Influence of oxalic acid and CTAB on the structural and optical properties of nanocrystalline tungsten oxide synthesized via co-precipitation method

Herein, we report the oxalic acid and cetyl trimethyl ammonium bromide (CTAB) assisted co-precipitation synthesis of nanocrystalline tungsten oxide (WO₃). Different annealing temperatures were selected systematically based on the thermo-gravimetric analysis (TGA) of the precursors. The high crystallinity of the samples was revealed from the intense and narrow X-ray diffraction (XRD) peaks. Oxalic acid-assisted WO₃ showed a considerable reduction in crystallite size. The increase in crystallite size with annealing temperature was also evident in both samples. The change of surfactant and annealing temperature resulted in a modification of surface morphology that was identified using high-resolution resolution-scanning electron microscopy (HR-SEM). The formation of WO₃ was further established by the Raman spectra of the samples. Size strain plot (SSP) analysis of the samples showed a decrease of microstrain with an increase in annealing temperature. The bandgap energy obtained from the diffused reflectance spectra of the samples showed a red shift with an increase in annealing temperature. The X-ray photoelectron spectroscopy (XPS) analysis confirmed the existence of a pure oxidation state of W⁶⁺ in oxalic acid-assisted WO₃ and mixed oxidation states of W⁶⁺ and W⁵⁺ in CTAB-assisted WO₃ samples. The mesoporous nature and specific surface area of the samples are inferred from Brunauer–Emmett–Teller (BET) analysis. The reduced crystallite size, stable oxidation state, and higher specific surface area of the oxalic acid-assisted WO₃ samples suggest its possible use as a supercapacitor and photocatalyst.

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