Melt polymerization COFs membrane and preparation method thereof

Abstract

According to the melt polymerization COFs membrane and the preparation method thereof provided by the invention, the melt polymerization COFs membrane prepared by the preparation method of the melt polymerization COFs membrane can be applied to wastewater treatment, gas separation and the like, and efficient removal of organic pollutants and efficient separation of different gases can be realized.

Description

Technical Field

[0001] The invention belongs to the field of organic functional materials and analytical chemistry, and particularly relates to a melt-polymerized COFs membrane and applications thereof. Background Art

[0002] Covalent organic framework (COF) materials were first reported in the early 21st century. They are crystalline porous materials with a periodic network structure formed by small organic molecules connected by covalent bonds. They have the characteristics of high specific surface area, precisely designed pore structure, good chemical stability and thermal stability, and show great application potential in gas storage and separation, catalysis, sensing, optoelectronics and other fields. With the deepening of research on COF materials, researchers began to try to prepare COF membranes to expand their application range. Early COF membrane preparation mainly focused on the use of solution methods to form membrane materials by growing or depositing COF on a substrate. These membrane materials have shown certain performance advantages in molecular separation, ion conduction and other aspects, but they also face some problems, such as membrane integrity, thickness uniformity and bonding with the substrate.

[0003] The traditional solution method for preparing COF membranes requires a large amount of organic solvent to dissolve the monomers and promote the reaction. This not only increases costs but also pollutes the environment. In addition, certain organic solvents may affect the structure and properties of COF. COF membranes prepared by the solution method often have problems such as low crystallinity and many defects, resulting in the membrane's selectivity and permeability being difficult to achieve ideal. In addition, stress is easily generated during the volatilization of the solution, causing cracks and holes in the membrane, affecting the integrity and stability of the membrane. On the other hand, the interfacial polymerization method is to prepare COF membranes by performing a polymerization reaction at the interface of two immiscible solvents. This method requires extremely high control of reaction conditions, such as solvent selection, monomer concentration, reaction temperature and time. A slight change in any of these parameters may lead to unstable membrane quality. The interfacial polymerization method is difficult to achieve large-scale, continuous membrane preparation, which is not conducive to industrial production. Moreover, the prepared membranes are usually thin and have low mechanical strength, making them easily damaged in practical applications.

[0004] Melt polymerization is a method that conducts polymerization reactions while the monomer is molten. Compared to solution polymerization, it does not require the use of large amounts of solvents, thus avoiding a series of problems caused by solvents. During melt polymerization, monomer molecules have high activity and fluidity at high temperatures, which is conducive to the formation of highly crystalline polymers. Melt polymerization technology has been widely used in the field of polymer materials, such as the preparation of polyesters and polyamides. Through melt polymerization, polymer materials with excellent mechanical properties and processing properties can be prepared. These successful experiences provide reference and reference for the introduction of melt polymerization technology into the preparation of COF membranes. The application of melt polymerization technology to the preparation of COF membranes is expected to overcome the limitations of traditional methods. The reaction in the high-temperature molten state can promote the growth and orientation of COF crystals, improving the crystallinity and order of the membrane. At the same time, the thickness and uniformity of the membrane can be better controlled during the melt polymerization process, resulting in the preparation of COF membranes with excellent performance. Summary of the Invention

[0005] The purpose of the present invention is to provide a melt-polymerized COFs membrane and a preparation method thereof. The melt-polymerized COFs membrane prepared by the preparation method of the melt-polymerized COFs membrane can be applied to wastewater treatment and gas separation, and can achieve efficient separation of dyes and gases.

[0006] To solve the above technical problems, the present invention provides a method for preparing a melt-polymerized COFs film, comprising the following steps:

[0007] S1. Using at least two organic monomers, mixing them under the catalytic action of a catalyst to prepare a melt-polymerized COFs matrix;

[0008] S2, performing a preforming process on the melt-polymerized COFs matrix to obtain a preformed film;

[0009] S3, performing a liquid sealing treatment on the preformed film using an inert low-melting-point and high-boiling-point liquid, so that the inert low-melting-point and high-boiling-point liquid completely covers the surface of the preformed film;

[0010] S4. Continue the reaction at the set temperature to prepare a formed film, clean the formed film, and obtain the melt-polymerized COFs film.

[0011] As a further improvement of the present invention, the S1 specifically comprises: reacting at least two organic monomers under the catalytic action of the catalyst at a temperature of 120 to 250° C. for 5 to 30 minutes to prepare a melt-polymerized COFs matrix.

[0012] As a further improvement of the present invention, in S1, the organic monomer includes a first organic monomer and a second organic monomer, the first organic monomer is any one of 2,4,6-trimethylpyridine, ligustrazine or a C3 / C2 symmetrical methyl monomer; the second organic monomer is any one of terephthalaldehyde, 4,4'-biphenyldicarboxaldehyde, trimesic acid or a C2 / C3 symmetrical aldehyde monomer; the catalyst is any one of benzoic acid, benzoic anhydride, acetic acid, acetic anhydride, and maleic anhydride.

[0013] As a further improvement of the present invention, S2 is specifically:

[0014] S21, heating the melt-polymerized COFs matrix in S1 at a temperature of 120 to 250° C. for 5 to 30 minutes to obtain the melt-polymerized COFs matrix in liquid form;

[0015] S22, transferring the liquid melt-polymerized COFs matrix to a sheet forming device for cooling to obtain the preformed film.

[0016] As a further improvement of the present invention, S2 is specifically:

[0017] S21′, heating the melt-polymerized COFs matrix in S1 at a temperature of 80 to 250° C. for 10 to 60 minutes to obtain the melt-polymerized COFs matrix in liquid form;

[0018] S22', coating the liquid melt-polymerized COFs matrix on a forming substrate to obtain the preformed film.

[0019] As a further improvement of the present invention, the forming substrate is an organic forming film, and the organic forming film can be any one of organic films such as polyvinylidene fluoride film, glass fiber film, electrospun polyvinylidene fluoride film, nylon film, polyacrylonitrile film, polyethersulfone film and polytetrafluoroethylene film.

[0020] As a further improvement of the present invention, the forming substrate is an inorganic forming film, and the inorganic forming film is an anodized aluminum inorganic film.

[0021] As a further improvement of the present invention, in S3, the inert low melting point and high boiling point liquid is any one of a low melting point tin-lead alloy, dimethyl silicone oil, benzyl silicone oil, vinyl silicone oil, and hydroxy silicone oil.

[0022] As a further improvement of the present invention, the S4 is specifically:

[0023] S41. Continue the reaction at the set temperature to obtain a formed film, clean the surface of the formed film with toluene or petroleum ether, and then clean it again with a mixture of N,N-dimethylformamide, methanol and tetrahydrofuran, or a mixture of N,N-dimethylformamide, ethanol and tetrahydrofuran; wherein the volume ratio of methanol to tetrahydrofuran is 1:1 to 1:2; and the volume ratio of ethanol to tetrahydrofuran is 1:1 to 1:2;

[0024] S42, immersing the cleaned formed film in the methanol or ethanol for standby use, or drying by vacuum hot pressing to obtain a dry melt-polymerized COFs film.

[0025] In order to solve the above technical problems, the present invention also provides a melt-polymerized COFs membrane for removing organic pollutants. The melt-polymerized COFs membrane is prepared using the aforementioned melt-polymerized COFs membrane preparation method, and the melt-polymerized COFs membrane has a retention rate of greater than 90% for organic pollutants.

[0026] By adopting the above technical solution, the present invention has the following beneficial effects:

[0027] The method for preparing a melt-polymerized COFs membrane of the present invention utilizes a liquid sealing strategy to replace the vacuuming step in the traditional melt-polymerized COFs material preparation process, making the melt-polymerized COFs material preparation process more controllable. Furthermore, by regulating the shape of the molten liquid during the melt-polymerized COFs material preparation process, a uniform, continuous melt-polymerized COFs membrane is successfully prepared, thereby resolving the problem that traditional preparation methods can only produce melt-polymerized COFs powders and cannot form other forms. Furthermore, the melt-polymerized COFs membrane prepared using the method for preparing a melt-polymerized COFs membrane of the present invention can be applied to wastewater treatment and gas separation, achieving efficient removal of organic pollutants and efficient separation of different gases. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] In order to more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the specific embodiments or the description of the prior art. Obviously, the drawings described below are some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0029] Figure 1 Flow chart of the preparation method of melt polymerization COFs film of the present invention;

[0030] Figure 2 1 is the PXRD pattern of the melt-polymerized NKCOF-41 film prepared in Example 1.

[0031] Figure 3 1 and 2 are PXRD patterns of the polyvinylidene fluoride film, NKCOF-41, and melt-polymerized NKCOF-41 / polyvinylidene fluoride film in Example 2.

[0032] Figure 4 This is the PXRD pattern of the melt-polymerized NKCOF-41 / anodized aluminum oxide film in Example 3.

[0033] Figure 5 These are the PXRD patterns of the glass fiber membrane, NKCOF-41, and melt-polymerized NKCOF-41 / glass fiber membrane in Example 4.

[0034] Figure 6 The dye separation performance test results of melt polymerization NKCOF-41 membrane.

[0035] Figure 7 These are the test results of dye separation performance of melt-polymerized NKCOF-41 / polyvinylidene fluoride membrane.

[0036] Figure 8 These are the test results of the gas separation performance of melt-polymerized COFs membrane. DETAILED DESCRIPTION

[0037] The technical solution of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the embodiments described are only some embodiments of the present invention, not all embodiments. All other embodiments obtained by ordinary technicians in this field based on the embodiments of the present invention without making any creative efforts shall fall within the scope of protection of the present invention.

[0038] See also Figure 1 As shown, a method for preparing a melt-polymerized COFs film provided by the present invention comprises the following steps:

[0039] S1. Using at least two organic monomers, mixing them under the catalytic action of a catalyst to prepare a melt-polymerized COFs matrix;

[0040] S2, performing a preforming process on the melt-polymerized COFs matrix to obtain a preformed film;

[0041] S3, performing a liquid sealing treatment on the preformed film using an inert low-melting-point and high-boiling-point liquid, so that the inert low-melting-point and high-boiling-point liquid completely covers the surface of the preformed film;

[0042] S4. Continue the reaction at the set temperature to prepare a formed film, clean the formed film, and obtain the melt-polymerized COFs film.

[0043] The S1 specifically comprises: reacting at least two organic monomers under the catalytic action of the catalyst at a temperature of 120 to 250° C. for 5 to 30 minutes to prepare a melt-polymerized COFs matrix.

[0044] Specifically, the organic monomer includes a first organic monomer and a second organic monomer, wherein the first organic monomer is any one of 2,4,6-trimethylpyridine, ligustrazine or a C3 / C2 symmetrical methyl monomer; the second organic monomer is any one of terephthalaldehyde, 4,4'-biphenyldicarboxaldehyde, trimesic acid or a C2 / C3 symmetrical aldehyde monomer.

[0045] Furthermore, the catalyst is any one of benzoic acid, benzoic anhydride, acetic acid, acetic anhydride, and maleic anhydride.

[0046] In S1, the molar ratio of the first organic monomer to the second organic monomer is 1:1 to 1:4; preferably, the molar ratio of the first organic monomer to the second organic monomer is 1:1.5 or 1.5:1. The molar equivalent of the catalyst benzoic acid or benzoic anhydride is 1.5 to 5 eq of the first organic monomer equivalent; preferably, the molar equivalent of the catalyst benzoic acid or benzoic anhydride is 1.5 to 3 eq of the first organic monomer equivalent.

[0047] The step S2 is to prepare a preformed film based on the melt-polymerized COFs matrix obtained in step S1. In the present application, the preformed film can be a monomer film or a composite film.

[0048] In a preferred embodiment of the present application, the preformed film is a monomer film, and S2 is specifically:

[0049] S21, heating the melt-polymerized COFs matrix in S1 at a temperature of 120 to 250° C. for 5 to 30 minutes to obtain the melt-polymerized COFs matrix in liquid form;

[0050] S22, transferring the liquid melt-polymerized COFs matrix to a sheet forming device for cooling to obtain the preformed film.

[0051] Preferably, in S21, the liquid melt-polymerized COFs matrix is ​​obtained by heating the melt-polymerized COFs matrix in S1 at a temperature of 120 to 200° C. for 10 to 20 minutes.

[0052] In another preferred embodiment of the present application, the preformed film is a composite film, and S2 is specifically:

[0053] S21′, heating the melt-polymerized COFs matrix in S1 at a temperature of 80 to 250° C. for 10 to 60 minutes to obtain the melt-polymerized COFs matrix in liquid form;

[0054] S22', coating the liquid melt-polymerized COFs matrix on a formed matrix to obtain the preformed film.

[0055] Preferably, in S21', the liquid melt-polymerized COFs matrix is ​​obtained by heating the melt-polymerized COFs matrix in S1 at a temperature of 120 to 200°C for 10 to 40 minutes.

[0056] Furthermore, the formed film in S22' can be an organic formed film or an inorganic formed film.

[0057] In a preferred embodiment of the present application, the forming substrate is an organic forming film, which can be any one of organic films such as polyvinylidene fluoride film, glass fiber film, electrospun polyvinylidene fluoride film, nylon film, polyacrylonitrile film, polyethersulfone film and polytetrafluoroethylene film.

[0058] In a preferred embodiment of the present application, the forming substrate is an inorganic forming film, and the inorganic forming film is an anodized aluminum inorganic film.

[0059] The S3 specifically comprises: covering the preformed film in the S2 with an inert low melting point and high boiling point liquid under the conditions of 80-200° C. and 0-1 atm, and continuing the reaction for 48-144 hours.

[0060] In a preferred embodiment of the present application, S4 specifically comprises: covering the preformed film in S2 with an inert low melting point and high boiling point liquid under the conditions of 100-140° C. and 0-1 atm, and continuing the reaction for 72-120 hours.

[0061] In the present application, the inert low melting point and high boiling point liquid is any one of a low melting point tin-lead alloy, dimethyl silicone oil, benzyl silicone oil, vinyl silicone oil, and hydroxy silicone oil.

[0062] The S4 is specifically:

[0063] S41. Continue the reaction at the set temperature to obtain a formed film, clean the surface of the formed film with toluene or petroleum ether, and then clean it again with a mixture of N,N-dimethylformamide, methanol and tetrahydrofuran, or a mixture of N,N-dimethylformamide, ethanol and tetrahydrofuran; wherein the volume ratio of methanol to tetrahydrofuran is 1:1 to 1:2; and the volume ratio of ethanol to tetrahydrofuran is 1:1 to 1:2;

[0064] S42, immersing the cleaned formed film in the methanol or ethanol for standby use, or drying by vacuum hot pressing to obtain a dry melt-polymerized COFs film.

[0065] It should be noted that after the reaction is completed and the formed film is taken out from the inert low-melting point and high-boiling point liquid, the inert low-melting point and high-boiling point liquid can be recovered for next use. In this way, the inert low-melting point and high-boiling point liquid can be reused, further reducing the preparation cost of the melt-polymerized covalent organic framework fiber.

[0066] The following description will further illustrate the preparation method of the melt-polymerized COFs film of the present application through specific examples.

[0067] Example 1

[0068] S1. A method for preparing a melt-polymerized COFs matrix NKCOF-41 film by mixing at least two organic monomers under the catalytic action of a catalyst. The specific implementation steps are as follows:

[0069] S1. Weigh 804 mg of terephthalaldehyde, 800 μL of 2,4,6-trimethylpyridine, and 2700 mg of benzoic anhydride, grind and mix them evenly, and react them at 180° C. for 10-40 minutes to obtain a melt-polymerized NKCOF-41 membrane matrix;

[0070] S2, maintaining the temperature of the melt-polymerized NKCOF-41 film substrate, transferring the melt-polymerized NKCOF-41 film substrate in a liquid state to a molding device for molding, and allowing it to cool to obtain the preformed film;

[0071] S3, using an inert low melting point and high boiling point liquid to cover the preformed film for liquid sealing;

[0072] S4. Place the preformed film covered with an inert low-melting-point and high-boiling-point liquid in an oven at 180°C for further reaction for 120 hours; use toluene or petroleum ether to clean the surface of the formed film, and then use a mixture of N,N-dimethylformamide, methanol and tetrahydrofuran or a mixture of N,N-dimethylformamide, ethanol and tetrahydrofuran to clean it again; immerse the cleaned formed film in the methanol or ethanol for standby use, or use vacuum hot pressing to dry it to obtain a dry melt-polymerized NKCOF-41 film.

[0073] See also Figure 2As shown, this is the PXRD pattern of the melt-polymerized NKCOF-41 film obtained in Example 1. It can be seen that the melt-polymerized NKCOF-41 film prepared using the melt-polymerized COFs film preparation method of the present application in Example 1 has good crystallinity.

[0074] Example 2

[0075] S1. Weigh 804 mg of terephthalaldehyde, 800 μL of 2,4,6-trimethylpyridine, and 2700 mg of benzoic anhydride, grind and mix them evenly, and react them at 180° C. for 10-40 minutes to obtain a melt-polymerized NKCOF-41 membrane matrix;

[0076] S2. Maintaining the temperature of the melt-polymerized NKCOF-41 film substrate, immersing a polyvinylidene fluoride (PVDF) film in the liquid melt-polymerized NKCOF-41 film substrate, slowly lifting the polyvinylidene fluoride film attached to the melt-polymerized NKCOF-41 film substrate, placing it on tin foil, and allowing it to cool to room temperature, obtaining the preformed film, and wrapping the preformed film with tin foil, and flattening and placing it in a container with a horizontal surface;

[0077] S3, using an inert low melting point and high boiling point liquid to cover the preformed film for liquid sealing;

[0078] S4. Place the preformed film covered with an inert low-melting-point and high-boiling-point liquid in an oven at 180°C for further reaction for 120 hours; use toluene or petroleum ether to clean the surface of the formed film, and then use a mixture of N,N-dimethylformamide, methanol and tetrahydrofuran or a mixture of N,N-dimethylformamide, ethanol and tetrahydrofuran to clean it again; immerse the cleaned formed film in the methanol or ethanol for standby use, or use vacuum hot pressing to dry it to obtain a dry melt-polymerized NKCOF-41 / polyvinylidene fluoride film.

[0079] See also Figure 3 As shown, this is the PXRD pattern of the melt-polymerized NKCOF-41 / polyvinylidene fluoride film obtained in Example 2. It can be seen that the melt-polymerized NKCOF-41 / polyvinylidene fluoride film prepared using the melt-polymerized COFs film preparation method of the present application in Example 2 has good crystallinity.

[0080] Example 3

[0081] S1. Weigh 804 mg of terephthalaldehyde, 800 μL of 2,4,6-trimethylpyridine, and 2700 mg of benzoic anhydride, grind and mix them evenly, and react them at 180° C. for 10-40 minutes to obtain a melt-polymerized NKCOF-41 membrane matrix;

[0082] S2. Maintaining the temperature of the melt-polymerized NKCOF-41 film substrate, coating the melt-polymerized NKCOF-41 film substrate on one side of an anodic aluminum oxide (AAO) film, placing the film on tinfoil, and allowing the film to cool to room temperature, obtaining the preformed film, wrapping the preformed film with tinfoil, and flattening the preformed film in a container with a horizontal surface;

[0083] S3, using an inert low melting point and high boiling point liquid to cover the preformed film for liquid sealing;

[0084] S4. Place the preformed film covered with an inert low-melting-point and high-boiling-point liquid in an oven at 180°C for further reaction for 120 hours; use toluene or petroleum ether to clean the surface of the formed film, and then use a mixture of N,N-dimethylformamide, methanol and tetrahydrofuran or a mixture of N,N-dimethylformamide, ethanol and tetrahydrofuran to clean it again; immerse the cleaned formed film in the methanol or ethanol for standby use, or use vacuum hot pressing to dry it to obtain a dry melt-polymerized NKCOF-41 / anodized aluminum oxide film.

[0085] See also Figure 4 As shown, this is the PXRD pattern of the melt-polymerized NKCOF-41 / anodized aluminum oxide film obtained in Example 3. It can be seen that the melt-polymerized NKCOF-41 / anodized aluminum oxide film prepared in Example 3 using the preparation method of the melt-polymerized COFs film of the present application has good crystallinity, density and integrity.

[0086] Example 4

[0087] S1. Weigh 804 mg of terephthalaldehyde, 800 μL of 2,4,6-trimethylpyridine, and 2700 mg of benzoic anhydride, grind and mix them evenly, and react them at 180° C. for 10-40 minutes to obtain a melt-polymerized NKCOF-41 membrane matrix;

[0088] S2. Maintaining the temperature of the melt-polymerized NKCOF-41 membrane substrate, immersing a glass fiber (GFM) membrane into the liquid melt-polymerized NKCOF-41 membrane substrate, slowly lifting the glass fiber membrane attached with the melt-polymerized NKCOF-41 membrane substrate, placing it on tin foil, and allowing it to cool to room temperature, obtaining the preformed film, and wrapping the preformed film with tin foil, and flattening and placing it in a container with a horizontal surface;

[0089] S3, using an inert low melting point and high boiling point liquid to cover the preformed film for liquid sealing;

[0090] S4. Place the preformed film covered with an inert low-melting-point and high-boiling-point liquid in an oven at 180°C for further reaction for 120 hours; use toluene or petroleum ether to clean the surface of the formed film, and then use a mixture of N,N-dimethylformamide, methanol and tetrahydrofuran or a mixture of N,N-dimethylformamide, ethanol and tetrahydrofuran to clean it again; immerse the cleaned formed film in the methanol or ethanol for standby use, or use vacuum hot pressing to dry it to obtain a dry melt-polymerized NKCOF-41 / glass fiber membrane.

[0091] See also Figure 5 As shown, this is the PXRD pattern of the melt-polymerized NKCOF-41 / glass fiber membrane obtained in Example 4. It can be seen that the melt-polymerized NKCOF-41 / glass fiber membrane prepared in Example 4 using the preparation method of the melt-polymerized COFs membrane of the present application has good crystallinity and density.

[0092] In order to verify the practicality of the melt-polymerized COFs membrane prepared using the preparation method of the melt-polymerized COFs membrane of the present application, the prepared melt-polymerized COFs membrane was placed in a dye solution to conduct a dye separation experiment.

[0093] Specifically, the melt-polymerized COFs membrane, NKCOF-41 / polyvinylidene fluoride membrane, was used as an example to conduct an organic pollutant removal test, and two dyes were selected as model molecules for testing.

[0094] Furthermore, 50 ppm aqueous solutions of dyes such as Congo red and Coomassie Brilliant Blue G250 were prepared respectively, a melt-polymerized NKCOF-41 / polyvinylidene fluoride membrane was fixed in a detachable dead-end filtration device, the dye solution was added to the filter cup, a vacuum water circulation pump was used to apply a suction force of -0.5 bar to 0.8 bar, and the filtrate after passing through the membrane was collected. The solution before and after passing through the melt-polymerized NKCOF-41 / polyvinylidene fluoride membrane was scanned at a full wavelength of 200 to 800 nm by ultraviolet light, and the dye retention rate of the melt-polymerized NKCOF-41 / polyvinylidene fluoride membrane was calculated using the change in the absorbance value of the dye at the maximum absorption wavelength, as shown in FIG. Figure 6 and Figure 7 As shown, the absorbance of various dyes at their maximum absorption wavelength is significantly reduced after filtration through the melt-polymerized NKCOF-41 / polyvinylidene fluoride membrane. Calculation results indicate that the melt-polymerized NKCOF-41 / polyvinylidene fluoride membrane has excellent retention of various dyes, with retention rates exceeding 90%. The specific retention rates are shown in Table 1.

[0095] Table 1 Dye rejection rate of melt polymerization NKCOF-41 / polyvinylidene fluoride membrane

[0096]

[0097] Further, such as Figure 8 As shown, the experimental results of the gas separation experiment of the melt polymerization COFs membrane prepared by the preparation method of the melt polymerization COFs membrane of the present application are shown. Specifically: the gas permeation performance of the membrane is tested using a gas permeation device. The pure gas permeation performance of the prepared melt polymerization COFs membrane is tested using a constant volume variable pressure method. The melt polymerization COFs membrane is installed in the testing instrument, then purged with N2 and left under vacuum overnight. The pure gas permeability test is carried out in the order of N2 and CO2. The test is repeated no less than 3 times under each condition, such as Figure 8 This indicates that melt-polymerized COFs membranes are expected to be used in the field of gas separation in the future.

[0098] In summary, the method for preparing the melt-polymerized COFs membrane of the present invention utilizes a liquid sealing strategy to replace the vacuuming step in the preparation process of the traditional melt-polymerized COFs material, making the preparation process of the melt-polymerized COFs material more controllable. By regulating the shape of the molten liquid during the preparation process of the melt-polymerized COFs material, a uniform and continuous melt-polymerized COFs membrane is successfully prepared, thereby solving the problem that the traditional preparation method can only prepare melt-polymerized COFs powder and cannot form other forms. At the same time, the melt-polymerized COFs membrane prepared using the method for preparing the melt-polymerized COFs membrane of the present invention can be applied to wastewater treatment and gas separation, etc., to achieve efficient separation of dyes and gases.

[0099] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the above embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the above embodiments, or replace some or all of the technical features therein with equivalents. However, these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for preparing a melt-polymerized COFs film, characterized in that: The following steps are involved: S1. Using at least two organic monomers, mixing them under the catalytic action of a catalyst to prepare a melt-polymerized COFs matrix; S2, performing a preforming process on the melt-polymerized COFs matrix to obtain a preformed film; S3, performing a liquid sealing treatment on the preformed film using an inert low-melting-point and high-boiling-point liquid, so that the inert low-melting-point and high-boiling-point liquid completely covers the surface of the preformed film; S4. Continue the reaction at the set temperature to prepare a formed film, clean the formed film, and obtain the melt-polymerized COFs film.

2. The method for preparing a melt-polymerized COFs film according to claim 1, wherein: The S1 specifically comprises: reacting at least two organic monomers under the catalytic action of the catalyst at a temperature of 120 to 250° C. for 5 to 30 minutes to prepare a melt-polymerized COFs matrix.

3. The method for preparing a melt-polymerized COFs film according to claim 1, wherein: In S1, the organic monomer includes a first organic monomer and a second organic monomer, the first organic monomer is any one of 2,4,6-trimethylpyridine, ligustrazine or a C3 / C2 symmetrical methyl monomer; the second organic monomer is any one of terephthalaldehyde, 4,4'-biphenyldicarboxaldehyde, trimesic acid or a C2 / C3 symmetrical aldehyde monomer; the catalyst is any one of benzoic acid, benzoic anhydride, acetic acid, acetic anhydride, and maleic anhydride.

4. The method for preparing a melt-polymerized COFs film according to claim 1, wherein: The S2 is specifically: S21, heating the melt-polymerized COFs matrix in S1 at a temperature of 120 to 250° C. for 5 to 30 minutes to obtain a liquid melt-polymerized COFs matrix; S22, transferring the liquid melt-polymerized COFs matrix to a sheet forming device for cooling to obtain the preformed film.

5. The method for preparing a melt-polymerized COFs film according to claim 1, wherein: The S2 is specifically: S21′, heating the melt-polymerized COFs matrix in S1 at a temperature of 80 to 250° C. for 10 to 60 minutes to obtain the melt-polymerized COFs matrix in liquid form; S22', coating the liquid melt-polymerized COFs matrix on a formed film to obtain the preformed film.

6. The method for preparing a melt-polymerized COFs film according to claim 5, wherein: The forming substrate is an organic forming film, which can be any one of organic films such as polyvinylidene fluoride film, glass fiber film, electrospun polyvinylidene fluoride film, nylon film, polyacrylonitrile film, polyethersulfone film and polytetrafluoroethylene film.

7. The method for preparing a melt-polymerized COFs film according to claim 5, wherein: The forming substrate is an inorganic forming film, and the inorganic forming film is an anodized aluminum inorganic film.

8. The method for preparing a melt-polymerized COFs film according to claim 1, wherein: In S3, the inert low melting point and high boiling point liquid is any one of low melting point tin-lead alloy, dimethyl silicone oil, phenylmethyl silicone oil, vinyl silicone oil, and hydroxy silicone oil.

9. The method for preparing a melt-polymerized COFs film according to claim 1, wherein: The S4 is specifically: S41. Continue the reaction at the set temperature to obtain a formed film, clean the surface of the formed film with toluene or petroleum ether, and then clean it again with a mixture of N,N-dimethylformamide, methanol and tetrahydrofuran, or a mixture of N,N-dimethylformamide, ethanol and tetrahydrofuran; wherein the volume ratio of methanol to tetrahydrofuran is 1:1 to 1:2; and the volume ratio of ethanol to tetrahydrofuran is 1:1 to 1:2; S42, immersing the cleaned formed film in the methanol or ethanol for standby use, or drying by vacuum hot pressing to obtain a dry melt-polymerized COFs film.

10. A melt-polymerized COFs membrane for separating organic pollutants, characterized by: The melt-polymerized COFs membrane is prepared by the method for preparing a melt-polymerized COFs membrane according to any one of claims 1 to 9, and the rejection rate of the melt-polymerized COFs membrane for organic pollutants is greater than 90%.

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