Sandeep Bose

All Publications

• Electric field-driven interfacial reduction of metal ions in microdroplets: gold, silver, and nickel. Chemical science Bose, S., Zare, R. N. 2025

  Abstract

  A bulk aqueous solution containing 100 μM HAuCl4 has been shown to spontaneously form gold nanoparticles (Au NPs) in 2-3 days when stored at room temperature. We demonstrate that Au NPs can be spontaneously formed within a few microseconds to milliseconds when the same solution is sprayed in the form of microdroplets (10-30 μm in diameter) using N2 as the nebulizing gas under ambient conditions. The rapid formation of Au NPs establishes that the air-water interface of microdroplets plays a dominant role. The reduction of metal ions in water microdroplets is driven by electron transfer at the air-water interface of water microdroplets aided by the strong electric field and the lack of three-dimensional solvation at the surface. The reduction of metal is accompanied by the formation of H2O2 resulting in part from the recombination of OH˙ produced at the interface. We observed that the size of the Au NPs increases when the distance between the tip and collector increases suggesting the rapid nucleation and growth of Au NPs within the microdroplets. The nanoparticle generation in microdroplets is not limited to Au, and we extend the scope of this method to other metals such as silver (Ag) and nickel (Ni) indicating a minimal role of the metal's position in the electrochemical series. When polar protic solvents such as CH3OH, and C2H5OH replace water as a solvent, Au NPs are seen to be formed but at a much slower rate whereas in acetonitrile (ACN), the Au NPs' formation is negligible.

  View details for DOI 10.1039/d5sc04995d

  View details for PubMedID 40740743

  View details for PubMedCentralID PMC12305125

• Selective Photochemical Conversion of Carbon Dioxide to Formic Acid at Gas-Water Interface of Microbubbles. Journal of the American Chemical Society Bose, S., Mehrgardi, M. A., Zare, R. N. 2025

  Abstract

  We report a selective photochemical conversion of carbon dioxide (CO2) to formic acid (HCOOH, FA) at the gas-water interface (GWI) of microbubbles. The microbubbles with an average diameter of 42 μm are produced by passing CO2 gas through a porous thermoplastic bubbler immersed in an aqueous solution of the copper(II)-phenanthroline complex [Cu(Phen)2]2+. The average FA production rate at room temperature is found to be 47.5 μM h-1 for 5 mM of [Cu(Phen)2]2+. When 5 mM iodide (I-) is added to the system, the FA production rate increases to a maximum value of 63.8 μM h-1. We also demonstrated that both acidic and alkaline conditions stimulate FA formation. Mechanistic investigations indicate that H• at the GWI plays a crucial role in the reduction of CO2 via the formation of the •COOH intermediate, which was captured using (2,2,6,6-tetramethylpiperidin-1-yl)oxyl (TEMPO) as a spin trap as well as by the molecular copper catalyst. As microbubbles are continuously formed in water, the reactions at the GWI of microbubbles can be sustained over extended periods, making it easier to scale up production, which often is an issue with droplet-generated products. These findings demonstrate the promising potential of gas microbubbles in water to drive unexpected chemistry, thereby removing a greenhouse gas such as CO2 by converting it into valuable products. The present study is a first step toward a practical demonstration, but does not constitute an industrial process at present.

  View details for DOI 10.1021/jacs.5c04912

  View details for PubMedID 40696304

• Cross-Coupling between Arylboronic Acids and Terminal Alkynes in Water Microdroplets. Journal of the American Chemical Society Bose, S., Mofidfar, M., Zare, R. N., Gnanamani, E. 2025

  Abstract

  We report a cross-coupling reaction between terminal alkyne and arylboronic acid to form the C-C bond in water microdroplets under mild, catalyst-free conditions. A solution containing phenylacetylene (50 μM) and 4-methoxyphenylboronic acid (50 μM) in a 4:1 (H2O: ACN) mixture was electrosprayed at +1.5 kV, and the reaction products were analyzed using a mass spectrometer (MS). We observed C(sp2)-C(sp) coupling reaction products within milliseconds, which were characterized by tandem mass spectrometry (MS2). Based on in situ reaction studies and radical experiments, we determined the reaction mechanism for the coupling reaction. Our approach offers a sustainable and environmentally benign pathway for the synthesis of internal aryl alkynes, making it a suitable building block for the preparation of various pharmaceutical drugs.

  View details for DOI 10.1021/jacs.5c07509

  View details for PubMedID 40629730

• Catalyst-Free Production of Urea from Nitrate and Carbon Dioxide in Water Microdroplets. Environmental science & technology Bose, S., Xu, J., Lee, K., Zare, R. N. 2025

  Abstract

  We report a simple, one-step selective process for producing urea (NH2CONH2) from nitrate (NO3-) dissolved in aqueous microdroplets when sprayed with carbon dioxide (CO2) as the nebulizing gas. This synthesis is accomplished without any catalyst or application of any external electric potential or radiation. The electric field at the gas-water interface is believed to drive the reaction process, resulting in urea being dissolved in the water microdroplets, which is the source of hydrogen for this conversion. The highest urea production rate of 118 muM h-1 is achieved with optimized parameters. The selectivity of urea formation in this process is >99%. Mass spectrometric studies were conducted to identify the reaction intermediates involved in the conversion. Density functional theory (DFT) calculations support our experimental observations by providing insights into the reaction pathways for the transformation. This eco-friendly approach for urea synthesis consumes CO2, thereby transforming a greenhouse gas into a value-added product.

  View details for DOI 10.1021/acs.est.5c01478

  View details for PubMedID 40415335

• Continuous Flow Contact Electrocatalysis for Hydrogen Peroxide Production JOURNAL OF PHYSICAL CHEMISTRY C Lee, K., Bose, S., Song, X., Choi, S. Q., Zare, R. N. 2025

  View details for DOI 10.1021/acs.jpcc.5c00163

  View details for Web of Science ID 001450111400001

• Sustainable Recovery of Rare Earth Metals from Smartphone Display using Nanoengineered Cellulose ADVANCED SUSTAINABLE SYSTEMS Bose, S., Ariya, P. A. 2024

  View details for DOI 10.1002/adsu.202400887

  View details for Web of Science ID 001370088500001

• Handheld portable device for delivering capped silver nanoparticles for antimicrobial applications. QRB discovery Naveen, K., Bose, S., Basheer, C., Zare, R. N., Gnanamani, E. 2024; 5: e9

  Abstract

  We describe a simple, cost-effective, green method for producing capped silver nanoparticles (Ag NPs) using a handheld portable mesh nebulizer. The precursor solution containing a 1:1 mixture of silver nitrate (AgNO3) and ligand (glycerol or sodium alginate) was sprayed using the nebulizer. The Ag NPs were generated in the water microdroplets within a few milliseconds under ambient conditions without any external reducing agent or action of a radiation source. The synthesized nanoparticles were characterized by using high-resolution transmission electron microscopy (HR-TEM), X-ray photoelectron spectroscopy (XPS), and X-ray diffraction analysis (XRD), which validated the formation of Ag NPs. The synthesized glycerate-capped silver nanoparticles (Ag-gly NPs) were used as a catalyst to show the oxidative coupling of aniline to form azobenzene products with a yield of up to 61%. Experiments conducted using Ag NPs produced in the droplets demonstrated more than 99% antibacterial activity when contacting Escherichia Coli. Our in-situ synthesis-cum-fabrication technique using a portable sprayer represents a viable alternative to the existing fiber or hydrogel-based antimicrobial wound healing.

  View details for DOI 10.1017/qrd.2024.9

  View details for PubMedID 39687232

  View details for PubMedCentralID PMC11649374

• Understanding the formation of nitrate from nitrogen at the interface of gas-water microbubbles. Chemical science Bose, S., Xia, Y., Zare, R. N. 2024

  Abstract

  Water microbubbles containing Fe2+ ions have been found to efficiently transform nitrogen (N2) to nitrate (NO3 -) by initiating Fenton's reaction at the gas-water interface. Herein, we elucidate the mechanism of the formation of nitrate (NO3 -) from nitrogen (N2) at the microbubble interface. Several experimental studies were conducted to identify the intermediates formed during the conversion. Our investigation shows the formation of H2N2O2, NO, NO2, and NO2 - intermediates before yielding NO3 - as the final product. Density functional theory (DFT) calculations provide additional support to our observation by providing insights into the energy profiles of the reaction intermediates. We believe that this work not only provides valuable insight into the abiotic nitrogen fixation in microbubbles but also helps in suggesting the modification of parameters to create a more reactive interface that leads to the enhanced production of nitric acid (HNO3).

  View details for DOI 10.1039/d4sc06989g

  View details for PubMedID 39568950

  View details for PubMedCentralID PMC11575618

• Direct Conversion of N2 and Air to Nitric Acid in Gas-Water Microbubbles. Journal of the American Chemical Society Bose, S., Mofidfar, M., Zare, R. N. 2024

  Abstract

  We report a simple, direct, and green conversion of air/N2 to nitric acid by bubbling the gas through an aqueous solution containing 50 μM Fe2+ ions. Air stone, along with ultrasonication, was employed to generate gas microbubbles. H2O2 produced at the water-gas interface undergoes Fenton's reaction with Fe2+ ions to produce OH• that efficiently activates N2, yielding nitric acid as the final product. Nitrate (NO3-) formation occurs without the use of any external electric potential or radiation. The concentration of NO3- increased linearly with time over a period of 132 h. The average NO3- production rate is found to be 12.9 ± 0.05 μM h-1. We envision that this nitrogen fixation strategy that produces nitric acid in an eco-friendly way might open the possibility for the energy-efficient and green production of nitric acid.

  View details for DOI 10.1021/jacs.4c11899

  View details for PubMedID 39315452