Flexible covalent organic frameworks (COFs) are intriguing for their dynamic properties distinctive from rigid counterparts but still suffer from limited accessibility. Especially, controlling ...flexibility of COFs is challenging and the impact of different flexibility on properties of COFs has rarely been unveiled. This article reports stepwise adjustment on flexibility of two-dimensional COFs, which is realized by the designed synthesis of rigid COF (R-COF), semi-flexible COF (SF-COF), and flexible COF (F-COF) through polymerization, linker exchange, and linkage conversion with a newly developed method for reduction of hydrazone, respectively. Significant difference in breathing behavior and self-adaptive capability of the three COFs are uncovered through vapor response and iodine capture experiments. Gas sorption experiments indicate that the porosity of F-COF could switch from "close" state in nitrogen to "open" state in carbon dioxide, which are not observed for R-COF and SF-COF. This study not only develops a strategy to adjust the flexibility of COFs by tuning their linkers and linkages, but also provides a deep insight into the impact of different flexibility on properties of COFs, which lays a foundation for the development of this new class of dynamic porous materials.
Exploring new linkage chemistry for covalent organic frameworks (COFs) provides a strong driving force to promote the development of this emerging class of crystalline porous organic materials. ...Herein we report a strategy to synthesize COFs with azo linkage, one of the most important functional unit in materials science but having not yet been exploited as a linkage of COFs. This strategy is developed on the basis of in situ linker exchange, by which imine-linked COFs are completely transformed into azo-linked COFs (Azo-COFs). Moreover, distinct properties of Azo-COFs from their corresponding imine-linked precursors are observed, indicating unique property of Azo-COFs. This strategy provides a useful approach to develop new linkage chemistry for COFs. It also has established a synthetic method for azo-linked COFs, which not only enriches the family of COFs but also offers a platform to explore properties and applications of this class of crystalline porous conjugated polymers.
Constructing two-dimensional (2D) polymers with complex tessellation patterns via synthetic chemistry makes a significant contribution not only to the understanding of the emergence of complex ...hierarchical systems in living organisms, but also to the fabrication of advanced hierarchical materials. However, to achieve such tasks is a great challenge. In this communication we report a facile and general approach to tessellate 2D covalent organic frameworks (COFs) by three or four geometric shapes/sizes, which affords 2D COFs bearing three or four different kinds of pores and increases structural complexity in tessellations of 2D polymers to a much higher level. The complex tessellation patterns of the COFs are elucidated by powder X-ray diffraction studies, theoretical simulations and high-resolution TEM.
Covalent organic frameworks (COFs) are an emerging class of crystalline porous organic materials which are fabricated via reticular chemistry. Their topologic structures can be precisely predicted on ...the basis of the structures of building blocks. However, constructing COFs with complicated structures has remained a great challenge, due to the limited strategies that can access to the structural complexity of COFs. In this work, we have developed a new approach to produce COFs bearing three different kinds of pores. The design is fulfilled by the combination of vertex-truncation with multiple-linking-site strategy. On the basis of this design, a “V”-shaped building block carrying two aldehyde groups on the end of each branch has been synthesized. Condensation of it with 1,4-diaminobenzene or benzidine leads to the formation of two triple-pore COFs, TP-COF-DAB and TP-COF-BZ, respectively. The topological structures of the triple-pore COFs have been confirmed by PXRD studies, synchrotron small-angle X-ray scattering (SAXS) experiments, theoretical simulations, and pore size distribution analyses. Furthermore, for the first time, an in situ COF-to-COF transformation has also been achieved by heating TP-COF-BZ with 1,4-diaminobenzene under solvothermal condition, which leads to the formation of TP-COF-DAB via in situ replacing the benzidine linkers in TP-COF-BZ with 1,4-diaminobenzene linkers.
Covalent organic frameworks (COFs) have emerged as a new class of cathode materials for energy storage in recent years. However, they are limited to two‐dimensional (2D) or three‐dimensional (3D) ...framework structures. Herein, this work reports designed synthesis of a redox‐active one‐dimensional (1D) COF and its composites with 1D carbon nanotubes (CNTs) via in situ growth. Used as cathode materials for Li‐ion batteries, the 1D COF@CNT composites with unique dendritic core–shell structure can provide abundant and easily accessible redox‐active sites, which contribute to improve diffusion rate of lithium ions and the corresponding specific capacity. This synergistic structural design enables excellent electrochemical performance of the cathodes, giving rise to 95% utilization of redox‐active sites, high rate capability (81% capacity retention at 10 C), and long cycling stability (86% retention after 600 cycles at 5 C). As the first example to explore the application of 1D COFs in the field of energy storage, this study demonstrates the great potential of this novel type of linear crystalline porous polymers in battery technologies.
One‐dimensional (1D) covalent organic framework (COF) has been explored as electrode materials for Li‐ion batteries. The cathodes exhibit excellent electrochemical performance, ultrahigh utilization of redox‐active sites, long cycling stability, and high rate capability. This work discloses the great application potential of 1D COF in high‐performance batteries.
Covalent organic frameworks (COFs) are an emerging class of crystalline porous organic polymers with potential for innovative applications. Here we report the use of COFs as precursors for the ...fabrication of well-defined tubular nanomaterials. A proof-of-concept study is presented for the controllable fabrication of organic nanotubes through selective disassembly of two-dimensional heteropore COFs. Two dual-pore COFs are constructed based on orthogonal reactions. Each COF possesses two different kinds of pores, which are formed by linking all-hydrzaone-bonded nanopores with boroxines. Selectively hydrolyzing boroxine rings in the COFs while keeping hydrazone linkages untouched gives rise to organic nanotubes with diameters and shapes corresponding to the nanochannels of the COFs.
Oily water caused in the process of industry leads to not only the waste of resources, but also environmental pollution. Membrane separation, as a facile and efficient separation technology, has ...attracted widespread attention in the field of oil/water separation. The development of membrane materials with high separation performance is one of the key elements to improve separation efficiency. In this work, a superhydrophobic membrane composited with a trifluoromethyl‐containing covalent organic framework (COF) is prepared, which exhibits excellent performance on separations of oil/water mixtures and water‐in‐oil emulsions. For different composition of oil/water mixtures, the highest flux of oil is up to 32 000 L m−2 h−1 and oil/water separation efficiency is above 99%. Moreover, the high oil/water separation efficiency remains unchanged after successive cycles. This work provides a feasible scheme for the design of high‐efficiency oil/water separation membranes.
A superhydrophobic membrane composited with a trifluoromethyl‐containing COF is prepared. The membrane exhibits excellent performance on separations of oil/water mixtures and water‐in‐oil emulsions. For different composition of oil/water mixtures, the highest flux of oil is up to 32 000 L m−2 h−1 and oil/water separation efficiency is above 99%. Moreover, the high oil/water separation efficiency remains unchanged after successive cycles.
Covalent organic framework nanosheets (COF NSs or CONs), as compared to their bulk counterparts two-dimensional (2D) covalent organic frameworks (COFs), exhibit superior performance in many aspects ...due to their fully accessible active sites benefiting from their ultrathin porous 2D structures. The development of a scalable synthetic methodology for CONs is crucial to further exploration of their unique properties and practical applications. Herein, we report an efficient strategy to fabricate ultrathin CONs through direct polycondensation of monomers under ultrasonic treatment and mild conditions. This method is facile and scalable, which is demonstrated by gram-scale synthesis of two ultrathin 2D CONs in several hours. Moreover, the as-prepared ultrathin CONs show excellent heterogeneous photocatalytic performance for the degradation of organic pollutants (dyes as representatives), remarkably superior to the bulk COFs prepared from the corresponding monomers under solvothermal conditions. This research provides a new roadmap for the scalable and facile synthesis of ultrathin CONs, which is of paramount importance for fully exploring the tremendous potential of this emerging type of 2D material.
We develop a strategy to efficiently fabricate ultrathin covalent organic framework nanosheets (CONs) through direct polycondensation of monomers under ultrasonic treatment. The CONs exhibit excellent photocatalytic performance for the degradation of organic pollutants.
The topology of a covalent organic framework (COF) is generally believed to be dictated by the symmetries of the monomers used for the condensation reaction. In this context, the use of monomers with ...different symmetries is usually required to afford COFs with different topologies. Herein, we report a conceptual strategy to regulate the topology of 2D COFs by introducing alkyl substituents into the skeleton of a parent monomer. The resulting monomers, sharing the same
symmetry, were assembled with a
symmetric tetraamine to generate a dual-pore COF or single-pore COFs, depending on the sizes of the substituents, which were evidenced using PXRD studies and pore size distribution analyses. These results demonstrate that the substituent is able to exert a significant influence on the topology of COFs, which is crucial for their application.
Accurate control of the layer number of orderly stacked 2D polymers has been an unsettled challenge in self‐assembly. Herein we describe the fabrication of a bilayer 2D supramolecular organic ...framework from a monolayer 2D supramolecular organic framework in water by utilizing the cooperative coordination of a rod‐like bipyridine ligands to zinc porphyrin subunits of the monolayer network. The monolayer supramolecular framework is prepared from the co‐assembly of an octacationic zinc porphyrin monomer and cucurbit8uril (CB8) in water through CB8‐encapsulation‐promoted dimerization of 4‐phenylpyridiunium subunits that the zinc porphyrin monomer bear. The bilayer 2D supramolecular organic framework exhibits structural regularity in both solution and the solid state, which is characterized by synchrotron small‐angle X‐ray scattering and high‐resolution transmission electron microscopic techniques. Atomic force microscopic imaging confirms that the bilayer character of the 2D supramolecular organic framework can be realized selectively on the micrometer scale.
Generation of a bilayer 2D supramolecular organic framework is realized by hierarchical assembly in water. The coordination of a rod‐like bipyridine ligand to the zinc porphyrin subunits of a monolayer supramolecular network has been utilized to selectively produce ordered bilayer supramolecular architectures with controlled thickness.
PDF
