Gordon Brown

All Publications

• (in press) Reservoir oxidation by geologically sequestered CO2. Geochim. Cosmochim. Acta Nielsen, L. C., Maher, K., Brown, Jr., G. E., Bird, D. K., Thomas, B., Johnson, N. C., Rosenbauer, R. J. 2105
• Oxide- and Silicate-Water Interfaces and Their Roles in Technology and the Environment. Chemical reviews Bañuelos, J. L., Borguet, E., Brown, G. E., Cygan, R. T., DeYoreo, J. J., Dove, P. M., Gaigeot, M. P., Geiger, F. M., Gibbs, J. M., Grassian, V. H., Ilgen, A. G., Jun, Y. S., Kabengi, N., Katz, L., Kubicki, J. D., Lützenkirchen, J., Putnis, C. V., Remsing, R. C., Rosso, K. M., Rother, G., Sulpizi, M., Villalobos, M., Zhang, H. 2023

  Abstract

  Interfacial reactions drive all elemental cycling on Earth and play pivotal roles in human activities such as agriculture, water purification, energy production and storage, environmental contaminant remediation, and nuclear waste repository management. The onset of the 21st century marked the beginning of a more detailed understanding of mineral aqueous interfaces enabled by advances in techniques that use tunable high-flux focused ultrafast laser and X-ray sources to provide near-atomic measurement resolution, as well as by nanofabrication approaches that enable transmission electron microscopy in a liquid cell. This leap into atomic- and nanometer-scale measurements has uncovered scale-dependent phenomena whose reaction thermodynamics, kinetics, and pathways deviate from previous observations made on larger systems. A second key advance is new experimental evidence for what scientists hypothesized but could not test previously, namely, interfacial chemical reactions are frequently driven by "anomalies" or "non-idealities" such as defects, nanoconfinement, and other nontypical chemical structures. Third, progress in computational chemistry has yielded new insights that allow a move beyond simple schematics, leading to a molecular model of these complex interfaces. In combination with surface-sensitive measurements, we have gained knowledge of the interfacial structure and dynamics, including the underlying solid surface and the immediately adjacent water and aqueous ions, enabling a better definition of what constitutes the oxide- and silicate-water interfaces. This critical review discusses how science progresses from understanding ideal solid-water interfaces to more realistic systems, focusing on accomplishments in the last 20 years and identifying challenges and future opportunities for the community to address. We anticipate that the next 20 years will focus on understanding and predicting dynamic transient and reactive structures over greater spatial and temporal ranges as well as systems of greater structural and chemical complexity. Closer collaborations of theoretical and experimental experts across disciplines will continue to be critical to achieving this great aspiration.

  View details for DOI 10.1021/acs.chemrev.2c00130

  View details for PubMedID 37186959

• Pauling's rules for oxide-based minerals: A re-examination based on quantum mechanical constraints and modern applications of bond-valence theory to Earth materials AMERICAN MINERALOGIST Gibbs, G., Hawthorne, F. C., Brown, G. E. 2022; 107 (7): 1219-1248

  View details for DOI 10.2138/am-2021-7938

  View details for Web of Science ID 000819593000002

• Mechanism of Arsenic Partitioning During Sulfidation of As-Sorbed Ferrihydrite Nanoparticles. ACS earth & space chemistry Kumar, N., Noël, V., Besold, J., Planer-Friedrich, B., Boye, K., Fendorf, S., Brown, G. E. 2022; 6 (7): 1666-1673

  Abstract

  Knowledge of how arsenic (As) partitions among various phases in Fe-rich sulfidic environments is critical for understanding the fate and mobility of As in such environments. We studied the reaction of arsenite and arsenate sorbed on ferrihydrite nanoparticle surfaces with dissolved sulfide at varying S/Fe ratios (0.1-2.0) to understand the fate and transformation mechanism of As during sulfidation of ferrihydrite. By using aqueous As speciation analysis by IC-ICP-MS and solid-phase As speciation analysis by synchrotron-based X-ray absorption spectroscopy (XAS), we were able to discern the mechanism and pathways of As partitioning and thio-arsenic species formation. Our results provide a mechanistic understanding of the fate and transformation of arsenic during the codiagenesis of As, Fe, and S in reducing environments. Our aqueous-phase As speciation data, combined with solid-phase speciation data, indicate that sulfidation of As-sorbed ferrihydrite nanoparticles results in their transformation to trithioarsenate and arsenite, independent of the initial arsenic species used. The nature and extent of transformation and the thioarsenate species formed were controlled by S/Fe ratios in our experiments. However, arsenate was reduced to arsenite before transformation to trithioarsenate.

  View details for DOI 10.1021/acsearthspacechem.1c00373

  View details for PubMedID 35903782

  View details for PubMedCentralID PMC9310089

• Mechanism of Arsenic Partitioning During Sulfidation of As-Sorbed Ferrihydrite Nanoparticles ACS EARTH AND SPACE CHEMISTRY Kumar, N., Noel, V., Besold, J., Planer-Friedrich, B., Boye, K., Fendorf, S., Brown Jr, G. E. 2022

  View details for DOI 10.1021/acsearthspacechem.1c00373

  View details for Web of Science ID 000826418100001

• Chemical and Reactive Transport Processes Associated with Hydraulic Fracturing of Unconventional Oil/Gas Shales. Chemical reviews Jew, A. D., Druhan, J. L., Ihme, M., Kovscek, A. R., Battiato, I., Kaszuba, J. P., Bargar, J. R., Brown, G. E. 2022

  Abstract

  Hydraulic fracturing of unconventional oil/gas shales has changed the energy landscape of the U.S. Recovery of hydrocarbons from tight, hydraulically fractured shales is a highly inefficient process, with estimated recoveries of <25% for natural gas and <5% for oil. This review focuses on the complex chemical interactions of additives in hydraulic fracturing fluid (HFF) with minerals and organic matter in oil/gas shales. These interactions are intended to increase hydrocarbon recovery by increasing porosities and permeabilities of tight shales. However, fluid-shale interactions result in the dissolution of shale minerals and the release and transport of chemical components. They also result in mineral precipitation in the shale matrix, which can reduce permeability, porosity, and hydrocarbon recovery. Competition between mineral dissolution and mineral precipitation processes influences the amounts of oil and gas recovered. We review the temporal/spatial origins and distribution of unconventional oil/gas shales from mudstones and shales, followed by discussion of their global and U.S. distributions and compositional differences from different U.S. sedimentary basins. We discuss the major types of chemical additives in HFF with their intended purposes, including drilling muds. Fracture distribution, porosity, permeability, and the identity and molecular-level speciation of minerals and organic matter in oil/gas shales throughout the hydraulic fracturing process are discussed. Also discussed are analysis methods used in characterizing oil/gas shales before and after hydraulic fracturing, including permeametry and porosimetry measurements, X-ray diffraction/Rietveld refinement, X-ray computed tomography, scanning/transmission electron microscopy, and laboratory- and synchrotron-based imaging/spectroscopic methods. Reactive transport and spatial scaling are discussed in some detail in order to relate fundamental molecular-scale processes to fluid transport. Our review concludes with a discussion of potential environmental impacts of hydraulic fracturing and important knowledge gaps that must be bridged to achieve improved mechanistic understanding of fluid transport in oil/gas shales.

  View details for DOI 10.1021/acs.chemrev.1c00504

  View details for PubMedID 35404590

• Reply to the Comment on "FeS colloids - formation and mobilization pathways in natural waters" by S. Peiffer, D0EN00967A ENVIRONMENTAL SCIENCE-NANO Noel, V., Kumar, N., Boye, K., Lezama-Pacheco, J. S., Brown, G. E., Bargara, J. R. 2021; 8 (6): 1817-1821

  View details for DOI 10.1039/d1en00278c

  View details for Web of Science ID 000662712900024

• Global Sensitivity Analysis of a Reactive Transport Model for Mineral Scale Formation During Hydraulic Fracturing Environmental Engineering Science Li, Q., Wang, L., Perzan, Z., Caers, J., Brown Jr., G. E., Bargar, J. R., Maher, K. 2021

  View details for DOI 10.1089/ees.2020.0365

• FeS colloids - formation and mobilization pathways in natural waters ENVIRONMENTAL SCIENCE-NANO Noel, V., Kumar, N., Boye, K., Barragan, L., Lezama-Pacheco, J. S., Chu, R., Tolic, N., Brown, G. E., Bargar, J. R. 2020; 7 (7): 2102–16

  View details for DOI 10.1039/c9en01427f

  View details for Web of Science ID 000549099000015

• Reactive Transport Modeling of Shale-Fluid Interactions after Imbibition of Fracturing Fluids ENERGY & FUELS Li, Q., Jew, A. D., Brown, G. E., Bargar, J. R., Maher, K. 2020; 34 (5): 5511–23

  View details for DOI 10.1021/acs.energyfuels.9b04542

  View details for Web of Science ID 000537407200035

• Chemical Speciation and Stability of Uranium in Unconventional Shales: Impact of Hydraulic Fracture Fluid. Environmental science & technology Jew, A. D., Besançon, C. J., Roycroft, S. J., Noel, V. S., Bargar, J. R., Brown, G. E. 2020

  Abstract

  Uranium and other radionuclides are prominent in many unconventional oil/gas shales and is a potential contaminant in flowback/produced waters due to the large volumes/types of chemicals injected into the subsurface during stimulation. To understand the stability of U before and after stimulation, a geochemical study of U speciation was carried out on three shales (Marcellus, Green River, and Barnett). Two types of samples for each shale were subjected to sequential chemical extractions: unreacted and shale-reacted with a synthetic hydraulic fracture fluid. A significant proportion of the total U (20-57%) was released from these three shales after reaction with fracture fluid, indicating that U is readily leachable. The total U released exceeds labile water-soluble and exchangeable fractions in unreacted samples, indicating that fluids leach more recalcitrant phases in the shale. Radiographic analysis of unreacted Marcellus shale thin sections shows U associated with detrital quartz and the clay matrix in the shale. Detrital zircon and TiO2 identified by an electron microprobe could account for the hot spots. This study shows that significant proportions of U in three shales are mobile upon stimulation. In addition, the extent of mobilization of U depends on the U species in these rocks.

  View details for DOI 10.1021/acs.est.0c01022

  View details for PubMedID 32401022

• Redox Heterogeneities Promote Thioarsenate Formation and Release into Groundwater from Low Arsenic Sediments. Environmental science & technology Kumar, N. n., Noël, V. n., Planer-Friedrich, B. n., Besold, J. n., Lezama-Pacheco, J. n., Bargar, J. R., Brown, G. E., Fendorf, S. n., Boye, K. n. 2020

  Abstract

  Groundwater contamination by As from natural and anthropogenic sources is a worldwide concern. Redox heterogeneities over space and time are common and can influence the molecular-level speciation of As, and thus, As release/retention but are largely unexplored. Here, we present results from a dual-domain column experiment, with natural organic-rich, fine-grained, and sulfidic sediments embedded as lenses (referred to as "reducing lenses") within natural aquifer sand. We show that redox interfaces in sulfur-rich, alkaline aquifers may release concerning levels of As, even when sediment As concentration is low (<2 mg/kg), due to the formation of mobile thioarsenates at aqueous sulfide/Fe molar ratios <1. In our experiments, this behavior occurred in the aquifer sand between reducing lenses and was attributed to the spreading of sulfidic conditions and subsequent Fe reductive dissolution. In contrast, inside reducing lenses (and some locations in the aquifer) the aqueous sulfide/Fe molar ratios exceeded 1 and aqueous sulfide/As molar ratios exceeded 100, which partitioned As(III)-S to the solid phase (associated with organics or as realgar (As4S4)). These results highlight the importance of thioarsenates in natural sediments and indicate that redox interfaces and sediment heterogeneities could locally degrade groundwater quality, even in aquifers with unconcerning solid-phase As concentrations.

  View details for DOI 10.1021/acs.est.9b06502

  View details for PubMedID 32069033

• Thicknesses of Chemically Altered Zones in Shale Matrices Resulting from Interactions with Hydraulic Fracturing Fluid ENERGY & FUELS Li, Q., Jew, A. D., Kohli, A., Maher, K., Brown, G. E., Bargar, J. R. 2019; 33 (8): 6878–89

  View details for DOI 10.1021/acs.energyfuels.8b04527

  View details for Web of Science ID 000481569100004

• Alteration depths from the shale surface into the matrix Li, Q., Jew, A., Kohli, A., Brown, G., Maher, K., Bargar, J. AMER CHEMICAL SOC. 2019

  View details for Web of Science ID 000478861200803

• Shale Kerogen: Hydraulic Fracturing Fluid Interactions and Contaminant Release ENERGY & FUELS Dustin, M. K., Bargar, J. R., Jew, A. D., Harrison, A. L., Joe-Wong, C., Thomas, D. L., Brown, G. E., Maher, K. 2018; 32 (9): 8966–77

  View details for DOI 10.1021/acs.energyfuels.8b01037

  View details for Web of Science ID 000445711700006

• Sulfidation mechanisms of Fe(III)-(oxyhydr)oxide nanoparticles: a spectroscopic study ENVIRONMENTAL SCIENCE-NANO Kumar, N., Pacheco, J., Noel, V., Dublet, G., Brown, G. E. 2018; 5 (4): 1012–26

  View details for DOI 10.1039/c7en01109a

  View details for Web of Science ID 000435963000016

• Theoretical and experimental investigations of mercury adsorption on hematite surfaces JOURNAL OF THE AIR & WASTE MANAGEMENT ASSOCIATION Jung, J., Liguori, S., Jew, A. D., Brown, G. E., Wilcox, J. 2018; 68 (1): 39–53

  Abstract

  One of the biggest environmental concerns caused by coal-fired power plants is the emission of mercury (Hg), which is toxic metal. To control the emission of Hg from coal-derived flue gas, it is important to understand the behavior and speciation of Hg as well as the interaction between Hg and solid materials in the flue gas stream. In this study, atomic-scale theoretical investigations using density functional theory (DFT) were carried out in conjunction with laboratory-scale experimental studies to investigate the adsorption behavior of Hg on hematite (α-Fe2O3). According to the DFT simulation, the adsorption energy calculation proposes that Hg physisorbs to the α-Fe2O3(0001) surface with an adsorption energy of -0.278 eV, and the subsequent Bader charge analysis confirms that Hg is slightly oxidized. In addition, Cl introduced to the Hg-adsorbed surface strengthens the Hg stability on the α-Fe2O3(0001) surface, as evidenced by a shortened Hg-surface equilibrium distance. The projected density of states (PDOS) analysis also suggests that Cl enhances the chemical bonding between the surface and the adsorbate, thereby increasing the adsorption strength. In summary, α-Fe2O3 has the ability to adsorb and oxidize Hg, and this reactivity is enhanced in the presence of Cl. For the laboratory-scale experiments, three types of α-Fe2O3 nanoparticles were prepared using the precursors Fe(NO3)3, Fe(ClO4)3, and FeCl3, respectively. The particle shapes varied from diamond to irregular stepped and subrounded, and particle size ranged from 20 to 500 nm depending on the precursor used. The nanoparticles had the highest surface area (84.5 m2/g) due to their highly stepped surface morphology. Packed-bed reactor Hg exposure experiments resulted in this nanoparticles adsorbing more than 300 μg Hg/g. The Hg LIII-edge extended X-ray absorption fine structure spectroscopy also indicated that HgCl2 physisorbed onto the α-Fe2O3 nanoparticles.Atomic-scale theoretical simulations proposes that Hg physisorbs to the α-Fe2O3(0001) surface with an adsorption energy of -0.278 eV, and the subsequent Bader charge analysis confirms that Hg is slightly oxidized. In addition, Cl introduced to the Hg-adsorbed surface strengthens the Hg stability on the α-Fe2O3(0001) surface, as evidenced by a shortened Hg-surface equilibrium distance. The PDOS analysis also suggests that Cl enhances the chemical bonding between the surface and the adsorbate, thereby increasing the adsorption strength. Following laboratory-scale experiment of Hg sorption also shows that HgCl2 physisorbs onto α-Fe2O3 nanoparticles which have highly stepped structure.

  View details for PubMedID 28829689

• Effects of nano-confinement on Zn(II) adsorption to nanoporous silica Geochimica et Cosmochimica Acta Nelson, J., Bargar, J. R., Wasylenki, L., Brown Jr., G. E., Maher, K. 2018; 240: 80-97

  View details for DOI 10.1016/j.gca.2018.08.017

• Partitioning of uranyl between ferrihydrite and humic substances at acidic and circum-neutral pH GEOCHIMICA ET COSMOCHIMICA ACTA Dublet, G., Pacheco, J., Bargar, J. R., Fendorf, S., Kumar, N., Lowry, G. V., Brown, G. E. 2017; 215: 122–40

  View details for DOI 10.1016/j.gca.2017.07.013

  View details for Web of Science ID 000409107900008

• Kinetics and Products of Chromium(VI) Reduction by Iron(II/III)-Bearing Clay Minerals ENVIRONMENTAL SCIENCE & TECHNOLOGY Joe-Wong, C., Brown, G. E., Maher, K. 2017; 51 (17): 9817–25

  Abstract

  Hexavalent chromium is a water-soluble pollutant, the mobility of which can be controlled by reduction of Cr(VI) to less soluble, environmentally benign Cr(III). Iron(II/III)-bearing clay minerals are widespread potential reductants of Cr(VI), but the kinetics and pathways of Cr(VI) reduction by such clay minerals are poorly understood. We reacted aqueous Cr(VI) with two abiotically reduced clay minerals: an Fe-poor montmorillonite and an Fe-rich nontronite. The effects of ionic strength, pH, total Fe content, and the fraction of reduced structural Fe(II) [Fe(II)/Fe(total)] were examined. The last variable had the largest effect on Cr(VI) reduction kinetics: for both clay minerals, the rate constant of Cr(VI) reduction varies by more than 3 orders of magnitude with Fe(II)/Fe(total) and is described by a linear free energy relationship. Under all conditions examined, Cr and Fe K-edge X-ray absorption near-edge structure spectra show that the main Cr-bearing product is a Cr(III)-hydroxide and that Fe remains in the clay structure after reacting with Cr(VI). This study helps to quantify our understanding of the kinetics of Cr(VI) reduction by Fe(II/III)-bearing clay minerals and may improve predictions of Cr(VI) behavior in subsurface environments.

  View details for PubMedID 28783317

• Impact of Organics and Carbonates on the Oxidation and Precipitation of Iron during Hydraulic Fracturing of Shale ENERGY & FUELS Jew, A. D., Dustin, M. K., Harrison, A. L., Joe-Wong, C. M., Thomas, D. L., Maher, K., Brown, G. E., Bargar, J. R. 2017; 31 (4): 3643-3658

  View details for DOI 10.1021/acs.energyfuels.6b03220

  View details for Web of Science ID 000400039800031

• Effects of surface structural disorder and surface coverage on isotopic fractionation during Zn(II) adsorption onto quartz and amorphous silica surfaces Geochimica et Cosmochimica Acta Nelson, J., Wasylenki, L., Bargar, J. R., Brown Jr., G. E., Maher, K. 2017; 215: 354-376

  View details for DOI 10.1016/j.gca.2017.08.003

• Clumped-isotope thermometry of magnesium carbonates in ultramafic rocks GEOCHIMICA ET COSMOCHIMICA ACTA del Real, P. G., Maher, K., Kluge, T., Bird, D. K., Brown, G. E., John, C. M. 2016; 193: 222-250

  View details for DOI 10.1016/j.gca.2016.08.003

  View details for Web of Science ID 000385507900013

• Effect of biofilm coatings at metal-oxide/water interfaces II: Competitive sorption between Pb(II) and Zn(II) at Shewanella oneidensis/metal-oxide/water interfaces GEOCHIMICA ET COSMOCHIMICA ACTA Wang, Y., Gelabert, A., Michel, F. M., Choi, Y., Eng, P. J., Spormann, A. M., Brown, G. E. 2016; 188: 393-406

  View details for DOI 10.1016/j.gca.2016.04.054

  View details for Web of Science ID 000380752700022

• Pb, Cu, and Zn distributions at humic acid-coated metal-oxide surfaces GEOCHIMICA ET COSMOCHIMICA ACTA Wang, Y., Michel, F. M., Choi, Y., Eng, P. J., Levard, C., Siebner, H., Gu, B., Bargar, J. R., Brown, G. E. 2016; 188: 407-423

  View details for DOI 10.1016/j.gca.2016.05.009

  View details for Web of Science ID 000380752700023

• Effect of biofilm coatings at metal-oxide/water interfaces I: Pb(II) and Zn(II) partitioning and speciation at Shewanella oneidensis/metal-oxide/water interfaces GEOCHIMICA ET COSMOCHIMICA ACTA Wang, Y., Gelabert, A., Michel, F. M., Choi, Y., Gescher, J., Ona-Nguema, G., Eng, P. J., Bargar, J. R., Farges, F., Spormann, A. M., Brown, G. E. 2016; 188: 368-392

  View details for DOI 10.1016/j.gca.2016.04.052

  View details for Web of Science ID 000380752700021

• Comparison of isoelectric points of single-crystal and polycrystalline alpha-Al2O3 and alpha-Fe2O3 surfaces AMERICAN MINERALOGIST Wang, Y., Persson, P., Michel, F. M., Brown, G. E. 2016; 101 (9-10): 2248-2259

  View details for DOI 10.2138/am-2016-5531

  View details for Web of Science ID 000385605100028

• Uranium Immobilization and Nanofilm Formation on Magnesium Rich Minerals ENVIRONMENTAL SCIENCE & TECHNOLOGY van Veelen, A., Bargar, J. R., Law, G. T., Brown, G. E., Wogelius, R. A. 2016; 50 (7): 3435-3443

  Abstract

  Polarization-dependent grazing incidence X-ray absorption spectroscopy (XAS) measurements were completed on oriented single crystals of magnesite [MgCO3] and brucite [Mg(OH)2] reacted with aqueous uranyl chloride above and below the solubility boundaries of schoepite (500, 50, and 5 ppm) at pH 8.3 and at ambient (PCO2 = 10(-3.5)) or reduced partial pressures of carbon dioxide (PCO2 = 10(-4.5)). X-ray absorption near edge structure (XANES) spectra show a striking polarization dependence (χ = 0° and 90° relative to the polarization plane of the incident beam) and consistently demonstrated that the uranyl molecule was preferentially oriented with its Oaxial═U(VI)═Oaxial linkage at high angles (60-80°) to both magnesite (101̅4) and brucite (0001). Extended X-ray absorption fine structure (EXAFS) analysis shows that the "effective" number of U(VI) axial oxygens is the most strongly affected fitting parameter as a function of polarization. Furthermore, axial tilt in the surface thin films (thickness ∼ 21 Å) is correlated with surface roughness [σ]. Our results show that hydrated uranyl(-carbonate) complexes polymerize on all of our experimental surfaces and that this process is controlled by surface hydroxylation. These results provide new insights into the bonding configuration expected for uranyl complexes on the environmentally significant carbonate and hydroxide mineral surfaces.

  View details for DOI 10.1021/acs.est.5b06041

  View details for Web of Science ID 000373655800017

  View details for PubMedID 26990311

• A spatially resolved surface kinetic model for forsterite dissolution GEOCHIMICA ET COSMOCHIMICA ACTA Maher, K., Johnson, N. C., Jackson, A., Lammers, L. N., Torchinsky, A. B., Weaver, K. L., Bird, D. K., Brown, G. E. 2016; 174: 313-334

  View details for DOI 10.1016/j.gca.2015.11.019

  View details for Web of Science ID 000368819800021

• Silver Sulfidation in Thermophilic Anaerobic Digesters and Effects on Antibiotic Resistance Genes ENVIRONMENTAL ENGINEERING SCIENCE Kim, B., Miller, J. H., Monsegue, N., Levard, C., Hong, Y., Hull, M. S., Murayama, M., Brown, G. E., Vikesland, P. J., Knocke, W. R., Pruden, A., Hochella, M. F. 2016; 33 (1): 1-10

  View details for DOI 10.1089/ees.2015.0226

  View details for Web of Science ID 000372753900001

• First-Principles Investigation of Mercury Adsorption on the alpha-Fe2O3(1(1)over-bar02) Surface JOURNAL OF PHYSICAL CHEMISTRY C Jung, J., Geatches, D., Lee, K., Aboud, S., Brown, G. E., Wilcox, J. 2015; 119 (47): 26512-26518

  View details for DOI 10.1021/acs.jpcc.5b07827

  View details for Web of Science ID 000366006400031

• Ni cycling in mangrove sediments from New Caledonia GEOCHIMICA ET COSMOCHIMICA ACTA Noel, V., Morin, G., Juillot, F., Marchand, C., Brest, J., Bargar, J. R., Munoz, M., Marakovic, G., Ardo, S., Brown, G. E. 2015; 169: 82-98

  View details for DOI 10.1016/j.gca.2015.07.024

  View details for Web of Science ID 000362975700006

• Mercury Interaction with the Fine Fraction of Coal-Combustion Fly Ash in a Simulated Coal Power Plant Flue Gas Stream ENERGY & FUELS Jew, A. D., Rupp, E. C., Geatches, D. L., Jung, J., Farfan, G., Bahet, L., Hower, J. C., Brown, G. E., Wilcox, J. 2015; 29 (9): 6025-6038

  View details for DOI 10.1021/acs.energyfuels.5b01253

  View details for Web of Science ID 000363068200053

• Goethite aging explains Ni depletion in upper units of ultramafic lateritic ores from New Caledonia GEOCHIMICA ET COSMOCHIMICA ACTA Dublet, G., Juillot, F., Morin, G., Fritsch, E., Fandeur, D., Brown, G. E. 2015; 160: 1-15

  View details for DOI 10.1016/j.gca.2015.03.015

  View details for Web of Science ID 000354879400001

• Sedimentary reservoir oxidation during geologic CO2 sequestration GEOCHIMICA ET COSMOCHIMICA ACTA Lammers, L. N., Brown, G. E., Bird, D. K., Thomas, R. B., Johnson, N. C., Rosenbauer, R. J., Maher, K. 2015; 155: 30-46

  View details for DOI 10.1016/j.gca.2015.02.001

  View details for Web of Science ID 000351732800003

• Stable Hg Isotope Signatures in Creek Sediments Impacted by a Former Hg Mine ENVIRONMENTAL SCIENCE & TECHNOLOGY Smith, R. S., Wiederhold, J. G., Jew, A. D., Brown, G. E., Bourdon, B., Kretzschmar, R. 2015; 49 (2): 767-776

  Abstract

  The goal of this study was to investigate the Hg stable isotope signatures of sediments in San Carlos Creek downstream of the former Hg mine New Idria, CA, USA and to relate the results to previously studied Hg isotope signatures of unroasted ore waste and calcine materials in the mining area. New Idria unroasted ore waste was reported to have a narrow δ(202)Hg range (−0.09 to 0.16‰), while roasted calcine materials exhibited a very large variability in δ(202)Hg (−5.96 to 14.5‰). In this study, creek sediment samples were collected in the stream bed from two depths (0–10 and 10–20 cm) at 10 locations between the mine adit and 28 km downstream. The sediment samples were size-fractionated into sand, silt, and (if possible) clay fractions as well as hand-picked calcine pebbles. The sediment samples contained highly elevated Hg concentrations (8.2 to 647 μg g(–1)) and displayed relatively narrow mass-dependent fractionation (MDF, δ(202)Hg; ± 0.08‰, 2SD) ranges (−0.58 to 0.24‰) and little to no mass-independent fractionation (MIF, Δ(199)Hg; ± 0.04‰, 2SD) (0.00 to 0.10‰), similar to what was observed previously for the unroasted ore waste. However, due to the highly variable and overlapping δ(202)Hg signatures of the calcines, they could not be ruled out as source of Hg to the creek sediments. Overall, our results suggest that analyzing creek sediments downstream of former Hg mines can provide a more reliable Hg isotope source signature for tracing studies at larger spatial scales, than analyzing the isotopically highly heterogeneous tailing piles typically found at former mining sites. Creek sediments carry an integrated isotope signature of Hg transported away from the mine with runoff into the creek, eventually affecting ecosystems downstream.

  View details for DOI 10.1021/es503442p

  View details for Web of Science ID 000348332400010

• As(III) and As(V) speciation during transformation of lepidocrocite to magnetite. Environmental Science & Technology Wang, Y., Morin, G., Ona-Nguema, G., Brown, Jr., G. E. 2015; 48 (24): 14282-14290
• (in press) The role of the Si-rich surface layer in forsterite dissolution. 2: An “ion-by-ion” model for dissolution and Mg isotope fractionation. Geochimica et Cosmochimica Acta Maher, K., Nielsen-Lammers, L. C., Johnson, N. C., Torchinsky, A. B., Weaver, K. I., Bird, D. K., Brown, Jr., G. E. 2015
• (in press) Ni cycling in mangrove sediments from New Caledonia. Environmental Science & Technology Noel, V., Morin, G., Juillot, F., Marchand, C., Brest, J., Bargar, J. R., Munoz, M., Marakovic, G., Ardo, S., Brown, Jr., G. E. 2015
• (submitted) Goethite aging explains Ni depletion in upper units of ultramafic lateritic ores from New Caledonia. Geochimica et Cosmochimica Acta Dublet, G., Juillot, F., Morin, G., Fritsch, E., Fandeur, D., Brown, Jr., G. E. 2015
• Stable Hg isotope signatures in creek sediments impacted by a former Hg mine. Environmental Science & Technology Smith, R. S., Wiederhold, J. G., Jew, A. D., Brown, Jr., G. E., Bourdon, B., Kretszchmer, R. 2015; 49 (2): 767-776
• (submitted) The role of the Si-rich layer in forsterite dissolution. 3: Spatially and temporally resolved incorporation of an isotopic tracer. Geochimica et Cosmochimica Acta Johnson, N. C., Rosenbauer, R. J., Bird, D. K., Brown, Jr., G. E., Chidsey, C. E., Maher, K. 2015
• Arsenic(III) and Arsenic(V) Speciation during Transformation of Lepidocrocite to Magnetite ENVIRONMENTAL SCIENCE & TECHNOLOGY Wang, Y., Morin, G., Ona-Nguema, G., Brown, G. E. 2014; 48 (24): 14282-14290

  Abstract

  Bioreduction of As(V) and As-bearing iron oxides is considered to be one of the key processes leading to arsenic pollution in groundwaters in South and Southeast Asia. Recent laboratory studies with simple aqueous media showed that secondary Fe(II)-bearing phases (e.g., magnetite and green rust), which commonly precipitate during bioreduction of iron oxides, captured arsenic species. The aim of the present study was to follow arsenic speciation during the abiotic Fe(II)-induced transformation of As(III)- and As(V)-doped lepidocrocite to magnetite, and to evaluate the influence of arsenic on the transformation kinetics and pathway. We found green rust formation is an intermediate phase in the transformation. Both As(III) and As(V) slowed the transformation, with the effect being greater for As(III) than for As(V). Prior to the formation of magnetite, As(III) adsorbed on both lepidocrocite and green rust, whereas As(V) associated exclusively with green rust, When magnetite precipitated, As(III) formed surface complexes on magnetite nanoparticles and As(V) is thought to have been incorporated into the magnetite structure. These processes dramatically lowered the availability of As in the anoxic systems studied. These results provide insights into the behavior of arsenic during magnetite precipitation in reducing environments. We also found that As(V) removal from solution was higher than As(III) removal following magnetite formation, which suggests that conversion of As(III) to As(V) is preferred when using As-magnetite precipitation to treat As-contaminated groundwaters.

  View details for DOI 10.1021/es5033629

  View details for Web of Science ID 000346686100028

  View details for PubMedID 25425339

• Preparation, Structure, and Orientation of Pyrite FeS2{100} Surfaces: Anisotropy, Sulfur Monomers, Dimer Vacancies, and a Possible FeS Surface Phase JOURNAL OF PHYSICAL CHEMISTRY C Andersson, K. J., Ogasawara, H., Nordlund, D., Brown, G. E., Nilsson, A. 2014; 118 (38): 21896-21903

  View details for DOI 10.1021/jp5005924

  View details for Web of Science ID 000342396300019

• Sulfidation of copper oxide nanoparticles and properties of resulting copper sulfide ENVIRONMENTAL SCIENCE-NANO Ma, R., Stegemeier, J., Levard, C., Dale, J. G., Noack, C. W., Yang, T., Brown, G. E., Lowry, G. V. 2014; 1 (4): 347-357

  View details for DOI 10.1039/c4en00018h

  View details for Web of Science ID 000347974200005

• Small-scale studies of roasted ore waste reveal extreme ranges of stable mercury isotope signatures GEOCHIMICA ET COSMOCHIMICA ACTA Smith, R. S., Wiederhold, J. G., Jew, A. D., Brown, G. E., Bourdon, B., Kretzschmar, R. 2014; 137: 1-17

  View details for DOI 10.1016/j.gca.2014.03.037

  View details for Web of Science ID 000338424000001

• Properties of impurity-bearing ferrihydrite III. Effects of Si on the structure of 2-line ferrihydrite GEOCHIMICA ET COSMOCHIMICA ACTA Cismasu, A. C., Michel, F. M., Tcaciuc, A. P., Brown, G. E. 2014; 133: 168-185

  View details for DOI 10.1016/j.gca.2014.02.018

  View details for Web of Science ID 000334833600010

• Olivine dissolution and carbonation under conditions relevant for in situ carbon storage CHEMICAL GEOLOGY Johnson, N. C., Thomas, B., Maher, K., Rosenbauer, R. J., Bird, D., Brown, G. E. 2014; 373: 93-105

  View details for DOI 10.1016/j.chemgeo.2014.02.026

  View details for Web of Science ID 000334737200009

• Integrated Approaches of X-Ray Absorption Spectroscopic and Electron Microscopic Techniques on Zinc Speciation and Characterization in a Final Sewage Sludge Product JOURNAL OF ENVIRONMENTAL QUALITY Kim, B., Levard, C., Murayama, M., Brown, G. E., Hochella, M. F. 2014; 43 (3): 908-916

  Abstract

  Integration of complementary techniques can be powerful for the investigation of metal speciation and characterization in complex and heterogeneous environmental samples, such as sewage sludge products. In the present study, we combined analytical transmission electron microscopy (TEM)-based techniques with X-ray absorption spectroscopy (XAS) to identify and characterize nanocrystalline zinc sulfide (ZnS), considered to be the dominant Zn-containing phase in the final stage of sewage sludge material of a full-scale municipal wastewater treatment plant. We also developed sample preparation procedures to preserve the organic and sulfur-rich nature of sewage sludge matrices for microscopic and spectroscopic analyses. Analytical TEM results indicate individual ZnS nanocrystals to be in the size range of 2.5 to 7.5 nm in diameter, forming aggregates of a few hundred nanometers. Observed lattice spacings match sphalerite. The ratio of S to Zn for the ZnS nanocrystals is estimated to be 1.4, suggesting that S is present in excess. The XAS results on the Zn speciation in the bulk sludge material also support the TEM observation that approximately 80% of the total Zn has the local structure of a 3-nm ZnS nanoparticle reference material. Because sewage sludge is frequently used as a soil amendment on agricultural lands, future studies that investigate the oxidative dissolution rate of ZnS nanoparticles as a function of size and aggregation state and the change of Zn speciation during post sludge-processing and soil residency are warranted to help determine the bioavailability of sludge-born Zn in the soil environment.

  View details for DOI 10.2134/jeq2013.10.0418

  View details for Web of Science ID 000336275700013

  View details for PubMedID 25602819

• Olivine carbonation kinetics. Part 1. Inhibition of the reaction by SiO2 Chemical Geology Johnson, N. C., Thomas, B., Maher, K., Bird, D., Rosenbauer, R. J., Brown, Jr., G. E. 2014; 373: 95-103
• XAS evidence for Ni sequestration by siderite in a lateritic Ni-deposit from New Caledonia AMERICAN MINERALOGIST Dublet, G., Juillot, F., Morin, G., Fritsch, E., Noel, V., Brest, J., Brown, G. E. 2014; 99 (1): 225-234

  View details for DOI 10.2138/am.2014.4625

  View details for Web of Science ID 000329416700028

• Microbially enhanced dissolution of HgS in an acid mine drainage system in the California Coast Range GEOBIOLOGY Jew, A. D., Behrens, S. F., Rytuba, J. J., Kappler, A., Spormann, A. M., Brown, G. E. 2014; 12 (1): 20-33

  View details for DOI 10.1111/gbi.12066

  View details for Web of Science ID 000328088500002

  View details for PubMedID 24224806

• Integrated approaches of x-ray absorption spectroscopic and electron microscopic techniques in zinc speciation and characterization in a final sewage sludge product J. Environ. Qual. Kim, B., Levard, C., Murayama, M., Brown, Jr., G. E., Hochella, Jr., M. F. 2014; 43 (3): 908-916
• Sulfidation of copper oxide nanoparticles and properties of the resulting copper sulfide Environmental Science: Nano Ma, R., Stegemeier, J., Levard, C., Dae, J. D., Yang, T., Brown, Jr., G. E., Lowry, G. V. 2014; 1 (4): 347-357
• Preparation, structure, and orientation of single crystal pyrite FeS2(100) J. Phys. Chem. C Andersson, K., Ogasawara, H., Kendelewicz, T., Brown, Jr., G. E., Nilsson, A. 2014; 118 (38): 21896-21903

  View details for DOI 10.1021/jp5005924

• Properties of impurity-bearing ferrihydrites III. Effects of Si and precipitation rate on the structure of 2-line ferrihydrite Geochimica Cosmochimica Acta Cismasu, A. C., Michel, F. M., Tcaciuc, A. P., Brown, Jr., G. E. 2014; 133: 168-185
• Competitive adsorption of Pb(II) and Zn(II) at polyacrylic acid-coated aluminum oxide surfaces Environmental Science & Technology Wang, Y., Michel, F. M., Levard, C., Choi, Y., Eng, P. J., Brown, Jr., G. E. 2014; 47: 12131-12139

  View details for DOI 10.1021/es401353y

• Microbially enhanced dissolution of HgS in an acid mine drainage system in the California Coast Range Geobiology Jew, A. D., Kühner, P., Behrens, S. F., Rytuba, J. J., Kappler, A., Spormann, A. M., Brown, Jr., G. E. 2014; 12: 20-33

  View details for DOI 10.1111/gbi.12066

• Sulfidation of silver nanoparticles: Natural antidote to their toxicity Environ. Sci. Technol. Levard, C., Hotze, E. M., Colman, B. P., Truong, L., Yang, X., Bone, A., Brown, Jr., G. E., Tanguay, R. L., Di Giulio, R. T., Bernhardt, E. S., Meyer, J. N., Wiesner, M. R., Lowry, G. V. 2014; 47: 13440-13448

  View details for DOI 10.1021/es403527n

• XAS evidence for Ni sequestration by siderite in lateritic regolith from New Caledonia American Mineralogist Dublet, G., Juillot, F., Morin, G., Fritsch, E., Brown, Jr., G. E. 2014; 99 (1): 225-234

  View details for DOI 10.2138/am/2014.4625

• Small-scale studies on roasted ore waste reveal extreme ranges of mercury isotope signatures Geochimica et Cosmochimica Acta Smith, R. S., Wiederhold, J. G., Jew, A. D., Brown, Jr., G. E., Bourdon, B., Kretzschmar, R. 2014; 137: 1-17
• Sulfidation of Silver Nanoparticles: Natural Antidote to Their Toxicity ENVIRONMENTAL SCIENCE & TECHNOLOGY Levard, C., Hotze, E. M., Colman, B. P., Dale, A. L., Truong, L., Yang, X. Y., Bone, A. J., Brown, G. E., Tanguay, R. L., Di Giulio, R. T., Bernhardt, E. S., Meyer, J. N., Wiesner, M. R., Lowry, G. V. 2013; 47 (23): 13440-13448

  Abstract

  Nanomaterials are highly dynamic in biological and environmental media. A critical need for advancing environmental health and safety research for nanomaterials is to identify physical and chemical transformations that affect the nanomaterial properties and their toxicity. Silver nanoparticles, one of the most toxic and well-studied nanomaterials, readily react with sulfide to form Ag(0)/Ag2S core-shell particles. Here, we show that sulfidation decreased silver nanoparticle toxicity to four diverse types of aquatic and terrestrial eukaryotic organisms (Danio rerio (zebrafish), Fundulus heteroclitus (killifish), Caenorhabditis elegans (nematode worm), and the aquatic plant Lemna minuta (least duckweed)). Toxicity reduction, which was dramatic in killifish and duckweed even for low extents of sulfidation (about 2 mol % S), is primarily associated with a decrease in Ag(+) concentration after sulfidation due to the lower solubility of Ag2S relative to elemental Ag (Ag(0)). These results suggest that even partial sulfidation of AgNP will decrease the toxicity of AgNPs relative to their pristine counterparts. We also show that, for a given organism, the presence of chloride in the exposure media strongly affects the toxicity results by affecting Ag speciation. These results highlight the need to consider environmental transformations of NPs in assessing their toxicity to accurately portray their potential environmental risks.

  View details for DOI 10.1021/es403527n

  View details for Web of Science ID 000327999400031

  View details for PubMedID 24180218

• Competitive Sorption of Pb(II) and Zn(II) on Polyacrylic Acid-Coated Hydrated Aluminum-Oxide Surfaces ENVIRONMENTAL SCIENCE & TECHNOLOGY Wang, Y., Michel, F. M., Levard, C., Choi, Y., Eng, P. J., Brown, G. E. 2013; 47 (21): 12131-12139

  Abstract

  Natural organic matter (NOM) often forms coatings on minerals. Such coatings are expected to affect metal-ion sorption due to abundant sorption sites in NOM and potential modifications to mineral surfaces, but such effects are poorly understood in complex multicomponent systems. Using poly(acrylic acid) (PAA), a simplified analog of NOM containing only carboxylic groups, Pb(II) and Zn(II) partitioning between PAA coatings and α-Al2O3 (1-102) and (0001) surfaces was investigated using long-period X-ray standing wave-florescence yield spectroscopy. In the single-metal-ion systems, PAA was the dominant sink for Pb(II) and Zn(II) for α-Al2O3(1-102) (63% and 69%, respectively, at 0.5 μM metal ions and pH 6.0). In equi-molar mixed-Pb(II)-Zn(II) systems, partitioning of both ions onto α-Al2O3(1-102) decreased compared with the single-metal-ion systems; however, Zn(II) decreased Pb(II) sorption to a greater extent than vice versa, suggesting that Zn(II) outcompeted Pb(II) for α-Al2O3(1-102) sorption sites. In contrast, >99% of both metal ions sorbed to PAA when equi-molar Pb(II) and Zn(II) were added simultaneously to PAA/α-Al2O3(0001). PAA outcompeted both α-Al2O3 surfaces for metal sorption but did not alter their intrinsic order of reactivity. This study suggests that single-metal-ion sorption results cannot be used to predict multimetal-ion sorption at NOM/metal-oxide interfaces when NOM is dominated by carboxylic groups.

  View details for DOI 10.1021/es401353y

  View details for Web of Science ID 000326711300034

  View details for PubMedID 24024496

• Properties of impurity-bearing ferrihydrite II: Insights into the surface structure and composition of pure, Al- and Si-bearing ferrihydrite from Zn(II) sorption experiments and Zn K-edge X-ray absorption spectroscopy GEOCHIMICA ET COSMOCHIMICA ACTA Cismasu, A. C., Levard, C., Michel, F. M., Brown, G. E. 2013; 119: 46-60

  View details for DOI 10.1016/j.gca.2013.05.040

  View details for Web of Science ID 000324036200004

• Quantification of the ferric/ferrous iron ratio in silicates by scanning transmission X-ray microscopy at the Fe L-2,L-3 edges CONTRIBUTIONS TO MINERALOGY AND PETROLOGY Bourdelle, F., Benzerara, K., Beyssac, O., Cosmidis, J., Neuville, D. R., Brown, G. E., Paineau, E. 2013; 166 (2): 423-434

  View details for DOI 10.1007/s00410-013-0883-4

  View details for Web of Science ID 000322027100005

• Mercury Isotope Signatures as Tracers for Hg Cycling at the New Idria Hg Mine ENVIRONMENTAL SCIENCE & TECHNOLOGY Wiederhold, J. G., Smith, R. S., Siebner, H., Jew, A. D., Brown, G. E., Bourdon, B., Kretzschmar, R. 2013; 47 (12): 6137-6145

  Abstract

  Mass-dependent fractionation (MDF) and mass-independent fractionation (MIF) of Hg isotopes provides a new tool for tracing Hg in contaminated environments such as mining sites, which represent major point sources of Hg pollution into surrounding ecosystems. Here, we present Hg isotope ratios of unroasted ore waste, calcine (roasted ore), and poplar leaves collected at a closed Hg mine (New Idria, CA, U.S.A.). Unroasted ore waste was isotopically uniform with δ(202)Hg values from -0.09 to 0.16‰ (± 0.10‰, 2 SD), close to the estimated initial composition of the HgS ore (-0.26‰). In contrast, calcine samples exhibited variable δ(202)Hg values ranging from -1.91‰ to +2.10‰. Small MIF signatures in the calcine were consistent with nuclear volume fractionation of Hg isotopes during or after the roasting process. The poplar leaves exhibited negative MDF (-3.18 to -1.22‰) and small positive MIF values (Δ(199)Hg of 0.02 to 0.21‰). Sequential extractions combined with Hg isotope analysis revealed higher δ(202)Hg values for the more soluble Hg pools in calcines compared with residual HgS phases. Our data provide novel insights into possible in situ transformations of Hg phases and suggest that isotopically heavy secondary Hg phases were formed in the calcine, which will influence the isotope composition of Hg leached from the site.

  View details for DOI 10.1021/es305245z

  View details for Web of Science ID 000320749000010

  View details for PubMedID 23662941

• Effect of Chloride on the Dissolution Rate of Silver Nanoparticles and Toxicity to E. coli. Environmental science & technology Levard, C., Mitra, S., Yang, T., Jew, A. D., Badireddy, A. R., Lowry, G. V., Brown, G. E. 2013; 47 (11): 5738-5745

  Abstract

  Pristine silver nanoparticles (AgNPs) are not chemically stable in the environment and react strongly with inorganic ligands such as sulfide and chloride once the silver is oxidized. Understanding the environmental transformations of AgNPs in the presence of specific inorganic ligands is crucial to determining their fate and toxicity in the environment. Chloride (Cl(-)) is a ubiquitous ligand with a strong affinity for oxidized silver and is often present in natural waters and in bacterial growth media. Though chloride can strongly affect toxicity results for AgNPs, their interaction is rarely considered and is challenging to study because of the numerous soluble and solid Ag-Cl species that can form depending on the Cl/Ag ratio. Consequently, little is known about the stability and dissolution kinetics of AgNPs in the presence of chloride ions. Our study focuses on the dissolution behavior of AgNPs in chloride-containing systems and also investigates the effect of chloride on the growth inhibition of E.coli (ATCC strain 33876) caused by Ag toxicity. Our results suggest that the kinetics of dissolution are strongly dependent on the Cl/Ag ratio and can be interpreted using the thermodynamically expected speciation of Ag in the presence of chloride. We also show that the toxicity of AgNPs to E.coli at various Cl(-) concentrations is governed by the amount of dissolved AgCl(x)((x-1)-) species suggesting an ion effect rather than a nanoparticle effect.

  View details for DOI 10.1021/es400396f

  View details for PubMedID 23641814

• Presentation of the Mineralogical Society of America Award for 2012 to Karim Benzerara AMERICAN MINERALOGIST Brown, G. E. 2013; 98 (5-6): 1088-1088

  View details for DOI 10.2138/am.2013.610

  View details for Web of Science ID 000319306900032

• Environmental Speciation of Actinides INORGANIC CHEMISTRY Maher, K., Bargar, J. R., Brown, G. E. 2013; 52 (7): 3510-3532

  Abstract

  Although minor in abundance in Earth's crust (U, 2-4 ppm; Th, 10-15 ppm) and in seawater (U, 0.003 ppm; Th, 0.0007 ppm), light actinides (Th, Pa, U, Np, Pu, Am, and Cm) are important environmental contaminants associated with anthropogenic activities such as the mining and milling of uranium ores, generation of nuclear energy, and storage of legacy waste resulting from the manufacturing and testing of nuclear weapons. In this review, we discuss the abundance, production, and environmental sources of naturally occurring and some man-made light actinides. As is the case with other environmental contaminants, the solubility, transport properties, bioavailability, and toxicity of actinides are dependent on their speciation (composition, oxidation state, molecular-level structure, and nature of the phase in which the contaminant element or molecule occurs). We review the aqueous speciation of U, Np, and Pu as a function of pH and Eh, their interaction with common inorganic and organic ligands in natural waters, and some of the common U-containing minerals. We also discuss the interaction of U, Np, Pu, and Am solution complexes with common Earth materials, including minerals, colloids, gels, natural organic matter (NOM), and microbial organisms, based on simplified model system studies. These surface interactions can inhibit (e.g., sorption to mineral surfaces, formation of insoluble biominerals) or enhance (e.g., colloid-facilitated transport) the dispersal of light actinides in the biosphere and in some cases (e.g., interaction with dissimilatory metal-reducing bacteria, NOM, or Mn- and Fe-containing minerals) can modify the oxidation states and, consequently, the behavior of redox-sensitive light actinides (U, Np, and Pu). Finally, we review the speciation of U and Pu, their chemical transformations, and cleanup histories at several U.S. Department of Energy field sites that have been used to mill U ores, produce fissile materials for reactors and weapons, and store high-level nuclear waste from both civilian and defense operations, including Hanford, WA; Rifle, CO; Oak Ridge, TN; Fernald, OH; Fry Canyon, UT; and Rocky Flats, CO.

  View details for DOI 10.1021/ic301686d

  View details for Web of Science ID 000317094300009

  View details for PubMedID 23137032

• Sulfidation Mechanism for Zinc Oxide Nanoparticles and the Effect of Sulfidation on Their Solubility ENVIRONMENTAL SCIENCE & TECHNOLOGY Ma, R., Levard, C., Michel, F. M., Brown, G. E., Lowry, G. V. 2013; 47 (6): 2527-2534

  Abstract

  Environmental transformations of nanoparticles (NPs) affect their properties and toxicity potential. Sulfidation is an important transformation process affecting the fate of NPs containing metal cations with an affinity for sulfide. Here, the extent and mechanism of sulfidation of ZnO NPs were investigated, and the properties of resulting products were carefully characterized. Synchrotron X-ray absorption spectroscopy and X-ray diffraction analysis reveal that transformation of ZnO to ZnS occurs readily at ambient temperature in the presence of inorganic sulfide. The extent of sulfidation depends on sulfide concentration, and close to 100% conversion can be obtained in 5 days given sufficient addition of sulfide. X-ray diffraction and transmission electron microscopy showed formation of primarily ZnS NPs smaller than 5 nm, indicating that sulfidation of ZnO NPs occurs by a dissolution and reprecipitation mechanism. The solubility of partially sulfidized ZnO NPs is controlled by the remaining ZnO core and not quenched by a ZnS shell formed as was observed for partially sulfidized Ag NPs. Sulfidation also led to NP aggregation and a decrease of surface charge. These changes suggest that sulfidation of ZnO NPs alters the behavior, fate, and toxicity of ZnO NPs in the environment. The reactivity and fate of the resulting <5 nm ZnS particles remains to be determined.

  View details for DOI 10.1021/es3035347

  View details for Web of Science ID 000316594000013

  View details for PubMedID 23425191

• Structure and reactivity of As(III)- and As(V)-rich schwertmannites and amorphous ferric arsenate sulfate from the Carnoules acid mine drainage, France: Comparison with biotic and abiotic model compounds and implications for As remediation GEOCHIMICA ET COSMOCHIMICA ACTA Maillot, F., Morin, G., Juillot, F., Bruneel, O., Casiot, C., Ona-Nguema, G., Wang, Y., Lebrun, S., Aubry, E., Vlaic, G., Brown, G. E. 2013; 104: 310-329

  View details for DOI 10.1016/j.gca.2012.11.016

  View details for Web of Science ID 000314664500020

• X-ray Photoemission and Density Functional Theory Study of the Interaction of Water Vapor with the Fe3O4(001) Surface at Near-Ambient Conditions JOURNAL OF PHYSICAL CHEMISTRY C Kendelewicz, T., Kaya, S., Newberg, J. T., Bluhm, H., Mulakaluri, N., Moritz, W., Scheffler, M., Nilsson, A., Pentcheva, R., Brown, G. E. 2013; 117 (6): 2719-2733

  View details for DOI 10.1021/jp3078024

  View details for Web of Science ID 000315181800040

• Highly Compressed Two-Dimensional Form of Water at Ambient Conditions SCIENTIFIC REPORTS Kaya, S., Schlesinger, D., Yamamoto, S., Newberg, J. T., Bluhm, H., Ogasawara, H., Kendelewicz, T., Brown, G. E., Pettersson, L. G., Nilsson, A. 2013; 3

  Abstract

  The structure of thin-film water on a BaF(2)(111) surface under ambient conditions was studied using x-ray absorption spectroscopy from ambient to supercooled temperatures at relative humidity up to 95%. No hexagonal ice-like structure was observed in spite of the expected templating effect of the lattice-matched (111) surface. The oxygen K-edge x-ray absorption spectrum of liquid thin-film water on BaF(2) exhibits, at all temperatures, a strong resemblance to that of high-density phases for which the observed spectroscopic features correlate linearly with the density. Surprisingly, the highly compressed, high-density thin-film liquid water is found to be stable from ambient (300 K) to supercooled (259 K) temperatures, although a lower-density liquid would be expected at supercooled conditions. Molecular dynamics simulations indicate that the first layer water on BaF(2)(111) is indeed in a unique local structure that resembles high-density water, with a strongly collapsed second coordination shell.

  View details for DOI 10.1038/srep01074

  View details for Web of Science ID 000313551300002

  View details for PubMedID 23323216

  View details for PubMedCentralID PMC3545261

• Effect of chloride on the dissolution rate and toxicity of silver nanoparticles to E. coli Environmental Science & Technology Levard, C., Mitra, S., Yang, T., Jew, A. D., Badireddy, A. R., Lowry, G. V., Brown, Jr., G. E. 2013; 47 (1): 5738-5745

  View details for DOI 10.102/es400396f

• A sequential chemical extraction and spectroscopic assessment of the potential bioavailability of mercury released from the inoperative New Idria Mercury Mine, San Benito, Co., CA Geochimica et Cosmochimica Acta Jew, A. D., Luong, P. M., Rytuba, J. J., Brown, Jr., G. E. 2013
• Structure and reactivity of As(III)- and As(V)-rich schwertmannites and ferric arsenate sulfate from the Carnoules acid mine drainage, France: Comparison with biotic and abiotic model compounds and implications for As remediation Geochimica et Cosmochimica Acta Maillot, F., Morin, G., Juillot, F., Buneel, O., Casiot, C., Ona-Nguema, G., Wang, Y., Lebrun, S., Aubrey, E., Vlaic, G., Brown, Jr., G. E. 2013; 104: 310-329
• Opportunities with Synchrotron Radiation at the Mesoscale Synchrotron Radiation News Bargar, J. R., Brown, Jr., G. E., Crabtree, G. W. 2013; 26 (4)
• Photoemission and DFT study of the reaction of water vapor with the Fe3O4 (100) surface at near-ambient conditions Journal of Physical Chemistry C Kendelewicz, T., Kaya, S., Newberg, J. E., Bluhm, H., Mulakluri, N., Mortitz, W., Scheffler, M., Nilsson, A., Pentcheva, R., Brown, Jr., G. E. 2013; 117: 2719-2733
• Ni speciation in a New Caledonian lateritic regolith: A quantitative X-ray absorption spectroscopy investigation GEOCHIMICA ET COSMOCHIMICA ACTA Dublet, G., Juillot, F., Morin, G., Fritsch, E., Fandeur, D., Ona-Nguema, G., Brown, G. E. 2012; 95: 119-133

  View details for DOI 10.1016/j.gca.2012.07.030

  View details for Web of Science ID 000309591500010

• MINERAL-AQUEOUS SOLUTION INTERFACES AND THEIR IMPACT ON THE ENVIRONMENT GEOCHEMICAL PERSPECTIVES Brown, G. E., Calas, G. 2012; 1 (4-5): 483-742

  View details for DOI 10.7185/geochempersp.1.4

  View details for Web of Science ID 000326942000001

• Properties of impurity-bearing ferrihydrite I. Effects of Al content and precipitation rate on the structure of 2-line ferrihydrite GEOCHIMICA ET COSMOCHIMICA ACTA Cismasu, A. C., Michel, F. M., Stebbins, J. F., Levard, C., Brown, G. E. 2012; 92: 275-291

  View details for DOI 10.1016/j.gca.2012.06.010

  View details for Web of Science ID 000307885900019

• Environmental Transformations of Silver Nanoparticles: Impact on Stability and Toxicity ENVIRONMENTAL SCIENCE & TECHNOLOGY Levard, C., Hotze, E. M., Lowry, G. V., Brown, G. E. 2012; 46 (13): 6900-6914

  Abstract

  Silver nanoparticles (Ag-NPs) readily transform in the environment, which modifies their properties and alters their transport, fate, and toxicity. It is essential to consider such transformations when assessing the potential environmental impact of Ag-NPs. This review discusses the major transformation processes of Ag-NPs in various aqueous environments, particularly transformations of the metallic Ag cores caused by reactions with (in)organic ligands, and the effects of such transformations on physical and chemical stability and toxicity. Thermodynamic arguments are used to predict what forms of oxidized silver will predominate in various environmental scenarios. Silver binds strongly to sulfur (both organic and inorganic) in natural systems (fresh and sea waters) as well as in wastewater treatment plants, where most Ag-NPs are expected to be concentrated and then released. Sulfidation of Ag-NPs results in a significant decrease in their toxicity due to the lower solubility of silver sulfide, potentially limiting their short-term environmental impact. This review also discusses some of the major unanswered questions about Ag-NPs, which, when answered, will improve predictions about their potential environmental impacts. Research needed to address these questions includes fundamental molecular-level studies of Ag-NPs and their transformation products, particularly Ag(2)S-NPs, in simplified model systems containing common (in)organic ligands, as well as under more realistic environmental conditions using microcosm/mesocosm-type experiments. Toxicology studies of Ag-NP transformation products, including different states of aggregation and sulfidation, are also required. In addition, there is the need to characterize the surface structures, compositions, and morphologies of Ag-NPs and Ag(2)S-NPs to the extent possible because they control properties such as solubility and reactivity.

  View details for DOI 10.1021/es2037405

  View details for Web of Science ID 000305876500003

  View details for PubMedID 22339502

• Sulfidation of Silver Nanoparticles Decreases Escherichia coli Growth Inhibition ENVIRONMENTAL SCIENCE & TECHNOLOGY Reinsch, B. C., Levard, C., Li, Z., Ma, R., Wise, A., Gregory, K. B., Brown, G. E., Lowry, G. V. 2012; 46 (13): 6992-7000

  Abstract

  Sulfidation of metallic nanoparticles such as silver nanoparticles (AgNPs) released to the environment may be an important detoxification mechanism. Two types of AgNPs-an engineered polydisperse and aggregated AgNP powder, and a laboratory-synthesized, relatively monodisperse AgNP aqueous dispersion-were studied. The particles were sulfidized to varying degrees and characterized to determine the effect of initial AgNP polydispersity and aggregation state on AgNP sulfidation, and then exposed to Escherichia coli to determine if the degree of sulfidation of pristine AgNPs affects growth inhibition of bacteria. The extent of sulfidation was found to depend on the HS(-)/Ag ratio. However, for the same reaction times, the more monodisperse particles were fully transformed to Ag(2)S, and the polydisperse, aggregated particles were not fully sulfidized, thus preserving the toxic potential of Ag(0) in the aggregates. A higher Ag(2)S:Ag(0) ratio in the sulfidized nanoparticles resulted in less growth inhibition of E. coli over 6 h of exposure. These results suggest that the initial properties of AgNPs can affect sulfidation products, which in turn affect microbial growth inhibition, and that these properties should be considered in assessing the environmental impact of AgNPs.

  View details for DOI 10.1021/es203732x

  View details for Web of Science ID 000305876500013

  View details for PubMedID 22296331

• An Early-Branching Microbialite Cyanobacterium Forms Intracellular Carbonates SCIENCE Couradeau, E., Benzerara, K., Gerard, E., Moreira, D., Bernard, S., Brown, G. E., Lopez-Garcia, P. 2012; 336 (6080): 459-462

  Abstract

  Cyanobacteria have affected major geochemical cycles (carbon, nitrogen, and oxygen) on Earth for billions of years. In particular, they have played a major role in the formation of calcium carbonates (i.e., calcification), which has been considered to be an extracellular process. We identified a cyanobacterium in modern microbialites in Lake Alchichica (Mexico) that forms intracellular amorphous calcium-magnesium-strontium-barium carbonate inclusions about 270 nanometers in average diameter, revealing an unexplored pathway for calcification. Phylogenetic analyses place this cyanobacterium within the deeply divergent order Gloeobacterales. The chemical composition and structure of the intracellular precipitates suggest some level of cellular control on the biomineralization process. This discovery expands the diversity of organisms capable of forming amorphous calcium carbonates.

  View details for DOI 10.1126/science.1216171

  View details for Web of Science ID 000303233400043

  View details for PubMedID 22539718

• X-ray Absorption Fine Structure Evidence for Amorphous Zinc Sulfide as a Major Zinc Species in Suspended Matter from the Seine River Downstream of Paris, Ile-de-France, France ENVIRONMENTAL SCIENCE & TECHNOLOGY Priadi, C., Le Pape, P., Morin, G., Ayrault, S., Maillot, F., Juillot, F., Hochreutener, R., Llorens, I., Testemale, D., Proux, O., Brown, G. E. 2012; 46 (7): 3712-3720

  Abstract

  Zinc is one of the most widespread trace metals (TMs) in Earth surface environments and is the most concentrated TM in the downstream section of the Seine River (France) due to significant anthropogenic input from the Paris conurbation. In order to better identify the sources and cycling processes of Zn in this River basin, we investigated seasonal and spatial variations of Zn speciation in suspended particulate matter (SPM) in the oxic water column of the Seine River from upstream to downstream of Paris using synchrotron-based extend X-ray absorption fine structure (EXAFS) spectroscopy at the Zn K-edge. First-neighbor contributions to the EXAFS were analyzed in SPM samples, dried and stored under a dry nitrogen atmosphere or under an ambient oxygenated atmosphere. We found a sulfur first coordination environment around Zn (in the form of amorphous zinc sulfide) in the raw SPM samples stored under dry nitrogen vs an oxygen first coordination environment around Zn in the samples stored in an oxygenated atmosphere. These findings are supported by scanning electron microscopy and energy dispersive X-ray spectrometry observations. Linear combination fitting of the EXAFS data for SPM samples, using a large set of EXAFS spectra of Zn model compounds, indicates dramatic changes in the Zn speciation from upstream to downstream of Paris, with amorphous ZnS particles becoming dominant dowstream. In contrast, Zn species associated with calcite (either adsorbed or incorporated in the structure) are dominant upstream. Other Zn species representing about half of the Zn pool in the SPM consist of Zn-sorbed on iron oxyhydroxides (ferrihydrite and goethite) and, to a lesser extent, Zn-Al layered double hydroxides, Zn incorporated in dioctahedral layers of clay minerals and Zn sorbed to amorphous silica. Our results highlight the importance of preserving the oxidation state in TM speciation studies when sampling suspended matter, even in an oxic water column.

  View details for DOI 10.1021/es2041652

  View details for Web of Science ID 000302850400018

  View details for PubMedID 22360369

• Morphological preservation of carbonaceous plant fossils in blueschist metamorphic rocks from New Zealand GEOBIOLOGY Galvez, M. E., Beyssac, O., Benzerara, K., Bernard, S., Menguy, N., Cox, S. C., Martinez, I., Johnston, M. R., Brown, G. E. 2012; 10 (2): 118-129

  Abstract

  Morphological and chemical evidence of ancient life is widespread in sedimentary rocks retrieved from shallow depths in the Earth's crust. Metamorphism is highly detrimental to the preservation of biological information in rocks, thus limiting the geological record in which traces of life might be found. Deformation and increasing pressure/temperature during deep burial may alter the morphology as well as the composition and structure of both the organic and mineral constituents of fossils. However, microspore fossils have been previously observed in intensely metamorphosed rocks. It has been suggested that their small size, and/or the nature of the polymer composing their wall, and/or the mineralogy of their surrounding matrix were key parameters explaining their exceptional preservation. Here, we describe the remarkable morphological preservation of plant macrofossils in blueschist metamorphic rocks from New Zealand containing lawsonite. Leaves and stems can be easily identified at the macroscale. At the microscale, polygonal structures with walls mineralized by micas within the leaf midribs and blades may derive from the original cellular ultrastructure or, alternatively, from the shrinkage during burial of the gelified remnants of the leaves in an abiotic process. Processes and important parameters involved in the remarkable preservation of these fossils during metamorphism are discussed. Despite the excellent morphological preservation, the initial biological polymers have been completely transformed to graphitic carbonaceous matter down to the nanometer scale. This occurrence demonstrates that plant macrofossils may experience major geodynamic processes such as metamorphism and exhumation involving deep changes and homogenization of their carbon chemistry and structure but still retain their morphology with remarkable integrity even if they are not shielded by any hard-mineralized concretion.

  View details for DOI 10.1111/j.1472-4669.2011.00316.x

  View details for Web of Science ID 000299941800002

  View details for PubMedID 22299653

• Size-Controlled Dissolution of Organic-Coated Silver Nanoparticles ENVIRONMENTAL SCIENCE & TECHNOLOGY Ma, R., Levard, C., Marinakos, S. M., Cheng, Y., Liu, J., Michel, F. M., Brown, G. E., Lowry, G. V. 2012; 46 (2): 752-759

  Abstract

  The solubility of Ag NPs can affect their toxicity and persistence in the environment. We measured the solubility of organic-coated silver nanoparticles (Ag NPs) having particle diameters ranging from 5 to 80 nm that were synthesized using various methods, and with different organic polymer coatings including poly(vinylpyrrolidone) and gum arabic. The size and morphology of Ag NPs were characterized by transmission electron microscopy (TEM). X-ray absorption fine structure (XAFS) spectroscopy and synchrotron-based total X-ray scattering and pair distribution function (PDF) analysis were used to determine the local structure around Ag and evaluate changes in crystal lattice parameters and structure as a function of NP size. Ag NP solubility dispersed in 1 mM NaHCO(3) at pH 8 was found to be well correlated with particle size based on the distribution of measured TEM sizes as predicted by the modified Kelvin equation. Solubility of Ag NPs was not affected by the synthesis method and coating as much as by their size. Based on the modified Kelvin equation, the surface tension of Ag NPs was found to be ∼1 J/m(2), which is expected for bulk fcc (face centered cubic) silver. Analysis of XAFS, X-ray scattering, and PDFs confirm that the lattice parameter, a, of the fcc crystal structure of Ag NPs did not change with particle size for Ag NPs as small as 6 nm, indicating the absence of lattice strain. These results are consistent with the finding that Ag NP solubility can be estimated based on TEM-derived particle size using the modified Kelvin equation for particles in the size range of 5-40 nm in diameter.

  View details for DOI 10.1021/es201686j

  View details for Web of Science ID 000299136200026

  View details for PubMedID 22142034

• Sulfidation decreases silver nanoparticle growth inhibition effect for Escherichia coli Environmental Science & Technology Reinsch, B. C., Levard, C. M., Li, Z., Ma, R., Wise, A., Gregory, K. B., Brown, Jr., G. E., Lowry, G. V. 2012; 46 (3): 6992-7000
• From Quanta to the Continuum: Opportunities for Mesoscale Science A Report for the Basic Energy Sciences Advisory Committee, Mesoscale Science Subcommittee Crabtree, G. W., Sarrao, J., Alivisatos, P., Barletta, W., Bates, F., Brown, Jr., G. E., French, R., Green, L., Hemminger, J., Kastner, M., Kay, B., Lewis, J., Ratner, M., Rollett, A., Rubloff, G., Spence, J., Tobias, D., Tranquada, J. U.S. Department of Energy. 2012
• Mineral-aqueous solution interfaces and their impact on the environment Geochemical Perspectives Brown, Jr., G. E., Calas, G. 2012; 1: 483-742
• EXAFS and SEM evidence for zinc sulfide solid phases in riverine suspended matter from the Seine River, France Environmental Science & Technology Priadi, C., Morin, G., Ayrault, S., Maillot, F., Juillot, F., Alliot, I., Testemale, D., Proux, O., Bonté, P., Brown, Jr., G. E. 2012; 46: 3712-3720
• Neutron Pair Distribution Function Study of Two-Line Ferrihydrite ENVIRONMENTAL SCIENCE & TECHNOLOGY Harrington, R., Hausner, D. B., Xu, W., Bhandari, N., Michel, F. M., Brown, G. E., Strongin, D. R., Parise, J. B. 2011; 45 (23): 9883-9890

  Abstract

  Pair distribution function (PDF) analysis of neutron total scattering data from deuterated two-line ferrihydrite is consistent with the Keggin-related structural model for ferrihydrite published by Michel et al. (2007). Other models proposed in the literature, such as that of Drits et al. (1993), lead to inferior fits. Bond valence sums indicate that O(1) is bonded to a hydrogen atom, but the quality of the data is such that the exact position of the hydrogen could not be elucidated with confidence.

  View details for DOI 10.1021/es2020633

  View details for Web of Science ID 000297382700012

  View details for PubMedID 21955257

• Probing Ag nanoparticle surface oxidation in contact with (in)organics: an X-ray scattering and fluorescence yield approach JOURNAL OF SYNCHROTRON RADIATION Levard, C., Michel, F. M., Wang, Y., Choi, Y., Eng, P., Brown, G. E. 2011; 18: 871-878

  Abstract

  Characterizing interfacial reactions is a crucial part of understanding the behavior of nanoparticles in nature and for unlocking their functional potential. Here, an advanced nanostructure characterization approach to study the corrosion processes of silver nanoparticles (Ag-Nps), currently the most highly produced nanoparticle for nanotechnology, is presented. Corrosion of Ag-Nps under aqueous conditions, in particular in the presence of organic matter and halide species common to many natural environments, is of particular importance because the release of toxic Ag(+) from oxidation/dissolution of Ag-Nps may strongly impact ecosystems. In this context, Ag-Nps capped with polyvinolpyrrolidone (PVP) in contact with a simple proxy of organic matter in natural waters [polyacrylic acid (PAA) and Cl(-) in solution] has been investigated. A combination of synchrotron-based X-ray standing-wave fluorescence yield- and X-ray diffraction-based experiments on a sample consisting of an approximately single-particle layer of Ag-Nps deposited on a silicon substrate and coated by a thin film of PAA containing Cl revealed the formation of a stable AgCl corrosion product despite the presence of potential surface stabilizers (PVP and PAA). Diffusion and precipitation processes at the Ag-Nps-PAA interface were characterized with a high spatial resolution using this new approach.

  View details for DOI 10.1107/S090904951103843X

  View details for Web of Science ID 000296736400006

  View details for PubMedID 21997911

• Molecular-level modes of As binding to Fe(III) (oxyhydr)oxides precipitated by the anaerobic nitrate-reducing Fe(II)-oxidizing Acidovorax sp strain BoFeN1 GEOCHIMICA ET COSMOCHIMICA ACTA Hohmann, C., Morin, G., Ona-Nguema, G., Guigner, J., Brown, G. E., Kappler, A. 2011; 75 (17): 4699-4712

  View details for DOI 10.1016/j.gca.2011.02.044

  View details for Web of Science ID 000293732500001

• Distinctive Arsenic(V) Trapping Modes by Magnetite Nanoparticles Induced by Different Sorption Processes ENVIRONMENTAL SCIENCE & TECHNOLOGY Wang, Y., Morin, G., Ona-Nguema, G., Juillot, F., Calas, G., Brown, G. E. 2011; 45 (17): 7258-7266

  Abstract

  Arsenic sorption onto iron oxide spinels such as magnetite may contribute to arsenic immobilization at redox fronts in soils, sediments, and aquifers, as well as in putative remediation and water treatment technologies. We have investigated As(V) speciation resulting from different sorption processes on magnetite nanoparticles, including both adsorption and precipitation, using X-ray absorption fine structure (XAFS) spectroscopy and transmission electron microscopy (TEM). XAFS results suggest that AsO(4) tetrahedra form predominantly inner-sphere bidentate corner-sharing ((2)C) complexes and outer-sphere complexes on magnetite in the adsorption experiments. In the precipitation experiments, an increasing fraction of AsO(4) tetrahedra appears to be incorporated in clusters having a magnetite-like local structure with increasing As loading, the remaining fraction of As being adsorbed at the surface of magnetite particles. In the sample with the highest As loading (15.7 μmol/m(2)) XAFS data indicate that As(V) is fully incorporated in such clusters. Such processes help to explain the significantly higher arsenic uptake in precipitation samples compared to those generated in adsorption experiments. In addition, for the precipitation samples, TEM observations indicate the formation of amorphous coatings and small (~3 nm) nanoparticles associated with larger (~20-40 nm) magnetite nanoparticles, which are absent in the adsorption samples. These results suggest that As(V) could form complexes at the surfaces of the small nanoparticles and could be progressively incorporated in their structure with increasing As loading. These results provide some of the fundamental knowledge about As(V)-magnetite interactions that is essential for developing effective water treatment technologies for arsenic.

  View details for DOI 10.1021/es200299f

  View details for Web of Science ID 000294373400025

  View details for PubMedID 21809819

• Autocatalytic Surface Hydroxylation of MgO(100) Terrace Sites Observed under Ambient Conditions JOURNAL OF PHYSICAL CHEMISTRY C Newberg, J. T., Starr, D. E., Yamamoto, S., Kaya, S., Kendelewicz, T., Mysak, E. R., Porsgaard, S., Salmeron, M. B., Brown, G. E., Nisson, A., Bluhm, H. 2011; 115 (26): 12864-12872

  View details for DOI 10.1021/jp200235v

  View details for Web of Science ID 000292281100024

• Study of the crystallographic architecture of corals at the nanoscale by scanning transmission X-ray microscopy and transmission electron microscopy ULTRAMICROSCOPY Benzerara, K., Menguy, N., Obst, M., Stolarski, J., Mazur, M., Tylisczak, T., Brown, G. E., Meibom, A. 2011; 111 (8): 1268-1275

  Abstract

  We have investigated the nanotexture and crystallographic orientation of aragonite in a coral skeleton using synchrotron-based scanning transmission X-ray microscopy (STXM) and transmission electron microscopy (TEM). Polarization-dependent STXM imaging at 40-nm spatial resolution was used to obtain an orientation map of the c-axis of aragonite on a focused ion beam milled ultrathin section of a Porites coral. This imaging showed that one of the basic units of coral skeletons, referred to as the center of calcification (COC), consists of a cluster of 100-nm aragonite globules crystallographically aligned over several micrometers with a fan-like distribution and with the properties of single crystals at the mesoscale. The remainder of the skeleton consists of aragonite single-crystal fibers in crystallographic continuity with the nanoglobules comprising the COC. Our observation provides information on the nm-scale processes that led to biomineral formation in this sample. Importantly, the present study illustrates how the methodology described here, which combines HRTEM and polarization-dependent synchrotron-based STXM imaging, offers an interesting new approach for investigating biomineralizing systems at the nm-scale.

  View details for DOI 10.1016/j.ultramic.2011.03.023

  View details for Web of Science ID 000300461100040

  View details for PubMedID 21864767

• Sulfidation Processes of PVP-Coated Silver Nanoparticles in Aqueous Solution: Impact on Dissolution Rate ENVIRONMENTAL SCIENCE & TECHNOLOGY Levard, C., Reinsch, B. C., Michel, F. M., Oumahi, C., Lowry, G. V., Brown, G. E. 2011; 45 (12): 5260-5266

  Abstract

  Despite the increasing use of silver nanoparticles (Ag-NPs) in nanotechnology and their toxicity to invertebrates, the transformations and fate of Ag-NPs in the environment are poorly understood. This work focuses on the sulfidation processes of PVP-coated Ag-NPs, one of the most likely corrosion phenomena that may happen in the environment. The sulfur to Ag-NPs ratio was varied in order to control the extent of Ag-NPs transformation to silver sulfide (Ag₂S). A combination of synchrotron-based X-ray Diffraction (XRD) and Extended X-ray Absorption Fine Structure spectroscopy shows the increasing formation of Ag₂S with an increasing sulfur to Ag-NPs ratio. TEM observations show that Ag₂S forms nanobridges between the Ag-NPs leading to chain-like structures. In addition, sulfidation strongly affects surface properties of the Ag-NPs in terms of surface charge and dissolution rate. Both may affect the reactivity, transport, and toxicity of Ag-NPs in soils. In particular, the decrease of dissolution rate as a function of sulfide exposure may strongly limit Ag-NPs toxicity since released Ag⁺ ions are known to be a major factor in the toxicity of Ag-NPs.

  View details for DOI 10.1021/es2007758

  View details for Web of Science ID 000291422200030

  View details for PubMedID 21598969

• Characterization of the Active Bacterial Community Involved in Natural Attenuation Processes in Arsenic-Rich Creek Sediments MICROBIAL ECOLOGY Bruneel, O., Volant, A., Gallien, S., Chaumande, B., Casiot, C., Carapito, C., Bardil, A., Morin, G., Brown, G. E., Personne, C. J., Le Paslier, D., Schaeffer, C., Van Dorsselaer, A., Bertin, P. N., Elbaz-Poulichet, F., Arsene-Ploetze, F. 2011; 61 (4): 793-810

  Abstract

  Acid mine drainage of the Carnoulès mine (France) is characterized by acid waters containing high concentrations of arsenic and iron. In the first 30 m along the Reigous, a small creek draining the site, more than 38% of the dissolved arsenic was removed by co-precipitation with Fe(III), in agreement with previous studies, which suggest a role of microbial activities in the co-precipitation of As(III) and As(V) with Fe(III) and sulfate. To investigate how this particular ecosystem functions, the bacterial community was characterized in water and sediments by 16S rRNA encoding gene library analysis. Based on the results obtained using a metaproteomic approach on sediments combined with high-sensitivity HPLC-chip spectrometry, several GroEL orthologs expressed by the community were characterized, and the active members of the prokaryotic community inhabiting the creek sediments were identified. Many of these bacteria are β-proteobacteria such as Gallionella and Thiomonas, but γ-proteobacteria such as Acidithiobacillus ferrooxidans and α-proteobacteria such as Acidiphilium, Actinobacteria, and Firmicutes were also detected.

  View details for DOI 10.1007/s00248-011-9808-9

  View details for Web of Science ID 000290811600008

  View details for PubMedID 21318282

• Contrasting isotopic signatures between anthropogenic and geogenic Zn and evidence for post-depositional fractionation processes in smelter-impacted soils from Northern France GEOCHIMICA ET COSMOCHIMICA ACTA Juillot, F., Marechal, C., Morin, G., Jouvin, D., Cacaly, S., Telouk, P., Benedetti, M. F., Ildefonse, P., Sutton, S., Guyot, F., Brown, G. E. 2011; 75 (9): 2295-2308

  View details for DOI 10.1016/j.gca.2011.02.004

  View details for Web of Science ID 000293033300004

• Density functional theory investigation of the interaction of water with alpha-Al2O3 and alpha-Fe2O3 (1(1)over-bar02) surfaces: Implications for surface reactivity PHYSICAL REVIEW B Aboud, S., Wilcox, J., Brown, G. E. 2011; 83 (12)

  View details for DOI 10.1103/PhysRevB.83.125407

  View details for Web of Science ID 000288511400005

• Composition and structural aspects of naturally occurring ferrihydrite COMPTES RENDUS GEOSCIENCE Cismasu, A. C., Michel, F. M., Tcaciuc, A. P., Tyliszczak, T., Brown, G. E. 2011; 343 (2-3): 210-218

  View details for DOI 10.1016/j.crte.2010.11.001

  View details for Web of Science ID 000289880800011

• Environmental mineralogy - Understanding element behavior in ecosystems COMPTES RENDUS GEOSCIENCE Brown, G. E., Calas, G. 2011; 343 (2-3): 90-112

  View details for DOI 10.1016/j.crte.2010.12.005

  View details for Web of Science ID 000289880800002

• Environmental mineralogy COMPTES RENDUS GEOSCIENCE Calas, G., Brown, G. E. 2011; 343 (2-3): 83-89

  View details for DOI 10.1016/j.crte.2010.12.003

  View details for Web of Science ID 000289880800001

• New Technique for Quantification of Elemental Hg in Mine Wastes and Its Implications for Mercury Evasion Into the Atmosphere ENVIRONMENTAL SCIENCE & TECHNOLOGY Jew, A. D., Kim, C. S., Rytuba, J. J., Gustin, M. S., Brown, G. E. 2011; 45 (2): 412-417

  Abstract

  Mercury in the environment is of prime concern to both ecosystem and human health. Determination of the molecular-level speciation of Hg in soils and mine wastes is important for understanding its sequestration, mobility, and availability for methylation. Extended X-ray absorption fine structure (EXAFS) spectroscopy carried out under ambient P-T conditions has been used in a number of past studies to determine Hg speciation in complex mine wastes and associated soils. However, this approach cannot detect elemental (liquid) mercury in Hg-polluted soils and sediments due to the significant structural disorder of liquid Hg at ambient-temperature. A new sample preparation protocol involving slow cooling through the crystallization temperature of Hg(0) (234 K) results in its transformation to crystalline α-Hg(0). The presence and proportion of Hg(0), relative to other crystalline Hg-bearing phases, in samples prepared in this way can be quantified by low-temperature (77 K) EXAFS spectroscopy. Using this approach, we have determined the relative concentrations of liquid Hg(0) in Hg mine wastes from several sites in the California Coast Range and have found that they correlate well with measured fluxes of gaseous Hg released during light and dark exposure of the same samples, with higher evasion ratios from samples containing higher concentrations of liquid Hg(0). Two different linear relationships are observed in plots of the ratio of Hg emission under light and dark conditions vs % Hg(0), corresponding to silica-carbonate- and hot springs-type Hg deposits, with the hot springs-type samples exhibiting higher evasion fluxes than silica-carbonate type samples at similar Hg(0) concentrations. Our findings help explain significant differences in Hg evasion data for different mine sites in the California Coast Range.

  View details for DOI 10.1021/es1023527

  View details for Web of Science ID 000286090500014

  View details for PubMedID 21121657

  View details for PubMedCentralID PMC3030447

• Nanomaterials and the Environment: The Chemistry and Materials Perspective NSF-Chemistry Workshop on Nanomaterials and the Environment: The Chemistry and Materials Perspective Grassian, V., Hamers, R., Brown, Jr., G. E., Fairbrother, H., Johnston, M., Penn, R. L. 2011
• Water reaction with MgO(100) probed by ambient pressure XPS Journal of Physical Chemistry C Newberg, J. T., Starr, D. E., Posgaard, S., Yamamoto, S., Kaya, S., Kendelewicz, T., Mysak, E., Salmeron, M. B., Nilsson, A., Brown, Jr., G. E., Bluhm, H. 2011; 115: 12864-12872
• Evidence for contrasted isotopic signatures between anthropogenic and natural Zn in smelter-impacted soils from Northern France Geochimica et Cosmochimica Acta Juillot, F., Maréchal, C., Morin, G., Jouvin, D., Cacaly, S., Telouk, P., Benedetti, M. F., Ildefonse, P., Sutton, S., Guyot, F., Brown, Jr., G. E. 2011; 75: 2295-2308
• Formation of hydroxyl and water layers on MgO films studied with ambient pressure XPS SURFACE SCIENCE Newberg, J. T., Starr, D. E., Yamamoto, S., Kaya, S., Kendelewicz, T., Mysak, E. R., Porsgaard, S., Salmeron, M. B., Brown, G. E., Nilsson, A., Bluhm, H. 2011; 605 (1-2): 89-94

  View details for DOI 10.1016/j.susc.2010.10.004

  View details for Web of Science ID 000286021000013

• Multiscale characterization of pyritized plant tissues in blueschist facies metamorphic rocks GEOCHIMICA ET COSMOCHIMICA ACTA Bernard, S., Benzerara, K., Beyssac, O., Brown, G. E. 2010; 74 (17): 5054-5068

  View details for DOI 10.1016/j.gca.2010.06.011

  View details for Web of Science ID 000280751400011

• XANES, Raman and XRD study of anthracene-based cokes and saccharose-based chars submitted to high-temperature pyrolysis CARBON Bernard, S., Beyssac, O., Benzerara, K., Findling, N., Tzvetkov, G., Brown, G. E. 2010; 48 (9): 2506-2516

  View details for DOI 10.1016/j.carbon.2010.03.024

  View details for Web of Science ID 000278585400016

• XANES Evidence for Rapid Arsenic(III) Oxidation at Magnetite and Ferrihydrite Surfaces by Dissolved O-2 via Fe2+-Mediated Reactions ENVIRONMENTAL SCIENCE & TECHNOLOGY Ona-Nguema, G., Morin, G., Wang, Y., Foster, A. L., Juillot, F., Calas, G., Brown, G. E. 2010; 44 (14): 5416-5422

  Abstract

  To reduce the adverse effects of arsenic on humans, various technologies are used to remove arsenic from groundwater, most relying on As adsorption on Fe-(oxyhydr)oxides and concomitant oxidation of As(III) by dissolved O(2). This reaction can be catalyzed by microbial activity or by strongly oxidizing radical species known to form upon oxidation of Fe(II) by dissolved O(2). Such catalyzed oxidation reactions have been invoked to explain the enhanced kinetics of As(III) oxidation in aerated water, in the presence of zerovalent iron or dissolved Fe(II). In the present study, we used arsenic K-edge X-ray absorption near edge structure (XANES) spectroscopy to investigate the role of Fe(II) in the oxidation of As(III) at the surface of magnetite and ferrihydrite under oxygenated conditions. Our results show rapid oxidation of As(III) to As(V) upon sorption onto magnetite under oxic conditions at neutral pH. Moreover, under similar oxic conditions, As(III) oxidized upon sorption onto ferrihydrite only after addition of Fe(II)(aq) within the investigated time frame of 24 h. These results confirm that Fe(II) is able to catalyze As(III) oxidation in the presence of dissolved O(2) and suggest that oxidation of As(III) upon sorption on magnetite under oxic conditions can be explained by an Fe(2+)-mediated Fenton-like reactions. Thus, the present study shows that magnetite might be an efficient alternative to the current use of oxidants and Fe(II) to remove As from aerated water. In addition, this study emphasizes that special care is needed to preserve arsenic oxidation state during laboratory sorption experiments as well as in collecting As-bearing samples from natural environments.

  View details for DOI 10.1021/es1000616

  View details for Web of Science ID 000279747100020

  View details for PubMedID 20666402

• Presentation of the Mineralogical Society of America Award for 2009 Thomas Patrick Trainor AMERICAN MINERALOGIST Brown, G. E. 2010; 95 (4): 662-663

  View details for DOI 10.2138/am.2010.559

  View details for Web of Science ID 000276269900032

• Ordered ferrimagnetic form of ferrihydrite reveals links among structure, composition, and magnetism PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA Michel, F. M., Barron, V., Torrent, J., Morales, M. P., Serna, C. J., Boily, J., Liu, Q., Ambrosini, A., Cismasu, A. C., Brown, G. E. 2010; 107 (7): 2787-2792

  Abstract

  The natural nanomineral ferrihydrite is an important component of many environmental and soil systems and has been implicated as the inorganic core of ferritin in biological systems. Knowledge of its basic structure, composition, and extent of structural disorder is essential for understanding its reactivity, stability, and magnetic behavior, as well as changes in these properties during aging. Here we investigate compositional, structural, and magnetic changes that occur upon aging of "2-line" ferrihydrite in the presence of adsorbed citrate at elevated temperature. Whereas aging under these conditions ultimately results in the formation of hematite, analysis of the atomic pair distribution function and complementary physicochemical and magnetic data indicate formation of an intermediate ferrihydrite phase of larger particle size with few defects, more structural relaxation and electron spin ordering, and pronounced ferrimagnetism relative to its disordered ferrihydrite precursor. Our results represent an important conceptual advance in understanding the nature of structural disorder in ferrihydrite and its relation to the magnetic structure and also serve to validate a controversial, recently proposed structural model for this phase. In addition, the pathway we identify for forming ferrimagnetic ferrihydrite potentially explains the magnetic enhancement that typically precedes formation of hematite in aerobic soil and weathering environments. Such magnetic enhancement has been attributed to the formation of poorly understood, nano-sized ferrimagnets from a ferrihydrite precursor. Whereas elevated temperatures drive the transformation on timescales feasible for laboratory studies, our results also suggest that ferrimagnetic ferrihydrite could form naturally at ambient temperature given sufficient time.

  View details for DOI 10.1073/pnas.0910170107

  View details for Web of Science ID 000274599500017

  View details for PubMedID 20133643

  View details for PubMedCentralID PMC2840321

• Water Adsorption on alpha-Fe2O3(0001) at near Ambient Conditions JOURNAL OF PHYSICAL CHEMISTRY C Yamamoto, S., Kendelewicz, T., Newberg, J. T., Ketteler, G., Starr, D. E., Mysak, E. R., Andersson, K. J., Ogasawara, H., Bluhm, H., Salmeron, M., Brown, G. E., Nilsson, A. 2010; 114 (5): 2256-2266

  View details for DOI 10.1021/jp909876t

  View details for Web of Science ID 000274269700040

• Role of extracellular polymeric substances in metal ion complexation on Shewanella oneidensis: Batch uptake, thermodynamic modeling, ATR-FTIR, and EXAFS study GEOCHIMICA ET COSMOCHIMICA ACTA Ha, J., Gelabert, A., Spormann, A. M., Brown, G. E. 2010; 74 (1): 1-15

  View details for DOI 10.1016/j.gca.2009.06.031

  View details for Web of Science ID 000273109700001

• Nanotextures of aragonite in stromatolites from the quasi-marine Satonda crater lake, Indonesia Tufas and Speleothems: Unraveling the Microbial and Physical Controls Benzerara, K., Meibom, A., Gautier, Q., Kazmierczak, J., Stolarski, J., Lopez-Garcia, P., Menguy, N., Brown, Jr., G. E. edited by Pedley, H. M., Rogerson, M. Geological Society of London. 2010: 211–224
• Extended x-ray absorption fine structure analysis of arsenite and arsenate adsorption on green rust Environmental Science & Technology Wang, Y., Morin, G., Ona-Nguema, G., Juillot, F., Guyot, F., Calas, G., Brown, Jr., G. E. 2010; 44: 109-115
• Evidence for Different Surface Speciation of Arsenite and Arsenate on Green Rust: An EXAFS and XANES Study ENVIRONMENTAL SCIENCE & TECHNOLOGY Wang, Y., Morin, G., Ona-Nguema, G., Juillot, F., Guyot, F., Calas, G., Brown, G. E. 2010; 44 (1): 109-115

  Abstract

  The knowledge of arsenic speciation at the surface of green rusts (GRs), [Fe(II)((1-x))Fe(III)(x) (OH)(2)](x+) (CO(3), Cl, SO(4))(x-), is environmentally relevant because arsenic sorption onto GRs could contribute to arsenic retention in anoxic environments (hydromorphic soils, marine sediments, etc.). The nature of arsenic adsorption complexes on hydroxychloride green rust 1 (GR1Cl) at near-neutral pH under anoxic conditions was investigated using extended X-ray absorption fine structure (EXAFS) spectroscopy at the As K-edge. Sorption data indicate that As(V) sorbs more efficiently than As(III) at the studied As loadings (0.27 micromol m(-2) and 2.7 micromol m(-2)). EXAFS results indicate that arsenite [As(III)] and arsenate [As(V)] form inner-sphere complexes on the surface of GR1Cl at arsenic surface coverages of 0.27 and 2.70 micromol m(-2), with distinct types of As(III) and As(V) sorption complexes, which change in relative concentration as a function of arsenic loading. For As(V), the EXAFS-derived As-Fe distances (3.34 +/- 0.02 and 3.49 +/- 0.02 A) suggest the presence of binuclear bidentate double-corner complexes ((2)C) and monodentate mononuclear corner-sharing complexes ((1)V). For As(III), EXAFS-derived As-As distance (3.32 +/- 0.02 A) and As-Fe distances (3.49 +/- 0.02 and 4.72 +/- 0.02 A) are consistent with the presence of dimers of As(III) pyramids binding to the edges of the GR1Cl layers by corner sharing with FeO(6) octahedra. However, (2)C and (1)V As(III) complexes cannot be excluded. These results improve our knowledge of the mode of As(V) and As(III) inner-sphere adsorption on green rusts, which will help to constrain sorption modeling of arsenic in soils, sediments, and aquifers.

  View details for DOI 10.1021/es901627e

  View details for Web of Science ID 000273267000022

  View details for PubMedID 20039740

• Organic matter heterogeneities in 2.72 Ga stromatolites: Alteration versus preservation by sulfur incorporation GEOCHIMICA ET COSMOCHIMICA ACTA Lepot, K., Benzerara, K., Rividi, N., Cotte, M., Brown, G. E., Philippot, P. 2009; 73 (21): 6579-6599

  View details for DOI 10.1016/j.gca.2009.08.014

  View details for Web of Science ID 000273416600009

• Uranyl-chlorite sorption/desorption: Evaluation of different U(VI) sequestration processes GEOCHIMICA ET COSMOCHIMICA ACTA Singer, D. M., Maher, K., Brown, G. E. 2009; 73 (20): 5989-6007

  View details for DOI 10.1016/j.gca.2009.07.002

  View details for Web of Science ID 000273416500003

• XANES Evidence for Oxidation of Cr(III)) to Cr(VI) by Mn-Oxides in a Lateritic Regolith Developed on Serpentinized Ultramafic Rocks of New Caledonia ENVIRONMENTAL SCIENCE & TECHNOLOGY Fandeur, D., Juillot, F., Morin, G., Olivi, L., Cognigni, A., Webb, S. M., Ambrosi, J., Fritsch, E., Guyot, F., Brown, G. E. 2009; 43 (19): 7384-7390

  Abstract

  Although several laboratory studies showed that Mn-oxides are capable of oxidizing Cr(II) to Cr(VI), very few have reported evidence for such a reaction in natural systems. This study presents new evidence for this redox reaction between Cr(III) and Mn-oxides in a lateritic regolith developed on ultramafic rocks in New Caledonia. The studied lateritic regolith presents several units with contrasting amounts of major (Fe, Al, Si, and Mg) and trace (Mn, Cr, Ni, Co) elements, which are related to varying mineralogical compositions. Bulk XANES analyses show the occurrence of Cr(VI) (up to 20 wt % of total chromium) in the unit of the regolith which is also enriched in Mn (up to 21.7 wt % MnO), whereas almost no Cr(VI) is detected elsewhere. X-ray powder diffraction indicates that the large amounts of Mn in this unit of the regolith are due to the occurrence of Mn-oxides (identified as a mixture of asbolane, lithiophorite and birnessite) and Mn K-edge XANES data indicate that Mn occurs mainly as Mn(IV) in this unit, although small amounts of Mn(III) could also be detected. These results strongly suggest a direct role of the Mn-oxides on the occurrence of Cr(VI) through a redox reaction between Cr(III) and Mn(IV) and/or Mn(III). Owing to the much larger toxicity and solubility of Cr(VI), such a co-occurrence of Cr and Mn-oxides in these soils could then represent an important risk for the environment. However, the significant amounts of Cr(VI) released after reacting the samples from the studied sequence with a 0.1 M (NH)4H2PO4 solution, designed to remove tightly sorbed chromate species, suggest that Cr(VI) mainly occurs as sorption complexes. This hypothesis is reinforced by spatially resolved XANES analyses, which show that Cr(VI) is associated with both Mn- and Fe-oxides, and especially at the boundary between these two mineral species. Such a distribution of Cr(VI) suggests a possible readsorption of Cr(VI) onto surrounding Fe-oxyhydroxides (mainly goethite) after oxidation by the Mn(IV)-oxides. These results, added to leaching tests with a 0.01 M CaCl2 solution indicative of low exchangeability of Cr in the investigated samples, suggest that secondary sorption reactions onto Fe-oxides might significantly decrease the environmental impact of the oxidation of Cr(III) to Cr(VI) by Mn-oxides.

  View details for DOI 10.1021/es900498r

  View details for Web of Science ID 000270136500038

  View details for PubMedID 19848150

• EXAFS and HRTEM Evidence for As(III)-Containing Surface Precipitates on Nanocrystalline Magnetite: Implications for As Sequestration LANGMUIR Morin, G., Wang, Y., Ona-Nguema, G., Juillot, F., Calas, G., Menguy, N., Aubry, E., Bargar, J. R., Brown, G. E. 2009; 25 (16): 9119-9128

  Abstract

  Arsenic sorption onto iron oxide spinels such as magnetite could contribute to immobilization of arsenite (AsO3(3-)), the reduced, highly toxic form of arsenic in contaminated anoxic groundwaters, as well as to putative remediation processes. Nanocrystalline magnetite (<20 nm) is known to exhibit higher efficiency for arsenite sorption than larger particles, sorbing as much as approximately 20 micromol/m2 of arsenite. To improve our understanding of this process, we investigated the molecular level structure of As(III)-containing sorption products on two types of fine-grained magnetite: (1) a biogenic one with an average particle diameter of 34 nm produced by reduction of lepidocrocite (gamma-FeOOH) by Shewanella putrefaciens and (2) a synthetic, abiotic, nanocrystalline magnetite with an average particle diameter of 11 nm. Results from extended X-ray absorption spectroscopy (EXAFS) for both types of magnetite with As(III) surface coverages of up to 5 micromol/m2 indicate that As(III) forms dominantly inner-sphere, tridentate, hexanuclear, corner-sharing surface complexes (3C) in which AsO3 pyramids occupy vacant tetrahedral sites on octahedrally terminated {111} surfaces of magnetite. Formation of this type of surface complex results in a decrease in dissolved As(III) concentration below the maximum concentration level recommended by the World Health Organization (10 microg/L), which corresponds to As(III) surface coverages of 0.16 and 0.19 micromol/m2 in our experiments. In addition, high-resolution transmission electron microscopy (HRTEM) coupled with energy dispersive X-ray spectroscopy (EDXS) analyses revealed the occurrence of an amorphous As(III)-rich surface precipitate forming at As(III) surface coverages as low as 1.61 micromol/m2. This phase hosts the majority of adsorbed arsenite at surface coverages exceeding the theoretical maximum site density of vacant tetrahedral sites on the magnetite {111} surface (3.2 sites/nm2 or 5.3 micromol/m2). This finding helps to explain the exceptional As(III) sorption capacity of nanocrystalline magnetite particles (>10 micromol/m2). However, the higher solubility of the amorphous surface precipitate compared to the 3C surface complexes causes a dramatic increase of dissolved As concentration for coverages above 1.9 micromol/m2.

  View details for DOI 10.1021/la900655v

  View details for Web of Science ID 000268719900046

  View details for PubMedID 19601563

• Cation field strength effects on high pressure aluminosilicate glass structure: Multinuclear NMR and La XAFS results GEOCHIMICA ET COSMOCHIMICA ACTA Kelsey, K. E., Stebbins, J. F., Singer, D. M., Brown, G. E., Mosenfelder, J. L., Asimow, P. D. 2009; 73 (13): 3914-3933

  View details for DOI 10.1016/j.gca.2009.03.040

  View details for Web of Science ID 000267229800014

• Ultrastructural and chemical study of modern and fossil sporoderms by Scanning Transmission X-ray Microscopy (STXM) REVIEW OF PALAEOBOTANY AND PALYNOLOGY Bernard, S., Benzerara, K., Beyssac, O., Brown, G. E., Stamm, L. G., Duringer, P. 2009; 156 (1-2): 248-261

  View details for DOI 10.1016/j.revpalbo.2008.09.002

  View details for Web of Science ID 000267570500022

• Biogenic nanoparticulate UO2: Synthesis, characterization, and factors affecting surface reactivity GEOCHIMICA ET COSMOCHIMICA ACTA Singer, D. M., Farges, F., Brown, G. E. 2009; 73 (12): 3593-3611

  View details for DOI 10.1016/j.gca.2009.03.031

  View details for Web of Science ID 000266455400006

• Arsenic(III) polymerization upon sorption on iron(II,III)-(hydr)oxides surfaces: Implications for arsenic mobility under reducing conditions 19th Annual VM Goldschmidt Conference Morin, G., Ona-Nguema, G., Wang, Y., Juillot, F., Menguy, N., CALAS, G., Brown, G. E. PERGAMON-ELSEVIER SCIENCE LTD. 2009: A906–A906

  View details for Web of Science ID 000267229902272

• Photoemission study of the reaction of Fe3O4(100) with water at near ambient conditions 19th Annual VM Goldschmidt Conference Kendelewicz, T., Kaya, S., Newberg, J., Bluhm, H., Nilsson, A., Brown, G. E., Pentcheva, R., Moritz, W. PERGAMON-ELSEVIER SCIENCE LTD. 2009: A638–A638

  View details for Web of Science ID 000267229901508

• Study of mineral-microbe assemblages down to the nm-scale in carbonate microbialites 19th Annual VM Goldschmidt Conference Benzerara, K., Meibom, A., Lopez-Garcia, P., Kazmierczak, J., Brown, G. E. PERGAMON-ELSEVIER SCIENCE LTD. 2009: A110–A110

  View details for Web of Science ID 000267229900233

• Iron biomineralization by neutrophilic nitrate-reducing iron-oxidizing bacteria 19th Annual VM Goldschmidt Conference Miot, J., Benzerara, K., Morin, G., Kappler, A., Obst, M., Brown, G. E., Guyot, F. PERGAMON-ELSEVIER SCIENCE LTD. 2009: A884–A884

  View details for Web of Science ID 000267229902228

• Interaction of Zn(II) with Hematite Nanoparticles and Microparticles: Part 2. ATR-FTIR and EXAFS Study of the Aqueous Zn(II)/Oxalate/Hematite Ternary System LANGMUIR Ha, J., Trainor, T. P., Farges, F., Brown, G. E. 2009; 25 (10): 5586-5593

  Abstract

  Sorption of Zn(II) to hematite nanoparticles (HN) (av diam=10.5 nm) and microparticles (HM) (av diam=550 nm) was studied in the presence of oxalate anions (Ox2-(aq)) in aqueous solutions as a function of total Zn(II)(aq) to total Ox2-(aq) concentration ratio (R=[Zn(II)(aq)]tot/[Ox2-(aq)]tot) at pH 5.5. Zn(II) uptake is similar in extent for both the Zn(II)/Ox/HN and Zn(II)/Ox/HM ternary systems and the Zn(II)/HN binary system at [Zn(II)(aq)](tot)<4 mM, whereas it is 50-100% higher for the Zn(II)/Ox/HN system than for the Zn(II)/Ox/HM ternary and the Zn(II)/HN and Zn(II)/HM binary systems at [Zn(II)(aq)]tot>4 mM. In contrast, Zn(II) uptake for the Zn(II)/HM binary system is a factor of 2 greater than that for the Zn(II)/Ox/HM and Zn(II)/Ox/HN ternary systems and the Zn(II)/HN binary system at [Zn(II)(aq)]tot<4 mM. In the Zn(II)/Ox/HM ternary system at both R values examined (0.16 and 0.68), attenuated total reflectance Fourier transform infrared (ATR-FTIR) results are consistent with the presence of inner-sphere oxalate complexes and outer-sphere ZnOx(aq) complexes, and/or type A ternary complexes. In addition, extended X-ray absorption fine structure (EXAFS) spectroscopic results suggest that type A ternary surface complexes (i.e., >O2-Zn-Ox) are present. In the Zn(II)/Ox/HN ternary system at R=0.15, ATR-FTIR results indicate the presence of inner-sphere oxalate and outer-sphere ZnOx(aq) complexes; the EXAFS results provide no evidence for inner-sphere Zn(II) complexes or type A ternary complexes. In contrast, ATR-FTIR results for the Zn/Ox/HN sample with R = 0.68 are consistent with a ZnOx(s)-like surface precipitate and possibly type B ternary surface complexes (i.e., >O2-Ox-Zn). EXAFS results are also consistent with the presence of ZnOx(s)-like precipitates. We ascribe the observed increase of Zn(II)(aq) uptake in the Zn(II)/Ox/HN ternary system at [Zn(II)(aq)]tot>or=4 mM relative to the Zn(II)/Ox/HM ternary system to formation of a ZnOx(s)-like precipitate at the hematite nanoparticle/water interface.

  View details for DOI 10.1021/la802895a

  View details for Web of Science ID 000266081000026

  View details for PubMedID 19326938

• Interaction of Aqueous Zn(II) with Hematite Nanoparticles and Microparticles. Part 1. EXAFS Study of Zn(II) Adsorption and Precipitation LANGMUIR Ha, J., Trainor, T. P., Farges, F., Brown, G. E. 2009; 25 (10): 5574-5585

  Abstract

  Sorption of Zn(II)(aq) on hematite (alpha-Fe2O3) nanoparticles (average diameter 10.5 nm) and microparticles (average diameter 550 nm) has been examined over a range of total Zn(II)(aq) concentrations (0.4-7.6 mM) using Zn K-edge EXAFS spectroscopy and selective chemical extractions. When ZnCl2 aqueous solutions were reacted with hematite nanoparticles (HN) at pH 5.5, Zn(II) formed a mixture of four- and six-coordinated surface complexes [Zn(O,OH)4 and Zn(O,OH)6] with an average Zn-O distance of 2.04+/-0.02 A at low sorption densities (Gammaor=3.38 micromol/m2), we observed the formation of Zn(O,OH)6 surface complexes, with an average Zn-O distance of 2.09+/-0.02 A, a Zn-Zn distance of 3.16+/-0.02 A, and a linear multiple-scattering feature at 6.12+/-0.06 A. Formation of a Zn(OH)2(am) precipitate for the higher sorption density samples (Gamma>or=3.38 micromol/m2) is suggested on the basis of comparison of the EXAFS spectra of the sorption samples with that of synthetic Zn(OH)2am. In contrast, EXAFS spectra of Zn(II) sorbed on hematite microparticles (HM) under similar experimental conditions showed no evidence of surface precipitates even at the same total [Zn(II)(aq)] that resulted in precipitate formation in the nanoparticle system. Instead, Zn(O,OH)6 octahedra (d(Zn-O)=2.10+/-0.02 A) were found to sorb dominantly in an inner-sphere, bidentate, edge-sharing fashion on Fe3+(O,OH)6 octahedra at hematite microparticle surfaces, based on an EXAFS-derived Zn-Fe3+ distance of 3.44+/-0.02 A. CaCl2 selective extraction experiments showed that 10-15% of the sorbed Zn(II) was released from Zn/HN sorption samples, and about 40% was released from a Zn/HM sorption sample. These fractions of Zn(II) are interpreted as weakly bound, outer-sphere adsorption complexes. The combined EXAFS and selective chemical extraction results indicate that (1) both Zn(O,OH)4 and Zn(O,OH)6 adsorption complexes are present in the Zn/HN system, whereas dominantly Zn(O,OH)6 adsorption complexes are present in the Zn/HM system; (2) a higher proportion of outer-sphere Zn(II) surface complexes is present in the Zn/HM system; and (3) Zn-containing precipitates similar to Zn(OH)2(am) form in the nanoparticle system but not in the microparticle system, suggesting a difference in reactivity of the hematite nanoparticles vs microparticles with respect to Zn(II)(aq).

  View details for DOI 10.1021/la8028947

  View details for Web of Science ID 000266081000025

  View details for PubMedID 19371051

• Speciation of Arsenic in Euglena gracilis Cells Exposed to As(V) ENVIRONMENTAL SCIENCE & TECHNOLOGY Miot, J., Morin, G., Skouri-Panet, F., Ferard, C., Poitevin, A., Aubry, E., Ona-Nguema, G., Juillot, F., Guyot, F., Brown, G. E. 2009; 43 (9): 3315-3321

  Abstract

  Euglena gracilis is a photosynthetic eukaryote ubiquitous in arsenic-polluted acid mine drainages and is locally exposed to As(III) and As(V) concentrations up to 250 and 100 mg L(-1), respectively. Here, arsenic speciation in E. graciliswas determined by X-ray absorption spectroscopy and selected (bio)chemical methods on cells grown at nonlimiting phosphate concentrations. Our results suggest the following detoxification scheme: (1) uptake of As(V) from solution in competition with phosphate, (2) intracellular reduction to As(III), (3) complexation by cytoplasmic proteic thiol ligands of low molecular weight, and (4) As(III) export from the cell. However, at As(V) concentrations >100 mg L(-1), growth rate is markedly lowered and As(V) remains mostly unreduced during the extended lag period. Intracellular As(V) is found to be exclusively concentrated in the membrane + nucleus fraction, suggesting that arsenate could substitute for phosphate groups in membranes or in phosphate-containing macromolecules. Thus, arsenic species are partitioned, with As(III)-thiol compounds concentrated in the cytoplasmic proteic pool and As(V)-compounds associated with the membrane + nucleus fraction. The increasing growth delay observed with increasing initial As(V) concentration in the culture medium is proposed to result from the combination of a higher As(V) uptake and limiting intracellular As(V) reduction rate and As(III) export rate. Under high As(V) exposure conditions (200 mg L(-1)) the reduction step is found to be the most limiting step for detoxification.

  View details for DOI 10.1021/es802833s

  View details for Web of Science ID 000265781100056

  View details for PubMedID 19534152

• Uranyl-chlorite sorption/desorption: Evaluation of different U(VI) sequestration processes Singer, D. M., Maher, K., Brown, G. E. AMER CHEMICAL SOC. 2009

  View details for Web of Science ID 000207857804384

• Arsenite sequestration at the surface of nano-Fe(OH)(2), ferrous-carbonate hydroxide, and green-rust after bioreduction of arsenic-sorbed lepidocrocite by Shewanella putrefaciens GEOCHIMICA ET COSMOCHIMICA ACTA Ona-Nguema, G., Morin, G., Wang, Y., Menguy, N., Juillot, F., Olivi, L., Aquilanti, G., Abdelmoula, M., Ruby, C., Bargar, J. R., Guyot, F., Calas, G., Brown, G. E. 2009; 73 (5): 1359-1381

  View details for DOI 10.1016/j.gca.2008.12.005

  View details for Web of Science ID 000263714300011

• Uranium Speciation As a Function of Depth in Contaminated Hanford Sediments - A Micro-XRF, Micro-XRD, and Micro- And Bulk-XAFS Study ENVIRONMENTAL SCIENCE & TECHNOLOGY Singer, D. M., Zachara, J. M., Brown, G. E. 2009; 43 (3): 630-636

  Abstract

  The distribution and speciation of U and Cu in contaminated vadose zone and aquifer sediments from the U.S. DOE Hanford site (300 Area) were determined using a combination of synchrotron-based micro-X-ray fluorescence (microXRF) imaging, micro-X-ray absorption near edge structure (microXANES) spectroscopy, and micro-X-ray diffraction (microXRD) techniques combined with bulk U LIII-edge X-ray absorption fine structure (XAFS) spectroscopy. Samples were collected from within the inactive North Process Pond (NPP2) at 8 ft (2.4 m, NPP2-8) depth and 12 ft (3.7 m, NPP2-12) depth in the vadose zone, and fines were isolated from turbid groundwater just below the water Table (12-14 ft, approximately 4 m, NPP2-GW). microXRF imaging, microXRD, and microXANES spectroscopy revealed two major U occurrences within the vadose and groundwater zones: (1) low to moderate concentrations of U(VI) associated with fine-textured grain coatings that were consistently found to contain clinochlore (referred to here as chlorite) observed in all three samples, and (2) U(VI)-Cu(II) hotspots consisting of micrometer-sized particles associated with surface coatings on grains of muscovite and chlorite observed in samples NPP2-8' and NPP2-GW. In the aquifer fines (NPP2-GW), these particles were identified as cuprosklodowskite (cps: Cu[(UO2)(SiO2OH)]2 x 6H2O) and metatorbernite (mtb: Cu(UO2)2(PO4)2 x 8H2O). In contrast, the U-Cu-containing particles in the vadose zone were X-ray amorphous. Analyses of U LIII-edge XAFS spectra by linear-combination fitting indicated that U speciation consisted of (1) approximately 75% uranyl sorbed to chlorite and approximately 25% mtb-like X-ray amorphous U-Cu-phosphates (8 ft depth), (2) nearly 100% sorbed uranyl (12 ft depth), and (3) approximately 70% uranyl sorbed to chlorite and approximately 30% cps/mtb (groundwater zone). These findings suggest that dissolution of U(VI)-Cu(II)-bearing solids as well as desorption of U(VI), mainly from phyllosilicates, are important persistent sources of U(VI) to the associated uranium groundwater plume in Hanford Area 300.

  View details for DOI 10.1021/es8021045

  View details for Web of Science ID 000262926400020

  View details for PubMedID 19244994

• Iron biomineralization by anaerobic neutrophilic iron-oxidizing bacteria GEOCHIMICA ET COSMOCHIMICA ACTA Miot, J., Benzerara, K., Morin, G., Kappler, A., Bernard, S., Obst, M., Ferard, C., Skouri-Panet, F., Guigner, J., Posth, N., Galvez, M., Brown, G. E., Guyot, F. 2009; 73 (3): 696-711

  View details for DOI 10.1016/j.gca.2008.10.033

  View details for Web of Science ID 000262877000006

• EXAFS and HRTEM evidence for surface precipitation of arsenic(III) on nanocrystalline magnetite: Implications for As sequestration Langmuir Morin, G., Wang, Y., Ona-Nguema, G., Juillot, F., Calas, G., Menguy, N., Aubry, E., Bargar, J. R., Brown, Jr., G. E. 2009; 25: 9119-9128
• A pre-edge analysis of Mn K-edge XANES spectra to help determine the speciation of manganese in minerals and glasses CONTRIBUTIONS TO MINERALOGY AND PETROLOGY Chalmin, E., Farges, F., Brown, G. E. 2009; 157 (1): 111-126

  View details for DOI 10.1007/s00410-008-0323-z

  View details for Web of Science ID 000260836600007

• Study of iodide adsorption on organobentonite using x-ray absorption spectroscopy Journal of the Mineral Society of Korea Yoon, J., Ha, J., Hwang, J., Hwang, B-H., Brown, Jr., G. E. 2009; 22: 23-34
• Sequestration of Sr(II) by calcium oxalate - A batch uptake study and EXAFS analysis of model compounds and reaction products GEOCHIMICA ET COSMOCHIMICA ACTA Singer, D. M., Johnson, S. B., Catalano, J. G., Farges, F., Brown, G. E. 2008; 72 (20): 5055-5069

  View details for DOI 10.1016/j.gca.2008.07.020

  View details for Web of Science ID 000260038200012

• Nanoscale study of As biomineralization in an acid mine drainage system GEOCHIMICA ET COSMOCHIMICA ACTA Benzerara, K., Morin, G., Yoon, T. H., Miot, J., Tyliszczak, T., Casiot, C., Bruneel, O., Farges, F., Brown, G. E. 2008; 72 (16): 3949-3963

  View details for DOI 10.1016/j.gca.2008.05.046

  View details for Web of Science ID 000258614400003

• XAS study of arsenic coordination in Euglena gracilis exposed to arsenite ENVIRONMENTAL SCIENCE & TECHNOLOGY Miot, J., Morin, G., Skouri-Panet, F., Ferard, C., Aubry, E., Briand, J., Wang, Y., Ona-Nguema, G., Guyot, F., Brown, G. E. 2008; 42 (14): 5342-5347

  Abstract

  Among the few eukaryotes adapted to the extreme conditions prevailing in acid mine drainage, Euglenae are ubiquitous in these metal(loid)-impacted environments, where they can be exposed to As(III) concentrations up to a few hundreds of mg x L(-1). In order to evaluate their resistance to this toxic metalloid and to identify associated detoxification mechanisms, we investigated arsenic coordination in the model photosynthetic protozoan, Euglena gracilis, cultured at pH 3.2 and exposed to As(III) at concentrations ranging from 10 to 500 mg x L(-1). E. gracilis is shown to tolerate As(III) concentrations up to 200 mg * L(-1), without accumulating this metalloid. X-ray absorption spectroscopy at the As K-edge shows that, in the cells, arsenic mainly binds to sulfur ligands, likely in the form of arsenic-trisglutathione (As-(GS)3) or arsenic-phytochelatin (As-PC) complexes, and to a much lesser extent to carbon ligands, presumably in the form of methylated As(III)-compounds. The key role of the glutathione pathway in As(III) detoxification is confirmed by the lower growth rate of E. gracilis cultures exposed to arsenic, in the presence of buthionine sulfoximine, an inhibitor of glutathione synthesis. This study provides the first investigation at the molecular scale of intracellular arsenic speciation in E. gracilis and thus contributes to the understanding of arsenic detoxification mechanisms in a eukaryotic microorganism under extreme acid mine drainage conditions.

  View details for DOI 10.1021/es703072d

  View details for Web of Science ID 000257620000053

  View details for PubMedID 18754391

• Acceptance of the 2007 Clair C. Patterson Award GEOCHIMICA ET COSMOCHIMICA ACTA Brown, G. E. 2008; 72 (12): S10-S11

  View details for DOI 10.1016/j.gca.2008.01.036

  View details for Web of Science ID 000257301600006

• Changes in arsenic speciation through a contaminated soil profile: A XAS based study SCIENCE OF THE TOTAL ENVIRONMENT Cances, B., Juillot, F., Morin, G., Laperche, V., Polya, D., Vaughan, D. J., Hazemann, J., Proux, O., Brown, G. E., CALAS, G. 2008; 397 (1-3): 178-189

  Abstract

  An impacted soil located near an industrial waste site in the Massif Central near Auzon, France, where arsenical pesticides were manufactured, has been studied in order to determine the speciation (chemical forms) of arsenic as a function of soil depth. Bulk As concentrations range from 8780 mg kg(-1) in the topsoil horizon to 150 mg kg(-1) at 60 cm depth. As ores (orpiment As2S3, realgar AsS, arsenopyrite FeAsS) and former Pb- and Al-arsenate pesticides have been identified by XRD at the site and are suspected to be the sources of As contamination for this soil. As speciation was found to vary with depth, based on XRD, SEM-EDS, EPMA measurements and selective chemical extractions. Based on oxalate extraction, As is mainly associated with amorphous Fe oxides through the soil profile, except in the topsoil horizons where As is hosted by another phase. SEM-EDS and EPMA analyses led to the identification of arseniosiderite (Ca2Fe3+3(AsVO4)3O2.3H2O), a secondary mineral that forms upon oxidation of primary As-bearing minerals like arsenopyrite, in these topsoil horizons. These mineralogical and chemical results were confirmed by synchrotron-based X-ray absorption spectroscopy. XANES spectra of soil samples indicate that As occurs exclusively as As(V), and EXAFS results yield direct evidence of changes in As speciation with depth. Linear combination fits of EXAFS spectra of soil samples with those of various model compounds indicate that As occurs mainly As-bearing Fe(III)-(hydr)oxides (65%) and arseniosiderite (35%) in the topsoil horizon (0-5 cm depth). Similar analyses also revealed that there is very little arseniosiderite below 15 cm depth and that As(V) is associated primarily with amorphous Fe oxides below this depth. This vertical change of As speciation likely reflects a series of chemical reactions downward in the soil profile. Arseniosiderite, formed most likely by oxidation of arsenopyrite, is progressively dissolved and replaced by less soluble As-bearing poorly ordered Fe oxides, which are the main hosts for As in well aerated soils.

  View details for DOI 10.1016/j.scitotenv.2008.02.023

  View details for Web of Science ID 000256923000018

  View details for PubMedID 18406447

• Impact of S-oneidensis MR-1 biofilm coatings on trace element partitioning at metal-oxide/water interfaces: A long period XSW-FY study 18th Annual V M Goldschmidt Conference Wang, Y., Gelabert, A., Ha, J., Ona-Nguema, G., Gescher, J., Cordova-Ardy, C., Bargar, J. R., Rogers, J., Eng, P. J., Ghose, S. K., Spormann, A. M., Brown, G. E. PERGAMON-ELSEVIER SCIENCE LTD. 2008: A1003–A1003

  View details for Web of Science ID 000257301602531

• Synchrotron X-ray studies of bacteria-mineral-metal ion interactions 18th Annual V M Goldschmidt Conference Brown, G. E., Gelabert, A., Wang, Y., Cismasu, C., Ha, J., Ona-Nguema, G., Benzerara, K., Morin, G., Yang, Y., Juillot, F., Guyot, F., CALAS, G., Yoon, T. H., Bargar, J. R., Eng, P. J., Templeton, A. S., Trainor, T. P., Spormann, A. M. PERGAMON-ELSEVIER SCIENCE LTD. 2008: A116–A116

  View details for Web of Science ID 000257301600239

• Adsorption of organic matter at mineral/water interfaces: 7. ATR-FTIR and quantum chemical study of lactate interactions with hematite nanoparticles LANGMUIR Ha, J., Yoon, T. H., Wang, Y., Musgrave, C. B., Brown, G. E. 2008; 24 (13): 6683-6692

  Abstract

  The interaction of the l-lactate ion ( l-CH3CH(OH)COO(-), lact(-1)) with hematite (alpha-Fe2O3) nanoparticles (average diameter 11 nm) in the presence of bulk water at pH 5 and 25 degrees C was examined using a combination of (1) macroscopic uptake measurements, (2) in situ attenuated total reflectance-Fourier transform infrared (ATR-FTIR) spectroscopy, and (3) density functional theory modeling at the B3LYP/6-31+G* level. Uptake measurements indicate that increasing [ lact(-1)]aq results in an increase in lact(-1) uptake and a concomitant increase in Fe(III) release as a result of the dissolution of the hematite nanoparticles. The ATR-FTIR spectra of aqueous lact(-1) and lact(-1) adsorbed onto hematite nanoparticles at coverages ranging from 0.52 to 5.21 micromol/m2 showed significant differences in peak positions and shapes of carboxyl group stretches. On the basis of Gaussian fits of the spectra, we conclude that lact(-1) is present as both outer-sphere and inner-sphere complexes on the hematite nanoparticles. No significant dependence of the extent of lact(-1) adsorption on background electrolyte concentration was found, suggesting that the dominant adsorption mode for lact(-1) is inner sphere under these conditions. On the basis of quantum chemical modeling, we suggest that inner-sphere complexes of lact(-1) adsorbed on hematite nanoparticles occur dominantly as monodentate, mononuclear complexes with the hydroxyl functional group pointing away from the Fe(III) center.

  View details for DOI 10.1021/la800122v

  View details for Web of Science ID 000257101100042

  View details for PubMedID 18522441

• Arsenite sorption at the magnetite-water interface during aqueous precipitation of magnetite: EXAFS evidence for a new arsenite surface complex GEOCHIMICA ET COSMOCHIMICA ACTA Wang, Y., Morin, G., Ona-Nguema, G., Menguy, N., Juillot, F., Aubry, E., Guyot, F., Calas, G., Brown, G. E. 2008; 72 (11): 2573-2586

  View details for DOI 10.1016/j.gca.2008.03.011

  View details for Web of Science ID 000256464400001

• Acceptance of the Mineralogical Society of America Roebling Medal for 2007 AMERICAN MINERALOGIST Brown, G. E. 2008; 93 (5-6): 956-957

  View details for DOI 10.2138/am.2008.515

  View details for Web of Science ID 000256133500029

• Extended X-ray absorption fine structure analysis of arsenite and arsenate adsorption on maghemite ENVIRONMENTAL SCIENCE & TECHNOLOGY Morin, G., Ona-Nguema, G., Wang, Y., Menguy, N., Juillot, F., Proux, O., Guyot, F., Calas, G., Brown, G. E. 2008; 42 (7): 2361-2366

  Abstract

  Arsenic sorption onto maghemite potentially contributes to arsenic retention in magnetite-based arsenic removal processes because maghemite is the most common oxidation product of magnetite and may form a coating on magnetite surfaces. Such a sorption reaction could also favor arsenic immobilization at redox boundaries in groundwaters. The nature of arsenic adsorption complexes on maghemite particles, at near-neutral pH under anoxic conditions, was investigated using X-ray absorption fine structure (XAFS) spectroscopy at the As K-edge. X-ray absorption near edge structure spectra indicate that As(III) does notoxidize after 24 h in any of the sorption experiments, as already observed in previous studies of As(III) sorption on ferric (oxyhydr)oxides under anoxic conditions. The absence of oxygen in our sorption experiments also limited Fenton oxidation of As(III). Extended XAFS (EXAFS) results indicate that both As(III) and As(V) form inner-sphere complexes on the surface of maghemite, under high surface coverage conditions (approximately 0.6 to 1.0 monolayer), with distinctly different sorption complexes for As(III) and As(V). For As(V), the EXAFS-derived As-Fe distance (approximately 3.35 +/- 0.03 A) indicates the predominance of single binuclear bidentate double-corner complexes (2C). For As(III), the distribution of the As-Fe distance suggests a coexistence of various types of surface complexes characterized by As-Fe distances of approximately 2.90 (+/-0.03) A and approximately 3.45 (+/-0.03) A. This distribution can be interpreted as being due to a dominant contribution from bidentate binuclear double-corner complexes (2C), with additional contributions from bidentate mononuclear edge-sharing (2E) complexes and monodentate mononuclear corner-sharing complexes (1V). The present results yield useful constraints on As(V) and As(III) adsorption on high surface-area powdered maghemite, which may help in modeling the behavior of arsenic at the maghemite-water interface.

  View details for DOI 10.1021/es072057s

  View details for Web of Science ID 000254492800026

  View details for PubMedID 18504966

• Microbially influenced formation of 2,724-million-year-old stromatolites NATURE GEOSCIENCE Lepot, K., Benzerara, K., Brown, G. E., Philippot, P. 2008; 1 (2): 118-121

  View details for DOI 10.1038/ngeo107

  View details for Web of Science ID 000256433300016

• Synchrotron X-ray studies of heavy metal mineral-microbe interactions 8th International Symposium on the Geochemistry of the Earths Surface (GES-8) Brown, G. E., Wang, Y., Gelabert, A., Ha, J., Cismasu, C., Ona-Nguema, G., Benzerara, K., Miot, J., Menguy, N., Morin, G., Juillot, F., Guyot, F., CALAS, G., Farges, F., Trainor, T. P., Gescher, J., Cordova, C., Spormann, A. M. MINERALOGICAL SOC. 2008: 169–73

  View details for DOI 10.1180/minmag.2008.072.1.169

  View details for Web of Science ID 000258945900037

• EXAFS analysis of arsenite and arsenate adsorption on maghemite Environmental Science & Technology Morin, G., Ona-Nguema, G., Wang, Y., Menguy, N., Juillot, F., Proux, O., Guyot, F., Calas, G., Brown, Jr., G. E. 2008; 42: 2361-2366
• Arsenite adsorption at the magnetite-water interface during aqueous precipitation of magnetite: EXAFS evidence for a new arsenite surface compolex Geochimica et Cosmochimica Acta Wang, Y., Morin, G., Ona-Nguema, G., Menguy, N., Juillot, F., Aubry, E., Guyot, F., Calas, G., Brown, Jr., G. E. 2008; 72: 2573-2586
• SSRL Workshop on STXM and X-ray Nanoprobe Capabilities and Needs in the Environmental, Geological, and Biomedical Sciences Synchrotron Radiation News Bargar, J. R., Brown, Jr., G. E., DeBeer-George, S., Ohldag, H. 2008; 21: 22-24
• Nanoscale study of As transformations by bacteria in an acid mine drainage system Geochimica et Cosmochimica Acta Benzerara, K., Morin, G., TYoon, T. H., Miot, J., Tyliszczak, T., Casiot, C., Farges, F., Brown, Jr., G. E. 2008; 72: 3949-3963
• Change in arsenic speciation through a contaminated soil profile: an XAS based study Science of the Total Environment Cancès, B., Juillot, F., Morin, G., Laperche, V., Polya, D., Vaughan, D. J., Hazemann, J-L., Proux, O., Brown, Jr., G.E., Calas, G. 2008; 397: 178-189
• Exceptional preservation of fossil plant spores in high-pressure metamorphic rocks EARTH AND PLANETARY SCIENCE LETTERS Bernard, S., Benzerara, K., Beyssac, O., Menguy, N., Guyot, F., Brown, G. E., Goffe, B. 2007; 262 (1-2): 257-272

  View details for DOI 10.1016/j.epsl.2007.07.041

  View details for Web of Science ID 000250652900018

• Speciation and colloid transport of arsenic from mine tailings APPLIED GEOCHEMISTRY Slowey, A. J., Johnson, S. B., Newville, M., Brown, G. E. 2007; 22 (9): 1884-1898

  View details for DOI 10.1016/j.apgeochem.2007.03.053

  View details for Web of Science ID 000249906600004

• Alteration of submarine basaltic glass from the Ontong Java Plateau: A STXM and TEM study EARTH AND PLANETARY SCIENCE LETTERS Benzerara, K., Menguy, N., Banerjee, N. R., Tyliszczak, T., Brown, G. E., Guyot, F. 2007; 260 (1-2): 187-200

  View details for DOI 10.1016/j.epsl.2007.05.029

  View details for Web of Science ID 000248883300015

• Citation for presentation of the 2006 F. W. Clarke Award to Alexis S. Templeton GEOCHIMICA ET COSMOCHIMICA ACTA Brown, G. E. 2007; 71 (15): S22-S23

  View details for DOI 10.1016/j.gca.2007.06.007

  View details for Web of Science ID 000248789900011

• Study at the nanoscale of the alteration of submarine basaltic glass from the Ontong Java Plateau 17th Annual V M Goldschmidt Conference Miot, J., Benzerara, K., Banerjee, N. R., Menguy, N., Tyliszczak, T., Brown, G. E., Guyot, F. PERGAMON-ELSEVIER SCIENCE LTD. 2007: A671–A671

  View details for Web of Science ID 000248789901557

• Speciation of mercury in mining environments 17th Annual V M Goldschmidt Conference Brown, G. E., Slowey, A., Jew, A., Kim, C. S., Lowry, G. V., Shaw, S., Gustin, M. S., Rytuba, J. J. PERGAMON-ELSEVIER SCIENCE LTD. 2007: A126–A126

  View details for Web of Science ID 000248789900266

• Transformations of mercury, iron, and sulfur during the reductive dissolution of iron oxyhydroxide by sulfide GEOCHIMICA ET COSMOCHIMICA ACTA Slowey, A. J., Brown, G. E. 2007; 71 (4): 877-894

  View details for DOI 10.1016/j.gca.2006.11.011

  View details for Web of Science ID 000244259500006

• Surface diffraction study of the hydrated hematite (1(1)over-bar-02) surface SURFACE SCIENCE Tanwar, K. S., Lo, C. S., Eng, P. J., Catalano, J. G., Walko, D. A., Brown, G. E., Waychunas, G. A., Chaka, A. M., Trainor, T. P. 2007; 601 (2): 460-474

  View details for DOI 10.1016/j.susc.2006.10.021

  View details for Web of Science ID 000244006200021

• Adsorption and precipitation of aqueous Zn(II) on hematite nano- and microparticles 13th International Conference on X-Ray Absorption Fine Structure (XAFS13) Ha, J., Farges, F., Brown, G. E. AMER INST PHYSICS. 2007: 238–240

  View details for Web of Science ID 000245805900065

• BiogenicUO(2) - Characterization and surface reactivity 13th International Conference on X-Ray Absorption Fine Structure (XAFS13) Singer, D. M., Farges, F., Brown, G. E. AMER INST PHYSICS. 2007: 277–279

  View details for Web of Science ID 000245805900078

• EXAFS signatures of structural Zn at trace levels in layered minerals 13th International Conference on X-Ray Absorption Fine Structure (XAFS13) Juillot, F., Morin, G., Hazemann, J., Proux, O., Belin, S., Briois, V., Brown, G. E., Calas, G. AMER INST PHYSICS. 2007: 247–249

  View details for Web of Science ID 000245805900068

• Durability of silicate glasses: An historical approach 13th International Conference on X-Ray Absorption Fine Structure (XAFS13) Farges, F., Etcheverry, M., Haddi, A., Trocellie, P., Curti, E., Brown, G. E. AMER INST PHYSICS. 2007: 44–50

  View details for Web of Science ID 000245805900008

• On the coordination of actinides and fission products in silicate glasses 13th International Conference on X-Ray Absorption Fine Structure (XAFS13) Haddi, A., Farges, F., Trocellier, P., Curti, E., Harfouche, M., Brown, G. E. AMER INST PHYSICS. 2007: 256–258

  View details for Web of Science ID 000245805900071

• Adsorption mechanisms of trivalent gold onto iron Oxy-Hydroxides: From the molecular scale to the model 13th International Conference on X-Ray Absorption Fine Structure (XAFS13) Cances, B., Benedetti, M., Farges, F., Brown, G. E. AMER INST PHYSICS. 2007: 217–219

  View details for Web of Science ID 000245805900058

• Discovery of unusual minerals in paleolithic black pigments from lascaux (France) and Ekain (Spain) 13th International Conference on X-Ray Absorption Fine Structure (XAFS13) Chalmin, E., Farges, F., Vignaud, C., Susini, J., Menu, M., Brown, G. E. AMER INST PHYSICS. 2007: 220–222

  View details for Web of Science ID 000245805900059

• Selenium speciation in biofilms from granular sludge bed reactors used for wastewater treatment 13th International Conference on X-Ray Absorption Fine Structure (XAFS13) van Hullenbusch, E., Farges, F., Lenz, M., Lens, P., Brown, G. E. AMER INST PHYSICS. 2007: 229–231

  View details for Web of Science ID 000245805900062

• Chrysocolla redefined as spertiniite 13th International Conference on X-Ray Absorption Fine Structure (XAFS13) Farges, F., Benzerara, K., Brown, G. E. AMER INST PHYSICS. 2007: 223–225

  View details for Web of Science ID 000245805900060

• Geochemistry of mineral surfaces and factors affecting their chemical reactivity Chemical Bonding at Surfaces and Interfaces Brown, Jr., G. E., Trainor, T. P., Chaka, A. M., Nilsson (ed.), A., Pettersson (ed.), L. M., Norskov (ed.), J. Elsevier, New York. 2007: 457–509
• Biogenic UO2 characterization and surface reactivity Am. Inst. Phys. Conf. Proc., 13th Int. XAFS Conf. 882 Singer, D. M., Farges, F., Brown, Jr., G. E. 2007: 277-279
• Exceptional preservation of fossil plants spores in high-pressure metamorphic rocks Earth and Planetary Science Letters Bernard, S., Benzerara, K., Beyssac, O., Menguy, N., Guyot, F., Brown, Jr., G. E., Goffe, B. 2007; 262: 257-272
• Study of interactions between microbes and minerals by scanning transmission X-ray microscopy (STXM) 13th International Conference on X-Ray Absorption Fine Structure (XAFS13) Benzerara, K., Tyliszczak, T., Brown, G. E. AMER INST PHYSICS. 2007: 726–730

  View details for Web of Science ID 000245805900217

• Coordination environments of higly charged cations (Ti, Cr, and Light REEís) in borosilicate glass/melts to 1120°C Am. Inst. Phys. Conf. Proc., 13th Int. XAFS Conf. 882 Farges, F., Brown, Jr., G. E. 2007: 208-210
• Recent advances in surface, interface, and environmental geochemistry 12th International Symposium on Water-Rock Interaction (WRI-12) Brown, G. E., Kendelewicz, T., Trainor, T. P., Tanwar, K. S., Chaka, A. M., Eng, P. J., Yamamoto, S., Nilsson, A., Bluhm, H., Starr, D. E., Salmeron, M., Catalano, J. G., Yoon, T. H., Benzerara, K., Morin, G., Ona-Nguema, G., Juillot, F., Cances, B., Farges, F., CALAS, G. TAYLOR & FRANCIS LTD. 2007: 3–11

  View details for Web of Science ID 000252215500001

• Search for microbial signatures within human and microbial calcifications using soft X-ray spectromicroscopy Symposium on Pathological Calcification - Crystallization, Infection, or Cellular Transdifferentiation Benzerara, K., Miller, V. M., Barell, G., Kumar, V., Miot, J., Brown, G. E., Lieske, J. C. LIPPINCOTT WILLIAMS & WILKINS. 2006: 367–79

  Abstract

  The origin of advanced arterial and renal calcification remains poorly understood. Self-replicating, calcifying entities have been detected and isolated from calcified human tissues, including blood vessels and kidney stones, and are referred to as nanobacteria. However, the microbiologic nature of putative nanobacteria continues to be debated, in part because of the difficulty in discriminating biomineralized microbes from minerals nucleated on anything else (eg, macromolecules, cell membranes). To address this controversy, the use of techniques capable of characterizing the organic and mineral content of these self-replicated structures at the submicrometer scale would be beneficial.Calcifying gram-negative bacteria (Caulobacter crescentus, Ramlibacter tataouinensis) used as references and self-replicating calcified nanoparticles cultured from human samples of calcified aneurysms were examined using a scanning transmission x-ray microscope (STXM) at the Advanced Light Source at Lawrence Berkeley National Laboratory. This microscope uses a monochromated and focused synchrotron x-ray beam (80-2,200 eV) to yield microscopic and spectroscopic information on both organic compounds and minerals at the 25 nm scale.High-spatial and energy resolution near-edge x-ray absorption fine structure (NEXAFS) spectra indicative of elemental speciation acquired at the C K-edge, N K-edge, and Ca L(2,3)-edge on a single-cell scale from calcified C. crescentus and R. tataouinensis displayed unique spectral signatures different from that of nonbiologic hydroxyapatite (Ca(10)(PO(4))(6)(OH)(2)). Further, preliminary NEXAFS measurements of calcium, carbon, and nitrogen functional groups of cultured calcified nanoparticles from humans revealed evidence of organics, likely peptides or proteins, specifically associated with hydroxyapatite minerals.Using NEXAFS at the 25 nm spatial scale, it is possible to define a biochemical signature for cultured calcified bacteria, including proteins, polysaccharides, nucleic acids, and hydroxyapatite. These preliminary studies suggest that nanoparticles isolated from human samples share spectroscopic characteristics with calcified proteins.

  View details for DOI 10.2310/6650.2006.06016

  View details for Web of Science ID 000243556000015

  View details for PubMedID 17169258

• Nanometer-scale chemical heterogeneities of black carbon materials and their impacts on PCB sorption properties: Soft X-ray spectromicroscopy study ENVIRONMENTAL SCIENCE & TECHNOLOGY Yoon, T. H., Benzerara, K., Ahn, S., Luthy, R. G., Tyliszczak, T., Brown, G. E. 2006; 40 (19): 5923-5929

  Abstract

  Synchrotron-based soft X-ray spectromicroscopy was used to probe nanometer-scale chemical heterogeneities of black carbon (BC) materials, including anthracite coal, coke, and activated carbon (AC), and to study their impact on the partitioning of one type of polychlorinated biphenyls (PCB-166: 2,3,4,4',5,6 hexachloro biphenyl) onto AC particles. Various carbon species (e.g., aromatic, ketonic/ phenolic, and carboxylic functional groups) were found in all of the BC materials examined, and impurities (e.g., carbonate and potassium ions in anthracite coal) were identified in nanometer-scale regions of these samples. We show that these chemical heterogeneities in AC particles influence their sorption of hydrophobic organic compounds (HOCs). PCB-166 was found to accumulate preferentially on AC particles with the highest content of aromatic functionalities. These new findings from X-ray spectromicroscopy have the following implications for the role of BC materials in the environment: (1) the functional groups of BC materials vary on a 25-nanometer scale, and so does the abundance of the HOCs; (2) molecular-level characterization of HOC sorption preferences on AC will lead to an improved understanding of AC sorption properties for the remediation of HOCs in soils and sediments.

  View details for DOI 10.1021/es060173+

  View details for Web of Science ID 000240826000022

  View details for PubMedID 17051780

• COLL 420-Structure of the iron-oxide aqueous solution interface via coupled surface X-ray diffraction and density functional theory Trainor, T. P., Eng, P., Chaka, A. M., Brown, G. E., Tanwar, K., Petitto, S. C., Lo, C. S., Ghose, S. K., Waychunas, G. A. AMER CHEMICAL SOC. 2006

  View details for Web of Science ID 000207781603484

• EXAFS signature of structural Zn at trace levels in natural and synthetic trioctahedral 2 : 1 phyllosilicates AMERICAN MINERALOGIST Juillot, F., Morin, G., Ildefonse, P., Calas, G., Brown, G. E. 2006; 91 (8-9): 1432-1441

  View details for DOI 10.2138/am.2006.1923

  View details for Web of Science ID 000240068700023

• Applications of synchrotron radiation to processes at environmental interfaces 16th Annual V M Goldschmidt Conference Brown, G. E., Benzerara, K., Yoon, T. H., Ha, J., Cordova, C. D., Spormann, A. M., Tyliszcak, T., Tanwar, K. S., Trainor, T. P., Eng, P. J., Kendelewicz, T., Yamamoto, S., Bluhm, H., Ketteler, G., Salmeron, M., Nilsson, A. PERGAMON-ELSEVIER SCIENCE LTD. 2006: A69–A69

  View details for DOI 10.1016/j.gca.2006.06.242

  View details for Web of Science ID 000241374200148

• Nanoscale detection of organic signatures in carbonate microbialites PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA Benzerara, K., Menguy, N., Lopez-Garcia, P., Yoon, T., Kazmierczak, J., Tyliszczak, T., Guyot, F., Brown, G. E. 2006; 103 (25): 9440-9445

  Abstract

  Microbialites are sedimentary deposits associated with microbial mat communities and are thought to be evidence of some of the oldest life on Earth. Despite extensive studies of such deposits, little is known about the role of microorganisms in their formation. In addition, unambiguous criteria proving their biogenicity have yet to be established. In this study, we characterize modern calcareous microbialites from the alkaline Lake Van, Turkey, at the nanometer scale by combining x-ray and electron microscopies. We describe a simple way to locate microorganisms entombed in calcium carbonate precipitates by probing aromatic carbon functional groups and peptide bonds. Near-edge x-ray absorption fine structure spectra at the C and N K-edges provide unique signatures for microbes. Aragonite crystals, which range in size from 30 to 100 nm, comprise the largest part of the microbialites. These crystals are surrounded by a 10-nm-thick amorphous calcium carbonate layer containing organic molecules and are embedded in an organic matrix, likely consisting of polysaccharides, which helps explain the unusual sizes and shapes of these crystals. These results provide biosignatures for these deposits and suggest that microbial organisms significantly impacted the mineralogy of Lake Van carbonates.

  View details for Web of Science ID 000238660400013

  View details for PubMedID 16772379

  View details for PubMedCentralID PMC1480426

• Structural environments around molybdenum in silicate glasses and melts. II. Effect of temperature, pressure, H2O, halogens and sulfur Conference on Rare-Element Geochemistry and Mineral Deposits held at the 2004 GAC-MAC Annual Meeting Farges, F., Siewert, R., Ponader, C. W., Brown, G. E., Pichavant, M., Behrens, H. MINERALOGICAL ASSOC CANADA. 2006: 755–773

  View details for Web of Science ID 000240268300010

• Structural environments around molybdenum in silicate glasses and melts. I. Influence of composition and oxygen fugacity on the local structure of molybdenum Conference on Rare-Element Geochemistry and Mineral Deposits held at the 2004 GAC-MAC Annual Meeting Farges, F., Siewert, R., Brown, G. E., Guesdon, A., Morin, G. MINERALOGICAL ASSOC CANADA. 2006: 731–753

  View details for Web of Science ID 000240268300009

• Redox and speciation of tin in hydrous silicate glasses: A comparison with Nb, Ta, Mo and W Conference on Rare-Element Geochemistry and Mineral Deposits held at the 2004 GAC-MAC Annual Meeting Farges, F., Linnen, R. L., Brown, G. E. MINERALOGICAL ASSOC CANADA. 2006: 795–810

  View details for Web of Science ID 000240268300012

• Structural environment of Nb5+ in dry and fluid-rich (H2O, F) silicate glasses: A combined XANES and EXAFS study Conference on Rare-Element Geochemistry and Mineral Deposits held at the 2004 GAC-MAC Annual Meeting Piilonen, P. C., Farges, F., Linnen, R. L., Brown, G. E., Pawlak, M., Pratt, A. MINERALOGICAL ASSOC CANADA. 2006: 775–794

  View details for Web of Science ID 000240268300011

• Changes in uranium speciation through a depth sequence of contaminated Hanford sediments ENVIRONMENTAL SCIENCE & TECHNOLOGY Catalano, J. G., McKinley, J. P., Zachara, J. M., Heald, S. M., Smith, S. C., Brown, G. E. 2006; 40 (8): 2517-2524

  Abstract

  The disposal of basic sodium aluminate and acidic U(VI)-Cu(ll) wastes in the now-dry North and South 300 A Process Ponds atthe Hanford site resulted in a groundwater plume of U(VI). To gain insight into the geochemical processes that occurred during waste disposal and those affecting the current and future fate and transport of this uranium plume, the solid-phase speciation of uranium in a depth sequence of sediments from the base of the North Process Pond through the vadose zone to groundwater was investigated using standard chemical and mineralogical analyses, electron and X-ray microprobe measurements, and X-ray absorption fine structure spectroscopy. Near-surface sediments contained uranium coprecipitated with calcite, which formed due to overneutralization of the waste ponds with base (NaOH). At intermediate depths in the vadose zone, metatorbernite [Cu(UO2PO4)2 x 8H2O] precipitated, likely during pond operations. Uranium occurred predominantly sorbed onto phyllosilicates in the deeper vadose zone and groundwater; sorbed uranium was also an important component at intermediate depths. Since the calcite-bearing pond sediments have been removed in remediation efforts, uranium fate and transport will be controlled primarily by desorption of the sorbed uranium and dissolution of metatorbernite.

  View details for Web of Science ID 000236992700009

  View details for PubMedID 16683586

• User facilities around the world ELEMENTS Brown, G. E., Sutton, S. R., Calas, G. 2006; 2 (1): 9-14

  View details for Web of Science ID 000235478900005

• New opportunities at emerging facilities ELEMENTS Parise, J. B., Brown, G. E. 2006; 2 (1): 37-42

  View details for Web of Science ID 000235478900009

• Soft X-ray microscopy and spectroscopy at the molecular environmental science beamline at the Advanced Light Source JOURNAL OF ELECTRON SPECTROSCOPY AND RELATED PHENOMENA Bluhm, H., Andersson, K., Araki, T., Benzerara, K., Brown, G. E., Dynes, J. J., Ghosal, S., Gilles, M. K., Hansen, H. C., Hemminger, J. C., Hitchcock, A. P., Ketteler, G., Kilcoyne, A. L., Kneedler, E., Lawrence, J. R., Leppard, G. G., Majzlan, J., Mun, B. S., Myneni, S. C., Nilsson, A., Ogasawara, H., Ogletree, D. F., Pecher, K., Salmeron, M., Shuh, D. K., Tonner, B., Tyliszczak, T., Warwick, T., Yoon, T. H. 2006; 150 (2-3): 86-104

  View details for DOI 10.1016/j.elspec.2005.07.005

  View details for Web of Science ID 000234191300004

• Scientific advances made possible by user facilities ELEMENTS Brown, G. E., Calas, G., Hemley, R. J. 2006; 2 (1): 23-30

  View details for Web of Science ID 000235478900007

• The Stanford Environmental Molecular Science Institute: A Focus on Chemical and Microbial Processes at Environmental Interfaces The Geochemical News Brown, Jr., G. E., Nilsson, A., Spormann, A. M., Addiego, W. P., Benzerara, K., Bergmann, U., Bluhm, H., Brown, B. A., Calas, G., Chaka, A. M., Constantz, B. R., Farges, F., Fendorf, S. E., Foster, A. L., Juillot, F., Morin, G., Myneni, S. C. B., Pettersson, L. G. M., Rosso, K. M., Rytuba, J. J., Salmeron, M., Saltzman, J., Toney, M., Trainor, T. P., Yoon, T-H. 2006; 128: 7-30
• XAS evidence of As(V) association with iron oxyhydroxides in a contaminated soil at a former arsenical pesticide processing plant ENVIRONMENTAL SCIENCE & TECHNOLOGY Cances, B., Juillot, F., Morin, G., Laperche, V., ALVAREZ, L., Proux, O., Hazemann, J. L., Brown, G. E., CALAS, G. 2005; 39 (24): 9398-9405

  Abstract

  The molecular-level speciation of arsenic has been determined in a soil profile in the Massif Central near Auzon, France that was impacted by As-based pesticides by combining conventional techniques (XRD, selective chemical extractions) with X-ray absorption spectroscopy (XAS). The arsenic concentration is very high at the top (>7000 mg kg(-1)) and decreases rapidly downward to a few hundreds of milligrams per kilogram. A thin layer of schultenite (PbHAsO4), a lead arsenate commonly used as an insecticide until the middle of the 20th century, was found at 10 cm depth. Despite the occurrence of this As-bearing mineral, oxalate extraction indicated that more than 65% of the arsenic was released upon dissolution of amorphous iron oxides, suggesting a major association of arsenic with these phases within the soil profile. Since oxalate extraction cannot unambiguously distinguish among the various chemical forms of arsenic, these results were confirmed by a direct in situ determination of arsenic speciation using XAS analysis. XANES data indicate that arsenic occurs mainly as As(V) along the soil profile except for the topsoil sample where a minor amount (7%) of As(III) was detected. EXAFS spectra of soil samples were fit by linear combinations of model compounds spectra and by a shell-by-shell method. These procedures clearly confirmed that As(V) is mainly (at least 80 wt %) associated with amorphous Fe(III) oxides as coprecipitates within the soil profile. If any, the proportion of schultenite, which was evidenced by XRD in a separate thin white layer, does not account for more than 10 wt % of arsenic in soil samples. This study emphasizes the importance of iron oxides in restricting arsenic dispersal within soils following dissolution of primary As-bearing solids manufactured for use as pesticides and released into the soils.

  View details for DOI 10.1021/es050920n

  View details for Web of Science ID 000234133300007

  View details for PubMedID 16475314

• EXAFS analysis of arsenite adsorption onto two-line ferrihydrite, hematite, goethite, and lepidocrocite ENVIRONMENTAL SCIENCE & TECHNOLOGY Ona-Nguema, G., Morin, G., Juillot, F., CALAS, G., Brown, G. E. 2005; 39 (23): 9147-9155

  Abstract

  The modes of As(III) sorption onto two-line ferrihydrite (Fh), hematite (Hm), goethite (Gt), and lepidocrocite (Lp) have been investigated under anoxic condition using X-ray absorption spectroscopy (XAS). X-ray absorption near-edge structure spectroscopy (XANES) indicates that the absence of oxygen minimized As(III) oxidation due to Fenton reactions. Extended X-ray absorption fine structure spectroscopy (EXAFS) indicates thatAs(III)forms similar inner-sphere surface complexes on two-line ferrihydrite and hematite that differ from those formed on goethite and lepidocrocite. At high surface coverage, the dominant complex types on Fh and Hm are bidentate mononuclear edge-sharing (2E) and bidentate binuclear corner-sharing (2C), with As-Fe distances of 2.90 +/- 0.05 and 3.35 +/- 0.05 A, respectively. The same surface complexes are observed for ferrihydrite at low surface coverage. In contrast, As(III) forms dominantly bidentate binuclear corner-sharing (2C) sorption complexes on Gt and Lp [d(As-Fe) = 3.3-3.4 A], with a minor amount of monodentate mononuclear corner-sharing (1V) complexes [d(As-Fe) = 3.5-3.6 A]. Bidentate mononuclear edge-sharing (2E) complexes are virtually absent in Gt and Lp at the high surface coverages that were investigated in the present study. These results are compared with available literature data and discussed in terms of the reactivity of iron(III) (oxyhydr)oxide surface sites.

  View details for DOI 10.1021/es050889p

  View details for Web of Science ID 000233712700027

  View details for PubMedID 16382936

• Role of organic acids in promoting colloidal transport of mercury from mine tailings ENVIRONMENTAL SCIENCE & TECHNOLOGY Slowey, A. J., Johnson, S. B., Rytuba, J. J., Brown, G. E. 2005; 39 (20): 7869-7874

  Abstract

  A number of factors affect the transport of dissolved and particulate mercury (Hg) from inoperative Hg mines, including the presence of organic acids in the rooting zone of vegetated mine waste. We examined the role of the two most common organic acids in soils (oxalic and citric acid) on Hg transport from such waste by pumping a mixed organic acid solution (pH 5.7) at 1 mL/min through Hg mine tailings columns. For the two total organic acid concentrations investigated (20 microM and 1 mM), particle-associated Hg was mobilized, with the onset of particulate Hg transport occurring later for the lower organic acid concentration. Chemical analyses of column effluent indicate that 98 wt % of Hg mobilized from the column was particulate. Hg speciation was determined using extended X-ray absorption fine structure spectroscopy and transmission electron microscopy, showing that HgS minerals are dominant in the mobilized particles. Hg adsorbed to colloids is another likely mode of transport due to the abundance of Fe-(oxyhydr)oxides, Fe-sulfides, alunite, and jarosite in the tailings to which Hg(II) adsorbs. Organic acids produced by plants are likely to enhance the transport of colloid-associated Hg from vegetated Hg mine tailings by dissolving cements to enable colloid release.

  View details for DOI 10.1021/es0504643

  View details for Web of Science ID 000232758400020

  View details for PubMedID 16295849

• In situ analysis of thioarsenite complexes in neutral to alkaline arsenic sulphide solutions Conference on Environmental Mineralogy, Geochemistry and Human Health Bostick, B. C., Fendorf, S., Brown, G. E. MINERALOGICAL SOC. 2005: 781–95

  View details for DOI 10.1180/0026461056950288

  View details for Web of Science ID 000235009100021

• Multi-spectroscopic study of Fe(II) in silicate glasses: Implications for the coordination environment of Fe(II) in silicate melts GEOCHIMICA ET COSMOCHIMICA ACTA Jackson, W. E., Farges, F., Yeager, M., Mabrouk, P. A., Rossano, S., WAYCHUNAS, G. A., SOLOMON, E. I., Brown, G. E. 2005; 69 (17): 4315-4332

  View details for DOI 10.1016/j.gca.2005.01.008

  View details for Web of Science ID 000231894800011

• Surface complexation studied via combined grazing-incidence EXAFS and surface diffraction: arsenate an hematite (0001) and (10-12) ANALYTICAL AND BIOANALYTICAL CHEMISTRY Waychunas, G., Trainor, T., Eng, P., Catalano, J., Brown, G., Davis, J., Rogers, J., Bargar, J. 2005; 383 (1): 12-27

  Abstract

  X-ray diffraction [crystal-truncation-rod (CTR)] studies of the surface structure of moisture-equilibrated hematite reveal sites for complexation not present on the bulk oxygen-terminated surface, and impose constraints on the types of inner-sphere sorption topologies. We have used this improved model of the hematite surface to analyze grazing-incidence EXAFS results for arsenate sorption on the c (0001) and r (10-12) surfaces measured in two electric vector polarizations. This work shows that the reconfiguration of the surface under moist conditions is responsible for an increased adsorption density of arsenate complexes on the (0001) surface relative to predicted ideal termination, and an abundance of "edge-sharing" bidentate complexes on both studied surfaces. We consider possible limitations on combining the methods due to differing surface sensitivities, and discuss further analysis possibilities using both methods.

  View details for DOI 10.1007/s00216-005-3393-z

  View details for Web of Science ID 000232952600005

  View details for PubMedID 16142422

• Water in silicate glasses and melts of environmental interest: from volcanoes to cathedrals 9th International Conference on the Structure of Non-Crystalline Materials (NCM9) Farges, F., Djanarthany, S., De Wispelaere, S., Munoz, M., Magassouba, B., Haddi, A., Wilke, M., Schmidt, C., Borchert, M., Trocellier, P., Crichton, W., Simionovici, A., Petit, P. E., Mezouar, M., Etcheverry, M. P., Pallot-Frossard, I., Bargar, J. R., Brown, G. E., Grolimund, D., Scheidegger, A. SOC GLASS TECHNOLOGY. 2005: 350–53

  View details for Web of Science ID 000234597300009

• CTR diffraction and grazing-incidence EXAFS study of U(VI) adsorption onto alpha-Al2O3 and alpha-Fe2O3 (1(1)over-bar02) surfaces GEOCHIMICA ET COSMOCHIMICA ACTA Catalano, J. G., Trainor, T. P., Eng, P. J., WAYCHUNAS, G. A., Brown, G. E. 2005; 69 (14): 3555-3572

  View details for DOI 10.1016/j.gca.2005.03.044

  View details for Web of Science ID 000230635000009

• Adsorption of organic matter at mineral/water interfaces. 6. Effect of inner-sphere versus outer-sphere adsorption on colloidal stability LANGMUIR Johnson, S. B., Brown, G. E., HEALY, T. W., Scales, P. J. 2005; 21 (14): 6356-6365

  Abstract

  The effects of the adsorption modes of several low molecular weight (LMW) organic anions (maleate, oxalate, and citrate) on the colloidal stability of corundum-water suspensions have been examined using electrokinetic and shear yield stress (tau(y)) measurements over a broad range of pH conditions and LMW organic anion concentrations. Consistent with previous studies, increasing concentrations of maleate, oxalate, and citrate progressively shift the electrokinetic isoelectric point and pH of the maximum shear yield stress (tau(y,max)) to more acidic conditions. Due to its predominant electrostatic driving force for adsorption, outer-spherically adsorbed maleate possesses a very limited ability to charge reverse the corundum-water interface or bind to the negatively charged corundum surface. By contrast, inner-spherically adsorbed oxalate and citrate can significantly charge reverse the corundum-water interface, with the extent of charge reversal being related to the relative binding strengths of the oxalate and citrate anions. Adsorbed maleate, oxalate, and citrate generate steric barriers to interparticle approach, leading to substantial reductions in the magnitude of tau(y,max) at low to intermediate concentrations of those LMW anions. At the highest anion concentrations investigated, however, increases in tau(y,max) are observed, and can be attributed to the formation of bridging Al(III)-organic surface precipitates, as suggested by in situ attenuated total reflectance Fourier transform infrared spectroscopic measurements of corundum-oxalate suspensions at high oxalate concentrations. The extent of precipitate formation is greatest for the corundum-oxalate system due to the strong dissolution-enhancing properties of the inner-spherically adsorbed oxalate anion (i.e., its ability to generate enhanced concentrations of dissolved Al(III) which can then participate in precipitate formation). The effects of the LMW organic anion adsorption modes on both the forms of the measured tau(y) versus pH data, and the ability to quantitatively compare tau(y) and zeta potential data measured at different corundum concentrations, are also discussed.

  View details for DOI 10.1021/la047030q

  View details for Web of Science ID 000230248500036

  View details for PubMedID 15982042

• Uranyl adsorption onto montmorillonite: Evaluation of binding sites and carbonate complexation GEOCHIMICA ET COSMOCHIMICA ACTA Catalano, J. G., Brown, G. E. 2005; 69 (12): 2995-3005

  View details for DOI 10.1016/j.gca.2005.01.025

  View details for Web of Science ID 000230156600005

• Adsorption of organic matter at mineral/water interfaces. IV. Adsorption of humic substances at boehmite/water interfaces and impact on boehmite dissolution LANGMUIR Yoon, T. H., Johnson, S. B., Brown, G. E. 2005; 21 (11): 5002-5012

  Abstract

  The adsorption of Suwannee River fulvic acid (SRFA) and Pahokee peat humic acid (PPHA) at the boehmite (gamma-AlOOH)/water interface and the impact of SRFA on boehmite dissolution have been examined over a wide range of solution pH conditions (pH 2-12), SRFA surface coverages (Gamma(SRFA), total SRFA binding site concentration normalized by the boehmite surface area) of 0.0-5.33 micromol m(-2), and PPHA surface coverages (Gamma(PPHA), PPHA binding site concentration normalized by boehmite surface area) of 0.0-4.0 micromol m(-2), using macroscopic adsorption and in situ attenuated total reflectance-Fourier transform infrared (ATR-FTIR) spectroscopy. At relatively high SRFA surface coverages (Gamma(SRFA) = 5.33 micromol m(-2)), in situ ATR-FTIR spectral features of adsorbed SRFA are very similar to those measured for SRFA in solution at approximately 1-3 pH units higher. At sub-monolayer surface coverages (Gamma(SRFA) = 1.20 and 2.20 micromol m(-2)), several new peaks and enhancements of the intensities of a number of existing peaks are observed. The latter spectral changes arise from several nonorganic extrinsic species (i.e., adsorbed carbonate and water, for alkaline solution conditions), partially protonated SRFA carboxyl functional groups (near-neutral pH conditions), and small quantities of inner-spherically adsorbed SRFA carboxyl groups and/or Al(III)-SRFA complexes (for acidic conditions). The spectra of PPHA adsorbed at boehmite/water interfaces also showed changes generally consistent with our observations for SRFA sorbed on boehmite. These observations confirm that SRFA and PPHA are predominantly adsorbed at the boehmite/water interface in an outer-sphere fashion, with minor inner-sphere adsorption complexes being formed only under quite acidic conditions. They also suggest that the positively charged boehmite/water interface stabilizes SRFA and PPHA carboxyl functional groups against protonation at lower pH. Measurements of the concentration of dissolved Al(III) ions in the absence and presence of SRFA showed that the boehmite dissolution process is clearly inhibited by the adsorption of SRFA, which is consistent with previous observations that outer-spherically adsorbed organic anions inhibit Al-(oxyhydr)oxide dissolution.

  View details for DOI 10.1021/la0476276

  View details for Web of Science ID 000229243800038

  View details for PubMedID 15896043

• Trace metal ion partitioning at polymer film-metal oxide interfaces: Long-period X-ray standing wave study LANGMUIR Yoon, T. H., Trainor, T. P., Eng, P. J., Bargar, J. R., Brown, G. E. 2005; 21 (10): 4503-4511

  Abstract

  The distributions of Pb(II) and As(V)O4(3-) ions in the interfacial region between thin poly(acrylic acid) (PAA) coatings and aalpha-A12O3(0001), alpha-Al2O3(1-102), and alpha-Fe2O3(0001) single-crystal substrates were studied using long-period X-ray standing wave fluorescent yield (XSW-FY) and X-ray reflectivity techniques. The PAA film serves as a simplified analogue of natural organic matter (NOM) coatings on mineral surfaces. Such coatings are often assumed to play an important role in the partitioning and speciation of trace heavy metals in soils and aquatic systems. On the alpha-Al2O3(1-102) surface, Pb(II) ions were found to preferentially bind to the PAA coating, even at sub-micromolar Pb(II) concentrations, and to partition increasingly onto the metal oxide surface as the Pb(II) concentration was increased ([Pb(II)] = 5 x 10(-8) to 2 x 10(-5) M, pH = 4.5; 0.01 M NaCl background electrolyte). This observation suggests that the binding sites in the PAA coating outcompete those on the alpha-Al2O3(1-102) surface for Pb(II) under these conditions. The As(V)O4(3-) oxoanion partitions preferentially to the L-Al2O3(1-102) surface for the As(V)O4(3-) concentrations examined (1 x 10(-7) to 5 x 10(-7) M, pH = 4.5; 0.01 M NaCl background electrolyte). Partitioning of Pb(II) (at 1 x 10(-7) M and pH 4.5) was also examined at PAA/alpha-Al2O3(0001), and PAA/alpha-Fe2O3(0001) interfaces using XSW-FY measurements. Our results show that the PAA coating was the dominant sink for Pb(II) in all three samples; however, the relative order of reactivity of these metal oxide surfaces with respect to Pb(II) sorption is alpha-Fe2O3(0001) > alpha-Al2O3(1-102) > alpha-Al2O3(0001). This order is consistent with that found in previous studies of the PAA-free surfaces. These XSW results strongly suggest that the characteristics of the organic film (i.e., binding affinity, type, and density of binding sites) as well as metal oxide substrate reactivity are key factors determining the distribution and speciation of Pb(II) and As(V)O4(3-) at organic film/metal oxide interfaces.

  View details for DOI 10.1021/la047271y

  View details for Web of Science ID 000228983700039

  View details for PubMedID 16032866

• Structure and reactivity of hydroxylated hematite surfaces: Application of surface x-ray diffraction and spectroscopy 15th Annual V M Goldschmidt Conference Trainor, T. P., Eng, P. J., Chaka, A. M., Lo, C. S., Tanwar, K., Ghose, S. K., Brown, G. E., Catalano, J. G., Waychunas, G. A., Tempelton, A. S. PERGAMON-ELSEVIER SCIENCE LTD. 2005: A486–A486

  View details for Web of Science ID 000229399701355

• Soft X-ray spectromicroscopy study of chemical heterogeneities in iron precipitates formed at or near bacterial cells 15th Annual V M Goldschmidt Conference Yoon, T. H., Borch, T., Benzerara, K., Fendorf, S., Tyliszczak, T., Brown, G. E. PERGAMON-ELSEVIER SCIENCE LTD. 2005: A598–A598

  View details for Web of Science ID 000229399701570

• Adsorption of organic matter at mineral/water interfaces: 5. Effects of adsorbed natural organic matter analogues on mineral dissolution LANGMUIR Johnson, S. B., Yoon, T. H., Brown, G. E. 2005; 21 (7): 2811-2821

  Abstract

  The effects of the adsorption of pyromellitate, an analogue for natural organic matter, on the dissolution behavior of corundum (alpha-Al2O3) have been examined over a wide range of pyromellitate concentrations (0-2.5 mM) and pH conditions (2-10). The adsorption modes of pyromellitate on corundum have first been examined using in situ attenuated total reflectance Fourier transform infrared (ATR-FTIR) spectroscopy and are shown to be dominated by a fully deprotonated, outer-sphere pyromellitate species ([triple bond]AlOH2+. . .Pyr4-) at pH >/= 5.0. At lower pH conditions, however, an additional protonated outer-sphere species ([triple bond]AlOH2+. . .H2Pyr2-) and an inner-sphere species are also evident. In accordance with the ATR-FTIR findings, modeling of macroscopic pyromellitate adsorption data using an extended constant capacitance treatment was possible using two outer-sphere ([triple bond]AlOH2+. . .Pyr4- and [triple bond]AlOH2+. . .H2Pyr2-) and one inner-sphere ([triple bond]AlPyr3-) adsorbed pyromellitate species. The presence of adsorbed pyromellitate strongly inhibited the dissolution of corundum under acidic (pH < 5) conditions, consistent with a mechanism previously proposed by Johnson et al. whereby outer-spherically adsorbed Pyr4- species sterically protect dissolution-active surface sites from attack by dissolution-promoting species such as protons. A reduction in the protolytic dissolution rate of corundum results. A reference Suwannee River fulvic acid, which also adsorbs to aluminum (oxyhydr)oxide surfaces in a predominantly outer-sphere manner, was similarly shown to strongly inhibit the dissolution of corundum at pH = 3.

  View details for DOI 10.1021/la0481041

  View details for Web of Science ID 000228042400031

  View details for PubMedID 15779953

• Speciation of mercury and mode of transport from placer gold mine tailings ENVIRONMENTAL SCIENCE & TECHNOLOGY Slowey, A. J., Rytuba, J. J., Brown, G. E. 2005; 39 (6): 1547-1554

  Abstract

  Historic placer gold mining in the Clear Creek tributary to the Sacramento River (Redding, CA) has highly impacted the hydrology and ecology of an important salmonid spawning stream. Restoration of the watershed utilized dredge tailings contaminated with mercury (Hg) introduced during gold mining, posing the possibility of persistent Hg release to the surrounding environment, including the San Francisco Bay Delta. Column experiments have been performed to evaluate the extent of Hg transport under chemical conditions potentially similar to those in river restoration projects utilizing dredge tailings such as at Clear Creek. Physicochemical perturbations, in the form of shifts in column influent ionic strength and the presence of a low molecular weight organic acid, were applied to coarse and fine sand placer tailings containing 109-194 and 69-90 ng of Hg/g, respectively. Significant concentrations of mercury, up to 16 microg/L, leach from these sediments in dissolved and particle-associated forms. Sequential chemical extractions (SCE) of these tailings indicate that elemental Hg initially introduced during gold mining has been transformed to readily soluble species, such as mercury oxides and chlorides (3-4%), intermediately extractable phases that likely include (in)organic sorption complexes and amalgams (75-87%), and fractions of highly insoluble forms such as mercury sulfides (6-20%; e.g., cinnabar and metacinnabar). Extended X-ray absorption fine structure (EXAFS) spectroscopic analysis of colloids obtained from column effluent identified cinnabar particles as the dominant mobile mercury-bearing phase. The fraction of intermediately extractable Hg phases also likely includes mobile colloids to which Hg is adsorbed.

  View details for DOI 10.1021/es049113z

  View details for Web of Science ID 000227636300028

  View details for PubMedID 15819208

• Role of organic molecules and microbial organisms in metal ion sorption processes. 229th National Meeting of the American-Chemical-Society (ACS) Brown, G. E., Yoon, T. H., Johnson, S. B., Templeton, A. S., Trainor, T. P., Benzerara, K., Bostick, B. C., Kendelewicz, T., Doyle, C. S., Spormann, A. M. AMER CHEMICAL SOC. 2005: U784–U785

  View details for Web of Science ID 000235066603535

• ATR-FTIR investigation of the mechanism(s) of lactate adsorption on hematite (alpha-FE2O3) nanoparticles at water/lactate/mineral interface. 229th National Meeting of the American-Chemical-Society (ACS) Ha, J., Johnson, S. B., Yoon, T. H., Brown, G. E. AMER CHEMICAL SOC. 2005: U654–U654

  View details for Web of Science ID 000228177704314

• Soft x-ray spectromicroscopy study of carbonaceous materials: Characterization of their chemical heterogeneities in sub-micrometer scale 229th National Meeting of the American-Chemical-Society (ACS) Yoon, T. H., Benzerara, K., Ahn, S. W., Luthy, R. G., Tyliszczak, T., Brown, G. E. AMER CHEMICAL SOC. 2005: U860–U860

  View details for Web of Science ID 000228177706191

• Nanoscale environments associated with bioweathering of a Mg-Fe-pyroxene PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA Benzerara, K., Yoon, T. H., Menguy, N., Tyliszczak, T., Brown, G. E. 2005; 102 (4): 979-982

  Abstract

  Microorganisms are believed to create microenvironments leading to reaction products not predictable from equilibrium thermodynamics and to unique biomineral morphologies. Unambiguous evidence for such environments is, however, rare in natural samples. We have used scanning transmission x-ray microscopy and spectromicroscopy at the sub-40-nm scale, coupled with transmission electron microscopy, to examine bioweathering products on a meteoritic Fe-Mg-orthopyroxene colonized by a filamentous microorganism. Our measurements reveal an amorphous Al-rich layer beneath the microorganism, calcium carbonates of unique morphology intimately associated with polysaccharides adjacent to the microorganism, and regions surrounding the microorganism with different iron oxidation states. Our results confirm the presence of different microenvironments at this microorganism-mineral interface and provide unique nanometer-scale views of microbially controlled pyroxene weathering products.

  View details for DOI 10.1073/pnas.0409029102

  View details for Web of Science ID 000226617900006

  View details for PubMedID 15647362

  View details for PubMedCentralID PMC545861

• Environmental interfaces, heavy metals, microbes, and plants: Applications of XAFS spectroscopy and related synchrotron radiation methods to environmental science PHYSICA SCRIPTA Brown, G. E., Catalano, J. G., Templeton, A. S., Trainor, T. P., Farges, F., Bostick, B. C., Kendelewicz, T., Doyle, C. S., Spormann, A. M., Revill, K., Morin, G., Juillot, F., Calas, G. 2005; T115: 80-87

  View details for Web of Science ID 000204272100015

• Sorption and precipitation of Co(II) in Hanford sediments and alkaline aluminate solutions APPLIED GEOCHEMISTRY Catalano, J. G., Warner, J. A., Brown, G. E. 2005; 20 (1): 193-205

  View details for DOI 10.1016/j.apgeochem.2004.06.002

  View details for Web of Science ID 000226312100014

• Tin and niobium in dry and fluid-rich (H2O, F) silicate glasses PHYSICA SCRIPTA Piilonen, P. C., Farges, F., Linnen, R. L., Brown, G. E. 2005; T115: 405-407

  View details for Web of Science ID 000204272100116

• Iron in silicate glasses: a systematic analysis of pre-edge, XANES and EXAFS features PHYSICA SCRIPTA Farges, F., Rossano, S., Lefrere, Y., Wilke, M., Brown, G. E. 2005; T115: 957-959

  View details for Web of Science ID 000204272100289

• Archeological applications of XAFS: Prehistorical paintings and medieval glasses PHYSICA SCRIPTA Farges, F., Chalmin, E., Vignaud, C., Pallot-Frossard, I., Susini, J., Bargar, J., Brown, G. E., Menu, M. 2005; T115: 885-887

  View details for Web of Science ID 000204272100265

• Surface complexation studied via combined grazing-incidence EXAFS and surface diffraction: arsenate on hematite (0001) and (1-102) Analytical and Bioanalytical Chemistry Waychunas, G. A., Trainor, T. P., Eng, P., Catalano, J. G., Brown, Jr., G. E., Davis, J. A., Rogers, J., Bargar, J. R. 2005; 383: 12-27
• CTR diffraction and grazing incidence XAFS study of U(VI) adsorption to α-Al2O3 and α-Fe2O3 (1-102) surfaces Geochimica et Cosmochimica Acta Catalano, J. G., Trainor, T. P., Eng, P. J., Waychunas, G. A., Brown, Jr., G. E. 2005; 69: 3555-3572
• Sorption and precipitation of Co(II) in alkali aluminate solutions and Hanford sediments Applied Geochemistry Catalano, J. G., Warner, J. A., Brown, Jr., G. E. 2005; 20: 193-205
• Adsorption of organic matter at mineral/water interfaces: 3. Implications of surface dissolution for adsorption of oxalate LANGMUIR Johnson, S. B., Yoon, T. H., Slowey, A. J., Brown, G. E. 2004; 20 (26): 11480-11492

  Abstract

  The adsorption of oxalate on a model aluminum oxide, corundum (alpha-Al2O3), has been examined over a broad range of oxalate concentrations (0.125-25.0 mM) and pH conditions (2-10). In situ attenuated total reflectance Fourier transform infrared (ATR-FTIR) measurements indicate that at low to intermediate concentrations ([oxalate] < or = 2.50 mM), oxalate adsorbs to corundum predominantly as a bidentate, mononuclear, inner-sphere complex involving both carboxyl groups. Significant contributions from outer-spherically bound oxalate and aqueous Ox(2-) are additionally observed at higher oxalate concentrations. Consistent with the ATR-FTIR findings, macroscopic adsorption data measured for oxalate concentrations of 0.125-2.50 mM can be generally well modeled with a single bidentate, inner-sphere oxalate complex using the charge distribution multisite complexation (CD-MUSIC) model. However, at intermediate oxalate concentrations (0.50 and 1.25 mM) and pH <5, the extent of oxalate adsorption measured experimentally is found to fall significantly below that predicted by CD-MUSIC simulations. The latter finding is interpreted in terms of competition for oxalate from dissolved Al(III), the formation of which is promoted by the dissolution-enhancing properties of the adsorbed oxalate anion. In accordance with this expectation, increasing concentrations of dissolved Al(III) in solution are found to significantly decrease the extent of oxalate adsorption on corundum under acidic pH conditions, presumably through promoting the formation of Al(III)-oxalate complexes with reduced affinities for the corundum surface compared with the uncomplexed oxalate anion.

  View details for DOI 10.1021/la048559q

  View details for Web of Science ID 000225816800030

  View details for PubMedID 15595773

• Structure and reactivity of the hydrated hematite (0001) surface SURFACE SCIENCE Trainor, T. P., Chaka, A. M., Eng, P. J., Newville, M., WAYCHUNAS, G. A., Catalano, J. G., Brown, G. E. 2004; 573 (2): 204-224

  View details for DOI 10.1016/j.susc.2004.09.040

  View details for Web of Science ID 000225612600010

• In situ characterization of aluminum-containing mineral-microorganism aqueous suspensions using scanning transmission X-ray microscopy LANGMUIR Yoon, T. H., Johnson, S. B., Benzerara, K., Doyle, C. S., Tyliszczak, T., Shuh, D. K., Brown, G. E. 2004; 20 (24): 10361-10366

  Abstract

  In situ characterization of colloidal particles under hydrous conditions is one of the key requirements for understanding their state of aggregation and impact on the transport of pollutants in aqueous environments. Scanning transmission X-ray microscopy (STXM) is one of the few techniques that can satisfy this need by providing element- and chemical-state-specific 2-D maps at a spatial resolution better than 50 nm using soft X-rays from synchrotron radiation wiggler or undulator sources tuned to the absorption edges of different elements. X-ray absorption near-edge structure (XANES) spectra can also be collected simultaneously at a similar spatial resolution and can provide phase identification in many cases. In this study, we report STXM images and XANES spectroscopy measurements at or above the Al K-edge (E = 1559.6 eV) of various Al-containing minerals and synthetic oxides [alpha-Al2O3 (corundum), gamma-Al2O3, gamma-AlOOH (boehmite), alpha-Al(OH)3 (bayerite), KAl2(AlSi3O10)(OH)2 (muscovite), (Al,Mg)8(Si4O10)4(OH)8.nH2O (montmorillonite), and Mg6Al2(OH)16CO3.4H2O (hydrotalcite)] and demonstrate the capability of this spectromicroscopic tool to identify different Al-containing mineral colloids in multiphase mixtures in aqueous solution. We also demonstrate that STXM imaging at or above the C K-edge (E = 284.2 eV) and Al K-edge can provide unique information on the interactions between bacteria and Al-containing nanoparticles in aqueous suspensions. STXM images of a mixture of Caulobacter crescentus and montmorillonite and corundum particles just above the C and Al K-edges show that the mineral particles and bacteria are closely associated in aggregates, which is likely due to the binding of bacteria to clay and corundum particles by extracellular polysaccharides.

  View details for DOI 10.1021/la048558y

  View details for Web of Science ID 000225207400001

  View details for PubMedID 15544358

• Adsorption of organic matter at mineral/water interfaces: I. ATR-FTIR spectroscopic and quantum chemical study of oxalate adsorbed at boehmite/water and corundum/water interfaces GEOCHIMICA ET COSMOCHIMICA ACTA Yoon, T. H., Johnson, S. B., Musgrave, C. B., Brown, G. E. 2004; 68 (22): 4505-4518

  View details for DOI 10.1016/j.gca.2004.04.025

  View details for Web of Science ID 000224980000001

• Experimental and theoretical characterization of the structure of defects at the pyrite FeS2(100) surface PHYSICAL REVIEW B Andersson, K., Nyberg, M., Ogasawara, H., Nordlund, D., Kendelewicz, T., Doyle, C. S., Brown, G. E., Pettersson, L. G., Nilsson, A. 2004; 70 (19)

  View details for DOI 10.1103/PhysRevB.70.195404

  View details for Web of Science ID 000225477800128

• Soft X-ray spectroscopic studies of the reaction of fractured pyrite surfaces with Cr(Vl)-containing aqueous solutions GEOCHIMICA ET COSMOCHIMICA ACTA Doyle, C. S., Kendelewicz, T., Bostick, B. C., Brown, G. E. 2004; 68 (21): 4287-4299

  View details for DOI 10.1016/j.gca.2004.02.015

  View details for Web of Science ID 000224698000001

• Macroscopic and microscopic observations of particle-facilitated mercury transport from new idria and sulphur bank mercury mine tailings ENVIRONMENTAL SCIENCE & TECHNOLOGY Lowry, G. V., Shaw, S., Kim, C. S., Rytuba, J. J., Brown, G. E. 2004; 38 (19): 5101-5111

  Abstract

  Mercury (Hg) release from inoperative Hg mines in the California Coast Range has been documented, but little is known about the release and transport mechanisms. In this study, tailings from Hg mines located in different geologic settings--New Idria (NI), a Si-carbonate Hg deposit, and Sulphur Bank (SB), a hot-spring Hg deposit--were characterized, and particle release from these wastes was studied in column experiments to (1) investigate the mechanisms of Hg release from NI and SB mine wastes, (2) determine the speciation of particle-bound Hg released from the mine wastes, and (3) determine the effect of calcinations on Hg release processes. The physical and chemical properties of tailings and the colloids released from them were determined using chemical analyses, selective chemical extractions, XRD, SEM, TEM, and X-ray absorption spectroscopy techniques. The total Hg concentration in tailings increased with decreasing particle size in NI and SB calcines (roasted ore), but reached a maximum at an intermediate particle size in the SB waste rock (unroasted ore). Hg in the tailings exists predominantly as low-solubility HgS (cinnabar and metacinnabar), with NI calcines having >50% HgS, SB calcines having >89% HgS, and SB waste rock having approximately 100% HgS. Leaching experiments with a high-ionic-strength solution (0.1 M NaCl) resulted in a rapid but brief release of soluble and particulate Hg. Lowering the ionic strength of the leach solution (0.005 M NaCI) resulted in the release of colloidal Hg from two of the three mine wastes studied (NI calcines and SB waste rock). Colloid-associated Hg accounts for as much as 95% of the Hg released during episodic particle release. Colloids generated from the NI calcines are produced by a breakup and release mechanism and consist of hematite, jarosite/alunite, and Al-Si gel with particle sizes of 10-200 nm. ATEM and XAFS analyses indicate that the majority (approximately 78%) of the mercury is present in the form of HgS. SB calcines also produced HgS colloids. The colloids generated from the SB waste rockwere heterogeneous and varied in composition according to the column influent composition. ATEM and XAFS results indicate that Hg is entirely in the HgS form. Data from this study identify colloidal HgS as the dominant transported form of Hg from these mine waste materials.

  View details for DOI 10.1021/es034636c

  View details for Web of Science ID 000224234100035

  View details for PubMedID 15506205

• The effect of redox state on the local structural environment of iron in silicate glasses: a molecular dynamics, combined XAFS spectroscopy, and bond valence study JOURNAL OF NON-CRYSTALLINE SOLIDS Farges, F., Lefrere, Y., Rossano, S., Berthereau, A., CALAS, G., Brown, G. E. 2004; 344 (3): 176-188

  View details for DOI 10.1016/j.jnoncrysol.2004.07.050

  View details for Web of Science ID 000224628100010

• Scanning transmission X-ray microscopy study of microbial calcification GEOBIOLOGY Benzerara, K., Yoon, T. H., Tyliszczak, T., Constantz, B., Spormann, A. M., Brown, G. E. 2004; 2 (4): 249-259

  View details for DOI 10.1111/j.1472-4677.2004.00039.x

  View details for Web of Science ID 000207171600006

• Adsorption of Suwannee River fulvic acid on aluminum oxyhydroxide surfaces: An in situ ATR-FTIR study LANGMUIR Yoon, T. H., Johnson, S. B., Brown, G. E. 2004; 20 (14): 5655-5658

  Abstract

  The adsorption of Suwannee River fulvic acid (SRFA) on boehmite, gamma-AlO(OH), has been examined by both macroscopic adsorption and in situ ATR-FTIR spectroscopic techniques. At a SRFA concentration approaching surface saturation (F = 5.3 micromol m(-2)), adsorption is at a maximum at low pH and decreases as pH is increased. The ATR-FTIR spectral features of adsorbed SRFA are very similar to those measured approximately 1-2 pH units higher in solution, indicating that (i) the SRFA appears to be predominantly adsorbed at the boehmite/water interface in an outer-sphere complexation mode and (ii) the positively charged boehmite/water interface stabilizes SRFA molecules against protonation at low pH.

  View details for DOI 10.1021/la0499214

  View details for Web of Science ID 000222429200004

  View details for PubMedID 16459573

• Adsorption mechanisms of trivalent gold on iron- and aluminum-(oxy)hydroxides. Part 1: X-ray absorption and Raman scattering spectroscopic studies of Au(III) adsorbed on ferrihydrite, goethite, and boehmite GEOCHIMICA ET COSMOCHIMICA ACTA Berrodier, I., Farges, F., Benedetti, M., Winterer, M., Brown, G. E., Deveughele, M. 2004; 68 (14): 3019-3042

  View details for DOI 10.1016/j.gca.2004.02.009

  View details for Web of Science ID 000222460800005

• Analysis of uranyl-bearing phases by EXAFS spectroscopy: Interferences, multiple scattering, accuracy of structural parameters, and spectral differences AMERICAN MINERALOGIST Catalano, J. G., Brown, G. E. 2004; 89 (7): 1004-1021

  View details for Web of Science ID 000222708200011

• Adsorption of organic matter at mineral/water interfaces. 2. Outer-sphere adsorption of maleate and implications for dissolution processes LANGMUIR Johnson, S. B., Yoon, T. H., Kocar, B. D., Brown, G. E. 2004; 20 (12): 4996-5006

  Abstract

  The effects of the adsorption of a simple dicarboxylate low molecular weight organic anion, maleate, on the dissolution of a model aluminum oxide, corundum (alpha-Al2O3), have been examined over a range of different maleate concentrations (0.125-5.0 mM) and pH conditions (2-10). In situ attenuated total reflectance Fourier transform infrared (ATR-FTIR) spectroscopic measurements indicate that maleate binds predominantly as an outer-sphere, fully deprotonated complex ([triple bond]AlOH2+ -Mal2-) at the corundum surface over the entire range of maleate concentrations and pH conditions investigated. In accordance with the ATR-FTIR findings, macroscopic adsorption data can be modeled as a function of maleate concentration and pH using an extended constant capacitance approach and a single [triple bond]AlOH2+ -Mal2- species. Outer-sphere adsorption of maleate is found to significantly reduce the protolytic dissolution rate of corundum under acidic conditions (pH < 5). A likely mechanism involves steric protection of dissolution-active surface sites, whereby strong outer-sphere interactions with maleate hinder attack on those surface sites by dissolution-promoting species.

  View details for DOI 10.1021/la036288y

  View details for Web of Science ID 000221846000032

  View details for PubMedID 15984260

• Initial oxidation of fractured surfaces of FeS2(100) by molecular oxygen, water vapor, and air SURFACE SCIENCE Kendelewicz, T., Doyle, C. S., Bostick, B. C., Brown, G. E. 2004; 558 (1-3): 80-88

  View details for DOI 10.1016/j.susc.2004.03.045

  View details for Web of Science ID 000221728000009

• The role of organic molecules and microbial organisms in metal ion sorption processes 14th Annual V M Goldschmidt Conference Brown, G. E., Yoon, T. H., Johnson, S. B., Templeton, A. S., Trainor, T. P., Bostick, B. C., Kendelewicz, T., Doyle, C. S., Spormann, A. M. PERGAMON-ELSEVIER SCIENCE LTD. 2004: A160–A160

  View details for Web of Science ID 000221923400256

• Inhibition of the reduction of Cr(VI) at the magnetite-water interface by calcium carbonate coatings APPLIED SURFACE SCIENCE Doyle, C. S., Kendelewicz, T., Brown, G. E. 2004; 230 (1-4): 260-271

  View details for DOI 10.1016/j.apsusc.2004.02.035

  View details for Web of Science ID 000221968100033

• Spectroscopic and diffraction study of uranium speciation in contaminated vadose zone sediments from the Hanford site, Washington state ENVIRONMENTAL SCIENCE & TECHNOLOGY Catalano, J. G., Heald, S. M., Zachara, J. M., Brown, G. E. 2004; 38 (10): 2822-2828

  Abstract

  Contamination of vadose zone sediments under tank BX-102 at the Hanford site, Washington, resulted from the accidental release of 7-8 metric tons of uranium dissolved in caustic aqueous sludge in 1951. We have applied synchrotron-based X-ray spectroscopic and diffraction techniques to characterize the speciation of uranium in samples of these contaminated sediments. UIII-edge X-ray absorption fine structure (XAFS) spectroscopic studies demonstrate that uranium occurs predominantly as a uranium(VI) silicate from the uranophane group of minerals. XAFS cannot distinguish between the members of this mineral group due to the near identical local coordination environments of uranium in these phases. However, these phases differ crystallographically, and can be distinguished using X-ray diffraction (XRD) methods. As the concentration of uranium was too low for conventional XRD to detect these phases, X-ray microdiffraction (microXRD) was used to collect diffraction patterns on approximately 20 microm diameter areas of localized high uranium concentration found using microscanning X-ray fluorescence (microSXRF). Only sodium boltwoodite, Na(UO2)(SiO3OH) x 1.5H20, was observed; no other uranophane group minerals were present. Sodium boltwoodite formation has effectively sequestered uranium in these sediments under the current geochemical and hydrologic conditions. Attempts to remediate the uranium contamination will likely face significant difficulties because of the speciation and distribution of uranium in the sediments.

  View details for DOI 10.1021/es049963e

  View details for Web of Science ID 000221502800019

  View details for PubMedID 15212255

• ATR-FTIR and macroscopic investigation of humic acid adsorption on goethite. 227th National Meeting of the American-Chemical Society Johnson, S. B., Yoon, T. H., Brown, G. E. AMER CHEMICAL SOC. 2004: U1218–U1218

  View details for Web of Science ID 000223655604027

• In situ grazing-incidence extended X-ray absorption fine structure study of Pb(II) chemisorption on hematite (0001) and (1-102) surfaces LANGMUIR Bargar, J. R., Trainor, T. P., Fitts, J. P., Chambers, S. A., Brown, G. E. 2004; 20 (5): 1667-1673

  View details for DOI 10.1021/la0354133

  View details for Web of Science ID 000189241500020

• EXAFS study of mercury(II) sorption to Fe- and Al-(hydr)oxides I. Effects of pH JOURNAL OF COLLOID AND INTERFACE SCIENCE Kim, C. S., Rytuba, J. J., Brown, G. E. 2004; 271 (1): 1-15

  Abstract

  The study of mercury sorption products in model systems using appropriate in situ molecular-scale probes can provide detailed information on the modes of sorption at mineral/water interfaces. Such studies are essential for assessing the influence of sorption processes on the transport of Hg in contaminated natural systems. Macroscopic uptake of Hg(II) on goethite (alpha-FeOOH), gamma-alumina (gamma-Al(2)O(3)), and bayerite (beta-Al(OH)(3)) as a function of pH has been combined with Hg L(III)-edge EXAFS spectroscopy, FTIR spectroscopy, and bond valence analysis of possible sorption products to provide this type of information. Macroscopic uptake measurements show that Hg(II) sorbs strongly to fine-grained powders of synthetic goethite (Hg sorption density Gamma=0.39-0.42 micromol/m(2)) and bayerite (Gamma=0.39-0.44 micromol/m(2)), while sorbing more weakly to gamma-alumina (Gamma=0.04-0.13 micromol/m(2)). EXAFS spectroscopy on the sorption samples shows that the dominant mode of Hg sorption on these phases is as monodentate and bidentate inner-sphere complexes. The mode of Hg(II) sorption to goethite was similar over the pH range 4.3-7.4, as were those of Hg(II) sorption to bayerite over the pH range 5.1-7.9. Conversion of the gamma-Al(2)O(3) sorbent to a bayerite-like phase in addition to the apparent reduction of Hg(II) to Hg(I), possibly by photoreduction during EXAFS data collection, resulted in enhanced Hg uptake from pH 5.2-7.8 and changes in the modes of sorption that correlate with the formation of the bayerite-like phase. Bond valence calculations are consistent with the sorption modes proposed from EXAFS analysis. EXAFS analysis of Hg(II) sorption products on a natural Fe oxyhydroxide precipitate and Al/Si-bearing flocculent material showed sorption products and modes of surface attachment similar to those for the model substrates, indicating that the model substrates are useful surrogates for the natural sediments.

  View details for DOI 10.1016/S0021-9797(03)00330-8

  View details for Web of Science ID 000188778600001

  View details for PubMedID 14757070

• Geological and anthropogenic factors influencing mercury speciation in mine wastes: an EXAFS spectroscopy study APPLIED GEOCHEMISTRY Kim, C. S., Rytuba, J. J., Brown, G. E. 2004; 19 (3): 379-393

  View details for DOI 10.1016/S0883-2927(03)00147-1

  View details for Web of Science ID 000189101300008

• EXAFS study of mercury(II) sorption to Fe- and Al-(hydr)oxides - II. Effects of chloride and sulfate JOURNAL OF COLLOID AND INTERFACE SCIENCE Kim, C. S., Rytuba, J., Brown, G. E. 2004; 270 (1): 9-20

  Abstract

  Common complexing ligands such as chloride and sulfate can significantly impact the sorption of Hg(II) to particle surfaces in aqueous environmental systems. To examine the effects of these ligands on Hg(II) sorption to mineral sorbents, macroscopic Hg(II) uptake measurements were conducted at pH 6 and [Hg](i)=0.5 mM on goethite (alpha-FeOOH), gamma-alumina (gamma-Al(2)O(3)), and bayerite (beta-Al(OH)(3)) in the presence of chloride or sulfate, and the sorption products were characterized by extended X-ray absorption fine structure (EXAFS) spectroscopy. The presence of chloride resulted in reduced uptake of Hg(II) on all three substrates over the Cl(-) concentration ([Cl(-)]) range 10(-5) to 10(-2) M, lowering Hg surface coverages on goethite, gamma-alumina, and bayerite from 0.42 to 0.07 micromol/m(2), 0.06 to 0.006 micromol/m(2), and 0.55 to 0.39 micromol/m(2) ([Cl(-)]=10(-5) to 10(-3) M only), respectively. This reduction in Hg(II) uptake is primarily a result of the formation of stable, nonsorbing aqueous HgCl(2) complexes in solution, limiting the amount of free Hg(II) available to sorb. At higher [Cl(-)] beam reduction of Hg(II) to Hg(I) was observed, resulting in the possible formation of aqueous Hg(2)Cl(2) species and the precipitation of calomel, Hg(2)Cl(2(s)). The presence of sulfate caused enhanced Hg(II) uptake over the sulfate concentration ([SO(4)(2-)]) range 10(-5) to 0.9 M, increasing Hg surface coverages on goethite, gamma-alumina, and bayerite from 0.39 to 0.45 micromol/m(2), 0.11 to 0.38 micromol/m(2), and 0.36 to 3.33 micromol/m(2), respectively. This effect is likely due to the direct sorption or accumulation of sulfate ions at the substrate interface, effectively reducing the positive surface charge that electrostatically inhibits Hg(II) sorption. Spectroscopic evidence for ternary surface complexation was observed in isolated cases, specifically in the Hg-goethite-sulfate system at high [SO(4)(2-)] and in the Hg-goethite-chloride system.

  View details for DOI 10.1016/j.jcis.2003.07.029

  View details for Web of Science ID 000187883900002

  View details for PubMedID 14693130

• In-situ grazing incidence EXAFS study of Pb(II) chemisorption on hematite (0001) and (1-102) Langmuir Bargar, J. R., Trainor, T. P., Fitts, J. P., Chambers, S. A., Brown, Jr., G. E. 2004; 20: 1667-1673
• Chromium speciation and mobility in a high level nuclear waste vadose zone plume GEOCHIMICA ET COSMOCHIMICA ACTA Zachara, J. M., Ainsworth, C. C., Brown, G. E., Catalano, J. G., McKinley, J. P., Qafoku, O., Smith, S. C., Szecsody, J. E., Traina, S. J., Warner, J. A. 2004; 68 (1): 13-30

  View details for DOI 10.1016/S0016-7037(03)00417-4

  View details for Web of Science ID 000187851900002

• A novel spectrometer system for hard x-ray interfacial environmental chemistry 8th International Conference on Synchrotron Radiation Instrumentation (SRI 2003) Rogers, J. H., Bargar, J. R., WAYCHUNAS, G. A., Yoon, T. H., Brown, G. E. AMER INST PHYSICS. 2004: 981–984

  View details for Web of Science ID 000222089000241

• Molecular Environmental Science: An Assessment of Research Accomplishments, Available Synchrotron Radiation Facilities, and Needs A Report Prepared on Behalf of EnviroSync - A National Organization Representing Molecular Environmental Science Users of Synchrotron Radiation Sources Brown, Jr., G. E., Sutton, S. R., Bargar, J. R., Shuh, D. K., Bassett, W. A., Bertsch, P. M., Bisognano, J., Bleam, W. F., Clark, D. L., De Stasio, P., Fendorf , S. E., Fenter, P. A., Fontes, E., Hormes, J., Kemner, K. M., Myneni, S. B., O'Day, P. A., Pecher, K. H., Reeder, R. J., Roy, A., Traina, S. J., Willson, C., Zachara, J. M. SLAC. 2004: 60p.
• Soft X-ray scanning transmission microscope working in an extended energy range at the advanced light source 8th International Conference on Synchrotron Radiation Instrumentation (SRI 2003) Tyliszczak, T., Warwick, T., Kilcoyne, A. L., Fakra, S., Shuh, D. K., Yoon, T. H., Brown, G. E., Andrews, S., Chernbrolu, V., Strachan, J., Acremann, Y. AMER INST PHYSICS. 2004: 1356–1359

  View details for Web of Science ID 000222089000333

• EXAFS study of uranyl adsorption on Wyoming montmorillonite 11th Internat. Symp. on Water-Rock Interaction Catalano, J. G., Brown, Jr., G. E., Wanty (ed.), R. B., Seal, II (ed.), R. R. 2004: 665–69
• Synchrotron-based studies of microbe-metal ion-mineral interactions. 11th Internat. Symp. on Water-Rock Interaction Brown, Jr., , G. E., Templeton, A. S., Trainor, T. P., Spormann, A. M., Yoon, T. H., Benzerara, K. edited by Wanty, R. B., Seal II, R. R. 2004: 1069–77
• Mercury speciation by X-ray absorption fine structure spectroscopy and sequential chemical extractions: A comparison of speciation methods ENVIRONMENTAL SCIENCE & TECHNOLOGY Kim, C. S., Bloom, N. S., Rytuba, J. J., Brown, G. E. 2003; 37 (22): 5102-5108

  Abstract

  Determining the chemical speciation of mercury in contaminated mining and industrial environments is essential for predicting its solubility, transport behavior, and potential bioavailability as well as for designing effective remediation strategies. In this study, two techniques for determining Hg speciation--X-ray absorption fine structure (XAFS) spectroscopy and sequential chemical extractions (SCE)--are independently applied to a set of samples with Hg concentrations ranging from 132 to 7539 mg/kg to determine if the two techniques provide comparable Hg speciation results. Generally, the proportions of insoluble HgS (cinnabar, metacinnabar) and HgSe identified by XAFS correlate well with the proportion of Hg removed in the aqua regia extraction demonstrated to remove HgS and HgSe. Statistically significant (>10%) differences are observed however in samples containing more soluble Hg-containing phases (HgCl2, HgO, Hg3S2O4). Such differences may be related to matrix, particle size, or crystallinity effects, which could affect the apparent solubility of Hg phases present. In more highly concentrated samples, microscopy techniques can help characterize the Hg-bearing species in complex multiphase natural samples.

  View details for DOI 10.1021/es0341485

  View details for Web of Science ID 000186601300004

  View details for PubMedID 14655695

• Selenium speciation and partitioning within Burkholderia cepacia biofilms formed on alpha-Al2O3 surfaces GEOCHIMICA ET COSMOCHIMICA ACTA Templeton, A. S., Trainor, T. P., Spormann, A. M., Brown, G. E. 2003; 67 (19): 3547-3557

  View details for DOI 10.1016/S0016-7037(03)00212-6

  View details for Web of Science ID 000185734600002

• Rapid oxidation of pyrite surfaces by thiobacillus ferrooxidans and T. thiooxidans. 226th National Meeting of the American-Chemical-Society Bostick, B. C., Lester, K., Doyle, C., Kendelewicz, T., Brown, G. E., Fendorf, S., Spormann, A. M. AMER CHEMICAL SOC. 2003: U591–U591

  View details for Web of Science ID 000187062402801

• Effect of sulfate and phosphate on oxalate adsorption on boehmite 226th National Meeting of the American-Chemical-Society Ha, J. Y., Yoon, T. H., Brown, G. E. AMER CHEMICAL SOC. 2003: U494–U494

  View details for Web of Science ID 000187062402362

• X-ray absorption fine structure study of As(V) and Se(IV) sorption complexes on hydrous Mn oxides GEOCHIMICA ET COSMOCHIMICA ACTA Foster, A. L., Brown, G. E., Parks, G. A. 2003; 67 (11): 1937-1953

  View details for DOI 10.1016/S0016-7037(00)01301-7

  View details for Web of Science ID 000182951900001

• Speciation of Pb(II) sorbed by Burkholderia cepacia/goethite composites ENVIRONMENTAL SCIENCE & TECHNOLOGY Templeton, A. S., Spormann, A. M., Brown, G. E. 2003; 37 (10): 2166-2172

  Abstract

  Bacterial-mineral composites are important in the retention of heavy metals such as Pb due to their large sorption capacity under a wide range of environmental conditions. However, the partitioning of heavy metals between components in such composites is not probed directly. Using Burkholderia cepacia biofilms coated with goethite (alpha-FeOOH) particles, the partitioning of Pb(II) between the biological and iron-(oxyhydr)oxide surfaces has been measured using an X-ray spectroscopic approach. EXAFS spectra were fit to quantitatively determine the fraction of Pb(II) associated with each component as a function of pH and [Pb]. At pH < 5.5, at least 50% of the total sorbed Pb(II) is associated with the biofilm component, whereas the total uptake within the composite is dominated by goethite (> 70% Pb/goethite) above pH 6. Direct comparison can be made between the amount of Pb(II) bound to each component in the composite vs separate binary systems (i.e., Pb/biofilm or Pb/goethite). At high pH, Pb(II) uptake on the biofilm is dramatically decreased due to competition with the goethite surface. In contrast, Pb uptake on goethite is significantly enhanced at low pH (2-fold increase at pH 5) compared to systems with no complexing ligands. The mode of Pb(II)-binding to the goethite component changes from low to high [Pb]. Structural fitting of the EXAFS spectra collected from 10(-5.6) to 10(-3.6) M [Pb]eq at pH 6 shows that the Pb-goethite surface complexes at low [Pb] are dominated by inner-sphere bidentate, binuclear complexes bridging two adjacent singly coordinated surface oxygens, giving rise to Pb-Fe distances of approximately 3.9 A. At high [Pb], the dominant Pb(II) inner-sphere complexes on the goethite surface shift to bidentate edge-sharing complexes with Pb-Fe distances of approximately 3.3 A.

  View details for DOI 10.1021/es026081b

  View details for Web of Science ID 000182866000020

  View details for PubMedID 12785522

• Occurrence of Zn/Al hydrotalcite in smelter-impacted soils from northern France: Evidence from EXAFS spectroscopy and chemical extractions AMERICAN MINERALOGIST Juillot, F., Morin, G., Ildefonse, P., Trainor, T. P., Benedetti, M., Galoisy, L., CALAS, G., Brown, G. E. 2003; 88 (4): 509-526

  View details for Web of Science ID 000182214400005

• Effect of simple organic acid adsorption on the stability of aqueous metal oxide systems 225th National Meeting of the American-Chemical-Society Johnson, S. B., Yoon, T. H., Brown, G. E., Scales, P. J., HEALY, T. W. AMER CHEMICAL SOC. 2003: U799–U799

  View details for Web of Science ID 000187917803731

• Sorption versus biomineralization of Pb(II) within Burkholderia cepacia biofilms ENVIRONMENTAL SCIENCE & TECHNOLOGY Templeton, A. S., Trainor, T. P., Spormann, A. M., Newville, M., Sutton, S. R., Dohnalkova, A., Gorby, Y., Brown, G. E. 2003; 37 (2): 300-307

  Abstract

  X-ray spectroscopy measurements have been combined with macroscopic uptake data and transmission electron microscopy (TEM) results to show that Pb(II) uptake by Burkholderia cepacia is due to simultaneous sorption and biomineralization processes. X-ray microprobe mapping of B. cepacia biofilms formed on alpha-Al2O3 surfaces shows that Pb(II) is distributed heterogeneously throughout the biofilms because of the formation of Pb "hot spots". EXAFS data and TEM observations show that the enhanced Pb accumulation is due to the formation of nanoscale crystals of pyromorphite (Pb5(PO4)3(OH)) adjacent to the outer-membrane of a fraction of the total population of B. cepacia cells. In contrast, B. cepacia cell suspensions or biofilms that were heat-killed or pretreated with X-rays do not form pyromorphite, which suggests that metabolic activity is required. Precipitation of pyromorphite occurs over several orders of magnitude in [H-] and [Pb] and accounts for approximately 90% of the total Pb uptake below pH 4.5 but only 45-60% at near-neutral pH because of the formation of additional Pb(II) adsorption complexes. Structural fits of Pb L(III) EXAFS data collected for heat-treated cells at near-neutral pH suggest that Pb(II) forms inner-sphere adsorption complexes with carboxyl functional groups in the biofilms.

  View details for DOI 10.1021/es025972g

  View details for Web of Science ID 000180501500014

  View details for PubMedID 12564901

• XAFS study of As(V) and Se(IV) sorption complexes on hydrous Mn oxides Geochimica et Cosmochimica Acta Foster, A. L., Brown, Jr., G. E., Parks, G. A. 2003; 67: 1937-1953
• Role of arsenic in pyrite oxidation Bostick, B. C., Doyle, C., Fendorf, S., Kendelewicz, T., Bargar, J., Brown, G. E. PERGAMON-ELSEVIER SCIENCE LTD. 2002: A95–A95

  View details for Web of Science ID 000177423400184

• Application of the long-period X-ray standing wave technique to the analysis of surface reactivity: Pb(II) sorption at alpha-Al2O3/aqueous solution interfaces in the presence and absence of Se(VI) LANGMUIR Trainor, T. P., Templeton, A. S., Brown, G. E., Parks, G. A. 2002; 18 (15): 5782-5791

  View details for DOI 10.1021/la015740f

  View details for Web of Science ID 000176903500024

• Bond valence in silicate glasses 5th Brazilian Symposium on Glasses and Related Materials/1st International Symposium on Non-Crystalline Solids in Brazil Rossano, R., Farges, F., Ramos, A., Delaye, J. M., Brown, G. E. ELSEVIER SCIENCE BV. 2002: 167–73

  View details for Web of Science ID 000176121200024

• Molecular beam epitaxial growth and properties of CoFe2O4 on MgO(001) JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS Chambers, S. A., Farrow, R. F., Maat, S., Toney, M. F., Folks, L., Catalano, J. G., Trainor, T. P., Brown, G. E. 2002; 246 (1-2): 124-139

  View details for Web of Science ID 000176154000019

• Crystal truncation rod diffraction study of the alpha-Al2O3 (1(1)over-bar-0 2) surface SURFACE SCIENCE Trainor, T. P., Eng, P. J., Brown, G. E., Robinson, I. K., De Santis, M. 2002; 496 (3): 238-250

  View details for Web of Science ID 000173286100010

• Actinides in silicate glasses and melts and on mineral surfaces: Information on local coordination environments from XAFS spectroscopy and bond valence theory Brown, Jr., G. E., Farges, F., Bargar, J. R., Berbeco, H. T., 2002 Nuclear Energy Agency/Organization for Economic Co-operation and Development, AEN/NEA 2002. 2002: 10–12
• An overview of synchrotron radiation applications to low temperature geochemistry and environmental science Conference on Synchrotron Applications to Low-Temperature Geochemistry and Environmental Science held at the American-Geophysical-Union Fall Meeting Brown, G. E., Sturchio, N. C. MINERALOGICAL SOC AMER. 2002: 1–115

  View details for Web of Science ID 000180779900001

• Crystal truncation rod diffraction study of the clean and hydrated α-Al2O3 (1-102) surface Surface Science Trainor, T. P., Eng, P., Brown, Jr., G. E., Robinson, I. K., De Santis, M. 2002; 496: 238-250
• Grazing-incidence XAFS study of aqueous Zn(II) sorption on alpha-Al2O3 single crystals Journal of Colloid and Interface Science Trainor, T. P., Fitts, J. P., Templeton, A. S., Grolimund, D., Brown, Jr., G. E. 2002; 244: 239-244
• A new hard x-ray XAFS spectroscopy facility for environmental samples, including actinides, at the Stanford Synchrotron Radiation Laboratory Bargar, J. R., Brown, Jr., G. E., Evans, I., Rabedeau, T., Rowen, M., Rogers, J. Nuclear Energy Agency/Organization for Economic Co-operation and Development, AEN/NEA 2002. 2002: 10–12
• Actinides in earth materials: The importance of natural analogues Farges, F., Harfouche, M., Petit, P-E., Brown, Jr., G. E. Nuclear Energy Agency/Organization for Economic Co-operation and Development, AEN/NEA 2002. 2002: 10–12
• Grazing-incidence XAFS study of aqueous Zn(II) sorption on alpha-Al2O3 single crystals JOURNAL OF COLLOID AND INTERFACE SCIENCE Trainor, T. P., Fitts, J. P., Templeton, A. S., Grolimund, D., Brown, G. E. 2001; 244 (2): 239-244

  View details for DOI 10.1006/jcis.2001.7951

  View details for Web of Science ID 000172745100003

• Pb(II) distributions at biofilm-metal oxide interfaces PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA Templeton, A. S., Trainor, T. P., Traina, S. J., Spormann, A. M., Brown, G. E. 2001; 98 (21): 11897-11902

  Abstract

  The distribution of aqueous Pb(II) sorbed at the interface between Burkholderia cepacia biofilms and hematite (alpha-Fe(2)O(3)) or corundum (alpha-Al(2)O(3)) surfaces has been probed by using an application of the long-period x-ray standing wave technique. Attached bacteria and adsorbed organic matter may interfere with sorption processes on metal oxide surfaces by changing the characteristics of the electrical double layer at the solid-solution interface, blocking surface sites, or providing a variety of new sites for metal binding. In this work, Pb L(alpha) fluorescence yield profiles for samples equilibrated with 10(-7) to 10(-3.8) M Pb(II) were measured and modeled to determine quantitatively the partitioning of Pb(II) at the biofilm-metal oxide interface. Our data show that the reactive sites on the metal oxide surfaces were not passivated by the formation of a monolayer biofilm. Instead, high-energy surface sites on the metal oxides form the dominant sink for Pb(II) at submicromolar concentrations, following the trend alpha-Fe(2)O(3) (0001) > alpha-Al(2)O(3) (1102) > alpha-Al(2)O(3) (0001), despite the greater site density within the overlying biofilms. At [Pb] > 10(-6) M, significant Pb uptake by the biofilms was observed.

  View details for Web of Science ID 000171558900016

  View details for PubMedID 11572932

  View details for PubMedCentralID PMC59817

• Surface science - How minerals react with water SCIENCE Brown, G. E. 2001; 294 (5540): 67-?

  View details for Web of Science ID 000171448800029

  View details for PubMedID 11588241

• Transition elements in water-bearing silicate glasses/melts. Part II. Ni in water-bearing glasses GEOCHIMICA ET COSMOCHIMICA ACTA Farges, F., Munoz, M., Siewert, R., Malavergne, V., Brown, G. E., Behrens, H., Nowak, M., Petit, P. E. 2001; 65 (10): 1679-1693

  View details for Web of Science ID 000168762600011

• Oxidation state and coordination of Fe in minerals: An FeK-XANES spectroscopic study AMERICAN MINERALOGIST Wilke, M., Farges, F., Petit, P. E., Brown, G. E., Martin, F. 2001; 86 (5-6): 714-730

  View details for Web of Science ID 000168554800012

• Transition elements in water-bearing silicate glasses/melts. Part I. A high-resolution and anharmonic analysis of Ni coordination environments in crystals, glasses, and melts GEOCHIMICA ET COSMOCHIMICA ACTA Farges, F., Brown, G. E., Petit, P. E., Munoz, M. 2001; 65 (10): 1665-1678

  View details for Web of Science ID 000168762600010

• Sorption of trace elements from aqueous media: Modern perspectives from spectroscopic studies and comments on adsorption in the marine environment International Geology Review Brown, Jr., G. E., Parks, G. A. 2001; 43: 867-976
• Mineralogy of lead in a soil developed on a Pb-mineralized sandstone (Largentiere, France) AMERICAN MINERALOGIST Morin, G., Juillot, F., Ildefonse, P., CALAS, G., Samama, J. C., Chevallier, P., Brown, G. E. 2001; 86 (1-2): 92-104

  View details for Web of Science ID 000166355700010

• Interaction of water and aqueous chromium ions with iron oxide surfaces Nuclear Site Remediation - First Accomplishments of the Environmental Management Science Program Brown, Jr. , G. E., Chambers, S. A., Amonette, J. E., Rustad, J. R., Kendelewicz, T., Liu, P., Doyle, C. S., Grolimund, D., Foster-Mills, N. S., Joyce, S.A., S. A., Thevuthasan, S. edited by Eller, P. G., Heineman, W. R. Am. Chem. Soc., Columbus, OH. 2001: 212–246
• Transition elements in water-bearing silicate glasses/melts. Part I. A high resolution and anharmonic EXAFS analysis of Ni coordination environments in crystals, glasses, and melts Geochimica et Cosmochimica Acta Farges, F., Brown, Jr., G. E., Petit, P.-E., Munoz, M. 2001; 65: 1665-1678
• Oxidation state and coordination of Fe in minerals: an Fe K-XANES study American Mineralogist Wilke, M., Farges, F., Petit, P-E., Brown, Jr., G. E., Martin, F. 2001; 86: 714-730
• Inside rocks Geotimes, American Geological Institute Astheimer, R., Kristin, B., Brown, Jr., G. E., Hoy, J., Jones, K. W., Sturchio, N. C., Sutton, S. R., Waychunas, G. A., Woodward, N. B. 2001: 20-23
• Transition elements in water-bearing silicate glasses/melts. Part II. Ni in water-bearing glasses Geochimica et Cosmochimica Acta Farges, F., Munoz, M., Siewert, R., Malavergne, V., Brown, Jr., G. E., Behrens, H., Nowak, M., Petit, P.-E. 2001; 65: 1679-1693
• Structural evolution of Cr(III) polymeric species at the gamma-Al2O3/water interface ENVIRONMENTAL SCIENCE & TECHNOLOGY Fitts, J. P., Brown, G. E., Parks, G. A. 2000; 34 (24): 5122-5128

  View details for DOI 10.1021/es9914285

  View details for Web of Science ID 000165887800009

• Spectroscopic study of the reaction of aqueous Cr(VI) with Fe3O4(111) surfaces SURFACE SCIENCE Kendelewicz, T., Liu, P., Doyle, C. S., Brown, G. E. 2000; 469 (2-3): 144-163

  View details for Web of Science ID 000166194900006

• Adsorption and Precipitation of Aqueous Zn(II) on Alumina Powders. Journal of colloid and interface science Trainor, T. P., Brown, G. E., Parks, G. A. 2000; 231 (2): 359-372

  Abstract

  The products of aqueous Zn(II) sorption on high-surface-area alumina powders (Linde-A) have been studied using XAFS spectroscopy as a function of Zn(II) sorption density (Gamma=0.2 to 3.3 µmol/m(2)) at pH values of 7.0 to 8.2. Over equilibration times of 15-111 h, we find that at low sorption densities (Gamma=0.2-1.1 µmol/m(2)) Zn(II) forms predominantly inner-sphere bidentate surface complexes with AlO(6) polyhedra, whereas at higher sorption densities (Gamma=1.5 to 3.5 µmol/m(2)), we find evidence for the formation of a mixed-metal Zn(II)-Al(III) hydroxide coprecipitate with a hydrotalcite-type local structure. These conclusions are based on an analysis of first- and second-neighbor interatomic distances derived from EXAFS spectra collected under ambient conditions on wet samples. At low sorption densities the sorption mechanism involves a transformation from six-coordinated Zn-hexaaquo solution complexes (with an average Zn-O distance of 2.07 Å) to four-coordinated surface complexes (with an average Zn-O distance of 1.97 Å) as described by the reaction identical withAl(OH(a))(OH(b))+Zn (H(2)O)(6)(2+)--> identical withAl(OH(a)') (OH(b)')Zn(OH(c)')(OH(d)'+4H(2)O+zH(+), where identical withAl(OH(a))(OH(b)) represents edge-sharing sites of Al(O,OH,OH(2))(6) octahedra to which Zn(O,OH,OH(2))(4) bonds in a bidentate fashion. The proton release consistent with this reaction (z=a-a'+b-b'+4-c'-d'), and with bond valence analysis falls in the range of 0 to 2 H(+)/Zn(II) when hydrolysis of the adsorbed Zn(II) complex is neglected. This interpretation suggests that proton release is likely a strong function of the coordination chemistry of the surface hydroxyl groups. At higher sorption densities (1.5 to 3.5 µmol/m(2)), a high-amplitude, second-shell feature in the Fourier transform of the EXAFS spectra indicates the formation of a three-dimensional mixed-metal coprecipitate, with a hydrotalcite-like local structure. Nitrate anions presumably satisfy the positive layer charge of the Al(III)-Zn(II) hydroxide layers in which the Zn/Al ratio falls in the range of 1 : 1 to 2 : 1. Our results for the higher Gamma-value sorption samples suggest that Zn-hydrotalcite-like phases may be a significant sink for Zn(II) in natural or catalytic systems containing soluble alumina compounds. Copyright 2000 Academic Press.

  View details for DOI 10.1006/jcis.2000.7111

  View details for PubMedID 11049686

• Adsorption and precipitation of aqueous Zn(II) on alumina powders JOURNAL OF COLLOID AND INTERFACE SCIENCE Trainor, T. P., Brown, G. E., Parks, G. A. 2000; 231 (2): 359-372

  View details for DOI 10.1006/jcis.2000.7111

  View details for Web of Science ID 000165199200017

• Characterization and speciation of mercury-bearing mine wastes using X-ray absorption spectroscopy 5th International Conference on Mercury as a Global Pollutant Kim, C. S., Brown, G. E., Rytuba, J. J. ELSEVIER SCIENCE BV. 2000: 157–68

  Abstract

  Mining of mercury deposits located in the California Coast Range has resulted in the release of mercury to the local environment and water supplies. The solubility, transport, and potential bioavailability of mercury are controlled by its chemical speciation, which can be directly determined for samples with total mercury concentrations greater than 100 mg kg(-1) (ppm) using X-ray absorption spectroscopy (XAS). This technique has the additional benefits of being non-destructive to the sample, element-specific, relatively sensitive at low concentrations, and requiring minimal sample preparation. In this study, Hg L(III)-edge extended X-ray absorption fine structure (EXAFS) spectra were collected for several mercury mine tailings (calcines) in the California Coast Range. Total mercury concentrations of samples analyzed ranged from 230 to 1060 ppm. Speciation data (mercury phases present and relative abundances) were obtained by comparing the spectra from heterogeneous, roasted (calcined) mine tailings samples with a spectral database of mercury minerals and sorbed mercury complexes. Speciation analyses were also conducted on known mixtures of pure mercury minerals in order to assess the quantitative accuracy of the technique. While some calcine samples were found to consist exclusively of mercuric sulfide, others contain additional, more soluble mercury phases, indicating a greater potential for the release of mercury into solution. Also, a correlation was observed between samples from hot-spring mercury deposits, in which chloride levels are elevated, and the presence of mercury-chloride species as detected by the speciation analysis. The speciation results demonstrate the ability of XAS to identify multiple mercury phases in a heterogeneous sample, with a quantitative accuracy of +/-25% for the mercury-containing phases considered. Use of this technique, in conjunction with standard microanalytical techniques such as X-ray diffraction and electron probe microanalysis, is beneficial in the prioritization and remediation of mercury-contaminated mine sites.

  View details for Web of Science ID 000089587200016

  View details for PubMedID 11036987

• Inorganic Ligand Effects on Pb(II) Sorption to Goethite (alpha-FeOOH). Journal of colloid and interface science Ostergren, J. D., Trainor, T. P., Bargar, J. R., Brown, G. E., Parks, G. A. 2000; 225 (2): 466-482

  Abstract

  Macroscopic measurements show that Pb(II) uptake on iron-(hydr)oxides can be altered significantly by dissolved carbonate (enhanced up to 18% at pH 5 and decreased above pH approximately 6.5 in analyses at 1 atm CO(2)). This study elucidates the molecular-scale processes giving rise to these macroscopic effects by characterizing the structures of Pb(II) sorption complexes formed on goethite (alpha-FeOOH) in the presence of carbonate using in situ Pb L(III)-EXAFS and ATR-FTIR spectroscopies. Bond valence and structural constraints are applied to develop mineral surface site-specific models for Pb sorption. Under all conditions studied (pH 5-7, Gamma(Pb)=0.4-4µmol/m(2), and P(CO(2))=0-1 atm), Pb(II) forms predominantly inner-sphere edge-sharing (bidentate and/or tridentate) complexes with Fe(O,OH)(6) octahedra (R(Pb-Fe) approximately 3.3 Å). Corner-sharing complexes (R(Pb-Fe) approximately 3.9 Å) are observed only in low pH (5) samples (P(CO(2)) 0-1 atm). Consistent with this pH sensitivity, site-specific analyses suggest that the relative abundance of corner-sharing sites reflects changes in the proton affinity of triply coordinated sites on the goethite (110) surface as suggested previously. FTIR results suggest the existence of ternary surface complexes in which carbonate groups bond to Pb as monodentate ligands. EXAFS data indicate that these ternary complexes are bound to the surface through Pb, forming metal-bridged (Type A) complexes. Findings are summarized as structural models and corresponding mineral surface site-specific chemical reactions. Copyright 2000 Academic Press.

  View details for PubMedID 11254287

• Inorganic ligand effects on Pb(II) sorption to goethite (alpha-FeOOH) - I. Carbonate JOURNAL OF COLLOID AND INTERFACE SCIENCE Ostergren, J. D., Trainor, T. P., Bargar, J. R., Brown, G. E., Parks, G. A. 2000; 225 (2): 466-482

  View details for Web of Science ID 000086988300027

• Inorganic ligand effects on Pb(II) sorption to goethite (alpha-FeOOH) - II. Sulfate JOURNAL OF COLLOID AND INTERFACE SCIENCE Ostergren, J. D., Brown, G. E., Parks, G. A., Persson, P. 2000; 225 (2): 483-493

  View details for Web of Science ID 000086988300028

• Inorganic Ligand Effects on Pb(II) Sorption to Goethite (alpha-FeOOH). Journal of colloid and interface science Ostergren, J. D., Brown, G. E., Parks, G. A., Persson, P. 2000; 225 (2): 483-493

  Abstract

  The effects of sulfate anions on the uptake of Pb(II) onto goethite were investigated at the molecular level using in situ Pb L(III)-EXAFS and ATR-FTIR spectroscopies. Macroscopic uptake data show that Pb uptake can be enhanced by at least 30% at pH 5 in the presence of 3.16 mM sulfate and that sulfate uptake at pH 7 can be enhanced by more than a factor of 3 in the presence of 1.0 mM Pb. Consistent with behavior in sulfate-free systems, Pb(II) forms inner-sphere complexes sharing either corners or edges with Fe(O,OH)(6) octahedra under all conditions studied. The relative fraction of corner-sharing complexes is, however, significantly enhanced in the presence of sulfate at pH 5, 6, and 7 (all conditions studied) and additional sulfate species with C(3v) or lower point symmetry were noted in the presence of Pb by ATR-FTIR. Drawing on bond valence and structural constraints developed in J. D. Ostergren et al. (2000, J. Colloid Interface Science 224, 000-000), these results indicate formation of Type A ternary complexes bonded to the surface through Pb that is bound as a bridging bidenate complex to two adjacent A-type (singly coordinated) surface oxygens (( identical withFe-O)(2)-Pb-OSO(3)). Copyright 2000 Academic Press.

  View details for DOI 10.1006/jcis.1999.6702

  View details for PubMedID 11254288

• Structure of the hydrated alpha-Al(2)O(3) (0001) surface Science (New York, N.Y.) Eng, P. J., Trainor, T. P., Brown, G. E., Waychunas, G. A., Newville, M., Sutton, S. R., Rivers, M. L. 2000; 288 (5468): 1029-33

  Abstract

  The physical and chemical properties of the hydrated alpha-Al(2)O(3) (0001) surface are important for understanding the reactivity of natural and synthetic aluminum-containing oxides. The structure of this surface was determined in the presence of water vapor at 300 kelvin by crystal truncation rod diffraction at a third-generation synchrotron x-ray source. The fully hydrated surface is oxygen terminated, with a 53% contracted double Al layer directly below. The structure is an intermediate between alpha-Al(2)O(3) and gamma-Al(OH)(3), a fully hydroxylated form of alumina. A semiordered oxygen layer about 2.3 angstroms above the terminal oxygen layer is interpreted as adsorbed water. The clean alpha-Al(2)O(3) (0001) surface, in contrast, is Al terminated and significantly relaxed relative to the bulk structure. These differences explain the different reactivities of the clean and hydroxylated surfaces.

  View details for PubMedID 10807569

• Structure of the hydrated alpha-Al2O3 (0001) surface SCIENCE Eng, P. J., Trainor, T. P., Brown, G. E., WAYCHUNAS, G. A., Newville, M., Sutton, S. R., Rivers, M. L. 2000; 288 (5468): 1029-1033

  View details for Web of Science ID 000086988400031

• Reaction of water with the (100) and (111) surfaces of Fe3O4 SURFACE SCIENCE Kendelewicz, T., Liu, P., Doyle, C. S., Brown, G. E., Nelson, E. J., Chambers, S. A. 2000; 453 (1-3): 32-46

  View details for Web of Science ID 000087302400013

• Growth and electronic structure of vanadium on alpha-Al2O3(0001) SURFACE SCIENCE Biener, J., Baumer, M., Madix, R. J., Liu, P., Nelson, E., Kendelewisz, T., Brown, G. 2000; 449 (1-3): 50-60

  View details for Web of Science ID 000086056800013

• Formation and Release of Cobalt(II) Sorption and Precipitation Products in Aging Kaolinite-Water Slurries. Journal of colloid and interface science Thompson, H. A., Parks, G. A., Brown, G. E. 2000; 222 (2): 241-253

  Abstract

  The uptake and release behavior of cobalt(II) was studied over thousands of hours in CO(2)-free aqueous suspensions of kaolinite under three pairs of total cobalt concentration (Co(T)) and near-neutral pH (7.5-7.8) conditions. Dissolved cobalt, aluminum, and silicon concentrations were monitored by ICPMS, and cobalt-containing products were identified by EXAFS spectroscopy. In each uptake experiment, cobalt sorbed to kaolinite as a mixture of surface-adsorbed monomers or polymers and hydrotalcite-like precipitates of the approximate composition Co(x)Al(OH)(2x+2)(A(n-))(1/n), where 2

  View details for DOI 10.1006/jcis.1999.6631

  View details for PubMedID 10662519

• Spectroscopic study of the reaction of Cr(VI)aqueous with Fe3O4 (111) surfaces Surface Science Kendelewicz, T., Liu, P., Doyle, C. S., Brown, Jr., G. E. 2000; 469: 144-163
• XAFS study of Cu model compounds and Cu2+ sorption products on amorphous SiO2, gamma-Al2O3, and anatase AMERICAN MINERALOGIST Cheah, S. F., Brown, G. E., Parks, G. A. 2000; 85 (1): 118-132

  View details for Web of Science ID 000084714000013

• XAFS study of copper model compounds and copper(II) sorption on amorphous SiO2, α-Al2O3, and anatase American Mineralogist Cheah, S.-F., Brown, Jr., G. E., Parks, G. A. 2000; 85: 118-132
• Structure and Bonding of Cu(II)-Glutamate Complexes at the gamma-Al(2)O(3)-Water Interface. Journal of colloid and interface science Fitts, J. P., Persson, P., Brown, G. E., Parks, G. A. 1999; 220 (1): 133-147

  Abstract

  Thecomposition and mode of attachment of Cu(II) complexes at the gamma-Al(2)O(3)-water interface in suspensions containing a simple amino acid (glutamate) were characterized with EXAFS and FTIR spectroscopies. The spectroscopic results indicate that two types of Cu(II)-glutamate-alumina interactions are primarily responsible for Cu(II) and glutamate uptake between pH 4 and 9. In acidic suspensions of alumina, glutamate forms a bridge between Cu(II) ions and the (hydr)oxide surface (Type B complex). In this Type B surface complex, Cu(II) is bonded to amino acid headgroups (i.e., (+)H(3)NCHRCOO(-)) of two glutamate molecules. Spectroscopic and ionic strength dependent uptake results are combined to propose that the nonbonded side chain carboxylate groups of this complex are attracted to the oxide surface through long-range forces, leading to enhanced Cu(II) uptake relative to the glutamate-free system. In alkaline suspensions the relative amount of surface-bound Cu(II) complexed by glutamate decreases, and a direct Cu(II)-surface bond becomes the dominant mode of attachment (Type A complex). These surface complexes differ markedly from the species found in the alumina-free Cu(II)-glutamate aqueous system under similar solution conditions, where Cu(H(2)O)(2+)(6) and Cu(glutamate)(2-)(2) are the dominant species in acidic and alkaline solutions, respectively. Based on these spectroscopic results, surface complexation reactions are proposed for the Cu(II) and glutamate ternary interactions with the alumina surface in this system. Similarities between the results of this study and Cu(II) uptake behavior and complexation in the presence of natural organic material (NOM) indicate that Cu(II)-glutamate interactions mimic those in more complex Cu(II)-NOM-mineral-water systems. Copyright 1999 Academic Press.

  View details for DOI 10.1006/jcis.1999.6521

  View details for PubMedID 10550251

• The interaction of carbon dioxide with single crystal CaO(100) surfaces 6th International Conference on the Structure of Surfaces (ICSOS-6) Doyle, C. S., Kendelewicz, T., Carrier, X., Brown, G. E. WORLD SCIENTIFIC PUBL CO PTE LTD. 1999: 1247–54

  View details for Web of Science ID 000086557100039

• Reaction of water with clean surfaces of MnO(100) 6th International Conference on the Structure of Surfaces (ICSOS-6) Kendelewicz, T., Doyle, C. S., Carrier, X., Brown, G. E. WORLD SCIENTIFIC PUBL CO PTE LTD. 1999: 1255–63

  View details for Web of Science ID 000086557100040

• Reaction of CO2 with MgO(100) surfaces 6th International Conference on the Structure of Surfaces (ICSOS-6) Carrier, X., Doyle, C. S., Kendelewicz, T., Brown, G. E. WORLD SCIENTIFIC PUBL CO PTE LTD. 1999: 1237–45

  View details for Web of Science ID 000086557100038

• A synchrotron study of the growth of vanadium oxide on Al2O3(0001) SURFACE SCIENCE Biener, J., Baumer, M., Madix, R. J., Liu, P., Nelson, E. J., Kendelewicz, T., Brown, G. E. 1999; 441 (1): 1-9

  View details for Web of Science ID 000083385000004

• Outer-sphere adsorption of Pb(II)EDTA on goethite GEOCHIMICA ET COSMOCHIMICA ACTA Bargar, J. R., Persson, P., Brown, G. E. 1999; 63 (19-20): 2957-2969

  View details for Web of Science ID 000083824200010

• Structural investigation of platinum solubility in silicate glasses AMERICAN MINERALOGIST Farges, F., Neuville, D. R., Brown, G. E. 1999; 84 (10): 1562-1568

  View details for Web of Science ID 000083078900009

• Structure and composition of copper(II)-2,2 '-bipyridine sorption complexes on amorphous SiO2 GEOCHIMICA ET COSMOCHIMICA ACTA Cheah, S. F., Brown, G. E., Parks, G. A. 1999; 63 (19-20): 3229-3246

  View details for Web of Science ID 000083824200035

• Sorption of Co(II) on Metal Oxide Surfaces. Journal of colloid and interface science Towle, S. N., Bargar, J. R., Brown, G. E., Parks, G. A. 1999; 217 (2): 312-321

  Abstract

  We have characterized the adsorption of Co(II) on the (0001) and (1102) surfaces of alpha-Al(2)O(3) single crystals under ambient conditions using polarization-dependent grazing-incidence X-ray absorption fine structure spectroscopy, in combination with bond valence modeling. Co(II) ions were found to be adsorbed on both surfaces in an inner-sphere fashion. Adions were found to adsorb dominantly in a tridentate fashion (i.e., bonded to three surface oxygens) on the (0001) surface and dominantly in a tetradentate fashion on the (1102) surface. Based on EXAFS results and bond valence analysis, plausible surface complexation reactions for Co(II) sorption on these two surfaces can be written as represent surface water molecules, hydroxyl groups, and oxygens bonded to one, two, and three Al cations, respectively. Copyright 1999 Academic Press.

  View details for DOI 10.1006/jcis.1999.6351

  View details for PubMedID 10469539

• Sorption of Co(II) on metal oxide surfaces I. Identification of specific binding sites of Co(II) on (110) and (001) surfaces of TiO2 (rutile) by grazing-incidence XAFS spectroscopy JOURNAL OF COLLOID AND INTERFACE SCIENCE Towle, S. N., Brown, G. E., Parks, G. A. 1999; 217 (2): 299-311

  View details for Web of Science ID 000082789900008

• Sorption of Co(II) on Metal Oxide Surfaces. Journal of colloid and interface science Towle, S. N., Brown, G. E., Parks, G. A. 1999; 217 (2): 299-311

  Abstract

  We have examined the molecular-scale details of aqueous Co(II) surface complexes and the types of surface sites to which these complexes bind on the (110) and (001) surfaces of single-crystal TiO(2) (rutile) using polarization-dependent grazing-incidence X-ray absorption fine structure (GI-XAFS) spectroscopy under ambient conditions in a humid atmosphere. On both surfaces, Co(II) adsorbs at sites corresponding to Ti-equivalent positions in an extension of the rutile structure. This result suggests that even if different crystallographic surfaces of metal oxides have strongly differing adsorption properties for gaseous species in ultra-high vacuum, they can have similar properties for adsorption of metal ions in aqueous solution, probably due to the tendency of liquid water to heal defects and satisfy the bonding requirements of coordinatively unsaturated surface atoms. Using a bond valence approach in combination with the XAFS results, we have proposed specific surface reactions for sorption of Co(II) on the (110) and (001) rutile surfaces as a function of pH and Co surface concentration. No evidence was found for well-ordered Co(II)-hydroxide-like precipitates that would show Co-Co pair correlations, or for Co-Ti pair correlations similar to those in anatase, as have been observed in other studies. These results demonstrate the utility of GI-XAFS spectroscopy on adsorbed metal ions at submonolayer surface coverages for determining the types of reactive sorption sites on metal oxide surfaces. Copyright 1999 Academic Press.

  View details for DOI 10.1006/jcis.1999.6264

  View details for PubMedID 10469538

• Ambient-temperature synthesis, evolution, and characterization of cobalt-aluminum hydrotalcite-like solids CLAYS AND CLAY MINERALS Thompson, H. A., Parks, G. A., Brown, G. E. 1999; 47 (4): 425-438

  View details for Web of Science ID 000082326300005

• Dynamic interactions of dissolution, surface adsorption, and precipitation in an aging cobalt(II)-clay-water system GEOCHIMICA ET COSMOCHIMICA ACTA Thompson, H. A., Parks, G. A., Brown, G. E. 1999; 63 (11-12): 1767-1779

  View details for Web of Science ID 000082080100012

• Quantitative speciation of lead in selected mine tailings from Leadville, CO ENVIRONMENTAL SCIENCE & TECHNOLOGY Ostergren, J. D., Brown, G. E., Parks, G. A., Tingle, T. N. 1999; 33 (10): 1627-1636

  View details for Web of Science ID 000080311400011

• Grazing-incidence XAFS investigations of Cu(II) sorption products at alpha-Al2O3-water and alpha-SiO2-water interfaces JOURNAL OF SYNCHROTRON RADIATION Fitts, J. P., Trainor, T. P., Grolimund, D., Bargar, J. R., Parks, G. A., Brown, G. E. 1999; 6: 627-629

  View details for Web of Science ID 000081221700181

  View details for PubMedID 15263403

• XAFS and XSW study of the distribution of Pb(II) sorbed to biofilms on alpha-Al2O3 and alpha-FeOOH surfaces 10th International Conference on XAFS (XAFS X) Templeton, A. S., Ostergren, J. D., Trainor, T. P., Foster, A. L., Traina, S. J., Spormann, A., Brown, G. E. WILEY-BLACKWELL. 1999: 642–644

  View details for Web of Science ID 000081221700186

  View details for PubMedID 15263408

• Adsorption of Au ferrihydrites using Au-L-III edge XAFS spectroscopy 10th International Conference on XAFS (XAFS X) Berrodier, I., Farges, F., Benedetti, M., Brown, G. WILEY-BLACKWELL. 1999: 651–652

  View details for Web of Science ID 000081221700189

  View details for PubMedID 15263411

• XANES studies at the Al K-edge of aluminium-rich surface phases in the soil environment JOURNAL OF SYNCHROTRON RADIATION Doyle, C. S., Traina, S. J., Ruppert, H., Kendelewicz, T., Rehr, J. J., Brown, G. E. 1999; 6: 621-623

  View details for Web of Science ID 000081221700179

  View details for PubMedID 15263401

• Identification of Cr species at the aqueous solution-hematite interface after Cr(VI)-Cr(III) reduction using GI-XAFS and Cr L-edge NEXAFS JOURNAL OF SYNCHROTRON RADIATION Grolimund, D., Trainor, T. P., Fitts, J. P., Kendelewicz, T., Liu, P., Chambers, S. A., Brown, G. E. 1999; 6: 612-614

  View details for Web of Science ID 000081221700176

  View details for PubMedID 15263398

• Utility of EXAFS in characterization and speciation of mercury-bearing mine wastes 10th International Conference on XAFS (XAFS X) Kim, C. S., Rytuba, J. J., Brown, G. E. WILEY-BLACKWELL. 1999: 648–650

  View details for Web of Science ID 000081221700188

  View details for PubMedID 15263410

• Combined EXAFS and FTIR investigation of sulfate and carbonate effects on Pb(II) sorption to goethite (alpha-FeOOH) 10th International Conference on XAFS (XAFS X) Ostergren, J. D., Bargar, J. R., Brown, G. E., Parks, G. A. WILEY-BLACKWELL. 1999: 645–647

  View details for Web of Science ID 000081221700187

  View details for PubMedID 15263409

• Grazing-incidence XAFS studies of aqueous Zn(II) on sapphire single crystals 10th International Conference on XAFS (XAFS X) Trainor, T. P., Fitts, J. P., Grolimund, D., Bargar, J. R., Brown, G. E. WILEY-BLACKWELL. 1999: 618–620

  View details for Web of Science ID 000081221700178

  View details for PubMedID 15263400

• Surface structure of MBE-grown alpha-Fe2O3(0001) by intermediate-energy X-ray photoelectron diffraction SURFACE SCIENCE Thevuthasan, S., Kim, Y. J., Yi, S. I., Chambers, S. A., Morais, J., Denecke, R., Fadley, C. S., Liu, P., Kendelewicz, T., Brown, G. E. 1999; 425 (2-3): 276-286

  View details for Web of Science ID 000080080200014

• X-ray absorption and photoemission study of the adsorption of aqueous Cr(VI) on single crystal hematite and magnetite surfaces SURFACE SCIENCE Kendelewicz, T., Liu, P., Doyle, C. S., Brown, G. E., Nelson, E. J., Chambers, S. A. 1999; 424 (2-3): 219-231

  View details for Web of Science ID 000079712000015

• Mineral surfaces and bioavailability of heavy metals: A molecular-scale perspective National-Academy-of-Sciences Colloquium on Geology, Mineralogy, and Human Welfare Brown, G. E., Foster, A. L., Ostergren, J. D. NATL ACAD SCIENCES. 1999: 3388–95

  Abstract

  There is a continual influx of heavy metal contaminants and pollutants into the biosphere from both natural and anthropogenic sources. A complex variety of abiotic and biotic processes affects their speciation and distribution, including adsorption onto and desorption from mineral surfaces, incorporation in precipitates or coprecipitates, release through the dissolution of minerals, and interactions with plants and microbes. Some of these processes can effectively isolate heavy metals from the biosphere, whereas others cause their release or transformation to different species that may be more (or less) bioavailable and/or toxic to organisms. Here we focus on abiotic adsorption and precipitation or coprecipitation processes involving the common heavy metal contaminant lead and the metalloids arsenic and selenium in mine tailings and contaminated soils. We have used extremely intense x-rays from synchrotron sources and a structure-sensitive method known as x-ray absorption fine structure (XAFS) spectroscopy to determine the molecular-level speciation of these elements at concentrations of 50 to several thousand ppm in the contaminated environmental samples as well as in synthetic sorption samples. Our XAFS studies of As and Pb in the mine tailings show that up to 50% of these contaminants in the samples studied may be present as adsorbed species on mineral surfaces, which makes them potentially more bioavailable than when present in sparingly soluble solid phases. Our XAFS studies of Se(VI) sorption on Fe2+-containing sulfates show that this element undergoes redox reactions that transform it into less bioavailable and less toxic species. This type of information on molecular-level speciation of heavy metal and metalloid contaminants in various environmental settings is needed to prioritize remediation efforts and to assess their potential hazard to humans and other organisms.

  View details for Web of Science ID 000079507900013

  View details for PubMedID 10097048

• XAFS determination of the chemical form of lead in smelter-contaminated soils and mine tailings: Importance of adsorption processes AMERICAN MINERALOGIST Morin, G., Ostergren, J. D., Juillot, F., Ildefonse, P., CALAS, G., Brown, G. E. 1999; 84 (3): 420-434

  View details for Web of Science ID 000078741000028

• Identification of Cr species at the solution-hematite interface after Cr(VI)-Cr(III) reduction using GI-XAFS and Cr L-edge NEXAFS Journal of Synchrotron Radiation Grolimund, D., Kendelewicz, T., Trainor, T. P., Liu, P., Fitts, J. P., Chambers, S. A., Brown, Jr., G. E. 1999; 6: 612-614
• Metal oxide surfaces and their interactions with aqueous solutions and microbial organisms CHEMICAL REVIEWS Brown, G. E., Henrich, V. E., Casey, W. H., Clark, D. L., Eggleston, C., Felmy, A., Goodman, D. W., Gratzel, M., Maciel, G., McCarthy, M. I., Nealson, K. H., Sverjensky, D. A., Toney, M. F., Zachara, J. M. 1999; 99 (1): 77-174

  View details for Web of Science ID 000078984500003

• XAFS and XSW studies of the distribution and chemical speciation of Pb sorbed to biofilms on α-Al2O3 and α-FeOOH surfaces Journal of Synchrotron Radiation Templeton, A. S., Ostergren, J. D., Trainor, T. P., Foster, A. L., Traina, S. J., Spormann, A., Brown, Jr., G. E. 1999; 6: 642-644
• Adsorption of Au on iron oxy-hydroxides using Au L3-edge XAFS spectroscopy Journal of Synchrotron Radiation Berrodier, I., Farges, F., Benedetti, M., Brown, Jr., G. E. 1999; 6: 651-652
• Quantitative lead speciation in selected mine tailings from Leadville, CO Environmental Science & Technology Ostergren, J. D., Brown, Jr., G. E., Parks, G. A., Tingle, T. N. 1999; 33: 1627-1636
• Al-XANES studies of aluminum-rich surface phases in the soil environment Journal of Synchrotron Radiation Doyle, C. S., Traina, S. J., Ruppert, H., Kendelewicz, T., Rehr, J. J., Brown, Jr., G. E. 1999; 6: 621-623
• Grazing-incidence XAFS investigations of Cu(II) sorption products at the oxide-water interface Journal of Synchrotron Radiation Fitts, J. P., Trainor, T. P., Grolimund, D., Bargar, J. R., Parks, G. A., Brown, Jr., G. E. 1999; 6: 627-629
• XAFS Spectroscopy Study of Cu(II) Sorption on Amorphous SiO2 and gamma-Al2O3: Effect of Substrate and Time on Sorption Complexes. Journal of colloid and interface science Cheah, S. F., Brown, G. E., Parks, G. A. 1998; 208 (1): 110-128

  Abstract

  We have used X-ray absorption fine structure (XAFS) spectroscopy to investigate Cu(II) sorption complexes on high surface area amorphous silica (am-SiO2) and gamma-Al2O3. For Cu(II) on gamma-Al2O3, analysis of XAFS data collected after a solution-solid total contact time of 80-170 h showed that monomeric Cu(II) species predominate at surface coverages of 0.007 and 0.05 µmol m-2. Cu(II) on the gamma-Al2O3 surface has aluminum second neighbors at about 2.8 Å. Geometrical considerations indicate that this distance is consistent with models of Cu(II) binding to the gamma-Al2O3 surface in inner-sphere bidentate or monodentate modes on Al(O,OH)6 octahedra. For Cu(II) sorbed on am-SiO2, analysis of XAFS data collected after a solution-solid total contact time of 80-110 h showed that a dimeric Cu(II)-surface complex predominates, along with a minority monomeric Cu(II) surface species, at 0.03 and 0.05 µmol m-2. The XAFS-derived Cu-Si distance is in the range of 2.98 to 3.05 Å, suggesting that Cu(II) binds to am-SiO2 in an inner-sphere, monodentate fashion. XAFS spectra of Cu(II) sorbed on am-SiO2 collected after 20-30 h total contact time are quantitatively different from those collected after 80-90 h contact time. Analyses of these spectra indicate that the ratio of dimeric to monomeric Cu(II) surface complexes has increased with contact time. A discussion of the processes responsible for the different Cu(II) complexes on am-SiO2 and gamma-Al2O3 is presented. Copyright 1998 Academic Press.

  View details for DOI 10.1006/jcis.1998.5678

  View details for PubMedID 9820755

• XAFS spectroscopy study of Cu(II) sorption on amorphous SiO2 and gamma-Al2O3: Effect of substrate and time on sorption complexes JOURNAL OF COLLOID AND INTERFACE SCIENCE Cheah, S. F., Brown, G. E., Parks, G. A. 1998; 208 (1): 110-128

  View details for Web of Science ID 000077359300013

• Reaction of water vapor with alpha-Al2O3(0001) and alpha-Fe2O3(0001) surfaces: synchrotron X-ray photoemission studies and thermodynamic calculations SURFACE SCIENCE Liu, P., Kendelewicz, T., Brown, G. E., Nelson, E. J., Chambers, S. A. 1998; 417 (1): 53-65

  View details for Web of Science ID 000077100900010

• Reaction of water with vacuum-cleaved CaO(100) surfaces: an X-ray photoemission spectroscopy study SURFACE SCIENCE Liu, P., Kendelewicz, T., Brown, G. E., Parks, G. A., Pianetta, P. 1998; 416 (1-2): 326-340

  View details for Web of Science ID 000076828200032

• Reaction of water with MgO(100) surfaces: Part III. X-ray standing wave studies SURFACE SCIENCE Liu, P., Kendelewicz, T., Nelson, E. J., Brown, G. E. 1998; 415 (1-2): 156-169

  View details for Web of Science ID 000076645000020

• Reaction of water with MgO(100) surfaces. Part I: Synchrotron X-ray photoemission studies of low-defect surfaces SURFACE SCIENCE Liu, P., Kendelewicz, T., Gordon, G. E., Parks, G. A. 1998; 412-13: 287-314

  View details for Web of Science ID 000076086700027

• Reaction of water with MgO(100) surfaces. Part II: Synchrotron photoemission studies of defective surfaces SURFACE SCIENCE Liu, P., Kendelewicz, T., Brown, G. E. 1998; 412-13: 315-332

  View details for Web of Science ID 000076086700028

• Interaction of sodium overlayers with the PbS(100) (galena) surface: evidence for a Na <-> Pb exchange reaction SURFACE SCIENCE Kendelewicz, T., Liu, P., Brown, G. E., Nelson, E. J. 1998; 411 (1-2): 10-22

  View details for Web of Science ID 000075652000016

• X-ray absorption fine-structure spectroscopy study of photocatalyzed, heterogeneous As(III) oxidation on kaolin and anatase ENVIRONMENTAL SCIENCE & TECHNOLOGY Foster, A. L., Brown, G. E., Parks, G. A. 1998; 32 (10): 1444-1452

  View details for Web of Science ID 000073648700013

• Quantitative arsenic speciation in mine tailings using X-ray absorption spectroscopy AMERICAN MINERALOGIST Foster, A. L., Brown, G. E., Tingle, T. N., Parks, G. A. 1998; 83 (5-6): 553-568

  View details for Web of Science ID 000073289400016

• Atomic geometry of the PbS(100) surface SURFACE SCIENCE Kendelewicz, T., Liu, P., Brown, G. E., Nelson, E. J. 1998; 395 (2-3): 229-238

  View details for Web of Science ID 000072194000015

• Use of x-ray absorption spectroscopy to study reaction mechanisms at metal oxide-water interfaces Am. Chem. Soc. Symposium Series 715, Kinetics and Mechanisms of Reactions at the Mineral/Water Interface Brown, Jr., G. E., Parks, G. A., Bargar, J. R., Towle, S. N. edited by Sparks, D. L., Grundl, T. 1998: 14–37
• Surface complexation of Pb(II) at oxide-water interfaces: III. XAFS determination of Pb(II) and Pb(II)-chloro adsorption complexes on goethite and alumina GEOCHIMICA ET COSMOCHIMICA ACTA Bargar, J. R., Brown, G. E., Parks, G. A. 1998; 62 (2): 193-207

  View details for Web of Science ID 000072512100002

• Structure and composition of uranium(VI) sorption complexes at the kaolinite-water interface Adsorption of Metals by Geomedia, Variables, Mechanisms, and Model Applications Thompson, H. A., Parks, G. A., Brown, Jr., G. E., Jenne (ed.), E. A. Academic Press. 1998: 349–370
• Abiotic selenium redox transformations in the presence of Fe(II,III) oxides SCIENCE Myneni, S. C., TOKUNAGA, T. K., Brown, G. E. 1997; 278 (5340): 1106-1109

  View details for Web of Science ID A1997YE65200046

• Prediction of extended x-ray-absorption fine-structure spectra from molecular interaction models: Na+(H2O)(n)-MgO (100) interface PHYSICAL REVIEW B McCarthy, M. I., Schenter, G. K., CHACONTAYLOR, M. R., Rehr, J. J., Brown, G. E. 1997; 56 (15): 9925-9936

  View details for Web of Science ID A1997YC39100105

• Differential redox and sorption of Cr(III/VI) on natural silicate and oxide minerals: EXAFS and XANES results GEOCHIMICA ET COSMOCHIMICA ACTA Peterson, M. L., Brown, G. E., Parks, G. A., Stein, C. L. 1997; 61 (16): 3399-3412

  View details for Web of Science ID A1997XY43900010

• Ti K-edge XANES studies of Ti coordination and disorder in oxide compounds: Comparison between theory and experiment PHYSICAL REVIEW B Farges, F., Brown, G. E., Rehr, J. J. 1997; 56 (4): 1809-1819

  View details for Web of Science ID A1997XY36600027

• Surface complexation of Pb(II) at oxide-water interfaces .1. XAFS and bond-valence determination of mononuclear and polynuclear Pb(II) sorption products on aluminum oxides GEOCHIMICA ET COSMOCHIMICA ACTA Bargar, J. R., Brown, G. E., Parks, G. A. 1997; 61 (13): 2617-2637

  View details for Web of Science ID A1997XN63700008

• Surface complexation of Pb(II) at oxide-water interfaces .2. XAFS and bond-valence determination of mononuclear Pb(II) sorption products and surface functional groups on iron oxides GEOCHIMICA ET COSMOCHIMICA ACTA Bargar, J. R., Brown, G. E., Parks, G. A. 1997; 61 (13): 2639-2652

  View details for Web of Science ID A1997XN63700009

• XAFS spectroscopic study of uranyl coordination in solids and aqueous solution AMERICAN MINERALOGIST Thompson, H. A., Brown, G. E., Parks, G. A. 1997; 82 (5-6): 483-496

  View details for Web of Science ID A1997XE09000007

• Selenium redox reactions and transport between ponded waters and sediments ENVIRONMENTAL SCIENCE & TECHNOLOGY TOKUNAGA, T. K., Brown, G. E., Pickering, I. J., Sutton, S. R., Bait, S. 1997; 31 (5): 1419-1425

  View details for Web of Science ID A1997WW94800040

• Surface passivation of magnetite by reaction with aqueous Cr(VI): XAFS and TEM results ENVIRONMENTAL SCIENCE & TECHNOLOGY Peterson, M. L., White, A. F., Brown, G. E., Parks, G. A. 1997; 31 (5): 1573-1576

  View details for Web of Science ID A1997WW94800061

• Coordination chemistry of titanium(IV) in silicate glasses and melts .4. XANES studies of synthetic and natural volcanic glasses and tektites at ambient temperature and pressure GEOCHIMICA ET COSMOCHIMICA ACTA Farges, F., Brown, G. E. 1997; 61 (9): 1863-1870

  View details for Web of Science ID A1997XA88700007

• Characterization of outer-sphere EDTA and Pb(II)EDTA surface complexes on goethite by FTIR and XAFS spectroscopy. Bargar, J. R., Persson, P., Brown, G. E. AMER CHEMICAL SOC. 1997: 135-GEOC

  View details for Web of Science ID A1997WP18503575

• XAFS determination of As(V) associated with Fe(III) oxyhydroxides in weathered mine tailings and contaminated soil from California, USA 9th International Conference on X-Ray Absorption Fine Structure Foster, A. L., Brown, G. E., Parks, G. A., Tingle, T. N., Voigt, D. E., Brantley, S. L. EDP SCIENCES S A. 1997: 815–16

  View details for Web of Science ID A1997XQ95200045

• XAFS studies of Pb(II)-chloro and Hg(II)-chloro ternary complexes on goethite 9th International Conference on X-Ray Absorption Fine Structure Bargar, J. R., Persson, P., Brown, G. E. EDP SCIENCES S A. 1997: 825–26

  View details for Web of Science ID A1997XQ95200050

• Ti K-edge XANES studies of oxides: Theory vs. experiment 9th International Conference on X-Ray Absorption Fine Structure Farges, F., Brown, G. E., Rehr, J. J. EDP SCIENCES S A. 1997: 191–93

  View details for Web of Science ID A1997XQ95100040

• Coordination of actinides in silicate melts 9th International Conference on X-Ray Absorption Fine Structure Farges, F., Brown, G. E., Wu, Z. EDP SCIENCES S A. 1997: 1009–10

  View details for Web of Science ID A1997XQ95200120

• Oxidation state, local structure, and ab-initio XAFS modeling of chromium in contaminated soils and model compounds 9th International Conference on X-Ray Absorption Fine Structure Peterson, M. L., Brown, G. E., Parks, G. A. EDP SCIENCES S A. 1997: 781–83

  View details for Web of Science ID A1997XQ95200036

• XAFS study of Cu(II) at the water-goethite (alpha-FeOOH) interface 9th International Conference on X-Ray Absorption Fine Structure Bochatay, L., Persson, P., Lovgren, L., Brown, G. E. EDP SCIENCES S A. 1997: 819–20

  View details for Web of Science ID A1997XQ95200047

• Surface Precipitation of Co(II)(aq) on Al2O3 Journal of colloid and interface science Towle, S. N., Bargar, J. R., Brown, G. E., Parks, G. A. 1997; 187 (1): 62-82

  Abstract

  Surface precipitation is an important process in many areas of science and technology, including modeling contaminant segregation from groundwater to solid phases and dispersion of active phases on catalyst supports. XAFS, TEM, and XPS measurements of Co(II) sorbed on Al2O3 demonstrate that surface precipitates have formed from solutions that are undersaturated with respect to any known bulk solid phase. The precipitates have a structure similar to that of Co(OH)2(s), but are disordered and have a high concentration of Co vacancies. The data plus thermodynamic reasoning have been used to analyze the plausibility of various models for surface precipitation and to show that for Co(II)/Al2O3 it occurs by forming a double-hydroxide phase containing substrate-derived Al(III) ions. This idea was corroborated by mixing aqueous solutions of Al(III) and Co(II) at the pH and concentration of the sorption samples, forming a stable colloidal precipitate that is less soluble than either Al(OH)3 or Co(OH)2. The Co XAFS of this material was similar to that of the sorption samples. Successful quantitative models of metal ion transport in groundwater need to include the possibility of forming ternary and higher order precipitates that include ions derived from sparingly soluble solids. For catalyst impregnation, surface coprecipitation can prevent production of a well-dispersed precursor material.

  View details for PubMedID 9245316

• XAFS and Bond-Valence Determination of the Structures and Compositions of Surface Functional Groups and Pb(II) and Co(II) Sorption Products on Single-Crystal alpha-Al2O3 Journal of colloid and interface science Bargar, J. R., Towle, S. N., Brown, G. E., Parks, G. A. 1997; 185 (2): 473-92

  Abstract

  The structures and compositions of Pb(II) adsorption complexes and surface binding sites on alpha-Al2O3 (0001) and (1&1macr;02) surfaces were investigated in the presence of water using grazing-incidence X-ray absorption fine structure (GI-XAFS) spectroscopy. Pb(II) ions were found to adsorb in an inner-sphere mode on alpha-Al2O3 (1&1macr;02) but as outer-sphere complexes on alpha-Al2O3 (0001). The distance between the outer-sphere complexes and the surface places useful constraints on double-layer properties of water. A bond-valence model is described that relates the reactivities of surface functional groups and adsorption complexes to their molecular structures and compositions, and places constraints on the stoichiometries of adsorption reactions, including proton release. The EXAFS and modeling results suggest that Pb(II) and Co(II) ions bond to [AlAlAl-->O-1/2--> and [Al-OH+1/22] surface functional groups. In contrast, [AlAl > OH] groups complex Co(II) but not Pb(II). The results indicate the importance of using structurally defined surface sites to describe reactions at oxide-water interfaces.

  View details for PubMedID 9028903

• XAFS and bond-valence determination of the structures and compositions of surface functional groups and Pb(II) and Co(II) sorption products on single-crystal alpha-Al2O3 JOURNAL OF COLLOID AND INTERFACE SCIENCE Bargar, J. R., Towle, S. N., Brown, G. E., Parks, G. A. 1997; 185 (2): 473-492

  View details for Web of Science ID A1997WD50200024

• Selenium transport between ponded waters and sediments Environmental Science & Technology Tokunaga, T. K., Brown, Jr., G. E., Pickering, I. J., Sutton, S. R., Bajt, S. 1997; 31: 1419-1425
• Ca X-ray absorption spectroscopy of C-S-H and some model compounds ADVANCES IN CEMENT RESEARCH Kirkpatrick, R. J., Brown, G. E., Xu, N., Cong, X. D. 1997; 9 (33): 31-36

  View details for Web of Science ID A1997XD74500005

• Quantitative determination of chromium valence in environmental samples using XAFS spectroscopy Symposium on Aqueous Chemistry and Geochemistry of Oxides, Oxyhydroxides, and Related Materials, at the 1996 MRS Spring Meeting Peterson, M. L., Brown, G. E., Parks, G. A. MATERIALS RESEARCH SOCIETY. 1997: 75–80

  View details for Web of Science ID A1997BH43B00010

• The effect of substrate type and 2,2'-bipyridine on the sorption of copper(II) on silica and alumina Symposium on Aqueous Chemistry and Geochemistry of Oxides, Oxyhydroxides, and Related Materials, at the 1996 MRS Spring Meeting Cheah, S. F., Brown, G. E., Parks, G. A. MATERIALS RESEARCH SOCIETY. 1997: 231–236

  View details for Web of Science ID A1997BH43B00031

• Surface precipitation in the Co(II)/Al2O3 sorption system Symposium on Aqueous Chemistry and Geochemistry of Oxides, Oxyhydroxides, and Related Materials, at the 1996 MRS Spring Meeting Towle, S. N., Bargar, J. R., Persson, P., Brown, G. E., Parks, G. A. MATERIALS RESEARCH SOCIETY. 1997: 237–242

  View details for Web of Science ID A1997BH43B00032

• XAFS study of Pb(II)-chloro- and Hg(II)-chloro- ternary complexes on goethite Journal de Physique IV, Colloque C Bargar, J. R., Persson, P., Brown, Jr., G. E. 1997; 2: 825-826
• Structure, composition, and reactivity of Pb(II) and Co(II) sorption products and surface functional groups on single-crystal α-Al2O3 Journal of Colloid and Interface Science Bargar, J. R., Towle, S. N., Brown, Jr., G. E., Parks, G. A. 1997; 185: 473-493
• Co(II) sorption at the calcite-water interface .1. X-ray photoelectron spectroscopic study GEOCHIMICA ET COSMOCHIMICA ACTA Xu, N., Hochella, M. F., Brown, G. E., Parks, G. A. 1996; 60 (15): 2801-2815

  View details for Web of Science ID A1996VC08800007

• Coordination chemistry of Ti(IV) in silicate glasses and melts .1. XAFS study of titanium coordination in oxide model compounds GEOCHIMICA ET COSMOCHIMICA ACTA Farges, F., Brown, G. E., Rehr, J. J. 1996; 60 (16): 3023-3038

  View details for Web of Science ID A1996VC98000007

• Coordination chemistry of Ti(IV) in silicate glasses and melts .2. Glasses at ambient temperature and pressure GEOCHIMICA ET COSMOCHIMICA ACTA Farges, F., Brown, G. E., NAVROTSKY, A., Gan, H., Rehr, J. J. 1996; 60 (16): 3039-3053

  View details for Web of Science ID A1996VC98000008

• Coordination chemistry of Ti(IV) in silicate glasses and melts .3. Glasses and melts from ambient to high temperatures GEOCHIMICA ET COSMOCHIMICA ACTA Farges, F., Brown, G. E., NAVROTSKY, A., Gan, H., Rehr, J. R. 1996; 60 (16): 3055-3065

  View details for Web of Science ID A1996VC98000009

• X-ray absorption spectroscopy of Co(II) sorption complexes on quartz (alpha-SiO2) and rutile (TiO2) GEOCHIMICA ET COSMOCHIMICA ACTA ODAY, P. A., CHISHOLMBRAUSE, C. J., Towle, S. N., Parks, G. A., Brown, G. E. 1996; 60 (14): 2515-2532

  View details for Web of Science ID A1996UY09800004

• An empirical model for the anharmonic analysis of high-temperature XAFS spectra of oxide compounds with applications to the coordination environment of Ni in NiO, gamma-Ni2SiO4 and Ni-bearing Na-disilicate glass and melt 5th Silicate Melt Workshop Farges, F., Brown, G. E. ELSEVIER SCIENCE BV. 1996: 93–106

  View details for Web of Science ID A1996UV56100008

• Photoemission study of Na and Cs adsorption on MgO(100)1 x 1 15th European Conference on Surface Science Kendelewicz, T., Liu, P., Brown, G. E., Nelson, E. J., Pianetta, P. ELSEVIER SCIENCE BV. 1996: 451–456

  View details for Web of Science ID A1996UV25400087

• Selenium transformations in ponded sediments SOIL SCIENCE SOCIETY OF AMERICA JOURNAL TOKUNAGA, T. K., Pickering, I. J., Brown, G. E. 1996; 60 (3): 781-790

  View details for Web of Science ID A1996UK98900013

• Direct XAFS evidence for heterogeneous redox reaction at the aqueous chromium/magnetite interface Symposium on Colloidal and Interfacial Phenomena to Aquatic Environments, at the 209th National Meeting of the American-Chemical-Society Peterson, M. L., Brown, G. E., Parks, G. A. ELSEVIER SCIENCE BV. 1996: 77–88

  View details for Web of Science ID A1996TW02100004

• Outer-sphere lead(II) adsorbed at specific surface sites on single crystal α-alumina Geochimica et Cosmochimica Acta Bargar, J. R., Towle, S. N., Brown, Jr., G. E., Parks, G. A. 1996; 60: 3541-3547
• Coordination chemistry of titanium(IV) in silicate glasses and melts. I. XAFS study of Ti coordination in oxide model compounds Geochimica et Cosmochimica Acta Farges, F., Brown, Jr., G. E., Rehr, J. J. 1996; 60: 3023-3038
• Coordination chemistry of titanium(IV) in silicate glasses and melts. Part III. Glasses and melts from ambient to high temperatures Geochimica et Cosmochimica Acta Farges, F., Brown, Jr., G. E., Navrotsky, A., Gan, H., Rehr, J.J. 1996; 60: 3055-3065
• X-ray absorption spectroscopy studies of selenium transformations in ponded sediments Soil Science Society of America Journal Tokunaga, T. K., Pickering, I. J., Brown, Jr., G. E. 1996; 60: 781-790
• Coordination chemistry of titanium(IV) in silicate glasses and melts. Part II. Glasses at ambient temperature and pressure Geochimica et Cosmochimica Acta Farges, F., Brown, Jr., G. E., Navrotsky, A., Gan, H., Rehr, J.J. 1996; 60: 3039-3053
• ADSORPTION AND STRUCTURAL ENVIRONMENT OF CO(II) AT THE ZINC OXIDE-AQUEOUS AND ZINC SULFIDE-AQUEOUS SOLUTION INTERFACES LANGMUIR Persson, P., Parks, G. A., Brown, G. E. 1995; 11 (10): 3782-3794

  View details for Web of Science ID A1995TC04000032

• X-RAY-ABSORPTION SPECTROSCOPIC STUDIES OF CADMIUM AND SELENITE ADSORPTION ON ALUMINUM-OXIDES LANGMUIR Papelis, C., Brown, G. E., Parks, G. A., Leckie, J. O. 1995; 11 (6): 2041-2048

  View details for Web of Science ID A1995RF22300033

• CATIONS IN GLASSES UNDER AMBIENT AND NON-AMBIENT CONDITIONS 1st European Conference on Synchrotron Radiation in Materials Science CALAS, G., Brown, G. E., Farges, F., Galoisy, L., Itie, J. P., Polian, A. ELSEVIER SCIENCE BV. 1995: 155–61

  View details for Web of Science ID A1995RF15800035

• XAFS STUDY OF CO(II) SORPTION AT THE ALPHA-AL2O3-WATER INTERFACE 8th International Conference on X-Ray Absorption Fine Structure (XAFS VIII) Towle, S. N., BARGAR, J. A., Persson, P., Brown, G. E., Parks, G. A. ELSEVIER SCIENCE BV. 1995: 439–40

  View details for Web of Science ID A1995QP96100170

• COORDINATION CHANGE AROUND 2WT-PERCENT NI IN NA2SI2O5 GLASS MELT SYSTEMS 8th International Conference on X-Ray Absorption Fine Structure (XAFS VIII) Farges, F., Brown, G. E., CALAS, G., Galoisy, L., WAYCHUNAS, G. A. ELSEVIER SCIENCE BV. 1995: 381–82

  View details for Web of Science ID A1995QP96100146

• XAFS STUDY OF CO(II) AT THE ZNO-AQUEOUS AND ZNS-AQUEOUS INTERFACES 8th International Conference on X-Ray Absorption Fine Structure (XAFS VIII) Persson, P., Parks, G. A., Brown, G. E. ELSEVIER SCIENCE BV. 1995: 453–54

  View details for Web of Science ID A1995QP96100177

• AL AND SI K-ABSORPTION EDGES OF AL2SIO5 POLYMORPHS USING THE NEW YB66 SOFT-X-RAY MONOCHROMATOR 8th International Conference on X-Ray Absorption Fine Structure (XAFS VIII) Froba, M., Wong, J., Rowen, M., Brown, G. E., Tanaka, T., Rek, Z. ELSEVIER SCIENCE BV. 1995: 555–56

  View details for Web of Science ID A1995QP96100218

• XAFS STUDY OF PB(II) SORPTION AT THE ALPHA-AL2O3-WATER INTERFACE 8th International Conference on X-Ray Absorption Fine Structure (XAFS VIII) Bargar, J. R., Brown, G. E., Parks, G. A. ELSEVIER SCIENCE BV. 1995: 455–56

  View details for Web of Science ID A1995QP96100178

• LOW AND AMBIENT-TEMPERATURE XAFS STUDY OF U(VI) IN SOLIDS AND AQUEOUS-SOLUTION 8th International Conference on X-Ray Absorption Fine Structure (XAFS VIII) Thompson, H. A., Brown, G. E., Parks, G. A. ELSEVIER SCIENCE BV. 1995: 167–68

  View details for Web of Science ID A1995QP96100061

• NEW OPPORTUNITIES IN 1-2-KEV SPECTROSCOPY 8th International Conference on X-Ray Absorption Fine Structure (XAFS VIII) Wong, J., Rek, Z. U., Rowen, M., Tanaka, T., Schafers, F., Muller, B., George, G. N., Pickering, I. J., Via, G., DeVries, B., Brown, G. E., Froba, M. ELSEVIER SCIENCE BV. 1995: 220–22

  View details for Web of Science ID A1995QP96100079

• SURFACE EXAFS AND X-RAY STANDING-WAVE STUDY OF THE CLEAVED CAO(100) SURFACE 8th International Conference on X-Ray Absorption Fine Structure (XAFS VIII) Kendelewicz, T., Liu, P., LABIOSA, W. B., Brown, G. E. ELSEVIER SCIENCE BV. 1995: 441–42

  View details for Web of Science ID A1995QP96100171

• Intracrystalline distribution of nickel in San Carlos olivine: An EXAFS study American Mineralogist Galoisy, L., Calas, G., Brown, Jr., G. E. 1995; 80: 1089-1092
• SORPTION AT MINERAL WATER INTERFACES - MACROSCOPIC AND MICROSCOPIC PERSPECTIVES Mineralogical-Society Winter Conference on Mineralogical Applications of Surface Science Brown, G. E., Parks, G. A., ODAY, P. A. CHAPMAN & HALL. 1995: 129–183

  View details for Web of Science ID A1995BD13E00005

• Coordination change around 2 wt% Ni in Na2Si2O5 glass/melt systems Physica B Farges, F., Brown, Jr., G. E., Calas, G., Galoisy, L., Waychunas, G. A. 1995; 208/209: 381-382
• X-ray scattering and x-ray spectroscopy studies of silicate melts STRUCTURE, DYNAMICS AND PROPERTIES OF SILICATE MELTS Brown, G. E., Farges, F., CALAS, G. 1995; 32: 317-410

  View details for Web of Science ID A1995BE38D00009

• Molecular Environmental Science: Speciation, Reactivity, and Mobility of Environmental Contaminants Report of the DOE Molecular Environmental Science Workshop, July 5-8, 1995, Airlie Center, VA edited by Brown, Jr., G. E., Chiamelli, R., Stock, L., Stults, R., Sutton, S. R., Traina, S. J. SLAC, Menlo Park, CA. 1995
• Adsorption and local environment of Co(II) at the zinc oxide- and zinc sulfide-aqueous interfaces Langmuir Persson, P., Parks, G. A., Brown, Jr., G. E. 1995; 11: 3782-3794
• X-ray absorption spectroscopy of selenium transformations in Kesterson Reservoir soils Environmental Science & Technology Pickering, I.J., Brown, Jr., G. E., Tokunaga, T.K. 1995; 29: 2456-2459
• Effect of surface structure on the adsorption of Co(II) on alpha-Al2O3: A glancing angle XAFS study Symposium on Structure and Properties of Interfaces in Ceramics, at the 1994 Fall Meeting of the Materials-Research-Society Towle, S. N., Bargar, J. R., Brown, G. E., Parks, G. A., Barbee, T. W. MATERIALS RESEARCH SOC. 1995: 23–28

  View details for Web of Science ID A1995BD52Z00004

• NEW OPPORTUNITIES IN XAFS INVESTIGATION IN THE 1-2-KEV REGION SOLID STATE COMMUNICATIONS Wong, J., George, G. N., Pickering, I. J., Rek, Z. U., Rowen, M., Tanaka, T., VIA, G. H., DeVries, B., Vaughan, D. E., Brown, G. E. 1994; 92 (7): 559-562

  View details for Web of Science ID A1994PN94100003

• STRUCTURAL TRANSFORMATION IN NI-BEARING NA2SI2O5 GLASS AND MELT GEOPHYSICAL RESEARCH LETTERS Farges, F., Brown, G. E., CALAS, G., Galoisy, L., WAYCHUNAS, G. A. 1994; 21 (18): 1931-1934

  View details for Web of Science ID A1994PE82400002

• STRUCTURAL ENVIRONMENT OF ZR IN 2 INOSILICATES FROM CAMEROON - MINERALOGICAL AND GEOCHEMICAL IMPLICATIONS AMERICAN MINERALOGIST Farges, F., Brown, G. E., Velde, D. 1994; 79 (9-10): 838-847

  View details for Web of Science ID A1994PM15900005

• X-RAY-ABSORPTION SPECTROSCOPY OF COBALT(II) MULTINUCLEAR SURFACE COMPLEXES AND SURFACE PRECIPITATES ON KAOLINITE JOURNAL OF COLLOID AND INTERFACE SCIENCE ODAY, P. A., Brown, G. E., Parks, G. A. 1994; 165 (2): 269-289

  View details for Web of Science ID A1994NR28700003

• MOLECULAR-STRUCTURE AND BINDING-SITES OF COBALT(II) SURFACE COMPLEXES ON KAOLINITE FROM X-RAY-ABSORPTION SPECTROSCOPY CLAYS AND CLAY MINERALS ODAY, P. A., Parks, G. A., Brown, G. E. 1994; 42 (3): 337-355

  View details for Web of Science ID A1994PB15300012

• EXTENDED X-RAY-ABSORPTION FINE-STRUCTURE (EXAFS) ANALYSIS OF DISORDER AND MULTIPLE-SCATTERING IN COMPLEX CRYSTALLINE SOLIDS JOURNAL OF THE AMERICAN CHEMICAL SOCIETY ODAY, P. A., Rehr, J. J., Zabinsky, S. I., Brown, G. E. 1994; 116 (7): 2938-2949

  View details for Web of Science ID A1994NG37800026

• Structural transformations in Ni-bearing Na2Si2O5 glass and melt Geophysical Research Letters Farges, F., Brown, Jr., G. E., Calas, G., Galoisy, L., Waychunas, G. A. 1994; 21: 1931-1934
• FLUORESCENCE YIELD XANES AND EXAFS EXPERIMENTS - APPLICATION TO HIGHLY DILUTE AND SURFACE SAMPLES 31st Annual Conference on Applications of X-Ray Analysis WAYCHUNAS, G. A., Brown, G. E. PLENUM PRESS DIV PLENUM PUBLISHING CORP. 1994: 607–617

  View details for Web of Science ID A1994BB55S00073

• New XAFS spectroscopic investigations in the 1-2 keV region Solid State Communications Wong, J., George, G. N., Pickering, I. J., Rek, Z. U., Rowen, M., Tanaka, T., Via, G. H., DeVries, B., Vaughan, D. E. W., Brown, Jr., G. E. 1994; 92: 559-562
• X-ray spectroscopic study of the structural environment of Zr in two inosilicates from Cameroon: implications for substitution mechanisms and Zr-partitioning American Mineralogist Farges, F., Brown, Jr., G. E., Velde, D. 1994; 79: 838-847
• HIGH-TEMPERATURE XAS STUDY OF FE2SIO4 LIQUID - REDUCED COORDINATION OF FERROUS IRON SCIENCE Jackson, W. E., DeLeon, J. M., Brown, G. E., WAYCHUNAS, G. A., Conradson, S. D., Combes, J. M. 1993; 262 (5131): 229-233

  Abstract

  X-ray absorption spectroscopy (XAS) of Fe(2+) in Fe(2)SiO(4) liquid at 1575 kelvin and 10(-4) gigapascal (1 bar) shows that the Fe(2+) -O bond length is 1.98 +/- 0.02 angstroms compared with approximately 2.22 angstroms in crystalline Fe(2)SiO(4) (fayalite) at the melting point (1478 kelvin), which indicates a decrease in average Fe(2+) coordination number from six in fayalite to four in the liquid. Anharmonicity in the liquid was accounted for using a data analysis procedure. This reduction in coordination number is similar to that observed on the melting of certain ionic salts. These results are used to develop a model of the medium-range structural environment of Fe(2+) in olivine-composition melts, which helps explain some of the properties of Fe(2)SiO(4) liquid, including density, viscosity, and the partitioning of iron and nickel between silicate melts and crystalline olivines. Some of the implications of this model for silicate melts in the Earth's crust and mantle are discussed.

  View details for Web of Science ID A1993MA66500031

  View details for PubMedID 17841870

• THE STRUCTURE OF APERIODIC, METAMICT (CA,TH)ZRTI2O7 (ZIRCONOLITE) - AN EXAFS STUDY OF THE ZR-SITES, TH-SITES AND U-SITES JOURNAL OF MATERIALS RESEARCH Farges, F., Ewing, R. C., Brown, G. E. 1993; 8 (8): 1983-1995

  View details for Web of Science ID A1993LR03900029

• GRAZING-INCIDENCE EXAFS SPECTROSCOPY OF METAL-ION SORPTION ON SINGLE-CRYSTAL ALPHA-AL2O3 Towle, S. N., Bargar, J. R., Brown, G. E., Parks, G. A., Persson, P., WAYCHUNAS, G. A., Barbee, T. W. AMER CHEMICAL SOC. 1993: 105-GEOC

  View details for Web of Science ID A1993KQ98102071

• LOCAL ENVIRONMENT AROUND GOLD(III) IN AQUEOUS CHLORIDE SOLUTIONS - AN EXAFS SPECTROSCOPY STUDY GEOCHIMICA ET COSMOCHIMICA ACTA Farges, F., SHARPS, J. A., Brown, G. E. 1993; 57 (6): 1243-1252

  View details for Web of Science ID A1993KW20300007

• KINETICS AND MECHANISM OF LIGAND-EXCHANGE OF AU(III), ZN(II), AND CD(II) CHLORIDES IN AQUEOUS-SOLUTION - AN NMR-STUDY FROM 28-98-DEGREES-C GEOCHIMICA ET COSMOCHIMICA ACTA SHARPS, J. A., Brown, G. E., Stebbins, J. F. 1993; 57 (4): 721-731

  View details for Web of Science ID A1993KN41200001

• The structure of aperiodic, metamict, (Ca,Th)2Zr2Ti4O14: an EXAFS study of the Zr, Th, and U sites Journal of Materials Research Farges, F., Ewing, R. C., Brown, Jr., G. E. 1993; 8: 1983-1995
• First XAFS spectra with a YB66 monochromator Synchrotron Radiation News Rowen, M., Rek, Z. U., Wong, J., Tanaka, T., George, G. N., Pickering, I. J., Via, G.H., Brown, Jr., G.E. 1993; 6: 25-27
• STRUCTURAL ENVIRONMENTS OF INCOMPATIBLE ELEMENTS IN SILICATE GLASS MELT SYSTEMS .2. UIV, UV, AND UVI GEOCHIMICA ET COSMOCHIMICA ACTA Farges, F., Ponader, C. W., CALAS, G., Brown, G. E. 1992; 56 (12): 4205-4220

  View details for Web of Science ID A1992KF60200007

• X-RAY ABSORPTION SPECTROSCOPIC STUDY OF SELENITE AND CADMIUM(II) COMPLEXES AT ALUMINUM-OXIDE WATER INTERFACES Papelis, C., Brown, G. E., Parks, G. A., Leckie, J. O. AMER CHEMICAL SOC. 1992: 50-GEOC

  View details for Web of Science ID A1992HK16102520

• EXAFS SPECTROSCOPIC STUDY OF NEPTUNIUM(V) SORPTION AT THE ALPHA-FEOOH WATER INTERFACE ENVIRONMENTAL SCIENCE & TECHNOLOGY Combes, J. M., CHISHOLMBRAUSE, C. J., Brown, G. E., Parks, G. A., Conradson, S. D., Eller, P. G., Triay, I. R., Hobart, D. E., Meijer, A. 1992; 26 (2): 376-382

  View details for Web of Science ID A1992HB87100027

• Synchrotron radiation in the earth sciences Encyclopedia of Earth Systems Science (Vol 4) Bassett, W. A., Brown, Jr., G. E. Academic Press. 1992: 339–350
• STRUCTURAL ENVIRONMENTS OF INCOMPATIBLE ELEMENTS IN SILICATE GLASS MELT SYSTEMS .1. ZIRCONIUM AT TRACE LEVELS GEOCHIMICA ET COSMOCHIMICA ACTA Farges, F., Ponader, C. W., Brown, G. E. 1991; 55 (6): 1563-1574

  View details for Web of Science ID A1991FU77200007

• SPECIATION OF AQUEOUS GOLD(III) CHLORIDES FROM ULTRAVIOLET VISIBLE ABSORPTION AND RAMAN RESONANCE RAMAN SPECTROSCOPIES GEOCHIMICA ET COSMOCHIMICA ACTA Peck, J. A., Tait, C. D., Swanson, B. I., Brown, G. E. 1991; 55 (3): 671-676

  View details for Web of Science ID A1991FD75200003

• INSITU X-RAY ABSORPTION STUDY OF LEAD-ION SURFACE COMPLEXES AT THE GOETHITE WATER INTERFACE LANGMUIR Roe, A. L., Hayes, K. F., CHISHOLMBRAUSE, C., Brown, G. E., Parks, G. A., Hodgson, K. O., Leckie, J. O. 1991; 7 (2): 367-373

  View details for Web of Science ID A1991EY64000029

• X-ray absorption study of lead complexes at α-FeOOH/water interfaces Langmuir Roe, A. L., Hayes, K. F., Chisholm-Brause, C. J., Brown, Jr., G. E., Hodgson, K. O., Parks, G. A., O., Leckie J. 1991; 7: 367-373
• EXAFS study of aqueous Co(II) sorption complexes on kaolinite and quartz surfaces XAFS VI, Sixth Internat. Conf. on X-ray Absorption Fine Structure O'Day, P. A., Brown, Jr., G. E., Parks, G. A., Hasnain, , S. S. Ellis Horwood Ltd. 1991: 260–262
• In-situ EXAFS study of changes in Co(II) sorption complexes on gamma-Al2O3 with increasing sorption densities XAFS VI, Sixth Internat. Conf. on X-ray Absorption Fine Structure Chisholm-Brause, C. J., Brown, Jr., G. E., Parks, G. A., Hasnain, S. S. Ellis Horwood Ltd. 1991: 263–265
• X-ray absorption and Raman-UV/visible spectroscopic study of Au(III) complexes in chloride solutions: direct evidence for chlorine and oxychlorine complexes XAFS VI, Sixth Internat. Conf. on X-ray Absorption Fine Structure Farges, F., Peck, J. A., Brown, Jr., G. E., Hasnain (ed.), S. S. Ellis Horwood Ltd. 1991: 478–480
• EXAFS study of the structural environments of trace levels of Zr4+, Mo6+, and U6+/U5+/U4+ in silicate glass/melt systems XAFS VI, Sixth Internat. Conf. on X-ray Absorption Fine Structure Farges, F., Brown, Jr., G. E., Ponader, C. W., Hasnain (ed.), S. S. Ellis Horwood Ltd. 1991: 309–311
• XAFS analysis in the anharmonic limit: Applications to Hi-Tc superconductors and ferrosilicates XAFS VI, Sixth Internat. Conf. on X-ray Absorption Fine Structure Mustre de Leon, J., Conradson, S. D., Batistic, I., Bishop, A. R., Raistrick, I., Jackson, W. E., Brown, Jr., G. E., Waychunas, G. A., Hasnain, S. S. Ellis Horwood Ltd. 1991: 54–57
• In-situ high temperature x-ray absorption study of ferrous iron in orthosilicates crystals and liquids XAFS VI, Sixth Internat. Conf. on X-ray Absorption Fine Structure Jackson, W. W., Brown, Jr., G. E., Waychunas, G. A., Mustre de Leon, J., Conradson, S. D., Combes, J., Hasnain (ed.), S. S. Ellis Horwood Ltd. 1991: 298–301
• X-ray absorption study of the local Ca environment in silicate glasses XAFS VI, Sixth Internat. Conf. on X-ray Absorption Fine Structure Combes, J. M., Brown, Jr., G. E., Waychunas, G. A. edited by Hasnain, S. S. Ellis Horwood, Ltd. 1991: 312–314
• X-RAY ABSORPTION FINE-STRUCTURE OF SYSTEMS IN THE ANHARMONIC LIMIT CONF ON X-RAYS IN MATERIALS ANALYSIS 2 : NOVEL APPLICATIONS AND RECENT DEVELOPMENTS DeLeon, J. M., Conradson, S. D., Batistic, I., Bishop, A. R., Raistrick, I., Jackson, W. E., Brown, G. SPIE - INT SOC OPTICAL ENGINEERING. 1991: 85–96

  View details for Web of Science ID A1991BU90T00011

• EVIDENCE FOR MULTINUCLEAR METAL-ION COMPLEXES AT SOLID WATER INTERFACES FROM X-RAY ABSORPTION-SPECTROSCOPY NATURE CHISHOLMBRAUSE, C. J., ODAY, P. A., Brown, G. E., Parks, G. A. 1990; 348 (6301): 528-531

  Abstract

  Metals dissolved in natural waters often become sorbed onto oxide or clay minerals, so that prediction of their chemical behaviour and transport properties requires knowledge of the structure and bonding of metal species at the solid/water interface. For many sorption systems, X-ray absorption spectroscopy (XAS) can be used to determine the identity and number of nearest-neighbour atoms and interatomic distances in aqueous complexes on solid surfaces, and thus to identify the dominant type of surface complex and the partitioning mechanism. Here we describe an XAS study of divalent cobalt (Co(II)) complexes sorbed on three different solids, gamma-Al2O3, rutile (TiO2) and kaolinite (Al2Si2O5(OH)4). We find direct evidence for the presence of multinuclear sorption complexes at surface coverages below one monolayer of Co(II) atoms. Our spectroscopic data reveal distinct differences in the number of coordinating atoms and interatomic distances in the surface complexes formed on each of the solids at the same sorption density. These results suggest that different oxide and clay surfaces influence the structure and properties of aqueous surface complexes, and therefore must be accounted for in models of metal-ion sorption.

  View details for Web of Science ID A1990EL76000058

  View details for PubMedID 2247162

• SPECTROSCOPIC INVESTIGATION OF PB(II) COMPLEXES AT THE GAMMA-AL2O3 WATER INTERFACE GEOCHIMICA ET COSMOCHIMICA ACTA CHISHOLMBRAUSE, C. J., Hayes, K. F., Roe, A. L., Brown, G. E., Parks, G. A., Leckie, J. O. 1990; 54 (7): 1897-1909

  View details for Web of Science ID A1990DQ21100004

• SYNCHROTRON RADIATION - APPLICATIONS IN THE EARTH SCIENCES ANNUAL REVIEW OF EARTH AND PLANETARY SCIENCES Bassett, W. A., Brown, G. E. 1990; 18: 387-447

  View details for Web of Science ID A1990DD77600012

• POLARIZED X-RAY ABSORPTION-SPECTROSCOPY OF METAL-IONS IN MINERALS - APPLICATIONS TO SITE GEOMETRY AND ELECTRONIC-STRUCTURE DETERMINATION PHYSICS AND CHEMISTRY OF MINERALS WAYCHUNAS, G. A., Brown, G. E. 1990; 17 (5): 420-430

  View details for Web of Science ID A1990EL78200008

• SPECTROSCOPIC STUDIES OF CHEMISORPTION REACTION-MECHANISMS AT OXIDE-WATER INTERFACES SHORT COURSE ON MINERAL-WATER INTERFACE GEOCHEMISTRY Brown, G. E. MINERALOGICAL SOC AMERICA. 1990: 309–363

  View details for Web of Science ID A1990BS23W00008

• RARE-EARTH ELEMENTS IN SILICATE GLASS MELT SYSTEMS .2. INTERACTIONS OF LA, GD, AND YB WITH HALOGENS GEOCHIMICA ET COSMOCHIMICA ACTA Ponader, C. W., Brown, G. E. 1989; 53 (11): 2905-2914

  View details for Web of Science ID A1989CB52000012

• MINERALOGY IN 2 DIMENSIONS - SCANNING TUNNELING MICROSCOPY OF SEMICONDUCTING MINERALS WITH IMPLICATIONS FOR GEOCHEMICAL REACTIVITY AMERICAN MINERALOGIST Hochella, M. F., Eggleston, C. M., Elings, V. B., Parks, G. A., Brown, G. E., Wu, C. M., Kjoller, K. 1989; 74 (11-12): 1233-1246

  View details for Web of Science ID A1989CH04800001

• SYNCHROTRON-BASED X-RAY ABSORPTION STUDIES OF CATION ENVIRONMENTS IN EARTH MATERIALS REVIEWS OF GEOPHYSICS Brown, G. E., Parks, G. A. 1989; 27 (4): 519-533

  View details for Web of Science ID A1989CL31000005

• RARE-EARTH ELEMENTS IN SILICATE GLASS MELT SYSTEMS .1. EFFECTS OF COMPOSITION ON THE COORDINATION ENVIRONMENTS OF LA, GD, AND YB GEOCHIMICA ET COSMOCHIMICA ACTA Ponader, C. W., Brown, G. E. 1989; 53 (11): 2893-2903

  View details for Web of Science ID A1989CB52000011

• INSITU X-RAY ABSORPTION SPECTROSCOPIC STUDIES OF IONS AT OXIDE-WATER INTERFACES CHIMIA Brown, G. E., Parks, G. A., CHISHOLMBRAUSE, C. J. 1989; 43 (9): 248-256

  View details for Web of Science ID A1989AW28500001

• INSITU HIGH-TEMPERATURE X-RAY ABSORPTION STUDY OF IRON IN ALKALI SILICATE MELTS AND GLASSES PHYSICA B-CONDENSED MATTER WAYCHUNAS, G. A., Brown, G. E., Jackson, W. E., Ponader, C. W. 1989; 158 (1-3): 67-68

  View details for Web of Science ID A1989AE26500023

• EXAFS INVESTIGATION OF AQUEOUS CO(II) ADSORBED ON OXIDE SURFACES INSITU PHYSICA B-CONDENSED MATTER CHISHOLMBRAUSE, C. J., Brown, G. E., Parks, G. A. 1989; 158 (1-3): 646-648

  View details for Web of Science ID A1989AE26500244

• XANES AND EXAFS STUDY OF AQUEOUS PB(II) ADSORBED ON OXIDE SURFACES PHYSICA B-CONDENSED MATTER CHISHOLMBRAUSE, C. J., Roe, A. L., Hayes, K. F., Brown, G. E., Parks, G. A., Leckie, J. O. 1989; 158 (1-3): 674-675

  View details for Web of Science ID A1989AE26500257

• Mineralogy in two dimensions: Scanning tunneling microscopy of semiconducting minerals with implications for geochemical reactivity American Mineralogist M. F. Hochella, Jr., Eggleston, C. M., Elings, V. B., Parks, G. A., Brown, Jr., G. E., Wu, C. M., Kjoller, K. 1989; 74: 1235-1248
• Synchrotron radiation: applications in the earth sciences Report of the Mineral Physics Committee, American Geophysical Union Bassett, W. A., Brown, Jr., G. E. 1989: 1-28
• Synchrotron radiation facilities: opportunities in the earth sciences Frontiers in Mineral Physics Brown, Jr., G. E., Bassett, W. A., Manghnani, M. H., Mao, H., Shankland, T. J. edited by Mackwell, S. J., Bassett, W. A., McMillan, P. F. American Geophysical Union. 1989: 87–96
• X-RAY ABSORPTION-SPECTROSCOPY OF IONS AT SOLID WATER INTERFACES Brown, G. E., Chisholm, C. J., Parks, G. A., Hayes, K. F., Leckie, J. O., Roe, A. L. AMER CHEMICAL SOC. 1988: 66-GEOC

  View details for Web of Science ID A1988P814201649

• ASPECTS OF SILICATE SURFACE AND BULK STRUCTURE-ANALYSIS USING X-RAY PHOTOELECTRON-SPECTROSCOPY (XPS) GEOCHIMICA ET COSMOCHIMICA ACTA Hochella, M. F., Brown, G. E. 1988; 52 (6): 1641-1648

  View details for Web of Science ID A1988P060400030

• EVIDENCE FROM X-RAY ABSORPTION FOR NETWORK-FORMING FE-2+ IN MOLTEN ALKALI SILICATES NATURE WAYCHUNAS, G. A., Brown, G. E., Ponader, C. W., Jackson, W. E. 1988; 332 (6161): 251-253

  View details for Web of Science ID A1988M540400054

• ELECTRONIC ABSORPTIONS IN THE HIGH-TC SUPERCONDUCTOR YBA2CU3OX JOURNAL OF THE AMERICAN CHEMICAL SOCIETY Little, W. A., Collman, J. P., Yee, G. T., Holcomb, M. J., McDevitt, J. T., Brown, G. E. 1988; 110 (4): 1301-1302

  View details for Web of Science ID A1988M188300054

• Synchrotron x-ray sources in the earth sciences EOS, Transactions American Geophysical Union Sutton, S. R., Rivers, M. L., Smith, J. V., Brown, Jr., G. E., Jones, K. W. 1988; 69: 1666-1675

  View details for DOI 10.1029/88EO01258

• X-RAY ABSORPTION-SPECTROSCOPY AND ITS APPLICATIONS IN MINERALOGY AND GEOCHEMISTRY REVIEWS IN MINERALOGY Brown, G. E., CALAS, G., WAYCHUNAS, G. A., PETIAU, J. 1988; 18: 431-512

  View details for Web of Science ID A1988N680300011

• X-ray absorption spectroscopy and its applications in mineralogy and geochemistry Spectroscopic Methods in Mineralogy and Geology Brown, Jr., G. E., Calas, G., Waychunas, G. A., Petiau, J. F. edited by Hawthorne, F. Mineralogical Society of America, Washington, DC. 1988: 431–512
• INSITU X-RAY ABSORPTION STUDY OF SURFACE COMPLEXES - SELENIUM OXYANIONS ON ALPHA-FEOOH SCIENCE Hayes, K. F., Roe, A. L., Brown, G. E., Hodgson, K. O., Leckie, J. O., Parks, G. A. 1987; 238 (4828): 783-786

  Abstract

  A novel application of x-ray absorption spectroscopy has provided structural information for ions sorbed at oxide-water interfaces. As an example, in situ extended x-ray absorption fine structure (EXAFS) measurements of adsorbed selenate and selenite ions at ah alpha-FeOOH(goethite)-water interface have been performed; these measurements show that selenate forms a weakly bonded, outer-sphere complex and that selenite forms a strongly bonded, inner-sphere complex. The selenite ion is bonded directly to the goethite surface in a bidentate fashion with two iron atoms 3.38 angstroms from the selenium atom. Adsorbed selenate has no iron atom in the second coordination shell of selenium, which indicates retention of its hydration sphere upon sorption. This method provides direct structural information for adsorbed species at solid-liquid interfaces.

  View details for Web of Science ID A1987K681000027

  View details for PubMedID 17814706

• X-RAY ABSORPTION STUDY OF THE POTASSIUM COORDINATION ENVIRONMENT IN GLASSES FROM THE NAALSI3O8-KALSI3O8 BINARY - STRUCTURAL IMPLICATIONS FOR THE MIXED-ALKALI EFFECT JOURNAL OF NON-CRYSTALLINE SOLIDS Jackson, W. E., Brown, G. E., Ponader, C. W. 1987; 93 (2-3): 311-322

  View details for Web of Science ID A1987K386900011

• LEAD ADSORPTION AT AQUEOUS OXIDE INTERFACES - AN EXAFS STUDY Roe, A. L., Hayes, K. F., Brown, G. E., Hodgson, K. O., Leckie, J. O., Parks, G. A. AMER CHEMICAL SOC. 1987: 95-COLL

  View details for Web of Science ID A1987G289600887

• PARTITIONING OF FE WITHIN HIGH-PRESSURE SILICATE PEROVSKITE - EVIDENCE FOR UNUSUAL GEOCHEMISTRY IN THE LOWER MANTLE GEOPHYSICAL RESEARCH LETTERS Jackson, W. E., Knittle, E., Brown, G. E., Jeanloz, R. 1987; 14 (3): 224-226

  View details for Web of Science ID A1987G753700015

• X-RAY ABSORPTION SPECTROSCOPIC STUDIES OF SILICATE-GLASSES AND MINERALS PHYSICS AND CHEMISTRY OF MINERALS CALAS, G., Brown, G. E., WAYCHUNAS, G. A., PETIAU, J. 1987; 15 (1): 19-29

  View details for Web of Science ID A1987K482000002

• NEAR-EDGE STRUCTURE OF OXYGEN IN INORGANIC OXIDES: EFFECT OF LOCAL GEOMETRY AND CATION TYPE JOURNAL DE PHYSIQUE Brown, G. E., WAYCHUNAS, G. A., Stohr, J., Sette, F. 1986; 47 (C-8): 163-167

  View details for DOI 10.1051/jphyscol:19868129

  View details for Web of Science ID 000208129900032

• ELECTRONIC-STRUCTURE FROM X-RAY K-EDGES IN ZNS-FE AND CUFES2 JOURNAL DE PHYSIQUE Sainctavit, P., CALAS, G., PETIAU, J., KARNATAK, R., Esteva, J. M., Brown, G. E. 1986; 47 (C-8): 411-414

  View details for Web of Science ID A1986G515900082

• EXAFS AND NEXAFS STUDIES OF CATION ENVIRONMENTS IN OXIDE GLASSES JOURNAL DE PHYSIQUE Brown, G. E., WAYCHUNAS, G. A., Ponader, C. W., Jackson, W. E., McKeown, D. A. 1986; 47 (C-8): 140-147

  View details for DOI 10.1051/jphyscol:19868125

  View details for Web of Science ID 000208129900028

• LITHIOPHILITE FORMATION IN GRANITIC PEGMATITES - A RECONNAISSANCE EXPERIMENTAL-STUDY OF PHOSPHATE CRYSTALLIZATION FROM HYDROUS ALUMINOSILICATE MELTS AMERICAN MINERALOGIST Shigley, J. E., Brown, G. E. 1986; 71 (3-4): 356-366

  View details for Web of Science ID A1986C098000010

• JAHNS,R.H. MEMORIAL ISSUE - THE MINERALOGY, PETROLOGY, AND GEOCHEMISTRY OF GRANITIC PEGMATITES AND RELATED GRANITIC-ROCKS - INTRODUCTION AMERICAN MINERALOGIST Brown, G. E., Ewing, R. C. 1986; 71 (3-4): 233-238

  View details for Web of Science ID A1986C098000001

• HIGH-TEMPERATURE STRUCTURE AND CRYSTAL-CHEMISTRY OF HYDROUS ALKALI-RICH BERYL FROM THE HARDING PEGMATITE, TAOS COUNTY, NEW-MEXICO AMERICAN MINERALOGIST Brown, G. E., MILLS, B. A. 1986; 71 (3-4): 547-556

  View details for Web of Science ID A1986C098000022

• MINERALOGY AND GEOCHEMICAL EVOLUTION OF THE LITTLE 3 PEGMATITE-APLITE LAYERED INTRUSIVE, RAMONA, CALIFORNIA AMERICAN MINERALOGIST Stern, L. A., Brown, G. E., Bird, D. K., JAHNS, R. H., Foord, E. E., Shigley, J. E., SPAULDING, L. B. 1986; 71 (3-4): 406-427

  View details for Web of Science ID A1986C098000014

• STRUCTURAL MECHANISMS OF ANOMALOUS THERMAL-EXPANSION OF CORDIERITE-BERYL AND OTHER FRAMEWORK SILICATES JOURNAL OF THE AMERICAN CERAMIC SOCIETY Hochella, M. F., Brown, G. E. 1986; 69 (1): 13-18

  View details for Web of Science ID A1986AXV0400004

• X-RAY K-EDGE ABSORPTION-SPECTRA OF FE MINERALS AND MODEL COMPOUNDS .2. EXAFS PHYSICS AND CHEMISTRY OF MINERALS WAYCHUNAS, G. A., Brown, G. E., Apted, M. J. 1986; 13 (1): 31-47

  View details for Web of Science ID A1986AXX1000005

• EXAFS STUDY OF THE COORDINATION ENVIRONMENT OF ALUMINUM IN A SERIES OF SILICA-RICH GLASSES AND SELECTED MINERALS WITHIN THE NA2O-AL2O3-SIO2 SYSTEM JOURNAL OF NON-CRYSTALLINE SOLIDS McKeown, D. A., WAYCHUNAS, G. A., Brown, G. E. 1985; 74 (2-3): 349-371

  View details for Web of Science ID A1985AUE6400016

• THE STRUCTURES OF ALBITE AND JADEITE COMPOSITION GLASSES QUENCHED FROM HIGH-PRESSURE GEOCHIMICA ET COSMOCHIMICA ACTA Hochella, M. F., Brown, G. E. 1985; 49 (5): 1137-1142

  View details for Web of Science ID A1985AHJ0300004

• EXAFS AND XANES STUDY OF THE LOCAL COORDINATION ENVIRONMENT OF SODIUM IN A SERIES OF SILICA-RICH GLASSES AND SELECTED MINERALS WITHIN THE NA2O-AL2O3-SIO2 SYSTEM JOURNAL OF NON-CRYSTALLINE SOLIDS McKeown, D. A., WAYCHUNAS, G. A., Brown, G. E. 1985; 74 (2-3): 325-348

  View details for Web of Science ID A1985AUE6400015

• STRUCTURE AND SPECIFICATION OF IRON COMPLEXES IN AQUEOUS-SOLUTIONS DETERMINED BY X-RAY ABSORPTION-SPECTROSCOPY GEOCHIMICA ET COSMOCHIMICA ACTA Apted, M. J., WAYCHUNAS, G. A., Brown, G. E. 1985; 49 (10): 2081-2089

  View details for Web of Science ID A1985ATC6300007

• OCCURRENCE AND ALTERATION OF PHOSPHATE MINERALS AT THE STEWART PEGMATITE, PALA DISTRICT, SAN-DIEGO COUNTY, CALIFORNIA AMERICAN MINERALOGIST Shigley, J. E., Brown, G. E. 1985; 70 (3-4): 395-408

  View details for Web of Science ID A1985AGG2200018

• RAMAN STUDIES OF AL COORDINATION IN SILICA-RICH SODIUM ALUMINOSILICATE GLASSES AND SOME RELATED MINERALS JOURNAL OF NON-CRYSTALLINE SOLIDS McKeown, D. A., GALEENER, F. L., Brown, G. E. 1984; 68 (2-3): 361-378

  View details for Web of Science ID A1984TV05700017

• Applications of EXAFS and XANES spectroscopy to problems in mineralogy and geochemistry EXAFS and Near Edge Structure III Waychunas, G. A., Brown, Jr., G. E. edited by Hodgson, K. O., Hedman, B., Penner-Hahn, J. E. Springer-Verlag. 1984: 336–342

  View details for DOI 10.1007/978-3-642-46522-2_86

• STRUCTURE AND VISCOSITY OF RHYOLITIC COMPOSITION MELTS GEOCHIMICA ET COSMOCHIMICA ACTA Hochella, M. F., Brown, G. E. 1984; 48 (12): 2631-2640

  View details for Web of Science ID A1984TY25900018

• Local coordination environment of Na in a series of silica-rich glasses and selected minerals within the Na2O-Al2O3-SiO2 system EXAFS and Near Edge Structure III McKeown, D. A., Brown, Jr., G. E., Waychunas, G. A. edited by Hodgson, K. O., Hedman, B., Penner-Hahn, J. E. Springer-Verlag. 1984: 308–310

  View details for DOI 10.1007/978-3-642-46522-2_78

• Total electron yield K-XANES and EXAFS investigation of aluminum in amorphous and crystalline aluminosilicates Stanford Synchrotron Radiation Laboratory Report 83/01 Brown, Jr., G. E., Dikmen, F. D., Waychunas, G. A. 1983: 148-149
• X-RAY K-EDGE ABSORPTION-SPECTRA OF FE MINERALS AND MODEL COMPOUNDS - NEAR-EDGE STRUCTURE PHYSICS AND CHEMISTRY OF MINERALS WAYCHUNAS, G. A., Apted, M. J., Brown, G. E. 1983; 10 (1): 1-9

  View details for Web of Science ID A1983RH98100001

• POLYMERIZATION OF SILICATE AND ALUMINATE TETRAHEDRA IN GLASSES, MELTS, AND AQUEOUS-SOLUTIONS .3. LOCAL SILICON ENVIRONMENTS AND INTERNAL NUCLEATION IN SILICATE-GLASSES GEOCHIMICA ET COSMOCHIMICA ACTA DEJONG, B. H., Keefer, K. D., Brown, G. E., Taylor, C. M. 1981; 45 (8): 1291-1308

  View details for Web of Science ID A1981MC70800004

• POLYMERIZATION OF SILICATE AND ALUMINATE TETRAHEDRA IN GLASSES, MELTS AND AQUEOUS-SOLUTIONS .2. THE NETWORK MODIFYING EFFECTS OF MG2+, K+, NA+, LI+, H+, OH-, F-, CL-, H2O, CO2 AND H3O+ ON SILICATE POLYMERS GEOCHIMICA ET COSMOCHIMICA ACTA DEJONG, B. H., Brown, G. E. 1980; 44 (11): 1627-1642

  View details for Web of Science ID A1980KT66800001

• Crystal chemistry of the olivines and silicate spinels Mineralogy (2nd edition, 1982) Brown, Jr. , G. E., Ribbe (ed.), P. H. Mineralogical Society of America. 1980: 275–381
• A neutron and x-ray diffraction study of Amelia low albite American Mineralogist Harlow, G. E., Brown, Jr., G. E. 1980; 65: 986-995
• CRYSTAL-STRUCTURE OF RASVUMITE, KFE2S3 AMERICAN MINERALOGIST Clark, J. R., Brown, G. E. 1980; 65 (5-6): 477-482

  View details for Web of Science ID A1980JW87100008

• STRUCTURE OF MINERAL GLASSES .3. NAALSI3O8 SUPERCOOLED LIQUID AT 805-DEGREES-C AND THE EFFECTS OF THERMAL HISTORY GEOCHIMICA ET COSMOCHIMICA ACTA Taylor, M., Brown, G. E., FENN, P. M. 1980; 44 (1): 109-117

  View details for Web of Science ID A1980JA85100009

• POLYMERIZATION OF SILICATE AND ALUMINATE TETRAHEDRA IN GLASSES, MELTS, AND AQUEOUS-SOLUTIONS .1. ELECTRONIC-STRUCTURE OF H6SI2O7, H6ALSIO-1-(7), AND H6AL2O-2-(7) GEOCHIMICA ET COSMOCHIMICA ACTA DEJONG, B. H., Brown, G. E. 1980; 44 (3): 491-511

  View details for Web of Science ID A1980JH64700008

• STRUCTURE OF MINERAL GLASSES .1. FELDSPAR GLASSES NAALSI3O8, KALSI3O8, CAAL2SI2O8 GEOCHIMICA ET COSMOCHIMICA ACTA Taylor, M., Brown, G. E. 1979; 43 (1): 61-75

  View details for Web of Science ID A1979GA96900007

• HIGH-TEMPERATURE CRYSTAL-CHEMISTRY OF HYDROUS MG-CORDIERITES AND FE-CORDIERITES AMERICAN MINERALOGIST Hochella, M. F., Brown, G. E., Ross, F. K., Gibbs, G. V. 1979; 64 (3-4): 337-351

  View details for Web of Science ID A1979GS91900009

• STRUCTURE OF MINERAL GLASSES .2. SIO2-NAALSIO4 JOIN GEOCHIMICA ET COSMOCHIMICA ACTA Taylor, M., Brown, G. E. 1979; 43 (9): 1467-1473

  View details for Web of Science ID A1979HL12200008

• STRUCTURE ENERGIES OF THE ALKALI FELDSPARS PHYSICS AND CHEMISTRY OF MINERALS Brown, G. E., FENN, P. M. 1979; 4 (1): 83-100

  View details for Web of Science ID A1979GQ12700008

• CRYSTAL-STRUCTURE OF HYDROCHLORBORITE, CA2[B3O3(OH)4.OB(OH)3]CL.7H2O, A SEASONAL EVAPORITE MINERAL AMERICAN MINERALOGIST Brown, G. E., Clark, J. R. 1978; 63 (9-10): 814-823

  View details for Web of Science ID A1978FU40000002

• CRYSTAL-STRUCTURES AND COMPOSITIONS OF SANIDINE AND HIGH ALBITE IN CRYPTOPERTHITIC INTERGROWTH AMERICAN MINERALOGIST Keefer, K. D., Brown, G. E. 1978; 63 (11-1): 1264-1273

  View details for Web of Science ID A1978GC19900024

• CRYSTAL-STRUCTURE OF A SYNTHETIC, COMPOSITIONALLY INTERMEDIATE, HYPERSOLVUS ALKALI FELDSPAR - EVIDENCE FOR NA,K SITE ORDERING ZEITSCHRIFT FUR KRISTALLOGRAPHIE FENN, P. M., Brown, G. E. 1977; 145 (1-2): 124-145

  View details for Web of Science ID A1977DS79500011

• HIGH-TEMPERATURE STRUCTURAL STUDY OF P21-AREVERSIBLEA2-A PHASE-TRANSITION IN SYNTHETIC TITANITE, CATISIO5 AMERICAN MINERALOGIST Taylor, M., Brown, G. E. 1976; 61 (5-6): 435-447

  View details for Web of Science ID A1976BV34500013

• CATION ORDERING IN NI-MG OLIVINE AMERICAN MINERALOGIST Rajamani, V., Brown, G. E., Prewitt, C. T. 1975; 60 (3-4): 292-299

  View details for Web of Science ID A1975W298800016

• PYROXENES IN SHAW (L-7) CHONDRITE GEOCHIMICA ET COSMOCHIMICA ACTA DODD, R. T., Grover, J. E., Brown, G. E. 1975; 39 (12): 1585-?

  View details for Web of Science ID A1975AY90600001

• The Feldspars, NATO Advanced Studies Institute on Feldspars Brown, Jr., G. E., Hamilton, W. C., Prewitt, C. T., Sueno, S. Manchester University Press. 1974: 68–80
• FRANKDICKSONITE, BAF2, A NEW MINERAL FROM NEVADA AMERICAN MINERALOGIST Radtke, A. S., Brown, G. E. 1974; 59 (9-10): 885-888

  View details for Web of Science ID A1974U569700001

• HIGH TEMPERATURE CRYSTAL-CHEMISTRY OF SPHENE Taylor, M., Brown, G. E. AMER GEOPHYSICAL UNION. 1974: 1201–

  View details for Web of Science ID A1974U698100818

• Earth Materials Geology Today Brown, Jr., G. E., Ernst, W. G. Del Mar Books, Del Mar, California. 1974: 91–113
• Crystallography of pigeonites from basaltic vitrophyre 15597 Geochimica et Cosmochimica Acta Brown, Jr., G. E., Wechsler, B. A. 1973: 887-900
• HIGH-TEMPERATURE CRYSTAL-CHEMISTRY OF HORTONOLITE AMERICAN MINERALOGIST Brown, G. E., Prewitt, C. T. 1973; 58 (7-8): 577-587

  View details for Web of Science ID A1973Q517100001

• NEW SINGLE-CRYSTAL HEATER FOR PRECESSION CAMERA AND 4-CIRCLE DIFFRACTOMETER AMERICAN MINERALOGIST Brown, G. E., Sueno, S., Prewitt, C. T. 1973; 58 (7-8): 698-704

  View details for Web of Science ID A1973Q517100011

• Apollo 12 clinopyroxenes: high temperature x-ray diffraction studies Proceedings of the 2nd Lunar Science Conference Prewitt, C. T., Brown, Jr., G. E., Papike, J. J. 1972; 1: 59-68
• COMPARISON OF STRUCTURES OF LOW AND HIGH PIGEONITE JOURNAL OF GEOPHYSICAL RESEARCH Brown, G. E., Papike, J. J., Prewitt, C. T., Sueno, S. 1972; 77 (29): 5778-?

  View details for Web of Science ID A1972N791700014

• CRYSTAL-STRUCTURE OF HIGH CUMMINGTONITE JOURNAL OF GEOPHYSICAL RESEARCH Sueno, S., Brown, G. E., Prewitt, C. T., Papike, J. J. 1972; 77 (29): 5767-?

  View details for Web of Science ID A1972N791700013

• APOLLO-12 CLINOPYROXENES - EXSOLUTION AND EPITAXY EARTH AND PLANETARY SCIENCE LETTERS Papike, J. J., Bence, A. E., Brown, G. E., Prewitt, C. T., Wu, C. H. 1971; 10 (3): 307-?

  View details for Web of Science ID A1971I675000004

• STEREOCHEMISTRY AND ORDERING IN TETRAHEDRAL PORTION OF SILICATES AMERICAN MINERALOGIST Brown, G. E., Gibbs, G. V. 1970; 55 (9-10): 1587-?

  View details for Web of Science ID A1970H812400011

• REFINEMENT OF CRYSTAL STRUCTURE OF OSUMILITE AMERICAN MINERALOGIST Brown, G. E., Gibbs, G. V. 1969; 54 (1-2): 101-?

  View details for Web of Science ID A1969C856300009

• NATURE AND VARIATION IN LENGTH OF SI-O AND AL-O BONDS IN FRAMEWORK SILICATES Brown, G. E., Gibbs, G. V., Ribbe, P. H. AMER GEOPHYSICAL UNION. 1969: 358-?

  View details for Web of Science ID A1969C982701189

• NATURE AND VARIATION IN LENGTH OF SI-O AND AL-O BONDS IN FRAMEWORK SILICATES AMERICAN MINERALOGIST Brown, G. E., Gibbs, G. V., Ribbe, P. H. 1969; 54 (7-8): 1044-?

  View details for Web of Science ID A1969E184600005

• OXYGEN COORDINATION AND SI-O BOND AMERICAN MINERALOGIST Brown, G. E., Gibbs, G. V. 1969; 54 (11-1): 1528-?

  View details for Web of Science ID A1969F327200003