Structure, morphology and photocatalytic performance of europium-doped bismuth vanadate

Europium-doped bismuth vanadate EBVO-x (0 <= x <= 7) with different crystalline phases has been successfully synthesized via a simple one-pot hydrothermal method. X-ray diffractometry, Raman scattering and scanning electron microscopy revealed that the crystal phase transformed from the monoclinic phase to the tetragonal phase, probably owing to the substitution of europium ions in the Bi3+ positions. Significant changes in the physical-chemical characteristics of the material with the initial molar ratio of Eu to Bi were observed. Adding the europium causes alteration of the BiVO4 structure from a monoclinic scheelite (x < 3) to a tetragonal zircon (x >= 3) structure with a mixed-phase state between them. The photocatalytic activities of the prepared samples were evaluated by degrading methylene blue (MB) under visible light irradiation and the best performance was attained for the EBVO-5 material with a phase transition trend. The results of the photoluminescence spectroscopy demonstrated that the recombination of photogenerated charges was greatly depressed and the photocatalytic activity was improved by the substitution of Eu for Bi in BiVO4. Furthermore, the proposed mechanism of the enhanced photocatalytic activity was discussed.