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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.

Multi-element nanoparticles (NPs) consisting of five or more elements have been increasingly studied in the past five years. Their emergence is taking materials science one step further because they exhibit superior properties to those of conventional NPs in a range of respects, including catalysis. This Review focuses on the recent progress in multi-element NPs regarding synthesis, especially with regard to chemical synthesis, characterization, and properties. We begin with a brief introduction of multi-element NPs and an overview of their synthesis methods. Then, we present representative examples of multi-element alloy NPs and ceramic NPs, including oxide NPs prepared by chemical syntheses. This Review intends to provide useful insights into the chemical methods that are used to synthesize multi-element NPs, and includes a discussion on the possibilities arising from their use in new functional materials.

We report on Cu/amUiO-66, a composite made of Cu nanoparticles (NPs) and amorphous [Zr6 O4 (OH)4 (BDC)6 ] (amUiO-66, BDC=1,4-benzenedicarboxylate), and Cu-ZnO/amUiO-66 made of Cu-ZnO nanocomposites and amUiO-66. Both structures were obtained via a spray-drying method and characterized using high-resolution transmission electron microscopy, energy dispersive spectra, powder X-ray diffraction and extended X-ray absorption fine structure. The catalytic activity of Cu/amUiO-66 for CO2 hydrogenation to methanol was 3-fold that of Cu/crystalline UiO-66. Moreover, Cu-ZnO/amUiO-66 enhanced the methanol production rate by 1.5-fold compared with Cu/amUiO-66 and 2.5-fold compared with γ-Al2 O3 -supported Cu-ZnO nanocomposites (Cu-ZnO/γ-Al2 O3 ) as the representative hydrogenation catalyst. The high catalytic performance was investigated using in situ Fourier transform IR spectra. This is a first report of a catalyst comprising metal NPs and an amorphous metal-organic framework in a gas-phase reaction.

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.

Recently, mixed-metal metal–organic frameworks (MOFs) have been attracting much attention in various fields. In this study, we have systematically investigated the magnetic properties of CoxNi₁–x-MOF-74 [Co₂xNi₂(₁–x)(dhtp), where H₄dhtp = 2, 5-dihydroxyterephthalic acid] with two different kinds of metals (Co and Ni) across the composition range 0 ≤ x ≤ 1. Bimetallic CoxNi₁–x-MOF-74 (x = 0.752, 0.458, and 0.233) were successfully synthesized and confirmed to have homogeneous metal distributions. Weak ferromagnetic (canted antiferromagnetic) behavior was exhibited, while homometallic Co-MOF-74 and Ni-MOF-74 are antiferromagnetic. We also investigated the effects of C₂H₄ sorption on the magnetic properties and found that C₂H₄-adsorbed Co₀.₅Ni₀.₅-MOF-74 exhibited a change in the interchain magnetic interaction.

Metal-organic frameworks (MOFs) provide highly selective catalytic activity because of their porous crystalline structure. There is particular interest in metal nanoparticle-MOF composites (MNP@MOF) that could take advantage of synergistic effects for enhanced catalytic properties. We present an investigation into the local geometry and electronic properties of thermally decomposed Ni-MOF-74 calcined at different temperatures and time durations. Pair distribution function analysis using high-energy X-ray diffraction reveals the formation of fcc-Ni nanoparticles with a mixture of MOF phase in samples heated at 623 K for 12 h. Elevating the calcination temperature and lengthening the time duration assisted complete precipitation of Ni nanoparticles in the MOF matrix. Local structures and valence states were investigated using X-ray absorption fine structure spectroscopy. Evidence of ligand-to-metal charge transfer and gradual reduction of Ni2+ is apparent for those samples heated above 623 K for 12 h. In addition, the Ni lattice was found to be slightly compressed as a result of surface stresses in the nanosized particles or surface ligand environment. Electronic structure investigation using hard X-ray photoelectron spectroscopy shows a significant narrowing of the valence band and a decrease in the d-band center (toward the Fermi level) when the heating temperature is increased, thus suggesting promising catalytic properties for NiNP@MOF composite.

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.