Randomly-oriented covalent organic framework film as well as preparation method and application thereof

Abstract

The invention belongs to the technical field of filtering membranes, and particularly relates to a randomly oriented covalent organic framework membrane as well as a preparation method and application thereof. The preparation method of the frame membrane comprises the following steps that a substrate makes contact with a precursor solution, heating treatment is conducted, an LDH template is obtained, and the precursor solution comprises cobalt salt, aluminum salt, urea, NH4F and water; treating the LDH template to generate-OH terminal groups on the surface of the LDH template; enabling the obtained LDH template to be in contact with a functional liquid phase to obtain a-NH2 functionalized LDH template; the functional liquid is prepared from methylbenzene and 3-amino propyl triethoxy silane; and contacting the-NH2 functionalized LDH template with a solution containing a diamine monomer, an aldehyde monomer, acetic acid and an organic solvent to obtain the randomly oriented covalent organic framework membrane. The framework membrane has the beneficial effects that the framework membrane has relatively high lithium ion selectivity, lithium ions can be accurately extracted from a complex salt lake brine solution, and a wide prospect is developed for application of a lithium ion extraction technology in a complex environment.

Description

Technical Field

[0001] The present invention belongs to the technical field of filtration membranes, and in particular relates to a randomly oriented covalent organic framework membrane and a preparation method and application thereof. Background Art

[0002] In terms of lithium extraction from salt lakes, if Li+ is to be screened out from other alkaline ions, the membrane used must achieve one of the following two effects: First, it allows Li + Pass, while retaining Na + and K + ; Second, allow Na + and K + Through, while intercepting Li + The first method requires the membrane to be Li + / Na + and Li + / K + The selectivity must be much higher than that of Na + / Li + and K + / Li + The ratio of (10 and 10 respectively 3 ), Li + Only through a single separation process can it be screened out. Otherwise, it is necessary to rely on repeated separation operations to achieve the goal. The second method is to use the membrane to filter out Na + / Li + and K + / Li+ selectivity needs to be nearly perfect. Because unlike the first method, once Li + If the wastewater leaks into the effluent, it will be difficult to recover it through multiple processes. Due to the above disadvantages, these two methods cannot be widely used. Summary of the Invention

[0003] The present application provides a randomly oriented covalent organic framework membrane and its preparation method and application, aiming to solve the problem of insufficient selectivity of salt lake lithium extraction membranes. Existing membrane extraction technology has to rely on repeated separation operations to achieve salt lake lithium extraction, which undoubtedly greatly increases the cost.

[0004] The first aspect of the present application provides a method for preparing a randomly oriented covalent organic framework film, comprising the following steps:

[0005] (1) contacting a substrate with a precursor solution and performing a heating treatment to obtain an LDH template, wherein the precursor solution includes a cobalt salt, an aluminum salt, urea, NH4F and water;

[0006] (2) treating the LDH template to generate -OH terminal groups on its surface;

[0007] (3) contacting the LDH template obtained in step (2) with a functional liquid to obtain an -NH2-functionalized LDH template; the functional liquid comprises toluene and 3-aminopropyltriethoxysilane;

[0008] (4) The -NH2-functionalized LDH template is contacted with a solution containing a diamine monomer, an aldehyde monomer, acetic acid, and an organic solvent to obtain a randomly oriented covalent organic framework film.

[0009] According to some embodiments of the method for preparing a randomly oriented covalent organic framework film described in the present application, in step (1), the substrate includes an aluminum oxide substrate or a silicon substrate.

[0010] According to some embodiments of the method for preparing a randomly oriented covalent organic framework film described in the present application, the molar ratio of the aluminum salt to the cobalt salt in the precursor solution is 1:(2-4).

[0011] According to some embodiments of the method for preparing a randomly oriented covalent organic framework membrane described in the present application, the molar ratio of the aluminum salt to the urea is 1:(8-12).

[0012] According to some embodiments of the method for preparing the randomly oriented covalent organic framework membrane described in the present application, the molar ratio of the aluminum salt to the NH4F is 1:(12-16).

[0013] According to some embodiments of the method for preparing a randomly oriented covalent organic framework membrane described in the present application, the mass ratio of the aluminum salt to water is 1:(90-100).

[0014] According to some embodiments of the method for preparing the randomly oriented covalent organic framework film described in the present application, the aluminum salt includes aluminum nitrate or aluminum chloride and hydrates of the above compounds.

[0015] According to some embodiments of the method for preparing the randomly oriented covalent organic framework film described in the present application, the cobalt salt includes cobalt nitrate or cobalt chloride and hydrates of the above compounds.

[0016] According to some embodiments of the method for preparing the randomly oriented covalent organic framework membrane described in the present application, the water is deionized water.

[0017] According to some embodiments of the method for preparing a randomly oriented covalent organic framework film described in the present application, in step (1), the temperature of the heating treatment is 100-150° C., and the time of the heating treatment is 20-30 hours.

[0018] According to some embodiments of the method for preparing a randomly oriented covalent organic framework membrane described in the present application, in step (2), the LDH template is treated with oxygen plasma to generate -OH terminal groups on its surface.

[0019] According to some embodiments of the method for preparing a randomly oriented covalent organic framework film described in the present application, the power of the oxygen plasma treatment is 40-50 W, and the time of the oxygen plasma treatment is 3-5 min.

[0020] According to some embodiments of the method for preparing a randomly oriented covalent organic framework film described in the present application, in step (3), the volume ratio of toluene and 3-aminopropyltriethoxysilane in the functional liquid is (2-4):1.

[0021] According to some embodiments of the method for preparing a randomly oriented covalent organic framework film described in the present application, in step (3), the contact temperature is 20-30° C., and the contact time is 20-30 h.

[0022] According to some embodiments of the method for preparing a randomly oriented covalent organic framework membrane described in the present application, in step (4), the diamine monomer includes sulfonic acid p-phenylenediamine.

[0023] According to some embodiments of the method for preparing a randomly oriented covalent organic framework film described herein, the aldehyde monomer includes 1,3,5-triformylphloroglucinol.

[0024] According to some embodiments of the method for preparing a randomly oriented covalent organic framework film described in the present application, the organic solvent includes 1,4-dioxane and mesitylene; preferably, the volume ratio of 1,4-dioxane to mesitylene is 1:1.

[0025] According to some embodiments of the method for preparing a randomly oriented covalent organic framework membrane described in the present application, in step (4), the mass ratio of the diamine monomer to the aldehyde monomer in the solution is: (1-3):1.

[0026] According to some embodiments of the method for preparing a randomly oriented covalent organic framework membrane described in the present application, the mass ratio of the diamine monomer to the acetic acid in the solution is 1:(40-60).

[0027] According to some embodiments of the method for preparing a randomly oriented covalent organic framework membrane described in the present application, the mass ratio of the diamine monomer to the organic solvent in the solution is 1:(200-600).

[0028] According to some embodiments of the method for preparing a randomly oriented covalent organic framework film described in the present application, in step (4), the contact temperature is 100-150° C., and the contact time is 70-75 hours.

[0029] The second aspect of the present application provides a randomly oriented covalent organic framework film, which is prepared by the preparation method described in the first aspect of the present application.

[0030] The third aspect of the present application provides a randomly oriented covalent organic framework film obtained by the preparation method of the first aspect of the present application or the randomly oriented covalent organic framework film of the second aspect of the present application in screening Li + Application in this area.

[0031] According to some embodiments of the application described in this application, the randomly oriented covalent organic framework membrane is used in electrodialysis screening of Li + Application in this area. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Figure 1a This is a scanning electron microscope image of the -NH2-functionalized LDH template obtained during the preparation of the randomly oriented covalent organic framework membrane described in Example 1 of the present application;

[0033] Figure 1b This is a scanning electron microscope image of the -NH2-functionalized LDH template obtained during the preparation of the randomly oriented covalent organic framework membrane described in Example 2 of the present application;

[0034] Figure 1c This is a scanning electron microscope image of the -NH2-functionalized LDH template obtained during the preparation of the randomly oriented covalent organic framework membrane described in Example 3 of the present application;

[0035] Figure 2a This is a scanning electron microscope image of the randomly oriented covalent organic framework film described in Example 2 of the present application;

[0036] Figure 2b This is a scanning electron microscope image of the randomly oriented covalent organic framework film described in Example 3 of the present application;

[0037] Figure 3a This is a scanning electron microscope image of the -NH2-functionalized LDH template obtained during the preparation of the randomly oriented covalent organic framework membrane described in Example 4 of the present application;

[0038] Figure 3b This is a scanning electron microscope image of the -NH2-functionalized LDH template obtained during the preparation of the randomly oriented covalent organic framework membrane described in Example 5 of the present application;

[0039] Figure 3c This is a scanning electron microscope image of the -NH2-functionalized LDH template obtained during the preparation of the randomly oriented covalent organic framework membrane described in Example 6 of the present application;

[0040] Figure 4a This is a scanning electron microscope image of the randomly oriented covalent organic framework film described in Comparative Example 1 of the present application;

[0041] Figure 4b This is a scanning electron microscope image of the randomly oriented covalent organic framework film described in Comparative Example 2 of the present application;

[0042] Figure 5a This is a graph showing the results of studying the ion selectivity of the randomly oriented covalent organic framework membrane described in Example 1 of the present application;

[0043] Figure 5b This is a graph showing the results of studying the ion selectivity of the randomly oriented covalent organic framework membrane described in Comparative Example 2 of this application;

[0044] Figure 6 This is a graph showing the ion selectivity study results of the randomly oriented covalent organic framework membrane described in Example 1 of the present application after continuous operation for 120 hours;

[0045] Figure 7 Separation of Li from salt lake water by the randomly oriented covalent organic framework membrane described in Example 1 of this application + Figure 2 shows the results of the effect study. DETAILED DESCRIPTION

[0046] The embodiments of the present invention are described in detail below. The examples of the embodiments are exemplary and intended to be used to explain the present invention, but should not be understood as limiting the present invention.

[0047] In the present invention, the terms "one embodiment", "some embodiments", "examples", "specific examples", or "some examples" mean that the specific features, structures, materials or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic expressions of the above terms do not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described can be combined in any one or more embodiments or examples in a suitable manner. In addition, those skilled in the art can combine and combine different embodiments or examples described in this specification and the features of different embodiments or examples without contradiction.

[0048] The present invention provides a method for preparing a randomly oriented covalent organic framework film, comprising the following steps:

[0049] (1) contacting a substrate with a precursor solution and performing a heating treatment to obtain an LDH template, wherein the precursor solution includes a cobalt salt, an aluminum salt, urea, NH4F and water;

[0050] (2) treating the LDH template to generate -OH terminal groups on its surface;

[0051] (3) contacting the LDH template obtained in step (2) with a functional liquid to obtain an -NH2-functionalized LDH template; the functional liquid comprises toluene and 3-aminopropyltriethoxysilane;

[0052] (4) The -NH2-functionalized LDH template is contacted with a solution containing a diamine monomer, an aldehyde monomer, acetic acid, and an organic solvent to obtain a randomly oriented covalent organic framework film.

[0053] In some embodiments of the present application, in step (1), the substrate comprises an aluminum oxide substrate or a silicon substrate. In the present application, the AAO substrate has higher reactivity and its inherent nanoscale pores are conducive to ion transport.

[0054] In some embodiments of the present application, the molar ratio of the aluminum salt to the cobalt salt in the precursor solution is 1:(2-4); for example, 1:2, 1:3, 1:4, etc.

[0055] In some embodiments of the present application, the molar ratio of the aluminum salt to the urea is 1:(8-12); for example, 1:8, 1:9, 1:10, 1:12, etc.

[0056] In some embodiments of the present application, the molar ratio of the aluminum salt to the NH4F is 1:(12-16); for example, 1:12, 1:13, 1:14, 1:16, etc.

[0057] In some embodiments of the present application, the mass ratio of the aluminum salt to water is 1:(90-100); for example, 1:90, 1:92, 1:95, 1:98, 1:100, etc.

[0058] In some embodiments of the present application, the aluminum salt includes aluminum nitrate or aluminum chloride and hydrates of the above compounds.

[0059] In some embodiments of the present application, the cobalt salt includes cobalt nitrate or cobalt chloride and hydrates of the above compounds.

[0060] In some embodiments of the present application, the water is deionized water.

[0061] In some embodiments of the present application, in step (1), the temperature of the heating treatment is 100-150°C, for example, 100°C, 120°C, 130°C, 140°C, 150°C, etc., and the time of the heating treatment is 20-30h, for example, 20h, 25h, 28h, 30h, etc.

[0062] In some embodiments of the present application, in step (2), the LDH template is treated with oxygen plasma to generate -OH terminal groups on its surface.

[0063] In some embodiments of the present application, the power of the oxygen plasma treatment is 40-50W, such as 40W, 43W, 45W, 48W, 50W, etc., and the time of the oxygen plasma treatment is 3-5min, such as 3min, 4min, 5min, etc.

[0064] In some embodiments of the present application, in step (3), the volume ratio of toluene and 3-aminopropyltriethoxysilane in the functional liquid is (2-4):1; for example, 2:1, 3:1, 4:1, etc., for functionalization treatment to cover a layer of NH2 groups.

[0065] In some embodiments of the present application, in step (3), the contact temperature is 20-30°C, for example, 20°C, 25°C, 28°C, 30°C, etc., and the contact time is 20-30h, for example, 20h, 25h, 28h, 30h, etc.

[0066] In some embodiments of the present application, in step (4), the diamine monomer includes sulfonic acid p-phenylenediamine.

[0067] In some embodiments of the present application, the aldehyde monomer includes 1,3,5-triformylphloroglucinol.

[0068] In some embodiments of the present application, the organic solvent includes 1,4-dioxane and mesitylene; preferably, the volume ratio of 1,4-dioxane to mesitylene is 1:1.

[0069] In some embodiments of the present application, in step (4), the mass ratio of the diamine monomer to the aldehyde monomer in the solution is (1-3):1; for example, 1:1, 2:1, 3:1, etc.

[0070] In some embodiments of the present application, the mass ratio of the diamine monomer to the acetic acid in the solution is 1:(40-60); for example, 1:40, 1:45, 1:48, 1:50, etc.

[0071] In some embodiments of the present application, the mass ratio of the diamine monomer to the organic solvent in the solution is 1:(200-600), for example, 1:200, 1:210, 1:220, 1:230, 1:250, etc.

[0072] In some embodiments of the present application, in step (4), the contact temperature is 100-150°C, for example, 100°C, 120°C, 128°C, 135°C, 140°C, 143°C, 150°C, etc., and the contact time is 70-75h, for example, 70h, 72h, 73h, 75h, etc.

[0073] An embodiment of the present application also provides a randomly oriented covalent organic framework film, which is prepared by the preparation method described in the first aspect of the present application.

[0074] The present application also provides a randomly oriented covalent organic framework film obtained by the preparation method of the first aspect of the present application or the randomly oriented covalent organic framework film of the second aspect of the present application in screening Li + Application in this area.

[0075] In some embodiments of the present application, the randomly oriented covalent organic framework membrane is used in electrodialysis screening of Li + Application in this area.

[0076] The technical solution of this application will be further described below with reference to specific embodiments.

[0077] Example 1

[0078] A method for preparing a randomly oriented covalent organic framework film comprises the following steps:

[0079] (1) An alumina substrate was immersed in a precursor solution (the precursor solution included 244.4 mg Co(NO3)2·6H2O, 105.0 mg Al(NO3)3·9H2O, 168.2 mg urea, 148.2 mg NH4F, and 35 ml deionized water), then heated at 120°C for 24 h and then naturally cooled to room temperature to obtain an LDH template;

[0080] (2) Treating the LDH template with oxygen plasma at a working power of 45 W for 3 min to generate -OH terminal groups on its surface;

[0081] (3) Soaking the LDH template obtained in step (2) in a functional liquid (comprising toluene and 3-aminopropyltriethoxysilane in a volume ratio of 2:1) at a temperature of 25° C. for 24 h to obtain an -NH2-functionalized LDH template;

[0082] (4) The -NH2-functionalized LDH template was placed in a solution (including 28.2 mg of diamine monomer sulfonic acid p-phenylenediamine, 21.0 mg of 1,3,5-triformyl phloroglucinol, 1.6 ml of acetic acid, 8 ml of 1,4-dioxane and 8 ml of mesitylene) and reacted at 120 °C for 72 h to obtain a randomly oriented covalent organic framework film.

[0083] Example 2

[0084] The only difference between the randomly oriented covalent organic framework membrane described in Example 2 and Example 1 is that the contact temperature between the LDH template and the functional liquid during the preparation process of the randomly oriented covalent organic framework membrane described in Example 2 is 10°.

[0085] Example 3

[0086] The only difference between the randomly oriented covalent organic framework membrane described in Example 3 and Example 1 is that the contact temperature between the LDH template and the functional liquid during the preparation process of the randomly oriented covalent organic framework membrane described in Example 3 is 50°.

[0087] Example 4

[0088] The only difference between the randomly oriented covalent organic framework membrane described in Example 4 and that in Example 1 is that the contact time between the LDH template and the functional liquid during the preparation process of the randomly oriented covalent organic framework membrane described in Example 4 is 12 hours.

[0089] Example 5

[0090] The only difference between the randomly oriented covalent organic framework membrane described in Example 5 and that in Example 1 is that the contact time between the LDH template and the functional liquid during the preparation process of the randomly oriented covalent organic framework membrane described in Example 5 is 30 h.

[0091] Example 6

[0092] The only difference between the randomly oriented covalent organic framework membrane described in Example 6 and that in Example 1 is that the contact time between the LDH template and the functional liquid during the preparation process of the randomly oriented covalent organic framework membrane described in Example 6 is 50 h.

[0093] Comparative Example 1

[0094] The only difference between the randomly oriented covalent organic framework membrane described in Comparative Example 1 and Example 1 is that the LDH template is not treated to generate -OH terminal groups on its surface during the preparation of the randomly oriented covalent organic framework membrane described in Comparative Example 1, and the LDH template is not brought into contact with the functional liquid.

[0095] Specific operation methods include:

[0096] (1) An alumina substrate was immersed in a precursor solution (the precursor solution included 244.4 mg Co(NO3)2·6H2O, 105.0 mg Al(NO3)3·9H2O, 168.2 mg urea, 148.2 mg NH4F, and 35 ml deionized water), then heated at 120°C for 24 h and then naturally cooled to room temperature to obtain an LDH template;

[0097] (2) The LDH template was placed in a solution (including 28.2 mg of diamine monomer sulfonic acid p-phenylenediamine, 21.0 mg of 1,3,5-triformyl phloroglucinol, 1.6 ml of acetic acid, 8 ml of 1,4-dioxane and 8 ml of mesitylene) and reacted at 120°C for 72 hours to obtain a randomly oriented covalent organic framework film.

[0098] Comparative Example 2

[0099] The only difference between the randomly oriented covalent organic framework membrane described in Comparative Example 2 and Example 1 is that the LDH template is not modified with sulfonyl functional groups during the preparation of the randomly oriented covalent organic framework membrane described in Comparative Example 2.

[0100] Specific operation methods include:

[0101] (1) An alumina substrate was immersed in a precursor solution (the precursor solution included 244.4 mg Co(NO3)2·6H2O, 105.0 mg Al(NO3)3·9H2O, 168.2 mg urea, 148.2 mg NH4F, and 35 ml deionized water), then heated at 120°C for 24 h and then naturally cooled to room temperature to obtain an LDH template;

[0102] (2) Treating the LDH template with oxygen plasma at a working power of 45 W for 3 min to generate -OH terminal groups on its surface;

[0103] (3) Soaking the LDH template obtained in step (2) in a functional liquid (including toluene and 3-aminopropyltriethoxysilane in a volume ratio of 2:1) at a temperature of 25° C. for 24 h to obtain an -NH2 functionalized LDH template.

[0104] Study on the performance of randomly oriented covalent organic framework films described in Examples 1-6 and Comparative Examples 1-2 of the present application

[0105] 1. The electron microscope scanning images of the -NH2 functionalized LDH templates prepared in Examples 1-3 of the present application are as follows: Figure 1a-Figure 1c As shown; the electron microscope scanning image of the randomly oriented covalent organic framework film prepared in Example 2-3 of the present application is as shown Figure 2a-2b shown.

[0106] from Figure 1a-Figure 1c It can be seen that the optimal contact temperature between the LDH template and the functional liquid during the preparation of the randomly oriented covalent organic framework membrane is 25°. When the contact temperature is 10°, the LDH template does not fully contact the functional liquid, resulting in incomplete functionalization and failure to grow into a uniform COF membrane ( Figure 2a When the contact temperature is 50°, the LDH template is too damaged, which is not conducive to the subsequent growth of the COF film, resulting in significant damage to the COF film structure ( Figure 2b shown).

[0107] 2. During the preparation of the randomly oriented covalent organic framework membranes described in Examples 4-6 of the present application, the electron microscope scanning images of the -NH2 functionalized LDH templates obtained are as follows: Figure 3a-3c shown.

[0108] from Figure 3a-3cThe results show that the optimal contact time between the LDH template and the functional solution during the preparation of the COF membrane is 24 hours. A 12-hour contact time is too short, resulting in incomplete functionalization and causing some collapse in the subsequently grown COF membrane. A 30-hour contact time is too long, slightly affecting the structure of the LDH template and causing some damage. A 50-hour contact time results in significant structural damage to the LDH, hindering subsequent COF membrane growth.

[0109] 3. The electron microscope scanning images of the randomly oriented covalent organic framework films described in Comparative Examples 1 and 2 of the present application are as follows: Figure 4a Figure 4b shown.

[0110] from Figure 4a and Figure 4b As can be seen, the randomly oriented COF membrane described in Comparative Example 1 differs only from Example 1 in that the LDH template was not treated to generate -OH terminal groups on its surface during the preparation process, and the LDH template was not exposed to a functional liquid. Without functionalization of the LDH, a COF membrane could not be formed; however, a COF membrane could be formed in Comparative Example 2.

[0111] 4. Study on the stability of the randomly oriented covalent organic framework film described in this application:

[0112] 0.1M KCl and 0.1M LiCl were mixed in a polytetrafluoroethylene permeation cell to evaluate the ion selectivity of the randomly oriented covalent organic framework membranes described in Example 1 and Comparative Example 2. The results are as follows: Figure 5a and Figure 5b shown.

[0113] from Figure 5a and Figure 5b It can be seen that: the raw material pool where the randomly oriented covalent organic framework membrane described in Comparative Example 2 of this application is located is mixed with 0.1MK + and 0.1M Li + , K cannot be detected + , Li + This is because the COF membrane without sulfonate groups has poor hydrophilicity and cannot provide groups for K ion transport; the randomly oriented covalent organic framework membrane described in Comparative Example 2 has no ion selectivity.

[0114] In order to evaluate the long-term stability of the selectivity of the randomly oriented covalent organic framework film described in Example 1 of the present application, this test example was tested continuously for 120 hours. The test results are as follows: Figure 6 shown.

[0115] from Figure 6 It can be seen that in order to verify the ability of COF to operate continuously, the test was conducted for 120 hours, and K + The flux changes little, and no Li + , which proves that the COF membrane has good performance retention ability, that is, the randomly oriented covalent organic framework membrane described in this application has good stability.

[0116] 5. The random oriented covalent organic framework membrane described in this application is used to separate Li from salt lake water. + Effect

[0117] Experimental method: A bias voltage is applied to a pair of Ag / AgCl electrodes on the reservoir of the electrodialysis device, with the working electrode on the permeate side. This electrode can reversibly store and release Cl - , the electrical neutrality of the two reservoirs is maintained during the electrodialysis process. The results of the test on the separation of Li+ from salt lake brine (composition see Table 1) are as follows Figure 7 shown.

[0118] Table 1

[0119] <![CDATA[Li + ]]> <![CDATA[Na + ]]> <![CDATA[K + ]]> <![CDATA[Ca 2+ ]]> <![CDATA[Mg 2+ ]]> 0.035 2.17 0.38 0.2 0.022

[0120] from Figure 7 It can be seen that at the point solution voltage of 4.5 V, all competing ions (K + 、Na + Mg 2+ , Ca 2+ ) can be transported through the randomly oriented covalent organic framework membrane, leaving only Li + That is, the randomly oriented covalent organic framework membrane described in this application exhibits almost perfect selectivity.

[0121] Although the above embodiments have been shown and described, it is understood that the above embodiments are illustrative and are not to be construed as limitations on the present invention. Changes, modifications, substitutions and variations of the above embodiments by those skilled in the art are all within the scope of protection of the present invention.

Claims

1. A method for preparing a randomly oriented covalent organic framework film, characterized in that: The following steps are involved: (1) contacting a substrate with a precursor solution and performing a heating treatment to obtain an LDH template, wherein the precursor solution includes a cobalt salt, an aluminum salt, urea, NH4F and water; (2) treating the LDH template to generate -OH terminal groups on its surface; (3) contacting the LDH template obtained in step (2) with a functional liquid to obtain an -NH2-functionalized LDH template; the functional liquid comprises toluene and 3-aminopropyltriethoxysilane; (4) The -NH2-functionalized LDH template is contacted with a solution containing a diamine monomer, an aldehyde monomer, acetic acid, and an organic solvent to obtain a randomly oriented covalent organic framework film.

2. The method for preparing the randomly oriented covalent organic framework film according to claim 1, characterized in that: In step (1), the substrate includes an aluminum oxide substrate or a silicon substrate; and / or, the molar ratio of aluminum salt to cobalt salt in the precursor solution is 1:(2-4); and / or, the molar ratio of the aluminum salt to the urea is 1:(8-12); and / or, the molar ratio of the aluminum salt to the NH4F is 1:(12-16); And / or, the mass ratio of the aluminum salt to water is 1:(90-100); Preferably, the aluminum salt includes aluminum nitrate or aluminum chloride and hydrates of the above compounds; Preferably, the cobalt salt includes cobalt nitrate or cobalt chloride and hydrates of the above compounds; Preferably, the water is deionized water.

3. The method for preparing the randomly oriented covalent organic framework film according to claim 1, characterized in that: In step (1), the temperature of the heating treatment is 100-150° C., and the time of the heating treatment is 20-30 hours.

4. The method for preparing the randomly oriented covalent organic framework film according to claim 1, characterized in that: In step (2), the LDH template is treated with oxygen plasma to generate -OH terminal groups on its surface; Preferably, the power of the oxygen plasma treatment is 40-50 W, and the time of the oxygen plasma treatment is 3-5 min.

5. The method for preparing the randomly oriented covalent organic framework film according to claim 1, characterized in that: In step (3), the volume ratio of toluene and 3-aminopropyltriethoxysilane in the functional liquid is (2-4):1; And / or, in step (3), the contact temperature is 20-30°C, and the contact time is 20-30h.

6. The method for preparing the randomly oriented covalent organic framework film according to claim 1, characterized in that: In step (4), the diamine monomer includes p-phenylenediamine sulfonate; and / or, the aldehyde monomer comprises 1,3,5-triformylphloroglucinol; And / or, the organic solvent includes 1,4-dioxane and mesitylene; preferably, the volume ratio of 1,4-dioxane to mesitylene is 1:

1.

7. The method for preparing the randomly oriented covalent organic framework film according to claim 1, characterized in that: In step (4), the mass ratio of the diamine monomer to the aldehyde monomer in the solution is: (1-3): 1; and / or, the mass ratio of the diamine monomer to the acetic acid in the solution is 1:(40-60); And / or, the mass ratio of the diamine monomer to the organic solvent in the solution is 1:(200-600).

8. The method for preparing the randomly oriented covalent organic framework film according to claim 1, characterized in that: In step (4), the contact temperature is 100-150° C., and the contact time is 70-75 hours.

9. A randomly oriented covalent organic framework film, characterized in that The compound is prepared by the preparation method according to any one of claims 1 to 8.

10. The randomly oriented covalent organic framework film obtained by the preparation method according to any one of claims 1 to 8 or the randomly oriented covalent organic framework film according to claim 9 is screened for Li + Application in this area; Preferably, the randomly oriented covalent organic framework membrane is subjected to electrodialysis screening of Li + Application in this area.

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