Abstract
Magnetite (Fe(3)O(4)) 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 (H(2)O(2)) 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 (Fe(4+)═O)-remains under debate. Here, surface-specific spectroscopy with density functional theory (DFT) calculations is used to elucidate the mechanism of H(2)O(2) activation on Fe(3)O(4)(001) surfaces. It is found that •OH production is driven by electron transfer from subsurface Fe(2)⁺ centers to adsorbed H(2)O(2), 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 Fe(3)O(4) nanozymes and offer mechanistic insight to guide the rational design of next-generation oxide-based catalysts for environmental and biomedical applications.