Degradation Of Iopamidol By Fes Catalyzed Peroxymonosulfate:Surface Reaction Mechanism And Pathway Analysis

Iodinated X-ray Contrast Medias(ICM)is used to enhance the imaging of organs such as blood vessels,soft tissues and internal organs during diagnostic procedures.Due to its chemical stability and biological inertness,ICM is frequently detected in various water bodies after excretion.ICM is also the main precursor of iodinated disinfection by-products(I-DBPs)formation.Therefore,the residue and transformation of ICM has attracted a lot of attention.In this paper,the non-ionic ICM-iopamidol(IPM)was selected as the object pollutant,a heterogeneous ferrous sulfide(FeS)/peroxymonosulfate(PMS)catalytic system was constructed to degrade IPM,and compared with that of homogeneous Fe(Ⅱ)/PMS,the surf’ce catalytic reaction mechanism of FeS was investigated.The study will provide some reference for the application of sulfur-containing metal minerals in controlling organics pollutanted water.The contents of the paper are as follows:(1)Compared with Fe(Ⅱ)/PMS,heterogeneous FeS/PMS is more conducive to the degradation of IPM.Under the experimental conditions:IPM concentration 10 μmol/L,500 r/min,initial pH of 6.5,25℃,FeS dosage 0.06 g/L,PMS concentration 0.6 mmol/L,IPM degradation achieved 92.8%in 30 min,in the FeS/PMS system.The degradation process conformed to the first-order reaction kinetics,with the reaction kinetic constant k of 8.36×10-2 min-1(R2>0.996).IPM degradation rate oin the[Fe(II)]=6 mg/L)/PMS system was 59.8%based on Ksp(FeS)=6×10-18,and 26.8%in FeS leachate([Fe(Ⅱ)]=0.28 mg/L)catalyzed PMS system under the same experimental conditions,.Which indicated that Fe(II)in solution and FeS surface Fe(Ⅱ)leaching were all involved in PMS activation.Increasing PMS concentration(0.1～1.2 mmol/L)and FeS dosage(0.02～0.12 g/L)were conducive to IPM degradation.IPM degradation in FeS/PMS and Fe(Ⅱ)/PMS systems all decreased with initial pH(3.0～11.0).However,FeS/PMS maintained higher catalytic activity in the range of pH 3～6.5.(2)The influence of water quality factors showed that:Cl-showed a slight inhibitory effect on FeS/PMS degrading IPM,and the inhibitory effect was almost the same at concentrations of 3 and 5 mmol/L.In the Fe(II)/PMS system,the inhibitory effect enhanced with Clconcentration(0～5 mmol/L).HCO3-inhibited IPM degradation in FeS/PMS and Fe(II)/PMS system,and the inhibitory effect increased with HCO3-concentration(0～5 mmol/L).Humic acid(HA)existed little effect.The degradation ability of FeS/PMS on IPM in sewage plant effluent and lake water decreased,IPM degradation rate would increased unless more FeS and PMSwere added.Which indicated that FeS/PMS can be used for the removal of IPM in actual water.(3)The radical quenching,electron paramagnetic resonance(EPR),X-ray diffraction(XRD),X-ray photoelectron spectroscopy(XPS),and Fourier infrared(FTIR)before and after FeS reaction were exployed to investigate IPM degradation mechanism under FeS/PMS system.The results showed that SO4-·,·OH,1O2 and·O2-all contributes to IPM degradation.Fe(Ⅱ)-activated PMS on FeS surface is the main way to form active species,and sulfur S promotes the recycling of Fe(III)/Fe(II)as an electron donor.Experimental and and the calculation of radical contribution indicated that surface·OHads and SO4-·ads are the main pathways oxidatives for IPM degradation.Density functional calculation(DFT),HPLC/MS/MS analysis showed that IPM degradation pathways includes:side-chain amide hydrolysis and oxidation,dehydrogenation,deiodine and hydroxyl addition,a total of 10 intermediate products were generated.Ecostructural Active Software(ECOSAR)predictions showed the degradation products of IPM pose certain ecological risks.Compared with that of PMS(1.40 μg/L)and Fe(Ⅱ)/PMS(1.24 μg/L)systems,the formation of iodoform(CHI3)in FeS/PMS system was the least(0.74 μg/L).In the FeS/PMS/IPM system containing Cl-,seven chlorine-containing intermediates were generated However,they existed lower ecological risksthrough ECOSAR prediction.The results of the paper provide a theoretical basis and technical support for the wide application of advanced oxidation technology based on ferrous sulfide catalyzed persulfate.