A super-hydrophobic oleophilic silica nanofiber membrane, a preparation method and an oil-water separation method

Abstract

The application discloses a preparation method of super-hydrophobic lipophilic silica nanofiber membranes for oil-water separation. First, the SiO2 nanofiber membrane is modified by impregnation with alkenyl silane coupling agent, and a silane nanospherical microstructure with a double bond group is introduced to the surface, then a long carbon chain mercaptan is grafted by initiating a double bond-mercaptan "click reaction" under ultraviolet auxiliary irradiation. The method effectively improves the surface roughness of the membrane and reduces the surface energy of the membrane, so that the prepared membrane material has excellent super-hydrophobic lipophilic performance, and also has excellent oil-water separation performance and repeated use stability.

Description

Technical Field

[0001] This invention relates to the field of functional membrane material preparation, and specifically to a method for preparing a superhydrophobic and oleophilic silica nanofiber membrane for oil-water separation. Background Technology

[0002] Electrospinning, as a simple and efficient technology, can produce nanofiber membranes with high porosity, large specific surface area, and nanoscale diameter. It also possesses unique advantages in composition control, structural design, and functional modification, meeting the needs of various fields. SiO2, with its excellent chemical stability, thermal stability, and solvent resistance, is one of the most commonly used materials for electrospinning nanofiber membranes, and also an ideal choice for preparing oil-water separation membranes. However, SiO2 itself has hydrophilic and oleophilic properties, making it unsuitable for direct application in oil / water separation. Modifying the surface of SiO2 membranes to be hydrophobic while maintaining its oleophilic properties is one of the most effective methods.

[0003] The most common method for constructing hydrophobic surfaces is to coat or graft perfluorolong-chain alkanes onto the surface. Li et al. (Langmuir, 2013, 29: 8093-8102) modified PDMS membranes by impregnating them with perfluorooctyltriethoxysilane. The silane was adsorbed on the membrane surface and reacted with Si-OH, successfully forming a perfluorosilane monolayer on the PDMS / PSF membrane, thus enhancing hydrophobicity. However, simply grafting perfluorolong-chain alkanes does not achieve a superhydrophobic effect.

[0004] Studies have shown that besides low surface energy, a suitable rough structure plays a crucial role in the preparation of superhydrophobic surfaces. Huang et al. (J. Mater. Chem. A, 2013, 1: 14071) constructed a superhydrophobic-superoleophilic nanofiber membrane by forming a functional layer of F-PBZ / Al2O3 nanoparticles on the surface of a SiO2 nanofiber membrane through in-situ polymerization. Zhang et al. (J. Mater. Chem. A, 2021, 9: 15310-15320) anchored BiOBr microspheres onto SiO2 / PANI nanofibers, thereby preparing a superhydrophobic-oleophilic nanofiber membrane with high porosity, submicron pore size, and a hierarchical wettability structure. However, the above-mentioned two-dimensional nanofiber membranes used to construct superhydrophobic-oleophilic membranes still suffer from low separation flux and limited separation efficiency. For example, Chinese invention patent CN111632581A discloses a method for modifying cotton fibers with dopamine hydrochloride, then preparing raspberry-like nanoparticles by combining two modified particles, and finally modifying the cotton fibers again to achieve superhydrophobic and oleophilic modification. The preparation process of this invention patent is too cumbersome and costly, making it unsuitable for industrial scale-up and production. Summary of the Invention

[0005] The purpose of this invention is to overcome the problems of complex preparation process and weak bonding between nanostructures and fibers. A two-step impregnation method that is easy to operate and scale up is used to grow silane nanospheres with double bond groups in situ on the surface of SiO2 nanofiber membranes, and then graft long carbon chain thiols, which improves the surface roughness of the membrane and reduces the surface energy, thus successfully preparing a superhydrophobic and oleophilic silica nanofiber membrane.

[0006] The technical solution is:

[0007] A superhydrophobic and oleophilic silica nanofiber membrane includes a silica nanofiber base membrane, on which silane microspheres are distributed, and the surface of the silane microspheres is modified with alkyl thiols with or without substituents.

[0008] The substituent refers to fluorine.

[0009] The particle size range of the silane microspheres is 200-2000 nm.

[0010] The superhydrophobic and oleophilic silica nanofiber membrane has a water contact angle range of 140-175° and an oil contact angle range of 0-10°.

[0011] The preparation method of the above-mentioned superhydrophobic and oleophilic silica nanofiber membrane includes the following steps:

[0012] Step 1: Obtain the water-in-oil emulsion;

[0013] Step 2: Place the silica nanofiber membrane in a water-in-oil emulsion, let it stand, add a silane coupling agent with C=C bonds on the main chain, modify the surface, remove it, clean and dry it.

[0014] Step 3: Immerse the membrane in a solution of thiols for the grafting reaction, then remove, clean, and dry it.

[0015] In step 1, the water-in-oil emulsion is a toluene-in-water emulsion with a water content of 0.1%-1%, obtained by ultrasonic emulsification; preferably, the water / toluene volume ratio is 20-60 μL / 10 mL.

[0016] The silane coupling agent with C=C bonds on its main chain is selected from any one of vinyltrimethoxysilane, allyltrimethoxysilane, allyltrichlorosilane, vinyltriethoxysilane, vinyltrichlorosilane, and allyltriethoxysilane.

[0017] In step 2, the standing time is 10-100 min; the amount of double bond silane modifier in each 100 mL toluene-in-water emulsion is 0.5-6 mL, and the surface modification time is 1-20 min.

[0018] In step 3, the molecular formula of the alkyl thiol is CH3(CH2). m SH, where m is an integer from 11 to 18, and the molecular formula of perfluoroalkyl thiols is C1. n F 2(n-2)+1 H4SH, where n represents an integer from 9 to 15; specifically, it can be perfluorododecyl mercaptan, perfluorooctyl mercaptan, n-tetradecyl mercaptan, perfluorodecyl mercaptan, or n-octadecyl mercaptan.

[0019] The volume percentage of thiols in a solution is 10%-60%.

[0020] The grafting reaction was carried out under ultraviolet light for 0.5-3 hours.

[0021] An oil-water separation method involves filtering an oil- and water-containing raw material liquid through the aforementioned superhydrophobic and oleophilic silica nanofiber membrane, allowing the oil to pass through while retaining the water.

[0022] Beneficial effects

[0023] The superhydrophobic and oleophilic SiO2 nanofiber membrane prepared by this invention is simple to prepare, low in cost, fast in separation speed, high in efficiency, easy to clean, and reusable.

[0024] The superhydrophobic and oleophilic SiO2 nanofiber membrane prepared by this invention can be used for rapid and efficient separation of oil-water mixtures.

[0025] This invention utilizes the most common electrospun SiO2 nanofiber membrane. By hydrolyzing a double-bonded silane modifier and polycondensing it on the surface of the SiO2 nanofiber membrane, silane nanospheres with double-bonded groups were successfully grown in situ on the SiO2 nanofiber membrane surface, improving the membrane surface roughness while reducing surface energy. Furthermore, long-chain hydrophobic groups were introduced through a UV-initiated "click reaction" of olefins and thiols, successfully preparing a superhydrophobic and oleophilic silica nanofiber membrane.

[0026] This invention also has the following advantages: the process is simple and easy to operate. It has strong versatility, applicable not only to SiO2 nanofiber membranes but also to surfaces rich in hydroxyl groups such as ZrO2, Al2O3, SiO2-ZrO2, and cotton fibers. The superhydrophobic and oleophilic membrane prepared by the method of this invention has a water contact angle greater than 160° and an oil contact angle of 0°.

[0027] The superhydrophobic and oleophilic SiO2 nanofiber membrane prepared by this invention can also separate water-in-oil (W / O) emulsions stabilized with surfactants, including petroleum ether / water, cyclohexane / water, n-hexane / water, and toluene / water emulsions.

[0028] The superhydrophobic and oleophilic SiO2 nanofiber membrane prepared by this invention maintains an oil-water separation efficiency of over 99.5% after 10 separation cycles. Attached Figure Description

[0029] Figure 1 Yes (ac). SEM images of VTC-SiO2 after adding 20 μL, 40 μL and 60 μL of water to toluene;

[0030] Figure 2 This is a diagram of the water-oil contact angle of the superhydrophobic and oleophilic silica nanofiber membrane in the embodiment;

[0031] Figure 3 Yes (ad). SEM images of VTC-SiO2 modified with concentrations of 0.5 wt.%, 1 wt.%, 2 wt.%, and 3 wt.%.

[0032] Figure 4 The contact angle of VTC-SiO2 modified with concentrations of 0.5 wt.%, 1 wt.%, 2 wt.%, and 3 wt.% is (ad).

[0033] Figure 5 Yes (af). SEM images of VTC-SiO2 modified after impregnation times of 0 min, 2 min, 4 min, 6 min, 8 min and 10 min;

[0034] Figure 6 The contact angles of VTC-SiO2 after impregnation times of 2 min, 4 min, 6 min, 8 min and 10 min are shown.

[0035] Figure 7 Yes (ac). SEM images of F-VTC-SiO2 modified with concentrations of 10%, 20%, and 30%;

[0036] Figure 8 The contact angles of F-VTC-SiO2 modified with concentrations of 10%, 20%, and 30% are (ac).

[0037] Figure 9 Yes (ac). SEM images of F-VTC-SiO2 modified after illumination for 30 min, 1.0 h, and 2.0 h;

[0038] Figure 10 Yes (ac). Contact angles of F-VTC-SiO2 modified after illumination times of 30 min, 1.0 h, and 2.0 h;

[0039] Figure 11 This is a graph showing the oil-water separation flux and efficiency of the superhydrophobic and oleophilic silica nanofiber membrane obtained in Example 4.

[0040] Figure 12This is a graph showing the emulsion separation flux and efficiency of the superhydrophobic and oleophilic silica nanofiber membrane obtained in Example 4;

[0041] Figure 13 This is a schematic diagram of the fabrication process;

[0042] Figure 14 This is a schematic diagram of an oil-water separation method. Detailed Implementation

[0043] In some typical implementations, the technical solution of this patent is as follows:

[0044] A method for preparing a superhydrophobic and oleophilic silica nanofiber membrane for oil-water separation, the specific steps of which are as follows:

[0045] (1) Emulsion preparation: Add a small amount of deionized water to toluene and perform ultrasonic emulsification at room temperature to obtain a stable toluene-in-water emulsion. The purpose of this step is to prepare toluene emulsion. In the subsequent preparation process, by utilizing the specific solubility and dispersion characteristics of toluene emulsion for silane coupling agents, the silane coupling agents can be dispersed in the emulsion droplets, so that the silane is modified to form microspheres.

[0046] (2) Silane modification: After the silica nanofiber membrane is immersed in the toluene emulsion prepared in step (1), a silane modifier is added dropwise to the emulsion for impregnation and modification. After stirring at room temperature for a period of time, a modified silica nanofiber membrane with double bond microspheres is obtained. In this step, the main chain of the silane coupling agent should have C=C bonds. On the one hand, the microspheres will form a modified layer with a certain roughness after being modified on the surface of the nanofiber membrane, which can improve the hydrophobicity. On the other hand, the C=C on the surface of the microspheres can react and crosslink with the subsequent thiol, so that the surface is further modified by hydrophobic groups.

[0047] (3) Vacuum drying: After repeatedly washing the modified silica nanofiber membrane from step (2), place it in a vacuum drying oven to dry;

[0048] (4) Thiol grafting: The modified silica nanofiber membrane dried in step (3) is immersed in an ethanol solution of thiol and grafted under a UV curing lamp. After a period of time, the fiber membrane is taken out, and after repeated washing and drying, a superhydrophobic and oleophilic silica nanofiber membrane is obtained.

[0049] The reaction principle in the above preparation process is as follows: Figure 13 As shown.

[0050] In step (1), the amount of water added to the toluene emulsion is 20-60 μL / 10 mL, specifically 20, 40, or 60 μL of water can be added to 10 mL of toluene. The ultrasonic emulsification time is 1-3 h, specifically 1-2 h, 1 h, 1.5 h, or 2 h.

[0051] In step (2), the silica nanofiber membrane is impregnated for 30 minutes. The silane coupling agent is selected from any one of vinyltrimethoxysilane, allyltrimethoxysilane, allyltrichlorosilane, vinyltriethoxysilane, vinyltrichlorosilane, and allyltriethoxysilane. Specifically, it can be allyltrichlorosilane or vinyltrichlorosilane.

[0052] In step (2), the amount of double-bonded silane modifier in each 100 mL of toluene-in-water emulsion is 0.5-6 mL, specifically 0.5-3%, 0.5%, 1%, 2%, or 3%. The impregnation modification time is 1-20 min, specifically 2-10 min, 2, 4, 6, 8, or 10 min.

[0053] The solvent used for cleaning in step (3) is anhydrous ethanol or toluene. The drying temperature is 60-120 °C, specifically 60 or 120 °C. The drying time is 4-6 hours, specifically 4 hours or 6 hours.

[0054] In step (4), the thiol is either an alkyl thiol or a perfluoroalkyl thiol. The alkyl thiol has the molecular formula CH3(CH2)mSH, where m is an integer from 11 to 18. The perfluoroalkyl thiol has the molecular formula C... n F 2(n-2)+1 H4SH, where n represents an integer from 9 to 15. Specifically, it can be perfluorododecylthiol, perfluorooctylthiol, n-tetradecylthiol, perfluorodecylthiol, or n-octadecylthiol.

[0055] In step (4), the volume percentage of thiol compounds is 10%-60%, specifically 10%-30%, 10%, 20%, or 30%. The UV curing time is 0.5-3 hours, specifically 0.5-2 hours, 0.5 hours, 1 hour, or 2 hours.

[0056] The cleaning solvent in step (4) is anhydrous ethanol, and the drying temperature is 60-120°C, specifically 60 or 120°C. The drying time is 3-5 hours, specifically 3 hours or 5 hours.

[0057] Example 1

[0058] (1) Add 20 μL of deionized water to 10 mL of toluene and sonicate for 1.5 h at room temperature to obtain a stable toluene-in-water emulsion;

[0059] (2) Immerse a 5cm×5cm electrospun silica nanofiber membrane into the toluene emulsion prepared in step (1) for 30 minutes. Then slowly add vinyltrichlorosilane coupling agent (concentration of 0.5%) to the emulsion for impregnation and modification. After stirring at room temperature for 2 minutes, precipitate the solution to obtain a modified silica nanofiber membrane with double bond microspheres.

[0060] (3) The modified silica nanofiber membrane in step (2) is first rinsed with toluene three times, and then rinsed with ethanol three times to remove the residual silane coupling agent. It is then placed in a vacuum drying oven to dry at 60 °C for 4 hours.

[0061] (4) The modified silica nanofiber membrane dried in step (3) was immersed in an ethanol solution containing 10% perfluorododecyl mercaptan by volume. Under ultraviolet curing, a "click reaction" of olefin-thiol was initiated to carry out superhydrophobic grafting. After 30 min, the fiber membrane was removed and repeatedly washed with anhydrous ethanol to remove residual perfluorododecyl mercaptan. It was then dried. The drying temperature was 60 °C and the drying time was 3 h to obtain a superhydrophobic and oleophilic silica nanofiber membrane.

[0062] Effect of water content on the morphology of VTC-SiO2 nanofiber membranes

[0063] To investigate the effect of moisture content on microstructure, corresponding moisture content gradient tests were conducted. In this part of the experiment, additional 20 μL, 40 μL, and 60 μL of water were added to 10 mL of toluene. Figure 1 As shown, different microstructures were formed on the silica film by adjusting the amount of water added. When 20 μL of water was added, only a small number of silane nanospheres were fixed on the surface, indicating that VTC was not completely hydrolyzed and condensed. When the amount of water increased to 40 μL, the number of silane nanospheres increased significantly. The increase in silane nanospheres can be explained by the reaction solvent system, given the low solubility of water in toluene. Although the added water was not completely soluble in toluene, the entire reaction solvent system formed a toluene-water emulsion during the sonication process. Vinyltrichlorosilane was in excess compared to the added water. When the silica film entered the water-in-oil emulsion system, VTC in the water droplets underwent hydrolysis and further combined with hydroxyl groups on the silica surface. Therefore, more water caused more VTC hydrolysis, resulting in the formation of more silane nanospheres on the surface. However, as the water volume increases further, in addition to the continuous increase in the number of silane nanospheres, they will also fill the gaps in the fiber membrane, which is not conducive to the hydrophobic modification of the silica membrane in the later stage. Therefore, this experiment determined the amount of water to be added to be 40 μL / 10 mL through the water content gradient experiment.

[0064] Effect of vinyltrichlorosilane modification concentration on the morphology of VTC-SiO2 nanofiber membranes

[0065] To investigate the effect of vinyltrichlorosilane concentration on the surface morphology of the membrane, this experiment explored the influence of a series of impregnation concentrations (0.5 wt.%, 1 wt.%, 2 wt.%, and 3 wt.%) on the surface morphology of VTC-SiO2 nanofiber membranes. Figure 3 It can be seen that when the concentration is 0.5 wt.%, only a small number of silane nanospheres are distributed on the membrane surface. As the VTC concentration increases to 1 wt.%, a large number of silane nanospheres are generated on the fiber surface, and the distribution is relatively uniform. When the concentration continues to increase to 2 wt.% and 3 wt.%, the silane nanospheres on the fiber surface begin to agglomerate, become larger, and block the pores, which is detrimental to subsequent modification and separation. We further determined the optimal modification parameters based on the hydrophobic angle. Figure 4 As shown, the water contact angles of VTC-SiO2 increased to 152°, 153.2°, 148.9° and 147.8° respectively with increasing concentration. It can be seen that the water contact angle first increases and then decreases with increasing concentration from 0.5% to 3%. Taking all factors into consideration, the optimal impregnation concentration of vinyltrichlorosilane was determined to be 1 wt.%.

[0066] Effect of vinyltrichlorosilane modification time on the morphology of VTC-SiO2 nanofiber membranes

[0067] To investigate the effect of vinyltrichlorosilane impregnation time on the microstructure of nanofiber membranes, this experiment used 1 wt.% vinyltrichlorosilane to explore the influence of impregnation times (2 min, 4 min, 6 min, 8 min, and 10 min) on the surface morphology of VTC-SiO2 nanofiber membranes. The morphology and structure of the VTC-SiO2 membranes prepared at different modification times were observed using scanning electron microscopy. Figure 5 As shown, the surface of the SiO2 nanofiber membrane is smooth, while the surface of the VTC-SiO2 fiber membrane is coated with a rough structure. When the modification time is 2 min-6 min, we found that only a small number of seed-like particles are distributed on the membrane surface and do not form spheres. As the time increases to 8 min, silane nanospheres are generated on the fiber surface and are more uniformly distributed. When the time is further extended to 10 min, the silane nanospheres on the fiber surface slowly increase in size and begin to aggregate. We further determined the optimal modification parameters based on the hydrophobic angle. Figure 6 As shown, the WCA of the VTC-SiO2 film increased slightly from approximately 152.3° to approximately 156.4° as the impregnation time increased from 2 min to 8 min. However, as the impregnation time was extended to 10 min, the WCA of the samples decreased to 152.8°, which may be attributed to the aggregation of silane nanospheres. Furthermore, the OCA of all samples was 0°, indicating that all samples exhibited oleophilicity. Taking all factors into consideration, a modification time of 8 min was finally determined.

[0068] Effect of perfluorodecylthiol concentration on the morphology of F-VTC-SiO2 nanofiber membranes

[0069] To investigate the effect of perfluorodecyl mercaptan (PFDM) concentration on the surface morphology of F-VTC-SiO2 nanofiber membranes, this experiment explored the influence of PFDM concentrations with ethanol volume percentages ranging from 10% to 30% (10%, 20%, and 30%, respectively) on the surface morphology of the membranes. The morphology and structure of the F-VTC-SiO2 membranes prepared with different concentrations were observed using scanning electron microscopy. Figure 7 As shown, silane nanospheres are attached to the surface of the F-VTC-SiO2 fiber membrane. With increasing thiol concentration, the silane nano-rough structure on the fiber surface shows no significant change. We further determined the optimal modification parameters based on the hydrophobic angle. Figure 8 As shown, the water contact angles of F-VTC-SiO2 increased to 158.2°, 161.4° and 162.6° with increasing concentration. It can be seen that the increase in contact angle is not very significant when the concentration ranges from 10% to 30%. Taking all factors into consideration, the ethanol volume percentage of perfluorodecyl mercaptan is 20%.

[0070] Effect of UV irradiation time on the morphology of F-VTC-SiO2 nanofiber membranes

[0071] To investigate the effect of UV irradiation time on the surface morphology of F-VTC-SiO2 nanofiber membranes, this experiment explored the influence of time gradients of 30 min–2 h (30 min, 1.0 h, and 2.0 h, respectively) on the surface morphology of the membranes. The morphology and structure of the F-VTC-SiO2 membranes prepared with different irradiation times were observed using scanning electron microscopy. Figure 9 As shown, silane nanospheres adhered to the surface of the F-VTC-SiO2 fiber membrane over time, with no significant difference between them. We further determined the optimal modification parameters based on the hydrophobic angle. Figure 10 As shown, with the extension of illumination time, the water contact angles of F-VTC-SiO2 were 158.6°, 161.5°, and 159.9°, respectively, showing a pattern of first increasing and then decreasing. Considering all factors, the UV illumination time was 1 hour.

[0072] Oil-water separation experiment

[0073] Oil-water separation tests of the F-VTC-SiO2 nanofiber membrane were conducted in a glass filtration apparatus, and all performance tests were performed solely by gravity. Dead-end filtration equipment was used throughout the separation process. Figure 14As shown, the gravity-driven separation device consists of a quartz filter cup with an F-VTC-SiO2 nanofiber membrane sandwiched between it and a glass beaker for collecting the filtrate. Carbon tetrachloride, dichloromethane, and 1,2-dichloroethane were used as the oil phase for testing. Water and oil (dichloromethane) were stained with methylene blue and brilliant yellow, respectively. The oil and water were mixed in a 1:1 ratio to obtain the desired non-emulsified oil-water mixture. The F-VTC-SiO2 nanofiber membrane was fixed in the filter jacket; the yellow oil fell into the beaker solely by gravity, while the blue water was retained on the surface due to the superhydrophobicity of the fiber membrane.

[0074] To prepare the emulsified oil-water mixture for testing, oil and water were mixed at a ratio of 99:1 (v / v). Then, 0.2 mg / L Span-80 was added as an emulsifier. The mixture was stirred at 3000 rpm / min for 3 hours to form a surfactant-stabilized water-in-oil emulsion.

[0075] The superhydrophobic and oleophilic silica nanofiber membrane prepared under the preferred conditions in this embodiment has a water contact angle of 161.4°, an oil contact angle of 0°, an oil-water mixture separation efficiency of 99.71%, a petroleum ether / water emulsion separation efficiency of 99.75%, and separation efficiencies for cyclohexane / water, n-hexane / water, and toluene / water emulsions.

[0076] Example 2

[0077] (1) Add 20 μL of deionized water to 10 mL of toluene and sonicate for 2 h at room temperature to obtain a stable toluene-in-water emulsion;

[0078] (2) Immerse a 5cm×5cm electrospun silica nanofiber membrane into the toluene emulsion prepared in step (1) for 30 minutes. Then slowly add allyl trichlorosilane coupling agent (concentration of 3%) to the emulsion for impregnation and modification. After stirring at room temperature for 4 minutes, precipitate the solution to obtain a modified silica nanofiber membrane with double bond microspheres.

[0079] (3) The modified silica nanofiber membrane in step (2) is first rinsed with toluene three times, and then rinsed with ethanol three times to remove the residual silane coupling agent. It is then placed in a vacuum drying oven to dry at 60°C for 4 hours.

[0080] (4) The modified silica nanofiber membrane dried in step (3) was immersed in an ethanol solution containing 20% ​​perfluorooctanethiol by volume. Under ultraviolet curing, an olefin-thiol "click reaction" was initiated to perform superhydrophobic grafting. After 45 min, the fiber membrane was removed and washed three times with anhydrous ethanol to remove residual perfluorooctanethiol. The membrane was then dried. The drying temperature was 80°C and the drying time was 5 h to obtain a superhydrophobic and oleophilic silica nanofiber membrane.

[0081] The superhydrophobic and oleophilic silica nanofiber membrane prepared in this embodiment has a water contact angle of 162.8°, an oil contact angle of 0°, an oil-water mixture separation efficiency of 99.68%, and a cyclohexane / water emulsion separation efficiency of 99.72%.

[0082] Example 3

[0083] (1) Add 40 μL of deionized water to 10 mL of toluene and sonicate for 3 h at room temperature to obtain a stable toluene-in-water emulsion;

[0084] (2) Immerse a 5cm×5cm electrospun silica nanofiber membrane into the toluene emulsion prepared in step (1) for 30 minutes. Then slowly add vinyltrichlorosilane coupling agent (concentration of 3%) to the emulsion for impregnation and modification. After stirring at room temperature for 6 minutes, precipitate the solution to obtain a modified silica nanofiber membrane with double bond microspheres.

[0085] (3) The modified silica nanofiber membrane in step (2) is first rinsed with toluene three times, and then rinsed with ethanol three times to remove the residual silane coupling agent. It is then placed in a vacuum drying oven to dry at 60°C for 6 hours.

[0086] (4) The modified silica nanofiber membrane dried in step (3) was immersed in an ethanol solution containing 30% n-tetradecyl mercaptan by volume. Under ultraviolet curing, a "click reaction" of olefin-thiol was initiated to carry out superhydrophobic grafting. After 1 hour, the fiber membrane was removed and washed three times with anhydrous ethanol to remove residual n-tetradecyl mercaptan. The membrane was then dried. The drying temperature was 60°C and the drying time was 3 hours to obtain a superhydrophobic and oleophilic silica nanofiber membrane.

[0087] The superhydrophobic and oleophilic silica nanofiber membrane prepared in this embodiment has a water contact angle of 160.3°, an oil contact angle of 0°, an oil-water mixture separation efficiency of 99.69%, and a hexane / water emulsion separation efficiency of 99.77%.

[0088] Example 4

[0089] (1) Add 60 μL of deionized water to 10 mL of toluene and sonicate for 2 h at room temperature to obtain a stable toluene-in-water emulsion;

[0090] (2) Immerse a 5cm×5cm electrospun silica nanofiber membrane into the toluene emulsion prepared in step (1) for 30 minutes. Then slowly add vinyltrichlorosilane coupling agent (concentration of 1%) to the emulsion for impregnation and modification. After stirring at room temperature for 8 minutes, precipitate the solution to obtain a modified silica nanofiber membrane with double bond microspheres.

[0091] (3) The modified silica nanofiber membrane in step (2) is first rinsed with toluene three times, and then rinsed with ethanol three times to remove the residual silane coupling agent. It is then placed in a vacuum drying oven to dry at 60°C for 6 hours.

[0092] (4) The modified silica nanofiber membrane dried in step (3) was immersed in an ethanol solution containing 20% ​​perfluorodecyl mercaptan by volume. Under ultraviolet curing, a "click reaction" of olefin-thiol was initiated to carry out superhydrophobic grafting. After 1.5 h, the fiber membrane was removed and washed three times with anhydrous ethanol to remove residual perfluorodecyl mercaptan. It was then dried. The drying temperature was 80°C and the drying time was 5 h to obtain a superhydrophobic and oleophilic silica nanofiber membrane.

[0093] The superhydrophobic and oleophilic silica nanofiber membrane prepared in this embodiment has a water contact angle of 161.9°, an oil contact angle of 0°, an oil-water mixture separation efficiency of 99.76%, and a toluene / water emulsion separation efficiency of 99.74%.

[0094] Example 5

[0095] (1) Add 40 μL of deionized water to 10 mL of toluene and sonicate for 2 h at room temperature to obtain a stable toluene-in-water emulsion;

[0096] (2) Immerse a 5cm×5cm electrospun silica nanofiber membrane into the toluene emulsion prepared in step (1) for 30 minutes. Then slowly add vinyltrichlorosilane coupling agent (concentration of 2%) to the emulsion for impregnation and modification. After stirring at room temperature for 10 minutes, precipitate the solution to obtain a modified silica nanofiber membrane with double bond microspheres.

[0097] (3) The modified silica nanofiber membrane in step (2) is first rinsed with toluene three times, and then rinsed with ethanol three times to remove the residual silane coupling agent. It is then placed in a vacuum drying oven to dry at 60°C for 4 hours.

[0098] (4) The modified silica nanofiber membrane dried in step (3) was immersed in an ethanol solution containing 30% n-octadecyl mercaptan by volume. Under ultraviolet curing, a "click reaction" of olefin-thiol was initiated to carry out superhydrophobic grafting. After 2 hours, the fiber membrane was removed and washed three times with anhydrous ethanol to remove residual n-octadecyl mercaptan. The membrane was then dried. The drying temperature was 60°C and the drying time was 3 hours to obtain a superhydrophobic and oleophilic silica nanofiber membrane.

[0099] The superhydrophobic and oleophilic silica nanofiber membrane prepared in this embodiment has a water contact angle of 162.6°, an oil contact angle of 0°, an oil-water mixture separation efficiency of 99.53%, and a hexane / water emulsion separation efficiency of 99.73%.

Claims

1. A method for preparing a superhydrophobic and oleophilic silica nanofiber membrane for oil-water separation, comprising the following specific steps: (1) Emulsion preparation: Add a small amount of deionized water to toluene and perform ultrasonic emulsification at room temperature to obtain a stable toluene-in-water emulsion with a water / toluene volume ratio of 20-60 μL / 10 mL. (2) Silane modification: After the silica nanofiber base film is immersed in the toluene-in-water emulsion prepared in step (1), a silane coupling agent with C=C bonds on the main chain is added dropwise to the emulsion for surface modification. After stirring at room temperature for a period of time, a modified silica nanofiber film with double bond microspheres is obtained. The amount of double bond silane coupling agent in each 100 mL toluene-in-water emulsion is 0.5-6 mL. (3) Vacuum drying: After repeatedly washing the modified silica nanofiber membrane from step (2), place it in a vacuum drying oven to dry. (4) Thiol grafting: The modified silica nanofiber membrane dried in step (3) is immersed in an ethanol solution of alkyl thiols with or without substituents, and the grafting reaction is carried out under a UV curing lamp. After a period of time, the fiber membrane is taken out, and after repeated washing and drying, a superhydrophobic and oleophilic silica nanofiber membrane is obtained.

2. The preparation method according to claim 1, characterized in that, In step (1), the toluene-in-water emulsion is obtained by ultrasonic emulsification.

3. The preparation method according to claim 1, characterized in that, The substituent is fluorine.

4. The preparation method according to claim 1, characterized in that, In step (2), the silane coupling agent with C=C bonds on the main chain is selected from any one of vinyltrimethoxysilane, allyltrimethoxysilane, allyltrichlorosilane, vinyltriethoxysilane, vinyltrichlorosilane, and allyltriethoxysilane; the wetting time is 10-100 min; and the surface modification time is 1-20 min.

5. The preparation method according to claim 1, characterized in that, In step (4), the molecular formula of the alkyl thiol without substituents is CH3(CH2). m SH, where m is an integer from 11 to 18.

6. The preparation method according to claim 1, characterized in that, The alkyl thiol is selected from any one of perfluorododecyl thiol, perfluorooctyl thiol, n-tetradecyl thiol, perfluorodecyl thiol, or n-octadecyl thiol.

7. The preparation method according to claim 1, characterized in that, The grafting reaction time is 0.5-3 hours.

8. A superhydrophobic and oleophilic silica nanofiber membrane for oil-water separation, characterized in that, The superhydrophobic and oleophilic silica nanofiber membrane prepared by any one of claims 1-7 comprises a silica nanofiber base membrane, on which silane microspheres are distributed, and the surface of the silane microspheres is modified with alkyl thiols with or without substituents.

9. The superhydrophobic and oleophilic silica nanofiber membrane according to claim 8, characterized in that, The particle size range of the silane microspheres is 200-2000 nm.

10. The superhydrophobic and oleophilic silica nanofiber membrane according to claim 8, characterized in that, The superhydrophobic and oleophilic silica nanofiber membrane has a water contact angle of 140-175° and an oil contact angle of 0-10°.

11. An oil-water separation method, wherein an oil- and water-containing raw material liquid is filtered through the superhydrophobic and oleophilic silica nanofiber membrane as described in claim 8, allowing oil to pass through while retaining water.

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