Efficient Separation and High Ion Selectivity Graphene Oxide Membrane and Preparation Method and Application

Abstract

The present invention belongs to the technical field of material preparation, and discloses a highly efficient separation and highly ion-selective graphene oxide membrane, a preparation method and an application thereof. The tensile strength of the highly efficient separation and highly ion-selective graphene oxide membrane is 50 - 750 MPa, the interlayer spacing is 0.3 - 0.4 nm, the height of the sheet stacking domain is 5 - 12 nm, the Herman's orientation factor is 0.3 - 0.95, and the interlayer spacing increases to 0.32 - 0.37 nm after swelling in water. The preparation method is as follows: after the formed graphene oxide membrane material is simultaneously subjected to isotropic stretching and steam plasticization orientation treatment, it is placed in a vacuum environment at 80 - 150 °C for low-temperature reduction to obtain the highly efficient separation and highly ion-selective graphene oxide membrane; its application is: used as an ion separation membrane. The present invention can simultaneously improve the orderliness of sheet stacking and the stacking orientation in the membrane, thereby enhancing the mechanical stability and chemical stability of the membrane, and having good application prospects.

Description

Technical Field

[0001] The present invention belongs to the technical field of material preparation, and relates to a graphene oxide membrane with high-efficiency separation and high ion selectivity, a preparation method thereof, and an application thereof. Background Art

[0002] Membrane separation technology is considered to be one of the most important scientific methods to solve the global water crisis, and the performance of membrane materials is one of the key factors for the development of membrane separation technology. In recent years, nanomaterials such as nano-silica, nano-titanium dioxide, nano-silver, and carbon nanotubes (CNT) have been widely used in the development of high-performance membrane materials. In addition, due to their atomic thickness, porous or non-porous structure, solution processability, chemical stability, and thermal stability, two-dimensional (2D) materials have been studied to achieve advanced separation performance.

[0003] Two-dimensional materials such as graphene-based materials, transition metal dichalcogenides, covalent organic frameworks, metal-organic frameworks (MOF), MXenes, layered double hydroxides (LDH), and layered silicates have shown great potential in ion transport applications, especially in ion separation and storage, due to their excellent properties. In particular, 2D nanosheets are ideal materials for constructing ultrathin membranes due to their atomic thickness and micron-scale lateral dimensions. The 2D channels formed by stacking these nanosheets enable rapid and selective transport of ions or molecules.

[0004] Researchers have discovered the sieving characteristics of graphene oxide membranes (GO membranes) through research. These membranes can effectively block solutes with a radius greater than 0.45 nm, while allowing ions with a smaller hydration radius to pass through. Subsequent research further confirmed the key role of interlayer channels in the selective transport of ions and molecules. It was also proven that an ideal separation membrane should have the advantages of short channels with high permeability, precisely controllable selective channel sizes, and high chemical and mechanical stability. Therefore, the reasonable regulation of interlayer channels is crucial.

[0005] Graphene-based materials are the most studied nanoporous membranes, multilayer membranes, and mixed matrix membranes. Molecular dynamics simulation results show that the water permeability of nanoporous graphene is several orders of magnitude higher than that of traditional reverse osmosis membranes. On the other hand, like most nanomaterials, graphene-based materials have been modified for conventional separation membranes such as ultrafiltration (UF), nanofiltration (NF), reverse osmosis (RO), forward osmosis (FO), ion exchange, pervaporation, and gas separation.

[0006] GO membranes assembled from GO nanosheets exhibit excellent potential for separation performance, and the large-scale production cost of GO nanosheets is low and easy to study. However, GO membranes are vulnerable to the hydrophilicity of GO nanosheets, resulting in easy insertion of water molecules into the interlayer channels, destruction of the ordered structure of the membrane, and reduction of separation performance. The original interlayer distance of the GO membrane is about 0.45 nm, but in an aqueous solution, due to the hydration of oxygen-containing groups on the GO nanosheets, the interlayer distance will expand to about 0.9 nm, which makes the membrane unable to effectively block the transport of hydrated ions. Therefore, how to prevent the expansion of GO nanosheets during the separation process and maintain high separation performance is the key challenge faced by GO membranes.

[0007] During the preparation of GO membranes, due to the low Young's modulus and shear modulus of GO sheets, small bending stiffness and thin film elastic modulus, morphological problems such as folding, curling, and wrinkling may occur during the assembly process, as well as wrinkles caused by the edge-to-edge interaction between adjacent GO sheets, which in turn lead to problems such as low order of sheet assembly, low stacking orientation, high porosity, and uncontrollable pore distribution in the GO membrane. These problems also result in defects that hinder stress transfer in the membrane, as well as pores of different sizes and tortuous paths, reducing the ion transport efficiency and ion selectivity, and then affecting the mechanical stability and chemical stability of the graphene oxide membrane, as well as the separation efficiency and separation selectivity. Therefore, how to precisely regulate the interlayer nanochannels in the graphene oxide membrane and shorten the interlayer distance, while improving the order of sheet assembly and stacking orientation, is crucial for improving stability and separation performance.

[0008] In order to fully exploit the theoretical advantages of GO membranes, researchers have proposed various technologies aimed at developing stable, scalable, and highly permeable / selective GO membranes to ensure precise regulation of the interlayer nanochannels in the GO membrane, shortening the interlayer distance, while improving the order of sheet assembly and stacking orientation, thus significantly enhancing the stability and separation performance of GO membranes is crucial.

[0009] Reference 1 (ACS Nano, 2022, 16(6): 8869-8880) proposed a chemical structure engineering strategy to reduce the edge carboxyl groups of GO to achieve the spontaneous ordered stacking of GO (GO-m) with trace edge carboxyl groups, improving the packing density. This is because the reduction of edge carboxyl groups weakens the interlayer hydrogen bond interaction, reduces the interfacial friction at the atomic scale between the sheets, helps to improve the packing density, and the GO membrane obtained from low-carboxyl GO has a higher degree of orientation, with a Herman's orientation factor of 0.94 (greater than 0.87 of the high-carboxyl content membrane), the full width at half maximum (FWHM) is reduced by 7°, with a higher degree of orientation, a tensile strength of 631 MPa, and a fracture energy of 3.47 MJ·m -3However, there are still limitations in further improving the sheet stacking density and eliminating the pores between stacks, making it difficult to elevate the orderliness and orientation of the stacking structure to a higher level.

[0010] In reference 2 (Nano Letter 2017, 17, 2928−2933), the self-assembly arrangement of GO was regulated by controlling the deposition rate, making the π-π domains on the sheets opposite to each other and the oxidized regions opposite to each other, achieving a good interlayer nanostructure, with the desalination rate increased by 1.8 - 4 times, the water permeation rate 2.5 - 4 times faster, and better size-dependent sieving performance (Na + rejection rate increased to 2 times). However, this method cannot increase the stacking density between sheets to a greater extent and cannot regulate the stacking orientation.

[0011] Reference 3 (Nano Lett. 2023, 23, 9641-9650) mentioned that the wrinkles on the GO sheets were flattened by vortex shear, and they were tightly stacked into a super-flat GO membrane with a Newton's ring interference pattern. As the mechanical stirring speed increased, the interlayer spacing of the GO membrane decreased, the stability of the interlayer structure increased, the water flux increased by 3 times, and for K + / Mg 2+ ions, the separation factor was about 57.92, and for Li + / Mg 2+ and K + / Mg 2+ in actual brine, it showed good separation effects, and the separation factors reached about 68.02 and 379.17 respectively at 9 h. However, the process of flattening by vortex shear is difficult to precisely control the stacking of different thicknesses, resulting in inconsistent interlayer spacing and orientation distribution in the GO membrane, affecting the overall separation performance of the membrane. In addition, this method cannot prepare high-orientation membranes on a large scale.

[0012] Patent CN118239483A discloses a method for preparing a self-supporting graphite film and a soft X-ray detector. This method mentions using the circumferential shear formed during the centrifugal escape of the solvent to orient the sheets, preparing a composite film with controllable size, orientation, and humidity, and then using a controllable phase separation technique to achieve the rapid separation of the GO film and the substrate. The film prepared by this method has a high degree of orientation, which can reach 98.6%. However, the time for preparing the film by this method is long, and the cost and energy consumption are high, making it impossible to be popularized on a large scale.

[0013] Reference 4 (Nano-Micro Lett. 2024, 16:17) mentions that in-plane mechanical stretching is performed during the drying process to inhibit the inward shrinkage caused by capillary forces generated during solvent evaporation, eliminate wrinkles in graphene oxide nanosheets, and achieve high in-plane orientation of graphene oxide nanosheets. After reduction, a graphene film is obtained for high thermal conductivity applications. However, when the external force is unloaded, the induced orientation structure may partially rebound and cannot maintain a stable in-membrane structure.

[0014] Reference 5 (Environmental Science & Technology Letters, 2020, 7(4): 273-279) mentions using three different reduction methods to study the influence of the wrinkle density of GO membranes. Compared with rGO membranes reduced by thermal annealing in vacuum and HI (hydroiodic acid) vapor, the rGO membrane prepared by thermal reduction in air exhibits the highest water permeability and NaCl rejection rate. This is because the rGO membrane reduced in air has the lowest wrinkle density, which inhibits the penetration of non-selective ions and improves the separation selectivity. The water permeability is 1.05 LMH / bar, and the NaCl removal rate reaches 83%. However, the increase in membrane pores and the decrease in lamellar order during the reduction process cannot meet the requirements of finer sieving.

[0015] Therefore, it is of great significance to develop a graphene oxide membrane with high separation efficiency and high ion selectivity, as well as its preparation method and application, to solve the above problems. Summary of the Invention

[0016] The object of the present invention is to solve the problems existing in the prior art and provide a graphene oxide membrane with high separation efficiency and high ion selectivity, as well as its preparation method and application.

[0017] To achieve the above object, the technical solution adopted by the present invention is as follows:

[0018] A preparation method of a graphene oxide membrane with high separation efficiency and high ion selectivity. After the formed graphene oxide membrane material is simultaneously subjected to isotropic stretching and steam treatment, it is placed in a vacuum environment at 80-150 °C for low-temperature reduction to obtain a partially reduced graphene oxide membrane, that is, a graphene oxide membrane with high separation efficiency and high ion selectivity.

[0019] The steam used for steam treatment is plasticizing steam, which is formed by the evaporation of a plasticizing solvent that has a plasticizing effect on the graphene oxide membrane material. The plasticizing solvent is ethanol or isopropanol.

[0020] When the thickness of the graphene oxide membrane material is ≤ 10 μm, the device for simultaneously performing isotropic stretching and steam treatment on the graphene oxide membrane material includes a solvent pool a and a heating device a; the top of the solvent pool a is a vertically arranged cylinder a, which is divided into upper and lower layers and is detachably connected by 2m membrane fixing screws a, where m > 2, and the 2m membrane fixing screws a are circumferentially and evenly distributed around the central axis of the cylinder a; the heating device a is used to heat the solvent pool a; after the solvent vapor stress in the closed environment contacts the graphene oxide membrane material fixed above, it is transformed into an isotropic tensile stress, thereby realizing the simultaneous isotropic stretching and steam treatment of the graphene oxide membrane material; the amount of the plasticizing solvent is 30 - 100 mL, the heat preservation temperature after the plasticizing solvent vaporizes is 90 - 105 °C, the generated vapor pressure stress is 1200 - 20000 mmHg, and the heat preservation time after the plasticizing solvent vaporizes is 12 - 24 h. When using this device, since the thickness of the graphene oxide membrane material is relatively thin, the steam can penetrate into the membrane. As the reaction time prolongs, uniform heating is ensured, and the vapor pressure generated by the rapid diffusion of solvent molecules assists in stress control at the membrane edge, enabling tensile stress to be generated along the perimeter of the membrane. Therefore, coplanar tensile orientation under the assistance of vapor pressure is achieved;

[0021] When the thickness of the graphene oxide membrane material is > 10 μm, the device for simultaneously performing isotropic stretching and steam treatment on the graphene oxide membrane material includes a solvent pool b, a heating device b, a deformable tube, and a regulator; the bottom of the deformable tube is hermetically connected to the top of the solvent pool b, the top of the deformable tube is a vertically arranged cylinder b, which is divided into upper and lower layers and is detachably connected by 2m membrane fixing screws b, where m > 2, and the 2m membrane fixing screws b are circumferentially and evenly distributed around the central axis of the cylinder b; the regulator is used to control the radial outward expansion of the cylinder b; the heating device b is used to heat the solvent pool b; by controlling the outward extension of the deformable tube through the regulator, during the extension process of the deformable tube, it generates an epitaxial biaxial tensile displacement of 1.5 mm - 3 mm on the circumferential boundary of the graphene oxide membrane material in contact with it, thereby realizing the simultaneous isotropic stretching and steam treatment of the graphene oxide membrane material. Since the thickness of the graphene oxide membrane material is too large, the steam penetration effect will be weakened, making it impossible to complete the plasticizing tensile orientation inside and on the upper layer of the membrane. Therefore, an additional in-plane isotropic stretch needs to be applied to the graphene oxide membrane material to ensure that the graphene oxide membrane material completes the plasticizing orientation process under a uniform mixed steam environment and isotropic stretching;

[0022] Adjust the volume of the plasticizing solvent according to the area and thickness of the graphene oxide membrane material, which can be simplified to adjust the volume of the plasticizing solvent according to the mass area density (D): when 0 < D ≤ 5, 30 mL; when 5 < D ≤ 10, 50 mL; when D > 10, 100 mL; the unit of D is mg·cm -2 .

[0023] When the film thickness ≤ 10 μm, the hydrogen bond network between GO sheets dominates, and the in-plane fracture toughness is relatively low (~1 MPa·m¹ / ²), but the isotropic tensile stress generated by the vapor is sufficient to initiate elastic-dominated uniform deformation; while when the film thickness > 10 μm, the stress non-uniformity (the ratio of the stress on the film interior to that on the film surface) under pure vapor loading is large, and an external mechanical tension is required to provide a compensating stress gradient. That is, due to the excessive thickness, the diffusion path of the plasticized vapor in the film increases, and the permeation effect is significantly weakened, making it impossible to complete the tensile orientation of the interior and outer layers of the film. Therefore, an additional in-plane isotropic tension needs to be applied to the graphene oxide film material to ensure that the graphene oxide film material completes the reduction orientation process under a uniform mixed vapor environment and isotropic tension.

[0024] When the thickness of the graphene oxide film material ≤ 10 μm, the graphene oxide film forms a closed cylindrical reaction chamber after being circumferentially fixed by vertically arranged cylinders a and film fixing screws a, forming an axisymmetric constraint boundary condition system. The saturated vapor pressure of the plasticized solvent in the system is controlled by the constant temperature field. When the volume and temperature of the solvent reach the conditions for generating the saturated vapor pressure, its vapor molecules penetrate into the interlayer domain of graphene oxide through Knudsen diffusion. The plasticized vapor penetration reduces the interlayer slip barrier, making the film enter a highly plastic state and generating a vapor plasticization effect; at the same time, the vapor pressure difference inside and outside generates a uniform normal stress distribution in the film plane. Constrained by the axisymmetric boundary, the graphene oxide film undergoes plane equibiaxial tensile deformation, and its strain tensor satisfies the isotropic condition. Therefore, the isotropic tension and vapor treatment of the graphene oxide film material are achieved simultaneously.

[0025] When the thickness of the graphene oxide film material > 10 μm, a circumferential displacement loading component (deformable tube and regulator) is integrated on the basis of the original closed vapor chamber. When the outward extension of the deformable tube is controlled by the regulator, during the extension of the deformable tube, it generates an external equibiaxial tensile displacement (△L) on the circumferential boundary of the film in contact with it, thereby generating an external tensile stress. The external tensile stress forms a uniform strain field in the plane. Therefore, the isotropic tension and vapor treatment of the graphene oxide film material are achieved simultaneously.

[0026] When the present invention simultaneously performs isotropic stretching and steam treatment on the formed graphene oxide membrane material, the plasticizing steam molecules can penetrate between the graphene oxide layers to weaken the intermolecular van der Waals forces and improve the deformability of the sheets. Isotropic stretching can remove or reduce the wrinkles, creases and other irregularities of the sheets, enabling them to be aligned and assembled more uniformly, improving the assembly orderliness of the sheets (more compact and orderly interlayer assembly), increasing the interlayer bonding force (decreasing the interlayer spacing), and increasing the orientation degree of the sheet stacking domain (increasing the stacking domain density and reducing the internal pores). The improvement of the interlayer assembly orderliness, the reduction of the interlayer spacing and the increase of the orientation degree of the sheet stacking domain make the penetration path of water and ions in the membrane shorter, accelerate the penetration rate, and significantly improve the transport efficiency. At the same time, the water permeation flux and rejection rate are improved; in addition, the finely adjustable interlayer spacing can achieve high selectivity for screening specific substances, so that the high-efficiency separation and high ion selectivity graphene oxide membrane shows more excellent performance in ion separation applications.

[0027] The specific action mechanism of the plasticizing steam is as follows: As Figure 1 shown in (a) below, when performing monovalent / divalent ion aqueous solution dialysis separation on untreated graphene oxide, due to the disordered stacking of the interlayer sheets in the membrane and many irregular voids, the monovalent and divalent ions cannot be completely separated, and the penetration path of water is tortuous and the penetration rate is slow; as Figure 1 shown in (b) below, when performing plasticizing solvent steam-assisted coplanar stretching on the graphene oxide membrane, the plasticizing steam molecules can penetrate between the graphene oxide sheets through diffusion. When using ethanol or isopropanol as the plasticizing solvent, the solvent molecules generate hydrogen bonds, van der Waals forces and wetting effects with the oxygen-containing functional groups on the graphene oxide, can penetrate between the graphene oxide sheets, and generate hydrogen bond and van der Waals force interactions with the sheets, reducing the interlayer cohesive force and the interlayer slip resistance, thereby improving the deformability and slip ability of the sheets; at the same time, the solvent molecules replace the positions occupied by some of the water molecules bound in the layer, reducing the number of water molecules bound between the layers; the plasticizing steam can promote the increase of the molecular mobility on the sheet surface, and some molecular segments are "softened" by the plasticizing steam molecules in the steam. This softening effect promotes the increase of the translational entropy, rotational entropy and motion entropy of the sheets, and the sheets are more likely to reach an ordered stacking state after being flattened and stretched; at the same time, due to the wetting effect of the plasticizing steam molecules, part of the internal stress is released, as Figure 1As shown in (c), under isotropic stretching, the lamellae unfold more uniformly, eliminating the wrinkles within the lamellae and the irregular stacking between the lamellae, thereby forming a more compact and ordered assembly structure. Further, under continuous isotropic stretching, the lamellae are guided to be flatter in all directions within the plane, and the lamellae are more uniformly arranged, avoiding the anisotropy formed by directional rearrangement, reducing the overall disorder of stacking, promoting uniform stacking arrangement, and increasing the stacking orientation. In addition, after the plasticization is completed, as the plasticization vapor slowly volatilizes, the lamellae tend to rearrange into a more compact structure, causing the stacking height to continuously increase and the layer spacing to gradually decrease accordingly. This change leads to a gradual increase in the binding force between the lamellae and an increase in the failure stress of interfacial slip. Further, the ordered arrangement and orientation of the stacking domains of the lamellae are enhanced with rearrangement, resulting in a gradual reduction of the disordered pores within the membrane and an increase in the failure stress at the domain interfaces. Therefore, the overall tensile strength of the membrane increases, as Figure 1 shown in (d). At this time, when the treated graphene oxide membrane is subjected to dialysis separation in a monovalent / divalent ion aqueous solution, small-sized monovalent ions can be more fully separated, and the separation selectivity of monovalent / divalent ions is greatly increased. Moreover, the permeation path of water molecules within the lamellae is shorter and more efficient, and the water permeability is correspondingly increased. Based on the above analysis, the overall layer spacing within the membrane is precisely controllable, the interlayer binding force is increased, and the disordered defects are reduced, enhancing the mechanical stability and chemical stability of the membrane.

[0028] Isotropic stretching is more conducive to improving the performance of graphene oxide membrane materials compared to uniaxial and biaxial stretching in the prior art. Because during isotropic stretching, the tensile stress on the periphery of the membrane is evenly distributed in all directions. Compared with uniaxial and biaxial stretching, there are obvious differences in the influence of the stress distribution in the membrane and the lamellar orientation: (1) Isotropic stretching: When isotropic stretching is performed on the membrane, the stress will be evenly distributed from the center outwards, and will not preferentially stretch the lamellae in a specific direction. The uniform stretching will cause the lamellae in the membrane to be simultaneously subjected to the same tensile force in all directions, flatten and stretch along all directions in the plane, releasing wrinkles and folds caused by uneven stress. The multi-directional stress helps to flatten the lamellae comprehensively and reduce uneven folds. Isotropic stretching helps to form an ordered packing without deviation in a specific direction, which can prompt the lamellae to more easily reach a stable ordered state and reduce complex entanglements. Under isotropic stretching, the lamellae are guided to be more evenly arranged in all directions within the plane, avoiding anisotropy formed by directional rearrangement, reducing the disorder of the overall packing domain, and promoting the uniform arrangement of the packing domain. Therefore, the lamellar orientation will be evenly distributed in the plane direction, without causing inconsistent packing domain distribution due to obvious single orientation, and avoiding stress concentration in any local direction. (2) Uniaxial stretching: The stress is applied in a single direction, causing the stress to concentrate in the stretching direction. The lamellae in the membrane flatten along the uniaxial direction and are roughly parallel to the stretching direction and rearrange, while shrinkage (Poisson effect) will occur in the direction perpendicular to the uniaxial direction, resulting in an increase in the order and orientation of the lamellae along the stretching direction, but being significantly insufficient in the direction perpendicular to the stretching direction; (3) Biaxial stretching: Stress is applied in orthogonal directions, and it is necessary to control the stress to be consistent in two directions. The lamellae in the membrane tend to flatten and rearrange along the biaxial directions, enhancing the ordered packing and orientation of the lamellae to a certain extent, especially in the two principal axis directions. However, the release of wrinkles and the ordered arrangement in the non-principal stress axes are not as good as isotropic stretching, which is prone to the problem of excessive local direction stress concentration load.

[0029] After the graphene oxide membrane undergoes steam plasticization and isotropically stretching, the order and controllability of the internal structure of the membrane increase. During the aqueous phase separation process of the graphene oxide membrane, it will inevitably be swollen by water molecules. The swelling stems from the hydrogen bond interaction between the oxygen-containing functional groups on graphene oxide and water molecules or other polar solvents. In the swollen state, the interlayer spacing of the graphene oxide membrane increases (15 - 60 Å, specifically depending on the pH value of the solution, ionic strength, or external pressure), significantly reducing the separation ability and selectivity of the membrane, and even leading to the dissociation of the membrane. Therefore, in order to maintain the high-efficiency separation and high selectivity of the graphene oxide membrane, the graphene oxide membrane is reductively treated at low temperature to partially remove the oxygen-containing functional groups (hydroxyl and epoxy groups) on the sheets, so as to reduce its interaction with water molecules or other polar solvents, thereby inhibiting swelling. Meanwhile, the π-π structure on the partially reduced graphene layers increases, and the interlayer π-π interaction is enhanced, improving the overall stability of the membrane. At the same time, the partially reduced GO shows higher hydrophobicity, increasing the water permeation rate between the layers and stabilizing the separation selectivity of the membrane.

[0030] As a preferred technical solution:

[0031] For the preparation method of the high-efficiency separation and high ion-selectivity graphene oxide membrane as described above, the thickness of the graphene oxide membrane material is 10 nm - 50 μm.

[0032] For the preparation method of the high-efficiency separation and high ion-selectivity graphene oxide membrane as described above, the regulator includes a displacement bracket, a pressing disk, an upper bracket, a limiting structure, and a lower bracket;

[0033] The displacement bracket is a conical cap-shaped structure with the tip facing upward, including 2n inclined rods I, where n > 3. The upper ends of the 2n inclined rods I are simultaneously connected to the center of the lower surface of the pressing disk, and the lower ends are circumferentially distributed around a point o, and the point o is located on the central axis of the pressing disk. The pressing disk is coaxial with the cylinder b;

[0034] The upper bracket includes 2n horizontal rods, and the 2n horizontal rods are radially distributed around the point o. The two ends of the horizontal rod are respectively denoted as the a end and the b end, and the a end is closer to the point o than the b end. The a ends of the 2n horizontal rods are respectively hinged to the lower ends of the 2n inclined rods I in one-to-one correspondence;

[0035] The limiting structure restricts the 2n horizontal rods to move only along their own length directions;

[0036] The b ends of adjacent two horizontal rods are each connected by one arc bar. At least one group of opposite arc bars consists of left, middle, and right sections. The middle section consists of a separated inner layer and outer layer. The outer layer of the middle section is fixedly connected to the left section, and the inner layer of the middle section is fixedly connected to the right section; all the arc bars enclose a ring, and the ring extends vertically downward to form a circular tube;

[0037] The lower bracket includes 2n inclined rods II. The 2n inclined rods II are distributed in an umbrella shape around the central axis of the cylinder b. The angle between the inclined rod II and the central axis of the cylinder b is 100-105°. The lower layer of the cylinder b extends radially outward and is connected to the upper ends of the 2n inclined rods II. The lower ends of the 2n inclined rods II are connected to the circular tube.

[0038] When the pressing plate is subjected to a downward pressure, it will undergo a downward displacement. This displacement is transmitted to the upper bracket through the displacement bracket, causing the upper bracket to also move outward. Then, the displacement of the upper bracket is transmitted to the lower bracket, causing the lower bracket to also move outward. Finally, the displacement of the lower bracket is transmitted to the deformable tube, causing the deformable tube to extend outward. During the outward extension of the deformable tube, it exerts a coplanar tensile displacement on the edge of the membrane in contact with it, thereby generating tensile stress.

[0039] For graphene oxide membrane materials with a thickness greater than 10 μm, due to the large thickness, the steam penetration effect is weakened, and it is impossible to complete the plasticization and tensile orientation inside and on the upper layer of the graphene oxide membrane material. It is necessary to start the stretching device to apply an additional in-plane isotropic stretch to the graphene oxide membrane material to ensure that the graphene oxide membrane material completes the plasticization and tensile orientation process under a uniform mixed steam environment and isotropic stretch. Among them, the maximum tensile displacement (△L) is determined by the initial diameter L0 of the graphene oxide membrane material, and the shrinkage rate of the unstretched membrane on the plane before and after plasticization and tensile orientation is , the maximum tensile displacement △L = (L0 * ) / 2.

[0040] The shrinkage rate of the graphene oxide membrane material on the plane (%) can be calculated through experiments (that is, placing the graphene oxide membrane material in a vacuum environment at 100 °C for 12 h, continuously evacuating during this period, and measuring its average diameter L after taking it out and cooling it to room temperature T ), and the calculation formula for the shrinkage rate is as follows:

[0041] ;

[0042] The tensile displacement is controlled by the pressing plate above the device. Under the pressing plate is the length S of the inclined rod I that can control the edge to move outward (the initial angle between the inclined rod I and the pressing plate is 45°), which is used to control the outward movement of the upper bracket and the lower bracket. When controlling the downward pressing distance (the height measuring bracket can record the change), the outward movement of the lower bracket causes the deformable tube to extend outward, and then generates an outward coplanar tensile displacement on the graphene oxide membrane material fixed on the deformable tube. Since the maximum tensile displacement is related to the maximum pressing displacement, the calculation formula for the maximum pressing displacement △H is as follows:

[0043] ;

[0044] Wherein, S is the length of the inclined rod I of the displacement bracket, and H is the initial height of the displacement bracket (i.e., the vertical distance between the pressing plate and the upper bracket);

[0045] Substitute the planar shrinkage rate and the calculation formula of the initial diameter L0 of the graphene oxide membrane material, and the final calculation formula is:

[0046] ;

[0047] Therefore, after determining the length S of the displacement bracket and the initial height H of the displacement bracket, the maximum pressing displacement can be adjusted according to the initial diameter L0 of the graphene oxide membrane material and the diameter L of the graphene oxide membrane material after shrinkage T to adjust the maximum pressing displacement, and the actual pressing displacement does not exceed the maximum pressing displacement, which is adjusted according to the required stretching ratio. The stretching ratio is y (0 < y < 1), and the actual pressing displacement is y * △H. Adjust the actual pressing displacement according to the application requirements.

[0048] In the present invention, the designed lower bracket includes 2n inclined rods II. On the one hand, it is to disperse the extended external force to the entire plane, reduce the stress concentration in a single direction, and avoid stress overload in a local direction; on the other hand, it is to provide a small displacement to cause a small deformation of the deformable tube.

[0049] In the preparation method of the high-efficiency separation and high-ion-selectivity graphene oxide membrane as described above, the regulator further includes a height measuring bracket, which is vertically arranged on one side of the pressing plate and fixedly connected to the upper bracket.

[0050] In the preparation method of the high-efficiency separation and high-ion-selectivity graphene oxide membrane as described above, the forming method of the graphene oxide membrane material is: vacuum filtering the graphene oxide aqueous solution into a film, spin-coating multiple times to form a film, casting on a substrate and evaporating to assemble into a film, or continuously scraping to form a film, and then drying and forming to obtain the graphene oxide membrane material; wherein, when using vacuum filtration to form a film, the concentration of the graphene oxide aqueous solution used is 0.5 - 1.5 mg·g -1 , when using spin-coating multiple times to form a film, the concentration of the graphene oxide aqueous solution used is 1 - 5 mg·g -1 , when using casting on a substrate and evaporating to assemble into a film, the concentration of the graphene oxide aqueous solution used is 6 - 8 mg·g -1 , when using continuous scraping to form a film, the concentration of the graphene oxide aqueous solution used is 20 - 40 mg·g -1 .

[0051] The preparation method of the highly efficient separation and highly ion-selective graphene oxide membrane as described above, the interlayer spacing of the graphene oxide membrane material is 0.35 - 0.8 nm, the tensile strength is 20 - 300 MPa, the height of the lamellar stacking domain is 3 - 9 nm, and the Herman's orientation factor is 0.2 - 0.5; after the graphene oxide membrane material swells in water, the interlayer spacing increases to 0.45 - 1 nm.

[0052] The present invention also provides a highly efficient separation and highly ion-selective graphene oxide membrane prepared by using the preparation method described in any one of the above. The tensile strength of the highly efficient separation and highly ion-selective graphene oxide membrane is 50 - 750 MPa, indicating that the mechanical stability has been improved. The interlayer spacing is 0.3 - 0.4 nm, the height of the lamellar stacking domain is 5 - 12 nm, and the Herman's orientation factor is 0.3 - 0.95; after the highly efficient separation and highly ion-selective graphene oxide membrane swells in water, the interlayer spacing increases to 0.32 - 0.45 nm. "The height of the membrane stacking domain" characterizes the orderliness of lamellar stacking; "the Herman's orientation parameter S of the membrane" characterizes the spatial arrangement and orientation distribution of two-dimensional lamellae, quantifies whether the two-dimensional lamellar stacking domain has a consistent arrangement direction, that is, the degree of orientation of the internal structure. The range of the orientation factor is 0 - 1. When the orientation factor is 0, the lamellar stacking domain is distributed in a completely random manner. When the orientation factor is 0.5, the lamellar stacking domain shows a partially ordered arrangement, but there are still randomly distributed stacking domains. When the orientation factor is 1, the lamellar stacking domain is arranged along a consistent direction.

[0053] The present invention also provides the application of the highly efficient separation and highly ion-selective graphene oxide membrane as described above, used as an ion separation membrane;

[0054] Using the graphene oxide membrane material as an ion separation membrane, the water permeability is 10 - 93 LMH / bar, the interception rate of inorganic salts is 10 - 50%, the interception rate of dyes is 70 - 90%, and the divalent / monovalent ion sieving selectivity factor is 1 - 3; after 120 hours of continuous testing, the water permeability of the graphene oxide membrane material decreases by 50 - 80%;

[0055] The water permeability of the graphene oxide membrane with high-efficiency separation and high ion selectivity is 30 - 600 LMH / bar. LMH represents liters per square meter per hour (L / m²·h), and bar is a pressure unit. LMH / bar is used to describe the water permeation ability of the graphene oxide membrane with selectivity under a unit pressure difference. A higher LMH / bar indicates a larger water flux under a lower pressure difference, suggesting more efficient separation ability and lower energy consumption. The rejection rate of inorganic salts is 70 - 95%, the rejection rate of dyes is 85 - 99%, and the divalent / monovalent ion sieving selectivity factor is 10 - 50. After 120 hours of continuous testing, the water permeability of the graphene oxide membrane with high-efficiency separation and high ion selectivity decreased by 10 - 20%, indicating a significant improvement in chemical stability.

[0056] Beneficial effects:

[0057] (1) The steam-assisted isotropic stretching and orientation method adopted in the present invention can simultaneously improve the in-plane lamellar packing order and stacking orientation of the membrane, thereby enhancing the mechanical stability and chemical stability of the membrane, and precisely regulating the interlayer nanochannels to improve the permeation efficiency and separation selectivity.

[0058] (2) The finely adjustable interlayer spacing of the present invention can achieve high selectivity for screening specific substances, so that the graphene oxide membrane with high-efficiency separation and high ion selectivity exhibits more excellent performance in ion separation applications. Description of the drawings

[0059] Figure 1 It is a schematic diagram of the changes in the in-plane structure, water transport, and ion sieving selectivity of the graphene oxide membrane of the present invention before and after steam plasticization stretching; in the figure, a represents the disordered packing between irregular GO sheets in the graphene oxide membrane, and the water transport channels are tortuous and cannot screen specific ions; b represents that solvent molecules penetrate the interlayer of the graphene oxide membrane to weaken the interlayer van der Waals force and improve the sheet slip ability; c represents that the sheets in the graphene oxide membrane tend to be flatly assembled, the interlayer spacing decreases, and the in-plane assembly order and stacking orientation increase; d represents that the transport path in the graphene oxide membrane is shortened, the water permeation flux increases, the solute rejection rate increases, and the ion selectivity increases;

[0060] Figure 2 It is a schematic diagram of the isotropic stretching and steam treatment device in Example A1 of the present invention;

[0061] Figure 3 It is a top view of the isotropic stretching and steam treatment device in Example A1 of the present invention;

[0062] Figure 4Schematic diagram of the isotropic stretching and steam treatment device in Embodiment A2 of the present invention; in the figure, 45° is the initial angle; S is the length of the inclined rod I of the displacement bracket; H is the initial height of the displacement bracket, that is, the vertical distance between the pressing disc and the upper bracket; △H is the maximum pressing displacement; △L is the maximum stretching displacement;

[0063] Figure 5 Top view of the regulator in Embodiment A2 of the present invention;

[0064] Figure 6 Side view of the middle section of the arc strip in the upper bracket of the present invention;

[0065] Among them, 1 - solvent pool a, 2 - cylinder a, 3 - membrane fixing screw a, 4 - arc strip, 5 - solvent pool b, 6 - height measuring bracket, 7 - limiting structure, 8 - membrane fixing screw b, 9 - deformable tube, 10 - displacement bracket, 11 - pressing disc, 12 - upper bracket, 13 - lower bracket. Specific embodiments

[0066] The present invention will be further described below in conjunction with specific embodiments. It should be understood that these embodiments are only used to illustrate the present invention and not to limit the scope of the present invention. In addition, it should be understood that after reading the content taught by the present invention, those skilled in the art can make various changes or modifications to the present invention, and these equivalent forms also fall within the scope defined by the appended claims of this application.

[0067] The test methods for relevant performance indicators in the following examples and comparative examples are as follows:

[0068] Mass area density D: Mass area density D = concentration of graphene oxide aqueous solution (mg·g -1 ) × mass of graphene oxide aqueous solution (g) / area of graphene oxide membrane material (cm 2 ), with the unit of mg·cm -2 .

[0069] Layer spacing: The highly efficient separation and highly ion-selective graphene oxide membranes and graphene oxide membrane materials prepared in each example were used as specimens respectively, and then the specimens were subjected to X-ray diffraction (XRD) tests. According to the obtained diffraction patterns, combined with the Bragg's law equation (nλ = 2dsinθ), the layer spacing d was calculated by substituting the ray wavelength λ, diffraction angle θ, and diffraction order n (n is 1).

[0070] Height of the lamellar stacking domain: The highly efficient separation and highly ion-selective graphene oxide membranes and graphene oxide membrane materials prepared in each example were used as specimens respectively, and then the specimens were subjected to XRD tests. According to the obtained diffraction patterns, combined with the Scherrer formula (L c= Kλ / FWHM·cosθ), substitute the Scherrer constant K (K value is taken as 0.9), the X-ray wavelength λ, the diffraction peak position angle θ of the ordered stacking domain, and the full width at half maximum FWHM of the XRD diffraction peak (that is, the difference in the diffraction angle 2θ at half of the diffraction peak peak value is the full width at half maximum of the XRD diffraction peak) to calculate the stacking domain height L c 。

[0071] Tensile strength: Take the highly efficient separation and highly ion-selective graphene oxide membranes and graphene oxide membrane materials prepared in each example as specimens respectively. When the thickness of the specimen ≤ 10 μm, use a tensile-compression force tester (model Mark-10 IntelliMESUR 2.3.1 from the United States) to test the tensile strength of the specimen. When the thickness of the specimen > 10 μm, use an electronic universal material testing machine (model INSTRON 5969) to test the tensile strength of the specimen.

[0072] Herman's orientation factor: Take the highly efficient separation and highly ion-selective graphene oxide membranes and graphene oxide membrane materials prepared in each example as specimens respectively. Then use a small-angle X-ray scattering instrument (SAXS) at the BL16B1 beamline of the Shanghai Synchrotron Radiation Facility to obtain the scattering image of the specimen, obtain the scattering intensity distribution of the diffraction spot, and finally process the scattering intensity distribution with the azimuth angle as a variable to obtain the scattering intensity I( ), obtain the weighted average ⟨cos 2 > of the scattering intensity at different azimuth angles through integration, and obtain Herman's orientation factor according to the calculation formula of Herman's orientation factor. The calculation formula is: Herman's orientation factor = 。

[0073] Water permeability: Take the graphene oxide membranes prepared in each example and the highly efficient separation and highly ion-selective graphene oxide membranes used as ion separation membranes as specimens respectively. Then install the specimens on a nanofiltration test device and use ultrapure water (conductivity below 0.1 μS / cm) to test at a set pressure. The pressure range is 1 - 10 bar (adjusted according to the thickness of the specimen), record the amount of water passing through the specimen at certain time intervals, and calculate the water permeation flux J (L / m²·h) according to the formula. The calculation formula is: , where V is the volume of the permeate, in L; A is the effective filtration area of the specimen, in m 2 ; △t is the filtration time, in h.

[0074] Inorganic salt rejection rate: Take the highly efficient separation and highly ion-selective graphene oxide membranes used as ion separation membranes in each example as specimens respectively. The effective test area of the specimen is 13.8 cm 2, first configure Solution A (the concentration of lithium chloride is 2 g / L -1 , the concentration of potassium chloride is 2 g / L -1 , the concentration of sodium chloride is 2 g / L -1 , and the solvent is water). Then, fix the sample in the middle of the nanofiltration membrane test device through anodic aluminum oxide membranes (pore size 100 nm, porosity 10%) above and below the sample. Load 50 mL of Solution A into the left cell of the device as the feed liquid, and load 50 mL of ultrapure water (driving solution) into the right cell of the device. To reduce concentration polarization, place magnetic stirrers in both cells of the device and stir at a speed of 500 rpm. Apply a pressure of 0.5 MPa at 25 °C for 1 h to obtain a stable flux. Subsequently, regularly extract 1 mL of solution from both the left and right sides, and use inductively coupled plasma optical emission spectrometry (ICP-OES) to measure the changes in the concentrations of lithium ions, potassium ions, and sodium ions in the solutions on both sides until the concentrations of the solutions in two consecutive samplings do not change, then stop sampling and testing. Finally, collect the permeate and the concentrate, use ICP-OES to measure the ion concentrations in the permeate in the right cell and the concentrate in the left cell, and then obtain the rejection rate of the solute (i.e., the rejection rate of inorganic salts) according to the calculation formula. Then, test the rejection rate of the solute for the samples prepared in the same example as described above and finally calculate the average value (thoroughly clean the pipeline with deionized water after each test to ensure the accuracy of the experimental results); among them, the calculation formula for the rejection rate of inorganic salts is: , where, C P is the mass concentration of the solute in the permeate, is the mass concentration of the solute in the feed liquid.

[0075] Dye rejection rate: Use the highly efficient separation and highly ion-selective graphene oxide membranes used as ion separation membranes in each example as samples respectively. The effective test area of the sample is 13.8 cm 2 , first configure Solution B (the concentration is 100 mg / L -1of methylene blue solution with water as the solvent), and then fix the sample in the middle of the nanofiltration membrane test device through anodic aluminum oxide membranes (manufactured by Whatman, with an average pore size of 0.02 μm) above and below the sample. Fill 50 mL of solution B into the left cell of the device as the feed solution, and fill 50 mL of ultrapure water (driving solution) into the right cell of the device. To reduce concentration polarization, place magnetic stirrers in both cells of the device for uniform stirring. Apply a pressure of 0.5 MPa at 25 °C for 1 h to obtain a stable flux. Regularly extract 1 mL of solution from both the left and right sides, and use a UV-vis-NIR spectrophotometer (Thermo Fisher Genesys 150) to measure the concentration change of the dye in the solutions on both sides until the concentration of the solutions in two consecutive samplings does not change, then stop sampling and testing. Finally, collect the permeate and concentrate, use ICP-OES to measure the dye concentration in the permeate in the right cell and the concentrate in the left cell, and then obtain the rejection rate of the solute (i.e., the dye rejection rate) according to the calculation formula. Then, test the rejection rate of the solute for the samples prepared in the same example 5 according to the aforementioned method and finally calculate the average value (thoroughly clean the pipeline with deionized water after each test to ensure the accuracy of the experimental results); among them, the calculation formula for the dye rejection rate is: , where C P is the mass concentration of the solute in the permeate, is the mass concentration of the solute in the feed solution.

[0076] Divalent / monovalent ion sieving selectivity factor: Take the highly efficient separation and highly ion-selective graphene oxide membranes used as ion separation membranes in each example as samples. First, mix NaCl (Na + ), MgSO4 (Mg 2+ ) and water evenly to obtain solution C (the concentration of NaCl is 500 mg L -1 , and the concentration of MgSO4 is 500 mg L -1), and then fix the sample in the middle of the nanofiltration membrane test device through anodic aluminum oxide membranes (pore size 100 nm, porosity 10%) above and below the sample. Load 50 mL of solution C into the left cell of the device as the feed liquid, and load 50 mL of ultrapure water (driving solution) into the right cell of the device. To reduce concentration polarization, place magnetic stirrers in both cells of the device for uniform stirring. Apply a pressure of 0.5 MPa at 25 °C for 1 h to obtain a stable flux. Regularly extract 1 mL of solution from both the left and right sides, and use inductively coupled plasma optical emission spectrometry (ICP-OES) to measure the changes in the concentrations of lithium ions, potassium ions, and sodium ions in the solutions on both sides until the concentrations of the solutions in two consecutive samplings do not change, then stop sampling and testing. Finally, collect the permeate and the concentrate, and use ICP-OES to measure the ion concentrations in the permeate in the right cell and the concentrate in the left cell. Subsequently, calculate the ion rejection rate according to the measured results (the calculation formula is: , where C P is the solute mass concentration of a specific ion in the permeate, is the solute mass concentration of a specific ion in the feed liquid), and then calculate the divalent / monovalent ion sieving selectivity factor of the sample according to the rejection rates of different ions obtained. The calculation formula is: , where is the rejection rate of divalent ions (Mg 2+ ), is the rejection rate of monovalent ions (Na + ).

[0077] Example A1

[0078] The device for simultaneously performing isotropic stretching and steam treatment on graphene oxide membrane materials with a thickness ≤ 10 μm, as shown in Figure 2 , Figure 3 , includes a solvent cell a1 and a heating device a;

[0079] The top of the solvent cell a is a vertically arranged cylinder a2. The cylinder a2 is divided into upper and lower layers and is detachably connected by 2m membrane fixing screws a3, where m > 2, and the 2m membrane fixing screws a3 are circumferentially and evenly distributed around the central axis of the cylinder a2;

[0080] The heating device a is used to heat the solvent cell a1.

[0081] Example A2

[0082] The device for simultaneously performing isotropic stretching and steam treatment on graphene oxide membrane materials with a thickness > 10 μm, as shown in Figure 4 , Figure 5 , includes a solvent cell b5, a heating device b, a deformable tube 9, and a regulator;

[0083] The bottom of the deformable tube 9 is hermetically connected to the top of the solvent pool b 5. The top of the deformable tube 9 is a vertically arranged cylinder b. The cylinder b is divided into upper and lower layers and is detachably connected by 2m membrane fixing screws b 8, where m > 2, and the 2m membrane fixing screws b 8 are circumferentially and evenly distributed around the central axis of the cylinder b;

[0084] The heating device b is used to heat the solvent pool b 5;

[0085] The regulator is used to control the cylinder b to expand radially outward along the cylinder b;

[0086] The regulator includes a displacement bracket 10, a pressing disc 11, an upper layer bracket 12, a limiting structure 7, a lower layer bracket 13 and a height measuring bracket 6;

[0087] The displacement bracket 10 is a conical cap-shaped structure with the tip upward, including 2n inclined rods I, where n > 3. The upper ends of the 2n inclined rods I are simultaneously connected to the center of the lower surface of the pressing disc 11, and the lower ends are circumferentially and evenly distributed around a point o, and the point o is located on the central axis of the pressing disc 11. The pressing disc 11 is coaxial with the cylinder b;

[0088] The upper layer bracket 12 includes 2n horizontal rods, and the 2n horizontal rods are radially distributed around the point o. The two ends of the horizontal rod are respectively denoted as the a end and the b end, and the a end is closer to the point o than the b end. The a ends of the 2n horizontal rods are respectively hinged to the lower ends of the 2n inclined rods I in one-to-one correspondence;

[0089] The limiting structure 7 restricts the 2n horizontal rods to move only along their own length directions;

[0090] As Figure 5 、 Figure 6 shown, the b ends of adjacent 2 horizontal rods are each connected by 1 arc bar 4. At least one group of opposite arc bars 4 consists of left, middle and right sections. The middle section consists of a separated inner layer and an outer layer. The outer layer of the middle section is fixedly connected to the left section, and the inner layer of the middle section is fixedly connected to the right section; all the arc bars 4 enclose a ring, and the ring extends vertically downward to form a circular tube;

[0091] The lower layer bracket 13 includes 2n inclined rods II. The 2n inclined rods II are distributed in an umbrella shape around the central axis of the cylinder b. The included angle between the inclined rods II and the central axis of the cylinder b is 100 - 105°. The lower layer of the cylinder b extends radially outward and is connected to the upper ends of the 2n inclined rods II, and the lower ends of the 2n inclined rods II are connected to the circular tube.

[0092] Example B1

[0093] A method for preparing a highly efficient separation and highly ion-selective graphene oxide membrane, the steps are as follows:

[0094] (1) Preparation of raw materials and the devices used;

[0095] Aqueous solution of graphene oxide: The solute is graphene oxide. The sheet size of graphene oxide is 0.2 - 0.5 μm, the sheet thickness is 0.8 nm, and the atomic ratio of carbon to oxygen is 2:1;

[0096] Device for isotropic stretching and steam treatment: The device described in Example A1, where m = 3, the height of solvent pool a is 10 cm, and the volume is 30 mL;

[0097] Plasticizing solvent: Isopropyl alcohol;

[0098] Filter membrane: Celgard 3501 membrane, with an average pore size of 0.22 μm, an effective filtration diameter of 4 cm, and an area of 12.57 cm 2 ;

[0099] (2) Preparation of graphene oxide membrane material;

[0100] The aqueous solution of graphene oxide with a concentration of 0.5 mg·g -1 was subjected to vacuum filtration using a filter membrane, dried at 35 °C for 24 h after filtration, and then the filter membrane was removed to obtain a graphene oxide membrane material with a thickness of 1 μm.

[0101] The obtained graphene oxide membrane material has a water permeability of 65 LMH / bar, a mass area density D of 3 mg·cm -2 , a layer spacing of 0.45 nm, a tensile strength of 210 MPa, a sheet stacking domain height of 5.8 nm, and a Herman's orientation factor of 0.4; The graphene oxide membrane material swells after being immersed in water for 12 h, and the layer spacing of the swollen graphene oxide membrane material increases to 0.58 nm;

[0102] (3) When simultaneously performing isotropic stretching and steam treatment on the graphene oxide membrane material prepared in step (2), first add 30 mL of plasticizing solvent to the solvent pool a, then fix the graphene oxide membrane material between the upper and lower cylinders a through the membrane fixing screw a and adjust the membrane fixing screw a to keep the two-dimensional sheet macroscopic assembly membrane in a taut state. Then heat it to 100 °C and keep it warm for 12 h (the vapor pressure stress during the warming process is 17000 mmHg) through the heating device a until the plasticizing solvent vaporizes. Finally, take out the plasticized graphene oxide membrane material and place it in a vacuum environment at 80 °C for low-temperature reduction for 24 h to obtain a highly efficient separation and high ion-selective graphene oxide membrane.

[0103] The tensile strength of the finally obtained graphene oxide membrane with high separation efficiency and high ion selectivity is 500 MPa, the interlayer spacing is 0.34 nm, the height of the sheet stacking domain is 9.4 nm, and the Herman's orientation factor is 0.7; after the graphene oxide membrane with high separation efficiency and high ion selectivity is immersed in water for 12 h, swelling occurs, and the interlayer spacing of the swollen graphene oxide membrane with high separation efficiency and high ion selectivity increases to 0.36 nm.

[0104] Application of the graphene oxide membrane with high separation efficiency and high ion selectivity: The above-prepared graphene oxide membrane with high separation efficiency and high ion selectivity is used as an ion separation membrane.

[0105] When the graphene oxide membrane with high separation efficiency and high ion selectivity is used as an ion separation membrane, it can be known that the water permeability of the graphene oxide membrane with high separation efficiency and high ion selectivity is 390 LMH / bar, the interception rate of inorganic salts is 89%, the interception rate of dyes is 93%, and the divalent / monovalent ion sieving selectivity factor is 40; after 120 hours of continuous testing (that is, when the graphene oxide membrane with high separation efficiency and high ion selectivity is used as an ion separation membrane and continuously used for 120 hours), the water permeability of the graphene oxide membrane with high separation efficiency and high ion selectivity decreases by 13%.

[0106] Example B2

[0107] Preparation method of the graphene oxide membrane with high separation efficiency and high ion selectivity, the steps are as follows:

[0108] (1) Preparation of raw materials and devices used;

[0109] Aqueous solution of graphene oxide: The solute is graphene oxide, the sheet size of graphene oxide is 0.5 - 1 μm, the sheet thickness is 1 nm, and the atomic ratio of carbon to oxygen is 2:1;

[0110] Device for isotropic stretching and steam treatment: The device described in Example A1, m = 3, the height of solvent pool a is 8 cm, and the volume is 30 mL;

[0111] Plasticizing solvent: Ethanol;

[0112] (2) Preparation of graphene oxide membrane materials;

[0113] A clean silicon wafer is vacuum adsorbed on a spin coater, and the concentration is 2 mg·g -1Drop the aqueous solution of graphene oxide on a glass slide, then start the spin coater. First, spin at a speed of 1000 rpm for 30 s, and then spin at a speed of 3000 rpm for 60 s to spin the aqueous solution of graphene oxide into a flat film. After the film is formed, place the silicon wafer on a heating stage and dry it at 80 °C for 1 min. After drying, repeat this process until a film with a thickness of 10 nm is obtained. Finally, put it into an oven and dry it at 35 °C for 24 h to obtain the graphene oxide membrane material; where the amount added each time is 100 μL;

[0114] The water permeability of the obtained graphene oxide membrane material is 93 LMH / bar, and the mass areal density D is 0.3 mg·cm -2 , the interlayer spacing is 0.4 nm, the tensile strength is 250 MPa, the height of the sheet stacking domain is 7.5 nm, and the Herman's orientation factor is 0.43; the graphene oxide membrane material swells after being immersed in water for 12 h, and the interlayer spacing of the swollen graphene oxide membrane material increases to 0.5 nm;

[0115] When performing isotropic stretching and steam treatment on the graphene oxide membrane material prepared in step (2) at the same time, first add 30 mL of plasticizing solvent to the solvent pool a, then fix the graphene oxide membrane material between the upper and lower cylinders a through the membrane fixing screw a and adjust the membrane fixing screw a to keep the two-dimensional sheet macroscopic assembly membrane in a taut state. Then heat it to 90 °C for 18 h (the vapor pressure stress during the heat preservation process is 1200 mmHg) after the plasticizing solvent vaporizes through the heating device a. Finally, take out the plasticized graphene oxide membrane material and place the plasticized graphene oxide membrane material in a vacuum environment at 120 °C for low-temperature reduction for 18 h to obtain a highly efficient separation and highly ion-selective graphene oxide membrane.

[0116] The tensile strength of the finally obtained highly efficient separation and highly ion-selective graphene oxide membrane is 650 MPa, the interlayer spacing is 0.3 nm, the height of the sheet stacking domain is 10.8 nm, and the Herman's orientation factor is 0.83; the highly efficient separation and highly ion-selective graphene oxide membrane swells after being immersed in water for 12 h, and the interlayer spacing of the swollen highly efficient separation and highly ion-selective graphene oxide membrane increases to 0.33 nm.

[0117] Application of the highly efficient separation and highly ion-selective graphene oxide membrane: Use the above-prepared highly efficient separation and highly ion-selective graphene oxide membrane as an ion separation membrane.

[0118] When a graphene oxide membrane with high separation efficiency and high ion selectivity is used as an ion separation membrane, the water permeability of the graphene oxide membrane with high separation efficiency and high ion selectivity is 520 LMH / bar, the rejection rate of inorganic salts is 91%, the rejection rate of dyes is 97%, and the divalent / monovalent ion sieving selectivity factor is 45; after 120 hours of continuous testing, the water permeability of the graphene oxide membrane with high separation efficiency and high ion selectivity decreases by 11%.

[0119] Example B3

[0120] A method for preparing a graphene oxide membrane with high separation efficiency and high ion selectivity comprises the following steps:

[0121] (1) Preparation of raw materials and apparatuses used;

[0122] Aqueous graphene oxide solution: The solute is graphene oxide, the sheet size of graphene oxide is 1 - 5 μm, the sheet thickness is 2 nm, and the atomic ratio of carbon to oxygen is 3:1;

[0123] Apparatuses for isotropic stretching and steam treatment: The apparatuses described in Example A2, where n = 5, m = 4, the height of solvent pool b is 12 cm, the volume is 150 mL, and the angle between the inclined rod II and the central axis of cylinder b is 100°;

[0124] Plasticizing solvent: Ethanol;

[0125] (2) Preparation of graphene oxide membrane materials;

[0126] An aqueous graphene oxide solution with a concentration of 7 mg·g -1 is cast on a quartz watch glass as a casting substrate, and after casting, it is dried at 45 °C for 12 h. After removing the casting substrate, a graphene oxide membrane material with a thickness of 35 μm is obtained;

[0127] The obtained graphene oxide membrane material has a water permeability of 30 LMH / bar, a mass area density D of 15 mg·cm -2 , a layer spacing of 0.6 nm, a tensile strength of 120 MPa, a lamellar stacking domain height of 4.2 nm, and a Herman's orientation factor of 0.24; when the graphene oxide membrane material is immersed in water for 18 h, it swells, and the layer spacing of the swollen graphene oxide membrane material increases to 0.72 nm;

[0128] (3)When simultaneously performing isotropic stretching and steam treatment on the graphene oxide membrane material obtained in step (2), first add 100 mL of plasticizing solvent to solvent pool b. Subsequently, fix the graphene oxide membrane material between the upper and lower cylinders b through membrane fixing screw b and adjust membrane fixing screw b to keep the two-dimensional sheet macroscopic assembly membrane in a taut state. Then, heat it to vaporize the plasticizing solvent through heating device b. At the same time, press down the pressing plate and keep it at 95 °C for 24 h (after the insulation ends, the maximum tensile displacement △L of the two-dimensional sheet macroscopic assembly membrane is 2 mm). Finally, take out the plasticized graphene oxide membrane material and place the plasticized graphene oxide membrane material in a vacuum environment at 150 °C for low-temperature reduction for 12 h to obtain a graphene oxide membrane with high separation efficiency and high ion selectivity.

[0129] The tensile strength of the finally obtained graphene oxide membrane with high separation efficiency and high ion selectivity is 150 MPa, the layer spacing is 0.38 nm, the height of the sheet stacking domain is 6.2 nm, and the Herman's orientation factor is 0.45; after the graphene oxide membrane with high separation efficiency and high ion selectivity is immersed in water for 18 h, it swells, and the layer spacing of the swollen graphene oxide membrane with high separation efficiency and high ion selectivity increases to 0.4 nm.

[0130] Application of the graphene oxide membrane with high separation efficiency and high ion selectivity: Use the above-prepared graphene oxide membrane with high separation efficiency and high ion selectivity as an ion separation membrane.

[0131] When using the graphene oxide membrane with high separation efficiency and high ion selectivity as an ion separation membrane, it can be known that the water permeability of the graphene oxide membrane with high separation efficiency and high ion selectivity is 196 LMH / bar, the interception rate of inorganic salts is 75%, the interception rate of dyes is 88%, and the divalent / monovalent ion sieving selectivity factor is 25; after 120 hours of continuous testing, the water permeability of the graphene oxide membrane with high separation efficiency and high ion selectivity decreases by 17%.

[0132] Example B4

[0133] Preparation method of the graphene oxide membrane with high separation efficiency and high ion selectivity, the steps are as follows:

[0134] (1)Preparation of raw materials and devices used;

[0135] Aqueous solution of graphene oxide: The solute is graphene oxide, the sheet size of graphene oxide is 5 - 10 μm, the sheet thickness is 5 nm, and the atomic ratio of carbon to oxygen is 3:1;

[0136] Devices used for isotropic stretching and steam treatment: The devices described in Example A2, n is 4, m is 3, the height of solvent pool b is 10 cm, the volume is 150 mL, and the included angle between the inclined rod II and the central axis of cylinder b is 105°;

[0137] Plasticizing solvent: isopropyl alcohol;

[0138] (2) Prepare a graphene oxide membrane material;

[0139] Take an aqueous solution of graphene oxide with a concentration of 40 mg·g -1 , and using a doctor blade coating process, with glass as the substrate, after doctor blade coating, dry it at 35 °C for 24 h, and after removing the glass substrate, obtain a graphene oxide membrane material with a thickness of 50 μm;

[0140] The water permeability of the obtained graphene oxide membrane material is 10 LMH / bar, the mass areal density D is 20 mg·cm -2 , the interlayer spacing is 0.8 nm, the tensile strength is 20 MPa, the height of the lamellar stacking domain is 3 nm, and the Herman's orientation factor is 0.2; the graphene oxide membrane material swells after being immersed in water for 24 h, and the interlayer spacing of the swollen graphene oxide membrane material increases to 1 nm;

[0141] (3) When simultaneously performing isotropic stretching and steam treatment on the graphene oxide membrane material prepared in step (2), first add 100 mL of the plasticizing solvent to the solvent pool b, then fix the graphene oxide membrane material between the upper and lower cylinders b through the membrane fixing screw b and adjust the membrane fixing screw b to keep the two-dimensional sheet macroscopic assembly membrane in a taut state, then heat it to vaporize the plasticizing solvent through the heating device b, and at the same time press down the pressing plate and keep it at 105 °C for 24 h (the tensile displacement of the two-dimensional sheet macroscopic assembly membrane is 3 mm after the heat preservation ends), finally take out the plasticized graphene oxide membrane material, and place the plasticized graphene oxide membrane material in a vacuum environment at 80 °C for low-temperature reduction for 24 h to prepare a highly efficient separation and highly ion-selective graphene oxide membrane.

[0142] The tensile strength of the finally prepared highly efficient separation and highly ion-selective graphene oxide membrane is 50 MPa, the interlayer spacing is 0.4 nm, the height of the lamellar stacking domain is 5 nm, and the Herman's orientation factor is 0.3; the highly efficient separation and highly ion-selective graphene oxide membrane swells after being immersed in water for 24 h, and the interlayer spacing of the swollen highly efficient separation and highly ion-selective graphene oxide membrane increases to 0.45 nm.

[0143] Application of the highly efficient separation and highly ion-selective graphene oxide membrane, using the above-prepared highly efficient separation and highly ion-selective graphene oxide membrane as an ion separation membrane.

[0144] When the graphene oxide membrane with high separation efficiency and high ion selectivity is used as an ion separation membrane, it is known that the water permeability of the graphene oxide membrane with high separation efficiency and high ion selectivity is 30 LMH / bar, the interception rate of inorganic salts is 70%, the interception rate of dyes is 85%, and the divalent / monovalent ion sieving selectivity factor is 10; after 120 hours of continuous testing, the water permeability of the graphene oxide membrane with high separation efficiency and high ion selectivity decreases by 20%.

[0145] Example B5

[0146] A preparation method of a graphene oxide membrane with high separation efficiency and high ion selectivity comprises the following steps:

[0147] (1) Preparation of raw materials and devices used;

[0148] Aqueous graphene oxide solution: the solute is graphene oxide, the sheet size of graphene oxide is 10 - 15 μm, the sheet thickness is 8 nm, and the atomic ratio of carbon to oxygen is 4:1;

[0149] Devices for isotropic stretching and steam treatment: the devices described in Example A1, m is 4, the height of solvent pool a is 10 cm, and the volume is 100 mL;

[0150] Plasticizing solvent: isopropyl alcohol;

[0151] Filter membrane: Celgard 3501 membrane, with an average pore size of 0.22 μm, an effective suction filtration diameter of 4 cm, and an area of 12.57 cm 2 ;

[0152] (2) Preparation of graphene oxide membrane materials;

[0153] The aqueous graphene oxide solution with a concentration of 1.5 mg·g -1 is subjected to vacuum suction filtration using a filter membrane, and after suction filtration, it is dried at 40 °C for 18 h. After removing the filter membrane, graphene oxide membrane materials with a thickness of 10 nm are obtained.

[0154] The obtained graphene oxide membrane materials have a water permeability of 85 LMH / bar, a mass area density D of 0.3 mg·cm -2 , a layer spacing of 0.35 nm, a tensile strength of 300 MPa, a height of the sheet stacking domain of 9 nm, and a Herman's orientation factor of 0.5; the graphene oxide membrane materials swell after being immersed in water for 12 h, and the layer spacing of the swollen graphene oxide membrane materials increases to 0.45 nm;

[0155] (3)When subjecting the graphene oxide membrane material obtained in step (2) to isotropic stretching and steam treatment simultaneously, first add 30 mL of plasticizing solvent to the solvent pool a, then fix the graphene oxide membrane material between the upper and lower cylinders a through the membrane fixing screw a and adjust the membrane fixing screw a to keep the two-dimensional sheet macroscopic assembly membrane in a taut state. Then heat it through the heating device a until the plasticizing solvent vaporizes and keep it at 105 °C for 12 h (the vapor pressure stress during the heat preservation process is 20,000 mmHg). Finally, take out the plasticized graphene oxide membrane material, and place the plasticized graphene oxide membrane material in a vacuum environment at 150 °C for low-temperature reduction for 12 h to obtain a graphene oxide membrane with high separation efficiency and high ion selectivity.

[0156] The tensile strength of the finally obtained graphene oxide membrane with high separation efficiency and high ion selectivity is 750 MPa, the layer spacing is 0.3 nm, the height of the sheet stacking domain is 12 nm, and the Herman's orientation factor is 0.95; after the graphene oxide membrane with high separation efficiency and high ion selectivity is immersed in water for 12 h, it swells, and the layer spacing of the swollen graphene oxide membrane with high separation efficiency and high ion selectivity increases to 0.32 nm.

[0157] Application of the graphene oxide membrane with high separation efficiency and high ion selectivity: Use the above-prepared graphene oxide membrane with high separation efficiency and high ion selectivity as an ion separation membrane.

[0158] When using the graphene oxide membrane with high separation efficiency and high ion selectivity as an ion separation membrane, it can be known that the water permeability of the graphene oxide membrane with high separation efficiency and high ion selectivity is 600 LMH / bar, the interception rate of inorganic salts is 95%, the interception rate of dyes is 99%, and the divalent / monovalent ion sieving selectivity factor is 50; after 120 hours of continuous testing, the water permeability of the graphene oxide membrane with high separation efficiency and high ion selectivity decreases by 10%.

[0159] Example B6

[0160] Preparation method of the graphene oxide membrane with high separation efficiency and high ion selectivity, the steps are as follows:

[0161] (1)Preparation of raw materials and devices used;

[0162] Aqueous solution of graphene oxide: The solute is graphene oxide, the sheet size of graphene oxide is 15 - 20 μm, the sheet thickness is 10 nm, and the atomic ratio of carbon to oxygen is 4:1;

[0163] Devices used for isotropic stretching and steam treatment: The devices described in Example A2, n is 4, m is 3, the height of the solvent pool b is 8 cm, the volume is 100 mL, and the included angle between the inclined rod II and the central axis of the cylinder b is 102.5°;

[0164] Plasticizing solvent: ethanol;

[0165] (2) Prepare a graphene oxide membrane material;

[0166] A graphene oxide aqueous solution with a concentration of 8 mg·g -1 was cast on a quartz watch glass as the casting substrate, dried at 45 °C for 12 h after casting, and a graphene oxide membrane material with a thickness of 20 μm was obtained after removing the casting substrate;

[0167] The water permeability of the obtained graphene oxide membrane material was 50 LMH / bar, the mass areal density D was 10 mg·cm -2 , the interlayer spacing was 0.55 nm, the tensile strength was 150 MPa, the height of the lamellar stacking domain was 4.9 nm, and the Herman's orientation factor was 0.35; the graphene oxide membrane material swelled after being immersed in water for 18 h, and the interlayer spacing of the swollen graphene oxide membrane material increased to 0.64 nm;

[0168] (3) When simultaneously performing isotropic stretching and steam treatment on the graphene oxide membrane material prepared in step (2), first add 50 mL of the plasticizing solvent to the solvent pool b, then fix the graphene oxide membrane material between the upper and lower cylinders b through the membrane fixing screw b and adjust the membrane fixing screw b to keep the two-dimensional sheet macroscopic assembly membrane in a taut state, and then heat it to vaporize the plasticizing solvent through the heating device b. At the same time, press down the pressing plate and keep it at 90 °C for 18 h (the tensile displacement of the two-dimensional sheet macroscopic assembly membrane after the heat preservation is 1.5 mm). Finally, take out the plasticized graphene oxide membrane material and place the plasticized graphene oxide membrane material in a vacuum environment at 120 °C for low-temperature reduction for 18 h to prepare a highly efficient separation and high ion-selective graphene oxide membrane.

[0169] The tensile strength of the finally prepared highly efficient separation and high ion-selective graphene oxide membrane was 300 MPa, the interlayer spacing was 0.36 nm, the height of the lamellar stacking domain was 7.8 nm, and the Herman's orientation factor was 0.59; the highly efficient separation and high ion-selective graphene oxide membrane swelled after being immersed in water for 18 h, and the interlayer spacing of the swollen highly efficient separation and high ion-selective graphene oxide membrane increased to 0.38 nm.

[0170] Application of the highly efficient separation and high ion-selective graphene oxide membrane: Use the above-prepared highly efficient separation and high ion-selective graphene oxide membrane as an ion separation membrane.

[0171] When the graphene oxide membrane with high separation efficiency and high ion selectivity is used as an ion separation membrane, it can be seen that the water permeability of the graphene oxide membrane with high separation efficiency and high ion selectivity is 280 LMH / bar, the interception rate of inorganic salts is 82%, the interception rate of dyes is 90%, and the divalent / monovalent ion sieving selectivity factor is 36; after 120 hours of continuous testing, the water permeability of the graphene oxide membrane with high separation efficiency and high ion selectivity decreases by 15%.

Claims

1. A method for preparing a graphene oxide membrane with high separation efficiency and high ion selectivity, characterized in that: The formed graphene oxide membrane material is isotropically stretched and steam treated at the same time, and then placed in a vacuum environment at 80-150°C for low-temperature reduction to obtain a graphene oxide membrane with high separation efficiency and high ion selectivity. The steam used in the steam treatment is plasticizing steam, which is formed by evaporating a plasticizing solvent having a plasticizing effect on the graphene oxide film material, and the plasticizing solvent is ethanol or isopropanol; When the thickness of the graphene oxide film material is ≤10 μm, the device used for isotropically stretching and steam-treating the graphene oxide film material at the same time includes a solvent pool a and a heating device a; the top of the solvent pool a is a vertically arranged cylinder a, the cylinder a is divided into an upper and a lower layer and is detachably connected by 2m film fixing screws a, m>2, and the 2m film fixing screws a are evenly distributed around the circumference of the central axis of the cylinder a; the heating device a is used to heat the solvent pool a; the solvent vapor stress in a closed environment is converted into an isotropic tensile stress after contacting the graphene oxide film material fixed above, thereby realizing isotropic stretching and steam-treating the graphene oxide film material at the same time; the amount of the plasticizing solvent is 30 to 100 mL, the insulation temperature after the plasticizing solvent is vaporized is 90 to 105° C., the generated vapor pressure stress is 1200 to 20000 mmHg, and the insulation time after the plasticizing solvent is vaporized is 12 to 24 h; When the thickness of the graphene oxide film material is greater than 10 μm, the device used for simultaneously performing isotropic stretching and steam treatment on the graphene oxide film material includes a solvent pool b, a heating device b, a deformable tube and a regulator; the bottom of the deformable tube is sealed and connected to the top of the solvent pool b, the top of the deformable tube is a vertically arranged cylinder b, the cylinder b is divided into an upper and lower layer and is detachably connected by 2m membrane fixing screws b, m>2, and the 2m membrane fixing screws b are evenly distributed around the circumference of the central axis of the cylinder b; the regulator is used to control the radial outward expansion of the cylinder b; the heating device b is used to heat the solvent pool b; the outward extension of the deformable tube is controlled by the regulator, and during the extension of the deformable tube, it produces an epitaxial equibiaxial tensile displacement on the circumferential boundary of the graphene oxide film material in contact with it, and the tensile displacement is 1.5 mm to 3 mm, thereby realizing simultaneous isotropic stretching and steam treatment of the graphene oxide film material.

2. The method for preparing a highly efficient separation and highly ion-selective graphene oxide membrane according to claim 1, characterized in that: The thickness of the graphene oxide film material is 10 nm to 50 μm.

3. The method for preparing a graphene oxide membrane with high separation efficiency and high ion selectivity according to claim 2, characterized in that: The regulator includes a displacement bracket, a pressing plate, an upper bracket, a limiting structure and a lower bracket; The displacement bracket is a conical cap-shaped structure with the tip at the top, comprising 2n inclined rods I, n>3, the upper ends of the 2n inclined rods I are simultaneously connected to the center of the lower surface of the pressing plate, and the lower ends are evenly distributed around a point o, the point o is located on the central axis of the pressing plate, and the pressing plate is coaxial with the cylinder b; The upper support includes 2n horizontal rods, which are radially distributed around point o. The two ends of the horizontal rods are respectively marked as end a and end b. End a is closer to point o than end b. The ends a of the 2n horizontal rods are respectively hinged to the lower ends of the 2n oblique rods I in a one-to-one correspondence. The limiting structure restricts the 2n horizontal rods to move only along their own length direction; The b ends of two adjacent horizontal rods are each connected by an arc bar, and at least one set of opposite arc bars is composed of three sections: left, middle and right. The middle section is composed of a separated inner layer and outer layer. The outer layer of the middle section is fixedly connected to the left section, and the inner layer of the middle section is fixedly connected to the right section. All the arc bars form a circular ring, and the circular ring extends vertically downward to form a circular tube. The lower support includes 2n oblique rods II, which are distributed in an umbrella shape around the central axis of the cylinder b. The angle between the oblique rods II and the central axis of the cylinder b is 100-105°. The lower layer of the cylinder b extends radially outward and is connected to the upper ends of the 2n oblique rods II, and the lower ends of the 2n oblique rods II are connected to the circular tube.

4. The method for preparing a highly efficient separation and highly ion-selective graphene oxide membrane according to claim 3, characterized in that: The regulator also includes a height measuring bracket, which is vertically arranged on one side of the pressing plate and fixedly connected to the upper bracket.

5. The method for preparing a graphene oxide membrane with high separation efficiency and high ion selectivity according to claim 1, characterized in that: The forming method of the graphene oxide film material is: vacuum filtering the graphene oxide aqueous solution into a film, spin coating it multiple times into a film, pouring it on a substrate to evaporate and assemble it into a film or continuously scraping it into a film, and then drying and forming it to obtain the graphene oxide film material.

6. The method for preparing a graphene oxide membrane with high separation efficiency and high ion selectivity according to claim 5, characterized in that: The interlayer spacing of the graphene oxide film material is 0.35-0.8nm, the tensile strength is 20-300MPa, the sheet stacking domain height is 3-9nm, and the Herman orientation factor is 0.2-0.5; after the graphene oxide film material swells in water, the interlayer spacing increases to 0.45-1nm.

7. A highly efficient separation and highly ion-selective graphene oxide membrane prepared by the preparation method according to any one of claims 1 to 5, characterized in that: The tensile strength of the high-efficiency separation and high-ion selectivity graphene oxide membrane is 50-750MPa, the interlayer spacing is 0.3-0.4nm, the layer stacking domain height is 5-12nm, and the Hermann orientation factor is 0.3-0.95; after the high-efficiency separation and high-ion selectivity graphene oxide membrane swells in water, the interlayer spacing increases to 0.32-0.45nm.

8. The use of the highly efficient separation and highly ion-selective graphene oxide membrane according to claim 7, characterized in that: Used as ion separation membrane; The water permeability of the high-efficiency separation and high-ion selectivity graphene oxide membrane is 30-600LMH / bar, the inorganic salt retention rate is 70-95%, the dye retention rate is 85-99%, and the divalent / monovalent ion screening selectivity factor is 10-50; after 120 hours of continuous testing, the water permeability of the high-efficiency separation and high-ion selectivity graphene oxide membrane decreased by 10-20%.

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