Preparation method of covalent organic framework film based on interlayer modification

Abstract

The invention discloses a preparation method of a covalent organic framework membrane based on interlayer modification. The preparation method comprises the steps of in-situ growth of a COFs layer, COFs modification, heat treatment, chemical crosslinking and solvent activation. According to the method, COFs are synthesized by only adopting an organic phase solution instead of adopting an aqueous phase solution, and acyl chloride or carboxylic acid is used for modifying the COFs to repair defects in a COFs layer and reduce the pore diameter of the COFs, so that the separation performance of the composite membrane is remarkably improved. The method is small in material consumption, simple in process, wide in application range, easy to amplify and realize industrial production, and has a good application prospect in the field of organic solvent system separation.

Description

Technical Field

[0001] The present invention belongs to the technical field of membrane separation, and particularly relates to a preparation method of a covalent organic framework membrane based on interlayer modification. Background Art

[0002] A large amount of organic solvents are used in the production of industries such as chemical engineering, petrochemical, and medicine, generating a large amount of waste organic solutions. Compared with traditional separation technologies, membrane separation technology has the advantages of being green, environmentally friendly, low-carbon, and sustainable. Solvent-resistant nanofiltration (OSN) technology is a pressure-driven membrane separation technology that is suitable for the separation and purification of organic solvents and is green and low-energy-consuming. Solvent-resistant nanofiltration membranes have good separation performance for small organic molecules with a molecular weight greater than 200 Dalton. Existing solvent-resistant nanofiltration membranes often have problems such as low flux and poor solvent resistance when applied to organic solution systems.

[0003] Two-dimensional covalent organic frameworks (COFs) are a new type of crystalline framework material composed of rigid molecular structural units, connected by strong in-layer covalent bonds and π-π interactions between layers, showing excellent solvent resistance. In addition, COF materials have regular channels, a high specific surface area, and a highly ordered periodic structure, making them ideal candidate materials for developing separation membranes.

[0004] However, compared with the preparation of polyamide membranes by traditional interfacial polymerization processes, the reaction time for generating COFs is generally longer, and the current research on solvent-resistant nanofiltration membranes based on COF materials is not yet mature. Although many researchers have achieved the morphological transformation of COF materials from powder to thin film through interfacial polymerization between water and oil phases, the growth time is long (greater than 48 h), and it is difficult to control the reaction process and the structure of solvent-resistant nanofiltration membranes. Moreover, due to the lack of obvious physical or chemical bonding between COFs and the substrate membrane, the separation of the skin layer from the substrate membrane is likely to occur, and the long-term operation stability is not guaranteed.

[0005] Synthesizing COF thin films by in-situ growth on the surface of the substrate membrane is a simple and fast method, and many researchers have used this method to prepare COF membranes for separating dye molecules in aqueous solution systems. However, due to the extremely short reaction time, which is much lower than the time required for preparing COF materials to reach thermodynamic equilibrium in general literature, it is difficult to form a continuous and ultrathin porous structure. Therefore, the membranes prepared by this method do not have an ideal retention performance for dye molecules in organic solvent systems such as ethanol. To sum up, the existing preparation methods of COF solvent-resistant nanofiltration membranes cannot prepare membranes with a short reaction time, good symbiosis with the substrate membrane, and high practicality. Summary of the Invention

[0006] In view of the deficiencies existing in the above-mentioned background art, the present invention provides a method for preparing a covalent organic framework membrane based on interlayer modification. Specifically, the present invention synthesizes COFs layers by in-situ growth, and modifies them with acyl chloride or carboxylic acid to repair the defects in the COFs layers and reduce the pore size of the COFs, thereby improving the rejection performance of the membrane. The membrane prepared by the present invention has an ultrasmooth separation layer and has good separation performance and stability in an organic solvent system. Moreover, the preparation method is simple and the preparation time is short, which is of great significance for the efficient utilization of resources and sustainable development.

[0007] The technical solution of the present invention is as follows.

[0008] The present invention discloses a method for preparing a covalent organic framework composite membrane based on interlayer modification, comprising the following steps: Step 1, in-situ growth of COFs layer: Prepare a solution of the first organic solvent of COFs monomer 1 and a solution of the second organic solvent of COFs monomer 2 respectively, then mix these two solutions in a certain proportion and bring them into full contact with the substrate membrane for a certain time, and then grow a layer of COFs layer in-situ on the surface of the substrate membrane, and then rinse the membrane surface with the first organic solvent; Step 2, COFs layer modification: Bring the COFs membrane obtained in Step 1 into full contact with a solution of the third organic solvent containing a polyvalent (including divalent, the same below) acyl chloride or polyvalent carboxylic acid compound for a certain time, and then remove the organic phase solution on the membrane surface; Step 3, heat treatment: Heat the COFs membrane obtained in Step 2 at a certain temperature for a certain time; Step 4, chemical crosslinking: Carry out overall chemical crosslinking of the COFs membrane obtained in Step 3 in a mixed solution of a crosslinking agent and a fourth organic solvent for a certain time, take it out, and rinse the membrane surface with the fourth organic solvent; Step 5, solvent activation: Activate the COFs membrane in Step 4 in a fifth organic solvent at a certain temperature for a certain time, take it out, and then rinse and displace it with a replacement solvent to obtain a modified covalent organic framework membrane.

[0009] Preferably, the COFs monomer 1 is an amine compound; preferably, the amine compound includes p-phenylenediamine, 2,5-dimethyl-p-phenylenediamine, benzidine, or a combination of any two or more of the above.

[0010] Preferably, the COFs monomer 2 is an aldehyde compound; preferably, the aldehyde compound includes phloroglucinol trialdehyde, 2,4-dihydroxy-1,3,5-benzenetricarboxaldehyde, 2-hydroxy-1,3,5-benzenetricarboxaldehyde, benzene-1,3,5-tricarboxaldehyde, or a combination of any two or more of the above.

[0011] Preferably, the polyvalent acyl chloride or polyvalent carboxylic acid compound includes trimesoyl chloride, trimesic acid or other compounds containing two or more acyl chloride groups or carboxyl groups, or a combination of any two or more of the above.

[0012] Preferably, the crosslinking agent includes ethylenediamine or hexamethylenediamine.

[0013] Preferably, the first organic solvent includes alkanes and other solvents capable of dissolving COFs monomer 1, or a combination thereof; more preferably, the first organic solvent is n-hexane.

[0014] Preferably, the second organic solvent includes alkanes and other solvents capable of dissolving COFs monomer 2, or a combination thereof; more preferably, the second organic solvent is n-hexane.

[0015] Preferably, the third organic solvent includes alkanes and other solvents capable of dissolving polyacyl chloride or polycarboxylic acid, or a combination thereof; more preferably, the third organic solvent is n-hexane.

[0016] Preferably, the fourth organic solvent includes isopropanol.

[0017] Preferably, the fifth organic solvent includes N,N-dimethylformamide (DMF), N-methylpyrrolidone (NMP), dimethylacetamide (DMAc), dimethyl sulfoxide (DMSO), tetrahydrofuran (THF), or a combination of any two or more of the above.

[0018] Preferably, the displacement solvent includes water, alcohol, or a mixture thereof.

[0019] Preferably, the concentration of COFs monomer 1 in the solution of the first organic solvent containing COFs monomer 1 is 0.02% - 0.15% (mass percentage concentration, the same hereinafter); more preferably, the concentration of COFs monomer 1 in the solution of the first organic solvent containing monomer 1 is 0.05% - 0.1%.

[0020] Preferably, the concentration of COFs monomer 2 in the solution of the second organic solvent containing COFs monomer 2 is 0.01% - 0.1%; more preferably, the concentration of COFs monomer 2 in the solution of the second organic solvent containing COFs monomer 2 is 0.01% - 0.5%.

[0021] Preferably, the heat treatment time is 0 - 10 min, and the heat treatment temperature is 40 - 120 °C; more preferably, the heat treatment time is 2 - 5 min, and the heat treatment temperature is 60 - 100 °C.

[0022] Preferably, the concentration of the solution of the third organic solvent containing polyacyl chloride or polycarboxylic acid compound is 0.1% - 0.4%; more preferably, the concentration of the solution of the third organic solvent containing polyacyl chloride or polycarboxylic acid compound is 0.1% - 0.2%.

[0023] The technical solution of the present invention has achieved remarkable technical effects and progress, and has substantial features.

[0024] One of the technical features of the present invention is that the COFs monomers are separately dissolved in organic solvents and then mixed for reaction. During the reaction process, a relatively complete COFs layer can be obtained in a short time using an extremely low monomer concentration. Moreover, this method can break through the limitation of the need for water-soluble monomers in traditional interfacial polymerization processes, enabling some water-insoluble COFs monomers to participate in the reaction, and the generated COFs layer is very smooth.

[0025] Another technical feature of the present invention is that a layer of COFs is synthesized by directly in-situ growing an organic phase solution containing COFs on the surface of the base membrane. This can enable the monomer solution to spread better on the membrane surface, making the distribution of COFs on the membrane surface more uniform, thereby improving the separation performance of the membrane.

[0026] The third technical feature of the present invention is that a step of contacting the base membrane with an aqueous solution containing a catalyst is omitted, reducing the process flow and saving the cost of the catalyst. At the same time, it avoids the problem that a high concentration of catalyst in the aqueous phase, such as acetic acid, may damage the base membrane and cause defects in the subsequent separation layer. Moreover, it also avoids the problem that the solvent resistance of the membrane is poor due to the possible formation of an interlayer after the base membrane contacts the aqueous solution containing the catalyst, resulting in poor bonding between the COFs layer and the base membrane.

[0027] The fourth technical feature of the present invention is to use polyfunctional acyl chloride monomers to repair the defects in the COFs layer and reduce the pore size of COFs, thereby greatly improving the rejection performance of the COFs membrane. The inherent pore structure of COFs itself can promote the rapid passage of solvents, greatly improving the permeation performance of the membrane.

[0028] The fifth technical feature of the present invention is not to use an aqueous solution but only an organic phase solution. This can enable the COFs monomers to directly contact the surface of the base membrane, so that some molecules of the COFs monomers react with the base membrane to form strong covalent bonds, improving the solvent resistance of the membrane. Moreover, the COFs layer and the base membrane are connected by covalent bonds through an overall cross-linking method, making the skin layer not easily fall off from the base membrane, enhancing the mechanical properties and solvent resistance of the membrane. At the same time, the monomer concentration required in the preparation process is low, the preparation method is simple, the applicable range is wide, and it is easy to scale up and realize industrial production.

[0029] Through the above technical innovations, the present invention has made remarkable technical progress and has excellent application prospects in the field of separation in organic solvent systems. Detailed implementation mode

[0030] The present invention will be further described below through specific examples.

[0031] Comparative Example 1

[0032] Dissolve 0.6 wt% of p-phenylenediamine (Pa), 1.0 wt% of acetic acid catalyst, and 0.005 wt% of cetyltrimethylammonium bromide surfactant in water to form an aqueous solution phase.

[0033] Dissolve phloroglucinol trialdehyde (Tp) in n-hexane organic solvent to form an organic phase monomer solution with a mass percentage concentration of 0.055%.

[0034] Pour 25 mL of the aqueous monomer solution onto the polyimide substrate film and immerse it for 30 s; remove the aqueous monomer solution on the surface of the substrate film, use a glass roller to evenly coat the remaining aqueous solution on the surface of the substrate film, and then dry it in air; pour 20 mL of the organic phase monomer solution onto the surface of the substrate film, after reacting for 40 s, remove the organic phase monomer solution; place the film in an oven at 60 °C for post-treatment for 5 min, and the subsequent chemical cross-linking and solvent activation steps are the same as those in the examples.

[0035] The rejection rate of the prepared membrane for fast green (809 Da) in a 100 mg / L fast green - ethanol solution is 96.2%, and the ethanol flux is 58.0 LMH.

[0036] Example 1

[0037] Dissolve 2,5-dimethyl-1,4-phenylenediamine (Pa-2) in n-hexane organic solvent to form an organic phase monomer solution with a mass percentage concentration of 0.08%.

[0038] Dissolve phloroglucinol trialdehyde (Tp) in n-hexane organic solvent to form an organic phase monomer solution with a mass percentage concentration of 0.02%.

[0039] Dissolve trimesoyl chloride (TMC) in n-hexane organic solvent to form an organic phase solution with a mass percentage concentration of 0.15%.

[0040] Dissolve hexamethylenediamine in isopropyl alcohol organic solvent to form a cross-linking agent solution with a mass percentage concentration of 10%.

[0041] Preparation of Interlayer-Modified Covalent Organic Framework Membrane: 1. In-situ growth of COFs layer: After mixing the Pa-2 monomer solution and the Tp monomer solution and fully contacting the surface of the polyimide-based membrane for 1 min, a layer of COFs is grown in-situ on the membrane surface, and then the membrane surface is rinsed with n-hexane; 2. COFs modification: After fully contacting the obtained COFs membrane with the TMC solution for 1 min, the organic phase solution on the membrane surface is removed; 3. Heat treatment: The obtained COFs membrane is taken out after being heated in an oven at 80 °C for 3 min; 4. Chemical crosslinking: The membrane after heat treatment is directly immersed in a crosslinking agent at 60 °C for 30 min and then taken out, and the membrane surface is rinsed with isopropanol; 5. Solvent activation: After the crosslinked membrane is activated with DMF at 80 °C for 30 min and then replaced in ethanol for 4 hours, the final interlayer-modified covalent organic framework membrane is obtained.

[0042] The prepared covalent organic framework membrane has a rejection rate of 97.0% for rhodamine B in a 100 mg / L rhodamine B (479 Da)-ethanol solution and an ethanol flux of 77.2 L / (m2·h) (abbreviated as LMH) at 25 °C and a transmembrane pressure difference of 1.0 MPa.

[0043] The above examples and comparative examples show that the performance of the membrane prepared by dissolving COFs monomers in organic solvents and modifying the generated COFs layer is greatly improved. The prepared solvent-resistant nanofiltration membrane has excellent performance, achieving remarkable technical effects and progress.

[0044] It should be noted that the above examples are only specific preferred embodiments of the present invention and do not constitute a limitation to the present invention. Any implementation manner that falls within the protection scope of the present invention constituted by the features of the claims of the present invention or equivalent features constitutes an infringement of the patent right of the present invention.

Claims

1. A preparation method of a COF film based on interlayer modification, characterized in that, It includes the following steps: Step 1, in-situ growth of a COFs layer: Prepare a solution of COFs monomer 1 in a first organic solvent and a solution of COFs monomer 2 in a second organic solvent respectively. Then mix these two solutions in a certain proportion and keep them in full contact with the substrate membrane for a certain time. After that, grow a layer of COFs on the surface of the substrate membrane in-situ, and then rinse the membrane surface with the first organic solvent. Step 2, COFs layer modification: Keep the COFs membrane obtained in Step 1 in full contact with a solution of a poly-acyl chloride (including di-acyl chloride, the same below) or poly-carboxylic acid compound in a third organic solvent for a certain time, and then remove the organic phase solution on the membrane surface. Step 3, heat treatment: Heat the COFs membrane obtained in Step 2 at a certain temperature for a certain time. Step 4, chemical cross-linking: Immerse the COFs membrane obtained in Step 3 in a mixed solution of a cross-linking agent and a fourth organic solvent for overall chemical cross-linking for a certain time, take it out, and rinse the membrane surface with the fourth organic solvent. Step 5, solvent activation: Immerse the COFs membrane obtained in Step 4 in a fifth organic solvent at a certain temperature for activation for a certain time, take it out, and then rinse and displace it with a displacement solvent to obtain a modified covalent organic framework membrane.

2. The preparation method of a COFs film based on interlayer modification according to claim 1, characterized in that, The COFs monomer 1 includes p-phenylenediamine, 2,5-dimethyl-p-phenylenediamine, benzidine, or a combination of any two or more of the above.

3. The preparation method of a COFs membrane based on interlayer modification according to claim 1, wherein The COFs monomer 2 includes phloroglucinol trialdehyde, 2,4-dihydroxy-1,3,5-benzenetricarbaldehyde, 2-hydroxy-1,3,5-benzenetricarbaldehyde, benzene-1,3,5-tricarbaldehyde, or a combination of any two or more of the above.

4. The preparation method of a COFs membrane based on interlayer modification according to claim 1, wherein, The concentration of COFs monomer 1 in the solution of the first organic solvent containing COFs monomer 1 is 0.02% - 0.15% (mass percentage concentration, the same below), and the concentration of COFs monomer 2 in the solution of the second organic solvent containing COFs monomer 2 is 0.01% - 0.1%.

5. The preparation method of a COFs membrane based on interlayer modification according to claim 1, characterized in that, The poly-acyl chloride or poly-carboxylic acid compound includes benzene-1,3,5-tricarbonyl chloride, benzene-1,3,5-tricarboxylic acid, other compounds containing two or more acyl chloride groups or carboxyl groups, or a combination of any two or more of the above.

6. The preparation method of a COFs membrane based on interlayer modification according to claim 1, characterized in that the cross-linking agent includes ethylenediamine or hexamethylenediamine; the first organic solvent includes alkanes and other solvents capable of dissolving monomer 1, or a combination of any two or more of the above; the second organic solvent includes alkanes and other solvents capable of dissolving monomer 2, or a combination of any two or more of the above; the third organic solvent includes alkanes and other solvents capable of dissolving poly-acyl chloride or poly-carboxylic acid compounds, or a combination of any two or more of the above; the fourth organic solvent includes isopropanol; the fifth organic solvent includes N,N-dimethylformamide (DMF), N-methylpyrrolidone (NMP), dimethylacetamide (DMAc), dimethyl sulfoxide (DMSO), tetrahydrofuran (THF), or a combination of any two or more of the above; the displacement solvent includes water, alcohol, or a mixture thereof.