Synthesis and characterisation of bismuth(III) vanadate

Modified hydrothermal and ‘wet’ precipitation routes at room temperature were employed to synthesise pure monoclinic BiVO4 powders of varying particle morphologies. Monoclinic BiVO4 powder was also prepared by a solid-state reaction at 700°C. Depending on the synthesis conditions, the colour of BiVO4 varies from inhomogeneously yellow–brown to homogeneously and intensive lemon yellow. BiVO4 prepared by solid-state reaction consisted of large compact particles about 15 μm in size and of irregular shape. At higher magnification, the formation of domains with smooth terrace-like surfaces was observed. These domains ended with well-defined walls, and the edges of these walls were relatively very sharp. BiVO4 synthesised by the hydrothermal and an aqueous process at RT consisted of smaller particles (0.3–1.2 μm) and of much bigger regular crystals with a well-defined crystal habit. A continuous shift of the most intense Raman band to lower wavenumbers reveals that the average short range symmetry of the VO4 tetrahedra becomes more regular. The values of FWHM for the same Raman band increase from sample prepared by solid-state reaction to sample obtained at RT. The Raman results suggested that a sample prepared at high temperature consisted of less symmetric VO4 tetrahedra than samples prepared at low temperature and that the high-temperature sample showed better crystallinity with less defects than the samples prepared by an aqueous process under mild conditions. FT-IR spectra showed main features typical of the vanadates of other metal(3+) cations. However, the position of IR bands recorded for BiVO4 depended on the synthesis route.