Study On Preparation And Catalytic Mechanism Of Bismuth-enriched Halogenated Bismuth Oxide Magnetic Composite Photocatalyst

Ecological security is a significant component of national security and the basis of defense security,political safety and economic security.With the rapid development of society.It is imperative that something urgent should be done to protect the ecological environment because the ecological damage is becoming more and more serious.Quite obviously,the human demand for water is increasing gradually,and has caused a lot of problems that harm the water environment security.Water pollution,as a prominent problem,has posed a serious threat to human health.And among the many sewage treatment methods,photocatalytic technology has become a research hotspot due to its advantages of low energy consumption,mild reaction conditions and simple operation.In recent years,bismuth-based nano-semiconductor materials have become popular photocatalytic materials owing to their unique electronic structure and excellent absorption capacity of sunlight.However,conventional semiconductor photocatalysts are difficult to be separated and reused when they dispersed in liquid,which restricts its practical application seriously.For this reason,this paper takes Bi₅O₇I,Bi₃O₄Cl and Bi₄O₅Br₂ as photocatalysts and Mn_xZn_1-xFe₂O₄ and SrFe₁₂O₁₉ as magnetic substrates to prepare bismuth-enriched halogenated bismuth oxide magnetic composite photocatalyst with excellent photocatalytic performance and efficient physical recovery.The photocatalytic activity and kinetic characteristics were studied by photo-degradation of Rh B under the simulated sunlight irradiation,and the active components in the photocatalytic reaction system were identified by capturing experiments.Meanwhile,the magnetic properties of the photocatalyst were researched by means of vibrating magnetometer and the stability of the photocatalyst was investigated by cyclic experiment.In addition,the microstructure of the photocatalyst was characterized by XRD,XPS,SEM and TEM,and the pore characteristics were studied by aperture and specific surface area analyzer.On the basis of the above characterization,the crystal type,atomic spatial distribution,interface bonding mode and morphology of the photocatalyst were analyzed.In order to explore the photo-absorption characteristics of the catalyst and the migration state of photogenic carriers,the parameters of Uv-vis DRS,PL,EIS and I-t of the samples were tested.Finally,the photodegradate mechanism of pollutants by magnetic composite photocatalyst was elucidated.Bi₅O₇I/Mn_xZn_1-xFe₂O₄ and Bi₅O₇I/SrFe₁₂O₁₉ magnetic composite photocatalyst were prepared by hydrothermal-roasting method.Among them,the photocatalytic activity of 10%Mn_xZn_1-xFe₂O₄/Bi₅O₇I and 10%SrFe₁₂O₁₉/Bi₅O₇I in their respective experimental groups was the best,and the degradation rate of Rh B within 120 min reached 96.7%and 96.6%respectively,which was close to that of Bi₅O₇I(97.6%).Meanwhile,the results of microstructure and morphology analysis showed that Bi₅O₇I/Mn_xZn_1-xFe₂O₄ and Bi₅O₇I/SrFe₁₂O₁₉ heterojunction structures were formed in the prepared composite photocatalyst,respectively.Compared with Bi₅O₇I,although the specific surface area increased and the band gap width decreased,the conductivity and electron mobility decreased slightly of Bi₅O₇I/Mn_xZn_1-xFe₂O₄ and Bi₅O₇I/SrFe₁₂O₁₉composite photocatalyst.The cyclic experiments showed that Bi₅O₇I/Mn_xZn_1-xFe₂O₄and Bi₅O₇I/SrFe₁₂O₁₉ composite photocatalyst had better magnetic recovery performance and photocatalytic stability.Combined with the results of the free radical capture experiment,it can be concluded that the heterojunction formed in Bi₅O₇I/Mn_xZn_1-xFe₂O₄ and Bi₅O₇I/SrFe₁₂O₁₉ magnetic composite photocatalyst are all Z-scheme,and Rh B was degraded under the joint action of h⁺,·OH and?O₂^-.Two kinds of magnetic composite photocatalysts Bi₃O₄Cl/Mn_xZn_1-xFe₂O₄ and Bi₃O₄Cl/SrFe₁₂O₁₉ were synthesized by hydrothermal-roasting processing.The degradation rate of Rh B by 10%Bi₃O₄Cl/Mn_xZn_1-xFe₂O₄ was 99.5%within 100 min,and that by 20%SrFe₁₂O₁₉/Bi₃O₄Cl reached 99.7%within 80 min.The results indicated that the heterostructure of Bi₃O₄Cl/Mn_xZn_1-xFe₂O₄ and Bi₃O₄Cl/SrFe₁₂O₁₉ has been formed in the prepared magnetic composite photocatalyst.Meanwhile,the BET specific surface area of Bi₃O₄Cl/Mn_xZn_1-xFe₂O₄ and Bi₃O₄Cl/SrFe₁₂O₁₉ composite photocatalyst was greater than Bi₃O₄Cl.The magnetic recovery ratio of Bi₃O₄Cl/Mn_xZn_1-xFe₂O₄ and Bi₃O₄Cl/SrFe₁₂O₁₉ composite photocatalyst was 91.3%and 92.4%respectively,and the degradation rate of Rh B was still as high as 82.2%and 84.1%after five cycles.All the results presented that Bi₃O₄Cl/Mn_xZn_1-xFe₂O₄ and Bi₃O₄Cl/SrFe₁₂O₁₉ had great magnetic recovery and photocatalytic stability.In the end,Z-scheme heterostructure was formed in Bi₃O₄Cl/Mn_xZn_1-xFe₂O₄ and Bi₃O₄Cl/SrFe₁₂O₁₉ magnetic composite photocatalyst,and h⁺,·OH and?O₂^-.were all the active substances.Composite photocatalysts Bi₄O₅Br₂/Mn_xZn_1-xFe₂O₄ and Bi₄O₅Br₂/SrFe₁₂O₁₉ were prepared by microemulsion method,and the degradation rates of Rh B by7.5%Mn_xZn_1-xFe₂O₄/Bi₄O₅Br₂ and 5%SrFe₁₂O₁₉/Bi₄O₅Br₂were 99.4%and 99.5%respectively within 60 min,which were slightly better than Bi₄O₅Br₂(98.6%).According to the analysis,the prepared magnetic composite photocatalysts has generated type-?scheme Bi₄O₅Br₂/Mn_xZn_1-xFe₂O₄ and Bi₄O₅Br₂/SrFe₁₂O₁₉heterojunction structure.And the Rh B was degraded under the joint action of h⁺,and?O₂^-.Also,internal electric fields were formed in both Bi₄O₅Br₂/Mn_xZn_1-xFe₂O₄ and Bi₄O₅Br₂/SrFe₁₂O₁₉ heterojunction,and the lifetime of e^-and h⁺were increased under the traction of internal electric fields,which enhanced the photocatalytic activity of the magnetic composite photocatalyst.Meanwhile,the increased specific surface area of Bi₄O₅Br₂/Mn_xZn_1-xFe₂O₄ and Bi₄O₅Br₂/SrFe₁₂O₁₉ composite photocatalysts in comparison with Bi₄O₅Br₂is conducive to the adsorption of Rh B on the surface to promote photocatalytic degradation.And,the photocatalytic activity of Bi₄O₅Br₂/Mn_xZn_1-xFe₂O₄ and Bi₄O₅Br₂/SrFe₁₂O₁₉ is enhanced by the narrowing of band gap width,the reduction of photogenic carrier recombination rate,the increase of electrical conductivity and electron mobility.In addition,Bi₄O₅Br₂/Mn_xZn_1-xFe₂O₄ and Bi₄O₅Br₂/SrFe₁₂O₁₉ composite photocatalysts have excellent magnetic recovery performance and photocatalytic stability.