Efficient and sustainable methods for carbon dioxide capture are highly sought after. Mature technologies involve chemical reactions that absorb CO
but they have many drawbacks. Energy-efficient ...alternatives may be realised by porous physisorbents with void spaces that are complementary in size and electrostatic potential to molecular CO
. Here, we present a robust, recyclable and inexpensive adsorbent termed MUF-16. This metal-organic framework captures CO
with a high affinity in its one-dimensional channels, as determined by adsorption isotherms, X-ray crystallography and density-functional theory calculations. Its low affinity for other competing gases delivers high selectivity for the adsorption of CO
over methane, acetylene, ethylene, ethane, propylene and propane. For equimolar mixtures of CO
/CH
and CO
/C
H
, the selectivity is 6690 and 510, respectively. Breakthrough gas separations under dynamic conditions benefit from short time lags in the elution of the weakly-adsorbed component to deliver high-purity hydrocarbon products, including pure methane and acetylene.
We report a molecular simulation study for the separation of industrially important gas mixtures (CO2/H2, CO2/CH4, and CO2/N2) in rho zeolite-like metal-organic framework (rho-ZMOF). Rho-ZMOF ...contains a wide-open anionic framework and charge-balancing extraframework Na+ ions. Two types of binding sites for Na+ ions are identified in the framework. Site I is in the single eight-membered ring, whereas site II is in the α-cage. Na+ ions at site I have a stronger affinity for the framework and thus a smaller mobility. The binding sites in rho-ZMOF resemble those in its inorganic counterpart rho-zeolite. CO2 is adsorbed predominantly over other gases because of its strong electrostatic interactions with the charged framework and the presence of Na+ ions acting as additional adsorption sites. At ambient temperature and pressure, the CO2 selectivities are 1800 for the CO2/H2 mixture, 80 for the CO2/CH4 mixture, and 500 for the CO2/N2 mixture. Compared with other MOFs and nanoporous materials reported to date, rho-ZMOF exhibits unprecedentedly high selective adsorption for these gas mixtures. This work represents the first simulation study to characterize extraframework ions and examine gas separation in a charged ZMOF. The simulation results reveal that rho-ZMOF is a promising candidate for the separation of syngas, natural gas, and flue gas.
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The separation of acetylene, ethylene, and carbon dioxide is a great challenge in view of their similar sizes and physical properties. Recently, adsorptive separations using porous metal–organic ...frameworks have risen to prominence. Here, we report a novel microporous metal–organic framework, termed MUF-17, that selectively adsorbs acetylene in the presence of ethylene or carbon dioxide. MUF-17 possesses one-dimensional zig-zag pores that are lined with amino and carboxylate groups, and coordinated water molecules. This pore surface is highly polar and has appropriate dimensions to interact optimally with guest acetylene molecules. Dispersion-corrected density functional theory calculations confirm the strong interactions between the framework and acetylene and illustrate the electrostatic basis for its lower affinity for other gases. The application of MUF-17 to gas separations was demonstrated by dynamic breakthrough measurements. It is a multipurpose adsorbent, removing trace quantities of acetylene from ethylene and sequestering bulk quantities in the presence of carbon dioxide. Its excellent performance fruitfully couples high selectivity with uptake capacity. Advantageously, MUF-17 is straightforward, robust, and inexpensive to prepare. Its recyclability and high stability render it a high-performance material for sustainable and energy-efficient separation processes.
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Two new chemically stable functional crystalline covalent organic frameworkds (COFs) (Tp-Azo and Tp-Stb) were synthesized using the Schiff base reaction between triformylphloroglucinol (Tp) and ...4,4′-azodianiline (Azo) or 4,4′-diaminostilbene (Stb), respectively. Both COFs show the expected keto-enamine form, and high stability toward boiling water, strong acidic, and basic media. H3PO4 doping in Tp-Azo leads to immobilization of the acid within the porous framework, which facilitates proton conduction in both the hydrous (σ = 9.9 × 10–4 S cm–1) and anhydrous state (σ = 6.7 × 10–5 S cm–1). This report constitutes the first emergence of COFs as proton conducting materials.
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A series of five thermally and chemically stable functionalized covalent organic frameworks (COFs), namely, TpPa-NO2, TpPa-F4, TpBD-(NO2)2, TpBD-Me2, and TpBD-(OMe)2 were synthesized by employing the ...solvothermal aldehyde-amine Schiff base condensation reaction. In order to complete the series, previously reported TpPa-1, TpPa-2, and TpBD have also been synthesized, and altogether, eight COFs were fully characterized through powder X-ray diffraction (PXRD), Fourier transform IR (FT-IR) spectroscopy, 13C solid-state NMR spectroscopy, and thermogravimetric analysis. These COFs are crystalline, permanently porous, and stable in boiling water, acid (9 N HCl), and base (3 N NaOH). The synthesized COFs (all eight) were successfully delaminated using a simple, safe, and environmentally friendly mechanical grinding route to transform into covalent organic nanosheets (CONs) and were well characterized via transmission electron microscopy and atomic force microscopy. Further PXRD and FT-IR analyses confirm that these CONs retain their structural integrity throughout the delamination process and also remain stable in aqueous, acidic, and basic media like the parent COFs. These exfoliated CONs have graphene-like layered morphology (delaminated layers), unlike the COFs from which they were synthesized.
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CO2 uptake in zirconium MOF UiO-66 almost doubles with post-synthetic exchange of Zr by Ti. This was due to smaller pore size and higher adsorption enthalpy, with good complementarity between ...experiment and simulation. Furthermore, the full effect is obtained with ~50% Ti loading, precluding the need to fully substitute frameworks for CO2 capture.
Recently we have investigated the storage and adsorption selectivity of CO2 and CH4 in three different classes of nanoporous materialssilicalite, IRMOF-1, and C168 schwarzite through Monte Carlo ...simulation (Babarao, R.; Hu, Z.; Jiang, J. Langmuir, 2007, 23, 659). In this work, the self-, corrected, and transport diffusivities of CO2 and CH4 in these materials are examined using molecular dynamics simulation. The activation energies at infinite dilution are evaluated from the Arrhenius fits to the diffusivities at various temperatures. As loading increases, the self-diffusivities in the three frameworks decrease as a result of the steric hindrance; the corrected diffusivities remain nearly constant or decrease approximately linearly depending on the adsorbate and framework; and the transport diffusivities generally increase except for CO2 in IRMOF-1. The correlation effects are identified to reduce from MFI, C168 to IRMOF-1, in accordance with the porosity increasing in the three frameworks. Predictions of self-, corrected, and transport diffusivities for pure CO2 and CH4 from the Maxwell−Stefan formulation match the simulation results well. In a CO2/CH4 mixture, the self-diffusivities decreases with loading, and good agreement is found between simulated and predicted results. On the basis of the adsorption and self-diffusivity in the mixture, the permselectivity is found to be marginal in IRMOF-1, slightly enhanced in MFI, and greatest in C168 schwarzite. Although IRMOF-1 has the largest storage capacity for CH4 and CO2, its selectivity is not satisfactory.
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Heterogeneous catalysts for CO2 reduction derived from porous, crystalline frameworks have emerged as efficient systems with comparable activity and superior selectivity to their inorganic ...counterparts. The spatial arrangement of active sites in such catalytically active frameworks is critical to their performance in CO2 reduction. This review presents a comprehensive and critical analysis of (thermal) CO2 reduction over catalysts derived from porous, crystalline frameworks, whose structural and chemical diversity offers unprecedented opportunities to regulate reactivity. Thermodyamic considerations and the impact of process parameters on reaction intermediates, governing mechanisms for CO2 reduction and catalyst stability are discussed. Strategies for leveraging the flexibility of porous, crystalline frameworks to improve their stability and promote CO2 reduction are presented which include: use as sacrificial precursors to an active phase; integration within composites; and as hosts for nanoparticle encapsulation. Finally, future challenges and research prospects are highlighted.
The high surface area and porosity, and limitless compound and network combinations between the metal ions and organic ligands making up metal-organic frameworks (MOFs) offer tremendous opportunities ...for their use in many applications. While numerous methods have been proposed for the synthesis of MOF powders, it is often difficult to obtain oriented crystals with these techniques. Further, the need for additional post-synthesis steps to activate the crystals and release them from the substrate presents a considerable production challenge. Here, we report an acoustically-driven microcentrifugation platform that facilitates fast convective solutal transport, allowing the synthesis of MOF crystals in as short as five minutes. The crystals are not only oriented due to long-range out-of-plane superlattice ordering aided by molecular dipole polarization under the acoustoelectric coupling, but also simultaneously activated during the synthesis process.
We report the development of metal–organic framework (MOF)-based probes for the direct and rapid detection and quantification of perfluorooctanoic acid (PFOA) by mass spectrometry. Four ...water-resistant MOFsZIF-8, UiO-66, MIL88-A, and Tb2(BDC)3were coated on poly(dopamine) precoated stainless steel needles and used to rapidly preconcentrate PFOA from water for direct analysis by nanoelectrospray ionization mass spectrometry. The analytical performance of each MOF for detecting PFOA was correlated with both the calculated binding energy of the MOF for PFOA and the relative change in the surface area of the MOF upon exposure to PFOA. MOF-functionalized probes can be used for the rapid (<5 min) and sensitive quantification of PFOA molecules at low ng L–1 levels in environmental water samples (i.e., tap water, rainwater, and seawater) with no sample preparation. The limit of detection of PFOA in ultrapure water was 11.0 ng L–1. Comparable accuracy to an accredited analytical method was achieved, despite the MOF-functionalized probe approach being ∼40 times quicker and requiring ∼10 times less sample. These features indicate that MOF-coated probes are promising for the direct and rapid monitoring of polyfluorinated substances and other pollutants in the field.
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