Growth Of Covalent Organic Frameworks Research Articles

Porphyrin COF and its mechanical pressing-prepared carbon fiber hybrid membrane for ratiometric detection, removal and enrichment of Cd2+

A nitrogen (N), oxygen (O)-rich porphyrin-based covalent organic framework (COF), in which interlayer porphyrin molecules are vertically stacked, is prepared and characterized. As-prepared N,O-rich TpTph COF shows a high adsorption capacity for Cd2+ due to the abundant coordination sites. More interesting, it is found that the formation of COF enlarges the porphyrin ring center space, thus facilitating the Cd2+coordination, and the resulting optical signal changes make the ratiometric detection of Cd2+ possible. Furthermore, using carbon fiber (CF) filaments, which are obtained from low cost and easy-to-obtain actived carbon mask, as support, porphyrin COF-based CF@TpTph membrane is prepared through in-situ growth of COF on the support followed by simple mechanical pressing. The CF@TpTph membrane is demonstrated to work well for both Cd2+ removal and enrichment from soil and water samples, and shows the advantages of ease of handling, robust stability, reduced secondary pollution risk to samples, and good reusability. This work provides a powerful tool for Cd2+ removal and enrichment, exhibits that preparing porphyrin-based COFs is a feasible way to promote the interactions between porphyrin ring and Cd2+, and demonstrates that mechanical pressing is a promising strategy for the design of COF-based monolithic materials to promote the practical applications of COFs.

In Situ Growth of COF on PAN Nanofibers to Improve Proton Conductivity and Dimensional Stability in Proton Exchange Membranes

Perfluorosulfonic acid (PFSA) polymer is considered as a proton exchange membrane material with great potential. Nevertheless, excessive water absorption caused by abundant sulfonic acid groups makes PFSA have low dimensional stabilities. In order to improve the dimensional stability of PFSA membranes, nanofibers are introduced into PFSA membranes. However, because nanofibers lack proton conducting groups, it usually reduces the proton conductivities of PFSA membranes. It is a challenge to improve dimensional stabilities while maintaining high proton conductivities. Due to the structural designability, covalent organic frameworks (COFs) with proton conductive groups are chosen to improve the overall performance of PFSA membranes. Herein, COFs synthesized in situ on three-dimensional PAN nanofibers were introduced into PFSA to prepare PFSA@PAN/TpPa-SO3H sandwiched membranes. The PFSA@PAN/TpPa-SO3H-5 composite membrane exhibited outstanding proton conductivity, which reached 260.81 mS·cm−1 at 80 °C and 100% RH, and only decreased by 4.7% in 264 h. The power density of a single fuel cell with PFSA@PAN/TpPa-SO3H-5 was as high as 392.7 mW·cm−2. Compared with the pristine PFSA membrane, the conductivity of PFSA@PAN/TpPa-SO3H-5 increased by 70.0 mS·cm−1, and the area swelling ratio decreased by 8.1%. Our work provides a novel strategy to prepare continuous proton transport channels to simultaneously improve conductivities and dimensional stabilities of proton exchange membranes.

Rapid in-situ growth of covalent organic frameworks on hollow fiber substrates with Janus-like characteristics for efficient organic solvent nanofiltration

Chemically stable covalent organic frameworks (COFs) with uniform and tailorable channels fast in-situ grown on polymeric hollow fiber substrates were reported to efficiently separate organic solvents under a low transmembrane pressure. A tris(4-aminophenyl)amine (TAPA) aqueous solution and a benzene-1,3,5-tricarboxaldehyde (BTCA) organic solution were circulated along the shell and lumen sides of hollow fiber modules, respectively. An imine-based COF was synthesized on the cross-linked polyimide (cPI) substrates because TAPA reacted with BTCA at their interface. The synthesis of COF took place on the inner surface of substrates and also generated crystallites in the matrix, forming an interpenetrating Janus-like network combining the cPI polymer and microporous COFs. The interpenetrating polymer networks not only reinforces the self-mechanical properties of the hollow fiber membranes, but also creates Janus-like characteristics so that the membranes have dramatically enhanced solute retention and super-high permeability in polar and nonpolar solvents. In addition, compared to the traditional synthesis of COF membranes, it took less than 1/6 duration (i.e., 240 min) to fabricate the inner-selective COF composite hollow fiber membranes (HFMs). The optimal composite hollow fiber has a molecular weight cut-off (MWCO) of 784 g mol−1 in isopropanol. This study opens a new strategy to rapidly grow COFs on polymeric hollow fiber substrates and obtain Janus-like characteristics for efficient purification of various organic solvents.

Micro/Nano‐Scaled Covalent Organic Frameworks: Polymerization, Crystallization and Self‐Assembly

AbstractIn the past decade, considerable efforts have been extended on covalent organic frameworks (COFs), however, the basic research about the nucleation and crystal growth of COF materials has been greatly ignored. This review aims at providing an overview over the theoretical foundation and experimental observation of the multi‐scale structural engineering of COF materials, which includes complex polymerization, crystallization and self‐assembly processes. In this perspective, we first highlighted the latest advances on basic knowledge about the nucleation and growth of COFs, including classical and non‐classical crystallization mechanism as well as the synthesis of COF single crystals. Subsequently, we surveyed the effects of synthesis conditions, such as catalysts, monomer adding modes, heating methods, modulator and supramolecular interaction on the formation of COF materials. In the last, the research on the synthesis of COF nanoparticles, nanofibers and nanosheets based on the knowledge of crystal growth are reviewed in detail. The understanding related to the polymerization, crystallization and self‐assembly process during COF formation will surely make it easier to realize COFs with designed hierarchical architectures for targeted applications.

Efficient extraction of trace organochlorine pesticides from environmental samples by a polyacrylonitrile electrospun nanofiber membrane modified with covalent organic framework

Detecting and analyzing of the trace organochlorine pesticides (OCPs) in the real water has become a big challenge. In this work, a novel functional electrospun nanofiber membrane (PAN@COFs) was synthesized through the in situ growth of covalent organic frameworks (COFs) on a polyacrylonitrile electrospun nanofiber membranes under room temperature and used in the solid-phase micro-extraction (SPME) to enrich trace organochlorine pesticides (OCPs) in water. The resulted PAN@COFs composite consisted of numerous nanofibers coated ample porous COFs spheres (~ 500 nm) and owned stable crystal structure, abundant functional groups, good stability. In addition, the enrichment experiments clearly revealed that PAN@COFs exhibited rather outstanding performance on adsorbing the trace OCPs (as low as 10 ng L−1) with the enrichment of 482–2686 times. Besides, PAN@COFs displayed good reusability and could be reused 100 times. Notably, in the real water samples (sea water and river water), the high enrichment factors and recovery rates strongly confirmed the feasibility of PAN@COFs for detecting the trace OCPs. Furthermore, due to the synergy of π-π stacking interaction and hydrophobic interaction between the OCPs molecules and PAN@COFs, the OCPs could be efficiently adsorbed on PAN@COFs, even under the extremely low driving force.

Vapor-liquid interfacial polymerization of covalent organic framework membranes for efficient alcohol dehydration

Covalent organic frameworks (COFs) with well-ordered pore structures and versatile functionalities hold tremendous promise as membrane building blocks. The facile and controllable fabrication of COF membranes remains a critical challenge. Herein, we presented a one-step vapor-liquid interfacial polymerization (VLIP) method to in-situ fabricate COF membranes on substrates under mild conditions. This VLIP method features controllable COF growth at the vapor-liquid interface, acquiring COF membranes with tunable physicochemical structure. The time-dependent amorphous-to-crystalline COF growth improved the crystallinity of COF membranes, thus improving the molecular sieving property. The increased monomer concentration endowed COF membranes with higher hydrophilicity, intensifying the water sorption ability. The resultant COF membranes conferred numerous hydrophilic pathways for water-selective transport, exhibited a high and stable n-butanol dehydration performance with permeation flux of 8160 g m−2 h−1 and separation factor of 1023 over 14 days. This VLIP method may evolve into a generic platform technique to fabricate COF membranes for efficient molecular separation.

Porous graphene oxide functionalized by covalent organic framework for the application in adsorption and electrochemical: The effect of C-F bonds to structure

Hybrid composites based on porous graphene oxide (PGO) and covalent organic framework (COF) were fabricated via a simple solvothermal method. PGO was applied as a platform to load COF based on melamine and p-phthalaldehyde (o-phthalaldehyde, 4-fluorobenzaldehyde, 4-trifluoromehylbenzaldehyde). These composites not only fine-tuned the pore properties but made it easy control the growth of COF by the introduction of C-F bonds. Besides, the combination of COF and PGO possessed both pore structures of PGO and pore properties of COF. In addition to the high surface area, the adjustability of cation–π interaction between COF and PGO resulted in better stability and selective adsorption for analytes. The Brunauer Emmett Teller (BET) N2 adsorption-desorption analysis proved that four COF@PGO composites contained both microporous and mesoporous structures, and COFTFA@PGO had the largest specific surface area (up to 450 m2g−1). Moreover, the excellent selective adsorption capacity of the obtained materials was evaluated by static adsorption test, and COFTFA@PGO displayed the best selective adsorption capacitance for organic acids. (16.99 μg/mL for chlorogenic acid and and 17.17 μg/mL for caffeic acid). Electrochemical performance of the materials was evaluated by cyclic voltammetry (CV) measurements and electrochemical impedance spectroscopy (EIS), respectively. And composites showed better performance in the frequency range of 105-10 Hz. This method offers a potential strategy to fabricate PGO and COF@PGO composites.

Imparting multi-functionality to covalent organic framework nanoparticles by the dual-ligand assistant encapsulation strategy

The potential applications of covalent organic frameworks (COFs) can be further developed by encapsulating functional nanoparticles within the frameworks. However, the synthesis of monodispersed core@shell structured COF nanocomposites without agglomeration remains a significant challenge. Herein, we present a versatile dual-ligand assistant strategy for interfacial growth of COFs on the functional nanoparticles with abundant physicochemical properties. Regardless of the composition, geometry or surface properties of the core, the obtained core@shell structured nanocomposites with controllable shell-thickness are very uniform without agglomeration. The derived bowl-shape, yolk@shell, core@satellites@shell nanostructures can also be fabricated delicately. As a promising type of photosensitizer for photodynamic therapy (PDT), the porphyrin-based COFs were grown onto upconversion nanoparticles (UCNPs). With the assistance of the near-infrared (NIR) to visible optical property of UCNPs core and the intrinsic porosity of COF shell, the core@shell nanocomposites can be applied as a nanoplatform for NIR-activated PDT with deep tissue penetration and chemotherapeutic drug delivery.

Low Power, Low Temperature and Atmospheric Pressure Plasma-Induced Polymerization: Facile Synthesis and Crystal Regulation of Covalent Organic Frameworks.

Low temperature and atmospheric pressure plasma-induced polymerization was demonstrated as a fast and facile strategy for tailoring of packing phase of COF-1 as well as preparing diverse covalent organic frameworks (COFs) including both two-dimensional (2D) COFs and three-dimensional (3D) COFs. By regulating the solvents, the fast construction of well-ordered AB staggered COF-1 and AA eclipsed COF-1 was facilely realized in minutes. The plasma approach presented here led to the rapid preparation of eight classical 2D COFs, including boronate ester-linkage (COF-5, COF-8 and COF-10), azine-linkage (NUS-2), β-ketoenamine-linkage (TpPa, TPBD), imine-linkage (ILCOF-1, Py-COF), and 3D-COF-102 (boroxine linkage) in less than 1 hour. Different from conventional methods, the proposed methodology required much less time, lower power, no extra heating, inert-gas protection and pressure. The fast nucleation and growth of COFs with good crystallinity, morphology and thermal stability can be achieved under mild conditions.

Low Power, Low Temperature and Atmospheric Pressure Plasma‐Induced Polymerization: Facile Synthesis and Crystal Regulation of Covalent Organic Frameworks

AbstractLow temperature and atmospheric pressure plasma‐induced polymerization was demonstrated as a fast and facile strategy for tailoring of packing phase of COF‐1 as well as preparing diverse covalent organic frameworks (COFs) including both two‐dimensional (2D) COFs and three‐dimensional (3D) COFs. By regulating the solvents, the fast construction of well‐ordered AB staggered COF‐1 and AA eclipsed COF‐1 was facilely realized in minutes. The plasma approach presented here led to the rapid preparation of eight classical 2D COFs, including boronate ester‐linkage (COF‐5, COF‐8 and COF‐10), azine‐linkage (NUS‐2), β‐ketoenamine‐linkage (TpPa, TPBD), imine‐linkage (ILCOF‐1, Py‐COF), and 3D‐COF‐102 (boroxine linkage) in less than 1 hour. Different from conventional methods, the proposed methodology required much less time, lower power, no extra heating, inert‐gas protection and pressure. The fast nucleation and growth of COFs with good crystallinity, morphology and thermal stability can be achieved under mild conditions.

Room-temperature growth of covalent organic frameworks as the stationary phase for open-tubular capillary electrochromatography.

Covalent organic frameworks (COFs) are a class of porous materials with high surface area, high porosity, good stability and tunable structure that have been widely used in the separation area. In this work, we have proposed the in situ synthesis of a novel COF composed of 4,4',4''-(1,3,5-triazine-2,4,6-triyl)trianiline (Tz) and 1,4-dihydroxyterephthalaldehyde (Da) onto the capillary inner surface for electrochromatographic separation. Fourier transform infrared (FT-IR) spectroscopy, elemental analysis (EA) and scanning electron microscopy (SEM) have facilitated the characterization of the prepared capillary columns. The COF (TzDa) modified OT-CEC column exhibited satisfactory separation selectivity towards neutral compounds (such as chlorobenzenes and alkylbenzenes), acidic and basic compounds (such as phenols and anilines), food additives (vanillin and its analogues) and small biomolecules (such as amino acids and polypeptides). Furthermore, the TzDa modified capillary was quite stable and reproducible. The relative standard deviations for retention times of the test analytes (alkylbenzenes) were as follows: for intra-day (n = 3) runs (≤1.74%), inter-day (n = 3) runs (≤2.25%) and between columns (n = 3) (≤4.83%). This new type of COF-based stationary phase has tremendous potential in separation science.

Nature‐Inspired Construction of MOF@COF Nanozyme with Active Sites in Tailored Microenvironment and Pseudopodia‐Like Surface for Enhanced Bacterial Inhibition

AbstractMetal–organic frameworks (MOFs) have sparked increasing interest in mimicking the structure and function of natural enzymes. However, their catalytic and therapeutic efficiency are unsatisfactory due to the relatively lower catalytic activity. Herein, inspired by nature, a MOF@COF nanozyme has been designed as a high‐efficiency peroxidase mimic, with the metallic nodes of MOFs as active centres, the hierarchical nanocavities produced by the growth of covalent organic frameworks (COFs) as binding pockets to form tailored pore microenvironment around active sites for enriching and activating substrate molecules, to perform enhanced bacterial inhibition. Furthermore, the pseudopodia‐like surface of the COFs “skin” enabled the system to catch the bacteria effectively for further amplifying the therapeutic efficiency of MOF‐based nanozyme. We believe that the present study will not only facilitate the design of novel nanozymes, but also broaden the biological usage of MOF/COF‐based hybrid materials.

Nature-Inspired Construction of MOF@COF Nanozyme with Active Sites in Tailored Microenvironment and Pseudopodia-Like Surface for Enhanced Bacterial Inhibition.

Metal-organic frameworks (MOFs) have sparked increasing interest in mimicking the structure and function of natural enzymes. However, their catalytic and therapeutic efficiency are unsatisfactory due to the relatively lower catalytic activity. Herein, inspired by nature, a MOF@COF nanozyme has been designed as a high-efficiency peroxidase mimic, with the metallic nodes of MOFs as active centres, the hierarchical nanocavities produced by the growth of covalent organic frameworks (COFs) as binding pockets to form tailored pore microenvironment around active sites for enriching and activating substrate molecules, to perform enhanced bacterial inhibition. Furthermore, the pseudopodia-like surface of the COFs "skin" enabled the system to catch the bacteria effectively for further amplifying the therapeutic efficiency of MOF-based nanozyme. We believe that the present study will not only facilitate the design of novel nanozymes, but also broaden the biological usage of MOF/COF-based hybrid materials.

Non-Interpenetrated Single-Crystal Covalent Organic Frameworks.

Growth of covalent organic frameworks (COFs) as single crystals is extremely challenging. Inaccessibility of open-structured single-crystal COFs prevents the exploration of structure-oriented applications. Herein we report for the first time a non-interpenetrated single-crystal COF, LZU-306, which possesses the open structure constructed exclusively via covalent assembly. With a high void volume of 80 %, LZU-306 was applied to investigate the intrinsic dynamics of reticulated tetraphenylethylene (TPE) as the individual aggregation-induced-emission moiety. Solid-state 2 H NMR investigation has determined that the rotation of benzene rings in TPE, being the freest among the reported cases, is as fast as 1.0×104 Hz at 203 K to 1.5×107 Hz at 293 K. This research not only explores a new paradigm for single-crystal growth of open frameworks, but also provides a unique matrix-isolation platform to reticulate functional moieties into a well-defined and isolated state.

Determination of Benzo[a]pyrene in Roast Meat by In Situ Growth of Covalent Organic Framework on Titanium Wire for Solid-Phase Microextraction Coupled with GC-FID

Benzo[a]pyrene (BaP) is a kind of trace pollutant commonly found in environment, food, and organism. It has been widely concerned because of its strong carcinogenicity to the human body. In this paper, covalent organic framework TpBD, in situ growth on titanium wire, was used as the coating of solid-phase microextraction (SPME) fiber and coupled with gas chromatography–flame ionization detector (GC-FID) for the detection of trace BaP in roast meat samples. The linear range of the developed method under the optimized experimental conditions was 0.02–15 μg L−1, the detection limit (S/N = 3) was 0.006 μg L−1, and the limit of quantification (S/N = 10) was 0.02 μg L−1. The intra-day and inter-day precision of a single fiber were 1.73% and 2.27%, respectively. The relative standard deviation (RSD) between fiber-to-fiber was investigated by three as-fabricated fibers was 6.09%. Moreover, the enrichment factor of the fabricated TpBD SPME fiber for BaP was 4914, and the fiber can withstand at least 150 cycles of adsorption and desorption without significantly decrease in extraction efficiency (< 3.6%). Finally, the developed method was successfully applied to the detection of BaP in roast meat samples with the recoveries from 95.4 to 108.5%.

Self-Controlled Growth of Covalent Organic Frameworks by Repolymerization

The growth of covalent organic frameworks (COFs) normally goes through a fast polymerization process, which quickly forms amorphous powder and then slowly crystallizes to obtain nanometer-sized cry...

Facile Removal of Phytochromes and Efficient Recovery of Pesticides Using Heteropore Covalent Organic Framework-Based Magnetic Nanospheres and Electrospun Films.

Nontargeted analysis of food safety requires selective removal of interference matrices and highly efficient recovery of chemical hazards. Porous materials such as covalent organic frameworks (COFs) show great promise in selective adsorption of matrix molecules via size selectivity. Considering the complexity of interference matrices, we prepared crystalline heteropore COFs whose two kinds of pores have comparable sizes to those of several common phytochromes, main interference matrices in vegetable sample analysis. By controlling the growth of COFs on the surface of Fe3O4 nanoparticles or by utilizing a facile co-electrospinning method, heteropore COF-based magnetic nanospheres or electrospun nanofiber films were prepared, respectively. Both the nanospheres and the films maintain the dual-pore structures of COFs and show good stability and excellent reusability. Via simple magnetic separation or immersion operation, respectively, they were successfully used for the complete removal of phytochromes and highly efficient recovery of 15 pesticides from the extracts of four vegetable samples, and the recoveries are in the range of 83.10-114.00 and 60.52-107.35%, respectively. Film-based immersion operation gives better sample pretreatment performance than the film-based filtration one. This work highlights the great application potentials of heteropore COFs in sample pretreatment for nontargeted analysis, thus opening up a new way to achieve high-performance sample preparation in many fields such as food safety analysis, environment monitoring, and so on.

Secondary growth of covalent organic frameworks (COFs) on porous substrates for fast desalination

Covalent organic frameworks (COFs) has emerged as a highly promising platform material for the manufacturing of molecule-separating membranes. However, COF membranes are predominantly used in the separation of dyes from water or organic solvents and there are very few reports on COF-enabled membranes for desalination. In this work, the secondary growth approach based on unidirectional diffusion synthesis is developed to grow continuous thin films of a COF with an intrinsic pore size of 0.8 nm on macroporous substrates to prepare COF membranes for desalination. The amino-modified polymer microfiltration substrate is fixed in a diffusion cell to separate the oil phase containing the aldehyde precursor (1,3,5-triformylphloroglucinol, Tp) and the aqueous phase containing both the amino precursor (hydrazine, Hz) and the catalyst. Because of the immiscible bi-phase solutions and the high molar ratio of Hz to Tp, the unidirectional diffusion of Hz molecules in the pore channel of the substrate is achieved and the polycondensation between the two precursors occurs at the phase interface. The unidirectional diffusion synthesis is sequentially performed for two times and the secondary growth is essential to ensure the formation of a defect-free, continuous thin film of COF (TpHz) on the top surface of the substrate. Cladding COF coatings are also formed along the skeleton in the near-surface region of the substrate. Such an asymmetric structure ensures both a good permselectivity and a strong adhesion between the grown COF layers and the substrates. The continuous COF thin film grown on the substrates serves as the selective layer, and the COF membrane prepared under the optimized condition exhibits an appreciable Na2SO4 rejection of 58.3% and a water permeance of 40.5 L∙m−2∙h−1∙MPa−1 which are ~ ten times higher than other membranes with similar rejections. This study not only demonstrates the potential of COFs in desalination but also showcases an efficient strategy to grow continuous thin films of COFs on porous substrates which are desired in diverse applications.

Application of GO/COF as a novel, efficient and recoverable catalyst in the Knoevenagel reaction

AbstractHybrid composite based on graphene oxide (GO) and covalent organic framework (COF) [GO/COF] was developed via a simple solvothermal method, at which GO was applied as a platform to load COF based on melamine and terephthaldehyde. The synthesized hybrid nanocomposite was characterized by FT‐IR, XRD, EDX and SEM techniques. Morphological analyses carried out by SEM confirm the successful growth of COF over GO. Then, the resultant composite was employed as an amazing and cost‐effective catalyst in the condensation of several aldehydes with malononitrile and produced the corresponding coupling products in high yields (up to 84%) at room temperature under solvent‐free conditions with an amount of catalyst, 15 mg in a very short reaction time of 10 min. The catalyst could be reused without a noteworthy drop in catalytic activity at least eight times. The use of GO/COF catalyst outcomes under mild reaction conditions in very short reaction time, exceptional catalytic activity, high recyclability and an easy work‐up process for the Knoevenagel condensation.

In situ growth of covalent organic framework on titanium fiber for headspace solid-phase microextraction of 11 phthalate esters in vegetables

Vegetables are easily contaminated by phthalate esters (PAEs) from the environment, agricultural films and fertilizers, affecting human health. In this paper, titanium dioxide (TiO2) nanotube arrays were prepared by electrochemical anodic oxidation on the surface of titanium wire. Covalent organic framework of TpBD was in situ bonded to the titanium wire via TiO2 nanotube arrays using monomers of 1,3,5-trimethylphloroglucinol (Tp) and benzidine (BD). The fabricated TpBD-TiO2 coated titanium wire was used as the solid-phase microextraction fiber to extract 11 PAEs in vegetable samples. Coupled with gas chromatography-tandem mass spectrometry (GC–MS/MS), the limits of detection for PAEs were from 0.001 (di-n-butyl phthalate) to 0.430 (butyl benzyl phthalate) μg/L (S/N = 3) and enrichment factors were between 226 (dimethyl phthalate) and 2154 (di-n-butyl phthalate). Our fabricated TpBD-TiO2 fiber can be used at least 150 times without significant loss of extraction efficiency (<4.8%). Quantitative determination of PAEs in vegetable samples (tomato, lettuce, cucumber) was achieved by standard addition.