Iron Single-Atom Catalyst Actuates PMS/O3 Activation Process: Nonradical Generation Path for Synergistic Multiperoxides

Abstract

Singlet oxygen (¹O₂) is an excellent reactive oxygen species in advanced oxidation processes for water purification due to its excellent environmental suitability and selectivity. However, its generation and conversion mechanisms remain unclear. Herein, we have constructed a high-yield system for ¹O₂ by introducing ozone (O₃) into an iron single-atom catalyst/peroxymonosulfate (PMS) system. The steady-state concentration of ¹O₂ in the system was increased by 53.2% at O₃ concentration below 0.5 mg/L. The formation of ¹O₂ from high-valent iron-oxo species (Fe^IV═O) was revealed by electron paramagnetic resonance analysis, where Fe^IV═O was found by probe experiment via the activation of PMS on iron single-atom sites. The developed in situ singlet oxygen fluorescence imaging technique observed that the addition of O₃ has promoted the conversion process of Fe^IV═O to ¹O₂. Density functional theory calculations further demonstrated the low energy barrier for the formation of the key intermediate OO* in this process. These findings help to further understand the mechanism of ¹O₂ production at the molecular level and guide the design of efficient advanced oxidation reaction systems for water purification.