Preparation And Performance Of Nickel Magnetic Composite Bismuth-enriched Halogenated Bismuth Oxide Photocatalyst

Water is the source of all things and an indispensable condition for biological growth.But,with the rapid development of globalization and industrialization,the untreated wastewater containing a large amount of organic pollutants is discharged into the natural ecosystem without restraint,which greatly exceeds the self-purification capacity of water bodies,and has an impact on the ecological environment and human health.Caused serious impact and irreparable harm.Therefore,the removal and prevention of organic pollutants in water is imperative.Among the existing water pollution treatment technologies,semiconductor photocatalytic technology has great potential in eliminating environmental pollutants due to its advantages such as green safety,mild reaction conditions,and high efficiency.The bismuth-rich oxygen halide compound Bi_xO_yX_z（X=Cl,Br,I）is considered to be an emerging photocatalyst system due to its flexible layered structure and adjustable energy band structure.For the purpose of conduct a comprehensive analysis of bismuth-rich oxyhalides,this paper specially selected Bi₁₂O₁₅Cl₆,Bi₂₄O₃₁Br₁₀ and Bi₄O₅I₂ as three different levels of bismuth for specific research.At the same time,in order to effectively and simply recover the photocatalyst in the reaction system,to achieve the purpose of reusing and suppressing secondary pollution,this paper combines Bi₁₂O₁₅Cl₆,Bi₂₄O₃₁Br₁₀ and Bi₄O₅I₂ halogen oxy-polybismuth photocatalysts with the magnetic semiconductor material NiFe₂O₄,respectively.Finally obtain three kinds of different magnitude and excellent performance composite magnetic photocatalyst.The effect of mass ratio of NiFe₂O₄ on the photocatalytic performance of the composite was evaluated by simulating the degradation efficiency of Rh B solution under sunlight.XRD,SEM,TEM,XPS,BET,UV-Vis,PL,EIS,VSM and other testing methods were used to evaluate the microstructure and structure characteristics of the material,light absorption characteristics,photo-generated carrier recombination,transfer and separation efficiency and magnetic properties.Based on the above conclusions and combined with the results of the capture experiment,the photodegradation mechanism of the composite photocatalyst was comprehensively elucidated.Bi₁₂O₁₅Cl₆/NiFe₂O₄ was successfully synthesized by hydrothermal method,and the compound with a mass ratio of NiFe₂O₄ of 5%had the best photocatalytic activity.The degradation rate of Rh B reached 98.2%after 90min of irradiation,which was better than that of other samples.The structure and morphology test showed that the（312）crystal plane was the preferred orientation crystal plane for the experimentally prepared Bi₁₂O₁₅Cl₆/NiFe₂O₄ photocatalyst,and the NiFe₂O₄ inside the Bi₁₂O₁₅Cl₆/NiFe₂O₄composite was contained in the cluster structure of Bi₁₂O₁₅Cl₆ nanosheets in the form of particles.Through the direct combination of Bi₁₂O₁₅Cl₆ nanosheets and NiFe₂O₄nanoparticles to form a heterojunction structure,the recombination rate of photogenerated carriers can be reduced,the separation of photogenerated electron-hole pairs can be enhanced,and the charge transfer efficiency in the transport process can be improved.Photocatalytic mechanism studies have shown that the degradation of Rh B by Bi₁₂O₁₅Cl₆/NiFe₂O₄ does not conform to the type-Ⅱelectron transport mechanism but follows the Z-type heterojunction mechanism.During the photocatalytic reaction,superoxide radicals（·O₂^-）is the main active substance active in the reaction process,followed by holes（h⁺）,and finally hydroxyl radicals（·OH）.The Bi₂₄O₃₁Br₁₀/NiFe₂O₄ magnetic composite photocatalyst was successfully synthesized by hydrothermal method.When the mass ratio of NiFe₂O₄ is 10%,the photocatalytic performance of the Bi₂₄O₃₁Br₁₀/NiFe₂O₄ composite is the best.It can degrade 99.8%of Rh B in 40 minutes,which is better than other samples in the experimental group.Microscopic morphology and structure tests show that NiFe₂O₄was successfully introduced into the system and embedded in the Bi₂₄O₃₁Br₁₀nanosheets as particles.The heterojunction structure formed by the combination of two semiconductor materials can increase the specific surface area of the composite and broaden the absorption edge wavelength of the photocatalyst,reduce the band gap energy,promote the separation and transfer of photogenerated carriers,which is beneficial to the improvement of the photocatalytic performance of the material.The Bi₂₄O₃₁Br₁₀/NiFe₂O₄ composite photocatalyst has excellent magnetic properties and cycle stability and can still achieve a photocatalytic degradation efficiency of more than90%after five times of recovery.The separation and recombination process of photogenerated carriers in Bi₂₄O₃₁Br₁₀/NiFe₂O₄ composites follows the direct Z-scheme mechanism,and·O₂^-,h⁺,·OH participated in the reaction as an active substance.The Bi₄O₅I₂/NiFe₂O₄ composite was synthesized by a simple hydrothermal method.When the mass ratio of NiFe₂O₄ was 5%,the photocatalytic effect of the Bi₄O₅I₂/NiFe₂O₄ composite was the best.It can effectively degrade 99.4%of the Rh B solution in 70 minutes,which is better than pure Bi₄O₅I₂（94.3%）.The results show that Bi₄O₅I₂ nanosheets and NiFe₂O₄ nanoparticles have extensive contact and fusion at the micro level,resulting in an increase in the specific surface area of the composite.Bi₄O₅I₂/NiFe₂O₄ magnetic catalyst has good magnetic properties and repeatability stability,which can meet Separation and recovery requirements under the action of an external magnet.The Z-type heterojunction structure is constructed between Bi₄O₅I₂and NiFe₂O₄,which is conducive to the separation and transfer of photogenerated electrons and holes,reduces the possibility of recombination,and is conducive to speeding up photocatalysis.The process makes Rh B degrade under the combined action of·O₂^-,h⁺and·OH.