Axial Nitrogen Coordination Engineering of Fe Single-Atom Catalyst for Enhanced Peroxidase-like Activity.

Mimicking the hierarchical structure as well as the asymmetric Fe-N5 sites in natural horseradish peroxidase (HRP) is of great importance in developing Fe1/CN with high peroxidase-like (POD-like) activity. In this work, Fe1/CN with an asymmetric FeN5 moiety and ordered porous structure (FeN5/CN) is fabricated by an ammonia-assisted redispersion strategy, which shows high structural similarity with HRP. Therefore, FeN5/CN shows an excellent catalytic efficiency (specific activity = 117.9 U/mg, kcat/Km = 2185 mM-1 s-1) and selectivity (Km = 0.059 mM) in a POD-like reaction. Based on the high catalytic properties of FeN5/CN, a sensor for the detection of carbosulfan with a low limit of detection of 3.1 nM is assembled. Interestingly, FeN5/CN activates H2O2 via a superoxide pathway, while ·OH, 1O2, and ·O2- can all be detected in the FeN4/CN involved catalytic system. Mechanistic study by density functional theory calculations combined with experimental results illustrates that Fe-N5 sites provide moderate adsorption of *OH, enlarging and decreasing the reaction energy to form ·OH and ·O2-, respectively, while Fe-N4 sites exhibited higher affinity toward the OH* intermediate, resulting in the facile O-O bond cleavage from H2O2 molecule and prohibited the process of *OH desorption to ·OH.