Defect-Mediated Growth of Noble-Metal (Ag, Pt, and Pd) Nanoparticles on TiO₂ with Oxygen Vacancies for Photocatalytic Redox Reactions under Visible Light

A synergistic strategy involving oxygen-vacancy generation and noble-metal deposition is developed to improve the photocatalytic performance of TiO₂ under visible-light irradiation. Through a redox reaction between the reductive TiO₂ with oxygen vacancies (TiO₂-OV) and metal salt precursors, noble-metal nanoparticles (Ag, Pt, and Pd) are uniformly deposited on the defective TiO₂-OV surface in the absence of any reducing agents or stabilizing ligands. The resulting M-TiO₂-OV (M = Ag, Pt, and Pd) nanocomposites are used as visible-light-driven photocatalysts for selective oxidation of benzyl alcohol and reduction of heavy metal ions Cr­(VI). The results show that the oxygen vacancy creation obviously enhances the visible-light absorption of semiconductor TiO₂. Meanwhile, the noble-metal deposition can effectively improve charge-separation efficiency of TiO₂-OV under visible-light irradiation, thereby enhancing the photoactivity. In particular, Pd-TiO₂-OV, having the average Pd particle size of 2 nm, shows the highest visible-light photoactivity, which can be attributed to the more efficient charge-carrier separation of Pd-TiO₂-OV than Ag-TiO₂-OV and Pt-TiO₂-OV. The possible reaction mechanism for photocatalytic selective oxidation of benzyl alcohol and reduction of Cr­(VI) over M-TiO₂-OV (M = Ag, Pt, and Pd) has also been studied. It is hoped that our work could offer a simple strategy on fabricating defect-based nanostructures and their applications in solar energy conversion.