Zwitterionic covalent organic framework nanofiltration membrane and method of making same

Abstract

The application belongs to the technical field of separation membrane materials, and discloses a zwitterionic covalent organic framework nanofiltration membrane and a preparation method thereof, which is prepared through the following steps: 1) dissolving aldehyde monomers, sulfonated amino monomers and pyridyl amino monomers in an organic solvent, adding a catalyst and an amine reagent, and obtaining a homogeneous reaction solution through ultrasonic; 2) taking a colloidal solution of the covalent organic framework as a casting solution, and coating the casting solution on the surface of a base film through a scraping method to prepare a nanofiltration membrane precursor; and 3) drying through a two-step drying process of a heating plate and an oven, and then immersing the membrane in water to obtain the zwitterionic covalent organic framework nanofiltration membrane. The zwitterionic covalent organic framework colloidal solution is synthesized through a single-phase method, the phase compatibility of the solvent and the substrate is utilized, and the construction of a surface selection layer is realized through the scraping method. The prepared zwitterionic covalent organic framework nanofiltration membrane has high water flux and dye rejection rate.

Description

Technical Field

[0001] This invention belongs to the technical field of separation membrane materials, and specifically relates to a zwitterionic covalent organic framework nanofiltration membrane and its preparation method. Background Technology

[0002] Water pollution poses a significant threat to human survival, with textile wastewater accounting for one-fifth of commercial wastewater. Due to the complexity of pollutant composition and potential hazards to organisms, effective treatment of textile wastewater is crucial. Nanofiltration (NF) is a pressure-driven membrane filtration process with pore sizes of 1-2 nm. Because the pore size of nanofiltration membranes closely matches the molecular size of dyes, it has attracted widespread attention in the field of textile wastewater treatment. In recent years, advanced nanofiltration membranes with precisely cut molecular weight (MWCO) have shown significant advantages in precision molecular sieving, enabling complex molecular separation for the sustainable molecular recovery and purification or high-value-added reuse of textile wastewater.

[0003] Covalent organic frameworks (COFs) possess the advantages of periodic pore structures and pre-designed functional groups, making them the preferred microporous framework materials for customizing highly selective nanofiltration membranes for precise molecular screening. Among reported COFs, imine-based COFs have been extensively studied due to their high crystallinity and reversible framework structure. However, most COFs prepared by solvothermal synthesis are unprocessable powders and cannot form well-structured membranes. For typical COF membranes linked by imine bonds, bottom-up strategies require interface-assisted synthesis, including the formation, aggregation, and crystal transformation of amorphous nanoparticles. In these processes, heterogeneous reversible reactions lead to time-consuming crystal formation of COF films and affect the control of COF film thickness. This can be avoided in homogeneous liquid-phase reaction systems. Colloidal COFs have attracted attention due to their good solution processability and the absence of the aggregation problem of COF powders.

[0004] This application proposes a simple, mild, and widely applicable method for preparing zwitterionic covalent organic framework nanofiltration membranes and the method thereof. Summary of the Invention

[0005] In view of the above-mentioned technical problems existing in the prior art, the purpose of this invention is to provide a simple, mild, and widely applicable zwitterionic covalently based framework nanofiltration membrane and its preparation method.

[0006] The method for preparing a zwitterionic covalently based nanofiltration membrane is characterized by comprising the following steps:

[0007] Step 1) Preparation of colloidal solution: Aldehyde monomer, sulfonated amino monomer and pyridinized amino monomer are dissolved in organic solvent. After complete dissolution, catalyst and quaternization reagent are added, and the mixture is sonicated for 5-30 min to obtain a reaction solution. The solution is then placed in an environment of 30℃ and allowed to stand for 1-3 days to obtain a covalent organic framework colloid.

[0008] Step 2) Using a colloidal solution of a covalent organic framework as the casting solution and a pre-fabricated ultrafiltration membrane as the base membrane, the height of the 100-400 μm doctor blade is adjusted, and the casting solution is coated onto the surface of the base membrane by a doctor blade to prepare a nanofiltration membrane precursor.

[0009] Step 3) Place the nanofiltration membrane precursor on a heating plate at a certain temperature for a certain period of time to pre-evaporate, and then transfer it to a constant temperature, humidity and windless environment to evaporate until dry, thus obtaining a zwitterionic covalent organic framework nanofiltration membrane.

[0010] In step 1), the reaction solution is prepared by using trialdehyde phloroglucinol as the aldehyde monomer, 2,5-diaminobenzenesulfonic acid as the sulfonated amino monomer, 2,5-diaminopyridine as the pyridinized amino monomer, formaldehyde solution as the quaternizing agent, trifluoroacetic acid solution as the catalyst, and dimethyl sulfoxide or N,N-dimethylformamide as the organic solvent.

[0011] In step 1), the ratio of the selected sulfonated amino monomer to the aldehyde monomer is 3:1 to 1:1, and the ratio of the sulfonated amino monomer to the pyridinized amino monomer is 1:0 to 0:1.

[0012] In step 1), the reaction solution is dispersed by ultrasound or pretreated for 3-20 minutes using a cell disruptor.

[0013] In step 2), the base membrane carrier can be a PES, PAN, PVDF or PSF ultrafiltration membrane.

[0014] In step 2), the height of the scraper used is 100μm to 400μm.

[0015] In step 3), the temperature of the pre-evaporation heating plate is 40-80℃, and the heating time is 1-10min.

[0016] The zwitterionic covalent organic framework nanofiltration membrane prepared according to the above method is divided into upper and lower parts, the upper part being a zwitterionic covalent organic framework and the lower part being the PES, PAN, PVDF or PSF ultrafiltration membrane.

[0017] Advantages and beneficial effects of the present invention:

[0018] This invention innovatively employs a single-phase synthesis system, benefiting from the ability of the charged nature of covalent organic frameworks to generate nanosheet colloids in the reaction solution. Using a simple blade coating method, covalent organic framework nanosheets can be coated onto the membrane surface. Due to the miscibility of ultrafiltration membranes in solvents, the covalent organic framework can effectively form a stable functional layer. The preparation method is simple, the reaction conditions are mild, and it has strong applicability. The prepared covalent organic framework nanofiltration membrane exhibits high water flux and excellent dye rejection. Attached Figure Description

[0019] Figure 1 This is a schematic diagram of the preparation process of the covalent organic framework nanofiltration membrane of the present invention;

[0020] Figure 2 This is an electron microscope image of the covalent organic framework nanosheets of Example 1 of the present invention;

[0021] Figure 3 These are scanning electron microscope and transmission electron microscope images of the membrane prepared in Example 1 of the present invention;

[0022] Figure 4 The infrared spectrum of the membrane prepared in Example 1 of this invention is shown. Detailed Implementation

[0023] The present invention will be further described below with reference to specific embodiments, but the scope of protection of the present invention is not limited thereto.

[0024] like Figure 1 As shown, the zwitterionic covalent organic framework nanofiltration membrane and its preparation method include the following steps:

[0025] 1) Preparation of colloidal solution: Aldehyde monomer, sulfonated amino monomer and pyridinized amino monomer are dissolved in organic solvent. After complete dissolution, catalyst and quaternization reagent are added, and the mixture is sonicated for 5-30 min to obtain a reaction solution. The solution is then placed in an environment of 30℃ and allowed to stand for 1-3 days to obtain a covalent organic framework colloid.

[0026] 2) Using a colloidal solution of a covalent organic framework as the casting solution and a pre-fabricated ultrafiltration membrane as the base membrane, the height of the 100-400 μm doctor blade is adjusted, and the casting solution is coated onto the surface of the base membrane by a doctor blade to prepare a nanofiltration membrane precursor.

[0027] 3) Place the nanofiltration membrane precursor on a heating plate at a certain temperature for a certain period of time to pre-evaporate, and then transfer it to a constant temperature, humidity and windless environment to evaporate until dry, thus obtaining a zwitterionic covalent organic framework nanofiltration membrane.

[0028] In step 1), the reaction solution is prepared by using trialdehyde phloroglucinol as the aldehyde monomer, 2,5-diaminobenzenesulfonic acid as the sulfonated amino monomer, 2,5-diaminopyridine as the pyridinized amino monomer, formaldehyde solution as the quaternizing agent, trifluoroacetic acid solution as the catalyst, and dimethyl sulfoxide or N,N-dimethylformamide as the organic solvent.

[0029] The zwitterionic covalent organic framework nanofiltration membrane and its preparation method are characterized in that, in step 1), the ratio of the selected amino monomer to the aldehyde monomer is 3:1 to 1:1, and the ratio of the sulfonated amino monomer to the pyridinized amino monomer is 1:0 to 0:1.

[0030] The zwitterionic covalent organic framework nanofiltration membrane and its preparation method are characterized in that, in step 1), the reaction solution is ultrasonically dispersed or pretreated using a cell disruptor for 3-20 minutes.

[0031] The zwitterionic covalent organic framework nanofiltration membrane and its preparation method are characterized in that, in step 2), the base membrane carrier can be a PES, PAN, PVDF or PSF ultrafiltration membrane.

[0032] The zwitterionic covalent organic framework nanofiltration membrane and its preparation method are characterized in that, in step 2), the scraper used is 100 μm to 400 μm.

[0033] The zwitterionic covalent organic framework nanofiltration membrane and its preparation method are characterized in that, in step 3, the temperature of the pre-evaporation heating plate is 40-80℃ and the heating time is 1-10min.

[0034] Example 1

[0035] 1) Preparation of colloidal solution: 0.2 mmol of trialdehyde phloroglucinol, 0.15 mmol of 2,5-diaminobenzenesulfonic acid, 0.15 mmol of 2,5-diaminopyridine, 100 μL of formaldehyde solution, and 100 μL of trifluoroacetic acid solution were dissolved in 50 mL of dimethyl sulfoxide and sonicated for 30 min to obtain a clear reaction solution. The reaction solution was placed in an environment of 30 °C and allowed to stand for 3 days to obtain a covalent organic framework colloid.

[0036] 2) Using a colloidal solution of a covalent organic framework as the casting solution and PAN as the base membrane, the casting solution was coated onto the surface of the base membrane by adjusting the height of a 100 μm doctor blade to prepare a nanofiltration membrane precursor.

[0037] 3) Place the nanofiltration membrane precursor on a 60°C heating plate for pre-evaporation for 2.5 min, and then transfer it to a 40°C windless environment to evaporate until dry, thus obtaining a zwitterionic covalent organic framework nanofiltration membrane.

[0038] Example 2

[0039] The preparation method of the covalent organic framework nanofiltration membrane in Example 2 is the same as that in Example 1, except that in the preparation of the colloidal solution in step 1) of Example 1, 0.15 mmol of 2,5-diaminobenzenesulfonic acid and 0.15 mmol of 2,5-diaminopyridine are replaced with 0.3 mmol of 2,5-diaminobenzenesulfonic acid, and the molar ratio of 2,5-diaminobenzenesulfonic acid to 2,5-diaminopyridine is 1:0. No catalyst or quaternizing agent is added. Other operations are the same as in Example 1, and the covalent organic framework nanofiltration membrane is finally obtained.

[0040] Example 3

[0041] The preparation method of the covalent organic framework nanofiltration membrane in Example 3 is the same as that in Example 1, except that in step 1) of Example 1, the preparation of the colloidal solution is carried out by replacing 0.15 mmol of 2,5-diaminobenzenesulfonic acid and 0.15 mmol of 2,5-diaminopyridine with 0.225 mmol of 2,5-diaminobenzenesulfonic acid and 0.075 mmol of 2,5-diaminopyridine, and the molar ratio of 2,5-diaminobenzenesulfonic acid to 2,5-diaminopyridine is 3:1. The other operations are the same as in Example 1, and the covalent organic framework nanofiltration membrane is finally obtained.

[0042] Example 4

[0043] The preparation method of the covalent organic framework nanofiltration membrane in Example 4 is the same as that in Example 1, except that in step 1) of Example 1, the preparation of the colloidal solution is carried out by replacing 0.15 mmol of 2,5-diaminobenzenesulfonic acid and 0.15 mmol of 2,5-diaminopyridine with 0.075 mmol of 2,5-diaminobenzenesulfonic acid and 0.225 mmol of 2,5-diaminopyridine, and the molar ratio of 2,5-diaminobenzenesulfonic acid to 2,5-diaminopyridine is 1:3. The other operations are the same as in Example 1, and the covalent organic framework nanofiltration membrane is finally obtained.

[0044] Example 5

[0045] The preparation method of the covalent organic framework nanofiltration membrane in Example 5 is the same as that in Example 1, except that in step 1) of Example 1, the preparation of the colloidal solution is carried out by replacing 0.15 mmol of 2,5-diaminobenzenesulfonic acid and 0.15 mmol of 2,5-diaminopyridine with 0.3 mmol of 2,5-diaminopyridine, and the molar ratio of 2,5-diaminobenzenesulfonic acid to 2,5-diaminopyridine is 0:1. The other operations are the same as in Example 1, and the covalent organic framework nanofiltration membrane is finally obtained.

[0046] Example 6

[0047] The preparation method of the covalent organic framework nanofiltration membrane in Example 6 is the same as that in Example 1, except that in the preparation of the colloidal solution in step 1) of Example 1, 50 mL of dimethyl sulfoxide is replaced with 50 mL of N,N-dimethylformamide. The other operations are the same as in Example 1, and the covalent organic framework nanofiltration membrane is finally obtained.

[0048] Example 7

[0049] The preparation method of the covalent organic framework nanofiltration membrane in Example 7 is the same as that in Example 1, except that in the preparation of colloidal solution in step 2) of Example 1, the PAN ultrafiltration membrane is replaced with a PES ultrafiltration membrane. The other operations are the same as in Example 1, and the covalent organic framework nanofiltration membrane is finally obtained.

[0050] Example 8

[0051] The preparation method of the covalent organic framework nanofiltration membrane in Example 8 is the same as that in Example 1, except that in the preparation of colloidal solution in step 2) of Example 1, the PAN ultrafiltration membrane is replaced with a PVDF ultrafiltration membrane. The other operations are the same as in Example 1, and the covalent organic framework nanofiltration membrane is finally obtained.

[0052] Example 9

[0053] The preparation method of the covalent organic framework nanofiltration membrane in Example 9 is the same as that in Example 1, except that in the preparation of colloidal solution in step 2) of Example 1, the PAN ultrafiltration membrane is replaced with a PSF ultrafiltration membrane. The other operations are the same as in Example 1, and the covalent organic framework nanofiltration membrane is finally obtained.

[0054] Example 10

[0055] The preparation method of the covalent organic framework nanofiltration membrane in Example 10 is the same as that in Example 1, except that in the preparation of colloidal solution in step 2) of Example 1, the 100 μm scraper is replaced with a 200 μm scraper. The other operations are the same as in Example 1, and the covalent organic framework nanofiltration membrane is finally obtained.

[0056] Example 11

[0057] The preparation method of the covalent organic framework nanofiltration membrane in Example 11 is the same as that in Example 1, except that in the preparation of colloidal solution in step 2) of Example 1, the 100 μm scraper is replaced with a 300 μm scraper. The other operations are the same as in Example 1, and the covalent organic framework nanofiltration membrane is finally obtained.

[0058] Example 12

[0059] The preparation method of the covalent organic framework nanofiltration membrane in Example 12 is the same as that in Example 1, except that in the preparation of colloidal solution in step 2) of Example 1, the 100 μm scraper is replaced with a 400 μm scraper. The other operations are the same as in Example 1, and the covalent organic framework nanofiltration membrane is finally obtained.

[0060] The zwitterionic covalently based framework nanofiltration membranes prepared by varying the ratio of sulfonated amino monomers to pyridinized amino monomers were tested for separation of 100 ppm dye aqueous solution at 25 °C and 0.45 MPa. The results are shown in Table 1.

[0061] Table 1: Performance comparison of zwitterionic covalent organic framework nanofiltration membranes prepared in Examples 1-5

[0062]

[0063] The separation results of zwitterionic covalently based framework nanofiltration membranes prepared by changing the solvent type for 100 ppm dye aqueous solution at 25℃ and 0.45 MPa are shown in Table 2.

[0064] Table 2: Performance comparison of zwitterionic covalent organic framework nanofiltration membranes prepared in Examples 1 and 6

[0065]

[0066]

[0067] The separation results of zwitterionic covalently based framework nanofiltration membranes prepared by changing the substrate type for 100 ppm dye aqueous solution at 25℃ and 0.45 MPa are shown in Table 2.

[0068] Table 3: Performance comparison of zwitterionic covalent organic framework nanofiltration membranes prepared in Examples 1 and 7-9

[0069]

[0070] The separation results of zwitterionic covalently based framework nanofiltration membranes prepared by varying the scraper height for 100 ppm dye aqueous solution at 25℃ and 0.45 MPa are shown in Table 4.

[0071] Table 4: Performance comparison of zwitterionic covalent organic framework nanofiltration membranes prepared in Examples 1 and 10-12

[0072]

[0073] Application testing experiments:

[0074] 1. Determination of flux of dye aqueous solution

[0075] The specific method is as follows: A 1cm diameter COF nanofiltration membrane is fixed in a dead-end filtration device. A 100ppm methylene blue aqueous solution is tested at 0.45MPa (N2) at room temperature. Pre-pressurize for 3 minutes, then collect 10mL of the supernatant. Record the time taken to collect 10mL of supernatant. Calculate the osmotic flux.

[0076] Application testing experiments:

[0077] 1. Determination of flux of dye aqueous solution

[0078] The specific method is as follows: A 1cm diameter COF nanofiltration membrane is fixed in a dead-end filtration device. A 100ppm dye aqueous solution is tested at 0.45MPa (N2) at room temperature. Pre-pressurize for 3 minutes, then collect 10mL of the supernatant. Record the time taken to collect 10mL of supernatant. Calculate the permeation flux.

[0079]

[0080] In the formula, V is the permeate flow rate; A is the effective area of ​​the membrane; t is the filtration time; and ΔP is the osmotic pressure.

[0081] 2. The method for determining the membrane rejection rate is as follows:

[0082] The specific method is as follows: A COF nanofiltration membrane with a diameter of 1 cm is fixed in a dead-end filtration device. A 100 ppm methylene blue aqueous solution is tested at 0.45 MPa (N2) at room temperature. Pre-pressure is applied for 3 minutes, and then 10 mL of the supernatant is collected. The absorbance of the collected supernatant and the original solution is measured using a UV absorption spectrometer to determine the concentrations of the original solution and the supernatant. The membrane rejection rate R is calculated using the following formula.

[0083]

[0084] In the formula, Cp and Cf represent the concentrations of the permeate and the original solution, respectively.

[0085] The membrane performance test results show that the membrane has high permeation flux and retention for small molecule solutes, which indicates that COF, as a porous material, has excellent separation performance and has important application value in the research of nanofiltration membranes.

[0086] The above description is only a preferred embodiment of the present invention and is not intended to limit the implementation of the present invention. Those skilled in the art can easily make corresponding modifications or alterations based on the main concept and spirit of the present invention. Therefore, the scope of protection of the present invention should be determined by the scope of protection claimed in the claims.

Claims

1. A method for preparing a zwitterionic covalent organic framework nanofiltration membrane, characterized in that... Includes the following steps: 1) Preparation of colloidal solution: Aldehyde monomer, sulfonated amino monomer and pyridinized amino monomer are dissolved in organic solvent. After complete dissolution, catalyst and quaternization reagent are added, and the mixture is sonicated for 5-30 min to obtain reaction solution. The solution is then placed in an environment of 30℃ and allowed to stand for 1-3 days to obtain a covalent organic framework colloid. 2) Using a colloidal solution of a covalent organic framework as the casting solution and a pre-fabricated ultrafiltration membrane as the base membrane carrier, the height of the doctor blade is adjusted, and the casting solution is coated onto the surface of the base membrane by a doctor blade to prepare a nanofiltration membrane precursor. 3) Place the nanofiltration membrane precursor on a heating plate at a certain temperature for a certain period of time to pre-evaporate, and then transfer it to a constant temperature, humidity and windless environment to evaporate until dry, thus obtaining a zwitterionic covalent organic framework nanofiltration membrane. In step 1), the reaction solution is prepared by using trialdehyde phloroglucinol as the aldehyde monomer, 2,5-diaminobenzenesulfonic acid as the sulfonated amino monomer, 2,5-diaminopyridine as the pyridinized amino monomer, formaldehyde solution as the quaternizing agent, trifluoroacetic acid solution as the catalyst, and dimethyl sulfoxide or N,N-dimethylformamide as the organic solvent.

2. The method for preparing a zwitterionic covalent organic framework nanofiltration membrane as described in claim 1, characterized in that in step 1), the molar ratio of the selected sulfonated amino monomer and aldehyde monomer is 3:1 to 1:1, and the molar ratio of the sulfonated amino monomer and pyridinized amino monomer is 1:

1.

3. The method for preparing a zwitterionic covalent organic framework nanofiltration membrane as described in claim 1, characterized in that in step 1), the reaction solution is ultrasonically dispersed or pretreated using a cell disruptor for 3-20 minutes.

4. The method for preparing a zwitterionic covalent organic framework nanofiltration membrane as described in claim 1, characterized in that in step 2), the base membrane carrier is a PES, PAN, PVDF or PSF ultrafiltration membrane.

5. The method for preparing a zwitterionic covalent organic framework nanofiltration membrane as described in claim 1, characterized in that in step 2), the height of the scraper used is 100 μm to 400 μm.

6. The method for preparing a zwitterionic covalent organic framework nanofiltration membrane as described in claim 1, characterized in that in step 3), the temperature of the pre-evaporation heating plate is 40-80℃ and the heating time is 1-10min.

7. A zwitterionic covalent organic framework nanofiltration membrane, characterized in that, Prepared by the method according to any one of claims 1-6.

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