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

Abstract

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 (O-vac) 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 O-vac 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 O-vac and Au could improve the photocatalytic performance.