High-loading inducing Fe-dimer on carbon nitride promotes the generation of ·O2−

The research on metal dimer clusters is of great importance, owing to the potential in modulating the adsorption behavior towards reaction intermediates. Here, we develop a loading heightening strategy to obtain a 32.5 wt% Fe-dimer catalyst (Fe-32.5). The co-anchoring of two Fe atoms in a single triazine ring of carbon nitride with an atomic spacing of ∼0.23 nm is proved. Fe atoms occupy the pores of the triazine ring in the lower iron content sample (Fe-12.9 and Fe-17.1). However, with the increase of iron content to 32.5 wt%, two Fe atoms simultaneously occupy one triazine ring. For Fe-32.5, besides the main peak located at ∼1.5 Å corresponding to the Fe-N interaction, a peak attributed to Fe-Fe bonding is observed at ∼2.2 Å in Fourier-transformed k 3 -weithted extended X-ray absorption fine structure. Density functional theoretical (DFT) calculations reveal that Fe-dimer in Fe-32.5 induces a charge redistribution compared with that in Fe-12.9 and Fe-17.1. H 2 O* is adsorbed on O* via hydrogen bonding in Fe-12.9 and Fe-17.1. However, H 2 O*and O* in Fe-32.5 are adsorbed on Fe-Fe dimer, resulting in a decrease in the total energy of the reaction process. For the two former, O 2 - * adsorbs on individual Fe atoms. Fe-dimer in Fe-32.5 adsorbs O 2 - * in the form of bridge bonds, which facilitates the ·O 2 - release. Furthermore, an enhanced affinity for the substrate 3,3',5,5'-tetramethylbenzidine and higher peroxidase-like activity were displayed. This work provides an effective mean to synthesize metal dimer clusters through high loading. By increasing Fe loading, two iron atoms simultaneously occupy a triazine ring, Fe-dimer formed in single atom catalysts. Fe-dimer adsorbs ·O 2 - produced by the decomposition of H 2 O 2 in the form of a bridge bond, thus promoting the release of ·O 2 - . • Fe-dimer catalysts with 32.5 wt% of iron (Fe-32.5) were synthesized by the high loading SACs. • For Fe-32.5, on the one hand, H 2 O* and O* was adsorbed on Fe-Fe owing to the charge redistribution, which reduced the total reaction energy barrier; on the other hand, ·O 2 - * was adsorbed on Fe-Fe in the form of bridge bonds to promote the ·O 2 - release. • An enhanced affinity for the substrate 3,3',5,5'-tetramethylbenzidine (TMB) on Fe-dimer catalysts was shown.