Covalent organic polymer composite membrane for organic solvent nanofiltration and method for preparing the same

Abstract

The application discloses a kind of covalent organic polymer composite membrane for organic solvent nanofiltration and preparation method thereof, comprising the following steps: acyl chloride monomer and diamine monomer are respectively prepared into solution, then aldehyde monomer and amine monomer are respectively prepared into solution, and equal molar amount of acetic acid is added therein;Substrate is first immersed in acyl chloride solution, and then taken out and washed, then substrate is immersed in diamine monomer solution, and then taken out and washed, and heat treatment is carried out;Aminated substrate is first immersed in aldehyde monomer solution, and then taken out and washed, then substrate is immersed in amine monomer solution, and then taken out and washed, and repeated for a certain number of times, substrate is heat treated, and finally covalent organic polymer composite membrane is obtained.The covalent organic polymer composite membrane with high porosity and high cross-linking structure similar to covalent organic framework is quickly prepared by kinetic control method, has excellent organic solvent resistance, and can accurately screen solute molecules at sub-nanometer scale with high permeability.

Description

Technical Field

[0001] The present invention relates to the technical field of functional membrane materials and membrane separation, and in particular to a covalent organic polymer composite membrane for organic solvent nanofiltration and a preparation method thereof. Background Art

[0002] The separation, purification, and concentration of solute molecules in organic solvents are essential processes in fields such as petrochemicals, food processing, and biopharmaceuticals. Common separation techniques currently used include distillation, evaporation, and recrystallization. However, these techniques involve phase transitions, often resulting in high energy consumption, high separation costs, and significant carbon emissions. Nanofiltration membrane separation technology, driven by pressure at room temperature, effectively retains solute molecules with a molecular weight of 200 to 1200 Daltons. Its high efficiency and low energy consumption have made it a vital player in fields such as seawater desalination and drinking water purification. Nanofiltration membrane separation technology implemented in organic solvents not only opens up new areas and brings technological innovation to the chemical industry, but also lays a solid foundation for my country to achieve its carbon neutrality goals. However, existing organic solvent nanofiltration membrane materials still face challenges, particularly the limitations of high permeability and selectivity, precise molecular sieving, and long-term stability in both highly polar and non-polar solvents.

[0003] Covalent organic framework materials (Science, 310 (2005) 1166-1170), which have been developed over the past decade, are microporous polymers composed primarily of carbon, hydrogen, oxygen, and nitrogen elements with ordered molecular chains. They exhibit characteristics such as uniform pore size, large specific surface area, high porosity, and strong designability. It is foreseeable that these materials will have enormous application prospects in the field of membrane separation. The framework chemical structure can be rationally designed to control pore size and pore surface properties based on diverse application requirements, such as gas separation, water purification, fuel cells, and organic solvent nanofiltration. Although the inherent pores and high stability of covalent organic framework materials perfectly match the requirements of organic nanofiltration membrane materials, and the current synthesis routes for powdered covalent organic framework materials are relatively mature and there are numerous related reports, the preparation of defect-free, large-area, and high-strength covalent organic framework membranes remains a significant challenge. Existing covalent organic framework materials typically have pore sizes between 1 and 5 nm, which cannot meet the requirements of molecular separation at the subnanometer scale.

[0004] Some of the technologies currently reported can solve some of the above problems. For example, the free interfacial polymerization method is used to dissolve two monomers in mutually immiscible solvents, and react at the phase interface to prepare a complete covalent organic framework membrane. However, it usually requires a long reaction time, it is difficult to obtain a large-area membrane, and it needs to be tediously transferred to the substrate to be useful. The in situ interfacial polymerization method is to grow directly on the surface of the porous membrane substrate, avoiding the transfer process and thus obtaining a covalent organic framework composite membrane, but due to its fast reaction rate and short reaction time, it is difficult to obtain a highly crystalline covalent organic framework membrane. At the same time, the interfacial polymerization method faces the limitation of the solubility of amine monomers in water, and it is difficult to apply some monomers of new structures, and it is impossible to construct a membrane material with high porosity and high specific surface area. In response to the above problems, a solution is proposed below. Summary of the Invention

[0005] The purpose of the present invention is to provide a covalent organic polymer composite membrane for organic solvent nanofiltration and a preparation method thereof, which has the advantages that the prepared composite membrane material has excellent solvent resistance, high separation accuracy and high permeability.

[0006] The above technical objectives of the present invention are achieved through the following technical solutions:

[0007] A covalent organic polymer composite membrane for organic solvent nanofiltration and a preparation method thereof, comprising the following steps:

[0008] (1) preparing an acyl chloride monomer and a diamine monomer for amination into a trimesoyl chloride solution and a p-phenylenediamine monomer solution, respectively; then preparing an aldehyde monomer and an amine monomer into an aldehyde monomer solution and an amine monomer solution, respectively; after the aldehyde monomer and the amine monomer are dissolved, an equimolar amount of acetic acid is added thereto as a catalyst;

[0009] (2) The substrate was immersed in a trimesoyl chloride solution for 30 seconds, then removed and cleaned in a corresponding solvent for 30 seconds, then immersed in a p-phenylenediamine monomer solution for 30 seconds, then removed and cleaned in a corresponding pure solvent for 30 seconds, and finally heat-treated at 60°C for 2 minutes to complete the amination of the substrate surface;

[0010] (3) At a certain reaction temperature, the surface amino-modified substrate is first immersed in an aldehyde monomer solution for a certain period of time, then taken out and washed twice in a corresponding solvent; then the substrate is immersed in an amine monomer solution for a certain period of time, then taken out and washed twice in a corresponding solvent to complete a cycle. After repeating a certain number of cycles, the substrate is heat-treated at 60°C for 5 minutes to preliminarily prepare a covalent organic polymer composite membrane; the preliminarily prepared covalent organic polymer composite membrane is placed in an activation solvent and immersed for 16 hours. After taking it out, it is placed in ethanol for exchange for 4 hours to obtain a final covalent organic polymer composite membrane.

[0011] Preferably, the acyl chloride monomer and the diamine monomer in step (1) are trimesoyl chloride and p-phenylenediamine, respectively, and their concentrations are both 0.1-0.3 wt%.

[0012] Preferably, the amine monomer in step (1) is any one of 5,5'-diamino-2,2'-bipyridine, p-diaminoazobenzene, and 1,3-bis(3-aminophenoxy)benzene, and the concentration of the amine monomer solution in step (1) is 3 mmol / L.

[0013] Preferably, the aldehyde monomer in step (1) is any one of trialdehyde phloroglucinol, tris(4-formylphenyl)amine, and 1,3,5-tris(2-formylpyridin-5-yl)benzene, and the concentration of the aldehyde monomer solution in step (1) is 2 mmol / L.

[0014] Preferably, the solvent for dissolving the monomer in step (1) is any one of tetrahydrofuran, dioxane, and mesitylene.

[0015] Preferably, in step (2), the substrate is a cross-linked polyimide ultrafiltration membrane.

[0016] Preferably, the immersion time in the aldehyde monomer solution and the amine monomer solution in step (3) is 1 to 2 minutes, and the reaction temperature in step (3) is 30 to 50°C.

[0017] Preferably, the activation solvent in step (3) is N,N-dimethylformamide.

[0018] Preferably, the covalent organic polymer composite membrane in step (3) is prepared based on Schiff base reaction and β-ketoenamination reaction.

[0019] The present invention provides the following beneficial effects: The substrate is pre-aminated. Only when the substrate surface has been aminated or has a high density of amino groups can the first layer of aromatic amino reactive sites be grafted. Without these sites, the aldehyde monomer can only be adsorbed on the substrate surface through weak hydrophobic or electrostatic interactions, resulting in uneven subsequent reactions and the inability to form a film with a complete and defect-free surface.

[0020] The covalent organic polymer composite membrane provided by the present invention is prepared by in-situ layer-by-layer crosslinking based on Schiff base and β-ketoenamination reactions. The Schiff base reaction is a nucleophilic substitution reaction between an amino group and an aldehyde group. Amine monomers are nucleophiles, and the greater their acidity value (Pka), the faster the reaction rate. The Schiff base reaction is reversible to a certain extent, and water needs to be continuously removed during the reaction process to ensure that the reaction proceeds in the forward direction. If a hydroxyl group is introduced next to the aldehyde group, a β-ketoenamination reaction will further occur after the Schiff base reaction, accelerating the reaction rate to form an irreversible stable chemical crosslinked structure. At the same time, the designed amine monomers and aldehyde monomers accelerate the reaction time by sacrificing a certain degree of crystallinity, thereby forming a partially ordered structure. The covalent organic polymer composite membrane finally formed has excellent solvent tolerance and high solvent permeability. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 A method for preparing a covalent organic polymer composite membrane;

[0022] Figure 2 Schematic diagram of the structure of amine and aldehyde monomers;

[0023] Figure 3 Scanning electron micrographs of the surface and cross section of the covalent organic polymer composite membrane prepared in Example 1;

[0024] Figure 4 Transmission electron microscopy image of a cross section of the covalent organic polymer composite membrane prepared in Example 1. DETAILED DESCRIPTION

[0025] The following is only a preferred embodiment of the present invention, and the scope of protection is not limited to this embodiment. All technical solutions under the concept of the present invention should fall within the scope of protection of the present invention. The same parts are represented by the same figure marks. It should be noted that the words "front", "rear", "left", "right", "up" and "down" used in the following description refer to the directions in the accompanying drawings, and the words "bottom" and "top", "inside" and "outside" refer to the directions toward or away from the geometric center of a specific component, respectively.

[0026] Example 1:

[0027] Trimesoyl chloride and p-phenylenediamine monomers, used for surface grafting initiation, were dissolved in tetrahydrofuran to a concentration of 0.1 wt%. Trialdehyde phloroglucinol and 5,5'-diamino-2,2'-bipyridine were then dissolved in tetrahydrofuran to concentrations of 0.2 and 0.3 mmol / L, respectively. After dissolution, an equimolar amount of acetic acid was added as a catalyst. A cross-linked polyimide ultrafiltration membrane was immersed in the trimesoyl chloride solution for 30 seconds, then removed and rinsed in the corresponding solvent for 30 seconds. The membrane was then immersed in the p-phenylenediamine solution for 30 seconds, removed and rinsed in the corresponding solvent for 30 seconds, and finally heat-treated at 60°C for 2 minutes. At 30°C, the amino-modified polyimide ultrafiltration membrane was first immersed in a trialdehyde phloroglucinol solution for 1 minute, then taken out and washed twice in a corresponding solvent; then it was immersed in a 5,5′-diamino-2,2′-bipyridine solution for 1 minute, then taken out and washed twice in a corresponding solvent. The above was one cycle. After repeating 10 cycles, the substrate was heat-treated at 60°C for 5 minutes to finally obtain a covalent organic polymer composite membrane.

[0028] The surface and cross-sectional morphologies of the prepared composite membranes are shown in Figure 2. Figure 3 and Figure 4 As shown, the membrane surface is very dense, exhibiting a uniform protrusion structure. The pore structure of the substrate is not lost during the preparation process. The covalent organic polymer membrane is supported on a cross-linked polyimide substrate with a thickness of approximately 25 nm, achieving ultra-thinness. This facilitates rapid penetration of organic solvents and enables high-performance organic solvent nanofiltration.

[0029] Example 2:

[0030] Trimesoyl chloride and p-phenylenediamine, monomers used for surface grafting initiation, were dissolved in tetrahydrofuran to a concentration of 0.1 wt%. Trialdehyde phloroglucinol and p-diaminoazobenzene were then dissolved in tetrahydrofuran to concentrations of 0.2 and 0.3 mmol / L, respectively. After dissolution, an equimolar amount of acetic acid was added as a catalyst. A cross-linked polyimide ultrafiltration membrane was immersed in the trimesoyl chloride solution for 30 seconds, then removed and rinsed in the corresponding solvent for 30 seconds. The membrane was then immersed in the p-phenylenediamine solution for 30 seconds, removed and rinsed in the corresponding solvent for 30 seconds, and finally heat-treated at 60°C for 2 minutes. At 40°C, the amino-modified polyimide ultrafiltration membrane was first immersed in a trialdehyde phloroglucinol solution for 1 minute, then taken out and washed twice in a corresponding solvent; then it was immersed in a p-diaminoazobenzene solution for 1 minute, then taken out and washed twice in a corresponding solvent. The above was one cycle. After repeating 10 cycles, the substrate was heat-treated at 60°C for 5 minutes to finally obtain a covalent organic polymer composite membrane.

[0031] Example 3:

[0032] Trimesoyl chloride and p-phenylenediamine monomers, used for surface grafting initiation, were dissolved in tetrahydrofuran to a concentration of 0.1 wt%. Trialdehyde phloroglucinol and 1,3-bis(3-aminophenoxy)benzene were then dissolved in tetrahydrofuran to concentrations of 0.2 and 0.3 mmol / L, respectively. After dissolution, an equimolar amount of acetic acid was added as a catalyst. A cross-linked polyimide ultrafiltration membrane was immersed in the trimesoyl chloride solution for 30 seconds, then removed and rinsed in the corresponding solvent for 30 seconds. The membrane was then immersed in a p-phenylenediamine solution for 30 seconds, removed and rinsed in the corresponding solvent for 30 seconds, and finally heat-treated at 60°C for 2 minutes. At 50°C, the amino-modified polyimide ultrafiltration membrane was first immersed in a trialdehyde phloroglucinol solution for 1 minute, then taken out and washed twice in a corresponding solvent; then it was immersed in a p-diaminoazobenzene solution for 1 minute, then taken out and washed twice in a corresponding solvent. The above was one cycle. After repeating 10 cycles, the substrate was heat-treated at 60°C for 5 minutes to finally obtain a covalent organic polymer composite membrane.

[0033] Example 4:

[0034] Trimesoyl chloride and p-phenylenediamine, monomers used for surface grafting initiation, were dissolved in dioxane to a concentration of 0.2 wt%. Tris(4-formylphenyl)amine and 5,5'-diamino-2,2'-bipyridine were then dissolved in dioxane to concentrations of 0.2 and 0.3 mmol / L, respectively. After dissolution, an equimolar amount of acetic acid was added as a catalyst. A cross-linked polyimide ultrafiltration membrane was immersed in the trimesoyl chloride solution for 30 seconds, then removed and rinsed in the corresponding solvent for 30 seconds. The membrane was then immersed in the p-phenylenediamine solution for 30 seconds, removed and rinsed in the corresponding solvent for 30 seconds, and finally heat-treated at 60°C for 2 minutes. At 50°C, the amino-modified polyimide ultrafiltration membrane was first immersed in a tri(4-formylphenyl)amine solution for 2 minutes, then taken out and washed twice in a corresponding solvent; then it was immersed in a 5,5′-diamino-2,2′-bipyridine solution for 2 minutes, then taken out and washed twice in a corresponding solvent. The above was one cycle. After repeating 15 cycles, the substrate was heat-treated at 60°C for 5 minutes to finally obtain a covalent organic polymer membrane.

[0035] Example 5:

[0036] Trimesoyl chloride and p-phenylenediamine, monomers used for surface grafting initiation, were dissolved in dioxane to a concentration of 0.1 wt%. Tris(4-formylphenyl)amine and p-diaminoazobenzene were then dissolved in dioxane to concentrations of 0.2 and 0.3 mmol / L, respectively. After dissolution, an equimolar amount of acetic acid was added as a catalyst. A cross-linked polyimide ultrafiltration membrane was immersed in the trimesoyl chloride solution for 30 seconds, then removed and rinsed in the corresponding solvent for 30 seconds. The membrane was then immersed in a p-phenylenediamine solution for 30 seconds, removed and rinsed in the corresponding solvent for 30 seconds, and finally heat-treated at 60°C for 2 minutes. At 50°C, the amino-modified polyimide ultrafiltration membrane was first immersed in a tri(4-formylphenyl)amine solution for 2 minutes, then taken out and washed twice in a corresponding solvent; then it was immersed in a p-diaminoazobenzene solution for 2 minutes, then taken out and washed twice in a corresponding solvent. The above was one cycle. After repeating 15 cycles, the substrate was heat-treated at 60°C for 5 minutes to finally obtain a covalent organic polymer membrane.

[0037] Example 6:

[0038] Trimesoyl chloride and p-phenylenediamine, monomers used for surface grafting initiation, were dissolved in acetone to a concentration of 0.1 wt%. Tris(4-formylphenyl)amine and bis(3-aminophenoxy)benzene were then dissolved in acetone to concentrations of 0.2 and 0.3 mmol / L, respectively. After dissolution, an equimolar amount of acetic acid was added as a catalyst. A cross-linked polyimide ultrafiltration membrane was then immersed in the trimesoyl chloride solution for 30 seconds, then removed and rinsed in the corresponding solvent for 30 seconds. The membrane was then immersed in a p-phenylenediamine solution for 30 seconds, removed and rinsed in the corresponding solvent for 30 seconds, and finally heat-treated at 60°C for 2 minutes. At 40°C, the amino-modified polyimide ultrafiltration membrane was first immersed in a tri(4-formylphenyl)amine solution for 2 minutes, then taken out and washed twice in a corresponding solvent; then it was immersed in a 1,3-bis(3-aminophenoxy)benzene solution for 2 minutes, then taken out and washed twice in a corresponding solvent. The above was one cycle. After repeating 15 cycles, the substrate was heat-treated at 60°C for 5 minutes to finally obtain a covalent organic polymer membrane.

[0039] Example 7:

[0040] Trimesoyl chloride and p-phenylenediamine monomers, used for surface grafting initiation, were dissolved in acetone to a concentration of 0.3 wt%. 1,3,5-Tris(2-formylpyridin-5-yl)benzene and 5,5'-diamino-2,2'-bipyridine were then dissolved in acetone to concentrations of 0.2 and 0.3 mmol / L, respectively. After dissolution, an equimolar amount of acetic acid was added as a catalyst. A cross-linked polyimide ultrafiltration membrane was then immersed in the trimesoyl chloride solution for 30 seconds, removed and rinsed in the corresponding solvent for 30 seconds, then immersed in the p-phenylenediamine solution for 30 seconds, removed and rinsed in the corresponding solvent for 30 seconds, and finally heat-treated at 60°C for 2 minutes. At 50°C, the amino-modified polyimide ultrafiltration membrane was first immersed in a 1,3,5-tris(2-formylpyridin-5-yl)benzene solution for 1 minute, then taken out and washed twice in a corresponding solvent; then it was immersed in a 5,5′-diamino-2,2′-bipyridine solution for 1 minute, then taken out and washed twice in a corresponding solvent. The above was one cycle. After repeating 10 cycles, the substrate was heat-treated at 60°C for 5 minutes to finally obtain a covalent organic polymer membrane.

[0041] Example 8:

[0042] Trimesoyl chloride and p-phenylenediamine monomers, used for surface grafting initiation, were dissolved in acetone to a concentration of 0.3 wt%. 1,3,5-Tris(2-formylpyridin-5-yl)benzene and p-diaminoazobenzene were then dissolved in acetone to concentrations of 0.2 and 0.3 mmol / L, respectively. After dissolution, an equimolar amount of acetic acid was added as a catalyst. A cross-linked polyimide ultrafiltration membrane was then immersed in the trimesoyl chloride solution for 30 seconds, then removed and rinsed in the corresponding solvent for 30 seconds. The membrane was then immersed in the p-phenylenediamine solution for 30 seconds, removed and rinsed in the corresponding solvent for 30 seconds, and finally heat-treated at 60°C for 2 minutes. At 50°C, the amino-modified polyimide ultrafiltration membrane was first immersed in a 1,3,5-tris(2-formylpyridin-5-yl)benzene solution for 2 minutes, then taken out and washed twice in a corresponding solvent; then it was immersed in a p-diaminoazobenzene solution for 2 minutes, then taken out and washed twice in a corresponding solvent. The above was one cycle. After repeating 10 cycles, the substrate was heat-treated at 60°C for 5 minutes to finally obtain a covalent organic polymer membrane.

[0043] Example 9:

[0044] Trimesoyl chloride and p-phenylenediamine monomers, used for surface grafting initiation, were dissolved in acetone to a concentration of 0.3 wt %. 1,3,5-Tris(2-formylpyridin-5-yl)benzene and 1,3-bis(3-aminophenoxy)benzene were then dissolved in acetone to concentrations of 0.2 and 0.3 mmol / L, respectively. After dissolution, an equimolar amount of acetic acid was added as a catalyst. A cross-linked polyimide ultrafiltration membrane was then immersed in the trimesoyl chloride solution for 30 seconds, removed and rinsed in the corresponding solvent for 30 seconds, then immersed in the p-phenylenediamine solution for 30 seconds, removed and rinsed in the corresponding solvent for 30 seconds, and finally heat-treated at 60°C for 2 minutes. At 40°C, the amino-modified polyimide ultrafiltration membrane was first immersed in a 1,3,5-tris(2-formylpyridin-5-yl)benzene solution for 1 minute, then taken out and washed twice in a corresponding solvent; then it was immersed in a 1,3-bis(3-aminophenoxy)benzene solution for 1 minute, then taken out and washed twice in a corresponding solvent. The above was one cycle. After repeating 15 cycles, the substrate was heat-treated at 60°C for 5 minutes to finally obtain a covalent organic polymer membrane.

[0045] Table 1 Properties of the covalent organic polymer films prepared in Examples 1 to 9

[0046]

[0047] The specific embodiments described above further illustrate the technical problems, technical solutions and beneficial effects solved by the present invention. It should be understood that the above are only specific embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A covalent organic polymer composite membrane for organic solvent nanofiltration and a preparation method thereof, characterized in that: The following steps are involved: (1) preparing the acyl chloride monomer and the diamine monomer for amination into a trimesoyl chloride solution and a p-phenylenediamine monomer solution respectively; Then, the aldehyde monomer and the amine monomer are prepared into an aldehyde monomer solution and an amine monomer solution respectively, and after the solution is dissolved, an equimolar amount of acetic acid is added thereto as a catalyst; The acyl chloride monomer and the diamine monomer are trimesoyl chloride and p-phenylenediamine, respectively, and their concentrations are both 0.1-0.3 wt %; The amine monomer is any one of 5,5'-diamino-2,2'-bipyridine, p-diaminoazobenzene, and 1,3-bis(3-aminophenoxy)benzene, and the concentration of the amine monomer solution in step (1) is 3 mmol / L; (2) Immerse the substrate in a solution of trimesoyl chloride for 30 seconds, then remove it and wash it in a corresponding solvent for 30 seconds, then immerse the substrate in a p-phenylenediamine monomer solution for 30 seconds, then remove it and wash it in a corresponding pure solvent for 30 seconds, and finally heat treat the substrate at 60°C for 2 minutes to complete the amination of the substrate surface; (3) At a certain reaction temperature, the surface amino-modified substrate is first immersed in an aldehyde monomer solution for a certain period of time, then taken out and washed twice in a corresponding solvent; then the substrate is immersed in an amine monomer solution for a certain period of time, then taken out and washed twice in a corresponding solvent to complete a cycle. After repeating a certain number of cycles, the substrate is heat-treated at 60°C for 5 minutes to preliminarily prepare a covalent organic polymer composite membrane; the preliminarily prepared covalent organic polymer composite membrane is placed in an activation solvent and immersed for 16 hours. After taking it out, it is placed in ethanol for exchange for 4 hours to obtain a final covalent organic polymer composite membrane; the activation solvent is N,N-dimethylformamide.

2. A covalent organic polymer composite membrane for organic solvent nanofiltration and a preparation method thereof according to claim 1, characterized in that: The aldehyde monomer in step (1) is any one of trialdehyde phloroglucinol, tris(4-formylphenyl)amine, and 1,3,5-tris(2-formylpyridin-5-yl)benzene, and the concentration of the aldehyde monomer solution in step (1) is 2 mmol / L.

3. A covalent organic polymer composite membrane for organic solvent nanofiltration and a preparation method thereof according to claim 2, characterized in that: The solvent for dissolving the monomer in step (1) is any one of tetrahydrofuran, dioxane, and mesitylene.

4. A covalent organic polymer composite membrane for organic solvent nanofiltration and a preparation method thereof according to claim 1, characterized in that: In the step (2), the substrate is a cross-linked polyimide ultrafiltration membrane.

5. A covalent organic polymer composite membrane for organic solvent nanofiltration and a preparation method thereof according to claim 1, characterized in that: The immersion time in the aldehyde monomer solution and the amine monomer solution in step (3) is 1-2 minutes, and the reaction temperature in step (3) is 30-50°C.

6. A covalent organic polymer composite membrane for organic solvent nanofiltration and a preparation method thereof according to claim 1, characterized in that: In the step (3), the covalent organic polymer composite membrane is prepared based on Schiff base reaction and β-ketoenamination reaction.

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