Iron 3D-Orbital Configuration Dependent Electron Transfer for Efficient Fenton-Like Catalysis

Transition metals are excellent active sites to activate peroxymonosulfate (PMS) for water treatment, but the favorable electronic structures governing reaction mechanism still remain elusive. Herein, the authors construct typical d-orbital configurations on iron octahedral (FeOh) and tetrahedral (FeTd) sites in spinel ZnFe2O4 and FeAl2O4, respectively. ZnFe2O4 (136.58 min-1 F-1 cm2) presented higher specific activity than FeAl2O4 (97.47 min-1 F-1 cm2) for tetracycline removal by PMS activation. Considering orbital features of charge amount, spin state, and orbital arrangement by magnetic spectroscopic analysis, ZnFe2O4 has a larger bond order to decompose PMS. Using this descriptor, high-spin FeOh is assumed to activate PMS mainly to produce nonradical reactive oxygen species (ROS) while high-spin FeTd prefers to induce radical species. This hypothesis is confirmed by the selective predominant ROS of 1O2 on ZnFe2O4 and O2 & BULL;- on FeAl2O4 via quenching experiments. Electrochemical determinations reveal that FeOh has superior capability than FeTd for feasible valence transformation of iron cations and fast interfacial electron transfer. DFT calculations further suggest octahedral d-orbital configuration of ZnFe2O4 is beneficial to enhancing Fe-O covalence for electron exchange. This work attempts to understand the d-orbital configuration-dependent PMS activation to design efficient catalysts. The intrinsic activity of iron cation towards decontamination via peroxymonosulfate activation depends on its orbital configurations including the factors of charge amount, spin state, as well as orbital arrangement.image