Preparation and characterization of TiO₂/BiVO₄ composite: Can this photocatalyst, under visible light, be able to eliminate rhodamine B from water and why?

Bismuth vanadate (BiVO₄) can be composited with titanium dioxide (TiO₂) to obtain a photocatalyst that can be activated by visible light. Such photocatalyst may be operated by solar light, principally, a free photon source. Many researchers have been working hard to find a stable, efficient, and low cost photocatalytic systems. In this presentation, we will report our effort to prepare and characterize TiO₂/BiVO₄ composite, which is responsive under visible light. The TiO₂/BiVO₄ composite was prepared by co-precipitation method, in which the self-prepared TiO₂ nanotubes was immersed in solution containing bismuth (III) and vanadate ions under certain pH. The freshly obtained TiO₂/BiVO₄ was dried and subjected to a heat treatment, then was characterized by XRD, UV-visible diffuse reflectance spectrophotometer, SEM, and photo-electro-chemical working station. The results showed a crystal phase mixture of TiO₂/BiVO₄ composite system, which are anatase (2θ of 27.5°, 36.1°, 54.3°) and monoclinic scheelite, bismuth vanadate (2θ of 19°, 29°). The photocurrent evolution under visible light exposure was investigated carefully. The results showed that the composite system is active under visible light, due to visible light absorption by narrow bandgap semiconductor, namely BiVO₄. While the heterojunction system in TiO₂/BiVO₄ composite enhanced the separation of electron and charge, eventually, the electron would flow from the conduction band of BiVO₄ to conduction band of TiO₂, so the photocurrent will be enhanced. When this composite was being applied to the photoelectrocatalytic reactor system, containing aqueous rhodamine B, the enhancement of photo-catalytic degradation of rhodamine B was also significantly observed. The influence of bias potential applied during photoelectrocatalytic degradation process will be further discussed.