Study On Preparation And Their Visible Photocatalytic Properties Of Bismuth Halide Heterojunction Nanomaterials

BiOX?X=Cl,Br,I?,as an economical and efficient photocatalyst,has attracted wide attention in energy conversion and environmental governance.The ability of absorbing visible light,the adsorption of pollutant,the separation and transmission efficiency of photogenerated electrons and holes could affect the photocatalytic efficiency of the photocatalysts.The construction of heterojunction can effectively improve the specific surface area of the photocatalyst and the separation efficiency of photogenerated electron and holes.In this paper,the development of photocatalytic technology and the research progress of BiOX had been reviewed.The photocatalytic activity of bismuth halide with three halogen atoms solid solution?BiOXs,X=Cl,Br and I?had improved by forming heterojunction with new semiconductor g-C₃N₄photocatalyst and traditional semiconductor TiO₂ photocatalyst.Here,BiOXs photocatalyst was synthesized by solvothermal method,and g-C₃N₄was prepared by thermal polymerization.Because of the surface inertia of g-C₃N₄,it is difficult to compound with other substances.Therefore,hydrogen peroxide was used to hydroxylate its surface to improve its surface activity.Then,a series of BiOXs and hydroxylated g-C₃N₄ heterojunctions?BiOXs/x%g-C₃N₄?OH?,x=0.5,1.0,1.5,2.0,5.0?were synthesized by the solvothermal method.The morphology and composition of the samples were characterized by X-ray diffraction?XRD?,Fourier transform infrared spectroscopy?FT-IR?,scanning electron microscopy?SEM?and X-ray photoelectron spectroscopy?XPS?.It was found that the samples were successfully prepared.The optical properties were characterized by ultraviolet-visible diffuse reflectance spectroscopy?DRS?and fluorescence spectroscopy?PL?.It was found that the band gap was improved after recombination,and the BiOXs/1.0%g-C₃N₄?OH?heterojunction exhibited the best separation efficiency of photogenerated carriers.The photocatalytic activity of the photocatalysts to degrading 20 mg/L methyl orange?MO?simulated pollutant was tested.It was found that BiOXs/1.0%g-C₃N₄?OH?displayed the highest degradation efficiency among the as-prepared samples and the degradation rate of BiOXs/1.0%g-C₃N₄?OH?reached 67%.Then,BiOXs and TiO₂ heterojunction photocatalysts?BiOXs/x%TiO₂,x=0.1,0.25,0.5,1.0,1.5,2.0?were in-situ composited by the solvothermal method.The morphologies of the samples were characterized by XRD,SEM,EDS and XPS.The corre photogenerated sponding results proved that the heterojunctions were successfully prepared.The results of DRS and PL exhibited that the band gaps of the composite samples decreased,and the fluorescence intensity of BiOXs/1.0%TiO₂ was lowest among the samples.BiOXs/1.0%TiO₂ exhibited the highest degradation efficiency towards 20 mg/L MO,15 mg/L bisphenol A?BPA?and 30 mg/L tetracycline?TET?simulated pollutants,and the degradation efficiency reached 92%,72%and 90%,respectively.BET,ESR analysis and free radical trapping experiments showed that the main active radicals during the process of photocatalytic degradation were photogenerated holes?h⁺?,then superoxide radicals?·O₂^-?,and then hydroxyl radicals?·OH?.The results suggested that the formation of heterojunction could improve the band gap,the separation efficiency of photogenerated electrons and holes,and the visible light catalytic activity.