Bismuth vanadate (BiVO4) hierarchical spheres were synthesized successfully by a facile hydrothermal approach without any additive by using novel vanadium-based nanosheets as precursors. The results indicated that as-prepared BiVO4 samples have monoclinic structure with high crystallinity. Scanning electron microscopy images show that the spheres were self-assembled by dozens of nanosheets with good dispersibility and uniform particle size. Meanwhile, the photocatalytic activities of the resulting BiVO4 were evaluated by photodegradation of methylene blue (MB) under visible light irradiation and exhibited enhanced catalytic efficiency. The excellent performance can be attributed to the high purity, the huge specific surface area, and the novel hierarchical structure. It was also found that the photodegradation of dye pollution is attributed to the oxidation process of the generated hydroxyl radicals and the action of ${\rm{h}}_{{\rm{vb}}}^{\rm{ + }}$ via direct hole oxidation.

X-ray powder diffraction data for the high temperature phase of NaBi3V2O10 obtained from in situ high temperature XRD studies are presented. NaBi3V2O10 undergoes a phase transition from triclinic to monoclinic at about 600 °C. The unit cell parameters of the high temperature monoclinic phase at 600 °C are: a=12.3899(21), b=5.5642(10), c=7.1543(18) Å and β=98.393(16)°, V=487.94(13) Å3 and Z=2, ρcal=6.20 g∕cc. On further increasing the temperature, it partially decomposes to a γ-Bi4V2O11 type phase. The details of this phase as well as the stability of NaBi3V2O10 are discussed.