Graphene oxide modified hollow fiber membrane for oily wastewater treatment and preparation method of graphene oxide modified hollow fiber membrane

Abstract

The invention belongs to the technical field of separation membrane materials, and discloses a graphene oxide modified hollow fiber membrane for oily wastewater treatment and a preparation method of the graphene oxide modified hollow fiber membrane. Firstly, a hollow fiber base membrane is prepared through a phase inversion method; then performing oxygen plasma pretreatment to activate the surface; immersing the activated base membrane into a Tris-HCl buffer solution of dopamine and polyethyleneimine, and forming a polydopamine intermediate layer on the surface of the membrane through auto-polymerization of dopamine; and finally, firmly loading the graphene oxide nanosheets on the surface of the base membrane by using the intermediate layer to form a graphene oxide functional surface layer, and carrying out vacuum drying to obtain a final product. A three-layer gradient structure of'base membrane-polydopamine middle layer-graphene oxide surface layer 'is constructed, the hydrophilicity of graphene oxide is utilized to form a water membrane on the surface of the membrane, oil drops are repelled, the anti-pollution performance of the membrane is improved, the problem that the coating is easy to fall off is solved by means of the adhesion of polydopamine, and the preparation process is simple and controllable and is suitable for large-scale production.

Description

Technical Field

[0001] This invention belongs to the field of separation membrane material technology, specifically relating to a graphene oxide modified hollow fiber membrane for oily wastewater treatment and its preparation method. Background Technology

[0002] Oily wastewater is a typical source of pollution generated in industrial production and daily life, widely originating from fields such as oil extraction, machinery processing, metal smelting, and catering services. The oil in this type of wastewater exists mainly in three forms: free oil, dispersed oil, and emulsified oil. Among these, emulsified oil, due to its extremely small particle size (0.1-10 μm) and the stable electric double layer formed by surfactants, is the most difficult component to treat. If discharged directly without effective treatment, the oil will form a dense oil film on the water surface, hindering oxygen exchange between the atmosphere and the water, leading to oxygen deprivation and death of aquatic organisms. Simultaneously, toxic and harmful substances such as polycyclic aromatic hydrocarbons and heavy metals contained in the oil will accumulate through the food chain, ultimately endangering human health. In ultrafiltration membrane materials, polyethersulfone (PES) and polyvinylidene fluoride (PVDF) hollow fiber membranes are widely used in oily wastewater treatment due to their high mechanical strength, excellent chemical resistance, and high porosity. However, PES and PVDF membranes are inherently hydrophobic, which presents a key drawback when treating oily wastewater: oil is easily adsorbed onto the membrane surface through hydrophobic-hydrophobic interactions, and at the same time forms a dense oil-solid composite filter cake layer with suspended solids in the water (such as silt and metal debris), leading to severe membrane fouling. This manifests as a short-term decline in membrane flux, high cleaning frequency, and short service life, which greatly limits their economic efficiency and stability in oily wastewater treatment.

[0003] Oily wastewater treatment technologies can be divided into pretreatment technologies and advanced treatment technologies:

[0004] 1. Pretreatment technologies: These include oil separators (removing free oil, efficiency >80%), air flotation (dispersing oil through microbubble adsorption, oil removal rate 60%-80%), and coagulation sedimentation (adding aluminum / iron salts to disrupt the stability of emulsified oil, oil removal rate 70%-90%). However, these technologies have limited effectiveness in removing emulsified oil (effluent oil concentration often >50mg / L), and require the addition of large amounts of chemicals, resulting in secondary sludge pollution, making it difficult to meet the needs of advanced treatment.

[0005] 2. Advanced Treatment Technology: Ultrafiltration membrane technology, thanks to its pore size sieving effect, can effectively retain emulsified oil (removal rate > 95%), reducing the oil concentration in the effluent to below 10 mg / L. While commercially available PES / PVDF hollow fiber membranes possess basic separation performance, their antifouling properties are insufficient.

[0006] Current technologies for modifying PES / PVDF hollow fiber membranes to resist oil fouling all revolve around improving the hydrophilicity of the membrane surface to reduce oil adsorption. However, they generally suffer from key drawbacks: hydrophilic polymer coating modification (such as coating with PEG or PVA) can improve hydrophilicity in the short term, but because the polymer and the base membrane are only physically adsorbed, they are easily detached during high-pressure water jets or chemical cleaning. Furthermore, PEG chains are easily encapsulated by oil, leading to a decrease in antifouling performance. Nanoparticle-supported modification (such as TiO2 or SiO2) utilizes nanoparticles... While high specific surface area enhances hydrophilicity, the high surface energy of nanoparticles makes them prone to aggregation, potentially clogging membrane pores and reducing flux. Furthermore, uneven aggregation can lead to gradual detachment, and some particles require UV excitation, limiting their application scenarios. Surface grafting modification (such as UV- or plasma-induced grafting of acrylic acid) can form hydrophilic grafted layers through chemical bonding, but it requires complex equipment, and the grafted layer thickness is difficult to control precisely (too thick reduces flux, too thin provides insufficient antifouling). Additionally, monomer residues may cause secondary water pollution, hindering large-scale industrial production. In summary, current technologies have not yet overcome the core bottlenecks of weak adhesion between the modified coating and the base membrane, long-term stable anti-oil pollution performance, and easy industrialization of the preparation process, thus failing to meet the long-term stability requirements of membrane materials for oily wastewater treatment. Summary of the Invention

[0007] To address the problems mentioned in the background art, this invention proposes a graphene oxide-modified hollow fiber membrane for oily wastewater treatment and its preparation method. The graphene oxide surface layer of this application, through its super hydrophilicity, can form a stable hydration layer on the membrane surface, effectively repelling the adsorption and wetting of oil droplets, exhibiting excellent and long-lasting anti-fouling performance, which is significantly better than traditional hydrophobic polymer membranes.

[0008] The technical solution adopted by this invention to solve its technical problem is: a method for preparing graphene oxide modified hollow fiber membrane for oily wastewater treatment, comprising the following steps:

[0009] S1. Preparation of hollow fiber base membrane: The spinning solution is prepared by dissolving the matrix polymer and pore-forming agent in N,N-dimethylacetamide. After uniform dissolution, the solution is extruded through a spinneret and then passed through a coagulation bath to obtain a hollow fiber base membrane.

[0010] S2. Oxygen plasma treatment of hollow fiber base membrane;

[0011] S3. The pretreated base film is immersed in a dopamine solution prepared with Tris-HCl buffer solution to react with a mixture of dopamine and polyethyleneimine, so that dopamine self-polymerizes on the surface of the base film to form a polydopamine intermediate layer.

[0012] S4. Immerse the base film with the polydopamine interlayer in the graphene oxide dispersion to carry out the loading reaction, so that the graphene oxide is fixed on the surface of the base film through the polydopamine interlayer to form the graphene oxide surface layer.

[0013] S5. The loaded membrane is vacuum dried to obtain the graphene oxide modified hollow fiber membrane.

[0014] Furthermore, in step S1, the matrix polymer is polysulfone, polyethersulfone, or polyvinylidene fluoride.

[0015] Furthermore, in step S1, the amount of the matrix polymer is 65-69 wt%;

[0016] The porogen is a mixture of PVP-K30 and PEG200; the amount of PVP-K30 is 6wt%-10wt%; the amount of PEG200 is 10wt%-14wt%.

[0017] The balance is N,N-dimethylacetamide;

[0018] The dissolution temperature is 105±5℃, and the stirring speed is 300r / min.

[0019] Furthermore, in step S2, the power of the oxygen plasma treatment is 10-30W, and the treatment time is 5-15s.

[0020] Furthermore, in step S3, the pH of the Tris-HCl buffer solution is 8.0-8.5, and the concentration of the dopamine solution is 0.5-2 g / L.

[0021] Furthermore, in step S3:

[0022] The concentration of the graphene oxide dispersion is 0.1-0.5 g / L;

[0023] The graphene oxide dispersion was prepared by ultrasonication at 300-500W power for 30-60 minutes.

[0024] The loading reaction temperature is 25-40℃, and the reaction time is 2-6h;

[0025] The concentration of polyethyleneimine is 0.5-1 g / L.

[0026] Furthermore, in step S4, the vacuum drying temperature is 60-80℃, and the drying time is 2-4 hours.

[0027] This invention also provides a graphene oxide-modified hollow fiber membrane for treating oily wastewater, the composite membrane having a three-layer gradient structure, from the inside out as follows:

[0028] The polymer-based film layer serves as a support.

[0029] A polydopamine intermediate layer, which is firmly bonded to the surface of the plasma-pretreated base film layer by covalent bonds, serves as a functional connecting layer;

[0030] The graphene oxide surface layer is stably loaded through the multiple intermolecular forces of the polydopamine intermediate layer, forming a dense nanoscale anti-fouling functional layer.

[0031] The polydopamine intermediate layer and the graphene oxide surface layer together form a synergistic anti-oil contamination interface. The ultra-high hydrophilicity of the graphene oxide surface layer generates a strong hydration layer to repel oil droplets, and the physical barrier effect of its nanosheets jointly prevents the adsorption and wetting of oil on the membrane surface.

[0032] Furthermore, the covalent bond between the polydopamine intermediate layer and the base film layer is formed by the reaction of the catechol groups of polydopamine with the oxygen-containing functional groups introduced on the surface of the base film by plasma pretreatment.

[0033] Compared with the prior art, the beneficial effects of the present invention are:

[0034] (1) The graphene oxide surface layer of this application can form a stable hydration layer on the membrane surface through its super hydrophilicity, effectively repelling the adsorption and wetting of oil droplets, showing excellent and long-lasting anti-fouling performance, which is significantly better than traditional hydrophobic polymer membranes.

[0035] (2) This application achieves a strong bond between graphene oxide and the base film through oxygen plasma pretreatment and the construction of a polydopamine interlayer. Plasma activation introduces oxygen-containing functional groups on the surface of the base film, forming covalent bonds with polydopamine; the polydopamine interlayer further stabilizes the loaded graphene oxide nanosheets through multiple forces such as π-π stacking and hydrogen bonding. After multiple rinsings, the coating retention rate is higher than 90%, effectively solving the common problem of easy coating detachment in traditional physical coating or nanoparticle loading.

[0036] (3) The graphene oxide surface layer and the polydopamine intermediate layer of this application together constitute a dense nanoscale functional layer. Through the synergistic effect of size sieving and hydrophilic repulsion, it has an extremely high retention rate for components such as emulsified oil in oily wastewater. The oil removal rate of oily wastewater in all embodiments exceeds 99%, and the oil concentration of the effluent meets the requirements for reuse or discharge in compliance with standards. Detailed Implementation

[0037] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0038] Example 1:

[0039] S1. Preparation of hollow fiber membrane: A spinning solution was prepared by dissolving the matrix polymer polysulfone (68 wt%), pore-forming agent PVP-K30 (8 wt%), and PEG200 (12 wt%) in N,N-dimethylacetamide (balance). The dissolution temperature was 105℃, and the stirring speed was 300 r / min. After uniform dissolution, the solution was extruded through a spinneret and passed through a coagulation bath to obtain a hollow fiber membrane.

[0040] S2. The hollow fiber base membrane is subjected to oxygen plasma treatment with a power of 20W and a treatment time of 10s.

[0041] S3. Immerse the pretreated base film in a mixture of dopamine (concentration 1 g / L) and polyethyleneimine (concentration 0.75 g / L) prepared in Tris-HCl buffer solution at pH 8.2, and react at room temperature for 2 h to allow dopamine to self-polymerize on the base film surface to form a polydopamine intermediate layer.

[0042] S4. Immerse the base film with the polydopamine interlayer in a graphene oxide dispersion (concentration 0.3 g / L, prepared by ultrasonication at 400 W for 45 min) and react at 30 °C for 4 h to fix the graphene oxide onto the surface of the base film through the polydopamine interlayer, forming a graphene oxide surface layer.

[0043] S5. The loaded membrane is vacuum dried at a temperature of 70°C for 3 hours to obtain a graphene oxide modified hollow fiber membrane.

[0044] Example 2:

[0045] S1. Preparation of hollow fiber membrane: A spinning solution was prepared by dissolving the matrix polymer polyethersulfone (66 wt%), pore-forming agent PVP-K30 (7 wt%), and PEG200 (11 wt%) in N,N-dimethylacetamide (balance). The dissolution temperature was 100℃, and the stirring speed was 300 r / min. After uniform dissolution, the solution was extruded through a spinneret and passed through a coagulation bath to obtain a hollow fiber membrane.

[0046] S2. The hollow fiber base membrane is subjected to oxygen plasma treatment with a power of 10W for a treatment time of 15s.

[0047] S3. Immerse the pretreated base film in a mixture of dopamine (concentration 0.5 g / L) and polyethyleneimine (concentration 0.5 g / L) prepared in Tris-HCl buffer solution at pH 8.0, and react at room temperature for 2 h to allow dopamine to self-polymerize on the base film surface to form a polydopamine intermediate layer.

[0048] S4. Immerse the base film with the polydopamine interlayer in a graphene oxide dispersion (concentration 0.1 g / L, prepared by ultrasonication at 300 W for 60 min) and react at 25 °C for 6 h to fix the graphene oxide onto the surface of the base film through the polydopamine interlayer, forming a graphene oxide surface layer.

[0049] S5. The loaded membrane is vacuum dried at a temperature of 60°C for 4 hours to obtain a graphene oxide modified hollow fiber membrane.

[0050] Example 3:

[0051] S1. Preparation of hollow fiber base membrane: A spinning solution was prepared by dissolving the matrix polymer polyvinylidene fluoride (69 wt%), pore-forming agent PVP-K30 (10 wt%), and PEG200 (14 wt%) in N,N-dimethylacetamide (balance). The dissolution temperature was 110℃, and the stirring speed was 300 r / min. After uniform dissolution, the solution was extruded through a spinneret and passed through a coagulation bath to obtain a hollow fiber base membrane.

[0052] S2. The hollow fiber base membrane is subjected to oxygen plasma treatment with a power of 30W and a treatment time of 5s.

[0053] S3. Immerse the pretreated base film in a mixture of dopamine (concentration 2 g / L) and polyethyleneimine (concentration 1 g / L) prepared in Tris-HCl buffer solution at pH 8.5, and react at room temperature for 2 h to allow dopamine to self-polymerize on the base film surface to form a polydopamine intermediate layer.

[0054] S4. Immerse the base film with the polydopamine interlayer in a graphene oxide dispersion (concentration 0.5 g / L, prepared by ultrasonication at 500 W for 30 min) and react at 40 °C for 2 h to fix the graphene oxide onto the surface of the base film through the polydopamine interlayer, forming a graphene oxide surface layer.

[0055] S5. The loaded membrane is vacuum dried at 80℃ for 2 hours to obtain a graphene oxide modified hollow fiber membrane.

[0056] Example 4:

[0057] S1. Preparation of hollow fiber membrane: A spinning solution was prepared by dissolving the matrix polymer polysulfone (65 wt%), pore-forming agent PVP-K30 (6 wt%), and PEG200 (10 wt%) in N,N-dimethylacetamide (balance). The dissolution temperature was 105℃, and the stirring speed was 300 r / min. After uniform dissolution, the solution was extruded through a spinneret and passed through a coagulation bath to obtain a hollow fiber membrane.

[0058] S2. The hollow fiber base membrane is subjected to oxygen plasma treatment with a power of 15W and a treatment time of 12s.

[0059] S3. Immerse the pretreated base film in a mixture of dopamine (concentration 1.5 g / L) and polyethyleneimine (concentration 0.8 g / L) prepared in Tris-HCl buffer solution at pH 8.1, and react at room temperature for 2 h to allow dopamine to self-polymerize on the base film surface to form a polydopamine intermediate layer.

[0060] S4. Immerse the base film with the polydopamine interlayer in a graphene oxide dispersion (concentration 0.2 g / L, prepared by ultrasonication at 350 W for 50 min) and react at 28 °C for 5 h to fix the graphene oxide onto the surface of the base film through the polydopamine interlayer, forming a graphene oxide surface layer.

[0061] S5. The loaded membrane is vacuum dried at a temperature of 65℃ for 3.5 hours to obtain a graphene oxide modified hollow fiber membrane.

[0062] Example 5:

[0063] S1. Preparation of hollow fiber membrane: A spinning solution was prepared by dissolving the matrix polymer polyethersulfone (67 wt%), pore-forming agent PVP-K30 (9 wt%), and PEG200 (13 wt%) in N,N-dimethylacetamide (balance). The dissolution temperature was 105℃, and the stirring speed was 300 r / min. After uniform dissolution, the solution was extruded through a spinneret and passed through a coagulation bath to obtain a hollow fiber membrane.

[0064] S2. The hollow fiber base membrane is subjected to oxygen plasma treatment with a power of 25W and a treatment time of 8s.

[0065] S3. Immerse the pretreated base film in a mixture of dopamine (concentration 1.2 g / L) and polyethyleneimine (concentration 0.9 g / L) prepared in Tris-HCl buffer solution at pH 8.3, and react at room temperature for 2 h to allow dopamine to self-polymerize on the base film surface to form a polydopamine intermediate layer.

[0066] S4. Immerse the base film with the polydopamine interlayer in a graphene oxide dispersion (concentration 0.4 g / L, prepared by ultrasonication at 450 W for 40 min) and react at 35 °C for 3 h to fix the graphene oxide onto the surface of the base film through the polydopamine interlayer, forming a graphene oxide surface layer.

[0067] S5. The loaded membrane is vacuum dried at a temperature of 75°C for 2.5 hours to obtain a graphene oxide modified hollow fiber membrane.

[0068] Example 6:

[0069] S1. Preparation of hollow fiber membrane: A spinning solution was prepared by dissolving the matrix polymer polyvinylidene fluoride (68.5 wt%), pore-forming agent PVP-K30 (8.5 wt%), and PEG200 (11.5 wt%) in N,N-dimethylacetamide (balance). The dissolution temperature was 105℃, and the stirring speed was 300 r / min. After uniform dissolution, the solution was extruded through a spinneret and passed through a coagulation bath to obtain a hollow fiber membrane.

[0070] S2. The hollow fiber base membrane is subjected to oxygen plasma treatment with a power of 18W and a treatment time of 14s.

[0071] S3. Immerse the pretreated base film in a mixture of dopamine (concentration 1.8 g / L) and polyethyleneimine (concentration 0.6 g / L) prepared in Tris-HCl buffer solution at pH 8.4, and react at room temperature for 2 h to allow dopamine to self-polymerize on the surface of the base film to form a polydopamine intermediate layer.

[0072] S4. Immerse the base film with the polydopamine interlayer in a graphene oxide dispersion (concentration 0.25 g / L, prepared by ultrasonication at 320 W for 55 min) and react at 32 °C for 4.5 h to fix the graphene oxide on the surface of the base film through the polydopamine interlayer, forming a graphene oxide surface layer.

[0073] S5. The loaded membrane is vacuum dried at a temperature of 68°C for 3.2 hours to obtain a graphene oxide modified hollow fiber membrane.

[0074] Example 7:

[0075] S1. Preparation of hollow fiber membrane: A spinning solution was prepared by dissolving the matrix polymer polysulfone (69 wt%), pore-forming agent PVP-K30 (10 wt%), and PEG200 (14 wt%) in N,N-dimethylacetamide (balance). The dissolution temperature was 105℃, and the stirring speed was 300 r / min. After uniform dissolution, the solution was extruded through a spinneret and passed through a coagulation bath to obtain a hollow fiber membrane.

[0076] S2. The hollow fiber base membrane is subjected to oxygen plasma treatment with a power of 12W and a treatment time of 13s.

[0077] S3. Immerse the pretreated base film in a mixture of dopamine (concentration 0.8 g / L) and polyethyleneimine (concentration 0.7 g / L) prepared in Tris-HCl buffer solution at pH 8.2, and react at room temperature for 2 h to allow dopamine to self-polymerize on the base film surface to form a polydopamine intermediate layer.

[0078] S4. Immerse the base film with the polydopamine interlayer in a graphene oxide dispersion (concentration 0.35 g / L, prepared by ultrasonication at 380 W for 35 min) and react at 38 °C for 3.5 h to fix the graphene oxide onto the surface of the base film through the polydopamine interlayer, forming a graphene oxide surface layer.

[0079] S5. The loaded membrane is vacuum dried at a temperature of 72℃ for 2.8 hours to obtain a graphene oxide modified hollow fiber membrane.

[0080] Key performance tests were conducted on the graphene oxide-modified hollow fiber membranes obtained in Examples 1-7. The test results are shown in the table below:

[0081]

[0082] Test Result Analysis:

[0083] Antifouling performance: The 24-hour flux decay rate of the hollow fiber membranes prepared in Examples 1-7 was ≤15%, indicating that the graphene oxide coating effectively improved the hydrophilicity and anti-oil adsorption capacity of the membrane. Among them, the parameter combination of Example 3 (higher plasma treatment power, dopamine concentration, and reaction temperature) showed the best antifouling performance and the lowest flux decay rate.

[0084] Coating stability: The coating retention rates of Examples 1-7 were all >90%, demonstrating that the interlayer design based on the "universal adhesion" of polydopamine can firmly fix the graphene oxide surface layer, solving the problem of easy coating detachment in traditional modification methods. Example 3 also showed the best performance in this aspect.

[0085] Treatment Results: Examples 1-7 all achieved oil removal rates exceeding 99% for oily wastewater, demonstrating very high separation precision. The treated effluent can be directly reused or discharged in compliance with standards. Example 3 showed the highest oil removal rate.

[0086] Conclusion: The test data from Examples 1-7 fully verify that the graphene oxide-modified hollow fiber membranes obtained by this preparation method possess excellent antifouling properties, high coating stability, and outstanding oil-water separation performance. Although membrane performance fluctuates under different parameter combinations, it still meets the design requirements, with the combination of preparation parameters in Example 3 exhibiting the most outstanding overall performance.

[0087] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A method for preparing a graphene oxide-modified hollow fiber membrane for treating oily wastewater, characterized in that, Includes the following steps: S1. Preparation of hollow fiber base membrane: The spinning solution is prepared by dissolving the matrix polymer and pore-forming agent in N,N-dimethylacetamide. After uniform dissolution, the solution is extruded through a spinneret and then passed through a coagulation bath to obtain a hollow fiber base membrane. S2. Oxygen plasma treatment of hollow fiber base membrane; S3. The pretreated base film is immersed in a mixture of dopamine and polyethyleneimine prepared with Tris-HCl buffer solution to react, so that dopamine self-polymerizes on the surface of the base film to form a polydopamine intermediate layer. S4. Immerse the base film with the polydopamine interlayer in the graphene oxide dispersion to carry out the loading reaction, so that the graphene oxide is fixed on the surface of the base film through the polydopamine interlayer to form the graphene oxide surface layer. S5. The loaded membrane is vacuum dried to obtain the graphene oxide modified hollow fiber membrane.

2. The method for preparing a graphene oxide-modified hollow fiber membrane for treating oily wastewater according to claim 1, characterized in that: In step S1, the matrix polymer is polysulfone, polyethersulfone, or polyvinylidene fluoride.

3. The method for preparing a graphene oxide-modified hollow fiber membrane for treating oily wastewater according to claim 1, characterized in that: In step S1, the amount of the matrix polymer is 65-69 wt%; The porogen is a mixture of PVP-K30 and PEG200; the amount of PVP-K30 is 6wt%-10wt%; the amount of PEG200 is 10wt%-14wt%. The balance is N,N-dimethylacetamide; The dissolution temperature is 105±5℃, and the stirring speed is 300r / min.

4. The method for preparing a graphene oxide-modified hollow fiber membrane for treating oily wastewater according to claim 1, characterized in that: In step S2, the power of the oxygen plasma treatment is 10-30W, and the treatment time is 5-15s.

5. The method for preparing a graphene oxide-modified hollow fiber membrane for treating oily wastewater according to claim 1, characterized in that: In step S3, the pH of the Tris-HCl buffer solution is 8.0-8.5, and the concentration of the dopamine solution is 0.5-2 g / L.

6. The method for preparing a graphene oxide-modified hollow fiber membrane for treating oily wastewater according to claim 1, characterized in that, In step S3: The concentration of the graphene oxide dispersion is 0.1-0.5 g / L; The graphene oxide dispersion was prepared by ultrasonication at 300-500W power for 30-60 minutes. The loading reaction temperature is 25-40℃, and the reaction time is 2-6h; The concentration of polyethyleneimine is 0.5-1 g / L.

7. The method for preparing a graphene oxide-modified hollow fiber membrane for treating oily wastewater according to claim 1, characterized in that, In step S4, the vacuum drying temperature is 60-80℃ and the drying time is 2-4 hours.

8. A graphene oxide-modified hollow fiber membrane for treating oily wastewater, characterized in that, The composite membrane has a three-layer gradient structure, which, from the inside out, consists of: The polymer-based film layer serves as a support. A polydopamine intermediate layer, which is firmly bonded to the surface of the plasma-pretreated base film layer by covalent bonds, serves as a functional connecting layer; The graphene oxide surface layer is stably loaded through the multiple intermolecular forces of the polydopamine intermediate layer, forming a dense nanoscale anti-fouling functional layer. The polydopamine intermediate layer and the graphene oxide surface layer together form a synergistic anti-oil contamination interface. The ultra-high hydrophilicity of the graphene oxide surface layer generates a strong hydration layer to repel oil droplets, and the physical barrier effect of its nanosheets jointly prevents the adsorption and wetting of oil on the membrane surface.

9. A graphene oxide-modified hollow fiber membrane for treating oily wastewater according to claim 8, characterized in that, The covalent bonds between the polydopamine intermediate layer and the base film layer are formed by the reaction of the catechol groups of polydopamine with the oxygen-containing functional groups introduced on the surface of the base film by plasma pretreatment.

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