Seawater desalination reverse osmosis membrane based on graphene-polyamide material and preparation method thereof

Abstract

The invention belongs to the technical field of semipermeable membranes, and particularly relates to a seawater desalination reverse osmosis membrane based on a graphene-polyamide material and a preparation method of the seawater desalination reverse osmosis membrane. Uniformly coating the upper surface of a polyester non-woven fabric with the membrane casting solution, soaking the polyester non-woven fabric in deionized water, taking out the polyester non-woven fabric, washing the polyester non-woven fabric, and drying the polyester non-woven fabric to obtain a composite layer of a supporting layer and a reinforcing layer; uniformly spraying the transition layer coating liquid on the surface of the supporting layer in the composite layer of the supporting layer and the reinforcing layer, and drying to obtain a composite film; soaking, taking out and blow-drying the composite membrane in the water-phase solution A, soaking the composite membrane in the oil-phase solution for primary reaction, taking out the composite membrane, soaking the composite membrane in the water-phase solution B for secondary reaction, taking out the composite membrane and blow-drying the composite membrane to obtain a reverse osmosis membrane precursor; washing, drying, cutting and packaging the reverse osmosis membrane precursor to obtain the seawater desalination reverse osmosis membrane based on the graphene-polyamide material. The graphene of the seawater desalination reverse osmosis membrane based on the graphene-polyamide material is uniformly dispersed, the interface bonding is tight, and the comprehensive performance is excellent.

Description

Technical Field

[0001] This invention belongs to the field of semi-permeable membrane technology, specifically relating to a seawater desalination reverse osmosis membrane based on graphene-polyamide material and its preparation method. Background Technology

[0002] The global shortage of freshwater resources has become a key bottleneck restricting the sustainable development of society and the economy. Seawater desalination is one of the effective ways to solve the freshwater resource crisis. Reverse osmosis has become the most widely used seawater desalination technology due to its advantages such as low energy consumption, high desalination efficiency, and simple operation. Its core component is the reverse osmosis membrane. Currently, commercial reverse osmosis membranes mainly use polyamide as the core separation layer. However, traditional polyamide reverse osmosis membranes have obvious defects: First, it is difficult to balance water flux and desalination rate. In order to improve the desalination effect, water flux is often reduced. Second, the antifouling performance is poor. Organic matter, microorganisms, and colloids coexisting in seawater are easy to adhere to the membrane surface, leading to membrane fouling and clogging, shortening the service life and increasing operating costs. Third, the chemical stability is limited. It is easy to degrade in high-salt and strong oxidizing environments, affecting the long-term stability of membrane separation performance.

[0003] Graphene, a carbon material with a single-atom-layer hexagonal close-packed structure, has a theoretical specific surface area as high as 2630 m². 2 With an atomic-level sieving channel of approximately 0.34 nm, graphene can efficiently separate water molecules from salt ions, while also possessing excellent mechanical strength, good chemical stability, and resistance to acid and alkali corrosion, demonstrating great potential in the field of membrane separation. Combining graphene with polyamide can optimize membrane separation performance through their synergistic effect—graphene's molecular sieving ability enhances desalination, while polyamide's excellent film-forming properties ensure the integrity of the membrane structure. However, existing composite technologies face several bottlenecks: firstly, strong van der Waals forces exist between graphene sheets, easily leading to aggregation and the formation of defective channels within the membrane, reducing the desalination rate; secondly, the inert surface of graphene results in weak interfacial bonding with polyamide, making it prone to interlayer delamination during long-term operation; and thirdly, the dispersion concentration of graphene during the composite process is difficult to control—excessive concentration leads to membrane pore blockage, while insufficient concentration fails to achieve the desired enhancement effect. These problems severely limit the industrial application of graphene-polyamide composite technology.

[0004] Currently, the market demand for high-performance reverse osmosis membranes is growing at an annual rate of 12%, while the performance improvement of existing reverse osmosis membrane products has reached a plateau. Chinese patent CN119588185A discloses a polyamide reverse osmosis membrane for high-salt wastewater treatment and its preparation method, solving the problem that polyamide reverse osmosis membranes cannot simultaneously achieve desalination rate and water flux. However, this patent is difficult to prepare, with a complex process and stringent conditions, resulting in low yield, high equipment investment, and high costs. Furthermore, pore structure control is challenging, and there is a contradiction between mechanical strength and flexibility. Although graphene membranes have high tensile strength, they are brittle and prone to micro-cracks due to mechanical stress in spiral-wound membrane modules, affecting long-term stability. Large-scale application is limited, making it unsuitable for mass production. Summary of the Invention

[0005] The purpose of this invention is to provide a seawater desalination reverse osmosis membrane based on graphene-polyamide material, which has uniform graphene dispersion, tight interfacial bonding, and excellent overall performance; this invention also provides a method for preparing the seawater desalination reverse osmosis membrane based on graphene-polyamide material.

[0006] The seawater desalination reverse osmosis membrane based on graphene-polyamide material described in this invention has an asymmetric composite structure. This structure consists of a surface functional layer, a transition layer, a support layer, and a reinforcing layer connected sequentially from the outside to the inside. The layers are tightly bonded through chemical bonding and physical nesting, with no obvious interface defects. The surface functional layer is a modified graphene-polyamide composite layer and is the core component for seawater desalination. The surface functional layer consists of a surface layer and an inner layer. The surface layer contains 0.8-1.2 wt.% modified graphene, with the remainder being polyamide. The inner layer contains 0.2-0.4 wt.% modified graphene, with the remainder being polyamide. The modified graphene content decreases gradually from 0.8-1.2 wt.% in the surface layer to 0.2-0.4 wt.% in the inner layer. The high content of modified graphene in the surface layer forms a dense sieve network, while the low content in the inner layer constructs efficient mass transfer channels. The transition layer is made of alumina nanoparticles and polyethylene glycol.

[0007] The surface functional layer has a thickness of 50-100 nm. The surface of the surface functional layer naturally forms a composite rough structure of micron-sized protrusions and nano-sized wrinkles through interfacial polymerization reaction, with a contact angle as low as about 32°, which significantly improves the hydrophilicity and antifouling ability of the surface functional layer. The modified graphene in the surface functional layer has a dispersion particle size of 100-200 nm in polyamide, the transition layer has a thickness of 200-300 nm, and the hydroxyl alumina nanoparticles in the transition layer have a particle size of 50-80 nm. The hydroxyl alumina nanoparticles are bonded to the support layer through hydrogen bonds, and at the same time, their surface hydroxyl groups form coordination bonds with the amino groups of the surface functional layer, which effectively enhances the bonding force between the surface functional layer and the support layer. The peel strength is more than 45% higher than that of the structure without the transition layer. The introduction of polyethylene glycol can further reduce the mass transfer resistance of the transition layer and ensure water flux.

[0008] The support layer has a thickness of 35-50 μm and is a modified polysulfone microporous membrane. The pore structure is controlled by adding the pore-forming agent to the casting solution.

[0009] The reinforcing layer has a thickness of 65-100μm and is made of polyester nonwoven fabric. A layer of polyester nonwoven fabric is laminated at the bottom of the support layer as a reinforcing layer, which can improve the tensile properties of the membrane and meet the needs of industrial spiral wound membrane module preparation.

[0010] The method for preparing a seawater desalination reverse osmosis membrane based on graphene-polyamide material according to the present invention includes the following steps: (1) Add anhydrous ethanol to the graphene oxide dispersion and ultrasonically disperse it. Then add silane coupling agent and stir evenly. Stir the reaction, centrifuge, wash, freeze dry to obtain aminated modified graphene powder. (2) DMF (N,N-dimethylformamide) and polyethylene glycol were added to polysulfone and stirred to remove bubbles, and a casting solution was obtained. The casting solution was uniformly coated on the upper surface of the polyester nonwoven fabric and then immersed in deionized water. The fabric was then removed, washed, and dried to obtain a composite layer of support layer and reinforcement layer. (3) Hydroxyalumina nanoparticles were ultrasonically dispersed with anhydrous ethanol, and then polyethylene glycol was added and stirred to dissolve them to obtain a transition layer coating liquid; the transition layer coating liquid was uniformly sprayed on the surface of the support layer in the composite layer of support layer and reinforcement layer, and dried to obtain a composite film; (4) The composite membrane is immersed in aqueous solution A, taken out, dried, immersed in oil solution for one reaction, taken out, immersed in aqueous solution B for a second reaction, taken out, dried, and the reverse osmosis membrane precursor is obtained. (5) The reverse osmosis membrane precursor is washed, dried, cut, and packaged to obtain a seawater desalination reverse osmosis membrane based on graphene-polyamide material.

[0011] In step (1), the volume ratio of graphene oxide dispersion, anhydrous ethanol, and silane coupling agent is 19-21:9-11:0.1; the concentration of graphene oxide dispersion is 0.5-0.55 mg / mL; the silane coupling agent is KH-550; the ultrasonic dispersion time is 20-30 min; the stirring reaction time is 4-5 hours; the stirring reaction temperature is 80-90℃; the centrifugation speed is 8000-8500 r / min; the centrifugation time is 15-20 min; washing is performed with anhydrous ethanol 3-4 times; and the freeze-drying time is 48-50 hours. The freeze-drying temperature is -50 to -45℃; in step (2), the ratio of polysulfone, DMF and polyethylene glycol is 3-4:15-16:1, where polysulfone and polyethylene glycol are expressed in g, DMF in mL, the stirring temperature is 70-75℃, the stirring time is 8-9 hours, the degassing temperature is 60-65℃, the degassing time is 2-3 hours, the soaking temperature is 23-27℃, the soaking time is 24-25 hours, the washing is done with deionized water, the number of washings is 3-4 times, the drying temperature is 40-45℃, the drying time is 10-12 hours, and polyethylene glycol is preferably polyethylene glycol 400.

[0012] In step (3), the ratio of alumina hydroxyl oxide nanoparticles, anhydrous ethanol, and polyethylene glycol is 2-2.5:100-105:1, where alumina hydroxyl oxide nanoparticles and polyethylene glycol are expressed in g, anhydrous ethanol in mL, the ultrasonic dispersion time is 30-40 min, the ultrasonic dispersion power is 200-220 W, the drying temperature is 60-65 ℃, and the drying time is 30-40 min.

[0013] In step (4), the aqueous solution A is prepared by adding aminated graphene powder to a 1.5-1.6 wt.% m-phenylenediamine aqueous solution and ultrasonically dispersing for 40-45 min to obtain a m-phenylenediamine-graphene mixed solution, denoted as aqueous solution A. The mass ratio of the 1.5-1.6 wt.% m-phenylenediamine aqueous solution to the aminated graphene is 2-2.1:1. The aqueous solution B is prepared by adding aminated graphene powder to a 0.5-0.6 wt.% m-phenylenediamine aqueous solution and ultrasonically dispersing for 40-45 min to obtain a m-phenylenediamine-graphene mixed solution, denoted as aqueous solution B. The mass ratio of the 0.5-0.6 wt.% m-phenylenediamine aqueous solution to the aminated graphene is 2. 4-2.6:1; The preparation method of the oil phase solution is to dissolve pyromellitic chloride in n-hexane by stirring to obtain the oil phase solution. The concentration of the oil phase solution is 0.1-0.12 wt.%. The soaking time in the aqueous phase solution A is 10-12 min, the reaction time is 30-45 s, and the reaction temperature is 25-35℃. The soaking time in the aqueous phase solution B is 5-6 min, and the reaction temperature is 25-35℃. The volume ratio of the aqueous phase solution A, aqueous phase solution B and oil phase solution is 1-1.1:1-1.1:1. The drying is done with nitrogen gas. In step (5), the washing is to rinse with deionized water 3-4 times and then rinse with anhydrous ethanol 2-3 times. The drying temperature is 55-60℃ and the drying time is 2-3 hours.

[0014] In step (4), the composite membrane is first immersed in aqueous solution A, then removed, dried, and immersed in oil solution for a primary reaction. At this time, a primary polymerization layer is formed on the surface of the composite membrane. Then, it is immersed in aqueous solution B. At this time, the m-phenylenediamine and aminated modified graphene in aqueous solution B gradually wet and diffuse from the outside to the inside on the surface of the primary polymerization layer. During the diffusion process, m-phenylenediamine and trimesoyl chloride undergo a secondary polymerization reaction to generate polyamide. As the content of m-phenylenediamine and aminated modified graphene in the primary polymerization layer gradually decreases from the outside to the inside during the diffusion process, a modified graphene-polyamide composite layer with a gradient concentration structure is formed on the surface of the composite membrane. The content of aminated modified graphene in the surface layer of the modified graphene-polyamide composite layer is 0.8-1.2 wt.%, and the rest is polyamide. The content of aminated modified graphene in the inner layer of the modified graphene-polyamide composite layer is 0.2-0.4 wt.%.

[0015] The preparation method of the graphene oxide dispersion in step (1) includes the following steps: (a) Concentrated sulfuric acid was added to flake graphite and stirred, then potassium permanganate was added and stirred to react, resulting in mixture 1; (b) Mixture 1 is stirred to produce mixture 2; (c) Add deionized water to mixture 2, stir and react to obtain mixture 3; (d) Deionized water was first added to mixture 3, followed by hydrogen peroxide solution. The mixture was stirred and reacted to obtain mixture 4. (e) The mixture was centrifuged, separated, washed, and a precipitate was obtained; (f) The precipitate was ultrasonically exfoliated in deionized water to obtain a graphene oxide dispersion.

[0016] In step (a), the ratio of flake graphite, concentrated sulfuric acid, and potassium permanganate is 1:22-23:3-4, where flake graphite and potassium permanganate are expressed in g, and concentrated sulfuric acid in mL. The stirring time is 30-40 min, the stirring temperature is 0-5℃, the reaction time is 2-3 hours, and the reaction temperature is 0-10℃. In step (b), the stirring time is 30-40 min, and the reaction temperature is 35-38℃. In step (c), the volume ratio of deionized water to concentrated sulfuric acid in step (a) is 2-2.5:1, the addition rate is 1-1.2 mL / min, the addition temperature is 35-38℃, the stirring time is 15-18 min, and the reaction temperature is 98-100℃. In step (d)... The concentration of hydrogen peroxide solution in step (a) is 30-32 wt.%, and the ratio of deionized water, hydrogen peroxide solution and flake graphite in step (a) is 100-110:5-5.5:1. The deionized water and hydrogen peroxide solution are expressed in mL, and the flake graphite is expressed in g. The stirring reaction time is 30-35 min, and the stirring reaction temperature is 25-26℃. In step (e), the centrifugation speed is 5000-6000 r / min, the centrifugation time is 10-15 min, and the washing is first washed with 5-7 wt.% hydrochloric acid solution 3-4 times, and then repeatedly washed with deionized water until the pH of the washing solution is neutral. In step (f), the ultrasonic peeling time is 60-70 min, and the ultrasonic peeling power is 300-350 W.

[0017] The beneficial effects of this invention are as follows: 1. Two-step graphene modification technology: A two-step modification process of "oxidation activation-amino grafting" is used. The first step involves oxidizing the graphene, introducing a large number of oxygen-containing functional groups such as hydroxyl (-OH) and carboxyl (-COOH) groups onto its surface to obtain graphene oxide (GO). This disrupts the van der Waals forces between graphene sheets, improving dispersibility. The second step uses a silane coupling agent (KH-550) to aminate the graphene oxide. The siloxane groups of KH-550 react with the hydroxyl groups of the graphene oxide. In a synthesis reaction, amino groups (-NH2) are grafted onto the surface of graphene to obtain aminated modified graphene (NH2-GO). Aminated modified graphene (modified graphene) can form a synergistic reaction with the amino group of polyamide monomer (m-phenylenediamine) and undergo an amidation reaction with the acyl chloride group (-COCl) of trimesoyl chloride to form a stable covalent bond. This solves the problems of uneven graphene dispersion and weak interfacial bonding. The particle size of modified graphene in polyamide can be controlled within 100-200 nm. (1) The silane coupling agent (KH-550) is γ-aminopropyltriethoxysilane. Its reaction mechanism with graphene oxide and polyamide is as follows: the ethoxy group (-OCH2CH3) attached to the Si atom is hydrolyzed to generate silanol (-SiOH), which then condenses with the hydroxyl group (-OH) on the surface of graphene oxide to form a stable Si-O-Si covalent bond; at the same time, the amino group (-NH2) at the other end combines with the polyamide monomer (m-phenylenediamine) through hydrogen bonding or electrostatic interaction, and finally undergoes an amidation reaction with the acyl chloride group (-COCl) of trimesoyl chloride to form a covalent cross-linked network; (2) The graphene oxidation reaction is: C + H2SO4 + KMnO4 → GO + CO2 + H2O; (3) The condensation reaction formula is: Si(OC2H5)3+GO-OH→Si-O-GO+C2H5OH; (4) The amidation reaction formula is: -NH2+-COCl→-CONH-+HCl.

[0018] 2. Precise Construction of Gradient Composite Structure: A precise gradient distribution of aminated modified graphene in the surface functional layer is achieved through dynamic interface polymerization. Specifically, by controlling the concentration gradient of the m-phenylenediamine-graphene mixed solution and the polymerization reaction time gradient, the modified graphene naturally forms a decreasing content distribution from the surface to the inside within the surface functional layer. The high content of modified graphene in the surface layer constructs a dense sieve network, increasing the desalination rate to over 99.5%; the low content of modified graphene in the inner layer reduces mass transfer resistance, increasing water flux by over 30% compared to traditional polyamide reverse osmosis membranes, achieving simultaneous optimization of desalination rate and water flux.

[0019] 3. Antifouling surface micro / nano structure design: By controlling the time of the two interfacial polymerization reactions to 30-45s and 5-6min respectively during the preparation of the surface functional layer, a composite rough structure of "2-5μm diameter micron protrusions + 50-100nm height nanon wrinkles" is formed on the membrane surface. Combined with the synergistic effect of the hydrophilic groups of graphene and polyamide, the membrane surface contact angle is reduced from about 65° of traditional polyamide membranes to about 32°, and the hydrophilicity is significantly improved. At the same time, the composite rough structure reduces the contact area between pollutants and the membrane surface by more than 40%, and the capillary action of the rough surface accelerates the spread of water molecules, forming a stable water film barrier and inhibiting pollutant adsorption. Compared with traditional polyamide reverse osmosis membranes, the flux attenuation rate is reduced to 9.3-10%.

[0020] 4. Multi-layer composite reinforcement system: A four-layer composite system of "surface functional layer - transition layer - support layer - reinforcement layer" is constructed. The hydroxyl alumina nanoparticles and polyethylene glycol composite system in the transition layer achieve a strong bond between the surface functional layer and the support layer. The modified polysulfone microporous membrane in the support layer ensures mass transfer efficiency, and the polyester nonwoven fabric in the reinforcement layer improves mechanical properties. This enables the seawater desalination reverse osmosis membrane based on graphene-polyamide material to achieve an elongation at break of more than 15%, which is more than 20% higher than the elongation at break of traditional mainstream polyamide reverse osmosis membranes on the market, meeting the pressure impact requirements in industrial operation.

[0021] In this invention, the transition layer is made of alumina hydroxyl oxide nanoparticles and polyethylene glycol (PEG), solving the problems of structural damage and short service life caused by insufficient interlayer bonding in traditional reverse osmosis membranes. If the transition layer consists only of alumina hydroxyl oxide nanoparticles, the accumulation of these nanoparticles may lead to a decrease in porosity and an increase in density, thereby increasing the mass transfer resistance of water molecules and reducing water flux. The introduction of PEG improves the pore structure of the transition layer, reduces the resistance to water molecule penetration, and ensures that water flux does not decrease while enhancing structural stability. Furthermore, alumina hydroxyl oxide nanoparticles have a tendency to aggregate; severe aggregation can lead to uneven distribution of interlayer bonding and localized delamination failure. PEG molecular chains can bind to the hydroxyl groups on the surface of alumina hydroxyl oxide nanoparticles through hydrogen bonds, acting as a steric hindrance to inhibit particle aggregation and make the transition layer structure more uniform. This ensures both the stability of interlayer bonding and a smoother mass transfer path for water molecules. The synergistic effect of alumina hydroxyl oxide nanoparticles and PEG achieves a balance between the structural stability and separation performance of the reverse osmosis membrane, avoiding the technical defects of a single-component transition layer.

[0022] This invention presents a high-flux, high-desalination-rate, fouling-resistant polyamide reverse osmosis membrane based on graphene-polyamide materials. Its core design concept revolves around "interface regulation, structural optimization, and performance synergy." This invention employs a two-step surface modification process (oxidation activation + amino grafting) to construct active functional groups on the graphene surface. This improves the dispersibility and compatibility of graphene in polyamide and provides reaction sites for interfacial covalent bonding. A dynamic interfacial polymerization process is used to wet and diffuse m-phenylenediamine with aminated modified graphene, constructing a modified graphene-polyamide surface functional layer with a gradient concentration structure, achieving a gradient distribution of graphene within the membrane layer. Combined with the support layer structure design and surface hydrophilic modification, synergistic performance improvements are achieved in three dimensions: mass transfer resistance, separation accuracy, and fouling resistance, resolving the core contradiction of the inverse relationship between water flux and desalination rate in traditional reverse osmosis membranes. This invention breaks through the limitations of single-performance optimization in existing reverse osmosis membrane preparation, and achieves a leapfrog improvement in the comprehensive performance of reverse osmosis membrane materials through multi-dimensional regulation.

[0023] The seawater desalination reverse osmosis membrane based on graphene-polyamide material in this invention has a four-layer structure (surface functional layer, transition layer, support layer, and reinforcement layer). The layers are tightly bonded together with no obvious interface gaps. The modified graphene content in the surface functional layer decreases gradually from the surface layer to the inner layer. The modified graphene in the surface layer is densely distributed, while the modified graphene in the inner layer is sparsely distributed. The alumina nanoparticles in the transition layer are uniformly dispersed, forming a bridge structure connecting the surface functional layer and the support layer. Attached Figure Description

[0024] Figure 1 This is a cross-sectional schematic diagram of the seawater desalination reverse osmosis membrane based on graphene-polyamide material in Example 1. In the figure, 1 is the surface functional layer, 2 is the transition layer, 3 is the support layer, and 4 is the reinforcement layer.

[0025] Figure 2 The graph shows the effect of different operating pressures on membrane separation performance.

[0026] Figure 3 The images show SEM images of the surface morphology of the seawater desalination reverse osmosis membrane based on graphene-polyamide material in Example 1. In the images, (a) is an SEM image with a scale bar of 200 nm, (b) is an SEM image with a scale bar of 50 nm, (c) is an SEM image with a scale bar of 10 μm, and (d) is an SEM image with a scale bar of 3 μm. Detailed Implementation

[0027] The present invention will be further described below with reference to embodiments.

[0028] Example 1 Graphene oxide (GO) was prepared using a modified Hummers method, with the following specific steps: (a) Place 50g of natural flake graphite in a 500mL beaker, add 200mL of 1mol / L hydrochloric acid solution, stir at 60℃ for 2h to remove metallic impurities from the natural flake graphite, then wash with deionized water until the pH of the washing solution is neutral, and vacuum dry at 80℃ for 12h to obtain pretreated natural flake graphite; add 2g of pretreated natural flake graphite to a 500mL three-necked flask equipped with a mechanical stirrer, thermometer and condenser, slowly add 46mL of concentrated sulfuric acid, stir for 30min under ice bath conditions of 0-5℃ to fully impregnate the natural flake graphite; then slowly add 6g of potassium permanganate, control the reaction temperature at 0-10℃ and continue stirring for 2h, at which point the reaction system is a purplish-black paste, to obtain mixture 1; (b) Remove the three-necked flask from the ice bath and place it in a 35°C constant temperature water bath. Continue stirring for 30 minutes. The reaction system gradually turns brown and the viscosity increases, yielding mixture 2. (c) Slowly add 92 mL of deionized water to a three-necked flask at 35 °C, with the addition rate controlled at 1 mL / min to prevent a sudden temperature rise; after the addition is complete, raise the water bath temperature to 98 °C and stir the reaction for 15 min. At this time, the reaction system is bright yellow, and mixture 3 is obtained. (d) Quickly remove the three-necked flask from the constant temperature water bath, add 200 mL of deionized water to terminate the reaction, then add 10 mL of 30 wt.% hydrogen peroxide solution, stir the reaction at 25 °C for 30 min to remove excess potassium permanganate, the reaction system turns golden yellow, and mixture 4 is obtained. (e) The mixture 4 obtained in step (d) was centrifuged at a speed of 5000 r / min for 10 min to remove the supernatant and obtain a solid product. The solid product was then washed three times with 5 wt.% hydrochloric acid solution to remove residual sulfate ions. It was then washed repeatedly with deionized water until the pH of the washing solution was neutral to obtain a precipitate. (f) The precipitate was dispersed in deionized water and ultrasonically exfoliated for 60 min at a power of 300 W to obtain a graphene oxide dispersion with a concentration of 0.5 mg / mL. The dispersion was sealed and stored for later use. The graphene oxide was observed to be transparent and wrinkled sheet structure with no obvious graphite particles remaining when observed by scanning electron microscopy (SEM).

[0029] Preparation of seawater desalination reverse osmosis membranes based on graphene-polyamide materials: (1) Preparation of aminated modified graphene (NH2-GO) powder Take 100 mL of a 0.5 mg / mL graphene oxide dispersion, add 50 mL of anhydrous ethanol, and sonicate for 20 min. Then add 0.5 mL of KH-550 and stir until homogeneous to obtain a mixed solution. Transfer the above mixed solution to a 250 mL three-necked flask and reflux and stir at 80 °C for 4 h to allow the siloxane groups of KH-550 to undergo a condensation reaction with the hydroxyl groups on the surface of graphene oxide, and the amino groups to be grafted onto the surface of graphene oxide. After the reaction is complete, the reaction product is centrifuged at 8000 r / min for 15 min to obtain a precipitate. The precipitate is washed three times with anhydrous ethanol to remove unreacted KH-550. Then disperse the washed precipitate in deionized water and freeze-dry at -45 °C for 48 h to obtain a fluffy aminated modified graphene powder. (2) Preparation of modified polysulfone microporous membrane Polysulfone particles were dried in a vacuum drying oven at 120°C for 24 hours to remove residual moisture and prevent the generation of large amounts of bubbles during the preparation of the casting solution, resulting in pretreated polysulfone. In a 250mL three-necked flask equipped with a mechanical stirrer, 15g of the pretreated polysulfone was added, followed by 80mL of DMF and 5g of polyethylene glycol 400. The mixture was stirred in a 70°C water bath for 8 hours until the polysulfone was completely dissolved. The mixture was then placed in a vacuum drying oven at 60°C for 2 hours to remove bubbles generated during stirring, forming a uniform, transparent, and bubble-free casting solution. A 65μm thick polyester nonwoven fabric was then fixed onto a glass substrate. On the board, an automatic coating machine was used to uniformly coat the casting solution onto the upper surface of the polyester nonwoven fabric at a coating speed of 5 cm / s and a coating thickness of 70 μm. Then, the glass substrate was quickly immersed in a deionized water coagulation bath at 25°C. The DMF in the casting solution rapidly diffused into the water, and the polysulfone underwent phase separation and solidified to form a microporous structure. The immersion was carried out for 24 hours to ensure full curing and solvent removal. The solidified polysulfone support layer and the polyester nonwoven fabric were peeled off from the glass substrate together, rinsed three times with deionized water, and then vacuum dried at 40°C for 12 hours to obtain a composite layer of modified polysulfone microporous membrane and reinforcing layer, i.e., a composite layer of support layer and reinforcing layer. (3) Modification of the transition layer 10g of alumina hydroxyl oxide nanoparticles were ultrasonically dispersed in 100mL of anhydrous ethanol for 30min, then stirred and evaporated at 80℃ to dryness, removing impurities adsorbed on the surface of the alumina hydroxyl oxide nanoparticles and improving their dispersibility in the transition layer, resulting in pretreated alumina hydroxyl oxide nanoparticles. 2g of the pretreated alumina hydroxyl oxide nanoparticles were added to 100mL of anhydrous ethanol and ultrasonically dispersed for 30min at a power of 200W. Then, 1g of polyethylene glycol was added and stirred to dissolve, resulting in a uniform transition layer coating solution. The composite layer of the support layer and the reinforcement layer was fixed on a spraying table and coated using an air... The transition layer coating liquid was uniformly sprayed onto the surface of the support layer in the composite layer of support and reinforcement layers using an air spraying method. The nozzle diameter was 0.5 mm, the spraying pressure was 0.3 MPa, the spraying distance was 15 cm, and the spraying speed was 10 cm / s. The composite layer of support and reinforcement layers coated with the transition layer coating liquid was placed in an oven at 60 °C and dried for 30 min to form a transition layer with a thickness of 200 nm, thus obtaining a composite film. The hydroxyl alumina nanoparticles in the transition layer had a particle size of 50 nm. At this point, the surface hydroxyl content of the composite layer of support and reinforcement layers was significantly increased, and the hydrophilicity was enhanced, laying the foundation for subsequent bonding with surface functional layers. (4) A surface functional layer (NH2-GO / polyamide composite layer) is constructed using a dynamic interface polymerization process. Dissolve 1.5 g of m-phenylenediamine in 100 mL of deionized water by stirring to obtain a 1.5 wt.% aqueous solution of m-phenylenediamine. Add 10 g of aminated graphene powder to 20 g of the 1.5 wt.% aqueous solution of m-phenylenediamine and ultrasonically disperse for 40 min to obtain a uniform aqueous dispersion, which is used as the surface wetting solution and is denoted as aqueous solution A. Dissolve 0.5 g of m-phenylenediamine in 100 mL of deionized water by stirring to obtain a 0.5 wt.% aqueous solution of m-phenylenediamine. Add 10 g of aminated graphene powder to 24 g of the 0.5 wt.% aqueous solution of m-phenylenediamine and ultrasonically disperse for 40 min to obtain a uniform aqueous dispersion, which is used as the inner wetting solution and is denoted as aqueous solution B. Dissolve 0.1 g of trimesoyl chloride in 100 mL of n-hexane by stirring to obtain an oil phase solution with a concentration of 0.1 wt.%. The composite membrane in step (3) is first immersed in 100 mL of aqueous solution A for 10 min to allow m-phenylenediamine and aminated graphene to be fully adsorbed on the surface of the transition layer. After removal, the excess solution on the surface is dried with nitrogen gas. Then, it is immersed in 100 mL of oil solution and reacted at 25 °C for 30 s to carry out the first interfacial polymerization reaction. Afterward, it is quickly transferred to 100 mL of aqueous solution B and immersed at 25 °C for 5 min to carry out the second interfacial polymerization reaction. Finally, it is removed and the surface is dried with nitrogen gas to obtain the reverse osmosis membrane precursor. (5) Post-processing and finished product preparation The reverse osmosis membrane precursor was first rinsed three times with deionized water, then twice with anhydrous ethanol to remove residual n-hexane, unreacted m-phenylenediamine, and trimesoyl chloride from the membrane surface. It was then dried in a vacuum drying oven at 60°C for 2 hours to make the membrane structure more compact and stable. It was then cut into different sizes according to requirements and packaged in clean polyethylene bags, stored in a dry environment to obtain a seawater desalination reverse osmosis membrane based on graphene-polyamide material. Testing showed that the surface functional layer of the graphene-polyamide-based seawater desalination reverse osmosis membrane contained 0.8 wt.% modified graphene, with the remainder being polyamide; the inner layer contained 0.2 wt.% modified graphene, with the remainder being polyamide; the thickness of the surface functional layer was 50 nm, and the dispersion particle size of the modified graphene in the polyamide was 100 nm; the thickness of the support layer was 35 μm. A cross-sectional schematic diagram of the graphene-polyamide-based seawater desalination reverse osmosis membrane is shown below. Figure 1 .

[0030] Example 2 Graphene oxide (GO) was prepared using a modified Hummers method, with the following specific steps: (a) Place 50g of natural flake graphite in a 500mL beaker, add 200mL of 1mol / L hydrochloric acid solution, stir at 60℃ for 2h to remove metallic impurities from the natural flake graphite, then wash with deionized water until the pH of the washing solution is neutral, and vacuum dry at 80℃ for 12h to obtain pretreated natural flake graphite; add 2g of pretreated natural flake graphite to a 500mL three-necked flask equipped with a mechanical stirrer, thermometer and condenser, slowly add 44mL of concentrated sulfuric acid, stir for 40min under ice bath conditions of 0-5℃ to fully impregnate the natural flake graphite; then slowly add 8g of potassium permanganate, control the reaction temperature at 0-10℃ and continue stirring for 3h, at which point the reaction system is a purplish-black paste, to obtain mixture 1; (b) Remove the three-necked flask from the ice bath and place it in a 38°C constant temperature water bath. Continue stirring for 40 minutes. The reaction system gradually turns brown and the viscosity increases, yielding mixture 2. (c) Slowly add 110 mL of deionized water to a three-necked flask at 38 °C, with the addition rate controlled at 1.2 mL / min to prevent a sudden temperature rise; after the addition is complete, raise the water bath temperature to 100 °C and stir the reaction for 18 min. At this time, the reaction system is bright yellow, and mixture 3 is obtained. (d) Quickly remove the three-necked flask from the constant temperature water bath, add 220 mL of deionized water to terminate the reaction, then add 11 mL of 32 wt.% hydrogen peroxide solution, stir the reaction at 25.5 °C for 35 min to remove excess potassium permanganate, the reaction system turns golden yellow, and mixture 4 is obtained. (e) The mixture 4 obtained in step (d) was centrifuged at a speed of 6000 r / min for 15 min to remove the supernatant and obtain a solid product. The solid product was then washed four times with 7 wt.% hydrochloric acid solution to remove residual sulfate ions. It was then washed repeatedly with deionized water until the pH of the washing solution was neutral to obtain a precipitate. (f) The precipitate was dispersed in deionized water and ultrasonically exfoliated for 70 min at a power of 350 W to obtain a graphene oxide dispersion with a concentration of 0.55 mg / mL. The dispersion was then sealed and stored for later use.

[0031] Preparation of seawater desalination reverse osmosis membranes based on graphene-polyamide materials: (1) Preparation of aminated modified graphene (NH2-GO) powder Take 105 mL of a 0.55 mg / mL graphene oxide dispersion, add 55 mL of anhydrous ethanol, and sonicate for 30 min. Then add 0.5 mL of KH-550 and stir until homogeneous to obtain a mixed solution. Transfer the above mixed solution to a 250 mL three-necked flask and reflux and stir at 90 °C for 5 h to allow the siloxane groups of KH-550 to undergo a condensation reaction with the hydroxyl groups on the surface of graphene oxide, and the amino groups to be grafted onto the surface of graphene oxide. After the reaction is complete, the reaction product is centrifuged at 8500 r / min for 20 min to obtain a precipitate. The precipitate is washed four times with anhydrous ethanol to remove unreacted KH-550. Then disperse the washed precipitate in deionized water and freeze-dry at -48 °C for 50 h to obtain a fluffy aminated modified graphene powder. (2) Preparation of modified polysulfone microporous membrane Polysulfone particles were dried in a vacuum drying oven at 120°C for 24 hours to remove residual moisture and prevent the formation of numerous bubbles during the preparation of the casting solution, resulting in pretreated polysulfone. 20g of the pretreated polysulfone was added to a 250mL three-necked flask equipped with a mechanical stirrer, followed by 75mL of DMF and 5g of polyethylene glycol 400. The mixture was stirred in a 75°C water bath for 9 hours until the polysulfone was completely dissolved. The mixture was then placed in a vacuum drying oven at 65°C for 3 hours to remove bubbles generated during stirring, resulting in a uniform, transparent, and bubble-free casting solution. A 100μm thick polyester nonwoven fabric was then fixed onto a glass substrate. On the board, an automatic coating machine was used to uniformly coat the casting solution onto the upper surface of the polyester nonwoven fabric at a coating speed of 5 cm / s and a coating thickness of 100 μm. Then, the glass substrate was quickly immersed in a deionized water coagulation bath at 27°C. The DMF in the casting solution rapidly diffused into the water, and the polysulfone underwent phase separation and solidified to form a microporous structure. The immersion was carried out for 25 hours to ensure full curing and solvent removal. The solidified polysulfone support layer and the polyester nonwoven fabric were peeled off from the glass substrate together, rinsed with deionized water 4 times, and then vacuum dried at 45°C for 11 hours to obtain a composite layer of modified polysulfone microporous membrane and reinforcing layer, i.e., a composite layer of support layer and reinforcing layer. (3) Modification of the transition layer 10g of alumina hydroxyl oxide nanoparticles were ultrasonically dispersed in 100mL of anhydrous ethanol for 30min, followed by stirring and evaporation at 80℃ until dry to remove impurities adsorbed on the surface of the alumina hydroxyl oxide nanoparticles and improve their dispersibility in the transition layer, resulting in pretreated alumina hydroxyl oxide nanoparticles. 2.5g of the pretreated alumina hydroxyl oxide nanoparticles were then ultrasonically dispersed in 105mL of anhydrous ethanol for 40min at a power of 220W. 1g of polyethylene glycol was then added and stirred to dissolve, resulting in a uniform transition layer coating solution. The composite layer of the support layer and the reinforcement layer was fixed on a spraying table and then... The transition layer coating liquid was uniformly sprayed onto the surface of the support layer in the composite layer of support and reinforcement layers using an air spraying method. The nozzle diameter was 0.5 mm, the spraying pressure was 0.3 MPa, the spraying distance was 15 cm, and the spraying speed was 10 cm / s. The composite layer of support and reinforcement layers coated with the transition layer coating liquid was placed in an oven at 65°C and dried for 40 min to form a transition layer with a thickness of 300 nm, thus obtaining a composite film. The hydroxyl alumina nanoparticles in the transition layer had a particle size of 80 nm. At this point, the surface hydroxyl content of the composite layer of support and reinforcement layers was significantly increased, and the hydrophilicity was enhanced, laying the foundation for subsequent bonding with surface functional layers. (4) A surface functional layer (NH2-GO / polyamide composite layer) is constructed using a dynamic interface polymerization process. Dissolve 1.6 g of m-phenylenediamine in 100 mL of deionized water by stirring to obtain a 1.6 wt.% aqueous solution of m-phenylenediamine. Add 10 g of aminated graphene powder to 21 g of the 1.6 wt.% aqueous solution of m-phenylenediamine and ultrasonically disperse for 42 min to obtain a uniform aqueous dispersion, which is used as the surface wetting solution and is denoted as aqueous solution A. Dissolve 0.6 g of m-phenylenediamine in 100 mL of deionized water by stirring to obtain a 0.6 wt.% aqueous solution of m-phenylenediamine. Add 10 g of aminated graphene powder to 26 g of the 0.6 wt.% aqueous solution of m-phenylenediamine and ultrasonically disperse for 42 min to obtain a uniform aqueous dispersion, which is used as the inner wetting solution and is denoted as aqueous solution B. Dissolve 0.12 g of trimesoyl chloride in 100 mL of n-hexane by stirring to obtain an oil solution with a concentration of 0.12 wt.%. The composite membrane in step (3) is first immersed in 110 mL of aqueous solution A for 12 min to allow m-phenylenediamine and aminated graphene to be fully adsorbed on the surface of the transition layer. After removal, the excess solution on the surface is dried with nitrogen gas. Then, it is immersed in 100 mL of oil solution and reacted at 35 °C for 45 s to carry out the first interfacial polymerization reaction. Afterward, it is quickly transferred to 110 mL of aqueous solution B and immersed at 35 °C for 6 min to carry out the second interfacial polymerization. Finally, it is removed and the surface is dried with nitrogen gas to obtain the reverse osmosis membrane precursor. (5) Post-processing and finished product preparation The reverse osmosis membrane precursor was first rinsed four times with deionized water, then three times with anhydrous ethanol to remove residual n-hexane, unreacted m-phenylenediamine, and trimesoyl chloride from the membrane surface. It was then dried in a vacuum drying oven at 58°C for 3 hours to make the membrane structure more compact and stable. The membrane was then cut to different sizes as needed and packaged in clean polyethylene bags, stored in a dry environment to obtain a seawater desalination reverse osmosis membrane based on graphene-polyamide material. Testing showed that the surface functional layer of the graphene-polyamide-based seawater desalination reverse osmosis membrane contained 1.2 wt.% modified graphene, with the remainder being polyamide; the inner layer contained 0.4 wt.% modified graphene, with the remainder being polyamide; the thickness of the surface functional layer was 100 nm, and the dispersion particle size of the modified graphene in the polyamide was 200 nm; the thickness of the support layer was 50 μm.

[0032] Example 3 Graphene oxide (GO) was prepared using a modified Hummers method, with the following specific steps: (a) Place 50g of natural flake graphite in a 500mL beaker, add 200mL of 1mol / L hydrochloric acid solution, stir at 60℃ for 2h to remove metallic impurities from the natural flake graphite, then wash with deionized water until the pH of the washing solution is neutral, and vacuum dry at 80℃ for 12h to obtain pretreated natural flake graphite; add 2g of pretreated natural flake graphite to a 500mL three-necked flask equipped with a mechanical stirrer, thermometer and condenser, slowly add 45mL of concentrated sulfuric acid, stir for 35min under ice bath conditions of 0-5℃ to fully impregnate the natural flake graphite; then slowly add 7g of potassium permanganate, control the reaction temperature at 0-10℃ and continue stirring for 2.5h, at which point the reaction system is a purplish-black paste, to obtain mixture 1; (b) Remove the three-necked flask from the ice bath and place it in a 36°C constant temperature water bath. Continue stirring for 35 minutes. The reaction system gradually turns brown and the viscosity increases, yielding mixture 2. (c) Slowly add 105 mL of deionized water to a three-necked flask at 36 °C, with the dropping rate controlled at 1.1 mL / min to prevent a sudden temperature rise; after the addition is complete, raise the water bath temperature to 99 °C and stir the reaction for 16 min. At this time, the reaction system is bright yellow, and mixture 3 is obtained. (d) Quickly remove the three-necked flask from the constant temperature water bath, add 210 mL of deionized water to terminate the reaction, then add 10.5 mL of 31 wt.% hydrogen peroxide solution, stir the reaction at 25.5 °C for 34 min to remove excess potassium permanganate, the reaction system turns golden yellow, and mixture 4 is obtained. (e) The mixture 4 obtained in step (d) was centrifuged at a speed of 5800 r / min for 12 min to remove the supernatant and obtain a solid product. The solid product was then washed four times with a 6 wt.% hydrochloric acid solution to remove residual sulfate ions. It was then repeatedly washed with deionized water until the pH of the washing solution was neutral to obtain a precipitate. (f) The precipitate was dispersed in deionized water and ultrasonically exfoliated for 65 min at a power of 320 W to obtain a graphene oxide dispersion with a concentration of 0.52 mg / mL. The dispersion was sealed and stored for later use.

[0033] Preparation of seawater desalination reverse osmosis membranes based on graphene-polyamide materials: (1) Preparation of aminated modified graphene (NH2-GO) powder Take 95 mL of a 0.52 mg / mL graphene oxide dispersion, add 45 mL of anhydrous ethanol, and sonicate for 25 min. Then add 0.5 mL of KH-550 and stir until homogeneous to obtain a mixed solution. Transfer the above mixed solution to a 250 mL three-necked flask and reflux and stir at 85 °C for 4.5 h to allow the siloxane groups of KH-550 to undergo a condensation reaction with the hydroxyl groups on the surface of graphene oxide, and the amino groups to be grafted onto the surface of graphene oxide. After the reaction is complete, the reaction product is centrifuged at 8300 r / min for 16 min to obtain a precipitate. The precipitate is washed four times with anhydrous ethanol to remove unreacted KH-550. Then disperse the washed precipitate in deionized water and freeze-dry at -50 °C for 49 h to obtain a fluffy aminated modified graphene powder. (2) Preparation of modified polysulfone microporous membrane Polysulfone particles were dried in a vacuum drying oven at 120°C for 24 hours to remove residual moisture and prevent the formation of numerous bubbles during the preparation of the casting solution, resulting in pretreated polysulfone. In a 250mL three-necked flask equipped with a mechanical stirrer, 16g of the pretreated polysulfone was added, followed by 78mL of DMF and 5g of polyethylene glycol 400. The mixture was stirred in a 72°C water bath for 8.5 hours until the polysulfone was completely dissolved. The mixture was then placed in a vacuum drying oven at 62°C for 2.5 hours to remove bubbles generated during stirring, resulting in a uniform, transparent, and bubble-free casting solution. An 80μm thick polyester nonwoven fabric was then fixed onto a glass substrate. On the substrate, an automatic coating machine was used to uniformly coat the casting solution onto the upper surface of the polyester nonwoven fabric at a coating speed of 5 cm / s and a coating thickness of 80 μm. The glass substrate was then rapidly immersed in a deionized water coagulation bath at 23°C. The DMF in the casting solution rapidly diffused into the water, and the polysulfone underwent phase separation and solidified to form a microporous structure. The immersion time was 24.5 h to ensure full curing and solvent removal. The solidified polysulfone support layer and the polyester nonwoven fabric were then peeled off from the glass substrate and rinsed four times with deionized water. Subsequently, the substrate was vacuum dried at 42°C for 10 h to obtain a composite layer of modified polysulfone microporous membrane and reinforcing layer, i.e., a composite layer of support layer and reinforcing layer. (3) Modification of the transition layer 10g of alumina hydroxyl oxide nanoparticles were ultrasonically dispersed in 100mL of anhydrous ethanol for 30min, then stirred and evaporated at 80℃ to remove impurities adsorbed on the surface of the alumina hydroxyl oxide nanoparticles, improving their dispersibility in the transition layer, thus obtaining pretreated alumina hydroxyl oxide nanoparticles. 2.3g of the pretreated alumina hydroxyl oxide nanoparticles were added to 102mL of anhydrous ethanol and ultrasonically dispersed for 35min at a power of 210W. Then, 1g of polyethylene glycol was added and stirred to dissolve, resulting in a uniform transition layer coating solution. The composite layer of the support layer and the reinforcement layer was fixed on a spraying table and then... The transition layer coating liquid was uniformly sprayed onto the surface of the support layer in the composite layer of support and reinforcement layers using an air spraying method. The nozzle diameter was 0.5 mm, the spraying pressure was 0.3 MPa, the spraying distance was 15 cm, and the spraying speed was 10 cm / s. The composite layer of support and reinforcement layers coated with the transition layer coating liquid was placed in an oven at 62°C and dried for 35 min to form a transition layer with a thickness of 250 nm, thus obtaining a composite film. The hydroxyl alumina nanoparticles in the transition layer had a particle size of 70 nm. At this point, the surface hydroxyl content of the composite layer of support and reinforcement layers was significantly increased, and the hydrophilicity was enhanced, laying the foundation for subsequent bonding with surface functional layers. (4) A surface functional layer (NH2-GO / polyamide composite layer) is constructed using a dynamic interface polymerization process. Dissolve 1.55 g of m-phenylenediamine in 100 mL of deionized water by stirring to obtain a 1.55 wt.% aqueous solution of m-phenylenediamine. Add 10 g of aminated modified graphene powder to 20.5 g of the 1.55 wt.% aqueous solution of m-phenylenediamine and ultrasonically disperse for 45 min to obtain a uniform aqueous dispersion, which is used as the surface wetting solution and is denoted as aqueous solution A. Dissolve 0.55 g of m-phenylenediamine in 100 mL of deionized water by stirring to obtain a 0.55 wt.% aqueous solution of m-phenylenediamine. Add 10 g of aminated modified graphene powder to 25 g of the 0.55 wt.% aqueous solution of m-phenylenediamine and ultrasonically disperse for 45 min to obtain a uniform aqueous dispersion, which is used as the inner wetting solution and is denoted as aqueous solution B. Dissolve 0.11 g of trimesoyl chloride in 100 mL of n-hexane by stirring to obtain an oil phase solution with a concentration of 0.11 wt.%. The composite membrane in step (3) is first immersed in 105 mL of aqueous solution A for 11 min to allow m-phenylenediamine and aminated graphene to be fully adsorbed on the surface of the transition layer. After removal, the excess solution on the surface is dried with nitrogen gas. Then, it is immersed in 100 mL of oil solution and reacted at 30 °C for 40 s to carry out the first interfacial polymerization reaction. Afterward, it is quickly transferred to 105 mL of aqueous solution B and immersed at 30 °C for 5.5 min to carry out the second interfacial polymerization. Finally, it is removed and the surface is dried with nitrogen gas to obtain the reverse osmosis membrane precursor. (5) Post-processing and finished product preparation The reverse osmosis membrane precursor was first rinsed four times with deionized water, then three times with anhydrous ethanol to remove residual n-hexane, unreacted m-phenylenediamine, and trimesoyl chloride from the membrane surface. It was then dried in a vacuum drying oven at 55°C for 2.5 hours to make the membrane structure more compact and stable. The membrane was then cut to different sizes as needed and packaged in clean polyethylene bags, stored in a dry environment to obtain a seawater desalination reverse osmosis membrane based on graphene-polyamide material. Testing revealed that the surface functional layer of the graphene-polyamide-based seawater desalination reverse osmosis membrane contained 1.0 wt.% modified graphene, with the remainder being polyamide; the inner layer contained 0.3 wt.% modified graphene, with the remainder being polyamide; the surface functional layer had a thickness of 80 nm, and the modified graphene in the polyamide had a dispersion particle size of 150 nm; the support layer had a thickness of 40 μm.

[0034] Comparative Example 1 Replace aqueous solution B in step (4) with aqueous solution A, and follow the same steps as in Example 1 to obtain a reverse osmosis membrane.

[0035] Experimental Test 1. Experimental setup and parameter settings (1) The experimental setup is a reverse osmosis experimental setup. Before the experiment, the sealing performance of the experimental setup was tested: the setup was filled with deionized water, the product water valve was closed, the pressure was increased to 2.0 MPa and maintained for 30 min. If the pressure drop did not exceed 0.05 MPa, it indicated that the setup was well sealed. Then the setup pipeline was flushed with deionized water for 30 min to remove impurities and oil stains from the pipeline. (2) Feed liquid parameters: Simulated seawater was used as the feed liquid. Its formula was based on GB / T 32359-2015 "Test and Evaluation Method of Seawater Desalination Reverse Osmosis Membrane Device". The specific components are as follows: NaCl 35g / L, MgCl2 3.0g / L, CaCl2 1.0g / L, KCl 0.5g / L and Na2SO4 0.5g / L. It was prepared with deionized water, and the pH value was adjusted to 6.9-7.1. The temperature was controlled at 24.9-25.1℃. In order to verify the performance of the reverse osmosis membrane under different salt concentrations, simulated seawater with NaCl concentrations of 20g / L and 50g / L was prepared as auxiliary feed liquid. (3) Operating parameters: The conventional experimental operating pressure is set to 1.5MPa, and pressure gradients of 1.0MPa, 2.0MPa and 2.5MPa are set to conduct pressure effect experiments; the feed liquid flow rate is fixed at 1.0L / min, cross-flow filtration is adopted, the concentrate is returned to the feed liquid storage tank, and the product water is collected to the product water storage tank. (4) Control and experimental group settings: The control group used a commercially available mainstream polyamide reverse osmosis membrane (composed of a polyamide functional layer, a polysulfone support layer, and a non-woven fabric reinforcement layer, with a relatively dense structure), which achieved a desalination rate of 99.2% and a water flux of 35 L / (m²) under conditions of 1.5 MPa and 25 °C. 2 •h); The experimental group used the seawater desalination reverse osmosis membrane based on graphene-polyamide material prepared in Example 1, and the comparative example 1 group used the reverse osmosis membrane prepared in Comparative Example 1. The effective area, installation method and experimental conditions of the reverse osmosis membranes in the control group, experimental group and comparative example 1 group were completely consistent to ensure the comparability of experimental data.

[0036] 2. Experimental Procedure (1) Membrane pretreatment: After the reverse osmosis membrane is installed in the experimental device, it is first rinsed with deionized water at a pressure of 0.5 MPa for 30 min to remove the protective agent and impurities on the membrane surface and make the membrane performance reach a stable state. (2) Parameter adjustment: Inject the prepared simulated seawater into the feed liquid storage tank, turn on the constant temperature water bath to raise the temperature to 25°C, turn on the high pressure plunger pump, gradually adjust the pressure to the set value, and at the same time adjust the feed liquid flow rate to 1.0L / min. Run stably for 30 minutes to make the membrane system reach a steady state. (3) Data acquisition: During steady-state operation, data were collected every 10 minutes, including permeate flow rate, concentrate flow rate, and conductivity of feed liquid and permeate; three sets of parallel data were collected under each experimental condition, and the average value was taken as the final experimental result to reduce experimental error; (4) Change of conditions: When changing experimental conditions (such as pressure or salt concentration), the apparatus should be rinsed with deionized water for 20 minutes, then adjusted to the new experimental conditions, and run stably for 30 minutes before data acquisition, so as to avoid the previous experimental conditions from interfering with the subsequent results.

[0037] Separation performance test Separation performance is the core indicator of reverse osmosis membranes, mainly including desalination rate (SR) and water flux (J). The calculation methods for desalination rate and water flux are as follows: Desalination rate SR(%) = [(C f -C p ) / C f ]×100% Water flux J [L / (m 2 ·h)]=V / (A×t), Among them, C f The conductivity of the feed liquid is expressed in μS / cm. C p The conductivity of the produced water (μS / cm). V represents the volume of produced water (L). A is the effective area of ​​the membrane (m²)2 ), t represents the water production time (h); (1) The comparison data of membrane separation performance under normal conditions of 1.5MPa, 25℃ and NaCl concentration of 35g / L are shown in Table 1.

[0038] Table 1 Comparison of membrane separation performance under conventional conditions

[0039] Table 1 shows that the desalination rate of the experimental group membrane reached 99.70%, which was 0.50% higher than that of the control group; the water flux reached 65.6 L / (m²). 2 The desalination rate (·h) was improved by 30.6% compared to the control group, achieving simultaneous optimization of desalination rate and water flux, and solving the problem of the traditional membrane desalination rate and water flux being inversely constrained.

[0040] (2) Effect of pressure on separation performance: The effect of different operating pressures on membrane separation performance at 25℃ and NaCl concentration of 35 g / L is shown in the figure. Figure 2 The results showed that as the operating pressure increased from 1.0 MPa to 2.5 MPa, the water flux of both the experimental and control groups exhibited a linear increasing trend. The water flux of the experimental group was consistently higher than that of the control group, reaching 112 L / (m²) at an operating pressure of 2.5 MPa. 2 Regarding the desalination rate, the experimental group maintained a rate above 99.5% under all pressures, while the control group's desalination rate began to decline after the pressure exceeded 2.0 MPa, dropping to 99.0% at 2.5 MPa. This is because the modified graphene-reinforced structure of the seawater desalination reverse osmosis membrane based on graphene-polyamide material in the experimental group improved the membrane's pressure resistance, avoiding the decrease in desalination rate caused by membrane pore deformation under high pressure.

[0041] (3) The effect of different NaCl concentrations on membrane separation performance under the conditions of 1.5 MPa and 25 °C is shown in Table 2.

[0042] Table 2 Effect of different NaCl concentrations on membrane separation performance

[0043] As shown in Table 2, the water flux of the membrane in both the experimental and control groups decreased with increasing NaCl concentration, but the decrease was smaller in the experimental group. From NaCl concentration of 20 g / L to 50 g / L, the water flux of the experimental group decreased by 15.17%, while that of the control group decreased by 34.51%. In terms of desalination rate, the membrane in the experimental group maintained a high desalination rate of 99.62% even at a high salt concentration of 50 g / L, while that in the control group decreased to 98.95%. This indicates that the modified graphene sieving network of the seawater desalination reverse osmosis membrane based on graphene-polyamide material in this invention has a stronger salt ion retention capacity.

[0044] Anti-pollution performance test The antifouling performance of the membrane was tested using three typical contaminants (bovine serum albumin BSA, simulating protein contaminants; humic acid HA, simulating natural organic matter; and sodium alginate SA, simulating polysaccharide contaminants). The experimental conditions were 1.5 MPa, 25℃, and a contaminant concentration of 100 mg / L. The water flux after fouling was measured first, then the reverse osmosis membrane was cleaned, and the water flux after cleaning was measured. The membrane's antifouling performance was evaluated by flux decay rate and flux recovery rate. The calculation methods for flux decay rate and flux recovery rate are as follows: Flux decay rate (%) = [(Jo-Jt) / Jo] × 100% Flux recovery rate (%) = [(Jr-Jt) / (Jo-Jt)] × 100%, Where Jo is the initial water flux, Jt is the water flux after contamination, and Jr is the water flux after cleaning; The results of the membrane's antifouling performance test are shown in Table 3.

[0045] Table 3. Test results of the antifouling performance of the membrane.

[0046] As shown in Table 3, the flux decay rate of the seawater desalination reverse osmosis membrane based on graphene-polyamide material in the experimental group was less than 10% in all three pollutant systems, while the flux decay rate of the membrane in the control group exceeded 37%. After cleaning, the flux recovery rate of the membrane in the experimental group was higher than 92%, while that in the control group was lower than 84%. This is because the hydrophilic micro-nano rough structure (contact angle of about 32°) on the surface of the seawater desalination reverse osmosis membrane based on graphene-polyamide material in this invention forms a stable water film barrier, reducing the adsorption of pollutants. At the same time, the hydrophobic regulation effect of modified graphene inhibits the hydrophobic binding of organic matter, thus exhibiting excellent antifouling performance.

[0047] Stability test Stability testing includes long-term operational stability testing, acid-base stability testing, and oxidative stability testing. Specific test conditions and results are as follows: (1) Long-term operational stability test: The membrane was continuously operated for 90 days under conditions of 1.5 MPa, 25℃ and simulated seawater (NaCl concentration of 35 g / L), and the desalination rate and water flux were measured periodically. The results showed that during the 90-day operation, the desalination rate of the membrane in the experimental group decreased from 99.70% to 99.58%, with a fluctuation range of only 0.12%; the water flux decreased from 65.6 L / (m²) to 99.58%. 2 The concentration of ·h) decreased to 63.2 L / (m 2The membrane in the control group showed excellent long-term stability with a fluctuation range of 3.6% (·h); while the desalination rate of the membrane in the control group decreased from 99.2% to 98.75% after 90 days, and the water flux decreased from 35 L / (m³). 2 The concentration of ·h) decreased to 28.5 L / (m 2 The fluctuation range is significantly larger (·h). (2) Acid-base stability test: The membrane was immersed in hydrochloric acid solution (pH=2) and sodium hydroxide solution (pH=11) for 72 hours, respectively, and then the separation performance of the membrane was tested. The results showed that the desalination rate of the membrane in the experimental group was 99.70% and the water flux was 65.6 L / (m²) under normal conditions. 2 •h); Under pH=2 conditions, the desalination rate was 99.65%, and the water flux was 64.1 L / (m³). 2 •h); Under pH=11 conditions, the desalination rate was 99.60%, and the water flux was 63.5 L / (m²). 2 The membrane in the control group showed almost no performance degradation under normal conditions (·h); while the membrane in the control group had a desalination rate of 99.2% and a water flux of 35 L / (m³). 2 ·h); Under pH=2 and pH=11 conditions, the desalination rate dropped to 98.80% and 98.65% respectively, and the water flux decreased by more than 5%, with significant performance degradation; This is because the chemical stability of the modified graphene in the seawater desalination reverse osmosis membrane based on graphene-polyamide material in this invention improves the acid and alkali tolerance of the reverse osmosis membrane. (3) Oxidative stability test: The membrane was immersed in a 200 mg / L sodium hypochlorite solution to simulate the oxidative environment in seawater desalination for 24 hours, and then the separation performance of the membrane was tested. The desalination rate of the membrane in the experimental group was 99.70% and the water flux was 65.6 L / (m²) before immersion. 2 •h); The desalination rate after soaking was 99.45%, and the water flux was 62.8 L / (m³). 2 The performance degradation was minimal (·h); the desalination rate of the membrane in the control group was 99.2% before immersion, and the water flux was 35 L / (m²). 2 ·h); After soaking, the desalination rate decreased from 99.2% to 98.20%, and the water flux decreased by 8%, indicating a significant performance degradation. This shows that the modified graphene in the functional layer of the seawater desalination reverse osmosis membrane based on graphene-polyamide material in this invention effectively inhibits the oxidative degradation of polyamide.

[0048] Mechanical performance testing The mechanical properties of the membranes in the experimental and control groups were tested using a tensile testing machine. The samples were fixed on the tensile testing machine and stretched at a constant speed until they broke. The maximum tensile force was recorded. The sample type was set to dumbbell type, the gauge length was 25 mm, and the tensile speed was 5 mm / min. Five parallel samples were tested for each membrane sample, and the average value was taken. The results of the membrane mechanical property test are shown in Table 4.

[0049] Table 4. Membrane mechanical property test results

[0050] As shown in Table 4, the tensile strength, elongation at break, and Young's modulus of the membrane in the experimental group were all superior to those in the control group. Compared with the control group, the tensile strength of the membrane in the experimental group increased by 27.8%, and the Young's modulus increased by 50%. This is because the excellent mechanical properties of graphene in the seawater desalination reverse osmosis membrane based on graphene-polyamide material in this invention are transferred to polyamide through covalent bonding. At the same time, the gradient composite structure reduces stress concentration, thereby significantly improving the mechanical properties of the reverse osmosis membrane and meeting the mechanical strength requirements in the preparation and operation of industrial spiral wound membrane modules.

[0051] Scanning electron microscopy (SEM) analysis The surface morphology of the reverse osmosis membrane in the experimental group was observed using field emission scanning electron microscopy (FET). The accelerating voltage of the FET was 5 kV, and the sample was sputter-coated with gold (5 nm thick) to enhance conductivity.

[0052] Surface morphology: SEM images of the surface morphology of the seawater desalination reverse osmosis membrane based on graphene-polyamide material in the experimental group are shown below. Figure 3 As can be seen from the figure, the surface of the reverse osmosis membrane exhibits a composite rough structure of "micron-sized protrusions + nano-sized wrinkles". The diameter of the protrusions is about 2-5 μm and the height of the wrinkles is about 50-100 nm. The aminated modified graphene is uniformly dispersed in the polyamide without obvious agglomeration. The composite rough structure of the reverse osmosis membrane increases the specific surface area of ​​the membrane and provides more mass transfer channels for water molecules, thereby improving the water flux.

Claims

1. A seawater desalination reverse osmosis membrane based on graphene-polyamide material, characterized in that... Its structure consists of a surface functional layer, a transition layer, a support layer, and a reinforcing layer connected sequentially from the outside to the inside. The surface functional layer is a modified graphene-polyamide composite layer. The surface functional layer consists of a surface layer and an inner layer. The modified graphene content in the surface layer is 0.8-1.2 wt.%, and the remainder is polyamide. The modified graphene content in the inner layer is 0.2-0.4 wt.%, and the remainder is polyamide. The transition layer is made of alumina hydroxyl nanoparticles and polyethylene glycol.

2. The seawater desalination reverse osmosis membrane based on graphene-polyamide material according to claim 1, characterized in that... The thickness of the surface functional layer is 50-100 nm, the particle size of the modified graphene in the surface functional layer in the polyamide is 100-200 nm, the thickness of the transition layer is 200-300 nm, and the particle size of the hydroxyalumina nanoparticles in the transition layer is 50-80 nm.

3. The seawater desalination reverse osmosis membrane based on graphene-polyamide material according to claim 1, characterized in that... The thickness of the support layer is 35-50μm, and the support layer is a modified polysulfone microporous membrane.

4. The seawater desalination reverse osmosis membrane based on graphene-polyamide material according to claim 1, characterized in that... The thickness of the reinforcing layer is 65-100μm, and the reinforcing layer is made of polyester nonwoven fabric.

5. A method for preparing a seawater desalination reverse osmosis membrane based on graphene-polyamide material as described in claims 1-4, characterized in that... Includes the following steps: (1) Add anhydrous ethanol to the graphene oxide dispersion and ultrasonically disperse it. Then add silane coupling agent and stir evenly. Stir the reaction, centrifuge, wash, freeze dry to obtain aminated modified graphene powder. (2) DMF and polyethylene glycol are added to polysulfone and stirred to remove bubbles, and casting solution is obtained. The casting solution is uniformly coated on the upper surface of polyester nonwoven fabric and then immersed in deionized water. The fabric is then removed, washed, and dried to obtain a composite layer of support layer and reinforcement layer. (3) Hydroxyalumina nanoparticles were ultrasonically dispersed with anhydrous ethanol, and then polyethylene glycol was added and stirred to dissolve them to obtain a transition layer coating liquid; the transition layer coating liquid was uniformly sprayed on the surface of the support layer in the composite layer of support layer and reinforcement layer, and dried to obtain a composite film; (4) The composite membrane is immersed in aqueous solution A, taken out, dried, immersed in oil solution for one reaction, taken out, immersed in aqueous solution B for a second reaction, taken out, dried, and the reverse osmosis membrane precursor is obtained. (5) The reverse osmosis membrane precursor is washed, dried, cut, and packaged to obtain a seawater desalination reverse osmosis membrane based on graphene-polyamide material.

6. The method for preparing a seawater desalination reverse osmosis membrane based on graphene-polyamide material according to claim 5, characterized in that... In step (1), the volume ratio of graphene oxide dispersion, anhydrous ethanol, and silane coupling agent is 19-21:9-11:0.1; the concentration of graphene oxide dispersion is 0.5-0.55 mg / mL; the silane coupling agent is KH-550; the ultrasonic dispersion time is 20-30 min; the stirring reaction time is 4-5 hours; the stirring reaction temperature is 80-90℃; the centrifugation speed is 8000-8500 r / min; the centrifugation time is 15-20 min; washing is performed with anhydrous ethanol 3-4 times; and the freeze-drying time is 4 hours. The freeze-drying process takes 8-50 hours and the freeze-drying temperature is -50 to -45℃. In step (2), the ratio of polysulfone, DMF and polyethylene glycol is 3-4:15-16:1, where polysulfone and polyethylene glycol are expressed in g and DMF in mL. The stirring temperature is 70-75℃ and the stirring time is 8-9 hours. The degassing temperature is 60-65℃ and the degassing time is 2-3 hours. The soaking temperature is 23-27℃ and the soaking time is 24-25 hours. The washing is done with deionized water and the number of washings is 3-4 times. The drying temperature is 40-45℃ and the drying time is 10-12 hours.

7. The method for preparing a seawater desalination reverse osmosis membrane based on graphene-polyamide material according to claim 5, characterized in that... In step (3), the ratio of alumina hydroxyl oxide nanoparticles, anhydrous ethanol, and polyethylene glycol is 2-2.5:100-105:1, where alumina hydroxyl oxide nanoparticles and polyethylene glycol are expressed in g, anhydrous ethanol in mL, the ultrasonic dispersion time is 30-40 min, the ultrasonic dispersion power is 200-220 W, the drying temperature is 60-65 ℃, and the drying time is 30-40 min.

8. The method for preparing a seawater desalination reverse osmosis membrane based on graphene-polyamide material according to claim 5, characterized in that... In step (4), the aqueous solution A is prepared by adding aminated graphene powder to a 1.5-1.6 wt.% m-phenylenediamine aqueous solution and ultrasonically dispersing for 40-45 min to obtain aqueous solution A, with a mass ratio of m-phenylenediamine aqueous solution to aminated graphene of 2-2.1:1; the aqueous solution B is prepared by adding aminated graphene powder to a 0.5-0.6 wt.% m-phenylenediamine aqueous solution and ultrasonically dispersing for 40-45 min to obtain aqueous solution B, with a mass ratio of m-phenylenediamine aqueous solution to aminated graphene of 2.4-2.6:1; the oil phase solution is prepared by reacting pyromellitic acid chloride in n-hexane. Stir to dissolve and obtain an oil phase solution with a concentration of 0.1-0.12 wt.%. Soak in aqueous solution A for 10-12 min, react for 30-45 s, and react at 25-35 ℃. Soak in aqueous solution B for 5-6 min, react at 25-35 ℃. The volume ratio of aqueous solution A, aqueous solution B and oil phase solution is 1-1.1:1-1.1:

1. All drying is done with nitrogen. In step (5), the washing is done by rinsing with deionized water 3-4 times and then with anhydrous ethanol 2-3 times. The drying temperature is 55-60 ℃ and the drying time is 2-3 hours.

9. The method for preparing a seawater desalination reverse osmosis membrane based on graphene-polyamide material according to claim 5, characterized in that... The preparation method of the graphene oxide dispersion in step (1) includes the following steps: (a) Concentrated sulfuric acid was added to flake graphite and stirred, then potassium permanganate was added and stirred to react, resulting in mixture 1; (b) Mixture 1 is stirred to produce mixture 2; (c) Add deionized water to mixture 2, stir and react to obtain mixture 3; (d) Deionized water was first added to mixture 3, followed by hydrogen peroxide solution. The mixture was stirred and reacted to obtain mixture 4. (e) The mixture was centrifuged, separated, washed, and a precipitate was obtained; (f) The precipitate was ultrasonically exfoliated in deionized water to obtain a graphene oxide dispersion.

10. The method for preparing a seawater desalination reverse osmosis membrane based on graphene-polyamide material according to claim 9, characterized in that... In step (a), the ratio of flake graphite, concentrated sulfuric acid, and potassium permanganate is 1:22-23:3-4, where flake graphite and potassium permanganate are expressed in g, and concentrated sulfuric acid in mL. The stirring time is 30-40 min, the stirring temperature is 0-5℃, the reaction time is 2-3 hours, and the reaction temperature is 0-10℃. In step (b), the stirring time is 30-40 min, and the reaction temperature is 35-38℃. In step (c), the volume ratio of deionized water to concentrated sulfuric acid in step (a) is 2-2.5:1, the addition rate is 1-1.2 mL / min, the addition temperature is 35-38℃, the stirring time is 15-18 min, and the reaction temperature is 98-100℃. In step (d)... The concentration of hydrogen peroxide solution in step (a) is 30-32 wt.%, and the ratio of deionized water, hydrogen peroxide solution and flake graphite in step (a) is 100-110:5-5.5:

1. The deionized water and hydrogen peroxide solution are expressed in mL, and the flake graphite is expressed in g. The stirring reaction time is 30-35 min, and the stirring reaction temperature is 25-26℃. In step (e), the centrifugation speed is 5000-6000 r / min, the centrifugation time is 10-15 min, and the washing is first washed with 5-7 wt.% hydrochloric acid solution 3-4 times, and then repeatedly washed with deionized water until the pH of the washing solution is neutral. In step (f), the ultrasonic peeling time is 60-70 min, and the ultrasonic peeling power is 300-350 W.

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