Add time:08/16/2019         Source:sciencedirect.com

The widespread occurrence of sulfonamides (SAs) in natural waters, wastewater, soil and sediment has raised increasing concerns about their potential risks to human health and ecological systems. Sulfate radical (SO4−)-based advanced oxidation processes (SR-AOPs) have become promising technologies to remove such contaminants in the environment. The present study systematically investigated the degradation of four selected SAs with different five-membered heterocyclic rings, namely, sulfamethoxazole (SMX), sulfisoxazole (SIX), sulfathiazole (STZ), and sulfamethizole (SMT), by thermo-activated persulfate (PS) process, and the role of heterocyclic rings was assessed particularly. The results revealed that all the selected SAs could be degraded efficiently by thermo-activated PS process, the decay rates of four SAs were appreciably increased with increasing temperature. For instance, degradation rates of STZ increased from 0.3 × 10−3 to 19.5 × 10−3 min−1 as the temperature was increased from 30 to 60 °C. Under the same experimental conditions, degradation rates of four SAs followed the order of SIX > SMX ≈ STZ > SMT, which is in accordance with decay rates of their R-NH2 moieties. The kinetic results indicated that five-membered heterocyclic rings could serve as reactive moieties toward SO4− attack, which were confirmed by frontier electron density (FED) calculations. Based on the transformation products identified by high-resolution mass spectrometry (HR-MS), five different oxidation pathways, including hydroxylation, aniline moiety oxidation, dimerization, sulfonamide bond cleavage, and heterocyclic ring oxidation/cleavage were proposed. Moreover, the degradation efficiency in real surface water (RSW) was found to be slight slower than that in artificial surface water (ASW), suggesting that SR-AOPs could be an efficient approach for the remediation of soil and water contaminated by these SAs.

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