A polyamide-PVA-polyamine COF composite film and its preparation method

Abstract

The application provides a polyamide-PVA-polyamine COF composite film and a preparation method thereof, and belongs to the technical field of membrane separation. The polyamide-PVA-polyamine COF composite film provided by the application comprises a polyamide COF film and a polyamine COF film, and the polyamide COF film is bonded to the polyamine COF film through PVA. The main body of the polyamide-PVA-polyamine COF composite film provided by the application is composed of a crystalline porous polymer-covalent organic framework (COF) with an ordered pore structure, the units are connected to each other through amide bonds, and the internal rich and highly ordered pores make the COF composite film exhibit high separation precision.

Description

Technical Field

[0001] This invention belongs to the field of membrane separation technology, specifically relating to a polyamide-PVA-polyamine COF composite membrane and its preparation method. Background Technology

[0002] With the increasing prominence of environmental issues, membrane separation technology is being applied more and more widely in industrial production. Membrane separation is a novel and efficient fluid separation technology that plays a vital role in water supply engineering, industrial wastewater treatment, the medical industry, the food industry, and the energy industry. Developing effective separation technologies is one way to alleviate environmental pressure, and membrane separation has attracted widespread attention in the field of separation technology due to its simplicity, efficiency, energy saving, and environmental friendliness.

[0003] Polyamides are an important type of membrane material in separation technology, but currently used polyamide membranes are amorphous, and their disordered pore structure reduces their separation performance. Summary of the Invention

[0004] In view of this, the purpose of this invention is to provide a polyamide-PVA-polyamine COF composite membrane and its preparation method. The polyamide-PVA-polyamine COF composite membrane provided by this invention has good crystallinity, an ordered pore structure, and high separation accuracy.

[0005] To achieve the above-mentioned objectives, the present invention provides the following technical solution:

[0006] This invention provides a polyamide-PVA-polyamine COF composite film, comprising a polyamide COF film and a polyamine COF film, wherein the polyamide COF film is bonded to the polyamine COF film via PVA; the polyamide COF film is formed from a polymer having the structure shown in Formula I, and the polyamine COF film is formed from a polymer having the structure shown in Formula II.

[0007]

[0008] Preferably, the thickness of the polyamide COF film and the polyamine COF film is independently 100-400 nm.

[0009] This invention provides a method for preparing the polyamide-PVA-polyamine COF composite film described above, comprising the following steps:

[0010] A trialdehyde-based phloroglucinol solution was added to an acetonitrile-water solution of 2,4,6-tris(4-aminophenyl)-1,3,5-triazine to carry out an interfacial polymerization reaction, thereby obtaining an imine COF film; the trialdehyde-based phloroglucinol solution was obtained by dissolving trialdehyde-based phloroglucinol in dichloromethane or in trichloromethane.

[0011] The imine COF membrane, the first organic solvent, the first catalyst, and the oxidant are mixed and subjected to an oxidation reaction to obtain a polyamide COF membrane. The polyamide COF membrane is then immersed in a polyvinyl alcohol solution to obtain an immersed polyamide COF membrane.

[0012] The imine COF membrane, the second organic solvent, the second catalyst, and the reducing agent are mixed and a reduction reaction is carried out to obtain a polyamine COF membrane. The polyamine COF membrane is then immersed in a polyvinyl alcohol solution to obtain an immersed polyamine COF membrane.

[0013] The impregnated polyamide COF film and the impregnated polyamine COF film are stacked and dried to obtain the polyamide-PVA-polyamine COF composite film.

[0014] Preferably, the molar ratio of the trialdehyde phloroglucinol to 2,4,6-tris(4-aminophenyl)-1,3,5-triazine is 1:1; and the interfacial polymerization reaction time is 48-72 h.

[0015] Preferably, the first organic solvent comprises N,N-dimethylformamide; the first catalyst comprises acetic acid; and the oxidant comprises KHSO5.

[0016] Preferably, when preparing the polyamide COF membrane, the molar amount of the imine COF membrane is calculated based on the molar amount of trialdehyde phloroglucinol used in preparing the imine COF membrane, the volume ratio of the molar amount of the imine COF membrane to the first catalyst is 0.05 mmol: 2 mL, and the molar ratio of the imine COF membrane to the oxidant is 0.05: 0.86.

[0017] Preferably, the oxidation reaction takes 36 to 48 hours.

[0018] Preferably, the second organic solvent comprises methanol; the second catalyst comprises terephthalic acid; and the reducing agent comprises NaBH4.

[0019] Preferably, when preparing the polyamine COF membrane, the molar amount of the imine COF membrane is calculated based on the molar amount of trialdehyde phloroglucinol used in preparing the imine COF membrane, the molar ratio of the imine COF membrane to the second catalyst is 0.05:0.17, and the molar ratio of the imine COF membrane to the reducing agent is 0.05:6.5.

[0020] Preferably, the reduction reaction takes 11 to 13 hours.

[0021] This invention provides a polyamide-PVA-polyamine COF composite membrane, comprising a polyamide COF membrane and a polyamine COF membrane, wherein the polyamide COF membrane is bonded to the polyamine COF membrane via PVA; the polyamide COF membrane is formed from a polymer having the structure shown in Formula I, and the polyamine COF membrane is formed from a polymer having the structure shown in Formula II. The main body of the polyamide-PVA-polyamine COF composite membrane provided by this invention is composed of a crystalline porous polymer-covalent organic framework (COF) with an ordered pore structure. The polyamide COF membrane units are connected to each other by amide bonds, and the abundant and highly ordered channels within the amide bonds enable the COF composite membrane to exhibit high separation accuracy; the polyamine COF membrane, due to its flexible amine bonds, results in channel narrowing, which further improves the accuracy.

[0022] Furthermore, within the polyamide COF membrane, the amide units themselves possess a certain degree of rigidity, while strong hydrogen bonds form between the C=O and NH groups in the interlayer, further enhancing the membrane's rigidity. This increased strength suppresses membrane deformation under pressure, facilitating membrane separation. Therefore, the strong hydrogen bonds between amide units contribute to the high chemical stability of the polyamide COF membrane. Even after treatment under harsh conditions, the polyamide COF membrane maintains high separation performance, and due to the hydrogen bonds in its internal structure, it also exhibits good mechanical properties and excellent hydrophilicity.

[0023] Furthermore, the amine bonds in polyamine COF are highly flexible chains, possessing both resistance to chlorine degradation and excellent thermal stability. Therefore, combining polyamide COF films with polyamine COF films compensates for the chlorine resistance of polyamide films, while polyamine films offer good flexibility and high thermal stability.

[0024] This invention provides a method for preparing the polyamide-PVA-polyamine COF composite film described above. The dichloromethane / water or trichloromethane / water interfacial polymerization method of this invention is based on monomer self-assembly and polymerization at a sharp interface formed between two immiscible solvents. This interface strictly confines the monomer within a single layer, which is crucial for precise thickness control. The interfacial polymerization process of this invention is mild, requires no other external conditions, and does not damage the COF structure.

[0025] Furthermore, in the layered assembly polymerization process (i.e., interfacial polymerization), the present invention regulates the interfacial polymerization reaction by precisely controlling the rate at which the trialdehyde phloroglucinol solution is added to the acetonitrile-water solution of 2,4,6-tris(4-aminophenyl)-1,3,5-triazine, the type and amount of solvent, and the reaction conditions, thereby adjusting the thermodynamic equilibrium in the covalent bond formation process and forming a stable polymer crystal structure.

[0026] This invention introduces amine-aldehyde functional groups of varying lengths into the membrane, forming COFs with different pore sizes. This design not only overcomes the bottleneck of COF membranes simultaneously exhibiting high permeability and high selectivity, but also prevents the loss of functional groups within the membrane and maintains stability. The bond energies are far greater than the interlayer π-π stacking interactions, preventing damage to the crystalline covalent network structure during exfoliation and significantly improving membrane stability. Therefore, interfacial polymerization can be used to prepare covalent organic framework separation membranes with tunable pore size and stable morphology.

[0027] Liquid-liquid interfacial polymerization is an effective method for synthesizing COF membranes. Due to its scalability, relatively mild reaction conditions, and efficient product collection from the reaction system, coupled with the absence of energy consumption during the reaction, it is advantageous for preparing defect-free membranes with high separation performance and high permeability. Therefore, the preparation method provided by this invention is simple, low-cost, and offers high separation accuracy, allowing for the production of independently supported membranes without the need for any substrate.

[0028] Nanofiltration membranes prepared in existing technologies are unstable in terms of the Schiff base structure formed by interfacial polymerization, and in-situ growth requires high temperatures and is complex. In contrast, the preparation process of this invention is carried out at room temperature and pressure, and the polyamide possesses excellent mechanical properties, good stability, and hydrophilicity. Furthermore, the addition of a polyamine membrane layer gives the composite membrane good flexibility and chlorine resistance. Attached Figure Description

[0029] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0030] Figure 1 Transmission electron microscope (TEM) images of (a) imine COF membrane, (b) polyamide COF membrane, and (c) polyamine COF membrane prepared by interfacial polymerization in Example 1, and cross-sectional TEM image of (d) polyamide-PVA-polyamine COF composite membrane.

[0031] Figure 2 The image shows the XRD pattern of the imine COF membrane prepared by interfacial polymerization in Example 1.

[0032] Figure 3 Images of a) imine COF membrane, b) polyamide COF membrane, c) polyamine COF membrane and d) polyamide-PVA-polyamine COF composite membrane prepared by interfacial polymerization in Example 1;

[0033] Figure 4The infrared spectra of TAPT monomer, TP monomer, imine COF film, polyamide COF film, and polyamine COF film in Example 1 are shown. Detailed Implementation

[0034] This invention provides a polyamide-PVA-polyamine COF composite membrane based on interfacial polymerization, comprising a polyamide COF membrane and a polyamine COF membrane, wherein the polyamide COF membrane is bonded to the polyamine COF membrane via PVA; the polyamide COF membrane is formed from a polymer having the structure shown in Formula I, and the polyamine COF membrane is formed from a polymer having the structure shown in Formula II.

[0035]

[0036] In this invention, the polyamide COF film is bonded to the polyamine COF film via PVA; simultaneously, the polyamide COF film and PVA molecules are connected by hydrogen bonds; the polyamine COF film and PVA molecules are also connected by hydrogen bonds. In this invention, the thicknesses of the polyamide COF film and the polyamine COF film are independently 100–400 nm, preferably 150–350 nm, and more preferably 200–300 nm.

[0037] The polyamide-PVA-polyamine COF composite membrane provided by this invention is primarily composed of a crystalline porous polymer-covalent organic framework (COF) with an ordered pore structure. The polyamide COF membrane units are interconnected by amide bonds. The formation of these amide bonds is achieved through an imine COF oxidative conversion method. The abundant and highly ordered internal pores enable the COF composite membrane to exhibit high separation precision. Furthermore, the flexible amine bonds in the polyamine COF membrane lead to pore size reduction, further enhancing the precision.

[0038] Furthermore, the interlayer hydrogen bonding between amide units in the polyamide COF membrane, coupled with the inherent rigidity of the amide units themselves and the strong hydrogen bonding between C=O and NH atoms in the interlayer, further enhances the membrane's rigidity. This increased strength suppresses membrane deformation under pressure, facilitating membrane separation. Therefore, the strong hydrogen bonding between amide units contributes to the high chemical stability of the polyamide COF membrane. Even after treatment under harsh conditions, the polyamide COF membrane maintains high separation performance. Moreover, the hydrogen bonding within its internal structure also gives it good mechanical properties and excellent hydrophilicity.

[0039] Furthermore, the amine bonds in polyamine COF are highly flexible chains, possessing both resistance to chlorine degradation and excellent thermal stability. Therefore, polyamine films compensate for the chlorine resistance of polyamide films, while also exhibiting good flexibility and high thermal stability.

[0040] This invention provides a method for preparing the polyamide-PVA-polyamine COF composite film described above, comprising the following steps:

[0041] A trialdehyde phloroglucinol solution was added to an acetonitrile-water solution of 2,4,6-tris(4-aminophenyl)-1,3,5-triazine to carry out an interfacial polymerization reaction, resulting in an imine COF film.

[0042] The trialdehyde phloroglucinol solution is obtained by dissolving trialdehyde phloroglucinol in dichloromethane or in trichloromethane;

[0043] The imine COF membrane, the first organic solvent, the first catalyst, and the oxidant are mixed and subjected to an oxidation reaction to obtain a polyamide COF membrane. The polyamide COF membrane is then immersed in a polyvinyl alcohol solution to obtain an immersed polyamide COF membrane.

[0044] The imine COF membrane, the second organic solvent, the second catalyst, and the reducing agent are mixed and a reduction reaction is carried out to obtain a polyamine COF membrane. The polyamine COF membrane is then immersed in a polyvinyl alcohol solution to obtain an immersed polyamine COF membrane.

[0045] The impregnated polyamide COF film and the impregnated polyamine COF film are stacked and dried to obtain the polyamide-PVA-polyamine COF composite film.

[0046] In this invention, a trialdehyde phloroglucinol solution is added to an acetonitrile-water solution of 2,4,6-tris(4-aminophenyl)-1,3,5-triazine to carry out an interfacial polymerization reaction to obtain an imine COF film.

[0047] In this invention, the trialdehyde-based phloroglucinol solution is obtained by dissolving trialdehyde-based phloroglucinol in dichloromethane or trichloromethane and then sonicating it, preferably by dissolving trialdehyde-based phloroglucinol in dichloromethane and then sonicating it. This invention does not have particular requirements on the amount of dichloromethane or trichloromethane used, as long as it is sufficient to dissolve the trialdehyde-based phloroglucinol. In this invention, the acetonitrile-water solution of 2,4,6-tris(4-aminophenyl)-1,3,5-triazine is preferably obtained by dissolving 2,4,6-tris(4-aminophenyl)-1,3,5-triazine in an acetonitrile-water solution and then sonicating it. This invention does not have particular requirements on the amount of acetonitrile-water solution used, as long as it is sufficient to dissolve 2,4,6-tris(4-aminophenyl)-1,3,5-triazine. In this invention, the volume ratio of acetonitrile to water in the acetonitrile-water solution is preferably 3:7. The present invention does not have special requirements for the time and power of the ultrasound, as long as it can dissolve the trialdehyde phloroglucinol and 2,4,6-tris(4-aminophenyl)-1,3,5-triazine.

[0048] In this invention, the molar ratio of the trialdehyde-based phloroglucinol to 2,4,6-tris(4-aminophenyl)-1,3,5-triazine is preferably 1:1. In this invention, it is preferable to add the trialdehyde-based phloroglucinol solution dropwise into the acetonitrile-water solution of the 2,4,6-tris(4-aminophenyl)-1,3,5-triazine; the dropwise addition rate is preferably 1–2 mL / min. In this invention, the interfacial polymerization reaction time is preferably 48–72 h, more preferably 52–68 h, and even more preferably 57–65 h; the interfacial reaction temperature is preferably room temperature. In this invention, the interfacial reaction is preferably carried out under static conditions.

[0049] The dichloromethane / water or trichloromethane / water interfacial polymerization method of the present invention is based on monomer self-assembly and polymerization at a sharp interface formed between two immiscible solvents. This interface strictly confines the monomers (trialdehyde phloroglucinol and 2,4,6-tris(4-aminophenyl)-1,3,5-triazine) within a single monolayer, which is crucial for precise thickness control. The interfacial polymerization process of the present invention is mild, requires no other external conditions, and does not damage the COF structure.

[0050] During interfacial polymerization, this invention precisely controls the rate at which the trialdehyde phloroglucinol solution is added to an acetonitrile-water solution of 2,4,6-tris(4-aminophenyl)-1,3,5-triazine, the type and amount of solvent, and the reaction conditions within the above-mentioned ranges. This allows for the regulation of the thermodynamic equilibrium during covalent bond formation, resulting in a stable polymer crystal structure.

[0051] This invention introduces amine-aldehyde functional groups of varying lengths into the membrane, forming COFs with different pore sizes. This design not only overcomes the bottleneck of COF membranes simultaneously exhibiting high permeability and high selectivity, but also prevents the loss of functional groups within the membrane and maintains stability. The bond energies are far greater than the interlayer π-π stacking interactions, preventing damage to the crystalline covalent network structure during exfoliation and significantly improving membrane stability. Therefore, interfacial polymerization can be used to prepare covalent organic framework separation membranes with tunable pore size and stable morphology.

[0052] After the interfacial reaction is completed, a thin layer is formed at the interface between water and dichloromethane or water and trichloromethane. Preferably, the top aqueous phase is removed using a dropper, and the thin layer is washed sequentially with dichloromethane, tetrahydrofuran, and acetone. After washing, the thin layer is preferably collected and dried using an ethanol-wetted nylon membrane to obtain the imine COF membrane. In this invention, the pore size of the nylon membrane is preferably 0.1 μm.

[0053] In this invention, the drying temperature is preferably 50–60°C, more preferably 52–58°C, and even more preferably 55–57°C. This invention removes residual solvent through drying. This invention does not have special requirements for the washing process; processes well-known in the art can be used.

[0054] After obtaining the imine COF membrane, the present invention mixes the imine COF membrane, a first organic solvent, a first catalyst and an oxidant to carry out an oxidation reaction to obtain a polyamide COF membrane, and then immerses the polyamide COF membrane in a polyvinyl alcohol solution to obtain an immersed polyamide COF membrane.

[0055] In preparing the polyamide COF membrane, the molar amount of the imine COF membrane is preferably calculated based on the molar amount of trialdehyde phloroglucinol used in preparing the imine COF membrane. The volume ratio of the molar amount of the imine COF membrane to the first catalyst is preferably 0.05 mmol: 2 mL; the molar ratio of the imine COF membrane to the oxidant is preferably 0.05:0.86. In this invention, the first organic solvent preferably includes N,N-dimethylformamide; the first catalyst preferably includes acetic acid; and the oxidant preferably includes KHSO5. This invention does not have particular requirements on the amount of the first organic solvent, as long as it is sufficient to immerse the imine COF membrane. In this invention, the oxidation reaction time is 36–48 h, more preferably 38–45 h, and more preferably 40–43 h; the oxidation reaction temperature is preferably room temperature. In this invention, the oxidation reaction is preferably carried out under static conditions. During the oxidation reaction, the imine COF membrane is oxidized into a polyamide COF membrane.

[0056] After the oxidation reaction is completed, the thin film is preferably washed sequentially with dichloromethane, tetrahydrofuran, and acetone. After washing, the thin film is preferably collected and dried using an ethanol-wetted nylon membrane to obtain the polyamide COF membrane. In this invention, the pore size of the nylon membrane is preferably 0.1 μm.

[0057] In this invention, the drying temperature is preferably 50–60°C, more preferably 52–58°C, and even more preferably 55–57°C. This invention removes residual solvent through drying. This invention does not have special requirements for the washing process; processes well-known in the art can be used.

[0058] After obtaining the imine COF membrane, the present invention mixes the imine COF membrane, the second organic solvent, the second catalyst and the reducing agent to carry out a reduction reaction to obtain a polyamine COF membrane. The polyamine COF membrane is then immersed in a polyvinyl alcohol solution to obtain an immersed polyamine COF membrane.

[0059] In the preparation of the polyamine COF membrane, the molar amount of the imine COF membrane is preferably calculated based on the molar amount of trialdehyde-resorcinol used in the preparation of the imine COF membrane. The molar ratio of the imine COF membrane to the second catalyst is preferably 0.05:0.17; the molar ratio of the imine COF membrane to the reducing agent is preferably 0.05:6.5. In this invention, the second organic solvent preferably includes methanol; the second catalyst preferably includes terephthalic acid; and the reducing agent preferably includes NaBH4. This invention does not have particular requirements on the amount of the second organic solvent, as long as it is sufficient to immerse the imine COF membrane.

[0060] In this invention, mixing the imine COF membrane, the second organic solvent, the second catalyst, and the reducing agent preferably includes: dissolving the second catalyst in the second organic solvent to obtain a mixed solution; immersing the imine COF membrane in the mixed solution and cooling it to -15 to -20°C; and then adding the reducing agent in batches. In this invention, the number of batch additions is preferably 10 to 15 times. This invention does not have particular requirements on the amount added in each batch; amounts well-known in the art can be used. This invention, by adding the reducing agent in batches, enables a more complete reduction reaction.

[0061] In this invention, the reduction reaction preferably includes: after the second catalyst has been added, maintaining the temperature at -15 to -20°C for 1 hour, and then maintaining it at room temperature for 10 to 12 hours. During the reduction reaction, the reducing agent reduces the imine COF membrane to a polyamine COF membrane. This invention reduces reactivity through low-temperature reaction to prevent the reaction from becoming too rapid.

[0062] After the reduction reaction is completed, the thin film is preferably washed sequentially with dichloromethane, tetrahydrofuran, and acetone. After washing, the thin film is preferably collected and dried using an ethanol-wetted nylon membrane to obtain the polyamine COF membrane. In this invention, the pore size of the nylon membrane is preferably 0.1 μm.

[0063] In this invention, the drying temperature is preferably 50–60°C, more preferably 52–58°C, and even more preferably 55–57°C. This invention removes residual solvent through drying. This invention does not have special requirements for the washing process; processes well-known in the art can be used.

[0064] The present invention does not have any special requirements on the amount of polyvinyl alcohol solution used, as long as it is sufficient to wet the polyamide COF membrane or the polyamine COF membrane.

[0065] After obtaining the impregnated polyamide COF film and the impregnated polyamine COF film, the present invention stacks the impregnated polyamide COF film and the impregnated polyamine COF film and dries them to obtain the polyamide-PVA-polyamine COF composite film.

[0066] In this invention, the drying temperature is preferably 110-120°C, more preferably 113-118°C, and even more preferably 115-118°C.

[0067] To further illustrate the present invention, the polyamide-PVA-polyamine COF composite film and its preparation method provided by the present invention will be described in detail below with reference to the accompanying drawings and embodiments, but these should not be construed as limiting the scope of protection of the present invention.

[0068] Example 1

[0069] Trialdehyde phloroglucinol (TP, 10.51 mg, 0.05 mmol) was dissolved in dichloromethane (20 mL) and sonicated to obtain a dichloromethane solution of trialdehyde phloroglucinol.

[0070] 2,4,6-Tris(4-aminophenyl)-1,3,5-triazine (TAPT, 17.72 mg, 0.05 mmol) was dissolved in an acetonitrile-water solution (acetonitrile:water = 3:7 (v:v), 20 mL), and sonicated to obtain an acetonitrile-water solution of 2,4,6-tris(4-aminophenyl)-1,3,5-triazine.

[0071] The dichloromethane solution of the trialdehyde phloroglucinol was slowly added dropwise along the container wall to the acetonitrile-aqueous solution of 2,4,6-tris(4-aminophenyl)-1,3,5-triazine (dropping rate: 1-2 mL / min). The mixture separated into layers and was allowed to stand at room temperature for 72 h to carry out interfacial polymerization. A thin layer was observed to form at the interface between water and dichloromethane. The top aqueous phase was then removed with a dropper, and the thin layer was washed sequentially with dichloromethane, tetrahydrofuran, and acetone. The thin layer was then collected through an ethanol-wetted nylon membrane (pore size: 0.1 μm). Finally, the thin layer was dried in a vacuum drying oven at 60 °C to remove residual solvent, yielding an imine COF membrane.

[0072] The imine COF membrane was immersed in N,N-dimethylformamide solution (10 mL), and KHSO5 (0.13 g, 0.86 mmol) and acetic acid (2 mL) were added. The membrane was allowed to stand at room temperature for 48 h. After washing the thin film with dichloromethane, tetrahydrofuran, and acetone, respectively, the thin film was collected through an ethanol-wetted nylon membrane (pore size: 0.1 μm). Finally, the thin film was dried in a vacuum drying oven at 60 °C to remove residual solvent, yielding a polyamide COF membrane. The polyamide COF membrane was then immersed in a polyvinyl alcohol solution to obtain an immersed polyamide COF membrane.

[0073] The imine COF membrane was immersed in a methanol solution (25 mL) containing terephthalic acid (28.5 mg, 0.17 mmol). The mixture was then immersed at -15°C for 5 min, followed by the addition of NaBH4 (0.25 g, 6.5 mmol) in portions over 10 min. The mixture was then immersed at -15°C for 1 h and then at room temperature for another 10 h. The thin film was washed with dichloromethane, tetrahydrofuran, and acetone, respectively, and collected through an ethanol-wetted nylon membrane (pore size: 0.1 μm). Finally, the thin film was dried in a vacuum drying oven at 60°C to remove residual solvent, yielding a polyamine COF membrane. The polyamine COF membrane was then immersed in a polyvinyl alcohol solution to obtain an impregnated polyamine COF membrane.

[0074] The impregnated polyamide COF film is stacked with the impregnated polyamine COF film and dried in a vacuum drying oven at 110°C to obtain the polyamide-PVA-polyamine COF composite film.

[0075] Example 2

[0076] Trialdehyde phloroglucinol (TP, 10.51 mg, 0.05 mmol) was dissolved in dichloromethane (20 mL) and sonicated to obtain a dichloromethane solution of trialdehyde phloroglucinol.

[0077] 2,4,6-Tris(4-aminophenyl)-1,3,5-triazine (TAPT, 17.72 mg, 0.05 mmol) was dissolved in an acetonitrile-water solution (acetonitrile:water = 3:7 (v:v), 20 mL), and sonicated to obtain an acetonitrile-water solution of 2,4,6-tris(4-aminophenyl)-1,3,5-triazine.

[0078] The dichloromethane solution of the trialdehyde phloroglucinol was slowly added dropwise along the container wall to the acetonitrile-aqueous solution of 2,4,6-tris(4-aminophenyl)-1,3,5-triazine (dropping rate: 1-2 mL / min). The mixture separated into layers and was allowed to stand at room temperature for 48 h to carry out interfacial polymerization. A thin layer was observed to form at the interface between water and dichloromethane. The top aqueous phase was then removed with a dropper, and the thin layer was washed sequentially with dichloromethane, tetrahydrofuran, and acetone. The thin layer was then collected through an ethanol-wetted nylon membrane (pore size: 0.1 μm). Finally, the thin layer was dried in a vacuum drying oven at 60 °C to remove residual solvent.

[0079] The imine COF membrane was immersed in N,N-dimethylformamide solution (10 mL), and KHSO5 (0.13 g, 0.86 mmol) and acetic acid (2 mL) were added. The membrane was allowed to stand at room temperature for 48 h. After washing the thin film with dichloromethane, tetrahydrofuran, and acetone, respectively, the thin film was collected through an ethanol-wetted nylon membrane (pore size: 0.1 μm). Finally, the thin film was dried in a vacuum drying oven at 60 °C to remove residual solvent, yielding a polyamide COF membrane. The polyamide COF membrane was then immersed in a polyvinyl alcohol solution to obtain an immersed polyamide COF membrane.

[0080] The imine COF membrane was immersed in a methanol solution (25 mL) containing terephthalic acid (28.5 mg, 0.17 mmol). The mixture was then immersed at -15°C for 5 min, followed by the addition of NaBH4 (0.25 g, 6.5 mmol) in portions over 10 min. The mixture was then immersed at -15°C for 1 h and then at room temperature for another 10 h. The thin film was washed with dichloromethane, tetrahydrofuran, and acetone, respectively, and collected through an ethanol-wetted nylon membrane (pore size: 0.1 μm). Finally, the thin film was dried in a vacuum drying oven at 60°C to remove residual solvent, yielding a polyamine COF membrane. The polyamine COF membrane was then immersed in a polyvinyl alcohol solution to obtain an impregnated polyamine COF membrane.

[0081] The impregnated polyamide COF film is stacked with the impregnated polyamine COF film and dried in a vacuum drying oven at 110°C to obtain the polyamide-PVA-polyamine COF composite film.

[0082] Example 3

[0083] Trialdehyde phloroglucinol (TP, 10.51 mg, 0.05 mmol) was dissolved in dichloromethane (20 mL) and sonicated to obtain a dichloromethane solution of trialdehyde phloroglucinol.

[0084] 2,4,6-Tris(4-aminophenyl)-1,3,5-triazine (TAPT, 17.72 mg, 0.05 mmol) was dissolved in an acetonitrile-water solution (acetonitrile:water = 3:7 (v:v), 20 mL), and sonicated to obtain an acetonitrile-water solution of 2,4,6-tris(4-aminophenyl)-1,3,5-triazine.

[0085] The dichloromethane solution of the trialdehyde phloroglucinol was slowly added dropwise along the container wall to the acetonitrile-aqueous solution of 2,4,6-tris(4-aminophenyl)-1,3,5-triazine (dropping rate: 1-2 mL / min). The mixture separated into layers and was allowed to stand at room temperature for 36 h to carry out interfacial polymerization. A thin layer was observed to form at the interface between water and dichloromethane. The top aqueous phase was then removed with a dropper, and the thin layer was washed sequentially with dichloromethane, tetrahydrofuran, and acetone. The thin layer was then collected through an ethanol-wetted nylon membrane (pore size: 0.1 μm). Finally, the thin layer was dried in a vacuum drying oven at 60 °C to remove residual solvent, yielding an imine COF membrane.

[0086] The imine COF membrane was immersed in N,N-dimethylformamide solution (10 mL), and KHSO5 (0.13 g, 0.86 mmol) and acetic acid (2 mL) were added. The membrane was allowed to stand at room temperature for 48 h. After washing the thin film with dichloromethane, tetrahydrofuran, and acetone, respectively, the thin film was collected through an ethanol-wetted nylon membrane (pore size: 0.1 μm). Finally, the thin film was dried in a vacuum drying oven at 60 °C to remove residual solvent, yielding a polyamide COF membrane. The polyamide COF membrane was then immersed in a polyvinyl alcohol solution to obtain an immersed polyamide COF membrane.

[0087] The imine COF membrane was immersed in a methanol solution (25 mL) containing terephthalic acid (28.5 mg, 0.17 mmol). The mixture was then immersed at -15°C for 5 min, followed by the addition of NaBH4 (0.25 g, 6.5 mmol) in portions over 10 min. The mixture was then immersed at -15°C for 1 h and then at room temperature for another 10 h. The thin film was washed with dichloromethane, tetrahydrofuran, and acetone, respectively, and collected through an ethanol-wetted nylon membrane (pore size: 0.1 μm). Finally, the thin film was dried in a vacuum drying oven at 60°C to remove residual solvent, yielding a polyamine COF membrane. The polyamine COF membrane was then immersed in a polyvinyl alcohol solution to obtain an impregnated polyamine COF membrane.

[0088] The impregnated polyamide COF film is stacked with the impregnated polyamine COF film and dried in a vacuum drying oven at 110°C to obtain the polyamide-PVA-polyamine COF composite film.

[0089] Performance and structural characterization

[0090] Figure 1 Transmission electron microscopy (TEM) images of (a) an imine COF film, (b) a polyamide COF film, and (c) a polyamine COF film prepared by interfacial polymerization in Example 1, and a cross-sectional TEM image of (d) a polyamide-PVA-polyamine COF composite film. The images show that the integrity and periodicity of the exfoliated sheet-like COF remain unchanged. The TEM images reveal large flakes of polycrystalline COF with lattice fringes running throughout the entire structure.

[0091] Figure 2 The image shows the XRD pattern of the imine COF membrane prepared by interfacial polymerization in Example 1. The XRD pattern was analyzed using a Miniflex 600 X-ray diffractometer (Rigaku Corporation, Japan). The XRD pattern demonstrates that the synthesized covalent organic framework membrane exhibits good crystallinity.

[0092] Figure 3 Images of the following membranes prepared by interfacial polymerization in Example 1 are shown: a) imine COF membrane, b) polyamide COF membrane, c) polyamine COF membrane, and d) polyamide-PVA-polyamine COF composite membrane. As can be seen from the images, the prepared imine COF, polyamide COF, polyamine COF, and polyamide-PVA-polyamine COF composite membranes are ultra-thin, have a large area, and a smooth surface.

[0093] Figure 4 The Fourier transform infrared (FT-IR) spectra of the TAPT monomer, TP monomer, imine COF film, polyamide COF film, and polyamine COF film of Example 1 are shown in the figure. As can be seen from the figure, for the monomer TAPT, at 1640 cm⁻¹... -1 The C=N peak at 3300-3500 cm⁻¹ and the peak at 3300-3500 cm⁻¹ -1 The NH peak disappears at 2900 cm⁻¹; for monomeric TP, the peak disappears at 2900 cm⁻¹. -1 The O=CH peak at 1635 cm⁻¹ -1 The disappearance of the C=O peak at 1505 cm⁻¹; for imine COF membranes at 1505 cm⁻¹ -1 C = C and 1280cm at the location -1 The appearance of the NH peak at 3425 cm⁻¹ confirms the presence of imine bonds and the synthesis of the imine COF membrane; the FT-IR spectra of the polyamide COF membrane and the polyamine COF membrane show a peak at 3425 cm⁻¹. -1 The appearance of the OH stretching vibration peak at 1662 cm⁻¹ -1 A new C=O vibrational peak appeared at 1635 cm⁻¹, further confirming the synthesis of the polyamide COF film; -1 The disappearance of the C=O vibration peak at the point proves the synthesis of the polyamine COF film.

[0094] Although the above embodiments have provided a detailed description of the present invention, they are only some embodiments of the present invention, and not all embodiments. People can obtain other embodiments based on these embodiments without creative effort, and these embodiments all fall within the protection scope of the present invention.

Claims

1. A polyamide-PVA-polyamine COF composite film, comprising a polyamide COF film and a polyamine COF film, the polyamide COF film being bonded to the polyamine COF film by PVA; the polyamide COF film being formed by a polymer having a structure shown in Formula I, and the polyamine COF film being formed by a polymer having a structure shown in Formula II: Formula I Formula II; the film layer thickness of the polyamide COF film and the polyamine COF film being independently 100-400 nm.

2. The polyamide-PVA-polyamine COF composite film according to claim 1, characterized in that, 3.A method for preparing the polyamide-PVA-polyamine COF composite film according to any one of claims 1-2, comprising the following steps: adding a triformylphloroglucinol solution into an acetonitrile-water solution of 2,4,6-tris(4-aminophenyl)-1,3,5-triazine to perform an interfacial polymerization reaction to obtain an imine COF film; the triformylphloroglucinol solution being obtained by dissolving triformylphloroglucinol in dichloromethane or trichloromethane; mixing the imine COF film, a first organic solvent, a first catalyst and an oxidizing agent to perform an oxidation reaction to obtain a polyamide COF film, and immersing the polyamide COF film in a polyvinyl alcohol solution to obtain an immersed polyamide COF film; mixing the imine COF film, a second organic solvent, a second catalyst and a reducing agent to perform a reduction reaction to obtain a polyamine COF film, and immersing the polyamine COF film in a polyvinyl alcohol solution to obtain an immersed polyamine COF film; and stacking the immersed polyamide COF film and the immersed polyamine COF film, and drying to obtain the polyamide-PVA-polyamine COF composite film. The molar ratio of the triformylphloroglucinol to 2,4,6-tris(4-aminophenyl)-1,3,5-triazine is 1:1, and the interfacial polymerization reaction is performed for 48-72 h. The first organic solvent comprises N,N-dimethylformamide; the first catalyst comprises acetic acid; and the oxidizing agent comprises KHSO5. When preparing the polyamide COF film, the molar amount of the imine COF film is based on the molar amount of the triformylphloroglucinol used when preparing the imine COF film, the molar amount of the imine COF film to the volume of the first catalyst is 0.05 mmol:2 mL, and the molar amount ratio of the imine COF film to the oxidizing agent is 0.05:0.

86. The oxidation reaction is performed for 36-48 h. The second organic solvent comprises methanol; the second catalyst comprises terephthalic acid; and the reducing agent comprises NaBH4.

4. The production method according to claim 3, characterized by, When preparing the polyamine COF film, the molar amount of the imine COF film is based on the molar amount of the triformylphloroglucinol used when preparing the imine COF film, the molar amount ratio of the imine COF film to the second catalyst is 0.05:0.17, and the molar amount ratio of the imine COF film to the reducing agent is 0.05:6.

5.

5. The preparation method according to claim 3, characterized in that, The reduction reaction is performed for 11-13 h.

6. The production method according to claim 3 or 5, characterized by, ​ 7. The production method according to claim 3 or 5, characterized by, ​ 8. The preparation method according to claim 3, characterized in that, ​ 9. The production method according to claim 3 or 8, characterized by, ​ 10. The production method according to claim 3 or 8, characterized by, ​

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