Preparation And Photocatalytic Performance Of BiOBr Based Semiconductor Composite Materials

With the rapid development of the economy,a large amount of organic waste liquid has been discharged into the environment,enriching in the organism,this has posed a significant threat to human health and ecological environment.Photocatalytic oxidation technology has become one of the widely used wastewater treatment technologies due to its advantages of high efficiency,green and pollution-free.As a new bismuth-based semiconductor material,bismuth bromide oxide（BiOBr）has been proven to have excellent photocatalytic activity under visible light excitation because of its green and non-toxic,suitable band gap,and simple preparation method.However,the disadvantages of BiOBr are a narrow visible light absorption range,low carrier separation efficiency,weak redox ability,and limited active species in the system.In order to the above issues,three BiOBr based composite photocatalysts,BiOBr/reduced graphene oxide（r GO）,g-C₃N₄/BiOBr and Cu₂O/BiOBr S-scheme heterojunction,were prepared and applied to dye degradation in water environment,providing a new idea for the treatment of organic waste liquid.The specific research content is as follows:（1）Reduced graphene oxide with excellent conductivity can be as electron transfer channels,promoting the separation of electrons and holes in photocatalysts.The r GO/BiOBr catalyst was synthesized by hydrothermal method.Explored the effect of hydrothermal time and the amount of r GO on the photocatalytic performance.The introduction of r GO improves the absorption of visible light and carrier separation of BiOBr.When the load of r GO was0.75%,the 0.75%r GO/BiOBr composite catalyst exhibited the highest photocatalytic degradation performance for methylene blue,the degradation efficiency was 90.67%under visible light irradiation within 90 min,the photocatalytic reaction rate k was 0.0227 min^-1,which was 1.32 times that of BiOBr.（2）The S-scheme heterojunction with band matching can promote the separation of electrons and holes,preserve the oxidation and reduction properties,and improve photocatalytic efficiency.The g-C₃N₄/BiOBr S-scheme heterojunction was synthesized by calcination and hydrothermal methods.The formation of S-scheme heterojunctions caused the CB position of the reducing semiconductor g-C₃N₄ to be sufficiently negative（-0.94 V）,and the VB position of the oxidizing semiconductor BiOBr to be sufficiently positive（0.33V）.The strong redox quality of g-C₃N₄/BiOBr is reserved and the problems of narrow visible light absorption range and low carrier separation efficiency are solved.When the mass fraction of g-C₃N₄ in BiOBr was 60%,the 60%g-C₃N₄/BiOBr composite catalyst exhibits the highest photocatalytic degradation performance for MB,the degradation efficiency was 90.77%under visible light irradiation within 90 min,the photocatalytic reaction rate k was 0.0269min^-1,which was 1.56 times that of BiOBr.（3）Cu₂O is a reducing semiconductor and Fenton-like catalyst,which can generate（·OH）with H₂O₂.The Cu₂O/BiOBr was synthesized using the chemical bath coprecipitation method.The Cu₂O/BiOBr S-scheme heterojunction and photo-Fenton system improves the redox ability of BiOBr,and increases the concentration of active species in the system further,resulting in efficient degradation of MB.When the mass fraction of Cu₂O in BiOBr was 15%,the 15%Cu₂O/BiOBr composite catalyst exhibited the highest photocatalytic degradation performance for MB,the degradation efficiency reached 98.30%at the catalyst dosage of 0.5g L^-1 within 50 min of visible light irradiation,the photocatalytic reaction rate k was 0.0787min^-1,which is 3.37 times that of BiOBr.The catalyst showed excellent photodegradation performance for MB in the range of p H=4～10.In addition,the photocatalytic activity was little affected by different anions(H₂PO₄^-,Cl^-,NO₃^-,SO₄^2-)and water quality（deionized water,tap water,lake water and river water）.And the catalyst had excellent photocatalytic degradation performance for other single and mixed organic pollutants.After four cycles,the photocatalytic efficiency decreased from 98.30%to 60.10%.the degradation efficiency of MB by the catalyst increased to 89.98%after the glucose reduction method,indicating that the composite catalyst has excellent cyclic regeneration performance.