Lewis-acid activation of persulfate enables oxidation of antibiotics: a new green low-cost advanced oxidation process.

Developing advanced oxidation processes (AOPs) that operate efficiently under environmentally relevant conditions remains a key challenge in water treatment. The results presented herein demonstrate that the -O-O- bond in persulfate is activated to react with substrates by forming (H2O)4Mg(OS(O)2OOSO3)/H(OS(O)2OOSO3)- that oxidise antibiotics (ciprofloxacin and ofloxacin). At pH 7.4, Mg2+/PDS achieved 75% degradation of ciprofloxacin and 89% degradation of ofloxacin after 24 h, with pseudo-first-order rate constants of 2.7 × 10-3 and 5.0 × 10-4 min-1, respectively. These values represent over a twentyfold enhancement over PDS alone at the same pH. In addition, for the reaction with DMSO, a novel mechanism was found, in which the oxidation processes are initiated by Lewis acid activation and do not involve initial radical formation; the substrates react directly with the activated O-O bond. Thus, its reactions with sulfoxides form the corresponding sulfones. This mechanism, for the reaction with DMSO is supported by DFT calculations. In contrast, the calculations indicate a radical mechanism for the reaction with phenol, suggesting that the substrate oxidation mechanism depends on the nature of the substrate. The results prove that peroxides can be activated towards oxidation processes not only via energy transfer (e.g., heat or light) or redox processes (e.g., Fenton-like or electrochemistry) but also via Lewis acid activation. The results establish an additional pathway for peroxide activation and provide a mechanistic basis for further exploring the development of potentially cost-effective and environmentally compatible advanced oxidation processes. This study highlights magnesium and protons as effective activators of persulfate for robust contaminant degradation in aqueous systems.