Enhancement of Titania Photoanode Performance by Sandwiching Copper between Two Titania Layers

Vacancies in semiconductors can play a versatile role in boosting their photocatalytic activity. In this work, a novel TiO₂/Cu/TiO₂ sandwich structure is designed and constructed. Abundant vacancies were introduced in TiO₂ lattice by Cu reduction under heat treatment. Meanwhile, Cu atom could diffuse into TiO₂ to form Cu-doped TiO₂. The synergistic effect between oxygen vacancies and Cu atoms achieved about 2.4 times improved photocurrent of TiO₂/Cu/TiO₂ sandwich structure compared to bare TiO₂ thin film. The enhanced photoactivity may be attributed to regulated electron structure of TiO₂ by oxygen vacancies and Cu dopant from experimental results and density functional theory calculations. Oxygen vacancies and Cu dopant in TiO₂ formed through copper metal reduction can introduce impurity levels and narrow the band gap of TiO₂, thus improve the visible light response. More importantly, the Cu²⁺ and oxygen vacancies in TiO₂ lattice can dramatically increase the charge density around conduction band and promote separation of photo-induced charge carriers. Furthermore, the oxygen vacancies on the surface may serve as active site for sufficient chemical reaction. This work presents a novel method to prepare doped metal oxides catalysts with abundant vacancies for improving photocatalytic activity.