Faculty Publications
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Item Novel Fe-Ni-Graphene composite electrode for hydrogen production(Elsevier Ltd, 2015) Badrayyana, S.; Bhat, D.K.; Shenoy, U.S.; Ullal, Y.; Hegde, A.We have developed a novel, efficient and economical composite electrode for hydrogen production. The electrode has been formed by embedding graphene in the Fe-Ni matrix via room temperature electrodeposition. The obtained active coatings have been tested for their efficiency and performance as electrode surfaces for hydrogen evolution reaction (HER) in 6 M KOH by cyclic voltammetry and chronopotentiometry techniques. The coating obtained at 60 mA cm-2 exhibited approximately 3 times higher activity for hydrogen production than that of binary Fe-Ni alloy. Addition of graphene to electrolyte bath resulted in porous 3D projections of nano-sized spheres of Fe-Ni on the surface of graphene, which effectively increased the electrochemically active surface area. XPS analysis results showed the equal distribution of both Ni metal and NiO active sites on the composite. The addition of graphene favoured the deposition of metallic nickel, which accelerated the rate determining proton discharge reaction. All these factors remarkably enhanced the HER activity of Fe-Ni-Graphene (Fe-Ni-G) composite electrode. The Tafel slope analysis showed that the HER follows Volmer-Tafel mechanism. The structure-property relationship of Fe-Ni-G coating has been discussed by interpreting field emission scanning electron microscopy (FESEM), X-ray photoelectron spectroscopy (XPS) and X-ray diffraction (XRD) analysis results. © 2015 Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.Item Novel RGO-ZnWO4-Fe3O4 nanocomposite as high performance visible light photocatalyst(Royal Society of Chemistry, 2016) Mohamed, M.M.J.; Shenoy, U.S.; Bhat, D.K.A novel RGO-ZnWO4-Fe3O4 nanocomposite is synthesized by a microwave irradiation method and its catalytic activity for the photo degradation of Methylene Blue (MB) is investigated. The prepared nanocomposites are characterized by powder X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), high resolution transmission electron microscopy (HRTEM), transmission electron microscopy (TEM), field emission scanning electron microscopy (FESEM), Raman spectroscopy, photoluminescence spectroscopy (PL) and UV-visible spectroscopy. The visible light photocatalytic activities of the prepared nanocomposites are investigated using a MB dye solution. It is noteworthy that RGO-ZnWO4-Fe3O4 nanocomposites exhibited relatively high photocatalytic activity compared to ZnWO4-RGO and pure ZnWO4 on MB in aqueous solution. This enhanced rate is due to the ability of the graphene in the RGO-ZnWO4-Fe3O4 composite to support carrier exploitation efficiently by tolerating the photo excited electron-hole pairs and thus encouraging oxidative degradation of the pollutants. This work could be extended to other organic pollutants as well and could provide new insights into ternary nanocomposites as high performance photocatalysts and their application in waste water treatment. © 2016 The Royal Society of Chemistry.Item Direct synthesis of nanofluids containing novel hexagonal disc shaped copper nanoparticles(American Scientific Publishers order@aspbs.com, 2017) Shenoy, U.S.; Nityananda Shetty, A.N.Copper nanofluids have been prepared by single step solution phase reduction of copper sulphate by ascorbic acid in the presence of polyvinylpyrrolidone. The synthesized hexagonal disc shaped nanostructures of copper are novel and were characterized by diffraction techniques, microscopic techniques and spectroscopic analysis. Thermal conductivity and rheological measurements were also carried out. Sedimentation measurements showed that the nanofluid was stable up to a period of 3 weeks. The copper nanofluid exhibited Newtonian behavior and enhanced thermal conductivity. The nanofluid showed thermal conductivity of 0.827 Wm?1K?1when the weight fraction of copper nanoparticles was as low as 0.096% owing to higher conductivity of copper, its nano size and uniform distribution of the particles in the fluid. The method is found to be facile, expeditious, economic and reliable technique for synthesis of nanofluids. © 2017 by American Scientific Publishers All rights reserved.Item High Thermoelectric Performance of Co-Doped Tin Telluride Due to Synergistic Effect of Magnesium and Indium(American Chemical Society service@acs.org, 2017) Bhat, D.K.; Shenoy, U.S.Thermoelectric (TE) materials are considered go-to materials lately in addressing the worldwide energy crisis. We report a study on the effect of co-doping of magnesium and indium in lead-free SnTe both experimentally and theoretically. We show how the resonant levels introduced by indium increase the Seebeck coefficient at lower temperatures and how magnesium enhances the Seebeck at higher temperatures by opening the band gap and decreasing the energy difference between the light and heavy hole valence sub-bands. Synergistically, the effects of band engineering lead to the co-doped sample having high thermoelectric figure of merit (ZT) over a wide range of temperature and record a high power factor of ?42 ?W cm-1 K-2 for SnTe based materials. For the very first time we show the effect of site occupied by the dopant on the electronic structure of the material. The resulting high ZT of 1.5 at 840 K makes SnTe a very suitable material for thermoelectric applications. (Graph Presented). © 2017 American Chemical Society.Item Enhanced photocatalytic performance of N-doped RGO-FeWO4/Fe3O4 ternary nanocomposite in environmental applications(Elsevier Ltd, 2017) Mohamed, M.; Shenoy, U.S.; Bhat, D.K.Nitrogen doped RGO- FeWO4/Fe3O4 (NRGO-FeWO4/Fe3O4) ternary nanocomposite was synthesized by rapid single step microwave irradiation approach using iron acetate, ammonium tungstate and graphene oxide as precursors. The synthesized materials were thoroughly characterized by diffraction, microscopic and spectroscopic techniques. The materials were tested for their catalytic efficiency in photo degradation of Methylene Blue (MB) dye and in reduction of 4-nitrophenol (4-NP) to 4-aminophenol (4-AP). MB was mineralized within 100 minutes of visible light irradiation time in the presence of the ternary composite, apart from excellent stability and efficiency even after 10 consecutive cycles. The composite also had the capacity to convert 4-NP into 4-AP within 45 seconds and showed very good catalytic activity even after 20 cycles. The results revealed that ternary composite has way more efficiency than the component materials and can act as a promising catalyst for various environmental and engineering applications. © 2017 Elsevier LtdItem NiWO4-ZnO-NRGO ternary nanocomposite as an efficient photocatalyst for degradation of methylene blue and reduction of 4-nitro phenol(Elsevier Ltd, 2017) Mohamed, M.; Shenoy, U.S.; Bhat, D.K.A novel NiWO4-ZnO-NRGO ternary nanocomposite has been efficiently synthesized by decorating nitrogen doped reduced graphene oxide (NRGO) with zinc oxide and nickel tungstate nanoparticles via a facile microwave irradiation technique and its capability to catalyze photodegradation of methylene blue (MB) dye in aqueous solution and reduction of 4-nitro phenol (4-NP) to 4-amino phenol (4-AP) using sodium borohydride was explored. The as-synthesized nanocomposite was characterized by X-ray diffraction (XRD), Raman spectroscopy, Brunauer-Emmett-Teller (BET) analysis, energy dispersive X-ray (EDX) analysis, field emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM), high-resolution transmission electron microscopy (HRTEM), X-ray photoelectron spectroscopy (XPS), photoluminescence (PL) spectroscopy and diffuse reflectance spectroscopy (DRS) techniques. The photocatalytic activity of the as-synthesized nanocomposite estimated through the photodegradation of MB under visible light irradiation showed 9 times improvement over pure NiWO4. It also showed excellent catalytic activity in reduction of 4-NP to 4-AP. The material also showed excellent stability and reusability. The entire study revealed that the novel NiWO4-ZnO-NRGO ternary nanocomposite can act as a promising bifunctional photocatalyst for environmental remediation and industrial application. © 2017 Elsevier LtdItem Enhanced Bulk Thermoelectric Performance of Pb0.6Sn0.4Te: Effect of Magnesium Doping(American Chemical Society service@acs.org, 2017) Shenoy, U.S.; Bhat, D.K.Thermoelectric (TE) materials are promising in the context of renewable power generation as they can directly convert waste heat into electricity. Although PbTe is the best known TE material, its use is not encouraged due to concerns of environmental toxicity of lead. A combination of modified self-propagating high-temperature synthesis (SHS) and field-assisted sintering technique (FAST) is employed for the very first time to synthesize a solid solution of PbTe and SnTe. We show that doping of Pb0.6Sn0.4Te with Mg breaks crystal mirror symmetry and opens up band gap. This results in suppression of bipolar diffusion. Also the increase in degeneracy of valence sub-bands improves Seebeck coefficient. Both these synergistically leads to remarkable enhancement in figure of merit ZT (?2 at 840 K) and ZTavg (?1.2 between 500 and 840 K) rendering it into high-performance thermoelectric material by successfully engineering electronic structure. Most importantly, the ZT here is comparable to that of Mg-doped PbTe but has lesser lead content and hence is more environment friendly. The most probable configuration of Pb0.6Sn0.4Te was also determined for the very first time using site occupancy disorder (SOD) technique. © 2017 American Chemical Society.Item Tuning the Photocatalytic Activity of SrTiO3 by Varying the Sr/Ti Ratio: Unusual Effect of Viscosity of the Synthesis Medium(American Chemical Society service@acs.org, 2018) Bantawal, H.; Shenoy, U.S.; Bhat, D.K.SrTiO3 nanostructures were successfully synthesized in various alcohols as cosolvent as well as surfactant by a facile solvothermal method. The as-synthesized catalysts were characterized by X-ray diffraction technique, scanning electron microscopy, energy-dispersive X-ray analysis, Brunauer-Emmett-Teller analysis, diffuse reflectance spectroscopy, and photoluminescence spectroscopy. The possible formation mechanism of SrTiO3 in the presence of these alcohols is discussed, and the effect of these alcohols on the structure, Sr/Ti atomic ratio, and optical properties is related to the photocatalytic activity. First principles calculations were made use of to determine the effect of defects on the electronic structure and the band gap. The photocatalytic activity of these catalysts was evaluated by taking methylene blue as a model pollutant under visible light irradiation. It was found that the photocatalytic activity of ethanol-mediated SrTiO3 was found to be higher than the other samples because of the synergistic effect of high surface area and lesser defects. © 2018 American Chemical Society.Item Synthesis of BaWO4/NRGO–g-C3N4 nanocomposites with excellent multifunctional catalytic performance via microwave approach(Higher Education Press, 2018) Mohamed, M.M.J.; Shenoy, U.S.; Bhat, D.K.Novel barium tungstate/nitrogen-doped reduced graphene oxide-graphitic carbon nitride (BaWO4/NRGO-g-C3N4) nanocomposite has been synthesized by a simple one-pot microwave technique. The synthesized nanocomposites are well characterized by diffraction, microscopic and spectroscopic techniques to study its crystal structure, elemental composition, morphological features and optical properties. The material prepared is tested for its performance as an electrocatalyst, photocatalyst and reduction catalyst. The nanocomposite catalyzed the photodegradation of methylene blue (MB) dye in 120 min, reduction of 4-nitro phenol (4-NP) to 4-amino phenol (4-AP) in 60 s, showed an impressive Tafel slope of 62 mV/dec for hydrogen evolution reaction (HER). The observed results suggest that the nanocomposite acts as an efficient multifunctional catalyst. The reported approach provides fundamental insights which can be extended to other metal tungstate-based ternary composites for applications in the field of clean energy and environment in the future. © 2018, Higher Education Press and Springer-Verlag GmbH Germany, part of Springer Nature.Item Band Engineering of SrTiO3: Effect of Synthetic Technique and Site Occupancy of Doped Rhodium(American Chemical Society service@acs.org, 2018) Shenoy, U.S.; Bantawal, H.; Bhat, D.K.It is well known that doping of Rh into the SrTiO3 lattice introduces 4d donor levels within the band gap, which causes reduction in the gap and extends the photocatalytic activity to the visible region of the solar spectrum. The mid-gap states formed also act as recombination centers and diminish the efficiency of the material. Herein, we present a combined theoretical and experimental approach to avoid the formation of the so-called acceptor mid-gap states. For the first time, we study the effect of occupancy of Rh in the Sr site. First-principles calculations reveal that mixed occupancies of Rh into Sr and Ti sites lead to the introduction of acceptor levels within the band gap, leading to decrease in photocatalytic efficiency. A facile one-pot solvothermal approach by avoiding high-temperature calcinations is reported to obtain Rh-doped SrTiO3 nanoparticles in Rh3+ states, suppressing the formation of Rh4+ states by directing Rh toward Sr sites. The photocatalytic activity of Rh-doped SrTiO3 nanoparticles is studied in the case of degradation of methylene blue, wherein the 1.0 Rh sample was found to be highly efficient. © 2018 American Chemical Society.