Enhanced photocatalytic activity of nc-TiO2 by promoting photogenerated electrons captured by the adsorbed oxygen

Nanocrystalline TiO2 (nc-TiO2) was modified by a simple post treatment with monometallic sodium orthophosphate solution. It is shown that the surface modification with an appropriate amount of phosphate obviously enhances the surface photovoltage responses of nc-TiO2 in the presence of O-2, clearly indicating that the separation of photogenerated charges is greatly improved by promoting the photoelectrons captured by the adsorbed O-2. This is well responsible for its much high photocatalytic activity for degrading representative gas-phase acetaldehyde, liquid-phase phenol and rhodamine B of phosphate-modified nc-TiO2, compared with the unmodified nc-TiO2. Moreover, it is demonstrated that the amount of O-2 adsorbed on the surfaces of nc-TiO2 is greatly increased after phosphate modification based on the O-2 temperature programmed desorption curves, which is attributed to the substitution of Ti OH with -Ti-O-P-OH. It is suggested for the first time that the phosphate modification favors the O-2 adsorbed on TiO2 so as to further promote the photogenerated electrons captured. This work would provide feasible routes to further improve the photocatalytic performance for degrading pollutants of oxide-based semiconductors.