Faculty Publications
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Item Advanced two-dimensional heterojunction photocatalysts of stoichiometric and non-stoichiometric bismuth oxyhalides with graphitic carbon nitride for sustainable energy and environmental applications(MDPI, 2021) Sridharan, K.; Shenoy, S.; Girish Kumar, S.G.; Terashima, C.; Fujishima, A.; Pitchaimuthu, S.Semiconductor-based photocatalysis has been identified as an encouraging approach for solving the two main challenging problems, viz., remedying our polluted environment and the generation of sustainable chemical energy. Stoichiometric and non-stoichiometric bismuth oxyhalides (BiOX and BixOyXz where X = Cl, Br, and I) are a relatively new class of semiconductors that have attracted considerable interest for photocatalysis applications due to attributes, viz., high stability, suitable band structure, modifiable energy bandgap and two-dimensional layered structure capable of generating an internal electric field. Recently, the construction of heterojunction photocatalysts, especially 2D/2D systems, has convincingly drawn momentous attention practicably owing to the productive influence of having two dissimilar layered semiconductors in face-to-face contact with each other. This review has systematically summarized the recent progress on the 2D/2D heterojunction constructed between BiOX/BixOyXz with graphitic carbon nitride (g-C3N4). The band structure of individual components, various fabrication methods, different strategies developed for improving the photocatalytic performance and their applications in the degradation of various organic contaminants, hydrogen (H2) evolution, carbon dioxide (CO2) reduction, nitrogen (N2) fixation and the organic synthesis of clean chemicals are summarized. The perspectives and plausible opportunities for developing high performance BiOX/BixOyXz-g-C3N4 heterojunction photocatalysts are also discussed. © 2021 by the authors. Licensee MDPI, Basel, Switzerland.Item Melt quenched vanadium oxide embedded in graphene oxide sheets as composite electrodes for amperometric dopamine sensing and lithium ion battery applications(Elsevier B.V., 2017) Moolayadukkam, M.; Shenoy, S.; Sridharan, K.; Kufian, D.; Arof, A.K.; Nagaraja, H.S.Electrochemical sensors and lithium-ion batteries are two important topics in electrochemistry that have attracted much attention owing to their extensive applications in enzyme-free biosensors and portable electronic devices. Herein, we report a simple hydrothermal approach for synthesizing composites of melt quenched vanadium oxide embedded on graphene oxide of equal proportion (MVGO50) for the fabrication of electrodes for nonenzymatic amperometic dopamine sensor and lithium-ion battery applications. The sensing performance of MVGO50 electrodes through chronoamperometry studies in 0.1 M PBS solution (at pH 7) over a wide range of dopamine concentration exhibited a highest sensitivity of 25.02 ?A mM ?1 cm ?2 with the lowest detection limit of 0.07 ?M. In addition, the selective sensing capability of MVGO50 was also tested through chronoamperometry studies by the addition of a very small concentration of dopamine (10 ?M) in the presence of a fairly higher concentration of uric acid (10 mM) as the interfering species. Furthermore, the reversible lithium cycling properties of MVGO50 are evaluated by galvanostatic charge-discharge cycling studies. MVGO50 electrodes exhibited enhanced rate capacity of up to 200 mAhg ?1 at a current of 0.1C rate and remained stable during cycling. These results indicate that MVGO composites are potential candidates for electrochemical device applications. © 2017 Elsevier B.V.Item Porous cobalt chalcogenide nanostructures as high performance pseudo-capacitor electrodes(Elsevier Ltd, 2017) Bhat, K.S.; Shenoy, S.; Nagaraja, H.S.; Sridharan, K.Electrochemical supercapacitor is an essential technology that is pivotal for the development of reliable energy storage devices. Herein, we report the fabrication of supercapacitor electrodes using nanostructured porous cobalt chalcogenide (CoTe2 and CoSe2) electrodes, anticipating an enhanced performance owing to their higher contact area with electrolyte and large pore volume enabling shorter diffusion paths for ion exchange. In this regard, we synthesized CoTe2 and CoSe2 nanostructures via an anion-exchange-reaction between pre-synthesized Co(OH)2 hexagonal nanosheets and chalcogen (tellurium and selenium) ions under hydrothermal conditions. Structural, morphological and compositional properties of the as-synthesized materials are examined using X-ray diffraction, Raman spectroscopy, scanning electron microscopy, high resolution transmission electron microscopy and energy dispersive X-ray spectroscopy. Pseudo-capacitive properties of CoTe2 and CoSe2 nanostructures as working electrodes are studied through cyclic voltammetry and galvanostatic charge-discharge methods using an electrochemical workstation. CoSe2 electrode delivered a specific capacitance of 951 F g?1 at a scan rate of 5 mV s?1, which surprisingly is almost three times higher in comparison to CoTe2 electrode (360 F g?1). Both CoTe2 and CoSe2 electrodes exhibited good capacitance retention capability for 2500 CV cycles. The superior electrochemical performance of the nanoporous CoSe2 electrode indicate their applicability for high-performance energy storage device applications. © 2017 Elsevier LtdItem A simple single-step approach towards synthesis of nanofluids containing cuboctahedral cuprous oxide particles using glucose reduction(Higher Education Press, 2018) Shenoy, S.; Nityananda Shetty, A.Enhancement of thermal properties of conventional heat transfer fluids has become one of the important technical challenges. Since nanofluids offer a promising help in this regard, development of simpler and hassle free routes for their synthesis is of utmost importance. Synthesis of nanofluids using a hassle free route with greener chemicals has been reported. The single-step chemical approach reported here overcomes the drawbacks of the two-step procedures in the synthesis of nanofluids. The resulting Newtonian nanofluids prepared contained cuboctahedral particles of cuprous oxide and exhibited a thermal conductivity of 2.852 W·m-1·K-1. Polyvinylpyrrolidone (PVP) used during the synthesis acted as a stabilizing agent rendering the nanofluid a stability of 9 weeks. © 2018, Higher Education Press and Springer-Verlag GmbH Germany, part of Springer Nature.Item Enhanced thermoelectric performance of bulk tin telluride: Synergistic effect of calcium and indium co-doping(Elsevier Ltd, 2018) Bhat, D.K.; Shenoy, S.SnTe based materials are considered recently as a lead-free replacement of the well-known PbTe based thermoelectric (TE) materials in addressing the energy crisis worldwide. Herein we report both experimental and theoretical study on the effect of co-doping of calcium and indium on electronic structure and TE properties of SnTe. We show that the resonant levels introduced by indium and band gap opening caused by calcium, valence band convergence induced by both calcium and indium, synergistically increases the Seebeck coefficient for a wide range of temperatures. The co-doped SnTe with a high ZT of ?1.65 at 840 K and record high power factor of ?47 ?Wcm?1K?2 for SnTe based materials make it a promising material for TE applications. © 2018 Elsevier LtdItem Novel NRGO-CoWO4-Fe2O3 nanocomposite as an efficient catalyst for dye degradation and reduction of 4-nitrophenol(Elsevier Ltd, 2018) Mohamed, M.M.J.; Shenoy, S.; Bhat, D.K.Novel NRGO-CoWO4-Fe2O3 (N-doped reduced graphene oxide-cobalt tungstate-iron oxide) ternary nanocomposite was prepared by using simple microwave method. The synthesized materials were thoroughly characterized by X-ray diffraction (XRD) studies, Brunauer-Emmett-Teller (BET) analysis, transmission electron microscopy (TEM), high-resolution transmission electron microscopy (HRTEM), X-ray photoelectron spectroscopy (XPS), Raman spectroscopy, photoluminescence (PL) and UV-Visible spectroscopy. The nanocomposite was studied for its catalytic activity in degradation of methylene blue (MB) and reduction of 4-Nitrophenol (4-NP) to 4-Aminophenol (4-AP). The observed results of catalytic efficiency and rate constants indicated that the NRGO-CoWO4-Fe2O3 nanocomposite can perform as an excellent catalyst compared to other composite materials. The detailed experimental study revealed that this ternary nanocomposite shows a great promise as a candidate for various environmental applications. © 2018 Elsevier B.V.Item Cadmium sulfide nanostructures: Influence of morphology on the photocatalytic degradation of erioglaucine and hydrogen generation(Elsevier B.V., 2019) Shenoy, S.; Jang, E.; Park, T.J.; Gopinath, C.S.; Sridharan, K.Size and shape of inorganic materials are known to have great effects on their physical and chemical properties. Here, for the first time we report the visible light driven photocatalytic degradation of erioglaucine – a stable organic dye molecule in the presence of chemically synthesized nanoscale CdS with 1D (nanorods), 2D (nanosheets) and 3D (hierarchical) morphology. Visible light driven photocatalytic degradation efficiency of both 1D and 3D CdS in the removal of erioglaucine are identical. Surprisingly, with 5 min of sonication, the highly crystalline 3D CdS stacked with many thin nanowires containing numerous active surface sites exhibited four-fold enhanced photodegradation efficiency in comparison to 1D and 2D CdS. Scavenger studies revealed that electrons and superoxide radicals are primary reactive species involved in the photodegradation of erioglaucine, while cyclic photodegradation studies revealed the good stability of 3D CdS against photocorrosion. Further, the photocatalytic hydrogen evolution studies also revealed the excellent activity of 3D CdS in comparison to 1D and 2D CdS. Thus, we find that the morphology indeed influences the photocatalytic activity. These results reveal that 3D CdS nanostructures investigated in the present work are efficient photocatalysts that could be fine-tuned for both environmental remediation and hydrogen generation applications. © 2019 Elsevier B.V.Item Structure-sensitive electrocatalytic reduction of co2 to methanol over carbon-supported intermetallic ptzn nano-alloys(American Chemical Society service@acs.org, 2020) Payra, S.; Shenoy, S.; Chakraborty, C.; Tarafder, K.; Roy, S.The electrochemical reduction of CO2 (CO2RR) to produce valuable synthetic fuel like CH3OH not only mitigates the accumulated greenhouse gas from the environment but is also a promising direction toward attenuating our continuous reliance on fossil fuels. However, CO2RR to yield CH3OH suffers because of large overpotential, competitive H2 evolution reaction (HER), and poor product selectivity. In this regard, intermetallic alloy catalysts open up a wide possibility of fine-tuning the electronic property and attain appropriate structures that facilitate selective CO2RR. Here, we report for the first time the CO2RR over carbon-supported PtZn nano-alloys and probed the crucial role of structures and interfaces as active sites. PtZn/C, Pt3Zn/C, and PtxZn/C (1 < x < 3) synthesized from the metal-organic framework material were characterized structurally and morphologically. The catalysts demonstrated structure dependency toward CH3OH selectivity, as the mixed-phase PtxZn/C outperformed the phase-pure PtZn/C and Pt3Zn/C. The structure-dependent reaction mechanism and the kinetics were elucidated over the synthesized catalysts with the help of detail experiments and associated density functional theory calculations. Results showed that in spite of low electrochemically active surface area, PtxZn could not only have facilitated the single electron transfer to adsorbed CO2 but also showed better binding of the intermediate CO2 •- over its surface. Moreover, the lower bond energy between the mixed-phase surface and -OCH3 compared to the phase-pure catalysts has enabled higher CH3OH selectivity over PtxZn. This work opens a wide possibility of studying the role of interfaces between phase-pure nano-alloys toward CO2RR. © 2020 American Chemical SocietyItem Bismuth oxybromide nanoplates embedded on activated charcoal as effective visible light driven photocatalyst(Elsevier B.V., 2020) Shenoy, S.; Sridharan, K.Nanostructured bismuth oxybromide (BiOBr) are one among the most significantly researched visible light driven photocatalyst, but their low specific surface area hinders higher rate of photodegradation. Herein, a single-step solution based synthesis technique is adopted to embed BiOBr on very little quantities of activated charcoal (AC), thereby improving its specific surface area and visible light absorption range. Nanoplate morphology of BiOBr and their embedment on AC are confirmed from electron microscopy. Interestingly, the embedment of BiOBr on just 0.5 wt% of AC (BiOBr-AC0.5) significantly enhanced the rate of salicylic acid photodegradation, which was six-fold higher than that of pristine BiOBr. © 2020 Elsevier B.V.Item Enhanced photocatalytic efficiency of layered CdS/CdSe heterostructures: Insights from first principles electronic structure calculations(Institute of Physics Publishing helen.craven@iop.org, 2020) Shenoy, S.; Tarafder, K.Metal sulfides are emerging as an important class of materials for photocatalytic applications, because of their high photo responsive nature in the wide visible light range. In this class of materials, CdS with a direct band gap of 2.4 eV, has gained special attention due to the relative position of its conduction band minimum, which is very close to the energies of the reduced protons. However, the photogenerated holes in the valence band of CdS are prone to oxidation and destroy its structure during photocatalysis. Thus constructing a CdS based heterostructure would be an effective strategy for improving the photocatalytic performance. In this work we have done a detail theoretical investigation based on hybrid density functional theory calculation to get insight into the energy band structure, mobility and charge transfer across the CdS/CdSe heterojunction. The results indicate that CdS/CdSe forms type-II heterostructure that has several advantages in improving the photocatalytic efficiency under visible light irradiation. © 2020 IOP Publishing Ltd.