Construction Of Structure Of BiVO₄-based Composite Cayalysts And Regulation Of Photocayalytic Performance

In the last few years,due to the increase of severe human-living environment and global shortage of energy,photocatalytic water splitting is an excellent strategy to solve above problems.Therefore,it is essential to synthesize a serise of photocatalysts with efficient photocatalytic performance.However,photocatalysts usually display the disadvantages of low visible-light response and high recombination of electron-hole pairs.Therefore,lots of efforts such as metal doping or non-metal doping,the deposition of noble metal,the construction of heterojunction and so on have frequently been taken,which makes it possible to greatly enhance the photocatalytic performance of semiconductors.In this thesis,monoclinic BiVO₄ with strong oxidizability and high stability was selected as the main material,and the composites were synthesized by coupling with Bi₂MoO₆,ZnIn₂S₄,Zn₂In₂S₅ and Zn₃In₂S₆ via a simple hydrothermal method,respectively.Eventually,the successful construction of Z-scheme heterojunction excellently improves the photocatalytic performance under visible light irradiation.The main contents in this thesis are discussed below:（1）The synthesis of Z-scheme heterojunction composites through two semiconductor photocatalysts possessing matched band structures is an effective regulation-strategy that can regulate the band gap and eventually promote the efficiency of separation between photoelectron and hole.What is more,monoclinic BiVO₄ has been widely studied as a photocatalytic semiconductor material to evaluate the photocatalytic oxygen production under visible light irradiation.In this chapter,a new approach for the formation of BiVO₄/Bi₂MoO₆ Z-scheme heterojunction via a simple hydrothermal method is firstly proposed to prevent the recombination of photo-generated electron-hole pair.As a result,BMO/BVO7represents the highest photocatalytic performance whose oxygen production reached5028.76μmol g^-11 among the series of samples.Accordingly,the highest photocurrent density of BMO/BVO7(0.4μA cm^-2)under visible light irradiation was 6.7 times bigger than that of Bi₂MoO₆(0.06μA cm^-2)and 1.4 times higher than that of the pristine BiVO₄(0.28μA cm^-2).The ESR test shows that the ability of generating superoxide radical of composition is promoted and the efficiency of separated electron-hole pairs is enhanced,which eventually improves the photocatalytic performance.（2）BiVO₄/ZnIn₂S₄ composites are successfully prepared via a hydrothermal method between nanosheets ZnIn₂S₄ and decahedron monoclinic BiVO₄.Among the different composites with different mass weights,BVO/ZIS1-11 shows the optimal photocatalytic activity under the visible light irradiation.Besides,the hydrogen production of BVO/ZIS1-11 reached 22.86 mmol·g^-1,which was about 3.6 times bigger than that of pristine ZIS1(6.33 mmol·g^-1).Moreover,the apparent quantum efficiency of BVO/ZIS1-11 composite reached 22.33%at 435 nm.Interestingly,BVO/ZIS1-11 composite showed the best photocatalytic performance which is attributed to the construction of Z-scheme photocatalysts between BiVO₄ and ZnIn₂S₄.As a result,the photocatalytic activity of BVO/ZIS1-11 composites is greatly promoted owing to the high separation efficiency of photogenerated electrons and holes.（3）In this chapter,decahedron monoclinic BiVO₄ and nanosheet like Zn_x In₂S_x+3（x=2-3）are also synthesized via a hydrothermal method with different mass weights.The photocatalytic activity of pure Zn_xIn₂S_x+3（x=2-3）and its composites are measured by the hydrogen production of photocatalytic water splitting.Among different weights ratio of composites,BVO/ZIS2-5 shows the highest photocatalytic hydrogen production whose production is 50.55 mmol·g^-1.At the same time,BVO/ZIS3-9 shows the best photocatalytic activity and its hydrogen production reaches 32.88 mmol·g^-1.Moreover,it is notably that the BVO/ZIS2-5 composite samples show relatively excellent chemical stability compared with BVO/ZIS3-9.Besides,the ESR test shows that the two kinds of composites are successfully constructed to the Z-scheme heterojunction,which further promotes the separation efficiency of photo-generated carriers and effectively improves the photocatalytic performance of catalysts.