Applications Of Covalent Organic Frameworks Research Articles

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

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

Europium chelate-anionic exchange functionalized covalent organic frameworks for the sensing of aristolochic acid a in humans and sulfamethoxazole/trimethoprim in surface water

The application of covalent organic frameworks (COFs) in fluorescence detection is of great interest. Herein, we have synthesized the ionic covalent organic framework TGH+·PD: Eu(TTA)4 with the characteristic emission of lanthanides by a straightforward ion-exchange method. This is the first time that aristolochic acid A (AA), a key biomarker for absorption and metabolism in the body for early diagnosis of diseases, has been detected by using COF as a fluorescent probe, which exhibits a good linear correlation with the AA concentration over a range from 5.0 to 1000 μM with a detection limit of 0.0808 μM. In addition, the selective response to sulfamethoxazole (SMZ)/trimethoprim (TMP) is achieved by varying the excitation wavelength with detection lines of 30.2 nM and 2.898 μM, respectively. It is worth mentioning that BNPP has been developed for the accurate determination of SMZ in uncertain samples. In a word, the prepared TGH+·PD: Eu(TTA)4-based sensor can be used for the quantitative detection of AA and SMZ/TMP, separately, effectively extending the application of COFs in the field of fluorescence sensing.

Recent Progress of Covalent Organic Frameworks Applied in Electrochemical Sensors.

As an emerging porous crystalline organic material, the covalent organic frameworks (COFs) are given more and more attention in many fields, such as gas storage and separation, catalysis, energy storage and conversion, luminescent devices, drug delivery, pollutant adsorption and removal, analysis and detection due to their special advantages of high crystallinity, flexible designability, controllable porosities and topologies, intrinsic chemical and thermal stability. In recent years, the COFs are applied in analytical chemistry, for instance, chromatography, solid-phase microextraction, luminescent and colorimetric sensing, surface-enhanced Raman scattering and electroanalytical chemistry. The COFs decorated electrodes show high performance for detecting trace substances with remarkable selectivity and sensitivity, such as heavy metal ions, glucose, hydrogen peroxide, drugs, antibiotics, explosives, phenolic compounds, pesticides, disease metabolites and so on. This review mainly summarized the application of COF based electrochemical sensor according to different target analytes.

Synthesis, characterization, and hydrazine sensing property of two covalent organic frameworks

AbstractSensitive and efficient detection of hydrazine is of great significance because hydrazine is a highly toxic organic molecule, which can pose great threats to human health. Herein, two covalent organic frameworks (COFs) modified with ester groups in the pores, TAPB‐DHE and TAPT‐DHE, have been successfully synthesized via esterification reaction. Both of the two COFs have good crystallinity, thermal stability, and fluorescence properties. TAPB‐DHE can be used as a turn‐on fluorescence sensor for the sensitive detection of trace hydrazine in aqueous solution with a detection limit of 0.40 μM and a wide linear range of 0–100 μM due to the fluorescence enhancement of TAPB‐DHE caused by the chemical reaction between hydrazine and TAPB‐DHE, in which the ester group of the COF is converted into hydroxyl group, leading to the restriction of the intramolecular charge transfer (ICT) effect. This work provides a reference for the design of COFs with hydrazine recognition function and a helpful expansion for the practical application of COFs.

Guest Molecular Assembly Strategy in Covalent Organic Frameworks for Electrochemiluminescence Sensing of Uranyl

The application of covalent organic frameworks (COFs) in electrochemiluminescence (ECL) is promising in environmental monitoring. Developing an emerging design strategy to expand the class of COF-based ECL luminophores is highly desirable. Here, a COF-based host-guest system was constructed through guest molecular assembly to deal with nuclear contamination analysis. The efficient charge transport network was formed by inserting an electron-withdrawing guest tetracyanoquinodimethane (TCNQ) into the open space of the COF host (TP-TBDA; TP = 2,4,6-trihydroxy-1,3,5-benzenetricarbaldehyde and TBDA = 2,5-di(thiophen-2-yl)benzene-1,4-diamine) with an electron-donating property; the construction of the COF-based host-guest system (TP-TBDA@TCNQ) triggered the ECL emission of non-emitting TP-TBDA. Furthermore, the dense active sites in TP-TBDA were utilized to capture the target substance UO22+. The presence of UO22+ broke the charge-transfer effect in TP-TBDA@TCNQ, resulting in the weakening of the ECL signal, thus the established ECL system integrating the low detection limit with high selectivity monitors UO22+. This COF-based host-guest system provides a novel material platform for constructing late-model ECL luminophores and creates an opportunity for the vigorous ECL technology.

Piezochromism in Dynamic Three-Dimensional Covalent Organic Frameworks.

Piezochromic materials with pressure-dependent photoluminescence tuning properties are important in many fields, such as mechanical sensors, security papers, and storage devices. Covalent organic frameworks (COFs), as an emerging class of crystalline porous materials (CPMs) with structural dynamics and tunable photophysical properties, are suitable for designing piezochromic materials, but there are few related studies. Herein, we report two dynamic three-dimensional COFs based on aggregation-induced emission (AIE) or aggregation-caused quenching (ACQ) chromophores, termed JUC-635 and JUC-636 (JUC = Jilin University China), and for the first time, study their piezochromic behavior by diamond anvil cell technique. Due to the various luminescent groups, JUC-635 has completely different solvatochromism and molecular aggregation behavior in the solvents. More importantly, JUC-635 with AIE effect exhibits a sustained fluorescence upon pressure increase (~3 GPa), and reversible sensitivity with high-contrast emission differences (Δλem = 187 nm) up to 12 GPa, superior to other CPMs reported so far. Therefore, this study will open a new gate to expand the potential applications of COFs as exceptional piezochromic materials in pressure sensing, barcoding, and signal switching.

Piezochromism in Dynamic Three‐Dimensional Covalent Organic Frameworks

AbstractPiezochromic materials with pressure‐dependent photoluminescence tuning properties are important in many fields, such as mechanical sensors, security papers, and storage devices. Covalent organic frameworks (COFs), as an emerging class of crystalline porous materials (CPMs) with structural dynamics and tunable photophysical properties, are suitable for designing piezochromic materials, but there are few related studies. Herein, we report two dynamic three‐dimensional COFs based on aggregation‐induced emission (AIE) or aggregation‐caused quenching (ACQ) chromophores, termed JUC‐635 and JUC‐636 (JUC=Jilin University China), and for the first time, study their piezochromic behavior by diamond anvil cell technique. Due to the various luminescent groups, JUC‐635 has completely different solvatochromism and molecular aggregation behavior in the solvents. More importantly, JUC‐635 with AIE effect exhibits a sustained fluorescence upon pressure increase (≈3 GPa), and reversible sensitivity with high‐contrast emission differences (Δλem=187 nm) up to 12 GPa, superior to other CPMs reported so far. Therefore, this study will open a new gate to expand the potential applications of COFs as exceptional piezochromic materials in pressure sensing, barcoding, and signal switching.

Efficient selective removal of uremic toxin precursor by olefin-linked covalent organic frameworks for nephropathy treatment

Indoxyl sulfate is a protein-bound uremic toxin synthesized from indole that cannot be efficiently removed by the hemodialysis method and thus becomes a key risk factor for the progression of chronic kidney disease. Here, we develop a non-dialysis treatment strategy to fabricate an ultramicroporous olefin-linked covalent organic framework with high crystallinity in a green and scalable fashion for selectively removing the indoxyl sulfate precursor (i.e., indole) from the intestine. Various analyses show that the resulting material exhibits excellent gastrointestinal fluid stability, high adsorption efficiency, and good biocompatibility. Notably, it realizes the efficient and selective removal of indole from the intestine and significantly attenuates serum indoxyl sulfate level in vivo. More importantly, the selective removal efficacy of indole is substantially higher than that of the commercial adsorbent AST-120 used in the clinic. The present study opens up a new avenue to eliminate indoxyl sulfate by a non-dialysis strategy and further expands the in vivo applications of covalent organic frameworks.

Synthesis of size-controllable urchin-like covalent organic frameworks for adsorption of nitrophenols

The adsorption of nitrophenols by covalent organic frameworks (COFs) has gained increasing attention, due to their feasible designability, which could provide abundant open active sites for their binding to nitrophenols. Herein, we developed a novel method to synthesize uniform urchin-like COFs (TTA-DVA-COF) with tunable sizes using a temperature-controlling method at atmospheric pressure. The size of the TTA-DVA-COF can be tuned and controlled gradually from 0.95 μm to 2.85 μm as the synthesis temperature decreases from 80 °C to 20 °C. By using the principle that the interlaced benzene rings, imine bonds (C=N) and triazine structures of TTA-DVA-COF can capture free nitrophenols through hydrogen bonding and conjugation interaction, the COFs can be used as an efficient adsorbent for adsorption and removal of nitrophenols, especially,o-nitrophenol. The research provides a new strategy for the controllable synthesis of uniform COFs and extends the application of COFs as efficient adsorbents for the removal of nitrophenols.

Post-synthetic thiol modification of covalent organic frameworks for mercury(II) removal from water.

Various materials have been developed for environmental remediation of mercury ion pollution. Among these materials, covalent organic frameworks (COFs) can efficiently adsorb Hg(II) from water. Herein, two thiol-modified COFs (COF-S-SH and COF-OH-SH) were prepared, through the reaction between 2,5-divinylterephthalaldehyde and 1,3,5-tris-(4-aminophenyl)benzene, followed by post-synthetic modification using bis(2-mercaptoethyl) sulfide and dithiothreitol, respectively. The modified COFs showed excellent Hg(II) adsorption abilities with maximum adsorption capacities of 586.3 and 535.5mgg-1 for COF-S-SH and COF-OH-SH, respectively. The prepared materials showed excellent selective absorbability for Hg(II) against multiple cationic metals in water. Unexpectedly, the experimental data showed that both co-existing toxic anionic diclofenac sodium (DCF) and Hg(II) performed positive effect for capturing another pollutant by these two modified COFs. Thus, a synergistic adsorption mechanism between Hg(II) and DCF on COFs was proposed. Moreover, density functional theory calculations revealed that synergistic adsorption occurred between Hg(II) and DCF, which resulted in a significant reduction in the adsorption system's energy. This work highlights a new direction for application of COFs to simultaneous removal of heavy metals and co-existing organic pollutants from water.

Application of Covalent Organic Frameworks (COFs) as Dyes and Additives for Dye-Sensitized Solar Cells (DSSCs).

Five Covalent Organic Frameworks (COFs) were synthesized and applied to Dye-Sensitized Solar Cells (DSSCs) as dyes and additives. These porous nanomaterials are based on cheap, abundant commercially available ionic dyes (thionin acetate RIO-43, Bismarck brown Y RIO-55 and pararosaniline hydrochloride RIO-70), and antibiotics (dapsone RIO-60) are used as building blocks. The reticular innovative organic framework RIO-60 is the most promising dye for DSSCs. It possesses a short-circuit current density (Jsc) of 1.00 mA/cm2, an open-circuit voltage (Voc) of 329 mV, a fill factor (FF) of 0.59, and a cell efficiency (η) of 0.19%. These values are higher than those previously reported for COFs in similar devices. This first approach using the RIO family provides a good perspective on its application in DSSCs as a dye or photoanode dye enhancer, helping to increase the cell's lifespan.

High efficient removal of U(VI) by covalent organic frameworks fabricated by mechanochemical method: Adsorption process, mechanism and surface complexation modeling

Herein, covalent organic frameworks (i.e., TpBD) were fabricated by mechanical delamination of 1, 3, 5-triformylphloroglucinol (Tp) and benzidine (BD) using NaHCO3 as foaming agent. The batch characterizations revealed that flower-like TpBD nanosheets exhibited the large porosity, high BET specific area (139 m2/g), small pore size (∼ 14 Å), remarkable stability and keto form. The adsorption process of U(VI) removal by TpBD displayed the fast sorption rate (equilibrium within 0.5 h), high adsorption capacity (167 mg/g) and good re-usability (no significant difference after five cycles). According to analysis of X-ray photoelectron spectroscopy (XPS) and surface complexation modeling, the removal mechanism of U(VI) by TpBD was chemisorption and inner-sphere surface complexation. These findings are of great importance for the application of covalent organic frameworks fabricated with rapid and easy-to-operate mechanochemical method in actual environmental cleanup.

A Fluorinated Covalent Organic Framework with Accelerated Oxygen Transfer Nanochannels for High-Performance Zinc-Air Batteries.

The establishment of abundant three-phase interfaces with accelerated mass transfer in air cathodes is highly desirable for the development of high-rate and long-cycling rechargeablezinc-air batteries (ZABs). Covalent organic frameworks (COFs) exhibit tailored nanopore structures, facilitating the rational tuning of their specific properties. Here, by finely tuning the fluorinated nanopores of a COF, a novel air cathode for rechargeable ZABs is unprecedentedly designed and synthesized. COFnanosheets are decorated with fluorinated alkyl chains, which shows high affinity to oxygen (O2 ), in its nanopores (fluorinated COF). The fluorinated COFnanosheets are stacked into well-defined O2 -transport channels, which are then assembled into aerophilic "nano-islands" on the hydrophilic FeNi layered-double-hydroxide (FeNi LDH) electrocatalyst surface. Therefore, the mass-transport "highway" for O2 and water is segregated on the nanoscale, which significantly enlarges the area of three-phase boundaries and greatly promotes the mass-transfer therein. ZABs based on the COF-modified air cathode deliver a small charge/discharge voltage gap (0.64V at 5mAcm-2 ), a peak power density (118mWcm-2 ), and a stable cyclability. This work provides a feasible approach for the design of the air cathodes for high-performance ZABs, and will expand the new application of COFs.

High sensitivity for detecting trace Sn2+ in canned food using novel covalent organic frameworks

Tin (Sn) element plays a vital role in the human body, and its detection is a mandatory inspection item for canned food. The application of covalent organic frameworks (COFs) in fluorescence detection has received extensive attentions. In this work, we designed a kind of novel COFs (COF-ETTA-DMTA) with high specific surface area (353.13 m2/g) by solvothermal synthesis using 2,5-dimethoxy-1,4-dialdehyde and tetra (4-aminophenyl) ethylene as precursors. It shows fast response time (about 50 s), low detection limit (228 nM) and good linearity (R2 = 0.9968) for the detection of Sn2+. Via coordination behavior, the recognition mechanism of COFs toward Sn2+ was simulated and verified by the small molecule with the same functional unit. More importantly, this COFs was successfully applied to identify Sn2+ in solid canned food (luncheon pork, canned fish, canned red kidney beans) with satisfactory results. This work provides a new approach for determining metal ions with COFs taking the advantage of their natural rich reaction set and specific surface area, improving the detection sensitivity and capacity.

2D Covalent Organic Frameworks Based on Heteroacene Units.

Covalent organic frameworks (COFs) are a unique new class of porous materials that arrange building units into periodic ordered frameworks through strong covalent bonds. Accompanied with structural rigidity and well-defined geometry, heteroacene-based COFs have natural advantages in constructing COFs with high stability and crystallinity. Heteroacene-based COFs usually have high physical and chemical properties, and their extended π-conjugation also leads to relatively low energy gap, effectively promoting π-electron delocalization between network units. Owing to excellent electron-withdrawing or -donating ability, heteroacene units have incomparable advantages in the preparation of donor-acceptor type COFs. Therefore, the physicochemical robust and fully conjugated heteroacene-based COFs solve the problem of traditional COFs lacking π-π interaction and chemical stability. In recent years, significant breakthroughs are made in this field, the choice of various linking modes and building blocks has fundamentally ensured the final applications of COFs. It is of great significance to summarize the heteroacene-based COFs for improving its complexity and controllability. This review first introduces the linkages in heteroacene-based COFs, including reversible and irreversible linkages. Subsequently, some representative building blocks are summarized, and their related applications are especially emphasized. Finally, conclusion and perspectives for future research on heteroacene-based COFs are presented.

Covalent organic frameworks

The dream to prepare well-defined materials drives the methodological evolution for molecular synthesis, structural control and materials manufacturing. Among various methods, chemical approaches to design, synthesize, control and engineer small molecules, polymers and networks offer the fundamental strategies. Merging covalent bonds and non-covalent interactions into one method to establish a complex structural composition for specific functions, mimicking biological systems such as DNA, RNA and proteins, is at the centre of chemistry and materials science. Covalent organic frameworks (COFs) are a class of crystalline porous polymers that enable the integration of organic units into highly ordered structures via polymerization. This polymerization system is unique as it deploys covalent bonds to construct the primary order structures of polymeric backbones via polycondensation and leverages on non-covalent interactions to create the high order structures of polymeric networks via supramolecular polymerization in a one-pot reaction system. This Primer covers all aspects of the field of COFs from chemistry to physics, materials and applications, and outlines the design principle, experimental methods, characterization and applications, with an aim to show a concise yet full picture of the field. The key fundamental issues to be addressed are analysed with an outlook on the future major directions from different perspectives. Covalent organic frameworks (COFs) are a class of crystalline porous polymers consisting of highly ordered organic structures formed by polymerization. In this Primer, Tan et al. discuss the design principle, experimental methods, characterization and applications of COFs.

Covalent Organic Frameworks (COFs) as Multi-Target Multifunctional Frameworks.

Covalent organic frameworks (COFs), synthesized from organic monomers, are porous crystalline polymers. Monomers get attached through strong covalent bonds to form 2D and 3D structures. The adjustable pore size, high stability (chemical and thermal), and metal-free nature of COFs make their applications wider. This review article briefly elaborates the synthesis, types, and applications (catalysis, environmental Remediation, sensors) of COFs. Furthermore, the applications of COFs as biomaterials are comprehensively discussed. There are several reported COFs having good results in anti-cancer and anti-bacterial treatments. At the end, some newly reported COFs having anti-viral and wound healing properties are also discussed.

Covalent organic frameworks for next-generation of lithium-ion batteries

The demand to develop lithium-ion batteries (LIBs) is growing as their consumption in various applications rises. In this regard, it is very important to pay attention to materials with suitable properties for use in LIBs. The energy storage capacity, cycle life, weight, and recycling of aging batteries are expected to improve with these materials. Recently, covalent organic frameworks (COFs) have shown great promise for use in cathode, anode, electrolyte, and separators of LIBs due to their numerous properties, including porosity and excellent physical and chemical stability. This review discusses the application of COFs in the next-generation of LIBs. First of all, the Main components, working principles, and characteristics of LIBs are described. After that, the advantages, applications, and synthesis methods of COFs are discussed. Finally, the application of COFs in various parts of LIBs by key features and the associated challenges is highlighted. In this review, we focus on improving batteries by introducing and developing COFs as a new-generation of materials for energy storage applications to overcome the current limitations and provide promising alternatives for current LIBs.

Design, synthesis, and application of covalent organic frameworks as catalysts

Unique properties make COFs suitable for catalytic activities. There are several approaches to synthesizing COFs. This review highlights the latest applications of COFs as catalysts with an emphasis on synthetic approaches.

Covalent organic framework-MnO2 nanoparticle composites for shape-selective sensing of bithiols.

Covalent organic frameworks (COFs) for detecting biological macromolecules in water or biological environments are generally challenging. In this work, a composite material IEP-MnO2 is obtained by combining manganese dioxide (MnO2) nanocrystals and a fluorescent COF (IEP), which is synthesized by using 2,4,6-tris(4-aminophenyl)-s-triazine and 2,5-dimethoxyterephthalaldehyde. By the addition of biothiols, such as glutathione, cysteine or homocysteine with different sizes, the fluorescence emission spectra of IEP-MnO2 changed ("turn-on" or "turn-off") via different mechanisms. The fluorescence emission of IEP-MnO2 increased in the presence of GSH by the elimination of the FRET (Förster resonance energy transfer) effect between MnO2 and IEP. Surprisingly, due to the formation of a hydrogen bond between Cys/Hcy and IEP, the fluorescence quenching for IEP-MnO2 + Cys/Hcy may be explained via the photoelectron transfer (PET) process, which endows IEP-MnO2 with specificity in distinguishing the detection of GSH and Cys/Hcy compared to other MnO2 complex materials. Therefore, IEP-MnO2 was used to detect GSH and Cys in human whole blood and serum, respectively. The limit of detection for GSH in whole blood and Cys in human serum was calculated to be 25.58 μM and 4.43 μM, which indicates that IEP-MnO2 can be used to investigate some diseases related to GSH and Cys concentration. Moreover, the research expands the application of covalent organic frameworks in the fluorescence sensing field.