The Performance And Mechanism For Photo-fenton Sulfonamide Antibiotics Decomposition By Magnetic MgFe₂O₄/MIL-88A Composites

In recent years,as the use of antibiotics has increased each year,more and more antibiotics are being discharged into the water environment through a variety of routes.As a major class of antibiotic drugs,sulfonamide antibiotics are frequently detected in the aquatic environment.Amongst them,sulfamethoxazole（SMX）has been listed by the United States Geological Survey as one of the 30 most common wastewater pollutants with half-lives of 85-100 days or more,making the removal of SMX a pressing issue.Photo-Fenton based advanced oxidation processes can produce many active species that break down pollutants into small molecules or even mineralize them completely,which has been widely used for the removal of difficult to degrade organic pollutants.Metal-organic skeleton materials（MOFs）are widely used in advanced oxidation process to remove antibiotics from water because of their abundant active sites,ultra-high specific surface area and diverse structures.However,the traditional powder photocatalysts face the problem of fast recombination of photo-generated carrier,and are often separated from aqueous solution by filtration,centrifugation,which is difficult to recover and easy to cause secondary pollution.To enhance the degradation performance of photocatalysts and improve the recovery of powder catalysts,this study combined the metal organic skeleton material（MOFs）with the magnetic material,using the photo-Fenton technology to degrade SMX,improve the degradation performance and at the same time give the material magnetism,so that it can achieve the effect of magnetic separation and recovery.The successful preparation of the materials was demonstrated by various characterization techniques,the optimal reaction conditions of the composites were explored,and finally the reaction mechanism was proposed.The main work of this paper is as follows:（1）The magnetic MgFe₂O₄ and MIL-88A materials were first prepared by solvothermal method,and then the magnetic materials were compounded with MOFs by the mechanical ball milling method to produce MgFe₂O₄/MIL-88A composites.The successful preparation of the materials was demonstrated by the characterization of MgFe₂O₄,MIL-88A and MgFe₂O₄/MIL-88A by powder X-ray diffraction,Fourier infrared spectroscopy,scanning electron microscopy,transmission electron microscopy,high power transmission electron microscopy,UV-Vis diffuse reflectance spectroscopy,X-ray photoelectron spectroscopy,specific surface area and zeta potential.And the prepared composites have good magnetic properties,which can achieve rapid separation and recovery from aqueous solutions.（2）The performance of MgFe₂O₄/MIL-88A photo-Fenton degradation of SMX was tested under low power visible light.The synergistic effect between the MF140M60（140:60 mass ratio of MgFe₂O₄ and MIL-88A）material,H₂O₂ and visible light in this system were confirmed by controlled experiments.The effects of different influencing factors such as different composite ratios,different solution initial p H,different catalyst dosages and different H₂O₂concentrations on their performance were systematically investigated.The results show that 0.4g/L MF140M60 with 2.94 mmol/L H₂O₂ can degrade 99.8%of SMX in 20 min at an initial p H with 350 m W low power visible light irradiation.The effects of different wavelength light sources,real sunlight,different anions and in real water were investigated,the MF140M60material showed excellent practical application capabilities.The recyclability of the material was tested and MF140M60 was able to maintain 100%degradation efficiency after 5 rounds of cycling,demonstrating its excellent stability.Broad-spectrum experiments confirmed its potential for practical applications,as well as speculating on the degradation pathway and toxicity of intermediates.（3）The reaction mechanism of MF140M60 photo-Fenton degradation of SMX was investigated by active matter capture,electron spin resonance analysis,fluorescence probe,photoluminescence spectroscopy,electrochemical impedance,transient photocurrent,homogeneous photo-Fenton,and Mottled-Schottky.The formation of a type II heterojunction between MgFe₂O₄ and MIL-88A was postulated and confirmed,explaining the superior degradability of the composite MF140M60 compared to the material alone.The main reactive species of the MF140M60/H₂O₂/light system were postulated to be·OH and ¹O₂.Finally,the reaction mechanism of the MF140M60/H₂O₂/light degradation of SMX was postulated.