Preparation method of crown ether polymer containing carboxyl and PEO and lithium ion selective positive membrane

Abstract

The invention discloses a preparation method of a crown ether polymer containing carboxyl and PEO and a lithium ion selective cation membrane, and belongs to the technical field of preparation of selective electrodialysis cation exchange membranes. According to the invention, specific selection of lithium ions is realized through complexation of crown ether and alkali metal; a hydrophilic group carboxyl is introduced, so that a hydrogen bond network is constructed in the polymer, and a lithium ion selective transmission channel is constructed; meanwhile, carboxyl is dissociated into-COO <-> under the action of an electric field, so that the polymer is negatively charged, the passing of monovalent and divalent cations is promoted, and the highest lithium-magnesium selectivity can reach 200. PEO is introduced, so that lithium ion transmission sites are further increased, and establishment of a lithium ion selective transmission channel is promoted; and PEO may form a hydrogen bond network with an amide group or a carboxylic acid group to improve the intermolecular force and the coordination effect of a C-O-C bond on a PEO side chain and lithium ions to promote further improvement of the lithium-magnesium permeation selectivity, the highest selectivity can reach 577, and the trade-off effect is broken through.

Description

Technical Field

[0001] The present invention belongs to the technical field of the preparation of cation exchange membranes for selective electrodialysis, and particularly relates to a crown ether polymer containing carboxyl and PEO and a preparation method of a lithium ion selective cation membrane. Background Art

[0003] At present, the enrichment and separation technologies of lithium in salt lake brine mainly include chemical precipitation method, solvent extraction method, adsorption method and membrane separation method. The chemical precipitation method and the solvent extraction method require a large amount of chemical solvents, while the adsorption method usually requires complex post-treatment procedures. In contrast, the membrane separation technology is more clean and environmentally friendly, has a small floor area, can operate continuously, and is easy to operate on a large scale. However, the separation of lithium by membrane method usually utilizes the particle size screening effect or charge repulsion of a specific membrane, and the separation efficiency is extremely vulnerable to the influence of interfering ions. In addition, the trade-off effect between the selectivity and permeability of the cation exchange membrane is also a major problem that needs to be solved urgently.

[0004] Therefore, there is an urgent need to design a selective ion exchange membrane with the function of specifically recognizing lithium ions. Summary of the Invention

[0005] Aiming at the problems of difficult lithium-magnesium separation and low separation efficiency, the present invention provides a crown ether polymer containing carboxyl and PEO and a preparation method of a lithium ion selective cation membrane.

[0006] To solve the above technical problems, the present invention adopts the following technical solutions:

[0007] A crown ether polymer containing carboxyl, the structural formula of which is as follows:

[0008]

[0009] Wherein: x is the degree of functionalization; 0 < x ≤ 1.

[0010] A preparation method of a crown ether polymer containing carboxyl, comprising the following steps:

[0011] Step 1, at room temperature, an aromatic monomer containing a crown ether ring and a ketone monomer are dispersed in dichloromethane in a certain proportion to obtain a mixed solution;

[0012] The aromatic monomer containing a crown ether ring is

[0013] The ketone monomer is one or two of the following monomers:

[0014]

[0015] Step 2: At 0 °C, trifluoroacetic acid and trifluoromethanesulfonic acid were added to the mixed solution obtained in Step 1, and the mixture was reacted for 1 - 2 h to obtain a viscous mixed solution. The obtained viscous mixed solution was poured into a poor solvent to obtain a fibrous product. The fibrous product was soaked in deionized water, washed thoroughly, filtered, and dried to obtain a carboxyl-containing crown ether polymer.

[0016] Furthermore, the molar ratio of the aromatic monomer containing a crown ether ring to the ketone monomer is 1:1.1.

[0017] Furthermore, the volume ratio of dichloromethane, trifluoroacetic acid, and trifluoromethanesulfonic acid is 1.3 - 1.4:1.3 - 1.4:1.

[0018] Furthermore, the poor solvent is methanol, ethanol, or deionized water.

[0019] The carboxyl-containing and poly(ethylene oxide) (PEO)-containing crown ether polymer has the following structural formula:

[0020]

[0021] Wherein: m is the number of repeating units of -O-CH2-CH2-, 2 ≤ m ≤ 7; Y and Z are the functionalization degrees of carboxyl and PEO, respectively.

[0022] A method for preparing a carboxyl-containing and poly(ethylene oxide) (PEO)-containing crown ether polymer, using the carboxyl-containing crown ether polymer described above, includes the following steps:

[0023] Step 1: The carboxyl-containing crown ether polymer was dissolved in an organic solvent at 60 °C to obtain a solution with a mass-to-volume ratio of 5 - 10%.

[0024] Step 2: An acid amide condensing agent was added to the solution and reacted for 3 h. Then, poly(ethylene oxide) (PEO) monomer was added and reacted for 3 h.

[0025] Step 3: After the reaction was completed, the reaction solution was cooled to room temperature and then poured into a precipitating agent to obtain a white granular product. The final product was soaked in a potassium carbonate solution, then soaked in a hydrochloric acid solution, and then washed with deionized water until neutral to obtain a carboxyl-containing and poly(ethylene oxide) (PEO)-containing crown ether polymer.

[0026] Furthermore, the organic solvent is N-methylpyrrolidone or dimethyl sulfoxide.

[0027] Furthermore, the ratio of poly(ethylene oxide) (PEO) to COOH is 1:2.

[0028] Furthermore, the acid amide condensing agent is N,N'-carbonyldiimidazole.

[0029] Further, the precipitating agent is a mixed solution of ethanol and deionized water.

[0030] The preparation method of the lithium ion selective cationic membrane comprises the following steps: dissolving the crown ether polymer containing carboxyl or the crown ether polymer containing carboxyl and polyethylene oxide (PEO) in an organic solvent respectively to obtain a transparent and homogeneous casting solution; casting the casting solution on a glass plate, drying to form a film at a certain temperature, and then immersing it in deionized water to make the film fall off from the mold, so as to obtain the lithium ion selective cationic membrane.

[0031] Further, the organic solvent is N-methylpyrrolidone or dimethyl sulfoxide.

[0032] Further, the mass concentration of the casting solution is 0.05-0.10 g / mL.

[0033] Further, the temperature for drying to form a film is 60-80 °C, and the time is 24 hours.

[0034] Compared with the prior art, the present invention has the following advantages:

[0035] In the present invention, dibenzo-18-crown-6 ether (DB18C6) and a ketone monomer are selected to prepare a series of crown ether polymers containing carboxyl through a superacid-catalyzed polymerization reaction. Through the synergistic effect of DB18C6 and -COOH groups, an ordered lithium ion transport channel is formed to construct a hydrogen bond network. The lithium ion selective cationic membrane prepared thereby shows excellent performance in electrodialysis tests. Taking the crown ether polymer with a side chain carboxylic acid content of 40% as an example, the Li + / Mg 2+ permeation selectivity of the prepared lithium ion selective cationic membrane can reach 200.66, and the lithium ion flux reaches 1.78×10 -8 mol·cm -2 ·s -1 , achieving a double improvement in flux and selectivity and solving the trade-off effect between permeability and selectivity common in ion exchange membranes. Introducing the hydrophilic segment PEO into the crown ether polymer containing carboxyl increases the lithium ion transport sites, thereby promoting the passage of lithium ions through the ion exchange membrane; increasing the hydrophilic region makes its microphase separation structure more obvious and promotes the establishment of the lithium ion transport channel; and PEO may form a hydrogen bond network with amide groups or carboxylic acid groups, and the coordination of C-O-C bonds on the PEO side chain with lithium ions promotes a further improvement in lithium-magnesium selectivity and permeability. The Li + / Mg 2+ permeation selectivity can reach 577, and the lithium ion flux can reach 1.81×10 -8 mol·cm -2 ·s -1 .

[0036] The present invention mainly provides a preparation method of a crown ether polymer with a crown ether ring in the main chain and carboxyl and PEO in the side chain. The preparation method is simple and easy to operate, and the subsequent treatment is relatively clean and environmentally friendly. It does not require the use of a large amount of chemical reagents, and the product has a high purity. Brief Description of the Drawings

[0037] In order to more clearly illustrate the technical solutions in the embodiments of the present application, the following will briefly introduce the drawings required for the description of the embodiments. Obviously, the following drawings are only some embodiments of the present application. For those of ordinary skill in the art, without creative efforts, other drawings can also be obtained based on these drawings.

[0038] Figure 1 It is the nuclear magnetic resonance hydrogen spectrum of the polymer in Example 1.

[0039] Figure 2 It is the nuclear magnetic resonance hydrogen spectrum of the polymer in Example 2.

[0040] Figure 3 It is the nuclear magnetic resonance hydrogen spectrum of the polymer in Example 3.

[0041] Figure 4 It is the nuclear magnetic resonance hydrogen spectrum of the polymer in Example 4.

[0042] Figure 5 It is the water absorption and swelling diagram of the polymers in Examples 1, 2, 3, and 4. Detailed Description of the Embodiments

[0043] In order to deeply understand the present invention, we will describe it comprehensively and meticulously. However, the present invention has various implementation manners and is not limited to the specific examples listed herein. The presentation of these examples aims to deepen the comprehensive understanding of the disclosed content of the present invention.

[0044] Many specific details are set forth in the following description in order to fully understand the present invention, but the present invention can also be implemented in other ways different from those described herein; obviously, the following embodiments are only used to better understand the technical solutions of the present invention and should not be construed as a limitation of the present invention.

[0045] The present invention provides a specific embodiment of a crown ether polymer containing carboxyl, and its structural formula is as follows:

[0046]

[0047] Wherein: x is the degree of functionalization; 0 < x ≤ 1.

[0048] The present invention also provides a preparation method of the above-mentioned crown ether polymer containing carboxyl, which includes the following steps:

[0049] Step 1, at room temperature, an aromatic monomer containing a crown ether ring and a ketone monomer are dispersed in dichloromethane in a certain ratio to obtain a mixed solution;

[0050] The aromatic monomer containing a crown ether ring is:

[0051] The ketone monomer is one or two of the following monomers:

[0052]

[0053] Step 2, at 0 °C, trifluoroacetic acid and trifluoromethanesulfonic acid are added to the mixed solution obtained in Step 1, and the reaction is carried out for 1 - 2 h to obtain a viscous mixed solution; the obtained viscous mixed solution is poured into a poor solvent to obtain a fibrous product; the fibrous product is soaked in deionized water, washed, filtered, and dried sufficiently to obtain a crown ether polymer containing carboxyl groups;

[0054] The poor solvent is methanol, ethanol, or deionized water;

[0055] The molar ratio of the aromatic monomer containing a crown ether ring to the ketone monomer is 1:1.1.

[0056] The volume ratio of dichloromethane, trifluoroacetic acid, and trifluoromethanesulfonic acid is 1.3 - 1.4:1.3 - 1.4:1.

[0057] In the present invention, the soaking time of the fibrous product in deionized water can be any suitable time, preferably 24 - 96 h. And the soaking temperature of the fibrous product in deionized water can be a temperature higher than room temperature, preferably 50 - 100 °C, more preferably 80 °C.

[0058] The present invention provides a specific embodiment of a crown ether polymer containing carboxyl groups: a crown ether polymer containing carboxyl groups and polyethylene oxide (PEO), and its structural formula is as follows:

[0059]

[0060] Wherein: m is the number of repeating units of -O-CH2-CH2-, 2 ≤ m ≤ 7; Y and Z are the functionalization degrees of carboxyl groups and polyethylene oxide (PEO) respectively.

[0061] The present invention also provides a preparation method of the above-mentioned crown ether polymer containing carboxyl groups and polyethylene oxide (PEO), including the following steps:

[0062] Step 1, dissolve the crown ether polymer containing carboxyl groups in an organic solvent at 60 °C to obtain a solution with a mass-to-volume ratio of 5 - 10%;

[0063] Step 2: Add an acid amide condensing agent to the solution and react for 3 h; then add polyethylene oxide (PEO) monomer and react for 3 h.

[0064] Step 3: After the reaction is completed, cool the reaction solution to room temperature and pour it into a precipitant to obtain a white granular product; soak the final product with a potassium carbonate solution, then soak it with a hydrochloric acid solution, and then wash it with deionized water until neutral to obtain a crown ether polymer containing carboxyl groups and polyethylene oxide (PEO).

[0065] The ratio of the polyethylene oxide (PEO) to COOH is 1:2; the acid amide condensing agent is N,N'-carbonyldiimidazole; the precipitant is a mixed solution of ethanol and deionized water.

[0066] The present invention further provides a method for preparing a lithium ion selective membrane, which comprises the following steps:

[0067] The crown ether polymer containing carboxyl groups or the crown ether polymer containing carboxyl groups and polyethylene oxide is respectively dissolved in an organic solvent to obtain a transparent and homogeneous casting solution; the casting solution is cast on a glass plate and dried into a film at a certain temperature, and then immersed in deionized water to make the film fall off from the mold to obtain a lithium ion selective cationic membrane.

[0068] The organic solvent is N-methylpyrrolidone or dimethyl sulfoxide; the mass concentration of the casting solution is 0.05 - 0.10 g / mL; the temperature for drying into a film is 60 - 80 °C, and the time is 12 - 24 hours.

[0069] Example 1

[0070] In this example, the polymerization monomers are dibenzo-18-crown-6 ether and 2,3-dioxoindoline (isatin), and the structural formulas are as follows:

[0071]

[0072] The preparation method of the above polymer is as follows:

[0073] Step 1: In a dry three-necked flask, add 1.62 g (11 mmol) of 2,3-dioxoindoline (isatin) and 3.68 g (10 mmol) of dibenzo-18-crown-6 ether, and add 8 mL of dichloromethane to the container for dissolution, and stir at 0 °C for 30 min to ensure uniform mixing.

[0074] Step 2: Keep the reaction system in Step 1 at 0 °C, add 8 mL of trifluoroacetic acid to the system, and then gradually add 6 mL of trifluoromethanesulfonic acid dropwise using a constant-pressure dropping funnel. After the addition is complete, stir the reaction for 1 h. As the reaction proceeds, the system becomes increasingly viscous. Slowly pour the highly viscous solution into ethanol, wash it 3 times with deionized water at 80 °C, and soak it for 24 h. Filter the white fibrous polymer and dry it under vacuum at 60 °C for 24 h to obtain a carboxyl-containing crown ether polymer.

[0075] A method for preparing a lithium-ion selective membrane, specifically:

[0076] Dissolve the above carboxyl-containing crown ether polymer in dimethyl sulfoxide, control the mass fraction to be 5 wt%, and obtain a homogeneous solution without insoluble matter. Subsequently, pour this solution onto a clean and horizontally placed glass plate to ensure that the solution can spread evenly. Dry it at 60 °C for 24 h to ensure that the solvent can completely evaporate, and obtain a polymer film with a uniform thickness.

[0077] Perform electrodialysis testing, and test its Li + / Mg 2+ selectivity for the binary mixture through electrodialysis. The dilute chamber is filled with 100 mL of a mixed solution, which is 0.1 M LiCl and 0.1 M MgCl2, and the concentrated chamber is 100 mL of a solution with a concentration of 0.01 M KCl. The electrode chamber is filled with 200 mL of a solution with a concentration of 0.3 M Na2SO4. The effective membrane area between the two electrodes is 9 cm 2 . Turn on the DC power supply to apply a certain current density, run the device for 1 h, turn off the DC power supply, and collect the liquid in the concentrated chamber. Use ICP-OES to measure the collected liquid to determine the contents of lithium ions and magnesium ions.

[0078] The calculation formula is:

[0079] Lithium ion flux:

[0080] Magnesium ion flux:

[0081] Li + / Mg 2+ Selectivity:

[0082] Where: is the change value of the solution concentration before and after the test; V is the volume of the solution in the test chamber; A m is the effective membrane area during the test; t is the test time.

[0083] The hydrophilicity of the membrane was investigated by testing the swelling degree. Before the test, the membrane sample was cut into small flakes with dimensions of 1 cm × 4 cm, and then the membrane flakes were immersed in deionized water at 25 °C. To ensure that the membrane flakes were fully wetted, the immersion time should be 24 h. After that, the water on the surface was wiped off with lint-free paper, and the swelling ratio (SR) of the membrane was measured using the length difference between the dry membrane (L dry ) and the wet membrane (L wet ). The calculation formula is as follows:

[0084] Swelling ratio:

[0085] Example 2

[0086] In this example, the polymerization monomers are dibenzo-18-crown-6 ether, 2,3-diketodihydroindole (isatin), and 2,3-dioxoindoline-7-carboxylic acid. Among them, the content of 2,3-diketodihydroindole (isatin) is 60%, and the content of 2,3-dioxoindoline-7-carboxylic acid is 40% (this ratio represents the percentage of each ketone monomer in the total amount of ketone monomers). The structural formulas are as follows:

[0087]

[0088] The preparation method of the above polymer is as follows:

[0089] Step 1, in a dry three-necked flask, add 0.97 g (6.6 mmol) of 2,3-diketodihydroindole (isatin), 0.88 g (4.4 mmol) of 2,3-dioxoindoline-7-carboxylic acid, and 3.68 g (10 mmol) of dibenzo-18-crown-6 ether. Then add 8 mL of dichloromethane to the container for dissolution, and stir at 0 °C for 30 min to ensure uniform mixing.

[0090] Step 2, keep the reaction system in Step 1 at 0 °C, add 8 mL of trifluoroacetic acid to the system, and then slowly dropwise add 6 mL of trifluoromethanesulfonic acid using a constant pressure dropping funnel. After the addition is complete, stir the reaction for 1 h. As the reaction progresses, the system becomes more and more viscous. Slowly pour the highly viscous solution into ethanol, wash it 3 times with deionized water at 80 °C, and soak it for 24 h. Filter the white fibrous polymer and vacuum dry it at 60 °C for 24 h to obtain a crown ether polymer containing carboxyl groups.

[0091] A preparation method of a lithium ion selective membrane is as follows:

[0092] Dissolve the above carboxyl-containing crown ether polymer in dimethyl sulfoxide, control the mass fraction to be 5 wt%, and obtain a homogeneous solution without insolubles. Subsequently, pour this solution onto a clean and horizontally placed glass plate to ensure that the solution can spread evenly. Dry it at 60 °C for 24 h to ensure that the solvent can completely evaporate, and obtain a polymer film with a uniform thickness.

[0093] Conduct electrodialysis testing, following the steps in Example 1.

[0094] Conduct swelling degree testing, following the steps in Example 1.

[0095] Example 3

[0096] In this example, the polymerization monomers are dibenzo-18-crown-6 ether and 2,3-dioxoindoline-7-carboxylic acid, and the structural formula is as follows:

[0097]

[0098] The preparation method of the above polymer is as follows:

[0099] Step 1, in a dry three-necked flask, add 2.19 g (11 mmol) of 2,3-dioxoindoline-7-carboxylic acid and 3.68 g (10 mmol) of dibenzo-18-crown-6 ether, and add 8 mL of dichloromethane to the container for dissolution. Stir at 0 °C for 30 min to ensure uniform mixing.

[0100] Step 2, keep the reaction system in Step 1 at 0 °C, add 8 mL of trifluoroacetic acid to the system, and then gradually add 6 mL of trifluoromethanesulfonic acid dropwise using a constant-pressure dropping funnel. After the addition is complete, stir and react for 1 h. As the reaction proceeds, the system becomes more and more viscous. Slowly pour the highly viscous solution into ethanol, wash it 3 times with deionized water at 80 °C, and soak it for 24 h. Filter the white fibrous polymer and dry it in vacuo at 60 °C for 24 h to obtain the carboxyl-containing crown ether polymer.

[0101] A preparation method of a lithium ion selective membrane, specifically:

[0102] Dissolve the above carboxyl-containing crown ether polymer in dimethyl sulfoxide, control the mass fraction to be 5 wt%, and obtain a homogeneous solution without insolubles. Subsequently, pour this solution onto a clean and horizontally placed glass plate to ensure that the solution can spread evenly. Dry it at 60 °C for 24 h to ensure that the solvent can completely evaporate, and obtain a polymer film with a uniform thickness.

[0103] Conduct electrodialysis testing, following the steps in Example 1.

[0104] Conduct swelling degree testing, following the steps in Example 1.

[0105] Example 4

[0106] In this example, the polymerization monomers are dibenzo-18-crown-6 ether, isatin, 2,3-dioxoindoline-7-carboxylic acid, and 3,6,9-trioxa-1-aminodecane, and the structural formulas are as follows:

[0107]

[0108] The preparation method of the above polymer is as follows:

[0109] Step 1: Take 1 g of the crown ether polymer with a carboxyl content of 40% in Example 2, dissolve it in 10 mL of DMSO at 60 °C, and wait for it to dissolve completely.

[0110] Step 2: After complete dissolution, add 0.0755 g of N,N'-carbonyldiimidazole (CDI) and react for about 3 h; then add 0.0691 g of 3,6,9-trioxa-1-aminodecane (PEO:COOH = 1:2), and continue to react for 3 h.

[0111] Step 3: After the reaction is completed, cool it to room temperature and pour it into a mixed solution of ethanol and deionized water to obtain a white granular product. Then soak the product in a potassium carbonate solution for 24 h, and then soak it in 0.1 M HCl for 3 h; finally, wash it with deionized water until it is neutral to obtain a crown ether polymer containing carboxyl and polyethylene oxide.

[0112] In summary, the present invention provides a crown ether polymer containing carboxyl and polyethylene oxide (PEO) and a preparation method of a lithium ion selective cationic membrane. The flux of the lithium ion selective cationic membrane prepared from the crown ether polymer (taking the example with a side chain carboxylic acid content of 40%) reaches 1.78 mmol·m -2 ·s -1 , and the Li + / Mg 2+ permeation selectivity of the membrane can reach 200.66. The flux of the lithium ion selective cationic membrane prepared with a PEO content of 20% (Example 4) reaches 1.81 mmol·m -2 ·s -1 , and the Li + / Mg 2+ permeation selectivity of the membrane can reach 577. It can be seen from this that the present invention has certain practical significance for lithium extraction from salt lakes, and the present invention realizes the double improvement of flux and selectivity, solving the "trade-off" effect between permeability and selectivity commonly found in ion exchange membranes. In addition, the preparation method of the present invention is simple and easy to operate, and the product has high purity and has good application development prospects.

[0113] A preparation method of a lithium ion selective membrane is specifically as follows:

[0114] Dissolve the above-mentioned crown ether polymer containing carboxyl and PEO in dimethyl sulfoxide, control the mass fraction to be 5 wt%, and obtain a homogeneous solution without insoluble substances. Subsequently, pour this solution onto a clean and horizontally placed glass plate to ensure that the solution can spread evenly. Dry it at 60 °C for 24 h to ensure that the solvent can completely evaporate, and obtain a polymer film with a uniform thickness.

[0115] Conduct electrodialysis tests following the steps in Example 1.

[0116] Conduct swelling degree tests following the steps in Example 1.

[0117] In summary, through the superacid-catalyzed polymerization reaction, the present invention synthesizes a series of crown ether polymers with crown ether rings in the main chain and carboxylic acid groups in the side chain. Due to the specific binding property of crown ethers, they are widely used in selective cation transport. This is mainly because the ion-dipole interaction between positively charged metal ions and electron-rich oxygen atoms allows crown ethers to selectively bind to specific cations. The present invention precisely introduces crown ethers to exert their specific binding effect with alkali metals, thereby achieving the specific selection of lithium ions. The introduction of carboxyl groups increases the content of hydrophilic groups, which is beneficial for constructing hydrophilic-hydrophobic ion transport channels within the membrane. The carboxyl groups form acid-base pairs with isatin groups, which helps to inhibit the swelling of the membrane and reduce the ion transport channels within the membrane, thereby enhancing the size sieving effect of the ion exchange membrane. Moreover, the carboxylic acid groups will dissociate under the action of an electric field to generate -COO - -, thereby making the polymer carry a certain negative charge and promoting the transport of divalent cations. The lithium ion-selective cationic membrane prepared from this crown ether polymer exhibits excellent performance in electrodialysis tests. Taking the crown ether polymer with a side-chain carboxylic acid content of 40% as an example, the flux of the lithium ion-selective cationic membrane prepared therefrom reaches 1.78 mmol·m -2 ·s -1 -, and the Li + / Mg 2+ permeation selectivity of the membrane can reach 200.66.

[0118] To further optimize the performance of the lithium ion-selective cationic membrane, a hydrophilic chain segment PEO is introduced into the crown ether polymer containing carboxyl groups. The introduction of PEO can increase the lithium ion transport sites, construct a microphase separation structure, and promote the establishment of lithium ion-selective transport channels; and PEO may further improve the lithium-magnesium selectivity by forming hydrogen bond networks with amide groups or carboxylic acid groups to increase the intermolecular force and the coordination of C-O-C bonds on the PEO side chain with lithium ions. The Li + / Mg 2+The permeation selectivity can reach 577, and the lithium ion flux can reach 1.81×10 -8 mmol·m -2 ·s -1 , achieving a double improvement in flux and selectivity and solving the trade-off effect between permeability and selectivity commonly seen in ion exchange membranes.

[0119] The content not described in detail in the specification of the present invention belongs to the prior art well-known to those skilled in the art. Although the illustrative specific embodiments of the present invention have been described above for the understanding of those skilled in the art of the present technology, it should be clear that the present invention is not limited to the scope of the specific embodiments. For those of ordinary skill in the art of the present technology, as long as various changes are within the spirit and scope of the present invention defined and determined by the appended claims, these changes are obvious, and all inventions made using the concept of the present invention are within the scope of protection.

Claims

1. A carboxyl-containing crown ether polymer, characterized in that, The structural formula is as follows: Wherein: x is the degree of functionalization; 0 < x ≤ 1.

2. A method for preparing a carboxyl-containing crown ether polymer as described in claim 1, characterized in that, It includes the following steps: Step 1, at room temperature, disperse the aromatic monomer containing a crown ether ring and the ketone monomer in a certain ratio in dichloromethane to obtain a mixed solution; The aromatic monomer containing a crown ether ring is as follows: The ketone monomer is one or two of the following monomers: Step 2, at 0 °C, add trifluoroacetic acid and trifluoromethanesulfonic acid to the mixed solution obtained in Step 1, react for 1 - 2 h to obtain a viscous mixed solution; pour the obtained viscous mixed solution into a poor solvent to obtain a fibrous product; soak the fibrous product in deionized water, wash, filter, and dry it sufficiently to obtain a crown ether polymer containing carboxyl groups.

3. The preparation method of the carboxyl-containing crown ether polymer according to claim 1, characterized in that: The molar ratio of the aromatic monomer containing a crown ether ring to the ketone monomer is 1:1.

1.

4. The preparation method of the carboxyl-containing crown ether polymer according to claim 1, wherein: The volume ratio of dichloromethane, trifluoroacetic acid, and trifluoromethanesulfonic acid is 1.3 - 1.4:1.3 - 1.4:

1.

5. The preparation method of the carboxyl-containing crown ether polymer according to claim 1, characterized in that: The poor solvent is methanol, ethanol, or deionized water.

6. A crown ether polymer containing a carboxyl group and polyethylene oxide, characterized in that, The structural formula is as follows: Wherein: m is the number of repeating units of -O-CH2-CH2-; 2 ≤ m ≤ 7; Y and Z are the degrees of functionalization of carboxyl group and polyethylene oxide respectively.

7. A method for preparing a crown ether polymer containing a carboxyl group and polyethylene oxide as described in claim 6, using the crown ether polymer containing a carboxyl group as described in claim 1, characterized in that, It includes the following steps: Step 1, dissolve the crown ether polymer containing carboxyl groups in an organic solvent at 60 °C to obtain a solution with a mass-volume ratio of 5 - 10%; Step 2, add an acid amide condensing agent to the solution and react for 3 h; then add polyethylene oxide monomer and react for 3 h; Step 3, after the reaction is completed, cool the reaction solution to room temperature and pour it into a precipitating agent to obtain a white granular product; Soak the final product in a potassium carbonate solution, then soak it in a hydrochloric acid solution, and then wash it with deionized water until it is neutral to obtain a crown ether polymer containing carboxyl groups and polyethylene oxide.

8. The preparation method of the crown ether polymer containing carboxyl and polyethylene oxide according to claim 7, characterized in that: The organic solvent is N-methylpyrrolidone or dimethyl sulfoxide; the ratio of polyethylene oxide to COOH is 1:2; the acid amide condensing agent is N,N'-carbonyldiimidazole; the precipitating agent is a mixed solution of ethanol and deionized water.

9. A method for preparing a lithium ion selective cationic membrane, characterized in that, It includes the following steps: Dissolve the crown ether polymer containing carboxyl groups described in Claim 1 or the crown ether polymer containing carboxyl groups and polyethylene oxide described in Claim 3 in an organic solvent respectively to obtain a transparent and homogeneous casting solution; pour the casting solution on a glass plate, dry it into a film at a certain temperature, and then immerse it in deionized water to make the film fall off from the mold to obtain a lithium ion selective cationic membrane.

10. The preparation method of the lithium ion selective cationic membrane according to claim 9, characterized in that, The organic solvent is N-methylpyrrolidone or dimethyl sulfoxide; the mass concentration of the casting solution is 0.05 - 0.10 g / mL; the temperature for drying into a film is 60 - 80 °C, and the time is 24 hours.

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