Interfacial properties and band alignment of noble-metal/anatase TiO2(1 0 1) hetero-structures

Abstract

Metal-semiconductor hetero-structures have been extensively studied because of taking full advantage of their respective advantages in many fields. For photocatalysis, the most significant advantage of supported noble metal co-catalyst is the effective separation for the photo-generated electron-hole pairs, which can obviously improve the quantum efficiency. However, it is very difficult to characterize and analyze the interfacial properties of the hetero-structure consisted by noble metal co-catalyst and photocatalyst. In this article, eight noble metals are chosen as the co-catalyst for the photocatalyst of anatase TiO2, meaning that eight kinds of hetero-structures should be established. The micro-structure, interfacial energy, and electronic structures have been systematically investigated and compared using DFT calculations. Importantly, the interfacial relaxation obviously induces the distribution of space charge, producing interfacial electric dipole moment. The electron transfer across interface leads to the formation of the built-in electric field, which can promote the separation of photo-generated carriers. Furthermore, NM/TiO2 hetero-structures demonstrate upward band bending. The electronic wave function of Pd-4d or Pt-5d state can extend to the band gap of the TiO2 interfacial layer, resulting in the metallic properties and reduce the Schottky barrier height. These findings illustrate the mechanism about the role of noble metals in photocatalysis from the reported experiments, and providing theoretical reference to the design of novel highly efficient hetero-structures in the field of photocatalysis.