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

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@HKUST1@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.