Preparation And Photocatalytic Properties Of Bismuth Vanadate Composites

In recent years,photocatalytic technology has been considered as a promising technology for environmental purification and clean energy production.Bismuth Vanadate?BiVO₄?,a kind of catalyst with strong photoresponse ability in the visible light region,has been a research focus of researchers due to its non-toxic,good stability.However,the development and application of BiVO₄ is greatly limited because the pure BiVO₄ excits some defects including the small specific surface area and high recombination rate of photo-generated electrons and holes.Therefore,this article attempts to compound BiVO₄ with some non-metal semiconductors to effectively inhibit the recombination of electron-hole pairs and enhance the photocatalytic degradation of organic pollutants.The main research content is as follows:?1?BiVO₄/g-C₃N₄ composite photocatalysts with different mass ratios were synthesized by using high temperature calcination combined with hydrothermal method.The photocatalytic activity of the BiVO₄/g-C₃N₄ composite photocatalyst was evaluated by degrading RhB under visible light.The results showed that 10 wt.%BiVO₄/g-C₃N₄ exhibited the strongest efficiency of photodegradation.The photodegradation of RhB reached 100%after 80 min,which was about 2.35 times that of g-C₃N₄ at the same conditions.The photocatalytic degradation mechanism of 10 wt.%BiVO₄/g-C₃N₄ was investigated by radical trapping experiments.The results showed that h⁺and O₂^-played the major role in the degradation process.It was observed by HRTEM that the surface of BiVO ₄ was covered with g-C₃N₄ layer with thickness of about 3 nm,which might contribut to the charge transfer between BiVO₄ and g-C₃N₄.It was clearly seen thatBiVO₄/g-C₃N₄ heterojunction was formed between the?121?plane of BiVO₄ and the?100?plane of g-C₃N₄.Moreover,XPS results showed that oxygen played as a bridge role in BiVO₄ and g-C₃N₄ heterojunction forming.Photoelectrochemical experiments further confirmed that the heterojunction promoted the efficient separation of photogenerated electron-hole pairs.In addition,the characteristic peaks of XRD,FTIR,and Raman all presented shifted,demonstrating the existence of forces between the two materials,meaning the formation of heterojunction.BET results demonstrated that the specific surface area has no effect on catalyst degradation.Finally,through the DRS test and empirical formula calculations,the migration path of photogenerated electron-hole pairs was obtained.?2?Using SeO₂ as the source of Se,hydrazine hydrate as a reducing agent,the Se N Rs was prepared by ethanol ripening.Then the Se NRs/BiVO₄ composite with n-n homojunction was prepared by hydrothermal method.Photocatalytic degradation of RhB under visible light irradiation was used to evaluate its photocatalytic property.The results showed that the photodegradation rate of RhBwith Se NRs/BiVO₄ composite was nearly 70%after 120 min under visible light irradiation.The degradation rate was 6.1 and 3.4 times higher than those of pure Se NRs and BiVO₄,respectively.The degradation reaction rate constants were K _Se=0.0015 min^-1,K_BVO=0.0027 min^-1and K_Se/BVO=0.0091 min^-1,respectively.By testing the fluorescence intensity of terephthalic acid with·O H,it was concluded that OH played a major role in the visible light degradation process of RhB.Moreover,the results of UV-Vis-DRS and Tauc diagrams showed the Se NRs/BiVO₄ composite was a Z-type heterojunction.The Z-type heterostructure can enhance the redox capacity of catalyst and lead to the increase of·OH content.In addition,SEM,XRD,TEM,electrochemical test and other characterizations have also fully confirmed that the heterojunction promoted the effective separation of photoelectron pairs.