Hydrophilic and hydrophobic composite Janus membrane preparation method and hydrophilic and hydrophobic composite Janus membrane

Abstract

The invention discloses a preparation method of a hydrophilic and hydrophobic composite Janus membrane and the hydrophilic and hydrophobic composite Janus membrane, and belongs to the technical field of membranes. The preparation method comprises the following steps: firstly, sequentially and respectively rinsing a hydrophobic porous base membrane by adopting an organic solvent and deionized water, drying to obtain a clean hydrophobic porous base membrane, then diluting a hydrophilic coating water-based dispersion liquid by utilizing a dispersing agent to obtain a diluted hydrophilic coating water-based dispersion liquid, and drying to obtain the hydrophilic coating water-based dispersion liquid. The preparation method comprises the following steps: diluting a hydrophilic coating aqueous dispersion liquid, placing the diluted hydrophilic coating aqueous dispersion liquid in a gas-phase spray gun, finally horizontally spreading a clean hydrophobic porous base membrane on a constant-temperature heating table, carrying out a gas-phase deposition process on the surface of the clean hydrophobic porous base membrane by using the gas-phase spray gun, and drying to obtain the hydrophilic and hydrophobic composite Janus membrane. The method has the advantages that the preparation speed is high, the operation is simple, the prepared hydrophilic and hydrophobic composite Janus membrane has the advantages of high flux, excellent desalination performance and the like, and experimental determination shows that the hydrophilic and 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 invention belongs to the technical field of membrane separation, and in particular relates to a method for preparing a hydrophilic-hydrophobic composite Janus membrane and the hydrophilic-hydrophobic composite Janus membrane. Background Art

[0002] In order to alleviate the problem of water shortage, water desalination and reuse technology has become a key method to solve this problem. At present, water desalination technology is mainly based on membrane distillation technology. In the membrane distillation process, low-temperature fresh water and high-temperature treated water are physically separated by a hydrophobic porous membrane. The liquid on both sides of the membrane cannot enter the hydrophobic membrane pores. Only the water vapor on the high-temperature treated water side can be transferred across the membrane under the drive of thermal osmotic force and condensed on the low-temperature fresh water side. Therefore, the membrane distillation process has a 100% interception effect on non-volatile substances in theory. However, in actual application, hydrophobic porous membranes often have a high osmotic pressure, which will cause the water vapor generated on the high-temperature treated water side to be difficult to enter the hydrophobic porous membrane, resulting in low treatment efficiency and other problems. For this reason, hydrophilic-hydrophobic composite Janus membranes have been proposed in recent years to solve the problem of water vapor having difficulty entering the interior of the hydrophobic porous membrane. CN115253717A discloses a method for preparing a hydrophilic-hydrophobic composite Janus membrane based on interfacial polymerization technology, and proposes a method for triggering an interfacial polymerization reaction without surface pretreatment of the hydrophobic porous membrane, that is, utilizing the characteristic that the oil phase monomer solution can completely wet the hydrophobic porous membrane, first immersing the hydrophobic porous membrane in the oil phase monomer solution, taking it out and then contacting it with the water phase monomer solution to trigger the interfacial polymerization reaction, thereby coating the surface of the hydrophobic porous membrane with an ultra-thin hydrophilic coating to prepare a hydrophilic-hydrophobic composite Janus membrane. However, when the feed liquid contains a low surface tension substance such as a surfactant, the wetting resistance of the hydrophilic-hydrophobic composite Janus membrane obtained by this method is unknown; at the same time, due to the direct contact interfacial polymerization reaction, the micropores inside the hydrophobic porous membrane are easily 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, wherein the method prepares a hydrophilic spinning solution and a hydrophobic spinning solution containing zwitterions respectively, spins through a microinjection pump to obtain a hydrophilic layer fiber membrane, and then continuously spins a 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 wetting resistance of the hydrophilic and hydrophobic composite Janus fiber membrane obtained by this method is unknown, and the preparation process is complicated and the controllability is poor, which is not conducive to large-scale production and product quality control.

[0003] Therefore, developing a preparation method with a simple preparation process and a stable structure of the hydrophilic and hydrophobic composite Janus membrane is an urgent technical problem that needs to be solved. Vapor deposition technology is a new technology that uses physical and chemical processes occurring in the gas phase to change the surface composition of the base membrane and form a coating of compounds with special properties on the surface. The use of vapor deposition technology can overcome the problem that related technologies are too complicated when processing the surface of hydrophobic porous base membranes, and the prepared hydrophilic and hydrophobic composite Janus membrane has the advantages of good uniformity, not easy to block the pores of the hydrophobic porous base membrane, and high membrane flux. Summary of the invention

[0004] The present invention proposes a method for preparing a hydrophilic-hydrophobic composite Janus membrane, which is used to solve the problems of low evaporation rate of conventional hydrophobic porous membranes. That is, by performing hydrophilic modification on one side of a conventional hydrophobic porous membrane, a hydrophobic porous membrane with hydrophobic properties on both sides is transformed 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 osmosis.

[0005] In a first aspect, the present invention provides a method for preparing a hydrophilic-hydrophobic composite Janus membrane, the preparation method comprising the following steps: (1) placing a hydrophobic porous base membrane in an organic solvent and deionized water for immersion in turn, placing the washed hydrophobic porous base membrane in a drying oven for drying 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 vapor phase spray gun; (4) spreading the clean hydrophobic porous membrane on a constant temperature heating table, performing vapor deposition treatment on the upper surface of the clean hydrophobic porous membrane with a vapor phase spray gun, and obtaining a hydrophilic-hydrophobic composite Janus membrane after drying.

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

[0007] According to the method for preparing the hydrophilic-hydrophobic composite Janus membrane provided by the present invention, the organic solvent in step (1) comprises any one of ethanol, ether, acetone or petroleum ether or a combination of at least two thereof;

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

[0009] According to the method for preparing the hydrophilic-hydrophobic composite Janus membrane provided by the present invention, the concentration of the diluted hydrophilic coating aqueous dispersion in step (2) is 0.1-5wt%;

[0010] According to the method for preparing the hydrophilic-hydrophobic composite Janus membrane provided by the present invention, the jet flow rate 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 membrane provided by the present invention, the temperature of the constant temperature heating platform in step (4) is set to 60-150° C.; preferably, the time for the clean hydrophobic porous membrane to be vapor-deposited on the constant temperature heating platform is 10-360 s; the amount of the diluted hydrophilic coating aqueous dispersion used for the vapor-deposited treatment of the clean hydrophobic porous base membrane on the constant temperature heating platform is 0.04-0.4 ml / cm 2 ;

[0012] According to the method for preparing the hydrophilic-hydrophobic composite Janus membrane provided by the present invention, the temperature of drying the clean hydrophobic porous membrane after the vapor deposition treatment in step (4) is not higher than 80°C.

[0013] In a second aspect, the present invention further provides a hydrophilic-hydrophobic composite Janus membrane, which is prepared by the preparation method of the first aspect.

[0014] The present invention provides a method for preparing a hydrophilic-hydrophobic composite Janus membrane and a hydrophilic-hydrophobic composite Janus membrane, wherein a hydrophobic porous base membrane is sequentially placed in an organic solvent and deionized water for leaching, and the hydrophobic porous base membrane after leaching is placed in a drying oven for drying treatment to obtain a clean hydrophobic porous membrane; a hydrophilic coating aqueous dispersion is diluted with a dispersant to obtain a diluted hydrophilic coating aqueous dispersion; the diluted hydrophilic coating aqueous dispersion is placed in a gas phase spray gun; the clean hydrophobic porous membrane is flattened on a constant temperature heating table, and the upper surface of the clean hydrophobic porous membrane is subjected to a vapor deposition treatment with a gas phase spray gun, and a hydrophilic-hydrophobic composite Janus membrane is obtained after drying treatment. The above-mentioned preparation method has the characteristics of cheap raw materials, low production cost, and simple operation of the preparation method. Compared with the hydrophobic porous membrane used in the experiment and conventional water treatment technology, the water production rate can be significantly improved. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1 A schematic flow chart of a method for preparing a hydrophilic-hydrophobic composite Janus membrane provided in Example 1 of the present invention;

[0016] Figure 2 The contact angle test graph and surface morphology graph of the PTFE / MWCNTS-COOH hydrophilic-hydrophobic composite Janus membrane prepared in Example 1 of the present invention before and after vapor deposition treatment;

[0017] Figure 3 This is a graph showing the change of desalination effect over time during a 12-hour water desalination process using the PTFE / MWCNTS-COOH hydrophilic-hydrophobic composite Janus membrane prepared in Example 1 of the present invention;

[0018] Figure 4 This is a graph showing the change in ion concentration of salt water before and after treatment obtained by conducting a water desalination experiment at a temperature difference of 40K using the PTFE / MWCNTS-COOH hydrophilic-hydrophobic composite Janus membrane prepared in Example 1 of the present invention;

[0019] Figure 5 The graphs show the water production rates at different temperature differences obtained by conducting a water desalination experiment using the PTFE / MWCNTS-COOH hydrophilic-hydrophobic composite Janus membrane prepared in Example 1 of the present invention and a clean polytetrafluoroethylene (PTFE) microfiltration membrane that has not been treated with vapor deposition. DETAILED DESCRIPTION

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

[0021] Example 1

[0022] Figure 1 The schematic flow diagram of a method for preparing a hydrophilic-hydrophobic composite Janus membrane provided in Example 1 is shown. The hydrophobic porous base membrane used in Example 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 uses a 5 wt % multi-walled carbon nanotube (MWCNTs-COOH) aqueous dispersion. The multi-walled carbon nanotube has a length of 10-30 μm, 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 soaked in acetone to remove residual grease on the surface, then soaked in deionized water, and then placed in a forced air drying oven at a temperature of 50° C. for 8 minutes to obtain a clean polytetrafluoroethylene (PTFE) microfiltration membrane.

[0024] Step 102: Take a 5 wt % aqueous dispersion of multi-walled carbon nanotubes (MWCNTs-COOH) and mix it with deionized water, and stir it in a stirred tank for 10 minutes to obtain a 0.1 wt % aqueous dispersion of multi-walled carbon nanotubes (MWCNTs-COOH).

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

[0026] Step 104: The temperature of the constant temperature heating platform is set to 80° C. After the temperature reaches the set temperature, the clean polytetrafluoroethylene (PTFE) microfiltration membrane obtained after the drying treatment in step 101 is spread flat on the constant temperature heating platform. At the same time, the direction of the vapor phase spray gun was adjusted so that the spray surface of the nozzle was evenly facing the upper surface of the clean polytetrafluoroethylene (PTFE) microfiltration membrane, and the vapor deposition treatment time was set to 60s, that is, 0.1ml of 0.1wt% multi-walled carbon nanotube (MWCNTs-COOH) aqueous dispersion was vapor deposited on the upper surface of the clean polytetrafluoroethylene (PTFE) microfiltration membrane per square centimeter. The vapor deposition treatment time can be flexibly adjusted according to the air flow rate of the vapor phase spray gun and the strength of the hydrophilic properties of the hydrophilic coating to be prepared. After the vapor deposition treatment, the obtained PTFE / MWCNTS-COOH hydrophilic and hydrophobic composite Janus membrane was placed in a vacuum drying oven and dried at a temperature of 50°C for 600s to finally obtain a PTFE / MWCNTS-COOH hydrophilic and hydrophobic composite Janus membrane.

[0027] The contact angle of the prepared PTFE / MWCNTS-COOH hydrophilic and hydrophobic composite Janus membrane is measured to verify whether the preparation is successful. 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 urban wastewater treatment, biomass solution concentration, etc.

[0028] The performance analysis of the PTFE / MWCNTS-COOH hydrophilic and hydrophobic composite Janus membrane prepared in Example 1 is as follows:

[0029] Figure 2 1 is a sample diagram of a clean tetrafluoroethylene (PTFE) microfiltration membrane and a PTFE / MWCNTS-COOH hydrophilic and hydrophobic Janus membrane prepared in Example 1. Figure 2 (a) and Figure 2 As can be seen from (b), the upper and lower surfaces of the clean polytetrafluoroethylene (PTFE) microfiltration membrane have different contact angles, but both are highly hydrophobic; Figure 2 (c) is the hydrophilic surface of the PTFE / MWCNTS-COOH hydrophilic and hydrophobic Janus membrane prepared in Example 1, and its contact angle is significantly reduced, showing strong hydrophilicity.

[0030] Figure 3The conductivity change diagram of the produced water under different time periods obtained by using the PTFE / MWCNTS-COOH hydrophilic and hydrophobic composite Janus membrane prepared in Example 1 of the present invention to carry out a water desalination treatment experiment. Under the condition that the temperature of the low temperature end is constant at 298.15K and the temperature of the high temperature end is constant at 338.15K, and artificial seawater with a salinity of 30‰ is artificially configured using seawater (purchased from Jiangxi Yantong Technology Co., Ltd.) as the water to be desalinated, the PTFE / MWCNTS-COOH hydrophilic and hydrophobic composite Janus membrane prepared in Example 1 of the present invention is subjected to a water desalination treatment experiment based on the principle of thermal osmosis at a temperature difference of 40K. At the same time, in order to reduce the error as much as possible, each working condition is independently carried out 3 times, and the average value of the 3 experimental results is taken as the final experimental result. The results show that the experiment lasted for 12 hours with a unit time of 2 hours. Within 12 hours, the conductivity of the treated water only changed slightly, and at the 12th hour, the average conductivity of the treated water was only 17.5μs / cm. According to the provisions of my country's "Drinking Water Hygiene Standard" (GB5749-2006), the conductivity of drinking water should be below 250μs / cm. This result shows that the PTFE / MWCNTS-COOH hydrophilic-hydrophobic composite Janus membrane prepared by Example 1 of the present invention can still maintain a stable desalination effect during a long-term water desalination treatment process.

[0031] Figure 4 The data diagram of the purification effect of the PTFE / MWCNTS-COOH hydrophilic-hydrophobic composite Janus membrane prepared by the present invention is shown. Under the condition that the temperature at the low temperature end is constant at 298.15K and the temperature at the high temperature end is constant at 338.15K, artificial seawater is used as the brine to be treated, and a water desalination treatment experiment based on the principle of thermal osmosis using the PTFE / MWCNTS-COOH hydrophilic-hydrophobic composite Janus membrane is carried out, and the artificial seawater before desalination treatment and the water after continuous 12 hours of desalination treatment are tested for 4 kinds of metal salt ions. As shown in the figure, compared with the water before desalination treatment, the ion concentration in the brine obtained after water desalination treatment is reduced by 99.9%, indicating that the PTFE / MWCNTS-COOH hydrophilic-hydrophobic composite Janus membrane prepared by the present invention has extremely high reliability in water desalination treatment.

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

Claims

1. A method for preparing a hydrophilic-hydrophobic composite Janus membrane, characterized in that: The preparation method comprises the following steps: (1) washing the hydrophobic porous base membrane in an organic solvent and deionized water respectively, and drying the washed hydrophobic porous base membrane in a drying oven to obtain a clean hydrophobic porous membrane; (2) diluting the hydrophilic coating aqueous dispersion using 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) Spreading the clean hydrophobic porous membrane flat on a constant temperature heating table, performing vapor deposition treatment on the upper surface of the clean hydrophobic porous membrane using the vapor phase spray gun, and obtaining the hydrophilic-hydrophobic composite Janus membrane after drying.

2. The preparation method according to claim 1, characterized in that: The hydrophobic porous base membrane is any one of an organic hydrophobic porous base membrane, an inorganic hydrophobic porous base membrane or an organic-inorganic composite hydrophobic porous base membrane; Preferably, the material of the hydrophobic porous base membrane includes any one of fluorine polymers, alkane polymers, olefin polymers, sulfone polymers, carbon nanotubes, graphene or phosphorene, or a combination of at least two thereof; preferably, the hydrophobic porous base membrane includes any one of polytetrafluoroethylene hydrophobic porous base membrane, polyvinylidene fluoride hydrophobic porous base membrane, polypropylene hydrophobic porous base membrane, polyethylene hydrophobic porous base membrane, polysulfone hydrophobic porous base membrane or polyethersulfone hydrophobic porous base membrane; Preferably, the hydrophobic porous base membrane includes any one of a flat sheet hydrophobic porous base membrane, a hollow fiber hydrophobic porous base membrane, a tubular hydrophobic porous base membrane or a rolled hydrophobic porous base membrane; Preferably, the pore size of the hydrophobic porous base membrane is 0.05-1.0 μm.

3. The preparation method according to claim 1, characterized in that: The solute of the hydrophilic coating aqueous dispersion includes any one of single-walled carbon nanotubes, double-walled carbon nanotubes and multi-walled carbon nanotubes modified with functional groups; 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, double-walled carbon nanotubes and multi-walled carbon nanotubes is 0.5-30 μm; Preferably, the outer diameters of the single-walled carbon nanotubes, double-walled carbon nanotubes and multi-walled carbon nanotubes are 2-80 nm.

4. The preparation method according to claim 1, characterized in that: The concentration of the diluted hydrophilic coating aqueous dispersion is 0.1-5wt%; Preferably, the gas phase spray gun has a jet flow rate of 0.5-7.5 L / min.

5. The preparation method according to claim 1, characterized in that: The temperature of the constant temperature heating stage is set to 60-150°C; Preferably, the clean hydrophobic porous membrane is subjected to vapor deposition treatment on the constant temperature heating platform for 10-360 seconds; Preferably, the amount of the diluted hydrophilic coating aqueous dispersion used for the vapor deposition treatment of the clean hydrophobic porous base membrane on the constant temperature heating table is 0.04-0.4 ml / cm 2 .

6. The preparation method according to claim 1, characterized in that: The organic solvent includes any one of ethanol, ether, acetone or petroleum ether, or a combination of at least two thereof; Preferably, the temperature at which the clean hydrophobic porous membrane after the vapor deposition process is dried is no higher than 80°C.

7. A hydrophilic-hydrophobic composite Janus membrane, characterized in that: The hydrophilic-hydrophobic composite Janus membrane is prepared by the preparation method according to any one of claims 1 to 6.

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