A monovalent selective cation exchange membrane containing a covalent organic framework modified layer and a preparation method and application thereof

Abstract

The application discloses a kind of monovalent selective cation exchange membrane containing covalent organic framework modification layer and preparation method and application thereof.The preparation method comprises the following steps: (1) ethidium bromide monomer, catalyst is dissolved in deionized water to obtain aqueous solution;(2) aldehyde monomer is dissolved in organic solvent, to obtain organic phase solution;(3) sulfonated polyether ether ketone-based film is immersed into aqueous solution, after taking out, film surface water droplet is blown dry, then immersed into organic phase solution, take out and air dry, obtain monovalent selective cation exchange membrane containing covalent organic framework modification layer.The application provides the application of the monovalent selective cation exchange membrane containing covalent organic framework modification layer in electrodialysis separation single multivalent cation.Under the condition of ensuring that the monovalent ion of the membrane has higher permeation flux, the membrane surface resistance is small, the tensile strength of the membrane is improved, the water absorption of the membrane is reduced, and the single multivalent selection performance of the membrane is significantly improved.

Description

Technical Field

[0001] This invention relates to the field of polymer materials, specifically to a monovalent selective cation exchange membrane containing a covalent organic framework modified layer, its preparation method, and its application. Background Technology

[0002] Ion exchange membranes (IEMs) are typically composed of a hydrophobic polymer matrix, fixed charged ion exchange groups, and mobile counterions. Since the last century, ion exchange membranes have been widely used as a new type of ion separation material in seawater desalination, environmental protection, resource recovery and energy production[4], which has attracted widespread attention (Chinese Journal of Chemical Engineering 25 (2017) 1606-1615).

[0003] Typically, ordinary ion exchange membranes can only separate different charged ions. For example, conventional cation exchange membranes, driven by a DC electric field, can only simultaneously allow monovalent cations (such as Na+) to pass through indiscriminately. + K + Li + ), divalent cations (such as Ca) 2+ Mg 2+ ) and trivalent cations (such as Al) 3+ Cations of different valence states, such as monovalent ions, can pass through a selective cation exchange membrane. Monovalent ions will preferentially allow monovalent ions to pass through, while blocking most divalent or higher valence ions.

[0004] The sieving mechanism of monovalent ion-selective ion exchange membranes mainly consists of the size sieving effect and the Donnan effect. The size sieving effect refers to the ability of a surface selective layer with a small pore size to sieve hydrated ions of different radii. The Donnan effect refers to the effective separation of monovalent and polyvalent ions by constructing a surface selective layer with opposite charges on the membrane. (ACS Applied Materials & Interfaces 11 (2019) 17730-17741)

[0005] However, while constructing a surface selectivity layer with opposite charges on the membrane can improve the membrane's permeation selectivity and increase the permeation flux of monovalent ions, it also brings about the problem of high membrane surface resistance. Summary of the Invention

[0006] In view of this, the present invention provides a monovalent selective cation exchange membrane containing a covalent organic framework modified layer, its preparation method and application.

[0007] To solve the above-mentioned technical problems, the present invention adopts the following technical solution:

[0008] In a first aspect, the present invention provides a method for preparing a monovalent selective cation exchange membrane containing a covalent organic framework modified layer, comprising the following steps:

[0009] (1) Preparation of aqueous solution: Ethidium bromide monomer and catalyst are dissolved in deionized water to obtain an aqueous solution, wherein the catalyst is one of glacial acetic acid and toluenesulfonic acid;

[0010] (2) Preparation of organic phase solution: Dissolve the aldehyde monomer in an organic solvent to obtain an organic phase solution;

[0011] (3) Interfacial polymerization reaction: The sulfonated polyether ether ketone-based membrane is immersed in the aqueous solution prepared in step (1), and after being taken out, the water droplets on the membrane surface are dried. Then it is immersed in the organic solution prepared in step (2), and after being taken out and air-dried, a monovalent selective cation exchange membrane containing a covalent organic framework modified layer is obtained.

[0012] According to the literature (Angewandte Chemie International Edition (2018) 8443-8447) and the experimental evidence of the present invention, the modified layer on the surface of the monovalent selective cation exchange membrane generates the structure shown in formula (I):

[0013]

[0014] Preferably, in step (1), the concentration of ethidium bromide in the aqueous solution is 0.1-0.4M, and the concentration of the catalyst is 0.5-0.7M.

[0015] Preferably, in step (2), the aldehyde monomer is one of phorbolaldehyde and 1,3,5-trialdehyde phloroglucinol, and the organic solvent is at least one of dichloromethane, n-hexane, and ethanol. More preferably, in step (2), the concentration of the aldehyde monomer in the organic phase solution is 0.05–0.3 M.

[0016] Preferably, in step (3), the soaking time in the aqueous solution and the organic solution is 10 to 30 minutes, more preferably 10 minutes.

[0017] In this invention, the sulfonated polyether ether ketone-based film can be obtained in the following manner:

[0018] (a) Sulfonation of polyetheretherketone:

[0019] Polyether ether ketone powder and concentrated sulfuric acid were added to a reaction vessel in a certain proportion and dissolved by mechanical stirring at a certain temperature. The solution was then poured into deionized water to obtain a solid, which was repeatedly washed with deionized water until neutral and dried to obtain sulfonated polyether ether ketone.

[0020] (b) Preparation of sulfonated polyether ether ketone-based films:

[0021] The sulfonated polyether ether ketone obtained in step (a) is dissolved in an organic solvent to obtain a solution with a mass fraction of 10% to 15%, and then filtered and degassed to obtain a casting solution. The obtained casting solution is poured onto a glass plate and dried at 70 to 200°C for 12 to 48 hours. After cooling, the membrane is peeled off from the glass plate in water to obtain the sulfonated polyether ether ketone-based membrane.

[0022] Preferably, in step (a), the mass-to-volume ratio of the polyether ether ketone to concentrated sulfuric acid is 1 g: 20 mL, and the heating reaction time is 4 to 12 h.

[0023] Preferably, the ion exchange capacity of the sulfonated polyether ether ketone-based membrane is 1.5–2.0 mmol·g. -1 .

[0024] Preferably, in step (b), the organic solvent is one or more of DMF, DMAc, and NMP.

[0025] In a second aspect, the present invention provides a monovalent selective cation exchange membrane containing a covalent organic framework modified layer, prepared according to the preparation method described in the first aspect.

[0026] Thirdly, the present invention provides the application of the monovalent selective cation exchange membrane containing a covalent organic framework modified layer as described in the second aspect in the electrodialysis separation of monovalent and multivalent cations.

[0027] In a specific embodiment of the present invention, the monovalent or polyvalent cation is Li. + and Mg 2+ .

[0028] Compared with the prior art, the beneficial effects of the present invention are as follows: The monovalent selective cation exchange membrane containing a covalent organic framework modified layer provided by the present invention introduces a covalent organic framework modified layer on the surface of a sulfonated polyether ether ketone-based membrane that does not have monovalent or multivalent selectivity. Under the condition of ensuring that monovalent ions have a high permeation flux, the membrane surface resistance is low, the tensile strength of the membrane is improved, the water absorption rate of the membrane is reduced, and the monovalent or multivalent selectivity of the membrane is significantly improved. Attached Figure Description

[0029] Figure 1 The figure shows the Cl s XPS spectrum of the modified ion exchange membrane prepared in Example 3. As can be seen from the figure, it can be divided into four fitting curves, which belong to C=C or CC (~284.7eV), CN (~285.5eV), CO (~286.5eV) and C=O (~287.9eV), respectively. They correspond one-to-one with the structure of formula (I), indicating the successful preparation of the COF modified layer.

[0030] Figure 2 This is a TEM image of the brownish-red powder EB-TFP prepared in Example 6.

[0031] Specific implementation methods

[0032] To further illustrate the technical solution of the present invention, the preferred embodiments of the present invention are described below in conjunction with specific examples. However, it should be understood that these descriptions are only for further illustrating the features and advantages of the present invention, and not for limiting the claims of the present invention.

[0033] Example 1:

[0034] Sulfonation of polyetheretherketone: Polyetheretherketone powder and concentrated sulfuric acid were added to a round-bottom flask at a mass-volume ratio of 1g:20mL and mechanically stirred at 50℃ to dissolve. The solution was poured into deionized water to obtain a white solid, which was repeatedly washed with deionized water until neutral and then dried to obtain sulfonated polyetheretherketone polymer.

[0035] Preparation of sulfonated polyether ether ketone: 15g of sulfonated polyether ether ketone polymer was dissolved in 100mL of NMP to prepare a 15% mass fraction solution. The solution was then filtered using a sintered glass funnel and degassed to obtain a casting solution. The casting solution was poured onto a glass plate and dried at 80℃ for 24h. After cooling, the membrane was peeled off the glass plate in water to obtain the sulfonated polyether ether ketone base membrane.

[0036] The sheet resistivity of the prepared sulfonated polyether ether ketone ion exchange membrane, as measured experimentally using national standard methods, is 2.23 Ω·cm. 2 The tensile strength is 31.2 MPa, the water swelling rate is 25.1%, and the ion exchange capacity is 1.81 mmol·g. -1 The ion flux of electrodialysis (initial solution in the concentration chamber: a mixed solution of 0.05 M LiCl and MgCl2) was 10.32 × 10⁻⁶. -8 mol·cm -2 ·s -1 The selectivity was 0.21. (For specific test methods, please refer to the literature report: ACS Applied materials & Interfaces 16(2024), 18019-18029).

[0037] Example 2:

[0038] Sulfonation of polyether ether ketone: Sulfonated polyether ether ketone polymers were prepared using the same preparation process as in Example 1.

[0039] Preparation of sulfonated polyether ether ketone: Sulfonated polyether ether ketone base film was prepared using the same preparation process as in Example 1.

[0040] Preparation of aqueous solution: Dissolve 2.7 mmol ethidium bromide monomer and 2 mL 6M glacial acetic acid in 18 mL deionized water to obtain an aqueous solution.

[0041] Preparation of organic phase solution: Dissolve 1.8 mmol of 1,3,5-trialdehyde phloroglucinol monomer in 20 mL of dichloromethane to obtain organic phase solution.

[0042] Interfacial polymerization reaction: The sulfonated polyether ether ketone-based membrane was immersed in the prepared aqueous solution for 10 min, removed and dried by blowing off water droplets on the membrane surface, and then immersed in the prepared organic solution for 10 min. After removal and air drying, the modified ion exchange membrane was obtained.

[0043] The sheet resistivity of the modified ion exchange membrane, as measured experimentally using national standard methods, is 4.73 Ω·cm. 2 The tensile strength is 39.2 MPa, the water swelling rate is 20.1%, and the ion exchange capacity is 1.78 mmol·g. -1 The ion flux of electrodialysis (initial solution in the concentration chamber: a mixed solution of 0.05M LiCl and MgCl2) was 8.64 × 10⁻⁶. -8 mol·cm -2 ·s -1 The selectivity was 10.72. (For specific test methods, please refer to the literature report: ACS Applied materials & Interfaces 16(2024), 18019-18029).

[0044] Example 3:

[0045] Sulfonation of polyether ether ketone: Sulfonated polyether ether ketone polymers were prepared using the same preparation process as in Example 1.

[0046] Preparation of sulfonated polyether ether ketone: Sulfonated polyether ether ketone base film was prepared using the same preparation process as in Example 1.

[0047] Preparation of aqueous solution: The same preparation process as in Example 2 was used, except that 5.4 mmol ethidium bromide monomer and 2 mL 6M glacial acetic acid were dissolved in 18 mL deionized water to obtain an aqueous solution.

[0048] Preparation of organic phase solution: The same preparation process as in Example 2 was used, except that 3.6 mmol of 1,3,5-trialdehyde phloroglucinol monomer was dissolved in 20 mL of dichloromethane to obtain organic phase solution.

[0049] Interfacial polymerization reaction: The modified ion exchange membrane was obtained using the same preparation process as in Example 2.

[0050] The sheet resistivity of the modified ion exchange membrane, as measured experimentally using national standard methods, is 8.46 Ω·cm. 2 The tensile strength is 43.5 MPa, the water swelling rate is 13.7%, and the ion exchange capacity is 1.64 mmol·g. -1 The ion flux of electrodialysis (initial solution in the concentration chamber: a mixed solution of 0.05 M LiCl and MgCl2) was 6.21 × 10⁻⁶. -8 mol·cm -2 ·s -1 The selectivity was 13.55. (For specific test methods, please refer to the literature report: ACS Applied materials & Interfaces 16(2024), 18019-18029).

[0051] Example 4:

[0052] Sulfonation of polyether ether ketone: Sulfonated polyether ether ketone polymers were prepared using the same preparation process as in Example 1.

[0053] Preparation of sulfonated polyether ether ketone: Sulfonated polyether ether ketone base film was prepared using the same preparation process as in Example 1.

[0054] Preparation of aqueous solution: The same preparation process as in Example 3 was used, except that 7.2 mmol ethidium bromide monomer and 2 mL 6M glacial acetic acid were dissolved in 18 mL deionized water to obtain an aqueous solution.

[0055] Preparation of organic phase solution: The organic phase solution was prepared using the same preparation process as in Example 3.

[0056] Interfacial polymerization reaction: The modified ion exchange membrane was obtained using the same preparation process as in Example 3.

[0057] The sheet resistivity of the modified ion exchange membrane, as measured experimentally using national standard methods, is 10.43 Ω·cm. 2 The tensile strength is 40.7 MPa, the water swelling rate is 16.2%, and the ion exchange capacity is 1.43 mmol·g. -1 The ion flux of electrodialysis (initial solution in the concentration chamber: a mixed solution of 0.05M LiCl and MgCl2) was 5.77 × 10⁻⁶. -8 mol·cm -2 ·s -1 The selectivity was 17.28. (For specific test methods, please refer to the literature report: ACS Applied materials & Interfaces 16(2024), 18019-18029)

[0058] Example 5:

[0059] Sulfonation of polyether ether ketone: Sulfonated polyether ether ketone polymers were prepared using the same preparation process as in Example 1.

[0060] Preparation of sulfonated polyether ether ketone: Sulfonated polyether ether ketone base film was prepared using the same preparation process as in Example 1.

[0061] Preparation of aqueous solution: The aqueous solution was prepared using the same preparation process as in Example 3.

[0062] Preparation of organic phase solution: The same preparation process as in Example 3 was used, except that 5.4 mmol of 1,3,5-trialdehyde phloroglucinol monomer was dissolved in 20 mL of dichloromethane to obtain organic phase solution.

[0063] Interfacial polymerization reaction: The modified ion exchange membrane was obtained using the same preparation process as in Example 3.

[0064] The sheet resistivity of the modified ion exchange membrane, as measured experimentally using national standard methods, is 10.73 Ω·cm. 2 The tensile strength is 47.3 MPa, the water swelling rate is 10.8%, and the ion exchange capacity is 1.57 mmol·g. -1 The ion flux of electrodialysis (initial solution in the concentration chamber: a mixed solution of 0.05 M LiCl and MgCl2) was 5.91 × 10⁻⁶. -8 mol·cm -2 ·s -1 The selectivity was 15.168. (For specific test methods, please refer to the literature report: ACS Applied materials & Interfaces 16(2024), 18019-18029)

[0065] Example 6

[0066] To verify the modified layer structure, the following experiment is provided:

[0067] 2,4,6-Trialdehyde phloroglucinol (63 mg, 0.3 mmol), ethidium bromide (177.32 mg, 0.45 mmol), 1.5 mL m-xylene, 1.5 mL 1,4-dioxane, and 0.5 mL 3M acetic acid aqueous solution were added to a hydrothermal reactor. The mixture was sonicated for 10 minutes to obtain a homogeneous dispersion. The reactor was then sealed and heated at 120 °C for 3 days. The resulting brown precipitate was collected by centrifugation and washed repeatedly with deionized water 10-15 times. The collected powder was then purified by Soxhlet extraction using a series of solvents including acetone, tetrahydrofuran, and methanol. The obtained solid was dried under vacuum at 100 °C for 24 hours to obtain a brownish-red powder, EB-TFP. A TEM image of this powder is shown below. Figure 2 As shown. Figure 2It can be proven that the obtained EB-TFP is a porous ring structure.

[0068] Table 1

[0069]

Claims

1. A method for preparing a monovalent selective cation exchange membrane containing a covalent organic framework modified layer, characterized in that: The preparation method includes the following steps: (1) Preparation of aqueous solution: Ethidium bromide monomer and catalyst are dissolved in deionized water to obtain an aqueous solution, wherein the catalyst is one of glacial acetic acid and toluenesulfonic acid; in the aqueous solution, the concentration of ethidium bromide is 0.1-0.4 M and the concentration of catalyst is 0.5-0.7 M; (2) Preparation of organic phase solution: Dissolve the aldehyde monomer in an organic solvent to obtain an organic phase solution; the aldehyde monomer is one of phorbol m-phenyleneformaldehyde and 1,3,5-trialdehyde phloroglucinol; the concentration of the aldehyde monomer in the organic phase solution is 0.05-0.3M; (3) Interfacial polymerization reaction: The sulfonated polyether ether ketone (PEEK) membrane is immersed in the aqueous solution prepared in step (1), wherein the ion exchange capacity of the sulfonated PEEK membrane is 1.5~2.0 mmol·g. -1 The membrane is soaked in an aqueous solution for 10 to 30 minutes. After removing it, the water droplets on the membrane surface are dried. Then it is immersed in the organic phase solution prepared in step (2) for 10 to 30 minutes. After removing it, it is air-dried to obtain a monovalent selective cation exchange membrane containing a covalent organic framework modified layer.

2. The preparation method according to claim 1, characterized in that: In step (2), the organic solvent is at least one of dichloromethane, n-hexane, and ethanol.

3. The preparation method according to claim 1, characterized in that: In step (3), the soaking time in the aqueous solution and the organic solution is 10 min, respectively.

4. A monovalent selective cation exchange membrane containing a covalent organic framework modified layer, prepared by the preparation method according to any one of claims 1-3.

5. The application of the monovalent selective cation exchange membrane containing a covalent organic framework modified layer as described in claim 4 in the electrodialysis separation of monovalent and polyvalent cations.

6. The application as described in claim 5, characterized in that: The monovalent or polyvalent cation is Li + and Mg 2+ .

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