Dinesh Rangappa
Visvesvaraya Technological University, Nanotechnology, Faculty Member
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Starch was isolated from ragi grains using alkali extraction method. Crystallinity of isolated ragi starch (RGS) was studied using X-ray diffraction technique, and thermal properties of RGS were characterized by differential scanning... more
Starch was isolated from ragi grains using alkali extraction method. Crystallinity of isolated ragi starch (RGS) was studied using X-ray diffraction technique, and thermal properties of RGS were characterized by differential scanning calorimetry. Novel ragi starch (RGS) based gel electrolyte for dye-sensitized solar cells (DSSCs) was prepared and characterized for the first time. In the first part, the effects of additives guanidinium thiocyanate (GSCN) and N-methylbenzimidazole (NMBI) on the photovoltaic performance of DSSC were investigated. Considerable improvement of open circuit voltage was found in the addition of only NMBI to the electrolyte, while only addition of GSCN has an influence on the short circuit current. Synergetic effects were observed when NMBI and GSCN were used together in the gel electrolyte. In the second part, various weight percentages of multiwalled carbon nanotubes (MWCNTs) were added to observe the cell performance. DSSCs fabricated with the optimum weight percentage (1 wt%) of MWCNT achieved a maximum conversion efficiency of 4.34%, an open circuit voltage (Voc) of 0.803 V, short circuit current density (Jsc) of 9.54 mA cm–2 and fill factor (FF) of 56.59%. Here we reported the novel ragi starch-based gel electrolytes for DSSC application along with the effect of different additives, such as GSCN, NMBI, and various weight percentages of MWCNTs incorporated into the gel electrolyte.
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ABSTRACT Alkaline earth molybdates, such as BaMoO4 and SrMoO4, films have been successfully fabricated on a Mo metal substrate in AOH (A = Ba, Sr) solutions by a ball-rotation-assisted solution reaction, at room temperature. The... more
ABSTRACT Alkaline earth molybdates, such as BaMoO4 and SrMoO4, films have been successfully fabricated on a Mo metal substrate in AOH (A = Ba, Sr) solutions by a ball-rotation-assisted solution reaction, at room temperature. The dissolution of Mo was mainly controlled by the concentration of the H2O2 oxidizing agent and ball-rotation to form MoO42− in the solution. AMoO4 was deposited on the substrate by the reaction between MoO42− and A2+ ions without any high energy or high-temperature treatment. Also, the mass transport of alkaline earth ions onto the solid/solution interface was improved as a result of the vigorous solution agitation by the ball-rotation. Therefore, the rate of deposition of the AMoO4 films was accelerated by the ball-rotation. A decrease in the grain size of the film was observed with an excessive ball-rotation.
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This paper presents guanidine-functionalized Fe3O4 magnetic nanoparticle-supported palladium (II) (Fe3O4@Guanidine-Pd) as an effective catalyst for Suzuki–Miyaura cross-coupling of aryl halides using phenylboronic acids and also for... more
This paper presents guanidine-functionalized Fe3O4 magnetic nanoparticle-supported palladium (II) (Fe3O4@Guanidine-Pd) as an effective catalyst for Suzuki–Miyaura cross-coupling of aryl halides using phenylboronic acids and also for selective reduction of nitroarenes to their corresponding amines. Fe3O4@Guanidine-Pd synthesized is well characterized using FT-IR spectroscopy, XRD, SEM, TEM, EDX, thermal gravimetric analysis, XPS, inductively coupled plasma-optical emission spectroscopy, and vibrating sample magnetometry analysis. The prepared Fe3O4@Guanidine-Pd showed effective catalytic performance in the Suzuki–Miyaura coupling reactions by converting aryl halides to their corresponding biaryl derivatives in an aqueous environment in a shorter reaction time and with a meagerly small amount of catalyst (0.22 mol %). Also, the prepared Fe3O4@Guanidine-Pd effectively reduced nitroarenes to their corresponding amino derivatives in aqueous media at room temperature with a high turnover number and turnover frequency with the least amount of catalyst (0.13 mol %). The most prominent feature of Fe3O4@Guanidine-Pd as a catalyst is the ease of separation of the catalyst from the reaction mixture after the reaction with the help of an external magnet with good recovery yield and also reuse of the recovered catalyst for a few cycles without significant loss in its catalytic activity.
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ABSTRACT LiCoPO4, a high voltage cathode material, was synthesized by supercritical solvothermal method at 400 °C for 4 min of reaction time. The synthesized plate like particles showed 50–200 nm in width, 100–300 nm in length and side... more
ABSTRACT LiCoPO4, a high voltage cathode material, was synthesized by supercritical solvothermal method at 400 °C for 4 min of reaction time. The synthesized plate like particles showed 50–200 nm in width, 100–300 nm in length and side length from 5 to 15 nm. The single phase of pristine particles was confirmed by powder X-ray diffraction analysis; the morphology and size were investigated by transmission electron microscopy. The use of oleylamine played a vital role in designing the plate like morphology. The electrochemical property was investigated for carbon coated plate like LiCoPO4 cathode by galvanostatic charge–discharge method. The carbon coated LiCoPO4 particles exhibited 130 mAh g−1 for the first cycle and 98 mAh g−1 for the 10th cycle. The capacity fade was observed with cycle performance and rate performance was also investigated.
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ABSTRACT We demonstrate a rapid and one-pot solvothermal synthesis of LiFePO4 hierarchical nanorods and flowers like microstructures in a short reaction time (4–10min) at temperature as low as 300–400°C, without any high temperature... more
ABSTRACT We demonstrate a rapid and one-pot solvothermal synthesis of LiFePO4 hierarchical nanorods and flowers like microstructures in a short reaction time (4–10min) at temperature as low as 300–400°C, without any high temperature post-annealing. The ethylene glycol was used as a solvent with hexane and oleic acid as co-solvent and surfactant, respectively. Addition of the co-solvent and/or surfactant played a key role in controlling the morphology and microstructures of the LiFePO4 nanocrystals. The EG and oleic acid were acted as the size and morphology controlling agents and carbon source when annealed at 600°C. Sample exhibited about 90% specific capacity at 0.5°C and showed good cyclic performance. The high-resolution TEM image revealed that these nanorods were self-assembled to form flower like microstructure in presence of oleic acid during the synthesis.
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A Cobalt disulfide–reduced graphene oxide (CoS2-RGO) nanocomposite was prepared by a simple hydrothermal method and the prepared nanocomposite was characterized using various techniques like XRD, SEM and FTIR. The results of these... more
A Cobalt disulfide–reduced graphene oxide (CoS2-RGO) nanocomposite was prepared by a simple hydrothermal method and the prepared nanocomposite was characterized using various techniques like XRD, SEM and FTIR. The results of these techniques indicated the uniform deposition of CoS2 nanoparticles on Graphene sheets. Further, the prepared nanocomposites were tested for its activity towards energy storage and the test results showed a specific capacitance of 28[Formula: see text]F/g in an aqueous 20% KOH electrolyte at a current density of 0.5[Formula: see text]A/g. All these materials showed highly reversible charge–discharge cycles. The overall electrochemical performance of this composite is shown to be drastically improved when compared to bare CoS2 nanoparticles. Thus with the good electrochemical properties, CoS2–RGO nanocomposites could be effectively used as an electrode material for supercapacitors.
Research Interests: Engineering, Chemical Engineering, Materials Science, Technology, Electrochemistry, and 13 moreNanoparticle, Graphene, Nanotechnology, Nanocomposite, Nanoscience, Physical sciences, CHEMICAL SCIENCES, Oxide, Fourier transform infrared spectroscopy, Cobalt Oxide, Supercapacitor, Electrolyte, and Biochemistry and cell biology
Novel ultrathin Li(2)MnSiO(4) nanosheets have been prepared in a rapid one pot supercritical fluid synthesis method. Nanosheets structured cathode material exhibits a discharge capacity of ~340 mAh/g at 45 ± 5 °C. This result shows two... more
Novel ultrathin Li(2)MnSiO(4) nanosheets have been prepared in a rapid one pot supercritical fluid synthesis method. Nanosheets structured cathode material exhibits a discharge capacity of ~340 mAh/g at 45 ± 5 °C. This result shows two lithium extraction/insertion performances with good cycle ability without any structural instability up to 20 cycles. The two-dimensional nanosheets structure enables us to overcome structural instability problem in the lithium metal silicate based cathode materials and allows successful insertion/extraction of two complete lithium ions.
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This work describes the heat transfer process from a heated microcantilever to a substrate. A platinum-resistance thermometer with a 140nm width was fabricated on a SiO2-coated silicon substrate. The temperature coefficient of resistance... more
This work describes the heat transfer process from a heated microcantilever to a substrate. A platinum-resistance thermometer with a 140nm width was fabricated on a SiO2-coated silicon substrate. The temperature coefficient of resistance estimated from the measurement was 7×10−4K−1, about one-fifth of the bulk value of platinum. The temperature distribution on the substrate was obtained from the thermometer reading, as the cantilever raster scanned the substrate. Comparison between the measurement and calculation reveals that up to 75% of the cantilever power is directly transferred to the substrate through the air gap. From the force-displacement experiment, the effective tip-specimen contact thermal conductance was estimated to be around 40nW∕K. The findings from this study should help understand the thermal interaction between the heated cantilever and the substrate, which is essential to many nanoscale technologies using heated cantilevers.
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Non-stoichiometric ferrite magnetic nanoparticles Mg0.5+xLi1−2xFe2O4 (x = 0, 0.15, 0.35) were prepared using low-cost sol–gel method and annealed at temperature 700 °C. Thermal analysis measurement confirms that there is a decrease in... more
Non-stoichiometric ferrite magnetic nanoparticles Mg0.5+xLi1−2xFe2O4 (x = 0, 0.15, 0.35) were prepared using low-cost sol–gel method and annealed at temperature 700 °C. Thermal analysis measurement confirms that there is a decrease in weight with an increase in temperature which becomes thermally stable till 600 °C. The XRD study confirms that prepared nanoparticles are a cubic spinel structure having Fd3m space group. The crystallite size lies in the range of 26.41–31 nm. Lattice parameter was found to increase with decreasing molar ratio of Li ion. The FTIR spectroscopy confirms the spinel nature of ferrite nanomaterial having characteristics absorption peaks at 588 and 435 cm−1. HRTEM and SEM image confirms the cubic spinel structure and porosity in the material. The indirect energy band gap was evaluated for all samples using tauc plot and found to be 2.25, 1.89 and 2.03 eV respectively for x = 0, 0.15 and 0.35. The energy band gap was found function of crystallite size. Strong luminescence was observed in the visible range of 580–610 nm. The non-molar ratio of Li = 0, 0.15 and 0.35 mol leads to a systematic increase in all the magnetic parameters. The magnetization increases from 15.53 to 33.75 emu/g, retentivity from 2.66 to 7.11 emu/g and coercivity increases 116.56–161.37 Gauss, respectively. Prepared nanomaterial possesses pure phase porous crystal with luminescent property in the visible range, energy band gap in the range of 2.03–2.25 eV and uniform increase in the magnetic parameter. Hence, materials may be potential candidate for magneto-optical device, humidity sensor, hydroelectric cell applications and some other realted fields.
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The LiMn 2 O 4 graphene hybrid cathode material has been synthesized by spray drying combustion process. The spinel structure cubic phase LiMn 2 O 4 graphene hybrid material was prepared by spray drying process at 120 ℃ and subsequent... more
The LiMn 2 O 4 graphene hybrid cathode material has been synthesized by spray drying combustion process. The spinel structure cubic phase LiMn 2 O 4 graphene hybrid material was prepared by spray drying process at 120 ℃ and subsequent heat treatment at 700 ℃ for 1 hour. The result indicates that the spinel shaped LiMn 2 O 4 particles wrapped with graphene sheets were formed with particle size in the range of 60-70 nm. The charge-discharge measurement indicates that the LiMn 2 O 4 graphene hybrid material shows an improved discharge capacity of 139 mAh/g at 0.1C rate. The pristine LiMn 2 O 4 nano crystals present only about 132 mAh/g discharge capacity. The LiMn 2 O 4 graphene hybrid samples show good cyclic performance with only 13% of capacity fading in 30 cycles when compared to the pristine LiMn 2 O 4 that shows 22% of capacity fading in 30 cycles. The capacity retention of the LiMn 2 O 4 graphene hybrid samples is about 10% higher than the pristine cycle after 30 cycles.
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In this study, we achieve the direct conversion of metallic Cu-In films to compound semiconductor CuInSe(2) films, at quite low temperature around 300 °C using less hazardous metalorganic selenium source in supercritical fluid (SCF). We... more
In this study, we achieve the direct conversion of metallic Cu-In films to compound semiconductor CuInSe(2) films, at quite low temperature around 300 °C using less hazardous metalorganic selenium source in supercritical fluid (SCF). We investigated the effects of temperature and fluid (ethanol) density, and found that supercritical ethanol plays a crucial role in this low-temperature selenization reaction. Such SCF-assisted direct conversion reactions can facilitate large-scale, low-temperature, and rapid synthesis of CuInSe(2) films, which can potentially lead to the low-cost production of solar cells.
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In this paper, we are reporting a combustion method to prepare carbon coated LiFePO4 nanoparticles using urea as fuel and sucrose as carbon source. The process involves exothermic decomposition of a viscous liquid, containing fuel to... more
In this paper, we are reporting a combustion method to prepare carbon coated LiFePO4 nanoparticles using urea as fuel and sucrose as carbon source. The process involves exothermic decomposition of a viscous liquid, containing fuel to oxidizer molar ratio of 1:1 at 300 ℃, followed by heat treatment at 600 ℃ for 6 h, under Ar (95%) and H2 (5%) mixed gas atmosphere. The resultant products are characterized by Thermogravimetric analysis (TG-DSC), Field emission-scanning Electron microscopy (SEM), Transmission electron microscopy (TEM), X-Ray diffraction (XRD), Raman Spectroscopy, Fourier transformation infrared spectroscopy (FTIR), and Moss-Bauer spectroscopy. The investigation reveals that the prepared sample has ordered olivine structure|with average crystallite size in the range of 30-40 nm. The SEM and TEM images show porous network type morphology with the size of the individual particles in range of 30-40 nm with spherical and oval shape morphology. The cathode obtained by combustion method exhibits a high discharge capacity (~156 mAhg-1) with a good cyclic performance and rate capability.
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ABSTRACT Styrene–maleic amide (SMA) encapsulated cobalt blue nanocrystals were synthesised by the supercritical water method using a flow type reactor. A monodisperse, water dispersible nanocrystal blue pigment with the particle size of 5... more
ABSTRACT Styrene–maleic amide (SMA) encapsulated cobalt blue nanocrystals were synthesised by the supercritical water method using a flow type reactor. A monodisperse, water dispersible nanocrystal blue pigment with the particle size of 5 nm was obtained by SMA encapsulation. Influence of different reaction conditions such as polymer concentration, pH, encapsulation temperature, etc., on the encapsulation and optical property of the cobalt blue nanocrystals is studied in detail. About 6–8 wt-% SMA concentration and the encapsulation temperature between 270 and 300uC were found to be favourable conditions for successful SMA encapsulation. This novel polymer encapsulation process could be used for mass production of different polymer inorganic hybrid materials that can be used in a variety of applications such as metallic finishing, contrast enhancing luminescent pigments, paint production, electronics and high end optical filters.
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ABSTRACT We report on the crystallographic structure and magnetism of 5-nm Co–Al–O spinel nanocrystals synthesized under supercritical hydrothermal conditions. Structural examination using powder X-ray diffraction and chemical analysis... more
ABSTRACT We report on the crystallographic structure and magnetism of 5-nm Co–Al–O spinel nanocrystals synthesized under supercritical hydrothermal conditions. Structural examination using powder X-ray diffraction and chemical analysis showed the composition of the sample to be Co0.47Al2.36O4 rather than the stoichiometric composition of CoAl2O4 . The site occupancy of Co on the A-site forming the diamond lattice was 0.47, which is slightly larger than the site percolation limit. Magnetization measurements showed that magnetic clusters emerged below 40 K. At temperatures below 40 K, a Griffiths-phase-like inhomogeneous state appeared in the sample in which magnetic clusters and paramagnetic spins coexisted. The dc-paramagnetic and ac-susceptibilities exhibited an anomaly below 7 K.