A confined imprinting covalent organic framework membrane and its application in selective separation of egcg

Abstract

The application discloses a confined imprinting covalent organic framework membrane and application thereof in selective separation of EGCG. A preparation method of the organic framework membrane comprises the following steps: firstly, growing a vinyl functionalized covalent organic framework layer in situ on the surface and in the channel of a nylon membrane to obtain a composite base membrane; then, preassembling a template molecule and an imprinting functional monomer to form a complex, adding a crosslinking agent and an initiator to initiate a thermal crosslinking polymerization reaction, and obtaining an imprinting polymerization membrane; finally, eluting and removing the template molecule in the imprinting polymerization membrane to obtain the confined imprinting covalent organic framework membrane. The method utilizes the double confined effects of the regular channel of the COF and the large pore of the nylon membrane, realizes uniform distribution and efficient construction of the imprinting site, and endows the membrane material with high selective recognition ability. When the template molecule is selected as epigallocatechin gallate and the imprinting functional monomer is selected as acrylamide, the obtained membrane is used for high selective separation and purification of EGCG, and the adsorption selectivity coefficient of the membrane for EGCG is above 90.

Description

Technical Field

[0001] This invention relates to the field of functional materials technology, and in particular to a confined imprinted covalent organic framework membrane and its application in the selective separation of EGCG. Background Technology

[0002] Epigallocatechin gallate (EGCG) is the most abundant and bioactive catechin compound in tea, possessing significant antioxidant, anti-inflammatory, anticancer, and metabolic regulatory pharmacological effects. It is widely used as a pharmaceutical intermediate, functional food additive, and cosmetic raw material. However, EGCG in tea extracts often coexists with structurally similar epigallocatechin (EGC) and epicatechin (EC), differing by only one or two phenolic hydroxyl groups, and exhibiting extremely similar molecular sizes and polarities. Traditional solvent extraction and column chromatography methods struggle to achieve highly selective purification, resulting in high costs and low efficiency in the preparation of high-purity EGCG, becoming a technological bottleneck restricting its in-depth development and high-value utilization.

[0003] Covalent organic framework (COF) membranes have attracted much attention in the field of membrane separation due to their advantages such as high specific surface area, uniform and tunable pore size, and ease of functionalization of organic frameworks. However, the separation selectivity of COF membranes mainly relies on physical sieving effects. For highly similar homologues such as EGCG, EGC, and EC with a kinetic diameter difference of less than 0.2 nm, pore size exclusion alone cannot effectively distinguish them. Molecular imprinting technology, by forming a pre-organized complex between a template molecule and a functional monomer, and then removing the template after polymerization, can construct a three-dimensional cavity within the material that is precisely complementary to the template in size, shape, and functional groups, giving the material a "key-and-lock" recognition capability. However, existing EGCG molecularly imprinted polymers are usually in powder or granular form, facing problems such as difficulty in recycling, easy secondary pollution, and difficulty in continuous operation. Theoretically, grafting the selectivity of molecular imprinting into the ordered channels of COF can overcome the dilemma of homologue separation, but the preparation of existing COF-based imprinted membranes often faces problems such as uneven distribution of imprinted sites, high mass transfer resistance within the channels, and low imprinting efficiency, thus failing to achieve highly selective separation and purification of EGCG. Summary of the Invention

[0004] To address the challenge of highly selective separation and purification of EGCG, this invention provides a confined imprinted covalent organic framework membrane, which can achieve highly selective separation and purification of EGCG.

[0005] The "confined imprinting" scheme proposed in this invention involves: firstly, growing a vinyl-functionalized COF thin layer in situ within the pores of a nylon membrane. This COF thin layer serves as both an ordered confined substrate and provides abundant polymerizable grafting sites. Subsequently, imprinting polymerization is carried out within the dual confined space formed by the COF nanopores and the nylon micropores, forcing the imprinting reaction to be confined to the restricted region, inhibiting disordered overgrowth, and ensuring that the imprinted cavities are uniformly distributed along the mass transfer path. This scheme not only improves the accessibility and utilization of imprinted sites but also enhances the structural stability of the membrane through the chemical bonding between the rigid COF framework and the imprinted polymer, ultimately achieving efficient and highly selective separation of EGCG.

[0006] The confined-imprinted covalent organic framework membrane of the present invention is prepared by the following method: S1. The nylon membrane activated by acid solution is added to an acetonitrile solution of 2,5-divinyl terephthalaldehyde and allowed to stand at room temperature for 2-3 hours. Then, scandium trifluoromethanesulfonate and 1,3,5-tris(4-aminophenyl)benzene are added, dissolved by ultrasonication, and allowed to stand in the dark for 2-6 hours. Vinyl functionalized covalent organic frameworks are grown in situ on the surface and in the pores of the nylon membrane to obtain a vinyl functionalized COF-nylon composite membrane.

[0007] The nylon membrane has a pore size of 0.3-0.6 μm, and preferably, the nylon membrane is activated by hydrochloric acid solution.

[0008] The preferred molar ratio of 2,5-divinyl terephthalaldehyde, 1,3,5-tris(4-aminophenyl)benzene, and scandium trifluoromethanesulfonate is 1.5–6:1–4:0.5–16.

[0009] S2. Dissolve the template molecule and the imprinted functional monomer in an organic solvent and stir for 1-2 hours under nitrogen protection to perform pre-assembly, so that the template molecule and the functional monomer form a complex through non-covalent interaction.

[0010] S3. Immerse the vinyl-functionalized COF-nylon composite membrane obtained in step S1 into the pre-assembled solution obtained in step S2. Add crosslinking agent and initiator under nitrogen protection, heat to 60-70℃, and carry out thermal crosslinking polymerization reaction in the confined space (within the COF channels and membrane channels) for 6-48 hours to allow the imprinted layer to polymerize in situ in the confined space, thereby obtaining the imprinted polymerized membrane.

[0011] S4. The template molecules in the imprinted polymer membrane obtained in step S3 are eluted and removed to obtain a confined imprinted covalent organic framework membrane.

[0012] The prepared confined imprinted covalent organic framework membrane exhibits specific selectivity for template molecules and can be used for the selective separation and purification of template molecules.

[0013] In step S2, when the template molecule is selected as epigallocatechin gallate (EGCG) and the imprinting functional monomer is selected as acrylamide, the resulting confined imprinted covalent organic framework membrane has high selectivity for EGCG and can be used for the selective separation and purification of EGCG.

[0014] Preferably, in step S2, the molar ratio of epigallocatechin gallate to acrylamide is 1:4 to 16, and acetonitrile is used as the organic solvent.

[0015] In step S3, the crosslinking agent is preferably ethylene glycol dimethacrylate. The initiator is preferably azobisisobutyronitrile, and the preferred polymerization conditions are: heating to 60°C for 6 hours for thermal crosslinking polymerization.

[0016] In step S4, a mixture of ethanol and acetic acid is used as the eluent, and the preferred volume ratio of methanol to acetic acid is 95:5.

[0017] Acrylamide was chosen as the imprinting functional monomer primarily because: its small molecular size and low steric hindrance allow it to easily enter the dual confinement space formed by COF nanopores and nylon micropores, ensuring uniform distribution of imprinted sites along the mass transfer pathway; its amide group possesses strong hydrogen bond acceptor capabilities, forming a stable and high-strength hydrogen-bonded pre-organized complex with EGCG rich in phenolic hydroxyl groups, and this hydrogen bond interaction is not easily weakened by solvent molecules in the acetonitrile polar system, ensuring pre-assembly efficiency. Other functional monomers, such as methacrylic acid, exhibit significantly reduced hydrogen bonding with the template in polar solvents, resulting in insufficient recognition ability; while aromatic ring monomers such as 4-vinylpyridine have higher binding energies, their large molecular size makes it difficult to effectively enter the COF confinement channels, hindering the uniform construction of confinement imprints.

[0018] Compared with the prior art, the advantages of the present invention are: (1) The confined-imprinted covalent organic framework membrane prepared by this invention has outstanding advantages such as easy recovery, convenient subsequent separation, no secondary pollution to the separated substances, and applicability to continuous cross-flow filtration processes. It effectively solves the shortcomings of traditional powdered or granular EGCG molecularly imprinted polymers, such as difficulty in recovery, easy secondary pollution, and difficulty in continuous operation. More importantly, the confined-imprinted membrane prepared by this invention has extremely high selective recognition ability for EGCG: in a mixed system of EGCG, EGC, and EC, the adsorption selectivity coefficient can reach more than 90, which is far superior to conventional EGCG imprinting reported in the literature. It can efficiently and accurately separate EGCG from structurally very similar catechin homologues.

[0019] (2) This invention is based on the in-situ confined growth of vinyl-functionalized COF within the pores of a nylon membrane, combined with molecular imprinting polymerization technology, to construct a confined-space imprinted covalent organic framework membrane with dual confined spaces of "COF nanopores + nylon micropores". This achieves uniform distribution and efficient construction of imprinted sites along the mass transfer path, significantly improving the accessibility and utilization of imprinted sites. Furthermore, the adsorption behavior conforms to the Langmuir model, indicating uniform imprinted sites and specific recognition, thus endowing the membrane material with high selective recognition capability. In addition, due to the vinyl chemical bonding between the rigid COF framework and the imprinted polymer layer, the structural stability and service life of the membrane are significantly enhanced; after five cycles of cross-flow testing, the adsorption performance only decreased by approximately 3.1%. This performance advantage makes this invention a promising candidate for efficient, continuous, and stable separation of EGCG in complex natural product systems for industrial application.

[0020] Other advantages, objectives and features of the present invention will become apparent in part from the following description, and in part from those skilled in the art through study and practice of the invention. Attached Figure Description

[0021] Figure 1 This is the isothermal adsorption curve of the confined imprinted covalent organic framework membrane in Example 1. Figure 2 This is the isothermal adsorption curve of the confined imprinted covalent organic framework membrane in Example 2.

[0022] Figure 3 This is the isothermal adsorption curve of the confined imprinted covalent organic framework membrane in Example 3.

[0023] Figure 4 The image shows the isothermal adsorption curves of the confined imprinted covalent organic framework membrane in Comparative Example 1.

[0024] Figure 5 This is a graph showing the adsorption selectivity coefficient of the confined imprinted covalent organic framework membrane in Example 2.

[0025] Figure 6 This is the kinetic adsorption curve of the confined imprinted covalent organic framework membrane in Example 2.

[0026] Figure 7 This is a cross-current cycling test breakthrough curve of the confined imprinted covalent organic framework membrane in Example 2.

[0027] Figure 8 In the figure, a, b, and c are high-performance liquid chromatograms of the feed solution, exudate, and eluent of the confined imprinted covalent organic framework membrane crossflow test in Example 2, respectively. Detailed Implementation

[0028] The preferred embodiments of the present invention will be described below with reference to the accompanying drawings. It should be understood that the preferred embodiments described herein are for illustration and explanation only and are not intended to limit the present invention.

[0029] Example 1 A confined imprinted covalent organic framework membrane for highly selective separation of EGCG is prepared as follows: (1) A nylon membrane with a pore size of 0.45 μm was placed in a 1 M hydrochloric acid solution and activated for 24 h. After drying, it was placed in 30 ml of an acetonitrile solution containing 0.15 mmol of 2,5-divinyl terephthalaldehyde and allowed to stand for 2 h at room temperature. Then, 0.05 mmol of scandium trifluoromethanesulfonate and 0.1 mmol of 1,3,5-tris(4-aminophenyl)benzene were added, and the membrane was dissolved by sonication and allowed to stand in the dark for 2 h. In this way, a vinyl-functionalized covalent organic framework (COF) layer was grown in situ on the surface and in the pores of the nylon membrane to obtain a vinyl-functionalized COF-nylon composite membrane.

[0030] (2) Dissolve 0.1 mmol epigallocatechin gallate (template molecule) and 0.4 mmol acrylamide (functional monomer) in 50 ml acetonitrile. Under nitrogen protection, stir at room temperature for 1 hour to carry out pre-assembly, so that the template molecule and the functional monomer form a pre-assembled complex through non-covalent interactions such as hydrogen bonding.

[0031] (3) Immerse the vinyl-functionalized COF-nylon composite membrane obtained in step (1) into the pre-assembled solution obtained in step (2), add 4 mmol of ethylene glycol dimethacrylate and 20 mg of azobisisobutyronitrile under nitrogen protection, and heat to 60°C for 6 hours to carry out thermal crosslinking polymerization reaction, so that the imprinted layer is polymerized in situ in the confined space to obtain the imprinted polymerized membrane.

[0032] (4) The epigallocatechin gallate in the imprinted polymer membrane was eluted with a methanol-acetic acid mixed solution with a volume ratio of 95:5 to obtain a confined imprinted covalent organic framework membrane.

[0033] Example 2 A confined imprinted covalent organic framework membrane for highly selective separation of EGCG is prepared as follows: (1) A nylon membrane with a pore size of 0.45 μm was placed in a 1 M hydrochloric acid solution and activated for 24 h. After drying, it was placed in 30 mL of an acetonitrile solution containing 0.24 mmol of 2,5-divinyl terephthalaldehyde and allowed to stand at room temperature for 2 h. Then, 0.48 mmol of scandium trifluoromethanesulfonate and 0.16 mmol of 1,3,5-tris(4-aminophenyl)benzene were added, dissolved by sonication, and allowed to stand in the dark for 4 h. In this way, a vinyl-functionalized covalent organic framework (COF) layer was grown in situ on the surface and in the pores of the nylon membrane to obtain a vinyl-functionalized COF-nylon composite membrane.

[0034] (2) Dissolve 0.1 mmol epigallocatechin gallate (template molecule) and 1.6 mmol acrylamide (functional monomer) in 50 ml acetonitrile. Under nitrogen protection, stir at room temperature for 1 hour to carry out pre-assembly, so that the template molecule and the functional monomer form a pre-assembled complex through non-covalent interactions such as hydrogen bonding.

[0035] (3) Immerse the vinyl-functionalized COF-nylon composite membrane obtained in step (1) into the pre-assembled solution obtained in step (2), add 4.5 mmol of ethylene glycol dimethacrylate and 20 mg of azobisisobutyronitrile under nitrogen protection, and heat to 60°C for 24 hours to carry out thermal crosslinking polymerization reaction, so that the imprinted layer is polymerized in situ in the confined space to obtain the imprinted polymerized membrane.

[0036] (4) The epigallocatechin gallate in the imprinted polymer membrane was eluted with a methanol-acetic acid mixed solution with a volume ratio of 95:5 to obtain a confined imprinted covalent organic framework membrane.

[0037] Example 3 A confined imprinted covalent organic framework membrane for highly selective separation of EGCG is prepared as follows: (1) A nylon membrane with a pore size of 0.45 μm was placed in a 1 M hydrochloric acid solution and activated for 24 h. After drying, it was placed in 30 mL of an acetonitrile solution containing 0.6 mmol of 2,5-divinyl terephthalaldehyde and allowed to stand at room temperature for 2 h. Then, 1.6 mmol of scandium trifluoromethanesulfonate and 0.4 mmol of 1,3,5-tris(4-aminophenyl)benzene were added, and the membrane was dissolved by sonication and allowed to stand in the dark for 6 h. In this way, a vinyl-functionalized covalent organic framework (COF) layer was grown in situ on the surface and in the pores of the nylon membrane to obtain a vinyl-functionalized COF-nylon composite membrane.

[0038] (2) Dissolve 0.1 mmol epigallocatechin gallate (template molecule) and 1.4 mmol acrylamide (functional monomer) in 50 ml acetonitrile. Under nitrogen protection, stir the reaction at room temperature for 1 hour to carry out pre-assembly, so that the template molecule and the functional monomer form a pre-assembled complex through non-covalent interactions such as hydrogen bonding.

[0039] (3) Immerse the vinyl-functionalized COF-nylon composite membrane obtained in step (1) into the pre-assembled solution obtained in step (2), add 6 mmol of ethylene glycol dimethacrylate and 20 mg of azobisisobutyronitrile under nitrogen protection, and heat to 60°C for 48 hours to carry out thermal crosslinking polymerization reaction, so that the imprinted layer is polymerized in situ in the confined space to obtain the imprinted polymerized membrane.

[0040] (4) The epigallocatechin gallate in the imprinted polymer membrane was eluted with a methanol-acetic acid mixed solution with a volume ratio of 95:5 to obtain a confined imprinted covalent organic framework membrane.

[0041] Comparative Example 1 Following the preparation method of Example 2, but without using a nylon membrane, all other steps remain unchanged. The specific method is as follows: (1) Dissolve 0.24 mmol of 2,5-divinyl terephthalaldehyde in 30 mL of acetonitrile solution, let it stand at room temperature for 2 hours, then add 0.48 mmol of scandium trifluoromethanesulfonate and 0.16 mmol of 1,3,5-tris(4-aminophenyl)benzene, sonicate to dissolve, and then let it stand in the dark for 4 hours to obtain vinyl-functionalized COF.

[0042] (2) Dissolve 0.1 mmol epigallocatechin gallate (template molecule) and 1.6 mmol acrylamide (functional monomer) in 50 ml acetonitrile. Under nitrogen protection, stir at room temperature for 1 hour to carry out pre-assembly, so that the template molecule and the functional monomer form a pre-assembled complex through non-covalent interactions such as hydrogen bonding.

[0043] (3) Add the vinyl-functionalized COF obtained in step (1) to the pre-assembled solution obtained in step (2), add 4.5 mmol of ethylene glycol dimethacrylate and 20 mg of azobisisobutyronitrile under nitrogen protection, and heat to 60°C for 24 hours to carry out thermal crosslinking polymerization reaction to obtain the imprinted polymer.

[0044] (4) The epigallocatechin gallate in the imprinted polymer was eluted with a methanol-acetic acid mixture with a volume ratio of 95:5 to obtain the imprinted covalent organic framework polymer.

[0045] The materials prepared in the above embodiments and comparative examples were subjected to performance tests: (1) Isothermal adsorption experiment The test method is as follows: Eight confined-imprinted covalent organic framework membranes prepared in Example 1 were immersed in 10 mL of EGCG aqueous solutions of eight different concentrations: 5, 10, 25, 50, 75, 100, 150, and 200 mg / L. After immersion for 8 h, the concentration of unadsorbed EGCG in the solution was determined by UV-Vis spectrophotometer. C e And calculate the adsorption amount according to formula (1) Q e (mg / g).

[0046] (1) in, C 0 and C e The values ​​are the initial concentration of EGCG aqueous solution and the concentration after soaking and adsorption, respectively, in mg / L; V The volume of the aqueous solution is expressed in L; m represents the mass of the confined-imprinted covalent organic framework membrane used, in g.

[0047] Concentration of unadsorbed EGCG in solution C e The method for determining the concentration is as follows: Before the experiment, a standard curve relating the UV absorption intensity to the concentration of EGCG is prepared. After the immersion experiment, the concentration of EGCG is determined from the standard curve based on the UV absorption intensity measured by a UV-Vis spectrophotometer. The method for determining the concentrations of EGC and EC is the same.

[0048] Following the same experimental method described above, the EGCG aqueous solution was replaced with EGC and EC aqueous solutions, and the eight different concentration values ​​remained 5, 10, 25, 50, 75, 100, 150 and 200 mg / L; the adsorption capacity of EGC and EC was finally calculated.

[0049] Based on the experimental results, the isothermal adsorption curves of EGCG, EGC, and EC for the confined imprinted covalent organic framework membrane in Example 1 are shown below. Figure 1 As shown.

[0050] Furthermore, the materials prepared in Examples 2, 3, and Comparative Example 1 were used in the above experiments, and the final results were obtained. Figure 2 , Figure 3 and Figure 4 The isothermal adsorption curve is shown.

[0051] Figure 1-3The adsorption capacities of the confined-imprinted covalent organic framework membranes prepared in the three examples for epigallocatechin gallate (EGCG), epigallocatechin, and epicatechin in mixed solutions with concentrations of 5, 10, 25, 50, 75, 100, 150, and 200 mg / L for 8 h are shown. The experimental results indicate that the prepared confined-imprinted covalent organic framework membranes exhibit higher adsorption capacities for EGCG than for epigallocatechin (EGC) and epicatechin (EC) in mixed solutions with concentrations ranging from 5 to 200 mg / L, demonstrating highly selective adsorption and separation of EGCG. Compared to Examples 1 and 3, the adsorption capacity of the imprinted membrane obtained in Example 2 for EGCG was increased by more than 24% and 35%, respectively. Figure 4 The results showed that the organic framework polymer material prepared in Comparative Example 1 had a higher adsorption capacity for EGCG than EGC and EC in mixed solutions with concentrations ranging from 5 to 200 mg / L, and exhibited selective adsorption and separation of EGCG. However, its effect was significantly weaker than that of Examples 1, 2, and 3. This indicates that the lack of confinement effect from the nylon membrane reduced the selective separation effect of the prepared imprinted covalent organic framework polymer on EGCG.

[0052] Based on the experimental results of Example 2, the selectivity coefficient α of the confined imprinted covalent organic framework membrane was further calculated using the following formula: Calculate according to formula (2) , and Then, the selectivity coefficient is calculated according to formula (3). and : (2) ( i = EGC, EC (3) Based on the calculation results, Figure 5 As can be seen, the confined imprinted covalent organic framework membrane prepared in Example 2 exhibits excellent adsorption selectivity, with a maximum adsorption selectivity of 98%.

[0053] (2) Kinetic adsorption experiment Thirteen portions of confined-imprinted covalent organic framework membranes were weighed and placed in test tubes. 10 mL of a 100 mg / L aqueous solution of epigallocatechin gallate was added to each test tube. After standing at room temperature for 0, 5, 10, 15, 30, 60, 90, 120, 180, 240, 360, 480, 600, and 720 min, the concentration of unadsorbed epigallocatechin gallate in the solution was measured using a UV-Vis spectrophotometer. The adsorption capacity was calculated based on the results. Q t (mg / g): (4) in C 0 and C t The concentrations of epigallocatechin gallate in the solution before and after adsorption are shown in mg / L. V Let L be the volume of the aqueous solution. m The mass, in g, is the mass of the confined-imprinted covalent organic framework membrane used.

[0054] Following the same experimental method described above, the EGCG aqueous solution was replaced with EGC aqueous solution and EC aqueous solution, and the adsorption amounts of EGC and EC were finally calculated.

[0055] The calculations were based on the experimental results of the confined imprinted covalent organic framework membrane in Example 2. Figure 6 The kinetic adsorption curves of the confined-imprinted covalent organic framework membrane are shown. Experimental results indicate that the confined-imprinted covalent organic framework membrane prepared in Example 2 adsorbs higher amounts of epigallocatechin gallate than epigallocatechin and epicatechin within a concentration range of 5–720 min, demonstrating selective adsorption and separation of epigallocatechin gallate. Furthermore, the kinetic model conforms to the Langmuir model, indicating that the adsorption behavior of epigallocatechin gallate by this membrane is chemisorption and monolayer adsorption.

[0056] (3) Cross-flow filtration test Place a confined-imprinted covalent organic framework membrane into the membrane module. Connect the assembled device to the peristaltic pump and feed it with a solution containing 100 mg / L each of epigallocatechin gallate (EGCG), epigallocatechin (EGC), and epicatechin (EC). -1 The mixed solution was prepared at 200 mL / min. -1 The flow rate was continuously pumped into the tube for 120 minutes of cross-flow filtration. To collect the eluted EGCG, the confined-imprinted covalent organic framework membrane was immersed in a 10 mL mixture of methanol and acetic acid (95:5, v / v) for 3 hours. This procedure was repeated three times, and the eluates were then combined. The eluted membrane was then subjected to another cross-flow test, and the concentrations of EGCG, EGC, and EC in the filtrate and eluate were determined by high-performance liquid chromatography (HPLC).

[0057] Figure 7 The image shows the breakthrough curve of the confined imprinted covalent organic framework membrane in Example 2 after a cross-current cycling test. It can be seen that after five cycles of cross-current testing, the adsorption performance decreased by only about 3.1%, indicating good performance stability.

[0058] Figure 8In Figures a, b, and c, respectively, are the high-performance liquid chromatograms of the feed solution, exudate, and eluent from the cross-flow test of the confined-imprinted covalent organic framework membrane in Example 2. The results show that the confined-imprinted covalent organic framework membrane can efficiently separate and enrich EGCG in a mixed solution of EGCG, EGC, and EC.

[0059] In summary, this invention combines the confined growth of vinyl-functionalized covalent organic frameworks with molecular imprinting technology to construct imprinted sites within the dual confined space of nylon membrane pores and COF pores, achieving uniform distribution and efficient construction of imprinted sites. The introduction of vinyl-functionalized COF provides abundant grafting sites for imprinting polymerization, enhances the chemical bonding between the imprinted layer and COF, and improves the structural stability and lifespan of the imprinted membrane. The confined imprinted membrane obtained by this invention exhibits excellent molecular recognition ability for EGCG, with an adsorption selectivity exceeding 90%. Moreover, the preparation method of this invention is simple to operate, operates under mild conditions, and is easy to scale up for production, showing promising prospects for industrial application.

[0060] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any way. Although the present invention has been disclosed above with reference to preferred embodiments, it is not intended to limit the present invention. Any person skilled in the art can make some modifications or alterations to the above-disclosed technical content to create equivalent embodiments without departing from the scope of the present invention. Any simple modifications, equivalent changes, and alterations made to the above embodiments based on the technical essence of the present invention without departing from the scope of the present invention shall still fall within the scope of the present invention.

Claims

1. A confined-imprinted covalent organic framework membrane, characterized in that, Made by the following method: S1. The nylon membrane activated by acid solution is added to an acetonitrile solution of 2,5-divinyl terephthalaldehyde and allowed to stand at room temperature for 2-3 hours. Then, scandium trifluoromethanesulfonate and 1,3,5-tris(4-aminophenyl)benzene are added, dissolved by ultrasonication, and allowed to stand in the dark for 2-6 hours. Vinyl functionalized covalent organic frameworks are grown in situ on the surface and in the pores of the nylon membrane to obtain a vinyl functionalized COF-nylon composite membrane. S2. Dissolve the template molecule and the imprinted functional monomer in an organic solvent and stir for 1-2 hours under nitrogen protection to perform pre-assembly, so that the template molecule and the functional monomer form a complex through non-covalent interaction. S3. Immerse the vinyl-functionalized COF-nylon composite membrane obtained in step S1 into the pre-assembled solution obtained in step S2, add crosslinking agent and initiator under nitrogen protection, and heat to 60-70℃ for thermal crosslinking polymerization reaction for 6-48 hours to allow the imprinted layer to polymerize in situ in the COF channels and membrane channels to obtain the imprinted polymerized membrane. S4. Use an eluent to elute the template molecules in the imprinted polymer membrane obtained in step S3 to obtain a confined imprinted covalent organic framework membrane.

2. The confined imprinted covalent organic framework membrane as described in claim 1, characterized in that, In step S1, the nylon membrane has a pore size of 0.3-0.6 μm and is activated using hydrochloric acid solution.

3. The confined-imprinted covalent organic framework membrane as described in claim 2, characterized in that, The molar ratio of 2,5-divinyl terephthalaldehyde, 1,3,5-tris(4-aminophenyl)benzene, and scandium trifluoromethanesulfonate is 1.5–6:1–4:0.5–16.

4. The confined imprinted covalent organic framework membrane as described in claim 1, characterized in that, In step S2, the template molecule is epigallocatechin gallate, the imprinting functional monomer is acrylamide, and the organic solvent is acetonitrile.

5. The confined-imprinted covalent organic framework membrane as described in claim 4, characterized in that, The molar ratio of epigallocatechin gallate to acrylamide is 1:4 to 16.

6. The confined imprinted covalent organic framework membrane as described in claim 4, characterized in that, In step S3, the crosslinking agent is ethylene glycol dimethacrylate, and the initiator is azobisisobutyronitrile.

7. The confined-imprinted covalent organic framework membrane as described in claim 6, characterized in that, In step S3, the temperature is raised to 60°C for a thermal crosslinking polymerization reaction for 6 hours.

8. The confined imprinted covalent organic framework membrane as described in claim 1, characterized in that, In step S4, the eluent is a mixture of methanol and acetic acid in a volume ratio of 95:

5.

9. An application of the confined imprinted covalent organic framework membrane as described in any one of claims 1-3, characterized in that, Used for selectively separating the template molecules.

10. The application of a confined imprinted covalent organic framework membrane as described in any one of claims 4-8 in the selective separation of epigallocatechin gallate esters.

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