Composite separation membrane and its preparation method and application

Abstract

The present application relates to the field of membrane separation technology, and specifically to a composite separation membrane and its preparation method and application. The composite separation membrane of the present application includes a hollow polymer-based membrane and a modified layer attached to the outer surface of the hollow polymer-based membrane; wherein, the surface of the hollow polymer-based membrane has a plurality of membrane pores, and at least part of the modified layer forms a depression in the membrane pores; the modified layer includes graphene oxide nanosheets, nanocellulose and sulfonated succinic acid; at least part of the nanocellulose is fixed between the layers of the graphene oxide nanosheets, and at least part of the sulfonated succinic acid is fixed between the layers of the graphene oxide nanosheets; the modified layer in the composite separation membrane of the present application and the hollow polymer-based membrane have good bonding strength and good stability, and it has good hydrophilicity, which can effectively improve the separation efficiency.

Description

Technical Field

[0001] The present application relates to the field of membrane separation technology, and in particular to a composite separation membrane and a preparation method and application thereof. Background Art

[0002] Membrane separation technology has emerged to achieve efficient separation and purification of substances in a variety of fields, including water treatment, food and beverages, biopharmaceuticals, and chemicals. Compared to traditional separation methods such as distillation, evaporation, adsorption, extraction, and chromatography, membrane separation technology offers advantages such as high separation precision, fast filtration speed, low operating pressure, and strong adaptability.

[0003] The basic principle of membrane separation technology is to utilize its microporous structure to intercept suspended solids, colloids, and macromolecular contaminants while allowing small molecules such as water to pass through, thereby achieving separation and purification. Membranes are the core of membrane separation technology. Currently, the most commonly used membrane materials include polyvinylidene fluoride (PVDF), polyethylene (PE), and polypropylene (PP). However, these polymers have low surface energy and are highly hydrophobic. Therefore, they are prone to adsorbing hydrophobic organic matter such as humic acid or microorganisms. This can easily lead to severe membrane fouling and significant flux attenuation (typically 50%). At present, there are mainly the following methods for hydrophilic modification of hydrophobic membrane materials: (1) introducing hydrophilic polymers such as polyvinyl pyrrolidone as a modification layer to improve the hydrophilicity of the hydrophobic material surface, but the above modification methods have the disadvantage that the modification layer is easy to fall off; (2) introducing materials such as titanium dioxide and carbon nanotubes to improve hydrophilicity, but the agglomerates of titanium dioxide nanoparticles and carbon nanotubes can easily cause membrane pore blockage, thereby reducing membrane separation efficiency; (3) introducing a modification layer prepared from raw materials including graphene oxide or graphene, organosilicon compounds and surfactants, but the above modification layer also has the disadvantage of insufficient bonding strength with the base membrane and easy peeling. Summary of the Invention

[0004] Based on this, the present application provides a composite separation membrane, a preparation method, and applications thereof. The composite separation membrane provided herein has the advantages of good bonding strength and stability between the modified layer and the hollow polymer-based membrane. Furthermore, the composite separation membrane has good hydrophilicity, effectively improving separation efficiency.

[0005] In a first aspect of the present application, a composite separation membrane is provided, comprising a hollow polymer-based membrane and a modified layer attached to the outer surface of the hollow polymer-based membrane;

[0006] The surface of the hollow polymer-based membrane has a plurality of membrane pores, and at least part of the modified layer forms a depression in the membrane pores;

[0007] The modified layer includes graphene oxide nanosheets, nanocellulose and sulfonated succinic acid; at least part of the nanocellulose is fixed between the sheets of the graphene oxide nanosheets, and at least part of the sulfonated succinic acid is fixed between the sheets of the graphene oxide nanosheets.

[0008] In one embodiment, the depth of the depression formed by the modified layer in the membrane pore is 50 nm to 200 nm.

[0009] In one embodiment, the modified layer has a two-dimensional network structure.

[0010] In one embodiment, the fixing method of the nanocellulose includes at least one of physical adsorption, coupling connection between the nanocellulose and the active sites of the graphene oxide nanosheets, coupling connection between the nanocellulose and the oxygen-containing functional groups of the graphene oxide nanosheets, and intermolecular interaction between the nanocellulose and the graphene oxide nanosheets.

[0011] In one embodiment, the immobilization method of the sulfonated succinic acid includes at least one of: physical adsorption, coupling connection between the sulfonated succinic acid and the active sites of the graphene oxide nanosheets, coupling connection between the sulfonated succinic acid and the oxygen-containing functional groups of the graphene oxide nanosheets, and intermolecular interaction between the sulfonated succinic acid and the graphene oxide nanosheets.

[0012] In one embodiment, the mass ratio of the graphene oxide nanosheets to the nanocellulose is (0.1-0.5): (0.05-0.2).

[0013] In one embodiment, the mass ratio of the graphene oxide nanosheets to the sulfonated succinic acid is (0.1-0.5): (0.2-0.8).

[0014] In one embodiment, the outer diameter of the hollow polymer-based membrane is 500 μm to 600 μm.

[0015] In one embodiment, the inner diameter of the hollow polymer-based membrane is 200 μm to 300 μm.

[0016] In one embodiment, the pore size of the membrane pore is 0.3 μm to 0.8 μm.

[0017] In one embodiment, the material of the hollow polymer-based membrane includes one or more of polyvinylidene fluoride, polypropylene and polyacrylonitrile.

[0018] In one embodiment, the contact angle of static water on the surface of the composite separation membrane is ≤40°.

[0019] In one embodiment, the static adsorption amount of humic acid on the surface of the composite separation membrane is 40 mg / m 2 ~170 mg / m 2 .

[0020] In one embodiment, the composite separation membrane has a retention rate of 90% to 98% for humic acid.

[0021] A second aspect of the present application provides a method for preparing the composite separation membrane according to any one of the first aspects of the present application, comprising the following steps:

[0022] The graphene oxide nanosheets and the nanocellulose are mixed in a solvent, and after ultrasonic treatment, the sulfonated succinic acid is added thereto for mixing reaction to prepare a casting solution;

[0023] The casting liquid is coated on the surface of the hollow polymer-based membrane, and negative pressure is applied in the hollow cavity of the hollow polymer-based membrane to form a depression of the casting liquid in at least part of the membrane pores of the hollow polymer-based membrane; after thermal curing, at least part of the nanocellulose is fixed between the layers of the graphene oxide nanosheets, and at least part of the sulfonated succinic acid is fixed between the layers of the graphene oxide nanosheets to form the modified layer, thereby preparing the composite separation membrane.

[0024] In one embodiment, the negative pressure is -0.1 MPa to -0.05 MPa.

[0025] In one embodiment, the process parameters of the thermal curing include: a thermal curing temperature of 60° C. to 80° C., and a thermal curing time of 1 hour to 2 hours.

[0026] In one embodiment, the process parameters of the ultrasonic treatment include: ultrasonic time is 30min~60min.

[0027] In one embodiment, the process parameters of the mixing reaction include: mixing time of 2h~4h, and rotation speed of 500r / min~800r / min.

[0028] In one embodiment, the mass ratio of the graphene oxide nanosheets to the nanocellulose is (0.1-0.5): (0.05-0.2).

[0029] In one embodiment, the mass ratio of the graphene oxide nanosheets to the sulfonated succinic acid is (0.1-0.5): (0.2-0.8).

[0030] In one embodiment, the solvent includes deionized water and an alcohol solvent in a volume ratio of (5-8): (2-5).

[0031] In one embodiment, before the step of applying the casting solution to the surface of the hollow polymer base membrane, the process further includes: soaking the hollow polymer base membrane in an organic solvent, washing, and drying;

[0032] The process parameters of the infiltration treatment include: time is 10min~30min.

[0033] The third aspect of the present application provides an application of the composite separation membrane described in any embodiment of the first aspect of the present application in the field of water treatment, biomedicine, food processing or chemical purification.

[0034] The beneficial effects of the composite separation membrane provided in this application include at least:

[0035] The composite separation membrane of the present application includes a hollow polymer-based membrane and a modified layer attached to the outer surface of the hollow polymer-based membrane, wherein the hollow polymer-based membrane can effectively intercept organic macromolecules, thereby ensuring the interception capacity of the composite separation membrane.

[0036] At least part of the modified layer forms a semi-immersed recessed anchoring structure at the membrane pores of the hollow polymer base membrane. This structure can effectively enhance the bonding strength between the modified layer and the hollow polymer membrane layer through a mechanical interlocking effect and synergistic chemical bonding between the modified layer and the hollow polymer base membrane, thereby improving the stability of the composite separation membrane.

[0037] Furthermore, at least a portion of the nanocellulose is immobilized between the graphene oxide nanosheets. This can be achieved through physical adsorption, chemical bonds (coupling) formed between the nanocellulose and oxygen-containing functional groups on the graphene oxide nanosheets through dehydration condensation, coupling between the nanocellulose and active sites of the graphene oxide nanosheets, or intermolecular interactions between the nanocellulose and graphene oxide. Simultaneously, at least a portion of the sulfonated succinic acid is immobilized between the graphene oxide nanosheets. This can be achieved through physical adsorption, coupling between the sulfonated succinic acid and active sites of the graphene oxide nanosheets, coupling between the sulfonated succinic acid and oxygen-containing functional groups of the graphene oxide nanosheets, or hydrogen bonding between the sulfonic groups of the sulfonated succinic acid and the graphene oxide nanosheets. The synergistic effect between the nanocellulose and the sulfonated succinic acid forms a stable cross-linked structure in the modified layer, thereby ensuring the stability of the modified layer. In addition, nanocellulose and sulfonated succinic acid are fixed between the sheets of graphene oxide nanosheets, which can form selective water channels, thereby allowing water molecules to quickly pass through the hydrophilic modified layer and improve water flux.

[0038] Furthermore, the introduction of the hydrophilic modified layer can reduce the adsorption of organic pollutants. At this time, the accumulation rate of organic pollutants on the surface of the composite separation membrane is significantly reduced, thereby delaying the membrane cleaning cycle, reducing the flux attenuation rate of the composite separation membrane, and improving the separation effect.

[0039] In summary, the modified layer and the hollow polymer-based membrane in the composite separation membrane provided by the present application have good bonding strength and good stability, and the above-mentioned composite separation membrane has good hydrophilicity, and has both good water flux and good retention capacity of organic macromolecules; it can effectively improve the separation efficiency and reduce the membrane cleaning cycle. BRIEF DESCRIPTION OF THE DRAWINGS

[0040] Figure 1 A schematic structural diagram of a modified layer provided as an example of this application;

[0041] Figure 2 A schematic structural diagram of a hollow polymer-based membrane provided as an example of this application;

[0042] Figure 3 A schematic structural diagram of a composite separation membrane provided as an example of this application;

[0043] Figure 4 This is an electron microscope image of a concave structure formed by the modified layer at the membrane pores of a hollow polymer-based membrane in an example of the present application;

[0044] Figure 5 This is a schematic diagram of the working principle of the composite separation membrane of this application when used for water purification.

[0045] In the figure, 10, hollow polymer base membrane; 20, modified layer; 201, sulfonated succinic acid; 202, nanocellulose; 203, graphene oxide nanosheets; A, water inlet side; B, permeate side; C, water molecule flow direction. DETAILED DESCRIPTION

[0046] The following provides a more complete and clear description of the composite separation membrane, its preparation method, and its applications, using specific examples. This application can be implemented in many different forms and is not limited to the embodiments described herein. Rather, these embodiments are provided to provide a more thorough and comprehensive understanding of the disclosure.

[0047] It will be understood that, in this application, "flux" refers to the amount of water passing through the membrane.

[0048] It can be understood that in this application, "retention capacity" refers to the retention capacity of the membrane for organic matter.

[0049] As a high-efficiency separation technology, hollow fiber ultrafiltration membranes are widely used in water treatment, medicine, food and beverage and other fields. Their core principle is to intercept suspended matter, colloids and macromolecular pollutants through microporous structures while allowing water molecules to pass through. The current mainstream materials are mainly hydrophobic polymers such as polyvinylidene fluoride (PVDF), polypropylene, and polyacrylonitrile (PAN). Although they have excellent chemical stability, the surface hydrophobicity leads to prominent membrane fouling problems, which are specifically manifested as follows: (1) Insufficient hydrophilicity: Taking traditional PVDF as an example, the static water contact angle of PVDF membrane is as high as about 80°, which easily adsorbs hydrophobic organic matter (such as humic acid) and microorganisms, forming an irreversible pollution layer, and the flux attenuation rate is significant (the total attenuation rate is generally about 50%). (2) Limited anti-pollution performance: The static adsorption capacity of humic acid by traditional membrane materials is as high as 295.0 mg / m 2 , pollutants easily accumulate on the membrane surface, requiring frequent chemical cleaning, resulting in a shortened membrane life and increased operating costs. (3) Low flux recovery efficiency: The flux recovery rate of conventional membranes after hydraulic backwashing is only 69%, making it difficult to effectively remove deep-seated pollutants and insufficient long-term operational stability. (4) Conflict between retention performance and operating cycle (flux): Traditional membranes have a low retention rate for micropollutants (e.g., the retention rate for humic acid is about 81%), and the retention rate needs to be increased by reducing the pore size, but this will result in a decrease in flux and a shortened filtration cycle.

[0050] Graphene oxide (GO) has a high specific surface area, excellent hydrophilicity, and a rich surface rich in oxygen-containing functional groups (-OH, -COOH). Therefore, GO has been explored for membrane modification. Studies have shown that GO coatings can reduce the contact angle of membrane surfaces to approximately 40°–50°. However, current GO-containing coatings lack sufficient bonding strength to the substrate membrane, making them prone to delamination during long-term operation. Furthermore, the scalable preparation process is not yet mature, hindering improved production efficiency.

[0051] In a first aspect of the present application, a composite separation membrane is provided, comprising a hollow polymer-based membrane and a modified layer attached to an outer surface of the hollow polymer-based membrane.

[0052] The surface of the hollow polymer-based membrane has a plurality of membrane pores, and at least a portion of the modified layer forms depressions in the membrane pores.

[0053] See Figure 1 The modified layer 20 includes graphene oxide nanosheets 203, nanocellulose 202, and sulfonated succinic acid 201. At least a portion of the nanocellulose 202 is fixed between the sheets of the graphene oxide nanosheets 203. At least a portion of the sulfonated succinic acid 201 is fixed between the sheets of the graphene oxide nanosheets 203.

[0054] The fixing methods of the nanocellulose and the sulfonated succinic acid independently include at least one of physical adsorption, coupling connection and intermolecular interaction.

[0055] The composite separation membrane of the present application includes a hollow polymer-based membrane and a modified layer attached to the outer surface of the hollow polymer-based membrane, wherein the hollow polymer-based membrane can effectively intercept organic macromolecules, thereby ensuring the interception capacity of the composite separation membrane.

[0056] The modified layer includes graphene oxide nanosheets, nanocellulose, and sulfonated succinic acid. The three work together to make the modified layer rich in hydrophilic groups such as hydroxyl groups and carboxylic acid groups, effectively reducing the static contact angle of the membrane surface, thereby reducing the adsorption of hydrophobic organic pollutants. The static adsorption of humic acid by the composite separation membrane is reduced by 60%, delaying the formation of the pollutant layer, thereby delaying the membrane cleaning cycle, reducing the flux attenuation rate of the composite separation membrane, and improving the separation effect. Moreover, due to the reduced adsorption of hydrophobic organic pollutants, the filtration cycle of the membrane is increased, the cleaning rate is reduced, and the flux recovery rate after membrane cleaning is effectively increased.

[0057] At least a portion of the modified layer forms a semi-submerged, recessed anchoring structure within the pores of the hollow polymer-based membrane. This structure, through a mechanical interlocking effect and synergistic chemical bonding between the modified layer and the hollow polymer-based membrane, effectively enhances the bonding strength between the modified layer and the hollow polymer membrane, thereby improving the stability of the composite separation membrane. Specifically, the modified layer of the composite separation membrane of the present application shows no noticeable delamination under long-term high-pressure operation (>0.5 MPa) and acid-base cleaning (pH 2-12), demonstrating significantly superior stability compared to conventional GO coating technology.

[0058] Furthermore, at least a portion of the nanocellulose is immobilized between the graphene oxide nanosheets. This can be achieved through physical adsorption, chemical bonds (coupling) formed between the nanocellulose and oxygen-containing functional groups on the graphene oxide nanosheets through dehydration condensation, coupling between the nanocellulose and active sites of the graphene oxide nanosheets, or intermolecular interactions between the nanocellulose and graphene oxide. Simultaneously, at least a portion of the sulfonated succinic acid is immobilized between the graphene oxide nanosheets. This can be achieved through physical adsorption, coupling between the sulfonated succinic acid and active sites of the graphene oxide nanosheets, coupling between the sulfonated succinic acid and oxygen-containing functional groups of the graphene oxide nanosheets, or hydrogen bonding between the sulfonic groups of the sulfonated succinic acid and the graphene oxide nanosheets. The synergistic effect between the nanocellulose and sulfonated succinic acid creates a stable three-dimensional cross-linked structure in the modified layer, inhibiting swelling of the graphene oxide sheets in water and thereby ensuring the stability of the modified layer. In addition, nanocellulose and sulfonated succinic acid are fixed between the layers of graphene oxide nanosheets, which can form selective water channels and cooperate with the traditional mass transfer mode of hollow polymer-based membranes to enable water molecules to quickly pass through the hydrophilic modified layer to improve flux.

[0059] In summary, the modified layer and the hollow polymer-based membrane in the composite separation membrane provided by the present application have good bonding strength and good stability, and the above-mentioned composite separation membrane has good hydrophilicity, and has both good water flux and good retention capacity of organic macromolecules; it can effectively improve the separation efficiency and reduce the membrane cleaning cycle.

[0060] Nanocellulose (CNF) is a cellulose material with a nanoscale structure that is extracted and further processed from natural cellulose raw materials (such as wood, cotton, bamboo, etc.) through physical, chemical or biological methods. Its diameter is usually between a few nanometers and tens of nanometers, and its length can reach micrometers. It has many excellent properties such as high specific surface area, high crystallinity, high strength, high elastic modulus, good biocompatibility, biodegradability and renewability.

[0061] In one example, the depth of the depression formed by the modified layer in the membrane pore is 50nm~200nm. It is understandable that the depth of the depression formed by the modified layer in the membrane pore can be selected from any value between 50nm~200nm. For example, the depth of the depression formed by the modified layer in the membrane pore includes but is not limited to 50nm, 80nm, 100nm, 120nm, 150nm, 180nm or 200nm, or within the range consisting of any two of the above point values as endpoint values. The modified layer of the present application forms a semi-immersed depression anchoring structure at the membrane pore of the hollow polymer-based membrane, which can achieve a close combination of the modified layer and the hollow polymer-based membrane.

[0062] In one example, the modified layer has a two-dimensional network structure.

[0063] In one example, the fixation method of the nanocellulose includes at least one of: physical adsorption, coupling connection between the nanocellulose and the active sites of the graphene oxide nanosheets, coupling connection between the nanocellulose and the oxygen-containing functional groups of the graphene oxide nanosheets, and intermolecular interaction between the nanocellulose and the graphene oxide nanosheets.

[0064] In one example, the immobilization method of the sulfonated succinic acid includes at least one of: physical adsorption, coupling connection between the sulfonated succinic acid and the active sites of the graphene oxide nanosheets, coupling connection between the sulfonated succinic acid and the oxygen-containing functional groups of the graphene oxide nanosheets, and intermolecular interaction between the sulfonated succinic acid and the graphene oxide nanosheets.

[0065] As can be understood, the graphene oxide nanosheets contain oxygen-containing functional groups and active sites on their surfaces, allowing them to be immobilized via coupling with nanocellulose and sulfonated succinic acid. Furthermore, the sulfonic acid groups of sulfonated succinic acid can form intermolecular interactions such as hydrogen bonds with the graphene oxide nanosheets, further enabling immobilization.

[0066] In one example, the mass ratio of the graphene oxide nanosheets to the nanocellulose is (0.1-0.5): (0.05-0.2). Defining the mass ratio of the graphene oxide nanosheets to the nanocellulose enables the graphene oxide nanosheets to provide hydrophilic groups and to synergistically exert the modification effect of the nanographene to improve the mechanical strength of the modified layer, and to form water channels between the nanocellulose sheets to improve the flux. For example, the mass ratio of the graphene oxide nanosheets to the nanocellulose includes but is not limited to 0.1:0.05, 0.1:0.1, 0.15:0.1, 0.2:01, 0.3:0.1, 0.4:0.1, 0.45:0.15 or 0.5:0.2, or within the range formed by any two of the above point values as endpoint values.

[0067] In one example, the mass ratio of the graphene oxide nanosheets to the sulfonated succinic acid is (0.1-0.5):(0.2-0.8). The mass ratio of the graphene oxide nanosheets to the sulfonated succinic acid includes, but is not limited to, 0.1:0.2, 0.2:0.3, 0.2:0.4, 0.4:0.7, or 0.5:0.8, or a range consisting of any two of the above endpoints.

[0068] The hydrophilic molecules CNF and sulfosuccinate (SSA) are used as composite crosslinkers in the two-dimensional structure of GO, forming a composite crosslinked structure that provides strong structural stability and controllable GO interlayer spacing. This hydrophilic modification of the membrane surface effectively reduces the adsorption of pollutants on the membrane surface and improves the membrane's anti-wetting properties.

[0069] In one example, the outer diameter of the hollow polymer-based membrane is 500 μm to 600 μm. For example, the outer diameter of the hollow polymer-based membrane includes but is not limited to 500 μm, 520 μm, 550 μm, 580 μm or 600 μm, or a range formed by any two of the above points as endpoints.

[0070] In one example, the inner diameter of the hollow polymer-based membrane is 200 μm to 300 μm. For example, the inner diameter of the hollow polymer-based membrane includes but is not limited to 200 μm, 210 μm, 220 μm, 230 μm, 250 μm, 270 μm, 290 μm or 300 μm, or a range formed by any two of the above points as endpoints.

[0071] In order to ensure that the modified layer forms a depression at the membrane pore, it is necessary to ensure the thickness of the hollow polymer-based membrane and limit the inner and outer diameters of the hollow polymer-based membrane, which is also conducive to ensuring the water flux and the chemical and mechanical stability of the membrane.

[0072] In one example, the pore size of the membrane pore is 0.3 μm to 0.8 μm. It is understandable that the pore size of the membrane pore can be selected from any value between 0.3 μm and 0.8 μm. For example, the pore size of the membrane pore includes but is not limited to 0.3 μm, 0.4 μm, 0.5 μm, 0.6 μm, 0.7 μm or 0.8 μm, or a range formed by any two of the above point values as endpoint values. Figure 2 The hollow polymer-based membrane has a hollow channel inside and multiple membrane pores on its surface. The hollow polymer-based membrane screens the particles flowing through it by the size of the membrane pores, allowing only molecules of a specific size or smaller to pass through. During the membrane separation process, the raw liquid is subjected to the action of static pressure difference on one side of the composite separation membrane. The solvent and small molecular solutes pass through the membrane pores to become the filtrate, while the large molecular solutes are retained by the membrane, thereby achieving the purpose of substance separation and concentration. Therefore, limiting the pore size of the membrane plays an important role in ensuring the retention capacity and flux of the composite separation membrane.

[0073] In one example, the material of the hollow polymer-based membrane includes one or more of polyvinylidene fluoride, polypropylene, and polyacrylonitrile.

[0074] Preferably, the material of the hollow polymer-based membrane includes polyvinylidene fluoride.

[0075] The material of the hollow polymer base membrane is a semi-crystalline thermoplastic polymer. The hollow fiber membrane structure formed by it is as follows Figure 2 As shown, it is a tiny hollow fiber filament separation membrane.

[0076] See Figure 3 In the present application, the composite separation membrane includes a hollow polymer-based membrane 10 and a modified layer 20 attached to the outer surface of the hollow polymer-based membrane 10. In one example, the thickness of the modified layer 20 is 50 nm to 200 nm. For example, the thickness of the modified layer includes but is not limited to 50 nm, 80 nm, 100 nm, 120 nm, 150 nm, 180 nm, or 200 nm, or a range formed by any two of the above-mentioned endpoints.

[0077] In one example, the contact angle of static water on the composite separation membrane surface was ≤40°. The contact angle of static water on traditional membrane surfaces is approximately 80°. The modified layer of this application, rich in hydrophilic groups such as hydroxyl and carboxyl groups, can effectively reduce the static water contact angle on the membrane surface to ≤40°, thereby reducing the adsorption tendency of hydrophobic pollutants.

[0078] In one example, the static adsorption amount of humic acid on the surface of the composite separation membrane is 40 mg / m 2 ~170 mg / m 2 The static adsorption amount of humic acid on the surface of the composite separation membrane includes but is not limited to 50 mg / m 2 , 80mg / m 2 , 100mg / m 2 , 120mg / m 2 , 140mg / m 2 , 160mg / m 2 or 170 mg / m 2 , or any two of the above points are used as endpoints. The static adsorption capacity of humic acid on the surface of traditional separation membrane is about 295 mg / m 2 The composite separation membrane of the present application can effectively reduce the adsorption of organic pollutants such as humic acid, significantly slow down the accumulation rate of pollutants on the membrane surface, and thus extend the membrane cleaning cycle.

[0079] In one example, the composite separation membrane has a retention rate of 90% to 98% for humic acid. The modified layer of this application includes nanocellulose and sulfonated succinic acid fixed between graphene oxide sheets, which can form a nanochannel structure in the modified layer, which easily ensures water flux and the retention rate of organic matter such as humic acid. Furthermore, the initial flux of the composite separation membrane of this application can be increased by 20% compared to the unmodified separation membrane, overcoming the "flux-retention" contradiction in traditional technologies.

[0080] In addition, the composite separation membrane provided by the present application also has other beneficial effects. For example, the above beneficial effects include but are not limited to: (1) Reduced operating costs: Since the composite separation membrane of the present application can effectively reduce the adsorption of organic pollutants, the frequency of chemical cleaning can be effectively reduced, such as the simultaneous reduction of reagent consumption and labor maintenance costs. At the same time, due to the slowdown in pollution rate and the reduction in cleaning damage, the membrane replacement cycle is extended by 30% to 40%. Moreover, the service life of the composite separation membrane, that is, the filtration cycle, is extended, the water production per unit time is increased, and the unit water treatment cost is reduced. Furthermore, the GO dosage per unit membrane area of the composite separation membrane of the present application is only 0.05 to 0.2 g / m 2 , the raw material cost accounts for a relatively low proportion. (2) Significant environmental benefits: The reduction in the frequency of chemical cleaning of the composite separation membrane of this application can directly reduce the discharge of acid / alkali cleaning waste liquid and reduce the risk of secondary pollution to the water body. In addition, the increase in flux and the reduction in separation operating pressure can reduce the energy consumption of the water treatment system. In addition, the retention rate of micropollutants (such as humic acid and antibiotics) is increased to more than 90%, which can provide technical guarantees for drinking water safety. In addition, the reduction in the frequency of membrane replacement can reduce the amount of solid waste generated, which is in line with the concept of circular economy.

[0081] Currently, the preparation of modified graphene oxide layers primarily relies on chemical modification or vacuum filtration. However, chemical modification requires precise control of reaction conditions and involves multiple chemical steps, while vacuum filtration requires specialized equipment and has low production efficiency. Consequently, traditional methods for preparing modified graphene oxide layers are complex and difficult to commercialize.

[0082] A second aspect of the present application provides a method for preparing the composite separation membrane according to any one of the first aspects of the present application, comprising the following steps:

[0083] S10: mixing the graphene oxide nanosheets and the nanocellulose in a solvent, performing ultrasonic treatment, and then adding the sulfonated succinic acid to carry out a mixing reaction to prepare a casting solution.

[0084] S20: Coating the casting liquid on the surface of the hollow polymer-based membrane, applying negative pressure in the hollow cavity of the hollow polymer-based membrane, so that the casting liquid forms a depression in at least part of the membrane pores of the hollow polymer-based membrane; after thermal curing, fixing at least part of the nanocellulose between the layers of the graphene oxide nanosheets, and fixing at least part of the sulfonated succinic acid between the layers of the graphene oxide nanosheets to form the modified layer, thereby preparing the composite separation membrane.

[0085] The present application prepares a composite separation membrane by a negative pressure and heat curing method. The preparation method does not require complicated equipment and is simple and easy to implement industrial production.

[0086] In one example, the step of coating the casting liquid on the surface of the hollow polymer base membrane includes: immersing the hollow polymer base membrane in the casting liquid for 10 minutes to 20 minutes.

[0087] In this application, the negative pressure applied within the hollow polymer-based membrane cavity plays an important role in utilizing suction filtration to allow the casting solution to penetrate the membrane pore surface and form depressions. In one example, the negative pressure is -0.1MPa to -0.05MPa. This application limits the negative pressure to the above range to ensure effective penetration of the casting solution and prevent blockage caused by excessive pressure infiltration into the pores.

[0088] For example, the negative pressure includes but is not limited to -0.1 MPa, -0.08 MPa, -0.06 MPa or -0.05 MPa, or a range formed by any two of the above point values as endpoints.

[0089] In one example, the thermal curing process parameters include: a thermal curing temperature of 60°C to 80°C. Thermal curing temperatures include but are not limited to 60°C, 63°C, 65°C, 68°C, 70°C, 72°C, 75°C, 78°C, or 80°C, or a range formed by any two of the above points as endpoints. Defining the thermal curing process parameters plays an important role in ensuring that nanocellulose or sulfonated succinic acid is fixed between the layers of graphene oxide nanosheets. For example, it can ensure that hydrogen bonds and ester groups are fully formed between graphene oxide and nanocellulose or sulfonated cellulose.

[0090] In one example, the thermal curing process parameters include: a thermal curing time of 1 hour to 2 hours. The thermal curing time includes but is not limited to 1 hour, 1.2 hours, 1.5 hours, 1.8 hours, or 2 hours, or a range formed by any two of the above points as endpoints.

[0091] The electron microscope image of the concave structure formed by the modified layer of the present application at the membrane pore of the hollow polymer base membrane is as follows Figure 4 The formation of the concave structure during the above preparation process mainly involves: during the filtration process, the casting liquid is driven into the membrane pores by negative pressure, and the GO sheets are oriented at the edge of the pore due to capillary forces; after thermal curing, the GO sheets form a "concave" structure at the pore mouth, which strengthens the bonding strength between the coating and the hollow polymer base membrane through a mechanical interlocking effect.

[0092] In one example, the process parameters of the ultrasonic treatment include: ultrasonic time is 30min~60min.

[0093] In one example, the process parameters of the mixing reaction include: a mixing time of 2 hours to 4 hours, and a rotation speed of 500 rpm to 800 rpm. For example, the rotation speed of the mixing reaction includes but is not limited to 500 rpm, 600 rpm, 700 rpm, or 800 rpm.

[0094] In one example, the mass ratio of the graphene oxide nanosheets to the nanocellulose is (0.1-0.5): (0.05-0.2).

[0095] In one example, the mass ratio of the graphene oxide nanosheets to the sulfonated succinic acid is (0.1-0.5): (0.2-0.8).

[0096] In one example, the mass fraction of graphene oxide in the casting solution is 0.1% to 0.5%. Specifically, the mass fraction of graphene oxide in the casting solution includes but is not limited to 0.1%, 0.2%, 0.3%, 0.4% or 0.5%, or a range formed by any two of the above points as endpoints.

[0097] In one example, the mass fraction of the nanocellulose in the casting solution is 0.05% to 0.2%. Specifically, the mass fraction of the nanocellulose in the casting solution includes, but is not limited to, 0.05%, 0.1%, 0.2%, 0.3%, 0.4%, or 0.5%, or a range formed by any two of the above endpoints.

[0098] In one example, the mass fraction of sulfonated succinic acid in the casting solution is 0.2% to 0.8%. Specifically, the mass fraction of sulfonated succinic acid includes, but is not limited to, 0.2%, 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, or 0.8%, or a range formed by any two of the above endpoints.

[0099] In one example, the solvent includes deionized water and an alcohol solvent in a volume ratio of (5-8):(2-5). For example, the alcohol solvent includes, but is not limited to, ethanol. Specifically, the volume ratio of deionized water to alcohol solvent includes, but is not limited to, 5:5, 6:4, 7:3, or 8:2, or a range formed by any two of the aforementioned endpoints.

[0100] In one example, before the step of coating the casting liquid on the surface of the hollow polymer base membrane, the method further includes: soaking the hollow polymer base membrane in an organic solvent, washing, and drying.

[0101] For example, the organic solvent is an alcohol solvent. The alcohol solvent includes but is not limited to ethanol. Furthermore, the organic solvent is ethanol with a mass concentration of 50% to 80%.

[0102] The process parameters of the immersion treatment include: a time of 10 minutes to 30 minutes. For example, the immersion treatment time includes but is not limited to 10 minutes, 15 minutes, 20 minutes, 25 minutes or 30 minutes, or a range formed by any two of the above points as endpoints.

[0103] Using alcohol solvent to pre-treat the hollow polymer base membrane can effectively reduce the surface tension of the base membrane, fully wet and open the membrane pores, and avoid the subsequent casting liquid from clogging the pores due to capillary action; and the alcohol solvent can also dissolve the amorphous area on the surface of the base membrane, exposing more active sites of the base membrane, such as the CF bond in the PVDF base membrane, thereby enhancing the bonding force with the modified layer.

[0104] The third aspect of the present application provides an application of the composite separation membrane described in any example of the first aspect of the present application in the field of water treatment, biomedicine, food processing or chemical purification.

[0105] The composite separation membrane of the present application and the composite separation membrane prepared by the above preparation method can be used as a membrane distillation hollow fiber membrane. Figure 5 During the separation process, water on the inlet side A, i.e., the inlet water, first permeates through the hydrophilic modified layer 20, reaches the membrane pores of the hollow polymer-based membrane 10, and ultimately permeates the membrane to the permeate side B, completing the hydrophilic-hydrophobic pathway of water molecule transfer along the water molecule flow direction C. When applied to water treatment, the composite separation membrane of the present application is suitable for various industrial wastewater treatment, seawater desalination, ultrapure water production, and the concentration and separation of volatile substance aqueous solutions.

[0106] For example, in the biomedicine field, the hollow polymer-based membranes of this application can be used to separate and purify biomacromolecules, such as proteins, DNA, and vaccines. In the food processing field, the hollow polymer-based membranes of this application can be used to separate nutrients from concentrated juices and dairy products, improving product quality. In the chemical purification field, the hollow polymer-based membranes of this application can achieve precise separation of substances of different molecular weights or polarities in the production of fine chemicals.

[0107] The following further specific examples are provided to illustrate the present application in detail. It should also be understood that the following examples are only used to further illustrate the present application and cannot be understood as limiting the scope of protection of the present application. Some non-essential improvements and adjustments made by those skilled in the art based on the above content of the present application belong to the scope of protection of the present application. The specific process parameters and the like in the following embodiments are only examples within a suitable range, that is, those skilled in the art can make a selection within a suitable range through the description herein, and are not necessarily limited to the specific values of the embodiments below.

[0108] Example 1

[0109] (1) Pretreatment of hollow polymer-based membrane: Take a hollow fiber ultrafiltration membrane (hollow polymer-based membrane, PVDF material), wherein the outer diameter of the hollow fiber ultrafiltration membrane is 500μm~600μm, the inner diameter of the hollow fiber ultrafiltration membrane is 200μm~300μm, and the pore size of the membrane pores on the surface of the hollow fiber ultrafiltration membrane is 0.3μm~0.8μm. Immerse the hollow fiber ultrafiltration membrane in a 70% mass concentration ethanol solution and wet it for 20 minutes to reduce the surface tension of the hollow fiber ultrafiltration membrane, dissolve the amorphous region of the hollow fiber ultrafiltration membrane, and expose active sites such as C-F bonds.

[0110] (2) Preparation of casting solution: Graphene oxide nanosheets and nanocellulose were mixed in a solvent (water:ethanol = 7:3, v / v), ultrasonically treated for 50 min, and then sulfonated succinic acid was added and reacted for 2 h to 4 h to prepare a casting solution. The mass concentration of graphene oxide in the casting solution was 0.3%, the mass concentration of nanocellulose was 0.1%, and the mass concentration of sulfonated succinic acid was 0.5%.

[0111] (3) Preparation of modified layer by negative pressure-filtration: The pretreated hollow fiber ultrafiltration membrane was immersed in the casting solution for 15 minutes, and a negative pressure of -0.08 MPa was applied to the hollow inner cavity of the hollow fiber ultrafiltration membrane. The casting solution was used to form a depression in the membrane pores of the hollow fiber ultrafiltration membrane (depth of about 80 nm~120 nm) by filtration; after thermal curing at 70°C for 1.5 hours, at least part of the nanocellulose was fixed between the layers of the graphene oxide nanosheets, and at least part of the sulfonated succinic acid was fixed between the layers of the graphene oxide nanosheets to form a modified layer, thereby preparing a composite separation membrane.

[0112] Comparative Example 1

[0113] In Comparative Example 1, only the hollow fiber ultrafiltration membrane of Example 1 was used.

[0114] Comparative Example 2

[0115] Comparative Example 2 is substantially the same as Example 1, with the main difference being that the preparation steps of the composite separation membrane of Comparative Example 2 do not include nanocellulose.

[0116] (1) Pretreatment of hollow polymer-based membrane: Take a hollow fiber ultrafiltration membrane (hollow polymer-based membrane, PVDF material), wherein the outer diameter of the hollow fiber ultrafiltration membrane is 500μm~600μm, the inner diameter of the hollow fiber ultrafiltration membrane is 200μm~300μm, and the pore size of the membrane pores on the surface of the hollow fiber ultrafiltration membrane is 0.3μm~0.8μm. Immerse the hollow fiber ultrafiltration membrane in a 70% mass concentration ethanol solution and wet it for 20 minutes to reduce the surface tension of the hollow fiber ultrafiltration membrane, dissolve the amorphous region of the hollow fiber ultrafiltration membrane, and expose active sites such as C-F bonds.

[0117] (2) Preparation of casting solution: Graphene oxide nanosheets were mixed in a solvent (water:ethanol = 7:3, v / v), ultrasonically treated for 50 min, and then sulfonated succinic acid was added and reacted for 2 h to 4 h to prepare a casting solution. The mass concentration of graphene oxide in the casting solution was 0.3%, and the mass concentration of sulfonated succinic acid was 0.5%.

[0118] (3) Preparation of modified layer by negative pressure-filtration: The pretreated hollow fiber ultrafiltration membrane was immersed in the casting solution for 15 minutes, and a negative pressure of -0.08 MPa was applied to the hollow inner cavity of the hollow fiber ultrafiltration membrane. The casting solution was used to form a depression in the membrane pores of the hollow fiber ultrafiltration membrane (depth of about 80 nm~120 nm) by filtration. After thermal curing at 70°C for 1.5 hours, at least part of the sulfonated succinic acid was fixed between the layers of the graphene oxide nanosheets to form a modified layer, and a composite separation membrane was prepared.

[0119] Comparative Example 3

[0120] Comparative Example 3 is substantially the same as Example 1, with the main difference being that the preparation steps of the composite separation membrane of Comparative Example 3 do not include sulfonated succinic acid.

[0121] (1) Pretreatment of hollow polymer-based membrane: Take a hollow fiber ultrafiltration membrane (hollow polymer-based membrane, PVDF material), wherein the outer diameter of the hollow fiber ultrafiltration membrane is 500μm~600μm, the inner diameter of the hollow fiber ultrafiltration membrane is 200μm~300μm, and the pore size of the membrane pores on the surface of the hollow fiber ultrafiltration membrane is 0.3μm~0.8μm. Immerse the hollow fiber ultrafiltration membrane in a 70% mass concentration ethanol solution and wet it for 20 minutes to reduce the surface tension of the hollow fiber ultrafiltration membrane, dissolve the amorphous region of the hollow fiber ultrafiltration membrane, and expose active sites such as C-F bonds.

[0122] (2) Preparation of casting solution: Graphene oxide nanosheets and nanocellulose were mixed in a solvent (water:ethanol = 7:3, v / v) and ultrasonically treated for 50 min to prepare a casting solution. The mass concentration of graphene oxide in the casting solution was 0.3%, and the mass concentration of nanocellulose was 0.1%.

[0123] (3) Preparation of modified layer by negative pressure-filtration: The pretreated hollow fiber ultrafiltration membrane was immersed in the casting liquid for 15 minutes, and a negative pressure of -0.08 MPa was applied to the hollow inner cavity of the hollow fiber ultrafiltration membrane. The casting liquid was used to form a depression in the membrane pores of the hollow fiber ultrafiltration membrane (depth of about 80 nm~120 nm) by filtration; after thermal curing at 70°C for 1.5 hours, at least part of the nanocellulose was fixed between the layers of the graphene oxide nanosheets to form a modified layer, and a composite separation membrane was prepared.

[0124] Test Case

[0125] The ultrafiltration membranes of the examples and comparative examples were contaminated with a 500 ppm humic acid solution for 2 hours to test their filtration performance. Furthermore, the bonding strength between the modified layer and the hollow fiber ultrafiltration membrane was tested under high pressure (>0.5 MPa), acidic (pH 2), and alkaline (pH 12) conditions for 100 hours. The corresponding test results are shown in Table 1.

[0126] Table 1 Comparison of membrane filtration performance

[0127]

[0128] As can be seen from Table 1, the composite separation membrane provided in the embodiment of the present application has more excellent membrane filtration performance, and the bonding strength between the modified layer and the hollow polymer base membrane is relatively high, and it has excellent stability, which can effectively improve the water production efficiency and reduce the operating cost.

[0129] The technical features of the above-mentioned embodiments can be combined arbitrarily. In order to make the description concise, not all possible combinations of the technical features in the above-mentioned embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0130] The embodiments described above only express several implementation methods of the present application, which are convenient for understanding the technical solutions of the present application in a specific and detailed manner, but they cannot be understood as limiting the scope of protection of the invention patent. It should be pointed out that for ordinary technicians in this field, without departing from the concept of the present application, several variations and improvements can be made, which all fall within the scope of protection of the present application. It should be understood that the technical solutions obtained by those skilled in the art through logical analysis, reasoning or limited experiments on the basis of the technical solutions provided in the present application are all within the scope of protection of the claims attached to the present application. Therefore, the scope of protection of the patent of this application shall be based on the content of the attached claims, and the description can be used to interpret the content of the claims.

Claims

1. A composite separation membrane, characterized in that The composite separation membrane comprises a hollow polymer base membrane and a modified layer attached to the outer surface of the hollow polymer base membrane; the modified layer has a two-dimensional network structure; The surface of the hollow polymer-based membrane has a plurality of membrane pores, and at least part of the modified layer forms a depression in the membrane pores; the depth of the depression formed by the modified layer in the membrane pores is 50 nm to 200 nm; The modified layer includes graphene oxide nanosheets, nanocellulose and sulfonated succinic acid; at least part of the nanocellulose is fixed between the sheets of the graphene oxide nanosheets, and at least part of the sulfonated succinic acid is fixed between the sheets of the graphene oxide nanosheets.

2. The composite separation membrane according to claim 1, characterized in that The fixing method of the nanocellulose includes: intermolecular interaction between the nanocellulose and the graphene oxide nanosheets; And / or, the immobilization method of the sulfonated succinic acid includes: intermolecular interaction between the sulfonated succinic acid and the graphene oxide nanosheets.

3. The composite separation membrane according to claim 2, characterized in that The fixing method of the nanocellulose includes at least one of physical adsorption and coupling connection between the nanocellulose and the active sites of the graphene oxide nanosheets; And / or, the immobilization method of the sulfonated succinic acid includes at least one of physical adsorption and coupling connection between the sulfonated succinic acid and the active sites of the graphene oxide nanosheets.

4. The composite separation membrane according to claim 3, characterized in that The fixing method of the nanocellulose includes: coupling connection between the nanocellulose and the oxygen-containing functional groups of the graphene oxide nanosheets; And / or, the immobilization method of the sulfonated succinic acid includes: coupling connection between the sulfonated succinic acid and the oxygen-containing functional groups of the graphene oxide nanosheets.

5. The composite separation membrane according to claim 1, characterized in that The mass ratio of the graphene oxide nanosheets to the nanocellulose is (0.1-0.5): (0.05-0.2); And / or, the mass ratio of the graphene oxide nanosheets to the sulfonated succinic acid is (0.1-0.5): (0.2-0.8).

6. The composite separation membrane according to any one of claims 1 to 5, characterized in that The hollow polymer-based membrane has one or more of the following characteristics: (1) The outer diameter of the hollow polymer-based membrane is 500 μm to 600 μm; (2) The inner diameter of the hollow polymer-based membrane is 200 μm to 300 μm; (3) The pore size of the membrane is 0.3 μm to 0.8 μm; (4) The material of the hollow polymer base membrane includes one or more of polyvinylidene fluoride, polypropylene and polyacrylonitrile.

7. The composite separation membrane according to any one of claims 1 to 5, characterized in that The composite separation membrane has one or more of the following characteristics: (1) The contact angle of static water on the surface of the composite separation membrane is ≤40°; (2) The static adsorption amount of humic acid on the surface of the composite separation membrane is 40 mg / m 2 ~170 mg / m 2 ; (3) The retention rate of humic acid by the composite separation membrane is 90%~98%.

8. A method for preparing a composite separation membrane according to any one of claims 1 to 7, characterized in that: The following steps are involved: The graphene oxide nanosheets and the nanocellulose are mixed in a solvent, and after ultrasonic treatment, the sulfonated succinic acid is added thereto for mixing reaction to prepare a casting solution; The casting liquid is coated on the surface of the hollow polymer-based membrane, and negative pressure is applied in the hollow cavity of the hollow polymer-based membrane to form a depression of the casting liquid in at least part of the membrane pores of the hollow polymer-based membrane; after thermal curing, at least part of the nanocellulose is fixed between the layers of the graphene oxide nanosheets, and at least part of the sulfonated succinic acid is fixed between the layers of the graphene oxide nanosheets to form the modified layer, thereby preparing the composite separation membrane.

9. The method for preparing a composite separation membrane according to claim 8, wherein: The negative pressure is -0.1MPa~-0.05MPa; And / or, the process parameters of the thermal curing include: a thermal curing temperature of 60° C. to 80° C., and a thermal curing time of 1 hour to 2 hours.

10. The method for preparing a composite separation membrane according to claim 8, wherein: The preparation method has one or more of the following characteristics: (1) The process parameters of the ultrasonic treatment include: ultrasonic time of 30min~60min; (2) The process parameters of the mixing reaction include: mixing time of 2 h to 4 h, rotation speed of 500 r / min to 800 r / min; (3) The mass ratio of the graphene oxide nanosheets to the nanocellulose is (0.1-0.5): (0.05-0.2); (4) The mass ratio of the graphene oxide nanosheets to the sulfonated succinic acid is (0.1-0.5): (0.2-0.8); (5) The solvent includes deionized water and an alcohol solvent in a volume ratio of (5-8): (2-5).

11. The method for preparing a composite separation membrane according to any one of claims 8 to 10, characterized in that: Before the step of coating the casting solution on the surface of the hollow polymer base membrane, the method further includes: soaking the hollow polymer base membrane in an organic solvent, washing, and drying; The process parameters of the infiltration treatment include: time is 10min~30min.

12. Use of the composite separation membrane according to any one of claims 1 to 7 in the fields of water treatment, biomedicine, food processing or chemical purification.

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