Revealing the mechanism of singlet oxygen formation during the activation of Peroxymonosulfate by Feco dual-atom catalysts

The development of selective reactive oxygen species is crucial for the efficient removal of organic contaminants. Iron‑cobalt dual-atom catalysts (FeCoDACs) show great promise for generating singlet oxygen (1O₂), a highly selective species, through the activation of peroxymonosulfate (PMS), but the formation mechanism remains unclear. In this study, FeCoDACs were synthesized via a facile pyrolysis method, and the activation of PMS by these catalysts for pollutant degradation and ¹O₂ generation was systematically investigated. Near-complete degradation of sulfamethoxazole was achieved after 30 min of reaction in the presence of 0.5 mM PMS and 0.05 g/L FeCoDACs. The formation of ¹O₂ during PMS activation was confirmed by electron paramagnetic resonance spectroscopy, and the formation kinetics were examined through quantification of 2,2,6,6-tetramethylpiperidine 1-oxide. Due to the high selectivity of ¹O₂, the presence of common water constituents—except for natural organic matter—did not adversely affect the treatment performance. For the same reason, the oxidative system performed well in treating real water matrices. Density functional theory calculations revealed that cleavage of the SO bond in PMS, rather than the peroxone bond occurred during activation by FeCoDACs, leading to the formation of high-valent iron-oxo species as a key intermediate for ¹O₂. The oxygen in the iron-oxo species then combined with oxygen from an adjacent site to form an OO* intermediate, which dissociated from the catalyst surface, resulting in the formation of ¹O₂. These findings are expected to enhance understanding of ¹O₂ formation during PMS activation by DACs