Effect of pH, temperature and autoclave reactor volume on the synthesis of h-WO3 by the hydrothermal method

In this research work, the effect of pH on the formation of the hexagonal phase of tungsten oxide was systematically studied using the hydrothermal method. The pH of the precursor solution was varied at 1, 2 and 3 and a 50 and 200 ml hydrothermal autoclave reactor was used. Post synthesis heat treatments were performed at 350 degrees C and 400 degrees C for a time of 2 hours. The FE-SEM results show the effect of pH on the morphology, observing the formation of nanowhiskers at pH 1, nanorods at pH 2 and nanotubes at pH 3. Similarly, from the NTA results, particle size growth is observed with increasing heat treatment temperature, regardless of the pH value. Similarly, by increasing the volume of the hydrothermal autoclave reactor, an increase in the diameter of the nanotubes is observed. From the analysis of the XRD results, the formation of the hexagonal phase is observed as a predominant phase in all samples. At pH 1 and 2 the monoclinic and orthorhombic phase is also observed, respectively, and at pH 3 only the hexagonal phase is present.