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

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 (center dot 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.