Gas Sorption Performances Research Articles

Cationic effect study in acetate-based ionic liquids/ZIF-8 composites for CO2 sorption

Several strategies can be considered for the mitigation of carbon dioxide (CO2) emissions to the atmosphere, and among them is its post-combustion capture/separation from flue gas emitted from coal-fired power plants. In this work, six imidazolium, ammonium- and DABCO-based ionic liquids (ILs) containing the acetate anion were used to impregnate the metal-organic framework (MOF) ZIF-8. The cationic effect was studied to determine how the different cationic families and side alkyl chain size influence the gas sorption performance of the produced IL@MOF composites. The combination of different characterization techniques confirmed IL impregnation, and that the composite materials were microporous and crystalline. Single-component CO2 and nitrogen (N2) sorption-desorption equilibrium measurements were performed at 303 K for ZIF-8 and the IL@ZIF-8 materials. At the low-pressure regime (0–1 bar), synergy was observed for the imidazolium-based composites, especially for the one with the long-side alkyl chain. The ideal CO2/N2 selectivity was calculated for post-combustion composition, and, at 1 bar, [C10MIM][Ac]@ZIF-8 was over four times more selective than ZIF-8, while the selectivity of [C2MIM][Ac]@ZIF-8 at this pressure almost tripled when compared to the MOF. A chemical reaction between CO2 and the imidazolium ILs explained the results.

Synthesis of ultra-porous zeolitic imidazolate Framework-300 under different synthesis conditions for sorption of CO2

We examined here how different ratios of precursors, temperature, time, and synthesis environment affected the crystal structure, texture, and CO2/N2 sorption behavior of the ZIF-300 samples synthesized. We found that a higher bmim/meIm molar ratio resulted in larger particle size, increased pore volume, and higher BET surface area due to a more crystalline structure and well-shaped pore structure. This was attributed to a decrease in the pH of the synthesis solution caused by the higher bmim/meIm molar ratio, which lowered the ζ potential and reduced electrostatic repulsion between particles, leading to the formation of larger particles with a more crystalline structure. Increasing the temperature of the synthesis solution resulted in smaller particles due to a decrease in supersaturation levels and the formation of smaller nuclei. The duration of synthesis had a positive effect on particle size as both growth and aggregation of smaller particles occurred over time. NMP and DMA were found to be unsuitable synthesis environments as they produced large particles with poor gas sorption performance. In terms of texture, ZIF-300 samples synthesized with a higher bmim/meIm molar ratio and at lower temperatures exhibited higher BET surface area and pore volume compared to other samples. Additionally, samples synthesized with a molar ratio of bmim/meIm = 4/1 and 2/1 showed better selectivity for CO2/N2 solubility compared to similar cases reported in previous studies.

Emissive fluoren-triangles for solid-state fluorochromism and selective gas sorption

•A fluorescent fluoren-triangle macrocycle is crafted •Intriguing solid-state fluorochromism capabilities are shown •Selective gas sorption performance is demonstrated In this work, we first present a new class of fluorescent synthetic macrocycle, named fluoren-triangle (FT), which we designed by creatively integrating the fluorene fluorophore into the resorcinarene backbone. Single-crystal analysis of FT revealed isosceles-triangle conformations accompanied by a layer-like molecular assembly in the solid state. Fluorescence experiments demonstrated its aggregation-induced emission character and tunable solid-state fluorescence emission, and per-methylated FT (MeFT) also exhibited an intriguing excitation-wavelength-dependent (Ex-De) capability with different emission color-switching processes. Significantly, the activated powders of per-hydroxylated FT (OHFT) and MeFT with both nonporous and amorphous features displayed remarkable potential in constructing adsorptive separation materials for CO2 and CH4 capture, affording good selectivities of 31/1 for CO2/N2 (by OHFT) and 8/1 for CH4/CO2 (by MeFT), respectively. The discovery of FT will provide new perspectives in constructing novel fluorescent macrocycles and functional photo-responsive materials, unleashing new inspirations in molecular sorbents for gas adsorption and separation. In this work, we first present a new class of fluorescent synthetic macrocycle, named fluoren-triangle (FT), which we designed by creatively integrating the fluorene fluorophore into the resorcinarene backbone. Single-crystal analysis of FT revealed isosceles-triangle conformations accompanied by a layer-like molecular assembly in the solid state. Fluorescence experiments demonstrated its aggregation-induced emission character and tunable solid-state fluorescence emission, and per-methylated FT (MeFT) also exhibited an intriguing excitation-wavelength-dependent (Ex-De) capability with different emission color-switching processes. Significantly, the activated powders of per-hydroxylated FT (OHFT) and MeFT with both nonporous and amorphous features displayed remarkable potential in constructing adsorptive separation materials for CO2 and CH4 capture, affording good selectivities of 31/1 for CO2/N2 (by OHFT) and 8/1 for CH4/CO2 (by MeFT), respectively. The discovery of FT will provide new perspectives in constructing novel fluorescent macrocycles and functional photo-responsive materials, unleashing new inspirations in molecular sorbents for gas adsorption and separation.

Precise Modulation of Surface Layer Dynamics for Tunable Flowability and Gas Absorption Properties of Molecular Porous Liquids

AbstractPorous liquids (PLs) have improved the understanding of the porous properties of matter; however, rational tuning of the viscosities and gas absorption properties of PLs lag far behind the explosive growth of PL applications. Herein, neat molecular PLs are constructed by grafting polymers onto the surface of 2 nm molecular nanocages with precisely tuned graft densities and molecular weights Mws. The flowability of the PLs showed a non‐monotonic dependence on the Mw of the polymers due to the interplay between the surface confinement effect and polymer chain entanglements, enabling optimization of their viscosities, similar to those of conventional liquids. The surface layer dynamics and gas absorption kinetics are quantified, correlation between the two properties is confirmed, and gas permeation process is regulated by surface layer dynamics. From the understanding of the structure–property relationship, the surface layer grafting densities are tuned to promote surface layer dynamics to achieve improved gas sorption performance.

Different Benzendicarboxylate-Directed Structural Variations and Properties of Four New Porous Cd(II)-Pyridyl-Triazole Coordination Polymers.

Four new different porous crystalline Cd(II)-based coordination polymers (CPs), i. e., [Cd(mdpt)2]·2H2O (1), [Cd2(mdpt)2(m-bdc)(H2O)2] (2), [Cd(Hmdpt)(p-bdc)]·2H2O (3), and [Cd3(mdpt)2(bpdc)2]·2.5NMP (4), were obtained successfully by the assembly of Cd(II) ions and bitopic 3-(3-methyl-2-pyridyl)-5-(4-pyridyl)-1,2,4-triazole (Hmdpt) in the presence of various benzendicarboxylate ligands, i.e., 1,3/1,4-benzenedicarboxylic acid (m-H2bdc, p-H2bdc) and biphenyl-4,4′-bicarboxylate (H2bpdc). Herein, complex 1 is a porous 2-fold interpenetrated four-connected 3D NbO topological framework based on the mdpt− ligand; 2 reveals a two-dimensional (2D) hcb network. Interestingly, 3 presents a three-dimensional (3D) rare interpenetrated double-insertion supramolecular net via 2D ···ABAB··· layers and can be viewed as an fsh topological net, while complex 4 displays a 3D sqc117 framework. Then, the different gas sorption performances were carried out carefully for complexes 1 and 4, the results of which showed 4 has preferable sorption than that of 1 and can be the potential CO2 storage and separation material. Furthermore, the stability and luminescence of four complexes were performed carefully in the solid state.

Microporous polymer networks constructed from cross-linkable linear polyimides for CO2 adsorption

In recent years, linear polyimides of intrinsic microporosity have been widely used in the field of gas adsorption and separation because of their high BET surface area and microporous structures. Most of the microporous structures come from the twisted main-chain structures in the linear polyimides of intrinsic microporosity. Therefore, most linear polyimides (PI) without twisted structure have no porosity. Herein, to construct the linear polyimide with microporous structure, a sequence of microporous polyimides (PIs-CL) were constructed from the flexible linear polyimide precursors through the thermal crosslinking reaction. The polyimide precursors without twisted structure were synthesized from a well-designed diamine TFVBPA with cross-linkable ethynyl groups and several commercial dianhydrides (ODPA, BPDA, PMDA and 6FDA) by polycondensation to research the influence of the main-chain structure on the porous characters. The introduction of crosslinked structures gives the linear crosslinked polyimides (PIs-CL) with porous structures. The PIs-CL show obviously improved porosity (0.52–1.71 nm) and higher BET surface area (337–618 m2 g−1) than those of the uncrosslinked polyimides (PIs). Moreover, PIs-CL have favorable CO2 adsorption (5.7–9.3 wt%) as well as good CO2/N2 selectivity (34.4–58.5) at 273 K, which are better than other polyimides materials. The introduction of crosslinked structures is an effective way to improve microporous porosity and gas sorption performance.

Metal-Organic Material Polymer Coatings for Enhanced Gas Sorption Performance and Hydrolytic Stability under Humid Conditions.

Physisorbent metal-organic materials (MOMs) have shown benchmark performance for highly selective CO2 capture from bulk and trace gas mixtures. However, gas stream moisture can be detrimental to both adsorbent performance and hydrolytic stability. One of the most effective methods to solve this issue is to transform the adsorbent surface from hydrophilic to hydrophobic. Herein, we present a facile approach for coating MOMs with organic polymers to afford improved hydrophobicity and hydrolytic stability under humid conditions. The impact of gas stream moisture on CO2 capture for the composite materials was found to be negligible under both bulk and trace CO2 capture conditions with significant improvements in regeneration times and energy requirements.

Bimetallic metal-organic frameworks (MOFs) synthesized using the spray method for tunable CO2 adsorption

A microdroplet-based spray process was applied for the fast and facile synthesis of a range of bimetallic metal–organic frameworks (MOFs), including Cu-TMA(Fe), Cu-TMA(Co), Cu-TMA(Mg), Cu-TMA(Al), and Cu-TPA(Fe) (TMA: trimesic acid; TPA: terephthalic acid). By forming M-O (M: metal, O: oxygen) bonds with the ligands, the secondary metal sites were incorporated into the framework partially substituting the original Cu sites in the parent MOF (i.e., Cu-TMA), which induced changes in surface areas, pore structures, and gas sorption properties. In particular, the bimetallic MOFs exhibited slightly higher surface areas than the parent MOF, which was attributable to the expansion of the unit cells, specifically because of the elongated M-O bonds. Meanwhile, the pore volumes of the MOFs showed a positive correlation with the atomic radii of the metal sites, suggesting that the metal substitution is an effective method to adjust the pore structures of the MOFs. Additionally, diverse gas sorption performances were observed among the bimetallic MOFs and the parent MOF, which was mainly associated with the different electrostatic interaction between the gas molecules and the frameworks induced by the incorporation of various secondary metal sites. Specifically, metal sites with larger electronegativity have a higher impact on the properties of the adsorbed CO2, such as CO bond length and OCO bond angle, leading to more asymmetric geometry and polarization of the adsorbed CO2 molecules. As a result, the gas sorption capacity, selectivity, and isosteric heat of adsorption vary with various secondary metal sites inside the framework. The results from this work offer an alternative method for the rapid synthesis of bimetallic MOFs and add new aspects to the fundamental understanding of gas sorption using bimetallic MOFs.

Metal−organic framework with dual-functionalized sites for efficient C2H2/CO2 separation

By virtue of a 4-connected rectangular-planar organic ligand 3,3′,5,5′-azobenzenetetracar-boxylate (ABTC4−), a new porous metal-organic framework (MOF) with the chemical formula of {[Zn2(ABTC)(H2O)2](DMA)3(H2O)3}n (1) has been prepared. This MOF is constructed from the {Zn2(CO2)4} cluster-based unit and shows two types of cages (octahedral and cuboctahedral cages) in the framework. Due to its cage-type network, open Zn2+ functional sites along with the azo groups functionalized pores, the resulting activated 1a displays high C2H2 storage capacity of C2H2 (179 cm3/g) at 298 K and 1 bar as well as a moderate high separation selectivity for equimolar C2H2/CO2 at 298 K. In addition, the molecular simulations were further performed to understand the different gas sorption performances.

Porous liquid zeolites: hydrogen bonding-stabilized H-ZSM-5 in branched ionic liquids.

Porous liquids, as a newly emerging type of porous material, have great potential in gas separation and storage. However, the examples and synthetic strategies reported so far likely represent only the tip of the iceberg due to the great difficulty and challenge in engineering permanent porosity in liquid matrices. Here, by taking advantage of the hydrogen bonding interaction between the alkane chains of branched ionic liquids and the Brønsted sites in H-form zeolites, as well as the mechanical bond of the long alkyl chain of the cation penetrated into the zeolite channel at the interface, the H-form zeolites can be uniformly stabilized in branched ionic liquids to form porous liquid zeolites, which not only significantly improve their gas sorption performance, but also change the gas sorption-desorption behavior because of the preserved permanent porosity. Furthermore, such a facile synthetic strategy can be extended to fabricate other types of H-form zeolite-based porous liquids by taking advantage of the tunability of the counter-anion (e.g., NTf2-, BF4-, EtSO4-, etc.) in branched ionic liquids, thus opening up new opportunities for porous liquids for specific applications in energy and environment.

The effect of centred versus offset interpenetration on C2H2 sorption in hybrid ultramicroporous materials.

Fine-tuning of hybrid ultramicroporous materials (HUMs) can significantly impact their gas sorption performance. This study reveals that offset interpenetration can be antagonistic with respect to C2H2 separation from C2H2/C2H4 gas mixtures.

Porous Organic Materials: Strategic Design and Structure-Function Correlation.

Porous organic materials have garnered colossal interest with the scientific fraternity due to their excellent gas sorption performances, catalytic abilities, energy storage capacities, and other intriguing applications. This review encompasses the recent significant breakthroughs and the conventional functions and practices in the field of porous organic materials to find useful applications and imparts a comprehensive understanding of the strategic evolution of the design and synthetic approaches of porous organic materials with tunable characteristics. We present an exhaustive analysis of the design strategies with special emphasis on the topologies of crystalline and amorphous porous organic materials. In addition to elucidating the structure-function correlation and state-of-the-art applications of porous organic materials, we address the challenges and restrictions that prevent us from realizing porous organic materials with tailored structures and properties for useful applications.

Systematic and Dramatic Tuning on Gas Sorption Performance in Heterometallic Metal–Organic Frameworks

Despite their having much greater potential for compositional and structural diversity, heterometallic metal-organic frameworks (MOFs) reported so far have lagged far behind their homometallic counterparts in terms of CO2 uptake performance. Now the power of heterometallic MOFs is in full display, as shown by a series of new materials (denoted CPM-200s) with superior CO2 uptake capacity (up to 207.6 cm(3)/g at 273 K and 1 bar), close to the all-time record set by MOF-74-Mg. The isosteric heat of adsorption can also be tuned from -16.4 kJ/mol for CPM-200-Sc/Mg to -79.6 kJ/mol for CPM-200-V/Mg. The latter value is the highest reported for MOFs with Lewis acid sites. Some members of the CPM-200s family consist of combinations of metal ions (e.g., Mg/Ga, Mg/Fe, Mg/V, Mg/Sc) that have never been shown to coexist in any known crystalline porous materials. Such previously unseen combinations become reality through a cooperative crystallization process, which leads to the most intimate form of integration between even highly dissimilar metals, such as Mg(2+) and V(3+). The synergistic effects of heterometals bestow CPM-200s with the highest CO2 uptake capacity among known heterometallic MOFs and place them in striking distance of the all-time CO2 uptake record.

A bracket approach to improve the stability and gas sorption performance of a metal-organic framework via in situ incorporating the size-matching molecular building blocks.

Incorporating the in situ formed size-matching molecular building blocks (MBBs) into the open channels will remarkably improve the robustness and gas sorption performance of an evacuated metal-organic framework. As a result, such MBBs can transfer the open metal sites from the framework walls to the channel centers and separate the large channels into multiple smaller voids, leading to a molecular sieving effect and high-performance gas-separation of the modified material.