The Construction Of Bi₂WO₆-based Heterojunction And The Study Of Photocatalysis Theory

Bismuth tungstate?Bi₂WO₆?is regarded as a promising visible-light-driven photocatalyst due to the unique layer structure and suitable bandgap structure.Unfortunately,the quick recombination of photogenerated charge carriers and narrow light response range limit the practical applications of pure Bi₂WO₆.Constructing semiconductor heterostructure photocatalytic materials is one of the effective ways to overcome the inherent defects of traditional photocatalysts.In light of this,the paper takes Bi₂WO₆ as the research object,adopts the first principle based on density functional theory to construct Bi₂WO₆/Bi₂MoO₆,Bi₂WO₆/MX₂?M=Mo,W;X=S,Se?,Bi₂WO₆/Cu₂O semiconductor heterojunction interface structure and discusses the interface structure,charge transfer,energy band offset and other related characteristics of the composite photocatalytic materials.According to the above conclusions,the mechanism of enhanced photocatalytic activity of heterojunction is summarized.The study of B_i2WO₆?010?/Bi₂MoO₆?010?heterojunction structure shows that due to the difference of work functions,electrons are transferred in the process of forming the heterojunction.After the interface reaches thermal equilibrium,the built-in electric field of the heterojunction is directed from Bi₂MoO₆ layer to Bi₂WO₆ layer so that the semiconductor energy bands on both sides of the heterojunction shift,and the shift results in the formation of the Step-Scheme heterojunction.The existence of the built-in electric field realizes the effective separation of useful photo-generated electrons and holes at the heterojunction interface.Thereby effectively improving the photocatalytic performance.The experimental results further prove that the degradation effect of Bi₂WO₆/Bi₂MoO₆ porous heterogeneous microspheres on rhodamine B is significantly better than that of pure Bi₂WO₆ or Bi₂MoO₆.For Bi₂WO₆?010?/MX₂?001??M=Mo,W;X=S,Se?Four heterojunction studies indicate that heterojunction interfaces can exist stably and electron transfer occurs at the interface during the formation of heterojunction?all of which are composed of MX₂?M=Mo,W;X=S,Se?to Bi₂WO₆?.As a result,the band edge position is shifted and the built-in electric field from MX₂ to Bi₂WO₆ is generated.Due to the different band gaps,work functions,and Fermi levels of the four MX₂ compounds,the combination of Bi₂WO₆ causes the band edge positions to shift to different degrees.Bi₂WO₆/MoS₂ conforms to the Step-Scheme heterojunction photocatalytic mechanism,while Bi₂WO6/WS₂,Bi₂WO₆/MoSe₂,and Bi₂WO₆/WSe₂ conform to the I-type heterojunction photocatalytic mechanism.According to the study on the electron structure and interface structure of Bi₂WO₆/Cu₂O heterojunction photocatalyst,Bi₂WO₆ forms a stable heterojunction with Cu₂O during the formation of the heterojunction,the electrons on the Cu₂O transfer to the Bi₂WO₆ and the interface therefore generates a built-in electric field from the Cu₂O to Bi₂WO₆.Band offset and built-in electric field lead to the spontaneous aggregation of photogenerated electrons to Cu₂O side after excited transition,while built-in electric field accelerates the aggregation of electrons to Cu₂O side.The Bi₂WO₆/Cu₂O heterojunction can effectively inhibit the photogenerated electron hole recombination and improve the efficiency of the catalyst.