Tailored Ni–O–Ni dimers drive radical/non-radical pathways in peroxymonosulfate oxidation processes to remove emerging contaminants

Single-atom catalysts (SACs) have emerged as promising candidates for peroxymonosulfate (PMS)-based advanced oxidation processes (AOPs), offering high activity and atomic efficiency for environmental remediation. However, achieving SACs with robust structural stability, wide pH tolerance, and resistance to matrix interference remains a formidable challenge. Here, we report a loading-controlled strategy to construct oxygen-bridged bimetallic Ni–O–Ni sites on a carbon nitride framework via a coordination-recrystallization-static-air pyrolysis route. The Ni loading critically modulates the local coordination environment: while moderate loading promotes the formation of active Ni–O–Ni moieties, excess Ni leads to the emergence of less active Ni–N3 configurations. The optimized Ni–O–Ni SAC exhibits exceptional catalytic performance for PMS activation, achieving 5.9- and 28.9-fold enhancements in the degradation of oxytetracycline (OTC) and rhodamine B (RhB), respectively, relative to pristine C3N5, and surpassing all 41 previously reported catalysts for OTC or RhB degradation. The catalyst also demonstrates excellent operational stability across a wide pH range (2.0–11.0) and strong resistance to common anionic interferences. Mechanistic investigations, including radical quenching experiments and density functional theory (DFT) calculations, reveal that the Ni–O–Ni site facilitates the selective generation of singlet oxygen (1O2) and superoxide radicals (·O2−) by lowering activation barriers. This work highlights the critical role of metal-oxygen-metal motifs in dictating reaction pathways and offers a versatile design principle for next-generation AOP catalysts toward sustainable water treatment.