Effects of pH on the Hierarchical Structures and Photocatalytic Performance of BiVO4 Powders Prepared via the Microwave Hydrothermal Method

BiVO4 powders with hierarchical structures were prepared by the microwave hydrothermal method at different pHs, using Bi(NO3)3·5H2O and NH4VO3 as raw materials. The results show that, when the pH value of the precursor is 0.59, the as-prepared powders are monoclinic BiVO4 crystals with octahedron and decahedron morphologies. Spherical and polyhedral BiVO4 with particle sizes in the range of 2-4 μm can be prepared under the strong acid condition (pH = 0.70-1.21) and possess a mixed crystal consisting of tetragonal and monoclinic phases, whereas rodlike and dendritic BiVO4 with a pure monoclinic phase can be obtained within a very wide pH range (pH = 4.26-9.76). The phase transformation from tetragonal phase to monoclinic phase occurs at pH 3.65. At pH >9.76, the powders are the nonstoichiometric crystals between the mixed-phase BiVO4 and non-BiVO4. The photocatalytic efficiencies were evaluated by the degradation of Rhodamine B (RhB) under UV and simulated sunlight irradiation. The corresponding relationship among pH values of the precursor, crystalline phase, morphology, and photocatalytic performance of the powders was also discussed.