Selective degradation of sulfonamide antibiotics by peroxymonosulfate alone: Direct oxidation and nonradical mechanisms

In this study, peroxymonosulfate (PMS) alone process was systematically demonstrated as nonradical processes for the first time and PMS direct oxidation was firstly verified by the combination of theoretical calculation and experimental detection as well, which were found to selectively degrade sulfonamide antibiotics (SAs) with high efficiency. Compared with the negligible decrease in other compounds, more than 95% of selected SAs were removed by PMS alone. In comparison with the little impacts of methanol or tert-butanol on SAs degradation, NaN₃ can almost completely quench the oxidation processes, demonstrating the nonradical oxidation processes (¹O₂ and PMS direct oxidation) may be responsible for SAs degradation by PMS alone rather than conventional radical oxidation. However, phenol, which can be efficiently degraded by ¹O₂, only showed 6.2% removal rate by PMS alone, suggesting the limited contribution of ¹O₂. Thus PMS direct oxidation would be the dominant nonradical oxidation process of PMS alone for efficient SAs degradation. Then electron paramagnetic resonance (EPR) experiments also verified the high SAs degradation efficiency was attributed to PMS direct oxidation. Furthermore, density functional theory (DFT) calculation and SAs pathways also indirectly confirmed PMS nonradical oxidation, where SAs were selectively attacked at the N atom on the benzene ring to form chromogenic products and S atom of the sulfanilamide groups by PMS direct oxidation. This study gives new insight into selectivity, performances and mechanisms of PMS self-oxidation on sulfonamide antibiotics degradation.