Method for preparing polyquaternary ammonium nanofiltration membrane based on door shut gold reaction interface polymerization and application

Abstract

The application discloses a method for preparing a polyquaternary ammonium nanofiltration membrane based on a Stober gold reaction interface polymerization, which comprises the following steps: dissolving a surfactant in a tris(2-dimethylaminoethyl) aqueous solution to prepare an aqueous monomer solution; using a 1,3,5-tris(bromomethyl)benzene n-heptane solution as an oil monomer solution; and causing the aqueous monomer solution and the oil monomer solution to undergo a Stober gold reaction and rapid cross-linking to form a polymer network at an oil-water interface, thereby constructing an ultrathin polyquaternary ammonium separation layer on the surface of a base film and preparing the polyquaternary ammonium nanofiltration membrane. The polyquaternary ammonium nanofiltration membrane has a narrow pore size distribution and a high positive electric density, and can thus synergistically enhance the size screening effect and the Donnan effect, thereby achieving excellent water flux and divalent cation rejection. In addition, the polyquaternary ammonium nanofiltration membrane does not contain easily hydrolyzable groups and has good acid-base stability. The polyquaternary ammonium nanofiltration membrane can be applied to nanofiltration treatment of salt lake water and lithium battery positive electrode material leaching liquid, realizes double-source lithium extraction, and has a simple preparation process and is easy to prepare on an industrial scale.

Description

Technical Field

[0001] This invention relates to the field of nanofiltration membrane separation technology, and in particular to a method for preparing and applying a positively charged nanofiltration membrane based on the Menshutkin reaction. Background Technology

[0002] With the shift to electric transportation, the increasing use of consumer electronics, the growing demand for renewable energy, and the positive drivers of carbon neutrality and peak carbon emissions, the demand for lithium-ion batteries is rapidly increasing, exacerbating the supply pressure on lithium resources. Salt lake brines account for approximately 70% of global lithium reserves, but the technical challenges of magnesium / lithium separation make their development difficult. Simultaneously, the rapid expansion of lithium battery applications generates a large number of waste batteries annually, posing the dual challenges of environmental pollution and resource depletion. The waste battery treatment process requires treating the cathode material with strong acid to obtain an acidic solution containing lithium ions and several divalent cations such as cobalt, manganese, and nickel.

[0003] Nanofiltration membranes can achieve efficient ion separation by synergistically combining the Donnan effect and size sieving. Their positive charge and suitable pore size are crucial for the separation of monovalent and divalent cations. Furthermore, the weakly alkaline nature of brine in salt lakes and the strong acidity of lithium-ion battery cathode material leachates place higher demands on the acid-base stability of nanofiltration membranes. Traditional polyamide nanofiltration membrane materials have a surface positive charge dependent on the protonation of amino groups, are highly susceptible to environmental acidity and alkalinity, and the residual acyl chloride groups are easily hydrolyzed, leading to a negative surface charge. Moreover, the amide groups are easily hydrolyzed in acidic or alkaline environments, causing structural damage. Therefore, their application in lithium extraction from salt lakes and the recycling of waste lithium-ion batteries is limited.

[0004] The Menshutkin reaction is a nucleophilic substitution reaction between tertiary amines and haloalkanes, which can generate quaternary ammonium salts. Interfacial polymerization based on the Menshutkin reaction can form a highly positively charged cross-linked network that does not contain easily hydrolyzable groups, and has great development potential in applications that achieve the separation of monovalent and divalent cations under acid and alkaline conditions. Summary of the Invention

[0005] In view of the above-mentioned prior art, the present invention provides a method for preparing polyquaternary ammonium nanofiltration membranes based on the Menshutkin reaction interfacial polymerization. The preparation method involves interfacial polymerization of tris(2-dimethylaminoethyl)amine and 1,3,5-tris(bromomethyl)benzene to obtain nanofiltration membranes that simultaneously possess high divalent cation rejection rate, high water permeation flux, and excellent stability under acidic and alkaline environments.

[0006] To address the aforementioned technical problems, this invention proposes a method for preparing polyquaternary ammonium nanofiltration membranes based on the Menshutkin reaction interfacial polymerization. Sodium dodecyl sulfate is used as a surfactant, dissolved in a tris(2-dimethylaminoethyl) aqueous solution to obtain an aqueous monomer solution; a 1,3,5-tris(bromomethyl)phenyl-heptane solution is used as an oil-phase monomer solution. With the assistance of the surfactant, the aqueous and oil-phase monomers undergo a Menshutkin reaction at the oil-water interface, rapidly crosslinking to form a polymer network. This constructs an ultrathin polyquaternary ammonium separation layer on the surface of a polyacrylonitrile substrate, thereby preparing the polyquaternary ammonium nanofiltration membrane. The specific steps are as follows:

[0007] Step 1) Prepare a 2.5-10% tris(2-dimethylaminoethyl) / water solution. Add sodium dodecyl sulfate to the 2.5-10% tris(2-dimethylaminoethyl) / water solution at a mass fraction of 0.01%, and sonicate for 10-20 minutes to obtain an aqueous monomer solution.

[0008] Step 2) Prepare a 0.6% (w / w) 1,3,5-tris(bromomethyl)benzene / n-heptane solution, sonicate for 20-30 min to obtain an oil phase monomer solution;

[0009] Step 3) Fix the polyacrylonitrile membrane in a plastic mold, add the aqueous monomer solution prepared in step 1) to the mold, and seal the mold. The ratio of the amount of aqueous monomer solution to the exposed area of ​​the membrane is 0.2 mL / cm². 2 After soaking and reacting for 30 minutes, the membrane was removed and the residual liquid on the membrane surface was removed.

[0010] Step 4) Fix the membrane treated in Step 3) in a plastic mold, add the oil phase monomer solution prepared in Step 2) into the mold, and seal the mold. The ratio of the amount of oil phase monomer solution to the exposed area of ​​the membrane is 0.2 mL / cm². 2 After soaking and reacting for 4 hours, the membrane was removed, washed with n-heptane, and placed in an oven for thermal crosslinking reaction to obtain a polyquaternary ammonium nanofiltration membrane.

[0011] Furthermore, in the preparation method described in this invention, wherein:

[0012] In step 1), the mass fraction of the tris(2-dimethylaminoethyl) / water solution is 5%. The ultrasonic time is 10 min; in step 2), the ultrasonic time is 20 min.

[0013] In step 3), the molecular weight cutoff of the polyacrylonitrile substrate is 15 kDa.

[0014] In step 4), the oven temperature is 60℃ and the thermal crosslinking reaction time is 10min.

[0015] In steps 3) and 4), the soaking reaction temperature is 20–30°C.

[0016] Compared with the prior art, the advantages of the present invention are as follows:

[0017] In this invention, the preparation method uses tris(2-dimethylaminoethyl)amine, a tertiary amine monomer, as the aqueous phase monomer and 1,3,5-tris(bromomethyl)benzene as the oil phase monomer. A Menshutkin reaction is performed at the oil-water interface to generate quaternary ammonium groups. Both monomers have a tripod symmetrical structure, which easily crosslinks to form a dense polymer network containing sub-nanopores. The high-density surface positive charge and narrow pore size distribution fully utilize the Donnan effect and size sieving function to achieve efficient retention of divalent cations. Simultaneously, the ultrathin separation layer and strong hydrophilicity achieve high water permeability. Furthermore, the positive charge of the prepared polyquaternary ammonium nanofiltration membrane is independent of protonation, and its structure does not contain easily hydrolyzable groups, exhibiting high charge stability and structural stability under both acidic and alkaline environments. The prepared nanofiltration membrane is used in the lithium extraction from salt lakes and the recycling of waste lithium batteries, efficiently retaining divalent cations in the feed solution while allowing lithium ions to pass through, achieving efficient extraction and utilization of lithium resources. The materials used are readily available, and the preparation process is simple, facilitating industrial-scale production.

[0018] The pure water flux of the polyquaternium nanofiltration membrane prepared by the method of the present invention is 29-33 L / m². -2 h -1 bar -1 Mg 2+ Retention rate 98.9–99.5%, Mn 2+ Co 2+ and Ni 2+ The retention rates of all Li were greater than 98%. + The rejection rate was 45.1%–54.1%; after the polyquaternary ammonium nanofiltration membrane was soaked in an acidic solution with pH=0 or an alkaline solution with pH=12 for 60 days, it showed a high rejection rate for Mg. 2+ The retention rate decreased by only 1.0–1.2%, and the water flux decreased by only 0.6–2.7 L / m³. -2 h -1 bar -1 The performance is basically stable, such as Figure 9 , Figure 10 As shown in Table 2, the polyquaternary ammonium nanofiltration membrane prepared by this invention is applied to nanofiltration treatment of salt lake water and lithium battery cathode material leachate to achieve dual-source lithium extraction. This includes using the polyquaternary ammonium nanofiltration membrane to perform nanofiltration treatment on pretreated clarified salt lake water to obtain a lithium ion solution, thereby achieving lithium extraction from the salt lake; and using the nanofiltration membrane to perform nanofiltration treatment on the leachate obtained after acid dissolution of waste lithium battery cathode material to obtain a lithium ion solution, thereby achieving efficient extraction and utilization of lithium resources. Attached Figure Description

[0019] Figure 1 This diagram illustrates the preparation of polyquaternary ammonium nanofiltration membranes by interfacial polymerization based on the Menshutkin reaction according to the present invention.

[0020] Figure 2 Fourier transform infrared spectra of the nanofiltration membrane and polyacrylonitrile substrate membrane in Example 2;

[0021] Figure 3 The X-ray electron spectrum of the nanofiltration membrane surface obtained in Example 2;

[0022] Figure 4 a and b are scanning electron microscope images of the polyacrylonitrile substrate membrane and the nanofiltration membrane prepared in Example 2, respectively.

[0023] Figure 5 The separation layer thickness of the nanofiltration membrane prepared in Example 2;

[0024] Figure 6 This is a diagram of the static water contact angle on the surface of the nanofiltration membrane obtained in Example 2;

[0025] Figure 7 The zeta potential of the nanofiltration membrane and polyacrylonitrile substrate prepared in Example 2 varies with pH.

[0026] Figure 8 The graph shows the rejection rates of different monovalent and divalent cations for the nanofiltration membrane prepared in Example 2.

[0027] Figure 9 The effect of tris(2-dimethylaminoethyl) concentration on the MgCl2 retention performance of nanofiltration membrane in the preparation method of this invention;

[0028] Figure 10 This invention relates to the effect of 1,3,5-tris(bromomethyl)benzene concentration on the MgCl2 retention performance of nanofiltration membranes in the preparation method of this invention. Detailed Implementation

[0029] The proposed method for preparing polyquaternary ammonium nanofiltration membranes based on the Menschutkin reaction involves a Menschutkin reaction between the tertiary amine groups of the aqueous monomer and the halogenated hydrocarbon at the oil-water interface, generating a polymer network rich in quaternary ammonium. Tris(2-dimethylaminoethyl)amine is used as the aqueous monomer, and 1,3,5-tris(bromomethyl)benzene is used as the oil monomer; both have a tripod symmetrical structure. An aqueous solution of tris(2-dimethylaminoethyl)amine is used as the aqueous monomer solution, and a solution of 1,3,5-tris(bromomethyl)benzene in n-heptane is used as the oil monomer solution. Sodium dodecyl sulfate is used as a surfactant. With the assistance of the surfactant, the aqueous and oil monomers undergo a Menschutkin reaction at the oil-water interface, rapidly crosslinking to form a polymer network. An ultrathin polyquaternary ammonium separation layer is constructed on the surface of a polyacrylonitrile substrate, thereby preparing the polyquaternary ammonium nanofiltration membrane.

[0030] The present invention will be further described below with reference to the accompanying drawings and specific embodiments, but the following embodiments are by no means intended to limit the present invention.

[0031] Example 1

[0032] A polyquaternary ammonium nanofiltration membrane was prepared using in-situ interfacial polymerization based on the Menshutkin reaction, such as... Figure 1 As shown in Figure a, the preparation steps of this nanofiltration membrane are as follows:

[0033] Step 1: Weigh 0.125g of tris(2-dimethylaminoethyl), add 4.875g of pure water, then add 0.005g of sodium dodecyl sulfate, and sonicate for 20min to obtain an aqueous monomer solution with a tris(2-dimethylaminoethyl) mass fraction of 2.5%.

[0034] Step 2: Weigh 0.03g of 1,3,5-tris(bromomethyl)benzene, add 4.97g of n-heptane, and sonicate for 20min to obtain an oil-phase monomer solution with a mass fraction of 0.6% for 1,3,5-tris(bromomethyl)benzene.

[0035] Step 3: After rinsing the polyacrylonitrile substrate three times with pure water, fix it in a plastic mold. Add an appropriate amount of aqueous monomer solution to the mold so that the solution volume to the exposed substrate area is 0.2 mL / cm². 2 After soaking the bottom film for 30 minutes, remove the mold and use a rubber roller to remove any residual liquid on the surface, ensuring that there are no visible droplets on the film surface.

[0036] Step 4: After assembling the mold in Step 3, add an appropriate amount of oil phase monomer solution and seal the mold, ensuring the solution volume to exposed substrate area ratio is 0.2 mL / cm². 2 After reacting for 4 hours, the treated bottom film was removed.

[0037] Step 5: After washing the treated bottom membrane three times with n-heptane, place it in an oven for thermal crosslinking for 10 minutes to obtain a polyquaternary ammonium nanofiltration membrane, denoted as PQA-2.5-0.6 membrane.

[0038] The separation performance of the prepared PQA-2.5-0.6 membrane was evaluated using a cross-flow apparatus, with salt rejection rate and water flux as the two main evaluation indicators.

[0039] Retention rate calculation formula: R = (1 - C) p / C f )×100%, where R represents the retention rate, C p and C f These are the salt concentrations (ppm) in the permeate and feed liquid, respectively. Unless otherwise specified, the salt concentration used is 1000 ppm.

[0040] Water flux (L m-2 h -1 bar -1 Defined as: the volume of water passing through a unit effective membrane area per unit pressure and unit time under certain operating pressure conditions, with a test pressure of 4 bar.

[0041] Example 2

[0042] A polyquaternary ammonium nanofiltration membrane was prepared using in-situ interfacial polymerization based on the Menshutkin reaction. The preparation process of Example 2 was basically the same as that of Example 1, except that in step one, the mass of tris(2-dimethylaminoethyl) was changed from 0.125g to 0.250g, and the mass of pure water was changed from 4.875g to 4.750g, resulting in an aqueous monomer solution with a tris(2-dimethylaminoethyl) mass fraction of 5%. The final nanofiltration membrane was designated as PQA-5-0.6 membrane.

[0043] Example 3

[0044] A polyquaternary ammonium nanofiltration membrane was prepared using in-situ interfacial polymerization based on the Menshutkin reaction. The preparation process of Example 3 was basically the same as that of Example 1, except that in step one, the mass of tris(2-dimethylaminoethyl) was changed from 0.125g to 0.375g, and the mass of pure water was changed from 4.875g to 4.625g, resulting in an aqueous monomer solution with a tris(2-dimethylaminoethyl) mass fraction of 7.5%. The final nanofiltration membrane was designated as PQA-7.5-0.6 membrane.

[0045] Example 4

[0046] A polyquaternary ammonium nanofiltration membrane was prepared using in-situ interfacial polymerization based on the Menshutkin reaction. The preparation process of Example 4 was basically the same as that of Example 1, except that in step one, the mass of tris(2-dimethylaminoethyl) was changed from 0.125g to 0.500g, and the mass of pure water was changed from 4.875g to 4.500g, resulting in an aqueous monomer solution with a tris(2-dimethylaminoethyl) mass fraction of 10%. The final nanofiltration membrane was designated as PQA-10-0.6 membrane.

[0047] Example 5

[0048] A polyquaternary ammonium nanofiltration membrane was prepared using in-situ interfacial polymerization based on the Menshutkin reaction. The preparation process of Example 5 was basically the same as that of Example 2, except that in step two, the mass of 1,3,5-tris(bromomethyl)benzene was changed from 0.03g to 0.01g, and the mass of n-heptane was changed from 4.97g to 4.99g, resulting in an oil-phase monomer solution with a mass fraction of 0.2% for 1,3,5-tris(bromomethyl)benzene. The final nanofiltration membrane was designated as PQA-5-0.2 membrane.

[0049] Example 6

[0050] A polyquaternary ammonium nanofiltration membrane was prepared using in-situ interfacial polymerization based on the Menshutkin reaction. The preparation process of Example 6 was basically the same as that of Example 2, except that in step two, the mass of 1,3,5-tris(bromomethyl)benzene was changed from 0.03g to 0.02g, and the mass of n-heptane was changed from 4.97g to 4.98g, resulting in an oil-phase monomer solution with a mass fraction of 0.4% for 1,3,5-tris(bromomethyl)benzene. The final nanofiltration membrane was designated as PQA-5-0.4 membrane.

[0051] Example 7

[0052] A polyquaternary ammonium nanofiltration membrane was prepared using in-situ interfacial polymerization based on the Menshutkin reaction. The preparation process of Example 7 was basically the same as that of Example 2, except that in step two, the mass of 1,3,5-tris(bromomethyl)benzene was changed from 0.03g to 0.04g, and the mass of n-heptane was changed from 4.97g to 4.96g, resulting in an oil-phase monomer solution with a mass fraction of 0.8% for 1,3,5-tris(bromomethyl)benzene. The final nanofiltration membrane was designated as PQA-5-0.8 membrane.

[0053] Example 8

[0054] A polyquaternary ammonium nanofiltration membrane was prepared using in-situ interfacial polymerization based on the Menshutkin reaction. The nanofiltration membrane obtained in Example 2 was immersed in hydrochloric acid solution with pH=0 for 60 days, then removed and rinsed 5 times with water. The resulting nanofiltration membrane was designated as PQA acid-impregnated membrane.

[0055] Example 9

[0056] A polyquaternary ammonium nanofiltration membrane was prepared using in-situ interfacial polymerization based on the Menshutkin reaction. The nanofiltration membrane obtained in Example 2 was immersed in a sodium hydroxide solution with pH=12 for 60 days, then removed and rinsed 5 times with water. The resulting nanofiltration membrane was designated as PQA alkaline-impregnated membrane.

[0057] Comparative Example 1

[0058] A polyquaternary ammonium nanofiltration membrane was prepared using in-situ interfacial polymerization based on the Menshutkin reaction. The preparation process of Comparative Example 1 was basically the same as that of Example 2, except that in step one, the aqueous monomer was changed from tris(2-dimethylaminoethyl) to 1,1,4,7,10,10-hexamethyltriethylenetetramine, resulting in an aqueous monomer solution with a mass of 5% 1,1,4,7,10,10-hexamethyltriethylenetetramine. The final nanofiltration membrane was designated as PQA-H membrane.

[0059] The formulations of the aqueous and oil phase monomer solutions of Examples 1-9 and Comparative Example 1 are shown in Table 1. Specifically, the aqueous phase monomer in Examples 1-9 is tris(2-dimethylaminoethyl), and the aqueous phase monomer in Comparative Example 1 is 1,1,4,7,10,10-hexamethyltriethylenetetramine. The ion separation performance test results of the nanofiltration membranes prepared in Examples 1-9 and Comparative Example 1 are shown in Table 1. Figure 9 , Figure 10 And Table 2.

[0060] Table 1

[0061]

[0062] Table 2

[0063]

[0064]

[0065] The structure and performance of the polyquaternary ammonium nanofiltration membranes prepared in the examples and comparative examples are evaluated through characterization and testing.

[0066] (I) The polyquaternary ammonium nanofiltration membrane and polyacrylonitrile substrate membrane prepared in Example 2 were characterized by infrared spectroscopy, and the results are as follows: Figure 2 As shown.

[0067] Fourier transform infrared spectroscopy (FT-IR) was used to demonstrate the successful occurrence of the Menshutkin reaction. The FT-IR spectra of the prepared PQA-5-0.6 membrane and the polyacrylonitrile substrate are shown below. Figure 2 As shown. The comparison results show that the PQA-5-0.6 membrane, under 3400 (OH stretching) and 3022 (crosslinked CN) conditions, + ) and 1383cm -1 A peak is shown at (unreacted CN); these peaks were not observed in the PAN spectrum. FT-IR results confirm the successful occurrence of the Menshutkin reaction and the successful preparation of the polyquaternary ammonium separation layer containing unreacted tertiary amines and crosslinked quaternary ammonium groups conjugated with OH- anti-anions.

[0068] (II) X-ray photoelectron spectroscopy (XPS) was performed on the polyquaternary ammonium nanofiltration membrane and polyacrylonitrile substrate membrane prepared in Example 2. The results are as follows: Figure 3 As shown.

[0069] X-ray photoelectron spectroscopy (XPS) is used to characterize the chemical composition and content of membrane surfaces. The high-resolution N1s XPS spectrum of the polyquaternary ammonium membrane shows two peaks at 402 and 399 eV, representing the cross-linked quaternary ammonium groups (CN-N, C, and E), respectively. + ) and unreacted tertiary amines (CN), according to their CN +The percentage estimate of the XPS peak area indicates that the near-surface crosslinking degree of the PQA separation layer is approximately 70%, confirming its highly crosslinked structure and high density of quaternary ammonium groups near the surface.

[0070] (III) The surface morphology of the polyquaternary ammonium nanofiltration membrane and polyacrylonitrile substrate membrane prepared in Example 2 was observed using a scanning electron microscope. The results are as follows: Figure 4 a and Figure 4 As shown in b.

[0071] Scanning electron microscopy (SEM) is used to observe the surface morphology of films. From Figure 4 As can be seen, numerous pores (10-50 nm) are randomly distributed on the polyacrylonitrile substrate. From Figure 4 As can be seen from b, the surface of the prepared PQA-5-0.6 membrane is very dense with no obvious pores, and the overall membrane surface is relatively smooth, which confirms the successful synthesis of a dense polyquaternary ammonium separation layer on the surface of the polyacrylonitrile substrate membrane.

[0072] (iv) The cross-section of the polyquaternary ammonium nanofiltration membrane prepared in Example 2 was observed using a transmission electron microscope, and the results are as follows: Figure 5 As shown.

[0073] Transmission electron microscopy (TEM) is used to observe the thickness of the separation layer in a membrane. From... Figure 5 It can be seen that the separation layer thickness of the PQA-5-0.6 membrane is only 12.4 nm, and its ultra-thin separation layer is conducive to achieving high water permeability.

[0074] (V) The static water contact angle of the polyquaternary ammonium nanofiltration membrane prepared in Example 2 was tested, and the results are as follows: Figure 6 As shown.

[0075] The static water contact angle at the instant a water droplet contacts the membrane surface is used to evaluate the membrane's hydrophilicity. From Figure 6 It can be seen that the water contact angle of the PQA-5-0.6 membrane is very small, only 23°, which confirms that the prepared polyquaternary ammonium nanofiltration membrane has good hydrophilicity.

[0076] (vi) The zeta potential of the polyquaternary ammonium nanofiltration membrane and the polyacrylonitrile substrate membrane prepared in Example 2 was tested, and the results are as follows: Figure 7 As shown.

[0077] The zeta potential of the polyacrylonitrile substrate membrane decreased sharply with increasing pH and remained negative throughout the pH range (3-10). In contrast, the potential of the PQA-5-0.6 membrane decreased gradually with increasing pH and maintained a positive surface charge at pH 10, confirming the high density of positive charge on the membrane surface and its stability under acidic and alkaline conditions.

[0078] (vii) The polyquaternary ammonium nanofiltration membrane prepared in Example 2 was tested for different ion separation performances, such as... Figure 8 As shown.

[0079] PQA-5-0.6 membrane for divalent cations (Mn) with different hydration radii 2+ Zn 2+ Mg 2+ Co 2+ Cu 2+ Ca 2+ and Ni 2+ The repulsion rate of ions is relatively high, around 97%, while the repulsion rate of monovalent ions (Li) is relatively high. + Na + K + and Cs + The repulsion rate of the polyquaternary ammonium film was relatively low, around 55%. This further confirmed that the prepared polyquaternary ammonium film had a high-density positive charge on its surface, resulting in a greater repulsion force on divalent ions than on monovalent ions, thus leading to a higher repulsion rate for divalent ions. Specifically, the repulsion rate for Mg... 2+ Mn 2+ Co 2+ and Ni 2+ The rejection rates were all greater than 98%, indicating that the prepared polyquaternary ammonium nanofiltration membrane can efficiently remove divalent cations from salt lakes and leachate from waste lithium battery cathodes.

[0080] Although the present invention has been described above in conjunction with the accompanying drawings, the present invention is not limited to the specific embodiments described above. The specific embodiments described above are merely illustrative and not restrictive. Those skilled in the art can make many improvements and changes under the guidance of the present invention without departing from the spirit of the present invention, and these improvements and changes are all within the protection scope of the present invention.

Claims

1. A method for preparing polymeric quaternary ammonium nanofiltration membranes based on the reaction interface of Gouy-Chaplyse, characterized in that: Sodium dodecyl sulfate is used as a surfactant, and the surfactant is dissolved in a tris(2-dimethylaminoethyl) aqueous solution to prepare an aqueous monomer solution; 1,3,5-tris(bromomethyl)benzene / n-heptane solution is used as an oil phase monomer solution; under the assistance of a surfactant, the aqueous monomer and the oil phase monomer undergo a door shutter reaction and rapid crosslinking at an oil-water interface to form a polymer network, and an ultra-thin polyquaternary ammonium separation layer is constructed on the surface of a polyacrylonitrile base film, so that a polyquaternary ammonium nanofiltration membrane is prepared; the method comprises the following steps: Step 1) A tris(2-dimethylaminoethyl) / water solution with a mass fraction of 2.5-10% is prepared, 0.1% sodium dodecyl sulfate is added to the tris(2-dimethylaminoethyl) / water solution according to a mass fraction, and ultrasonic treatment is performed for 10-20 min to obtain an aqueous monomer solution; Step 2) A 1,3,5-tris(bromomethyl)benzene / n-heptane solution with a mass fraction of 0.2-0.8% is prepared, and ultrasonic treatment is performed for 20-30 min to obtain an oil phase monomer solution; Step 3) fixing the polyacrylonitrile film in a plastic mold, adding the aqueous monomer solution prepared in Step 1) into the mold, and sealing the mold, the amount of the aqueous monomer solution used being 0.2 mL / cm2 of the exposed area of the film 2 After 30 min of the immersion reaction, the film was removed and the residual liquid on the surface of the film was removed. Step 4) The membrane treated in Step 3) is fixed in a plastic mold, the oil phase monomer solution prepared in Step 2) is added to the mold, and the mold is sealed, the amount of the oil phase monomer solution being 0.2 mL / cm2 of the exposed area of the membrane 2 After the membrane is taken out, it is washed with n-heptane and is put into an oven for a thermal crosslinking reaction to obtain a polyquaternary ammonium nanofiltration membrane.

2. The method of claim 1, wherein: In step 1), the mass fraction of the tris(2-dimethylaminoethyl) is 5%.

3. The method of claim 1, wherein: In step 2), the mass fraction of the 1,3,5-tris(bromomethyl)benzene is 0.6%.

4. The method of claim 1, wherein: In step 1), the ultrasonic treatment time is 10 min; in step 2), the ultrasonic treatment time is 20 min.

5. The method of claim 1, wherein: In step 3), the molecular weight cut-off of the polyacrylonitrile base film is 15 kDa.

6. The method of claim 1, wherein: In step 4), the temperature of the oven is 60°C, and the heat crosslinking reaction time is 10 min.

7. The method of claim 1, wherein: In steps 3) and 4), the temperature of the soaking reaction is 20-30°C.

8. Use of a polyquaternary ammonium nanofiltration membrane, characterized in that, The polyquaternary ammonium nanofiltration membrane prepared by the method according to any one of claims 1-7 has a pure water flux of 29-33 L m - ² h -1 bar -1 , Mg 2+ The rejection rate of Mn 2+ , Co 2+ and Ni 2+ is greater than 98%, and the rejection rate of Li + is 45.1-54.1%. The polyquaternary ammonium nanofiltration membrane has a Mg 2+ The rejection rate only decreases by 1.0-1.2%, and the water flux only decreases by 0.6-2.7 L m -2 h -1 bar -1 , and the performance is basically stable; The polyquaternary ammonium nanofiltration membrane is applied to nanofiltration treatment of salt lake water and lithium battery positive electrode material leaching solution to realize double-source lithium extraction.

9. Use of a polyquaternary ammonium nanofiltration membrane according to claim 8, characterized in that, The polyquaternary ammonium nanofiltration membrane is used for nanofiltration treatment of pretreated clear salt lake water, or the polyquaternary ammonium nanofiltration membrane is used for nanofiltration treatment of leaching solution obtained after acid dissolution of waste lithium battery positive electrode material, and lithium ion solution is obtained in both cases.

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