Browsing by Author "Chaudhury, S.K."

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    A study on the kinetics and structure of tungsten oxide nanopowder synthesized by an electrochemical oxidation process
    (John Wiley and Sons Inc, 2025) Salot, M.; Santhy, K.; Mandal, D.; Pramanick, A.K.; Rajasekaran, B.; Avasthi, G.; Chaudhury, S.K.
    Tungsten oxide possesses unique properties owing to its multiple oxidation states. They are produced by several techniques with each having their advantages and limitations. In this study, the hydrated tungsten oxide nanopowders with varied morphology were synthesized by electrochemical oxidation of WC-6Co scrap at room temperature. This process is efficient and requires low capital investment. The effect of processing parameters, namely voltage, molarity, temperature, and electrolyte stirring on yield, structure, morphology, and energy bandgap is studied. The X-ray diffraction (XRD) analysis showed that at low voltage and low molarity monoclinic WO3.2H2O nanoparticles are synthesized. In contrast, at high molarity and high voltage, orthorhombic WO3.H2O nanoparticles are synthesized. Further, the size of crystal decreases with the increase in voltage during electrochemical oxidation of WC-6Co pellet. The in-situ XRD analysis showed progressive transformation of as-synthesized nanopowder from orthorhombic to cubic crystal structure. Thermal treatments using microwave radiation and muffle furnace resulted in partial phase transformation of hydrated tungsten oxide to cubic WO3.H0.5 phase. The scanning electron microscopy and transmission electron microscopy analyses confirmed the formation of nanoplates, nanorods, and quantum dots depending on the processing parameters. The ultraviolet-visible spectroscopy showed a relatively lower energy bandgap of as-synthesized tungsten oxide nanopowder. © 2025 The American Ceramic Society.
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    Effect of microwave treatment on structural characteristics and energy bandgap of electrochemically synthesized hydrated tungsten oxide quantum dots
    (Elsevier Ltd, 2024) Salot, M.; Santhy, K.; Pramanick, A.K.; Rajasekaran, B.; Awasthi, G.; Singh, S.G.; Chaudhury, S.K.
    Quantum Dots (QDs) of hydrated tungsten oxide were synthesized via electrolysis using sintered tungsten carbide-6 wt% cobalt (WC–6Co) scrap as anode, Ti plate as cathode, and sulfuric acid as electrolyte at room temperature. The as-synthesized powder was characterized using X-ray diffraction (XRD), Transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), Fourier transform infrared spectroscopy (FTIR), Raman spectroscopy, Electron paramagnetic resonance spectroscopy (EPR), and Ultraviolet–visible spectroscopy (UV–Vis). The XRD analysis confirmed the formation of orthorhombic hydrated tungsten oxide (WO3.H2O) QDs via electrochemical oxidation of WC. As-synthesized WO3.H2O QDs were thermally-treated using microwave radiation and conventional furnace at 150 °C for 8 min and 45 min, respectively. Thermal treatment of as-synthesized QDs produced partially dehydrated powder consisting of both orthorhombic WO3.H2O and cubic WO3.H0.5 crystal structures. The TEM analysis showed that the average particle size of QDs was 7.60 nm. Further, an increase in lattice strain was observed on microwave treatment owing to the non-equilibrium phase transformation (i.e., rapid heating) from orthorhombic to cubic crystal structure resulting in the generation of oxygen vacancies. The increase in oxygen vacancy concentrations in QDs on microwave heating was confirmed by XPS, FTIR, EPR, and Raman spectroscopy. The energy bandgaps of as-synthesized and thermally-treated QDs were in the range of 2.4307–2.4979 eV. The relatively low energy bandgap of QDs is attributed to the change in crystal structure and increase in the oxygen vacancy concentration. An improved CO gas sensing characteristics of microwave-treated QDs was noted. © 2024 Elsevier Ltd and Techna Group S.r.l.