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

Abstract

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 O₂, clearly indicating that the separation of photogenerated charges is greatly improved by promoting the photoelectrons captured by the adsorbed O₂. 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 O₂ adsorbed on the surfaces of nc-TiO₂ is greatly increased after phosphate modification based on the O₂ 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 O₂ 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.