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Activation of Peroxymonosulfate by Benzoquinone: A Novel Nonradical Oxidation Process
- Zhou, Yang, Jiang, Jin, Gao, Yuan, Ma, Jun, Pang, Su-Yan, Li, Juan, Lu, Xue-Ting, Yuan, Li-Peng
- Environmental Science & Technology 2015 v.49 no.21 pp. 12941-12950
- antibiotics, benzoquinones, electron paramagnetic resonance spectroscopy, hydroxyl radicals, kinetics, liquid chromatography, models, oxidation, pH, singlet oxygen, sulfamethoxazole, sulfates
- The reactions between peroxymonosulfate (PMS) and quinones were investigated for the first time in this work, where benzoquinone (BQ) was selected as a model quinone. It was demonstrated that BQ could efficiently activate PMS for the degradation of sulfamethoxazole (SMX; a frequently detected antibiotic in the environments), and the degradation rate increased with solution pH from 7 to 10. Interestingly, quenching studies suggested that neither hydroxyl radical (•OH) nor sulfate radical (SO₄•–) was produced therein. Instead, the generation of singlet oxygen (¹O₂) was proved by using two chemical probes (i.e., 2,2,6,6-tetramethyl-4-piperidinol and 9,10-diphenylanthracene) with the appearance of ¹O₂ indicative products detected by electron paramagnetic resonance spectrometry and liquid chromatography mass spectrometry, respectively. A catalytic mechanism was proposed involving the formation of a dioxirane intermediate between PMS and BQ and the subsequent decomposition of this intermediate into ¹O₂. Accordingly, a kinetic model was developed, and it well described the experimental observation that the pH-dependent decomposition rate of PMS was first-order with respect to BQ. These findings have important implications for the development of novel nonradical oxidation processes based on PMS, because ¹O₂ as a moderately reactive electrophile may suffer less interference from background organic matters compared with nonselective •OH and SO₄•–.