Fenton-like Reactivity on Fe₃O₄ Nanozymes Driven by Charge Transfer and Interfacial Water

Magnetite (Fe₃O₄) nanoparticles, widely recognized as inorganic nanozymes due to their enzyme-like catalytic activity, are emerging as effective heterogeneous catalysts for Fenton-like reactions, in which lattice iron activates hydrogen peroxide (H₂O₂) to generate reactive oxygen species. While hydroxyl radicals (•OH) are generally considered the primary reactive species, the underlying mechanism-particularly the possible involvement of a high-valent ferryl intermediate (Fe⁴⁺═O)-remains under debate. Here, surface-specific spectroscopy with density functional theory (DFT) calculations is used to elucidate the mechanism of H₂O₂ activation on Fe₃O₄(001) surfaces. It is found that •OH production is driven by electron transfer from subsurface Fe²⁺ centers to adsorbed H₂O₂, accompanied by the transient formation of a ferryl species. Moreover, interfacial water plays an active role in modulating surface reactivity and stabilizing key reaction intermediates. These findings clarify the origin of radical formation in Fe₃O₄ nanozymes and offer mechanistic insight to guide the rational design of next-generation oxide-based catalysts for environmental and biomedical applications.