Gas Separation Applications Research Articles

An ethynyl-modified interpenetrated metal-organic framework for highly efficient selective gas adsorption.

An ethynyl-modified interpenetrated MOF material with lvt topology, [Cu2(BTEB)(NMF)2]·NMF·8H2O (compound 1, H4BTEB = 4,4',4'',4'''-(benzene-1,2,4,5-tetrayltetrakis(ethyne-2,1-diyl))tetrabenzoic acid, NMF = N-Methylformamide), was successfully synthesized by using an alkynyl-functionalized H4BTEB organic ligand under solvothermal conditions. Structural analysis shows that compound 1, consisting of a tetradentate carboxylic acid ligand and classical [Cu2(CO2)4] paddle-wheel structure building units, has a rare 4-connected lvt topology with dual interpenetrating structure, which can improve the framework stability, as well as the gas adsorption capacity and selectivity due to the restricted pore channel. According to the study of gas adsorption performance, compound 1 with a larger surface area, boasts a superior adsorption capacity for small gas molecules. Also, ideal adsorption solution theory (IAST) computational simulation shows that compound 1 has good gas adsorption selectivity for C3H8/CH4, indicating its potential application in gas separation.

The Mechanical Property of 2D Materials and Potential Application in Gas Separation

The Mechanical Property of 2D Materials and Potential Application in Gas Separation

Fabrication and Characterization of Nanoscale Metal-Organic Frameworks (MOFs) for Gas Storage and Separation

In recent years, Metal-Organic Frameworks (MOFs) have emerged as a promising class of materials for gas storage and separation applications due to their high surface area, tunable pore size, and chemical functionality. In this study, we report the successful fabrication and characterization of nanoscale MOFs for enhanced gas storage and separation performance. We synthesized a series of MOFs with varying metal nodes and organic linkers, and systematically investigated their structural, thermal, and chemical stability. Advanced characterization techniques, including X-ray diffraction, scanning electron microscopy, and gas adsorption isotherms, were employed to elucidate the structural and morphological features of the synthesized MOFs. The gas storage capacities of the MOFs were evaluated for hydrogen, methane, and carbon dioxide, revealing a significant enhancement in storage capacity compared to bulk MOFs. Furthermore, we investigated the gas separation performance of the MOFs for CO2/CH4 and CO2/N2 mixtures, demonstrating high selectivity and separation efficiency. The results of this study provide valuable insights into the design and fabrication of nanoscale MOFs for gas storage and separation applications, and pave the way for the development of next-generation materials for clean energy and environmental applications.

Zeolites and metal-organic frameworks for gas separation: the possibility of translating adsorbents into membranes.

Zeolites and metal-organic frameworks (MOFs) represent an attractive class of crystalline porous materials that possesses regular pore structures. The inherent porosity of these materials has led to an increasing focus on gas separation applications, encompassing adsorption and membrane separation techniques. Here, a brief overview of the critical properties and fabrication approaches for zeolites and MOFs as adsorbents and membranes is given. The separation mechanisms, based on pore sizes and the chemical properties of nanochannels, are explored in depth, considering the distinct characteristics of adsorption and membrane separation. Recommendations for judicious selection and design of zeolites and MOFs for gas separation purposes are emphasized. By examining the similarities and differences between the roles of nanoporous materials as adsorbents and membranes, the feasibility of zeolites and MOFs from adsorption separation to membrane separation is discussed. With the rapid development of zeolites and MOFs towards adsorption and membrane separation, challenges and perspectives of this cutting-edge area are also addressed.

Recent advances in the chemistry and applications of fluorinated metal-organic frameworks (F-MOFs).

Metal-organic frameworks are a class of porous crystalline materials based on the ordered connection of metal centers or metal clusters by organic linkers with comprehensive functionalities. The interest in these materials is rapidly moving towards their application in industry and real life. In this context, cheap and sustainable synthetic strategies of MOFs with tailored structures and functions are nowadays a topic widely studied from different points of view. In this review, fluorinated MOFs (F-MOFs) and their applications are investigated. The principal aim is to provide an overview of the structural features and the main application of MOFs containing fluorine atoms both as anionic units or as coordinating elements of more complex inorganic units and, therefore, directly linked to the structural metals or as part of fluorinated linkers used in the synthesis of MOFs. Herein we present a review of F-MOFs reported in the recent literature compared to benchmark compounds published over the last 10 years. The compounds are discussed in terms of their structure and properties according to the aforementioned classification, with an insight into the different chemical nature of the bonds. The application fields of F-MOFs, especially in sustainability related issues, such as harmful gas sorption and separation, will also be discussed. F-MOFs are compounds containing fluorine atoms in their framework and they can be based on: (a) fluorinated metallic or semi-metallic anionic clusters or: (b) fluorinated organic linkers or (c) eventually containing both the building blocks. The nature of a covalent C-F bond in terms of length, charge separation and dipole moment sensibly differs from that of a partly ionic M-F (M = metal) one so that the two classes of materials (points a and b) have different properties and they find various application fields. The study shows how the insertion of polar M-F and C-F bonds in the MOF structure may confer several advantages in terms of interaction with gaseous molecules and the compounds can find application in gas sorption and separation. In addition, hydrophobicity tends to increase compared to non-fluorinated analogues, resulting in an overall improvement in moisture stability.

Modular metallotecton for engineering permanently porous frameworks: supernumerary role of ancillary ion.

The formation of robust supramolecular frameworks built from hetero-polytopic metal complexes and interacting with different ancillary ions remains a long-standing and underexplored desire. Herein, the secondary sphere interaction chemistry of [Ru(5-oxido-6-hydroxy-1,10-phenanthroline)a(5,6-dihydroxy-1,10-phenanthroline)(3-a)]-(a-2) (1) (a = 1, 3) coordination ion is reported, where the π-conjugated phenanthroline ligands are functionalized with catecholate groups used as H-bond donors and ligands. The deprotonation of the catechols is found to control the overall charge stoichiometry in 1, acting as a metallotecton to interact with anions of different basicity (Cl- in 1.Cl and Br- in 1.Br) as well as with Li+ cations (in 1.Li+). These interactions lead to the formation of 2D porous honeycomb networks without any significant alteration in the molecular packing. This implies that the self-assembly process is controlled by complementary intermolecular non-covalent interactions making the choice of the ancillary ion insignificant. The robust porous structure of the frameworks is established by uptake of D2O and I2 molecules within the microporous channels. This work demonstrates that supramolecular frameworks appear as flexible candidates for applications in gas sorption, separation and chemical sensing.

Post-synthetic modifications of covalent organic frameworks (COFs) for diverse applications.

Covalent organic frameworks (COFs) are porous and crystalline organic polymers, which have found usage in various fields. These frameworks are tailorable through the introduction of diverse functionalities into the platform. Indeed, functionality plays a key role in their different applications. However, sometimes functional groups are not compatible with reaction conditions or can compete and interfere with other groups of monomers in the direct synthetic method. Also, pre-synthesis of bulky moieties in COFs can negatively affect crystal formation. To avoid these problems a post-synthetic modification (PSM) approach is a helpful tactic. Also, with the assistance of this strategy porous size can be tunable and stability can be improved without considerable effect on the crystallite. In addition, conductivity, hydrophobicity/ hydrophilicity, and chirality are among the features that can be reformed with this method. In this review, different types of PSM strategies based on recent articles have been divided into four categories: (i) post-functionalization, (ii) post-metalation, (iii) chemical locking, and (iv) host-guest post-modifications. Post-functionalization and chemical locking methods are based on covalent bond formation while in post-metalation and host-guest post-modifications, non-covalent bonds are formed. Also, the potential of these post-modified COFs in energy storage and conversion (lithium-sulfur batteries, hydrogen storage, proton-exchange membrane fuel cells, and water splitting), heterogeneous catalysts, food safety evaluation, gas separation, environmental domains (greenhouse gas capture, radioactive element uptake, and water remediation), and biological applications (drug delivery, biosensors, biomarker capture, chiral column chromatography, and solid-state smart nanochannels) have been discussed.

Synthesis and characterization of a high-performance bio-based Pebax membrane for gas separation applications

Synthesis of biobased membranes for gas separation applications. The Pebax® Rnew® 30R51 membrane holds potential for CO2 separation. Increasing the polymer concentration enhanced the gas selectivity to 91 and 26 for CO2/N2 and CO2/CH4, respectively.

A study of the permeation barrier of nanoporous Graphene

Nanoporous Graphene, due to its single atom thickness and good mechanical strength is an emerging candidate for efficient and reliable gas separation applications. The permeation of the gas molecules through the pores can be seen as an activated process, whereby the gas molecules have to overcome a threshold barrier before it can pass through the pore. Here, we study and compare the Single Point Energy of the CO2 molecule as it approaches a nanoporous Graphene sheet comprising of 6 Carbon atoms removed contiguously to create what is known as the Type A nanopore. The distance of the single molecule from the pore is varied continuously for 2 configurations of the gas molecule, one parallel and other perpendicular to the nanopore, positioned vertically above the centre of the 6-pore, by means of ab-initio simulations based on Density Functional Theory. The permeation barrier of the CO2 molecule is estimated. It is found that orientation of incident molecule along with the pore geometry, plays an important role in gas permeation and penetration barriers, and thereby in all applications that crucially depend upon the rate of gas permeation, like gas separation for example.

3D ceramic structure fabrication by Stereolithography and physicochemical characterization

In this study, a methodology for 3D printing of Silica (SiO2) structures for potential gas separation applications (either as membranes or as substrates for selective layers deposition) utilizing Stereolithography (SLA) is presented. The porosity, morphology and crystallinity of the 3D printed samples structure were optimized by the parametric study of the calcination profile of the printed ceramic SiO2 resin; the printed material was calcined at 450, 600 and 1250 °C by different residence times at different temperature steps. The microstructure of the 3D printed samples was characterized with Scanning Electron Microscopy (SEM) and Energy Dispersive X-ray Spectroscopy (EDS). Structural characterization (crystallinity and average crystal size) was performed by X-Ray Diffraction (XRD). The porosity and the specific surface area of the 3D printed samples were determined through the Brunauer–Emmett–Teller (BET) technique, which revealed that the surface area was gradually increased by increasing final calcination temperature. Permeability tests with flat sheet printed samples were performed in a constant pressure (isobaric) gas permeation system to quantify pure gases’ (e.g., CO2, N2, O2, Ar) permeances. Permselectivities of binary gaseous mixtures were obtained for printed samples calcined under different temperature profiles. The outcomes open new opportunities in 3D printing of versatile ceramic structures which can be exploited either as substrates for gas separation ceramic membranes or as membrane contactors for gas–liquid applications.

Revisiting Competitive Adsorption of Small Molecules in the Metal–Organic Framework Ni-MOF-74

To precisely evaluate the potential of metal-organic frameworks (MOFs) for gas separation and purification applications, it is crucial to understand how various molecules competitively adsorb inside MOFs. In this paper, we combine in situ infrared spectroscopy with ab initio calculations to investigate the mechanisms associated with coadsorption of several small molecules, including CO, NO, and CO2 inside the prototypical structure Ni-MOF-74. Surprisingly, we find that the displacement of CO bound inside Ni-MOF-74 (binding energy of 53 kJ/mol) is readily driven by CO2 exposure, even though CO2 has a noticeably weaker binding energy of only 41 kJ/mol; meanwhile, the significantly more strongly binding NO molecule (90 kJ/mol) is not able to easily displace bound CO inside Ni-MOF74. These results show that single-phase binding energies of a molecule inside the MOF cannot completely describe their interaction with the MOF in the presence of other guest molecules. We unveil many crucial factors, such as the kinetic barrier, partial pressure, secondary binding sites, and guest-host/lateral interactions that control the coadsorption process and, combined with the binding energy, are better descriptors of the behavior and adsorption of gas mixtures inside MOFs.

A comprehensive review on zeolite-based mixed matrix membranes for CO2/CH4 separation

Biogas consisting of carbon dioxide/methane (CO2/CH4) gas mixtures has emerged as an alternative renewable fuel to natural gas. The presence of CO2 can decrease the calorific value and generate greenhouse gas. Hence, separating CO2 from CH4 is a vital step in enhancing the use of biogas. Zeolite and zeolite-based mixed matrix membrane (MMM) is considered an auspicious candidate for CO2/CH4 separation due to thermal and chemical stability. This review initially addresses the development of zeolite and zeolite-based MMM for the CO2/CH4 separation. The highest performance in terms of CO2 permeance and CO2/CH4 selectivity was achieved using zeolite and zeolite-based MMM, which exhibited CO2 permeance in the range of 2.0 × 10− 7–7.0 × 10− 6 mol m− 2 s− 1 Pa− 1 with CO2/CH4 selectivity ranging from 3 to 300. Current trends directed toward improving CO2/CH4 selectivity via modification methods including post-treatment, ion-exchanged, amino silane-grafted, and ionic liquid encapsulated of zeolite-based MMM. Those modification methods improved the defect-free and interfacial adhesions between zeolite particulates and polymer matrices and subsequently enhanced the CO2/CH4 selectivity. The modifications via ionic liquid and silane methods more influenced the CO2/CH4 selectivity with 90 and 660, respectively. This review also focuses on the possible applications of zeolite-based MMM, which include the purification and treatment of water as well as biomedical applications. Lastly, future advances and opportunities for gas separation applications are also briefly discussed. This review aims to share knowledge regarding zeolite-based MMM and inspire new industrial applications.

Polymer materials derived from the SEAr reaction for gas separation applications

A set of linear polymers were synthesized utilizing an electrophilic aromatic substitution reaction (SEAr) between biphenyl and ketone containing electron-withdrawing groups (isatin, IS; N-methylisatin, MeIS; and 4,5-diazafluoren-9-one, DF). Optimization of the polycondensation reaction was made to obtain high molecular weight products when using DF, which has not previously been used for linear polymer synthesis. Due to the absence of chemically labile units, these polymers exhibited excellent chemical and thermal stability. Linear SEAr polymers were blended with porous polymer networks derived from IS and MeIS, and both neat/mixed materials were tested as membranes for gas separation. The gas separation properties of both pristine polymers and mixed matrix membranes were good, showing some polymer membrane CO2 permeability values higher than 200 barrer.

Poly(vinyl alcohol) mediated bifunctional ZIF-BN nanocomposite for the high-selectivity H2 separation membrane

We combined the advantages of the 2-methylimidazole zinc salt (ZIF-8) and hydroxylated boron nitride (OH-BN) materials to prepare a new bifunctional separation material, namely ZIF-BN. In this, spherical ZIF-8 materials fill the macroporous structure of OH-BN sheets by coordination bonds due to the edge effect. Furthermore, a series of ZIF-BN/PVA membranes were prepared using the vacuum-assisted filtration of the layer-by-layer for the gas separation study. The trace amounts of PVA connect adjacent ZIF-BN sheets through hydrogen bonds, without covering the pore structures of ZIF-8 materials. Based on this exclusive strategy for preparing membranes, the obtained membranes exhibit superior H2 separation performances. Compared with the pure PVA membrane, the H2 permeability, H2/CO2 selectivity, and H2/N2 selectivity of the ZIF-BN/PVA-8 membrane have increased (54, 13, & 12)-fold, to (600 Barrer, 97.2, & 173.6), respectively. This strategy provides a facile way to design new bifunctional membranes for gas separation applications.

Synthesis of a Highly Crystalline Amide‐Linked Covalent Organic Framework

Comprehensive SummaryThe dilemma for the synthesis of covalent organic frameworks (COFs) is crystallinity and stability. Herein, we present the synthesis of a single‐crystalline amide‐linked COF, and demonstrate its excellent chemical as well as thermal stabilities. This study will inspire the synthesis of a wide spectrum of highly crystalline and stable COFs, promote their structure‐property investigations and boost their applications in selective gas adsorption, storage and separation.

Aromatic Polyimide Membranes with tert-Butyl and Carboxylic Side Groups for Gas Separation Applications-Covalent Crosslinking Study.

A set of aromatic copolyimides was obtained by reaction of 4,4'-(hexafluoroisopropylidene) diphthalic anhydride (6FDA), and mixtures of the diamines 1,4-bis(4-amino-2-trifluoromethylphenoxy)-2,5-di-tert-butylbenzene (CF3TBAPB) and 3,5-diamino benzoic acid (DABA). These polymers were characterized and compared with the homopolymer derived from 6FDA and CF3TBAPB. All copolyimides showed high molecular weight values and good mechanical properties. The presence of carboxylic groups in these copolymers allowed their chemical crosslinking by reaction with 1,4-butanediol. Glass transition temperatures (Tg) were higher than 260 °C, showing the non-crosslinked copolyimides had the highest Tg values. Degradation temperature of crosslinked copolyimides was lower than their corresponding non-crosslinked ones. Mechanical properties of all polymers were good, and thus, copolyimide (precursor, and crosslinked ones) films could be tested as gas separation membranes. It was observed that CO2 permeability values were around 100 barrer. Finally, the plasticization resistance of the crosslinked material having a large number of carboxylic groups was excellent.

Deep eutectic solvents as reusable catalysts and promoter for the greener syntheses of small molecules: Recent advances

Deep eutectic solvents (DESs) are significant environmentally benign media in the field of green chemistry. They are known not only for their inexpensive nature, biodegradability, non-toxicity, and bioavailability, but also for recyclability and their ease of preparation and purification. DESs are made up of hydrogen bond donor substituents (such as urea, carboxylic acid, glycerol, metals, etc.) and hydrogen bond acceptor substituents such as halide salts; they have a lower melting point than each substituent comprising the mixture. DESs find applications in biotransformation, gas separation, biomass valorization, electrochemistry, extraction, and dissolution process as well as in material chemistry and other assorted fields of chemistry. Interestingly, DESs fulfil a unique dual role as green solvents, promoters and catalysts in organic syntheses. Thus, it is noteworthy that chemical progresses and transformation with external catalysts in cross-coupling reactions, oxidations and reductions are not covered in this overview. This review mostly focuses on leading-edge applications of DES as a reusable catalyst in the expeditious synthesis of assorted small molecules central in the assembly of broad-spectrum pharmaceuticals, and total synthesis of common natural products.

A Cavity-Tailored Metal-Organic Tetrahedral Nanocage and Gas Adsorption Property.

Porous organometallic nanomaterials are a new class of materials based on a three-dimensional structure. They have excellent applications in different fields, but their applications in gas storage and separation have not been fully developed. CO2 adsorption storage and hydrocarbon separation has been a challenging industrial problem. Several typical molecular adsorbents have been used to study the separation, but the problems of long-term stability, high selectivity and synthetic complexity of these adsorbents remain to be solved. Here, we have designed and synthesized tetrahedral metal supramolecular nanocage with custom cavities based on the unique rigid structure of triptycene derivatives. Using the unique discrete porous structure of tetrahedral metal nanocages, the gas adsorption and separation performance of the metal supramolecular nanocage was investigated. By analyzing the adsorption and desorption isotherms and the multi-component competitive adsorption curves, we noticed that the tetrahedral supramolecular nanocages had good CO2 storage capacity and good separation capacity for C2H2/CO2 and C2H2/N2. All these indicate that porous organic metal nanomaterials are expected to be a new energy saving separation material.

Flexibility of Mixed Ligand Zeolitic Imidazolate Frameworks (ZIF-7-8) under CO2 Pressure: An Investigation Using Positron Annihilation Lifetime Spectroscopy.

Fine tuning of the pore architecture and flexibility of zeolitic imidazolate frameworks (ZIFs) is highly crucial for realizing their applications in molecular gas separation. Mixed ligand frameworks (ZIF-7-8) synthesized by mixing 2-methylimidazole (2meIm) and benzimidazole (bIm) ligands show enhanced gas separation performance, attributable to pore and flexibility tuning. In the present study, positron annihilation lifetime spectroscopy (PALS) measurements under CO2 pressure have been used to experimentally investigate the tuning of the pore architecture and flexibility of mixed ligand frameworks ZIF-7-8 having a ZIF-8 structure and similar morphology with varying bIm content up to 18.2%. The aperture and cavity of frameworks begin to open up with an increasing bIm ligand content followed by a decrease at a higher content. On the contrary, flexibility of the frameworks indexed from PALS measurements carried out under CO2 pressure shows a decreasing trend followed by an increase. The present study shows that mixed ligand frameworks having a larger aperture size are less flexible as a result of inherent open configurations of ligands in the framework lattice. On the other hand, frameworks having a comparatively smaller aperture size show higher flexibility as a result of a possibility of twisting of the ligands under CO2 pressure, resulting in aperture opening. The pore-opening phenomenon as a result of lattice flexibility under CO2 pressure is observed to be fully reversible for ZIF-7-8.

In-situ interfacial crosslinking of NH2-MIL-53 and polyimide in MOF-incorporated mixed matrix membranes for efficient H2 purification

The key issue to avoiding the degradation of gas separation performance due to the formation of non-selective defects in mixed matrix membranes (MMMs) is to promote the interfacial compatibility of fillers with the continuous polymer matrix. In this work, we report an efficient and simple method to prepare MMMs by crosslinking metal organic frameworks (MOF) and polyamic acid (PAA) (the precursor of polyimide), in which NH2-MIL-53 particles are thermally crosslinked with the PAA during the imidization reaction, forming hydrogen bonds and amide bonds at the interface. The resulting enhanced interfacial force greatly improves the interfacial compatibility of the membrane, which is also more conducive to the separation of H2/CO2. Among the as-prepared samples, PI-NH2-MIL-53 MMMs loaded with 30 wt% MOF exhibit excellent H2 permeability (384.1 Barrer) and H2/CO2 permeation selectivity (16.7), which are significantly higher than the 2008 Robeson upper bound. The membranes also display enhanced mechanical characteristics and long-term stability. Here, building strong interactions on MOF/polymer MMMs using an in-situ cross-linking strategy to enhance membrane performance provides a new opportunity to develop advanced membranes for industrial gas separation applications.