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Versatile materials like metal–organic frameworks require careful characterization. Transmission electron microscopy is a very powerful method that can address a multitude of investigative challenges. In this review we present TEM studies that yielded valuable insights into the investigated MOFs to illustrate the potential of TEM despite the sensitivity of MOFs to the electron beam. [ABSTRACT FROM AUTHOR]

By employing the mixed-component, solid-solution approach, various functionalized ditopic isophthalate (ip) defect-generating linkers denoted 5-X-ipH2, where X=OH ( 1), H ( 2), NH2 ( 3), Br ( 4), were introduced into the mixed-valent ruthenium analogue of [Cu3(btc)2] n (HKUST-1, btc=benzene-1,3,5-tricarboxylate) to yield Ru-DEMOFs (defect-engineered metal-organic frameworks) of the general empirical formula [Ru3(btc)2− x(5-X-ip) xY y] n. Framework incorporation of 5-X-ip was confirmed by powder XRD, FTIR spectroscopy, ultrahigh-vacuum IR spectroscopy, thermogravimetric analysis, 1H NMR spectroscopy, N2 sorption, and X-ray absorption near edge structure. Interestingly, Ru-DEMOF 1 c with 32 % framework incorporation of 5-OH-ip shows the highest BET surface area (≈1300 m2 g−1, N2 adsorption, 77 K) among all materials (including the parent framework [Ru3(btc)2Y y] n). The characterization data are consistent with two kinds of structural defects induced by framework incorporation of 5-X-ip: modified paddlewheel nodes featuring reduced ruthenium sites (Ru δ+, 0< δ<2, type A) and missing nodes leading to enhanced porosity (type B). Their relative abundances depend on the choice of the functional group X in the defect linkers. Defects A and B also appeared to play a key role in sorption of small molecules (i.e., CO2, CO, H2) and the catalytic properties of the materials (i.e., ethylene dimerization and the Paal-Knorr reaction). [ABSTRACT FROM AUTHOR]

Nanostructure engineering has been demonstrated to improve the electrochemical performance of iron oxide based electrodes in Li-ion batteries (LIBs). However, the synthesis of advanced functional materials often requires multiple steps. Herein, we present a facile one-pot synthesis of carbon-coated nanostructured iron oxide on few-layer graphene through high-pressure pyrolysis of ferrocene in the presence of pristine graphene. The ferrocene precursor supplies both iron and carbon to form the carbon-coated iron oxide, while the graphene acts as a high-surface-area anchor to achieve small metal oxide nanoparticles. When evaluated as a negative-electrode material for LIBs, our composite showed improved electrochemical performance compared to commercial iron oxide nanopowders, especially at fast charge/discharge rates. [ABSTRACT FROM AUTHOR]

The zinc-imidazolate-based framework ZIF-8 was loaded with preformed surfactant-stabilized bimetallic Pd/Au nanoparticles and its corresponding monometallic counterparts Au and Pd by a controlled encapsulation process during the ZIF-8 crystal growth. The nanoparticle-loaded materials were characterized by powder X-ray diffraction (PXRD), FTIR spectroscopy, N2-sorption measurements, as well as by transmission electron microscopy (TEM). The ZIF-8 matrix material remained intact and the NP@ZIF-8 materials revealed the permanent porosity of Brunauer-Emmett-Teller (BET) surface areas above 1100 m2 g-1. The nanoparticles are exclusively found inside the volume of the nanocrystals and exhibit unchanged composition and size distribution as revealed by TEM investigations. Additionally, scanning transmission electron microscopy (STEM) coupled with energy-dispersive X-ray spectroscopy (EDX) confirmed the solid solution-type alloying of Pd and Au in the embedded Pd/Au nanoparticles. The materials were briefly evaluated in aqueous-phase aerobic alcohol oxidation to investigate the synergetic effects of alloyed Pd/Au nanoparticles and the microporous, hydrophobic matrix ZIF-8. [ABSTRACT FROM AUTHOR]

Three-dimensional covalent organic frameworks (COFs) have been demonstrated as a new class of templates for nanoparticles. Photodecomposition of the [Pd(η3-C3H5)(η5-C5H5)]@COF-102 inclusion compound (synthesized by a gas-phase infiltration method) led to the formation of the Pd@COF-102 hybrid material. Advanced electron microscopy techniques (including high-angle annular dark-field scanning transmission electron microscopy and electron tomography) along with other conventional characterization techniques unambiguously showed that highly monodisperse Pd nanoparticles ((2.4±0.5) nm) were evenly distributed inside the COF-102 framework. The Pd@COF-102 hybrid material is a rare example of a metal-nanoparticle-loaded porous crystalline material with a very narrow size distribution without any larger agglomerates even at high loadings (30 wt %). Two samples with moderate Pd content (3.5 and 9.5 wt %) were used to study the hydrogen storage properties of the metal-decorated COF surface. The uptakes at room temperature from these samples were higher than those of similar systems such as Pd@metal-organic frameworks (MOFs). The studies show that the H2 capacities were enhanced by a factor of 2-3 through Pd impregnation on COF-102 at room temperature and 20 bar. This remarkable enhancement is not just due to Pd hydride formation and can be mainly ascribed to hydrogenation of residual organic compounds, such as bicyclopentadiene. The significantly higher reversible hydrogen storage capacity that comes from decomposed products of the employed organometallic Pd precursor suggests that this discovery may be relevant to the discussion of the spillover phenomenon in metal/MOFs and related systems. [ABSTRACT FROM AUTHOR]

Porous solids with organized multiple porosity are of scientific and technological importance for broadening the application range from traditional areas of catalysis and adsorption/separation to drug release and biomedical imaging. Synthesis of crystalline porous materials offering a network of uniform micro- and mesopores remains a major scientific challenge. One strategy is based on variation of synthesis parameters of microporous networks, such as, for example, zeolites or metal-organic frameworks (MOFs). Here, we show the rational development of an hierarchical variant of the microporous cubic Cu3(BTC)2 (BTC= 1,3,5-benzenetricarboxylate) HKUST-1 MOF having strictly repetitive 5 nm wide mesopores separated by uniform microporous walls in a single crystal structure. This new material coined COK-15 (COK = Centrum voor Oppervlaktechemie en Katalyse) was synthesized via a dual-templating approach. Stability was enhanced by Keggin type phosphotungstate (HPW) systematically occluded in the cavities constituting the walls between the mesopores. [ABSTRACT FROM AUTHOR]

Solvent mixture controlled rapid room temperature syntheses for facile access to uniformzeolitic-imidazolate framework nanocrystals (ZIF-7, ZIF-65-Zn and ZIF-71) are reported. ZIF thin film devices for sensing volatile organic chemicals were fabricated by dip-coating nano-ZIF (80-130 nm) suspensions. [ABSTRACT FROM AUTHOR]

N-Lewis base mediated room temperature synthesis of covalent organic frameworks (COFs) starting from a solution of building blocks instead of partially soluble building blocks was developed. This protocol shifts COF synthetic chemistry from sealed tubes to open beakers. Non-conventional inclusion compounds of COF-1 were obtained by vapor phase infiltration of ferrocene and azobenzene, and solvation like effects were established. [ABSTRACT FROM AUTHOR]

Electrochemically exfoliated graphene (e-G) thin films on Nafion membranes exhibit a selective barrier effect against undesirable fuel crossover. This approach combines the high proton conductivity of state-of-the-art Nafion and the ability of e-G layers to effectively block the transport of methanol and hydrogen. Nafion membranes are coated with aqueous dispersions of e-G on the anode side, making use of a facile and scalable spray process. Scanning transmission electron microscopy and electron energy-loss spectroscopy confirm the formation of a dense percolated graphene flake network, which acts as a diffusion barrier. The maximum power density in direct methanol fuel cell (DMFC) operation with e-G-coated Nafion N115 is 3.9 times higher than that of the Nafion N115 reference (39 vs 10 mW cm -2 @0.3 V) at a 5M methanol feed concentration. This suggests the application of e-G-coated Nafion membranes for portable DMFCs, where the use of highly concentrated methanol is desirable., Competing Interests: The authors declare no competing financial interest., (© 2023 The Authors. Published by American Chemical Society.)

Efforts to replace noble-metal catalysts by low-cost alternatives are of constant interest. The organometallic, non-aqueous wet-chemical synthesis of various hitherto unknown nanocrystalline Ni/Ga intermetallic materials and the use of NiGa for the selective semihydrogenation of alkynes to alkenes are reported. Thermal co-hydrogenolysis of the all-hydrocarbon precursors [Ni(COD)2] (COD = 1,5-cyclooctadiene) and GaCp* (Cp* = pentamethylcyclopentadienyl) in high-boiling organic solvents mesitylene and n-decane in molar ratios of 1 : 1, 2 : 3 and 3 : 1 yields the nano-crystalline powder materials of the over-all compositions NiGa, Ni2Ga3 and Ni3Ga, respectively. Microwave induced co-pyrolysis of the same precursors without additional hydrogen in the ionic liquid [BMIm][BF4] (BMIm = 1-butyl-3-methyl-imidazolium) selectively yields the intermetallic phases NiGa and Ni3Ga from the respective 1 : 1 and 3 : 1 molar ratios of the precursors. The obtained materials are characterized by transmission electron microscopy (TEM), energy dispersive X-ray spectroscopy (EDX), IR, powder X-ray diffraction (PXRD) and atomic absorption spectroscopy (AAS). The single-source precursor [Ni(GaCp*)(PMe3)3] with a fixed Ni : Ga stoichiometry of 1 : 1 was employed as well. In comparison with the co-hydrogenolytic dual precursor source approach it turned out to be less practical due to inefficient nickel incorporation caused by the parasitic formation of stable [Ni(PMe3)4]. The use of ionic liquid [BMIm][BF4] as a non-conventional solvent to control the reaction and stabilize the nanoparticles proved to be particularly advantageous and stable colloids of the nanoalloys NiGa and Ni3Ga were obtained. A phase-selective Ni/Ga colloid synthesis in conventional solvents and in the presence of surfactants such as hexadecylamine (HDA) was not feasible due to the undesired reactivity of HDA with GaCp* leading to inefficient gallium incorporation. Recyclable NiGa nanoparticles selectively semihydrogenate 1-octyne and diphenylacetylene (tolan) to 1-octene and diphenylethylene, respectively, with a yield of about 90% and selectivities of up to 94 and 87%. Ni-NPs yield alkanes with a selectivity of 97 or 78%, respectively, under the same conditions.

Silver nitrate induces spontaneous room temperature transformation of ZIF-8 into a composite of ZnO nanorods embedded in a ZIF-8 matrix. This first example of reverse transformation of ZIF-8 into ZnO is a convenient method for generating fixed ZnO nanoparticles in powders as well as films and coatings. The fabricated ZnO nanorod@ZIF-8 is photocatalytically active.