Study On The Mechanism Of Photoassisted Fenton-like Degradation Of Antibiotics By MIL-53Fe-based Composites

With the development of technology and the improvement of people’s quality,health issues have become the primary concern of the people,and the concept of green and sustainable development involves all aspects of life.At present,the harm of organic pollutants to the water environment is becoming increasingly serious,posing a threat to human health.However,the commonly used water treatment technologies have more or less shortcomings and cannot effectively remove organic pollutants.Photocatalytic technology is an environmentally friendly water treatment technology that utilizes solar energy to efficiently remove pollutants,and has great potential in water environmental purification.Due to the large proportion of visible light in sunlight,photocatalysts with visible light response ability are more favored.The metal organic framework is a porous material with a simple structure and convenient preparation,which has the ability to respond to visible light,thus becoming the research focus of new photocatalysts.In this paper,MIL-53 Fe photocatalyst was prepared by solvothermal method,and its photocatalytic degradation performance was investigated using Tetracycline antibiotics（tetracycline hydrochloride and Oxytetracycline hydrochloride）.Titanium dioxide and Graphitic carbon nitride were used as UV and visible light responsive photocatalysts respectively to support MIL-53 Fe surface,and heterojunction was constructed to form MIL-53Fe/compound composites,and on this basis,they cooperated with Fenton like advanced oxidation technology.The synergistic Fenton like technology of composite materials and the mechanism of degradation of Tetracycline antibiotics under visible light assisted conditions were systematically explored.The research conclusion is as follows:（1）After constructing heterojunction with UV-responsive TiO₂,the morphology and structure of MIL-53 Fe itself did not change.However,as the molar ratio of Fe source and Ti source in MIL-53 Fe and TiO₂ increased from 1 : 1 to 1 : 4,the XRD diffraction peak of MIL-53 Fe in the composite decreased,indicating that some planes of MIL-53 Fe may be inhibited,affecting its crystallinity.The introduction of UV-responsive TiO₂ improves the degradation rate of tetracycline hydrochloride by a single MIL-53 Fe under visible light irradiation,and when the molar ratio of Fe source to Ti source is 1 : 2,the composite has the best degradation rate.This is because the introduction of TiO₂ can not only promote the separation and migration of photogenerated carriers,but also block the light,resulting in the degradation rate of tetracycline hydrochloride less than 1 : 2 when the molar ratio of Fe source to Ti source is 1 : 4.At the same time,the peak position of the composite material in the fluorescence spectrum has a significant blue shift,indicating that the survival time of the photogenerated e-/h+ in the material becomes longer.The MIL-53Fe@TiO₂/PMS system was constructed by synergistic Fenton-like technology under the assistance of visible light.The experimental results showed that the optimal addition amount of PMS in the system was 0.2 mmol,and the MIL-53Fe@TiO₂/PMS/Vis system made the degradation rate of tetracycline hydrochloride more than 70 % within 1 hour.The Fe element in the composite was analyzed by XPS.The analysis of Fe elements in composite by XPS indicates the recycling between Fe（II）/ Fe（III）and Fe（III）in the system,which is beneficial to the activation of PMS.The results of free radical capture experiment and EPR detection analysis showed that the main substances in the degradation of tetracycline hydrochloride by MIL-53Fe@TiO₂/ PMS/Vis system were photogenerated holes and sulfate radicals.（2）MIL-53Fe@g-C₃N₄ was prepared by introducing visible light responsive g-C₃N₄.XRD test results showed that the composite material had good crystallinity and the crystal structure of MIL-53 Fe did not change.The degradation rate of oxytetracycline hydrochloride by three different MIL-53 Fe and g-C₃N₄ composites was significantly higher than that of single MIL-53 Fe.Mott-Schottky and UV diffuse reflectance characterization results show that MIL-53 Fe and g-C₃N₄ have matching energy band positions.The optimum addition amount of PMS in MIL-53Fe@g-C₃N₄/PMS/Vis system is 0.1 mmol.MIL-53Fe@g-C₃N₄/PMS/Vis system has good photocatalytic degradation performance under different temperature,concentration,p H and anion conditions.Compared with MIL-53Fe@g-C₃N₄/PMS/Vis and MIL-53Fe@g-C₃N₄/H2O2/Vis systems,the degradation rate of oxytetracycline hydrochloride in MIL-53 Fe @g-C₃N₄/PMS/Vis system is higher.This is because PMS is easier to be activated than PS and the oxidation of sulfate radicals is stronger than that of hydroxyl radicals.The results of free radical capture experiment and EPR detection showed that hydroxyl radicals existed in the degradation of oxytetracycline hydrochloride in MIL-53Fe@g-C₃N₄/PMS/Vis system,but photogenerated holes and sulfate radicals played a key role.The synergistic activation of PMS by photogenerated electrons and transition metal Fe under visible light accelerated the degradation of oxytetracycline hydrochloride,and the degradation rate of oxytetracycline hydrochloride was 32 times higher than that of single MIL-53 Fe.