Gas Separation Membranes Research Articles

Tuning the Stacking Modes of Ultrathin Two-Dimensional Metal-Organic Framework Nanosheet Membranes for Highly Efficient Hydrogen Separation.

Two-dimensional (2D) metal-organic framework (MOF) membranes are considered potential gas separation membranes of the next generation due to their structural diversity and geometrical functionality. However, achieving a rational structure design for a 2D MOF membrane and understanding the impact of MOF nanosheet stacking modes on membrane separation performance remain challenging tasks. Here, we report a novel kind of 2D MOF membrane based on [Cu2 Br(IN)2 ]n (IN=isonicotinato) nanosheets and propose that synergetic stacking modes of nanosheets have a significant influence on gas separation performance. The stacking of the 2D MOF nanosheets is controlled by solvent droplet dynamic behaviors at different temperatures of drop coating. Our 2D MOF nanosheet membranes exhibit high gas separation performances for H2 /CH4 (selectivity >290 with H2 permeance >520 GPU) and H2 /CO2 (selectivity >190 with H2 permeance >590 GPU) surpassing the Robeson upper bounds, paving a potential way for eco-friendly H2 separation.

Enhanced mechanical robustness and separation performance in triptycene modulated thermally rearranged copolyimide membranes

Thermally rearranged (TR) polymers have seen a growing role in gas separation membranes. Further exploitation of TR membranes with enhanced mechanical properties and gas separation performance are urgently demanded. Herein, a new series of TR polymers incorporating rigid triptycene units were prepared containing amino-functionalized neighbored benzene propellers and thermally rearrangeable o-hydroxy groups. The resultant TR membranes exhibit increased chain d-spacing and gas permeability with the increase of thermal arrangement temperatures. Moreover, the presence of triptycene enhances the mechanical strength of TR polymers due to the π-π stacking effect of triptycene moieties. The 400 °C TR polymer 6FDA-6FAP:DAT(2:1) displays a H2 permeability of 345.3 Barrer with a H2/CH4 selectivity of 83.6, 440% and 118% higher than the precursor, respectively, exceeding the latest Robeson upper bound. The design principle of TR membranes in this work provides an alternative route for the development of mechanically robust and high performance membranes with potentials for energy efficient gas separations.

Effect of Mixing Technique on Physico-Chemical Characteristics of Blended Membranes for Gas Separation

Polymer blending has attracted considerable attention because of its ability to overcome the permeability–selectivity trade-off in gas separation applications. In this study, polysulfone (PSU)-modified cellulose acetate (CA) membranes were prepared using N-methyl-2-pyrrolidone (NMP) and tetrahydrofuran (THF) using a dry–wet phase inversion technique. The membranes were characterized using scanning electron microscopy (SEM) for morphological analysis, thermogravimetric analysis (TGA) for thermal stability, and Fourier transform infrared spectroscopy (FTIR) to identify the chemical changes on the surface of the membranes. Our analyses confirmed that the mixing method (the route chosen for preparing the casting solution for the blended membranes) significantly influences the morphological and thermal properties of the resultant membranes. The blended membranes exhibited a transition from a finger-like pore structure to a dense substructure in the presence of macrovoids. Similarly, thermal analysis confirmed the improved residual weight (up to 7%) and higher onset degradation temperature (up to 10 °C) of the synthesized membranes. Finally, spectral analysis confirmed that the blending of both polymers was physical only.

Molecular simulation study on permeation behavior of small molecules in graphyne/polypyrrole mixed matrix membrane

AbstractThe research on the permeation behavior of small molecules in mixed matrix membranes (MMMs) is an important part of the research of MMMs. Graphyne, a new two‐dimensional carbon material, was used as the filler, and polypyrrole was used as polymer matrix to construct a MMM. In order to clarify the permeation behavior of common small molecules in MMM at room temperature and constant pressure, the adsorption and diffusion properties of H2O, CO2, and O2 in graphyne/polypyrrole MMM were investigated by combining the Giant Canonical Monte Carlo (GCMC) and molecular dynamics (MD). The results show that: (1) the order of adsorption capacity of the three molecules is H2O > CO2 > O2; (2) the diffusion ability of the three molecules is influenced by the doping content of graphyne. Oxygen diffusion and permeation in MMMs are optimal when the graphyne filling level is 15%. The filling of graphyne affects the permeation of gases. It will shed light on application areas such as coating membranes for electronics in special environments, gas separation membranes, and gas sensor membranes.Highlights A new two‐dimensional carbon nano filler—graphyne was used. A simulation method using a combination of GCMC and MD. The diffusion and permeation behaviors are analyzed from multiple perspectives. The permeation behavior conforms to the solution‐diffusion theory. The graphyne‐filled MMM is conducive to oxygen molecular diffusion.

Unit-cell-thick zeolitic imidazolate framework films for membrane application

Zeolitic imidazolate frameworks (ZIFs) are a subset of metal–organic frameworks with more than 200 characterized crystalline and amorphous networks made of divalent transition metal centres (for example, Zn2+ and Co2+) linked by imidazolate linkers. ZIF thin films have been intensively pursued, motivated by the desire to prepare membranes for selective gas and liquid separations. To achieve membranes with high throughput, as in ångström-scale biological channels with nanometre-scale path lengths, ZIF films with the minimum possible thickness—down to just one unit cell—are highly desired. However, the state-of-the-art methods yield membranes where ZIF films have thickness exceeding 50 nm. Here we report a crystallization method from ultradilute precursor mixtures, which exploits registry with the underlying crystalline substrate, yielding (within minutes) crystalline ZIF films with thickness down to that of a single structural building unit (2 nm). The film crystallized on graphene has a rigid aperture made of a six-membered zinc imidazolate coordination ring, enabling high-permselective H2 separation performance. The method reported here will probably accelerate the development of two-dimensional metal–organic framework films for efficient membrane separation.

A New Era of Modeling MOF‐Based Membranes: Cooperation of Theory and Data Science

AbstractMembrane‐based separation can offer significant energy savings over conventional separation methods. Given their highly customizable and porous structures, metal–organic frameworks‐ (MOFs) are considered as next‐generation membrane materials that can bring about high separation performance and energy efficiency in various separation applications. Yet, the enormously large number of possible MOF structures necessitates the development and implementation of efficient modeling approaches to expedite the design, discovery, and selection of optimal MOF‐based membranes via directing the experimental efforts, time, and resources to the potentially useful membrane materials. With the recent developments in the field of atomic simulations and artificial intelligence methods, a new era of membrane modeling has started. This review focuses on the recent advances made and key strategies used in the modeling of MOF‐based membranes and highlight the huge potential of combining atomistic modeling of MOFs with machine learning to explore very large number of MOF membranes and MOF/polymer composite membranes for gas separation. Opportunities and challenges related to the implementation of data‐driven approaches to extract useful structure–property relations of MOF‐based membranes and to produce design principles for the high‐performing MOF‐based membranes are discussed.

Molecular simulations of hybrid cross-linked membranes for H2S gas separation at very high temperatures and pressure: Binary 90%/10% N2/H2S and CH4/H2S, ternary 90%/9%/1% N2/CO2/H2S and CH4/CO2/H2S mixtures

Molecular dynamics (MD) simulations have previously identified four hybrid inorganic-organic membranes based on POSS or OAPS silsesquioxanes hyper-cross-linked with small PMDA or 6FDA imides, which are able to maintain reasonable CO2/N2 and CO2/CH4 permselectivities at very high temperatures (300 °C and 400 °C) and pressure (60 bar). Experimentally, the polyPOSS-imides are known to degrade above 300 °C while the polyOAPS-imides can resist up to above 400 °C. In the present work, the same four model polyOAPS/POSS-imide networks are further tested for their gas separation abilities of H2S-containing mixtures. Indeed, hydrogen sulfide is a hazardous gas present in many gas feeds, and, within the context of a toxic penetrant under harsh conditions, simulations are a useful task to perform before embarking on difficult experiments.The separations of H2S with respect to N2, CH4 and CO2 by the polyOAPS/POSS-imide matrices were studied at 300 °C, 400 °C and at 60 bar, firstly with H2S as a single-gas in order to obtain its ideal permselectivities, secondly as part of binary 90%/10% N2/H2S and CH4/H2S feeds and thirdly as part of ternary 90%/9%/1% N2/CO2/H2S and CH4/CO2/H2S feeds. They were compared to separations of binary 90%/10% N2/CO2 and CH4/CO2 feeds under exactly the same conditions.At 300 °C, H2S is much more soluble in the networks than the other three penetrants. It is the only one leading to a non-negligible volume swelling at 60 bar, although this does not happen for the mixed-gas feeds due to their low H2S partial pressures. Differences are attenuated at 400 °C because of the decrease in solubilities upon heating. The linear N2 and CO2 move faster than the non-linear CH4 and H2S penetrants, but the diffusion selectivities are moderate. As such, the ideal permselectivities under harsh conditions are mainly governed by the solubility selectivities. With binary 90%/10% N2/H2S, CH4/H2S, N2/CO2 and CH4/CO2 feeds, the transport parameters of the major N2 or CH4 components remain similar to their ideal values, whereas the solubilities of the minor H2S and CO2 components increase. This leads to some of the real separation factors for H2S being different from their ideal permselectivities, and approximately twice as high as those with CO2. In the ternary 90%/9%/1% N2/CO2/H2S and CH4/CO2/H2S mixtures, replacing 1% CO2 by 1% H2S in the feeds leads to small changes but, in pratice, these are not significant enough to make a difference. Under the conditions tested, the ternary separation factors are the same than for the 90%/10% binary mixtures.In all cases, the denser polyPOSS-imides show better sieving properties than the more open polyOAPS-imides. As such, the former should preferably be used in applications up to 300 °C, i.e. in the temperature range below their degradation. However, it is also possible to use the polyOAPS-imides at higher temperatures, since they still manage maintaining separation factors between 2 and 6 for CO2 and H2S at 400 °C, which is outstanding for polymer-based membranes at such high temperatures.

Simultaneously enhanced gas separation and anti-aging performance of intrinsic microporous polyimide by dibromo substitution

Physical aging is a huge challenge hindering the practical gas separation application of high-performance intrinsic microporous polyimides (PIM-PIs). Herein, through precise molecular design, bromine was introduced into the PIM-PI chain to both improve its separation and anti-aging properties. To clarify the anti-aging effect of bromo groups in PIM-PIs, two fluorene-based diamine isomer monomers, 9,9-bis(3-bromo-4-aminophenyl)-fluorene (BBAPF), 2,7-dibromo-9,9-bis(4-aminophenyl)-fluorene (DBBAPF), and their corresponding PIM-PIs (BAPI, BBPI, DBPI) were synthesized. Compared with pristine BAPI membrane, the permeability of BBPI is improved about 50%, which can be attributed to the bromo groups near the amino group suppressing chain densification packing and providing more free volume element (FVE). In addition, the substituted bromo group increased the chain rigidity of the polymer and hindered its rotation, resulting in a lower release of fractional free volume (FFV) during aging process. Particularly, the permeability of the BBPI was maintained at approximately ∼70% with slightly increased selectivity after 250 days, while the pristine BAPI only retained about 50% permeability of N2 (CH4). Our findings proposed an effective strategy for designing microporous polymers with improved permeability and anti-aging properties for practical applications in gas separation membranes.

Cross-Linked Polymer Membranes for Energy-Efficient Gas Separation: Innovations and Perspectives

Cross-Linked Polymer Membranes for Energy-Efficient Gas Separation: Innovations and Perspectives

Small molecule DOPO-p-DP crosslinked 6FDA-DAM-Br-85% carbon molecular sieve membrane with superior aging for efficient gas separation

Carbon molecular sieve (CMS), as the gas separation membrane materials, still faces challenges for regulation pore diameter precisely. In this work, we propose to reconstruct the 6FDA-DAM-Br-85% polyimide CMS membranes by introducing 6,6'-(1,4-phenylenebis(((4-hydroxyphenyl)amino)methylene))bis(dibenzo[c,e][1,2] oxaphosphinine6-oxide) small molecule compound (DOPO-p-DP) as crosslinking agent to regulate the pore distribution. The crosslinked precursors were obtained via the reaction between C–Br bond in 6FDA-DAM-Br-85% polyimide and N–H bond in DOPO-p-DP compound, the precursors and CMS membranes (550 °C- 2 h) were characterized with ATR-TFIR, XRD and XPS. The pore size distribution of crosslinked CMS membranes was range in 4.5–8.0 Å from the N2 adsorption data. The crosslinked CMS membranes exhibited excellent gas separation performance, which was strongly dependent on the mass fraction of DOPO-p-DP, an increasing mass fraction of DOPO-p-DP leaded to improve in gas selectivity, while reduced its permeability. The 6FDA-DAM-Br-85%/DOPO-p-DP-20% CMS membrane showed the impressive permeability and superior gas selectivity, the permeabilities of O2, CO2, and H2 are 798, 3018, and 13560 Barrer combined with the O2/N2, CO2/CH4, and H2/CH4 selectivities of 7.8, 65.6, and 294.8 respectively, the separation performances surpassed the latest trade-off relationship. In addition, the 20% of the DOPO-p-DP crosslinked CMS membrane revealed the superior aging behaviour than that of the 6FDA-DAM-Br-85% CMS membrane over 480 h aging under vacuum conditions.

Sub-Tg cross-linked thermally rearranged polybenzoxazole derived from phenolphthalein diamine for natural gas purification

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 CO2 permeability of 122 barrer and a CO2/CH4 selectivity of 40.4 for pure gases. Moreover, the XTR PBO was not plasticized at a CO2 pressure of 30 atm. After aged for 60 days, the CO2 permeability decreased to 100 barrer and the CO2/CH4 selectivity increased to 44. When separating CO2/CH4 (1:1) mixed gases, the CO2 permeability gradually decreased from 120 to 74 barrer with a decrement in the CO2/CH4 selectivity from 47 to 26 because of the progressively saturated Langmuir sorption sites and the competitive sorption by CH4 decreasing the solubility of CO2. The excellent and stable CO2/CH4 separation property makes the sub-Tg XTR PBO an ideal material for fabricating hollow fiber gas separation membranes.

Gas permeation through carbon membranes: Model development and experimental validation

With a growing interest in carbon membranes for gas separation, understanding their performance and behaviour is essential for proper design of the membrane separation. Currently not many models exist that correctly describe transport through carbon membranes due to its complex nature. This work attempts to implement a general modelling approach which describes several key transport phenomena inside carbon membranes. The approach assumes a membrane wall to be a bundle of pores with parallel transport mechanisms using the pore size distribution as a weight factor to sum the different transport phenomena. This work adapts this approach specifically for carbon membranes, additionally accounting for molecular sieving and pore blocking effects. Imposing realistic boundary conditions, the model is solved using global optimization algorithms. For testing, four different CMSMs have been produced with hydroquinone and novolac precursors. Pure- and mixed gas permeation tests are done for these CMSMs with H2, N2, and CO2 and the model is fit to this permeation data. Fitting results with pure gas measurements show the model is able to predict the contributions of different mass transport mechanism for the different membranes. This is validated by comparing these results to gas-pair permselectivity data. The model is furthermore fit to mixed gas data. Existence of multi-component effects shows that the model could be further improved. Overall, the model presented in this work is shown to be able to describe complex mass transport behaviour for various different carbon membranes.

Polyimide blend metal–organic framework‐based mixed matrix membrane for gas separation: A review

AbstractPolyimide (PI), a glassy polymer, suffers from permeability–selectivity trade‐off and plasticization, which restrict its gas separation performance. Instead of exploring new materials, polymer blend and mixed matrix membrane (MMM) emerge as promising approaches in improving membrane gas separation efficiency attributed to their simplicity and cost efficiency. However, polymer immiscibility and polymer‐filler incompatibility are the main challenges encountered in these two approaches, respectively. Thus far, only limited reviews target the comparison between PI/glassy and PI/rubbery polymer blends. Besides, the review on improving the compatibility between polymer and filler in PI‐metal–organic framework (MOF) MMM is also lacking. Hence, this review aims to assess the gas separation characteristics of PI blended with glassy and rubbery polymers, focusing on the blend miscibility. It was discovered that the casting solvent's solubility parameter and solvent volatility play a part in governing the blend miscibility. Meanwhile, the efficiency of surface functionalization and ionic liquid addition in improving the polymer–filler compatibility in MMM is also reviewed. The wet method for filler incorporation demonstrates a more homogeneous filler dispersion within the membrane. Hence, its employment in MOF‐based MMM fabrication can be explored further.

Effect of uniaxial stretching on gas separation performance of polyimide membranes

Fine-tuning of the physical stacking structure for microporous polyimide (PI) membranes via the stretching processing is a practical way of achieving advanced membrane materials with improved aging resistance as well as high gas separation performance. Here, a fluorinated polyimide 6FDA:BPDA-TFDB(1:1:2) is used as a prototype and a series of stretched membranes X%-PI are fabricated by uniaxially stretching the membrane to different elongation ratio and then annealing. Based on birefringence and wide-angle X-ray diffraction measurements, it's found that regular orientation of polymer chains along the stretching direction and fine-tuning of d-spaces from interchain packing and π-π stacking happen during the uniaxial stretching process. As such, compared to pristine PI membrane, the stretched membranes show better mechanical and thermal stability, especially for the one with higher stretching ratio. In addition, owing to the increased packing density of polymer chains, the highly stretched membrane of 40%-PI shows significantly improved gas perm-selectivity by 32.8%, 24.3%, and 12.6% for He/CH4, H2/CH4, and CO2/CH4 gas pairs, respectively, in comparison to pristine membrane. Furthermore, 40%-PI exhibits much higher gas permeability retention rate than that of other membranes after three months' aging. We expect that this work can offer polymer materials processing guidance for the preparation of high-performance gas separation membrane in future.

Print-Assisted Layer - by - Layer Fabrication of Mixed-Matrix Membrane for Gas Separation

The process intensification principles of optimizing the driving forces/resistances at every scale and the spatial domain were investigated using a print-assisted technique. The investigation was done by using a LaserJet printer to fabricate structured mixed-matrix membranes for gas separation. The physico-chemical properties of the fabricated membranes were evaluated using FTIR, and XRD. The microstructure of the membrane was evaluated using Scanning Electron Microscope (SEM) and optical microscope. The separation performance was evaluated using constant-pressure gas permeation test. The capability of the membrane to separate a mixture of two gases were tested using CO2 and CH4. The results from optical microscope analysis showed that membrane fabricated using print-assisted method possessed a well-structured morphology which can enhance the predictability of their performance. The gas permeations results showed that the transport mechanism of the membranes changed from Knudsen to molecular sieve as the number of print layers was increased from 0 to 7 layers. Overall, the fabricated membrane showed some potentials for separating CO2/CH4 mixture.

Cathodic Deposition of Thickness-Controllable ZIF-62 Film and Its Vitrification

Glass metal-organic framework (MOF) membrane is a newly developed material that is promising for separation works like ionic sieving and gas separation. Compared with its crystalline counterpart, the glass MOF membrane takes the advantage of its grain-boundary-free nature that greatly benefits the separation performance. However, the fabrication of the glass MOF membrane requires the pre-preparation of the mother crystalline MOF film, which remains a challenge. Taking the deposition of the iconic ZIF-62 (Zn-imidazole, melting point: 711 K) film as an example, this area remained silent until Jiang et al. reported the first example in 2018.1,2 They achieved the ZIF-62 deposition on anodic aluminum oxide (AAO) membrane by a solvothermal method. Nevertheless, this approach is limited by the low yield of the generated MOF crystals on the substrate and the time/energy-consuming process. To mitigate the existing dilemma, here we show an economic cathodic deposition approach to the preparation of ZIF-62 film with a controllable thickness. Thanks to the addition of hydrogen peroxide as a probase, the pure ZIF-62 film can be deposited without the co-deposition of metallic Zn. In the proposed deposition, a nucleation-Ostwald ripening-crystallization ternary process can be observed, which is different from the cathodic deposition of other MOF species like MOF-5. Also, it is found that the crystallinity of the deposited ZIF-62 film improves with the deposition temperature and the thickness of it can be well-tuned by the deposition time from a range of ~1 µm to ~15 µm. The cathodically deposited ZIF-62 film can be directly used as the mother material for the preparation of glass MOF membrane via a vitrification process. Systematic annealing experiments indicate that the heating temperature and dwelling time are crucial to the quality of the glass MOF membrane. At the optimized conditions (713 K, 4 hours), the dense and bulb-free glass MOF membrane with a flat surface can be obtained, which is ideal for separation works. Wang, Y.; Jin, H.; Ma, Q.; Mo, K.; Mao, H.; Feldhoff, A.; Cao, X.; Li, Y.; Pan, F.; Jiang, Z., A MOF glass membrane for gas separation. Angewandte Chemie 2020, 132 (11), 4395-4399. Bennett, T. D.; Yue, Y. Z.; Li, P.; Qiao, A.; Tao, H. Z.; Greaves, N. G.; Richards, T.; Lampronti, G. I.; Redfern, S. A. T.; Blanc, F.; Farha, O. K.; Hupp, J. T.; Cheetharm, A. K.; Keen, D. A., Melt-Quenched Glasses of Metal-Organic Frameworks. Journal of the American Chemical Society 2016, 138 (10), 3484-3492.

Polymer architecture effect on rheology and segmental dynamics in poly (methyl methacrylate)-silica nanocomposite melts.

Architecturally different polymer chains lead to fundamentally different rheological responses and internal dynamics, which can be utilized to rationalize advanced thermoplastic nanocomposites with tunable mechanical behavior. In this work, three model poly (methyl methacrylate) (PMMA) polymers with linear, bottlebrush, and star architectures with the same total molar mass were investigated in their neat form, and nanocomposites with well-dispersed silica nanoparticles using rheology and broadband dielectric spectroscopy (BDS). The master curves of the dynamic moduli obtained by time-temperature superposition (TTS) over the entire range from the Rouse regime to the terminal flow and a sequence of significantly different relaxation modes were observed for the samples with linear and branch chains. While linear chains form an entangled polymer network, the branched bottlebrush, and star chains show a viscoelastic response with no sign of rubbery entanglement plateau and a weak arm relaxation regime between Rouse and terminal flow, akin to other branched polymers. Moreover, branched chains showed a higher fragility index (m = 3.46 for the bottlebrush and 5.36 for the star) compared to linear chains (m = 3.29) due to dynamical heterogeneities induced by arm relaxation. The addition of nanoparticles affects only the terminal relaxation regime, where the whole chain motion is hindered by the attractive nanoparticles. The dynamics of the polymer segment were investigated by performing broadband dielectric spectroscopy (BDS) at a frequency range from 10-2 Hz to 107 Hz. The results revealed more than 10 times slower segmental relaxation for the star homopolymers and a slowdown in the α-relaxation process for all three architectures in their composite form. The dynamical slowdown in the composites is temperature dependent and more pronounced at low temperatures (leading to approximately equal to 80 times slower dynamics for nanocomposite with bottlebrush PMMA at 150 °C) due to prolonged relaxation of the interfacial polymer compared to the matrix chains. The results from this study have practical applications in fields such as gas separation and polymeric electrolyte membranes, where simultaneous improvement of segmental mobility and mechanical moduli is highly desired.

Effect of incorporated hybrid MIL-53(Al) and MWCNT into PES membrane for CO2/CH4 and CO2/N2 separation

In this study, MIL-53(Al) particles and –COOH functionalized multi-walled carbon nanotube (MWCNT) were combined as the dispersed phase to synthesize a hybrid structure, MIL-53(Al)@MWCNT. In the next step, MIL-53(Al)@MWCNT was embedded in a polyethersulfone (PES) polymer matrix to prepare PES/MIL-53(Al)@MWCNT mixed matrix membrane (MMM) for CO2/CH4 and CO2/N2 separation. Different techniques, including SEM, XRD, FT-IR, BET, and TGA, were used to confirm the successful synthesis of MMMs. Adding MWCNTs prevented MIL-53(Al) aggregation in the polymer matrix and enhanced membrane mechanical properties and gas separation efficiency. Furthermore, the correlation between MWCNT and MIL-53(Al) created a rapid transfer channel for CO2 molecules. According to the results, the MMM containing 5 wt% of MIL-53(Al)@MWCNT showed high CO2/N2 and CO2/CH4 ideal selectivity of 87 and 58.6 along with a desired permeability of 183 barrer than the pure PES membrane indicating a favorable CO2 separation efficiency. Moreover, performance shifted towards the corresponding upper bounds.

1D-2D intercalated network CMC@g-C3N4/IL membrane with high permeability and selectivity for the CO2 capture

The structural advantages of the membrane material itself are critical to the membrane separation performance. Two-dimensional (2D) graphitic carbon nitride (g-C3N4) nanosheets can achieve minimal mass-transfer barrier and high gas sieving performance due to their ultra-thin thickness, inherent surface porosity and abundance of amine groups. However, the 2D g-C3N4 nanosheets are prone to stacking during the self-assembly process, which reduces the membrane permeability. Based on this line, herein, we proposed a concept of construction of 1D-2D intercalated network supported ionic liquid membrane composed by one-dimensional (1D) carboxymethylcellulose (CMC) and g-C3N4 nanosheets to overcome the low permeability of 2D graphitic carbon nitride membrane in separating CO2/N2 and CO2/CH4. The as-prepared 1D-2D intercalated network supported ionic liquid gas separation membrane exhibits superior CO2 permeance of 953.96 GPU, CO2/N2 selectivity of 55.46 in separation of CO2/N2, and CO2 permeance of 854.00 GPU, CO2/CH4 selectivity of 50.62 in separation of CO2/CH4. In addition, the resulting CMC@g-C3N4/IL membrane has excellent durability. After 120 h of testing, it still has outstanding separation performance. In short, this concept in this study provides an effective modulation of molecular sieving of g-C3N4 membrane for high-efficiency CO2 capture by combination of the advantages of the 1D (CMC) and 2D (g-C3N4) materials.

Effect of Thermally Reduced Graphene on the Characteristics and Performance of Polysulfone Mixed Matrix Ultrafiltration Membranes

Ultrafiltration (UF) polymeric membranes are widely used in water treatment and support desalination and gas separation membranes. In this article, we enhance the performance of Polysulfone (PSF) mixed matrix membranes (MMMs) by dispersing different concentrations of thermally reduced graphene (TRG) nanofillers. The UF PSF-TRG MMMs were fabricated via the phase inversion process, and the impact of TRG loading on the characteristics of the membrane, including hydrophilicity, porosity, roughness, and morphology, were analyzed using a contact angle measurement, atomic force microscopy (AFM), scanning electron microscopy (SEM), and dynamic mechanical analysis. Incorporating TRG into the PSF matrix led to favorable effects in the instantaneous de-mixing during phase inversion, increasing the porosity and hydrophilicity of MMMs and improving the mechanical properties of the membranes. Moreover, membrane performance was examined to remove dispersed oil from oil–water emulsion and support air-dehumidification membranes. MMM performance in terms of flux and oil rejection was superior to the control PSF membrane. Incorporating 0.25% TRG into PSF resulted in a 70% water flux increase and higher oil rejection compared to the control PSF membrane. As a support for air-dehumidification membranes, the MMM also demonstrated enhanced humidity reduction and an over 20% increase in water vapor permeance over the control PSF membrane. These results indicate that the PSF-TRG MMMs are an excellent candidate for reliable oil–water separation and as a support for air-dehumidification membranes.