Coupling Effect of Au Nanoparticles with the Oxygen Vacancies of TiO2–x for Enhanced Charge Transfer

Interface structure plays an extremely important role in the charge-transfer and photocatalytic performances in plasmonic metal/semiconductor systems. Defect engineering by introducing an oxygen vacancy (Ovac) is an effective way to modulate the interface structure. Here, a representative photocatalyst system including TiO2, TiO2–x, Au-TiO2 and Au-TiO2–x as designed delicately to reveal the detailed mechanism of the plasmon-resonance-induced charge separation in interfacial defect structure from the nanoscale. The local charge transfer via a conducting amorphous-like interface layer is visualized as the arched valence change from Ti3+ to Ti4+ at the Au-TiO2–x interface after Schottky contact. This phenomenon eventually leads to the enhancement of localized surface plasmon resonance (LSPR) at 2.3 eV, and the introduction of Ovac reduces the Schottky barrier height of Au-TiO2–x by 5 mV compared with that of Au-TiO2. Under visible light, Au-TiO2–x excites the most photogenerated carriers to the surface, which is larger than that of TiO2–x and Au-TiO2. It can be concluded that the changes in electronic structure eventually promote charge transfer in visible light and explain the original reason that the coupling of Ovac and Au could improve the photocatalytic performance.