Covalent organic framework composite membrane as well as preparation method and application thereof
By constructing an ionic liquid-water interface on the outer wall of a tubular support to carry out the Schiff base reaction, the problem of non-uniform density of COF membranes in traditional methods was solved, achieving efficient liquid separation and nanofiltration performance, and extending the preparation of COF membranes on curved substrates.
Patent Information
- Application Number
- CN202511758340.5
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-11-27
- Publication Date
- 2026-01-02
AI Technical Summary
Existing technologies make it difficult to prepare uniform and dense covalent organic framework (COF) membranes on porous supports such as tubular Al2O3, resulting in poor separation performance. Furthermore, traditional organic solvents are highly toxic and have a fast diffusion rate, making it difficult to control the thickness and density of the membrane.
By replacing traditional organic solvents with ionic liquids, a stable "ionic liquid-water" interface is constructed on the outer wall of a tubular support through reverse diffusion, and a Schiff base reaction is carried out to form a uniform and dense COF membrane.
A COF membrane with high crystallinity, few defects, and uniform density was obtained, exhibiting excellent nanofiltration separation performance and suitable for liquid separation, nanofiltration, and water treatment.
Smart Images
Figure CN121244033A_ABST
Abstract
Description
Technical Field
[0001] This invention belongs to the field of membrane material technology, specifically relating to a covalent organic framework composite membrane, its preparation method and application. Background Technology
[0002] Covalent organic frameworks (COFs) are a class of novel crystalline porous materials with periodic two- or three-dimensional pore structures, composed of lightweight elements (such as C, H, O, N, and B) linked by strong covalent bonds. Due to their high specific surface area, regular pore structure, excellent structural designability, and good stability, COF materials have shown great application potential in gas storage, chemical separation, catalysis, sensing, and optoelectronics. However, COF materials are usually in powder form, and processing them into macroscopic, continuous, defect-free thin films (i.e., COF membranes) is the key and challenge for their large-scale application in practical separation processes.
[0003] Loading COF membranes onto porous supports with high mechanical strength to form composite membranes is the mainstream strategy for solving this problem. Among these, tubular Al2O3 supports are ideal choices due to their excellent mechanical strength, thermal stability, and chemical stability. Currently, common methods for preparing COF composite membranes on porous supports such as tubular Al2O3 mainly include in-situ growth and liquid-solid interface polymerization. In-situ growth involves immersing the support in a solution containing all the reactants, and then using methods such as heating to allow COF crystals to directly nucleate and grow on the support surface or within the pores. While this method is simple, it is difficult to precisely control the membrane thickness and density, easily leading to discontinuous, defective membranes or thick crystal layers, resulting in poor separation performance.
[0004] Liquid-solid interfacial polymerization involves immersing a support in an aqueous solution of one monomer, removing it and cleaning off any residual droplets, and then immersing it in an organic solution of another monomer. The two monomers react at the liquid-solid interface on the support surface to form a COF film. Existing literature often uses toxic and harmful solvents immiscible with water, such as benzene, toluene, dichloromethane, and n-hexane, as the organic solvent. These solvents have low viscosity and fast monomer diffusion rates, leading to overly vigorous interfacial reactions, rapid nucleation but poor order. This easily results in amorphous polymers or polycrystalline films with many defects, and makes it difficult to obtain ultrathin, continuous, and ideal film structures.
[0005] Therefore, developing a new method that is green, controllable, and capable of forming uniform and dense COF membranes on tubular carriers is of great practical significance. Summary of the Invention
[0006] The purpose of this invention is to provide a covalent organic framework composite membrane, its preparation method and application. The preparation method uses ionic liquid to replace traditional organic solvent and constructs a stable "ionic liquid-water" interface on the outer wall of a tubular support through reverse diffusion, and performs Schiff base reaction to successfully construct a uniform and dense COF membrane on the outer wall of the tubular support.
[0007] To achieve the above objectives, a specific embodiment of the present invention provides the following technical solution:
[0008] A method for preparing a covalent organic framework composite membrane, the method comprising the following steps:
[0009] The amino monomer, catalyst, and deionized water are mixed to obtain an aqueous solution;
[0010] An aldehyde monomer and an ionic liquid are mixed to obtain an ionic liquid phase solution.
[0011] Take a tubular carrier, place it in an aqueous solution, and then remove and dry it to obtain a pretreated tubular carrier;
[0012] Aqueous solution was filled into the pretreated tubular carrier, and both ends of the pretreated tubular carrier were sealed.
[0013] A pretreated tubular support sealed at both ends is placed in an ionic liquid phase solution for reaction to obtain a covalent organic framework composite membrane.
[0014] In one or more embodiments of the present invention, the tubular carrier contains pores, and the pore size of the pores in the tubular carrier decreases sequentially from the inside to the outside;
[0015] The pore size on the inner wall of the tubular carrier is 1μm-5μm, and the pore size on the outer wall is 50nm-100nm.
[0016] In one or more embodiments of the present invention, the tubular carrier is made of any one of alumina, zirconium oxide, titanium oxide, and silicon oxide; and / or,
[0017] The tubular carrier has an outer diameter of 11mm-15mm and an inner diameter of 5mm-9mm.
[0018] In one or more embodiments of the present invention, the step of immersing the tubular carrier in an aqueous solution and then removing and drying it is repeated 2-3 times, with each immersion time being 5-10 minutes; and / or,
[0019] The drying conditions after the tubular carrier is removed from the aqueous solution are: temperature 60℃-80℃, time 8min-12min.
[0020] In one or more embodiments of the present invention, the reaction temperature is 20°C-30°C, and the reaction time is 24h-120h; and / or,
[0021] After the reaction was completed, the covalent organic framework composite membrane was washed alternately with ethanol and deionized water, and then vacuum dried at 60℃-80℃ for 3h-6h.
[0022] In one or more embodiments of the present invention, the amino monomer is one or more selected from p-phenylenediamine, benzidine, 5,5'-diamino-2,2'-bipyridine, and 1,3,5-tris(4-aminophenyl)benzene; and / or,
[0023] The catalyst is one or both of acetic acid and p-toluenesulfonic acid; and / or,
[0024] The aldehyde monomer is one or more selected from trialdehyde phloroglucinol, pyromellitic terephthalaldehyde, and 2,5-dihydroxyterephthalaldehyde; and / or...
[0025] The ionic liquid is one or both of 1-butyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide salt and 1-butyl-3-methylimidazolium hexafluorophosphate.
[0026] In one or more embodiments of the present invention, the concentration of the amino monomer in the aqueous solution is 13 mmol / L-40 mmol / L, and the concentration of the catalyst is 0.2 mol / L-0.6 mol / L; and / or,
[0027] In the ionic liquid phase solution, the concentration of the aldehyde monomer is 5 mmol / L-20 mmol / L.
[0028] In one or more embodiments of the present invention, the outer surface of the tubular carrier is pre-modified with polydopamine, an amino-containing silane coupling agent, or polyethyleneimine.
[0029] Another specific embodiment of the present invention provides the following technical solution:
[0030] A covalent organic framework composite membrane, wherein the covalent organic framework composite membrane is prepared by the above-described preparation method.
[0031] Another specific embodiment of the present invention provides the following technical solution:
[0032] Application of a covalent organic framework composite membrane in liquid separation, nanofiltration, and water treatment.
[0033] Compared with existing technologies, this invention places the aqueous solution inside a tubular carrier and the ionic liquid solution outside the carrier. Utilizing the difference in their physical properties (viscosity, permeability), a stable ionic liquid-water reaction interface is constructed on the outer wall of the tubular carrier, achieving interfacial polymerization to form a COF membrane. Furthermore, this invention utilizes the high viscosity of the ionic liquid to limit the diffusion rate of aldehyde monomers to the interface, thereby slowing down the interfacial polymerization reaction rate. This is beneficial for the ordered nucleation and growth of COF crystals, ultimately obtaining a COF membrane with high crystallinity, few defects, and uniform density. The COF composite membrane obtained by this solution placement method and interfacial polymerization membrane formation exhibits excellent separation performance in nanofiltration and can be effectively applied in liquid separation, nanofiltration, and water treatment. Moreover, this method can be extended not only to prepare COF membranes on curved substrates but also to prepare COF membranes on planar substrates. Attached Figure Description
[0034] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments recorded in the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.
[0035] Figures 1-10 These are SEM images of the COF composite membranes in Examples 1-6 and Comparative Examples 1-4 of the present invention;
[0036] Figure 11 The images show the infrared spectrum and XRD pattern of the TpBpy composite film in Example 1 of this invention. Detailed Implementation
[0037] To enable those skilled in the art to better understand the technical solutions in this disclosure, the technical solutions in the embodiments of this disclosure are described clearly and completely below. Obviously, the described embodiments are only some embodiments of this disclosure, and not all embodiments. Based on the embodiments in this disclosure, all other embodiments obtained by those skilled in the art without creative effort should fall within the scope of protection of this disclosure.
[0038] To achieve the green and controllable preparation of uniform and dense COF membranes on tubular supports, this invention replaces traditional organic solvents with ionic liquids and constructs a stable "ionic liquid-water" interface on the outer wall of the tubular support through a reverse diffusion method, thereby carrying out a Schiff base reaction and successfully constructing a uniform and dense COF membrane on the outer wall of the tubular support.
[0039] A specific embodiment of the present invention provides a method for preparing a covalent organic framework composite membrane, comprising the following steps:
[0040] Step 1: Pretreatment of tubular carriers.
[0041] Specifically, the tubular carrier is made of any one of alumina, zirconium oxide, titanium oxide, and silicon oxide, with alumina being preferred. The outer diameter of the tubular carrier is 11mm-15mm, and the inner diameter is 5mm-9mm. The specific specifications are not limited to the scope disclosed in this invention and can be selected according to actual needs.
[0042] Furthermore, the tubular support contains pores, and the pore size decreases progressively from the inside to the outside. Specifically, the pore size on the inner wall of the tubular support is 1μm-5μm, the pore size on the outer wall is 50nm-100nm, and the average pore size is 50nm-200nm. This pore size distribution promotes the diffusion of the aqueous solution inside the tubular support to the outer wall, while hindering the diffusion of the ionic liquid outside the tubular support to the inside, thereby forming a stable "ionic liquid-water" interface on the outer surface of the tubular support, and ultimately forming a dense COF film.
[0043] Furthermore, the outer surface of the tubular carrier is pre-modified with polydopamine, amino-containing silane coupling agent, or polyethyleneimine. The purpose is to introduce amino groups to modify the carrier, thereby enhancing the bonding force between the carrier and the COF membrane and preventing detachment. The introduced amino and other functional groups can also serve as nucleation sites, inducing COF crystals to grow vertically and uniformly on the carrier surface.
[0044] Taking the use of polydopamine-modified tubular carriers as an example, polydopamine is loaded onto the outer surface of the tubular carrier, allowing it to be firmly fixed to the outer surface of the tubular carrier through chemical bonds, forming an active interface with functional groups such as amino and phenolic hydroxyl groups. This step aims to provide numerous specific binding sites for COF film formation, improve the adhesion between the carrier surface and the COF film, thereby promoting a more uniform and stable anchoring of the COF film to the outer surface of the tubular carrier.
[0045] Specifically, the tubular carrier is sealed at both ends with stoppers and placed in an open container. An appropriate amount of dopamine hydrochloride is weighed, dissolved in Tris-HCl buffer solution, and then poured into the container. The container is then placed in a constant-temperature water bath shaker to allow the dopamine to self-polymerize at room temperature, forming polydopamine on the outer surface of the tubular carrier. After the reaction is complete, the surface is repeatedly rinsed with deionized water to remove any unadhered particles, and then the carrier is soaked in water for later use.
[0046] Step 2: Prepare the aqueous phase solution and the ionic liquid phase solution.
[0047] Specifically, amino monomers, catalysts, and deionized water are mixed to obtain an aqueous solution with an amino monomer concentration of 13 mmol / L–40 mmol / L and a catalyst concentration of 0.2 mol / L–0.6 mol / L. Aldehyde monomers and ionic liquids are mixed to obtain an ionic liquid solution with an aldehyde monomer concentration of 5 mmol / L–20 mmol / L.
[0048] The amino monomer is one or more of p-phenylenediamine, benzidine, 5,5'-diamino-2,2'-bipyridine, and 1,3,5-tris(4-aminophenyl)benzene; the catalyst is one or two of acetic acid and p-toluenesulfonic acid; the aldehyde monomer is one or more of trialdehyde-resorcinol, pyromellitic pyroxenaldehyde, and 2,5-dihydroxy-terephthalaldehyde; and the ionic liquid is one or two of 1-butyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide salt and 1-butyl-3-methylimidazolium hexafluorophosphate.
[0049] This invention preferably uses ionic liquids such as imidazoles and pyridines, which are liquids at room temperature, and whose anion can be Tf₂N. - PF6 - BF4 - These types of ionic liquids are immiscible with water, can fully dissolve aldehyde monomers, and have suitable viscosity (typically between 50 mPa·s and 200 mPa·s). Choosing an acidic catalyst can promote imine bond formation, thereby increasing the reaction rate and crystallinity.
[0050] Step 3, reverse diffusion interface aggregation.
[0051] Specifically, a tubular support is placed in an aqueous solution, then removed and dried. This process is repeated 2-4 times, with each immersion lasting 5-10 minutes. This allows sufficient amino monomers to be adsorbed onto the surface of the tubular support. When the tubular support comes into contact with the ionic liquid solution containing aldehyde monomers, an amorphous primary layer rapidly forms on the surface. This primary layer has significant defects, which are gradually repaired and form a crystalline COF film during subsequent back diffusion. Furthermore, the presence of the primary layer further restricts diffusion. Although the rapidly formed primary layer film on the support surface is not dense and has defects, it limits the diffusion rate of amino monomers from the inside to the outside of the tube in the aqueous solution, thus providing more time for molecules to stack in an orderly manner and ultimately improving the crystallinity of the COF film.
[0052] Next, seal one end of the tubular carrier with a stopper, filling the tubular carrier with the aqueous solution, and then seal the other end. Place the sealed tubular carrier in a container filled with the ionic liquid solution, ensuring the outer wall of the tubular carrier is completely submerged in the ionic liquid solution. Due to the high viscosity of the ionic liquid and the small pore size of the tubular carrier, the aqueous solution inside the tube easily permeates to the outer wall, while the ionic liquid solution has difficulty permeating to the inside, thus creating an ionic liquid-water interface on the outer wall of the tubular carrier.
[0053] At the ionic liquid-water interface, aldehyde and amino monomers undergo Schiff base polymerization at a temperature controlled between 20°C and 30°C for 24-120 hours. As the reaction proceeds, a continuous COF membrane gradually forms on the outer wall of the tubular support. After the reaction, the prepared COF composite membrane is removed from the solution and rinsed repeatedly with alternating ethanol and deionized water to remove residual monomers and ionic liquids from the surface. It is then vacuum-dried at 60°C-80°C for 3-6 hours to obtain the final COF composite membrane.
[0054] Another specific embodiment of the present invention provides a covalent organic framework composite membrane, which is prepared by the above preparation method.
[0055] Another specific embodiment of the present invention provides an application of a covalent organic framework composite membrane in liquid separation, nanofiltration, and water treatment.
[0056] The present invention will be further described in detail below with reference to specific embodiments.
[0057] Example 1
[0058] The method for preparing the covalent organic framework composite membrane in this embodiment includes the following steps:
[0059] (1) Carrier pretreatment: An Al2O3 tube with an outer diameter of 12 nm and an inner diameter of 8 mm was sealed at both ends and placed in an open container. 200 mg of dopamine hydrochloride was weighed and dissolved in 100 mL of Tris-HCl buffer solution (0.01 M pH=8.5), and poured into the container. The container was then placed in a constant temperature water bath shaker to allow the dopamine to undergo a self-polymerization reaction at 25 °C. After 4 h of reaction, the Al2O3 tube was removed, and the surface was repeatedly rinsed with deionized water to remove unadhered particles. It was then soaked in water for later use.
[0060] (2) Preparation of TpBpy composite membrane: Weigh 200 mg of 5,5'-diamino-2,2'-bipyridine (Bpy) and 1 mL of acetic acid into a 50 mL centrifuge tube, add 40 mL of deionized water, and sonicate for 5 minutes to promote complete dissolution of monomers and catalysts. This is recorded as solution A (Bpy is approximately 26 mmol / L, and acetic acid is approximately 0.4 mol / L). Weigh 25 mg of trialdehyde phloroglucinol (Tp) into a 20 mL centrifuge tube, add 12 mL of 1-butyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide salt ([BMIm]NTf2), and sonicate for 30 minutes to promote complete dissolution. This is recorded as solution B (approximately 10 mmol / L).
[0061] The modified Al2O3 tube was immersed in solution A for 10 minutes, then removed and dried in a 60 °C oven for 10 minutes. This immersion and drying process was repeated three times to ensure sufficient monomer adsorption on the Al2O3 tube surface. One end of the Al2O3 tube was then sealed, and 4 mL of solution A was added inside. The other end was then sealed, and the sealed tube was placed in solution B. After reacting at room temperature for 4 days, the membrane was removed and washed with anhydrous ethanol to remove residual ionic liquid and unreacted monomer from the membrane surface. Finally, the membrane was dried in a 60 °C vacuum oven to obtain the TpBpy composite membrane, as shown in the SEM image. Figure 1 As shown, the infrared spectrum and XRD pattern are as follows: Figure 11 As shown.
[0062] Example 2
[0063] The method for preparing the covalent organic framework composite membrane in this embodiment includes the following steps:
[0064] (1) Carrier pretreatment: An Al2O3 tube with an outer diameter of 12 nm and an inner diameter of 8 mm was sealed at both ends and placed in an open container. 200 mg of dopamine hydrochloride was weighed and dissolved in 100 mL of Tris-HCl buffer solution (0.01 M pH=8.5), and poured into the container. The container was then placed in a constant temperature water bath shaker to allow the dopamine to undergo a self-polymerization reaction at 25 °C. After 4 h of reaction, the Al2O3 tube was removed, and the surface was repeatedly rinsed with deionized water to remove unadhered particles. It was then soaked in water for later use.
[0065] (2) Preparation of TpPa-1 composite membrane: Weigh 150 mg of p-phenylenediamine (Pa-1) and 1 mL of acetic acid into a 50 mL centrifuge tube, add 40 mL of deionized water, and sonicate for 5 minutes to promote complete dissolution of monomers and catalysts. This is recorded as solution A (p-phenylenediamine is approximately 34 mmol / L, and acetic acid is approximately 0.4 mol / L). Weigh 25 mg of trialdehyde phloroglucinol (Tp) into a 20 mL centrifuge tube, add 12 mL of 1-butyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide salt ([BMIm]NTf2), and sonicate for 30 minutes to promote complete dissolution. This is recorded as solution B (approximately 10 mmol / L).
[0066] The modified Al2O3 tube was immersed in solution A for 10 minutes, then removed and dried in a 60 °C oven for 10 minutes. This immersion and drying process was repeated three times to ensure sufficient monomer adsorption on the Al2O3 tube surface. One end of the Al2O3 tube was then sealed, and 4 mL of solution A was added inside. The other end was then sealed, and the sealed tube was placed in solution B. After reacting at room temperature for 4 days, the membrane was removed and washed with anhydrous ethanol to remove residual ionic liquid and unreacted monomer from the membrane surface. Finally, the membrane was dried in a 60 °C vacuum oven to obtain the TpPa-1 composite membrane, as shown in the SEM image. Figure 2 As shown.
[0067] Example 3
[0068] The method for preparing the covalent organic framework composite membrane in this embodiment includes the following steps:
[0069] (1) Carrier pretreatment: An Al2O3 tube with an outer diameter of 12 nm and an inner diameter of 8 mm was sealed at both ends and placed in an open container. 200 mg of dopamine hydrochloride was weighed and dissolved in 100 mL of Tris-HCl buffer solution (0.01 M pH=8.5), and poured into the container. The container was then placed in a constant temperature water bath shaker to allow the dopamine to undergo a self-polymerization reaction at 25 °C. After 4 h of reaction, the Al2O3 tube was removed, and the surface was repeatedly rinsed with deionized water to remove unadhered particles. It was then soaked in water for later use.
[0070] (2) Preparation of TpBD composite membrane: Weigh 200 mg benzidine (BD) and 1 mL acetic acid into a 50 mL centrifuge tube, add 40 mL deionized water, and sonicate for 5 minutes to promote complete dissolution of monomers and catalysts. This is recorded as solution A (benzidine is approximately 26 mmol / L, and acetic acid is approximately 0.4 mol / L). Weigh 25 mg trialdehyde phloroglucinol (Tp) into a 20 mL centrifuge tube, add 12 mL 1-butyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide salt ([BMIm]NTf2), and sonicate for 30 minutes to promote complete dissolution. This is recorded as solution B (approximately 10 mmol / L).
[0071] The modified Al2O3 tube was placed in solution A and immersed for 10 minutes. Afterward, the Al2O3 tube was removed and dried in a 60 °C oven for 10 minutes. This immersion and drying process was repeated three times to ensure sufficient monomer adsorption onto the Al2O3 tube surface. Then, one end of the Al2O3 tube was sealed, and 4 mL of solution A was added inside. The other end was then sealed, and the sealed Al2O3 tube was placed in solution B. After reacting at room temperature for 4 days, the tube was removed and the composite membrane was washed with anhydrous ethanol to remove residual ionic liquid and unreacted monomer from the membrane surface. Finally, the membrane was dried in a 60 °C vacuum oven to obtain the TpBD composite membrane, the SEM image of which is shown below. Figure 3 As shown.
[0072] Example 4
[0073] The method for preparing the covalent organic framework composite membrane in this embodiment includes the following steps:
[0074] (1) Carrier pretreatment: An Al2O3 tube with an outer diameter of 12 nm and an inner diameter of 8 mm was sealed at both ends and placed in an open container. 200 mg of dopamine hydrochloride was weighed and dissolved in 100 mL of Tris-HCl buffer solution (0.01 M pH=8.5), and poured into the container. The container was then placed in a constant temperature water bath shaker to allow the dopamine to undergo a self-polymerization reaction at 25 °C. After 4 h of reaction, the Al2O3 tube was removed, and the surface was repeatedly rinsed with deionized water to remove unadhered particles. It was then soaked in water for later use.
[0075] (2) Preparation of TFB-TAPB composite membrane: Weigh 300 mg of 1,3,5-tris(4-aminophenyl)benzene (TAPB) and 1 mL of acetic acid into a 50 mL centrifuge tube, add 40 mL of deionized water, and sonicate for 5 minutes to promote complete dissolution of monomers and catalysts. This is recorded as solution A (TAPB is approximately 21 mmol / L, and acetic acid is approximately 0.4 mol / L). Weigh 20 mg of trimethylbenzaldehyde (TFB) into a 20 mL centrifuge tube, add 12 mL of 1-butyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide salt ([BMIm]NTf2), and sonicate for 30 minutes to promote complete dissolution. This is recorded as solution B (approximately 10 mmol / L).
[0076] The modified Al2O3 tube was immersed in solution A for 10 minutes, then removed and dried in a 60 °C oven for 10 minutes. This immersion and drying process was repeated three times to ensure sufficient monomer adsorption on the Al2O3 tube surface. One end of the Al2O3 tube was then sealed, and 4 mL of solution A was added inside. The other end was then sealed, and the sealed tube was placed in solution B. After reacting at room temperature for 4 days, the membrane was removed and washed with anhydrous ethanol to remove residual ionic liquid and unreacted monomer from the membrane surface. Finally, the membrane was dried in a 60 °C vacuum oven to obtain the TFB-TAPB composite membrane, as shown in the SEM image. Figure 4 As shown.
[0077] Example 5
[0078] The method for preparing the covalent organic framework composite membrane in this embodiment includes the following steps:
[0079] (1) Carrier pretreatment: An Al2O3 tube with an outer diameter of 12 nm and an inner diameter of 8 mm was sealed at both ends and placed in an open container. 200 mg of dopamine hydrochloride was weighed and dissolved in 100 mL of Tris-HCl buffer solution (0.01 M pH=8.5), and poured into the container. The container was then placed in a constant temperature water bath shaker to allow the dopamine to undergo a self-polymerization reaction at 25 °C. After 4 h of reaction, the Al2O3 tube was removed, and the surface was repeatedly rinsed with deionized water to remove unadhered particles. It was then soaked in water for later use.
[0080] (2) Preparation of TpBpy composite membrane: Weigh 100 mg of 5,5'-diamino-2,2'-bipyridine (Bpy) and 0.5 mL of acetic acid into a 50 mL centrifuge tube, add 40 mL of deionized water, and sonicate for 5 minutes to promote complete dissolution of monomers and catalysts. This is recorded as solution A (Bpy is approximately 13 mmol / L, and acetic acid is approximately 0.2 mol / L). Weigh 25 mg of trialdehyde phloroglucinol (Tp) into a 20 mL centrifuge tube, add 12 mL of 1-butyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide salt ([BMIm]NTf2), and sonicate for 30 minutes to promote complete dissolution. This is recorded as solution B (approximately 10 mmol / L).
[0081] The modified Al2O3 tube was immersed in solution A for 10 minutes, then removed and dried in a 60 °C oven for 10 minutes. This immersion and drying process was repeated three times to ensure sufficient monomer adsorption on the Al2O3 tube surface. One end of the Al2O3 tube was then sealed, and 4 mL of solution A was added inside. The other end was then sealed, and the sealed tube was placed in solution B. After reacting at room temperature for 4 days, the membrane was removed and washed with anhydrous ethanol to remove residual ionic liquid and unreacted monomer from the membrane surface. Finally, the membrane was dried in a 60 °C vacuum oven to obtain the TpBpy composite membrane, as shown in the SEM image. Figure 5 As shown.
[0082] Example 6
[0083] The method for preparing the covalent organic framework composite membrane in this embodiment includes the following steps:
[0084] (1) Carrier pretreatment: An Al2O3 tube with an outer diameter of 12 nm and an inner diameter of 8 mm was sealed at both ends and placed in an open container. 200 mg of dopamine hydrochloride was weighed and dissolved in 100 mL of Tris-HCl buffer solution (0.01 M pH=8.5), and poured into the container. The container was then placed in a constant temperature water bath shaker to allow the dopamine to undergo a self-polymerization reaction at 25 °C. After 4 h of reaction, the Al2O3 tube was removed, and the surface was repeatedly rinsed with deionized water to remove unadhered particles. It was then soaked in water for later use.
[0085] (2) Preparation of TpBpy composite membrane: Weigh 300 mg of 5,5'-diamino-2,2'-bipyridine (Bpy) and 1.5 mL of acetic acid into a 50 mL centrifuge tube, add 40 mL of deionized water, and sonicate for 5 minutes to promote complete dissolution of monomers and catalysts. This is recorded as solution A (Bpy is approximately 39 mmol / L, and acetic acid is approximately 0.6 mol / L). Weigh 25 mg of trialdehyde phloroglucinol (Tp) into a 20 mL centrifuge tube, add 12 mL of 1-butyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide salt ([BMIm]NTf2), and sonicate for 30 minutes to promote complete dissolution. This is recorded as solution B (approximately 10 mmol / L).
[0086] The modified Al2O3 tube was immersed in solution A for 10 minutes, then removed and dried in a 60 °C oven for 10 minutes. This immersion and drying process was repeated three times to ensure sufficient monomer adsorption on the Al2O3 tube surface. One end of the Al2O3 tube was then sealed, and 4 mL of solution A was added inside. The other end was then sealed, and the sealed tube was placed in solution B. After reacting at room temperature for 4 days, the membrane was removed and washed with anhydrous ethanol to remove residual ionic liquid and unreacted monomer from the membrane surface. Finally, the membrane was dried in a 60 °C vacuum oven to obtain the TpBpy composite membrane, as shown in the SEM image. Figure 6 As shown.
[0087] Comparative Example 1
[0088] The preparation method of the covalent organic framework composite membrane in this comparative example includes the following steps:
[0089] (1) Carrier pretreatment: An Al2O3 tube with an outer diameter of 12 nm and an inner diameter of 8 mm was sealed at both ends and placed in an open container. 200 mg of dopamine hydrochloride was weighed and dissolved in 100 mL of Tris-HCl buffer solution (0.01 M pH=8.5), and poured into the container. The container was then placed in a constant temperature water bath shaker to allow the dopamine to undergo a self-polymerization reaction at 25 °C. After 4 h of reaction, the Al2O3 tube was removed, and the surface was repeatedly rinsed with deionized water to remove unadhered particles. It was then soaked in water for later use.
[0090] (2) Preparation of TpBpy composite membrane: Weigh 200 mg of 5,5'-diamino-2,2'-bipyridine (Bpy) and 1 mL of acetic acid into a 50 mL centrifuge tube, add 40 mL of deionized water, and sonicate for 5 minutes to promote complete dissolution of monomer and catalyst. This is recorded as solution A. Weigh 25 mg of trialdehyde phloroglucinol (Tp) into a 20 mL centrifuge tube, add 12 mL of toluene, and sonicate for 30 minutes to promote complete dissolution. This is recorded as solution B.
[0091] The modified Al2O3 tube was immersed in solution A for 10 minutes, then removed and dried in a 60 °C oven for 10 minutes. This immersion and drying process was repeated three times to ensure sufficient monomer adsorption on the Al2O3 tube surface. One end of the Al2O3 tube was then sealed, and 4 mL of solution A was added inside. The other end was then sealed, and the sealed tube was placed in solution B. After reacting at room temperature for 4 days, the membrane was removed and washed with anhydrous ethanol to remove residual organic solvent and unreacted monomer. Finally, the membrane was dried in a 60 °C vacuum oven to obtain the TpBpy composite membrane, as shown in the SEM image. Figure 7 As shown.
[0092] Comparative Example 2
[0093] The preparation method of the covalent organic framework composite membrane in this comparative example includes the following steps:
[0094] (1) Carrier pretreatment: An Al2O3 tube with an outer diameter of 12 nm and an inner diameter of 8 mm was sealed at both ends and placed in an open container. 200 mg of dopamine hydrochloride was weighed and dissolved in 100 mL of Tris-HCl buffer solution (0.01 M pH=8.5), and poured into the container. The container was then placed in a constant temperature water bath shaker to allow the dopamine to undergo a self-polymerization reaction at 25 °C. After 4 h of reaction, the Al2O3 tube was removed, and the surface was repeatedly rinsed with deionized water to remove unadhered particles. It was then soaked in water for later use.
[0095] (2) Preparation of TpBpy composite membrane: Weigh 200 mg of 5,5'-diamino-2,2'-bipyridine (Bpy) and 1 mL of acetic acid into a 50 mL centrifuge tube, add 40 mL of deionized water, and sonicate for 5 minutes to promote complete dissolution of monomers and catalysts. This is recorded as solution A. Weigh 25 mg of trialdehyde phloroglucinol (Tp) into a 20 mL centrifuge tube, add 12 mL of 1-butyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide salt ([BMIm]NTf2), and sonicate for 30 minutes to promote complete dissolution. This is recorded as solution B.
[0096] The modified Al2O3 tube was immersed in solution A for 10 minutes, then removed and dried in a 60 °C oven for 10 minutes. This immersion and drying process was repeated three times to ensure sufficient monomer adsorption onto the Al2O3 tube surface. The Al2O3 tube was then sealed at both ends and placed in solution B. After reacting at room temperature for 4 days, the membrane was removed and washed with anhydrous ethanol to remove residual ionic liquid and unreacted monomer from the membrane surface. Finally, the membrane was dried in a 60 °C vacuum oven to obtain the TpBpy composite membrane, as shown in the SEM image below. Figure 8 As shown.
[0097] Comparative Example 3
[0098] The preparation method of the covalent organic framework composite membrane in this comparative example includes the following steps:
[0099] (1) Carrier pretreatment: An Al2O3 tube with an outer diameter of 12 nm and an inner diameter of 8 mm was sealed at both ends and placed in an open container. 200 mg of dopamine hydrochloride was weighed and dissolved in 100 mL of Tris-HCl buffer solution (0.01 M pH=8.5), and poured into the container. The container was then placed in a constant temperature water bath shaker to allow the dopamine to undergo a self-polymerization reaction at 25 °C. After 4 h of reaction, the Al2O3 tube was removed, and the surface was repeatedly rinsed with deionized water to remove unadhered particles. It was then soaked in water for later use.
[0100] (2) Preparation of TpBpy composite membrane: Weigh 50 mg of 5,5'-diamino-2,2'-bipyridine (Bpy) and 0.25 mL of acetic acid into a 50 mL centrifuge tube, add 4 mL of deionized water, and sonicate for 5 minutes to promote complete dissolution of monomers and catalysts. This is recorded as solution A (Bpy is approximately 26 mmol / L, and acetic acid is approximately 0.4 mol / L). Weigh 25 mg of trialdehyde phloroglucinol (Tp) into a 20 mL centrifuge tube, add 12 mL of 1-butyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide salt ([BMIm]NTf2), and sonicate for 30 minutes to promote complete dissolution. This is recorded as solution B (approximately 10 mmol / L).
[0101] One end of a modified Al2O3 tube was sealed, and solution A was added inside. The other end was then sealed, and the sealed Al2O3 tube was placed in solution B. After reacting at room temperature for 4 days, the tube was removed, and the composite membrane was washed with anhydrous ethanol to remove residual ionic liquid and unreacted monomers from the membrane surface. Finally, the membrane was dried in a vacuum oven at 60 °C to obtain the TpBpy composite membrane, as shown in the SEM image below. Figure 9 As shown.
[0102] Comparative Example 4
[0103] The preparation method of the covalent organic framework composite membrane in this comparative example includes the following steps:
[0104] (1) Carrier pretreatment: An Al2O3 tube with an outer diameter of 12 nm and an inner diameter of 8 mm was sealed at both ends and placed in an open container. 200 mg of dopamine hydrochloride was weighed and dissolved in 100 mL of Tris-HCl buffer solution (0.01 M pH=8.5), and poured into the container. The container was then placed in a constant temperature water bath shaker to allow the dopamine to undergo a self-polymerization reaction at 25 °C. After 4 h of reaction, the Al2O3 tube was removed, and the surface was repeatedly rinsed with deionized water to remove unadhered particles. It was then soaked in water for later use.
[0105] (2) Preparation of TpBpy composite membrane: Weigh 50 mg of 5,5'-diamino-2,2'-bipyridine (Bpy) and 0.2 mL of acetic acid into a 50 mL centrifuge tube, add 40 mL of deionized water, and sonicate for 5 minutes to promote complete dissolution of monomer and catalyst. This is recorded as solution A (Bpy is approximately 6.7 mmol / L, and acetic acid is approximately 0.08 mol / L). Weigh 25 mg of trialdehyde phloroglucinol (Tp) into a 20 mL centrifuge tube, add 12 mL of 1-butyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide salt ([BMIm]NTf2), and sonicate for 30 minutes to promote complete dissolution. This is recorded as solution B (approximately 10 mmol / L).
[0106] The modified Al2O3 tube was immersed in solution A for 10 minutes, then removed and dried in a 60 °C oven for 10 minutes. This immersion and drying process was repeated three times to ensure sufficient monomer adsorption on the Al2O3 tube surface. One end of the Al2O3 tube was then sealed, and 4 mL of solution A was added inside. The other end was then sealed, and the sealed tube was placed in solution B. After reacting at room temperature for 4 days, the membrane was removed and washed with anhydrous ethanol to remove residual ionic liquid and unreacted monomer from the membrane surface. Finally, the membrane was dried in a 60 °C vacuum oven to obtain the TpBpy composite membrane, as shown in the SEM image. Figure 10 As shown.
[0107] Nanofiltration separation performance: The COF membranes prepared in the examples and comparative examples were applied to organic solvent nanofiltration. An ethanol solution containing 100 ppm Evans blue was selected as the separation target. The Evans blue rejection rate and ethanol permeation flux of the COF membrane were measured at 6 bar. The results are shown in Table 1.
[0108] Table 1. Test results of nanofiltration separation performance
[0109]
[0110] As can be seen from Table 1, the COF composite membranes in the embodiments of the present invention all exhibit excellent retention effects and high ethanol permeation flux, indicating that the COF composite membranes have low mass transfer resistance and high processing efficiency.
[0111] In Comparative Example 1, the COF composite membrane obtained by mixing aldehyde monomers with an organic solution had a rejection rate of only 4.3% for Evans blue, far lower than the rejection rate in the embodiments of this invention. Although Comparative Example 2 showed a higher rejection rate, the ethanol permeation flux was low, indicating significant mass transfer resistance and low treatment efficiency. In Comparative Example 3, the Al2O3 tube was not pre-soaked in the aqueous solution, resulting in a slightly poorer rejection effect of the COF composite membrane, indicating certain defects in the COF membrane formed on the outer wall of the Al2O3 tube. In Comparative Example 4, the concentration of amino monomers in the aqueous solution was low, resulting in a poor rejection performance of the COF membrane, indicating that insufficient amino monomer dosage led to defects in the COF membrane formed on the outer wall of the Al2O3 tube, thus degrading its performance.
[0112] In summary, unlike commonly used in-situ growth methods and liquid-solid interfacial polymerization methods, this invention places the aqueous solution inside an Al2O3 tube and the ionic liquid solution outside the tube. Utilizing the difference in their physical properties (viscosity, permeability), a stable ionic liquid-water reaction interface is constructed on the outer wall of the Al2O3 tube, achieving interfacial polymerization to form a COF membrane. Furthermore, this invention utilizes the high viscosity of the ionic liquid to limit the diffusion rate of aldehyde monomers to the interface, thereby slowing down the interfacial polymerization reaction rate. This is beneficial for the ordered nucleation and growth of COF crystals, ultimately yielding a COF membrane with high crystallinity, few defects, and uniform density. The COF composite membrane obtained through this solution placement method and interfacial polymerization film formation exhibits excellent separation performance in nanofiltration and can be effectively applied in liquid separation, nanofiltration, and water treatment.
[0113] It will be apparent to those skilled in the art that this disclosure is not limited to the details of the exemplary embodiments described above, and that this disclosure can be implemented in other specific forms without departing from the spirit or essential characteristics of this disclosure. Therefore, the embodiments should be considered in all respects as exemplary and non-limiting, and the scope of this disclosure is defined by the appended claims rather than the foregoing description. Thus, it is intended that all variations falling within the meaning and scope of equivalents of the claims be included within this disclosure.
[0114] Furthermore, it should be understood that although this specification describes embodiments, not every embodiment contains only one independent technical solution. This narrative style is merely for clarity. Those skilled in the art should consider the specification as a whole, and the technical solutions in each embodiment can also be appropriately combined to form other embodiments that can be understood by those skilled in the art.
Claims
1. A method for preparing a covalent organic framework composite membrane, characterized in that, The preparation method includes the following steps: The amino monomer, catalyst, and deionized water are mixed to obtain an aqueous solution; An aldehyde monomer and an ionic liquid are mixed to obtain an ionic liquid phase solution. Take a tubular carrier, place it in an aqueous solution, and then remove and dry it to obtain a pretreated tubular carrier; Aqueous solution was filled into the pretreated tubular carrier, and both ends of the pretreated tubular carrier were sealed. A pretreated tubular support sealed at both ends is placed in an ionic liquid phase solution for reaction to obtain a covalent organic framework composite membrane.
2. The method for preparing the covalent organic framework composite membrane according to claim 1, characterized in that, The tubular carrier contains pores, and the pore size in the tubular carrier decreases sequentially from the inside to the outside; The pore size on the inner wall of the tubular carrier is 1μm-5μm, and the pore size on the outer wall is 50nm-100nm.
3. The method for preparing the covalent organic framework composite membrane according to claim 1, characterized in that, The tubular carrier is made of any one of alumina, zirconium oxide, titanium dioxide, and silicon dioxide; and / or, The tubular carrier has an outer diameter of 11mm-15mm and an inner diameter of 5mm-9mm.
4. The method for preparing the covalent organic framework composite membrane according to claim 1, characterized in that, The step of immersing the tubular carrier in an aqueous solution and then removing and drying it is repeated 2-3 times, with each immersion time being 5-10 minutes; and / or, The drying conditions after the tubular carrier is removed from the aqueous solution are: temperature 60℃-80℃, time 8min-12min.
5. The method for preparing a covalent organic framework composite membrane according to claim 1, characterized in that, The reaction temperature is 20℃-30℃, and the reaction time is 24h-120h; and / or, After the reaction was completed, the covalent organic framework composite membrane was washed alternately with ethanol and deionized water, and then vacuum dried at 60℃-80℃ for 3h-6h.
6. The method for preparing the covalent organic framework composite membrane according to claim 1, characterized in that, The amino monomer is one or more selected from p-phenylenediamine, benzidine, 5,5'-diamino-2,2'-bipyridine, and 1,3,5-tris(4-aminophenyl)benzene; and / or, The catalyst is one or both of acetic acid and p-toluenesulfonic acid; and / or, The aldehyde monomer is one or more selected from trialdehyde phloroglucinol, pyromellitic terephthalaldehyde, and 2,5-dihydroxyterephthalaldehyde; and / or... The ionic liquid is one or both of 1-butyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide salt and 1-butyl-3-methylimidazolium hexafluorophosphate.
7. The method for preparing a covalent organic framework composite membrane according to claim 1, characterized in that, In the aqueous solution, the concentration of the amino monomer is 13 mmol / L-40 mmol / L, and the concentration of the catalyst is 0.2 mol / L-0.6 mol / L; and / or, In the ionic liquid phase solution, the concentration of the aldehyde monomer is 5 mmol / L-20 mmol / L.
8. The method for preparing a covalent organic framework composite membrane according to claim 1, characterized in that, The outer surface of the tubular carrier is pre-modified with polydopamine, an amino-containing silane coupling agent, or polyethyleneimine.
9. A covalent organic framework composite membrane, characterized in that, The covalent organic framework composite membrane is prepared by the preparation method described in claim 1.
10. The application of the covalent organic framework composite membrane according to claim 9 in liquid separation, nanofiltration, and water treatment.