Switchable Na+ and K+ selectivity in an amino acid functionalized 2D covalent organic framework membrane

Covalent organic frameworks for metal ion separation: Nanoarchitectonics, mechanisms, applications, and future perspectives

Covalent organic frameworks (COFs) are a class of porous crystalline materials with high surface areas, tunable pore sizes, and customizable surface chemistry, making them ideal for selective metal ion separation. This review explores the nanoarchitectonics, mechanisms, and applications of COFs in metal ion separation. We highlight the diverse bonding types (e.g., imine, boronic ester) and topologies (2D and 3D) that enable precise separation for alkali, alkaline earth, transition, and precious metals. The influence of COFs' pore characteristics, such as surface area, pore size, and distribution, on their adsorption capacity and selectivity is discussed. Additionally, surface functionalization enhances ion adsorption through electrostatic, coordination, and polarity interactions. Despite significant progress, challenges remain, including optimizing functional design for complex metal systems, improving material stability, and developing cost-effective synthesis methods. COFs also show promise in energy material recovery, biomedical diagnostics, and environmental remediation. Combining COFs with other separation technologies can enhance performance, and integrating AI and robotics in COF design may address current limitations, enabling broader industrial and environmental applications.

Oriented PolyMOFs Enabled by Bridging Coligand for CO2 Separation

Despite enormous research efforts in recent years, polymer-metal-organic framework (polyMOF) development still faces several drawbacks, such as the substantial decrease in surface area, poor crystallinity, and monophyletic chemical structure of polyMOFs. Herein, we overcome the constraints of the coordination mode of conventional polyMOFs and report a bridging coligand strategy to prepare new types of polyMOFs, where the MOFs featuring accessible CuII sites are compelled to orientally regrow within the confined channels of semirigid PIM-1 in dimethyl sulfoxide. Coordination-substitution characteristics and solvent-modulated synthesis enable the Cu centers in MOFs to coordinate with the N atoms from PIM-1 by bridging coligand mode. The reduced particle size, enhanced ultramicroporosity, preferential orientation, and superior filler-matrix compatibility endow the polyMOF-based mixed matrix membrane with excellent CO2 separation performance, with a CO2 permeability of 4669 Barrer, and with a CO2/N2 selectivity of ∼30. This polyMOF design concept exploits a viable avenue for developing more inorganic-organic hybrid materials.

Construction of Guanidinium-Functionalized Covalent Organic Frameworks via Phototriggered Click Reaction as a Dual-Mode Accurate Sensor for Malondialdehyde

Malondialdehyde (MDA) serves as a pivotal indicator to estimate the lipid peroxidation status and as a biomarker for the assessment of oxidative stress and screening of disease by people excretion. However, most of the existing analytical methods for MDA suffer from complicated derivation, leading to poor accuracy and inconvenience. In this work, the guanidinium-functionalized covalent organic framework (COF) was delicacy-designed and used to tune the modular structure by the building blocks with condensation, phototriggered click reaction, and further guanidylation process. A methoxy-group-containing linker in the skeleton was adopted to form lone-pair delocalized oxygen atoms, trigger the resonance effect, attenuate the polarization of the C═N bond linkages, and weaken the interlayer repulsion, supporting the stability of the guest gating COF. The available guanidino groups grew from the ordered pore walls of the COF and served as the customized talon with an enhanced interaction site density to rapidly grab the target guest by charge-assisted strong hydrogen bonds and electrostatic attraction forces. This distinctive feature significantly bolstered sensitive signal transduction, enabling rapid MDA sensing (within 120 s) without derivation treatment, and achieved a calculated limit of detection (LOD) as low as 0.08 μM. With the accessible image-data transmission process, the portable dual-channel sensing platform achieved sensitive and accurate MDA monitoring.

Power-Sustainable and Portable Electrochemical Sensing Platforms for Complex Outdoor Environment Applications

Portable sensor technologies are indispensable in personalized healthcare and environmental monitoring as they enable the continuous tracking of key analytes. Human sweat contains valuable physiological information, and previously developed noninvasive sweat-based sensors have effectively monitored single or multiple biomarkers. By successfully detecting biochemicals in sweat, portable sensors could also significantly broaden their application scope, encompassing non-biological fluids commonly encountered in daily life, such as mineral water. However, developing a portable electrochemical sensing system with sustainable power remains a challenge for real-time, on-site analysis in complex outdoor applications. Here, we present a power-sustainable and portable electrochemical sensing platform, composed of multiple electrochemical sensors, a multichannel data acquisition circuit, a microfluidic module, and a power supply module, that is designed to conform onto the human body for daily use. The device enables simultaneous and selective measurement of Na+, K+, and pH levels in sweat and outdoor environments wirelessly. Additionally, we utilize a dual power supply module composed of a lithium-ion battery and a solar cell, offering a sustainable power supply for various application scenarios. Looking forward, this novel platform can serve as a bridge between monitoring biological fluids and detecting nonbiological fluids in complex outdoor environments.

Highly Selective and Excitable Artificial Ion Channel for Spike Generation

Cation channels of the neuron can be excited by neurotransmitters and have high ionic selectivity, which are crucial for the generation of spikes. Intuitively, if a channel has both a high ionic selectivity and excitability, it may be used to generate spikes. However, integrating the high selectivity and excitability in a single channel remains highly challenging. In this work, we demonstrate an artificial ion channel based on a wetting film between an oil droplet and a glass substrate. The channel height is dominated by the repulsive electrostatic interaction between the glass/water and water/oil interfaces and is therefore highly adaptable to ambient ions and charged surfactant, setting the basis for flexible control of the open/close state and ion selectivity. The channel stays in a closed state unless excited by an anionic surfactant. Once excited, the channel opens wide for monovalent ions but narrows for divalent ions, exhibiting a selectivity up to >6800. By exploiting such excitability and selectivity, we constructed a prototype artificial neuron for spike generation. Using the anionic surfactant to simulate the neurotransmitter, our artificial neuron can automatically and step-wisely open and close the channel, generating a current spike with adjustable magnitude. We expect our work to inspire the development of biomimetic devices for potential neuromorphic computing applications.

Comediation of voltage gating and ion charge in MXene membrane for controllable and selective monovalent cation separation

Artificial ion channels with controllable mono/monovalent cation separation fulfill important roles in biomedicine, ion separation, and energy conversion. However, it remains a daunting challenge to develop an artificial ion channel similar to biological ion channels due to ion-ion competitive transport and lack of ion-gating ability of channels. Here, we report a conductive MXene membrane with polydopamine-confined angstrom-scale channels and propose a voltage gating and ion charge comediation strategy to concurrently achieve gated and selective mono/monovalent cation separation. The membrane shows a highly switchable "on-off" ratio of ∼9.9 for K+ transport and an excellent K+/Li+ selectivity of 40.9, outperforming the ion selectivity of reported membranes with electrical gating (typically 1.5 to 6). Theoretical simulations reveal that the introduced high-charge cations such as Mg2+ enable the preferential distribution of target K+ over competing Li+ at the channel entrance, and the surface potential reduces the ionic transport energy barrier for allowing K+ to pass quickly through the channel.

Precise Separation of Complex Ultrafine Molecules through Solvating Two-Dimensional Covalent Organic Framework Membranes

Isoporous nanomaterials, with their proven potential for accurate molecular sieving, are of substantial interest in propelling sustainable membrane techniques. Covalent organic frameworks (COFs) are prominent due to their customizable isopores and chemistry. Still, the discrepancy in experimental and theoretical structures poses a challenge to developing COF membranes for molecular separations. Here, we report high-selectivity sieving of complex ultrafine molecules through solvating pore-to-pore-aligned two-dimensional COF membranes. Our structurally oriented membrane shows reversible interlayer expansion with intralayer shift in response to solvent exposure. This dynamic deformation induced by solvents leads to a reduction in the aperture of the membrane's sieving pores, which correlates with the number of COF layers. The resultant membranes yield largely improved molecular selectivity to discriminate binary and trinary complex mixtures, exceeding the conventional COF membranes. The membrane's robustness against solvents and physical aging permits extremely stable microporosity and reliable operation for over 3000 h. This exceptional performance positions our membrane as an alternative to enriching and purifying value-added chemicals, such as active pharmaceutical ingredients.

Heterogeneous Covalent Organic Framework Membranes Mediated by Polycations for Efficient Ions Separation

Precise ions sieving at angstrom-scale is gaining tremendous attention thanks to its significant impact at the water-energy nexus. Herein, a novel polycation-modulated interfacial polymerization (IP) strategy is developed to prepare a heterogeneously charged covalent organic frameworks (COFs) membrane. Cationic poly(diallyldimethylammonium chloride) (PDDA) regulates the growth and assembly of anionic COFs nanosheets, which thus provides a negative, smooth top surface and positive, rough bottom surface, indicating the presence of heterogeneously charged angstrom-scale channels through the membrane. Experiments and simulations are conducted to understand the facilitated ions transport behavior relative to specific interactions raised by heterogeneously charged channels and angstrom-scale steric hinderance as well, rendering the membrane with robust mono-/divalent cations sieving capabilities. The selectivity (61.6) of Li+ to Mg2+ in mixed saline under the continuous cross-flow filtration mode is superior to most of the reported nanofiltration membranes. This polycation-mediated interfacial polymerization strategy offers a compelling opportunity to develop versatile heterogeneously charged COF membranes for exquisite ion sieving.

Reverse-Selective Anion Separation Relies on Charged "Hourglass" Gate

According to the hydration size and charge property of separated ions, the transport channel can be constructed to achieve precision ion separation, but the ion geometry as a separation parameter to design the channel structure is rarely reported. Herein, a reverse-selective anion separation membrane composed of a metal-organic frameworks (MOFs) layer with a charged "hourglass" channel as an ion-selective switch to manipulate oxoanion transport is developed. The gate in "hourglass" with tetrahedral geometry similar to the oxoanion (such as SO2- 4, Cr 2O2- 7, and MnO- 4) boosts the transmission effect oxoanion much larger than Cl- through geometric matching and Coulomb interaction. Specific channel structure exhibits an abnormal selectivity for SO2- 4/Cl- of 20, Cr 2O2- 7/Cl- of 6.6, and MnO- 4/Cl- of 4.0 in a binary-ion system. The transfer behavior of SO2- 4 in the channel revealed by molecular dynamics simulation and density functional theory calculation further indicates the mechanism of the abnormal separation performance. The universality of the membrane structure is validated by the formation of different nitrogen-containing modified layers, which also achieves in situ growth of the MOFs layer, and exhibits similar reversal separation performance. The geometric configuration control of ion transport channels presents a novel effective strategy to realize the precise separation of target ions.

A Bioinspired Membrane with Ultrahigh Li+/Na+ and Li+/K+ Separations Enables Direct Lithium Extraction from Brine

Membranes with precise Li+/Na+ and Li+/K+ separations are imperative for lithium extraction from brine to address the lithium supply shortage. However, achieving this goal remains a daunting challenge due to the similar valence, chemical properties, and subtle atomic-scale distinctions among these monovalent cations. Herein, inspired by the strict size-sieving effect of biological ion channels, a membrane is presented based on nonporous crystalline materials featuring structurally rigid, dimensionally confined, and long-range ordered ion channels that exclusively permeate naked Li+ but block Na+ and K+. This naked-Li+-sieving behavior not only enables unprecedented Li+/Na+ and Li+/K+ selectivities up to 2707.4 and 5109.8, respectively, even surpassing the state-of-the-art membranes by at least two orders of magnitude, but also demonstrates impressive Li+/Mg2+ and Li+/Ca2+ separation capabilities. Moreover, this bioinspired membrane has to be utilized for creating a one-step lithium extraction strategy from natural brines rich in Na+, K+, and Mg2+ without utilizing chemicals or creating solid waste, and it simultaneously produces hydrogen. This research has proposed a new type of ion-sieving membrane and also provides an envisioning of the design paradigm and development of advanced membranes, ion separation, and lithium extraction.

Synthesis of a cysteine functional covalent organic framework via facile click reaction for the efficient solid phase extraction of substituted p-phenylenediamine-derived quinones

N,N'-Substituted p-phenylenediamine quinones (PPD-Qs) are the emerging toxicant, which transform from the rubber tire antioxidant N,N'-substituted p-phenylenediamines (PPDs). Because of their potential toxic and widespread occurrence in the environment, PPD-Qs have received great attention. However, efficiently extracting PPD-Qs from complex samples is still a challenge. Herein, a cysteine functional covalent organic framework (Cys-COF) designed according to the "donor-acceptor" sites of hydrogen bonding of PPD-Qs was synthesized via click reaction and then used as solid-phase extraction (SPE) adsorbent. Cys-COF can form the seven-member ring adsorption structure with PPD-Qs via hydrogen bonding. The adsorption mechanism was tentatively revealed by density functional theory (DFT). After optimizing the Cys-COF-SPE parameters, PPD-Qs were efficiently extracted from water, soil, sediment, and fish, followed by detection using ultra-performance liquid chromatography-tandem mass spectrometry (UHPLC-MS/MS). The Cys-COF-SPE-UHPLC-MS/MS method exhibited ideal linearity (R2 ≥ 0.9932), high relative recoveries (80.4-111 %), and low limits of detection (0.0001-0.0013 ng mL-1). In addition, the bioconcentration kinetics in goldfish provides a feasible platform to investigate the toxicity and accumulated ability of PPD-Qs.

Microporous polyarylate membranes based on 3D phenolphthalein for molecular sieving

Thin-film composite (TFC) membranes have gradually replaced some traditional technologies in the extraction, separation, and concentration of high value-added pharmaceutical ingredients due to their controllable microstructure. Nevertheless, devising solvent-stable, scalable TFC membranes with high permeance and efficient molecule selectivity is urgently needed to improve the separation efficiency in the separation process. Here, we propose phenolphthalein, a commercial acid-base indicator, as an economical monomer for optimizing the micropore structure of selective layers with thickness down to 30 nanometers formed by in situ interfacial reactions. Molecular dynamics simulations indicate that the polyarylate membranes prepared using three-dimensional phenolphthalein monomers exhibit tunable microporosity and higher pore interconnectivity. Moreover, the TFC membranes show a high methanol permeance (9.9 ± 0.1 liters per square meter per hour per bar) and small molecular weight cutoff (≈289 daltons) for organic micropollutants in organic solvent systems. The polyarylate membranes exhibit higher mechanical strength (2.4 versus 0.8 gigapascals) compared to the traditional polyamide membrane.

Elucidating the transport of water and ions in the nanochannel of covalent organic frameworks by molecular dynamics

Inspired by biological channels, achieving precise separation of ion/water and ion/ion requires finely tuned pore sizes at molecular dimensions and deliberate exposure of charged groups. Covalent organic frameworks (COFs), a class of porous crystalline materials, offer well-defined nanoscale pores and diverse structures, making them excellent candidates for nanofluidic channels that facilitate ion and water transport. In this study, we perform molecular simulations to investigate the structure and kinetics of water and ions confined within the typical COFs with varied exposure of charged groups. The COFs exhibit vertically arrayed nanochannels, enabling diffusion coefficients of water molecules within COFs to remain within the same order of magnitude as in the bulk. The motion of water molecules manifests in two distinct modes, creating a mobile hydration layer around acid groups. The ion diffusion within COFs displays a notable disparity between monovalent (M+) and divalent (M2+) cations. As a result, the selectivity of M+/M2+ can exceed 100, while differentiation among M+ is less pronounced. In addition, our simulations indicate a high rejection (R > 98%) in COFs, indicating their potential as ideal materials for desalination. The chemical flexibility of COFs indicates that would hold significant promise as candidates for advanced artificial ion channels and separation membranes.

Thiol-Ene Click Reaction in Constructing Liquid Separation Membranes for Water Treatment

In the evolving landscape of water treatment, membrane technology has ascended to an instrumental role, underscored by its unmatched efficacy and ubiquity. Diverse synthesis and modification techniques are employed to fabricate state-of-the-art liquid separation membranes. Click reactions, distinguished by their rapid kinetics, minimal byproduct generation, and simple reaction condition, emerge as a potent paradigm for devising eco-functional materials. While the metal-free thiol-ene click reaction is acknowledged as a viable approach for membrane material innovation, a systematic elucidation of its applicability in liquid separation membrane development remains conspicuously absent. This review elucidates the pre-functionalization strategies of substrate materials tailored for thiol-ene reactions, notably highlighting thiolation and introducing unsaturated moieties. The consequential implications of thiol-ene reactions on membrane properties-including trade-off effect, surface wettability, and antifouling property-are discussed. The application of thiol-ene reaction in fabricating various liquid separation membranes for different water treatment processes, including wastewater treatment, oil/water separation, and ion separation, are reviewed. Finally, the prospects of thiol-ene reaction in designing novel liquid separation membrane, including pre-functionalization, products prediction, and solute-solute separation membrane, are proposed. This review endeavors to furnish invaluable insights, paving the way for expanding the horizons of thiol-ene reaction application in liquid separation membrane fabrication.

Ionic Current Saturation Enabled by Cation Gating Effect in Metal-Organic-Framework Membranes

Ion transport through nanoporous two-dimensional (2D) membranes is predicted to be tunable by controlling the charging status of the membranes' planar surfaces, the behavior of which though remains to be assessed experimentally. Here we investigate ion transport through intrinsically porous membranes made of 2D metal-organic-framework layers. In the presence of certain cations, we observe a linear-to-nonlinear transition of the ionic current in response to the applied electric field, the behavior of which is analogous to the cation gating effect in the biological ion channels. Specifically, the ionic currents saturate at transmembrane voltages exceeding a few hundreds of millivolts, depending on the concentration of the gating cations. This is attributed to the binding of cations at the membranes' surfaces, tuning the charging states there and affecting the entry/exit process of translocating ions. Our work also provides 2D membranes as candidates for building nanofluidic devices with tunable transport properties.

Bio-Inspired Subnanofluidics: Advanced Fabrication and Functionalization

Biological ion channels can realize high-speed and high-selective ion transport through the protein filter with the sub-1-nanometer channel. Inspired by biological ion channels, various kinds of artificial subnanopores, subnanochannels, and subnanoslits with improved ion selectivity and permeability are recently developed for efficient separation, energy conversion, and biosensing. This review article discusses the advanced fabrication and functionalization methods for constructing subnanofluidic pores, channels, tubes, and slits, which have shown great potential for various applications. Novel fabrication methods for producing subnanofluidics, including top-down techniques such as electron beam etching, ion irradiation, and electrochemical etching, as well as bottom-up approaches starting from advanced microporous frameworks, microporous polymers, lipid bilayer embedded subnanochannels, and stacked 2D materials are well summarized. Meanwhile, the functionalization methods of subnanochannels are discussed based on the introduction of functional groups, which are classified into direct synthesis, covalent bond modifications, and functional molecule fillings. These methods have enabled the construction of subnanochannels with precise control of structure, size, and functionality. The current progress, challenges, and future directions in the field of subnanofluidic are also discussed.

Conformational Locking as a Strategy to Reverse Ion Recognition Selectivity

This study delves into the ion recognition capabilities of a novel host molecule, emphasizing the role of conformational locking in dictating ion selectivity. By employing the Buchwald-Hartwig cross-coupling reaction, we have notably shifted the ion receptor's selectivity from K+ to Na+. The findings are supported by computational simulations that reveal differences in binding energies and molecular strain impacting ion recognition. This innovative structural modification broadens the scope for alterations at the calix[4]arene's lower rim, paving the way for new methods and strategies in modulating ion recognition selectivity.

Regulating ion affinity and dehydration of metal-organic framework sub-nanochannels for high-precision ion separation

Membrane consisting of ordered sub-nanochannels has been pursued in ion separation technology to achieve applications including desalination, environment management, and energy conversion. However, high-precision ion separation has not yet been achieved owing to the lack of deep understanding of ion transport mechanism in confined environments. Biological ion channels can conduct ions with ultrahigh permeability and selectivity, which is inseparable from the important role of channel size and "ion-channel" interaction. Here, inspired by the biological systems, we report the high-precision separation of monovalent and divalent cations in functionalized metal-organic framework (MOF) membranes (UiO-66-(X)2, X = NH2, SH, OH and OCH3). We find that the functional group (X) and size of the MOF sub-nanochannel synergistically regulate the ion binding affinity and dehydration process, which is the key in enlarging the transport activation energy difference between target and interference ions to improve the separation performance. The K+/Mg2+ selectivity of the UiO-66-(OCH3)2 membrane reaches as high as 1567.8. This work provides a gateway to the understanding of ion transport mechanism and development of high-precision ion separation membranes.

Advancing Ion Selective Membranes with Micropore Ion Channels in the Interaction Confinement Regime

Ion exchange membranes allowing the passage of charge-carrying ions have established their critical role in water, environmental, and energy-relevant applications. The design strategies for high-performance ion exchange membranes have evolved beyond creating microphase-separated membrane morphologies, which include advanced ion exchange membranes to ion-selective membranes. The properties and functions of ion-selective membranes have been repeatedly updated by the emergence of materials with subnanometer-sized pores and the understanding of ion movement under confined micropore ion channels. These research progresses have motivated researchers to consider even greater aims in the field, i.e., replicating the functions of ion channels in living cells with exotic materials or at least targeting fast and ion-specific transmembrane conduction. To help realize such goals, we briefly outline and comment on the fundamentals of rationally designing membrane pore channels for ultrafast and specific ion conduction, pore architecture/chemistry, and membrane materials. Challenges are discussed, and perspectives and outlooks are given.

Porous organic framework membranes based on interface-induced polymerisation: design, synthesis and applications

Porous organic frameworks (POFs) are novel porous materials that have attracted much attention due to their extraordinary properties, such as high specific surface area, tunable pore size, high stability and ease of functionalisation. However, conventional synthesised POFs are mostly large-sized particles or insoluble powders, which are difficult to recycle and have low mass transfer efficiencies, limiting the development of their cutting-edge applications. Therefore, processing POF materials into membrane structures is of great significance. In recent years, interface engineering strategies have proved to be efficient methods for the formation of POF membranes. In this perspective, recent advances in the use of interfaces to prepare POF membranes are reviewed. The challenges of this strategy and the potential applications of the formed POF membranes are discussed.

Tuning Pore Size in Graphene in the Angstrom Regime for Highly Selective Ion-Ion Separation

Zero-dimensional pores spanning only a few angstroms in size in two-dimensional materials such as graphene are some of the most promising systems for designing ion-ion selective membranes. However, the key challenge in the field is that so far a crack-free macroscopic graphene membrane for ion-ion separation has not been realized. Further, methods to tune the pores in the Å-regime to achieve a large ion-ion selectivity from the graphene pore have not been realized. Herein, we report an Å-scale pore size tuning tool for single layer graphene, which incorporates a high density of ion-ion selective pores between 3.5 and 8.5 Å while minimizing the nonselective pores above 10 Å. These pores impose a strong confinement for ions, which results in extremely high selectivity from centimeter-scale porous graphene between monovalent and bivalent ions and near complete blockage of ions with the hydration diameter, DH, greater than 9.0 Å. The ion diffusion study reveals the presence of an energy barrier corresponding to partial dehydration of ions with the barrier increasing with DH. We observe a reversal of K+/Li+ selectivity at elevated temperature and attribute this to the relative size of the dehydrated ions. These results underscore the promise of porous two-dimensional materials for solute-solute separation when Å-scale pores can be incorporated in a precise manner.

Ultra-fast supercritically solvothermal polymerization for large single-crystalline covalent organic frameworks

Crystalline polymer materials, e.g., hyper-crosslinked polystyrene, conjugate microporous polymers and covalent organic frameworks, are used as catalyst carriers, organic electronic devices and molecular sieves. Their properties and applications are highly dependent on their crystallinity. An efficient polymerization strategy for the rapid preparation of highly or single-crystalline materials is beneficial not only to structure-property studies but also to practical applications. However, polymerization usually leads to the formation of amorphous or poorly crystalline products with small grain sizes. It has been a challenging task to efficiently and precisely assemble organic molecules into a single crystal through polymerization. To address this issue, we developed a supercritically solvothermal method that uses supercritical carbon dioxide (sc-CO2) as the reaction medium for polymerization. Sc-CO2 accelerates crystal growth due to its high diffusivity and low viscosity compared with traditional organic solvents. Six covalent organic frameworks with different topologies, linkages and crystal structures are synthesized by this method. The as-synthesized products feature polarized photoluminescence and second-harmonic generation, indicating their high-quality single-crystal nature. This method holds advantages such as rapid growth rate, high productivity, easy accessibility, industrial compatibility and environmental friendliness. In this protocol, we provide a step-by-step procedure including preparation of monomer dispersion, polymerization in sc-CO2, purification and characterization of the single crystals. By following this protocol, it takes 1-5 min to grow sub-mm-sized single crystals by polymerization. The procedure takes ~4 h from preparation of monomer dispersion and polymerization in sc-CO2 to purification and drying of the product.

Polysulfonated covalent organic framework as active electrode host for mobile cation guests in electrochemical soft actuator

Tailoring transfer dynamics of mobile cations across solid-state electrolyte-electrode interfaces is crucial for high-performance electrochemical soft actuators. In general, actuation performance is directly proportional to the affinity of cations and anions in the electrolyte for the opposite electrode surfaces under an applied field. Herein, to maximize electrochemical actuation, we report an electronically conjugated polysulfonated covalent organic framework (pS-COF) used as a common electrolyte-electrode host for 1-ethyl-3-methylimidazolium cation embedded into a Nafion membrane. The pS-COF-based electrochemical actuator exhibits remarkable bending deflection at near-zero voltage (~0.01 V) and previously unattainable blocking force, which is 34 times higher than its own weight. The ultrafast step response shows a very short rising time of 1.59 seconds without back-relaxation, and substantial ultralow-voltage actuation at higher frequencies up to 5.0 hertz demonstrates good application prospects of common electrolyte-electrode hosts. A soft fluidic switch is constructed using the proposed soft actuator as a potential engineering application.

Function-Led Design of Covalent-Organic-Framework Membranes for Precise Ion Separation

Insufficient access to clean water and resources has emerged as one of the most pressing issues affecting people globally. Membrane-based ion separation has become a focal point of research for the generation of fresh water and the extraction of energy elements. This Review encapsulates recent advancements in the selective ion transport of covalent organic framework (COF) membranes, accomplished by strategically pairing diverse monomers to create membranes with various pore sizes and environments for specific purposes. We first discuss the merits of using COF materials as a basis for fabricating membranes for ion separation. We then explore the development of COF membranes in areas such as desalination, acid recovery, and energy element extraction, with a particular emphasis on the fundamental principles of membrane design. Lastly, we address both theoretical and practical challenges, as well as potential opportunities in the targeted design of ion-selective membranes. The goal of this Review is to stimulate future investigative efforts in this field, which is of significant scientific and strategic importance.

Continuous Covalent Organic Frameworks Membranes: From Preparation Strategies to Applications

Covalent organic frameworks (COFs) are porous crystalline polymeric materials formed by the covalent bonding of organic units. The abundant organic units library gives the COFs species diversity, easily tuned pore channels, and pore sizes. In addition, the periodic arrangement of organic units endows COFs regular and highly connected pore channels, which has led to the rapid development of COFs in membrane separations. Continuous defect-free and high crystallinity of COF membranes is the key to their application in separations, which is the most important issue to be addressed in the research. This review article describes the linkage types of covalent bonds, synthesis methods, and pore size regulation strategies of COFs materials. Further, the preparation strategies of continuous COFs membranes are highlighted, including layer-by-layer (LBL) stacking, in situ growth, interfacial polymerization (IP), and solvent casting. The applications in separation fields of continuous COFs membranes are also discussed, including gas separation, water treatment, organic solvent nanofiltration, ion conduction, and energy battery membranes. Finally, the research results are summarized and the future prospect for the development of COFs membranes are outlined. More attention may be paid to the large-scale preparation of COFs membranes and the development of conductive COFs membranes in future research.