Monovalent selective cation exchange membrane containing covalent organic framework modified layer as well as preparation method and application of monovalent selective cation exchange membrane

Abstract

The invention discloses a monovalent selective cation exchange membrane containing a covalent organic framework modified layer as well as a preparation method and application of the monovalent selective cation exchange membrane. The preparation method comprises the following steps: (1) dissolving an ethidium bromide monomer and a catalyst in deionized water to obtain a water-phase solution; (2) dissolving an aldehyde monomer in an organic solvent to obtain an organic phase solution; and (3) immersing the sulfonated polyetheretherketone base membrane into the water phase solution, taking out the sulfonated polyetheretherketone base membrane, blow-drying water drops on the surface of the membrane, then immersing the sulfonated polyetheretherketone base membrane into the organic phase solution, taking out the sulfonated polyetheretherketone base membrane, and naturally airing to obtain the monovalent selective cation exchange membrane containing the covalent organic framework modified layer. The invention provides application of the monovalent selective cation exchange membrane containing the covalent organic framework modified layer in electrodialysis separation of monovalent and multivalent cations. Under the condition of ensuring that monovalent ions of the membrane have relatively high permeation flux, the membrane surface resistance is small, the tensile strength of the membrane is improved, the water absorption rate of the membrane is reduced, and the monovalent and multivalent selectivity of the membrane is remarkably improved.

Description

Technical Field

[0001] The invention relates to the field of high molecular polymer materials, and in particular to a monovalent selective cation exchange membrane containing a covalent organic framework modified layer, and a preparation method and application thereof. Background Art

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

[0003] Generally, ordinary ion exchange membranes can only separate different charged ions. For example, conventional cation exchange membranes can only simultaneously pass monovalent cations (such as Na + , K + , Li + ), divalent cations (such as Ca 2+ Mg 2+ ) and trivalent cations (such as Al 3+ ) and other cations of different valences, while the monovalent ion selective cation exchange membrane will preferentially pass monovalent cations and prevent the penetration of most divalent or higher valent cations.

[0004] The screening mechanism of monovalent ion selective ion exchange membranes is mainly the size screening effect and the Donnan effect. The size screening effect refers to the fact that the surface selective layer of the separation membrane with a smaller pore size can screen hydrated ions with different radii. The Donnan effect refers to the fact that after constructing a surface selective layer with opposite charges on the membrane, monovalent and multivalent ions can be effectively separated. (ACS Applied Materials & Interfaces 11 (2019) 17730-17741)

[0005] However, although constructing a surface selective layer with opposite charges on the membrane can improve the membrane's permeability selectivity and increase the permeability 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, and a preparation method and application thereof.

[0007] In order to solve the above technical problems, the present invention adopts the following technical solutions:

[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) preparing an aqueous solution: dissolving ethidium bromide monomer and a catalyst in deionized water to obtain an aqueous solution, wherein the catalyst is one of glacial acetic acid and toluenesulfonic acid;

[0010] (2) preparing an organic phase solution: dissolving the aldehyde monomer in an organic solvent to obtain an organic phase solution;

[0011] (3) Interfacial polymerization reaction: immerse the sulfonated polyetheretherketone-based membrane into the aqueous solution prepared in step (1), take it out and blow dry the water droplets on the membrane surface, then immerse it into the organic solution prepared in step (2), take it out and air-dry it naturally, and obtain a monovalent selective cation exchange membrane containing a covalent organic framework modified layer.

[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 a structure shown in formula (I):

[0013]

[0014] Preferably, in step (1), in the aqueous solution, the concentration of ethidium bromide 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 trimesaldehyde and 1,3,5-trialdehyde phloroglucinol, and the organic solvent is at least one of dichloromethane, n-hexane, and ethanol. Further preferably, in step (2), the aldehyde monomer concentration in the organic phase solution is 0.05 to 0.3M.

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

[0017] In the present invention, the sulfonated polyetheretherketone base membrane can be obtained by the following method:

[0018] (a) Sulfonation of polyetheretherketone:

[0019] Add polyetheretherketone powder and concentrated sulfuric acid in a certain proportion to a reaction vessel, stir mechanically at a certain temperature to dissolve, then pour the solution into deionized water to obtain a solid, wash it repeatedly with deionized water until it is neutral, and dry it to obtain sulfonated polyetheretherketone:

[0020] (b) Preparation of sulfonated polyetheretherketone based membrane:

[0021] The sulfonated polyetheretherketone prepared 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 liquid; the obtained casting liquid is poured on a glass plate, dried at 70 to 200° C. for 12 to 48 hours, and after cooling, the film is peeled off from the glass plate in water to obtain a sulfonated polyetheretherketone base film.

[0022] Preferably, in step (a), the mass volume ratio of the polyetheretherketone 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 polyetheretherketone-based membrane is 1.5 to 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, which is prepared according to the preparation method described in the first aspect.

[0026] In a third aspect, the present invention provides the use of the monovalent selective cation exchange membrane containing a covalent organic framework modified layer described in the second aspect in the electrodialysis separation of monovalent and polyvalent cations.

[0027] In a specific embodiment of the present invention, the monovalent 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 polyetheretherketone based membrane that does not have monovalent or polyvalent selectivity. Under the condition of ensuring that the monovalent ions have a high permeation flux, the membrane surface resistance is small, the tensile strength of the membrane is improved, the water absorption rate of the membrane is reduced, and the monovalent or polyvalent selectivity of the membrane is significantly improved. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 This is the Cl s XPS spectrum of the modified ion exchange membrane prepared in Example 3. It can be seen from the figure that it can be divided into four fitting curves, belonging to C=C or CC (~284.7 eV), CN (~285.5 eV), CO (~286.5 eV) and C=O (~287.9 ​​eV), which 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 brown-red powder EB-TFP prepared in Example 6.

[0031] Specific embodiment

[0032] To further illustrate the technical solution of the present invention, the preferred implementation scheme of the present invention is described below in conjunction with specific examples, but it should be understood that these descriptions are only to further illustrate the features and advantages of the present invention, rather than to limit the claims of the present invention.

[0033] Embodiment 1:

[0034] Sulfonation of polyetheretherketone: Add polyetheretherketone powder and concentrated sulfuric acid in a mass volume ratio of 1g:20mL into a round-bottom flask, stir mechanically to dissolve at 50°C, pour the solution into deionized water to obtain a white solid, and repeatedly wash with deionized water until neutral, and dry to obtain a sulfonated polyetheretherketone polymer.

[0035] Preparation of sulfonated polyetheretherketone: Take 15g of sulfonated polyetheretherketone polymer and use 100mLNMP to dissolve it to obtain a solution with a mass fraction of 15%, and use a sand core funnel to filter and degas to obtain a casting liquid. The obtained casting liquid is poured on a glass plate and dried at 80°C for 24h. After cooling, the membrane is peeled off from the glass plate in water to obtain a sulfonated polyetheretherketone base membrane.

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

[0037] Embodiment 2:

[0038] Sulfonation of polyetheretherketone: The sulfonated polyetheretherketone polymer was prepared by the same preparation process as in Example 1.

[0039] Preparation of sulfonated polyetheretherketone: The sulfonated polyetheretherketone base membrane was prepared by the same preparation process as in Example 1.

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

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

[0042] Interfacial polymerization reaction: immerse the sulfonated polyetheretherketone-based membrane in the prepared aqueous phase solution for 10 minutes, take it out and blow dry the water droplets on the membrane surface, then immerse it in the prepared organic phase solution for 10 minutes, take it out and air-dry it naturally to obtain the modified ion exchange membrane.

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

[0044] Embodiment 3:

[0045] Sulfonation of polyetheretherketone: The sulfonated polyetheretherketone polymer was prepared by the same preparation process as in Example 1.

[0046] Preparation of sulfonated polyetheretherketone: The sulfonated polyetheretherketone base membrane was prepared by the same preparation process as in Example 1.

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

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

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

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

[0051] Embodiment 4:

[0052] Sulfonation of polyetheretherketone: The sulfonated polyetheretherketone polymer was prepared by the same preparation process as in Example 1.

[0053] Preparation of sulfonated polyetheretherketone: The sulfonated polyetheretherketone base membrane was prepared by the same preparation process as in Example 1.

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

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

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

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

[0058] Embodiment 5:

[0059] Sulfonation of polyetheretherketone: The sulfonated polyetheretherketone polymer was prepared by the same preparation process as in Example 1.

[0060] Preparation of sulfonated polyetheretherketone: The sulfonated polyetheretherketone base membrane was prepared by the same preparation process as in Example 1.

[0061] Prepare the 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 adopted, except that 5.4 mmol of 1,3,5-trialdehyde phloroglucinol monomer was dissolved in 20 mL of dichloromethane to obtain an organic phase solution.

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

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

[0065] Example 6

[0066] In order to verify the modified layer structure, the following experiments are provided:

[0067] 2,4,6-trialdehyde pyrogallol (63 mg, 0.3 mmol), ethidium bromide (177.32 mg, 0.45 mmol), 1.5 mL of m-xylene, 1.5 mL of 1,4-dioxane and 0.5 mL of 3M acetic acid aqueous solution were added to the hydrothermal reactor. The mixture was ultrasonicated for 10 minutes to obtain a uniform dispersion. The reactor was then sealed and heated at 120°C for 3 days. The brown precipitate formed was collected by centrifugation and washed repeatedly with deionized water for 10-15 times. The collected powder was then purified by Soxhlet extraction using a series of solvents such as acetone, tetrahydrofuran and methanol. The obtained solid was vacuum dried at 100°C for 24 hours to obtain a brown-red powder EB-TFP, the TEM image of which is shown in the figure. Figure 2 shown. Figure 2It can be proved that the obtained EB-TFP is a ring structure with holes.

[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 comprises the following steps: (1) preparing an aqueous solution: dissolving ethidium bromide monomer and a catalyst in deionized water to obtain an aqueous solution, wherein the catalyst is one of glacial acetic acid and toluenesulfonic acid; (2) preparing an organic phase solution: dissolving the aldehyde monomer in an organic solvent to obtain an organic phase solution; (3) Interfacial polymerization reaction: immerse the sulfonated polyetheretherketone-based membrane into the aqueous solution prepared in step (1), take it out and blow dry the water droplets on the membrane surface, then immerse it into the organic solution prepared in step (2), take it out and air-dry it naturally, and 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 (1), in the aqueous solution, the concentration of ethidium bromide is 0.1-0.4M, and the concentration of the catalyst is 0.5-0.7M.

3. The preparation method according to claim 1, characterized in that: In step (2), the aldehyde monomer is one of trimesaldehyde and 1,3,5-trialdehyde phloroglucinol, and the organic solvent is at least one of dichloromethane, n-hexane, and ethanol.

4. The preparation method according to claim 3, characterized in that: In step (2), the concentration of aldehyde monomer in the organic phase solution is 0.05-0.3M.

5. The preparation method according to claim 1, characterized in that: In step (3), the immersion time in the aqueous solution and the organic solution is respectively 10 to 30 minutes.

6. The preparation method according to claim 5, characterized in that: In step (3), the immersion time in the aqueous solution and the organic solution is 10 min respectively.

7. The preparation method according to claim 1, characterized in that: The ion exchange capacity of the sulfonated polyetheretherketone based membrane is 1.5 to 2.0 mmol·g -1 .

8. A monovalent selective cation exchange membrane containing a covalent organic framework modified layer obtained according to the preparation method of any one of claims 1 to 7.

9. Use of the monovalent selective cation exchange membrane containing a covalent organic framework modified layer as claimed in claim 8 in electrodialysis separation of monovalent and polyvalent cations.

10. The use according to claim 9, characterized in that: The monovalent cation is Li + and Mg 2+ .

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