Activation of Peroxymonosulfate by Benzoquinone: A Novel Nonradical Oxidation Process

TLDR

The study investigates the first reactions between peroxymonosulfate (PMS) and quinones, using benzoquinone (BQ) as a model compound. A catalytic mechanism is proposed in which a dioxirane intermediate forms between PMS and BQ and decomposes to singlet oxygen, with a kinetic model showing first‑order dependence on BQ and pH‑dependent PMS decomposition. BQ efficiently activates PMS to degrade sulfamethoxazole, with rates increasing from pH 7 to 10, proceeding via singlet oxygen rather than hydroxyl or sulfate radicals, thereby providing a less interfering nonradical oxidation approach.

Abstract

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•–.