Preparation method of hydrophilic-hydrophobic composite Janus membrane and hydrophilic-hydrophobic composite Janus membrane

Abstract

The application relates to a preparation method of a hydrophilic-hydrophobic composite Janus membrane and the hydrophilic-hydrophobic composite Janus membrane, and belongs to the technical field of membranes. The preparation method comprises the following steps: firstly, a hydrophobic porous base membrane is immersed and washed with an organic solvent and deionized water in sequence, and the cleaned hydrophobic porous base membrane is obtained after drying; then, a hydrophilic coating aqueous dispersion is diluted by using a dispersing agent to obtain diluted hydrophilic coating aqueous dispersion; the diluted hydrophilic coating aqueous dispersion is placed in a gas phase spraying gun; finally, the cleaned hydrophobic porous base membrane is horizontally laid on a constant-temperature heating table, a gas phase spraying gun is used to perform a gas phase deposition process on the surface of the cleaned hydrophobic porous base membrane, and the hydrophilic-hydrophobic composite Janus membrane is obtained after drying. The method has the advantages of fast preparation speed, simple operation, high flux and excellent desalination performance of the prepared hydrophilic-hydrophobic composite Janus membrane, and the like. Experimental determination shows that the hydrophilic-hydrophobic composite Janus membrane can greatly improve the water production rate in the process, and the desalination rate reaches 99.9%.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of membrane separation, and particularly relates to a preparation method of a hydrophilic-hydrophobic composite Janus membrane and the hydrophilic-hydrophobic composite Janus membrane. BACKGROUND

[0002] To alleviate the problem of water resource shortage, water desalination treatment and reuse technology has become a key method to solve the problem. At present, the water desalination treatment technology mainly takes membrane distillation technology as the main method. In the membrane distillation process, the low-temperature fresh water and the high-temperature water to be treated are physically separated by a hydrophobic porous membrane. The liquids on both sides of the membrane cannot enter the inside of the hydrophobic membrane hole, and only the water vapor on the high-temperature water to be treated side can be transferred across the membrane under the driving of the heat penetration force and condensed on the low-temperature fresh water side. Therefore, the membrane distillation process theoretically has 100% rejection effect on non-volatile substances. However, in the actual application process, the hydrophobic porous membrane often has a high penetration pressure, which causes the water vapor generated on the high-temperature water to be treated side to be difficult to enter the inside of the hydrophobic porous membrane, thereby causing problems such as low treatment efficiency. Therefore, in recent years, a hydrophilic-hydrophobic composite Janus membrane has been proposed to solve the problem that the water vapor is difficult to enter the inside of the hydrophobic porous membrane. CN115253717A discloses a preparation method of a hydrophilic-hydrophobic composite Janus membrane based on an interfacial polymerization technology. The method proposes a method for triggering an interfacial polymerization reaction without surface pretreatment of the hydrophobic porous membrane, that is, by utilizing the characteristic that the oil phase monomer solution can completely wet the hydrophobic porous membrane, the hydrophobic porous membrane is first immersed in the oil phase monomer solution, and then taken out and contacted with the water phase monomer solution to trigger the interfacial polymerization reaction. In this way, an ultrathin hydrophilic coating layer is coated on the surface of the hydrophobic porous membrane to form a hydrophilic-hydrophobic composite Janus membrane. However, when the feed liquid contains a low-surface-tension substance such as a surfactant, the moisture resistance of the hydrophilic-hydrophobic composite Janus membrane obtained by the method is unknown. At the same time, due to the direct contact of the interfacial polymerization reaction, the micropores in the hydrophobic porous membrane are easy to be blocked, thereby affecting the membrane flux. CN118422418A discloses a technology for preparing a composite Janus fiber membrane with hydrophilicity and hydrophobicity by an asymmetric distribution spinning method. The method prepares a hydrophilic spinning solution containing a zwitterion and a hydrophobic spinning solution respectively, spins by a micro-injection pump to obtain a hydrophilic layer fiber membrane, and then continuously spins the hydrophobic solution on the hydrophilic layer fiber membrane to form a hydrophobic layer fiber membrane, thereby obtaining a composite Janus fiber membrane with hydrophilicity and hydrophobicity. Similarly, the moisture resistance of the hydrophilic-hydrophobic composite Janus fiber membrane obtained by the method is unknown, and the preparation process is complex, the controllability is poor, and it is not conducive to large-scale production and product quality control.

[0003] Therefore, it is urgent to develop a preparation method of a hydrophilic-hydrophobic composite Janus membrane with simple preparation process and stable structure. The gas deposition technology is a new technology for forming a coating layer with special performance on the surface of a substrate by changing the surface composition of the substrate through physical and chemical processes in the gas phase. The gas deposition technology can overcome the complex problem of treating the surface of a hydrophobic porous substrate, and the prepared hydrophilic-hydrophobic composite Janus membrane has the advantages of good uniformity, low risk of blocking the pores of the hydrophobic porous substrate, and high membrane flux. SUMMARY

[0004] The application provides a preparation method of a hydrophilic-hydrophobic composite Janus membrane to solve the problem of low evaporation rate of a conventional hydrophobic porous membrane. The conventional hydrophobic porous membrane is modified on one side to have hydrophilic properties, so that the hydrophobic porous membrane with hydrophobic properties on both sides is changed into a hydrophilic-hydrophobic composite Janus membrane with hydrophobic properties on one side and hydrophilic properties on the other side. Experimental verification shows that the prepared hydrophilic-hydrophobic composite Janus membrane can effectively improve the water production rate of a water desalination process based on the principle of thermal permeation.

[0005] In a first aspect, the application provides a preparation method of a hydrophilic-hydrophobic composite Janus membrane, which comprises the following steps: (1) immersing and washing a hydrophobic porous substrate in an organic solvent and deionized water, respectively, drying the hydrophobic porous substrate in a drying box after immersion and washing to obtain a clean hydrophobic porous membrane; (2) diluting a hydrophilic coating aqueous dispersion to obtain a diluted hydrophilic coating aqueous dispersion; (3) placing the diluted hydrophilic coating aqueous dispersion in a gas phase spray gun; (4) placing the clean hydrophobic porous membrane on a constant temperature heating table, and performing gas phase deposition treatment on the upper surface of the clean hydrophobic porous membrane with the gas phase spray gun to obtain a hydrophilic-hydrophobic composite Janus membrane after drying treatment.

[0006] In the preparation method of the hydrophilic-hydrophobic composite Janus membrane provided by the application, the hydrophobic porous substrate in step (1) is any one of an organic hydrophobic porous substrate, an inorganic hydrophobic porous substrate, or an organic-inorganic composite hydrophobic porous substrate; preferably, the material of the hydrophobic porous substrate comprises any one or a combination of at least two of fluorine-based polymers, alkane-based polymers, olefin-based polymers, sulfone-based polymers, carbon nanotubes, graphene, or phosphorene; further preferably, the hydrophobic porous substrate comprises any one of a polytetrafluoroethylene hydrophobic porous substrate, a polyvinylidene fluoride hydrophobic porous substrate, a polypropylene hydrophobic porous substrate, a polyethylene hydrophobic porous substrate, a polysulfone hydrophobic porous substrate, or a polyether sulfone hydrophobic porous substrate; preferably, the hydrophobic porous substrate comprises any one of a flat sheet hydrophobic porous substrate, a hollow fiber hydrophobic porous substrate, a tubular hydrophobic porous substrate, or a rolled hydrophobic porous substrate; and preferably, the pore size of the hydrophobic porous substrate is 0.05-1.0 μm.

[0007] According to the preparation method of the hydrophilic-hydrophobic composite Janus film provided by the application, the organic solvent in step (1) comprises any one or a combination of at least two of ethanol, diethyl ether, acetone or petroleum ether.

[0008] According to the preparation method of the hydrophilic-hydrophobic composite Janus film provided by the application, the dispersoid of the hydrophilic coating aqueous dispersion in step (2) comprises any one of single-walled carbon nanotubes, double-walled carbon nanotubes and multi-walled carbon nanotubes modified by a functional group; preferably, the modified functional group is at least one of a carboxyl group (-COOH), a hydroxyl group (-OH) and a carbonyl group (-C=O); preferably, the length of the single-walled carbon nanotubes, the double-walled carbon nanotubes and the multi-walled carbon nanotubes is 0.5-30 μm; preferably, the outer diameter of the single-walled carbon nanotubes, the double-walled carbon nanotubes and the multi-walled carbon nanotubes is 2-80 nm.

[0009] According to the preparation method of the hydrophilic-hydrophobic composite Janus film provided by the application, the concentration of the diluted hydrophilic coating aqueous dispersion in step (2) is 0.1-5 wt%.

[0010] According to the preparation method of the hydrophilic-hydrophobic composite Janus film provided by the application, the air flow of the gas-phase spray gun in step (3) is 0.5-7.5 L / min.

[0011] According to the preparation method of the hydrophilic-hydrophobic composite Janus film provided by the application, the temperature of the constant-temperature heating table in step (4) is set to 60-150℃; preferably, the time for which the clean hydrophobic porous film is subjected to the gas-phase deposition treatment on the constant-temperature heating table is 10-360 s; and preferably, the amount of the diluted hydrophilic coating aqueous dispersion used for the gas-phase deposition treatment of the clean hydrophobic porous base film on the constant-temperature heating table is 0.04-0.4 ml / cm 2 ;

[0012] According to the preparation method of the hydrophilic-hydrophobic composite Janus film provided by the application, the temperature for drying the clean hydrophobic porous film after the gas-phase deposition treatment in step (4) is not higher than 80℃.

[0013] In a second aspect, the application further provides a hydrophilic-hydrophobic composite Janus film, which is prepared by the preparation method according to the first aspect.

[0014] The application provides a preparation method of a hydrophobic-hydrophilic composite Janus membrane and the hydrophobic-hydrophilic composite Janus membrane, and the preparation method comprises the following steps: sequentially immersing and washing a hydrophobic porous base film in an organic solvent and deionized water, and drying the hydrophobic porous base film after immersion and washing in a drying box to obtain a clean hydrophobic porous membrane; diluting a hydrophilic coating aqueous dispersion liquid by using a dispersing agent to obtain a diluted hydrophilic coating aqueous dispersion liquid; placing the diluted hydrophilic coating aqueous dispersion liquid in a gas phase spray gun; placing the clean hydrophobic porous membrane on a constant temperature heating table, and performing gas phase deposition treatment on the upper surface of the clean hydrophobic porous membrane by using the gas phase spray gun, so that the hydrophobic-hydrophilic composite Janus membrane is obtained after drying treatment. The preparation method has the characteristics of low cost of raw materials, low production cost and simple operation, and the water production rate can be significantly improved compared with the hydrophobic porous membrane used in conventional water treatment technology. BRIEF DESCRIPTION OF DRAWINGS

[0015] Figure 1 A flowchart of a preparation method of a hydrophobic-hydrophilic composite Janus membrane provided for the embodiment 1 of the application is shown in the figure.

[0016] Figure 2 The contact angle test figures and the surface morphology figures of the PTFE / MWCNTS-COOH hydrophobic-hydrophilic composite Janus membrane prepared in the embodiment 1 of the application before and after the gas phase deposition treatment are shown in the figures.

[0017] Figure 3 The figure showing the change of the desalination effect with time during the water desalination treatment process lasting for 12 hours by using the PTFE / MWCNTS-COOH hydrophobic-hydrophilic composite Janus membrane prepared in the embodiment 1 of the application is shown in the figure.

[0018] Figure 4 The figure showing the change of the ion concentration of the salt water before and after the treatment by using the PTFE / MWCNTS-COOH hydrophobic-hydrophilic composite Janus membrane prepared in the embodiment 1 of the application to carry out the water desalination experiment under a temperature difference of 40K is shown in the figure.

[0019] Figure 5 The figure showing the water production rate under different temperature differences by using the PTFE / MWCNTS-COOH hydrophobic-hydrophilic composite Janus membrane prepared in the embodiment 1 of the application and the clean polytetrafluoroethylene (PTFE) microfiltration membrane without gas phase deposition treatment to carry out the water desalination experiment is shown in the figure. DETAILED DESCRIPTION

[0020] The application will be further described in conjunction with specific examples and drawings. It should be understood that these examples are only used to illustrate the application and not used to limit the scope of the application. In addition, it should be understood that those skilled in the art can make various modifications or changes to the application after reading the content of the application, and these equivalent forms also fall within the scope of the appended claims.

[0021] Example 1

[0022] Figure 1 A flowchart of a method for preparing a hydrophilic-hydrophobic composite Janus membrane is shown. The hydrophobic porous base membrane used in this embodiment 1 is a polytetrafluoroethylene (PTFE) microfiltration membrane with a pore size of 0.45 μm and a membrane thickness of 150 μm. The hydrophilic coating aqueous dispersion used is a 5 wt% multi-walled carbon nanotube (MWCNTs-COOH) aqueous dispersion. The multi-walled carbon nanotube has a length of 10-30 um, an outer diameter of 5-15 nm, and a carboxyl (-COOH) content of 3.86 wt%. The preparation steps are as follows:

[0023] Step 101: First, the polytetrafluoroethylene (PTFE) microfiltration membrane is immersed in acetone to remove residual grease on the surface, then immersed in deionized water, and then placed in a forced air drying oven for drying treatment at a temperature of 50°C for 8 min to obtain a clean polytetrafluoroethylene (PTFE) microfiltration membrane.

[0024] Step 102: Mix the 5 wt% multi-walled carbon nanotube (MWCNTs-COOH) aqueous dispersion with deionized water, and stir in a stirred tank for 10 min to obtain a 0.1 wt% multi-walled carbon nanotube (MWCNTs-COOH) aqueous dispersion.

[0025] Step 103: Place the 0.1 wt% multi-walled carbon nanotube (MWCNTs-COOH) aqueous dispersion obtained in step 102 in a gas phase spray gun, and adjust the air flow of the gas phase spray gun to 7 L / min.

[0026] Step 104: Set the temperature of the constant temperature heating table to 80℃, and after the temperature reaches the set temperature, the clean polytetrafluoroethylene (PTFE) microfiltration membrane obtained after the drying treatment in step 101 is laid flat on the constant temperature heating table. At the same time, adjust the direction of the gas phase spray gun so that the spray head is evenly opposite to the upper surface of the clean polytetrafluoroethylene (PTFE) microfiltration membrane, and set the time for gas phase deposition treatment to 60s, i.e. 0.1ml of 0.1wt% multi-walled carbon nanotube (MWCNTs-COOH) aqueous dispersion solution is corresponding to the upper surface of each square centimeter of the clean polytetrafluoroethylene (PTFE) microfiltration membrane for gas phase deposition. The gas phase deposition treatment time can be flexibly adjusted according to the air flow of the gas phase spray gun and the strength of the hydrophilic properties of the hydrophilic coating to be prepared. After the gas phase deposition treatment is completed, the obtained PTFE / MWCNTS-COOH hydrophilic and hydrophobic composite Janus membrane is placed in a vacuum drying box for drying treatment at a temperature of 50℃ for a time of 600s, and finally the PTFE / MWCNTS-COOH hydrophilic and hydrophobic composite Janus membrane is obtained.

[0027] The contact angle of the PTFE / MWCNTS-COOH hydrophilic and hydrophobic composite Janus membrane prepared above is measured to verify whether it is successfully prepared. The prepared PTFE / MWCNTS-COOH hydrophilic and hydrophobic composite Janus membrane can be applied to direct contact membrane distillation processes, such as seawater desalination, industrial or municipal wastewater treatment, biomass solution concentration, etc.

[0028] Performance analysis of the PTFE / MWCNTS-COOH hydrophilic and hydrophobic composite Janus membrane prepared in Example 1 is carried out.

[0029] Figure 2 is a sample diagram of a clean polytetrafluoroethylene (PTFE) microfiltration membrane and a PTFE / MWCNTS-COOH hydrophilic and hydrophobic Janus membrane prepared in Example 1. From Figure 2 (a) and Figure 2 (b) of it can be seen that the upper surface and the lower surface of the clean polytetrafluoroethylene (PTFE) microfiltration membrane have different contact angles, but both exhibit strong hydrophobicity; Figure 2 (c) of it is the hydrophilic surface of the PTFE / MWCNTS-COOH hydrophilic and hydrophobic Janus membrane prepared in Example 1, which has a significant decrease in contact angle and exhibits strong hydrophilicity.

[0030] Figure 3The conductivity change graph of the produced water at different time periods obtained by using the PTFE / MWCNTS-COOH hydrophilic and hydrophobic composite Janus film prepared in Embodiment 1 to perform water desalination treatment experiment. The experiment was performed under the condition that the low-temperature end temperature was constant at 298.15 K and the high-temperature end temperature was constant at 338.15 K, and artificial seawater with a salinity of 30 ‰ was artificially configured by using seawater element (purchased from Jiangxi Yantong Technology Co., Ltd.) as the water to be desalinated, and the PTFE / MWCNTS-COOH hydrophilic and hydrophobic composite Janus film prepared in Embodiment 1 was subjected to water desalination treatment experiment based on the heat penetration principle under a temperature difference of 40 K. In order to minimize errors as much as possible, each working condition was independently subjected to 3 experiments, and the average value of the results of the 3 experiments was taken as the final experimental result. The results show that, in the case of every 2 hours as a unit of time, the experiment was continuously performed for 12 hours, and within 12 hours, the conductivity of the treated water only had a slight change, and at the 12th hour, the average conductivity of the treated water was only 17.5 μs / cm. According to the provisions of the “Drinking Water Health Standards” (GB5749-2006) of China, the conductivity of drinking water should be below 250 μs / cm, and the results show that the PTFE / MWCNTS-COOH hydrophilic and hydrophobic composite Janus film prepared in Embodiment 1 can still maintain stable desalination effect in the long-term water desalination treatment process.

[0031] Figure 4 The purification effect data graph of the PTFE / MWCNTS-COOH hydrophilic and hydrophobic composite Janus film prepared by the application. Under the condition that the low-temperature end temperature was constant at 298.15 K and the high-temperature end temperature was constant at 338.15 K, artificial seawater was used as the salt water to be treated, and the PTFE / MWCNTS-COOH hydrophilic and hydrophobic composite Janus film was subjected to water desalination treatment experiment based on the heat penetration principle, and the four kinds of metal salt ions of the artificial seawater before desalination treatment and the water after 12 hours of continuous desalination treatment were determined. The results are shown in the figure. Compared with before desalination treatment, the ion concentration in the salt water obtained after water desalination treatment was reduced by 99.9%, which shows that the PTFE / MWCNTS-COOH hydrophilic and hydrophobic composite Janus film prepared by the application has high reliability in water desalination treatment.

[0032] Figure 5A water production rate diagram under different temperature differences obtained by using the PTFE / MWCNTS-COOH hydrophilic-hydrophobic composite Janus membrane prepared in Embodiment 1 of the present application and a clean polytetrafluoroethylene (PTFE) microfiltration membrane for water desalination treatment experiments. The experiment is carried out under the condition that the low-temperature end temperature is kept constant at 298.15 K, the high-temperature end temperature is increased, and artificial seawater is used as water to be desalinated. The water desalination treatment experiment based on the heat penetration principle is carried out on the two membranes under different temperature differences. The results show that the water production rate of the PTFE / MWCNTS-COOH hydrophilic-hydrophobic composite Janus membrane is higher than that of the clean polytetrafluoroethylene (PTFE) microfiltration membrane within 12 hours, which proves that the PTFE / MWCNTS-COOH hydrophilic-hydrophobic composite Janus membrane prepared in the present application has a higher water production rate than the clean polytetrafluoroethylene (PTFE) microfiltration membrane used in the traditional process in the water desalination treatment process.

Claims

1. A method for preparing a hydrophilic-hydrophobic composite Janus membrane, characterized in that, The preparation method comprises the following steps: (1) sequentially immersing and washing a hydrophobic porous base film in an organic solvent and deionized water, and drying the hydrophobic porous base film after immersion and washing in a drying box to obtain a clean hydrophobic porous membrane; (2) diluting a hydrophilic coating aqueous dispersion with a dispersant to obtain a diluted hydrophilic coating aqueous dispersion; (3) placing the diluted hydrophilic coating aqueous dispersion in a gas phase spray gun; (4) placing the clean hydrophobic porous membrane on a constant temperature heating table, and performing gas phase deposition treatment on the upper surface of the clean hydrophobic porous membrane with the gas phase spray gun, and obtaining the hydrophilic-hydrophobic composite Janus membrane after drying treatment; The solute of the hydrophilic coating aqueous dispersion in step (2) comprises any one of a single-walled carbon nanotube, a double-walled carbon nanotube, and a multi-walled carbon nanotube modified by a functional group, and the functional group is at least one of a carboxyl group, a hydroxyl group, and a carbonyl group; the concentration of the diluted hydrophilic coating aqueous dispersion is 0.1-5 wt%.

2. The production method according to claim 1, characterized by, The hydrophobic porous base film is any one of an organic hydrophobic porous base film, an inorganic hydrophobic porous base film, or an organic-inorganic composite hydrophobic porous base film; The material of the hydrophobic porous base film comprises any one or a combination of at least two of a fluorine-based polymer, an alkane-based polymer, an olefin-based polymer, a sulfone-based polymer, a carbon nanotube, graphene, or phosphorene; The hydrophobic porous base film comprises any one of a flat sheet type hydrophobic porous base film, a hollow fiber type hydrophobic porous base film, a tube type hydrophobic porous base film, or a roll type hydrophobic porous base film; The pore size of the hydrophobic porous base film is 0.05-1.0 μm.

3. The preparation method according to claim 2, characterized in that, The hydrophobic porous base film comprises any one of a polytetrafluoroethylene hydrophobic porous base film, a polyvinylidene fluoride hydrophobic porous base film, a polypropylene hydrophobic porous base film, a polyethylene hydrophobic porous base film, a polysulfone hydrophobic porous base film, or a polyether sulfone hydrophobic porous base film.

4. The method of claim 1, wherein, The length of the single-walled carbon nanotube, the double-walled carbon nanotube, and the multi-walled carbon nanotube is 0.5-30 μm; and the outer diameter of the single-walled carbon nanotube, the double-walled carbon nanotube, and the multi-walled carbon nanotube is 2-80 nm.

5. The preparation method according to claim 1, characterized in that, The gas flow rate of the gas phase spray gun is 0.5-7.5 L / min.

6. The method of claim 1, wherein, The temperature of the constant temperature heating table is set to 60-150℃; The time for which the clean hydrophobic porous membrane is subjected to gas phase deposition treatment on the constant temperature heating table is 10-360 s; The amount of diluted hydrophilic coating aqueous dispersion used for the vapor deposition treatment of the clean hydrophobic porous membrane on the constant temperature heating table is 0.04-0.4 ml / cm 2 .

7. The preparation method according to claim 1, characterized in that, The organic solvent comprises any one or a combination of at least two of ethanol, diethyl ether, acetone, or petroleum ether; The temperature for drying the clean hydrophobic porous membrane after gas phase deposition treatment is not higher than 80℃.

8. A hydrophilic-hydrophobic composite Janus membrane, characterized in that, The hydrophilic-hydrophobic composite Janus membrane is prepared by the preparation method of any one of claims 1-7.

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