Fabrication of Integrated Cu₂O@HKUST-1@Au Nanocatalysts via Galvanic Replacements toward Alcohols Oxidation...

Metastable Cu₂O is an attractive material for the architectural design of integrated nanomaterials. In this context, the in situ growth of microporous metal-organic frameworks (MOFs) on Cu₂O nanocrystals with well-defined shapes (such as octahedron, truncated octahedron, and corner-truncated cube) was conducted under ambient conditions by using sacrificial Cu₂O nanocrystals as a copper ion source for the construction of HKUST-1. It was found that the growth rate of HKUST-1 on the (111) facet of octahedral Cu₂O was much faster than that on the (100) facet of cubic Cu₂O. A subsequent etching process on the core-shell-structured Cu₂O@HKUST-1 to remove Cu₂O results in hollow HKUST-1 with hierarchical pores, where the shapes of cavities are tailored depending on the original Cu₂O crystals. Importantly, it was found that the integrated Cu₂O@HKUST-1@Au nanocatalysts could be fabricated by galvanic replacement reaction between Cu₂O and AuCl₄^-, wherein the copper(I) ions from Cu₂O etching diffuse through the microporous MOF shell and reach to the external surface to reduce AuCl₄^- ions, thereby forming Au nanoparticles exclusively on the MOF external surface. Furthermore, the catalytic applications of Cu₂O@HKUST-1@Au toward liquid-phase oxidation of both aromatic and aliphatic alcohols were studied. Notably, 100% selectivities of aldehyde products were achieved without any further oxidation byproducts such as acid and ester.