Nanoporous Metal-organic Framework Research Articles

Multi-Component Uptake of Dye Molecules by Films of Nanoporous Metal-Organic Frameworks.

Nanoporous materials, such as metal-organic frameworks (MOFs), enable the separation of various molecular mixtures. Thus, detailed knowledge of multi-component diffusion properties of the guest molecules in the pores is vital. Here, UV/Vis absorption spectroscopy combined with step-by-step-synthesized MOF films with high transparency are used to measure the multi-component dye uptake and diffusion in a straightforward fashion. The time-resolved single-component, binary- and ternary-mixture uptakes of methylene blue (MB), nuclear fast red (NFR) and acid yellow 17 (AY) by MOF films of type HKUST-1 from ethanolic solutions with low dye concentrations were investigated. It was found that the diffusion of MB is approximately one order of magnitude slower than the diffusion of NFR or AY, independent of whether it is a single-component uptake or a mixture uptake.

One-step synthesis of Pd-NPs@Cu2(BDC)2DABCO as efficient heterogeneous catalyst for the Suzuki–Miyaura cross-coupling reaction

A new heterogeneous palladium catalyst has been synthesized by one-step encapsulation in nanoporous metal-organic framework Cu2(BDC)2(DABCO) (BDC = 1,4-benzenedicarboxylate, DABCO = 1,4-diazabicyclo[2.2.2]octane) under a temperature control program. Supported Pd nanoparticles (Pd-NPs@Cu2(BDC)2(DABCO)) were characterized by X-ray diffraction, BET analysis, field emission scanning electron microscopy, transmission electron microscopy, inductively coupled plasma atomic emission and X-ray photoelectron spectroscopy (XPS). The Highly dispersed Pd particles (Pd-NPs@Cu2(BDC)2(DABCO)) offered a very efficient catalytic activity towards the Suzuki–Miyaura cross-coupling reaction.

Solvothermal synthesis, nanostructural characterization and gas cryo-adsorption studies in a metal–organic framework (IRMOF-1) material

A nanoporous metal–organic framework material, exhibiting an IRMOF-1 type crystalline structure, was prepared by following a direct solvothermal synthesis approach, using zinc nitrate and terephthalic acid as precursors and dimethylformamide as solvent, combined with supercritical CO2 activation and vacuum outgassing procedures. A series of advanced characterization methods were employed, including scanning electron microscopy, Fourier-transform infrared radiation spectroscopy and X-ray diffraction, in order to study the morphology, surface chemistry and structure of the IRMOF-1 material directly upon its synthesis. Porosity properties, such as Brunauer–Emmet–Teller (BET) specific area (∼520 m2/g) and micropore volume (∼0.2 cm3/g), were calculated for the activated sample based on N2 gas sorption data collected at 77 K. The H2 storage performance was preliminary assessed by low-pressure (0–1 bar) H2 gas adsorption and desorption measurements at 77 K. The activated IRMOF-1 material of this study demonstrated a fully reversible H2 sorption behavior combined with an adequate gravimetric H2 uptake relative to its BET specific area, thus achieving a value of ∼1 wt.% under close-to-atmospheric pressure conditions.

Building Nanoporous Metal-Organic Frameworks "Armor" on Fibers for High-Performance Composite Materials.

The nanoporous metal-organic frameworks (MOFs) "armor" is in situ intergrown onto the surfaces of carbon fibers (CFs) by nitric acid oxidization to supply nucleation sites and serves as a novel interfacial linker between the fiber and polymer matrix and a smart cushion to release interior and exterior applied forces. Simultaneous enhancements of the interfacial and interlaminar shear strength as well as the tensile strength of CFs were achieved. With the aid of an ultrasonic "cleaning" process, the optimized surface energy and tensile strength of CFs with a MOF "armor" are 83.79 mN m-1 and 5.09 GPa, for an increase of 102% and 11.6%, respectively. Our work finds that the template-induced nucleation of 3D MOF onto 1D fibers is a general and promising approach toward advanced composite materials for diverse applications to meet scientific and technical demands.

Correction: Materials with high proton conductivity above 200 °C based on a nanoporous metal–organic framework and non-aqueous ionic media

Correction for ‘Materials with high proton conductivity above 200 °C based on a nanoporous metal–organic framework and non-aqueous ionic media’ by Valentina G. Ponomareva et al., RSC Adv., 2017, 7, 403–407.

Materials with high proton conductivity above 200 °C based on a nanoporous metal–organic framework and non-aqueous ionic media

MOF-based composite material features superior proton conductivity at temperatures above 200 °C in dry atmosphere.

Post-synthetic ion-exchange process in nanoporous metal–organic frameworks; an effective way for modulating their structures and properties

In this review paper, we considered all of the reports on the ion-exchange process which occur in the pores of MOFs. A comparison between MOFs before and after-exchange process and their applications were addressed.

Solvent-free and melt aerobic oxidation of benzyl alcohols using Pd/Cu2(BDC)2DABCO–MOF prepared by one-step and through reduction by dimethylformamide

In this paper we report an efficient method for the aerobic oxidation of benzyl alcohols to aldehydes by supported palladium nanoparticles in nanoporous metal–organic framework Cu2(BDC)2(DABCO) that Pd(ii) in MOF reduced without using any external reducing agent.

Interactions of SO2-Containing Acid Gases with ZIF-8: Structural Changes and Mechanistic Investigations

Zeolitic imidazolate frameworks (ZIFs) are a set of nanoporous metal–organic frameworks (MOFs) with tunable porosity and functionality. Among MOFs, they also show relatively good stability with respect to temperature and humidity. These characteristics lead to their possible applications in separation processes. In many practical separation processes, adsorbents are exposed to a variety of molecular species including acid gases. However, there is little knowledge of the effects of such acid gas exposure on the adsorption and separation properties of ZIFs. Here, the stability of a model ZIF material (ZIF-8) under SO2 exposure in dry, humid, and aqueous environments has been investigated in detail. Combined characterization by several techniques (PXRD, N2 physisorption, EDX, XPS, and FTIR) allowed us to track the structural and compositional properties of ZIF-8 before and after SO2 exposure. ZIF-8 is stable after prolonged exposure in dry SO2 and in humid air without SO2. However, exposure to 10–20 ppm conc...

Mechanochemically synthesized nanoporous metal-organic framework Cu2(BDC)2(DABCO): An efficient heterogeneous catalyst for preparation of carbamates

Nanoporous metal-organic frameworks Cu2(BDC)2(DABCO) (BDC = 1,4-benzenedicarboxylate, DABCO = 1,4- diazabicyclo[2.2.2]octane) was synthesized by ball milling technique and characterized by techniques such as Scanning Electron Microscopy (SEM), Transmission Electron Microscopy (TEM), Powder X-ray Diffraction (PXRD), Fourier Transform Infrared Spectroscopy (FT-IR) and Nitrogen adsorption/desorption analysis, CHN elemental analysis, and Inductively Coupled Plasma Spectrometry (ICP). The copper-catalyzed oxidative coupling reaction of 2-substituted phenols with DMF or N-formyl morpholine was then investigated by employing the synthesized Cu2(BDC)2(DABCO) as a heterogeneous catalyst to form carbamates through C-H activation. The catalyst was recovered and frequently reused without significant decrease in its catalytic activity. In addition, the surface area of the synthesized catalyst in this approach was considerably higher in comparison with the most given values in the literature for this compound.

Improved Interfacial Affinity and CO2 Separation Performance of Asymmetric Mixed Matrix Membranes by Incorporating Postmodified MIL-53(Al).

Asymmetric mixed matrix membranes(MMMs) with MOFs hold great application potential for energy-efficient gas separations. However, the particle aggregation and nonselective interfacial microvoids restrict the gas separation performance of asymmetric MMMs. Herein, nanoporous metal-organic framework (MOF) of MIL-53(Al) was modified with aminosilane after solvothermal synthesis. The postfunctionalization by grafting alkyl chains can form hydrogen bonds with polymer chains to enhance the affinity with polymer matrix and facilitate the preferential adsorption of CO2 by dipole-quadrupole interaction with the functional group. Then the postmodified MIL-53(Al) was incorporated as filler into poly(ether imide) Ultem1000 to fabricate high-quality asymmetric MMMs with well dispersed particles in polymer matrix and good adhesion at the MOFs-polymer interface. The Ultem/S-MIL-53(Al) asymmetric MMMs exhibited remarkable combinations of gas permeance and ideal selectivity for CO2/N2 separation at 10 wt % filler loading. The CO2 permeance achieved 24.1 GPU, an increase of 165% compared with pure Ultem membrane. Meanwhile, the ideal CO2/N2 selectivity also increased from 31.0 up to 41.1. The strategy of post covalent modification for MOFs provides an effective way to improve the interfacial affinity and gas separation performance.

Anionic dyes removal from aqueous solution using TMU-16 and TMU-16-NH2 as isoreticular nanoporous metal organic frameworks

The adsorptive removal of anionic dyes were investigated over two isoreticular nanoporous Zn(II)-MOFs known as TMU-16 and TMU-16-NH2 in view of the influence of an amine group on the adsorption capacity. Adsorption isotherms, thermodynamics and kinetics parameters of the sorbents were studied and also effective factors on dye adsorption have been optimized. Thermodynamic and kinetic results revealed adsorption over two MOFs is spontaneous and pseudo-second order, as well as TMU-16-NH2 showed higher removal yield to TMU-16 because of forming hydrogen bonding between dyes and amine groups. These MOFs showed great adsorption uptakes for anionic dyes than other porous materials that reported previously. Adsorption mechanism could be explained by electrostatic and hydrogen bonding interactions. Importantly TMU-16 and TMU-16-NH2 due to high adsorption capacity and stability of structures could be employed as excellent sorbents to remove harmful dyes in contaminated water.

Superexchange Charge Transport in Loaded Metal Organic Frameworks.

In the past, nanoporous metal-organic frameworks (MOFs) have been mostly studied for their huge potential with regard to gas storage and separation. More recently, the discovery that the electrical conductivity of a widely studied, highly insulating MOF, HKUST-1, improves dramatically when loaded with guest molecules has triggered a huge interest in the charge carrier transport properties of MOFs. The observed high conductivity, however, is difficult to reconcile with conventional transport mechanisms: neither simple hopping nor band transport models are consistent with the available experimental data. Here, we combine theoretical results and new experimental data to demonstrate that the observed conductivity can be explained by an extended hopping transport model including virtual hops through localized MOF states or molecular superexchange. Predictions of this model agree well with precise conductivity measurements, where experimental artifacts and the influence of defects are largely avoided by using well-defined samples and the Hg-drop junction approach.

H3PW12O40 Encapsulation by Nanoporous Metal Organic Framework HKUST-1: Synthesis, Characterization, Activity and Stability.

Hybrid composite material was obtained through encapsulation of H3PW12O40 (PW) into HKUST-1 (Cu3(BTC)2, BTC = 1,3,5-benzenetricarboxylic acid), in molar composition of 5 Cu(NO3)2 · 3H2O/2.8 BTC/0.3 PW/0.6 CTAB by adding solutions of PW and copper salts to mixture of BTC and surfactant. The catalyst was characterized by various techniques including powder X-ray diffraction (XRD), Fourier transform infrared (FT-IR), scanning electron microscopy (SEM), energy dispersive X-ray (EDX), laser particle size analyzer, Brunauer Emmett-Teller (BET). The acidity of the catalyst was measured by a potentiometric titration with n-butylamine and PW/HKUST-1 presented very strong acidic sites with Ei > 100 mV. This nano catalyst was successfully used for the synthesis of various β-keto enol ethers at 45 °C with 51-98% yield after 5-75 min. The catalyst was easily recycled and reused at least four times without significant loss of its activity (94% yield after forth run). The presence of the PW in PW/HKUST-1 and reused PW/HKUST-1 structure, eliminating any doubt about collapse of the HKUST-1 after catalytic reaction and can be followed by FT-IR, XRD and SEM techniques. Brönsted and Lewis acidity of the PW/HKUST-1 catalyst was distinguished by studying the FT-IR and determined by chemisorption of pyridine. The strength and dispersion of the protons on PW/HKUST-1 was considerably high and active surface protons became more available for reactant.

Metal–Organic Frameworks as Highly Active Electrocatalysts for High-Energy Density, Aqueous Zinc-Polyiodide Redox Flow Batteries

The new aqueous zinc-polyiodide redox flow battery (RFB) system with highly soluble active materials as well as ambipolar and bifunctional designs demonstrated significantly enhanced energy density, which shows great potential to reduce RFB cost. However, the poor kinetic reversibility and electrochemical activity of the redox reaction of I3(-)/I(-) couples on graphite felts (GFs) electrode can result in low energy efficiency. Two nanoporous metal-organic frameworks (MOFs), MIL-125-NH2 and UiO-66-CH3, that have high surface areas when introduced to GF surfaces accelerated the I3(-)/I(-) redox reaction. The flow cell with MOF-modified GFs serving as a positive electrode showed higher energy efficiency than the pristine GFs; increases of about 6.4% and 2.7% occurred at the current density of 30 mA/cm(2) for MIL-125-NH2 and UiO-66-CH3, respectively. Moreover, UiO-66-CH3 is more promising due to its excellent chemical stability in the weakly acidic electrolyte. This letter highlights a way for MOFs to be used in the field of RFBs.

Fabrication of mixed-matrix membrane containing metal–organic framework composite with task-specific ionic liquid for efficient CO2 separation

Gas permeability and selectivity for CO2/N2 separation were improved simultaneously in mixed-matrix membranes formed by a nanoporous metal–organic framework with a task-specific ionic liquid in PIM-1.

Capture and immobilisation of iodine (I2) utilising polymer-based ZIF-8 nanocomposite membranes

Polymer nanocomposites made up of nanoporous metal–organic frameworks (MOFs) are fast becoming a staple of next generation hybrid composites, and are currently being intensely developed for gas capture and separation.

Ultraselective Gas Separation by Nanoporous Metal-Organic Frameworks Embedded in Gas-Barrier Nanocellulose Films.

Metal-organic frameworks (MOFs) are synthesized at carboxy groups on crystalline TEMPO-oxidized cellulose nanofibers (TOCNs). MOF-TOCN films coated on a paper filter have a hierarchical structure from the nano- to macroscale, and demonstrate a high CO2 /CH4 selectivity, over 120 for CO2 at a high gas flux, by the combination of the nanoporous MOFs and the gas-barrier TOCNs, which have strong affinity with each other.

Photoswitchable Adsorption in Metal-Organic Frameworks Based on Polar Guest-Host Interactions.

Reversible remote-controlled switching of the properties of nanoporous metal-organic frameworks (MOFs) is enabled by incorporating photoswitchable azobenzene. The interaction of the host material with different guest molecules, which is crucial for all applications, is precisely studied using thin MOF films of the type Cu2 (BDC)2 (AzoBipyB). A molecule-specific effect of the photoswitching, based on dipole-dipole interactions, is found.

Ammonia Adsorption and Co-adsorption with Water in HKUST-1: Spectroscopic Evidence for Cooperative Interactions

Ammonia interactions and competition with water at the interface of nanoporous metal organic framework thin films of HKUST-1 (Cu3Btc2, Btc = 1,3,5-benzenedicarboxylate) are investigated with ambient pressure X-ray photoelectron spectroscopy (APXPS). In the absence of water, ammonia adsorption at the Cu2+ metal center weakens the metal–linker bond of the framework. In the presence of water, due to the higher binding energy (adsorption strength) of ammonia compared to water, ammonia replaces water at the unsaturated Cu2+ metal centers. The water molecules remaining in the pores are stabilized by hydrogen bonding to ammonia. Hydrogen bonding between the water and ammonia strengthens the metal–ammonia interaction due to cooperative interactions. Cooperative interactions result in a reduction in the metal center oxidation state facilitating linker replacement by other species explaining the previously reported structure degradation.