Effects of Interface Defects on Charge Transfer and Photoinduced Properties of TiO₂ Bilayer Films

Abstract

By a combination of cold plasma treatment and sol–gel dip-coating technology, defective TiO 2 bilayer films were successfully prepared, and then the defect was characterized by X-ray photoelectron spectroscopy and electron spin resonance. The photocatalytic activity and photoinduced superhydrophilicity of the films were evaluated by the photocatalytic degradation of organic dyes and water contact angle measurement in air, respectively. Compared to the conventional TiO 2 film, the TiO 2 bilayer films with defects provide much higher efficiency in photocatalysis and photoinduced hydrophilicity. Moreover, it is found that the introduction of defect sites at the interface of two TiO 2 layers results in a significant improvement in the photonic efficiency due to the generation of electron trapping states. The defect sites can inhibit the recombination of electron–hole pairs and thereby increase the concentration of photogenerated carriers at the film surface, leading to an enhancement of quantum efficiency of TiO 2 films under UV irradiation. Furthermore, the defects located at the interface between two TiO 2 layers show higher stability as compared with that located at the outermost surface of TiO 2 films. In addition, the fabrication of the interface defective TiO 2 multilayer film is convenient and of low cost. The study demonstrates that this modified strategy is practical for promoting the photoinduced properties of TiO 2 multilayer films.