Facile synthesis of oxygen-deficient nano-TiO2 coordinated by acetate ligands for enhanced visible-light photocatalytic performance

To date, various methods have been adopted to enhance the visible-light photocatalytic activity of nano-TiO2. However, a more facile and moderate method is still highly desirable. In this work, a series of defective nano-TiO2 photocatalysts with surface oxygen vacancy defects (SOVDs) coordinated by surface acetate ligands (SALs) were synthesized via a facile low-temperature sol-hydrothermal method without more complicated modifications. The low synthesis temperature not only results in the preservation of SALs derived from the protective agent acetic acid, but also results in a considerable amount of SOVDs due to low crystallinity and small particle size. The SALs are coordinated to nano-TiO2 in both bidentate chelating and bidentate bridging modes. The electron-withdrawing carboxyl groups can induce the splitting of the impurity states introduced by the SOVDs when the SALs and SOVDs coexist on the surface of TiO2. The split impurity states contribute mainly to the formation of valence band (VB) tail states, which can significantly narrow the bandgap of TiO2. Furthermore, the SOVDs and SALs synergistically result in the positive shift of the main VB edge of TiO2, which can significantly enhance the oxidizing capability of the photogenerated holes. Meanwhile, an appropriate amount of SOVDs can effectively promote the separation of photogenerated charge carriers. The synergistic effect of the above factors significantly enhances the photocatalytic activity of the oxygen-deficient nano-TiO2 for phenol degradation.