Zwitterionic covalent organic framework membranes and methods of making and using the same

Abstract

The application discloses a kind of zwitterionic covalent organic framework membranes and preparation method and application thereof, belong to the technical field of separation membrane material, continuous covalent organic framework membrane is in-situ constructed on the surface of porous support base film by interfacial polymerization reaction, then the membrane is sequentially soaked in organic phase solution containing polyacyl chloride and aqueous solution containing zwitterion, and zwitterionic covalent organic framework membrane is obtained after heat treatment.The continuous covalent organic framework membrane hole channel is through, can be used as the rapid transfer channel of molecule, it is favorable to obtain high permeation flux;Zwitterionic is carried out on its surface, on the one hand, the hydrophilicity of membrane surface can be improved, on the other hand, the pore structure of membrane surface can be controlled, while forming water selective transport channel, competitive alcohol molecules are excluded.The preparation method of the application is simple and controllable, and the prepared composite membrane is used in pervaporation ethanol dehydration process, and excellent separation performance and long-term operation stability are shown.

Description

Technical Field

[0001] This invention relates to the fields of membrane material preparation and membrane separation technology, specifically to a zwitterionic covalent organic framework membrane, its preparation method, and its application. Background Technology

[0002] Pervaporation membranes, as an emerging membrane separation technology, offer advantages such as high efficiency, energy saving, environmental friendliness, and flexible operation. They are commonly used for separating liquid mixtures, particularly suitable for near-boiling or azeotropic systems that are difficult to separate using traditional distillation. They also demonstrate significant advantages in removing trace impurities from liquid mixtures. Membrane materials are the core of membrane separation technology; ideal membrane materials should possess high permeability, high selectivity, and high stability. Currently, commercially available membrane materials are traditional polymers, but these suffer from problems such as small free volume within the membrane, discontinuous channels, and easy swelling. Furthermore, they are limited by the trade-off effect, where permeability and selectivity cannot be simultaneously improved, making it difficult to achieve highly efficient separation performance. Therefore, the development and design of novel porous membrane materials are of great significance.

[0003] Covalent organic frameworks (COFrames) possess characteristics such as regular pores, high porosity, controllable structure, and ease of functionalization. They exhibit significantly higher permeability than traditional polymer membranes, and their strong covalent bonding allows them to maintain structural stability in harsh liquid environments, demonstrating great potential in liquid separation and the possibility of overcoming the trade-off effect. Compared to discontinuous COFrame membranes prepared by blending, continuous COFrame membranes prepared by interfacial polymerization can leverage the advantages of their pore structure in separation. However, the intrinsic building block structure of COFrames results in insufficient hydrophilicity, and their relatively large pore size makes effective separation of small liquid molecule mixtures difficult, especially for mixtures with coupling effects and similar molecular sizes. Therefore, the research and development of continuous COFrame membranes suitable for separating small liquid molecule mixtures has become a focus in the field of separation. Summary of the Invention

[0004] The purpose of this section is to outline some aspects of embodiments of the present invention and to briefly describe some preferred embodiments. Simplifications or omissions may be made in this section, as well as in the abstract and title of this application, to avoid obscuring the purpose of these documents; however, such simplifications or omissions should not be construed as limiting the scope of the invention.

[0005] In view of the problems existing in the above and / or prior art, the present invention is proposed.

[0006] Therefore, the purpose of this invention is to overcome the shortcomings of the prior art and provide a method for preparing zwitterionic covalent organic framework membranes.

[0007] To solve the above-mentioned technical problems, the present invention provides the following technical solution: including,

[0008] The porous support substrate membrane is immersed in an aqueous solution of amine monomers containing a catalyst and tumbled dry with a rubber roller until there are no water stains on the surface; then it is immersed in an organic solution of aldehyde monomers to carry out a polymerization reaction, and after the reaction, it is dried and heat-treated to obtain a covalent organic framework membrane.

[0009] The covalent organic framework membrane is first immersed in a polyacrylamide chloride organic phase solution and then immersed in a zwitterionic aqueous phase solution. After being dried by rubber rollers, it is subjected to heat treatment to obtain a zwitterionic covalent organic framework membrane.

[0010] The concentration of the zwitterionic material in the zwitterionic aqueous solution is 0.01–2 wt%, and the zwitterionic material is prepared from N-aminoethylpiperazine and 1,3-propanesulfonate lactone.

[0011] As a preferred embodiment of the method for preparing the zwitterionic covalent organic framework membrane of the present invention, the porous supporting substrate membrane includes one of polyacrylonitrile ultrafiltration membrane, polyvinyl alcohol ultrafiltration membrane, and polyvinylidene fluoride ultrafiltration membrane.

[0012] As a preferred embodiment of the preparation method of the zwitterionic covalent organic framework membrane of the present invention, when the porous supporting base membrane is a polyacrylonitrile ultrafiltration membrane, it is first subjected to heat treatment with sodium hydroxide solution to obtain a hydrolyzed polyacrylonitrile ultrafiltration membrane, wherein the heat treatment temperature is 50-60°C, the treatment time is 0.5-1.5h, and the concentration of the sodium hydroxide solution used is 1-2M.

[0013] In a preferred embodiment of the method for preparing the zwitterionic covalent organic framework membrane of the present invention, the following steps are performed: immersion in an aqueous solution of an amine monomer containing a catalyst, wherein the catalyst comprises one of acetic acid and p-toluenesulfonic acid, with a concentration of 0.01–2 wt%; the amine monomer comprises one of hydrazine hydrate, p-phenylenediamine, and biphenylenediamine, with a concentration of 0.001–2 wt%; and the immersion time is 1–10 min.

[0014] In a preferred embodiment of the method for preparing the zwitterionic covalent organic framework membrane of the present invention, the immersion in an aldehyde monomer organic phase solution, wherein the aldehyde monomer includes one of pyromellitic terephthalaldehyde, trialdehyde-resorcinol, terephthalaldehyde, and 2,5-dihydroxyterephthalaldehyde, with a concentration of 0.001-1 wt%, the organic phase includes one of n-hexane and n-heptane, and the immersion time is 30-300 s.

[0015] As a preferred embodiment of the method for preparing the zwitterionic covalent organic framework membrane of the present invention, wherein: the polyacrylamide chloride organic phase solution includes one of trimesoyl chloride, terephthaloyl chloride, and isophthaloyl chloride, with a concentration of 0.01-0.2 wt%, and the organic phase includes one of n-hexane and n-heptane.

[0016] As a preferred embodiment of the method for preparing the zwitterionic covalent organic framework membrane of the present invention, the soaking time of the covalent organic framework membrane in the polyacyl chloride organic phase solution is 1-10 min, and the soaking time in the zwitterionic aqueous phase solution is 1-10 min.

[0017] As a preferred embodiment of the preparation method of the zwitterionic covalent organic framework membrane of the present invention, the heat treatment temperature of the ultrafiltration membrane after polymerization reaction is 50-100℃ and the time is 1-20min; the heat treatment temperature of the covalent organic framework membrane after immersion in a polyacrylamide chloride organic phase solution and a zwitterionic aqueous phase solution is 50-100℃ and the heat treatment time is 1-20min.

[0018] Another object of the present invention is to provide a zwitterionic covalent organic framework membrane.

[0019] Another object of the present invention is to provide an application of zwitterionic covalent organic framework membrane in pervaporation ethanol dehydration separation.

[0020] As a preferred embodiment of the application of the zwitterionic covalent organic framework membrane described in this invention in the pervaporation and dehydration separation of ethanol, wherein:

[0021] Under conditions of 76°C and a feed solution water content of 10 wt%, the permeation flux of the zwitterionic covalent organic framework membrane is 3000–4000 gm³. -2 h -1 The separation factor is 1000-3000, and its separation performance remains stable within 130 hours.

[0022] Beneficial effects of this invention:

[0023] This invention provides a zwitterionic covalent organic framework membrane, its preparation method, and its application. The method is simple and controllable, and can realize the transformation of covalent organic framework from fibrous thin layer to two-dimensional film. The membrane thickness is very thin, and the obtained continuous covalent organic framework membrane has high porosity and interconnected pores, which is beneficial to obtaining high permeability.

[0024] The amphoteric ionization of the covalent organic framework membrane surface prepared by this invention endows the membrane surface with high hydrophilicity, enhances the dissolution process of water molecules on the membrane surface, and can also reduce the pore size of the membrane surface and improve the selective diffusion process of water molecules.

[0025] The prepared zwitterionic covalent organic framework membrane was used in the pervaporation ethanol dehydration process, exhibiting high permeation flux and high separation factor. Furthermore, due to the covalent bonding mode of the covalent organic framework, its structure has high stability and can resist the adverse evolution of the membrane structure in the liquid environment. In application, it also showed good long-term operational stability. Attached Figure Description

[0026] To more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings used in the following description of the embodiments will be briefly introduced. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort. Wherein:

[0027] Figure 1 This is a scanning electron microscope image of the zwitterionic covalent organic framework membrane prepared in Example 1 of the present invention.

[0028] Figure 2 This is a scanning electron microscope (SEM) image of a cross-section of the zwitterionic covalent organic framework membrane prepared in Example 1 of this invention.

[0029] Figure 3 This is a scanning electron microscope image of the surface of the covalent organic framework membrane prepared in Comparative Example 1;

[0030] Figure 4 This is a scanning electron microscope image of the surface of the covalent organic framework membrane prepared in Comparative Example 2;

[0031] Figure 5 This is a scanning electron microscope image of the cross-section of the covalent organic framework membrane prepared in Comparative Example 2;

[0032] Figure 6 This is a graph showing the long-term operational stability of the zwitterionic covalent organic framework membrane prepared in Example 1. Detailed Implementation

[0033] To make the above-mentioned objects, features and advantages of the present invention more apparent and understandable, the specific embodiments of the present invention will be described in detail below with reference to the examples in the specification.

[0034] Many specific details are set forth in the following description in order to provide a full understanding of the invention. However, the invention may also be practiced in other ways different from those described herein, and those skilled in the art can make similar extensions without departing from the spirit of the invention. Therefore, the invention is not limited to the specific embodiments disclosed below.

[0035] Secondly, the term "one embodiment" or "embodiment" as used herein refers to a specific feature, structure, or characteristic that may be included in at least one implementation of the present invention. The phrase "in one embodiment" appearing in different places in this specification does not necessarily refer to the same embodiment, nor is it a single or selective embodiment that is mutually exclusive with other embodiments.

[0036] Unless otherwise specified, all raw materials used in this invention are commercially available in the art.

[0037] The method for testing the separation performance of the membrane in this invention is as follows:

[0038] The prepared membrane material was used in a pervaporation ethanol-water solution system at a temperature of 76℃ and a water content of 10wt% in the feed solution. The permeation flux and separation factor of the composite membrane were then measured.

[0039] Example 1

[0040] This embodiment provides a method for preparing zwitterionic covalent organic framework membranes, specifically as follows:

[0041] 1) Preparation of zwitterionic materials: 0.06 mol of N-aminoethylpiperazine and 0.05 mol of 1,3-propanesulfonate lactone were dissolved in 60 mL and 20 mL of acetonitrile, respectively. Then, the 1,3-propanesulfonate lactone solution was added to the N-aminoethylpiperazine solution and reacted at 30 °C for 7 h. After the reaction was completed, the crude product was collected and then extracted with acetonitrile using a Soxhlet method. The purified product was obtained by vacuum drying, which is the zwitterionic material.

[0042] 2) The porous supporting base membrane polyacrylonitrile ultrafiltration membrane was placed in a sodium hydroxide solution with a concentration of 1.5M and a temperature of 55℃ for 1 hour for heat treatment, and then repeatedly washed with deionized water until the pH was neutral to obtain the hydrolyzed polyacrylonitrile ultrafiltration membrane.

[0043] 3) The hydrolyzed polyacrylonitrile ultrafiltration membrane was immersed in an aqueous solution containing 0.05 wt% acetic acid and 0.2 wt% p-phenylenediamine for 1 min, and then rolled dry with a rubber roller until there were no water stains on the surface; then it was immersed in a heptane solution of 0.005 wt% trialdehyde resorcinol for 150 s to carry out the polymerization reaction. After the reaction, it was naturally dried and heat-treated at 80℃ for 3 min to obtain a covalent organic framework membrane.

[0044] 4) The covalent organic framework membrane was first immersed in a 0.1 wt% solution of trimesoyl chloride in n-heptane for 3 min, and then immersed in a 0.2 wt% zwitterionic aqueous solution for 3 min. After being dried by a rubber roller, the membrane was heat-treated at 60℃ for 10 min to obtain a zwitterionic covalent organic framework membrane, which is denoted as membrane 1. Figure 1 and Figure 2 The images shown are scanning electron microscope (SEM) images of the surface and cross-section of membrane 1, respectively.

[0045] Comparative Example 1

[0046] This comparative example provides a method for preparing a covalent organic framework membrane, which differs from Example 1 in that steps 1) and 4) are omitted, and the concentrations of the amine monomer aqueous solution and the aldehyde monomer organic solution containing the catalyst are adjusted. The specific steps are as follows:

[0047] The porous supporting substrate polyacrylonitrile ultrafiltration membrane was heat-treated in a sodium hydroxide solution with a concentration of 1.5M and a temperature of 55℃ for 1 hour, and then repeatedly washed with deionized water until the pH was neutral to obtain the hydrolyzed polyacrylonitrile ultrafiltration membrane.

[0048] The hydrolyzed polyacrylonitrile ultrafiltration membrane was immersed in an aqueous solution containing 0.5 wt% acetic acid and 0.5 wt% p-phenylenediamine for 1 min, and then rolled dry with a rubber roller until there were no water stains on the surface. It was then immersed in a heptane solution of 0.05 wt% trialdehyde resorcinol for 150 s to carry out the polymerization reaction. After natural drying, the membrane was heat-treated at 80℃ for 3 min to obtain a covalent organic framework membrane, which was designated as control membrane 1. Figure 3 For comparison, see the surface scanning electron microscope image of film 1.

[0049] Comparative Example 2

[0050] The difference between this comparative example and Example 1 is that steps 1) and 4) are omitted. The remaining steps are the same as in Example 1, and the specific steps are as follows:

[0051] The porous supporting substrate polyacrylonitrile ultrafiltration membrane was heat-treated in a sodium hydroxide solution with a concentration of 1.5M and a temperature of 55℃ for 1 hour, and then repeatedly washed with deionized water until the pH was neutral to obtain the hydrolyzed polyacrylonitrile ultrafiltration membrane.

[0052] The hydrolyzed polyacrylonitrile ultrafiltration membrane was immersed in an aqueous solution containing 0.05 wt% acetic acid and 0.2 wt% p-phenylenediamine for 1 min, and then rolled dry with a rubber roller until there were no water stains on the surface. It was then immersed in a heptane solution of 0.005 wt% trialdehyde phloroglucinol for 150 s to carry out the polymerization reaction. After the reaction, it was naturally dried and heat-treated at 80℃ for 3 min to obtain a covalent organic framework membrane, which was designated as control membrane 2. Figure 4 and Figure 5 The images shown are scanning electron microscope (SEM) images of the surface and cross-section of contrast membrane 2, respectively.

[0053] The separation performance of the membranes prepared in Example 1, Comparative Example 1, and Comparative Example 2 was tested, and the results are shown in Table 1.

[0054] Table 1

[0055] membrane <![CDATA[Permeation flux (gm -2 h -1 )]]> Separation factor Example 1 3309 2839 Comparative Example 1 1308 550 Comparative Example 2 2866 438

[0056] From Table 1 and Figures 1-5As can be seen, compared with covalent organic framework membranes, zwitterionic covalent organic framework membranes exhibit superior separation performance, with improvements in both permeation flux and separation factor to varying degrees. This is because the present invention can control the transformation of the covalent organic framework from a fibrous thin layer to a two-dimensional film by adjusting the interfacial polymerization reaction parameters, thereby successfully preparing a continuous and defect-free covalent organic framework membrane. Furthermore, zwitterionic modification of the covalent organic framework membrane surface can regulate the pore structure of the membrane surface, forming water-selective transport channels while repelling competing alcohol molecules.

[0057] Figure 6 The diagram shows the long-term operational stability of the zwitterionic covalent organic framework membrane prepared in Example 1. It can be seen that the zwitterionic covalent organic framework membrane prepared in this invention exhibits good separation stability during long-term operation.

[0058] Example 2

[0059] The difference between this embodiment and Embodiment 1 is that the concentration of zwitterionic material in the zwitterionic aqueous solution in step 4) is adjusted to 0.05 wt%, while the remaining steps are the same as in Embodiment 1, to obtain the zwitterionic covalent organic framework membrane of this embodiment.

[0060] Example 3

[0061] The difference between this embodiment and Embodiment 1 is that the concentration of zwitterionic material in the zwitterionic aqueous solution in step 4) is adjusted to 0.1 wt%, while the remaining steps are the same as in Embodiment 1, to obtain the zwitterionic covalent organic framework membrane of this embodiment.

[0062] Example 4

[0063] The difference between this embodiment and Embodiment 1 is that the concentration of zwitterionic material in the zwitterionic aqueous solution in step 4) is adjusted to 0.15wt%, while the remaining steps are the same as in Embodiment 1, to obtain the zwitterionic covalent organic framework membrane of this embodiment.

[0064] Example 5

[0065] The difference between this embodiment and Embodiment 1 is that the concentration of zwitterionic material in the zwitterionic aqueous solution in step 4) is adjusted to 0.3 wt%, while the remaining steps are the same as in Embodiment 1, to obtain the zwitterionic covalent organic framework membrane of this embodiment.

[0066] The separation performance of the zwitterionic covalent organic framework membranes prepared in Examples 2-5 was tested and compared with that in Example 1. The results are shown in Table 2.

[0067] Table 2

[0068] membrane <![CDATA[Permeation flux (gm -2 h -1 )]]> Separation factor Example 1 3309 2839 Example 2 3330 1007 Example 3 3239 1320 Example 4 3508 1282 Example 5 3387 2624

[0069] As shown in Table 2, with the increase of zwitterion concentration, the separation factor first increases and then remains basically unchanged, while the membrane permeation flux changes little. On the one hand, zwitterions can increase the hydrophilicity of the covalent organic framework membrane surface, which is beneficial to the dissolution process of water molecules on the membrane surface; on the other hand, zwitterions have a modifying effect on the pore structure of the covalent organic framework membrane surface, reducing the pore size and increasing the resistance to molecular transport, which is detrimental to permeability, but enhances the selective diffusion process of water molecules. The above factors jointly affect the membrane separation performance. When the zwitterion modification on the membrane surface reaches a threshold, the membrane separation performance remains basically unchanged.

[0070] Comparative Example 3

[0071] The difference between this comparative example and Example 1 is that the concentration of acetic acid in step 3) is adjusted to 0.5 wt%, while the remaining steps are the same as in Example 1, to obtain the zwitterionic covalent organic framework membrane of this comparative example.

[0072] Comparative Example 4

[0073] The difference between this comparative example and Example 1 is that the concentration of acetic acid in step 3) is adjusted to 0.5 wt%, the concentration of trialdehyde phloroglucinol is adjusted to 0.05 wt%, and the remaining steps are the same as in Example 1, to obtain the zwitterionic covalent organic framework membrane of this comparative example.

[0074] Comparative Example 5

[0075] The difference between this comparative example and Example 1 is that the concentration of acetic acid in step 3) is adjusted to 0.5 wt%, the concentration of phenylenediamine is 0.5 wt%, and the concentration of trialdehyde phloroglucinol is 0.05 wt%. The remaining steps are the same as in Example 1, and the zwitterionic covalent organic framework membrane of this comparative example is obtained.

[0076] Comparative Example 6

[0077] The difference between this comparative example and Example 1 is that the concentration of acetic acid in step 3) is adjusted to 0.5wt%, the concentration of phenylenediamine is 0.5wt%, the concentration of trialdehyde resorcinol is 0.05wt%, and the soaking time in the n-heptane solution of trialdehyde resorcinol is 90s. The remaining steps are the same as in Example 1, and the zwitterionic covalent organic framework membrane of this comparative example is obtained.

[0078] The separation performance of the zwitterionic covalent organic framework membranes prepared in Comparative Examples 3-6 was tested and compared with that in Example 1. The results are shown in Table 3.

[0079] Table 3

[0080] membrane <![CDATA[Permeation flux (gm -2 h -1 )]]> Separation factor Example 1 3309 2839 Comparative Example 3 3051 695 Comparative Example 4 2298 872 Comparative Example 5 1576 1083 Comparative Example 6 3510 481

[0081] As shown in Table 3, the concentration of reactants, catalyst concentration, and reaction time affect the formation process of covalent organic framework (COF) membranes, and consequently, the separation performance of zwitterionic COF membranes. Improper control of reactant and catalyst concentrations leads to the formation of fibrous COF layers on the porous support substrate surface instead of continuous two-dimensional layers. Reaction time affects the COF interfacial polymerization process; shorter reaction times result in incomplete formation of the two-dimensional COF layer, leading to numerous defects and poor separation performance. Zwitterionic ionization of discontinuous COF membrane surfaces cannot achieve high separation performance. Therefore, proper control of reaction parameters is beneficial for forming continuous COF membrane structures on the porous support substrate surface, thereby obtaining zwitterionic COF membranes with high separation performance.

[0082] In summary, the zwitterionic covalent organic framework membrane provided by this invention possesses continuous, interconnected pore channels, which can serve as rapid molecular transport channels, facilitating the achievement of high permeation flux. Zwitterionicizing its surface enhances the membrane's hydrophilicity and modulates the pore structure, creating water-selective transport channels while repelling competing alcohol molecules. The prepared composite membrane overcomes the technical bottleneck of covalent organic framework materials in the separation of small liquid molecules. The preparation method of this invention is simple and controllable. When the composite membrane prepared by this invention is used in the pervaporation ethanol dehydration process, it exhibits excellent separation performance and long-term operational stability, demonstrating broad application potential in the field of organic solvent dehydration.

[0083] It should be noted that 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 preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the spirit and scope of the technical solutions of the present invention, and all such modifications or substitutions should be covered within the scope of the claims of the present invention.

Claims

1. A method for preparing a zwitterionic covalent organic framework membrane, characterized in that: include, The porous support base membrane is immersed in an aqueous solution of amine monomers containing catalyst and then tumbled dry with a rubber roller until there are no water stains on the surface. The membrane is then immersed in an aldehyde monomer organic phase solution for polymerization. After the reaction, it is dried and heat-treated to obtain a covalent organic framework membrane. The porous support base membrane includes one of polyacrylonitrile ultrafiltration membrane, polyvinyl alcohol ultrafiltration membrane, and polyvinylidene fluoride ultrafiltration membrane. The covalent organic framework membrane is first immersed in a polyacrylamide chloride organic phase solution and then immersed in a zwitterionic aqueous phase solution. After being dried by rubber rollers, it is subjected to heat treatment to obtain a zwitterionic covalent organic framework membrane. The concentration of the zwitterionic material in the zwitterionic aqueous solution is 0.01–2 wt%, and the zwitterionic material is prepared from N-aminoethylpiperazine and 1,3-propanesulfonate lactone.

2. The method for preparing zwitterionic covalent organic framework membranes as described in claim 1, characterized in that: When the porous supporting substrate membrane is a polyacrylonitrile ultrafiltration membrane, it is first heat-treated with sodium hydroxide solution to obtain a hydrolyzed polyacrylonitrile ultrafiltration membrane. The heat treatment temperature is 50~60 ℃, the treatment time is 0.5~1.5 h, and the concentration of the sodium hydroxide solution used is 1~2 M.

3. The method for preparing zwitterionic covalent organic framework membranes as described in claim 1, characterized in that: The immersion is carried out in an aqueous solution of an amine monomer containing a catalyst, wherein the catalyst includes one of acetic acid and p-toluenesulfonic acid, with a concentration of 0.01-2 wt%; the amine monomer includes one of hydrazine hydrate, p-phenylenediamine, and biphenylenediamine, with a concentration of 0.001-2 wt%; and the immersion time is 1-10 min.

4. The method for preparing a zwitterionic covalent organic framework membrane as described in claim 1, characterized in that: The immersion is carried out in an aldehyde monomer organic phase solution, wherein the aldehyde monomer includes one of pyromellitic terephthalaldehyde, trialdehyde-resorcinol, terephthalaldehyde, and 2,5-dihydroxyterephthalaldehyde, with a concentration of 0.001-1 wt%, and the organic phase includes one of n-hexane and n-heptane, and the immersion time is 30-300 s.

5. The method for preparing a zwitterionic covalent organic framework membrane as described in claim 1, characterized in that: The polyacrylamide chloride organic phase solution includes one of pyromellitic chloride, terephthaloyl chloride, and isophthaloyl chloride, with a concentration of 0.01–0.2 wt%, and the organic phase includes one of n-hexane and n-heptane.

6. The method for preparing zwitterionic covalent organic framework membranes as described in claim 1, characterized in that: The covalent organic framework membrane is immersed in a polyacrylamide chloride organic phase solution for 1–10 min, and in a zwitterionic aqueous phase solution for 1–10 min.

7. The method for preparing a zwitterionic covalent organic framework membrane as described in claim 1, characterized in that: The porous support membrane is heat-treated at a temperature of 50–100 °C for 1–20 min after being immersed in an aldehyde monomer organic phase solution for polymerization. The covalent organic framework membrane is heat-treated at a temperature of 50–100 °C for 1–20 min after being immersed in a polyacrylamide chloride organic phase solution and a zwitterionic aqueous phase solution.

8. The zwitterionic covalent organic framework membrane prepared by any one of claims 1 to 7.

9. The application of the zwitterionic covalent organic framework membrane as described in claim 8 in the dehydration separation of pervaporated ethanol, characterized in that: Under conditions of 76℃ and a feed solution water content of 10 wt%, the permeation flux of the zwitterionic covalent organic framework membrane is 3000–4000 gm³. -2 h -1 The separation factor is 1000–3000, and its separation performance remains stable within 130 h.

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