Citrate-ball milled Cu-Fe oxides activate O2 triggering selective non-radical mechanism: A boosted strategy coupling oxygen vacancies with surface carboxyl

Realizing efficiently sustainable generation of singlet oxygen ( 1 O 2 ) in the O 2 activation-based systems is crucial, since 1 O 2 can oxidize many organic pollutants via a non-radical pathway that is preferable in complex water matrices e.g. saline wastewaters. In this study, a boosted strategy that introduced oxygen vacancies (OVs) and surface carboxyl groups (−COOH) onto electron-rich copper‑iron oxides, was proposed by a facile mechanochemical ball-milling process with citrate ligands (Cit). Notably, the resulting Cit@CuFe 2.5 O x catalyst enabled efficient O 2 activation via a selective non-radical pathway, achieving a standardized pseudo-first-order rate constant ( k obs ) of 0.073 min −1 ·g −1 for sulfamethoxazole (SMX) degradation, with over 90 % of the oxidative contribution attributed to 1 O 2 . The ball-milling procedure with Cit could cause the generation of abundant OVs for O 2 adsorption and activation . Mechanistic analysis and theoretical calculations revealed that the OVs accelerated electron transfer from adjacent Cu(I) atoms to adsorbed O 2, facilitating the generation of O 2 − and markedly lowering the free energy barrier for its subsequent conversion to 1 O 2 other than H 2 O 2 . Additionally, the surface-bound −COOH groups facilitated the transformation of molecular O 2 to adsorbed O 2 at OVs sites, further lowering the thermodynamic barrier of the O 2  ⟶ O 2 −  ⟶  1 O 2 pathway. This study provides a simple and cost-effective promotional strategy for O 2 activation by ball-milled electron-rich materials, offering an easily obtained method to induce 1 O 2 -dominated oxidation of recalcitrant organic pollutants in the treatment of high-salinity wastewater.