Synthesis, Characterization, and DFT Calculations of a Novel Craft Axially Coordinated Fe–Fe Dual-Atom Oxidase-like Nanozyme for Colorimetric Sensing

Metal dual-atom nanozymes (DAzymes) with two sites commonly offer more advantages over single-atom nanozymes (SAzymes) in terms of electronic structure modification and synergy. However, the design of DAzymes remains challenging. Herein, we present a novel ion-imprinting strategy for preparing an axially coordinated Fe–Fe DAzyme (CNBFe-3-800) with an unreported configuration of Fe 2 N 6 B 2 active sites on a N,B-doped carbon support. The active sites comprise coplanar Fe 2 N 4 B 2 units with two axial N atoms (one on each Fe atom). The exact configuration of CNBFe-3-800 was compellingly confirmed by robust characterizations including aberration-corrected transmission electron microscopy and X-ray absorption near-edge structure spectroscopy. SAzymes demonstrate peroxidase-like activity, catalyzing the oxidation of organic substrates using reactive oxygen species (ROS) generated by H 2 O 2 decomposition. Contrastingly, DAzymes often show oxidase-like activity, favorably generating ROS from O 2 without the need for toxic H 2 O 2 . As a proof of concept, a three-channel colorimetric sensor array based on CNBFe-3-800 possessing excellent oxidase-like activity was developed for the discrimination and sensitive quantitation of tetracycline pollutants (tetracycline, oxytetracycline, and aureomycin). Principal component analysis enabled detection of these three tetracyclines at concentrations ranging from 8 to 2000 μM. Density functional theory calculations indicated that the Fe–Fe sites in CNBFe-3-800 exhibited a stronger adsorption energy for O 2 than the single Fe sites in iron phthalocyanine, with the enhanced oxidase-like activity of CNBFe-3-800 originating from an optimized bonding distance between the Fe–Fe dual-atom sites and the O intermediates, thus lowering the activation barrier of the rate-determining step (H 2 O desorption) on the binuclear iron sites. This work offers novel valuable insights for constructing dual-atom nanozymes.