Preparation Of Visible-light-responsive Magnetic Fe₃O₄/BiOX?X=Br,I? Photocatalysts And Their Performance For RhB Degradation

Nowdays,energy shortages and environmental pollution are two serious problems which threaten the future development of human society.It's an important task to control environmental pollution and develop and use new clean energy.Synthetic dyes are one of the most common organic pollutants in water environment,and account for about 35%of the total discharge of industrial wastewater.About 80%of organic dyes belong to nitrogen-containing dyes which are resistant to biological degradation and result in high chromatism,high COD,high biological toxicity and other aquatic environment problems.Therefore,it is necessary to develop a reasonable and efficient process to remove dyes from wastewater.Photocatalysis technology has attracted much attention due to its green,environmental protection and low energy consumption.The core of photocatalysis technology is that semiconductor photocatalyst can degrade the dye molecules into non-toxic and harmless carbon dioxide,water and other small molecules under illumination.With the development of photocatalysis technology,it is found that if we want to use renewable solar energy,the band gap of semiconductor photocatalyst is moderate.The way of semiconductor recombination can not only maximize the use of visible light in solar energy,but also reduce the recombination rate of photogenerated electrons and holes.In recent years,a new type of nano photocatalyst Bi OX?x=BR,I?has attracted extensive attention of researchers.Because of its unique layered structure,good built-in electric field and excellent photocatalytic efficiency,it has become a research hotspot.However,the separation of nano catalysts still restricts the practical application of the photocatalysis technology.Therefore,it is our research goal to make the high activity nano photocatalyst magnetic,which can solve the problem of catalyst separation,at the same time,it can use solar energy efficiently and promote the application progress of photocatalysis technology.In this study,BiOBr was taken as the main research line,Fe₃O₄was selected as the magnetic material and the aim was to magnetize and enhance the activity of single component BiOBr.Firstly,binary composite photocatalytic material Fe₃O₄/BiOBr was synthesized to solve the problem of low activity and difficult separation of single component BiOBr.Then BiOBr/BiOI?3:1?was synthesized,which greatly improved the photocatalytic activity of BiOBr.To solve the separation problem of BiOBr/BiOI?3:1?with high photocatalytic activity,Fe₃O₄?co-precipitation?/BiOBr/BiOI was synthesized.In order to discuss the differences between Fe₃O₄ prepared by different methods as the magnetic material of magnetized BiOBr/BiOI?3:1?,ternary magnetic material Fe₃O₄?solvent thermal method?/BiOBr/BiOI was synthesized,the photocatalytic properties of two ternary magnetic materials were compared.The results confirmed that Fe₃O₄synthesized by co-precipitation method was more suitable as the magnetic material of magnetized BiOBr/BiOI?3:1?.The research contents are as follows:?1?Binary magnetic material Fe₃O₄?co-precipitation?/BiOBr was synthesized by two-step method.Firstly,Fe₃O₄ was synthesized by co-precipitation method,and then Fe₃O₄/BiOBr?the molar ratios were 3:1,2:1,3:2,2:2,2:3,1:2 and 1:3?was synthesized by solvothermal method.The effects of different Fe₃O₄contents on the properties of Fe₃O₄/BiOBr composites were studied by XRD,SEM,HR-TEM,EDS,XPS,Uv-vis,PL and BET.When the molar ratio of Fe₃O₄ and BiOBr was 0.5:1,Fe₃O₄ nanoparticles were evenly distributed on the surface of BiOBr petal-like sheet.The degradation rate of RhB by Fe₃O₄/BiOBr?0.5:1?was 99.6%under visible light for 140 min?82.3%for pure BiOBr?.Fe₃O₄/BiOBr?0.5:1?could be rapidly separated from water after 30s under a magnetic field.In addition,Fe₃O₄/BiOBr?0.5:1?owned good stability.After ten recycling experiments,the degradation activity of RhB decreased from99.6%to 90.1%.Finally,the degradation mechanism and pathway of RhB were studied by free radical capture experiments,semiconductor band theory and liquid chromatography mass spectrometry?LC-MS?analysis.?2?Binary composite photocatalyst BiOBr/BiOI was synthesized by one-step method.Binary compound BiOBr/BiOI?3:1,2:1,3:2,2:2,2:3,1:2 and 1:3?with different molar ratios were synthesized by one-step solvothermal method.The physical and chemical properties of binary composites BiOBr/BiOI with different molar ratios were studied by XRD,Raman,SEM,EDS,TEM,HR-TEM,BET,Uv-vis DRS and PL.When the molar ratio of BiOBr and BiOI was 3:1,they compounded to form a uniform 3D olive flower-like structure.BiOBr/BiOI?3:1?with uniform flower-like structure had the best degradation effect on RhB.The degradation rate of RhB reached 99.8%after 80 min under visible light,and the degradation kinetics constant K was 28 times that of pure BiOBr.This result was closely related to its uniform flower structure and large specific surface area(44.21 m².g^-1).Besides,the affecting factors?p H,NO₃^-,Cl^-and HCO₃^-?the photocatalytic performance of BiOBr/BiOI?3:1?were explored.In addition,the possible degradation mechanism was determined by free radical trapping experiment,EPR and semiconductor structure analysis.?3?Ternary magnetic photocatalyst Fe₃O₄?co-precipitation?/BiOBr/BiOI was synthesized by two-step method.The ternary magnetic Fe₃O₄/BiOBr/BiOI composite photocatalyst was synthesized by solvothermal method combining Fe₃O₄ synthesized by precipitation method and BiOBr/BiOI?3:1?.The effects of different molar ratios of Fe₃O₄?x=0.7,0.9,1.1,1.3 and 1.5?on the properties of ternary magnetic Fe₃O₄/BiOBr/BiOI?x:3:1?materials were studied by XRD,SEM,EDS,TEM,HR-TEM,XPS,BET,VSM,Uv-vis DRS and PL.Among them,Fe₃O₄/BiOBr/BiOI?1.1:3:1?had the best degradation ability on RhB.Compared with the previously synthesized binary magnetic composite Fe₃O₄/BiOBr?0.5:1?,the adsorption capacity and the first-order rate constant K were 2.6 and 1.5 times that of Fe₃O₄/BiOBr?0.5:1?,respectively.In addition,several factors?p H,HCO₃^-and NO₃^-?affecting the catalytic performance of Fe₃O₄/BiOBr/BiOI?1.1:3:1?were explored.After ten recycling experiments,the crystal structure,morphology and magnetic property of Fe₃O₄/BiOBr/BiOI?1.1:3:1?remained good,and the photocatalytic activity remained high.Finally,the photocatalytic degradation mechanism of RhB by Fe₃O₄/BiOBr/BiOI?1.1:3:1?was discussed.?4?TernarymagneticphotocatalystFe₃O₄?solvothermal method?/BiOBr/BiOI was synthesized by two-step method.In order to further explore the effect of Fe₃O₄ prepared by different methods as magnetic material on the properties of BiOBr/BiOI?3:1?composite.In this part,Fe₃O₄ synthesized by solvothermal method was compounded with BiOBr/BiOI?3:1?.The screened Fe₃O₄?solvothermal method?/BiOBr/BiOI?0.4:3:1?has obvious advantages over binary magnetic Fe₃O₄?co-precipitation?/BiOBr?0.5:1?in photocatalytic activity and adsorption capacity.However,compared with Fe₃O₄?co-precipitation?/BiOBr/BiOI?1.1:3:1?,the magnetic property,degradation activity and stability were weaker.The results show that Fe₃O₄ synthesized by co-precipitation method was more suitable for the magnetic material of BiOBr/BiOI?3:1?.