Hollow fiber membrane for treating printing and dyeing wastewater and preparation method thereof

Abstract

The invention discloses a hollow fiber membrane for treating printing and dyeing wastewater and a preparation method thereof, and relates to the technical field of sewage treatment.The hollow fiber membrane for treating printing and dyeing wastewater comprises a polyether sulfone hollow fiber base membrane, and hydrophilic groups and hydrophobic groups are grafted on the surface and the thickness direction of the polyether sulfone hollow fiber base membrane; the number of the hydrophilic groups positioned on the outer surface of the polyether sulfone hollow fiber base membrane is higher than that of the hydrophilic groups positioned on the inner surface of the polyether sulfone hollow fiber base membrane; the number of the hydrophobic groups positioned on the inner surface of the polyether sulfone hollow fiber base membrane is higher than that of the hydrophobic groups positioned on the outer surface of the polyether sulfone hollow fiber base membrane. The hollow fiber membrane has the effects of improving the removal performance of the hollow fiber membrane on water-soluble dyes and grease impurities in printing and dyeing wastewater and having better durability and self-cleaning performance.

Description

Technical Field

[0001] The invention relates to a hollow fiber membrane for treating printing and dyeing wastewater and a preparation method thereof, belonging to the technical field of sewage treatment. Background Art

[0002] The treatment of printing and dyeing wastewater has received increasing attention, especially when the wastewater contains a large amount of water-soluble dyes, oils and other organic pollutants. Traditional sewage treatment methods are often difficult to effectively remove these pollutants. In particular, some special pollutants, such as water-soluble dyes and emulsified oils, are difficult to achieve the expected treatment effect with conventional physical and chemical methods due to the particularity of their molecular structure and physical and chemical properties. In order to improve the efficiency and effect of wastewater treatment, it is particularly urgent to develop new membrane materials and membrane technologies that can specifically remove these pollutants.

[0003] At present, membrane separation technology has been widely used in the field of sewage treatment. As a form of membrane separation technology, hollow fiber membrane has gradually become an important tool for treating wastewater, especially printing and dyeing wastewater, because of its high specific surface area, excellent filtration performance and easy modular design. The performance of hollow fiber membrane is affected by factors such as the membrane material itself, the membrane surface structure and the pore size distribution. Existing hollow fiber membranes mostly use a single membrane material or a simple surface modification method, which leads to certain limitations in treating specific wastewater. Summary of the invention

[0004] In view of the shortcomings of the prior art, the object of the present invention is to provide a hollow fiber membrane for treating printing and dyeing wastewater and a preparation method thereof.

[0005] The above object of the present invention is achieved through the following technical solutions: A hollow fiber membrane for treating printing and dyeing wastewater, comprising a polyethersulfone hollow fiber-based membrane, wherein the polyethersulfone hollow fiber-based membrane is grafted with hydrophilic groups and hydrophobic groups on its surface and in the thickness direction; The hydrophilic group is selected from aminopropionic acid (APTES) or polyvinyl alcohol (PVA), and the hydrophobic group is selected from fluorinated alkyltrimethylsilane (FAS) or long-chain alkyltrimethylammonium chloride (CTAC); The number of the hydrophilic groups on the outer surface of the polyethersulfone hollow fiber-based membrane is greater than the number of the hydrophilic groups on the inner surface of the polyethersulfone hollow fiber-based membrane, and the hydrophilic groups decrease gradually from the outside to the inside along the thickness direction of the polyethersulfone hollow fiber-based membrane; The number of the hydrophobic groups on the inner surface of the polyethersulfone hollow fiber-based membrane is greater than that on the outer surface of the polyethersulfone hollow fiber-based membrane, and the hydrophobic groups decrease gradually from inside to outside along the thickness direction of the polyethersulfone hollow fiber-based membrane.

[0006] The hollow fiber membrane for treating printing and dyeing wastewater provided by the present invention has a unique surface and inner layer structure design, which can efficiently remove water-soluble dyes and oil impurities, thereby improving the effect of wastewater treatment. First, the affinity of the membrane for water molecules is enhanced by grafting hydrophilic groups (such as aminopropionic acid (APTES) or polyvinyl alcohol (PVA)) on the outer surface of the membrane. The hydrophilic group can effectively adsorb water-soluble dyes or other water-soluble pollutants in the wastewater through hydrogen bonds or electrostatic effects. The presence of the hydrophilic group not only improves the adsorption capacity of water-soluble dyes, but also reduces the deposition of water-soluble pollutants on the membrane surface, thereby avoiding membrane pollution and maintaining the long-term stability and flux of the membrane.

[0007] In addition, the present invention can effectively treat hydrophobic pollutants such as grease by precisely controlling the membrane pore size and designing the structure of the membrane. The pore size of the membrane is designed to be between 0.1-0.5 μm, so that larger grease particles can be effectively blocked by the physical barrier effect, thereby preventing grease from passing through the pores of the membrane. However, for fine grease particles and emulsified oil, the role of the hydrophobic groups of the membrane (such as fluorinated alkyltrimethylsilane (FAS) or long-chain alkyltrimethylammonium chloride (CTAC)) is more critical. The hydrophobic groups reduce the affinity between the inner surface of the membrane and grease, making it easier for grease substances to pass through the membrane, and during the backwashing process, the grease can be smoothly discharged from the inner surface area of ​​the membrane to avoid the accumulation of grease on the membrane surface. The hydrophobic groups can effectively reduce grease contamination by reducing the adhesion of grease to the membrane, thereby improving the flux and service life of the membrane.

[0008] In the present invention, the gradient distribution design of hydrophilic and hydrophobic groups between the outer surface and the inner surface enables the membrane to achieve graded removal of water-soluble pollutants and oily pollutants in wastewater. Specifically, the hydrophilic groups of the outer layer of the membrane are conducive to the adsorption of pollutants such as water-soluble dyes, while the hydrophobic groups of the inner layer of the membrane can repel oily pollutants, ensuring that different areas of the membrane can handle different types of pollutants. This design enables the membrane to efficiently and selectively remove multiple pollutants in complex wastewater treatment, thereby improving the overall efficiency of wastewater treatment.

[0009] In addition, the gradient structure of the membrane also has a positive impact on the self-cleaning performance. Due to the clever design of the hydrophilic and hydrophobic groups, when the membrane surface is flushed or cleaned by external water flow, the difference between the hydrophilic and hydrophobic areas makes it easier to remove the attached pollutants on the membrane surface. This structural design improves the self-cleaning ability of the membrane and effectively reduces the deposition of pollutants on the membrane surface, thereby extending the service life of the membrane and improving the operating efficiency of the membrane.

[0010] Furthermore, the average pore size of the polyethersulfone hollow fiber-based membrane decreases gradually from the outside to the inside along the thickness direction.

[0011] The pore size of the polyethersulfone hollow fiber membrane is a gradient decreasing structure along the thickness of the membrane. This design effectively optimizes the wastewater treatment process, especially in filtering and removing different types of pollutants. Specifically, the larger pore size of the outer layer of the membrane can effectively intercept larger particles and pollutants in the wastewater, reducing the accumulation of these large particles on the membrane surface, thereby effectively avoiding the initial blockage problem on the membrane surface. This not only helps to maintain a high flux of the membrane, but also prolongs the service life of the membrane and reduces the need for frequent cleaning.

[0012] The smaller pore size of the inner layer plays a more delicate screening role, further improving the membrane's ability to intercept fine particles, micropollutants and water-soluble dyes. The pore size design of the membrane is particularly important when dealing with hydrophobic pollutants such as oils and fats. Oil pollutants are mainly intercepted by the pore size of the membrane, while the larger pore size of the outer layer can effectively avoid the rapid accumulation of oily substances, slow down the pollution rate of the membrane, and ensure the cleanliness of the membrane surface and stable flux. At the same time, the smaller pore size of the inner layer can prevent oily substances and other fine pollutants from further penetrating into the interior of the membrane, thereby improving the filtration accuracy and overall performance of the membrane.

[0013] This gradient structure design is also of great significance for the membrane's backwashing process. During backwashing, the larger pore size of the outer layer helps to quickly remove large particle pollutants on the membrane surface, reducing the pollution burden on the membrane surface; while the smaller pore size of the inner layer further helps to remove fine grease and other hydrophobic substances, ensuring that during backwashing, grease and other hydrophobic pollutants can be easily discharged from the inner surface area of ​​the membrane, thereby improving the membrane's anti-pollution ability and extending the membrane's service life.

[0014] In addition, the outer layer of the polyethersulfone hollow fiber membrane is grafted with a high content of hydrophilic groups. These hydrophilic groups can strongly adsorb water-soluble dye molecules, significantly improving the membrane's removal efficiency for water-soluble dye impurities. The larger pore size design of the outer layer not only helps the membrane to efficiently intercept large particle pollutants, but also enhances the adsorption and removal capacity of water-soluble dyes through the action of hydrophilic groups. Combined with the membrane pore size gradient structure, the hydrophilic groups in the outer layer make the membrane more effective in removing water-soluble dyes, ensuring the efficient removal of water-soluble dyes in wastewater.

[0015] Furthermore, the average pore size of the outer surface of the polyethersulfone hollow fiber-based membrane is 0.1-0.5 μm, and the average pore size of the inner surface of the polyethersulfone hollow fiber-based membrane is 0.05-0.2 μm.

[0016] The pore sizes of the outer and inner surfaces of the hollow fiber membrane are designed to be between 0.1-0.5μm and 0.05-0.2μm, which further optimizes the filtration performance of the membrane, especially in removing different types of pollutants in wastewater. The larger pore size (0.1-0.5μm) on the outer surface of the membrane can effectively intercept larger particulate pollutants, including grease particles, suspended matter, etc., to prevent these pollutants from accumulating on the membrane surface and reduce the risk of clogging on the membrane surface. This helps to maintain a higher flux on the one hand, and on the other hand, it also reduces the pollution burden of the membrane and extends the service life of the membrane.

[0017] The smaller pore size (0.05-0.2μm) on the inner surface of the membrane facilitates finer screening, especially for the removal of water-soluble pollutants such as tiny particles and emulsified oil. The smaller pore size can prevent the penetration of fine pollutants, and at the same time improve the removal efficiency of the membrane through fine filtering, ensuring the efficient removal of water-soluble pollutants in wastewater, and further improving the filtration accuracy and processing capacity of the membrane.

[0018] This pore size gradient design can effectively optimize the filtration and pollutant removal process in wastewater treatment, ensure the efficient separation of pollutants of different particle sizes, help reduce the maintenance frequency of the membrane and extend the service life of the membrane.

[0019] Furthermore, the contact angle A1 of the outer surface of the hollow fiber membrane is 60°-80°, and the contact angle A2 of the inner surface of the hollow fiber membrane is 100°-120°.

[0020] The contact angle A1 of the outer surface of the hollow fiber membrane is controlled to be 60°-80°, and the contact angle A2 of the inner surface is controlled to be 100°-120°, so that the membrane has excellent hydrophilic and hydrophobic properties during the water treatment process. Specifically, the lower contact angle of the outer surface (60°-80°) makes the membrane surface more hydrophilic, enhances the interaction between the membrane and water molecules, and promotes the adsorption and removal of water-soluble dyes and other water-soluble pollutants. The lower contact angle helps keep the membrane surface clean, reduces the deposition of water-soluble pollutants, and thus avoids membrane surface contamination, thereby improving the flux and stability of the membrane.

[0021] The higher contact angle (100°-120°) of the inner surface shows stronger hydrophobicity, which effectively reduces the affinity of oil and grease pollutants to the membrane surface, making it easier for hydrophobic substances such as oil and grease to be washed out of the inner surface area of ​​the membrane through reverse washing, and is less likely to cause irreversible flux loss.

[0022] Furthermore, a cellulose nanocrystal complex is grafted or adsorbed on the outer surface of the polyethersulfone hollow fiber-based membrane. The preparation method of the cellulose nanocrystal complex is as follows: (1) Surface oxidation: cellulose nanocrystals were immersed in hydrogen peroxide solution for 1-2 hours, then washed with deionized water and dried; (2) Mixing laccase and cellulose nanocrystals: Prepare a surface oxidized cellulose nanocrystal solution with a mass concentration of 1-2 wt%, and mix it evenly with 50-80 U / mL laccase and 100-200 U / mL lipase solution; (3) Cross-linking: Add 0.1-0.5 wt% glutaraldehyde cross-linking agent to the mixed solution, adjust the pH to 4-5, and stir at room temperature for 6-12 hours.

[0023] (4) Separation and drying: The mixed solution after the reaction is separated by centrifugation and then dried at 40°C to obtain a cellulose nanocrystal complex.

[0024] The outer surface of the hollow fiber membrane is grafted or adsorbed with cellulose nanocrystal complexes, which further improves the hydrophilicity of the outer surface of the hollow fiber membrane and enhances the pollutant removal ability of the membrane, especially in the treatment of water-soluble dyes and oil pollutants. The introduction of cellulose nanocrystal complexes not only enhances the hydrophilicity of the membrane surface, but also plays a catalytic role of laccase and lipase to degrade and remove harmful substances and oil impurities in wastewater.

[0025] The preparation method of the cellulose nanocrystal complex involves effectively combining laccase, lipase and cellulose nanocrystals through specific chemical reaction steps. When laccase is mixed with surface-oxidized cellulose nanocrystals, lipase can catalyze the hydrolysis of fatty acids, thereby enhancing the affinity of the cellulose nanocrystal surface and providing more contact sites for laccase. The action of lipase can also promote the binding of laccase to cellulose nanocrystals, thereby improving the distribution and activity of laccase in the complex and enhancing the catalytic performance of the complex.

[0026] Through this preparation method, laccase, lipase and cellulose nanocrystals form a stable composite structure at the molecular level, giving the membrane higher hydrophilicity and pollutant removal ability.

[0027] Furthermore, the step of grafting the cellulose nanocrystal complex onto the outer surface of the polyethersulfone hollow fiber base membrane is as follows: (1) Prepare 0.5-2 mg / mL cellulose nanocrystal complex solution; (2) Soaking the outer surface of the polyethersulfone hollow fiber membrane base membrane in the cellulose nanocrystal complex solution for a soaking time of 30-60 minutes, and then exposing the membrane to 40°C for drying.

[0028] By grafting cellulose nanocrystal complexes onto the outer surface of polyethersulfone hollow fiber-based membranes, the performance of the membranes was further enhanced, especially when treating wastewater containing water-soluble dyes and oil-based pollutants. By controlling the grafting concentration and soaking time of the cellulose nanocrystal complexes, the uniform distribution of the complexes on the outer surface area of ​​the membrane was ensured, thereby greatly improving the hydrophilicity of the membrane and its adsorption capacity for water-soluble pollutants.

[0029] In this step, the grafting of cellulose nanocrystal complex effectively increases the catalytic sites on the membrane surface, which not only enhances the removal ability of water-soluble dyes, but also improves the cleaning ability of the membrane surface. Laccase, as a catalyst, can degrade certain organic pollutants, reduce the pollution of the membrane surface, and maintain the efficient operation of the membrane. Lipase can effectively degrade certain oil impurities attached to the membrane, so that the removal effect of oil impurities can be effectively improved during the backwashing process.

[0030] Furthermore, the polyethersulfone hollow fiber-based membrane is first grafted with hydrophilic groups and hydrophobic groups, and then grafted with cellulose nanocrystal complexes.

[0031] The main purpose of grafting the hydrophilic group and the hydrophobic group first and then the cellulose nanocrystal complex is to increase the grafting amount of the cellulose nanocrystal complex and ensure that the complex has more grafting sites on the membrane surface. The grafting of hydrophilic groups and hydrophobic groups can provide a surface functionalized gradient structure for the membrane surface, so that the surface forms dual characteristics of both hydrophilicity and hydrophobicity. Specifically, the hydrophilic areas formed by the hydrophilic groups on the membrane surface can effectively enhance the contact of the complex and provide more chemical reaction sites; while the hydrophobic groups form hydrophobic areas on the membrane surface, improving the stability of the complex in these areas and the grafting efficiency.

[0032] The hydrophilic groups facilitate the grafting of cellulose nanocrystal complexes by providing a higher polar environment, especially enabling the laccase part to be more stably attached to the membrane surface, thus improving the affinity of the complex. Therefore, more complexes can be effectively chemically grafted in the hydrophilic area, thereby increasing the grafting amount.

[0033] The hydrophobic groups provide a non-polar environment that helps the grafting of cellulose nanocrystals on the membrane surface. Since cellulose nanocrystals have good hydrophobicity, they can interact with the hydrophobic groups on the membrane surface to ensure that the complex has stronger adsorption in the hydrophobic area. This effect not only increases the stability of the complex, but also increases its grafting amount, making the distribution of the entire complex on the membrane surface more uniform.

[0034] By controlling the sequential grafting of hydrophilic and hydrophobic groups, the composite can have a higher grafting density on the membrane surface, especially in the hydrophilic area of ​​the membrane surface, where the grafting amount of laccase and cellulose nanocrystals is significantly increased. This design optimizes the catalytic and adsorption properties of the composite and further improves the overall performance of the membrane.

[0035] Due to the synergistic effect of the hydrophilic and hydrophobic regions on the surface during the grafting of the complex, the grafting amount of the cellulose nanocrystal complex is significantly increased compared with the traditional method. The functionalized gradient structure formed on the membrane surface can provide more grafting sites and optimize the distribution of the complex, thereby increasing the grafting amount and improving the catalytic degradation and adsorption effects of the membrane. This increase in the grafting amount not only improves the pollutant removal efficiency of the membrane in the wastewater treatment process, but also enhances the stability and pollution resistance of the membrane after long-term use, extending the service life of the membrane.

[0036] Furthermore, the contact angle A3 of the outer surface of the hollow fiber membrane is 0.5 to 0.9×A1, and the contact angle A4 of the inner surface of the hollow fiber membrane is 0.98 to 1.1×A2.

[0037] By controlling the ratio of the contact angles A3 and A1 on the outer surface to 0.5 to 0.9 times, and the ratio of the contact angles A4 and A2 on the inner surface to 0.98 to 1.1 times, the hydrophilicity of the outer surface of the membrane is greatly improved, while the hydrophobicity of the inner surface of the membrane is not excessively reduced. Specifically, the increased hydrophilicity of the outer surface can enhance the interaction between the membrane and water-soluble pollutants, thereby optimizing the pollutant removal efficiency during wastewater treatment. At the same time, the contact angle ratio of the inner surface is kept unchanged to ensure that the membrane can still maintain good hydrophobicity when treating oily wastewater. The lower contact angle change on the inner surface (the ratio of A4 to A2 is 0.98 to 1.1 times) ensures that the hydrophobicity of the membrane is not affected too much, thereby effectively avoiding the deposition of oil and fat pollutants on the inner surface of the membrane, and improving the membrane's anti-pollution ability and backwashing effect.

[0038] A method for preparing a hollow fiber membrane for treating printing and dyeing wastewater comprises the following steps: S1 base membrane activation: plasma treatment of polyethersulfone hollow fiber base membrane; plasma power: 50-100W; treatment time: 2-5 minutes; S2 hydrophilic group grafting: (1) The two ends of the activated polyethersulfone hollow fiber-based membrane are sealed, and the outer surface is immersed in a hydrophilic group grafting solution, and reacted at 50° C. for 4-6 hours; the hydrophilic group is selected from aminopropionic acid (APTES) or polyvinyl alcohol (PVA), and the mass fraction of the hydrophilic group grafting solution is 0.5%-2%; (2) Wash the membrane surface with deionized water to remove unreacted monomers; (3) Dry at 60°C for 12 hours; S3 hydrophobic group grafting: (1) The hydrophobic group grafting solution is filled into the interior of the polyethersulfone hollow fiber-based membrane after the hydrophilic group grafting, and reacted at 40° C. for 3-5 hours; the hydrophobic group is selected from fluorinated alkyltrimethylsilane (FAS) or long-chain alkyltrimethylammonium chloride (CTAC), and the concentration of the hydrophobic group grafting solution is controlled to be 0.1%-0.5%; (2) Wash the membrane surface with deionized water to remove ungrafted groups; (3) Dry at 60°C for 24 hours.

[0039] Through plasma treatment and the grafting of hydrophilic and hydrophobic groups, the surface properties of the membrane are optimized, enabling it to efficiently remove water-soluble dyes and oil pollutants in wastewater. The plasma treatment step can effectively activate the membrane surface, improve the grafting effect of hydrophilic and hydrophobic groups, ensure that the membrane surface has excellent hydrophilicity and hydrophobicity, and thus improve the pollutant removal efficiency of the membrane.

[0040] After the hydrophilic groups are grafted, the membrane surface can enhance the adsorption capacity of water-soluble pollutants and effectively remove soluble substances in water; while the grafting of hydrophobic groups improves the hydrophobicity of the membrane and promotes the separation of oil and fat pollutants. This method can not only improve the separation performance of the membrane, but also improve the self-cleaning property of the membrane, reduce the deposition of pollutants on the membrane surface, and extend the service life of the membrane.

[0041] Furthermore, the method further comprises the following steps: (1) soaking a polyethersulfone hollow fiber-based membrane grafted with hydrophilic groups and hydrophobic groups in a solution containing a surfactant, wherein the surfactant is a polyvinyl alcohol surfactant, and the solution concentration is 0.01%-0.1%; (2) The surfactant is evenly coated on the membrane surface by spin coating to form a thin and uniform surfactant film to adjust the hydrophilicity and hydrophobicity gradient of the membrane; (3) Drying the coated film at 40°C to ensure that the surfactant layer is firmly fixed on the film surface; (4) Finally, the membrane surface is cleaned with deionized water to remove unreacted surfactant and ensure that there is no excess residue on the membrane surface.

[0042] Surfactants can form a uniform film on the membrane surface, reduce the surface tension of the membrane, and make the membrane surface more wettable, thereby improving the hydrophilicity of the membrane. Increasing the hydrophilicity of the membrane can effectively reduce scaling on the membrane surface and the adsorption of pollutants, reduce the occurrence of membrane pollution, and extend the service life of the membrane. As a highly efficient dispersant, polyvinyl alcohol surfactant can effectively disperse impurities that may appear on the membrane surface during the coating process, preventing these impurities from reacting adversely with the membrane surface or forming a scaling layer. By coating a uniform surfactant film, it can help optimize the surface microstructure of the membrane, reduce scaling and blocking of the membrane, and improve the stability and performance of the membrane.

[0043] Compared with the prior art, the beneficial effects of the present invention are mainly reflected in the following aspects: 1. By grafting hydrophilic groups (such as aminopropionic acid (APTES) or polyvinyl alcohol (PVA)) onto the outer surface of the polyethersulfone hollow fiber membrane and grafting hydrophobic groups (such as fluorinated alkyltrimethylsilane (FAS) or long-chain alkyltrimethylammonium chloride (CTAC)) onto the inner surface, the present invention achieves a gradient change in the distribution of groups on the inner and outer surfaces of the membrane. This design can effectively remove water-soluble dyes and oily pollutants in a graded manner. Specifically, the higher hydrophilic groups on the outer surface help to adsorb water-soluble dyes and other water-soluble pollutants, thereby improving the removal efficiency of the membrane for these pollutants and avoiding the pollution problem of deposition on the membrane surface. The higher hydrophobic groups on the inner surface effectively reduce the affinity of oily pollutants to the membrane, prevent oily pollutants from accumulating on the membrane surface, thereby extending the service life of the membrane and improving the membrane's anti-pollution ability.

[0044] 2. In order to further improve the performance of the membrane, the present invention grafts or adsorbs cellulose nanocrystal complexes on the outer surface of the membrane. This complex forms a cross-linked structure through surface oxidation treatment and the action of enzymes such as laccase and lipase, which can further enhance the filtration performance of the membrane, especially in removing water-soluble pollutants and improving the anti-pollution ability of the membrane. The introduction of cellulose nanocrystal complexes not only improves the hydrophilicity of the membrane, but also improves the stability and anti-pollution property of the membrane, ensuring the high efficiency of the membrane in long-term use. DETAILED DESCRIPTION

[0045] The present invention is described in detail below in conjunction with embodiments.

[0046] The polyethersulfone hollow fiber base membrane adopts PES-HF-8040 from DuPont de Nemours, Inc.; The fluorinated alkyltrimethylsilane used was Dynasylan® F8261 produced by Evonik Industries AG of Germany; Polyvinyl alcohol used was PVA-217 produced by Kuraray Co., Ltd. of Japan; The long-chain alkyl trimethyl ammonium chloride is Luviquat® FC 370 produced by BASF SE; AJIPURE® L-Alanine produced by Ajinomoto Co., Inc. was used as the aminopropionic acid. Cellulose nanocrystals were BioNano-12 from FPInnovations Inc., Canada; Laccase used was NS51003-LT from Novozymes A / S; The lipase used was CALB-L produced by Chr. Hansen A / S.

[0047] Example 1 The hollow fiber membrane preparation method in this embodiment is as follows: S1 membrane activation: The polyethersulfone hollow fiber membrane was treated with plasma, and the average pore size of the outer surface was 0.5 μm, and the average pore size of the inner surface was 0.05 μm; Plasma power: 70W; treatment time: 3 minutes; S2 hydrophilic group grafting: (1) The two ends of the activated polyethersulfone hollow fiber-based membrane are sealed, and the outer surface is immersed in a hydrophilic group grafting solution, and reacted at 50°C for 4 hours; the hydrophilic group is polyvinyl alcohol (PVA), and the solvent is deionized water. The mass fraction of the hydrophilic group grafting solution is 0.5%; (2) Wash the membrane surface with deionized water to remove unreacted monomers; (3) Dry at 60°C for 12 hours; S3 hydrophobic group grafting: (1) The hydrophobic group grafting solution is filled into the interior of the polyethersulfone hollow fiber-based membrane after the hydrophilic group grafting, and reacted at 40° C. for 3 hours; the hydrophobic group is fluorinated alkyltrimethylsilane (FAS), and the concentration of the hydrophobic group grafting solution is controlled to be 0.5%; (2) Wash the membrane surface with deionized water to remove ungrafted groups; (3) Dry at 60°C for 24 hours.

[0048] The outer surface contact angle A1 of the prepared hollow fiber membrane was 80°, and the inner surface contact angle A2 was 120°.

[0049] Example 2 The hollow fiber membrane preparation method in this embodiment is as follows: S1 membrane activation: The polyethersulfone hollow fiber membrane was treated with plasma, and the average pore size of the outer surface was 0.3 μm, and the average pore size of the inner surface was 0.13 μm; Plasma power: 70W; treatment time: 3 minutes; S2 hydrophilic group grafting: (1) The two ends of the activated polyethersulfone hollow fiber-based membrane are sealed, and the outer surface is immersed in a hydrophilic group grafting solution, and reacted at 50°C for 4 hours; the hydrophilic group is polyvinyl alcohol (PVA), and the solvent is deionized water. The mass fraction of the hydrophilic group grafting solution is 1.2%; (2) Wash the membrane surface with deionized water to remove unreacted monomers; (3) Dry at 60°C for 12 hours; S3 hydrophobic group grafting: (1) The interior of the polyethersulfone hollow fiber-based membrane grafted with hydrophilic groups is filled with a grafting solution of hydrophobic groups, and reacted at 40° C. for 3 hours; the hydrophobic groups are fluorinated alkyltrimethylsilane (FAS), and the concentration of the grafting solution of the hydrophobic groups is controlled to be 0.4%; (2) Wash the membrane surface with deionized water to remove ungrafted groups; (3) Dry at 60°C for 24 hours.

[0050] The outer surface contact angle A1 of the prepared hollow fiber membrane was 75°, and the inner surface contact angle A2 was 110°.

[0051] Example 3 The hollow fiber membrane preparation method in this embodiment is as follows: S1 membrane activation: The polyethersulfone hollow fiber membrane was treated with plasma, and the average pore size of the outer surface was 0.2 μm, and the average pore size of the inner surface was 0.1 μm; Plasma power: 70W; treatment time: 3 minutes; S2 hydrophilic group grafting: (1) The two ends of the activated polyethersulfone hollow fiber-based membrane are sealed, and the outer surface is immersed in a hydrophilic group grafting solution, and reacted at 50°C for 4 hours; the hydrophilic group is polyvinyl alcohol (PVA), and the solvent is deionized water. The mass fraction of the hydrophilic group grafting solution is 2%; (2) Wash the membrane surface with deionized water to remove unreacted monomers; (3) Dry at 60°C for 12 hours; S3 hydrophobic group grafting: (1) The hydrophobic group grafting solution is filled into the interior of the polyethersulfone hollow fiber-based membrane after the hydrophilic group grafting, and reacted at 40° C. for 3 hours; the hydrophobic group is fluorinated alkyltrimethylsilane (FAS), and the concentration of the hydrophobic group grafting solution is controlled to be 0.1%; (2) Wash the membrane surface with deionized water to remove ungrafted groups; (3) Dry at 60°C for 24 hours.

[0052] The outer surface contact angle A1 of the prepared hollow fiber membrane was 60°, and the inner surface contact angle A2 was 100°.

[0053] Example 4 The hollow fiber membrane preparation method in this embodiment is as follows: S1 membrane activation: plasma treatment of polyethersulfone hollow fiber membrane, polyethersulfone hollow fiber membrane is a symmetrical membrane with an average pore size of 0.1 μm; Plasma power: 70W; treatment time: 3 minutes; S2 hydrophilic group grafting: (1) The two ends of the activated polyethersulfone hollow fiber-based membrane are sealed, and the outer surface is immersed in a hydrophilic group grafting solution, and reacted at 50°C for 4 hours; the hydrophilic group is polyvinyl alcohol (PVA), and the solvent is deionized water. The mass fraction of the hydrophilic group grafting solution is 2%; (2) Wash the membrane surface with deionized water to remove unreacted monomers; (3) Dry at 60°C for 12 hours; S3 hydrophobic group grafting: (1) The hydrophobic group grafting solution is filled into the interior of the polyethersulfone hollow fiber-based membrane after the hydrophilic group grafting, and reacted at 40° C. for 3 hours; the hydrophobic group is fluorinated alkyltrimethylsilane (FAS), and the concentration of the hydrophobic group grafting solution is controlled to be 0.1%; (2) Wash the membrane surface with deionized water to remove ungrafted groups; (3) Dry at 60°C for 24 hours.

[0054] The outer surface contact angle A1 of the prepared hollow fiber membrane was 60°, and the inner surface contact angle A2 was 110°.

[0055] Example 5 The hollow fiber membrane preparation method in this embodiment is as follows: S1 membrane activation: The polyethersulfone hollow fiber membrane was treated with plasma, and the average pore size of the outer surface was 0.6 μm, and the average pore size of the inner surface was 0.02 μm; Plasma power: 70W; treatment time: 3 minutes; S2 hydrophilic group grafting: (1) The two ends of the activated polyethersulfone hollow fiber-based membrane are sealed, and the outer surface is immersed in a hydrophilic group grafting solution, and reacted at 50°C for 4 hours; the hydrophilic group is polyvinyl alcohol (PVA), and the solvent is deionized water. The mass fraction of the hydrophilic group grafting solution is 2%; (2) Wash the membrane surface with deionized water to remove unreacted monomers; (3) Dry at 60°C for 12 hours; S3 hydrophobic group grafting: (1) The hydrophobic group grafting solution is filled into the interior of the polyethersulfone hollow fiber-based membrane after the hydrophilic group grafting, and reacted at 40° C. for 3 hours; the hydrophobic group is fluorinated alkyltrimethylsilane (FAS), and the concentration of the hydrophobic group grafting solution is controlled to be 0.3%; (2) Wash the membrane surface with deionized water to remove ungrafted groups; (3) Dry at 60°C for 24 hours.

[0056] The outer surface contact angle A1 of the prepared hollow fiber membrane was 70°, and the inner surface contact angle A2 was 115°.

[0057] Example 6 The hollow fiber membrane preparation method in this embodiment is as follows: S1 membrane activation: The polyethersulfone hollow fiber membrane was treated with plasma, and the average pore size of the outer surface was 0.5 μm, and the average pore size of the inner surface was 0.06 μm; Plasma power: 70W; treatment time: 3 minutes; S2 hydrophilic group grafting: (1) The two ends of the activated polyethersulfone hollow fiber-based membrane are sealed, and the outer surface is immersed in a hydrophilic group grafting solution, and reacted at 50°C for 4 hours; the hydrophilic group is polyvinyl alcohol (PVA), and the solvent is deionized water. The mass fraction of the hydrophilic group grafting solution is 0.9%; (2) Wash the membrane surface with deionized water to remove unreacted monomers; (3) Dry at 60°C for 12 hours; S3 hydrophobic group grafting: (1) The hydrophobic group grafting solution is filled into the interior of the polyethersulfone hollow fiber-based membrane after the hydrophilic group grafting, and reacted at 40° C. for 3 hours; the hydrophobic group is fluorinated alkyltrimethylsilane (FAS), and the concentration of the hydrophobic group grafting solution is controlled to be 0.3%; (2) Wash the membrane surface with deionized water to remove ungrafted groups; (3) Dry at 60°C for 24 hours.

[0058] The outer surface contact angle A1 of the prepared hollow fiber membrane was 85°, and the inner surface contact angle A2 was 95°.

[0059] Example 7 The hollow fiber membrane preparation method in this embodiment is as follows: S1 membrane activation: The polyethersulfone hollow fiber membrane was treated with plasma, and the average pore size of the outer surface was 0.45 μm, and the average pore size of the inner surface was 0.05 μm; Plasma power: 70W; treatment time: 3 minutes; S2 hydrophilic group grafting: (1) The two ends of the activated polyethersulfone hollow fiber-based membrane are sealed, and the outer surface is immersed in a hydrophilic group grafting solution, and reacted at 50°C for 4 hours; the hydrophilic group is polyvinyl alcohol (PVA), and the solvent is deionized water. The mass fraction of the hydrophilic group grafting solution is 2%; (2) Wash the membrane surface with deionized water to remove unreacted monomers; (3) Dry at 60°C for 12 hours; S3 hydrophobic group grafting: (1) The hydrophobic group grafting solution is filled into the interior of the polyethersulfone hollow fiber-based membrane after the hydrophilic group grafting, and reacted at 40° C. for 3 hours; the hydrophobic group is fluorinated alkyltrimethylsilane (FAS), and the concentration of the hydrophobic group grafting solution is controlled to be 0.5%; (2) Wash the membrane surface with deionized water to remove ungrafted groups; (3) Dry at 60°C for 24 hours.

[0060] S4 cellulose nanocrystal complex is grafted onto the outer surface of the polyethersulfone hollow fiber base membrane: (1) Prepare 0.5 mg / mL cellulose nanocrystal complex solution; (2) The outer surface of the polyethersulfone hollow fiber membrane base membrane is immersed in the cellulose nanocrystal complex solution for 60 minutes. After the immersion, the membrane is exposed to 40°C for drying.

[0061] The preparation method of the cellulose nanocrystal complex is as follows: (1) Surface oxidation: Cellulose nanocrystals were immersed in a hydrogen peroxide solution for oxidation reaction for 1 hour, then washed with deionized water and dried; (2) Mixing laccase and cellulose nanocrystals: Prepare a surface oxidized cellulose nanocrystal solution with a mass concentration of 1 wt%, and mix it evenly with 50 U / mL laccase and 100 U / mL lipase solution; (3) Cross-linking: Add 0.1 wt% glutaraldehyde cross-linking agent to the mixed solution, adjust the pH to 4, and stir at room temperature for 8 hours.

[0062] (4) Separation and drying: The mixed solution after the reaction is separated by centrifugation and then dried at 40°C to obtain a cellulose nanocrystal complex.

[0063] The outer surface contact angle A1 of the prepared hollow fiber membrane was 50°, and the inner surface contact angle A2 was 115°.

[0064] Example 8 The hollow fiber membrane preparation method in this embodiment is as follows: S1 membrane activation: The polyethersulfone hollow fiber membrane was treated with plasma, and the average pore size of the outer surface was 0.45 μm, and the average pore size of the inner surface was 0.05 μm; Plasma power: 70W; treatment time: 3 minutes; S2 hydrophilic group grafting: (1) The two ends of the activated polyethersulfone hollow fiber-based membrane are sealed, and the outer surface is immersed in a hydrophilic group grafting solution, and reacted at 50°C for 4 hours; the hydrophilic group is aminopropionic acid (APTES), and the solvent is deionized water. The mass fraction of the hydrophilic group grafting solution is 2%; (2) Wash the membrane surface with deionized water to remove unreacted monomers; (3) Dry at 60°C for 12 hours; S3 hydrophobic group grafting: (1) The hydrophobic group grafting solution is filled into the interior of the polyethersulfone hollow fiber-based membrane after the hydrophilic group grafting, and reacted at 40° C. for 3 hours; the hydrophobic group is long-chain alkyl trimethyl ammonium chloride (CTAC), and the concentration of the hydrophobic group grafting solution is controlled to be 0.5%; (2) Wash the membrane surface with deionized water to remove ungrafted groups; (3) Dry at 60°C for 24 hours.

[0065] S4 cellulose nanocrystal complex is grafted onto the outer surface of the polyethersulfone hollow fiber base membrane: (1) Prepare 1.2 mg / mL cellulose nanocrystal complex solution; (2) The outer surface of the polyethersulfone hollow fiber membrane base membrane is immersed in the cellulose nanocrystal complex solution for 40 minutes. After the immersion, the membrane is exposed to 40° C. for drying.

[0066] The preparation method of the cellulose nanocrystal complex is as follows: (1) Surface oxidation: Cellulose nanocrystals were immersed in a hydrogen peroxide solution for oxidation reaction for 1 hour, then washed with deionized water and dried; (2) Mixing laccase and cellulose nanocrystals: Prepare a surface oxidized cellulose nanocrystal solution with a mass concentration of 1 wt%, and mix it evenly with 70 U / mL laccase and 130 U / mL lipase solution; (3) Cross-linking: Add 0.3 wt % glutaraldehyde cross-linking agent to the mixed solution, adjust the pH to 4, and stir at room temperature for 8 hours.

[0067] (4) Separation and drying: The mixed solution after the reaction is separated by centrifugation and then dried at 40°C to obtain a cellulose nanocrystal complex.

[0068] The outer surface contact angle A1 of the prepared hollow fiber membrane was 43°, and the inner surface contact angle A2 was 110°.

[0069] Example 9 The hollow fiber membrane preparation method in this embodiment is as follows: S1 membrane activation: The polyethersulfone hollow fiber membrane was treated with plasma, and the average pore size of the outer surface was 0.2 μm, and the average pore size of the inner surface was 0.1 μm; Plasma power: 70W; treatment time: 3 minutes; S2 hydrophilic group grafting: (1) The two ends of the activated polyethersulfone hollow fiber-based membrane are sealed, and the outer surface is immersed in a hydrophilic group grafting solution, and reacted at 50°C for 4 hours; the hydrophilic group is polyvinyl alcohol (PVA), and the solvent is deionized water. The mass fraction of the hydrophilic group grafting solution is 2%; (2) Wash the membrane surface with deionized water to remove unreacted monomers; (3) Dry at 60°C for 12 hours; S3 hydrophobic group grafting: (1) The hydrophobic group grafting solution is filled into the interior of the polyethersulfone hollow fiber-based membrane after the hydrophilic group grafting, and reacted at 40° C. for 3 hours; the hydrophobic group is fluorinated alkyltrimethylsilane (FAS), and the concentration of the hydrophobic group grafting solution is controlled to be 0.5%; (2) Wash the membrane surface with deionized water to remove ungrafted groups; (3) Dry at 60°C for 24 hours.

[0070] S4 cellulose nanocrystal complex is grafted onto the outer surface of the polyethersulfone hollow fiber base membrane: (1) Prepare 2 mg / mL cellulose nanocrystal complex solution; (2) The outer surface of the polyethersulfone hollow fiber membrane base membrane is immersed in the cellulose nanocrystal complex solution for 30 minutes. After the immersion, the membrane is exposed to 40°C for drying.

[0071] The preparation method of the cellulose nanocrystal complex is as follows: (1) Surface oxidation: Cellulose nanocrystals were immersed in a hydrogen peroxide solution for oxidation reaction for 1 hour, then washed with deionized water and dried; (2) Mixing laccase and cellulose nanocrystals: Prepare a surface oxidized cellulose nanocrystal solution with a mass concentration of 1 wt%, and mix it evenly with 80 U / mL laccase and 200 U / mL lipase solution; (3) Cross-linking: Add 0.5 wt % glutaraldehyde cross-linking agent to the mixed solution, adjust the pH to 4, and stir at room temperature for 8 hours.

[0072] (4) Separation and drying: The mixed solution after the reaction is separated by centrifugation and then dried at 40°C to obtain a cellulose nanocrystal complex.

[0073] The outer surface contact angle A1 of the prepared hollow fiber membrane was 38°, and the inner surface contact angle A2 was 107°.

[0074] Example 10 The hollow fiber membrane preparation method in this embodiment is as follows: S1 membrane activation: The polyethersulfone hollow fiber membrane was treated with plasma, and the average pore size of the outer surface was 0.2 μm, and the average pore size of the inner surface was 0.1 μm; Plasma power: 70W; treatment time: 3 minutes; S2 cellulose nanocrystal complex is grafted onto the outer surface of the polyethersulfone hollow fiber base membrane: (1) Prepare 2 mg / mL cellulose nanocrystal complex solution; (2) The outer surface of the polyethersulfone hollow fiber membrane base membrane is immersed in the cellulose nanocrystal complex solution for 30 minutes. After the immersion, the membrane is exposed to 40°C for drying.

[0075] The preparation method of the cellulose nanocrystal complex is as follows: (1) Surface oxidation: Cellulose nanocrystals were immersed in a hydrogen peroxide solution for oxidation reaction for 1 hour, then washed with deionized water and dried; (2) Mixing laccase and cellulose nanocrystals: Prepare a surface oxidized cellulose nanocrystal solution with a mass concentration of 1 wt%, and mix it evenly with 80 U / mL laccase and 200 U / mL lipase solution; (3) Cross-linking: Add 0.5 wt % glutaraldehyde cross-linking agent to the mixed solution, adjust the pH to 4, and stir at room temperature for 8 hours.

[0076] (4) Separation and drying: The mixed solution after the reaction is separated by centrifugation and then dried at 40°C to obtain a cellulose nanocrystal complex.

[0077] S3 hydrophilic group grafting: (1) The two ends of the polyethersulfone hollow fiber-based membrane are sealed, and the outer surface is immersed in a hydrophilic group grafting solution, and reacted at 50°C for 4 hours; the hydrophilic group is polyvinyl alcohol (PVA), and the solvent is deionized water. The mass fraction of the hydrophilic group grafting solution is 2%; (2) Wash the membrane surface with deionized water to remove unreacted monomers; (3) Dry at 60°C for 12 hours; S4 hydrophobic group grafting: (1) The hydrophobic group grafting solution is filled into the interior of the polyethersulfone hollow fiber-based membrane after the hydrophilic group grafting, and reacted at 40° C. for 3 hours; the hydrophobic group is fluorinated alkyltrimethylsilane (FAS), and the concentration of the hydrophobic group grafting solution is controlled to be 0.5%; (2) Wash the membrane surface with deionized water to remove ungrafted groups; (3) Dry at 60°C for 24 hours.

[0078] The outer surface contact angle A1 of the prepared hollow fiber membrane was 45°, and the inner surface contact angle A2 was 116°.

[0079] Embodiment 11 The hollow fiber membrane preparation method in this embodiment is as follows: S1 membrane activation: The polyethersulfone hollow fiber membrane was treated with plasma, and the average pore size of the outer surface was 0.2 μm, and the average pore size of the inner surface was 0.1 μm; Plasma power: 70W; treatment time: 3 minutes; S2 hydrophilic group grafting: (1) The two ends of the activated polyethersulfone hollow fiber-based membrane are sealed, and the outer surface is immersed in a hydrophilic group grafting solution, and reacted at 50°C for 4 hours; the hydrophilic group is polyvinyl alcohol (PVA), and the solvent is deionized water. The mass fraction of the hydrophilic group grafting solution is 2%; (2) Wash the membrane surface with deionized water to remove unreacted monomers; (3) Dry at 60°C for 12 hours; S3 hydrophobic group grafting: (1) The hydrophobic group grafting solution is filled into the interior of the polyethersulfone hollow fiber-based membrane after the hydrophilic group grafting, and reacted at 40° C. for 3 hours; the hydrophobic group is fluorinated alkyltrimethylsilane (FAS), and the concentration of the hydrophobic group grafting solution is controlled to be 0.5%; (2) Wash the membrane surface with deionized water to remove ungrafted groups; (3) Dry at 60°C for 24 hours.

[0080] S4 cellulose nanocrystal complex is grafted onto the outer surface of the polyethersulfone hollow fiber base membrane: (1) Prepare 2 mg / mL cellulose nanocrystal complex solution; (2) The outer surface of the polyethersulfone hollow fiber membrane base membrane is immersed in the cellulose nanocrystal complex solution for 30 minutes. After the immersion, the membrane is exposed to 40°C for drying.

[0081] The preparation method of the cellulose nanocrystal complex is as follows: (1) Surface oxidation: Cellulose nanocrystals were immersed in a hydrogen peroxide solution for oxidation reaction for 1 hour, then washed with deionized water and dried; (2) Mixing laccase and cellulose nanocrystals: Prepare a surface oxidized cellulose nanocrystal solution with a mass concentration of 1 wt%, and mix it evenly with 80 U / mL laccase and 200 U / mL lipase solution; (3) Cross-linking: Add 0.5 wt % glutaraldehyde cross-linking agent to the mixed solution, adjust the pH to 4, and stir at room temperature for 8 hours.

[0082] (4) Separation and drying: The mixed solution after the reaction is separated by centrifugation and then dried at 40°C to obtain a cellulose nanocrystal complex.

[0083] S5 Surfactant Treatment: (1) soaking a polyethersulfone hollow fiber-based membrane grafted with hydrophilic groups and hydrophobic groups in a solution containing a surfactant, wherein the surfactant is a polyvinyl alcohol surfactant, and the solution concentration is 0.06%; (2) The surfactant is evenly coated on the membrane surface by spin coating to form a thin and uniform surfactant film to adjust the hydrophilicity and hydrophobicity gradient of the membrane; (3) Drying the coated film at 40°C to ensure that the surfactant layer is firmly fixed on the film surface; (4) Finally, the membrane surface is cleaned with deionized water to remove unreacted surfactant and ensure that there is no excess residue on the membrane surface.

[0084] The outer surface contact angle A1 of the prepared hollow fiber membrane was 35°, and the inner surface contact angle A2 was 105°.

[0085] Comparative Example 1 The preparation method of the hollow fiber membrane in this comparative example is as follows: S1 membrane activation: The polyethersulfone hollow fiber membrane was treated with plasma, and the average pore size of the outer surface was 0.5 μm, and the average pore size of the inner surface was 0.05 μm; Plasma power: 70W; treatment time: 3 minutes; S2 hydrophilic group grafting: (1) The two ends of the activated polyethersulfone hollow fiber-based membrane are sealed, and the outer surface is immersed in a hydrophilic group grafting solution, and reacted at 50°C for 4 hours; the hydrophilic group is polyvinyl alcohol (PVA), and the solvent is deionized water. The mass fraction of the hydrophilic group grafting solution is 0.5%; (2) Wash the membrane surface with deionized water to remove unreacted monomers; (3) Dry at 60°C for 12 hours.

[0086] Comparative Example 2 The hollow fiber membrane preparation method in this embodiment is as follows: S1 membrane activation: The polyethersulfone hollow fiber membrane was treated with plasma, and the average pore size of the outer surface was 0.5 μm, and the average pore size of the inner surface was 0.05 μm; Plasma power: 70W; treatment time: 3 minutes; S2 hydrophilic group grafting: (1) The two ends of the activated polyethersulfone hollow fiber-based membrane are sealed, and the outer surface is immersed in a hydrophilic group grafting solution, and reacted at 50°C for 4 hours; the hydrophilic group is polyvinyl alcohol (PVA), and the solvent is deionized water. The mass fraction of the hydrophilic group grafting solution is 0.5%; (2) Wash the membrane surface with deionized water to remove unreacted monomers; (3) Dry at 60°C for 12 hours; S3 hydrophobic group grafting: (1) The two ends of the polyethersulfone hollow fiber-based membrane grafted with hydrophilic groups are sealed, and the outer surface is immersed in a grafting solution of hydrophobic groups, and reacted at 40° C. for 3 hours; the hydrophobic group is fluorinated alkyltrimethylsilane (FAS), and the concentration of the grafting solution of the hydrophobic group is controlled to be 0.5%; (2) Wash the membrane surface with deionized water to remove ungrafted groups; (3) Dry at 60°C for 24 hours.

[0087] The outer surface contact angle A1 of the prepared hollow fiber membrane was 89°, and the inner surface contact angle A2 was 92°.

[0088] Detection Methods 1. Pretreatment: The hollow fiber membrane samples of Examples 1-11 and Comparative Examples 1-2 were pre-soaked in pure water at 25° C. for 24 hours and operated at a pressure of 0.15 MPa for 2 hours.

[0089] 2. Initial removal rate test: Standard wastewater with an initial concentration of 100 mg / L of methylene blue, Congo red reactive dye, and an initial concentration of 500 mg / L of emulsified oil were respectively passed through a membrane filtration device composed of the hollow fiber membrane samples of Examples 1-11 and Comparative Examples 1-2. After continuous operation for 24 hours, the effluent concentrations of methylene blue, Congo red, and emulsified oil were tested, and the removal rates were calculated.

[0090] Removal rate = (1-outlet concentration / inlet concentration) × 100% 3. Regeneration performance test: The above membrane filter device is backwashed to remove impurities on the hollow fiber membrane.

[0091] Back pressure: 0.15MPa.

[0092] Pulse frequency: 3 times / minute. Recoil time accounts for 10% of the operating cycle.

[0093] After backwashing, the removal rates of methylene blue, Congo red and emulsified oil were tested again, and the average recovery rate (%) was calculated.

[0094] Recovery rate = (removal rate after backwashing / initial removal rate) × 100% The results of removal and recovery rates are shown in Table 1.

[0095] Table 1 The hollow fiber membrane of the present invention effectively improves the sewage treatment performance, pollutant removal efficiency and regeneration performance after backwashing of the membrane by accurately designing the gradient distribution of hydrophilic and hydrophobic groups and combining the grafting of cellulose nanocrystal complexes.

[0096] The above is only a preferred embodiment of the present invention, and the protection scope of the present invention is not limited to the above embodiments. All technical solutions under the concept of the present invention belong to the protection scope of the present invention. It should be pointed out that for ordinary technicians in this technical field, some improvements and modifications without departing from the principle of the present invention should also be regarded as the protection scope of the present invention.

Claims

1. A hollow fiber membrane for treating printing and dyeing wastewater, characterized in that: The invention comprises a polyethersulfone hollow fiber-based membrane, wherein the polyethersulfone hollow fiber-based membrane is grafted with hydrophilic groups and hydrophobic groups on its surface and in the thickness direction; The hydrophilic group is selected from aminopropionic acid or polyvinyl alcohol, and the hydrophobic group is selected from fluorinated alkyltrimethylsilane or long-chain alkyltrimethylammonium chloride; The number of the hydrophilic groups on the outer surface of the polyethersulfone hollow fiber-based membrane is greater than the number of the hydrophilic groups on the inner surface of the polyethersulfone hollow fiber-based membrane, and the hydrophilic groups decrease gradually from the outside to the inside along the thickness direction of the polyethersulfone hollow fiber-based membrane; The number of the hydrophobic groups on the inner surface of the polyethersulfone hollow fiber-based membrane is greater than that on the outer surface of the polyethersulfone hollow fiber-based membrane, and the hydrophobic groups decrease gradually from inside to outside along the thickness direction of the polyethersulfone hollow fiber-based membrane.

2. The hollow fiber membrane for treating printing and dyeing wastewater according to claim 1, characterized in that: The average pore size of the polyethersulfone hollow fiber-based membrane decreases gradually from the outside to the inside along the thickness direction.

3. A hollow fiber membrane for treating printing and dyeing wastewater according to claim 2, characterized in that: The average pore size of the outer surface of the polyethersulfone hollow fiber-based membrane is 0.1-0.5 μm, and the average pore size of the inner surface of the polyethersulfone hollow fiber-based membrane is 0.05-0.2 μm.

4. The hollow fiber membrane for treating printing and dyeing wastewater according to claim 1, characterized in that: The contact angle A1 of the outer surface of the hollow fiber membrane is 60°-80°, and the contact angle A2 of the inner surface of the hollow fiber membrane is 100°-120°.

5. The hollow fiber membrane for treating printing and dyeing wastewater according to claim 1, characterized in that: A cellulose nanocrystal complex is also grafted or adsorbed on the outer surface of the polyethersulfone hollow fiber-based membrane. The preparation method of the cellulose nanocrystal complex is as follows: (1) Surface oxidation: cellulose nanocrystals were immersed in hydrogen peroxide solution for 1-2 hours, then washed with deionized water and dried; (2) Mixing laccase and cellulose nanocrystals: Prepare a surface oxidized cellulose nanocrystal solution with a mass concentration of 1-2 wt%, and mix it evenly with 50-80 U / mL laccase and 100-200 U / mL lipase solution; (3) Cross-linking: add 0.1-0.5 wt% glutaraldehyde cross-linking agent to the mixed solution, adjust the pH to 4-5, and stir at room temperature for 6-12 hours; (4) Separation and drying: The mixed solution after the reaction is separated by centrifugation and then dried at 40°C to obtain a cellulose nanocrystal complex.

6. The hollow fiber membrane for treating printing and dyeing wastewater according to claim 5, characterized in that: The steps of grafting the cellulose nanocrystal complex onto the outer surface of the polyethersulfone hollow fiber base membrane are as follows: (1) Prepare 0.5-2 mg / mL cellulose nanocrystal complex solution; (2) Soaking the outer surface of the polyethersulfone hollow fiber membrane base membrane in the cellulose nanocrystal complex solution for a soaking time of 30-60 minutes, and then exposing the membrane to 40°C for drying.

7. A hollow fiber membrane for treating printing and dyeing wastewater according to claim 6, characterized in that: The polyethersulfone hollow fiber-based membrane is firstly grafted with a hydrophilic group and a hydrophobic group, and then grafted with a cellulose nanocrystal complex.

8. The hollow fiber membrane for treating printing and dyeing wastewater according to claim 7, characterized in that: The contact angle A3 of the outer surface of the hollow fiber membrane is 0.5 to 0.9×A1, and the contact angle A4 of the inner surface of the hollow fiber membrane is 0.98 to 1.1×A2.

9. A method for preparing a hollow fiber membrane for treating printing and dyeing wastewater according to any one of claims 1 to 8, characterized in that: The following steps are involved: S1 base membrane activation: plasma treatment of polyethersulfone hollow fiber base membrane; plasma power: 50-100W; treatment time: 2-5 minutes; S2 hydrophilic group grafting: (1) The two ends of the activated polyethersulfone hollow fiber-based membrane are sealed, and the outer surface is immersed in a grafting solution of a hydrophilic group, and reacted at 50° C. for 4-6 hours; the hydrophilic group is selected from aminopropionic acid or polyvinyl alcohol, and the mass fraction of the grafting solution of the hydrophilic group is 0.5%-2%; (2) Wash the membrane surface with deionized water to remove unreacted monomers; (3) Dry at 60°C for 12 hours; S3 hydrophobic group grafting: (1) Filling the interior of the polyethersulfone hollow fiber-based membrane grafted with hydrophilic groups with a grafting solution of hydrophobic groups, and reacting at 40° C. for 3-5 hours; the hydrophobic groups are selected from fluorinated alkyltrimethylsilane or long-chain alkyltrimethylammonium chloride, and the concentration of the grafting solution of the hydrophobic groups is controlled to be 0.1%-0.5%; (2) Wash the membrane surface with deionized water to remove ungrafted groups; (3) Dry at 60°C for 24 hours.

10. The method for preparing a hollow fiber membrane for treating printing and dyeing wastewater according to claim 9, characterized in that: After steps S2 and S3, the following steps are further included: (1) soaking a polyethersulfone hollow fiber-based membrane grafted with hydrophilic groups and hydrophobic groups in a solution containing a surfactant, wherein the surfactant is a polyvinyl alcohol surfactant, and the solution concentration is 0.01%-0.1%; (2) The surfactant is evenly coated on the membrane surface by spin coating to form a thin and uniform surfactant film to adjust the hydrophilicity and hydrophobicity gradient of the membrane; (3) Drying the coated film at 40°C to ensure that the surfactant layer is firmly fixed on the film surface; (4) Finally, the membrane surface is cleaned with deionized water to remove unreacted surfactant and ensure that there is no excess residue on the membrane surface.

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