Heteromorphic covalent organic framework film as well as preparation method and application thereof

Abstract

The invention discloses a heteromorphic covalent organic framework membrane as well as a preparation method and application thereof, and belongs to the technical field of separation membrane materials. The method comprises the following steps: firstly, synthesizing a COF nanosheet colloidal solution through a homogeneous solution method; then carrying out suction filtration on the colloidal solution to a porous supporting base membrane to form a crystalline COF layer; and finally, growing an amorphous COF layer on the surface of the crystalline COF layer in situ through interfacial polymerization, and carrying out heat treatment to obtain the heteromorphic covalent organic framework film. According to the invention, the rigid crystalline COF is used for providing a long-range ordered pore channel, the flexible amorphous COF is used for strengthening the controllable processability to make up the defect, a rigid-flexible heteromorphic configuration is formed, and the construction of the continuous defect-free COF film is realized. The preparation method is simple, the characteristics of a crystalline state and an amorphous state are coupled, a multi-layer sub-nanometer mass transfer channel is formed in the membrane, high permeability and high rejection rate are shown in the separation process of organic pollutants in water, and good long-term separation stability is achieved.

Description

Technical Field

[0001] This invention belongs to the field of novel separation membrane materials technology, specifically relating to a heterocrystalline covalent organic framework membrane, its preparation method, and its application. Background Technology

[0002] Rapid economic and social development has led to increased industrial intensity, and wastewater discharged during industrial production processes causes water quality deterioration, threatening water safety and hindering sustainable development. Membrane separation technology, with its significant advantages such as high efficiency, environmental friendliness, and low energy consumption, is considered one of the most competitive technologies in water treatment.

[0003] Membrane materials are crucial for the efficient operation of membrane separation technology. High-performance membrane materials should possess high permeability, high selectivity, and high stability. However, currently mainstream polymer membranes such as polyamides have low porosity and uneven pore size, making it difficult to achieve both high permeability and high selectivity. Covalent organic frameworks (COFs), as a novel type of crystalline porous polymer material, ensure high permeability through their long-range ordered and uniformly sized interconnected pore structure, while the covalent interactions within the structural units endow them with excellent chemical stability. These characteristics make COFs ideal materials for constructing separation membranes. However, for crystalline materials, their rigid framework is prone to connection errors during growth, easily forming intergranular defects, making it difficult to form continuous, defect-free COF membranes. Reducing crystallinity can reduce intergranular defects, but it sacrifices the high permeability of the ordered pores.

[0004] To address this issue, existing technologies involve introducing amorphous polymers to chemically stitch together grain boundary defects in crystalline COF layers, resulting in molecularly welded COF membranes with crystalline-amorphous heterojunction interfaces, which can enhance organic solvent nanofiltration (OSN) performance (Advanced Membranes, 2024, 4, 100110). However, this technology involves heterogeneous material composites for organic solvent systems, presenting not only heterojunction compatibility issues but also complex process complexity due to the often intricate solvothermal treatments or specific monomer matching involved in molecular welding. Furthermore, its hydrophobic framework makes it difficult to directly apply to high-efficiency water treatment processes. In water treatment, membrane materials require excellent hydrophilicity to ensure high water flux and antifouling performance. How to solve the inherent intergranular defect problem of COF membranes using a simple and controllable process while simultaneously achieving efficient screening of organic pollutants in water remains a key technical challenge in this field. Summary of the Invention

[0005] In view of the above problems, the application adopts a homogeneous material as a film building unit to provide a preparation method of a heteromorphic covalent organic framework film. Based on the differences in channel and film forming properties of different crystal structures of the same material, i.e. rigid crystal COF provides long-range ordered pore channels, flexible amorphous COF strengthens controllable processability to make up for defects, forming a rigid-flexible heteromorphic configuration; and due to the homology of the material, the problem of poor interface compatibility of heterogeneous materials is avoided, realizing the construction of a continuous and defect-free COF film. The difference between the crystal structure and the amorphous structure of the homogeneous material is used to construct a multi-level sub-nanometer mass transfer channel, and the hydrophilic ion groups on the channel wall are adapted to the demand of water treatment, strengthening the precise screening of water molecules, which can realize the high permeability and high selectivity separation target. The preparation process of the application is simple and exhibits excellent separation performance in the removal of organic pollutants in water.

[0006] In order to achieve the purpose of the application, the technical scheme adopted is as follows:

[0007] The preparation method of the heteromorphic covalent organic framework film prepared by the application comprises the following steps:

[0008] Step one, the amine monomer and the aldehyde monomer are dissolved in an organic solvent respectively, and are blended and reacted for 12-72 hours to obtain a COF nanosheet colloidal solution;

[0009] Step two, the COF nanosheet colloidal solution is dispersed in deionized water, and the obtained dispersion is suction filtered onto a porous support film to obtain a crystal COF layer;

[0010] Step three, the crystal COF layer surface is sequentially soaked in an amine monomer solution and an aldehyde monomer solution for interfacial polymerization reaction, and after heat treatment under air condition, a heteromorphic covalent organic framework film is obtained.

[0011] As a preferred scheme of the preparation method of the heteromorphic covalent organic framework film, in step one, the amine monomer is one of 2,5-diaminobenzenesulfonic acid and 2,2'-diphenylamine disulfonic acid, the aldehyde monomer is one of tri-aldehyde-based phloroglucinol and triformylphenol, the molar ratio of the amine monomer and the aldehyde monomer is 3:2, and the organic solvent is one of dimethyl sulfoxide and N,N-dimethylformamide.

[0012] As a preferred scheme of the preparation method of the heteromorphic covalent organic framework film, in step two, the porous support film is one of polyacrylonitrile, polytetrafluoroethylene, polyvinylidene fluoride and polyether sulfone.

[0013] As a preferred scheme of the preparation method of the heteroepitaxial covalent organic framework film, in the step three, the amine monomer is one of 2,5-diaminobenzenesulfonic acid and 2,2'-diphenylamine disulfonic acid, the concentration of the amine monomer is 0.03-3.0 mmol / L, the aldehyde monomer is one of triformylphloroglucinol and trimesaldehyde, and the concentration of the aldehyde monomer is 0.02-2.0 mmol / L.

[0014] More preferably, the concentration of the amine monomer is 0.12-3.0 mmol / L, and the concentration of the aldehyde monomer is 0.8-2.0 mmol / L.

[0015] More preferably, the concentration of the amine monomer is 0.12-3.0 mmol / L, and the concentration of the aldehyde monomer is 0.8-2.0 mmol / L.

[0016] More preferably, the concentration of the amine monomer is 0.12-3.0 mmol / L, and the concentration of the aldehyde monomer is 0.8-2.0 mmol / L.

[0017] As a preferred scheme of the preparation method of the heteroepitaxial covalent organic framework film, in the step three, the amine monomer is one of 2,5-diaminobenzenesulfonic acid and 2,2'-diphenylamine disulfonic acid, the concentration of the amine monomer is 0.03-3.0 mmol / L, the aldehyde monomer is one of triformylphloroglucinol and trimesaldehyde, and the concentration of the aldehyde monomer is 0.02-2.0 mmol / L.

[0018] More preferably, the concentration of the amine monomer is 0.12-3.0 mmol / L, and the concentration of the aldehyde monomer is 0.8-2.0 mmol / L.

[0019] Another object of the present application is to provide a heteroepitaxial covalent organic framework film.

[0020] Another object of the present application is to provide a heteroepitaxial covalent organic framework film for separating and removing organic pollutants in water.

[0021] Compared with the prior art, the present application has the following advantages:

[0022] In view of the problem that rigid crystalline COF is difficult to prepare to form a continuous COF film without defects, based on the differences between crystalline and amorphous in the pore and film forming, the characteristics of coupling rigid crystalline COF to build long-range ordered pore channels and flexible amorphous to make up for intercrystalline defects to help film forming are proposed to prepare continuous and defect-free hetero-crystalline COF film. In particular, the crystalline COF layer in the application has long-range ordered and uniform through-pores, and the crystalline COF layer is used as a high-flux intermediate layer to provide an efficient mass transfer channel. The hetero-crystalline covalent organic framework film prepared by the application has high water permeability and high rejection of organic dyes, and has good separation stability in the long-term operation of the film. The hetero-crystalline covalent organic framework film of the application is simple to prepare, and has important enlightenment and reference value for the structure design and construction of continuous and defect-free organic framework film. BRIEF DESCRIPTION OF DRAWINGS

[0023] In order to more clearly illustrate the technical solutions of the embodiments of the present application, the drawings needed in the embodiment description will be briefly introduced as follows. Obviously, the drawings in the following description are only some embodiments of the present application, and those skilled in the art can also obtain other drawings according to these drawings without creative labor. Among them:

[0024] Figure 1 XRD diagram of the film of Comparative Example 1, Comparative Example 2 and Example 1;

[0025] Figure 2 Surface scanning electron microscope diagram of the film of Example 1;

[0026] Figure 3 Surface scanning electron microscope diagram of the film of Comparative Example 1;

[0027] Figure 4 Surface scanning electron microscope diagram of the film of Comparative Example 2;

[0028] Figure 5 Long-term separation stability diagram of Example 1. DETAILED DESCRIPTION

[0029] In order to further understand the purpose, content and advantages of the present application, the specific embodiments of the present application will be described in detail as follows, but it cannot be limited to the following examples, and should be freely combined according to the actual situation. The endpoints and any value of the range disclosed in this paper are not limited to the exact range and value. For numerical ranges, the endpoints of each range, the endpoints of each range and individual point values, and individual point values can be combined with each other to obtain one or more new numerical ranges, which should be regarded as specifically disclosed in this paper.

[0030] The separation performance test method of the film in the following examples and comparative examples is:

[0031] The prepared membrane material is applied to dye separation, the dye type is Congo red, chrome black T and Alcian blue, the dye concentration is 100 ppm, and the permeation flux and dye retention rate of the heteroepitaxial covalent organic framework membrane are determined.

[0032] It should be noted that the test method is only for the convenience of parallel comparison of the performance of the membrane material, and does not mean that the membrane material provided by the application can only be used for dye separation under the above conditions. The membrane material provided by the application can separate any concentration of dyes required in the art.

[0033] The application provides a preparation method of a heteroepitaxial covalent organic framework membrane.

[0034] Step one, the amine monomer and the aldehyde monomer are respectively dissolved in an organic solvent, and are blended and reacted for 12-72 h to obtain a COF nanosheet colloidal solution;

[0035] Step two, the COF nanosheet colloidal solution is dispersed in deionized water, and the obtained dispersion is suction-filtered onto a porous support base membrane to obtain a crystalline COF layer;

[0036] Step three, the crystalline COF layer is sequentially soaked in an amine monomer solution and an aldehyde monomer solution for interfacial polymerization reaction, and after heat treatment, a heteroepitaxial covalent organic framework membrane is obtained.

[0037] The following specific examples and comparative examples are further described in detail:

[0038] The porous support base membrane described below is a polyacrylonitrile base membrane.

[0039] Example 1

[0040] The application provides a preparation method of a heteroepitaxial covalent organic framework membrane, specifically:

[0041] Step one, 0.15 mmol of 2,5-diaminobenzenesulfonic acid and 0.1 mmol of triformylphloroglucinol are respectively dissolved in 5 mL of dimethyl sulfoxide, and are blended and placed for reaction for 24 h to obtain a COF nanosheet colloidal solution;

[0042] Step two, 0.2 mg of the COF nanosheet colloidal solution is dispersed in deionized water, and the obtained dispersion is suction-filtered onto a porous support base membrane to obtain a crystalline COF layer;

[0043] Step three, the surface of the crystalline COF layer was sequentially immersed in 0.9 mmol / L 2,5-diaminobenzenesulfonic acid aqueous solution for 1 h and 0.6 mmol / L tricarbonyl phloroglucinol n-hexane solution for 6 h for interfacial polymerization, and was heated at 80 ℃ for 3 min to obtain the heteromorphic covalent organic framework membrane.

[0044] The water flux of Example 1 was 298.88 L m -2 h -1 bar -1 The Congo red rejection rate was 98.47 %, the chrome black T rejection rate was 97.45 %, and the Alcian blue rejection rate was 99.87 %. Figure 1 and Figure 2 The XRD pattern and the membrane surface scanning electron microscope pattern of Example 1 are shown in FIGS. 1 and 2, respectively.

[0045] The XRD pattern of Example 1 retained a similar characteristic peak at 2θ = 4.7° with slightly lower intensity than that of Comparative Example 1, proving that the amorphous COF layer was successfully constructed on the surface of the crystalline COF layer by interfacial polymerization in Step three, and the ordered structure of the crystalline COF layer in the membrane was not destroyed. The surface of the heteromorphic COF membrane was slightly rougher than that of the crystalline COF layer.

[0046] Example 2

[0047] The difference between this example and Example 1 is that the mass of the COF nanosheet in Step two is adjusted to 0.05 mg, and the rest of the step process refers to Example 1 to obtain the heteromorphic covalent organic framework membrane of this example.

[0048] The water flux of Example 2 was 344.49 L m -2 h -1 bar -1 The Congo red rejection rate was 92.13 %, the chrome black T rejection rate was 94.85 %, and the Alcian blue rejection rate was 99.64 %.

[0049] Example 3

[0050] The difference between this example and Example 1 is that the mass of the COF nanosheet in Step two is adjusted to 0.1 mg, and the rest of the step process refers to Example 1 to obtain the heteromorphic covalent organic framework membrane of this example.

[0051] The water flux of Example 3 was 322.50 L m -2 h -1 bar -1 The Congo red rejection rate was 96.34 %, the chrome black T rejection rate was 96.67 %, and the Alcian blue rejection rate was 99.82 %.

[0052] Example 4

[0053] The difference between this example and Example 1 is that the mass of COF nanosheets in step two is adjusted to 0.3 mg, and the rest of the process steps refer to Example 1 to obtain the heteroepitaxial covalent organic framework film of this example.

[0054] The water flux of Example 4 is 220.59 L m -2 h -1 bar -1 The rejection rate for Congo red is 98.63 %, the rejection rate for chrome black T is 98.08 %, and the rejection rate for Alcian blue is 99.95 %.

[0055] Example 5

[0056] The difference between this example and Example 1 is that the mass of COF nanosheets in step two is adjusted to 0.5 mg, and the rest of the process steps refer to Example 1 to obtain the heteroepitaxial covalent organic framework film of this example.

[0057] The water flux of Example 5 is 195.40 L m -2 h -1 bar -1 The rejection rate for Congo red is 99.03 %, the rejection rate for chrome black T is 98.30 %, and the rejection rate for Alcian blue is 99.95 %.

[0058] Table 1

[0059]

[0060] From Table 1, it can be seen that as the amount of COF nanosheets deposited increases, the water flux of the film gradually decreases, and the rejection rates for Congo red, chrome black T and Alcian blue gradually increase. This is because as the COF nanosheets are gradually deposited, the COF film layer becomes thicker, the sheet layer interlacing also reduces the pore size, the water molecule mass transfer resistance increases, and the large size dye molecules are trapped.

[0061] Example 6

[0062] The difference between this example and Example 1 is that the concentrations of 2,5-diaminobenzenesulfonic acid and triformylphloroglucinol in step three are adjusted to 0.15 mmol / L and 0.1 mmol / L, respectively, and the rest of the process steps refer to Example 1 to obtain the heteroepitaxial covalent organic framework film of this example.

[0063] The water flux of Example 6 is 370.99 L m -2 h -1 bar -1The rejection rates for Congo Red were 94.68%, for Chrome Black T 90.34%, and for Alsin Blue 99.49%.

[0064] Example 7

[0065] The difference between this embodiment and Example 1 is that the concentrations of 2,5-diaminobenzenesulfonic acid and trialdehyde phloroglucinol in step three are adjusted to 0.6 mmol / L and 0.4 mmol / L, respectively. The remaining steps are the same as in Example 1, resulting in the heterocrystalline covalent organic framework membrane of this embodiment.

[0066] The water flux in Example 7 was 308.44 L / m³. -2 h -1 bar -1 The rejection rates for Congo Red were 96.59%, for Chrome Black T 92.27%, and for Alsin Blue 99.65%.

[0067] Example 8

[0068] The difference between this embodiment and Example 1 is that the concentrations of 2,5-diaminobenzenesulfonic acid and trialdehyde phloroglucinol in step three are adjusted to 1.2 mmol / L and 0.8 mmol / L, respectively. The remaining steps are the same as in Example 1, resulting in the heterocrystalline covalent organic framework membrane of this embodiment.

[0069] The water flux in Example 8 was 310.24 L / m³. -2 h -1 bar -1 The rejection rates for Congo Red were 97.35%, for Chrome Black T 97.27%, and for Alsin Blue 99.79%.

[0070] Example 9

[0071] The difference between this embodiment and Example 1 is that the concentrations of 2,5-diaminobenzenesulfonic acid and trialdehyde phloroglucinol in step three are adjusted to 1.5 mmol / L and 1.0 mmol / L, respectively. The remaining steps are the same as in Example 1, resulting in the heterocrystalline covalent organic framework membrane of this embodiment.

[0072] The water flux in Example 9 was 340.07 L / m³. -2 h -1 bar -1 The rejection rates for Congo Red were 96.96%, for Chrome Black T were 96.97%, and for Alsin Blue were 99.63%.

[0073] Table 2

[0074]

[0075] From Table 2, it can be seen that as the monomer concentration increases, the water flux of the membrane first decreases and then increases, while the rejection rates of Congo red, chrome black T and Alcian blue first increase and then decrease. The monomer concentration affects the formation structure of COF. If the monomer concentration is too low, the complete amorphous COF layer cannot be formed; if the monomer concentration is too high, the polymerization reaction speed will be too fast, the disorder degree of COF channel will increase, and the rejection rate will decrease. Precise control of the monomer concentration plays an important role in building a good structure of amorphous COF layer and optimizing the separation performance.

[0076] Example 10

[0077] The difference between this example and Example 1 is that the test dye concentration is adjusted to 50 ppm, and the remaining process steps are all referred to Example 1 to obtain the crystalline covalent organic framework membrane of this example.

[0078] The rejection rate of Congo red in Example 10 is 98.63 %, the rejection rate of chrome black T is 97.62 %, and the rejection rate of Alcian blue is 99.91 %.

[0079] Example 11

[0080] The difference between this example and Example 1 is that the test dye concentration is adjusted to 500 ppm, and the remaining process steps are all referred to Example 1 to obtain the crystalline covalent organic framework membrane of this example.

[0081] The rejection rate of Congo red in Example 11 is 98.34 %, the rejection rate of chrome black T is 96.83 %, and the rejection rate of Alcian blue is 99.83 %.

[0082] Example 12

[0083] The difference between this example and Example 1 is that the test dye concentration is adjusted to 2000 ppm, and the remaining process steps are all referred to Example 1 to obtain the crystalline covalent organic framework membrane of this example.

[0084] The rejection rate of Congo red in Example 12 is 97.82 %, the rejection rate of chrome black T is 96.17 %, and the rejection rate of Alcian blue is 99.74 %.

[0085] Table 3

[0086]

[0087] From Table 3, it can be seen that the isomorphic covalent organic framework film prepared in the application has high separation performance for dyes of different concentrations, and the rejection rates of Congo red, chrome black T and Alcian blue can still be maintained above 96%, indicating that the isomorphic covalent organic framework film has high efficient organic pollutant removal capacity.

[0088] Comparative Example 1

[0089] The difference between the present comparative example and Example 1 is that step three is no longer performed, and the remaining step processes all refer to Example 1 to obtain the crystalline covalent organic framework film of the present comparative example.

[0090] The water flux of Comparative Example 1 is 335.77 L m -2 h -1 bar -1 The rejection rate of Congo red is 90.81%, the rejection rate of chrome black T is 87.91%, and the rejection rate of Alcian blue is 98.92%. Figure 1 and Figure 3 are the XRD pattern and the membrane surface scanning electron microscope pattern of Comparative Example 1, respectively.

[0091] The XRD pattern of Comparative Example 1 has a strong peak at 2θ=4.7° corresponding to the (100) crystal face, indicating that it has a good ordered crystal structure. The crystalline COF membrane surface is smooth and flat.

[0092] Comparative Example 2

[0093] The difference between the present comparative example and Example 1 is that steps one and two are no longer performed, and the crystalline COF membrane in step three is adjusted to a porous support base film, and the remaining step processes all refer to Example 1 to obtain the amorphous covalent organic framework film of the present comparative example.

[0094] The water flux of Comparative Example 2 is 209.28 L m -2 h -1 bar -1 The rejection rate of Congo red is 91.84%, the rejection rate of chrome black T is 94.61%, and the rejection rate of Alcian blue is 99.58%.

[0095] Figure 1 and Figure 4 are the XRD pattern and the membrane surface scanning electron microscope pattern of Comparative Example 2, respectively.

[0096] The XRD pattern of Comparative Example 2 does not have a peak at 2θ=4.7°, indicating its amorphous state. The amorphous COF membrane surface is rougher than the crystalline COF membrane and the isomorphic COF membrane.

[0097] Table 4

[0098] ​

[0099] As can be seen from Table 4, the dye rejection rate of Example 1 is higher than that of the comparative examples. As can be seen from Comparative Example 2, the crystalline COF layer in the application plays a key role as a high-flux intermediate layer, and the crystalline COF layer has long-range order, uniform size through-pore channels, much higher porosity than the amorphous layer prepared directly on the porous support base film, efficient mass transfer channels, and reduced water molecule migration resistance; in addition, the flexible amorphous COF layer can effectively compensate for intercrystalline defects. Coupling the crystalline and amorphous characteristics, the hetero-crystal covalent organic framework membrane realizes efficient separation and removal of organic dyes in water, and still maintains relatively stable separation performance in the long-term operation process. Figure 5 ).

[0100] Although the application has been described in conjunction with the specific embodiments thereof, it is evident that many alternatives, modifications and variations will be apparent to those skilled in the art in the light of the foregoing description. Accordingly, it is intended to embrace all such alternatives, modifications and variations as fall within the scope of the application. All publications, patents and patent applications mentioned in this specification are herein incorporated by reference in their entirety for the purpose of describing and disclosing, for example, the methodologies described in such publications, which might be used in connection with the application.

[0101] The above description is merely illustrative of the application and is not intended to limit the scope of the application. Any modifications and variations that fall within the scope of the application are intended to be included herein. It is to be understood that the application can be carried out by specifically different embodiments and equivalents without departing from the spirit and scope of the application. Therefore, the scope of the application shall be limited only by the appended claims.

Claims

1. A method for preparing a heterocrystalline covalent organic framework membrane, characterized in that, First, a colloidal solution of COF nanosheets is synthesized by homogeneous solution method; then, the colloidal solution is filtered onto a porous support substrate to form a crystalline COF layer; finally, an amorphous COF layer is grown in situ on the surface of the crystalline COF layer by interfacial polymerization, and after heat treatment, a COF membrane with a composite structure of crystalline and amorphous structures is obtained, which is a heterocrystalline covalent organic framework membrane.

2. The method for preparing heterocrystalline covalent organic framework membranes according to claim 1, characterized in that: Includes the following steps: Step 1: Dissolve the amine monomer and aldehyde monomer separately in an organic solvent and react them together for 12-72 h to obtain a COF nanosheet colloidal solution; wherein the amine monomer is an aromatic diamine or polyamine containing a sulfonic acid group; and the aldehyde monomer is an aromatic trialdehyde or polyaldehyde. Step 2: Disperse the COF nanosheet colloidal solution in water, and filter the resulting dispersion onto a porous support membrane to obtain a crystalline COF layer; Step 3: The surface of the crystalline COF layer is sequentially immersed in amine monomer solution and aldehyde monomer solution to carry out interfacial polymerization reaction. After heat treatment, a heterocrystalline covalent organic framework film is obtained.

3. The method for preparing heterocrystalline covalent organic framework membranes according to claim 2, characterized in that: The amine monomer mentioned in step one is one of 2,5-diaminobenzenesulfonic acid and 2,2'-benzidinedisulfonic acid, the aldehyde monomer is one of trialdehyde phloroglucinol and pyromellitic methyl ester, the molar ratio of the amine monomer and the aldehyde monomer is 1:1-2:1, and the organic solvent is one of dimethyl sulfoxide and N,N-dimethylformamide.

4. The method for preparing heterocrystalline covalent organic framework membranes according to claim 2, characterized in that: The porous support base membrane mentioned in step two is one of polyacrylonitrile, polytetrafluoroethylene, polyvinylidene fluoride, and polyethersulfone.

5. The method for preparing heterocrystalline covalent organic framework membranes according to claim 2, characterized in that: The amine monomer mentioned in step three is one of 2,5-diaminobenzenesulfonic acid and 2,2'-benzidinedisulfonic acid, and the concentration of the amine monomer is 0.03-3.0 mmol / L. The aldehyde monomer is one of trialdehyde phloroglucinol and pyromellitic methyl aldehyde, and the concentration of the aldehyde monomer is 0.02-2.0 mmol / L.

6. The method for preparing heterocrystalline covalent organic framework membranes according to claim 2, characterized in that: In step three, the solvent for the amine monomer solution is water, and the solvent for the aldehyde monomer solution is n-hexane.

7. The method for preparing heterocrystalline covalent organic framework membranes according to claim 2, characterized in that: In step three, the soaking time in the amine monomer solution is 0.5-3 h, the soaking time in the aldehyde monomer solution is 3-12 h, the heat treatment temperature is 50-90 ℃, and the heat treatment time is 1-10 min.

8. The heterocrystalline covalent organic framework membrane prepared by the method according to any one of claims 1-7.

9. The heterocrystalline covalent organic framework membrane prepared by the method according to any one of claims 1-7 is applied to the separation and removal of organic pollutants in water.

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