One-Step Template-Free Fabrication of Ultrathin Mixed-Valence Polyoxovanadate-Incorporated Metal–Organic Framework Nanosheets for Highly Efficient Selective Oxidation Catalysis in Air

Abstract

Polyoxometalate (POM)-based metal-organic frameworks (MOFs) with nanostructure represent a class of promising heterogeneous nanocatalysts. As yet, direct one-step controllable synthesis of pure nanoscale POM-MOFs catalysts is an extremely huge challenge owing to highly complicated synthetic conditions. Herein, for the first time, we fabricated ultrathin (∼5 nm) mixed-valence {V₁₆} clusters-incorporated metal-organic framework nanosheets [Ni(4,4'-bpy)₂]₂ [V₇^IVV₉^VO₃₈Cl]·(4,4'-bpy)·6H₂O (NENU-MV-1a) via one-step template-free strategy and successfully achieved one-step removal of all impurities from the multicomponent complex system. The obtained NENU-MV-1a nanosheets possess dramatically different physiochemical properties from bulk crystal, including larger lateral area, and more active sites originated from their nanostructures. As a proof-of-concept application, NENU-MV-1a was applied in olefin epoxidation in air and exhibited more excellent catalytic activity (95% conversion) than the bulk crystal (35%). In addition, detailed catalytic mechanism studies revealed the structure-property correlations of NENU-MV-1a and proposed V^IV-V^V synergistic catalytic effect. Our investigations are of great significance for the development of more active and/or selective mixed-valence metal-oxygen cluster-based MOF nanocatalysts.