Preparation And Performance Study Of BiOX-system Visible-light Heterogeneous Photocatalysts

Nowadays,it is difficult for the earth to pay for the growing energy demand of mankind.Semiconductor photocatalysis,which has brought the dawn of mankinds,solve the environment and energy problems.However,the preparation of visible-light driven photocatalysis that can make full use of sunlight is a difficult problem in the area of photocatalysis.Bismuth oxyhalides BiOX?X=Cl,Br,I?is a novel V-VI-VII ternary semiconductor photocatalyst of which crystal belongs to tetragonal form and has a fluorochloride lead layer structure.Its excellent photocatalytic performance is due to:?1?the open layered structure and the indirect transition bandgap,which is beneficial to the separation and transfer of electrons-holes;?2?The lower band gap,(Eg_BiOCl=3.2e V,Eg_{Bi OBr}=2.7eV,Eg_BiOI=1.7eV).However,photocatalysis is a systematic project involving photogenerated charge,surface interface catalysis,and catalyst recovery.So far,none of the single semiconductors can complete the entire project independently.In this paper,BiOX as the object,by microstucture modulation,design solid solution and composite photocatalyst,to improve its visible light responsiveness.The morphology and structure of BiOX series composite photocatalysts were characterized by X-ray diffraction,scanning electron microscopy,infrared spectroscopy,N₂ physical adsorption-desorption X-ray photoelectron spectroscopy,and UV-visible diffuse reflection.And the photocatalytic degradation of methyl orange were carried out to evaluate their photocatalytic performance.Details is as follows.1.BiOBr as the research object,we regulate the microstructure of BiOBr by adjusting pH and solvent.The obtained BiOBr with different facets and dimension demonstrated diffurent reactivity toward decomposition of MO,which is used to evaluate their photocatalytic mechanism of the impact of microsructure.The results show that different dimensions have great influence on the photocatalytic performance of BiOBr,and the three-dimensional has higher specific surface than that of 2D.The different facets have great influence on the photocatalytic activity of BiOBr,and 110-BiOBr has higher of the surface area and open surface atomic characteristics,which for its visible light indirect sensitized degradation of dyes are of great help.2.BiOCl as the research object,the solid solution photocatalyst of BiOCl/Br was prepared in one step by using ethylene glycol/dodecyltrimethylammonium bromide?EG/DTAB?as the co-template.The results show that the BiOCl/Br solid solution obtained by DTAB/EG co-template method has a more obvious layered structure than that of prepared by solvothermal method.This may result in the formation of regular micelles due to the interaction of the EG/DTAB template,which is directed to the BiOCl lattice skeleton by strong coordination.So that the high exposure of{110}crystal face and promote the dissociation of graded microspheres.At the same time,the Br^-of DTAB will be inserted into the lattice of BiOCl forming the structure of solid solution,which reduce the bandgap and inhibit the recombination of electron hole.When the mole ratio of DTAB KCl is 0.75,the degrading rate of RhB was97.2%with 8 min.under visible light,and the degrading rate of MO was 83.6%with1 hour under visible light.3.Firstly,self-assembled"ultrasonic-stirring-cooling-heating"integrated reaction device was used to prepare GO,which is the method of ultrasonic assisted Hummers.BiOCl/Br-RGO and BiOCl/Br@RGO composites were prepared by one-step in situ growth method and two-step electrostatic self-assembly method respectively.The results show that BiOCl/Br/RGO composite photocatalyst can reduce the band gap of BiOCl and enhance the visible light absorption performance of BiOCl/Br solid solution.What's more,the composite of GO enhance the crystallinity of the BiOCl/Br solid solution.Effectively improve their photocatalytic performance.While,The photocatalytic activity of BiOCl/Br-RGO prepared by one-step in-situ growth method is better than that of BiOCl/Br RGO prepared by two-step electrostatic self-assembly.The degradation efficiency of MO is up to 99.7%at 26min,which may effectively reduce the number of defects in the composite system to improve the stability of the composite system.4.BiOI as the research object,through electrostatic self-assembly method to prepare TiO₂@BiOI composite photocatalyst,building p-n heterojunction structure.The results show that TiO₂@BiOI has a narrow band gap and higher specific surface area than TiO₂ and BiOI.At the same time,TiO₂@BiOI improves the aggregation of BiOI and greatly increases the visible light of photocatalyst catalytic performance.The interfacial contact between TiO₂ and BiOI is enhanced by electrostatic self-assembly method.This core-shell structure can form a large area of effective contact between the semiconductors.This is a prerequisite for ensuring the smooth migration and separation of the photocharged charge at the same time.What's more,wrapping BiOI with TiO₂ achieve mass production.The main work of this paper is to study the modification of BiOX catalyst and improve their photocatalytic activity.The photocatalytic performance of BiOX was improved from the aspects of crystal surface,dimension,solid solution and composite materials.The visible light response of BiOX was improved from the aspects of enhanced adsorption capacity and improved optical and electrical properties.