The Construction And Photocatalytic Mechanism Of BiVO₄-Based Z-Scheme Heterojunction Photocatalysts

Photocatalytic technology using solar energy has great prospects in the removal of environmental pollutants.As a novel visible light responsive photocatalysts,BiVO₄ has attracted wide attention due to its unique crystal structure,electronic structure,visible light response and high transfer rate of photogenerated carriers.However,the high recombination rate of photogenerated electron-holes and low reducing ability are the obstacles to achieve a satisfactory photocatalytic efficiency for BiVO₄.Therefore,in this work,BiVO₄ as the main research object,the light absorption ability,carriers separation ability and mechanism of photocatalytic enhancement of BiVO₄-based photocatalysts have been studied.The main contents are summarized as follows:1.A direct Z-scheme BiVO₄/2D g-C₃N₄ heterojunction photocatalysts via a facile electrostatic self-assembly method is successfully synthesized.The as-synthesized BiVO₄/2D g-C₃N₄ heterojunction exhibits excellent photocatalytic performance with the93.0%Rhodamine B（RhB）removed after 40 min visible light irradiation,and the photocatalytic reaction rate is about 19.76 and 8.96 times as high as that of BiVO₄ and 2D g-C₃N₄,respectively.2.Through both experimental and first-principle calculations,we clearly reveal that the high photocatalytic performance of BiVO₄/2D g-C₃N₄ photocatalysts can be attributed to effective light harvesting,large specific surface area and formed intimate interface between BiVO₄ and 2D g-C₃N₄.The strong electronic coupling in BiVO₄/2D g-C₃N₄interface could induce charge transfer from 2D g-C₃N₄ to BiVO₄.As a result,the formation of built-in electric field and the opposite bands bending around interface region leading to the high efficiencies for separation and transport of photogenerated charge carriers.Moreover,the photocatalytic mechanism follow a Z-scheme system which provided an efficient transfer pathway for charge carriers meanwhile endow the heterojunction with strong redox ability.3.A novel ternary BiVO₄/protonated g-C₃N₄/AgI photocatalyst with a double Z-scheme mechanism is successfully constructed by electrostatic self-assembly method loading of BiVO₄ onto protonated g-C₃N₄（pCN）and subsequently via a in-situ precipitation route.Moreover,the as-prepared ternary sample exhibit excellent photocatalyticperformance and high stability.Using RhB as the target of elimination,BiVO₄/pCN/AgI displays excellent photocatalytic performance with the 94.67%removal after 60 min visible light irradiation,which is higher than pure BiVO₄（1.74%）.4.The charge transfer of BiVO₄/pCN/AgI composite follows a direct double Z-scheme.Due to the band gap matchment,this reaction system owns improved light absorption,faster charge carrier separation and transportation as well as more powerful redox ability,leading to improved photocatalytic activity.Meanwhile,the active speciestrapping experiment and ESR analysis confirm that·O₂^-,h⁺and·OH are produced in theternary photocatalytic system.