Organic Framework Membranes Research Articles

Spatial Size Manipulation of 1D/2D Channels in Covalent Organic Framework Membranes Through Dopamine Chemistry for Ion Separations

AbstractCovalent organic framework (COF) membranes feature with well‐developed 1D in‐plane pores and parallelly arranged 2D interlayer gallery, presenting promising platform for precise separations. However, it remains a formidable challenge to construct and regulate membrane channels at angstrom scale. Herein, pH‐sensitive dopamine is taken advantage to elaborately engineer the spatial size of 1D/2D channels in COF membranes for the separations of alkali metal ions. Acid treatment allows monomolecular dopamine to segment 1D in‐plane pores of COF membrane, achieving ultramicroporous regulation from 1.25 nm to 0.71 nm, which enables high selectivity of 18.7 for K+/Li+ separation. Molecular dynamics simulations reveal the higher dehydration degree, weaker channel‐cation interaction and faster diffusion coefficient of K+ than Li+. For alkaline treatment, dopamine self‐polymerizes to form nanoparticles between COF layers, which enlarges the 2D interlayer channels from 0.33 nm to 0.45 nm in COF membrane, enabling high‐permeance ion/molecule separations. The water permeance increases 86.7% to 404 L m−2 h−1 bar−1, without the sacrifice of membrane sieving ability. Both cation separation and ion/molecule separation performances outperform the current state‐of‐the‐art membranes. This dopamine‐mediated channel engineering strategy may provide the new insights for the design of membrane channels in precise separations.

Cell membrane-inspired COF/AAO hybrid nanofluidic membrane with ion current rectification properties for ultrasensitive detection of E. coli

Nanofluidic membranes hold great prospects in sensitive and rapid detection of bioanalysts, while remaining lacking robust and general approaches for specificity. In this work, we introduce a cell membrane-inspired nanofluidic membrane with excellent ion current rectification properties as a simple and robust platform for label-free and ultrasensitive biosensing. The asymmetric nanofluidic membrane is prepared by coupling a two-dimensional covalent organic framework (COF) membrane to an anodic aluminum oxide (AAO) nanochannel via hydrogen bonding. The prepared COF/AAO membrane presents selective ion transport due to the asymmetric structure and anion selectivity of COF. With the large surface area and abundant functional modification sites of COF, further grafting of the recognition unit can be easily achieved to mimic the recognition process of receptors and ligands on cell membranes. As a proof of concept, the application in bacterial detection is demonstrated by covalently bonded Concanavalin A as recognition units. The highly amplified ionic current based on ion current rectification properties of the COF/AAO membrane allows sensitive and selective bioanalysis. Specifically, the proposed asymmetric nanofluidic membrane presents a linear detection range from 10 to 106 CFU/mL with an ultralow detection limit of 7 CFU/mL for E. coli. This work reveals the great potential of COF/AAO hybrid nanofluidic membrane as a sensor for rapid and precise bioanalysis.

Freestanding Hydrogen-Bonded Organic Framework Membrane for Efficient Wound Healing.

Hydrogen-bonded organic frameworks (HOFs) are emerging as multifunctional materials with exceptional biocompatibility, abundant active sites, and tunable porosity, which are highly beneficial for advanced wound care. However, a significant challenge involves transforming pristine HOFs powders into lightweight, ultrathin, freestanding membranes compatible with soft biological systems. Herein, the study successfully develops shape-adaptive HOF-based matrix membranes (HMMs) using a polymer-assisted liquid-air interface technique. The HMMs conform seamlessly to tissues of different sizes and shapes, effectively stopping bleeding, and provide high water-vapor permeability. Notably, both in vitro and in vivo studies with mice wound models demonstrated that these tissue-conformable HMMs significantly accelerate wound healing by modulating the inflammatory environment of the injured tissue and promoting rapid re-epithelialization. Furthermore, RNA-seq analysis and mechanistic studies revealed that HMMs effectively reduce inflammation and facilitate the tissue transition from the proliferative stage to the remodeling stage of skin development. This work not only opens up new avenues for advanced wound care materials but also establishes a foundation for hybridizing HOFs with polymers for a wide range of potential applications.

Alkoxy-functionalized covalent organic Framework membranes for efficient molecular sieving with high water permeance

The presence of various trace water-soluble organic pollutants, such as dyes, poses significant potential risks to human health and ecosystems. Membrane technology presents a promising and sustainable approach for their removal from aqueous environments. However, the amorphous structure of most commercial membranes makes it challenging to achieve effective separation with high water flux. Here, we present a novel series of hydrophilic COF membranes with different alkoxy sidechain lengths for the first time. These alkoxy sidechain functional COF membranes exhibit efficient rejection of water-soluble organic dyes, including rose bengal (> 50 %), congo red (> 98 %), brilliant blue R250 (> 99 %), and alcian blue (> 99 %). Moreover, these membranes demonstrate a high water flux exceeding 291.8 L m-2h−1 bar−1 and exceptional long-term operational stability lasting at least 2880 min. The superior performance of COF membranes is attributed to their optimal pore size, excellent hydrophilicity, and high crystallinity. This finding offers a promising approach for effectively eliminating water-soluble organic pollutants, thereby ensuring the safety and sustainability of the water supply.

Covalent Organic Framework Membranes with Regulated Orientation for Monovalent Cation Sieving.

Continuous covalent organic framework (COF) thin membranes have garnered broad concern over the past few years due to their merits of low energy requirements, operational simplicity, ecofriendliness, and high separation efficiency in the application process. This study marks the first instance of fabricating two distinct, self-supporting COF membranes from identical building blocks through solvent modulation. Notably, the precision of the COF membrane's separation capabilities is substantially enhanced by altering the pore alignment from a random to a vertical orientation. Within these confined channels, the membrane with vertically aligned pores and micron-scale stacking thickness demonstrates rapid and selective transportation of Li+ ions over Na+ and K+ ions, achieving Li+/K+ and Li+/Na+ selectivity ratios of 38.7 and 7.2, respectively. This research not only reveals regulated orientation and layer stacking in COF membranes via strategic solvent selection but also offers a potent approach for developing membranes specialized in Li+ ion separation.

Giant gateable thermoelectric conversion by tuning the ion linkage interactions in covalent organic framework membranes

Efficient energy conversion using ions as carriers necessitates membranes that sustain high permselectivity in high salinity conditions, which presents a significant challenge. This study addresses the issue by manipulating the linkages in covalent-organic-framework membranes, altering the distribution of electrostatic potentials and thereby influencing the short-range interactions between ions and membranes. We show that a charge-neutral covalent-organic-framework membrane with β-ketoenamine linkages achieves record permselectivity in high salinity environments. Additionally, the membrane retains its permselectivity under temperature gradients, providing a method for converting low-grade waste heat into electrical energy. Experiments reveal that with a 3 M KCl solution and a 50 K temperature difference, the membrane generates an output power density of 5.70 W m−2. Furthermore, guided by a short-range ionic screening mechanism, the membrane exhibits adaptable permselectivity, allowing reversible and controllable operations by finely adjusting charge polarity and magnitude on the membrane’s channel surfaces via ion adsorption. Notably, treatment with K3PO4 solutions significantly enhances permselectivity, resulting in a giant output power density of 20.22 W m−2, a 3.6-fold increase over the untreated membrane, setting a benchmark for converting low-grade heat into electrical energy.

The role of one-dimensional materials in modulating the selective mass transport of covalent organic framework membranes for nanofiltration

Two-dimensional covalent organic frameworks (2D COFs) membranes have well-ordered nanochannels for selective molecular sieving. One-dimensional (1D) materials have been proposed to link the loosely packed COFs nanosheet for enhancing the separation performance of COFs membranes. However, it remains unclear how the enhancement arises. Herein, we demonstrate the role of 1D materials in modulating the microstructure and interlayer force of 2D COFs membranes. The optimized composite membrane, assembled from 2D COFs and chitosan exhibits a 75% enhancement in permeance without sacrificing selectivity towards different dyes. Our results show that the interaction forces between COFs and 1D materials are directly correlated to the transport nanochannels. When the interaction forces are stronger, the microstructure is more densely packed. Meanwhile, the shielding effect of 1D materials on the intrinsic channels of 2D COFs is more significant, resulting in narrow transport channels for mass transfer. In contrast, the weaker interaction forces prevent the excessive shrinkage of nanochannels, facilitating fast mass transfer and maintaining the high molecular selectivity. The work unravels the interaction forces between 2D COFs and 1D materials leading to the shaping of mass transfer nanochannels, offering a new perspective for the advancement of COFs membrane for nanofiltration.

Ionic Covalent Organic Framework Membrane as Active Separator for Highly Reversible Zinc-Sulfur Battery.

Zinc-sulfur (Zn-S) batteries exhibit a high theoretical energy density, nontoxicity, and cost-effectiveness, demonstrating significant potential for integration into large-scale energy storage systems. However, the phenomenon of polysulfide (including dissolved S8 and Sx2-) shuttling is a major issue that results in rapid capacity decay and a short lifespan, limiting the practical performance of sulfur-based batteries. Herein, we fabricated an ionic covalent organic framework (iCOF) membrane as an active separator for the Zn-S battery. Sulfonic acid groups were introduced to the COF membrane, providing abundant negative charge sites in its pore wall. By combining size sieving and charge interaction between the polysulfide and pore wall, the iCOF membrane inhibited the crossover of polysulfides to the Zn metal anode without affecting the transport of metal ions. The Zn-S battery with the iCOF membrane as the separator shows a high-performance and low attenuation rate of 0.05% per cycle over 300 cycles at 2.5 A g-1. This study emphasizes the significance of separator design in enhancing Zn-S batteries and showcases the potential of functionalized framework materials for the development of high-performance energy storage systems.

Alkaline-resistant covalent organic framework membranes for selective hydroxide ion separation

Alkali holds a pivotal role in the chemical industry, however, the substantial discharge of alkaline wastewater causes a severe waste of resources and environmental pollution. Conventional polymer membranes have ether bonded backbones and form randomly assembled nanochannels, suffering from a weak alkali resistance and a low hydroxide ion selectivity. Covalent organic frameworks (COFs), known for their robust framework structure, highly ordered channels, and tunable channel chemistry, have been considered as the competent candidate for alkaline-resistant membranes for selective hydroxide ion separation. Herein, we fabricate a β-ketoenamine COF (TpTAPB) membrane with a high alkaline resistance via the interfacial growth strategy. After post-sulfonation, the negatively charged channels of sulfonated TpTAPB membrane allows OH- with smaller size and lower charges to pass through while repulsing WO42- ions, achieving a selectivity of OH-/WO42- up to ∼ 60 and surpassing commercial and most reported polymeric membranes. This work expands the application scope of COF membranes in selective alkali separation.

Covalent organic framework membranes achieving Mg/Li separation by permeating Mg2+ while retaining Li+

Due to the growing demand for lithium in the new energy industry, significant attention has been focused on developing lithium extraction technologies from salt-lake brine. However, the high Mg/Li ratio in salt-lake brine presents challenges for membrane separation technology. If a membrane can allow Mg2+ and water molecules to pass through while retaining Li+, the retained brine will have concentrated Li+ with a reduced Mg/Li ratio, creating the facilitation of further lithium extraction. In this study, we discovered through non-equilibrium molecular dynamics simulations that strongly hydrophilic covalent organic frameworks membranes capture Li+ in their pores, preventing additional Li+ from entering the nanopores. Meanwhile, Mg2+ can freely penetrate these nanopores along with water molecules. This adsorption of Li+ and the free permeation of Mg2+ with water molecules result in the effective separation of Li+ and Mg2+. Consequently, the retained brine becomes lithium-rich with reduced Mg/Li ratio. The findings of this work provide valuable guidance for designing nanofiltration membranes for extracting lithium from salt lakes with high Mg/Li ratio.

A cationic three-dimensional covalent organic framework membrane for nanofiltration of molecules and rare Earth ions

Permanently microporous materials have evolved as focal point of research for tackling issues in separation science and membrane technology. Covalent organic frameworks (COFs) stand out for their distinctive synergy of crystalline nature, uniform channels, and structural diversities. Three-dimensional (3D) COFs, distinguished by angstrom-sized and interconnected channels, hold special promise for separating small targets; however, this potential remains underexplored. Here, we report feasible growth of cationic 3D COF membranes on a flexible polymer substrate for versatile nanofiltration toward both molecules and ions. Through comprehensive performance evaluations, we reveal that the resultant membrane exhibits durable and prominent molecular selectivity to separate fine species with molecular weights above 300 g mol−1 at fast methanol permeation. Lanthanide ions of industrial value also can be harvested by the membrane with rejection rates of up to 91.4%. Together with its nonselectivity to competing ions, our membrane implements efficient extraction of rare earth elements from ion mixtures. These findings illuminate the potential of 3D COFs for liquid separation and offer a solution to building versatile membranes.

Assembly-Dissociation-Reconstruction Synthesis of Covalent Organic Framework Membranes with High Continuity for Efficient CO2 Separation.

Covalent organic frameworks (COFs), at the forefront of porous materials, hold tremendous potential in membrane separation; however, achieving high continuity in COF membranes remains crucial for efficient gas separation. Here, we present a unique approach termed assembly-dissociation-reconstruction for fabricating COF membranes tailored for CO2/N2 separation. A parent COF is designed from two-node aldehyde and three-node amine monomers and dissociated to high-aspect-ratio nanosheets. Subsequently, COF nanosheets are orderly reconstructed into a crack-free membrane by surface reaction under water evaporation. The membrane exhibits high crystallinity, open pores and a strong affinity for CO2 adsorption over N2, resulting in CO2 permeance exceeding 1060 GPU and CO2/N2 selectivity surpassing 30.6. The efficacy of this strategy offers valuable guidance for the precise fabrication of gas-separation membranes.

Assembly‐Dissociation‐Reconstruction Synthesis of Covalent Organic Framework Membranes with High Continuity for Efficient CO2 Separation

AbstractCovalent organic frameworks (COFs), at the forefront of porous materials, hold tremendous potential in membrane separation; however, achieving high continuity in COF membranes remains crucial for efficient gas separation. Here, we present a unique approach termed assembly‐dissociation‐reconstruction for fabricating COF membranes tailored for CO2/N2 separation. A parent COF is designed from two‐node aldehyde and three‐node amine monomers and dissociated to high‐aspect‐ratio nanosheets. Subsequently, COF nanosheets are orderly reconstructed into a crack‐free membrane by surface reaction under water evaporation. The membrane exhibits high crystallinity, open pores and a strong affinity for CO2 adsorption over N2, resulting in CO2 permeance exceeding 1060 GPU and CO2/N2 selectivity surpassing 30.6. The efficacy of this strategy offers valuable guidance for the precise fabrication of gas‐separation membranes.

Polyelectrolyte intercalated two-dimensional covalent organic framework membranes for efficient desalination

Two-dimensional covalent organic frameworks (2D COFs) have been proven to be ideal membrane materials for highly efficient separation. However, synergistic manipulation of the in-plane pores and interlayer channel structures of 2D COF membranes (COFMs) to acquire both high permeability and selectivity has rarely been reported. In this work, we synthesized TbTG COF nanosheets with intrinsic sub-nanometer pores, which were assembled with polyelectrolytes to form intercalated 2D COFMs. The sub-nanometer in-plane pores of the COF nanosheets endowed the COFM with size sieving capacity toward hydrated multivalent ions. The polyelectrolyte introduces numerous charged groups to the interlayer channels, enhancing the Donnan effect for desalination and also enlarging the interlayer distance to facilitate permeability. Accordingly, the in-plane pores and interlayer channels of the 2D COFM were synergistically engineered to simultaneously enhance the selectivity and permeability of COFMs. By adjusting the polyelectrolytes with different charged groups, the intercalated COFMs exhibited a high Na2SO4 rejection of 97.5 % and MgCl2 rejection of 99.4 %, respectively, as well as about a fourfold increase in permeability. Compared with the pure COFM. This work highlights the significance of interlayer channel structure of 2D COFMs for precise separations, providing new guidelines on the design and construction of advanced COFMs.

Theoretical investigation of supramolecular organic framework membranes for hydrogen purification

Given that SOF materials have both inorganic and organic properties and are easy to prepare and structurally designable, this paper carries out the microbehavioral analysis and membrane design of SOF-8, SOF-9, and SOF-10 membranes for the hydrogen purification process of RMFCs. Since three materials have complementary performance characteristics for hydrogen purification, this paper focuses on the gas separation behavior of these three composite membranes using molecular dynamics simulations. Results showed that the SOF-9a+10a composite membranes could 100% block CO2 and CO, and displayed an excellent H2 permeability of 6.118 × 105 GPU during H2/CO2 separation, which exceeded the industry standard by nearly 105 times. Additionally, the SOF-9a+8 and SOF-10a+8 composite membranes improved gas selectivity and maintained high H2 permeability. Moreover, microdiffusion analyses revealed that the small pore sizes and irregular-shaped pore channels effectively hindered CO2 and CO transport. Microscopic analysis shows the potential of SOF composite membranes for gas separation.

A robust COF membrane on polyethylene support via ethanol-assisted self-assembly of COF nanosheets for efficient desalination

Fabrication of high-rejection covalent organic framework (COF) membranes for desalination remains a significant challenge, due to processing limitations and substrate mismatches. Herein, we report an ethanol-assisted self-assembly strategy for preparing high-rejection COF membranes from anionic TpPa-SO3Na COF (SCOF) nanosheets. This method promotes SCOF dispersion in ethanol with high aspect-ratio structures and elimination of interlayer charge, thus facilitating the formation of defect-free SCOF membranes (COFMs). Furthermore, polyvinyl alcohol (PVA) was used to modify commercial polyethylene (PE) supports ensuring compatibility with the high-rejection SCOF layers. The hydrophilic PVA@PE support with appropriate surface pore induces the SCOF nanosheets to form a complete stacking structure. The resultant COFM (MEtOH) exhibit an impressive Na2SO4 rejection rate of 98.83 % and a pure water flux of 4.35 L m−2 h−1, demonstrate exceptional rejection stability under elevated pressure, acidic or alkaline conditions, and high salt concentrations. The superior desalination performance of the COFMs surpasses the most reported 2D desalination membranes.

Homogeneously assembled covalent organic framework membrane co-stitched by β-cyclodextrin and chitosan for dye separation

Covalent organic frameworks (COFs) based membranes have demonstrated great potential in molecular separation. However, COFs are usually synthesized as powders, and difficult to form large-area and highly crystalline membranes. There normally exists unfavorable crystal flaws and stacking defects in membranes, impairing their rejection performance. The severe reaction conditions of solvothermal synthesis also inhibit their fabrication. Here, a comprehensive strategy was developed to fabricate a homogeneously assembled COF membrane co-stitched by β-cyclodextrin (β-CD) and chitosan (CS). Specifically, the COF crystallites (named TATP) were homogeneously formed and assembled to be films at room temperature under the control of n-propylamine; The aminated CS chemically bonded the TATP crystallites on the substrate and helped assemble them to form dense films. β-CD molecules were subsequently embedded into the TATP layer and crosslinked to further stitch membrane defects. The prepared CD-TATP-NH2CS/nylon membrane demonstrated enhanced excellent rejection performance. It could reject 100 % of R250 (BB), Congo red, Direct blue15, and 99.4 % of Alcian blue. It also could selectively separate Methyl orange (MO) and BB mixed solutions with only MO passing through, owing to the co-stitching of the membrane defects by β-CD and CS. This study provides a significant concept and strategy for fabricating high-performance COF membranes.

Covalent organic framework membrane reactor for boosting catalytic performance

Membrane reactors are known for their efficiency and superior operability compared to traditional batch processes, but their limited diversity poses challenges in meeting various reaction requirements. Herein, we leverage the molecular tunability of covalent organic frameworks (COFs) to broaden their applicability in membrane reactors. Our COF membrane demonstrates an exceptional ability to achieve complete conversion in just 0.63 s at room temperature—a benchmark in efficiency for Knoevenagel condensation. This performance significantly surpasses that of the corresponding homogeneous catalyst and COF powder by factors of 176 and 375 in turnover frequency, respectively. The enhanced concentration of reactants and the rapid removal of generated water within the membrane greatly accelerate the reaction, reducing the apparent activation energy. Consequently, this membrane reactor enables reactions that are unattainable using both COF powders and homogeneous catalysts. Considering the versatility, our findings highlight the substantial promise of COF-based membrane reactors in organic transformations.

Tunable Wettability of a Dual-Faced Covalent Organic Framework Membrane for Enhanced Water Filtration.

Membrane technology plays a central role in advancing separation processes, particularly in water treatment. Covalent organic frameworks (COFs) have transformative potential in this field due to their adjustable structures and robustness. However, conventional COF membrane synthesis methods are often associated with challenges, such as time-consuming processes and limited control over surface properties. Our study demonstrates a rapid, microwave-assisted method to synthesize self-standing COF membranes within minutes. This approach allows control over the wettability of the surface and achieves superhydrophilic and near-hydrophobic properties. A thorough characterization of the membrane allows a detailed analysis of the membrane properties and the difference in wettability between its two faces. Microwave activation accelerates the self-assembly of the COF nanosheets, whereby the thickness of the membrane can be controlled by adjusting the time of the reaction. The superhydrophilic vapor side of the membrane results from -NH2 reactions with acetic acid, while the nearly hydrophobic dioxane side has terminal aldehyde groups. Leveraging the superhydrophilic face, water filtration at high water flux, complete oil removal, increased rejection with anionic dye size, and resistance to organic fouling were achieved. The TTA-DFP-COF membrane opens new avenues for research to address the urgent need for water purification, distinguished by its synthesis speed, simplicity, and superior separation capabilities.

Congo red stitched covalent organic framework membrane for dye separation

Covalent organic framework (COF) membranes have shown great potential in dyes’ separation. However, COFs are difficult to form large-area and highly crystalline membranes, therefore there normally exists crystal and stacking defects in COF membranes, impairing their rejection performance. Herein, we discovered the prepared COF-TATP membranes have exceptional high rejection to Congo red (CR) solution. Further study showed the presence of small proportion of CR in other dye solutions also could enhance the rejection to those dyes. 3:100 CR/Brilliant blue R250 (BB) solution could obtain 99.81% rejection to BB. Characterizations indicated CR molecules could well merged into the COF layer and strongly bonded with its N/O groups via plentiful hydrogen bonds. Inspired by the finding, we proposed a strategy of using CR to stitch the defects in COF layer. Specifically, CR was embedded into and then chemically crosslinked with COF-TATP layer by glutaraldehyde to prepare LCR-TATP-NH2CS/nylon membranes. The membranes showed obviously enhanced rejection to all dyes tested, typically BB rejection of 99.75%. It also could selectively separate BB/Methyl orange mixed solutions. This study reveals some insights into dyes’ behavior on COF membranes, and provides a simple and feasible strategy for stitching COF membranes’ defects to enhance their performance.