Efficient degradation of organic pollutant with WO x modified nano TiO 2 under visible irradiation

Abstract

Nanocrystalline tungsten oxide-doped titanium dioxide (WO x -TiO 2) powders were prepared by a sol-mixing method. The photooxidation efficiencies of WO x -TiO 2 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 WO x -TiO 2 under visible light irradiation, especially when the pH value of the solution was over 6. It was found that an optimal WO x dosage of 1% in WO x -TiO 2 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 TiO 2 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 (W x O y ) with W n+ (4 < n < 6), which could easily substitute Ti 4+ in the lattice of TiO 2 because of the similarity in the ion radius of W n+ and Ti 4+ to form non-stiochiometric solid solution of W x Ti 1− x O 2. The light absorption band of TiO 2 changed from the near UV to the visible light range (2.98 eV in 1.0% WO x -TiO 2) because of the tungsten impurity energy level induced by W x Ti 1− x O 2.