Synthesis of BiVO4–TiO2–BiVO4 three-layer composite photocatalyst: effect of layered heterojunction structure on the enhancement of photocatalytic activity

Abstract

BiVO₄–TiO₂–BiVO₄ three-layer heterostructure photocatalyst was successfully synthesized by a simple sol–gel method with a glass substrate. The structural and optical properties of the as-prepared samples were relatively characterized. UV-vis diffuse reflectance spectroscopy indicated that the BiVO₄–TiO₂–BiVO₄ three-layer composite possessed strong visible-light absorption. Compared to pure TiO₂, BiVO₄ and BiVO₄–TiO₂ bilayer composites, the BiVO₄–TiO₂–BiVO₄ three-layer composite photocatalyst exhibited much higher photocatalytic activity in decomposition of methylene blue and rhodamine B under visible light irradiation. The results of photoluminescence spectroscopy and photocurrent measurement indicated that three-layer structure could distinctly improve the separation and transmission of the photogenerated charges, which led to the enhanced activity. Moreover, the active species trapping experiments demonstrated holes (h⁺) and superoxide radicals (˙O²⁻) were major active species in the degradation process. Then, a possible reaction mechanism accounting for the excellent photocatalytic activity was proposed on the basis of the energy band structure of the composites.