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.
Keywords: HKUST-1; MOFs; alcohol oxidation; cuprous oxide; gold; hollow materials.