Biochar-Fe-Mn Oxide Composite Material As Persulfate Activator For The Degradation Of Tetracycline

Antibiotics are widely used in the medical treatment of microbial infectious diseases,and are also one of the additives to promote animal growth.Tetracycline（TC）,as the second most widely used antibiotic in the world,is often used in human and animal diseases and as an additive to promote animal growth.In recent years,advanced oxidation techniques（AOPs）have been widely used to remove refractory organic pollutants.Biochar,a renewable resource,has good economic and environmental benefits.It is mainly prepared from crop residues,wood biomass,animal litter,and solid waste by thermochemical methods.Due to its rich surface functional groups,porous structure and high specific surface area,biochar can be used as a persulfate（PS）activator in AOPs.In this study,the dipping method and co-pyrolysis technology were used to combine the transition metals iron（Fe）and manganese（Mn）with biochar to prepare biochar-Fe-Mn oxide composite material（MMBC）,and used MMBC to activate PS to degrade TC.The specific research contents are as follows:（1）Biochar-Fe-Mn oxide composite material with different Mn doping amount（BC,MBC,MMBC-5 and MMBC-10）and biochar-Fe-Mn oxide composite material with different pyrolysis conditions（MMBC-900-2h（MMBC-10）,MMBC-700-2h,MMBC-500-2h,MMBC-900-1.5h and MMBC-900-1h）were prepared by dipping method.The surface morphology,functional groups,elements and other properties of the prepared material were analyzed by scanning electron microscope-energy spectroscopy（SEM-EDS）,x-ray diffractometer（XRD）,Raman spectroscopy（Raman）and other methods.Fe and Mn were attached to the surface of biochar in the form of metal oxides Mn Fe₂O₄,Mn₃O₄ and Fe₂O₃.The introduction of Fe reduced the specific surface area（SSA）of biochar,but SSA increased with the increase of Mn doping.After the introduction of Fe and Mn in BC,the material formed a layered porous structure composed of micropores and mesopores,w hich was conducive to promoting the transport of pollutants in the catalyst.The oxygen-containing functional groups（metal-O,O-H,C-O-C,etc.）in MMBC were affected by the pyrolysis temperature and Mn doping amount,and the content was higher under the c onditions of higher pyrolysis temperature and high concentration Mn doping.（2）The performance of prepared materials as a PS activator to degrade TC was investigated.The performance of biochar-Fe-Mn oxide composite material activated PS to degrade TC was affected by the introduction of metal Fe and Mn,pyrolysis conditions（pyrolysis temperature and residence time）.MMBC-10,obtained by pyrolysis of bamboo immersed with 0.01 M KMn O₄and then pyrolyzed at 900℃ for2 h,showed the best removal of TC and the removal rate reached 93.2%.（3）Electron spin resonance（ESR）and quenching results indicated that SO ₄^·-and·OH were produced in the MMBC-PS system,and the main free radical was·OH.In addition,the results of linear sweep voltammetry（LSV）proved t hat MMBC was highly conductive and the existence of electron transport in the degradation.Surface oxygen-containing functional groups,the defect structure of the material and the iron-manganese oxide were sites of MMBC to activate PS.（4）After 4 catalytic experiments,the removal rate of TC by MMBC-PS system was still above 75%,indicating that MMBC has reusability and stability.In addition,the removal rate of TC by the MMBC-PS system in real water was over 80%,indicating that the MMBC-PS system can be used in the actual antibiotic wastewater treatment process.It was worth mentioning that MMBC has excellent magnetic properties and can be removed from the water environment using magnets without causing secondary pollution to the environment.