Improved degradation of iohexol using electro-enhanced activation of persulfate by a CuxO-loaded carbon felt with carbon nanotubes as an interlayer

Abstract

Persulfate (PS) activation by means of transition metals has been extensively applied to eliminate persistent organic pollutants, but the slow rate of metal redox cycling between high-valence and low-valence states inhibits the degradation reaction. Here, a CuxO-loaded carbon felt with carboxylated multi-walled carbon nanotubes (MWCNT-COOH) as an interlayer (CuxO/CNT/CF) has been successfully prepared. This assembly was then employed in a process of peroxymonosulfate (PMS) activation with the assistance of an electric field (CuxO/CNT/CF-PMS-EC). PMS could be effectively activated by the electrically enhanced CuxO/CNT/CF due to faster metal redox cycling, and the system could be applied over a broad pH range (3.0–11.0). The degradation efficiency of iohexol (IOH) could reach 100 % within 25 min, and around 62.7 % of total organic carbon (TOC) was removed within 120 min in the CuxO/CNT/CF-PMS-EC system. Both non-radical (1O2)- and radical-mediated (·SO4-, ·O2–, and ·OH) PS activation are involved in the degradation process. According to the results of DFT calculations and LC-MS, the degradation of IOH involves deiodination, amide hydrolysis, amine oxidation, C-OH oxidation, addition of –OH, hydrogen abstraction, and elimination reactions. The present study shows electrocatalysis coupled with transition-metal-activated PS to be a highly efficient technique for the removal of iodinated contrast media (ICMs).