Nanofiltration membrane with double-layer multi-dimensional structure and preparation method of nanofiltration membrane

Abstract

The invention provides a nanofiltration membrane with a double-layer multi-dimensional structure and a preparation method of the nanofiltration membrane, and belongs to the technical field of nanofiltration membranes. According to the preparation method, a lithium salt-alkali composite catalyst is added into a water-phase solution, and the interfacial polymerization rate, the molecular diffusion behavior and the interfacial reaction kinetics are regulated by regulating and controlling the ionic strength, the pH dynamic balance and the oriented growth of a nanostructure, so that the high-performance polyamide nanofiltration membrane with a layered multi-dimensional structure is prepared. The high-performance polyamide nanofiltration membrane with the layered multi-dimensional structure shows an excellent separation effect in a natural surface water treatment process, particularly shows excellent performance in the aspect of removing perfluoro and polyfluoroalkyl substances, and has wide application potential.

Description

Technical Field

[0001] The present invention relates to the technical field of nanofiltration membranes, and particularly relates to a nanofiltration membrane with a double-layer multi-dimensional structure and a preparation method thereof. Background Art

[0002] With the rapid development of industrialization in modern society, the water environment is facing increasingly complex and diverse pollution problems. In recent years, persistent organic pollutants - fluorine and per- and polyfluoroalkyl substances (PFAS) have attracted wide attention. Due to their excellent persistence, chemical stability and bioaccumulation potential, PFAS are widely used in industrial production and daily life. A large number of research and monitoring data show that PFAS are widely distributed globally, and their negative impacts have become the research focus in the fields of environmental science and public health. Therefore, the efficient removal of PFAS has become an important research direction in the current water treatment field.

[0003] As a pressure-driven liquid phase separation method, membrane treatment technology is widely used in the treatment of natural surface water and the preparation of healthy drinking water due to its advantages such as environmental protection, pollution-free and small land occupation. In recent years, research has shown that membrane technology has high efficiency in the removal of PFAS. Reverse osmosis membranes and nanofiltration membranes are the main technologies for PFAS removal. Research shows that reverse osmosis membranes have a higher PFAS removal rate than nanofiltration membranes. However, due to the dense active layer of reverse osmosis membranes, they have a large mass transfer resistance and require a high operating pressure, which makes the operating cost high during long-term operation. While nanofiltration membranes have a lower operating pressure and have significant advantages in the removal of organic compounds and emerging pollutants. The molecular weights of most PFAS are between 200 - 900 Da and they are negatively charged in aqueous solutions. Therefore, polyamide nanofiltration membranes show significant advantages in PFAS removal.

[0004] Traditional polyamide nanofiltration membranes are usually synthesized by the interfacial polymerization reaction of aqueous monomers and organic monomers. In recent years, researchers have begun to pay attention to the influence of surface morphology on the performance of polyamide nanofiltration membranes. Polyamide nanofiltration membranes with a wrinkled surface morphology have attracted wide attention. Common wrinkled surface morphologies include nodular, striped and circular ring structures, etc. The formation of the wrinkled morphology is mainly caused by the interfacial instability mechanism, including reaction diffusion, convective flow and the formation of nanobubbles, etc. By adjusting the reaction conditions of interfacial polymerization, interfacial instability and turbulent phenomena can be effectively induced, thereby forming a polyamide membrane with special morphological characteristics. Nanofiltration membranes with a double-layer microstructure have been proven to have potential in PFAS removal, but in-depth research on the influence of the double-layer membrane morphology on PFAS retention performance is still limited. Therefore, designing a nanofiltration membrane with a double-layer microstructure to improve the PFAS removal rate has become an important research topic at present. Summary of the Invention

[0005] Aiming at the deficiencies of the above prior art, the present invention provides a nanofiltration membrane with a double-layer multi-dimensional structure and a preparation method thereof. By adding a lithium salt regulator to the aqueous solution and combining the synergistic effect of an alkali catalyst, the reaction rate is precisely controlled by adjusting the content and type of the lithium salt, so as to successfully prepare a high-performance nanofiltration membrane with a double-layer multi-dimensional structure in the interfacial polymerization reaction.

[0006] To achieve the above object, the specific technical solution of the present invention is as follows:

[0007] In the first aspect, the present invention provides a preparation method of a nanofiltration membrane with a double-layer multi-dimensional structure, comprising the following steps:

[0008] Immerse the base membrane in an aqueous solution for treatment, take it out, dry it, then immerse it in an oil phase solution for treatment, take it out, and perform heat treatment. After soaking, washing and drying with water, a nanofiltration membrane with a double-layer multi-dimensional structure is obtained;

[0009] Wherein, the aqueous solution includes an aromatic polyfunctional amine, a lithium salt and an alkali catalyst; the oil phase solution includes an aromatic polyfunctional acyl halide.

[0010] In the present invention, a lithium salt-alkali composite catalyst is constructed by adding a lithium salt and an alkali catalyst to the aqueous solution to regulate the ionic strength, pH dynamic balance and nano-structure directional growth, so as to precisely adjust the reaction rate, molecular diffusion behavior and interfacial reaction kinetics of interfacial polymerization, and realize the decoupled control of monomer diffusion-reaction kinetics in the interfacial polymerization reaction (the reaction rate is reduced by 40%-60%), providing a kinetic basis for constructing a heterogeneous structure; at the same time, the present invention utilizes the coordination effect, electrostatic shielding effect, template pore formation, hydrogen bond network regulation of the lithium salt with the carbonyl group in trimesoyl chloride, as well as the multiple effects of the lithium salt and the alkali catalyst on monomer activation and diffusion rate regulation, etc., to enable the synergistic construction of nano-crystal directional growth and amorphous region cross-linking in the polyamide network, forming a double-layer heterogeneous structure with wrinkled macropores on the upper layer and nodular sub-nanometer channels on the lower layer, and obtaining a high-performance nanofiltration membrane with a hierarchical multi-dimensional morphology feature; in addition, the surface of the high-performance nanofiltration membrane with a hierarchical multi-dimensional morphology feature is rich in fluorine adsorption sites, forming a size screening-chemical adsorption dual interception mechanism with the multi-dimensional pores, effectively improving the removal rate of PFAS. The method of the present invention has the advantages of simple operation, high polymerization rate, short reaction time, strong controllability, etc., and is suitable for large-scale production.

[0011] Preferably, the base membrane includes, but is not limited to, a polyethersulfone membrane, a polysulfone membrane, a sulfonated polysulfone membrane, a poly sulfate ester membrane or a polyacrylonitrile membrane.

[0012] Preferably, the aromatic polyfunctional amine includes, but is not limited to, at least one of piperazine, homopiperazine, 2-methylpiperazine, N-aminoethylpiperazine, 2,2-dimethylpiperazine.

[0013] Preferably, the lithium salt includes but is not limited to at least one of lithium carbonate (Li2CO3), lithium nitrate (LiNO3), lithium sulfate (Li2SO4), lithium fluoride (LiF), and lithium phosphate (Li3PO4). When selecting a metal salt, the cation's charge density, hydration ability, and target membrane properties need to be weighed. Among them, lithium salts are preferred for regulating the polyamide structure due to their unique ionic properties. The CO3 in the lithium salt 2- , NO3⁻, SO4 2- , F - and PO4 3- ions can significantly reduce the diffusion rate of aromatic polyfunctional amines in the aqueous solution due to their large volume or stronger hydration ability, enabling a hierarchical multi-dimensional morphological feature to be formed after the interfacial polymerization reaction. In particular, when the lithium salt is lithium chloride, since chloride ions (Cl - ) can form hydrogen bonds or electrostatic interactions with amine monomers (such as piperazine) in the aqueous phase, they cannot effectively delay its diffusion rate, resulting in only a relatively loose structure on the surface of the prepared nanofiltration membrane, leading to poor separation performance.

[0014] Preferably, the base catalyst is a strong base, and the base catalyst includes but is not limited to at least one of sodium hydroxide (NaOH), potassium hydroxide (KOH), and calcium hydroxide (Ca(OH)2).

[0015] Preferably, in the aqueous solution, the mass concentration of the aromatic polyfunctional amine is 0.5%wt - 0.8wt%, the mass concentration of the lithium salt is 0.1wt% - 0.5wt%, and the mass concentration of the base catalyst is 0.5wt% - 1.0wt%.

[0016] Preferably, the aromatic polyfunctional acyl halide includes but is not limited to at least one of trimesoyl chloride, isophthaloyl chloride, phthaloyl chloride, and phthalene disulfonyl chloride.

[0017] Preferably, in the oil phase solution, the mass concentration of the aromatic polyfunctional acyl halide is 0.05wt% - 0.15wt%.

[0018] Preferably, the solvent used in the oil phase solution includes but is not limited to at least one of n-hexane, cyclohexane, isoparaffin IsoparG, isoparaffin Isopar H, and isoparaffin Isopar L.

[0019] Preferably, the time for the substrate membrane to be immersed in the aqueous solution for treatment is 20 - 40 s.

[0020] Preferably, the time for the substrate membrane to be immersed in the oil phase solution for treatment is 30 - 50 s.

[0021] Preferably, the temperature of the heat treatment is 60 to 80 °C and the time is 2 to 10 min.

[0022] In a second aspect, the present invention provides a nanofiltration membrane with a double-layer multi-dimensional structure prepared by the method.

[0023] Preferably, under the conditions of a temperature of 25 °C and a test pressure of 4 bar, the desalination rate of the nanofiltration membrane with a double-layer multi-dimensional structure for 2000 ppm NaCl is 30% to 70%; the desalination rate for 2000 ppm MgCl2 is 50% to 80%; the desalination rate for 2000 ppm MgSO4 or Na2SO4 is 90% to 99%; the removal rate of perfluorooctanoic acid exceeds 90%; the water flux is greater than 15 L m -2 h -1 bar -1 。

[0024] In a third aspect, the present invention provides the application of the nanofiltration membrane with a double-layer multi-dimensional structure in sewage treatment.

[0025] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0026] (1) By adding a lithium salt-alkali composite catalyst in an aqueous solution, the present invention regulates the ionic strength, pH dynamic balance, and directional growth of nanostructures, thereby adjusting the interfacial polymerization rate, molecular diffusion behavior, and interfacial reaction kinetics, and preparing a high-performance polyamide nanofiltration membrane with a hierarchical multi-dimensional structure. The high-performance polyamide nanofiltration membrane with a hierarchical multi-dimensional structure exhibits excellent separation effects during the treatment of natural surface water, especially shows excellent performance in removing perfluoro- and polyfluoroalkyl substances, and has broad application potential.

[0027] (2) The method of the present invention has the advantages of simple operation, high polymerization rate, short reaction time, and strong controllability, and is suitable for large-scale production.

[0028] (3) Based on the research on the efficient removal of PFAS by the nanofiltration membrane with a unique surface microstructure, the present invention proposes an interfacial regulation strategy, which provides a new mechanism perspective for revealing the relationship between the interfacial microstructure and the performance of the nanofiltration membrane, and also opens up a new way for the application of designing efficient nanofiltration membranes in water treatment. Description of the Drawings

[0029] Figure 1 It is the surface SEM image of the nanofiltration membrane with a double-layer multi-dimensional structure for Example 4;

[0030] Figure 2 It is the surface SEM image of the nanofiltration membrane for Comparative Example 1;

[0031] Figure 3SEM image of the surface of the nanofiltration membrane of Comparative Example 2;

[0032] Figure 4 SEM image of the surface of the nanofiltration membrane of Comparative Example 3;

[0033] Figure 5 Filtration effect diagram of surface water by the nanofiltration membrane with a double-layer multi-dimensional structure of Example 4. Detailed implementation manners

[0034] The technical solutions of the present invention will be described clearly and completely below. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts belong to the protection scope of the present invention.

[0035] Before introducing the specific implementation manners of the present invention, it should be clear that the protection scope of the present invention is not limited to the specific implementation manners described below. At the same time, the terms used in the present invention are for the convenience of describing specific embodiments, rather than for limiting the scope of the invention. Unless otherwise defined, all technical terms in the present invention should be interpreted according to the general understanding of those skilled in the art in this technical field. For the experimental methods not specifically listed in the embodiments, they should generally be operated under conventional conditions or the recommended conditions of the equipment manufacturer. In addition to the specific methods, equipment, and materials used in the embodiments, the implementation of the present invention can also be achieved by using existing technical solutions similar or equivalent to the methods, equipment, and materials described in the embodiments.

[0036] The present invention provides a preparation method of a nanofiltration membrane with a double-layer multi-dimensional structure, including the following steps:

[0037] Immerse the base membrane in an aqueous solution for treatment, take it out, dry it, then immerse it in an oil phase solution for treatment, take it out, and perform heat treatment. After soaking, cleaning, and drying with water, a nanofiltration membrane with a double-layer multi-dimensional structure is obtained;

[0038] Wherein, the aqueous solution includes aromatic polyfunctional amine, lithium salt, and base catalyst; the oil phase solution includes aromatic polyfunctional acyl halide.

[0039] In some examples, the base film includes, but is not limited to, a polyethersulfone membrane, a polysulfone membrane, a sulfonated polysulfone membrane, a polysulfate membrane, or a polyacrylonitrile membrane; the aromatic polyfunctional amine includes, but is not limited to, at least one of piperazine, homopiperazine, 2-methylpiperazine, N-aminoethylpiperazine, 2,2-dimethylpiperazine; the lithium salt includes, but is not limited to, at least one of lithium carbonate (Li2CO3), lithium nitrate (LiNO3), lithium sulfate (Li2SO4), lithium fluoride (LiF), lithium phosphate (Li3PO4); the base catalyst is a strong base, and the base catalyst includes, but is not limited to, at least one of sodium hydroxide (NaOH), potassium hydroxide (KOH), calcium hydroxide (Ca(OH)2); the aromatic polyfunctional acyl halide includes, but is not limited to, at least one of trimesoyl chloride, isophthaloyl chloride, phthaloyl chloride, phthalene disulfonyl chloride; the solvent used in the oil phase solution includes, but is not limited to, at least one of n-hexane, cyclohexane, isoparaffin Isopar G, isoparaffin Isopar H, isoparaffin Isopar L.

[0040] In some examples, in the aqueous solution, the mass concentration of the aromatic polyfunctional amine is 0.5%wt - 0.8wt%, the mass concentration of the lithium salt is 0.1wt% - 0.5wt%, and the mass concentration of the base catalyst is 0.5wt% - 1.0wt%; in the oil phase solution, the mass concentration of the aromatic polyfunctional acyl halide is 0.05wt% - 0.15wt%.

[0041] In some examples, the time for the base film to be immersed in the aqueous solution for treatment is 20 - 40 s; the time for the base film to be immersed in the oil phase solution for treatment is 30 - 50 s; the temperature of the heat treatment is 60 - 80 °C, and the time is 2 - 10 min.

[0042] In some examples, under the conditions of a temperature of 25 °C and a test pressure of 4 bar, the desalination rate of the nanofiltration membrane with a double-layer multi-dimensional structure for 2000 ppm NaCl is 30% - 70%; the desalination rate for 2000 ppm MgCl2 is 50% - 80%; the desalination rate for 2000 ppm MgSO4 or Na2SO4 is 90% - 99%; the removal rate of perfluorooctanoic acid exceeds 90%; the water flux is greater than 15 L m -2 h -1 bar -1 。

[0043] In the following specific embodiments, the base membrane is a polyethersulfone membrane (purchased from Minard Membrane Technology (Xiamen) Co., Ltd.). In the present invention, the base membrane is first immersed in an aqueous solution and then in an oil-phase solution. The two phases undergo an interfacial polymerization reaction to obtain a polyamide reactive layer, and finally, through subsequent heat treatment and cleaning, a composite nanofiltration membrane with a double-layer multi-dimensional structure is obtained. The key technology of the present invention lies in controlling the type and content of lithium salts in the aqueous solution, simultaneously coordinating with alkali metal salts and controlling the reaction time to obtain a nanofiltration membrane with high water flux, high PFAS removal rate, and controllable desalination rate under ultra-low pressure driving. The following will be described in detail with specific examples.

[0044] Examples 1 - 11

[0045] A nanofiltration membrane with a double-layer multi-dimensional structure is prepared as follows:

[0046] (1) Immerse the polyethersulfone membrane in a 20% isopropanol solution for 5 min to remove any protective chemicals; subsequently, thoroughly rinse the pretreated porous polyethersulfone support base membrane with deionized water and set it aside for use.

[0047] (2) Immerse the porous polyethersulfone support base membrane in an aqueous solution containing a lithium salt (the content and type of the lithium salt are shown in Table 1), 0.5 wt% piperazine, and 0.5 wt% sodium hydroxide for 30 s. Subsequently, use an air knife to blow dry the excess solution on the surface.

[0048] (3) Immerse the porous polyethersulfone support base membrane obtained in step (2) in a 0.1 wt% hexane solution of trimesoyl chloride for 10 s to form a separation layer. Finally, heat-treat the composite membrane in an oven at 70 °C for 3 min, soak it in pure water, clean it, and dry it to obtain a nanofiltration membrane with a double-layer multi-dimensional structure.

[0049] Comparative Example 1

[0050] The difference between this Comparative Example 1 and Example 4 is that the aqueous solution does not contain a lithium salt.

[0051] Comparative Example 2

[0052] The difference between this Comparative Example 1 and Example 4 is that the aqueous solution does not contain an alkali catalyst.

[0053] Comparative Example 3

[0054] The difference between this Comparative Example 3 and Example 4 is that the lithium salt used is lithium chloride (LiCl).

[0055] Comparative Example 4

[0056] The difference between this Comparative Example 4 and Example 4 is that the lithium salt used is sodium chloride (NaCl).

[0057] Comparative Example 5

[0058] The difference between this Comparative Example 5 and Example 4 is that the lithium salt used is magnesium chloride (MgCl).

[0059] Comparative Example 6

[0060] The difference between this Comparative Example 6 and Example 4 is that the lithium salt used is potassium chloride (KCl).

[0061] Comparative Example 7

[0062] The difference between this Comparative Example 7 and Example 4 is that the alkali catalyst used is sodium carbonate (Na2CO3).

[0063] Comparative Example 8

[0064] The difference between this Comparative Example 8 and Example 4 is that the alkali catalyst used is sodium phosphate (Na3PO4).

[0065] Comparative Example 9

[0066] The difference between this Comparative Example 9 and Example 4 is that the alkali catalyst used is triethylamine.

[0067] Comparative Example 10

[0068] The difference between this Comparative Example 10 and Example 5 is that the alkali catalyst used is sodium bicarbonate (NaHCO3).

[0069] The surface structures of the nanofiltration membranes prepared in Example 4 and Comparative Examples 1-3 were characterized, and the results are as follows Figures 1-4 shown. It can be seen from the figure that the nanofiltration membrane with a double-layer multi-dimensional structure of the present invention has the morphological characteristics of a fractal nested "pocket" with a large-folded outer layer structure and a dense small nodule inner layer structure. When the nanofiltration membrane is used for filtration treatment, its large-folded outer layer structure intercepts pollutant molecules, and at the same time, the dense small nodule structure inside it plays a role in secondary interception, effectively inhibiting the transmembrane mass transfer of pollutant molecules, greatly improving the interception effect of pollutants, and avoiding the problem of low pollutant interception efficiency caused by the single-layer interception of traditional limited membranes.

[0070] The nanofiltration membranes prepared in Examples 1-11 and Comparative Examples 1-10 were subjected to performance tests. Under the conditions of an operating pressure of 4 bar and a temperature of 25 °C, a membrane filtration experiment was carried out on an aqueous solution containing NaCl (2 g / L), MgCl2 (2 g / L), MgSO4 (2 g / L), Na2SO4 (2 g / L), and perfluorooctanoic acid (PFOA, 50 μg / L). The test results are shown in Table 1.

[0071] Table 1: Performance test results of the nanofiltration membranes of Examples 1-11 and Comparative Examples 1-10

[0072]

[0073] From the data in Table 1, it can be seen that under the conditions of a temperature of 25 °C and a test pressure of 4 bar, the nanofiltration membrane with a bilayer multi-dimensional structure prepared by the present invention has a moderate desalination rate for 2000 ppm (i.e., 2 g / L) of NaCl, which is 30% - 70%; the desalination rate for 2000 ppm of MgCl2 is 50% - 80%; the desalination rate for 2000 ppm of MgSO4 or Na2SO4 is 90% - 99%; the removal rate of perfluorooctanoic acid exceeds 90%; and the water flux is greater than 15 L m -2 h -1 bar -1 -1 bar-1. This result shows that the nanofiltration membrane with a bilayer multi-dimensional structure of the present invention has excellent separation performance, and by changing the type and concentration of the lithium salt, the performance of the nanofiltration membrane can be regulated, and it has great potential in practical applications.

[0074] Application Example

[0075] The nanofiltration membrane with a bilayer multi-dimensional structure prepared in Example 4 was used to purify surface water (TOC: 5.65 mg / L, TDS: 845 mg / L, Ca 2+ : 425 mg / L, Mg 2+ : 344 mg / L) for a purification test with a single cycle.

[0076] The specific steps are as follows:

[0077] a. Pretreatment of surface water with a microfiltration membrane: The surface water was filtered and pretreated with a commercial microfiltration membrane. The purpose was to remove impurities and suspended particles in the raw water to prevent clogging of the nanofiltration membrane. The operating pressure was 0.02 Mpa. The pore size of the microfiltration membrane was 0.45 μm, which was much larger than the pore size of the nanofiltration membrane and could not retain dissolved substances and ions in the water. Therefore, it would not affect the interception experimental data of subsequent Ca 2+ and Mg 2+ and other ions. The permeate obtained after microfiltration was used as the feed water for the nanofiltration membrane with a bilayer multi-dimensional structure.

[0078] b. The surface water pretreated by microfiltration entered the feed water tank and was deeply filtered using the nanofiltration membrane with a bilayer multi-dimensional structure prepared in Example 4 of the present invention under a pressure of 0.4 Mpa.

[0079] The effluent of the nanofiltration membrane was collected, and the collected solution was measured and analyzed for TOC and TDS. At the same time, an ion chromatograph was used to detect and calculate Ca 2+ and Mg in the raw water and the collected solution2+ Content; The removal effect of the nanofiltration membrane of the present invention on perfluorooctanoic acid (PFOA) was tested using a triple quadrupole mass spectrometer.

[0080] The test results are shown in Figure 5 , and the figure shows that the removal rate of the nanofiltration membrane of the present invention for TOC is 89.76%, the removal rate for total dissolved solids (TDS) in water is 87.34%, the removal rate for Ca 2+ is 78.45%, the removal rate for Mg 2+ is 90.12%, and the removal rate for PFOA is 90.12%.

[0081] In summary, the present invention adds a lithium salt-alkali composite catalyst in an aqueous solution to regulate the ionic strength, pH dynamic balance, and the directional growth of nanostructures, thereby adjusting the interfacial polymerization rate, molecular diffusion behavior, and interfacial reaction kinetics, and preparing a high-performance polyamide nanofiltration membrane with a hierarchical multi-dimensional structure. Moreover, by changing the type and concentration of the lithium salt, the performance of the nanofiltration membrane can be regulated. The high-performance polyamide nanofiltration membrane with a hierarchical multi-dimensional structure exhibits excellent separation effects during the treatment of natural surface water, especially shows excellent performance in removing perfluoro- and polyfluoroalkyl substances, and has broad application potential.

[0082] The above specific embodiments have described the implementation of the present invention in detail. However, the present invention is not limited to the specific details in the above embodiments. Within the scope of the claims and technical concept of the present invention, various simple modifications and changes can be made to the technical solutions of the present invention, and these simple variations all belong to the protection scope of the present invention.

Claims

1. A preparation method of a nanofiltration membrane with a double-layer multi-dimensional structure, characterized in that, It includes the following steps: Immerse the base membrane in an aqueous solution for treatment, take it out, dry it, then immerse it in an oil-phase solution for treatment, take it out, and perform heat treatment. After soaking in water, washing, and drying, a nanofiltration membrane with a double-layer multi-dimensional structure is obtained; Among them, the aqueous solution includes aromatic polyfunctional amines, lithium salts, and base catalysts; The oil-phase solution includes aromatic polyfunctional acyl halides.

2. The preparation method of a nanofiltration membrane with a double-layer multi-dimensional structure according to claim 1, characterized in that, The aromatic polyfunctional amines include but are not limited to at least one of piperazine, homopiperazine, 2-methylpiperazine, N-aminoethylpiperazine, 2,2-dimethylpiperazine; the lithium salts include but are not limited to at least one of lithium carbonate, lithium nitrate, lithium sulfate, lithium fluoride, lithium phosphate; the base catalysts include but are not limited to at least one of sodium hydroxide, potassium hydroxide, calcium hydroxide; the aromatic polyfunctional acyl halides include but are not limited to at least one of trimesoyl chloride, isophthaloyl chloride, phthaloyl chloride, phthalene disulfonyl chloride; the base membrane includes but is not limited to a polyethersulfone membrane, a polysulfone membrane, a sulfonated polysulfone membrane, a poly sulfate ester membrane, or a polyacrylonitrile membrane; the solvents used in the oil-phase solution include but are not limited to at least one of n-hexane, cyclohexane, isoparaffin Isopar G, isoparaffin Isopar H, isoparaffin Isopar L.

3. The preparation method of a nanofiltration membrane with a double-layer multi-dimensional structure according to claim 1, characterized in that, In the aqueous solution, the mass concentration of the aromatic polyfunctional amine is 0.5%wt - 0.8wt%, the mass concentration of the lithium salt is 0.1wt% - 0.5wt%, and the mass concentration of the base catalyst is 0.5wt% - 1.0wt%.

4. A preparation method of a nanofiltration membrane with a double-layer multi-dimensional structure according to claim 1, characterized in that, In the oil-phase solution, the mass concentration of the aromatic polyfunctional acyl halide is 0.05wt% - 0.15wt%.

5. The preparation method of a nanofiltration membrane with a double-layer multi-dimensional structure according to claim 1, characterized in that, The time for the base membrane to be immersed in the aqueous solution for treatment is 20 - 40 s; the time for the base membrane to be immersed in the oil-phase solution for treatment is 30 - 50 s; the temperature of the heat treatment is 60 - 80 °C, and the time is 2 - 10 min.

6. A nanofiltration membrane with a double-layer multi-dimensional structure prepared by the method according to any one of claims 1 - 5.

7. The nanofiltration membrane with a double-layer multi-dimensional structure according to claim 6, characterized in that, Under the conditions of a temperature of 25 °C and a test pressure of 4 bar, the desalination rate of the nanofiltration membrane with a double-layer multi-dimensional structure for 2000 ppm NaCl is 30% - 70%; the desalination rate for 2000 ppm MgCl2 is 50% - 80%; the desalination rate for 2000 ppm MgSO4 or Na2SO4 is 90% - 99%; the removal rate for perfluorooctanoic acid exceeds 90%; the water flux is greater than 15 L m -2 h -1 bar -1 。 8. Application of the nanofiltration membrane with a double-layer multi-dimensional structure according to claim 6 in sewage treatment.

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