A modified polyvinylidene fluoride membrane for adsorbing heavy metals and a preparation method thereof

Abstract

This invention discloses a modified polyvinylidene fluoride (PVDF) membrane for adsorbing heavy metals and its preparation method, relating to the field of functional nanomaterials technology. The preparation method of the modified PVDF membrane is as follows: mercapto-polypyrrole and PVDF are mixed in a solvent to obtain an electrospinning solution. The electrospinning solution is then subjected to electrospinning treatment to obtain a PVDF-PPySH membrane. The membrane is then activated by immersion in anhydrous ethanol. Finally, the PVDF-PPySH membrane is soaked in a dopamine solution to obtain the modified PVDF membrane. The modified PVDF membrane prepared by this invention exhibits excellent Hg(II) ion adsorption performance and good hydrophilicity, showing significant application potential in the removal of mercury ions from wastewater. Furthermore, the preparation method is simple and suitable for industrial application.

Description

Technical Field

[0001] This invention relates to the field of functional nanomaterials technology, and in particular to a modified polyvinylidene fluoride membrane for adsorbing heavy metals and its preparation method. Background Technology

[0002] With the continuous development of industry, the discharge of heavy metal wastewater is increasing daily. Its toxicity and bioaccumulation have a significant environmental impact on nature and cause serious physiological health problems for organisms. Mercury, in particular, is a highly toxic heavy metal and is classified as a Class I pollutant among many environmental pollutant indicators. Mercury has inherent solubility and stability, and can accumulate in organisms even at very low concentrations. Water pollution caused by mercury is mainly due to human activities, the most important of which is the arbitrary discharge of industrial wastewater from factories that produce mercury or use mercury compounds. Mercury (Hg(II)) ions in water are highly reactive and easily methylated. Methylmercury is rapidly absorbed into the body of animals and accumulates in the brain, liver, and kidneys, exhibiting extreme toxicity. Therefore, reducing the mercury ion content in wastewater before discharge is a key research focus in the field of mercury pollution control in water environments.

[0003] Traditional adsorbent materials suffer from low adsorption capacity and are not recyclable. Designing and synthesizing an adsorbent material with high adsorption capacity, high efficiency, and recyclability is a pressing issue. Membrane adsorption is a novel adsorption technology that combines membrane technology with chemisorption technology. It creates a membrane adsorbent by attaching functional groups to the surface and pore walls of a polymer membrane. Target pollutants can be selectively adsorbed by the functional groups on the membrane adsorbent, effectively separating them from polluted water. Membrane adsorption offers advantages such as low cost, high removal efficiency, and strong operability. Moreover, membrane filtration can be achieved simultaneously with membrane adsorption, greatly simplifying the wastewater treatment process.

[0004] There are various methods for preparing thin films, such as phase separation, self-assembly, and electrospinning. Among these, electrospinned films possess advantages such as high porosity, extremely large surface area, excellent mechanical properties, controllable thickness and biological properties, and a wide availability of raw materials. By changing the relevant electrospinning process parameters, the surface morphology, orientation, and mechanical properties of electrospinned films can be controlled. Methods for modifying membrane materials mainly include surface coating, physical blending, and surface grafting. These modification methods can significantly improve the hydrophilicity, antifouling properties, and other properties of the membrane; however, existing technologies suffer from problems such as complex preparation methods and easy loss of added functional monomers.

[0005] In summary, there is an urgent need to develop an adsorption membrane that is simple to prepare, has excellent mechanical properties, high stability, and good adsorption performance, as well as a preparation method thereof. Summary of the Invention

[0006] The purpose of this invention is to provide a modified polyvinylidene fluoride membrane for adsorbing heavy metals and its preparation method, so as to solve the problems existing in the prior art and achieve efficient removal of mercury ions from water bodies polluted with mercury ions.

[0007] To achieve the above objectives, the present invention provides the following solution:

[0008] This invention provides a method for preparing a modified polyvinylidene fluoride (PVDF) membrane, comprising the following steps:

[0009] The electrospinning solution is obtained by blending mercapto-polypyrrole and polyvinylidene fluoride in a solvent.

[0010] The electrospinning solution was subjected to electrospinning treatment to obtain a PVDF-PPySH membrane;

[0011] The PVDF-PPySH membrane was immersed in anhydrous ethanol to obtain the activated PVDF-PPySH membrane;

[0012] The activated PVDF-PPySH membrane was immersed in a dopamine solution to obtain the modified polyvinylidene fluoride membrane.

[0013] As a further preferred embodiment of the present invention, the thiol-modified polypyrrole is obtained by oxidative polymerization of thiol acetate and pyrrole. More specifically, thiol acetate is added to an aqueous pyrrole solution, and after oxidative polymerization, washing and drying, thiol-grafted polypyrrole is obtained, i.e., thiol-modified polypyrrole;

[0014] As a further preferred embodiment of the present invention, the solvent includes dimethyl sulfoxide, N,N-dimethylformamide, or acetone.

[0015] More preferably, mercaptopolypyrrole and polyvinylidene fluoride are first dissolved by heating in solvent A (dimethyl sulfoxide or N,N-dimethylformamide), and then solvent B (acetone) is added to obtain a spinning solution. The preferred heating and dissolving temperature is 70°C.

[0016] More preferably, the volume ratio of solvent A to solvent B is 8 mL: 4-6 mL.

[0017] As a further preferred embodiment of the present invention, the ambient temperature of the electrospinning treatment is 25-30°C, and the voltage is 10-12kV, more preferably 11kV.

[0018] The preferred electrospinning parameters are: ambient temperature of 25-30℃, receiving distance of 10-12cm, feed flow rate of 0.70mL / h, spinning time of 5 hours, voltage of 11kV, roller speed of 400r / min, and slide table scanning speed of 30mm / s.

[0019] As a further preferred embodiment of the present invention, the mercaptopolypyrrole and polyvinylidene fluoride (CH2CF2) are... n The mass ratio is 0.05g-0.55g:1g. The molecular weight of polyvinylidene fluoride is 500,000-1,000,000, more preferably 700,000.

[0020] As a further preferred embodiment of the present invention, the PVDF-PPySH membrane is immersed in anhydrous ethanol for 1 hour.

[0021] As a further preferred embodiment of the present invention, the concentration of the dopamine solution is 4 mg / mL.

[0022] As a further preferred embodiment of the present invention, the soaking time is 7 hours.

[0023] The present invention also provides a modified polyvinylidene fluoride membrane prepared by the above preparation method.

[0024] The present invention further provides the application of the above-mentioned modified polyvinylidene fluoride membrane in the removal of Hg(II) ions from water.

[0025] Polyvinylidene fluoride (PVDF) has good film-forming properties, is thermally stable, and resistant to chemical corrosion, making it one of the main film-forming materials. However, its inherent hydrophobicity and the absence of active functional groups on its surface limit its application in the adsorption field.

[0026] This invention involves bulk blending mercapto-polypyrrole in a polyvinylidene fluoride spinning solution and spinning it into a film using electrospinning technology. Subsequently, a polydopamine (PDA) layer is deposited on the surface of the base film using the self-polymerization effect of dopamine (DA), thereby giving the material hydrophilicity.

[0027] In this invention, the thiol functional group containing thioglycolic acid plays an important role in the mercury removal process due to its strong binding ability between soft acid mercury and soft basic thiol.

[0028] The present invention discloses the following technical effects:

[0029] This invention addresses the performance defects of polyvinylidene fluoride (PVDF) by making a technical improvement. The PVDF bulk is blended with mercapto-polypyrrole, and the membrane material is obtained by electrospinning. Then, a polydopamine layer is deposited on the surface of the membrane material through the dopamine self-polymerization effect. The modified PVDF membrane prepared by this invention has excellent Hg(II) ion adsorption effect and good hydrophilicity, and has important application prospects in the removal of mercury ions in wastewater.

[0030] The preparation method of this invention is simple and suitable for industrial application. Attached Figure Description

[0031] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0032] Figure 1 This is a physical image of the modified polyvinylidene fluoride membrane (PVDF-PPySH-PDA membrane) prepared in Example 3 of the present invention.

[0033] Figure 2 This is a physical image of the PVDF membrane prepared in Comparative Example 3 of the present invention.

[0034] Figure 3 The infrared spectra of the modified polyvinylidene fluoride membrane (PVDF-PPySH-PDA membrane) prepared in Example 3 of this invention before and after adsorption of Hg(II) ions are shown.

[0035] Figure 4 This is a SEM image of the modified polyvinylidene fluoride membrane (PVDF-PPySH-PDA membrane) prepared in Example 3 of the present invention.

[0036] Figure 5 The contact angles of the modified polyvinylidene fluoride membrane (PVDF-PPySH-PDA membrane) prepared in Example 3 of the present invention, the PVDF-PDA membrane prepared in Comparative Example 1, the PVDF-PPySH membrane prepared in Comparative Example 2, and the PVDF membrane prepared in Comparative Example 3 are shown. Detailed Implementation

[0037] Various exemplary embodiments of the present invention will now be described in detail. This detailed description should not be considered as a limitation of the present invention, but rather as a more detailed description of certain aspects, features, and embodiments of the present invention.

[0038] It should be understood that the terminology used in this invention is merely for describing particular embodiments and is not intended to limit the invention. Furthermore, with respect to numerical ranges in this invention, it should be understood that each intermediate value between the upper and lower limits of the range is also specifically disclosed. Any stated value or intermediate value within a stated range, as well as each smaller range between any other stated value or intermediate value within said range, is also included in this invention. The upper and lower limits of these smaller ranges may be independently included or excluded from the range.

[0039] Unless otherwise stated, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art. While only preferred methods and materials have been described herein, any methods and materials similar or equivalent to those described herein may be used in the implementation or testing of this invention. All references to this specification are incorporated by way of citation to disclose and describe methods and / or materials associated with those references. In the event of any conflict with any incorporated reference, the content of this specification shall prevail.

[0040] Various modifications and variations can be made to the specific embodiments described in this specification without departing from the scope or spirit of the invention, as will be apparent to those skilled in the art. Other embodiments derived from this specification will also be readily apparent to those skilled in the art. This specification and embodiments are merely exemplary.

[0041] The terms “include,” “including,” “have,” “contain,” etc., used in this article are all open-ended terms, meaning that they include but are not limited to.

[0042] Example 1

[0043] The preparation steps of the modified polyvinylidene fluoride membrane are as follows:

[0044] (1) Preparation of thiol-based polypyrrole (adsorption functional polymer):

[0045] 0.5 mL of pyrrole (Py) monomer was added to 30 mL of deionized water and stirred for 3 h to obtain a pyrrole aqueous solution. 1 mL of mercaptoacetic acid was added and stirring was continued for 3 h to obtain a pyrrole-mercapto-water solution. 4 g of ammonium persulfate was dissolved in 10 mL of deionized water to obtain an ammonium persulfate solution, which was used as an initiator. The ammonium persulfate solution was then slowly added dropwise to the pyrrole-mercapto-water solution and stirred slowly for 6 h. After standing overnight, the precipitate was collected, washed repeatedly with distilled water and ethanol, and dried to obtain mercapto-polypyrrole powder PPySH.

[0046] (2) Preparation of bulk blended modified polyvinylidene fluoride membrane:

[0047] a. Add 0.05g of mercaptopolypyrrole powder to 8mL of dimethyl sulfoxide (DMSO), disperse it evenly by ultrasonication, then add 1g of polyvinylidene fluoride (molecular weight 700,000), heat and stir (70℃) for 3h to dissolve it evenly, then stop heating, add 4mL of acetone and continue stirring for 4h to obtain the spinning solution;

[0048] b. Place the prepared spinning solution into an electrospinning apparatus for spinning, using aluminum foil as the receiving device. Ambient temperature: 25℃, receiving distance: 12cm, feed rate: 0.70mL / h, spinning time: 5 hours, voltage: 11kV, roller speed: 400r / min, slide scanning speed: 30mm / s.

[0049] c. Place the spun film evenly in deionized water and perform solid-liquid phase transformation through phase inversion to obtain a PVDF-PPySH adsorption membrane. Finally, soak the adsorption membrane in deionized water.

[0050] d. Cut the membrane into 3*3cm pieces and soak them in 15mL of anhydrous ethanol for 1 hour. Then remove and clean them thoroughly.

[0051] (3) Hydrophilic modification of the membrane:

[0052] Dopamine was dissolved in 1.5M Tris-HCl buffer solution to prepare a dopamine solution with a concentration of 4 mg / mL. The adsorption membrane prepared in step (2) was then immersed in the dopamine solution and placed in a shaker. It was kept at a constant temperature and shaken for 7 hours in an aerobic environment to polymerize a layer of hydrophilic dopamine on the surface of the membrane. The membrane was then washed with deionized water and dried to obtain a modified polyvinylidene fluoride membrane (PVDF-PPySH-PDA membrane).

[0053] The adsorption experiment was carried out in a constant temperature shaker at 30℃ and 100 rpm. 20 mL of mercury ion solution with an initial concentration of 50 mg / L was taken and placed into 20 mg of modified polyvinylidene fluoride membrane. The results showed that the removal rate of Hg(II) ions reached 77.74% after 1 h and 78.6% after 4 h.

[0054] Example 2

[0055] The preparation steps of the modified polyvinylidene fluoride membrane are as follows:

[0056] (1) Preparation of thiol-based polypyrrole (adsorption functional polymer):

[0057] 0.5 mL of pyrrole (Py) monomer was added to 30 mL of deionized water and stirred for 3 h to obtain a pyrrole aqueous solution. 1 mL of mercaptoacetic acid was added and stirring was continued for 3 h to obtain a pyrrole-mercapto-water solution. 4 g of ammonium persulfate was dissolved in 10 mL of deionized water to obtain an ammonium persulfate solution, which was used as an initiator. The ammonium persulfate solution was then slowly added dropwise to the pyrrole-mercapto-water solution and stirred slowly for 6 h. After standing overnight, the precipitate was collected, washed repeatedly with distilled water and ethanol, and dried to obtain mercapto-polypyrrole powder PPySH.

[0058] (2) Preparation of bulk blended modified polyvinylidene fluoride membrane:

[0059] a. Add 0.15g of mercaptopolypyrrole powder to 8mL of dimethyl sulfoxide (DMSO), disperse it evenly by ultrasonication, then add 1g of polyvinylidene fluoride (molecular weight 700,000), heat and stir (70℃) for 3h to dissolve it evenly, then stop heating, add 4mL of acetone and continue stirring for 4h to obtain the spinning solution;

[0060] b. Place the prepared spinning solution into an electrospinning apparatus for spinning, using aluminum foil as the receiving device. Ambient temperature: 27℃, receiving distance: 12cm, feed rate: 0.70mL / h, spinning time: 5 hours, voltage: 11kV, roller speed: 400r / min, slide scanning speed: 30mm / s.

[0061] c. Place the spun film evenly in deionized water and perform solid-liquid phase transformation through phase inversion to obtain a PVDF-PPySH adsorption membrane. Finally, soak the adsorption membrane in deionized water.

[0062] d. Cut the membrane into 3*3cm pieces and soak them in 15mL of anhydrous ethanol for 1 hour. Then remove and clean them thoroughly.

[0063] (3) Hydrophilic modification of the membrane:

[0064] Dopamine was dissolved in 1.5M Tris-HCl buffer solution to prepare a dopamine solution with a concentration of 4 mg / mL. The adsorption membrane prepared in step (2) was then immersed in the dopamine solution and placed in a shaker. It was kept at a constant temperature and shaken for 7 hours in an aerobic environment to polymerize a layer of hydrophilic dopamine on the surface of the membrane. The membrane was then washed with deionized water and dried to obtain a modified polyvinylidene fluoride membrane (PVDF-PPySH-PDA membrane).

[0065] The adsorption experiment was carried out in a constant temperature shaker at 30℃ and 100 rpm. 20 mL of mercury ion solution with an initial concentration of 50 mg / L was taken and placed into 20 mg of modified polyvinylidene fluoride membrane. The results showed that the removal rate of Hg(II) ions reached 90.6% after 1 h and 97.08% after 4 h.

[0066] Example 3

[0067] The preparation steps of the modified polyvinylidene fluoride membrane are as follows:

[0068] (1) Preparation of thiol-based polypyrrole (adsorption functional polymer):

[0069] 0.5 mL of pyrrole (Py) monomer was added to 30 mL of deionized water and stirred for 3 h to obtain a pyrrole aqueous solution. 1 mL of mercaptoacetic acid was added and stirring was continued for 3 h to obtain a pyrrole-mercapto-water solution. 4 g of ammonium persulfate was dissolved in 10 mL of deionized water to obtain an ammonium persulfate solution, which was used as an initiator. The ammonium persulfate solution was then slowly added dropwise to the pyrrole-mercapto-water solution and stirred slowly for 6 h. After standing overnight, the precipitate was collected, washed repeatedly with distilled water and ethanol, and dried to obtain mercapto-polypyrrole powder PPySH.

[0070] (2) Preparation of bulk blended modified polyvinylidene fluoride membrane:

[0071] a. Add 0.25g of mercaptopolypyrrole powder to 8mL of dimethyl sulfoxide (DMSO), disperse it evenly by ultrasonication, then add 1g of polyvinylidene fluoride (molecular weight 700,000), heat and stir (70℃) for 3h to dissolve it evenly, then stop heating, add 4mL of acetone and continue stirring for 4h to obtain the spinning solution;

[0072] b. Place the prepared spinning solution into an electrospinning apparatus for spinning, using aluminum foil as the receiving device. Ambient temperature: 30℃, receiving distance: 12cm, feed rate: 0.70mL / h, spinning time: 5 hours, voltage: 11kV, roller speed: 400r / min, slide scanning speed: 30mm / s.

[0073] c. Place the spun film evenly in deionized water and perform solid-liquid phase transformation through phase inversion to obtain a PVDF-PPySH adsorption membrane. Finally, soak the adsorption membrane in deionized water.

[0074] d. Cut the membrane into 3*3cm pieces and soak them in 15mL of anhydrous ethanol for 1 hour. Then remove and clean them thoroughly.

[0075] (3) Hydrophilic modification of the membrane:

[0076] Dopamine was dissolved in 1.5M Tris-HCl buffer solution to prepare a dopamine solution with a concentration of 4 mg / mL. The adsorption membrane prepared in step (2) was then immersed in the dopamine solution and placed in a shaker. It was kept at a constant temperature and shaken for 7 hours in an aerobic environment to polymerize a layer of hydrophilic dopamine on the surface of the membrane. The membrane was then washed with deionized water and dried to obtain a modified polyvinylidene fluoride membrane (PVDF-PPySH-PDA membrane).

[0077] The modified polyvinylidene fluoride membrane prepared in Example 3 of this invention exhibits excellent Hg(II) ion removal capability:

[0078] The adsorption experiment was carried out in a constant temperature shaker at 30℃ and 100 rpm. 20 mL of mercury ion solution with an initial concentration of 50 mg / L was taken and placed into 20 mg of modified polyvinylidene fluoride membrane. The results showed that the removal rate of Hg(II) ions reached 93.28% after 1 h and 99.26% after 4 h.

[0079] The modified polyvinylidene fluoride membrane prepared in Example 3 of this invention also exhibits good hydrophilicity, with a water contact angle of 15.76° after ionized water contacts the membrane surface for 1 second.

[0080] Figure 1 This is a physical image of the modified polyvinylidene fluoride membrane (PVDF-PPySH-PDA membrane) prepared in Example 3 of the present invention.

[0081] Figure 3The infrared spectra of the modified polyvinylidene fluoride membrane (PVDF-PPySH-PDA membrane) prepared in Example 3 of this invention before and after adsorption of Hg(II) ions are shown.

[0082] Figure 4 This is a SEM image of the modified polyvinylidene fluoride membrane (PVDF-PPySH-PDA membrane) prepared in Example 3 of the present invention.

[0083] Example 4

[0084] The preparation steps of the modified polyvinylidene fluoride membrane are as follows:

[0085] (1) Preparation of thiol-based polypyrrole (adsorption functional polymer):

[0086] 0.5 mL of pyrrole (Py) monomer was added to 30 mL of deionized water and stirred for 3 h to obtain a pyrrole aqueous solution. 1 mL of mercaptoacetic acid was added and stirring was continued for 3 h to obtain a pyrrole-mercapto-water solution. 4 g of ammonium persulfate was dissolved in 10 mL of deionized water to obtain an ammonium persulfate solution, which was used as an initiator. The ammonium persulfate solution was then slowly added dropwise to the pyrrole-mercapto-water solution and stirred slowly for 6 h. After standing overnight, the precipitate was collected, washed repeatedly with distilled water and ethanol, and dried to obtain mercapto-polypyrrole powder PPySH.

[0087] (2) Preparation of bulk blended modified polyvinylidene fluoride membrane:

[0088] a. Add 0.35g of mercaptopolypyrrole powder to 8mL of dimethyl sulfoxide (DMSO), disperse it evenly by ultrasonication, then add 1g of polyvinylidene fluoride (molecular weight 700,000), heat and stir (70℃) for 3h to dissolve it evenly, then stop heating, add 4mL of acetone and continue stirring for 4h to obtain the spinning solution;

[0089] b. Place the prepared spinning solution into an electrospinning apparatus for spinning, using aluminum foil as the receiving device. Ambient temperature: 28℃, receiving distance: 11cm, feed rate: 0.70mL / h, spinning time: 5 hours, voltage: 11kV, roller speed: 400r / min, slide scanning speed: 30mm / s.

[0090] c. Place the spun film evenly in deionized water and perform solid-liquid phase transformation through phase inversion to obtain a PVDF-PPySH adsorption membrane. Finally, soak the adsorption membrane in deionized water.

[0091] d. Cut the membrane into 3*3cm pieces and soak them in 15mL of anhydrous ethanol for 1 hour. Then remove and clean them thoroughly.

[0092] (3) Hydrophilic modification of the membrane:

[0093] Dopamine was dissolved in 1.5M Tris-HCl buffer solution to prepare a dopamine solution with a concentration of 4 mg / mL. The adsorption membrane prepared in step (2) was then immersed in the dopamine solution and placed in a shaker. It was kept at a constant temperature and shaken for 7 hours in an aerobic environment to polymerize a layer of hydrophilic dopamine on the surface of the membrane. The membrane was then washed with deionized water and dried to obtain a modified polyvinylidene fluoride membrane (PVDF-PPySH-PDA membrane).

[0094] The adsorption experiment was carried out in a constant temperature shaker at 30℃ and 100 rpm. 20 mL of mercury ion solution with an initial concentration of 50 mg / L was taken and placed into 20 mg of modified polyvinylidene fluoride membrane. The results showed that the removal rate of Hg(II) ions reached 96.68% after 1 h and 99.54% after 4 h.

[0095] Example 5

[0096] The preparation steps of the modified polyvinylidene fluoride membrane are as follows:

[0097] (1) Preparation of thiol-based polypyrrole (adsorption functional polymer):

[0098] 0.5 mL of pyrrole (Py) monomer was added to 30 mL of deionized water and stirred for 3 h to obtain a pyrrole aqueous solution. 1 mL of mercaptoacetic acid was added and stirring was continued for 3 h to obtain a pyrrole-mercapto-water solution. 4 g of ammonium persulfate was dissolved in 10 mL of deionized water to obtain an ammonium persulfate solution, which was used as an initiator. The ammonium persulfate solution was then slowly added dropwise to the pyrrole-mercapto-water solution and stirred slowly for 6 h. After standing overnight, the precipitate was collected, washed repeatedly with distilled water and ethanol, and dried to obtain mercapto-polypyrrole powder PPySH.

[0099] (2) Preparation of bulk blended modified polyvinylidene fluoride membrane:

[0100] a. Add 0.45g of mercaptopolypyrrole powder to 8mL of dimethyl sulfoxide (DMSO), disperse it evenly by ultrasonication, then add 1g of polyvinylidene fluoride (molecular weight 700,000), heat and stir (70℃) for 3h to dissolve it evenly, then stop heating, add 4mL of acetone and continue stirring for 4h to obtain the spinning solution;

[0101] b. Place the prepared spinning solution into an electrospinning apparatus for spinning, using aluminum foil as the receiving device. Ambient temperature: 25℃, receiving distance: 10cm, feed rate: 0.70mL / h, spinning time: 5 hours, voltage: 11kV, roller speed: 400r / min, slide scanning speed: 30mm / s.

[0102] c. Place the spun film evenly in deionized water and perform solid-liquid phase transformation through phase inversion to obtain a PVDF-PPySH adsorption membrane. Finally, soak the adsorption membrane in deionized water.

[0103] d. Cut the membrane into 3*3cm pieces and soak them in 15mL of anhydrous ethanol for 1 hour. Then remove and clean them thoroughly.

[0104] (3) Hydrophilic modification of the membrane:

[0105] Dopamine was dissolved in 1.5M Tris-HCl buffer solution to prepare a dopamine solution with a concentration of 4 mg / mL. The adsorption membrane prepared in step (2) was then immersed in the dopamine solution and placed in a shaker. It was kept at a constant temperature and shaken for 7 hours in an aerobic environment to polymerize a layer of hydrophilic dopamine on the surface of the membrane. The membrane was then washed with deionized water and dried to obtain a modified polyvinylidene fluoride membrane (PVDF-PPySH-PDA membrane).

[0106] The adsorption experiment was carried out in a constant temperature shaker at 30℃ and 100 rpm. 20 mL of mercury ion solution with an initial concentration of 50 mg / L was taken and placed into 20 mg of modified polyvinylidene fluoride membrane. The results showed that the removal rate of Hg(II) ions reached 95.87% after 1 h and 98.68% after 4 h.

[0107] Example 6

[0108] The preparation steps of the modified polyvinylidene fluoride membrane are as follows:

[0109] (1) Preparation of thiol-based polypyrrole (adsorption functional polymer):

[0110] 0.5 mL of pyrrole (Py) monomer was added to 30 mL of deionized water and stirred for 3 h to obtain a pyrrole aqueous solution. 1 mL of mercaptoacetic acid was added and stirring was continued for 3 h to obtain a pyrrole-mercapto-water solution. 4 g of ammonium persulfate was dissolved in 10 mL of deionized water to obtain an ammonium persulfate solution, which was used as an initiator. The ammonium persulfate solution was then slowly added dropwise to the pyrrole-mercapto-water solution and stirred slowly for 6 h. After standing overnight, the precipitate was collected, washed repeatedly with distilled water and ethanol, and dried to obtain mercapto-polypyrrole powder PPySH.

[0111] (2) Preparation of bulk blended modified polyvinylidene fluoride membrane:

[0112] a. Add 0.55g of mercaptopolypyrrole powder to 8mL of dimethyl sulfoxide (DMSO), disperse it evenly by ultrasonication, then add 1g of polyvinylidene fluoride (molecular weight 700,000), heat and stir (70℃) for 3h to dissolve it evenly, then stop heating, add 4mL of acetone and continue stirring for 4h to obtain the spinning solution.

[0113] b. Place the prepared spinning solution into an electrospinning apparatus for spinning, using aluminum foil as the receiving device. Ambient temperature: 30℃, receiving distance: 12cm, feed rate: 0.70mL / h, spinning time: 5 hours, voltage: 11kV, roller speed: 400r / min, slide scanning speed: 30mm / s.

[0114] c. Place the spun film evenly in deionized water and perform solid-liquid phase transformation through phase inversion to obtain a PVDF-PPySH adsorption membrane. Finally, soak the adsorption membrane in deionized water.

[0115] d. Cut the membrane into 3*3cm pieces and soak them in 15mL of anhydrous ethanol for 1 hour. Then remove and clean them thoroughly.

[0116] (3) Hydrophilic modification of the membrane:

[0117] Dopamine was dissolved in 1.5M Tris-HCl buffer solution to prepare a dopamine solution with a concentration of 4 mg / mL. The adsorption membrane prepared in step (2) was then immersed in the dopamine solution and placed in a shaker. It was kept at a constant temperature and shaken for 7 hours in an aerobic environment to polymerize a layer of hydrophilic dopamine on the surface of the membrane. The membrane was then washed with deionized water and dried to obtain a modified polyvinylidene fluoride membrane (PVDF-PPySH-PDA membrane).

[0118] The adsorption experiment was carried out in a constant temperature shaker at 30℃ and 100 rpm. 20 mL of mercury ion solution with an initial concentration of 50 mg / L was taken and placed in 20 mg of modified polyvinylidene fluoride membrane. The results showed that the removal rate of Hg(II) ions reached 95.73% after 1 h and 98.82% after 4 h.

[0119] Comparative Example 1

[0120] The preparation steps of PVDF-PDA membrane are as follows:

[0121] (1) Membrane preparation:

[0122] a. Add 1g of polyvinylidene fluoride (molecular weight 700,000) to 8mL of dimethyl sulfoxide (DMSO), heat and stir (70℃) for 3h to dissolve it evenly, then stop heating, add 4mL of acetone and continue stirring for 4h to obtain the spinning solution;

[0123] b. Place the prepared spinning solution into an electrospinning apparatus for spinning, using aluminum foil as the receiving device. Ambient temperature: 30℃, receiving distance: 12cm, feed rate: 0.70mL / h, spinning time: 5 hours, voltage: 11kV, roller speed: 400r / min, slide scanning speed: 30mm / s.

[0124] c. Place the spun film evenly in deionized water and perform solid-liquid phase transformation through phase inversion to obtain a PVDF membrane, which is then soaked in deionized water.

[0125] d. Cut the membrane into 3*3cm pieces and soak them in 15mL of anhydrous ethanol for 1 hour. Then remove and clean them thoroughly.

[0126] (2) Hydrophilic modification of the membrane:

[0127] Dopamine was dissolved in 1.5M Tris-HCl buffer solution to prepare a dopamine solution with a concentration of 4 mg / mL. The adsorption membrane prepared in step (1) was then immersed in the dopamine solution and placed in a shaker. It was kept at a constant temperature and shaken for 7 hours in an aerobic environment to polymerize a layer of hydrophilic dopamine on the surface of the membrane. The membrane was then washed with deionized water and dried to obtain a PVDF-PDA membrane.

[0128] Comparative Example 2

[0129] The preparation steps of PVDF-PPySH are as follows:

[0130] (1) Preparation of thiol-based polypyrrole (adsorption functional polymer):

[0131] 0.5 mL of pyrrole (Py) monomer was added to 30 mL of deionized water and stirred for 3 h to obtain a pyrrole aqueous solution. 1 mL of mercaptoacetic acid was added and stirring was continued for 3 h to obtain a pyrrole-mercapto-water solution. 4 g of ammonium persulfate was dissolved in 10 mL of deionized water to obtain an ammonium persulfate solution, which was used as an initiator. The ammonium persulfate solution was then slowly added dropwise to the pyrrole-mercapto-water solution and stirred slowly for 6 h. After standing overnight, the precipitate was collected, washed repeatedly with distilled water and ethanol, and dried to obtain mercapto-polypyrrole powder PPySH.

[0132] (2) Preparation of bulk blended modified polyvinylidene fluoride membrane:

[0133] a. Add 0.25g of mercaptopolypyrrole powder to 8mL of dimethyl sulfoxide (DMSO), disperse it evenly by ultrasonication, then add 1g of polyvinylidene fluoride (molecular weight 700,000), heat and stir (70℃) for 3h to dissolve it evenly, then stop heating, add 4mL of acetone and continue stirring for 4h to obtain the spinning solution;

[0134] b. Place the prepared spinning solution into an electrospinning apparatus for spinning, using aluminum foil as the receiving device. Ambient temperature: 30℃, receiving distance: 12cm, feed rate: 0.70mL / h, spinning time: 5 hours, voltage: 11kV, roller speed: 400r / min, slide scanning speed: 30mm / s.

[0135] c. Place the spun film evenly in deionized water and perform solid-liquid phase transformation through phase inversion to obtain a PVDF-PPySH membrane. Finally, soak the adsorption membrane in deionized water.

[0136] Comparative Example 3

[0137] The preparation steps of PVDF electrospun film are as follows:

[0138] (1) Membrane preparation:

[0139] a. Add 1g of polyvinylidene fluoride (molecular weight 700,000) to 8mL of dimethyl sulfoxide (DMSO), heat and stir (70℃) for 3h to dissolve it evenly, then stop heating, add 4mL of acetone and continue stirring for 4h to obtain the spinning solution;

[0140] b. Place the prepared spinning solution into an electrospinning apparatus for spinning, using aluminum foil as the receiving device. Ambient temperature: 30℃, receiving distance: 12cm, feed rate: 0.70mL / h, spinning time: 5 hours, voltage: 11kV, roller speed: 400r / min, slide scanning speed: 30mm / s.

[0141] c. Place the spun film evenly in deionized water and perform solid-liquid phase transformation through phase inversion to obtain a PVDF membrane, which is then soaked in deionized water.

[0142] Figure 2 This is a physical image of the PVDF membrane prepared in Comparative Example 3 of the present invention.

[0143] Figure 5 The contact angles of the modified polyvinylidene fluoride membrane (PVDF-PPySH-PDA membrane) prepared in Example 3 of the present invention, the PVDF-PDA membrane prepared in Comparative Example 1, the PVDF-PPySH membrane prepared in Comparative Example 2, and the PVDF membrane prepared in Comparative Example 3 are shown.

[0144] The embodiments described above are merely preferred embodiments of the present invention and are not intended to limit the scope of the present invention. Various modifications and improvements made by those skilled in the art to the technical solutions of the present invention without departing from the spirit of the present invention should fall within the protection scope defined by the claims of the present invention.

Claims

1. A method for preparing a modified polyvinylidene fluoride membrane, characterized in that, Includes the following steps: The electrospinning solution is obtained by blending mercapto-polypyrrole and polyvinylidene fluoride in a solvent. The electrospinning solution was subjected to electrospinning treatment to obtain a PVDF-PPySH membrane; The PVDF-PPySH membrane was immersed in anhydrous ethanol to obtain the activated PVDF-PPySH membrane; The activated PVDF-PPySH membrane was immersed in a dopamine solution to obtain the modified polyvinylidene fluoride membrane.

2. The preparation method according to claim 1, characterized in that, The thiol polypyrrole is obtained by oxidative polymerization of thioglycolic acid and pyrrole.

3. The preparation method according to claim 1, characterized in that, The solvent includes dimethyl sulfoxide, N,N-dimethylformamide, or acetone.

4. The preparation method according to claim 1, characterized in that, The electrospinning process is carried out at an ambient temperature of 25–30°C and a voltage of 10–12 kV.

5. The preparation method according to claim 1, characterized in that, The mass ratio of the mercaptopolypyrrole to polyvinylidene fluoride is 0.05g-0.55g:1g.

6. The preparation method according to claim 1, characterized in that, The concentration of the dopamine solution is 4 mg / mL.

7. The preparation method according to claim 1, characterized in that, The soaking time in the dopamine solution was 7 hours; the soaking time in the anhydrous ethanol was 1 hour.

8. The modified polyvinylidene fluoride membrane prepared by the preparation method according to any one of claims 1-7.

9. The application of the modified polyvinylidene fluoride membrane as described in claim 8 in the removal of Hg(II) ions from water.

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