Morphology control of BiVO4 photocatalysts: pH optimization vs. self-organization

The influence of the pH value on the hydrothermal formation of BiVO4 photocatalysts from Bi(NO3)3·5H2O and NH4VO3 was investigated. Optimal nanostructuring and surface area values are obtained for BiVO4 nanoplatelets synthesized at pH 4. Screening of phosphorus-containing templates brought forward dimethyl methylphosphonate (DMMP) as the most efficient surfactant to fine-tune the synthesis of hierarchically structured BiVO4 architectures. Their growth processes were subsequently monitored with ex situ studies. The formation of different BiVO4 microsphere types proceeds via a gradual transformation of zircon-type BiVO4 precursors into self-organized hollow shells of monoclinic BiVO4 crystallites. A slight variation of the synthetic conditions induces the formation of dumbbell-shaped BiVO4 particles consisting of small BiVO4 building blocks arranged around a cylindrical core unit via a different pathway. Catalytic test series for organic dye degradation and water oxidation show that template-free BiVO4 nanoplatelets obtained at pH 4 exhibit optimal activity in both processes. Their MB degradation performance is further improved in alkaline media and the influence of synthetic parameter tuning on BiVO4 catalyst growth and reactivity is discussed.