Preparation method of amino acid composite covalent organic framework nanofiltration membrane with amino acid in-situ anchoring

Abstract

The application discloses a preparation method of an amino acid composite covalent organic framework nanofiltration membrane, and the preparation method comprises the following steps: synthesizing a primary nano covalent organic framework colloidal solution by an aldehyde group monomer and an amino monomer in a polar aprotic organic solvent; subsequently, adding an amino acid aqueous solution to provide in-situ anchoring sites of the amino acid by virtue of active aldehyde groups and amino groups which are rich on the edges of the primary nano covalent organic framework, and realizing in-situ anchoring of the amino acid synchronously with the crystallization growth of subsequent covalent organic framework nanosheets; finally, the prepared covalent organic framework nanosheets are deposited on the surface of an ultrafiltration base film through vacuum-assisted deposition, and the covalent organic framework nanosheets are subjected to soaking treatment in an alkaline solution, cleaning and drying to obtain the amino acid composite covalent organic framework nanofiltration membrane. The application develops a simple and universal preparation method of the amino acid composite covalent organic framework nanofiltration membrane, and different nanofiltration membrane materials with different water fluxes and rejection performances can be obtained by changing monomer types and amino acid types.

Description

Technical Field

[0001] This invention relates to a method for preparing an amino acid-in-situ anchored amino acid composite covalent organic framework nanofiltration membrane, belonging to the field of nanofiltration membrane technology. Background Technology

[0002] Nanofiltration membrane separation technology is widely used in fine chemical separation and organic resource recovery due to its advantages such as low energy consumption, simple operation, and high separation efficiency. Among them, achieving efficient retention and high selective fractionation of fine chemicals is its key application direction. At present, conventional polymer thin-layer composite nanofiltration membranes have problems such as wide pore size distribution and insufficient sieving accuracy, making it difficult to achieve both high throughput and effective retention. Although inorganic ceramic nanofiltration membranes have good chemical stability, their preparation cost is high, they are brittle, and their surface functionalization modification is difficult, which limits their large-scale promotion in dye separation.

[0003] Covalent organic frameworks (COFs), as a novel class of crystalline porous organic materials, possess advantages such as highly ordered pores, tunable pore size, and strong chemical stability, making them ideal substrates for constructing high-performance nanofiltration membranes. Currently, COF nanofiltration membranes are mostly prepared using interfacial polymerization and nanoassembly methods. Through pore structure regulation and pore function compositing, it is hoped that the comprehensive improvement of membrane separation performance can be achieved, but key issues still exist: On the one hand, pore function compositing of COFs usually requires its framework to have highly reactive sites, but the types of such COFs are limited, and the effectiveness of pore function compositing of COFs is limited by the accessibility of reactive sites, resulting in low controllability and making it difficult for membrane performance to meet separation requirements; on the other hand, amorphous networks or defects are easily generated during COF membrane formation, leading to non-uniform membrane pore structures, which limits the simultaneous improvement of separation accuracy and flux. Furthermore, balancing membrane pore structure regulation and functional compositing usually requires multi-step synthesis or processing, increasing the complexity of membrane preparation.

[0004] Constructing COF membranes using COF nanosheets as the main membrane structure allows for the integration of functional molecules as side chains into the COF framework, achieving pore-functional composites while preserving the intrinsic crystalline porous structure of COF. This endows the membrane material with superior adaptability to target separation systems. Currently reported COF nanosheet pore-functional composites mainly employ side-linking grafting methods, which involve first synthesizing the COF framework structure and then grafting functional molecules onto the highly reactive sites of the framework side chains. This method typically requires multi-step synthesis or stringent grafting conditions and is highly dependent on side-chain monomers with specific reactive sites, thus lacking versatility. In-situ introduction of functional molecules during the synthesis of COF nanosheets promises to achieve more efficient pore-functional composites. On one hand, the intrinsically rich reactive aldehyde and amino groups at the edges of the COF nanosheet framework during growth provide abundant binding sites for the in-situ anchoring of functional molecules (such as amino acids). This allows for pore-functional composites of COF nanosheets using conventional monomers and mild reaction conditions, eliminating the dependence on highly reactive monomer side chains and complex grafting conditions inherent in conventional COF nanosheet pore-functional composite methods. On the other hand, in-situ anchored functional molecules (such as amino acids) can occupy defect sites in COF nanosheets, simultaneously regulating pore size and pore wall chemical environment (such as polarity, hydrophilicity, and charge), thus endowing the membrane with greater tunability in permeability and selectivity. Amino acids, as functional small molecules containing multiple reactive functional groups, polar groups, and charged groups such as amino, carboxyl, and thiol groups, offer greater freedom in the tunability of COF membrane structure and the composite nature of its functions. Currently, no research has been reported on the design and synthesis of in-situ anchored amino acid COF nanosheets as the main body for constructing COF membranes. This patent application proposes a method for preparing an amino acid-in-situ anchored amino acid composite covalent organic framework nanofiltration membrane. The membrane structure is based on amino acid-in-situ anchored amino acid composite COF nanosheets. This method is simple and universal. By changing the monomer type and amino acid type, the separation performance of the COF nanofiltration membrane can be improved, providing a flexible and selectable technical solution for the targeted preparation of COF nanofiltration membranes for different application needs. Summary of the Invention

[0005] To address the aforementioned technical problems, this invention provides a method for preparing an amino acid-in-situ anchored amino acid composite covalent organic framework nanofiltration membrane. The amino acid composite covalent organic framework nanofiltration membrane is prepared by vacuum-assisted deposition using amino acid-in-situ anchored amino acid composite covalent organic framework nanosheets as the membrane structure host. The specific technical solution is as follows: A method for preparing an amino acid-modified covalent organic framework composite membrane includes the following steps: Step 1: Preparation of amino acid-based covalent organic framework (COF) nanosheets: Aldehyde monomers were dissolved in a polar aprotic solvent. Amino monomers were dissolved in an equal volume of polar aprotic solvent with an appropriate catalyst added, and both solutions were sonicated until completely dissolved. The two concentrated monomer solutions were then mixed to form a homogeneous solution. The reaction was allowed to proceed at room temperature to obtain a primary COF colloidal solution. Subsequently, amino acids were dissolved in water and sonicated until completely dissolved to obtain an amino acid solution. This amino acid solution was added to the primary COF colloidal solution, and crystallization was performed at room temperature to obtain a covalent organic framework (COF) nanosheet colloidal solution. Step 2: Preparation of amino acid composite covalent organic framework nanofiltration membrane: Take an appropriate amount of the COF nanosheet colloidal solution grown in Step 1, dilute it with water, and sonicate it until it is evenly dispersed. Vacuum filter and deposit it on the base membrane to obtain a COF composite membrane. Then, immerse the composite membrane in an alkaline environment for a certain period of time, wash it with methanol and acetone, and dry it in a vacuum oven to obtain an amino acid composite covalent organic framework nanofiltration membrane.

[0006] The in-situ anchoring mechanism of amino acids in step one is as follows: The COF backbone is formed by the condensation polymerization of amino and aldehyde monomers through Michael addition reaction into a covalent network with hexagonal topology and imine (C=N) bonds. The formation of imine bonds is reversible. On the one hand, the continuous "breaking and recombination" of imine bonds allows the COF to repeatedly correct errors during growth, ultimately resulting in a thermodynamically stable, long-range ordered crystalline network. On the other hand, the continuous "breaking and recombination" process of imine bonds can form abundant free amino and aldehyde sites on the COF backbone, which can react with the carboxyl and amino groups on amino acids, respectively, to achieve in-situ anchoring of amino acids on the COF backbone. This anchoring process utilizes the active amino and aldehyde sites generated by the dynamic breaking and recombination of imine bonds.

[0007] Furthermore, in step two, the composite membrane is immersed in an alkaline environment for a certain period of time to provide a favorable reaction environment for the covalent anchoring of amino acids, promote the amidation reaction of free amino groups of COF skeleton to carboxyl groups of amino acids and the Michael addition reaction of free aldehydes of COF skeleton to amino groups of amino acids, so as to stabilize the covalent anchoring structure of amino acids.

[0008] This invention develops a simple and universal method for preparing covalent organic framework nanofiltration membranes using amino acid composite covalent organic framework nanosheets as the main membrane structure. By changing the monomer type and amino acid type, a series of covalent organic framework nanofiltration membranes with different pore structures can be obtained. The prepared covalent organic framework nanofiltration membranes have both high water flux and high dye rejection rate, providing a simple and effective preparation strategy for the development of high-performance nanofiltration membranes.

[0009] Furthermore, in step one, the aldehyde monomer is 2,3,5,6-tetrafluoroterephthalaldehyde, 2,5-dihydroxyterephthalaldehyde, 2,3-dihydroxyterephthalaldehyde, 2,6-pyridinedicarboxaldehyde, or 2,4,6-tricarboxymethylphloroglucinol; the amino monomer is triaminoguanidine hydrochloride or 2,5-diaminobenzenesulfonic acid; the amino acid is cysteine, tyrosine, arginine, or lysine; and the catalyst is trifluoroacetic acid, acetic acid, terephthalic acid, or KOH. Furthermore, the polar aprotic solvent in step one is acetonitrile, dichloromethane, or dimethyl sulfoxide; Furthermore, in step one, the ratio of the amounts of aldehyde monomer, amino monomer, catalyst, and amino acid is 0.03~0.3 mmol: 0.02~0.2 mmol: 0.25~2.5 mmol: 0.06~0.6 mmol.

[0010] Furthermore, in step one, when mixing the monomer solutions, the amino monomer solution is poured into the aldehyde monomer solution, and the initial nano-COF is allowed to stand for 1 to 3 days. After the amino acid solution is added to the COF colloidal solution, the amino acid composite nanosheet crystallization growth time is 2 to 7 days. Furthermore, in step two, the base membrane is a PES ultrafiltration membrane, a PVDF ultrafiltration membrane, or a PAN ultrafiltration membrane; Furthermore, the alkaline solution in step two is a K2CO3 solution with a concentration of 1 g / L to 50 g / L, and the soaking time is 0.5 to 2 h; Compared with the prior art, the present invention has the following advantages: This invention utilizes in-situ anchored amino acid-based composite COF nanosheets as the main membrane structure to prepare COF membranes. The preparation method is simple, universal, and operates under mild reaction conditions, without relying on specific monomer side-chain reactive groups or complex grafting processes. The covalent composite of amino acids on the nanosheets can fill nanosheet defects, regulate membrane pore size and pore wall chemical environment, and synergistically enhance membrane permeability and selectivity by leveraging the inherent pore structure advantages of COF and the intrapore amino acid chemical environment (mimicking aquaporins where amino acid residues provide water activation sites). The electrostatic association between amino acid molecules enhances the nanosheet binding stability, improving the long-term performance of the membrane. This process is simple, easy to control, and low-cost, suitable for large-scale production. The resulting nanofiltration membrane exhibits both high water flux and high dye rejection rate, enabling efficient and precise dye separation and fractionation. Attached Figure Description

[0011] Figure 1 This is a flowchart illustrating the preparation process and mechanism of the amino acid in-situ anchored amino acid composite covalent organic framework nanofiltration membrane of the present invention.

[0012] Figure 2This is a schematic diagram of the molecular structure of the nanofiltration membrane prepared by the composite covalent organic framework in Example 1.

[0013] Figure 3 The image shows the ATR-FTIR image of the composite covalent organic framework nanofiltration membrane in Example 1.

[0014] Figure 4 The images show the surface and cross-sectional views of the composite covalent organic framework nanofiltration membrane from Example 1. Figure 5 The image shows the XRD pattern of the composite covalent organic framework nanofiltration membrane from Example 1.

[0015] Figure 6 The graph shows the methylene blue separation performance of Examples 1-9. Detailed Implementation

[0016] The specific embodiments of the present invention will be further described below with reference to the accompanying drawings. The specific examples described are only for illustrative purposes and are not intended to limit the present invention.

[0017] Example 1: In this embodiment, a method for preparing an amino acid-in-situ anchored amino acid composite covalent organic framework nanofiltration membrane is as follows: Step 1: Preparation of amino acid-based covalent organic framework nanosheets: 0.06 mmol of the aldehyde monomer 2,3,5,6-tetrafluoroterephthalaldehyde was dissolved in 10 ml of dimethyl sulfoxide solution. 0.04 mmol of the amino monomer triaminoguanidine hydrochloride was dissolved in an equal volume of solvent, and 37.5 µL of trifluoroacetic acid was added. Both solutions were sonicated until completely dissolved. The aldehyde monomer solution was then poured into the amino monomer solution and mixed to form a homogeneous solution. The reaction was allowed to stand at room temperature for 3 days to obtain a COF nanosheet colloidal solution. Subsequently, 7.27 mg of cysteine ​​was dissolved in 300 µL of water and sonicated for 20 min to obtain a cysteine ​​solution. The cysteine ​​solution was added to the COF colloidal solution, and the mixture was allowed to stand at room temperature for another 4 days for growth. Step 2: Take out 400 µL of the COF nanosheet colloidal solution grown in Step 1, dilute it with water to 20 ml, and sonicate it until it is evenly dispersed. Vacuum filter and deposit it on the PAN base membrane to obtain a COF composite membrane. Then, immerse the composite membrane in K2CO3 solution for 30 min, and then wash it three times with methanol and acetone respectively to remove unreacted monomers. After drying in a vacuum oven, an amino acid composite covalent organic framework nanofiltration membrane is obtained.

[0018] The preparation process of amino acid composite covalent organic framework nanofiltration membrane is as follows: Figure 1 As shown. Figure 2The molecular structure in the reaction process of Example 1 is as follows: a polyfluorinated aromatic aldehyde monomer and an aminoguanidine salt monomer undergo a Schiff base (imine condensation) reaction to obtain an imine-linked COF skeleton structure. Subsequently, amino acids are grafted onto the free aldehyde and amino sites of the skeleton to obtain a covalently anchored amino acid covalent organic skeleton structure. Figure 3 The infrared spectrum of Example 1 shows the characteristic absorption peaks of imine belonging to COF and carboxyl groups belonging to amino acids, confirming the successful synthesis of in-situ anchored COF nanosheets with amino acids. Figure 4 The images show the SEM surface and cross-section of Example 1. The COF film has a smooth, dense, and defect-free surface with uniform thickness. Figure 5 The XRD pattern of Example 1 shows that the nanosheet has good crystallinity and structural order. Figure 6 The retention performance of the composite membranes prepared in Examples 1-9 for methylene blue demonstrates the good nanofiltration performance and ease of use of the amino acid grafting method for preparing covalent organic framework composite membranes.

[0019] Application testing experiments: The COF nanofiltration membrane prepared in Example 1 was tested for its permeation flux and dye molecule rejection rate. The effective area of ​​the filtration unit was 0.98 cm². 2 The filtration unit can provide an operating pressure of 3–6 bar. The obtained permeation flux is the average of three repeated experiments on the COF membrane. The water permeation flux is calculated using equation (1): (1) Where P(L·m) -2 ·h -1 ·bar -1 V(L) is the osmotic flux, A(m³) is the volume of the permeate, and V(L) is the volume of the permeate. 2 ) is the effective area of ​​the membrane, Δt(h) is the permeation time, and ΔP(bar) is the operating pressure.

[0020] The retention rate of the COF membrane was tested against dye molecules. The dye molecule concentration was 100 mg / L, and the results were evaluated using UV absorption curves. The membrane retention rate was tested using a single dye solution as the feed solution, which was stirred at 600 rpm to minimize concentration polarization. The retention rate was calculated using formula (2): (2) Where R(%) is the retention rate, C p (mg / L) is the concentration of the permeate, C f (mg / L) represents the concentration of the feed solution.

[0021] The COF nanofiltration membrane prepared in Example 1 was subjected to tests on the retention and permeation flux of dyes Evans Blue (EB), Acid Blue (AB), Methylene Blue (MB), Alizarin Green (AG), and Congo Red (CR). The test results are listed in Table 1.

[0022] Table 1: Performance of the nanofiltration membrane prepared in Example 1 Example 2 In this embodiment, the preparation method of the amino acid in-situ anchored amino acid composite covalent organic framework nanofiltration membrane is the same as that in Example 1. The only difference is that in step one of Example 2, the aldehyde monomer is replaced with 2,5-dihydroxyterephthalaldehyde, the catalyst is replaced with acetic acid, and the amount remains the same. Other operations are the same as in Example 1, and finally the amino acid composite covalent organic framework nanofiltration membrane is obtained.

[0023] The COF nanofiltration membrane prepared in Example 2 was subjected to tests on the retention and permeation flux of dyes Evans Blue (EB), Acid Blue (AB), Methylene Blue (MB), Alizarin Green (AG), and Congo Red (CR). The test results are listed in Table 2.

[0024] Table 2: Performance of the nanofiltration membrane prepared in Example 2 Example 3 In this embodiment, the preparation method of the amino acid composite covalent organic framework nanofiltration membrane with in-situ anchored amino acids is the same as that in Example 1. The only difference is that in step one of Example 1, the aldehyde monomer is replaced with 2,3-dihydroxyterephthalaldehyde, the catalyst is replaced with terephthalic acid, and the amount remains the same. Other operations are the same as in Example 1, and the amino acid composite covalent organic framework nanofiltration membrane is finally obtained.

[0025] The COF nanofiltration membrane prepared in Example 3 was subjected to tests for the retention and permeation flux of dyes Evans Blue (EB), Acid Blue (AB), Methylene Blue (MB), Alizarin Green (AG), and Congo Red (CR). The test results are listed in Table 3.

[0026] Table 3: Performance of the nanofiltration membrane prepared in Example 3 Example 4 In this embodiment, the preparation method of the amino acid composite covalent organic framework nanofiltration membrane with in-situ anchored amino acids is the same as that in Example 1. The only difference is that in step one of Example 1, the aldehyde monomer is replaced with 2,6-pyridinedicarboxaldehyde, while the concentration remains unchanged. Other operations are the same as in Example 1, and the amino acid composite covalent organic framework nanofiltration membrane is finally obtained.

[0027] The COF nanofiltration membrane prepared in Example 4 was subjected to tests on the retention and permeation flux of dyes Evans Blue (EB), Acid Blue (AB), Methylene Blue (MB), Alizarin Green (AG), and Congo Red (CR). The test results are listed in Table 4.

[0028] Table 4: Performance of the nanofiltration membrane prepared in Example 4 Example 5 In this embodiment, the preparation method of the amino acid in-situ anchored amino acid composite covalent organic framework nanofiltration membrane is the same as that in Example 1. The only difference is that in step one of Example 1, the aldehyde monomer is replaced with 2,4,6-tricarboxymethyl phloroglucinol, the amine monomer is replaced with 2,5-diaminobenzenesulfonic acid, the amount of aldehyde monomer remains unchanged, and the amount of amine monomer is 0.06 mmol. Other operations are the same as in Example 1, and the amino acid composite covalent organic framework nanofiltration membrane is finally obtained.

[0029] The COF nanofiltration membrane prepared in Example 5 was subjected to tests for the retention and permeation flux of dyes Evans Blue (EB), Acid Blue (AB), Methylene Blue (MB), Alizarin Green (AG), and Congo Red (CR). The test results are listed in Table 5.

[0030] Table 5: Performance of the nanofiltration membrane prepared in Example 5 Example 6 In this embodiment, the preparation method of the amino acid composite covalent organic framework nanofiltration membrane with in-situ anchored amino acids is the same as that in Example 1. The only difference is that in step one of Example 1, the catalyst is replaced with 2.832 mg of KOH. Other operations are the same as in Example 1, and finally, the amino acid composite covalent organic framework nanofiltration membrane is obtained.

[0031] The COF nanofiltration membrane prepared in Example 6 was subjected to tests for the retention and permeation flux of dyes Evans Blue (EB), Acid Blue (AB), Methylene Blue (MB), Alizarin Green (AG), and Congo Red (CR). The test results are listed in Table 6.

[0032] Table 6: Performance of the nanofiltration membrane prepared in Example 6 Example 7 In this embodiment, the preparation method of the amino acid composite covalent organic framework nanofiltration membrane with in-situ anchored amino acids is the same as that in Example 1. The only difference is that the amino acid added in step one of Example 1 is replaced with arginine, the amount is changed to 0.12 mmol, and the polar aprotic solvent is replaced with N,N-dimethylformamide. Other operations are the same as in Example 1, and the amino acid composite covalent organic framework nanofiltration membrane is finally obtained.

[0033] The COF nanofiltration membrane prepared in Example 7 was subjected to retention and permeation flux tests for the dyes Evans Blue (EB), Acid Blue (AB), Methyl Blue (MB), Alizarin Green (AG), and Congo Red (CR). The test results are listed in Table 7.

[0034] Table 7: Performance of the nanofiltration membrane prepared in Example 7 Example 8 In this embodiment, the preparation method of the amino acid composite covalent organic framework nanofiltration membrane with in-situ anchored amino acids is the same as that in Example 1. The only difference is that the amino acid added in step one of Example 1 is replaced with tyrosine, and the polar aprotic solvent is replaced with acetonitrile. Other operations are the same as in Example 1, and finally, the amino acid composite covalent organic framework nanofiltration membrane is obtained.

[0035] The COF nanofiltration membrane prepared in Example 8 was subjected to tests for the retention and permeation flux of dyes Evans Blue (EB), Acid Blue (AB), Methylene Blue (MB), Alizarin Green (AG), and Congo Red (CR). The test results are listed in Table 8.

[0036] Table 8: Performance of the nanofiltration membrane prepared in Example 8 Example 9 In this embodiment, the preparation method of the amino acid composite covalent organic framework nanofiltration membrane with in-situ anchored amino acids is the same as that in Example 1. The only difference is that the amino acid added in step one of Example 1 is replaced with lysine. Other operations are the same as in Example 1, and finally, the amino acid composite covalent organic framework nanofiltration membrane is obtained.

[0037] The COF nanofiltration membrane prepared in Example 9 was subjected to tests for the retention and permeation flux of dyes Evans Blue (EB), Acid Blue (AB), Methylene Blue (MB), Alizarin Green (AG), and Congo Red (CR). The test results are listed in Table 9.

[0038] Table 9: Performance of the nanofiltration membrane prepared in Example 9 The contents described in this specification are merely an enumeration of the implementation forms of the inventive concept, and the scope of protection of this invention should not be regarded as limited to the specific forms described in the embodiments.

Claims

1. A method for preparing an amino acid-in-situ anchored amino acid composite covalent organic framework nanofiltration membrane, characterized in that, Includes the following steps: Step 1: Dissolve the aldehyde monomer, amino monomer and catalyst in a polar aprotic solvent, mix thoroughly to obtain a homogeneous solution, allow the reaction to stand, and then obtain a primary nano-covalent organic framework colloidal solution; then dissolve the amino acid in water to obtain an amino acid solution, add the amino acid solution to the primary nano-covalent organic framework colloidal solution, crystallize and grow, and obtain a grown COF nanosheet colloidal solution. Step 2: Take out the COF nanosheet colloidal solution grown in Step 1, dilute it with water, and sonicate it until it is evenly dispersed. Vacuum filter it and deposit it on the base membrane to obtain a COF composite membrane. Then, immerse the COF composite membrane in an alkaline environment, and after cleaning and drying in a vacuum oven, obtain an amino acid in-situ anchored amino acid composite covalent organic framework nanofiltration membrane.

2. The method for preparing an amino acid-in-situ anchored amino acid composite covalent organic framework nanofiltration membrane according to claim 1, characterized in that, In step one, the aldehyde monomer is 2,3,5,6-tetrafluoroterephthalaldehyde, 2,5-dihydroxyterephthalaldehyde, 2,3-dihydroxyterephthalaldehyde, 2,6-pyridinedicarboxaldehyde, or 2,4,6-tricarboxymethyl phloroglucinol.

3. The method for preparing an amino acid-in-situ anchored amino acid composite covalent organic framework nanofiltration membrane according to claim 1, characterized in that, In step one, the amino monomer is triaminoguanidine hydrochloride or 2,5-diaminobenzenesulfonic acid.

4. The method for preparing an amino acid-in-situ anchored amino acid composite covalent organic framework nanofiltration membrane according to claim 1, characterized in that, In step one, the amino acid is cysteine, tyrosine, arginine, or lysine.

5. The method for preparing an amino acid-in-situ anchored amino acid composite covalent organic framework nanofiltration membrane according to claim 1, characterized in that, In step one, the catalyst is trifluoroacetic acid, acetic acid, terephthalic acid, or KOH.

6. The method for preparing an amino acid-in-situ anchored amino acid composite covalent organic framework nanofiltration membrane according to claim 1, characterized in that, In step one, the polar aprotic solvent is dimethyl sulfoxide, acetonitrile, or N,N-dimethylformamide.

7. The method for preparing an amino acid-in-situ anchored amino acid composite covalent organic framework nanofiltration membrane according to claim 1, characterized in that, In step one, the ratio of the amounts of aldehyde monomer, amino monomer, catalyst, and amino acid is 0.03~0.3 mmol: 0.02~0.2 mmol: 0.25~2.5 mmol: 0.06~0.6 mmol.

8. The method for preparing an amino acid-in-situ anchored amino acid composite covalent organic framework nanofiltration membrane according to claim 1, characterized in that, In step one, the initial growth time of the nano-COF in the static reaction is 1 to 3 days.

9. The method for preparing an amino acid-in-situ anchored amino acid composite covalent organic framework nanofiltration membrane according to claim 1, characterized in that, In step one, the crystal growth time is 2 to 7 days.

10. The method for preparing an amino acid-in-situ anchored amino acid composite covalent organic framework nanofiltration membrane according to claim 1, characterized in that, In step two, the alkaline solution used is a K2CO3 solution with a concentration of 1 g / L to 50 g / L, and the soaking time is 0.5 to 2 h.

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