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.