Engineering Hexacoordination-Structured Co Single-Atom Sites (Co–N4+2) to Boost Peroxydisulfate Activation in Advanced Oxidation Processes

The effectiveness of single-atom catalysts (SACs) in organic pollutant oxidation is largely dependent on the coordination number of the single-atom sites. A new nitrogen–cobalt (Co)-doped carbon (Co1–N4+2–C) catalyst was synthesized via pyrolysis of a 1,10-phenanthroline coordinated Co compound, using the template method. The Co single-atom sites in Co1–N4+2–C have a hexacoordination structure, which was confirmed through extended X-ray absorption fine structure (EXAFS) and density functional theory (DFT) analysis. This new catalyst was able to efficiently oxidize peroxydisulfate (PDS) and achieved a 100% degradation of 10 mg L–1 of bisphenol A (BPA) within 5 min, with singlet oxygen (1O2) as the major reactive oxygen species. The Co1–N4+2–C demonstrated favorable durability in six cycle experiments and applicability in actual wastewater treatment, thanks to its unique active sites. DFT calculations showed that PDS adsorbed more favorably on Co–N4+2 than on the conventional Co–N4 structural model. This paper can guide the modulation of the coordination number of SACs to enhance PDS activation and organic degradation, which has significant potential in the field of environmental remediation.