Fabrication of Au25(SG)18–ZIF-8 Nanocomposites: A Facile Strategy to Position Au25(SG)18 Nanoclusters Inside and Outside ZIF-8

Abstract

Multifunctional composite materials are currently highly desired for sustainable energy applications. A general strategy to integrate atomically precise Au₂₅(SG)₁₈ with ZIF-8 (Zn(MeIm)₂, MeIm = 2-methylimidazole), is developed via the typical Zn-carboxylate type of linkage. Au₂₅(SG)₁₈ are uniformly encapsulated into a ZIF-8 framework (Au₂₅(SG)₁₈@ZIF-8) by coordination-assisted self-assembly. In contrast, Au₂₅(SG)₁₈ integrated by simple impregnation is oriented along the outer surface of ZIF-8 (Au₂₅(SG)₁₈/ZIF-8). The porous structure and thermal stability of these nanocomposites are characterized by N₂ adsorption–desorption isothermal analysis and thermal gravimetric analysis. The distribution of Au₂₅(SG)₁₈ in the two nanocomposites is confirmed by electron microscopy, and the accessibility of Au₂₅(SG)₁₈ is evaluated by the 4-nitrophenol reduction reaction. The as-prepared nanocomposites retain the high porosity and thermal stability of the ZIF-8 matrix, while also exhibiting the desired catalytic and optical properties derived from the integrated Au₂₅(SG)₁₈ nanoclusters (NCs). Au₂₅(SG)₁₈@ZIF-8 with isolated Au₂₅ sites is a promising heterogenous catalyst with size selectivity imparted by the ZIF-8 matrix. The structural distinction between Au₂₅(SG)₁₈@ZIF-8 and Au₂₅(SG)₁₈/ZIF-8 determines their different emission features, and provides a new strategy to adjust the optical behavior of Au₂₅(SG)₁₈ for applications in bioimaging and biotherapy.

The controlled embedding of nanoclusters into metal–organic frameworks is one of the major obstacles for the application of nanoclusters in catalysis. A general strategy to position Au₂₅(SG)₁₈ inside and outside ZIF-8 (Zn(MeIm)₂, MeIm = 2-methylimidazole) is developed via the typical Zn-carboxylate type of linkage. The catalytic and optical properties of such nanocomposites are further investigated.

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