Thin-layer composite separation membrane with high magnesium-lithium separation ratio as well as preparation method and application of thin-layer composite separation membrane

Abstract

The invention discloses a thin-layer composite separation membrane with a high magnesium-lithium separation ratio and a preparation method of the thin-layer composite separation membrane. The preparation method comprises the following steps: carrying out solution blending on ionic liquid and polyether sulfone, carrying out vacuum drying, and then carrying out irradiation through Co-gamma rays; performing extraction and vacuum drying on the grafted blend obtained by irradiation to prepare a membrane casting solution, coating a substrate with the membrane casting solution, immersing the substrate in a coagulating bath, and performing phase splitting and membrane forming to obtain a polymer bottom membrane; dissolving a polyamine monomer in deionized water to obtain a water phase solution; dissolving a multi-acyl chloride monomer in an organic solvent to obtain an organic phase solution; loading the aqueous phase solution into a polymer base membrane; the organic phase solution is coated on the polymer base membrane, and the polyamine monomer in the water phase solution and the polyacyl chloride monomer in the organic phase solution are subjected to interfacial polymerization reaction to form an active polyamide separation layer. The thin-layer composite separation membrane disclosed by the invention has high positively charged property, narrow pore size distribution and relatively good magnesium-lithium selectivity, and can be applied to magnesium-lithium separation.

Description

Technical Field

[0001] This invention relates to the field of membrane separation technology, and in particular to a thin-layer composite separation membrane with a high magnesium-lithium separation ratio, its preparation method, and its application. Background Technology

[0002] Lithium is the lightest and smallest metallic element on Earth. It is widely used in portable electronic devices, power tools, electric vehicles, and grid storage. Exploring new technologies and materials for lithium extraction from brine with a high magnesium-to-lithium mass ratio, as well as for wastewater treatment in the lithium battery industry, is of great significance. Currently, methods for lithium-ion extraction mainly include neutralization precipitation, adsorption, thermal decomposition, solvent extraction, and membrane separation. Membrane separation, due to its low investment, low energy consumption, simple operation, high efficiency, and environmental friendliness, has become a promising lithium extraction technology from brine lakes.

[0003] Nanofiltration is a pressure-driven membrane separation technology with a molecular weight cutoff range of 200-1000 Da. It features low operating pressure and high separation capacity for both monovalent and polyvalent cations. Nanofiltration membranes, based on pore size sieving and the Donnan effect, can repel polyvalent cations but allow monovalent cations to pass through, making them suitable for separating lithium and magnesium ions in salt lake brines.

[0004] Patent CN118577145A discloses a method for preparing a surfactant-self-assembled positively charged nanofiltration membrane. By utilizing the dynamic self-assembly network of sodium dodecyl sulfate surfactant, it facilitates faster and more uniform diffusion of amine monomers at the hexane interface during interfacial polymerization. The resulting composite nanofiltration membrane achieves a magnesium ion rejection rate as high as 98.2%. Patent CN118001941A discloses a magnesium-lithium separation composite nanofiltration membrane, its preparation method, and its application. By co-depositing dopamine hydrochloride and iron molecular cages, the prepared intermediate layer can control the release and diffusion rate of polyethyleneimine monomers during interfacial polymerization, thereby reducing the thickness of the selective separation layer, increasing the permeation flux of the nanofiltration membrane, and simultaneously improving the magnesium ion rejection rate. Patent CN119113809A discloses a method for preparing a high-performance magnesium-lithium separation membrane. First, piperazine and acyl chloride monomers are interfacially polymerized on a polysulfone membrane surface to form a polyamide film. A solution of small-molecule quaternary ammonium salt and amine monomers is then poured onto the resulting polyamide film as a secondary interfacial polymerization solution. A positively charged separation layer is formed through this secondary interfacial polymerization. Finally, the membrane is cured at high temperature to obtain a nanofiltration membrane. The prepared nanofiltration membrane maintains good separation performance (separation coefficient 37) even at high salt concentrations.

[0005] Currently, numerous studies have explored methods such as introducing surfactants, nanoparticles, and constructing intermediate layers to regulate interfacial polymerization reactions, or to further modify prepared polyamide separation layers to enhance the separation performance of nanofiltration membranes. However, research on controlling the interfacial polymerization process through the properties of the substrate membrane structure to prepare nanofiltration membranes with high magnesium-lithium separation selectivity remains relatively scarce. Summary of the Invention

[0006] This invention provides a thin-layer composite separation membrane with a high magnesium-lithium separation ratio, its preparation method, and its application. The thin-layer composite separation membrane of this invention has high positive charge and narrow pore size distribution, which further improves the problem of low magnesium-lithium selectivity of traditional polyamide thin-layer composite membranes.

[0007] The technical solution of the present invention is as follows: A method for preparing a thin-layer composite separation membrane with a high magnesium-to-lithium separation ratio includes the following steps: (1) The ionic liquid and polyethersulfone were solution-blended, dried under vacuum, and then irradiated with Co-γ rays; (2) The grafted blend obtained by irradiation is extracted, vacuum dried and then prepared into a casting solution. The casting solution is coated on the substrate and immersed in a coagulation bath to separate phases and form a film, thus obtaining a polymer substrate film. (3) Dissolve the polyamine monomer in deionized water to obtain an aqueous solution; dissolve the polyacrylamide chloride monomer in an organic solvent to obtain an organic solution; (4) Load the aqueous solution onto the polymer substrate; (5) The organic phase solution is coated on the polymer substrate. The polyamine monomer in the aqueous phase solution and the polyacrylamide monomer in the organic phase solution undergo interfacial polymerization reaction to form an active polyamide separation layer, which is then obtained.

[0008] This invention discloses a method for preparing a thin-layer composite membrane with a permanently highly positively charged surface and a membrane body. First, an ionic liquid is fixed onto the molecular chain of a matrix polymer through chemical bonding by a Co-γ radiation grafting chemical modification method. Then, an asymmetric porous polymer substrate with ionic liquid properties on the surface and substrate is obtained through immersion precipitation phase transformation. Finally, an active polyamide separation layer is generated on the polymer substrate through vacuum-assisted interfacial polymerization to obtain a polyamide thin-layer composite membrane.

[0009] The ionic liquid grafted onto polyethersulfone (PES) improves the hydrophilicity of both the PES membrane surface and bulk, influencing the PES membrane structure (pore size and distribution) and achieving charge reversal (from negative to highly positive). The hydrophilicity and highly positive surface charge of the PES membrane affect the spreading of aqueous monomers on the membrane, slowing the diffusion rate of the aqueous monomer polyethyleneimine to the water-oil interface. This reduces the amount of aqueous monomer diffusing to the reaction interface, slowing down the interfacial polymerization rate and ensuring uniform polymerization, resulting in a thin-skinned, narrow-pore-distribution polyamide separation layer. Simultaneously, the positive surface charge of the PES membrane imparts a positive charge to the polyamide skin layer, resulting in a high magnesium-lithium separation ratio and high flux of the prepared polyamide thin-layer composite membrane.

[0010] Preferably, the ionic liquid contains unsaturated bonds.

[0011] Furthermore, the ionic liquid is at least one of 1-vinyl-3-methylimidazolium tetrafluoroborate, 1-vinyl-3-propylimidazolium tetrafluoroborate, 1-vinyl-3-butylimidazolium tetrafluoroborate, 1-vinyl-3-methylimidazolium hexafluoroborate, 1-vinyl-3-propylimidazolium hexafluoroborate, and 1-vinyl-3-butylimidazolium hexafluoroborate.

[0012] Preferably, in step (1), the mass ratio of ionic liquid to polyethersulfone in the blend solution is 1:5~50.

[0013] Preferably, in step (1), the Co-γ irradiation dose is 10~100 kGy and the irradiation time is 1~24 h.

[0014] Preferably, in step (2), the extraction includes: performing methanol Soxhlet extraction on the irradiated graft blend.

[0015] Preferably, in step (2), the concentration of the grafted blend in the casting solution is 10-30%.

[0016] Preferably, the mass percentage concentration of the polyamine monomer in the aqueous solution is 0.5~5 wt.%.

[0017] The concentration of polyamine monomers affects their solubility in water, as well as their diffusion and reaction rates at the interface, thereby influencing the thickness, crosslinking degree, and surface amine number of the polyamide layer. Excessive polyamine monomer concentration by mass percentage will increase the polyamide layer thickness, reducing the flux of the composite membrane; conversely, insufficient concentration by mass percentage will result in an underlying, incomplete, or reduced surface amine number polyamide layer, decreasing its positive charge.

[0018] More preferably, the polyamine monomer is polyethyleneimine. The polyethyleneimine can be linear or branched.

[0019] More preferably, the molecular weight of the polyamine monomer is 300~70000 Da; more preferably, it is 300~2000 Da.

[0020] Preferably, the mass percentage concentration of the polyacrylamide chloride monomer in the organic phase solution is 0.05~0.5 wt.%.

[0021] The concentration of polyacryl chloride monomers affects the thickness, degree of crosslinking, charge, and pore size of polyamide skins prepared by interfacial polymerization. Excessive concentration of polyacryl chloride monomers intensifies the interfacial polymerization reaction, leading to a decrease in the pore size of the polyamide layer. Simultaneously, excessive hydrolysis of acryl chlorides enhances the negative charge. Conversely, insufficient concentration of polyacryl chloride monomers weakens the interfacial polymerization reaction, increases the pore size of the polyamide layer, and a small amount of hydrolysis of acryl chlorides enhances the positive charge of the membrane.

[0022] Preferably, the polyacrylamide chloride monomer is at least one selected from pyromellitic trimethylolpropionate chloride, terephthaloyl chloride, isophthaloyl chloride, orthophthaloyl chloride, 1,5-naphthalenedisulfonyl chloride, 1,3,6-naphthalenedisulfonyl chloride, 1,3,5-cyclohexanetrimethylolpropionate chloride, and pyromellitic tetramethylolpropionate chloride.

[0023] Preferably, the functionality of the acyl chloride group in the polyacyl chloride monomer is 2 to 3.

[0024] Preferably, in the organic phase solution, the organic solvent is an alkane solvent (such as n-hexane, isoalkanes) or toluene.

[0025] Preferably, step (4) includes: immersing the polymer substrate in an aqueous solution for 1 to 10 minutes and then performing vacuum filtration; the vacuum filtration pressure is 0.1 to 0.15 MPa; and the vacuum filtration time is 1 to 10 minutes.

[0026] Preferably, in step (5), the organic phase solution is coated onto the polymer substrate, and after the interfacial polymerization reaction is carried out for 0.5 to 30 minutes, the organic phase solution is poured out, heat-cured and dried to form an active polyamide separation layer, which is then obtained.

[0027] More preferably, the thermosetting temperature is 50~70℃ and the thermosetting time is 1~10 min.

[0028] Further preferred, the drying temperature is 50~80℃ and the drying time is 2~12 h.

[0029] The present invention also provides a polyamide thin-film composite film prepared by the preparation method described above.

[0030] The present invention also provides the application of the polyamide thin-film composite membrane in magnesium-lithium separation.

[0031] Compared with the prior art, the beneficial effects of the present invention are as follows: (1) The polyamide thin-film composite film provided by the present invention improves the hydrophilicity of the substrate by using ionic liquid grafted polyethersulfone as the polymer substrate and realizes the charge reversal of the substrate. (2) The polyethersulfone substrate after grafting ionic liquid can regulate the diffusion rate of aqueous monomers to the water-oil interface, thereby regulating the interfacial polymerization reaction. The prepared polyamide separation layer has a narrower pore size distribution, higher crosslinking degree, smaller thickness and higher salt rejection performance, while also having better magnesium-lithium separation selectivity. Attached Figure Description

[0032] Figure 1 The diagram shows the degree of crosslinking of the polyamide skin prepared in Comparative Example 1 and Examples 1-4; Figure 2 The films prepared for Comparative Example 1 and Examples 1-4 are used to prepare Mg 2+ and Li + Retention rate graph; Figure 3 The magnesium-lithium separation selectivity diagrams are shown for the membranes prepared in Comparative Example 1 and Examples 1-4. Figure 4 The image shows the antibacterial performance of the membranes prepared in Comparative Example 1, Example 1, and Example 4. Detailed Implementation

[0033] The present invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be noted that the embodiments described below are intended to facilitate the understanding of the present invention and do not limit it in any way.

[0034] Unless otherwise specified, the experimental methods used in the following examples are conventional methods; unless otherwise specified, the reagents and materials used in the following examples are commercially available.

[0035] The materials used in the examples and comparative examples are as follows: Polyethersulfone: Mw=75000, Mw / Mn=3.4, BASF; 1-Vinyl-3-butylimidazolium tetrafluoroborate: Lanzhou Institute of Chemical Physics, Chinese Academy of Sciences; Polyethyleneimine: PEI300, 99%, Beijing Puxitang Biotechnology Co., Ltd.; Trimethylbenzene chloride: 98%, Sinopharm Chemical Reagent Co., Ltd.; n-Hexane: 97%, Sinopharm Chemical Reagent Co., Ltd.; N,N-Dimethylacetamide: 99%, Sinopharm Group Chemical Reagent Co., Ltd.; The polyamide thin-film composite membrane of the present invention comprises a polymer base film and a polyamide skin layer coated on the polymer base film. First, a chemically bonded ionic liquid is uniformly distributed on the surface of a polyethersulfone material using a Co-γ radiation grafting chemical modification method. Then, an asymmetric porous membrane is prepared by an immersion precipitation phase inversion method. Next, an aqueous solution containing dissolved polyamine monomers is vacuum filtered into the polymer base film. Then, an organic phase solution containing dissolved polyacrylamide chlorides is spread on the polymer base film to undergo interfacial polymerization, thereby generating an active polyamide thin-film composite membrane in one step.

[0036] Example 1 (1) First, 9.8 g of polyethersulfone (PES), 0.2 g of 1-vinyl-3-butylimidazolium tetrafluoroborate and 25 g of dimethylacetamide (DMAc) were added to the reaction flask and the solution was mixed at 60°C for 6 h. Then, after the solution was cooled to room temperature, it was poured into a PTFE mold and vacuum dried for 24 h to evaporate the solvent. Co-γ was used as the radiation source and room temperature irradiation was carried out at an irradiation dose of 30 kGy for 17 h.

[0037] (2) The grafted blend obtained by the above irradiation was extracted with methanol by Soxhlet extraction for 48 h, and then dried under vacuum. The solution was prepared with N,N-dimethylacetamide as solvent to form a casting solution with a concentration of 16.7%. The casting solution was then coated on a glass plate and immersed in a coagulation bath (deionized water at 25°C) to form a phase-separated film.

[0038] (3) Fix the prepared bottom membrane on a vacuum filtration device, and pour in a polyamine (PEI) with a mass percentage concentration of 5 wt.%. 300 Aqueous solution. After wetting the substrate membrane for 1 min, vacuum filter the solution into the pores of the porous membrane.

[0039] (4) Pour in a 0.15 wt.% hexane solution of polyacrylamide chloride (trimethylammonium chloride) to carry out interfacial polymerization. After reacting for 1 min, pour out the oil phase solution, take it out and place it in a 70℃ oven for heat treatment for 7 min.

[0040] (5) The prepared composite film was placed in an oven to dry the moisture and dried at 60°C for 12 h to obtain a polyamide thin-film composite film.

[0041] Example 2 (1) First, 9.6 g PES, 0.4 g 1-vinyl-3-butylimidazolium tetrafluoroborate and 25 g DMAc were added to the reaction flask and the solution was mixed at 60°C for 6 h. Then, after the solution was cooled to room temperature, it was poured into a PTFE mold and vacuum dried for 24 h to evaporate the solvent. Co-γ was used as the radiation source and room temperature irradiation was carried out at an irradiation dose of 30 kGy for 17 h.

[0042] (2) The grafted blend obtained by the above irradiation was extracted with methanol by Soxhlet extraction for 48 h, and then dried under vacuum. The solution was prepared with N,N-dimethylacetamide as solvent to form a casting solution with a concentration of 16.7%. The casting solution was then coated on a glass plate and immersed in a coagulation bath (deionized water at 25°C) to form a phase-separated film.

[0043] (3) Fix the prepared bottom membrane on a vacuum filtration device, and pour in a polyamine (PEI) with a mass percentage concentration of 5 wt.%. 300 Aqueous solution. After wetting the substrate membrane for 1 min, vacuum filter the solution into the pores of the porous membrane.

[0044] (4) Pour in a 0.15 wt.% hexane solution of polyacrylamide chloride (trimethylammonium chloride) to carry out interfacial polymerization. After reacting for 1 min, pour out the oil phase solution, take it out and place it in a 70℃ oven for heat treatment for 7 min.

[0045] (5) The prepared composite film was placed in an oven to dry the moisture and dried at 60°C for 12 h to obtain a polyamide thin-film composite film.

[0046] Example 3 (1) First, 9.4 g PES, 0.6 g 1-vinyl-3-butylimidazolium tetrafluoroborate and 25 g DMAc were added to the reaction flask and the solution was mixed at 60°C for 6 h. Then, after the solution was cooled to room temperature, it was poured into a PTFE mold and vacuum dried for 24 h to evaporate the solvent. Co-γ was used as the radiation source and room temperature irradiation was carried out at an irradiation dose of 30 kGy for 17 h.

[0047] (2) The grafted blend obtained by the above irradiation was extracted with methanol by Soxhlet extraction for 48 h, and then dried under vacuum. The solution was prepared with N,N-dimethylacetamide as solvent to form a casting solution with a concentration of 16.7%. The casting solution was then coated on a glass plate and immersed in a coagulation bath (deionized water at 25 °C) to form a phase-separated film.

[0048] (3) Fix the prepared bottom membrane on a vacuum filtration device, and pour in a polyamine (PEI) with a mass percentage concentration of 5 wt.%. 300 Aqueous solution. After wetting the substrate membrane for 1 min, vacuum filter the solution into the pores of the porous membrane.

[0049] (4) Pour in a 0.15 wt.% hexane solution of polyacrylamide chloride (trimethylammonium chloride) to carry out interfacial polymerization. After reacting for 1 min, pour out the oil phase solution, take it out and place it in a 70℃ oven for heat treatment for 7 min.

[0050] (5) The prepared composite film was placed in an oven to dry the moisture and dried at 60°C for 12 h to obtain a polyamide thin-film composite film.

[0051] Example 4 (1) First, 9.0 g PES, 1.0 g 1-vinyl-3-butylimidazolium tetrafluoroborate and 25 g DMAc were added to the reaction flask and the solution was mixed at 60°C for 6 h. Then, after the solution was cooled to room temperature, it was poured into a PTFE mold and vacuum dried for 24 h to evaporate the solvent. Co-γ was used as the radiation source and room temperature irradiation was carried out at an irradiation dose of 30 kGy for 17 h.

[0052] (2) The grafted blend obtained by the above irradiation was extracted with methanol by Soxhlet extraction for 48 h, and then dried under vacuum. The solution was prepared with N,N-dimethylacetamide as solvent to form a casting solution with a concentration of 16.7%. The casting solution was then coated on a glass plate and immersed in a coagulation bath (deionized water at 25 °C) to form a phase-separated film.

[0053] (3) Fix the prepared bottom membrane on a vacuum filtration device, and pour in a polyamine (PEI) with a mass percentage concentration of 5 wt.%. 300 Aqueous solution. After wetting the substrate membrane for 1 min, vacuum filter the solution into the pores of the porous membrane.

[0054] (4) Pour in a 0.15 wt.% hexane solution of polyacrylamide chloride (trimethylammonium chloride) to carry out interfacial polymerization. After reacting for 1 min, pour out the oil phase solution, take it out and place it in a 70℃ oven for heat treatment for 7 min.

[0055] (5) The prepared composite film was placed in an oven to dry the moisture and dried at 60°C for 12 h to obtain a polyamide thin-film composite film.

[0056] Comparative Example 1 This comparative example provides a traditional polyamide thin-film composite membrane, which is prepared by vacuum filtration.

[0057] The preparation method includes the following steps: (1) After vacuum drying of polyethersulfone powder, N,N-dimethylacetamide was used as solvent to prepare a casting solution with a concentration of 16.7%. The casting solution was then coated onto a glass plate and immersed in a coagulation bath (deionized water at 25°C) to form a phase-separated film.

[0058] (2) Fix the prepared bottom membrane on a vacuum filtration device, and pour in a polyamine (PEI) with a mass percentage concentration of 5 wt.%. 300 Aqueous solution. After wetting the substrate membrane for 1 min, vacuum filter the solution into the pores of the porous membrane.

[0059] (3) Pour in a 0.15 wt.% hexane solution of polyacrylamide chloride (trimethylammonium chloride) to carry out interfacial polymerization. After reacting for 1 min, pour out the oil phase solution, take it out and place it in a 70℃ oven for heat treatment for 7 min.

[0060] (4) The prepared composite film was placed in an oven to dry the moisture and dried at 60°C for 12 h to obtain a polyamide thin-film composite film.

[0061] Performance testing Test Example 1: Grafting rate of ionic liquids on polyethersulfone substrate films The grafting ratio of the ionic liquid is calculated using the relative integral area of ​​the NMR spectrum on the polyethersulfone substrate. The formula is as follows: Among them, A Ha A is the integral area of ​​the characteristic peak on the ionic liquid; Hb This represents the integral area of ​​the corresponding grafting site on the polyethersulfone.

[0062] The grafting rates of ionic liquids on the polyethersulfone substrates prepared in Examples 1, 2, 3, and 4 were tested and found to be 0.33%, 0.75%, 0.83%, and 0.92%, respectively.

[0063] Test Example 1: Degree of crosslinking of polyamide layer The degree of crosslinking of polyamide films was calculated using XPS peak analysis. Polyamide film structures are classified into linear and crosslinked structures. The linear structure involves the hydrolysis of acyl chlorides leading to the formation of carboxyl groups, while the crosslinked structure involves the crosslinking of acyl chlorides with polyethyleneimine monomers to form polyamide. Therefore, the degree of crosslinking of the polyamide skin can be obtained from the nitrogen to oxygen ratio in XPS analysis, as shown in the following formula: Cross-linking degree = The degree of crosslinking of the polyamide skin layers in Comparative Example 1, Example 1, Example 2, Example 3, and Example 4 was tested, such as... Figure 1 As shown, with the increase of ionic liquid grafting rate, the hydrophilicity of the grafted ionic liquid bottom film and the positive charge on the surface become stronger, which further slows down the diffusion rate of the aqueous monomer polyethyleneimine (PEI), making the interfacial polymerization reaction more uniform and resulting in a higher degree of crosslinking.

[0064] Test Example 2: Magnesium-Lithium Separation Performance Test The magnesium-lithium separation performance of the polyamide thin-film composite membrane was measured using a cross-flow filtration device. 1 g / L magnesium chloride and lithium chloride were dissolved separately in deionized water to prepare feed solutions. The polyamide thin-film composite membrane to be tested was placed in the membrane tank and pre-pressed at the operating pressure for 30 min. After stabilization, performance testing began at a temperature of 25℃ and a flow rate of 30 L / h. The concentrations of the feed solution and filtrate were measured using a conductivity meter, and the rejection rate was determined. R Flux J and ideal magnesium-lithium separation selectivity The calculation formula is as follows: The magnesium-lithium separation performance of Comparative Example 1, Example 1, Example 2, Example 3, and Example 4 was tested, such as... Figure 2 , 3 As shown, Mg in Comparative Example 1 2+ The retention rate was 90.8%. With the increase of ionic liquid grafting rate, the positive charge of the polyamide skin layer became stronger, and the degree of cross-linking of the skin layer also increased. Under the combined effect of the Donnan effect and pore size sieving, the composite membrane effectively retained Mg... 2+ The retention rate is getting higher and higher, reaching as high as 98.6%, while the Donan effect applies to monovalent Li + The retention of magnesium and lithium has no significant impact, thus achieving efficient magnesium-lithium separation.

[0065] Test Example 3: Antibacterial Performance Test of Composite Membrane Dilute the bacterial culture to 10 using 1 / 500 NB liquid medium. 5 Add 314 μL of bacterial suspension (CFU / mL) evenly to the sample surface. Using sterile forceps, place a sterile covering film over each sample, ensuring it is spread evenly and that the bacterial suspension does not extend beyond the edge of the film. Incubate at 37°C for 24 h. After incubation, elute the bacterial suspension with 3.14 mL of sterile PBS solution. Perform a 10-fold serial dilution of the eluent, and spread 100 μL of the diluted solution evenly onto LB agar plates. Incubate at 37°C for 18 h, then photograph and record the colony count.

[0066] The antibacterial properties of Comparative Example 1, Example 1, and Example 4 were tested, such as... Figure 4 As shown, the antibacterial rate against Escherichia coli reached 99.99%, and the antibacterial rate against Staphylococcus aureus reached over 94.47%. This is because the surfaces of the comparative examples and the embodiments are covered with a highly charged polyamide skin layer. The polyamide layer can destroy cell structure through electrostatic interaction, thereby leading to cell death.

[0067] The embodiments described above provide a detailed explanation of the technical solutions and beneficial effects of the present invention. It should be understood that the above descriptions are merely specific embodiments of the present invention and are not intended to limit the present invention. Any modifications, additions, and equivalent substitutions made within the scope of the principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for preparing a thin-layer composite separation membrane with a high magnesium-to-lithium separation ratio, characterized in that, Includes the following steps: (1) The ionic liquid and polyethersulfone were solution-blended, dried under vacuum, and then irradiated with Co-γ rays; (2) The grafted blend obtained by irradiation is extracted, vacuum dried and then prepared into a casting solution. The casting solution is coated on the substrate and immersed in a coagulation bath to separate phases and form a film, thus obtaining a polymer substrate film. (3) Dissolve the polyamine monomer in deionized water to obtain an aqueous solution; The polyacryl chloride monomer is dissolved in an organic solvent to obtain an organic phase solution; (4) Load the aqueous solution onto the polymer substrate; (5) The organic phase solution is coated on the polymer substrate. The polyamine monomer in the aqueous phase solution and the polyacrylamide monomer in the organic phase solution undergo interfacial polymerization reaction to form an active polyamide separation layer, which is then obtained.

2. The method for preparing a thin-layer composite separation membrane with a high magnesium-to-lithium separation ratio according to claim 1, characterized in that, The ionic liquid is at least one of 1-vinyl-3-methylimidazolium tetrafluoroborate, 1-vinyl-3-propylimidazolium tetrafluoroborate, 1-vinyl-3-butylimidazolium tetrafluoroborate, 1-vinyl-3-methylimidazolium hexafluoroborate, 1-vinyl-3-propylimidazolium hexafluoroborate, and 1-vinyl-3-butylimidazolium hexafluoroborate.

3. The method for preparing a thin-layer composite separation membrane with a high magnesium-to-lithium separation ratio according to claim 1 or 2, characterized in that, In step (1), the mass ratio of ionic liquid to polyethersulfone in the blended solution is 1:5~50.

4. The method for preparing a thin-layer composite separation membrane with a high magnesium-to-lithium separation ratio according to claim 1, characterized in that, In step (1), the Co-γ irradiation dose is 10~100 kGy and the irradiation time is 1~24 h.

5. The method for preparing a thin-layer composite separation membrane with a high magnesium-to-lithium separation ratio according to claim 1, characterized in that, In step (2), the concentration of the grafted blend in the casting solution is 10-30%.

6. The method for preparing a thin-layer composite separation membrane with a high magnesium-to-lithium separation ratio according to claim 1, characterized in that, The polyamine monomer is polyethyleneimine; the mass percentage concentration of the polyamine monomer in the aqueous solution is 0.5~5 wt.%.

7. The method for preparing a thin-layer composite separation membrane with a high magnesium-to-lithium separation ratio according to claim 1, characterized in that, The polyacrylamide chloride monomer is at least one selected from pyromellitic trimethylolpropionate chloride, terephthaloyl chloride, isophthaloyl chloride, orthophthaloyl chloride, 1,5-naphthalenedisulfonyl chloride, 1,3,6-naphthalenedisulfonyl chloride, 1,3,5-cyclohexanetrimethylolpropionate chloride, and pyromellitic tetramethylolpropionate chloride; the mass percentage concentration of the polyacrylamide chloride monomer in the organic phase solution is 0.05~0.5 wt.%.

8. The method for preparing a thin-layer composite separation membrane with a high magnesium-to-lithium separation ratio according to claim 1, characterized in that, In the organic phase solution, the organic solvent is an alkane solvent or toluene.

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

10. The application of the polyamide thin-film composite membrane according to claim 9 in magnesium-lithium separation.

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