The Nature of Molecular Hybridizations in Nanodiamonds for Boosted Fe(III)/Fe(II) Circulation

Reducing agents have been frequently utilized as electron donors for Fe(II) generation to resolve the sluggish Fe(III) reduction in Fenton-like reactions, while their irreversible consumption necessitates a robust catalytic system that utilizes green electron donors such as H₂O₂. In this study, we used annealed nanodiamonds (NDs) as a collection of model catalysts with different sp²/sp³ ratios to investigate the roles of the molecular structure in boosting the Fenton-like reactions. The annealed NDs acted as an electron mediator to transfer electrons from H₂O₂ to surface-adsorbed Fe(III) for Fe(II) generation as well as an electron donor for direct Fe(III) reduction, driving Fe(II)-catalyzed H₂O₂ decomposition to produce massive hydroxyl radicals, demonstrating potential in the real-water matrixes. Galvanic cell experiments show that the contribution ratio of mediation and electron donation is 2.75:1, indicating that the majority of Fe(II) was generated through electron transfer from H₂O₂. Additionally, different carbon configurations (sp-sp²-sp³ hybridizations) were compared to assess the molecular structure-performance relationships in Fe(III) reduction. This study unveils the distinct functions of carbon molecular structures in driving Fe(III)/Fe(II) circulation and provides insights into sustainable Fenton oxidation driven by metal-free catalysis.