CN111111447A - Nanofiltration membrane preparation method with adjustable and controllable desalination rate and prepared nanofiltration membrane - Google Patents
Nanofiltration membrane preparation method with adjustable and controllable desalination rate and prepared nanofiltration membrane Download PDFInfo
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Abstract
The invention provides a method for preparing a nanofiltration membrane with adjustable desalination rate, which comprises the following steps: dissolving 11-15 wt% of polyether sulfone in dimethylacetamide, adding 0.5-5 wt% of pore-forming agent, cooling, blade-coating the cooled pore-forming agent on the surface of non-woven fabric, adding hydrogel, and rinsing to obtain a support layer; dissolving 0.5-3 wt% of one or more aromatic, aliphatic or alicyclic polyfunctional amines in water, adding 1.5-2 wt% of camphorsulfonic acid, and adjusting pH to 10-12 with triethylamine; dissolving one or more aromatic, aliphatic or alicyclic polyfunctional acyl halides in an amount of 0.05-0.4 wt% in aliphatic hydrocarbon, cycloaliphatic hydrocarbon or aromatic hydrocarbon to obtain an oil phase liquid; and immersing the back surface of the supporting layer into the water phase liquid, taking out and drying, coating the oil phase liquid on the front surface of the supporting layer, and drying. The invention can prepare nanofiltration membranes with different desalination rates.
Description
Technical Field
The invention belongs to the technical field of water treatment, and particularly relates to a nanofiltration membrane preparation method with adjustable and controllable desalination rate and a prepared nanofiltration membrane.
Background
Nanofiltration (NF) is a new membrane separation technology developed in the middle of the 80 th century, between ultrafiltration and reverse osmosis, and belongs to pressure driving, and has been widely used in the fields of petrochemical, biochemical and medical industries, food, paper making, textile printing and dyeing, and the like, and in water treatment processes. With the continuous development of separation technology, the separation performance requirements of nanofiltration membranes in different separation fields are different.
At present, commercial nanofiltration membranes are basically prepared by an interfacial polymerization method, most of reaction monomers are piperazine as a main component, and the surfaces of the prepared nanofiltration membranes are generally negatively charged. The removal rate of monovalent salt is low (40-60 percent) and the monovalent salt is not easy to control, thus the application of the nanofiltration membrane in different separation requirement fields is seriously limited. In addition, the nanofiltration membrane preparation method in the prior art is to perform interfacial polymerization reaction on the outer surface layer of the polyethersulfone or polyethersulfone basement membrane to form a multilayer composite nanofiltration membrane. Because the interfacial polymerization reaction occurs on the outer surface layer of the polyether sulfone or polyether sulfone basement membrane, the characteristics of high reaction rate and difficult regulation exist, and therefore, the entrapment rate of substances with different molecular weights cannot be accurately controlled.
In summary, there is an urgent need to develop a method for preparing a nanofiltration membrane with adjustable and controllable desalination rate and a nanofiltration membrane prepared by the method, so as to enrich the types of commercial nanofiltration membranes, better meet the requirements of the field of material separation for nanofiltration membranes with different desalination rates, and solve the problems in the prior art.
The invention content is as follows:
the invention aims to provide a nanofiltration membrane preparation method with adjustable and controllable desalination rate, which is characterized in that a brand-new preparation process is adopted to prepare a polyethersulfone-polypiperazine amide embedded nanofiltration membrane, interfacial polymerization reaction on the surface layer of a polyethersulfone basement membrane supporting layer in the prior art is introduced into a polyethersulfone layer for carrying out, and the nanofiltration membranes with different separation capacities and desalination rates can be prepared by adjusting the porosity and pore size of the polyethersulfone layer and the formula of the polymerization reaction.
In order to achieve the purpose, the invention adopts the following technical scheme:
a preparation method of a nanofiltration membrane with adjustable desalination rate comprises the following steps:
(1) preparing a support layer: dissolving polyether sulfone in dimethyl acetamide, wherein the weight percentage of polyether sulfone in dimethyl acetamide is 11-15%, adding 0.5-5% of pore-forming agent, stirring uniformly, standing and cooling to form a casting solution; coating the casting solution on the surface of the non-woven fabric, adding hydrogel, and rinsing to prepare a supporting layer;
(2) preparing an aqueous phase liquid: dissolving one or more of aromatic, aliphatic or alicyclic polyfunctional amines in water, wherein the weight percentage of the polyfunctional amines in the water is 0.5-3%, adding 1.5-2% by weight of camphorsulfonic acid, and adding triethylamine to adjust the pH value to 10-12 to obtain aqueous phase liquid;
(3) preparing oil phase liquid: dissolving one or more aromatic, aliphatic or alicyclic polyfunctional acyl halides in aliphatic hydrocarbon, cycloaliphatic hydrocarbon or aromatic hydrocarbon, wherein the weight percentage of the polyfunctional acyl halides is 0.05-0.4%, and obtaining oil phase liquid;
(4) preparing a nanofiltration membrane: and immersing the back surface of the supporting layer into the water phase liquid, controlling the water phase liquid not to exceed the front surface of the supporting layer, taking out and drying, coating the oil phase liquid on the front surface of the supporting layer, removing redundant oil phase liquid, and drying to obtain the nanofiltration membrane with adjustable desalination rate. And when the oil phase liquid is coated, the thickness of the oil phase liquid is ensured to completely cover the front surface of the supporting layer.
Preferably, the thickness of the non-woven fabric in the step (1) is 110 microns, and the thickness of the polyether sulfone layer is 50-60 microns.
Preferably, the pore-forming agent in step (1) is one or two of lithium bromide and acetone. When LiBr and acetone are added simultaneously, the mass ratio of the LiBr to the acetone is 1: 1.
preferably, the average pore diameter of the support layer prepared in the step (1) is 110nm-250nm, and the porosity is 45% -65%.
Preferably, the aromatic, aliphatic or alicyclic polyfunctional amine in step (2) is one or more of piperazine, m-phenylenediamine, o-toluidine, 2, 4-dimethylaniline, 2, 6-dimethylaniline and trimesamine.
Preferably, the aromatic, aliphatic or alicyclic polyfunctional acyl halide in the step (3) is trimesoyl chloride.
Preferably, in the step (4), the back surface of the support layer is immersed in the aqueous liquid for 2-5 min.
Preferably, in the step (4), the back surface of the support layer is immersed in the aqueous phase to a depth of 100-150 μm.
Preferably, in the step (4), the oil phase liquid is coated on the front surface of the support layer and then stands still for 1-5 min.
The invention also provides the nanofiltration membrane prepared by the nanofiltration membrane preparation method with the adjustable and controllable desalination rate, and the water phase liquid and the oil phase liquid are subjected to interfacial polymerization reaction in the supporting layer to form the nanofiltration membrane with polyether sulfone and polypiperazine amide embedded in each other.
Preferably, the desalination rate of the nanofiltration membrane is adjustable, the desalination rate of the nanofiltration membrane on monovalent salt is adjustable to be 30% -90%, and the desalination rate on divalent salt is more than 90%.
The technical scheme of the invention at least has the following beneficial effects:
the preparation method of the nanofiltration membrane with adjustable desalination rate comprises the following steps: firstly, a loose polyethersulfone layer is prepared by adopting a phase inversion method, and then interfacial polymerization reaction is carried out in the polyethersulfone layer to prepare the polyethersulfone-polypiperazine amide embedded nanofiltration membrane. The method is different from the traditional preparation method of the polypiperazine amide nanofiltration membrane, the interfacial polymerization reaction is introduced into the polyether sulfone layer from the traditional polyether sulfone/polyether sulfone surface layer, and the accurate regulation and control of the interception capability of the nanofiltration membrane are realized. The method has simple process, realizes the regulation and control of the speed and the path of the polypiperazine amide polymerization reaction by regulating the pore diameter structure in the polyether sulfone layer, thereby achieving the preparation of the nanofiltration membrane with different separation capacities, has simple operation, common raw materials, easy large-scale production and commercialization, enriches the types of commercial nanofiltration membranes, can better meet the requirements of the material separation field on the nanofiltration membranes with different desalination rates, and provides a new method for the development of the commercial nanofiltration membranes. The nanofiltration membrane prepared by the method can be controlled in a specific desalination rate range according to needs.
Drawings
FIG. 1 is an SEM sectional view of a nanofiltration membrane with controllable desalination rate in example 1;
fig. 2 is an SEM cross-sectional morphology of the nanofiltration membrane with controllable salt rejection in comparative example 1.
Detailed Description
The following preferred embodiments of the present invention are provided to aid in a further understanding of the invention. It should be understood by those skilled in the art that the description of the embodiments of the present invention is by way of example only, and not by way of limitation.
The method adopts a self-made porous polyether sulfone basement membrane supporting layer, then one side of a non-woven fabric is soaked in a water phase liquid, and then the polyether sulfone basement membrane is soaked in an oil phase liquid. Because the average pore diameter and the porosity of the polyether sulfone base membrane supporting layer are large, the surface interfacial polymerization reaction can occur in the polyether sulfone base membrane supporting layer, the rate and the degree of the interfacial polymerization reaction can be regulated and controlled by adjusting the porosity and the average pore diameter of the polyether sulfone base membrane, and meanwhile, different water phase monomers and monomer concentrations are regulated, so that the composite nanofiltration membrane with different selective separation capacities can be prepared. See examples 1-5 for specific methods of operation.
Example 1:
1. preparing a support layer: weighing 130g of polyether sulfone, dissolving the polyether sulfone in 986g of DMAc (Dimethylacetamide), stirring at 70 ℃ until the polyether sulfone is completely dissolved, adding 10g of LiBr, uniformly mixing, standing and cooling for 24 hours to form a casting solution; uniformly coating the cooled casting membrane liquid on the surface of the non-woven fabric by adopting a scraper, adding hydrogel and rinsing to prepare a polyether sulfone basement membrane supporting layer; wherein the thickness of the non-woven fabric is 110 microns, the thickness of the polyether sulfone layer is 50 microns, the average pore diameter of the polyether sulfone base membrane supporting layer is 170nm, and the porosity is 54%.
2. Preparing a water phase liquid: completely dissolving 8g of piperazine and 2g of m-phenylenediamine in 972g of distilled water, adding 18g of camphorsulfonic acid after completely dissolving, stirring, adjusting the pH value of the solution to 11.5 by using triethylamine, and uniformly stirring to obtain an aqueous phase solution.
3. Preparing an oil phase liquid: 2g of trimesoyl chloride is dissolved in 998g of IsoparG solvent (which belongs to isoparaffin solvent and is purchased from Exxon Mobil manufacturers), and oil phase liquid is obtained after uniform stirring.
4. Preparing a nanofiltration membrane: the first step is as follows: fixing a polyether sulfone base membrane supporting layer on a metal frame, then soaking the side of a non-woven fabric into aqueous phase liquid for 3min, controlling the soaking depth to be about 130 microns, removing redundant solution on the surface by using a low-pressure air knife, and then blowing and drying the aqueous phase liquid in the polyether sulfone base membrane supporting layer for 2 min; the second step is that: and (3) coating the oil phase liquid on the surface of the polyether sulfone layer of the supporting layer, standing for 2min so that substances in the water phase liquid and the oil phase liquid are subjected to polymerization reaction in the polyether sulfone layer of the supporting layer, removing redundant solution on the surface by using a low-pressure air knife, then placing the solution in a drying oven at 100 ℃ for keeping for 4min, and drying the oil phase liquid to prepare the nanofiltration membrane with the adjustable desalination rate.
SEM (scanning electron microscope) section scanning is carried out on the nanofiltration membrane prepared in the embodiment, and the result is shown in figure 1.
Example 2:
1. preparing a support layer: weighing 130g of polyether sulfone, dissolving the polyether sulfone in 982g of DMAc, stirring and dissolving at 70 ℃, adding 20g of LiBr, uniformly mixing, standing and cooling for 24 hours to obtain a membrane casting solution; uniformly coating the cooled casting membrane liquid on the surface of the non-woven fabric by adopting a scraper, adding hydrogel and rinsing to prepare a polyether sulfone basement membrane supporting layer; wherein the thickness of the non-woven fabric is 110 microns, the thickness of the polyether sulfone layer is 50 microns, the average pore diameter of the polyether sulfone base membrane supporting layer is 210nm, and the porosity is 57%.
2. Preparing a water phase liquid: the same as in example 1.
3. Preparing an oil phase liquid: the same as in example 1.
4. Preparing a nanofiltration membrane: the same as in example 1.
Example 3:
1. preparing a support layer: weighing 120g of polyether sulfone, dissolving the polyether sulfone in 982g of DMAc, stirring and dissolving at 70 ℃, adding 20g of LiBr, uniformly mixing, standing and cooling for 24 hours; uniformly coating the cooled casting membrane liquid on the surface of the non-woven fabric by adopting a scraper, adding hydrogel and rinsing to prepare a polyether sulfone basement membrane supporting layer; wherein the thickness of the non-woven fabric is 110 microns, the thickness of the polyether sulfone layer is 50 microns, the average pore diameter of the polyether sulfone base membrane supporting layer is 240nm, and the porosity is 62%.
2. Preparing a water phase liquid: the same as in example 1.
3. Preparing an oil phase liquid: the same as in example 1.
4. Preparing a nanofiltration membrane: the same as in example 1.
Example 4
1. Preparing a support layer: weighing 180g of polyether sulfone, dissolving in 960g of DMAc, stirring and dissolving at 65 ℃, adding 40g of LiBr and 20g of acetone, uniformly mixing, standing and cooling for 24 hours; uniformly coating the cooled casting membrane liquid on the surface of the non-woven fabric by adopting a scraper, adding hydrogel and rinsing to prepare a polyether sulfone basement membrane supporting layer; wherein the thickness of the non-woven fabric is 110 microns, the thickness of the polyether sulfone layer is 60 microns, the average pore diameter of the polyether sulfone base membrane supporting layer is 110nm, and the porosity is 43%.
2. Preparing a water phase liquid: 4g of 2, 6-dimethylaniline and 2g of pyromellitic triamine are completely dissolved in 184g of distilled water, after the materials are completely dissolved, 1g of camphorsulfonic acid is added and stirred until the materials are dissolved, and triethylamine is added to adjust the pH value of the solution to 10.5, so that aqueous phase liquid is obtained.
3. Preparing an oil phase liquid: dissolving 3g of trimesoyl chloride in 998g of IsoparG solvent (belonging to isoparaffin solvent), and uniformly stirring to obtain an oil phase liquid.
4. Preparing a nanofiltration membrane: the first step is as follows: fixing a polyether sulfone base membrane supporting layer on a metal frame, then soaking the side of a non-woven fabric into aqueous phase liquid for 3min, controlling the soaking depth to be about 150 microns, then removing redundant solution on the surface by using a low-pressure air knife, and then blowing and drying the aqueous phase liquid in the polyether sulfone base membrane supporting layer for 3 min; the second step is that: and (3) coating the oil phase liquid on the surface of the polyether sulfone layer of the supporting layer, standing for 3min so that substances in the water phase liquid and the oil phase liquid are subjected to polymerization reaction in the polyether sulfone layer of the supporting layer, removing redundant solution on the surface by using a low-pressure air knife, drying in an oven at 80 ℃ for 5min, and drying the oil phase liquid to prepare the nanofiltration membrane with adjustable desalination rate.
Example 5
1. Preparing a support layer: weighing 88g of polyether sulfone, dissolving in 708g of DMAc, stirring and dissolving at 60 ℃, adding 2g of LiBr and 2g of acetone, uniformly mixing, standing and cooling for 24 hours; uniformly coating the cooled casting membrane liquid on the surface of the non-woven fabric by adopting a scraper, adding hydrogel and rinsing to prepare a polyether sulfone basement membrane supporting layer; wherein the thickness of the non-woven fabric is 110 microns, the thickness of the polyether sulfone layer is 50 microns, the average pore diameter of the polyether sulfone base membrane supporting layer is 250nm, and the porosity is 64%.
2. Preparing a water phase liquid: completely dissolving 2g of o-toluidine and 2g of 2, 4-dimethylaniline in 794.8g of distilled water, adding 1.2g of camphorsulfonic acid after the o-toluidine and the 2, 4-dimethylaniline are completely dissolved, stirring until the mixture is dissolved, adding triethylamine to adjust the pH value of the solution to 12, and obtaining aqueous phase liquid.
3. Preparing an oil phase liquid: 1g of trimesoyl chloride is dissolved in 1999g of IsoparG solvent (belonging to isoparaffin solvent), and the mixture is stirred uniformly to obtain an oil phase liquid.
4. Preparing a nanofiltration membrane: the first step is as follows: fixing a polyether sulfone base membrane supporting layer on a metal frame, then soaking the side of a non-woven fabric into aqueous phase liquid for 2min, controlling the soaking depth to be about 120 microns, then removing redundant solution on the surface by using a low-pressure air knife, and then blowing and drying the aqueous phase liquid in the polyether sulfone base membrane supporting layer for 2 min; the second step is that: and (3) coating the oil phase liquid on the surface of the polyether sulfone layer of the supporting layer, standing for 3min so that substances in the water phase liquid and the oil phase liquid are subjected to polymerization reaction in the polyether sulfone layer of the supporting layer, removing redundant solution on the surface by using a low-pressure air knife, drying in an oven at 80 ℃ for 3min, and drying the oil phase liquid to prepare the nanofiltration membrane with adjustable desalination rate.
The comparative example adopts the preparation method of the polypiperazine amide composite nanofiltration membrane in the prior art:
1. preparing a polyether sulfone base membrane supporting layer: weighing 140g of polyether sulfone, dissolving the polyether sulfone in 982g of DMAc, stirring and dissolving at 70 ℃, standing and cooling for 24 hours; uniformly coating the cooled casting membrane liquid on the surface of the non-woven fabric by adopting a scraper, adding hydrogel and rinsing to prepare a polyether sulfone basement membrane supporting layer; wherein the thickness of the non-woven fabric is 110 microns, the thickness of the polyether sulfone layer is 50 microns, the average pore diameter of the polyether sulfone layer is 120nm, and the porosity is 49%.
2. Preparing a water phase liquid: adding 10g of piperazine and 18g of camphorsulfonic acid into 972g of water, adjusting the pH value to 11.5 by using triethylamine, and uniformly stirring to obtain an aqueous phase solution.
3. Preparing an oil phase liquid: dissolving 2g of trimesoyl chloride in 998g of IsoparG solvent (belonging to isoparaffin solvent), and uniformly stirring to obtain an oil phase liquid.
4. Preparing a nanofiltration membrane: firstly, coating a water phase solution on a polyether sulfone support layer, removing redundant solution on the surface by using a low-pressure air knife, then allowing the polyether sulfone base membrane adsorbed with the water phase solution to pass through a closed space with a heat supply and air exhaust system, controlling the internal temperature of the closed space to be 30 ℃, controlling the relative humidity to be 40-60%, and allowing the water on the membrane surface to further volatilize within 1 min. And then, coating the oil phase liquid on the water phase liquid, removing a part of the oil phase liquid on the surface by using a low-pressure air knife, then placing the mixture in a 100 ℃ oven for 4min, and drying the oil phase liquid to form the composite nanofiltration membrane.
SEM (scanning electron microscope) section scanning is carried out on the nanofiltration membrane prepared in the comparative example, and the result is shown in figure 2.
Comparing the scanning results of the cross section shape of the nanofiltration membrane in the attached figure 1 (example 1), it can be seen that the nanofiltration membrane in the example 1 has a compact structure and a uniform pore diameter, and presents a "sponge-like condition", because the interfacial polymerization reaction is deep into the polyethersulfone layer, and the high porosity of the polyethersulfone provides a uniform place for the interfacial polymerization reaction, so as to prepare the polyethersulfone-polypiperazine amide embedded nanofiltration membrane; the nanofiltration membrane in the comparative example shown in the attached figure 2 has a loose structure, obvious layering and an irregular structure, the upper layer of the membrane is an interface polymerization reaction to generate a polypiperazine amide layer, and the lower layer of the membrane is a finger-like hole structure of polyether sulfone.
The method for detecting the performance of the nanofiltration membrane prepared by the methods of the above examples 1 to 3 and comparative example is as follows: 500ppm NaCl solution and 2000ppm MgSO4 solution, pH value of 7.5-8, temperature of 25 ℃ and test pressure of 70psi, and respectively testing the salt rejection rate and corresponding water yield of membrane NaCl and MgSO 4. The results of the measurements are shown in Table 1 below.
TABLE 1 nanofiltration membrane test results prepared in examples 1-3 and comparative examples
The relationship between the porosity and the aperture of the bottom membrane and the desalination rate of the prepared nanofiltration membrane is as follows: the porosity of the basement membrane is high, the pore size distribution is more uniform, so that the water phase monomers can be more favorably immersed into the basement membrane layer, the immersion depth can be ensured to be consistent, the reaction rate and the polymerization degree can be more effectively adjusted, and the influence of the water phase monomers and the concentration on the desalination rate is shown in the detection data of the table 1.
From the detection results in table 1, it can be seen that in examples 1 to 3, the rate and degree of interfacial polymerization can be adjusted and controlled by adjusting the porosity and the average pore diameter of the bottom membrane, and the composite nanofiltration membranes with different selective separation capacities can be prepared by adjusting different aqueous phase monomers and monomer concentrations.
The preparation method of the nanofiltration membrane is different from the traditional preparation method of the polypiperazine amide nanofiltration membrane, the interfacial polymerization reaction is introduced into the polyether sulfone layer from the surface layer of the traditional polyether sulfone or polyether sulfone, and the speed and the path of the polypiperazine amide polymerization reaction are regulated and controlled by adjusting the pore diameter structure in the polyether sulfone layer, so that the nanofiltration membrane with different separation capacities is prepared, wherein the desalination rate of the nanofiltration membrane on monovalent salt (NaCl) can be effectively controlled to be between 30 and 90 percent, and divalent salt (MgSO) can be effectively controlled4) The removal range is maintained at a high level. The method is simple to operate, common in raw materials, easy for large-scale production commercialization, capable of enriching the types of commercial nanofiltration membranes and capable of better meeting the requirements of the field of material separation on nanofiltration membranes with different desalination rates.
Finally, it should be noted that the above embodiments are only used for illustrating the technical solutions of the present application and not for limiting the protection scope thereof, and although the present application is described in detail with reference to the above embodiments, those of ordinary skill in the art should understand that: numerous variations, modifications, and equivalents will occur to those skilled in the art upon reading the present application and are within the scope of the claims as issued or as granted.
Claims (10)
1. A method for preparing a nanofiltration membrane with adjustable desalination rate is characterized by comprising the following steps:
(1) preparing a support layer: dissolving polyether sulfone in dimethyl acetamide, wherein the weight percentage of polyether sulfone in dimethyl acetamide is 11-15%, adding 0.5-5% of pore-forming agent, stirring uniformly, standing and cooling to form a casting solution; coating the casting solution on the surface of the non-woven fabric, adding hydrogel, and rinsing to prepare a supporting layer;
(2) preparing an aqueous phase liquid: dissolving one or more of aromatic, aliphatic or alicyclic polyfunctional amines in water, wherein the weight percentage of the polyfunctional amines in the water is 0.5-3%, adding 1.5-2% by weight of camphorsulfonic acid, and adding triethylamine to adjust the pH value to 10-12 to obtain aqueous phase liquid;
(3) preparing oil phase liquid: dissolving one of aromatic, aliphatic or alicyclic polyfunctional acyl halide in aliphatic hydrocarbon, cycloaliphatic hydrocarbon or aromatic hydrocarbon, wherein the weight percentage of the polyfunctional acyl halide is 0.05-0.4%, and obtaining oil phase liquid;
(4) preparing a nanofiltration membrane: and immersing the back surface of the supporting layer into the water phase liquid, controlling the water phase liquid not to exceed the front surface of the supporting layer, taking out and drying, coating the oil phase liquid on the front surface of the supporting layer, removing redundant oil phase liquid, and drying to obtain the nanofiltration membrane with adjustable desalination rate.
2. The method for preparing a nanofiltration membrane according to claim 1, wherein the pore-forming agent in step (1) is one or both of lithium bromide and acetone.
3. The method for preparing a nanofiltration membrane according to claim 2, wherein the support layer prepared in the step (1) has an average pore size of 110nm to 250nm and a porosity of 45% to 65%.
4. The method for preparing a nanofiltration membrane according to claim 3, wherein the aromatic, aliphatic or alicyclic polyfunctional amine in the step (2) is one or more of piperazine, m-phenylenediamine, o-toluidine, 2, 4-dimethylaniline, 2, 6-dimethylaniline and trimesamine.
5. The method for preparing a nanofiltration membrane according to claim 4, wherein the aromatic, aliphatic or alicyclic polyfunctional acyl halide in the step (3) is trimesoyl chloride.
6. The method for preparing a nanofiltration membrane according to claim 1, wherein in the step (4), the back surface of the support layer is immersed in the aqueous liquid for 2-5 min.
7. The method for preparing a nanofiltration membrane according to claim 6, wherein in the step (4), the back surface of the support layer is immersed into the aqueous phase to a depth of 100-150 μm.
8. The method for preparing a nanofiltration membrane according to claim 6, wherein in the step (4), the oil phase liquid is coated on the front surface of the support layer and then is kept still for 1-5 min.
9. The nanofiltration membrane according to any one of claims 1 to 8, wherein the nanofiltration membrane comprises polyether sulfone and polypiperazine amide embedded in a support layer.
10. The nanofiltration membrane of claim 9, wherein the nanofiltration membrane has a controllable desalination rate, the nanofiltration membrane has a monovalent salt desalination rate of 30-90%, and a divalent salt desalination rate of more than 90%.
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| CN112742215A (en) * | 2020-12-25 | 2021-05-04 | 恩泰环保科技（常州）有限公司 | High-performance positively-charged nanofiltration membrane for removing multivalent cations and preparation method thereof |
| CN114669194A (en) * | 2021-12-27 | 2022-06-28 | 浙江易膜新材料科技有限公司 | Preparation method of single-multivalent ion high-resolution nanofiltration membrane |
| CN115155327A (en) * | 2022-05-10 | 2022-10-11 | 广东奥斯博膜材料技术有限公司 | Nanofiltration membrane suitable for low-temperature pretreatment of salt lake brine and preparation method thereof |
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