Synthesis Of MIL-100(Fe)-based Composites And Their Performance For Photocatalytic Degradation Of Tetracycline

Tetracycline,an important broad-spectrum antibiotic,has been widely applied in medical health and animal breeding.However,due to the mass production and widespread use,the residue problems of tetracycline are becoming more and more serious around the world,highly threatening the ecological environment and human health.The environmental-friendly photocatalytic technology,which can convert solar energy into chemical energy for eliminating pollutants,has far-reaching development prospect and research significance in the field of environmental remediation.Recently,metal-organic frameworks(MOFs) has attracted much attention because of their excellent properties such as large surface areas,high porosity and tunable structure.Among them,MIL-100(Fe)with great visible-light response,low toxicity and hydrothermal stability exhibits potential application prospects for environmental photocatalysis.However,the separation efficiency of photo-generated electron-hole for MIL-100(Fe)is too low,resulting in weak photocatalytic activity.Therefore,MIL-100(Fe)was modified by compounding with semiconductors in this dissertation.Two photocatalysts with different heterostructures were prepared and applied for the removal of tetracycline in water.Not only the propertity and transformation path of intermediate products were analyzed,but also the photocatalytic performance and mechanisms of these two MIL-100(Fe)-based photocatalysts were explored.The main findings are summarized as follows:(1)The In₂S₃/MIL-100(Fe) photocatalyst was successfully synthesized by solvothermal method and In₂S₃ nanoparticles were proved to be wrapped on the surface of MIL-100(Fe)with the aid of multiple characterization technologies.Under visible light radiation,the rate constant of ISMIL-16 for photocatalytic degradation of tetracycline was 1.231×10-2 min^-1,which was respectively 3.9 and 2.3 times than that of MIL-100(Fe)and In₂S₃,indicating the enhanced photocatalytic activity of composites.Although ISMIL-16 had a smaller specific surface area and pore volume,the formed type-II heterojunction between MIL-100(Fe)and In₂S₃ effectively improved the separation efficiency of photogenerated carriers.As a result,the photocatalytic activity of composites was much enhanced.Based on the results of the trapping experiments,h⁺and·O₂^-played a dominant role in the photocatalytic degradation of tetracycline,while·OH has a small contribution.(2)Compared with the type-?heterojunction,the Z-scheme heterojunction can retain a higher redox potential,which is more conducive to the degradation of pollutants.In this study,a Z-scheme heterojunction photocatalyst was obtained by conbining MIL-100(Fe)and Bi₂WO₆ nanosheets.Under natural sunlight,BMIL-12exhibited the strongest photocatalytic activity and its rate constant for degradating tetracycline was 16.1 and 3.9 times than that of MIL-100(Fe)and Bi₂WO₆,respectively.Based on the experimental results,BMIL-12 is not only suitable for various environmental conditions,but also possessed good stability and repeatability.In addition,we found that the intermediate products of tetracycline belonged to humic acid-like substances and fulvic acid-like substances,which were continuously mineralized during photocatalytic degradation process,and their biotoxicity would become stronger and then be weaker.The introduction of MIL-100(Fe)not only effectively improved the specific surface area and light absorption capacity of the composites,but also formed a Z-scheme heterostructure with Bi₂WO₆ nanosheets,which promoted the spatial separation of photo-generated electrons and holes,resulting in stronger photocatalytic activity,and improved the redox capability of the composites,favoring the degradation of pollutants.