Linking the Doping-Induced Trap States to the Concentration of Surface-Reaching Photoexcited Holes in Transition-Metal-Doped TiO₂ Nanoparticles

Abstract

Transition-metal doping has been demonstrated to be effective for tuning the photocatalytic activity of semiconductors. Nonetheless, the impact of doping-induced trap states on the concentration of surface-reaching photoexcited charges remains a topic of debate. In this study, through time-resolved spectroscopies and kinetic analysis, we found that the concentration of surface-reaching photoholes (<i>C</i>_h+(surf)) in doped TiO₂ nanoparticles sensitively relies on the type of dopants and their associated trap states. Among the studied dopants (Fe, Cu, and Co), Fe doping resulted in the most significant increase in <i>C</i>_h+(surf), nearly double that of Co or Cu doping. Fe-doping induced more effective hole trap states, acting as the mediator for interfacial charge transfer, thus accelerating charge separation and consequently enriching <i>C</i>_h+(surf). This work provides valuable insight into understanding and controlling <i>C</i>_h+(surf) in transition-metal-doped TiO₂ materials.