Method for customizing nano-channels by grafting ether oxygen groups in COFs (covalent organic frameworks) membrane pores

Abstract

The invention belongs to the technical field of gas membrane separation, and discloses a method for customizing nano channels by grafting ether oxygen groups in COFs membrane pores. Phenolic hydroxyl groups of COFs and brominated OE are subjected to a Williamson cross-linking reaction, ether oxygen chains of different lengths and types are introduced to accurately regulate and control the pore size of the COFs membrane, the ether oxygen chains of different lengths occupy the space in pores, a steric effect is formed, large CO2 molecules are prevented from passing through the membrane, and small H2 is allowed to pass through. Meanwhile, the existence of ether bonds greatly enhances the adsorption of CO2, inhibits the diffusion of CO2, realizes the coordinated regulation and control of the steric hindrance effect and dynamic screening in membrane pores, and the introduction of flexible ether oxygen groups does not significantly reduce the permeability of hydrogen under the condition of high-density grafting, thereby realizing the efficient separation of H2 / CO2. The method is simple in preparation process, stable in structure and suitable for most phenolic hydroxyl COFs.

Description

Technical Field

[0001] The present invention belongs to the technical field of gas membrane separation, and relates to a method for customizing nanochannels by grafting ether oxygen groups inside the pores of COFs membranes. Specifically, it designs a method for preparing defect-free COFs membranes by grafting small molecule ether oxygen groups inside the COFs pores, reducing the pore size of COFs, and simultaneously adsorbing CO 2 , thereby improving the H 2 permeability and gas selectivity of the composite membrane. Background Art

[0002] With the development of the times, the excessive consumption of increasing fossil fuels has triggered serious energy crises and environmental pollutions, highlighting the urgency of establishing a clean, low-carbon, safe and efficient energy system. The surging of intermittent renewable energy such as wind energy and solar energy is driving the momentum of the "hydrogen economy". As an energy carrier, hydrogen has always been regarded as the most promising alternative to fossil fuels due to its pollution-free, high calorific value and diverse sources. Currently, there are diverse hydrogen production methods, more than 96% of which are produced from fossil fuels, usually through the steam-methane reforming (SMR) process and then obtained through the water-gas shift (WGS) process. This process produces a gas mixture of carbon dioxide and hydrogen. Therefore, it is very important to purify hydrogen from carbon dioxide. Membrane separation technology is a new and efficient separation technology applied in industrial production. Compared with traditional separation methods, it has advantages such as high efficiency and easy coupling. It requires relatively low operating energy during the separation process and is a very competitive separation method, attracting much attention. Its core is to prepare separation membrane materials with high separation performance.

[0003] A composite membrane is composed of a selective layer that undertakes the separation function and a substrate layer that plays a supporting role. The materials of the selective layer and the support layer can be designed separately to achieve the best effects in terms of selectivity, permeability and mechanical properties. Due to the existence of the support layer, an ultrathin selective layer is more easily achieved, thereby improving the separation performance of the membrane. The performance of a gas separation membrane is usually limited by the trade-off relationship between the permeability (P) and the selectivity (S).

[0004] Covalent organic frameworks (COFs), as a new type of porous crystalline material, are connected by covalent bonds formed by light elements (such as C, H, O, N, B) through thermodynamic control. COFs have a regular periodic structure, a high specific surface area, adjustable pore sizes, high thermal and chemical stability, and are easy to functionalize. Due to the above unique properties of COFs, COF membranes have been used as important separation platforms for gas capture and separation. However, the inherent pore sizes of the vast majority of COFs are greater than 0.5 nm, while the kinetic diameters of most gas molecules are in the range of 0.25 - 0.4 nm. The mismatch between the two pore sizes makes the separation of gas molecules extremely challenging. Therefore, there is an urgent need to increase the channel size of COF membranes to improve selectivity and achieve efficient gas separation. Wang Shaofei et al. from Hunan University invented a hydrogen-bond crosslinked covalent organic framework composite membrane and its preparation method and application (CN202410430964.3). By blending a polyhydroxy polymer with COF nanosheets and filtering them into a membrane, due to the hydrogen bonds between the polyhydroxy polymer and COFs, a composite membrane with a molecular weaving structure is formed, improving selectivity. However, due to the weak interaction between the two, during the membrane preparation process, there will inevitably be a loss of polyhydroxy polymer, thus affecting the separation performance. Jiang Zhongyi et al. from Tianjin University invented a preparation method for functionalized covalent organic framework membranes (CN202411334050.3). By blending an ionic liquid with COF materials and spin-coating them into a composite membrane, the presence of the ionic liquid repairs the defects of the membrane and improves the solubility of carbon dioxide. The excessive introduction of the ionic liquid will cause blockage of the COF pores, increase the mass transfer resistance, and reduce the gas flux.

[0005] Based on the above technical problems, it is of great significance to prepare a new type of membrane using porous materials with customizable pores to improve the membrane performance. The present invention provides a method for preparing a COF membrane by grafting ether oxygen bonds in the pores of COFs to customize nanochannels. Summary of the Invention

[0006] The present invention proposes a method for grafting ether oxygen groups in the pores of COF membranes to customize nanochannels. Utilize the phenolic hydroxyl groups of COFs to undergo Williamson crosslinking reaction with OE bromide to introduce ether oxygen groups with different lengths and types to precisely regulate the pore size of COF membranes, thereby customizing nanochannels. At the same time, the presence of ether bonds 2 achieves strong adsorption and inhibits the diffusion rate of CO 2 , improving selectivity. In addition, the introduction of flexible ether oxygen groups will not significantly reduce the hydrogen permeability under the condition of high-density grafting. Realize the synergistic regulation of the steric hindrance effect and adsorption effect in the pores of the membrane, and achieve the efficient separation of H 2 / CO 2 .

[0007] The technical solution of the present invention:

[0008] A method for customizing nanochannels by grafting ether oxygen groups inside the pores of a COFs membrane, the steps are as follows:

[0009] (1) Prepare ionic DhaTG by the three-phase "oil-water-oil" interfacial polymerization method Cl nanosheets

[0010] First, dissolve the aldehyde monomer in dichloromethane (CH 2 Cl 2 ), ultrasonicate for 30 min, and record it as solution A as the bottom oil phase; add aqueous acetic acid solution (AcOH) above solution A as solution B; subsequently, dissolve the amine monomer in N,N-dimethylformamide (DMF) as solution C, ultrasonicate for 30 min, and add it dropwise onto solution B as the top oil phase; keep it undisturbed at room temperature for 7 days. The aqueous phase becomes a dark yellow transparent solution, and the middle phase is collected with a dropper after removing the top organic phase. The obtained DhaTG Cl nanosheets are loaded into a dialysis bag and dialyzed in deionized water for 3 days to remove residual aldehyde and amine monomers and any small fragments, obtaining a yellow transparent solution;

[0011] Furthermore, in the step (1), the aldehyde monomer is 2,5-dihydroxyterephthalaldehyde or / and 2-hydroxyterephthalaldehyde or / and 2,3-dihydroxyterephthalaldehyde;

[0012] Furthermore, in the step (1), the amine monomer is triaminoguanidine hydrochloride;

[0013] Furthermore, in the step (1), the molar ratio of 2,5-dihydroxyterephthalaldehyde to triaminoguanidine hydrochloride is 3:2.

[0014] Furthermore, in the step (1), a dialysis bag with a molecular weight cut-off (MWCO) of 30000 is used for dialysis.

[0015] (2) Prepare ionic OE n -DhaTG Cl nanosheets

[0016] OE n -DhaTG Cl nanosheets are synthesized by grafting OE bromide with different chain lengths onto the pore walls of DhaTG Cl nanosheets, where n represents the number of ethylene oxide repeating units; specifically, the DMF dispersion of OE n -DhaTG Cl nanosheets is first prepared by the solvent exchange method. Add an aprotic solvent (THF) to DhaTG ClA water dispersion of nanosheets was obtained to achieve the corresponding deposition; after centrifugation, the supernatant was removed; subsequently, the wet deposit was redissolved in DMF to effect solvent exchange. Then OE bromide and K 2 CO 3 were added to the DMF dispersion of DhaTG Cl nanosheets, and the mixture was heated at 80 °C for 6 - 12 h. After cooling to room temperature, the DMF dispersion was loaded into a dialysis bag and dialyzed in deionized water for 3 days to obtain a water dispersion of OE n -DhaTG Cl again.

[0017] Furthermore, in the step (2), the OE bromides with different chain lengths are respectively: 2-bromoethyl methyl ether, 1-bromo-2-(2-methoxyethoxy)ethane, diethylene glycol-2-bromoethyl methyl ether, and triethylene glycol 2-bromoethyl methyl ether

[0018] Furthermore, in the step (2), the molar ratios of the OE bromides with different chain lengths to the aldehyde monomer are 4:1, 3:1, and 2:1.

[0019] Furthermore, in the step (2), the molar ratio of K 2 CO 3 to the aldehyde monomer is 4.2:1.

[0020] (3) Preparation of OE n -DhaTG Cl membrane

[0021] A COFs membrane was prepared by a vacuum-assisted self-assembly method. The specific steps were as follows: the dispersion obtained in step (2) was diluted to a dispersion of 0.02 mg / mL, and a certain amount of OE n -DhaTG Cl nanosheets were vacuum-filtered onto a polyacrylonitrile (PAN) membrane and then dried at 60 °C for 1 h. A composite membrane with a thickness of 380 - 420 nm was obtained.

[0022] Advantages of the present invention: The method of the present invention utilizes the Williamson cross-linking reaction between the phenolic hydroxyl group of COFs and OE bromide to precisely regulate the pore size of the COFs membrane by introducing ether oxygen chains of different lengths and types. The ether oxygen chains of different lengths occupy the space inside the pores, forming a hindrance effect to prevent larger CO 2 molecules from passing through the membrane and allowing smaller H 2 to pass through. At the same time, the presence of ether bonds greatly enhances the adsorption of CO 2 and inhibits the diffusion of CO 2 , realizing the synergistic regulation of the spatial hindrance effect and adsorption effect inside the membrane. The introduction of flexible ether oxygen groups does not significantly reduce the hydrogen permeability under the condition of high-density grafting, achieving H2 / CO 2 Efficient separation. The preparation process of this method is simple and the structure is stable, which is applicable to most phenolic hydroxyl COFs. Description of the Drawings

[0023] Figure 1 It is the pore size distribution diagram of COFs grafted with ether oxygen chains of different lengths.

[0024] Figure 2 is OE 4 -DhaTG Cl Scanning electron micrograph of OE-DhaTG nanosheets.

[0025] Figure 3 is OE 4 -DhaTG Cl Scanning electron micrograph of the cross-section of the OE-DhaTG membrane.

[0026] Figure 4 is the H / CO gas separation performance diagram of COFs grafted with ether oxygen chains of different lengths. 2 / CO 2 Gas separation performance diagram. Detailed Embodiments

[0027] The following further illustrates the detailed embodiments of the present invention in combination with the drawings and technical solutions.

[0028] Example 1:

[0029] A method for grafting ether oxygen groups in the pores of a COFs membrane to customize nanochannels, the specific process includes the following steps:

[0030] Step 1: First, dissolve 24.9 mg of 2,5-dihydroxyterephthalaldehyde in 50 mL of dichloromethane, sonicate for 30 min, and use it as solution A and place it in a glass beaker as the bottom oil phase. Add 30 mL of 3 M / L acetic acid aqueous solution above solution A as solution B. Subsequently, dissolve 14 mg of triaminoguanidine hydrochloride in 50 mL of N,N-dimethylformamide as solution C, sonicate for 30 min, and dropwise add it onto the acetic acid aqueous solution B as the top oil phase. The three-phase system is kept undisturbed at room temperature for 7 days. The aqueous phase becomes a dark yellow transparent solution, which is collected with a dropper after removing the top organic phase. Using a dialysis bag with a molecular weight cut-off (MWCO) of 30000, the obtained DhaTG Cl nanosheets are dialyzed in deionized water for 3 days to remove residual aldehyde and amine monomers and any small fragments, obtaining a yellow transparent solution.

[0031] Step 2: OE n -DhaTG Cl Nanosheets are obtained by grafting OE bromides with different chain lengths onto DhaTG Clsynthesized on the pore walls of the nanosheets, where n represents the number of ethylene oxide repeating units. OE n -DhaTG Cl The DMF dispersion of the nanosheets was first prepared by a solvent exchange method. 10 mL of the aprotic solvent THF was added to 20 mL of the DhaTG Cl aqueous dispersion of the nanosheets to obtain the corresponding deposition. After centrifugation, the supernatant was removed. Subsequently, the wet deposit was redissolved in 20 mL of DMF to effect solvent exchange. Then 0.049 g of 2-bromoethyl methyl ether and 0.087 g of K 2 CO 3 were added to the DMF dispersion of the DhaTG Cl nanosheets, and the mixture was heated at 80 °C for 6 - 12 hours. After cooling to room temperature, an aqueous dispersion of OE 1 -DhaTG Cl was obtained again by solvent exchange using a dialysis membrane with a molecular weight cut-off (MWCO) of 30,000, and further purified by dialysis for 3 days.

[0032] Step 3: Prepare the COFs membrane using a vacuum-assisted self-assembly method. The specific steps are as follows: Take 1 mL of the dispersion obtained in Step 2 and dilute it to a dispersion of 0.02 mg / mL. A certain amount of OE n -DhaTG Cl nanosheets were vacuum-assisted filtered onto a PAN membrane at a pressure of 1 Bar, and then dried at 60 °C for 1 h. A composite membrane (membrane 1) with a thickness of about 380 - 420 nm was obtained.

[0033] Example 2:

[0034] A method for customizing nanochannels by grafting ether oxygen groups inside the pores of a COFs membrane, the specific process comprising the following steps:

[0035] Step 1: First, dissolve 24.9 mg of 2,5-dihydroxyterephthalaldehyde in 50 mL of dichloromethane, sonicate for 30 min, and use it as solution A and place it in a glass beaker as the bottom oil phase. Add 30 mL of 3 M / L aqueous acetic acid solution above solution A as solution B. Subsequently, dissolve 14 mg of triaminoguanidine hydrochloride in 50 mL of N,N-dimethylformamide as solution C, sonicate for 30 min, and add it dropwise onto the aqueous acetic acid solution B as the top oil phase. The three-phase system was left undisturbed at room temperature for 7 days. The aqueous phase became a dark yellow transparent solution, which was collected with a dropper after removing the top organic phase. Using a dialysis membrane with a molecular weight cut-off (MWCO) of 30,000, the obtained DhaTG Cl nanosheets were dialyzed in deionized water for 3 days to remove residual aldehyde and amine monomers and any small fragments, obtaining a yellow transparent solution.

[0036] Step 2, OE n -DhaTG Cl The nanosheets were synthesized by grafting OE with different chain lengths onto the pore walls of DhaTG Cl nanosheets, where n represents the number of ethylene oxide repeating units. DhaTG Cl The DMF dispersion of DhaTG nanosheets was first prepared by the solvent exchange method. 10 mL of aprotic solvent THF was added to 20 mL of the aqueous dispersion of DhaTG Cl nanosheets to obtain the corresponding deposition. After centrifugation, the supernatant was removed. Subsequently, the wet deposit was redissolved in 20 mL of DMF to achieve solvent exchange. Then 0.0647 g of 1-bromo-2-(2-methoxyethoxy)ethane and 0.087 g of K 2 CO 3 were added to the DMF dispersion of DhaTG Cl nanosheets, and the mixture was heated at 80 °C for 6 - 12 h. After cooling to room temperature, a dialysis bag with a molecular weight cut-off (MWCO) of 30,000 was used to obtain the aqueous dispersion of OE 2 -DhaTG Cl again by solvent exchange and further purified by dialysis for 3 days.

[0037] Step 3, Preparation of COFs membrane by vacuum-assisted self-assembly method. The specific steps are as follows: 1 mL of the dispersion obtained in Step 2 was diluted to a dispersion of 0.02 mg / mL, and a certain amount of OE n -DhaTG Cl nanosheets were vacuum-assisted filtered onto the PAN membrane at a pressure of 1 Bar and then dried at 60 °C for 1 h. A composite membrane (membrane 2) with a thickness of about 380 - 420 nm was obtained.

[0038] Example 3:

[0039] A method for customizing nanochannels by grafting ether oxygen groups inside the pores of a COFs membrane, and the specific process includes the following steps:

[0040] Step 1: First, dissolve 24.9 mg of 2,5-dihydroxyterephthalaldehyde in 50 mL of dichloromethane, and ultrasonicate for 30 min to obtain Solution A, which is placed in a glass beaker as the bottom oil phase. Add 30 mL of 3 M / L acetic acid aqueous solution above Solution A as Solution B. Subsequently, dissolve 14 mg of triaminoguanidine hydrochloride in 50 mL of N,N-dimethylformamide as Solution C, ultrasonicate for 30 min, and add it dropwise onto the acetic acid aqueous solution B as the top oil phase. The three-phase system is kept undisturbed at room temperature for 7 days. The aqueous phase turns into a dark yellow transparent solution, which is collected with a dropper after removing the top organic phase. Using a dialysis bag with a molecular weight cut-off (MWCO) of 30,000, the obtained DhaTG Cl nanosheets are dialyzed in deionized water for 3 days to remove residual aldehyde and amine monomers and any small fragments, obtaining a yellow transparent solution.

[0041] Step 2: OE n -DhaTG Cl nanosheets are synthesized by grafting OE bromides with different chain lengths onto the pore walls of DhaTG Cl nanosheets, where n represents the number of ethylene oxide repeating units. The DMF dispersion of DhaTG Cl nanosheets is first prepared by the solvent exchange method. Add 10 mL of aprotic solvent THF to 20 mL of the aqueous dispersion of DhaTG Cl nanosheets to obtain the corresponding deposition. After centrifugation, remove the supernatant. Subsequently, redissolve the wet deposit with 20 mL of DMF to achieve solvent exchange. Then add 0.0857 g of diethylene glycol-2-bromoethyl methyl ether and 0.087 g of K 2 CO 3 to the DMF dispersion of DhaTG Cl nanosheets, and heat the mixture at 80 °C for 6 - 12 h. After cooling to room temperature, using a dialysis bag with a molecular weight cut-off (MWCO) of 30,000, an aqueous dispersion of OE 3 -DhaTG Cl is obtained again through solvent exchange and further purified by dialysis for 3 days.

[0042] Step 3: Prepare the COFs membrane by the vacuum-assisted self-assembly method. The specific steps are as follows: Take 1 mL of the dispersion obtained in Step 2 and dilute it to a dispersion of 0.02 mg / mL. Filter a certain amount of OE n -DhaTG Cl nanosheets onto the PAN membrane under a pressure of 1 Bar by vacuum-assisted filtration, and then dry at 60 °C for 1 h. A composite membrane (Membrane 3) with a thickness of about 380 - 420 nm is obtained.

[0043] Example 4:

[0044] A method for customizing nanochannels by grafting ether oxygen groups inside the pores of a COFs membrane, and the specific process includes the following steps:

[0045] Step 1: First, dissolve 24.9 mg of 2,5-dihydroxyterephthalaldehyde in 50 mL of dichloromethane, and ultrasonicate for 30 min to obtain solution A, which is placed in a glass beaker as the bottom oil phase. Add 30 mL of 3 M / L acetic acid aqueous solution above solution A as solution B. Subsequently, dissolve 14 mg of triaminoguanidine hydrochloride in 50 mL of N,N-dimethylformamide as solution C, ultrasonicate for 30 min, and add it dropwise onto the acetic acid aqueous solution B as the top oil phase. The three-phase system is kept undisturbed at room temperature for 7 days. The aqueous phase turns into a dark yellow transparent solution, which is collected with a dropper after removing the top organic phase. Using a dialysis bag with a molecular weight cut-off (MWCO) of 30000, the obtained DhaTG Cl nanosheets are dialyzed in deionized water for 3 days to remove residual aldehyde and amine monomers and any small fragments, obtaining a yellow transparent solution.

[0046] Step 2: OE n -DhaTG Cl nanosheets are synthesized by grafting OE with different chain lengths onto the pore walls of DhaTG Cl nanosheets, where n represents the number of ethylene oxide repeating units. The DMF dispersion of DhaTG Cl nanosheets is first prepared by the solvent exchange method. Add 10 mL of aprotic solvent THF to 20 mL of the aqueous dispersion of DhaTG Cl nanosheets to obtain the corresponding deposition. After centrifugation, remove the supernatant. Subsequently, redissolve the wet deposit with 20 mL of DMF to achieve solvent exchange. Then add 0.1023 g of triethylene glycol 2-bromoethyl methyl ether and 0.087 g of K 2 CO 3 to the DMF dispersion of DhaTG Cl nanosheets, and heat the mixture at 80 °C for 6 - 12 hours. After cooling to room temperature, using a dialysis bag with a molecular weight cut-off (MWCO) of 30000, the aqueous dispersion of OE 4 -DhaTG Cl is obtained again through solvent exchange and further purified by dialysis for 3 days.

[0047] Step 3: Prepare the COFs membrane using the vacuum-assisted self-assembly method. The specific steps are as follows: Take 1 mL of the dispersion obtained in Step 2 and dilute it to a dispersion of 0.02 mg / mL. Take a certain amount of OE n -DhaTG ClThe nanosheets were filtered onto the PAN membrane under a pressure of 1 Bar by vacuum-assisted filtration and then dried at 60 °C for 1 h. A composite membrane (membrane 4) with a thickness of about 380 - 420 nm was obtained.

[0048] Comparative Example 1:

[0049] A method for customizing nanochannels by grafting ether oxygen groups inside the pores of a COFs membrane, the specific process comprising the following steps:

[0050] Step 1: First, dissolve 24.9 mg of 2,5-dihydroxyterephthalaldehyde in 50 mL of dichloromethane, sonicate for 30 min, and use it as solution A and place it in a glass beaker as the bottom oil phase. Add 30 mL of 3 M / L aqueous acetic acid solution on top of the aldehyde solution as solution B. Subsequently, dissolve 14 mg of triaminoguanidine hydrochloride in 50 mL of N,N-dimethylformamide as solution C, sonicate for 30 min, and add it dropwise onto the aqueous acetic acid solution B as the top phase. The three-phase system was left undisturbed at room temperature for 7 days. The aqueous phase turned into a dark yellow transparent solution, which was collected with a dropper after removing the top organic phase. Using a dialysis bag with a molecular weight cut-off (MWCO) of 30000, the obtained DhaTG Cl The nanosheets were dialyzed in deionized water for 3 days to remove residual aldehyde and amine monomers and any small fragments, obtaining a yellow transparent solution.

[0051] Step 2: Prepare the COFs membrane using the vacuum-assisted self-assembly method. The specific steps are as follows: Take 1 mL of the dispersion obtained in Step 1 and dilute it to a dispersion of 0.02 mg / mL. Add a certain amount of DhaTG Cl The nanosheets were filtered onto the PAN membrane under a pressure of 1 Bar by vacuum-assisted filtration and then dried at 60 °C for 1 h. A composite membrane (membrane 5) with a thickness of about 400 nm was obtained.

[0052] By comparing the examples and the comparative examples, it can be seen that the method of the present invention for preparing a COFs membrane by customizing nanochannels by grafting ether oxygen bonds inside the COFs pores significantly improves the separation performance. The pore sizes of the nanosheets before and after grafting were characterized. It can be Figure 1 seen that the introduction of the ether oxygen chain reduced the pore size of the nanosheets from 1.51 nm to 0.56 nm. Ether oxygen chains of different lengths occupied the space inside the pores, forming a steric effect that prevented larger CO 2 molecules from passing through the membrane. At the same time, the presence of the ether bond greatly enhanced the adsorption of CO 2 and inhibited the diffusion of CO 2 , achieving the synergistic regulation of the spatial hindrance effect and the adsorption effect inside the membrane, and realizing the efficient separation of H 2 / CO 2 . It can be seen from the scanning electron microscope images that in the OE prepared in Example 44 -DhaTG Cl The nanosheet morphology is uniform, which helps to construct a dense and defect-free COFs membrane. In addition, the COFs membrane modified with ether oxygen chains can repair the stacking defects of the internal structure of the membrane to a certain extent, so there are no problems such as stacking bulges on the cross-section of the membrane. Through Figure 4 the gas separation performance diagram, it can be seen that compared with the DhaTG Cl composite membrane prepared in Comparative Example 1, the OE 4 -DhaTG Cl composite membrane prepared in Example 4 has better H 2 / CO 2 separation performance, and the H 2 / CO 2 selectivity is much higher than that of the DhaTG Cl composite membrane prepared in Comparative Example 1, which also proves that the introduction of flexible ether oxygen groups will not significantly reduce the hydrogen permeability under the condition of high-density grafting.

Claims

1. A method for customizing nanochannels by grafting ether oxygen groups in COFs membrane pores, characterized in that: Here are the steps: (1) Preparation of ionic DhaTG by three-phase "oil-water-oil" interfacial polymerization Cl Aqueous dispersion of nanosheets (2) Preparation of ionic OE n -DhaTG Cl Nanosheets Grafting of brominated OE with different chain lengths onto DhaTG Cl Synthesis of OE on the pore walls of nanosheets n -DhaTG Cl Nanosheets, wherein n represents the number of ethylene oxide repeating units; specifically as follows: to DhaTG Cl THF was added to the aqueous dispersion of nanosheets, and after centrifugation, the supernatant was removed to obtain a wet precipitate; then, the wet precipitate was redissolved with DMF to achieve solvent exchange to obtain DhaTG Cl DMF dispersion of nanosheets; then OE bromide and K2CO3 were added to DhaTG Cl The nanosheets were dispersed in DMF and heated at 80 °C for 6-12 h. After cooling to room temperature, the dispersion was placed in a dialysis bag and dialyzed in deionized water for 3 days to obtain ionic OE again. n -DhaTG Cl Aqueous dispersion of nanosheets; (3) Preparation of OE n -DhaTG Cl membrane COFs films were prepared using vacuum-assisted self-assembly method.

2. The method according to claim 1, characterized in that The specific steps of step (1) are as follows: First, the aldehyde monomer was dissolved in dichloromethane and ultrasonicated for 30 minutes, which was recorded as solution A as the bottom oil phase; acetic acid aqueous solution was added to solution A as solution B; then, the amine monomer was dissolved in N, N-dimethylformamide as solution C, ultrasonicated for 30 minutes, and added dropwise to solution B as the top oil phase; it was kept undisturbed at room temperature for 7 days; the aqueous phase turned into a dark yellow transparent solution, and the middle phase was collected with a dropper after removing the top organic phase; the obtained DhaTG Cl The nanosheets were placed in a dialysis bag and dialyzed in deionized water for 3 days to remove the residual aldehyde monomers, amine monomers and any small fragments, and a yellow transparent solution was obtained, which was ionic DhaTG. Cl Aqueous dispersion of nanosheets.

3. The method according to claim 2, characterized in that In step (1), The aldehyde monomer is 2,5-dihydroxyterephthalaldehyde or / and 2-hydroxyterephthalaldehyde or / and 2,3-dihydroxyterephthalaldehyde; The amine monomer is triaminoguanidine chloride hydrochloride; The molar ratio of the aldehyde monomer to the amine monomer is 3:

2.

4. The method according to claim 2, characterized in that: In step (1), a dialysis bag with a molecular weight cut-off of 30,000 is used for dialysis.

5. The method according to claim 1, characterized in that In step (2), the brominated OEs with different chain lengths are: 2-bromoethyl methyl ether, 1-bromo-2-(2-methoxyethoxy)ethane, diethylene glycol-2-bromoethyl methyl ether, and triethylene glycol-2-bromoethyl methyl ether.

6. The method according to claim 1, characterized in that In step (2), the molar ratio of brominated OE with different chain lengths to aldehyde monomer is 4:1-2:

1.

7. The method according to claim 1, characterized in that In step (2), the molar ratio of K2CO3 to aldehyde monomer is 4.2:

1.

8. The method according to claim 1, characterized in that The specific steps of step (3) are as follows: The ion OE obtained in step (2) n -DhaTG Cl The aqueous dispersion of nanosheets was diluted to 0.02 mg / mL dispersion, filtered onto a polyacrylonitrile membrane by vacuum filtration, and then dried at 60 °C for 1 h.

9. The method according to claim 8, characterized in that The thickness of the polyacrylonitrile membrane is a composite membrane of 380-420 nm.

10. The method according to claim 8, characterized in that The substrate for vacuum filtration is polyacrylonitrile, polypropylene or polyethersulfone.

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