Janus pvdf hollow fiber ultrafiltration membrane and preparation method thereof

Abstract

The application relates to a Janus PVDF hollow fiber ultrafiltration membrane and a preparation method thereof, the Janus PVDF hollow fiber ultrafiltration membrane comprising a PVDF hollow fiber ultrafiltration base film and Janus particles; the PVDF hollow fiber ultrafiltration base film is prepared by hydrophilic modification of a polyester fiber hollow braided tube and a PVDF polymer casting solution; one side of the Janus particles is TiO2-PVDF, and the other side is modified epoxy resin; the TiO2-PVDF is prepared from a first spinning solution, and the first spinning solution comprises TiO2 nanoparticles and PVDF; the modified epoxy resin is prepared from a second spinning solution, and the second spinning solution comprises epoxy resin, an epoxy-containing silane coupling agent and an amine curing agent. The Janus PVDF hollow fiber ultrafiltration membrane has the advantages that the Janus particle TiO2-PVDF side plays a role in improving the hydrophilicity and antibacterial property of the membrane, the modified epoxy resin side mainly plays a bonding role, the hydrophilicity of the membrane is further improved, and the problem of material loss caused by poor compatibility is overcome.

Description

Technical Field

[0001] This invention relates to the field of membrane materials technology, and in particular to a Janus PVDF hollow fiber ultrafiltration membrane and its preparation method. Background Technology

[0002] Membrane separation technology, as a highly efficient and pollution-free purification technology that integrates concentration and separation, features simple operation, convenient maintenance, low energy consumption, and strong adaptability, and has been widely used in chemical, electronics, food, medical, and environmental protection fields. Among commonly used membrane materials, polyvinylidene fluoride (PVDF) is an emerging membrane material with excellent comprehensive performance. Due to its high mechanical strength, good resistance to acid and alkali corrosion, and good chemical stability, it has broad application prospects.

[0003] Currently, most commercially available PVDF hollow fiber ultrafiltration membranes are hydrophobic due to the strong CF bonds in PVDF, which result in poor surface hydrophilicity. Hydrophobic membranes require frequent physical and chemical cleaning during operation, increasing operating costs. Over long-term use, oily substances easily accumulate on the membrane surface, leading to severe fouling, a significant and irreversible reduction in membrane flux, and shortened membrane lifespan, especially in MBR systems with poor water quality. Furthermore, microorganisms adhere to or deposit on the membrane surface, forming a biofilm. The number of live bacteria on the membrane surface increases with the thickness of the biofilm, and the fouling layer becomes more compact due to the metabolic products. Therefore, developing a PVDF membrane material with both hydrophilic and antibacterial properties is crucial for preventing fouling.

[0004] For example, Chinese patent CN106215723A discloses a method for preparing a superhydrophilic composite PVDF ultrafiltration membrane. This method involves grafting silica nanoparticles modified with ammonium salt end groups onto the PVDF membrane surface with self-peptide and aromatic polyacrylamide chloride, resulting in a hydrophilic composite PVDF ultrafiltration membrane. When the nanoparticle mass fraction is 0.08 wt%, the contact angle decreases to 46°. Chinese patent CN102516584A discloses a method for modifying polyvinylidene fluoride (PVDF) membranes to resist protein fouling. This method involves forming a zwitterionic copolymer layer on the PVDF membrane surface through a two-step polymerization grafting method, with a grafting rate of zwitterionic 3-(methacrylamide)propyl-dimethyl(3-sulfopropyl)amine of 522 μg / cm³. 2The contact angle decreased to 29.1°. Chinese patent CN102205209A discloses an antibacterial polymeric ultrafiltration membrane and its preparation method. This method involves adding antibacterial agent particles with long-term sustained-release properties, composed of an inorganic carrier and an antibacterial agent, to the polymeric membrane-forming solution to prepare a polymeric ultrafiltration membrane with long-term antibacterial effects. In the above method, while introducing a modifier through blending improves the hydrophilicity and antibacterial properties of the PVDF membrane, it suffers from problems such as poor compatibility between the modifier and the membrane matrix, leading to raw material loss. Grafting modification, on the other hand, has disadvantages such as a cumbersome process and high cost.

[0005] In this context, Janus materials integrating two different components or structures have attracted increasing attention from researchers, including Janus particles, Janus films, and Janus sheets. For example, one part of such particles is hydrophilic, while the other part is hydrophobic. Compared with other single homogeneous materials, Janus materials can provide bifunctional effects, but the preparation methods of these materials require high compatibility between the materials. Therefore, finding a novel Janus PVDF membrane material that is compatible with PVDF membranes, suitable for large-scale industrial applications, and can achieve both hydrophilic and antibacterial functions is of significant practical importance. Summary of the Invention

[0006] The technical problem to be solved by the present invention is: the present invention provides a Janus PVDF hollow fiber ultrafiltration membrane and its preparation method, so as to improve the problems of poor compatibility between membrane materials and complex process, and prepare Janus PVDF membrane material with dual functions of hydrophilicity and antibacterial properties.

[0007] To solve the above-mentioned technical problems, the technical solution adopted by the present invention is as follows:

[0008] In a first aspect, the present invention provides a Janus PVDF hollow fiber ultrafiltration membrane, the Janus PVDF hollow fiber ultrafiltration membrane comprising a PVDF hollow fiber ultrafiltration base membrane and Janus particles; the PVDF hollow fiber ultrafiltration base membrane is formed by hydrophilic modification of polyester fiber hollow braided tube and PVDF polymer casting solution; one side of the Janus particles is TiO2-PVDF and the other side is modified epoxy resin;

[0009] The TiO2-PVDF is prepared by a first spinning solution, which includes TiO2 nanoparticles and PVDF.

[0010] The modified epoxy resin is prepared from a second spinning solution, which includes epoxy resin, an epoxy-containing silane coupling agent, and an amine curing agent.

[0011] This invention proposes a Janus PVDF hollow fiber ultrafiltration membrane, which is obtained by modifying a PVDF hollow fiber ultrafiltration base membrane with Janus particles that have different structures at both ends. For the TiO2-PVDF solid side of the Janus particles, since it inherently contains PVDF, there is essentially no compatibility issue with the PVDF hollow fiber ultrafiltration base membrane. Furthermore, the TiO2 nanoparticles impart hydrophilicity and antibacterial properties to the PVDF hollow fiber ultrafiltration base membrane. The strong bond between the TiO2-PVDF solid side and the PVDF hollow fiber ultrafiltration membrane is mainly attributed to the curing effect of the modified epoxy resin slurry side: the modified epoxy resin slurry side automatically turns outward, where the epoxy functional group end of the epoxy-containing silane coupling agent reacts with part of the amino group of the amine curing agent, and the remaining part of the amino group of the amine curing agent reacts with the epoxy resin, thereby grafting the epoxy-containing silane coupling agent onto the epoxy resin. This overcomes the compatibility problem with the PVDF hollow fiber ultrafiltration membrane and prevents raw material loss during use. The silane end of the epoxy-containing silane coupling agent hydrolyzes into the hydrophilic silanol group, further enhancing the hydrophilicity of the PVDF hollow fiber ultrafiltration membrane. Finally, Janus PVDF hollow fiber ultrafiltration membrane with excellent hydrophilicity, antibacterial properties, and antifouling properties is obtained.

[0012] Optionally, the PVDF polymer casting solution comprises, by weight: 100 parts PVDF, 10-15 parts polysorbate, 360-400 parts dimethylacetamide, 25-30 parts polyvinyl chloride K30, and 5-10 parts vinyl chloride.

[0013] Optionally, the first spinning solution and the second spinning solution further include an organic solvent, wherein the organic solvent is a mixture of dimethylacetamide and acetone, wherein the dimethylacetamide and acetone are mixed in a volume ratio of 2.8-3.2:1.

[0014] Optionally, the TiO2 nanoparticles in the first spinning solution are anatase nano-TiO2 with a particle size of 1-30 nm, and their mass fraction in the first spinning solution is 0.1-2 wt%.

[0015] The molecular weight of PVDF in the first spinning solution is 1×10⁻⁶. 5 g / mol, its mass concentration is 10%.

[0016] Optionally, the epoxy resin, epoxy-containing silane coupling agent, and amine curing agent in the second spinning solution are mixed in a mass ratio of 8-10:2.4-2.6:1.

[0017] The total mass concentration of the epoxy resin and amine curing agent is 40%.

[0018] The epoxy-containing silane coupling agent is at least one of KH560, KH561, KH530, KH531 and 3-[(2,3)-epoxypropoxy]propylmethyldimethoxysilane;

[0019] The amine curing agent is at least one of triethylenetetramine, ethylenediamine, diethylenetriamine, and hexamethylenediamine.

[0020] Optionally, the molecular weight of PVDF in the PVDF polymer casting solution is 5 × 10⁻⁶. 5 -7×10 5 g / mol.

[0021] Secondly, the present invention provides a method for preparing a Janus PVDF hollow fiber ultrafiltration membrane, comprising the following steps:

[0022] S1. Preparation of PVDF hollow fiber ultrafiltration membrane:

[0023] PVDF, polysorbate, dimethylacetamide, povidone K30, and vinyl chloride are formulated into a PVDF polymer casting solution according to the specified ratio. The bubble-free and impurity-free casting solution is extruded from spinneret A and uniformly coated onto the outer surface of a polyester fiber hollow braided tube at a temperature of 65-90℃. After passing through an air section of 2-14cm in length, the tube is immersed in a gel bath at 20-40℃. After curing, a PVDF hollow fiber ultrafiltration base membrane is obtained.

[0024] S2. Preparation of spinning solution:

[0025] First spinning solution: Add PVDF and organic solvent to a flask according to the ratio, heat at 70-80℃ for 24h until the solution turns light yellow, then add TiO2 nanoparticles to obtain the first spinning solution, and sonicate for 4h for later use.

[0026] Second spinning solution: Dissolve epoxy resin, epoxy-containing silane coupling agent and amine curing agent in an organic solvent according to the formula, stir for 1 hour to obtain the second spinning solution for later use.

[0027] S3. Preparation of Janus PVDF hollow fiber ultrafiltration membrane:

[0028] A dual-fluid parallel electro-spraying process is adopted. The first and second spinning solutions are placed in two injection pumps respectively and collected through hoses at the eccentric spinneret B. The solution is then uniformly sprayed onto the PVDF hollow fiber ultrafiltration membrane, and the electro-sprayed hybrid Janus particles are uniformly deposited on the surface of the PVDF hollow fiber ultrafiltration membrane. Finally, the membrane is immersed in water for washing and then air-dried for 72 hours to obtain the Janus PVDF hollow fiber ultrafiltration membrane product.

[0029] The spinneret B is an eccentric nozzle consisting of two nested and fixed metal capillaries with different inner diameters. One side of its cross-section is circular, and the other side is crescent-shaped.

[0030] This invention proposes a method for preparing Janus PVDF hollow fiber ultrafiltration membranes. It employs a two-fluid parallel electrospraying process. To ensure a large contact area between the first and second spinning solutions and prevent separation, the spinneret B is designed as a metal capillary with an irregular cross-section, creating an integrated Janus structure. This avoids the diffusion and mixing phenomena between the two spinning solutions during traditional biaxial parallel electrospinning, and successfully confines the first and second spinning solutions to their respective areas, reducing adverse mutual influences.

[0031] Optionally, in step S3, a plurality of the spinnerets B are evenly distributed circumferentially around the spinneret A.

[0032] Optionally, in step S3, the first spinning solution is sprayed out through a circular channel, and the second spinning solution is sprayed out through a crescent-shaped channel; the flow rate of the first spinning solution is 1.0-1.3 mL / h, and the flow rate of the second spinning solution is 0.27-0.35 mL / h.

[0033] Optionally, in step S3, the spinning voltage is 12kV and the distance between the spinneret B and the collector electrode is 16cm. Attached Figure Description

[0034] Figure 1 This is a schematic diagram of step S1 in the method described in this invention, which involves the preparation of a PVDF hollow fiber ultrafiltration membrane.

[0035] Figure 2 This is a schematic diagram of step S3 in the method of the present invention for preparing Janus PVDF hollow fiber ultrafiltration membrane;

[0036] Figure 3 These are test diagrams of the anti-pollution and antibacterial properties of Examples 1-3 and Comparative Examples 1-3 of the present invention. Detailed Implementation

[0037] To better understand the above technical solutions, exemplary embodiments of the present invention will be described in more detail below with reference to the accompanying drawings. Although exemplary embodiments of the present invention are shown in the drawings, it should be understood that the present invention can be implemented in various forms and should not be limited to the embodiments set forth herein. Rather, these embodiments are provided so that the present invention can be understood more clearly and thoroughly, and that the scope of the present invention can be fully conveyed to those skilled in the art.

[0038] Example 1

[0039] A Janus PVDF hollow fiber ultrafiltration membrane, comprising a PVDF hollow fiber ultrafiltration base membrane and Janus particles; the PVDF hollow fiber ultrafiltration base membrane is formed by hydrophilic modification of polyester fiber hollow braided tube and PVDF polymer casting solution; one side of the Janus particles is TiO2-PVDF and the other side is modified epoxy resin;

[0040] The TiO2-PVDF is prepared by a first spinning solution, which includes TiO2 nanoparticles and PVDF.

[0041] The modified epoxy resin is prepared from a second spinning solution, which includes epoxy resin, an epoxy-containing silane coupling agent, and an amine curing agent.

[0042] The PVDF polymer casting solution comprises, by weight: 100 parts PVDF, 10 parts polysorbate, 360 parts dimethylacetamide, 25 parts polyvinyl chloride K30, and 5 parts vinyl chloride.

[0043] The first spinning solution and the second spinning solution also include an organic solvent, which is a mixture of dimethylacetamide and acetone, wherein the dimethylacetamide and acetone are mixed in a volume ratio of 3:1.

[0044] The TiO2 nanoparticles in the first spinning solution are anatase nano-TiO2 with a particle size of 1-30 nm, and their mass fraction in the first spinning solution is 0.1 wt%.

[0045] The molecular weight of PVDF in the first spinning solution is 1×10⁻⁶. 5 g / mol, its mass concentration is 10%.

[0046] In the second spinning solution, epoxy resin, epoxy-containing silane coupling agent, and amine curing agent are mixed in a mass ratio of 10:2.6:1;

[0047] The total mass concentration of the epoxy resin and amine curing agent is 40%.

[0048] The epoxy-containing silane coupling agent is KH560;

[0049] The amine curing agent is triethylenetetramine.

[0050] The molecular weight of PVDF in the PVDF polymer casting solution is 5 × 10⁻⁶. 5 -7×10 5 g / mol.

[0051] It is prepared through the following steps:

[0052] S1. Preparation of PVDF hollow fiber ultrafiltration membrane (see...) Figure 1 ):

[0053] PVDF, polysorbate, dimethylacetamide, povidone K30, and vinyl chloride are formulated into a PVDF polymer casting solution according to the specified ratio. The bubble-free and impurity-free casting solution is extruded from spinneret A and uniformly coated onto the outer surface of a polyester fiber hollow braided tube at a temperature of 65-90℃. After passing through an air section of 2-14cm in length, the tube is immersed in a gel bath at 20-40℃. After curing, a PVDF hollow fiber ultrafiltration base membrane is obtained.

[0054] S2. Preparation of spinning solution:

[0055] First spinning solution: Add PVDF and organic solvent to a flask according to the ratio, heat at 70-80℃ for 24h until the solution turns light yellow, then add TiO2 nanoparticles to obtain the first spinning solution, and sonicate for 4h for later use.

[0056] Second spinning solution: Dissolve epoxy resin, epoxy-containing silane coupling agent and amine curing agent in an organic solvent according to the formula, stir for 1 hour to obtain the second spinning solution for later use.

[0057] S3. Preparation of Janus PVDF hollow fiber ultrafiltration membrane (see...) Figure 2 ):

[0058] A dual-fluid parallel electro-spraying process is adopted. The first and second spinning solutions are placed in two injection pumps respectively and collected through hoses at the eccentric spinneret B. The solution is then uniformly sprayed onto the PVDF hollow fiber ultrafiltration membrane, and the electro-sprayed hybrid Janus particles are uniformly deposited on the surface of the PVDF hollow fiber ultrafiltration membrane. Finally, the membrane is immersed in water for washing and then air-dried for 72 hours to obtain the Janus PVDF hollow fiber ultrafiltration membrane product.

[0059] The spinneret B is an eccentric nozzle consisting of two nested and fixed metal capillaries with different inner diameters. One side of its cross-section is circular, and the other side is crescent-shaped.

[0060] In step S3, several spinnerets B are evenly distributed in a circle around spinneret A.

[0061] In step S3, the first spinning solution is sprayed out through a circular channel, and the second spinning solution is sprayed out through a crescent-shaped channel; the flow rate of the first spinning solution is 1.3 mL / h, and the flow rate of the second spinning solution is 0.35 mL / h.

[0062] In step S3, the spinning voltage is 12kV and the distance between the spinneret B and the collector electrode is 16cm.

[0063] Example 2

[0064] The difference between this embodiment and Embodiment 1 is that the mass fraction of TiO2 nanoparticles in the first spinning solution is 1 wt%.

[0065] Example 3

[0066] The difference between this embodiment and Embodiment 1 is that the mass fraction of TiO2 nanoparticles in the first spinning solution is 2 wt%.

[0067] Comparative Example 1

[0068] The difference between this comparative example and Example 1 is that the first spinning solution does not contain TiO2 nanoparticles.

[0069] Comparative Example 2

[0070] The difference between this comparative example and Example 1 is that it does not contain a second spinning solution and uses a conventional electrostatic spinning spraying device.

[0071] Comparative Example 3

[0072] The difference between this comparative example and Example 1 is that the second spinning solution contains only epoxy resin and amine curing agent.

[0073] Performance tests were conducted on Examples 1-3 and Comparative Examples 1-3, and the specific testing methods are as follows:

[0074] 1. Pure water flux test: Under certain operating pressure and normal temperature, test the pure water permeation per unit time and per unit membrane area. The test method is specified in industry standard HY / T051-1999.

[0075] 2. Contact angle test: The contact angle between the prepared ultrafiltration membrane and water was measured using a contact angle tester.

[0076] 3. Antifouling performance test: The test was conducted using a UV-Vis spectrophotometer at 0.1 MPa using an external pressure method. A certain concentration of bovine serum albumin was used as the test subject. The residual amount of bovine serum albumin on the membrane was measured, and the rejection rate of the ultrafiltration membrane was calculated according to the following formula 1:

[0077]

[0078] In the formula, R represents the retention rate, %.

[0079] C f - Concentration of bovine serum albumin in the feed solution, mg / L;

[0080] C p - The concentration of bovine serum albumin in the osmotic fluid, in mg / L.

[0081] 4. Antibacterial performance test: Janus PVDF hollow fiber ultrafiltration membrane was cut into 1×1cm pieces. 2Square samples were sterilized by irradiation with 15W ultraviolet light for 30 minutes. *E. coli* was cultured in LB broth at 37°C (shaking 220 times per minute) until the OD600 of the strain reached approximately 0.6. The microbial culture (10⁸ CFU / mL) was diluted 1:1000 to a final concentration of 10⁵ CFU / mL. The sterilized sample was placed in 3 mL of the bacterial solution and completely immersed. The culture was then incubated at 37°C and 220 rpm for 24 hours, after which the OD value was measured. Three independent experiments were performed on each fabric sample. The inhibition rate (%) was calculated according to the following formula 2:

[0082]

[0083] The test results for pure water flux and contact angle are shown in Table 1. The test results for antifouling performance and antibacterial performance are shown in Table 2. Figure 3 .

[0084] Table 1

[0085]

[0086] From Table 1 and Figure 3 It can be seen that the Janus PVDF hollow fiber ultrafiltration membrane obtained in the embodiments of the present invention has a small contact angle, high rejection rate, and excellent hydrophilicity and antifouling properties. In Comparative Example 1, due to the lack of TiO2 modification, the antibacterial and hydrophilic properties of the obtained ultrafiltration membrane are significantly reduced. In Comparative Example 2, due to the absence of the second spinning solution, the curing effect of the modified epoxy resin is lacking, which weakens the bonding force between TiO2 particles and the base membrane, resulting in a certain degree of decrease in the hydrophilicity of the obtained ultrafiltration membrane. In Comparative Example 3, although the second spinning solution contains epoxy resin and curing agent, the hydrophilicity of the obtained Janus PVDF hollow fiber ultrafiltration membrane is still reduced to a certain extent compared with Example 1. This indicates that the introduction of the second spinning solution can further improve the hydrophilicity of the ultrafiltration membrane mainly due to the hydrolysis of the silane end of the epoxy-containing silane coupling agent into the hydrophilic silanol group, while the introduction of epoxy resin and curing agent mainly improves the depth and adhesion of the cross-linking reaction between each component and the base membrane.

[0087] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A Janus PVDF hollow fiber ultrafiltration membrane, characterized in that, The Janus PVDF hollow fiber ultrafiltration membrane comprises a PVDF hollow fiber ultrafiltration base membrane and Janus particles; the PVDF hollow fiber ultrafiltration base membrane is formed by hydrophilic modification of polyester fiber hollow braided tube and PVDF polymer casting solution; one side of the Janus particles is TiO2-PVDF and the other side is modified epoxy resin. The TiO2-PVDF is prepared by a first spinning solution, which includes TiO2 nanoparticles and PVDF. The modified epoxy resin is prepared from a second spinning solution, which includes epoxy resin, an epoxy-containing silane coupling agent, and an amine curing agent.

2. The Janus PVDF hollow fiber ultrafiltration membrane as described in claim 1, characterized in that, The PVDF polymer casting solution comprises, by weight: 100 parts PVDF, 10-15 parts polysorbate, 360-400 parts dimethylacetamide, 25-30 parts povidone K30, and 5-10 parts vinyl chloride.

3. The Janus PVDF hollow fiber ultrafiltration membrane as described in claim 1, characterized in that, The first spinning solution and the second spinning solution also include an organic solvent, which is a mixture of dimethylacetamide and acetone, wherein the dimethylacetamide and acetone are mixed in a volume ratio of 2.8-3.2:

1.

4. The Janus PVDF hollow fiber ultrafiltration membrane as described in claim 1, characterized in that, The TiO2 nanoparticles in the first spinning solution are anatase nano-TiO2 with a particle size of 1-30 nm, and their mass fraction in the first spinning solution is 0.1-2 wt%. The molecular weight of PVDF in the first spinning solution is 1×10⁻⁶. 5 g / mol, its mass concentration is 10%.

5. The Janus PVDF hollow fiber ultrafiltration membrane as described in claim 1, characterized in that, In the second spinning solution, epoxy resin, epoxy-containing silane coupling agent, and amine curing agent are mixed in a mass ratio of 8-10:2.4-2.6:

1. The total mass concentration of the epoxy resin and amine curing agent is 40%. The epoxy-containing silane coupling agent is at least one of KH560, KH561, KH530, KH531 and 3-[(2,3)-epoxypropoxy]propylmethyldimethoxysilane; The amine curing agent is at least one of triethylenetetramine, ethylenediamine, diethylenetriamine, and hexamethylenediamine.

6. The Janus PVDF hollow fiber ultrafiltration membrane as described in claim 2, characterized in that, The molecular weight of PVDF in the PVDF polymer casting solution is 5 × 10⁻⁶. 5 -7×10 5 g / mol.

7. A method for preparing a Janus PVDF hollow fiber ultrafiltration membrane as described in any one of claims 1-6, comprising the following steps: S1. Preparation of PVDF hollow fiber ultrafiltration membrane: PVDF, polysorbate, dimethylacetamide, povidone K30, and vinyl chloride are formulated into a PVDF polymer casting solution according to the specified ratio. The bubble-free and impurity-free casting solution is extruded from spinneret A and uniformly coated onto the outer surface of a polyester fiber hollow braided tube at a temperature of 65-90℃. After passing through an air section of 2-14cm in length, the tube is immersed in a gel bath at 20-40℃. After curing, a PVDF hollow fiber ultrafiltration base membrane is obtained. S2. Preparation of spinning solution: First spinning solution: Add PVDF and organic solvent to a flask according to the ratio, heat at 70-80℃ for 24h until the solution turns light yellow, then add TiO2 nanoparticles to obtain the first spinning solution, and sonicate for 4h for later use. Second spinning solution: Dissolve epoxy resin, epoxy-containing silane coupling agent and amine curing agent in an organic solvent according to the formula, stir for 1 hour to obtain the second spinning solution for later use. S3. Preparation of Janus PVDF hollow fiber ultrafiltration membrane: A dual-fluid parallel electro-spraying process is adopted. The first and second spinning solutions are placed in two injection pumps respectively, and collected through a hose at the eccentric spinneret B. The solution is then uniformly sprayed onto the PVDF hollow fiber ultrafiltration membrane, and the electro-sprayed hybrid Janus particles are uniformly deposited on the surface of the PVDF hollow fiber ultrafiltration membrane. Finally, the membrane is immersed in water for cleaning and then air-dried for 72 hours to obtain the JanusPVDF hollow fiber ultrafiltration membrane product. The spinneret B is an eccentric nozzle consisting of two nested and fixed metal capillaries with different inner diameters. One side of its cross-section is circular, and the other side is crescent-shaped.

8. The method for preparing the Janus PVDF hollow fiber ultrafiltration membrane as described in claim 7, characterized in that, In step S3, several spinnerets B are evenly distributed in a circle around spinneret A.

9. The method for preparing the Janus PVDF hollow fiber ultrafiltration membrane as described in claim 7, characterized in that, In step S3, the first spinning solution is ejected through a circular channel, and the second spinning solution is ejected through a crescent-shaped channel; the flow rate of the first spinning solution is 1.0-1.3 mL / h, and the flow rate of the second spinning solution is 0.27-0.35 mL / h.

10. The method for preparing the Janus PVDF hollow fiber ultrafiltration membrane as described in claim 7, characterized in that, In step S3, the spinning voltage is 12kV and the distance between the spinneret B and the collector electrode is 16cm.

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