Vijaykumar V. Jadhav

A coordination chemistry approach for shape controlled synthesis of indium oxide nanostructures and their photoelectrochemical properties

Indium oxide (In2O3) is an important wide band-gap semiconductor having applications in a variety of optoelectronic devices. We report here on the low temperature solution deposition of In(OH)3 and In(SO4)(OH)·H2O architectures with various shapes such as cubes, maize corns and giant crystals. The In2O3 nanostructures are then obtained by solid state transformation of In(OH)3 and In(SO4)(OH)·H2O architectures. Shape control is achieved by controlling the local concentration of In3+ ions available for reaction by applying the principles of coordination chemistry, thereby obviating the need of any shape controlling agents. The phase and surface composition is obtained by X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) measurements. The XPS is used to probe the defect structure of In2O3 architecture. Optical properties of the films, studied by UV-Vis absorption and photoluminescence (PL) spectroscopy measurements, show that the different morphologies have different band-gaps. Furthermore current–voltage characteristics of In2O3–CdSe photoelectrochemical cells are studied, which show that cube–CdSe samples display excellent photovoltaic behaviour, exhibiting a short circuit current density in excess of 10 mA cm−2. The charge transport properties of the In2O3–CdSe photoanodes are studied by impedance spectroscopy, which shows that cube–CdSe samples have lowest resistance to charge transfer.

A simple, room temperature, solid-state synthesis route for metal oxide nanostructures

In this work, we demonstrate an extremely simple but highly effective strategy for the synthesis of various functional metal oxides (MOs) such as ZnO, In2O3, Bi2O3, and SnO2 nanoparticles with various distinct shapes at room temperature via a solid-state reaction method. The method involves only mixing and stirring of the corresponding metal salt and NaOH together in the solid phase, which yields highly crystalline metal oxides within 5–10 min of reaction time. The obtained paste can be directly doctor-bladed onto a variety of substrates for photoelectrochemical applications. The crystal structure and surface composition of the MOs are obtained by X-ray diffraction patterns, energy dispersive analysis and X-ray photoelectron spectroscopy, respectively. The surface morphology is confirmed from the scanning electron microscopy surface photo-images. The surface area and pore size distribution are studied by the N2 adsorption method. As a proof-of-concept demonstration for the application, ZnO nanoplate structures are envisaged in DSSCs as photoanodes, which enables us to obtain excellent photovoltaic properties with a power conversion efficiency of 5%. The proposed method does not require a sophisticated instrumental setup or harsh conditions, and the method is easily scalable. Hence, it can be applied for the cost-effective and large-scale production of MO nanoparticles with high crystallinity.

The structural and magnetic properties of dual phase cobalt ferrite

The bismuth (Bi3+)-doped cobalt ferrite nanostructures with dual phase, i.e. cubic spinel with space group Fd3m and perovskite with space group R3c, have been successfully engineered via self-ignited sol-gel combustion route. To obtain information about the phase analysis and structural parameters, like lattice constant, Rietveld refinement process is applied. The replacement of divalent Co2+ by trivalent Bi3+ cations have been confirmed from energy dispersive analysis of the ferrite samples. The micro-structural evolution of cobalt ferrite powders at room temperature under various Bi3+ doping levels have been identified from the digital photoimages recorded using scanning electron microscopy. The hyperfine interactions, like isomer shift, quadrupole splitting and magnetic hyperfine fields, and cation distribution are confirmed from the Mossbauer spectra. Saturation magnetization is increased with Bi3+-addition up to x = 0.15 and then is decreased when x = 0.2. The coercivity is increased from 1457 to 2277 G with increasing Bi3+-doping level. The saturation magnetization, coercivity and remanent ratio for x = 0.15 sample is found to be the highest, indicating the potential of Bi3+-doping in enhancing the magnetic properties of cobalt ferrite.

Hybrid composite polyaniline-nickel hydroxide electrode materials for supercapacitor applications

Pristine and nanocomposite (NC) hybrid electrodes of polyaniline (PANI)-nickel hydroxide [Ni(OH)2] have been prepared by single and two-step electrodeposition processes, respectively, onto stainless-steel (SS) substrates. Enhanced reversibility and stability of amorphous PANI- Ni(OH)2 NC electrodes compared to single electrode materials have been explored. PANI has a nanofibrous morphology, Ni(OH)2 has nanoplatelet-type morphology, and the NC electrodes retain an overall nanofibrous morphology. The maximum specific capacitance (SC), obtained from integrated charge under voltammetric conditions, for PANI (electro-deposited for 5 min), NC (electrodeposition of Ni(OH)2 for 10 min and 20 min onto PANI electrode surface) and Ni(OH)2 (electrodeposited for 10 min) electrodes, are 0.59, 39.06, 32.36, and 113.8 F/g, respectively, suggesting higher electrochemical performance of Ni(OH)2 electrode compared to PANI and NC electrodes. The retention in SC values with faster scan rates from 10 to 100 mV/s for PANI, NC (10 min), NC (20 min) and Ni(OH)2 are 38.7, 61.1, 52.4, and 29.0 %, respectively, explicitly confirming a higher reversibility in NC electrodes. The retention in SC values with increase of cycle number up to 1000 for PANI, NC (10 min), NC (20 min) and Ni(OH)2 electrodes are 34.9, 61.5, 67.5, and 40.7 % respectively, demonstrating higher electrochemical stability of NC electrodes over pure-phase electrodes. Nearly 2.15, 79.36, 66.66 and 406.83 mC/cm2 charges on PANI, NC (10 min), NC (20 min) and Ni(OH)2 electrodes, respectively, are obtained. Inner to total charge and outer to total charge ratios have been used to explain contributing sites to total charge in pristine and NC electrodes.

An eco-friendly physicocultural-based rapid synthesis of selenium nanoparticles

The eco-friendly, safe, and cost-effective synthesis of selenium (Se) nanoparticles (NPs) by microorganisms is an important branch of nanotechnology and is considered to be a green synthesis. Functional biosynthesized Se NPs find various applications if they are have definite shapes and sizes, which can be obtained by controlling the cultural conditions and physical operation parameters during the biosynthesis process. We depict the rapid (∼12 h) synthesis of Se NPs using a tryptic soy broth culture under the experimental conditions of pH ∼9, temperature ∼50 °C, in sunlight. The optimized conditions helped us to synthesize chemically and environmentally stable Se NPs. The main aim of the present study is to optimize the different cultural media, temperature, pH, light intensity, concentration of selenium dioxide, and the time of reaction for the rapid blend of Se NPs by Pantoea agglomerans.