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

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 (K_sp) 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 K_sp 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.