Nanocrystalline MOFs Embedded in the Crystals of Other MOFs and Their Multifunctional Performance for Molecular Encapsulation and Energy-Carrier Storage

A metal–organic framework (MOF) with a specific construction and pores was demonstrated to have many advanced properties, but still limited to having unique aspects arising from the combination of different MOFs in a single body. Here, we report a facile method to produce MOF-5 crystals with nanocrystalline HKUST-1 (nHKUST-1) embedded into them in what is termed the “nHKUST-1⊂MOF-5” structure. The results show that the nHKUST-1⊂MOF-5 structure is capable of molecular encapsulation by trapping dye molecules in nHKUST-1 particles and embedding them in MOF-5 crystals. Moreover, the gravimetric uptake capacity of nHKUST-1⊂MOF-5 for methane (CH₄) was found to be enhanced as compared to that of MOF-5 or nHKUST-1 alone such that the nHKUST-1⊂MOF-5 structure exhibits a volumetric capacity of 250% for fuel storage deliverable by the CNG tank at room temperature and 80 bar. Furthermore, it showed robust capacity retention for reversible CH₄ uptake cycles at room temperature

Metal-Independent Coherent Electron Tunneling through Polymerized Fullerene Chains

We employ a first-principles computational approach to explore the potential of polymerized one-dimensional [60]fullerene chains as the channel material for improved nanoelectronics applications. Coherent electron transmissions of the fullerene wires obtained from [2+2] cycloaddition are calculated at different numbers of fullerene units (from one to four), electrode materials (Au and Al), and contact configurations (contact distances and symmetries). We find that metal-induced gap states are localized within the first side fullerenes in contact with the electrodes, so conclude that polymerized fullerene wires including more than three units should show a robust device characteristic irrespective of the type of electrode metals and contact configurations. Transmission channels are analyzed in terms of the density of states projected onto each fullerene unit, and for the three-unit chain case they are further characterized via the orbital distributions. We demonstrate that the comparison of the projected density of states in the energy viewpoint and the orbitals in the real-space viewpoint can provide a heuristic approach to understand the charge transport phenomena in the nanoscale junctions

Fast Charge Transfer and High Stability via Hybridization of Hygroscopic Cu-BTC Metal–Organic Framework Nanocrystals with a Light-Absorbing Layer for Perovskite Solar Cells

Perovskite solar cells (PSCs) have great potential as an efficient solar energy harvesting system due to their outstanding optoelectronic properties, but the charge accumulation and recombination, as well as the moisture-induced degradation of the light-absorbing perovskite layers, remain great bottlenecks in practical applications for future technology. As a solution to this challenge, here we report a strategy to realize moisture-stable PSCs allowing fast charge transfer that, in turn, leads to high power conversion efficiency (PCE). Hybridization of hygroscopic copper­(II) benzene-1,3,5-tricarboxylate metal–organic frameworks (Cu-BTC MOFs) with a light-absorbing perovskite layer for PSCs, where a moderate level of moisture attracted by Cu-BTC MOFs during the synthesis step, leads to enhanced perovskite crystallization. Besides, the perovskite–MOF hybrid facilitates the transfer of photoexcited electrons from the perovskite to TiO2 by providing additional channels for electron extraction. This enables a high PCE of 20.5% in a triple-cation perovskite–MOF device with negligible hysteresis compared to reference devices. Moreover, the perovskite–MOF hybrid exhibits high stability in ambient air under dark conditions over a long period (up to 22 months), while the unmodified counterpart quickly decomposes into PbI2. Consequently, this work provides a promising clue to realizeing fast charge transfer and high stability for high-performance PSCs

Heterogeneity within Order in Crystals of a Porous Metal–Organic Framework

Generally, crystals of synthetic porous materials such as metal–organic frameworks (MOFs) are commonly made up from one kind of repeating pore structure which predominates the whole material. Surprisingly, little is known about how to introduce heterogeneously arranged pores within a crystal of homogeneous pores without losing the crystalline nature of the material. Here, we outline a strategy for producing crystals of MOF-5 in which a system of meso- and macropores either permeates the whole crystal to make sponge-like crystals or is entirely enclosed by a thick crystalline microporous MOF-5 sheath to make pomegranate-like crystals. These new forms of crystals represent a new class of materials in which micro-, meso-, and macroporosity are juxtaposed and are directly linked unique arrangements known to be useful in natural systems but heretofore unknown in synthetic crystals

Hydrogen Storage Property on Nickel-Atom-Dispersed Organosilica Nanotubes

Hydrogen Storage Property on Nickel-Atom-Dispersed Organosilica Nanotube

Facile Route to Synthesize Large-Mesoporous γ-Alumina by Room Temperature Ionic Liquids

A large mesoporous γ-alumina was fabricated through a thermal process without postaddition of molecular or organic solvents at ambient pressure in an open container by using the dual functions of 1-hexadecyl-3-methylimidazolium chloride (C16MimCl) as room-temperature ionic liquids (RTILs), i.e., templating and cosolvent functions. In this synthesis, a thermal process with the assistance of RTILs was the key technology for induction of the nanostructure of aluminum hydroxide and transformation to boehmite crystallites by means of intermolecular interaction. Both C16MimCl/boehmite hybrid and γ-alumina displayed the nanostructure consisting of randomly debundled nanofibers embedded in wormlike porous networks. Nanofibers of C16MimCl/boehmite hybrid and γ-alumina exhibited a length of ca. 40−60 nm and a diameter of ca. 1.5−3 nm. In particular, γ-alumina had good thermal stability and reasonable acidic sites. After conversion from boehmite crystallites into γ-phase by calcination, this nanostructured γ-alumina obtained the largest surface area and pore volume among large mesoporous γ-aluminas around 10 nm pore size, i.e., 470 m2 g-1 in surface area, 1.46 cm3 g-1 in pore volume, and 9.9 nm in pore size by calcination at 550 °C. Therefore, this synthetic method is a facile way to synthesize various nanostructured inorganic materials with the enhanced physical properties

Nitrogen-Doped Multiwall Carbon Nanotubes for Lithium Storage with Extremely High Capacity

The increasing demands on high performance energy storage systems have raised a new class of devices, so-called lithium ion capacitors (LICs). As its name says, LIC is an intermediate system between lithium ion batteries and supercapacitors, designed for taking advantages of both types of energy storage systems. Herein, as a quest to improve the Li storage capability compared to that of other existing carbon nanomaterials, we have developed extrinsically defective multiwall carbon nanotubes by nitrogen-doping. Nitrogen-doped carbon nanotubes contain wall defects through which lithium ions can diffuse so as to occupy a large portion of the interwall space as storage regions. Furthermore, when integrated with 3 nm nickel oxide nanoparticles for a further capacity boost, nitrogen doping enables unprecedented cell performance by engaging anomalous electrochemical phenomena such as nanoparticles division into even smaller ones, their agglomeration-free diffusion between nitrogen-doped sites as well as capacity rise with cycles. The final cells exhibit a capacity as high as 3500 mAh/g, a cycle life of greater than 10 000 times, and a discharge rate capability of 1.5 min while retaining a capacity of 350 mAh/g

Understanding Adsorption Behavior of Periodic Mesoporous Organosilica Having a Heterogeneous Chemical Environment: Selective Coverage and Interpenetration of Adsorbates inside the Channel Wall

Gas adsorption of periodic mesoporous organosilica (PMO) containing bipyridine ligands within the framework (BPy-PMO) has been studied by in situ gas adsorption powder X-ray diffraction (XRD) analysis. Both Ar and CO2 molecules showed strong affinity with organic moiety than silica during monolayer adsorption, even though CO2 is localized more than Ar due to the strong interaction with bipyridine. During multilayer adsorption, adsorbates tend to be located on the silica layers rather than organic and uniformly distributed on the framework surface at the end of this process. The interpenetration of adsorbates within the organic domain of BPy-PMO pore wall enhances rigidity of the framework until capillary condensation, confirmed by decrease of full width at half-maxima (FWHM) of XRD peaks. A molecular simulation study supported the in situ XRD data, and these results provided a full understanding of how the framework environment influences the adsorption behavior of different adsorbates

Network of Heterogeneous Catalyst Arrays on the Nitrogen-Doped Graphene for Synergistic Solar Energy Harvesting of Hydrogen from Water

Combination of different nanoparticles has been suggested as a promising approach to realize advanced functionalities for many applications. Herein, we report a new method to make uniform sized nanoparticle arrays in a network by arranging a micelle monolayer in an ordered fashion on the conductive nitrogen-doped graphene (NG). Moreover, coarrangement of two different arrays using both metal and metal oxide nanoparticles on the conductive graphene is found to result in the synergistic and cooperative photocatalytic activity for production of hydrogen from water using solar energy, with the excellent performance attributed to efficient electron transfer from one nanoparticle through the conductive NG to the other nanoparticle in a single-layer network. Consequently, this work suggests a promising solution to design high-performance catalysts in a network of different nanoparticle arrays on thin and flexible conductive substrates

Acetylene Gas Mediated Conjugated Microporous Polymers (ACMPs): First Use of Acetylene Gas as a Building Unit

Acetylene Gas Mediated Conjugated Microporous Polymers (ACMPs): First Use of Acetylene Gas as a Building Uni