Removal Of Antibiotic In Water Via Peroxymonosulfate Activation With Bimetal-organic Frameworks Derived Catalysts

The control of antibiotic pollutants in water is a hot topic in the field of environment.Advanced oxidation technology based on persulfate can effectively remove refractory organic pollutants in water.Catalysts are the key factors affecting the catalytic oxidation efficiency of persulfate.Therefore,the development of catalysts with high activity and easy recovery is of great significance.This paper did optimization to the metal organic framework materials（MOFs）as precursors with high specific surface area,easy-control structure,the synthetic route was developed with pre-synthetic modification and post-synthetic modification,the key parameters were optimized,in that the bimetal organic frameworks-derived catalysts were prepared.The structure-activity relationship between structure and catalytic efficiency was further analyzed through the structure characterization and theory calculation,which clarified the mechanism of bimetal coordination and active species generated path.The work provided the theory instruction of preparation and application of the efficient and easy-recycle catalysts.The following work was carried out based on the catalytic degradation of typical antibiotic sulfamethazine（SMT）in the paper.Four types of MOFs,ZIF-67,ZIF-8,MOF-74 and MIL-88A,are tested from the following three aspects,the compatibility of different metals,specific surface area and the activation of PMS to degrade SMT.ZIF-67,ZIF-8 and MOF-74 have a wonderful compatibility of different metals,metal nodes can be grew in accordance with the setting percentage.ZIF-67 and MOF-74 have large specific surface area,which is conducive to the distribution of active sites.ZIF-67 and MOF-74 have better activation performance in the pre-experiment of SMT degradation by PMS.Based on the above,ZIF-67 and MOF-74 were selected as precursors for the next step of material synthesis.The cobalt-based hollow bimetal sulfide polyhedron material(M_xCo_3-xS₄)was prepared by sulfurization reaction and subsequent calcination with ZIF-67 as precursor.The high density active site distribution of the hollow structure and the synergistic effect of bimetals make the catalyst show excellent catalytic activity and M_xCo_3-xS₄ can effectively activate PMS to degrade SMT.The k value of the first-order reaction kinetic constant reached 0.363 min^-1 at the highest,which was 3-4 times higher than the similar reports.Quenching experiments and electron spin resonance spectra showed that sulfate radical(SO₄^·-),superoxide radical(O₂^·-)and singlet oxygen（¹O₂）were the main reactive species involved in the degradation reaction.The XPS characterization and theoretical calculation reveal the bimetal synergistic effect from two aspects:the introduction of substitution metals accelerates the electronic recycling,besides,the adsorption energy between the catalysts and PMS was increased,and the positive charge density of metal species on the catalysts got larger,thus facilitating the binding between the catalytic active center and PMS.The magnetic material（Fe_xMn_y-z NCNT）of in-situ N-doped carbon nanotubes encapsulating metal nanoparticles was prepared by means of calcining reaction with different amounts of melamine.The saturated magnetization intensity was 0.23 emu/g,which was convenient for recycling.The magnetic material can activate PMS to degrade SMT,and the removal rate is 97.0%within 30 min,and the TOC removal rate reaches 48.8%.The SEM images of the catalysts are used to analyze the main roles of iron and manganese in the preparation of magnetic materials.Iron promotes the stacking of carbon layers and serves as the main encapsulated metal,while manganese promotes the growth and extension of carbon nanotubes.The hollow nitrogen-doped carbon nanotubes（Mn-100NCNT）was produced in the same growth environment of Fe Mn-100NCNT,which laid the foundation for the study of free radical and non-free radical initiation mechanisms.The active species quenching experiment and EPR results show that the active species in the Mn-100NCNT catalytic system include only¹O₂ and SO₄^·-,while the active species in the Fe Mn-100NCNT catalytic system are more abundant including ¹O₂,SO₄^·-,·OH and O₂^·-.It is proved that metals mainly initiate free radical reaction pathways,and nitrogen-doped carbon nanotubes initiate non-free radical pathways.The catalysts after the reaction are easy to be magnetically recovered and thermally regenerated.It can still maintain excellent PMS activation function after repeated use,and the removal rate of SMT can reach 90.2%within 20minutes.In summary,this paper optimized the bimetallic ZIF-67 and MOF-74 as precursors,and independently designed and prepared the composite catalysts with hollow structured bimetallic sulfide polyhedron and carbon nanotube encapsulated metal nanoparticles.Taking activated PMS as the model reaction for catalytic degradation of SMT,the two optimized catalysts Mn_0.3Co_2.7S₄ and Fe Mn-100NCNT showed significant advantages of high activity and easy recovery.It revealed key mechanisms such as accelerating the electron cycle,enhancing the specific binding between PMS and catalysts,and initiating free radical and non-free radical pathways,providing scientific guidance for the research and development of highly active and easily recoverable catalysts.