Department of Chemistry

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Ag2S/Ag Heterostructure: A Promising Electrocatalyst for the Hydrogen Evolution Reaction
(ACS, 2017) Basu, Mrinmoyee; Pande, Surojit; Gangopadhyay, Subhashis
Different metal chalcogenides, being a potential candidate for hydrogen evolution catalysts, have attracted enormous attention in the field of water splitting. In the present study, Ag2S/Ag is revealed as an efficient catalyst for hydrogen evolution. When a sacrificial template of the CuS nanostructure is used, Ag2S/Ag heterostructures are synthesized following a simple wet-chemical technique. Two different routes, wet chemical and hydrothermal, are followed to modulate the morphology of the CuS templates from flower ball to wirelike structures, which subsequently results in the formation of Ag2S nanostructure. Finally, the Ag layer is deposited on Ag2S with the help of a photoreduction technique. The unique heterostructure of Ag2S/Ag shows efficient catalytic activity in the H2 evolution reaction. A Ag2S/Ag wire can successfully generate a 10 mA/cm2 current density at a −0.199 V potential. Ag2S/Ag contains the micronanostructure where nanoplates of Ag2S/Ag assemble to give rise to microstructures such as flower balls and wire.
Decoration of Pd and Pt nanoparticles on a carbon nitride (C3N4) surface for nitro-compounds reduction and hydrogen evolution reaction
(RSC, 2017) Basu, Mrinmoyee; Gangopadhyay, Subhashis; Pande, Surojit
Herein, we propose the synthesis of Pd and Pt monometallic nanoparticles on a carbon nitride (C3N4) surface for the reduction of nitro compounds as well as for electrocatalysis. For the synthesis of C3N4/Pd and C3N4/Pt, metal ions were initially adsorbed on the C3N4 surface and then subsequently reduced by NaBH4. The as-synthesized heterostructures were authenticated by different characterization techniques: UV-vis, PXRD, XPS, TEM, FESEM, and EDS. Decorations of monometallic NPs on C3N4 not only improved the reduction efficiency of nitro-compounds but also enhanced the electrocatalytic activity in the hydrogen evolution reaction. C3N4/Pt proved to be an efficient electrocatalyst as it requires a potential of −0.339 V to attain a current density of 10 mA cm−2; whereas, C3N4/Pd requires −0.371 V to reach a current density of 10 mA cm−2vs. Ag/AgCl. Both C3N4/Pd and Pt heterostructures are better than bare C3N4, which needs −0.596 V to achieve a current density of 10 mA cm−2vs. Ag/AgCl. On the other hand, C3N4/Pd showed a better performance in nitro-compound reduction compared to C3N4/Pt and bare C3N4. The kinetic study reveals that the rate constant using a C3N4/Pd catalyst is 6.7 × 10−1 min−1 for p-nitroaniline reduction, which is 101 times higher compared to bare C3N4 and 4.7 times higher in comparison to C3N4/Pt.
Study on metal nanoparticles synthesis and orientation of gemini surfactant molecules used as stabilizer
(Elsiever, 2015-05-01) Pande, Surojit; Saha, Subit Kumar; Gangopadhyay, Subhashis
In the present study, we report the synthesis of gold (Au), silver (Ag), and gold–silver alloy (Au–Ag) nanoparticles (NPs) by seed-mediated method using gemini surfactant, containing diethyl ether spacer group as a stabilizer. As-synthesized NPs are found very much stable and have been characterized using UV–vis spectroscopy, X-ray photoelectron spectroscopy (XPS), transmission electron microscopy (TEM), energy dispersive spectroscopy (EDS), and zeta potential techniques. The orientation of gemini surfactant molecules surrounding the metal NPs has been investigated exploiting twisted intramolecular charge transfer (TICT) fluorescence properties of a probe 4-(N,N-dimethylamino) cinnamaldehyde (DMACA). The quenching efficiencies of different NPs have been performed in the fluorescence of DMACA and are found to be different. This effect can be related to the location of DMACA as well as the electro-negativity of the metals as the extent of orientation of the surfactant molecules around NPs controls the location of DMACA in a bilayer. To support the location of DMACA, fluorescence quenching studies with cetylpyridinium chloride (CPC) as an external quencher have also been carried out.
Synthesis of Monometallic (Au and Pd) and Bimetallic (AuPd) Nanoparticles Using Carbon Nitride (C3N4) Quantum Dots via the Photochemical Route for Nitrophenol Reduction
(ACS, 2016) Basu, Mrinmoyee; Gangopadhyay, Subhashis; Pande, Surojit
In this study, we report the synthesis of monometallic (Au and Pd) and bimetallic (AuPd) nanoparticles (NPs) using graphitic carbon nitride (g-C3N4) quantum dots (QDs) and photochemical routes. Eliminating the necessity of any extra stabilizer or reducing agent, the photochemical reactions have been carried out using a UV light source of 365 nm where C3N4 QD itself functions as a suitable stabilizer as well as a reducing agent. The g-C3N4 QDs are excited upon irradiation with UV light and produce photogenerated electrons, which further facilitate the reduction of metal ions. The successful formation of Au, Pd, and AuPd alloy nanoparticles is evidenced by UV–vis, powder X-ray diffraction, X-ray photon spectroscopy, and energy-dispersive spectroscopy techniques. The morphology and distribution of metal nanoparticles over the C3N4 QD surface has been systematically investigated by high-resolution transmission electron microscopy (HRTEM) and SAED analysis. To explore the catalytic activity of the as-prepared samples, the reduction reaction of 4-nitrophenol with excellent performance is also investigated. It is noteworthy that the synthesis of both monometallic and bimetallic NPs can be accomplished by using a very small amount of g-C3N4, which can be used as a promising photoreducing material as well as a stabilizer for the synthesis of various metal nanoparticles.
Synthesis of ZnO/Au and ZnO/Ag nanoparticles and their photocatalytic application using UV and visible light
(RSC, 2014-05-20) Pande, Surojit; Gangopadhyay, Subhashis
We report a simple and convenient method for the synthesis of a ZnO/Au and ZnO/Ag heterostructure nanoflower by applying a surfactant mediated route. Initially, pure ZnO nanoflowers have been synthesized followed by Au and Ag deposition on ZnO surface using hydrazine hydrate as reducing agent. Structure, crystallinity, and morphology have been assessed by X-ray diffraction, X-ray photoelectron spectroscopy, and electron microscopy techniques. The influences of the deposited metal nanoparticles (Au and Ag) on the surface of ZnO have been emphasized by applying the as-synthesized nanostructure in dye degradation under illumination of UV and visible light. The basic motivation behind this work is to find a superior photocatalyst, which can work under UV as well as visible light i.e., to cover the whole range of the solar spectrum. Photocatalytic performances of bare ZnO, ZnO/Au, and ZnO/Ag have been studied thoroughly. Photodegradation results under UV and visible light demonstrated that the incorporation of noble metal nanoparticles significantly (or drastically) increases the catalytic efficiency by promoting the photogenerated charge carrier separation. The main advantage of the proposed ZnO/Au and ZnO/Ag semiconductor is that it delays the recombination process of the electron–hole pairs generated by the photon absorption, which in lieu increases the photocatalytic efficiency. It is a challenging issue to fabricate stable photocatalysts which can work under visible light as it covers 43% of sunlight. To investigate the role of photogenerated electrons and holes in dye degradation, scavenging experiments using different scavengers have also been performed.