Synthesis, characterization and photocatalytic activities of rare earth-loaded BiVO4 catalysts

The BiVO4-based photocatalysts loaded with rare earth (RE=Ho, Sm, Yb, Eu, Gd, Nd, Ce and La) were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), diffuse reflectance spectroscopy (DRS), nitrogen adsorption for the BET specific surface area and X-ray photoelectron spectroscopy (XPS). The photocatalytic activities of the samples were evaluated by decolorization of methylene blue (MB) under visible light irradiation. The results of XRD, SEM and XPS analysis deduced that the rare earth ions were present as RE2O3 in the samples. The DRS analysis showed the shift in the absorbption edge from the UV to the visible range: Ho3+-BiVO4 < Sm3+-BiVO4 < Yb3+-BiVO4 < Eu3+-BiVO4 < Gd3+-BiVO4 < Nd3+-BiVO4 < La3+-BiVO4 < Ce3+-BiVO4 < BiVO4. Gd3+-BiVO4 had the highest photocatalytic activity among all the RE3+-BiVO4 catalysts. The optimal Gd content was 8 at% under visible light irradiation. This beneficial effect was attributed to the specific electron structure characteristics of gadolinium and the increasing in the separation efficiency of the electron-hole pairs. On the contrast, the other rare earth ions had the detrimental effect on the photocatalytic decolorization of MB.