Significant role of high-valent iron-oxo species in the degradation and detoxification of indomethacine

A novel high-valent iron-oxo species (Fe(IV) = O) generated from Iron hexadecachlorophthalocyanine (FePcCl16)-mediated peroxymonosulfate (PMS) activation under visible light illumination for the degradation of a special group of compounds, indomethacine (IDM), containing methoxy, carboxyl, chloro, and amide groups was investigated. The experimental results indicate that Fe(IV) = O was able to selectively attack the carbonyl C-N bond on twisted amide groups, which exerts a strong toxic effect, and could therefore, effectively degrade and detoxify IDM and its byproducts. Twelve byproducts were identified by HPLC/MS/MS and calculation of frontier electron densities (FEDs), with all amide-group breakage products detected, and the possible pathways were deduced, which mainly consisted of Fe(IV) = O-induced cleavage of amide groups and radicals-induced reactions. Ecological risk assessment further confirmed a decrease in toxicity towards IDM degradation, which provides a promising Fe(IV) = O species for selective oxidation and detoxification of destabilized ground-state amides in drinking-water and wastewater treatment. (C) 2020 Elsevier Ltd. All rights reserved.