Construction And Modification Of BiVO₄ Homogeneous Junction Photocatalyst

Bismuth vanadate（BiVO₄）is an n-type visible-light-responsive bimetal oxide semiconductor with the advantages of non-toxicity and chemical stability.The light absorption range of single BiVO₄ is relatively narrow,and the photogenerated carriers are easy to recombine,which greatly hinder its photocatalytic performance.The construction of BiVO₄-based composite photocatalysts is one of the effective ways to improve their performance,however,the current research on BiVO₄ homojunction is not in-depth.Focusing on the above bottlenecks that limit the photocatalytic reaction,in this work,g-BiVO₄/y-BiVO₄ homojunction was constructed and modified by g-C₃N₄to construct a ternary composite photocatalyst,and the microstructure,morphology,and photoresponse ability,carrier separation efficiency of the composite photocatalyst were investigated,to establish the corresponding structure-activity relationship.The main contents and results are as follows:1.The g-BiVO₄/y-BiVO₄ homojunction with excellent photocatalytic performance under simulated sunlight was synthesized by sonochemical method.The degradation efficiency of Rh B by g-BiVO₄/y-BiVO₄ reaches 95.0%under illumination for 210 min,which is 2.21 times and 4.24 times higher than that of the four-pointed star-shaped BiVO₄（g-BiVO₄）and the grass-shaped BiVO₄（y-BiVO₄）,respectively.During the reaction,h⁺and·O₂^-are the main active species of g-BiVO₄/y-BiVO₄ homojunction.2.At the interface of g-BiVO₄/y-BiVO₄,the charges satisfy the type-II transfer mechanism.The photogenerated electrons transfer from the conduction band of the four-pointed star-shaped g-BiVO₄ to the conduction band of the grass-like y-BiVO₄,and the transfer direction of the holes in the valence band is opposite.This type-II mechanism can help the spatial separation of the photogenerated carriers and promote the enhancement of the photocatalytic activity of g-BiVO₄/y-BiVO₄ homojunction.3.The g-C₃N₄/g-BiVO₄/y-BiVO₄ternary composite photocatalyst with excellent degradation performance was synthesized by sonochemical method.Under the illumination of simulated sunlight for 100 min,the degradation efficiency of Rh B by g-C₃N₄/g-BiVO₄/y-BiVO₄ reaches 99.6%,and the apparent reaction rate constant is 8.55 times higher than that of g-BiVO₄/y-BiVO₄ homojunction.After 4 cycles,the degradation activity remains 85.7%.h⁺,·O₂^-,·OH play a role in the degradation of Rh B.4.The g-C₃N₄/g-BiVO₄/y-BiVO₄ ternary composites follow the Z-scheme charge transfer mechanism.The photogenerated electrons in the conduction band of g-BiVO₄ react with O₂to generate strong oxidizing·O₂^-,and the holes in the valence band of g-C₃N₄interact with OH^-to generate strong oxidizing·OH,which retains a high redox ability and exhibits more excellent photocatalytic ability.