A nanofiber membrane and a preparation method and application thereof

Abstract

The application relates to a preparation method and application of a nanofiber membrane, and the preparation of the nanofiber membrane comprises the steps of electrospinning, high-temperature curing, hydrothermal growth of magnesium-aluminum hydrotalcite and the like. Compared with common electrospun nanofiber membranes, the nanofiber membrane prepared through electrospinning in the application is subjected to high-temperature curing after the electrospinning, and the mechanical property of the nanofiber membrane is improved by nearly one time compared with that of an untreated nanofiber membrane; a subsequent hydrophilic modification process enables the nanofiber membrane to have emulsion separation and photodegradation dye performance. Based on excellent emulsion separation performance and mechanical stability, combined with the current environment of treating organic pollutants in water, the nanofiber membrane in the application can be prepared and popularized on a large scale.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of nanofiber membrane preparation, in particular to a preparation method and application of nanofiber membrane. BACKGROUND

[0002] In recent years, with the acceleration of industrialization process, the development of marine transportation industry, oil industry, catering industry and machinery industry will produce oil-water emulsion, resulting in a large loss of oil resources. Water exists in the form of free water, dissolved water or emulsified water in oil, free water and dissolved water can be removed by gravity separation method, due to the action of surfactant, the particle size of emulsion is generally less than 20 microns, which can be dispersed in oil for a long time, forming a complex emulsion state, which is difficult to be destroyed, and macromolecular dyes such as methylene blue are easily dissolved in water and difficult to remove in water, which also has a great impact on the environment. How to remove the emulsified water in oil is the key and difficulty of oil-water emulsion separation research.

[0003] At present, the treatment technology of oil-water emulsion mainly adopts membrane separation technology, uses membrane materials with specific pore size, utilizes the characteristics that the pore size is larger than the diameter of water molecules and smaller than the diameter of emulsified oil, so that water molecules can smoothly pass through the membrane material, while emulsified oil droplets are intercepted on the other side of the membrane material, to achieve the effect of emulsion separation. However, the existing membrane separation technology has problems such as low separation efficiency and long separation time, and cannot remove macromolecular dyes dissolved in water. SUMMARY

[0004] The present application provides a preparation method and application of nanofiber membrane, polyacrylonitrile and polyvinylidene fluoride-hexafluoropropylene nanofiber membrane are obtained by electrospinning technology, after high temperature curing, magnesium aluminum hydrotalcite is in-situ grown by hydrothermal method, and is modified by tannic acid, to obtain nanofiber membrane with super hydrophilicity and excellent mechanical properties. The nanofiber membrane can realize rapid separation and efficient separation of emulsion, and has excellent mechanical properties, which can be mass produced and popularized combined with the current electrospinning technology.

[0005] The solution to the above technical problem is as follows: a preparation method of nanofiber membrane, comprising the following steps:

[0006] 1) Dissolve polyacrylonitrile and polyvinylidene fluoride-hexafluoropropylene in a solvent to prepare a spinning solution;

[0007] 2) Inject the spinning solution into an electrospinning machine, spin into a film on a single shaft, and then vacuum dry;

[0008] 3) High temperature curing of the dried primary nanofiber membrane;

[0009] 4) Prepare a mixed aqueous solution of magnesium nitrate and aluminum nitrate, stir until the solution is stable, and then add the high temperature cured nanofiber membrane for hydrothermal treatment;

[0010] 5) The nanofiber membrane after hydrothermal treatment is first immersed in a tannic acid solution, and then immersed in a sodium periodate aqueous solution to promote tannic acid chelation, and after drying, the final nanofiber membrane is obtained.

[0011] The primary nanofiber membrane prepared by electrospinning is improved in mechanical properties after high-temperature curing. The cured nanofiber membrane is composed of polyvinylidene hexafluoropropylene wrapped polyacrylonitrile fibers, and after hydrothermal treatment, layered double hydroxide nanoparticles grow on the membrane. The obtained nanofiber membrane has a small pore size (<2 microns) and can realize the screening of small particle size emulsions. In addition, the positive charge on the surface of magnesium-aluminum hydrotalcite particles can attract the negative charge on the surface of emulsion droplets, promote the deformation and rupture of emulsion droplets, realize the demulsification effect of emulsion, and thus accelerate the separation of emulsion. Finally, the nanofiber membrane is hydrophilically modified by tannic acid to have more excellent emulsion separation effect and photodegradation of dyes.

[0012] Preferably, in step 1), the solvent is one or a mixture of several of N,N-dimethylformamide, N,N-dimethylacetamide, N-methylpyrrolidone, acetone. Further preferably, in step 1), the solvent is N,N-dimethylformamide.

[0013] Preferably, in step 1), the mass ratio of the solvent, polyacrylonitrile and polyvinylidene hexafluoropropylene is 75:2-5:2-5. Further preferably, in step 1), the mass ratio of the solvent, polyacrylonitrile and polyvinylidene hexafluoropropylene is 75:5:3. The solvent is used in a larger amount, on the one hand, the density of the solvent is larger, and the raw material is in powder form and has a smaller mass; on the other hand, the total mass of the solute is about 10% of the solvent, and after forming the spinning solution, the viscosity is moderate, there is no problem of very dilute solution, difficult to diffuse after pressurization, or very high voltage required to form a filamentous fiber when the viscosity is larger.

[0014] Preferably, in step 2), the voltage for electrospinning is 10-16 kilovolts. Further preferably, in step 2), the voltage for electrospinning is 12 kilovolts. Other electrospinning film forming parameters are: the rotating speed of the receiving roller is 200 revolutions per minute, the pumping speed is 1.5 milliliters per hour, the distance between the needle and the receiving roller is 15 centimeters, the temperature is maintained at 25±2 degrees Celsius, and the humidity is maintained at 30%±5%.

[0015] Preferably, the vacuum drying temperature is 40-80 degrees Celsius, and the time is 8-16 hours. Further preferably, the vacuum drying temperature is 60 degrees Celsius, and the time is 12 hours.

[0016] Preferably, in the step 3), the curing temperature is 160-240 degrees Celsius, and the curing time is 20-40 minutes. Further preferably, in the step 3), the curing temperature is 200 degrees Celsius, and the curing time is 30 minutes.

[0017] Preferably, in the step 4), the concentration of magnesium nitrate in the mixed aqueous solution is 25-30 mg / ml, and the concentration of aluminum nitrate is 10-20 mg / ml. Further preferably, in the step 4), the concentration of magnesium nitrate in the mixed aqueous solution is 30 mg / ml, and the concentration of aluminum nitrate is 16 mg / ml.

[0018] Preferably, the hydrothermal treatment temperature is 80-160 degrees Celsius, and the time is 8-16 hours. Preferably, the hydrothermal treatment temperature is 120 degrees Celsius, and the time is 12 hours.

[0019] Preferably, in the step 5), the concentration of the tannic acid aqueous solution is 0.1-25 mg / ml, the concentration of the sodium periodate solution is 5-15 mg / ml, and the soaking time is 5-20 minutes.

[0020] The nanofiber membrane prepared by the preparation method of the nanofiber membrane as described above is applied to the separation of emulsion in polluted water bodies.

[0021] The nanofiber membrane prepared by the preparation method of the nanofiber membrane as described above is applied to the degradation of macromolecular dyes in polluted water.

[0022] The beneficial effects of the present application are as follows:

[0023] (1) The present application obtains a nanofiber membrane with superhydrophilicity and underwater oleophobicity by performing superhydrophilic treatment on the surface of the nanofiber membrane, allowing water in various oil-water mixtures to pass through and preventing oil from passing through, thereby achieving the purpose of separating oil-water mixtures.

[0024] (2) In the curing process of the present application, polyvinylidene fluoride-hexafluoropropylene is crosslinked on the surface of polyacrylonitrile, greatly improving the mechanical properties of the nanofiber membrane.

[0025] (3) The nanofiber membrane of the present application has the advantages of high efficiency, high throughput, good repeatability, and the like.

[0026] (4) The nanofiber membrane of the present application contains magnesium-aluminum hydrotalcite with photocatalytic activity, which can realize the degradation of macromolecular dyes such as methylene blue, and can realize water purification.

[0027] The above description is only a summary of the technical solutions of the present application. In order to make the technical means of the present application clearer and can be implemented according to the content of the description, the following will be described in detail with the preferred embodiments of the present application and the accompanying drawings. The specific embodiments of the present application are given in detail by the following examples and the accompanying drawings. BRIEF DESCRIPTION OF DRAWINGS

[0028] The accompanying drawings, which are included to provide a further understanding of the present application and constitute a part of this application, illustrate the exemplary embodiments of the present application and are used to explain the present application, and do not constitute an improper limitation on the present application. In the drawings:

[0029] Figure 1 The SEM images of the nanofiber membranes obtained in different steps in Example 1 have a resolution of 1 micrometer; wherein a is the nanofiber membrane obtained by the electrospinning machine, b is the nanofiber membrane after high-temperature curing, c is the nanofiber membrane after hydrothermal treatment, and d is the nanofiber membrane after tannic acid modification;

[0030] Figure 2 The stress-strain curve diagrams of the nanofiber membranes obtained in different steps in Example 1 are shown;

[0031] Figure 3 The optical microscope photos of the separated emulsions of the nanofiber membranes prepared in Example 1 and Step 2 of Example 1 are shown; wherein a is the n-hexane emulsion before separation, b is the liquid separated by the nanofiber membrane prepared in Example 1, and c is the liquid separated by the nanofiber membrane prepared in Step 2 of Example 1;

[0032] Figure 4 The separation effect diagrams of various oil-water emulsions by Example 1 are shown;

[0033] Figure 5 The cycle effect diagrams of two kinds of oil-water emulsions separated by Example 1 are shown; wherein a is the cyclohexane emulsion, and b is the isooctane emulsion.

[0034] Figure 6 The underwater oil contact angle diagram of Example 1 is shown;

[0035] Figure 7 The underwater oil dynamic wetting process diagram of Example 1 is shown;

[0036] Figure 8 The photodegradation efficiency diagram of the methylene blue solution by Example 1 is shown.

[0037] Figure 9 The SEM images of the nanofiber membranes obtained in Examples 1-4 are shown; wherein a is the SEM image obtained in Example 1, and the resolution is 20 micrometers, at this time the electrospinning voltage is 12 kilovolts; b, c, and d are the SEM images obtained in Examples 2-4, and the resolution is 20 micrometers, at this time the electrospinning voltages are 10, 14, and 16 kilovolts, respectively.

[0038] Figure 10 Stress-strain curve of the sample in Example 1 and Examples 5-7;

[0039] Figure 11 Droplet spreading time graph of Example 1 and Examples 8-12. DETAILED DESCRIPTION

[0040] The principles and features of the present application are described below in conjunction with the accompanying drawings, in which the examples are used to explain the present application and are not intended to limit the scope of the present application.

[0041] Example 1

[0042] This example provides a nanofiber membrane, the preparation steps are as follows:

[0043] 1. Prepare a spinning solution for electrospinning: weigh N, N-dimethylformamide, polyacrylonitrile and polyvinylidene fluoride-hexafluoropropylene according to the mass ratio of 75:5:3, and mix uniformly to prepare the spinning solution.

[0044] 2. Inject the spinning solution into the electrospinning machine, and set the film forming parameters as follows: the rotating speed of the receiving roller is 200 revolutions per minute, the voltage is 12 kilovolts, the pumping speed is 1.5 milliliters per hour, the distance between the needle and the receiving roller is 15 centimeters, the temperature is kept at 25±2 degrees Celsius, and the humidity is kept at 30%±5%; after uniaxial spinning film forming, vacuum dry at 60 degrees Celsius for 12 hours.

[0045] 3. Dry and shape the nanofiber membrane at 200 degrees Celsius for 30 minutes, and set the temperature rising speed to 5 degrees Celsius per minute.

[0046] 4. Put the cured nanofiber membrane into a mixed aqueous solution of magnesium nitrate and aluminum nitrate for hydrothermal treatment at 120 degrees Celsius for 12 hours, wherein the concentration of magnesium nitrate is 30 milligrams per milliliter, and the concentration of aluminum nitrate is 16 milligrams per milliliter.

[0047] 5. Soak the cured nanofiber membrane in a tannic acid solution with a concentration of 20 milligrams per milliliter and a sodium periodate solution with a concentration of 10 milligrams per milliliter for 10 minutes, respectively.

[0048] The nanofiber membrane obtained after completing steps 2, 3, 4, and 5 of this example is tested for morphology, and the scanning electron microscope photos are shown in Figure 1 a, b, c, d, after high temperature curing, the crosslinking degree of the fiber increases, after hydrothermal treatment, magnesium aluminum hydrotalcite grows on the surface, after hydrophilic treatment, the nanofiber and magnesium aluminum hydrotalcite surface are more rough.

[0049] The nanofiber membrane obtained after completing steps 2, 3, 4, and 5 of this example is tested for stress-strain, and the results are as followsFigure 2 As shown in FIG. 11B, the mechanical property of the nanofiber membrane after high-temperature curing is improved by 90%.

[0050] The nanofiber membranes obtained in steps 2 and 5 of this example were subjected to emulsion separation. The optical micrographs of the n-hexane (water / oil volume ratio of 99:1) emulsion before and after separation are shown in FIGS. 11A and 11B, respectively. Figure 3 a, as shown in FIG. 11A, Figure 3 b is the optical micrograph of the liquid after the nanofiber membrane obtained in step 5 of this example was subjected to emulsion separation, as shown in FIG. 11B, Figure 3 b is the optical micrograph of the liquid after the nanofiber membrane obtained in step 2 of this example was subjected to emulsion separation, as shown in FIG. 11A, and it can be seen that both of the nanofiber membranes have excellent separation performance.

[0051] To further test the separation performance of the nanofiber membrane prepared in Example 1, cyclohexane, n-hexane, isooctane, dimethyl silicone oil, and n-heptane were used to prepare emulsions for separation. The water / oil volume ratio of the emulsion was 99:1, and 1 mg / ml of surfactant (sodium dodecyl sulfate) was added to stabilize the emulsion. The nanofiber membrane prepared in Example 1 was used to separate the oil / water emulsion multiple times, and the results are shown in FIG. 12. Figures 4-5 As shown in FIG. 12, the nanofiber membrane of Example 1 has good separation efficiency (>99%) and high separation flux (>2500 L / m2·h·bar) for various oil / water emulsions, and can maintain high efficiency and flux after multiple cycles. The nanofiber membrane after curing is composed of polyvinylidene fluoride-hexafluoropropylene-coated polyacrylonitrile fibers, and after hydrothermal treatment to grow layered double hydroxide nanosheets, the nanofiber membrane has a demulsification effect, and after modification with tannic acid, the membrane has superhydrophilicity. In summary, the final product is a superhydrophilic nanofiber membrane with a demulsification effect, which can realize the separation of emulsions.

[0052] The wettability of the nanofiber membrane of Example 1 is shown in FIG. 13. Figures 6-7 As shown in FIG. 13, the underwater oil contact angle of various organic oils is greater than 150 degrees. The dynamic wetting process of the oil droplets shows that the nanofiber membrane has very small adhesion to the oil droplets.

[0053] The nanofiber membrane prepared in Example 1 was immersed in a 15 mg / ml methylene blue aqueous solution, and the photodegradation performance was tested every 30 minutes under ultraviolet light. As shown in FIG. 14, Figure 8 As shown in FIG. 14, it can be found that after 150 minutes, the decomposition rate of methylene blue can reach 90%.

[0054] Example 2

[0055] This example is basically the same as Example 1, except that the voltage during the electrospinning process in step 2 is set to 10 kV.

[0056] Example 3

[0057] The steps of this example are basically the same as those of Example 1, except that in the electrospinning process of Step 2, the voltage is set to 14 kilovolts.

[0058] Example 4

[0059] The steps of this example are basically the same as those of Example 1, except that in the electrospinning process of Step 2, the voltage is set to 16 kilovolts.

[0060] Figure 9 a is the SEM image of the nanofiber membrane prepared in Example 1, Figure 9 b is the SEM image of the nanofiber membrane prepared in Example 2, Figure 9 c is the SEM image of the nanofiber membrane prepared in Example 3, Figure 9 d is the SEM image of the nanofiber membrane prepared in Example 4. As can be seen from the figures, the surface topographies of Examples 1 and 2-4 obtained under different voltage conditions are different. The nanofibers of Example 1 are the most uniform, and the beaded structure is the least. The uniformity of the nanofibers in Examples 2-4 is low, and the beaded structure is more. Voltage affects the electrostatic force of the system, thereby affecting the splitting ability of the spinning solution droplets. Appropriate voltage can obtain uniform nanofibers, which is conducive to obtaining nanofiber membranes with stable mechanical properties and uniform pore size.

[0061] Example 5

[0062] The steps of this example are basically the same as those of Example 1, except that in the high-temperature curing process of Step 3, the temperature is set to 120°C.

[0063] Example 6

[0064] The steps of this example are basically the same as those of Example 1, except that in the high-temperature curing process of Step 3, the temperature is set to 160°C.

[0065] Example 7

[0066] The steps of this example are basically the same as those of Example 1, except that in the high-temperature curing process of Step 3, the temperature is set to 240°C.

[0067] The nanofiber membranes prepared in Examples 1 and 5-7 were subjected to tensile test, and the results are shown in Table 1. Figure 10 As can be seen, between 120°C and 160°C, the tensile resistance of the membrane becomes better as the temperature rises. When the temperature reaches 240°C, the tensile resistance of the nanofiber membrane is weakened due to the partial decomposition of polyvinylidene fluoride-hexafluoropropylene.

[0068] Example 8

[0069] The steps of this example are basically the same as those of Example 1, except that in Step 5, the aqueous tannin solution is not used.

[0070] Example 9

[0071] The steps of this example are basically the same as those of Example 1, except that a tannic acid aqueous solution with a concentration of 5 mg / ml is used in step 5.

[0072] Example 10

[0073] The steps of this example are basically the same as those of Example 1, except that a tannic acid aqueous solution with a concentration of 10 mg / ml is used in step 5.

[0074] Example 11

[0075] The steps of this example are basically the same as those of Example 1, except that a tannic acid aqueous solution with a concentration of 15 mg / ml is used in step 5.

[0076] Example 12

[0077] The steps of this example are basically the same as those of Example 1, except that a tannic acid aqueous solution with a concentration of 25 mg / ml is used in step 5.

[0078] Figure 11 From the liquid drop spreading time diagrams of Examples 1 and 8-12, it can be seen that Example 1 has the fastest liquid drop spreading time and the best hydrophilicity.

[0079] The above description is only the preferred embodiments of the present application and is not intended to limit the present application in any form. Those skilled in the art can easily implement the present application according to the drawings and the above description. However, any equivalent changes, modifications and evolutions made by those skilled in the art within the scope of the technical solutions of the present application, using the above disclosed technical contents, are equivalent embodiments of the present application. Meanwhile, any equivalent changes, modifications and evolutions made by those skilled in the art according to the essence of the present application, to the above embodiments, are still within the protection scope of the technical solutions of the present application.

Claims

1. A method for producing a nanofiber membrane, characterized by, The method comprises the following steps: 1) mixing N, N-dimethylformamide, polyacrylonitrile and polyvinylidene fluoride-hexafluoropropylene in a mass ratio of 75:2-5:2-5 to prepare a spinning solution; 2) injecting the spinning solution into an electrostatic spinning machine, spinning into a film on a single shaft and vacuum drying; 3) curing the dried primary nanofiber film at 160-240 degrees Celsius; 4) preparing a mixed aqueous solution of magnesium nitrate and aluminum nitrate, stirring until the solution is stable, and then adding the nanofiber film cured at high temperature for hydrothermal treatment; 5) immersing the nanofiber film after hydrothermal treatment in a tannic acid solution first, and then in a sodium periodate aqueous solution, and drying to obtain the final nanofiber film.

2. The method of claim 1, wherein the nanofiber membrane is prepared by electrospinning. In the step 2), the voltage for electrostatic spinning is 10-16 kilovolts; in the step 2), the vacuum drying temperature is 40-80 degrees Celsius, and the time is 8-16 hours.

3. The method of claim 1, wherein the nanofiber membrane is prepared by electrospinning. In the step 3), the curing time is 20-40 minutes.

4. The method of claim 1, wherein the nanofiber membrane is prepared by electrospinning. In the step 4), in the mixed aqueous solution, the concentration of magnesium nitrate is 25-30 milligrams / milliliter, and the concentration of aluminum nitrate is 10-20 milligrams / milliliter.

5. The method of claim 1, wherein the nanofiber membrane is prepared by electrospinning. In the step 4), the temperature for hydrothermal treatment is 80-160 degrees Celsius, and the time is 8-16 hours.

6. The method of claim 1, wherein the nanofiber membrane is prepared by electrospinning. In the step 5), the concentration of the tannic acid aqueous solution is 0.1-25 milligrams / milliliter, the concentration of the sodium periodate solution is 5-15 milligrams / milliliter, and the immersion time is 5-20 minutes.

7. The application of the nanofiber film prepared by the method for preparing a nanofiber film according to any one of claims 1-6 in emulsion separation of contaminated water bodies.

8. The application of the nanofiber film prepared by the method for preparing a nanofiber film according to any one of claims 1-6 in degrading macromolecular dyes in contaminated water.

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