Efficiency And Mechanism Of Cathode/Fe³⁺/peroxymonosulfate On Iohexol Degradation

In recent years,the abuse of medicines and personal care productshas drawn increasing attentions.Contrast medias are commonly used medicines involved in interventional radiology operation,and iodinated contrast media（ICM）is the most commonly used contrast agents.As a representative of ICM,iohexol is widely used clinically for its advantages of less toxicity and good body tolerance.However,iohexol may act as a precursor,reacting with disinfectants to produce iodinated disinfection by-products.In this thesis,iohexol was used selected as the target contaminant and different Cathode/Ferric Iron/peroxymonosulfate systems were established,namely Pt-cathode/Fe³⁺/PMS system,Cu-cathode/Fe³⁺/PMS system,and Fe-cathode/Fe³⁺/PMS system for the degradation of iohexol.One aim of this study is to investigate whether non-inert electrodes are involved in the reactions and to find out the conditions of participation.The variation of iohexol,inorganic iodide,metal ion concentration,and PMS consumption were examined.With intermediates identification,electrochemical analysis and electrode materials characterization,he iohexol degradation pathways and reaction mechanisms in different systems were discussed.The main findings of this thesis are as follows:（1）The Pt-cathode/Fe³⁺/PMS,Cu-cathode/Fe³⁺/PMS and Fe-cathode/Fe³⁺/PMS systems are all efficient on iohexol degradation.The optimal reaction conditions of Pt-cathode/Fe³⁺/PMS system are determined to be 3.0 mM of PMS dosage,2.0 mM of Fe³⁺dosage,and 2.00mA/cm² of current density.The optimal reaction conditions of Cu-cathode/Fe³⁺/PMS system are determined to be 3.0 mM of PMS dosage,1.0 mM of Fe³⁺dosage,and 0.50 mA/cm² of current density.The optimal reaction conditions of Fe-cathode/Fe³⁺/PMS are determined to be6.0 mM of PMS dosage,1.0 mM of Fe³⁺dosage,and 1.00 mA/cm² of current density.（2）The non-inertial electrode participates in the reaction and contributes to iohexol degradation at low current density.The Cu-cathode has participated in Fe²⁺regeneration and PMS activation via both cathodic reduction and the surface Cu（0）-Cu（I）-Cu（II）-Cu（0）redox cycle in Cu-cathode/Fe³⁺/PMS process,and then enhances the iohexol degradation.In Fe-cathode/Fe³⁺/PMS system,the reaction between Fe-cathode and PMS promotes the iohexol degradation.（3）SO₄^·-and^·OH are involved in the iohexol degradation in the three systems.Both SO₄^·-and^·OH make important contributions to the degradation iohexol in Pt-cathode/Fe³⁺/PMS and Fe-cathode/Fe³⁺/PMS systems,while SO₄^·-plays a dominant role for the iohexol degradation in Cu-cathode/Fe³⁺/PMS system and^·OH plays a dominant role for the iohexol degradation in Fe-cathode/Fe³⁺/PMS system.Six types of reactions are involved in the iohexol transformation,including（a）amide hydrolysis,（b）amino oxidation,（c）hydrogen abstraction,（d）deiodination,（e）^·OH attack,and（f）oxidation of C-OH.