Facilely Tuning the First-Shell Coordination Microenvironment in Iron Single-Atom for Fenton-like Chemistry toward Highly Efficient Wastewater Purification

Precisely identifying the atomic structures in single-atom sites and establishing authentic structure-activity relationships for single-atom catalyst (SAC) coordination are significant challenges. Here, theoretical calculations first predicted the underlying catalytic activity of Fe-N_xC_4-x sites with diverse first-shell coordination environments. Substituting N with C to coordinate with the central Fe atom induces an inferior Fenton-like catalytic efficiency. Then, Fe-SACs carrying three configurations (Fe-N₂C₂, Fe-N₃C₁, and Fe-N₄) fabricate facilely and demonstrate that optimized coordination environments of Fe-N_xC_4-x significantly promote the Fenton-like catalytic activity. Specifically, the reaction rate constant increases from 0.064 to 0.318 min^-1 as the coordination number of Fe-N increases from 2 to 4, slightly influencing the nonradical reaction mechanism dominated by ¹O₂. In-depth theoretical calculations unveil that the modulated coordination environments of Fe-SACs from Fe-N₂C₂ to Fe-N₄ optimize the d-band electronic structures and regulate the binding strength of peroxymonosulfate on Fe-N_xC_4-x sites, resulting in a reduced energy barrier and enhanced Fenton-like catalytic activity. The catalytic stability and the actual hospital sewage treatment capacity also showed strong coordination dependency. This strategy of local coordination engineering offers a vivid example of modulating SACs with well-regulated coordination environments, ultimately maximizing their catalytic efficiency.