Faculty Publications
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Publications by NITK Faculty
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Item Miscibility studies of starch and poly(4-styrene sulfonic acid) blend system(Sphinx Knowledge House info@sphinxsai.com, 2014) Sudhakar, Y.N.; Bhat, D.; Muthu, M.Polymeric solutions were prepared using blends of starch with poly(4-styrene sulfonic acid) (PSSA) in water and their miscibility was determined by viscosity studies at 30 °C, 40 °C and 50 °C. Using interaction parameters such as Krigbaum’s (?b), Hong’s (?kAB), Chee’s (?), Sun’s (?), polymer-polymer, blend-solvent and heat of mixing there was the existence of positive interactions in the blend polymer solutions only up to 80% PSSA content. A significant variation of miscibility was observed with increase in temperature in the sample containing 70% PSSA content. Polymer blend films obtained by solution casting showed hydrogen bonding in Fourier transform infrared (FTIR) studies. Differential thermal analysis (DTA) and thermogravimetric analysis (TGA) studies also supported the results. A uniform surface of the miscible blend films were observed in scanning electron microscopy images, whereas segregation was observed for the immiscible blends. © 2014, Sphinx Knowledge House. All Rights Reserved.Item Reduced graphene oxide derived from used cell graphite and its green fabrication as an eco-friendly supercapacitor(Royal Society of Chemistry, 2014) Sudhakar, Y.N.; Muthu, M.; Bhat, D.; Senthil Kumar, S.Graphite extracted from a used primary cell was converted into reduced graphene oxide (rGO) using calcium carbonate together with rapid and local Joule heating by microwave irradiation. Electrodes were prepared by ultrasonically dispersing rGO in biodegradable poly(vinylpyrrolidone) (PVP) binder and coating this on recyclable poly(ethyleneterephthalate) (PET) sheet using a low cost screen printing technique. The use of the same polymer (PVP) as a binder, in addition to as the solid polymer electrolyte (SPE), enhances the compatibility and ionic conductivity of the hydrophobic rGO electrode in the supercapacitor system. Further, the phosphoric acid (H3PO4)-doped biodegradable SPE was screen printed for the first time on the rGO electrodes. Ionic conductivity and dielectric studies of the SPE were carried out at different temperatures and different dopant acid concentrations. The morphology, composition and structure of the graphene electrode components were characterized using Fourier transform infrared spectroscopy (FTIR), Raman spectroscopy, X-ray diffraction (XRD), scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS) methods. Transmission electron microscopy (TEM) images showed a single layer or a few layers of rGO sheets and selected area electron diffraction showed the presence of slight defects. The fabricated environmentally friendly, industrially favorable and green supercapacitor showed a specific capacitance of 201 F g-1 and cyclic stability with 97% retention of the initial capacitance over 2000 cycles. Furthermore, the performance of this green supercapacitor is comparable to that of those fabricated using rGO synthesized from commercial graphite and in other literature reports. © 2014 The Royal Society of Chemistry.Item Partial molar volumes and compressibilities of glycine betaine in aqueous NaCl solutions at temperatures T=(288.15-318.15)K(Elsevier, 2014) Karanth, V.R.; Bhat, D.The partial molar volumes, partial molar isentropic compressibilities, transfer molar volumes and transfer molar isentropic compressibilities of the system: glycine betaine in aqueous (0.1, 0.2, 0.3, 0.4 and 0.5molkg-1) NaCl solutions at different temperatures were determined using the experimental values of density and speed of sound. The positive transfer molar volumes of the systems indicated the presence of strong solute-solvent interactions. The electrostatic charge-charge interactions (among Na+/Cl- ions and amino/carboxylic groups of glycine betaine) were found to be predominant over the ionic-hydrophobic interactions (among Na+/Cl- ions and CH2/CH3 groups of the glycine betaine) in aqueous solutions. Size of the metal ion was found to influence the volumetric properties to an appreciable extent. © 2014 Elsevier B.V.Item Novel one-pot green synthesis of graphene in aqueous medium under microwave irradiation using a regenerative catalyst and the study of its electrochemical properties(Royal Society of Chemistry, 2015) Subramanya, B.; Bhat, D.In this work we report an economic, eco-friendly, high yielding and facile one-pot method for the large scale synthesis of few layer graphene (FLG) nanosheets directly from graphite in aqueous medium using a regenerative catalyst, sodium tungstate. This method is fast and makes use of environmental friendly chemicals and microwave radiation. The as-synthesized FLG nanosheets are characterized by field emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), Raman spectroscopy, X-ray photoelectron spectroscopy (XPS) and Brunauer-Emmett-Teller (BET) surface area analysis. Raman analysis indicates that the as-synthesized graphene is bilayered with a smaller domain size of 3.9 nm which is responsible for a higher specific surface area of FLG nanosheets (1103.62 m2 g-1). Moreover, XPS analysis of FLG nanosheets shows a high C:O ratio (?9.6) which is the best among the graphene prepared from green chemicals. The electrochemical performance of as-synthesized FLG nanosheets is analysed by cyclic voltammetry (CV), chronopotentiometry and electrochemical impedance spectroscopy (EIS) in neat 1-ethyl-3-methylimidazolium tetrafluoroborate (EMIMBF4) electrolyte. The superior capacitive performance with large capacitance (219 F g-1), high energy density (83.56 W h kg-1) and excellent cyclability (3000 cycles) exhibited by these graphene nanosheets make them an excellent candidate for supercapacitor material. © The Royal Society of Chemistry and the Centre National de la Recherche Scientifique 2015.Item Lithium salts doped biodegradable gel polymer electrolytes for supercapacitor application(Universite Mohammed Premier Oujda jmaterenvironsci@gmail.com, 2015) Sudhakar, Y.N.; Muthu, M.; Bhat, D.A biodegradable gel polymer (GPE) consisting of Xanthan gum (XG), glycerol, lithium salts like lithium perchlorate and lithium tetraborate were prepared. Using Fourier transform infrared spectroscopy (FTIR), thermal and scanning electron microscopy characterizations the interactions between the components in the gel matrix were studied. Furthermore, a unique electrochemical property was exhibited by GPEs as measured by AC impedance and dielectric studies. The role of anion in the enhancement of conductivity was important in the present study and highest conductivity of 6.4×10-2 S cm-1 at 333K was achieved among lithium salts. Supercapacitor was fabricated using GPE and tested for its electrochemical properties. Supercapacitor showed specific capacitance of was 82 Fg-1 at a scan rate of 5 mV s-1 for Li2B4O7 and 74 Fg-1 at a scan rate of 5 mV s-1. specific energy and specific power. Galvanostatic charge-discharge studies showed excellent cyclic stability.Item Novel Co-Ni-graphene composite electrodes for hydrogen production(Royal Society of Chemistry, 2015) Subramanya, B.; Ullal, Y.; Shenoy, S.U.; Bhat, D.; Hegde, A.C.Active, stable and cost-effective electrocatalysts are key to water splitting for hydrogen production through electrolysis. Herein, we report the facile preparation of highly porous Co-Ni-graphene (Co-Ni-G) composite electrodes by electrodeposition for electrocatalytic applications. The incorporation of graphene into the Co-Ni matrix enhances the catalyst's activity for the hydrogen evolution reaction (HER) in an alkaline solution. The best coating exhibits a maximum current density of -850 mA cm-2 at -1.6 V, which is approximately 4 times better than that of the binary Co-Ni alloy indicating higher activity for hydrogen production. The addition of graphene to an electrolyte bath results in a porous encapsulated bundle of alloy nano-particles within the graphene network which effectively increases the electrochemically active surface area. As indicated by XPS analysis results, on addition of graphene the Co(0) and Ni(0) content in the deposit increases and as a result both cobalt/cobalt oxide and nickel/nickel oxide sites are evenly distributed on the Co-Ni-G electrode surface which is responsible for increased HER activity. The Tafel slope analysis showed that the HER follows a Volmer-Tafel mechanism. The structure-property relationship of the Co-Ni-G composite coating has been discussed by interpreting field emission scanning electron microscopy (FESEM), X-ray photoelectron spectroscopy (XPS) and X-ray diffraction (XRD) analysis results. © The Royal Society of Chemistry 2015.Item Development of multilayer Sn-Ni alloy coating by pulsed sonoelectrolysis for enhanced corrosion protection(Royal Society of Chemistry, 2016) Shetty, S.; Mohamed, M.J.; Bhat, D.; Hegde, A.C.Multilayer Sn-Ni alloy coating has been developed electrochemically on mild steel using an ultrasound effect, as a tool to modulate mass transfer process at electrical double layer, during deposition. Sn-Ni coatings having alternate layers of alloys of different compositions were developed on a nano/micrometric scale by pulsing sonicator ON (tON) and OFF (tOFF), periodically. The composition modulated multilayer alloy (CMMA) Sn-Ni coatings have been deposited by inducing the ultrasound field periodically at optimal current density. Corrosion performances of ultrasound-assisted multilayer Sn-Ni alloy coatings have been evaluated by electrochemical methods. Corrosion data revealed that CMMA Sn-Ni coating, developed using pulsed ultrasonic field and having 150 layers, represented as (Sn-Ni)2/2/150, is the most corrosion resistant, compared to its monolayer alloy coatings developed by both with/without ultrasound effect. Corrosion protection efficacy of multilayer coatings was found to be decreased at high degree of layering due to diffusion of layers. Improved corrosion resistance of multilayer Sn-Ni coatings is attributed to an increase in the number of layers, or interfaces separating alloys of the same metals, but of different composition, surface morphologies and phase structures, supported by energy dispersive spectroscopy, field emission scanning electron microscopy and X-ray diffraction study, respectively. The better corrosion protection of CMMA Sn-Ni coatings, compared to monolayer counterparts, is attributed to an increase in the number of layers, hence phase boundaries between layers, and experimental results are discussed. © 2018 The Royal Society of Chemistry.Item Ionic conductivity and dielectric studies of acid doped cellulose acetate propionate solid electrolyte for supercapacitor(John Wiley and Sons Inc, 2016) Sudhakar, Y.N.; Bhat, D.; Muthu, M.Phosphoric acid doped cellulose acetate propionate (CAP) consisting of poly(ethylene glycol) (PEG) as plasticizer was investigated. Ionic conductivities and dielectric studies were carried at different temperature with varying concentration of H3PO4 using AC impedance method. The highest conductivity was 8.1 × 10-4 S cm-1 at 343 K and a long tail was featured in dielectric studies indicating good capacitance nature of the electrolyte. Interactions between added constituents were observed in FTIR and differential scanning calorimetry studies. Thin and compact fabricated supercapacitor demonstrated specific capacitance of 64 F g-1 using cyclic voltammetry. Furthermore, the supercapacitor properties like AC impedance and charge-discharge were studied. Stability was up to 96% at 1000th cycle. POLYM. ENG. SCI., 56:196-203, 2016. © 2015 Society of Plastics Engineers.