A method for preparing highly crystalline covalent organic framework materials

Abstract

This invention discloses a method for preparing highly crystalline covalent organic framework materials using a eutectic solvent. Addressing the shortcomings of existing methods for preparing covalent organic framework materials, which involve harsh conditions, complex operations, and low crystallinity, this invention provides a method with mild synthesis conditions, simple operation, and highly crystalline covalent organic framework materials. The method includes the following steps: (1) Preparation of the eutectic solvent: A hydrogen bond donor and a hydrogen bond acceptor are mixed and heated to form a colorless, transparent homogeneous solution, thus obtaining the eutectic solvent. (2) Two-step preparation of the covalent organic framework material: An organic amine and the above-mentioned eutectic solvent are mixed and ground, and then an organic aldehyde is added and ground further. The ground mixture is then transferred to a reaction vessel for reaction. After the reaction, the crude covalent organic framework product is subjected to Soxhlet extraction and activated using supercritical carbon dioxide.

Description

Technical Field

[0001] This invention relates to the field of materials preparation technology, and in particular to a method for preparing highly crystalline covalent organic framework materials. Background Technology

[0002] Covalent organic frameworks (COFs) are a class of porous 2D or 3D organic materials with periodically ordered structures. They are constructed from monomers containing light elements (such as C, H, O, N, B, etc.) through covalent bonds and have been extensively studied in various fields such as adsorption separation, catalysis, drug delivery, and proton conduction. Among them, COFs linked by imine bonds formed by the dehydration condensation of organic amines and aldehyde monomers exhibit superior chemical stability compared to other types of COFs. With the continuous deepening of COF research, imine-linked COFs have become the most widely studied type. Currently, imine-linked COFs can be synthesized by various methods, including mechanical grinding, melting, and solvothermal methods. Among these, the solvothermal method is the most commonly used. However, the organic solvents commonly used in solvothermal synthesis, such as trimethylbenzene, o-dichlorobenzene, dioxane, and N,N-dimethylformamide, are highly toxic and pose a significant threat to health. In addition, the solvothermal method requires strict reaction conditions, including high temperature, high pressure, and long reaction time. Moreover, the success of this method is highly dependent on precise control of solvent composition and catalyst dosage, and careful optimization is required to obtain highly crystalline products from different monomers. Therefore, from both a green chemistry perspective and an economic standpoint, it is necessary to develop a universally applicable green solvent system for the synthesis of imine COFs.

[0003] Current research on the green synthesis of imine-based COFs mainly focuses on solvents and catalysts, but these two areas of research are relatively independent. Eutectic solvents (DES) are a novel analogue of ionic liquids (ILs) and are considered another new type of environmentally friendly liquid material besides traditional ILs. DES is formed by hydrogen bond acceptors (HBAs) and hydrogen bond donors (HBDs) linked by hydrogen bonds. It requires neither further purification with organic solvents nor subsequent processing; it can be used immediately after synthesis, and its atom utilization rate is 100%, making it a truly green solvent. Similar to ILs, DES possesses characteristics such as low vapor pressure, high thermal stability, non-flammability, and ease of preparation. Furthermore, DES also offers advantages such as low cost, non-toxicity, and biodegradability.

[0004] Existing technology CN113817116B discloses a method for preparing covalent organic framework materials, which involves dissolving organic aldehydes and organic amines in a eutectic solvent, adding acetic acid as a catalyst, and preparing the covalent organic framework material at room temperature. However, the PXRD pattern of the prepared covalent organic framework material shows only weak diffraction peaks at the corresponding crystal planes. Furthermore, no obvious lattice fringes were observed in the transmission electron microscopy (TEM) image, indicating that the covalent organic framework material prepared by this prior art has poor crystallinity and low crystallinity.

[0005] Existing technology CN110894299B discloses a method for synthesizing covalent organic framework materials using a eutectic solvent. This method involves adding organic aldehydes and amines to a DES (diethyl ether ester), freezing the reactor with liquid nitrogen, and then flame-sealing it under vacuum to obtain the crude product. However, this method is complex to operate.

[0006] Existing technology CN119060282A discloses a covalent organic framework material, its preparation method, and its application. This method uses a two-component eutectic solvent composed of menthol and acetic acid to condense organic aldehydes and organic amines in the eutectic solvent to obtain the covalent organic framework material. However, this method requires soaking in cyclohexane, and the resulting product has an irregular morphology.

[0007] To address the above problems, this invention proposes a green method for preparing highly crystalline covalent organic framework materials through a two-step process using a eutectic solvent. Summary of the Invention

[0008] In view of this, in order to overcome the defects and shortcomings of existing covalent organic framework material preparation methods, such as harsh conditions, complex operations, and low crystallinity of the prepared covalent organic framework materials, this invention provides a method for preparing covalent organic framework materials.

[0009] The above-mentioned objective of this invention is achieved through the following technical solution:

[0010] A method for preparing a highly crystalline covalent organic framework material, comprising the following steps:

[0011] S1. Preparation of eutectic solvent: Mix hydrogen bond donor and hydrogen bond acceptor and react under heating conditions for 0.5~1.5h to form a colorless and transparent homogeneous solution, which is the eutectic solvent.

[0012] S2. Preparation of covalent mailing frame materials:

[0013] a. Mix the organic amine and the above-mentioned eutectic solvent and grind them, then add the organic aldehyde and continue grinding;

[0014] b. Transfer the ground mixture to a reaction vessel and react at 80~120℃ for 2~72h. After the reaction is completed, wash, purify and dry to obtain the covalent organic framework material.

[0015] Furthermore, the hydrogen bond donor is one of benzoic acid, urea, and ethylene glycol, and the hydrogen bond acceptor is choline chloride.

[0016] Preferably, the hydrogen bond donor is benzoic acid, the hydrogen bond acceptor is choline chloride, and the molar ratio of choline chloride to the hydrogen bond donor is 1:(0.75-1.5). More preferably, the molar ratio is 1:1.

[0017] Further, the organic amine is one of p-phenylenediamine, tris(4-aminophenyl)amine, 1,3,5-tris(4-aminophenyl)benzene, and 1,3,5-tris(4-aminophenyl)triazine; the organic aldehyde is one of trialdehyde-resorcinol, 1,4-terephthalaldehyde, 2,5-dimethoxy-1,4-benzenedialdehyde, and 2,5-dihydroxy-1,4-dicarboxaldehyde.

[0018] Preferably, the molar ratio of the organic amine to the organic aldehyde is 1:1, 1:1.5, or 1.5:1.

[0019] Preferably, the total concentration of the organic aldehyde and organic amine in the eutectic solvent is 0.02-1.5 mmol / mL.

[0020] Furthermore, the purification process involves washing the crude covalent organic framework product with water and ethanol, followed by Soxhlet extraction with tetrahydrofuran.

[0021] Preferably, it also includes post-processing, specifically: activating the covalent organic framework product after Soxhlet extraction using supercritical carbon dioxide to increase the specific surface area.

[0022] The above technical solution has the following beneficial effects:

[0023] The preparation method of this invention features mild synthesis conditions and simple operation. Furthermore, it does not use organic solvents and eliminates the need for complex operations such as vacuuming. The resulting covalent organic framework material exhibits a regular morphology and high crystallinity. Compared to traditional synthesis methods, this method is less polluting, has milder reaction conditions, is simple to operate, has good versatility, and is conducive to large-scale industrial production, aligning with the principles of green chemistry. Attached Figure Description

[0024] Figure 1 XRD pattern of covalent organic framework material;

[0025] Figure 2 Scanning electron microscopy of covalent organic framework materials;

[0026] Figure 3 This is a structural diagram of the covalent organic framework material in Example 2. Detailed Implementation

[0027] To explain in detail the technical content, structural features, objectives, and effects of the technical solution, the following detailed description is provided in conjunction with specific embodiments.

[0028] Example 1

[0029] (1) Preparation of eutectic solvent: Benzoic acid (0.1 M) and choline chloride (0.1 M) are mixed and stirred and heated at 90°C for 0.5 h to form a colorless and transparent homogeneous solution, which is the eutectic solvent of choline chloride-benzoic acid. The solvent is stored in a vacuum drying oven for later use.

[0030] (2) Preparation of covalent organic framework material: 3 g of DES solvent was placed in a mortar, 0.1 mM 1,3,5-tris(4-aminophenyl)benzene was added, and the mixture was ground for 5 min. Then, 0.15 mM 1,4-terephthalaldehyde was added and ground for another 5 min to form a slurry. The slurry was transferred to a hydrothermal reactor and reacted at 100℃ for 1 day. After washing with water and ethanol, the covalent organic framework material was obtained by Soxhlet extraction with tetrahydrofuran. Its XRD pattern is shown below. Figure 1 As shown, it exhibits high crystallinity; the scanning electron microscope image is as follows. Figure 2 As shown, the prepared material exhibits a regular rod shape.

[0031] Example 2

[0032] (1) Preparation of eutectic solvent: Same as in Example 1.

[0033] (2) Preparation of covalent organic framework material: 3 g of DES solvent was placed in a mortar, 0.15 mM p-phenylenediamine was added and ground for 5 min, then 0.1 mM trialdehyde phloroglucinol was added and ground for 5 min to form a slurry; the slurry was transferred to a hydrothermal reactor and reacted at 120℃ for 1 day, then removed; after washing with water and ethanol, the covalent organic framework material was obtained by Soxhlet extraction with tetrahydrofuran, and the structural diagram is shown below. Figure 3 As shown.

[0034] Example 3

[0035] (1) Preparation of eutectic solvent: Benzoic acid (0.075 M) and choline chloride (0.1 M) were mixed and stirred and heated at 90°C for 0.5 h to form a colorless and transparent homogeneous solution, which is the eutectic solvent of choline chloride-benzoic acid. The solvent was stored in a vacuum drying oven for later use.

[0036] (2) Preparation of covalent organic framework material: 10 g of DES solvent was placed in a mortar, 1 mM 1,3,5-tris(4-aminophenyl)triazine was added and ground for 5 min, and then 1.5 mM 2,5-dimethoxy-1,4-benzaldehyde was added and ground for 5 min to form a slurry. The slurry was transferred to a hydrothermal reactor and reacted at 100℃ for 2 days. After washing with water and ethanol, the covalent organic framework material was obtained by Soxhlet extraction with tetrahydrofuran.

[0037] Example 4

[0038] (1) Preparation of eutectic solvent: Same as in Example 3.

[0039] (2) Preparation of covalent organic framework material: 10 g of DES solvent was placed in a mortar, 1 mM tris(4-aminophenyl)amine was added and ground for 5 min, and then 1.5 mM 2,5-dihydroxy-1,4-dicarboxaldehyde was added and ground for 5 min to form a slurry. The slurry was transferred to a hydrothermal reactor and reacted at 90℃ for 12 h. After washing with water and ethanol, the covalent organic framework material was obtained by Soxhlet extraction with tetrahydrofuran.

[0040] Example 5

[0041] (1) Preparation of eutectic solvent: urea (0.15 M) and choline chloride (0.1 M) are mixed and heated at 90°C for 0.5 h to form a colorless and transparent homogeneous solution, which is the eutectic solvent of choline chloride-urea. The solvent is stored in a vacuum drying oven for later use.

[0042] (2) Preparation of covalent organic framework material: 5 g of DES solvent was placed in a mortar, 1.5 mM 1,3,5-tris(4-aminophenyl)benzene was added and ground for 5 min, and then 1.5 mM trialdehyde phloroglucinol was added and ground for 5 min to form a slurry. The slurry was transferred to a hydrothermal reactor and reacted at 80℃ for 2 days. After washing with water and ethanol, the covalent organic framework material was obtained by Soxhlet extraction with tetrahydrofuran.

[0043] Example 6

[0044] (1) Preparation of eutectic solvent: Ethylene glycol and choline chloride are mixed in a molar ratio of 1:1 and stirred and heated at 70°C for 0.5 h to form a colorless and transparent homogeneous solution, which is the eutectic solvent of choline chloride-urea. The solvent is stored in a vacuum drying oven for later use.

[0045] (2) Preparation of covalent organic framework material: 5 g of DES solvent was placed in a mortar, 1 mM 1,3,5-tris(4-aminophenyl)amine was added and ground for 5 min, and then 1.5 mM 2,5-dimethoxy-1,4-benzaldehyde was added and ground for 5 min to form a slurry. The slurry was transferred to a hydrothermal reactor and reacted at 80℃ for 2 days. After washing with water and ethanol, the covalent organic framework material was obtained by Soxhlet extraction with tetrahydrofuran.

[0046] The above embodiments are preferred embodiments of the present invention, but the embodiments of the present invention are not limited to the above embodiments. Any changes, modifications, substitutions, combinations, or simplifications made without departing from the spirit and principle of the present invention shall be considered equivalent substitutions and shall be included within the protection scope of the present invention.

Claims

1. A method for preparing a highly crystalline covalent organic framework material, characterized in that, The steps are as follows: S1. Preparation of eutectic solvent: Mix hydrogen bond donor and hydrogen bond acceptor and react under heating conditions for 0.5~1.5h to form a colorless and transparent homogeneous solution, which is the eutectic solvent. S2. Preparation of covalent mailing frame materials: a. Mix the organic amine and the above-mentioned eutectic solvent and grind them, then add the organic aldehyde and continue grinding; b. Transfer the ground mixture to a reaction vessel and react at 80~120℃ for 2~72h. After the reaction is completed, wash, purify and dry to obtain the covalent organic framework material.

2. The preparation method according to claim 1, characterized in that, The hydrogen bond donor is one of benzoic acid, urea, or ethylene glycol, and the hydrogen bond acceptor is choline chloride.

3. The preparation method according to claim 2, characterized in that, The molar ratio of choline chloride to hydrogen bond donor is 1:(0.75-1.5).

4. The preparation method according to claim 1, characterized in that, The organic amine is one of p-phenylenediamine, tris(4-aminophenyl)amine, 1,3,5-tris(4-aminophenyl)benzene, and 1,3,5-tris(4-aminophenyl)triazine; the organic aldehyde is one of trialdehyde-resorcinol, 1,4-terephthalaldehyde, 2,5-dimethoxy-1,4-benzenedialdehyde, and 2,5-dihydroxy-1,4-dicarboxaldehyde.

5. The preparation method according to claim 4, characterized in that, The molar ratio of the organic amine to the organic aldehyde is 1:1, 1:1.5, or 1.5:

1.

6. The preparation method according to claim 5, characterized in that, The total concentration of the organic aldehydes and organic amines in the eutectic solvent is 0.02-1.5 mmol / mL.

7. The preparation method according to claim 1, characterized in that, The purification method is as follows: the crude covalent organic framework product is washed with water and ethanol, and then Soxhlet extracted with tetrahydrofuran.

8. The preparation method according to claim 7, characterized in that, It also includes post-processing, specifically the activation of the covalent organic framework product after Soxhlet extraction using supercritical carbon dioxide.

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