Supramolecular ion separation membrane with asymmetric functionalized nano-channel structure as well as preparation method and application of supramolecular ion separation membrane

Abstract

The invention provides a supramolecular ion separation membrane with an asymmetric functionalized nano-channel structure as well as a preparation method and application thereof, and relates to the field of separation membranes. The preparation method of the supramolecular ion separation membrane comprises the following steps: flatly attaching a covalent organic framework ion separation membrane to a polyacrylonitrile substrate to obtain a composite membrane; the membrane is installed in an H-shaped reactor, and only one side of the membrane is exposed in a reaction solution environment; the preparation method comprises the following steps: dissolving 1, 3-propane sultone in an organic solvent to obtain a sultone solution; injecting the sultone solution into a reaction chamber, close to the surface of a membrane, in an H-type reactor, so that the sultone solution and the-NH-active sites exposed on the surface of the membrane are subjected to a ring-opening reaction; after the reaction is completed, washing the obtained membrane sample with methanol and water; and drying to obtain the target supramolecular ion separation membrane. The membrane material provided by the invention is good in performance, can still maintain stable ion screening performance in a high-salt environment, can be applied to water treatment, and has a good industrial application prospect.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of separation membranes, in particular to a supramolecular ion separation membrane with an asymmetrically functionalized nanochannel structure and a preparation method and application thereof. BACKGROUND

[0002] With the rapid development of industrial wastewater treatment, seawater desalination, salt lake resource exploitation, and lithium battery recycling, selective extraction of specific ions from high-salinity solutions or complex salt systems has become an important direction for resource utilization and zero-emission technology. Among them, the direct selective ion extraction process based on membrane separation has the advantages of simplified process, low energy consumption, continuous operation, and is considered as an important means to realize efficient separation and resource recovery.

[0003] Existing ion-selective membranes (ISMs) mainly rely on weak interactions such as dielectric exclusion and size sieving to achieve ion separation. However, under high-concentration salt solution conditions, due to strong charge shielding effects and partial dehydration behavior during transmembrane migration, the above-mentioned weak interactions are difficult to maintain effective ion sieving ability, resulting in a significant decrease in ion separation selectivity, making it difficult to be applied in high-salinity environments. Therefore, enhancing the interaction between ions and channels has become an important research direction to improve the separation performance of membranes.

[0004] In recent years, researchers have introduced crown ethers, coordination groups or charged functional groups into membrane channels to strengthen the specific recognition ability of target ions, thereby improving the ion separation selectivity of the membrane. However, existing studies have shown that although the enhanced ion-channel interaction helps to improve selectivity, it also significantly increases the transmission resistance, resulting in a decrease in ion transmembrane permeation rate, presenting an inherent trade-off relationship between selectivity and permeation flux. In particular, when ions bind to strong interaction sites, their transmission process is prone to retention or capture, further inhibiting transmembrane transmission efficiency, thereby limiting the overall separation performance of the membrane in actual complex systems.

[0005] In addition, some current studies adjust the membrane pore size, channel size or introduce charge regulation structures to improve separation performance, but it is still difficult to achieve fast ion migration and efficient selective separation at the same time. The existing membrane materials lack adjustable structural gradients or functional site differences, resulting in decoupling of ion capture and release processes, making it difficult to achieve efficient transmembrane transport.

[0006] Therefore, how to construct a nanochannel structure with a functional distribution inside the membrane material, regulate the capture, transmission and release process of ions in the channel, and thus break through the bottleneck of the incompatibility of selectivity and flux in traditional membrane separation, has become a key scientific and engineering problem to be solved in the field of ion-selective membrane technology. SUMMARY

[0007] In view of this, the present invention proposes a supramolecular ion separation membrane with an asymmetric functionalized nanochannel structure, its preparation method and application.

[0008] The technical solution of this invention is implemented as follows: A method for preparing a supramolecular ion separation membrane with an asymmetric functionalized nanochannel structure includes the following steps: (1) A covalent organic framework ion separation membrane is flatly attached to a polyacrylonitrile substrate to obtain a composite membrane; the composite membrane is installed in an H-type reactor so that only one side of the membrane is exposed to the reaction solution environment to form a single-sided selective modification structure. (2) Dissolve 1,3-propanesulfonyl lactone in an organic solvent to prepare a homogeneous and transparent sulfonyl lactone solution; (3) Inject the sulfonyl lactone solution into the reaction chamber near the membrane surface in the H-type reactor so that it can undergo a ring-opening reaction with the exposed -NH- active sites on the membrane surface; (4) After the reaction is complete, the obtained membrane sample is repeatedly rinsed with methanol to remove unreacted monomers; then the membrane sample is immersed in deionized water and dried to obtain the target supramolecular ion separation membrane.

[0009] Furthermore, in step (1), the polyacrylonitrile substrate is circular with a diameter of 1.8-2.2 cm; the channel inner diameter of the H-type reactor is 0.9-1.1 cm, and the cross-sectional dimension is 1.8-2.2 cm; the electrolytic cell of the H-type reactor has an inner diameter of 2.0-2.5 cm, an outer diameter of 2.3-2.8 cm, and a height of 8-10 cm.

[0010] Furthermore, in step (2), the organic solvent is methanol, and the mass-volume ratio of 1,3-propanesulfonyl lactone to the organic solvent is 1:30-40 (g / mL).

[0011] Furthermore, in step (3), the reaction temperature is 55-65℃ and the reaction time is 4-8h.

[0012] Furthermore, in step (4), the drying process specifically involves: the treated sample being naturally dried at room temperature.

[0013] Furthermore, in step (1), the preparation method of the covalent organic framework ion separation membrane includes the following steps: S1. Add 2,3-dihydroxyterephthalic acid to anhydrous ethanol, add concentrated sulfuric acid, reflux, cool, and allow the crude product to precipitate as a white crystalline solid; filter, collect the precipitate, dry, and obtain compound 1. S2. Compound 1 and potassium carbonate were added to acetonitrile. The solution system was controlled at 68-72℃. Di-p-toluenesulfonic acid pentylene glycol solution was added dropwise. The reaction was continued by stirring. After cooling and filtration, the filtrate was dried under reduced pressure to obtain the product. The product was purified by silica gel column chromatography (using ethyl acetate and dichloromethane in a volume ratio of 38-42:58-62 as eluent) to obtain compound 2. S3. Compound 2 was added to anhydrous ethanol, hydrazine hydrate was added, the mixture was heated to reflux, cooled, and dried under reduced pressure to obtain the product, a monomer Tph-18C6 containing an hydrazone structure. S4. Add the monomer Tph-18C6 to the acetic acid solution and allow it to dissolve completely to prepare the base phase solution; S5. Add the aldehyde monomer to a mixed solvent composed of ethyl acetate and m-trimethylbenzene, dissolve it completely, and prepare a top phase solution; S6. Add the top phase solution to the surface of the bottom phase solution to form a stable interface between the two phases and allow the reaction to stand to obtain a COF film. S7. Remove the COF membrane from the reaction system and clean it to remove unreacted monomers, residual catalysts and organic solvents. A covalent organic framework ion separation membrane was obtained.

[0014] Synthetic route of the monomer Tph-18C6 of this invention .

[0015] Further, in step S1, the mass-to-volume ratio (g / mL) of 2,3-dihydroxyterephthalic acid and ethanol is 1:38-42; the mass-to-volume ratio (g / mL) of 2,3-dihydroxyterephthalic acid and concentrated sulfuric acid is 1:2-3; the mass concentration of the concentrated sulfuric acid is 95%-99%; the reflux temperature is 90-95℃, and the reflux time is 8-12 h; after collecting the precipitate, it is recrystallized 2-3 times with ethanol; the drying temperature is 50-60℃, and the drying time is 12-36 h. In step S2, the mass ratio of compound 1 to potassium carbonate is 1:2.7-3.3; the mass-to-volume ratio of compound 1 to acetonitrile (g / mL) is 1:90-110; the di-p-toluenesulfonic acid pentylene glycol solution is composed of di-p-toluenesulfonic acid pentylene glycol and acetonitrile (g / mL) in a mass-to-volume ratio of pentylenesulfonic acid pentylene glycol (g / mL) of 1:20-25; the mass ratio of compound 1 to di-p-toluenesulfonic acid pentylene glycol is 1:2.1-2.5; the time for adding the di-p-toluenesulfonic acid pentylene glycol solution is 1.5-2.5 h; the stirring temperature is 68-72 °C, and the stirring time is 24-60 h, preferably 45-55 h; and the mixture is cooled to room temperature.

[0016] Further, in step S3, the mass-to-volume ratio of compound 2 to anhydrous ethanol (g / mL) is 1:50-60; the mass ratio of compound 2 to hydrazine hydrate solution is 1:9-13; the mass concentration of hydrazine hydrate solution is 70%-80%, preferably 75%-80%; the heating and reflux temperature is 90-95℃, and the reflux time is 14-16h; and the mixture is cooled to room temperature.

[0017] Furthermore, the mass ratio of monomer Tph-18C6 in step S4 to aldehyde monomer in step S5 is 6-7:2-3. In step S4, the mass-to-volume ratio of Tph-18C6 to acetic acid solution (g / mL) is 6-7:20-25; the concentration of the acetic acid solution is 0.9-1.1 mol / L. In step S5, the volume ratio of ethyl acetate to m-thallium in the mixed solvent is 0.9-1.1:8-10; the mass-volume ratio of the aldehyde monomer to the mixed solvent (g / mL) is 2-3:20-30; and the aldehyde monomer is trialdehyde phloroglucinol. In step S6, the reaction time is 5-7 days and the reaction temperature is 33-37℃; In step S7, the cleaning process specifically involves washing with ethanol, methanol, and deionized water 2-4 times each.

[0018] A supramolecular ion separation membrane with an asymmetric functionalized nanochannel structure is prepared by any one of the preparation methods described in this invention.

[0019] The supramolecular ion separation membrane with asymmetric functionalized nanochannel structure described in this invention is used in water treatment.

[0020] Compared with the prior art, the beneficial effects of the present invention are: (1) This invention achieves a synergistic effect of strong coordination recognition and weak charge regulation by constructing a supramolecular ion separation membrane with an asymmetric functionalized nanochannel structure. The crown ether groups inside the membrane channel can selectively recognize and capture specific ions, while the charged groups introduced at the end of the channel can promote the rapid release of target ions, thereby effectively avoiding problems such as ion retention and increased transport resistance.

[0021] (2) By controlling the spatial distribution of the channel structure and its active sites, this invention achieves a situation where selectivity and permeation flux are no longer mutually restrictive. In a high-salt environment, the membrane can still maintain stable ion sieving performance, and has high selectivity, high flux and anti-charge shielding ability, overcoming the technical defects of existing ion-selective membranes such as easy failure in high-concentration salt solutions, low transmembrane migration rate and difficulty in achieving selectivity control.

[0022] (3) The membrane material provided by the present invention can be applied to the fields of high-salt wastewater resource utilization, lithium extraction from salt lakes, seawater desalination and selective extraction of target metal ions in concentrated salt systems, and has good industrial application prospects. Attached Figure Description

[0023] Figure 1 This is a synthetic route diagram for the monomer Tph-18C6 of this invention; Figure 2 This is the NMR spectrum of compound 1 of the present invention; Figure 3 This is the NMR spectrum of compound 2 of the present invention; Figure 4 This is the NMR spectrum of the monomer Tph-18C6 of this invention; Figure 5 This is a diagram of the H-type reactor apparatus of the present invention; Figure 6 This is a surface elemental distribution diagram of the supramolecular ion separation membrane with asymmetric functionalized nanochannel structure obtained in Example 2; Figure 7 Fourier transform infrared (FTIR) spectrum of the supramolecular ion separation membrane with asymmetric functionalized nanochannel structure obtained in Example 2; Figure 8 The image shows the X-ray photoelectron spectroscopy (XPS) spectrum of the supramolecular ion separation membrane with asymmetric functionalized nanochannel structure obtained in Example 2.

[0024] Figure 9 The contact angle diagram shows the supramolecular ion separation membrane with asymmetric functionalized nanochannel structure obtained in Example 2. Figure 10 Fourier transform infrared (FTIR) spectra of supramolecular ion separation membranes with asymmetric functionalized nanochannel structures obtained in Examples 1-3; Figure 11 The contact angle diagrams are for the supramolecular ion separation membranes with asymmetric functionalized nanochannel structures prepared in Examples 1-3; wherein, 18C6-COF-S 4h The modification time is 4 hours, 18C6-COF-S 6h The modification time is 6 hours, 18C6-COF-S 8h The editing time is 8 hours.

[0025] Figure 12 The unit system performance diagram (permeation flux) of the supramolecular ion separation membrane with asymmetric functionalized nanochannel structure prepared in Example 2. Figure 13 The unit system performance diagram (selective) of the supramolecular ion separation membrane with asymmetric functionalized nanochannel structure prepared in Example 2; Figure 14 The diagram shows the ion separation performance of the mixed salt system of the supramolecular ion separation membrane with asymmetric functionalized nanochannel structure prepared in Example 2. Detailed Implementation

[0026] Unless otherwise specified, the experimental methods used in the embodiments of this invention are conventional methods; Unless otherwise specified, all materials and reagents used in the embodiments of this invention are commercially available.

[0027] According to the modification time of 4 hours, 6 hours, and 8 hours, the present invention is named 18C6-COF-S. 4h 18C6-COF-S 6h 18C6-COF-S 8h .

[0028] In the implementation of this invention, the post-modification time of the membrane is at most 8 hours to ensure that functionalization only occurs on one side of the membrane surface; when the modification time exceeds 8 hours, functionalization may extend to the other surface of the membrane. Therefore, this invention only studies post-modification reactions that do not exceed 8 hours.

[0029] The compound name of the aldehyde monomer Tp in this embodiment of the invention is trialdehyde-resorcinol; The concentrated sulfuric acid used in this embodiment of the invention has a mass concentration of 98%.

[0030] The hydrazine hydrate solution used in this embodiment of the invention has a mass concentration of 80%.

[0031] The H-type reactor used in this embodiment of the invention has an inner diameter of about 1 cm and a cross-sectional dimension of about 2 cm; the electrolytic cell of the H-type reactor has an inner diameter of about 2.3 cm, an outer diameter of about 2.5 cm, and a height of about 9 cm.

[0032] The room temperature range of this invention is 20-30℃.

[0033] Example 1 This embodiment describes a method for preparing a supramolecular ion separation membrane with an asymmetric functionalized nanochannel structure, comprising the following steps: S1. In a 500 mL round-bottom flask, 5.0 g of 2,3-dihydroxyterephthalic acid was dissolved in 200 mL of anhydrous ethanol, and 12 mL of concentrated sulfuric acid was added. The solution was then refluxed at 95 °C for 12 h and cooled until a crude product precipitated as white crystalline flakes. The reaction system was filtered and the precipitate was collected. The precipitate was recrystallized twice with ethanol and dried at 50 °C for 24 h to obtain target compound 1. S2. Compound 1 (2 g) and potassium carbonate (5.97 g) were added to a 500 mL three-necked flask equipped with a magnetic stirrer. After evacuating the reaction flask and circulating nitrogen three times, 200 mL of acetonitrile was added. Subsequently, 4.73 g of pentylene-2-toluenesulfonate dissolved in 100 mL of acetonitrile was added dropwise at 70 °C over 2 hours. After the addition was complete, the reaction was stirred at the same temperature for 48 hours. After the reaction was completed, the mixture was cooled to room temperature and filtered. The filtrate was evaporated to dryness under reduced pressure. The crude product was purified by silica gel column chromatography (using ethyl acetate and dichloromethane in a volume ratio of 40:60 as eluents) to obtain compound 2. S3. Compound 2 (1 g) was dissolved in 50 mL of anhydrous ethanol, 9.87 g of hydrazine hydrate solution was added, and the mixture was heated to 95 °C and refluxed for 15 hours. After the reaction was completed, the mixture was cooled to room temperature, and the solvent was evaporated under reduced pressure to obtain product Tph-18C6. S4. Add 6.4 mg of monomer Tph-18C6 to 20 mL of 1 M acetic acid aqueous solution and allow it to dissolve completely to prepare a base phase solution; S5. Add 2.1 mg of aldehyde monomer Tp to a mixed solvent consisting of 2 ml ethyl acetate and 18 ml m-trimethylbenzene, and dissolve it completely to prepare a top phase solution. S6. Slowly add the top phase solution to the surface of the bottom phase solution, control the reaction temperature at 35 ℃, keep the two phases in interfacial contact and let them stand for 6 days to allow the film to gradually form and grow at the phase interface. S7. After the reaction is complete, the COF film formed at the interface is removed from the reaction system and washed three times in sequence with ethanol, methanol and deionized water to remove unreacted monomers, residual catalyst and organic solvent. S8. The 18C6-COF membrane obtained above is flatly attached to a polyacrylonitrile (PAN) substrate with a diameter of 2 cm, and the composite membrane is installed in an H-type reactor so that only one side of the membrane is exposed to the reaction solution environment to form a single-sided selective modification structure. S9. Weigh 0.6 g of 1,3-propanesulfonyl lactone and dissolve it in 20 ml of methanol to prepare a homogeneous and transparent sulfonyl lactone reaction solution. S10. The sulfonyl lactone solution is injected into the reaction chamber near the membrane surface in the H-type reactor, so that it undergoes a ring-opening reaction with the exposed -NH- active sites on the membrane surface. The reaction temperature is 60°C and the reaction time is 4 hours. S11. After the reaction is complete, the obtained membrane sample is repeatedly washed with methanol to remove unreacted monomers; then the membrane is continuously immersed in deionized water. S12. The membrane sample treated in S11 can be naturally dried at room temperature to obtain a supramolecular ion separation membrane with an asymmetric functionalized nanochannel structure, denoted as 18C6-COF-S. 4h .

[0034] Example 2 This embodiment describes a supramolecular ion separation membrane with an asymmetric functionalized nanochannel structure and its preparation method, including the following steps: S1. In a 500 mL round-bottom flask, 5.0 g of 2,3-dihydroxyterephthalic acid was dissolved in 200 mL of anhydrous ethanol, and 12 mL of concentrated sulfuric acid was added. The solution was then refluxed at 95 °C for 12 h and cooled until a crude product precipitated as white crystalline flakes. The reaction system was filtered and the precipitate was collected. The precipitate was recrystallized twice with ethanol and dried at 50 °C for 24 h to obtain target compound 1. S2. Compound 1 (2 g) and potassium carbonate (5.97 g) were added to a 500 mL three-necked flask equipped with a magnetic stirrer. After evacuating the reaction flask and circulating nitrogen three times, 200 mL of acetonitrile was added. Subsequently, 4.73 g of pentylene-2-toluenesulfonate dissolved in 100 mL of acetonitrile was added dropwise at 70 °C over 2 hours. After the addition was complete, the reaction was stirred at the same temperature for 48 hours. After the reaction was completed, the mixture was cooled to room temperature and filtered. The filtrate was evaporated to dryness under reduced pressure. The crude product was purified by silica gel column chromatography (using ethyl acetate and dichloromethane in a volume ratio of 40:60 as eluents) to obtain compound 2. S3. Compound 2 (1 g) was dissolved in 50 mL of anhydrous ethanol, 9.87 g of hydrazine hydrate solution was added, and the mixture was heated to 95 °C and refluxed for 15 hours. After the reaction was completed, the mixture was cooled to room temperature, and the solvent was evaporated under reduced pressure to obtain product Tph-18C6. S4. Add 6.4 mg of monomer Tph-18C6 to 20 mL of 1 M acetic acid aqueous solution and allow it to dissolve completely to prepare a base phase solution; S5. Add 2.1 mg of aldehyde monomer Tp to a mixed solvent consisting of 2 ml ethyl acetate and 18 ml m-trimethylbenzene, and dissolve it completely to prepare a top phase solution. S6. Slowly add the top phase solution to the surface of the bottom phase solution, control the reaction temperature at 35 ℃, keep the two phases in interfacial contact and let them stand for 6 days to allow the film to gradually form and grow at the phase interface. S7. After the reaction is complete, the COF film formed at the interface is removed from the reaction system and washed three times in sequence with ethanol, methanol and deionized water to remove unreacted monomers, residual catalyst and organic solvent. S8. The 18C6-COF membrane obtained above is flatly attached to a polyacrylonitrile (PAN) substrate with a diameter of 2 cm, and the composite membrane is installed in an H-type reactor so that only one side of the membrane is exposed to the reaction solution environment to form a single-sided selective modification structure. S9. Weigh 0.6 g of 1,3-propanesulfonyl lactone and dissolve it in 20 ml of methanol to prepare a homogeneous and transparent sulfonyl lactone reaction solution. S10. The above-mentioned sulfonyl lactone solution is injected into the reaction chamber near the membrane surface in the H-type reactor, so that it can undergo a ring-opening reaction with the exposed -NH- active sites on the membrane surface. The reaction temperature is 60°C and the reaction time is 6 hours. S11. After the reaction is complete, the obtained membrane sample is repeatedly washed with methanol to remove unreacted monomers; then the membrane is continuously immersed in deionized water. S12. The membrane sample treated in S11 can be naturally dried at room temperature to obtain a supramolecular ion separation membrane with an asymmetric functionalized nanochannel structure, denoted as 18C6-COF-S. 6h .

[0035] Example 3 This embodiment describes a supramolecular ion separation membrane with an asymmetric functionalized nanochannel structure and its preparation method, including the following steps: S1. In a 500 mL round-bottom flask, 2,3-dihydroxyterephthalic acid (5.0 g, 25 mmol) was dissolved in 200 mL of anhydrous ethanol, and 12 mL of concentrated sulfuric acid was added. The solution was then refluxed at 95 °C for 12 h and cooled until a crude product precipitated as white crystalline flakes. The reaction system was filtered and the precipitate was collected. The precipitate was recrystallized twice with ethanol and dried at 50 °C for 24 h to obtain target compound 1. S2. Compound 1 (2 g) and potassium carbonate (5.97 g) were added to a 500 mL three-necked flask equipped with a magnetic stirrer. After evacuating the reaction flask and circulating nitrogen three times, 200 mL of acetonitrile was added. Subsequently, 4.73 g of pentylene-2-toluenesulfonate dissolved in 100 mL of acetonitrile was added dropwise at 70 °C over 2 hours. After the addition was complete, the reaction was stirred at the same temperature for 48 hours. After the reaction was completed, the mixture was cooled to room temperature and filtered. The filtrate was evaporated to dryness under reduced pressure. The crude product was purified by silica gel column chromatography (using ethyl acetate and dichloromethane in a volume ratio of 40:60 as eluents) to obtain compound 2. S3. Compound 2 (1 g, 2.2 mmol) was dissolved in 50 mL of anhydrous ethanol, and 9.87 g of hydrazine hydrate solution was added. The mixture was heated to 95 °C and refluxed for 15 hours. After the reaction was completed, the mixture was cooled to room temperature, and the solvent was evaporated under reduced pressure to give the product Tph-18C6. S4. Add 6.4 mg of monomer Tph-18C6 to 20 mL of 1 M acetic acid aqueous solution and allow it to dissolve completely to prepare a base phase solution; S5. Add 2.1 mg of aldehyde monomer Tp to a mixed solvent consisting of 2 ml ethyl acetate and 18 ml m-trimethylbenzene, and dissolve it completely to prepare a top phase solution. S6. Slowly add the top phase solution to the surface of the bottom phase solution, control the reaction temperature at 35 ℃, keep the two phases in interfacial contact and let them stand for 6 days to allow the film to gradually form and grow at the phase interface. S7. After the reaction is complete, the COF film formed at the interface is removed from the reaction system and washed three times in sequence with ethanol, methanol and deionized water to remove unreacted monomers, residual catalyst and organic solvent. S8. The 18C6-COF membrane obtained above is flatly attached to a polyacrylonitrile (PAN) substrate with a diameter of 2 cm, and the composite membrane is installed in an H-type reactor so that only one side of the membrane is exposed to the reaction solution environment to form a single-sided selective modification structure. S9. Weigh 0.6 g of 1,3-propanesulfonyl lactone and dissolve it in 20 ml of methanol to prepare a homogeneous and transparent sulfonyl lactone reaction solution. S10. The sulfonyl lactone solution is injected into the reaction chamber near the membrane surface in the H-type reactor, so that it undergoes a ring-opening reaction with the exposed -NH- active sites on the membrane surface. The reaction temperature is 60°C and the reaction time is 8 hours. S11. After the reaction is complete, the obtained membrane sample is repeatedly washed with methanol to remove unreacted monomers and byproducts; then the membrane is continuously immersed in deionized water. S12. The membrane sample treated in S11 can be naturally dried at room temperature to obtain a supramolecular ion separation membrane with an asymmetric functionalized nanochannel structure, denoted as 18C6-COF-S. 8h .

[0036] Comparative Example The preparation method of this comparative example is the same as that of Example 1, except that the 1,3-propanesulfonyl lactone modification step is not performed, and the other steps are the same as those of Example 1.

[0037] The preparation method of a supramolecular ion separation membrane with an asymmetric functionalized nanochannel structure in this comparative example includes the following steps: S1. In a 500 mL round-bottom flask, 2,3-dihydroxyterephthalic acid (5.0 g, 25 mmol) was dissolved in 200 mL of anhydrous ethanol, and 12 mL of concentrated sulfuric acid was added. The solution was then refluxed at 95 °C for 12 h and cooled until a crude product precipitated as white crystalline flakes. The reaction system was filtered and the precipitate was collected. The precipitate was recrystallized twice with ethanol and dried at 50 °C for 24 h to obtain target compound 1. S2. Compound 1 (2 g) and potassium carbonate (5.97 g) were added to a 500 mL three-necked flask equipped with a magnetic stirrer. After evacuating the reaction flask and circulating nitrogen three times, 200 mL of acetonitrile was added. Subsequently, 4.73 g of pentylene-2-toluenesulfonate dissolved in 100 mL of acetonitrile was added dropwise at 70 °C over 2 hours. After the addition was complete, the reaction was stirred at the same temperature for 48 hours. After the reaction was completed, the mixture was cooled to room temperature and filtered. The filtrate was evaporated to dryness under reduced pressure. The crude product was purified by silica gel column chromatography (using ethyl acetate and dichloromethane in a volume ratio of 40:60 as eluents) to obtain compound 2. S3. Compound 2 (1 g, 2.2 mmol) was dissolved in 50 mL of anhydrous ethanol, and 9.87 g of hydrazine hydrate solution was added. The mixture was heated to 95 °C and refluxed for 15 hours. After the reaction was completed, the mixture was cooled to room temperature, and the solvent was evaporated under reduced pressure to give the product Tph-18C6. S4. Add 6.4 mg of monomer Tph-18C6 to 20 mL of 1 M acetic acid aqueous solution and allow it to dissolve completely to prepare a base phase solution; S5. Add 2.1 mg of aldehyde monomer Tp to a mixed solvent consisting of 2 ml ethyl acetate and 18 ml m-trimethylbenzene, and dissolve it completely to prepare a top phase solution. S6. The top phase solution is slowly added to the surface of the bottom phase solution, and the reaction temperature is controlled at 35 °C. The two phases are kept in interfacial contact and allowed to stand for 6 days to allow the film to gradually form and grow at the phase interface. S7. After the reaction is complete, the COF membrane formed at the interface is removed from the reaction system and washed three times in sequence with ethanol, methanol and deionized water to remove unreacted monomers, residual catalyst and organic solvent, and finally a supramolecular ion separation membrane with nanochannel structure is obtained, denoted as 18C6-COF.

[0038] Test case 1. The structure of compound 1 obtained in Example 1 was analyzed by nuclear magnetic resonance (NMR) technique. Figure 2 As can be seen, the analysis of the 1H NMR spectrum of compound 1 shows a high degree of agreement with the target structure. A singlet with a chemical shift of 11.02 ppm was observed in the low-field region, corresponding to 2H, which can be clearly attributed to the two phenolic hydroxyl groups. This signal is a typical feature of ortho-diphenol structures. Only one singlet (δ 7.33 ppm, 2H) exists in the aromatic region, indicating that the chemical environments of the two hydrogen atoms on the benzene ring are completely identical. In addition, the characteristic signal of the ethyl ester group is clearly visible in the spectrum: the quartet (4H) at δ 4.43 ppm belongs to the methylene group attached to oxygen, while the triplet (6H) at δ 1.43 ppm corresponds to the terminal methyl group. The integral ratio of the two sets of signals is consistent with the two identical ethyl ester group structures. In summary, the NMR data consistently confirm the synthesized compound 1.

[0039] 2. The structure of compound 2 obtained in Example 1 was analyzed using nuclear magnetic resonance (NMR) technology. Figure 3 As can be seen, analysis of the 1H NMR spectrum of compound 2 shows that its structure is in complete agreement with expectations. The most crucial evidence is the complete disappearance of the characteristic signal of the phenolic hydroxyl group at 11.02 ppm in compound 1, confirming that the phenolic hydroxyl group successfully participated in the reaction. Only a singlet (2H) at δ 7.49 ppm was observed in the aromatic region, attributed to two hydrogen atoms with the same chemical environment on the benzene ring. The spectrum clearly retains the characteristic signals of the ethyl ester group at δ 1.38 ppm (triplet, 6H) and δ 4.37 ppm (quartet, 4H), indicating that the ester group remained stable during the reaction. Multiple characteristic signals of the PEG chain appeared in the δ 3.5–4.3 ppm range: the singlet (4H) at δ 3.67 ppm was attributed to the methylene group directly attached to the benzene ring; the triplets (4H each) at δ 4.27 ppm and δ 3.94 ppm corresponded to the methylene groups adjacent to the aryl ether bond and the chain terminus, respectively; and the strong signal (8H) at δ 3.74 ppm came from the methylene group of the repeating unit in the middle of the PEG chain. The integral ratios of all signals were perfectly matched, fully confirming the successful synthesis of compound 2.

[0040] 3. The monomer Tph-18C6 obtained in Example 1 was subjected to structural analysis using nuclear magnetic resonance (NMR) technology. From... Figure 4As can be seen, the data clearly confirm the successful conversion from compound 2 to the target product. The most significant change is the complete disappearance of the ethyl ester group signal (the signals at δ 1.38 ppm and 4.37 ppm in compound 2 are no longer present), which directly verifies that the hydrazine hydrolysis reaction between hydrazine hydrate and the ester group has been completed. Simultaneously, a singlet (2H) at δ 9.48 ppm appears in the low-field region. This signal can be clearly attributed to the amide proton in the newly formed acylhydrazine group (-CONHNH2), providing direct evidence that the reaction occurred. The aromatic hydrogen signal appears at δ 7.31 ppm (singlet, 2H), and its chemical shift is significantly higher than that of compound 2 (δ 7.50 ppm). This is because the strongly electron-withdrawing ester group transforms into a weakly electron-donating acylhydrazine group, increasing the electron cloud density of the benzene ring, a change completely consistent with expectations. Furthermore, the PEG chain signal representing the macrocyclic ether skeleton was fully preserved: multiple signals at δ 3.55 ppm (single, 4H), 3.61 ppm (triple, 8H), 3.79 ppm (triple, 4H), and 4.14 ppm (triple, 4H), whose splitting modes and integral ratios are highly consistent with the symmetric structure similar to that of 18-crown-6-ether (18C6). In summary, the NMR data consistently demonstrate the successful synthesis of the monomer Tph-18C6.

[0041] 4. Surface elemental distribution analysis was performed on the supramolecular ion separation membrane with asymmetric functionalized nanochannel structure obtained in Example 2. From... Figure 6 As can be seen, the characteristic element S on the surface of the modified sample is uniformly distributed, indicating that the sulfonic acid groups have been successfully introduced and grafted onto the membrane surface.

[0042] 5. The supramolecular ion separation membrane with asymmetric functionalized nanochannel structure obtained in Example 2 was subjected to Fourier transform infrared spectroscopy (FTIR) testing. Figure 7 It can be seen that 18C6-S 6h - Lower surface at 1039 cm -1 The location shows obvious -SO3 - Characteristic absorption peaks, and its 18C6-S 6h The spectrum of the upper surface is basically consistent with that of the unmodified 18C6-COF. These results indicate that the sulfonic acid groups were successfully grafted onto only one side of the membrane surface, demonstrating that the membrane structure possesses asymmetric functionalization characteristics.

[0043] 6. The supramolecular ion separation membrane with asymmetric functionalized nanochannel structure obtained in Example 2 was subjected to X-ray photoelectron spectroscopy (XPS) testing. Figure 8 It can be seen that 18C6-S 6h - A distinct S2p characteristic peak appears on the lower surface, while 18C6-S 6h- No S2p signal was detected on the upper surface, with only a weak background vibration peak. This result indicates that sulfur exists only on one side of the membrane surface, further verifying the excellent asymmetric functionalization characteristics of the membrane structure.

[0044] 7. The contact angle of the supramolecular ion separation membrane with asymmetric functionalized nanochannel structure obtained in Example 2 was tested. Figure 9 It can be seen that 18C6-S 6h - The contact angle on the lower surface is significantly reduced, while 18C6-S 6h - The upper surface remains close to the original 18C6-COF. This significant difference in wettability fully demonstrates that the membrane prepared in this invention has asymmetric functionalization characteristics, providing a structural basis for realizing ion transport and selective separation.

[0045] 8. The supramolecular ion separation membranes with asymmetric functionalized nanochannel structures obtained in Examples 1-3 were analyzed by Fourier transform infrared spectroscopy (FTIR). Figure 10 It can be seen that as the reaction time increases, the characteristic absorption peaks corresponding to the sulfonic acid groups gradually increase, indicating that the amount of sulfonic acid groups introduced increases with the reaction time, and the degree of grafting shows a gradual increasing trend.

[0046] 9. Contact angle tests were performed on the supramolecular ion separation membranes with asymmetric functionalized nanochannel structures prepared in Examples 1-3. Figure 11 It can be seen that the contact angle of the membrane surface gradually decreases with the extension of reaction time. This trend indicates that the amount of sulfonic acid groups grafted increases with the increase of reaction time, thereby enhancing the hydrophilicity of the membrane surface.

[0047] 10. The supramolecular ion separation membrane with asymmetric functionalized nanochannel structure prepared in Example 2 was subjected to unit system ion separation tests. Salt solutions of KCl, NaCl, LiCl, and MgCl2 were placed on one side of the membrane, while pure water was placed on the other side. Separation was performed by driving ion diffusion through concentration difference. Figure 12 As can be seen from this, monovalent cations (such as K) + Na + Li + The permeation rate of ions with increasing concentration is significantly higher than that of divalent ions (such as Mg). 2+ This indicates that the membrane can overcome the charge shielding effect, effectively distinguish ions of different valence states, and has excellent ion sieving ability. 11. The supramolecular ion separation membrane with asymmetric functionalized nanochannel structure prepared in Example 2 was subjected to unit system ion separation tests. KCl and MgCl2 solutions of different concentrations were placed on one side of the membrane, while pure water was placed on the other side. Ion diffusion was driven by the concentration difference for separation testing. Figure 13As can be seen, the membrane can still maintain high selectivity in a high-salt environment.

[0048] 12. The supramolecular ion separation membrane with asymmetric functionalized nanochannel structure prepared in Example 2 was subjected to mixed salt system ion separation test. Mixed solutions of KCl / MgCl2, NaCl / MgCl2 and LiCl / MgCl2 (KCl, NaCl, LiCl and MgCl2 concentrations of 1M) were placed on one side of the membrane and pure water was placed on the other side. Ion diffusion was driven by concentration difference to evaluate its separation performance.

[0049] from Figure 14 As can be seen, the modification of sulfonic acid groups into supramolecular ion separation membranes (18C6-COF-S) with asymmetric functionalized nanochannel structures has a significant effect. 6h After that, in the 1 M mixed salt separation experiment, its K + / Mg 2+ The selectivity is further improved. This performance demonstrates that the membrane can maintain or even enhance separation selectivity in complex systems with strong salt shielding effects and more intense ion competition, indicating that its COF membrane possesses good stability. Therefore, this membrane is not only suitable for experimental conditions but also has potential advantages for practical applications such as high-salt wastewater treatment, salt lake resource extraction, and zero-liquidity discharge.

[0050] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the scope of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for preparing a supramolecular ion separation membrane having an asymmetrically functionalized nanochannel structure, characterized by, The method comprises the following steps: (1) a covalent organic framework ion separation membrane is flatly attached to a polyacrylonitrile substrate to obtain a composite membrane; the composite membrane is installed in an H-shaped reactor so that only one side of the membrane is exposed to a reaction solution environment; (2) 1,3-propane sultone is dissolved in an organic solvent to obtain a sultone solution; (3) the sultone solution is injected into a reaction chamber close to the surface of the membrane in the H-shaped reactor to undergo ring-opening reaction with the -NH- active sites exposed on the surface of the membrane; (4) after the reaction is completed, the obtained membrane sample is washed with methanol; then the membrane sample is immersed in deionized water; and drying is performed to obtain a target supramolecular ion separation membrane.

2. The method for preparing a supramolecular ion separation membrane having an asymmetrically functionalized nanochannel structure according to claim 1, characterized by, In step (1), the polyacrylonitrile substrate is in a circular shape with a diameter of 1.8-2.2 cm; the channel inner diameter of the H-shaped reactor is 0.9-1.1 cm, and the cross-sectional size is 1.8-2.2 cm; the electrolytic cell of the H-shaped reactor has an inner diameter of 2.0-2.5 cm, an outer diameter of 2.3-2.8 cm, and a height of 8-10 cm.

3. The method for preparing a supramolecular ion separation membrane having an asymmetrically functionalized nanochannel structure according to claim 1, characterized by, In step (2), the organic solvent is methanol, and the mass / volume ratio g / mL of 1,3-propane sultone and the organic solvent is 1:30-40.

4. The method of claim 1, wherein the method is characterized by: In step (3), the reaction temperature is 55-65℃, and the reaction time is 4-8 h.

5. The method of claim 1, wherein the method is characterized by: In step (4), the drying is specifically that the treated sample is dried at room temperature.

6. The method of claim 1, wherein the method is characterized by: In step (1), the preparation method of the covalent organic framework ion separation membrane comprises the following steps: S1, 2,3-dihydroxyterephthalic acid is added to anhydrous ethanol, concentrated sulfuric acid is added, refluxing is performed, cooling is performed, the precipitate is collected and dried to obtain compound 1; S2, compound 1 and potassium carbonate are added to acetonitrile, the solution system is controlled at 68-72℃, and di-p-toluenesulfonic acid pentanediol solution is added dropwise, and the stirring reaction is continued, and then cooling and filtration are performed, and the filtrate is dried under reduced pressure to obtain a product, which is purified by silica gel column chromatography to obtain compound 2; S3, compound 2 is added to anhydrous ethanol, hydrazine hydrate is added, heating refluxing is performed, cooling is performed, and drying under reduced pressure is performed to obtain product Tph-18C6; S4, Tph-18C6 is added to an acetic acid solution to prepare a bottom phase solution; S5, an aldehyde monomer is added to a mixed solvent composed of ethyl acetate and m-trimethylbenzene to prepare a top phase solution; S6, the top phase solution is added to the surface of the bottom phase solution, and standing reaction is performed to obtain a COF membrane; S7, the COF membrane is taken out of the reaction system, washed, and a covalent organic framework ion separation membrane is obtained; the structural formula of the compound 1 is shown in formula (1); （1）； the structural formula of the compound 2 is shown in formula (2); （2）； the structural formula of the Tph-18C6 is shown in formula (3): （3）。 7. The method of claim 5, wherein the method further comprises the step of: 5 introducing a functional group into the nanochannel structure. In step S1, the mass-volume ratio g / mL of 2,3-dihydroxyterephthalic acid and anhydrous ethanol is 1:38-42; the mass-volume ratio g / mL of 2,3-dihydroxyterephthalic acid and concentrated sulfuric acid is 1:2-3; the mass concentration of the concentrated sulfuric acid is 95%-99%; the reflux temperature is 90-95℃, and the reflux time is 8-12h; the precipitate is collected and recrystallized with ethanol for 2-3 times; the drying temperature is 50-60℃, and the drying time is 12-36h; In step S2, the mass ratio of the compound 1 and potassium carbonate is 1:2.7-3.3; the mass-volume ratio g / mL of the compound 1 and acetonitrile is 1:90-110; the pentylene glycol solution of di-p-toluenesulfonic acid is composed of the mass-volume ratio g / mL of pentylene glycol and di-p-toluenesulfonic acid and acetonitrile is 1:20-25; the mass ratio of the compound 1 and pentylene glycol solution of di-p-toluenesulfonic acid is 1:2.1-2.5; the time for dropping the pentylene glycol solution of di-p-toluenesulfonic acid is 1.5-2.5h; the stirring temperature is 68-72℃, and the stirring time is 24-60h; and the cooling to room temperature.

8. The method of claim 5, wherein the method further comprises the step of: In step S3, the mass-volume ratio g / mL of the compound 2 and anhydrous ethanol is 1:50-60; the mass ratio of the compound 2 and hydrazine hydrate solution is 1:9-13, and the mass concentration of the hydrazine hydrate solution is 70%-80%; the heating reflux temperature is 90-95℃, and the reflux time is 14-16h; and the cooling to room temperature. In step S4, the mass ratio of the monomer Tph-18C6 and the aldehyde monomer in step S5 is 6-7:2-3; In step S4, the mass-volume ratio g / mL of the Tph-18C6 and acetic acid solution is 6-7:20-25; and the concentration of the acetic acid solution is 0.9-1.1mol / L; In step S5, the volume ratio of ethyl acetate and m-trimethylbenzene in the mixed solvent is 0.9-1.1:8-10; the mass-volume ratio g / mL of the aldehyde monomer and the mixed solvent is 2-3:20-30; and the aldehyde monomer is trihydroxybenzene; In step S6, the reaction time is 5-7d, and the reaction temperature is 33-37℃; In step S7, the washing specifically comprises: sequentially washing 2-4 times with ethanol, methanol and deionized water.

9. A supramolecular ion separation membrane having asymmetrically functionalized nanochannel structures, characterized in that, Prepared by the preparation method in any one of claims 1-8.

10. The application of the supramolecular ion separation membrane with asymmetric functionalized nanochannel structure in water treatment in claim 9.

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