Synergistic Effects of Bi/S Codoping on Visible Light-Activated Anatase TiO2 Photocatalysts from First Principles

The electronic properties and photocatalytic activity of S and/or Bi-doped anatase TiO2 are investigated by first-principles density functional theory calculations. For S-doped TiO2, S 3p states locate above the top of the valence band and mix with O 2p states, leading to band gap narrowing. For Bi-doped anatase, the energy levels of the impurity Bi 6s states lie below the bottom of the conduction band while the Fermi level EF lies above the gap states, indicating the gap states are fully occupied. The transition from Bi 6s to Ti 3d states is responsible for a red-shift of the visible light absorption edge. In Bi/S-doped TiO2, both S 3p acceptor states and partially occupied Bi 6s donor states hybridized with S 3p appear simultaneously; this observation suggests that photocatalytic efficiency would be improved significantly due to greater separation of electron−hole pairs. These findings present a reasonable explanation of recent experimental results.