High-performance phospholipid interlayer lithium-magnesium separation membrane as well as preparation method and application thereof

Abstract

The invention belongs to the technical field of nanofiltration membranes, and particularly relates to a high-performance phospholipid interlayer lithium-magnesium separation membrane as well as a preparation method and application thereof. The high-performance phospholipid interlayer lithium-magnesium separation membrane is prepared according to the following method: taking a polyethersulfone ultrafiltration membrane as a substrate, introducing a phospholipid interlayer, then performing interfacial polymerization through polyethyleneimine and trimesoyl chloride to form a polyamide separation layer, and finally performing heat treatment to obtain the high-performance phospholipid interlayer lithium-magnesium separation membrane. The phospholipid middle layer is a positively charged phospholipid double-layer membrane formed by spreading phospholipid vesicles on the surface of the polyethersulfone supporting layer. The phospholipid in the phospholipid vesicles is one of dioleoyl phosphatidylcholine, dioleoyl phosphatidyl ethanolamine and 1, 2-dioleoyl-3-trimethylamine propane hydrochloride. The transmittance of the lithium-magnesium separation membrane with the phospholipid interlayer is higher than 11L. M <-2 >. H <-1 >. Bar <-1 >, and the separation factor is greater than or equal to 29.5.

Description

Technical Field

[0001] This invention belongs to the field of nanofiltration technology, specifically relating to a high-performance phospholipid intermediate layer lithium-magnesium separation membrane, its preparation method, and its application. Background Technology

[0002] Lithium batteries are an important means of solving the traditional energy crisis. However, the development of lithium resources is currently weak.

[0003] Nanofiltration membrane technology, as an emerging technology between ultrafiltration and reverse osmosis, exhibits unique advantages in seawater softening, removal of trace pollutants, and retention of beneficial minerals due to the synergistic effect of nanoscale pore diameter sieving and charge effects. Since its conception in the 1960s, nanofiltration membranes have evolved from loose reverse osmosis membranes to polyamide composite membranes, and currently comprise two main systems: organic and inorganic membranes. Industrial applications are achieved through processes such as phase inversion and interfacial polymerization. However, polymer membranes are constrained by the "Robeson upper limit," and positively charged polyamide membranes struggle to simultaneously achieve high permeability and high selectivity. Furthermore, the positive charge on the membrane surface also affects Li... + A repulsive effect is generated; excessively high charge strength is detrimental to Li. + Osmosis recovery.

[0004] However, due to the similar chemical properties of magnesium and lithium, existing nanofiltration membrane technologies struggle to balance high permeability and high rejection rate when separating lithium and magnesium, resulting in low efficiency of lithium-magnesium separation membranes. Summary of the Invention

[0005] To address the aforementioned technical problems, this invention provides a high-performance phospholipid interlayer lithium-magnesium separation membrane, its preparation method, and its application.

[0006] To facilitate understanding of the present invention, the substances used in the present invention and their abbreviations are listed below: Dioleoylphosphatidylethanolamine (DOPE) is abbreviated as DOPE. Dioleoylphosphatidylcholine (DOPC) is abbreviated as DOPC. Trimethyl-2,3-dioleoyloxypropylammonium bromide (DOTAP) is abbreviated as DOTAP. Polyethersulfone ultrafiltration membrane is abbreviated as PS membrane. Polyethylene glycol (PEG) is abbreviated as PEG. Polyethyleneimine (PEI) is abbreviated as PEI. Tristyroyl chloride (TMC) is abbreviated as TMC. Sodium dodecyl sulfate (SDS) is abbreviated as SDS. Phosphate buffered saline (PBS) is abbreviated as PBS.

[0007] The first objective of this invention is to provide a high-performance phospholipid interlayer lithium-magnesium separation membrane, comprising a lower polyethersulfone support layer, a phospholipid interlayer, and an upper polyamide separation layer. The polyethersulfone support layer provides support, stabilizing the structure of the high-performance phospholipid interlayer lithium-magnesium separation membrane. The phospholipid interlayer can regulate the interfacial polymerization process, and the polyamide separation layer can separate lithium and magnesium ions.

[0008] The high-performance phospholipid interlayer lithium-magnesium separation membrane is prepared by the following method: a phospholipid interlayer is introduced into a PS membrane as a substrate, and then a polyamide separation layer is formed by interfacial polymerization of polyethyleneimine and trimesoyl chloride. Finally, the membrane is heat-treated to obtain the high-performance phospholipid interlayer lithium-magnesium separation membrane.

[0009] The phospholipid interlayer is a positively charged phospholipid bilayer film formed by phospholipid vesicles spreading on the surface of the polyethersulfone support layer. The function of the phospholipid interlayer is to modify the physicochemical properties of the PS film surface, such as hydrophilicity, smoothness, and to regulate the surface porosity and pore diameter, thereby affecting the reaction rate and extent of the interfacial polymerization process.

[0010] The phospholipids in the phospholipid vesicles are one of DOPC, DOPE, and DOTAP.

[0011] The phospholipid vesicles are obtained by repeatedly extruding a phospholipid hydrate solution through a filter membrane with a pore diameter of 200nm~600nm to make the vesicle size uniform.

[0012] The term "high performance" refers to a transmittance higher than 11 L·m. -2 ·h -1 ·bar -1 The separation factor is greater than 29.5.

[0013] Preferably, the thickness of the polyethersulfone support layer is 150µm~200µm, the thickness of the phospholipid intermediate layer is 6nm~24nm, and the thickness of the polyamide separation layer is 50nm~60nm.

[0014] Preferably, the method for preparing the phospholipid vesicles includes the following steps: A phospholipid solution is added to a container to form a film, thus obtaining a phospholipid film.

[0015] A phosphate buffer solution was used to hydrate the phospholipid membrane to obtain a hydrated phospholipid solution. The hydration reaction involved using ultrasound, mechanical vibration, and freeze-thaw cycles to rearrange the phospholipid molecules into vesicle structures.

[0016] The phospholipid hydrate solution is repeatedly squeezed through a filter membrane to make the vesicles uniform in size, thus obtaining a phospholipid vesicle solution.

[0017] Phospholipid powder was dissolved in chloroform to obtain a phospholipid solution. The phospholipid solution was added to a container, dried to form a film, and then vacuum dried to obtain a phospholipid film. The phospholipid film was hydrated with PBS, and subjected to sonication, mechanical vibration, and freeze-thaw cycles to allow the phospholipid molecules to rearrange and initially form vesicle structures, thus hydrating the phospholipid film and obtaining a hydrated phospholipid solution. The hydrated phospholipid vesicle solution was repeatedly extruded through a filter membrane to make the size of the hydrated phospholipid vesicles more uniform. PBS was added to dilute the solution, obtaining a phospholipid vesicle solution.

[0018] Preferably, the concentration of the phospholipid solution is 1 mg / mL to 10 mg / mL, and the solvent is chloroform.

[0019] The film formation conditions are: first blow-drying followed by vacuum drying, with the blow-drying time being 10 min to 30 min, the vacuum drying pressure being 10 kPa to 100 kPa, the time being 4 h to 6 h, and the temperature being 40 ℃ to 60 ℃.

[0020] The volume ratio of the phospholipid solution to PBS buffer is 1:1~19.

[0021] The ultrasound power is 200W~400W, and the duration is 10min~15min.

[0022] The mechanical vibration speed is 500rpm~1500rpm, the amplitude is 1mm~2mm, and the duration is 5min~10min.

[0023] The freezing temperature for the freeze-thaw cycle is -20℃ to -10℃, the thawing temperature is 60℃ to 80℃, the time is 15min to 30min, and the number of cycles is 5 to 10.

[0024] The filter membrane is a polycarbonate membrane.

[0025] The number of extrusions is 10 to 30 times.

[0026] The concentration of the phospholipid vesicle solution is 0.1 mg / mL to 0.2 mg / mL.

[0027] Preferably, the concentration of the phospholipid vesicle solution is 0.1 mg / mL, 0.16 mg / mL, or 0.20 mg / mL.

[0028] The second objective of this invention is to provide a method for preparing a high-performance phospholipid interlayer lithium-magnesium separation membrane, comprising the following steps: A phospholipid vesicle solution is added to the surface of a PS membrane, and vacuum membrane is performed. After all the phospholipid vesicle solution has passed through the membrane, the filtrate is repeatedly passed through the membrane to obtain a polyethersulfone-phospholipid interlayer modified base membrane. The polyethersulfone-phospholipid interlayer modified base membrane includes a lower polyethersulfone support layer and a phospholipid layer located on the upper surface of the polyethersulfone support layer. The polyethersulfone-phospholipid interlayer modified base membrane was immersed in PEI solution, allowing PEI to bind to the phospholipid interlayer surface of the polyethersulfone-phospholipid interlayer modified base membrane through hydrogen bonding. After removal and drying, the surface of the phospholipid interlayer side of the polyethersulfone-phospholipid interlayer modified base membrane was brought into contact with an organic solution, allowing PEI to undergo a polymerization reaction with the oil phase monomers in the organic solution to form a polyamide separation layer. Heat treatment was then performed to stabilize the polymerization of PEI in the polyamide separation layer with the oil phase monomers in the organic solution, resulting in a high-performance phospholipid interlayer lithium magnesium separation membrane.

[0029] Preferably, the ratio of the amount of PS membrane to phospholipid vesicle solution is 0.5 mg to 5 mg of phospholipid vesicles per square centimeter of PS membrane.

[0030] The PEI solution contains 0.1 wt% sodium dodecyl sulfate and 0.1 wt% sodium carbonate, and the soaking time is 3 min to 5 min.

[0031] Preferably, the PEI solution soaking time is 5 minutes.

[0032] The organic solution is a hexane solution of pyromellitic chloride with a concentration of 0.05wt%~0.3wt%, and the contact time is 1min~3min.

[0033] Preferably, the organic solution is a hexane solution of 0.15 wt% trimesoyl chloride, and the contact time is 3 min.

[0034] Preferably, the heat treatment temperature is 60℃~80℃ and the time is 8min~12min.

[0035] Preferably, the heat treatment temperature is 60°C and the time is 10 minutes.

[0036] Preferably, the PS membrane is first soaked in a 4wt% sodium bisulfite solution for 12h~24h, and then soaked in ultrapure water for 6h~24h.

[0037] Preferably, the soaking time in ultrapure water is 6 hours.

[0038] Preferably, the pressure of the vacuum membrane is 0.05MPa~0.1MPa.

[0039] Preferably, the pressure of the vacuum filter is 0.1 MPa.

[0040] Preferably, the number of times the membrane is repeated is 2 to 5 times.

[0041] Preferably, the membrane is repeated twice.

[0042] The third objective of this invention is to provide an application of a high-performance phospholipid interlayer lithium-magnesium separation membrane in the separation of lithium and magnesium.

[0043] Compared with the prior art, the present invention has the following beneficial effects: 1. The high-performance phospholipid interlayer lithium-magnesium separation membrane of the present invention comprises a lower polyethersulfone support layer, a phospholipid interlayer, and an upper polyamide separation layer. The polyethersulfone support layer provides support, stabilizing the structure of the high-performance phospholipid interlayer lithium-magnesium separation membrane. The phospholipid interlayer regulates the interfacial polymerization process, and the polyamide separation layer separates lithium and magnesium ions. The high-performance phospholipid interlayer lithium-magnesium separation membrane is prepared by the following method: using a PS membrane as a substrate, a phospholipid interlayer is introduced, followed by interfacial polymerization of polyethyleneimine and trimesoyl chloride to form a polyamide separation layer, and finally heat treatment to obtain the high-performance phospholipid interlayer lithium-magnesium separation membrane. The phospholipid interlayer is a positively charged phospholipid bilayer membrane formed by phospholipid vesicles spreading on the surface of the polyethersulfone support layer. The function of the phospholipid interlayer is to modify the physicochemical properties of the PS membrane surface, such as hydrophilicity and smoothness, and to regulate the surface porosity and pore diameter, thereby affecting the reaction rate and degree of the interfacial polymerization process. The phospholipid interlayer is a phospholipid bilayer membrane formed by phospholipid vesicles spreading on the surface of a polyethersulfone support layer. This phospholipid bilayer membrane can modify the physicochemical properties of the base membrane surface, such as hydrophilicity, smoothness, and regulate surface porosity and pore diameter, thereby further influencing the reaction rate and extent of the interfacial polymerization process. The construction of the phospholipid interlayer effectively reduces the pore diameter of the membrane and enhances the pore diameter sieving effect. The construction of the phospholipid interlayer also facilitates a reduction in the thickness of the interfacial polymerization layer, reducing the transmembrane path of water molecules and increasing water flux. The phospholipid in the phospholipid vesicles is one of DOPC, DOPE, and DOTAP. High performance refers to a permeability higher than 11 L·m⁻¹. -2 ·h -1 ·bar -1 The separation factor is greater than 29.5. Phospholipid vesicles were introduced to construct biomimetic water channels with diameters ranging from 0.5 nm to 2 nm, increasing the water permeability of the lithium-magnesium separation nanofiltration membrane to 4.12 L·m⁻². -2 ·h -1 ·bar -1 The permeability is 1.93 times higher than that of traditional membranes. The permeability of the TFNi0.1 membrane prepared in Example 1 of this invention is 15.22 L·m⁻¹. -2 ·h -1 ·bar -1 It is 1.45 times more efficient than TFC membranes, with removal rates of 97.6% for MgCl2 and 32.8% for LiCl. The high-performance phospholipid intermediate layer lithium-magnesium separation membrane of the present invention has high permeability and high rejection rate, and can efficiently separate lithium from lithium-magnesium mixed solutions.

[0044] 2. The method for preparing phospholipid vesicles provided by this invention involves dissolving phospholipid powder in chloroform to obtain a phospholipid solution. The phospholipid solution is added to a container, dried to form a film, and then vacuum dried to obtain a phospholipid film. Dissolving the phospholipid in an organic solvent, followed by drying with nitrogen and vacuum drying, ensures the uniformity of the phospholipid molecular film and effectively removes the organic solvent, providing clean reaction conditions for the hydration reaction. The phospholipid film is hydrated with PBS buffer, and subjected to five cycles of sonication, mechanical vibration, and freeze-thaw cycles to allow the phospholipid molecules to rearrange and initially form vesicle structures, thus hydrating the phospholipid film to obtain a hydrated phospholipid solution. Hydration with PBS buffer utilizes the hydrophilic and hydrophobic properties of phospholipid molecules to gradually transform the phospholipid film into phospholipid vesicles. At this stage, the phospholipid vesicles have a wide diameter distribution and large size differences. The hydrated phospholipid vesicle solution is repeatedly extruded through a filter membrane to make the size of the hydrated phospholipid vesicles more uniform. When phospholipid vesicles pass through a filter membrane with a fixed pore diameter, the shearing action causes larger phospholipid vesicles to break down into smaller ones, resulting in a more uniform phospholipid vesicle solution. Adding PBS buffer yields a phospholipid vesicle solution with a gradient concentration. Diluting with PBS buffer further stabilizes the phospholipid vesicle solution, making it easier to form a membrane.

[0045] The method for preparing phospholipid vesicles in this invention provides an important raw material for preparing high-performance phospholipid intermediate lithium-magnesium separation membranes, which is key to achieving high permeability and high rejection rate, and is therefore very important to this invention.

[0046] 3. The preparation method of the high-performance phospholipid interlayer lithium-magnesium separation membrane of the present invention involves immersing a PS membrane in a sodium bisulfite solution, removing the PS membrane, washing it, and then immersing the PS membrane in ultrapure water. Immersion and washing remove unstable substances from the surface of the PS membrane, providing a clean adhesion surface for the phospholipid layer. Using the PS membrane as a filter membrane, a gradient concentration of phospholipid vesicle solution is added sequentially from low to high concentration, and vacuum filtration is performed. After all the vesicle solution is filtered, the filtrate is collected and filtered repeatedly to obtain the phospholipid interlayer. Multiple filtrations of the phospholipid vesicle solution through the PS membrane allow the phospholipid vesicles to gradually form a phospholipid layer on the PS membrane surface, resulting in a more uniform phospholipid layer. The PS membrane and phospholipid interlayer are then immersed in a PEI solution, removed, and dried. The polyamide nanofiltration membrane containing the phospholipid interlayer is then contacted with an organic solution to induce a polymerization reaction on the surface of the phospholipid interlayer, yielding a polyamide nanofiltration membrane containing the phospholipid interlayer. The polyamide nanofiltration membrane containing the phospholipid interlayer is then heat-treated to obtain the lithium-magnesium separation nanofiltration membrane.

[0047] The high-performance phospholipid interlayer lithium-magnesium separation membrane prepared by the preparation method and conditions of the present invention has a stable structure and a high lithium-magnesium separation coefficient.

[0048] 4. The high-performance phospholipid intermediate layer lithium-magnesium separation membrane and its preparation method provided by this invention lay the foundation for the preparation of nanofiltration membranes with high permeability and high selectivity for lithium and magnesium ions. Attached Figure Description

[0049] Figure 1 This is a distribution diagram of the PEI on the surface of membranes prepared with different phospholipid vesicle concentrations according to the present invention.

[0050] Figure 2 TFC film and TFNi prepared for Example 1 of the present invention 0.1 MWCO diagram of the membrane.

[0051] Figure 3 TFNi prepared in Example 1 of the present invention 0.1 Electron micrographs of the membrane and the polyamide nanofiltration membrane without a phospholipid interlayer. A is the polyamide nanofiltration membrane without a phospholipid interlayer, and B is the high-performance lithium-magnesium separation membrane with a phospholipid interlayer.

[0052] Figure 4 The TFC membrane prepared for the embodiments of the present invention and the TFNi prepared for Examples 1-3 and Comparative Example 1 0.1 membrane, TFNi 0.16 membrane, TFNi 0.2 membrane, TFNi 0.04 Membrane permeability diagram.

[0053] Figure 5 The TFC membrane prepared in Example 1 of the present invention and the TFNi membrane prepared in Examples 1 to 3 and Comparative Example 1 are examples of the present invention. 0.1 membrane, TFNi 0.16 membrane, TFNi 0.2 membrane, TFNi 0.04 The membrane separation performance diagram. Where A is the water permeability coefficient and B is the magnesium chloride rejection rate.

[0054] Figure 6 TFC and TFNi prepared for Example 1 of the present invention 0.1 Lithium-magnesium separation factor diagram of the membrane. Detailed Implementation

[0055] To enable those skilled in the art to better understand and implement the technical solutions of the present invention, the following detailed description, in conjunction with preferred embodiments and accompanying drawings, provides a clear and complete account of the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of them. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are within the scope of protection of the present invention.

[0056] It should be noted that all technical terms used in this invention are for the purpose of describing specific embodiments only and are not intended to limit the scope of protection of this invention. Unless otherwise specified, all raw materials, reagents, instruments and equipment used in the following embodiments of this invention can be purchased from the market or prepared by existing methods.

[0057] Example 1 A method for preparing a high-performance phospholipid interlayer lithium-magnesium separation membrane includes the following steps: Preparation of phospholipid vesicle solution: Dissolve 100 mg of DOPE in chloroform and bring the volume to 100 mL to obtain a DOPE solution. Add 20 mL of the DOPE solution to a flask and purge with nitrogen for 10 min to allow the phospholipids to adhere to the flask wall and form a DOPE film. Vacuum the flask at 10 kPa and 40 °C for 4 h to thoroughly remove the chloroform and obtain a DOPE film. React the DOPE film with 20 mL of PBS under ultrasonic power of 200 W for 10 min, then mechanically vibrate at 500 rpm for 1 mm, freeze at -20 °C for 15 min, and thaw at 60 °C. Repeat the freeze-thaw cycle 5 times to obtain a hydrated DOPE solution. Extrude the hydrated DOPE solution repeatedly 12 times through a polycarbonate membrane with a pore diameter of 400 nm, and dilute with PBS to obtain a 0.1 mg / mL DOPE vesicle solution.

[0058] Preparation of a high-performance phospholipid interlayer lithium-magnesium separation membrane: A PS membrane was immersed in a 4 wt% sodium bisulfite solution for 12 h to remove contaminants from its surface. The membrane was then removed, washed with water, and soaked in ultrapure water for 6 h. Using the PS membrane as a filter, 50 mL of a 0.1 mg / mL DOPE vesicle solution was passed through the membrane at 0.1 MPa pressure, and the filtrate was collected. The filtrate was passed through the membrane twice more to obtain the DOPE interlayer, denoted as PS-DOPEx. The PS-DOPEx membrane with the PS membrane as the substrate is the polyethersulfone-phospholipid interlayer modified base membrane, denoted as TFC membrane.

[0059] The TFC membrane was immersed in a 0.3 wt% PEI solution for 5 min, allowing polyethyleneimine to bond to the phospholipid interlayer surface of the polysulfone-phospholipid interlayer modified base membrane via hydrogen bonding. The membrane was then removed and air-dried. Next, the surface of the phospholipid interlayer of the TFC membrane was contacted with a 0.15 wt% hexane organic phase of trimesoyl chloride for 3 min, causing the polyethyleneimine to polymerize with the oil-phase monomers in the organic solution, forming a polyamide separation layer. This layer was then heat-treated at 60°C for 10 min to obtain a high-performance phospholipid interlayer lithium-magnesium separation membrane, denoted as TFNi. 0.1 Among them, TFNi 0.1The polyethersulfone support layer has a thickness of 150 µm, the phospholipid interlayer has a thickness of 19 nm, and the polyamide release layer has a thickness of 50 nm. The transmittance is 15.22 L·m⁻¹. -2 ·h -1 ·bar -1 The separation factor is 35.4.

[0060] Example 2 A method for preparing a high-performance phospholipid interlayer lithium-magnesium separation membrane includes the following steps: Preparation of phospholipid vesicle solution: 500 mg of DOPE was dissolved in chloroform and the volume was adjusted to 100 mL to obtain a DOPE solution. 20 mL of the DOPE solution was added to a flask, and nitrogen gas was purged through the flask to dry it for 20 min, allowing the phospholipids to adhere to the flask wall and form a DOPE film. The flask was then vacuum-treated at 50 kPa and 70 °C for 5 h to thoroughly remove the chloroform, yielding a DOPE film. The DOPE film was reacted with 20 mL of PBS buffer at 300 W ultrasonic power for 13 min, followed by mechanical vibration at 1000 rpm for 1.5 mm, freezing at -10 °C for 30 min, and thawing at 70 °C. This freeze-thaw cycle was repeated 10 times to obtain a hydrated DOPE solution. The hydrated DOPE solution was repeatedly extruded through a polycarbonate membrane with a pore diameter of 200 nm 10 times, and diluted with PBS buffer to obtain a gradient DOPE vesicle solution with a concentration of 0.16 mg / mL.

[0061] Preparation of a high-performance phospholipid interlayer lithium-magnesium separation membrane: A PS membrane was immersed in a 4% sodium bisulfite solution for 16 hours to remove contaminants from its surface. The membrane was then removed, washed with water, and soaked in ultrapure water for 12 hours. Using the PS membrane as a filter, 50 mL of a 0.16 mg / mL DOPE vesicle solution was passed through the membrane at a pressure of 0.05 MPa, and the filtrate was collected. The filtrate was passed through the membrane four times to obtain the DOPE interlayer, denoted as PS-DOPEx. The PS-DOPEx membrane with the PS membrane as the substrate is the polyethersulfone-phospholipid interlayer modified base membrane, denoted as TFC membrane.

[0062] The TFC membrane was immersed in a 0.3 wt% PEI solution for 4 min, allowing polyethyleneimine to bond to the phospholipid interlayer surface of the polysulfone-phospholipid interlayer modified base membrane via hydrogen bonding. The membrane was then removed and air-dried. Next, the surface of the phospholipid interlayer of the TFC membrane was contacted with a 0.15 wt% hexane organic phase of trimesoyl chloride for 1 min, causing the polyethyleneimine to polymerize with the oil-phase monomers in the organic solution, forming a polyamide separation layer. This layer was then heat-treated at 70°C for 8 min to obtain a high-performance phospholipid interlayer lithium-magnesium separation membrane, denoted as TFNi. 0.16 Among them, TFNi 0.16The polyethersulfone support layer has a thickness of 170 µm, the phospholipid interlayer has a thickness of 6 nm, and the polyamide separator layer has a thickness of 55 nm. The transmittance is 13.04 L·m. -2 ·h -1 ·bar -1 The separation factor is 31.7.

[0063] Example 3 A method for preparing a high-performance phospholipid interlayer lithium-magnesium separation membrane includes the following steps: Preparation of phospholipid vesicle solution: 1000 mg of DOPE was dissolved in chloroform and the volume was adjusted to 100 mL to obtain a DOPE solution. 20 mL of the DOPE solution was added to a flask, and nitrogen gas was purged through to dry the flask, allowing the phospholipids to adhere to the flask wall and form a DOPE film. The flask was vacuum-treated at 100 kPa and 60 °C for 6 h to thoroughly remove the chloroform, obtaining a DOPE film. The DOPE film was reacted with 20 mL of PBS buffer at 400 W ultrasonic power for 15 min, followed by mechanical vibration at 1500 rpm and a 2 mm amplitude for min, then frozen at -15 °C for 20 min, and thawed at 80 °C. This freezing and thawing process was repeated 8 times, followed by 5 freeze-thaw cycles at 80 °C to obtain a hydrated DOPE solution. The hydrated DOPE solution was repeatedly extruded through a polycarbonate membrane with a pore diameter of 400 nm 30 times, and diluted with PBS buffer to obtain a gradient DOPE vesicle solution with a concentration of 0.20 mg / mL.

[0064] Preparation of a high-performance phospholipid interlayer lithium-magnesium separation membrane: A PS membrane was immersed in a 4% sodium bisulfite solution for 24 hours to remove contaminants from its surface. The membrane was then removed, washed with water, and soaked in ultrapure water for 24 hours. Using the PS membrane as a filter, 50 mL of a 0.2 mg / mL DOPE vesicle solution was passed through the membrane at a pressure of 0.07 MPa, and the filtrate was collected. The filtrate was passed through the membrane five times to obtain the DOPE interlayer, denoted as PS-DOPEx. The PS-DOPEx membrane with the PS membrane as the substrate is the polyethersulfone-phospholipid interlayer modified base membrane, denoted as TFC membrane.

[0065] The TFC membrane was immersed in a 0.3 wt% PEI solution for 3 min, allowing polyethyleneimine to bond to the phospholipid interlayer surface of the polysulfone-phospholipid interlayer modified base membrane via hydrogen bonding. The membrane was then removed and air-dried. Next, the surface of the phospholipid interlayer of the TFC membrane was contacted with a 0.05 wt% hexane organic phase of trimesoyl chloride for 2 min, causing the polyethyleneimine to polymerize with the oil-phase monomers in the organic solution, forming a polyamide separation layer. This layer was then heat-treated at 80°C for 12 min to obtain a high-performance phospholipid interlayer lithium-magnesium separation membrane, denoted as TFNi. 0.2 Among them, TFNi 0.1The polyethersulfone support layer has a thickness of 200 µm, the phospholipid interlayer has a thickness of 24 nm, and the polyamide separator layer has a thickness of 60 nm. The transmittance is 11.16 L·m⁻¹. -2 ·h -1 ·bar -1 The separation factor was 29.5.

[0066] Example 4 A method for preparing a high-performance phospholipid interlayer lithium-magnesium separation membrane includes the following steps: adjusting the DOPE vesicle solution in Example 1 to 0.18 mg / mL, and preparing the high-performance phospholipid interlayer lithium-magnesium separation membrane, denoted as TFNi. 0.18 The remaining conditions are the same as in Example 1.

[0067] The high-performance phospholipid interlayer lithium-magnesium separation membrane prepared is denoted as TFNi. 0.16 The thickness of the polyethersulfone support layer is 150 µm, the thickness of the phospholipid interlayer is 19 nm, and the thickness of the polyamide separator layer is 60 nm. The transmittance is 12.35 L / m². 2 The separation factor is 30.2, calculated as h·bar.

[0068] Comparative Example 1 A method for preparing a high-performance phospholipid interlayer lithium-magnesium separation membrane includes the following steps: adjusting the DOPE vesicle solution in Example 3 to 0.04 mg / mL, and preparing the high-performance phospholipid interlayer lithium-magnesium separation membrane, denoted as TFNi. 0.04 The remaining conditions are the same as in Example 3.

[0069] Prepared TFNi 0.04 The polyethersulfone support layer in the membrane has a thickness of 150 µm, the phospholipid interlayer has a thickness of 19 nm, and the polyamide separator layer has a thickness of 60 nm. The transmittance is 9.88 L·m. -2 ·h -1 ·bar -1 The separation factor is 18.3.

[0070] Comparative Example 2 A method for preparing a high-performance phospholipid interlayer lithium-magnesium separation membrane includes the following steps: The DOPE vesicle solution in Example 3 was adjusted to 0.06 mg / mL to prepare a high-performance phospholipid interlayer lithium-magnesium separation membrane, denoted as TFNi. 0.06 The remaining conditions are the same as in Example 3.

[0071] Prepared TFNi 0.06The polyethersulfone support layer in the membrane has a thickness of 150 µm, the phospholipid interlayer has a thickness of 19 nm, and the polyamide separator layer has a thickness of 60 nm. The permeability is 10.1 L / m². 2 The separation factor is 19.7 (h·bar).

[0072] Comparative Example 3 A method for preparing a high-performance phospholipid interlayer lithium-magnesium separation membrane includes the following steps: The DOPE vesicle solution in Example 3 was adjusted to 0.08 mg / mL to prepare a high-performance phospholipid interlayer lithium-magnesium separation membrane, denoted as TFNi. 0.08 The remaining conditions are the same as in Example 3.

[0073] Prepared TFNi 0.08 The polyethersulfone support layer in the membrane has a thickness of 150 µm, the phospholipid interlayer has a thickness of 19 nm, and the polyamide separator layer has a thickness of 60 nm. The transmittance is 9.05 L·m. -2 ·h -1 ·bar -1 The separation factor is 17.1.

[0074] To illustrate the beneficial effects of the present invention, the following experiment was also conducted.

[0075] I. Materials and Equipment 1. Experimental Materials The main materials used in this invention are PS film, DOPE, polyethylene glycol, polyethyleneimine, trimesoyl chloride, lithium chloride, magnesium chloride, n-hexane, and sodium dodecyl sulfate.

[0076] The following materials were purchased: PS membrane with a molecular weight cutoff of 50,000 Da from Beijing OriginWater Technology Co., Ltd.; DOPE with a purity >99% from Avanti Polar Lipids, USA; polyethylene glycol with molecular weights of 200 Da, 400 Da, 600 Da, 800 Da, and 1000 Da from TCI Chemical Co., Ltd., Japan; polyethyleneimine with a molecular weight of 600 Da from Sigma-Aldrich, USA; trimesoyl chloride with a purity ≥98% from Sigma-Aldrich, USA; and lithium chloride with a purity ≥99%, magnesium chloride with a purity ≥99.9%, n-hexane with a purity ≥98%, and sodium dodecyl sulfate from Shanghai Sinopharm Chemical Reagent Co., Ltd., China.

[0077] II. Experimental Methods 1. Morphological characterization of the phospholipid interlayer The TFC membrane and TFNi prepared in Example 1 0.1The membrane structure was characterized. The surface morphology and cross-sectional structure of the phospholipid interlayer were characterized using scanning electron microscopy. Atomic force microscopy was used to determine the surface roughness of the membrane; at least three different points were tested on each membrane, and the average value was taken to ensure accuracy.

[0078] 2. Permeability and separation performance of lithium-magnesium separation nanofiltration membranes This invention uses ultrapure water as the feed liquid to evaluate the water permeability of membranes. The membrane prepared in Example 1 has an area of ​​24 cm². 2 TFNi 0.1 The water flux and salt rejection rate of the membrane were tested at 25℃. First, the membrane was pre-compressed at 0.6MPa for 0.5h to achieve a stable water permeability, and then the operating pressure was adjusted to 0.4MPa for testing. The separation performance of the nanofiltration membrane was determined using a typical salt solution of 2000ppm MgCl2 and LiCl. The water flux, water permeability, and salt rejection rate can be calculated using formulas (1) to (3). The unit of water flux is L·m -2 ·h -1 The unit of water permeability is L·m. -2 ·h -1 ·bar -1 The unit for salt rejection rate is %.

[0079] Formula (1): ; Formula (2): ; Formula (3): ; In the formula, J v ΔV is the water flux; ΔV is the solution permeate flow rate; S is the membrane area; ΔT is the sample collection time interval; A is the water permeability coefficient; ΔP is the transmembrane pressure difference; R is the salt rejection rate; C p It is the concentration of the solute in the liquid; C f It refers to the solute concentration in the raw material solution.

[0080] 3. Separation coefficient of lithium-magnesium separation nanofiltration membrane The TFC membrane and TFNi prepared in Example 1 were evaluated using a mixed solution of magnesium chloride and lithium chloride. 0.1 Membrane, TFNi 0.16 Membrane, TFNi 0.2 Membrane, TFNi 0.04 The separation coefficient of the membrane. For Mg 2+ and Li + The separation selectivity was assessed. Inductively coupled plasma atomic emission spectrometry (ICP-AES) using a PerkinElmer 8300 system was employed to determine the Mg content in the feed solution and permeate. 2+ and Li + The concentration of Mg. 2+ and Li+ The separation factor is calculated using formula (4).

[0081] Formula (4):

[0082] In the formula: S Mg，Li It is the lithium-magnesium separation factor; C + p Li represents the concentration of lithium ions permeated by the liquid; C 2+ p Mg is the concentration of magnesium ions permeated through the liquid; C + f Li represents the lithium-ion concentration in the feed solution; C 2+ f Mg is the concentration of magnesium ions in the raw material solution.

[0083] III. Experimental Results 1. Morphological characterization of the phospholipid layer The effect of constructing phospholipid layers of different concentrations on the morphology and structure of the interfacial polymerization layer is as follows: Figures 1-3 As shown. Figure 1 In the study, when the phospholipid vesicle solution concentration was 0.1 mg / mL, the PEI distribution was more uniform after constructing the phospholipid layer, and the surface showed a uniform red color. When the phospholipid vesicle solution concentration was 0.04 mg / mL, the membrane edge showed a darker red color, while the center was lighter, indicating uneven PEI distribution. Figure 2 The polyamide nanofiltration membrane containing a phospholipid interlayer with a concentration of 0.1 wt% is denoted as TFNi. 0.1 Membrane. TFNi 0.1 The pore diameter decreased from 0.62 nm in the TFC membrane to 0.40 nm. Figure 3 In the TFNi nanofiltration membrane, the polyamide separation layer thickness without a phospholipid interlayer is approximately 49.3 nm, while... 0.1 The polyamide separation layer of the membrane is approximately 26.4 nm thick. The construction of the phospholipid layer effectively improves the physicochemical properties of the base membrane, resulting in a reduced interfacial polymerization rate and a more uniform reaction.

[0084] 2. Permeability of lithium-magnesium separation nanofiltration membranes The effect of phospholipid layer construction on the permeability of composite membranes, such as Figure 4 As shown. Figure 4 In this study, the water permeability of the TFC membrane was 9.05 L·m. -2 ·h -1 ·bar -1 This is within the normal range compared to commercial NF membranes. When a DOPE interlayer is introduced, water permeability gradually increases until the DOPE concentration reaches 0.1 mg / mL. TFNi 0.1 The membrane exhibited the highest permeability, at 15.22 L·m⁻². -2 ·h -1·bar -1 It is 1.45 times that of TFC membranes. This is because the construction of the phospholipid interlayer facilitates the reduction of the thickness of the interfacial polymerization layer, reduces the transmembrane path of water molecules, and thus increases water flux.

[0085] 3. Separation performance of lithium-magnesium separation nanofiltration membrane The effect of phospholipid layer construction on the separation performance of composite membranes, such as Figure 5 As shown. Figure 5 In the study, the TFC membrane achieved removal rates of 78.1% for MgCl2 and 27.1% for LiCl, while TFNi... 0.1 The membrane removed 97.6% of MgCl2 and 32.8% of LiCl. This is because the construction of the phospholipid interlayer effectively reduced the membrane pore diameter and enhanced the pore diameter sieving effect.

[0086] 4. Separation coefficient of lithium-magnesium separation nanofiltration membrane The effect of phospholipid layer construction on the separation coefficient of lithium-magnesium separation nanofiltration membranes is as follows: Figure 6 As shown. Figure 6 In the simulated salt water, when Mg 2+ and Li + When the mass concentration ratios are 1:1, 10:1, 20:1 and 40:1, TFNi 0.1 The separation coefficients of the membranes were 54.9, 41.4, 35.4, and 27.1, respectively. The results indicate that, compared to TFC, TFNi... 0.1 Positive interlayer NF membrane for Li + and Mg 2+ The separation exhibits good selectivity.

[0087] IV. Discussion of Results The high-performance phospholipid interlayer lithium-magnesium separation membrane of the present invention utilizes phospholipid vesicles to form an interlayer, enhancing the permeability of the filter membrane while also exhibiting selective permeability for lithium and magnesium ions. Simultaneously, the construction of the phospholipid interlayer effectively reduces the membrane pore diameter, enhancing the pore diameter sieving effect. The construction of the phospholipid interlayer facilitates a reduction in the thickness of the interfacial polymerization layer, decreasing the transmembrane path of water molecules and thus increasing water flux. Therefore, the TFNi prepared in Example 1 of the present invention… 0.1 The membrane permeability is 15.22 L·m⁻². -2 ·h -1 ·bar -1 It is 1.45 times more efficient than TFC membranes, achieving removal rates of 97.6% for MgCl2 and 32.8% for LiCl. Therefore, the lithium-magnesium separation nanofiltration membrane of this invention can efficiently separate lithium and magnesium in a lithium-magnesium mixed solution. Nanofiltration membrane separation technology features low energy consumption and high equipment integration. In the lithium-magnesium separation process, the nanofiltration membrane amplifies the interaction between the nanofiltration membrane and MgCl2. 2+ and Li +The difference in function achieves the goal of "blocking magnesium and allowing lithium to pass through".

[0088] It should be noted that when numerical ranges are involved in this invention, it should be understood that both endpoints of each numerical range and any value between the two endpoints can be selected. Since the steps and methods used are the same as in the embodiments, preferred embodiments are described in this invention to avoid redundancy. Although preferred embodiments of this invention have been described, those skilled in the art, once they understand the inventive concept of this invention, can make other changes and modifications to these embodiments, and all such changes and modifications fall within the scope of this invention.

[0089] Obviously, those skilled in the art can make various modifications and variations to this invention without departing from its spirit and scope. If such modifications and variations fall within the scope of equivalents of this invention, then this invention also intends to include these modifications and variations.

Claims

1. A high-performance phospholipid interlayer lithium-magnesium separation membrane, characterized in that, It includes a lower polyethersulfone support layer, a phospholipid intermediate layer, and an upper polyamide separation layer; The high-performance phospholipid interlayer lithium-magnesium separation membrane is prepared by the following method: a phospholipid interlayer is introduced into a polyethersulfone ultrafiltration membrane as a substrate, and then a polyamide separation layer is formed by interfacial polymerization of polyethyleneimine and trimesoyl chloride. Finally, the membrane is heat-treated to obtain the high-performance phospholipid interlayer lithium-magnesium separation membrane. The phospholipid intermediate layer is a positively charged phospholipid bilayer film formed by phospholipid vesicles spreading on the surface of the polyethersulfone support layer. The phospholipid in the phospholipid vesicles is one of dioleoylphosphatidylcholine, dioleoylphosphatidylethanolamine and 1,2-dioleoyl-3-trimethylaminopropane hydrochloride; The phospholipid vesicles are obtained by repeatedly extruding a phospholipid hydrate solution through a filter membrane with a pore diameter of 200nm~600nm to make the vesicle size uniform. The term "high performance" refers to a transmittance higher than 11 L·m. -2 ·h -1 ·bar -1 The separation factor is greater than or equal to 29.

5.

2. The high-performance phospholipid interlayer lithium-magnesium separation membrane according to claim 1, characterized in that, The thickness of the polyethersulfone support layer is 150µm~200µm, the thickness of the phospholipid intermediate layer is 6nm~24nm, and the thickness of the polyamide separation layer is 50nm~60nm.

3. The high-performance phospholipid interlayer lithium-magnesium separation membrane according to claim 1, characterized in that, The method for preparing the phospholipid vesicles includes the following steps: A phospholipid solution is added to a container to form a film, thus obtaining a phospholipid film. A phosphate buffer solution was used to hydrate the phospholipid membrane to obtain a hydrated phospholipid solution. The hydration reaction refers to the rearrangement of phospholipid molecules to form vesicle structures by means of ultrasound, mechanical vibration and freeze-thaw. The phospholipid hydrate solution is repeatedly squeezed through a filter membrane to make the vesicles uniform in size, thus obtaining a phospholipid vesicle solution.

4. The high-performance phospholipid interlayer lithium-magnesium separation membrane according to claim 3, characterized in that, The phospholipid solution has a concentration of 1 mg / mL to 10 mg / mL, and the solvent is chloroform. The film formation conditions are: first blow-drying followed by vacuum drying, with the blow-drying time being 10 min to 30 min, the vacuum drying pressure being 10 kPa to 100 kPa, the time being 4 h to 6 h, and the temperature being 40 ℃ to 60 ℃. The volume ratio of the phospholipid solution to the PBS buffer is 1:1~19; The power of the ultrasound is 200W~400W, and the duration is 10min~15min; The mechanical vibration speed is 500rpm~1500rpm, the amplitude is 1mm~2mm, and the duration is 5min~10min; The freezing temperature for the freeze-thaw cycle is -20℃ to -10℃, the thawing temperature is 60℃ to 80℃, the time is 15min to 30min, and the number of cycles is 5 to 10. The filter membrane is a polycarbonate membrane; The number of extrusions is 10 to 30 times; The concentration of the phospholipid vesicle solution is 0.1 mg / mL to 0.2 mg / mL.

5. The method for preparing a high-performance phospholipid interlayer lithium-magnesium separation membrane according to claim 1, characterized in that, Includes the following steps: A phospholipid vesicle solution was added to the surface of a polyethersulfone ultrafiltration membrane, and vacuum membrane was performed. After all the phospholipid vesicle solution had passed through the membrane, the filtrate was repeatedly passed through the membrane to obtain a polyethersulfone-phospholipid intermediate modified base membrane. The polyethersulfone-phospholipid interlayer modified base film includes a lower polyethersulfone support layer and a phospholipid layer located on the upper surface of the polyethersulfone support layer. The polyethersulfone-phospholipid interlayer modified base membrane was immersed in a polyethyleneimine solution, allowing the polyethyleneimine to bind to the phospholipid interlayer surface of the polyethersulfone-phospholipid interlayer modified base membrane through hydrogen bonding. After removal and drying, the surface of one side of the phospholipid interlayer of the polyethersulfone-phospholipid interlayer modified base membrane was brought into contact with an organic solution, causing the polyethyleneimine to undergo a polymerization reaction with the oil phase monomers in the organic solution to form a polyamide separation layer. Heat treatment was then performed to stabilize the polymerization of the polyethyleneimine in the polyamide separation layer with the oil phase monomers in the organic solution, resulting in a high-performance phospholipid interlayer lithium-magnesium separation membrane.

6. The method for preparing a high-performance phospholipid interlayer lithium-magnesium separation membrane according to claim 5, characterized in that, The ratio of the amount of polyethersulfone ultrafiltration membrane to the amount of phospholipid vesicle solution is 0.5 mg to 5 mg of phospholipid vesicles per square centimeter of polyethersulfone ultrafiltration membrane. The immersion time in the polyethyleneimine solution is 3 to 5 minutes. The organic solution is a hexane solution of pyromellitic trimethylol chloride with a concentration of 0.05wt%~0.3wt%, and the contact time is 1min~3min.

7. The method for preparing a high-performance phospholipid interlayer lithium-magnesium separation membrane according to claim 5, characterized in that, The heat treatment temperature is 60℃~80℃, and the time is 8min~12min.

8. The method for preparing a high-performance phospholipid interlayer lithium-magnesium separation membrane according to claim 5, characterized in that, The pressure of the vacuum membrane is 0.05MPa~0.1MPa.

9. The method for preparing a high-performance phospholipid interlayer lithium-magnesium separation membrane according to claim 5, characterized in that, The number of times the membrane is repeated is 2 to 5.

10. The application of the high-performance phospholipid intermediate layer lithium-magnesium separation membrane according to claim 5 in the separation of lithium and magnesium.

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