Coordination-Diverse Fe-N ₄ Single-Atom Catalysts Regulate High-Valent Iron–Oxo Generation for Ultrafast Fenton-like Reactions

In practical catalyst synthesis, single-atom catalysts (SACs) typically possess complex coordination environments, where multiple coordination configurations coexist within a single catalyst. However, the mechanisms of these diverse coordination structures during oxidant activation and reactive oxygen species (ROS) generation remain largely unclear, hindering the rational design of SACs with controllable ROS pathways. Herein, we developed a SAC based on sludge-based activated carbon (SBAC-SAC) that simultaneously stabilized three Fe coordination configurations (Fe-N 4, Fe 2 N 6, and 2Fe-N 4 ) for efficient peracetic acid (PAA) activation. The optimized SBAC-SAC/PAA system achieved rapid phenol degradation with an apparent rate constant of 1.9829 min –1 and 86.12% PAA utilization efficiency. Theoretical calculations further revealed that the Fe 2 N 6 configuration, with a narrowed band gap and high Fe spin states, achieved an optimal balance between adsorption strength and electron transfer for the formation of high-valent iron–oxo species compared with other configurations. The long-term steady operation demonstrated outstanding stability in continuous-flow applications, maintaining 100% removal efficiency for 312 h with negligible iron leaching. Life cycle assessment (LCA) showed the feasibility and environmental promise of this catalyst for practical wastewater treatment. This work provides fundamental insights into the catalytic roles of coordination-diverse Fe-N 4 sites and offers a sustainable strategy for designing SACs toward efficient environmental remediation.