A polyelectrolyte nanofiltration membrane with permanent structure stamp and preparation method and application thereof
By growing a nano-manganese oxide template layer in situ on a porous substrate and then self-assembling a polyelectrolyte layer layer by layer, a polyelectrolyte nanofiltration membrane with a permanent structural imprint was prepared. This solved the problem of achieving both high water flux and high rejection rate, improved the membrane's long-term stability and antifouling ability, and achieved a highly efficient water treatment effect.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- HARBIN INST OF TECH
- Filing Date
- 2026-03-27
- Publication Date
- 2026-06-16
AI Technical Summary
Existing polyelectrolyte nanofiltration membranes struggle to achieve a balance between water flux and retention rate, and their structure is prone to ion exchange and loss under long-term operation or high-salt conditions, leading to performance degradation.
A manganese oxide nanofiltration membrane with a permanent structural imprint is formed by in-situ growth of a nano-manganese oxide template layer on a porous substrate and layer-by-layer self-assembly to form a polyelectrolyte layer. The manganese oxide-polyelectrolyte composite nanofiltration membrane is prepared by filling the gaps between the nano-manganese oxide particles with positively and negatively charged polyelectrolytes.
It achieves a balance between high throughput and high rejection rate, improves long-term stability, enhances anti-fouling ability, and has an environmentally friendly and simple preparation process.
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Figure CN122209231A_ABST
Abstract
Description
Technical Field
[0001] This invention belongs to the field of membrane separation technology, specifically relating to a polyelectrolyte nanofiltration membrane with a permanent structural imprint, its preparation method, and its application. Background Technology
[0002] Polyelectrolyte layer-by-layer self-assembled nanofiltration membranes (PEMs) have shown broad application prospects in water treatment fields such as micro-pollutant removal, seawater pretreatment, and resource recovery due to their advantages such as tunable selectivity, mild preparation conditions, and no need for organic solvents. Compared to traditional polyamide nanofiltration membranes, PEMs can finely control the membrane's pore size, surface charge, and hydrophilicity / hydrophobicity by selecting different polyelectrolyte pairs and assembly conditions. However, the practical application of PEM membranes has long been hampered by a fundamental problem: the trade-off between water flux and rejection rate. An ideal PEM structure requires polycationic and polyanionic segments to form an intrinsic compensation network through close ion pairing. This structure endows the membrane with excellent selectivity but also leads to excessively dense segment stacking and limited free volume, which is the fundamental reason why PEM membrane flux is generally lower than that of commercial polyamide membranes. To improve flux, researchers often introduce small-molecule counterions, such as sodium chloride, during the assembly process to form "external compensation." These external compensation ions insert between the segments, expanding the network structure and increasing free volume, thereby increasing flux. However, external compensation is a double-edged sword. Low salt concentrations cause polymer chains to become more coiled and denser, leading to increased retention; while high salt concentrations result in excessive external compensation, causing a looser structure and larger membrane pores, leading to decreased retention. More critically, the external compensation state is highly dependent on the liquid environment, and ion exchange and loss easily occur under long-term operation or high-salt conditions, leading to structural relaxation and performance degradation. To address these challenges, there is an urgent need to develop a novel nanofiltration membrane that combines high throughput, high stability, and excellent separation performance to overcome existing performance bottlenecks and expand its application in complex systems (such as high-salt wastewater and lithium-magnesium separation). Summary of the Invention
[0003] The purpose of this invention is to solve the technical problems of structural instability, long-term performance degradation, and difficulty in achieving both flux and retention in existing polyelectrolyte nanofiltration membranes due to external compensation dynamic changes. The invention provides a polyelectrolyte nanofiltration membrane with a permanent structural imprint, its preparation method, and its application.
[0004] A polyelectrolyte nanofiltration membrane with a permanent structural imprint includes a porous substrate, a template layer, and a functional layer; the template layer is grown in situ on the porous substrate; and the functional layers are self-assembled layer by layer on the template layer.
[0005] The template layer is nano-manganese oxide;
[0006] The functional layer is a polyelectrolyte layer.
[0007] A method for preparing a polyelectrolyte nanofiltration membrane with a permanent structural imprint, characterized in that the preparation method is specifically carried out according to the following steps:
[0008] I. Pretreatment of porous substrates:
[0009] The porous substrate was cleaned with deionized water to obtain a pretreated porous substrate.
[0010] II. In-situ reaction to generate template layer:
[0011] When the porous substrate is a flat sheet membrane, the in-situ reaction to generate the template layer is specifically accomplished according to the following steps:
[0012] ① Immerse the flat sheet membrane in a polycationic solution and react for a period of time. A layer of polycations is adsorbed on the flat sheet membrane. Then rinse with deionized water to obtain a flat sheet membrane adsorbed with polycations.
[0013] ② The sheet membrane with adsorbed polycations is immersed in potassium permanganate solution and reacted for a period of time. Brownish-brown nano-manganese oxide is generated in situ on the sheet membrane. Then it is rinsed with deionized water and then immersed in glycerol aqueous solution for storage. When used, it is taken out and dried at room temperature to obtain a sheet membrane with an in situ grown template layer.
[0014] When the porous substrate is a hollow fiber ultrafiltration membrane, the in-situ reaction to generate the template layer is specifically accomplished according to the following steps:
[0015] (1) The polycation solution is injected into and flows through the inner wall of the hollow fiber ultrafiltration membrane. After reacting for a period of time, a layer of polycations is adsorbed on the inner wall of the hollow fiber ultrafiltration membrane. Then, deionized water is continuously injected to rinse the inner wall of the hollow fiber ultrafiltration membrane to obtain a hollow fiber ultrafiltration membrane adsorbed with polycations.
[0016] (2) Potassium permanganate solution is injected into and flows through the inner wall of the hollow fiber ultrafiltration membrane adsorbed with polycations.
[0017] After reacting for a period of time, brownish-yellow nano-manganese oxide is generated in situ. Then, deionized water is continuously injected to rinse the inner wall of the hollow fiber ultrafiltration membrane. Glycerol aqueous solution is then injected and stored. When using, deionized water is continuously injected to rinse the inner wall of the hollow fiber ultrafiltration membrane to obtain a hollow fiber ultrafiltration membrane with an in situ grown template layer.
[0018] III. Assemble the polyelectrolyte layer layer by layer:
[0019] When the porous substrate is a flat sheet membrane, the layer-by-layer assembly of the polyelectrolyte layer is carried out according to the following steps:
[0020] ① Immerse the flat sheet membrane with the in-situ grown template layer in a polycationic solution for a period of time, then rinse it several times with NaCl solution after taking it out, and then immerse it in a polyanionic solution for a period of time, and then rinse it several times with NaCl solution after taking it out.
[0021] ② Repeat step 3① to assemble the polyelectrolyte layer by layer; after assembly, immerse it in a glycerol aqueous solution for storage. When using, take it out and air dry at room temperature to obtain a polyelectrolyte nanofiltration membrane with a permanent structural imprint.
[0022] When the porous substrate is a hollow fiber ultrafiltration membrane, the layer-by-layer assembly of the polyelectrolyte layer is carried out according to the following steps:
[0023] (1) The polycationic solution is injected into and flows through the inner wall of the hollow fiber ultrafiltration membrane with the in-situ growth template layer. After reacting for a period of time, NaCl solution is continuously injected to rinse the inner wall of the hollow fiber ultrafiltration membrane. Then the polyanionic solution is injected into and flows through the inner wall of the hollow fiber ultrafiltration membrane. After reacting for a period of time, NaCl solution is continuously injected to rinse the inner wall of the hollow fiber ultrafiltration membrane.
[0024] (2) Repeat step 3 (1) to assemble the polyelectrolyte layer layer by layer; after assembly, inject glycerol aqueous solution and store it. When using, continuously inject deionized water to rinse the inner wall of the hollow fiber ultrafiltration membrane to obtain a polyelectrolyte nanofiltration membrane with a permanent structural imprint.
[0025] A polyelectrolyte nanofiltration membrane with a permanent structural imprint is used to remove micropollutants, perfluoroalkyl substances, divalent salts, or for seawater pretreatment.
[0026] The principle of this invention:
[0027] This invention reacts a cleaned porous substrate with a mixture of polycations, NaCl, and deionized water, followed by a reaction with a potassium permanganate solution. In this step, potassium permanganate and polycations undergo a redox reaction, generating nano-manganese oxide in situ, which is then anchored onto a hollow fiber ultrafiltration membrane. A polyelectrolyte layer then undergoes surface self-assembly at the nano-interface containing manganese oxide particles, i.e., by sequentially passing through a polycationic solution and a polyanionic solution. The gaps between the in-situ manganese oxide nanoparticles are filled with positively and negatively charged polyelectrolytes, thus preparing a manganese oxide-polyelectrolyte composite nanofiltration membrane. The gaps between the manganese oxide nanoparticles are further reduced until salt ions are retained. Under the dual effects of size sieving and electrorepulsion, it exhibits high throughput and high retention rate.
[0028] The beneficial effects of this invention are:
[0029] I. Simultaneous Achievement of High Flux and High Retention: The polyelectrolyte nanofiltration membrane with permanent structural imprint prepared in this invention breaks through the flux-retention trade-off of traditional PEM membranes; while maintaining a Na2SO4 retention rate of >95%, the pure water flux can reach 30m³ / s. -2 h -1 bar -1 above;
[0030] II. Permanent structural impression, enhancing long-term stability: Template layer (MnO) x The optimized PEM structure induced by the intermediate layer is permanent; long-term operation (>7 days) and high salt immersion tests show that the membrane flux and retention performance degradation rate of the present invention are significantly lower than those of the control membrane, solving the problem of structural instability caused by external compensation dynamic loss;
[0031] III. Enhanced antifouling ability: The optimized PEM structure of this invention has a more uniform surface charge distribution and improved hydrophilicity, which reduces the adsorption and deposition of pollutants on the membrane surface; humic acid pollution experiments show that the membrane flux recovery rate of this invention is higher and there is less irreversible pollution.
[0032] IV. Environmentally friendly and simple process: The preparation process uses water as a solvent and does not require organic solvents; the in-situ oxidation-reduction method is simple and controllable and easy to scale up for production. Attached Figure Description
[0033] Figure 1 These are scanning electron microscope (SEM) images of the inner surfaces of the original and modified membranes. In the image, A is the polyethersulfone hollow fiber ultrafiltration membrane, and B is the MnO obtained in step two of Example 1. x -PES composite membrane, C is MnO obtained in step three of Example 1. x -PEM composite nanofiltration membrane, D is MnO obtained from control example 2. x -PEM-acid composite nanofiltration membrane;
[0034] Figure 2 This is a particle size distribution diagram of the nano-manganese oxide obtained in step two of Example 1;
[0035] Figure 3 This is a diagram showing the zeta potential transition on the inner surface of the membrane during assembly.
[0036] Figure 4 MnO prepared in Example 1 x -PEM composite nanofiltration membrane, the PEM-control composite nanofiltration membrane prepared in Comparative Example 1 and the MnO prepared in Comparative Example 2 x Flux-salt rejection ratio of PEM-acid composite nanofiltration membrane. Detailed Implementation
[0037] Specific Implementation Method 1: This implementation method is a polyelectrolyte nanofiltration membrane with a permanent structural imprint, which includes a porous substrate, a template layer, and a functional layer; the template layer is grown in situ on the porous substrate; the functional layers are self-assembled layer by layer on the template layer;
[0038] The template layer is nano-manganese oxide;
[0039] The functional layer is a polyelectrolyte layer.
[0040] Specific Implementation Method Two: This implementation method differs from Specific Implementation Method One in that the template layer is a surface-confined porous structure with a thickness of 10nm~200nm; the particle size of the nano-manganese oxide is 5nm~30nm. Other steps are the same as in Specific Implementation Method One.
[0041] Specific Implementation Method Three: This implementation method differs from Specific Implementation Method One or Two in that the porous substrate is a flat sheet membrane or a hollow fiber ultrafiltration membrane, and the material is polyethersulfone, polyacrylonitrile, or polysulfone. Other steps are the same as in Specific Implementation Method One or Two.
[0042] Specific Implementation Method Four: This implementation method differs from Specific Implementation Methods One to Three in that: the polyelectrolyte layer is formed by the self-assembly of polycations and polyanions layer by layer, with 2 to 10 bilayers; the polycation is polyallylamine hydrochloride, polydiallyldimethylammonium chloride, or polyethyleneimine; the polyanion is sodium polystyrene sulfonate. Other steps are the same as in Specific Implementation Methods One to Three.
[0043] Specific Implementation Method 5: This implementation method is a method for preparing a polyelectrolyte nanofiltration membrane with a permanent structural imprint, specifically completed according to the following steps:
[0044] I. Pretreatment of porous substrates:
[0045] The porous substrate was cleaned with deionized water to obtain a pretreated porous substrate.
[0046] II. In-situ reaction to generate template layer:
[0047] When the porous substrate is a flat sheet membrane, the in-situ reaction to generate the template layer is specifically accomplished according to the following steps:
[0048] ① Immerse the flat sheet membrane in a polycationic solution and react for a period of time. A layer of polycations is adsorbed on the flat sheet membrane. Then rinse with deionized water to obtain a flat sheet membrane adsorbed with polycations.
[0049] ② The sheet membrane with adsorbed polycations is immersed in potassium permanganate solution and reacted for a period of time. Brownish-brown nano-manganese oxide is generated in situ on the sheet membrane. Then it is rinsed with deionized water and then immersed in glycerol aqueous solution for storage. When used, it is taken out and dried at room temperature to obtain a sheet membrane with an in situ grown template layer.
[0050] When the porous substrate is a hollow fiber ultrafiltration membrane, the in-situ reaction to generate the template layer is specifically accomplished according to the following steps:
[0051] (1) The polycation solution is injected into and flows through the inner wall of the hollow fiber ultrafiltration membrane. After reacting for a period of time, a layer of polycations is adsorbed on the inner wall of the hollow fiber ultrafiltration membrane. Then, deionized water is continuously injected to rinse the inner wall of the hollow fiber ultrafiltration membrane to obtain a hollow fiber ultrafiltration membrane adsorbed with polycations.
[0052] (2) Potassium permanganate solution is injected into and flows through the inner wall of the hollow fiber ultrafiltration membrane adsorbed with polycations.
[0053] After reacting for a period of time, brownish-yellow nano-manganese oxide is generated in situ. Then, deionized water is continuously injected to rinse the inner wall of the hollow fiber ultrafiltration membrane. Glycerol aqueous solution is then injected and stored. When using, deionized water is continuously injected to rinse the inner wall of the hollow fiber ultrafiltration membrane to obtain a hollow fiber ultrafiltration membrane with an in situ grown template layer.
[0054] III. Assemble the polyelectrolyte layer layer by layer:
[0055] When the porous substrate is a flat sheet membrane, the layer-by-layer assembly of the polyelectrolyte layer is carried out according to the following steps:
[0056] ① Immerse the flat sheet membrane with the in-situ grown template layer in a polycationic solution for a period of time, then rinse it several times with NaCl solution after taking it out, and then immerse it in a polyanionic solution for a period of time, and then rinse it several times with NaCl solution after taking it out.
[0057] ② Repeat step 3① to assemble the polyelectrolyte layer by layer; after assembly, immerse it in a glycerol aqueous solution for storage. When using, take it out and air dry at room temperature to obtain a polyelectrolyte nanofiltration membrane with a permanent structural imprint.
[0058] When the porous substrate is a hollow fiber ultrafiltration membrane, the layer-by-layer assembly of the polyelectrolyte layer is carried out according to the following steps:
[0059] (1) The polycationic solution is injected into and flows through the inner wall of the hollow fiber ultrafiltration membrane with the in-situ growth template layer. After reacting for a period of time, NaCl solution is continuously injected to rinse the inner wall of the hollow fiber ultrafiltration membrane. Then the polyanionic solution is injected into and flows through the inner wall of the hollow fiber ultrafiltration membrane. After reacting for a period of time, NaCl solution is continuously injected to rinse the inner wall of the hollow fiber ultrafiltration membrane.
[0060] (2) Repeat step 3 (1) to assemble the polyelectrolyte layer layer by layer; after assembly, inject glycerol aqueous solution and store it. When using, continuously inject deionized water to rinse the inner wall of the hollow fiber ultrafiltration membrane to obtain a polyelectrolyte nanofiltration membrane with a permanent structural imprint.
[0061] Specific Implementation Method Six: The differences between this implementation method and Specific Implementation Methods One to Five are as follows: the cleaning time in step one is 20 min to 40 min; the polycationic solution in step two is a mixture of polycationic acid, NaCl, and deionized water, wherein the concentration of polycationic acid is 0.5 g / L to 10 g / L, and the concentration of NaCl is 0.5 mol / L to 1 mol / L; the reaction time in step two is 5 min to 15 min; the number of times the deionized water is rinsed in step two (1) is 2 to 4 times; the time for continuously injecting deionized water to rinse the inner wall of the hollow fiber ultrafiltration membrane in steps two (1) and two (2) is 2 min to 3 min. Other steps are the same as in Specific Implementation Methods One to Five.
[0062] Specific Implementation Method Seven: The differences between this implementation method and Specific Implementation Methods One to Six are as follows: the concentration of the potassium permanganate solution in step two is 0.1 g / L to 2 g / L; the reaction time in step two is 2 min to 10 min; the mass fraction of the glycerol aqueous solution in step two is 20% to 50%, and the storage time is 3 h to 4 h; the reaction time in step three is 5 min to 30 min; the number of rinsings in step three (①) is 1 to 3 times; the time for each rinsing is 5 min to 10 min; the time for continuously injecting NaCl solution to rinse the inner wall of the hollow fiber ultrafiltration membrane in step three (1) is 2 min to 3 min; and the time for continuously injecting deionized water to rinse the inner wall of the hollow fiber ultrafiltration membrane in step three (2) is 30 min to 60 min. Other steps are the same as in Specific Implementation Methods One to Six.
[0063] Specific Implementation Method Eight: The difference between this implementation method and Specific Implementation Methods One to Seven is that: the polycationic solution in step three is a mixture of polycationic acid, NaCl, and deionized water, wherein the concentration of polycationic acid is 0.1 g / L to 10 g / L, and the concentration of NaCl is 0.1 mol / L to 1 mol / L; the polyanionic solution in step three is a mixture of polyanionic acid, NaCl, and deionized water, wherein the concentration of polyanionic acid is 0.1 g / L to 10 g / L, and the concentration of NaCl is 0.1 mol / L to 0.5 mol / L; step three ① is repeated 1 to 9 times in step three ②; the mass fraction of the glycerol aqueous solution in step three is 20% to 50%, and the storage time is 3 to 4 hours; step three (2) is repeated 1 to 9 times in step three (1). Other steps are the same as in Specific Implementation Methods One to Seven.
[0064] Specific Implementation Method Nine: This implementation method is a polyelectrolyte nanofiltration membrane with a permanent structural imprint for removing micropollutants, perfluoroalkyl substances, divalent salts from water or for seawater pretreatment.
[0065] Specific Implementation Method Ten: The difference between this implementation method and Specific Implementation Methods One through Nine is that a polyelectrolyte nanofiltration membrane with a permanent structural impression has a pure water flux greater than 30 L·m³ at an operating pressure of 6 bar to 10 bar. -2 ·h -1 bar -1 The retention rate of magnesium chloride is greater than 95%. Other steps are the same as those in specific implementation methods one through nine.
[0066] The beneficial effects of the present invention are verified using the following embodiments:
[0067] Example 1: A method for preparing a polyelectrolyte nanofiltration membrane with a permanent structural imprint, specifically comprising the following steps:
[0068] I. Pretreatment of porous substrates:
[0069] The porous substrate was cleaned with deionized water for 30 minutes to obtain the pretreated porous substrate.
[0070] The porous substrate mentioned in step one is a hollow fiber ultrafiltration membrane made of polyethersulfone (PES).
[0071] II. In-situ reaction to generate template layer:
[0072] (1) The polycation solution was injected into and flowed through the inner wall of the hollow fiber ultrafiltration membrane using an injection pump. After reacting for 10 minutes, a layer of polyallylamine hydrochloride was adsorbed on the inner wall of the hollow fiber ultrafiltration membrane. Then, the inner wall of the hollow fiber ultrafiltration membrane was continuously rinsed with deionized water using an injection pump for 3 minutes to obtain a hollow fiber ultrafiltration membrane adsorbed with polycations.
[0073] The polycationic solution mentioned in step 2① is a mixture of polyallylamine hydrochloride, NaCl and deionized water, wherein the concentration of polyallylamine hydrochloride is 10 g / L and the concentration of NaCl is 0.5 mol / L.
[0074] (2) Using a syringe pump, potassium permanganate solution is injected and flows through the inner wall of the hollow fiber ultrafiltration membrane adsorbed with polycations. The reaction is allowed to proceed for 2 minutes, resulting in the in-situ formation of brown nano-manganese oxide. Then, deionized water is continuously injected into the inner wall of the hollow fiber ultrafiltration membrane for 3 minutes. Next, a 20% glycerol aqueous solution is injected and stored for 4 hours. When using the membrane, deionized water is continuously injected into the inner wall for 30 minutes to obtain a hollow fiber ultrafiltration membrane with an in-situ grown template layer (i.e., MnO). x-PES composite membrane);
[0075] The concentration of the potassium permanganate solution mentioned in step 2 (2) is 0.5 g / L;
[0076] III. Assemble the polyelectrolyte layer layer by layer:
[0077] (1) The polycationic solution was injected into and flowed through the inner wall of the hollow fiber ultrafiltration membrane with the in-situ growth template layer using a syringe pump. The reaction was carried out for 15 min. Then, the inner wall of the hollow fiber ultrafiltration membrane was rinsed with 0.5 mol / L NaCl solution continuously injected into the syringe pump for 3 min. Then, the polyanionic solution was injected into and flowed through the inner wall of the hollow fiber ultrafiltration membrane using a syringe pump. The reaction was carried out for 15 min. Finally, the inner wall of the hollow fiber ultrafiltration membrane was rinsed with 0.5 mol / L NaCl solution continuously injected into the syringe pump for 3 min.
[0078] The polycationic solution mentioned in step 3 (1) is a mixture of polyallylamine hydrochloride, NaCl and deionized water, wherein the concentration of polyallylamine hydrochloride is 10 g / L and the concentration of NaCl is 0.5 mol / L;
[0079] The polyanionic solution mentioned in step three (1) is a mixture of sodium polystyrene sulfonate, NaCl and deionized water, wherein the concentration of sodium polystyrene sulfonate is 10 g / L and the concentration of NaCl is 0.5 mol / L.
[0080] (2) Repeat step 3 (1) twice to assemble the polyelectrolyte layer layer by layer; after assembly, inject a 20% glycerol aqueous solution using a syringe pump and store for 4 hours. When using, continuously inject deionized water using a syringe pump to rinse the inner wall of the hollow fiber ultrafiltration membrane for 30 minutes to obtain a polyelectrolyte nanofiltration membrane (i.e., MnO4) with a permanent structural imprint. x -PEM composite nanofiltration membrane).
[0081] Comparing with Example 1: The preparation method of the PEM-control composite nanofiltration membrane is specifically completed according to the following steps:
[0082] I. Pretreatment of porous substrates:
[0083] The porous substrate was cleaned with deionized water for 30 minutes to obtain the pretreated porous substrate.
[0084] The porous substrate mentioned in step one is a hollow fiber ultrafiltration membrane made of polyethersulfone (PES).
[0085] II. Assemble the polyelectrolyte layer layer by layer:
[0086] (1) The polycationic solution was injected into and flowed through the inner wall of the hollow fiber ultrafiltration membrane with the in-situ growth template layer using a syringe pump. The reaction was carried out for 15 min. Then, the inner wall of the hollow fiber ultrafiltration membrane was rinsed with 0.5 mol / L NaCl solution continuously injected into the syringe pump for 3 min. Then, the polyanionic solution was injected into and flowed through the inner wall of the hollow fiber ultrafiltration membrane using a syringe pump. The reaction was carried out for 15 min. Finally, the inner wall of the hollow fiber ultrafiltration membrane was rinsed with 0.5 mol / L NaCl solution continuously injected into the syringe pump for 3 min.
[0087] The polycationic solution mentioned in step 2 (1) is a mixture of polyallylamine hydrochloride, NaCl and deionized water, wherein the concentration of polyallylamine hydrochloride is 10 g / L and the concentration of NaCl is 0.5 mol / L.
[0088] The polyanionic solution mentioned in step 2 (1) is a mixture of sodium polystyrene sulfonate, NaCl and deionized water, wherein the concentration of sodium polystyrene sulfonate is 10 g / L and the concentration of NaCl is 0.5 mol / L.
[0089] (2) Repeat step 2 (1) twice to assemble the polyelectrolyte layer layer by layer. After assembly, inject a 20% glycerol aqueous solution using an injection pump and store for 4 hours. When using, continuously inject deionized water using an injection pump to rinse the inner wall of the hollow fiber ultrafiltration membrane for 30 minutes to obtain the PEM-control composite nanofiltration membrane.
[0090] Compare with Example 2: MnO x The preparation method of the PEM-acid composite nanofiltration membrane is carried out according to the following steps:
[0091] A 0.1 mol / L ascorbic acid solution was injected into the polyelectrolyte nanofiltration membrane (i.e., MnO4) with a permanent structural imprint prepared in Example 1 using a syringe pump. x The MnO was dissolved in the inner wall of the PEM composite nanofiltration membrane for 5 minutes. x Intermediate layer, to obtain MnO x -PEM-acid composite nanofiltration membrane.
[0092] Figure 1 These are scanning electron microscope (SEM) images of the inner surfaces of the original and modified membranes. In the image, A is the polyethersulfone hollow fiber ultrafiltration membrane, and B is the MnO obtained in step two of Example 1. x -PES composite membrane, C is MnO obtained in step three of Example 1. x -PEM composite nanofiltration membrane, D is MnO obtained from control example 2. x -PEM-acid composite nanofiltration membrane;
[0093] from Figure 1 MnO obtained by growing B nano-manganese oxidex - The PES composite membrane shows that the pores of the original hollow fiber ultrafiltration membrane are covered, providing a smoother substrate for the polyelectrolyte, which is beneficial to the self-assembly process of the polyelectrolyte membrane at the nano-manganese oxide interface. Figure 1 As shown in C, after assembling the polyelectrolyte layer, larger nanoparticle clusters are generated, which increases the roughness of the membrane surface and is beneficial to increasing the specific surface area of the membrane, thereby increasing the water flux. Figure 1 D is the SEM image of the membrane surface after pickling. According to the SEM images of the membrane surface before and after pickling, the polyelectrolyte membrane structure is preserved, and the nano-manganese oxide serves as a permanent template layer, enabling the polyelectrolyte layer to maintain a better stacking mode.
[0094] Figure 2 This is a particle size distribution diagram of the nano-manganese oxide obtained in step two of Example 1;
[0095] from Figure 2 It can be seen that the particle size distribution of the nano-manganese oxide particles obtained in step two of Example 1 is 10 nm; the nano-manganese oxide (MnO) x The nanolayers, acting as a rigid inorganic framework, form permanent, incompressible open channels. Even if the polyelectrolyte layer undergoes some degree of swelling or shrinkage, the manganese oxide framework maintains structural stability, ensuring the long-term unobstructed flow of water molecules. This "structural imprinting" effect significantly reduces the flux decay rate of the membrane during long-term operation.
[0096] Figure 3 This is a diagram showing the zeta potential transition on the inner surface of the membrane during assembly.
[0097] from Figure 3 It is evident that the alternating positive and negative changes in zeta potential are the most direct evidence for the successful self-assembly of polyelectrolytes (LbL). During the assembly process, the nano-manganese oxide layer exhibits a weak negative charge, which facilitates its binding with positively charged polycations through electrostatic interactions.
[0098] Nanofiltration performance test:
[0099] ① Pure water flux test:
[0100] Test Example 1 prepared MnO x -PEM composite nanofiltration membrane, PEM-control composite nanofiltration membrane prepared in Comparative Example 1, and MnO prepared in Comparative Example 2 x The pure water flux of the PEM-acid composite nanofiltration membrane was measured by the following method: pure water was passed through the composite nanofiltration membrane, and after pressing at an operating pressure of 3 bar and a temperature of 25°C for 1 hour, the pure water flux was measured. ,See Figure 4 As shown;
[0101] The formula for testing pure water flux is: ;
[0102] Where V is the volume of permeated water, in liters (L);
[0103] T is the filtration time, in hours (h).
[0104] S is the effective membrane area, measured in m². 2 ;
[0105] This represents the transmembrane pressure difference.
[0106] ② Salt Retention Test:
[0107] The rejection rates R for 500 mg / L Na₂SO₄ solution and 500 mg / L MgCl₂ solution were tested respectively, see [reference]. Figure 4 As shown; calculations were performed using the conductivity of the permeate and the prepared salt solution;
[0108] ;
[0109] in It is the conductivity of the prepared salt solution. It is the conductivity of the permeate.
[0110] Figure 4 MnO prepared in Example 1 x -PEM composite nanofiltration membrane, the PEM-control composite nanofiltration membrane prepared in Comparative Example 1 and the MnO prepared in Comparative Example 2 x Flux-salt rejection ratio of PEM-acid composite nanofiltration membrane;
[0111] from Figure 4 It can be seen that the MnO prepared in Example 1 x The flux of the PEM composite nanofiltration membrane is 34.8 L·m. -2 ·h -1 ·bar -1 In contrast, the flux of the PEM-control composite nanofiltration membrane prepared in Comparative Example 1 was only 15 L·m⁻¹. -2 ·h -1 bar -1 MnO x The PEM composite nanofiltration membrane showed a rejection rate of 44.66% for 500 mg / L Na₂SO₄ solution, while the PEM-control composite nanofiltration membrane showed a rejection rate of 20.39% for the same solution. (MnO₂) x The PEM composite nanofiltration membrane exhibits a 95% rejection rate for 500 mg / L MgCl2 solution, while the PEM-control composite nanofiltration membrane shows a 75% rejection rate. Therefore, it can be concluded that MnO...x - The PEM composite nanofiltration membrane not only significantly increases flux but also improves retention rate.
[0112] MnO prepared according to Example 2 x The flux of the PEM-acid composite nanofiltration membrane for pure water is 41 L·m⁻¹. -2 ·h -1 ·bar -1 The retention rate for 500 mg / L Na₂SO₄ solution was 35%. (This is in contrast to the retention rate of MnO₂ before acid treatment.) x Compared to PEM-control composite nanofiltration membranes, the flux is increased while the rejection rate is somewhat reduced; however, compared to PEM-control composite nanofiltration membranes, the performance is still significantly better. This indicates that MnO x It plays a "mold-making" role in the assembly process, inducing the formation of an optimized PEM structure, and this structure is in MnO x Even after being removed, it remains permanently "locked" in the membrane, such as Figure 1 As shown in Figure D, the membrane surface retains its original morphology after acid treatment.
Claims
1. A polyelectrolyte nanofiltration membrane with a permanent structural imprint, characterized in that... The polyelectrolyte nanofiltration membrane with a permanent structural imprint comprises a porous substrate, a template layer, and a functional layer; the template layer is grown in situ on the porous substrate; and the functional layers are self-assembled layer by layer on the template layer. The template layer is nano-manganese oxide; The functional layer is a polyelectrolyte layer.
2. The polyelectrolyte nanofiltration membrane with a permanent structural impression according to claim 1, characterized in that... The template layer is a surface-confined porous structure with a thickness of 10nm~200nm; the nano-manganese oxide has a particle size of 5nm~30nm.
3. The polyelectrolyte nanofiltration membrane with a permanent structural impression according to claim 1, characterized in that... The porous substrate is a flat sheet membrane or a hollow fiber ultrafiltration membrane, and the material is polyethersulfone, polyacrylonitrile, or polysulfone.
4. A polyelectrolyte nanofiltration membrane with a permanent structural impression according to claim 1, characterized in that... The polyelectrolyte layer is formed by the self-assembly of polycations and polyanions layer by layer, with 2 to 10 bilayers; the polycation is polyallylamine hydrochloride, polydiallyldimethylammonium chloride, or polyethyleneimine; the polyanion is sodium polystyrene sulfonate.
5. The method for preparing a polyelectrolyte nanofiltration membrane with a permanent structural imprint as described in claim 1, characterized in that... The preparation method is specifically carried out according to the following steps: I. Pretreatment of porous substrates: The porous substrate was cleaned with deionized water to obtain a pretreated porous substrate. II. In-situ reaction to generate template layer: When the porous substrate is a flat sheet membrane, the in-situ reaction to generate the template layer is specifically accomplished according to the following steps: ① Immerse the flat sheet membrane in a polycationic solution and react for a period of time. A layer of polycations is adsorbed on the flat sheet membrane. Then rinse with deionized water to obtain a flat sheet membrane adsorbed with polycations. ② The sheet membrane with adsorbed polycations is immersed in potassium permanganate solution and reacted for a period of time. Brownish-brown nano-manganese oxide is generated in situ on the sheet membrane. Then it is rinsed with deionized water and then immersed in glycerol aqueous solution for storage. When used, it is taken out and dried at room temperature to obtain a sheet membrane with an in situ grown template layer. When the porous substrate is a hollow fiber ultrafiltration membrane, the in-situ reaction to generate the template layer is specifically accomplished according to the following steps: (1) The polycation solution is injected into and flows through the inner wall of the hollow fiber ultrafiltration membrane. After reacting for a period of time, a layer of polycations is adsorbed on the inner wall of the hollow fiber ultrafiltration membrane. Then, deionized water is continuously injected to rinse the inner wall of the hollow fiber ultrafiltration membrane to obtain a hollow fiber ultrafiltration membrane adsorbed with polycations. (2) Potassium permanganate solution is injected into and flows through the inner wall of the hollow fiber ultrafiltration membrane adsorbed with polycations. After reacting for a period of time, brownish-yellow nano-manganese oxide is generated in situ. Then, deionized water is continuously injected to rinse the inner wall of the hollow fiber ultrafiltration membrane. Glycerol aqueous solution is then injected and stored. When using, deionized water is continuously injected to rinse the inner wall of the hollow fiber ultrafiltration membrane to obtain a hollow fiber ultrafiltration membrane with an in situ grown template layer. III. Assemble the polyelectrolyte layer layer by layer: When the porous substrate is a flat sheet membrane, the layer-by-layer assembly of the polyelectrolyte layer is carried out according to the following steps: ① Immerse the flat sheet membrane with the in-situ grown template layer in a polycationic solution for a period of time, then rinse it several times with NaCl solution after taking it out, and then immerse it in a polyanionic solution for a period of time, and then rinse it several times with NaCl solution after taking it out. ② Repeat step 3① to assemble the polyelectrolyte layer by layer; after assembly, immerse it in a glycerol aqueous solution for storage. When using, take it out and air dry at room temperature to obtain a polyelectrolyte nanofiltration membrane with a permanent structural imprint. When the porous substrate is a hollow fiber ultrafiltration membrane, the layer-by-layer assembly of the polyelectrolyte layer is carried out according to the following steps: (1) The polycationic solution is injected into and flows through the inner wall of the hollow fiber ultrafiltration membrane with the in-situ growth template layer. After reacting for a period of time, NaCl solution is continuously injected to rinse the inner wall of the hollow fiber ultrafiltration membrane. Then the polyanionic solution is injected into and flows through the inner wall of the hollow fiber ultrafiltration membrane. After reacting for a period of time, NaCl solution is continuously injected to rinse the inner wall of the hollow fiber ultrafiltration membrane. (2) Repeat step 3 (1) to assemble the polyelectrolyte layer layer by layer; after assembly, inject glycerol aqueous solution and store it. When using, continuously inject deionized water to rinse the inner wall of the hollow fiber ultrafiltration membrane to obtain a polyelectrolyte nanofiltration membrane with a permanent structural imprint.
6. A polyelectrolyte nanofiltration membrane with a permanent structural impression according to claim 5, characterized in that... The cleaning time in step one is 20 min to 40 min; the polycationic solution in step two is a mixture of polycationic acid, NaCl and deionized water, wherein the concentration of polycationic acid is 0.5 g / L to 10 g / L and the concentration of NaCl is 0.5 mol / L to 1 mol / L; the reaction time in step two is 5 min to 15 min; the number of times the deionized water is rinsed in step two ① is 2 to 4 times; the time for continuously injecting deionized water to rinse the inner wall of the hollow fiber ultrafiltration membrane in steps two (1) and two (2) is 2 min to 3 min.
7. A polyelectrolyte nanofiltration membrane with a permanent structural impression according to claim 5, characterized in that... The concentration of the potassium permanganate solution in step two is 0.1 g / L to 2 g / L; the reaction time in step two is 2 min to 10 min; the mass fraction of the glycerol aqueous solution in step two is 20% to 50%, and the storage time is 3 h to 4 h; the reaction time in step three is 5 min to 30 min; the number of times to rinse in step three ① is 1 to 3 times; the time for each rinse is 5 min to 10 min; the time for continuously injecting NaCl solution to rinse the inner wall of the hollow fiber ultrafiltration membrane in step three (1) is 2 min to 3 min; when using in step three (2), continuously injecting deionized water to rinse the inner wall of the hollow fiber ultrafiltration membrane for 30 min to 60 min.
8. A polyelectrolyte nanofiltration membrane with a permanent structural impression according to claim 5, characterized in that... The polycationic solution mentioned in step three is a mixture of polycationic acid, NaCl and deionized water, wherein the concentration of polycationic acid is 0.1 g / L to 10 g / L and the concentration of NaCl is 0.1 mol / L to 1 mol / L; the polyanionic solution mentioned in step three is a mixture of polyanionic acid, NaCl and deionized water, wherein the concentration of polyanionic acid is 0.1 g / L to 10 g / L and the concentration of NaCl is 0.1 mol / L to 0.5 mol / L; step three ① is repeated 1 to 9 times in step three ②; the mass fraction of the glycerol aqueous solution mentioned in step three is 20% to 50%, and the storage time is 3h to 4h; step three (2) is repeated 1 to 9 times in step three (1).
9. The application of a polyelectrolyte nanofiltration membrane with a permanent structural impression as described in claim 1, characterized in that... A polyelectrolyte nanofiltration membrane with a permanent structural imprint is used to remove micropollutants, perfluoroalkyl substances, divalent salts, or for seawater pretreatment.
10. The application of a polyelectrolyte nanofiltration membrane with a permanent structural impression according to claim 1, characterized in that... A polyelectrolyte nanofiltration membrane with a permanent structural imprint exhibits a pure water flux greater than 30 L·m³ at an operating pressure of 6 bar to 10 bar. -2 ·h -1 ·bar -1 The retention rate of magnesium chloride is greater than 95%.