科研之友
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摘要
We have systematically investigated the modification mechanism of anatase TiO(2) doped with nitrogen using the plane-wave ultrasoft pseudopotentials method based on density functional theory. The crystal structure, impurity formation energy, electronic structure and optical properties of TiO(2) supercells containing subsitutional nitrogen, interstitial nitrogen or oxygen vacancies were calculated. TiO(2) doped with substitutional nitrogen has shallow acceptor states above the valence band. In contrast, TiO(2) doped with interstitial nitrogen has isolated impurity states in the middle of the band gap. These impurity energy levels are mainly hybridized by N 2p states with O 2p states and Ti 3d states. TiO(2) containing oxygen vacancy has shallow donor states below the conduction band, which consists of Ti 3d states. Except for containing oxygen vacancies, the band gaps of N-doped TiO(2) are narrowed in the range 0.03-0.23 eV, and thus their fundamental absorption edges extend to the visible-light region. By nitrogen doping, the octahedral dipole moments in TiO(2) increase due to the changes in lattice parameters, bond length and charges on atoms, which is very effective for the separation of photoexcited electron-hole pairs. The calculated results are consistent with the existing experimental data. Based on these results, the effects on the electronic structure and photocatalytic activity of anatase TiO(2) doped with nitrogen were analysed and compared in detail, and the mechanism by which anatase TiO(2) doped with nitrogen has higher photocatalytic activity than that of pure TiO(2) was explained. The conclusions have important significance for understanding and further developing TiO(2) photocatalysts that are active under visible-light irradiation.
- 出版日期2008-1-21
- 单位云南大学
