Densely Isolated FeN₄ Sites for Peroxidase Mimicking

Despite the breakthroughs of transition-metal catalysts in enzyme mimicking, fundamental investigation on the design of efficient nanozymes at the atomic scale is still required for boosting their intrinsic activities to fill in gaps from enzymes to nanozymes. Herein, we developed a universal salt-template strategy for the fabrication of atomically dispersed Fe atoms on ultrathin nitrogen-doped carbon nanosheets characterized by a dramatically high concentration of 13.5 wt %. The proposed Fe-N-C nanozymes with densely isolated FeN4 sites show high peroxidase-like activities and exhibit a specific activity of 25.33 U/mg, superior to Zn(Co)-N-C nanozymes. Both experiments and theoretical analysis revealed that FeN4 sites not only lead to the strong adsorption of H2O2 molecules but also weaken the bonding interaction between single Fe atom and two absorbed hydroxyl groups, lowering the energy barrier of the formation of hydroxyl radicals and therefore boosting their peroxidase-like activities. As expected, utilizing the peroxidase-like activity of Fe-N-C nanozymes, good sensitivity and selectivity for the intracellular H2O2 monitoring were realized. It offers a versatile approach for the construction of densely isolated M-N-C single-atom catalysts and achieves better understanding of single sites for the peroxidase-like catalytic mechanisms.