Synergistic Effects in La/N Codoped TiO2 Anatase (101) Surface Correlated with Enhanced Visible-Light Photocatalytic Activity

Abstract

The interaction between implanted La, substitutional N, and an oxygen vacancy at TiO(2) anatase (101) surface has been investigated by means of first-principles density function theory calculations to investigate the origin of enhanced visible-light photocatalytic activity of La/N-codoped anatase observed in experiments. Our calculations suggest that both the adsorptive and substitutional La-doped TiO(2) anatase (101) surfaces are probably defective configurations in experiments. The h-Cave-adsorbed La doping decreases the formation energy for the substitutional N implantation and vice versa, while the charge compensation effects do not take effect between the adsorptive La and substitutional N dopants, resulting in some partially occupied states in the band gap acting as traps of the photoexcited electrons. The Ti(5c)-substituted La doping decreases the energy required for the substitutional N implantation, and the substitutional La and N codoping promotes the formation of an oxygen vacancy, which migrates from the O(sb-3c) site at the inner layer toward the surface O(b) site. For the substitutional La/N-codoped (Ti(5c)_O(3c-down)) surface, the charge compensation between the substitutional La and substitutional N leads to the formation of two isolated occupied N(s)-O π* impurity levels in the gap, while the excitation energy from the higher impurity level to the CBM decreases by about 0.89 eV. After further considering an oxygen vacancy on the Ti(5c)_O(3c-down) surface, the two electrons on the double donor levels (O(b) vacancy) passivate the same amount of holes on the acceptor levels (substitutional La and N), forming the acceptor-donor-acceptor compensation pair, which provides a reasonable mechanism for the enhanced visible-light photocatalytic activity of La/N codoped TiO(2) anatase. This knowledge may aid the further design and construction of new effective visible-light photocatalysts.