Effects of pH value on the surface morphology of BiVO4 microspheres and removal of methylene blue under visible light

Bismuth vanadate (BiVO4) microspheres with different surface morphology were hydrothermally synthesised at different pH value. The resulting sample was characterised by X-ray diffraction, scanning electron micrographs, transmission electron microscopy, N-2 adsorption and UV-Vis diffuse reflectance spectroscopy. On the basis of characterisation results, we found that the pH value exhibits a great influence on the surface morphology and photocatalytic activity of the BiVO4 microspheres. The acid condition may play a more important role on the sample morphology compared with alkaline condition. BiVO4 3D architectures prepared at pH=5 composed of many random grown nanosheets show an excellent photocatalytic activity. Thanks to the 3D architectures and narrow bandgap, the photocatalytic performance was significantly improved as compared with the other BiVO4 microspheres. Several possible reasons for the higher photocatalytic activity have been taken into consideration, namely, the unique features of high surface area, quantum-size effect and high surface-to-volume ratios of nanosheets.