Spectroscopic Kinetic Insights into the Critical Role of Metal–Oxide Interfaces in Enhancing the Concentration of Surface-Reaching Photoexcited Charges

Surface modification of semiconductors with noble metals has been shown to effectively tune their photocatalytic activity. However, the photoinduced charge transfer processes at the metal/semiconductor interface and their impact on the concentration of surface-reaching photoexcited charges remain subjects of ongoing debate. In this study, we used time-resolved spectroscopy and kinetic analysis to investigate the behavior of surface-reaching photoholes in metal-loaded TiO₂ nanoparticles. Our results reveal that the concentration of surface-reaching photoholes (C_h+(surf)) is highly dependent upon the type of metal and the resulting metal–oxide interface. Among the noble metals studied (Pt, Au, and Ag), Pt loading led to the most significant increase in C_h+(surf), with a nearly 3-fold enhancement compared to pristine TiO₂. This enhancement was attributed to the generation of more abundant Ti³⁺ defects at the metal–oxide interface, which serve as hole trap states, thereby accelerating interfacial charge transfer, improving charge separation, and enriching C_h+(surf). These findings underscore the critical role of the metal–oxide interface in enhancing surface-reaching photoexcited charges, offering valuable insights for the design of advanced materials for solar energy conversion.