Dissolution behaviors of a visible-light-responsive photocatalyst BiVO4: Measurements and chemical equilibrium modeling

Despite of the extensive research in semiconductor photocatalysis with respect to material and device innovations, much of the fundamental aquatic chemistry of those new materials that governs their environmental hazard and implications remains poorly understood. BiVO4 has long been recognized as a promising visible-light-responsive photocatalyst. However, the solubility product (Ksp) of BiVO4 and the mechanistic understanding of the non-stoichiometric dissolution of BiVO4 remain unclear. Here, we investigated the solubility of BiVO4 via the observation on its non-stoichiometric dissolution in the pH range of 4-9. Combining dissolution experiments, adsorption behavior and thermodynamic equilibrium calculations, the Ksp of BiVO4 was determined to be 10-35.81±0.51. The solubility and stability of BiVO4 were strongly pH-dependent, with the lowest solubility and highest stability near pH 5. Furthermore, we tested the effect of illumination on the dissolution of BiVO4, which was significantly enhanced by light. Under both dark and illumination conditions, adsorption of dissolved bismuth by BiVO4 solids was the main reason for the non-stoichiometric dissolution of BiVO4, and could be modeled by including an additional surface complexation reaction. Thus, the results highlighted the importance of considering the dissolution of photocatalysts, and presented a feasible method to evaluate environmental stability and risks of other semiconductor materials.