Effect of pH on the Properties of BiVO_4 by Hydrothermal Synthesis Method

摘要

Bismuth vanadate (BiVO_4) powders were synthesized using Bi(NO_3)_3·5H_2O and NH_4VO_3 as raw materials, NaOH and HNO_3 for pH adjustment. The samples were characterized by X-ray diffraction ( XRD ), scanning electron microscopy (SEM ) and UV-vis diffuse reflectance spectra techniques. The results show that the pH of precursor solution has great effect on the composition and morphology of products. Synthetic product was BiVO_4 with two kinds of crystal shape ( monoclinic and tetragonal ) with pH of 3; synthetic product was pure monoclinic phase BiVO_4 when the pH is between 5-9. Whereas, V_2O_5 and Bi_2O_3 appeared when the pH was 11; synthetic product was a mixture of V_2O_5 and Bi_2O_3 with pH of 13, and BiVO_4 didn't exist. The photocatalytic activity was evaluated by the degradation of methylene blue solution. It is shown that the synthetic sample has the best photocatalytic ability with pH of 5. The degradation of methylene blue reaches 84.7% when irradiated for 240 min by high pressure mercury lamp, and the sample synthesized at 13 for pH has strong adsorption capacity and poor photocatalytic ability.