Dominant Influence of the Surface on the Photoactivity of Shape-Controlled Anatase TiO2 Nanocrystals

Shape-controlled anatase TiO 2 nanocrystals with large {001} facets are synthesized by a hydrothermal method using HF as a shape-controlling agent. The photoactivity of the TiO 2 nanocrystals is evaluated from the photodegradation rate of methylene blue in aqueous solution under UV irradiation. Here, we observe higher photoactivities for the TiO 2 nanocrystals with a {001} ratio of close to 60%, which is the shape effect in photoactivity. In addition, we observe that the photoactivity is further enhanced when the TiO 2 nanocrystals are treated in a dilute NaOH (HF) solution. Our SEM, XPS, and EPR analyses reveal that the etching in the NaOH (HF) solution can induce significant changes in the surface defects as well as in the surface morphology. We find that the enhanced photoactivity is closely related to the changes in the surface defects, which favor the formation of surface O – species under ambient conditions.