Covalent organic framework nanofiltration membrane for molecular separation and preparation method thereof

Abstract

The invention belongs to the field of membrane separation, and particularly relates to a covalent organic framework nanofiltration membrane for molecular separation and a preparation method of the covalent organic framework nanofiltration membrane. The nanofiltration membrane takes colloidal COFs as a separation layer, and the colloidal COFs are loaded on the surface of a base membrane. The prepared colloid COFs nanofiltration membrane has excellent polymer affinity and stability, the porous colloid COFs are introduced into the base membrane, an additional water molecule transmission channel can be provided, and the method for preparing the nanofiltration membrane by utilizing the colloid COFs has obvious advantages.

Description

Technical Field

[0001] The present invention belongs to the field of membrane separation, and in particular relates to a covalent organic skeleton nanofiltration membrane for molecular separation and a preparation method thereof. Background Art

[0002] Covalent organic frameworks (COFs) are an emerging crystalline material with a well-defined structure, ordered pores, and adjustable pore size. They have good application prospects in a variety of applications such as storage, separation, and catalysis. The atomically smooth channels of COFs are conducive to the rapid transport of ions / molecules, and the long-range ordered structure gives the COF membrane a narrow channel size distribution, so it has significant nanofiltration performance. The channel size of COFs can be fine-tuned in the range of 0.5-5.0nm, which creates a high degree of freedom for membrane construction to separate target ions. In addition, COFs have rich monodisperse functional groups, making it easier to combine multiple physical and chemical interactions to improve the recognition ability of target ions / molecules.

[0003] To date, a large amount of work has been devoted to the preparation of free-standing or pure-phase COFs membranes. Current methods for constructing continuous COFs membranes mainly include in situ growth, back diffusion, and interfacial polymerization. However, most covalently linked COF powders are usually synthesized in the form of insoluble powders, which limits their application in functional materials and devices and hinders their further processing into large-area uniform membranes. Therefore, it is of great significance to develop membrane preparation methods that are compatible with COF structures and avoid tedious post-deposition processing. Summary of the Invention

[0004] The purpose of the present invention is to provide a covalent organic framework nanofiltration membrane for molecular separation, which can improve the processability of the COF composite membrane and better separate macromolecular pollutants in water.

[0005] In order to solve the above technical problems, the technical solutions adopted by the present invention are as follows:

[0006] A covalent organic framework nanofiltration membrane for molecular separation uses colloidal COFs as a separation layer and is specifically obtained by loading the colloidal COFs on the surface of a base membrane.

[0007] Furthermore, the colloidal COFs are boric acid colloidal COFs.

[0008] Preferably, COF-OEt colloid, COF-OAl colloid and COF-5 colloid can be selected.

[0009] Specifically, colloidal COFs can be prepared by a solvothermal method.

[0010] For example, the COF-OEt colloid preparation method is as follows: 3,5-diformylphenylboronic acid (10.0-30.0 mg, 0.056-0.168 mmol), 2,5-diethoxyterephthaloylhydrazide (16.2-48.6 mg, 0.056-0.168 mmol), n-butanol and o-dichlorobenzene (1 / 1, 1.5-4.5 mL) are added to a glass tube (10 mL); the glass tube is subjected to three freeze-pump-thaw cycles and vacuum-sealed; the mixed solution is reacted at 150° C. for 3-5 days to obtain a COF-OEt colloid.

[0011] The COF-OAl colloid was prepared as follows: 3,5-dicarboxyphenylboronic acid (10.0-30.0 mg, 0.056-0.168 mmol), 2,5-bis(allyloxy)terephthalic acid hydrazine (7.2-21.6 mg, 0.056-0.168 mmol), n-butanol, and o-dichlorobenzene (1 / 1, 1.5-4.5 mL) were added to a 10 mL glass tube. The tube was then subjected to three freeze-pump-thaw cycles and sealed under vacuum. The mixed solution was reacted at 120°C-150°C for 3-5 days to obtain a yellow COF-OAl colloid.

[0012] COF-5 colloid was prepared as follows: 1,4-Benzenebis(boronic acid) (41-123 mg, 0.25-0.75 mmol) and CH3OH (0.099-0.297 mL, 2.5-7.5 mmol) were mixed in a small glass vial. A dioxane / trimethylbenzene solution (4:1 v / v, 16-48 mL) of 2,3,6,7,10,11-hexahydroxytriphenyl (53-159 mg, 0.16-0.48 mmol) was then added. The mixture was then filtered through a 0.45 μm PTFE microfiltration membrane to remove any residual particulate matter. Additional CH3CN and / or a dioxane / trimethylbenzene blank solvent were added to the mixture. The mixture was reacted at 90°C for 1-2 days to yield COF-5 colloid.

[0013] During preparation, it is particularly necessary to directly coat the colloidal COFs in a colloidal state onto the base film.

[0014] No drying steps are required before application.

[0015] The present invention creatively utilizes colloidal COFs in a colloidal state for coating, rather than preparing a casting solution from the powder obtained after drying the colloidal COFs for coating. The effect obtained by the present invention is completely different.

[0016] The coating method is scraping, and the scraping times are 1-2 times; or the coating method is spin coating, and the spin coating times are 1-2 times; the coating method is brush coating, and the brush coating times are 2-3 times.

[0017] Preferably, after the colloidal COFs are coated on the base film, the thickness of the colloidal COF active layer prepared by the doctor blade method is 200-600 nm, the thickness of the colloidal COF active layer prepared by the spin coating method is 50-600 nm, and the thickness of the colloidal COF active layer prepared by the brush coating method is 200-600 nm.

[0018] Furthermore, after the colloidal COFs are coated on the base film, they are treated at 50-100° C. for 12-24 hours, and then unreacted modifiers and solvents in the colloidal COFs film are removed.

[0019] Specifically, the colloidal COFs membrane can be rinsed alternately with ethanol and deionized water to remove unreacted modifiers and solvents.

[0020] In the method for preparing colloidal COFs nanofiltration membrane of the present invention, different types of colloidal COFs do not need to be pretreated and can be directly loaded onto the surface of the base membrane by coating to prepare the colloidal COFs nanofiltration membrane for molecular separation.

[0021] The base membrane can be made of corrosion-resistant nylon or polytetrafluoroethylene (PTFE).

[0022] The present invention can construct colloidal COFs with a dual-pore structure through hydrazone bonds / hydroxyl bonds and boric acid polymerization. The colloidal COF suspension has multiple advantages over COF powder. Colloidal COFs are compatible with polymer materials, thereby promoting the formation of nanocomposite functional materials. Colloidal COFs have a highly ordered channel structure, and the channel pore size of its structure can be flexibly adjusted between a few angstroms and a few nanometers. Precise regulation can be achieved at the atomic level by simply changing the size of the building blocks. In addition, the colloidal COF suspension can be separated, washed and resuspended into a stable solvent formula, which makes it show great potential in applications such as thin film preparation.

[0023] The present invention first prepares colloidal COFs, and then uses a coating method to load them on the surface of a base membrane to construct a colloidal COFs nanofiltration membrane with stable structure and high selectivity. The obtained colloidal COFs nanofiltration membrane has a regular pore structure and a large specific surface area, which makes it have significant advantages in the fields of gas storage and separation, catalysis, sensing, etc. Since the colloidal COFs nanofiltration membrane is connected by covalent bonds, it has good chemical and thermal stability and can maintain structural and performance stability under a wide range of temperature and chemical environments. The structure and function of the colloidal COFs nanofiltration membrane can be designed and regulated by selecting different organic building blocks and connection methods. In addition, as a colloidal form of COFs, the colloidal COFs nanofiltration membrane has a particle size of nanometer or micrometer level and exhibits good dispersibility and stability, which is easy to process and apply, and also improves the utilization rate of the material. The pore size of the colloidal COF nanofiltration membrane is adjustable and can intercept large molecular pollutants of different molecular weights in water, which is of great significance in the field of molecular separation.

[0024] The present invention uses coating methods (spin coating, brush coating and blade coating) to prepare continuous colloidal COFs nanofiltration membrane films. By changing the reaction monomer structure and reaction parameters, the influence of monomer geometry and polymerization conditions on the molecular separation performance of the colloidal COFs nanofiltration membrane is explored.

[0025] Compared with the prior art, the present invention has the following advantages:

[0026] The colloidal COFs nanofiltration membrane prepared by the present invention has excellent polymer affinity and stability. The introduction of porous colloidal COFs on the base membrane can provide additional water molecule transmission channels. The use of colloidal COFs to prepare nanofiltration membranes has obvious advantages: (1) good processing performance, COF films can be directly prepared from COFs precursors; (2) the preparation process is simple and does not require further treatment and modification; (3) it has unique COF crystallinity, adjustable particle size, and excellent polymer affinity, which prevents the formation of non-selective defects and provides additional selective transport channels, which is of great significance for improving the processability of COF composite membranes and in molecular separation and other aspects; (4) structural flexibility, which can improve the interfacial adhesion between the separation layer and the underlying base membrane. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 This is a physical picture of the colloidal COFs prepared in Example 1;

[0028] Figure 2 The actual images of colloidal COFs obtained by different preparation methods are shown in Examples 1, 3, and 5 respectively;

[0029] Figure 3 TEM images of colloidal COFs suspensions were obtained for Example 1;

[0030] Figure 4 TEM elemental analysis images of the colloidal COFs suspension obtained for Example 1;

[0031] Figure 5 The SEM images of colloidal COFs nanofiltration membranes obtained by different preparation methods in Example 1, Example 3 and Example 5 are respectively shown. DETAILED DESCRIPTION

[0032] The following specific embodiments are used to illustrate the technical solution of the present invention, but the protection scope of the present invention is not limited thereto: Example 1

[0033] A covalent organic framework nanofiltration membrane for molecular separation, the preparation method of which comprises the following specific steps:

[0034] 1) 3,5-Diformylphenylboronic acid (10.0 mg, 0.056 mmol), 2,5-diethoxyterephthaloylhydrazide (16.2 mg, 0.056 mmol), n-butanol, and o-dichlorobenzene (1 / 1 volume ratio, total 1.5 mL) were added to a 10 mL glass tube. The tube was then subjected to three freeze-pump-thaw cycles and sealed under vacuum. The mixed solution was reacted at 150°C for 3-5 days to obtain a COF-OEt colloid.

[0035] 2) Fixing the PTFE base film on a glass plate, manually scraping the film with a scraper (thickness of 300 nm, scraper thickness), and loading the above-mentioned COF-OEt colloidal suspension on the surface of the PTFE base film by a scraping method, the scraping number of times is 1;

[0036] 3) The nanofiltration membrane was heat-treated in an oven at 80°C for 12 hours. The colloidal COFs membrane was then rinsed alternately with ethanol and deionized water to remove unreacted modifier and solvent, thereby obtaining a colloidal COFs composite nanofiltration membrane, designated as COF-OEt Colloid-1 membrane. The resulting membrane had a thickness of 200-400 nm.

[0037] Example 2

[0038] A method for preparing a colloidal covalent organic framework nanofiltration membrane for molecular separation comprises the following specific steps:

[0039] 1) Same as Example 1;

[0040] 2) Fixing the PTFE base film on a glass plate, manually scraping the film with a scraper, and loading the above-mentioned COF-OEt colloidal suspension on the surface of the base film by a scraping method, the scraping times are 2 times;

[0041] 3) The nanofiltration membrane was heat-treated in an oven at 80°C for 12 hours. The colloidal COFs membrane was rinsed alternately with ethanol and deionized water to remove unreacted modifier and solvent, thereby obtaining a colloidal COFs composite nanofiltration membrane, designated COF-OEt Colloid-2 membrane. The resulting membrane had a thickness of 400-600 nm.

[0042] Example 3

[0043] A method for preparing a colloidal covalent organic framework nanofiltration membrane for molecular separation comprises the following specific steps:

[0044] 1) Same as Example 1;

[0045] 2) The COF-OEt colloidal suspension was loaded on the surface of the PTFE base film by spin coating, and the spin coating number was 1;

[0046] 3) The nanofiltration membrane was heat-treated in an oven at 80°C for 12 hours. The colloidal COFs membrane was rinsed alternately with ethanol and deionized water to remove unreacted modifier and solvent, thereby obtaining a colloidal COFs composite nanofiltration membrane, labeled COF-OEt Colloid-3 membrane. The resulting membrane had a thickness of 50-300 nm.

[0047] Example 4

[0048] A method for preparing a colloidal covalent organic framework nanofiltration membrane for molecular separation comprises the following specific steps:

[0049] 1) Same as Example 1;

[0050] 2) The COF-OEt colloidal suspension was loaded onto the surface of the PTFE base film by spin coating, and the spin coating times were 2 times;

[0051] 3) The nanofiltration membrane was heat-treated in an oven at 80°C for 12 hours. The colloidal COFs membrane was rinsed alternately with ethanol and deionized water to remove unreacted modifier and solvent, thereby obtaining a colloidal COFs composite nanofiltration membrane, labeled COF-OEt Colloid-4 membrane. The resulting membrane had a thickness of 100-600 nm.

[0052] Example 5

[0053] A method for preparing a colloidal covalent organic framework nanofiltration membrane for molecular separation comprises the following specific steps:

[0054] 1) Same as Example 1;

[0055] 2) Fixing a PTFE base film on a glass plate, and applying the COF-OEt colloidal suspension on the surface of the base film using a brush, with the brushing times being 2 times;

[0056] 3) The nanofiltration membrane was heat-treated in an oven at 80°C for 12 hours. The colloidal COFs membrane was rinsed alternately with ethanol and deionized water to remove unreacted modifier and solvent, thereby obtaining a colloidal COFs composite nanofiltration membrane, labeled COF-OEt Colloid-5 membrane. The resulting membrane had a thickness of 200-400 nm.

[0057] Example 6

[0058] A method for preparing a colloidal covalent organic framework nanofiltration membrane for molecular separation comprises the following specific steps:

[0059] 1) Same as Example 1;

[0060] 2) Fixing a PTFE base film on a glass plate, and applying the COF-OEt colloidal suspension on the surface of the base film using a brush, with the brushing times being 3 times;

[0061] 3) The nanofiltration membrane was heat-treated in an oven at 80°C for 12 hours. The colloidal COFs membrane was rinsed alternately with ethanol and deionized water to remove unreacted modifier and solvent, thereby obtaining a colloidal COFs composite nanofiltration membrane, labeled COF-OEt Colloid-6 membrane. The resulting membrane had a thickness of 300-600 nm.

[0062] Example 7

[0063] A method for preparing a colloidal covalent organic framework nanofiltration membrane for molecular separation comprises the following specific steps:

[0064] 1) Same as Example 1;

[0065] 2) Fixing the PTFE base film on a glass plate, manually scraping the film with a scraper, and loading the above-mentioned COF-OEt colloidal suspension on the surface of the base film by a scraping method, the scraping number of times is 1;

[0066] 3) The nanofiltration membrane was heat-treated in an oven at 50°C for 12 hours. The colloidal COFs membrane was rinsed alternately with ethanol and deionized water to remove unreacted modifier and solvent, thereby obtaining a colloidal COFs composite nanofiltration membrane, designated COF-OEt Colloid-7 membrane. The resulting membrane had a thickness of 400-600 nm.

[0067] Example 8

[0068] A method for preparing a colloidal covalent organic framework nanofiltration membrane for molecular separation comprises the following specific steps:

[0069] 1) Same as Example 1;

[0070] 2) The COF-OEt colloidal suspension was loaded on the surface of the PTFE base film by spin coating, and the spin coating number was 1;

[0071] 3) The nanofiltration membrane was heat-treated in an oven at 50°C for 12 hours. The colloidal COFs membrane was rinsed alternately with ethanol and deionized water to remove unreacted modifier and solvent, thereby obtaining a colloidal COFs composite nanofiltration membrane, labeled COF-OEt Colloid-8 membrane. The resulting membrane had a thickness of 50-300 nm.

[0072] Example 9

[0073] A method for preparing a colloidal covalent organic framework nanofiltration membrane for molecular separation comprises the following specific steps:

[0074] 1) Same as Example 1;

[0075] 2) Fixing a PTFE base film on a glass plate, and applying the COF-OEt colloidal suspension on the surface of the base film using a brush, with the brushing times being 2 times;

[0076] 3) The nanofiltration membrane was heat-treated in an oven at 50°C for 12 hours. The colloidal COFs membrane was rinsed alternately with ethanol and deionized water to remove unreacted modifier and solvent, thereby obtaining a colloidal COFs composite nanofiltration membrane, labeled COF-OEt Colloid-9 membrane. The resulting membrane had a thickness of 200-400 nm.

[0077] Example 10

[0078] A method for preparing a colloidal covalent organic framework nanofiltration membrane for molecular separation comprises the following specific steps:

[0079] 1) 3,5-Dicarboxyphenylboronic acid (10.0 mg, 0.056 mmol), 2,5-bis(allyloxy)terephthalic acid hydrazine (7.2 mg, 0.056 mmol), n-butanol, and o-dichlorobenzene (1 / 1 volume ratio, 1.5 mL total) were added to a 10 mL glass tube. The tube was then subjected to three freeze-pump-thaw cycles and sealed under vacuum. The mixed solution was reacted at 120°C for 5 days to obtain a yellow COF-OAl colloid.

[0080] 2) Fixing the PTFE base film on a glass plate, manually scraping the film with a scraper (thickness of 300 nm), and loading the above-mentioned COF-OAl colloidal suspension on the surface of the PTFE base film by a scraping method, the scraping number of times is 1;

[0081] 3) The nanofiltration membrane was heat-treated in an oven at 80°C for 12 hours. The colloidal COFs membrane was rinsed alternately with ethanol and deionized water to remove unreacted modifier and solvent, thereby obtaining a colloidal COFs composite nanofiltration membrane, designated COF-OAl Colloid-1 membrane. The resulting membrane had a thickness of 200-400 nm.

[0082] Example 11

[0083] A method for preparing a colloidal covalent organic framework nanofiltration membrane for molecular separation comprises the following specific steps:

[0084] 1) Same as Example 10;

[0085] 2) The COF-OAl colloidal suspension is loaded on the surface of the PTFE base film by spin coating, and the spin coating is performed once;

[0086] 3) The nanofiltration membrane was heat-treated in an oven at 80°C for 12 hours. The colloidal COFs membrane was rinsed alternately with ethanol and deionized water to remove unreacted modifier and solvent, thereby obtaining a colloidal COFs composite nanofiltration membrane, labeled COF-OAl Colloid-2 membrane. The resulting membrane had a thickness of 50-300 nm.

[0087] Example 12

[0088] A method for preparing a colloidal covalent organic framework nanofiltration membrane for molecular separation comprises the following specific steps:

[0089] 1) Same as Example 10;

[0090] 2) Fixing a PTFE base film on a glass plate, and applying the COF-OAl colloidal suspension on the surface of the base film using a brush, with the brushing times being 2 times;

[0091] 3) The nanofiltration membrane was heat-treated in an oven at 80°C for 12 hours. The colloidal COFs membrane was rinsed alternately with ethanol and deionized water to remove unreacted modifier and solvent, thereby obtaining a colloidal COFs composite nanofiltration membrane, labeled COF-OAl Colloid-3 membrane. The resulting membrane had a thickness of 200-400 nm.

[0092] Example 13

[0093] A method for preparing a colloidal covalent organic framework nanofiltration membrane for molecular separation comprises the following specific steps:

[0094] 1) 1,4-Benzenebis(boronic acid) (41 mg, 0.25 mmol) and CH3OH (0.099 mL, 2.5 mmol) were mixed in a small glass vial, followed by the addition of a dioxane / trimethylbenzene solution (4:1 v / v, 16 mL) of 2,3,6,7,10,11-hexahydroxytriphenyl (53 mg, 0.16 mmol). The mixed solution was then filtered through a 0.45 μm PTFE microfiltration membrane to remove trace residual particles. Additional CH3CN and / or dioxane / trimethylbenzene blank solvent were added to the mixed solution. The mixed solution was reacted at 90°C for 2 days to obtain COF-5 colloid;

[0095] 2) Fixing the PTFE base film on a glass plate, manually scraping the film with a scraper (thickness of 300 nm), and loading the above-mentioned COF-5 colloidal suspension on the surface of the PTFE base film by a scraping method, the scraping number of times is 1;

[0096] 3) The nanofiltration membrane was heat-treated in an oven at 80°C for 12 hours. The colloidal COFs membrane was rinsed alternately with ethanol and deionized water to remove unreacted modifier and solvent, thereby obtaining a colloidal COFs composite nanofiltration membrane, designated COF-5 Colloid-1 membrane. The resulting membrane had a thickness of 200-400 nm.

[0097] Example 14

[0098] A method for preparing a colloidal covalent organic framework nanofiltration membrane for molecular separation comprises the following specific steps:

[0099] 1) Same as Example 13;

[0100] 2) The COF-5 colloidal suspension was loaded onto the surface of the PTFE base film by spin coating, with the spin coating number being 1;

[0101] 3) The nanofiltration membrane was heat-treated in an oven at 80°C for 12 hours. The colloidal COFs membrane was rinsed alternately with ethanol and deionized water to remove unreacted modifier and solvent, thereby obtaining a colloidal COFs composite nanofiltration membrane, designated COF-5 Colloid-2 membrane. The resulting membrane had a thickness of 50-300 nm.

[0102] Example 15

[0103] A method for preparing a colloidal covalent organic framework nanofiltration membrane for molecular separation comprises the following specific steps:

[0104] 1) Same as Example 13;

[0105] 2) Fixing the PTFE base film on a glass plate, and applying the COF-5 colloidal suspension on the surface of the base film using a brush, with the brushing times being 2 times;

[0106] 3) The nanofiltration membrane was heat-treated in an oven at 80°C for 12 hours. The colloidal COFs membrane was rinsed alternately with ethanol and deionized water to remove unreacted modifier and solvent, thereby obtaining a colloidal COFs composite nanofiltration membrane, designated COF-5 Colloid-3 membrane. The resulting membrane had a thickness of 200-400 nm.

[0107] Comparative Example 1

[0108] The preparation process of COF-OEt-1 membrane is as follows:

[0109] 1) 3,5-diformylphenylboronic acid (10.0 mg, 0.056 mmol), 2,5-diethoxyterephthaloylhydrazide (16.2 mg, 0.056 mmol), n-butanol and o-dichlorobenzene (volume ratio 1 / 1, total 1.5 mL) were added to a glass tube (10 mL). Subsequently, the glass tube was subjected to three freeze-pump-thaw cycles and vacuum-sealed. The mixed solution was reacted at 150°C for 3-5 days to obtain COF-OEt colloid. After cooling to room temperature, the colloid was collected and dried in a vacuum drying oven at 120°C for 4 hours to obtain a COF crude product. The synthesized COF was further washed 3 times with ethanol and methanol (1 / 1, 8 mL) to remove excess impurities to obtain COF-OEt powder;

[0110] 2) Fixing the PTFE base film on a glass plate, manually scraping the film with a scraper (thickness of 300 nm, scraper thickness), and loading the aqueous dispersion of COF-OEt powder obtained in step 1) above on the surface of the PTFE base film by a scraping method, the scraping number of times is 1;

[0111] 3) The nanofiltration membrane was heat-treated in an oven at 80° C. for 12 h; the COFs were alternately rinsed with ethanol and deionized water to remove unreacted modifier and solvent, thereby obtaining a COFs composite nanofiltration membrane, which was labeled as COF-OEt-1 membrane.

[0112] Comparative Example 2

[0113] The preparation process of COF-OEt-2 membrane is as follows:

[0114] 1) Same as Comparative Example 1;

[0115] 2) The COF-OEt powder-water dispersion is loaded on the surface of the PTFE base film by spin coating, and the spin coating is performed once;

[0116] 3) The nanofiltration membrane was heat-treated in an oven at 80°C for 12 hours. The COFs were alternately rinsed with ethanol and deionized water to remove unreacted modifier and solvent, thereby obtaining a COFs composite nanofiltration membrane, labeled as COF-OEt-2 membrane.

[0117] Comparative Example 3

[0118] The preparation process of COF-OEt-3 membrane is as follows:

[0119] 1) Same as Comparative Example 1;

[0120] 2) Fixing a PTFE base film on a glass plate, and applying the COF-OEt-water dispersion on the surface of the base film using a brush, the number of brushing times being 2 times;

[0121] 3) The nanofiltration membrane was heat-treated in an oven at 80°C for 12 hours. The COFs were rinsed alternately with ethanol and deionized water to remove unreacted modifier and solvent, thereby obtaining a COFs composite nanofiltration membrane, labeled as COF-OEt-3 membrane.

[0122] The permeability and wastewater dye retention rates of the colloidal COFs nanofiltration membranes prepared in Examples 1-15 and the COFs nanofiltration membranes prepared in Comparative Examples 1-3 were tested, and the data errors were all within a reasonable error range. The results are shown in Table 1. The tests were conducted in a cross-flow apparatus at room temperature and a pressure of 0.2 MPa.

[0123] Table 1

[0124]

[0125]

[0126] As shown in the table, the colloidal COFs nanofiltration membranes prepared by the three coating methods exhibit high permeability and dye retention. The permeability of the colloidal COFs prepared by the blade coating method was slightly higher than that of the spin coating and brush coating methods. This is likely due to the more uniform surface of the membranes prepared by the blade coating method due to the preparation technique and process parameters. For four macromolecular dyes (Eriochrome Black T, Brilliant Blue, Reactive Black 5, and Congo Red), the colloidal COFs nanofiltration membranes prepared by the three coating techniques achieved retention rates exceeding 95%, demonstrating excellent molecular retention. Furthermore, the performance of the COF-OEt colloidal nanofiltration membrane was superior to that of the COF-OAl and COF-5 colloidal membranes. This is likely due to the more uniform colloidal structure of the COF-OEt composite membrane and the larger pore size and specific surface area, resulting in a looser membrane surface. Drying conditions also affect the performance of the colloidal COFs composite membranes. Drying at higher temperatures results in a denser membrane surface and higher retention rates. After drying, the colloidal COFs exhibit a powdery structure, and the composite nanofiltration membrane prepared from them fails to form a complete active layer. The performance results of the nanofiltration membranes prepared in the comparative example show that compared to the colloidal COFs composite membranes, the COFs membranes have lower separation performance and are unable to effectively separate large molecular dyes from water.

Claims

1. A method for preparing a covalent organic framework nanofiltration membrane for molecular separation, characterized in that: Colloidal COFs are used as the separation layer and loaded on the surface of the basement membrane.

2. The method for preparing a covalent organic framework nanofiltration membrane for molecular separation according to claim 1, wherein: The colloidal COFs are boric acid colloidal COFs.

3. The method for preparing a covalent organic framework nanofiltration membrane for molecular separation according to claim 2, wherein: The colloidal COFs are COF-OEt colloid, COF-OAl colloid and COF-5 colloid.

4. The method for preparing a covalent organic framework nanofiltration membrane for molecular separation according to claim 3, wherein: Colloidal COFs were prepared by a solvothermal method.

5. The method for preparing a covalent organic framework nanofiltration membrane for molecular separation according to claim 1, wherein: The colloidal COFs in a colloidal state are directly coated on the base film.

6. The method for preparing a covalent organic framework nanofiltration membrane for molecular separation according to claim 5, wherein: The coating method is scraping, and the scraping times are 1-2 times; or the coating method is spin coating, and the spin coating times are 1-2 times; the coating method is brush coating, and the brush coating times are 2-3 times.

7. The method for preparing a covalent organic framework nanofiltration membrane for molecular separation according to claim 6, wherein: After the colloidal COFs were coated on the base film, the colloidal COF active layer with a thickness of 200-600 nm was prepared by blade coating, the colloidal COF active layer with a thickness of 50-600 nm was prepared by spin coating, and the colloidal COF active layer with a thickness of 200-600 nm was prepared by brush coating.

8. The method for preparing a covalent organic framework nanofiltration membrane for molecular separation according to claim 7, wherein: After the colloidal COFs are coated on the base film, they are treated at 50-100° C. for 12-24 hours, and then the unreacted modifier and solvent in the colloidal COFs film are removed.

9. A covalent organic framework nanofiltration membrane for molecular separation obtained by the preparation method according to any one of claims 1 to 8.

Images