Super-amphiphobic polytetrafluoroethylene micro-nano fiber membrane, preparation method and use thereof

Abstract

The application provides a kind of super-amphiphobic polytetrafluoroethylene micro-nano fiber membrane and its preparation method and use.The preparation method comprises the following steps: electrospinning is carried out using spinning solution, after spinning polytetrafluoroethylene micro-nano fiber membrane, polytetrafluoroethylene micro-nano fiber membrane is chemically crosslinked and modified, and then fluorination modification treatment is carried out, and finally super-amphiphobic polytetrafluoroethylene micro-nano fiber membrane is obtained.The applicant of the present application directly carries out chemical modification on polytetrafluoroethylene fiber membrane containing spinning aid, forms super-amphiphobic polytetrafluoroethylene micro-nano fiber membrane with excellent hydrophobic and oleophobic effects.The technical means of calcining treatment to remove spinning aid in the prior art is abandoned, and there is no need to additionally use nanoparticles.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of micro-nano fiber composite membranes, and particularly relates to a super-biphobic polytetrafluoroethylene micro-nano fiber membrane and a preparation method and application thereof. BACKGROUND

[0002] Membrane distillation (MD) has been identified as a promising technology for its unique advantages such as the ability to treat high-salinity solutions, theoretically 100% solute rejection, and mild operating conditions. However, flat cast membranes prepared by phase inversion and wet-spun hollow fiber membranes have some disadvantages such as insufficient hydrophobicity, small pore size, low porosity, and non-interconnected structure between pores, which ultimately lead to low permeation flux and wetting of membrane pores, resulting in loss of rejection effect in membrane distillation technology. This is one of the main factors limiting the large-scale industrialization of membrane distillation technology.

[0003] In addition, compared with hydrophilic filter membranes, the variety of materials and the membrane preparation process for membrane distillation are very limited. How to broaden the material sources of membrane distillation membranes, especially how to obtain membrane materials with high stability, large-scale preparation, and operation in harsh chemical and thermal environments without aging and degradation, and how to improve their permeability and selectivity, are the problems to be solved in the field of membrane distillation.

[0004] In the prior art, the conventional treatment method for PTFE hydrophobic membranes used in membrane distillation processes is high-temperature calcination or adding nanoparticles to increase the hydrophobicity and roughness of the fiber surface. However, these operation steps are complicated, and the removal of hydrophilic substances easily leads to the loss of the roughness of PTFE fibers themselves. Therefore, there is an urgent need for a preparation method for PTFE hydrophobic membranes that is controllable in process conditions, simple and easy to operate, convenient for production, and does not use large and precise equipment during the preparation process. SUMMARY

[0005] In view of the above-mentioned shortcomings of the prior art, the present application aims to provide a super-biphobic polytetrafluoroethylene micro-nano fiber membrane and a preparation method and application thereof, to solve the problems of insufficient hydrophobicity, small pore size, low porosity, poor stability, and high production cost of micro-nano fiber composite membranes in the prior art.

[0006] To achieve the above-mentioned and other related purposes, the present application is obtained by the following technical solutions.

[0007] The present application provides a preparation method for a super-biphobic polytetrafluoroethylene micro-nano fiber membrane. The preparation method uses a spinning solution for electrospinning, and after obtaining a polytetrafluoroethylene micro-nano fiber membrane, the polytetrafluoroethylene micro-nano fiber membrane is subjected to chemical crosslinking modification and then fluorination modification treatment, to finally obtain a super-biphobic polytetrafluoroethylene micro-nano fiber membrane.

[0008] According to the above-mentioned preparation method, the spinning solution comprises a spinning aid and polytetrafluoroethylene. The spinning aid is used to adjust the viscosity, surface tension, electrical conductivity and other properties of the spinning solution.

[0009] Preferably, the polytetrafluoroethylene emulsion used in the spinning solution is a mixture of polytetrafluoroethylene and water.

[0010] Preferably, the concentration of the polytetrafluoroethylene emulsion is 50-70 wt%. For example, it can be 50-55 wt%, 55-63 wt%, 63-70 wt%, and in a specific embodiment, 60 wt%.

[0011] Preferably, the spinning aid is selected from one or more of polyvinyl alcohol (PVA), chitosan (CS), cellulose nanocrystal (CNC), and polyethylene oxide (PEO). The addition of the spinning aid can improve the fiber-forming property of the polytetrafluoroethylene micro-nano fiber membrane, and after the combination of the polytetrafluoroethylene micro-nano fiber membrane and the spinning aid is chemically cross-linked and fluorinated, the hydrophobic anti-pollution performance of the polytetrafluoroethylene micro-nano fiber membrane can be improved.

[0012] Preferably, the polyvinyl alcohol aqueous solution is used in the spinning solution. Preferably, the number average molecular weight of the polyvinyl alcohol is 80-130 thousand. The number average molecular weight in this application is obtained by GPC test. Preferably, the alcoholysis degree of the polyvinyl alcohol is 70-95%. Preferably, the concentration of the polyvinyl alcohol aqueous solution is 5-15 wt% based on the mass of the polyvinyl alcohol aqueous solution. For example, it can be 5-8 wt%, 8-12 wt%, 12-15 wt%, and in a specific embodiment, 10 wt%.

[0013] Preferably, the number average molecular weight of the chitosan is 50-100 thousand. More preferably, the degree of deacetylation of the chitosan is 80-90%. In a specific embodiment, a chitosan solution is used to form the spinning solution, and the solvent of the chitosan solution is a mixture of acetic acid and water. Preferably, the content of the chitosan is 5-15 wt% based on the mass of the chitosan solution.

[0014] Preferably, the number average molecular weight of the cellulose nanocrystal is 1-100 thousand. In a specific embodiment, a cellulose nanocrystal aqueous solution is used in the spinning solution. The content of the cellulose nanocrystal is 2-5 wt% based on the mass of the cellulose nanocrystal aqueous solution.

[0015] Preferably, the number average molecular weight of the polyethylene oxide is 1-50 thousand. In a specific embodiment, a polyethylene oxide aqueous solution is used in the spinning solution. The content of the polyethylene oxide is 3-10 wt% based on the mass of the polyethylene oxide aqueous solution.

[0016] Preferably, the spinning solution further comprises boric acid. The boric acid can increase the viscosity of the polyvinyl alcohol aqueous solution, so that the solution has higher viscosity. This helps the fiber to form more elongated and uniform morphology during the stretching process.

[0017] Preferably, the content of boric acid is not more than 5wt% based on the total mass of the spinning solution. For example, it can be 0.01-0.02wt%, 0.02-0.04wt%, 0.04-0.06wt%, 0.06-0.10wt%, 0.10-0.20wt%, 0.20-0.50wt%, 0.50-0.1wt%, 0.10-0.50wt%, 0.50-1wt%, 1-2wt%, 2-3wt%, 3-4wt%, 4-5wt%, and in a specific embodiment, it is 0.03wt%.

[0018] In one embodiment, by preparing a spinning solution in which the spinning aid, boric acid and polytetrafluoroethylene emulsion are dispersed, electrospinning can be carried out, so that the diameter size distribution of the polytetrafluoroethylene fiber is uniform and the morphology is stable.

[0019] According to the preparation method described above, in the spinning solution, the mass ratio of the spinning aid and polytetrafluoroethylene is 1:4-10. For example, it can be 1:4, 1:5, 1:6, 1:7, 1:8, 1:9, 1:10.

[0020] According to the preparation method described above, the voltage during electrospinning is 12-25kV, and the receiving distance is 10-40cm.

[0021] According to the preparation method described above, during the chemical crosslinking modification, the crosslinking temperature is 30-80℃. For example, it can be 30-40℃, 40-45℃, 45-55℃, 55-60℃, 60-70℃, 70-80℃, and in a specific embodiment, it is 50℃. Crosslinking at this temperature is conducive to removing the spinning aid on the polytetrafluoroethylene micro-nano fiber membrane. If the crosslinking temperature is too high, the hydroxyl curing speed will be too fast, and the overall mechanical properties of the membrane will be reduced. On the contrary, if the temperature is too low, the crosslinking reaction will not proceed well.

[0022] Preferably, after the crosslinking is completed, water washing is performed to remove excess polyvinyl alcohol, which helps to make the polytetrafluoroethylene micro-nano fiber membrane rough after forming, and is conducive to the hydrophobicity of the polytetrafluoroethylene micro-nano fiber membrane.

[0023] According to the preparation method described above, during the chemical crosslinking modification, a crosslinking agent is used.

[0024] Preferably, the crosslinking agent is selected from one or more of dicumyl peroxide, benzoyl peroxide, and glutaraldehyde. The crosslinking agent is used to modify the crosslinking reaction with the hydroxyl group in the spinning aid to enhance the hydrophobicity of the polytetrafluoroethylene micro-nano fiber membrane.

[0025] Preferably, the chemical crosslinking agent is modified by using a reaction medium, which is an organic solvent. More preferably, the organic solvent is acetone. Acetone as a crosslinking solvent can provide an effective site for chemical crosslinking.

[0026] Preferably, the chemical crosslinking agent is modified by using hydrochloric acid. The addition of hydrochloric acid is conducive to improving the stability and formability of the fiber membrane structure.

[0027] Preferably, the molar ratio of the hydroxyl content in the auxiliary spinning agent to the crosslinking agent is ≤2. This ratio of the crosslinking agent is conducive to improving the conversion rate of hydroxyl groups and improving the hydrophobic and anti-pollution performance of the polytetrafluoroethylene micro-nano fiber membrane.

[0028] According to the preparation method described above, the fluorinated modifier used in the fluorinated modification process is selected from one or more of trichloro(3,3,3-trifluoropropyl)silane, trichloro(1H,1H,2H,2H-tridecafluoro-n-octyl)silane or 1H,1H,2H,2H-perfluorodecyltrimethoxysilane. The fluorinated modification process is to form a C-O-Si bond to further improve the hydrophobicity of the polytetrafluoroethylene micro-nano fiber membrane.

[0029] Preferably, the molar ratio of the hydroxyl content in the auxiliary spinning agent to the fluorinated modifier is ≤1.

[0030] Preferably, the conditions for the fluorinated modification process are: performed under vacuum; the treatment temperature is: 60-150℃. Such as 60-80℃, 80-100℃, 100-120℃, 120-140℃, 140-150℃, and in a specific embodiment, 60℃. Such as performed at 60-90kPa, and also can be 60-70kPa, 75-85kPa, 85-90kPa, and in a specific embodiment, 80kPa. Such as the treatment time is: 6-24h, and also can be 6-10h, 10-13h, 13-18h, 18-21h, 21-24h, and in a specific embodiment, 6, 12, 24h. When the temperature is higher and the time is longer, the fluorination reaction can be fully carried out to ensure the full conversion of hydroxyl groups in the polytetrafluoroethylene micro-nano fiber membrane.

[0031] The second aspect of the present application provides a super-amphiphobic polytetrafluoroethylene micro-nano fiber membrane prepared by the above preparation method.

[0032] Preferably, the water contact angle of the super-amphiphobic polytetrafluoroethylene micro-nano fiber membrane is ≥140°. More preferably, the water contact angle of the super-amphiphobic polytetrafluoroethylene micro-nano fiber membrane is ≥150°.

[0033] Preferably, the oil contact angle of the super-amphiphobic polytetrafluoroethylene micro-nanofiber membrane is ≥95°. More preferably, the oil contact angle of the super-amphiphobic polytetrafluoroethylene micro-nanofiber membrane is ≥130°.

[0034] Preferably, the porosity of the super-amphiphobic polytetrafluoroethylene micro-nanofiber membrane is 73-90%. More preferably, the porosity of the super-amphiphobic polytetrafluoroethylene micro-nanofiber membrane is 78-90%.

[0035] The third aspect of the present application provides the use of the super-amphiphobic polytetrafluoroethylene micro-nanofiber membrane as described above as a separation membrane material for seawater desalination, wastewater treatment, and separation of azeotropic mixture.

[0036] As described above, the present application provides a super-amphiphobic polytetrafluoroethylene micro-nanofiber membrane, a preparation method thereof, and a use thereof. The applicant of the present application directly performs chemical modification on a polytetrafluoroethylene fiber membrane containing a spinning aid to form a super-amphiphobic polytetrafluoroethylene micro-nanofiber membrane with excellent hydrophobic and oleophobic effects. The technical means of calcining treatment to remove the spinning aid from the polytetrafluoroethylene fiber membrane containing the spinning aid in the prior art is abandoned, and no additional nanoparticles are needed. Specifically,

[0037] The present application has the following beneficial effects, including the following aspects:

[0038] 1) By preparing a spinning solution with a specific composition for electrospinning, the diameter size distribution of the polytetrafluoroethylene fiber can be uniform and the morphology is stable.

[0039] 2) The chemical treatment in the present application not only ensures the mechanical properties of the super-amphiphobic polytetrafluoroethylene micro-nanofiber membrane, but also ensures its good hydrophobic and oleophobic properties.

[0040] 3) The process conditions of the preparation method in the present application are controllable, thereby ensuring the stability of the performance of the super-amphiphobic polytetrafluoroethylene micro-nanofiber membrane, and large precision equipment is not used in the preparation process, so the production cost is low and the operation is simple and easy to implement.

[0041] 4) The super-amphiphobic polytetrafluoroethylene micro-nanofiber membrane obtained by using the preparation method in the present application can improve the morphology, diameter size, and mechanical properties of the polytetrafluoroethylene micro-nanofiber membrane in the prior art. It has been proved by tests that the super-amphiphobic polytetrafluoroethylene micro-nanofiber membrane provided in the technical scheme of the present application exhibits stable flux and excellent salt rejection performance in the treatment of high-salt solutions, salt solutions containing surfactants, and oily salt solutions, and exhibits good stability and reusability in the cyclic use test. Therefore, the super-amphiphobic polytetrafluoroethylene micro-nanofiber membrane provided in the present application has good application prospects in the treatment of high-salt and heavily polluted water. BRIEF DESCRIPTION OF DRAWINGS

[0042] Figure 1 The water-oil contact angle test results of the polytetrafluoroethylene micro-nanofiber membrane prepared in the present application comparative examples 1-3 and example 3 are shown in the figure.

[0043] Figure 2 The scanning electron microscope images of the polytetrafluoroethylene micro-nanofiber membranes of the present application examples 1-4 are shown. Figure 3 The membrane distillation performance test results (a), water-oil contact angle test results (b) and physical display (c) of the super-amphiphobic polytetrafluoroethylene micro-nanofiber membrane prepared in the present application examples 1-4 are shown.

[0044] Figure 4 The membrane distillation performance test results of the super-amphiphobic polytetrafluoroethylene micro-nanofiber membrane prepared in the present application example 5 for high-concentration salt water are shown.

[0045] Figure 5 The pollution resistance test results of the super-amphiphobic polytetrafluoroethylene micro-nanofiber membrane prepared in the present application example 6 are shown. DETAILED DESCRIPTION

[0046] The embodiments of the present application are described below by specific examples, which are used to verify the practical feasibility of the method of the present application. Those skilled in the art can easily understand other advantages and effects of the present application from the disclosure of the present specification. The present application can also be implemented or applied by other different specific embodiments, and the details in the present specification can be modified or changed based on different views and applications without departing from the spirit of the present application.

[0047] It should be understood that the process equipment or device not specifically mentioned in the following examples is the conventional equipment or device in the art. In addition, it should be understood that the protection scope of the present application is not limited to the following specific embodiments, and one or more method steps mentioned in the present application do not exclude that there can be other method steps before and after the combination steps or other method steps can be inserted between the explicitly mentioned steps, unless otherwise specified. It should also be understood that the terms used in the embodiments of the present application are for the purpose of describing the specific embodiments, and are not intended to limit the protection scope of the present application. The test methods in the following examples without specific conditions are generally carried out under conventional conditions or under the conditions recommended by the manufacturers.

[0048] A specific preparation method is used in the following specific examples of the present application, which includes the following steps:

[0049] 1) using a spinning solution containing a polyvinyl alcohol aqueous solution, boric acid and a polytetrafluoroethylene emulsion;

[0050] 2) electrospinning the spinning solution to obtain a polytetrafluoroethylene micro-nanofiber membrane;

[0051] 3) chemically crosslinking the polytetrafluoroethylene micro-nano fiber membrane to obtain a pre-processed polytetrafluoroethylene micro-nano fiber membrane;

[0052] 4) fluorinating the pre-processed polytetrafluoroethylene micro-nano fiber membrane to obtain a super-amphiphobic polytetrafluoroethylene micro-nano fiber membrane.

[0053] The method for preparing the spinning solution is not particularly specified in the present application.

[0054] Specifically, a specific preparation method is used in the following specific embodiments of the present application, which comprises the following steps:

[0055] 1-1) dissolving polyvinyl alcohol in water at a temperature of 90°C for 6-10 h to obtain a polyvinyl alcohol aqueous solution;

[0056] 1-2) adding boric acid and polytetrafluoroethylene emulsion into the polyvinyl alcohol aqueous solution in time and stirring for 6-8 h to obtain a spinning solution.

[0057] According to the above-mentioned preparation method, in step 2), when electrospinning is performed, the process parameters of the electrospinning machine are set as follows: voltage 12-25 kV, receiving distance 10-40 cm, perfusion speed 5-30 μL / min, drum rotation speed 20-100 r / min, and receiving distance 10-40 cm.

[0058] The morphology and diameter of the polytetrafluoroethylene micro-nano fiber membrane can be controlled by the preparation of the spinning solution and the setting of the electrospinning process parameters, so as to ensure that the formed polytetrafluoroethylene micro-nano fiber membrane has stable diameter size and morphology characteristics.

[0059] According to the above-mentioned preparation method, in step 3), the crosslinking temperature of the chemical crosslinking modification is 30-80°C, and the crosslinking time is 0.5-3 h. Crosslinking under this temperature condition is conducive to removing polyvinyl alcohol on the formed polytetrafluoroethylene micro-nano fiber membrane and ensuring the full conversion of hydroxyl groups in the polytetrafluoroethylene micro-nano fiber membrane.

[0060] Preferably, water washing is performed after the crosslinking is completed to ensure the formation of the polytetrafluoroethylene micro-nano fiber membrane.

[0061] According to the above-mentioned preparation method, in step 3), a crosslinking agent is used when the chemical crosslinking modification is performed.

[0062] Preferably, the crosslinking agent is selected from one or more of dicumyl peroxide, benzoyl peroxide, and glutaraldehyde.

[0063] Preferably, the molar ratio of the hydroxyl content in the auxiliary spinning agent to the crosslinking agent is ≤2.

[0064] Preferably, the chemical cross-linking modification is also performed with an acetone solution. The acetone as a cross-linking solvent can provide an effective site for the chemical cross-linking.

[0065] Preferably, the chemical cross-linking modification is also performed with hydrochloric acid. The hydrochloric acid is beneficial to improve the stability and formability of the fiber membrane structure.

[0066] According to the preparation method described above, in step 4), the fluorination treatment is performed in a vacuum oven, the vacuum degree is 80 kPa, the oven temperature is 60-150℃, and the holding time is 6-24h, which ensures the sufficient conversion of the hydroxyl groups in the pretreated polytetrafluoroethylene micro-nano fiber membrane, so that it has higher hydrophobic and anti-pollution performance.

[0067] According to the preparation method described above, in step 4), the fluorination treatment is performed with a fluorination modifier.

[0068] Preferably, the fluorination modifier is one or more of trichloro(3,3,3-trifluoropropyl)silane, trichloro(1H,1H,2H,2H-tridecafluoro-n-octyl)silane or 1H,1H,2H,2H-perfluorodecyltrimethoxysilane.

[0069] Preferably, the molar ratio between the hydroxyl content in the polyvinyl alcohol and the fluorination agent is ≤1.

[0070] In the following examples of the present application, the alcoholysis degree of the polyvinyl alcohol is 87-89%, and the number average molecular mass is 85,000-124,000.

[0071] Example 1

[0072] The present example 1 provides a preparation method of a super-biphobic polytetrafluoroethylene micro-nano fiber membrane, which specifically comprises the following steps:

[0073] 1) Prepare a spinning solution containing polyvinyl alcohol aqueous solution, boric acid and polytetrafluoroethylene emulsion.

[0074] 2) Electrospinning the spinning solution, and drying the polytetrafluoroethylene micro-nano fiber membrane after spinning to obtain a polytetrafluoroethylene micro-nano fiber membrane for standby. During electrospinning, the parameter settings of the electrospinning machine are as follows: voltage is 20 kV, infusion speed is 20 μL / min, drum rotation speed is 60 r / min, receiving distance is 25 cm, and drying temperature is 60℃.

[0075] 3) The polytetrafluoroethylene micro-nano fiber film prepared in step 2) is placed in a crosslinking agent solution for chemical crosslinking modification, and the crosslinking agent is glutaraldehyde. During the crosslinking process, the crosslinking temperature is 50°C, the crosslinking time is 20 min, then water washing in 90°C water for 1 min, and drying for standby use. The component contents in the crosslinking solution are: polytetrafluoroethylene micro-nano fiber film 4.5wt%, glutaraldehyde 0.3wt%, hydrochloric acid 0.2wt%, and acetone 95wt%.

[0076] 4) The crosslinked polytetrafluoroethylene micro-nano fiber film prepared in step 3) is placed in a dry dish together with a fluorination modifier, and is kept at a temperature of 60°C in a vacuum of 80kPa for 6h, so that the polytetrafluoroethylene micro-nano fiber film has high hydrophobic and anti-pollution performance. The fluorination modifier is trichloro(1H,1H,2H,2H-tridecafluoro-n-octyl)silane, and the molar ratio of the fluorination modifier to polyvinyl alcohol is 1.

[0077] Specifically, in the present embodiment 1, the preparation method of the above spinning solution is as follows:

[0078] 1-1) Dissolve polyvinyl alcohol in 90°C water for 8h to obtain a polyvinyl alcohol aqueous solution, and the concentration of the final polyvinyl alcohol aqueous solution is 10wt% based on the total mass of the polyvinyl alcohol aqueous solution;

[0079] 1-2) Take a certain amount of polyvinyl alcohol aqueous solution, and add boric acid and polytetrafluoroethylene emulsion to it in turn, the concentration of the polytetrafluoroethylene emulsion is 60wt%, and stir at room temperature for 8h to obtain a spinning solution. The mass ratio of polyvinyl alcohol aqueous solution to polytetrafluoroethylene emulsion is 3:2. The content of boric acid is 0.03wt% based on the total mass of polyvinyl alcohol aqueous solution and polytetrafluoroethylene emulsion.

[0080] so that the mass ratio of polyvinyl alcohol to polytetrafluoroethylene is 1:4, and the super-amphiphobic polytetrafluoroethylene micro-nano fiber film obtained in the present embodiment 1 is marked as P1-P4 NFM, and its structure is characterized, and the results are shown in Table a. Figure 2 Figure 2 -a1 is a scanning electron microscope image of the super-amphiphobic polytetrafluoroethylene micro-nano fiber film P1-P4 NFM magnified by 50,000 times; Figure 2 -a2 is a scanning electron microscope image of the super-amphiphobic polytetrafluoroethylene micro-nano fiber film P1-P4 NFM magnified by 10,000 times.

[0081] According to the above Figure 2 It can be seen from a1 to a2 that: the fiber film morphology is well formed as a whole, no stringing phenomenon is observed, and the structure is stable. However, the fiber diameter is relatively thick, reaching 730nm, and the fiber surface has no strong grainy feeling, and no obvious concave-convex points are observed, indicating that the polyvinyl alcohol content is relatively high, and the polytetrafluoroethylene particles are not exposed to the fiber surface after post-processing. ​

[0082] Example 2

[0083] The present example 2 provides a method for preparing a super-biphobic polytetrafluoroethylene micro-nano fiber membrane, which specifically comprises the following steps:

[0084] 1) A spinning solution containing polyvinyl alcohol aqueous solution, boric acid and polytetrafluoroethylene emulsion is prepared.

[0085] 2) The spinning solution is electrospun, and after spinning is completed, the polytetrafluoroethylene micro-nano fiber membrane is dried to obtain a polytetrafluoroethylene micro-nano fiber membrane for standby. During electrospinning, the parameter settings of the electrospinning machine are as follows: voltage 20 kV, infusion speed 20 μL / min, drum rotation speed 60 r / min, and receiving distance 25 cm; the drying temperature is 60°C.

[0086] 3) The polytetrafluoroethylene micro-nano fiber membrane prepared in step 2) is placed in a crosslinking solution for chemical crosslinking modification. During crosslinking, the crosslinking temperature is 50°C, the crosslinking time is 20 min, then water washing is performed in 90°C water for 1 min, and drying is performed for standby. The component contents in the crosslinking solution are as follows: polytetrafluoroethylene micro-nano fiber membrane 4.5 wt%, glutaraldehyde 0.3 wt%, hydrochloric acid 0.2 wt%, and acetone 95 wt%.

[0087] 4) The polytetrafluoroethylene micro-nano fiber membrane prepared in step 3) is placed in a dry dish together with a fluorination modifier, and is incubated in a vacuum of 80 kPa and a temperature environment of 60°C for 24 h, so that the polytetrafluoroethylene micro-nano fiber membrane has high hydrophobic and anti-pollution properties. The fluorination modifier is trichloro(1H,1H,2H,2H-tridecafluoro-n-octyl)silane, and the molar ratio of the fluorination modifier to polyvinyl alcohol is 1.

[0088] Specifically, in the present example 2, the preparation method of the above spinning solution is as follows:

[0089] 1-1) Polyvinyl alcohol is dissolved in 90°C water for 8 h to obtain a polyvinyl alcohol aqueous solution. The concentration of the final polyvinyl alcohol aqueous solution is 10 wt% based on the total mass of the polyvinyl alcohol aqueous solution;

[0090] 1-2) A certain amount of polyvinyl alcohol aqueous solution is taken, boric acid and polytetrafluoroethylene emulsion with a concentration of 60 wt% are sequentially added thereto, and stirring is performed at room temperature for 8 h to obtain a spinning solution. The mass ratio of the polyvinyl alcohol aqueous solution to the polytetrafluoroethylene emulsion is 1:1. The boric acid content is 0.03 wt% based on the total mass of the polyvinyl alcohol aqueous solution and the polytetrafluoroethylene emulsion.

[0091] The mass ratio of the final polyvinyl alcohol and polytetrafluoroethylene is 1:6, and the super-amphiphobic polytetrafluoroethylene micro-nano fiber membrane obtained in Example 2 is marked as P1-P6 NFM, and structural characterization is performed, and the results are Figure 2 b is shown. Among them, Figure 2 b1 is a scanning electron microscope image of the super-amphiphobic polytetrafluoroethylene micro-nano fiber membrane P1-P6 NFM magnified by 50,000 times; Figure 2 b2 is a scanning electron microscope image of the super-amphiphobic polytetrafluoroethylene micro-nano fiber membrane P1-P6 NFM magnified by 10,000 times.

[0092] According to Figure 2 b1 to b2 can be seen: the fiber membrane morphology is well shaped as a whole, and there is no obvious beading phenomenon, and the structure is stable. The fiber diameter has a decreasing trend, reaching 612 nm, and the fiber surface graininess is enhanced, and obvious concave-convex points can be seen, indicating that the reduction of polyvinyl alcohol content makes the polytetrafluoroethylene particles exposed on the fiber surface after post-processing.

[0093] Example 3

[0094] The present embodiment 3 provides a preparation method of a super-amphiphobic polytetrafluoroethylene micro-nano fiber membrane, which specifically comprises the following steps:

[0095] 1) Prepare a spinning solution containing polyvinyl alcohol aqueous solution, boric acid and polytetrafluoroethylene emulsion.

[0096] 2) Electrospinning the spinning solution, and drying the polytetrafluoroethylene micro-nano fiber membrane after spinning to obtain a polytetrafluoroethylene micro-nano fiber membrane for standby. Wherein, when electrospinning, the parameter settings of the electrospinning machine are: voltage 20kV, perfusion speed 20μL / min, drum rotation speed 60r / min, receiving distance 25cm; the drying temperature is 60℃.

[0097] 3) Put the polytetrafluoroethylene micro-nano fiber membrane prepared in step 2) into a crosslinking solution for chemical crosslinking modification. During the crosslinking process, the crosslinking temperature is 50℃, and the crosslinking time is 1h, then washed in 90℃ water for 1min, and dried for standby. Wherein, the component content in the crosslinking solution is respectively: polytetrafluoroethylene micro-nano fiber membrane 4.5wt%, glutaraldehyde 0.3wt%, hydrochloric acid 0.2wt%, acetone 95wt%.

[0098] 4) Put the polytetrafluoroethylene micro-nano fiber membrane prepared in step 3) and fluorination modifier into a dry dish, and keep it in a vacuum of 80kPa and a temperature environment of 60℃ for 12h, so that the polytetrafluoroethylene micro-nano fiber membrane has high hydrophobic and anti-pollution performance. Wherein, the fluorination modifier is trichloro(1H,1H,2H,2H-tridecafluoro-n-octyl)silane, and the molar ratio of fluorination modifier to polyvinyl alcohol is 1.

[0099] Specifically, in this embodiment 3, the preparation method of the spinning solution is as follows:

[0100] 1-1) Dissolve polyvinyl alcohol in water at 90°C for 8h to obtain a polyvinyl alcohol aqueous solution, and the concentration of the final polyvinyl alcohol aqueous solution is 10wt% based on the total mass of the polyvinyl alcohol aqueous solution;

[0101] 1-2) Take a certain amount of polyvinyl alcohol aqueous solution, and sequentially add boric acid and polytetrafluoroethylene emulsion (the concentration of the polytetrafluoroethylene emulsion is 60wt%) to the polyvinyl alcohol aqueous solution, and stir at room temperature for 8h to obtain a spinning solution. The mass ratio of the polyvinyl alcohol aqueous solution to the polytetrafluoroethylene emulsion is 2:3. The amount of boric acid is 0.03wt% based on the total mass of the polyvinyl alcohol aqueous solution and the polytetrafluoroethylene emulsion.

[0102] so that the mass ratio of the final polyvinyl alcohol to polytetrafluoroethylene is 1:8, and the super-amphiphobic polytetrafluoroethylene micro-nanofiber membrane obtained in this embodiment 3 is marked as P1-P8 NFM, and the structure is characterized, and the results are shown in Table 1 and Figures c1-c8. Figure 2 Figure 2 -c1 is a scanning electron microscope image of the super-amphiphobic polytetrafluoroethylene micro-nanofiber membrane P1-P8 NFM magnified by 50,000 times; Figure 2 -c2 is a scanning electron microscope image of the super-amphiphobic polytetrafluoroethylene micro-nanofiber membrane P1-P8 NFM magnified by 10,000 times; Figure 2 is a super-amphiphobic polytetrafluoroethylene micro-nanofiber membrane real object picture.

[0103] According to Figure 2 As can be seen from c1 to c2, the fiber membrane morphology is well formed as a whole, no beaded phenomenon is observed, and the structure is stable. The fiber diameter has a significant decreasing trend, reaching 468nm, and in addition, the fiber surface grain is clearer, and obvious concave-convex points can be seen, indicating that the increase of the polytetrafluoroethylene emulsion content makes the polytetrafluoroethylene particles more obviously exposed on the fiber surface after post-processing. Figure 3 It can be seen that the fiber has good film-forming property and the surface is relatively smooth, and can be directly used for membrane distillation test.

[0104] Embodiment 4

[0105] The embodiment 4 provides a preparation method of a super-amphiphobic polytetrafluoroethylene micro-nanofiber membrane, which specifically comprises the following steps:

[0106] 1) Preparing a spinning solution containing polyvinyl alcohol aqueous solution, boric acid and polytetrafluoroethylene emulsion.

[0107] ​2) The spinning solution is electrospun, and after spinning is completed, the polytetrafluoroethylene micro-nanofiber membrane is dried to obtain a polytetrafluoroethylene micro-nanofiber membrane for standby. During electrospinning, the parameter settings of the electrospinning machine are: voltage 20 kV, infusion speed 20 μL / min, drum rotation speed 60 r / min, and receiving distance 25 cm; the drying temperature is 60°C.

[0108] 3) The polytetrafluoroethylene micro-nanofiber membrane prepared in step 2) is placed in a crosslinking solution for chemical crosslinking modification. During crosslinking, the crosslinking temperature is 50°C, and the crosslinking time is 3 h, followed by water washing in 90°C water for 1 min and drying for standby. The component contents in the crosslinking solution are: polytetrafluoroethylene micro-nanofiber membrane 4.5 wt%, glutaraldehyde 0.3 wt%, hydrochloric acid 0.2 wt%, and acetone 95 wt%.

[0109] 4) The polytetrafluoroethylene micro-nanofiber membrane prepared in step 3) is placed in a dry dish together with a fluorination modifier, and is incubated in a vacuum of 80 kPa and a temperature environment of 60°C for 24 h, so that the polytetrafluoroethylene micro-nanofiber membrane has high hydrophobic and anti-pollution properties. The molar ratio of the fluorination modifier, which is trichloro(1H,1H,2H,2H-tridecafluoro-n-octyl)silane fluorination modifier, to polyvinyl alcohol, is 1.

[0110] Specifically, in this embodiment 4, the preparation method of the spinning solution is as follows:

[0111] S101: Dissolve polyvinyl alcohol in 90°C water for 8 h to obtain a polyvinyl alcohol aqueous solution. The concentration of the final polyvinyl alcohol aqueous solution is 10 wt% based on the total mass of the polyvinyl alcohol aqueous solution;

[0112] S102: Take a certain amount of polyvinyl alcohol aqueous solution, and sequentially add boric acid and polytetrafluoroethylene emulsion (the concentration of the polytetrafluoroethylene emulsion is 60 wt%) to it, and stir at room temperature for 8 h to obtain a spinning solution. The mass ratio of the polyvinyl alcohol aqueous solution to the polytetrafluoroethylene emulsion is 3:7. The boric acid content is 0.03 wt% based on the total mass of the polyvinyl alcohol aqueous solution and the polytetrafluoroethylene emulsion.

[0113] so that the mass ratio of the final polyvinyl alcohol to polytetrafluoroethylene is 1:10. The super-amphiphobic polytetrafluoroethylene micro-nanofiber membrane obtained in this embodiment 4 is marked as P1-P10 NFM, and is subjected to structure characterization, and the results are shown in Table 1 and Figs. 1-2. Figure 2 Table 1: Structure characterization results of the super-amphiphobic polytetrafluoroethylene micro-nanofiber membranes P1-P10 NFM Figure 2 - d1 is a scanning electron microscope image of the super-amphiphobic polytetrafluoroethylene micro-nanofiber membrane P1-P10 NFM at 50,000 times magnification; Figure 2 - d2 is a scanning electron microscope image of the super-amphiphobic polytetrafluoroethylene micro-nanofiber membrane P1-P10 NFM at 10,000 times magnification.

[0114] According to Figure 2 It can be seen from d1 to d2 that the fiber film morphology is well shaped as a whole, no stringing phenomenon is observed, and the structure is still relatively stable. The fiber diameter has no obvious decreasing trend of 467 nm, and the fiber surface particles are clearer, and obvious concave and convex points can be observed, indicating that the increase of the content of the polytetrafluoroethylene emulsion makes the polytetrafluoroethylene particles more obviously exposed on the fiber surface after post-processing.

[0115] Example 5

[0116] The example 5 provides a membrane distillation high-concentration brine test method of the super-amphiphobic polytetrafluoroethylene micro-nano fiber film, which specifically includes the following steps:

[0117] The super-amphiphobic polytetrafluoroethylene micro-nano fiber film marked as P1-P8 NFM in example 3 is used for membrane distillation high-concentration brine (25wt% NaCl solution) test, and the specific results of the test are shown in Figure 4 .

[0118] As Figure 4 shown, the polytetrafluoroethylene micro-nano fiber film prepared by the preparation method of the application has good performance in separating and filtering the salt solution containing 25wt%, and still maintains a low permeation flux and a good interception performance after continuous working for 24 hours. It is explained that it is not easy to be contaminated and infiltrated, and can be used for long time in the separation and purification of high-salt-content solution.

[0119] Example 6

[0120] The example 6 provides a membrane distillation anti-fouling performance test method of the super-amphiphobic polytetrafluoroethylene micro-nano fiber film, which specifically includes the following steps:

[0121] The super-amphiphobic polytetrafluoroethylene micro-nano fiber film marked as P1-P8 NFM in example 3 is used for membrane distillation anti-fouling performance (3.5wt% NaCl solution + 0.1mM SDS) test, and the specific results of the test are shown in Figure 5 .

[0122] As Figure 5 can be seen, the polytetrafluoroethylene micro-nano fiber film has good performance in separating and filtering the salt solution containing surfactant, and still maintains a low permeation flux and a good interception performance after continuous working for 24 hours. It is explained that it is not easy to be contaminated and infiltrated, and can be used for long time in the separation and purification of high-salt-content solution.

[0123] Comparative Example 1

[0124] The comparative example 1 provides a preparation method of a super-amphiphobic polytetrafluoroethylene micro-nano fiber film, which specifically includes the following steps:

[0125] Steps 1) and 2) are exactly the same as in Example 3.

[0126] 3) The polytetrafluoroethylene (PTFE) micro / nanofiber membrane obtained in step 2) was placed together with the fluorination modifier in a desiccator and kept at a vacuum of 80 kPa and a temperature of 60°C for 12 hours to give the PTFE micro / nanofiber membrane high hydrophobic and antifouling properties. The fluorination modifier was trichloro(1H,1H,2H,2H-tridecylfluorooctyl)silane, and the molar ratio of the fluorination modifier to polyvinyl alcohol was 1.

[0127] Specifically, in Comparative Example 1, the preparation method of the spinning solution is exactly the same as that in Example 3.

[0128] The superhydrophobic polytetrafluoroethylene micro / nanofiber membrane obtained in this comparative example is labeled as No. 1.

[0129] Comparative Example 2

[0130] Comparative Example 2 provides a method for preparing a superhydrophobic polytetrafluoroethylene micro / nanofiber membrane, specifically including the following steps:

[0131] Steps 1), 2), and 3) are exactly the same as in Example 3, but Comparative Example 2 does not have the fluorination modification treatment in step 4). The remaining treatments are exactly the same as in Example 3.

[0132] Specifically, in Comparative Example 2, the preparation method of the spinning solution is exactly the same as that in Example 3.

[0133] The superhydrophobic polytetrafluoroethylene micro / nanofiber membrane obtained in this comparative example is labeled as No. 2.

[0134] Comparative Example 3

[0135] Comparative Example 3 provides a method for preparing a superhydrophobic polytetrafluoroethylene micro / nanofiber membrane, specifically including the following steps:

[0136] Steps 1) and 2) are exactly the same as in Example 3.

[0137] 3) The polytetrafluoroethylene (PTFE) micro / nanofiber membrane obtained in step 2) was placed together with the fluorination modifier in a desiccator and kept at a vacuum of 80 kPa and a temperature of 60°C for 12 hours to give the PTFE micro / nanofiber membrane high hydrophobic and antifouling properties. The fluorination modifier was trichloro(1H,1H,2H,2H-tridecylfluorooctyl)silane, and the molar ratio of the fluorination modifier to polyvinyl alcohol was 1.

[0138] 4) The polytetrafluoroethylene (PTFE) micro / nanofiber membrane prepared in step 3) was placed in a crosslinking solution for chemical crosslinking modification. During the crosslinking process, the crosslinking temperature was 50℃ and the crosslinking time was 1 hour. It was then washed with water at 90℃ for 1 minute and dried for later use. The component contents of the crosslinking solution were: PTFE micro / nanofiber membrane 4.5 wt%, glutaraldehyde 0.3 wt%, hydrochloric acid 0.2 wt%, and acetone 95 wt%.

[0139] Specifically, in Comparative Example 3, the preparation method of the spinning solution is exactly the same as that in Example 3.

[0140] The superhydrophobic polytetrafluoroethylene micro / nanofiber membrane obtained in this comparative example is labeled as No. 3.

[0141] The inventors tested the water-oil contact angle of the superhydrophobic polytetrafluoroethylene micro / nanofiber membranes prepared in Comparative Examples 1-3 and Example 3. Specific test results are shown below. Figure 1 Among them, No. 1 is the super-dihydrophobic polytetrafluoroethylene micro / nanofiber membrane prepared in Comparative Example 1, No. 2 is the super-dihydrophobic polytetrafluoroethylene micro / nanofiber membrane prepared in Comparative Example 2, No. 3 is the super-dihydrophobic polytetrafluoroethylene micro / nanofiber membrane prepared in Comparative Example 3, and No. 4 is the super-dihydrophobic polytetrafluoroethylene micro / nanofiber membrane prepared in Example 3.

[0142] The specific test method for the water-oil contact angle is as follows:

[0143] The surface water-oil contact angle of superhydrophobic polytetrafluoroethylene micro / nanofiber membranes (NFMs numbered 1, 2, 3, and P1-P8) was measured using a dynamic contact angle meter (SL200B, Kino Corporation, USA) to characterize the hydrophobicity of the membrane surface. Measurements were taken in five different regions of each sample, and the average value was recorded.

[0144] Depend on Figure 1 It can be seen that in Example 3, when crosslinking and fluorination modification are used simultaneously, and crosslinking treatment is used first followed by fluorination modification treatment, a better effect can be achieved on the hydrophobic and oleophobic dual-repellent properties of the membrane. See [link to example]. Figure 1 Number 4;

[0145] In Comparative Example 1, when only fluorination modification was performed without chemical crosslinking modification, the hydrophobic and oleophobic properties of the prepared polytetrafluoroethylene micro / nanofiber membrane were significantly reduced, and the water contact angle was less than 140°. See details... Figure 1 Middle number 1;

[0146] In Comparative Example 2, when only chemical crosslinking modification was performed without fluorination modification, the hydrophobic and oleophobic properties of the prepared polytetrafluoroethylene micro / nanofiber membrane were significantly further reduced. For details, please refer to [link to relevant documentation]. Figure 1 Number 2;

[0147] In Comparative Example 3, when fluorination modification was performed first, followed by chemical crosslinking modification, the resulting polytetrafluoroethylene micro / nanofiber membrane exhibited poor hydrophobic and oleophobic properties. See details below. Figure 1 Number 3.

[0148] Therefore, it can be seen that only when both crosslinking and fluorination modification are used, and crosslinking is used first followed by fluorination modification, can the hydrophobic and oleophobic properties of the membrane achieve a better effect.

[0149] The inventors tested the water-oil contact angle, mechanical properties, porosity, and membrane distillation of the superhydrophobic polytetrafluoroethylene micro / nanofiber membranes prepared in Examples 1-4. (Table 1 and...) Figure 3 The results show that the superhydrophobic polytetrafluoroethylene micro / nano fiber membrane prepared in Example 3 (i.e., when the mass ratio of polyvinyl alcohol and polytetrafluoroethylene is 1:8) has excellent water-oil contact angle, mechanical properties, porosity, and brine test results of membrane distillation.

[0150] Therefore, the superhydrophobic polytetrafluoroethylene micro / nanofiber membrane prepared in Example 3 was subjected to membrane distillation high salt concentration and antifouling performance tests, and the test methods were as in Examples 5 and 6, respectively.

[0151] The specific test methods for water-oil contact angle, mechanical properties, porosity, and membrane distillation are as follows:

[0152] 1) Water-oil contact angle: The surface water-oil contact angle of the superhydrophobic polytetrafluoroethylene micro / nanofiber membranes obtained in Examples 1-4 was tested using a dynamic contact angle meter (SL200B, Kino Corporation, USA) to characterize the hydrophobicity of the membrane surface. Measurements were taken in five different regions of each sample, and the average value was recorded. The water contact angle data for each example are shown in Table 1 and [Table data would be inserted here]. Figure 3 Image b.

[0153] 2) Mechanical Properties: The tensile strength and elongation at break of the tensile films were determined using a JBDL200 tensile testing machine (Yangzhou, China) at room temperature. The films were cut into 1×5cm (width×length) strips, and the tensile rate was 10 mm / min. Each sample was tested five times, and the average value was taken. The results of tensile strength and elongation at break for each embodiment are shown in Table 1.

[0154] 3) Porosity: To ensure that the filling fluid fully fills the membrane pores and reduce measurement errors and deviations, the membrane sample was immersed in isopropanol for 48 hours, and the size and thickness of the membrane sample were measured with a precision micrometer. The mass of the wet sample and the dry sample were weighed with an electronic balance, and then the porosity ε was calculated according to the following formula (1).

[0155]

[0156] In the formula, W1 and W2 are the wet and dry masses of the membrane, respectively (g); D i D represents the density of an aqueous solution of isopropanol. i =0.7855g / cm 3 ;D p This is the density of the polymer, expressed in g / cm³. 3 It is calculated from the weighted average of the polymer mass in the synthesized membrane, specifically the weighted average of the mass of polytetrafluoroethylene and polyvinyl alcohol.

[0157] The porosity results for each embodiment are shown in Table 1.

[0158] 4) Membrane distillation: The DCMD performance of the membrane was evaluated using a laboratory-scale direct contact membrane distillation (DCMD) experimental setup with an effective contact area of ​​3 cm². 2 The feed solutions were (3.5 wt% NaCl solution, 25 wt% NaCl solution, and 3.5 wt% NaCl solution + 0.1 mM sodium dodecyl sulfonate), and the permeate was distilled water. The temperature difference between the two sides was 40°C, and the flow rate was maintained at 0.2 L / min. -1 The transmembrane water flux and salt rejection were calculated by continuously monitoring the weight and conductivity of the permeate. Transmembrane water flux (J) w ,L·m -2 ·h -1 The salt rejection (R,%) and salt retention (R,%) are determined by equations (2) and (3), respectively:

[0159]

[0160]

[0161] In the formula, Δm (kg) represents the change in the weight of the permeate over a period of time; A (m 2 ) represents the effective area of ​​the membrane; C f and C p (g·L -1 ) represent the salt concentrations of the feed solution and the permeate, respectively, which can be converted using the solution conductivity.

[0162] The membrane distillation test results of Examples 1-6 are shown below. Figure 3 Figure a and Figure 4 , Figure 5 .

[0163] Table 1

[0164]

[0165] According to Table 1 and Figure 3It can be seen that the superhydrophobic polytetrafluoroethylene micro / nanofiber membrane prepared by the method provided in this application has a water contact angle ≥145°, exhibiting excellent hydrophobic properties. In terms of mechanical properties, it meets the basic requirements for membrane distillation testing, and its porosity can be maintained above 73%.

[0166] At the same time, Figure 3 In Figure a, the left ordinate represents osmotic flux, and the right ordinate represents electrical conductivity (solid graphs represent osmotic flux test results, and corresponding hollow graphs represent electrical conductivity test results). Figure 3 As shown in Figure a, the permeation flux of the superhydrophobic polytetrafluoroethylene micro / nanofiber membranes prepared by the preparation method provided in this application is significantly lower than that of commercially available polytetrafluoroethylene micro / nanofiber membranes in the prior art. Furthermore, no obvious wetting fouling phenomenon was observed after 24 hours of membrane distillation testing. In contrast, the conductivity of polytetrafluoroethylene micro / nanofiber membranes in the prior art gradually increases with time, indicating that they are wetted and fouled.

[0167] Depend on Figure 3 As shown in Figure c, when the test liquid is water, milk, ink, pump oil, hexadecane, KOH, or HNO3, the test liquid forms circular droplets on the membrane, proving that the superhydrophobic polytetrafluoroethylene micro / nanofiber membrane prepared in Example 3 has a large water-oil contact angle and good hydrophobic and oleophobic properties.

[0168] In addition, Figure 4 and Figure 5 In the diagram, the left vertical axis represents osmotic flux, and the right vertical axis represents electrical conductivity (solid graphs represent osmotic flux test results, and corresponding hollow graphs represent electrical conductivity test results). Figure 4 and Figure 5 It can be seen that the superhydrophobic polytetrafluoroethylene micro / nanofiber membrane prepared by the method of the present invention exhibits stable flux and excellent salt removal performance in the treatment of high-salt solutions, salt solutions containing surfactants, and oily salt solutions. In contrast, the permeation flux of commercial polytetrafluoroethylene micro / nanofiber membranes in the prior art drops sharply and the conductivity increases significantly under the same test conditions, indicating that commercial polytetrafluoroethylene micro / nanofiber membranes are easily wetted and not resistant to fouling.

[0169] In summary, this invention provides a superhydrophobic polytetrafluoroethylene (PTFE) micro / nanofiber membrane, its preparation method, and its applications. The preparation method of the superhydrophobic PTFE micro / nanofiber membrane provided by this invention features controllable process conditions, simple and easy operation, and is convenient for production, without the need for large-scale precision equipment. Furthermore, the superhydrophobic PTFE micro / nanofiber membrane obtained using this method exhibits stable flux and excellent salt removal performance in treating high-salt solutions, surfactant-containing salt solutions, and oily salt solutions. It also demonstrates good stability and reusability in cyclic use tests, showing promising application prospects in membrane distillation processes, especially in harsh environments.

[0170] Therefore, this invention effectively overcomes the various shortcomings of the prior art and has high industrial application value.

[0171] The above embodiments are merely illustrative of the principles and effects of the present invention and are not intended to limit the invention. Any person skilled in the art can modify or alter the above embodiments without departing from the spirit and scope of the present invention. Therefore, all equivalent modifications or alterations made by those skilled in the art without departing from the spirit and technical concept disclosed in the present invention should still be covered by the claims of the present invention.

Claims

1. A method for preparing a superhydrophobic polytetrafluoroethylene micro / nanofiber membrane, characterized in that, The preparation method includes the following steps: After obtaining a polytetrafluoroethylene micro-nano fiber membrane by electrospinning with spinning solution, the polytetrafluoroethylene micro-nano fiber membrane is chemically crosslinked and then fluorinated to finally obtain a superhydrophobic polytetrafluoroethylene micro-nano fiber membrane. The spinning solution includes a spinning aid and polytetrafluoroethylene, wherein the spinning aid is selected from one or more of polyvinyl alcohol, chitosan, cellulose nanocrystals, and polyethylene oxide. The spinning solution also includes boric acid; The chemical crosslinking modification uses a crosslinking agent.

2. The preparation method according to claim 1, characterized in that, The spinning solution uses a polytetrafluoroethylene emulsion, which is a mixture of polytetrafluoroethylene and water. And / or, based on the total mass of the spinning aid and polytetrafluoroethylene, the content of boric acid shall not exceed 5 wt%; And / or, in the spinning solution, the mass ratio of the spinning aid to polytetrafluoroethylene is 1:4 to 10.

3. The preparation method according to claim 2, characterized in that, The concentration of the polytetrafluoroethylene emulsion is 50–70 wt%.

4. The preparation method according to claim 1, characterized in that, The voltage during electrospinning is 12-25kV, and the receiving distance is 10-40cm.

5. The preparation method according to claim 1, characterized in that, During the chemical crosslinking modification, the crosslinking temperature is 30-80℃; And / or, the crosslinking agent is selected from one or more of dicumyl peroxide, benzoyl peroxide, and glutaraldehyde; And / or, when the chemical crosslinking agent is used for modification, a reaction medium is used, and the reaction medium is an organic solvent.

6. The preparation method according to claim 5, characterized in that, The molar ratio of hydroxyl content to crosslinking agent in the spinning aid is ≤2.

7. The preparation method according to claim 1, characterized in that, It also includes one or more of the following features: 1) The fluorination modification treatment uses a fluorination modifier; the fluorination modifier is selected from one or more of trichloro(3,3,3-trifluoropropyl)silane, trichloro(1H,1H,2H,2H-tridecyl octyl)silane or 1H,1H,2H,2H-perfluorodecyltrimethoxysilane. 2) The molar ratio of hydroxyl content to fluorinated modifier in the spinning aid is ≤1; 3) The fluorination modification treatment is carried out under vacuum conditions at a temperature of 60-150℃.

8. A superhydrophobic polytetrafluoroethylene micro / nanofiber membrane obtained by the preparation method according to any one of claims 1 to 7.

9. The use of the superhydrophobic polytetrafluoroethylene micro / nano fiber membrane as described in claim 8 as a membrane separation material in seawater desalination, wastewater treatment, and azeotropic mixture separation.

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