Synthesis, characterization and photocatalytic activity of porous WO3/TiO2 hollow microspheres

Porous WO3/TiO2 hollow microspheres were prepared by a spray drying method for photodegradation of methylene blue and phenol. The catalysts were characterized by X-ray diffraction, Field Emission Scanning Electron Microscope, High Resolution Transmission Electron Microscope, N2 adsorption-desorption measurements, Raman spectrometer, UV-Vis Diffuse Reflectance Spectroscopy and Zeta-Meter measurements. The results showed that the tungsten oxides mainly existed in highly dispersed amorphous form on anatase when the loading amount of tungsten oxide was below 3 mol%. The improved photocatalytic activity under UV light irradiation of the WO3/TiO2 catalyst mainly arises from the enhanced charge separation efficiency rather than the improved light absorbance by highly dispersed amorphous tungsten oxides. Highly dispersed amorphous WOx can form a shallowly trapped site due to its similar band structure with TiO2. The strongly electron-withdrawing of tungsten oxide in highly dispersed state facilitates the electron transition between titanium and WOx, and consequently improves the charge separation. The enhanced acidity of catalyst by WOx in reactant environment also improved the charge separation efficiency due to the timely transition of holes and electrons accumulated on TiO2 and WOx, respectively. However, the improved photocatalytic activity under visible light irradiation of the WO3/TiO2 catalyst mainly arises from light harvest. TiO2 containing 3 mol% WO3 displayed the highest photocatalytic activity under UV light irradiation while that containing 4 mol% WO3 present highest activity under visible light irradiation.