CN116020280A - A preparation method for anti-wetting, anti-fouling and anti-fouling hydrogel Janus membrane - Google Patents

Abstract

The present invention relates to a kind of anti-wetting, anti-pollution, anti-scaling hydrogel Janus membrane preparation method, the invention adopts hydrogel solution, polyvinyl alcohol (PVA) and tannic acid (TA) are dissolved in water and In the mixed solvent of ethanol, through the slow volatilization of ethanol, the hydrogen bond between PVA, TA and CNC is reconstructed, and hydrogel is formed in situ on the hydrophilic surface of the hydrophobic membrane, and a hydrogel Janus membrane is prepared. Compared with the traditional PTFE membrane, due to the strong hydrophilicity of the hydrogel layer, the hydrophilicity of the surface of the hydrogel Janus membrane is greatly increased, so that the adhesion of the membrane to dirt is small, so the oil resistance ability Very strong. In addition, the surface of the hydrogel layer is very dense, which can prevent surfactants and salt crystals from contacting the hydrophobic base film, so it has strong anti-wetting and anti-fouling capabilities. At the same time, it is on the hydrophilic surface of the hydrophobic film. The hydrogel is formed in situ, which enhances the binding force between the hydrogel layer and the hydrophobic membrane, avoids the detachment of the hydrogel layer, and enhances the operation stability of the membrane.

Description

A preparation method for anti-wetting, anti-fouling and anti-fouling hydrogel Janus membrane

technical field

The invention relates to a preparation method of a hydrogel Janus membrane with anti-wetting, anti-pollution and anti-scaling properties, and belongs to the technical field of membrane preparation.

Background technique

Freshwater scarcity has become a thorny issue due to population growth, climate change and industrialization. Seawater desalination and wastewater treatment are one of the effective ways to solve the problem of fresh water shortage. Membrane distillation is an emerging seawater desalination technology. Compared with other membrane separation technologies, membrane distillation has unique advantages. It uses waste heat or low-grade heat energy, is insensitive to pollutant concentration and does not require additional pressure. It is widely used in wastewater treatment. Applications. However, membrane wetting, fouling, and fouling are key issues that limit the development of membrane distillation. Compared with traditional hydrophobic membranes, composite Janus membranes have better membrane distillation performance and become the focus of people's research.

Hydrogel is a three-dimensional polymer cross-linked network with water as the dispersion medium, and its unique spatial structure allows the free diffusion and evaporation of water molecules. The hydrogel itself has excellent hydrophilicity and a dense surface, which can prevent the attachment of proteins, oil droplets, salt crystals and microorganisms on the membrane surface, forming an anti-pollution protective layer. On the other hand, hydrogel can effectively block and slow down the contact of surfactant molecules, solvents and inorganic salts with hydrophobic microporous membranes through the "molecular confinement effect" to prevent membrane wetting. In addition, the three-dimensional structure and surface properties of hydrogels can be precisely tuned, which can enhance the performance of hydrogels on demand. Therefore, combining hydrogels with hydrophobic membranes is expected to construct high-flux, excellent anti-wetting and anti-fouling membrane distillation membranes.

Existing studies have found that superimposing preformed agar hydrogel on polytetrafluoroethylene (PTFE) commercial membranes can reduce the wetting tendency of membrane distillation membranes when treating printing and dyeing wastewater containing surfactants. Lin Shihong's team prepared a superhydrophilic, underwater oleophobic composite membrane by spraying SiO ₂ , nanoparticles, chitosan hydrogel and fluoropolymer on the surface of PVDF membrane, which can effectively treat the environment with high concentration of organic pollutants. High-salt wastewater. M. Peyravi's research group deposited polydiallyl dimethyl chloride/polyacrylic acid semi-interpenetrating hydrogel on the surface of PVDF membrane, and constructed a composite membrane distillation membrane that resists wetting by different surfactants, which is expected to be used in oil and gas Produced water treatment.

However, the hydrogel layer has the problems of poor stability and poor binding force with the hydrophobic base membrane, and the temperature difference polarization phenomenon caused by the low heat transfer coefficient reduces the mass transfer driving force to a certain extent, resulting in the distillation of the hydrogel composite membrane. Membranes face the problems of poor stability and low permeation flux in actual use.

Therefore, the poor stability of the hydrogel layer and the poor binding force with the hydrophobic base membrane lead to poor stability and low permeation flux of the hydrogel composite membrane distillation membrane, which is an urgent problem to be solved for the composite membrane distillation membrane.

Contents of the invention

Aiming at the deficiencies of the prior art, the invention provides a preparation method of a hydrogel Janus membrane with anti-wetting, anti-pollution and anti-fouling properties.

The hydrogel Janus membrane obtained by the present invention has a strong binding force between the hydrogel layer and the hydrophobic membrane, and the Janus membrane has high stability, can run stably for a long time in the membrane distillation process and has strong anti-wetting and anti-pollution properties at the same time And anti-fouling ability, with high flux, excellent performance of salt interception rate.

The present invention is achieved through the following technical solutions:

A preparation method for anti-wetting, anti-pollution, and anti-scaling hydrogel Janus membranes, comprising the following steps:

(1) Preparation of hydrogel solution

Dissolving polyvinyl alcohol (PVA) and tannic acid (TA) in a mixed solvent, stirring at a certain temperature, then adding cellulose nanocrystals (CNC), stirring evenly, to obtain a PVA/TA/CNC hydrogel solution;

(2) Preparation of hydrogel membrane

Coat the PVA/TA/CNC hydrogel solution obtained in step (1) on the hydrophilic layer of a hydrophobic microporous membrane with hydrophilic modification on one side, form a hydrogel in situ on the hydrophilic surface layer, and let it dry naturally , to obtain Janus hydrogel membrane with anti-wetting, anti-pollution and anti-fouling properties.

According to the present invention, preferably, in step (1), the mixed solvent is a mixed solution of ultrapure water and ethanol with a volume ratio of (1-2):(1-2).

Most preferably, in step (1), the mixed solvent is a mixed solution of ultrapure water and ethanol with a volume ratio of 1:1.

According to the present invention, preferably, in step (1), the mass percent of polyvinyl alcohol in PVA/TA/CNC hydrogel solution is 1%～5%, the mass ratio of tannic acid and polyvinyl alcohol is (1～5%) 4): 1.

Further preferably, in step (1), the mass percentage of polyvinyl alcohol in the PVA/TA/CNC hydrogel solution is 2%～3%, and the mass ratio of tannic acid and polyvinyl alcohol is (1～2): 1.

According to the present invention, preferably, in step (1), the stirring temperature is 80-100°C, and the stirring time is 4-8h.

According to the present invention, preferably, in step (1), after adding cellulose nanocrystals (CNC), the concentration of CNC in the PVA/TA/CNC hydrogel solution is 0.1-1.8 wt%.

Preferably, in step (1), after adding cellulose nanocrystals (CNC), the concentration of CNC in the PVA/TA/CNC hydrogel solution is 0.5-1 wt%.

According to the present invention, preferably, in step (2), the hydrophilic modification treatment method of the hydrophobic microporous membrane with one hydrophilic modification is wet chemical, plasma treatment, radiation treatment or atomic deposition modification.

According to the present invention, preferably, in step (2), the wet chemical modification is specifically: dissolving dopamine DA and polyethyleneimine PEI in a Tris-HCl buffer solution, stirring fully to obtain a coating solution, and using a coating The solution only soaks the surface of the hydrophobic membrane, and finally rinses it with ultrapure water, and dries it at room temperature; the concentration of dopamine DA in the coating solution is 2g/L, the concentration of polyethyleneimine PEI is 2g/L, and the concentration of Tris-HCl buffer solution is 50mmol /L, the pH is 8.5, the stirring speed is 400-600rpm/min, the stirring time is 10-20min, the soaking time is 2-24h, and the drying time at room temperature is 10h.

According to the present invention, preferably, the hydrophobic membrane is polyvinylidene fluoride, polytetrafluoroethylene or polypropylene microfiltration membrane.

According to the present invention, preferably, in step (2), the natural drying time is 1-2 hours.

According to the present invention, preferably, in step (2), the coating method is doctor blade coating, drop coating, spray coating, or spin coating.

A hydrogel Janus membrane with anti-wetting, anti-pollution and anti-scaling properties is prepared by the above-mentioned method.

The preparation method of the present invention adopts a hydrophobic microporous membrane modified by hydrophilicity on one side to enhance the binding force between the hydrogel layer and the hydrophobic membrane, increase the binding force between the hydrogel layer and the hydrophobic membrane, and enhance the stability of the Janus membrane. Polyvinyl alcohol (PVA) and tannic acid (TA) are dissolved in a mixed solvent of water and ethanol, through the slow volatilization of ethanol, the hydrogen bond between PVA, TA and CNC is restructured, and the original The formation of hydrogel further enhances the bonding force between the hydrogel layer and the hydrophobic membrane, avoiding the detachment of the hydrogel layer, the hydrogel layer has a strong hydration ability and a dense surface, which makes the Janus membrane anti-wetting at the same time , anti-pollution and anti-fouling properties; the selection and addition of CNC make the surface of Janus membrane rough and dense, and a porous structure appears inside the hydrogel, so that the permeation flux is basically the same as that of PTFE membrane, without significant decrease. In summary, the hydrogel Janus membrane obtained by the present invention has a strong binding force between the hydrogel layer and the hydrophobic membrane, and the Janus membrane has high stability, and can run stably for a long time during the membrane distillation process and has strong anti-wetting properties at the same time , Anti-pollution and anti-scaling capabilities, with high flux and excellent salt interception performance.

The beneficial effects of the present invention are as follows:

1. The present invention adopts hydrogel solution, polyvinyl alcohol (PVA) and tannic acid (TA) are dissolved in the mixed solvent of water and ethanol, slowly volatilizes by ethanol, the hydrogen bond reconstruction between PVA, TA and CNC , a hydrogel Janus membrane was prepared by in situ formation of hydrogel on the hydrophilic surface of the hydrophobic membrane. Compared with the traditional PTFE membrane, due to the strong hydrophilicity of the hydrogel layer, the hydrophilicity of the surface of the hydrogel Janus membrane is greatly increased, so that the adhesion of the membrane to dirt is small, so the oil resistance ability Very strong. In addition, the surface of the hydrogel layer is very dense, which can prevent surfactants and salt crystals from contacting the hydrophobic base film, so it has strong anti-wetting and anti-fouling capabilities. At the same time, it is on the hydrophilic surface of the hydrophobic film. The hydrogel is formed in situ, which enhances the binding force between the hydrogel layer and the hydrophobic membrane, avoids the detachment of the hydrogel layer, and enhances the operation stability of the membrane.

2. The gel layer on the surface of the hydrogel Janus membrane prepared by the present invention can effectively reduce the evaporation enthalpy, thereby reducing the energy required for water evaporation; at the same time, due to the existence of CNC, the inside of the hydrogel layer is a porous structure ; Therefore, the hydrogel Janus membrane has a high flux (20.43kg m ^-2 h ^-1 ), which can be kept stable in a 100h continuous experiment.

3. The hydrogel Janus membrane prepared by the present invention can maintain a stable flux (20.41kg m ^-2 h ^-1 ) and an excellent salt rejection rate (99%) when dealing with a variety of actual wastewater with complex components, conducive to practical application.

4. The preparation process of the present invention is simple, does not require complicated instruments and equipment, and has a short process cycle, and the raw materials are green and environmentally friendly with low cost, and are suitable for industrial production.

5. The hydrogel Janus membrane obtained by the present invention has a strong binding force between the hydrogel layer and the hydrophobic membrane, and the Janus membrane has high stability, and can run stably for a long time in the membrane distillation process and has strong anti-wetting, Anti-pollution and anti-scaling capabilities, with high flux and excellent salt interception performance.

Description of drawings

Fig. 1 is the surface scanning electron microscope (SEM) picture of the polytetrafluoroethylene membrane without any modification;

Fig. 2 is the surface scanning electron micrograph of the hydrogel Janus membrane that the embodiment of the present invention 1 makes;

Fig. 3 is the scanning electron micrograph of the section of the hydrogel Janus membrane that the embodiment of the present invention 1 makes;

Fig. 4 is the comparative figure of water contact angle (WCA) and underwater oil contact angle (UOCA) of the hydrogel Janus membrane that the embodiment of the present invention makes and the polytetrafluoroethylene membrane without any modification;

Fig. 5 is the permeation flux and the electrical conductivity figure of the hydrogel Janus membrane that the embodiment of the present invention 1 makes in membrane distillation experiment, uses oil-water emulsion (3.5wt% sodium chloride, 0.4mM sodium lauryl sulfate and 1000ppm mineral oil) as the feed solution with a temperature difference of 45°C.

Figure 6 is a comparison chart of the normalized permeation flux and conductivity of the hydrogel Janus membrane and the polytetrafluoroethylene membrane prepared in Example 1 of the present invention in the concentrated membrane distillation experiment, using a solution with a high gypsum scaling tendency (20 mM calcium chloride, 20 mM sodium sulfate, and 600 mM sodium chloride), as the feed solution, with a temperature difference of 45 °C.

Figure 7 is the normalized permeate flux and conductivity diagram of the hydrogel Janus membrane prepared in Example 1 of the present invention during the operation duration of 100 h, using actual wastewater-oilfield produced water as the feed solution, and the temperature difference is 45°C .

Fig. 8 is a flux comparison diagram of hydrogel Janus membranes and polytetrafluoroethylene membranes with different additions of cellulose nanocrystals.

Fig. 9 is the permeation flux and electric conductivity figure of the hydrogel Janus membrane that comparative example 4 makes in membrane distillation experiment, uses oil-water emulsion (3.5wt% sodium chloride, 0.4mM sodium lauryl sulfate and 1000ppm mineral oil), as the feed solution, with a temperature difference of 45°C.

Detailed ways

In order to enable those skilled in the art to fully understand the technical solutions and beneficial effects of the present invention, further description will be made below in conjunction with the accompanying drawings and specific embodiments.

Example 1

A preparation method for a hydrogel Janus membrane with anti-wetting, anti-pollution and anti-scaling, the steps are as follows:

(1) Preparation of hydrophobic microporous membrane with hydrophilic modification on one side

Dissolve DA and PEI in 50mM Tris-HCl buffer solution, fully stir at 500rpm/min for 15min, with the help of a polytetrafluoroethylene mold, soak only the surface of the hydrophobic membrane with the coating solution, and finally use ultrapure Rinse with water and dry at room temperature; the concentration of dopamine DA in the coating solution is 2g/L, the concentration of polyethyleneimine PEI is 2g/L, and the pH of the Tris-HCl buffer solution is 8.5 to obtain a hydrophobic microporous membrane with a hydrophilic modification on one side;

(2) Preparation of hydrogel solution

Dissolve 3g polyvinyl alcohol (PVA) and 3g tannic acid (TA) in 105ml mixed solvent, the mixed solvent is a solvent mixed with ultrapure water and ethanol at a volume ratio of 1:1, and stir at room temperature, then add fiber Prime nanocrystal (CNC), stir 6h at 90 ℃, obtain PVA/TA/CNC hydrogel solution, the concentration of CNC in the PVA/TA/CNC hydrogel solution is 1wt%;

(3) Preparation of Hydrogel Janus Membrane

The PVA/TA/CNC hydrogel solution obtained in step (2) is scraped and coated on the hydrophilic surface of the hydrophobic microporous membrane with hydrophilic modification on one side of step (1) with a gap of 100 μm, and dried naturally to obtain Hydrogel Janus membrane, denoted as: HC ₁ -PTFE.

The surface scanning electron microscope (SEM) picture of the polytetrafluoroethylene membrane without any modification is shown in Figure 1, and the surface scanning electron microscope picture and cross-sectional scanning electron microscope picture of the prepared hydrogel Janus membrane are shown in Figure 2 and Figure 3.

From Figures 1 to 3, it can be seen that the PTFE membrane has a fibrous network microporous structure, while the surface of the prepared hydrogel Janus membrane coating is dense and rough and has many nanostructured protrusions. The section shows that the thickness of the hydrogel layer is 11.54 μm left and right, and presents a porous structure.

The smaller the initial water contact angle, the better the hydrophilicity of the film; the initial water contact angle of the hydrogel Janus film of Example 1 is 39.5°, which shows that the hydrogel Janus film prepared by the present invention has a strong hydrophilicity. Water-based, the contact angle of underwater oil is 142.7, indicating underwater super-oleophobic (Figure 4).

With the oil-water emulsion containing 3.5% sodium chloride, 0.1g/L mineral oil and 0.4mM sodium lauryl sulfate as the feed liquid, using a direct contact membrane distillation device, the hydrogel layer faces the feed liquid, and the test is obtained The anti-wetting and anti-fouling properties of the hydrogel Janus membrane were monitored in real time by cold measurement of conductivity and flux changes. The test results are shown in Figure 5.

It can be seen from Figure 5 that the obtained hydrogel Janus membrane maintained a stable permeation flux of 19.43kg m ^-2 h ^-1 during the oil-water emulsion treatment process, and the conductivity remained stable after 24 hours, with a salt cut-off rate as high as 99.99 %, indicating that the hydrogel Janus membrane has excellent anti-wetting and anti-fouling properties.

The oil-water emulsion containing 3.5% sodium chloride, 20mM sodium sulfate and 20mM calcium chloride was used as the feed liquid to test the anti-fouling performance of the obtained hydrogel Janus membrane, and the test results are shown in Figure 6.

It can be seen from Figure 6 that the initial permeation flux of the hydrogel Janus membrane was 22.64kg m ^-2 h ^-1 , and the permeation flux dropped to 60% after treating 800mL feed solution, and the conductivity remained stable at 1.68μs /cm, indicating that the hydrogel Janus membrane has excellent anti-fouling properties. However, the permeation flux of PTFE membrane decreased to 11%, and the conductivity increased to 31.7μs/cm after treating 736mL of feed solution.

The actual wastewater oilfield produced water was used as the feed liquid to test the anti-wetting, anti-pollution and anti-fouling properties of the obtained hydrogel Janus membrane. The test results are shown in Figure 7.

It can be seen from Figure 7 that the initial permeation flux of the hydrogel Janus membrane is 20.41kg m ^-2 h ^-1 , and the salt rejection rate is 99.9% within 100h, indicating that the hydrogel Janus membrane has excellent anti-fouling properties performance.

Example 2

With the method described in embodiment 1, difference is:

Step (1) Clean the PTFE membrane with acetone in an ultrasonic bath for 30 minutes to remove surface impurities. Before the treatment, vacuum the chamber to less than 1×10 ^-4 Pa, then introduce nitrogen gas into the chamber, modify the surface of the PTFE film with a base bias voltage of 800V, and use the plasma enhanced chemical vapor deposition method to treat the PTFE film Plasma modification was carried out, the duty ratio was 60%, the treatment time was 2 hours, and the treatment was completed and cooled for 3 hours to obtain a hydrophobic microporous membrane with one side of hydrophilic modification.

Step (2), step (3) carry out by embodiment 1.

With the oil-water emulsion containing 3.5% sodium chloride, 0.1g/L mineral oil and 0.4mM sodium lauryl sulfate as feed liquid, according to the film performance test mode among the embodiment 1, evaluate the hydrogel Janus film that obtains Anti-wetting and anti-pollution properties.

The obtained hydrogel Janus membrane maintained a stable permeation flux of 19.86kgm ^-2 h ^-1 during the oil-water emulsion treatment process, and the salt interception rate was still as high as 99.99% after 24 hours, indicating that the hydrogel Janus membrane has excellent resistance to Wetting and anti-fouling properties.

Example 3

With the method described in embodiment 1, difference is:

The concentration of CNC in the PVA/TA/CNC hydrogel solution is 0.5wt%, and the others are carried out as in Example 1.

Example 4

With the method described in embodiment 1, difference is:

The concentration of CNC in the PVA/TA/CNC hydrogel solution was 1.5wt%, and the others were carried out as in Example 1.

Comparative example 1

Using an untreated polytetrafluoroethylene membrane, an oil-water emulsion containing 3.5% sodium chloride and 0.1 g/L mineral oil was used as the feed liquid, and a membrane distillation experiment was carried out according to Example 1.

The results showed that the initial permeation flux of the membrane was as low as 4.86kg m ^-2 h ^-1 , and dropped to zero after 16min, indicating that the PTFE membrane was seriously fouled by oil, which was due to the hydrophobic and lipophilic properties of the PTFE membrane (Fig. 4 ), so it is not suitable for treating oily wastewater.

Comparative example 2

With the method described in embodiment 1, difference is:

Dissolve 3 g of polyvinyl alcohol (PVA) and 3 g of tannic acid (TA) in 105 ml of a mixed solvent (1:1 ultrapure water/ethanol by volume), and stir at room temperature. Then, 2wt% cellulose nanocrystals (CNC) were added and stirred at 90°C for 6h.

Others are carried out according to Example 1, and the obtained membrane is recorded as: HC ₂ -PTFE.

With the oil-water emulsion containing 3.5% sodium chloride, 0.1g/L mineral oil and 0.4mM sodium lauryl sulfate as feed liquid, according to the membrane distillation method in the embodiment 1, when measuring CNC concentration is 2%, water Properties of Gel Janus Membranes. In addition, the permeation flux was measured with a solution containing 3.5% sodium chloride as the feed solution, and the test results are shown in FIG. 8 .

The results show that when dealing with oil-water emulsion, the wetting phenomenon obviously occurs, the conductivity increases, 14.45μS/cm; and the permeation flux is 7.43kg m ^-2 h ^-1 , which is significantly lower than that of the hydrogel with a CNC concentration of 1%. Janus membrane (Fig. 8).

Comparative example 3

With the method described in embodiment 1, difference is:

Dissolve 3g polyvinyl alcohol (PVA) and 3g tannic acid (TA) in 105ml mixed solvent (1:1 ultrapure water/ethanol by volume), and stir at 90°C for 6h.

Others are carried out according to Example 1, and the obtained membrane is recorded as: HC ₀ -PTFE.

With the oil-water emulsion containing 3.5% sodium chloride, 0.1g/L mineral oil and 0.4mM sodium lauryl sulfate as feed liquid, according to the membrane distillation method in the embodiment 1, when measuring without adding CNC, hydrogel Properties of Janus membranes. In addition, the permeate flux was measured with a solution containing 3.5% NaCl as the feed solution.

The results showed that the hydrogel solution without adding CNC was thin, with poor film-forming properties and prone to defects.

When dealing with oil-water emulsion, the wetting phenomenon obviously occurs, the conductivity increases, 53.42μs/cm; and the permeation flux is 12.57kg m ^-2 h ^-1 , which is significantly lower than that of the hydrogel Janus membrane with a CNC concentration of 1% ( Figure 8).

Comparative example 4

With the method described in embodiment 1, difference is:

The cellulose nanocrystals (CNC) in step (2) were replaced with silicon dioxide, and other methods and steps were carried out as in Example 1.

With the oil-water emulsion containing 3.5% sodium chloride, 0.1g/L mineral oil and 0.4mM sodium lauryl sulfate as feed liquid, utilize direct contact membrane distillation device, hydrogel layer is towards feed liquid, test this The anti-wetting and anti-fouling properties of the hydrogel Janus membrane of the comparative example were monitored in real time by cold measurement of conductivity and flux changes, and the test results are shown in Figure 9.

The results show that when the oil-water emulsion is treated, the wetting phenomenon obviously occurs, the electrical conductivity increases significantly from 1.71μS/cm to 429.79μS/cm; and the permeation flux is only 5.57kg m ^-2 h ^-1 (Fig. 9 ), indicating that replacing CNC with other substances will significantly increase the conductivity and reduce the flux.

The above-described embodiments are preferred embodiments of the present invention, and are not intended to limit the present invention. Any modifications, equivalent replacements or improvements made within the spirit and principles of the present invention should be included in the protection of the present invention. within range.

Claims (10)

1. A preparation method with anti-wetting, anti-pollution, and anti-fouling hydrogel Janus membranes, comprising the following steps: (1) Preparation of hydrogel solution Dissolving polyvinyl alcohol (PVA) and tannic acid (TA) in a mixed solvent, stirring at a certain temperature, then adding cellulose nanocrystals (CNC), stirring evenly, to obtain a PVA/TA/CNC hydrogel solution; (2) Preparation of hydrogel membrane Coat the PVA/TA/CNC hydrogel solution obtained in step (1) on the hydrophilic layer of a hydrophobic microporous membrane with hydrophilic modification on one side, form a hydrogel in situ on the hydrophilic surface layer, and let it dry naturally , to obtain Janus hydrogel membrane with anti-wetting, anti-pollution and anti-fouling properties. 2. method according to claim 1, is characterized in that, in step (1), mixed solvent is the mixed solution that volume ratio is (1-2): (1-2) ultrapure water and ethanol mix, preferably Yes, the mixed solvent is a mixture of ultrapure water and ethanol with a volume ratio of 1:1. 3. The method according to claim 1, characterized in that, in step (1), the mass percent of polyvinyl alcohol in the PVA/TA/CNC hydrogel solution is 1% to 5%, and tannic acid and polyethylene The mass ratio of alcohol is (1-4):1. 4. The method according to claim 1, characterized in that, in step (1), the stirring temperature is 80-100°C, and the stirring time is 4-8h. 5. The method according to claim 1, characterized in that, in step (1), after the cellulose nanocrystal (CNC) is added, the concentration of CNC in the PVA/TA/CNC hydrogel solution is 0.1～1.8wt% . 6. The method according to claim 1, characterized in that, in step (1), after adding cellulose nanocrystals (CNC), the concentration of CNC in the PVA/TA/CNC hydrogel solution is 0.5-1 wt%. 7. The method according to claim 1, characterized in that, in step (2), the hydrophilic modification treatment mode of the hydrophobic microporous membrane of one side hydrophilic modification is wet chemical, plasma treatment, radiation treatment or atomic deposition modification. 8. The method according to claim 7, characterized in that, in step (2), the wet chemical modification is specifically: dopamine DA and polyethyleneimine PEI are dissolved in Tris-HCl buffer solution, fully stirred, Obtain the coating solution, use the coating solution to soak only the surface of the hydrophobic membrane, finally rinse with ultrapure water, and dry at room temperature; the concentration of dopamine DA in the coating solution is 2g/L, and the concentration of polyethyleneimine PEI is 2g/L. The concentration of the Tris-HCl buffer solution is 50mmol/L, the pH is 8.5, the stirring speed is 400-600rpm/min, the stirring time is 10-20min, the soaking time is 2-24h, and the drying time at room temperature is 10h. 9. The method according to claim 1, characterized in that, in step (2), the natural drying time is 1 to 2 hours, and the coating method is scraping, dripping, spraying, or spin coating. 10. A hydrogel Janus membrane with anti-wetting, anti-pollution and anti-fouling properties, which is prepared by the method described in claims 1-9.

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