Stable Covalent Organic Frameworks Research Articles

Boron removal by water molecules inside covalent organic framework (COF) multilayers

Removal of small neutral solutes (SNSs) by reverse osmosis membranes is crucial but challenging. Common consideration of narrowing pore sizes works very little as SNSs have close sizes to the one of water molecules. The most serious drawback of narrowing pore sizes is the reduction of permeance, which dramatically enhances the energy input per volume of permeate water. In this work, an alternative strategy of driving water molecules to reject SNSs is proposed. Using non-equilibrium molecular dynamics simulations, we reveal that inside the nanopores of TpTG multilayers, stable imine-linked covalent organic frameworks, water molecules will preferentially adsorb via the hydrogen bonding interaction. In that way, water molecules in TpTG multilayers other than TpTG themselves can completely reject SNSs, e.g. boric acid. The permeance of TpTG multilayers is excellent as the nanopores are fulfilled with fluidic water. The findings in this work will inspire researchers with an alternative way to design the membranes for SNS removal.

Are Highly Stable Covalent Organic Frameworks the Key to Universal Chiral Stationary Phases for Liquid and Gas Chromatographic Separations?

High-performance liquid chromatography (HPLC) and gas chromatography (GC) over chiral stationary phases (CSPs) represent the most popular and highly applicable technology in the field of chiral separation, but there are currently no CSPs that can be used for both liquid and gas chromatography simultaneously. We demonstrate here that two olefin-linked covalent organic frameworks (COFs) featuring chiral crown ether groups can be general CSPs for extensive separation not only in GC but also in normal-phase and reversed-phase HPLC. Both COFs have the same 2D layered porous structure but channels of different sizes and display high stability under different chemical environments including water, organic solvents, acids, and bases. Chiral crown ethers are periodically aligned within the COF channels, allowing for enantioselective recognition of guest molecules through intermolecular interactions. The COF-packed HPLC and GC columns show excellent complementarity and each affords high resolution, selectivity, and durability for the separation of a wide range of racemic compounds, including amino acids, esters, lactones, amides, alcohols, aldehydes, ketones, and drugs. The resolution performances are comparable to and the versatility is superior to those of the most widely used commercial chiral columns, showing promises for practical applications. This work thus advances COFs with high stability as potential universal CSPs for chromatography that are otherwise hard or impossible to produce.

Metal Nanoparticles@Covalent Organic Framework@Enzymes: A Universal Platform for Fabricating a Metal-Enzyme Integrated Nanocatalyst.

Cascade catalysis that combines chemical catalysis and biocatalysis has received extensive attention in recent years, especially the integration of metal nanoparticles (MNPs) with enzymes. However, the compatibility between MNPs and enzymes, and the stability of the integrated nanocatalyst should be improved to promote the application. Therefore, in this study, we proposed a strategy to space-separately co-immobilize MNPs and enzymes to the pores and surface of a highly stable covalent organic framework (COF), respectively. Typically, Pd NPs that were prepared by in situ reduction with triazinyl as the nucleation site were distributed in COF (Tz-Da), and organophosphorus hydrolase (OPH) was immobilized on the surface of Tz-Da by a covalent method to improve its stability. The obtained integrated nanocatalyst Pd@Tz-Da@OPH showed high catalytic efficiency and reusability in the cascade degradation of organophosphate nerve agents. Furthermore, the versatility of the preparation strategy of COF-based integrated nanocatalyst has been preliminarily expanded: (1) Pd NPs and OPH were immobilized in the triazinyl COF (TTB-DHBD) with different pore sizes for cascade degradation of organophosphate nerve agent and the particle size of MNPs can be regulated. (2) Pt NPs and glucose oxidase were immobilized in COF (Tz-Da) to obtain an integrated nanocatalyst for efficient colorimetric detection of phenol.

Frontispiece: Near‐Equilibrium Growth of Chemically Stable Covalent Organic Framework/Graphene Oxide Hybrid Materials for the Hydrogen Evolution Reaction

Covalent Organic Frameworks Near-equilibrium growth of chemically stable covalent organic framework–graphene oxide hybrid materials for the hydrogen evolution reaction is reported in the Communication by Jianyi Chen, Jichen Dong, Yunqi Liu et al. (e202113067).

Synthesis of phenol esters by direct C–H activation of aldehydes using a highly efficient and reusable copper-immobilized polyimide covalent organic framework (Cu@PI-COF)

In the present study, we report the design and fabrication of a thermally and chemically stable copper-based polyimide covalent organic framework (Cu@PI-COF) via a facile and straightforward synthetic approach for the oxidative esterification of aldehydes.

Low-temperature and gram-scale synthesis of chemically stable covalent organic frameworks in an aqueous medium

A facile and green scalable approach for production of chemically stable covalent organic frameworks (COFs) in aqueous medium at room temperature was reported by exploring an ionic liquid ([Bmim][N(CN)2) as the superior catalyst.

A Stable Covalent Organic Framework Cathode Enables Ultra-Long Cycle Life for Alkali and Multivalent Metal Rechargeable Batteries

A Stable Covalent Organic Framework Cathode Enables Ultra-Long Cycle Life for Alkali and Multivalent Metal Rechargeable Batteries

Achieving a stable COF with the combination of “flat” and “twist” large-size rigid synthons for selective gas adsorption and separation

A new type of covalent organic framework (COF) was achieved using combination of structrally rigid and conformationally othorganal building blocks. The N-2-aryl-substituted triazole derivative (NAT-CHO) was prepared with co-planar conformation among the three aromatic rings as the “flat” building block. The 4,4′,4′′,4′′′-(ethene-1,1,2,2-tetrayl)tetraaniline) (ETTA) was applied as the “twist” building block. A 2D sheet of network was obtained through imine formation. The resulting NAT-COF gave excellent thermal and chemical stability, survived aqueous solutions from pH 5 to 13. With large-size building blocks, the porous framework NAT-COF gave efficient gas adsorption with excellent selectivity of C3 propane over C1 me-thane, suggesting its potential application for selective gas capture and separation.

Near-Equilibrium Growth of Chemically Stable Covalent Organic Framework/Graphene Oxide Hybrid Materials for the Hydrogen Evolution Reaction.

Facile synthesis and post-processing of covalent organic frameworks (COFs) under mild synthetic conditions are highly sought after and important for widespread utilizations in catalysis and energy storage. Here we report the synthesis of the chemically stable aza-fused COFs BPT-COF and PT-COF by a liquid-phase method. The process involves the spontaneous polycondensation of vicinal diamines and vicinal diketones, and is driven by the near-equilibrium growth of COF domains at a very low monomer concentration. The method permits in situ assembly of COFs and COF-GO hybrid materials and leads to the formation of a uniform conducting film on arbitrary substrates on vacuum filtration. When used as electrocatalysts, the as-prepared membranes show a fast hydrogen evolution reaction (HER) with a low overpotential (45 mV at 10 mA cm-2 ) and a small Tafel slope (53 mV dec-1 ), which are the best among metal-free catalysts. Our results may open a new route towards the preparation of highly π-conjugated COFs for multifunctional applications.

A novel covalent organic framework with multiple adsorption sites for removal of Hg2+ and sensitive detection of nitrofural

It is urgent to control serious drug pollution and heavy metal ion pollution. Covalent organic framework (COF) is becoming a promising material for the removal of heavy metal ion and adsorption of organic small molecule because of the designed functional sites, ordered pore channel, high specific surface area and abundant π electrons. Herein, 2,4,6-triformylphloroglucinol (TFP) and benzene-1,3,5-tricarbohydrazide (BTH) was used to design a stable yet efficient beta-ketoenamine COF (COFTFP-BTH) adsorbent, which would provide multiple adsorption sites of Hg2+ by dense acylhydrazine. The maximum adsorption capacity of COFTFP-BTH toward Hg2+ achieved 909 mg g−1, coinciding with Langmuir adsorption and pseudo-second-order adsorption kinetic model, with the h value as high as 71.43 mg g−1 min−1. COFTFP-BTH was also grown on NH2-carbon nanotubes (CNT) to form a novel COFTFP-BTH@NH2-CNT composite for sensitive detection of nitrofural (NF). The NF sensor based on COFTFP-BTH@NH2-CNT showed a low detection limit (3.2 nM) and a wide linear range (9.6 nM-100 μM). The excellent performances were also attributed to the ordered channels of COFTFP-BTH exposing more adsorption sites of Hg2+ and NF, as well as the good stability of beta-ketoenamine COFTFP-BTH.

Covalent Organic Framework Nanofilm-Based Laser Desorption/Ionization Mass Spectrometry for 5-Fluorouracil Analysis and Tissue Imaging.

Although matrix-assisted laser desorption/ionization mass spectrometry (MALDI-MS) has become a ubiquitous and effective tool for macromolecules, direct analysis of small molecules by MALDI-MS using conventional organic matrices poses a challenge. Herein, a large-area, uniform, and stable covalent organic framework (COF) nanofilm prepared directly on indium-tin oxide (ITO) glass was first introduced as a substrate for LDI-MS, which showed enhanced sensitivity, no background interference, and high reproducibility in the analysis of diverse small molecules. Taking into account all these merits, an attractive approach of COF nanofilm-based LDI-MS was developed to quantitatively evaluate the pharmacokinetics of 5-fluorouracil (5-FU) in mouse plasma. A good linear relationship (10-20,000 ng/mL) and a low limit of detection (LOD) for 5-FU (∼100 pg/mL) were achieved. In view of the fact that the COF nanofilm was uniform and without the requirement of additional matrix spraying, it was further extended for LDI-MS imaging (LDI-MSI) to visualize the spatial distribution of 5-FU in mouse liver at different interval times after intravenous and intragastric administrations. The results indicated that the decay of 5-FU in mouse liver obtained with the COF nanofilm-based LDI-MSI was consistent with the tendency of 5-FU pharmacokinetics. This work not only offers an alternative solution for LDI-MS/MSI analysis of small molecules but also extends the application fields of COF nanofilm in MS research.

A New Covalent Organic Framework of Dicyandiamide-Benzaldehyde Nanocatalytic Amplification SERS/RRS Aptamer Assay for Ultratrace Oxytetracycline with the Nanogold Indicator Reaction of Polyethylene Glycol 600.

In this paper, dicyandiamide (Dd) and p-benzaldehyde (Bd) were heated at 180 °C for 3 h to prepare a new type of stable covalent organic framework (COF) DdBd nanosol with high catalysis. It was characterized by molecular spectroscopy and electron microscopy. The study found that DdBd had a strong catalytic effect on the new indicator reaction of polyethylene glycol 600 (PEG600)-chloroauric acid to form gold nanoparticles (AuNPs). AuNPs have strong resonance Rayleigh scattering (RRS) activity, and in the presence of Victoria Blue B (VBB) molecular probes, they also have a strong surface-enhanced Raman scattering (SERS) effect. Combined with a highly selective oxytetracycline (OTC) aptamer (Apt) reaction, new dual-mode scattering SERS/RRS methods were developed to quantitatively analyze ultratrace OTC. The linear range of RRS is 3.00 × 10−3 –6.00 × 10−2 nmol/L, the detection limit is 1.1 × 10−3 nmol/L, the linear range of SERS is 3.00 × 10−3–7.00 × 10−2 nmol/L, and the detection limit is 9.0 × 10−4 nmol/L. Using the SERS method to analyze OTC in soil samples, the relative standard deviation is 1.35–4.78%, and the recovery rate is 94.3–104.9%.

Chemically Stable Carbazole-Based Imine Covalent Organic Frameworks with Acidochromic Response for Humidity Control Applications.

Isoreticular chemically stable two-dimensional imine covalent organic frameworks (COFs), further denoted as DUT-175 and DUT-176, are obtained in a reaction of 4,4′-bis(9H-carbazol-9-yl)biphenyl tetraaldehyde with phenyldiamine and benzidine. The crystal structures, solved and refined from the powder X-ray diffraction data and confirmed by high-resolution transmission electron microscopy, indicate AA-stacked layer structures. Both structures feature distorted hexagonal channel pores, assuring remarkable porosity (SBET = 1071 m2 g–1 for DUT-175 and SBET = 1062 m2 g–1 for DUT-176), as confirmed by adsorption of gases and vapors. The complex conjugated π system of the COFs involves electron-rich carbazole building units, which in combination with the imine groups allow reversible pH-dependent protonation of the frameworks, accompanied by charge transfer and shift of the absorption bands in the UV–vis spectrum. The sigmoidal shape of the water vapor adsorption and desorption isotherms with a steep adsorption step at p/p0 = 0.4–0.6 in combination with excellent stability over dozens of adsorption and desorption cycles ranks these COFs among the best materials for indoor humidity control applications.

Stable Bimetallic Polyphthalocyanine Covalent Organic Frameworks as Superior Electrocatalysts

The development of highly stable covalent organic frameworks (COFs) is extremely compelling for their implementation in practical application. In this work, we rationally designed and synthesized new kinds of ultrastable bimetallic polyphthalocyanine COFs, which are constructed with the dioxin linkage through the nucleophilic aromatic substitution between octahydroxylphthalocyanine and hexadecafluorophthalocyanine. The resulting bimetallic CuPcF8-CoPc-COF and CuPcF8-CoNPc-COF exhibited strong robustness under harsh conditions. The eclipsed stacking mode of metallophthalocyanine units supplies a high-speed pathway for electron transfer. With these structural advantages, both COFs displayed considerable activity, selectivity, and stability toward electrocatalytic CO2 reduction in an aqueous system. Notably, CuPcF8-CoNPc-COF showed a faradaic efficiency of 97% and an exceptionally high turnover frequency of 2.87 s-1, which is superior to most COF-based electrocatalysts. Furthermore, the catalytic mechanism was well demonstrated by using a theoretical calculation. This work not only expanded the variety of dioxin-linked COFs, but also constituted a new step toward their practical use in carbon cycle.

Chelating effect between uranyl and pyridine N containing covalent organic frameworks: A combined experimental and DFT approach

Covalent organic frameworks (COFs) are promising adsorbents for removing heavy metal ions, and have high crystallinity, a porous structure, and conjugated stability. N-containing functional groups are known to have great affinity for uranyl ions. In this work, to explore the peculiarity of the pyridine N structure as an efficient adsorbent, we chose 2,2′-dipyridine-5,5′-diamine (Bpy) and pyridine-2,5′-diamine (Py) as the core skeletons, and 1,3,5-triformylphloroglucinol (Tp) as the linker to synthesize two crystalline and stable N-containing COFs named TpBpy and TpPy, respectively, through a facile solvothermal method. Characterization results demonstrated that TpBpy and TpPy possessed regularly growing pore sizes, large specific surface areas and relatively strong thermal resistances. The results of batch experiments showed that both COF materials were capable of the effective removal of uranyl with uptake capacities of 115.45 mg g−1 and 291.79 mg g−1, respectively. In addition, density functional theory (DFT) simulations highlighted the beneficial chelation effect of the double N structure in pyridine monomers for removing uranyl ions. Combining systematic experimental and theoretical analyses, the adsorption process and interaction mode of porous COFs and UO22+ were revealed, to provide predictable support for the application of pyridine N-containing COFs in the field of environmental remediation.

Microporous and stable covalent organic framework for effective gas uptake

Covalent organic frameworks (COFs) are a new class of crystalline porous materials, maintaining porosity, stability, uniform pore channel, and well-designed skeletons. These features trait to be well suited as a platform for effective adsorption and separation of sorbents. Here, we reported microporous and stable COF with high-density N and O atoms that are implanted via the linker and vertex design. The new COF possessed high crystallinity, permanent micropores, excellent thermal and chemical stability, and high-density N and O atoms on the walls. Interestingly, the new COF is able to capture CO2 of 14.2 wt%, and iodine vapor of 456 wt%. These results evolve structural designs of COFs as effective gas uptake scaffolds.

Studying the adsorption mechanisms of nanoplastics on covalent organic frameworks via molecular dynamics simulations

Covalent organic frameworks (COFs) with well-defined supramolecular structures and high surface-area-to-volume ratio have received extensive attention on their adsorption of contaminants from micro- to nano-size. Here, we studied the adsorption mechanisms of three typical nanoplastics (NP), including polyethylene (PE), nylon-6 (PA 6), and polyethylene terephthalate (PET) on chemically stable COFs (TpPa-X, X = H, CH3, OH, NO2 and F) by molecular dynamics simulations. Depending on molecular structure and surface composition, two distinct interactions–electrostatic interaction and van der Waals (vdW) interaction–are identified to be responsible for the adsorption of different NP pollutants on TpPa-X. The vdW interaction is dominant during the adsorption process, while polar groups in polymers and COFs can enhance the adsorption because of the electrostatic interaction. Compared with other functional COFs, we found that TpPa-OH shows the strongest adsorption with the NP pollutants employed in this study. This work reveals the COF-polymer adsorption behavior and properties at atomic scale, which is crucial to the development of promising COF materials to deal with NP pollution.

Catalyst‐ and Solvent‐Free Synthesis of a Chemically Stable Aza‐Bridged Bis(phenanthroline) Macrocycle‐Linked Covalent Organic Framework

AbstractDeveloping new linkage‐based covalent organic frameworks (COFs) is one of the major topics in reticular chemistry. Electrically conductive COFs have enabled applications in energy storage and electrochemical catalysis, which are not feasible using insulating COFs. Despite significant advances, the construction of chemically stable conductive COFs by the formation of new linkages remains relatively unexplored and challenging. Here we report the solvent‐ and catalyst‐free synthesis of a two‐dimensional aza‐bridged bis(phenanthroline) macrocycle‐linked COF (ABBPM‐COF) from the thermally induced poly‐condensation of a tri‐topic monomer and ammonia gas. The ABBPM‐COF structure was elucidated using multiple techniques, including X‐ray diffraction analysis combined with structural simulation, revealing its crystalline nature with an ABC stacking mode. Further experiments demonstrated its excellent chemical stability in acid/base solutions. Electrical‐conductivity measurements showed that the insulating ABBPM‐COF becomes a semiconducting material after exposure to iodine vapor.

Catalyst- and Solvent-Free Synthesis of a Chemically Stable Aza-Bridged Bis(phenanthroline) Macrocycle-Linked Covalent Organic Framework.

Developing new linkage-based covalent organic frameworks (COFs) is one of the major topics in reticular chemistry. Electrically conductive COFs have enabled applications in energy storage and electrochemical catalysis, which are not feasible using insulating COFs. Despite significant advances, the construction of chemically stable conductive COFs by the formation of new linkages remains relatively unexplored and challenging. Here we report the solvent- and catalyst-free synthesis of a two-dimensional aza-bridged bis(phenanthroline) macrocycle-linked COF (ABBPM-COF) from the thermally induced poly-condensation of a tri-topic monomer and ammonia gas. The ABBPM-COF structure was elucidated using multiple techniques, including X-ray diffraction analysis combined with structural simulation, revealing its crystalline nature with an ABC stacking mode. Further experiments demonstrated its excellent chemical stability in acid/base solutions. Electrical-conductivity measurements showed that the insulating ABBPM-COF becomes a semiconducting material after exposure to iodine vapor.

A Perspective on the Application of Covalent Organic Frameworks for Detection and Water Treatment.

Global population growth and water resource scarcity are significant social problems currently being studied by many researchers focusing on finding new materials for water treatment. The aim is to obtain quality water suitable for drinking and industrial consumption. In this sense, an emergent class of crystalline porous materials known as Covalent-Organic Frameworks (COFs) offers a wide range of possibilities since their structures can be designed on demand for specific applications. Indeed, in the last decade, many efforts have been made for their use in water treatment. This perspective article aims to overview the state-of-the-art COFs collecting the most recent results in the field for water detection of pollutants and water treatment. After the introduction, where we overview the classical design strategies on COF design and synthesis for obtaining chemically stable COFs, we summarize the different experimental methodologies used for COFs processing in the form of supported and free-standing membranes and colloids. Finally, we describe the use of COFs in processes involving the detection of pollutants in water and wastewater treatment, such as the capture of organic compounds, heavy metals, and dyes, the degradation of organic pollutants, as well as in desalination processes. Finally, we provide a perspective on the field and the potential technological use of these novel materials.