New insight into the enhanced visible-light photocatalytic activities of B-, C- and B/C-doped anatase TiO2 by first-principles

The geometry structures, formation energies and electronic properties of the B-, C- and B/C-doped anatase TiO2 were investigated by the density functional theory (DFT) calculations of first-principles. The results indicated that the visible-light absorption and photocatalytic activities of the B-, C- and B/C-doped anatase TiO2 were not only influenced by the energy gaps (E-g) and the distributions of impurity states, but also affected by the locations of Fermi levels (E-F) and the energies of the edges of band gaps (E-v for the top of valence bands and E-c for the bottom of conduction bands). However, the above four factors changed with the doped models of TiO2. The impurity states in the band gaps reduced the maximum energy gaps in the band gaps, which is responsible for the absorption of visible light. The Fermi levels at the bottom of conduction bands indicated the existence of Ti3+ ions, which enhanced the separation rates of photogenerated electrons and holes. Further, the energies of the edges of band gaps, determining the dominant types of oxidants (O-2(-), hole, (OH)-O-center dot) in the photocatalytic degradation, were discussed. Moreover, the stability of the doped TiO2 depended on its growth conditions (O-rich or Ti-rich environment). The O-rich growth condition is beneficial to the substitutional B and C atoms to Ti atoms, while the Ti-rich growth condition is favorable to the other doped TiO2 including the most stable co-doped TiO2 with the interstitial B atom and the substitutional C atom to O atom. In addition, our results also showed that the B/C-doped TiO2 inherited the partial electronic properties of single-doped TiO2, but also exhibited many new electronic properties, implying that the electronic properties of co-doped systems are not a mechanical mixture of those of both single-doped systems.