A super-hydrophilic-underwater super-oleophobic polyacrylonitrile nanofiber membrane and its preparation method and application

Abstract

The present invention discloses a kind of super-hydrophilic underwater super-oleophobic polyacrylonitrile nanofiber membrane and its preparation method and application, comprise the following steps: S1, hydrophilic acrylate is added to the organic solution of polyacrylonitrile, prepare and obtain electrostatic spinning solution;S2, the electrostatic spinning solution is electrostatically spun to obtain electrostatically spun nanofiber membrane;S3, the electrostatically spun nanofiber membrane is immersed in the solution containing photoinitiator and carries out ultraviolet illumination, then takes out and is immersed in alkaline solution, washes, dries and obtains the super-hydrophilic underwater super-oleophobic polyacrylonitrile nanofiber membrane.Above-mentioned preparation method is simple, efficient, is suitable for batch production;And the polyacrylonitrile nanofiber membrane prepared is cross-linked by light alkali collaborative double network structure, effectively improves the chemical stability of polyacrylonitrile nanofiber membrane in organic solvent, and shows super-hydrophilic, underwater super-oleophobic characteristics, can realize efficient separation of oil-in-water emulsion only under the action of gravity.

Description

Technical Field

[0001] The present invention relates to the technical field of oil-water separation material preparation, and in particular to a method for preparing a super-hydrophilic-underwater super-oleophobic polyacrylonitrile nanofiber membrane, and its application in oil-water separation. Background Art

[0002] In recent years, the discharge of wastewater, oil spills, and industrial oily wastewater generated by daily life has posed a serious threat to the ecological environment and human survival. Efficient oil-water separation materials are key to addressing these challenges. Membrane separation materials, characterized by ease of operation, high efficiency, and low energy consumption, are ideal for efficient oil-water separation. However, oil droplet sizes and distributions in oily wastewater vary widely, ranging from large, easily separated floating oil (>150 μm) and dispersed oil (20-150 μm) to smaller, more difficult-to-separate emulsified oil (<20 μm). Traditional separation membranes based on pore size screening and low selective wettability not only require additional pressure to separate emulsified oily wastewater, but also easily become contaminated and clogged by oil on the surface and internal pores, making subsequent removal difficult. This inevitably leads to a decrease in separation efficiency and flux, making sustained, efficient oil-water separation difficult. Developing separation membrane materials with micro- and nanopore structures and highly selective wettability is an ideal solution for addressing these challenges and achieving high-efficiency, low-energy purification of oily wastewater.

[0003] Electrospinning technology has become a leading technique for preparing nanofiber membranes due to its simple equipment, ease of operation, low spinning costs, and wide variety of spinnable materials. It can directly form fiber membranes with high specific surface area, highly interconnected porous structures, and unique micro-nano roughened surfaces. Among them, electrospun polyacrylonitrile membranes are widely used in membrane separation due to their low cost, large specific surface area, high porosity, and relatively stable structure. However, polyacrylonitrile nanofiber membranes have poor hydrophilicity, are easily contaminated during oil-water separation, have low flux, and exhibit poor solvent resistance, further limiting their application environments.

[0004] With the development of special impregnating materials, a series of superhydrophilic / underwater superoleophobic electrospun membrane materials with high selective wettability have been prepared by adding inorganic nanomaterials such as silicon dioxide and titanium dioxide to the electrospinning solution for electrospinning, or by coating, grafting and other post-finishing techniques on the electrospun membrane to increase the micro-nano roughness and surface chemical energy of the electrospun membrane. These materials have been applied to the separation of emulsified oily wastewater. The super wettability of the surface of this type of membrane allows water to quickly pass through and form a dense water film on the membrane surface, blocking the permeation of the membrane, and achieving efficient purification of oily wastewater under the action of gravity. However, the stability of this type of membrane material is poor. The modified material on the membrane surface is easy to fall off during oil-water separation, and it will swell and dissolve in the presence of organic solvents when filtering wastewater, which can easily lead to serious membrane pollution and short service life.

[0005] Based on this, there is an urgent need for a superhydrophilic-underwater superoleophobic electrospun membrane material that has high selective wettability, resistance to organic solvents, long service life, and can achieve efficient separation of emulsified oily wastewater without applying additional pressure. Summary of the Invention

[0006] To solve the above problems, the present invention provides a super-hydrophilic-underwater super-oleophobic polyacrylonitrile nanofiber membrane and its preparation method and application, by electrostatic spinning of polyacrylonitrile and hydrophilic acrylate compound blended into a film, in the presence of a photoinitiator, ultraviolet irradiation induces the multifunctional hydrophilic acrylate copolymerization uniformly dispersed in polyacrylonitrile to obtain an electrostatically spun nanofiber membrane, and further alkali treatment is performed to induce the hydrolysis of polyacrylonitrile and the multifunctional hydrophilic acrylate network to form an interfacial chemical bond, thereby effectively improving the organic dissolution resistance of the fiber membrane. The preparation method is simple, the chemical reaction is rapid, and it is suitable for mass production, and the prepared polyacrylonitrile nanofiber membrane is resistant to organic solvents, and can achieve efficient separation of oily wastewater only under the action of gravity, and has good application prospects in oil-water separation materials.

[0007] Specifically, the following technical solutions are provided:

[0008] A first aspect of the present invention provides a method for preparing a super-hydrophilic-underwater super-oleophobic polyacrylonitrile nanofiber membrane, comprising the following steps:

[0009] S1. Evenly mixing an organic solution of hydrophilic acrylate and polyacrylonitrile to prepare an electrospinning solution; wherein the mass ratio of hydrophilic acrylate to polyacrylonitrile in the electrospinning solution is 1:10-3:1 (e.g., 1:10, 1:5, 1:1, 2:1, 3:1, etc.);

[0010] S2, electrospinning the electrospinning solution to obtain an electrospun nanofiber membrane;

[0011] S3, immersing the electrospun nanofiber membrane in a solution containing a photoinitiator and irradiating it with ultraviolet light, transferring it to an alkaline solution for immersion treatment after irradiation, washing it, and drying it to obtain the super hydrophilic-underwater super oleophobic polyacrylonitrile nanofiber membrane;

[0012] The hydrophilic acrylate is an acrylate compound containing at least two carbon-carbon double bonds.

[0013] The existing polyacrylonitrile nanofiber membrane has poor hydrophilicity and poor solvent resistance, and is prone to contamination and low flux during the oil-water separation process. The existing superhydrophilic / underwater superoleophobic electrospun membrane materials with high selective wettability have modified materials on the membrane surface that easily fall off during the oil-water separation process, and swell and dissolve in the presence of organic solvents when filtering wastewater, resulting in serious membrane pollution and a short service life (poor stability). In order to solve the above problems, the present invention electrostatically spins polyacrylonitrile and hydrophilic acrylate compounds into a membrane, and the two components are evenly distributed in the nanofiber membrane, and then immersed in a solution containing a photoinitiator for ultraviolet light treatment, so that the multifunctional hydrophilic acrylate evenly distributed in the nanofiber membrane undergoes free radical polymerization to form a first cross-linked network; on this basis, the nanofiber membrane after ultraviolet light treatment is further immersed in an alkaline solution. Under the action of the alkaline reagent, the cyanide group in the polyacrylonitrile chain segment in the nanofiber membrane is hydrolyzed into a carboxyl group, and the carboxyl group undergoes esterification or amidation reaction with the active groups (such as hydroxyl and amino) in the hydrophilic acrylate cross-linked network, forming a chemical bond at the interface of the two materials, thereby constructing a stable double network structure. The formation of this double network structure can effectively inhibit the swelling and penetration of the molecular chain by the organic solvent, and at the same time, the hydrophilic carboxyl salt (-COO - Na + ) synergistically with the hydrophilic groups of the cross-linked network to endow the membrane with superhydrophilic properties.

[0014] It should be noted that in the above preparation method, the feed ratio of the two raw materials, polyacrylonitrile and hydrophilic acrylate compounds, needs to be controlled. If the polyacrylonitrile content in the formed nanofiber membrane is too high, the hydrophilicity of the prepared nanofiber membrane will be poor, which will affect the wetting performance of the nanofiber membrane. Under water, the affinity of oil molecules is higher than that of water, which can expel the water molecules in the membrane and penetrate into the interior of the membrane to contaminate the membrane material, thereby failing to efficiently separate oil and water and being easily contaminated, with poor recycling performance; but the content of hydrophilic acrylate compounds in the nanofiber membrane should not be too high, otherwise adhesion will occur between the fibers of the nanofiber membrane, and even the fiber structure cannot be observed. This is because a small amount of polyacrylonitrile cannot provide sufficient viscoelasticity required for spinning, and the spinning solution is sprayed in the form of droplets, and the receiving device forms a porous nanofiber membrane. Although the liquid is hydrophilic after drying, there is no obvious pore structure and the solvent resistance is poor, so it cannot be used as an oil-water separation membrane material. Therefore, in order to obtain a polyacrylonitrile nanofiber membrane that can efficiently separate oily wastewater, the mass ratio of hydrophilic acrylate to polyacrylonitrile needs to be controlled in the range of 1:10-3:1.

[0015] The present invention controls the feed ratio of polyacrylonitrile and hydrophilic acrylic ester compounds and combines the light-alkali synergistic effect to prepare an integrated, structurally stable nanofiber membrane. The polyacrylonitrile nanofiber membrane not only has good resistance to organic solvents, but also exhibits excellent oil-water separation ability and long-term stability.

[0016] Furthermore, in step S1, the hydrophilic acrylate is selected from one or more of polyethylene glycol diacrylate, pentaerythritol triacrylate, trimethylolpropane triacrylate, glycerol propoxy triacrylate, ethoxylated trimethylolpropane triacrylate, ditrimethylolpropane tetraacrylate, ethoxylated pentaerythritol tetraacrylate, dipentaerythritol pentaacrylate, and dipentaerythritol hexaacrylate.

[0017] Furthermore, in step S1, the organic solution of polyacrylonitrile is obtained by dissolving polyacrylonitrile in an organic solvent; wherein the organic solvent includes but is not limited to N,N-dimethylformamide.

[0018] Furthermore, in step S1, the mass proportion of polyacrylonitrile in the organic solution of polyacrylonitrile is 5%-30%, for example, 5%, 10%, 15%, 20%, 25%, 30%, etc., including but not limited to the mass proportions listed above.

[0019] Furthermore, in step S1, the mass ratio of hydrophilic acrylate to polyacrylonitrile in the electrospinning solution is preferably 1:10-2:1; when the mass ratio of hydrophilic acrylate to polyacrylonitrile in the electrospinning solution is 1:10-1:3, the super hydrophilic-underwater super oleophobic polyacrylonitrile nanofiber membrane also has a super hydrophobic effect under oil.

[0020] Furthermore, in step S2, the process parameters of the electrospinning are: spinning voltage 8-35 kV, spinning distance 5-20 cm, spinning speed 0.1-3 mL / h, and needle diameter 0.2-3.5 mm.

[0021] Furthermore, in step S3, the photoinitiator is selected from one or more of 2-hydroxy-2-methyl-1-phenyl-1-propanone, 2,4,6-trimethylbenzoyldiphenoxyphosphine, a,a,-dimethylbenzil ketal, benzophenone, 1-hydroxycyclohexyl benzophenone and bis(2,4,6-trimethylbenzoyl)phenylphosphine oxide.

[0022] Furthermore, in step S3, the mass proportion of the photoinitiator in the photoinitiator-containing solution is preferably 0.5%-10%, for example, 0.5%, 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10%, etc., including but not limited to the mass proportions listed above.

[0023] Furthermore, in step S3, in the ultraviolet irradiation step: the wavelength of the ultraviolet light is 200-500 nm, and the irradiation intensity is 10-100 W / cm 2 The irradiation time is 5 min-120 min.

[0024] Furthermore, in step S3, the alkaline solution is obtained by dissolving an alkali in water; preferably, the alkali is selected from one or more of sodium hydroxide, potassium hydroxide, sodium carbonate, tetramethylammonium hydroxide, and ammonia water.

[0025] Furthermore, in step S3, the concentration of the alkaline solution used to hydrolyze polyacrylonitrile cannot be too low. Too low a concentration of the alkaline solution will result in insufficient hydrolysis of the carboxyl groups, which will not be able to fully bond with the active groups in the hydrophilic acrylate cross-linked network to form a double network structure, and the prepared nanofiber membrane will have poor solvent resistance; however, the concentration of the alkaline solution used to hydrolyze polyacrylonitrile cannot be too high. High concentrations of alkali will destroy hydrogen bonds, causing the polyacrylonitrile segments to swell violently, leading to rupture of the fiber membrane. Preferably, the mass proportion of the alkali in the alkaline solution is controlled within the range of 5%-40%, such as 5%, 10%, 15%, 20%, 25%, 30%, 35%, 40%, etc., including but not limited to the mass proportions listed above.

[0026] Furthermore, in step S3, the soaking temperature is 30-80°C, and the soaking time is preferably 0.2 h-12 h, such as 0.2 h, 1 h, 2 h, 4 h, 6 h, 8 h, 10 h, 12 h, etc., including but not limited to the times listed above. In the present invention, the hydrolysis temperature should not be too high, as such a high temperature may cause fiber collapse; and the soaking time should not be too long, as such a long time may lead to excessive hydrolysis and embrittlement.

[0027] Furthermore, in step S3, the washing solvent is water; and the drying temperature is preferably 20-80°C.

[0028] The second aspect of the present invention provides a super-hydrophilic-underwater super-oleophobic polyacrylonitrile nanofiber membrane, which is prepared by the preparation method described in the first aspect.

[0029] The third aspect of the present invention provides an application of the super-hydrophilic-underwater super-oleophobic polyacrylonitrile nanofiber membrane described in the second aspect in an oil-water separation material.

[0030] Furthermore, the superhydrophilic-underwater superoleophobic polyacrylonitrile nanofiber membrane can achieve a separation efficiency of up to 99.9% for oil-water mixture under gravity, and a separation flux of up to 3.5×10 4 L·m -2 ·h -1 The separation efficiency of oil-in-water emulsion can reach up to 98.5%, and the separation flux can reach 5.7×10 3 L·m -2 ·h -1 .

[0031] Beneficial effects of the present invention:

[0032] The present invention provides a method for preparing a super-hydrophilic-underwater super-oleophobic polyacrylonitrile nanofiber membrane. Polyacrylonitrile and a hydrophilic acrylate compound are used as raw materials. A super-hydrophilic-underwater super-oleophobic polyacrylonitrile nanofiber membrane with a double-network integrated structure can be prepared through electrospinning and a two-step impregnation operation. The preparation method is simple to operate, efficient, easy to control conditions and low cost, and is suitable for mass production.

[0033] The super-hydrophilic-underwater super-oleophobic polyacrylonitrile nanofiber membrane prepared by the present invention has a stable structure and good resistance to organic solvents. It can not only be used to separate oil-water mixtures, but also can separate emulsified oily wastewater with low energy consumption and high efficiency without applying additional pressure. The separation efficiency and flux of emulsified oily wastewater can reach as high as 98.5% and 5700 L·m respectively under the action of gravity alone. -2 ·h -1At the same time, the super-hydrophilic-underwater super-oleophobic polyacrylonitrile nanofiber membrane prepared by the present invention has self-cleaning properties, which can quickly remove oil stains on the surface of the material and increase the service life of the material. After 10 cycles of separation and emulsification of oily wastewater, it can still maintain a separation efficiency of 95.3%, which has broader application prospects in the field of oil-water separation. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Figure 1 is a scanning electron microscope (SEM) image of the polyacrylonitrile nanofiber membrane prepared in Example 1 of the present invention;

[0035] Figure 2 This is a test of the water wettability of the polyacrylonitrile nanofiber membrane prepared in Example 1 of the present invention;

[0036] Figure 3 This is a contact angle test of the polyacrylonitrile nanofiber membrane prepared in Example 1 of the present invention on hexadecane underwater;

[0037] Figure 4 This is a test of the adhesion of the polyacrylonitrile nanofiber membrane prepared in Example 1 of the present invention to hexadecane under water;

[0038] Figure 5 This is a test of the self-cleaning performance of the polyacrylonitrile nanofiber membrane prepared in Example 1 of the present invention after being contaminated with hexadecane in water;

[0039] Figure 6 This is the state of the polyacrylonitrile nanofiber membrane obtained in step (2) of Example 1 of the present invention after being immersed in DMF for 5 seconds;

[0040] Figure 7 The polyacrylonitrile nanofiber membrane prepared in step (3) of Example 1 of the present invention without alkali treatment is in a state after being immersed in DMF for 2 minutes;

[0041] Figure 8 This is the state of the polyacrylonitrile nanofiber membrane prepared in Example 1 of the present invention after being immersed in DMF for 2 hours;

[0042] Figure 9 This is a SEM image of the polyacrylonitrile nanofiber membrane prepared in Comparative Example 1 of the present invention. DETAILED DESCRIPTION

[0043] Unless otherwise defined, all technical and scientific terms used herein have the same meanings as commonly understood by those skilled in the art to which this invention pertains. The terms used in this specification of the present invention are for the purpose of describing specific embodiments only and are not intended to limit the present invention. The term "and / or" as used herein includes any and all combinations of one or more of the associated listed items. The terms "including" or "comprising" as used herein may also be replaced by the enclosed form "being" or "consisting of."

[0044] The present invention will be further described below with reference to the accompanying drawings and specific embodiments so that those skilled in the art can better understand the present invention and implement it. However, the embodiments are not intended to limit the present invention.

[0045] Example 1: This example relates to the preparation of a super-hydrophilic-underwater super-oleophobic polyacrylonitrile nanofiber membrane, which specifically includes the following steps:

[0046] (1) Polyethylene glycol diacrylate was added to a 15% solid content polyacrylonitrile N,N-dimethylformamide solution and stirred evenly to obtain an electrospinning solution; the mass ratio of polyethylene glycol diacrylate to polyacrylonitrile was 1:3, and the solid content of the electrospinning solution was 20%.

[0047] (2) The electrospinning solution prepared in step (1) was electrospun to obtain a polyacrylonitrile / polyethylene glycol diacrylate electrospinning nanofiber membrane, wherein the electrospinning process parameters were: spinning voltage 25 kV, spinning distance 15 cm, spinning speed 1 mL / h, and needle diameter 0.86 mm.

[0048] (3) The polyacrylonitrile / polyethylene glycol diacrylate electrospun nanofiber membrane prepared in step (2) was immersed in a 1% 2-hydroxy-4-(2-hydroxyethoxy)-2-methylpropiophenone aqueous solution and irradiated with ultraviolet light for 20 min, with a UV wavelength of 365 nm and a UV intensity of 50 W / cm 2 After illumination, the membrane was immersed in a 5% sodium hydroxide solution and treated at 60 °C for 0.5 h, then washed and dried at 60 °C to obtain a super-hydrophilic-underwater super-oleophobic polyacrylonitrile / polyethylene glycol diacrylate nanofiber membrane.

[0049] The SEM image of the super hydrophilic-underwater super oleophobic polyacrylonitrile / polyethylene glycol diacrylate electrospun nanofiber membrane prepared in this example is shown in FIG. Figure 1 As shown in the figure, the fibers are uniform and smooth, and the fiber membrane has a good pore structure.

[0050] In addition, the contact angles of the nanofiber membrane prepared in this example to water in air and to oil underwater were tested, and the results were as follows: Figure 2 、 3 As shown, the time it takes for a water droplet to completely spread on the nanofiber membrane surface is less than 0.1 s ( Figure 2 ), showing excellent superhydrophilic properties, and the contact angle of oil droplets (hexadecane) on the surface of the nanofiber membrane under water is greater than 150° ( Figure 3 ), showing underwater superoleophobic properties.

[0051] Figure 4 The figure shows the adhesion test of the nanofiber membrane prepared in this example to hexadecane under water. As can be seen from the figure, the oil droplets adhering to the surface of the nanofiber membrane in water will automatically fall off. To further study the self-cleaning ability of the nanofiber membrane prepared in this example, the surface of the nanofiber membrane was first contaminated with hexadecane, and then the contaminated nanofiber membrane was immersed in water. Figure 5 As shown in the figure, when the nanofiber membrane is immersed in water, the hexadecane on its surface automatically leaves, which also shows that the super hydrophilic-underwater super oleophobic polyacrylonitrile nanofiber membrane has self-cleaning properties and can quickly remove oil stains on the surface of the material.

[0052] In addition, by Figure 6-8 It can be seen that the polyacrylonitrile / polyethylene glycol diacrylate electrospun nanofiber membrane prepared in step (2) of this embodiment is completely dissolved after being immersed in DMF solution for 5 s (e.g. Figure 6 As shown); the polyacrylonitrile / polyethylene glycol diacrylate electrospun nanofiber membrane prepared by UV irradiation but without alkali treatment in step (3) of this embodiment was immersed in DMF for 2 minutes, as shown Figure 7 As shown in FIG, the membrane is completely dissolved. The nanofiber membrane prepared in this example after UV irradiation and alkali treatment is immersed in DMF solution for 2 h. Figure 8 As shown, no dissolution of the membrane occurred.

[0053] It can be seen that the nanofiber membrane prepared in this embodiment not only has superhydrophilic / underwater superoleophobic properties, but also has self-cleaning and organic solvent resistance properties.

[0054] Example 2: This example relates to the preparation of a superhydrophilic-underwater superoleophobic polyacrylonitrile nanofiber membrane. The only difference from Example 1 is that in step (1), the mass ratio of polyethylene glycol diacrylate to polyacrylonitrile is 2:1, and the other conditions are the same to prepare the corresponding nanofiber membrane.

[0055] The nanofiber membrane prepared in this example was tested for its morphology and contact angles with water in air and oil underwater. The results showed partial adhesion between fibers and decreased fiber diameter uniformity. The membrane took less than 0.1 seconds for water to fully spread on the surface, and the contact angle with oil underwater was greater than 150°, demonstrating superhydrophilicity and underwater superoleophobicity. The nanofiber membrane remained insoluble in a DMF solution, demonstrating resistance to organic solvents.

[0056] Example 3: This example relates to the preparation of a superhydrophilic-underwater superoleophobic polyacrylonitrile nanofiber membrane. The only difference from Example 1 is that in step (1), the mass ratio of polyethylene glycol diacrylate to polyacrylonitrile is 1:7, and the other conditions are the same to prepare the corresponding nanofiber membrane.

[0057] The nanofiber membrane prepared in this example was tested for its morphology and contact angles with water in air and oil underwater. The results showed that the fibers were smooth and had uniform fiber diameters. It took approximately 1 second for water in air to completely spread across the nanofiber membrane surface, and the contact angle with oil underwater was greater than 150°, demonstrating superhydrophilicity and underwater superoleophobicity. The nanofiber membrane remained insoluble in a DMF solution, demonstrating its resistance to organic solvents.

[0058] Example 4: This example relates to the preparation of a super-hydrophilic-underwater super-oleophobic polyacrylonitrile nanofiber membrane. The only difference from Example 1 is that the hydrophilic acrylate in step (1) is pentaerythritol triacrylate, and the other conditions are the same to prepare the corresponding nanofiber membrane.

[0059] The nanofiber membrane prepared in this example was tested for its morphology and contact angles with water in air and oil underwater. The results showed that the fibers were smooth and had uniform fiber diameters. The membrane took less than 0.2 seconds for water to fully spread on the surface, and the contact angle with oil underwater was greater than 150°, demonstrating superhydrophilicity and underwater superoleophobicity. The nanofiber membrane remained insoluble in a DMF solution, demonstrating resistance to organic solvents.

[0060] Example 5: This example relates to the preparation of a super-hydrophilic-underwater super-oleophobic polyacrylonitrile nanofiber membrane. The only difference from Example 1 is that the hydrophilic acrylate in step (1) is dipentaerythritol hexaacrylate, and the other conditions are the same to prepare the corresponding nanofiber membrane.

[0061] The nanofiber membrane prepared in this example was tested for its morphology and contact angles with water in air and oil underwater. The results showed that the fibers were smooth and had uniform fiber diameters. The membrane took less than 0.1 seconds for water to fully spread on the surface, and the contact angle with oil underwater was greater than 150°, demonstrating superhydrophilic and underwater superoleophobic properties. The nanofiber membrane remained insoluble in a DMF solution, demonstrating its resistance to organic solvents.

[0062] Comparative Example 1: This comparative example relates to the preparation of a polyacrylonitrile nanofiber membrane. The only difference from Example 1 is that in step (1), the mass ratio of polyethylene glycol diacrylate to polyacrylonitrile is 6:1, and the other conditions are the same, and the corresponding nanofiber membrane is prepared.

[0063] The morphology of the nanofiber membrane prepared in this comparative example, the contact angles of water in air and oil under water were tested, and the results showed that the silk liquid was ejected in the form of droplets, and the receiving device formed a non-porous film (such as Figure 9 As shown in the figure, nanofibers could not be formed, the membrane was brittle, and the membrane broke during the photocuring and alkali treatment in step (3), making subsequent contact angle measurement impossible. When the nanofiber membrane was immersed in DMF solution, the membrane completely dissolved, and the organic solvent resistance was poor.

[0064] Comparative Example 2: This comparative example relates to the preparation of a superhydrophilic-underwater superoleophobic polyacrylonitrile nanofiber membrane. The only difference from Example 1 is that in step (1), the mass ratio of polyethylene glycol diacrylate to polyacrylonitrile is 1:18, and the other conditions are the same, and the corresponding nanofiber membrane is prepared.

[0065] The nanofiber membrane prepared in this comparative example was tested for its morphology and contact angles with water in air and oil underwater. The results showed that the fibers were smooth and had uniform fiber diameters. It took approximately 3 seconds for water in air to fully spread on the nanofiber membrane surface, and the contact angle with oil underwater was less than 150°, demonstrating superhydrophilic / underwater oleophobic properties. However, when the nanofiber membrane was immersed in a DMF solution, the membrane partially dissolved, indicating poor resistance to organic solvents.

[0066] Comparative Example 3: This comparative example relates to the preparation of a super-hydrophilic-underwater super-oleophobic polyacrylonitrile nanofiber membrane. The only difference from Example 1 is that there is no sodium hydroxide solution treatment in step (3). The other conditions are the same, and the corresponding nanofiber membrane is prepared.

[0067] The nanofiber membrane prepared in this comparative example was tested for its morphology and contact angles with water in air and oil underwater. The results showed that the fibers were smooth and had uniform fiber diameters. The membrane took less than 0.1 s for water to completely spread on the surface, and the contact angle with oil underwater was greater than 150°, demonstrating superhydrophilic / underwater oleophobic properties. However, the membrane completely dissolved when immersed in a DMF solution, indicating poor resistance to organic solvents.

[0068] Comparative Example 4: This comparative example relates to the preparation of a super-hydrophilic-underwater super-oleophobic polyacrylonitrile nanofiber membrane. The only difference from Example 1 is that there is no ultraviolet irradiation treatment in step (3). The other conditions are the same, and the corresponding nanofiber membrane is prepared.

[0069] The nanofiber membrane prepared in this comparative example was tested for its morphology and contact angles with both airborne water and underwater oil. The results showed interfiber adhesion and localized fiber defects. It took approximately 0.5 seconds for airborne water to completely spread on the nanofiber membrane surface, and the underwater oil contact angle was greater than 150°, demonstrating superhydrophilic / underwater oleophobic properties. When immersed in a DMF solution, the nanofiber membrane completely dissolved, indicating poor resistance to organic solvents.

[0070] Comparative Example 5: This comparative example relates to the preparation of a polyacrylonitrile nanofiber membrane. The only difference from Example 1 is that an equal amount of polyacrylonitrile is used to replace polyethylene glycol diacrylate in step (1), and the operation in step (3) is not included. The other conditions are the same, and the corresponding nanofiber membrane is prepared.

[0071] The nanofiber membrane prepared in this comparative example was tested for its morphology and contact angles with water in air and oil underwater. The results showed that the fibers were smooth and had uniform fiber diameters. The contact angles of water in air on the nanofiber membrane surface were 53°, and the contact angle with oil underwater was less than 90°, indicating both hydrophilic and lipophilic properties. When immersed in a DMF solution, the nanofiber membrane immediately dissolved, indicating poor resistance to organic solvents.

[0072] Comparative Example 6: This comparative example relates to the preparation of a polyacrylonitrile nanofiber membrane. The only difference from Example 1 is that an equal amount of polyacrylonitrile is used instead of polyethylene glycol diacrylate in step (1), and step (3) does not include the operation of ultraviolet irradiation. The other conditions are the same, and the corresponding nanofiber membrane is prepared.

[0073] The nanofiber membrane prepared in this example was tested for its morphology and contact angles with water in air and oil underwater. The results showed that the fibers were smooth and had uniform fiber diameters. The membrane took approximately 2.5 seconds for water in air to fully spread across the surface, and the contact angle with oil underwater was less than 90°, demonstrating superhydrophilicity and underwater oleophilicity. When the nanofiber membrane was immersed in a DMF solution, the membrane completely dissolved, indicating poor resistance to organic solvents.

[0074] The test results of the wettability or contact angle of the polyacrylonitrile nanofiber membranes prepared in the above examples and comparative examples to water in the air and the contact angle of oil under water are shown in Table 1 below.

[0075] Table 1

[0076]

[0077] In the table: "undissolved" means the membrane did not dissolve after being immersed in DMF for 2 h; "completely dissolved" means the membrane was completely dissolved within 5 min after being immersed in DMF; "immediately dissolved" means the membrane was completely dissolved after being immersed in DMF for 5 s.

[0078] Application Example: The nanofiber membranes prepared in Example 1 and Comparative Examples 2 and 6 were named nanofiber membranes 1, 2, and 3, respectively. Nanofiber membranes 1, 2, and 3 were tested for separation efficiency, separation flux, and durability on oil-water mixtures and oil-in-water emulsions, respectively. The test process is as follows:

[0079] Preparation of oil-water mixture: 50 g of water and 50 g of hexadecane were mixed to prepare an oil-water mixture.

[0080] Test method for separation efficiency of oil-water mixture: weigh the weight of the separated oil on a balance, and use the formula Calculate the separation efficiency of the oil-water mixture, where E is the separation efficiency of the oil-water mixture, C1 is the mass of the oil after separation, and C0 is the mass of the oil before separation.

[0081] Preparation of oil-in-water emulsion: 0.1 g of sodium lauryl sulfate, 100 g of water and 1 g of diesel were ultrasonically cleaned in an ultrasonic cleaner for 24 h to form a stable emulsion. The prepared emulsion remained stable for at least 48 h.

[0082] Test method for separation efficiency of oil-in-water emulsion: The test instrument is an infrared oil analyzer (Qingdao Juchuang Environmental Protection Group Co., Ltd.); 100 mL of the filtrate before and after filtration were taken, the treated extract was injected into a quartz cuvette, placed in the instrument sample cell, and the absorbance at 2930 cm⁻¹ was measured. The initial concentration of oil in the emulsion before treatment and the residual concentration of oil in the aqueous phase after filtration were measured as C0 and C1 (in ppm), respectively. Finally, according to , the separation efficiency is calculated.

[0083] Separation flux test method: the volume of permeate passing through unit membrane area per unit time, according to the formula Calculate the separation flux J, where V is the permeate volume in L and A is the effective membrane area in m 2 ; t is the running time, in hours.

[0084] Durability test method: Repeat the above separation operation for the above oil-water mixture and oil-in-water emulsion 2 times and 10 times, and calculate the corresponding separation efficiency after 2 or 10 cycles respectively.

[0085] The test results are shown in Table 2 below:

[0086] Table 2

[0087]

[0088] As shown in Table 2, the nanofiber membrane 1 forms a dense chemical cross-linking network due to its high polyethylene glycol diacrylate content, and cooperates with polyacrylonitrile to form a double cross-linking structure. After alkali treatment, a large amount of -COO- , forming a stable hydrophilic layer and a strong negatively charged surface, effectively blocking oil droplets through hydration repulsion and electrostatic repulsion, while the double network inhibits swelling and deformation, ensuring high porosity and small pore size, and achieving high flux and anti-pollution cycle stability; while the insufficient polyethylene glycol diacrylate in nanofiber membrane 2 leads to weak hydrophilicity and charge shielding, and the membrane has weak repulsion to oil underwater, and cannot achieve superoleophobicity, making oil droplets easy to adhere and clog, and the adsorption of cationic surfactants induces hydrophilicity, the flux drops sharply and fails after circulation.

[0089] In addition, compared with the nanofiber membrane 1 prepared in Example 1, the nanofiber membrane 3 prepared in Comparative Example 6 has lower initial separation efficiency and initial separation flux for oil-water mixture and oil-in-water emulsion than nanofiber membrane 1, and has poor durability. After two cycles, the separation effect of oil-water mixture and oil-in-water emulsion is greatly reduced; while the separation efficiency of nanofiber membrane 1 for oil-water mixture and oil-in-water emulsion does not decrease after two cycles, and after 10 cycles, the separation efficiency of oil-water mixture and oil-in-water emulsion is still greater than 95%.

[0090] The above embodiments are merely preferred embodiments for the purpose of fully illustrating the present invention, and the scope of protection of the present invention is not limited thereto. Equivalent substitutions or modifications made by those skilled in the art based on the present invention are within the scope of protection of the present invention. The scope of protection of the present invention shall be subject to the claims.

Claims

1. A method for preparing a super-hydrophilic-underwater super-oleophobic polyacrylonitrile nanofiber membrane, characterized in that: The following steps are involved: S1, uniformly mixing the hydrophilic acrylate and the organic solution of polyacrylonitrile to prepare an electrospinning solution; The hydrophilic acrylate is an acrylate compound containing at least two carbon-carbon double bonds; the mass ratio of the hydrophilic acrylate to polyacrylonitrile in the electrospinning solution is 1:10-3:1; S2, electrospinning the electrospinning solution to obtain an electrospun nanofiber membrane; S3, immersing the electrospun nanofiber membrane in a solution containing a photoinitiator and irradiating it with ultraviolet light, transferring it to an alkaline solution for immersion treatment after irradiation, washing and drying it to obtain the super hydrophilic-underwater super oleophobic polyacrylonitrile nanofiber membrane.

2. The preparation method according to claim 1, characterized in that In step S1, the hydrophilic acrylate is selected from one or more of polyethylene glycol diacrylate, pentaerythritol triacrylate, trimethylolpropane triacrylate, glycerol propoxy triacrylate, ethoxylated trimethylolpropane triacrylate, ditrimethylolpropane tetraacrylate, ethoxylated pentaerythritol tetraacrylate, dipentaerythritol pentaacrylate, and dipentaerythritol hexaacrylate.

3. The preparation method according to claim 1, characterized in that In step S1, the organic solution of polyacrylonitrile is obtained by dissolving polyacrylonitrile in an organic solvent; The organic solvent includes N,N-dimethylformamide; The mass proportion of polyacrylonitrile in the organic solution of polyacrylonitrile is 5%-30%.

4. The preparation method according to claim 1, characterized in that In step S1, the mass ratio of hydrophilic acrylate to polyacrylonitrile in the electrospinning solution is 1:10-1:

3.

5. The preparation method according to claim 1, characterized in that In step S2, the electrospinning process parameters are: spinning voltage 8-35 kV, spinning distance 5-20 cm, spinning speed 0.1-3 mL / h, and needle diameter 0.2-3.5 mm.

6. The preparation method according to claim 1, characterized in that In step S3, the photoinitiator is selected from one or more of 2-hydroxy-2-methyl-1-phenyl-1-propanone, 2,4,6-trimethylbenzoyldiphenoxyphosphine, α,α,-dimethylbenzil ketal, benzophenone, 1-hydroxycyclohexylbenzophenone and bis(2,4,6-trimethylbenzoyl)phenylphosphine oxide; The mass proportion of the photoinitiator in the photoinitiator-containing solution is 0.5%-10%; In the ultraviolet irradiation step, the wavelength of the ultraviolet light is 200-500 nm, and the irradiation intensity is 10-100 W / cm 2 The irradiation time is 5 min-120 min.

7. The preparation method according to claim 1, characterized in that In step S3, the alkaline solution is obtained by dissolving an alkali in water; The base is selected from one or more of sodium hydroxide, potassium hydroxide, sodium carbonate, tetramethylammonium hydroxide, and ammonia water; The mass proportion of alkali in the alkaline solution is 5%-40%; The soaking treatment temperature is 30-80° C., and the soaking treatment time is 0.2 h-12 h.

8. The preparation method according to claim 1, characterized in that In step S3, the washing solvent is water; and the drying temperature is 20-80°C.

9. A super-hydrophilic-underwater super-oleophobic polyacrylonitrile nanofiber membrane, characterized in that: The compound is prepared by the preparation method according to any one of claims 1 to 8.

10. Use of the super-hydrophilic-underwater super-oleophobic polyacrylonitrile nanofiber membrane according to claim 9 in oil-water separation materials.

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