Preparation method and application of oriented nanofiber composite membrane with self-cleaning function

Abstract

The application provides a preparation method and application of an oriented nanofiber composite membrane with a self-cleaning function. First, polymer nanofibers are frozen by liquid nitrogen, and the polymer nanofibers and multi-walled carbon tubes are placed in a sealed container with a substrate attached to the inner wall, and high-speed rotation is performed to apply centrifugal force to the polymer nanofibers and multi-walled carbon tubes. Finally, the substrate is removed, and a conductive metal is sprayed on the surface of the material to obtain an oriented nanofiber composite membrane with a self-cleaning function. The oriented nanofiber composite membrane can be used for emulsion separation, and after multiple applications, it can be connected to a closed circuit of a direct current power supply for self-cleaning. The oriented nanofiber composite membrane achieves good filtering performance while realizing self-cleaning ability, and has the advantage of being recyclable. The preparation method is simple, the device is simple and easy to operate, and there is no need to adapt to the spinning equipment, realizing dry film forming technology and providing a new method for existing emulsion separation membrane materials.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of functional membrane materials, in particular to a preparation method and application of an oriented nanofiber composite membrane with self-cleaning function. BACKGROUND

[0002] At present, environmental governance, waste liquid treatment and recycling and water recycling are of great significance to ecological development. Whether it is industrial waste liquid or domestic sewage, the oil stains in it become a problem in sewage treatment. In recent years, nanofiber membranes have become an effective method for treating oil-water emulsions because of their high separation efficiency, low cost, simple operation and environmental friendliness. Therefore, emulsion separation membrane materials that can be used for sewage treatment have become a major research hotspot in the field.

[0003] At present, the invention patent (application number CN 202011306936.9) discloses a glass fiber membrane for oil-water emulsion separation and a preparation method thereof. First, the surface of the glass fiber membrane is modified by KH550, then the modified glass fiber membrane is immersed in an organic solvent dispersion liquid of modified silica particles modified by KH560, and finally the glass fiber membrane is immersed in a random copolymer solution of acrylic acid and glycidyl methacrylate, thereby obtaining a glass fiber membrane for oil-water emulsion separation. The method has complex process steps, and multiple immersion methods are used for treatment. If used in industry, a large amount of chemical waste liquid will be produced, and the environmental friendliness is poor.

[0004] In the prior art, SHAHABADI S S M et al. used electrostatic spraying technology to spray carbon nanoparticles on the surface of polyvinylidene fluoride-co-hexafluoropropylene (PVDF-HFP) nanofiber support membrane, and constructed a superhydrophobic / superoleophilic composite nanofiber membrane with multi-level rough surface by interlayer composite method (Bio-inspired Superhydrophobic and Superoleophilic Nanofibrous Membranes for Non-aqueous Solvent and Oil Separation from Water. Separation and Purification Technology, 2019, 210: 587-599.). However, the above-mentioned methods all rely on traditional electrospinning process to prepare membrane materials, and there are problems of easy agglomeration and difficult dispersion of nanomaterials, which affect the structural uniformity of nanofiber membranes, and there is often a problem of oil stain accumulation on the surface of the membrane during emulsion separation, which reduces the filtration performance.

[0005] In the prior art, the self-cleaning of nanofiber membranes is mainly realized by photocatalysis. Wenxuan Cao et al. prepared a hierarchical structure superhydrophilic / underwater superoleophobic nanofiber membrane with antifouling and visible light-induced self-cleaning performance by combining electrospun silver / b-cyclodextrin / polyacrylonitrile (Ag / b-CD / PAN) nanofiber with in-situ grown zinc oxide (ZnO) (Multifunctional nanofiber membranes with sunlight-driven self-cleaning performance for complex oily wastewater remediation. J Colloid Interface Sci 2022, 608 (Pt 1), 164-174). However, due to the low energy conversion efficiency of light, the self-cleaning efficiency of the fiber membrane is low.

[0006] Therefore, it is necessary to design an improved preparation method and application of oriented nanofiber composite membrane with self-cleaning function to solve the above problems. SUMMARY

[0007] The purpose of the present application is to provide a preparation method and application of oriented nanofiber composite membrane with self-cleaning function. The polymer nanofiber frozen by liquid nitrogen and the multi-walled carbon tube are placed in a sealed container, and the oriented selection of nanofiber is realized under the action of high-speed shearing force. The centrifugal force is applied to the two, so that they adhere to the substrate on the inner wall of the container. Finally, a conductive metal film is sprayed on the surface of the material to prepare a polymer nanofiber / multi-walled carbon tube composite membrane with oriented structure. The composite membrane can be used for emulsion separation, and when it is connected to a direct current circuit, it can perform a self-cleaning process, and has the advantage of multiple recycling.

[0008] To achieve the above-mentioned purpose of the application, the present application provides a preparation method of oriented nanofiber composite membrane with self-cleaning function, comprising the following steps:

[0009] S1, pretreat the polymer nanofiber, and freeze it with liquid nitrogen for 15-20 min;

[0010] S2, place the polymer nanofiber treated in step S1 and the multi-walled carbon tube in a sealed container with a substrate attached to the inner wall, and rotate at high speed for 100-180 s; the mass ratio of the polymer nanofiber to the multi-walled carbon tube is (18-22):1;

[0011] The sealed container is provided with a rotating assembly for crushing the polymer nanofiber and applying centrifugal force to the polymer nanofiber and the multi-walled carbon tube;

[0012] S3, taking off the substrate on the inner wall of the sealed container, the surface of which is compounded with oriented polymer nanofiber and multi-walled carbon tube;

[0013] S4, spraying conductive metal on the surface of the material obtained in step S3, to obtain oriented nanofiber composite film with self-cleaning function.

[0014] As a further improvement of the present application, in step S2, the sealed container keeps the internal temperature below -10℃ during high-speed rotation, to maintain the frozen state of the polymer nanofiber inside.

[0015] As a further improvement of the present application, the multi-walled carbon tube is in long fiber structure, with diameter of 30-100 nm and aspect ratio of (10-20):1; the diameter of the polymer nanofiber is 100 nm-6 μm, preferably 200-300 nm.

[0016] As a further improvement of the present application, in step S1, the pre-treatment of the polymer nanofiber is performed by grafting small molecule substance with benzene ring structure on the surface of the polymer nanofiber; the small molecule substance with benzene ring structure includes pyromellitic anhydride.

[0017] As a further improvement of the present application, in step S2, the surface roughness of the substrate is 10-100 nm; the rotation speed of the high-speed rotation is greater than 30000 rpm, preferably 35000 rpm.

[0018] As a further improvement of the present application, in step S4, the time for spraying conductive metal on the surface of the material is 100-150 s, and the resistance of the material surface after spraying metal is less than 600 Ω.

[0019] As a further improvement of the present application, in step S2, the rotating assembly includes at least one layer of planar rotating blade and at least one layer of inclined rotating blade; the number of blades of a single layer of the inclined rotating blade is 1-3, and the inclination angle is 20°-60°; the thickness of the planar rotating blade and the inclined rotating blade is 0.5-3.0 μm, preferably 2.0 μm.

[0020] As a further improvement of the present application, the polymer nanofiber includes one or more of polyvinyl alcohol-polyethylene copolymer, nylon and its derivatives, and polypropylene nanofiber.

[0021] As a further improvement of the present application, the substrate includes one of metal film substrate and polymer film substrate; the polymer film substrate includes one of polypropylene film, polyurethane film, polyvinyl chloride film, polystyrene film, and polyethylene terephthalate film.

[0022] The application further provides application of the oriented nanofiber composite membrane with the self-cleaning function, which is prepared by the preparation method of any one of the above, and is used for emulsion separation; after the oriented nanofiber composite membrane is used for emulsion separation for multiple times, the oriented nanofiber composite membrane is connected to a closed circuit of a direct current power supply, and after being heated to 45-55 DEG C, a surfactant is added for flushing, so that the self-cleaning process of the oriented nanofiber composite membrane is performed; the surfactant is a 0.1% sodium dodecyl sulfate aqueous solution.

[0023] The application has the following beneficial effects:

[0024] 1. The preparation method of the oriented nanofiber composite membrane with the self-cleaning function, which comprises the following steps: freezing polymer nanofibers by using liquid nitrogen, giving certain brittleness and rigidity to the polymer nanofibers, placing the polymer nanofibers and multi-walled carbon tubes in a closed container with a substrate attached to the inner wall, and performing high-speed rotation; the closed container is provided with a rotating assembly for crushing the polymer nanofibers and applying centrifugal force to the polymer nanofibers and the multi-walled carbon tubes; finally, the substrate is removed, and a conductive metal is sprayed on the surface of the material, so that the oriented nanofiber composite membrane with the self-cleaning function is obtained. The oriented nanofiber composite membrane can be used for emulsion separation, and after being used for emulsion separation for multiple times, the composite membrane is connected to a closed circuit of a direct current power supply, heated and flushed with a surfactant, so that the self-cleaning of the oriented nanofiber composite membrane is performed, the good filtering performance is achieved, the self-cleaning ability is further realized, and the oriented nanofiber composite membrane has the advantage of multiple recycling.

[0025] 2. The flexible polymer nanofibers are frozen to give certain rigidity, so that the polymer nanofibers are crushed and oriented under the action of high-speed shearing force, and are adhered to the substrate on the wall under the action of centrifugal force, so that the oriented structure is formed; meanwhile, the multi-walled carbon tubes are selected, and the shape and length-diameter ratio of the multi-walled carbon tubes are limited, so that the multi-walled carbon tubes can be uniformly dispersed in the polymer nanofibers, and the pores are not blocked, and the separation efficiency of the membrane is not affected. The prepared oriented nanofiber composite membrane has high porosity, and most of the pores are slender holes, so that the flux is high, and the efficiency of emulsion separation is greatly improved; the multi-walled carbon tubes in the oriented nanofiber composite membrane have adsorption effect on the surfactant in the emulsion, can destroy the oil-in-water structure, and promote the separation of the emulsion. Under the synergistic cooperation of the oriented polymer nanofibers and the multi-walled carbon tubes, the oriented nanofiber composite membrane has high flux, high emulsion separation efficiency, and can be widely used in the fields of environmental governance and wastewater treatment.

[0026] 3、The oriented nanofiber composite film surface of the application sprays a conductive metal film, and after being used for emulsion separation for multiple times, the oriented nanofiber composite film can be self-cleaned; in the self-cleaning process, after the film is connected to an electric circuit and heated, because the oil stains are adsorbed around the multi-walled carbon tube, and the multi-walled carbon tube is a conductive and heat-conductive material, heating increases the fluidity of the oil, and the surfactant remaining on the multi-walled carbon tube can drive the oil to pass through the film efficiently, so that the self-cleaning effect of the composite film is improved, and the cleaned composite film still has high emulsion separation function, and has high practicability.

[0027] 4、The preparation method of the application is simple, the device is simple and easy to operate, and the device does not need to be matched with a spinning equipment, and in cooperation with the preparation process of the application, the emulsion separation composite film of different fiber materials can be efficiently prepared, the dependence on the electrostatic spinning process in the traditional method is overcome, other reagents do not need to be introduced, the green production advantage is achieved, the dry film forming technology is realized, and new equipment and new ideas are provided for the existing preparation of emulsion separation film materials. BRIEF DESCRIPTION OF DRAWINGS

[0028] Figure 1 The electron microscope graph of the oriented nanofiber / multi-walled carbon tube composite film with self-cleaning function prepared for example 1.

[0029] Figure 2 The change graph of the filtration flow rate value of the oriented nanofiber / multi-walled carbon tube composite film of example 1.

[0030] Figure 3 The liquid ultraviolet spectrum graph collected after each filtration and self-cleaning of the oriented nanofiber / multi-walled carbon tube composite film of example 1.

[0031] Figure 4 The structure and principle schematic diagram of the device for preparing the oriented nanofiber composite film of the application.

[0032] REFERENCE NUMERALS

[0033] 1-closed container; 2-rotating assembly; 21-flat rotating blade; 22-inclined rotating blade. DETAILED DESCRIPTION

[0034] In order to make the purpose, technical scheme and advantages of the application clearer, the application is described in detail below with reference to the drawings and specific examples.

[0035] Here, it also needs to be explained that in order to avoid the unnecessary details from blurring the application, only the structures and / or processing steps closely related to the scheme of the application are shown in the drawings, and other details not closely related to the application are omitted.

[0036] It is also important to note that the term "comprising" or "including" or any other variation thereof is intended to cover a non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements does not include only those elements but can also include other elements not expressly listed or inherent to such process, method, article, or apparatus.

[0037] A preparation method of an oriented nanofiber composite membrane with self-cleaning function, comprising the following steps:

[0038] S1, the polymer nanofiber is pretreated and frozen with liquid nitrogen for 15-20 min; the diameter of the polymer nanofiber is 100 nm-6 μm, preferably 200-300 nm; by adjusting the diameter of the polymer nanofiber, the thickness of the rotating blade is matched, so that the rotating blade has strong shear force on the nanofiber, and enough power is provided for the orientation and composite substrate of the nanofiber;

[0039] S2, the polymer nanofiber treated in step S1 and the multi-walled carbon tube are placed in a closed container 1 with a substrate attached to the inner wall, and are rotated at high speed for 100-180 s; the mass ratio of the polymer nanofiber to the multi-walled carbon tube is (18-22):1; the multi-walled carbon tube is a long fibrous structure, and the diameter is 30-100 nm, and the length-diameter ratio is (10-20):1;

[0040] Wherein, the closed container 1 is provided with a rotating assembly 2 inside, which is used for crushing the polymer nanofiber and applying centrifugal force to the polymer nanofiber and the multi-walled carbon tube; during high-speed rotation, the closed container 1 keeps the temperature inside lower than-10 DEG C, so as to maintain the frozen state of the polymer nanofiber inside;

[0041] S3, the substrate on the inner wall of the closed container 1 is taken off, and the oriented polymer nanofiber and multi-walled carbon tube on the surface of the substrate are obtained;

[0042] S4, the material surface obtained in step S3 is sprayed with conductive metal, the spraying time of the conductive metal is 100-150 s, and the resistance of the material surface after spraying the metal is less than 600 Ω, thereby obtaining the oriented nanofiber composite membrane with self-cleaning function.

[0043] In the present application, the polymer nanofiber in the oriented nanofiber membrane is mainly combined with the substrate through van der Waals force; in addition, after the oriented nanofiber composite membrane is taken out from the device, its temperature rises, so that the molecular chain segments inside the nanofiber are in a "thawing" state, that is, the movement of the molecular chain is strengthened, the activity of the side groups and functional groups is improved, and the interaction force between the substrate and the multi-walled carbon tube is generated, thereby further improving the overall stable combination of the membrane, so that the oriented nanofiber membrane has excellent mechanical properties, and its practicability and application value are improved.

[0044] Specifically, in step S1, the polymer nanofiber is pretreated by grafting a small molecule material with a benzene ring structure on the surface of the polymer nanofiber; the small molecule material with a benzene ring structure includes pyromellitic anhydride. The pyromellitic anhydride can be grafted with the hydroxyl group on the surface of the polymer nanofiber, and in the film preparation process, the pyromellitic anhydride can also be combined with the multi-walled carbon tube to form a connection between the multi-walled carbon tube and the polymer nanofiber, thereby providing the binding force of the two.

[0045] In some specific embodiments, the surface roughness of the substrate is 10-100 nm, and the binding force between the substrate and the polymer nanofiber is increased by controlling the roughness of the substrate, and the uniformity of the prepared oriented nanofiber composite film structure is ensured.

[0046] In step S2, the rotation speed of the high-speed rotation is greater than 30000 rpm, preferably 35000 rpm; the length of the fiber after breaking, the thickness and performance of the prepared oriented nanofiber film are controlled by adjusting the rotation speed and time of the closed container 1, and at the same time, the problem that the nanofiber cannot maintain a rigid state under freezing due to overheating of the device caused by too long processing time, and the problems of sticking to the blade, insufficient orientation and centrifugal power, and uneven fiber film are avoided.

[0047] Please refer to Figure 4 As shown in the figure, in the closed container 1 used for film preparation of the application, the rotating assembly 2 includes at least one layer of planar rotating blades 21 and at least one layer of inclined rotating blades 22; the number of blades of the single layer of inclined rotating blades 22 is 1-3, and the inclination angle is 20°-60°; the thickness of the planar rotating blades 21 and the inclined rotating blades 22 is 0.5-3.0 μm, preferably 2.0 μm. Among them, the planar rotating blades 21 break the agglomerated elongated polymer nanofiber into short fibers, the inclined rotating blades 22 are responsible for stirring and screening the nanofiber, and provide high-speed shearing force for the broken short fibers, so that they are oriented and compounded on the substrate to obtain an oriented nanofiber composite film uniformly compounded with the multi-walled carbon tube.

[0048] In some specific embodiments, the polymer nanofiber includes one or more of polyvinyl alcohol-polyethylene copolymer, nylon and its derivatives, and polypropylene nanofiber. The substrate includes one of a metal film substrate and a polymer film substrate; the polymer film substrate includes one of a polypropylene film, a polyurethane film, a polyvinyl chloride film, a polystyrene film, and a polyethylene terephthalate film.

[0049] The prepared oriented nanofiber composite membrane has high porosity, and the pores are mostly elongated pores. Because the fibers themselves have a certain bending degree, the connection between the pores is good, and larger pores that affect the emulsion separation effect will not be generated. The multi-walled carbon tube has an adsorption effect on the surfactant in the emulsion, can destroy the oil-in-water structure, and promote the separation of the emulsion. Under the synergistic cooperation of the oriented structure of the polymer nanofiber and the multi-walled carbon tube, the oriented nanofiber composite membrane has high flux, high emulsion separation efficiency, and can be widely used in the fields of environmental governance and wastewater treatment.

[0050] Specifically, the application of the oriented nanofiber composite membrane with self-cleaning function is prepared by any one of the preparation methods of the oriented nanofiber composite membrane, and the oriented nanofiber composite membrane is used for emulsion separation. After the oriented nanofiber composite membrane is used for emulsion separation for multiple times, the oriented nanofiber composite membrane is connected to a closed circuit of a direct current power supply of 30 V, and after being heated to 45-55 DEG C, a surfactant is added for flushing, and the self-cleaning process of the oriented nanofiber composite membrane is performed. The surfactant is a 0.1% sodium dodecyl sulfate aqueous solution.

[0051] After the oriented nanofiber composite membrane is used for emulsion separation for multiple times, there is a certain oil blockage. Because the surface of the oriented nanofiber composite membrane is sprayed with a conductive metal film, the oriented nanofiber composite membrane can be directly connected to an electric circuit for self-cleaning. In the self-cleaning process, after being heated, the oil stains are mostly adsorbed around the multi-walled carbon tube, and the multi-walled carbon tube is a conductive and heat-conductive material. Heating can increase the flowability of the oil, and at the same time, the surfactant remaining on the multi-walled carbon tube can drive the oil to pass through the membrane efficiently, so that the self-cleaning effect of the composite membrane can be improved. The cleaned composite membrane still has high emulsion separation function and high practicability.

[0052] Embodiment 1

[0053] The embodiment provides a preparation method of an oriented nanofiber composite membrane with self-cleaning function, which comprises the following steps:

[0054] S1, polyvinyl alcohol-polyethylene copolymer (PVA-co-PE) nanofiber is pretreated and frozen with liquid nitrogen for 20 min; the diameter of the nanofiber is 300 nm;

[0055] S2, the polyurethane base material used for preparing the oriented nanofiber membrane is cleaned and treated, and is attached to the inner wall of a closed container 1 of a device for preparing the oriented nanofiber membrane; 20 g of the polymer nanofiber treated in step S1 and 1 g of the multi-walled carbon tube are placed in the closed container 1 with the inner wall attached with the base material, and are subjected to high-speed rotation for 150 s; the diameter of the multi-walled carbon tube is 50 nm, and the length is 600 nm;

[0056] The closed container 1 is internally provided with a rotating assembly 2 for breaking the polymer nanofiber and applying centrifugal force to the polymer nanofiber and the multi-walled carbon tube; the closed container 1 keeps the internal temperature below -10℃ during high-speed rotation;

[0057] S3, the base material on the inner wall of the closed container 1 is removed, and the surface of the composite oriented polymer nanofiber and the multi-walled carbon tube is removed;

[0058] S4, the material surface obtained in step S3 is sprayed with gold, and the conductive metal is sprayed for 120s, and the resistance of the material surface after spraying metal is less than 600Ω, thereby obtaining the oriented nanofiber / multi-walled carbon tube composite film with self-cleaning function.

[0059] Referring to Figure 1 Figure, it can be seen that the orientation effect of PVA-co-PE nanofiber is good, and no concentrated multi-walled carbon tube is seen, which indicates that the oriented nanofiber composite film with uniformly dispersed multi-walled carbon tube is successfully prepared by the scheme.

[0060] Referring to Figure 2 Figure, Figure 2 The oriented nanofiber / multi-walled carbon tube composite film prepared in Example 1 is subjected to 5 times of emulsion separation and self-cleaning process, and the change of filtration flow rate value is obtained. As can be seen from the figure, after multiple emulsion separation, oil stains will cause certain blockage to the composite film, but after self-cleaning, the filtration flow rate of the oriented nanofiber / multi-walled carbon tube composite film returns to the original value, and still has good emulsion separation function.

[0061] Referring to Figure 3 Figure, for the oriented nanofiber / multi-walled carbon tube composite film prepared in Example 1 is continuously filtered for 5 times, and the ultraviolet spectrum of the liquid collected after each filtration and self-cleaning is collected. As can be seen from the figure, the oriented nanofiber / multi-walled carbon tube composite film prepared in Example 1 has good filtration effect, even after multiple filtration affecting the flow rate, the filtration effect is still good, which indicates that the oriented nanofiber / multi-walled carbon tube composite film has good reusability and high practicability.

[0062] Comparative Example 1

[0063] Comparative Example 1 provides a preparation method of an oriented nanofiber film with self-cleaning function, which is different from Example 1 in that no multi-walled carbon tube is added in step S2, and an oriented nanofiber single-component film is prepared, and the rest is substantially the same as Example 1, which will not be repeated here.

[0064] Example 2

[0065] The embodiment provides a preparation method of an oriented nanofiber composite membrane with a self-cleaning function, and compared with the embodiment 1, the difference is that in the step S2, the diameter of the multi-walled carbon tube is 100 nm, and the rest is basically the same as the embodiment 1, and details are not repeated here.

[0066] Embodiment 3

[0067] The embodiment provides a preparation method of an oriented nanofiber composite membrane with a self-cleaning function, and compared with the embodiment 1, the difference is that in the step S2, the length of the multi-walled carbon tube is 1 μm, and the rest is basically the same as the embodiment 1, and details are not repeated here.

[0068] Embodiments 4-5

[0069] The embodiments 4-5 provide a preparation method of an oriented nanofiber composite membrane with a self-cleaning function, and compared with the embodiment 1, the difference is that in the step S1, the length of the polymer nanofiber is 500 nm and 2 μm respectively, and the rest is basically the same as the embodiment 1, and details are not repeated here.

[0070] The oriented nanofiber membranes prepared in the embodiments 1-5 and the comparative example 1 are tested in terms of filtration efficiency and flow rate, and the obtained results are shown in the following table.

[0071] Table 1: Test results of the filtration efficiency and flow rate of the fiber membranes in the embodiments 1-5 and the comparative example 1

[0072] Filtration efficiency (%) Flow rate (L / m 2 • h • bar) Example 1 98.6％ 350 Example 2 96.7％ 342 Example 3 94.2％ 330 Example 4 97.2％ 345 Example 5 95.8％ 333 Comparative Example 1 Comparative Example 2 80.7％ 500

[0073] It can be known from the table 1 that the diameter and length of the multi-walled carbon tube and the diameter of the polymer nanofiber have influences on the filtration efficiency and flow rate of the prepared fiber membrane; in a certain range, the filtration efficiency can be increased by selecting the nanofiber with a small diameter. It can be known from the comparative example 1 that when the multi-walled carbon tube is not added, the filtration efficiency of the prepared fiber membrane is greatly reduced, and the flow rate is too large, which can have influences on the filtration effect of the fiber membrane; therefore, the addition of the multi-walled carbon tube dispersant can effectively increase the filtration efficiency of the fiber membrane and improve the filtration effect of the fiber membrane.

[0074] Comparative example 2

[0075] The comparative example 2 provides a preparation method of an oriented nanofiber composite membrane with a self-cleaning function, and compared with the embodiment 1, the difference is that the nanofiber is not subjected to the freeze drying in the step S1, and the rest is basically the same as the embodiment 1, and details are not repeated here.

[0076] In the experiment process of the comparative example 2, because the nanofiber is not subjected to the freeze drying, the entanglement between the fibers and between the fibers and the blade is serious, and the oriented nanofiber composite membrane is not successfully prepared.

[0077] Comparative Example 3

[0078] Comparative Example 3 provides a preparation method of an oriented nanofiber composite film with self-cleaning function, which is different from Example 1 in that the closed container is rotated at high speed for 200 s in step S2, and the rest is substantially the same as Example 1, which will not be repeated here.

[0079] Comparative Example 4

[0080] Comparative Example 4 provides a preparation method of an oriented nanofiber composite film with self-cleaning function, which is different from Example 1 in that the length of the polymer nanofiber is 8 μm in step S1, and the rest is substantially the same as Example 1, which will not be repeated here.

[0081] In Comparative Example 4, the polymer nanofiber film with a diameter of 8 μm is used to prepare the oriented film, and it is found that the oriented fiber film cannot be prepared due to the too large fiber diameter. In Comparative Example 3, the container starts to heat gradually in the later stage of high-speed rotation of the closed container 1, and the fibers gradually appear to be entangled and stick to the knife, so that the oriented nanofiber film cannot be continuously prepared.

[0082] In summary, the present application provides a preparation method and application of an oriented nanofiber composite film with self-cleaning function. The polymer nanofiber is first frozen with liquid nitrogen to give it certain brittleness and rigidity, and then it is placed with a multi-walled carbon tube in a closed container with a substrate attached to the inner wall, and is rotated at high speed. The closed container is provided with a rotating assembly for breaking the polymer nanofiber and applying centrifugal force to the polymer nanofiber and the multi-walled carbon tube. Finally, the substrate is removed, and a conductive metal is sprayed on the surface of the material to obtain an oriented nanofiber composite film with self-cleaning function. The oriented nanofiber composite film can be used for emulsion separation, and after being used for emulsion separation for many times, the composite film is connected to a closed circuit of a direct current source, heated and washed with a surfactant, and the oriented nanofiber composite film can be self-cleaned, achieving good filtration performance and further realizing self-cleaning ability, which has the advantage of being recyclable. The preparation method of the present application is simple, the device is simple and easy to operate, and it does not need to be adapted to the spinning equipment. Combined with the preparation process of the present application, emulsion separation composite films of different fiber materials can be efficiently prepared, overcoming the dependence on electrospinning process in traditional methods. Moreover, no other reagents are needed, and the production is green, realizing dry film forming technology, and providing new equipment and new ideas for existing emulsion separation film materials.

[0083] The above examples are only used to illustrate the technical solutions of the present application but not limit the present application. Although the present application is described in detail with reference to the preferred embodiments, those skilled in the art should understand that the technical solutions of the present application can be modified or equivalent replaced without departing from the spirit and scope of the technical solutions of the present application.

Claims

1. A method for preparing an oriented nanofiber composite membrane having a self-cleaning function, characterized by, The method comprises the following steps: S1, the polymer nanofiber is pretreated and frozen with liquid nitrogen for 15-20 min; the pretreatment method of the polymer nanofiber is that the small molecule substance with benzene ring structure is grafted on the surface of the polymer nanofiber; the small molecule substance with benzene ring structure comprises pyromellitic anhydride; the polymer nanofiber comprises one or more of polyvinyl alcohol-polyethylene copolymer, nylon and its derivative, and polypropylene nanofiber; S2, the polymer nanofiber treated in step S1 and the multi-walled carbon tube are placed in a closed container with a substrate attached to the inner wall, and high-speed rotation is performed for 100-180 s; the mass ratio of the polymer nanofiber to the multi-walled carbon tube is (18-22):1; The closed container is internally provided with a rotating assembly for breaking the polymer nanofiber and applying centrifugal force to the polymer nanofiber and the multi-walled carbon tube; During high-speed rotation, the internal temperature of the closed container is kept below -10℃ to maintain the frozen state of the polymer nanofiber inside; the substrate comprises one of a metal film substrate and a polymer film substrate; the polymer film substrate comprises one of a polypropylene film, a polyurethane film, a polyvinyl chloride film, a polystyrene film, and a polyethylene terephthalate film; S3, the substrate on the inner wall of the closed container is removed, and the surface of the substrate is compounded with oriented polymer nanofiber and multi-walled carbon tube; S4, the surface of the material obtained in step S3 is sprayed with a conductive metal to obtain an oriented nanofiber composite film with self-cleaning function.

2. The method of claim 1, wherein the method is characterized by: The multi-walled carbon tube has a long fiber structure, a diameter of 30-100 nm, and an aspect ratio of (10-20):1; the diameter of the polymer nanofiber is 100 nm-6 μm.

3. The method of claim 2, wherein the method is characterized by: The diameter of the polymer nanofiber is 200-300 nm.

4. The method of claim 1, wherein the method is characterized by: In step S2, the surface roughness of the substrate is 10-100 nm; the rotation speed of high-speed rotation is greater than 30,000 rpm.

5. The method of claim 4, wherein the method is characterized by: The rotation speed of high-speed rotation is 35,000 rpm.

6. The method for preparing the oriented nanofiber composite membrane with self-cleaning function according to claim 1, characterized in that, In step S4, the time for spraying a conductive metal on the surface of the material is 100-150 s, and the resistance of the surface of the material after spraying the metal is less than 600 Ω.

7. The method of claim 1, wherein the method is characterized by: In step S2, the rotating assembly comprises at least one layer of planar rotating blades and at least one layer of inclined rotating blades; The number of blades of a single layer of the inclined rotating blades is 1-3, and the inclination angle is 20°-60°; the thickness of the planar rotating blades and the inclined rotating blades is 0.5-3.0 μm.

8. The method of claim 7, wherein the method is characterized by: The thickness of the planar rotating blades and the inclined rotating blades is 2.0 μm.

9. Use of an oriented nanofiber composite membrane having a self-cleaning function, characterized in that, The oriented nanofiber composite film is prepared by the preparation method of any one of claims 1-8, the oriented nanofiber composite film is used for emulsion separation; after the oriented nanofiber composite film is used for emulsion separation for multiple times, it is connected to a closed circuit of a direct current source, heated to 45-55℃, and then a surfactant is added for flushing to perform a self-cleaning process of the oriented nanofiber composite film; the surfactant is a 0.1% aqueous solution of sodium dodecyl sulfate.

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