Method for preparing ionic covalent organic framework nanosheet and self-supporting proton exchange membrane of ionic covalent organic framework nanosheet through microemulsion interfacial polymerization

Abstract

The invention provides a method for preparing an ionic covalent organic framework (iCOF) nanosheet and a self-supporting proton exchange membrane thereof through microemulsion interfacial polymerization, and solves the problems that the macroscopic interfacial polymerization reaction efficiency is low, and thin ionic nanosheets are difficult to prepare through existing microemulsion interfacial polymerization. Liquid long-chain fatty acid with weak anionic surface activity is selected to dissolve an aldehyde monomer, and the aldehyde monomer is dispersed in a water phase to form oil-in-water (O / W) microemulsion droplets which are used as a polymerization reaction interface with a high specific surface area, so that the generation rate of iCOF is remarkably increased. The iCOF grown on the interface of the micro-emulsion droplet has high curvature and is stripped to a water phase to form a thin iCOF nanosheet with high aspect ratio. In the layer-by-layer stacking membrane preparation process, the thin nanosheets are more beneficial to pi-pi close packing between sheet layers and continuous reaction and assembly of active end groups, the strength and toughness of the iCOF self-supporting membrane are improved, the ultra-thin iCOF self-supporting proton exchange membrane is prepared, the structural advantages of an iCOF material intrinsic highly-ordered frame conduction channel are played to the maximum extent, and the application prospect is broad. And the material has high proton conductivity and excellent fuel cell performance. The method for preparing the iCOF nanosheet through microemulsion interfacial polymerization provides a promising platform technology for innovative application of the iCOF in energy materials and devices.

Description

Technical Field

[0001] This invention belongs to the field of energy materials, specifically relating to a method for preparing ionic covalent organic framework nanosheets and their self-supporting proton exchange membranes by microemulsion interfacial polymerization. Background Technology

[0002] Covalent organic frameworks (COFs) are a class of crystalline porous polymer materials based on covalent bonds, forming a crystalline network framework structure by organic building blocks connected by covalent bonds. They have attracted widespread attention due to their high porosity, regular and ordered pore structure, and easily tunable pore size. In particular, ionic covalent organic frameworks (iCOFs) with abundant ionic groups can construct continuous, low-resistance proton conduction channels through hydrogen bonding interactions between dense sulfonic acid groups and hydrated protons within ordered framework nanochannels. Simultaneously, the rigid crystalline framework structure of iCOFs results in extremely low water swelling. Therefore, iCOF self-supporting proton exchange membranes exhibit significantly higher proton conductivity and lower swelling ratios than polymer-based proton exchange membranes.

[0003] Currently, iCOF self-supporting proton exchange membranes are mainly prepared through methods such as monomer casting in-situ growth and physical stacking of iCOF nanosheets. For example, in the literature Angew. Chem. Int. Ed. Engl., 2023, 62(4): e202209306, iCOF self-supporting membranes are prepared by monomer casting in-situ growth, but the iCOF polymerization and crystallization process is coupled with the solvent evaporation film formation process, making it difficult to control independently. The iCOF nanosheet physical stacking method usually involves stacking iCOF nanosheets layer by layer to form a film using vacuum assistance or other methods. The key is to synthesize highly crystalline, ultrathin, and uniformly shaped nanosheets. In the literature Adv. Mater., 2020, 32(52): 2005565, a macroscopic oil-level interfacial polymerization system was established in a beaker to prepare an iCOF nanosheet dispersion. However, the macroscopic interfacial polymerization reaction area is small, which reduces the reaction efficiency. References such as J. Am. Chem. Soc., 2023145 (40): 21974-21982 and Angew. Chem. Int. Ed., 2025, 64(4): e202416980 utilize cationic surfactants to form stable oil-in-water emulsions, whose high specific surface area greatly expands the reaction interface and increases the reaction rate. However, the COF morphologies prepared by microemulsion interfacial polymerization reported in the literature are nanospheres, rods, bowls, hollow capsules, etc. There are no microemulsion systems designed for the morphology of ionic iCOF nanosheets, which makes it difficult to meet the application requirements of self-supporting iCOF proton exchange membranes. Summary of the Invention

[0004] This invention proposes a method for preparing ionic covalent organic framework nanosheets and their self-supporting proton exchange membranes via microemulsion interfacial polymerization. The microemulsion interfacial polymerization involves dissolving an aldehyde monomer in a liquid long-chain fatty acid with weak anionic surfactant activity to form an aldehyde monomer solution, which is then ultrasonically dispersed in water to form an oil-in-water microemulsion for micro-interfacial reaction. Water is the continuous phase, and the oil phase (oil phase) of the weak anionic surfactant solution of the aldehyde monomer is the dispersed phase. The microemulsion droplet size ranges from 150 to 2000 nm. Then, an aqueous solution of an ionic amine monomer is slowly added dropwise to the microemulsion, polymerizing on the surface of the microemulsion droplets to form iCOF. Ionic covalent organic framework nanosheets are obtained in the aqueous phase, and the iCOF dispersion is obtained after dialysis and washing. The iCOF self-supporting proton exchange membrane is then prepared by vacuum-assisted filtration and layer-by-layer stacking.

[0005] The technical solution of the present invention is as follows:

[0006] A method for preparing ionic covalent organic framework nanosheets via microemulsion interfacial polymerization involves dissolving aldehyde monomers in a liquid long-chain fatty acid with weak anionic surface activity and dispersing it in an aqueous phase to form an oil-in-water microemulsion. Then, an aqueous solution of an ionic amine monomer is slowly added dropwise to the microemulsion at room temperature, where it polymerizes on the surface of the microemulsion droplets to form an ionic covalent organic framework. The framework is then exfoliated into the aqueous phase to obtain a dispersion of ionic covalent organic framework nanosheets, thus yielding the ionic covalent organic framework nanosheets.

[0007] The aldehyde monomer is a multifunctional aldehyde monomer, specifically one or a mixture of two or more of the following: trialdehyde phloroglucinol, 1,3-dihydroxy-2,4,6-trialdehyde benzene, and pyromellitic methylaldehyde; the concentration of the aldehyde monomer in liquid long-chain fatty acids is 2 to 5 mmol / L.

[0008] The liquid long-chain fatty acid with weak anionic surface activity is octanoic acid;

[0009] The ionic amine monomer is a polyfunctional amine monomer, specifically one or a mixture of two or more of 2,5-diaminobenzenesulfonic acid, 4,4'-diamino-3,3'-biphenyldisulfonic acid, and 2,5-diamino-1,4-benzenedisulfonic acid, and the concentration of the aqueous solution of the ionic amine monomer is 2 to 5 mmol / L.

[0010] The microemulsion was added at a rate of 0.5 to 1.5 mL / min. After addition, the molar ratio of aldehyde monomer to ionic amine monomer was 2:3. The reaction was carried out at room temperature for 3 to 8 days, and the microemulsion droplet size ranged from 150 to 2000 nm.

[0011] The aforementioned ionic covalent organic framework nanosheets refer to covalent organic framework materials with sulfonic acid groups. The nanosheets have a size of 1 to 5 μm, a thickness of 1.3 to 20 nm, and a high aspect ratio.

[0012] A method for preparing a self-supporting proton exchange membrane of ionic covalent organic framework nanosheets via microemulsion interfacial polymerization involves dialysis and washing the ionic covalent organic framework nanosheets to obtain a dispersion. The dispersion is then prepared by vacuum-assisted filtration and layer-by-layer stacking to form the self-supporting proton exchange membrane of the ionic covalent organic framework nanosheets.

[0013] The concentration of the ionic covalent organic framework nanosheet dispersion is 1.5 ~ 2 mg / mL.

[0014] The aforementioned dialysis washing refers to transferring the ionic covalent organic framework nanosheet dispersion into a dialysis bag and washing it in deionized water to remove small molecule impurities.

[0015] The self-supporting proton exchange membrane of the ion-forming covalent organic framework nanosheets has a thickness of 3 ~ 13 μm and a filtration vacuum degree of -0.08 ~ -0.1 MPa.

[0016] The beneficial effects of this invention are:

[0017] Compared to macroscopic planar interface polymerization, microemulsions possess a high specific surface area, significantly increasing the interfacial polymerization reaction area and improving the reaction rate. Simultaneously, the high curvature of the microemulsion interface promotes the exfoliation of iCOF into the aqueous phase, forming thin nanosheets with high aspect ratios. This facilitates closer π-π packing between the sheets and continued reaction and assembly of active end groups, enhancing the strength and toughness of the iCOF self-supporting membrane. Ultrathin iCOF self-supporting proton exchange membranes can be prepared, maximizing the intrinsic structural advantages of iCOF materials. These membranes exhibit high toughness, high proton conductivity, and excellent fuel cell performance, with a conductivity of 150–350 mS / cm. -1 The preparation process of this invention is simple and facilitates the large-scale preparation of ionic covalent organic framework nanosheets and their ultrathin self-supporting proton exchange membranes, providing a promising platform technology for the innovative application of iCOF in energy materials and devices. Attached Figure Description

[0018] Figure 1 The images show the morphology of the ionic iCOF nanosheets and their self-supporting films in Example 1 of this invention; where (a) is a scanning electron microscope (SEM) image, (b) is an atomic force microscope (AFM) image, and (c) is a three-dimensional image of the iCOF nanosheets.

[0019] Figure 2 The image shows the morphology of the iCOF self-supporting membrane in Embodiment 1 of the present invention; wherein, (a) is a SEM image of the surface of the iCOF self-supporting membrane, (b) is a SEM image of the cross section of the iCOF self-supporting membrane, and (c) is a folded morphology image of the iCOF self-supporting membrane.

[0020] Figure 3 The proton conductivity is the iCOF self-supporting membrane in Embodiment 1 of the present invention.

[0021] Figure 4 The hydrogen-oxygen fuel cell performance of the iCOF self-supporting membrane in Embodiment 1 of the present invention is shown. Detailed Implementation

[0022] The specific implementation method of the present invention will be further described below with reference to the accompanying drawings and technical solutions.

[0023] Example 1

[0024] The aldehyde monomer trialdehyde phloroglucinol was dissolved in octanoic acid at a concentration of 5 mmol / L. This aldehyde monomer solution was dispersed in water and sonicated for 15 min to form an emulsion. The amine monomer 2,5-diaminobenzenesulfonate was dissolved in water at a concentration of 5 mmol / L. The amine monomer solution was then slowly added dropwise to the emulsion (dropping rate of 0.5 mL / min) to achieve a molar ratio of aldehyde monomer to ionic amine monomer of 2:3. The microemulsion interfacial polymerization system was reacted at room temperature for 3 days, followed by dialysis and washing with the aqueous phase for 5 days to obtain an ionic iCOF nanosheet dispersion with a concentration of 1.5 mg / mL. An appropriate amount of the dispersion was used to prepare an iCOF self-supported membrane with a thickness of 3 μm via vacuum-assisted filtration.

[0025] The morphology of the ionic iCOF nanosheets and their self-supporting films in this embodiment is as follows: Figure 1 As shown, the iCOF nanosheets prepared by microemulsion interfacial polymerization are large and thin (length and width greater than 3 μm, thickness approximately 1.3 nm). Furthermore, the morphology of the iCOF self-supporting film is as follows... Figure 2 As shown, the membrane surface and cross-section are dense and defect-free, with a thickness of approximately 10 μm. Furthermore, the membrane can be repeatedly bent, exhibiting good toughness. The proton conductivity of the iCOF self-supporting membrane is as follows: Figure 3 As shown, the iCOF self-supporting membrane possesses a rigid framework structure and high-density ordered proton-conducting groups, enabling rapid proton conduction. Its conductivity reaches 340 mS / cm at 80 °C. -1 It is 1.7 times that of Nafion 212 proton exchange membranes. The prepared iCOF self-supporting membrane was used in a hydrogen-oxygen fuel cell, and its performance was as follows: Figure 4 As shown, under the test conditions of 80 °C, H2 and O2 flow rates of 2000 mL / min, back pressure of 0.2 MPa, and relative humidity of 100%, the iCOF self-supporting membrane fuel cell achieves high current density of 4999.2 mA cm⁻¹. -2 At that time, the peak power density was 2017.5 mW / cm³. -2 .

[0026] Example 2

[0027] The aldehyde monomer 1,3-dihydroxy-2,4,6-trialdehydebenzene was dissolved in octanoic acid at a concentration of 3 mmol / L. This aldehyde monomer solution was dispersed in water and sonicated for 15 min to form an emulsion. The amine monomer 4,4'-diamino-3,3'-biphenyl disulfonic acid was dissolved in water at a concentration of 3 mmol / L. The amine monomer solution was then slowly added dropwise to the emulsion (dropping rate of 1 mL / min) to achieve a molar ratio of aldehyde monomer to ionic amine monomer of 2:3. The microemulsion interfacial polymerization system was reacted at room temperature for 5 days, followed by dialysis and washing of the aqueous phase for another 5 days to obtain an ionic iCOF nanosheet dispersion with a concentration of 1.8 mg / mL. An appropriate amount of the dispersion was used to prepare an iCOF self-supported membrane with a thickness of 8 μm and a proton conductivity of 150.2 mS·cm at room temperature. -1 Superior to commercial Nafion 212 membrane (87.9 mS·cm) -1 This indicates that the proton conductivity of the iCOF self-supporting membrane prepared by this invention is significantly improved.

[0028] Example 3

[0029] The aldehyde monomer pyromellitic aldehyde was dissolved in octanoic acid at a concentration of 2 mmol / L. This aldehyde monomer solution was dispersed in water and sonicated for 15 min to form an emulsion. The amine monomer 2,5-diamino-1,4-benzenedisulfonic acid was dissolved in water at a concentration of 2 mmol / L. The amine monomer solution was then slowly added dropwise to the emulsion (dropping rate of 1.5 mL / min) to achieve a molar ratio of aldehyde monomer to ionic amine monomer of 2:3. The microemulsion interfacial polymerization system was reacted at room temperature for 8 days, followed by dialysis and washing for 7 days to obtain an ionic iCOF nanosheet dispersion with a concentration of 2 mg / mL. An appropriate amount of the dispersion was used to prepare an iCOF self-supported membrane with a thickness of 13 μm and a proton conductivity of 180.4 mS·cm at room temperature. -1 Superior to commercially available Nafion 212 membrane (87.9 mS·cm) -1 This indicates that the proton conductivity of the COF self-supporting membrane prepared by this invention is significantly improved.

Claims

1. A method for preparing ionic covalent organic framework nanosheets via microemulsion interfacial polymerization, characterized in that, Aldehyde monomers were dissolved in a liquid long-chain fatty acid with weak anionic surface activity and dispersed in an aqueous phase to form an oil-in-water microemulsion. Then, an aqueous solution of an ionic amine monomer was slowly added dropwise to the microemulsion at room temperature. The ionic covalent organic framework was polymerized on the surface of the microemulsion droplets and exfoliated into the aqueous phase. After dialysis and washing, a dispersion of ionic covalent organic framework nanosheets was obtained, thus yielding ionic covalent organic framework nanosheets.

2. The method for preparing ionic covalent organic framework nanosheets by microemulsion interfacial polymerization according to claim 1, characterized in that, The aldehyde monomer is a multifunctional aldehyde monomer, specifically one or a mixture of two or more of the following: trialdehyde phloroglucinol, 1,3-dihydroxy-2,4,6-trialdehyde benzene, and pyromellitic methylaldehyde; the concentration of the aldehyde monomer in liquid long-chain fatty acids is 2 to 5 mmol / L.

3. The method for preparing ionic covalent organic framework nanosheets by microemulsion interfacial polymerization according to claim 1, characterized in that, The liquid long-chain fatty acid with weak anionic surface activity is octanoic acid.

4. The method for preparing ionic covalent organic framework nanosheets by microemulsion interfacial polymerization according to claim 1, characterized in that, The ionic amine monomer is a polyfunctional amine monomer, specifically one or a mixture of two or more of 2,5-diaminobenzenesulfonic acid, 4,4'-diamino-3,3'-biphenyldisulfonic acid, and 2,5-diamino-1,4-benzenedisulfonic acid, and the concentration of the aqueous solution of the ionic amine monomer is 2 to 5 mmol / L.

5. The method for preparing ionic covalent organic framework nanosheets by microemulsion interfacial polymerization according to claim 1, characterized in that, The microemulsion was added at a rate of 0.5 to 1.5 mL / min. After addition, the molar ratio of aldehyde monomer to ionic amine monomer was 2:

3. The reaction was carried out at room temperature for 3 to 8 days, and the microemulsion droplet size ranged from 150 to 2000 nm.

6. The method for preparing ionic covalent organic framework nanosheets by microemulsion interfacial polymerization according to claim 1, characterized in that, The aforementioned ionic covalent organic framework nanosheets refer to covalent organic framework materials with sulfonic acid groups, and the nanosheets have a size of 1 ~ 5 μm and a thickness of 1.3 ~ 20 nm.

7. A method for preparing self-supporting proton exchange membranes of ionic covalent organic framework nanosheets by microemulsion interfacial polymerization, characterized in that, The ionic covalent organic framework nanosheets prepared by the method according to any one of claims 1-6 are subjected to dialysis and washing to obtain an iCOF dispersion, which is then stacked layer by layer by vacuum-assisted filtration to prepare a self-supporting proton exchange membrane of ionic covalent organic framework nanosheets.

8. The method for preparing a self-supporting proton exchange membrane of ionic covalent organic framework nanosheets by microemulsion interfacial polymerization according to claim 7, characterized in that, The concentration of the ionic covalent organic framework nanosheet dispersion is 1.5 ~ 2 mg / mL.

9. The method for preparing a self-supporting proton exchange membrane of ionic covalent organic framework nanosheets by microemulsion interfacial polymerization according to claim 7, characterized in that, The aforementioned dialysis washing refers to transferring the ionic covalent organic framework nanosheet dispersion into a dialysis bag and washing it in deionized water to remove small molecule impurities.

10. The method for preparing a self-supporting proton exchange membrane of ionic covalent organic framework nanosheets by microemulsion interfacial polymerization according to claim 7, characterized in that, The self-supporting proton exchange membrane of the ionic covalent organic framework nanosheets has a thickness of 3~13μm and a filtration vacuum degree of -0.08~-0.1MPa.

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