Degradation Efficacy And Reaction Mechanism Of Iohexol By Activation Of Sulfite With Copper Oxides

Iodinated X-ray contrast media is frequently detected in the aquatic environment.Iodinated X-ray contrast media,as an important precursor of toxic iodinated disinfection by-products,is refractory in conventional sewage treatment process.Recently,advanced oxidation processes based on sulfate radical(SO₄^?-)have gained researchers’ attention regarding its high redox potential（2.5-3.1 V）,selectivity and reactivity towards organic contaminants.The precursors of SO₄^?-production are mainly persulfate and sulfite.Activation of sulfite is proposed for generating SO₄^?-due to the fact that sulfite is cost-effective,environmentally friendly and less toxic.At present,the sulfite activation methods are not effective for neutral conditions.Therefore,this paper proposed that copper oxide can activate sulfite auto-oxidation system under neutral conditions for iodinated X-ray contrast media（iohexol）degradation.Firstly,comparison of iohexol degradation efficiency by sulfite autoxidation activated with different metal oxides（Co₃O₄,CoO,α-Fe₂O₃,γ-Fe₂O₃,CuO and Cu₂O）indicates that CuO and Cu₂O with lower toxicity are efficient activators and removal efficiencies of over 90% can be obtained at pH 8.0.Secondly,in order to further enhance the activation efficiency and make it easy for separation and reuse for copper oxides,CuFe₂O₄ material(CuFe₂O_4MOF)prepared by MOF template method was proposed.The characterization of CuFe₂O_4MOFby SEM,TG,BET,XRD and VSM shows that CuFe₂O_4MOFis a rod-like material with magnetic,large specific surface area and large pore size.The removal efficiency of ⁸0% by CuFe₂O_4MOFactivated sulfite system for iohexol degradation can be obtained at pH 8.0 within 10 minutes.Effect of different parameters,radical identification,reaction mechanism,metal oxides stability and reusability and effect of real water matrixes by CuO/Cu₂O and CuFe₂O_4MOFactivated sulfite systems were studied.The main results are as follows: nitrogen atmosphere can inhibit iohexol degradation in copper oxides/sulfite systems,suggesting that dissolved oxygen is the essential substance.Electron paramagnetic resonance（EPR）characterization and radical quenching experiment confirm that SO₄^?-is the active radicals in copper oxides/sulfite systems determined as.The negative effects of common anions（HCO₃^-,Cl^-）and humic acid on iohexol degradation in copper oxides/sulfite systems were investigated.Based on the effect of ionic strength,FTIR spectra,copper leaching and valence changes of CuO and Cu₂O before and after use,the type of interaction between sulfite and copper oxides which is inner-sphere interaction was clarified.The possible iohexol transformation pathways are inferred through the major transformation products during the iohexol degradation process.This study shows that copper oxides can be used as a highly effective activator in heterogeneous activation of sulfite auto-oxidation,and this method can provide a new way for the advanced oxidative process of organic pollutants in water.