Preparation And Property Studies Of Bismuth Vanadate Based Heterojunction Photocatalytic Materials

Bismuth Vanadate（Bi VO₄）as a new kind of semiconductor photocatalytic materials has three kinds of crystal structures: monoclinic scheelite、tetragonal scheelite and quadrangular zirconium.Among these,monoclinic scheelite Bi VO₄ has attracted much attention in recent years because of its narrow bandgap（2.4 e V）and better response to visible-light.Yet,the poor adsorption and quickly recombination rate of photogenerated carriers result in the low photocatalytic activity.So modify the Bi VO₄-based with other semiconductors to form heterojunction to promote the separation of photogenerated electron and hole pairs and then to improve the photocatalytic activity.In this paper,the monoclinic scheelite Bi VO₄ power has been successfully prepared by hydrothermal method,Bi（NO₃）₃·5H₂O as the source of bismuth,NH₄VO₃ as the source of vanadium.And took XRD、SEM、HRTEM、XPS、UV-vis DRS、PL and I-t to characterize their crystal structure 、 surface morphology 、 opticalabsorption and photoelectric properties.Via the decolorization rate of Rhodamine B to evaluate the photocatalytic activity of Bi VO₄,the mechanism of photocatalytic reaction of composite photocatalyst was further studied.the main contents are as follows:（1）The Ag VO₃/Bi VO₄ heterojunction photocatalytic materials was synthetized by the chemical precipitation method and the prepared sample was characterized above.The results showed that Rh B used as a simulated pollutant,the degradation rates of pure Bi VO₄ and Ag VO₃ were 13.2 % and 54.2 %,respectively,while the photocatalytic activity of composite semiconductor was93.3 % with the irradiation of visible light for 2 h.Compared with the single Bi VO₄ and Ag VO₃,the Ag VO₃/Bi VO₄ heterojunction showed enhanced photocatalytic activity.The enhanced photocatalytic activity should be mainly attributed to the formation of the Type-II staggered heterojunction between Bi VO₄ and Ag VO₃,which accelerated the separation efficiency of photogenerated carriers.The mechanism of photocatalytic reaction was based on the trapping experiment of active species,indicating that h+ is the key active species during the process of the degradation Rh B.（2）Taking mercaptopropionic acid（MPA）as a surface modifier,the Ag₂S/Bi VO₄ composite photocatalysts with different mass ratio were prepared by chemical precipitation method and then the photocatalysts with different mass ratio were characterized by the above.The results showed that Rh B used as a simulated pollutant,the degradation efficiency of pure Bi VO₄ and Ag₂ Swere 12.4 % and 8.5 %,respectively,with the irradiation of visible light in 100 min and Rh B as a simulated pollutant.The Ag₂S/Bi VO₄ composite photocatalysts presents higher photocatalytic activity compared with pure Bi VO₄.However,when Ag₂ S was loaded to Bi VO₄,the photocatalytic activity of the composite increased first and then decreased with the increase of Ag₂ S.When Ag₂ S content was 0.5 wt%,the photocatalytic activity of Ag₂S/Bi VO₄ composite photocatalyst was the best,reaching 95.1 %.The 0.5 wt%Ag₂S/Bi VO₄ composite photocatalyst was also prepared by mechanical mixing method and the photocatalytic degradation rate was 22 %.The photocatalytic activity of composite photocatalyst prepared by chemical precipitation method is better,which attributed to the addition of surface modifier to increase the adsorption of Bi VO₄ and the loaded Ag₂ S to Bi VO₄ resulted in the formation of a suitable type-II staggered heterojunction between Ag₂ S and Bi VO₄ to improve the separation efficiency of photogenerated carriers.The reaction mechanism of Ag₂S/Bi VO₄ composite photocatalyst was further studied,indicating that h+ and O₂·- played a key role in the photocatalytic degradation of Rh B.