High-flux and high-interception composite nanofiltration membrane and preparation method thereof

Abstract

The invention discloses a high-flux and high-interception composite nanofiltration membrane and a preparation method thereof, and relates to a method for preparing the high-flux and high-interception composite nanofiltration membrane by adding amino modified inorganic nanoparticles, organic polymers, sodium lactate and isopropanol, coating the reverse side of a base material with a moisturizing solution, coating the front side of the base material with a precursor solution, and preparing the high-flux and high-interception composite nanofiltration membrane. And drying to obtain the high-flux and high-interception composite nanofiltration membrane, and storing the high-flux and high-interception composite nanofiltration membrane in water. The stability of the composite nanofiltration membrane is improved by adding the amino-modified inorganic nanoparticles, the synergistic effect is formed by regulating and controlling the adding proportion of the amino-modified inorganic nanoparticles and the moisturizing liquid, and the high flux is ensured while the high interception performance is obtained.

Description

Technical Field

[0001] The invention belongs to the field of separation membranes, and in particular relates to a high-flux and high-retention composite nanofiltration membrane and a preparation method thereof. Background Art

[0002] As the global water crisis becomes increasingly severe, the development of innovative water treatment technologies has become an urgent need. Among numerous desalination processes, nanofiltration technology has become a research focus due to its unique advantages. This technology can efficiently intercept harmful substances such as heavy metal ions and organic micropollutants with low energy consumption, significantly improving water purification efficiency. However, traditional nanofiltration membranes generally face a "selectivity-flux" performance paradox: increasing pollutant retention often leads to a significant decrease in water flux. This paradox severely restricts their potential for industrial application.

[0003] Chinese patent document CN117599610A discloses a chemically resistant polyphenylene sulfone nanofiltration membrane and its preparation method. The method involves introducing chemically stable organosilicon into biphenyl molecular chains, polymerizing them with diphenyl sulfone to form thermally stable polyphenylene sulfone. The introduced sulfonic acid groups then interact electrostatically with the amino groups of aminated graphene to form a cross-linked network system, resulting in a chemically resistant polyphenylene sulfone nanofiltration membrane. While this method improves the chemical resistance of the nanofiltration membrane, its synthesis process is complex and time-consuming, and the basic filtration performance of the resulting nanofiltration membrane has not been characterized. Summary of the Invention

[0004] In response to the shortcomings of the existing technology, the present invention provides a method for preparing a high-flux and high-retention composite nanofiltration membrane. The operation method is simple and convenient, the cost is low, and the preparation time is short. After adding amino-modified nanoparticles, the high retention of the composite nanofiltration membrane is ensured while also improving its pure water flux. The addition of moisturizing liquid also reduces the possibility of flux attenuation caused by pore shrinkage in the composite nanofiltration membrane during the drying process, and improves the overall stability of the nanofiltration membrane.

[0005] Based on this, the present invention provides a method for preparing a high-flux, high-retention composite nanofiltration membrane, comprising the following steps: 1) Ultrasonic dispersion of amino-modified inorganic nanoparticles in an organic solvent to prepare a dispersion; 2) Add the organic polymer to the dispersion and stir magnetically at room temperature for 4 hours to obtain a precursor solution after uniform dissolution; 3) Add sodium lactate and isopropyl alcohol to water and stir magnetically at room temperature for 2 hours to obtain a moisturizing solution after uniform dissolution. 4) After the moisturizing liquid is coated on the back side of the substrate and allowed to stand for a period of time, the excess moisturizing liquid is removed and the membrane is dried at a certain temperature; then, the precursor liquid is coated on the front side of the substrate and allowed to stand for a period of time, the excess precursor liquid is removed and the membrane is dried at a certain temperature; after drying, a high-flux and high-retention composite nanofiltration membrane is obtained and stored in water.

[0006] Preferably, the amino-modified inorganic nanoparticles include one or more of silicon dioxide, titanium dioxide, and aluminum oxide. Preferably, the organic solvent includes one or more of ethylene glycol methyl ether, propylene glycol methyl ether, N,N-dimethylformamide, N-methylpyrrolidone, tetrahydrofuran, and dimethyl sulfoxide. Preferably, the organic polymer includes one or more of sulfonated polysulfone, sulfonated polyethersulfone, and sulfonated polyetheretherketone.

[0007] Preferably, the mass ratio of the organic polymer to the organic solvent is 0.5-24%:1.

[0008] Preferably, in the dispersion, the mass fraction of the amino-modified inorganic nanoparticles is 5-30%, more preferably 5-10%.

[0009] Preferably, the coating time on the back side of the substrate in step 4) is 0.5-2 minutes, and the coating time on the front side of the substrate is 0.5-10 minutes, more preferably 2-4 minutes. Preferably, the drying temperature in step 4) is 40-150°C. Preferably, the coating method in step 4) is one or more of blade coating, dip coating, and spray coating.

[0010] Preferably, the substrate is one or more of a non-woven fabric and an ultrafiltration base membrane. More preferably, the ultrafiltration base membrane is a polysulfone ultrafiltration membrane with a molecular weight cut-off of 60,000 Da to 100,000 Da.

[0011] In the present invention, the method for preparing amino-modified inorganic nanoparticles is to add inorganic nanoparticles to anhydrous ethanol, ultrasonically disperse them uniformly, add a small amount of silane coupling agent and deionized water, and magnetically stir them at a temperature of 25-60°C for 5-8 hours until the modification is complete. The resulting suspension is filtered, centrifuged, washed, and dried to obtain amino-modified inorganic nanoparticles. The mass ratio of the inorganic nanoparticles is 1% to 10%, and the silane coupling agent is one or more of γ-aminopropyltriethoxysilane, γ-aminopropyltrimethoxysilane, and N-(β-aminoethyl)-γ-aminopropyltrimethoxysilane. In the examples of the present invention, for ease of illustration, silica nanoparticles are used as the inorganic nanoparticles, and γ-aminopropyltriethoxysilane is used as the silane coupling agent to prepare the amino-modified silica nanoparticles used in the examples.

[0012] The beneficial effects of the present invention are as follows: (1) The present invention prepares a composite nanofiltration membrane by a simple coating method, which is simple to operate, has readily available raw materials, and is easy to industrialize; (2) The addition of amino-modified inorganic nanoparticles improves the overall stability of the composite nanofiltration membrane; (3) The addition of amino-modified inorganic nanoparticles forms a synergistic effect with the moisturizing liquid, ensuring that the flux attenuation caused by pore shrinkage in the subsequent drying process is effectively improved, thereby achieving high retention performance while ensuring high flux. BRIEF DESCRIPTION OF THE DRAWINGS

[0013] Figure 1 This is a surface scanning electron microscope image of the high-flux, high-retention composite nanofiltration membrane prepared in Example 12.

[0014] Figure 2 The flux-retention performance diagram of the composite nanofiltration membrane at different coating times (1000 ppm Na2SO4 solution). DETAILED DESCRIPTION

[0015] The present invention will be further described below in conjunction with specific embodiments. It should be understood that these embodiments are only intended to illustrate the present invention and are not intended to limit the scope of the present invention. In addition, it should be understood that after reading the contents of the present invention, those skilled in the art may make various changes or modifications to the present invention, and these equivalent forms fall within the scope of the present invention.

[0016] The present invention relates to a method for preparing a high-flux and high-retention composite nanofiltration membrane, comprising the following steps: 1) Ultrasonic dispersion of amino-modified inorganic nanoparticles in an organic solvent to prepare a dispersion; 2) Add the organic polymer to the dispersion and stir magnetically at room temperature for 4 hours to obtain a precursor solution after uniform dissolution; 3) Add sodium lactate and isopropyl alcohol to water and stir magnetically at room temperature for 2 hours to obtain a moisturizing solution after uniform dissolution. 4) After the moisturizing liquid is coated on the back side of the substrate and allowed to stand for a period of time, the excess moisturizing liquid is removed and the membrane is dried at a certain temperature; then, the precursor liquid is coated on the front side of the substrate and allowed to stand for a period of time, the excess precursor liquid is removed and the membrane is dried at a certain temperature; after drying, a high-flux and high-retention composite nanofiltration membrane is obtained and stored in water.

[0017] Preferably, the amino-modified inorganic nanoparticles include one or more of silicon dioxide, titanium dioxide, and aluminum oxide. Preferably, the organic solvent includes one or more of ethylene glycol monomethyl ether, propylene glycol monomethyl ether, N,N-dimethylformamide, N-methylpyrrolidone, tetrahydrofuran, and dimethyl sulfoxide. Preferably, the organic polymer includes one or more of sulfonated polysulfone, sulfonated polyethersulfone, and sulfonated polyetheretherketone. Preferably, the substrate includes one or more of a non-woven fabric and an ultrafiltration base membrane. More preferably, the ultrafiltration base membrane is a polysulfone ultrafiltration membrane with a molecular weight cut-off of 60,000 to 100,000 Da.

[0018] Preferably, the mass ratio of the organic polymer to the organic solvent is 0.5-24%: 1. Preferably, in the dispersion, the mass fraction of the amino-modified inorganic nanoparticles is 5-30%, more preferably 5-10%.

[0019] Preferably, the coating time for the back side of the substrate in step 4) is 0.5-2 minutes, and the coating time for the front side of the substrate is 0.5-10 minutes, more preferably 2-4 minutes. Preferably, the drying temperature in step 4) is 40-150°C. Preferably, the coating method in step 4) is one or more of blade coating, dip coating, and spray coating.

[0020] Example 1

[0021] A method for preparing a high-flux, high-retention composite nanofiltration membrane is prepared by the following steps: 1) Add 5 wt % of amino-modified silica nanoparticles to ethylene glycol methyl ether and ultrasonically disperse for 5 min to prepare 50 g of dispersion.

[0022] 2) Add 1.2 wt% of sulfonated polysulfone to the dispersion and stir magnetically at room temperature for 4 h until the mixture is uniformly dissolved.

[0023] 3) Add 15% sodium lactate and 8.6% isopropanol to deionized water and stir magnetically at room temperature for 2 h until the solution is uniform.

[0024] 4) The moisturizing solution prepared in step 3) was dip-coated on the reverse side of a polysulfone ultrafiltration membrane (molecular weight cutoff of 60,000 Da to 100,000 Da), and allowed to stand for 1 minute. The excess moisturizing solution was removed, and the membrane was dried at 80°C. The precursor solution prepared in step 2) was then coated on the front side of the polysulfone ultrafiltration membrane for 2 minutes. The excess precursor solution was removed, and the membrane was dried at 80°C to obtain a high-flux, high-retention composite nanofiltration membrane, which was then stored in water.

[0025] Example 2

[0026] A method for preparing a high-flux, high-retention composite nanofiltration membrane is prepared by the following steps: 1) Add 5 wt % of amino-modified silica nanoparticles to ethylene glycol methyl ether and ultrasonically disperse for 5 minutes to prepare 50 g of dispersion.

[0027] 2) Add 1.2 wt% of sulfonated polysulfone to the dispersion and stir magnetically at room temperature for 4 h until the mixture is uniformly dissolved.

[0028] 3) Add 15% sodium lactate and 8.6% isopropanol to deionized water and stir magnetically at room temperature for 2 h until the solution is uniform.

[0029] 4) The moisturizing solution prepared in step 3) was dip-coated on the reverse side of a polysulfone ultrafiltration membrane (molecular weight cutoff of 60,000 Da to 100,000 Da), and allowed to stand for 1 minute. The excess moisturizing solution was removed, and the membrane was dried at 80°C. The precursor solution prepared in step 2) was then coated on the front side of the polysulfone ultrafiltration membrane for 4 minutes. The excess precursor solution was removed, and the membrane was dried at 80°C to obtain a high-flux, high-retention composite nanofiltration membrane, which was then stored in water.

[0030] Example 3

[0031] A method for preparing a high-flux, high-retention composite nanofiltration membrane is prepared by the following steps: 1) Add 5 wt % of amino-modified silica nanoparticles to ethylene glycol methyl ether and ultrasonically disperse for 5 minutes to prepare 50 g of dispersion.

[0032] 2) Add 1.2 wt% of sulfonated polysulfone to the dispersion and stir magnetically at room temperature for 4 h until the mixture is uniformly dissolved.

[0033] 3) Add 15% sodium lactate and 8.6% isopropanol to deionized water and stir magnetically at room temperature for 2 h until the solution is uniform.

[0034] 4) The moisturizing solution prepared in step 3) was dip-coated on the reverse side of a polysulfone ultrafiltration membrane (molecular weight cutoff of 60,000 Da to 100,000 Da), and allowed to stand for 1 minute. The excess moisturizing solution was removed, and the membrane was dried at 80°C. The precursor solution prepared in step 2) was then coated on the front side of the polysulfone ultrafiltration membrane for 6 minutes. The excess precursor solution was removed, and the membrane was dried at 80°C to obtain a high-flux, high-retention composite nanofiltration membrane, which was then stored in water.

[0035] Example 4

[0036] A method for preparing a high-flux, high-retention composite nanofiltration membrane is prepared by the following steps: 1) Add 5 wt % of amino-modified silica nanoparticles to ethylene glycol methyl ether and ultrasonically disperse for 5 minutes to prepare 50 g of dispersion.

[0037] 2) Add 1.2 wt% of sulfonated polysulfone to the dispersion and stir magnetically at room temperature for 4 h until the mixture is uniformly dissolved.

[0038] 3) Add 15% sodium lactate and 8.6% isopropanol to deionized water and stir magnetically at room temperature for 2 h until the solution is uniform.

[0039] 4) The moisturizing solution prepared in step 3) was dip-coated on the reverse side of a polysulfone ultrafiltration membrane (molecular weight cutoff of 60,000 Da to 100,000 Da), and allowed to stand for 1 minute. The excess moisturizing solution was removed, and the membrane was dried at 80°C. The precursor solution prepared in step 2) was then coated on the front side of the polysulfone ultrafiltration membrane for 8 minutes. The excess precursor solution was removed, and the membrane was dried at 80°C to obtain a high-flux, high-retention composite nanofiltration membrane, which was then stored in water.

[0040] Example 5

[0041] A method for preparing a high-flux, high-retention composite nanofiltration membrane is prepared by the following steps: 1) Add 10 wt % of amino-modified silica nanoparticles to ethylene glycol methyl ether and ultrasonically disperse for 5 minutes to prepare 50 g of dispersion.

[0042] 2) Add 1.2 wt% of sulfonated polysulfone to the dispersion and stir magnetically at room temperature for 4 h until the mixture is uniformly dissolved.

[0043] 3) Add 15% sodium lactate and 8.6% isopropanol to deionized water and stir magnetically at room temperature for 2 h until the solution is uniform.

[0044] 4) The moisturizing solution prepared in step 3) was dip-coated on the reverse side of a polysulfone ultrafiltration membrane (molecular weight cutoff of 60,000 Da to 100,000 Da), and allowed to stand for 1 minute. The excess moisturizing solution was removed, and the membrane was dried at 80°C. The precursor solution prepared in step 2) was then coated on the front side of the polysulfone ultrafiltration membrane for 2 minutes. The excess precursor solution was removed, and the membrane was dried at 80°C to obtain a high-flux, high-retention composite nanofiltration membrane, which was then stored in water.

[0045] Example 6

[0046] A method for preparing a high-flux, high-retention composite nanofiltration membrane is prepared by the following steps: 1) Add 10 wt % of amino-modified silica nanoparticles to ethylene glycol methyl ether and ultrasonically disperse for 5 minutes to prepare 50 g of dispersion.

[0047] 2) Add 1.2 wt% of sulfonated polysulfone to the dispersion and stir magnetically at room temperature for 4 h until the mixture is uniformly dissolved.

[0048] 3) Add 15% sodium lactate and 8.6% isopropanol to deionized water and stir magnetically at room temperature for 2 h until the solution is uniform.

[0049] 4) The moisturizing solution prepared in step 3) was dip-coated on the reverse side of a polysulfone ultrafiltration membrane (molecular weight cutoff of 60,000 Da to 100,000 Da), and allowed to stand for 1 minute. The excess moisturizing solution was removed, and the membrane was dried at 80°C. The precursor solution prepared in step 2) was then coated on the front side of the polysulfone ultrafiltration membrane for 4 minutes. The excess precursor solution was removed, and the membrane was dried at 80°C to obtain a high-flux, high-retention composite nanofiltration membrane, which was then stored in water.

[0050] Example 7

[0051] A method for preparing a high-flux, high-retention composite nanofiltration membrane is prepared by the following steps: 1) Add 10 wt % of amino-modified silica nanoparticles to ethylene glycol methyl ether and ultrasonically disperse for 5 minutes to prepare 50 g of dispersion.

[0052] 2) Add 1.2 wt% of sulfonated polysulfone to the dispersion and stir magnetically at room temperature for 4 h until the mixture is uniformly dissolved.

[0053] 3) Add 15% sodium lactate and 8.6% isopropanol to deionized water and stir magnetically at room temperature for 2 h until the solution is uniform.

[0054] 4) The moisturizing solution prepared in step 3) was dip-coated on the reverse side of a polysulfone ultrafiltration membrane (molecular weight cutoff of 60,000 Da to 100,000 Da), and allowed to stand for 1 minute. The excess moisturizing solution was removed, and the membrane was dried at 80°C. The precursor solution prepared in step 2) was then coated on the front side of the polysulfone ultrafiltration membrane for 6 minutes. The excess precursor solution was removed, and the membrane was dried at 80°C to obtain a high-flux, high-retention composite nanofiltration membrane, which was then stored in water.

[0055] Example 8

[0056] A method for preparing a high-flux, high-retention composite nanofiltration membrane is prepared by the following steps: 1) Add 10 wt % of amino-modified silica nanoparticles to ethylene glycol methyl ether and ultrasonically disperse for 5 minutes to prepare 50 g of dispersion.

[0057] 2) Add 1.2 wt% of sulfonated polysulfone to the dispersion and stir magnetically at room temperature for 4 h until the mixture is uniformly dissolved.

[0058] 3) Add 15% sodium lactate and 8.6% isopropanol to deionized water and stir magnetically at room temperature for 2 h until the solution is uniform.

[0059] 4) The moisturizing solution prepared in step 3) was dip-coated on the reverse side of a polysulfone ultrafiltration membrane (molecular weight cutoff of 60,000 Da to 100,000 Da), and allowed to stand for 1 minute. The excess moisturizing solution was removed, and the membrane was dried at 80°C. The precursor solution prepared in step 2) was then coated on the front side of the polysulfone ultrafiltration membrane for 8 minutes. The excess precursor solution was removed, and the membrane was dried at 80°C to obtain a high-flux, high-retention composite nanofiltration membrane, which was then stored in water.

[0060] Example 9

[0061] A method for preparing a high-flux, high-retention composite nanofiltration membrane is prepared by the following steps: 1) Add 5 wt % of amino-modified silica nanoparticles to ethylene glycol methyl ether and ultrasonically disperse for 5 minutes to prepare 50 g of dispersion.

[0062] 2) Add 1.2 wt% of sulfonated polysulfone to the dispersion and stir magnetically at room temperature for 4 h until the mixture is uniformly dissolved.

[0063] 3) Add 15% sodium lactate and 8.6% isopropanol to deionized water and stir magnetically at room temperature for 2 h until the solution is uniform.

[0064] 4) The moisturizing solution prepared in step 3) was dip-coated on the reverse side of a polysulfone ultrafiltration membrane (molecular weight cutoff of 60,000 Da to 100,000 Da), and allowed to stand for 1 minute. The excess moisturizing solution was removed, and the membrane was dried at 80°C. The precursor solution prepared in step 2) was then coated on the front side of the polysulfone ultrafiltration membrane for 2 minutes. The excess precursor solution was removed, and the membrane was dried at 120°C to obtain a high-flux, high-retention composite nanofiltration membrane, which was then stored in water.

[0065] Example 10

[0066] A method for preparing a high-flux, high-retention composite nanofiltration membrane is prepared by the following steps: 1) Add 5 wt % of amino-modified silica nanoparticles to ethylene glycol methyl ether and ultrasonically disperse for 5 minutes to prepare 50 g of dispersion.

[0067] 2) Add 1.2 wt% of sulfonated polysulfone to the dispersion and stir magnetically at room temperature for 4 h until the mixture is uniformly dissolved.

[0068] 3) Add 15% sodium lactate and 8.6% isopropanol to deionized water and stir magnetically at room temperature for 2 h until the solution is uniform.

[0069] 4) The moisturizing solution prepared in step 3) was dip-coated on the reverse side of a polysulfone ultrafiltration membrane (molecular weight cutoff of 60,000 Da to 100,000 Da), and allowed to stand for 1 minute. The excess moisturizing solution was removed, and the membrane was dried at 80°C. The precursor solution prepared in step 2) was then coated on the front side of the polysulfone ultrafiltration membrane for 4 minutes. The excess precursor solution was removed, and the membrane was dried at 120°C to obtain a high-flux, high-retention composite nanofiltration membrane, which was then stored in water.

[0070] Example 11

[0071] A method for preparing a high-flux, high-retention composite nanofiltration membrane is prepared by the following steps: 1) Add 5 wt % of amino-modified silica nanoparticles to ethylene glycol methyl ether and ultrasonically disperse for 5 minutes to prepare 50 g of dispersion.

[0072] 2) Add 1.2 wt% of sulfonated polysulfone to the dispersion and stir magnetically at room temperature for 4 h until the mixture is uniformly dissolved.

[0073] 3) Add 15% sodium lactate and 8.6% isopropanol to deionized water and stir magnetically at room temperature for 2 h until the solution is uniform.

[0074] 4) The moisturizing solution prepared in step 3) was dip-coated on the reverse side of a polysulfone ultrafiltration membrane (molecular weight cutoff of 60,000 Da to 100,000 Da), and allowed to stand for 1 minute. The excess moisturizing solution was removed, and the membrane was dried at 80°C. The precursor solution prepared in step 2) was then coated on the front side of the polysulfone ultrafiltration membrane for 6 minutes. The excess precursor solution was removed, and the membrane was dried at 120°C to obtain a high-flux, high-retention composite nanofiltration membrane, which was then stored in water.

[0075] Example 12

[0076] A method for preparing a high-flux, high-retention composite nanofiltration membrane is prepared by the following steps: 1) Add 5 wt % of amino-modified silica nanoparticles to ethylene glycol methyl ether and ultrasonically disperse for 5 minutes to prepare 50 g of dispersion.

[0077] 2) Add 1.2 wt% of sulfonated polysulfone to the dispersion and stir magnetically at room temperature for 4 h until the mixture is uniformly dissolved.

[0078] 3) Add 15% sodium lactate and 8.6% isopropanol to deionized water and stir magnetically at room temperature for 2 h until the solution is uniform.

[0079] 4) The moisturizing solution prepared in step 3) was dip-coated on the reverse side of a polysulfone ultrafiltration membrane (molecular weight cutoff of 60,000 Da to 100,000 Da), and allowed to stand for 1 minute. The excess moisturizing solution was removed, and the membrane was dried at 80°C. The precursor solution prepared in step 2) was then coated on the front side of the polysulfone ultrafiltration membrane for 8 minutes. The excess precursor solution was removed, and the membrane was dried at 120°C to obtain a high-flux, high-retention composite nanofiltration membrane, which was then stored in water.

[0080] The surface scanning electron microscopy image of the high-throughput and high-retention composite nanofiltration membrane prepared in Example 12 is as follows: Figure 1 As shown by Figure 1 It can be seen that the amino-modified silica nanoparticles are evenly distributed on the surface of the ultrafiltration base membrane. The porous structure of the base membrane surface and the amino-modified silica nanoparticles form a rough micro-nano structure, which further improves the pure water flux of the membrane.

[0081] Example 13: Performance Evaluation

[0082] Comparison of the flux and retention performance of the composite nanofiltration membranes prepared under different front coating times in Examples 9-12 when adding 1000ppm Na2SO4 solution. The experimental results are as follows: Figure 2 shown.

[0083] Depend on Figure 2 It can be seen that with the increase of the front coating time, the retention performance of the composite nanofiltration membrane is greatly improved, but the pure water flux is sacrificed. Taking all factors into consideration, when the coating time is 2 minutes or 4 minutes, it can simultaneously meet the requirements of high flux and high retention performance of the composite nanofiltration membrane.

[0084] Example 14: Preparation method as control example 1 As a comparative example 1, a method for preparing a high-flux and high-retention composite nanofiltration membrane is prepared by the following steps: 1) Add 1.2 wt % sulfonated polysulfone to ethylene glycol methyl ether and stir magnetically at room temperature for 4 h until uniformly dissolved to prepare 50 g of precursor solution.

[0085] 2) Prepare a moisturizing solution by adding 15% sodium lactate and 8.6% isopropyl alcohol to deionized water and stirring under magnetic stirring at room temperature for 2 h until the mixture is uniformly dissolved.

[0086] 3) The moisturizing solution prepared in step 2) is dip-coated on the reverse side of a polysulfone ultrafiltration membrane (molecular weight cutoff of 60,000 Da to 100,000 Da), and allowed to stand for 1 minute. Excess moisturizing solution is removed, and the membrane is dried at 80°C. The precursor solution prepared in step 1) is then coated on the front side of the polysulfone ultrafiltration membrane for 2 minutes. Excess precursor solution is removed, and the membrane is dried at 120°C to obtain a high-flux, high-retention composite nanofiltration membrane, which is then stored in water.

[0087] The flux and retention performance of the composite nanofiltration membranes prepared in Example 9 and Comparative Example 1 when 1000 ppm Na2SO4 solution was added were compared. The experimental results are shown in the following table:

[0088] As can be seen from the table above, the flux of the composite nanofiltration membrane with amino-modified silica nanoparticles increased from 36.73 L·m -2 ·h -1 Increased to 49.22 L·m -2 ·h -1 However, the retention performance decreased slightly, by only 1.57%. The addition of amino-modified silica nanoparticles increased the membrane surface roughness and the specific surface area. Furthermore, the amino-modified silica nanoparticles have good hydrophilicity, further improving the permeability of the composite nanofiltration membrane. However, a certain amount of amino-modified silica nanoparticles can make the nanofiltration membrane loose, resulting in a slight decrease in retention performance.

Claims

1. A method for preparing a high-flux, high-retention composite nanofiltration membrane, characterized in that: The following steps are involved: (1) Ultrasonic dispersion of amino-modified nanoparticles in an organic solvent to prepare a dispersion; (2) Adding the organic polymer to the dispersion, stirring it magnetically at room temperature for 4 h, and obtaining a precursor solution after uniform dissolution; (3) Sodium lactate and isopropyl alcohol were added to water and magnetically stirred at room temperature for 2 h to obtain a moisturizing solution after uniform dissolution; (4) After the moisturizing liquid is coated on the back of the substrate and allowed to stand for a period of time, the excess moisturizing liquid is removed and the substrate is dried at a certain temperature; then the precursor liquid is coated on the front of the substrate and allowed to stand for a period of time, the excess precursor liquid is removed and the substrate is dried at a certain temperature; after drying, a high-flux and high-retention composite nanofiltration membrane is obtained and stored in water.

2. The preparation method according to claim 1, characterized in that The amino-modified nanoparticles are one or more of silicon dioxide, titanium dioxide, and aluminum oxide.

3. The preparation method according to claim 1, characterized in that The organic solvent is one or more of ethylene glycol methyl ether, propylene glycol methyl ether, N,N-dimethylformamide, N-methylpyrrolidone, tetrahydrofuran, and dimethyl sulfoxide.

4. The preparation method according to claim 1, characterized in that The organic polymer is one or more of sulfonated polysulfone, sulfonated polyethersulfone, and sulfonated polyetheretherketone.

5. The preparation method according to claim 1, characterized in that The coating method is one or more of scraping, dipping and spraying.

6. The preparation method according to claim 1, characterized in that The substrate is one or more of non-woven fabric and ultrafiltration base membrane.

7. A high-flux, high-retention composite nanofiltration membrane, characterized in that: The composite nanofiltration membrane is prepared by the preparation method according to any one of claims 1 to 6.

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