Efficient degradation of organic pollutant with WOx modified nano TiO2 under visible irradiation

Nanocrystalline tungsten oxide-doped titanium dioxide (WOx-TiO2) powders were prepared by a sol-mixing method. The photooxidation efficiencies of WOx-TiO2 catalysts were evaluated by conducting a set of experiments of photodegrading Methylene blue (MB) in aqueous solution. The experiments demonstrated that the MB in aqueous solution was successfully degraded using WOx-TiO2 under visible light irradiation, especially when the pH value of the solution was over 6. It was found that an optimal WOx dosage of 1% in WOx-TiO2 achieved the highest photocatalytic activity in the conditions of this experiment, on which MB was photooxided completely within 1 h. Powders were characterized by X-ray diffraction (XRD), X-ray photoelectron emission spectroscopy (XPS), UV–vis absorption spectra, transmission electron micrograph (TEM) measurements. These results showed that tungsten oxides not only hindered the growth of TiO2 particles but greatly increased the transformation temperature (>800 °C) from anatase to rutile during sintering; the dominant fraction of tungsten oxides was non-stoichiometric tungsten oxide (WxOy) with Wn+ (4 < n < 6), which could easily substitute Ti4+ in the lattice of TiO2 because of the similarity in the ion radius of Wn+ and Ti4+ to form non-stiochiometric solid solution of WxTi1−xO2. The light absorption band of TiO2 changed from the near UV to the visible light range (2.98 eV in 1.0% WOx-TiO2) because of the tungsten impurity energy level induced by WxTi1−xO2.