A hollow fiber membrane for treating printing and dyeing wastewater and a preparation method thereof

Abstract

The present invention discloses a hollow fiber membrane for treating printing and dyeing wastewater and a preparation method thereof, relating to the technical field of sewage treatment. A hollow fiber membrane for treating printing and dyeing wastewater includes a polyethersulfone hollow fiber base membrane, and hydrophilic groups and hydrophobic groups are grafted on the surface and in the thickness direction of the polyethersulfone hollow fiber base membrane; moreover, the number of the hydrophilic groups on the outer surface of the polyethersulfone hollow fiber base membrane is higher than the number of the hydrophilic groups on the inner surface of the polyethersulfone hollow fiber base membrane, and the number of the hydrophobic groups on the inner surface of the polyethersulfone hollow fiber base membrane is higher than the number of the hydrophobic groups on the outer surface of the polyethersulfone hollow fiber base membrane. The present invention has the effects of improving the removal performance of the hollow fiber membrane for water-soluble dyes and oil impurities in printing and dyeing wastewater, as well as better durability and self-cleaning property.

Description

Technical Field

[0001] The present 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 attracted increasing attention. Especially when the wastewater contains a large amount of water-soluble dyes, oil substances and other organic pollutants, traditional sewage treatment methods are often difficult to effectively remove these pollutants. Especially for some special pollutants, such as water-soluble dyes and emulsified oil, due to the particularity of their molecular structure and physical and chemical properties, conventional physical and chemical methods are difficult to achieve the desired treatment effect. In order to improve the efficiency and effect of wastewater treatment, it has become 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 membranes have gradually become an important tool for treating wastewater, especially printing and dyeing wastewater, due to their high specific surface area, excellent filtration performance and easy modular design. The performance of hollow fiber membranes is affected by factors such as the membrane material itself, the surface structure of the membrane and the pore size distribution. Existing hollow fiber membranes mostly use a single membrane material or a simple surface modification method, resulting in certain limitations when treating specific wastewater. Summary of the Invention

[0004] Aiming at the deficiencies of the existing technology, the purpose 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 by the following technical solutions:

[0006] A hollow fiber membrane for treating printing and dyeing wastewater, comprising a polyethersulfone hollow fiber base membrane, and hydrophilic groups and hydrophobic groups are grafted on the surface and in the thickness direction of the polyethersulfone hollow fiber base membrane;

[0007] The hydrophilic groups are selected from 3-aminopropyltriethoxysilane (APTES) or polyvinyl alcohol (PVA), and the hydrophobic groups are selected from fluorinated alkyltrimethylsilane (FAS) or long-chain alkyltrimethylammonium chloride (CTAC);

[0008] And the number of the hydrophilic groups on the outer surface of the polyethersulfone hollow fiber base membrane is higher than the number of the hydrophilic groups on the inner surface of the polyethersulfone hollow fiber base membrane, and the hydrophilic groups gradually decrease from the outside to the inside along the thickness direction of the polyethersulfone hollow fiber base membrane;

[0009] The number of the hydrophobic groups located on the inner surface of the polyethersulfone hollow fiber base membrane is higher than that on the outer surface of the polyethersulfone hollow fiber base membrane, and the hydrophobic groups decrease in a gradient manner from the inside to the outside along the thickness direction of the polyethersulfone hollow fiber base membrane.

[0010] The hollow fiber membrane for treating printing and dyeing wastewater provided by the present invention has a unique surface and inner layer structure design, and can efficiently remove water-soluble dyes and oil impurities, thereby improving the effect of wastewater treatment. First, hydrophilic groups (such as 3-aminopropyltriethoxysilane (APTES) or polyvinyl alcohol (PVA)) are grafted on the outer surface of the membrane to enhance the affinity of the membrane for water molecules. The hydrophilic groups can effectively adsorb water-soluble dyes or other water-soluble pollutants in the wastewater through hydrogen bonding or electrostatic interaction. The presence of the hydrophilic groups 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 fouling and maintaining the long-term stability and flux of the membrane.

[0011] In addition, by precisely controlling the membrane pore size and designing the structure of the membrane, the oil-based hydrophobic pollutants can be effectively treated. The pore size of the membrane is designed to be between 0.1 - 0.5 μm, so that larger oil particles can be effectively blocked by the physical barrier effect, thereby preventing the oil from passing through the pores of the membrane. However, for fine oil particles and emulsified oil, the role of the hydrophobic groups (such as fluorinated alkyltrimethylsilane (FAS) or long-chain alkyltrimethylammonium chloride (CTAC)) of the membrane is more crucial. The hydrophobic groups reduce the affinity between the inner surface of the membrane and the oil, making it easier for the oil-based substances to pass through the membrane, and during the backwashing process, the oil can smoothly drain out of the inner surface area of the membrane, avoiding the accumulation of oil on the membrane surface. The hydrophobic groups can effectively reduce oil fouling by reducing the adhesion between the oil and the membrane, thereby improving the flux and service life of the membrane.

[0012] In the present invention, the gradient distribution design of the hydrophilic and hydrophobic groups between the outer surface and the inner surface enables the membrane to achieve the hierarchical removal of water-soluble pollutants and oil-based pollutants in the wastewater. Specifically, the hydrophilic groups on the outer layer of the membrane are beneficial to adsorb pollutants such as water-soluble dyes, while the hydrophobic groups on the inner layer of the membrane can repel oil-based pollutants, ensuring that different regions of the membrane can treat different types of pollutants. This design enables the membrane to efficiently and selectively remove various pollutants in complex wastewater treatment, thereby improving the overall efficiency of wastewater treatment.

[0013] In addition, the gradient structure of the membrane also has a positive impact on the self-cleaning performance. Due to the ingenious design of hydrophilic and hydrophobic groups, when the membrane surface is flushed or cleaned by external water flow, the difference between hydrophilic and hydrophobic regions enables the attachment of pollutants on the membrane surface to be more easily removed. The design of this structure improves the self-cleaning ability of the membrane, effectively reduces the deposition of pollutants on the membrane surface, thereby extending the service life of the membrane and enhancing the operating efficiency of the membrane.

[0014] Furthermore, the average pore size of the polyethersulfone hollow fiber-based membrane decreases gradually from the outside to the inside along the thickness direction.

[0015] The pore size of the polyethersulfone hollow fiber membrane shows a gradient decreasing structure along the membrane thickness direction. This design effectively optimizes the wastewater treatment process, especially in filtering and removing different types of pollutants. Specifically, the larger pore size in the outer layer of the membrane can efficiently intercept larger particulate matters and pollutants in the wastewater, reducing the accumulation of these large particulate substances on the membrane surface, thereby effectively avoiding the initial clogging problem on the membrane surface. This not only helps to maintain a relatively high flux of the membrane but also extends the service life of the membrane and reduces the need for frequent cleaning.

[0016] The smaller pore size in the inner layer plays a more refined sieving role, further improving the interception ability of the membrane for fine particulate matters, micro-pollutants, and water-soluble dyes. Especially when treating oil-based hydrophobic pollutants, the pore size design of the membrane is particularly important. Oil-based pollutants are mainly intercepted through the pore size of the membrane. The larger pore size in the outer layer can effectively avoid the rapid accumulation of oil-based substances, slow down the pollution rate of the membrane, and ensure the cleanliness and flux stability of the membrane surface. At the same time, the smaller pore size in the inner layer can prevent oil-based 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.

[0017] This gradient structure design is also of great significance for the backwashing process of the membrane. During backwashing, the larger pore size in the outer layer helps to quickly remove large particulate pollutants on the membrane surface, reducing the pollution burden on the membrane surface; while the smaller pore size in the inner layer further helps to remove fine oil-based hydrophobic substances, ensuring that oil and other hydrophobic pollutants can be easily discharged from the inner surface area of the membrane during backwashing, thereby enhancing the anti-pollution ability of the membrane and extending the service life of the membrane.

[0018] In addition, the outer layer of the polyethersulfone hollow fiber membrane is grafted with a high content of hydrophilic groups, which can have a strong adsorption effect on water-soluble dye molecules, significantly improving the removal efficiency of the membrane 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 ability of water-soluble dyes through the action of hydrophilic groups. Combining with the membrane pore size gradient structure, the hydrophilic groups on the outer layer make the removal effect of the membrane on water-soluble dyes more significant, ensuring the efficient removal of water-soluble dyes in wastewater.

[0019] Furthermore, the average pore size of the outer surface of the polyethersulfone hollow fiber base membrane is 0.1 - 0.5 μm, and the average pore size of the inner surface of the polyethersulfone hollow fiber base membrane is 0.05 - 0.2 μm.

[0020] The pore size design of the outer and inner surfaces of the hollow fiber membrane between 0.1 - 0.5 μm and 0.05 - 0.2 μm further optimizes the filtration performance of the membrane, especially in removing different types of pollutants in wastewater. The larger pore size (0.1 - 0.5 μm) on the outer surface of the membrane can efficiently intercept larger particle pollutants, including oil particles, suspended solids, etc., avoiding the accumulation of these pollutants on the membrane surface and reducing the risk of membrane surface blockage. On the one hand, this helps to maintain a higher flux, and on the other hand, it also reduces the pollution burden on the membrane and extends the service life of the membrane.

[0021] The smaller pore size (0.05 - 0.2 μm) on the inner surface of the membrane is helpful for a more refined sieving effect, especially having a better effect on the removal of water-soluble pollutants such as fine particles and emulsified oil. The smaller pore size can prevent the penetration of fine pollutants and improve the removal efficiency of the membrane through a fine filtration effect, ensuring the efficient removal of water-soluble pollutants in wastewater and further improving the filtration accuracy and treatment capacity of the membrane.

[0022] This pore size gradient design can effectively optimize the filtration and pollutant removal processes in wastewater treatment, ensure the efficient separation of pollutants with different particle sizes, help reduce the membrane maintenance frequency, and extend the service life of the membrane.

[0023] 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°.

[0024] The contact angle A1 on the outer surface of the hollow fiber membrane is controlled to be 60°-80°, and the contact angle A2 on 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 (60°-80°) on the outer surface 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 to keep the membrane surface clean, reduces the deposition of water-soluble pollutants, and thus avoids membrane surface fouling, thereby improving the flux and stability of the membrane.

[0025] The higher contact angle (100°-120°) on the inner surface shows strong hydrophobicity, effectively reducing the affinity between oil-based pollutants and the membrane surface, making it easier for hydrophobic substances such as oil to be backwashed out of the inner surface area of the membrane and less likely to cause irreversible flux loss.

[0026] Furthermore, a cellulose nanocrystal composite is grafted or adsorbed on the outer surface of the polyethersulfone hollow fiber-based membrane, and the preparation method of the cellulose nanocrystal composite is as follows:

[0027] (1) Surface oxidation: Immerse the cellulose nanocrystals in hydrogen peroxide solution for 1-2 hours of oxidation reaction, and then wash and dry with deionized water;

[0028] (2) Mixing of 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 of laccase and 100-200 U / mL of lipase solution;

[0029] (3) Crosslinking: Add 0.1-0.5 wt% of glutaraldehyde crosslinking agent to the mixed solution, adjust the pH to 4-5, and stir at room temperature for 6-12 hours.

[0030] (4) Separation and drying: Centrifuge the reacted mixed solution and dry it at 40 °C to obtain the cellulose nanocrystal composite.

[0031] The outer surface of the hollow fiber membrane is grafted or adsorbed with a cellulose nanocrystal composite, 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-based pollutants. The introduction of the cellulose nanocrystal composite not only enhances the hydrophilicity of the membrane surface but also can play the catalytic roles of laccase and lipase to degrade and remove harmful substances and oil-based impurities in the wastewater.

[0032] The preparation method of the cellulose nanocrystal composite involves effectively binding laccase, lipase with 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 on the surface of cellulose nanocrystals and providing more contact sites for laccase. The role of lipase can also promote the binding of laccase and cellulose nanocrystals, thus improving the distribution and activity of laccase in the composite and enhancing the catalytic performance of the composite.

[0033] Through this preparation method, laccase, lipase and cellulose nanocrystals form a stable composite structure at the molecular level, endowing the membrane with higher hydrophilicity and pollutant removal ability.

[0034] Furthermore, the steps of grafting the cellulose nanocrystal composite onto the outer surface of the polyethersulfone hollow fiber substrate membrane are as follows:

[0035] (1) Prepare a 0.5 - 2 mg / mL cellulose nanocrystal composite solution;

[0036] (2) Immerse the outer surface of the polyethersulfone hollow fiber membrane substrate in the cellulose nanocrystal composite solution, control the immersion time for 30 - 60 minutes, and after immersion, expose the membrane to 40 °C for drying.

[0037] By grafting the cellulose nanocrystal composite onto the outer surface of the polyethersulfone hollow fiber substrate membrane, the performance of the membrane is further enhanced, especially when treating wastewater containing water-soluble dyes and oil-based pollutants. By controlling the grafting concentration and immersion time of the cellulose nanocrystal composite, the uniform distribution of the composite in the outer surface area of the membrane is ensured, thus greatly improving the hydrophilicity of the membrane and its adsorption capacity for water-soluble pollutants.

[0038] In this step, the grafting of the cellulose nanocrystal composite effectively increases the catalytic sites on the membrane surface, not only enhancing the ability to remove water-soluble dyes, but also improving the cleaning ability of the membrane surface. As a catalyst, laccase can degrade certain organic pollutants, reduce the pollution on the membrane surface, and maintain the efficient operation of the membrane. Lipase can effectively degrade certain oil-based impurities attached to the membrane, so that the removal effect of oil-based impurities can be effectively improved during the backwashing process.

[0039] Furthermore, the polyethersulfone hollow fiber substrate membrane is first grafted with hydrophilic groups and hydrophobic groups, and then grafted with the cellulose nanocrystal composite.

[0040] The main purpose of grafting hydrophilic groups and hydrophobic groups first and then grafting cellulose nanocrystal composites is to increase the grafting amount of cellulose nanocrystal composites and ensure more grafting sites on the membrane surface. The grafting of hydrophilic groups and hydrophobic groups can provide a surface-functionalized gradient structure on the membrane surface, resulting in a dual property of both hydrophilicity and hydrophobicity on the surface. Specifically, the hydrophilic regions formed by hydrophilic groups on the membrane surface can effectively enhance the contact of the composites and provide more chemical reaction sites; while the hydrophobic groups form hydrophobic regions on the membrane surface, improving the stability and grafting efficiency of the composites in these regions.

[0041] The hydrophilic groups contribute to the grafting of cellulose nanocrystal composites by providing a highly polar environment, especially enabling the laccase part to adhere more stably to the membrane surface and enhancing the affinity of the composites. Therefore, more composites can undergo effective chemical grafting in the hydrophilic regions, increasing the grafting amount.

[0042] The hydrophobic groups provide a non-polar environment that facilitates the grafting of cellulose nanocrystals on the membrane surface. Due to the good hydrophobicity of cellulose nanocrystals, they can ensure a stronger adsorption force of the composites in the hydrophobic regions through interaction with the hydrophobic groups on the membrane surface. This effect not only increases the stability of the composites but also makes the distribution of the whole composites on the membrane surface more uniform by increasing the grafting amount.

[0043] By controlling the sequential grafting of hydrophilic and hydrophobic groups, the composites can have a higher grafting density on the membrane surface, especially in the hydrophilic regions of the membrane surface, where the grafting amounts of laccase and cellulose nanocrystals increase significantly. This design optimizes the catalytic and adsorption properties of the composites, further improving the overall performance of the membrane.

[0044] Due to the synergistic effect of the surface hydrophilic and hydrophobic regions during the grafting of the composites, the grafting amount of cellulose nanocrystal composites increases significantly compared with traditional methods. The functionalized gradient structure formed on the membrane surface can provide more grafting sites and optimize the distribution of the composites, thus increasing the grafting amount and enhancing 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 during wastewater treatment but also enhances the stability and anti-fouling ability of the membrane after long-term use, extending the service life of the membrane.

[0045] Furthermore, the contact angle A3 of the outer surface of the hollow fiber membrane is 0.5 - 0.9×A1, and the contact angle A4 of the inner surface of the hollow fiber membrane is 0.98 - 1.1×A2.

[0046] By controlling the ratio of the contact angle A3 to A1 on the outer surface to be 0.5 to 0.9 times, and the ratio of the contact angle A4 to A2 on the inner surface to be 0.98 to 1.1 times, the hydrophilicity of the outer surface of the membrane is greatly improved, while maintaining the hydrophobicity of the inner surface of the membrane from being overly 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 the wastewater treatment process. At the same time, keeping the contact angle ratio of the inner surface unchanged ensures that the membrane can still maintain good hydrophobicity when treating oily wastewater. The relatively low change in the contact angle of 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 overly affected, thus effectively avoiding the deposition of oil-based pollutants on the inner surface of the membrane and improving the anti-fouling ability and backwashing effect of the membrane.

[0047] A preparation method of a hollow fiber membrane for treating printing and dyeing wastewater, comprising the following steps:

[0048] S1 Base membrane activation: Treating a polyethersulfone hollow fiber base membrane with plasma; plasma power: 50 - 100 W; treatment time: 2 - 5 minutes;

[0049] S2 Grafting of hydrophilic groups:

[0050] (1) Sealing both ends of the activated polyethersulfone hollow fiber base membrane, immersing the outer surface in a grafting solution of hydrophilic groups, and reacting at 50°C for 4 - 6 hours; the hydrophilic groups are selected from 3-aminopropyltriethoxysilane (APTES) or polyvinyl alcohol (PVA), and the mass fraction of the grafting solution of hydrophilic groups is 0.5% - 2%;

[0051] (2) Cleaning the membrane surface with deionized water to remove unreacted monomers;

[0052] (3) Drying at 60°C for 12 hours;

[0053] S3 Grafting of hydrophobic groups:

[0054] (1) Filling the inside of the polyethersulfone hollow fiber base 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 (FAS) or long-chain alkyltrimethylammonium chloride (CTAC), and the concentration of the grafting solution of hydrophobic groups is controlled to be 0.1% - 0.5%;

[0055] (2) Cleaning the membrane surface with deionized water to remove ungrafted groups;

[0056] (3) Drying at 60°C for 24 hours.

[0057] Through the steps of plasma treatment and grafting of hydrophilic groups and hydrophobic groups, the surface properties of the membrane are optimized, enabling it to efficiently remove water-soluble dyes and oil-based pollutants in wastewater. The plasma treatment step can effectively activate the membrane surface, improve the grafting effect of hydrophilic groups and hydrophobic groups, ensure that the membrane surface has excellent hydrophilicity and hydrophobicity, and thus enhance the pollutant removal efficiency of the membrane.

[0058] After the grafting of hydrophilic groups, the membrane surface can enhance the adsorption capacity of water-soluble pollutants and effectively remove dissolved substances in water; while the grafting of hydrophobic groups improves the hydrophobicity of the membrane and promotes the separation of oil-based pollutants. This method can not only enhance the sorting 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.

[0059] Furthermore, it also includes the following steps:

[0060] (1) Immerse the polyethersulfone hollow fiber-based membrane grafted with hydrophilic groups and hydrophobic groups in a solution containing a surfactant, where the surfactant is a polyvinyl alcohol surfactant and the solution concentration is 0.01% - 0.1%;

[0061] (2) Uniformly coat the surfactant on the membrane surface by spin coating to form a thin and uniform surfactant film, and adjust the hydrophilicity-hydrophobicity gradient of the membrane;

[0062] (3) Dry the coated membrane at 40 °C to ensure that the surfactant layer is firmly fixed on the membrane surface;

[0063] (4) Finally, wash the membrane surface with deionized water to remove the unreacted surfactant and ensure that there are no excess residues on the membrane surface.

[0064] The surfactant can form a uniform thin film on the membrane surface, reduce the surface tension of the membrane, make the membrane surface more wettable, and thus improve the hydrophilicity of the membrane. Increasing the hydrophilicity of the membrane can effectively reduce fouling and pollutant adsorption on the membrane surface, reduce the occurrence of membrane fouling, and extend the service life of the membrane. As an efficient dispersant, the polyvinyl alcohol surfactant can effectively disperse impurities that may appear on the membrane surface during the coating process, preventing these impurities from reacting with the membrane surface or forming a fouling layer. By coating a uniform surfactant thin film, it can help optimize the surface microstructure of the membrane, reduce fouling and blocking phenomena of the membrane, and improve the stability and performance of the membrane.

[0065] Compared with the prior art, the beneficial effects of the present invention are mainly reflected in the following aspects:

[0066] 1. By grafting hydrophilic groups (such as 3-aminopropyltriethoxysilane (APTES) or polyvinyl alcohol (PVA)) onto the outer surface of the polyethersulfone hollow fiber membrane and 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 oil-based pollutants in a hierarchical manner. Specifically, the higher hydrophilic groups on the outer surface help adsorb water-soluble dyes and other water-soluble pollutants, thereby improving the removal efficiency of the membrane for these pollutants and avoiding the problem of fouling deposition on the membrane surface. The higher hydrophobic groups on the inner surface effectively reduce the affinity of oil-based pollutants for the membrane, preventing the accumulation of oil-based pollutants on the membrane surface, thus extending the service life of the membrane and improving the anti-fouling ability of the membrane.

[0067] 2. To further improve the performance of the membrane, the present invention grafts or adsorbs cellulose nanocrystal composites on the outer surface of the membrane. This composite 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-fouling ability of the membrane. The introduction of cellulose nanocrystal composites not only improves the hydrophilicity of the membrane but also enhances the stability and anti-fouling property of the membrane, ensuring the high efficiency of the membrane during long-term use. Detailed implementation mode

[0068] The present invention will be described in detail below in conjunction with embodiments.

[0069] The polyethersulfone hollow fiber base membrane uses PES-HF-8040 from DuPont de Nemours, Inc. in the United States;

[0070] The fluorinated alkyltrimethylsilane uses Dynasylan® F8261 from Evonik Industries AG in Germany;

[0071] The polyvinyl alcohol uses PVA-217 from Kuraray Co., Ltd. in Japan;

[0072] The long-chain alkyltrimethylammonium chloride uses Luviquat® FC 370 from BASF SE;

[0073] The 3-aminopropionic acid uses AJIPURE® L-Alanine from Ajinomoto Co., Inc.;

[0074] Cellulose nanocrystals were BioNano-12 from FPInnovations Inc. in Canada;

[0075] Laccase was NS51003-LT from Novozymes A / S;

[0076] Lipase was CALB-L from Chr. Hansen A / S.

[0077] Example 1

[0078] The preparation method of the hollow fiber membrane in this example is as follows:

[0079] S1 Substrate membrane activation: The polyethersulfone hollow fiber substrate membrane was treated with plasma. 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;

[0080] The plasma power was 70 W; the treatment time was 3 minutes;

[0081] S2 Grafting of hydrophilic groups:

[0082] (1) Both ends of the activated polyethersulfone hollow fiber substrate membrane were sealed, and the outer surface was immersed in the grafting solution of hydrophilic groups and reacted at 50 °C for 4 hours; the hydrophilic group was polyvinyl alcohol (PVA), and the solvent was deionized water. The mass fraction of the grafting solution of hydrophilic groups was 0.5%;

[0083] (2) The membrane surface was washed with deionized water to remove unreacted monomers;

[0084] (3) It was dried at 60 °C for 12 hours;

[0085] S3 Grafting of hydrophobic groups:

[0086] (1) The inside of the polyethersulfone hollow fiber substrate membrane grafted with hydrophilic groups was filled with the grafting solution of hydrophobic groups and reacted at 40 °C for 3 hours; the hydrophobic group was fluorinated alkyltrimethylsilane (FAS), and the concentration of the grafting solution of hydrophobic groups was controlled at 0.5%;

[0087] (2) The membrane surface was washed with deionized water to remove ungrafted groups;

[0088] (3) It was dried at 60 °C for 24 hours.

[0089] The contact angle A1 of the outer surface of the prepared hollow fiber membrane was 80°, and the contact angle A2 of the inner surface was 120°.

[0090] Example 2

[0091] The preparation method of the hollow fiber membrane in this embodiment is as follows:

[0092] S1 Substrate membrane activation: Treat the polyethersulfone hollow fiber substrate membrane with plasma. The average pore size of the outer surface is 0.3 μm, and the average pore size of the inner surface is 0.13 μm;

[0093] Plasma power: 70 W; Treatment time: 3 minutes;

[0094] S2 Grafting of hydrophilic groups:

[0095] (1) Seal both ends of the activated polyethersulfone hollow fiber substrate membrane, immerse the outer surface in the grafting solution of hydrophilic groups, and react at 50 °C for 4 hours; The hydrophilic group is polyvinyl alcohol (PVA), and the solvent is deionized water. The mass fraction of the grafting solution of hydrophilic groups is 1.2%;

[0096] (2) Wash the membrane surface with deionized water to remove unreacted monomers;

[0097] (3) Dry at 60 °C for 12 hours;

[0098] S3 Grafting of hydrophobic groups:

[0099] (1) Fill the inside of the polyethersulfone hollow fiber substrate membrane grafted with hydrophilic groups with the grafting solution of hydrophobic groups, and react at 40 °C for 3 hours; The hydrophobic group is fluorinated alkyltrimethylsilane (FAS), and the concentration of the grafting solution of hydrophobic groups is controlled at 0.4%;

[0100] (2) Wash the membrane surface with deionized water to remove ungrafted groups;

[0101] (3) Dry at 60 °C for 24 hours.

[0102] The contact angle A1 of the outer surface of the prepared hollow fiber membrane is 75°, and the contact angle A2 of the inner surface is 110°.

[0103] Example 3

[0104] The preparation method of the hollow fiber membrane in this embodiment is as follows:

[0105] S1 Substrate membrane activation: Treat the polyethersulfone hollow fiber substrate membrane with plasma. The average pore size of the outer surface is 0.2 μm, and the average pore size of the inner surface is 0.1 μm;

[0106] Plasma power: 70 W; Treatment time: 3 minutes;

[0107] S2 Grafting of hydrophilic groups:

[0108] (1) Seal both ends of the activated polyethersulfone hollow fiber substrate membrane, soak the outer surface in the grafting solution of hydrophilic groups, and react at 50 °C for 4 hours; the hydrophilic groups are polyvinyl alcohol (PVA), and the solvent is deionized water. The mass fraction of the grafting solution of hydrophilic groups is 2%;

[0109] (2) Wash the membrane surface with deionized water to remove unreacted monomers;

[0110] (3) Dry at 60 °C for 12 hours;

[0111] S3 Grafting of hydrophobic groups:

[0112] (1) Fill the inside of the polyethersulfone hollow fiber substrate membrane grafted with hydrophilic groups with the grafting solution of hydrophobic groups, and react at 40 °C for 3 hours; the hydrophobic groups are fluorinated alkyltrimethylsilane (FAS), and the concentration of the grafting solution of hydrophobic groups is controlled at 0.1%;

[0113] (2) Wash the membrane surface with deionized water to remove ungrafted groups;

[0114] (3) Dry at 60 °C for 24 hours.

[0115] The contact angle A1 of the outer surface of the prepared hollow fiber membrane is 60°, and the contact angle A2 of the inner surface is 100°.

[0116] Example 4

[0117] The preparation method of the hollow fiber membrane in this example is as follows:

[0118] S1 Substrate membrane activation: Treat the polyethersulfone hollow fiber substrate membrane with plasma. The polyethersulfone hollow fiber substrate membrane is a symmetric membrane with an average pore size of 0.1 μm;

[0119] Plasma power: 70 W; treatment time: 3 minutes;

[0120] S2 Grafting of hydrophilic groups:

[0121] (1) Seal both ends of the activated polyethersulfone hollow fiber substrate membrane, soak the outer surface in the grafting solution of hydrophilic groups, and react at 50 °C for 4 hours; the hydrophilic groups are polyvinyl alcohol (PVA), and the solvent is deionized water. The mass fraction of the grafting solution of hydrophilic groups is 2%;

[0122] (2) Wash the membrane surface with deionized water to remove unreacted monomers;

[0123] (3) Dry at 60 °C for 12 hours;

[0124] S3 Grafting of hydrophobic groups:

[0125] (1) Fill the inside of the polyethersulfone hollow fiber-based membrane grafted with hydrophilic groups with a grafting solution of hydrophobic groups, and react 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 0.1%;

[0126] (2) Wash the membrane surface with deionized water to remove the ungrafted groups;

[0127] (3) Dry at 60 °C for 24 hours.

[0128] The contact angle A1 of the outer surface of the prepared hollow fiber membrane is 60°, and the contact angle A2 of the inner surface is 110°.

[0129] Example 5

[0130] The preparation method of the hollow fiber membrane in this example is as follows:

[0131] S1 Base membrane activation: Treat the polyethersulfone hollow fiber-based membrane with plasma. The average pore size of the outer surface is 0.6 μm, and the average pore size of the inner surface is 0.02 μm;

[0132] Plasma power: 70 W; treatment time: 3 minutes;

[0133] S2 Hydrophilic group grafting:

[0134] (1) Seal both ends of the activated polyethersulfone hollow fiber-based membrane, immerse the outer surface in the grafting solution of hydrophilic groups, and react at 50 °C for 4 hours; the hydrophilic group is polyvinyl alcohol (PVA), and the solvent is deionized water. The mass fraction of the grafting solution of hydrophilic groups is 2%;

[0135] (2) Wash the membrane surface with deionized water to remove the unreacted monomers;

[0136] (3) Dry at 60 °C for 12 hours;

[0137] S3 Hydrophobic group grafting:

[0138] (1) Fill the inside of the polyethersulfone hollow fiber-based membrane grafted with hydrophilic groups with a grafting solution of hydrophobic groups, and react 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 0.3%;

[0139] (2) Wash the membrane surface with deionized water to remove the ungrafted groups;

[0140] (3) Dry at 60 °C for 24 hours.

[0141] The contact angle A1 of the outer surface of the prepared hollow fiber membrane is 70°, and the contact angle A2 of the inner surface is 115°.

[0142] Example 6

[0143] The preparation method of the hollow fiber membrane in this example is as follows:

[0144] S1 Substrate membrane activation: The polyethersulfone hollow fiber substrate membrane is treated with plasma. The average pore size of the outer surface is 0.5 μm, and the average pore size of the inner surface is 0.06 μm;

[0145] Plasma power: 70 W; treatment time: 3 minutes;

[0146] S2 Grafting of hydrophilic groups:

[0147] (1) Seal both ends of the activated polyethersulfone hollow fiber substrate membrane, soak the outer surface in the grafting solution of hydrophilic groups, and react at 50 °C for 4 hours; the hydrophilic group is polyvinyl alcohol (PVA), and the solvent is deionized water. The mass fraction of the grafting solution of hydrophilic groups is 0.9%;

[0148] (2) Wash the membrane surface with deionized water to remove unreacted monomers;

[0149] (3) Dry at 60 °C for 12 hours;

[0150] S3 Grafting of hydrophobic groups:

[0151] (1) Fill the inside of the polyethersulfone hollow fiber substrate membrane grafted with hydrophilic groups with the grafting solution of hydrophobic groups, and react at 40 °C for 3 hours; the hydrophobic group is fluorinated alkyltrimethylsilane (FAS), and the concentration of the grafting solution of hydrophobic groups is controlled at 0.3%;

[0152] (2) Wash the membrane surface with deionized water to remove ungrafted groups;

[0153] (3) Dry at 60 °C for 24 hours.

[0154] The contact angle A1 of the outer surface of the prepared hollow fiber membrane is 85°, and the contact angle A2 of the inner surface is 95°.

[0155] Example 7

[0156] The preparation method of the hollow fiber membrane in this example is as follows:

[0157] S1 Substrate membrane activation: The polyethersulfone hollow fiber substrate membrane is treated with plasma. The average pore size of the outer surface is 0.45 μm, and the average pore size of the inner surface is 0.05 μm;

[0158] Plasma power: 70 W; Processing time: 3 minutes;

[0159] Grafting of S2 hydrophilic groups:

[0160] (1) Seal both ends of the activated polyethersulfone hollow fiber substrate membrane, soak the outer surface in the grafting solution of hydrophilic groups, and react at 50 °C for 4 hours; the hydrophilic groups are polyvinyl alcohol (PVA), and the solvent is deionized water. The mass fraction of the grafting solution of hydrophilic groups is 2%;

[0161] (2) Wash the membrane surface with deionized water to remove unreacted monomers;

[0162] (3) Dry at 60 °C for 12 hours;

[0163] Grafting of S3 hydrophobic groups:

[0164] (1) Fill the inside of the polyethersulfone hollow fiber substrate membrane grafted with hydrophilic groups with the grafting solution of hydrophobic groups, and react at 40 °C for 3 hours; the hydrophobic groups are fluorinated alkyltrimethylsilane (FAS), and the concentration of the grafting solution of hydrophobic groups is controlled at 0.5%;

[0165] (2) Wash the membrane surface with deionized water to remove ungrafted groups;

[0166] (3) Dry at 60 °C for 24 hours.

[0167] Graft cellulose nanocrystal composite onto the outer surface of the polyethersulfone hollow fiber substrate membrane:

[0168] (1) Prepare a 0.5 mg / mL cellulose nanocrystal composite solution;

[0169] (2) Immerse the outer surface of the polyethersulfone hollow fiber membrane substrate in the cellulose nanocrystal composite solution, control the immersion time to 60 minutes, and dry the membrane by exposing it at 40 °C after immersion.

[0170] The preparation method of cellulose nanocrystal composite is as follows:

[0171] (1) Surface oxidation: Immerse cellulose nanocrystals in hydrogen peroxide solution, carry out oxidation reaction for 1 hour, and then wash and dry with deionized water;

[0172] (2) Mix laccase with 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;

[0173] (3) Crosslinking: Add 0.1 wt% glutaraldehyde crosslinking agent to the mixed solution, adjust the pH to 4, and stir at room temperature for 8 hours.

[0174] (4)Separation and drying: The mixed solution after the reaction was separated by centrifugation and dried at 40 °C to obtain the cellulose nanocrystal composite.

[0175] The contact angle A1 of the outer surface of the prepared hollow fiber membrane was 50°, and the contact angle A2 of the inner surface was 115°.

[0176] Example 8

[0177] The preparation method of the hollow fiber membrane in this example is as follows:

[0178] S1 Activation of the base membrane: The polyethersulfone hollow fiber base membrane was treated with plasma. 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;

[0179] Plasma power: 70 W; treatment time: 3 minutes;

[0180] S2 Grafting of hydrophilic groups:

[0181] (1)Both ends of the activated polyethersulfone hollow fiber base membrane were sealed, and the outer surface was immersed in the grafting solution of hydrophilic groups and reacted at 50 °C for 4 hours; the hydrophilic group was 3-aminopropyltriethoxysilane (APTES), and the solvent was deionized water. The mass fraction of the grafting solution of hydrophilic groups was 2%;

[0182] (2)The membrane surface was washed with deionized water to remove the unreacted monomers;

[0183] (3)Dried at 60 °C for 12 hours;

[0184] S3 Grafting of hydrophobic groups:

[0185] (1)The inside of the polyethersulfone hollow fiber base membrane grafted with hydrophilic groups was filled with the grafting solution of hydrophobic groups and reacted at 40 °C for 3 hours; the hydrophobic group was cetyltrimethylammonium chloride (CTAC), and the concentration of the grafting solution of hydrophobic groups was controlled at 0.5%;

[0186] (2)The membrane surface was washed with deionized water to remove the ungrafted groups;

[0187] (3)Dried at 60 °C for 24 hours.

[0188] S4 Grafting the cellulose nanocrystal composite onto the outer surface of the polyethersulfone hollow fiber base membrane:

[0189] (1)Prepare a 1.2 mg / mL cellulose nanocrystal composite solution;

[0190] (2) Immerse the outer surface of the polyethersulfone hollow fiber membrane substrate in the cellulose nanocrystal composite solution, control the immersion time to 40 minutes, and after immersion, expose the membrane to 40 °C for drying.

[0191] The preparation method of the cellulose nanocrystal composite is as follows:

[0192] (1) Surface oxidation: Immerse the cellulose nanocrystals in a hydrogen peroxide solution, carry out the oxidation reaction for 1 hour, and then wash and dry with deionized water;

[0193] (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 of laccase and 130 U / mL of lipase solution;

[0194] (3) Crosslinking: Add 0.3 wt% of glutaraldehyde crosslinking agent to the mixed solution, adjust the pH to 4, and stir at room temperature for 8 hours.

[0195] (4) Separation and drying: Centrifuge the reacted mixed solution and dry it at 40 °C to obtain the cellulose nanocrystal composite.

[0196] The contact angle A1 of the outer surface of the prepared hollow fiber membrane is 43°, and the contact angle A2 of the inner surface is 110°.

[0197] Example 9

[0198] The preparation method of the hollow fiber membrane in this example is as follows:

[0199] S1 Substrate activation: Treat the polyethersulfone hollow fiber substrate with plasma. The average pore size of the outer surface is 0.2 μm, and the average pore size of the inner surface is 0.1 μm;

[0200] Plasma power: 70 W; treatment time: 3 minutes;

[0201] S2 Grafting of hydrophilic groups:

[0202] (1) Seal both ends of the activated polyethersulfone hollow fiber substrate, immerse the outer surface in the grafting solution of hydrophilic groups, and react at 50 °C for 4 hours; the hydrophilic group is polyvinyl alcohol (PVA), and the solvent is deionized water. The mass fraction of the grafting solution of hydrophilic groups is 2%;

[0203] (2) Wash the membrane surface with deionized water to remove unreacted monomers;

[0204] (3) Dry at 60 °C for 12 hours;

[0205] S3 Grafting of hydrophobic groups:

[0206] (1) Fill the inside of the polyethersulfone hollow fiber-based membrane grafted with hydrophilic groups with a grafting solution of hydrophobic groups, and react at 40 °C for 3 hours; the hydrophobic group is fluorinated alkyltrimethylsilane (FAS), and the concentration of the grafting solution of hydrophobic groups is controlled at 0.5%;

[0207] (2) Wash the membrane surface with deionized water to remove the ungrafted groups;

[0208] (3) Dry at 60 °C for 24 hours.

[0209] S4 Graft cellulose nanocrystal composite onto the outer surface of the polyethersulfone hollow fiber-based membrane:

[0210] (1) Prepare a 2 mg / mL cellulose nanocrystal composite solution;

[0211] (2) Immerse the outer surface of the polyethersulfone hollow fiber membrane-based membrane in the cellulose nanocrystal composite solution, control the immersion time to 30 minutes, and dry the membrane by exposing it at 40 °C after immersion.

[0212] The preparation method of the cellulose nanocrystal composite is as follows:

[0213] (1) Surface oxidation: Immerse cellulose nanocrystals in hydrogen peroxide solution, carry out oxidation reaction for 1 hour, and then wash and dry with deionized water;

[0214] (2) Mix 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;

[0215] (3) Crosslinking: Add 0.5 wt% glutaraldehyde crosslinking agent to the mixed solution, adjust the pH to 4, and stir at room temperature for 8 hours.

[0216] (4) Separation and drying: Centrifuge the reacted mixed solution and dry it at 40 °C to obtain the cellulose nanocrystal composite.

[0217] The contact angle A1 of the outer surface of the prepared hollow fiber membrane is 38°, and the contact angle A2 of the inner surface is 107°.

[0218] Example 10

[0219] The preparation method of the hollow fiber membrane in this example is as follows:

[0220] S1 Activation of the base membrane: Treat the polyethersulfone hollow fiber-based membrane with plasma, the average pore size of the outer surface is 0.2 μm, and the average pore size of the inner surface is 0.1 μm;

[0221] Plasma power: 70 W; treatment time: 3 minutes;

[0222] The S2 cellulose nanocrystal composite is grafted onto the outer surface of the polyethersulfone hollow fiber substrate membrane:

[0223] (1) Prepare a 2 mg / mL cellulose nanocrystal composite solution;

[0224] (2) Immerse the outer surface of the polyethersulfone hollow fiber membrane substrate in the cellulose nanocrystal composite solution, control the immersion time to 30 minutes, and after immersion, expose the membrane to 40 °C for drying.

[0225] The preparation method of the cellulose nanocrystal composite is as follows:

[0226] (1) Surface oxidation: Immerse the cellulose nanocrystals in a hydrogen peroxide solution, carry out the oxidation reaction for 1 hour, and then wash and dry with deionized water;

[0227] (2) Mix 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;

[0228] (3) Crosslinking: Add 0.5 wt% glutaraldehyde crosslinking agent to the mixed solution, adjust the pH to 4, and stir at room temperature for 8 hours.

[0229] (4) Separation and drying: Centrifuge the reacted mixed solution and dry it at 40 °C to obtain the cellulose nanocrystal composite.

[0230] S3 Grafting of hydrophilic groups:

[0231] (1) Seal both ends of the polyethersulfone hollow fiber substrate membrane, immerse the outer surface in the grafting solution of hydrophilic groups, and react at 50 °C for 4 hours; the hydrophilic group is polyvinyl alcohol (PVA), and the solvent is deionized water. The mass fraction of the grafting solution of hydrophilic groups is 2%;

[0232] (2) Wash the membrane surface with deionized water to remove unreacted monomers;

[0233] (3) Dry at 60 °C for 12 hours;

[0234] S4 Grafting of hydrophobic groups:

[0235] (1) Fill the inside of the polyethersulfone hollow fiber substrate membrane grafted with hydrophilic groups with the grafting solution of hydrophobic groups, and react at 40 °C for 3 hours; the hydrophobic group is fluorinated alkyltrimethylsilane (FAS), and the concentration of the grafting solution of hydrophobic groups is controlled at 0.5%;

[0236] (2) Wash the membrane surface with deionized water to remove ungrafted groups;

[0237] (3) Dry for 24 hours at 60 °C.

[0238] The contact angle A1 of the outer surface of the prepared hollow fiber membrane is 45°, and the contact angle A2 of the inner surface is 116°.

[0239] Example 11

[0240] The preparation method of the hollow fiber membrane in this example is as follows:

[0241] S1 Substrate membrane activation: Treat the polyethersulfone hollow fiber substrate membrane with plasma. The average pore size of the outer surface is 0.2 μm, and the average pore size of the inner surface is 0.1 μm;

[0242] Plasma power: 70 W; treatment time: 3 minutes;

[0243] S2 Grafting of hydrophilic groups:

[0244] (1) Seal both ends of the activated polyethersulfone hollow fiber substrate membrane, immerse the outer surface in the grafting solution of hydrophilic groups, and react at 50 °C for 4 hours; the hydrophilic group is polyvinyl alcohol (PVA), and the solvent is deionized water. The mass fraction of the grafting solution of hydrophilic groups is 2%;

[0245] (2) Wash the membrane surface with deionized water to remove unreacted monomers;

[0246] (3) Dry at 60 °C for 12 hours;

[0247] S3 Grafting of hydrophobic groups:

[0248] (1) Fill the inside of the polyethersulfone hollow fiber substrate membrane grafted with hydrophilic groups with the grafting solution of hydrophobic groups, and react at 40 °C for 3 hours; the hydrophobic group is fluorinated alkyltrimethylsilane (FAS), and the concentration of the grafting solution of hydrophobic groups is controlled at 0.5%;

[0249] (2) Wash the membrane surface with deionized water to remove ungrafted groups;

[0250] (3) Dry at 60 °C for 24 hours.

[0251] S4 Graft the cellulose nanocrystal complex onto the outer surface of the polyethersulfone hollow fiber substrate membrane:

[0252] (1) Prepare a 2 mg / mL cellulose nanocrystal complex solution;

[0253] (2) Immerse the outer surface of the polyethersulfone hollow fiber membrane substrate in the cellulose nanocrystal complex solution, control the immersion time to 30 minutes, and dry the membrane by exposing it to 40 °C after immersion.

[0254] The preparation method of the cellulose nanocrystal composite is as follows:

[0255] (1) Surface oxidation: Immerse the cellulose nanocrystals in a hydrogen peroxide solution, carry out the oxidation reaction for 1 hour, and then wash and dry with deionized water;

[0256] (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 of laccase and 200 U / mL of lipase solution;

[0257] (3) Crosslinking: Add 0.5 wt% of glutaraldehyde crosslinking agent to the mixed solution, adjust the pH to 4, and stir at room temperature for 8 hours.

[0258] (4) Separation and drying: Centrifuge the reacted mixed solution and then dry it at 40 °C to obtain the cellulose nanocrystal composite.

[0259] S5 Surfactant treatment:

[0260] (1) Immerse the polyethersulfone hollow fiber-based membrane grafted with hydrophilic and hydrophobic groups in a solution containing a surfactant. The surfactant is a polyvinyl alcohol surfactant, and the solution concentration is 0.06%;

[0261] (2) Uniformly coat the surfactant on the membrane surface by spin coating to form a thin and uniform surfactant film, and adjust the hydrophilic-hydrophobic gradient of the membrane;

[0262] (3) Dry the coated membrane at 40 °C to ensure that the surfactant layer is firmly fixed on the membrane surface;

[0263] (4) Finally, wash the membrane surface with deionized water to remove the unreacted surfactant and ensure that there are no excess residues on the membrane surface.

[0264] The contact angle A1 of the outer surface of the prepared hollow fiber membrane is 35°, and the contact angle A2 of the inner surface is 105°.

[0265] Comparative Example 1

[0266] The preparation method of the hollow fiber membrane in this comparative example is as follows:

[0267] S1 Substrate membrane activation: Treat the polyethersulfone hollow fiber substrate membrane with plasma. The average pore size of the outer surface is 0.5 μm, and the average pore size of the inner surface is 0.05 μm;

[0268] Plasma power: 70 W; Treatment time: 3 minutes;

[0269] S2 Grafting of hydrophilic groups:

[0270] (1) Seal both ends of the activated polyethersulfone hollow fiber substrate membrane, soak the outer surface in the grafting solution of hydrophilic groups, and react at 50 °C for 4 hours; the hydrophilic groups are polyvinyl alcohol (PVA), and the solvent is deionized water. The mass fraction of the grafting solution of hydrophilic groups is 0.5%;

[0271] (2) Wash the membrane surface with deionized water to remove unreacted monomers;

[0272] (3) Dry at 60 °C for 12 hours.

[0273] Comparative Example 2

[0274] The preparation method of the hollow fiber membrane in this example is as follows:

[0275] S1 Substrate membrane activation: Treat the polyethersulfone hollow fiber substrate membrane with plasma. The average pore size of the outer surface is 0.5 μm, and the average pore size of the inner surface is 0.05 μm;

[0276] Plasma power: 70 W; Treatment time: 3 minutes;

[0277] S2 Hydrophilic group grafting:

[0278] (1) Seal both ends of the activated polyethersulfone hollow fiber substrate membrane, soak the outer surface in the grafting solution of hydrophilic groups, and react at 50 °C for 4 hours; the hydrophilic groups are polyvinyl alcohol (PVA), and the solvent is deionized water. The mass fraction of the grafting solution of hydrophilic groups is 0.5%;

[0279] (2) Wash the membrane surface with deionized water to remove unreacted monomers;

[0280] (3) Dry at 60 °C for 12 hours;

[0281] S3 Hydrophobic group grafting:

[0282] (1) Seal both ends of the polyethersulfone hollow fiber substrate membrane grafted with hydrophilic groups, soak the outer surface in the grafting solution of hydrophobic groups, and react at 40 °C for 3 hours; the hydrophobic groups are fluorinated alkyltrimethylsilane (FAS), and the concentration of the grafting solution of hydrophobic groups is controlled at 0.5%;

[0283] (2) Wash the membrane surface with deionized water to remove ungrafted groups;

[0284] (3) Dry at 60 °C for 24 hours.

[0285] The contact angle A1 of the outer surface of the prepared hollow fiber membrane is 89°, and the contact angle A2 of the inner surface is 92°.

[0286] Detection method

[0287] 1. Pretreatment: The hollow fiber membrane samples of Examples 1-11 and Comparative Examples 1-2 were pre-wetted in pure water at 25°C for 24 hours and operated at a pressure of 0.15 MPa for 2 hours.

[0288] 2. Initial removal rate test: Standard wastewater containing methylene blue and congo red active dyes with an initial concentration of 100 mg / L and emulsified oil with an initial concentration of 500 mg / L passed through the membrane filtration devices respectively 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 rate was calculated.

[0289] Removal rate = (1 - effluent concentration / influent concentration) × 100%

[0290] 3. Regeneration performance test: The above membrane filtration device was backwashed to remove impurities on the hollow fiber membrane.

[0291] Back pressure: 0.15 MPa.

[0292] Pulse frequency: 3 times / minute. The backwashing time accounted for 10% of the operation cycle.

[0293] After backwashing, the removal rates of methylene blue, congo red and emulsified oil were tested again, and the average recovery rate (%) was calculated.

[0294] Recovery rate = (removal rate after backwashing / initial removal rate) × 100%

[0295] The results of the removal rate and recovery rate are shown in Table 1.

[0296] Table 1

[0297]

[0298] By precisely designing the gradient distribution of hydrophilic and hydrophobic groups and combining with the grafting of cellulose nanocrystal composites, the hollow fiber membrane of the present invention effectively improves the sewage treatment performance, pollutant removal efficiency of the membrane and the regeneration performance after backwashing.

[0299] The above are only the preferred embodiments of the present invention, and the protection scope of the present invention is not limited to the above embodiments. All technical solutions falling within the idea of the present invention belong to the protection scope of the present invention. It should be noted that for those of ordinary skill in the art, without departing from the principle of the present invention, several improvements and modifications 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, It includes a polyethersulfone hollow fiber base membrane, and hydrophilic groups and hydrophobic groups are grafted on the surface and in the thickness direction of the polyethersulfone hollow fiber base membrane; The hydrophilic groups are selected from aminopropionic acid or polyvinyl alcohol, and the hydrophobic groups are selected from fluorinated alkyltrimethylsilane or long-chain alkyltrimethylammonium chloride; Moreover, the number of the hydrophilic groups on the outer surface of the polyethersulfone hollow fiber base membrane is higher than that on the inner surface of the polyethersulfone hollow fiber base membrane, and the hydrophilic groups decrease in a gradient from the outside to the inside along the thickness direction of the polyethersulfone hollow fiber base membrane; The number of the hydrophobic groups on the inner surface of the polyethersulfone hollow fiber base membrane is higher than that on the outer surface of the polyethersulfone hollow fiber base membrane, and the hydrophobic groups decrease in a gradient from the inside to the outside along the thickness direction of the polyethersulfone hollow fiber base membrane; A cellulose nanocrystal complex is also grafted or adsorbed on the outer surface of the polyethersulfone hollow fiber base membrane, and the preparation method of the cellulose nanocrystal complex is as follows: (1) Surface oxidation: Immerse cellulose nanocrystals in a hydrogen peroxide solution, carry out an oxidation reaction for 1-2 hours, and then wash and dry with deionized water; (2) Mixing of laccase and cellulose nanocrystals: Prepare a surface-oxidized cellulose nanocrystal solution with a mass concentration of 1-2 wt%, and mix it evenly with laccase at 50-80 U / mL and a lipase solution at 100-200 U / mL; (3) Crosslinking: Add 0.1-0.5 wt% glutaraldehyde crosslinking agent to the mixed solution, adjust the pH to 4-5, and stir at room temperature for 6-12 hours; (4) Separation and drying: Centrifuge the reacted mixed solution and then dry it at 40 °C to obtain a cellulose nanocrystal complex; The steps for grafting the cellulose nanocrystal complex onto the outer surface of the polyethersulfone hollow fiber base membrane are as follows: (1) Prepare a cellulose nanocrystal complex solution at 0.5-2 mg / mL; (2) Immerse the outer surface of the polyethersulfone hollow fiber membrane base membrane in the cellulose nanocrystal complex solution, control the immersion time to be 30-60 minutes, and after immersion, expose the membrane to 40 °C for drying.

2. The hollow fiber membrane for treating printing and dyeing wastewater according to claim 1, wherein: The average pore size of the polyethersulfone hollow fiber base membrane decreases in a gradient from the outside to the inside along the thickness direction.

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

4. A 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. A hollow fiber membrane for treating printing and dyeing wastewater according to claim 1, characterized in that: The polyethersulfone hollow fiber base membrane is first grafted with hydrophilic groups and hydrophobic groups, and then the cellulose nanocrystal complex is grafted.

6. The hollow fiber membrane for treating printing and dyeing wastewater according to claim 1, wherein: The contact angle A3 of the outer surface of the hollow fiber membrane is 0.5-0.9×A1, and the contact angle A4 of the inner surface of the hollow fiber membrane is 0.98-1.1×A2.

7. A method for preparing a hollow fiber membrane for treating printing and dyeing wastewater according to any one of claims 1 to 6, characterized in that, It includes the following steps: S1 Base membrane activation: Treat the polyethersulfone hollow fiber base membrane with plasma; Plasma power: 50-100 W; Treatment time: 2-5 minutes; S2 Grafting of hydrophilic groups: (1) Seal both ends of the activated polyethersulfone hollow fiber-based membrane, soak the outer surface in the grafting solution of hydrophilic groups, and react at 50 °C for 4 - 6 hours; the hydrophilic groups are selected from aminopropionic acid or polyvinyl alcohol, and the mass fraction of the grafting solution of hydrophilic groups 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) Fill the inside of the polyethersulfone hollow fiber-based membrane grafted with hydrophilic groups with the grafting solution of hydrophobic groups, and react 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 hydrophobic groups is controlled at 0.1% - 0.5%; (2) Wash the membrane surface with deionized water to remove ungrafted groups; (3) Dry at 60 °C for 24 hours.

8. The preparation method of a hollow fiber membrane for treating printing and dyeing wastewater according to claim 7, characterized in that: After steps S2 and S3, the following steps are further included: (1) Immerse the polyethersulfone hollow fiber-based membrane grafted with hydrophilic and hydrophobic groups in a solution containing a surfactant, the surfactant is a polyvinyl alcohol surfactant, and the solution concentration is 0.01% - 0.1%; (2) Uniformly coat the surfactant on the membrane surface by spin coating to form a thin and uniform surfactant film, and adjust the hydrophilic-hydrophobic gradient of the membrane; (3) Dry the coated membrane at 40 °C to ensure that the surfactant layer is firmly fixed on the membrane surface; (4) Finally, wash the membrane surface with deionized water to remove unreacted surfactant and ensure that there are no excess residues on the membrane surface.

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