Preparation method and application of covalent organic framework bipolar membrane

Abstract

The invention belongs to the technical field of membrane separation, and aims to provide a preparation method and application of a covalent organic framework bipolar membrane. The method comprises the following steps: combining at least one amine, hydrazide or aldehyde monomer containing ionic groups with a monomer without ionic groups, and respectively synthesizing covalent organic framework COF nanosheets with positive charges and negative charges through a one-pot method under the condition of coexistence of an acid catalyst and an organic solvent; sequentially depositing COF nanosheets with positive and negative charges on the surface of the porous carrier by a hot solvent evaporation method; by constructing two COF separation layers with regular pore channels and opposite electrical properties, the covalent organic framework bipolar membrane with charge asymmetry is finally obtained. The product provided by the invention has high selectivity, can realize efficient separation of protons and metal cations, and significantly improves the extraction and recovery purity of hydrochloric acid; through charge repulsion and pore size screening mechanisms, separation of different anions can be further realized, and selective recovery of acid molecules is enhanced.

Description

Technical Field

[0001] The present invention belongs to the technical field of membrane separation, and particularly relates to a preparation method of a bipolar membrane for selective ion separation and its application in industrial acid treatment. Background Art

[0002] Acids are important industrial raw materials, widely used in fields such as metal surface treatment, chemical engineering and metallurgy, and the electronics industry. Membrane separation technology has been attracting increasing attention due to its significant advantages in acid pollutant treatment and acid recovery. Especially under the dual demands of current environmental protection and resource recovery, membrane separation technology has become an efficient and low-energy-consuming separation method with important application value.

[0003] Membrane separation technology can achieve efficient acid purification with low energy consumption, reduce the use of neutralizing agents, and thus avoid the generation of secondary pollution. By concentrating the acid solution, its acidic components can be recycled and reused, which not only improves the resource utilization efficiency but also significantly reduces the production cost. In addition, this technology has a simple process, is easy to operate and maintain, and can support continuous and automated production.

[0004] Currently, acid recovery technologies based on membrane separation methods mainly focus on the separation of protons and metal ions (such as Fe 2+ 、Al 3+ 、Ti 4+ etc.), and the main materials used are anion exchange membranes. The separation mechanism of such membranes mainly relies on the Donnan exclusion effect and the size sieving mechanism. However, traditional anion exchange membranes show deficiencies in anion sieving separation performance, resulting in relatively low purity of the obtained acid solution, which limits their further application scope.

[0005] Therefore, the development of new membrane materials that can simultaneously achieve efficient selective separation of protons, metal ions, and anions has become an important problem that needs to be solved urgently. Summary of the Invention

[0006] The present invention aims to overcome the deficiencies in the prior art and provides a preparation method and application of a covalent organic framework bipolar membrane. This bipolar membrane can achieve selective transmembrane transport of different ions by regulating the type and distribution of charges, and simultaneously achieve efficient selective separation of protons, metal ions, and anions to improve the purity of acids.

[0007] To solve the above technical problems, the present invention proposes the following solutions:

[0008] Provided is a method for preparing a covalent organic framework bipolar membrane. An amine or hydrazide monomer containing ionic groups and an aldehyde monomer without ionic groups, or an aldehyde monomer containing ionic groups and an amine or hydrazide monomer without ionic groups are used. Under the coexistence of an acid catalyst and an organic solvent, positively charged and negatively charged covalent organic framework (COF) nanosheets are respectively synthesized by a one-pot method. Then, by the hot solvent evaporation method, the positively charged COF nanosheets are first deposited on the surface of a porous support, and then the negatively charged COF nanosheets are continuously deposited. By constructing two COF separation layers with regular pores and opposite electric charges, a covalent organic framework bipolar membrane with charge asymmetry is finally obtained.

[0009] As a preferred embodiment of the present invention, the method specifically includes:

[0010] (1) Synthesizing COF nanosheets

[0011] Select at least one amine, hydrazide or aldehyde monomer containing positively charged ionic groups, and at least one amine, hydrazide or aldehyde monomer containing negatively charged ionic groups. Then, monomer solutions are respectively prepared according to the combination mode of an amine or hydrazide monomer containing ionic groups and an aldehyde monomer without ionic groups, or according to the combination mode of an aldehyde monomer containing ionic groups and an amine or hydrazide monomer without ionic groups.

[0012] Under stirring conditions, the monomer solutions are mixed evenly according to the aforementioned combination mode, and then an appropriate amount of acid catalyst solution is added dropwise to the mixture. The reaction is carried out for 5 - 100 h under a constant temperature condition of 10 - 120 °C to generate COF nanosheets. The COF nanosheets are dialyzed with water to remove the catalyst, unreacted monomers and oligomers. Finally, the obtained aqueous solution contains positively charged or negatively charged COF nanosheets.

[0013] Control the dosages of the monomer solutions so that the amino groups in the amine monomers, the hydrazide groups in the hydrazide monomers or the aldehyde groups in the aldehyde monomers in the monomer combination are in an equimolar ratio.

[0014] (2) Preparing the bipolar membrane

[0015] Take two aqueous solutions of COF nanosheets, which respectively contain positively charged and negatively charged COF nanosheets. The positively charged COF nanosheets are first deposited on a porous support by the hot solvent evaporation method, and then the negatively charged COF nanosheets are continuously deposited. By constructing two COF separation layers with regular pores and opposite electric charges, a covalent organic framework bipolar membrane with charge asymmetry is finally obtained.

[0016] As a preferred embodiment of the present invention, the amine or hydrazide monomer is any one of the following: benzidine (BD), 1,3,5-tris(4-aminophenyl)benzene (TAPB), 2,5-diaminobenzenesulfonic acid (DAB-SA), 2,5-diaminobenzoic acid (DABA), 4-(4,4'-diamino-3'-hydroxy-[1,1'-biphenyl]-3-yl)oxy)butyric acid (DAHBP-BUA), trans-6,6'-(ethene-1,2-diyl)bis(3-aminobenzenesulfonic acid) (DABSAE), sodium 4,7-bis(4-aminophenyl)-2,5,6-trimethylbenzo[d]imidazol-1-olate (DAPTMINA), 3,3'-(2,5-bis(hydrazinecarbonyl)-1,4-phenylene)bis(aza-diyl)bis(propane-1-sulfonic acid) (DATH-BPSA), triaminoguanidine hydrochloride (TAGCL), 2,5-diamino-1-ethylpyridinium hydrochloride (DAEPYCL), 1H-1,2,4-triazole-3,5-diamine (DATZ), 1-(3,5-bis(hydrazinecarbonyl)phenyl)-N,N,N-trimethylmethanaminium hydrochloride (IDHT-MACL), 4-(2,5-bis(hydrazinecarbonyl)-4-hydroxyphenoxy)-N,N,N-trimethylbutan-1-aminium hydrochloride (DHTH-TMBACL), 2,2'-(2,5-bis(hydrazinecarbonyl)-1,4-phenylene)bis(oxy)bis(N,N,N-trimethylethan-1-aminium hydrochloride) (DHTH-DTMEACL), 4,4'-(2,5-bis(hydrazinecarbonyl)-1,4-phenylene)bis(oxy)bis(N,N,N-trimethylbutan-1-aminium hydrochloride) (DHTH-DTMBACL), 3-(2,5-bis(hydrazinecarbonyl)benzyl)-1-vinyl-1H-imidazol-3-ium hydrochloride (THB-VICL), 5,5'-diamino-1,1'-diethyl-[2,2'-bipyridine]-1,1'-diium hydrochloride (DADEBPYCL), 3,9-diaminoimidazo[1,5-a:3,4-a']bipyridin-5-ium hydrochloride (DAIBPYCL), 5,5'-diamino-1-(2-((1S,2R,5S)-2-isopropyl-5-methylcyclohexyloxy)-2-oxoethyl)-[2,2'-bipyridine]-1-ium hydrochloride (DAACMTBPYCL), 4-amino-N,N-bis(4-aminophenyl)-N-methylbenzenaminium iodate (TAPMAI), ethidium bromide (EB), (S)-2,4,6-tris(4-aminophenyl)-1-((1-(tert-butoxycarbonyl)pyrrolidin-2-yl)methoxy)carbonyl)pyridinium hydrochloride (TAPPYPRCL), N 1 ,N 1 ,N 4 ,N 4 tetrakis(4-aminophenyl)-N 1 ,N4 -Dimethylbenzene-1,4-diammonium hydrochloride (TAPDMTABCL).

[0017] As a preferred embodiment of the present invention, the aldehyde monomer is any one of the following: terephthalaldehyde (BDA), phloroglucinol trialdehyde (TP), 3-(2,5-diformyl-4-hydroxyphenoxy) propane-1-sulfonic acid (DHTA-PSA), 3,3'-(((2,5-diformyl-1,4-phenylene) bis(oxy)) bis(methylene)) bis(1H-1,2,3-triazole-4,1-diyl)) dipropionic acid (DHTA-DTZPA), 3,3'-((2,5-diformyl-1,4-phenylene) bis(oxy)) bis(propane-3,1-diyl) bis(1-methyl-1H-imidazol-3-ium) hydrochloride (DHTA-DPICL), 3,3'-((2,5-diformyl-1,4-phenylene) bis(oxy)) bis(ethane-2,1-diyl) bis(1-methyl-1H-imidazol-3-ium) hydrochloride (DHTA-DEICL), 2,2'-((2,5-diformyl-1,4-phenylene) bis(oxy)) bis(methylene) bis(1H-1,2,3-triazole-4,1-diyl) bis(N,N,N-trimethylethane-1-amine) (DHTA-DTZTMACL), 2-(2,4-diformyl-3,5-dihydroxyphenoxy)-N,N,N-triethylethane-1-amine (THIA-TEACL), 3-butyl-4,7-bis(4-formylphenyl)-1-methyl-1H-benzo[d]imidazol-3-ium hydrochloride (bu-DFPBICL), 4,7-bis(4-formylphenyl)-1,3-dimethyl-1H-benzo[d]imidazol-3-ium hydrochloride (me-DFPBICL), 4,4',4''-(benzene-1,3,5-triacyl) tris(1-(4-formylbenzyl)-4H-imidazol-1-ium) hydrochloride (TBFPICL), 1,1'-bis(4-formylphenyl)-[4,4'-bipyridine]-1,1'-diimine (DFPBPYCL).

[0018] As a preferred embodiment of the present invention, the ionic group is a positively charged tertiary ammonium group, or a negatively charged carboxyl group, sulfonic acid group or imidazole.

[0019] As a preferred embodiment of the present invention, the organic solvent is any one of the following: dimethyl sulfoxide (DMSO), N,N'-dimethylformamide (DMF), acetonitrile, dichloromethane (DCM), N-methylpyrrolidone (NMP), ethyl acetate (EA); the acid catalyst is any one of the following: acetic acid, p-toluenesulfonic acid, scandium trifluoromethanesulfonate, trifluoromethanesulfonic acid, trifluoroacetic acid, methanesulfonic acid; the addition amount of the acid catalyst and the molar ratio of the amino group, hydrazide group or aldehyde group is 1:0.3 - 3000.

[0020] As a preferred embodiment of the present invention, the porous support is a porous ultrafiltration base membrane made of any one of the following materials: polyacrylonitrile (PAN), polyetheretherketone (PEEK), polysulfone (PSF), polyethersulfone (PES), polyvinylidene fluoride (PVDF), aluminum oxide (Al 2 O 3 2O3); the pore size range of the porous ultrafiltration base membrane is 1.5 - 200 nm.

[0021] As a preferred embodiment of the present invention, amine, hydrazide, aldehyde monomers or acid catalysts are respectively dissolved in organic solvents to obtain corresponding solutions for the reaction of synthesizing COF nanosheets; among them, the concentration of the amine or hydrazide solution is 0.1 - 15 mmol / L; the concentration of the aldehyde solution is 0.1 - 10 mmol / L; the concentration of the acid catalyst solution is 0.01 - 5 mmol / L; the thickness of the COF nanosheets prepared by the synthesis reaction is 1.2 - 9.7 nm.

[0022] As a preferred embodiment of the present invention, the concentrations and dosages of two COF nanosheet aqueous solutions are controlled so that in the final COF bipolar membrane, the thickness of the COF separation layer is 100 nm - 3 μm, and the pore size is 0.5 - 2 nm.

[0023] The present invention further provides the application of the COF bipolar membrane prepared by the foregoing method in separating and recovering hydrochloric acid in waste acid solution.

[0024] Description of the invention principle:

[0025] 1. Among the amine, hydrazide, and aldehyde monomers used in the present invention, the charge attributes of the ionic groups contained are determined according to the reaction groups participating in the synthesis of COF nanosheets on the monomers. These reaction groups all carry additional ionic groups, such as positively charged tertiary ammonium groups, or negatively charged carboxyl or sulfonic acid groups.

[0026] When preparing COF nanosheets, "amine or hydrazide monomers containing ionic groups + aldehyde monomers without ionic groups" and "aldehyde monomers containing ionic groups + amine or hydrazide monomers without ionic groups" are used to respectively prepare a positively charged nanosheet solution and a negatively charged nanosheet solution. Then, the positively charged and negatively charged nanosheet solutions are successively deposited on the substrate membrane, and the obtained COF separation layer has regular pores and contains both positively charged groups and negatively charged groups.

[0027] Since these charged groups have different electrostatic forces with ions of different valences, they have a stronger charge repulsion effect on high-valence ions than on monovalent ions. Low-valence ions are more easily transported across the membrane due to weaker repulsion, thus achieving the separation of cations of different valences (such as protons and metal cations) and anions. It should be noted that when preparing bipolar membranes, positively charged monomers are deposited first, followed by negatively charged monomers; if this in turn affects the direction of the built-in electric field in the membrane, it will have a certain impact on product performance.

[0028] 2. In the COF bipolar membrane of the present invention, the COF separation layer has regular pores, specifically, the monomers in the nanosheets used for the reaction membrane are connected to each other by covalent bonds, forming a long-range ordered crystal structure, thereby forming regular pores, as can be seen in the SAXD diagram ( Figure 5 ).

[0029] Based on the size screening effect of the membrane pores and different host-guest forces, the present invention can also separate ions of the same valence. For example: because protons have a high diffusion coefficient, and the staggered pore structure of the bipolar membrane reduces the pore size, further limiting the transmission of metal cations, allowing protons to be quickly separated. For anions of the same valence, due to the differences in their molecular size, geometric structure, and charge distribution concentration, the pore structure of the membrane can achieve efficient screening and separation. Through the above mechanism, the present invention can achieve the separation of protons from metal cations and different anions, thereby extracting specific acid molecules in one step, solving the limitations of existing commercial ion exchange membranes in terms of acid purity.

[0030] 3. The COF bipolar membrane provided by the present invention has the ability to selectively separate highly specific acid (hydrochloric acid) molecules. The principle is as follows: in addition to the chloride ions and hydrogen ions of hydrochloric acid, industrial waste acid mainly contains more high-valent acid ions (sulfate ions, phosphate ions) or high-valent metal ions. When the waste acid passes through the COF bipolar membrane, the membrane layer containing positive charge has a strong force with the high-valent anions, so that the chloride ions are intercepted, and the chloride ions can pass smoothly. The membrane layer containing negative charge has a strong force with the high-valent metal ions, so that they are intercepted, and the hydrogen ions can pass smoothly.

[0031] 4. Due to the rigidity of the membrane skeleton, the membrane is not easy to swell and the pore structure is stable, the membrane product prepared by the present invention can maintain a constant separation ratio for a long time under high salt conditions.

[0032] Compared with the prior art, the present invention has the following advantages and innovations:

[0033] 1. The COF bipolar membrane of the present invention has high selectivity and can achieve efficient separation of protons and metal cations such as sodium, magnesium, iron, and aluminum, significantly improving the extraction and recovery purity of hydrochloric acid.

[0034] 2. Through the charge repulsion and pore size sieving mechanisms, the bipolar membrane of the present invention can further achieve the separation of different anions, enhancing the selective recovery of acid molecules.

[0035] 3. The preparation method of the present invention has a simple process, is suitable for large-scale production, and the prepared membrane products have high stability, and can operate stably for a long time under strong acidic and high-salt conditions and maintain a stable separation effect. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] Figure 1 It is a schematic diagram of the vacuum-assisted nanoflake deposition film-forming process.

[0037] Figure 2 It is a schematic diagram of the film-forming process by the hot solvent evaporation method.

[0038] Figure 3 It is an atomic force microscope (AFM) image of the one-pot acid-catalyzed preparation of COF-SA nanoflakes.

[0039] Figure 4 It is a cross-sectional scanning electron microscope (SEM) image (left side) and an S element distribution map (right side) of the COF-EBSA / PAN membrane in Example 1.

[0040] Figure 5 It is a small-angle X-ray scattering (SAXD) image of the COF-EBSA / PAN membrane in Example 1. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0041] The following further specifically describes the implementation of the present invention in conjunction with the drawings.

[0042] The preparation method of the covalent organic framework bipolar membrane of the present invention is to react an amine or hydrazide monomer containing an ionic group with an aldehyde monomer without an ionic group, or an aldehyde monomer containing an ionic group with an amine or hydrazide monomer without an ionic group, in the coexistence of an acid catalyst and an organic solvent, and respectively synthesize positively charged and negatively charged covalent organic framework COF nanoflakes by a one-pot method; then, by the hot solvent evaporation method, first deposit the positively charged COF nanoflakes on the surface of the porous carrier, and continue to deposit the negatively charged COF nanoflakes; by constructing two COF separation layers with regular pores and opposite electric charges, a covalent organic framework bipolar membrane with charge asymmetry is finally obtained.

[0043] This method specifically includes the following steps:

[0044] (1) Synthesis of COF nanoflakes

[0045] Select at least one amine, hydrazide or aldehyde monomer containing a positively charged ionic group, and at least one amine, hydrazide or aldehyde monomer containing a negatively charged ionic group; then prepare monomer solutions respectively according to the combination mode of amine or hydrazide monomers containing ionic groups and aldehyde monomers without ionic groups, or prepare monomer solutions respectively according to the combination mode of aldehyde monomers containing ionic groups and amine or hydrazide monomers without ionic groups;

[0046] Under stirring conditions, mix the monomer solutions evenly according to the aforementioned combination mode, and then drop an appropriate amount of acid catalyst solution into the mixture; react at a constant temperature of 10 - 120 °C for 5 - 100 h to generate COF nanosheets; dialyze the COF nanosheets with water to remove the catalyst, unreacted monomers and oligomers, and finally obtain an aqueous solution containing positively or negatively charged COF nanosheets.

[0047] Judging the charged situation of COF nanosheets according to the existing groups on the monomers is common knowledge. In the present invention, the charged situation of the reaction product after ionization in an aqueous solution can be clearly judged from the structural formula of the monomer. For example, a tertiary amino group is positively charged, and a carboxyl group, sulfonic acid group or imidazole is negatively charged.

[0048] Control the dosages of each monomer solution so that the amino groups in the amine monomers, hydrazide groups in the hydrazide monomers or aldehyde groups in the aldehyde monomers in the monomer combination are in an equimolar ratio; the molar ratio of the amount of the acid catalyst to the amino (hydrazide) or aldehyde group is 1:0.3 - 3000; the thickness of the COF nanosheets prepared by the synthesis reaction is 1.2 - 9.7 nm.

[0049] Among them, the organic solvent can be any one of the following: dimethyl sulfoxide (DMSO), N,N'-dimethylformamide (DMF), acetonitrile, dichloromethane (DCM), N-methylpyrrolidone (NMP), ethyl acetate (EA). The acid catalyst can be any one of the following: acetic acid, p-toluenesulfonic acid, scandium trifluoromethanesulfonate, trifluoromethanesulfonic acid, trifluoroacetic acid, methanesulfonic acid; the porous carrier can be a porous ultrafiltration base membrane made of any one of the following materials: polyacrylonitrile (PAN), polyetheretherketone (PEEK), polysulfone (PSF), polyethersulfone (PES), polyvinylidene fluoride (PVDF), aluminum oxide (Al 2 O 3 )). The concentration of the amine or hydrazide solution can be selected from 0.1 - 10 mmol / L; the concentration of the aldehyde solution can be selected from 0.1 - 10 mmol / L; the concentration of the acid catalyst solution can be selected from 0.01 - 20 mmol / L;

[0050] As an optional example, the structural formulas and their English abbreviations of the amine, hydrazide and aldehyde monomers used in the present invention are as follows:

[0051]

[0052]

[0053] (2) Preparation of bipolar membrane

[0054] Take two aqueous solutions of COF nanosheets, which contain positively charged and negatively charged COF nanosheets respectively; use the thermal solvent evaporation method (temperature controlled at 40 - 120 °C) to first deposit the positively charged COF nanosheets on the porous support, and then continue to deposit the negatively charged COF nanosheets; by constructing two COF separation layers with regular pores and opposite electrical charges, a covalent organic framework bipolar membrane with charge asymmetry is finally obtained.

[0055] During this process, control the concentration and dosage of the two aqueous solutions of COF nanosheets so that in the final COF bipolar membrane, the thickness of the COF separation layer is 100 nm - 3 μm, and the pore size is 0.5 - 2 nm.

[0056] In the present invention, a porous ultrafiltration base membrane is used as the base filtration membrane, and its pore size range is 1.5 - 200 nm, which can achieve precise material screening and filtration at the nanoscale and provide high - efficient ion separation ability. The porous ultrafiltration base membrane can be a commercial product or can be prepared by referring to the public literature (for example: Cai Bangxiao. A manufacturing method of a polyacrylonitrile membrane [P]. Zhejiang Province: CN94116066.1, 1999 - 06 - 09.).

[0057] Based on the COF bipolar membrane obtained by the above preparation method, the present invention further proposes to apply the COF bipolar membrane to the separation and recovery of hydrochloric acid in waste acid solution. The separation and recovery can use a separation and recovery device that meets the requirements of industrial applications, and the specific construction method can refer to the record of Sci.Adv.2023, 9, eadh0207.

[0058] In the following examples, the test device for acid separation performance is constructed with reference to the static diffusion device described in Sci.Adv.2023, 9, eadh0207. This device is designed to meet the operation requirements under high - salt - concentration and strong - acid - environment conditions, and can ensure the reliability and repeatability of test data.

[0059] In each example, control the dosage of each monomer solution so that the amino group in the amine monomer, the hydrazide group in the hydrazide monomer, or the aldehyde group in the aldehyde monomer in the monomer combination are in equimolar ratio; control the dosage of the acid catalyst so that the molar ratio of the acid catalyst to the amino, hydrazide, or aldehyde group is 1:0.3 - 3000.

[0060] Example 1:

[0061] (1) Preparation of COF - EB nanosheets

[0062] Prepare an ethyl acetate solution of TP with a concentration of 0.1 mmol / L. Prepare equal volumes of an NMP solution of EB with a concentration of 0.15 mmol / L and a DMF solution of scandium trifluoromethanesulfonate with a concentration of 0.1 mmol / L. While stirring, gradually dropwise mix the ethyl acetate solution of TP with the NMP solution of EB, and then dropwise add the DMF solution of scandium trifluoromethanesulfonate. Control the dosages of each monomer solution so that in the reaction system: the amino group and the aldehyde group are in an equimolar ratio, and the molar ratio of the acid catalyst to the amino group is 1:3.

[0063] After the dropping is completed, let the mixed reaction solution stand at 40 °C for 24 hours. The obtained reaction product is dialyzed with distilled water at room temperature for 24 hours to obtain an aqueous solution of COF-EB nanosheets, and the prepared nanosheets carry a positive charge. The AFM test results show that the thickness of the nanosheets contained in the solution is 2.1 nm.

[0064] (2) Preparation of COF-SA nanosheets

[0065] Prepare an acetonitrile solution of TP with a concentration of 1.0 mmol / L. Prepare equal volumes of a DMSO solution of DAB-SA with a concentration of 1.5 mmol / L and a DMF solution of scandium trifluoromethanesulfonate with a concentration of 0.01 mmol / L. While stirring, gradually dropwise mix the acetonitrile solution of TP with the DMSO solution of DAB-SA, and then dropwise add the DMF solution of scandium trifluoromethanesulfonate. Control the dosages of each monomer solution so that in the reaction system: the amino group and the aldehyde group are in an equimolar ratio, and the molar ratio of the acid catalyst to the amino group is 1:30.

[0066] After the dropping is completed, let the mixed reaction solution stand at 10 °C for 100 hours. The obtained reaction product is dialyzed with distilled water at room temperature for 24 hours to obtain an aqueous solution of COF-SA nanosheets, and the prepared nanosheets carry a negative charge. The AFM test results show that the thickness of the nanosheets contained in the solution is 3.3 nm.

[0067] (3) Preparation of bipolar membrane

[0068] Using the hot solvent evaporation method, uniformly drop 5 mL / cm 2 of the COF-EB nanosheet solution on the PAN substrate, and evaporate the water at 50 °C to form a positively charged COF-EB membrane. On the basis of the COF-EB membrane, uniformly drop 2 mL / cm 2 of the COF-SA nanosheet solution, and evaporate the water at 100 °C to form a bipolar membrane.

[0069] SEM cross-section results: The thicknesses of the COF-EB layer and the COF-SA layer are 600 nm and 500 nm respectively, and the membrane structure is clear and distinct. N 2 The adsorption result shows that the pore size is 0.5 nm.

[0070] (4) Acid separation performance test

[0071] Acid recovery separation performance test: Using 0.25 M hydrochloric acid, sulfuric acid, phosphoric acid, sodium chloride, ferrous chloride, and aluminum chloride as the feed solution, static diffusion for 3 hours, and the separation ratios of hydrochloric acid to sulfuric acid, phosphoric acid, sodium chloride, ferrous chloride, and aluminum chloride are 23, 136, 226, 1458, and 11567 respectively.

[0072] Example 2:

[0073] (1) Preparation of COF-TAG nanosheets

[0074] Prepare an ethyl acetate solution of BDA with a concentration of 0.15 mmol / L. Prepare equal volumes of a DMSO solution of TAGCL with a concentration of 0.1 mmol / L and a DMSO solution of methanesulfonic acid with a concentration of 0.1 mmol / L. Under stirring, gradually dropwise mix the ethyl acetate solution of BDA with the DMSO solution of TAGCL, and then dropwise add the DMSO solution of methanesulfonic acid. Control the dosage of each monomer solution so that in the reaction system: the amino group and the aldehyde group are in an equimolar ratio, and the molar ratio of the acid catalyst to the amino group is 1:3.

[0075] After the dropping is completed, let the mixed reaction solution stand at 25 °C for 10 hours. The obtained reaction product is dialyzed with distilled water at room temperature for 24 hours to obtain an aqueous solution of COF-TAG nanosheets, and the prepared nanosheets carry a positive charge. The AFM test results show that the thickness of the nanosheets contained in the solution is 1.8 nm.

[0076] (2) Preparation of COF-DABA nanosheets

[0077] Prepare an acetonitrile solution of TP with a concentration of 1.0 mmol / L. Prepare equal volumes of a DCM solution of DABA with a concentration of 1.5 mmol / L and a DMF solution of scandium trifluoromethanesulfonate with a concentration of 0.01 mmol / L. Under stirring, gradually dropwise mix the acetonitrile solution of TP with the DCM solution of DABA, and then dropwise add the DMF solution of scandium trifluoromethanesulfonate. Control the dosage of each monomer solution so that in the reaction system: the amino group and the aldehyde group are in an equimolar ratio, and the molar ratio of the acid catalyst to the amino group is 1:300.

[0078] After the dropping is completed, let the mixed reaction solution stand at 60 °C for 30 hours. The obtained reaction product is dialyzed with distilled water at room temperature for 24 hours to obtain an aqueous solution of COF-DABA nanosheets, and the prepared nanosheets carry a negative charge. The AFM test results show that the thickness of the nanosheets contained in the solution is 1.2 nm.

[0079] (3) Preparation of bipolar membrane

[0080] Using the hot solvent evaporation method, uniformly drop 10 mL / cm on the PAN substrate 2The COF-TAG nanosheet solution was volatilized at 60 °C to form a positively charged COF-TAG film. 1 mL / cm of the COF-DABA nanosheet solution was evenly dropped onto the COF-TAG film, and the water was volatilized at 80 °C to form a bipolar membrane. 2 The COF-DABA nanosheet solution was volatilized at 80 °C to form a bipolar membrane.

[0081] SEM cross-section results: The thicknesses of the COF-TAG layer and the COF-DABA layer were 500 nm and 200 nm respectively, and the membrane structure was clear and distinct. 2 The adsorption results showed that the pore size was 0.6 nm.

[0082] (4) Acid separation performance test

[0083] Acid recovery separation performance test: Using 0.25 M hydrochloric acid, sulfuric acid, phosphoric acid, sodium chloride, ferrous chloride, and aluminum chloride as the feed solution, static diffusion for 3 hours, the separation ratios of hydrochloric acid from sulfuric acid, phosphoric acid, sodium chloride, ferrous chloride, and aluminum chloride were 39, 154, 344, 1681, and 13458 respectively.

[0084] Example 3:

[0085] (1) Preparation of COF-DAEPY nanosheets

[0086] An ethyl acetate solution of TP with a concentration of 0.2 mmol / L was prepared. An equal volume of an NMP solution of DAEPYCL with a concentration of 0.3 mmol / L and a DMF solution of trifluoromethanesulfonic acid with a concentration of 0.1 mmol / L were prepared. Under stirring, the ethyl acetate solution of TP was gradually dropped into the NMP solution of DAEPYCL, and then the DMF solution of scandium trifluoromethanesulfonate was dropped. The amounts of each monomer solution were controlled so that in the reaction system: the amino group and the aldehyde group were in an equimolar ratio, and the molar ratio of the acid catalyst to the amino group was 1:6.

[0087] After the dropping was completed, the mixed reaction solution was allowed to stand at 80 °C for 48 hours. The obtained reaction product was dialyzed with distilled water at room temperature for 24 hours to obtain an aqueous solution of COF-DAEPY nanosheets, and the prepared nanosheets carried a positive charge. The AFM test results showed that the thickness of the nanosheets contained in the solution was 5.6 nm.

[0088] (2) Preparation of COF-DABSAE nanosheets

[0089] Prepare an NMP solution of TP with a concentration of 0.5 mmol / L. Prepare NMP solutions of DABSAE with a concentration of 0.75 mmol / L and p-toluenesulfonic acid with a concentration of 5 mmol / L in equal volumes. While stirring, gradually dropwise mix the acetonitrile solution of TP with the DMSO solution of DABSAE, and then dropwise add the DMF solution of p-toluenesulfonic acid. Control the dosages of each monomer solution so that in the reaction system: the amino group and the aldehyde group are in an equimolar ratio, and the molar ratio of the acid catalyst to the amino group is 1:0.3.

[0090] After the dropping is completed, let the mixed reaction solution stand at 80 °C for 5 hours. Dialyze the obtained reaction product through distilled water at room temperature for 24 hours to obtain an aqueous solution of COF-DABSAE nanosheets, and the prepared nanosheets carry negative charges. The AFM test results show that the thickness of the nanosheets contained in the solution is 4.1 nm.

[0091] (3) Preparation of bipolar membrane

[0092] Using the hot solvent evaporation method, uniformly drop 0.01 mL / cm 2 of the COF-DAEPY nanosheet solution on the PAN substrate, and evaporate the water at 40 °C to form a positively charged COF-DAEPY membrane. Uniformly drop 0.1 mL / cm 2 of the COF-DABSAE nanosheet solution on the basis of the COF-DAEPY membrane, and evaporate the water at 120 °C to form a bipolar membrane.

[0093] SEM cross-section results: The thicknesses of the COF-DAEPY layer and the COF-DABSAE layer are 100 nm and 200 nm respectively, and the membrane structure is clear and distinct. N 2 The adsorption results show that the pore size is 0.7 nm.

[0094] (4) Acid separation performance test

[0095] Acid recovery separation performance test: Using 0.25 M hydrochloric acid, sulfuric acid, phosphoric acid, sodium chloride, ferrous chloride, and aluminum chloride as the feed solution, perform static diffusion for 3 hours. The separation ratios of hydrochloric acid to sulfuric acid, phosphoric acid, sodium chloride, ferrous chloride, and aluminum chloride are 12, 98, 125, 763, and 3402 respectively.

[0096] Example 4:

[0097] (1) Preparation of COF-DATZ nanosheets

[0098] Prepare an ethyl acetate solution of TP with a concentration of 2 mmol / L. Prepare equal volumes of a DMF solution of DATZ with a concentration of 3 mmol / L and a DMF solution of trifluoroacetic acid with a concentration of 0.01 mmol / L. Dropwise mix the ethyl acetate solution of TP with the DMF solution of DATZ under stirring, and then add dropwise the DMF solution of trifluoroacetic acid. Control the dosages of each monomer solution so that in the reaction system: the amino group and the aldehyde group are in an equimolar ratio, and the molar ratio of the acid catalyst to the amino group is 1:600.

[0099] After the addition is completed, let the mixed reaction solution stand at 120 °C for 10 hours. The obtained reaction product is dialyzed with distilled water at room temperature for 24 hours to obtain an aqueous solution of COF-DATZ nanosheets, and the prepared nanosheets carry a positive charge. The AFM test results show that the thickness of the nanosheets contained in the solution is 9.7 nm.

[0100] (2) Preparation of COF-DHTA-PSA nanosheets

[0101] Prepare an acetonitrile solution of DHTA-PSA with a concentration of 1.5 mmol / L. Prepare equal volumes of an aqueous solution of TAPB with a concentration of 1 mmol / L and an aqueous solution of acetic acid with a concentration of 2 mmol / L. Dropwise mix the acetonitrile solution of DHTA-PSA with the aqueous solution of TAPB under stirring, and then add dropwise the aqueous solution of acetic acid. Control the dosages of each monomer solution so that in the reaction system: the amino group and the aldehyde group are in an equimolar ratio, and the molar ratio of the acid catalyst to the amino group is 1:1.5.

[0102] After the addition is completed, let the mixed reaction solution stand at 40 °C for 100 hours. The obtained reaction product is dialyzed with distilled water at room temperature for 24 hours to obtain an aqueous solution of COF-DHTA-PSA nanosheets, and the prepared nanosheets carry a negative charge. The AFM test results show that the thickness of the nanosheets contained in the solution is 3.4 nm.

[0103] (3) Preparation of bipolar membrane

[0104] Using the hot solvent evaporation method, uniformly drop 10 mL / cm 2 of the COF-DATZ nanosheet solution on the PSF substrate, and evaporate the water at 70 °C to form a positively charged COF-DATZ membrane. Uniformly drop 100 mL / cm 2 of the COF-DHTA-PSA nanosheet solution on the basis of the COF-EB membrane, and evaporate the water at 100 °C to form a bipolar membrane.

[0105] SEM cross-section results: The thicknesses of the COF-DATZ layer and the COF-DHTA-PSA layer are 1.2 μm and 3 μm respectively, and the membrane structure is clear and distinct. N 2 The adsorption results show that the pore size is 0.9 nm.

[0106] (4) Acid separation performance test

[0107] Acid recovery separation performance test: Using 0.25 M hydrochloric acid, sulfuric acid, phosphoric acid, sodium chloride, ferrous chloride, and aluminum chloride as the feed solution, static diffusion for 3 hours, and the separation ratios of hydrochloric acid from sulfuric acid, phosphoric acid, sodium chloride, ferrous chloride, and aluminum chloride are 55, 136, 226, 1458, and 11567 respectively.

[0108] Example 5:

[0109] (1) Preparation of COF-DHTH-TMBACL nanosheets

[0110] Prepare an ethyl acetate solution of TP with a concentration of 0.1 mmol / L. Prepare equal volumes of a DMF solution of DHTH-TMBACL with a concentration of 0.15 mmol / L and a DMF solution of acetic acid with a concentration of 0.1 mmol / L. Under stirring, gradually dropwise mix the ethyl acetate solution of TP with the DMF solution of DHTH-TMBACL, and then dropwise add the DMF solution of acetic acid. Control the dosage of each monomer solution so that in the reaction system: the hydrazide and aldehyde group are in an equimolar ratio, and the molar ratio of the acid catalyst to the hydrazide is 1:3.

[0111] After the dropping is completed, let the mixed reaction solution stand at 90 °C for 12 hours. The obtained reaction product is dialyzed with distilled water at room temperature for 24 hours to obtain an aqueous solution of COF-DHTH-TMBACL nanosheets. The prepared nanosheets carry a positive charge. The AFM test results show that the thickness of the nanosheets contained in the solution is 4.4 nm.

[0112] (2) Preparation of COF-DAPTMINA nanosheets

[0113] Prepare an acetonitrile solution of TP with a concentration of 1.0 mmol / L. Prepare equal volumes of a DMSO solution of DAB-DAPTMINA with a concentration of 1.5 mmol / L and a DMSO solution of scandium trifluoromethanesulfonate with a concentration of 0.01 mmol / L. Under stirring, gradually dropwise mix the acetonitrile solution of TP with the DMSO solution of DAB-DAPTMINA, and then dropwise add the DMSO solution of scandium trifluoromethanesulfonate. Control the dosage of each monomer solution so that in the reaction system: the amino group and the aldehyde group are in an equimolar ratio, and the molar ratio of the acid catalyst to the amino group is 1:300.

[0114] After the dropping is completed, let the mixed reaction solution stand at 10 °C for 100 hours. The obtained reaction product is dialyzed with distilled water at room temperature for 24 hours to obtain an aqueous solution of COF-DAPTMINA nanosheets. The prepared nanosheets carry a negative charge. The AFM test results show that the thickness of the nanosheets contained in the solution is 7.8 nm.

[0115] (3) Preparation of bipolar membrane

[0116] Using the hot solvent evaporation method, 1 mL / cm 2 of the COF-DHTH-TMBACL nanosheet solution was evenly dropped on the PAN substrate, and the water was evaporated at 50 °C to form a positively charged COF-DHTH-TMBACL membrane. On the basis of the COF-DHTH-TMBACL membrane, 1 mL / cm 2 of the COF-DAPTMINA nanosheet solution was evenly dropped, and the water was evaporated at 100 °C to form a bipolar membrane.

[0117] SEM cross-section results: The thicknesses of the COF-DHTH-TMBACL layer and the COF-DAPTMINA layer are 200 nm and 300 nm respectively, and the membrane structure is clear and distinct. N 2 The adsorption results show that the pore size is 1.1 nm.

[0118] (4) Acid separation performance test

[0119] Acid recovery separation performance test: Using 0.25 M hydrochloric acid, sulfuric acid, phosphoric acid, sodium chloride, ferrous chloride, and aluminum chloride as the feed solution, static diffusion for 3 hours, and the separation ratios of hydrochloric acid to sulfuric acid, phosphoric acid, sodium chloride, ferrous chloride, and aluminum chloride are 41, 163, 623, 2987, and 8912 respectively.

[0120] Example 6:

[0121] (1) Preparation of COF-DHTH-DTMBACL nanosheets

[0122] Prepare an ethyl acetate solution of TP with a concentration of 0.1 mmol / L. Prepare an equal volume of an NMP solution of DHTH-DTMBACL with a concentration of 0.15 mmol / L and a DMF solution of trifluoromethanesulfonic acid with a concentration of 0.1 mmol / L. Under stirring, the ethyl acetate solution of TP was gradually dropped into the NMP solution of EB, and then the DMF solution of trifluoromethanesulfonic acid was dropped. Control the dosage of each monomer solution so that in the reaction system: the hydrazide and the aldehyde group are in an equimolar ratio, and the molar ratio of the acid catalyst to the hydrazide is 1:3.

[0123] After the dropping was completed, the mixed reaction solution was allowed to stand at 40 °C for 24 hours. The obtained reaction product was dialyzed with distilled water at room temperature for 24 hours to obtain an aqueous solution of COF-DHTH-DTMBACL nanosheets, and the prepared nanosheets carried a positive charge. The AFM test results show that the thickness of the nanosheets contained in the solution is 2.6 nm.

[0124] (2) Preparation of COF-DAHBP-BUA nanosheets

[0125] Prepare an acetonitrile solution of TP with a concentration of 1.0 mmol / L. Prepare an equal volume of a DMSO solution of DAB-DAHBP-BUA with a concentration of 1.5 mmol / L and a DMF solution of scandium trifluoromethanesulfonate with a concentration of 0.01 mmol / L. Under stirring, gradually dropwise mix the acetonitrile solution of TP with the DMSO solution of DAB-DAHBP-BUA, and then dropwise add the DMF solution of scandium trifluoromethanesulfonate. Control the dosage of each monomer solution so that in the reaction system: the amino group and the aldehyde group are in an equimolar ratio, and the molar ratio of the acid catalyst to the amino group is 1:300.

[0126] After the dropping is completed, let the mixed reaction solution stand at 10 °C for 100 hours. The obtained reaction product is dialyzed with distilled water at room temperature for 24 hours to obtain an aqueous solution of COF-DAHBP-BUA nanosheets, and the prepared nanosheets carry a negative charge. The AFM test results show that the thickness of the nanosheets contained in the solution is 4.3 nm.

[0127] (3) Bipolar membrane preparation

[0128] Using the thermal solvent evaporation method, uniformly drop 1 mL / cm 2 of the COF-DHTH-DTMBACL nanosheet solution on the PEEK substrate, and evaporate the water at 50 °C to form a positively charged COF-DHTH-DTMBACL membrane. On the basis of the COF-DHTH-DTMBACL membrane, uniformly drop 1 mL / cm 2 of the COF-DAHBP-BUA nanosheet solution, and evaporate the water at 100 °C to form a bipolar membrane.

[0129] SEM cross-section results: The thicknesses of the COF-DHTH-DTMBACL layer and the COF-DAHBP-BUA layer are 300 nm and 400 nm respectively, and the membrane structure is clear and distinct. N 2 The adsorption results show that the pore size is 2.0 nm.

[0130] (4) Acid separation performance test

[0131] Acid recovery separation performance test: Using 0.25 M hydrochloric acid, sulfuric acid, phosphoric acid, sodium chloride, ferrous chloride, and copper chloride as the feed solution, static diffusion for 3 hours, and the separation ratios of hydrochloric acid to sulfuric acid, phosphoric acid, sodium chloride, ferrous chloride, and copper chloride are 58, 149, 205, 2123, and 1690 respectively.

[0132] Example 7:

[0133] (1) Preparation of COF-IDHT-MACL nanosheets

[0134] Prepare an ethyl acetate solution of TP with a concentration of 0.1 mmol / L. Prepare equal volumes of an NMP solution of EB with a concentration of 0.15 mmol / L and a DMF solution of methanesulfonic acid with a concentration of 0.1 mmol / L. While stirring, gradually dropwise mix the ethyl acetate solution of TP with the NMP solution of EB, and then dropwise add the DMF solution of methanesulfonic acid. Control the dosages of each monomer solution so that in the reaction system: the hydrazide and aldehyde group are in an equimolar ratio, and the molar ratio of the acid catalyst to the hydrazide is 1:3.

[0135] After the dropping is completed, let the mixed reaction solution stand at 40 °C for 24 hours. The obtained reaction product is dialyzed with distilled water at room temperature for 24 hours to obtain an aqueous solution of COF-IDHT-MACL nanosheets. The prepared nanosheets carry a positive charge. The AFM test results show that the thickness of the nanosheets contained in the solution is 2.1 nm.

[0136] (2) Preparation of COF-DAHBP-BUA nanosheets

[0137] Prepare an acetonitrile solution of TP with a concentration of 1.0 mmol / L. Prepare equal volumes of a DMSO solution of DAB-DAHBP-BUA with a concentration of 1.5 mmol / L and a DMF solution of scandium trifluoromethanesulfonate with a concentration of 0.01 mmol / L. While stirring, gradually dropwise mix the acetonitrile solution of TP with the DMSO solution of DAB-DAHBP-BUA, and then dropwise add the DMF solution of scandium trifluoromethanesulfonate. Control the dosages of each monomer solution so that in the reaction system: the amino group and the aldehyde group are in an equimolar ratio, and the molar ratio of the acid catalyst to the amino group is 1:300.

[0138] After the dropping is completed, let the mixed reaction solution stand at 10 °C for 100 hours. The obtained reaction product is dialyzed with distilled water at room temperature for 24 hours to obtain an aqueous solution of COF-DAHBP-BUA nanosheets. The prepared nanosheets carry a negative charge. The AFM test results show that the thickness of the nanosheets contained in the solution is 6.3 nm.

[0139] (3) Preparation of bipolar membrane

[0140] Using the hot solvent evaporation method, uniformly drop 5 mL / cm 2 of the COF-IDHT-MACL nanosheet solution on the PAN substrate, and evaporate the water at 50 °C to form a positively charged COF-IDHT-MACL membrane. On the basis of the COF-IDHT-MACL membrane, uniformly drop 2 mL / cm 2 of the COF-DAHBP-BUA nanosheet solution, and evaporate the water at 100 °C to form a bipolar membrane.

[0141] SEM cross-section results: The thicknesses of the COF-IDHT-MACL layer and the COF-DAHBP-BUA layer are 500 nm and 400 nm respectively, and the film structures are clearly distinct. N 2 The adsorption results show that the pore size is 1.4 nm.

[0142] (4) Acid separation performance test

[0143] Acid recovery separation performance test: Using 0.25 M hydrochloric acid, sulfuric acid, phosphoric acid, sodium chloride, ferrous chloride, and aluminum chloride as the feed solution, static diffusion for 3 hours, the separation ratios of hydrochloric acid with sulfuric acid, phosphoric acid, sodium chloride, ferrous chloride, and aluminum chloride are 34, 180, 546, 2456, and 10567 respectively.

[0144] Example 8:

[0145] (1) Preparation of COF-THIB-VICL nanosheets

[0146] Prepare an ethyl acetate solution of TP with a concentration of 5 mmol / L. Prepare an equal volume of an NMP solution of THIB-VICL with a concentration of 7.5 mmol / L and a DMF solution of scandium trifluoromethanesulfonate with a concentration of 0.1 mmol / L. Under stirring, gradually dropwise mix the ethyl acetate solution of TP with the NMP solution of THIB-VICL, and then dropwise add the DMF solution of scandium trifluoromethanesulfonate. Control the dosages of each monomer solution so that in the reaction system: the hydrazide and aldehyde group are in an equimolar ratio, and the molar ratio of the acid catalyst to the hydrazide is 1:150.

[0147] After the dropping is completed, let the mixed reaction solution stand at 40 °C for 24 hours. The obtained reaction product is dialyzed with distilled water at room temperature for 24 hours to obtain an aqueous solution of COF-THIB-VICL nanosheets, and the prepared nanosheets carry a positive charge. The AFM test results show that the thickness of the nanosheets contained in the solution is 8.9 nm.

[0148] (2) Preparation of COF-DATH-BPSA nanosheets

[0149] Prepare an acetonitrile solution of TP with a concentration of 5 mmol / L. Prepare an equal volume of a DMSO solution of DAB-DATH-BPSA with a concentration of 7.5 mmol / L and a DMF solution of scandium trifluoromethanesulfonate with a concentration of 0.01 mmol / L. Under stirring, gradually dropwise mix the acetonitrile solution of TP with the DMSO solution of DAB-DATH-BPSA, and then dropwise add the DMF solution of scandium trifluoromethanesulfonate. Control the dosages of each monomer solution so that in the reaction system: the amino group and aldehyde group are in an equimolar ratio, and the molar ratio of the acid catalyst to the amino group is 1:1500.

[0150] After the addition was completed, the mixed reaction solution was allowed to stand at 10 °C for 100 hours. The resulting reaction product was dialyzed against distilled water at room temperature for 24 hours to obtain an aqueous solution of COF-DATH-BPSA nanosheets, and the prepared nanosheets were negatively charged. The AFM test results showed that the thickness of the nanosheets contained in the solution was 5.3 nm.

[0151] (3) Preparation of bipolar membrane

[0152] Using the hot solvent evaporation method, 1 mL / cm of the COF-THIB-VICL nanosheet solution was uniformly dropped onto the PAN substrate, and the water was evaporated at 50 °C to form a positively charged COF-THIB-VICL membrane. On the basis of the COF-THIB-VICL membrane, 1 mL / cm of the COF-DATH-BPSA nanosheet solution was uniformly dropped, and the water was evaporated at 100 °C to form a bipolar membrane. 2 2

[0153] SEM cross-section results: The thicknesses of the COF-THIB-VICL layer and the COF-DATH-BPSA layer were 300 nm and 600 nm respectively, and the membrane structure was clear and distinct. The N 2 adsorption results showed that the pore size was 1.7 nm.

[0154] (4) Acid separation performance test

[0155] Acid recovery separation performance test: Using 0.25 M hydrochloric acid, sulfuric acid, phosphoric acid, sodium chloride, ferrous chloride, and aluminum chloride as the feed solution, static diffusion was carried out for 3 hours, and the separation ratios of hydrochloric acid to sulfuric acid, phosphoric acid, sodium chloride, ferrous chloride, and aluminum chloride were 41, 145, 456, 1890, and 7432 respectively.

[0156] Example 9:

[0157] (1) Preparation of COF-DADEBPYCL nanosheets

[0158] Prepare an ethyl acetate solution of TP with a concentration of 0.1 mmol / L. Prepare an equal volume of an NMP solution of DADEBPYCL with a concentration of 0.15 mmol / L and a DMF solution of scandium trifluoromethanesulfonate with a concentration of 0.1 mmol / L. Under stirring, the ethyl acetate solution of TP was gradually mixed dropwise with the NMP solution of DADEBPYCL, and then the DMF solution of scandium trifluoromethanesulfonate was added dropwise. Control the dosage of each monomer solution so that in the reaction system: the amino group and the aldehyde group are in an equimolar ratio, and the molar ratio of the acid catalyst to the amino group is 1:3.

[0159] ​​After the addition was completed, the mixed reaction solution was allowed to stand at 40 °C for 24 hours. The resulting reaction product was dialyzed against distilled water at room temperature for 24 hours to obtain an aqueous solution of COF-DADEBPYCL nanosheets, and the prepared nanosheets were positively charged. The AFM test results showed that the thickness of the nanosheets contained in the solution was 3.2 nm.

[0160] (2) Preparation of COF-DHTA-DTZPA nanosheets

[0161] Prepare an acetonitrile solution of DHTA-DTZPA with a concentration of 15 mmol / L. Prepare an equal volume of a DMSO solution of TAPB with a concentration of 10 mmol / L and a DMF solution of scandium trifluoromethanesulfonate with a concentration of 0.01 mmol / L. Under stirring, the acetonitrile solution of DHTA-DTZPA was gradually added dropwise to the DMSO solution of TAPB, and then the DMF solution of scandium trifluoromethanesulfonate was added dropwise. Control the dosage of each monomer solution so that in the reaction system: the hydrazide and aldehyde group are in an equimolar ratio, and the molar ratio of the acid catalyst to the hydrazide is 1:3000.

[0162] After the addition was completed, the mixed reaction solution was allowed to stand at 10 °C for 100 hours. The resulting reaction product was dialyzed against distilled water at room temperature for 24 hours to obtain an aqueous solution of COF-DHTA-DTZPA nanosheets, and the prepared nanosheets were negatively charged. The AFM test results showed that the thickness of the nanosheets contained in the solution was 6.7 nm.

[0163] (3) Preparation of bipolar membrane

[0164] Using the hot solvent evaporation method, 1 mL / cm 2 of the COF-DADEBPYCL nanosheet solution was uniformly dropped on the PES substrate, and the water was evaporated at 50 °C to form a positively charged COF-DADEBPYCL membrane. On the basis of the COF-DADEBPYCL membrane, 1 mL / cm 2 of the COF-DHTA-DTZPA nanosheet solution was uniformly dropped, and the water was evaporated at 100 °C to form a bipolar membrane.

[0165] SEM cross-section results: The thicknesses of the COF-DADEBPYCL layer and the COF-DHTA-DTZPA layer were 300 nm and 600 nm respectively, and the membrane structure was clear and distinct. N 2 The adsorption results showed that the pore size was 1.3 nm.

[0166] (4) Acid separation performance test

[0167] Acid recovery separation performance test: Using 0.25 M hydrochloric acid, sulfuric acid, phosphoric acid, sodium chloride, ferrous chloride, and aluminum chloride as the feed solution, static diffusion for 3 hours, the separation ratios of hydrochloric acid from sulfuric acid, phosphoric acid, sodium chloride, ferrous chloride, and aluminum chloride are 14, 198, 365, 2567, and 10123 respectively.

[0168] Example 10:

[0169] (1) Preparation of COF-DAIBPYCL nanosheets

[0170] Prepare an ethyl acetate solution of TP with a concentration of 0.1 mmol / L. Prepare an equal volume of an NMP solution of DAIBPYCL with a concentration of 0.15 mmol / L and a DMF solution of scandium trifluoromethanesulfonate with a concentration of 0.1 mmol / L. Under stirring, gradually dropwise mix the ethyl acetate solution of TP with the NMP solution of DAIBPYCL, and then dropwise add the DMF solution of scandium trifluoromethanesulfonate. Control the dosage of each monomer solution so that in the reaction system: the amino group and the aldehyde group are in an equimolar ratio, and the molar ratio of the acid catalyst to the amino group is 1:3.

[0171] After the dropping is completed, let the mixed reaction solution stand at 40 °C for 24 hours. The obtained reaction product is dialyzed with distilled water at room temperature for 24 hours to obtain an aqueous solution of COF-DAIBPYCL nanosheets. The prepared nanosheets carry a positive charge. The AFM test results show that the thickness of the nanosheets contained in the solution is 6.1 nm.

[0172] (2) Preparation of COF-SA nanosheets

[0173] Prepare an acetonitrile solution of TP with a concentration of 1.0 mmol / L. Prepare an equal volume of a DMSO solution of DAB-SA with a concentration of 1.5 mmol / L and a DMF solution of scandium trifluoromethanesulfonate with a concentration of 0.01 mmol / L. Under stirring, gradually dropwise mix the acetonitrile solution of TP with the DMSO solution of DAB-SA, and then dropwise add the DMF solution of scandium trifluoromethanesulfonate. Control the dosage of each monomer solution so that in the reaction system: the amino group and the aldehyde group are in an equimolar ratio, and the molar ratio of the acid catalyst to the amino group is 1:300.

[0174] After the dropping is completed, let the mixed reaction solution stand at 10 °C for 100 hours. The obtained reaction product is dialyzed with distilled water at room temperature for 24 hours to obtain an aqueous solution of COF-SA nanosheets. The prepared nanosheets carry a negative charge. The AFM test results show that the thickness of the nanosheets contained in the solution is 3.3 nm.

[0175] (3) Preparation of bipolar membrane

[0176] Using the hot solvent evaporation method, uniformly drop 1 mL / cm on the PAN substrate 2The COF-DAIBPYCL nanosheet solution was allowed to evaporate water at 50 °C to form a positively charged COF-DAIBPYCL film. On the basis of the COF-DAIBPYCL film, 1 mL / cm 2 of the COF-SA nanosheet solution was evenly added dropwise, and the water was evaporated at 100 °C to form a bipolar membrane.

[0177] SEM cross-section results: The thicknesses of the COF-DAIBPYCL layer and the COF-SA layer were 300 nm and 600 nm respectively, and the film structure was clear and distinct. N 2 The adsorption results showed that the pore size was 1.3 nm.

[0178] (4) Acid separation performance test

[0179] Acid recovery separation performance test: Using 0.25 M hydrochloric acid, sulfuric acid, phosphoric acid, sodium chloride, ferrous chloride, and aluminum chloride as the feed solution, static diffusion for 3 hours, and the separation ratios of hydrochloric acid to sulfuric acid, phosphoric acid, sodium chloride, ferrous chloride, and aluminum chloride were 44, 143, 437, 1975, and 10854 respectively.

[0180] Example 11:

[0181] (1) Preparation of COF-DAACMTBPY-TBFPICL nanosheets

[0182] An ethyl acetate solution of TBFPICL with a concentration of 0.1 mmol / L was prepared. An NMP solution of DAACMTBPYCL with a concentration of 0.15 mmol / L and a DMF solution of scandium trifluoromethanesulfonate with a concentration of 0.1 mmol / L with equal volumes were prepared. Under stirring, the ethyl acetate solution of TBFPICL was gradually mixed dropwise with the NMP solution of DAACMTBPYCL, and then the DMF solution of scandium trifluoromethanesulfonate was added dropwise. Control the dosage of each monomer solution so that in the reaction system: the amino group and the aldehyde group are in an equimolar ratio, and the molar ratio of the acid catalyst to the amino group is 1:3.

[0183] After the addition was completed, the mixed reaction solution was allowed to stand at 40 °C for 24 hours. The obtained reaction product was dialyzed with distilled water at room temperature for 24 hours to obtain an aqueous solution of COF-DAACMTBPYCL-TBFPICL nanosheets, and the prepared nanosheets carried a positive charge. The AFM test results showed that the thickness of the nanosheets contained in the solution was 3.1 nm.

[0184] (2) Preparation of COF-SA nanosheets

[0185] Prepare an acetonitrile solution of TP with a concentration of 1.0 mmol / L. Prepare an equal volume of a DMSO solution of DAB-SA with a concentration of 1.5 mmol / L and a DMF solution of scandium trifluoromethanesulfonate with a concentration of 0.01 mmol / L. While stirring, gradually dropwise mix the acetonitrile solution of TP with the DMSO solution of DAB-SA, and then dropwise add the DMF solution of scandium trifluoromethanesulfonate. Control the dosages of each monomer solution so that in the reaction system: the amino group and the aldehyde group are in an equimolar ratio, and the molar ratio of the acid catalyst to the amino group is 1:300.

[0186] After the dropping is completed, let the mixed reaction solution stand at 10 °C for 100 hours. The obtained reaction product is dialyzed with room temperature distilled water for 24 hours to obtain an aqueous solution of COF-SA nanosheets, and the prepared nanosheets carry negative charges. The AFM test results show that the thickness of the nanosheets contained in the solution is 3.3 nm.

[0187] (3) Preparation of bipolar membrane

[0188] Using the hot solvent evaporation method, uniformly drop 1 mL / cm 2 of the COF-DAACMTBPYCL-TBFPICL nanosheet solution on the PAN substrate, and evaporate the water at 50 °C to form a positively charged COF-DAACMTBPYCL-TBFPICL membrane. On the basis of the COF-DAACMTBPYCL-TBFPICL membrane, uniformly drop 1 mL / cm 2 of the COF-SA nanosheet solution, and evaporate the water at 100 °C to form a bipolar membrane.

[0189] SEM cross-section results: The thicknesses of the COF-DAACMTBPYCL-TBFPICL layer and the COF-SA layer are 300 nm and 600 nm respectively, and the membrane structure is clear and distinct. N 2 The adsorption results show that the pore size is 0.9 nm.

[0190] (4) Acid separation performance test

[0191] Acid recovery separation performance test: Using 0.25 M hydrochloric acid, sulfuric acid, phosphoric acid, sodium chloride, ferrous chloride and copper chloride as the feed solution, static diffusion for 3 hours, and the separation ratios of hydrochloric acid to sulfuric acid, phosphoric acid, sodium chloride, ferrous chloride and copper chloride are 71, 136, 591, 1311 and 672 respectively.

[0192] Example 12:

[0193] (1) Preparation of COF-TAPMAI-DHTA-DPICL nanosheets

[0194] Prepare an ethyl acetate solution of DHTA - DPICL with a concentration of 0.15 mmol / L. Prepare equal - volume NMP solutions of TAPMAI with a concentration of 0.1 mmol / L and DMF solutions of scandium trifluoromethanesulfonate with a concentration of 0.1 mmol / L. Under stirring, gradually drop - wise mix the ethyl acetate solution of TP with the NMP solution of TAPMAI, and then drop - wise add the DMF solution of scandium trifluoromethanesulfonate. Control the dosage of each monomer solution so that in the reaction system: the amino group and the aldehyde group are in an equimolar ratio, and the molar ratio of the acid catalyst to the amino group is 1:3.

[0195] After the dropping is completed, let the mixed reaction solution stand at 40 °C for 24 hours. The obtained reaction product is dialyzed with distilled water at room temperature for 24 hours to obtain an aqueous solution of COF - TAPMAI - DHTA - DPICL nanosheets. The prepared nanosheets carry positive charges. The AFM test results show that the thickness of the nanosheets contained in the solution is 5.1 nm.

[0196] (2) Preparation of COF - SA nanosheets

[0197] Prepare an acetonitrile solution of TP with a concentration of 1.0 mmol / L. Prepare equal - volume DMSO solutions of DAB - SA with a concentration of 1.5 mmol / L and DMF solutions of scandium trifluoromethanesulfonate with a concentration of 0.01 mmol / L. Under stirring, gradually drop - wise mix the acetonitrile solution of TP with the DMSO solution of DAB - SA, and then drop - wise add the DMF solution of scandium trifluoromethanesulfonate. Control the dosage of each monomer solution so that in the reaction system: the amino group and the aldehyde group are in an equimolar ratio, and the molar ratio of the acid catalyst to the amino group is 1:300.

[0198] After the dropping is completed, let the mixed reaction solution stand at 10 °C for 100 hours. The obtained reaction product is dialyzed with distilled water at room temperature for 24 hours to obtain an aqueous solution of COF - SA nanosheets. The prepared nanosheets carry negative charges. The AFM test results show that the thickness of the nanosheets contained in the solution is 3.3 nm.

[0199] (3) Preparation of bipolar membrane

[0200] Using the hot - solvent evaporation method, uniformly drop 1 mL / cm 2 of the COF - TAPMAI - DHTA - DPICL nanosheet solution on the PAN substrate, and evaporate the water at 50 °C to form a positively charged COF - TAPMAI - DHTA - DPICL membrane. On the basis of the COF - TAPMAI - DHTA - DPICL membrane, uniformly drop 1 mL / cm 2 of the COF - SA nanosheet solution, and evaporate the water at 100 °C to form a bipolar membrane.

[0201] SEM cross-section results: The thicknesses of the COF-TAPMAI-DHTA-DPICL layer and the COF-SA layer are 300 nm and 600 nm respectively, and the film structures are clearly distinct. N 2 The adsorption results show that the pore size is 1.1 nm.

[0202] (4) Acid separation performance test

[0203] Acid recovery separation performance test: Using 0.25 M hydrochloric acid, sulfuric acid, phosphoric acid, sodium chloride, ferrous chloride, and aluminum chloride as the feed solution, static diffusion for 3 hours, the separation ratios of hydrochloric acid with sulfuric acid, phosphoric acid, sodium chloride, ferrous chloride, and aluminum chloride are 21, 129, 543, 2356, and 8786 respectively.

[0204] Example 13:

[0205] (1) Preparation of COF-TAPPYPRCL-THIA-TEACL nanosheets

[0206] Prepare an ethyl acetate solution of THIA-TEACL with a concentration of 0.15 mmol / L. Prepare equal volumes of a DCM solution of TAPPYPRCL with a concentration of 0.1 mmol / L and a DMF solution of scandium trifluoromethanesulfonate with a concentration of 0.1 mmol / L. Under stirring, gradually dropwise mix the ethyl acetate solution of TP with the DCM solution of TAPPYPRCL, and then dropwise add the DMF solution of scandium trifluoromethanesulfonate. Control the dosage of each monomer solution so that in the reaction system: the amino group and the aldehyde group are in an equimolar ratio, and the molar ratio of the acid catalyst to the amino group is 1:3.

[0207] After the dropping is completed, let the mixed reaction solution stand at 40 °C for 24 hours. The obtained reaction product is dialyzed with distilled water at room temperature for 24 hours to obtain an aqueous solution of COF-TAPPYPRCL-THIA-TEACL nanosheets, and the prepared nanosheets carry a positive charge. The AFM test results show that the thickness of the nanosheets contained in the solution is 4.1 nm.

[0208] (2) Preparation of COF-SA nanosheets

[0209] Prepare an acetonitrile solution of TP with a concentration of 1.0 mmol / L. Prepare equal volumes of a DMSO solution of DAB-SA with a concentration of 1.5 mmol / L and a DMF solution of scandium trifluoromethanesulfonate with a concentration of 0.01 mmol / L. Under stirring, gradually dropwise mix the acetonitrile solution of TP with the DMSO solution of DAB-SA, and then dropwise add the DMF solution of scandium trifluoromethanesulfonate. Control the dosage of each monomer solution so that in the reaction system: the amino group and the aldehyde group are in an equimolar ratio, and the molar ratio of the acid catalyst to the amino group is 1:300.

[0210] After the addition was completed, the mixed reaction solution was allowed to stand at 10 °C for 100 hours. The resulting reaction product was dialyzed against distilled water at room temperature for 24 hours to obtain an aqueous solution of COF-SA nanosheets. The prepared nanosheets were negatively charged. The AFM test results showed that the thickness of the nanosheets contained in the solution was 3.3 nm.

[0211] (3) Preparation of bipolar membrane

[0212] Using the thermal solvent evaporation method, 1 mL / cm of the COF-TAPPYPRCL-THIA-TEACL nanosheet solution was uniformly dropped onto the PVDF substrate, and the water was evaporated at 50 °C to form a positively charged COF-TAPPYPRCL-THIA-TEACL membrane. On the basis of the COF-TAPPYPRCL-THIA-TEACL membrane, 1 mL / cm of the COF-SA nanosheet solution was uniformly dropped, and the water was evaporated at 100 °C to form a bipolar membrane. 2 2

[0213] SEM cross-section results: The thicknesses of the COF-TAPPYPRCL-THIA-TEACL layer and the COF-SA layer were 300 nm and 600 nm, respectively, and the membrane structure was clear and distinct. N 2 The adsorption results showed that the pore size was 0.8 nm.

[0214] (4) Acid separation performance test

[0215] Acid recovery separation performance test: Using 0.25 M hydrochloric acid, sulfuric acid, phosphoric acid, sodium chloride, ferrous chloride, and aluminum chloride as the feed solution, static diffusion was carried out for 3 hours. The separation ratios of hydrochloric acid to sulfuric acid, phosphoric acid, sodium chloride, ferrous chloride, and aluminum chloride were 13, 156, 357, 1122, and 8796, respectively.

[0216] Example 14:

[0217] (1) Preparation of COF-TAPDMTABCL-DHTA-DEICL nanosheets

[0218] Prepare an ethyl acetate solution of DHTA-DEICL with a concentration of 0.2 mmol / L. Prepare an equal volume of an NMP solution of TAPDMTABCL with a concentration of 0.1 mmol / L and a DMF solution of scandium trifluoromethanesulfonate with a concentration of 0.1 mmol / L. Under stirring, the ethyl acetate solution of TP was gradually mixed dropwise with the NMP solution of TAPDMTABCL, and then the DMF solution of scandium trifluoromethanesulfonate was added dropwise. Control the dosage of each monomer solution so that in the reaction system: the amino group and the aldehyde group are in an equimolar ratio, and the molar ratio of the acid catalyst to the amino group is 1:4.

[0219] ​​After the addition was completed, the mixed reaction solution was allowed to stand at 40 °C for 24 hours. The resulting reaction product was dialyzed against distilled water at room temperature for 24 hours to obtain an aqueous solution of COF-TAPDMTABCL-DHTA-DEICL nanosheets. The prepared nanosheets were positively charged. The AFM test results showed that the thickness of the nanosheets contained in the solution was 2.3 nm.

[0220] (2) Preparation of COF-SA nanosheets

[0221] Prepare an acetonitrile solution of TP with a concentration of 1.0 mmol / L. Prepare equal volumes of a DMSO solution of DAB-SA with a concentration of 1.5 mmol / L and a DMF solution of scandium trifluoromethanesulfonate with a concentration of 0.01 mmol / L. Under stirring, the acetonitrile solution of TP was gradually added dropwise to the DMSO solution of DAB-SA, and then the DMF solution of scandium trifluoromethanesulfonate was added dropwise. Control the dosage of each monomer solution so that in the reaction system: the amino group and the aldehyde group are in an equimolar ratio, and the molar ratio of the acid catalyst to the amino group is 1:300.

[0222] After the addition was completed, the mixed reaction solution was allowed to stand at 10 °C for 100 hours. The resulting reaction product was dialyzed against distilled water at room temperature for 24 hours to obtain an aqueous solution of COF-SA nanosheets. The prepared nanosheets were negatively charged. The AFM test results showed that the thickness of the nanosheets contained in the solution was 3.3 nm.

[0223] (3) Preparation of bipolar membrane

[0224] Using the hot solvent evaporation method, 1 mL / cm 2 of the COF-TAPDMTABCL-DHTA-DEICL nanosheet solution was uniformly dropped on the PAN substrate, and the water was evaporated at 50 °C to form a positively charged COF-TAPDMTABCL-DHTA-DEICL membrane. On the basis of the COF-EB membrane, 1 mL / cm 2 of the COF-SA nanosheet solution was uniformly dropped, and the water was evaporated at 100 °C to form a bipolar membrane.

[0225] SEM cross-section results: The thicknesses of the COF-TAPDMTABCL-DHTA-DEICL layer and the COF-SA layer were 300 nm and 600 nm respectively, and the membrane structure was clear and distinct. N 2 The adsorption results showed that the pore size was 0.7 nm.

[0226] (4) Acid separation performance test

[0227] Acid recovery separation performance test: Using 0.25 M hydrochloric acid, sulfuric acid, phosphoric acid, sodium chloride, ferrous chloride, and aluminum chloride as the feed solution, static diffusion for 3 hours, the separation ratios of hydrochloric acid from sulfuric acid, phosphoric acid, sodium chloride, ferrous chloride, and aluminum chloride are 38, 152, 632, 2463, and 9812 respectively.

[0228] Example 15:

[0229] (1) Preparation of COF-DHTA-DEICL nanosheets

[0230] Prepare an ethyl acetate solution of DHTA-DEICL with a concentration of 0.15 mmol / L. Prepare equal volumes of an NMP solution of TAPB with a concentration of 0.1 mmol / L and a DMF solution of scandium trifluoromethanesulfonate with a concentration of 0.1 mmol / L. Under stirring, gradually dropwise mix the ethyl acetate solution of DHTA-DEICL with the NMP solution of TAPB, and then dropwise add the DMF solution of scandium trifluoromethanesulfonate. Control the dosage of each monomer solution so that in the reaction system: the amino group and the aldehyde group are in an equimolar ratio, and the molar ratio of the acid catalyst to the amino group is 1:3.

[0231] After the dropping is completed, let the mixed reaction solution stand at 40 °C for 24 hours. The obtained reaction product is dialyzed with distilled water at room temperature for 24 hours to obtain an aqueous solution of COF-DHTA-DEICL nanosheets. The prepared nanosheets carry a positive charge. The AFM test results show that the thickness of the nanosheets contained in the solution is 2.8 nm.

[0232] (2) Preparation of COF-SA nanosheets

[0233] Prepare an acetonitrile solution of TP with a concentration of 1.0 mmol / L. Prepare equal volumes of a DMSO solution of DAB-SA with a concentration of 1.5 mmol / L and a DMF solution of scandium trifluoromethanesulfonate with a concentration of 0.01 mmol / L. Under stirring, gradually dropwise mix the acetonitrile solution of TP with the DMSO solution of DAB-SA, and then dropwise add the DMF solution of scandium trifluoromethanesulfonate. Control the dosage of each monomer solution so that in the reaction system: the amino group and the aldehyde group are in an equimolar ratio, and the molar ratio of the acid catalyst to the amino group is 1:300.

[0234] After the dropping is completed, let the mixed reaction solution stand at 10 °C for 100 hours. The obtained reaction product is dialyzed with distilled water at room temperature for 24 hours to obtain an aqueous solution of COF-SA nanosheets. The prepared nanosheets carry a negative charge. The AFM test results show that the thickness of the nanosheets contained in the solution is 3.3 nm.

[0235] (3) Preparation of bipolar membrane

[0236] Using the hot solvent evaporation method, on Al 2 O 31 mL / cm was uniformly dropped onto the substrate 2 of the COF-DHTA-DEICL nanosheet solution, and the water was evaporated at 50 °C to form a positively charged COF-DHTA-DEICL film. 1 mL / cm 2 of the COF-SA nanosheet solution was uniformly dropped onto the COF-DHTA-DEICL film, and the water was evaporated at 100 °C to form a bipolar membrane.

[0237] SEM cross-section results: The thicknesses of the COF-DHTA-DEICL layer and the COF-SA layer were 300 nm and 600 nm respectively, and the membrane structure was clear and distinct. N 2 The adsorption results showed that the pore size was 0.8 nm.

[0238] (4) Acid separation performance test

[0239] Acid recovery separation performance test: Using 0.25 M hydrochloric acid, sulfuric acid, phosphoric acid, sodium chloride, ferrous chloride and copper chloride as the feed solution, static diffusion for 3 hours, and the separation ratios of hydrochloric acid to sulfuric acid, phosphoric acid, sodium chloride, ferrous chloride and copper chloride were 71, 136, 591, 1089 and 891 respectively.

[0240] Example 16:

[0241] (1) Preparation of COF-DHTA-DEICL nanosheets

[0242] An ethyl acetate solution of DHTA-DEICL with a concentration of 0.15 mmol / L was prepared. An equal volume of an NMP solution of TAPB with a concentration of 0.1 mmol / L and a DMF solution of scandium trifluoromethanesulfonate with a concentration of 0.1 mmol / L were prepared. Under stirring, the ethyl acetate solution of DHTA-DEICL was gradually dropped into the NMP solution of TAPB, and then the DMF solution of scandium trifluoromethanesulfonate was dropped. The amounts of each monomer solution were controlled so that in the reaction system: the amino group and the aldehyde group were in an equimolar ratio, and the molar ratio of the acid catalyst to the amino group was 1:3.

[0243] After the dropping was completed, the mixed reaction solution was allowed to stand at 40 °C for 24 hours. The obtained reaction product was dialyzed with distilled water at room temperature for 24 hours to obtain an aqueous solution of COF-DHTA-DEICL nanosheets, and the prepared nanosheets carried a positive charge. The AFM test results showed that the thickness of the nanosheets contained in the solution was 3.9 nm.

[0244] (2) Preparation of COF-SA nanosheets

[0245] Prepare an acetonitrile solution of TP with a concentration of 1.0 mmol / L. Prepare equal volumes of a DMSO solution of DAB-SA with a concentration of 1.5 mmol / L and a DMF solution of scandium trifluoromethanesulfonate with a concentration of 0.01 mmol / L. While stirring, gradually dropwise mix the acetonitrile solution of TP with the DMSO solution of DAB-SA, and then dropwise add the DMF solution of scandium trifluoromethanesulfonate. Control the dosages of each monomer solution so that in the reaction system: the amino group and the aldehyde group are in an equimolar ratio, and the molar ratio of the acid catalyst to the amino group is 1:300.

[0246] After the dropping is completed, let the mixed reaction solution stand at 10 °C for 100 hours. The obtained reaction product is dialyzed with room temperature distilled water for 24 hours to obtain an aqueous solution of COF-SA nanosheets, and the prepared nanosheets carry a negative charge. The AFM test results show that the thickness of the nanosheets contained in the solution is 3.3 nm.

[0247] (3) Preparation of bipolar membrane

[0248] Adopt the hot solvent evaporation method, and uniformly drop 1 mL / cm 2 of the COF-DHTA-DEICL nanosheet solution on the PAN substrate, and evaporate the water at 50 °C to form a positively charged COF-DHTA-DEICL membrane. On the basis of the COF-DHTA-DEICL membrane, uniformly drop 1 mL / cm 2 of the COF-SA nanosheet solution, and evaporate the water at 100 °C to form a bipolar membrane.

[0249] SEM cross-section results: The thicknesses of the COF-DHTA-DEICL layer and the COF-SA layer are 300 nm and 600 nm respectively, and the membrane structure is clear and distinct. N 2 The adsorption results show that the pore size is 0.9 nm.

[0250] (4) Acid separation performance test

[0251] Acid recovery separation performance test: Using 0.25 M hydrochloric acid, sulfuric acid, phosphoric acid, sodium chloride, ferrous chloride, and aluminum chloride as the feed liquid, static diffusion for 3 hours, and the separation ratios of hydrochloric acid to sulfuric acid, phosphoric acid, sodium chloride, ferrous chloride, and aluminum chloride are 67, 177, 364, 4562, and 2893 respectively.

[0252] Example 17:

[0253] (1) Preparation of COF-DHTA-DTZTMACL nanosheets

[0254] Prepare an NMP solution of DHTA - DTZTMACL with a concentration of 3 mmol / L. Prepare an equal - volume NMP solution of TAPB with a concentration of 2 mmol / L and a DMF solution of scandium trifluoromethanesulfonate with a concentration of 0.1 mmol / L. Under stirring, gradually drop - wise mix the NMP solution of DHTA - DTZTMACL with the NMP solution of TAPB, and then drop - wise add the DMF solution of scandium trifluoromethanesulfonate. Control the dosage of each monomer solution so that in the reaction system: the amino group and the aldehyde group are in an equimolar ratio, and the molar ratio of the acid catalyst to the amino group is 1:60.

[0255] After the dropping is completed, let the mixed reaction solution stand at 25 °C for 24 hours. The obtained reaction product is dialyzed with distilled water at room temperature for 24 hours to obtain an aqueous solution of COF - DHTA - DTZTMACL nanosheets, and the prepared nanosheets carry a positive charge. The AFM test results show that the thickness of the nanosheets contained in the solution is 6.1 nm.

[0256] (2) Preparation of COF - SA nanosheets

[0257] Prepare an acetonitrile solution of TP with a concentration of 1.0 mmol / L. Prepare an equal - volume DMSO solution of DAB - SA with a concentration of 1.5 mmol / L and a DMF solution of scandium trifluoromethanesulfonate with a concentration of 0.01 mmol / L. Under stirring, gradually drop - wise mix the acetonitrile solution of TP with the DMSO solution of DAB - SA, and then drop - wise add the DMF solution of scandium trifluoromethanesulfonate. Control the dosage of each monomer solution so that in the reaction system: the amino group and the aldehyde group are in an equimolar ratio, and the molar ratio of the acid catalyst to the amino group is 1:300.

[0258] After the dropping is completed, let the mixed reaction solution stand at 10 °C for 100 hours. The obtained reaction product is dialyzed with distilled water at room temperature for 24 hours to obtain an aqueous solution of COF - SA nanosheets, and the prepared nanosheets carry a negative charge. The AFM test results show that the thickness of the nanosheets contained in the solution is 3.3 nm.

[0259] (3) Preparation of bipolar membrane

[0260] Adopt the hot - solvent evaporation method. Uniformly drop 1 mL / cm 2 of the COF - DHTA - DTZTMACL nanosheet solution on the PAN substrate, and evaporate the water at 50 °C to form a positively charged COF - DHTA - DTZTMACL membrane. On the basis of the COF - DHTA - DTZTMACL membrane, uniformly drop 1 mL / cm 2 of the COF - SA nanosheet solution, and evaporate the water at 100 °C to form a bipolar membrane.

[0261] SEM cross-section results: The thicknesses of the COF-DHTA-DTZTMACL layer and the COF-SA layer are 300 nm and 600 nm respectively, and the film structure is clear and distinct. N 2 The adsorption results show that the pore size is 1.2 nm.

[0262] (4) Acid separation performance test

[0263] Acid recovery separation performance test: Using 0.25 M hydrochloric acid, sulfuric acid, phosphoric acid, sodium chloride, ferrous chloride, and aluminum chloride as the feed solution, static diffusion for 3 hours, the separation ratios of hydrochloric acid with sulfuric acid, phosphoric acid, sodium chloride, ferrous chloride, and aluminum chloride are 21, 236, 256, 1878, and 12137 respectively.

[0264] Example 18:

[0265] (1) Preparation of COF-n-bu-DFPBICL nanosheets

[0266] Prepare a DMF solution of n-bu-DFPBICL with a concentration of 0.15 mmol / L. Prepare equal volumes of an NMP solution of TAPB with a concentration of 0.1 mmol / L and a DMF solution of scandium trifluoromethanesulfonate with a concentration of 0.1 mmol / L. Under stirring, gradually dropwise mix the DMF solution of n-bu-DFPBICL with the NMP solution of TAPB, and then dropwise add the DMF solution of scandium trifluoromethanesulfonate. Control the dosage of each monomer solution so that in the reaction system: the amino group and the aldehyde group are in an equimolar ratio, and the molar ratio of the acid catalyst to the amino group is 1:3.

[0267] After the dropping is completed, let the mixed reaction solution stand at 120 °C for 24 hours. The obtained reaction product is dialyzed with room temperature distilled water for 24 hours to obtain an aqueous solution of COF-n-bu-DFPBICL nanosheets, and the prepared nanosheets carry a positive charge. The AFM test results show that the thickness of the nanosheets contained in the solution is 5.3 nm.

[0268] (2) Preparation of COF-SA nanosheets

[0269] Prepare an acetonitrile solution of TP with a concentration of 1.0 mmol / L. Prepare equal volumes of a DMSO solution of DAB-SA with a concentration of 1.5 mmol / L and a DMF solution of scandium trifluoromethanesulfonate with a concentration of 0.01 mmol / L. Under stirring, gradually dropwise mix the acetonitrile solution of TP with the DMSO solution of DAB-SA, and then dropwise add the DMF solution of scandium trifluoromethanesulfonate. Control the dosage of each monomer solution so that in the reaction system: the amino group and the aldehyde group are in an equimolar ratio, and the molar ratio of the acid catalyst to the amino group is 1:300.

[0270] After the addition was completed, the mixed reaction solution was allowed to stand at 50 °C for 60 hours. The resulting reaction product was dialyzed against distilled water at room temperature for 24 hours to obtain an aqueous solution of COF-SA nanosheets, and the prepared nanosheets were negatively charged. The AFM test results showed that the thickness of the nanosheets contained in the solution was 3.3 nm.

[0271] (3) Preparation of bipolar membrane

[0272] Using the hot solvent evaporation method, 1 mL / cm of the COF-n-bu-DFPBICL nanosheet solution was uniformly dropped onto the PAN substrate, and the water was evaporated at 50 °C to form a positively charged COF-n-bu-DFPBICL membrane. On the basis of the COF-n-bu-DFPBICL membrane, 50 mL / cm of the COF-SA nanosheet solution was uniformly dropped, and the water was evaporated at 100 °C to form a bipolar membrane. 2 2

[0273] SEM cross-section results: The thicknesses of the COF-n-bu-DFPBICL layer and the COF-SA layer were 300 nm and 600 nm respectively, and the membrane structure was clear and distinct. N 2 The adsorption results showed that the pore size was 1.3 nm.

[0274] (4) Acid separation performance test

[0275] Acid recovery separation performance test: Using 0.25 M hydrochloric acid, sulfuric acid, phosphoric acid, sodium chloride, ferrous chloride, and aluminum chloride as the feed solution, static diffusion for 3 hours, and the separation ratios of hydrochloric acid to sulfuric acid, phosphoric acid, sodium chloride, ferrous chloride, and aluminum chloride were 45, 342, 549, 2491, and 7932 respectively.

[0276] Example 19:

[0277] (1) Preparation of COF-me-DFPBICL nanosheets

[0278] Prepare an ethyl acetate solution of me-DFPBICL with a concentration of 6 mmol / L. Prepare an equal volume of an NMP solution of TAPB with a concentration of 4 mmol / L and a DMF solution of scandium trifluoromethanesulfonate with a concentration of 0.1 mmol / L. Under stirring, the ethyl acetate solution of me-DFPBICL was gradually mixed dropwise with the NMP solution of TAPB, and then the DMF solution of scandium trifluoromethanesulfonate was added dropwise. Control the dosage of each monomer solution so that in the reaction system: the amino group and the aldehyde group are in an equimolar ratio, and the molar ratio of the acid catalyst to the amino group is 1:120.

[0279] ​​After the addition was completed, the mixed reaction solution was allowed to stand at 40 °C for 100 hours. The resulting reaction product was dialyzed against distilled water at room temperature for 24 hours to obtain an aqueous solution of COF-me-DFPBICL nanosheets. The prepared nanosheets carried a positive charge. The AFM test results showed that the thickness of the nanosheets contained in the solution was 7.8 nm.

[0280] (2) Preparation of COF-SA nanosheets

[0281] Prepare an acetonitrile solution of TP with a concentration of 1.0 mmol / L. Prepare an equal volume of a DMSO solution of DAB-SA with a concentration of 1.5 mmol / L and a DMF solution of scandium trifluoromethanesulfonate with a concentration of 0.01 mmol / L. Under stirring, the acetonitrile solution of TP was gradually added dropwise to the DMSO solution of DAB-SA, and then the DMF solution of scandium trifluoromethanesulfonate was added dropwise. Control the dosage of each monomer solution so that in the reaction system: the amino group and the aldehyde group are in an equimolar ratio, and the molar ratio of the acid catalyst to the amino group is 1:300.

[0282] After the addition was completed, the mixed reaction solution was allowed to stand at 10 °C for 100 hours. The resulting reaction product was dialyzed against distilled water at room temperature for 24 hours to obtain an aqueous solution of COF-SA nanosheets. The prepared nanosheets carried a negative charge. The AFM test results showed that the thickness of the nanosheets contained in the solution was 3.3 nm.

[0283] (3) Preparation of bipolar membrane

[0284] Using the hot solvent evaporation method, 1 mL / cm 2 of the COF-me-DFPBICL nanosheet solution was uniformly dropped on the PAN substrate, and the water was evaporated at 50 °C to form a positively charged COF-me-DFPBICL membrane. On the basis of the COF-me-DFPBICL membrane, 100 mL / cm 2 of the COF-SA nanosheet solution was uniformly dropped, and the water was evaporated at 100 °C to form a bipolar membrane.

[0285] SEM cross-section results: The thicknesses of the COF-me-DFPBICL layer and the COF-SA layer were 300 nm and 600 nm respectively, and the membrane structure was clear and distinct. N 2 The adsorption results showed that the pore size was 0.8 nm.

[0286] (4) Acid separation performance test

[0287] Acid recovery separation performance test: Using 0.25 M hydrochloric acid, sulfuric acid, phosphoric acid, sodium chloride, ferrous chloride and aluminum chloride as the feed solution, static diffusion for 3 hours, and the separation ratios of hydrochloric acid to sulfuric acid, phosphoric acid, sodium chloride, ferrous chloride and aluminum chloride were 239, 186, 223, 1890 and 5743 respectively.

[0288] Example 20:

[0289] (1) Preparation of COF-DFPBPYCL Nanosheets

[0290] Prepare an ethyl acetate solution of DFPBPYCL with a concentration of 10 mmol / L. Prepare equal volumes of an NMP solution of TAPB with a concentration of 6.77 mmol / L and a DMF solution of scandium trifluoromethanesulfonate with a concentration of 0.1 mmol / L. Under stirring, gradually dropwise mix the ethyl acetate solution of DFPBPYCL with the NMP solution of TAPB, and then dropwise add the DMF solution of scandium trifluoromethanesulfonate. Control the dosages of each monomer solution so that in the reaction system: the amino group and the aldehyde group are in an equimolar ratio, and the molar ratio of the acid catalyst to the amino group is 1:200.

[0291] After the dropping is completed, let the mixed reaction solution stand at 50 °C for 100 hours. The obtained reaction product is dialyzed with distilled water at room temperature for 24 hours to obtain an aqueous solution of COF-DFPBPYCL nanosheets, and the prepared nanosheets carry a positive charge. The AFM test results show that the thickness of the nanosheets contained in the solution is 8.5 nm.

[0292] (2) Preparation of COF-SA Nanosheets

[0293] Prepare an acetonitrile solution of TP with a concentration of 1.0 mmol / L. Prepare equal volumes of a DMSO solution of DAB-SA with a concentration of 1.5 mmol / L and a DMF solution of scandium trifluoromethanesulfonate with a concentration of 0.01 mmol / L. Under stirring, gradually dropwise mix the acetonitrile solution of TP with the DMSO solution of DAB-SA, and then dropwise add the DMF solution of scandium trifluoromethanesulfonate. Control the dosages of each monomer solution so that in the reaction system: the amino group and the aldehyde group are in an equimolar ratio, and the molar ratio of the acid catalyst to the amino group is 1:300.

[0294] After the dropping is completed, let the mixed reaction solution stand at 40 °C for 10 hours. The obtained reaction product is dialyzed with distilled water at room temperature for 24 hours to obtain an aqueous solution of COF-SA nanosheets, and the prepared nanosheets carry a negative charge. The AFM test results show that the thickness of the nanosheets contained in the solution is 3.3 nm.

[0295] (3) Preparation of Bipolar Membrane

[0296] Using the hot solvent evaporation method, uniformly drop 20 mL / cm 2 of the COF-DFPBPYCL nanosheet solution on the PAN substrate, and evaporate the water at 50 °C to form a positively charged COF-DFPBPYCL membrane. On the basis of the COF-DFPBPYCL membrane, uniformly drop 10 mL / cm 2 of the COF-SA nanosheet solution, and evaporate the water at 100 °C to form a bipolar membrane.

[0297] SEM cross-section results: The thicknesses of the COF-DFPBPYCL layer and the COF-SA layer are 3 μm and 900 nm respectively, and the film structure is clear and distinct. N 2 The adsorption results show that the pore size is 0.6 nm.

[0298] (4) Acid separation performance test

[0299] Acid recovery separation performance test: Using 0.25 M hydrochloric acid, sulfuric acid, phosphoric acid, sodium chloride, ferrous chloride, and aluminum chloride as the feed solution, static diffusion for 3 hours, the separation ratios of hydrochloric acid to sulfuric acid, phosphoric acid, sodium chloride, ferrous chloride, and aluminum chloride are 33, 177, 362, 2738, and 6345 respectively.

[0300] Comparative Example 1

[0301] Synthesize a cation exchange membrane material according to the method provided in the literature Separation and Purification Technology, 2018, 201, 336 - 345, and conduct acid separation performance tests on it with reference to the experimental operation process and electrolyte concentration in Example 1. The results are as follows: The separation ratios of hydrochloric acid to sulfuric acid, phosphoric acid, sodium chloride, ferrous chloride, and aluminum chloride are 1.1, 8.5, 9, 41, and 102 respectively.

[0302] Comparison of separation ratio data shows that:

[0303] Theoretically, separation can be achieved if the separation ratio is not equal to 1, and when the separation ratio reaches more than 10, it has practical industrial significance. However, there are still major technical bottlenecks in currently commercialized membrane materials, making it difficult to simultaneously achieve the following goals: (i) efficient separation of protons and metal ions; (ii) selective separation of different anions. The fundamental reason for the above problems is the non-uniform pore structure and relatively single membrane composition of current membrane materials, resulting in the following limitations: (i) easy to swell in an aqueous environment, unstable pore structure, weakening the separation ability; (ii) single host-guest interaction, unable to effectively distinguish ions with the same valence state. In contrast, the COF bipolar membrane prepared in the present invention exhibits the following significant advantages: (i) The membrane material has good crystallinity, regular and uniform pores, and a stable structure, avoiding the swelling phenomenon in an aqueous environment; (ii) The multi-polar linkage mode of the COF material can form specific dipole interactions with different ions to achieve selective separation of ions with the same valence state; (iii) Extracting single acid molecules from a complex mixed system, the separation ratio far exceeds that of existing membrane materials.

[0304] The product characteristics demonstrated by the separation ratio data in the above embodiments indicate that the bipolar membrane of the present invention not only shortens the separation process flow but also can quickly extract high-purity acid molecules, significantly enhancing the application value of such products in the industrial production process.

[0305] Durability experiment comparison:

[0306] Compare the durability performance of the bipolar membrane prepared in Example 1 of the present invention with that of the cation exchange membrane in the literature:

[0307] Referring to the operation process of Example 1, under the same feed liquid and diffusion conditions, the separation ratio change was tested after continuous operation for 10 days. After the bipolar membrane of the present invention was continuously operated for 10 days, the separation ratio of hydrochloric acid from other acids and salts almost remained constant, and the performance was stable. In the same way, after the cation exchange membrane in Example 1 was continuously operated for 10 days, the separation ratio decreased significantly. The separation ratios of hydrochloric acid and sulfuric acid, phosphoric acid, sodium chloride, ferrous chloride, and aluminum chloride decreased by 22.1%, 13.5%, 10.8%, <6.2%, and <5.6%, respectively.

[0308] Summary

[0309] The COF bipolar membrane of the present invention has significant separation performance advantages, can selectively extract single acid molecules from complex mixed systems, and meets industrial requirements. Compared with the cation exchange membrane in the literature, the separation ratio of the membrane material of the present invention is higher, and it is suitable for the efficient recovery of acids in acidic waste liquids. The membrane material of the present invention exhibits excellent stability at high salt concentrations, with a constant separation ratio, avoiding significant attenuation of operating performance. This characteristic makes it more suitable for the long-term stable operation of industrial production, reduces maintenance costs, and enhances application value. The bipolar membrane of the present invention is suitable for the selective recovery of acids in acidic waste liquids, the extraction of acids in high-salt environments, and the separation of single acid molecules in complex systems. In summary, the COF bipolar membrane of the present invention is superior to the prior art in terms of acid separation performance, stability, and industrial application value, and has broad market prospects and practical application potential.

Claims

1. A method for preparing a covalent organic framework bipolar membrane, characterized in that: Amine or hydrazide monomers containing ionic groups are reacted with aldehyde monomers without ionic groups, or aldehyde monomers containing ionic groups are reacted with amine or hydrazide monomers without ionic groups, in the coexistence of an acid catalyst and an organic solvent, to synthesize positively charged and negatively charged covalent organic framework (COF) nanosheets respectively through a one-pot method; then, the positively charged COF nanosheets are first deposited on the surface of a porous carrier by a hot solvent volatilization method, and the negatively charged COF nanosheets are continuously deposited; and finally, a covalent organic framework bipolar membrane with charge asymmetry is obtained by constructing two COF separation layers with regular pores and opposite charges.

2. The method according to claim 1, characterized in that The method specifically includes: (1) Synthesis of COF nanosheets Selecting at least one amine, hydrazide or aldehyde monomer containing a positively charged ionic group, and at least one amine, hydrazide or aldehyde monomer containing a negatively charged ionic group; then preparing monomer solutions respectively in the form of a combination of the amine or hydrazide monomer containing an ionic group and the aldehyde monomer without an ionic group, or preparing monomer solutions respectively in the form of a combination of the aldehyde monomer containing an ionic group and the amine or hydrazide monomer without an ionic group; Under stirring conditions, the monomer solution is mixed uniformly according to the aforementioned combination method, and then an appropriate amount of acid catalyst solution is added dropwise to the mixture; the reaction is carried out at a constant temperature of 10 to 120° C. for 5 to 100 hours to generate COF nanosheets; the COF nanosheets are dialyzed with water to remove the catalyst, unreacted monomers and oligomers, and the aqueous solution finally obtained contains COF nanosheets with positive or negative charges; Controlling the amount of each monomer solution so that the amino group in the amine monomer, the hydrazide in the hydrazide monomer or the aldehyde group in the aldehyde monomer in the monomer combination are in an equimolar ratio; (2) Preparation of bipolar membrane Take two COF nanosheet aqueous solutions, containing COF nanosheets with positive charge and negative charge respectively; use hot solvent evaporation method to first deposit the positively charged COF nanosheets on a porous carrier, and then continue to deposit the negatively charged COF nanosheets; by constructing two COF separation layers with regular pores and opposite charges, a covalent organic framework bipolar membrane with charge asymmetry is finally obtained.

3. The method according to claim 1 or 2, characterized in that: The amine or hydrazide monomer is any one of the following: benzidine (BD), 1,3,5-tris(4-aminophenyl)benzene (TAPB), 2,5-diaminobenzenesulfonic acid (DAB-SA), 2,5-diaminobenzoic acid (DABA), 4-(4,4'-diamino-3'-hydroxy-[1,1'-biphenyl]-3-yl)oxy)butyric acid (DAHBP-BUA), trans-6,6'-(ethylene-1,2-diyl)bis(3-aminobenzenesulfonic acid) (DABSAE), 4,7-bis(4-aminophenyl)-2,5,6-trimethylbenzo[d]imidazole-1-ether sodium salt (DAPTMINA), 3,3'- (2,5-di(hydrazinecarbonyl)-1,4-phenylene)bis(azadiyl)bis(propane-1-sulfonic acid) (DATH-BPSA), triaminoguanidine hydrochloride (TAGCL), 2,5-diamino-1-ethylpyridinium hydrochloride (DAEPYCL), 1H-1,2,4-triazole-3,5-diamine (DATZ), 1-(3,5-di(hydrazinecarbonyl)phenyl)-N,N,N-trimethylmethylammonium hydrochloride (IDHT-MACL), 4-(2,5-di(hydrazinecarbonyl)-4-hydroxyphenoxy)-N,N,N-trimethylbutyl-1-ammonium hydrochloride (DHTH-TMBACL), 2,2'-(2,5-di(hydrazinecarbonyl)phenyl)-N,N,N-trimethylbutyl-1-ammonium hydrochloride (DHTH-TMBACL), bis(2,5-di(hydrazinocarbonyl)benzyl)-1-vinyl-1H-imidazol-3-ium hydrochloride (THB-VICL), 5,5'-diamino-1,1'-diethyl-[2,2'-bipyridyl]-1,1'-diamine hydrochloride (DADEBPYCL), 3,9-diaminoimidazo[1, 5-a:3,4-a']bipyridinium-5-ol hydrochloride (DAIBPYCL), 5,5'-diamino-1-(2-((1S,2R,5S)-2-isopropyl-5-methylcyclohexyl)oxy)-2-oxoethyl)-[2,2'-bipyridinium]-1-ol hydrochloride (DAACMTBPYCL), 4-amino-N,N-bis(4-aminophenyl)-N-methylanilinium iodide (TAPMAI), ethidium bromide (EB), (S)-2,4,6-tris(4-aminophenyl)-1-((1-(tert-butyloxycarbonyl)pyrrolidin-2-ol)methoxy)carbonyl)pyridinium hydrochloride (TAPPYPRCL), N 1 ,N 1 ,N 4 ,N 4 Tetrakis(4-aminophenyl)-N 1 ,N 4 -Dimethylbenzene-1,4-diammonium hydrochloride (TAPDMTABCL).

4. The method according to claim 1 or 2, characterized in that: The aldehyde monomer is any one of the following: terephthalaldehyde (BDA), trialdehyde phloroglucinol (TP), 3-(2,5-diformyl-4-hydroxyphenoxy)propane-1-sulfonic acid (DHTA-PSA), 3,3'-(((2,5-diformyl-1,4-phenylene)bis(oxy))bis(methylene))bis(1H-1,2,3-triazole-4,1-diyl))dipropionic acid (DHTA-DTZPA), 3,3'-((2,5-diformyl-1,4-phenylene)bis(oxy))bis(methylene))bis(1H-1,2,3-triazole-4,1-diyl))dipropionic acid (DHTA-DTZPA), 3,3'-((2,5-diformyl-1,4-phenylene)bis(oxy))bis(propane-3,1-dialkyl)bis(1-methyl-1H-imidazol-3-ium) hydrochloride (DHTA-DPICL), 3,3'-((2,5-diformyl-1,4-phenylene)bis(oxy))bis(ethane-2,1-diyl)bis(1-methyl-1H-imidazol-3-ium) hydrochloride (DHTA-DEICL), 2,2'-((2,5-diformyl-1,4-phenylene)bis( bis(methylene)bis(1H-1,2,3-triazole-4,1-diyl)bis(N,N,N-trimethylethan-1-amine) (DHTA-DTZTMACL), 2-(2,4-diformyl-3,5-dihydroxyphenoxy)-N,N,N-triethylethan-1-amine (THIA-TEACL), 3-butyl-4,7-bis(4-formylphenyl)-1-methyl-1H-benzo[d]imidazol-3-ium hydrochloride (bu-DFP BICL), 4,7-bis(4-formylphenyl)-1,3-dimethyl-1H-benzo[d]imidazol-3-ium hydrochloride (me-DFPBICL), 4,4',4"-(benzene-1,3,5-triacyl)tris(1-(4-formylbenzyl)-4H-imidazol-1-ium) hydrochloride (TBFPICL), 1,1'-bis(4-formylphenyl)-[4,4'-bipyridine]-1,1'-diimide (DFPBPYCL).

5. The method according to claim 1 or 2, characterized in that: The ionic group is a positively charged tertiary ammonium group, or a negatively charged carboxyl group, sulfonic acid group or imidazole group.

6. The method according to claim 1 or 2, characterized in that: The organic solvent is any one of the following: dimethyl sulfoxide (DMSO), N,N'-dimethylformamide (DMF), acetonitrile, dichloromethane (DCM), N-methylpyrrolidone (NMP), ethyl acetate (EA); the acid catalyst is any one of the following: acetic acid, p-toluenesulfonic acid, scandium trifluoromethanesulfonate, trifluoromethanesulfonic acid, trifluoroacetic acid, methanesulfonic acid; the molar ratio of the added amount of the acid catalyst to the amino group, hydrazide or aldehyde group is 1:0.3 to 3000.

7. The method according to claim 1 or 2, characterized in that: The porous carrier is a porous ultrafiltration base membrane made of any one of the following materials: polyacrylonitrile (PAN), polyetheretherketone (PEEK), polysulfone (PSF), polyethersulfone (PES), polyvinylidene fluoride (PVDF), aluminum oxide (Al2O3); the pore size range of the porous ultrafiltration base membrane is 1.5 to 200 nm.

8. The method according to claim 1 or 2, characterized in that: Amines, hydrazides, aldehyde monomers or acid catalysts are dissolved in organic solvents respectively to obtain corresponding solutions for the reaction of synthesizing COF nanosheets; wherein the concentration of the amine or hydrazide solution is 0.1-15 mmol / L; the concentration of the aldehyde solution is 0.1-10 mmol / L; the concentration of the acid catalyst solution is 0.01-5 mmol / L; the thickness of the COF nanosheets obtained by the synthesis reaction is 1.2-9.7 nm.

9. The method according to claim 1 or 2, characterized in that: The concentration and dosage of the two COF nanosheet aqueous solutions are controlled so that the thickness of the COF separation layer in the final COF bipolar membrane is 100nm-3μm and the pore size is 0.5-2nm.

10. Use of the COF bipolar membrane prepared by the method of claim 1 or 2 in separating and recovering hydrochloric acid from waste acid solution.

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