Inorganic hydrogel / polyvinylidene fluoride oil-water separation membrane and preparation method and application thereof

Abstract

The application belongs to the technical field of wastewater treatment, and provides an inorganic hydrogel / polyvinylidene fluoride oil-water separation membrane and a preparation method and application thereof. The method comprises the following steps: sequentially immersing a PVDF membrane in anhydrous ethanol, an alkali solution, a tannic acid solution, a FeCl3·6H2O solution and a (NH4)6Mo7O 24 4H2O solution to obtain an inorganic hydrogel / polyvinylidene fluoride oil-water separation membrane. The PVDF / TA / Gel composite membrane prepared by the application has good biocompatibility and a simple preparation process, has superhydrophilicity, underwater superoleophobicity, anti-pollution, good oil-water emulsion separation efficiency, excellent regeneration performance and good stability after catalytic cleaning, and can be recycled for a long time.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of wastewater treatment, and particularly relates to an inorganic hydrogel / polyvinylidene fluoride oil-water separation membrane and a preparation method and application thereof. BACKGROUND

[0002] At present, oil spills and a large amount of oily wastewater generated in the chemical industry pose a serious threat to human health and global water resources. Therefore, effective treatment of oily wastewater is of great significance for alleviating water resource shortage and achieving sustainable development. Traditional separation methods, such as gravity separation, flotation, coagulation and centrifugation, although widely used, have the disadvantages of low separation efficiency, high energy consumption and high cost. In recent years, membrane separation technology has attracted widespread attention due to its high separation efficiency, low energy consumption, relatively low cost and strong controllability. However, membrane fouling is inevitable during a long oil-water separation process. Therefore, it is a research focus to use hydrophilic functional materials to alleviate membrane fouling and achieve efficient oil-water separation.

[0003] At present, hydrogel modified materials are considered to be ideal modified materials due to their excellent hydrophilicity, especially inorganic hydrogel materials, which usually have excellent durability and can maintain their structural integrity and properties during oil-water separation. However, during long-term operation, membrane fouling is still inevitable due to the deformation and aggregation of oil droplets. Relying solely on hydrophilic modification cannot achieve long-term efficient operation, and even if simple hydraulic cleaning is used, oil droplets inside the membrane pores are difficult to remove.

[0004] Therefore, it is necessary to realize superhydrophilicity and catalytic cleaning functionalization to complete the long-term filtration treatment of oily wastewater. SUMMARY

[0005] The present application aims at providing an inorganic hydrogel / polyvinylidene fluoride oil-water separation membrane and a preparation method and application thereof to overcome the deficiencies of the prior art.

[0006] In order to achieve the above-mentioned application purposes, the present application provides the following technical solutions:

[0007] The present application provides a preparation method of an inorganic hydrogel / polyvinylidene fluoride oil-water separation membrane, comprising the following steps:

[0008] 1) soaking a PVDF membrane in anhydrous ethanol to obtain a pretreated PVDF membrane;

[0009] 2) soaking the pretreated PVDF membrane in an alkali solution to obtain an alkali-treated PVDF membrane;

[0010] 3) soaking the alkali-treated PVDF membrane in a tannic acid solution to obtain a PVDF / TA membrane;

[0011] 4) soaking the PVDF / TA membrane in FeCl3 6H2O solution to obtain PVDF / TA / Fe 3+ membrane;

[0012] 5) soaking the PVDF / TA / Fe 3+ membrane in (NH4)6Mo7O 24 4H2O solution to obtain inorganic hydrogel / polyvinylidene fluoride oil-water separation membrane.

[0013] Preferably, the pore size of the PVDF membrane in step 1) is 0.1-0.5 μm, and the soaking time is 5-30 min.

[0014] Preferably, the alkali solution in step 2) is sodium hydroxide solution or potassium hydroxide solution, and the concentration of the alkali solution is 1-5 mol / L; the soaking time is 2-10 min.

[0015] Preferably, the concentration of the tannic acid solution in step 3) is 30-120 g / L, the concentration of the FeCl3 6H2O solution in step 4) is 0.5-3.5 mol / L, and the concentration of the (NH4)6Mo7O 24 4H2O solution in step 5) is 0.05-2.0 mol / L.

[0016] Preferably, the soaking time in steps 3)-5) is independently 0.5-4 h.

[0017] The application further provides the inorganic hydrogel / polyvinylidene fluoride oil-water separation membrane prepared by the preparation method.

[0018] The application further provides the application of the inorganic hydrogel / polyvinylidene fluoride oil-water separation membrane in oil-containing wastewater, wherein a surfactant, oil and water are mixed to obtain oil-containing wastewater, and the inorganic hydrogel / polyvinylidene fluoride oil-water separation membrane is used for oil-water filtration and separation of the oil-containing wastewater.

[0019] Preferably, the concentration of the surfactant in the oil-containing wastewater is 10-50 mg / L, and the concentration of the oil is 1000-5000 ppm.

[0020] Preferably, the surfactant is one or more of sodium dodecyl sulfate, stearic acid, sodium dodecyl benzene sulfonate and Tween 80; and the oil is one or more of isooctane, n-hexane, paraffin, soybean oil, hexadecane and dichloromethane.

[0021] Preferably, the inorganic hydrogel / polyvinylidene fluoride oil-water separation membrane contaminated with oil droplets after filtration is regenerated in a persulfate solution; the persulfate is potassium peroxymonosulfate and / or potassium persulfate; the concentration of the persulfate solution is 0.1–0.5 mmol / L, and the regeneration time is 5–30 min.

[0022] The beneficial effects of this invention include the following:

[0023] 1) The PVDF / TA / Gel composite membrane prepared in this invention uses TA, a common and inexpensive natural plant polyphenol, and inorganic hydrogel materials, which are two common inorganic salts, FeCl3·6H2O and (NH4)6Mo7O. 24 ·4H2O has good biocompatibility and is simple to prepare.

[0024] 2) The PVDF / TA / Gel composite membrane prepared by this invention has super hydrophilicity, underwater superoleophobic properties, antifouling properties, and good oil-water emulsion separation efficiency.

[0025] 3) The PVDF / TA / Gel composite membrane prepared by this invention has excellent regeneration performance and good stability after catalytic cleaning, and can be recycled for a long time. Attached Figure Description

[0026] Figure 1 SEM images of the PVDF / TA / Gel composite membrane prepared in Example 2 and the original PVDF membrane without any treatment are shown, where a is the PVDF / TA / Gel composite membrane of Example 2 and b is the original PVDF membrane.

[0027] Figure 2 The images show the water contact angles of the PVDF / TA / Gel composite membrane prepared in Example 2 and the original PVDF membrane without any treatment, where a is the original PVDF membrane and b is the PVDF / TA / Gel composite membrane.

[0028] Figure 3 The graph shows the flux and separation efficiency of the PVDF / TA / Gel composite membranes prepared in Examples 1-3 and the original PVDF membranes without any treatment for separating oily wastewater.

[0029] Figure 4 The graph shows the flux recovery rate and separation efficiency of the PVDF / TA / Gel composite membrane prepared in Example 2 for the separation of water-in-isooctane emulsion in circulating filtration.

[0030] Figure 5 The graph shows the flux recovery rate and separation efficiency of the PVDF / TA / Gel composite membrane prepared in Example 2 after circulating filtration and catalytic cleaning for separating water-encapsulated isooctane emulsion. Detailed Implementation

[0031] This invention provides a method for preparing an inorganic hydrogel / polyvinylidene fluoride oil-water separation membrane, comprising the following steps:

[0032] 1) The PVDF membrane was immersed in anhydrous ethanol to obtain a pretreated PVDF membrane;

[0033] 2) The pretreated PVDF membrane is immersed in an alkaline solution to obtain an alkaline-treated PVDF membrane;

[0034] 3) The alkali-treated PVDF membrane is immersed in tannic acid (TA) solution to obtain a PVDF / TA membrane;

[0035] 4) The PVDF / TA membrane was immersed in FeCl3·6H2O solution to obtain PVDF / TA / Fe 3+ membrane;

[0036] 5) Combine PVDF / TA / Fe 3+ The membrane is in (NH4)6Mo7O 24 Immersion in 4H2O solution yields an inorganic hydrogel / polyvinylidene fluoride oil-water separation membrane (PVDF / TA / Gel composite membrane).

[0037] In this invention, the pore size of the PVDF membrane in step 1) is preferably 0.1-0.5 μm, more preferably 0.2-0.45 μm, and even more preferably 0.22-0.35 μm. The soaking time is preferably 5-30 min, more preferably 10-25 min, and even more preferably 15-20 min.

[0038] In this invention, the alkaline solution in step 2) is preferably a sodium hydroxide solution or a potassium hydroxide solution, and the concentration of the alkaline solution is preferably 1-5 mol / L, more preferably 2-4 mol / L, and even more preferably 3 mol / L; the soaking time is preferably 2-10 min, more preferably 3-8 min, and even more preferably 5-6 min.

[0039] In this invention, the concentration of the tannic acid solution in step 3) is preferably 30–120 g / L, more preferably 60–100 g / L, and even more preferably 70–90 g / L; the concentration of the FeCl3·6H2O solution in step 4) is preferably 0.5–3.5 mol / L, more preferably 1–3 mol / L, and even more preferably 1.5–2.5 mol / L; the concentration of the (NH4)6Mo7O solution in step 5) is... 24 The concentration of the ·4H2O solution is preferably 0.05 to 2.0 mol / L, more preferably 0.14 to 1.5 mol / L, and even more preferably 0.3 to 1.0 mol / L.

[0040] In this invention, the soaking time in steps 3) to 5) is preferably 0.5 to 4 hours, more preferably 1 to 3 hours, and even more preferably 1.5 to 2.5 hours.

[0041] In this invention, after soaking in step 1), the membrane is preferably rinsed with water to obtain a pretreated PVDF membrane; after soaking in step 2), the membrane is preferably rinsed with water to obtain an alkali-treated PVDF membrane; after soaking in step 3), the membrane is preferably rinsed with water to obtain a PVDF / TA membrane; and after soaking in step 4), the membrane is preferably rinsed with water to obtain a PVDF / TA / Fe membrane. 3+ Membrane; after the soaking in step 5), it is preferable to wash the membrane with water to obtain an inorganic hydrogel / polyvinylidene fluoride oil-water separation membrane.

[0042] In this invention, the alkaline solution is an aqueous solution of an alkali, the tannic acid solution is an aqueous solution of tannic acid, the FeCl3·6H2O solution is an aqueous solution of FeCl3·6H2O, and (NH4)6Mo7O 24 The 4H2O solution is (NH4)6Mo7O 24 Aqueous solution of 4H2O.

[0043] The present invention also provides an inorganic hydrogel / polyvinylidene fluoride oil-water separation membrane prepared by the aforementioned preparation method.

[0044] The present invention also provides the application of the inorganic hydrogel / polyvinylidene fluoride oil-water separation membrane in oily wastewater, wherein surfactant, oil and water are mixed to obtain oily wastewater, and the inorganic hydrogel / polyvinylidene fluoride oil-water separation membrane is used to filter and separate the oil and water in the oily wastewater.

[0045] In this invention, the concentration of surfactant in the oily wastewater is preferably 10-50 mg / L, more preferably 20-40 mg / L, and even more preferably 30 mg / L; the concentration of oil is preferably 1000-5000 ppm, more preferably 2000-4000 rpm, and even more preferably 3000 rpm.

[0046] In this invention, the pH value of the oily wastewater is preferably 6 to 9, and more preferably 7 to 8.

[0047] In this invention, the surfactant is preferably one or more of sodium dodecyl sulfate, stearic acid, sodium dodecylbenzene sulfonate, and Tween 80; the oil is preferably one or more of isooctane, n-hexane, paraffin, soybean oil, hexadecane, and dichloromethane.

[0048] In this invention, the inorganic hydrogel / polyvinylidene fluoride oil-water separation membrane contaminated with oil droplets after filtration and separation is regenerated in a persulfate solution; the persulfate is preferably potassium peroxymonosulfate and / or potassium persulfate; the concentration of the persulfate solution is preferably 0.1-0.5 mmol / L, more preferably 0.2-0.4 mmol / L, more preferably 0.3 mmol / L, and the regeneration time is preferably 5-30 min, more preferably 10-25 min, and more preferably 15-20 min.

[0049] The technical solutions provided by the present invention will be described in detail below with reference to the embodiments, but they should not be construed as limiting the scope of protection of the present invention.

[0050] In this embodiment, the PVDF membrane is a hydrophilic PVDF membrane purchased from Haining Delu New Material Technology Co., Ltd.

[0051] Example 1

[0052] A PVDF membrane with a pore size of 0.45 μm was immersed in anhydrous ethanol for 10 min and then washed with deionized water to obtain a pretreated PVDF membrane.

[0053] The pretreated PVDF membrane was immersed in a 3 mol / L sodium hydroxide solution for 5 min, and then washed with deionized water to obtain an alkali-treated PVDF membrane.

[0054] The alkali-treated PVDF membrane was soaked in a 30 g / L tannic acid solution for 1 hour, and then washed with deionized water to obtain a PVDF / TA membrane.

[0055] The PVDF / TA membrane was immersed in a 1 mol / L FeCl3·6H2O solution for 1 h, followed by washing with deionized water to obtain the PVDF / TA / Fe... 3+ membrane;

[0056] PVDF / TA / Fe 3+ The membrane was in 0.14 mol / L (NH4)6Mo7O 24 The membrane was soaked in 4H2O solution for 1 hour, and then washed with deionized water to obtain a PVDF / TA / Gel composite membrane (PVDF / T3 / Gel).

[0057] Example 2

[0058] The concentration of the tannic acid solution in Example 1 was changed from 30 g / L to 60 g / L, while other process conditions remained the same as in Example 1, to obtain a PVDF / TA / Gel composite membrane (PVDF / T6 / Gel).

[0059] SEM images of the PVDF / TA / Gel composite membrane prepared in Example 2 and the original PVDF membrane without any treatment are shown below.Figure 1 As shown, a is the PVDF / TA / Gel composite membrane of Example 2, and b is the original PVDF membrane. Figure 1 It can be seen that both the PVDF membrane and the PVDF / TA / Gel composite membrane are porous structures. After modification with TA and inorganic hydrogel, the surface of the PVDF / TA / Gel composite membrane is loaded with TA and inorganic hydrogel particles.

[0060] Example 3

[0061] The concentration of the tannic acid solution in Example 1 was changed from 30 g / L to 90 g / L, while other process conditions remained the same as in Example 1, to obtain a PVDF / TA / Gel composite membrane (PVDF / T9 / Gel).

[0062] Example 4

[0063] A PVDF membrane with a pore size of 0.35 μm was immersed in anhydrous ethanol for 20 min and then washed with deionized water to obtain a pretreated PVDF membrane.

[0064] The pretreated PVDF membrane was immersed in a 2 mol / L potassium hydroxide solution for 8 min, and then washed with deionized water to obtain an alkali-treated PVDF membrane.

[0065] The alkali-treated PVDF membrane was soaked in a 70 g / L tannic acid solution for 1.5 h, and then washed with deionized water to obtain a PVDF / TA membrane.

[0066] The PVDF / TA membrane was immersed in a 2.5 mol / L FeCl3·6H2O solution for 1 h, followed by washing with deionized water to obtain the PVDF / TA / Fe... 3+ membrane;

[0067] PVDF / TA / Fe 3+ The membrane was in 1.0 mol / L (NH4)6Mo7O 24 The membrane was soaked in 4H2O solution for 0.5 h and then washed with deionized water to obtain a PVDF / TA / Gel composite membrane.

[0068] Example 5

[0069] A PVDF membrane with a pore size of 0.22 μm was immersed in anhydrous ethanol for 15 min and then washed with deionized water to obtain a pretreated PVDF membrane.

[0070] The pretreated PVDF membrane was immersed in a 4 mol / L sodium hydroxide solution for 3 min, and then washed with deionized water to obtain an alkali-treated PVDF membrane.

[0071] The alkali-treated PVDF membrane was soaked in a 100 g / L tannic acid solution for 2 hours, and then washed with deionized water to obtain a PVDF / TA membrane.

[0072] The PVDF / TA membrane was immersed in a 1.5 mol / L FeCl3·6H2O solution for 2 h, followed by washing with deionized water to obtain the PVDF / TA / Fe... 3+ membrane;

[0073] PVDF / TA / Fe 3+ The membrane was in 0.3 mol / L (NH4)6Mo7O 24 The membrane was soaked in 4H2O solution for 2 hours, and then washed with deionized water to obtain a PVDF / TA / Gel composite membrane.

[0074] Application Example 1: Evaluation of the hydrophilicity of the membrane using contact angle testing.

[0075] The wettability of the membrane was tested using a water contact angle meter. The PVDF / TA / Gel composite membrane prepared in Example 2 and the untreated original PVDF membrane were placed on a contact angle measurement platform. Using a German KRUSS contact angle meter, a 2 μL drop of ultrapure water was slowly dropped onto the membrane sample surface through a needle. When the water droplet began to contact the membrane surface, the instrument recorded the static contact angle, i.e., the initial contact angle between the water droplet and the membrane surface. Subsequently, the change in contact angle over time was measured until the contact angle stabilized.

[0076] The water contact angle (WCA) diagrams of the PVDF / TA / Gel composite membrane prepared in Example 2 and the original PVDF membrane without any treatment are shown below. Figure 2 As shown in Figure a, where a is the original PVDF membrane and b is the PVDF / TA / Gel composite membrane. Figure a shows that water completely permeates the original PVDF membrane within 34.27 s, indicating a certain degree of hydrophilicity. Figure b shows that water droplets completely disappear and permeate into the PVDF / TA / Gel composite membrane within 1.50 s, indicating that the PVDF / TA / Gel composite membrane prepared in Example 2 has good hydrophilicity.

[0077] Application Example 2: Permeation flux and separation efficiency of different oil-in-water emulsions

[0078] At room temperature, the PVDF / TA / Gel composite membrane prepared in Example 2 was placed in a cross-flow filtration membrane module to filter oily wastewater (oil-in-water emulsion). The membrane module was fixed with screws, and a peristaltic pump (Baoding Reif BT100L) was used to deliver the oil-in-water emulsion to the membrane module for oil-water separation. The effluent from the membrane module was connected to the peristaltic pump for filtrate collection. The oil-in-water emulsion consisted of isooctane (2000 ppm), liquid paraffin (3500 ppm), soybean oil (4250 ppm), and hexadecane (1900 ppm). The concentration of surfactant added to the oil-in-water emulsion was 25 mg / L, and the pH of the oily wastewater was 7. After filtration for 1 hour, the filtration volume was recorded and the flux through the emulsion was calculated. The same operation was performed using the PVDF / TA / Gel composite membranes prepared in Examples 1 and 3, as well as the original PVDF membrane without any treatment.

[0079] The flux and separation efficiency of the PVDF / TA / Gel composite membrane prepared in Examples 1-3 and the original PVDF membrane without any treatment for separating oily wastewater are shown in the figure below. Figure 3 As shown, PVDF / T3 / Gel corresponds to Example 1, PVDF / T6 / Gel corresponds to Example 2, and PVDF / T9 / Gel corresponds to Example 3. The bar chart represents flux, and ○, □, △, and ☆ represent separation efficiency. Figure 3 It can be seen that the PVDF / TA / Gel composite membrane achieves a separation efficiency of over 98.5% for various oil-in-water emulsions, which is significantly better than the original PVDF membrane. This indicates that the membrane modified with TA and inorganic hydrogel effectively improves the flux and separation efficiency.

[0080] Application Example 3

[0081] A cyclic filtration experiment was conducted using the PVDF / TA / Gel composite membrane prepared in Example 2. At room temperature, the PVDF / TA / Gel composite membrane prepared in Example 2 was placed in a cross-flow filtration membrane module for oil-in-water emulsion separation. The oil-in-water emulsion used was isooctane (2000 ppm). First, deionized water was filtered for 10 min, and the filtrate volume was recorded. Then, the isooctane emulsion was filtered for 1 h, and the filtrate volume was recorded. After each cycle, the contaminated membrane was removed from the membrane module, rinsed with deionized water for 5 min, and then placed back into the membrane module for filtration for another 10 min. The filtrate volume was recorded, and the flux recovery rate was calculated. This cycle was repeated 7 times.

[0082] The flux recovery rate and separation efficiency of the PVDF / TA / Gel composite membrane prepared in Example 2 for the circulating filtration of water-in-water isooctane emulsion are shown in the figure below. Figure 4 As shown. By Figure 4It can be seen that the flux recovery rate can reach 90.6% after 7 cycles of filtration, indicating that the PVDF / TA / Gel membrane has good antifouling performance. However, with long-term oil-water separation filtration, the oil droplets inside the membrane pores cannot be removed by simple hydraulic cleaning, which leads to a decrease in flux recovery rate after the 7th cycle.

[0083] Application Example 4

[0084] Catalytic cleaning and regeneration experiments were conducted using the PVDF / TA / Gel composite membrane prepared in Example 2. At room temperature, the PVDF / TA / Gel composite membrane prepared in Example 2 was placed in a cross-flow filtration membrane module for oil-in-water emulsion separation. The oil-in-water emulsion used was isooctane (2000 ppm). First, deionized water was filtered for 10 min, and the filtrate volume was recorded. Then, the isooctane emulsion was filtered for 1 h, and the filtrate volume was recorded. After each cycle, the contaminated membrane was removed from the membrane module, soaked in a 0.25 mmol / L persulfate aqueous solution for 5 min, and then placed back into the membrane module for filtration for another 10 min. The filtrate volume was recorded, and the flux recovery rate was calculated. This cycle was repeated 7 times.

[0085] The flux recovery and separation efficiency of the PVDF / TA / Gel composite membrane prepared in Example 2 after circulating filtration and catalytic cleaning for separating water-in-water isooctane emulsion are shown in the figure below. Figure 5 As shown. By Figure 5 It is known that the flux recovery rate can reach as high as 98.6% after 7 cycles of filtration. This is because the iron in the inorganic hydrogel loaded on the surface of the PVDF / TA / Gel composite membrane reacts with persulfate, providing sufficient active sites. The resulting active substances effectively decompose oil droplets into water and carbon dioxide, making them easier to remove from the membrane pores. The PVDF / TA / Gel composite membrane prepared by this invention has good catalytic regeneration performance and is suitable for the stable separation of oil-water emulsions over long periods.

[0086] This invention prepares a PVDF / TA / Gel composite membrane with high oil-water separation efficiency via an immersion method. First, the PVDF membrane is modified with TA, and then two common inorganic salts, FeCl3·6H2O and (NH4)6Mo7O, are introduced. 24 Gelization with 4H2O yields a PVDF / TA / Gel composite membrane. The inorganic hydrogel / PVDF composite membrane prepared in this invention exhibits excellent hydrophilicity and underwater superoleophobicity, demonstrating good separation performance for simulated oily wastewater. Through the coupling of inorganic hydrogel superhydrophilic modification with persulfate catalytic cleaning, the contaminated membrane generates reactive oxygen species during catalysis to decompose oil on the membrane surface and inside the pores. This results in good regenerability of the cleaned membrane, extending its service life and demonstrating promising application prospects in oil-water separation.

[0087] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A method for preparing an inorganic hydrogel / polyvinylidene fluoride oil-water separation membrane, characterized in that, It includes the following steps: 1) The PVDF membrane was immersed in anhydrous ethanol to obtain a pretreated PVDF membrane; 2) The pretreated PVDF membrane is immersed in an alkaline solution to obtain an alkaline-treated PVDF membrane; 3) The alkali-treated PVDF membrane is immersed in tannic acid solution to obtain a PVDF / TA membrane; 4) The PVDF / TA membrane was immersed in FeCl3·6H2O solution to obtain PVDF / TA / Fe 3+ membrane; 5) Combine PVDF / TA / Fe 3+ The membrane is in (NH4)6Mo7O 24 • Immersion in 4H2O solution yields an inorganic hydrogel / polyvinylidene fluoride oil-water separation membrane; Step 3) The concentration of the tannic acid solution is 30–120 g / L; Step 4) The concentration of the FeCl3·6H2O solution is 0.5–3.5 mol / L; Step 5) The concentration of the (NH4)6Mo7O solution is… 24 The concentration of the 4H2O solution is 0.05–2.0 mol / L.

2. The preparation method according to claim 1, characterized in that, Step 1) The PVDF membrane has a pore size of 0.1 to 0.5 μm, and the soaking time is 5 to 30 min.

3. The preparation method according to claim 1 or 2, characterized in that, Step 2) The alkaline solution is a sodium hydroxide solution or a potassium hydroxide solution, and the concentration of the alkaline solution is 1-5 mol / L; the soaking time is 2-10 min.

4. The preparation method according to claim 3, characterized in that, The soaking time in steps 3) to 5) is independently 0.5 to 4 hours.

5. The inorganic hydrogel / polyvinylidene fluoride oil-water separation membrane prepared by the preparation method according to any one of claims 1 to 4.

6. The application of the inorganic hydrogel / polyvinylidene fluoride oil-water separation membrane according to claim 5 in oily wastewater, characterized in that, Surfactants, oil, and water are mixed to obtain oily wastewater, which is then filtered and separated by an inorganic hydrogel / polyvinylidene fluoride oil-water separation membrane.

7. The application according to claim 6, characterized in that, The oily wastewater contains surfactants at a concentration of 10–50 mg / L and oil at a concentration of 1000–5000 ppm.

8. The application according to claim 6 or 7, characterized in that, The surfactant is one or more of sodium dodecyl sulfate, stearic acid, sodium dodecylbenzene sulfonate, and Tween 80; the oil is one or more of isooctane, n-hexane, paraffin, soybean oil, hexadecane, and dichloromethane.

9. The application according to claim 8, characterized in that, After filtration and separation, the inorganic hydrogel / polyvinylidene fluoride oil-water separation membrane contaminated with oil droplets is regenerated in a persulfate solution; the persulfate is potassium peroxymonosulfate and / or potassium persulfate; the concentration of the persulfate solution is 0.1-0.5 mmol / L, and the regeneration time is 5-30 min.

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