Preparation And Study Of Photocatalytic Activity Of Bismuth Oxyhalide Solid Solution

The increased massive emission of waste water and industrial waste with the development of industrial civilization and the burning of fossil fuels has an increasingly serious impact on the environment where we live in.Photocatalytic degradation,as a clean and efficient method,has been extensively studied to solve the problem.Titanium dioxide is the most extensively studied photocatalytic material,but its wide band gap makes it only absorb UV light for photocatalytic reactions.As a new type of photocatalysts,BiOX?X=Cl,Br,I?family has been discovered and researched in recent years.BiOI and BiOBr are potential photocatalysts for their narrow band gap that they have response to visible light.In this work,a one-step hydrothermal method is used to synthesize BiOI_xCl_1-x solid solutions by adjusting the ratios of chlorine source and iodine source in precursor.The phase structure,morphology,UV-visible absorption and photocatalytic properties of the BiOI_xCl_1-x solid solutions are characterized.The results show that the synthesized sample are a series of solid solutions instead of complexs.XRD patterns show that different main phase may dominate as x increase because of the huge differencnce between the radius of iodine atom and the chlorine atom.Photodegradation of Rhodamine B reveals that the BiOI_0.4Cl_0.6 solid solution holds the best photocatalytic performance.Under 60 min Xe lamp irradiation,80%RhB is degraded.And the band gap of the BiOI_0.4Cl_0.6 is about 2.31 eV.Subsequently,a series of BiOI_xBr_1-x solid solutions are synthesized by the same method.The XRD patterns show that the products are a series of solid solutions instead of two-phase composites,and the XRD characteristic peaks shifted regularly with the change of x.BiOI_0.3Br_0.7solid solution shows the best photocatalytic performance toward the degradation of Rhodamine B,98%RhB is degraded under 40 min Xe lamp irradiation,which is superior to the narrower band gap BiOI and wider band gap BiOBr monomer.The UV-visible absorption spectra proved the band width of x=0.3 sample is 2.36 eV,which is close to the BiOI_xCl_1-x solid solution system,and the mechanism insight is analyzed.BiOBr holds the highest photocatalytic activity among the three BiOX family.In order to improve its photocatalytic performance further,It was compounded with another photocatalyst Bi₂MoO₆ and purposed on formation of heterojuntion in between BiOBr and Bi₂MoO₆ by a two-step hydrothermal method.SEM result shows that BiOBr is nanospheres and Bi₂MoO₆ is nano-cake structures.A series of characterizations and testing confirm the formation of heterojunction.The photocatalytic performance of the composites is significantly enhanced.When the amount of Bi₂MoO₆ in composite is 20%,the composites show the best photocatalytic performance,83%RhB is degraded under 60 min visible light irradiation,which is due to the formation of the heterojunction.The photocatalytic efficiency of 20%Bi₂MoO₆/BiOI_0.3Br_0.7 reaches the most optimized value in our work,degrading 98%RhB under 50 min visible light irradiation.