Doping Mechanism and Visible-light Photocatalytic Activity of S-doped TiO_2 Nano Powders

S-doped TiO2 nanopowders were prepared by a sol-gel method with acid as the catalyst. The results of photocatalytic degradation methylene blue demonstrated that the doped TiO2 exhibited the highest photocatalytic activity when the mole ratio of thiourea and tetrabutyltitanate[Ti-(OC4H9)4] was 3.5 and the doped TiO2 was calcined at 500℃for 2h. The results from the X-ray diffraction (XRD), diffusion reflectance spectra (DRS) and X ray photoelectron spectroscopy (XPS) showed that sulfur doping controlled the increasing of nano TiO2 and restrained the transformation from anatase to rutile. S2- was oxidezed to S4+ during the thermal treatment. The trance of sulfur ions (S4+) substitued partially for the lattice titanium ions (Ti4+), which resulted in the localized crystal deformation of TiO2 and the bandgap between valence band and conduction band narrowed, and the absorption light transferred to visible light region.