Cindy Weng

All Publications

• Electrochemical Dechlorination of Municipal Wastewater Effluent. Environmental science & technology Weng, C., Hinkle, M. M., Mitch, W. A. 2023

  Abstract

  The use of sodium bisulfite as an electron donor to quench chloramine disinfectant residuals in municipal wastewater effluents prior to discharge incurs the cost of purchasing and transporting bisulfite to the utility and increases the loading of salts to the receiving water. In this study, degradation of chloramine residuals within authentic municipal wastewater effluents was achieved within a 30 min timescale using a reductive electrochemical reactor, which supplied electrons via a stainless-steel cathode under galvanostatic conditions without an ion exchange membrane separating the cathode and anode. Application of a 0.26 mA/cm2 cathodic current density reduced chloramines to ammonia and avoided oxidation at the IrO2-coated titanium anode of chloride to chlorine or chlorate and of ammonia to nitrite or nitrate. Net chloramine production was observed at a higher current density (2 mA/cm2). Chloramine degradation rates and Coulombic efficiencies were highest and electrical energy per order (EEO) values were lowest for the 304-grade stainless-steel cathode, which contains the highest nickel content, and for a stainless-steel cathode with a high surface area. Differences in ionic strength and pH were less important. For chloraminated municipal wastewater samples, the highest Coulombic efficiency was 4.1% and the lowest EEO value was 0.08 kWh/m3. An initial comparison indicated that the electricity cost associated with this EEO value would be comparable to the cost of sodium bisulfite for areas with low electricity costs.

  View details for DOI 10.1021/acs.est.2c02481

  View details for PubMedID 36626832

• Zero-order Catalysis in TAML-catalyzed Oxidation of Imidacloprid, a Neonicotinoid Pesticide. Chemistry (Weinheim an der Bergstrasse, Germany) Ryabov, A. D., Warner, G. R., Somasundar, Y., Weng, C., Akin, M. H., Collins, T. J. 2020

  Abstract

  Bis -sulfonamide bis -amide TAML activator [Fe{4-NO 2 C 6 H 3 -1,2-( N COCMe 2 N SO 2 ) 2 CHMe}] - ( 2 ) catalyzes oxidative degradation of the oxidation-resistant neonicotinoid insecticide, imidacloprid (IMI), by H 2 O 2 at pH 7 and 25 °C, whereas the tetrakis -amide TAML [Fe{4-NO 2 C 6 H 3 -1,2-( N COCMe 2 N CO) 2 CF 2 }] - ( 1 ) is inactive under the same conditions. At ultra-low concentrations of both IMI and 2 , 62% of the insecticide was oxidized in 2 h, at which time the catalyst is inactivated; oxidation resumes on addition of a new aliquot of 2 . Acetate and oxamate were detected by ion chromatography, suggesting deep oxidation of imidacloprid. Explored at concentrations [ 2 ] ≥ [IMI], the reaction kinetics revealed unusually low order in 2 (0.164±0.006) which is observed alongside with the first order in IMI and an ascending hyperbolic dependence in [H 2 O 2 ]. Actual independence of the reaction rate on the catalyst concentration is accounted for in terms of a reversible binding between a substrate and a catalyst, which usually results in substrate inhibition when [catalyst] << [substrate] but explains zero order in the catalyst when [ 2 ] > [IMI]. A plausible mechanism of the TAML-catalyzed oxidations of imidacloprid is discussed. Similar zero-order catalysis is presented for the oxidation of 3-methyl-4-nitrophenol by H 2 O 2 catalyzed by the analog of 1 without NO 2 -group in the aromatic ring.

  View details for DOI 10.1002/chem.202000384

  View details for PubMedID 32187755

• Reductive Electrochemical Activation of Hydrogen Peroxide as an Advanced Oxidation Process for Treatment of Reverse Osmosis Permeate during Potable Reuse. Environmental science & technology Weng, C. n., Chuang, Y. H., Davey, B. n., Mitch, W. A. 2020

  Abstract

  The UV/hydrogen peroxide (H2O2) advanced oxidation process (AOP) frequently employed to generate hydroxyl radical (•OH) to treat reverse osmosis permeate (ROP) in potable reuse treatment trains is inefficient, using only 10% of the H2O2. This study evaluated ·OH generation by electron transfer from a low-cost stainless steel cathode. In deionized water, the electrochemical system achieved 0.5 log removal of 1,4-dioxane, a benchmark for AOP validation for potable reuse, within 4 min using only 1.25 mg/L H2O2. Hydrogen peroxide and 1,4-dioxane degradations were maximized near -0.18 and + 0.02 V versus standard hydrogen electrode, respectively. Degradations of positively and negatively charged compounds were comparable to neutral 1,4-dioxane, indicating that degradation occurs by ·OH generation from neutral H2O2 and that electrostatic repulsion of contaminants from the electrode is not problematic. For ROP without chloramines, 0.5 log 1,4-dioxane removal was achieved in 6.7 min with 7 mM salts for ionic strength and 2.5 mg/L H2O2. For ROP with 1.4 mg/L as Cl2 chloramines, 0.5 log 1,4-dioxane removal was achieved in 13.2 min with 7 mM salts and 4.5 mg/L total H2O2 dosed in three separate injections in 5 min intervals. Initial estimates based on lab-scale electrochemical AOP treatment indicated that, except for the cost of salts, the electrochemical AOP featured lower reagent costs than the UV/H2O2 AOP but higher electricity costs that could be reduced by optimization of the electrochemical design.

  View details for DOI 10.1021/acs.est.0c02144

  View details for PubMedID 32822532

• Bioinspired, Multidisciplinary, Iterative Catalyst Design Creates the Highest Performance Peroxidase Mimics and the Field of Sustainable Ultradilute Oxidation Catalysis (SUDOC) ACS CATALYSIS Wamer, G. R., Somasundar, Y., Jansen, K. C., Kaaret, E. Z., Weng, C., Burton, A. E., Mills, M. R., Shen, L. Q., Ryabov, A. D., Pros, G., Pintauer, T., Biswas, S., Hendrich, M. P., Taylor, J. A., Vom Saal, F. S., Collins, T. J. 2019; 9 (8): 7023–37

  View details for DOI 10.1021/acscatal.9b01409

  View details for Web of Science ID 000480503700045

• Reactivity, Selectivity, and Long-Term Performance of Sulfidized Nanoscale Zerovalent Iron with Different Properties ENVIRONMENTAL SCIENCE & TECHNOLOGY Xu, J., Wang, Y., Weng, C., Bai, W., Jiao, Y., Kaegi, R., Lowry, G. 2019; 53 (10): 5936–45

  Abstract

  Sulfidized nanoscale zerovalent iron (SNZVI) has desirable properties for in situ groundwater remediation. However, there is limited understanding of how the sulfidation type and particle properties affect the reactivity and selectivity of SNZVI toward groundwater contaminants, or how reactivity changes as the particles age. Here, SNZVI synthesized by either a one-step (SNZVI-1) or two-step (SNZVI-2) process were characterized, and the reactivity of both fresh and aged (1d to 60 d) nanoparticles was assessed. The measured S/Fe ratio was 5.4 ± 0.5 mol % for SNZVI-1 and 0.8 ± 0.1 mol % for SNZVI-2. XPS analysis indicates S2-, S22-, and S n2- species on the surface of both SNZVI-1 and SNZVI-2, while S22- is the dominant species inside of the SNZVI nanoparticles. SNZVI-1 particles were hydrophobic (contact angle = 103 ± 3°), while the other materials were hydrophilic (contact angles were 18 ± 2° and 36 ± 3° for NZVI and SNZVI-2, respectively). SNZVI-1, with greater S content and hydrophobicity, was less reactive with water than either NZVI or SNZVI-2 over a 60 d period, resulting in less H2 evolution. It also had the highest reactivity with TCE and the lowest reactivity with nitrate, consistent with its higher hydrophobicity. In contrast, both NZVI and SNZVI-2 were reactive with both TCE and nitrate. Both types of SNZVI remained more reactive after aging in water over 60 d than NZVI. These data suggest that the properties of the SNZVI made from a one-step synthesis procedure may provide better reactivity, selectivity, and longevity than that made from a two-step process.

  View details for DOI 10.1021/acs.est.9b00511

  View details for Web of Science ID 000469288100045

  View details for PubMedID 31022346