Layered Covalent Organic Frameworks Research Articles

Preserving High Porosity of Covalent Organic Frameworks via Functional Polymer Guest Introduction.

Due to their high structural tunability, remarkable internal surface areas, readily accessible pore space, and host of possible applications, covalent organic frameworks (COFs) remain at the forefront of materials science research. Unfortunately, many COFs suffer from structural distortions or pore collapse during activation, which can lead to a substantial loss of crystallinity and functionality. Thus, herein, we demonstrate a facile method to address this issue by introducing polymer guests. The polymer adheres to the COF internal pore wall, acting as a supporting pillar during activation and effectively preserving the COF porosity and crystallinity. In fact, the surface area of one COF/polymer composite, known as TAPB-TA/PDA, was boosted by a factor of 16 when compared to the parent COF, TAPB-TA. More importantly, the now robust COF structure was able to resist layer shifting and order loss during both solvent immersion and removal. The introduction of functional polymer guests not only solidifies the COF structure and preserves its high porosity but is also shown to enhance the transport and separation of photogenerated charge carriers, thereby facilitating hydrogen evolution during photocatalytic water splitting. Molecular dynamics simulations further support experimental observations that the incorporation of PDA within the COF pores reinforces the walls, preventing its collapse. The proposed mechanism is based on the adsorption of PDA oligomers along the c direction of the unit cell, fastening the COF layers in place via van der Waals interactions. This kind of interaction locks -N═CH-Ph-CH═N- units in a trans-configuration in the COF pores.

Covalent organic framework membranes with vertically aligned nanorods for efficient separation of rare metal ions

Covalent organic frameworks (COFs) have emerged as promising platforms for membrane separations, while remaining challenging for separating ions in a fast and selective way. Here, we propose a concept of COF membranes with vertically aligned nanorods for efficient separation of rare metal ions. A quaternary ammonium-functionalized monomer is rationally designed to synthesize COF layers on porous substrates via interfacial synthesis. The COF layers possess an asymmetric structure, in which the upper part displays vertically aligned nanorods, while the lower part exhibits an ultrathin dense layer. The vertically aligned nanorods enlarge contact areas to harvest water and monovalent ions, and the ultrathin dense layer enables both high permeability and selectivity. The resulting membranes exhibit exceptional separation performances, for instance, a Cs+ permeation rate of 0.33 mol m−2 h−1, close to the value in porous substrates, and selectivities with Cs+/La3+ up to 75.9 and 69.8 in single and binary systems, highlighting the great potentials in the separation of rare metal ions.

Ultrafine Spatial Modulation of Diazapyrene-Based Two-Dimensional Conjugated Covalent Organic Frameworks.

Tailormade bottom-up synthesis of covalent organic frameworks (COFs) from various functional building blocks offer not only tunable topology and pore size but also multidimensional properties. High crystallinity is one of the prerequisites for their structures and associated physicochemical properties. Among different π-conjugated motifs for constructing COFs, pyrene-based tetragonal structures are effective in achieving highly ordered and crystalline states. In the present research, we demonstrated that the substitution of pyrene with 2,7-diazapyrene produces nearly "flat" structures of two-dimensional (2D) COF layers by controlling the torsional angle of linker molecules. Featuring finite pore diameters and excellent thermodynamic stability of ∼500 °C, ordered face-to-face (slipped AA) stacking arrangements were produced. Extended electrical conjugation spanning 2D frames with modest optical bandgaps (Eg) of ∼2.1 eV shows the planar character of diazapyrene-based COFs. The stacking of the conjugated 2D frames with small Eg values is also beneficial for the formation of highly stable conducting pathways in the crystalline state, which was confirmed by the results of the microwave conductivity measurements. Nitrogen centers in diazapyrene units also play a key role as the active sites for proton transfer, and the maximum proton conductivity of σ = 10-2 S cm-1 was achieved along the cocontinuous nanopore structures surrounded by the active sites. Results show that tetragonal COFs based on diazapyrene can be used as a highly crystalline two-dimensional material with special electrical and proton-conducting capabilities.

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.

Synthetic Strategies to Extended Aromatic Covalent Organic Frameworks.

π-Conjugated materials are highly attractive owing to their unique optical and electronic properties. Covalent organic frameworks (COFs) offer a great opportunity for precise arrangement of building units in a π-conjugated crystalline matrix and tuning of the properties through choice of functionalities or post-synthetic modification. With this review, we aim at summarizing both the most representative as well as emerging strategies for the synthesis of π-conjugated COFs. We give examples of direct synthesis using large, π-extended building blocks. COFs featuring fully conjugated linkages such as vinylene, pyrazine, and azole are discussed. Then, post-synthetic modification methods that result in the extension of the COF π-system are reviewed. Throughout, mechanistic insights are presented when available. In the context of their utilization as film devices, we conduct a concise survey of the prominent COF layer deposition techniques reported and their aptness for the deposition of fused aromatic systems.

Atomically Precise Regulation of the N-Heterocyclic Microenvironment in Triazine Covalent Organic Frameworks for Coenzyme Photocatalytic Regeneration.

Artificial photosynthesis represents a sustainable strategy for accessing high-value chemicals; however, the conversion efficiency is significantly limited by its difficulty in the cycle of coenzymes such as NADH. In this study, we report a series of isostructural triazine covalent organic frameworks (COFs) and explore their N-substituted microenvironment-dependent photocatalytic activity for NADH regeneration. We discovered that the rational alteration of N-heterocyclic species, which are linked to the triazine center through an imine linkage, can significantly regulate both the electron band structure and planarity of a COF layer. This results in different separation efficiencies of the photoinduced electron-hole pairs and electron transfer behavior within and between individual layers. The optimal COF catalyst herein achieves an NADH regeneration capacity of 89% within 20 min, outperforming most of the reported nanomaterial photocatalysts. Based on this, an artificial photosynthesis system is constructed for the green synthesis of a high-value compound, L-glutamate, and its conversion efficiency significantly surpasses the enzymatic approach without the NADH photocatalytic cycle. This work offers new insights into the coenzyme regeneration by means of regulating the distal heterocyclic microenvironment of a COF skeleton, holding great potential for the green photosynthesis of important chemicals.

Hierarchical Assembly of 2D Covalent Organic Frameworks into Janus Optical Devices

AbstractAssembly of 2D molecules into hierarchical structures opens new avenues for creating multifunctional materials, yet fabricating the optical materials with multiscale structural features, and extending functions in a controllable way remains a challenge. Here, an asynchronous liquid depositing strategy is introduced that enables the asymmetrical growth of 2D covalent organic frameworks (COFs) on a graphene substrate. This results in Janus composite (JC) materials with independently controlled mesoscopic features, such as the COF layer thickness (100–300 nm), and its nanoflake length (0–200 nm), and thickness (0–30 nm). The JCs exhibit impressive light coupling capabilities and display a wide range of angle‐independent structural colors. These colors can be dynamically and reversibly changed in 10 ms when exposed to volatile organic compounds (VOCs). They also demonstrate remarkable tailorability to form both random and ordered patterns which shows excellent information processing potential. These unique properties make JCs highly suitable as novel responsive optical devices for collecting and processing information about their surroundings, as demonstrated by visual and real‐time VOC monitoring and localization in both open and confined spaces. It is believed that the controlled assembly of 2D components into composites with well‐organized hierarchical structures will facilitate the future development of extraordinary materials with extensive applications.

Probing Self-Diffusion of Guest Molecules in a Covalent Organic Framework: Simulation and Experiment.

Covalent organic frameworks (COFs) are a class of porous materials whose sorption properties have so far been studied primarily by physisorption. Quantifying the self-diffusion of guest molecules inside their nanometer-sized pores allows for a better understanding of confinement effects or transport limitations and is thus essential for various applications ranging from molecular separation to catalysis. Using a combination of pulsed field gradient nuclear magnetic resonance measurements and molecular dynamics simulations, we have studied the self-diffusion of acetonitrile and chloroform in the 1D pore channels of two imine-linked COFs (PI-3-COF) with different levels of crystallinity and porosity. The higher crystallinity and porosity sample exhibited anisotropic diffusion for MeCN parallel to the pore direction, with a diffusion coefficient of Dpar = 6.1(3) × 10-10 m2 s-1 at 300 K, indicating 1D transport and a 7.4-fold reduction in self-diffusion compared to the bulk liquid. This finding aligns with molecular dynamics simulations predicting 5.4-fold reduction, assuming an offset-stacked COF layer arrangement. In the low-porosity sample, more frequent diffusion barriers result in isotropic, yet significantly reduced diffusivities (DB = 1.4(1) × 10-11 m2 s-1). Diffusion coefficients for chloroform at 300 K in the pores of the high- (Dpar = 1.1(2) × 10-10 m2 s-1) and low-porosity (DB = 4.5(1) × 10-12 m2 s-1) samples reproduce these trends. Our multimodal study thus highlights the significant influence of real structure effects such as stacking faults and grain boundaries on the long-range diffusivity of molecular guest species while suggesting efficient intracrystalline transport at short diffusion times.

Covalent organic framework membranes modified by end-capping monomers for organic solvent nanofiltration

Covalent organic frameworks (COFs) with excellent solvent stability, high porosity, and well-designed pore size, are competitive candidates for organic solvent nanofiltration (OSN). To manipulate their structures, pre-synthetic and post-synthetic modifications are commonly used. Nevertheless, pre-synthetic modifications may alter the stacking fashion of COF nanosheets; post-synthetic modifications are constrained by limited pre-functionalities and can hardly achieve complete conversion. In contrast, defect engineering is a facile method to modify the structure of COFs through defects generated by the breakage of linkages or the usage of end-capping molecules. In this study, we adopted defect engineering to improve the OSN performance of TpPa-COF membranes constructed of 2,4,6-triformylphloroglucinol (Tp) and p-phenylenediamine (Pa) monomers with end-capping molecules—aniline (An). The membrane synthesized with 30 percent of An molecules (TpPaAn-30/HPAN membrane) maintained a continuous COF layer with a thickness of ∼20 nm but lower density or more free channels, compared to the control membrane. The optimized TpPaAn-30/HPAN membrane had improved permeance for various organic solvents (e.g., 31.8 L m−2 h−1 bar−1 for methanol, fourfold of the control membrane) but maintained rejection towards methyl blue (>90 %). It also allowed the passage of rhodamine B but blocked methyl blue when filtrating a mixed-dye methanolic solution. Herein, the usage of end-capping monomers is proven to be an efficient method to introduce transport channels and improve the separation performance of COF membranes.

Interlayer Polymerization to Construct a Fully Conjugated Covalent Organic Framework as a Metal-Free Oxygen Reduction Reaction Catalyst for Anion Exchange Membrane Fuel Cells.

Two-dimensional (2D) covalent organic frameworks (COFs) have a multilayer skeleton with a periodic π-conjugated molecular array, which can facilitate charge carrier transport within a COF layer. However, the lack of an effective charge carrier transmission pathway between 2D COF layers greatly limits their applications in electrocatalysis. Herein, by employing a side-chain polymerization strategy to form polythiophene along the nanochannels, a conjugated bridge is constructed between the COF layers. The as-synthesized fully conjugated COF (PTh-COF) exhibits high oxygen reduction reaction (ORR) activity with narrowed energy band gaps. Correspondingly, PTh-COF is tested as a metal-free cathode catalyst for anion exchange membrane fuel cells (AEMFCs) which showed a maximum power density of 176mWcm-2 under a current density of 533mAcm-2. The density functional theory (DFT) calculation reveals that interlayer conjugated polythiophene optimizes the electron cloud distribution, which therefore enhances the ORR performance. This work not only provides new insight into the construction of a fully conjugated covalent organic framework but also promotes the development of new metal-free ORR catalysts.

Spatially confined coordination platform in covalent organic framework for selective uranium adsorption from aqueous solutions

The use of covalent organic frameworks (COFs) to remove uranium from nuclear wastewater, especially capture uranium by well-defined nanopores and customizable groups, is highly desired. The development of an ideal binding site with optimal balance between adsorption capacity and selectivity has remained an attractive challenge. Herein, a staggered stacking self-assembly approach was adapted to control the pore size and confine space of dioxin-linked COF-316 with modified functional groups to achieve higher capture efficiency. EXAFS analysis suggested that COF-316-COOH and COF-316-AO both have high affinities toward U(VI) owing to inner-sphere surface complexation by two or three atoms, DFT calculations further revealed that the uranyl cation was coordinated by = NOH or –COOH groups from two adjacent COF layers. The synergistic coordination in multi-confined interlaminar position provides an ideal spatial coordination platform for uranium, and the merits of capacity, selectivity and stability underscore the potential application of COF-316-AO for efficient uranium removal.

Decoupling synthesis and crystallization of covalent organic frameworks (COFs) for more crystalline layer targeting high efficiency dye separation

Covalent organic frameworks (COFs) are crystalline porous materials composed of organic building blocks linked by covalent bonds, which have attracted great attention for membrane–based separation applications. However, fabrication of COF membranes with high quality and performance remains a challenge, especially for the β–ketoenamine linked COFs. In the conventional IP methods, the synthesis process (the Schiff–base reaction of the monomers and the tautomerism of the oligomers) and the crystallization process (the self–assembly of the oligomers) of the COFs materials occur simultaneously on the surface of the support membrane, which can result in low crystallinity, high defect density, and poor separation performance of the COF layer. In this study, a novel strategy for fabricating large-area, defect–free COFs composite membranes by interfacial polymerization (IP) was presented to overcome this problem. By incorporating both the amine and aldehyde monomers in one organic phase, and dissolving organic acid catalyst in another phase (the water), the synthesis process mostly take place in the bulk of the organic phase, while the crystallization occurs on the surface of the support membrane under the influence of the organic acid catalyst. This strategy effectively decoupled the synthesis process with the crystallization, providing a stable growth region for crystalline layer, ultimately leading to the formation of a thin, defect–free and highly ordered COF layer on the support membrane. The strategy was demonstrate by synthesis of triformylphloroglucinol phenylenediamine (TpPa)–Ⅱ/Poly(m–phenylene isophthalaminde) (PMIA) composite membrane. We characterize the structure and morphology of the TpPa–Ⅱ/PMIA composite membrane by various analytical techniques to verify our hypothesis, and evaluate its separation performance using pure water permeance and dyes retention rate as indicators. The results show that the TpPa–Ⅱ/PMIA composite membrane has an 80 nm thick top-layer with regular COF structure and orderly pores. It exhibits an excellent dye separation performance, with a (pure water permeance) PWP of 105.6 L·m−2·h−1·bar−1 and CR rejection of 99.2 %, which surpasses most of the TpPa–type COFs composite membranes reported in literature, as well as the reference (TpPa–I/PMIA membrane) in this work. Moreover, the TpPa–Ⅱ/PMIA composite membrane maintains both its performance and structural stability during a 240–hour cross–flow filtration of the dye solution, demonstrating its excellent potential in the dye wastewater treatment.

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.

A novel high temperature resistance thin film composite polyamide reverse osmosis membrane with covalent organic frameworks intermediate layer

Both salt rejection and pressure-bearing properties of the conventional thin film composite (TFC) polyamide reverse osmosis (RO) membrane are easily weakened at high temperature. In order to improve the high temperature resistance, in this work, a polyamide TFC RO membrane with covalent organic frameworks (COFs) intermediate layer was prepared. Firstly, the COFs layer was decorated on polyether sulfone (PES) support membrane by a unidirectional diffusion method and further modified for shrinking the micropore via the chemical crosslinking reaction with 1,3-diamino-2-propanol (DAPL) or ethylenediamine (EDA), and then continued the conventional interfacial polymerization of m-phenylene diamine (MPD) and trimesoyl chloride (TMC) on the resultant COFs layer for preparing the RO membrane. Furthermore, the correlationship between the microstructure of COFs layer and the separation performance of modified RO membrane was systematically investigated. Due to the introduction of the COFTpPa-DAPL intermediate layer with more regular microstructure and specific hydrophilicity, the resultant TFC-COFTpPa-DAPL RO membrane exhibited improvement in water flux by 30 ​% (reached to 50.5 ​L ​m−2 ​h−1) and higher salt rejection (>99.5 ​%) as compared with the conventional polyamide RO membrane and other reported temperature resistance RO membranes. Meanwhile, this TFC-COFTpPa-DAPL membrane showed good long-term separation stability during the RO process for 160 ​h. Especially, its water flux increased to 98.8 ​L ​m−2 ​h−1 without weakening salt rejection (about 99.4 ​%) at 70 ​°C. This study provides an effective way to fabricate the high temperature resistance TFC polyamide RO membrane with good comprehensive separation performance based on COFs intermediate layer.

Orientation and morphology control in acid-catalyzed covalent organic framework thin films.

As thin films of semiconducting covalent organic frameworks (COFs) are demonstrating utility for ambipolar electronics, channel materials in organic electrochemical transistors (OECTs), and broadband photodetectors, control and modulation of their thin film properties is paramount. In this work, an interfacial growth technique is utilized to synthesize imine TAPB-PDA COF films at both the liquid-liquid interface as well as at the liquid-solid interface on a Si/SiO2 substrate. The concentration of acetic acid catalyst in the aqueous phase is shown to significantly influence the thin film morphology of the liquid-solid growth, with concentrations below 1 M resulting in no film nucleation, concentrations of 1-4 M enabling smooth film formation, and concentrations greater than 4 M resulting in films with a higher density of particulates on the surface. Importantly, while the films grown at the liquid-liquid interface are mixed-orientation, those grown directly at the liquid-solid interface on the Si/SiO2 surface have highly oriented COF layers aligned parallel to the substrate surface. Moreover, this liquid-solid growth process affords TAPB-PDA COF thin films with p-type charge transport having a transconductance of 10 μS at a gate voltage of -0.9 V in an OECT device structure.

Fabrication of monodisperse micron-sized and aldehyde-functionalized microspheres coating with covalent organic framework for efficient and rapid removal of copper ions from wastewater.

Covalent organic frameworks (COFs) possess an excellent ability for absorbing heavy metals, but their uneven particle size, difficult separation, and poor dispersion limit their wide application in the treatment of heavy metal pollution. In this paper, a monodisperse poly(4-allyloxybenzaldehyde-co-divinylbenzene) microsphere (denoted as PAD) was prepared with 4-allyloxybenzaldehyde as a functional monomer and divinylbenzene (DVB) as a crosslinker by one-step seed swelling polymerization. Subsequently, oxalyldihydrazide (ODH) and 2,4,6-trihydroxybenzene-1,3,5-tricarbaldehyde (Tp) were chosen as the precursors for coating the COF layer onto the surface of PAD through a one-pot method. The resulting monodisperse particles (diameter = 6.3 μm) with a core-shell structure were assigned as PAD@COF and possessed excellent dispersibility in water along with a high specific surface area of 163.8 m2 g-1. In isothermal and dynamic adsorption experiments, the maximum adsorption capacity of Cu2+ reached 270.9 mg g-1, with the adsorption amount reaching 93 mg g-1 after only 10 min. The Langmuir isothermal adsorption model and pseudo-second-order kinetic model were consistent with the adsorption process, indicating that the adsorption of Cu2+ on PAD@COF occurred as a monolayer and that the adsorption process was controlled by chemical processes.

Covalent organic frameworks as catalyst support: A case study of thermal, hydrothermal, and mechanical pressure stability of β-ketoenamine-linked TpBD-Me2

Covalent organic frameworks (COFs) are crystalline, ordered networks, that, due to their high surface areas and the opportunity for periodic placement of catalytically active sites, are interesting materials for catalysis. Despite the great interest in the use of COFs for this application, there is currently a lack of fundamental understanding on how catalytically relevant conditions affect the integrity of the materials. To gain insight into the stability of COFs as catalyst supports, we herein subjected a β-ketoenamine-linked COF to thermal treatment at high temperatures, to autogenous pressure in water at different temperatures, and to mechanical pressure during pelletizing, after which the materials were thoroughly characterized to gain insight into the structural changes occurring during these catalytically relevant treatments. The COF was largely stable under all hydrothermal conditions studied, highlighting the applicability of β-ketoenamine-linked COFs under aqueous and vapor conditions. On the other hand, thermal and pressure treatments led to a rapid decline in the surface area already at the lowest temperatures and pressures studied. Theoretical calculations indicated this loss to stem from interlayer rearrangement or buckling of the COF layers induced by the applied conditions. This study demonstrates the suitability of β-ketoenamine-linked COFs for use under hydrothermal conditions, and sheds light on the degradation pathways under thermal and pressure treatments, opening the path to the design of COFs with increased stability under such conditions.

PTSA-mediated interfacial catalytic polymerization of crystalline dense covalent organic framework membranes for enhanced desalination

Construction of covalent organic frameworks (COF) membranes for desalination applications was challenging, mainly due to the poor crystallinity and large intrinsic pore size of COFs. Herein, the p-toluenesulfonic acid (PTSA)-mediated interfacial catalytic polymerization (ICP) strategy was proposed to fabricate COF membranes with high crystallinity and sub-nano pores on the polysulfone substrate to enhance desalination and selectivity performance. The proposed PTSA-mediated ICP strategy facilitated the amorphous-to-crystalline transformation and regulated the stacking behavior of COF crystals. Via PTSA meditated ICP process, a ribbon-like crystal structure was observed on the membrane surface. The amorphous COF layers with a thickness of 122–412 nm transformed into crystalline COF layers with a thickness of approximately 245–390 nm, while the pore radius of the COF membranes decreased from 0.65-1.25 nm to 0.17–0.25 nm due to the multilayer stacking of COF crystals on the membrane surface. Meanwhile, the crystalline degree of these COF membranes increased from 21.45% to 73.95% with increasing PTSA concentration and ICP time. The optimal TpPa3%-15 membrane had a water permeability of approximately 3.74 L−1 m−2 h−1 bar−1 and substantial enhancement of Na2SO4 rejection from 19.7% to 90.4%. The 30-day duration of the cross-flow operation measurement demonstrated excellent stability and robust selectivity of SO42− and Cl− for the optimal TpPa3%-15 membrane. In addition, the optimal membrane exhibited excellent desalination performance for divalent ions in petrochemical wastewater and shale gas produced water than that of pristine membrane, rendering their applicability for industrial wastewater desalination. The mechanisms analysis verified that PTSA induced disorder multilayer stacking of crystalline COF crystals on the substrate surface, resulting in reduced pore sizes and increased desalination of the COF membranes. As the traditional IP process, this work proposed that PTSA mediated ICP process was a facile, scalable and time-saving approach for the construction of highly crystalline COF membranes with sub-nanometer pores to achieve enhanced desalination performance.

Carbonized paper-supported electrode with covalent organic framework layers on carbonized cellulose fibers for supercapacitor application

As a class of crystalline porous polymers, covalent organic frameworks (COFs) have shown great application potential in electrochemical energy storage due to their high specific surface area, porous structure, and multiple redox-active sites. However, there are some challenges for practical application of COFs, such as low electrical conductivity, easy stacking, weak mechanical strength, and poor processability. In this study, 2,6-diaminoanthraquinone-1,3,5-triformylphloroglucinol COF is synthesized on dialdehyde cellulose fibers with hyperbranched polyamide-amine (HPAMAM) as a stabilizer. After carbonization, the COF is uniformly and stably supported on the conductive carbon fibers (CCFs) for preparing composite paper electrode (CCF-HPAMAM-COF paper). The carbonized fibers provide mechanical support for the COF and improve the electron transfer efficiency. While the COF layers shorten the ion diffusion path for high utilization of redox-active sites due to their porous structure, the CCF-HPAMAM-COF paper exhibits high volume-specific capacitance (66.7 F/cm3 at 0.5 mA/cm2), good rate capability (capacitance retention of 82% with 10 times current density), and a long lifetime (a charge-discharge stability of 93.7% after 10,000 cycles). This work develops a carbonized paper-supported electrode with stable loading of COFs on carbonized fibers for new generation sustainable supercapacitors.

Ceramic hollow fibre supported covalent organic framework membranes prepared by direct interfacial polymerisation -potential for efficient dye removal from wastewater

Covalent organic frameworks (COFs) have emerged as promising membrane materials, owing to their tunable pore size and ease of functionalisation with potential applications in water purification and organic solvent nanofiltration. However, current COF membranes fabricated via interfacial polymerisation have primarily been limited to polymeric flat sheet substrates, which may not provide optimal mechanical stability over extended periods, as the COF materials are inherently brittle due to their rigid structures and hence prone to damage when applied them on flexible polymeric substrates. In this study, we utilized direct interfacial polymerisation to fabricate imine-linked COF-LZU1 membranes on pre-designed ceramic hollow fibres for efficient dye removal from aqueous solutions. The key parameters, i.e., reaction time and choice of organic solvents, were investigated to achieve a highly crystalline and defect-free COF layer. The resultant membranes exhibited a high pure water permeance of 28.5 L m−2 h−1 bar−1 with a rejection rate of over 90% for dyes with a molecular weight exceeding 500 g mol−1, highlighting the potential of the ceramic hollow fibre supported COF membranes for enhanced process intensification, i.e. high surface-to-volume ratio, better mechanical stability and structural integrity for long-term operations.