A method for improving crystallinity of a flexible covalent organic framework membrane by solvothermal treatment

Abstract

This invention discloses a method for improving the crystallinity of flexible covalent organic framework (COF) membranes through solvothermal treatment, relating to the field of flexible functional membrane materials. The method includes the following steps: (1) synthesizing a COF membrane; (2) immersing the COF membrane in a triethylamine-methanol solution to remove residual acidic components; and (3) placing the treated membrane in an acetic acid-acetonitrile solution and heating it at 100°C for 0.5-6 hours to improve the crystallinity of the membrane. This invention achieves the rearrangement of the backbone chain segments and the enhancement of crystallinity in the membrane through a mild two-step solution treatment process, significantly improving the XRD diffraction intensity, membrane density, and structural order of the COF membrane, while maintaining the flexibility and mechanical properties of the original membrane.

Description

Technical Field

[0001] This invention relates to the field of flexible functional membrane materials technology, and specifically to a method for improving the crystallinity of flexible covalent organic framework membranes through solvothermal treatment. Background Technology

[0002] Covalent organic frameworks (COFs) are a class of highly ordered, porous, and designable crystalline polymers composed of light elements (such as C, H, O, N, B, etc.) linked by dynamic covalent bonds to form organic molecular units. They have significant advantages in structural diversity, specific surface area, functionalization control, and thermal stability, and their application research has grown exponentially since they were first proposed in 2005.

[0003] Especially in the field of membrane materials, COF membranes, with their characteristics of tailorability, high molecular selectivity, and stability, have become a research hotspot in gas separation, proton exchange membranes, and flexible devices. However, there are still contradictions between the film formation rate, film uniformity, mechanical properties, and crystallinity of the flexible COF membranes currently prepared. In particular, COF membranes synthesized under rapid reaction conditions often exhibit a disordered or semi-crystalline state due to the rapid solidification speed and insufficient crystal nucleation. Their XRD patterns often show no obvious Bragg diffraction peaks or broad peaks, with only weak C=N functional group formation signals.

[0004] Current academic literature reports that methods such as solvent-assisted recrystallization, vapor-induced crystallization, and long-term heat treatment can improve the crystallinity of COF powder or film. However, these methods usually have problems such as long cycle time (24-72h), high energy consumption, and damage to film morphology.

[0005] Therefore, there is an urgent need to develop a crystallization enhancement method that is universally applicable, time-controllable, and does not damage the membrane structure, suitable for the post-processing of various flexible COF membranes, to improve their crystal integrity and application performance. Summary of the Invention

[0006] To address the aforementioned problems, this invention provides a method for improving the crystallinity of flexible covalent organic framework membranes through solvothermal treatment. This invention achieves the rearrangement of the backbone chain segments in the membrane and enhances the crystallinity through a mild two-step solution treatment process, significantly improving the XRD diffraction intensity, membrane compactness, and structural order of the COF membrane, while maintaining the flexibility and mechanical properties of the original membrane.

[0007] To achieve the above objectives, the present invention adopts the following technical solution:

[0008] A method for improving the crystallinity of flexible covalent organic framework membranes by solvothermal treatment, wherein the method comprises heat-treating the flexible covalent organic framework membrane in a mixed solution of acetic acid and acetonitrile for 0.5-6 hours.

[0009] The method of this invention achieves rearrangement of COF backbone segments in a heterogeneous environment, thereby improving its crystallinity. The XRD pattern of the treated film shows an increase in the main peak intensity of at least 3 times that before treatment, and the crystal plane indices (such as 100 and 110 planes) are clearly distinguishable.

[0010] Preferably, the heat treatment temperature is 60-160℃, more preferably 80-140℃, and the XRD is best when heat-treated at 100-120℃.

[0011] Preferably, the volume ratio of acetic acid to acetonitrile in the acetic acid-acetonitrile mixed solution is 1:10-50.

[0012] Preferably, the flexible covalent organic framework membrane needs to be deacidified before heat treatment to neutralize residual trifluoroacetic acid and prevent it from affecting the stability of the framework during subsequent heat treatment.

[0013] Preferably, the method for removing acid is as follows: the flexible covalent organic framework membrane is completely immersed in a triethylamine methanol solution and left to stand at room temperature for 10-30 minutes.

[0014] Preferably, the volume ratio of triethylamine to methanol in the triethylamine methanol solution is 1:9.

[0015] Preferably, the thickness of the flexible covalent organic framework membrane is 10-40 μm, it has good peelability, and its flexibility allows it to be bent at 180° without breaking.

[0016] Preferably, the method for preparing the flexible covalent organic framework membrane is as follows:

[0017] Aldehyde monomers and amine monomers are dissolved separately in an aqueous solution of trifluoroacetic acid and then mixed. The mixture is heated on a heating plate at 100°C for 3-5 minutes until the solvent has completely evaporated, thus forming a flexible covalent organic framework membrane.

[0018] If the temperature is too high during the preparation process, the resulting film is prone to cracking; if the temperature is too low, the solvent evaporates slowly and a gel is easily formed.

[0019] Preferably, the aldehyde monomer is at least one selected from isophthalaldehyde, terephthalaldehyde, 2,5-dihydroxyterephthalaldehyde, 2,5-dimethoxyterephthalaldehyde, tris(4-formylphenyl)amine, and trialdehyde-resorcinol.

[0020] The amine monomer is tris(4-aminophenyl)amine.

[0021] Preferably, the molar ratio of the aldehyde group in the aldehyde monomer to the amino group in the amine monomer is 1:1.

[0022] Preferably, the volume ratio of trifluoroacetic acid to water in the trifluoroacetic acid aqueous solution is 95:5. Any other ratio will not form a film and will only form powder.

[0023] Compared with the prior art, the present invention has the following beneficial effects:

[0024] (1) The method of the present invention is simple to operate, has a short reaction time, and can quickly improve the quality of the membrane crystals;

[0025] (2) The method of the present invention has mild conditions and does not damage the flexibility and surface structure integrity of the membrane;

[0026] (3) The method of the present invention has wide applicability to a variety of COF systems and is highly versatile;

[0027] (4) The method of the present invention can significantly improve the intensity of the main peak of XRD and realize crystal plane identification and structure simulation. Attached Figure Description

[0028] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. The drawings in this description are merely embodiments of the present invention.

[0029] Figure 1 This is an optical image of the TAPA-PDA COF film before heat treatment in Example 1 of the present invention;

[0030] Figure 2 The XRD patterns of the TAPA-PDA COF membrane before and after heat treatment in Example 1 of this invention are shown below.

[0031] Figure 3 This is an optical image of the TAPA-MDA COF film before heat treatment in Embodiment 2 of the present invention;

[0032] Figure 4 The XRD patterns of the TAPA-MDA COF membrane before and after heat treatment in Example 2 of this invention are shown.

[0033] Figure 5 This is an optical image of the TAPA-DHTA COF film before heat treatment in Example 3 of the present invention;

[0034] Figure 6 The XRD patterns of the TAPA-DHTA COF membrane before and after heat treatment in Example 3 of this invention are shown.

[0035] Figure 7 This is an optical image of the TAPA-DMeOTA COF film before heat treatment in Example 4 of the present invention;

[0036] Figure 8 The XRD patterns of the TAPA-DMeOTA COF membrane before and after heat treatment in Example 4 of this invention are shown.

[0037] Figure 9This is an optical image of the TpTAPA COF film before heat treatment in Embodiment 5 of the present invention;

[0038] Figure 10 The XRD patterns of the TpTAPA COF membrane before and after heat treatment in Example 5 of this invention are shown below.

[0039] Figure 11 This is an optical image of the TFPA-TAPA COF film before heat treatment in Embodiment 6 of the present invention;

[0040] Figure 12 The XRD patterns of the TFPA-TAPA COF membrane of Example 6 of the present invention at different heat treatment times;

[0041] Figure 13 The XRD patterns of the TAPA-PDA COF film at different heat treatment temperatures in Example 1 of this invention are shown.

[0042] Figure 14 This is an optical image of the TAPA-PDA COF film after heat treatment at 100°C in Example 1 of the present invention. Detailed Implementation

[0043] Embodiments of the present invention are described below, examples of which are shown in the accompanying drawings. The embodiments described with reference to the drawings are exemplary and intended to explain the present invention, but are not to be construed as limiting the present invention.

[0044] Example 1

[0045] This invention provides a method for improving the crystallinity of flexible covalent organic framework films through solvothermal treatment, specifically including the following steps:

[0046] (1) Film formation steps: Weigh 0.05 mol of tris(4-aminophenyl)amine and 0.075 mol of terephthalaldehyde, dissolve them separately in 500 μL of trifluoroacetic acid / water (volume ratio 95:5), disperse them by ultrasonication, mix them, pour them into a quartz mold, heat at 100℃ for 3 min, cool and peel off to obtain the film, which is named TAPA-PDA COF; the synthesis route is as follows:

[0047]

[0048] (2) Deacidification step: Immerse the membrane in 5 mL of triethylamine / methanol (volume ratio 1:9) for 20 min to neutralize the free acid, and then rinse with ethanol;

[0049] (3) Heat treatment steps: Transfer the deacidified membrane into 10 mL of acetic acid / acetonitrile (volume ratio 1:50), seal and place in a 100℃ oven for heat treatment for 6 hours. After cooling, wash and dry. Figure 1 Optical image of TAPA-PDA COF film before heat treatment. Figure 2 The XRD patterns of the TAPA-PDA COF film before and after heat treatment are shown in the figure. It can be seen from the figure that the intensity of the main COF peak is improved and the crystal diffraction peak is sharpened.

[0050] Figure 13 The XRD patterns of the TAPA-PDA COF film at different heat treatment temperatures in this embodiment of the invention are shown in the figure. As can be seen from the figure, the COF main peak intensity is best at 100℃.

[0051] Figure 14 The image shows an optical image of the TAPA-PDA COF film after heat treatment at 100°C according to an embodiment of the present invention. As can be seen from the image, the film remains intact after treatment in acetonitrile acetic acid solution at 100°C.

[0052] Example 2

[0053] This invention provides a method for improving the crystallinity of flexible covalent organic framework films through solvothermal treatment, specifically including the following steps:

[0054] (1) Film formation steps: Weigh 0.05 mol of tris(4-aminophenyl)amine and 0.075 mol of isophthalaldehyde, dissolve them separately in 500 μL of trifluoroacetic acid / water (volume ratio 95:5), disperse them by ultrasonication, mix them, pour them into a quartz mold, heat at 100℃ for 3 min, cool and peel off to obtain the film, which is named TAPA-MDA COF; the synthesis route is as follows:

[0055]

[0056] (2) Deacidification step: Immerse the membrane in 5 mL of triethylamine / methanol (volume ratio 1:9) for 20 min to neutralize the free acid, and then rinse with ethanol;

[0057] (3) Heat treatment steps: Transfer the deacidified membrane into 10 mL of acetic acid / acetonitrile (volume ratio 1:50), seal and place in a 100℃ oven for heat treatment for 6 hours. After cooling, wash and dry. Figure 3 Optical image of TAPA-MDA COF film before heat treatment. Figure 4 The images show the XRD patterns of the TAPA-MDA COF film before and after heat treatment. As can be seen from the images, the intensity of the COF main peak is increased, and the crystal diffraction peaks are sharpened.

[0058] Example 3

[0059] This invention provides a method for improving the crystallinity of flexible covalent organic framework films through solvothermal treatment, specifically including the following steps:

[0060] (1) Film formation steps: Weigh 0.05 mol of tris(4-aminophenyl)amine and 0.075 mol of 2,5-dihydroxyterephthalaldehyde, dissolve them separately in 500 μL of trifluoroacetic acid / water (volume ratio 95:5), disperse them by ultrasonication, mix them, pour them into a quartz mold, heat at 100℃ for 3 min, cool and peel off to obtain the film, which is named TAPA-DHTA COF; the synthesis route is as follows:

[0061]

[0062] (2) Deacidification step: Immerse the membrane in 5 mL of triethylamine / methanol (volume ratio 1:9) for 20 min to neutralize the free acid, and then rinse with ethanol;

[0063] (3) Heat treatment steps: Transfer the deacidified membrane into 10 mL of acetic acid / acetonitrile (volume ratio 1:50), seal and place in a 100℃ oven for heat treatment for 6 hours. After cooling, wash and dry. Figure 5 Optical image of TAPA-DHTA COF film before heat treatment. Figure 6 The images show the XRD patterns of the TAPA-DHTA COF film before and after heat treatment. As can be seen from the images, the intensity of the COF main peak is enhanced, and the crystal diffraction peaks are sharpened.

[0064] Example 4

[0065] This invention provides a method for improving the crystallinity of flexible covalent organic framework films through solvothermal treatment, specifically including the following steps:

[0066] (1) Film formation steps: Weigh 0.05 mol of tris(4-aminophenyl)amine and 0.075 mol of 2,5-dimethoxyterephthalaldehyde, and dissolve them separately in 500 μL of trifluoroacetic acid / water (volume ratio 95:5). After ultrasonic dispersion, mix the solutions, pour the mixture into a quartz mold, heat at 100℃ for 3 min, and peel off the membrane after cooling. Name the membrane TAPA-DMeOTA COF. The synthesis route is as follows:

[0067]

[0068] (2) Deacidification step: Immerse the membrane in 5 mL of triethylamine / methanol (volume ratio 1:9) for 20 min to neutralize the free acid, and then rinse with ethanol;

[0069] (3) Heat treatment steps: Transfer the deacidified membrane into 10 mL of acetic acid / acetonitrile (volume ratio 1:50), seal and place in a 100℃ oven for heat treatment for 6 hours. After cooling, wash and dry. Figure 7 Optical image of TAPA-DMeOTA COF film before heat treatment. Figure 8The images show the XRD patterns of the TAPA-DMeOTA COF film before and after heat treatment. As can be seen from the images, the intensity of the COF main peak is enhanced, and the crystal diffraction peaks are sharpened.

[0070] Example 5

[0071] This invention provides a method for improving the crystallinity of flexible covalent organic framework films through solvothermal treatment, specifically including the following steps:

[0072] (1) Film formation steps: Weigh 0.05 mol of tris(4-aminophenyl)amine and 0.05 mol of trialdehyde-resorcinol, dissolve them separately in 500 μL of trifluoroacetic acid / water (volume ratio 95:5), disperse them by ultrasonication, mix them, pour them into a quartz mold, heat at 100℃ for 3 min, cool and peel off to obtain the film, which is named TpTAPA COF; the synthesis route is as follows:

[0073]

[0074] (2) Deacidification step: Immerse the membrane in 5 mL of triethylamine / methanol (volume ratio 1:9) for 20 min to neutralize the free acid, and then rinse with ethanol;

[0075] (3) Heat treatment steps: Transfer the deacidified membrane into 10 mL of acetic acid / acetonitrile (volume ratio 1:50), seal and place in a 100℃ oven for heat treatment for 6 hours. After cooling, wash and dry. Figure 9 Optical image of TpTAPA COF film before heat treatment. Figure 10 The images show the XRD patterns of the TpTAPA COF film before and after heat treatment. As can be seen from the images, the intensity of the COF main peak is increased, and the crystal diffraction peaks are sharpened.

[0076] Example 6

[0077] This invention provides a method for improving the crystallinity of flexible covalent organic framework films through solvothermal treatment, specifically including the following steps:

[0078] (1) Film formation steps: Weigh 0.05 mol of tris(4-aminophenyl)amine and 0.05 mol of tris(4-formylphenyl)amine, dissolve them separately in 500 μL of trifluoroacetic acid / water (volume ratio 95:5), disperse them by ultrasonication, mix them, pour them into a quartz mold, heat at 100℃ for 3 min, cool and peel off to obtain the film, which is named TFPA-TAPA COF; the synthesis route is as follows:

[0079]

[0080] (2) Deacidification step: Immerse the membrane in 5 mL of triethylamine / methanol (volume ratio 1:9) for 20 min to neutralize the free acid, and then rinse with ethanol;

[0081] (3) Heat treatment steps: Transfer the deacidified membrane into 10 mL of acetic acid / acetonitrile (volume ratio 1:50), seal and place in a 100℃ oven for heat treatment for 0-6 hours. After cooling, wash and dry. Figure 11 Optical image of TFPA-TAPA COF film before heat treatment. Figure 12 The figure shows the XRD patterns of TFPA-TAPA COF films at different heat treatment times. As can be seen from the figure, the intensity of the COF main peak increases with the increase of heat treatment time.

[0082] As can be seen from the above, the solvothermal treatment strategy of the present invention can improve the crystallinity of COF membranes without changing the structural integrity and flexibility, providing a new approach for the large-scale production of multifunctional flexible COF membranes in high-performance applications.

[0083] The above embodiments are only used to illustrate the technical solutions of the present invention, and are not intended to limit it. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for improving the crystallinity of flexible covalent organic framework films by solvothermal treatment, characterized in that, The method involves heat-treating a flexible covalent organic framework membrane in a mixed solution of acetic acid and acetonitrile for 0.5-6 hours. The flexible covalent organic framework membrane needs to be deacidified before heat treatment; The flexible covalent organic framework membrane is prepared by dissolving aldehyde monomers and amine monomers in trifluoroacetic acid aqueous solution, mixing them, heating on a heating plate at 100°C, and forming a flexible covalent organic framework membrane after the solvent has completely evaporated.

2. The method for improving the crystallinity of flexible covalent organic framework films by solvothermal treatment according to claim 1, characterized in that, The heat treatment temperature is 60-160℃.

3. The method for improving the crystallinity of flexible covalent organic framework films by solvothermal treatment according to claim 1, characterized in that, The volume ratio of acetic acid to acetonitrile in the acetic acid-acetonitrile mixed solution is 1:10-50.

4. The method for improving the crystallinity of flexible covalent organic framework films by solvothermal treatment according to claim 1, characterized in that, The method for removing acid is as follows: immerse the flexible covalent organic framework membrane in a triethylamine methanol solution and let it stand at room temperature for 10-30 minutes.

5. The method for improving the crystallinity of flexible covalent organic framework films by solvothermal treatment according to claim 4, characterized in that, The volume ratio of triethylamine to methanol in the triethylamine methanol solution is 1:

9.

6. The method for improving the crystallinity of flexible covalent organic framework films by solvothermal treatment according to claim 1, characterized in that, The aldehyde monomer is at least one selected from isophthalaldehyde, terephthalaldehyde, 2,5-dihydroxyterephthalaldehyde, 2,5-dimethoxyterephthalaldehyde, tris(4-formylphenyl)amine, and trialdehyde-resorcinol. The amine monomer is tris(4-aminophenyl)amine.

7. The method for improving the crystallinity of flexible covalent organic framework films by solvothermal treatment according to claim 1, characterized in that, The molar ratio of the aldehyde group in the aldehyde monomer to the amino group in the amine monomer is 1:

1.

8. The method for improving the crystallinity of flexible covalent organic framework films by solvothermal treatment according to claim 1, characterized in that, The volume ratio of trifluoroacetic acid to water in the trifluoroacetic acid aqueous solution is 95:5.

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