Two-dimensional covalent organic framework separation membrane for electrocatalytic carbon dioxide reduction reaction system
By preparing a two-dimensional covalent organic framework separation membrane, the problem of carbonate ions entering the anode region was solved by utilizing electrostatic interactions and size sieving effects, thereby improving the reduction efficiency of the electrocatalytic carbon dioxide reduction reaction and the cathode product collection efficiency, and realizing efficient hydroxide ion transport and selective separation.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- WUHAN UNIV
- Filing Date
- 2026-01-20
- Publication Date
- 2026-04-10
AI Technical Summary
In the electrocatalytic carbon dioxide reduction reaction, carbonate ions reach the anode through the anion exchange membrane and undergo oxidation, affecting the anode half-reaction and reducing the collection efficiency of the cathode reduction products, thus leading to a decrease in reduction efficiency.
A two-dimensional covalent organic framework separation membrane was designed and fabricated. By using an oil-water-oil three-phase interface polymerization process and a vacuum-assisted assembly method, the membrane with electrostatic interaction and size sieving effect was developed by utilizing the size and charge difference between carbonate and hydroxide ions to prevent carbonate ions from entering the anode region.
It achieves effective separation of hydroxide and carbonate ions, reduces cross-reactions, improves the collection efficiency of cathode products and the reduction efficiency of electrocatalytic carbon dioxide reduction, and has high hydroxide ion transport capacity and OH-/CO32- selectivity, with a Faraday efficiency of 95%.
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Figure CN121819611A_ABST
Abstract
Description
Technical Field
[0001] This invention relates to the field of separation membrane technology, and in particular to a two-dimensional covalent organic framework separation membrane for electrocatalytic carbon dioxide reduction reaction systems. Background Technology
[0002] Electrocatalytic carbon dioxide reduction (CO2R) is considered a promising carbon conversion technology due to its advantages such as mild conversion conditions, controllable electrocatalytic process, abundant energy resources, and modular industrial applications. Electrocatalytic CO2R not only reduces carbon dioxide emissions but also allows for the storage of renewable electrical energy in easily transportable chemicals, solving the problem of the difficulty in storing intermittent electrical energy. Therefore, electrocatalytic CO2R provides an effective pathway to mitigate the greenhouse effect and achieve a green carbon cycle.
[0003] In the electrocatalytic reduction of carbon dioxide, neutral or alkaline electrolytes are typically used as the reaction solution to increase the solubility of carbon dioxide in the electrocatalytic system. However, due to the presence of a localized alkaline environment, the carbon dioxide introduced into the system reacts with hydroxide ions (OH-) in the electrolyte. - The reaction produces carbonates, and carbonate ions can pass through the anion exchange membrane to the anode to undergo oxidation. This phenomenon not only affects the formation of cross-reactions in the anodic half-reaction but also reduces the collection efficiency of the cathode reduction products, thereby reducing the reduction efficiency of the electrocatalytic carbon dioxide reduction reaction. Summary of the Invention
[0004] In view of the above-mentioned deficiencies of the prior art, the purpose of this invention is to design and develop a new technological approach to achieve effective separation of hydroxide ions and carbonate ions in an electrocatalytic system, prevent carbonate ions from entering the anode region through the anion exchange membrane, thereby reducing cross-reactions caused by the anode, improving the collection efficiency of cathode products, and improving the reduction efficiency of the electrocatalytic carbon dioxide reduction system.
[0005] To achieve the above objectives, the present invention adopts the following technical solution: In a first aspect of the present invention, a method for preparing a two-dimensional covalent organic framework separation membrane is provided, comprising the following steps: (1) A dichloromethane solution of 2,4,6-trihydroxybenzene-1,3,5-tricarboxaldehyde was used as the base phase oil solution; The intermediate phase aqueous solution includes solution A or solution B; solution A is an aqueous solution of sodium hydroxide, and solution B is an aqueous solution of acetic acid; The upper phase oil solution includes one of solution C, solution D, and solution E; solution C is an N,N-dimethylformamide solution of 2,5-diaminobenzoic acid, solution D is an N,N-dimethylformamide solution of 2,5-diaminobenzenesulfonic acid, and solution E is an N,N-dimethylformamide solution of 3,3'-((2,5-diamino-1,4-phenylene)bis(oxy))bis(propane-1-sulfonic acid); (2) Add the bottom phase oil solution, the intermediate phase aqueous solution and the upper phase oil solution to the container in the order from bottom to top. After assembly and purification, covalent organic framework nanosheets are obtained. When the upper phase oil solution is solution C, the intermediate phase aqueous solution is solution A; when the upper phase oil solution is solution D or solution E, the intermediate phase aqueous solution is solution B. (3) Using a vacuum-assisted assembly process, covalent organic framework nanosheets are assembled onto a porous substrate to obtain a two-dimensional covalent organic framework separation membrane.
[0006] Preferably, in step (1), the amount of 2,4,6-trihydroxybenzene-1,3,5-tricarboxaldehyde used to prepare the bottom phase oil solution is 0.08~0.12 mmol, and the amount of dichloromethane used is 60~100 mL.
[0007] Preferably, in step (1), solution A is 20-30 mL of sodium hydroxide aqueous solution with a concentration of 0.04-0.06 M; solution B is 20-30 mL of acetic acid aqueous solution with a concentration of 2-4 M.
[0008] Preferably, in step (1), the amount of 2,5-diaminobenzoic acid used in preparing 40-60 mL solution C is 0.12-0.18 mmol; the amount of 2,5-diaminobenzenesulfonic acid used in preparing 40-60 mL solution D is 0.12-0.18 mmol; and the amount of 3,3'-((2,5-diamino-1,4-phenylene)bis(oxy))bis(propane-1-sulfonic acid) used in preparing 40-60 mL solution E is 0.12-0.18 mmol.
[0009] Preferably, in step (2), the assembly step includes: standing at 25~27 ℃ for 72~80 h.
[0010] Preferably, in step (2), the purification step includes: dialysis in deionized water for 60-72 h.
[0011] In a second aspect of the present invention, a two-dimensional covalent organic framework separation membrane is provided, which is prepared using the preparation method of the first aspect of the present invention.
[0012] Preferably, the two-dimensional covalent organic framework separation membrane has an average pore size of 0.8~1.4 nm and a charge density of -4~-6.5 mC / m³. -2 .
[0013] In a third aspect of the invention, an application of the two-dimensional covalent organic framework separation membrane of the second aspect of the invention is provided, including: for electrocatalytic carbon dioxide reduction reaction.
[0014] Preferably, the application of the two-dimensional covalent organic framework separation membrane includes the following steps: in an electrolytic cell, the two-dimensional covalent organic framework separation membrane is used as an anion transport membrane, potassium hydroxide aqueous solution is used as the electrolyte, a catalyst for catalyzing the reduction of carbon dioxide is used as the cathode, and a voltage is applied to reduce the carbon dioxide introduced into the electrolytic cell.
[0015] The structural formula of 3,3'-((2,5-diamino-1,4-phenylene)bis(oxy))bis(propane-1-sulfonic acid) is as follows:
[0016] Based on the above technical solutions, the design concept and principle of this invention are as follows: This invention utilizes a molecular design strategy, based on the size and charge differences between carbonate and hydroxide ions, to develop and prepare a two-dimensional covalent organic framework (COF) separation membrane with tunable charge density. This COF separation membrane is composed of trialdehyde monomers and various diamine monomers. First, COF nanosheets are prepared via an oil-water-oil three-phase interfacial polymerization process. Then, the COF nanosheets are assembled onto a porous substrate using a vacuum-assisted assembly method to obtain the target two-dimensional COF separation membrane.
[0017] The covalent organic framework nanosheets of this invention are crystalline porous framework materials assembled through covalent bonds between organic precursors. By adjusting the organic precursors in the reaction process, the size and surface charge characteristics of the nanochannels in the covalent organic framework nanosheets can be effectively controlled. Based on the difference in charge between carbonate and hydroxide ions, this invention introduces functional groups (Pa monomers) with different charges onto the amine monomers of the framework, including 2,5-diaminobenzoic acid (Pa-COOH), 2,5-diaminobenzenesulfonic acid (Pa-SO3H), and 3,3'-((2,5-diamino-1,4-phenylene)bis(oxy))bis(propane-1-sulfonic acid) (Pa-OSO3H). The Pa monomers with different functional groups undergo a Schiff base reaction with the aldehyde monomers under solvent-induced assembly to assemble into two-dimensional covalent organic framework nanosheets, which are then used to form two-dimensional covalent organic framework separation membranes through assisted assembly.
[0018] Furthermore, the core reason for choosing dichloromethane as the solvent for the bottom phase oil solution is that its density is greater than water and it is immiscible with water. This allows it to act as a stable "bottom phase," forming a clear interface with the upper aqueous phase. This enables precise control of the slow, orderly polymerization reaction of the reactants at the liquid-liquid interface, which is crucial for preparing high-quality thin films or ordered materials. Simultaneously, it effectively dissolves the reactants, is chemically stable, and is easily removed subsequently. Depending on the reaction type of different raw materials, sodium hydroxide is used to construct the intermediate phase because its strongly alkaline environment is used to deprotonate and activate the amino monomers diffusing from the upper phase, significantly enhancing their nucleophilicity and enabling them to react efficiently with the lower aldehyde monomers. Acetic acid is used as the intermediate phase because its weakly acidic environment provides the most suitable catalytic conditions for the Schiff base reaction itself. The acidity activates the aldehyde groups and removes the generated water through a reversible process, thereby efficiently driving the formation and connection of imine bonds and controlling the polymerization reaction to mainly occur in the interfacial region near the bottom phase.
[0019] Hydroxide ions can form a continuous hydrogen bond network with sub-nanochannels containing flexible alkoxysulfonic acid groups to enhance the hydroxyl ion transport rate. Carbonate ions exhibit electrostatic interactions and size sieving effects with the sulfonic acid functional groups on the two-dimensional covalent organic framework nanochannels. These two interactions synergistically hinder the passage of carbonate ions, thereby achieving effective separation of hydroxide and carbonate ions in the electrocatalytic system. In application, the two-dimensional covalent organic framework separation membrane prevents carbonate ions from entering the anode region through the membrane via electrostatic interactions and size sieving effects, thus reducing the cross-reactions caused by the conversion of carbon dioxide at the cathode to carbonate ions and their diffusion to the anode. Therefore, the two-dimensional covalent organic framework separation membrane of this invention possesses excellent hydroxide ion transport capacity (3.62 mol L⁻¹). -1 h -1 ) and OH - / CO3 2- Selectivity (~36); used in electrocatalytic carbon dioxide reduction systems, with a Faraday efficiency of ~95%.
[0020] Compared with the prior art, the present invention has the following advantages and beneficial effects: This invention provides a method for preparing a two-dimensional covalent organic framework separation membrane. The method involves preparing covalent organic framework nanosheets through an oil-water-oil three-phase interface polymerization process, and then assembling them onto a porous substrate using a vacuum-assisted assembly method. This method has advantages such as convenient process and mild reaction conditions.
[0021] This invention provides a two-dimensional covalent organic framework separation membrane, which possesses excellent hydroxide ion transport capacity and OH ion transport capacity. - / CO3 2-The selectivity enables the effective separation of hydroxide and carbonate ions in the electrocatalytic system, preventing carbonate ions from entering the anode region through the anion exchange membrane, thereby reducing cross-reactions caused by the anode.
[0022] This invention provides an application of a two-dimensional covalent organic framework separation membrane, which improves the reduction efficiency of the electrocatalytic carbon dioxide reduction system and has good application prospects. Attached Figure Description
[0023] Figure 1 In the image, (a) to (c) are, in order, images of COF-COOH obtained by a scanning electron microscope (SEM) and a cross-sectional scanning electron microscope (SEM); (d) to (f) are, in order, images of COF-SO3H obtained by a scanning electron microscope (SEM) and a cross-sectional scanning electron microscope (SEM); and (g) to (i) are, in order, images of COF-OSO3H obtained by a scanning electron microscope (SEM) and a cross-sectional scanning electron microscope (SEM). Figure 2 In the image, (a) and (b) are transmission electron microscope (TEM) images of COF-COOH and high-resolution transmission electron microscope (HRTEM) images, respectively; (c) and (d) are transmission electron microscope (TEM) images of COF-SO3H and high-resolution transmission electron microscope (HRTEM) images, respectively; and (e) and (f) are TEM images of COF-OSO3H and high-resolution transmission electron microscope (HRTEM) images, respectively. Figure 3 In the diagram, (a) to (c) are the pore size distribution diagrams of COF-COOH, COF-SO3H, and COF-OSO3H, respectively. Figure 4 In the figure, (a) shows the Zeta potential of COF-COOH, COF-SO3H, and COF-OSO3H; (b) shows the surface charge characterization results of COF-COOH, COF-SO3H, and COF-OSO3H.
[0024] Figure 5 In the image, (a) shows the effects of COF-COOH, COF-SO3H, COF-OSO3H, and Fumasep membrane (commercial membrane) on OH-. - / CO3 2- Separation performance test results; (b)~(d) are the separation stability test results of COF-COOH, COF-SO3H and COF-OSO3H respectively; Figure 6 A schematic diagram illustrating the principle of using a two-dimensional covalent organic framework separation membrane as an anion transport membrane for electrocatalytic carbon dioxide reduction reaction; Figure 7 In the figure, (a) represents the current density of COF-COOH, COF-SO3H, COF-OSO3H and the commercial membrane at different reduction potentials; (b) represents the Faraday efficiency of COF-COOH, COF-SO3H, COF-OSO3H and the commercial membrane in the electrocatalytic reduction of carbon dioxide to formate. Detailed Implementation
[0025] The present invention is further illustrated below by way of embodiments, but the invention is not limited to the scope of the embodiments described herein. Experimental methods in the following embodiments that do not specify specific conditions were performed according to conventional methods and conditions, or as selected according to the product instructions.
[0026] In the following embodiments: Fumasep membrane, Suzhou Shengernuo Technology Co., Ltd.; Sustain membrane, Suzhou Shengernuo Technology Co., Ltd.
[0027] Example 1 This embodiment provides a method for preparing a two-dimensional covalent organic framework separation membrane, the steps of which are as follows: (1) Preparation of the bottom phase oil solution: Dissolve 0.1 mmol of 2,4,6-trihydroxybenzene-1,3,5-tricarboxaldehyde in 80 mL of dichloromethane, sonicate for 10 min, and record the resulting solution as the bottom phase oil solution; Preparation of intermediate phase aqueous solution: Prepare 20 mL of 0.05 M sodium hydroxide aqueous solution, sonicate for 10 min, and record the resulting solution as solution A; Preparation of the upper phase oil solution: Dissolve 0.15 mmol of 2,5-diaminobenzoic acid in 50 mL of N,N-dimethylformamide, sonicate for 10 min, and denote the resulting solution as solution C; (2) The bottom phase oil solution, the intermediate phase aqueous solution and the upper phase oil solution were slowly added to the beaker in the order from bottom to top for assembly. The mixture was allowed to stand at 25 °C for 72 h, and then purified by dialyzing in deionized water for 72 h to obtain covalent organic framework nanosheets that are water-soluble colloids. In this embodiment, the intermediate phase aqueous solution is solution A, and the upper phase oil solution is solution C; (3) A vacuum-assisted assembly process was adopted, and a filtration device (the diameter of the filtration device is 2.5 cm and the filtration pressure is controlled at 20 bar) was used to drive the permeation through the porous substrate under negative pressure. The covalent organic framework nanosheets were used to form a filter layer by utilizing the retention effect of the porous substrate, and the assembly was completed to obtain a two-dimensional covalent organic framework separation membrane, denoted as COF-COOH.
[0028] Example 2 This embodiment provides a method for preparing a two-dimensional covalent organic framework separation membrane, the steps of which are as follows: (1) Preparation of the bottom phase oil solution: Dissolve 0.1 mmol of 2,4,6-trihydroxybenzene-1,3,5-tricarboxaldehyde in 80 mL of dichloromethane, sonicate for 10 min, and record the resulting solution as the bottom phase oil solution; Preparation of intermediate phase aqueous solution: Prepare 20 mL of 3 M acetic acid aqueous solution, and denote the resulting solution as solution B; Preparation of the upper phase oil solution: Dissolve 0.15 mmol of 2,5-diaminobenzenesulfonic acid in 50 mL of N,N-dimethylformamide, sonicate for 10 min, and denote the resulting solution as solution D; (2) The bottom phase oil solution, the intermediate phase aqueous solution and the upper phase oil solution were slowly added to the beaker in the order from bottom to top for assembly. The mixture was allowed to stand at 25 °C for 72 h, and then purified by dialyzing in deionized water for 72 h to obtain covalent organic framework nanosheets that are water-soluble colloids. In this embodiment, the intermediate phase aqueous solution is solution B, and the upper phase oil solution is solution D; (3) A vacuum-assisted assembly process was adopted, and a filtration device (the diameter of the filtration device is 2.5 cm and the filtration pressure is controlled at 20 bar) was used to drive the permeation through the porous substrate under negative pressure. The covalent organic framework nanosheets were used to form a filter layer by utilizing the retention effect of the porous substrate, and the assembly was completed to obtain a two-dimensional covalent organic framework separation membrane, denoted as COF-SO3H.
[0029] Example 3 This embodiment provides a method for preparing a two-dimensional covalent organic framework separation membrane, the steps of which are as follows: (1) Preparation of the bottom phase oil solution: Dissolve 0.1 mmol of 2,4,6-trihydroxybenzene-1,3,5-tricarboxaldehyde in 80 mL of dichloromethane, sonicate for 10 min, and record the resulting solution as the bottom phase oil solution; Preparation of intermediate phase aqueous solution: Prepare 20 mL of 3 M acetic acid aqueous solution, and denote the resulting solution as solution B; Preparation of the upper phase oil solution: Dissolve 0.15 mmol of 3,3'-((2,5-diamino-1,4-phenylene)bis(oxy))bis(propane-1-sulfonic acid) in 50 mL of N,N-dimethylformamide, sonicate for 10 min, and the resulting solution is denoted as solution E; (2) The bottom phase oil solution, the intermediate phase aqueous solution and the upper phase oil solution were slowly added to the beaker in the order from bottom to top for assembly. The mixture was allowed to stand at 25 °C for 72 h, and then purified by dialyzing in deionized water for 72 h to obtain covalent organic framework nanosheets that are water-soluble colloids. In this embodiment, the intermediate phase aqueous solution is solution B, and the upper phase oil solution is solution E. (3) A vacuum-assisted assembly process was adopted, and a filtration device (the diameter of the filtration device is 2.5 cm and the filtration pressure is controlled at 20 bar) was used to drive the permeation through the porous substrate under negative pressure. The covalent organic framework nanosheets were used to form a filter layer by utilizing the retention effect of the porous substrate, and the assembly was completed to obtain a two-dimensional covalent organic framework separation membrane, denoted as COF-OSO3H.
[0030] In addition to the two-dimensional covalent organic framework separation membrane prepared in the above embodiments, within the preferred scope of the present invention, the corresponding two-dimensional covalent organic framework separation membrane can be successfully prepared by adjusting the amount of raw materials or the preparation parameters.
[0031] Example 4 This embodiment provides three two-dimensional covalent organic framework separation membranes, namely COF-COOH, COF-SO3H, and COF-OSO3H, prepared using the methods of Examples 1-3, and characterizes their morphology and structure.
[0032] In this embodiment, scanning electron microscopy was used to characterize the surface and cross-sectional micromorphology of COF-COOH, COF-SO3H, and COF-OSO3H. Figure 1 Images of COF-COOH, COF-SO3H, and COF-OSO3H, along with corresponding surface and cross-sectional scanning electron microscope (SEM) images, are shown. The images of the two-dimensional covalent organic framework (COF-COOH) separation membranes demonstrate that they maintain good structural integrity within a centimeter-scale range, without obvious cracks. The SEM images reveal that the surfaces of all three membranes exhibit a smooth and uniform morphology at the micrometer scale. Furthermore, the absence of obvious defects or gaps on the membrane surface indicates good continuity. Cross-sectional images show that the nanosheet assembly units of the three membranes are densely packed along the vertical direction, resulting in a COF-COOH separation membrane with a thickness of 2 μm, a COF-SO3H separation membrane with a thickness of 1 μm, and a COF-OSO3H separation membrane with a thickness of 1 μm.
[0033] In addition, this embodiment also uses transmission electron microscopy and high-resolution transmission electron microscopy to observe the microstructure of COF-COOH, COF-SO3H, and COF-OSO3H. Figure 2 The characterization results of the above-mentioned two-dimensional covalent organic framework separation membrane are shown. Figure 2 Transmission electron microscopy images confirmed the layered structure of the covalent organic framework nanosheets. In the high-resolution transmission electron microscopy images, the crystal faces showed clear periodic lattice fringes, indicating that the covalent organic framework material exhibits ordered molecular stacking along a specific direction.
[0034] Finally, in this embodiment, the pore sizes of three two-dimensional covalent organic framework separation membranes were measured using N2 adsorption-desorption isotherm testing, and the test curves are shown below. Figure 3 As shown. According to the test, the pore size of COF-COOH is 1.2 nm, the pore size of COF-SO3H is 1.4 nm, and the pore size of COF-OSO3H is 0.8 nm.
[0035] Example 5 In this embodiment, three two-dimensional covalent organic framework separation membranes, namely COF-COOH, COF-SO3H, and COF-OSO3H, were prepared based on the preparation methods of Examples 1 to 3, and were tested using a solid surface Zeta potential analyzer. Figure 4 In the figure, (a) shows the Zeta potential of three two-dimensional covalent organic framework separation membranes, and the error bar represents the standard deviation of three parallel experiments; (b) shows the surface charge characterization of the COF separation membrane. The results show that the charge densities of COF-COOH, COF-SO3H, and COF-OSO3H are -4.2 mC m -2 -5.1 mC m -2 and -6.2 mC m -2 .
[0036] This embodiment evaluated the ion transport and OH- ions of three two-dimensional covalent organic framework separation membranes using a four-chamber electrodialysis apparatus. - / CO3 2- Separation performance. The four chambers consist of electrode chambers on the left and right sides, a concentration chamber in the middle, and a desalination chamber. The effective membrane area is 0.78 cm². 2 100 mL of 0.3 M Na₂SO₄ solution was injected into each of the two polar chambers via a peristaltic pump. Simultaneously, 100 mL of a mixed solution of 0.1 M NaOH, 1 M NaOH, and 0.1 M Na₂CO₃ was injected into the concentration chamber and desalination chamber, respectively. Figure 5 As shown in (a), the three two-dimensional covalent organic framework separation membranes exhibit high ion fluxes for hydroxide ions, at 3.5, 3.6, and 3.8 mol L, respectively. -1 h-1 In contrast, carbonate ions have relatively low ion fluxes of 0.04, 0.03, and 0.01 mol L, respectively. -1 h -1 Among them, the COF-OSO3H separation membrane exhibited an ion selectivity as high as 36.4%. To investigate the long-term separation stability of the two-dimensional covalent organic framework (BOC) membranes, the ion separation performance of three different BOC membranes was tested repeatedly. Figure 5 As shown in (b) to (d), under the electrodialysis test conditions of 10 cycles and 1 hour each, the ion fluxes of hydroxide and carbonate ions of the three two-dimensional covalent organic framework membranes remained essentially unchanged, indicating that the two-dimensional covalent organic framework membranes still exhibit excellent OH flux after repeated cycles. - / CO3 2- Separation performance.
[0037] Example 6 This embodiment illustrates the application of a two-dimensional covalent organic framework separation membrane. Using COF-COOH, COF-SO3H, COF-OSO3H, and a commercially available membrane as examples, the current density of the electrocatalytic reduction of carbon dioxide to formate in an H-type electrolyzer (using 0.5 M KOH as the electrolyte) at different operating potentials was measured. The principle of this invention is as follows: Figure 6 As shown.
[0038] Structural changes of formate, a product of electrocatalytic carbon dioxide production, within an operating potential range of -0.7 to -0.9 V were quantitatively analyzed using liquid water peak suppression. Figure 7 As shown in (a), COF-COOH, COF-SO3H, and COF-OSO3H exhibit superior performance compared to commercial Fumasep and sustain membranes; among them, the average current densities of the COF-OSO3H separation membrane at operating potentials of -0.7, -0.8, and -0.9 V are -29.6, -38.4, and -48.4 mA cm⁻¹, respectively. -2 It is significantly higher than that of commercial Fumasep and Sustain membranes. Furthermore, as... Figure 7 As shown in (b), within the operating potential range of -0.7 to -0.9 V, all three two-dimensional covalent organic framework separation membranes can maintain a Faraday efficiency of approximately 95%, which is better than or close to the level of existing commercial membranes.
[0039] In summary, this invention synthesizes a covalent organic framework separation membrane material with tunable charge density through a molecular design strategy, achieving effective separation of hydroxide and carbonate ions in the electrocatalytic carbon dioxide reduction reaction system and improving the collection efficiency of cathode products in the electrocatalytic carbon dioxide reduction reaction system. The high charge density covalent organic framework separation membrane allows for rapid ion transport of hydroxide ions with minimal resistance under size sieving and electrostatic interactions, while effectively blocking the transport of carbonate ions. The interaction between hydroxide ions and sub-nanometer channels with flexible alkoxy chains lowers the energy barrier for hydroxide ion transmembrane transport, resulting in the covalent organic framework separation membrane exhibiting excellent hydroxide ion transport capacity and high OH- ion concentration. - / CO3 2- Selectivity. This invention provides a new strategy for ion / molecule separation, nanofluids, and high-efficiency ion separation in electrocatalytic systems, and has promising application prospects.
[0040] The preferred embodiments of the present invention have been described in detail above. It should be understood that those skilled in the art can make numerous modifications and variations based on the concept of the present invention without creative effort. Therefore, all technical solutions that can be obtained by those skilled in the art based on the concept of the present invention through logical analysis, reasoning, or limited experimentation on the basis of existing technology should be within the scope of protection defined by the claims.
Claims
1. A method for preparing a two-dimensional covalent organic framework separation membrane, characterized in that, Includes the following steps: (1) A dichloromethane solution of 2,4,6-trihydroxybenzene-1,3,5-tricarboxaldehyde was used as the base phase oil solution; The intermediate phase aqueous solution includes solution A or solution B; solution A is an aqueous solution of sodium hydroxide, and solution B is an aqueous solution of acetic acid; The upper phase oil solution includes one of solution C, solution D, and solution E; solution C is an N,N-dimethylformamide solution of 2,5-diaminobenzoic acid, solution D is an N,N-dimethylformamide solution of 2,5-diaminobenzenesulfonic acid, and solution E is an N,N-dimethylformamide solution of 3,3'-((2,5-diamino-1,4-phenylene)bis(oxy))bis(propane-1-sulfonic acid); (2) Add the bottom phase oil solution, the intermediate phase aqueous solution and the upper phase oil solution to the container in the order from bottom to top. After assembly and purification, covalent organic framework nanosheets are obtained. When the upper phase oil solution is solution C, the intermediate phase aqueous solution is solution A; When the upper phase oil solution is solution D or solution E, the intermediate phase aqueous solution is solution B; (3) Using a vacuum-assisted assembly process, covalent organic framework nanosheets are assembled onto a porous substrate to obtain a two-dimensional covalent organic framework separation membrane.
2. The method for preparing the two-dimensional covalent organic framework separation membrane according to claim 1, characterized in that: In step (1), the amount of 2,4,6-trihydroxybenzene-1,3,5-tricarboxaldehyde used to prepare the bottom phase oil solution is 0.08~0.12 mmol, and the amount of dichloromethane used is 60~100 mL.
3. The method for preparing the two-dimensional covalent organic framework separation membrane according to claim 1, characterized in that: In step (1), solution A is 20-30 mL of sodium hydroxide aqueous solution with a concentration of 0.04-0.06 M; solution B is 20-30 mL of acetic acid aqueous solution with a concentration of 2-4 M.
4. The method for preparing the two-dimensional covalent organic framework separation membrane according to claim 1, characterized in that: In step (1), the amount of 2,5-diaminobenzoic acid used in preparing 40-60 mL solution C is 0.12-0.18 mmol; the amount of 2,5-diaminobenzenesulfonic acid used in preparing 40-60 mL solution D is 0.12-0.18 mmol; and the amount of 3,3'-((2,5-diamino-1,4-phenylene)bis(oxy))bis(propane-1-sulfonic acid) used in preparing 40-60 mL solution E is 0.12-0.18 mmol.
5. The method for preparing the two-dimensional covalent organic framework separation membrane according to claim 1, characterized in that, In step (2), the assembly step includes: standing at 25~27 ℃ for 72~80 h.
6. The method for preparing the two-dimensional covalent organic framework separation membrane according to claim 1, characterized in that, In step (2), the purification step includes: dialysis in deionized water for 60-72 h.
7. A two-dimensional covalent organic framework separation membrane, characterized in that: It is prepared by any one of the preparation methods described in claims 1 to 6.
8. The two-dimensional covalent organic framework separation membrane according to claim 7, characterized in that: The two-dimensional covalent organic framework separation membrane has an average pore size of 0.8–1.4 nm and a charge density of -4 to -6.5 mC / m². -2 .
9. An application of the two-dimensional covalent organic framework separation membrane as described in claim 7 or 8, characterized in that, include: Used for electrocatalytic carbon dioxide reduction reaction.
10. The application of the two-dimensional covalent organic framework separation membrane according to claim 9, characterized in that, The process includes the following steps: In an electrolytic cell, a two-dimensional covalent organic framework separation membrane is used as an anion transport membrane, an aqueous solution of potassium hydroxide is used as the electrolyte, a catalyst for the reduction of carbon dioxide is used as the cathode, and a voltage is applied to reduce the carbon dioxide introduced into the electrolytic cell.