Enhanced high-permeability nanofiltration membrane and preparation method thereof
By integrating oxidized graphene into nanofiltration membranes, the challenges of energy loss and membrane performance in PRO systems are addressed, resulting in high water permeability and mechanical strength with reduced concentration polarization.
Patent Information
- Application Number
- CN202510403102.6
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-04-01
- Publication Date
- 2025-07-15
AI Technical Summary
The existing PRO power generation systems have large energy losses, low production capacity efficiency, and lack suitable membrane materials. Traditional membranes cannot take into account the properties of mechanical strength, water flux, low concentration polarization of membrane carriers, hydrophilicity and thin selective layers.
Graphene oxide was introduced into the support structure of the nanofiltration membrane, and by improving the support structure performance, a composite nanofiltration membrane with high hydrophilicity, high water permeability flux and good mechanical properties were prepared, and a porous and macroporous structure design was adopted to reduce the concentration polarization effect.
It realizes nanofiltration membrane with high permeability flux, low concentration difference polarization and high mechanical strength, which is suitable for large-scale application of PRO processes, reduces operation and maintenance costs, and improves energy conversion efficiency.
Smart Images
Figure SMS_3
Abstract
Description
Technical Field
[0001] The present invention relates to the technical field of nanofiltration membrane preparation, and particularly relates to an enhanced high-permeability nanofiltration membrane and a preparation method thereof. Background Art
[0002] Pressure Retarded Osmosis (PRO) is a salinity-gradient power generation technology that drives the transmembrane flow of water molecules through the osmotic pressure difference generated by a salinity gradient (such as seawater and fresh water, brine and fresh water), thereby converting chemical potential energy into mechanical energy (electric power generation). Its principle is to separate a high-salt solution (draw solution) from a low-salt solution (feed solution) through a semi-permeable membrane. Water molecules spontaneously migrate from the low-salt side to the high-salt side under the action of the osmotic pressure difference, and at the same time, the system pressure (lower than the osmotic pressure difference) is adjusted to drive turbine power generation. Due to its high theoretical power density (electricity generation per unit membrane area) and sustainability (utilizing renewable energy), PRO technology is regarded as an important direction for ocean energy development.
[0003] It has great potential in sustainable resources, but there are the following problems in the process of large-scale application: 1. The energy loss of the PRO power generation system is large, and the production efficiency is low; 2. There is a lack of a suitable membrane tailored for the PRO process; 3. Traditional PRO membranes (such as flat membranes made of thin film composites are usually manufactured in a spiral wound type.) cannot balance membrane performance parameters such as mechanical strength, water flux, low concentration polarization (CP) in the membrane support, high porosity, hydrophilicity, thin selective layer, and low structure.
[0004] 4. Since hollow fibers are self-supporting membranes and have no other supports, compared with spiral wound membrane modules, hollow fiber membranes can have a higher packing density, so hollow fiber membrane modules may be more suitable for the PRO process. Summary of the Invention
[0005] The purpose of the present invention is to provide an enhanced high-permeability nanofiltration membrane and a preparation method thereof. The present invention introduces graphene oxide into the support structure of the nanofiltration membrane, improves the performance of its support structure, realizes a composite nanofiltration membrane with high hydrophilicity, high water permeation flux, and good mechanical properties, and accelerates the large-scale use process of hollow fiber nanofiltration membranes in the PRO process.
[0006] To solve the above technical problems, the technical solution adopted by the present invention is: A method for preparing an enhanced high-permeability nanofiltration membrane, comprising the following steps: 1) Preparation of graphene oxide (GO): Mix graphite powder, sodium nitrate, sulfuric acid, and phosphoric acid, add potassium permanganate, and precisely control the temperature for the oxidation reaction. After a period of time, add hydrogen peroxide to terminate the reaction, and obtain GO nanosheets through centrifugation and washing; 2) Preparation of hollow fiber-based membrane: Mix a polymer, a solvent, graphene oxide, and an additive in proportion, stir to form a casting solution, prepare a hollow fiber membrane through a spinning process, and soak it in water, treat it with a glycerol aqueous solution, and dry it; 3) Construction of interfacial polymerization functional layer: Conduct an interfacial polymerization reaction on the inner layer of the hollow fiber membrane, sequentially introduce MPD solution and TMC solution. After completing the polymerization reaction, purge it with N2 gas and soak it for preservation.
[0007] Furthermore, in 1), the mass ratio of the graphite powder to sodium nitrate is 2:1, the volume ratio of sulfuric acid and phosphoric acid is 9:1 to form a mixed solution, the total mass of the solid is 0.1 times the mass of the mixed solution, add potassium permanganate (KMnO4) with a mass twice that of the solid, and control the reaction temperature at 0 - 5 °C, and the oxidation reaction time is 1.5 - 2.5 hours.
[0008] Furthermore, in 1), the preparation of the GO nanosheets also includes heating the reaction mixture to 40 ± 2 °C and holding for 0.8 - 1.2 hours, then heating to 80 ± 5 °C and holding for 1 hour. Finally, add deionized water to dilute to 1.5 - 2.0 times the original volume, and add 30 wt% hydrogen peroxide to terminate the reaction. After washing (pH > 6.0) and ultrasonic exfoliation, GO nanosheets are obtained.
[0009] Furthermore, in 2), the polymer is selected from one or more of PES, PVDF, and PSU, with a molecular weight of 40 - 60 kDa, the solvent is selected from one or more of DMAc, NMP, and DMSO, and the additive is selected from one or more of PEG, PVP, and graphene oxide.
[0010] Furthermore, in 2), the spinning process uses a three-hole spinneret. The core liquid layer is deionized water with 0.1 wt% sodium dodecyl sulfate (SDS), the middle layer is the casting solution, the outermost layer is a mixed solvent of solvent and glycerol with a volume ratio of 9:1, the coagulation bath is tap water at 25 °C, the extrusion rate ratio of the core liquid to the casting solution is 1:1 - 1:1.5, the air gap is 8 - 12 mm, the winding speed is 10 - 30 m / min. After spinning, the base membrane is post-treated with a 50 °C glycerol aqueous solution (20 wt%) for 12 hours, and after drying, a gradient pore structure base membrane with a porosity ≥ 75%, an average pore diameter of 20 ± 5 nm, a macroporous layer with an outer surface pore diameter of 50 - 100 nm, an intermediate transition layer pore diameter of 20 - 50 nm, and an inner surface dense layer pore diameter of 5 - 20 nm, and the porosity of the macroporous layer is 20% - 30% higher than that of the dense layer is obtained.
[0011] Further, in step 3), the construction of the interfacial polymerization functional layer includes the following steps: 1) Connect the inner cavity of the hollow fiber membrane to a pulsed microfluidic system, and introduce a mixed solution of 1.5 - 2.5 wt% m-phenylenediamine (MPD) and 0.1 - 0.2 wt% SDS at a flow rate of 4 - 6 mL / min, a pulse frequency of 10 Hz, and for 2 - 4 minutes; 2) Purge with N2 gas at a pressure of 0.1 - 0.2 MPa for 4 - 6 minutes to remove the excess solution; 3) Introduce an aqueous solution of 0.12 - 0.18 wt% trimesoyl chloride (TMC) at a flow rate of 2 - 3 mL / min, a pulse frequency of 5 Hz, and for 4 - 6 minutes to complete the interfacial polymerization reaction; 4) Purge with N2 gas at a pressure of 0.1 - 0.2 MPa for 20 - 35 seconds to finally obtain a polymeric functional separation layer with a thickness ≤ 50 nm and a Zeta potential ≤ -20 mV. Finally, immerse the membrane module in deionized water and store it at low temperature.
[0012] Further, the outer surface of the base membrane is formed into a porous and macroporous structure by extrusion with pure organic solvent to reduce the internal concentration polarization (ICP) effect during the pressure retarded osmosis (PRO) process.
[0013] In addition, the present invention also discloses an enhanced high - permeability nanofiltration membrane prepared by using the above - described method for preparing an enhanced high - permeability nanofiltration membrane.
[0014] Compared with the prior art, the present invention has the following beneficial effects: The present invention introduces graphene oxide into the support structure of the nanofiltration membrane, improves the performance of its support structure, realizes a composite nanofiltration membrane with high hydrophilicity, high water permeation flux, and good mechanical properties, and accelerates the large - scale application process of the hollow fiber nanofiltration membrane in the PRO process. The outer surface of the base membrane of the present invention is designed to be a porous and macroporous structure by extrusion with pure organic solvent to promote the rapid transmission of the solvent during the PRO process to reduce the ICP effect. Doping graphene oxide enhances hydrophilicity and increases the membrane permeation ability, and the addition of graphene oxide increases the mechanical strength of the membrane. Specific Embodiments
[0015] In the following, only some exemplary embodiments are simply described. As those skilled in the art can recognize, the described embodiments can be modified in various different ways without departing from the spirit or scope of the embodiments of the present invention. Example 1 This example discloses a method for preparing an enhanced high - permeability nanofiltration membrane, including the following steps: 1) Preparation of graphene oxide (GO): Mix graphite powder, sodium nitrate, sulfuric acid, and phosphoric acid, add potassium permanganate, and precisely control the temperature for the oxidation reaction. After a period of time, add hydrogen peroxide to terminate the reaction, and obtain GO nanosheets through centrifugation and washing; 2) Preparation of hollow fiber-based membrane: Mix the polymer, solvent, and additive in proportion, stir to form a casting solution, prepare a hollow fiber membrane through a spinning process, and soak it in clear water, treat it with a glycerol aqueous solution, and dry it; 3) Construction of interfacial polymerization functional layer: Conduct an interfacial polymerization reaction on the inner layer of the hollow fiber membrane, sequentially introduce the MPD solution and the TMC solution, and after completing the polymerization reaction, purge it with N2 gas and soak it for storage.
[0016] Among them, in 1), the mass ratio of the graphite powder to the sodium nitrate is 2:1, the volume ratio of the sulfuric acid to the phosphoric acid is 9:1, the reaction temperature is controlled below 5°C, and the oxidation reaction time is 1.5 - 2.5 hours.
[0017] Furthermore, in 1), the preparation of the GO nanosheets also includes heating the reaction mixture to 40 ± 2°C and holding for 0.8 - 1.2 hours, then heating to 80 ± 5°C and holding for 1 hour, and finally adding deionized water for dilution and adding 30% hydrogen peroxide to terminate the reaction.
[0018] Furthermore, in 2), the polymer is selected from one or more of polyethersulfone (PES), polyvinylidene fluoride (PVDF), and polysulfone (PSU), and the molecular weight is 40 - 60 kDa.
[0019] Furthermore, in 2), the solvent is selected from one or more of N,N-dimethylacetamide (DMAc), N-methylpyrrolidone (NMP), and dimethyl sulfoxide (DMSO), and the additive is selected from one or more of polyethylene glycol (PEG), polyvinylpyrrolidone (PVP), and graphene oxide (GO).
[0020] Furthermore, in 2), the spinning process uses a three-hole spinneret. The inner layer is a core liquid layer composed of deionized water, the middle layer is the casting solution, the outermost layer is an organic solvent, the coagulation bath is tap water, the extrusion rate ratio of the core liquid to the casting solution is 1:1 - 1:1.5, the air gap is 8 - 12 mm, and the winding rate is 10 - 30 m / min.
[0021] Furthermore, in 3), the interfacial polymerization reaction includes the following steps: 1) Connect the inner cavity of the hollow fiber membrane to a peristaltic pump, introduce a mixed solution of 1.5 - 2.5 wt% MPD and 0.1 - 0.2 wt% SDS, with a flow rate of 4 - 6 mL / min, and continue for 2 - 4 minutes; 2) Flush with N2 gas at a pressure of 0.1 - 0.2 MPa for 4 - 6 minutes to remove the excess solution; 3) Introduce an aqueous solution of 0.12 - 0.18 wt% TMC at a flow rate of 2 - 3 mL / min for 4 - 6 minutes to complete the interfacial polymerization reaction; 4) Flush with N2 gas at a pressure of 0.1 - 0.2 MPa for 20 - 35 seconds, and finally immerse the membrane module in deionized water for storage at low temperature.
[0022] Furthermore, the outer surface of the base membrane is formed into a porous and macroporous structure by extrusion with pure organic solvent to reduce the concentration polarization (ICP) effect during the pressure retarded osmosis (PRO) process.
[0023] An enhanced high - permeability nanofiltration membrane is prepared by using the preparation method of an enhanced high - permeability nanofiltration membrane described above.
[0024] An enhanced high - permeability nanofiltration membrane, the nanofiltration membrane is of a hollow - fiber structure, including: A self - supporting base membrane layer made of a polymer blend material containing graphene oxide (GO); A selective separation layer located inside the base membrane, formed by interfacial polymerization; The outer surface of the base membrane layer is a porous and macroporous structure, and the inner layer is a gradient pore structure.
[0025] The polymer material of the base membrane layer includes at least one of polyethersulfone (PES), polyvinylidene fluoride (PVDF), or polysulfone (PSU), with a molecular weight of 40 - 60 kDa and a graphene oxide doping amount of 0.1 - 0.2 wt%; The raw materials for preparing the base membrane layer include: 20 - 25 wt% of polymer; 20 - 40 wt% of solvent, the solvent is N,N - dimethylacetamide (DMAc), N - methylpyrrolidone (NMP), or dimethyl sulfoxide (DMSO); 40 - 60 wt% of additives, the additives include a combination of polyethylene glycol (PEG), polyvinylpyrrolidone (PVP), and graphene oxide.
[0026] Through the collaborative design of GO doping and porous structure, the contradictory requirements of high permeation flux, low concentration polarization (ICP), and high mechanical strength of the PRO membrane are simultaneously solved. At the same time, through the collaborative design of GO doping and porous structure, the contradictory requirements of high permeation flux, low concentration polarization (ICP), and high mechanical strength of the PRO membrane are simultaneously solved. Furthermore, through the collaborative design of GO doping and porous structure, the contradictory requirements of high permeation flux, low concentration polarization (ICP), and high mechanical strength of the PRO membrane are simultaneously solved.
[0027] To facilitate the further understanding of the present invention by those skilled in the art, the present invention will be further elaborated below in combination with specific implementation cases.
[0028] Case 1: (1) Preparation of graphene oxide (GO): Add 5 g of commercially available graphite powder and 2.5 g of sodium nitrate to a mixed solution of 120 mL of sulfuric acid and phosphoric acid (9:1), and continuously stir in an ice bath for 15 minutes. Then gently add 15 g of potassium permanganate to the mixture, keep the temperature < 5 °C, and react for 2 hours.
[0029] Raise the temperature of the reaction mixture to 40 °C in a water bath and keep it for 1 hour.
[0030] Then raise the temperature to 98 °C for 1 h, slowly add deionized water to make the final suspension volume reach 400 mL. After 1 hour, add 15 mL of 30% hydrogen peroxide to the mixed solution to terminate the reaction, and cool the reaction mixture to room temperature.
[0031] Finally, centrifuge at 4000 rpm and wash with a large amount of 5% hydrochloric acid and deionized water to remove chlorides and sulfates, recover GO nanosheets, and dry them overnight in an oven under vacuum at 70 °C for standby.
[0032] (2) Preparation of hollow fiber-based membrane: The polymer of the casting solution is polyethersulfone PES, polyvinylidene fluoride PVDF, polysulfone PSU, with a molecular weight of 40 - 60 kDa; The solvent is N,N-dimethylacetamide (DMAc), N-methylpyrrolidone (NMP), dimethyl sulfoxide (DMSO); The additive is PEG, PVP, GO; mix the polymer (20 - 25 wt%), solvent (20 - 40 wt%), and additive (40 - 60 wt%) according to the ratio, stir at a rotation speed of 500 - 800 rpm and a temperature of 60 - 80 °C for 12 - 24 h, and then cool to room temperature. For the spinning parameters, use a three-hole spinneret. The inner layer is the core liquid layer composed of deionized water, the middle layer is the casting solution, and the outermost layer is an organic solvent. The coagulation bath composition is tap water. Control the ratio of the core liquid casting solution extrusion rate to the core liquid extrusion rate within the range of 1:1 - 1:1.5, the air gap is 10 mm, and the winding speed is 10 - 30 m / min. After the obtained hollow fiber membrane is soaked / cleaned with clear water, soak it in a 50% glycerol aqueous solution for 48 h and dry it at room temperature to obtain the current product.
[0033] (3) Construction of interfacial polymerization functional layer: The nanofiltration membrane is designed as an internal pressure nanofiltration membrane, and interfacial polymerization occurs in the inner layer of the hollow fiber membrane. First, the inner cavity of the hollow fiber membrane is connected to a peristaltic pump, and a mixture of 2wt% MPD + 0.1wt% SDS is introduced at a flow rate of 5.0 mL / min for 3 min.
[0034] Then, it is purged with N2 gas at a pressure of 0.1 MPa for 5 min to remove the excess solution; Next, an aqueous solution of TMC (0.15wt%) is introduced at a flow rate of 2.5 mL / min for 5 min to provide sufficient time to complete the interfacial polymerization reaction with the remaining MPD. Finally, it is purged with N2 gas at a pressure of 0.1 MPa for 30 s.
[0035] Then, all membrane modules are immersed in deionized water and stored at low temperature.
[0036] Furthermore, the polymer of the casting solution is polyethersulfone PES (20wt%) with a molecular weight of 60 kDa; the solvent is N,N-dimethylacetamide (DMAc) (40wt%); the additives are PEG (40wt%), GO (0 wt%); after mixing, it is stirred at a rotation speed of 500 rpm and a temperature of 80 °C for 12 h, and then cooled to room temperature. For the spinning parameters, a three-hole spinneret is used. The inner layer is the core liquid layer composed of deionized water, the middle layer is the casting solution, and the outermost layer is the organic solvent DMAc. The coagulation bath composition is tap water. The ratio of the core liquid casting solution extrusion rate to the core liquid extrusion rate is controlled within the range of 1:1.5. The air gap is 10 mm, and the winding speed is 15 m / min. The obtained hollow fiber membrane is immersed / washed with clear water, then immersed in a 50% glycerol aqueous solution for 48 h, and dried at room temperature to obtain the current product denoted as R1.
[0037] As an option, the polymer of the casting solution is polyethersulfone PES (20wt%) with a molecular weight of 60 kDa; the solvent is N,N-dimethylacetamide (DMAc) (40wt%); the additives are PEG (40wt%), GO (0.1 wt%); after mixing, it is stirred at a rotation speed of 500 rpm and a temperature of 80 °C for 12 h, and then cooled to room temperature. For the spinning parameters, a three-hole spinneret is used. The inner layer is the core liquid layer composed of deionized water, the middle layer is the casting solution, and the outermost layer is the organic solvent DMAc. The coagulation bath composition is tap water. The ratio of the core liquid casting solution extrusion rate to the core liquid extrusion rate is controlled within the range of 1:1.5. The air gap is 10 mm, and the winding speed is 15 m / min. The obtained hollow fiber membrane is immersed / washed with clear water, then immersed in a 50% glycerol aqueous solution for 48 h, and dried at room temperature to obtain the current product denoted as R2.
[0038] As an option, the polymer of the casting solution is polyethersulfone PES (21 wt%), with a molecular weight of 60 kDa; the solvent is N,N-dimethylacetamide (DMAc) (39.5 wt%); the additives are PEG (39.5 wt%) and GO (0.2 wt%); after mixing, it is stirred at 500 rpm and 80 °C for 12 h, and then cooled to room temperature. For the spinning parameters, a three-hole spinneret is used. The inner layer is the core liquid layer composed of deionized water, the middle layer is the casting solution, and the outermost layer is the organic solvent DMAc. The flow rate is 1 / 5 of the casting solution. The coagulation bath composition is tap water. The ratio of the core liquid casting solution extrusion rate to the core liquid extrusion rate is controlled within the range of 1:1.5. The air gap is 10 mm, and the winding speed is 15 m / min. The obtained hollow fiber membrane is soaked / washed with clean water, soaked in a 50% glycerol aqueous solution for 48 h, and dried at room temperature to obtain the current product denoted as R3.
[0039] The process for evaluating the PRO performance of the products R1, R2, and R3 obtained above is as follows: The membrane is made into a module. 5 L of solution (driving solution DS, 1.0 mmol NaCl solution) is passed into the inner cavity side of the hollow fiber, and 2 L of solution (feed solution FS, deionized water) is passed into the outer side of the hollow fiber. The flow rates on both sides are set to 150 mL / min. Before the PRO test, the membrane is stabilized at 12 bar for 1 h (the pressure is lower than the critical point of each membrane). After the membrane is stabilized, each sample is gradually tested from 0 bar to the stable pressure. To confirm the stability and reproducibility of each test sample, a second operation is carried out immediately after the first run within the same applied pressure range. The reverse salt flux and power density are as follows: ; ; The detected performances of R1, R2, and R3 are as follows: R1, R2, and R3 have high mechanical strength and pressure tolerance. The mechanical strengths of R1 (5.0 ± 0.1 MPa), R2 (5.3 ± 0.2 MPa), and R3 (5.6 ± 0.2 MPa) all exceed 5 MPa. All samples passed the 1-hour pre-stabilization test at 12 bar without structural damage.
[0040] R1, R2, and R3 are flexible and have structural adaptability. The elongation rates of R1, R2, and R3 are 35.1%, 45.6%, and 46.0% respectively, all having a certain degree of ductility. Although the flexibility of R1 is slightly lower, all samples are non-brittle materials, capable of adapting to dynamic pressure changes and mechanical stresses during component assembly (such as the bending requirements of spiral wound or hollow fiber membrane modules), reducing the risk of accidental damage during installation or operation. They are suitable for industrial scenarios with complex flow channel designs or frequent pressure fluctuations.
[0041] R1, R2, and R3 have hydrophilic surface characteristics and anti-fouling potential, with contact angles all less than 90° (R1 is 73°, R2 is 65°, and R3 is 61°). All three reduce their hydrophobicity through surface modification (such as introducing hydrophilic groups, coatings, or blending techniques), reducing the adsorption of pollutants (such as organic substances, colloids), and delaying the rate of membrane fouling.
[0042] Application significance: When operating in impurity-containing water sources (such as wastewater, seawater), the cleaning cycle can be extended, reducing operation and maintenance costs.
[0043] The average pore sizes of R1, R2, and R3 range from 6.82 to 9.11 nm, and the PWP (pure water permeability) ranges from 350 to 423 L / (m²·h·bar). Although pore size differences affect selectivity, all three balance the permeation flux and salt rejection ability through optimized pore size distribution (such as narrow distribution or asymmetric structure), avoiding a sharp increase in reverse salt flux due to overly large pore sizes or restricting water flux due to overly small pore sizes. They achieve a compromise between efficient water transfer and salt rejection in the PRO process, meeting the core requirements of salinity gradient energy recovery. The prepared nanofiltration membranes are superior to traditional PRO membranes in key performance indicators such as mechanical strength (≥5 MPa), permeation flux (55.7 L / (m²·h)), and hydrophilicity (contact angle 61°), capable of meeting the large-scale application requirements of salinity gradient power generation scenarios.
[0044] Furthermore, in actual use, to further improve the performance of the products of the present invention, the present invention is further improved as follows: Improvement Example 1: Optimization of the dispersion and functionalization of graphene oxide (GO); 1) Amino-functionalization of GO: Take 10 g of the original GO dispersion (concentration 1 mg / mL), add 50 mL of concentrated nitric acid (65%), and reflux at 60°C for 6 hours to introduce carboxyl groups. After washing the carboxylated GO with deionized water until neutral, disperse it in 100 mL of ethylenediamine solution (concentration 5 wt%), add 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide (EDC, 0.1 mol / L) and N-hydroxysuccinimide (NHS, 0.05 mol / L), and stir at 25°C for 24 hours to complete the amino modification.
[0045] The amino-functionalized GO was centrifuged, washed three times with deionized water, and then freeze-dried for later use.
[0046] 2) Composite dispersion of GO and carbon nanotubes (CNT): The amino-functionalized GO and carboxylated CNT were mixed at a mass ratio of 1:1, and the total addition amount was 0.3 wt% (based on the total mass of the casting solution). The mixture was added to the DMAc solvent, and first mechanically stirred at 1000 rpm for 30 minutes. Then it was treated with an ultrasonic crusher (power 500 W, frequency 40 kHz) for 1 hour to ensure uniform dispersion of the nanomaterials.
[0047] 3) Casting solution formulation: Polymer: PES (22 wt%, molecular weight 60 kDa); Solvent: DMAc (40 wt%); Additive: PEG (37.5 wt%); Amino-functionalized GO / CNT composite (0.3 wt%).
[0048] Spinning process: The parameters were the same as those in Example 1, but the air gap was adjusted to 10 - 15 mm to adapt to the pore regulation of the composite material.
[0049] The test results were as follows using the test methods in the existing technology: Mechanical strength: 6.2 ± 0.3 MPa (a 10% increase compared to the original R3); Contact angle: 55° (significantly enhanced hydrophilicity); Power density: 17.1 W / m² (12 bar, a 9.6% increase compared to the original R3).
[0050] Improved Example 2: Optimization of the dispersion and functionalization of graphene oxide (GO); 1): Amino-functionalization of GO. Take 10 g of the original GO dispersion (concentration 1 mg / mL), add 50 mL of concentrated nitric acid (65%), and reflux at 60 °C for 6 hours to introduce carboxyl groups. After the carboxylated GO was washed with deionized water until neutral, it was dispersed in 100 mL of ethylenediamine solution (concentration 5 wt%), and 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide (EDC, 0.1 mol / L) and N-hydroxysuccinimide (NHS, 0.05 mol / L) were added and stirred at 25 °C for 24 hours to complete the amino-functionalization modification. The amino-functionalized GO was centrifuged, washed three times with deionized water, and then freeze-dried for later use.
[0051] 2): Composite dispersion of GO and carbon nanotubes (CNT). The aminated GO and carboxylated CNT were mixed at a mass ratio of 1:1, and the total addition amount was 0.3 wt% (based on the total mass of the casting solution). The mixture was added to the DMAc solvent and first mechanically stirred at 1000 rpm for 30 minutes. It was treated with an ultrasonic crusher (power 500 W, frequency 40 kHz) for 1 hour to ensure uniform dispersion of the nanomaterials.
[0052] 3): Casting solution formulation: Polymer: PES (22 wt%, molecular weight 60 kDa); Solvent: DMAc (40 wt%); Additive: PEG (37.5 wt%); Aminated GO / CNT composite (0.3 wt%); Spinning process: The same parameters as in Example 1, but the air gap was adjusted to 10 - 15 mm to adapt to the pore regulation of the composite material.
[0053] Test results: Mechanical strength: 6.2 ± 0.3 MPa (10% higher than the original R3); Contact angle: 55° (significantly enhanced hydrophilicity); Power density: 17.1 W / m² (12 bar, 9.6% higher than the original R3).
[0054] In Case 1 and Case 2, through amination modification and CNT composite, the interfacial compatibility and dispersion of GO were improved, and the mechanical properties and hydrophilicity of the membrane were significantly enhanced. Combining plasma activation and synchronous injection of dual monomers shortened the process time and improved the quality of the separation layer at the same time.
[0055] Although the preferred embodiments of the present invention have been described, those skilled in the art can make additional changes and modifications to these embodiments once they learn the basic creative concept. Therefore, the appended claims are intended to be construed as including the preferred embodiments and all changes and modifications falling within the scope of the present invention.
[0056] The above description is only the preferred embodiment of the present invention and is not intended to limit the present invention. It should be noted that any modifications, equivalent replacements, and improvements made within the spirit and principle of the present invention should be included within the protection scope of the present invention.
Claims
1. A preparation method of an enhanced high-permeability nanofiltration membrane, characterized in that It includes the following steps: 1) Preparation of graphene oxide (GO): Mix graphite powder, sodium nitrate, sulfuric acid and phosphoric acid, add potassium permanganate and precisely control the temperature for oxidation reaction. After a period of time, add hydrogen peroxide to terminate the reaction, and obtain GO nanosheets through centrifugation and washing; 2) Preparation of hollow fiber-based membrane: Mix polymer, solvent, graphene oxide and additive in proportion, stir to form a casting solution, prepare a hollow fiber membrane through a spinning process, and soak it in clear water, treat it with a glycerol aqueous solution and dry it; 3) Construction of interfacial polymerization functional layer: Conduct an interfacial polymerization reaction on the inner layer of the hollow fiber membrane, sequentially introduce MPD solution and TMC solution, after completing the polymerization reaction, purge it with N2 gas and soak it for preservation.
2. The preparation method of an enhanced high-permeability nanofiltration membrane according to claim 1, characterized in that: In 1), the mass ratio of the graphite powder to sodium nitrate is 2:1, the volume ratio of sulfuric acid and phosphoric acid is 9:1 to form a mixed solution, the total mass of the solid is 0.1 times the mass of the mixed solution, add potassium permanganate (KMnO4) with a mass twice that of the solid and control the reaction temperature at 0 - 5°C, and the oxidation reaction time is 1.5 - 2.5 hours.
3. The preparation method of an enhanced high-permeability nanofiltration membrane according to claim 1, characterized in that: In 1), the preparation of the GO nanosheets further includes heating the reaction mixture to 40 ± 2°C and maintaining it for 0.8 - 1.2 hours, then heating it to 80 ± 5°C and maintaining it for 1 hour, finally adding deionized water to dilute it to 1.5 - 2.0 times the original volume, and adding 30wt% hydrogen peroxide to terminate the reaction. After washing (pH > 6.0) and ultrasonic exfoliation, GO nanosheets are obtained.
4. The preparation method of an enhanced high-permeability nanofiltration membrane according to claim 1, wherein: In 2), the polymer is selected from one or more of PES, PVDF, PSU, with a molecular weight of 40 - 60 kDa, the solvent is selected from one or more of DMAc, NMP, DMSO, and the additive is selected from one or more of PEG, PVP, graphene oxide.
5. The preparation method of an enhanced high-permeability nanofiltration membrane according to claim 1, characterized in that: In 2), the spinning process uses a three-hole spinneret. The core liquid layer is deionized water with 0.1wt% sodium dodecyl sulfate (SDS), the middle layer is the casting solution, the outermost layer is a mixed solvent of solvent and glycerol with a volume ratio of 9:1, the coagulation bath is tap water at 25°C, the extrusion rate ratio of the core liquid to the casting solution is 1:1 - 1:1.5, the air gap is 8 - 12 mm, the winding speed is 10 - 30 m / min. After spinning, the base membrane is post-treated with a 50°C glycerol aqueous solution (20wt%) for 12 hours, and after drying, a gradient pore structure base membrane with a porosity ≥ 75%, an average pore diameter of 20 ± 5 nm, a macroporous layer with an outer surface pore diameter of 50 - 100 nm, an intermediate transition layer pore diameter of 20 - 50 nm, and an inner surface dense layer pore diameter of 5 - 20 nm, and the porosity of the macroporous layer is 20% - 30% higher than that of the dense layer is obtained.
6. The preparation method of an enhanced high-permeability nanofiltration membrane according to claim 1, characterized in that: In 3), the construction of the interfacial polymerization functional layer includes the following steps: 1) Connect the inner cavity of the hollow fiber membrane to a pulsed microfluidic system, introduce a mixed solution of 1.5 - 2.5wt% m-phenylenediamine (MPD) and 0.1 - 0.2wt% SDS, with a flow rate of 4 - 6 mL / min, a pulse frequency of 10 Hz, and continue for 2 - 4 minutes; 2) Purge it with N2 gas at a pressure of 0.1 - 0.2 MPa for 4 - 6 minutes to remove the excess solution; 3) Introduce an aqueous solution of 0.12 - 0.18 wt% trimesoyl chloride (TMC) at a flow rate of 2 - 3 mL / min with a pulse frequency of 5 Hz for 4 - 6 minutes to complete the interfacial polymerization reaction; 4) Purge with N2 gas at a pressure of 0.1 - 0.2 MPa for 20 - 35 seconds to finally obtain a polymeric functional separation layer with a thickness ≤ 50 nm and a Zeta potential ≤ -20 mV. Finally, immerse the membrane module in deionized water and store it at low temperature.
7. The preparation method of an enhanced high-permeability nanofiltration membrane according to claim 1, characterized in that: The outer surface of the base membrane is formed into a porous and macroporous structure by extrusion with pure organic solvents to reduce the internal concentration polarization (ICP) effect during the pressure retarded osmosis (PRO) process.
8. An enhanced high-permeability nanofiltration membrane, characterized in that: It is prepared by using the preparation method of an enhanced high - permeability nanofiltration membrane described in any one of claims 1 - 7.