Browsing by Author "Bhat, D.K."

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A case of perfect convergence of light and heavy hole valence bands in SnTe: the role of Ge and Zn co-dopants
(Royal Society of Chemistry, 2022) Shenoy, U.S.; D, G.K.; Bhat, D.K.
A dual step approach of decreasing the thermal conductivity and improving the power factor by using two different dopants has shown great promise in the development of high performance thermoelectrics. In this work, we dope Ge, which is well known to decrease the thermal conductivity of SnTe. Later, to this, we co-dope Zn to simultaneously improve the power factor. Zn, in the presence of Ge, introduces resonance levels, thus distorting the density of states near the Fermi level, improving the room temperature performance. In addition, it is also able to increase the band gap, thus preventing bipolar diffusion at high temperatures. The unique feature exhibited is the perfect convergence of light and heavy hole valence sub-bands achieved for the first time in SnTe promising a high performance throughout the temperature range. The transport property calculations reveal that in addition to p-type, it can also act as an outstanding n-type material by tuning its chemical potential, making it worth studying experimentally. © 2022 RSC.
A direct approach towards synthesis of copper nanofluid by one step solution phase method
(Elsevier B.V., 2024) Kumar, S.P.; Shenoy, U.S.; Bhat, D.K.
We adopted a simple one step approach to synthesize copper nanofluids by reduction of copper sulphate with fructose. The solution phase synthetic technique led to the formation of copper particles whose size was restricted to the nanodimensions by use of sodium lauryl sulphate. We studied the effect of various parameters on the formation and dispersion of the copper nanoparticles in the base fluid containing a 1:1 mixture of water and ethylene glycol. The resulting Newtonian nanofluid was found to be highly stable with increased thermal conductivity. Thus, the applied technique is found to be simple, economic, and extendable to other class of materials to obtain stable dispersions of nanofluids for heat transfer applications. © 2024 Elsevier B.V.
A facile microwave approach to synthesize RGO-BaWO4 composites for high performance visible light induced photocatalytic degradation of dyes
(AIMS Press Min.yu@aimspress.com, 2017) Mohamed, M.; Bhat, D.K.
Photocatalysts with enhanced efficiency for environmental remediation requires an effective separation of photogenerated electron hole pairs and optimum charge carrier transport. Based on the above criteria, a cost effective, facile one-pot microwave approach was made to synthesize RGO-BaWO4 composites with excellent stability and reusability in photodegradation of methylene blue (MB) and methyl orange (MO). A series of composites with varying composition with respect to RGO was synthesized and thoroughly characterized using various techniques. The composite with 2.5% RGO-BaWO4 showed maximum efficiency under visible light irradiation. The mechanism of charge transfer and kinetics of the reaction was also studied. The interfacial/interparticle charge transfer between the narrow elliptical BaWO4 particles and RGO is found to be responsible for the increased efficiency. The photo generated holes and the superoxide radical were found to play a key role in the degradation process. The synergistic action makes RGOBaWO4 composites a promising material as high performance photocatalyst for degradation of organic dyes. © 2017 Denthaje Krishna Bhat, et al.
A porous graphene-NiFe2O4nanocomposite with high electrochemical performance and high cycling stability for energy storage applications
(Royal Society of Chemistry orders@rsc.org, 2020) Sethi, M.; Shenoy, U.S.; Bhat, D.K.
It is well agreed that supercapacitors form an important class of energy storage devices catering to a variety of needs. However, designing the same using eco-friendly and earth abundant materials with high performance is still the dire need of the day. Here, we report a facile solvothermal synthesis of a porous graphene-NiFe2O4 (PGNF) nanocomposite. Thorough elemental, diffraction, microscopic and spectroscopic studies confirmed the formation of the PGNF composite, in which the NF nanoparticles are covered over the PG surface. The obtained 10 PGNF composite showed a surface area of 107 m2 g-1, with large pore volume which is favorable for charge storage properties. When utilizing the material as an electrode for a supercapacitor in a 2 M KOH aqueous electrolyte, the electrode displayed an impressive specific capacitance value of 1465.0 F g-1 at a scan rate of 5 mV s-1 along with a high capacitance retention of 94% after 10?000 discharge cycles. The fabricated symmetrical supercapacitor device exhibited an energy density of 4.0 W h kg-1 and a power density of 3600.0 W kg-1 at a high applied current density of 14 A g-1. The superior electrochemical performance is attributed to the synergetic effect of the composite components which not only provided enough electroactive channels for the smooth passage of electrolyte ions but also maintained the hybrid structure intact in the ongoing electrochemical process. The obtained results underpin the promising utility of this material for future electrochemical energy storage devices. © The Royal Society of Chemistry.
Acoustical and compressibility parameters of glycylglycine-FeCl3 in aqueous ethanol mixture at T = (293.15, 303.15, and 313.15) K
(2010) Santosh, M.S.; Bhat, D.K.
Ultrasonic velocity measurement is a reliable procedure that allows quick and easy determination of solvent concentrations in mixtures. This paper presents data of ultrasonic velocities and isentropic compressibilities of (glycylglcyine-FeCl3) in aqueous ethanol mixture at T = (293.15, 303.15, and 313.15) K. Various acoustical parameters were calculated, because of their importance in the study of specific molecular interactions. A less-compressible phase of the fluid and a closer packing of molecules is observed with changes in the intermolecular free length. Quantitative investigation suggests that the mixing of ethanol with an aqueous glycylglycine-FeCl3 solution causes the rupture of hydrogen bonds, with increasing S and Lf values (where the former represents the change in isentropic compressibility and the latter represents the intermolecular free length). Theoretically computed values of isentropic compressibility in the studied mixture using different models indicate the superiority of the very complex procedure. © 2010 American Chemical Society.
Activated carbon-polyethylenedioxythiophene composite electrodes for symmetrical supercapacitors
(2008) Muthu, M.S.; Bhat, D.K.
A symmetrical (p/p) supercapacitor has been fabricated by making use of activated carbon (AC)-poly-ethylenedioxythiophene (PEDPT)-composite electrodes for the first time. The composite electrodes have been prepared via electrochemical deposition of ?-napthalenesulphonate doped PEDPT onto AC electrodes. The characteristics of the electrodes and the fabricated supercapacitor have been investigated using cyclic voltammetry (CV) and AC impedance spectroscopy. The electrodes show a maximum specific capacitance of 158 Fg-1 at a scan rate of 10 mV s_1. This indicates that the in situ electro-polymerization of ethylenedioxythiophene (EDPT) onto AC could improve the performance of carbon electrodes for use in supercapacitors. © 2007 Wiley Periodicals, Inc.
Application of Prigogine-Flory-Patterson theory to volumetric, ultrasonic, and compressibility parameters of (glycylglycine + CuCl2) in aqueous ethanol mixtures
(2011) Santosh, M.S.; Bhat, D.K.
The molar volume and compressibility of (glycylglycine + CuCl2) in aqueous ethanol mixtures have been obtained at four different temperatures T = (288.15 to 318.15) K from ultrasonic velocity and density measurements. Excess molar volumes were found to be negative throughout the composition range indicating notable changes in hydrogen bonding and electrostatic interactions. Using the Prigogine-Flory-Patterson theory, quantitative estimation of different contributions, i.e. interactional, free volume, and P effect to VE have been obtained. The molar isentropic compressibility has been computed using the ultrasonic velocity and excess volume data. The trends in ?SE are affected by the size of the molecule leading to negative contributions. In order to compare the theoretical values of ultrasonic velocity, the equations of Nomoto and Junjie were used and found to predict the experimental data very well. © 2011 Elsevier Ltd. All rights reserved.
Asymmetric Thermoelectric Performance Tuning in Low-Cost ZrFexNi1-xSb Double Half-Heusler Materials
(American Chemical Society, 2023) Kahiu, J.N.; Kihoi, S.K.; Kim, H.; Shenoy, U.S.; Bhat, D.K.; Lee, H.S.
The new paradigm for increasing the commercial viability of thermoelectric materials in the energy sector is the theoretical prediction and subsequent experimental validation and optimization of cheaper and inherently more efficient compositions. Herein, the experimental validation of the recently theoretically predicted ZrFe0.50Ni0.50Sb double half-Heusler and the ability to intrinsically tune this system to optimized p- or n-type materials by varying the Fe/Ni ratio in the synthesized ZrFexNi1-xSb (x = 0.35-0.65) samples are demonstrated. The samples are synthesized by arc melting, hot pressing, and annealing. Subsequent microstructural analysis confirms the crystallization of the ZrFexNi1-xSb into the half-Heusler structure and reveals that the variation of the Fe/Ni ratio favors the Ni-rich side. Consequently, the best p-type x = 0.55 and n-type x = 0.35 samples exhibit higher power factor values stemming from an increased carrier concentration, higher density of state effective mass, and suppressed bipolar conduction, as indicated by the Hall data analysis and density functional theory simulations. The additional lattice disorders introduced by varying the Fe/Ni ratio suppress the thermal conductivity and increase the microhardness of the n-type samples. The ZrFe0.35Ni0.65Sb and ZrFe0.55Ni0.45Sb samples achieve maximum zTs of ∼0.43 and 0.06, respectively, which is a great improvement over the ∼0.001 value of the ZrFe0.50Ni0.50Sb sample. These results highlight the viability of tuning the performance of double half-Heuslers on the doubly doped site. They will be instrumental in demonstrating the feasibility of developing low-cost double half-Heusler materials with better intrinsic and highly tunable properties. © 2023 American Chemical Society.
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.
BaTiO3-graphene nanocomposite as a photocatalyst for the degradation of methylene blue
(American Institute of Physics Inc. subs@aip.org, 2020) Bantawal, H.; Bhat, D.K.
BaTiO3-graphene composite (BG) was synthesized by a facile two step solvothermal approach. The synthesized materials were thoroughly characterized by X-ray diffraction technique, field emission scanning electron microscopy, energy-dispersive X-ray analysis, Raman analysis, diffuse reflectance spectroscopy and photoluminescence spectroscopic techniques. The photocatalytic activity of 7.5 BG composite was found to be higher as compared to bare BaTiO3, which can be attributed to the enhanced visible light response., excellent adsorption of methylene blue dye via Ï€-Ï€interaction and low recombination rate of photoinduced charges. Â© 2020 Author(s).
Bi and Zn co-doped SnTe thermoelectrics: Interplay of resonance levels and heavy hole band dominance leading to enhanced performance and a record high room temperature: ZT
(Royal Society of Chemistry, 2020) Shenoy, U.S.; Bhat, D.K.
Lead free SnTe with a tunable electronic structure has become the front runner in eco-friendly thermoelectrics. Herein, we show through first-principles density functional theory calculations that Bi and Zn doping introduces a resonance level in SnTe. The dominance of the heavy hole valence band at room temperature in Bi-Zn co-doped SnTe leads to a record high room temperature ZT of ?0.3 (at 300 K) for SnTe based materials. The increase in the Seebeck coefficient value due to the interaction between the resonance states and formation of the nanoprecipitates leading to an appreciably low lattice thermal conductivity of 0.68 W m-1 K-1 results in a peak ZT of ?1.6 at 840 K. A record high ZTaverage of ?0.86 with 300 K and 840 K as cold and hot ends, respectively, makes Bi-Zn co-doped SnTe a potential material for thermoelectric applications. This strategy of using two resonant dopants, to not only improve the room temperature ZT but also high temperature values, can very well be extended to other systems. This journal is © The Royal Society of Chemistry.
Biodegradability of PMMA blends with some cellulose derivatives
(2006) Bhat, D.K.; Muthu, M.S.
High polymer blends of Polymethyl methacrylate (PMMA) with cellulose acetate (CA) and Cellulose acetate phthalate (CAP) of varying blend compositions have been prepared to study their biodegradation behavior and blend miscibility. Films of PMMA-CA, and PMMA-CAP blends have been prepared by solution casting using Acetone and Dimethyl formamide(DMF) as solvents respectively. Biodegradability of these blends has been studied by four different methods namely, soil burial test, enzymatic degradation, and degradation in phosphate buffer and activated sludge degradation followed by water absorption tests to support the degradation studies. Degradation analysis was done by weight loss method. The results of all the tests showed sufficient biodegradability of these blends. Degradability increased with the increase in CA and CAP content in the blend compositions. The miscibility of PMMA-CA and PMMA-CAP blends have been studied by solution viscometric and ultrasonic methods. The results obtained reveal that PMMA forms miscible blends with either CA or CAP in the entire composition range. Miscibility of the blends may be due to the formation of hydrogen bond between the carbonyl group of PMMA and the free hydroxyl group of CA and CAP. © Springer Science+Business Media, Inc. 2006.
Chitosan/NiO nanocomposites: A potential new dielectric material
(2011) Bhatt, A.S.; Bhat, D.K.; Santosh, M.S.; Tai, C.-W.
The study of electrochemical behavior of organic-inorganic nanocomposite materials remains a major challenge for application in energy storage devices. Here, new composite materials of chitosan and NiO nanoparticles have been fabricated. The NiO nanoparticles are well characterized by infrared spectroscopy, X-ray diffraction and transmission electron microscopy. The electrical properties of the films are studied by impedance spectroscopy at different temperatures; and thereby permittivity, electric modulus and conductivity data are obtained. By studying the variations in permittivity and electric modulus spectra with respect to applied frequency signal and temperature, the ionic conductivity of the material is investigated. The Correlated Barrier Hopping model is employed to understand the conduction mechanism. An admirable conductivity of 1.4 × 10-2 S cm -1 is obtained for a nanocomposite with 4 wt% NiO content. The activation energies of the composite films decrease with increase in NiO content, from 16.5 to 4.8 kJ mol-1. © 2011 The Royal Society of Chemistry.
Complementary effect of co-doping aliovalent elements Bi and Sb in self-compensated SnTe-based thermoelectric materials
(Royal Society of Chemistry, 2021) Kihoi, S.K.; Shenoy, U.S.; Bhat, D.K.; Lee, H.S.
Research on Pb-free thermoelectric materials as a potential eco-friendly and solid-state source of energy has continuously advanced over time, with SnTe-based materials having shown utmost promising properties owing to their tunable electronic structure and scalable thermal conductivity. In this study, we self-compensate Sn to reduce inherent Sn vacancies, and further tune the carrier concentration by doping with Bi. Sb is further alloyed to incorporate nanostructures that significantly reduce the thermal conductivity. Multiple aliovalent dopants result in a continually decreased carrier concentration and subsequent significantly decreased electrical conductivity. The Seebeck values are seen to increase with temperature, where a maximum value of ?171 ?V K?1is reported with a maximum power factor of ?22.7 ?W cm?1K?2. We show through first principles DFT calculations the synergistic effect of Bi and Sb to introduce resonance states and an additional valence band convergence effect with increasing Sb that contribute to improved electronic properties. A decreased phonon frequency with co-doping is also reported. A maximumZTof ?0.8 at 823 K is reported in the Sn0.90Bi0.03Sb0.10Te composition, showing good potential in Sb co-doped SnTe-based materials. © The Royal Society of Chemistry 2021.
Copper doping induced band structure and morphology transformation in CaTiO3 for textile dye photodegradation applications
(Elsevier Ltd, 2024) Shenoy, U.S.; Uma, P.I.; Bhat, D.K.
Semiconductor metal oxides with a wide bandgap like CaTiO3 can be exploited into an efficient visible light photocatalyst via cation doping. The type of dopant and the site of doping is known to greatly influence the photocatalytic activity of a material. Based on the intricacies of the density functional theory electronic structure study, we delve into the optimization of one-pot solvothermal synthesis to obtain Cu doped CaTiO3 nanocuboids. Doping of copper not only resulted in change in the electronic structure of the material but also led to change in the morphology. The uneven nanostep architecture resulted in increase in the surface area of the catalyst, which led to more active sites for the adsorption of the dyes and subsequent degradation. The reduced band gap and decreased recombination of charge carriers made the copper doped calcium titanate an efficient photocatalyst for degradation of both cationic (99.7% degradation of MV dye in 120 minutes) and anionic (99.8% degradation of RB in 45 minutes) dyes. © 2024 Elsevier B.V.
Crystallinity, conductivity, and magnetic properties of PVDF-Fe 3O4 composite films
(2011) Bhatt, A.S.; Bhat, D.K.; Santosh, M.S.
The formation of Fe3O4 nanoparticles by hydrothermal process has been studied. X-ray Diffraction measurements were carried out to distinguish between the phases formed during the synthesis. Using the synthesized Fe3O4 nanoparticles, poly(vinyledene fluoride)-Fe3O4 composite films were prepared by spin coating method. Scanning electron microscopy of the composite films showed the presence of Fe3O4 nanoparticles in the form of aggregates on the surface and inside of the porous polymer matrix. Differential Scanning calorimetry revealed that the crystallinity of PVDF decreased with the addition of Fe3O4. The conductitivity of the composite films was strongly influenced by the Fe3O4 content; conductivity increased with increase in Fe3O4 content. Vibration sample magnetometry results revealed the ferromagnetic behavior of the synthesized iron oxide nanoparticles with a Ms value of 74.50 emu/g. Also the presence of Fe3O4 nanoparticles rendered the composite films magnetic. © 2010 Wiley Periodicals, Inc.
Crystallinity, magnetic and electrochemical studies of PVDF/Co 3O4 polymer electrolyte
(Elsevier Ltd, 2012) Bhatt, A.S.; Bhat, D.K.
Organic-inorganic nanocomposites are gaining importance in the recent times as polymer electrolyte membranes. In the present work, composites were prepared by combining nano sized Co3O4 and poly(vinyledene fluoride) (PVDF), using spin coating technique. The surface of the PVDF/Co 3O4 system characterized through field emission scanning electron microscopy (FESEM) revealed a porous structure of the films. The nanoparticles tend to aggregate on the surface and inside the pores, leading to a decrease in the porosity with an increase in Co3O4 content. Co3O4 nanoparticles prohibit crystallization of the polymer. Differential scanning calorimetry (DSC) studies revealed a decrease in crystallinity of PVDF/Co3O4 system with an increase in the oxide content. Magnetic property studies of the composite films revealed that with an increase in Co3O4 content, the saturation magnetization values of the nanocomposites increased linearly, showing successful incorporation of the nanoparticles in the polymer matrix. Further, ionic conductivity of the composite films was evaluated from electrochemical impedance spectroscopy. Addition of Co3O4 nanoparticles enhanced the conductivity of PVDF/Co3O4 system. © 2011 Elsevier B.V. All rights reserved.
Design, synthesis, and characterization of stable copper nanofluid with enhanced thermal conductivity
(Elsevier Ltd, 2024) Bhat, D.K.; Kumar, S.P.; Shenoy, U.S.
Nanofluids, which are liquids that contain small particles with dimensions in the nanometer range, have gained significant attention in recent years due to their enhanced thermal properties in various applications such as thermal management and energy conversion. This article aims to provide insights into the design and optimization of copper nanofluid synthesis and it investigates the thermal and rheological properties at varying concentrations of nanoparticles and temperature. The method involves simultaneous use of fructose as reducing agent and polyvinyl pyrrolidone as stabilizing agent to enable synthesis of copper nanofluid from copper sulphate. The resulting Newtonian nanofluid had a stability of 3 months with enhanced thermal conductivity of up to ∼500 % compared to 1:1 mixture of water and ethylene glycol which served as the base fluid. The approach is suitable for producing large volume of nanofluid using cost effective materials. © 2024 Elsevier Ltd
Designing sustainable porous graphene-CaTiO3 nanocomposite for environmental remediation
(Elsevier B.V., 2024) Bhat, D.K.; Bantawal, H.; Uma, P.I.; Kumar, S.P.; Shenoy, U.S.
In the pursuit of sustainable energy and environmental solutions, photocatalysis has emerged as a transformative technology, harnessing the power of light to drive chemical transformations. Among the myriad photocatalytic materials, calcium titanate (CaTiO3) stands out as a promising candidate, holding the potential to revolutionize the landscape of photocatalysis. To further improvise the efficiency of CaTiO3 in this work, porous graphene-CaTiO3 nanocomposite was synthesized by a straightforward solvothermal method and its photocatalytic activity was tested for the degradation of methylene blue dye under visible light. The synthesized sample exhibited 98.1% degradation in 40 min with excellent cyclic stability. Experimental and computational analysis attributed the enhanced performance to the strong chemical interaction of CaTiO3 cuboids with PG sheets via Ti-O-C bond which led to efficient electron hole separation leading to enhanced lifetime of the charge carriers. This along with reduced band gap and increased surface area made the material a potent photocatalyst for the degradation of dyes in short duration. © 2024 The Authors
Doped BaTiO3 cuboctahedral nanoparticles: Role of copper in photocatalytic degradation of dyes
(Elsevier B.V., 2023) Uma, P.I.; Shenoy, U.S.; Bhat, D.K.
The discovery of perovskite oxides as photocatalysts has opened unique possibilities for the degradation of pollutants such as dyes. In this work, we carry out both theoretical and experimental study for the design and preparation of copper doped BaTiO3. To begin with, First principles electronic structure calculations revealed the presence of additional levels at the top of the valence band after doping copper, which considerably decreased the band gap making the oxide visible light active. Later, single pot synthesis of copper doped BaTiO3 led to production of a material which was photocatalytically active in degrading both cationic and anionic dyes. From our work, we found that the photocatalyst 0.5 CuBTO decomposed 98.2% of methylene blue dye in 120 min and 99.4% of rose bengal dye within 45 min. Such high efficiency was attributed to the high surface area, appropriate band gap and low recombination rate of the charge carriers. © 2023