Crown ether grafted polyarylether sulfone ion separation membrane as well as preparation method and application thereof

Abstract

The invention discloses a crown ether grafted polyarylether sulfone ion separation membrane as well as a preparation method and application thereof, and belongs to the technical field of ion separation membranes, collaborative optimization is realized through crown ether accurate grafting and ultrathin ordered membrane formation: a main chain of polyarylether sulfone is grafted with 4 '-aminobenzo-12-crown-4 to form an inherent channel adapted to Li, and the specific surface area of the main chain is increased; the ultrathin film is prepared by a water surface spreading method, and the ion transmission path is shortened. Finally, in a LiCl / MgCl system, Liion flux has high selectivity, high permeation-high selectivity cooperation is preliminarily realized, the chemical synthesis step can be amplified to a kilogram level, and after a DPAES-g-CE / dichloromethane solution is dropwise added to the water surface, the DPAES-g-CE / dichloromethane solution is rapidly spread to form a film without precise equipment; the raw materials are industrial-grade monomers and have no toxic residues, the membrane can be recycled and reused through dichloromethane, the equipment cost is reduced by about 90%, and industrialization is easy; the main chain of the polyaryl ether sulfone is high in rigidity and resistant to high temperature and chemical corrosion; crown ether grafting avoids molecular chain agglomeration, and the swelling rate is far lower than that of a traditional sulfonated membrane.

Description

Technical Field

[0001] This invention belongs to the field of ion separation membrane technology, specifically a crown ether-grafted polyarylether sulfone ion separation membrane, its preparation method, and its application. Background Technology

[0002] In the vast field of membrane separation technology, current technologies face severe challenges in achieving ion-selective separation, particularly for the efficient extraction of lithium from complex liquid resources such as brine in salt lakes. The core issue lies in the long-standing "permeability-selectivity" trade-off that has constrained membrane technology development: increasing the membrane's selectivity for target ions (such as lithium ions) often leads to a significant decrease in its permeate flux, and vice versa. Specifically, in the crucial category of lithium / magnesium separation, traditional separation membranes struggle to achieve efficient differentiation due to the similar hydrated ionic radii of lithium and magnesium ions. Existing research, such as using materials based on covalent organic frameworks, metal-organic frameworks, or modified nanofiltration membranes, has made some progress in improving lithium / magnesium selectivity, but their lithium ion permeation rates are generally below 1 mol / m³. ⁻² h ⁻¹ This makes it difficult to meet the high-throughput requirements of practical applications. Meanwhile, some nanofluidic devices with high permeation potential are limited by complex fabrication processes, high costs, and difficulties in large-scale production. Therefore, developing an ion separation membrane that can simultaneously achieve ultra-high ion permeation rates and high selectivity, and is easy to fabricate, has become a crucial technological bottleneck that urgently needs to be overcome in this sub-field.

[0003] Lithium, as a core strategic resource in the new energy field, is widely used in key areas such as lithium-ion batteries, aerospace, and energy storage equipment. Its resource supply has a significant impact on the global clean energy transition. Statistics show that approximately 70% of the world's lithium resources are stored in salt lake brines. Traditional methods such as solvent extraction and precipitation suffer from high energy consumption, low selectivity, and environmental pollution. Separation technologies like precipitation and solvent extraction rely on large amounts of chemical reagents to adjust the pH of the system or achieve phase transfer, resulting in low separation efficiency (lithium recovery rates are typically below 80%), high energy consumption (3000-5000 kWh of electricity is required to extract 1 ton of lithium), and the generation of wastewater and waste residue, causing environmental pollution and failing to meet the development needs of modern green industry. In contrast, membrane separation technology, due to its energy-saving, environmentally friendly, and sustainable characteristics, is considered an ideal alternative.

[0004] Membrane separation technology has become a research hotspot in the field of lithium extraction from salt lakes due to its advantages such as low energy consumption, environmental friendliness, and continuous operation. However, existing membrane technologies still face core challenges that restrict their industrial application. Mg is commonly found in brine. 2+ / Li + The problem of high molar ratios (typically >20), and Li + With Mg2+ The hydrated ionic radii are extremely close (Li + Hydration radius ≈ 3.8 Å, Mg 2+ The hydration radius is approximately 4.3 Å, which poses a challenge to lithium separation.

[0005] Since the beginning of the 21st century, the development of ion-selective membranes has been constrained by the trade-off between permeability and selectivity. Studies have shown that many laboratory-grade nanofiltration membranes typically exhibit lithium-ion permeability below 1 mol m⁻² h⁻¹ in lithium / magnesium separation. Although some studies have successfully improved Li⁺ / Mg²⁺ selectivity to high levels (some even exceeding 1000) by introducing precision sieving materials (such as MOFs and COFs) or utilizing differences in ion dehydration energy, their lithium-ion permeability is often extremely low (e.g., below 0.001 mol m⁻² h⁻¹), making it difficult to meet the flux requirements of practical applications. On the other hand, although some studies have maintained lithium selectivity at 31.9 by shortening ion migration paths or improving hydrophilicity, there is still room for improvement in ion permeability (approximately 1.73 mol m⁻² h⁻¹), and the complexity or cost of their fabrication processes limit large-scale applications. Commercial membranes such as Nafion 212 have a lithium-ion permeability of approximately 0.78 mol m⁻² h⁻¹, but the Li⁺ / Mg²⁺ selectivity is only 1.2, which is far from meeting the actual separation requirements.

[0006] However, existing crown ether-related membrane materials are mostly focused on improving the hydrophilicity and ionic conductivity of the membrane or as adsorbents. Achieving both ultra-high ion permeation rates and high-selectivity ion sieving, especially for efficient lithium-magnesium separation, still faces challenges.

[0007] The trade-off between ion flux and selectivity Existing membrane materials (such as nanofiltration membranes and MOF / COF membranes) generally suffer from the problem of balancing ion flux and selectivity. For example, the ion flux of laboratory-grade Li⁺ membranes is typically below 1 mol m⁻²h⁻¹, and the Li⁺ / Mg ratio is also problematic. 2+ Insufficient selectivity (approximately 20%), such as commercial membranes (e.g., Nafion 212) with a selectivity of only 1.2, cannot meet the demand for lithium extraction from salt lakes.

[0008] Complexity of the preparation process and challenges in scaling up Nanofluidic devices and MOF / COF membranes rely on sophisticated synthesis techniques (such as interfacial polymerization and vacuum filtration), which involve complex steps, high costs, and stringent production conditions, making large-scale production difficult. Commercial production conditions, however, determine the broad application prospects of polymer membranes.

[0009] Transport resistance caused by membrane structure disorder Traditional polymer membranes lack ordered ion channels and have large membrane thickness (micrometer scale), requiring ions to traverse long and tortuous paths, resulting in low ion flux.

[0010] Insufficient adaptability to real-world application scenarios Most membranes exhibit poor stability in high-salinity, multi-ion competing environments (such as brine in salt lakes), particularly the Li⁺ / Mg ratio. 2+ The separation efficiency decreased significantly. Summary of the Invention

[0011] This invention targets this specific problem, aiming to break the trade-off between permeability and selectivity through innovation in molecular design and preparation processes, and to provide a brand-new membrane technology solution for the economical and efficient extraction of lithium from liquid resources rich in interfering ions such as magnesium.

[0012] The technical solution of the present invention is as follows: an ion separation membrane, comprising: a self-supporting ultrathin film formed by grafting crown ether onto polyarylether sulfone polymer, wherein the thickness of the ultrathin film is 50-500 nm.

[0013] Furthermore, the backbone of the crown ether-grafted polyarylether sulfone polymer is formed by a nucleophilic polycondensation reaction of diallyl bisphenol A, 4,4'-dihydroxybiphenyl and 4-fluorophenyl sulfone.

[0014] Furthermore, the crown ether-grafted polyarylether sulfone polymer is prepared via the following steps: S1 epoxidizes the olefin groups on the side chains of the main chain to obtain epoxy-modified polyarylether sulfone; S2 induces an epoxy-modified polyarylene ether sulfone to undergo a ring-opening amination reaction with an aminobenzocrown ether to obtain a crown ether-grafted polyarylene ether sulfone polymer.

[0015] Furthermore, the aminobenzocrown ether is selected from at least one of 4'-aminobenzo-12-crown-4, 4'-aminobenzo-15-crown-5, or 4'-aminobenzo-18-crown-6.

[0016] Furthermore, the crown ether side chains in the ultrathin film are oriented and aligned along the film surface under shear force, forming an ordered ion transport channel.

[0017] A method for preparing an ion separation membrane includes the following steps: The crown ether-grafted polyarylether sulfone polymer is dissolved in an organic solvent that is immiscible with water to form a polymer solution. The polymer solution is then dropped onto the water surface, and the Marangoni effect is used to cause the polymer solution to spread on the water surface to form a liquid film. After the organic solvent evaporates, a self-supporting ultrathin film is formed.

[0018] Furthermore, the organic solvent is dichloromethane, 1,2-dichloroethane, or chloroform.

[0019] Furthermore, the concentration of the polymer solution is 5-25 mg / mL.

[0020] Furthermore, the volume of the droplets added to the water surface is 10-50 μL.

[0021] Application of an ion separation membrane in ion separation.

[0022] Furthermore, ion separation involves the selective separation of lithium ions from a mixed solution containing lithium ions and magnesium ions.

[0023] Furthermore, the molar ratio of Mg²⁺ / Li⁺ in the mixed solution is greater than 20.

[0024] Further applications include seawater desalination, recovery of valuable metals from waste batteries, and removal of heavy metals from industrial wastewater.

[0025] The beneficial effects of this invention are as follows: 1. Ultra-high ion flux: The 216 nm ultrathin film shortens the ion transport path, and the oriented crown ether channel provides a continuous transport path. The Li⁺ ion flux reaches 82 mol·m⁻²·h⁻¹, which is 104 times that of the commercial Nafion 212 film (0.78 mol·m⁻²·h⁻¹), and far exceeds that of existing MOF and COF base films (both <1 mol·m⁻²·h⁻¹).

[0026] 2. High selectivity: The inherent pore size of crown ether enables size sieving (12C4 pore size 1.2-1.5Å matches the hydration radius of Li⁺, while the difference in ion dehydration energy (Li⁺ 515 kJ / mol, Mg²⁺ 1828 kJ / mol) inhibits the transport of multivalent ions. The Li⁺ / Mg²⁺ selectivity is 32, which is 26 times that of Nafion 212 membrane (1.2).

[0027] 3. Feasibility of Scale-Up Preparation: The chemical synthesis steps can be scaled up to the kilogram level (DPAES batch production reaches 5 kg / batch). A 16.7 μL DPAES-g-CE / dichloromethane solution (10-20 mg / mL) added to the water surface spreads in 3 seconds and forms a film in 10 seconds, requiring no precision equipment. The raw materials are industrial-grade monomers (DBA, DPS), with no toxic residues. The membrane can be recycled and reused through dichloromethane recovery (utilization rate >85%), reducing equipment costs by approximately 90%. Ten 3 cm diameter membranes can be prepared in a single culture dish, and the process can be expanded to fluid circulation equipment for thin film preparation. The preparation cost is 60% lower than that of nanofluidic devices, making it easy to industrialize.

[0028] 4. Structural stability: The polyaryl ether sulfone backbone is rigid and resistant to high temperature and chemical corrosion; crown ether grafting avoids molecular chain aggregation, and the swelling rate is much lower than that of traditional sulfonated films. Attached Figure Description

[0029] Figure 1 This is a synthetic route for polyarylene ether sulfones (DPAES) containing olefins in their side chains.

[0030] Figure 2 This is a synthetic route for the polymer side chain epoxidation of DPAES-g-PO.

[0031] Figure 3 Synthetic route for polymer side-linked crown ether DPAES-g-CE.

[0032] Figure 4 The image shows the 1H NMR spectrum of polyarylene ether sulfones (DPAES) containing olefins in their side chains.

[0033] Figure 5 The image shows the 1H NMR spectrum of the polymer side chain epoxidized DPAES-g-PO.

[0034] Figure 6 Gel permeation chromatogram of polyarylether sulfone (DPAES).

[0035] Figure 7 Infrared spectra of polyarylene ether sulfones (DPAES), side-group epoxidized polyarylene ether sulfones (DPAES-g-PO), and side-linked crown ethers (DPAES-g-CE).

[0036] Figure 8 X-ray photoelectron spectra of the side-linked crown ether membrane DPAES-g-15C5.

[0037] Figure 9 Electron micrograph of the grafted crown ether polymer film, with cellulose acetate film substrate as a reference.

[0038] Figure 10 Transmission electron microscope image of grafted crown ether polymer film.

[0039] Figure 11 Ion flux and selectivity of grafted crown ether polymer films.

[0040] Figure 12 Schematic diagram of an ion separation performance testing device. Detailed Implementation

[0041] This invention uses a crown ether-grafted polyarylether sulfone (DPAES-g-CE) ion separation membrane as its core, and achieves efficient separation of lithium and magnesium ions through material design and process innovation. The specific technical solution is as follows: Polymer Material Design and Synthesis Using polyarylene ether sulfone (PAES) as the main chain, its molecular structure is a copolymer of diallyl bisphenol A (DBA), 4,4'-dihydroxybiphenyl (DBP), and 4-fluorophenyl sulfone (DPS), exhibiting excellent chemical stability and mechanical strength. Crown ether groups (12C4, 15C5, 18C6) are grafted onto the PAES side chains via an epoxidation-amine reaction, forming inherent ion channels.

[0042] Polymer thin film preparation process: water surface unfolding method Solution preparation: Dissolve DPAES-g-CE in dichloromethane (DCM) to prepare a homogeneous solution of 5–20 mg / mL.

[0043] Droplet spreading: The solution is dropped onto the water surface, and the Marangoni effect (DCM surface tension 27.2 mN / m, water 72.0 mN / m) drives the droplets to spread rapidly into an ultrathin film.

[0044] Oriented alignment: Shear force induces the crown ether side chains to align parallel to the water surface, and π-π interaction causes the main chain to stack in an orderly manner, forming oriented ion channels.

[0045] Solvent evaporation: After the DCM evaporates, it is peeled off to obtain a self-supporting ultrathin film (thickness 50–300 nm).

[0046] Film formation in seconds: The entire process takes less than 10 seconds and requires no complex equipment or post-processing.

[0047] Controllable structure: By adjusting the solution concentration (e.g., 10 mg / mL to prepare a 216 nm membrane) and the spreading area, the membrane thickness and channel density can be precisely controlled.

[0048] Membrane structure and performance characteristics Membrane structure orientation: TEM diffraction spots and SEM images show that the polymer chain segments are oriented.

[0049] Ion separation performance: In a mixed salt system (0.1 M LiCl / 0.1 M MgCl2), the Li⁺ ion flux of the DPAES-g-12C4 membrane is as high as 82 mol m⁻²h⁻¹, and the Li⁺ / Mg²⁺ selectivity is 32.

[0050] Multi-ion competition: In eight common mixed salt systems, the membrane has a rejection rate of more than 90% for high-valence ions such as Cu²⁺ and Ca²⁺, demonstrating the stability of the membrane in complex salt environments.

[0051] Application scenarios Lithium extraction from salt lakes: Directly treats brine with a Mg²⁺ / Li⁺ ratio > 20, eliminating the need for pretreatment and significantly reducing energy consumption and pollution.

[0052] The specific steps are as follows: First, a polyaryl ether sulfone containing a side-chain olefin (DPAES, diallyl bisphenol A-based polyaryl ether sulfone) was synthesized via nucleophilic condensation polymerization, providing reaction sites for subsequent functionalization modification. Second, the side-chain olefin of DPAES was converted into epoxy groups via oxidation to obtain epoxy-modified polyaryl ether sulfone (DPAES-g-PO), and the high reactivity of the epoxy groups was utilized to achieve directional grafting of crown ethers. Third, aminobenzocrown ethers with specific pore sizes (12-crown-4, 15-crown-5, 18-crown-6) were selected and combined with DP... A ring-opening grafting reaction was carried out with AES-g-PO to construct a crown ether-grafted polyaryl ether sulfone (DPAES-g-CE) polymer with inherent ion-screening channels. Then, an innovative water-spreading method was used to prepare an oriented ultrathin film, utilizing the Marangoni effect to arrange the crown ether side groups in an orderly manner to form continuous ion channels, while controlling the film thickness to be below 200 nm to shorten the ion transport path. Finally, a concentration-driven ion separation system based on this ultrathin film was built to achieve ultra-high ion flux and high selectivity separation of monovalent ions (especially lithium ions).

[0053] The overall technical solution comprises four core components: preparation of polyaryl ether sulfones (DPAES) containing side-chain olefins, preparation of epoxy-modified polyaryl ether sulfones (DPAES-g-PO), synthesis of intrinsic crown ether-grafted polyaryl ether sulfones (DPAES-g-CE) polymers, aqueous film formation, and the construction and testing of an ion separation system. All functions in this solution are supported by clear technical technologies. For example, "high selectivity" is achieved through the size sieving effect and ion coordination of crown ethers; "high ion flux" is achieved through ultrathin film thickness design and oriented ion channel construction; and "large-scale preparation" is achieved through standardized chemical synthesis and rapid aqueous film formation.

[0054] The following examples detail the complete conditions for the synthesis of DPAES, DPAES-g-PO, and DPAES-g-CE, their water surface spreading and film formation, and ion separation performance testing. Those skilled in the art can reproduce this invention accordingly. All commercial reagents require no further purification; the self-made polymers must meet specific molecular weight and purity requirements.

[0055] Example 1: Preparation of polyaryl ether sulfones (DPAES) containing side-chain olefins Raw materials: diallyl bisphenol A (DBA, 98% purity, Energy Chemical) 1.935 g (0.006 mol), 4,4'-dihydroxybiphenyl (DBP, 99% purity, Energy Chemical) 1.797 g (0.0096 mol), 4-fluorophenyl sulfone (DPS, 99% purity, Energy Chemical) 4.273 g (0.016 mol), anhydrous potassium carbonate (K2CO3, 99% purity, Sinopharm Group) 2.433 g (0.0176 mol), dimethylacetamide (DMAc, 99.5% purity, Aladdin) 32.8 mL, toluene (analytical grade, ≥99.5%, Beijing Chemical Plant) 10.4 mL.

[0056] Equipment: 250 mL three-necked flask (PTFE stopper), Dean-Stark water separator (with condenser), nitrogen generator (model GN-50, high-purity nitrogen 99.999%), thermostatic magnetic stirrer (model DF-101S, temperature control accuracy ±0.5℃), G-3 type sintered sand funnel, high-speed pulverizer (model FK-100, speed 10000rpm), vacuum drying oven (model DZF-6050, vacuum degree -0.095MPa), gel permeation chromatograph (GPC, model Waters 2414-1515, equipped with HT3, HT4, and HT5 columns, using dimethyl sulfoxide (DMSO) as the mobile phase), nuclear magnetic resonance spectrometer (¹H NMR, model Bruker AVANCE III 400 MHz, using CDCl3 as solvent).

[0057] Preparation steps Step 1: Setting up the nitrogen protection system. Purge high-purity nitrogen gas into a 250 mL three-necked flask at a flow rate of 50 mL / min, repeating this process three times to remove air. Then maintain the nitrogen atmosphere until the reaction is complete.

[0058] Step 2: Addition and dissolution of raw materials. Add DBA (1.935g), DBP (1.797g), and anhydrous K2CO3 (2.433g) in sequence, then add DMAc (32.8 mL) and toluene (10.4 mL). Turn on the magnetic stirrer (200 rpm) and stir at room temperature for 30 minutes until the solids are completely dissolved, forming a homogeneous pale yellow solution.

[0059] Step 3: Dehydration reaction. Connect the Dean-Stark water separator to the condenser and reflux at 135°C for 2.5 hours. Toluene and water form an azeotrope, which separates into layers after condensation. The aqueous phase is collected at the bottom of the water separator, with a final collection volume of approximately 0.32 mL, confirming complete removal of water from the system.

[0060] Step 4: Polymerization reaction. Gradually raise the temperature to 165°C to evaporate excess toluene (approximately 10 mL) from the system; at this point, the solution will be viscous. Maintain the temperature at 165°C and continue the reaction for 3 hours, taking samples every 30 minutes to monitor the solution viscosity. Stop the reaction when the viscosity reaches 500 cP or higher.

[0061] Step 5: Post-treatment and purification. Slowly pour the hot, viscous reaction solution into 200 mL of acidic deionized water (pH=2, adjusted with hydrochloric acid). White, strip-shaped polymers immediately precipitate. Let stand overnight. Pulverize the polymer into 1-2 mm particles using a high-speed grinder. Wash sequentially with boiling deionized water (200 mL × 3 times) and boiling ethanol (200 mL × 2 times) to remove residual salts and solvents. Dissolve the crude product in 50 mL of DMAc and filter three times through a G-3 sintered glass funnel. Pour the filtrate into 200 mL of ultrapure water to precipitate white, strip-shaped polymers. Repeat the pulverization-washing steps, then dry in a vacuum drying oven at 80°C for 24 hours to obtain DPAES, with the molecular formula as shown below. Figure 1 As shown.

[0062] Step 6: Product characterization. ¹H NMR spectrum ( Figure 4 The results show that the integral ratio of the ortho-sulfonate protons in the benzene ring to the protons inside the DBP biphenyl unit conforms to the designed structure; GPC testing indicates that ( Figure 5 The number-average molecular weight (Mn) was 75989 Da, the weight-average molecular weight (Mw) was 224108 Da, and the polydispersity index (PDI) was 2.95, confirming that high-purity, high-molecular-weight DPAES was synthesized and can be used for subsequent modification.

[0063] Example 2: Preparation of epoxy-modified polyaryl ether sulfone (DPAES-g-PO) Raw materials: 3 g of DPAES prepared in Example 1, 4.36 g of m-chloroperoxybenzoic acid (mCPBA, purity 97%, Aladdin), 70 mL of dichloromethane (DCM, analytical grade, ≥99.0%, Aladdin), and 400 mL of anhydrous ethanol (analytical grade, ≥99.7%, Beijing Chemical Plant).

[0064] Equipment: 250 mL round-bottom flask, calcium chloride drying tube, 50 mL dropping funnel, ice-water bath (temperature control accuracy ±0.1℃), magnetic stirrer (model 85-2, adjustable speed), Buchner funnel (diameter 10 cm), Fourier transform infrared spectrometer (FTIR, model Varian Excalibur 3100, scanning range 500-4000 cm⁻¹).

[0065] Preparation steps Step 1: Dissolve DPAES. Add 3 g of DPAES to a 250 mL round-bottom flask, add 30 mL of DCM, and stir at room temperature for 1 hour until completely dissolved to obtain a clear, pale yellow solution.

[0066] Step 2: Preparation of oxidant solution. Add 4.36 g mCPBA to a 50 mL beaker, add 40 mL DCM, stir for 30 minutes until dissolved to obtain an mCPBA / DCM solution, and transfer to a dropping funnel.

[0067] Step 3: Oxidation reaction. Place the round-bottom flask in an ice-water bath and cool to 0°C. While maintaining magnetic stirring (300 rpm), slowly add the mCPBA / DCM solution dropwise at a rate of 1 drop per 2 seconds, completing the addition over 30 minutes. Continue the reaction in the ice-water bath for 2 hours, then remove the ice-water bath and allow the reaction to proceed at room temperature for 30 hours. The solution color will gradually deepen to a deep yellow.

[0068] Step 4: Purification and Drying. Slowly pour the reaction solution into 400 mL of anhydrous ethanol and let it stand for 30 minutes, resulting in a white fibrous precipitate. Collect the precipitate by filtration using a Buchner funnel. Redissolve the precipitate in 20 mL of DCM, and then pour the solution into 200 mL of anhydrous ethanol to precipitate again. Repeat this process twice. Collect the final precipitate and dry it in a vacuum drying oven at 80 °C for 12 hours to obtain DPAES-g-PO, with a yield of approximately 2.9 g. The molecular formula is as follows: Figure 2 As shown.

[0069] Step 5: Product characterization. ¹H NMR spectrum ( Figure 5 The FTIR spectrum shows that the product corresponds to the molecular formula, indicating successful synthesis. Figure 7 The results showed a characteristic absorption peak of the epoxy group at 910 cm⁻¹, confirming that the side chain olefin of DPAES had been successfully oxidized to the epoxy group.

[0070] Example 3: Preparation of intrinsic crown ether grafted polyaryl ether sulfone (DPAES-g-CE) (taking 4'-aminobenzo-12-crown-4 as an example) Raw materials: 500 mg of DPAES-g-PO prepared in Example 2, 380 mg of 4'-aminobenzo-12-crown-4 (12C4, purity 98%, Jilin Putai Biotechnology Co., Ltd.), 20 mL of dimethylacetamide (DMAc, same as in Example 1), 200 mL of anhydrous ethanol (same as in Example 2), and 10 mL of dichloromethane (same as in Example 2).

[0071] Equipment: 100 mL round bottom flask, magnetic stirrer (model 85-2), oil bath (model HH-S, temperature control accuracy ±0.5℃), high-speed centrifuge (model TGL-16M, speed 8000 rpm), X-ray photoelectron spectrometer (XPS, model ThermoESCALAB 250Xi).

[0072] Preparation steps Step 1: Dissolve DPAES-g-PO. Add 500 mg of DPAES-g-PO to a 100 mL round-bottom flask, add 20 mL of DMAc, and stir at room temperature for 1 hour until completely dissolved to obtain a clear solution.

[0073] Step 2: Crown ether grafting reaction. Add 380 mg of 4'-aminobenzo-12-crown-4 to the above solution, stir for 10 minutes, then place the round-bottom flask in an oil bath, heat to 100°C, and maintain the temperature for 2 hours. During this time, the solution gradually turns pale yellow.

[0074] Step 3: Precipitation and purification. Cool the reaction solution to room temperature and slowly pour it into 200 mL of anhydrous ethanol. Let it stand for 1 hour, and a pale yellow precipitate will form. Centrifuge to collect the precipitate (8000 rpm, 5 minutes), dissolve the precipitate in 10 mL of DCM, and pour it into 100 mL of anhydrous ethanol again to precipitate. Repeat twice to remove unreacted crown ether monomers.

[0075] Step 4: Drying and Characterization. The precipitate was collected and dried in a vacuum drying oven at 80℃ for 24 hours to obtain DPAES-g-12C4, with the molecular formula as shown below. Figure 3 As shown, the yield was approximately 620 mg. XPS analysis ( Figure 8 The results showed that the ratio of sulfur atoms to nitrogen atoms was 2.5:1, and the calculated crown ether grafting rate was 49.3%, confirming that the crown ether grafting was successful.

[0076] Note: When grafting 4'-aminobenzo-15-crown-5 (15C5) or 4'-aminobenzo-18-crown-6 (18C6), only the type of crown ether monomer needs to be replaced; all other raw materials, equipment, and steps are completely the same.

[0077] Example 4: Preparation of DPAES-g-12C4 ultrathin films by water surface spreading method Raw materials: 0.2 g of DPAES-g-12C4 prepared in Example 3, 10 mL of dichloromethane (same as in Example 2), and 80 mL of deionized water (resistivity ≥18.2 MΩ·cm, prepared by an ultrapure water system (model UPT-I-20T)).

[0078] Equipment: 100 mL glass culture dish (15 cm in diameter), 20 μL microsyringe (HAMILTON 702RN, accuracy ±0.1 μL), optical microscope (Olympus CX43, magnification 100×), scanning electron microscope (SEM, Hitachi S-4800, accelerating voltage 5 kV), transmission electron microscope (TEM, JEM 2100, accelerating voltage 80 kV), atomic force microscope (AFM, Bruker Fastscan, phase mode).

[0079] Film formation steps Step 1: Preparation of polymer solution. Weigh 0.2 g DPAES-g-12C4, add 10 mL DCM, stir magnetically at room temperature for 2 hours until completely dissolved, filter through a 0.22 μm organic phase filter membrane to remove minor impurities, and obtain a transparent solution with a concentration of 20 mg / mL.

[0080] Step 2: Water surface preparation. Add 80 mL of deionized water to a 100 mL glass petri dish, control the water temperature at 25℃, and let it stand for 30 minutes until the water surface is completely calm to eliminate disturbances.

[0081] Step 3: Spreading and Film Formation on Water Surface. Using a microsyringe, draw 16.7 μL of polymer solution and slowly add it dropwise from a height of 5 mm above the water surface, avoiding contact between the needle and the water. Under the Marangoni effect, the droplet spreads into a circular liquid film with a diameter of 3-4 cm within 5 seconds. Allow it to stand at room temperature (25℃) and 50% humidity for 1 minute to allow the DCM to completely evaporate, forming a transparent, self-supporting ultrathin film.

[0082] Step 4: Membrane Transfer and Characterization. Using a quartz capillary tube with an inner diameter of 0.5 mm, the membrane was gently lifted along the edge and transferred to a 0.22 μm cellulose acetate filter membrane for surface testing. SEM observation was performed. Figure 9 The membrane surface appears smooth and flat, as observed by TEM. Figure 10 The interior shows an alternating light and dark structure, and the diffraction spots in the illustration are regularly arranged, confirming the successful formation of the orientation structure.

[0083] Note: The film thickness can be controlled by adjusting the polymer solution concentration. 10 mg / mL corresponds to a film thickness of 216±10 nm, 15 mg / mL corresponds to a film thickness of 337±9 nm, and 20 mg / mL corresponds to a film thickness of 416±5 nm.

[0084] Example 5: Ion separation performance test based on DPAES-g-12C4 membrane Testing system: Ion separation system, including feed chamber, permeation chamber, membrane clamping device, constant temperature water bath and detection unit.

[0085] Raw materials: mixed salt solution (0.1 M LiCl + 0.1 M MgCl2, prepared by LiCl (99% purity, Sinopharm Group), MgCl2 (99% purity, Sinopharm Group) and deionized water), deionized water (same as in Example 4).

[0086] Equipment: constant temperature water bath (model HH-S6, temperature control 80℃), magnetic stirrer (speed 300 rpm), inductively coupled plasma optical emission spectrometer (ICP-OES, model Agilent 5110), electronic balance (model Mettler AL204, accuracy 0.1mg).

[0087] Test steps and results Step 1: System Assembly. The DPAES-g-12C4 membrane prepared in Example 4 was cut into a circle with a diameter of 0.5 cm and installed in the membrane clamping device, ensuring that the membrane surface was flat and the water surface contact side faced the feed chamber.

[0088] Step 2: Solution addition. Add 20 mL of mixed salt solution to the feed chamber and 3.5 × 10⁻³ L of deionized water to the permeation chamber. Seal both chambers and place them in an 80℃ constant temperature water bath.

[0089] Step 3: Ion transport. Turn on the magnetic stirrer in the feed chamber (300 rpm) and keep it at this temperature for 24 hours. Ions will pass through the membrane into the permeation chamber by relying on the concentration difference.

[0090] Step 4: Concentration detection. Pipette 5 mL of the permeation chamber solution and determine the concentrations of Li⁺ and Mg²⁺ by ICP-OES. The Li⁺ concentration was 2.86 mol / L and the Mg²⁺ concentration was 0.089 mol / L.

[0091] Step 5: Performance Calculation. Calculate the ion flux (J) and selectivity (S) using the following formulas: Ion flux formula: J = [V×(Ct - C0)] / (Am×t), where V is the permeation chamber volume (3.5×10⁻³L), Ct is the concentration after testing, C0 is the initial concentration (0), and Am is the effective test area (1.96×10⁻³L). 7 m²), t is the test time (24h).

[0092] Selectivity formula: S(Li⁺ / Mg²⁺) = J(Li⁺) / J(Mg²⁺).

[0093] The calculations show that the Li⁺ ion flux is 82 mol·m⁻²·h⁻¹, the Mg²⁺ ion flux is 2.56 mol·m⁻²·h⁻¹, and the Li⁺ / Mg²⁺ selectivity is 32, confirming that the membrane has ultra-high lithium ion flux and high selectivity.

[0094] Key innovation points Precise Synthesis of Intrinsic Crown Ether Grafted Polyarylether Sulfone Polymers A three-step directional synthetic route was adopted, namely, "nucleophilic poly(arylene ether sulfone) (DPAES) containing side-chain olefins → olefin oxidation to epoxy groups (DPAES-g-PO) → epoxy ring-opening grafting of crown ethers with specific pore sizes." Functional side groups of 4'-aminobenzo-12-crown-4, 15-crown-5, or 18-crown-6 were introduced onto the poly(arylene ether sulfone) backbone to construct a DPAES-g-CE polymer with inherent ion-screening channels. The crown ether grafting rate was controlled at 45%-49.3%, ensuring both ion channel density and maintaining the rigidity and chemical stability of the polymer backbone, thus solving the problem of the lack of specific ion recognition sites in traditional sulfonated poly(arylene ether) membranes.

[0095] Innovation in the preparation of oriented ultrathin films using water-based spreading method Using deionized water as a flexible substrate, a 10-20 mg / mL DPAES-g-CE / dichloromethane solution was added dropwise at a dose of 16.7 μL. Utilizing the Marangoni effect (the surface tension difference between dichloromethane and water), the droplets spread and formed a film within 5 seconds. After solvent evaporation at room temperature, a self-supporting oriented film with a thickness of 108-413 nm was formed. This process induces the crown ether side groups to align parallel and orderly along the water surface through interfacial shear flow, forming continuous ion transport channels. Simultaneously, the ultrathin film thickness shortens the ion migration path, achieving a Li⁺ ion flux of 82 mol·m⁻²·h⁻¹ (104 times higher than the commercial Nafion 212 film), with a film surface roughness of only 5.2 nm and no micropore defects.

[0096] The high selectivity mechanism of crown ether size sieving and ion dehydration By utilizing the inherent pore size differences of different crown ethers (12C4: 1.2-1.5 Å, 15C5: 1.7-2.2 Å, 18C6: 2.6-3.2 Å), specific screening of monovalent ions such as Li⁺, Na⁺, and K⁺ is achieved. Simultaneously, by combining the differences in ion dehydration energy (Li⁺ dehydration energy 515 kJ / mol, Mg²⁺ dehydration energy 1828 kJ / mol), the permeation of divalent and polyvalent ions is suppressed. The DPAES-g-12C4 membrane achieves a Li⁺ / Mg²⁺ selectivity of 32, overcoming the technical bottleneck of traditional membranes where "high ion flux and high selectivity are difficult to achieve simultaneously."

[0097] Core protected points Material composition Polymers comprising a polyarylene ether sulfone backbone and grafted crown ether side chains (DPAES-g-CE) and their synthetic methods, specifically including Preparation of polyarylene ether sulfone backbone (nucleophilic polycondensation of diallyl bisphenol A, 4,4'-dihydroxybiphenyl and 4-fluorophenyl sulfone). Epoxy modification steps (oxidation of dipropylene side groups with m-chloroperoxybenzoic acid). Crown ether grafting step (ring-opening amination reaction of 4'-aminobenzocrown ether with epoxy group).

[0098] Membrane preparation process The process for preparing oriented ultrathin films based on water surface spreading includes: Solvent selection (dichloromethane), polymer solution concentration control (10-20 mg / mL); Film formation parameters (water temperature 20-30℃, humidity 45%-55%, droplet volume 10-50μL); Marangoni effect-driven molecular orientation control (shear flow-induced parallel alignment of crown ether side groups).

[0099] Membrane structure characteristics A homogeneous ultrathin film structure with a thickness of 100-420 nm, a surface roughness of ≤5.2 nm, and an ordered arrangement of crown ether channels (characteristic spacing of 13.36-16.53 nm).

[0100] Ion separation mechanisms and applications The membrane achieves multi-ion selective separation through the synergistic effect of crown ether size sieving and ion dehydration, with performance indicators of Li⁺ / Mg²⁺ selectivity coefficient ≥30 and Li⁺ ion flux ≥75 mol·m⁻²·h⁻¹.

[0101] The DPAES-g-CE membrane is used in applications such as lithium extraction from salt lakes, seawater desalination, and metal ion recovery. It is particularly suitable for the selective extraction of Li⁺ in systems with a high magnesium-to-lithium ratio (Mg²⁺ / Li⁺>20).

[0102] This invention has been experimentally verified to be feasible, and those skilled in the art can completely reproduce this invention by controlling the following key parameters: Raw material control: Commercial reagents must meet the purity requirements of the examples (e.g., DBA ≥ 98%, mCPBA ≥ 97%); self-made DPAES must meet the requirement of Mn = 7.0 × 10⁻⁶. 4 -8.0×10 4 Da, PDI = 2.5-3.0, otherwise adjust the polymerization temperature (160-170℃) or time (2-4 hours).

[0103] Equipment requirements: The reaction vessel must be made of polytetrafluoroethylene or glass to avoid metal ion contamination; the vacuum degree of the vacuum drying oven must be ≥-0.095 MPa, otherwise the drying time should be extended (36-48 hours).

[0104] Key process parameters: (1) DPAES synthesis: dehydration temperature 135±5℃, polymerization temperature 165±5℃, to ensure complete removal of water (water volume of water separator ≥ 90% of theoretical value). (2) Epoxy modification: reaction temperature 0±0.5℃, molar ratio of mCPBA to DPAES 2:1, to avoid excessive temperature causing epoxy ring opening; (3) Crown ether grafting: reaction temperature 100±2℃, molar ratio of crown ether to DPAES-g-PO 1.2:1, ensuring grafting rate ≥45%; (4) Water surface film formation: The solution concentration is 10-20 mg / mL, otherwise the film is prone to wrinkles or poor orientation.

[0105] Verification of the controllability of the film-forming process: DPAES-g-CE polymer was dissolved in DCM to prepare solutions of 10 mg / mL, 15 mg / mL, and 20 mg / mL. 16.7 μL of each solution was dropped onto the surface of deionized water. Utilizing the Marangoni effect (DCM surface tension 27.2 mN / m, water surface tension 72.0 mN / m), rapid spreading was achieved within 3 seconds, and complete solvent evaporation and film formation occurred within 10 seconds. Optical photographs showed that the film was transparent and flexible, and could be directly retrieved or transferred to substrates such as cellulose. SEM characterization showed that the film surface was smooth and flat, free of micropores, cracks, and other defects, and the cross-sectional structure was uniform and dense.

[0106] Verification of dynamic control of membrane thickness: The membrane thickness can be precisely controlled by changing the concentration of the polymer solution. Experimental data show that the membrane thickness is 215.9±5 nm for 10 mg / mL solution, 413.2±8 nm for 15 mg / mL solution, and 334.0±6 nm for 20 mg / mL solution, with a thickness error of ≤±5%. This proves that the membrane thickness parameters can be flexibly adjusted according to the actual separation requirements.

[0107] Verification of membrane structure orderliness: TEM characterization showed that the intracellular chain segments were oriented and could form ordered ion channels. Diffraction spots confirmed the existence of oriented structures in the polymer chains.

[0108] Ion separation performance verification: Test according to Example 5. If the Li⁺ ion flux is ≥75 mol·m⁻²·h⁻¹ and the Li⁺ / Mg²⁺ selectivity is ≥30, the reproduction is successful. If it does not meet the standard, check the crown ether grafting rate (≥45%) or the film thickness (150-250 nm), adjust and retest.

[0109] With "ion sieving function" as the core, single-ion system, mixed-ion system and dynamic control experiments were designed. Inductively coupled plasma optical emission spectrometry (ICP-OES) and Keithley 6487 semiconductor picoammeter were used to test the ion flux, selectivity and control performance of the membrane, and to verify the feasibility of the application of the present invention in actual separation scenarios.

[0110] This invention achieves synergistic optimization through "precise grafting of crown ethers + ultrathin ordered film formation": 4'-aminobenzo-12-crown-4 (pore size 1.2-1.5 Å) is grafted onto the polyarylene ether sulfone main body, forming an inherent channel adapted to Li⁺ (hydration radius 3.8 Å). A 216±5 nm ultrathin film is prepared using an aqueous spreading method, shortening the ion transport path. Ultimately, in a 0.1 M LiCl / 0.1 M MgCl₂ system, the Li⁺ ion flux reaches 82 mol·m⁻²·h⁻¹, and the Li⁺ / Mg²⁺ selectivity is 32, initially achieving a synergistic effect of "high permeability-high selectivity".

[0111] Partial ingredient substitution Crown ether monomer substitution Alternative solution: Replace the core functional units 4'-aminobenzo-12-crown-4, 15-crown-5, and 18-crown-6 with azacrown ethers (such as BN15C5 and BN18C6) or oxacrown ether derivatives (such as dibenzo-14-crown-4). Based on the "epoxy ring-opening grafting" reaction mechanism, these crown ethers all contain amino / hydroxyl groups that can react with epoxy groups and can be grafted onto the polyarylether sulfone backbone using the same process.

[0112] Polymer backbone substitution Alternative solution: Replace the polyarylene ether sulfone (PAES) backbone with sulfonated polyether ether ketone (SPEEK) or polyimide (PI). The core advantages of PAES are "high stability and modifiable side chains". SPEEK and PI also have solvent resistance and active side chain groups (hydroxyl and carboxyl groups). Crown ether grafting can be achieved through the "epoxidation-amine grafting" route, making them suitable for water surface spreading film formation processes.

[0113] Film-forming solvent substitution Alternative solution: Replace dichloromethane (DCM) with 1,2-dichloroethane or a chloroform / ethanol mixture (volume ratio 9:1), or solvents such as benzene that are immiscible with water. The "water surface spreading film formation mechanism" indicates that the key to film formation is the "surface tension difference between the solvent and water." 1,2-dichloroethane (surface tension 32.2 mN / m) and chloroform (27.1 mN / m) both meet this condition, driving the Marangoni effect for rapid spreading.

[0114] Changes in proportion and process parameters Monomer ratio adjustment Alternative solution: Adjust the molar ratio of diallyl bisphenol A (DBA) to 4,4'-dihydroxybiphenyl (DBP) in the synthesis of polyarylene ether sulfone backbone (original ratio 1:1.6) to a range of 1:1 to 1:2.5; the molar ratio of crown ether to epoxy-modified polyarylene ether sulfone (DPAES-g-PO) (original ratio 1.2:1) can be adjusted to 1:1 to 1.5:1.

[0115] Replacement of film formation process parameters Alternative solution: In the water surface spreading method, the polymer solution concentration (originally 10-20 mg / mL) can be adjusted to 5-25 mg / mL; the water temperature (originally 25℃) can be adjusted to 0-30℃. The correlation curve between film thickness and concentration shows that the film thickness of 5 mg / mL solution is 108 nm, and the film thickness of 25 mg / mL solution is 413 nm.

[0116] Method and step substitution Alternative solution: Replace the water surface spreading method with the Langmuir-Blodgett (LB) membrane transfer method. The core of the water surface spreading method is "interfacial shear flow-induced directional alignment," while the LB membrane transfer method can precisely control the membrane pressure (10-30 mN / m) through the Langmuir groove to achieve monolayer directional film formation, which is consistent with the principle of the original solution.

[0117] Alternative polymer synthesis routes Alternative approach: Replace the "nucleophilic condensation-epoxidation-amine grafting" route with a "free radical polymerization-click chemistry grafting" route (azide-alkynyl cycloaddition reaction). Polymer purification processes show that free radical polymerization can prepare polyarylene sulfones containing alkynyl side chains, which can then undergo a click reaction with azid-modified crown ethers.

[0118] Other uses Based on the material properties and ion separation mechanism, the technology of this invention can be extended to the following scenarios, and is not limited to lithium-magnesium separation: Seawater desalination and brackish water softening Application Basis: Data shows that the crown ether pore size is precisely matched to monovalent ions (Na⁺ hydration radius 3.58 Å, K⁺ hydration radius 3.31 Å), with a retention rate of >95% for Ca²⁺ and Mg²⁺. When treating high-salinity seawater (salt content 3.5%) or brackish water, it can remove divalent ions to achieve water softening, producing water with a hardness ≤50 mg / L (calculated as CaCO₃), meeting drinking water standards.

[0119] Used battery recycling Application Basis: DFT calculations show that the complexation energy of Li⁺ with 12-crown-4 (150 kJ / mol) is much higher than that of Co²⁺ (85 kJ / mol) and Ni²⁺ (78 kJ / mol). When separating and recovering Li⁺ from the leachate of spent lithium-ion batteries (containing Li⁺, Co²⁺, and Ni²⁺), the Li⁺ recovery rate is >90%, and the purity reaches 99.5%, making it suitable for battery material regeneration processes.

[0120] Industrial wastewater heavy metal treatment Application basis: Multi-ion system tests show that the membrane has a rejection rate of >98% for heavy metal ions such as Cu²⁺. When treating electroplating wastewater, the Cu²⁺ ion flux is <5 mol·m⁻²·h⁻¹, which can achieve heavy metal recovery and water purification.

[0121] fuel cell proton conduction membrane Application rationale: The ether bonds in the polymer backbone can form hydrogen bonds with protons, constructing a proton transport channel. When replacing commercial Nafion membranes, it achieves a proton conductivity of 85 mS / cm (80℃, 100%RH), improving battery stability.

[0122] Breaking the trade-off between ion flux and selectivity: A size-tunable (1.2–3.2 Å) intrinsic ion channel is constructed through crown ether grafting, achieving high selectivity by combining the difference between dehydration and complexation energies. Utilizing an ultrathin ordered structure (<300 nm) to shorten the ion migration path, the Li⁺ ion flux is increased to 82 mol m⁻² h⁻¹, with a Li⁺ / Mg²⁺ selectivity of 32 (mixed salt system).

[0123] Simplified preparation process and large-scale production: The water surface spreading method (Marangoni effect driven) shortens the film formation time to the second level. It does not require complex equipment or toxic monomers. The process is simple, environmentally friendly, and suitable for industrial applications.

[0124] Constructing ordered ion channels to reduce transport resistance: By inducing the directional alignment of crown ether side chains through shear force, ordered ion channels are formed, reducing friction and energy loss during ion migration and significantly improving permeation efficiency.

[0125] Enhanced adaptability to high-salinity environments: The polyarylethersulfone backbone provides excellent chemical stability, ensuring long-term stable operation of the membrane in high-salinity environments such as salt lake brines and avoiding performance degradation.

[0126] The above description is merely a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any modifications, equivalent substitutions, and improvements made by those skilled in the art within the scope of the technology disclosed in the present invention, and within the spirit and principles of the present invention, should be included within the scope of protection of the present invention. Furthermore, all content not described in detail in this specification is prior art known to those skilled in the art.

Claims

1. An ion separation membrane, characterized in that, include: Self-supporting ultrathin films formed by grafting crown ether onto polyarylether sulfone polymers, with a thickness of 50-500 nm.

2. The ion separation membrane according to claim 1, characterized in that, The backbone of the crown ether-grafted polyarylether sulfone polymer is formed by nucleophilic polycondensation of diallyl bisphenol A, 4,4'-dihydroxybiphenyl and 4-fluorophenyl sulfone.

3. The ion separation membrane according to claim 2, characterized in that, Crown ether-grafted polyarylether sulfone polymers are prepared via the following steps: S1 epoxidizes the olefin groups on the side chains of the main chain to obtain epoxy-modified polyarylether sulfone; S2 induces an epoxy-modified polyarylene ether sulfone to undergo a ring-opening amination reaction with an aminobenzocrown ether to obtain a crown ether-grafted polyarylene ether sulfone polymer.

4. The ion separation membrane according to claim 3, characterized in that, The aminobenzocrown ether is selected from at least one of 4'-aminobenzo-12-crown-4, 4'-aminobenzo-15-crown-5, or 4'-aminobenzo-18-crown-6.

5. The ion separation membrane according to claim 1, characterized in that, In ultrathin films, crown ether side chains align along the film surface under shear force, forming ordered ion transport channels.

6. A method for preparing an ion separation membrane as described in any one of claims 1-5, characterized in that, Includes the following steps: The crown ether-grafted polyarylether sulfone polymer is dissolved in an organic solvent that is immiscible with water to form a polymer solution. The polymer solution is then dropped onto the water surface, and the Marangoni effect is used to cause the polymer solution to spread on the water surface to form a liquid film. After the organic solvent evaporates, a self-supporting ultrathin film is formed.

7. The method according to claim 6, characterized in that, The organic solvent is dichloromethane, 1,2-dichloroethane, or chloroform, the concentration of the polymer solution is 5-25 mg / mL, and the volume of the droplet added to the water surface is 10-50 μL.

8. The application of the ion separation membrane as described in any one of claims 1-5 in ion separation.

9. The application according to claim 8, characterized in that, Ion separation is the selective separation of lithium ions from a mixed solution containing lithium ions and magnesium ions, wherein the molar ratio of Mg²⁺ / Li⁺ in the mixed solution is greater than 20.

10. The application according to claim 9, characterized in that, Applications include seawater desalination, recovery of valuable metals from waste batteries, and removal of heavy metals from industrial wastewater.

Images