Functional Covalent Organic Frameworks Research Articles

Functional Covalent Organic Frameworks' Microspheres Synthesized by Self-Limited Dynamic Linker Exchange for Stationary Phases.

Synthesizing uniform functional covalent organic framework (COF) microspheres is the prerequisite of applying COFs as novel stationary phases for liquid chromatography. However, the synthesis of functionalized COF microspheres is challenging due to the difficulty in maintaining microspheric morphology when conferring functions. Here, a facile and universal "self-limited dynamic linker exchange" strategy is developed to achieve surface functionalization of uniform COF microspheres. Six different types of COF microspheres are constructed, showing the universality and superiority of the strategy. The library of COF microspheres' stationary phases can be further enriched on demand by varying different functional building blocks. The "self-limited dynamic linker exchange" is attributed to the result of a delicate balance of reaction thermodynamics and molecular diffusion energy barrier. As a demonstration, the chiral functional COF microspheres are used as stationary phases of chiral chromatography and realized effective enantioseparation.

Metal-Catalyzed Multi-Component Approach to Quinoline-Linked Covalent Organic Frameworks

The development of new reaction chemistry is highly desirable to construct new structural and functional covalent organic frameworks (COFs). Benefiting from the extremely large database of metal-catalyzed reaction database, we herein develop a new synthetic strategy that can generate quinoline-linked COFs via a silver-catalyzed three-component one-pot reaction and achieve functionalization by the simple replacement of alcohols. This metal-catalyzed approach to the construction of robust COF structures characterized by extended π-conjugation holds the potential to pave a novel pathway in the synthesis of COF materials endowed with both heightened stability and functionality.

On topological analysis of two-dimensional covalent organic frameworks via M-polynomial

Covalent organic frameworks (ZnP-COFs) made of zinc-porphyrin have become effective materials with a variety of uses, including gas storage and catalysis. To simulate the structural and electrical features of ZnP-COFs, this study goes into the computation of polynomials utilizing degree-based indices. We gave a methodical study of these polynomial computations using Excel, illustrating the complex interrelationships between the various indices. Degree-based indices provide valuable insights into the connectivity of vertices within a network. M-polynomials, on the other hand, offer a mathematical framework for representing and studying the properties of 2D COFs. By encoding structural information into a polynomial form, M-polynomials facilitate the calculation of various topological indices, including the Wiener index, Zagreb indices, and more. The different behavior of ZnP-COFs based on degree-based indices was illustrated graphically, and this comparison provided insightful information for prospective applications and the construction of innovative ZnP-COF structures. Moreover, we discuss the relevance of these techniques in the broader context of materials science and the design of functional covalent organic frameworks.

Metal-free thiophene-based covalent organic frameworks achieve efficient photocatalytic hydrogen evolution by accelerating interfacial charge transfer

Photocatalysis is widely recognized as an efficient and environmentally friendly pathway for the conversion of solar energy into chemical energy. In recent years, designing efficient hydrogen evolution to obtain green clean energy has been one of the major challenges faced by researchers. Covalent organic frameworks (COFs) are considered as new and effective photocatalyst due to the inherent porosity, high crystallinity and structural adjustability. In this study, two metal-free thiophene-based covalent organic frameworks (JLNU-308 and JLNU-309) were constructed by solvothermal method through effective modulation sites. Because JLNU-COFs has a narrow band gap and good absorption capacity in the spectral range, the interfacial charge transfer speed is accelerated to solve the problem of low charge separation efficiency. Remarkably, JLNU-309 displays an impressive hydrogen evolution rate of 2868.57 μmol g−1 h−1 under visible light irradiation (λ > 420 nm). The superior hydrogen evolution reaction (HER) activity is due to the triazine units, which have high visible light absorption capacity, one-dimensional nanochannels of two-dimensional COFs and synergy with charge mobility. The photoelectrochemical measurements and calculation of density functional theory (DFT) supports the accuracy of the experiment. This work opens an avenue for constructing functional covalent organic frameworks for environmentally relevant critical applications. In addition, the simple synthesis process, excellent activity and high chemical stability indicate that JLNU-COFs are promising photocatalytic hydrogen production materials.

Shape-persistent COF-derived functional carbon microspheres for No-carrier added 177Lu separation

Porous carbon materials stemming from covalent organic frameworks (COFs) have emerged as pivotal candidates in various fields. However, no COF or relevant derivative has stepped into the recovery of no-carrier added (NCA) 177Lu, one of the most important radionuclides in modern medicine, from irradiated target. In this work, shape-persistent COF-derived carbon microsphere (COF-CMS) was successfully synthesized via self-templated carbonization and subsequently functionalized with active component 2-ethylhexyl phosphoric acid mono-2-ethylhexyl ester (P507). The prepared functional COF-CMS@P507 has shown high selectivity and fast adsorption kinetics for Yb3+/Lu3+ in static batch adsorption and great potential in dynamic column separation of Lu3+ from Yb3+. More importantly, based on plenty of tracer experiments and practical investigations, a separation process flow was established to realize the isolation of 177Lu from an irradiated 176Yb target. Consequently, 177Lu product can be effectively obtained in preferable recovery (86%) with high radinuclidic and chemical purity (≥99.99%). The present study provides a new idea for NCA 177Lu production, which is also valuable for the development of lanthanide separation and functional COFs.

Pore Space Partition Synthetic Strategy in Imine-linked Multivariate Covalent Organic Frameworks.

Partitioning the pores of covalent organic frameworks (COFs) is an attractive strategy for introducing microporosity and achieving new functionality, but it is technically challenging to achieve. Herein, we report a simple strategy for partitioning the micropores/mesopores of multivariate COFs. Our approach relies on the predesign and synthesis of multicomponent COFs through imine condensation reactions with aldehyde groups anchored in the COF pores, followed by inserting additional symmetric building blocks (with C2 or C3 symmetries) as pore partition agents. This approach allowed tetragonal or hexagonal pores to be partitioned into two or three smaller micropores, respectively. The synthesized library of pore-partitioned COFs was then applied for the capture of iodine pollutants (i.e., I2 and CH3I). This rich inventory allowed deep exploration of the relationships between the COF adsorbent composition, pore architecture, and adsorption capacity for I2 and CH3I capture under wide-ranging conditions. Notably, one of our developed pore-partitioned COFs (COF 3-2P) exhibited greatly enhanced dynamic I2 and CH3I adsorption performances compared to its parent COF (COF 3) in breakthrough tests, setting a new benchmark for COF-based adsorbents. Results present an effective design strategy toward functional COFs with tunable pore environments, functions, and properties.

Adsorption of Pb(II) on covalent organic frameworks: Overlooked sorption sites formed in the post-synthetic modification process

The post-synthesis strategy is frequently employed to create functional covalent organic frameworks (COFs) for the removal of heavy metals. Different post-synthesis methods can yield structurally distinct side chains. However, the potential adsorption role of these side chains is often overlooked, even though they can provide efficient adsorption sites that significantly enhance the adsorption performance of functional COFs for targeted pollutants. In this study, two post-modification reactions were conducted to introduce functional groups into the original COFs, namely acetylene COFs and ethylene COFs (referred to as COFV1 and COFV2). This resulted in the synthesis of modified MCOFV1 and MCOFV2 with emerging triazole and thioether groups, respectively. Subsequently, these modified COFs were characterized and employed to investigate the influence of the newly formed structures on the adsorption of Pb(II). Density functional theory (DFT) calculations were carried out to explore the adsorption mechanism and the binding energies between COFs and Pb(II). The results indicate that after modification, the specific surface area of COFV1 and COFV2 decreased by 8.08 and 2.05 times, reaching 204.9 m2 g–1 for MCOFV1 and 587.5 m2 g−1 for MCOFV2. However, their Pb(II) equilibrium adsorption capacity significantly increased, with MCOFV1 achieving 52.1 mg/g (11.5 times higher than COFV1) and MCOFV2 achieving 31.1 mg/g (1.6 times higher than COFV2) based on the pseudo-first-order model. This indicates that the triazole group, which is produced in the post-modification reaction, demonstrates greater efficacy in the removal of Pb(II) as compared to the thioether group. This study reveals that efficient bifunctional groups can be formed through suitable post-modification methods, enhancing the adsorption performance of COFs in environmental remediation.

Dual-Interface Modulation with Covalent Organic Framework Enables Efficient And Durable Perovskite Solar Cells.

Dual-interface modulation including buried interface as well as the top surface has recently been proven to be crucial for obtaining high photovoltaic performance in lead halide perovskite solar cells (PSCs). Herein, for the first time, we report the strategy of using functional covalent organic frameworks (COFs), namely HS-COFs, for dual-interface modulation, and further understand its intrinsic mechanisms in optimizing the bottom and top surfaces. Specifically, the buried HS-COFs layer can enhance the resistance against ultraviolet radiation, and more importantly, release the tensile strain, which is beneficial for enhancing device stability and improving the order of perovskite crystal growth. Furthermore, the detailed characterization results reveal that the HS-COFs on the top surface can effectively passivate the surface defects and suppress non-radiation recombination, as well as optimize the crystallization and growth of the perovskite film. Benefiting from the synergistic effects, the dual-interface modified device delivers a champion efficiency of 24.26% and 21.30% for 0.0725 cm2 and 1 cm2 -sized devices, respectively. Moreover, it retains 88% and 84% of their initial efficiency after aging for 2000 hours under the ambient conditions (25°C, relative humidity: 35- 45%) and a nitrogen atmosphere with heating at 65°C, respectively. This article is protected by copyright. All rights reserved.

Regulating the iodine adsorption performances of two- and three-component β-ketoenamine-linked covalent organic frameworks through tuning the proportion of monomers

The crystallinity, specific surface area, and amino content of NH2-ThX-Mth1−X-Tfp COFs have been effectively regulated by changing the mole ratio of NH2-Th and Mth. Interestingly, they showed different iodine vapour capture performances.

Anchoring ultrasmall Pd nanoparticles by bipyridine functional covalent organic frameworks for semihydrogenation of acetylene.

Acetylene hydrogenation is a well-accepted solution to reduce by-products in the ethylene production process, while one of the key technical difficulties lies in developing a catalyst that can provide highly dispersed active sites. In this work, a highly crystalline layered covalent organic framework (COF) material (TbBpy) with excellent thermal stability was synthesized and firstly applied as support for ultrasmall Pd nanoparticles to catalyze acetylene hydrogenation. 100% of C2H2 conversion and 88.2% of C2H4 selectivity can be obtained at 120 °C with the space velocity of 70 000 h-1. The reaction mechanism was elucidated by applying a series of characterization techniques and theoretical calculation. The results indicate that the coordination between Pd and N atom in the bipyridine functional groups of COFs successfully increased the dispersibility and stability of Pd particles, and the introduction of COFs not only improved the adsorption of acetylene and H2 onto catalyst surface, but enhanced the electron transfer process, which can be responsible for the high selectivity and activity of catalyst. This work, for the first time, reported the excellent performance of Pd@TbBpy as a catalyst for acetylene hydrogenation and will facilitate the development and application of COFs materials in the area of petrochemicals.

Functionalization of Covalent Organic Frameworks with Peptides by Polymer-Assisted Surface Modification and the Application for Protein Detection.

Although covalent organic frameworks (COFs) have received extensive attention for biomedical research due to their unique properties, their application is still hindered by the challenges of incorporating COFs with functional biomolecules. Since peptides have shown advantages in biomedical applications, herein, we propose the functionalization of COFs with peptides by a polymer-assisted surface modification strategy. Furthermore, a method based on the peptide-functionalized COFs for protein detection has also been developed to demonstrate their application potential. With the help of the polymers, peptides and horseradish peroxidase are attached onto COFs with a high surface density, and the developed method has achieved simple and sensitive detection of the secreted protein acidic and rich in cysteine. We speculate that the facile method proposed in this work to prepare peptide-functionalized COFs can not only benefit protein detection but also promote more biomedical applications of COFs.

Functionalization of Covalent Organic Frameworks with DNA via Covalent Modification and the Application to Exosomes Detection.

The functionalization of covalent organic frameworks (COFs) with biomacromolecules can extend their functions, which is the premise of their application in biomedical research. However, strategies to functionalize COFs with biomacromolecules, which can ensure the stability in complex medium and minimize the undesired effects, are still lacking. In this work, we have proposed a strategy to functionalize COFs with DNA by covalently linking DNA to the functional group on the COF surface through Cu(I)-catalyzed azide/alkyne cycloaddition (CuAAC) reaction. The as-prepared DNA-functionalized COFs (DNA-COFs) can exhibit good hybridization ability and cargo loading ability; thus, we have designed a DNA-COF-based nanoprobe and then fabricated an electrochemical biosensor for the detection of exosomes. In this design, the functionalization with DNA enables COFs to recognize and capture exosomes, and the encapsulation of a large number of methylene blue (MB) in COFs facilitates signal amplification, which can enhance the sensitivity of the biosensor. Moreover, by simply replacing the oligonucleotide sequences, the strategy proposed here can generally be used to build different DNA-COFs with diverse functions for broader biomedical applications.

Anchoring Ultrasmall Pd Nanoparticles by Bipyridine Functional Covalent Organic Frameworks for Semihydrogenation of Acetylene

Anchoring Ultrasmall Pd Nanoparticles by Bipyridine Functional Covalent Organic Frameworks for Semihydrogenation of Acetylene

Postsynthetic functionalization of covalent organic frameworks for dual channel fluorescence diagnosis of two indicators related to Parkinson's disease

Exploring facile analytical technologies with high reliability and precision to quantify targets is significant but remains great challenge for disease diagnosis. Several signal transduction pathways have stimulated the development of various target analysis system. However, many systems are limited by the single channel/mechanism method, it could lead to false positive/negative results. Herein, a dual channel-driven fluorescence sensor was designed for simultaneously analysing homovanillic acid (HVA) and Al3+, two effective indicators for the diagnosis of Parkinson's disease (PD). With two steps of postsynthetic modification (PSM) strategy for covalent organic framework (COF) TpBD-(OH)2, the excellent luminescent material TpBD-(COOH)2@EuTTA (1) still maintained good structural stability, further prepared hydrogel had also been applied to dual channel detect two analytes related to PD. The fluorescence sensor showed turn-off fluorescence response to HVA, and exhibited ratiometric identification approach to Al3+. Simultaneous and quantitative detection with dual channel for two indicators can greatly improve the accuracy of the diagnosis of PD. This study not only provides feasible strategy for versatile functionalization of COFs, but also reveals promising perspectives for the future of non-invasive and accurate disease diagnosis.

In-situ fabrication of a chlorine-functionalized covalent organic framework coating for solid-phase microextraction of polychlorinated biphenyls in surface water

The functionalization of covalent organic frameworks (COFs) identifies significant potential for developing selective coating materials for solid-phase microextraction (SPME). Herein, a chlorine-functionalized covalent organic framework (CF–COF) was in-situ synthesized by employing triformylphloroglucinol (Tp) and 2,5-dichloro-1,4-phenylenediamine (2,5-DCA) as monomers on an amino-functionalized stainless steel wire. The obtained CF-COF coated fiber exhibited a higher enrichment capacity for polychlorinated biphenyls (PCBs) than commercial fibers and non-chlorinated COF fiber, owing to a more hydrophobic surface, size-matching effect, a large number of micropores and the π–π stacking interactions between COF coating and analytes. As a practical application, the CF-COF coated fiber was applied to the headspace extraction of 17 PCBs prior to their quantification by GC/MS. The established analytical method offered a good linearity in the range of 0.1–1000 ng L−1, low detection limits of 0.0015–0.0088 ng L−1, and satisfactory enhancement factors (EFs) of 699–4281. The repeatability for single fiber and the fiber-to-fiber reproducibility was lower than 9.26% and 9.33%, respectively. The proposed method was verified to be sensitive, selective, and applicable for the analysis of ultra-trace PCBs in environmental surface water samples with the recoveries ranged from 78.7% to 124.0%.

Functionalized triazine-based covalent organic frameworks containing quinoline via aza-Diels-Alder reaction for enhanced lithium-sulfur batteries performance

The development of functional covalent organic frameworks (COFs) with specific properties is an emerging research field. In the current work, COF-SQ-Ph was synthesized through the aza-Diels-Alder reaction between phenylacetylene and the matrix COF-SQ (triazine-based COF) generated from the organic monomers 2, 4, 6-tris(4-aminophenyl)-1, 3, 5-triazine and 2, 5-dimethoxyterephthalaldehyde in flask. The functionalized COF-SQ-Ph with an extended π-conjugated structure and enhanced structural stability was used as the sulfur loading recipient to prepare sulfur cathodes for lithium-sulfur batteries. Sulfur-impregnated COF-SQ-Ph marked as COF-SQ-Ph-S displayed better cycling stability with a specific capacity of 618 mA h g−1 after 150 cycles due to the lithiophilic interaction between lithium polysulfides and nitrogen atoms from quinoline and triazine moieties in COF-SQ-Ph-S. The functionalization of triazine-based COFs through a cycloaddition reaction in flask could promote the large-scale preparation of tailored COFs and the post-synthesis modification of COF-SQ.

Nanocomposite based on graphene and intercalated covalent organic frameworks with hydrosulphonyl groups for electrochemical determination of heavy metal ions.

Anelectrochemical sensor constructed by intercalated composites was developed for determination of heavy metal ions. The intercalated composites were composed of hydrosulphonyl functional covalent organic frameworks (COF-SH) and graphene (G). The presence of numerous adsorption sites, such as 18 sulfur atoms and 30 nitrogen atoms per big circle of COFs on COF-SH, was beneficial for the accumulation of heavy metals, while the graphene enhanced the electrical conductivity. The obtained sensor under the optimal conditions successfully detected the presence of heavy metal ions in coastal water samples at concentrations ranging from 1 to 1000μgL-1. The detection limits of Cd (II), Pb (II), Cu (II), and Hg (II) were 0.3, 0.2, 0.2, and 1.1μgL-1, respectively. Furthermore, the sensor still exhibited good stability after multiple uses less than 5%. When it is used in the analysis of actual samples, the recovery of standard addition is higher than 95%. In sum, the combination of hydrosulphonyl functional COFs with graphene looks very promising for the assembly of sensors with high sensitivity toward the determination of heavy metal ions for coastal environmental monitoring.

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.

Fabrication of Two-Dimensional Functional Covalent Organic Frameworks via the Thiol-Ene "Click" Reaction as Lubricant Additives for Antiwear and Friction Reduction.

To address the energy wastage problem caused by friction, novel lubricant additives other than the traditional and basic used additives with outstanding performance are urgently needed. A facile and efficient postsynthetic strategy for modification of two-dimensional (2D) covalent organic frameworks (COFs) was proposed to obtain dialkyl dithiophosphate (DDP)-functionalized COFs (DDP@TD-COF) as lubricant additives. The DDP@TD-COF was prepared by amine-aldehyde condensation reaction of the triazine compound and vinyl-functionalized monomers through a solvothermal process to form a vinyl-functionalized 2D COF (TD-COF), followed by covalent bonding of commercial lubricating molecules (DDP) via the UV-induced thiol-ene "click" reaction. The as-obtained DDP@TD-COF with homogeneous distribution of N, P, and S elements exhibits exceptional dispersion stability in the 500SN base oil, which remains stable for over 6 days. With a trace amount addition of 0.05 wt %, superior friction and wear reduction of DDP@TD-COF are observed with the friction coefficient lessened to 0.096 from 0.19, wear volume loss declined by 94.9%, and load carrying ability increased from 150 to 650 N simultaneously. The mechanism studies show that the shear force can induce interlayer slipping during the friction process, and the stripped DDP@TD-COF can get involved in the contacting interface inducing tribo-chemical reactions via N, P, and S elements forming a protective layer on the surfaces. Consequently, the DDP@TD-COF demonstrated remarkable friction diminution and abrasion resistance abilities even with a trace amount addition, and this work provides a dependable and valid route for the design and preparation of functional COF-based nanoadditives.

Design of a new drug delivery platform based on surface functionalization 2D covalent organic frameworks

The adsorption mechanism of doxorubicin (DOX) on pristine covalent organic frameworks (COF) and functionalized COF (F-COF) is investigated by using molecular dynamics (MD) and Metadynamics simulations. MD simulations are performed to explore the loading of DOX into the COFs. To evaluate this process, a set of descriptors, including interaction energies, radial distribution function, and square mean displacement, the number of hydrogen bonds (HB) are calculated throughout the simulation trajectories. It is determined that HB interactions are the most important factors in stability of the investigated systems. The MD results show that the drug molecules move toward the COFs and form the stable complexes. Functionalization of COF with six and three hydroxyl groups increases its interaction energy with DOX from -16.87 to -264.95 and -139.87 kJ/mol, respectively. In this study, the free energy surface (FES) is also calculated by well-tempered metadynamics simulation technique. The PES landscapes confirm that the global minimum could be typically relevant to formation of the HB. The free energy values for the COF/DOX complexes in pristine and functionalization of COFs at their global minima are reached about -229.7, -260.46 (for six OH groups), and -243.37 (for three OH groups) kJ/mol, respectively. In addition, at the acidic condition, protonation of DOX causes that the interactions between DOXs and the COFs become weaker and drug molecules could release from the nanocarrier cavities.