Synthesis and Characterization of Twin Barrel-Like Tungsten Trioxide Obtained by Hydrothermal Treatment

Abstract

Various methods have been presented lately in literature for the elaboration of tungsten oxide (WO3) materials. Herein, WO3 was prepared under properly controlled conditions by hydrothermal route, using Na2WO4·2H2O as a raw material in the presence of different structure directing agents (SDAs) and by acidifying the medium with nitric acid to pH 1. The influence of the SDAs on the structure and morphology of the obtained tungsten oxide has been investigated by scanning electron microscopy (SEM), micro-Raman spectroscopy and X-ray powder diffraction. The obtained WO3 materials have a barrel-like morphology independently of the SDA used. However the crystalline structure obtained is a pure hexagonal WO3 with CoSO4·7H2O, CuSO4·5H2O, ZnSO4·7H2O and Zn(CH3COO)2·2H2O and a hydrated hexagonal WO3: WO3·1/3H2O with MnCl2·4H2O. The results demonstrate a noteworthy effect of the SDA anion on the crystalline structure of the synthesized tungsten oxide as compared to the minor effect from the cation of the SDA. Furthermore, a formation mechanism of the nanobarrel WO3 is proposed