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

Abstract

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 ( V_O) and the trivalent titanium (Ti³⁺) defects exist in TiO₂ after N₂ treatment (N-TiO₂). Meanwhile, mainly V_O 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 •O^2- 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 V_O with a suitable concentration in transferring photogenerated charges.