Super-hydrophilic / underwater super-oleophobic filter screen for oil-water separation as well as preparation method and application of super-hydrophilic / underwater super-oleophobic filter screen

Abstract

The invention discloses a super-hydrophilic / underwater super-oleophobic filter screen for oil-water separation as well as a preparation method and application of the super-hydrophilic / underwater super-oleophobic filter screen, and relates to the technical field of environment-friendly special wettability materials. The method comprises the following steps: 1) preparing a base material: selecting a stainless steel net film as the base material, soaking the stainless steel net film with inorganic acid, and then cleaning the stainless steel net film with deionized water for multiple times to remove oil stains and impurities on the surface; 2) surface modification: placing the cleaned stainless steel net film in a dopamine / ethanol / water mixed solution, then adjusting the pH value to alkalescence, and stirring for reaction to form a rough adhesion layer; 3) alginate hydrogel covering: alternately soaking the surface-modified filter screen in an alginate solution and a calcium chloride solution, and firmly covering the alginate hydrogel on the surface of the filter screen through strong hydrogen-bond interaction and cross-linking interaction; and 4) drying and curing: drying the filter screen covered with the alginate hydrogel in a drying oven to cure the hydrogel so as to prepare the super-hydrophilic / underwater super-oleophobic stainless steel filter screen. The invention provides a super-hydrophilic / underwater super-oleophobic filter screen for oil-water separation as well as a preparation method and application of the super-hydrophilic / underwater super-oleophobic filter screen. The filter screen has excellent oil-water separation performance, good chemical stability and environmental friendliness, the preparation process is simple and easy to implement, and the filter screen can be widely applied to large-scale efficient treatment of oil-containing wastewater. The invention provides a novel, efficient and environment-friendly material and technical support for the field of oil-water separation.

Description

Technical Field

[0001] The present invention relates to the technical field of environmentally friendly special wettability materials, and particularly to a superhydrophilic / underwater superoleophobic filter for oil-water separation and its environmentally friendly preparation method. Background Art

[0002] With the continuous advancement of society and industrialization, a large amount of oily wastewater has been generated in many fields such as oil exploitation, industrial manufacturing, and daily life. These wastewaters not only exacerbate environmental pollution but also have a negative impact on many industries. Therefore, the proper treatment of oily wastewater has gradually attracted the wide attention of researchers globally. In traditional oil-water separation methods, many methods (such as chemical treatment, biological enzyme degradation, gravity separation, adsorption, etc.) have disadvantages such as high cost, poor recovery rate, easy secondary pollution, and complex processes, and usually cannot treat oil pollution on a large scale.

[0003] By observing the surface energy of organisms such as fish and shrimp in nature, it is found that they have a hierarchical structure and random nanostructures at the microscale, which endows their surfaces with special wettability, being superhydrophilic in air and superoleophobic underwater. Therefore, these organisms can resist oil pollution in water. Inspired by this, materials with superhydrophilic / underwater superoleophobic surfaces can effectively resist oil pollution and thus separate it. The oil-water separation materials studied in existing patent applications, for example, in application No. 202410135619.7, copolymer micron particles and nano titanium dioxide particles are simply blended and then coated on the surface of a substrate to prepare a superhydrophilic / underwater superoleophobic membrane; in application No. 202410233650.4, it is mentioned that a mixed solution of nano zinc oxide / graphene oxide is filtered onto the surface of a base membrane and naturally dried to obtain an oil-water separation membrane; application No. 202311760474.1 generates silica nanoparticles on the surface of a PLA fiber membrane by sol-gel method to form a superhydrophilic PLA fiber membrane with submicron-sized pores. Most of these methods construct rough structures at the microscale by adding inorganic nanoparticles, but the shedding of these nanoparticles during the use of the materials will still cause a certain degree of pollution to the water body. Therefore, the development of materials that are cheap, efficient, environmentally friendly, and can achieve high-throughput continuous oil-water separation is of great significance in the sustainable development of society. Summary of the Invention

[0004] The main object of the present invention is to provide an environmentally friendly superhydrophilic / underwater superoleophobic filter for continuous oil-water separation, its preparation method and application, in view of the problems of high cost, environmental unfriendliness, and inability to treat a large amount of oily wastewater existing in existing oil-water separation materials. By adjusting the volume ratio of water to ethanol in the dopamine polymerization system, the microstructure and wetting performance of the target product are controlled, providing a new experimental technical route for realizing oil-water separation in various complex environments.

[0005] An environmentally friendly preparation method of a superhydrophilic / underwater superoleophobic filter for oil-water separation, comprising the following steps:

[0006] (1) Select a stainless steel mesh as the substrate, first soak it in inorganic acid, and then wash it with deionized water multiple times to remove surface oil stains and impurities;

[0007] (2) Place the washed stainless steel mesh in a dopamine / ethanol / water mixed solution, then adjust the pH to weakly alkaline, stir and react to form a rough adhesion layer;

[0008] (3) Alternately soak the filter obtained in step (2) in an alginate solution and a calcium chloride solution to firmly coat the alginate hydrogel on the surface of the filter;

[0009] (4) Dry the filter covered with the alginate hydrogel in step (3) to cure the hydrogel, thereby obtaining a superhydrophilic / underwater superoleophobic filter.

[0010] Preferably, the inorganic acid in step (1) is one or more of hydrochloric acid, sulfuric acid, carbonic acid, phosphoric acid, hydrofluoric acid, etc., preferably hydrochloric acid.

[0011] Preferably, the aperture of the stainless steel mesh in step (1) is 20-100 μm, preferably 20-50 μm;

[0012] Preferably, the dopamine-based substance selected for the dopamine / ethanol / water mixed solution in step (2) is one or more of dopamine hydrochloride, dopamine D4 hydrochloride, N-methyldopamine, 6-hydroxydopamine, 3-acryloyldopamine; preferably dopamine hydrochloride.

[0013] Preferably, the preparation method of the dopamine / ethanol / water mixed solution in step (2) is: mixing dopamine, absolute ethanol and deionized water in a mass ratio of 0.5:(0-70):(100-20), further preferably 0.5:(24-47):(40-70), and most preferably 0.5:24:70.

[0014] Preferably, the pH-adjusting substance in step (2) is preferably ammonia water, adding 0.01-0.05 parts by mass, and the final pH of the obtained dopamine solution is 7.5-10, preferably 8.0-9.

[0015] Preferably, the stirring reaction time in step (2) is 10-48 h, the rotation speed is 500-1000 rpm, and the reaction temperature is 25-50 °C.

[0016] Preferably, the alginate solution in step (3) is a mixed solution of alginate powder and deionized water in a mass ratio of 0.01-0.1:100; the alginate is sodium alginate.

[0017] Preferably, the temperature for preparing the alginate solution in step (3) is 85 - 95°C, and the stirring speed is 1000 - 1500 rpm.

[0018] Preferably, the calcium chloride solution in step (3) is a mixed solution of calcium chloride particles and deionized water with a mass ratio of 0.1 - 1:100.

[0019] Preferably, the specific method of alternately soaking the surface - modified filter screen in step (3) is as follows: first soak the filter screen in the sodium alginate solution for 10 - 30 min, take it out, rinse it with deionized water, and then transfer it to the calcium chloride solution for soaking for 10 - 30 min. This process needs to be repeated 2 - 5 times.

[0020] Preferably, in step (4), the filter screen with alginate attached is dried in an oven. The temperature of the oven is set at 50 - 100°C, and the drying time is 1 - 12 h.

[0021] Compared with the prior art, the present invention has the following advantages and beneficial effects:

[0022] 1. The present invention constructs the surface microstructure of the filter screen with polydopamine nanoparticles, replacing the addition of inorganic nanoparticles, which is more in line with the sustainable development route of green environmental protection.

[0023] 2. Polydopamine itself has strong adhesion to the substrate. Without adding additional adhesives, the stable loading of polydopamine nanoparticles can be achieved, so that it will not easily fall off during use and affect the surface wettability of the filter screen. While reducing costs, it also takes into account good reusability.

[0024] 3. The present invention constructs a hydrogel layer on the surface of the substrate by a simple alternate - soaking method, endowing the material surface with super - hydrophilic / underwater super - oleophobic properties, so that it has excellent efficiency and water permeation flux in continuous oil - water separation treatment. Description of the Drawings

[0025] Figure 1 Underwater static oil contact angles for each example and comparative example;

[0026] Figure 2 Scanning electron microscope images of Example 3 and the original stainless - steel mesh. Detailed Description of the Invention

[0027] The present invention will be further described in detail below in conjunction with examples, but the implementation manners of the present invention are not limited thereto.

[0028] Example 1: Place a 4*4 cm stainless steel mesh in hydrochloric acid for 5 min, then rinse with deionized water and dry for later use. Add 0.5 parts by mass of dopamine hydrochloride to a mixed solution of 20 parts by mass of deionized water and 63 parts by mass of absolute ethanol. After mixing evenly by ultrasound, add ammonia water to adjust the pH of the system to 8.0 - 8.5. Under normal temperature and pressure, immerse the stainless steel mesh in the above solution, stir and react for 16 h, then rinse with deionized water and set aside.

[0029] Take 0.1 part by mass of sodium alginate powder and add it to 100 parts by mass of deionized water. Stir at 90 °C until the system is uniform to obtain sodium alginate solution A. Take 1 part by mass of anhydrous calcium chloride particles and add them to 100 parts by mass of deionized water. Stir at normal temperature and pressure until the system is uniform to obtain calcium chloride solution B. Immerse the above stainless steel mesh in solution A for 15 min, then rinse with deionized water and dry. Subsequently, immerse it in solution B for 15 min, rinse with deionized water, and dry to obtain filter mesh SM1.

[0030] Example 2: Place a 4*4 cm stainless steel mesh in hydrochloric acid for 5 min, then rinse with deionized water and dry for later use. Add 0.5 parts by mass of dopamine hydrochloride to a mixed solution of 40 parts by mass of deionized water and 47 parts by mass of absolute ethanol. After mixing evenly by ultrasound, add ammonia water to adjust the pH of the system to 8.0 - 8.5. Under normal temperature and pressure, immerse the stainless steel mesh in the above solution, stir and react for 16 h, then rinse with deionized water and set aside.

[0031] Take 0.1 part by mass of sodium alginate powder and add it to 100 parts by mass of deionized water. Stir at 90 °C until the system is uniform to obtain sodium alginate solution A. Take 1 part by mass of anhydrous calcium chloride particles and add them to 100 parts by mass of deionized water. Stir at normal temperature and pressure until the system is uniform to obtain calcium chloride solution B. Immerse the above stainless steel mesh in solution A for 15 min, then rinse with deionized water and dry. Subsequently, immerse it in solution B for 15 min, rinse with deionized water, and dry to obtain filter mesh SM2.

[0032] Example 3: Place a 4*4 cm stainless steel mesh in hydrochloric acid for 5 min, then rinse with deionized water and dry for later use. Add 0.5 parts by mass of dopamine hydrochloride to a mixed solution of 70 parts by mass of deionized water and 24 parts by mass of absolute ethanol. After mixing evenly by ultrasound, add ammonia water to adjust the pH of the system to 8.0 - 8.5. Under normal temperature and pressure, immerse the stainless steel mesh in the above solution, stir and react for 16 h, then rinse with deionized water and set aside.

[0033] Take 0.1 part by mass of sodium alginate powder and add it to 100 parts by mass of deionized water. Stir at 90 °C until the system is homogeneous to obtain sodium alginate solution A. Take 1 part by mass of anhydrous calcium chloride particles and add them to 100 parts by mass of deionized water. Stir at normal temperature and pressure until the system is homogeneous to obtain calcium chloride solution B. Immerse the above stainless steel mesh in solution A for 15 min, then rinse with deionized water and dry. Subsequently, immerse it in solution B for 15 min, rinse with deionized water, and dry to obtain filter mesh SM3.

[0034] Example 4: Place a 4*4 cm stainless steel mesh in hydrochloric acid and clean for 5 min, then rinse with deionized water and dry for standby. Add 0.5 part by mass of dopamine hydrochloride to 100 parts by mass of deionized water. Mix them evenly by ultrasonic wave, and then add ammonia water to adjust the pH of the system to 8.0 - 8.5. At normal temperature and pressure, immerse the stainless steel mesh in the above solution, stir and react for 16 h, and rinse with deionized water for standby.

[0035] Take 0.1 part by mass of sodium alginate powder and add it to 100 parts by mass of deionized water. Stir at 90 °C until the system is homogeneous to obtain sodium alginate solution A. Take 1 part by mass of anhydrous calcium chloride particles and add them to 100 parts by mass of deionized water. Stir at normal temperature and pressure until the system is homogeneous to obtain calcium chloride solution B. Immerse the above stainless steel mesh in solution A for 15 min, then rinse with deionized water and dry. Subsequently, immerse it in solution B for 15 min, rinse with deionized water, and dry to obtain filter mesh SM4.

[0036] Example 5: Place a 4*4 cm stainless steel mesh in hydrochloric acid and clean for 5 min, then rinse with deionized water and dry for standby. Add 0.5 part by mass of dopamine hydrochloride to a mixed solution of 70 parts by mass of deionized water and 24 parts by mass of absolute ethanol. Mix them evenly by ultrasonic wave, and then add ammonia water to adjust the pH of the system to 8.0 - 8.5. At normal temperature and pressure, immerse the stainless steel mesh in the above solution, stir and react for 16 h, and rinse with deionized water for standby.

[0037] Take 0.05 part by mass of sodium alginate powder and add it to 100 parts by mass of deionized water. Stir at 90 °C until the system is homogeneous to obtain sodium alginate solution A. Take 0.5 part by mass of anhydrous calcium chloride particles and add them to 100 parts by mass of deionized water. Stir at normal temperature and pressure until the system is homogeneous to obtain calcium chloride solution B. Immerse the above stainless steel mesh in solution A for 15 min, then rinse with deionized water and dry. Subsequently, immerse it in solution B for 15 min, rinse with deionized water, and dry to obtain filter mesh SM5.

[0038] Example 6: A 4×4 cm stainless steel mesh was placed in hydrochloric acid and cleaned for 5 min, then rinsed with deionized water and dried for later use. 0.5 part by mass of dopamine hydrochloride was added to a mixed solution of 70 parts by mass of deionized water and 24 parts by mass of absolute ethanol. After mixing evenly by ultrasonic treatment, ammonia water was added dropwise to adjust the pH of the system to 8.0 - 8.5. Under normal temperature and pressure, the stainless steel mesh was immersed in the above solution and stirred for reaction for 16 h, then rinsed with deionized water and reserved for later use.

[0039] 0.01 part by mass of sodium alginate powder was added to 100 parts by mass of deionized water and stirred at 90 °C until the system was uniform to obtain sodium alginate solution A. 0.1 part by mass of anhydrous calcium chloride particles was added to 100 parts by mass of deionized water and stirred at normal temperature and pressure until the system was uniform to obtain calcium chloride solution B. The above stainless steel mesh was immersed in solution A for 15 min, then rinsed with deionized water and dried. Subsequently, it was placed in solution B and immersed for 15 min and rinsed with deionized water, and then dried to obtain filter mesh SM6.

[0040] Comparative Example 1: A 4×4 cm stainless steel mesh was placed in hydrochloric acid and cleaned for 5 min, then rinsed with deionized water and dried for later use. 0.1 part by mass of sodium alginate powder was added to 100 parts by mass of deionized water and stirred at 90 °C until the system was uniform to obtain sodium alginate solution A. 1 part by mass of anhydrous calcium chloride particles was added to 100 parts by mass of deionized water and stirred at normal temperature and pressure until the system was uniform to obtain calcium chloride solution B. The above stainless steel mesh was immersed in solution A for 15 min, then rinsed with deionized water and dried. Subsequently, it was placed in solution B and immersed for 15 min and rinsed with deionized water, and then dried to obtain filter mesh SM7.

[0041] Comparative Example 2: A 4×4 cm stainless steel mesh was placed in hydrochloric acid and cleaned for 5 min, then rinsed with deionized water and dried. 0.5 part by mass of dopamine hydrochloride was added to a mixed solution of 70 parts by mass of deionized water and 24 parts by mass of absolute ethanol. After mixing evenly by ultrasonic treatment, ammonia water was added dropwise to adjust the pH of the system to 8.0 - 8.5. Under normal temperature and pressure, the stainless steel mesh was immersed in the above solution and stirred for reaction for 16 h, then rinsed with deionized water and dried to obtain filter mesh SM8.

[0042] Comparative Example 3: A 4×4 cm stainless steel mesh was placed in hydrochloric acid and cleaned for 5 min, then rinsed with deionized water and dried for later use. 0.5 part by mass of dopamine hydrochloride was added to a mixed solution of 0 parts by mass of deionized water and 24 parts by mass of absolute ethanol. After mixing evenly by ultrasonic treatment, ammonia water was added dropwise to adjust the pH of the system to 8.0 - 8.5. Under normal temperature and pressure, the stainless steel mesh was immersed in the above solution and stirred for reaction for 16 h, then rinsed with deionized water and reserved for later use.

[0043] Take 0.1 part by mass of sodium alginate powder and add it to 100 parts by mass of deionized water. Stir at 90 °C until the system is uniform to obtain sodium alginate solution A. Take 1 part by mass of anhydrous calcium chloride particles and add them to 100 parts by mass of deionized water. Stir at normal temperature and pressure until the system is uniform to obtain calcium chloride solution B. Immerse the above stainless steel mesh in solution A for 15 min, then rinse with deionized water and dry. Subsequently, immerse it in solution B for 15 min and rinse with deionized water. After drying, the filter mesh SM9 is obtained.

[0044] Test Example 1: Through the detection of the static contact angle of underwater oil droplets and the water contact angle, the hydrophilic and oleophobic properties of the stainless steel meshes of each example and the comparative examples were tested. A German LAUDA Scientific LSA100S-T type instrument was used to test the underwater oil contact angle. In the test, the oil droplet was toluene and the test volume was 5 μL for all. The test results of the underwater oil contact angles of each example and Comparative Examples 1 and 2 are as Figure 1 shown. It can be seen from Figure 1 that the maximum contact angle of the oil (toluene) on the stainless steel mesh in water is about 165°, showing superhydrophilic / underwater superoleophobicity. The test results are shown in Table 1.

[0045] Table 1 Test results of water contact angle and underwater oil contact angle (toluene)

[0046]

[0047]

[0048] For Examples 1-6, the water contact angles in air are all 0°, which is the superhydrophilicity endued by the sodium alginate hydrogel. However, due to different dopamine polymerization conditions, the surface roughness of the materials is changed differently, thus affecting the underwater oil contact angles of Examples 1-6. The concentrations of the sodium alginate solution and the calcium chloride solution affect the formation of the superhydrophilic gel layer to a certain extent. In Examples 3, 5, and 6, due to the decrease in the concentrations of the two solutions, the thickness and integrity of the formed hydrogel layer are also reduced, thus affecting the underwater oil contact angles of the examples. The stainless steel filter meshes of each example all show a certain degree of superhydrophilic / underwater superoleophobic property, and the effect of Example 3 is more prominent. In Comparative Example 3, since absolute ethanol inhibits the polymerization of dopamine, poly-dopamine nanoparticles that can change the surface roughness of the material cannot be successfully self-polymerized to construct a micro / nano structure, so the effect of the example cannot be achieved, and it is the same as the effect of Comparative Example 1. In Comparative Example 2, without the coating of the sodium alginate hydrogel, it is difficult for the surface of the stainless steel mesh to reach a superhydrophilic state, and there is no "water film" formed by the hydrogel layer underwater to isolate oil stains, so its oleophobic effect cannot reach an ideal state.

[0049] Test Example 2: The morphologies of each example were observed by scanning electron microscopy. The SEM results of Example 3 and the original stainless steel mesh are as follows Figure 2 shown. It can be seen from Figure 2 that the skeleton of the original stainless steel mesh is very smooth without any protrusions, while the surface morphology of Example 3 has a large number of aggregated structural units. This indicates that due to the loading of polydopamine nanoparticles and the coating of alginate hydrogel, the surface roughness of the original smooth stainless steel mesh increases, and many micro / nano structures appear, meeting the construction conditions of special wettability structures.

[0050] Test Example 3: The water permeation flux and oil-water separation efficiency of each example and the stainless steel filter mesh of the comparative example were tested. Taking the filter mesh prepared in Example 3 as an example, the effective test area of the filter mesh to be tested is 12.56 cm 2 , and the oil-water separation test was completed by a self-made oil-water separation device. The test solution was a mixed solution of 20 mL of toluene (dyed with methyl red) and 40 mL of water. The filter mesh was placed between two 300 mL filter cups and fixed with a flange clamp, and a beaker was used to collect the filtered liquid below. The oil-water separation efficiency was calculated by dividing the mass fraction of the oil collected after separation by the mass fraction of the oil before separation. The test results are shown in Table 2.

[0051] Table 2 Test results of water permeation flux and oil-water separation efficiency

[0052] Sample Water permeation flux (LMH) Oil-water separation efficiency (%) SM1 5683 99.64 SM2 5779 99.45 SM3 5893 99.25 SM4 5872 98.79 SM5 5746 98.84 SM6 5893 98.06 SM7 4983 93.67 SM8 4375 74.69 SM9 4988 93.21

[0053] Each example has excellent water permeation flux. This is because the alginate hydrogel layer can quickly wet and penetrate the surface of the stainless steel mesh, while the unmodified stainless steel mesh will hinder the liquid passage to a certain extent due to the capillary effect of the micropores. At the same time, the "water film" formed after the water wets the surface of the filter mesh can prevent the oil from passing through, thus effectively separating the oil-water mixture.

[0054] Test Example 4: Considering the complex separation environment of oily wastewater, the chemical stability of the examples needs to be tested. Taking Example 3 as an example, the stainless steel meshes prepared according to this example were taken out after being placed in solutions with pH values of 1.0 - 13.0 for 24 h, and their underwater oil contact angles, water permeation fluxes, and oil-water separation efficiencies were tested respectively. The test results are shown in Table 3.

[0055] Table 3 Underwater oil contact angle, water permeation flux, and oil-water separation efficiency of Example 3 after soaking in different pH solutions for 24 h

[0056]

[0057]

[0058] This embodiment can still maintain an underwater oleophobic angle of more than 145° and considerable oil-water separation efficiency under strong acid and strong alkali corrosion, indicating that although the acid and alkali cause certain damage to the modified layer, it still does not affect its application in oil-water separation. Instead, the water permeation flux increases in a strong acid and strong alkali environment, which may be due to the destruction of the filter screen's own structure under the strong corrosion environment. The above results confirm that the stainless steel mesh of the present invention has excellent chemical stability and is expected to be applied to the treatment of complex oily wastewater.

[0059] Based on the above test examples, it can be seen that the superhydrophilic / underwater superoleophobic stainless steel mesh prepared by the present invention has an extremely high underwater oleophobic angle, excellent water flux and oil-water separation efficiency, and also has good chemical corrosion resistance and can be applied to complex environments. Moreover, the preparation process of the present invention is simple and convenient, with low cost, and the raw materials used are all environmentally friendly and non-toxic. Compared with the prior art, the present invention has progressiveness.

[0060] The above embodiments are preferred embodiments of the present invention, but the embodiments of the present invention are not limited to the above embodiments. Any other changes, modifications, substitutions, combinations, and simplifications made without departing from the spirit and principle of the present invention shall be equivalent replacement methods and are all included in the protection scope of the present invention.

Claims

1. A preparation method of a superhydrophilic / underwater superoleophobic filter for oil-water separation, characterized in that, It includes the following steps: (1) Select a stainless steel mesh as the substrate, soak it in inorganic acid first, and then wash it with deionized water multiple times to remove surface oil stains and impurities; (2) Place the washed stainless steel mesh in a dopamine / ethanol / water mixed solution, then adjust the pH to weakly alkaline, stir and react to form a rough adhesion layer; (3) Alternately soak the filter obtained in step (2) in an alginate solution and a calcium chloride solution to firmly coat the alginate hydrogel on the surface of the filter; (4) Dry the filter covered with the alginate hydrogel in step (3) to cure the hydrogel, thereby obtaining a superhydrophilic / underwater superoleophobic filter.

2. The method according to claim 1, wherein The inorganic acid described in step (1) is one or more of hydrochloric acid, sulfuric acid, carbonic acid, phosphoric acid, and hydrofluoric acid; the pore size of the stainless steel mesh is 20 - 100 μm.

3. The method according to claim 1, wherein The dopamine-like substance selected for the dopamine / ethanol / water mixed solution described in step (2) is one or more of dopamine hydrochloride, dopamine D4 hydrochloride, N-methyl dopamine, 6-hydroxy dopamine, and 3-acryloyl dopamine.

4. The method according to claim 1, wherein The preparation method of the dopamine / ethanol / water mixed solution described in step (2) is: mix dopamine, absolute ethanol, and deionized water in a mass ratio of 0.5:(0 - 70):(100 - 20).

5. The method according to claim 4, wherein In the dopamine / ethanol / water mixed solution described in step (2), the mass ratio of dopamine, absolute ethanol, and deionized water is 0.5:(24 - 47):(40 - 70).

6. The method according to claim 1, characterized in that, The pH-adjusting substance described in step (2) is one or more of ammonia water, triethanolamine, sodium bicarbonate, borax, sodium bicarbonate, sodium carbonate, disodium hydrogen phosphate, and calcium hydroxide, and the final pH of the obtained solution is 7.5 - 10; the stirring reaction time is 10 - 48 h, the rotation speed is 500 - 1000 rpm, and the reaction temperature is 25 - 50 °C.

7. The method according to claim 1, characterized in that, The alginate solution in step (3) is a solution prepared by mixing alginate powder and deionized water in a mass ratio of 0.01 - 0.1:100; the alginate is sodium alginate; the calcium chloride solution is a solution prepared by mixing calcium chloride particles and deionized water in a mass ratio of 0.1 - 1:

100.

8. The method according to claim 1, characterized in that, The preparation temperature of the alginate solution described in step (3) is 85 - 95 °C, and the stirring speed is 1000 - 1500 rpm; the specific method of alternate soaking is: first soak the filter in the sodium alginate solution for 10 - 30 min, take it out, rinse it with deionized water, and then transfer it to the calcium chloride solution for soaking for 10 - 30 min. This process needs to be repeated 2 - 5 times.

9. A superhydrophilic / underwater superoleophobic filter prepared by the method according to any one of claims 1 - 8.

10. Use of the superhydrophilic / underwater superoleophobic filter according to claim 9 in the preparation of an oil-water separation structure, an oil-proof coating structure, an oil separation structure, or an oil collection structure.

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