The Synthesis Of MIL-53（Fe） Modified By Ag₃PO₄ Nanoparticles And Its Removal For Antibiotics

Environmental pollution has become a major issue concerning people’s livelihood with the rapid development of the economy.And the increasingly serious pollution has received extensive attention of global citizens.As persistent organic pollutants,antibiotics are considered to be a great threat to human health and aquatic ecosystems because they are easy to be accumulated but difficult to be degraded.In recent years,photocatalysis is viewed as one of the most desirable strategy due to its cost-effectiveness and high efficiency.Metal-organic frameworks（MOFs）,a novel type of crystalline porous materials with high surface area and adjustable pore structure,have attracted a lot of researchers in the field of photocatalysis.Among them,MIL-53（Fe）,one of earth-abundant Fe（III）-based MOF stands out among numerous MOFs due to its semiconductor properties,visible light response,low cost and environment-friendly nature.Nevertheless,the photocatalytic performance of pristine MIL-53（Fe）is still unsatisfied owing to the rapid internal recombination of electron-hole pairs.And coupling with other suitable semiconductors to fabricate MIL-53（Fe）-based heterojunctions have been proved a feasible strategy to improve the performance of MIL-53（Fe）,which can promote the charge separation and transfer effectively.In this study,Ag₃PO₄ is selected to be combined with MIL-53（Fe）,the specific research contents are listed as follows:Firstly,novel heterostructure photocatalysts consisted of MIL-53（Fe）and Ag₃PO₄were successfully developed through a simple in situ precipitation strategy in this work.The photocatalytic activities of the as-synthesized samples were assessed via multiple antibiotics degradation,including tetracycline（TC）,oxytetracycline（OTC）,chlortetracycline（CTC）and deoxytetracycline（DCL）.All the obtained Ag₃PO₄/MIL-53（Fe）composites exhibited much more superior photocatalytic activities than pure MIL-53（Fe）and Ag₃PO₄.Especially,the optimal composite with1:3 mass ratio of Ag₃PO₄:MIL-53（Fe）（APM-3）displayed the best photocatalytic activity,for which the removal of antibiotics was 93.72%（TC）,90.12%（OTC）,85.54%（CTC）and 91.74%（DCL）under visible light irradiation for 1 h,and the concentration of all pollutants is 20 mg L^-1.In addition,the photocatalytic efficiency of APM-3composite is much higher than the simple physical mixture of Ag₃PO₄ and MIL-53（Fe）,and APM-3 still has great potential in TC or other pollutants treatment even at a comparatively higher concentration.The results of repeated experiments demonstrated that APM-3 has good photostability and recyclability after four recycling runs.Secondly,the prepared samples were characterized by XRD,FTIR,XPS,SEM,TEM,BET,TG,UV-vis DRS.The results confirmed the successful fabrication of Ag₃PO₄/MIL-53（Fe）.And Ag₃PO₄ nanoparticles were tightly adhered to the surface of MIL-53（Fe）.The TC degradation process was investigated by 3D EEMs and HPLC-MS was applied to further study the TC intermediates.Finally,the possible degradation pathway for TC was proposed.Thirdly,it was verified that·O₂^-,·OH and h⁺radicals all worked during the degradation process through trapping experiments and ESR measurement.The results of PL,PC and EIS test inferred that APM-3 composite has the highest photoinduced charge transfer and separation efficiency.Finally,based on the conduction band and valence band of Ag₃PO₄ and MIL-53（Fe）,a possible Z-scheme heterostructure model was proposed.In the Z-scheme system,the small reducible Ag nanoparticles functioned as a bridge for charge transportation.Powerful redox ability and effective separation of photoinduced carriers can be achieved in this Z-scheme heterostructure system.