Self-supporting COFs membrane based on DES-H2O interfacial polymerization, preparation method and application

Abstract

The present invention discloses a self-supporting COFs membrane based on a DES-H2O interfacial polymerization method. The membrane is prepared by a deep eutectic solvent-water interfacial polymerization method and has an imine structure or a β-ketoenamine structure. The membrane is made of a C2-symmetrical amine or a C3-symmetrical amine and triformyl phloroglucinol as raw materials, p-toluenesulfonic acid as a catalyst, a quaternary ammonium salt as a regulator, and an alkyl acid as a crystallization controller. The present invention develops a simple, effective, universal, and easily modifiable method. A series of COFs membranes with periodic structures of different thicknesses and crystallinities are prepared by means of a DES-H2O interface. By constructing an adjustable viscosity and interfacial tension system, the membrane growth process is coordinated with monomer diffusion, interfacial polymerization, and the orderly assembly of the crystalline framework, and the precise modulation of the crystalline polymer membrane structure is achieved. The method is applied to the efficient separation of pollutants such as dyes and fluoride ions.

Description

Technical Field

[0001] The present invention relates to the technical field of novel separation membrane materials, and in particular to a self-supporting COFs membrane based on a DES-H2O interfacial polymerization method, a preparation method and applications thereof. Background Art

[0002] Membrane separation has the advantages of low cost, high energy efficiency, small footprint, easy operation and regeneration, and environmental friendliness. Covalent organic frameworks (COFs) have the functions of low density, large specific surface area, adjustable pore size and structure, and easy customization, and have attracted increasing attention in fields such as membrane separation. However, most COFs are prepared by solvothermal methods under harsh reaction conditions (i.e., high temperature and high pressure, inert gas protection, sealed environment, indispensable solvents and catalysts), and most of them are refractory, difficult to dissolve, and difficult to process powders, which seriously hinders their possible application in industry. Therefore, developing an effective and simple method to prepare COFs films with periodic honeycomb structure is a research hotspot and scientific frontier in the field of membrane separation.

[0003] Highly crystalline COF thin films are ideal separation materials. However, the crystallinity of most polymer backbones often leads to internal structural defects due to their compositional heterogeneity, which significantly limits their industrial application in membrane separations. Therefore, further densification is required. To overcome this problem, several strategies, including top-down and bottom-up approaches, have been used to grow COF thin films on surfaces. However, these strategies require suitable substrates and expensive technologies, which limits their full-scale implementation in industrial applications. Liquid-liquid interfacial polymerization (IP) is an effective method for preparing COF membranes, offering advantages such as mild conditions and the ability to obtain products from a reaction system. However, most existing works use volatile organic solvents such as dichloromethane. The evaporation of these solvents can disrupt the liquid-liquid interface, affecting the crystallinity and specific surface area of ​​the COF membranes. Furthermore, the organic phase is highly hydrophobic and cannot dissolve polar monomers. The size of the interfacial region is difficult to adjust at the traditional dichloromethane (DCM)-water interface, making this type of interfacial polymerization lacking scalability. These issues limit the widespread application of liquid-liquid interfacial polymerization in the synthesis of COF membranes with diverse functionalities. Summary of the Invention

[0004] In view of the above-mentioned shortcomings, the present invention provides a self-supporting COFs membrane, preparation method and application based on the DES-H2O interfacial polymerization method. The present invention develops a simple, effective, universal and easy-to-adjust method: with the help of a low eutectic solvent (DES)-H2O interface, a series of covalent organic framework membranes with periodic structures of different thicknesses and crystallinity are prepared. By constructing an adjustable viscosity and interfacial tension system, coordinating the monomer diffusion, interfacial polymerization and membrane growth processes during the reaction, optimizing the orderly assembly of the crystalline framework, and realizing the precise adjustment of the crystalline polymer membrane structure. On the one hand, the construction of this system can provide new ideas and new methods for the film formation of crystalline materials. On the other hand, this type of membrane can be used for the efficient separation of pollutants such as dyes and fluoride ions, and can also bring new breakthroughs and new opportunities for industrial membrane separation applications. The present invention belongs to the key R&D plan of Hunan Province 2021GK2014, the research, development and application of separation membrane materials oriented to the deep treatment function of fluorine-containing wastewater.

[0005] In order to achieve the above-mentioned object, the present invention provides a self-supporting COFs membrane based on the DES-H2O interfacial polymerization method, wherein the self-supporting COFs membrane is a COFs membrane having an imine structure or a β-ketoenamine structure prepared based on the low eutectic solvent-water interfacial polymerization method; wherein the self-supporting COFs membrane uses a C2-symmetrical amine or a C3-symmetrical amine and triformylphloroglucinol as raw materials, p-toluenesulfonic acid as a catalyst, a quaternary ammonium salt as a regulator, and an alkyl acid as a crystallization controller.

[0006] According to one aspect of the present invention, the C2-symmetrical amine includes any one or more of p-phenylenediamine, benzyl diamine, 3,3-dihydroxybenzenediamine, hydrazine hydrate, bipyridine diamine, and diaminoguanidine hydrochloride.

[0007] According to one aspect of the present invention, the C3 symmetrical amine includes any one or more of tris(4-aminophenyl)amine, triazine triphenylamine, and triaminoguanidine hydrochloride.

[0008] According to one aspect of the present invention, the quaternary ammonium salt includes any one of tetrabutylammonium chloride, tetrabutylammonium bromide, and hexadecyltrimethyloctylammonium bromide.

[0009] According to one aspect of the present invention, the alkyl acid includes any one of acetic acid, levulinic acid, n-hexanoic acid, n-octanoic acid, n-decanoic acid, dodecanoic acid, and oleic acid.

[0010] Based on the same inventive concept, the present invention also provides a method for preparing the above-mentioned self-supporting COFs film based on the DES-H2O interfacial polymerization method, comprising the following steps:

[0011] Step 1: Add quaternary ammonium salt and alkyl acid into a container and heat in an oil bath. After the solution in the container becomes clear and transparent, place it in a vacuum oven and dry it until all moisture is removed to obtain DES.

[0012] Step 2: dissolving triformylphloroglucinol in the DES and sonicating until the DES is dissolved to obtain a reaction solution A;

[0013] Step 3: dissolving a C2-symmetrical amine or a C3-symmetrical amine and p-toluenesulfonic acid in distilled water, sonicating until dissolved, and then filling with inert gas to obtain a reaction solution B;

[0014] Step 4: Slowly add distilled water to the upper layer of reaction solution A to form a pure water layer; slowly add reaction solution B to the upper layer of the pure water layer, and ensure that the interface is left still without disturbance, and react at room temperature for 3-5 days.

[0015] According to one aspect of the present invention, in step 1, the oil bath heating temperature is 85-100°C; the molar ratio of the quaternary ammonium salt to the alkyl acid is 1:2; and the vacuum oven drying temperature is 75-110°C.

[0016] According to one aspect of the present invention, in step 2, the ultrasonication time is 10-15 minutes.

[0017] According to one aspect of the present invention, in step 3, the molar amount of the C2-symmetrical amine or the C3-symmetrical amine is based on the functionality of the reactive monomer, and the functionality of the reactive monomer of the C2-symmetrical amine or the C3-symmetrical amine is 100-150% of the functionality of the reactive monomer of the triformylphloroglucinol; the inert gas is nitrogen; and the ultrasonic time is 10-15 minutes.

[0018] Based on the same inventive concept, the present invention also discloses an application of any of the above-mentioned self-supporting COFs membranes based on the DES-H2O interfacial polymerization method or a self-supporting COFs membrane prepared by any of the above-mentioned preparation methods based on the DES-H2O interfacial polymerization method, wherein the self-supporting COFs membrane is used for the separation of dyes and fluoride ions.

[0019] The imine structure of the present application is formed by the condensation of amine and aldehyde (Schiff base reaction), and the β-ketoenamine structure is because the α-H of the aldehyde (trialdehyde phloroglucinol) becomes active due to the influence of the carbonyl group, and a transformation from an enol structure to a keto structure occurs.

[0020] Beneficial effects of the present invention:

[0021] The self-supporting COFs film of the present invention is a two-dimensional covalent organic framework film, which is a topological structure formed by the reaction of C2-symmetric and C3-symmetric amines with triformylphloroglucinol through a deep eutectic solvent (DES)-water (H2O) interface;

[0022] (1) The reaction is carried out at room temperature, the interface is relatively stable, the oil phase and the water phase are not easy to volatilize, and the prepared film is continuous and relatively dense;

[0023] (2) By changing the length of the alkyl chain, the viscosity of DES can be adjusted and the size of the interface area can be customized to achieve the effect of controllable reaction interface confinement;

[0024] (3) The two-dimensional covalent organic framework film prepared by the preparation method of the present application can efficiently separate pollutants such as dyes and fluoride ions;

[0025] (4) This invention is the first to utilize the DES-water interface to easily prepare different two-dimensional covalent organic framework separation membranes at room temperature. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 Schematic diagram of the structure of the two-dimensional covalent organic framework according to an embodiment of the present invention;

[0027] Figure 2 Schematic diagram of the preparation principle of the self-supporting COFs film based on the DES-H2O interfacial polymerization method described in an embodiment of the present invention;

[0028] Figure 3 (a) is a schematic diagram of the preparation of TPPa-1 in Example 3 of the present invention; Figure 3 (b) is a schematic diagram of the preparation of TPPa-1 according to Example 4 of the present invention; Figure 3 (c) is a schematic diagram of the preparation of TPPa-1 in Example 5 of the present invention;

[0029] Figure 4 Schematic diagrams of the COFs membrane of TPPa-1 prepared in Example 3 of the present application, the COFs membrane of TP-BD prepared in Example 6, the COFs membrane of TP-BD(OH)2 prepared in Example 7, and the COFs membrane of TP-TAPA prepared in Example 8;

[0030] Figure 5 (a) is the Raman spectrum of the TPPa-1 film prepared in Example 3-5 of the present invention; Figure 5 (b) is the infrared spectrum of the TPPa-1 film prepared in Example 3-5 of the present invention; Figure 5 (c) The crystallinity of the TPPa-1 films prepared in Examples 3-4 and 9-10 of the present invention;

[0031] Figure 6(a) Infrared spectra of the COFs film of TPPa-1 prepared in Example 3, the COFs film of TP-BD prepared in Example 6, the COFs film of TP-BD(OH)2 prepared in Example 7, and the COFs film of TP-TAPA prepared in Example 8; Figure 6 (b) Electron micrographs of the COFs membrane of TPPa-1 prepared in Example 3, the COFs membrane of TP-BD prepared in Example 6, the COFs membrane of TP-BD(OH)2 prepared in Example 7, and the COFs membrane of TP-TAPA prepared in Example 8;

[0032] Figure 7 (a) The COFs membranes prepared in Example 3 and Example 6 were subjected to dye separation in Example 11 of the present invention; Figure 7 (b) The COFs membranes prepared in Examples 7 and 8 were subjected to F ion separation in Example 12 of the present invention. DETAILED DESCRIPTION

[0033] To make the present invention easier to understand, the present invention is further described below with reference to specific examples. It should be understood that these examples are only used to illustrate the present invention and are not used to limit the scope of the present invention. Obviously, the embodiments described are only part of the embodiments of the present invention, rather than all of the embodiments. Based on the embodiments in the present invention, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present invention. Unless otherwise defined, the professional terms used below are consistent with the meanings understood by professional and technical personnel in this field; unless otherwise specified, the raw materials and reagents involved in this article can be purchased from the market or prepared by known methods.

[0034] It should be noted that the "trialdehyde phloroglucinol" and "triformyl phloroglucinol" in the present application are the same substance, but are named differently.

[0035] It should be noted that the triformylphloroglucinol in this application is abbreviated as TP, the p-phenylenediamine in this application is abbreviated as Pa, the benzyl diamine in this application is abbreviated as BD, the N,N-bis(4-aminophenyl)benzene-1,4-diamine in this application is abbreviated as TAPA, the 3,3-dihydroxybenzidine in this application is abbreviated as BD(OH)2, the tris(4-aminophenyl)amine in this application is abbreviated as TAPB, the triazine triphenylamine in this application is abbreviated as TAPT, the triphenylamine in this application is abbreviated as TD, the triaminoguanidine hydrochloride in this application is abbreviated as TG, and the diaminoguanidine hydrochloride in this application is abbreviated as DG.

[0036] It should be noted that the abbreviations in this application are not case sensitive.

[0037] It should be understood that "TP-TAPA" and "TPTAPA" in this application are equivalent and can be replaced with each other.

[0038] It should be noted that “TPPa-1” in this application is equivalent to “TPPa”.

[0039] Currently, most COF membranes are prepared via solvothermal methods under harsh reaction conditions (i.e., high temperature, high pressure, inert gas protection, sealed environments, and the presence of essential solvents and catalysts). Most of these membranes are difficult to melt, dissolve, and process, resulting in refractory powders. This severely hinders their potential industrial applications. Crystallization of most polymer backbones often results in internal structural defects due to compositional heterogeneity, significantly limiting their industrial applications and necessitating further densification. To overcome this issue, several strategies, including top-down and bottom-up approaches, have been employed to grow COF films on surfaces. However, these strategies require suitable substrates and expensive techniques, limiting their full-scale industrial implementation. Liquid-liquid interfacial polymerization (IP) is an effective method for preparing COF membranes, offering advantages such as mild conditions and the ability to obtain a product from the reaction system. However, most existing works utilize volatile organic solvents, such as dichloromethane, whose evaporation can disrupt the liquid-liquid interface, affecting the crystallinity and specific surface area of ​​the COF membranes. Furthermore, the organic phase is highly hydrophobic and cannot dissolve polar monomers. The size of the interfacial area is difficult to adjust at the traditional dichloromethane (DCM)-water interface, and this interfacial polymerization lacks scalability. These problems limit the widespread application of liquid-liquid interfacial polymerization in the synthesis of covalent organic framework membranes with different functions.

[0040] In order to solve the above problems, the present invention provides a self-supporting COFs film based on DES-H2O interfacial polymerization method, which has a periodic topological structure, specifically as follows Figure 1 As shown, Figure 1 They are TPPa-1 (raw materials are triformyl phloroglucinol and p-phenylenediamine), TP-BD (raw materials are triformyl phloroglucinol and benzyl diamine), TP-BD(OH)2 (raw materials are triformyl phloroglucinol and 3,3-dihydroxybenzidine BD(OH)2), TPTAPB (raw materials are triformyl phloroglucinol and tris(4-aminophenyl)amine), TPTAPT (raw materials are triformyl phloroglucinol and triazine triphenylamine), TP-TAPA (raw materials are triformyl phloroglucinol and N,N-bis(4-aminophenyl)benzene-1,4-diamine), TPDG (raw materials are triformyl phloroglucinol and diaminoguanidine hydrochloride), TPTG (raw materials are triformyl phloroglucinol and triaminoguanidine hydrochloride), and TPTD (raw materials are triformyl phloroglucinol and tris(benzidine). Figure 1It can be seen that the self-supporting COFs film of the present application has the structure of a highly crystalline COFS film.

[0041] In order to solve the above problems, the present invention also provides a method for preparing a self-supporting COFs film based on the DES-H2O interfacial polymerization method, the principle diagram of which is shown in FIG. Figure 2 As shown, the following steps are included:

[0042] Step 1: Add quaternary ammonium salt and alkyl acid into a container and heat in an oil bath. After the solution in the container becomes clear and transparent, place it in a vacuum oven and dry it until all moisture is removed to obtain DES.

[0043] Step 2: dissolving triformylphloroglucinol (abbreviated as TP) in the DES and sonicating until dissolved to obtain reaction solution A;

[0044] Step 3: dissolving a C2-symmetrical amine or a C3-symmetrical amine (such as p-phenylenediamine, abbreviated as Pa) and p-toluenesulfonic acid in distilled water, sonicating until dissolved, and then filling with inert gas to obtain a reaction solution B;

[0045] Step 4: Slowly add distilled water to the upper layer of reaction solution A to form a pure water layer; slowly add reaction solution B to the upper layer of the pure water layer, and ensure that the interface is left still without disturbance, and react at room temperature for 3-5 days.

[0046] It should be noted that Figure 2 “TP / DES” in the table represents reaction solution A, and “Pa / water” represents reaction solution B.

[0047] Example 1

[0048] This example relates to the synthesis of a deep eutectic solvent (DES):

[0049] Step 1: Tetrabutylammonium chloride (54.4 g, 0.2 mol), tetrabutylammonium bromide (64.5 g, 0.2 mol), and hexadecyltrimethyloctylammonium bromide (114.96 g, 0.2 mol) were respectively mixed with acetic acid (24 g, 0.4 mol), levulinic acid (46.4 g, 0.4 mol), n-hexanoic acid (46.5 g, 0.4 mol), n-octanoic acid (57.6 g, 0.4 mol), n-decanoic acid (68.8 g, 0.4 mol), dodecanoic acid (80.144 g, 0.4 mol), and oleic acid (112.8 g, 0.4 mol) of different alkyl chain lengths into a beaker containing a magnet, heated and stirred with a magnetic stirrer at a stirring rate of 300 r / min for 2 h, and then placed in a vacuum oven at 90°C for 12 h to obtain 21 DES.

[0050] Example 2

[0051] This example relates to the preparation of a two-dimensional covalent framework separation membrane at the interface of n-octanoic acid DES (tetrabutylammonium chloride + n-octanoic acid, referred to as DES-C8)-water:

[0052] Step 2: Dissolve trialdehyde phloroglucinol (4.2 mg, 0.2 mmol) in 10 ml of DES (tetrabutylammonium chloride + octanoic acid, abbreviated as DES-C8) and sonicate for 10 minutes to prepare reaction solution A1;

[0053] Step 3: Dissolve p-phenylenediamine (3.2 mg, 0.3 mmol), benzyldiamine (5.4 mg, 0.3 mol), and 12 mg of p-toluenesulfonic acid in 10 ml of water, sonicate for 15 minutes, and purge with nitrogen to obtain reaction solution B1;

[0054] Step 4: Slowly add 1 ml of distilled water to the reaction liquid A1, and slowly add the reaction liquid B1 into the bottle of reaction liquid A1. Keep the interface stable and undisturbed during the addition process. Let it stand at room temperature for 4 days to obtain a self-supporting COFs film.

[0055] Example 3

[0056] This example relates to the preparation of a two-dimensional covalent framework separation membrane at the interface of DES (tetrabutylammonium chloride + octanoic acid, referred to as DES-C8) and water:

[0057] Step 2: Dissolve trialdehyde phloroglucinol (4.2 mg, 0.2 mmol) in 10 ml of DES (tetrabutylammonium chloride + octanoic acid, abbreviated as DES-C8) and sonicate for 10 minutes to prepare reaction solution A1;

[0058] Step 3: Dissolve p-phenylenediamine (3.2 mg, 0.3 mmol) and 12 mg of p-toluenesulfonic acid in 10 ml of water, sonicate for 15 minutes, and purge with nitrogen to obtain reaction solution B1;

[0059] Step 4: Slowly add 1 ml of distilled water to the reaction solution A1, and slowly add the reaction solution B1 into the bottle of reaction solution A1. Keep the interface stable and undisturbed during the addition process. Let it stand at room temperature for 4 days to obtain a self-supporting COFs film. The physical diagram of the preparation of TPPa-1 (the raw materials are triformyl phloroglucinol and p-phenylenediamine) is shown as follows Figure 3 As shown in (a).

[0060] Example 4

[0061] This example relates to the preparation of a two-dimensional covalent framework separation membrane at the interface of n-decanoic acid DES (tetrabutylammonium chloride + decanoic acid, referred to as DES-C10) and water:

[0062] Step 2: Dissolve trialdehyde phloroglucinol (4.2 mg, 0.2 mmol) in 10 ml of DES-decanoate (DES-C9) and ultrasonicate for 10 minutes to prepare reaction solution A2.

[0063] Step 3: Dissolve p-phenylenediamine (3.2 mg, 0.3 mmol) and 12 mg of p-toluenesulfonic acid in 10 ml of water, sonicate for 15 minutes, and purge with nitrogen to obtain reaction solution B2;

[0064] Step 4: Slowly add 1 ml of distilled water to the reaction solution A2, and slowly add the reaction solution B2 into the bottle of reaction A2. Keep the interface stable and undisturbed during the addition process. Let it stand at room temperature for 4 days to obtain a self-supporting COFs film. The physical diagram of the preparation of TPPa-1 (the raw materials are triformyl phloroglucinol and p-phenylenediamine) is shown as follows Figure 3 (b) shown.

[0065] Example 5

[0066] This example relates to the preparation of a two-dimensional covalent framework separation membrane at the dodecanoic acid DES (tetrabutylammonium chloride + dodecanoic acid, referred to as DES-C12)-water interface:

[0067] Step 2: Dissolve trialdehyde phloroglucinol (4.2 mg, 0.2 mmol) in 10 ml of dodecanoic acid DES (abbreviated as DES-C10) and sonicate for 10 minutes to prepare reaction solution A3;

[0068] Step 3: Dissolve p-phenylenediamine (3.2 mg, 0.3 mmol) and 12 mg of p-toluenesulfonic acid in 10 ml of water, sonicate for 15 minutes, and purge with nitrogen to obtain reaction solution B3;

[0069] Step 4: Slowly add 1 ml of distilled water to the reaction solution A3, and slowly add the reaction solution B3 into the bottle of reaction A3. Keep the interface stable and undisturbed during the addition process. Let it stand at room temperature for 4 days to obtain a self-supporting COFs film. The physical diagram of the preparation of TPPa-1 (the raw materials are triformyl phloroglucinol and p-phenylenediamine) is shown as follows Figure 3 (c) shown.

[0070] Example 6

[0071] The difference between this embodiment and embodiment 3 is that the p-phenylenediamine in step 3 is replaced by benzyl diamine (BD for short), and the other steps are the same as those in embodiment 3.

[0072] Example 7

[0073] The difference between this embodiment and embodiment 3 is that the p-phenylenediamine in step 3 is replaced by 3,3-dihydroxybenzidine BD(OH)2 (abbreviated as BD(OH)2), and the other steps are the same as those in embodiment 3.

[0074] Example 8

[0075] The difference between this embodiment and embodiment 3 is that the p-phenylenediamine in step 3 is replaced by N,N-bis(4-aminophenyl)benzene-1,4-diamine (TAPA for short), and the other steps are the same as those in embodiment 3.

[0076] Example 9

[0077] The difference between this embodiment and embodiment 3 is that DES octanoate is replaced by DES acetic acid (tetrabutylammonium chloride + acetic acid, referred to as DES-C2), and the other steps are the same as those in embodiment 3.

[0078] Example 10

[0079] The difference between this embodiment and embodiment 3 is that DES octanoate is replaced by DES acetic acid (tetrabutylammonium chloride + n-hexanoic acid, referred to as DES-C6), and the other steps are the same as those in embodiment 3.

[0080] Example 11

[0081] This embodiment relates to the application of dye separation:

[0082] Five different dye feed aqueous solutions (30 mL) were passed through the ultrafiltration device at an upstream pressure of 0.5 bar. The effective separation area of ​​each membrane was (2.5 cm -1 The five different dye feed aqueous solutions were methyl orange (50 mg) (MO), methyl red (50 mg) (MR), methylene blue (50 mg) (MB), crystal violet (50 mg) (CV), and fluorescent yellow (50 mg) (FB), which were dissolved in 1 L of water to obtain 50 mg / L dye feed aqueous solutions.

[0083] 5 ml of the filtrate was collected for characterization.

[0084] The dye concentrations of the feed and permeate were measured by UV-Vis spectroscopy. The percent retention (R%) was calculated according to the formula:

[0085]

[0086] Among them, C F Indicates the dye concentration of the feed liquid; C P Indicates the permeate dye concentration.

[0087] Example 12

[0088] This embodiment relates to the application of fluoride ion separation:

[0089] 30 mL of F ion standard liquid was passed through the ultrafiltration device at an upstream pressure of 1 bar. The effective separation area of ​​each membrane was (2.5 cm-1 For the fluorine ion standard solution, place 0.0221 g of analytical grade sodium fluoride in a 1000 mL quantitative flask and add deionized water to the mark. This yields a 10 mg / L fluorine ion standard solution.

[0090] 5 ml of the filtrate was collected for characterization using a F ion detection instrument to calculate the membrane retention rate and flux.

[0091] Results detection and performance analysis:

[0092] Depend on Figure 3 It can be seen that TPPa-1 COFs membranes can be successfully prepared in different DES systems. Figure 4 Schematic diagram of the COFs membrane prepared in Example 3 and Examples 6-8. Figure 4 It can be seen that four different structures of highly crystalline COFs films can be successfully prepared in the DES-C8 system, indicating that the system of this application has universal applicability. The TPPa-1 films prepared in Examples 3-5 were subjected to Raman spectroscopy analysis, and the results are as follows: Figure 5 As shown in (a), the Raman spectrum of TPPa-1 film can be obtained at about 1180 -1 , 1400 -1 and 1608cm -1 Peaks appear at , which are the stretching vibration modes of CH, NH and CN bonds, respectively. The N–H and C–N bonds further prove the formation of β-ketoenamine, indicating the tautomerization of enol to ketone to obtain β-ketoenamine structure. The TPPa-1 film prepared in Example 3-5 was subjected to infrared spectroscopy analysis, and the results are as follows: Figure 5 As shown in (b), the infrared spectrum of TPPa-1 film can be obtained at 1580 cm -1 The stretching band of (C=C) and the 1262cm -1 The stretching band of (CN) indicates that the β-ketoamine skeleton structure is successfully formed. The crystallinity of the TPPa-1 films prepared in Examples 3-4 and 9-10 is analyzed, and the results are as follows: Figure 5 As shown in (c), Figure 5 (c) It can be seen that the crystallinity of TPPa-1 films prepared from DES with different alkyl chain lengths (DES-C2, DES-C6, DES-C10) is different. The crystallinity of the film prepared from the DES-C10 system is the highest. This allows for the rapid preparation of highly crystalline COFs films at room temperature, and the goal of achieving controllable film crystallinity through the system can be achieved. The COFs films prepared in Examples 3 and Examples 6-8 were subjected to infrared spectroscopy and scanning electron microscopy analysis. Figure 6 As shown by Figure 6 (a) It can be seen that 1580cm-1 The stretching band of (C=C) and the 1262cm -1 The stretching band of (CN) indicates the successful formation of β-ketoamine skeleton structure; Figure 6 (b) It can be seen that the membrane is continuous and dense. The COFs membranes prepared in Example 3 (TPPa) and Examples 6-8 (TPBD, TP-TAPA, TPBD(OH)2) were subjected to the dye separation step in Example 11. The results are shown in FIG. Figure 7 As shown in (a), Figure 7 (a) It can be seen that the TPPa-1 membrane has a high retention rate for methylene blue, reaching 98.8%. The TPTAPA membrane has a high retention rate for methyl red, reaching 94.7%. The pore sizes of the TPBD membrane and the TPBD(OH)2 membrane are consistent, making them more suitable for the retention of gentian violet dye, with retention rates of 84.2% and 86.3%, respectively. The prepared membranes have a high retention effect on dyes of specific sizes.

[0093] The COFs membranes prepared in Examples 3 and 6-8 (TPBD, TP-TAPA, TPBD(OH)2) were subjected to the F ion separation step in Example 12. The results are shown in Table 1 below:

[0094] Table 1:

[0095] COFs membrane TPPa-1 TPBD <![CDATA[TPBD(OH)2]]> TPTAPA Retention rate (%) 73.1 78.1 88.4 93.6 Flux LMH 51.7 42.3 58.6 51.2

[0096] As shown in Table 1, the retention rates of the four membranes for a standard F ion solution obtained through F ion separation experiments are as follows: TPPa-1 membrane achieved a 73.1% retention rate at a flux of 51.7 LMH; TPBD membrane achieved a 78.1% retention rate at a flux of 42.3 LMH; TPBD(OH)2 membrane achieved a 88.4% retention rate at a flux of 58.6 LMH; and TPTAPA membrane achieved a 93.6% retention rate at a flux of 51.2 LMH. All four membranes achieved a flux greater than 40 LMH and a retention rate greater than 70%, demonstrating excellent F ion separation performance.

[0097] The above description is merely a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any changes or substitutions that can be easily conceived by a person skilled in the art within the technical scope disclosed in the present invention should be included in the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be based on the scope of protection of the claims.

Claims

1. A self-supporting COFs film based on DES-H2O interfacial polymerization method, characterized in that: The self-supporting COFs membrane is a COFs membrane having an imine structure or a β-ketoenamine structure prepared by a low eutectic solvent-water interfacial polymerization method; wherein the self-supporting COFs membrane uses C2-symmetrical amine or C3-symmetrical amine and triformyl phloroglucinol as raw materials, p-toluenesulfonic acid as a catalyst, a quaternary ammonium salt as a regulator, and an alkyl acid as a crystallization control agent; the C2-symmetrical amine includes p-phenylenediamine, benzyldiamine, 3, Any one or more of 3-dihydroxybenzyl diamine, hydrazine hydrate, bipyridine diamine, and diaminoguanidine hydrochloride; the C3 symmetrical amine includes any one or more of tris(4-aminophenyl)amine, triazine triphenylamine, and triaminoguanidine hydrochloride; the quaternary ammonium salt includes any one of tetrabutylammonium chloride, tetrabutylammonium bromide, and hexadecyltrimethyloctylammonium bromide; the alkyl acid includes any one of acetic acid, levulinic acid, n-hexanoic acid, n-octanoic acid, n-decanoic acid, dodecanoic acid, and oleic acid; the method for preparing a self-supporting COFs film based on the DES-H2O interfacial polymerization method comprises the following steps: Step 1: Add quaternary ammonium salt and alkyl acid into a container and heat in an oil bath. After the solution in the container becomes clear and transparent, place it in a vacuum oven and dry it until all moisture is removed to obtain DES. Step 2: dissolving triformylphloroglucinol in the DES and sonicating until the DES is dissolved to obtain a reaction solution A; Step 3: dissolving a C2-symmetrical amine or a C3-symmetrical amine and p-toluenesulfonic acid in distilled water, sonicating until dissolved, and then filling with inert gas to obtain a reaction solution B; Step 4: Slowly add distilled water to the upper layer of reaction solution A to form a pure water layer; slowly add reaction solution B to the upper layer of the pure water layer, and ensure that the interface is left still without disturbance, and react at room temperature for 3-5 days.

2. The self-supporting COFs film based on the DES-H2O interfacial polymerization method according to claim 1, characterized in that: In step 1, the temperature of the oil bath heating is 85-100° C.; the molar ratio of the quaternary ammonium salt to the alkyl acid is 1:2; and the temperature of the vacuum oven drying is 75-110° C.

3. The self-supporting COFs film based on DES-H2O interfacial polymerization method according to claim 1, characterized in that: In step 2, the ultrasonication time is 10-15 minutes.

4. The self-supporting COFs film based on DES-H2O interfacial polymerization method according to claim 1, characterized in that In step 3, the molar amount of the C2-symmetrical amine or the C3-symmetrical amine is based on the functionality of the reactive monomer, and the functionality of the reactive monomer of the C2-symmetrical amine or the C3-symmetrical amine is 100-150% of the functionality of the reactive monomer of the triformylphloroglucinol; the inert gas is nitrogen; and the ultrasonication time is 10-15 minutes.

5. An application of a self-supporting COFs film based on the DES-H2O interfacial polymerization method according to any one of claims 1 to 4, characterized in that: The self-supporting COFs membrane is used for separation of dyes and fluoride ions.

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