Atomically Dispersed Fe–N4 Site as a Conductive Bridge Enables Efficient and Stable Activation of Peroxymonosulfate: Active Site Renewal, Anti-Oxidative Capacity, and Pathway Alternation Mechanism

Atomically dispersed metal sites anchored on nitrogen-doped carbonaceous substrates (M-NCs) have emerged as promising alternatives to conventional peroxymonosulfate (PMS) activators; however, the exact contribution of each site still remains elusive. Herein, isolated Fe-N₄ active site-decorated three-dimensional NC substrates (FeSA-NC) via a micropore confinement strategy are fabricated to initiate PMS oxidation reaction, achieving a specific activity of 5.16 × 10³ L·min^-1·g^-1 for the degradation of bisphenol A (BPA), which outperforms most of the state-of-the-art single-atom (SA) catalysts. Mechanism inquiry reveals enhanced chemisorption and electron transfer between PMS and FeSA-NC, enabling an inner electron shuttle mechanism in which Fe-N₄ serves as a conductive bridge. The Fe-N₄ sites reduce the energy barrier for the formation of SO₅* and H*, thereby transforming the reaction pathway from directly adjacent electron transfer into reactive oxygen species (ROS)-dominated oxidation. Theoretical calculations and dynamic simulations reveal that the Fe-N₄ sites induce facilitated desorption of reaction intermediates (PMS*/BPA*), which collectively contribute to the renewal of active sites and eventually enhance the catalytic durability. This work offers a reasonable interpretation for the important role of the Fe-N₄ moiety in altering the activation mechanism and enhancing the antioxidative capacity of NC materials, which fundamentally furnishes theoretical support for SA material design.