A Quantitative Study on the Effect of Fe Doping on the Surface-Available Photohole Concentration in TiO₂ Nanoparticles

Fe-doped TiO2 materials have recently emerged as robust catalysts with high photocatalytic activity, especially for oxidation reactions. Despite the fact that Fe doping plays a pivotal role in the oxidation process, there is still a lack of quantitative and in-depth research on how the Fe doping of TiO2 affects the surface-available photohole concentration. Herein, the adsorbate (methanol) surface elementary reaction kinetic analysis method was applied to quantify the surface-available photohole concentration in a library of Fe-doped TiO2 nanoparticles (0–0.5 wt %). Adsorbed methanol species on the Fe/TiO2 surface were photo-oxidized by surface-available photoholes, following first-order reaction kinetics. Thus, the concentration of surface-available photoholes in Fe/TiO2 nanoparticles could be directly reflected by measured reaction rate constants. It was found that optimized Fe-doped TiO2 nanoparticles showed the increased surface-available photoholes under light irradiation, representing nearly 1.5 times higher than that of the pristine TiO2 nanoparticles. Such a high concentration of surface-available photoholes in Fe/TiO2 nanoparticles was attributed to the enhanced photogenerated electron–hole separation induced by Fe doping. This work provides new insight into understanding and controlling the oxidation reaction process on Fe-doped TiO2 materials.