Selective Gas Adsorption Properties Research Articles

A Flexible Dihydrogen-Bonded Organic Framework with Selective Gas Adsorption Properties

A Flexible Dihydrogen-Bonded Organic Framework with Selective Gas Adsorption Properties

Two Cu(II) microporous frameworks based on a bifunctional linker and selective gas adsorption properties for CO2

Two microporous metal-organic frameworks assembled of Cu(II) ions and bifunctional imidazoly/carboxylate containing organic compound (4-(1H-imidazole-4-yl) benzoate), namely [Cu2(L)4]·DMA·3H2O (1) and [Cu(L)2]·2H2O (2), are structurally characterized. Compound 1 shows 3-fold interpenetrating binodal 4-connected CdSO4 microporous architecture with Point (Schläfli) symbol of (65·8), while complex 2 is a supramolecular framework by stacking in an ···AAA··· configuration from two-dimensional 44 layers with one-dimensional open channels with 11.99 ​× ​11.99 ​Å2. MOF 1 shows selective adsorption capacity for CO2 (32.24 ​cm3/g) over N2 and CH4, while 2 has the uptake of 45.67 ​cm3/g for CO2 and 23.81 ​cm3/g for CH4. The corresponding the heat of adsorption calculated by Clausius–Clapeyron equation are 28.5 and 32.3 ​kJ ​mol−1. The adsorption capacity of CO2 is comparative higher than CH4 and N2, ascribing to the electrostatic interactions between CO2 and narrow pores decorated with uncoordinated imidazoly-N atoms.

Coordination-Driven Self-Assembly of Complexes Constructed from Two Helical Ligands: Synthesis, Structures, and Selective Gas Adsorption Properties.

Two helical ligands (L1 and L2) were designed and synthesized by a Schiff base condensation reaction. Eight complexes, {[Zn(L1)I2]·H2O}n (1), [Cd2(L1)2I4(CH3OH)2] (2), [Hg2(L1)2I4] (3), [Ag(L1)NO3]n (4), [Ag2(L1)2(NO3)2DMSO]·H2O (5), {[Zn2(L2)2Cl4]·2CHCl3}n (6), {[Ag(L2)]·NO3}n (7), and {[Ag(L2)NO3]·CH3OH}n (8), were synthesized and characterized based on these two ligands. The crystal structures show that both Schiff base compounds exist as racemic ligands with equal amounts of P- and M-helicity, and the assembly of these racemic ligands with metal ions can lead to homochiral or heterochiral complexes via a chiral self-recognition or self-discrimination process. Complexes 2, 3, and 5 exist as heterochiral metallomacrocycles with a figure-eight conformation. Complexes 1, 6, and 8 exist as one-dimensional (1D) homochiral helical chain coordination polymers, while complexes 4 and 7 exist as 1D heterochiral helical chain coordination polymers. Furthermore, gas and vapor adsorption measurements show that all of the synthesized complexes exhibit good selective adsorption capacities toward methanol and ethanol vapor over N2, H2, and O2.

Selective CO2 adsorption and bathochromic shift in a phosphocholine-based lipid and conjugated polymer assembly.

We assemble a film of a phosphocholine-based lipid and a crystalline conjugated polymer using hydrophobic interactions between the alkyl tails of the lipid and alkyl side chains of the polymer, and demonstrated its selective gas adsorption properties and the polymer's improved light absorption properties. We show that a strong attractive interaction between the polar lipid heads and CO2 was responsible for 6 times more CO2 being adsorbed onto the assembly than N2, and that with repeated CO2 adsorption and vacuuming procedures, the assembly structures of the lipid-polymer assembly were irreversibly changed, as demonstrated by in situ grazing-incidence X-ray diffraction during the gas adsorption and desorption. Despite the disruption of the lipid structure caused by adsorbed polar gas molecules on polar head groups, gas adsorption could promote orderly alkyl chain packing by inducing compressive strain, resulting in enhanced electron delocalization of conjugated backbones and bathochromic light absorption. The findings suggest that merging the structures of the crystalline functional polymer and lipid bilayer is a viable option for solar energy-converting systems that use conjugated polymers as a light harvester and the polar heads as CO2-capturing sites.

A Series of Metal-Organic Framework Isomers Based on Pyridinedicarboxylate Ligands: Diversified Selective Gas Adsorption and the Positional Effect of Methyl Functionality.

Solvothermal assembly of copper(II) cations and 5-(pyridine-3-yl)isophthalate linkers bearing different position-substituted methyl groups afforded four ligand-induced metal-organic framework (MOF) isomers as a platform for investigating diverse selective gas adsorption properties and understanding the positional effect of methyl functionality. Single-crystal X-ray diffraction (SCXRD) analyses showed that, when the methyl substituent is at the para position with respect to the pyridinic N atom, the resultant framework compound ZJNU-27 features an eea-type topology, while the other three solids possess an isoreticular structure with an rtl-type topology when the methyl group is situated at the other positions. As revealed by N2 physi-adsorption measurements at 77 K, they exhibit moderate specific surface areas ranging from 584 to 1182 m2 g-1 and distinct degrees of framework flexibility, which are heavily dependent on the methyl position. Comprehensive gas adsorption studies show that they are capable of effectively separating three pairs of binary gas mixtures including C2H2-CH4, CO2-CH4, and CO2-N2 couples. Moreover, their uptake capacities and adsorption selectivities can be tailored by altering the methyl position. In addition, their framework hydro-stability is also influenced by the methyl position. Compared to ZJNU-27 and ZJNU-28, ZJNU-26 and ZJNU-29 exhibit poorer stability against H2O, although the methyl group is more close to inorganic secondary building units (SBUs), which are believed to originate from the steric effect of the methyl group. Overall, the four MOFs display the methyl position-dependent network architectures, framework flexibilities, and selective gas adsorption properties as well as hydrostabilities. The findings observed in this work not only demonstrate the importance of the positional effect of the functional group but also highlight that engineering the substituent position is a potential strategy for achieving the modulation of MOF structures and properties.

A Microporous MOF with Inorganic Nitrate Ions Immobilized on a Porous Surface Displaying Efficient C2H2 Separation and Purification

A microporous MOF based on a heterotopic ligand was successfully synthesized under solvothermal conditions and fully characterized using single‐crystal and powder X‐ray diffraction, TGA, FTIR, and microanalyses. Single‐crystal X‐ray diffraction analyses showed that the title MOF contains rich inorganic nitrate ions decorating the channel surface that can serve as C2H2 recognition sites. Its selective gas adsorption properties towards C2H2 over CO2 and CH4 were evaluated by single‐component equilibrium adsorption measurements and IAST calculations, establishing its promising potential for C2H2 separation and purification. At ambient conditions, the C2H2 uptake capacity reaches 92.2 cm3 (STP) g–1, while the IAST‐predicted adsorption selectivities are up to 30.6 and 4.5 for the equimolar C2H2‐CH4 and C2H2‐CO2 binary gas mixtures, respectively. Furthermore, DFT computation studies revealed that the inorganic nitrate ion plays a very important role for preferential adsorption of C2H2 over CO2 and CH4.

Dipyrrolylnaphthyridine-based Schiff-base cryptands and their selective gas adsorption properties

Presented here is the synthesis of three new Schiff-base cryptands, 4–6. Dynamic covalent imine bond formation via the condensation of a dialdehyde (7 or 8) with two different tris-amines allowed for the preparation of 4–6 in 84%, 80% and 83% yield, respectively. These systems were characterized by NMR spectroscopy, mass spectra, and, in the case of 5, single crystal X-ray diffraction analysis. These cages act as selective CO[Formula: see text] gas adsorbing materials in the solid state.

Construction and selective gas adsorption properties of two heteroSBU MOFs based on unsymmetrical tetracarboxylate linkers

Two homometallic pure-carboxylate hetero-SBU MOFs were constructed, displaying selective C2H2/CH4and CO2/CH4separation potential.

Shape-persistent pyrrole-based covalent organic cages: synthesis, structure and selective gas adsorption properties.

Two cryptand-like, shape persistent [2+3] imine cages (1 and 2) derived from oligopyrrolic precursors (diformyl dipyrrylpyridine 3 and diformyl bipyrrole 4) were prepared. These cages contain open cavities as inferred from solid state structural analyses and act as selective CO2 gas adsorbing materials in the solid state.

A rod-like phenolic π-conjugated polymer with pillar[5]arene units in its main chain

A new rigid rod-like phenolic π-conjugated polymer containing pillar[5]arene units in its main chain was prepared. First, a pillar[5]arene-containing π-conjugated polymer was prepared by Pd-catalyzed copolymerization of 4,4’-diphenyldiboronic acid with a pillar[5]arene bearing two triflate moieties in one hydroquinone unit and eight ethoxy groups in the other units. Then, deprotection of the ethyl moieties using BBr3 gave a rigid rod-like phenolic π-conjugated polymer. The phenolic polymer showed high thermal stability, with a 10 wt% loss temperature (T10) of 300 °C in a nitrogen atmosphere, which is higher than that of a pillar[5]arene containing 10 phenolic moieties (T10 = 164 °C). Moreover, the phenolic π-conjugated polymer showed selective gas adsorption properties: it was highly selective for the adsorption of CO2, but did not take up N2 or methane.

Expanded Porous MOF-505 Analogue Exhibiting Large Hydrogen Storage Capacity and Selective Carbon Dioxide Adsorption

An expanded 4,4-paddlewheel-connected porous MOF-505-type metal-organic framework (MOF), [Cu2(PDEB)(H2O)2]·xS (NJU-Bai12; NJU-Bai represents the Nanjing University Bai group and S represents noncoordinated solvent molecules) has been designed from a nanosized rectangular diisophthalate linker containing alkyne groups 5,5'-(1,4-phenylenedi-2,1-ethynediyl)bis(1,3-benzenecarboxylic acid). This MOF material possesses permanent microporosity with the highest Brunauer-Emmett-Teller surface area of 3038 m(2)·g(-1) and the largest unsaturated total hydrogen storage capacity of 62.7 mg·g(-1) at 77 K and 20 bar among reported MOF-505 analogues. Additionally, NJU-Bai12 also exhibits excellent carbon dioxide (CO2) uptake capacity (23.83 and 19.85 mmol·g(-1) at 20 bar for 273 and 298 K, respectively) and selective gas adsorption properties with CO2/CH4 selectivity of 5.0 and CO2/N2 selectivity of 24.6 at room temperature.

Four 3D Cd(II)-Based Metal Organic Hybrids with Different N,N′-Donor Spacers: Syntheses, Characterizations, and Selective Gas Adsorption Properties

Four new metal organic frameworks with bivalent cadmium, disodium succinate (Na2suc), and four different N,N′-donor ligands, i.e., {[Cd(L1)(suc)]·(H2O)3}n (1), {[Cd(L2)(suc)]·(H2O)2}n (2), {[Cd(L3)(suc)]·(H2O)4}n (3), {[Cd3(L4)3(suc)2(H2O)2]·(NO3)2 (H2O)4}n (4) [L1 = 2,5-bis-(4-pyridyl)-3,4-diaza-2,4-hexadiene, L2 = trans 4,4′-azobispyridine, L3 = 2,5-bis-(3-pyridyl)-3,4-diaza-2,4-hexadiene, L4 = 1, 2-bis(4-pyridyl) ethane and suc = succinate dianion] have been synthesized at room temperature and characterized by single-crystal X-ray diffraction and other physicochemical methods. Structure determination reveals that compounds 1 and 2 show honeycomb-like three-dimensional (3D) architecture with water-filled channels. The dehydrated frameworks of 1 and 2 exhibit hydrogen and carbon dioxide adsorption properties. In compound 3, change of linker (linear to bent) led to the blockage of such regular channels which also affected the porosity and adsorption properties of its dehydrated framework. In 4, the used spacer is linear but the resulting 3D framework contains blocked channels filled with nitrate (NO3–) anions and lattice water.

A Soft Copper(II) Porous Coordination Polymer with Unprecedented Aqua Bridge and Selective Adsorption Properties

Herein, the synthesis, crystal structure, and full characterization of a new soft porous coordination polymer (PCP) of ([Cu(2)(dmcapz)(2)(OH(2))]DMF(1.5))(n) (1) formulation, which is easily obtained in the reaction of CuX(2) (X = Cl, NO(3)) salts with 3,5-dimethyl-4-carboxypyrazole (H(2)dmcapz) is present. Compound 1 shows a copper(II) dinuclear secondary building unit (SBU), which is supported by two pyrazolate bridges and an unprecedented H(2)O bridge. The dinuclear SBUs are further bridged by the carboxylate ligands to build a diamondoid porous network. The structural transformations taking place in 1 framework upon guest removal/uptake has been studied in detail. Indeed, the removal of the bridging water molecules gives rise to a metastable evacuated phase (1 b) that transforms into an extremely stable porous material (1 c) after freezing at liquid-nitrogen temperature. The soaking of 1 c into water allows the complete and instantaneous recover of the water-exchanged material (1 a'). Remarkably, 1 b and 1 c materials possess structural bistability, which results in the switchable adsorptive functions. Therefore, the gas-adsorption properties of both materials have been studied by means of single-component gas adsorption isotherms as well as by variable-temperature pulse-gas chromatography. Both materials present permanent porosity and selective gas-adsorption properties towards a variety of gases and vapors of environmental and industrial interest. Moreover, the flexible nature of the coordination network and the presence of highly active convergent open metal sites confer on these materials intriguing gas-adsorption properties with guest-triggered framework-breathing phenomena being observed. The plasticity of Cu(II) metal center and its ability to form stable complexes with different coordination numbers is at the origin of the structural transformations and the selective-adsorption properties of the studied materials.

Solvent influences structural variation from a 3D 4-fold interpenetrated framework to a 2D layer-type porous coordination polymer: Structure analysis and highly selective gas adsorption properties

Two new complexes {[Co(dcpy)(bipy)0.5]·H2O} (1) and {[Co(dcpy)(bipy)0.5(H2O)]·2H2O} (2) constructed from the same initial materials Co(NO3)2·6H2O, 3-(2′,5′-dicarboxylphenyl)pyridine (H2dcpy) and 4,4′-bipyridine (bipy), exhibiting varying architectures from a 3D 4-fold interpenetrated framework to a 2D layer-type porous coordination polymer (PCP) were synthesized by changing the reaction solvent. In particular, the dehydrated 2 shows a high selective gas sorption for H2 over N2 at 77 K and high selectivity for CO2 over N2 and CH4 at 293 K.

Preparation and Gas Adsorption Characteristics of Zeolite MFI Crystals with Organic-Functionalized Interiors

We show that the selective gas adsorption properties of pure-silica MFI zeolite crystals are significantly altered by modifying their internal pore structure with molecules such as aliphatic alcohols, aromatic alcohols, amino-alcohols, and amines. NMR and TGA/DSC characterization indicates that the functional groups are chemisorbed to the internal pores, and the organic molecule loading is strongly dependent on the concentration of internal silanol sites. Adsorption isotherms of CO2, CH4, and N2 are measured for the functionalized samples up to 400 kPa. In the low pressure region (1–10 kPa), the organic-modified materials show gas adsorption behavior significantly different from that of the bare zeolite MFI, ranging from an enhancement in CO2/CH4 sorption selectivity in the amine-functionalized materials to an enhancement in CH4 adsorption in the aromatic-functionalized material. The CO2/N2 sorption selectivity decreases for all the modified materials compared to bare zeolite MFI. This investigation of organic-modified MFI zeolites points toward the tuning of adsorption and molecular sieving behavior of zeolites through internal modification of the pores.

Microporous Metal–Organic Framework Based on Supermolecular Building Blocks (SBBs): Structure Analysis and Selective Gas Adsorption Properties

A new supermolecular building blocks (SBBs) based microporous metal–organic framework (MOF) was prepared with both 1,3,5-benzenetricarboxylic acid (H3btc) and 2,4,6-tris(4-pyridyl)-1,3,5-triazine (tpt) as ligands. The obtained CoII MOF reveals an uncommon ftw-a-like structure from the assembly of cubohemioctahedra SBBs under the direction of tpt and exhibits selective gas adsorption properties depending on gas molecule diameter and temperature which might have application in gas separation purposes.

Three Coordination Polymers Based on 1H-Tetrazole (HTz) Generated via in Situ Decarboxylation: Synthesis, Structures, and Selective Gas Adsorption Properties

Three tetrazole-based coordination polymers, [Zn3(Tz)6(H2O)2]n (1), [Cu2(Tz)3(OH)]n (2), and {[Cu5(Tz)9](NO3)·8H2O}n (3) (Tz = tetrazolate) have been prepared under hydro(solvo)thermal conditions using ethyl tetrazolate-5-carboxylate and corresponding metal salts as building blocks, in which tetrazolate was generated via in situ decarboxylation. The results of X-ray single diffraction analyses indicate that 1 possesses a 2D layer structure with μ2-Tz− bridged six- and four-coordinated Zn(II), forming a rare kagome dual topological layer. Compound 2 is a 3D layer−pillar structure, in which the Cu(II) ions are bridged by μ3-Tz− anions to generate a 2D sheet, and the 2D sheets are further pillared by μ2-Tz− and μ2-OH− to form a 3D framework with a fsc topology net. Compound 3 is a 3D porous framework with an acs topology net. Compound 1 exhibits photoluminescent properties with an emission peak at 467 nm, and compound 3 shows selective H2 and CO2 over N2 adsorption.

Modulating Metal−Organic Frameworks To Breathe: A Postsynthetic Covalent Modification Approach

Postsynthetic covalent modification of a metal-organic framework (MOF) is shown to activate "breathing" behavior upon adsorption of certain gases. The findings reported suggest that chemical modification can be used to trigger, tune, and control the flexibility of MOFs in an unprecedented fashion. By manipulation of MOF breathing and flexibility, the development of new MOFs with selective gas adsorption properties may be realized.