Abstract: H2 WO4 precursor was prepared by precipitation method using ammonium tungstate as a starting material and nitric acid as the precipitation agent .WO3 photocatalysts with hexagonal and monoclinic phase were obtained by thermal-decomposition H2WO4 at different temperatures.Crystalline phase, morphology , particle size , chemical composition , surface area and optical properties during the phase transformation from H2WO4 to WO3 were investigated by X-ray diffraction(XRD), Raman spectroscopy, differential thermal analysis-thermogravimetry ( TG-DTA ) , scanning electronic microscopy ( SEM ) , N2 adsorption-desorption , X-ray photoelectron spectroscopy ( XPS ) , and UV-Vis diffuse reflectance spectroscopy ( UV-Vis DRS ) . The results show that H 2 WO4 undergoes the following process after calcination:H2WO4→hexagonal WO3→hexagonal/monoclinic WO3→monolinic WO3.Furthermore, the photodegradation of Rhodamine (RhB) as model reaction to investigate the photocatalytic activity of WO 3 with different crystalline phase . Compared with monoclinic WO 3 , hexagonal WO 3 exhibits higher photocatalytic activity .

Key words: H2 WO4 precursor was prepared by precipitation method using ammonium tungstate as a starting material and nitric acid as the precipitation agent .WO3 photocatalysts with hexagonal and monoclinic phase were obtained by thermal-decomposition H2WO4 at different temperatures.Crystalline phase, morphology , particle size , chemical composition , surface area and optical properties during the phase transformation from H2WO4 to WO3 were investigated by X-ray diffraction(XRD), Raman spectroscopy, differential thermal analysis-thermogravimetry ( TG-DTA ) , scanning electronic microscopy ( SEM ) , N2 adsorption-desorption , X-ray photoelectron spectroscopy ( XPS ) , and UV-Vis diffuse reflectance spectroscopy ( UV-Vis DRS ) . The results show that H 2 WO4 undergoes the following process after calcination:H2WO4→hexagonal WO3→hexagonal/monoclinic WO3→monolinic WO3.Furthermore, the photodegradation of Rhodamine (RhB) as model reaction to investigate the photocatalytic activity of WO 3 with different crystalline phase . Compared with monoclinic WO 3 , hexagonal WO 3 exhibits higher photocatalytic activity .