Introduction
Covalent organic frameworks (COFs) are designed and synthesized by combining organic monomers, also known as linkers. Monomers containing aldehyde functional groups are the one of most common and widely used types of COF linkers. Typically, according to the number of binding sites, aldehyde COFs linkers can be divided into ditopic aldehyde linkers, tritopic aldehyde linkers, tetratopic aldehyde linkers, multi-aldehyde linkers, etc. To be more specific, the ditopic aldehyde COFs linker is an aldehyde-containing monomer with two binding sites, and so forth. So far, aldehyde COFs linkers have been used to synthesize various types of COFs, and these COFs have been widely used in substance capture, storage or separation, energy storage and conversion, metal-ion/sulfur batteries or supercapacitors, photo/electro-catalysis, biomedicine, etc.
Fig. 1. Typical examples of COFs monomers with aldehyde functional groups.
Applications
COFs can be divided into many types by the form of linkage between monomers in COFs. Aldehyde-containing linkers can be condensed with other linkers to form different linkage forms, and thus can construct different types of COFs materials.
- Synthesis of imine-linked COFs: The condensation between kinds of aldehydes-containing monomers and amino groups has been proved to successfully generate imine-linked COFs. Among them, benzaldehyde and its derivatives are the most commonly used aldehydes-containing monomers, while the amino group is usually supplied by substances containing p-phenylenediamines and their derivatives [1]. In 2009, the first three-dimensional imine-based COFs, COF-300, was reported by Yaghi research group, which was obtained by dehydration condensation of p-phenyldiformaldehyde and tetra-(4-aminophenyl) methane. And this COF has high thermal stability and permanent porosity with a surface area of 1360 m2g-1.
Fig. 2. Synthesis of COF-300.
- Synthesis of azine-linked COFs: Aldehydes-containing monomers can react with hydrazine via thermodynamically controlled condensation reaction to obtain common azine-linked COFs with hexagonal, rhombic, and trigonal structures [2]. Generally, the obtained COFs have high crystallinity, porosity, and excellent chemical stability in polar and non-polar organic solvents, even in inorganic acids and bases (such as HCl and NaOH aqueous solution) [1].
Fig. 3. Schematics for the synthesis of azine-based COF by aldehydes-containing linkers.
- Synthesis of aminal-linked COFs: Aldehydes-containing monomers can react with secondary amine to construct aminal-linked COFs, which is a relatively new type of COFs material. Jiang et al.[3] reported the first two COFs using aminal as the linkages, termed Aminal-COF-1 and Aminal-COF-2. These two COFs have been synthesized by condensation of D2h-symmetric tetraaldehydes and piperazine, inspired by the reaction between benzaldehyde and piperidine. These aminal-COFs exhibit good thermal stability and high chemical stability under neutral and basic conditions.
Fig. 4. Synthesis of aminal-based COFs (Aminal-COF-1 and Aminal-COF-2) by aldehydes-containing linkers.
- Synthesis of C=C linked COFs: Two monomers of aldehydes monomer containing benzaldehyde group and cyanogen monomer containing methylene group have been widely proved to form cyanostilbene-linked COFs. A series of sp2c-COFs with different linkers has been synthesized by this strategy (as shown in Fig.5). Furthermore, the condensation between two monomers of aldehydes monomer with benzaldehyde group and pyridine and its derivatives monomer bearing arylmethyl carbon atoms can also be used to construct C=C linked COFs.
Fig. 5. Schematic for the synthesis of (A) sp2c-COF, sp2c-COF-2, and sp2c-COF-3 by aldehydes-containing linkers.
Alfa Chemistry offers a series of aldehyde COFs linkers such as ditopic aldehyde linkers, tritopic aldehyde linkers, tetratopic aldehyde linkers, multi-aldehyde linkers, etc. These linkers have been widely used to construct imine-linked COFs, azine-linked COFs, aminal-linked COFs, C=C linked COFs, etc. You can click on our product list for a detailed view. At the same time, we also offer product customization according to customer's detailed requirements. If you are interested in our products or have any questions or needs, please feel free to contact us. We will be happy to provide you with support and services.
References:
- Li S., et al. Covalent organic frameworks: from linkages to biomedical applications[J]. Chemical Engineering Journal, 2022, 446: 137148.
- Geng K., et al. Covalent organic frameworks: design, synthesis, and functions[J]. Chemical Reviews, 2020, 120(16): 8814-8933.
- Jiang S. Y., et al. Aminal-linked covalent organic frameworks through condensation of secondary amine with aldehyde[J]. Journal of the American Chemical Society, 2019, 141(38): 14981-14986.
