Mechanochemical degradation of UV-328 by solid oxidative reagents: Peroxydisulfate vs. peroxymonosulfate

Peroxydisulfate (PDS) and peroxymonosulfate (PMS) are crucial oxidative additives for mechanochemical (MC) treatment of persistent organic pollutants and contaminated soils. However, their differences between solid-phase mechanisms remain unclear. This study found that both PDS and PMS achieved comparable 2-(2H-Benzotriazol-2-yl)-4,6-bis(2-methyl-2-butanyl)phenol (UV-328) degradation (91.9 % in PDS and 94.1 % in PMS after 120 min of milling), but the variance observed at elevated milling intensities and persulfate-to-UV-328 mass ratios implies that PDS and PMS follow different working regimes. Alterations in surface-physicochemistry and structure of PDS are more pronounced than those of PMS. Conversely, PMS shows more obvious changes in infrared properties, presumably forming hydrogen bonds with the hydroxyl group of UV-328. Probe experiments, with quantum chemical calculations, indicate that PDS is more likely than PMS to achieve O-O bond cleavage to generate sulfate radicals, while PMS depends on direct oxidation capabilities to selectively oxidize electron-rich pollutants. Ultimately, PDS exhibited stronger mineralization efficiency (13.20 %) and more small-molecule production (e.g., benzotriazole, NH₄⁺) compared to PMS (9.87 %). Concerningly, both systems result in oligomer formation (more ethers in PDS, while more esters and ethers in PMS). This work may provide foundational knowledge for the MC treatment of organic waste with persulfates as co-milling agents.