Total mineralization of sulfamethoxazole and aromatic pollutants through Fe2+-montmorillonite catalyzed ozonation

Abstract The catalytic activity and selectivity of montmorillonite exchanged with Na + , Fe 2+ , Co 2+ , Ni 2+ and Cu 2+ cations were comparatively investigated in the ozonation of sulfamethoxazole (SMX). Chlorobenzene, benzoic acid, 4-nitrobenzoic acid, 3-hydroxybenzaldehyde, 4-nitrophenol and phenol were used as probe molecules having structural similarity with SMX oxidation intermediates. UV–vis spectrophometry and chemical oxygen demand (COD) measurements showed that Fe(II)–Mt and, to a lesser extent, Co(II)–Mt produce total mineralization of all organic substrates in less than 40 min. Combined HPLC–mass spectrometry revealed a reverse proportionality between the degradation time and molecular size of the organic substrates. Oxalic acid was recognized as a common bottleneck in the ozonation of any organic substrates. Ozonation initially obeyed a first order kinetics, but adsorption took place after 3–5 min, inducing changes in the mechanisms pathways. These findings may be useful for tailoring optimum oxidative treatment of waters without accumulation of hazardous derivatives.