Crown ether cation selective separation membrane and preparation method thereof

Abstract

The invention discloses a crown ether cation selective separation membrane and a preparation method thereof. The preparation method comprises the following steps: carrying out super acid catalysis on dibenzo-18-crown-6, terphenyl and isatin in dichloromethane to synthesize a precursor; carrying out affinity substitution reaction on the precursor and a flexible side chain with an ion exchange group through a pre-modification method to obtain a functional precursor; dissolving the functionalized precursor in an organic solvent to form a film casting solution, coating on a glass plate, and heating to volatilize the solvent so as to form a film through curing; and taking down the membrane from the glass plate, acidifying in an acidic aqueous solution, washing with deionized water, and extracting with deionized water to obtain the crown ether cation selective separation membrane. The crown ether cation selective separation membrane has the advantages of relatively high mechanical strength, physical and chemical stability and the like. Meanwhile, the crown ether cation selective separation membrane shows performance superior to that of a commercial membrane in the field of monovalent cation separation, and has wide application prospects in the fields of TMAH purification, salt lake lithium extraction, seawater salt extraction and the like.

Description

Technical Field

[0001] The present invention belongs to the technical field of ion exchange membranes, and particularly relates to a crown ether-based cation selective separation membrane and a preparation method thereof. Background Art

[0002] Ion selective separation involves fields such as the purification of TMAH, lithium extraction from salt lakes, salt extraction from seawater, and resource recovery, and is an important part of membrane separation technology. Electronic-grade tetramethylammonium hydroxide (TMAH), as a key type of electronic chemical, consists of tetramethylammonium ions (Me4N + ) and hydroxide (OH - ). TMAH has advantages such as a high etching rate, excellent selectivity, and environmental friendliness, and has gradually become the mainstream choice for three-dimensional structure etching. Breaking through the technical bottleneck of high-purity TMAH preparation and realizing the domestic substitution of key electronic chemicals have become urgent tasks to promote industrial upgrading. Given that the traditional methods for preparing tetramethylammonium hydroxide (TMAH) have problems such as high costs and high impurity ion content, since the 1990s, researchers and the industrial community have begun to explore and adopt the ion membrane electrolysis method to prepare TMAH. Constructing an ion selective separation membrane with ion flux and selectivity is the core to improve the separation efficiency.

[0003] The selective binding of ions to ion recognition groups has been widely studied in the field of supramolecular chemistry and has received increasing attention in the design and application of ion exchange membranes in recent years. Currently, covalent receptors based on crown ethers, cryptands, or calixarenes are considered ion recognition units with specific recognition capabilities, and the conformational isomers generated by these units have cavities of different sizes and various shapes. Compounds containing ion recognition groups can complex with specific ions, have high selectivity, and can be used as phase transfer catalysts, ion carriers, or ion exchangers.

[0004] Inspired by biological ion channels, incorporating ion selective sieving sites in the membrane and controlling the specific interaction between functional sites and ions have become the key research directions of artificial biomimetic membranes. Currently, modifying ion exchange membranes by using crown ethers as ion recognition groups in the membrane has received extensive attention in the field of ion separation.

[0005] Crown ether-based ion selective separation membranes have multiple advantages. First, crown ethers, as a type of ion recognition group, the conformational isomers generated by these units have cavities of different sizes and various shapes. Compounds containing crown ether ion recognition groups can complex with specific ions, have high selectivity, and can be used as phase transfer catalysts, ion carriers, or ion exchangers. Second, modifying the crown ether-containing precursor can obtain a crown ether-functionalized ion transport channel. Currently, modifying ion exchange membranes by using crown ethers as ion recognition groups in the membrane has received extensive attention in the field of ion separation. Summary of the Invention

[0006] The object of the present invention is to provide a crown ether-based cation selective separation membrane and a preparation method thereof. The prepared crown ether-based cation selective separation membrane has relatively high mechanical strength and physical and chemical stability. At the same time, the prepared crown ether-based cation selective separation membrane shows better performance than commercial membranes in the field of monovalent cation separation, and has broad application prospects in the purification of TMAH, lithium extraction from salt lakes, salt extraction from seawater, etc.

[0007] To achieve the above object, the present invention adopts the following technical solutions: A preparation method of a crown ether-based cation selective separation membrane, comprising the following steps: synthesizing a precursor PDTI polymer by superacid catalysis of a certain proportion of dibenzo-18-crown-6, terphenyl, and isatin in dichloromethane; through a pre-modification method, subjecting the precursor PDTI polymer to an affinity substitution reaction with a flexible side chain with an ion exchange group to obtain a functionalized precursor; dissolving the functionalized precursor in an organic solvent to form a casting solution, coating the solution on a glass plate, and heating to volatilize the solvent to solidify into a membrane; removing the membrane from the glass plate, acidifying it in an acidic aqueous solution, washing it with deionized water, and subjecting it to deionized water extraction to obtain a crown ether-based cation selective separation membrane; The molar ratio of the dibenzo-18-crown-6 to the terphenyl is x:1-x, where 0 < x < 1; The ion exchange group is selected from a sulfonic acid group -SO3 - 、a carboxylic acid group -COO - 、a phosphonic acid group -PO3H - 、a quaternary ammonium salt group -NR4 + 、a phosphonium group -PR4 + 、an imidazolium group -C3H5N2 + 、a pyridinium group -C5H5N + ; The organic solvent is any one of N-methylpyrrolidone, dimethyl sulfoxide, and N,N-dimethylformamide; the temperature of the nucleophilic substitution reaction is 60-110 °C and the time is 8-32 h; The concentration of the casting solution is 2 wt% - 20 wt%, the heating temperature is 60-90 °C and the time is 12-24 h; The acidic aqueous solution is a 1 M HCl aqueous solution, and the acidification time is 24 h.

[0008] A crown ether-based cation selective separation membrane prepared by the above preparation method.

[0009] The application of the above crown ether-based cation selective separation membrane in monovalent / monovalent ion separation and monovalent / divalent ion separation; The monovalent / monovalent ions include K+ / Me4N + 、Na + / Me4N + The monovalent / divalent ions include K + / Mg 2+ 、Na + / Mg 2 + 、Li + / Mg 2+ 。

[0010] The beneficial effects of the present invention are as follows: (1) The crown ether-based cation selective separation membrane of the present invention has relatively high mechanical strength and physicochemical stability.

[0011] (2) For the existing crown ether-based ion selective separation membranes, there are problems such as low transport efficiency, poor structural stability, being restricted by the mutual restriction effect between permeability and selectivity, and the unclear ion transport mechanism. The crown ether-based cation selective separation membrane prepared in the present invention introduces crown ether as an ion recognition group into the ion exchange membrane by polycondensation, and explores the actual industrial application potential of the functionalized crown ether-based ion selective separation membrane under the synergistic effect of ion binding sites and ion exchange sites.

[0012] (3) The present invention studies the novel synergistic hydrophilic network formed by dibenzo-18-crown-6 and sulfonic acid groups, and proposes that the binding effect between crown ether and ions affects the chain conformation through non-covalent interaction in the membrane containing cation exchange groups, constructing an ion selective channel with synergistic effect and having relatively high ion permeability. The ion transport channel constructed by crown ether and sulfonic acid groups in the flexible chain is studied, and it is proposed that in the case of flexible main chain, a double-periodic structure is formed inside the bifunctional membrane containing crown ether and sulfonic acid groups. Through comprehensive analysis by methods such as ion conductance and SAXS, the synergistic ion transport mechanism of the bifunctional ion channel jointly constructed by crown ether - sulfonic acid groups is proposed. BRIEF DESCRIPTION OF THE DRAWINGS

[0013] Figure 1 1H NMR spectra of PDTI 90 and SPDTI 90 at -1.0.

[0014] Figure 2 Full-spectrum scanning XPS and high-resolution scanning spectra in the S2p region of PDTI 90 and SPDTI 90 at -1.0.

[0015] Figure 3 1H NMR spectra of the base membrane of PDTI 90 and SPDTI 90SEM and TA-AFM images of -1.0. Detailed implementation manners

[0016] To make the content of the present invention easier to understand, the technical solutions of the present invention will be further described below in conjunction with specific implementation manners, but the present invention is not limited thereto.

[0017] The chemical reagents used in the embodiments of the present invention are all commercially available.

[0018] The synthesis steps of the precursor used in Example 1 of the present invention are as follows: First, add 3.3098 g (9 mmol) of dibenzo-18-crown-6, 0.2303 g (1 mmol) of p-terphenyl, 1.6184 g (11 mmol) of isatin and 25 ml of dichloromethane into a three-necked flask, and stir at room temperature for 2 h to disperse each component evenly. The dispersed liquid is added dropwise with 5 ml of TFA and 10 ml of TSFA at a rate of 2 - 3 s / drop under an ice bath (0 °C) condition, and continue to stir. When it is observed that the system changes from orange-red to dark green and finally turns to yellowish-brown, the reaction is terminated. The reaction product is precipitated in a liquid with a volume ratio of ethanol to water of 1:1, and then the precipitate is heated and stirred for washing at 70 °C for 12 h. The solid after filtration is then heated in a 0.01 M NaOH aqueous solution at 70 °C for 24 h. Finally, after washing with pure water and filtering and drying, the final product precursor PDTI is obtained. 90 .

[0019] Example 1: Dissolve 2 g of the precursor PDTI 90 in DMSO to prepare a 10 wt% solution, and then add 1.07 g of a flexible side chain with a sulfonic acid group (preparation method: add 5 g of 1,3-propane sultone and 5.85 g of potassium bromide into 75 mL of distilled water, react at 60 °C for 1 h, after the reaction, rotate to evaporate the solvent, wash the obtained crude product with absolute ethanol, and then recrystallize and purify with a mixed solution of absolute ethanol:water = 3:1 (volume ratio) to obtain a flexible side chain with a sulfonic acid group), heat to 60 °C and react for 8 h to obtain a functionalized precursor. The degree of modification of the functionalized precursor is measured to be 30%. Dissolve the functionalized precursor in DMSO to prepare a 5 wt% casting solution. The casting solution is coated on a clean and flat glass plate to form a film solution with a thickness of 200 μm, and then placed on a graphite plate and heated at 70 °C for 24 h to volatilize the solvent to solidify the film. Take the film off the glass plate, soak it in a 1 M HCl aqueous solution at room temperature for acidification treatment for 24 h, wash it with deionized water until neutral, and after extraction with deionized water, obtain a crown ether-based ion selective separation membrane SPDTI 90 -1.0. The ion exchange capacity (IEC) of the crown ether-based ion selective separation membrane is measured to be 0.486 mmol·g-1 , with a water content of 6.75%, a tensile strength of 28.38 MPa, and a membrane surface resistance of 42.35 Ω·cm 2 , and a transference number of 0.802.

[0020] An experiment on monovalent / monovalent ion separation was carried out using the prepared crown ether-based ion-selective separation membrane. The desalination chamber was a 200 mL mixed aqueous solution containing 0.1 M KCl and 0.1 M Me4N(HCO3), the concentration chamber was 200 mL of deionized water, the replenishing solution in the electrode chamber was 400 ml of 0.3 M Na2SO4 aqueous solution, and the circulation flow rate was 60 ml·min -1 , and the operating current was 10 mA. The Na + flux of the crown ether-based ion-selective separation membrane was measured to be 0.158 mol·m -2 ·h -1 , and the selectivity of Na + / Me4N + was 38.54. Compared with the commercial membrane (CIMS, with a Na + flux of 0.563 mol·m -2 ·h -1 , and a selectivity of Na + / Me4N + of 21.60), the selectivity was greatly improved.

[0021] Example 2: A crown ether-based ion-selective separation membrane was prepared by a method similar to that in Example 1, except that the functionalization reaction temperature was changed to 90 °C, and the degree of modification of the obtained functionalized precursor was 45%. The measured ion exchange capacity (IEC) of the prepared crown ether-based ion-selective separation membrane was 0.729 mmol·g -1 , with a water content of 14.58%, a tensile strength of 26.38 MPa, and a membrane surface resistance of 42.35 Ω·cm 2 , a transference number of 0.802, and a Na + flux of 0.192 mol·m -2 ·h -1 , and the selectivity of Na + / Me4N + was 38.54.

[0022] Example 3: A crown ether-based ion-selective separation membrane was prepared by a method similar to that in Example 1, except that the functionalization reaction temperature was changed to 90 °C and the functionalization reaction time was adjusted to 24 h, and the degree of modification of the obtained functionalized precursor was 70%. The measured ion exchange capacity (IEC) of the prepared crown ether-based ion-selective separation membrane was 1.145 mmol·g -1, the water content is 21.64%, the tensile strength is 22.72 MPa, and the membrane surface resistance is 2.8 Ω·cm 2 , the transference number is 0.927, Na + flux is 0.372 mol·m -2 ·h -1 , Na + / Me4N + selectivity is 46.93.

[0023] Combining Examples 1 to 3, the preparation requirements have been met under the conditions of a functionalization reaction temperature of 90 °C and a functionalization reaction time of 24 h. Further increasing the temperature and prolonging the time has little effect on the degree of modification.

[0024] Example 4: A crown ether-based ion-selective separation membrane was prepared by a method similar to that of Example 3, except that the molar ratio of dibenzo-18-crown-6 to terphenyl was adjusted to 8:2, and the degree of modification of the obtained functionalized precursor was 70%. The ion exchange capacity (IEC) of the prepared crown ether-based ion-selective separation membrane was measured to be 1.183 mmol·g -1 , the water content is 22.38%, the tensile strength is 14.54 MPa, and the membrane surface resistance is 2.71 Ω·cm 2 , the transference number is 0.931, Na + flux is 0.375 mol·m -2 ·h -1 , Na + / Me4N + selectivity is 47.38.

[0025] Example 5: A crown ether-based ion-selective separation membrane was prepared by a method similar to that of Example 3, except that the molar ratio of dibenzo-18-crown-6 to terphenyl was adjusted to 7:3, and the degree of modification of the obtained functionalized precursor was 70%. The ion exchange capacity (IEC) of the prepared crown ether-based ion-selective separation membrane was measured to be 1.211 mmol·g -1 , the water content is 22.87%, the tensile strength is 9.77 MPa, and the membrane surface resistance is 2.65 Ω·cm 2 , the transference number is 0.935, Na + flux is 0.381 mol·m -2 ·h -1 , Na + / Me4N + selectivity is 48.52.

[0026] Example 6: The crown ether-based ion-selective separation membrane was prepared by a method similar to that of Example 3, except that the molar ratio of dibenzo-18-crown-6 to terphenyl was adjusted to 6:4, and the degree of modification of the obtained functionalized precursor was 70%. The ion exchange capacity (IEC) of the prepared crown ether-based ion-selective separation membrane was measured to be 1.239 mmol·g -1 , the water content was 23.58%, the tensile strength was 6.52 MPa, and the membrane surface resistance was 2.54 Ω·cm 2 , the transference number was 0.939, and the Na + flux was 0.392 mol·m -2 ·h -1 , and the selectivity of Na + / Me4N + was 45.38.

[0027] From Examples 4 to 6, it is not difficult to find that by changing the ratio of dibenzo-18-crown-6 to terphenyl, a higher theoretical IEC can be obtained, thereby increasing the degree of membrane modification, increasing the actual IEC, increasing the ion exchange sites, and improving the selective separation performance of ions. However, as the proportion of terphenyl increases, the mechanical strength of the membrane decreases sharply. Therefore, the finally determined ratio of dibenzo-18-crown-6 to terphenyl is 9:1.

[0028] Example 7: The crown ether-based ion-selective separation membrane was prepared by a method similar to that of Example 3, except that the flexible side chain with a sulfonic acid group was changed to a flexible side chain with a carboxylic acid group (preparation method: acrylic acid and bromine gas were reacted at a molar ratio of 1:1 at room temperature for 40 min, and bromine would add to the β-carbon of acrylic acid (i.e., one carbon of the double bond) to form a flexible side chain with a carboxylic acid group), and the degree of modification of the obtained functionalized precursor was 72%. The ion exchange capacity (IEC) of the prepared crown ether-based ion-selective separation membrane was measured to be 1.152 mmol·g -1 , the water content was 23.72%, the tensile strength was 21.79 MPa, and the membrane surface resistance was 2.79 Ω·cm 2 , the transference number was 0.918, and the Na + flux was 0.358 mol·m -2 ·h -1 , and the selectivity of Na + / Me4N + was 38.52.

[0029] Example 8: The crown ether-based ion-selective separation membrane was prepared by a method similar to that of Example 3, except that the flexible side chain with a sulfonic acid group was changed to a flexible side chain with a phosphonic acid group (preparation method: 3-bromo-1-propanoic acid and diethyl phosphoric acid were reacted in dichloromethane at room temperature in a molar ratio of 1:1 for 24 h, and the reaction product was dried at 60 °C for 24 h to obtain a flexible side chain with a phosphonic acid group). The modification degree of the obtained functionalized precursor was 68%. The ion exchange capacity (IEC) of the prepared crown ether-based ion-selective separation membrane was 1.097 mmol·g -1 , the water content was 20.68%, the tensile strength was 22.54 MPa, and the membrane surface resistance was 2.92 Ω·cm 2 , the transference number was 0.908, and the Na + flux was 0.334 mol·m -2 ·h -1 , and the selectivity of Na + / Me4N + was 34.29.

[0030] Example 9: The crown ether-based ion-selective separation membrane was prepared by a method similar to that of Example 3, except that the flexible side chain with a sulfonic acid group was changed to a flexible side chain with a quaternary ammonium group (preparation method: 5 g of 1,4-dibromobutane was dissolved in 60 ml of tetrahydrofuran (THF) to obtain a 1,4-dibromobutane solution, 1.28 g of trimethylamine was dissolved in 60 ml of THF to obtain a trimethylamine solution, and then the trimethylamine solution was slowly dropped into the 1,4-dibromobutane solution through a constant pressure separating funnel and stirred at room temperature for 24 h. After the reaction, filtration was carried out, and the filter cake was dried to obtain a flexible side chain with a quaternary ammonium group). The modification degree of the obtained functionalized precursor was 90%. The ion exchange capacity (IEC) of the prepared crown ether-based ion-selective separation membrane was 1.364 mmol·g -1， The water content was 24.58%, the tensile strength was 18.21 MPa, and the membrane surface resistance was 1.54 Ω·cm 2 , the transference number was 0.952, and the Na + flux was 0.183 mol·m -2 ·h -1 , and the selectivity of Na + / Me4N + was 48.30.

[0031] Example 10: The crown ether-based ion-selective separation membrane was prepared by a method similar to that of Example 3, except that the flexible side chain with a sulfonic acid group was changed to a flexible side chain with a phosphonium group (preparation method: dissolve 5 g of 1,4-dibromobutane in 60 ml of THF to obtain a 1,4-dibromobutane solution, dissolve 1.65 g of trimethylphosphine in 60 ml of THF to obtain a trimethylphosphine solution, then slowly drip the trimethylphosphine solution into the 1,4-dibromobutane solution through a constant-pressure separatory funnel, stir and react at room temperature for 24 h, filter after the reaction is completed, and dry the filter cake to obtain a flexible side chain with a phosphonium group), and the modification degree of the obtained functionalized precursor was 90%. The ion exchange capacity (IEC) of the prepared crown ether-based ion-selective separation membrane was measured to be 1.318 mmol·g -1 , the water content was 23.28%, the tensile strength was 18.43 MPa, and the membrane surface resistance was 1.65 Ω·cm 2 , the transference number was 0.947, Na + flux was 0.179 mol·m -2 ·h -1 , Na + / Me4N + selectivity was 47.25.

[0032] Example 11: The crown ether-based ion-selective separation membrane was prepared by a method similar to that of Example 3, except that the flexible side chain with a sulfonic acid group was changed to a flexible side chain with a pyridinium group (preparation method: dissolve 5 g of 1,4-dibromobutane in 60 ml of THF to obtain a 1,4-dibromobutane solution, dissolve 1.71 g of pyridine in 60 ml of THF to obtain a pyridine solution, then slowly drip the pyridine solution into the 1,4-dibromobutane solution through a constant-pressure separatory funnel, stir and react at room temperature for 24 h, filter after the reaction is completed, and dry the filter cake to obtain a flexible side chain with a pyridinium group), and the modification degree of the obtained functionalized precursor was 89.79%. The ion exchange capacity (IEC) of the prepared crown ether-based ion-selective separation membrane was measured to be 1.342 mmol·g -1 , the water content was 22.49%, the tensile strength was 19.35 MPa, and the membrane surface resistance was 1.72 Ω·cm 2 , the transference number was 0.927, Na + flux was 0.164 mol·m -2 ·h -1 , Na + / Me4N + selectivity was 36.77.

[0033] Example 12: The crown ether-based ion-selective separation membrane was prepared by a method similar to that of Example 3, except that the flexible side chain with sulfonic acid groups was changed to a flexible side chain with imidazolium groups (preparation method: dissolve 5 g of 1,4-dibromobutane in 60 ml of THF to obtain a 1,4-dibromobutane solution, dissolve 2.08 g of 1,2-dimethylimidazole in 60 ml of THF to obtain a 1,2-dimethylimidazole solution, then slowly drop the 1,2-dimethylimidazole solution into the 1,4-dibromobutane solution through a constant-pressure separatory funnel, stir and react at room temperature for 24 h, filter after the reaction is completed, and dry the filter cake to obtain a flexible side chain with imidazolium groups), and the modification degree of the obtained functionalized precursor was 91.2%. The ion exchange capacity (IEC) of the prepared crown ether-based ion-selective separation membrane was measured to be 1.359 mmol·g -1 , the water content was 23.92%, the tensile strength was 18.97 MPa, and the membrane surface resistance was 1.62 Ω·cm 2 , the transference number was 0.945, and the Na + flux was 0.179 mol·m -2 ·h -1 , and the selectivity of Na + / Me4N + was 47.24.

[0034] Based on Examples 8 to 12, it is not difficult to find that, compared with the negatively charged cation exchange membrane, the positively charged anion exchange membrane has a greater modification degree than the cation exchange membrane and can reach a larger actual IEC value. Therefore, in the following exploration, the crown ether-based ion-selective separation membrane functionalized with imidazolium groups was selected for exploration.

[0035] Example 13: The crown ether-based ion-selective separation membrane was prepared by a method similar to that of Example 12, except that the separation system was changed to Na + / Mg 2+ . The ion separation performance of the prepared crown ether-based ion-selective separation membrane was measured to be that the Na + flux was 0.187 mol·m -2 ·h -1 , and the selectivity of Na + / Mg 2+ was 34.27.

[0036] Example 14: The crown ether-based ion-selective separation membrane was prepared by a method similar to that of Example 12, except that the separation system was changed to K + / Mg 2+ . The ion separation performance of the prepared crown ether-based ion-selective separation membrane was measured to be that the K + flux was 0.239 mol·m -2 ·h-1 , K + / Mg 2+ had a selectivity of 47.21.

[0037] Example 15: A crown ether-based ion-selective separation membrane was prepared using a method similar to that of Example 12, except that the separation system was changed to Li + / Mg 2+ . The ion separation performance of the prepared crown ether-based ion-selective separation membrane was measured as follows: the Li + flux was 0.084 mol·m -2 ·h -1 , and the selectivity of Li + / Mg 2+ was 11.43.

[0038] The chemical compositions of PDTI 1 and SPDTI 90 -1.0 were characterized by 90 1H NMR, and the results are shown in Figure 1 . It can be seen that between 8.0 - 6.0, characteristic peaks of Ar-H (H3-H 11 ) in the precursor appeared. Between 4.5 - 3.5, characteristic peaks of the hydrogen of the methylene group in the crown ether unit (H1, H2) were attributed, and the ratio of the two was 0.65, close to the theoretical value of 0.66. The chemical shift at 10.7 was attributed to the H (H 12 ) on the amide bond of isatin. The above results indicated the successful synthesis of the precursor PDTI 90 .

[0039] Figure 2 These are the XPS (a) full spectra and (b) high-resolution spectra of the S2p region of PDTI 90 and SPDTI 90 -1.0. It can be seen that characteristic peaks of the elements O1s, N 1s, and C 1s appeared at binding energies of 532.1 eV, 399.7 eV, and 284.2 eV for both, which was determined by the substances of the base membrane itself. After sulfonation modification of PDTI 90 , a characteristic peak of S2p appeared at 168.2 eV for SPDTI 90 -1.0, which was mainly attributed to the successful grafting of the -SO3 - group. In addition, two new peaks with an area ratio of 1:2 appeared in the high-resolution spectrum of the S2p region of SPDTI 90 -1.0 at binding energies of 168.7 eV and 167.3 eV (see Figure 2 (b)), which were respectively attributed to -SO3 --S-O and -S=O in the group. The XPS and FI-IR results are consistent, also proving that -SO3 - group was successfully grafted onto PDTI 90 to achieve the successful preparation of SPDTI 90 -1.0.

[0040] Figure 3 For the PDTI 90 base membrane, SPDTI 90 -1.0 surface SEM images and AFM-Phase diagrams. For the PDTI 90 base membrane and SPDTI 90 -1.0, the SEM images show that there are no significant differences in their microtopographies, all showing a uniform, dense and defect-free microstructure. In contrast, the AFM-Phase images of the PDTI 90 base membrane and SPDTI 90 -1.0 are significantly different. For the PDTI 90 base membrane, no common hydrophilic-hydrophobic microphase separation structure of ion exchange membranes is found in its phase diagram, which is directly related to its lack of hydrophilic groups. This result shows that the introduction of sulfonic acid groups forms channels for rapid ion transport inside SPDTI 90 -X. For the highly modified SPDTI 90 -1.0, an obvious hydrophilic-hydrophobic phase separation structure composed of dark regions and bright regions can be observed. Among them, the dark regions are formed by the aggregation of hydrophilic sulfonic acid groups, while the bright regions are formed by the aggregation of hydrophobic crown ether main chains, with certain mechanical stability. The proportion of its dark regions increases significantly, and the connectivity is greatly improved. This means that the number and aggregation degree of sulfonic acid groups increase significantly, thereby greatly reducing the resistance of ion transport.

[0041] The results of the above examples show that the optimal functionalization reaction temperature of the crown ether-based ion selective separation membrane prepared by the present invention is 90 °C, the optimal functionalization reaction time is 24 h, and for the functionalized crown ether-based ion selective separation membrane, a dual-functionalized ion channel jointly constructed by crown ether-ion exchange groups is formed inside the membrane, which has high ion permeability and ion selectivity. At the same time, there are few reports on the research of crown ether-type ion selective separation membranes in the field of TMAH purification. Therefore, the present invention has broad development prospects.

[0042] The above are only the preferred embodiments of the present invention. All equivalent changes and modifications made according to the scope of the patent application of the present invention shall fall within the scope covered by the present invention.

Claims

1. A preparation method of a crown ether-based cation-selective separation membrane, characterized in that: A precursor PDTI polymer is synthesized by catalytically reacting a certain proportion of dibenzo-18-crown-6, terphenyl, and isatin in dichloromethane with a superacid; through a pre-modification method, the precursor PDTI polymer is subjected to an affinity substitution reaction with a flexible side chain having an ion exchange group to obtain a functionalized precursor; the functionalized precursor is dissolved in an organic solvent to form a casting solution, which is coated on a glass plate, and the solvent is heated and volatilized to solidify into a film; the film is removed from the glass plate, acidified in an acidic aqueous solution, washed with deionized water, and extracted with deionized water to obtain a crown ether-based cation selective separation membrane.

2. The preparation method according to claim 1, wherein: The molar ratio of the dibenzo-18-crown-6 to the terphenyl is x:1 - x, where 0 < x < 1.

3. The preparation method according to claim 1, characterized in that: The ion exchange group is selected from a sulfonic acid group -SO3 - , a carboxylic acid group -COO - , a phosphonic acid group -PO3H - , a quaternary ammonium salt group -NR4 + , a phosphonium group -PR4 + , an imidazolium group -C3H5N2 + , a pyridinium group -C5H5N + .

4. The preparation method according to claim 1, characterized in that: The organic solvent is any one of N-methylpyrrolidone, dimethyl sulfoxide, and N,N-dimethylformamide.

5. The preparation method according to claim 1, wherein: The temperature of the nucleophilic substitution reaction is 60 - 110 °C and the time is 8 - 32 h.

6. The preparation method according to claim 1, characterized in that: The concentration of the casting solution is 2 wt% - 20 wt%, and the heating temperature is 60 - 90 °C and the time is 12 - 24 h.

7. The preparation method according to claim 1, characterized in that: The acidic aqueous solution is a 1 M HCl aqueous solution, and the acidification time is 24 h.

8. A crown ether-based cation selective separation membrane prepared by the preparation method according to any one of claims 1 - 7.

9. Use of a crown ether-based cation selective separation membrane as described in claim 8 in the separation of monovalent / divalent ions and monovalent / monovalent ions.

10. The application according to claim 9, characterized in that: The monovalent or univalent ion includes K + / Me4N + , Na + / Me4N + , and the monovalent or divalent ion includes K + / Mg 2+ , Na + / Mg 2+ , Li + / Mg 2+ .

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