Construction Of Covalent Organic Frameworks Research Articles

Hollow nanosphere construction of covalent organic frameworks for catalysis: (Pd/C)@TpPa COFs in Suzuki coupling reaction

A novel catalyst with a yolk-shell structure was designed to overcome the leaching of noble metals in heterogeneous catalysis. Through a template method, palladium (Pd) nanoparticles were encapsulated by hollow spherical covalent organic frameworks (COFs) consisting of 2,4,6-trihydroxybenzene-1,3,5-tricarbaldehyde (Tp) and p-phenylenediamine (Pa). The final catalyst with a yolk-shell structure was denoted as (Pd/C)@TpPa COFs. The unique morphology and chemical structure of this novel composite (Pd/C)@TpPa COFs were confirmed by a transmission electron microscope (TEM), a laser particle analyzer, X-ray diffraction (XRD), and N2 adsorption and desorption. Subsequently, to demonstrate its catalytic performance brought by structural design, this novel catalyst was applied to catalyze the Suzuki reaction. Interestingly, this catalyst exhibited a brilliant size cutoff efficiency for aryl benzene amounting to 100% and achieved a high conversion with only 0.05 mol% Pd loading. Besides, this catalyst could be readily recovered via filtration and reused for at least five consecutive cycles without any significant loss in its activity.

Rational construction of covalent organic frameworks with multi-site functional groups for highly efficient removal of low-concentration U(vi) from water

The multi-site chelation effect has successfully improved the affinity of COF-TpDd-AO2 towards low-concentration uranium.

In situ growth of covalent organic frameworks TpBD on electrode for electrochemical determination of aflatoxin M1

An in situ growth strategy for construction of covalent organic frameworks (COFs) TpBD on glassy carbon electrode using p-aminobenzoic acid and ethylenediamine as connector is introduced. The fabricated electrode was used for electrochemical biosensing of aflatoxin M1 in milk samples combined with magnetic nanoparticles, which acted as probe carriers. The developed electrochemical biosensor exhibited high selectivity and sensitivity toward aflatoxin M1 with a detection limit of 0.15 ng/mL (S/N = 3). Moreover, the covalent bonding of TpBD on the glassy carbon electrode has good stability, which retained 76% of the initial signal after 15 days storage at room temperature. This work provides a valuable case for in situ growth of COFs TpBD on the electrode, and the proposed synthetic route is expected to provide a powerful tool for the wide application of other functional COFs in electrochemical biosensor.

Crystalline, porous, covalent polyoxometalate-organic frameworks for lithium-ion batteries

Abstract The development of covalent organic frameworks (COFs) with new building units is of critical importance for enriching the structural diversity and expanding their functions. However, the construction of COFs has been thus far limited primarily to traditional organic linkers. Herein, we report three-dimensional porous crystalline covalent polyoxometalate-organic frameworks (CPOFs) constructed from both inorganic and organic building blocks with reversible covalent bonds. These highly crystalline CPOFs exhibited 3-fold interpenetrated diamondoid topology, permanent porosity and high stability. Furthermore, these CPOFs could be directly applied as anode materials for lithium-ion batteries (LIBs) and displayed high reversible capacity (as high as 550 mA h g−1), rate performance, and cycling stability (up to 500 cycles).

Twist Building Blocks from Planar to Tetrahedral for the Synthesis of Covalent Organic Frameworks.

Rational construction of covalent organic frameworks (COFs) with novel structures still remains a challenge. Herein, we report the designed synthesis of two COFs, 2D-BPTA-COF and 3D-BMTA-COF, starting from biphenyl-based precursors but with different groups at the ortho positions. Both COFs exhibited high crystallinity and large surface area, and interestingly, 2D-BPTA-COF crystallizes into 2D sheets with AB stacking mode while 3D-BMTA-COF adopts a 7-fold interpenetrated structure with pts topology. This structural difference could be ascribed to the introduction of methyl groups in the building blocks, as the dihedral angle of biphenyl rings in 2D-BPTA-COF is ∼0° while in 3D-BMTA-COF it is ∼60°. Therefore, it is possible to synthesize COFs with different structures by twisting building blocks from planar to tetrahedral with steric hindrance. We believe this result represents a general and straightforward way to expand the diversity of tetrahedral nodes for constructing 3D COFs in the future, and moreover, a new tetrahedral node for constructing 3D COFs is now available.

Construction of covalent organic framework with unique double-ring pore for size-matching adsorption of uranium.

The separation and recovery of key nuclides such as uranium and plutonium from effluents related to nuclear industry is of great significance for alleviating the shortage of nuclear energy resources and protecting the environment and human health. However, the high temperature, strong acidity and radioactivity of the nuclear effluents pose a severe challenge to the separation materials used in such conditions. The diversity of structure, flexibility of design, and excellent physicochemical stability of covalent organic framework materials (COFs) provide the possibility for the directional design and preparation of adsorbents for use under harsh conditions. Herein, three COFs with similar structure, different pore sizes and connecting modules were synthesized. The ingenious structure predesign enables Dp-COF to have three carboxyl groups oriented toward the pore center and laid out in appropriate spatial positions, which builds hydrogen-bonding bridges between carboxycarbonyl and hydroxyl groups, and thus constructs for the first time a unique COF material with a double-ring pore. The inner pore size of the "double-ring" is slightly larger than the diameter of uranyl hydrate, which leads to a size-matching adsorption of uranium by Dp-COF, thus greatly reducing the effect of protonation. Even in the simulated spent fuel reprocessing liquid with pH = 1.0, the adsorption capacity of Dp-COF for uranium can reach 66.3 mg g-1, and the adsorption capacity reaches 317.3 mg g-1 at pH = 4.5, which is very rare among the reported COFs. More excitingly, the removal rate for uranium reaches up to an unprecedented 99.8% due to the size-matching effect, more than any analogous adsorbents. This study not only proposes new ideas for the design and regulation of the microscopic configuration of COF materials, but also provides an alternative approach for the preparation of efficient uranium adsorbents.

Construction of Covalent-Organic Frameworks (COFs) from Amorphous Covalent Organic Polymers via Linkage Replacement.

Covalent-organic frameworks (COFs) as porous crystalline materials show promising potential applications. However, developing facile strategies for the construction of COFs directly from amorphous covalent organic polymers (COPs) is still a great challenge. To this end, we report a novel approach for easy preparation of COFs from amorphous COPs through the linkage replacement under different types of reactions. Four COFs with high crystallinity and porosity were constructed via the linkage substitution of polyimide-linked COPs to imine-linked COFs as well as imine-linked COPs to polyimide-linked COFs. The realization of the linkage substitution would significantly expand the research scope of COFs.

Construction of Covalent‐Organic Frameworks (COFs) from Amorphous Covalent Organic Polymers via Linkage Replacement

AbstractCovalent‐organic frameworks (COFs) as porous crystalline materials show promising potential applications. However, developing facile strategies for the construction of COFs directly from amorphous covalent organic polymers (COPs) is still a great challenge. To this end, we report a novel approach for easy preparation of COFs from amorphous COPs through the linkage replacement under different types of reactions. Four COFs with high crystallinity and porosity were constructed via the linkage substitution of polyimide‐linked COPs to imine‐linked COFs as well as imine‐linked COPs to polyimide‐linked COFs. The realization of the linkage substitution would significantly expand the research scope of COFs.

A Novel Strategy for the Construction of Covalent Organic Frameworks from Nonporous Covalent Organic Polymers

AbstractThe field of covalent organic frameworks (COFs) has been developed significantly in the past decade on account of their important characteristics and vast application potential. On the other hand, the discovery of novel synthetic methodology is still a challenging task to further promote the preparation of COFs. Herein, an interesting protocol for the conversion of amorphous nonporous covalent organic polymers (COPs) to COFs was established, affording four COFs with high crystallinity and porosity. Specifically, imine‐linked amorphous COP‐1 was successfully converted to COF‐1–4 by replacing one type of linker with other organic building blocks. The realization of this conversion provides a facile method for constructing COFs from COPs.

A Novel Strategy for the Construction of Covalent Organic Frameworks from Nonporous Covalent Organic Polymers.

The field of covalent organic frameworks (COFs) has been developed significantly in the past decade on account of their important characteristics and vast application potential. On the other hand, the discovery of novel synthetic methodology is still a challenging task to further promote the preparation of COFs. Herein, an interesting protocol for the conversion of amorphous nonporous covalent organic polymers (COPs) to COFs was established, affording four COFs with high crystallinity and porosity. Specifically, imine-linked amorphous COP-1 was successfully converted to COF-1-4 by replacing one type of linker with other organic building blocks. The realization of this conversion provides a facile method for constructing COFs from COPs.

Materials genomics methods for high-throughput construction of COFs and targeted synthesis

Materials genomics represents a research mode for materials development, for which reliable methods for efficient materials construction are essential. Here we present a methodology for high-throughput construction of covalent organic frameworks (COFs) based on materials genomics strategy, in which a gene partition method of genetic structural units (GSUs) with reactive sites and quasi-reactive assembly algorithms (QReaxAA) for structure generation were proposed by mimicking the natural growth processes of COFs, leading to a library of 130 GSUs and a database of ~470,000 materials containing structures with 10 unreported topologies as well as the existing COFs. As a proof-of-concept example, two generated 3D-COFs with ffc topology and two 2D-COFs with existing topologies were successfully synthesized. This work not only presents useful genomics methods for developing COFs and largely extended the COF structures, but also will stimulate the switch of materials development mode from trial-and-error to theoretical prediction-experimental validation.

Integrating Superwettability within Covalent Organic Frameworks for Functional Coating

Summary Despite the availability of a variety of skeletons for covalent organic frameworks (COFs), control of pore-surface wettability remains undeveloped, which could immensely expand their overall versatility. Herein, we contribute an effective strategy for imparting superwettability on COFs by chemically coating the pore surface with perfluoroalkyl groups to confer them with superhydrophobicity. Taking advantage of controllable modification, the resultant COFs retain the porosity and crystallinity of the pristine COFs. Benefiting from the bulk superhydrophobicity of the COF crystals and the feasibility of COF synthesis, they can be used as a coat or in situ integrated within various substrates; once applied, this renders them superhydrophobic. Given the modular nature, this protocol is compatible with the development of various specific wettabilities in COFs, which thereby constitutes a step for expanding the scope of COF applications and provides many opportunities for the processing of advanced materials and devices.

Multivariate Chiral Covalent Organic Frameworks with Controlled Crystallinity and Stability for Asymmetric Catalysis.

The modular construction of covalent organic frameworks (COFs) provides a convenient platform for designing high-performance functional materials, but the synthetic control over their chirality has been relatively barely studied. Here we report a multivariate strategy to prepare chiral COFs (CCOFs) with controlled crystallinity and stability for asymmetric catalysis. By crystallizing mixtures of triamines with and without chiral organocatalysts and with a dialdehyde, a family of two- and three-component 2D porous CCOFs that adopt two different stacking modes is prepared. The organocatalysts are periodically appended on the channel walls, and their contents, which can be synthetically tuned using a three-component condensation system, greatly affect the chemical stability and crystallinity of CCOFs. Specially, the ternary CCOFs displayed relatively high crystallinity and stability compared with the binary CCOFs. Under harsh conditions, the ternary CCOFs can serve as efficient heterogeneous catalysts for an asymmetric aminooxylation reaction, an aldol reaction, and the Diels-Alder reaction, with the stereoselectivity and diastereoselectivity rivaling or surpassing the homogeneous analogues. This work not only opens up a new synthetic route toward CCOFs, but also provides tunable control of COF crystallintity and stability and, in turn, the properties.

Precision Construction of 2D Heteropore Covalent Organic Frameworks by a Multiple-Linking-Site Strategy.

Integrating different kinds of pores into one covalent organic framework (COF) endows it with hierarchical porosity and thus generates a member of a new class of COFs, namely, heteropore COFs. Whereas the construction of COFs with homoporosity has already been well developed, the fabrication of heteropore COFs still faces great challenges. Although two strategies have recently been developed to successfully construct heteropore COFs from noncyclic building blocks, they suffer from the generation of COF isomers, which decreases the predictability and controllability of construction of this type of reticular materials. In this work, this drawback was overcome by a multiple-linking-site strategy that offers precision construction of heteropore COFs containing two kinds of hexagonal pores with different shapes and sizes. This strategy was developed by designing a building block in which double linking sites are introduced at each branch of a C3 -symmetric skeleton, the most widely used scaffold to construct COFs with homogeneous porosity. This design provides a general way to precisely construct heteropore COFs without formation of isomers. Furthermore, the as-prepared heteropore COFs have hollow-spherical morphology, which has rarely been observed for COFs, and an uncommon staggered AB stacking was observed for the layers of the 2D heteropore COFs.

Construction of Covalent Organic Frameworks Bearing Three Different Kinds of Pores through the Heterostructural Mixed Linker Strategy.

It is very important to create novel topologies and improve structural complexity for covalent organic frameworks (COFs) that might lead to unprecedented properties and applications. Despite the progress achieved over the past decade, the structural diversity and complexity of COFs are quite limited. In this Communication, we report the construction of COFs bearing three different kinds of pores through the heterostructural mixed linker strategy involving the condensation of a D2h-symmetric tetraamine and two C2-symmetric dialdehydes of different lengths. The complicated structures of the triple-pore COFs have been confirmed by powder X-ray diffraction and pore size distribution analyses.

Construction of Covalent Organic Framework for Catalysis: Pd/COF-LZU1 in Suzuki–Miyaura Coupling Reaction

Covalent organic frameworks (COFs) are crystalline porous solids with well-defined two- or three-dimensional molecular structures. Although the structural regularity provides this new type of porous material with high potentials in catalysis, no example has been presented so far. Herein, we report the first application of a new COF material, COF-LZU1, for highly efficient catalysis. The easily prepared imine-linked COF-LZU1 possesses a two-dimensional eclipsed layered-sheet structure, making its incorporation with metal ions feasible. Via a simple post-treatment, a Pd(II)-containing COF, Pd/COF-LZU1, was accordingly synthesized, which showed excellent catalytic activity in catalyzing the Suzuki-Miyaura coupling reaction. The superior utility of Pd/COF-LZU1 in catalysis was elucidated by the broad scope of the reactants and the excellent yields (96-98%) of the reaction products, together with the high stability and easy recyclability of the catalyst. We expect that our approach will further boost research on designing and employing functional COF materials for catalysis.