Manipulation of Cationic Group Density in Covalent Organic Framework Membranes for Efficient Anion Transport

Potassium-Selective Covalent Organic Framework Membranes Enable Dynamic Monitoring of Microbial K+ Metabolism

Ultraselective and rapid transport of potassium ion (K+) is crucial for maintaining life activities such as osmotic pressure equilibrium, protein synthesis regulation, microbial growth, and communication. However, it is challenging to achieve high efficiency and precise K+ transport due to the existence of competitive cations with similar size and valence. Here, a biomimetic K+ nanochannel based on sulfonated covalent organic frameworks (COF) is reported with high K+ screening selectivity to achieve dynamic microbial K+ metabolism monitoring. Similar to the structure and function of biological KcsA channels, sulfonated COF feature ordered nanochannels and abundant surface charges, facilitating effective sieving of K+ and sodium ions (Na+) through size screening and electrostatic interactions, achieving a K+/Na+ selectivity ratio of 17.3. Molecular dynamic simulations indicate that the K+/Na+ selectivity of the COF nanochannels arises from the interaction of K+ with the sulfonate functional groups on the nanochannels, resulting in a decreased energy barrier for K+. Given the excellent K+ screening selectivity and efficiency, the designed COF nanochannels enable real-time monitoring of K+ in complex microbial systems and provide guidance for the synthesis of high value-added products. These findings suggest approaches for developing efficient and selective nanochannels for ion separation, nanofluidic, and complex microbial metabolism systems.

Facilitating efficient catalytic conversion of polysulfides in lithium-sulfur batteries via self-assembled hydrogen-bond-rich covalent organic frameworks

The widespread commercialization of lithium-sulfur (Li-S) batteries is hindered by two critical challenges: sluggish redox kinetics and the detrimental polysulfide shuttle effect. In this study, we present a novel approach utilizing hydrogen-bond-rich covalent organic frameworks (TTP@PVDF50), synthesized through an in situ self-assembly process incorporating polymeric guest species. These covalent organic frameworks (COFs), when integrated into the separators of Li-S batteries, preserve their intrinsic porosity and crystallinity, while the abundant fluorine-rich sites and well-defined pore structures enhance lithium-ion (Li+) transport kinetics. The hydrogen-bond-rich nature of the COFs provides an effective strategy to mitigate the polysulfide shuttle, leveraging both spatial hindrance and strong polar interactions for enhanced adsorption. Density functional theory (DFT) calculations and in situ Raman spectroscopy reveal that the F∙∙∙OH hydrogen bonding network in the TTP@PVDF50 composite significantly accelerates Li+ migration and catalyzes the conversion of LiPSs. The modified separator demonstrates a high discharge capacity of 1420.2 mAh g-1 at 0.2 C (1 C=1675 mAh g-1), alongside remarkable anti-self-discharge performance with only 9.0% capacity loss. Notably, the Li-S battery with a high sulfur loading (4.59 mg cm-2) and a lean electrolyte (6 µL mg-1) retains over 83% of its capacity, underscoring the effectiveness of this strategy in advancing the performance and longevity of Li-S batteries.

Hydrogen Bond Network Assisted Ultrafast Ion Transport of Anion Exchange Membrane Grafting with Covalent Organic Frameworks for Hydrogen Conversion

The development of anion exchange membranes (AEMs) capable of facilitating rapid hydroxide ion transport, while maintaining robust mechanical stability, is considered a key direction for advancing hydrogen energy conversion systems. Herein, we synthesized a series of AEMs by grafting covalent organic frameworks (COFs) onto triphenylpiperidine copolymer and systematically evaluated the performance of AEMs. The tailored COFs, characterized by an extensive hydrogen bond network and high micro-porosity, created interconnected high-speed ion transport channels, significantly reducing the resistance to hydroxide ion conduction. Remarkably, the COF-grafted membranes exhibited superior ionic conductivity compared to pristine triphenylpiperidine, even at lower ion exchange capacities. Additionally, the crystalline and highly rigid structure of the grafted COFs effectively preserved the mechanical stability of the membranes. The optimized COF-grafted AEMs demonstrated outstanding performance, achieving a peak power density of 1.54 W cm-2 in H2-O2 fuel cells and exceptional current densities of 4.5 A cm-2 at 2.0 V in 1 m KOH and 1.1 A cm-2 at 2.0 V in pure water at 80 °C. The present work provides an effective strategy for enhancing AEM performance through the grafting of COFs.

Amphoteric Metal Ion-Coordinated Chitosan Membranes for Efficient Hydroxide Ion Transport

Hydroxide exchange membranes (HEMs) have attracted extensive attention in energy-related fields, such as fuel cells and water electrolysis, primarily due to their suitability for alkaline environments. However, the practical application of membranes is hindered significantly by their limited conductivity. In this study, a series of amphoteric metal ion-coordinated chitosan (CTS-AM) membranes with enhanced hydroxide ion conductivity are reported. The CTS-AM membranes are prepared using a simple soaking-drying method, exhibiting excellent mechanical strength and thermal stability due to the strong coordination bonds between amphoteric metal ions and chitosan chains. To the best of our knowledge, the Zn2+ coordinated chitosan membrane achieved the highest-ever reported hydroxide ion conductivity of 82.0 ± 5.4 mS cm-1 at 25 °C and 100% RH, with the value increasing to 301.0 ± 6.7 mS cm-1 at operating temperature (80 °C) and 100% RH. Through combined structural analysis and theoretical calculations, we propose that the formation of nanochannels and the lowered barrier for electron transfer are responsible for the high hydroxide ion conductivities of CTS-AM membranes. This study presents a viable approach to the design and fabrication of high-performance HEMs for energy storage devices and other applications.

Engineering Bipolar Covalent Organic Framework Membranes for Selective Acid Extraction

Nitric acid (HNO3) is a vital industrial chemical, and its recovery from complex waste streams is essential for sustainability and resource optimization. This study demonstrates the effectiveness of bipolar covalent organic framework (COF) membranes with tunable ionic site distributions as a solution for this challenge. The membranes are fabricated by layering anionic COF nanosheets on cationic COF layers, supported by a porous substrate. The resulting membranes exhibit significant rectifying behavior, driven by the asymmetric charge polarity and the intrinsic electric field, which enhances HNO3 transport. The transmembrane diffusion coefficient of 2.74 × 10-5 cm2 s-1 exceeds the self-diffusion rate of NO3 -, leading to increased HNO3 flux and selectivity compared to the individual anionic and cationic COF membranes. The optimized bipolar membrane configuration achieves remarkable separation factors, ranging from 22 to 242,000 for HNO₃, in comparison to other solutes such as HCl, H2SO4, H3PO4, and various metal salts in an eight-component mixed waste stream. This results in a substantial increase in HNO₃ purity, from 12.5% to 94.1% after a single membrane separation. With the broad range of COF materials and the versatility of the proposed membrane design, this work represents a significant advancement in chemical separation technologies.

Bioinspired Chloride-Assisted Protein Channels: Enhancing Proton Transport for Sustainable Energy Harvesting from Acidic Wastewater

Highly efficient proton transfer in biological processes has driven the pursuit of synthetic analogs; however, replicating high proton permeance in natural systems remains a significant challenge. Herein, inspired by the function of the ClC-ec1 protein, we report the design of Cl--assisted proton transport channels within a hybrid membrane composed of covalent organic frameworks (COFs) integrated with aramid nanofibers (ANFs). By leveraging buffer layer-mediated interfacial polymerization and the flocculation behavior of ANF in aqueous environments, we establish robust hydrogen-bonding interactions between COFs and ANFs. The hydride material enables Cl- binding, significantly accelerating proton transport in a manner similar to that of the ClC-ec1 protein channel. In the presence of a small concentration of Cl- ions (0.1% of the proton concentration), the proton permeation rate is enhanced approximately by 3 times, reaching 9.8 mol m-2 h-2. Notably, the membrane facilitates sustainable osmotic power generation from acidic wastewater, delivering an output power density of 434.8 W m-2. Theoretical calculations revealed that ANF preferentially binds Cl-, promoting proton hopping and lowering the energy barrier for proton transport. This study establishes a new paradigm for bioinspired ion-assisted proton transport, presenting an approach for sustainable energy harvesting from acidic wastewater.

Effects of Hydration Level and Hydrogen Bonds on Hydroxide Transport Mechanisms in Anion Exchange Membranes

The transport of hydroxide in anion exchange membranes (AEMs) is generally determined by multiple factors, including hydration levels, pore morphologies, and the hydration shells of cationic groups and hydroxides. Thus, clarifying the working mechanisms benefits the proposal of strategies for enhancing the hydroxide transport, thereby enabling a rational design of high-performance AEMs. Herein, by using ReaxFF molecular dynamics (MD) simulations and RDAnalyzer, this study explores the straightforward but effective correlations for steric hindrance versus hydration shell, hydration level versus free/associated diffusion, and strong (short) hydrogen bond (SHB) versus vehicular/Grotthuss diffusion. The theoretical investigations indicate that higher steric hindrance of cationic groups results in less water in the first hydration shell of cationic groups in AEMs. Meanwhile, a higher hydration level facilitates wider hydrophilic pores of AEMs and increases the ratio of the free diffusion mechanism of hydroxides. Interestingly, this study finds a strong correlation between the number of SHBs and the Grotthuss diffusion, thereby enhancing the understanding of the high conductivity of covalent organic framework (COF)-based AEMs that contain obvious SHBs. This work provides a theoretical view for fine-tuning the free/associated and vehicular/Grotthuss transport of hydroxide in AEMs.

Crystalline, Porous Figure-Eight-Noded Covalent Organic Frameworks

Figure-eight macrocycles represent a fascinating class of π-conjugated units characterized by unique aesthetics and non-contact molecular crossing at the center. Despite progress in synthesis over the past century, research into inorganic, organic, and polymeric figure-eight materials remains in its infancy. Here we report the first examples of figure-eight covalent organic frameworks by condensing figure-eight knots to create extended porous figure-eight π architectures. A distinct feature is that polymerization interweaves figure-eight knots into double-decker layers, which upon supramolecular polymerization organize well-defined layer frameworks. The figure-eight frameworks exhibit a band gap of 2.3 eV and emit bright orange florescence with benchmark quantum yields. Remarkably, the donor-acceptor figure-eight skeletons convert the figure-eight knots into reduction centers and the linkers into oxidation sites upon light irradiation, enable charge transport and accumulation through π columns, while the built-in hydrophilic micropores allow rapid water and oxygen delivery via capillary effect. With these distinct features, the figure-eight frameworks function as a photocatalyst to produce hydrogen peroxide at high rate and efficiency with water/saltwater, oxygen/air, and light as sole inputs. This work paves a way to a new class of molecular frameworks, underpinning the study of well-defined figure-eight materials to explore unprecedented structures and functions so far we untouched.

Noncovalent Complex Modulated Fabrication of COF Membrane for Organic Solvent Nanofiltration

Covalent organic framework (COF) has been recognized as a disruptive material for fabricating organic molecular sieve membranes. Acquiring crystalline and defect-free COF membranes directly on polymeric substrates is important for practical applications yet is highly challenging. In this study, a noncovalent complex (NCX) modulated fabrication of COF membrane on hydrolyzed polyacrylonitrile (HPAN) substrate via counter diffusion is proposed. The triaminoguanidine chloride-phytic acid noncovalent complex (Tg-PA NCX) is uniformly introduced onto the HPAN substrate, transferring the substrate into an ideal seeding layer and catalytic platform for COF nucleation and growth. Enhanced Tg monomer concentration derived from NCX enhance its concentration near the surface is observed, facilitating the heterogeneous nucleation for COF fabrication. In addition, the PA in the NCX acted as a catalyst, promoting the growth of the highly crystalline COF membrane afterward. The resulting TgTb/NCX/HPAN membrane shows a defect-free surface with high crystallinity. Also, it displays over 90% rejection to various dyes rejection rates (e.g., Evans blue, Methyl blue, Congo red, and Amido Black) and high solvent permeation for organic solvents (e.g., ethanol: 57.9 ± 2.1 L m-2h-1 bar-1, n-hexane: 215.0 ± 2.7 L m-2h-1 bar-1). This work holds great potential as a platform technology for fabricating high-performance organic molecular sieve membranes.

Regulation of Ion Binding Sites in Covalent Organic Framework Membranes for Enhanced Selectivity under High Ionic Competition

The strategic spatial positioning of ion affinity sites within biological ion channels and their cooperative binding with the targeted ions are pivotal for enhancing ion recognition and ensuring exceptional selectivity in high ionic competition scenarios. However, the application of these principles to artificial ion channels remains largely unexplored. Herein, we present a series of covalent organic framework (COF) membranes, engineered with oxygen functional groups aligned along the rims of oriented COF pore channels of varying sizes to achieve a precise spatial arrangement of ion affinity sites. A notable COF membrane, featuring subnanometer pores decorated alternately with carbonyl and amide groups, demonstrated outstanding selectivity, achieving a Li/Mg selectivity ratio of 513 under equal mole and electrodialysis conditions. Impressively, as the Mg/Li ratio in the source solution increased to 16.6, the selectivity ratio rose to 833, significantly exceeding the reductions typically seen in conventional selective electrodialysis and nanofiltration methods. Both simulation and experimental analyses indicate that this exceptional selectivity stems from the cooperative binding between the oxygen functional groups and Li+ ions within the confined nanochannels, facilitating the preferential transport of Li+ ions. These findings provide a promising approach for designing selective ion extraction systems that function effectively in highly competitive environments.

Advanced Anion Exchange Membranes: Structural Insights and Property Optimization

With the increasing demand for clean energy, driven by advancements in science and technology, anion exchange membrane fuel cells (AEMFCs) have emerged as a promising solution for efficient and clean energy conversion. As the core component of AEMFCs, anion exchange membranes (AEMs) are crucial for ion transport and the separation of the cathode and anode. The performance of AEMs primarily depends on two key factors: ionic conductivity and stability, which often require a delicate balance. The ion conduction process is closely linked to the membrane's microscopic structure. This concept article reviews the development of various AEM types, including homogeneous polymer membranes, hybrid membranes, and nanoporous framework membranes, with a focus on their structural characteristics. Additionally, it explores the design and optimization of AEMs in relation to key properties such as ionic conductivity, dimensional stability, and alkali resistance, providing a reference for future innovations in ion-exchange membranes for AEMFCs.

A Smart Polycage Membrane with Responsive Osmotic Energy Conversion Based on Synchronously Switchable Microporosity and Chargeability

Membranes with specific pore sizes are widely used in molecular separation, ion transport, and energy conversion. However, the molecular understanding of structure-property performance in membrane science has been an urgent and long-standing problem. A promising but challenging solution lies in the fine-tuning of the membrane microstructure and properties to control membrane performance. Here, we designed an exofunctionalized triskelion cage to construct smart polycage membranes with concurrently responsive pore apertures and charge property. The synthetic polyaza cage is decorated with exoextended aldehyde groups for membrane fabrication and multiple amine sites for postmodification. The engineered polycage membranes thereby are endowed with pH-responsive porosity and chargeability, which serve as excellent candidates to explore the influence of the pore size and charge properties on membrane performance. In this regard, we successfully demonstrated the responsive osmotic energy conversion of the polycage membrane with a power density increase of over fourfold. This result indicates that the chargeability here outcompetes microporosity in energy conversion performance, which is further supported by molecular simulations. Therefore, this smart polycage membrane not only offers a feasible strategy to regulate the membrane microstructure and charge property reversibly but also balances pore size and chargeability to control the membrane performance at the molecular level.

Synthesis of Carboxyl-Functionalized COFs with Alternate Stable β-Ketoenamine and Benzimidazole Linkages: Unraveling Exceptional Solvent Effects for Efficient Uranium Separation

The prevalent π-π interactions in 2D covalent organic frameworks (COFs) impart a certain flexibility to the structures, making the stacking of COF layers susceptible to external stimuli and introducing some structural disorder. Recent research indicates that the flexibility between COF layers and the associated disorder significantly influence their selective adsorption performance toward gas molecules. However, the adsorption process in a solution environment is more complex compared to gas-phase adsorption, involving interactions between adsorbents and adsorbates, as well as the solvation effects of flexible 2D COFs. Therefore, the inherent flexibility and disorder in 2D COFs under solution conditions and their impact on the adsorption performance of metal ions have not been observed yet. Herein, the synthesis of a novel carboxyl-functionalized COF featuring stable β-ketoenamine and benzimidazole linkages, named DMTP-COOH, is presented. DMTP-COOH exhibits excellent selective adsorption capability for uranium, with significantly different adsorption capacities observed after treatment with different solvents. This notable difference in adsorption capacity is observed under varying pH, concentration, time, and even in the presence of multiple competing ions. This work represents the first observation of the significant impact of solvent soaking treatment on the selective adsorption performance of COFs for uranium under liquid conditions.

Recyclable covalent organic frameworks/cellulose aerogels for efficient uranium adsorption

The advancement of efficient, recyclable adsorbents for the economical capture of uranium from seawater is critical for the sustainable progression of nuclear energy. In this work, a unique aerogel composed of covalent organic frameworks (COF-TpTHA)/cellulose nanofibrils (CNF) was synthesized under mild conditions for uranium adsorption. TpTHA/CNF aerogel resolves challenges related to the formability of COF. CNF utilized as the matrix to encapsulate COF-TpTHA in order to improve the dispersion and reinforce the composite materials. The introduction of COF-TpTHA endows CNF aerogel with sufficient active groups for uranium adsorption. X-ray diffraction (XRD) characterization confirmed the successful incorporation of COF while maintaining the type I structure of cellulose. Fourier-transform infrared (FT-IR) spectroscopy further validated the presence of hydrogen bonding interactions between COF and cellulose. The results demonstrated the excellent adsorption efficiency of TpTHA/CNF aerogel towards U(VI), with a maximum adsorption capacity of 177.90 mg g-1 (experiment) for U(VI). Meanwhile, TpTHA/CNF aerogel exhibited favorable adsorption selectivity and reusability. This cellulose-encapsulated COF approach offers a simple and promising method for uranium extraction from seawater, demonstrating its significant application potential.

Electrostatic Repulsion Facilitated Ion Transport in Covalent-Organic Framework Membranes

Covalent-organic framework (COF) membranes are increasingly used for many potential applications including ion separation, fuel cells, and ion batteries. It is of central importance to fundamentally and quantitatively understand ion transport in COF membranes. In this study, a series of COF membranes is designed with different densities and arrangements of functional groups and subsequently utilize molecular simulation to provide microscopic insights into ion transport in these membranes. The membrane with a single-sided layer exhibits the highest chloride ion (Cl-) conductivity of 77.2 mS cm-1 at 30 °C. Replacing the single-sided layer with a double-sided layer or changing layer arrangement leads to a decrease in Cl- conductivity up to 33% or 53%, respectively. It is revealed that the electrostatic repulsion between ions serves as a driving force to facilitate ion transport and the positions of functional groups determine the direction of electrostatic repulsion. Furthermore, the ordered pores generate concentrated ions and allow rapid ion transport. This study offers bottom-up inspiration on the design of new COF membranes with moderate density and proper arrangement of functional groups to achieve high ion conductivity.

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.

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.

Ultrafast Interfacial Self-Assembly toward Bioderived Polyester COF Membranes with Microstructure Optimization

The precise manipulation of the microstructure (pore size, free volume distribution, and connectivity of the free-volume elements), thickness, and mechanical characteristics of membranes holds paramount significance in facilitating the effective utilization of self-standing membranes. In this contribution, the synthesis of two innovative ester-linked covalent-organic framework (COF) membranes is first reported, which are generated through the selection of plant-derived ellagic acid and quercetin phenolic monomers in conjunction with terephthaloyl chloride as a building block. The optimization of the microstructure of these two COF membranes is systematically achieved through the application of three different interfacial electric field systems: electric neutrality, positive electricity, and negative electricity. It is observed that the positively charged system facilitates a record increase in the rate of membrane formation, resulting in a denser membrane with a uniform pore size and enhanced flexibility. In addition, a correlation is identified wherein an increase in the alkyl chain length of the surfactants leads to a more uniform pore size and a decrease in the molecular weight cutoff of the COF membrane. The resulting COF membrane exhibits an unprecedented combination of high water permeance, superior sieving capability, robust mechanical strength, chemical robustness for promising membrane-based separation science and technology.

Ionic Covalent Organic Frameworks in Adsorption and Catalysis

The ion extraction and electro/photo catalysis are promising methods to address environmental and energy issues. Covalent organic frameworks (COFs) are a class of promising template to construct absorbents and catalysts because of their stable frameworks, high surface areas, controllable pore environments, and well-defined catalytic sites. Among them, ionic COFs as unique class of crystalline porous materials, with charges in the frameworks or along the pore walls, have shown different properties and resulting performance in these applications with those from charge-neutral COFs. In this review, current research progress based on the ionic COFs for ion extraction and energy conversion, including cationic/anionic materials and electro/photo catalysis is reviewed in terms of the synthesis strategy, modification methods, mechanisms of adsorption and catalysis, as well as applications. Finally, we demonstrated the current challenges and future development of ionic COFs in design strategies and applications.

Ultrathin Free-Standing Porous Aromatic Framework Membranes for Efficient Anion Transport

Porous aromatic frameworks (PAFs) show promising potential in anionic conduction due to their high stability and customizable functionality. However, the insolubility of most PAFs presents a significant challenge in their processing into membranes and subsequent applications. In this study, continuous PAF membranes with adjustable thickness were successfully created using liquid-solid interfacial polymerization. The rigid backbone and the stable C-C coupling endow PAF membrane with superior chemical and dimensional stabilities over most conventional polymer membranes. Different quaternary ammonium functionalities were anchored to the backbone through flexible alkyl chains with tunable length. The optimal PAF membrane exhibited an OH- conductivity of 356.6 mS ⋅ cm-1 at 80 °C and 98 % relative humidity. Additionally, the PAF membrane exhibited outstanding alkaline stability, retaining 95 % of its OH- conductivity after 1000 hours in 1 M NaOH. To the best of our knowledge, this is the first application of PAF materials in anion exchange membranes, achieving the highest OH- conductivity and exceptional chemical/dimensional stability. This work provides the possibility for the potential of PAF materials in anionic conductive membranes.

Viologen-based solution-processable ionic porous polymers for electrochromic applications

Electrochromic porous thin films are promising for applications in smart windows and energy-efficient optical displays. However, their generally poor processing ability and excessive processing times remain grand challenges. Herein, we report the design and convenient synthesis of core-altered N-arylated viologens with aldehyde groups (πV-CHO) as new building blocks to prepare soluble, viologen-embedded ionic porous polymers. We also demonstrate that these polymers can be easily solution-processed by drop-coating to fabricate high-quality electrochromic films with tunable optoelectronic properties in a cost-effective fashion. The prepared films exhibit excellent electrochromic performance, including a low driving voltage (1.2-1.4 V), fast switching times (0.8-1.7 s), great coloration efficiency (73-268 cm2 C-1), remarkably high optical contrast up to 95.6%, long cycling stability, and tunable oxidation and reduction colors. This work sheds important light on a new molecular engineering approach to produce redox-active polymers with combined properties of intrinsic porosity, reversible and tunable redox activity, and solution processability. This provides the materials with an inherently broad utility in a variety of electrochemical devices for energy storage, sensors, and electronic applications.

Construction of Layer-Blocked Covalent Organic Framework Heterogenous Films via Surface-Initiated Polycondensations with Strongly Enhanced Photocatalytic Properties

Imine-linked covalent organic frameworks (COFs) usually show high crystallinity and porosity, while vinyl-linked COFs have excellent semiconducting properties and stability. Therefore, achieving the advantages of imine- and vinyl-linkages in a single COF material is highly interesting but remains challenging. Herein, we demonstrate the fabrication of a layer-blocked COF (LB-COF) heterogeneous film that is composed of imine- and vinyl-linkages through two successive surface-initiated polycondensations. In brief, the bottom layer of imine-linked COF film was constructed on an amino-functionalized substrate via Schiff-base polycondensation, in which the unreacted aldehyde edges could be utilized for initiating aldol polycondensation to prepare the second layer of vinyl-linked COF film. The resultant LB-COF film displays excellent ordering due to the crystalline templating effect from the bottom imine-linked COF layer; meanwhile, the upper vinyl-linked COF layer could strongly enhance its stability and photocatalytic properties. The LB COF also presents superior performance in photocatalytic uranium extraction (320 mg g-1), which is higher than the imine-linked (35 mg g-1) and the vinyl-linked (295 mg g-1) counterpart. This study provides a novel surface-initiated strategy to synthesize layer-blocked COF heterogeneous films that combine the advantages of each building block.

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.