Thin film composite nanofiltration membrane, preparation method and application thereof

Abstract

This invention discloses a thin-film composite nanofiltration membrane, its preparation method, and its application, belonging to the field of membrane separation technology. The preparation method specifically includes the following steps: (1) dissolving a negatively charged amine monomer and a negatively charged ionic liquid in pure water, adding an alkaline solution to obtain an aqueous monomer solution; (2) dissolving a polyacrylamide chloride in an organic solvent to obtain an organic phase solution; (3) immersing the surface of a porous ultrafiltration substrate in the aqueous phase solution; (4) immersing the substrate in the organic phase solution to carry out an interfacial polymerization reaction; (5) heat treatment, rinsing, and drying to obtain the final product. Compared with traditional nanofiltration membranes, this invention strengthens the negative charge intensity of the polyamide layer surface and regulates the porosity of the polyamide layer through the synergistic effect of the negatively charged amine monomer and the negatively charged ionic liquid. The resulting thin-film composite nanofiltration membrane exhibits high permeability, excellent monovalent / divalent anion selectivity, and strong antifouling ability, making it suitable for seawater desalination pretreatment and industrial wastewater treatment.

Description

Technical Field

[0001] This invention relates to the field of membrane separation technology, and more specifically to a thin-film composite nanofiltration membrane, its preparation method, and its application. Background Technology

[0002] In seawater desalination pretreatment and industrial wastewater treatment processes, high concentrations of divalent anions (such as SO42-) are present. 2- Monovalent / divalent anions typically lead to scaling, which increases the energy consumption of water treatment systems and poses environmental risks. Therefore, achieving effective separation of monovalent / divalent anions is crucial for ensuring the stable operation of water treatment systems.

[0003] Currently, nanofiltration membrane technology offers a promising method for separating monovalent / divalent anions due to its advantages such as low energy consumption, low carbon emissions, and high design flexibility. Polyamide membranes are the benchmark membranes for separating monovalent / divalent anions in nanofiltration. These membranes are typically prepared by interfacial polymerization of an aqueous amine monomer (such as piperazine) and an organic acyl chloride monomer (such as trimesoyl chloride) on a porous substrate, relying on steric hindrance and the Donnan effect to separate monovalent / divalent anions.

[0004] To significantly improve the selectivity of nanofiltration membranes for monovalent / divalent anions, existing technologies attempt to modify nanofiltration membranes by introducing ionic liquids during interfacial polymerization. For example, CN117000061A discloses a method for preparing polyamide film composite nanofiltration membranes using ionic liquids as aqueous phase additives. This technology directly adds ionic liquids to piperazine aqueous solutions and prepares nanofiltration membranes through one-step interfacial polymerization. However, this approach still has significant drawbacks: (1) Piperazine monomers have strong reactivity and a high interfacial polymerization rate, resulting in a relatively dense polyamide layer structure and low porosity, which is not conducive to improving water permeability and the release of monovalent anions (such as Cl-). - (2) Piperazine monomers themselves are uncharged, and the negative charge on the membrane surface comes only from the carboxyl groups generated by the hydrolysis of unreacted acyl chloride groups. The negative charge strength is still low, and it is not effective against divalent anions (such as SO42-). 2- (3) Insufficient electrostatic repulsion makes it difficult to further improve the selectivity of monovalent / divalent anions; (4) Insufficient hydrophilicity and negative charge strength of membrane surface result in limited improvement of antifouling ability.

[0005] Therefore, how to prepare a thin-film composite nanofiltration membrane with high permeability, excellent monovalent / divalent anion selectivity and strong antifouling ability is a key problem that technicians urgently need to solve. Summary of the Invention

[0006] In view of this, the purpose of the present invention is to provide a thin-film composite nanofiltration membrane, its preparation method and application, so as to overcome the shortcomings of the prior art.

[0007] To achieve the above objectives, the present invention adopts the following technical solution:

[0008] A method for preparing a thin-film composite nanofiltration membrane specifically includes the following steps: (1) Dissolve the negatively charged amine monomer and the negatively charged ionic liquid in pure water, add alkali solution to obtain an aqueous monomer solution for later use; (2) Dissolve the polyacryl chloride in an organic solvent to obtain an organic phase solution for later use; (3) First, immerse the surface of the porous ultrafiltration substrate in the aqueous solution, then pour off the excess aqueous solution and remove the droplets on the surface of the porous ultrafiltration substrate to obtain a porous ultrafiltration substrate that stores aqueous monomers in the pores. (4) First, immerse the surface of the porous ultrafiltration substrate containing aqueous monomers in an organic phase solution to carry out interfacial polymerization reaction. Then, pour off the excess organic phase solution and finally rinse with an organic solvent to obtain the nascent nanofiltration membrane. (5) First, heat-treat the nascent nanofiltration membrane, then rinse it with pure water and dry it to obtain the thin film composite nanofiltration membrane.

[0009] Further, in step (1) above, the negatively charged amine monomer is piperazine-2-carboxylic acid; the negatively charged ionic liquid is at least one of 1-ethyl-3-methylimidazolium chloride, 1-ethyl-3-methylimidazolium tetrafluoroborate, 1-butyl-3-methylimidazolium chloride, 1-butyl-3-methylimidazolium tetrafluoroborate, 1-butyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide, 1-hexyl-3-methylimidazolium chloride, and 1-octyl-3-methylimidazolium chloride, preferably 1-ethyl-3-methylimidazolium chloride; the alkaline solution is at least one of NaOH solution and KOH solution, preferably NaOH solution, with a mass fraction of 0.4%-4.0%, preferably 2.0%, added to a pH value of 10-13, preferably 12; in the aqueous monomer solution, the mass fraction of the negatively charged amine monomer is 0.05%-5.0%, preferably 1.0%, and the mass fraction of the negatively charged ionic liquid is 0.1%-5.0%. The preferred value is 2.0%.

[0010] The further beneficial effects of the above-mentioned method are that the carboxyl groups carried by the negatively charged amine monomer directly become part of the polyamide backbone; the negatively charged ionic liquid is oriented at the reaction interface, thereby reducing the interfacial energy barrier, promoting the transport of trimesoyl chloride molecules from the organic phase to the reaction interface and their accumulation at the interface, and hydrolyzing to generate a large number of additional carboxyl groups; the negatively charged ionic liquid and the negatively charged carboxyl groups generate electrostatic repulsion, inducing the negative charge orientation of the polyamide layer surface to be outward. The carboxyl groups carried by the piperazine-2-carboxylic acid monomer and the regulatory effect of the negatively charged ionic liquid synergistically enhance the density of negatively charged carboxyl groups on the membrane surface. In addition, the alkaline solution can act as an acceptor for hydrochloric acid generated during the interfacial polymerization process, and can strengthen the negative charge intensity of the negatively charged ionic liquid, enhance its electrostatic repulsion on the negatively charged carboxyl groups generated during the interfacial polymerization reaction, causing them to be oriented outward, thereby increasing the negative charge intensity of the membrane surface.

[0011] Furthermore, in step (2) above, the polyacrylamide chloride is at least one of isophthaloyl chloride and trimesoyl chloride, preferably trimesoyl chloride; the organic solvent is at least one of n-hexane, n-heptane, Isopar G, cyclohexane, toluene and n-octane, preferably n-hexane; the mass fraction of the organic phase monomer solution is 0.01%~0.3%, preferably 0.15%.

[0012] Furthermore, in step (3) above, the membrane material of the porous ultrafiltration substrate is polysulfone, polyethersulfone, polyvinylidene fluoride or polyacrylonitrile, preferably polyethersulfone.

[0013] Furthermore, in step (3) above, the immersion time is 0.5 to 20 minutes, preferably 3 minutes.

[0014] Furthermore, in step (4) above, the time for the interfacial polymerization reaction is 5~300s, preferably 3min.

[0015] Furthermore, in step (4) above, the organic solvent is at least one of n-hexane, n-heptane, Isopar G, cyclohexane, toluene and n-octane, preferably n-hexane; the rinsing time is 20~300s, preferably 30s.

[0016] Furthermore, in step (5) above, the heat treatment temperature is 40~80℃, preferably 70℃, and the time is 2~20min, preferably 5min; the pure water rinsing time is 20~300s, preferably 1min; the drying temperature is 30~80℃, preferably 50℃, and the time is 2~30min, preferably 2min.

[0017] This invention also claims protection for a thin-film composite nanofiltration membrane prepared by the above-described preparation method.

[0018] This invention also claims protection for the application of a thin-film composite nanofiltration membrane prepared by the above-described method in seawater desalination pretreatment and industrial wastewater treatment.

[0019] As can be seen from the above technical solution, compared with the prior art, the beneficial effects of the present invention are as follows: 1. The negatively charged amine monomer (piperazine-2-carboxylic acid) used in this invention has a large carboxyl group volume and significant steric hindrance, resulting in reduced interfacial polymerization activity with trimesoyl chloride. Simultaneously, the high-viscosity negatively charged ionic liquid hinders the Brownian motion of piperazine-2-carboxylic acid, slowing its diffusion rate to the reaction interface. The synergistic effect of the steric hindrance of the negatively charged amine monomer and the high-viscosity negatively charged ionic liquid weakens the interfacial polymerization rate, leading to the formation of a loose polyamide separation layer. The increased density of negatively charged carboxyl groups on the membrane surface enhances the electrostatic repulsion against divalent anions, and the loose separation layer structure allows monovalent anions to permeate more easily through the membrane, thereby significantly improving the monovalent / divalent anion selectivity of the membrane.

[0020] 2. The increased negative charge carboxyl group density on the surface of the membrane composite nanofiltration membrane of the present invention is beneficial to improving the hydrophilicity of the membrane surface and hindering the adsorption of pollutants. At the same time, the enhanced negative charge strength can improve the electrostatic repulsion of negatively charged pollutants (such as bovine serum albumin), thereby significantly improving the membrane's antifouling ability.

[0021] 3. Compared with traditional nanofiltration membranes, this invention enhances the negative charge intensity on the surface of the polyamide layer through the synergistic effect of negatively charged amine monomers and negatively charged ionic liquids, and controls the porosity of the polyamide layer. The resulting thin-film composite nanofiltration membrane has high permeability, excellent monovalent / divalent anion selectivity and strong antifouling ability, and is suitable for seawater desalination pretreatment and industrial wastewater treatment. Attached Figure Description

[0022] Figure 1 Scanning electron microscope (SEM) images of the surface of the nanofiltration membranes in Examples 1-2 and Comparative Examples 1-2; Figure 2 The surface carboxyl group density of the nanofiltration membranes in Examples 1-2 and Comparative Examples 1-2; Figure 3 The surface Zeta potential of the nanofiltration membranes in Examples 1-2 and Comparative Examples 1-2; Figure 4 The surface water contact angle of the nanofiltration membranes in Examples 1-2 and Comparative Examples 1-2; Figure 5 The molecular weight cutoff of the nanofiltration membranes in Examples 1-2 and Comparative Examples 1-2; Figure 6 The membrane pore size of the nanofiltration membranes in Examples 1-2 and Comparative Examples 1-2; Figure 7 The pure water flux of the nanofiltration membranes in Examples 1-2 and Comparative Examples 1-2; Figure 8 Salt rejection rates of nanofiltration membranes in Examples 1 and 2 and Comparative Examples 1-2; Figure 9 The NaCl / Na2SO4 selectivity of nanofiltration membranes in Examples 1-2 and Comparative Examples 1-2; Figure 10 The normalized flux for filtering bovine serum albumin solution using nanofiltration membranes in Examples 1-2 and Comparative Examples 1-2 is given. Detailed Implementation

[0023] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0024] Example The preparation method of the thin-film composite nanofiltration membrane specifically includes the following steps: (1) Dissolve 0.5 g piperazine-2-carboxylic acid and 0.70 mL of 1-ethyl-3-methylimidazolium chloride in 48.5 mL of pure water, and adjust the pH to 12 with 2.0% NaOH solution to obtain an aqueous solution with a piperazine-2-carboxylic acid mass fraction of 1.0% and a 1-ethyl-3-methylimidazolium chloride mass fraction of 2.0%, for later use; (2) Dissolve 0.05 g of trimesoyl chloride in 50 mL of n-hexane to obtain an organic phase solution with a mass fraction of 0.15%, and set aside for later use; (3) First, immerse the surface of the porous polyethersulfone ultrafiltration substrate in the aqueous solution for 3 minutes, then pour off the excess aqueous solution and remove the droplets on the surface of the porous ultrafiltration substrate to obtain a porous ultrafiltration substrate that stores aqueous monomers in the pores. (4) First, immerse the surface of the porous ultrafiltration substrate containing aqueous monomers in n-hexane for interfacial polymerization reaction for 3 min, then pour off the excess organic phase solution, and finally rinse with n-hexane for 30 s to obtain the nascent nanofiltration membrane. (5) First, heat-treat the nascent nanofiltration membrane at 70°C for 5 min, then rinse it with pure water for 1 min, and dry it at 50°C for 2 min to obtain the membrane composite nanofiltration membrane.

[0025] Comparative Example 1 The preparation method of the thin-film composite nanofiltration membrane (the only difference from the example is that piperazine-2-carboxylic acid is replaced with piperazine) specifically includes the following steps: (1) Dissolve 0.5 g piperazine and 0.70 mL of 1-ethyl-3-methylimidazolium chloride in 48.5 mL of pure water, and adjust the pH to 12 with 2.0% NaOH solution to obtain an aqueous solution with a piperazine mass fraction of 1.0% and a 1-ethyl-3-methylimidazolium chloride mass fraction of 2.0%, for later use; (2) Dissolve 0.05 g of pyromellitic chloride in 50 mL of n-hexane to obtain an organic phase pyromellitic chloride solution with a mass fraction of 0.15%, and set aside for later use; (3) First, immerse the surface of the porous polyethersulfone ultrafiltration substrate in the aqueous solution for 3 minutes, then pour off the excess aqueous solution and remove the droplets on the surface of the porous ultrafiltration substrate to obtain a porous ultrafiltration substrate that stores aqueous monomers in the pores. (4) First, immerse the surface of the porous ultrafiltration substrate containing aqueous monomers in n-hexane for interfacial polymerization reaction for 3 min, then pour off the excess organic phase solution, and finally rinse with n-hexane for 30 s to obtain the nascent nanofiltration membrane. (5) First, heat-treat the nascent nanofiltration membrane at 70°C for 5 min, then rinse it with pure water for 1 min, and dry it at 50°C for 2 min to obtain the membrane composite nanofiltration membrane.

[0026] Comparative Example 2 The preparation method of the thin-film composite nanofiltration membrane (the only difference from the example is that the aqueous solution does not contain 1-ethyl-3-methylimidazolium chloride) specifically includes the following steps: (1) Dissolve 0.5 g piperazine-2-carboxylic acid in 49.5 mL of pure water, and adjust the pH to 12 with 2.0% NaOH solution to obtain an aqueous solution with a piperazine-2-carboxylic acid mass fraction of 1.0%, for later use; (2) Dissolve 0.05 g of pyromellitic chloride in 50 mL of n-hexane to obtain an organic phase pyromellitic chloride solution with a mass fraction of 0.15%, and set aside for later use; (3) First, immerse the surface of the porous polyethersulfone ultrafiltration substrate in the aqueous solution for 3 minutes, then pour off the excess aqueous solution and remove the droplets on the surface of the porous ultrafiltration substrate to obtain a porous ultrafiltration substrate that stores aqueous monomers in the pores. (4) First, immerse the surface of the porous ultrafiltration substrate containing aqueous monomers in n-hexane for interfacial polymerization reaction for 3 min, then pour off the excess organic phase solution, and finally rinse with n-hexane for 30 s to obtain the nascent nanofiltration membrane. (5) First, heat-treat the nascent nanofiltration membrane at 70°C for 5 min, then rinse it with pure water for 1 min, and dry it at 50°C for 2 min to obtain the membrane composite nanofiltration membrane.

[0027] Performance testing 1. Membrane characterization The nanofiltration membranes prepared in Examples 1 and 2 were characterized for surface morphology, carboxyl density, zeta potential, water contact angle, molecular weight cutoff, and pore size. The results are as follows: Figure 1-6 As shown.

[0028] Depend on Figure 1 It can be seen that the nanofiltration membranes of the Examples have fewer nodules on their surface, which helps to slow down the deposition of pollutants on the nanofiltration membranes of the Examples; while the nanofiltration membranes of Comparative Examples 1-2 have more nodules on their surface.

[0029] Depend on Figure 2 It can be seen that the carboxyl group density on the surface of the nanofiltration membrane in the embodiment is 483 nm. -2 It is significantly higher than the 369 nm of the nanofiltration membrane in Comparative Example 1. -2 Compared with the 266 nm nanofiltration membrane of Comparative Example 2 -2 This indicates that the synergistic effect of the negatively charged amine monomer (piperazine-2-carboxylic acid) and the negatively charged ionic liquid (1-ethyl-3-methylimidazolium chloride) can significantly increase the surface carboxyl group density of the nanofiltration membrane in the examples.

[0030] Depend on Figure 3 It can be seen that at pH=7, the Zeta potential value of the nanofiltration membrane surface of the example is -107.4 mV, which is significantly higher than -81.9 mV of the nanofiltration membrane of Comparative Example 1 and -62.8 mV of the nanofiltration membrane of Comparative Example 2. This indicates that the increase in the carboxyl group density on the surface of the nanofiltration membrane of the example can significantly enhance the negative charge intensity of the membrane surface, which helps to strengthen the retention of divalent anions and enhance the electrostatic repulsion of negatively charged pollutants by the nanofiltration membrane of the example.

[0031] Depend on Figure 4 It can be seen that the water contact angle of the nanofiltration membrane surface in the embodiment is 10.7°, which is significantly lower than that of the nanofiltration membrane of Comparative Example 1 (19.4°) and the nanofiltration membrane of Comparative Example 2 (25.8°). This indicates that the increase in carboxyl group density on the surface of the nanofiltration membrane in the embodiment significantly improves the hydrophilicity of the membrane surface, which is beneficial to enhancing the antifouling ability of the nanofiltration membrane surface in the embodiment.

[0032] Depend on Figure 5 It can be seen that the molecular weight cutoff of the nanofiltration membrane in the example is 591 Da, which is significantly higher than that of the nanofiltration membrane of Comparative Example 1 (502 Da) and the nanofiltration membrane of Comparative Example 2 (415 Da). This indicates that the synergistic effect of the negatively charged amine monomer (piperazine-2-carboxylic acid) and the negatively charged ionic liquid (1-ethyl-3-methylimidazolium chloride) can effectively regulate the porosity of the polyamide layer of the nanofiltration membrane in the example.

[0033] Depend on Figure 6It can be seen that the pore size of the polyamide layer of the nanofiltration membrane in the embodiment is 0.586 nm, which is significantly larger than that of the nanofiltration membrane of Comparative Example 1 (0.535 nm) and the nanofiltration membrane of Comparative Example 2 (0.481 nm). This helps to improve the water permeability and monovalent anion permeation of the nanofiltration membrane in the embodiment.

[0034] 2. Water treatment efficiency test The nanofiltration membranes prepared in Examples 1 and 2 were subjected to water treatment performance tests, specifically including water permeability tests, salt rejection rate tests, and antifouling performance tests. The results are as follows: Figure 7-10 As shown.

[0035] The test conditions for water treatment efficiency testing are as follows: (1) When conducting water permeability (pure water flux) tests, the operating pressure is 0.6 MPa; the cross-flow velocity is 10 cm / s; and the water temperature is 25℃.

[0036] Pure water flux (PWF) refers to the volume (V) of pure water passing through a unit membrane area (A) per unit time (t) at a unit operating pressure (S), with units of L·m. -2 ·h -1 ·bar -1 PWF is used to measure the water permeability of nanofiltration membranes, and its calculation formula is: PWF=V / (A·t·S).

[0037] (2) When conducting the salt rejection test, the feed concentration is: 1000 mg / L NaCl solution, 1000 mg / L Na2SO4 solution; operating pressure is 6 bar; cross-flow velocity is 10 cm / s; solution pH is 7.0; water temperature is 25℃.

[0038] Retention rate (R) refers to the solute concentration (C) of the feed solution under a certain operating pressure. f ) and the concentration of solute in the permeate (C) p The ratio of the difference between the concentrations of inorganic salt ions (C and C) and the concentration of the solute in the feed solution is used to evaluate the removal capacity of nanofiltration membranes for inorganic salt ions. The calculation formula is: R(%) = (C / C) * ... f -C p ) / C f ×100%.

[0039] The selectivity of NaCl / Na2SO4 was used to evaluate the separation performance of nanofiltration membranes for monovalent / divalent anions. The calculation formula is: S(NaCl / Na2SO4)=(1-R NaCl ) / (1-R Na2SO4 ).

[0040] (3) When conducting the antifouling performance (normalized flux) test, the feed concentrations were: bovine serum albumin 100 mg / L, NaCl 1000 mg / L; and the initial flux was 100 L·m. -2 ·h -1 Cross-flow velocity 10 cm / s; solution pH 7.0; water temperature 25℃. Chemical cleaning conditions: 1.0% EDTA solution with pH=12, cross-flow velocity 20 cm / s; water temperature 25℃; duration 10 min.

[0041] Normalized flux (N) f ) refers to the membrane flux (J) during the fouling process. f The ratio of N to the initial membrane flux (J0) is used to evaluate the membrane's antifouling performance. The formula for calculating N is: f =J f / J0.

[0042] Depend on Figure 7 It can be seen that the pure water flux (L·m) of the nanofiltration membrane in the example is... -2 ·h -1 ·bar -1 The value was 54.4, which was much higher than the 37.8 of the nanofiltration membrane in Comparative Example 1 and the 22.2 of the nanofiltration membrane in Comparative Example 2.

[0043] Depend on Figure 8 It can be seen that the Na2SO4 rejection rate of the nanofiltration membrane in the example is 99.35%, which is significantly higher than that of the nanofiltration membrane in Comparative Example 1 (98.61%) and the nanofiltration membrane in Comparative Example 2 (98.00%); the NaCl rejection rate of the nanofiltration membrane in the example is 6.47%, which is significantly lower than that of the nanofiltration membrane in Comparative Example 1 (7.28%) and the nanofiltration membrane in Comparative Example 2 (12.51%).

[0044] Depend on Figure 9 It can be seen that the NaCl / Na2SO4 selectivity of the nanofiltration membrane in the example is 143.9, which is 2.2 times and 3.3 times that of the nanofiltration membrane of Comparative Example 1 (66.5) and Comparative Example 2 (43.7), respectively.

[0045] Depend on Figure 10 It can be seen that the normalized flux of the nanofiltration membrane in the example at the end of membrane fouling was 0.90, which was significantly higher than that of the nanofiltration membrane in Comparative Example 1 (0.74) and Comparative Example 2 (0.55). Furthermore, after chemical cleaning, the normalized flux of the nanofiltration membrane in the example was almost completely recovered, while the normalized flux of the nanofiltration membranes in Example 1 and Comparative Example 2 only recovered to 0.81 and 0.62, respectively.

[0046] The above description of the disclosed embodiments enables those skilled in the art to make or use the invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the invention. Therefore, the invention is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A method for preparing a thin-film composite nanofiltration membrane, characterized in that, Specifically, the following steps are included: (1) Dissolve the negatively charged amine monomer and the negatively charged ionic liquid in pure water, add alkali solution to obtain an aqueous monomer solution for later use; (2) Dissolve the polyacryl chloride in an organic solvent to obtain an organic phase solution for later use; (3) First, immerse the surface of the porous ultrafiltration substrate in the aqueous solution, then pour off the excess aqueous solution and remove the droplets on the surface of the porous ultrafiltration substrate to obtain a porous ultrafiltration substrate that stores aqueous monomers in the pores. (4) First, immerse the surface of the porous ultrafiltration substrate containing aqueous monomers in an organic phase solution to carry out interfacial polymerization reaction. Then, pour off the excess organic phase solution and finally rinse with an organic solvent to obtain the nascent nanofiltration membrane. (5) First, heat-treat the nascent nanofiltration membrane, then rinse it with pure water and dry it to obtain the thin film composite nanofiltration membrane.

2. The method for preparing a thin-film composite nanofiltration membrane according to claim 1, characterized in that, In step (1), the negatively charged amine monomer is piperazine-2-carboxylic acid; the negatively charged ionic liquid is at least one of 1-ethyl-3-methylimidazolium chloride, 1-ethyl-3-methylimidazolium tetrafluoroborate, 1-butyl-3-methylimidazolium chloride, 1-butyl-3-methylimidazolium tetrafluoroborate, 1-butyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide, 1-hexyl-3-methylimidazolium chloride, and 1-octyl-3-methylimidazolium chloride; the alkaline solution is at least one of NaOH solution and KOH solution, with a mass fraction of 0.4%-4.0%, added to a pH value of 10-13; in the aqueous monomer solution, the mass fraction of the negatively charged amine monomer is 0.05%-5.0%, and the mass fraction of the negatively charged ionic liquid is 0.1%-5.0%.

3. The method for preparing a thin-film composite nanofiltration membrane according to claim 1, characterized in that, In step (2), the polyacrylamide chloride is at least one of isophthaloyl chloride and trimesoyl chloride; the organic solvent is at least one of n-hexane, n-heptane, Isopar G, cyclohexane, toluene and n-octane; and the mass fraction of the organic phase monomer solution is 0.01%~0.3%.

4. The method for preparing a thin-film composite nanofiltration membrane according to claim 1, characterized in that, In step (3), the membrane material of the porous ultrafiltration substrate is polysulfone, polyethersulfone, polyvinylidene fluoride or polyacrylonitrile.

5. The method for preparing a thin-film composite nanofiltration membrane according to claim 1, characterized in that, In step (3), the immersion time is 0.5 to 20 minutes.

6. The method for preparing a thin-film composite nanofiltration membrane according to claim 1, characterized in that, In step (4), the time for the interfacial polymerization reaction is 5~300s.

7. The method for preparing a thin-film composite nanofiltration membrane according to claim 1, characterized in that, In step (4), the organic solvent is at least one of n-hexane, n-heptane, Isopar G, cyclohexane, toluene, and n-octane; the rinsing time is 20-300s.

8. The method for preparing a thin-film composite nanofiltration membrane according to claim 1, characterized in that, In step (5), the heat treatment temperature is 40~80℃ and the time is 2~20min; the pure water rinsing time is 20~300s; and the drying temperature is 30~80℃ and the time is 2~30min.

9. A thin-film composite nanofiltration membrane prepared by the preparation method according to any one of claims 1 to 8.

10. The application of a thin-film composite nanofiltration membrane prepared by the preparation method according to any one of claims 1 to 8 in seawater desalination pretreatment and industrial wastewater treatment.

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