The Nature of Molecular\nHybridizations in Nanodiamonds\nfor Boosted Fe(III)/Fe(II) Circulation

Reducing agents have been frequently utilized as electron\ndonors\nfor Fe(II) generation to resolve the sluggish Fe(III) reduction in\nFenton-like reactions, while their irreversible consumption necessitates\na robust catalytic system that utilizes green electron donors such\nas H<sub>2</sub>O<sub>2</sub>. In this study, we used annealed nanodiamonds\n(NDs) as a collection of model catalysts with different sp<sup>2</sup>/sp<sup>3</sup> ratios to investigate the roles of the molecular\nstructure in boosting the Fenton-like reactions. The annealed NDs\nacted as an electron mediator to transfer electrons from H<sub>2</sub>O<sub>2</sub> to surface-adsorbed Fe(III) for Fe(II) generation as\nwell as an electron donor for direct Fe(III) reduction, driving Fe(II)-catalyzed\nH<sub>2</sub>O<sub>2</sub> decomposition to produce massive hydroxyl\nradicals, demonstrating potential in the real-water matrixes. Galvanic\ncell experiments show that the contribution ratio of mediation and\nelectron donation is 2.75:1, indicating that the majority of Fe(II)\nwas generated through electron transfer from H<sub>2</sub>O<sub>2</sub>. Additionally, different carbon configurations (sp–sp<sup>2</sup>–sp<sup>3</sup> hybridizations) were compared to assess\nthe molecular structure-performance relationships in Fe(III) reduction.\nThis study unveils the distinct functions of carbon molecular structures\nin driving Fe(III)/Fe(II) circulation and provides insights into sustainable\nFenton oxidation driven by metal-free catalysis.