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Hybrid materials of metal-organic frameworks (MOFs) and nanoparticles (NPs) have attracted significant attention because of the wide variety of attractive properties derived from the two components. In the last decade, the development of synthesis techniques for NP/MOF composites was particularly significant. In the field of catalysis in particular, various synergistic effects that make the composites attractive catalysts have been reported. However, the role of MOFs in the composite catalysts is still not well understood and is being elucidated. In this feature article, we focus on recent progress in NP/MOF composite catalysts, concentrating on the analysis of the interaction between NPs and MOFs and the reaction mechanisms, together with the synthetic techniques used for NP/MOF hybrid materials.

We first report the facile synthesis of metal-carbon composites consisting of metal nanoparticles (NPs) and different types of carbon species: onion-like and amorphous carbon, Ni@onion-like carbon and Co@amorphous carbon. By simply changing the metal species in an isostructural metal-organic framework, thermal decompositions of MOF-74 directly afforded different types of metal NPs and carbon composites, which exhibited good electrical conductivity. In particular, the Ni@onion-like carbon, having a well-ordered carbon structure, had high electrical conductivity (sigma = 5.3 omega(-1) cm(-1) at 295 K), explained by a modified model of the Efros-Shklovskii variable range hopping.

We demonstrate a novel, simple synthetic method for metal (Ni) NPs in a MOF using the partial thermal decomposition of nickel(II) 2,5-dihydroxyterephthalate (Ni-MOF-74). The Ni NPs inside the Ni-MOF-74 are several nanometers in size, and the size can be precisely controlled by the heating conditions.