Arpan Kumar Nayak

Synthesis of In2S3 microspheres using a template-free and surfactant-less hydrothermal process and their visible light photocatalysis

Indium sulfide (In2S3) microspheres of (β-) tetragonal phase were synthesized by varying the indium precursors using a template-free and surfactant-less hydrothermal process at 150 °C. The as-synthesized samples were found to be crystalline and phase pure as confirmed by X-ray diffraction and X-ray photoelectron spectroscopy studies, respectively. Indium precursors play an important role in controlling the shape of the building blocks, i.e. nanoflakes or nanobricks, of In2S3 microspheres. The photocatalytic activity of as-synthesized In2S3 microspheres was tested for the degradation of methylene blue and crystal violet in the presence of visible light produced by an incandescent lamp. The terephthalic acid test using photoluminescence spectroscopy shows hydroxyl radicals as active species for the degradation of organic contaminants. Repeat photocatalysis measurements suggest the high stability of In2S3 microspheres without a change in their morphology and phase.

Enhanced ammonia sensing at room temperature with reduced graphene oxide/tin oxide hybrid films

Sensitive and selective detection of ammonia at room temperature is required for proper environmental monitoring and also to avoid any health hazards in the industrial areas. The excellent electrical properties of reduced graphene oxide (RGO) and sensing capabilities of SnO2 were combined to achieve enhanced ammonia sensitivity. RGO–SnO2 films were synthesized hydrothermally as well as prepared by mixing different amounts of hydrothermally synthesized SnO2 nanoparticles with graphene oxide (GO). It was observed that the response of the hybrid sensing layer was considerably better than intrinsic RGO or SnO2. However, the best performance was observed in the 10 : 8 (RGO–SnO2) sample. The sample was exposed to nine different concentrations of ammonia in the presence of 20% RH at room temperature. The response of the sensor varied from 1.4 times (25 ppm) to 22 times (2800 ppm) with quick recovery after purging with air. The composite formation was verified by characterizing the samples using field emission scanning electron microscopy (FESEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and high resolution transmission electron microscopy (HRTEM). The results and their significance have been discussed in detail.

Highly Active Tungsten Oxide Nanoplate Electrocatalysts for the Hydrogen Evolution Reaction in Acidic and Near Neutral Electrolytes

An efficient, cost-effective, and earth-abundant catalyst that could drive the production of hydrogen from water without or with little external energy is the ultimate goal toward hydrogen economy. Herein, nanoplates of tungsten oxide and its hydrates (WO3·H2O) as promising electrocatalysts for the hydrogen evolution reaction (HER) are reported. The square-shaped and stacked WO3·H2O nanoplates are synthesized at room temperature under air in ethanol only, making it as a promising green synthesis strategy. The repeated electrochemical cyclic voltammetry cycles modified the surface of WO3·H2O nanoplates to WO3 as confirmed by X-ray photoelectron and Auger spectroscopy, which leads to an improved HER activity. Hydrogen evolution is further achieved from distilled water (pH 5.67) producing 1 mA cm–2 at an overpotential of 15 mV versus the reversible hydrogen electrode. Moreover, WO3·H2O and WO3 nanoplates demonstrate excellent durability in acidic and neutral media, which is highly desirable for practical application. Improved hydrogen evolution by WO3(200) when compared to that by Pt(111) is further substantiated by the density functional theory calculations.

Understanding hydrothermal transformation from Mn2O3 particles to Na0.55Mn2O4·1.5H2O nanosheets, nanobelts, and single crystalline ultra-long Na4Mn9O18 nanowires

Manganese oxides are one of the most valuable materials for batteries, fuel cells and catalysis. Herein, we report the change in morphology and phase of as-synthesized Mn2O3 by inserting Na+ ions. In particular, Mn2O3 nanoparticles were first transformed to 2 nm thin Na0.55Mn2O4·1.5H2O nanosheets and nanobelts via hydrothermal exfoliation and Na cation intercalation, and finally to sub-mm ultra-long single crystalline Na4Mn9O18 nanowires. This paper reports the morphology and phase-dependent magnetic and catalytic (CO oxidation) properties of the as-synthesized nanostructured Na intercalated Mn-based materials.

Enhanced catalytic activity without the use of an external light source using microwave-synthesized CuO nanopetals

We report enhanced catalytic activity of CuO nanopetals synthesized by microwave-assisted wet chemical synthesis. The catalytic reaction of CuO nanopetals and H2O2 was studied with the application of external light source and also under dark conditions for the degradation of the hazardous dye methylene blue. The CuO nanopetals showed significant catalytic activity for the fast degradation of methylene blue and rhodamine B (RhB) under dark conditions, without the application of an external light source. This increased catalytic activity was attributed to the co-operative role of H2O2 and the large specific surface area (≈40 m2·g−1) of the nanopetals. We propose a detail mechanism for this fast degradation. A separate study of the effect of different H2O2 concentrations for the degradation of methylene blue under dark conditions is also illustrated.

Synthesis of Au-V2O5 composite nanowires through the shape transformation of a vanadium(III) metal complex for high-performance solid-state supercapacitors

A simple redox transformation between a vanadium(III) metal complex and gold(III) chloride aided by a cost-effective modified hydrothermal procedure has been adopted for the synthesis of Au-V2O5 composite nanowires. The stability of pseudocapacitive electrode materials in acidic electrolytes is a major challenge. However, the synthesized Au-V2O5 composite nanowires are stable in acidic electrolyte when compared to the precursor component, V2O5. Electrochemical measurement shows a specific capacitance of 419 F g−1 at 1 A g−1 current density in 0.5 M H2SO4 solution for the synthesized composite nanowires. However, the precursor component V2O5 shows a lower specific capacitance under identical conditions. The synthesized composite nanowires, as a pseudocapacitive electrode material, respond to a wide range of working potential windows (+1.6 V), resulting in maximum energy and power densities of 53.33 W h kg−1 and 3.85 kW kg−1 respectively. Moreover, the Au-V2O5 nanowires show high cyclic stability (89% specific capacitance retention) for up to 5000 consecutive charge–discharge (CD) cycles at 10 A g−1 constant current density, due to the composite formation by redox transformation, which reflects the stability of the composite in acidic electrolyte.