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 WO_x 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 WO_x, and consequently improves the charge separation. The enhanced acidity of catalyst by WO_x in reactant environment also improved the charge separation efficiency due to the timely transition of holes and electrons accumulated on TiO₂ and WO_x, 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