Mechanistic elucidation of Ta₃N₅/LaTiO₂N heterojunction formation for improving photocatalytic activity

A Ta₃N₅/LaTiO₂N junction is applied in photocatalytic reactions since the favorable band alignment of the two components promotes the separation of photogenerated carriers. This inference is mainly based on the properties of the two isolated, non-interacting materials. However, experiments reveal negligible information on the real nature of the interface, stoichiometry and composition of oxide layers and atomic arrangements in the heterojunction photocatalyst. In this work, we investigated the characteristics of Ta₃N₅/LaTiO₂N using density functional theory calculations. Heterojunction models include the Ta₃N₅(110) surface interfaced with the LaTiO₂N(010) surface and the Ta₃N₅(020) surface matched with the LaTiO₂N(002) surface. Results show that owing to strong interfacial covalent bonds, the formation of a Ta₃N₅/LaTiO₂N junction is an energetically favorable process. Ab initio molecular dynamics simulations also prove the stability of the studied interfacial structures. Light absorption becomes stronger and is extended after the formation of the heterojunction structure, which is favorable for enhancing the utilization efficiency of solar energy. Ta₃N₅/LaTiO₂N is expected to behave as a type II heterojunction, irrespective of the surfaces of the two semiconductors involved in the junction, in which the band edges of Ta₃N₅ are lower in energy than those of LaTiO₂N. This type of band alignment is favorable for the separation of photogenerated carriers upon photoexcitation, where electrons move toward Ta₃N₅ and holes toward LaTiO₂N. On account of the larger driving force for separating charge carriers, the Ta₃N₅(110)/LaTiO₂N(010) interface is predicted to outperform the Ta₃N₅(020)/LaTiO₂N(002) one. The formation of an interfacial structure between Ta₃N₅ and LaTiO₂N induces a more significant separation of photogenerated charge carriers, which may be the origin of an enhanced photocatalytic efficiency compared with isolated components.