Preparation method of solvent-resistant nanofiltration membrane with polydopamine / amino silicon dioxide middle layer

Abstract

The invention discloses a preparation method of a solvent-resistant nanofiltration membrane with a polydopamine / amino silicon dioxide middle layer, belongs to the technical field of membrane separation, and solves the technical problems of low flux and poor stability of the solvent-resistant nanofiltration membrane. The preparation method of the solvent-resistant nanofiltration membrane with the polydopamine / amino silicon dioxide middle layer comprises the following steps: preparing a polyetherimide-based membrane by a phase inversion method-crosslinking method; preparing amino silicon dioxide nanoparticles by adopting a sol-gel method; preparing a deposition solution containing dopamine, an oxidizing agent and amino silicon dioxide by using a Tris buffer solution; depositing the polydopamine / amino silicon dioxide intermediate layer on the upper surface of the polyetherimide base film; carrying out interfacial polymerization reaction of piperazine and trimesoyl chloride on the surface of the membrane deposited with the middle layer, and carrying out heat treatment to obtain a composite membrane; and immersing the composite membrane into an organic solvent for activation to obtain the solvent-resistant nanofiltration membrane with a polydopamine / amino silicon dioxide intermediate layer. The solvent-resistant nanofiltration membrane constructed by taking polyetherimide as a base membrane, polydopamine / amino silicon dioxide as a middle layer and polyamide as a separation layer has excellent flux and stability, and has a wide application prospect in the aspects of drug separation, organic solvent recovery and the like.

Description

Technical Field

[0001] The present invention relates to a method for preparing a solvent-resistant nanofiltration membrane with a polydopamine / amino silica interlayer, belonging to the technical field of membrane separation.

Background Art

[0002] Solvent-resistant nanofiltration (OSN) has been used in various industries, such as food, petrochemical, semiconductor, especially pharmaceutical. It not only aims to separate active pharmaceutical ingredients with molecular weights of 200 Da to 1000 Da from organic solvents, but also is used to recover valuable organic solvents in pharmaceutical and chemical syntheses. Solvent-resistant nanofiltration membranes mainly consist of an ultrafiltration substrate membrane and a separation layer. The polyamide separation layer formed by traditional interfacial polymerization processes is relatively thick, which will bring a large mass transfer resistance during application and is easily peeled off in organic solvents. Therefore, it is necessary to optimize the structure of the OSN membrane to improve the flux and stability.

[0003] Introducing an interlayer can have a significant impact on the structure (thickness and compactness) of the polyamide separation layer. Polydopamine (PDA), as a functional organic material, exhibits significant advantages in the preparation of the interlayer due to its unique biomimetic properties and chemical versatility. Liu et al. prepared a thin-film composite polyamide nanofiltration membrane with high permeability and selectivity by using sodium percarbonate-assisted dopamine oxidative self-polymerization to form a polydopamine interlayer. The hydrophilic PDA interlayer can regulate the interfacial polymerization process by controlling the diffusion and storage of amine monomers, and construct a uniform and defect-free separation layer as thin as 8 nm

Journal of Membrane Science, 2025, 718: 123686

[0004] Blending hydrophilic nanoparticles with polymers to construct an inorganic-organic interlayer can not only improve the hydrophilicity of the interlayer but also increase the free volume of the polymer, thereby providing additional solvent transport channels and further enhancing the flux. Among hydrophilic nanoparticles, silica has typical characteristics such as high stability and simple synthesis routes, and exhibits multiple advantages in the application of the interlayer. Wang et al. used polydopamine-coated silica microspheres as the interlayer to modify a poly(m-phenylene isophthalamide) substrate membrane, and then prepared a polyamide composite nanofiltration membrane through interfacial polymerization technology. Since both dopamine and silica contain a large number of hydroxyl groups, hydrogen bonding restricts the diffusion of aqueous monomers to the oil-water interface, so the surface of the nanofiltration membrane presents a nano-tubular Turing structure, and its pure water flux is 3 times that of traditional polyamide nanofiltration membranes

Separation and Purification Technology. 2022, 285: 120390

[0005] Therefore, based on the hydrophilicity and adhesion of polydopamine, this patent constructs a solvent-resistant nanofiltration membrane by introducing amino-functionalized silica nanoparticles into the polydopamine interlayer. Amino-functionalized silica can form regular packed pores in the interlayer, reduce the solvent transport resistance, and improve the flux. At the same time, the amino groups on its surface can not only participate in the interfacial polymerization reaction to inhibit the peeling of the separation layer but also enhance the binding strength with the substrate membrane through hydrogen bonding. In addition, the rigid inorganic framework can increase the elastic modulus of the interlayer, inhibit the swelling and deformation of the membrane in strongly polar solvents such as methanol, and enhance the stability.

Summary of the Invention

[0006] Aiming at the deficiencies of the prior art, the technical problem solved by the present invention is the low flux and poor stability of solvent-resistant nanofiltration membranes.

[0007] The technical solution of the present invention to solve the problems of low flux and poor stability of the solvent-resistant nanofiltration membrane is to provide a method for preparing a solvent-resistant nanofiltration membrane with a polydopamine / amino-functionalized silica interlayer, which is characterized by including the following steps:

[0008] a) Preparation of the substrate membrane: Pour 15 wt% - 19 wt% of polyetherimide particles into 100 mL - 120 mL of N,N-dimethylacetamide solvent, and at the same time add 2 wt% - 4 wt% of polyvinylpyrrolidone as a pore-forming agent; place the prepared solution in a 60°C constant-temperature magnetic stirrer and continuously stir for 8 h. After the solution is fully mixed and homogenized, stand for defoaming for 12 h; then, select a coating rod with a thickness of 120 μm - 250 μm, uniformly scrape the solution on the surface of the non-woven fabric, and quickly immerse it in a water bath. After phase inversion, immerse it in a 6 wt% - 12 wt% hexamethylenediamine / isopropanol solution for chemical cross-linking at 50°C - 80°C to obtain a polyetherimide substrate membrane;

[0009] b) Preparation of amino-functionalized silica nanoparticles: Add 50 mL of ethanol and 4 mL of deionized water into a round-bottom flask. After mixing evenly, add 0.1 mL to 2 mL of ammonia water. Fix the round-bottom flask above a magnetic stirrer and stir at a speed of 100 r / min to 150 r / min for 20 min. Subsequently, add 1 mL of tetraethyl orthosilicate into the round-bottom flask and stir for 5 h. Then add 0.1 mL to 1 mL of 3-aminopropyltriethoxysilane and stir for 12 h. After the stirring is completed, transfer the solution in the round-bottom flask to a 50 mL centrifuge tube, place it in a centrifuge, and centrifuge at a speed of 10000 r / min for 10 min. After centrifugation, pour out the upper-layer solution, add ethanol and ultrasonicate for 10 min, and then perform the centrifugation operation again. Repeat this process four times in total. Place the centrifuged solid in a drying oven and vacuum-dry it at room temperature (25 ± 1 °C) for 12 h to obtain amino-functionalized silica nanoparticles;

[0010] c) Preparation of the deposition solution: Prepare a Tris buffer solution with a molar concentration of 0.01 mol / L. Dissolve dopamine and an oxidant in the Tris buffer solution. The mass percentage of dopamine is 0.1 wt% to 2 wt%, and the mass ratio of the oxidant to dopamine is 1:10 to 10:1. Then add the amino-functionalized silica nanoparticles obtained in step b) with a mass percentage of 0.1 wt% to 10 wt%. After ultrasonication for 0.5 h, the deposition solution is obtained;

[0011] d) Preparation of the intermediate layer: Fix the base film obtained in step a) in a polytetrafluoroethylene frame. Then pour the deposition solution obtained in step c) onto the upper surface of the film for 0.5 h to 2.5 h, and keep the temperature of the deposition solution at 40 °C to 80 °C. After the deposition is completed, take out the film and ultrasonically clean it in deionized water for 10 min to obtain a deposited film;

[0012] e) Preparation of the polyamide layer: Fix the deposited film obtained in step d) in a polytetrafluoroethylene frame. Prepare an aqueous solution of piperazine with a mass percentage of 0.1 wt% to 1.5 wt%, pour it onto the surface of the film, let it stay for 5 min and then pour out the surface solution. Let it stand and dry at room temperature (25 ± 1 °C) for 10 min. Then prepare a solution of trimesoyl chloride / n-hexane with a mass percentage of 0.01 wt% to 0.5 wt%, pour it onto the surface of the film, let it stay for 3 min and then pour out the surface solution. Then place the film in an oven at 60 °C to 100 °C and dry it for 10 min to 60 min to obtain a composite film;

[0013] f) Activation treatment: Immerse the composite film obtained in e) in an organic solvent and soak it at 60 °C to 80 °C for 1 min to 30 min to obtain a solvent-resistant nanofiltration membrane with a polydopamine / amino-functionalized silica intermediate layer.

[0014] The oxidant in step c) of the present invention is one or more of ammonium persulfate, potassium persulfate, sodium periodate, potassium periodate, sodium perchlorate, and potassium perchlorate.

[0015] The organic solvent in step f) of the present invention is one or more of methanol, isopropanol, acetone, acetonitrile, tetrahydrofuran, dimethyl sulfoxide, dichloromethane, ethyl acetate, toluene, xylene, n-hexane, cyclohexane, dioxane, N,N-dimethylformamide, N-methylpyrrolidone, acetic acid, ethylene glycol, 1,4-dioxane, and propylene glycol methyl ether.

Specific Embodiments

[0016] Unless otherwise defined, the technical terms used in the following embodiments have the same meanings as commonly understood by those skilled in the art to which the present invention pertains. The experimental reagents used in the following embodiments are all conventional biochemical reagents unless otherwise specified; the experimental methods are all conventional methods unless otherwise specified.

[0017] The solvent-resistant nanofiltration membrane with a polydopamine / amino silica intermediate layer prepared by the present invention was measured for its permeation performance using a cross-flow filtration device, namely the flux and rejection rate of the membrane:

[0018] The flux and rejection rate jointly reflect the permeation performance of the membrane, J = V / (A×t), R = (1 - C p / C f )×100. In the formula, J is the flux of the membrane (L·m -2 ·h -1 ); R is the rejection rate of the membrane (%); V is the volume of the permeate on the permeate side (L); A is the effective area of the membrane (m 2 ); t is the permeation time (h); C f and C p are the concentrations of the solute components in the feed liquid and the permeate (mg / L), respectively.

[0019] The degree of swelling reflects the stability of the membrane, SD = (W wet / W dry -1)×100. In the formula, SD is the degree of swelling of the membrane (%); W dry and W wet are the masses of the membrane before and after immersion (mg), respectively.

[0020] The following introduces the specific embodiments of the present invention, but the present invention is not limited by the embodiments.

[0021] Example 1.

[0022] a) Preparation of the base membrane: Pour polyetherimide particles with a mass percentage of 17 wt% into 100 mL of N,N-dimethylacetamide solvent, and simultaneously add polyvinylpyrrolidone with a mass percentage of 2 wt% as a pore-forming agent; place the prepared solution in a 60°C constant-temperature magnetic stirrer and continuously stir for 8 h. After the solution is fully mixed and homogenized, let it stand for defoaming for 12 h; subsequently, select a coating rod with a thickness of 120 μm, uniformly scrape the solution on the surface of the non-woven fabric, and quickly immerse it in a water bath. After phase inversion, immerse it in a 10 wt% hexanediamine / isopropanol solution at 60°C for chemical cross-linking to obtain a polyetherimide base membrane;

[0023] b) Preparation of amino-functionalized silica nanoparticles: Add 50 mL of ethanol and 4 mL of deionized water to a round-bottom flask, mix them evenly and then add 0.75 mL of ammonia water; fix the round-bottom flask above a magnetic stirrer and stir at a speed of 100 r / min for 20 min: Subsequently, add 1 mL of tetraethyl orthosilicate to the round-bottom flask, stir for 5 h, and then add 1 mL of 3-aminopropyltriethoxysilane and stir for 12 h; after stirring is completed, transfer the solution in the round-bottom flask to a 50 mL centrifuge tube, place it in a centrifuge, and centrifuge at a speed of 10000 r / min for 10 min; after centrifugation, pour out the upper layer solution, add ethanol and ultrasonicate for 10 min, and perform the centrifugation operation again, repeating a total of four times; place the centrifuged solid in an oven and vacuum dry it at room temperature (25 ± 1°C) for 12 h to obtain amino-functionalized silica nanoparticles with a diameter of about 20 nm;

[0024] c) Preparation of the deposition solution: Prepare a Tris buffer solution with a molar concentration of 0.01 mol / L, dissolve dopamine and ammonium persulfate in the Tris buffer solution, the mass percentage of dopamine is 0.2 wt%, the mass ratio of ammonium persulfate to dopamine is 1:1, and then add the amino-functionalized silica nanoparticles obtained in step b) with a mass percentage of 0.1 wt%, and ultrasonicate for 0.5 h to obtain the deposition solution:

[0025] d) Preparation of the intermediate layer: Fix the base membrane obtained in step a) in a polytetrafluoroethylene frame, then pour the deposition solution obtained in step c) on the upper surface of the membrane for 0.5 h, keep the temperature of the deposition solution at 60°C, take out the membrane after deposition, and ultrasonically clean it in deionized water for 10 min to obtain a deposited membrane;

[0026] e) Preparation of the polyamide layer: Fix the deposited film obtained in step d) in a polytetrafluoroethylene frame. Prepare an aqueous piperazine solution with a mass percentage of 0.8 wt%, pour it on the film surface, let it stand for 5 min, then pour off the surface solution, and leave it to dry statically at room temperature (25 ± 1 °C) for 10 min. Then prepare a solution of trimesoyl chloride / n - hexane with a mass percentage of 0.2 wt%, pour it on the film surface, let it stand for 3 min, then pour off the surface solution, and then put the film into an oven at 80 °C and dry it for 10 min to obtain a composite film;

[0027] f) Activation treatment: Immerse the composite film obtained in e) in n - hexane and soak it at 80 °C for 5 min to obtain a solvent - resistant nanofiltration membrane with a polydopamine / aminosilica intermediate layer;

[0028] g) Test the permeation performance of the solvent - resistant nanofiltration membrane with a polydopamine / aminosilica intermediate layer obtained in step f) on a 50 mg / L drug / ethanol solution at room temperature (25 ± 1 °C) and an operating pressure of 0.5 MPa using a cross - flow filtration device. The results show that the flux of the membrane for ethanol is 16 L·m -2· h -1 , and the rejection rates for rifampicin, oxytetracycline, vitamin B1, and vitamin B12 are 99%, 88%, 89%, and 99% respectively; the swelling degrees after soaking in methanol, acetone, and toluene for 24 h are 1%, 2%, and 1% respectively.

[0029] Example 2.

[0030] a) Preparation of the base membrane: Pour polyetherimide particles with a mass percentage of 17 wt% into 100 mL of N,N - dimethylacetamide solvent, and at the same time add polyvinylpyrrolidone with a mass percentage of 2 wt% as a pore - forming agent; place the prepared solution in a 60 °C constant - temperature magnetic stirrer and continuously stir for 8 h. After the solution is fully mixed and homogenized, let it stand for defoaming for 12 h; then, select a coating rod with a thickness of 120 μm, uniformly scrape - coat the solution on the surface of the non - woven fabric, and quickly immerse it in a water bath. After phase inversion, immerse it in a 10 wt% hexanediamine / isopropanol solution at 60 °C for chemical cross - linking to obtain a polyetherimide base membrane;

[0031] b) Preparation of amino-functionalized silica nanoparticles: Add 50 mL of ethanol and 4 mL of deionized water to a round-bottom flask. After mixing evenly, add 1 mL of ammonia water. Fix the round-bottom flask above a magnetic stirrer and stir at a speed of 100 r / min for 20 min. Subsequently, add 1 mL of tetraethyl orthosilicate to the round-bottom flask and stir for 5 h. Then add 1 mL of 3-aminopropyltriethoxysilane and stir for 12 h. After stirring is completed, transfer the solution in the round-bottom flask to a 50 mL centrifuge tube, place it in a centrifuge, and centrifuge at a speed of 10,000 r / min for 10 min. After centrifugation, pour out the upper layer solution, add ethanol and ultrasonicate for 10 min, and then perform the centrifugation operation again. Repeat this process four times in total. Place the centrifuged solid in a drying oven and vacuum dry it at room temperature (25 ± 1 °C) for 12 h to obtain amino-functionalized silica nanoparticles with a diameter of approximately 40 nm;

[0032] c) Preparation of the deposition solution: Prepare a Tris buffer solution with a molar concentration of 0.01 mol / L. Dissolve dopamine and sodium periodate in the Tris buffer solution. The mass percentage of dopamine is 0.2 wt%, and the mass ratio of sodium periodate to dopamine is 1:1. Then add the amino-functionalized silica nanoparticles obtained in step b) with a mass percentage of 0.2 wt%. After ultrasonication for 0.5 h, the deposition solution is obtained;

[0033] d) Preparation of the intermediate layer: Fix the base film obtained in step a) in a polytetrafluoroethylene frame, and then pour the deposition solution obtained in step c) onto the upper surface of the film for 1 h. Keep the temperature of the deposition solution at 80 °C. After deposition, take out the film and ultrasonically clean it in deionized water for 10 min to obtain a deposited film;

[0034] e) Preparation of the polyamide layer: Fix the deposited film obtained in step d) in a polytetrafluoroethylene frame. Prepare an aqueous solution of piperazine with a mass percentage of 0.6 wt%, pour it onto the surface of the film, let it stand for 5 min, and then pour out the surface solution. Let it stand and dry at room temperature (25 ± 1 °C) for 10 min. Then prepare a solution of trimesoyl chloride / n-hexane with a mass percentage of 0.1 wt%, pour it onto the surface of the film, let it stand for 3 min, and then pour out the surface solution. Then place the film in an oven at 80 °C and dry it for 20 min to obtain a composite film;

[0035] f) Activation treatment: Immerse the composite film obtained in e) in N,N-dimethylformamide and soak it at 60 °C for 10 min to obtain a solvent-resistant nanofiltration membrane with a polydopamine / amino-functionalized silica intermediate layer;

[0036] g) Test the permeation performance of the solvent-resistant nanofiltration membrane with a polydopamine / amino-functionalized silica intermediate layer obtained in step f) for a 50 mg / L drug / ethanol solution at room temperature (25 ± 1 °C) and an operating pressure of 0.5 MPa using a cross-flow filtration device. The results show that the flux of ethanol through the membrane is 19 L·m-2 ·h -1 The rejection rates for rifampicin, oxytetracycline, vitamin B1, and vitamin B12 were 95%, 79%, 88%, and 96%, respectively; the swelling degrees after soaking in methanol, acetone, and toluene for 24 h were 1%, 3%, and 1%, respectively.

[0037] Example 3.

[0038] a) Preparation of the base membrane: Pour polyetherimide particles with a mass percentage of 18 wt% into 100 mL of N,N-dimethylacetamide solvent, and simultaneously add polyvinylpyrrolidone with a mass percentage of 4 wt% as a pore-forming agent; place the prepared solution in a 60 °C constant-temperature magnetic stirrer and continuously stir for 8 h. After the solution is fully mixed and uniform, let it stand for defoaming for 12 h; subsequently, select a coating rod with a thickness of 120 μm, uniformly scrape the solution on the surface of the non-woven fabric, and quickly immerse it in a water bath. After phase inversion, immerse it in a 6 wt% hexanediamine / isopropanol solution at 60 °C for chemical cross-linking to obtain a polyetherimide base membrane;

[0039] b) Preparation of amino-functionalized silica nanoparticles: Add 50 mL of ethanol and 4 mL of deionized water to a round-bottom flask, mix well, and then add 1.25 mL of ammonia water; fix the round-bottom flask above a magnetic stirrer and stir at a speed of 100 r / min for 20 min; subsequently, add 1 mL of tetraethyl orthosilicate to the round-bottom flask, stir for 5 h, and then add 1 mL of 3-aminopropyltriethoxysilane and stir for 12 h; after stirring is completed, transfer the solution in the round-bottom flask to a 50 mL centrifuge tube, place it in a centrifuge, and centrifuge at a speed of 10,000 r / min for 10 min; after centrifugation, pour out the upper layer solution, add ethanol and ultrasonicate for 10 min, and perform the centrifugation operation again, repeating a total of four times; place the centrifuged solid in an oven and vacuum dry it at room temperature (25 ± 1 °C) for 12 h to obtain amino-functionalized silica nanoparticles with a diameter of approximately 60 nm;

[0040] c) Preparation of the deposition solution: Prepare a Tris buffer solution with a molar concentration of 0.01 mol / L, dissolve dopamine and potassium persulfate in the Tris buffer solution, the mass percentage of dopamine is 0.2 wt%, the mass ratio of potassium persulfate to dopamine is 1:1, and then add the amino-functionalized silica nanoparticles obtained in step b) with a mass percentage of 0.3 wt%. After ultrasonication for 0.5 h, the deposition solution is obtained;

[0041] d) Preparation of the intermediate layer: Fix the base membrane obtained in step a) in a polytetrafluoroethylene frame, then pour the deposition solution obtained in step c) on the upper surface of the membrane for 1.5 h, keep the temperature of the deposition solution at 60 °C, after deposition, take out the membrane and ultrasonically clean it in deionized water for 10 min to obtain a deposited membrane;

[0042] e) Preparation of the polyamide layer: Fix the deposited film obtained in step d) in a polytetrafluoroethylene frame, prepare an aqueous piperazine solution with a mass percentage of 0.8 wt%, pour it on the surface of the film, pour off the surface solution after 5 min, and leave it to stand and dry at room temperature (25 ± 1 °C) for 10 min. Then prepare a solution of trimesoyl chloride / n - hexane with a mass percentage of 0.15 wt%, pour it on the surface of the film, pour off the surface solution after 3 min, and then put the film into an oven at 80 °C and dry it for 15 min to obtain a composite film;

[0043] f) Activation treatment: Immerse the composite film obtained in e) in isopropanol and soak it at 70 °C for 15 min to obtain a solvent - resistant nanofiltration membrane with a polydopamine / aminosilica intermediate layer;

[0044] g) Test the permeation performance of the solvent - resistant nanofiltration membrane with a polydopamine / aminosilica intermediate layer obtained in step f) on a 50 mg / L drug / ethanol solution at room temperature (25 ± 1 °C) and an operating pressure of 0.5 MPa using a cross - flow filtration device. The results show that the flux of ethanol through the membrane is 23 L·m -2· h -1 , and the rejection rates for rifampicin, oxytetracycline, vitamin B1, and vitamin B12 are 96%, 86%, 90%, and 97% respectively; the swelling degrees after soaking in methanol, acetone, and toluene for 24 h are 2%, 3%, and 2% respectively.

[0045] Example 4.

[0046] a) Preparation of the base membrane: Pour polyetherimide particles with a mass percentage of 18 wt% into 100 mL of N,N - dimethylacetamide solvent, and simultaneously add polyvinylpyrrolidone with a mass percentage of 4 wt% as a pore - forming agent; place the prepared solution in a 60 °C constant - temperature magnetic stirrer and continuously stir for 8 h. After the solution is fully mixed and homogenized, leave it to stand and defoam for 12 h; then, select a coating rod with a thickness of 250 μm, uniformly scrape - coat the solution on the surface of the non - woven fabric, and quickly immerse it in a water bath. After phase inversion, immerse it in a 12 wt% hexanediamine / isopropanol solution at 80 °C for chemical cross - linking to obtain a polyetherimide base membrane;

[0047] b) Preparation of amino-functionalized silica nanoparticles: Add 50 mL of ethanol and 4 mL of deionized water to a round-bottom flask. After mixing evenly, add 1.5 mL of ammonia water. Fix the round-bottom flask above a magnetic stirrer and stir at a speed of 100 r / min for 20 min. Subsequently, add 1 mL of tetraethyl orthosilicate to the round-bottom flask, stir for 5 h, then add 1 mL of 3-aminopropyltriethoxysilane, and stir for 12 h. After stirring is completed, transfer the solution in the round-bottom flask to a 50 mL centrifuge tube, place it in a centrifuge, and centrifuge at a speed of 10,000 r / min for 10 min. After centrifugation, pour out the upper layer solution, add ethanol and ultrasonicate for 10 min, and then perform the centrifugation operation again, repeating a total of four times. Place the centrifuged solid in an oven and vacuum dry it at room temperature (25 ± 1 °C) for 12 h to obtain amino-functionalized silica nanoparticles with a diameter of approximately 100 nm;

[0048] c) Preparation of the deposition solution: Prepare a Tris buffer solution with a molar concentration of 0.01 mol / L. Dissolve dopamine and ammonium persulfate in the Tris buffer solution. The mass percentage of dopamine is 0.2 wt%, and the mass ratio of ammonium persulfate to dopamine is 1:1. Then add the amino-functionalized silica nanoparticles obtained in step b) with a mass percentage of 0.5 wt%, and ultrasonicate for 0.5 h to obtain the deposition solution;

[0049] d) Preparation of the intermediate layer: Fix the base film obtained in step a) in a polytetrafluoroethylene frame, then pour the deposition solution obtained in step c) onto the upper surface of the film for 2.5 h, and keep the temperature of the deposition solution at 80 °C. After deposition, take out the film and ultrasonically clean it in deionized water for 10 min to obtain the deposited film;

[0050] e) Preparation of the polyamide layer: Fix the deposited film obtained in step d) in a polytetrafluoroethylene frame, prepare an aqueous piperazine solution with a mass percentage of 1.2 wt%, pour it onto the film surface, let it stay for 5 min and then pour out the surface solution, and leave it to dry at room temperature (25 ± 1 °C) for 10 min. Then prepare a solution of trimesoyl chloride / n-hexane with a mass percentage of 0.3 wt%, pour it onto the film surface, let it stay for 3 min and then pour out the surface solution, and then place the film in an oven at 80 °C and dry it for 25 min to obtain the composite film;

[0051] f) Activation treatment: Immerse the composite film obtained in e) in N-methylpyrrolidone and soak it at 80 °C for 20 min to obtain a solvent-resistant nanofiltration membrane with a polydopamine / amino-functionalized silica intermediate layer;

[0052] g) Test the permeation performance of the solvent-resistant nanofiltration membrane with a polydopamine / amino-functionalized silica intermediate layer obtained in step f) for a 50 mg / L drug / ethanol solution at room temperature (25 ± 1 °C) and an operating pressure of 0.5 MPa using a cross-flow filtration device. The results show that the flux of ethanol through the membrane is 14 L·m-2 ·h -1 The rejection rates for rifampicin, oxytetracycline, vitamin B1 and vitamin B12 were 94%, 79%, 69% and 93% respectively; the swelling degrees after soaking in methanol, acetone and toluene for 24 h were 5%, 5% and 2% respectively.

Claims

1. A preparation method of a solvent-resistant nanofiltration membrane with a polydopamine / amino silica intermediate layer, characterized in that: It includes the following steps: a) Preparation of the base film: Pour polyetherimide particles with a mass percentage of 15wt% - 19wt% into 100mL - 120mL of N,N-dimethylacetamide solvent, and simultaneously add polyvinylpyrrolidone with a mass percentage of 2wt% - 4wt% as a pore-forming agent; place the prepared solution in a 60°C constant-temperature magnetic stirrer and continuously stir for 8h. After the solution is fully mixed and uniform, let it stand for defoaming for 12h; Subsequently, select a coating rod with a thickness of 120μm - 250μm, uniformly scrape the solution on the surface of the non-woven fabric, and quickly immerse it in a water bath. After phase inversion, immerse it in a 6wt% - 12wt% hexanediamine / isopropanol solution for chemical cross-linking at 50°C - 80°C to obtain a polyetherimide base film; b) Preparation of amino-functionalized silica nanoparticles: Add 50mL of ethanol and 4mL of deionized water to a round-bottom flask, mix them evenly, and then add 0.1mL - 2mL of ammonia water; fix the round-bottom flask above a magnetic stirrer and stir at a speed of 100r / min - 150r / min for 20min; Subsequently, add 1mL of tetraethyl orthosilicate to the round-bottom flask and stir for 5h, then add 0.1mL - 1mL of 3-aminopropyltriethoxysilane and stir for 12h; after the stirring is completed, transfer the solution in the round-bottom flask to a 50mL centrifuge tube, place it in a centrifuge, and centrifuge at a speed of 10000r / min for 10min; after centrifugation, pour out the upper-layer solution, add ethanol and ultrasonicate for 10min, and perform the centrifugation operation again, repeating a total of four times; place the centrifuged solid in an oven and vacuum-dry it at room temperature (25 ± 1°C) for 12h to obtain amino-functionalized silica nanoparticles; c) Preparation of the deposition solution: Prepare a Tris buffer solution with a molar concentration of 0.01mol / L, dissolve dopamine and an oxidant in the Tris buffer solution, the mass percentage of dopamine is 0.1wt% - 2wt%, the mass ratio of the oxidant to dopamine is 1:10 - 10:1, and then add the amino-functionalized silica nanoparticles obtained in step b) with a mass percentage of 0.1wt% - 10wt%, and ultrasonicate for 0.5h to obtain the deposition solution; d) Preparation of the intermediate layer: Fix the base film obtained in step a) in a polytetrafluoroethylene frame, then pour the deposition solution obtained in step c) on the upper surface of the film for 0.5h - 2.5h, keep the temperature of the deposition solution at 40°C - 80°C, take out the film after deposition, and ultrasonically clean it in deionized water for 10min to obtain a deposited film; e) Preparation of the polyamide layer: Fix the deposited film obtained in step d) in a polytetrafluoroethylene frame, prepare an aqueous piperazine solution with a mass percentage of 0.1 wt% to 1.5 wt%, pour it onto the film surface, pour off the surface solution after 5 min, and leave it to stand and dry at room temperature (25 ± 1 °C) for 10 min. Then prepare a solution of trimesoyl chloride / n-hexane with a mass percentage of 0.01 wt% to 0.5 wt%, pour it onto the film surface, pour off the surface solution after 3 min, and then place the film in an oven at 60 °C to 100 °C and dry it for 10 min to 60 min to obtain a composite membrane; f) Activation treatment: Immerse the composite membrane obtained in e) in an organic solvent and soak it at 60 °C to 80 °C for 1 min to 30 min to obtain a solvent-resistant nanofiltration membrane with a polydopamine / aminosilica intermediate layer.

2. The preparation method of a solvent-resistant nanofiltration membrane with a polydopamine / amino silica interlayer according to claim 1, characterized in that: In step c), the oxidant is one or more of ammonium persulfate, potassium persulfate, sodium periodate, potassium periodate, sodium perchlorate, and potassium perchlorate.

3. The preparation method of a solvent-resistant nanofiltration membrane with a polydopamine / amino-silica intermediate layer according to claim 1, characterized in that: In step f), the organic solvent is one or more of methanol, isopropanol, acetone, acetonitrile, tetrahydrofuran, dimethyl sulfoxide, dichloromethane, ethyl acetate, toluene, xylene, n-hexane, cyclohexane, dioxane, N,N-dimethylformamide, N-methylpyrrolidone, acetic acid, ethylene glycol, 1,4-dioxane, and propylene glycol methyl ether.

4. The application of the solvent-resistant nanofiltration membrane with a polydopamine / aminosilica intermediate layer prepared by the preparation method according to any one of claims 1 to 3 in organic solvent recovery and drug purification.