Preparation Of Bismuth Oxyhalides Composite Photocatalysts And Study On Their Photocatalytic Degradation Of Tetracycline Wastewater

Antibiotics are widely used in the medical industry,aquaculture,and other agricultural activities due to their ability to interfere with cell development.However,the variety of antibiotics and the lack of understanding of antibiotics among the population have led to the abuse of antibiotics.The extensive abuse of antibiotics in clinical medicine,aquaculture,and agriculture has caused the remnants of antibiotics in the environment.The long-term existence of antibiotics in the aquatic environment not only poses a serious threat to microorganisms,animals,plants and humans,but also destroys the ecological balance.The composition of antibiotic wastewater is complex and has certain biological toxicity.Traditional physical,biological or chemical methods are not effective in degrading antibiotics.As a new type of advanced oxidation process,photocatalytic oxidation has the characteristics of environmental protection,economy,and high efficiency.It has become a research hotspot for the treatment of antibiotic wastewater.As typical bismuth-based semiconductor materials,bismuth Oxyhalides[BiOX?X=Cl,Br,I?]have been widely studied in recent years.BiOX exhibit excellent photocatalytic activity due to their unique lamellar structure,appropriate band gap,and sensitive response to visible light.They have great potentials in the field of photocatalytic oxidation.However,BiOCl,BiOBr and BiOI of BiOX hierarchy have problems such as non-response to visible light,electron-hole pair recombination,and weak redox ability,which limit their practical applications.Therefore,the photocatalytic performances of pure BiOX were studied in this thesis,and they were modified by constructing heterojunction structure and adopting magnetic substrates.Pure BiOX,BiOX/BiOY binary composites and ternary Fe₃O₄/BiOX/BiOY hybrid photocatalysts were prepared by the solvothermal method.XRD,SEM,FT-IR,UV-Vis,XPS and other characterization methods were used to analyze the morphology,structure,light absorption and elemental composition of the prepared samples.Taking tetracycline?TC?as the target pollutant,the photocatalyst degradation of tetracycline wastewater was investigated under a simulated light source of xenon lamp.And we also explored the mechanism of their photocatalytic reactions.The main research contents of this thesis are as follows:?1?Microspheres of pure BiOCl?BiOBr and BiOI were prepared by the solvothermal method.UV-vis analysis showed that BiOCl can only absorb ultraviolet light,and BiOBr and BiOI have visible light response.The results of photocatalytic degradation showed that the order of photocatalytic activity was BiOBr>BiOCl>BiOI.This was mainly related to the utilization of light by photocatalyst and the position of its conduction band and valence band.Although BiOI has visible light response,its conduction band is too positive,its valence band is too negative,and its redox ability is relatively weak.Therefore,BiOI has the lowest photocatalytic activity.?2?BiOCl/BiOBr,BiOCl/BiOI and BiOBr/BiOI composite photocatalysts with different ratios were prepared by solvothermal method using Bi?NO₃?₃·5H₂O and NaX as the bismuth and halogen sources.XRD and XPS analysis results indicated the formation of heterojunction structures.UV-vis analysis showed that the photo-absorption range of the binary composite photocatalyst was increased and the utilization of visible light was increased.The prepared BiOCl/BiOBr,BiOCl/BiOI and BiOBr/BiOI composite photocatalysts all exhibited good photocatalytic properties.At the optimal compound ratio?Cl/Br=3:7,Cl/I=3:7,Br/I=5:5?,the degradation rate of tetracycline on the composite photocatalysts were 83%,84%,and 82%,respectively,which were better than pure BiOCl,BiOBr,and BiOI.The improvement of the photocatalytic activity of composites is mainly attributed to the formation of heterojunction structures,which promotes the separation of photogenerated carriers and avoids the recombination of photogenerated electrons and holes.?3?Fe₃O₄ nanoparticles and ternary Fe₃O₄/BiOCl/BiOBr,Fe₃O₄/BiOCl/BiOI and Fe₃O₄/BiOBr/BiOI composite photocatalysts were prepared by solvothermal method.The SEM characterizations showed that the Fe₃O₄ nanoparticles were loaded on the surface of the BiOX/BiOY microspheres under the effect of ultrasonic waves;the XPS analysis results also demonstrated the presence of Fe₃O₄ in the ternary composite photocatalysts.The introduction of Fe₃O₄ not only broadened the response range of the catalyst to visible light,but also effectively improved the separation efficiency of photogenerated electrons and holes.At the same time,the composite material showed good magnetic response and can be quickly separated and recovered under the action of an external magnetic field.The catalytic activity of ternary Fe₃O₄/BiOX/BiOY composite photocatalysts had been significantly improved compared with pure BiOX and binary BiOX/BiOY.Among them,the photocatalytic activity of Fe₃O₄/BiOCl/BiOI was the highest:the degradation rate of tetracycline can reach 87%after light irradiation for 80 minutes.In addition,the recycling experiments showed that the ternary Fe₃O₄/BiOX/BiOY composite photocatalysts exhibited good stability and recycling performance.After five cycles,their photocatalytic activities still maintained a relatively high level.