Asymmetrically coordinated cobalt atom on oxygen-doped carbon nitride for enhanced peroxymonosulfate activation and pollutants degradation

Targeted regulation of metal-atom configurations is an effective strategy to modulate electronic structure and enhance peroxymonosulfate (PMS) activation. In this study, cobalt atom with an asymmetric coordination of five nitrogen atoms and one oxygen atom (Co-N5O1) anchored on oxygen-doped carbon nitride (OCN) surfaces was synthesized to activate PMS. Experimental and computational results revealed that the asymmetric N, O coordination of Co atoms not only facilitated PMS adsorption and activation, thereby generating more sulfate (SO₄^•–), superoxide radical (O₂^•–), and singlet oxygen (¹O₂) radicals; but also enabled dissolved oxygen to participate in radical generation and promoted the electron transfer from contaminants to the surface-bound PMS complexes. Under the main actions of SO₄^•–, ¹O₂, and electron transfer, the Co-N5O1/OCN + PMS system demonstrated remarkable degradation efficiency, achieving nearly 100% degradation for both electron-donating (ciprofloxacin, bisphenol A, sulfamethoxazole, 4-chlorophenol, tetracycline) and electron-withdrawing (p-nitrophenol, p-nitrobenzoic acid, metronidazole) pollutants at a concentration of 10 mg L⁻¹. In a continuous-flow operation, 90% of ciprofloxacin was removed within 150 min (100 mL solution) with minimal metal leaching (< 0.3 mg L⁻¹). This study elucidates the critical role of metal atom coordination in PMS activation and offers a promising catalyst for various types of contaminants degradation.