Removal Of Organic Pollutants By Activated Persulfate With Bimetallic MOF And Its Composites

In recent years,the water pollution with antibiotics and organic dyes as the main pollution sources has become increasingly serious.The massive discharge of various antibiotics and organic dye wastewater has led to the enrichment of drug resistance genes（ARGs）in water environment and the increase of cancer risk.Advanced oxidation process based on sulfate radical（SR-AOPs）,as a new pollution treatment method,has attracted extensive attention.SR-AOPs have the advantages of green,convenient and efficient,but lack of effective activation methods.MOFs materials have large specific surface area,rich metal active sites and high adjustability,and show excellent properties in SR-AOPs system.Compared with single metal MOFs,bimetallic MOFs can realize diversified functions,possess higher stability,and have stronger activation performance for peroxymonosulfate（PMS）.At present,the research on the application of bimetallic MOFs in SR-AOPs system mostly focuses on common transition metals such as Fe,Co,Cu and Ni,and the relevant catalytic mechanism is not perfect.Based on the above research status,this paper finds another way to carry out the research on new bimetallic MOFs with V,Nb and Co as the main metal elements.It is applied to SR-AOPs system to remove organic pollutants,and the following main results and conclusions are obtained:（1）Mixing metals de novo method was combined with stringent solvothermal conditions to synthesize macaroon-like Nb Co-MOF catalyst.Nb Co-MOF catalyst prepared with different atom ratios and growth time presented various morphology,structure,performance,and distinctive MTV-MOFs growth law which were confirmed by SEM,TEM,EDS,XRD,FTIR,raman spectra and UV-vis spectra.Besides,the removal performance test of tetracycline（TC）further determined the optimal conditions for the catalytic activation of PMS.Furthermore,the effects of anions(Cl^-,NO₃^-,HCO₃^-,and C₂O₄^2-)on Nb Co-MOF/PMS system were explored which were proved very limited.Particularly,the Co²⁺/Co³⁺cycle combining with the Nb⁴⁺/Nb⁵⁺cycle for PMS activation were verified by XPS.EPR and quenching experiment results indicated exists non-radical pathway（¹O₂）,but radical pathways are dominant（SO₄·^-O₂·^-,and·OH）.In terms of reusability,the TC removal rate exhibited no significant reduce after three times run（>99.5%）.Furthermore,Nb Co-MOF exhibited excellent decomposing ability towards methylene blue（MB）,tylosin tartrate（TT）and rhodamine B（Rh B）with the removal rate reaching to 100%,98.4%and 99.7%in 30 min respectively and also maintained good performance in actual water environment.（2）The synergistic effect between transition metal active sites and ion valence cycle rate in the catalyst have a significant impact on the catalytic activation efficiency of PMS.In this work,VCo-MOF was grown in situ on the surface of MXene by solvothermal method to prepare VCo-MOF@Ti₃C₂T_x composite catalyst.SEM,TEM,AFM,XRD,BET and FTIR tests systematically proved the successful preparation of the VCo-MOF@Ti₃C₂T_x,and alter MXene dosage caused the change of catalyst morphology and structure.Response surface methodology was used to optimize the experimental conditions to achieve the best catalytic performance.Only 5 mg VCo-MOF@Ti₃C₂T_x-4 could effectively activate PMS to remove96.14%ciprofloxacin（CIP,20 mg/L）.In addition,the fluorescence spectrum test also verified the effective removal of CIP.The possible reaction mechanism of VCo-MOF@Ti₃C₂T_x-4/PMS system was analyzed by XPS,contact angle,EPR test and free radical quenching experiment.The construction of efficient V-Co-Ti ternary system,as well as the excellent hydrophilicity and PMS adsorption capacity of Ti₃C₂T_x carrier,have greatly improved the removal efficiency of ciprofloxacin.At the same time,the generation of unique superoxide radical path further strengthens the oxidation capacity of VCo-MOF@Ti₃C₂T_x-4/PMS system.