Preparation,Characterization And Photocatalytic Performance Of Bismuth Vanadate-Based Composites

China is the country with the largest production and use of glyphosate herbicide.Glyphosate will cause pollution in the process of production and use,which has greatly affected the ecological balance of nature and the living environment and health of human beings.Therefore,it is urgent to seek out an efficient method to efficiently remove the glyphosate under sunlight irradiation.Photocatalysis has attracted extensive interest because of its advantages such as efficient and thorough degradation of pollutants,mild conditions and no secondary pollution.Bismuth vanadate（Bi VO₄）can be excited by visible light,but its photocatalytic activity is low due to the fast recombination of electrons and holes.Therefore,more and more researchers have pay attention to the design of high-efficient and stable visible-light-driven photocatalysts for the degradation of pollutants.In this paper,the modification of Bi VO₄ coupling with Mo Se₂,Cu S,In₂S₃,Bi₂S₃ and graphene was carried out,and the photocatalytic activity was evaluated by the degradation of glyphosate under visible light irradiation.The morphology,structure,crystal phase,luminescence and photoelectrochemical properties of Mo Se₂/Bi VO₄,Cu S/Bi VO₄,In₂S₃/Bi VO₄and Bi₂S₃/RGO/Bi VO₄photocatalysts were analyzed using scanning electron microscopy（SEM）,X-ray diffraction（XRD）,X-ray photoelectron spectroscopy（XPS）,fluorescence spectroscopy（PL）,photocurrent test（I-t）and electrochemical impedance test（EIS）.At the same time,the photocatalytic performance of the samples was tested by the glyphosate degradation under the visible light illumination.The results are as follows:（1）The Mo Se₂/Bi VO₄photocatalysts were successfully synthesized by a two-step hydrothermal method.XRD results showed that Bi VO₄ and Mo Se₂ were the monoclinic and hexagonal crystal phases,respectively.SEM results showed that the diameter and the length of peanut-Bi VO₄ was 0.5-2μm and 1-3μm,respectively.The photocatalytic degradation results showed that 0.15Mo Se₂/Bi VO₄catalyst exhibited the highest photocatalytic activity and the degradation rate of glyphosate was 86%after 3 h visible-light irradiation,which was 5.6 times and 2.2 times of pure Mo Se₂and Bi VO₄,respectively.The XRD and XPS results of 0.15Mo Se₂/Bi VO₄photocatalyst after four cycle experiment showed that the 0.15Mo Se₂/Bi VO₄photocatalyst possessed good stability and photo-corrosion resistance.The radical trapping experiment results showed that the holes（h⁺）and electrons（e^-）played an important role during the photocatalytic degradation of glyphosate.（2）The p-Cu S/n-Bi VO₄ p-n heterojunction catalysts were prepared by two-step hydrothermal method using Bi（NO₃）₃·5H₂O,NH₄VO₃,Cu（NO₃）₂·3H₂O and thiourea as raw materials.DRS results showed that the band gap energies of Cu S and Bi VO₄were 1.68 e V and 2.40 e V,respectively,which exhibited an excellent visible light absorption performance,and the doped amount of Cu S had an important influence on the photocatalytic performance of the samples.When the amount of Cu S was 8%,the degradation efficiency was 98%under the visible light irradiation for 180 min,which was 3.8 times than that of Bi VO₄.Owing to the conformation of the p-Cu S/n-Bi VO₄p-n heterojunctions,an internal electric field with the direction from n-type Bi VO₄ to p-type Cu S was formed and accelerated the effective separation and transfer of photogenerated charge carriers.（3）The tetragonal phase In₂S₃modified Bi VO₄ were synthesized by a two-step hydrothermal method.The photocatalytic degradation results showed that the degradation efficiency of 15%In₂S₃/Bi VO₄ catalyst exhibited better than Bi VO₄,In₂S₃and other In₂S₃/Bi VO₄ catalysts with different In₂S₃ contents.The PL,photocurrent and EIS results indicated that 15%In₂S₃/Bi VO₄ catalyst had excellent photoelectrochemical properties,further demonstrating the effective separation of photogenerated electrons and holes due to the formation of In₂S₃/Bi VO₄heterojunctions.（4）The Z-scheme Bi₂S₃/RGO/Bi VO₄ heterojunctions were prepared by one-pot hydrothermal method and anion exchange method,and the amouts of the electron mediator reduced graphene oxide（RGO）and sodium sulfide were optimized.The photocatalytic degradation results showed that the photocatalytic degradation rate of glyphosate presented an inverted U-shape.When the amounts of graphene oxide and sodium sulfide were 0.5 wt.%and 0.10 mmol,respectively,the photocatalytic activity of Bi₂S₃/RGO/Bi VO₄ was the highest.The photogenerated electrons in the conduction band of Bi VO₄ transferred via electron mediator RGO to recombine with the photogenerated holes of Bi₂S₃ at the interface,resulting in the accumulation of the holes with strong oxidation capalibity of Bi VO₄ and the electrons with strong reduction capalibity of Bi₂S₃.Therefore,the degradation efficiency of glyphosate was enhanced,indicating that the photocatalytic activity was improved.