Exploring the electro-oxidation of the iodinated contrast iopamidol on different electrode materials for wastewater treatment

Emerging contaminants in water pose a serious threat to the environment and human health, stressing the need of developing efficient treatment processes. In this work, the electrochemical degradation of iopamidol (IOPA), as model iodinated organic pollutant, and the formation of its by-products were investigated on different electrode materials, including commercial anodes (Ti/Pt and Si/BDD) and a synthetized Ti/SnO₂-Sb-Pt(13 %) electrode. The electrochemical behaviour and catalytic activity were studied in Na₂SO₄ by cyclic voltammetry, electrochemical impedance spectroscopy, and galvanostatic experiments in a filter-press reactor. The results show that IOPA can be effectively degraded with all the studied anodes by anodic treatment, involving both the direct and OHs-mediated oxidation routes. The degradation efficiency achieved after 3 h of electrolysis was found greater than 80 % for all electrodes, being Si/BDD the most efficient anode. By-products analyses with HPLC/MS and ionic chromatography demonstrate the selective dehalogenation of IOPA as the main reaction pathway, giving rise to the formation of non-toxic deiodinated organic compounds. The unselective and highly oxidizing capability of Si/BDD results in rapid and complete mineralization but promotes the accumulation of toxic oxidants and most oxidized inorganic products in the treated residue. By contrast, the lower but more controllable oxidative conditions associated to Pt-containing electrodes enable the conversion of pollutants into valuable compounds and the production of non-toxic aqueous residues. The promoted IOPA interaction and OHs generation induced by Pt and the SnO₂-Sb matrix, respectively, observed for Ti/SnO₂-Sb-Pt(13 %), together with its comparatively lower cost, make this anode a good candidate to revalorize or eliminate iodinated organic contrast media.