Covalent organic frameworks for separation applications

Development of an electrochemical sensor utilizing MWCNs-poly(2-aminothiophenol) @AgNPs nanocomposite for the simultaneous determination of Pb2+ and Cd2+ in food samples

This study focuses on the synthesis and characterization of the Multiwall Carbon Nanotubes-Poly(2-aminothiophenol) @silver nanoparticles nanocomposite (MWCNTs-PATP@AgNPs) using different analytical methods. The synthesized MWCNTs-PATP@AgNPs served as an electrocatalytic modifier, enabling the highly selective and sensitive detection of Pb2+ and Cd2+ ions at nanomolar levels using square wave anodic stripping voltammetry. The concentration of MWCNTs- PATP @AgNPs, the type and concentration of the electrolyte, the solution's pH, and the preconcentration conditions, were systematically optimized. A linear response was observed for Pb2+ and Cd2+ within the ranges of 0.5-60.0 nmolL-1 and 8.0-50.0 nmol L-1, respectively, with detection limits of 0.125 nmol L-1 for Pb2+ and 1.47 nmol L-1 for Cd2+. Furthermore, the MWCNTs-PATP@AgNPs sensor demonstrated the capability to selectively detect these target metals in the presence of various common interfering species. The sensor was effectively utilized for the detection of Pb2+ and Cd2+ ions across various real samples.

"Turn-on" mode fluorescence detection of amines based on a cationic covalent organic framework linked with C-C single bond

Developing methods to detect amine pollutants at trace levels is urgently needed due to their high toxicity to both human health and environment. Covalent organic frameworks (COFs) have emerged as promising candidates for amine sensing due to their exceptional stability when exposed to corrosive amines. While several COF-based sensors have recently been developed for amine detection, to the best of our knowledge, fluorescent "turn-on" sensors have been limited to imine-linked COFs. However, the relatively low stability of imine linkages may compromise structural integrity in the presence of corrosive amines. Here, for the first time, we constructed a cationic C-C single bond linked COF (CSBL-COF-4) through the reaction between cationic porphyrin TMPyP and terephthaldicarboxaldehyde. The abundant cationic sites distributing throughout the networks not only improved the dispersity of CSBL-COF-4 in aqueous solution but also provided numerous acidic sites to enhance the affinity with alkaline amines via Lewis acid-base interaction. CSBL-COF-4 exhibited an efficient response to amine solutions or vapors and was further utilized to evaluate the freshness of meat samples, highlighting its potential for practical applications. Our result would thus open up a new avenue towards constructing a broader class of COF-based sensors for the fluorescence "turn-on" detection of amines.

Efficient enrichment and sensitive determination of endocrine disruptors in PPCPs by novel magnetic covalent organic framework extraction coupled with HPLC-MS/MS

Endocrine-disrupting chemicals (EDCs) are a growing class of pollutants commonly found in environmental matrices due to their extensive use in pharmaceuticals and personal care products (PPCPs). In this study, a novel magnetic covalent organic framework (COF), Fe3O4-COOH@TFP-BHBD, was successfully synthesized and utilized as an adsorbent for magnetic solid-phase extraction (MSPE) of EDCs from PPCPs. The core-shell structured adsorbent demonstrated a high specific surface area, strong magnetic responsiveness and excellent stability. A COF-MSPE-high-performance liquid chromatography-tandem mass spectrometry (COF-MSPE-HPLC-MS/MS) method was developed for the quantitative analysis of EDCs in PPCPs. Under the optimized condition, the detection and quantification limits of this method reached as low as 0.001-0.007 ng/mL and 0.004-0.025 ng/mL, respectively. This method was validated and proven capable to analyze real PPCP samples, while the spiked recovery rates in ranged from 85.62 to 107.83 % with RSD of 2.28-8.58 %. Moreover, the adsorption mechanism was investigated using density functional theory (DFT) calculations. The DFT results revealed that the efficient enrichment capacity of Fe3O4-COOH@TFP-BHBD for EDCs can be attributed to π-π interactions and hydrogen bondings. This proposed method provides excellent adsorption ability and sensitivity for the extraction and precise detection of EDCs in PPCPs.

A new class of ultrastable dual hydrogen-bond-donor COF for improving the reaction activity

Dual hydrogen-bond-donor (HBD) molecules attracted considerable attention in the area of organocatalysts. Here, a novel and stable dual HBD TBP-COF has been developed by structural transformation from TB-COF by locking the reversible bond to form a heterocycle. The obtained dual HBD COF showed excellent hydrogen bond catalytic performance in promoting the Friedel-Crafts reaction. Postsynthetic engineering endows TBP-COF with exceptional stability, demonstrating 90% activity retention over 20 catalytic cycles.

Mechanochemically synthesized covalent organic frameworks as catalysts for the Suzuki-Miyaura coupling reaction

In this study, we present a mechanochemically assisted rapid synthesis of highly crystalline covalent organic frameworks (COFs), specifically the MC-Tab-Dva COF and the MC-Tz-Dva COF, achieved in an exceptionally short time of 30 to 60 min. Additionally, the synthesized COFs were post-modified to incorporate Pd(II), resulting in Pd(II)-containing COFs that demonstrated excellent catalytic activity in Suzuki-Miyaura coupling reactions.

Proton-Mediated ROS Amplification in Hydrazone-Linked Pillararene Microspheres for Photocatalysis

Smart materials that adapt to environmental stimuli have massive technological potential. Translating well-established molecular-level responsiveness to macroscopic systems, particularly complex systems for photocatalysis, remains a significant hurdle. Herein, we introduce a new approach using a hydrazone-linked pillararene microsphere (NP5-TF-HPM) as a smart stimuli-responsive photocatalyst. NP5-TF-HPM showcases unique proton responsiveness owing to electron-rich cavities, resulting in a proton-induced structural rearrangement from the enol-imine to keto-amine form. Experiments and density functional theory calculations reveal that pillararenes in the protonated framework function as activity amplifiers. These molecules donate π-electrons from their cavities to another building unit, not only shifting the framework's conduction band to a more negative potential, which enhances its electron-donating capability, but also inducing a nonuniform charge distribution in the donor-acceptor moiety, thereby resulting in an intramolecular built-in electric field. Consequently, protonated HPM exhibits amplified photo-oxidation activity, efficiently catalyzing sulfide photo-oxidation with high conversions (up to 99%).

Mass Transport Based on Covalent Organic Frameworks

ConspectusMass transport is fundamental to biological systems and industrial processes, governing chemical reactions, substance exchange, and energy conversion across various material scales. In biological systems, ion transport, such as proton migration through voltage-gated proton channels, regulates cellular potential, signaling, and metabolic balance. In industrial processes, transporting molecules through solid, liquid, or gas phases dictates reactant contact and diffusion rates, directly impacting reaction efficiency and conversion. Optimizing these processes necessitates the design of efficient interfaces or channels to enhance mass transport.Crystalline porous materials, particularly covalent organic frameworks (COFs), offer an excellent platform for investigating and optimizing mass transport. With ordered, pre-engineered nano- or subnanometer pores, COFs enable confined substance transport and garnered significant attention for energy conversion, catalysis, drug delivery, adsorption, and separation applications. Deeper investigations into the mass transport mechanism in COFs at the molecular level are crucial for advancing materials science, chemistry, and chemical engineering.Our group focuses on COFs to explore multisubstance cooperative transport mechanisms and structure-activity relationships for ions, water, and gases. We have expanded the linker chemistry of COFs by developing irreversible α-aminoketone-linked COFs and introducing the irreversible Suzuki coupling reaction into COF preparation. We proposed strategies such as side-chain-induced dipole-facilitated stacking and prenucleation and slow growth to achieve record large pore sizes and highly oriented nanochannels. We implemented exfoliation and an interwoven strategy to accelerate ion transport at complex interfaces, refined gas permeability in molecular sieve-based membranes through precise pore size engineering, and elucidated the effects of pore size and hydrophobicity/hydrophilicity on water phase transition and diffusion. Building on these insights, we designed novel open framework ionomers to tailor the microenvironment of electrocatalytic interfaces and uncovered multiple substance transport mechanisms. The synergistically enhanced transport of ions, water, and gas across three-phase interfaces effectively modulates the electrochemical CO2 reduction reaction pathway and significantly boosts the power density of proton-exchange membrane fuel cells (PEMFCs).In this Account, we summarize recent advances in COF-based ion and molecular transport, emphasizing nanochannel construction strategies, including linkage, pore size, orientation, and function gradient modulations. We discuss the functional design of COFs, correlations between pore structure and transport properties, and their applications in gas separation, energy storage, and catalysis. Finally, we outline current challenges and future opportunities in synthetic chemistry, mass transport mechanisms, and applications. By understanding mass transport phenomena from microscopic particles to macroscopic scales, this Account aims to provide molecular design strategies for optimizing multisubstance transport across three-phase interfaces, aligning mass transport with reaction processes and offering insights to enhance catalytic efficiency and energy conversion performance.

C2H2/CO2 Separation by a Carborane Hybrid 2D Metal-Organic Framework

The separation of acetylene (C2H2) from carbon dioxide (CO2) is important in industry but challenging due to their similar physical properties. Herein, a boron-rich 2D metal-organic framework ZNU-14 based on the carborane backbone was readily prepared by the supramolecular assembly of Zn2+, p-C2B10H10-(COOH)2, and di(pyridin-4-yl) amine under mild conditions for C2H2/CO2 separation. ZNU-14 displays a straight 1D channel (7.6 × 12.5 Å2) with an electronegative pore surface. Gas adsorption isotherms show that ZNU-14 has a good C2H2 adsorption capacity of 43.6 cm3 g-1, 181% of the CO2 uptake capacity. The calculated ideal adsorbed solution theory (IAST) selectivity is as high as 6.3-9.7, outperforming many popular materials. The moderate C2H2 adsorption heat of 34.3 kJ mol-1 facilitates the straightforward desorption and regeneration of ZNU-14. Furthermore, the theoretical study confirmed the stronger binding of C2H2 compared to that of CO2. The practical C2H2/CO2 separation performance was fully demonstrated by breakthrough experiments with excellent dynamic selectivity and recyclability under various conditions.

Fully Conjugated Benzobisoxazole-Bridged Covalent Organic Frameworks for Boosting Photocatalytic Hydrogen Evolution

2D covalent organic frameworks (2D-COFs) have attracted extensive interest in solar energy to hydrogen conversion. However, insufficient light harvesting and difficult exciton dissociation severely limit the improvement of photocatalytic activity for COFs, thereby impeding the progression of this advanced field. In this work, two benzobisoxazole-bridged and fully conjugated 2D-COFs with triazine (COF-JLU44) and pyrene (COF-JLU45) units were constructed for the first time via Knoevenagel polycondensation, and they hold long-range ordered structures, largely acceptable surface area, and fascinating photoelectric properties. Significantly, COF-JLU45 exhibits an impressive hydrogen evolution rate of 272.5 mmol g-1 h-1 and superior reusability in the presence of 1.0 wt% Pt under light irradiation, coupled with a remarkable apparent quantum yield of 12.9% at a long wavelength of 600 nm. Multiple spectroscopy and theoretical simulation demonstrate the ingenious design of COF-JLU45 widen its light absorption and effectively promote the exciton dissociation. This finding contributes valuable insights for constructing metal-free photocatalysts for solar energy conversion and utilization.

Electronegative Strategic Positions in Covalent Organic Frameworks: Unlocking High-Efficiency Gold Recovery

Gold (Au) concentrations accumulated from electronic waste (e-waste) and industrial leachates far surpass those found in natural ores, a highly valuable resource if efficient recovery methods can be developed. Despite advancements in covalent organic frameworks (COFs), achieving adsorbents with high selectivity, large capacity, and rapid adsorption kinetics remain challenging because of limitations in partial pore wall sites. Here, we present hexaazatriphenylene-based COFs (HATP-COFs) with an electronegative skeleton, specifically designed for selective Au recovery. The hexaazatriphenylene centers, imine linkages, and pyridine linkers within the COFs introduce electron-rich sites that extend across strategic positions-vertex, linkages, and linkers-thereby enhancing the overall structural integrity. These features facilitate efficient Au capture through electrostatic interactions, achieving an exceptional adsorption capacity exceeding 2366 mg g-1 with rapid kinetics, making HATP-COFs one of the most efficient pure COFs reported to date. Moreover, these HATP-COFs demonstrate remarkable selectivity, stability, and scalability. Theoretical calculations reveal that the electronegative skeleton introduces critical binding sites, promoting strong electrostatic interactions with Au3+ ions and improving adsorption kinetics. This work highlights the potential of charge-interface engineering in COFs as a transformative strategy for developing next-generation materials.

Recent Progress of Covalent Organic Frameworks-Based Materials Used for CO2 Electrocatalytic Reduction: A Review

The excessive CO2 emissions from human activities severely impact the natural environment and ecosystems. Among the various technologies available, electrocatalytic CO2 reduction is regarded as one of the most promising routes due to its exceptional environmental friendliness and sustainability. Covalent organic frameworks (COFs) are crystalline, porous organic networks that are formed through thermodynamically controlled reversible covalent polymerization of organic linkers via covalent bonding. These materials exhibit high porosity, large surface area, excellent chemical and thermal stability, sustainability, high electron transfer efficiency, and surface functionalization capabilities, making them particularly effective in electrocatalytic CO2 reduction. First, this review briefly introduces the fundamental principles of electrocatalysis and the mechanism of electrocatalytic CO2 reduction. Next, it discusses the composition, structure, and synthesis methods of COF-based materials, as well as their applications in electrocatalytic CO2 reduction. Furthermore, it reviews the research progress in this field from the perspective of different types of COF-based catalysts. Finally, in light of the current research status, the development prospects of COF-based catalysts are explored, providing a reference for the development of more efficient and stable COF electrocatalysts for CO2 reduction.

Benzotrithiophene-based covalent organic frameworks for sensitive fluorescence detection and efficient removal of Ag+ from drinking water

The simultaneous detection and removal of Ag+ from drinking water was crucial for preventing human health, while it was also extremely challenging due to bifunctional materials that combine both Ag+ adsorption and detection functions rarely being explored. In this study, a benzotrithiophene-based covalent organic framework (TAPA-BTT) was synthesized and applied to detect and remove Ag+. TAPA-BTT exhibited high crystallinity, a large specific surface area, and good thermal stability. As a fluorescent probe, TAPA-BTT had a low detection limit (0.14 μg/L), wide linear range (0.2-700 μg/L), and good linearity (R2 > 0.9948). It was also successfully applied to identify Ag+ in drinking water including tap, pure, and mineral water with satisfactory detection performance. Moreover, TAPA-BTT had a high efficiency in removing Ag+ from water, offering a high capacity for adsorption (344.83 mg/g) and a removal rate of 99.45 %. The adsorption of TAPA-BTT towards Ag+ can be well explained by the quasi-second-order kinetic model and the Langmuir isotherm model. In addition, experimental and theoretical studies revealed the interaction mechanism between TAPA-BTT and Ag+. The specific Ag+ detection by TAPA-BTT was assumed to be caused by the electron transfer from thiophene-S to Ag+, which enhanced the fluorescence of TAPA-BTT. The effective removal of Ag+ was attributed to the co-chelation of imine-N and thiophene-S on TAPA-BTT. These novel findings revealed the great potential of benzotrithiophene-based COFs in the detection and removal of Ag+, providing a new strategy and alternative material for monitoring and controlling Ag+ in drinking water.

Chiral Porous Organic Polymers (CPOPs): Design, Synthesis, and Applications in Asymmetric Catalysis

Since the recognition of the area of asymmetric synthesis in 2000, there has been a tremendous focus on the development of heterogeneous catalysts for asymmetric synthesis. Porous organic polymers (POPs) have emerged in recent years as inextricable materials of high physicochemical and hydrolytic stabilities, permitting infinite possibilities to modulate and tune reactivity, engineer porosity, regulate spatial environments and pore attributes, and maneuver material transport. With a diligent design of building blocks and the exploitation of organic reactions judiciously, the synthesis of POPs with BET surface areas of the order of a few thousand cm3/g has been demonstrated. The incorporation of reactive functional groups and chiral centers into the porous matrices of polymers offers opportunities to conduct asymmetric synthesis. Very high enantioselectivities of the order of 99% ee have been exemplified in the reactions mediated by chiral POPs (CPOPs). The design-driven tunability of POPs allows the development of catalytic materials for targeted applications in a tailor-made fashion. This review, while placing the development of chiral materials for asymmetric synthesis in the right perspective, delves into different design principles to pave the way for continued research on futuristic CPOP materials by a creative design, limited by one's imagination, for heretofore unprecedented results.

Converging the Complementary Traits of Metal-Organic Frameworks and Covalent Organic Frameworks

Since their discovery, metal-organic frameworks (MOFs) and covalent organic frameworks (COFs) featuring permanent nanopores have transformed the landscape of porous materials, excelling as platforms for catalysis, gas separation, and sensing thanks to their exceptional surface areas, adjustable pore sizes, and modular functionality. However, MOFs, while versatile, face stability challenges due to their coordination bonds, whereas COFs, although robust, lack metal sites, limiting their catalytic activity, redox functionality, and other metal-specific applications. To bridge these gaps, innovative porous materials, such as MCOFs, which incorporate metal ions into COF lattices; covalent cluster frameworks, formed by assembling metal clusters into covalent networks; and MOF-COF composites, which integrate the strengths of both systems, have emerged. This review explores the synthesis and design principles of these advanced materials, showcasing their applications and the unique advantages conferred by their composite nature. It provides insights into future directions and their potential to address key challenges in materials science and beyond.

Porphyrin-Based Covalent Organic Framework Encapsulating Multiwalled Carbon Nanotubes: A High-Performance Electrocatalyst for Oxygen Reduction Reaction

The development of efficient and cost-effective oxygen reduction reaction (ORR) catalysts is crucial for advancing fuel cell technologies, given the limitations of platinum-based catalysts. Here, we present a novel nanocomposite, cobalt-based porphyrinic covalent organic framework wrapped on multiwalled carbon nanotubes (Co-pCOF@MWCNTs), synthesized via template-directed in situ polymerization. This composite combines the high porosity and tunable catalytic properties of porphyrinic COFs with the excellent electrical conductivity of MWCNTs. The Co-pCOF@MWCNT demonstrates superior ORR activity, exhibiting an onset potential (Eonset) of 0.86 V vs RHE in 0.1 M KOH, surpassing the performance of its individual components (Co-pCOF and MWCNT) and other related materials. The enhanced catalytic efficiency is attributed to the synergistic interactions between the conductive MWCNT scaffold and the active porphyrinic COF nanolayers, which facilitate efficient charge transfer and increase catalytic site exposure. Furthermore, the nanocomposite exhibits high stability and methanol tolerance, establishing its potential as a cathodic material for fuel cells. This work highlights the promise of integrating COFs with conductive carbon materials and opens new avenues for the design of advanced ORR catalysts for energy conversion applications.

Randomly oriented covalent organic framework membrane for selective Li+ sieving from other ions

Certain biological channels exhibit remarkable selectivity, effectively distinguishing between competing cations. If artificial membranes could achieve similar precision in differentiating competing ions from Li+, it could advance sustainable technologies in lithium extraction. In this study, we present a covalent organic framework (COF) membrane featuring a randomly oriented structure that enables selective separation of major competing ions from Li+. The random orientation results in narrow pores, which impart size-based selectivity among alkaline ions. Additionally, the COF incorporates sulfonic groups that preferentially bind to Na+ and K+, facilitating their transport while retaining Li+. These synergistic mechanisms endow the membrane with a selectivity beyond detection limit for K+ and Na+ over Li+. When driven by an electrical potential, the ion flux through the membrane is enhanced by over an order of magnitude. Notably, the membrane also permits the transport of Mg2+ and Ca2+ while still rejecting Li+, leveraging differences in their ion mobility. This work should advance the design and construction of biomimetic materials for the extraction of valuable species from seawater and other aqueous sources.

Three-Dimensional Covalent Organic Frameworks with jcg Topology Based on a Trinodal Strategy

The development of three-dimensional (3D) covalent organic frameworks (COFs) holds significant promise for various applications, but the conventional uninodal or binodal design strategies limit their structural diversity. In this work, we present a novel trinodal strategy for the synthesis of 3D COFs featuring both microporous and mesoporous nanochannels. Using powder X-ray diffraction (PXRD), computational simulations, and high-resolution transmission electron microscopy (HR-TEM), we demonstrate that employing an 8-c building block with reduced symmetry, which can be considered as 4- and 3-connected subunits, along with planar 4-c building blocks, results in an unprecedented [4 + 3 + 4]-c jcg net. This structure features rare saddle-shaped eight-membered rings and mirror-symmetrical chains. Furthermore, the incorporation of chromophore pyrene and redox-active triphenylamine components, coupled with structural conjugation, imparts tunable photophysical and electronic properties to these COFs, making them promising candidates for photocatalytic H2O2 production. This work highlights the potential of the trinodal strategy in creating intricate COF architectures and enhances their applicability in heterogeneous photocatalysis.

Rolling two-dimensional covalent organic framework (COF) sheets into one-dimensional electronic and proton-conductive nanotubes

Mimicking the interconvertible carbon allotropes of 2-dimensional (2D) graphene and 1-dimensional (1D) carbon nanotubes (CNTs), herein we report the in situ transformation of 2D π-conjugated covalent organic frameworks (COFs) sheet into 1D nanotubular structures via self-assembly the sheets at solvent interfaces. The facile "roll-sheets" self-assembly resulted in coaxial nanotubes with uniform cross-sectional diameter, which was realized for diazapyrene-based COFs but not for the corresponding pyrene COF, although both possess similar chemical structures. Upon replacing the carbon atoms at 2,7-positions of pyrene with nitrogen, contrasting optical and electronic properties were realized, reflecting the rolled structure of the conjugated 2D sheets. The nanotubes exhibited concerted electronic- and proton-conducting nature with stable conducting pathways at ambient conditions. The nitrogen centers act simultaneously as the site for charge carrier doping and proton acceptors, as evidenced by the high photo- and electrical conductivity, as well as the record proton conductivity (σ = 1.98 S cm-1) results. The present diazapyrene-based 1D nanotubular COF serves as a unique materials platform with electronic conduction in the wall and proton conduction in the core, respectively.

The Development Prospects and Potential of High Specific Surface Area Materials: A Review of the Use of Porous Framework Materials for the Capture and Filtration of Ammonia

Ammonia is one of the most widely produced inorganic chemicals, with extensive applications in the military, agricultural, and industrial sectors. However, its strong stimulation and corrosive properties pose significant health risks, as long-term exposure to ammonia environments can lead to respiratory tract damage, loss of consciousness, and even cardiopulmonary dysfunction. Over the years, researchers have focused on exploring suitable materials for ammonia adsorption fields such as activated carbon and zeolites. Porous framework materials (PFMs), including metal-organic frameworks, covalent organic frameworks, and hydrogen-bonded organic frameworks, have emerged as possible ammonia adsorption materials due to their high specific surface area, pore size, and structural adjustability. This review focuses on the research and application of materials with excellent adsorption based on PFMs for ammonia adsorption, highlighting their potential applications and providing insights into future developments in this field.

Thiol-Functionalized Covalent Organic Framework for Efficient Metal Ion Removal in Water Treatment

Advanced water treatment technologies must offer selective, efficient, and cost-effective contaminant removal. In this study, TPB-DMTP-COF-SH, prepared from 1,3,5-tris(4-aminophenyl)benzene (TPB) and 2,5-dimethoxyterephaldehyde (DMTP), was synthesized via a two-step method and applied for the adsorption of aluminum (Al3+), iron (Fe2+), and manganese (Mn2+) ions from water. Adsorption performance was influenced by pH, initial concentration, and contact time, with optimal pH values of 3 for Al3+, 8 for Fe2+, and 10 for Mn2+. The adsorption data followed the Langmuir isotherm model, yielding maximum capacities of 3.27 mg g-1 (Al3+), 8.5 mg g-1 (Fe2+), and 0.67 mg g-1 (Mn2+). Kinetic studies indicated a pseudo-second-order mechanism, suggesting chemisorption as the dominant process. Equilibrium adsorption was reached at 15 min for Al3+ and Mn2+ and 20 min for Fe2+. As a proof of concept, we demonstrate that this thiol-functionalized COF not only effectively removes metals but also offers enhanced processability into composite beads and membranes, making it a strong candidate for real-world water treatment applications. These findings highlight TPB-DMTP-COF-SH as a promising and scalable solution for water purification.

Single-Crystal X-ray Structures of Homochiral Brønsted Acidic Covalent Organic Frameworks

Determining the crystal structures of covalent organic frameworks (COFs) with atomic precision is pivotal for uncovering their properties and optimizing functionalities. However, the synthesis of high-quality single crystals of COFs suitable for X-ray diffraction analysis, especially chiral COFs (CCOFs), remains a formidable challenge. In this work, we report two three-dimensional (3D) CCOFs synthesized via imine condensation of tetrahedral tetraamine and tetraaldehydes derived from optically active 1,1'-biphenol phosphoryl chloride or thiophosphoryl chloride. Single crystals of varying sizes are obtained through either a low-temperature modulation strategy, yielding large crystals up to 100 μm, or a solvothermal method. The large single crystals are structurally characterized by single-crystal X-ray diffraction, achieving a resolution of 0.90 Å. These two CCOFs are isostructural and each features a 4-fold interpenetrated diamondoid open framework with all phosphoric acid groups periodically aligned within tubular helical channels, displaying enhanced Brønsted acidity compared to non-immobilized acids. The frameworks exhibit permanent porosity, chemical resistance in boiling water, 14 M NaOH, and 0.1 M HCl, and thermal stability up to 400 °C. Notably, these CCOFs serve as efficient and recyclable heterogeneous Brønsted acid catalysts in the asymmetric addition to aromatic aldehydes, enantioselective transfer hydrogenation of ketimines, and three-component direct asymmetric Mannich reactions involving aldimines and cyclic ketones, achieving good to high enantioselectivities (up to 99.5% ee) that surpass those obtained in analogous systems with homogeneous catalysts. This work represents the first successful demonstration of single-crystal structures of homochiral COFs, paving the way for in-depth investigations into structure-property relationships in enantioselective processes and facilitating the design of novel functional chiral organic materials.

Machine Learning Accelerated Discovery of Covalent Organic Frameworks for Environmental and Energy Applications

Covalent organic frameworks (COFs) are porous crystalline materials obtained by linking organic ligands covalently. Their high surface area and adjustable pore sizes make them ideal for a range of applications, including CO2 capture, CH4 storage, gas separation, catalysis, etc. Traditional methods of material research, which mainly rely on manual experimentation, are not particularly efficient, while with advancements in computer science, high-throughput computational screening methods based on molecular simulation have become crucial in material discovery, yet they face limitations in terms of computational resources and time. Currently, machine learning (ML) has emerged as a transformative tool in many fields, capable of analyzing large data sets, identifying underlying patterns, and predicting material performance efficiently and accurately. This approach, termed "materials genomics", combines high-throughput computational screening with ML to predict and design high-performance materials, significantly speeding up the discovery process compared to traditional methods. This review discusses the functions of ML in the screening, design, and performance prediction of COFs and highlights their applications across various domains like CO2 capture, CH4 storage, gas separation, and catalysis, thereby providing new research directions and enhancing the understanding of COF materials and their applications.

Next-Generation Chromatography: Covalent Organic Frameworks in Biomedical Analysis

Chromatography, a cornerstone technique in analytical chemistry, continues to evolve with the emergence of novel stationary phases. Covalent organic frameworks (COFs) have garnered significant attention due to their unique properties and versatile applications. COFs, composed of covalently linked organic building blocks, exhibit high surface area, tunable porosity, and exceptional chemical stability. These attributes make them next-generation chromatographic techniques that leverage novel materials and methodologies to achieve significant improvements in separation efficiency, selectivity, speed, and/or sensitivity compared to traditional methods. COF stationary phases demonstrate remarkable selectivity for small molecules, peptides, proteins, and nucleic acids. Their use in drug discovery, metabolomics, proteomics, and clinical diagnostics is gaining momentum. In this review, we explored their synthesis strategies, emphasizing the design principles that enable tailoring of their physicochemical properties. Further, we discuss the immobilization of COFs onto solid supports, ensuring their compatibility with existing chromatographic systems. Furthermore, we highlighted case studies where COFs outperformed traditional stationary phases, improving sensitivity and resolution. We delve into the integration of COFs as stationary phases in biomedical analysis and explore various strategies for utilizing COFs as stationary phases in chromatographic separations.

Rapid and Large-Scale Synthesis of High-Crystalline Imide Covalent Organic Frameworks Accelerated by Self-Generated Water

Imide covalent organic frameworks (COFs) are considered promising materials in various fields due to their exceptional stability, large surface area, and high porosity. However, current synthesis methods of imide COFs typically involve complex vacuum operations, large amounts of solvents, and long reaction times at high temperatures, limiting their scalability for industrial production. Herein, a facile self-accelerated strategy is developed for rapid, low-cost, and large-scale synthesis of eight imide COFs (SACOFs) under solvent-free, vacuum-free, and low-temperature conditions. Mechanistic studies reveal that the self-accelerated synthesis is driven by the self-generated water under atmospheric conditions, which accelerates the reversible self-healing of disordered polymers, ultimately leading to the rapid synthesis of highly crystalline COFs. Notably, the only additive required besides the COF monomers is o-substituted benzoic acid, a small amount of which is grafted onto the imide COFs, enabling their straightforward functionalization. Thiol-functionalized SACOFs are synthesized as supports for anchoring Pd nanoparticles. The as-prepared Pd@SACOFs exhibit high activity and selectivity in the hydrogenation of substituted nitrobenzene due to the surface modulation of Pd by thiol groups. The self-accelerated synthetic strategy enables rapid, low-cost, and large-scale production of imide COFs, potentially paving the way for their transition from laboratory research to commercial applications.

Fluorinated Covalent Organic Framework Antifouling Nanofiltration Membranes Through Defect Engineering

Covalent organic framework (COF) membrane holds great promise in water treat-ment. Improving the antifouling property of COF membrane is critical for practical application while rare investigations have been reported. Grafting fluorinated chains on the COF membrane surface is expected an effective strategy but quite challenging due to the lack of grafting sites. In this work, the defect engineering strategy is adopted to generate free amino groups as grafting sites through the Schiff-base reaction between amine monomer and mixed aldehyde monomers, then perfluoroalkyl chains are grafted on the COF membrane surface through the reaction between the free amino groups and the perfluorooctanoyl chloride. The content of perfluoroalkyl chains can be regulated and optimized by controlling the amount of free amino groups. The fluorinated COF membrane shows superior antifouling performance with a significantly increased flux recovery ratio and reduced flux decline ratio against oil/water emulsions and humic acid (FRR ≈ 98%, DRt = 10%). Furthermore, the fluorinated COF membrane exhibits high water permeance up to ≈115 L m-2 h-1 bar-1 while acquiring a high salt/dye selective factor. This work affords an effective approach to the development of antifouling, high-separation-performance COF membranes, and other kinds of organic molecular sieve membranes.

Protonation of Nitrogen-Containing Covalent Organic Frameworks for Enhanced Catalysis

Covalent organic frameworks (COFs) are a class of porous crystalline materials with ordered structures and tunable properties, which have been widely explored in catalysis, sensing, gas storage, and separation. Among various post-synthetic modifications, protonation emerges as a simple yet effective strategy to fine-tune the properties of nitrogen-containing COFs, thereby enhancing their catalytic performance. This concept article highlights the contribution of protonation on the mass transfer kinetics, charge distribution, photo-response, charge transfer, and other properties related to photocatalysis and electrocatalysis. The applications of protonated COFs are explored in catalytic processes including hydrogen evolution, CO2 reduction, H2O2 synthesis, and singlet oxygen generation. We also emphasize the necessity of considering the protonation process when nitrogen-containing COFs are applied in acidic environments to accurately reveal the structure-activity relationship. By analyzing recent advancements in protonated COFs, this article underscores the potential and challenges of protonation as a powerful tool for advancing COF-based catalytic systems.

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.

Single-Molecule Detection via Pore Nanoconfinement of Covalent Organic Frameworks for Surface-Enhanced Raman Scattering

Surface-enhanced Raman scattering (SERS) offers significant advantages for single-molecule detection. However, stochastic molecular motion makes it challenging to consistently capture signals from single-molecule binding events, particularly in complex environments. Herein, we propose a novel SERS system via the pore nanoconfinement effect of covalent organic frameworks (COFs) to achieve reliable single-molecule detection. The self-assembled COF thin films on SERS metal substrates (Au/Ag) create a nanogap of 3 nm, allowing electric field enhancement. By precise tuning of the COF shell thickness, a molecular-scale pore volume is formed, effectively trapping individual molecules from molecular aggregates. Furthermore, the strong intermolecular forces within the COF pores significantly enhance the residence time of individual molecules, thereby increasing the probability of detecting single-molecule binding events. This innovative approach ensures consistent and reliable SERS single-molecule detection in complex mixtures, paving the way for advanced applications in biochemical sensing and diagnostics.

Enhanced CO2 Separation Performance of a Modified Composite Membrane Based on a Covalent Organic Framework by Molecular Simulation

This study investigates the mechanisms of CO2 adsorption and separation in COF (covalent organic framework) membranes modified with ionic liquids and DESs (deep eutectic solvents) under varying temperature and humidity conditions by molecular dynamics simulations. The results indicate that higher temperatures enhance the CO2 permeability, while an appropriate amount of water improves separation selectivity. The effects of DES and PEGIL (PEG-modified ionic liquid) solvents differ due to their distinct molecular structures. DES molecules are more uniform with shorter and less curved chains, resulting in denser membranes. In contrast, PEGIL molecules, characterized by longer and more curved chains, generate additional free volume. However, due to the strong interactions among PEGIL, COF, and CO2 gas molecules, more adsorption space is provided for gas molecules, resulting in decreased gas permeability. Humidity plays a dual role. In DES@COF membranes, small amounts of water selectively enhance the transport of CO2 while inhibiting N2 transport; in PEGIL@COF membranes, excessive water causes phase separation, which impedes gas transport. These findings offer practical insights for optimizing COF-based composite membranes for efficient CO2 separation in industrial applications.

Autocatalytic Interfacial Synthesis of Self-Standing Amide-Linked Covalent Organic Framework Membranes

The synthesis of crystalline covalent organic frameworks (COFs) has in principle relied on reversible dynamic chemistry. A general method to synthesize irreversibly bonded COFs is urgently demanded for driving the COF chemistry to a new era. Here we report a universal two-step method for the straightforward synthesis of irreversibly amide-linked COF (AmCOF) membranes by autocatalytic interfacial polymerization (AIP). Highly crystalline amide and imine bilinker COF (AICOF) membranes are readily synthesized by AIP strategy which ingeniously leverages interfacial polymerization to generate amide units followed by an autocatalytic condensation that forms imine bonds. Then, the fully amide-linked AmCOF membranes with Turing structures can be prepared through irreversible linker renovation. The universality of this method has been exemplified by nine AmCOF membranes. Among them, the AmCOF-1 membrane exhibits superior performance for H2O2 photosynthesis (4353 μmol g-1 h-1) and high stability, enabling continuous production of H2O2 under sunlight for 150 h without sacrificial agents. Mechanistic investigations reveal that the greatly improved properties are attributable to the built-in robust amide knots, facilitating full separation of electrons and holes, ultra-long exciton diffusion length, and fast dissociation of excitons within the AmCOF channels.

Temperature-Swing Synthesis of Highly Crystalline Covalent Organic Framework Films for Fast and Precise Molecular Separations

Producing crystalline covalent organic framework (COF) films is intimately related to the elusive nucleation and growth processes, which is desirable for efficient molecular transport. Rational control over these processes and insights into the mechanisms are crucial to improve synthetic methodology and achieve COF films with regular channels. Here, we report the controllable synthesis of COF films via the temperature-swing strategy and explore their crystallization from monomer assemblies to film formation. A detailed time-dependent study reveals that COF crystallites preferentially coalesce at low temperature, progressing from assembled nanospheres to continuous films through lateral and vertical interactions. Moreover, appropriately elevating the synthesis temperature promotes crystal growth and eliminate the defects of weakly crystalline regions, contributing to highly crystalline and porous COF film with a surface area of 746 m2 g-1. The prepared COF composite membrane exhibits a methanol permeance of 79 L m-2 h-1 bar-1, which is 4.5 times higher than the weakly crystalline counterpart. In addition, the molecular sieving test recognize great membrane selectivity to discriminate the antibiotic mixture with a high separation factor of 15.4. This work offers a feasible way for the rational design of the synthesis environment, enabling access to highly crystalline framework materials for targeting molecular separations.

Covalent organic frameworks as superior adsorbents for the removal of toxic substances

Developing new materials capable of the safe and efficient removal of toxic substances has become a research hotspot in the field of materials science, as these toxic substances pose a serious threat to human health, both directly and indirectly. Covalent organic frameworks (COFs), as an emerging class of crystalline porous materials, have advantages such as large specific surface area, tunable pore size, designable structure, and good biocompatibility, which have been proven to be a superior adsorbent design platform for toxic substances capture. This review will summarize the synthesis methods of COFs and the properties and characteristics of typical toxicants, discuss the design strategies of COF-based adsorbents for the removal of toxic substances, and highlight the recent advancements in COF-based adsorbents as robust candidates for the efficient removal of various types of toxicants, such as animal toxins, microbial toxins, phytotoxins, environmental toxins, etc. The adsorption performance and related mechanisms of COF-based adsorbents for different types of toxic substances will be discussed. The complex host-guest interactions mainly include electrostatic, π-π interactions, hydrogen bonding, hydrophobic interactions, and molecular sieving effects. In addition, the adsorption performance of various COF-based adsorbents will be compared, and strategies such as reasonable adjustment of pore size, introduction of functionalities, and preparation of composite materials can effectively improve the adsorption efficiency of toxins. Finally, we also point out the challenges and future development directions that COFs may face in the field of toxicant removal. It is expected that this review will provide valuable insights into the application of COF-based adsorbents in the removal of toxicants and the development of new materials.

Dimensional evolution of charge mobility and porosity in covalent organic frameworks

Covalent organic frameworks are an emerging class of covalently linked polymers with programmable lattices and well-defined nanopores. Developing covalent organic frameworks with both high porosity and excellent charge transport properties is crucial for widespread applications, including sensing, catalysis, and organic electronics. However, achieving the combination of both features remains challenging due to the lack of overarching structure-property correlations. Here, we report a strategy toward covalent organic frameworks with tunable dimensionality. The concept relies on splicing one-dimensional charge-conducting channels to form extended networks with tailorable substitution patterns. Such dimensional evolution and substitution control enable fine-tuning of electronic band structure, charge mobility, and porosity. According to surface-area characterization, high-frequency terahertz photoconductivity measurements, and theoretical calculations, the transition from one-dimensional to para-linked two-dimensional networks furnishes a substantial increase in surface area and a decrease in local charge mobility. The latter feature is assigned to substitution-induced electronic band flattening. A subtle balance of surface area (947 m2·g-1) and local charge mobility (49 ± 10 cm2·V-1·s-1) is achieved through the rational design of meta-linked analogs with mixed one-dimensional and two-dimensional superior nature. This work provides fundamental insights and new structural knobs for the design of conductive covalent organic frameworks.

The Feasibility of Using Electrostatic Interactions for Immobilizing Ru-bda Catalysts in Covalent Organic Framework: A Proof-of-Concept

Heterogenization of molecular catalysts effectively resolves the separation issues of homogeneous catalysts and expands their application scenarios. In recent years, more and more studies have been using non-covalent interactions to achieve the heterogenization of molecular catalysts. Herein, electrostatic attraction was used to immobilize molecular catalysts, Ru-bda small molecular catalysts in COF materials, where the charged Ru-bda catalysts were immobilized in the oppositely charged COF with a high [Ru] loading content of ~0.2 mmol [Ru] g-1 COF. The leakage experiment verified that the immobilization of Ru-bda catalysts in COF by electrostatic interactions is stable in 0.1 M HClO4 and less than 5 % of molecular Ru-bda catalysts were leached into the solution in 2 hours. The chemical water oxidation experiment was conducted as a model catalysis reaction to verify the feasibility of using electrostatic interactions for immobilizing Ru-bda catalysts in COFs. The prepared Ru(bda)@COFs demonstrate a high catalytic activity of 268 μmol L-1 s-1 O2 for chemical water oxidation, illustrating the electrostatic attractions between COF and small molecules that can be used to immobilize homogeneous catalysts in heterogeneous materials. However, the robustness of COF material itself under catalytic conditions should be considered in practical applications.

A Novel Gully-like Surface of Stainless-Steel Fiber Coated with COF-TPB-DMTP Nanoparticles for Solid-Phase Microextraction of Phthalic Acid Esters in Bottled Tea Beverages

A covalent organic framework TPB-DMTP was physically coated onto the gully-like surface of stainless-steel fiber. The fabricated TPB-DMTP-coated stainless-steel fiber was used to extract five phthalic acid esters (PAEs) prior to the GC-FID separation and determination in bottled tea beverages. The developed SPME-GC-FID method gave limits of detection (S/N = 3) from 0.04 µg·L-1 (DBP) to 0.44 µg·L-1 (BBP), with the enrichment factors from 268 (DEHP) to 2657 (DPP). The relative standard deviations (RSDs) of the built method for inter-day and fiber-to-fiber were 4.1-11.8% and 2.3-9.9%, respectively. The prepared TPB-DMTP-coated stainless-steel fibers could stand at least 180 cycles without a significant loss of extraction efficiency. The developed method was successfully applied for the determination of trace PAEs in different bottled tea beverages, with recoveries from 85.5% to 115%.

Integration of ratiometric, ultrafast, sensitive detection as well as rapid and efficient removal of tetracycline based on a novel Zn (II) functionalized magnetic covalent organic framework

BACKGROUND

Based on the low volatility and refractory nature of Tetracycline (TC), excessive use leads to its continuous accumulation in water environments, posing serious risks to the ecological environment and human health. Although a very limited number of nanomaterials capable of simultaneously detecting and removing TC have been fabricated, they generally exist issues associated with a single detection signal ("on" or "off") or low adsorption rates with low adsorption capacities. As a result, it is crucial to develop a reliable technique to achieve ratiometric detection as well as rapid and efficient removal of TC.

RESULTS

Herein, a novel Zn (II) Functionalized magnetic covalent organic framework (Fe3O4@COF@Zn) was created. As the role of a fluorescent probe, it had excellent characteristics of ratiometric (F529/F436), ultrafast response (1 min), and ultra-low detection limit (16 nM). As the role of an adsorbent, it demonstrated a high capacity of adsorption (414.94 mg/g) in the pH-neutral range, fast kinetics (10 min), desirable regeneration capability, and convenient magnetic separation. By theoretical and experimental analysis, the detection and adsorption mechanism for TC was systematically revealed. Moreover, as an attempt, Fe3O4@COF@Zn showed it potential for crop remediation by adsorbing TC-contaminated water.

SIGNIFICANCE

This work demonstrates the exceptional performance of Zn-functionalized fluorescent COF for ratiometric, ultrafast, sensitive detection as well as rapid and efficient removal of TC, thereby illustrating its significant potential for the rapid monitoring and treatment of TC contamination.

Surface Involvement in the Boosting of Chiral Organocatalysts for Efficient Asymmetric Catalysis

Nanostructures with curved surfaces and chiral-directing residues are highly desirable in the synthesis of asymmetric chemicals, but they remain challenging to synthesize without using unique templates due to the disfavored torsion energy of twisted architectures toward chiral centers. Here, a strategy for the facile fabrication of highly cured capsule-shaped catalysts with chiral interiors by the amplification of molecular chirality via the irreversible cross-linking of 2D asymmetric laminates is presented. The key to the success of these irregular 2D layers is the use of hierarchical assembly of chiral macrocycles, which can exactly regulate the cured nanostructures as well as asymmetric catalysis. The cross-linking of 2D laminates from the assembly of hexameric macrocycles with one proline edge gave rise to rarely curled capsules with a diameter of 200-400 nm and excellent enantioselectivities as well as diastereoselectivities for asymmetric aldol reactions (94% ee and 1:13 dr). The tetrameric macrocycles decorated with the chiral block produced further curled porous structures, giving an outstanding enantioselectivities (up to 98% ee and 1:17 dr). The strategy of mechanical surface folding will provide a new insight related to increasing the enantioselectivity of chiral organocatalysts.

Engineering fluorene-based covalent organic framework photocatalysts toward efficient and selective aerobic oxidation of amines

Covalent organic frameworks (COFs) have attracted significant interest due to diverse applications, relying on their versatile molecular building blocks like fluorenes. However, the twisted structures of fluorenes pose substantial challenges for the construction of porous crystalline materials like COFs. Here, the couplings of 1,3,5-triformylphloroglucinol (Tp) with 9H-fluorene-2,7-diamine (DAF), 9,9-dimethyl-9H-fluorene-2,7-diamine (MFC) and 9,9-difluoro-9H-fluorene-2,7-diamine (FFC) with a pyrrolidine catalyst afford three fluorene-based COFs, TpDAF-COF, TpMFC-COF and TpFFC-COF, respectively. The resulting COFs, with distinct functional groups, exhibit high crystallinity and porosity. Optoelectronic tests reveal that TpFFC-COF demonstrates the most intense photocurrent density and the lowest interfacial charge transfer resistance. When applied to the selective aerobic oxidation of amines to imines, the efficiency follows the order of TpFFC-COF > TpMFC-COF > TpDAF-COF, consistent with the observed optoelectronic properties. Additionally, the TpFFC-COF photocatalyst showcases excellent reusability and broad applicability. This work illuminates the potential of engineering COFs with functional groups toward efficient photocatalysts.

Exploring New Bioorthogonal Catalysts: Scaffold Diversity in Catalysis for Chemical Biology

Bioorthogonal catalysis has revolutionized the field of chemical biology by enabling selective and controlled chemical transformations within living systems. Research has converged on the development of innovative catalyst scaffolds, seeking to broaden the scope of bioorthogonal reactions, boost their efficiency, and surpass the limitations of conventional catalysts. This review provides a comprehensive overview of the latest advancements in bioorthogonal catalyst research based on different scaffold materials. Through an in-depth analysis of fabrication strategies and applications of bioorthogonal catalysts, this review discusses the design principles, mechanisms of action, and applications of these novel catalysts in chemical biology. Current challenges and future directions in exploring the scaffold diversity are also highlighted. The integration of diverse catalyst scaffolds offers exciting prospects for precise manipulation of biomolecules and the development of innovative therapeutic strategies in chemical biology. In addition, the review fills in the gaps in previous reviews, such as in fully summarizing the presented scaffold materials applied in bioorthogonal catalysts, emphasizing the potential impact on advancing bioorthogonal chemistry, and offering prospects for future development in this field.

Linkage Engineering of Semiconductive Covalent-Organic Frameworks toward Room-Temperature Ppb-Level Selective Ammonia Sensing

Rational design of molecular architectures is crucial for developing advanced materials such as covalent-organic frameworks (COFs) with excellent sensing performance. In this work, two isostructural COFs (β-keto-AnCOF and imine-AnCOF) with the same conjugated linkers but distinct linkages are constructed. Although both COFs have porous structure and semiconductor behavior conferred by the identical conjugated backbones, β-keto-AnCOF with ─C═O side groups exhibits superior room-temperature ammonia (NH3) sensing performance than imine-AnCOF and even the state-of-the-art dynamic and commercial NH3 sensors, i.e., high sensitivity up to 18.94% ppm-1, ultralow experimental detection limit of 1 ppb, outstanding selectivity, and remarkable response stability and reproducibility after 180 days. In situ spectroscopy and theoretical calculation reveal that the additional charge transfer between NH3 and ─C═O sites in β-keto-AnCOF effectively increases the distance between Fermi level and the valence band, enabling highly-sensitive NH3 detection at ppb levels. This work provides novel molecular architectures for next-generation high-performance sensors.

Industrialization of Covalent Organic Frameworks

Covalent organic frameworks (COFs) have attracted broad interest because of their well-defined, customizable, highly stable, and porous structures. COFs have shown significant potential for various practical applications, such as gas storage/purification, drug purification, water treatment, catalysis, and battery applications. Scaling up COFs is highly desirable to meet industrial application demands but is hindered by the limitations of synthesis methods and the high cost of reactants. Recently, emerging green synthesis methods, such as mechanochemical synthesis and flux synthesis, have offered promising solutions to these challenges (e.g., ton-scale production of COFs has been achieved by companies recently). This Perspective provides an overview of the state of the art with respect to the industrial production of COFs and discusses factors influencing the large-scale production of COFs. Directions and opportunities for improving the performance and sustainability of COFs toward industrial applications are also emphasized.

Synthesis of high quality two dimensional covalent organic frameworks through a self-sacrificing guest strategy

The quality of covalent organic frameworks (COFs) crucially influences their mechanistic research and subsequent practical implementations. However, it has been widely observed that the structure damage induced by the activation procedure could compromise the quality of COFs. Here we develop a self-sacrificing guest method for synthesizing high-quality two-dimensional COFs (SG-COFs) by incorporating salt guests into the pores of the COF structure. These introduced salts play an indispensable role in supporting COF pores and mitigating quality loss during the activation process. Interestingly, due to the unique characteristic of salts decomposing into gases upon heating, this method can ultimately enable the synthesis of highly pure, high-quality COFs without the presence of residual guest molecules. The resulting sixteen COFs display superior crystallinity and porosity compared to those synthesized using conventional routes. Moreover, these high-quality SG-COFs have demonstrated to be highly efficient adsorbents for removal of per- and polyfluoroalkyl substances.

From Fundamentals to Synthesis: Covalent Organic Frameworks as Promising Materials for CO2 Adsorption

Covalent organic frameworks (COFs) are highly crystalline polymers that possess exceptional porosity and surface area, making them a subject of significant research interest. COF materials are synthesized by chemically linking organic molecules in a repetitive arrangement, creating a highly effective porous crystalline structure that adsorbs and retains gases. They are highly effective in removing impurities, such as CO2, because of their desirable characteristics, such as durability, high reactivity, stable porosity, and increased surface area. This study offers a background overview, encompassing a concise discussion of the current issue of excessive carbon emissions, and a synopsis of the materials most frequently used for CO2 collection. This review provides a detailed overview of COF materials, particularly emphasizing their synthesis methods and applications in carbon capture. It presents the latest research findings on COFs synthesized using various covalent bond formation techniques. Moreover, it discusses emerging trends and future prospects in this particular field.

Synthesis of Sulfonyl Two-Dimensional Covalent Organic Frameworks for Supercapacitor Applications

Covalent organic frameworks (COFs) are attracting more attention for energy storage applications. COFs possess unique structural properties, such as highly ordered pore structures, abundant functionalization sites, and tunable chemical properties, making them ideal candidates for the development of novel energy storage materials. In this work, we synthesized sulfonyl two-dimensional (2D) covalent organic frameworks (SLD-COFs) using 4,4'-sulfonyldiphenylamine (SLD). SLD-COFs have a remarkable conjugated structure, which includes imine groups forming large π-bonds, and the conjugated structure can provide consecutive electron conduction paths, which enables SLD-COF to transfer charges more efficiently, thus improving the electrical conductivity. Additionally, the sulfonyl groups introduce redox-active sites, which participate in the redox process during electrochemical reactions and generate a pseudocapacitive effect. For a current of 0.5 A/g, the specific capacitance of the SLD-COF material was 31.5 F/g in an acidic electrolyte and 41.7 F/g in an alkaline electrolyte. The structural flexibility and good electrochemical properties of the COFs make them a potentially essential component of energy storage applications. Meanwhile, the capacitance retention of SLD-COFs reaches 78.3% after 1000 GCD cycles at a current density of 1 A/g, which indicates its good cycling stability.

Designed Synthesis of Covalent Organic Multicycles

Covalent organic multicycles (COMs) have been designed and synthesized via the covalent assembly of rigid three-arm Y-shaped and U-shaped building blocks. These COMs have a precise tricyclic structure and exhibit remarkable solubility in a range of common solvents. Featuring well-defined cavities with electron-rich structures, these COMs displayed good adsorption capabilities for iodine in both its vapor and liquid states. Moreover, the solution processability allows for the facile fabrication of these COMs as uniform films on different substrates via the spin coating methods.

Highly Efficient Chiral Separation Based on Alkali-proof Protein Immobilization by Covalent Organic Frameworks

Chiral separation plays a pivotal role in both practical applications and industrial productions. However, traditional chiral stationary phases (CSPs) exhibit inherent instability in alkaline environments, presenting a significant challenge despite their importance. Herein, basophilic alcalase is creatively developed to fabricate ultrastable protein-based CSPs that can efficiently work under alkaline conditions. An in-depth theoretical simulation is conducted to unveil the unique three-dimensional conformation of alcalase, showing selective affinity towards various enantiomers of chiral amino acids and drugs, especially acidic substrates. Subsequently, an in situ assembly strategy is used to immobilize alcalase within a hydrazone-linked covalent organic framework (COF) platform. The generated protein-based CSPs enable successful baseline separation (Rs≥1.50) for various value-added compounds (e.g., non-steroidal drug, RS-flurbiprofen; nucleotide analog, RS-tenofovir) via high-performance liquid chromatography, surpassing the commercial chiral column. Furthermore, a systematic study reveals that increasing hydrophilicity and pore sizes of COFs can enhance the separation performance. Remarkably, the obtained CSPs demonstrated exceptional durability, maintaining performance for >2,400 runs. This study provides a new member to the protein library for CSPs, and represents an innovative and effective platform for CSPs with immense potential for the enantioseparation of acidic drugs.

Highly Enantioselective Transportation Across Liquid Membranes Mediated by Porous Covalent Organic Frameworks

Chiral liquid membrane separation is crucial in pharmaceuticals and chemical synthesis for its simplicity and stability, yet designing membrane carriers that enable efficient enantioseparation remains a challenge. Here, we demonstrated for the first time that chiral porous materials can act as mobile carriers of bulk liquid membranes (BLMs) to enhance enantioselective transport and separation. We design and prepare three 2D chiral covalent organic frameworks (CCOFs) by imine condensations of a chiral dialdehyde with triamines containing ethyl, fluorine and/or isopropyl groups. These isostructural CCOFs feature ABC stacking, excellent water, acid and base tolerance, and chiral amine groups in 1D porous channels, promoting efficient enantioselective transportation of amino acid enantiomers. Among them, the CCOF with both -F and -iPr groups showing superior transport performance. Exfoliating the CCOF into chiral nanosheets creates flexible layers with accessible active sites, enabling nanosheet-mediated liquid membranes to separate chiral drug enantiomers, a feat unattainable with the pristine CCOF. This work establishes CCOFs as a promising platform for chiral BLM separations and will guide the design of high-performance BLMs using porous materials for enantioselective separation.

Molecular-Squeeze Triggers Guest Desorption from Sponge-Like Macrocycle Crystals

Desorption in conventional porous sorbents often employ external forces including inert gas blowing, heating, vacuum treatment to trigger guest release. We here report an unprecedented molecular-squeeze triggered guest release behavior from sponge-like macrocycle crystals. The crystals function as typical sponge to include guest molecules within their microscopic voids that are adaptively formed, thus acting as adsorbents for toluene/pyridine separations. Intriguingly, vaporized ethyl acetate (EA) molecules trigger the guest release from the crystals without entering the pores or voids of the crystals to replace the guests. Instead, they work as external forces applied directly onto the crystals themselves, ''squeezing" the materials to close the voids through supramolecular interactions between EA and macrocycles on the crystal surface and release the guest molecules. Various experimental techniques as well as molecular dynamics simulations reveal the mechanism of the molecular-squeeze induced guest release procedure. The EA-regenerated crystals can be recycled multiple times without the loss of separation performance. Compared with conventional guest release procedure, this method is manipulated in a mild condition, showing the potential in saving cost and energy.

Construction and Band Gap-Regulation of Ordered Macro-Microporous Single Crystals of an Amine-Linked Covalent Organic Framework

Heterogeneity engineering provides an effective route to manipulate the chemical and physical properties of covalent organic frameworks (COFs) but is still under development for their single-crystal form. Here, we report the strategy based on a combination of the template-assisted modulated synthesis with a one-pot crystallization-reduction method to directly construct ordered macro-microporous single crystals of an amine-linked three-dimensional (3D) COF (OM-COF-300-SR). In this strategy, the colloidal crystal-templating synthesis not only assists the formation of ordered macropores but also greatly facilitates the in situ conversion of linkages (from imine to amine) in the COF-300 single crystals. The as-synthesized OM-COF-300-SR120 exhibits a reversible symmetry change from a tetragonal I41/a to monoclinic I2/c space group after activation, which was not observed previously. On the other hand, this strategy allows for a flexible control over the degree of amination (from 0 to 100%, as determined by X-ray photoelectron spectroscopy (XPS) analysis) in COF-300 crystals to regulate their band gap (from 2.57 to 2.81 eV) for the optimization of photocatalytic activity. The high degree of amination and the embedded ordered macropores render OM-COF-300-SR120 with superior photocatalytic activity (with a reaction rate constant of 0.9572 min-1) to its nonmacroporous counterpart (NM-COF-300-SR120, 0.2303 min-1) for the degradation of rhodamine B. In addition, the significant contribution of ordered macropores to confront mass transfer resistance in COF single crystals was also confirmed by the much higher catalytic activity of Au/OM-COF-300-SR120 (with an activity parameter of 7.96 × 103 s-1 mol-1) as compared with Au/NM-COF-300-SR120 (1.43 × 103 s-1 mol-1) in the model reduction reaction of 4-nitrophenol by NaBH4.

Induced Charge-Compensation Effect for Boosting Photocatalytic Water Splitting in Covalent Organic Frameworks

Imine-based covalent organic frameworks (COFs) are promising for photocatalytic water splitting, but their performance is often constrained by inefficient charge separation due to the high electron localization nature of polar imine bonds. In this study, we have optimized the electron delocalization across the imine linkage within a COF by implementing a charge compensation effect. This effect is achieved when a strong electron-donating thieno[3,2-b]thiophene linker is directly attached to the iminic carbon of a zinc-porphyrinic COF. This modification significantly reduces the electron binding effect within the imine bonds of the COF, facilitating both in-plane charge separation and out-plane charge transfer to the catalytic site. Conversely, the use of strong electron-withdrawing pyrizine linker aggravates the electron localization at the imine linkage in the ZnP-Pz variant. Consequently, ZnP-Tt shows a substantially improved photocatalytic water-splitting activity under visible light irradiation, with a hydrogen evolution of 44288±2280 μmol g-1 in 4 h, which exceeds the ZnP-Pz counterpart by a factor of 10. These results offer fresh perspectives for the design of imine-based COFs to overcome their limitations in charge separation efficiency.