Preparation And Photocatalytic Activity Of Bismuth Vanadate-based Composite Photocatalysts

With the development of economy, industrial wastewater pollution had brought a lot of potential environmental problems. Compared with the traditional processing methods, semiconductor photocatalytic technology had attracted the wide attention for its mild reaction, no secondary pollution, clean energy and other advantages in recent years. As a representative of the new semiconductor materials, Bismuth vanadate had received extensive attention of the researchers. In order to solve the problems of dye wastewater, this paper set up a complex visible-light-responsive photocatalyst by modifying BiVO4 and methylene blue（MB） was used as the model pollutant to evaluate the performance of prepared photocatalysts. This paper took XRD, XPS, SEM, TEM and UV-vis to characterize the synthesized photocatalysts for studying their crystal structure, size, surface morphology, and corresponding photocatalytic mechanism. The results are as followings:（1） Monoclinic BiVO4 photocatalyst was prepared by hydrothermal treatment at different pH and hydrothermal time. The optimal sample of monoclinic BiVO4 was synthesized when pH was 1 and hydrothermal time was 24 h and could remove 63% of MB.（2） Ag2 O / BiVO4 was prepared by UV light reduction method. Its characterization showed the loading of Ag2 O had no effect on its crystal phase structure, instead decreased its crystal size. When the Ag2 O loading ratio was 4%, Ag2 O / BiVO4 could degrade 84% of MB. This is mainly because the excited conductance band（CB） electrons of Ag2 O transferred to the BiVO4 CB and the holes of BiVO4 transferred to the valence band（VB） of Ag2 O, and thus suppressed photo-excited electron-hole pairs recombination under the potential difference of energy level offset. It promoted Ag₂O/BiVO₄ generating strong oxidizing hydroxyl radicals under photo-irradiation and efficiently and rapidly decomposed target pollutants.（3） Eu doped BiVO4 photocatalyst was synthesized by one-step hydrothermal treatment method. Its characterization showed Eu dopant did not transform the crystalline structure of the prepared sample. The degradation efficiency of MB could be reached 77% when Eu doping content at 1%. This is mainly because Eu3+ and V5+ provided by the metavanadate competed for O. Finally, Eu3+ substituted V atom in BiVO4 crystal lattice and formed Eu-O. The Eu3+ doping in BiVO4 resulted in lattice defect and novel energy band, which enhanced the visible-light photoactivity of BiVO4.（4） Combined with the hydrothermal synthesis and UV reduction methods, Eu was doped into BiVO4 lattice and Ag2 O was loaded on the surface of Eu-BiVO4 crystal. The composite catalyst could remove 95% of MB and showed higher degradation rate. This is mainly due to the synergistic action between the above two modifying methods. The synergism had a positive effect on the photocatalytic performance of BiVO4 under visible-light irradiation.