Photoinduced Superhydrophilicity of Anatase TiO₂ Surface Uncovered by First-Principles Molecular Dynamics

TiO₂ is a prototype of photocatalyst materials. Interfacial water structure is critical to understand the chemical reactivity of TiO₂. By performing first-principles molecular dynamics simulations on the TiO₂(001)/water interface were performed, we found that the presence of a photogenerated hole at the interface increases the coverage of both the molecular and dissociative water adsorption by increasing the surface acidity and then shapes the layered and ordered water structure by enhancing the interfacial hydrogen bond network. The enhanced attachment of water in contact with the TiO₂ surface rationalizes the increase in the intensity of the sum frequency generation spectrum under ultraviolet illumination reported in the experiment. These findings provide a novel interpretation of the electronic effect for the photoinduced hydrophilic conversion of the TiO₂ surface at the atomistic level.