Degradation Of Tetracycline Antibiotics Through Activation Of Persulfate By MOF Derived Complex

Tetracycline antibiotics（TCs）（including tetracycline（TC）,oxytetracycline（OTC）and doxycycline（DOX））are a kind of common broad-spectrum antibiotics,which are widely used in animal husbandry,aquaculture and the treatment of human infectious diseases.However,the metabolic level of TCs in the body is limited.Most of the ingested TCs will be discharged from the body and re-enter the environment.Antibiotic wastewater from medicine and aquaculture will also be discharged into the water to pollute the water body.Excessive residues in the environment and a small amount of continuous intake of TCs can lead to a variety of adverse reactions such as liver injury,which also has an irreversible impact on the ecological community in the water.Therefore,it is urgent to find efficient solutions.Metal organic frameworks（MOFs）and their derivatives,as new porous materials,showed high reactivity in the field of catalysis.When it is used in the advanced oxidation process based on sulfate radical（SR-AOP）,it can effectively activate persulfate（PS）and remove pollutants from water.In this study,three MOF derived complexes were successfully prepared as catalysts,activated persulfate,and tetracycline antibiotics were used as target pollutants to study the degradation effect of antibiotic pollutants,explore the activation mechanism and possible active substances of PS,as well as the degradation pathway of pollutants.Firstly,MIL-88B-NH₂ was synthesized and Febased nitrogenous carbon material（Fe/NC）was prepared by pyrolysis at different temperatures to activate PS to remove OTC.Without adjusting p H,the removal rate of OTC was 89.18%when the dosage of catalyst was 0.2 g/L and the concentration of PS was 3 mmol/L.The sulfate radical(SO₄^·-)produced during its activation played a key role in the degradation of OTC.The Fe/NC material prepared at 900℃calcination temperature still maintained high catalytic activity after five times of reuse.Secondly,precursors of synthetic ZIF-67（cobalt nitrate and dimethyl imidazole）were hydrothermally and pyrolyzed with ginkgo biloba powder at high temperature to synthesize cobalt based nitrogen doped carbon material（Co/NBC）dispersed on ginkgo biloba biochar,and construct the reaction system of Co/NBC activated PS degradation of DOX.In Co/NBC,in addition to Co²⁺and Co³⁺provided by Co O and Co₃O₄ as active sites,pyrrole nitrogen and pyridine nitrogen were also formed as effective sites for activating PS to produce active substances.When the carbonization temperature was 800℃and the content of ZIF-67 was 10%,the reaction process can reach equilibrium within 30 minutes,and the removal rate of DOX was 93.45%.There were two reaction forms of free radical dominated by(SO₄^·-)and non-free radical dominated by singlet oxygen（¹O₂）in 10%Co/NBC-800/PS system.After five times of reuse,it still had a high degradation rate of DOX.Finally,nitrogen doped iron cobalt bimetallic MOF（FeCo/N-MOF）catalyst was synthesized by"one pot"hydrothermal method and applied to activate PS to degrade TC.Feand co bimetals in FeCo/N-MOF promoted the ion cycle and improved the degradation efficiency of the system.Under the conditions of no p H adjustment,catalyst dosage of 0.4 g/L and PS concentration of 5 mmol/L,TC can reach 99.28%degradation rate and mineralization rate of 67.33%within 60 minutes.When PS was5 mmol/L,the reaction stoichiometric efficiency（RSE）of PS can reach 6.13%.Superoxide radical（·O₂）dominated free radical pathway was dominant in FeCo/N-MOF/PS system.FeCo/N-MOF still had a high removal effect on TC after four cycle experiments.This study provides a new way for the application of MOF materials in water treatment and a new idea for the degradation of tetracycline antibiotics.