Search

Carbon molecular sieve (CMS) membranes show attractive potential for energy-efficient separation of C 2 H 4 /C 2 H 6 due to their unique slit-like pore structure. In this work, a novel precursor polymer of phenolphthalein-based poly(arylene ether ketone) (PEK-C) was introduced to prepare high-performance CMS membranes for C 2 H 4 /C 2 H 6 separation. Molecular insight into the effect of the sp 3/ sp 2 hybridized carbon ratio on the packing morphology of carbon layers, pore size and configuration, and C 2 H 4 /C 2 H 6 diffusion and separation properties of CMS membranes was investigated via using in-depth characterization techniques combined with molecular simulations. Results show that the carbon layers with more sp 3 hybridized carbons lead to forming a loose and disordered carbon structure and pore structure with large pore volume and micropore size (steric voids), resulting in low C 2 H 4 /C 2 H 6 permselectivity of CMS membrane. With the reduction of the sp 3/ sp 2 hybridized carbon ratio, a compact and graphite-like carbon structure with the two-dimensional slit-like ultramicropore structure is formed, and the C 2 H 4 /C 2 H 6 permselectivity is obviously enhanced. The CMS membranes derived from the novel precursor of PEK-C exhibit high C 2 H 4 permeability with superior C 2 H 4 /C 2 H 6 selectivity, which have surpassed the trade-off bounds of both polymeric membrane and CMS membrane, and reveal a great potential in the industrial applications of C 2 H 4 /C 2 H 6 separation. [Display omitted] • A novel precursor was introduced to prepare high-performance CMS membranes. • The structure-property relationships between microstructure and gas separation performance were investigated. • The sp3/ sp 2 hybridized carbon ratio obviously affects the C 2 H 4 /C 2 H 6 diffusion selectivity. • The C 2 H 4 /C 2 H 6 separation performance of CMS membranes exceed the trade-off bounds of polymeric and CMS membranes. [ABSTRACT FROM AUTHOR]

[Display omitted] • The electric field has a substantial impact on CO 2 molecules structure. • PEK-C(CN) membrane is electrically stable. • PEK-C(CN) membrane favored CO 2 adsorption both with and without electric field. • Flow velocity distribution aided locate connected pores, and transportation paths. • Electric field significantly enhanced CO 2 mass transport through the membrane pores. An important challenge in membrane technology for gas separation is to simultaneously improve their permeability and selectivity. Often, the increase in one performance leads to the decline of the other. This study presents a solution to that problem by utilizing electrical field coupling to improve CO 2 permeation through a nitrile-containing poly (arylene-ether-ketone) (PEK-C(CN)) carbon molecular sieve membrane. Density functional based tight binding simulations of CO 2 , CH 4 , and N 2 adsorption on PEK-C(CN) monolayer were conducted without and with electric field. The findings revealed that the electric field strength and orientation affected the molecules bond lengths, atomic charges, and bond angles. Investigation of their adsorption energy dominantly favored CO 2 adsorption. Analysis of the partial density of states confirmed that adsorption interactions with the membrane were due to CO 2 responses to the applied electric field. It additionally proved the electrical stability of PEK-C(CN) membrane. Computational fluid dynamics simulations of gas permeation through PEK-C(CN) membrane were performed without and with electric field. Results indicated an average pore distribution around 0.5 nm. The velocity flow distribution aided locate the interconnected pores, bringing to the fore the dominant transportation paths of gas molecules. It was uncovered that although the application of an electric field significantly improved the membrane gas permeability, it was not necessarily beneficial to its selectivity. −5 V was determined to be the optimum potential for an improvement of CO 2 permeability from 57.32 Barrer (no field) to 15924.91 Barrer, while also enhancing the selectivity. This work demonstrates the benefits of the electric field and its promising application in gas separation processes. [ABSTRACT FROM AUTHOR]

The MOF crystal-glass composites (CGC) membrane, comprising a MOF crystal and MOF glass matrix, represents a novel self-supported membrane that has been effectively applied in gas separation. Nevertheless, the typical MOF glass matrix requires a higher operating temperature (>400 °C), which constrains its combination with a multitude of MOF crystals characterized by high porosity and low decomposition. In this work, Zn–P-dmbIm (coordination polymer) was chosen as the glass matrix, and MIL-101 crystal with high porosity were integrated at an operating temperature of 190 °C. Furthermore, the intrinsic low porosity of a g Zn-P-dmbIm can be enhanced by the incorporation of higher porosity MIL-101, which possessed a high specific surface area (from ∼1.7 m2/g to 401 m2/g) and porosity (from ∼0.0014 cm³/g/nm to 0.5605 cm³/g/nm) of the CGC. The intimate combination of MIL-101 and a g Zn-P-dmbIm by in - situ melting to reduce the interfacial defects, which also provides a robust foundation for effective CO 2 /N 2 separation. In CO₂/N₂ (50/50, v/v) mixed gas conditions, the MIL-101/ a g Zn-P-dmbIm membrane demonstrated a impressively high CO₂ permeability of 18670 barrer and CO₂/N₂ selectivity of 61, exceeding the CO₂/N₂ upper bound. The variable pressure (1–12 bar) and long-term stability (120 h) of the CGC membrane exhibited enhancing separation stability. Hence, the self-supported MIL-101/ a g Zn-P-dmbIm membrane demonstrated effective CO₂/N₂ separation performance, which had the potential to significantly extend the scope of applications for MOF crystal-glass matrices. [Display omitted] • Highly porous MIL-101 integrated with Zn–P-dmbIm glass. • The operating temperature of crystal-glass composites was reduced to 190 °C. • MOF crystal-glass composites membrane were obtained by in - situ melting. • Significantly enhanced CO 2 diffusion in Zn–P-dmbIm composites glass membrane. • The membrane has CO 2 permeability of 18670 barrer and CO 2 /N 2 selectivity of 61. [ABSTRACT FROM AUTHOR]

Carbon molecular sieve (CMS) membranes demonstrate promising economic and environmental advantages in gas separation applications. In this work, we synthesized a novel polymer precursor of PEK-N and utilized it to fabricate a series of PEK-N derived CMS membranes. With varying carbonization temperature and time, the pore structures and gas separation performance were finely tuned. The gas separation properties of membranes with different carbonization temperature were comprehensively evaluated. In particular, by carbonizing the sample at 650 °C for 1 h, PEK-N derived CMS membranes (CMS-650-1) achieved the highest CO 2 permeability around 2176 Barrer, and selectivities of 48.2 for CO 2 /N 2 and 57.8 for CO 2 /CH 4 in their gas mixtures. Our study suggests that the use of rationally designed polymers has the potential to bring about high gas separation performance for polymer-derived carbon molecular sieve membranes. This study explores the use of a novel polymer of polyaryletherketone bearing tertiary amine group (PEK-N) for preparing carbon molecular sieve membranes through control of carbonization temperature and time. The optimized CMS membrane (CMS-650-1) exhibited a CO 2 permeability around 2176 Barrer, and CO 2 /N 2 and CO 2 /CH 4 gas selectivities of 48.2 and 57.8, respectively. [Display omitted] • Polyaryletherketone bearing tertiary amine group polymer was synthesized. • CMS membranes were fabricated using PEK-N polymer. • The structural features of CMS membranes could be tuned by adjusting the carbonization temperature and time. • The CMS membrane exhibited high separation performance for CO 2 /N 2 and CO 2 /CH 4. [ABSTRACT FROM AUTHOR]

• Pebax-based membranes containing different 2D materials for CO 2 capture. • The separation mechanism and properties of Pebax materials are discussed. • The transport mechanism of CO 2 in the membrane was explained. • The challenges and future directions of the Pebax gas separation field are presented. Since the onset of the industrial age, annual global CO 2 emissions have risen, significantly affecting the climate and natural ecosystems. Addressing this, the development of carbon capture, utilization, and storage (CCUS) technologies becomes crucial. Gas membrane separation, recognized for its efficiency, low energy consumption, and eco-friendly nature, is rapidly gaining prominence in global carbon capture efforts. Polyether-block-polyamide (Pebax), with its high CO 2 affinity and resilient mechanical properties (attributed to its elastic polyether and robust polyamide segments) is gaining traction in CO 2 separation research. Yet, the inherent trade-off effect poses challenges for its industrial application. This article delves into the current research landscape of gas separation membranes made of Pebax and assorted 2D nanomaterials for CO 2 separation. It outlines the separation mechanism of Pebax materials and elucidates the CO 2 separation membrane's transport mechanism. Further, the application of gas separation membranes formed by combining Pebax with various 2D nanomaterials for CO 2 capture is also described in detail. Relevant studies underscore that these gas separation membranes offer enhanced separation efficacy and stability, positioning them as potential leaders in CO 2 separation solutions. The paper concludes by highlighting challenges in Pebax-based research and suggesting future research avenues. [ABSTRACT FROM AUTHOR]

Crosslinked poly (ethylene oxide) (XLPEO) membranes are leading candidates for membrane post-combustion carbon capture, because of their high CO 2 /N 2 selectivity and CO 2 permeability. However, their crosslinked nature makes it difficult to process them into thin films through conventional coating techniques. In this study, interfacially initiated chain growth polymerization of epoxides is used to circumvent the XLPEO processing challenge whilst allowing in-situ crosslinking. The interfacial design strategy yields intrinsically crosslinked, epoxide-based PEO (eXLPEO) thin-film composite gas separation (GS) membranes consisting fully of CO 2 -philic ether bonds. An eXLPEO selective layer made from poly (ethylene glycol) diglycidyl ether was successfully deposited on a PAN support and, after introduction of densification steps and a PDMS sealing, gas selective membranes were obtained. Synthesis-structure-performance analysis revealed that multiple reaction condition combinations result in highly selective membranes with a tunable chemical structure. The best performing membranes showed CO 2 /N 2 separation factors of 58 at 35 °C, with a stable operation at pressures from 2 to 10 bar, and retaining a separation factor of 30 at 65 °C. However, all membranes had a low CO 2 permeance (<10 GPU), probably due to pore impregnation of the support layer. This work demonstrates for the first time the viability of interfacial polymerization for the synthesis of thin film eXLPEO GS membranes. [Display omitted] • Epoxide chemistry is a novel platform for thin-film composite (TFC) gas separation membrane synthesis. • Crosslinked poly (ethylene oxide) TFC were synthesized using epoxide interfacial polymerization. • The chemical structure of epoxide-TFC is controlled by the monomer/initatior ratio. • Membranes show high CO 2 /N 2 selectivity, even at elevated temperatures. • The hydrophilicity of the monomers caused pore impregnation. [ABSTRACT FROM AUTHOR]

• Review the macromolecular structures of microporous polymers for O 2 /N 2 separation. • Explore the aging behavior of innovative microporous materials. • Review the impacts of thermal treatments to reset microporosity and O 2 /N 2 separation. • Investigate the application of polymers and process design in membrane systems. This review summarizes the performance of recently developed microporous polymers for practical industrial O 2 /N 2 separations. The macromolecular design of innovative polymers of intrinsic porosity and derivatives is evaluated from the perspective of pore structure regulation for their outstanding O 2 /N 2 separation performance. The structural groups that could fine-tune the free volume elements are examined to discern the promising moiety and architectures to improve size-based sieving. The long-term aging behaviors of the state-of-the-art macromolecules are also screened to explore the impacts of improved pore/free volume configuration. The strategies using thermal treatments to reset the structure of microporosity are inspected for their potential to improve the gas permeability or enhance size-specific molecular sieving, including the thermal rearrangement of polymeric membranes and pyrolyzed carbon molecular membranes using pre-crosslinked precursors and PIM-derived precursors. Membrane process design and optimization are summarized to evaluate the prospects of these novel membrane materials for large-scale industrial applications. [ABSTRACT FROM AUTHOR]

Chemical structure and morphology of polymers are directly related with the membrane separation performance. Poly(imide)s (PIs) are the most widely used polymers in the preparation of membranes for gas separation applications; thus, research on the structural design of polymers is of great interest to develop new membranes. In the present work, we reported the synthesis, characterization, and measurement of the gas transport properties of a new co-poly(imide)s (PI-D2a-D2b-6FDA) prepared from a mixture of isomeric diamines. The co-poly(imide) synthetic route involved several steps, starting by a bromination reaction, followed by a double nucleophilic aromatic substitution giving an isomeric mixture of precursors, which suffered a Suzuki-Miyaura C–C cross-coupling reaction followed by the reduction of nitro groups to give two new isomeric diamines. Finally, diamines simultaneously reacted with the dianhydride 6FDA to obtain PI-D2a-D2b-6FDA. The co-poly(imide) had a M n of 47.7 kDa and a M w of 74.0 kDa with a PDI of 1.6. The sample exhibited a 10% weight loss at 540 °C, T g of 280 °C, BET surface area of 110 m2 g−1, and wide-angle X-ray diffraction (WAXD) interchain d- spacing at 9.5 Å and 6.3 Å. Tensile strength, elongation at break and Young's modulus were 109.6 MPa, 6.66% and 2.18 GPa, respectively. co-Poly(imide) was soluble in various polar aprotic organic solvents such as DMSO, NMP, DMF, DMAc, THF, and chloroform, forming a self-standing dense film whose gas transport properties were measured. Pure gas permeability coefficients for H 2 , CO 2 , O 2 , N 2 , and CH 4 , were 47.28, 24.04, 4.35, 1.02, and 0.76 (Barrer), respectively, which follows a decreasing order by the increasing kinetic diameters of the respective gases. Ideal gas selectivities H 2 /N 2 , O 2 /N 2 , CO 2 /CH 4 , and CO 2 /N 2 were 46.4, 4.3, 31.6, and 23.6, respectively. These gas transport properties were compared with the commercial polymer Matrimid®, showing higher gas permeability coefficients than Matrimid®. Synthetic route to obtain a new self-standing co-polyimide. [Display omitted] • A new co-poly(imide)s was prepared from a mixture of isomeric diamines (position monomers). • The co-poly(imide) was soluble even in low boiling point solvents like THF and chloroform, forming a self-standing dense film. • Isomeric structures in the polymer lead to irregular growth, achieving higher diffusion coefficients than Matrimid®. [ABSTRACT FROM AUTHOR]

Covalent organic frameworks (COF) are deemed as disruptive membrane materials owing to their versatile functionalities, high stability and ordered nanochannels. However, the size mismatch between the COF intrinsic pore and gas molecules becomes a grand challenge when using COF membrane for carbon capture. Herein, we propose a new type of polymer-functionalized COF laminar membranes through grafting CO 2 -phlic polyethyleneimine (PEI) polymer onto carboxylic acid COF (cCOF) laminar membranes. The cCOF nanosheets with high density of carboxyl groups are prepared via modified single phase solution method and then assembled to fabricate membranes. Further, the cCOF membranes are functionalized with PEI using 1-ethyl-3-(3-dimethylaminopropyl) carbodiimide/N-Hydroxysuccinimide (EDC/NHS) coupling chemistry. The introduction of abundant amino groups from PEI afford the affinity of membranes toward CO 2. Meanwhile, the graft of the PEI polymers reduces the defects or pinholes on the membrane surface. As a result, the PEI functionalized cCOF membranes exhibit a high CO 2 permeance of 1004 GPU and a CO 2 /N 2 selectivity of 33.7, which reach the carbon capture target performance and show great prospect for treating real flue gas. Our approach of functionalizing cCOF membranes with tailored functionalities may inspire the design of molecule-selective COF membranes. [Display omitted] • Carboxyl covalent organic framework (cCOF) nanosheets are assembled into membrane. • cCOF membranes are modified with CO 2 -philic PEI polymer under mild condition. • The membrane shows CO 2 permeance of 1004 GPU with CO 2 /N 2 selectivity of 33.7. • Our work will inspire the design and modification of diverse COF membranes. [ABSTRACT FROM AUTHOR]

• Demonstration of mixed matrix membrane using defective ZIF-78, a MOF with the highest CO 2 uptake reported in literature. • Different solvents used to prepare polysulfone lead to smooth or cracked fillers with different membrane free volume. • CO 2 permeability and CO 2 /N 2 selectivity enhanced by 140 % and 129 % with optimally loaded MMMs. Mixed matrix membranes (MMMs) provide a new possibility for membranes to exceed the tradeoff between permeability and selectivity found in pure polymeric membranes. Factors that enhance gas separation performance in MMMs include filler morphology and aspect ratio. High aspect ratio microporous ZIF-78, a metal-organic framework (MOF) demonstrated in literature to have one of the highest carbon dioxide uptake capacities, was successfully synthesized using a solvothermal method. These particles were incorporated into MMMs in non-defective and systematically defective forms by using two common solvents – chloroform and DMF. Detailed characterization of the various membranes was performed using BET, XRD, SEM, EDS, DSC, TGA, FTIR, and a custom-built gas permeability measurement apparatus. Introduction of crystals with no apparent defect results in a more tortuous pathway for permeating gas molecules, demonstrated by nitrogen permeation results. Conversely, for carbon dioxide, strong dipole-quadrupole interaction with ZIF-78 creates excellent permeation pathways through the crystal themselves. The defective system possesses more inter-filler free volume which allow all gas components to permeate more easily, in addition to the original mechanism. The gas separation performance of the resulting MMMs in this work displayed a 140 % improvement of CO 2 permeability and 129 % improvement of CO 2 /N 2 ideal selectivity over pure polysulfone membranes. This work shows the potential of using deliberately designed fillers to increase performance via special pathways for gas molecules. [Display omitted] [ABSTRACT FROM AUTHOR]

New PIM-1 copolymers with 2,3,6,7-anthracenetetrayl moiety have been synthesized as fine powders from 2,3,6,7-tetrahydroxy-9,10-di(p -fluorophenyl)anthracene monomer in DMSO, with crystal structure of the monomer as well as its precursors and the product of its model side crosslinking reaction being determined using X-ray diffraction. The microporosity and surface characteristics of the copolymers powders have been measured. As-cast membrane from the copolymer with 5 mol% of the monomer synthesized revealed promising gas separation properties as compared with original PIM-1. [ABSTRACT FROM AUTHOR]

In this work, Amine-functionalized CNF/UiO-66 (CNF–NH 2 /UiO-66) composite membranes were fabricated by incorporating UiO-66 nanoparticles in the CNF–NH 2 matrix. The CO 2 -facilitated transfer channels can be constructed in the CNF–NH 2 /UiO-66 composite membrane. As a natural polymer material, CNF–NH 2 would absorb water and form a gel-like structure under humidification. The adsorbed water can convert CO 2 into bicarbonate ions (HCO 3 −) through the catalysis of amino groups on CNF–NH 2. Moreover, in CNF–NH 2 /UiO-66 composite membranes, HCO 3 − could quickly migrate to the permeate side promoted by the porous UiO-66, facilitating CO 2 transport. The optimum membrane gave a CO 2 permeability of 257.0 Barrer with a CO 2 /CH 4 ideal selectivity of 71.3. [Display omitted] • Hydrogel material CNF–NH 2 was selected as membrane matrix for gas separation. • Adsorbed water molecules can act as fast moving carriers of CO 2. • Porous UiO-66 was incorporated in CNF–NH 2 matrix as a highway for CO 2 transport. • Significantly higher CO 2 permeability was observed for membranes in a humid state. [ABSTRACT FROM AUTHOR]

A novel gas separation membrane was fabricated from a commercially available polymer of phenolphthalein-based cardo poly (arylene ether ketone) (PEK-C). Thermal treatment was employed to improve the gas permeability and anti-plasticization property of PEK-C polymeric membrane via inducing interchain crosslinking. The changes of chemical structure, thermal crosslinking reaction, interchain distance, gas separation performance and anti-plasticization properties of PEK-C membranes were investigated by the FT-IR, XPS, TG-MS, XRD and gas permeation tests. Results show that the gas separation performance and anti-plasticization properties of PEK-C membranes are significantly enhanced after the thermal crosslinking, which is induced by the decomposition of the lactone rings in cardo moieties and crosslinking with the formation of biphenyl linkages. The dramatic enhancement in gas permeability for the crosslinked membrane is attributed to the enlargement of the interchain distance and free volume cavity, and the great improvement on the anti-plasticization property is due to the formation of a rigid crosslinked network structure. Compared to PEK-C polymeric membrane, the CO 2 permeability of the crosslinked membrane increased by more than 110 times with an adequate CO 2 /CH 4 selectivity, especially for the separation of CO 2 /CH 4 mixed gas (50:50 mol%). The CO 2 plasticization pressure substantially increased from 2 atm to the highest tested pressure of 30 atm. The gas separation performance of the crosslinked membrane surpassed the 2008 upper bound for CO 2 /CH 4 , exhibiting that the thermal crosslinking membrane derived from PEK-C membrane material is an attractive candidate for the natural gas purification. • A novel gas separation membrane was fabricated from a commercially available polymer. • Thermal crosslinking greatly enhances the gas permeability and anti-plasticization. • The CO 2 permeability increased by more than 110 times after crosslinking. • The CO 2 plasticization pressure of cross-linked membrane increased up to 30 atm. [ABSTRACT FROM AUTHOR]

Herein, the microporous structure and gas transport property of a new family of polyimides (PIs) containing bulky tetra- o -isopropyl and naphthalene groups prepared via a microwave-assisted polymerization process are reported. The polyimides were prepared from a naphthalene and isopropyl containing diamine, i.e., 4,4'-(naphthalen-1-ylmethylene)bis(2,6-diisopropylaniline)) (i.e., BAN-3) obtained via a one-step electrophilic substitution reaction, reacting with three commercial dianhydrides. Analysis of fractional free volume (FFV) in conjunction with positron annihilation lifetime spectroscopy (PALS) showed that the resultant BAN-3 based PIs had high FFV values of over 0.19 featuring a bimodal size distribution of microcavities with average diameters in the range of 8.0–9.0 Å and 5.6–6.3 Å, respectively. Wide angle X-ray diffraction (WXRD) further confirmed that the introduction of naphthalene and tetra- o -isopropyl groups effectively enhanced polymeric backbone rigidity and disrupted chain packing, leading to high gas permeabilities in all three PI films. For example, the PI-3F film had high H 2 and CO 2 permeability values of 722 and 849 barrer, respectively while maintaining comparable selectivities for H 2 /CH 4 and CO 2 /CH 4 gas pairs with other reported PIs of the same dianhydride. In addition, the PI-3B film displayed excellent gas separation performance for O 2 /N 2 gas pair approaching the 2008 Robeson upper bound. Image 1 • Robust and highly soluble polyimides containing isopropyl and naphthalene units were readily prepared. • The polyimides had high FFV values featuring a bimodal size distribution of microcavities. • The polyimides showed excellent gas selectivity for O2/N2, approaching the 2008 Robeson upper bound. [ABSTRACT FROM AUTHOR]

Polymer crosslinking via thermal oxidation is a well-established technique that enhances the gas selectivity of a polymer membrane, but usually at the expense of lower gas permeability. As thermal oxidation is typically performed at temperatures higher than the glass transition temperature (T g) of polymers, large energy footprints are incurred while pore structures in asymmetric membranes – the preferred physical configuration of polymer membranes are collapsed. To overcome these drawbacks, here we report a strategy to simultaneously enhance both gas permeability and selectivity via thermal oxidation at sub-T g temperatures. This was achieved with a copolymer consisting a component that enhanced T g , and another component with functional groups that decomposed and induced crosslinking at lower temperatures. We used a series of complementary characterization techniques to pinpoint the actual mechanism underpinning our sub-T g thermal oxidation approach. Crosslinking slightly reduced the d-space between polymer chains but increased polymer fractional free volume and most importantly, inhibited CO 2 -induced plasticization. The pure CO 2 permeability of the crosslinked polymer reached 88.5 Barrer with a CO 2 /CH 4 ideal selectivity of 38.8, while no plasticization behavior was detected at a CO 2 pressure up to 30 atm at 35 °C. When separating CO 2 :CH 4 (1:1) mixed gas at total pressures between 10 and 60 atm, the CO 2 permeability and CO 2 /CH 4 selectivity of this crosslinked polymer were reduced to 55 Barrer and 29 due to competitive permeation. Image 1 • Introducing Durene into 6FDA-MPP enhances T g and decreases crosslinking temperature. • Thermal oxidative crosslinking mechanism of the lactone ring based polyimide was elucidated. • Polyimide is crosslinked at 275 °C that is 75 °C lower than its T g. • Crosslinked polymer shows no plasticization at a CO 2 pressure of 30 atm. [ABSTRACT FROM AUTHOR]

[Display omitted] • This article reviewed the preparation strategies for large MXene flakes. • A systematic summary was conducted based on the preparation methods of MXene gas separation membranes. • An analysis on the influence of the surface groups on gas adsorption process and the adsorption in gas sensing was carried out. • The potential relationship between gas adsorption and separation as well as the application of computational simulation were explored. Recently, MXene, a novel two-dimensional (2D) material, shows promising potential in many fields. Among these fields, gas separation and adsorption have emerged as new application areas for MXene. The number of studies relevant to the application of MXene in gas separation and adsorption is gradually increasing, making it a hot spot in scientific research. Therefore, timely and systematic reviews of the strengths and weaknesses of MXene are crucial to its further development. This article focused on the application of MXene in gas separation and adsorption. In this review paper, we presented some preparation methods of large MXene layers and practicable strategies for utilizing them to enhance the operational stability of MXene membranes, and the latest research advancements in the application of MXene in gas separation and adsorption. In terms of gas separation, we provided a systematic summary of the research progress based on the techniques used to prepare MXene membranes. As for gas adsorption, we discussed the research progress from both experimental and theoretical perspectives. This discussion was divided into three parts: (1) exploration of the impact of the surface groups on gas adsorption process; (2) analysis on the effect of gas adsorption in gas sensing; and (3) study on theoretical calculation pertaining to gas adsorption and separation. Finally, we evaluated the advantages and disadvantages of using MXene in gas separation and adsorption and then outlined the potential avenues for the future development of MXene. It is expected that this review may provide valuable insights and guidance for the researchers engaged in promoting the intensive study and the broad application of MXene. [ABSTRACT FROM AUTHOR]

Thermally rearranged (TR) polymers have shown a great potential for gas separation. However, the temperature of TR reaction often goes beyond the glass transition temperature (Tg) of polymer precursor and results in pore collapsing and low gas permeance to asymmetric membranes. To solve this problem, we prepared a series of crosslinked thermally rearranged (XTR) polybenzoxazoles (PBO) at sub-Tg. We synthesized crosslinkable phenolphthalein-based polyimides via chemical imidization (EPPI) and azeotropic distillation (HPPI). The two polyimides were crosslinked at 300–335 °C to increase their Tg so that the subsequent TR reaction were accomplished at sub-Tg. The HPPBO-425 exhibited the best separation performance with a CO 2 permeability of 122 barrer and a CO 2 /CH 4 selectivity of 40.4 for pure gases. Moreover, the XTR PBO was not plasticized at a CO 2 pressure of 30 atm. After aged for 60 days, the CO 2 permeability decreased to 100 barrer and the CO 2 /CH 4 selectivity increased to 44. When separating CO 2 /CH 4 (1:1) mixed gases, the CO 2 permeability gradually decreased from 120 to 74 barrer with a decrement in the CO 2 /CH 4 selectivity from 47 to 26 because of the progressively saturated Langmuir sorption sites and the competitive sorption by CH 4 decreasing the solubility of CO 2. The excellent and stable CO 2 /CH 4 separation property makes the sub-Tg XTR PBO an ideal material for fabricating hollow fiber gas separation membranes. [Display omitted] • Crosslinked thermally rearranged PBOs were synthesized at sub-Tg. • Gas permeability increased by 20 times while maintained selectivity after TR. • XTR-PBO resists plasticization and good for nature gas separation. • Phenolphthalein based diamine is good platform to XTR polymer. [ABSTRACT FROM AUTHOR]

Metal-organic framework (MOF) membranes have become promising candidates for gas separation due to their adjustable structure, high separation performance, and environmental friendliness. However, the emergence of grain boundary defects, and interface defects between the support layer and separation layer significantly decrease the gas separation performance of MOF membranes. Herein, a self-supported ZIF (zeolitic imidazolate framework) glass membrane is fabricated, eliminating grain boundary defects and cracks through the molten-liquid phase. The fluorine-based linkers with high electronegativity and polarizability are introduced to enhance a g ZIF-62(a and g denote amorphous and glass, respectively) interaction of CO 2 and CH 4. The CO 2 /N 2 and CH 4 /N 2 ideal selectivity of a g ZIF-UC-4 membrane (fluorine-based, UC-4 named by Cambridge University) reach 36 and 6.2, respectively. In addition, the CO 2 and CH 4 permeance of the a g ZIF-UC-4 membrane with an independent separation layer and the non-grain boundary has improved to 4752 and 818 GPU, respectively. Under the mixed gas condition, a g ZIF-UC-4 membrane exhibits good separation performance, exceeding the 2019 Mckeown upper bond of CO 2 /N 2. Moreover, a g ZIF-UC-4 membrane has good stability for CO 2 /N 2 and CH 4 /N 2 under continuous operation and variable pressure testing. Hence, the self-supported a g ZIF-UC-4 membrane is a potential candidate for preparing MOF glass membranes with good gas separation performance. [Display omitted] • A self-supported a g ZIF-UC-4 glass membrane is fabricated for gas separation. • The glass membrane can eliminate grain boundary defects by the molten-liquid phase. • The a g ZIF-UC-4 membrane has enhanced CO 2 and CH 4 permeance of 4752 and 818 GPU, respectively. • The a g ZIF-UC-4 membrane has good stability for CO 2 /N 2 and CH 4 /N 2. • The performance of a g ZIF-UC-4 membrane surpasses the corresponding upper bounds. [ABSTRACT FROM AUTHOR]

A novel method to determine the individual diffusion coefficients of gases in a mixture during their permeation through polymeric membranes is described. The method was developed in two independent laboratories, using rubbery Pebax ® and glassy Hyflon ® AD60X membrane samples as standards, and validated using the Tröger's base containing Polymer of Intrinsic Microporosity, PIM-EA-TB. Monitoring of the permeate composition in real time by a quadrupole mass spectrometer allowed the analysis of the permeation transient for gas mixtures. Two operation modes, either with a vacuum in the permeate and a direct connection to the mass spectrometer via a heated restriction, or using a sweeping gas and a heated capillary sample inlet, give excellent agreement with the traditional time lag method for single gases. A complete overview of the method development, identification of the critical parameters, instruments calibration, data elaboration and estimation of the experimental accuracy are provided. Validation with PIM-EA-TB, shows that the method can also successfully detect anomalous phenomena, related to pressure and concentration dependency of the transport properties, physical aging or penetrant-induced dilation. Rapid online analysis of the permeate composition makes the method also very suitable for routine mixed gas permeability measurements. [ABSTRACT FROM AUTHOR]

A novel triptycene-based diamine, 2,6-diaminotriptycene-14-carboxylic acid, was synthesized and used for preparing carboxylic acid containing triptycene-based Tröger's base copolymers, CoPIM-TB-1 and CoPIM-TB-2, with another diamine monomer, 2,6-diaminotriptycene. The copolymers were subsequently post - crosslinked by glycidol to form C-CoPIM-TB-1 and C-CoPIM-TB-2. Glycidol crosslinking greatly impeded inter-chain mobility of the triptycene-based copolymers and subsequently restricted both physical aging rate and CO 2 induced plasticization. Gas permeabilities of 40 days old C-CoPIM-TB-2 film decreased by 7%, 5%, and 9%, to gases H 2 , CO 2 , and O 2 , respectively, which were slower than those of the uncrosslinked PIM-Trip-TB polymer of which permeabilities decreased by 21%, 42%, and 30%, respectively. Mixed gas permeation results showed no CO 2 induced plasticization at a CO 2 partial pressure up to 20 atm. Moreover, separation performance of C-CoPIM-TB-1 and C-CoPIM-TB-2 went over the Robeson 2008 upper bounds for gas pairs including O 2 /N 2 , CO 2 /CH 4 , CO 2 /N 2 and H 2 /N 2 . All these results indicated a great potential for the post-crosslinked Triptycene-Based Tröger's Base polymers for natural gas sweetening. [ABSTRACT FROM AUTHOR]

Because of their excellent thermal, chemical and physical properties, as well as high gas selectivity, polyimides are promising polymers for gas separation membranes. However, their commercial use is limited due to their relatively poor solubility and permeability. Here, 5-(2,5-dioxotetrahydrofuryl)-3-methyl-cyclohexane-1,2-dicarboxylic anhydride (DOCDA) was used to improve the solubility of the polyimides, and various methyl-substituted diamines were introduced to increase their permeability, due to the effect of the bulky methyl groups. Polyimides based on DOCDA (DOCDA-PIs), synthesized via one-step solution polymerization, exhibited high solubility in common organic solvents and improved gas permeability due to the non-planar structure of DOCDA and the presence of methyl groups, which disturbed chain packing, an effect that was correlated with increased fractional free volume (FFV) and d-spacing. Co-polyimides based on DOCDA, DOCDA-coPIs, exhibited high gas permeability and CO 2 /CH 4 and O 2 /N 2 selectivity, comparable to commercial polymeric membranes. [ABSTRACT FROM AUTHOR]

Butyl reclaimed rubber (BRR) was used as a novel precursor in the fabrication of a rubber membrane for CO 2 separation. Fully de-vulcanized BRR without impurities was produced from waste tire by regeneration. The properties of BRR were evaluated via systematic investigation of a number of experimental variables, and the effects of these variables on the molecular structure and the CO 2 separation performance of the membrane were assessed. The BRR-derived membrane was fabricated by simple solution-coating on an Al 2 O 3 support. The effect of the fabrication parameters, such as the solvent type, polymer concentration (8–12 wt%), and curing temperature (room temperature to 100 °C). The results indicate that the CO 2 /N 2 separation performance of the BRR-derived membrane prepared with a low concentration (<10 wt%) of coating dope in toluene solvent and cured at room temperature is competitive with that of membranes reported in previous studies due to the cis -isoprene structure. The CO 2 /N 2 ideal selectivity of 11.6, coupled with a CO 2 permeability of 86.9 Barrer, obtained with the 8RD-T25 membrane is comparable to that of a commercial rubber membrane. Furthermore, the use of BRR would decrease the use of non-renewable resources and aggregation of waste, with reduced environmental impact. [ABSTRACT FROM AUTHOR]

Herein, a series of novel triptycene-containing thermally rearranged poly(benzoxazole- co -imide) membranes (TPI-PBOs) with enhanced mechanical properties and gas separation performance are reported. The effects of chemical structures and poly(benzoxazole- co -imide) composition on the fractional free volume, polymer chain packing, microcavity size and size distribution, mechanical properties, and gas transport properties have been comprehensively investigated. Due to the incorporation of triptycene-containing non-TR-able polyimide segments, the resulting poly(benzoxazole- co -imide) films exhibited good mechanical properties even after being treated at 450 °C. The incorporation of bulky and rigid triptycene units led to significantly improved fractional free volume and gas transport properties compared to previously reported poly(benzoxazole- co -imide)s. Several triptycene-containing poly(benzoxazole- co -imide) films displayed excellent gas separation performance for H 2 /CH 4 , H 2 /N 2 , and CO 2 /CH 4 gas pairs that exceeded the 2008 upper bounds. [ABSTRACT FROM AUTHOR]

A proper increase of d -spacing after crosslinking is an effective strategy to enhance gas separation performance and anti-plasticization property of polymeric membranes. One way to achieve high chain distance is to design and prepare polymer precursors that have large side groups with crosslinkable functionality. Our previous research proved that the decarboxylation crosslinked polyimides connected by a biphenyl group showed enlarged d -spacing. However, the 100% crosslinking temperature is 425–450 °C that is higher than the glass transition temperature ( T g ) of most polymers and may cause problem for preparing asymmetric crosslink membranes. Here we proposed a thermal oxidative crosslinking method which had a lower crosslinking temperature than the decarboxylation crosslinking method. Specifically, we synthesized two phenolphthalein-based cardo diamines, MPP and PP, with or without CH 3 substituted groups and prepared the 6FDA-MPP and 6FDA-PP polyimides. The lactone ring in the cardo moiety decomposed and the crosslinking reaction took place by heating the polymer in an air purge atmosphere. A 100% conversion of the crosslinking reaction was obtained at 400 °C. In addition, the crosslinked polyimides showed increased d -spacing, high CO 2 permeability and CO 2 /CH 4 selectivity than before. The best result for pure gas test was achieved for 6FDA-MPP-400, which had a CO 2 permeability of 193.8 Barrer with a CO 2 /CH 4 ideal selectivity of 39.2. No plasticization was observed for the 6FDA-MPP-400 and 6FDA-PP-400 polyimides at a CO 2 pressure up to 450 psia. In addition, both 6FDA-MPP-400 and 6FDA-PP-400 showed excellent mixed gas selectivity of 35 at a partial CO 2 pressure of 147 psia. [ABSTRACT FROM AUTHOR]

Ion gel films were prepared by incorporating eight commercially available ionic liquids in two different cross-linked polymer matrices to evaluate their phase miscibility, gas permeability and ionic conductivity for potential applications as gas separation membranes and solid electrolyte materials. The ionic liquids cations were 1-ethyl-3-methylimidazolium, 1-ethyl-3-methylpyridinium, 1-butyl-1-methylpyrrolidinium, tributylmethylphosphonium, and butyltrimethylammonium with a common anion (bis(trifluoromethylsulfonyl)imide). In addition, ionic liquids with 1-ethyl-3-methylimidazolium cation with acetate, dicyanamide and tetrafluoroborate counterions were evaluated. The two polymers were cross-linked poly(ethylene oxide) and cross-linked poly(ethylene oxide)/siloxane copolymer. Differential scanning calorimetry, X-ray diffractometry and visual observations were performed to evaluate the ion gels’ miscibility, thermal stability and homogeneity. Ionic liquids with the least basic anion (bis(trifluoromethylsulfonyl)imide) and aromatic cations containing acidic proton (e.g. imidazolium and pyridinium) gave the most stable and miscible ion gels. Phase stability was shown to be a function of both ionic liquid content and temperature, with phase separation observed at elevated temperatures. Gas permeability testing with carbon dioxide and nitrogen and ionic conductivity measurements confirmed that these ionic liquids increased the gas permeability and ionic conductivity of the polymers. [ABSTRACT FROM AUTHOR]

[Display omitted] • Triptycene-based highly crosslinked and microporous nanofilms were fabricated on PES substrate. • Triptycene enhanced the microporosity and interconnectivity of the polymer networks. • PA-Trip nanofilms displayed outstanding gas separation performance for several gas pairs. • Microporosity and gas separation properties were highly tailorable by reaction condition. Highly permeable and selective synthetic polymer membranes are attractive for energy-efficient gas separations, while fabricating such membranes with well-defined micropore architecture and interconnectivity remains a significant challenge. We report the design and fabrication of highly crosslinked and microporous polymer nanofilms via engineering the bridged-bicyclic triptycene triamine moieties into the interfacially polymerized networks. The integrated polyamide nanofilms exhibited hierarchical pore structures with finely tuned microporosity (pore size 0.7–1.0 nm), ultramicroporosity (pore size 0.4–0.7 nm), and submicroporosity (pore size < 0.4 nm) and enhanced micropore interconnectivity due to triptycene-induced non-coplanar orientation and configurational free volume in the networks. Consequently, the composite membranes comprising polyamide nanofilms display exceptional gas separation performance for He and H 2 recovery with enhanced permeances and selectivities as well as notable plasticization resistance compared to current state-of-the-art highly crosslinked TFC membranes. It is also proved that the microporosity and gas transport properties of the composite nanofilms are highly tailorable by regulating the reaction conditions. Incorporating hierarchical triptycene units with well-defined and interconnected microvoids provides the potential to fabricate highly permselective thin-film composite membranes applicable for various important gas separations. [ABSTRACT FROM AUTHOR]

Carbon molecular sieve (CMS) membranes are ideal candidates for natural gas separation due to their rigid pore structures and stability. The chemical composite and spatial configuration of the used precursors for deriving CMS membranes can greatly influence the final microporous structure and separation performance of the membranes. Most CMS membranes are transformed from amorphous precursors such as polymers nowadays. Here, for the first time, we report a new type of CMS membrane derived from a crystalline porous hydrogen-bonded organic framework membrane (named HCMS). The conversion process has been studied with the characterization of TGA, FTIR, XRD, SEM, and pore size distribution. The effect of pyrolysis temperature on the membrane structure has been investigated to achieve optimized CO 2 /CH 4 separation performance. On the one hand, as the pyrolysis temperature increases from 550 to 650 °C, the pore size distribution of HCMS membrane is narrowed, which is conducive to improving the molecular sieving effect of the membrane. On the other hand, higher ratios of graphitic N and pyrrolic N, which show better affinity for CO 2 molecules than pyridinic N, are obtained on the HCMS membranes, leading to more favorable adsorption of CO 2. The optimized HCMS membrane pyrolyzed at 600 °C shows a remarkable CO 2 /CH 4 selectivity of 128 and excellent separation stability at varying temperatures and pressures. The HCMS membranes derived from the crystalline HOF precursor can also maintain a stable separation performance against physical aging. The results reported in this work may open the door to constructing CMS membranes with the precursor of crystalline porous membranes. Crystalline porous hydrogen-bonded organic framework membrane is employed as a new kind of precursor for the first time to derive carbon molecular sieve membrane with a narrow pore size distribution, which reveals good separation selectivity and stability for CO 2 /CH 4. [Display omitted] • For the first time, a HOF membrane is used as a precursor to derive HCMS membrane. • Ordered porosity of HOF leads to a narrow pore size distribution of HCMS membrane. • Effect of pyrolysis temperature on membrane structure and CO 2 affinity is studied. • The HCMS-600 membrane reveals the optimized CO 2 /CH 4 separation selectivity of 128. • The HCMS-600 membrane is long-term stable at variable temperatures and pressures. [ABSTRACT FROM AUTHOR]

Commercially available polycarbosilane has been chemically modified with primary and secondary amino silane derivatives in order to provide amine-functionalized polycarbosilane as hydrophobic solid sorbent capable of reversibly capturing CO 2 from flue gas streams. CO 2 uptake by the samples was investigated at the molecular level using thermogravimetric analysis under CO 2 atmosphere, in situ DRIFTS analysis, and CO 2 sorption isotherm. The reaction paths and sorption mechanisms were examined by comparing with the CO 2 adsorbing behaviors previously studied for amine-functionalized SiO 2 , and proven to be related to the presence of adsorbed water, as well as the nature of the grafted amino silanes. With effective CO 2 adsorption rate, regeneration capacity at 40–50 °C, and lesser sensitivity to moist due to its hydrophobic Si-C backbone, secondary amine-functionalized polycarbosilane hybrids have potential applications in membrane gas separation through facilitated transport of CO 2 . [ABSTRACT FROM AUTHOR]

A series of triptycene-based copolyimides with varying backbone rigidity was synthesized and evaluated for chain packing behavior and gas transport properties. These copolymers were composed of a rigid element with the triptycene skeleton directly linked to imide rings and a relatively flexible element containing ether linkage and CF 3 substituent groups. The ratio of the two components was systematically varied to investigate the effect of increasing triptycene density and steric hindrance while decreasing CF 3 and ether linkage density. Generally, increasing the percentage of the directly-linked triptycene component increased chain rigidity, interchain spacing, and fractional free volume due to more highly disrupted chain packing. Therefore, copolymers with a high fraction of the directly-linked component showed increased gas permeabilities compared to the relatively flexible homopolymer counterpart. Additionally, the increase in triptycene density introduced more ultra-fine microcavities to facilitate in sieving, allowing for a concurrent maintenance or increase in selectivity. [ABSTRACT FROM AUTHOR]

This study investigates the physical properties and gas separation performance of a series of PBO-based membranes derived from thermal conversion of blends containing ortho -OH polyamide (PHA) and polyimide (API) precursors. Homogeneous films were obtained in varying PHA/API molar ratios before and after thermal conversion, indicating good compatibility between the two precursors and resulting PBOs. This study reveals that PBO conversion efficiency, fractional free volume and gas transport properties of the resulting PBO-based blend films show an unexpected non-linear dependence on the blend composition (i.e., PHA/API ratio), due to an interplay between API thermal rearrangement (TR) process and PHA cyclodehydration process. Particularly, the B11 blend membrane, containing API and PHA in 1:1 M ratio, showed an optimal combination of gas separation performance and mechanical robustness, while the B31 blend (PHA:API = 3:1) showed little degradation of separation performance relative to both constituent polymers. This is possibly because of the localization of the excess PHA fraction that discourages the formation of inter-connected diffusive transport pathways. In summary, physical blending of API and PHA precursors at an optimal composition is demonstrated to be a simple yet instrumental approach to mitigate the mechanical deterioration issue of API-TR process while greatly improving the separation performance of the PBOs derived from the PHA cyclodehydration process. [ABSTRACT FROM AUTHOR]

Two series of novel aromatic polyimides ( PIs ) containing three polymers each one were prepared using two new aromatic silylated-diamine monomers. These monomeric diamines contain biphenylsilane units and biphenyl moieties in their structures. All PIs were obtained in high yield and the inherent viscosities were in the range of 0.44 to 0.82 dL/g. Polyimides showed excellent solubility in a wide variety of aprotic polar solvents, including THF and chloroform and were thermally stable with thermal decomposition temperature (TDT 10% ) over 500 °C and high glass transition temperatures (Tg) between 230 and 270 °C. Additionally, two films were prepared and gas transport properties were determined. These films offered a reasonably acceptable balance of permeability and selectivity with values close to a commercial polyimide (Matrimid), in particular for the CO 2 /N 2 gases pair. Experimental density of the films was measured and the fractional free volume was calculated. [ABSTRACT FROM AUTHOR]

Three spirobichroman-based diamines, FSBC, SBC and MSBC, with different substituted groups (-CF 3, -H, and -CH 3 ) were synthesized. The diamines were reacted with 4,4′-hexafluoroisopropylidene bisphthalic dianhydride (6FDA) to form 6FDA-FSBC, 6FDA-SBC, and 6FDA-MSBC polyimides, respectively. The organosolubilities, molecular weights ( M n ), densities, glass transition temperature (T g ), thermal stabilities, fractional free volume (FFV), d -spacing and gas separation properties of the spirobichroman-based polyimides were systematically studied. The three spirobichroman-based polyimides had high M n and T g , excellent thermal stabilities, and good solubilities in a wide range of organic solvents. 6FDA-FSBC exhibited the highest gas permeability which could be attributed to its insufficient chain packing conditions rooting from the incorporation of spriobichroman backbone with the spiro and non-coplaner nature, and the bulky CF 3 substituting group that increased the polymer FFV and decreased the polymer chain flexibility. 6FDA-MSBC had the highest H 2 /CH 4 selectivity due to the present of the CH 3 group in the diamine moiety which had the turnstile-like rotary thermal motion that inhibited the diffusion of large molecules like CH 4 but had little effect on the diffusion of small molecules like H 2 . [ABSTRACT FROM AUTHOR]

Graphical abstract Abstract Two-dimensional graphene nanopores have shown great promise as ultra-permeable molecular sieves based on their size-sieving effects. We design a nitrogen/hydrogen modified graphene nanopore and conduct a transient non-equilibrium molecular dynamics simulation on its molecular sieving effects. The distinct time-varying molecular crossing numbers show that this special nanopore can efficiently sieve CO 2 and H 2 S molecules from CH 4 molecules with high selectivity. By analyzing the molecular structure and pore functionalization-related molecular orientation and permeable zone in the nanopore, density distribution in the molecular adsorption layer on the graphene surface, as well as other features, the molecular sieving mechanisms of graphene nanopores are revealed. Finally, several implications on the design of highly-efficient graphene nanopores, especially for determining the porosity and chemical functionalization, as gas separation membranes are summarized based on the identified phenomena and mechanisms. [ABSTRACT FROM AUTHOR]

The fundamental gas transport properties and physical aging behavior of a series of triptycene-based polyimides with various substitution groups were investigated. Wide-angle x-ray diffraction revealed that the 6FDA-1,4-triptycene polyimides exhibit two chain packing domains with d -spacing values of ~6.7 Å and ~5.3 Å, corresponding to triptycene-induced chain packing disruption and chain segments lacking the triptycene moiety, respectively. Positron annihilation lifetime spectroscopy (PALS) showed a bimodal distribution of microcavity size made up of triptycene cleft cavities that are ~3 Å diameter and larger interchain cavities with an average diameter of ~7 Å. Additionally, PALS confirmed 6FDA-1,4-trip_CH 3 has the lowest fractional free volume, primarily due to smaller contributions from the interchain cavities, and 6FDA-1,4-trip_CF 3 has the largest fractional free volume. It was also found that the addition of substituent groups had a unique and positive effect on the aging properties over nine months, in which the addition of CH 3 and CF 3 groups led to permeability increases of ~20% and ~40%, respectively. This is caused by the combination of the lowered driving force for physical aging, the substituent groups sterically hindering tighter packing with time, and the interconnectivity and/or unblocking of free volume over time through small-scale, local chain motion. [ABSTRACT FROM AUTHOR]

Mixed matrix membranes (MMMs) with easy scale-up architectures have shown great potential to achieve superior CO 2 permeance, while their performances are often restricted by the poor interfacial compatibility between fillers and the matrix, and also by blocking of the original channel for gas transmission. Here, a rational design and facile construction of highly permeable MMMs is presented by dispersing triphenyltriazine-based β-ketoenamine-linked covalent organic framework (TpTta-COF) within solution-processable polymer of intrinsic microporosity (PIM-1). An intimate mixing was achieved by improved compatibility of the components induced by the hydrogen bond interaction between -N-H in TpTta-COF and C N of PIM-1. The good adhesion avoids the formation of interface defects, preserving the original gas transmission channel. TpTta-COF particles with strong CO 2 affinity are evenly distributed in the matrix, forming a fast and continuous channel for CO 2 transmission. The physical properties of MMMs were easily tuned, and the as-prepared PIM-1/TpTta–COF–6wt% demonstrates extraordinary stability, high CO 2 permeability and CO 2 /N 2 selectivity, surpassing the β-ketoenamine-free MMM counterparts. This study provides a feasibly pathway for the development of efficient and high performances separation membranes. A facile strategy to improve the compatibility between the matrix and filler through hydrogen-bonded interaction was presented for the construction of high performance MMMs with extraordinary long-term stability. [Display omitted] • A facile strategy to improve matrix-filler compatibility was developed through hydrogen-bonded interaction. • The CO 2 -philic COF fillers and defect-less interface provided fast channels for CO 2 diffusion. • The MMMs exhibited superior CO 2 permeability and CO 2 /N 2 and CO 2 /CH 4 selectivity than the β-ketoenamine-free counterparts. [ABSTRACT FROM AUTHOR]

High-performance polymer membranes with well-defined microporosity and size-sieving ability are especially attractive for helium and hydrogen recovery. Here we report novel macromolecular engineering of polybenzimidazole (PBI) membranes that integrate hierarchical triptycene units for high permeability and polyprotic acid doping for size sieving via controllable manipulation of microporous architecture. The triptycene moieties disrupt chain packing and introduce additional configurational free volume, leading to significantly boosted He and H 2 permeabilities compared to previously reported PBI membranes. The acid doping resulted in crosslinked PBI membranes via hydrogen bonding and proton transfer with dramatically enhanced gas selectivities. Via adjusting the H 3 PO 4 -doping level, triptycene-based polybenzimidazole (TPBI) composite membranes (TPBI-(H 3 PO 4) x) exhibit the highest gas selectivities for He enrichment (i.e., α (He/CH 4) = 7052 ± 156) and H 2 purification (i.e., α (H 2 /CH 4) = 5128 ± 110) among existing polymeric gas separation membranes. Additionally, under mixed-gas conditions at 150 °C, the TPBI-(H 3 PO 4) 0.98 membrane displays a H 2 permeability of 46.7 Barrer and a H 2 /CO 2 selectivity of 16, far beyond the Robeson's 2008 upper bound for H 2 /CO 2 separation. The facile and diverse tunability and excellent gas separation performance make TPBI-(H 3 PO 4) x membranes highly attractive for helium and hydrogen separation. Scheme demonstrating novel macromolecular engineering of polybenzimidazole (PBI) membranes via controllable manipulation of microporous architecture. Hierarchical triptycene moieties disrupt chain packing and introduce additional configurational free volumes for high permeability. Phosphoric acid doping enhances molecule sieving via hydrogen bonding and proton transfer. [Display omitted] • Novel triptycene-based polybenzimidazole was fabricated for gas separation membranes. • H 3 PO 4 doping enhanced size-sieving ability for hydrogen and helium separations. • TPBI-(H 3 PO 4) x membranes displayed extraordinary gas separation performance far beyond Robeson upper bounds. • TPBI and TPBI-(H 3 PO4) 0.98 membranes exhibited outstanding H 2 /CO 2 separation performance at 150 °C. [ABSTRACT FROM AUTHOR]

This paper reports comprehensive characterization and detailed analyses of microporous structure and fundamental gas transport properties for a series of new pentiptycene-containing polyimide gas separation membranes prepared from custom-synthesized pentiptycene-based diamines and 4,4′-hexafluoroisopropylidene bisphthalic dianhydride (6FDA) to identify the molecular origins for fast and selective gas transport. Both experimental characterizations of inter-chain spacing and microporosity and molecular modeling analysis of chain conformations and rigidity suggested that rigid H-shape pentiptycene units effectively disrupted chain packing, resulting in large fractional free volume and consequent high gas permeabilities in these membranes. Atomic-level detection of free volume architecture by positron annihilation lifetime spectroscopy (PALS) analysis revealed a bimodal microcavity size distribution with cavity sizes of d 4 ~7–8 Å and d 3 ~3–4 Å in this series of membranes. The microcavity size and size distribution were found to be sensitively affected by the substituent groups in the pentiptycene monomer structure based on the mechanism of “partial filling” of internal molecular cavities defined by the shape of pentiptycene units. Analysis of fundamental gas transport properties in terms of diffusivity ( D ) and solubility ( S ) coefficients demonstrated that size sieving mechanism (diffusivity contribution) dominates the gas transport in these polymers and bimodal microcavity size distribution with ultrafine microporosity is responsible for the excellent H 2 -related gas separation performance. Superior resistance against physical aging was observed for these high-free-volume polymers, which is ascribed to the stable, configuration-induced microcavity structure constructed by the rigid pentiptycene units. [ABSTRACT FROM AUTHOR]

Several families of hydrocarbon polymers (polysulfones, polycarbonates, cellulose acetates, polyamides, and polyimides) have been established as common industrial gas separation membranes over the past three decades. Fluoropolymer membranes have found commercial use because of their unique gas separation properties in addition to their extraordinary chemical resistance and thermo-oxidative stability. To date, studies of gas transport in fluoropolymers have been limited largely to variants of the commercially available perfluoropolymers: Teflon ® AF, Cytop™, and Hyflon ® AD. Here, we describe gas transport in composite membranes fabricated from copolymers of perfluoro(2-methylene-4,5-dimethyl-1,3-dioxolane) (PFMDD) and chlorotrifluoroethlyene (CTFE). This poly(PFMDD- co -CTFE)-based membranes have far superior gas separation performance compared to the commercial perfluoropolymers for a number of gas pairs, including H 2 /CH 4 , He/CH 4 , and CO 2 /CH 4 . The gas separation performance of the membranes depends strongly on the copolymer composition. Increasing the amount of CTFE up to 30 mol% in the copolymer increases the membrane selectivity and reduces permeance. The membranes based on 70 mol% PFMDD-30 mol% CTFE poly(PFMDD- co -CTFE) show H 2 /CH 4 and He/CH 4 selectivities of 210 and 480, respectively, values that far exceed those possible with the known commercial perfluoropolymers. [ABSTRACT FROM AUTHOR]

Polyoxyethylene (POE) exhibits great potential for selective CO 2 permeation and is tethered onto poly(methyl methacrylate) (PMMA) or poly(styrene- r -acrylonitrile) (PSt- r -PAN) by atom transfer radical polymerization (ATRP) of POE methacrylate (POEM) to endow preferential CO 2 permeability. The polymer backbones are first prepared from corresponding monomers and 4-(chloromethyl)styrene (Cl-St) with various mixture ratios by free radical polymerization. The POE grafting is then carried out by chain propagation of POEM from the Cl-St moiety by ATRP. The introduction of Cl-St to a polymer backbone is readily controlled when the monomer ratio was less than 2 mol%, and thus the average distance of POE graft chains can be tuned along the polymer backbone. ATRP also defines the length of the POE graft chains. CO 2 separation properties over N 2 of the well-defined hyper-branched polymers are investigated by comparing permeability of CO 2 and N 2 pure gases. The gas permeabilities increase with increase of POE content, and the resulting CO 2 /N 2 selectivity is also enhanced in comparison to the pristine polymers and 35 and 40 for PMMA-based and PSt- r -PAN-based hyper-branched copolymers, respectively. Higher POE content indeed gives higher diffusion coefficient for both of CO 2 and N 2 , but the CO 2 and N 2 diffusivities are almost the same. Thus the gas permeation progresses under solubility control. The CO 2 permeability is 135 Barrer with the CO 2 /N 2 selectivity 42, when the POE content is 76 wt% of PSt- r -PAN-based hyper-branched copolymer. [ABSTRACT FROM AUTHOR]

Here we report the synthesis of branched Tröger's base polymers (x -BTB) with different degree of tetraphenylmethane branch structure by incorporating varied amounts of tetrakis(4-aminopheny)methane into the main chains of Tröger's base polymer (TB). We show that branching increases porosity of x -BTB, leading to improved gas permeability. Specifically, the BET surface area and pore volume of x -BTB polymers increase continuously from 410 to 544 m2 g−1 and 0.584–0.607 cm3 g−1, respectively, for branched polymers containing progressively more branch structure. For CO 2 /N 2 , CO 2 /CH 4 , and O 2 /N 2 binary gas separation, a significant improvement in the gas permeability without obvious compromising the membrane selectivity is observed on the x -BTB membranes with higher branch degree. In particular, for CO 2 /N 2 binary gas separation, the CO 2 permeability of 5 wt%-BTB membrane is 145 Barrers, creating an enhancement of 64.8% as compared to TB membrane. Moreover, x -BTB membranes are much more resistant to physical aging than TB membrane. These results suggest that introduction of tetraphenylmethane branch structure is an effective strategy to fabricate polymeric membranes with high performance suitable for gas separation applications. [Display omitted] • Tetrakis(4-aminopheny)methane (TAPM) exhibited a rigid tetrahedral structure. • Incorporating TAPM into the backbones of TB yielded branched TB polymer (x -BTB). • x -BTB polymers exhibited higher BET surface area than that of TB polymer. • The obtained x -BTB membranes showed a significantly improved gas permeability. [ABSTRACT FROM AUTHOR]

• A novel phthalide-containing polyimide precursor was synthesized and employed to prepare the CMSMs for hydrogen purification. • The structural evolution from precursor to CMS was investigated. • The H 2 separation performance of CMSMs was optimized by the pyrolysis temperature. • The optimized CMSMs show a high H 2 permeability with superior H 2 separation property. Hydrogen-based economy has been considered as a potential solution for energy security and sustainability in the future. And the ever-increasing demand for high-purity hydrogen (H 2) provides an urgent force for the H 2 purification technologies. Herein, a novel polyimide (BATPPP-6FDA) with rigid and contorted structure was synthesized and used as a precursor to fabricate the carbon molecular sieve membranes (CMSMs) for H 2 purification. The structural changes from precursor to CMS were detected and the H 2 separation performance of the membranes was optimized by the pyrolysis temperature. The CMSM pyrolyzed at 550 °C exhibited the highest H 2 permeability of 10054.1 Barrer and moderate H 2 permselectivity due to its highly disordered and turbostratic carbon structure originated from the generally decomposition of thermally labile -CF 3 groups and the lactone rings of phthalide structure in the early stages (<550 °C) of pyrolysis. As the pyrolysis temperature raised, the H 2 permeability of the derived CMSM decreased, and the H 2 permselectivity enhanced greatly. The CMSM pyrolyzed at 800 °C demonstrated a high H 2 permeability of 2622.4 Barrer and superior selectivity with H 2 /N 2 of 524.48, H 2 /CH 4 of 1248.76 and H 2 /CO 2 of 7.51, respectively, which was attributed to the low densification of carbon structure resulting from the rigid and contorted structure of the BATPPP-6FDA precursor. The excellent H 2 separation performance showed a great potential in hydrogen purification application. [ABSTRACT FROM AUTHOR]

Thermally induced chemical crosslinking has attracted substantial attention for fabricating plasticization resistant membranes due to the facile structure tunability that enables the construction of robust and well-defined architecture for gas separation. In this study, we report a new series of dual thermally crosslinkable polyimides derived from 4,4′-diamino-2,2′-biphenyldicarboxylic acid (DCB) containing two carboxyl groups, and a systematic investigation of the thermal treatment above and below T g demonstrated the decarboxylation-induced crosslinking. The dual thermally crosslinked membranes were insoluble in common organic solvents and maintained excellent mechanical properties. Due to the evolution of CO 2 and collapse of chain segments during thermal treatment, the crosslinked membranes exhibited hierarchical microcavity size distribution featuring ultra-micropore size in the range of 2.0–6.0 Å and micropore size in the range of 6.5–10.0 Å. Gas transport properties of the crosslinked membranes were feasibly tuned through the chemical compositions and thermal treatment procedures. For instance, the CO 2 permeability of crosslinked 6FDA-DAM 0.7 -TFMB 0.1 -DCB 0.2 increased almost three-fold with only a slight decrease in CO 2 /CH 4 selectivity. The crosslinked membranes also demonstrated superior plasticization resistance with mixed-gas feed pressure up to 40 bar and excellent low-temperature gas separation performance at −30 °C, making them attractive for aggressive gas separations. [Display omitted] • Dual thermal crosslinking provides additional tunability toward membrane microporosity and gas separation performance. • Positron annihilation lifetime spectroscopy demonstrates hierarchical microcavity architecture of the crosslinked membranes. • Dual thermal crosslinking improves crosslinking efficiency and boosts the CO 2 permeability increment up to 444%. • Crosslinked membranes show superior anti-plasticization properties and excellent low-temperature gas separation performance. [ABSTRACT FROM AUTHOR]

This comparative study focuses on the cyclodehydration reaction of poly(hydroxyamide)s (PHAs) and the thermal rearrangement (TR) reaction of aromatic poly(hydroxyimide)s (APIs) to produce polybenzoxazoles (PBOs) for application as gas separation membranes. Systematic comparisons between the two routes showed that PHA cyclodehydration can produce fully converted PBO membranes at a temperature more than 100 °C lower than the API-TR route. Gas separation performance of PHA–PBOs is comparable to API-TR polymers, and PHA–PBOs are considerably more mechanically robust. More importantly, PBO films can be produced equally well in both air and inert atmospheres via the PHA cyclodehydration route. The PHA–PBOs formed in air have statistically the same physical and transport properties as those formed in N 2 . The present study provides fundamental information regarding the PHA-to-PBO cyclodehydration process. [ABSTRACT FROM AUTHOR]

An environmentally friendly magnesium fuel cell system using seawater electrolyte and atmospheric oxygen was tested under practical considerations for use as maritime power supply. The hydrogen rate and therefore the power density of the system were increased by a factor of two by using hydrogen evolution cathodes with a gas separation membrane instead of submerged cathodes without gas separation. Commercial magnesium AZ31 rolled sheet anodes can be dissolved in seawater for hydrogen production, down to a thickness below 100 μm thickness, resulting in hydrogen generation efficiency of the anode of over 80%. A practical specific energy/energy density of the alloy of more than 1200 Wh/kg/3000 Wh/l was achieved when coupled to a fuel cell with atmospheric air breathing cathode. The performance of several AZ31 alloy anodes was tested as well as the influence of temperature, electrolyte concentration and anode – cathode separation. The excess hydrogen produced by the magnesium hydrogen evolving cell, due to the negative difference effect, is proportional to the cell current in case of the AZ31 alloys, which simplifies system control considerably. Stable long-term operation of the system was demonstrated at low pressures which can be maintained in an open-seawater-submerged hydrogen generator. [ABSTRACT FROM AUTHOR]

A series of new pentiptycene-containing diamines with systematically varied substituent groups were designed and synthesized with high purity and high yields. These diamines were used to prepare a series of new polyimides with 4,4′-hexafluoroisopropylidene bisphthalic dianhydride (6FDA) by conventional condensation polymerization. The obtained pentiptycene-containing polyimides possessed high molecule weights, excellent thermal stability, good solubility in a wide range of organic solvents and thus excellent processability for membrane fabrication. Because of the excess amount of internal free volume associated with the molecular cavities in the pentiptycene moieties and the consequently disrupted chain packing, all the polyimides exhibited high fractional free volume (FFV) leading to high gas permeabilities as well as good selectivities that are highly desired for gas separation membranes. In addition, the comparisons between the pentiptycene-containing polyimides bearing various substituent groups indicated that free volume, the vital structural parameter for fast and selective molecular transport, was very sensitive to the size of the substituent groups. Large substituent groups such as CF 3 led to increased FFV, while relatively small substituent groups such as CH 3 resulted in reduced FFV, possibly due to the mechanism of “partial filling” of the molecular cavities of pentiptycene units by the substituent groups. Gas permeability data also supported this unusual trend of the dependence of free volume on the substituent groups. This finding provides a completely new and potentially novel means of molecular-level manipulations to predictably construct preferred free volume architecture that may maximize the separation performance of polymeric membranes. [ABSTRACT FROM AUTHOR]

ZIF-8 membranes are currently attracting attention for the separation of propylene/propane based on the molecular sieve effect. We have recently reported the preparation of ZIF-8 membranes using the counter-diffusion method, which is advantageous in reducing defects in the selective layer. In the present study, ZIF-8 membranes were prepared at the interface of miscible and immiscible pairs of solvents such as water/methanol and water/1-octanol, respectively. ZIF-8 membranes prepared from the immiscible pair of water and 1-octanol showed a propylene permeance of 5.2 × 10 −9 mol m −2 s −1 Pa −1 and a propylene/propane permselectivity of 7.2 at 25 °C. As for the ZIF-8 membrane prepared by the initial reaction using the immiscible pair of water/1-octanol and the successive reaction using the miscible pair of water/methanol mixture, the average propylene permeance and average propylene/propane permselectivity increased to 1.2 × 10 −8 mol m −2 s −1 Pa −1 and 20 at 25 °C, respectively. The successive reactions in water/1-octanol and water/methanol mixtures successfully decreased the defects in the ZIF-8 selective layer, resulting in high propylene permeance and high permselectivity for propylene/propane. The structure and gas permeation properties were also thoroughly characterized. [ABSTRACT FROM AUTHOR]

A series of cross-linkable membrane materials based on the 6FDA-DAM:DABA (3:2) polyimide with enhanced transport plasticization resistance were synthesized to separate CO 2 from CH 4 . Glycidol was used as a cross-linking agent to modify 6FDA-DAM:DABA (3:2) efficiently and form a transesterification reaction-based cross-linking. The conversion was calculated by solution 1 H NMR. These materials were also characterized via density, glass transition temperature, permeation, and sorption measurements. Pure (CO 2 , CH 4 ) and mixed gas (CO 2 /CH 4 ) permeation was studied on dense films of these materials up to 700 psia (1000 psia) for pure CO 2 (50%:50% CO 2 :CH 4 mixed gas) feed. Compared to the 6FDA-DAM:DABA (3:2) membrane, CO 2 -induced plasticization resistance for cross-linked membranes was enhanced in aggressive feed streams. Under CO 2 feed conditions at 35 °C, plasticization for the 41% glycidol-modified cross-linked membrane was not observed up to approximately 450 psia. Glycidol-induced cross-linking offers an excellent balance of selectivity, permeability, and plasticization resistance. The glycidol-modified 6FDA-DAM:DABA (3:2) is competitive with the earlier reported 1,3-propanediol modified materials. Possible issues such as resistance to contaminants may be final determinants in choice of approach; however, this topic was beyond the scope of the current study. [ABSTRACT FROM AUTHOR]

Carbon molecular sieve (CMS) membrane with high CO 2 separation performance were fabricated by pyrolysis of a novel hydroxyl-containing polyetherimide (BAHPPF-6FDA type HPEI) precursor. The thermal reactive ortho-OH group in HPEI resulted in the structural conversion when thermal treated at 450 °C, which simultaneously improved the chain rigidity and FFV of the precursor membrane. The structural evolution from HPEI precursor to intermediate polymer till CMS membrane was detected via TGA-MS, Py-GC/MS, FT-IR and WAXD. The pore structure, CO 2 separation performance and aging behavior of CMS membranes were characterized and analyzed by physisorption and gas permeation measurements. Results indicated that the structural properties of the intermediate TR-polymers, which depend on the thermal treatment protocol, have an obvious influence on the CMS membrane performance. Increased thermal soak time of HPEI at 450 °C leads to the increased chain rigidity and FFV, resulting in a more open pore structure and higher CO 2 permeability of derived CMS membranes. In addition, the prolonged soak time at 450 °C or increased pyrolysis temperature would result in the shrinkage of pore structure in CMS membranes and the enhanced molecular sieving performance. The high permeation CMS membrane prepared at the optimal thermal treatment protocol shows good performance stability under the mixed gas (50:50 mixture of CO 2 /N 2 or CO 2 /CH 4) feeds. The relative high CO 2 permeability of about 10000 Barrer and CO 2 /N 2 (or CH 4) selectivity over 30 were obtained after 60 days aging under vacuum, which exhibits a good potential for CO 2 separation application. [Display omitted] • A novel HPEI precursor was synthesized and employed to prepare the CMS membranes for CO 2 separations. • The structural evolution from HPEI to intermediate TR-polymer till CMS was detailed analyzed. • The effects of structural properties of the intermediate TR-polymers on the CMS membrane performance were investigated. • The CMS membrane shows high CO 2 separation performance under the mixed gas feeds after 60 days aging. [ABSTRACT FROM AUTHOR]

A series of aromatic polyimides were synthesized from three Cardo-based diamines, BAF, DDA, BAP, with different building blocks (ether linkage, dioxane linkage and C–C linkage), and commercially available dianhydride 6FDA. All polyimides were readily soluble in conventional aprotic and protic solvents, which guaranted the fabrication of self-standing membranes for gas separation applications. The Cardo-based polyimides also exhibited excellent thermal stability, with weight loss temperatures (T 5 %) of over 538 °C, and good mechanical properties, with tensile strength in the range of 41–64 MPa. Compared to 6FDA-BAF, the substitution of dioxane linkage for ether linkage resulted in increased chain rigidity, looser polymer chain packing, and larger fractional free volume. Consequently, as displayed by single gas permeation tests, 6FDA-DDA showed higher permeability coefficients without significantly sacrificing selectivity. In addition, the CO 2 permeability of 6FDA-BAP was around 2 times as high as that of 6FDA-BAF, while the CO 2 /CH 4 selectivity increased by 11%. This can be explained by the lower rotational mobility and the relatively higher imide content caused by the absence of the flexible ether linkage and dioxane linkage in polymer backbone. In short, fundamental insights into structure-property relationships of the Cardo-based polyimides observed in this study provided guidance for the molecular structure design of the gas separation membranes. [Display omitted] • Three Cardo-based polyimides containing different building blocks were successfully synthesized. • The effect of rigidity and microstructure on gas separation performance of the Cardo-based polyimides was elucidate. • The substitution of dioxane for ether linkage led to the increased chain rigidity and the looser chain packing. • The polyimide containing C–C linkage showed better combination of permeability and gas-pair selectivity. [ABSTRACT FROM AUTHOR]

Carbon dioxide-enriched air can be used to promote the photosynthesis of plants, accelerate plant growth and fix more carbon dioxide which means that it can solve the food crisis and the greenhouse effect at the same time. The carbon dioxide-enriched air permeance and CO 2 concentration in the permeate of the membrane must reach 2000 GPU and 800 ppm to meet the practical needs of accelerating the growth of plants. A polydimethylsiloxane (PDMS)/polysulfone (PSf) composite membrane with appropriate modification that can meet the set goals was successfully prepared. The structure of the membrane selective layer can be precisely adjusted by comprehensively surveying the thickness of the selective layer, the amount of crosslinking agent added, the UV/O 3 treatment time and the heat treatment. The carbon dioxide-enriched air permeance and CO 2 concentration in the permeate of the modified PDMS/PSf composite membrane reached 2336 GPU and 814 ppm, respectively. In this work, the prepared membrane was also applied to cultivate plants. Comparing Glebionis coronaria grown in an atmospheric environment with Glebionis coronaria grown in CO 2 -enriched air, the plant mass and plant height increased by 240% and 40%, respectively, after 4 weeks of growth. Experimental results show that the development of carbon dioxide-enriched PDMS/PSf-modified membranes has strong potential to capture CO 2 and accelerate the food production. [Display omitted] • Modification of the active layer of PDMS membrane using various techniques. • To see the impact of CO 2 enrichment on plants grown in CO 2 -enriched and regular air. • The integrated system resulted in reduced greenhouse gas emissions and faster plant growth. [ABSTRACT FROM AUTHOR]