Abstract
Precisely tailoring the molecular configurations of single-atom sites and elucidating their correlation with generated specific reactive species is crucial for advancing Fenton-like chemistry toward targeted remediation. Herein, we developed a facile approach to precisely modulate the distances between isolated Fe‒N(4) sites (d(Fe-Fe)) from nanometer (0.95 nm) to subnanometer (0.43 nm) to construct a family of well-defined Fe‒N(4) twins with manipulated ligand-field strength and spin states. Different Fe‒N(4) twin sites trigger a metal-loading-independent volcano-shaped Fenton-like activity trend. The optimal configuration, achieved at an Fe‒Fe distance of 0.43 nm (Fe(d0.43)SA), induces an intermediate-spin (t(2g)4e(g)1) configuration that optimizes e(g) orbital occupancy, thereby promoting peroxymonosulfate (PMS) adsorption to form *HSO(5) (-) and subsequently lowers the energy barrier for coupling with another PMS to selectively generate singlet oxygen ((1)O(2)). The robust molecular catalyst with Fe‒N(4) twin sites sustains over 120 h of continuous treatment of organic wastewater and demonstrates simultaneous disinfection and pharmaceutical removal of actual hospital wastewater. This work presents an advanced strategy for engineering single-atom sites with multi-site cooperativity to regulate Fenton-like catalysis, enabling rapid and real-world water purification.