The Confined Interlayer Growth of Ultrathin Two-Dimensional Fe₃O₄ Nanosheets with Enriched Oxygen Vacancies for Peroxymonosulfate Activation

Developing iron-based catalysts with superior activity and stability is a long-term goal for peroxymonosulfate (PMS) activation in advanced oxidation processes. Combining the confined interlayer growth strategy with melt infiltration under dry-chemical conditions, we successfully synthesized ultrathin 2D Fe3O4 nanosheets with a monolayer thickness of about 1 nm. Atomic force microscopy, CS-corrected high-resolution transmission electron microscopy, X-ray photoelectron spectroscopy, X-ray absorption fine structure, etc. jointly revealed that the 2D Fe3O4 nanosheets possessed special graphene-like morphology and enriched oxygen vacancies. As highly efficient AOP catalysts, a series of refractory organic pollutants, including phenolic compounds, antibiotics, and pharmaceuticals, were degraded and mineralized effectively via the activation of PMS. On the basis of radical quenching experiments, electrochemical analysis, and theory calculations, the radical generation (center dot OH and SO4 center dot-) and mediated electron transfer were verified to be key mechanisms in the reaction. The oxygen vacancy-rich ultrathin 2D Fe3O4 mediated the electron transfer between pollutions and oxidants, prompted the redox cycle of Fe3O4, and remarkably lowered the energy barrier for interfacial charge transfer. This work could generate 2D metal oxides nanosheets with sufficient oxygen vacancies in a large scale, leading the insight for boosting the activity of iron-based catalysts.