Gas Sorption Properties Research Articles

Windmill Co4{Co4(μ4‐O)} with 16 Divergent Branches Forming a Family of Metal–Organic Frameworks: Organic Metrics Control Topology, Gas Sorption, and Magnetism

A series of highly connected metal-organic frameworks (MOFs), [Co8 (O)(OH)4 (H2 O)4 (ina)8 ](NO3 )2 ⋅2 C2 H5 OH⋅4 H2 O (1), [Co8 (O)(OH)4 (H2 O)4 (pba)8 ](NO3 )2 ⋅8 C2 H5 OH⋅28 H2 O (2), and [Co8 (O)(OH)4 (H2 O)4 (pbba)8 ](NO3 )2 ⋅guest (3), in which ina=isonicotinate, pba=4-pyridylbenzoate, and pbba=4-(pyridine-4-yl)phenylbenzoate, is reported. These MOFs contain a new secondary building unit (SBU), with a square Co4 (μ4 -O) central unit having the rare μ4 -O(2-) motif, which is decorated by the other four peripheral cobalt atoms through μ3 -OH in a windmill-like shape. This SBU holds 16 divergent connecting organic ligands, pyridyl-carboxylates, to form three different frameworks. The high porosity of desolvated 2 is shown by the efficient gas absorption of N2 , CO2 , CH4 , and H2 . In addition, 1 and 2 exhibit unusual canted antiferromagnetic behavior with spin-glass-like relaxation, with blocking temperatures that are fairly high, 20 K (1) and 10 K (2), for cobalt materials. The relationship between the metal clusters and linkers has been studied, in which the size and rotational degrees of freedom of the ligands are found to control the topology, gas sorption, and magnetic properties.

Modulation of Gas Sorption Properties through Cation Exchange within an Anionic Metal-Organic Framework.

A novel 3D anionic metal-organic framework (MOF) of (Me2 NH2 )4 [Ni8 (PTCA)4 (μ3 -OH)4 (H2 O)4 ](DMF)5 (H2 O)13 (H4 PTCA=pyrene-1,3,6,8-tetracarboxylic acid) has been synthesized, in which Me2 NH2 + can be exchanged by Li+ ions. The results of gas sorption measurements indicate that the desolvated MOFs both before and after Li+ exchange show highly selective adsorption for CO2 over CH4 and N2 gases, and the Li+ -exchanged MOF exhibits enhanced CO2 , CH4 , and H2 storage properties.

Influence of Interpenetration in Diamondoid Metal–Organic Frameworks on the Photoreactivity and Sensing Properties

The degree of interpenetration is known to influence the gas sorption, catalytic, magnetic and nonlinear optical properties, chirality, and sensing of various molecules but not the solid-state [2 + 2] photocycloaddition reaction. In our previous studies of a solvothermal reaction using dimethylacetamide (DMA) as one of the solvents, a photoreactive 6-fold interpenetrated metal–organic framework with dia topology, [Zn(bpeb)(bdc)] (1) [bpeb = 1,4-bis[2-(4′-pyridyl)ethenyl]benzene; bdc = 1,4-benzenecarboxylate], was isolated. Because of the slip-stacked alignment of a dipyridyl ligand with two conjugated olefin bonds, the [2 + 2] cycloaddition reaction occurs under UV light leading to the formation of an organic polymer ligand fused with a coordination polymer, 2. On the contrary, under similar conditions when diethylformamide was used instead of DMA, a 5-fold interpenetrated structure, 3, with the same dia topology was obtained in this work. This has been found to be photostable as also predicted from the a...

Hg(II) Coordination Polymers Based on N,N'-bis(pyridine-4-yl)formamidine.

Reactions of N,N’-bis(pyridine-4-yl)formamidine (4-Hpyf) with HgX2 (X = Cl, Br, and I) afforded the formamidinate complex {[Hg(4-pyf)2]·(THF)}n, 1, and the formamidine complexes {[HgX2(4-Hpyf)]·(MeCN)}n (X = Br, 2; I, 3), which have been structurally characterized by X-ray crystallography. Complex 1 is a 2D layer with the {44·62}-sql topology and complexes 2 and 3 are helical chains. While the helical chains of 2 are linked through N–H···Br hydrogen bonds, those of 3 are linked through self-complementary double N–H···N hydrogen bonds, resulting in 2D supramolecular structures. The 4-pyf- ligands of 1 coordinate to the Hg(II) ions through one pyridyl and one adjacent amine nitrogen atoms and the 4-Hpyf ligands of 2 and 3 coordinate to the Hg(II) ions through two pyridyl nitrogen atoms, resulting in new bidentate binding modes. Complexes 1–3 provide a unique opportunity to envisage the effect of the halide anions of the starting Hg(II) salts on folding and unfolding the Hg(II) coordination polymers. Density function theory (DFT) calculation indicates that the emission of 1 is due to intraligand π→π * charge transfer between two different 4-pyf- ligands, whereas those of 2 and 3 can be ascribed to the charge transfer from non-bonding p-type orbitals of the halide anions to π * orbitals of the 4-pyf- ligands (n→π *). The gas sorption properties of the desolvated product of 1 are compared with the Cu analogues to show that the nature of the counteranion and the solvent-accessible volume are important in determining their adsorption capability.

Paddle Wheel Based Triazolyl Isophthalate MOFs: Impact of Linker Modification on Crystal Structure and Gas Sorption Properties.

Syntheses and comprehensive characterization of two closely related series of isomorphous metal-organic frameworks (MOFs) based on triazolyl isophthalate linkers with the general formula ∞(3)[M2(R(1)-R(2)-trz-ia)2] (M = Cu, Zn) are presented. Using solvothermal synthesis and synthesis of microcrystalline materials on the gram scale by refluxing a solution of the starting materials, 11 MOFs are readily available for a systematic investigation of structure-property relationships. The networks of the two series are assigned to rutile (rtl) (1-4) and α-PbO2 (apo) (5-9) topology, respectively. Due to the orientation of the triazole substituents toward the cavities, both the pore volume and the pore diameter can be adjusted by choice of the alkyl substituents. Compounds 1-9 exhibit pronounced microporosity with calculated porosities of 31-53% and show thermal stability up to 390 °C as confirmed by simultaneous thermal analysis. Systematic investigation of adsorption properties by CO2 (298 K) and N2 (77 K) adsorption studies reveal remarkable network flexibility induced by alkyl substituents on the linker. Fine-tuning of the gate opening pressure and of the hysteresis shape is possible by adjusting the substitution pattern and by choice of the metal ion.

ChemInform Abstract: Metal‐Organic Frameworks Derived Porous Carbons: Syntheses, Porosity and Gas Sorption Properties

AbstractReview: 111 refs.

Syntheses, structures and properties of zinc(II) and cadmium(II) coordination polymers with mixed organic ligands

Three new coordination polymers [Zn(tib)(BPDS)] (1), [Zn(tib) (BPDS) (H2O)]·6H2O (2) and [Zn2(tib) (TPDC-4CH3)2]·DMF·10H2O (3) (DMF = N, N-dimethylformamide), and a previously reported one [Cd(tib)2]·2NO3·4DMF (4) were synthesized by hydro/solvothermal reactions of corresponding metal salt with mixed organic ligands of 1, 3, 5-tris(1-imidazolyl)benzene (tib) and 4, 4'-biphenyldisulfonic acid (H2BPDS)/2′, 3′, 5′, 6′-tetramethylterphenyl-4, 4″-dicarboxylic acid (H2TPDC-4CH3). The complexes were characterized by elemental, thermogravimetric analyses, IR, single crystal and powder X-ray diffractions. 1 and 2 are 2D networks with {4·82} and {63} topologies, which are further assembled into 3D architectures through hydrogen bonding interactions. In 3, both tib and TPDC-4CH32− act as bidentate bridging ligands and link Zn(II) centers to form a 3-fold interpenetrating 3D framework, while 4 is a (3, 6)-connected binodal 3D net with the Schläfli symbol of {4·62}2{42·610·83}. Gas and dye sorption and photoluminescence properties of the complexes were investigated.

Mixed Matrix Membranes (MMMs) Comprising Exfoliated 2D Covalent Organic Frameworks (COFs) for Efficient CO2 Separation

Two water-stable covalent organic frameworks (COFs) named NUS-2 and NUS-3 having two-dimensional (2D) layered structures with different pore sizes were synthesized. These COFs were exfoliated into nanosheets and even monolayers with high aspect ratio. They were subsequently blended with commercial polymers poly(ether imide) (Ultem) or polybenzimidazole (PBI) into mixed matrix membranes (MMMs) exhibiting highly homogeneous textures due to the excellent compatibility between COF fillers and polymer matrixes. Thanks to the selective gas sorption properties of the porous COF fillers, the prepared MMMs exhibited increased gas permeabilities with NUS-2@PBI demonstrating an excellent H2/CO2 permselectivity that exceeded the 2008 Robeson upper bound. Our approach of using exfoliated 2D COFs as porous fillers in MMMs paves a novel way toward the tailored synthesis of advanced composite membrane materials for clean energy and environmental sustainability.

Metal‐Organic Frameworks Derived Porous Carbons: Syntheses, Porosity and Gas Sorption Properties

AbstractPorous carbon materials derived from metal‐organic frameworks (MOFs) have been brought into stage due to the intrinsic advantages of MOFs such as high porosity and tailorable structure diversity, which might provide infinite possibility in producing porous carbons with diverse structures and various decorations. Inherited from MOFs, the porosity in carbon materials is an important factor to evaluate the performances of porous carbons (e.g. gas sorption properties, electrochemical and catalytic behaviors). Factors that affect the porosity of porous carbon materials are mainly focused on the porosity of pristine MOFs, additives and conducting conditions. However, during past decades there were still no systematical reports on the influence factors of porosity in MOFs derived porous carbon materials and corresponding gas sorption properties. In this review, we will summarize the performances of MOF‐derived carbon materials (i.e. non‐doped porous carbons, heteroatoms doped porous carbons, metal/metal oxide decorated porous carbons) and give a detailed discussion about the connections between the properties and four major effects (calcination temperature, loading of additional precursor, post‐synthetic treatment as well as intrinsic properties of MOFs).

Ethylene/ethane permeation, diffusion and gas sorption properties of carbon molecular sieve membranes derived from the prototype ladder polymer of intrinsic microporosity (PIM-1)

Fine-tuning the microporosity of PIM-1 by heat treatment was applied to develop a suitable carbon molecular sieve membrane for ethylene/ethane separation. Pristine PIM-1 films were heated from 400 to 800°C under inert N2 atmosphere (<2ppm O2). At 400°C, PIM-1 self-cross-linked and developed polar carbonyl and hydroxyl groups due to partial dioxane splitting in the polymer backbone. Significant degradation occurred at 600°C due to carbonization of PIM-1 and resulted in 30% increase in cumulative surface area compared to its cross-linked predecessor. In addition, PIM-1-based CMS developed smaller ultramicropores with increasing pyrolysis temperature, which enhanced their molecular sieving capability by restricted diffusion of ethylene and ethane through the matrix due to microstructural carbon densification. Consequently, the pure-gas ethylene permeability (measured at 35°C and 2bar) decreased from 1600Barrer for the pristine PIM-1 to 1.3Barrer for the amorphous carbon generated at 800°C, whereas the ethylene/ethane pure-gas selectivity increased significantly from 1.8 to 13.

Crystal engineering of a family of hybrid ultramicroporous materials based upon interpenetration and dichromate linkers.

A new family of 2-fold interpenetrated primitive cubic (pcu) networks of formula [M(L)2(Cr2O7)] n (M = Co2+, Ni2+, Cu2+ and Zn2+; L = 4,4'-azopyridine), DICRO-3-M-i, has been synthesised and their structures, permanent porosity and gas sorption properties were comprehensively characterised. Molecular simulations indicate that CO2 molecules occupy both of the two distinct ultramicropores that run through this isostructural series. The orientation of the Cr2O72- pillars is thought to contribute to high isosteric enthalpy of adsorption (Qst) towards CO2 and temperature programmed desorption experiments reveal that DICRO-3-Ni-i selectively adsorbs CO2 from gas mixtures that simulate flue gas. Performance in this context is among the highest for physisorbents measured to date and these materials are readily regenerated at 50 °C.

Enhanced gas sorption and breathing properties of the new sulfone functionalized COMOC-2 metal organic framework.

A new sulfone functionalized vanadium metal-organic framework (MOF), denoted as SO2-COMOC-2, has been synthesized solvothermally. Its structural and gas sorption properties towards CO2 and CH4 have been evaluated and compared to those of the pristine COMOC-2 material. The SO2-COMOC-2 shows a remarkable increase in CO2 capacity at ambient pressure (2.13 mmol g(-1) at 273 K vs. 1.23 mmol g(-1) for the pristine COMOC-2). Additionally, the high pressure CO2 sorption isotherm shows a distinctive two-step sorption behavior with a final capacity of 12.45 mmol g(-1) for SO2-COMOC-2 at 303 K, while for CH4 a typical Type I isotherm was obtained with a capacity of 4.13 mmol g(-1). In situ synchrotron X-ray powder diffraction measurements have been carried out to characterize the structural flexibility of the materials, showing both the presence of large pore and narrow pore form. Furthermore, synchrotron XANES and a variety of spectroscopic techniques have been utilized to verify the presence of hydroxyl groups and the existence of the mixed vanadium oxidation states in the titled MOF structure.

Ameliorated synthetic methodology for crystalline lanthanoid–metalloporphyrin open frameworks based on a multitopic octacarboxy-porphyrin scaffold: structural, gas sorption and photophysical properties

A novel synthetic methodology has been applied to obtain sizeable single crystals of wide-pore porphyrin-based MOFs.

Metal ion induced porous HKUST-1 nano/microcrystals with controllable morphology and size

Porous coordination polymer HKUST-1 [Cu3(BTC)2] (H3BTC = 1,3,5-benzenetricarbocylic acid) nano/microcrystals have been fabricated by an environment friendly facile direct precipitation method at room temperature using inorganic salts such as NaNO3, NaCl, NaBr, KNO3, KCl and KBr as additives. It is found that the concentration of the inorganic salt has an important impact on the morphology and size of the HKUST-1 crystals, and their morphology changed from cube to cuboctahedron and finally to octahedron by increasing the concentration of inorganic salts. Gas adsorption measurements reveal that HKUST-1 nano/microcrystals with different morphologies show high specific surface areas, and their gas sorption properties depend on the crystal morphology and size.

Using neutron powder diffraction and first-principles calculations to understand the working mechanisms of porous coordination polymer sorbents.

Metal-organic frameworks (MOFs) are promising solid sorbents, showing gas selectivity and uptake capacities relevant to many important applications, notably in the energy sector. To improve and tailor the sorption properties of these materials for such applications, it is necessary to gain an understanding of their working mechanisms at the atomic and molecular scale. Specifically, it is important to understand how features such as framework porosity, topology, chemical functionality and flexibility underpin sorbent behaviour and performance. Such information is obtained through interrogation of structure-function relationships, with neutron powder diffraction (NPD) being a particularly powerful characterization tool. The combination of NPD with first-principles density functional theory (DFT) calculations enables a deep understanding of the sorption mechanisms, and the resulting insights can direct the future development of MOF sorbents. In this paper, experimental approaches and investigations of two example MOFs are summarized, which demonstrate the type of information and the understanding into their functional mechanisms that can be gained. Such information is critical to the strategic design of new materials with targeted gas-sorption properties.

Carbonization and oxidation of metal–organic frameworks based on 1,4-naphthalene dicarboxylates

Three new isostructural metal–organic frameworks (MOFs), [V(OH)(NDC)] (1), [Cr(OH)(NDC)] (2), and [Ga(OH)(NDC)] (3) have been synthesized hydrothermally using 1,4-naphthalene dicarboxylate (NDC) as the linker. These MOFs (1, 2 and 3) have been used as a template for the synthesis of metal-oxide-inserted nanoporous carbon materials. The newly synthesized MOFs and the resulting porous carbon hybrid functional materials have been characterized using powder x-ray diffraction, scanning electron microscopy, transmission electron microscopy, and energy dispersive x-ray spectroscopic analysis. Results show that compounds 2 and 3 form their respective metal oxide nanoparticles on the surface of the carbon materials during carbonization at 800 °C. The gas sorption properties of the new MOFs and their corresponding carbon frameworks have been reported.

Design of Pore Size and Functionality in Pillar-Layered Zn-Triazolate-Dicarboxylate Frameworks and Their High CO2/CH4 and C2 Hydrocarbons/CH4 Selectivity.

In the design of new materials, those with rare and exceptional compositional and structural features are often highly valued and sought after. On the other hand, materials with common and more accessible modes can often provide richer and unsurpassed compositional and structural variety that makes them a more suitable platform for systematically probing the composition-structure-property correlation. We focus here on one such class of materials, pillar-layered metal-organic frameworks (MOFs), because different pore size and shape as well as functionality can be controlled and adjusted by using pillars with different geometrical and chemical features. Our approach takes advantage of the readily accessible layered Zn-1,2,4-triazolate motif and diverse dicarboxylate ligands with variable length and functional groups, to prepare seven Zn-triazolate-dicarboxylate pillar-layered MOFs. Six different gases (N2, H2, CO2, C2H2, C2H4, and CH4) were used to systematically examine the dependency of gas sorption properties on chemical and geometrical properties of those MOFs as well as their potential applications in gas storage and separation. All of these pillar-layered MOFs show not only remarkable CO2 uptake capacity, but also high CO2 over CH4 and C2 hydrocarbons over CH4 selectivity. An interesting observation is that the BDC ligand (BDC = benzenedicarboxylate) led to a material with the CO2 uptake outperforming all other metal-triazolate-dicarboxylate MOFs, even though most of them are decorated with amino groups, generally believed to be a key factor for high CO2 uptake. Overall, the data show that the exploration of the synergistic effect resulting from combined tuning of functional groups and pore size may be a promising strategy to develop materials with the optimum integration of geometrical and chemical factors for the highest possible gas adsorption capacity and separation performance.

Temperature dependence of gas transport and sorption in carbon molecular sieve membranes derived from four 6FDA based polyimides: Entropic selectivity evaluation

Temperature dependences of gas transport and sorption properties on four previously isothermally studied 6FDA based carbon molecular sieve (CMS) membranes: 6FDA/DETDA, 6FDA:BPDA(1:1)/DETDA, 6FDA/DETDA:DABA(3:2) and 6FDA/1,5-ND:ODA(1:1), were examined over the temperature range from 35 °C to 50 °C. The permeability, sorption and diffusivity of these materials are reported, and activation energies of permeation and diffusion as well as heats of sorption for gases CO2, CH4, O2, and N2 of these materials are compared. Permselectivity of these materials at 35 °C was probed for three gas pairs: CO2/CH4, O2/N2, and N2/CH4, and results show that diffusion selectivity is the dominant factor in providing permselectivity. Diffusion selectivity can be factored further into an energetic selectivity and an entropic selectivity. The temperature dependence of both energetic and entropic selectivity and their contributions to overall diffusion selectivity are discussed in detail in this study. All four CMS membranes showed larger than unity entropic selectivity discriminations. 6FDA/DETDA derived CMS membrane, with the most compact structure, showed the largest entropic selectivity for CO2/CH4, O2/N2, and N2/CH4 as about 7.40, 4.24, and 2.17 respectively. Analysis of the selectivity factors provides insights into the effects of polymer precursor backbone structures on key transport and sorption properties in CMS materials.

Systematic Investigation of the Effect of Polymerization Routes on the Gas-Sorption Properties of Nanoporous Azobenzene Polymers.

Functional-group-oriented polymerization strategies have contributed significantly to the initial development of porous polymers and have led to the utilization of several well-known organic transformations in the synthesis of these polymers. Because there are multiple polymerization routes that can be used to introduce the same chemical functionality, it is very important to demonstrate the effect of different polymerization routes on the gas-sorption properties of these chemically similar polymers. Herein, we have studied the rich chemistry of azobenzenes and synthesized four chemically similar nanoporous azobenzene polymers (NABs) with surface areas of up to 1021 m(2) g(-1) . The polymerization routes have a significant impact on the pore-size distributions of the NABs, which directly affects the temperature dependence of the CO2 /N2 selectivity. A pore-width maximum of 6-8 Å, narrow pore-size distribution, and small particle size (20-30 nm) were very critical for high CO2 /N2 selectivity and N2 phobicity, which is associated with azo linkages and realized at warm temperatures. Our findings collectively suggest that an investigation of different polymerization routes for the same chemical functionalization is critical to understand fully the combined effect of textural properties, local environment, and chemical functionalization on the gas-sorption properties of nanoporous polymers.

ChemInform Abstract: In situ Synthesis of Amide‐imidate‐imidazolate Ligand and Formation of Metal‐Organic Frameworks: Application for Gas Storage

AbstractReview: 66 refs.