Preparation And Performance Of Bismuth Vanadate-based Photocatalytic Materials

In recent years,problems such as environmental pollution and energy shortage caused by the rapid development of industrial civilization have become increasingly prominent.As a green technology that can sustainably utilize the renewable solar energy for pollution control and environment protection,semiconductor photocatalytic technology can provide a feasible solution to solve the above problems.However,the wide bandgap of TiO₂（≈3.2 eV）makes it possible to use only the UV radiation which is just about 5%of the total solar radiation,and results in a low utilization efficiency of solar energy.BiVO₄ is a new type of visible light responsive semiconductor material,which can absorb the visible light.The development of BiVO₄ based composite photocatalysts with high visible light photocatalytic activity are of great significance for improving the utilization efficiency of solar energy.Therefore,the coupling modification and its photocatalytic mechanism of BiVO₄ semiconductor materials were studied in this article.The main research contents are as follows:The tetragonal scheelite bismuth vanadate（（t-s）BiVO₄）and graphite-like phase carbon nitride（g-C₃N₄）were prepared by a polyol method and thermal condensation method,respectively,and then the（t-s）BiVO₄/g-C₃N₄ composite photocatalysts with core-shell structure were successfully synthesized via a facile combination of ultrasonic and chemisorption treatment.The structure and properties of the as-obtained photocatalyst samples were characterized by XRD,SEM,FT-IR,XPS,PL and electrochemical tests.The photocatalytic activities of composite photocatalysts were investigated using Rhodamine B（RhB）as the target contaminant,and its photocatalytic mechanism was studied by the radical capture experiments.The experimental results showed that the photocatalytic performance of the composite photocatalysts had been significantly improved.When the mass ratio of（t-s）BiVO₄ to g-C₃N₄ was 1:16,the photocatalytic activity of the composite photocatalysts was highest.Under the simulated sunlight irradiation,the degradation efficiency for RhB was97.7%within 120 min.In addition,capture experiments showed that h⁺and·O₂^-were the main active species in the photocatalytic reaction process.（t-s）BiVO₄/g-C₃N₄ composite photocatalyst had an enhanced photocatalytic activity and stability.This can be attributed to the formation of the heterojunction structure at their interface,which can extend the light absorption range of the composite photocatalysts,promote the separation and suppress the recombination of photogenerated carriers to some extent.Graphene oxide（GO）was prepared by a modified Hummers method.The monoclinic scheelite type bismuth vanadate（（m-s）BiVO₄）was prepared by a calcining method,and then BiVO₄/RGO composite photocatalysts were prepared by 3-aminopropyltriethoxysilane（KH550）modification assisted solvothermal method.BiVO₄/RGO/Ag₃PO₄ composite photocatalysts were synthesized by in-situ ion sequential precipitation method.The structure and properties of the photocatalyst samples were characterized by XRD,SEM,FT-IR,XPS,UV-vis and PL.The photocatalytic activities of BiVO₄/RGO/Ag₃PO₄ composite photocatalysts were investigated using RhB and 4-nitrophenol（4-NP）as the target contaminants,and the photocatalytic mechanism was studied by the radical capture experiments.The experimental results showd that the photocatalytic activities of BiVO₄/RGO/Ag₃PO₄ composite photocatalysts with different mass ratios were higher than that of BiVO₄/Ag₃PO₄ composite photocatalysts,pure BiVO₄ and Ag₃PO₄,and the photocatalytic activity of the composite photocatalysts was highest,and the degradation efficiency for RhB was 98.2%in 45 min when the mass ratio of Ag₃PO₄ and BiVO₄/RGO was0.6:1.During the process of photocatalytic reaction,h⁺and·O₂^-were the dominant active species.The enhanced photocatalytic performance of BiVO₄/RGO/Ag₃PO₄ composite photocatalysts can be assigned to the synergy effect of BiVO₄ and Ag₃PO₄,incorporation of RGO which can promote the transfer ability of photogenerated electrons,inhibiting the recombination of photogenerated electron-hole pairs.