Activating peroxymonosulfate by halogenated and methylated quinones: performance and mechanism

Activation of peroxymonosulfate (PMS) by halogenated and methylated quinones for destroying sulfamethoxazole (SMX) was investigated, where 2,6-dimethyl-1,4-benzoquinone (DMBQ), 2,6-dichloro-1,4-benzoquinone (DCBQ), and tetrafluoro-1,4-benzoquinone (TFBQ) were chosen as model quinones. The PMS could be activated by halogenated and methylated quinones efficiently for SMX degradation, and the process showed high pH and quinones dependency. Different from PMS activated by ultraviolet (UV), singlet oxygen (¹O₂) instead of hydroxyl radical (˙OH) and sulfate radical (SO₄˙^-) was the primary oxidizing species in the activation process. The formation of ¹O₂ was confirmed by various quenching studies combined with chemical probes (9,10-diphenylanthracene (DPA)). By sampling in situ and monitoring in real time, droplet spray ionization mass spectrometry (DSI-MS) was applied to capture and identify the intermediates generated in the activation process. A possible mechanism for PMS activation was proposed accordingly. It was found that a series of reactions between PMS and halogenated/methylated quinones formed a dioxirane intermediate, and the subsequent decomposition of this intermediate produced the ¹O₂. These findings would help to better understand the interactions between PMS and quinones, and provide a novel activator for PMS activation toward environmental contaminants.