Performance of Cu-cathode/Fe³⁺/peroxymonosulfate process on iohexol degradation

Copper was used as a non-inert cathode material in a Cathode/Fe³⁺/peroxymonosulfate(PMS) system, and the performance of this novel Cu-cathode/Fe³⁺/PMS system was tested with a typical iodinated X-ray contrast media (iohexol) as target organics. The reaction mechanisms and the iohexol degradation pathways were investigated. The operational conditions of Cu-cathode/Fe³⁺/PMS process on iohexol degradation were optimized to be 1.0 mM Fe³⁺ dosage, 3.0 mM PMS dosage and 0.50 mA/cm² of current input. The much lower current applied in the present study than previous reports would help to save energy and be more economical. Compared with typical inert cathode (Pt-cathode), the Cu-cathode/Fe³⁺/PMS process has better performance on both iohexol removal and deiodination, due to that Cu-cathode participated in Fe²⁺ regeneration and PMS activation via surface Cu°-Cu⁺(s)-Cu²⁺-Cu° redox cycle. Fe²⁺ could be produced via reactions between Fe³⁺ and Cu/Cu⁺(s) as well as cathodic reduction of Fe³⁺. SO₄^- was generated from PMS activation by Fe²⁺, Cu/Cu⁺(s) and cathodic reduction. OH was also generated in this process but SO₄^- played a dominant role in iohexol degradation. The intermediate products of iohexol and its transformation pathways were complex due to the varied reaction mechanisms involving both oxidation and reduction in Cu-cathode/Fe³⁺/PMS process.