Structure, stability and visible light adsorption properties of N-doped anatase TiO ₂ for photocatalytic H ₂ production from DFT calculations

The extension of absorption properties of TiO ₂ photocatalytic materials to the visible part of the solar spectrum is of major importance for energy applications, eg in the photochemical water splitting reaction for hydrogen production. We carry out a systematic study of N-doped anatase TiO ₂ material with density functional theory using the range separated HSE06 functional. The thermodynamic stability is studied as a function of the oxygen chemical potential in relation with the chemical doping agents (H ₂, NH ₃ and H ₂H ₄). Diamagnetic dispersed substitutional N species with an associated half concentration of O vacancies appear as the configuration favored for NH ₃ or H ₂H ₄. The electronic analysis reveals a band gap narrowing of 0.6 eV from delocalized impurity states at the top of the valence band of TiO ₂. The calculated UV-visible absorption spectra demonstrates that these diamagnetic dispersed N species with O-vacancy are at the origin of the enhanced optical absorption in N-doped TiO ₂ under visible-light irradiation observed experimentally.