Preparation method and application of super-hydrophobic film with high-temperature self-repairing performance

Abstract

The application relates to a preparation method and application of a super-hydrophobic membrane with high-temperature self-repairing performance, and relates to a preparation method and application of a super-hydrophobic membrane.The application aims to solve the problems that the super-hydrophobic membrane used for membrane distillation will appear in flux decline and a large increase in the conductivity of the permeate after a long time of operation, and the water treatment performance of the membrane will be reduced after acid washing, and even the membrane cannot continue to operate.Method: I, Fenton reaction pretreatment;II, preparation of a bottom super-hydrophobic layer;III, preparation of a PVA middle layer;IV, preparation of a top super-hydrophobic layer.The super-hydrophobic membrane with high-temperature self-repairing performance is used as a membrane for membrane distillation.The prepared membrane with high-temperature self-repairing performance has high super-hydrophobic performance and self-repairing performance.A super-hydrophobic membrane with high-temperature self-repairing performance can be obtained.

Description

TECHNICAL FIELD

[0001] The application relates to a preparation method and application of a super-hydrophobic membrane. BACKGROUND

[0002] Membrane distillation (MD) is a high-efficiency separation technology integrating evaporation and membrane separation processes. In the face of the increasingly scarce water resources, the membrane distillation technology has the advantages of simple process, convenient operation and low power consumption. The micro-porous hydrophobic membrane is used as the driving force for the vapor pressure difference between the two sides of the membrane. The hot side of the membrane is in direct contact with the feed liquid. The water in the hot feed liquid evaporates into water vapor at the membrane surface and then enters the cold side through the membrane pores and is condensed. Other solute molecules cannot pass through the membrane, so that the separation or purification of the mixture is realized.

[0003] Due to the process flow of membrane distillation, the membrane used for membrane distillation must be a micro-porous hydrophobic membrane. The stronger the hydrophobicity, the more difficult it is for the pollutants in the feed liquid to adhere to the membrane surface, thereby greatly improving the running time. When the static contact angle of the membrane surface with water is greater than 150° and the rolling contact angle is less than 10°, the membrane can be called a super-hydrophobic membrane. The super-hydrophobic membrane can better avoid the flux reduction caused by the wetting of the membrane pores and the pollution of the membrane surface due to its excellent resistance and self-cleaning performance. However, the super-hydrophobic membrane will also be polluted to a certain extent after a long time of operation, resulting in a decrease in membrane flux and a large increase in the conductivity of the permeate. Washing the membrane surface by acid washing and the like can effectively restore the performance of the membrane, but the water treatment performance of the membrane will decrease after cleaning and even cannot continue to run. SUMMARY

[0004] The purpose of the present application is to solve the problems of the existing super-hydrophobic membrane for membrane distillation, i.e. the decrease in membrane flux and the large increase in the conductivity of the permeate after a long time of operation, and the decrease in the water treatment performance of the membrane after acid washing and even the inability to continue to run, and to provide a preparation method and application of a super-hydrophobic membrane with high-temperature self-repairing performance.

[0005] A preparation method of a super-hydrophobic membrane with high-temperature self-repairing performance, which is completed according to the following steps:

[0006] I. Fenton reaction pretreatment:

[0007] The PVDF-based membrane is immersed in a mixed solution of FeSO4·7H2O, H2O2, anhydrous ethanol and deionized water, then a Fenton reaction is carried out under heating, the PVDF-based membrane is cleaned with sulfuric acid, and finally vacuum drying is performed to obtain a pretreated PVDF-based membrane;

[0008] II. Preparation of a bottom super-hydrophobic layer:

[0009] ①, first, SiO2 nanoparticles are dissolved in cyclohexane, magnetic stirring, ultrasonic dispersion, then drop 1H, 1H, 2H, 2H-perfluorooctyltrichlorosilane, continue ultrasonic dispersion, to get PFTS / SiO2 solution;

[0010] ②, the pretreated PVDF base film is immersed in PFTS / SiO2 solution, and then vacuum dried after taking out, to obtain a composite film containing a bottom super-hydrophobic layer;

[0011] III. Preparation of PVA intermediate layer:

[0012] ①, polyvinyl alcohol and deionized water are mixed, then stirred under heating conditions, then anhydrous ethanol is added, to obtain a mixed solution;

[0013] ②, the mixed solution is uniformly cast on the composite film containing the bottom super-hydrophobic layer, then a film applicator is used to control the thickness of the mixed solution on the bottom super-hydrophobic layer, and finally dried at room temperature, to obtain a composite film containing a PVA intermediate layer;

[0014] IV. Preparation of top super-hydrophobic layer:

[0015] PFTS / SiO2 solution is sprayed on the surface of the composite film containing the PVA intermediate layer using a spray gun, left to stand, then air-dried, to obtain a super-hydrophobic film with high-temperature self-repairing performance.

[0016] A super-hydrophobic film with high-temperature self-repairing performance is used as a membrane for membrane distillation.

[0017] The principle of the present application is:

[0018] The application is to prepare a super-hydrophobic film with high-temperature self-repairing performance by grafting PFTS (1H, 1H, 2H, 2H-perfluorooctyltrichlorosilane) fluorinated SiO2 nanoparticles on the surface of the film to reduce the surface energy, then preparing an intermediate layer by dissolving PVA at high temperature in water with the aid of ethanol, and finally spraying the fluorinated SiO2 solution on the surface of the film by the spray deposition method. PVA, as an organic compound, will dissolve in the water environment above 85 DEG C. When the super-hydrophobic surface of the top layer is polluted or damaged, the super-hydrophobic surface of the top layer is rubbed off by sandpaper, and then the super-hydrophobic layer of the bottom film surface is exposed by treating it in the water environment above 85 DEG C for 30 min, so that the hydrophobic performance of the super-hydrophobic layer is restored. The polyvinyl alcohol film can permeate water vapor, but it is difficult to permeate alcohol vapor, and it cannot permeate organic solvent vapor, inert gas and the like. The water-soluble polyvinyl alcohol film has a water-soluble temperature above 85 DEG C, which is higher than the hot side temperature (60 DEG C) of the conventional membrane distillation process, and thus it is suitable for the modification process of the membrane for membrane distillation. Compared with the method of modifying the surface of the film by using fluorosilane alone, the film prepared in the application has high super-hydrophobic performance and self-repairing performance. The application provides a preparation method of a super-hydrophobic film with high-temperature self-repairing performance.

[0019] Advantages of the application:

[0020] I. The main purpose of the application is to solve the problem of poor durability in the conventional super-hydrophobic modification of the membrane in the membrane distillation technology, and a preparation method of a super-hydrophobic film with high-temperature self-repairing performance is provided. Specifically, the PVDF film is used as the substrate, the surface of the film is modified by grafting fluorinated SiO2, the PVA (polyvinyl alcohol) is cast on the surface of the film to form a PVA layer, and then the fluorinated SiO2 solution is sprayed on the PVA layer on the surface of the film by the spray deposition method using a spray gun to prepare a P-P-S self-repairing super-hydrophobic film (a super-hydrophobic film with high-temperature self-repairing performance). Due to the high-temperature water-soluble property of PVA, compared with the untreated PVDF base film, the P-P-S self-repairing film has excellent hydrophobic performance and high-temperature self-repairing performance. When the surface layer of the film is damaged, the PVA dissolves in water at a high temperature above 85 DEG C, the super-hydrophobic surface of the bottom is exposed, and the hydrophobicity of the film is restored.

[0021] II. The application is simple to operate, improves the hydrophobicity and durability of the film surface, and is beneficial to long-term and repeated operation of the film in the membrane separation process.

[0022] III. The super-hydrophobic film with high-temperature self-repairing performance in the application not only has stable water flux during the initial operation process, but also has a certain degree of improvement in water flux after the self-repairing process due to the decrease in the overall thickness of the film. BRIEF DESCRIPTION OF DRAWINGS

[0023] Figure 1 The process of preparing the super-hydrophobic membrane with high-temperature self-repairing property and the self-repairing process in Example 1;

[0024] Figure 2 The contact angle, (a) is the contact angle of the super-hydrophobic layer on the top of the super-hydrophobic membrane with high-temperature self-repairing property prepared in Example 1, (b) is the contact angle of the super-hydrophobic layer after being damaged, and (c) is the contact angle of the super-hydrophobic membrane with high-temperature self-repairing property prepared in Example 1 after being repaired at high temperature;

[0025] Figure 3 The SEM image of the super-hydrophobic layer on the bottom of the composite membrane prepared in step 2(ii) of Example 1;

[0026] Figure 4 The SEM image of the PVA intermediate layer on the composite membrane prepared in step 3(ii) of Example 1;

[0027] Figure 5 The SEM image of the super-hydrophobic layer on the top of the super-hydrophobic membrane with high-temperature self-repairing property prepared in step 4 of Example 1;

[0028] Figure 6 The water flux diagram, 1 is the water flux of the super-hydrophobic membrane with high-temperature self-repairing property prepared in step 4 of Example 1, and 2 is the water flux of the super-hydrophobic membrane with high-temperature self-repairing property prepared in Example 1 after being repaired at high temperature;

[0029] Figure 7 The permeate conductivity diagram, 1 is the permeate conductivity of the super-hydrophobic membrane with high-temperature self-repairing property prepared in step 4 of Example 1, and 2 is the permeate conductivity of the super-hydrophobic membrane with high-temperature self-repairing property prepared in Example 1 after being repaired at high temperature. DETAILED DESCRIPTION

[0030] The following examples further illustrate the present application, but should not be construed as limiting the application. Modifications and variations of the methods, steps and conditions of the application are possible without departing from the spirit of the application.

[0031] Specific embodiment one: a method for preparing a super-hydrophobic membrane with high-temperature self-repairing property, which is completed according to the following steps:

[0032] I. Fenton reaction pretreatment:

[0033] The PVDF base film is immersed in a mixed solution of FeSO4·7H2O, H2O2, anhydrous ethanol and deionized water, then a Fenton reaction is carried out under heating, the PVDF base film is cleaned with sulfuric acid, and finally vacuum drying is performed to obtain a pretreated PVDF base film;

[0034] II. Preparation of the bottom super-hydrophobic layer:

[0035] ①, first, the SiO2 nanoparticles are dissolved in cyclohexane, magnetically stirred, ultrasonically dispersed, and then 1H, 1H, 2H, 2H-perfluorooctyltrichlorosilane is added dropwise, and ultrasonic dispersion is continued to obtain a PFTS / SiO2 solution;

[0036] ②, the pretreated PVDF base film is immersed in the PFTS / SiO2 solution, and then vacuum dried after being taken out, to obtain a composite film containing a bottom super-hydrophobic layer;

[0037] III. Preparation of the PVA intermediate layer:

[0038] ①, polyvinyl alcohol and deionized water are mixed, then stirred under heating, and then anhydrous ethanol is added to obtain a mixed solution;

[0039] ②, the mixed solution is uniformly cast onto the composite film containing the bottom super-hydrophobic layer, and then a film applicator is used to control the thickness of the mixed solution on the bottom super-hydrophobic layer, and finally dried at room temperature to obtain a composite film containing a PVA intermediate layer;

[0040] IV. Preparation of the top super-hydrophobic layer:

[0041] The PFTS / SiO2 solution is sprayed onto the surface of the composite film containing the PVA intermediate layer using an airbrush, left to stand, and then air-dried to obtain a super-hydrophobic film with high-temperature self-repairing performance.

[0042] Specific implementation method two: the difference between this implementation method and specific implementation method one is that the mass and volume ratio of FeSO4·7H2O to H2O2 in step one is (1g-2g):(5mL-7mL); the volume ratio of H2O2, anhydrous ethanol and deionized water in step one is (5-7):(40-60):(40-60). The other steps are the same as specific implementation method one.

[0043] Specific implementation method three: the difference between this implementation method and one of specific implementation method one or two is that the mass fraction of H2O2 in step one is 30%; the temperature of the Fenton reaction in step one is 40℃-60℃, and the time of the Fenton reaction is 1h-2h; the mass fraction of sulfuric acid in step one is 98%; the temperature of vacuum drying in step one is 60℃-80℃. The other steps are the same as specific implementation method one or two.

[0044] Specific embodiment four: the difference between this embodiment and one of the specific embodiments one to three is that the mass ratio of SiO2 nanoparticles, 1H, 1H, 2H, 2H-perfluorooctyltrichlorosilane and cyclohexane in step two ① is 1:(1-2):50. The other steps are the same as specific embodiments one to three.

[0045] Specific embodiment five: the difference between this embodiment and one of the specific embodiments one to four is that the speed of magnetic stirring in step two ① is 40 r / min-60 r / min, and the time of magnetic stirring is 20 min-40 min; the time of ultrasonic dispersion in step two ① is 15 min-25 min, and the power of ultrasonic dispersion is 350 W-500 W. The other steps are the same as specific embodiments one to four.

[0046] Specific embodiment six: the difference between this embodiment and one of the specific embodiments one to five is that the pretreated PVDF base film is immersed in the PFTS / SiO2 solution for 3 h-5 h in step two ②; the temperature of vacuum drying in step two ② is 60℃-80℃. The other steps are the same as specific embodiments one to five.

[0047] Specific embodiment seven: the difference between this embodiment and one of the specific embodiments one to six is that the mass ratio of polyvinyl alcohol and deionized water in step three ① is 1:(6-8); the mass ratio of polyvinyl alcohol and the volume of anhydrous ethanol in step three ① is (1 g-2 g):1 mL; the temperature of stirring in step three ① is 70℃-80℃, and the time of stirring is 1 h-2 h. The other steps are the same as specific embodiments one to six.

[0048] Specific embodiment eight: the difference between this embodiment and one of the specific embodiments one to seven is that the thickness of the mixed solution on the super-hydrophobic composite film is controlled to be 400 μm-600 μm using a film applicator in step three ②. The other steps are the same as specific embodiments one to seven.

[0049] Specific embodiment nine: the difference between this embodiment and one of the specific embodiments one to eight is that the pressure of spraying in step four is 0.2 MPa-0.6 MPa, the spraying distance is 10 cm-17 cm, and the standing time after spraying is 20 min-40 min; the temperature of air drying in step four is 60℃-70℃, and the time of air drying is 3 h-5 h. The other steps are the same as specific embodiments one to eight.

[0050] Specific embodiment ten: this embodiment is a super-hydrophobic film with high-temperature self-repairing performance used as a membrane for membrane distillation.

[0051] The beneficial effects of the present application are verified by the following examples:

[0052] Embodiment 1: A method for preparing a super-hydrophobic film with high-temperature self-repairing performance, specifically completed according to the following steps:

[0053] I. Fenton reaction pretreatment:

[0054] The PVDF base film is immersed in a mixed solution of 1.39 g FeSO4·7H2O, 6 mL H2O2, 50 mL anhydrous ethanol and 50 mL deionized water, then Fenton reaction is carried out at 50℃ for 1 h, the PVDF base film is cleaned with sulfuric acid, and finally vacuum drying is carried out at 70℃ to obtain the pretreated PVDF base film;

[0055] The mass fraction of H2O2 in step one is 30%;

[0056] The mass fraction of sulfuric acid in step one is 98%;

[0057] II. Preparation of the bottom super-hydrophobic layer:

[0058] ①, First, the SiO2 nanoparticles are dissolved in cyclohexane, magnetically stirred at a stirring speed of 40 r / min for 30 min, ultrasonically dispersed at a power of 450 W for 20 min, and then 1H, 1H, 2H, 2H-perfluorooctyltrichlorosilane (PFTS) is added dropwise, and ultrasonic dispersion is continued to obtain a PFTS / SiO2 solution;

[0059] The mass ratio of SiO2 nanoparticles, 1H, 1H, 2H, 2H-perfluorooctyltrichlorosilane and cyclohexane in step two ① is 1:1.5:50;

[0060] ②, The pretreated PVDF base film is immersed in the PFTS / SiO2 solution for 4 h, and then vacuum dried at 70℃ to obtain a composite film containing a bottom super-hydrophobic layer;

[0061] III. Preparation of PVA intermediate layer:

[0062] ①, 1 g of polyvinyl alcohol and 7 g of deionized water are mixed, then stirred at 80℃ for 1 h, and then 1 mL of anhydrous ethanol is added to obtain a mixed solution;

[0063] ②, The mixed solution is uniformly cast onto the composite film containing the bottom super-hydrophobic layer, a film applicator is used to control the thickness of the mixed solution on the bottom super-hydrophobic layer, and finally dried at room temperature to obtain a composite film containing a PVA intermediate layer;

[0064] The thickness of the mixed solution on the super-hydrophobic composite film controlled by the film applicator in step three ② is 500 μm;

[0065] IV. Preparation of the top super-hydrophobic layer:

[0066] The PFTS / SiO2 solution was sprayed on the surface of the composite film containing the PVA intermediate layer using a spray gun, left to stand for 30 min, and then air-dried at 60°C for 4 h to obtain a super-hydrophobic film with high-temperature self-repairing performance (P-P-S film);

[0067] The spraying pressure in step four was 0.2 MPa, and the spraying distance was 10 cm.

[0068] Example 2: The difference between this example and Example 1 is that the mass ratio of the SiO2 nanoparticles, 1H, 1H, 2H, 2H-perfluorooctyltrichlorosilane and cyclohexane in step two ① is 1:2:50. The other steps and parameters are the same as those in Example 1.

[0069] Example 3: The difference between this example and Example 1 is that the spraying pressure in step four is 0.5 MPa, and the spraying distance is 15 cm. The other steps and parameters are the same as those in Example 1.

[0070] The super-hydrophobic layer on the top of the super-hydrophobic film with high-temperature self-repairing performance prepared in step four of Example 1 was rubbed off with sandpaper, and the hydrophobicity of the film itself was greatly reduced. At this time, the film was placed in a high-temperature water environment above 85°C, and due to the high-temperature solubility of PVA, the PVA intermediate layer was dissolved, exposing the bottom super-hydrophobic layer, and realizing the self-repairing process.

[0071] Figure 1 The process of preparing the super-hydrophobic film with high-temperature self-repairing performance in Example 1 and the self-repairing process;

[0072] Figure 2 The contact angle, (a) is the contact angle of the super-hydrophobic layer on the top of the super-hydrophobic film with high-temperature self-repairing performance prepared in Example 1, (b) is the contact angle of the super-hydrophobic layer on the top of the super-hydrophobic film with high-temperature self-repairing performance prepared in Example 1 after being damaged, and (c) is the contact angle of the super-hydrophobic film with high-temperature self-repairing performance prepared in Example 1 after being repaired at high temperature;

[0073] From Figure 2 It can be seen that after the high-temperature self-repairing process, the static water contact angle on the surface can be restored to the initial value.

[0074] Figure 3 The SEM image of the bottom super-hydrophobic layer on the composite film prepared in step two ② of Example 1;

[0075] Figure 4 The SEM image of the PVA intermediate layer on the composite film prepared in step three ② of Example 1;

[0076] Figure 5The image shows the top superhydrophobic layer of the superhydrophobic membrane with high-temperature self-healing properties prepared in step four of Example 1.

[0077] from Figures 3 to 5 It can be seen that the superhydrophobic membrane with high-temperature self-healing properties prepared in step four of Example 1 has a three-layer hierarchical structure. When the PVA layer is successfully prepared, the bottom superhydrophobic surface is covered and protected. The particle state of the top superhydrophobic surface prepared by the spray deposition method is different from that of the bottom superhydrophobic surface prepared by the surface grafting method, but both can greatly improve the hydrophobicity of the membrane.

[0078] Figure 6 The figure shows the water flux diagram. In the figure, 1 represents the water flux of the superhydrophobic membrane with high temperature self-healing properties prepared in step four of Example 1, and 2 represents the water flux of the superhydrophobic membrane with high temperature self-healing properties prepared in Example 1 after high temperature repair.

[0079] from Figure 6 It can be seen that the superhydrophobic membrane with high-temperature self-healing properties prepared in step four of Example 1 not only has a stable water flux during the initial operation, but also has a certain degree of increase in water flux after the self-healing process is completed due to the decrease in the overall thickness of the membrane.

[0080] Figure 7 The graph shows the permeate conductivity. In the graph, 1 represents the permeate conductivity of the superhydrophobic membrane with high-temperature self-healing properties prepared in step four of Example 1, and 2 represents the permeate conductivity of the superhydrophobic membrane with high-temperature self-healing properties prepared in Example 1 after high-temperature repair.

[0081] from Figure 7 It can be seen that the superhydrophobic membrane with high-temperature self-healing properties prepared in step four of Example 1 did not show a significant increase in the permeate conductivity after the self-healing process was completed.

Claims

1. Use of a superhydrophobic film having a high-temperature self-repairing property, characterized in that The application discloses a super-hydrophobic film with high-temperature self-repairing performance, which is used as a film for membrane distillation. The application further discloses a preparation method of the super-hydrophobic film with high-temperature self-repairing performance. I. Fenton reaction pretreatment The PVDF base film is immersed in a mixed solution of 1.39g FeSO4·7H2O, 6mL H2O2, 50mL anhydrous ethanol and 50mL deionized water, then Fenton reaction is carried out at 50 DEG C for 1h, the PVDF base film is cleaned by using sulfuric acid, and finally vacuum drying is carried out at 70 DEG C, so as to obtain the pretreated PVDF base film; The mass fraction of H2O2 in step one is 30%; The mass fraction of sulfuric acid in step one is 98%; II. Preparation of bottom super-hydrophobic layer ①, firstly, the SiO2 nanoparticles are dissolved in cyclohexane, magnetic stirring is carried out at a stirring speed of 40r / min for 30min, ultrasonic dispersion is carried out at a power of 450W for 20min, and then 1H, 1H, 2H, 2H-perfluorooctyltrichlorosilane is added dropwise, and ultrasonic dispersion is continued, so as to obtain the PFTS / SiO2 solution; The mass ratio of SiO2 nanoparticles, 1H, 1H, 2H, 2H-perfluorooctyltrichlorosilane and cyclohexane in step two ① is 1:1.5:50; ②, the pretreated PVDF base film is immersed in the PFTS / SiO2 solution for 4h, and then vacuum drying is carried out at 70 DEG C after being taken out, so as to obtain the composite film containing the bottom super-hydrophobic layer; III. Preparation of PVA intermediate layer ①, 1g polyvinyl alcohol and 7g deionized water are mixed, then stirring is carried out at 80 DEG C for 1h, and then 1mL anhydrous ethanol is added, so as to obtain a mixed solution; ②, the mixed solution is uniformly cast on the composite film containing the bottom super-hydrophobic layer, a film applicator is used to control the thickness of the mixed solution on the bottom super-hydrophobic layer, and finally drying is carried out at room temperature, so as to obtain the composite film containing the PVA intermediate layer; The thickness of the mixed solution on the super-hydrophobic composite film controlled by the film applicator in step three ② is 500μm; IV. Preparation of top super-hydrophobic layer The PFTS / SiO2 solution is sprayed on the surface of the composite film containing the PVA intermediate layer by using a spray gun, and then standing is carried out for 30min, air blowing drying is carried out at 60 DEG C for 4h, so as to obtain the super-hydrophobic film with high-temperature self-repairing performance; The pressure of spraying in step four is 0.2MPa, and the spraying distance is 10cm.

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