Nitrogen complex species and its chemical nature in TiO2 for visible-light sensitized photocatalysis

A photocatalyst with high reactivity under visible-light has been desired to utilize solar irradiation or interior lighting efficiently. Nitrogen-doped TiO2 revealed significant improvement in optical absorption and photocatalytic activity over TiO2 under visible light. We have performed the first-principles calculations to study the detailed N complex species introduced in TiO2. The results include stable geometries, densities of states, formation energies, and core levels. The present systematic studies account for the long-term controversial issue on N-doped TiO2, in particular, regarding the detailed assignment of N 1s binding energies observed in the XPS measurement. The detailed analyses of the formation energies show that introducing the N species more in a controlled way via process conditions is crucial to achieve the optimized photocatalytic performance.