Atomic-level mechanistic insights into singlet oxygen-dominated oxidation: Deciphering the pivotal role of Cu-N2 active sites for selective contaminant degradation

Sulfonamide antibiotics are highly toxic, persistent, and environmentally hazardous, necessitating effective remediation technologies for their removal from aquatic systems. Singlet oxygen ( 1 O 2 ), a selective and pH-tolerant reactive species, has emerged as a key oxidant in persulfate-based advanced oxidation processes (PS-AOPs). Herein, the systematic and novel pathway formation for the 1 O 2 on single Cu atom during PS-AOPs was elucidated. Nitrogen-doped biochar-supported single-atom Cu catalysts featuring low-coordination Cu-N 2 sites (SACu-N 2 @C) were synthesized via calcinating straw biomass, which showed remarkable catalytic efficiency towards sulfamethoxazole (SMX) oxidation even under high-salinity conditions. Results and further elucidated the 1 O 2 formation pathway, where the Cu-N 2 sites adsorbed and interacted the oxygen atom in S O group at the end of peroxymonosulfate (PMS) with lower adsorption energy. This process was accompanied by the generation of two SO 5 •− molecular intermediates, ultimately leading to the formation of 1 O 2 with the lowest energy barrier. Moreover, toxicity tests showed that the degraded SMX solution was ecologically safe with no significant toxic effects on zebrafish, rice and Escherichia coli ( E. coli ). This study provides atomic-level insights into 1 O 2 generation via Cu-N 2 coordination, advancing the design of efficient and environmentally benign Fenton-like systems for antibiotic wastewater treatment.