Double-layer separation membrane and method for producing the same

Abstract

The application relates to a double-layer separation membrane and a preparation method thereof. The preparation method of the double-layer separation membrane comprises the following steps: uniformly mixing ZIF-67 nanoparticles, polysulfone particles, a first organic solvent and deionized water under the condition of 5 DEG C to 20 DEG C to obtain an outer layer casting solution; dissolving the polysulfone particles in a second organic solvent and uniformly mixing under the condition of 60 DEG C to 80 DEG C to obtain an intermediate layer casting solution; simultaneously forming the outer layer casting solution and the intermediate layer casting solution on a base material by adopting a double-knife co-casting method to obtain a double-layer separation membrane precursor; and performing baking treatment on the double-layer separation membrane precursor under the condition of 40 DEG C to 60 DEG C to make the outer layer casting solution form a film; then immersing the double-layer separation membrane precursor into a coagulation bath to obtain the double-layer separation membrane after complete solidification. The double-layer separation membrane with specific structure and performance is prepared by adopting the double-knife co-casting method, the flux of the double-layer separation membrane is large, the double-layer separation membrane is suitable for water treatment, dye treatment, metal ion removal and the like, and is favorable for wide application.

Description

Technical Field

[0001] This invention relates to the field of membrane separation technology, and in particular to a bilayer separation membrane and its preparation method. Background Technology

[0002] Currently, water scarcity and pollution have become global challenges, severely hindering sustainable socio-economic development. Membrane separation technology, due to its advantages of low energy consumption, simple processes, and high automation, is widely used in water treatment. The preparation of organic polymer separation membranes typically employs methods such as solvent-inducing phase separation, thermally induced phase separation, and evaporation-inducing phase separation. While these methods have demonstrated practical value in water treatment, dye treatment, healthcare, and metal ion removal, there is still room for improvement.

[0003] Traditional single-layer membrane fabrication requires only a single casting process, resulting in a limited structural range that fails to meet the demands of diverse applications. While bilayer or multilayer membranes offer greater structural diversity, current fabrication methods, which involve the separate preparation of the casting solution, are complex and lack precision in controlling membrane structure and performance. Therefore, there is an urgent need to improve and optimize the membrane fabrication process to produce separation membranes that better meet application requirements. Summary of the Invention

[0004] Therefore, it is necessary to provide a novel bilayer separation membrane and its preparation method. The bilayer separation membrane with specific structure and performance can be prepared by a double-blade co-casting method. The bilayer separation membrane has a large flux and is suitable for water treatment, dye treatment, metal ion removal and other fields.

[0005] A method for preparing a bilayer separation membrane includes the following steps:

[0006] ZIF-67 nanoparticles, polysulfone particles, a first organic solvent and deionized water were mixed evenly at 5℃~20℃ to obtain the outer layer casting solution.

[0007] Polysulfone particles are dissolved in a second organic solvent and mixed evenly at 60℃~80℃ to obtain an intermediate layer casting solution.

[0008] The outer layer casting solution and the middle layer casting solution are simultaneously formed on a substrate using a dual-blade co-casting method to obtain a bilayer separation membrane precursor; and

[0009] The bilayer separation membrane precursor is baked at 40°C to 60°C to form the outer layer casting solution; then the bilayer separation membrane precursor is immersed in a coagulation bath and completely solidified to obtain the bilayer separation membrane.

[0010] This invention enables the preparation of a bilayer separation membrane with specific structure and performance through a double-blade co-casting method. This bilayer separation membrane has a large flux and is suitable for water treatment, dye treatment, metal ion removal and other fields, which is beneficial for its wide application.

[0011] In one embodiment, the outer casting solution contains ZIF-67 nanoparticles at a mass fraction of 0.1% to 1%, polysulfone particles at a mass fraction of 10% to 20%, and deionized water at a mass fraction of 1% to 5%.

[0012] In one embodiment, the process of uniformly mixing ZIF-67 nanoparticles, polysulfone particles, a first organic solvent, and deionized water at a temperature of 5°C to 20°C is as follows:

[0013] ZIF-67 nanoparticles were mixed evenly with a first organic solvent to obtain a first mixture.

[0014] Polysulfone particles were added to the first mixture and mixed thoroughly to obtain a second mixture; and

[0015] Add deionized water to the second mixture and mix thoroughly at 5℃~20℃. After defoaming, maintain the temperature at no higher than 20℃.

[0016] In one embodiment, the ZIF-67 nanoparticles are prepared by the following steps: cobalt nitrate hexahydrate and 2-methylimidazole are dissolved in a third organic solvent, and after sufficient reaction, solid-liquid separation is performed and the solid is retained, which is the ZIF-67 nanoparticles.

[0017] In one embodiment, the mass fraction of the polysulfone particles in the intermediate layer casting solution is 10% to 20%.

[0018] In one embodiment, the first organic solvent comprises one or a mixture of N-methylpyrrolidone, N,N-dimethylformamide, N,N-dimethylacetamide, and dimethyl sulfoxide;

[0019] The second organic solvent includes one or a mixture of N-methylpyrrolidone, N,N-dimethylformamide, N,N-dimethylacetamide and dimethyl sulfoxide.

[0020] In one embodiment, the operation of simultaneously forming the outer layer casting liquid and the middle layer casting liquid on the substrate using a dual-blade co-casting method to obtain the bilayer separation membrane precursor is as follows:

[0021] Fix the substrate to the work surface;

[0022] A first scraper, a second scraper, and a third scraper are provided, and the first scraper, the second scraper, and the third scraper are positioned on one side of the substrate at a predetermined distance from the substrate. The first and second scrapers are at the same distance from the substrate, and the third scraper is at a greater distance from the substrate than the second scraper. An intermediate layer casting solution is injected between the first and second scrapers, and an outer layer casting solution is injected between the second and third scrapers, while maintaining the temperature of the outer layer casting solution at 5°C to 20°C.

[0023] At room temperature, pressure is applied simultaneously to the first, second, and third scrapers, causing the intermediate layer casting liquid and the outer layer casting liquid to be extruded, and then a film is formed on the substrate by scraping.

[0024] In one embodiment, the distance between the first scraper, the second scraper and the substrate is 30μm~80μm, and the distance between the third scraper and the substrate is 60μm~160μm;

[0025] The film is scraped at a speed of 2m / min to 4m / min under conditions of 30℃ to 40℃.

[0026] In one embodiment, the baking time is 10s to 40s, and the time for immersing the bilayer separation membrane precursor in the coagulation bath is 1min to 10min.

[0027] A bilayer separation membrane is prepared using any of the above-mentioned methods for preparing bilayer separation membranes.

[0028] This invention enables the preparation of a bilayer separation membrane with specific structure and performance through a double-blade co-casting method. This bilayer separation membrane has a large flux and is suitable for water treatment, dye treatment, metal ion removal and other fields, which is beneficial for its wide application. Attached Figure Description

[0029] Figure 1 This is a flowchart of a method for preparing a bilayer separation membrane according to an embodiment of the present invention;

[0030] Figure 2 This is a schematic diagram of the scraper and substrate in the preparation method of the double-layer separation membrane according to an embodiment of the present invention. Detailed Implementation

[0031] To make the above-mentioned objects, features, and advantages of the present invention more apparent and understandable, specific embodiments of the present invention will be described in detail below with reference to the accompanying drawings. Many specific details are set forth in the following description to provide a thorough understanding of the present invention. However, the present invention can be practiced in many other ways different from those described herein, and those skilled in the art can make similar modifications without departing from the spirit of the present invention. Therefore, the present invention is not limited to the specific embodiments disclosed below.

[0032] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. The terminology used herein in the description of the invention is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. The term "and / or" as used herein includes any and all combinations of one or more of the associated listed items.

[0033] Please see Figure 1 The preparation method of the bilayer separation membrane according to one embodiment of the present invention includes the following steps:

[0034] S10. Mix ZIF-67 nanoparticles, polysulfone particles, the first organic solvent and deionized water evenly at 5℃~20℃ to obtain the outer layer casting solution.

[0035] The Chinese name for ZIF-67 nanoparticles is zeolite imidazole ester framework-67 nanoparticles. ZIF-67 is a metal-organic framework (MOF) material composed of cobalt ions (Co). 2+ It is composed of 2-methylimidazolium ions (Hmim) and has a cubic crystal system.

[0036] Among them, polysulfone (PSU) particles have good film-forming properties, excellent mechanical strength, chemical stability and heat resistance, providing a solid supporting foundation for composite membranes; the molecular structure of polysulfone is easy to be modified by blending, and it can be well compatible with ZIF-67 nanoparticles (through solvent action) to form a stable mixed matrix membrane.

[0037] The advantages of using ZIF-67 nanoparticles and polysulfone particles as the outer membrane material are as follows: ZIF-67 has a uniform microporous structure (pore size of approximately 0.34 nm) and hydrophilic imidazole groups, which can provide molecular sieving function and enhance the hydrophilicity of the membrane surface, thus potentially improving both the water flux and pollutant rejection rate of the membrane; its cobalt metal center may have selective adsorption effects on heavy metal ions. Polysulfone provides excellent film-forming properties, mechanical strength, and chemical stability, making it an ideal carrier for ZIF-67 and forming a stable hybrid matrix functional layer.

[0038] The combination of ZIF-67 nanoparticles and polysulfone particles aims to achieve a synergistic improvement in high throughput, high selectivity and antifouling performance. The effects are as follows: (1) Synergistic improvement of separation performance: ZIF-67 provides precise sieving and potential adsorption sites, while PSU provides a stable matrix. The combination of the two makes the outer membrane have the potential for both high throughput and high selectivity (high rejection rate); (2) Enhanced surface properties: The introduction of ZIF-67 can effectively improve the hydrophobicity of PSU membrane, reduce membrane fouling tendency, and improve long-term operational stability; (3) Provide a functionalization platform: Using ZIF-67 / PSU as a functional separation layer provides a basic platform for further functionalization (such as growing other MOF layers on its surface or grafting specific functional groups).

[0039] In one embodiment, the outer casting solution contains 0.1% to 1% ZIF-67 nanoparticles by mass, 10% to 20% polysulfone particles by mass, and 1% to 5% deionized water by mass. Further, the mass fraction of ZIF-67 nanoparticles may be, but is not limited to, 0.1%, 0.2%, 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, or 1%, the mass fraction of polysulfone particles may be, but is not limited to, 10%, 11%, 12%, 13%, 14%, 15%, 16%, 17%, 18%, 19%, or 20%, and the mass fraction of deionized water may be, but is not limited to, 1%, 2%, 3%, 4%, or 5%.

[0040] In one embodiment, the process of uniformly mixing ZIF-67 nanoparticles, polysulfone particles, a first organic solvent, and deionized water at a temperature of 5°C to 20°C is as follows:

[0041] ZIF-67 nanoparticles were mixed evenly with a first organic solvent to obtain a first mixture.

[0042] Polysulfone particles were added to the first mixture and mixed thoroughly to obtain a second mixture; and

[0043] Add deionized water to the second mixture and mix thoroughly at 5℃~20℃. After defoaming, maintain the temperature at no higher than 20℃.

[0044] In one embodiment, ZIF-67 nanoparticles are prepared by the following steps: cobalt nitrate hexahydrate and 2-methylimidazole are dissolved in a third organic solvent, and after sufficient reaction, solid-liquid separation is performed and the solid is retained, which is the ZIF-67 nanoparticle. The third organic solvent is methanol.

[0045] In one embodiment, the first organic solvent includes one or more of N-methylpyrrolidone, N,N-dimethylformamide, N,N-dimethylacetamide, and dimethyl sulfoxide.

[0046] It should be noted that in step S10, the process of mixing ZIF-67 nanoparticles, polysulfone particles, the first organic solvent, and deionized water at 5℃~20℃ can be combined with vacuum degassing to improve the quality of the subsequent casting of the outer layer casting solution.

[0047] S20. Dissolve polysulfone particles in a second organic solvent and mix them evenly at 60℃~80℃ to obtain an intermediate layer casting solution.

[0048] In one embodiment, the mass fraction of polysulfone particles in the intermediate layer casting solution is 10% to 20%. Further, the mass fraction of polysulfone particles may be, but is not limited to, 10%, 11%, 12%, 13%, 14%, 15%, 16%, 17%, 18%, 19%, or 20%.

[0049] In one embodiment, the second organic solvent includes one or a mixture of N-methylpyrrolidone, N,N-dimethylformamide, N,N-dimethylacetamide, and dimethyl sulfoxide.

[0050] It should be noted that in step S20, the operation of dissolving polysulfone particles in the second organic solvent and mixing them uniformly at 60℃~80℃ can be combined with a vacuum degassing operation to improve the quality of the subsequent casting of the intermediate layer casting solution.

[0051] S30. Using a double-blade co-casting method, the outer layer casting liquid obtained in step S10 and the intermediate layer casting liquid obtained in step S20 are simultaneously formed on the substrate to obtain a double-layer separation membrane precursor.

[0052] The substrate can be non-woven fabric or any other feasible substrate.

[0053] Please see also Figure 2 In one embodiment, the operation of simultaneously forming the outer layer casting solution and the middle layer casting solution on the substrate using a double-blade co-casting method to obtain the bilayer separation membrane precursor is as follows:

[0054] Fix the substrate 6 to the work surface;

[0055] A first scraper 1, a second scraper 2, and a third scraper 3 are provided. The first scraper 1, the second scraper 2, and the third scraper 3 are positioned on one side of the substrate 6 at a predetermined distance from the substrate 6. The distances between the first scraper 1 and the second scraper 2 and the substrate 6 are the same, and the distance between the third scraper 3 and the substrate 6 is greater than the distance between the second scraper 2 and the substrate 6. The intermediate layer casting liquid is injected between the first scraper and the second scraper (i.e., scraper opening 4), and the outer layer casting liquid is injected between the second scraper 2 and the third scraper 3 (i.e., scraper opening 5). The temperature of the outer layer casting liquid is maintained at 5℃~20℃.

[0056] At room temperature, pressure is applied to the first scraper 1, the second scraper 2, and the third scraper 3 simultaneously, causing the intermediate layer casting liquid and the outer layer casting liquid to be extruded, and then a film is formed on the substrate 6 by scraping.

[0057] In one embodiment, the distance between the first scraper 1, the second scraper 2 and the substrate 6 is 30μm~80μm, and the distance between the third scraper 3 and the substrate 6 is 60μm~160μm.

[0058] In one embodiment, the film is scraped at a speed of 2 m / min to 4 m / min under conditions of 30°C to 40°C.

[0059] S40. The bilayer separation membrane precursor obtained in step S30 is baked at 40℃~60℃ to form an outer layer of casting solution; then the bilayer separation membrane precursor is immersed in a coagulation bath and completely solidified to obtain a bilayer separation membrane.

[0060] In step S40, the coagulation bath includes pure water.

[0061] In one embodiment, the baking time is 10s to 40s, and the time for immersing the bilayer separation membrane precursor in the coagulation bath is 1min to 10min.

[0062] The bilayer composite membrane prepared according to this embodiment includes a substrate, an intermediate layer located on one side of the substrate, and an outer layer located on the side of the intermediate layer away from the substrate. The intermediate layer is a pure polysulfone support layer, providing mechanical support and low transport resistance; the outer layer is a polysulfone mixed matrix functional layer rich in ZIF-67 nanoparticles, responsible for the main separation function.

[0063] In the bilayer composite membrane of this embodiment, the synergistic effect between the intermediate layer (pure polysulfone layer) and the outer layer (a polysulfone mixed matrix functional layer containing ZIF-67 nanoparticles) is key to achieving a high-performance bilayer separation membrane. This synergy is not a simple physical superposition, but rather a result of complementary material properties and structural design, jointly enhancing the overall performance of the membrane. Specifically, the synergistic effect is manifested in the following aspects:

[0064] (1) The strong support of the middle layer effectively compensates for the loss of mechanical properties that may be caused by the addition of nanoparticles to the outer layer, ensuring the overall structural integrity and durability of the double membrane under long-term operation and use pressure.

[0065] (2) The pure polysulfone support layer in the middle layer has a larger pore size and higher porosity. Compared with the functional layer, it is more porous and provides low-resistance channels, which greatly reduces the transport resistance of water molecules and permeates from the functional layer to the downstream. This allows the outer layer to focus on achieving high selective separation while the middle layer maximizes the high permeation flux, which is the basis for achieving high flux while maintaining high selectivity.

[0066] (3) The same polymer matrix ensures good molecular compatibility between the outer mixed matrix layer and the middle pure polysulfone layer. During the double-blade co-casting and subsequent phase separation process, the polymer chains at the interface of the two layers can diffuse and entangle with each other to form a seamless, low-resistance interface. This avoids the additional transport resistance or delamination risk caused by interface mismatch in traditional multilayer film preparation.

[0067] (4) During co-casting, the two solutions simultaneously come into contact with the coagulation bath (or undergo pre-evaporation / baking). Due to the differences in composition, temperature, viscosity, and thermodynamic state of the two solutions, they undergo asynchronous but mutually influential phase separation processes: the outer layer contains non-solvent additives (water) and has a lower temperature, tending to undergo instantaneous phase separation more quickly, forming a denser functional layer or one with a specific surface pore structure (such as the top of finger-like pores); the middle layer has a higher temperature and relatively lower viscosity, and its phase separation speed may be slightly slower, tending to form a more open sponge-like or macroporous structure. This differentiated phase separation behavior is designed to simultaneously optimize the structure of the two layers in one-step molding: the outer layer obtains the desired selective surface, and the middle layer obtains a supporting macroporous structure; the co-casting process itself promotes interface fusion, allowing this structural gradient to transition naturally.

[0068] Therefore, polysulfone was chosen as the intermediate layer material, forming a highly synergistic "functional-support" integrated structure with the outer ZIF-67 / polysulfone functional layer. This design fully utilizes the mechanical properties and processing characteristics of polysulfone as a supporting substrate, while allowing ZIF-67 to focus on its separation function. The shared matrix ensures interfacial fusion and low resistance, ultimately achieving the comprehensive performance advantages of high throughput, high selectivity, and good mechanical stability that are difficult to achieve simultaneously with traditional single-layer membranes or non-optimized multilayer membranes.

[0069] This invention enables the precise construction of a dual-layer structure in a single step, avoiding the complex steps of multiple castings and interface treatments required in traditional multilayer film preparation. By precisely controlling the doctor blade spacing, the thickness of the functional layer and the support layer can be adjusted separately. By controlling the low-temperature conditions of the outer casting solution, it helps to stabilize the dispersion of ZIF-67 and regulate the phase separation process, forming a surface porous structure that is more conducive to high throughput.

[0070] This invention enables the preparation of a bilayer separation membrane with specific structure and performance through a double-blade co-casting method. This bilayer separation membrane has a large flux and is suitable for water treatment, dye treatment, metal ion removal and other fields, which is beneficial for its wide application.

[0071] The bilayer separation membrane of one embodiment is prepared using any of the above-described methods for preparing bilayer separation membranes.

[0072] The bilayer composite membrane of this embodiment includes a substrate, an intermediate layer located on one side of the substrate, and an outer layer located on the side of the intermediate layer away from the substrate. The intermediate layer is a pure polysulfone support layer, providing mechanical support and low transport resistance; the outer layer is a polysulfone mixed matrix functional layer rich in ZIF-67 nanoparticles, responsible for the main separation function.

[0073] The double-layer separation membrane of the present invention is prepared by a double-blade co-casting method. The double-layer separation membrane has a large flux and is suitable for water treatment, dye treatment, metal ion removal and other fields, which is conducive to its wide application.

[0074] Referring to the above embodiments, in order to make the technical solution of the present invention more specific, clear and easy to understand, examples of the technical solution of the present invention are given below. However, it should be noted that the content to be protected by the present invention is not limited to the following embodiments.

[0075] Example 1

[0076] 0.1g of ZIF-67 nanoparticles were dissolved in 80.9g of N,N-dimethylformamide, and the nanoparticles were uniformly mixed in the solvent by ultrasound. Then, 16g of polysulfone particles and 3g of deionized water were added, and the mixture was stirred at 20°C for 12h to form a uniform purple solution. The solution was then degassed under vacuum while maintaining the temperature below 20°C to obtain the outer casting solution, which was ready for use.

[0077] 16g of polysulfone particles were dissolved in 84g of N,N-dimethylformamide and stirred at 80℃ for 10h. Vacuum degassing was performed to obtain the intermediate layer casting solution, which was then set aside for use.

[0078] like Figure 2 The nonwoven fabric (i.e., substrate 6) is fixed on the operating table; the distance between the first scraper 1, the second scraper 2 and the nonwoven fabric is adjusted to 50μm, and the distance between the third scraper 3 and the nonwoven fabric is 100μm; the casting solution of the middle layer is poured onto the scraper nozzle 4, and the casting solution of the outer layer is poured onto the scraper nozzle 5, keeping the temperature of the outer layer casting solution at 20℃; at room temperature of 30℃, pressure is applied to the first scraper 1, the second scraper 2 and the third scraper 3 simultaneously, so that the casting solution is squeezed out from the scraper nozzle 4 and the scraper nozzle 5, and then the film is scraped to obtain the bilayer separation precursor.

[0079] After placing the bilayer separation membrane precursor in a 50°C oven for 20 seconds, the entire bilayer separation membrane precursor was immersed in a coagulation water bath and kept for 5 minutes to obtain the bilayer separation membrane of Example 1. The bilayer separation membrane was then soaked in deionized water for later use.

[0080] Example 2

[0081] 0.1g of ZIF-67 nanoparticles were dissolved in 80.9g of N,N-dimethylformamide, and the nanoparticles were uniformly mixed in the solvent by ultrasound. Then, 16g of polysulfone particles and 3g of deionized water were added, and the mixture was stirred at 20°C for 12h to form a uniform purple solution. The solution was then degassed under vacuum while maintaining the temperature below 20°C to obtain the outer casting solution, which was ready for use.

[0082] Dissolve 18g of polysulfone particles in 82g of N,N-dimethylformamide, stir at 80℃ for 10h, and degas under vacuum to obtain the intermediate layer casting solution for later use.

[0083] like Figure 2 The nonwoven fabric (i.e., substrate 6) is fixed on the operating table; the distance between the first scraper 1, the second scraper 2 and the nonwoven fabric is adjusted to 50μm, and the distance between the third scraper 3 and the nonwoven fabric is 100μm; the casting solution of the middle layer is poured onto the scraper nozzle 4, and the casting solution of the outer layer is poured onto the scraper nozzle 5, keeping the temperature of the outer layer casting solution at 20℃; at room temperature of 30℃, pressure is applied to the first scraper 1, the second scraper 2 and the third scraper 3 simultaneously, so that the casting solution is squeezed out from the scraper nozzle 4 and the scraper nozzle 5, and then the film is scraped to obtain the bilayer separation precursor.

[0084] After placing the bilayer separation membrane precursor in a 50°C oven for 20 seconds, the entire bilayer separation membrane precursor was immersed in a coagulation water bath and kept for 5 minutes to obtain the bilayer separation membrane of Example 2. The bilayer separation membrane was then soaked in deionized water for later use.

[0085] Example 3

[0086] 0.1g of ZIF-67 nanoparticles were dissolved in 80.9g of N,N-dimethylformamide, and the nanoparticles were uniformly mixed in the solvent by ultrasound. Then, 16g of polysulfone particles and 3g of deionized water were added, and the mixture was stirred at 20°C for 12h to form a uniform purple solution. The solution was then degassed under vacuum while maintaining the temperature below 20°C to obtain the outer casting solution, which was ready for use.

[0087] Dissolve 20g of polysulfone particles in 80g of N,N-dimethylformamide, stir at 80℃ for 10h, and degas under vacuum to obtain the intermediate layer casting solution, which is ready for use.

[0088] like Figure 2The nonwoven fabric (i.e., substrate 6) is fixed on the operating table; the distance between the first scraper 1, the second scraper 2 and the nonwoven fabric is adjusted to 50μm, and the distance between the third scraper 3 and the nonwoven fabric is 100μm; the casting solution of the middle layer is poured onto the scraper nozzle 4, and the casting solution of the outer layer is poured onto the scraper nozzle 5, keeping the temperature of the outer layer casting solution at 20℃; at room temperature of 30℃, pressure is applied to the first scraper 1, the second scraper 2 and the third scraper 3 simultaneously, so that the casting solution is squeezed out from the scraper nozzle 4 and the scraper nozzle 5, and then the film is scraped to obtain the bilayer separation precursor.

[0089] After placing the bilayer separation membrane precursor in a 50°C oven for 20 seconds, the entire bilayer separation membrane precursor was immersed in a coagulation water bath and kept for 5 minutes to obtain the bilayer separation membrane of Example 3. The bilayer separation membrane was then soaked in deionized water for later use.

[0090] Example 4

[0091] 0.3g of ZIF-67 nanoparticles were dissolved in 80.9g of N,N-dimethylformamide, and the nanoparticles were uniformly mixed in the solvent by ultrasound. Then, 16g of polysulfone particles and 3g of deionized water were added, and the mixture was stirred at 20°C for 12h to form a uniform purple solution. The solution was then degassed under vacuum while maintaining the temperature below 20°C to obtain the outer casting solution, which was ready for use.

[0092] Dissolve 18g of polysulfone particles in 82g of N,N-dimethylformamide, stir at 80℃ for 10h, and degas under vacuum to obtain the intermediate layer casting solution for later use.

[0093] like Figure 2 The nonwoven fabric (i.e., substrate 6) is fixed on the operating table; the distance between the first scraper 1, the second scraper 2 and the nonwoven fabric is adjusted to 50μm, and the distance between the third scraper 3 and the nonwoven fabric is 100μm; the casting solution of the middle layer is poured onto the scraper nozzle 4, and the casting solution of the outer layer is poured onto the scraper nozzle 5, keeping the temperature of the outer layer casting solution at 20℃; at room temperature of 30℃, pressure is applied to the first scraper 1, the second scraper 2 and the third scraper 3 simultaneously, so that the casting solution is squeezed out from the scraper nozzle 4 and the scraper nozzle 5, and then the film is scraped to obtain the bilayer separation precursor.

[0094] After placing the bilayer separation membrane precursor in a 50°C oven for 20 seconds, the entire bilayer separation membrane precursor was immersed in a coagulation water bath and kept for 5 minutes to obtain the bilayer separation membrane of Example 4. The bilayer separation membrane was then soaked in deionized water for later use.

[0095] Example 5

[0096] 0.5g of ZIF-67 nanoparticles were dissolved in 80.9g of N,N-dimethylformamide, and the nanoparticles were uniformly mixed in the solvent by ultrasound. Then, 16g of polysulfone particles and 3g of deionized water were added, and the mixture was stirred at 20°C for 12h to form a uniform purple solution. The solution was then degassed under vacuum while maintaining the temperature below 20°C to obtain the outer casting solution, which was ready for use.

[0097] Dissolve 18g of polysulfone particles in 82g of N,N-dimethylformamide, stir at 80℃ for 10h, and degas under vacuum to obtain the intermediate layer casting solution for later use.

[0098] like Figure 2 The nonwoven fabric (i.e., substrate 6) is fixed on the operating table; the distance between the first scraper 1, the second scraper 2 and the nonwoven fabric is adjusted to 50μm, and the distance between the third scraper 3 and the nonwoven fabric is 100μm; the casting solution of the middle layer is poured onto the scraper nozzle 4, and the casting solution of the outer layer is poured onto the scraper nozzle 5, keeping the temperature of the outer layer casting solution at 20℃; at room temperature of 30℃, pressure is applied to the first scraper 1, the second scraper 2 and the third scraper 3 simultaneously, so that the casting solution is squeezed out from the scraper nozzle 4 and the scraper nozzle 5, and then the film is scraped to obtain the bilayer separation precursor.

[0099] After placing the bilayer separation membrane precursor in a 50°C oven for 20 seconds, the entire bilayer separation membrane precursor was immersed in a coagulation water bath and kept for 5 minutes to obtain the bilayer separation membrane of Example 5. The bilayer separation membrane was then soaked in deionized water for later use.

[0100] Performance testing:

[0101] The water flux of the bilayer separation membranes in Examples 1-5 was tested. The test methods are as follows, and the test results are shown in Table 1.

[0102] Water flux test: The test pressure is 1 bar, the solution is deionized water, the solution temperature is 25°C, and the membrane runs in the cross-flow device for 10 minutes to measure the water flux.

[0103] Table 1

[0104]

[0105] The following conclusions can be drawn from Table 1:

[0106] (1) The bilayer separation membranes of Examples 1 to 5 of the present invention have a large flux, among which Example 4 has the best performance and the highest flux (560.72 LMH), which is beneficial for widespread application;

[0107] (2) From Example 1 to Example 2 and then to Example 3, the concentration of polysulfone in the intermediate layer increases (16g → 20g), which leads to a decrease in flux, indicating that the denser the support layer, the worse the water permeability;

[0108] (3) From Example 2 to Example 4, a moderate increase in ZIF-67 content (0.1g → 0.3g) can increase water flux, possibly due to the enhanced hydrophilicity and microporous structure of ZIF-67; however, excessive ZIF-67 (0.5g) leads to a decrease in flux (Example 4 → Example 5), possibly due to particle agglomeration or pore blockage.

[0109] The technical features of the above embodiments can be combined in any way. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0110] The embodiments described above are merely illustrative of several implementations of the present invention, and while the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the invention patent. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these all fall within the protection scope of the present invention. Therefore, the protection scope of this invention patent should be determined by the appended claims.

Claims

1. A method for preparing a double-layer separation membrane for water treatment, characterized in that, Includes the following steps: ZIF-67 nanoparticles, polysulfone particles, a first organic solvent, and deionized water are mixed uniformly at 5°C to 20°C to obtain an outer layer casting solution; in the outer layer casting solution, the mass fraction of ZIF-67 nanoparticles is 0.1% to 1%, the mass fraction of polysulfone particles is 10% to 20%, and the mass fraction of deionized water is 1% to 5%. Polysulfone particles are dissolved in a second organic solvent and mixed evenly at 60℃~80℃ to obtain an intermediate layer casting solution. The outer layer casting liquid and the middle layer casting liquid are simultaneously formed on the substrate using a double-blade co-casting method to obtain a double-layer separation membrane precursor. as well as The bilayer separation membrane precursor is baked at 40°C to 60°C to form the outer layer casting solution; then the bilayer separation membrane precursor is immersed in a coagulation bath and completely solidified to obtain the bilayer separation membrane. The operation of simultaneously forming the outer layer casting solution and the middle layer casting solution on the substrate using a double-blade co-casting method to obtain the double-layer separation membrane precursor is as follows: Fix the substrate to the work surface; A first scraper, a second scraper, and a third scraper are provided, and the first scraper, the second scraper, and the third scraper are positioned on one side of the substrate at a predetermined distance from the substrate. The first and second scrapers are at the same distance from the substrate, and the third scraper is at a greater distance from the substrate than the second scraper. An intermediate layer casting solution is injected between the first and second scrapers, and an outer layer casting solution is injected between the second and third scrapers, while maintaining the temperature of the outer layer casting solution at 5°C to 20°C. At room temperature, pressure is applied simultaneously to the first, second, and third scrapers, causing the intermediate layer casting liquid and the outer layer casting liquid to be extruded, and then a film is formed on the substrate by scraping.

2. The method for preparing the bilayer separation membrane according to claim 1, characterized in that, The procedure for uniformly mixing ZIF-67 nanoparticles, polysulfone particles, the first organic solvent, and deionized water at 5℃~20℃ is as follows: ZIF-67 nanoparticles were mixed evenly with a first organic solvent to obtain a first mixture. Polysulfone particles were added to the first mixture and mixed thoroughly to obtain a second mixture; and Add deionized water to the second mixture and mix thoroughly at 5℃~20℃. After defoaming, maintain the temperature at no higher than 20℃.

3. The method for preparing the bilayer separation membrane according to claim 1, characterized in that, The ZIF-67 nanoparticles were prepared by the following steps: cobalt nitrate hexahydrate and 2-methylimidazole were dissolved in a third organic solvent, and after the reaction was complete, solid-liquid separation was performed and the solid was retained. The solid was the ZIF-67 nanoparticles.

4. The method for preparing the bilayer separation membrane according to claim 1, characterized in that, In the intermediate layer casting solution, the mass fraction of the polysulfone particles is 10%~20%.

5. The method for preparing the bilayer separation membrane according to claim 1, characterized in that, The first organic solvent includes N Methylpyrrolidone, N,N Dimethylformamide, N,N A mixture of one or more of dimethylacetamide and dimethyl sulfoxide; The second organic solvent includes N Methylpyrrolidone, N,N Dimethylformamide, N,N A mixture of one or more of dimethylacetamide and dimethyl sulfoxide.

6. The method for preparing the bilayer separation membrane according to claim 1, characterized in that, The distance between the first and second scrapers and the substrate is 30μm~80μm, and the distance between the third scraper and the substrate is 60μm~160μm; The film is scraped at a speed of 2m / min to 4m / min under conditions of 30℃ to 40℃.

7. The method for preparing the bilayer separation membrane according to claim 1, characterized in that, The baking time is 10s~40s, and the time for immersing the double-layer separation membrane precursor in the coagulation bath is 1min~10min.

8. A double-layer separation membrane, characterized in that, The bilayer separation membrane was prepared using the method described in any one of claims 1 to 7.

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