[en] The effects of Fe–C/N co-doping on the electronic and optical properties of NaTaO${}_3$ are studied with density functional theory. Our calculations indicate that mono-doped and co-doped sodium tantalate are both thermodynamically stable. The co-doping sodium tantalate can reduce the energy band gap to a greater degree due to the synergistic effects of Fe and C(N) atoms than mono-doping sodium tantalate, and has a larger optical absorption of the whole visible spectrum. The band alignments for the doped NaTaO${}_3$ are well positioned for the feasibility of hydrogen production by water splitting. The Fe–C co-doping can enhance the absorption of the visible light and its photocatalytic activity more than Fe–N co-doping due to the different locations of impurity energy levels originating from their p–d hybridization effect. (paper)

[en] The electronic structures and absorption spectra have been studied with density functional theory plus U for isoelectronic impurities C/Si/Ge/Sn-doped anatase TiO₂. Our theoretical results show silicon atoms can attract electrons from the surrounding oxygen atoms due to their greater electronegativity than that of titanium atoms which leads to increasing the energy of 2p orbitals of the surrounding oxygen atoms and then forming new acceptor impurity level composed of oxygen 2p orbitals near the top of TiO₂ valence band. This new acceptor level can easily bind the photoexcited holes for a period of time, thus effectively preventing the recombination of photo-excited electron-hole pairs, which play a key role in achieving higher light photocatalytic activity than pure TiO₂ for degradation of contaminants in water. We also systematically described the electronic structure and optical properties of the germanium doped system and then explained experimental observations of absorption spectra with red-shift at a suitable Ge dopant concentration. Especially, compared with pure TiO₂, Sn-doped TiO₂ has better photocatalytic activity because of the synergistic effect of Sn atoms and oxygen vacancies. Our theoretical calculations not only explained the key role of isoelectronic defect in preventing the recombination of photo-excited electron-hole pairs but also provided a new way for enhance of photocatalytic activity.