Directional generation of singlet oxygen (1O2) for efficient antibiotic degradation via Cu-Co hierarchical activation of molecular oxygen

Abstract

Singlet oxygen (¹O₂) offers unique advantages for contaminant degradation owing to its high oxidative selectivity, long half-life, and pH-independent reactivity. However, the spin-forbidden transition between molecular oxygen (triplet state, ³O₂) and ¹O₂ severely limits their interconversion under energy-free conditions. Herein, we innovatively prepared a nitrogen-doped carbon-coated copper-cobalt alloy catalyst (CuCo@NC) that hierarchically activated molecular oxygen into ¹O₂. The optimized CuCo@NC600 demonstrated exceptional performance: achieving 96.79 %-98.91 % Norfloxacin (NOR) removal and ∼70 % mineralization within 40 min across a broad pH range of 3–11 under conditions of 1.0 g/L catalyst and 20 mg/L NOR. The catalyst exhibited remarkable versatility, degrading diverse organic pollutants (rhodamine B, tetracycline hydrochloride, etc.) with > 90 % efficiency and strong anti-interference capability against common ions and organic matter. No significant performance degradation was observed in both real wastewater and surface water systems. Radical quenching experiments confirmed ¹O₂ as the dominant reactive species generated through hierarchically activating O₂ by Cu-Co collaboration: molecular oxygen is initially activated at Cu sites, generating •O₂^– and •OH, which are then captured and converted to ¹O₂ at Co sites. The preserved catalytic stability (>70 % efficiency after 3 cycles) originated from the protective carbon matrix and self-compensating Cu⁺/Cu²⁺–Co²⁺/Co³⁺ valence transitions. LC-MS-identified intermediates revealed three detoxification pathways. This work provided an energy-efficient and environmentally friendly strategy for ¹O₂-dominated advanced oxidation processes, demonstrating significant potential for antibiotic-polluted water remediation.