A method for increasing the flux and hydrophobicity of an isotropic membrane using selective fluorination

Abstract

The application discloses a method for improving the flux and hydrophobicity of a uniform pore membrane by selective fluorination, comprising the following steps: immersing a uniform pore membrane with a pore size of 5-100 nm and containing carboxyl functional groups into a reaction solution, wherein the reaction solution comprises a silver salt catalyst with a mass concentration in the range of 0.1-3.5 wt%, a fluorination reagent with a mass concentration in the range of 0.15-5.5 wt%, an oxidizing agent with a mass concentration in the range of 0.05-7.5 wt%, a co-catalyst with a mass concentration in the range of 0.15-5.5 wt%, water and an organic solvent with a mass concentration in the range of 5-65 wt%; reacting at 4-60 DEG C for 15 min-72 h, taking out the membrane, and then sequentially cleaning the membrane with ethanol and deionized water to obtain a uniform pore membrane with good membrane flux and hydrophobicity. The application improves the permeability and separation selectivity of the uniform pore membrane by selective fluorination, and the uniform pore membrane is not damaged, and the method has universality.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of membrane materials, in particular to a method for improving the flux and hydrophobicity of a uniform pore membrane by selective fluorination. BACKGROUND

[0002] Uniform pore membranes are a new type of membrane material with uniform pore size and high porosity, which is the next generation of high-performance separation membranes that break through the traditional "Trade-off" effect (i.e., permeability selectivity cannot be simultaneously considered) and achieve precise separation. Uniform pore membranes prepared by block copolymer self-assembly technology have a self-supporting structure and have been widely used in the separation of high-value-added biological macromolecules in recent years. However, the uniform pore membranes prepared by combining block copolymer self-assembly and non-solvent induced phase separation often have high-density hydrophilic and water-soluble polymers enriched in the pores. These hydrophilic and water-soluble polymers swell excessively in the membrane pores, resulting in a sharp decrease in effective pore size, ultimately leading to low membrane permeability. The above shortcomings greatly restrict the application of uniform pore membranes in efficient and rapid separation.

[0003] Currently, the methods for improving the permeability of uniform pore membranes include the synthesis of new block copolymers, the addition of additives to the casting solution, and the modification of the membrane after formation. Synthesizing ideal copolymer materials is beneficial to solving the problem of poor permeability of uniform pore membranes from the source, but the synthesis of new copolymers is difficult, and the use of new copolymers to prepare uniform pore membranes generally requires the exploration of new membrane formation conditions, making this method have great limitations. In addition, there are also many studies on improving the flux of uniform pore membranes by introducing additives, which can improve the permeability of uniform pore membranes to a certain extent, but the upper limit of improvement is not high, and there is still a significant gap from the expected high flux and high retention. Finally, the modification of the uniform pore membrane after formation, such as the degradation and etching of the pore-forming block, can usually greatly improve the permeability of the membrane, but this method is only limited to a few uniform pore membranes with degradable blocks, and has poor universality. In view of the problems existing in the prior art, there is an urgent need for a method for directional hydrophobic modification of water-soluble blocks inside the membrane pores to efficiently and conveniently control the pore size and hydrophobicity of the uniform pore membrane, thereby more effectively utilizing the performance advantages of the uniform pore membrane in precise and rapid separation in the fields of protein separation and virus filtration. SUMMARY

[0004] In view of the shortcomings of the prior art, the present application provides a method for improving the flux and hydrophobicity of a uniform pore membrane by selective fluorination. The uniform pore membrane obtained by this method has increased pore size, enhanced hydrophobicity, and improved contact angle. This method has mild reaction conditions, simple steps, and strong universality, which is beneficial to the surface hydrophobic modification and directional functionalization of the uniform pore membrane, and overcomes the shortcomings of the prior art, such as the swelling of polymers in the pores of block copolymer uniform pore membranes, large pore flow resistance, low water flux, and low separation efficiency.

[0005] The specific technical solution is as follows:

[0006] A method for improving the flux and hydrophobicity of a uniform pore membrane by selective fluorination, comprising the following steps:

[0007] S1: immerse a uniform pore membrane containing carboxyl functional groups in the pores into a reaction solution, the reaction solution comprising: a silver salt catalyst, a fluorination reagent, an oxidizing agent, a co-catalyst, water, an organic solvent; the mass concentration of the silver salt catalyst ranges from 0.1 to 3.5 wt%, the mass concentration of the fluorination reagent ranges from 0.15 to 5.5 wt%, and the mass concentration of the oxidizing agent ranges from 0.05 to 7.5 wt%;

[0008] S2: after the uniform pore membrane is reacted in the reaction solution at 4-60℃ for 15min-72h, the membrane is taken out;

[0009] S3: sequentially clean with ethanol and deionized water to obtain a uniform pore membrane with improved flux and enhanced hydrophobicity.

[0010] Further, in S1, the uniform pore membrane is formed by self-assembly of amphiphilic block copolymer, and the pore size ranges from 5 to 100 nm, and the relative standard deviation of the pore size distribution is less than 20%. The pore size of the uniform pore membrane of amphiphilic block copolymer is precisely adjustable in the nanometer range, and precise separation of high value-added molecules can be achieved. The uniform pore membrane with a pore size standard deviation greater than 20% has poor separation selectivity and is difficult to use for precise separation.

[0011] Further, in S1, the block in the pores of the uniform pore membrane is composed of a hydrophilic polymer containing carboxyl functional groups, and the mass fraction of carboxyl in the hydrophilic block is not less than 2.5 wt%. Most of the hydrophilic polymers containing carboxyl functional groups have strong swelling properties, resulting in generally smaller effective pore size of the uniform pore membrane containing such polymers. At the same time, carboxyl can better undergo fluorination substitution reaction, which can effectively realize the transformation of water solubility. The modification effect of polymers with carboxyl content less than 2.5 wt% is not obvious, and the urgency of modification is lower.

[0012] Further, the silver salt catalyst is selected from any one of silver acetate, silver nitrate, silver sulfate, silver triflate, and silver tetrafluoroborate. The above silver salt catalysts are all efficient catalysts for selective fluorination. If the mass concentration is higher than 3.5 wt%, the fluorination rate and reaction degree are less affected; if it is lower than 0.1 wt%, the reaction rate is lower and the time to reach the predetermined conversion rate is too long (more than 48h).

[0013] Further, the fluorination reagent is selected from any one of diethylamino sulfide trifluoride, N-fluorobenzensulfonamide, 1-chloromethyl-4-fluoro-1,4-diazabicyclo[2.2.2]octane di(tetrafluoroborate) salt, and bispyridine tris(trifluoromethyl) copper. The fluorination reagent is a high-efficiency reaction reagent for selective fluorination. If the mass concentration of the fluorination reagent is higher than 5.5 wt%, the fluorination rate and the reaction degree are less affected, and the mass concentration is higher than the saturated solubility. If the mass concentration of the fluorination reagent is lower than 0.15 wt%, the reaction efficiency is low, and the time for reaching the predetermined conversion rate is too long (more than 48 h).

[0014] Further, the oxidizing agent is selected from any one of sodium persulfate, potassium persulfate, ammonium persulfate, and dibenzoyl peroxide. The oxidizing agent has high activity and low decomposition temperature, and can be decomposed into free radicals at the selected temperature to promote the fluorination reaction. The mass concentration of the oxidizing agent is selected in consideration of the reaction rate, the reaction conversion rate, and the economy. If the mass concentration of the oxidizing agent is higher than 7.5 wt%, the effect of accelerating the selective fluorination is not obvious.

[0015] Further, the co-catalyst is dimethyl zinc or diethyl zinc, and the mass concentration of the co-catalyst in the solution is 0.15-5.5 wt%. Dimethyl zinc and diethyl zinc are the most effective co-catalysts for selective fluorination of carboxyl-containing small organic molecules, and both of them are also effective in the selective fluorination of carboxyl groups on the uniform pore membrane. The preferred mass concentration range takes into account the solubility of the co-catalyst in the reaction solution and the effect on the reaction selectivity. If the mass concentration is higher than the above-mentioned concentration, the side reactions other than carboxyl substitution increase.

[0016] Further, the organic solvent is selected from any one of acetone, acetonitrile, and tetrahydrofuran, and the mass concentration of the organic solvent in the reaction solution is 5-65 wt%. The mixed solvent of acetone, acetonitrile, tetrahydrofuran, and water has the best solubility for the catalyst, the co-catalyst, the fluorination reagent, and the oxidizing agent, and can reach the concentration requirement of the above-mentioned solvents. The given mass concentration range takes into account the solubility of the reaction reagent and the maintenance of the uniform pore structure. If the content of the organic solvent is higher than 65 wt%, the uniform pore membrane is dissolved in the reaction solution, which changes the uniform pore structure. If the content of the organic solvent is lower than 5 wt%, the solubility of the fluorination reagent is poor.

[0017] Further, in S3, the uniform pore membrane is cleaned with ethanol for 1-2 times, cleaned with deionized water for 2-3 times, and finally soaked in a mixed solvent of water and glycerol for storage.

[0018] A uniform pore membrane with improved membrane flux and hydrophobicity is prepared according to the method for improving the membrane flux and hydrophobicity of the uniform pore membrane by selective fluorination. The mass content of fluorine in the uniform pore membrane is not less than 0.2 wt%, the effective pore size is increased by not less than 15% compared with the uniform pore membrane before modification, the flux is increased by more than 35%, and the contact angle is increased by not less than 5°.

[0019] The present application has the following advantages:

[0020] (1) The present application combines the characteristics of hydrophilic environment in the pores of the uniform pore membrane, which makes it easy for fluorinated reagents to enter the pores for continuous reaction, thereby selectively fluorinating the carboxyl functional group in the pores.

[0021] (2) The method provided by the present application improves the permeability and separation selectivity of the uniform pore membrane by selective fluorination. This method is universal and suitable for all uniform pore membranes containing carboxyl functional groups in the pores.

[0022] (3) The present application is a non-destructive modification method for uniform pore membranes, which does not change the original pore density and pore order of the uniform pore membranes.

[0023] (4) The present application has mild reaction conditions, simple steps, and strong universality, which is beneficial to the hydrophobic modification and directional functionalization of the uniform pore membrane, and has significant value for expanding the new applications of the uniform pore membrane in the hydrophobic field. BRIEF DESCRIPTION OF DRAWINGS

[0024] Figure 1 Figure 1 is a surface scanning electron microscope characterization of the uniform pore membrane before and after fluorination in Example 1 of the present application, wherein (a) is the surface scanning electron microscope characterization before fluorination, and (b) is the surface scanning electron microscope characterization after fluorination.

[0025] Figure 2 Figure 2 is a surface ATR-FTIR infrared spectrum characterization diagram of the uniform pore membrane before and after fluorination in Example 1 of the present application.

[0026] Figure 3 Figure 3 is a permeability column chart of the uniform pore membrane before and after fluorination in Example 1 of the present application.

[0027] Figure 4 Figure 4 is a data column chart of the rejection of polyethylene glycol by the uniform pore membrane before and after fluorination in Example 1 of the present application.

[0028] Figure 5 Figure 5 is a contact angle diagram of the uniform pore membrane before and after fluorination in Example 1 of the present application.

[0029] Figure 6 Figure 6 is the XPS test result of the uniform pore membrane after different reaction times in Example 1 of the present application. DETAILED DESCRIPTION

[0030] The present application will be described in detail below according to the drawings and preferred embodiments, and the purposes and effects of the present application will become more apparent. The present application will be further described in detail below in combination with the drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present application and do not limit the present application.

[0031] Example 1

[0032] A method for improving the flux and hydrophobicity of a uniform pore membrane by selective fluorination, comprising the following steps:

[0033] S1: Selective fluorination of the uniform pore membrane: A polystyrene-block-polyacrylic acid self-assembled uniform pore membrane with a pore size of 13.5 nm and carboxyl functional groups in the pores (polyacrylic acid block mass content of 15.7 wt%, carboxyl mass content of 9.8 wt%) is immersed in a water / acetone mixed solution (i.e. reaction solution) containing silver nitrate with a mass fraction of 3.5 wt%, diethylamino sulfur trifluoride with a mass fraction of 5 wt%, sodium persulfate with a mass fraction of 7 wt%, and dimethyl zinc with a mass fraction of 3 wt%, wherein the mass ratio of water to acetone is 50:50 (wt%:wt%).

[0034] S2: Fluorination reaction: After immersing the four pieces of uniform pore membrane in the above reaction solution, they are transferred to a 50°C water bath for reaction for 12, 24, 48, and 60 hours, respectively. After the reaction is completed, the membrane pieces are taken out in turn.

[0035] S3: Post-treatment: The membrane pieces are washed twice with an ethanol solution and then three times with deionized water to wash away the residual fluorination reagents in the membrane, obtaining a uniform pore membrane with good flux and hydrophobicity.

[0036] After the membrane pieces are completely dried, scanning electron microscopy is used to characterize the surface morphology of the uniform pore membrane before and after the reaction, and the results are shown in FIG. 1. It is found by statistics that the pore size before the reaction is 13±0.5 nm, and the relative standard deviation of the pore size distribution is 16.5%; after the reaction for 48 h, the pore size is 16±0.2 nm, and the relative standard deviation of the pore size distribution is 18.0%. The standard deviation value changes little, and the modified membrane still belongs to a uniform pore structure; compared with the original membrane, the flux of the modified membrane is about 12 times that of the original membrane. Figure 1 The surface of the membrane before and after the reaction is characterized by infrared spectroscopy, and the results are shown in FIG. 2. It is found that the carboxyl stretching vibration peak at 1710 nm in the original membrane is significantly weakened in the fluorinated membrane, confirming the successful fluorination modification of the carboxyl group. -1

[0037] Figure 2 The permeability of the membrane before and after fluorination is tested, and the results are shown in FIG. 3. It is found that the flux of the uniform pore membrane after fluorination is significantly improved, and compared with the original membrane, the flux is increased by about 12 times when the reaction time is 48 h.

[0038] Figure 3

[0039] FIG. 1 shows the surface morphology of the uniform pore membrane before and after the reaction. Figure 4 ​​​​The column chart of the rejection of PEG before and after fluorination of the uniform pore membrane shows that the rejection rate of the fluorinated membrane is significantly lower than that of the original membrane for PEG molecules of the same molecular weight, reflecting the increase in the effective pore size of the fluorinated membrane.

[0040] The Figure 5 The contact angle of the fluorinated membrane surface is significantly larger than that of the original membrane, indicating that the hydrophobicity of the membrane surface is enhanced.

[0041] The Figure 6 The fluorine element is present on the uniform pore membrane after fluorination, indicating that selective fluorination of the uniform pore membrane is successfully performed.

[0042] Example 2

[0043] A method for improving the flux and hydrophobicity of a uniform pore membrane by selective fluorination includes the following steps:

[0044] S1: Selective fluorination of the uniform pore membrane: A poly(methyl methacrylate)-block-poly(acrylic acid) self-assembled uniform pore membrane with a pore size of 15 nm and carboxyl functional groups in the pores is immersed in a water / acetone mixed solution containing silver sulfate at a mass fraction of 3.5 wt%, bipyridine tris(trifluoromethyl) copper at a mass fraction of 3.5 wt%, ammonium persulfate at a mass fraction of 5 wt%, and diethyl zinc at a mass fraction of 3 wt%, wherein the mass ratio of water to acetone is 60:40 (wt%:wt%).

[0045] S2: Fluorination reaction: After immersing the uniform pore membrane in the above reaction solution, it is transferred to a 60°C water bath for continuous reaction for 60 hours. After the reaction is completed, the membrane is removed.

[0046] S3: Post-treatment: The membrane is washed twice with ethanol solution and then three times with deionized water to remove the residual fluorination reagents from the membrane, obtaining a uniform pore membrane with good flux and hydrophobicity.

[0047] The surface morphology of the membrane before and after the reaction is characterized using a scanning electron microscope, and it is found that the pore size of the modified uniform pore membrane is significantly larger than that of the original membrane. The flux of the modified membrane is about 1.4 times that of the original membrane. PEG rejection tests on the uniform pore membranes before and after fluorination show that the rejection rate of the fluorinated membrane is significantly lower than that of the original membrane for PEG molecules of the same molecular weight, indicating an increase in the effective pore size of the fluorinated membrane. The surface contact angle test of the fluorinated membrane shows that the hydrophobicity of the membrane surface is enhanced.

[0048] Example 3

[0049] A method for improving the flux and hydrophobicity of a uniform pore membrane by selective fluorination includes the following steps:

[0050] S1: Selective fluorination of the uniform pore membrane: A polystyrene-block-polyacrylic acid self-assembled uniform pore membrane with a pore size of 13 nm and carboxyl functional groups in the pores was immersed in a water / acetone mixed solution containing silver triflate at a mass fraction of 0.1 wt%, N-fluorobenzenesulfonimide at a mass fraction of 5.5 wt%, dibenzoyl peroxide at a mass fraction of 0.15 wt%, and diethyl zinc at a mass fraction of 3.5 wt%, with a mass ratio of water to acetone of 70:30 (wt%:wt%).

[0051] S2: Fluorination reaction: After immersing the uniform pore membrane in the above reaction solution, it was transferred to a 40°C water bath for continuous reaction for 60 hours. After the reaction was completed, the membrane was taken out.

[0052] S3: Post-treatment: The membrane was washed twice with an ethanol solution and then three times with deionized water to wash away the residual fluorination reagents in the membrane, obtaining a uniform pore membrane with good membrane flux and hydrophobicity.

[0053] The surface morphology of the membrane before and after the reaction was characterized using a scanning electron microscope, and it was found that the pore size of the modified uniform pore membrane was significantly larger than that of the original membrane. Compared with the original membrane, the flux of the modified membrane was about 5 times that of the original membrane. PEG rejection tests were conducted on the uniform pore membranes before and after fluorination, and for the same molecular weight PEG molecules, the rejection rate of the fluorinated membrane was significantly lower than that of the original membrane, indicating that the effective pore size of the fluorinated membrane increased. The contact angle test of the fluorinated membrane surface showed that the hydrophobicity of the fluorinated membrane surface was enhanced.

[0054] Example 4

[0055] A method for improving the flux and hydrophobicity of a uniform pore membrane using selective fluorination, comprising the following steps:

[0056] S1: Selective fluorination of the uniform pore membrane: A polystyrene-block-polyacrylic acid self-assembled uniform pore membrane with a pore size of 13 nm and carboxyl functional groups in the pores was immersed in a water / acetone mixed solution containing silver triflate at a mass fraction of 0.1 wt%, N-fluorobenzenesulfonimide at a mass fraction of 5.5 wt%, dibenzoyl peroxide at a mass fraction of 0.15 wt%, and diethyl zinc at a mass fraction of 3.5 wt%, with a mass ratio of water to acetone of 70:30 (wt%:wt%).

[0057] S2: Fluorination reaction: After immersing the uniform pore membrane in the above reaction solution, it was transferred to a 40°C water bath for continuous reaction for 60 hours. After the reaction was completed, the membrane was taken out.

[0058] S3: Post-treatment: The membrane was washed twice with an ethanol solution and then three times with deionized water to wash away the residual fluorination reagents in the membrane, obtaining a uniform pore membrane with good membrane flux and hydrophobicity.

[0059] The surface morphology of the membrane before and after the reaction is characterized by using a scanning electron microscope, and it is found that the pore size of the modified membrane is significantly larger than that of the original membrane. Compared with the original membrane, the flux of the modified membrane is about 8 times that of the original membrane. The PEG rejection test is performed on the fluorinated and non-fluorinated membranes, and for the same molecular weight PEG molecule, the rejection rate of the fluorinated membrane is significantly less than that of the original membrane, indicating that the effective pore size of the fluorinated membrane is increased. The surface contact angle test of the fluorinated membrane shows that the hydrophobicity of the fluorinated membrane surface is enhanced.

[0060] Example 5

[0061] A method for improving the flux and hydrophobicity of a uniform pore membrane by selective fluorination, comprising the following steps:

[0062] S1: Selective fluorination of the uniform pore membrane: a poly(methyl methacrylate)-block-poly(acrylic acid) self-assembled uniform pore membrane with a pore size of 25 nm and carboxyl functional groups in the pores is immersed in a water / acetone mixed solution containing 0.1wt% silver acetate, 5wt% diethylamino sulfur trifluoride, 7.5wt% potassium persulfate, and 0.15wt% diethyl zinc, wherein the mass ratio of water to acetone is 95:5 (wt%:wt%).

[0063] S2: Fluorination reaction: after immersing the uniform pore membrane in the above reaction solution, it is transferred to a 5℃ water bath and continuously reacted for 48 hours. After the reaction is completed, the membrane is taken out.

[0064] S3: Post-treatment: washed twice with ethanol solution and then three times with deionized water to wash away the residual fluorination reagents in the membrane, obtaining a uniform pore membrane with good flux and hydrophobicity.

[0065] The surface morphology of the membrane before and after the reaction is characterized by using a scanning electron microscope, and it is found that the pore size of the modified membrane is significantly larger than that of the original membrane. Compared with the original membrane, the flux of the modified membrane is about 8 times that of the original membrane. The PEG rejection test is performed on the fluorinated and non-fluorinated membranes, and for the same molecular weight PEG molecule, the rejection rate of the fluorinated membrane is significantly less than that of the original membrane, indicating that the effective pore size of the fluorinated membrane is increased. The surface contact angle test of the fluorinated membrane shows that the hydrophobicity of the fluorinated membrane surface is enhanced.

[0066] Example 6

[0067] A method for improving the flux and hydrophobicity of a uniform pore membrane by selective fluorination, comprising the following steps:

[0068] S1: Selective fluorination of the homogeneous membrane: A polystyrene-block-poly(acrylic acid) self-assembled homogeneous membrane with a pore size of 100 nm and carboxyl functional groups in the pores (where the carboxyl mass content is 2.5 wt%) is immersed in a water / tetrahydrofuran mixed solution containing silver sulfate with a mass fraction of 3.5 wt%, bipyridine tris(trifluoromethyl) copper with a mass fraction of 3.5 wt%, sodium persulfate with a mass fraction of 0.05 wt%, and dimethyl zinc with a mass fraction of 3.5 wt%, where the mass ratio of water to tetrahydrofuran is 35:65 (wt%:wt%).

[0069] S2: Fluorination reaction: After immersing the homogeneous membrane in the above reaction solution, it is transferred to a 60°C water bath and the reaction is continued for 24 hours. After the reaction is completed, the membrane sheet is removed.

[0070] S3: Post-treatment: The membrane is washed twice with an ethanol solution and then three times with deionized water to wash away the residual fluorination reagents in the membrane, obtaining a homogeneous membrane with good membrane flux and hydrophobicity.

[0071] The surface morphology of the membrane before and after the reaction is characterized using a scanning electron microscope, and it is found that the pore size of the modified homogeneous membrane is significantly larger than that of the original membrane. Compared with the original membrane, the flux of the modified membrane is about 8 times that of the original membrane. PEG rejection tests are performed on the homogeneous membranes before and after fluorination, and for the same molecular weight PEG molecules, the rejection rate of the fluorinated membrane is significantly lower than that of the original membrane, indicating that the effective pore size of the fluorinated membrane has increased. The surface contact angle test of the fluorinated membrane shows that the hydrophobicity of the surface of the fluorinated membrane has been enhanced.

[0072] Example 7

[0073] A method for improving the flux and hydrophobicity of a homogeneous membrane using selective fluorination, comprising the following steps:

[0074] S1: Selective fluorination of the homogeneous membrane: A polystyrene-block-poly(acrylic acid) self-assembled homogeneous membrane with a pore size of 100 nm and carboxyl functional groups in the pores (where the carboxyl mass content is 2.5 wt%) is immersed in a water / tetrahydrofuran mixed solution containing silver sulfate with a mass fraction of 3.5 wt%, bipyridine tris(trifluoromethyl) copper with a mass fraction of 3.5 wt%, sodium persulfate with a mass fraction of 0.05 wt%, and dimethyl zinc with a mass fraction of 3.5 wt%, where the mass ratio of water to tetrahydrofuran is 35:65 (wt%:wt%).

[0075] S2: Fluorination reaction: After immersing the homogeneous membrane in the above reaction solution, it is transferred to a 60°C water bath and the reaction is continued for 24 hours. After the reaction is completed, the membrane sheet is removed.

[0076] S3: Post-treatment: The membrane is washed twice with an ethanol solution and then three times with deionized water to wash away the residual fluorination reagents in the membrane, obtaining a homogeneous membrane with good membrane flux and hydrophobicity.

[0077] The surface morphology of the membrane before and after the reaction was characterized using a scanning electron microscope, and it was found that the pore size of the modified membrane was significantly larger than that of the original membrane. Compared with the original membrane, the flux of the modified membrane was about 1.4 times that of the original membrane. PEG rejection tests were performed on the fluorinated and non-fluorinated membranes, and for the same molecular weight PEG molecules, the rejection rate of the fluorinated membrane was significantly lower than that of the original membrane, indicating that the effective pore size of the fluorinated membrane increased. The surface contact angle test of the fluorinated membrane showed that the hydrophobicity of the membrane surface was enhanced.

[0078] Example 8

[0079] A method for improving the flux and hydrophobicity of a uniform pore membrane by selective fluorination, comprising the following steps:

[0080] S1: Selective fluorination of the uniform pore membrane: a polystyrene-block-poly(acrylic acid-co-hydroxyethyl acrylate) self-assembled uniform pore membrane with a pore size of 12 nm and carboxyl functional groups in the pores (acrylic acid functional group content of 3.5 wt%) was immersed in a water / acetonitrile mixed solution containing silver nitrate with a mass fraction of 3.5 wt%, bipyridine tris(trifluoromethyl) copper with a mass fraction of 5 wt%, sodium persulfate with a mass fraction of 6 wt%, and dimethyl zinc with a mass fraction of 5.5 wt%, wherein the mass ratio of water to acetonitrile is 95:5 (wt%:wt%).

[0081] S2: Fluorination reaction: after immersing the uniform pore membrane in the above reaction solution, it was transferred to a 60°C water bath and the reaction was continued for 15 minutes. After the reaction was completed, the membrane was removed.

[0082] S3: Post-treatment: washed twice with ethanol solution and then three times with deionized water to wash away the residual fluorination reagents in the membrane, obtaining a uniform pore membrane with good flux and hydrophobicity.

[0083] The surface morphology of the membrane before and after the reaction was characterized using a scanning electron microscope, and it was found that the pore size of the modified membrane was significantly larger than that of the original membrane. Compared with the original membrane, the flux of the modified membrane was about 1.4 times that of the original membrane. PEG rejection tests were performed on the fluorinated and non-fluorinated membranes, and for the same molecular weight PEG molecules, the rejection rate of the fluorinated membrane was significantly lower than that of the original membrane, indicating that the effective pore size of the fluorinated membrane increased. The surface contact angle test of the fluorinated membrane showed that the hydrophobicity of the membrane surface was enhanced.

[0084] Those skilled in the art can understand that the above description is only a preferred example of the application and is not intended to limit the application, although the application has been described in detail with reference to the foregoing examples, those skilled in the art can still modify the technical solutions described in the foregoing examples or make equivalent replacements for part of the technical features. Any modifications, equivalent replacements, etc. made within the spirit and principles of the application shall be included in the protection scope of the application.

Claims

1. A method for improving the flux and hydrophobicity of uniformly porous membranes using selective fluorination, characterized in that, Includes the following steps: S1: Immerse a uniformly porous membrane containing carboxyl functional groups in the pores into a reaction solution, and selectively fluorinate the carboxyl functional groups in the pores. The reaction solution includes: silver salt catalyst, fluorination reagent, oxidant, cocatalyst, water, and organic solvent. The mass concentration range of the silver salt catalyst is 0.1~3.5 wt%, the mass concentration range of the fluorinating agent is 0.15~5.5 wt%, and the mass concentration range of the oxidant is 0.05~7.5 wt%. S2: The uniformly porous membrane is reacted in the reaction solution at 4~60℃ for 15min~72h, and then the membrane is removed; S3: Wash with ethanol and deionized water in sequence to obtain a uniformly porous membrane with improved membrane flux and enhanced hydrophobicity.

2. The method for improving the flux and hydrophobicity of uniformly porous membranes using selective fluorination according to claim 1, characterized in that, In S1, the uniformly porous membrane is formed by the self-assembly of an amphiphilic block copolymer, with a pore size range of 5-100 nm and a relative standard deviation of less than 20% for the pore size distribution.

3. The method for improving the flux and hydrophobicity of uniformly porous membranes using selective fluorination according to claim 2, characterized in that, In S1, the pore blocks of the uniformly porous membrane are composed of hydrophilic polymers containing carboxyl functional groups, and the mass percentage of the carboxyl groups in the hydrophilic blocks is not less than 2.5 wt%.

4. The method for improving the flux and hydrophobicity of uniformly porous membranes using selective fluorination according to claim 1, characterized in that, The silver salt catalyst is selected from any one of silver acetate, silver nitrate, silver sulfate, silver trifluoromethanesulfonate, and silver tetrafluoroborate.

5. The method for improving the flux and hydrophobicity of uniformly porous membranes using selective fluorination according to claim 1, characterized in that, The fluorinating agent is selected from any one of diethylaminosulfonium trifluoride, N-fluorobis(benzenesulfonamide), 1-chloromethyl-4-fluoro-1,4-diazabicyclo[2.2.2]octane di(tetrafluoroborate) salt, and bipyridine tri(trifluoromethyl)copper.

6. The method for improving the flux and hydrophobicity of a uniformly porous membrane using selective fluorination according to claim 1, characterized in that, The oxidant is selected from any one of sodium persulfate, potassium persulfate, ammonium persulfate, and benzoyl peroxide.

7. The method for improving the flux and hydrophobicity of uniformly porous membranes using selective fluorination according to claim 1, characterized in that, The cocatalyst is dimethyl zinc or diethyl zinc, with a mass concentration of 0.15~5.5 wt% in the solution.

8. The method for improving the flux and hydrophobicity of uniformly porous membranes using selective fluorination according to claim 1, characterized in that, The organic solvent is selected from any one of acetone, acetonitrile, and tetrahydrofuran, wherein the mass concentration of the organic solvent in the reaction solution is 5~65 wt%.

9. The method for improving the flux and hydrophobicity of a uniformly porous membrane using selective fluorination according to claim 1, characterized in that, In step S3, the sample is first washed with ethanol 1-2 times, then washed with deionized water 2-3 times, and finally soaked in a mixed solvent of water and glycerol for preservation.

10. A uniformly porous membrane with improved membrane flux and hydrophobicity, characterized in that, The membrane was prepared by the method according to any one of claims 1-9, which utilizes selective fluorination to improve the flux and hydrophobicity of the uniformly porous membrane.

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