Covalent organic framework membrane based on biomimetic mineralization strategy, preparation method and application of ion separation

Abstract

The present application relates to a kind of covalent organic framework film preparation based on biomimetic mineralization strategy and its application in ion separation.In the process of monovalent ion separation, methoxy forms stable interaction with monovalent ion through its unique coordination characteristics and electronegativity, significantly improves the transmission rate of monovalent ion. At the same time, the introduction of functionalized methoxy can also effectively inhibit the passage of divalent ion, so as to realize efficient ion separation. Biomimetic mineralization strategy can significantly improve the mechanical strength and chemical stability of COF membrane by compounding organic polymer with COF. Compared with traditional separation membrane, the biomimetic mineralized COF membrane provided by the present application exhibits higher separation efficiency, more excellent selectivity and longer service life, and is suitable for efficient extraction of lithium and other monovalent ion resources, battery material preparation and ion separation application in related industrial production process. The functionalized methoxy COF membrane material of the present application has the advantages of adjustable structure, simple preparation and potential for large-scale production.

Description

Technical Field

[0001] This invention relates to the preparation and application of a covalent organic framework membrane based on a biomimetic mineralization strategy, belonging to the field of covalent organic framework membrane technology. Background Technology

[0002] Monovalent ions (Li + Na + K + Lithium (MgO, MgO, MgO) is a crucial strategic resource for modern energy and technology industries, and a key raw material for the production of high-energy-density batteries. Its demand has increased significantly with the rapid growth of markets such as electric vehicles and portable electronic devices. However, the extraction of monovalent ions remains challenging. For example, in the development of lithium resources, extraction from salt lake brine is the primary method due to its advantages of low development costs, minimal environmental impact, and high economic benefits. Lithium resources in salt lake brine are often accompanied by magnesium ions (MgO). 2+ ), due to Mg 2+ With Li + Similar in physicochemical properties, especially in ionic radius and hydrate structure, these materials are difficult to separate effectively during extraction. In recent years, membrane separation technology has become a popular solution for Li-related problems due to its high efficiency, high selectivity, and environmental friendliness. + / Mg 2+ A potential approach to solving the separation problem. Compared with traditional separation methods, membrane separation technology can achieve highly selective separation of target ions by precisely controlling the pore size, surface chemical properties, and functionalization of membrane materials. Covalent organic framework (COF) membranes, due to their high porosity, high stability, and high tunability, have become a promising solution for Li... + / Mg 2+ A research hotspot in the field of separation. Functional modification of COF membranes, such as introducing methoxy and crown ether functional groups, can significantly improve the resorption capacity for Li. + Selective transport and reduced membrane sensitivity to Mg 2+ The permeability of COF membranes is crucial. Nature regulates mineralization processes through polymers, resulting in highly stable and dense hardened materials. This phenomenon provides a novel guiding principle for the transformation of COF from solution-phase monomers to solid-phase membranes. By uniformly introducing organic molecules onto or within the COF membrane surface, it is hoped that the membrane's structural stability can be enhanced, defects can be controlled, and novel membrane separation materials with high selectivity and high permeability can be developed, thus providing a basis for Li... + / Mg 2+ The plasma separation process has brought about a revolutionary breakthrough. Summary of the Invention

[0003] Based on the above technical background, the present invention provides a method for designing and preparing covalent organic framework membranes based on a biomimetic mineralization strategy.

[0004] This application relates to the preparation and application of a covalent organic framework (COF) membrane material. COF is a class of highly ordered crystalline porous materials formed by organic ligand molecules linked by covalent bonds. The structural design of COF materials is highly tunable; different combinations of organic units endow COF membranes with different pore characteristics and pore sizes. Therefore, precise design and customization can be carried out according to specific application requirements, making COF membranes exhibit broad application potential in the field of separation.

[0005] A covalent organic framework membrane based on a biomimetic mineralization strategy is designed and prepared, and its preparation method includes the following steps:

[0006] Step 1: Dissolve the aldehyde monomer in an organic solvent and add a catalyst to form solution 1. Solve the amino monomer in deionized water to form solution 2.

[0007] Step 2: Place the base membrane in the middle of the H-shaped diffusion cell and secure both sides of the diffusion cell with metal clips. Add solution 1 to the diffusion cell facing the front of the base membrane and solution 2 to the diffusion cell facing the back. Seal the diffusion cell and allow it to react under constant conditions for a period of time.

[0008] Step 3: After the reaction is complete, remove the COF membrane, clean its surface, and let it stand at room temperature for later use.

[0009] The aldehyde monomer in step one is selected from 2,4,6-tricarboxymethyl phloroglucinol and 1,3,5-trimethoxy-2,4,6-tricarboxymethyl benzene, and the amount of the selected monomer is 0.01 mmol-0.1 mmol.

[0010] The organic solvent may be selected from dichloromethane, mesitylene, dimethyl sulfoxide, anisole, or ethyl acetate, and the volume of the solvent shall be 5-50 mL to achieve complete solvent treatment of the monomer.

[0011] The catalyst used can be selected from octanoic acid, acetic acid, concentrated hydrochloric acid (35-37%), and concentrated sulfuric acid (93-98%), with a concentration of 1 mol / L-10 mol / L.

[0012] The amino monomer is selected from 2,5-diaminoanisole, 2,5-dimethoxy-p-phenylenediamine, and p-phenylenediamine. The amount of the selected monomer used is 0.01 mmol to 0.1 mmol, and the volume of deionized water used is 5 to 50 mL.

[0013] When the aldehyde monomers and amino monomers are combined, the aldehyde monomers contain methoxy groups. In addition, the combination of p-phenylenediamine and 2,4,6-tricarboxymethyl phloroglucinol is used as a control experiment.

[0014] The amount of PEI added to the solution is determined based on the mass of the amino monomer, ranging from 1% to 30% of the amino monomer mass, with a preferred addition amount of 10-20%, and more preferably 10%. The selected PEI has a molecular weight range of 1000 to 50000 Da to ensure that the formed membrane has high continuity and chemical stability; preferably, PEI with a molecular weight of 10000 Da. During the preparation process, PEI can be flexibly added to either side of the diffusion cell according to the characteristics of the base membrane: hydrophobic base membranes can be added to the solution side 1 on the front side of the base membrane, or the solution side 2 on the back side of the hydrophilic base membrane, both can perform their functions.

[0015] The base film material used in step two can be selected from a variety of polymeric materials such as polyacrylonitrile (PAN), polysulfone (PSU), polyethylene terephthalate (PET), polyamide (PA), and polytetrafluoroethylene (PTFE). Each of these base film materials possesses unique properties, providing excellent mechanical strength, chemical stability, and interfacial compatibility under different operating conditions. The specific base film material selected can be optimized according to the requirements of the final application. In this preparation method, constant reaction conditions are achieved by controlling the temperature to ensure the stability of the mineralization process and uniform mineral deposition. The reaction temperature range can be adjusted between 20°C and 100°C, with 50-60°C being the preferred temperature. The settling time can be adjusted between 1 and 5 days, with a preferred settling time of 2-4 days. Within this timeframe, the continuity of the COF membrane is ensured, while performance degradation due to over- or incomplete reaction is avoided.

[0016] In some preferred embodiments, the selection of amino and aldehyde monomers must include a class of monomers containing a methoxy group. When selecting monomers for preparation, if the aldehyde monomer is 2,4,6-tricarboxymethyl phloroglucinol and the amino monomer is 2,5-diaminoanisole, the corresponding COF membrane is TpPaOCH3@PEI (10 w%), where w% is the percentage of the mass of PEI to the mass of the amino monomer. For example, if the mass of PEI is 10% of the mass of the amino monomer, it is recorded as 10 w.

[0017] In some preferred embodiments, when the aldehyde monomer is 2,4,6-tricarboxymethyl phloroglucinol and the amino monomer is 2,5-dimethoxy-p-phenylenediamine, the corresponding COF membrane is TpPa(OCH3)2@PEI (10 w%), where w% is the percentage of the mass of PEI to the mass of the amino monomer. For example, if the mass of PEI is 10% of the mass of the amino monomer, it is recorded as 10 w.

[0018] In some preferred embodiments, when the aldehyde monomer is 2,4,6-tricarboxymethyl phloroglucinol and the amino monomer is p-phenylenediamine, the corresponding COF membrane is TpPa (10 w%), where w% is the percentage of the mass of PEI to the mass of the amino monomer. For example, if the mass of PEI is 10% of the mass of the amino monomer, it is recorded as 10 w.

[0019] In some preferred embodiments, when the amino monomer is p-phenylenediamine, the corresponding COF film is TMFBPa@PEI (10 w%), where w% is the percentage of the mass of PEI to the mass of the amino monomer. For example, if the mass of PEI is 10% of the mass of the amino monomer, it is recorded as 10 w.

[0020] Another technical solution of the present invention is to provide a COF membrane based on biomimetic mineralization, wherein the COF layer is formed by polymerization of amino monomer units and aldehyde monomer units, wherein the aldehyde monomer units and amino monomer units are respectively added to both sides of the base membrane and diffuse to the positive surface of the base membrane to undergo a polymerization reaction.

[0021] The monomer in the aldehyde monomer unit is selected from 2,4,6-tricarboxymethyl phloroglucinol and 1,3,5-trimethoxy-2,4,6-tricarboxymethyl benzene.

[0022] The monomer in the amino monomer unit is selected from any one of 2,5-diaminoanisole, 2,5-dimethoxy-p-phenylenediamine, and p-phenylenediamine.

[0023] In the examples above, the combination of p-phenylenediamine and 2,4,6-tricarboxymethylphloroglucinol served as a control experiment.

[0024] When the base membrane is hydrophobic, the aldehyde monomer is dissolved in an organic solvent and applied to the front side of the hydrophobic base membrane, while an aqueous solution is added to the other side. If the base membrane is hydrophilic, the amino monomer is dissolved in an aqueous solution and applied to the front side of the hydrophilic base membrane. In hydrophobic base membranes, PEI is preferably added to the solution side corresponding to the front side of the base membrane, while in hydrophilic base membranes, PEI is preferably added to the back side to fully utilize its role in promoting membrane structure stability and improving separation performance.

[0025] In some specific embodiments, the raw materials for the amino monomer unit also include a mixed solution formed by adding a catalyst to an organic solvent, wherein the organic solvent is selected from dichloromethane, mesitylene, dimethyl sulfoxide, anisole, and ethyl acetate, and the catalyst is selected from octanoic acid, acetic acid, hydrochloric acid (35-37%), and sulfuric acid (93-98%).

[0026] The amount of the aldehyde monomer used is 0.01 mmol-0.1 mmol, and the catalyst concentration is 1 mol / L-10 mol / L; the amount of the amino monomer used is 0.01 mmol-0.1 mmol.

[0027] The base film material is selected from any one of polyacrylonitrile (PAN), polysulfone (PSU), polyethylene terephthalate (PET), polyamide (PA), and polytetrafluoroethylene (PTFE).

[0028] The process of interfacial polymerization of aldehyde monomer units and amino monomer units on both sides of the base film refers to the process of impregnation and static diffusion of monomer units of the base film twice at a certain temperature.

[0029] In some embodiments, the diffusion temperature is adjusted between 20°C and 100°C, with 60-80°C being a preferred temperature; the settling reaction time can be adjusted between 1 and 5 days, with a preferred settling time of 2-4 days.

[0030] In some embodiments, the biomimetic mineralized COF film of the present invention is characterized by an X-ray diffraction (XRD) 2θ value including a characteristic peak at approximately 5° ± 0.2°, indicating that the COF film has an ordered crystal structure.

[0031] The X-ray diffraction (XRD) 2θ also includes 27 o The characteristic peak at ±0.4° represents the stacking effect of the crystalline structures between COFs.

[0032] Another technical solution of the present invention provides a new application of a biomimetic mineralized COF membrane, based on the application of the biomimetic mineralized COF membrane in ion separation, wherein the ions include two or more types of ions such as potassium ions, sodium ions, lithium ions, magnesium ions, and calcium ions. The metal salts used are halides, including chloride salts, bromide salts, and iodide salts, and it is ensured that the metal salts are of the same type of halide during separation.

[0033] In some embodiments, a halide concentration of 0.05-0.5 mol / L can achieve the effect of membrane separation.

[0034] In the technical solution of this invention, monovalent / divalent ions are separated, such as Li + / Mg 2+ Introducing oxygen-containing groups (such as methoxy groups, crown ethers, etc.) during the separation process can significantly improve separation performance. + Due to its small radius and high charge density, it interacts strongly with oxygen-containing groups, thereby promoting the Li + Highly efficient transport. Although Mg 2+ It has a higher charge number, but due to its larger ionic radius, its charge density is lower than that of Li.+ At the same time, its high degree of hydration makes Mg 2+ The coordination effect with oxygen-containing groups is relatively weak. Furthermore, the introduction of oxygen-containing groups also leads to a moderate reduction in the pore size of the COF membrane, which further inhibits the growth of Mg with a large hydration radius. 2+ The transmission efficiency is improved, enhancing the membrane's ability to transport Li. + The selectivity of Li is improved. Based on this mechanism, a functionalized methoxylated COF membrane was prepared in this invention. The introduction of methoxy groups significantly enhances the selectivity of Li. + The transmission rate was increased, and the Mg content was effectively reduced. 2+ The diffusion rate was significantly improved. Simultaneously, by introducing PEI as a regulator during the COF membrane preparation process, the growth process of the COF membrane was controlled, significantly enhancing the membrane's stability. PEI not only provides abundant amino sites during film formation but also forms strong chemical bonds with the organic matrix in the COF membrane, enhancing the membrane's stability and continuity. Even under harsh operating conditions, such as high temperature and strong acid / alkali environments, the membrane maintains its structural integrity.

[0035] By employing a biomimetic mineralization strategy, polymer regulation is introduced during the COF film formation process to repair intergranular defects and reduce reaction energy barriers. Simultaneously, methoxy functional groups are modified on the COF pore walls to enhance the selective transport performance of the membrane for monovalent ions.

[0036] This invention relates to the design and fabrication of a COF membrane based on a biomimetic mineralization strategy. The introduction of methoxy groups significantly improves the separation efficiency of monovalent / divalent ions in the membrane material. Using monovalent Li... + and Mg 2+ Taking selective separation as an example, the biomimetic mineralization strategy of this invention significantly improves the COF membrane of Li. + / Mg 2+ Selectivity and efficiency in separation. The membrane, through its interaction with Li... + The formation of relatively high interactions promotes Li + The rapid transmission of Mg 2+ Due to its large radius and low charge density, the interaction with methoxy groups is weak, resulting in a significantly reduced transport rate. Compared with traditional separation methods, the methoxy-coated COF membrane prepared in this invention exhibits higher selectivity and stability, making it suitable for efficient and environmentally friendly Li₂ separation. + / Mg 2+ The separation process. This method is simple and feasible, and the prepared membrane material is uniform and dense, showing broad application prospects and is expected to become a key component in Li₂. + / Mg 2+ A significant technological breakthrough in the field of separation. Attached Figure Description

[0037] Figure 1The images show scanning electron microscope (SEM) surface and cross-sectional views of the embodiments TMFBPa@PEI (10 w%), TpPa(OCH3)2@PEI (10 w%), and TpPaOCH3@PEI (10 w%). Images 1a and 1b are SEM images of the surface and cross-section of TMFBPa@PEI (10 w%), respectively. Figure 1 c and d are surface and cross-sectional electron micrographs of TpPa(OCH3)2@PEI (10 w%). Figure 1 e and f are electron micrographs of the surface and cross-section of TpPaOCH3@PEI (10 w%).

[0038] Figure 2 The infrared spectra of TMFBPa@PEI (10 w%), TpPa(OCH3)2@PEI (10 w%), and TpPaOCH3@PEI (10 w%) are shown in the examples. Figure 2 a is the TMFBPa@PEI (10 w%) infrared image. Figure 2 b is the infrared image of TpPa(OCH3)2@PEI (10 w%). Figure 2 c is the infrared image of TpPaOCH3@PEI (10 w%).

[0039] Figure 3 The XRD patterns of the examples TMFBPa@PEI (10 w%), TpPa(OCH3)2@PEI (10 w%), and TpPaOCH3@PEI (10 w%) are shown below, from top to bottom.

[0040] Figure 4 The following are BET pore size analysis diagrams for the examples TMFBPa@PEI (10 w%), TpPa(OCH3)2@PEI (10 w%), and TpPaOCH3@PEI (10 w%). Figure 4 a is the pore size distribution diagram of TMFBPa@PEI (10 w%). Figure 4 b is the pore size distribution diagram of TpPa(OCH3)2@PEI (10 w%). Figure 4 c is the pore size distribution diagram of TpPaOCH3@PEI (10 w%).

[0041] Figure 5 Li is shown in the embodiment of the present invention. + / Mg 2+ Comparison results of separation performance. Detailed Implementation

[0042] The specific embodiments of the present invention will be further described with reference to the accompanying drawings. The specific embodiments described are only used to explain the principles and implementation process of the present invention and do not constitute a limitation on the present invention.

[0043] Example 1: Preparation of TMFBPa@PEI (10 w%) membrane, the steps are as follows:

[0044] Step 1: Dissolve 0.5 mmol of 1,3,5-trimethoxy-2,4,6-tricarboxyphenyl in 15 mL of anisole, and add 0.1 mL of n-octanoic acid. Dissolve 0.75 mmol of p-phenylenediamine in 15 mL of deionized water. Sonicate both solutions separately for 2 min and set aside for later use.

[0045] Step 2: Place the polyacrylonitrile (PCA) membrane between diffusion cells and secure it with metal clamps. Pour the dispersed anisole solution into the diffusion cell on the front side of the PCA membrane, and pour the aqueous solution into the diffusion cell on the other side. Add 10% (w / w) of PEI (amino monomer by mass). Transfer the diffusion cells to a 60°C oven and allow the reaction to proceed for 4 days. After the reaction is complete, remove the COF membrane, wash it three times with ethanol and deionized water, and dry it at room temperature to obtain the TMFBPa@PEI (10 w%) membrane.

[0046] Figure 1 Images a and b show scanning electron microscope (SEM) images of the surface morphology and cross-sectional structure of the TMFBPa@PEI (10 w%) film, respectively. As can be seen from the images, the prepared TMFBPa@PEI (10 w%) film has a smooth surface without obvious defects and a uniform film thickness. Figure 2 a is the infrared spectrum of the TMFBPa@PEI (10 w%) film, where the characteristic peak at 1091 cm⁻¹ corresponds to the vibration of the CO bond, indicating that the methoxy-functionalized COF has been successfully synthesized, and the stretching vibration peak of -NH at 1590 cm⁻¹ indicates the successful recombination of PEI. Figure 3 The XRD pattern of the TMFBPa@PEI (10 w%) film is shown. The diffraction peaks near 5° reflect the high crystallinity of the COF film, confirming the formation of long-range ordered pore structure in the TMFBPa@PEI (10 w%) film. Figure 4 The diagram shows the BET pore size distribution of the TMFBPa@PEI (10 w%) membrane, indicating that the membrane has a minimal pore structure, further demonstrating that the introduction of methoxy groups effectively reduces the pore size of the COF membrane.

[0047] Example 2: Preparation of TpPa(OCH3)2@PEI (10 w%) membrane. The steps were basically the same as in Example 1, except that 1,3,5-trimethoxy-2,4,6-tricarboxyphenylene in step 1 was replaced with 2,4,6-tricarboxymethyl phloroglucinol, and p-phenylenediamine was replaced with 2,5-dimethoxy-p-phenylenediamine. The other steps remained the same.

[0048] Figure 1 Images c and d show the surface and cross-sectional electron micrographs of the TpPa(OCH3)2@PEI (10 w%) film, respectively. As can be seen from the images, the prepared TpPa(OCH3)2@PEI (10 w%) film has a smooth surface without obvious defects, and the film thickness is uniform. Figure 2 b is the infrared spectrum of the TpPa(OCH3)2@PEI (10 w%) film. The peak at 1093 cm⁻¹ corresponds to the characteristic of the CO bond, indicating the successful preparation of methoxy functionalized COF. The peak at 1585 cm⁻¹ is the stretching vibration peak of -NH, indicating the successful composite of PEI. Figure 3 The image shows the XRD pattern of the TpPa(OCH3)2@PEI (10 w%) membrane. The peak at around 5° indicates that the COF membrane has high crystallinity, which proves that the TpPa(OCH3)2@PEI (10 w%) membrane forms a long-range ordered pore structure. Figure 4 b is the BET pore size distribution of the TpPa(OCH3)2@PEI (10 w%) membrane, showing that the membrane has a smaller pore structure, but its pores are larger than those of the TMFBPa@PEI (10 w%) membrane. This indicates that the number of AX groups introduced will significantly affect the pore size of the COF membrane; the more AX groups introduced, the smaller the pore size.

[0049] Example 3: Preparation of TpPaOCH3@PEI (10 w%) membrane. The steps were basically the same as in Example 1, except that 1,3,5-trimethoxy-2,4,6-tricarboxyphenylene in step 1 was replaced with 2,4,6-tricarboxymethyl phloroglucinol, and p-phenylenediamine was replaced with 2,5-diaminoanisole. All other steps remained the same.

[0050] Figure 1 Images c and d show electron micrographs of the surface morphology and cross-sectional structure of the TpPaOCH3@PEI (10 w%) film, respectively. The images reveal that the prepared TpPaOCH3@PEI (10 w%) film has a smooth surface without obvious defects, and its thickness is uniform. Figure 2c is the infrared spectrum of the TpPaOCH3@PEI (10 w%) film, where the peak at 1096 cm⁻¹ corresponds to the characteristic vibration peak of the CO bond, verifying the successful introduction of the methoxy group into the COF structure, and the peak at 1580 cm⁻¹ is the stretching vibration peak of -NH, indicating the successful recombination of PEI. Figure 3 The XRD pattern of the TpPaOCH3@PEI (10 w%) film shows a diffraction peak at approximately 5°, indicating that the COF film has high crystallinity and a long-range ordered pore structure. Figure 4 a is the BET pore size distribution of the TpPaOCH3@PEI(10 w%) membrane. The results show that the membrane has a relatively small pore structure, but the pore size is larger than that of the TMFBPa@PEI(10 w%) membrane and the TpPa(OCH3)2 membrane. This further indicates the effect of the amount of methoxy groups introduced on the pore size of the COF membrane. As the amount of methoxy groups increases, the pore size tends to decrease.

[0051] Example 4: Preparation of TpPa@PEI (10 w%) membrane. The steps were basically the same as in Example 1, except that 1,3,5-trimethoxy-2,4,6-tricarboxyphenyl in step one was replaced with 2,4,6-tricarboxypyrogallol. All other steps remained the same. Its separation performance was as follows: Figure 5 As shown.

[0052] Example 5: Preparation of polyacrylonitrile (HPAN) membrane. No amino or aldehyde monomers were added in step one, and all other conditions remained the same as in Example 1. Its separation performance was as follows: Figure 5 As shown.

[0053] Step 3: Perform ion separation test.

[0054] Ion separation testing was conducted using an H-type electrolytic cell, the most commonly used ion self-diffusion separation testing system. The diffusion rate of ions was measured by connecting a conductivity meter. In the apparatus, the diffusion cell was divided into a feed side and a diffusion side. The feed side contained a certain volume of the analyte salt ion solution, with a concentration set at 0.1 mol / L, while the diffusion side contained an equal volume of deionized water. The conductivity change on the diffusion side was measured at preset time intervals, and the ion concentration diffused to the diffusion side was calculated based on these data. The ion diffusion rate could be calculated by the concentration change over a constant time. The separation effect was evaluated using a separation factor, which was the ratio of the diffusion rates of the two ions. For example, when testing Na… + With Li + To achieve the desired separation effect, sodium ions and Li ions need to be measured separately. + The diffusion rate of Na + Diffusion rate divided by Li + The diffusion rate of Na was determined to obtain the Na + / Li+ Separation factor. The larger the separation factor, the more significant the separation effect.

[0055] The test results based on the above embodiments are as follows: Figure 4 As shown in the figure, among all tested membranes, the MFBPa@PEI (10 w%) membrane with three methoxy groups exhibited the best lithium-magnesium separation performance. This was followed by the TpPa(OCH3)2@PEI (10 w%) membrane containing two methoxy groups and the TpPaOCH3@PEI (10 w%) membrane containing one methoxy group, while the TpPa@PEI (10 w%) membrane without any methoxy groups showed poor separation performance. This indicates that the number of methoxy groups significantly affects the separation performance of COF membranes in Li... + / Mg 2+ The separation performance is significantly affected; compared to traditional methoxyl-free TpPa@PEI (10 w%) membranes, increasing the number of methoxy groups effectively improves the membrane's separation performance. This achievement highlights the importance of methoxyl functionalization in COF membrane design and provides new insights for the development of future high-performance ion separation membranes.

[0056] Separation performance such as Figure 5 As shown. Among them, the TMFBPa@PEI (10 wt%) composite film with the highest methoxy content exhibits the best Li... + / Mg 2+ Separation effect. As the methoxy content in the membrane gradually decreases, Li + / Mg 2+ The separation performance decreased significantly, indicating that the methoxy group played a role in promoting the separation of Li + Transport plays a significant role and can effectively suppress Mg. 2+ The transport rate. Compared with the methoxyl-free COF membrane, the latter's Li + / Mg 2+ Its separation ability is extremely low, almost negligible. Meanwhile, the Li in the base film HPAN... + / Mg 2+ The separation performance was even worse, further confirming the effectiveness of COF membranes in Li + / Mg 2+ It played a major role in the separation process, demonstrating the key role of methoxyl functionalization in improving separation performance.

[0057] Although the invention has been described in detail above with reference to the accompanying drawings, the invention is not limited to the specific embodiments shown. These embodiments are merely examples and are not intended to be restrictive. Those skilled in the art, after understanding the basic principles of the invention, can make various modifications and adjustments without departing from the core idea of ​​the invention, and all such modifications and adjustments should be considered within the scope of protection of the invention.

Claims

1. A method for preparing a covalent organic framework membrane based on a biomimetic mineralization strategy, characterized in that, Includes the following steps: Step 1: Dissolve the aldehyde monomer in an organic solvent and add a catalyst to form solution 1. Dissolve the amino monomer in deionized water and disperse it evenly to form solution 2. The aldehyde monomer is 1,3,5-trimethoxy-2,4,6-tricarboxyphenyl; The amino monomer is selected from any one of 2,5-diaminoanisole, 2,5-dimethoxy-p-phenylenediamine, and p-phenylenediamine; The organic solvent is selected from any one of dichloromethane, mesitylene, dimethyl sulfoxide, anisole, and ethyl acetate, and the catalyst used is selected from one of octanoic acid, acetic acid, concentrated hydrochloric acid, and concentrated sulfuric acid; Step 2: Place the base film in the middle of the H-shaped diffusion cell. Add solution 1 to the diffusion cell facing the front of the base film and solution 2 to the diffusion cell facing the back. Then add a certain equivalent amount of polyethyleneimine (PEI) to the diffusion cell. The amount of PEI added is 1% to 30% of the mass of the amino monomer. Seal the diffusion cell and let it stand for a period of time under constant conditions. Step 3: After the reaction is complete, remove the COF membrane, clean its surface, and let it stand at room temperature for later use.

2. The method for preparing a covalent organic framework membrane based on a biomimetic mineralization strategy according to claim 1, characterized in that, The amount of aldehyde monomer used is 0.01 mmol-0.1 mmol, and the catalyst concentration is 1 mol / L-10 mol / L; The amount of the amino monomer used is 0.01 mmol to 0.1 mmol.

3. The method for preparing a covalent organic framework membrane based on a biomimetic mineralization strategy according to claim 1, characterized in that, In step two, the amount of PEI added is 10% of the mass of the amino monomer; the molecular weight of the selected PEI is between 1000 and 50000 Da.

4. The method for preparing a COF membrane based on biomimetic mineralization according to claim 1, characterized in that, The base film material mentioned in step two is selected from any one of polyacrylonitrile (PAN), polysulfone (PSU), polyethylene terephthalate (PET), polyamide (PA), and polytetrafluoroethylene (PTFE).

5. The method for preparing a COF membrane based on biomimetic mineralization according to claim 1, characterized in that, The reaction temperature range is adjusted between 20°C and 100°C; the standing reaction time is adjusted between 1 and 5 days.

6. A biomimetic mineralized COF membrane for ion separation, characterized in that, Including the biomimetic mineralized COF membrane prepared by the preparation method according to any one of claims 1-5.

7. A method for ion separation using a biomimetic mineralized COF membrane, characterized in that, The biomimetic mineralized COF membrane is prepared by the preparation method according to any one of claims 1-5; The ions include two or more types of ions such as potassium ions, sodium ions, lithium ions, magnesium ions, and calcium ions. The metal salts used are halides, including chloride salts, bromide salts, and iodide salts. During the separation, it is ensured that the metal salts are of the same type of halide.

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