Design And Preparation Of BiVO₄-based Ternary Visible Light Catalysts

Bulk BiVO₄ prepared by hydrothermal method suffers from rapid recombination of photogenerated carriers,low photochemical conversion efficiency,low specific surface area,poor conductivity,and weak adsorption capacity of dye.These features limited its application in photocatalysis.In recent years,the construction of heterojunction structures and indirect Z-scheme methods to improve the separation efficiency of photo-generated carriers has attracted much attention.The purpose of this paper is to build a Z-scheme and new type ? heterojunction structure based on BiVO₄,to accelerate the separation and transfer of wide-ranging carriers from the perspective of band structure,and greatly improve the photocatalytic performance.The main research contents of this article are as follows:?1?The ternary Z-scheme g-C₃N₄/RGO/BiVO₄ nanocomposites were successfully fabricated by in-situ electrostatic adsorption of g-C₃N₄ sheets on RGO/BiVO₄ surface using hydrothermal and thermal oxidations processes.The ternary Z-scheme g-C₃N₄/RGO/BiVO₄ nanocomposites were then tested for photodegradation of Rhodamine B?RhB?.The introduction of graphene into direct Z-scheme g-C₃N₄/BiVO₄ nanocomposites as an electronic accelerator efficiently enhanced the photocatalytic properties.The as-prepared g-C₃N₄/RGO/BiVO₄ composites exhibited optimal visible-light responses with significantly improved photocatalytic performances towards degradation of Rhodamine B?RhB?.The degradation efficiency using ternary photocatalyst reached 100 % after 20 min irradiation time.The reaction rate constant was estimated to 1.537,which was almost 29-and 20-folds higher than those of pure g-C₃N₄ and binary g-C₃N₄/BiVO₄,respectively.The synergistic effect between BiVO₄,RGO and g-C₃N₄yielded g-C₃N₄/RGO/BiVO₄composites with Z-scheme charge transfer mechanism,promoting rapid separation and slow recombination of photogenerated electron-hole pairs with strong photocatalytic activity.Overall,these findings look promising for design of future Z-scheme photocatalysts for environmental degradation of organic dyes.?2?The ternary ? Cu₂O/RGO/BiVO₄ composite photocatalytic material was prepared by hydrothermal method and polyol reduction method.Cu₂O nanoparticles were then grown in situ on the RGO/BiVO₄ surface to yield a heterojunction structure with an internal electric field,allowing movement of photogenerated electrons and holes in opposite directions to participate in redox reactions.The as-obtained optimized Cu₂O/RGO/BiVO₄ material exhibited excellent photocatalytic degradation performance towards organic pollutants.The reaction rate constant of RhB was estimated as 0.0324 min^-1,which was almost 5.94,5.15 and 1.94-fold higher than those of bare BiVO₄,4%RGO/BiVO₄ and 5%Cu₂O/BiVO₄,respectively.Moreover,the optimized material displayed good activity in the degradation of the colorless organic contaminant tetracycline hydrochloride?TC?.The reaction rate constant was estimated as 0.0219 min^-1,which was almost 1.60,1.40 and 1.63-fold higher than those of bare BiVO₄,4%RGO/BiVO₄ and 5%Cu₂O/BiVO₄,respectively.The hole and superoxide radical worked as active species for degradation of organic matter.Such a significant increase in degradation efficiencies was attributed not only to the formation of a heterojunction structure but also to rapid electron transfer between interfaces.