Unveiling the Role of Defects on Oxygen Activation and Photodegradation of Organic Pollutants.

The status of defects of TiO2 are of fundamental importance in determining its physicochemical properties. Here we report a simple chemical deposition method for controllable synthesis of defective anatase TiO2 nanocrystals under various calcination atmospheres. XPS and ESR analysis reveals that both the oxygen vacancies ( VO) and the trivalent titanium (Ti3+) defects exist in TiO2 after N2 treatment (N-TiO2). Meanwhile, mainly VO defects can be obtained in TiO2 with air calcination (A-TiO2). ESR spectra for reactive oxygen species determination, clearly show that the visible light catalytic activity is mainly caused by the efficient activation of oxygen molecules to •O2- species for A-TiO2, which play an important role in hindering the accumulation of intermediates during p-chlorophenol (4-CP) photodegradation process. However, the oxygen molecules cannot be activated for N-TiO2 even with superior visible light absorption and thus the photogenerated electron are reductant, which participated in the transformation of BQ to HQ via electron shuttle mechanism. Moreover, A-TiO2 exhibits higher separation efficiency of photogenerated carriers than that of N-TiO2, showing the critical role of VO with a suitable concentration in transferring photogenerated charges.