Improved H2/CO2 separation performance on mixed-linker ZIF-7 polycrystalline membranes

Nano-enabled gas separation membranes: Advancing sustainability in the energy-environment Nexus

Gas separation membranes serve as crucial to numerous industrial processes, including gas purification, energy production, and environmental protection. Recent advancements in nanomaterials have drastically revolutionized the process of developing tailored gas separation membranes, providing unreachable levels of control over the performance and characteristics of the membrane. The incorporation of cutting-edge nanomaterials into the composition of traditional polymer-based membranes has provided novel opportunities. This review critically analyses recent advancements, exploring the diverse types of nanomaterials employed, their synthesis techniques, and their integration into membrane matrices. The impact of nanomaterial incorporation on separation efficiency, selectivity, and structural integrity is evaluated across various gas separation scenarios. Furthermore, the underlying mechanisms behind nanomaterial-enhanced gas transport are examined, shedding light on the intricate interactions between nanoscale components and gas molecules. The review also discusses potential drawbacks and considerations associated with nanomaterial utilization in membrane development, including scalability and long-term stability. This review article highlights nanomaterials' significant impact in revolutionizing the field of selective gas separation membranes, offering the potential for innovation and future directions in this ever-evolving sector.

Wrinkled metal-organic framework thin films with tunable Turing patterns for pliable integration

Flexible integration spurs diverse applications in metal-organic frameworks (MOFs). However, current configurations suffer from the trade-off between MOF loadings and mechanical compliance. We report a wrinkled configuration of MOF thin films. We established an interfacial synthesis confined and controlled by a polymer topcoat and achieved multiple Turing motifs in the wrinkled thin films. These films have complete MOF surface coverage and exhibit strain tolerance up to 53.2%. The enhanced mechanical properties allow film transfer onto various substrates. We obtained membranes with large H2/CO2 selectivity (41.2) and high H2 permeance (8.46 × 103 gas permeation units), showcasing negligible defects after transfer. We also achieved soft humidity sensors on delicate electrodes by avoiding exposure to harsh MOF synthesis conditions. These results highlight the potential of wrinkled MOF thin films for plug-and-play integration.

Recent progress on CO2 separation membranes

Presently, excessive carbon dioxide emissions represent a critical environmental challenge. Thus, urgent efforts are required to develop environmentally friendly and low-energy technologies for carbon dioxide treatment. In this case, membrane separation technology stands out as a promising avenue for CO2 separation, with selective membrane materials of high permeability playing a pivotal role in this process. Herein, we categorize CO2 separation membranes into three groups: inorganic membranes, organic membranes, and emerging membranes. Moreover, representative high-performance membranes are introduced and their synthesis methods, gas separation performances, and applications are examined. Furthermore, a brief analysis of the challenges encountered by carbon dioxide separation membrane materials is provided together with a discussion on the future research direction. It is expected that this review will provide some potential insights and guidance for the future development of CO2 separation membranes, which can promote their development.

Modular Customization and Regulation of Metal-Organic Frameworks for Efficient Membrane Separations

Metal-organic frameworks (MOFs) are considered ideal membrane candidates for energy-efficient separations. However, the MOF membrane amount to date is only a drop in the bucket compared to the material collections. The fabrication of an arbitrary MOF membrane exhibiting inherent separation capacity of the material remains a long-standing challenge. Herein, we report a MOF modular customization strategy by employing four MOFs with diverse structures and physicochemical properties and achieving innovative defect-free membranes for efficient separation validation. Each membrane fully displays the separation potential according to the MOF pore/channel microenvironment, and consequently, an intriguing H2 /CO2 separation performance sequence is achieved (separation factor of 1656-5.4, H2 permeance of 964-2745 gas permeation unit). Taking advantage of this strategy, separation performance can be manipulated by a non-destructive modification separately towards the MOF module. This work establishes a universal full-chain demonstration for membrane fabrication-separation validation-microstructure modification and opens an avenue for exclusive customization of membranes for important separations.

Fabrication of Polycrystalline Zeolitic Imidazolate Framework Membranes by a Vapor-Phase Seeding Method

The reliable fabrication of polycrystalline zeolitic imidazolate framework (ZIF) membranes continues to pose challenges for their industrial applications. Here, we present a vapor-phase seeding approach that integrates atomic layer deposition (ALD) with ligand vapor treatment to synthesize ZIF membranes with high propylene/propane separation performance. This method began with depositing a ZnO coating onto the support surface via ALD. The support underwent treatment with 2-methylimidazole vapor to transform ZnO to ZIF-8, forming the seed layer. Subsequent secondary growth was employed at near-room temperature, allowing the seeds to grow into a continuous membrane. ZIF-8 membranes made on macroporous ceramic support by this method consistently demonstrated propylene permeances above 1 × 10-8 mol Pa-1 m-2 s-1 and a propylene/propane separation factor exceeding 50. Moreover, we demonstrated the effectiveness of the vapor-phase seeding method in producing the ZIF-67 membrane.

Ligand Substitution: An Effective Way for Tuning Structures of ZIF-7 Nanoparticles (NPs) and Improving Energy Recovery Performance of ZIF/PA TFN Membranes

It is an important initiative to reduce the building energy consumption using energy recovering ventilation (ERV) systems. The application of ERV systems is hindered by the low CO₂ barrier performance of commercial total heat exchange membranes (THEMs) that lead to unsatisfactory indoor air refreshing rate, and there is an urgent need for THEMs that have improved CO₂ barrier properties and effective energy recovery efficiencies. Here, we report the formation of novel ZIF/PA TFN THEMs based on ZIF-7-X nanoparticles (NPs) with "core-shell" structures and tunable particle sizes, formed from benzimidazole (BIM) ligands and BIM substituted by -NH₂, -CH₃, -C₂H₅, and -C₃H₇ functional groups. The NPs were mixed with pyr omellitic triformyl chloride (TMC) in the organic phase during the interface polymerization process to form ZIF/PA TFN membranes. The total heat exchange performance of ZIF/PA TFN membranes could be effectively modified by the type and quantity of ZIF-7-X NPs added. The CO₂ barrier properties and water vapor permeability of ZIF/PA TFN membranes could be improved by the addition of optimal levels of ZIF-7-X NPs, showing low CO₂ permeance of 7.76 GPU, high H₂O permeance of 663.8 GPU, and excellent enthalpy exchange efficiency of 72.1%. This work provided an effective strategy for tuning not only the nanostructures of ZIF-7 fillers but also the CO₂ barrier properties of the formed ZIF/PA TFN membranes.

Adsorption and diffusion of the H2/CO2/CO/MeOH/EtOH mixture into the ZIF-7 using molecular simulation

The adsorption and diffusion of synthesis gas components (methanol, ethanol, H₂, CO_2, and CO molecules) in ZIF-7 by grand canonical Monte Carlo and molecular dynamics simulation were investigated. The initial diffusion coefficient at the beginning of the process depends on the kinetic diameter of the guest molecules. Also, the diffusion coefficient at equilibrium conditions probably depends on the interaction between the guest molecules with the ZIF-7 framework. The radial distribution function results indicate that the distribution of guest molecules in the framework is affected by the interaction between the guest molecules. These results indicate that the CO, CO₂, and H₂ guest molecules are adsorbed on both the Zn metal atom and the organic linker (especially the C₁ atom). In contrast, the organic linker is the most favorable adsorption site for methanol and ethanol guest molecules. In addition, the diffusion coefficient of guest molecules in binary mixtures is related to the attraction or repulsion between the guest molecules.

Large-Scale Screening and Machine Learning for Metal–Organic Framework Membranes to Capture CO2 from Flue Gas

To combat global warming, as an energy-saving technology, membrane separation can be applied to capture CO₂ from flue gas. Metal–organic frameworks (MOFs) with characteristics like high porosity have great potential as membrane materials for gas mixture separation. In this work, through a combination of grand canonical Monte Carlo and molecular dynamics simulations, the permeability of three gases (CO₂, N₂, and O₂) was calculated and estimated in 6013 computation–ready experimental MOF membranes (CoRE–MOFMs). Then, the relationship between structural descriptors and permeance performance, and the importance of available permeance area to permeance performance of gas molecules with smaller kinetic diameters were found by univariate analysis. Furthermore, comparing the prediction accuracy of seven classification machine learning algorithms, XGBoost was selected to analyze the order of importance of six structural descriptors to permeance performance, through which the conclusion of the univariate analysis was demonstrated one more time. Finally, seven promising CoRE-MOFMs were selected, and their structural characteristics were analyzed. This work provides explicit directions and powerful guidelines to experimenters to accelerate the research on membrane separation for the purification of flue gas.

Development of coin-shaped ZIF-7 functionalized superhydrophobic polysulfone composite foams for continuous removal of oily contaminants from water

Development of efficient absorbent materials for oil spillage clean-up and environmental pollution remediation is highly desired but remains a challenge. In this work, superhydrophobic/superoleophilic polysulfone based ZIF-7 composite (SPZ) foams were fabricated via chemical modification of polysulfone and integrating with hydrophobic coin-shaped ZIF-7 particles. The synergistic approaches provided the SPZ foams with high porosity, low density and superhydrophobic/superoleophilic features (θ_water=162.3°, θ_oil=0°) and outstanding self-cleaning property. The as-prepared SPZ foams exhibited highly selective absorption capacity (up to 3800 wt%) for various kinds of oils and organic solvents. Furthermore, the SPZ foams still maintained 95.2% of its pristine absorption capacity and the θ_water remained at 143.6° after ten absorption/distillation cycles. The SPZ foam showed outstanding separation ability towards different types of emulsions with separation efficiency all above 97%. The high oil/water separation efficiency and robust reusability made the SPZ foams promising absorbent in dealing with practical oil spills.

Preparation and Evaluation of Nanocomposite Sodalite/α-Al2O3 Tubular Membranes for H2/CO2 Separation

Nanocomposite sodalite/ceramic membranes supported on α-Al₂O₃ tubular support were prepared via the pore-plugging hydrothermal (PPH) synthesis protocol using one interruption and two interruption steps. In parallel, thin-film membranes were prepared via the direct hydrothermal synthesis technique. The as-synthesized membranes were evaluated for H₂/CO₂ separation in the context of pre-combustion CO₂ capture. Scanning electron microscopy (SEM) was used to check the surface morphology while x-ray diffraction (XRD) was used to check the crystallinity of the sodalite crystals and as-synthesized membranes. Single gas permeation of H₂, CO₂, N₂ and mixture gas H₂/CO₂ was used to probe the quality of the membranes. Gas permeation results revealed nanocomposite membrane prepared via the PPH synthesis protocols using two interruption steps displayed the best performance. This was attributed to the enhanced pore-plugging effect of sodalite crystals in the pores of the support after the second interruption step. The nanocomposite membrane displayed H₂ permeance of 7.97 × 10⁻⁷ mol·s⁻¹·m⁻²·Pa⁻¹ at 100 °C and 0.48 MPa feed pressure with an ideal selectivity of 8.76. Regarding H₂/CO₂ mixture, the H₂ permeance reduced from 8.03 × 10⁻⁷ mol·s⁻¹·m⁻²·Pa⁻¹ to 1.06 × 10⁻⁷ mol·s⁻¹·m⁻²·Pa⁻¹ at 25 °C and feed pressure of 0.18 MPa. In the presence of CO₂, selectivity of the nanocomposite membrane reduced to 4.24.

Amino-Functionalized β-Cyclodextrin to Construct Green Metal-Organic Framework Materials for CO2 Capture

The adsorption of CO₂ by conventional liquid alkanolamine adsorbents does not meet the requirements for green-friendly development in industrial applications. In this work, we constructed NH₂-β-CD-MOF for the first time through the amino-functionalization of the lowest-priced, readily available, and biocompatible β-CD. Subsequently, the samples were characterized by single-crystal X-ray diffraction, powder X-ray diffraction, scanning electron microscopy, differential scanning calorimetry, thermogravimetric analysis, elemental analysis, and N₂ adsorption/desorption. The CO₂ adsorption capacity of NH₂-β-CD-MOF was found to be 12.3 cm³/g, which is 10 times that of β-CD-MOF. In addition, NH₂-β-CD-MOF has outstanding selective adsorption of CO₂/N₂ (947.52) compared with the reported materials. The adsorption mechanism of CO₂ was analyzed by X-ray photoelectron spectroscopy and Fourier transform infrared spectroscopy. Furthermore, we have found that NH₂-β-CD-MOF has better water stability relative to β-CD-MOF and γ-CD-MOF, and it can be recycled by an ultrasonic method.

Effects of different plasticizers on highly crosslinked NaAlg/PSSAMA membranes for pervaporative dehydration of tert-butanol

Polystyrene sulfonic acid-co-maleic acid (PSSAMA) crosslinked sodium alginate (NaAlg) membranes were developed by incorporating diethyl phthalate (DEP), dibutyl phthalate (DBP) and dioctyl phthalate (DOP).