Preparation Method of a PVDF Composite Ultrafiltration Membrane with Underwater Piezoelectric Activity

Abstract

The invention discloses a preparation method of a PVDF composite ultrafiltration membrane with underwater piezoelectric activity, belonging to the technical field of water treatment. The preparation method of the PVDF composite ultrafiltration membrane with underwater piezoelectric activity comprises the following steps: dispersing graphene oxide in an organic solvent, then adding a pore-forming agent and PVDF, heating and stirring until completely dissolved, and then degassing to obtain a casting solution; coating the casting solution on a flat plate, and then immersing it in a pure water coagulation bath arranged in a negative direct current electric field for phase separation and synchronous polarization to obtain a PVDF porous membrane; performing hydrophobic modification on the PVDF porous membrane to obtain a PVDF composite ultrafiltration membrane. By introducing GO during the forming process of the PVDF separation membrane and synchronously applying a negative electric field polarization effect, and then combining with the hydrophobic modification method, the invention finally prepares a PVDF composite ultrafiltration membrane with remarkable underwater piezoelectric activity and anti-pollution ability.

Description

Technical Field

[0001] The invention relates to the technical field of water treatment, and in particular to a method for preparing a PVDF composite ultrafiltration membrane with underwater piezoelectric activity. Background Art

[0002] In recent years, ultrafiltration technology has attracted widespread attention in water purification and comprehensive utilization of water resources due to its excellent removal performance for colloidal particles and pathogenic microorganisms. However, the pollution problems faced by ultrafiltration membranes in actual applications have restricted the further improvement of process efficiency. In response to the problem of ultrafiltration membrane pollution, electric field-assisted membrane pollution control technology has shown unique advantages in reducing chemical agent consumption, improving membrane separation efficiency, and slowing down membrane flux attenuation. However, traditional electric-assisted membrane pollution technology usually relies on external power supply, which aggravates energy consumption and is difficult to meet the development requirements of green and low-carbon membrane separation technology. In response to this problem, new membrane pollution control technologies based on the intrinsic piezoelectric properties of membrane materials have gradually become feasible alternatives. Especially for polyvinylidene fluoride (PVDF) ultrafiltration membranes, PVDF is not only one of the most widely used membrane-making polymers, but also a typical organic piezoelectric material (β-phase PVDF). Different from traditional conductive membrane or electric field assisted membrane pollution control technology, PVDF piezoelectric separation membrane can directly convert the redundant mechanical energy in the pressure-driven membrane separation process into membrane surface potential energy through its inherent electromechanical coupling characteristics (i.e., piezoelectric characteristics), thereby slowing down the development of membrane pollution through a series of electrochemical effects.

[0003] However, there are still some challenges in using the piezoelectric properties of PVDF for underwater membrane fouling control. On the one hand, the intrinsic piezoelectric coefficient of PVDF is low. 33 It is only about 33pC / N, which makes it difficult to obtain excellent output performance under low stress loads. Therefore, the existing technology usually chooses to mix inorganic dielectric particles or piezoelectric particles such as zinc oxide (ZnO) and barium titanate (BaTiO3) into the PVDF matrix to improve the overall piezoelectric performance of the mixed matrix. On the other hand, although the blended inorganic piezoelectric particles can effectively improve the piezoelectric performance of the PVDF mixed matrix in the air, it is difficult to achieve ideal results when the relevant strategies are applied to the water environment or water purification process. At present, when PVDF piezoelectric film is applied to water environment and membrane separation process, its underwater open circuit voltage is usually less than 150mV under conventional driving pressure (0.04~0.2MPa), which is only about one percent of its output voltage in the air, which seriously limits the underwater performance expression of PVDF piezoelectric film. At the same time, there is a lack of material preparation technology for improving the underwater output performance of piezoelectric materials at this stage, which further limits the application of PVDF piezoelectric materials in the fields of water treatment and membrane separation. Summary of the invention

[0004] The object of the present invention is to provide a preparation method of a PVDF composite ultrafiltration membrane with underwater piezoelectric activity to solve the problems existing in the above-mentioned prior art.

[0005] To achieve the above object, the present invention provides the following solutions:

[0006] One of the technical solutions of the present invention: A preparation method of a PVDF composite ultrafiltration membrane with underwater piezoelectric activity, comprising the following steps:

[0007] Prepare a casting solution using graphene oxide, an organic solvent, a pore-forming agent, and PVDF as raw materials;

[0008] Coat the casting solution on a flat plate and scrape it into a liquid film, and then immerse the above liquid film in a pure water coagulation bath arranged in a negative direct current electric field for phase separation and synchronous polarization to obtain a PVDF porous membrane;

[0009] Perform hydrophobic modification on the PVDF porous membrane to obtain the PVDF composite ultrafiltration membrane.

[0010] In the present invention, an appropriate amount of graphene oxide (GO) is mixed into the casting solution to induce the formation of polar PVDF-β phase, promote the generation of interfacial polarization at the organic-inorganic phase interface, and improve the dielectric properties (i.e., polarizable potential) of the casting solution; then, by applying a negative direct current electric field during the phase inversion process, the orientation of GO is promoted and the formation of out-of-plane orientation of PVDF molecular dipoles is induced, enhancing the intrinsic piezoelectric activity of the PVDF / GO matrix; finally, by performing hydrophobic modification on the PVDF / GO porous membrane, the interfacial double-layer structure and interfacial ion concentration in the water environment are improved, the dissipation effect of charged ions in water on the polarized charges of the piezoelectric membrane is reduced, and the expression of piezoelectric performance underwater is enhanced, and finally a piezoelectric separation membrane with excellent underwater piezoelectric activity and electrokinetic anti-pollution ability is obtained.

[0011] Further, the diameter of the graphene oxide is 0.5 - 100 nm.

[0012] Further, the organic solvent includes N-methylpyrrolidone (NMP), N,N-dimethylformamide (DMF), dimethyl sulfoxide (DMSO), or dimethylacetamide (DMAC); and / or, the pore-forming agent includes polyvinylpyrrolidone (PVP), polyethylene glycol (PEG), or lithium chloride (LiCl).

[0013] Further, the casting solution includes the following raw materials in mass percentages: graphene oxide 0.1 - 1.5%, PVDF 17 - 24%, pore-forming agent 0.5 - 4%, and the balance is the organic solvent.

[0014] The pore-forming agent is used for pore formation during the membrane preparation process.

[0015] Further, the graphene oxide, organic solvent, pore-forming agent, and PVDF are used to prepare the casting solution by heating and stirring; the temperature of the heating and stirring is 45 to 75 °C, the time is 6 to 10 h, and the stirring speed is 300 to 500 rpm;

[0016] The thickness of the casting solution on the flat plate is 150 to 350 μm.

[0017] Furthermore, the defoaming method is static defoaming, and the static time is ≥24 h.

[0018] Further, the intensity of the electric field is 200 to 800 V / mm, the temperature of the phase separation and synchronous polarization is 15 to 25 °C, and the time is 5 to 30 min.

[0019] Further, the hydrophobic modification method includes the following steps: uniformly coating the hydrophobic modification solution on the surface of the PVDF porous membrane and maintaining a pressure of 5 to 80 kPa during the coating process;

[0020] The dosage ratio of the hydrophobic modification solution to the area of the PVDF porous membrane is 1 to 7 mL: 1 cm 2 ;

[0021] The hydrophobic modification solution is composed of the following raw materials in mass percentage: 0.5 to 5% of long-chain silane and 95 to 99.5% of n-hexane.

[0022] Further, the long-chain silane includes triethoxy(1H,1H,2H,2H-nonafluorohexyl)silane (C 12 H 19 F9O3Si), trichloro(1H,1H,2H,2H-tridecafluorooctyl)silane (C8H4Cl3F 13 Si), or 1H,1H,2H,2H-perfluorodecyltriethoxysilane (C 16 H 19 F 17 O3Si).

[0023] The second technical solution of the present invention: a PVDF composite ultrafiltration membrane prepared by the above preparation method.

[0024] The third technical solution of the present invention: an application of the above PVDF composite ultrafiltration membrane in water purification.

[0025] The present invention discloses the following technical effects:

[0026] (1) By mixing GO into the casting solution and synchronously applying a negative DC electric field during the phase inversion process, the present invention improves the intrinsic piezoelectric properties of the material.

[0027] (2) By hydrophobically modifying the membrane material, the piezoelectric output performance of the membrane material in water is improved.

[0028] (3) Through the organic combination of methods such as GO blending, negative electrode DC electric field polarization, and hydrophobically modifying, a PVDF composite ultrafiltration membrane with significant underwater piezoelectric activity and electrokinetic anti-pollution ability is finally prepared. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings required to be used in the embodiments. Obviously, the drawings in the following description are only some embodiments of the present invention. For those of ordinary skill in the art, other drawings can be obtained based on these drawings without creative efforts.

[0030] Figure 1 FTIR diagrams of the PVDF composite ultrafiltration membranes prepared in Examples 1 - 6;

[0031] Figure 2 XRD diagrams of the PVDF composite ultrafiltration membranes prepared in Examples 1 - 6;

[0032] Figure 3 Schematic diagram of the device for testing the piezoelectric output signal in water;

[0033] Figure 4 Schematic diagram of the preparation process of the PVDF composite ultrafiltration membrane;

[0034] Figure 5 Electric signals of the PVDF composite ultrafiltration membranes (with different GO blending contents) prepared in Examples 1 - 6;

[0035] Figure 6 Electric signals of the PVDF composite ultrafiltration membranes prepared in Examples 2 - 4 (Poling), Examples 7 - 9 (nPoling);

[0036] Figure 7 Electric signals of the PVDF composite ultrafiltration membranes prepared in Examples 2 - 4 (Hob), Examples 10 - 12;

[0037] Figure 8 Electric signals of the PVDF composite ultrafiltration membranes (with different applied electric field intensities) prepared in Examples 4, 13;

[0038] Figure 9 Electric signals of the PVDF composite ultrafiltration membranes (with different silane chain lengths used for hydrophobic modification) prepared in Examples 4, 14;

[0039] Figure 10For the fouling resistance of bovine serum albumin (BSA) by the PVDF composite ultrafiltration membranes prepared in Example 1 (Hob-PM0-Poling), Example 9 (Hob-PM 0.5 -nPoling), Example 12 (PM 0.5 -Poling), and Example 4 (Hob-PM 0.5 -Poling).

[0040] Figure 11 For the electrical signals of the PVDF composite ultrafiltration membranes prepared in Example 2 and Examples 15 - 16;

[0041] Figure 12 For the electrical signals of the PVDF composite ultrafiltration membranes prepared in Example 2 and Example 17. Detailed Description of the Invention

[0042] Now, various exemplary embodiments of the present invention will 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, characteristics, and implementation manners of the present invention.

[0043] It should be understood that the terms used in the present invention are only for describing specific implementation manners and are not used to limit the present invention. Additionally, for the numerical ranges in the present invention, it should be understood that each intermediate value between the upper and lower limits of the range is also specifically disclosed. Each intermediate value within any stated value or stated range, as well as each smaller range between any other stated value or intermediate value within the stated range, is also included in the present invention. The upper and lower limits of these smaller ranges may be independently included or excluded from the range.

[0044] Unless otherwise specified, all technical and scientific terms used herein have the same meaning as commonly understood by those of ordinary skill in the art to which the present invention pertains. Although the present invention only describes preferred methods and materials, any methods and materials similar or equivalent to those described herein may also be used in the implementation or testing of the present invention. All documents mentioned in this specification are incorporated by reference to disclose and describe the methods and / or materials related to the documents. In case of conflict with any incorporated document, the content of this specification shall prevail.

[0045] Without departing from the scope or spirit of the present invention, various improvements and changes can be made to the specific implementation manners of the present invention specification, which are obvious to those skilled in the art. Other implementation manners obtained from the present invention specification are obvious to those skilled in the art. The present invention specification and examples are only exemplary.

[0046] Regarding the terms "comprising", "including", "having", "containing", etc. used herein, they are all open-ended terms, meaning including but not limited to.

[0047] In the following examples, "parts" refers to "parts by weight".

[0048] Example 1

[0049] A preparation method of a PVDF composite ultrafiltration membrane with underwater piezoelectric activity (without mixing graphene oxide):

[0050] (1) Mix the organic solvent NMP, the polymer PVDF, and the pore-forming agent PVP in a ratio of 76 wt%: 20 wt%: 4 wt% (the total mass percentage of NMP, PVDF, and PVP is 100%). Subsequently, heat in a water bath at 60 °C and dissolve with mechanical stirring at 400 rpm for 8 h, then let it stand for degassing for 24 h to obtain a casting solution.

[0051] (2) Coat the casting solution on a glass plate, and use a wet film former to make it into a flat shape with a thickness of 250 μm. Immerse the glass plate with the casting solution in a pure water coagulation bath set in a negative direct current electric field for phase separation and synchronous polarization. The electric field strength is 600 V / mm and the time is 15 min. Keep the temperature of the coagulation bath at room temperature (25 °C). Take out the membrane until the casting solution is completely gelled to obtain a PVDF porous membrane.

[0052] (3) Uniformly coat the hydrophobic modification solution on the surface of the PVDF porous membrane (the area ratio of the dosage of the hydrophobic modification solution to the PVDF porous membrane is 5 mL: 1 cm 2 ), and maintain a pressure of 10 kPa during the coating process. The coating time is 30 min. Then let the coated membrane stand at room temperature for 24 h to ensure that n-hexane completely volatilizes, and obtain a PVDF composite ultrafiltration membrane (denoted as PM0).

[0053] The hydrophobic modification solution consists of 2 wt% triethoxy(1H,1H,2H,2H-nonafluorohexyl)silane and 98 wt% n-hexane.

[0054] After drying the PVDF composite ultrafiltration membrane prepared in this example at 50 °C for 2 h, perform FTIR and XRD tests. The results are shown in Figure 1 and Figure 2 .

[0055] Use a platinum-titanium double electrode system to test the underwater electrical signal of the PVDF composite ultrafiltration membrane prepared in this example under the action of a peristaltic pump (see the schematic diagram of the underwater piezoelectric output signal test device in Figure 3 ), and the peristaltic pump provides a pulsed pressure of 90 kPa.

[0056] After testing, when graphene oxide was not added, it was found from the FTIR spectrum that at 763 cm -1There is a non-polar crystal form characteristic peak at [specific location]; it is found from the XRD pattern that the peak at 18.4° is the peak of the α phase. This indicates that when graphene oxide is not added, the film has a strong non-polarity. Combining with the measured average underwater piezoelectric output signal of the PVDF composite ultrafiltration membrane being 150 mV, the result is obtained: when graphene oxide is not added, the β-phase content of PVDF is low and has a non-polar characteristic peak, indicating that it does not have strong piezoelectric properties.

[0057] Example 2

[0058] A preparation method of a PVDF composite ultrafiltration membrane with underwater piezoelectric activity (the dosage of graphene oxide is 0.1 wt%):

[0059] (1) First, disperse 0.1 wt% graphene oxide (GO) (with a diameter of 50 nm) in 75.9 wt% organic solvent NMP under ultrasonic action. Then, add polymer PVDF and pore-forming agent PVP to this solution in a ratio of 20 wt%:4 wt% (the total mass percentage of GO, NMP, PVDF, and PVP is 100%). Subsequently, heat in a water bath at 60 °C and stir mechanically at 400 rpm for 8 h to dissolve, and let it stand for defoaming for 24 h to obtain a casting solution.

[0060] (2) Coat the casting solution on a glass plate, and use a wet film former to make it into a flat shape with a thickness of 250 μm. Immerse the glass plate with the casting solution in a pure water coagulation bath set in a negative DC electric field for phase separation and synchronous polarization. The electric field strength is 600 V / mm, and the time is 15 min. Keep the temperature of the coagulation bath at room temperature (25 °C). After the casting solution is completely gelled, take out the membrane to obtain a PVDF porous membrane.

[0061] (3) Uniformly coat the hydrophobic modification solution on the surface of the PVDF porous membrane (the dosage ratio of the hydrophobic modification solution to the area of the PVDF porous membrane is 5 mL:1 cm 2 ), and maintain a pressure of 10 kPa during the coating process. The coating time is 30 min. Then, let the coated membrane stand at room temperature for 24 h to ensure that n-hexane completely volatilizes, and obtain a PVDF composite ultrafiltration membrane (denoted as PM 0.1 ).

[0062] The hydrophobic modification solution consists of 2 wt% triethoxy(1H,1H,2H,2H-nonafluorohexyl)silane and 98 wt% n-hexane.

[0063] The schematic diagram of the preparation process of the PVDF composite ultrafiltration membrane is shown in Figure 4 .

[0064] After drying the PVDF composite ultrafiltration membrane prepared in this example at 50 °C for 2 h, perform FTIR and XRD tests. The results are shown in Figure 1 andFigure 2 。

[0065] The PVDF composite ultrafiltration membrane prepared in this example was used to test the underwater electrical signal under the action of a peristaltic pump with a platinum-titanium double-electrode system, and the peristaltic pump provided a pulsed pressure of 90 kPa.

[0066] After testing, after adding 0.1 wt% graphene oxide, it was found from the FTIR spectrum that the non-polar peak disappeared at 763 cm -1 , while the peak values of the polar peaks increased at 510 cm -1 and 840 cm -1 . It was found from the XRD pattern that at 18.4°, the α-phase crystal form decreased, and at 20.8°, the β-phase crystal form increased. Combining the measured average piezoelectric output signal of PVDF being 400 mV, the result was obtained: when 0.1 wt% graphene oxide was added, it was found from FTIR and XRD that the piezoelectric performance of PVDF itself was improved, indicating that blending graphene oxide could improve the piezoelectric performance of the PVDF composite ultrafiltration membrane itself.

[0067] Example 3

[0068] A preparation method of a PVDF composite ultrafiltration membrane with underwater piezoelectric activity (the dosage of graphene oxide is 0.3 wt%):

[0069] (1) First, 0.3 wt% graphene oxide (GO) (with a diameter of 50 nm) was dispersed in 75.7 wt% organic solvent NMP under ultrasonic action, and then polymer PVDF and pore-forming agent PVP were added to this solution in a ratio of 20 wt%:4 wt% (the total mass percentage of GO, NMP, PVDF, and PVP is 100%). Subsequently, it was heated in a water bath at 60 °C and dissolved with mechanical stirring at 400 rpm for 8 h, and then left to stand for defoaming for 24 h to obtain a casting solution.

[0070] (2) The casting solution was coated on a glass plate and made into a flat shape with a wet film maker, with a thickness of 250 μm. The glass plate with the casting solution was immersed in a pure water coagulation bath set in a negative DC electric field for phase separation and synchronous polarization. The electric field strength was 600 V / mm, and the time was 15 min. The temperature of the coagulation bath was maintained at room temperature (25 °C). After the casting solution was completely gelled, the membrane was taken out to obtain a PVDF porous membrane.

[0071] (3) The hydrophobic modification solution was uniformly coated on the surface of the PVDF porous membrane (the dosage ratio of the hydrophobic modification solution to the area of the PVDF porous membrane is 5 mL:1 cm 2 ), and a pressure of 10 kPa was maintained during the coating process. The coating time was 30 min. Subsequently, the coated membrane was left to stand at room temperature for 24 h to ensure that n-hexane completely volatilized, obtaining a PVDF composite ultrafiltration membrane (denoted as PM0.3 )。

[0072] The hydrophobic modified solution consists of 2 wt% triethoxy(1H,1H,2H,2H-nonafluorohexyl)silane and 98 wt% n-hexane.

[0073] The PVDF composite ultrafiltration membrane prepared in this example was dried at 50 °C for 2 h and then subjected to FTIR and XRD tests. The results are shown in Figure 1 and Figure 2 。

[0074] The PVDF composite ultrafiltration membrane prepared in this example was used to test the underwater electrical signal under the action of a peristaltic pump using a platinum-titanium double electrode system. The peristaltic pump provided a pulsed pressure of 90 kPa.

[0075] After testing, after adding 0.3 wt% graphene oxide, it was found from the FTIR spectrum that the non-polar peak disappeared at 763 cm -1 , and the peak values of the polar peaks at 510 cm -1 and 840 cm -1 were significantly increased compared with the peak values of the membrane without adding graphene oxide. It was found from the XRD spectrum that at 18.4°, the α-phase crystal form decreased close to no peak, and the β-phase crystal form at 20.8° increased. Combining the measured average piezoelectric output signal of PVDF being 600 mV, the result was obtained: when adding 0.3 wt% graphene oxide, it was found from FTIR and XRD that the piezoelectric properties of PVDF itself were improved, indicating that blending graphene oxide can improve the piezoelectric properties of the PVDF composite ultrafiltration membrane itself.

[0076] Example 4

[0077] A preparation method of a PVDF composite ultrafiltration membrane with underwater piezoelectric activity (the dosage of graphene oxide is 0.5 wt%):

[0078] (1) First, 0.5 wt% graphene oxide (GO) (with a diameter of 50 nm) was dispersed in 75.5 wt% organic solvent NMP under ultrasonic action. Then, the polymer PVDF and the pore-forming agent PVP were added to this solution in a ratio of 20 wt%:4 wt% (the total mass percentage of GO, NMP, PVDF, and PVP is 100%). Subsequently, it was heated in a water bath at 60 °C and dissolved with mechanical stirring at 400 rpm for 8 h, and left to stand for defoaming for 24 h to obtain a casting solution.

[0079] (2) Coat the casting solution on a glass plate and use a wet film former to make it into a flat shape with a thickness of 250 μm. Immerse the glass plate with the casting solution in a pure water coagulation bath set in a negative direct current electric field for phase separation and synchronous polarization. The electric field strength is 600 V / mm, and the time is 15 min. Keep the temperature of the coagulation bath at room temperature (25 °C). After the casting solution is completely gelled, take out the film to obtain a PVDF porous membrane.

[0080] (3) Uniformly coat the hydrophobic modification solution on the surface of the PVDF porous membrane (the dosage ratio of the hydrophobic modification solution to the area of the PVDF porous membrane is 5 mL:1 cm 2 ), and maintain a pressure of 10 kPa during the coating process. The coating time is 30 min. Then, leave the coated membrane standing at room temperature for 24 h to ensure that n-hexane completely volatilizes, obtaining a PVDF composite ultrafiltration membrane (denoted as PM 0.5 ).

[0081] The hydrophobic modification solution consists of 2 wt% triethoxy(1H,1H,2H,2H-nonafluorohexyl)silane and 98 wt% n-hexane.

[0082] Dry the PVDF composite ultrafiltration membrane prepared in this example at 50 °C for 2 h and then conduct FTIR and XRD tests. The results are shown in Figure 1 and Figure 2 .

[0083] Use a platinum-titanium double electrode system to test the underwater electrical signal of the PVDF composite ultrafiltration membrane prepared in this example under the action of a peristaltic pump. The peristaltic pump provides a pulsed pressure of 90 kPa.

[0084] After testing, after adding 0.5 wt% graphene oxide, it is found from the FTIR spectrum that the non-polar peak disappears at 763 cm -1 , while the peak values of the polar peaks at 510 cm -1 and 840 cm -1 are significantly increased compared to the membrane peak values without graphene oxide. It is found from the XRD spectrum that at 18.4°, the α-phase crystal form disappears, and at 20.8°, the β-phase crystal form increases. Combining with the measured average piezoelectric output signal of PVDF being 900 mV, the result is obtained: when adding 0.5 wt% graphene oxide, it is found from FTIR and XRD that the piezoelectric performance of PVDF itself is improved, indicating that blending graphene oxide can improve the piezoelectric performance of the PVDF composite ultrafiltration membrane itself.

[0085] Example 5

[0086] A preparation method of a PVDF composite ultrafiltration membrane with underwater piezoelectric activity (the dosage of graphene oxide is 1 wt%):

[0087] (1) First, 1 wt% graphene oxide (GO) (with a diameter of 50 nm) was dispersed in 75 wt% organic solvent NMP under ultrasonic action. Then, the polymer PVDF and the pore-forming agent PVP were added to this solution in a ratio of 20 wt%:4 wt% (the total mass percentage of GO, NMP, PVDF, and PVP is 100%). Subsequently, it was heated in a water bath at 60 °C and dissolved with mechanical stirring at 400 rpm for 8 h, and then left to stand and defoam for 24 h to obtain the casting solution.

[0088] (2) The casting solution was coated on a glass plate and made into a flat plate with a wet film former, with a thickness of 250 μm. The glass plate with the casting solution was immersed in a pure water coagulation bath set in a negative direct current electric field for phase separation and synchronous polarization. The electric field strength was 600 V / mm and the time was 15 min. The temperature of the coagulation bath was maintained at room temperature (25 °C). After the casting solution was completely gelled, the membrane was taken out to obtain the PVDF porous membrane.

[0089] (3) The hydrophobic modification solution was uniformly coated on the surface of the PVDF porous membrane (the ratio of the amount of the hydrophobic modification solution to the area of the PVDF porous membrane is 5 mL:1 cm 2 ), and a pressure of 10 kPa was maintained during the coating process. The coating time was 30 min. Subsequently, the coated membrane was left to stand at room temperature for 24 h to ensure that n-hexane completely volatilized, obtaining the PVDF composite ultrafiltration membrane (denoted as PM1).

[0090] The hydrophobic modification solution consists of 2 wt% triethoxy(1H,1H,2H,2H-nonafluorohexyl)silane and 98 wt% n-hexane.

[0091] The PVDF composite ultrafiltration membrane prepared in this example was dried at 50 °C for 2 h and then subjected to FTIR and XRD tests. The results are shown in Figure 1 and Figure 2 .

[0092] The PVDF composite ultrafiltration membrane prepared in this example was used to test the underwater electrical signal under the action of a peristaltic pump using a platinum-titanium double electrode system. The peristaltic pump provided a pulsed pressure of 90 kPa.

[0093] After testing, it was found from the FTIR spectrum that after adding 1 wt% graphene oxide, the non-polar peak disappeared at 763 cm -1 , while at 510 cm -1 and 840 cm -1The peak value of the piezoelectricity at this position is significantly increased compared with that of the membrane without adding graphene oxide. It is found from the XRD pattern that at 18.4°, the α-phase crystal form disappears, and at 20.8°, the β-phase crystal form increases. Combining with the measured average piezoelectric output signal of PVDF being 600 mV, the result is obtained that when 1 wt% graphene oxide is added, it is found from FTIR and XRD that the piezoelectric performance of PVDF itself is improved, indicating that blending graphene oxide can improve the piezoelectric performance of the PVDF composite ultrafiltration membrane itself.

[0094] Example 6

[0095] A preparation method of a PVDF composite ultrafiltration membrane with underwater piezoelectric activity (the dosage of graphene oxide is 1.5 wt%):

[0096] (1) First, disperse 1.5 wt% graphene oxide (GO) (with a diameter of 50 nm) in 74.5 wt% organic solvent NMP under ultrasonic action. Then, add polymer PVDF and pore-forming agent PVP to this solution in a ratio of 20 wt%:4 wt% (the total mass percentage of GO, NMP, PVDF, and PVP is 100%). Subsequently, heat it in a water bath at 60 °C, dissolve it with mechanical stirring at 400 rpm for 8 h, and let it stand for defoaming for 24 h to obtain a casting solution.

[0097] (2) Coat the casting solution on a glass plate, and use a wet film preparation device to make it into a flat shape with a thickness of 250 μm. Immerse the glass plate with the casting solution in a pure water coagulation bath set in a negative DC electric field for phase separation and synchronous polarization. The electric field strength is 600 V / mm, and the time is 15 min. Keep the temperature of the coagulation bath at room temperature (25 °C). After the casting solution is completely gelled, take out the membrane to obtain a PVDF porous membrane.

[0098] (3) Uniformly coat the hydrophobic modification solution on the surface of the PVDF porous membrane (the dosage ratio of the hydrophobic modification solution to the area of the PVDF porous membrane is 5 mL:1 cm 2 ), and maintain a pressure of 10 kPa during the coating process. The coating time is 30 min. Then, let the coated membrane stand at room temperature for 24 h to ensure that n-hexane completely volatilizes, and obtain a PVDF composite ultrafiltration membrane (denoted as PM 1.5 ).

[0099] The hydrophobic modification solution consists of 2 wt% triethoxy(1H,1H,2H,2H-nonafluorohexyl)silane and 98 wt% n-hexane.

[0100] Dry the PVDF composite ultrafiltration membrane prepared in this example at 50 °C for 2 h and then conduct FTIR and XRD tests. The results are shown in Figure 1 and Figure 2 .

[0101] The PVDF composite ultrafiltration membrane prepared in this example was used to test the underwater electrical signal under the action of a peristaltic pump using a platinum-titanium double-electrode system, and the peristaltic pump provided a pulsed pressure of 90 kPa.

[0102] After testing, after adding 1.5 wt% graphene oxide, it was found from the FTIR spectrum that the non-polar peak disappeared at 763 cm -1 while the peak values of the polar peaks at 510 cm -1 and 840 cm -1 were significantly increased compared to the peak values of the membrane without adding graphene oxide. It was found from the XRD pattern that at 18.4°, the α-phase crystal form disappeared, and the β-phase crystal form at 20.8° increased. Combining with the measured average piezoelectric output signal of PVDF being 400 mV, the result was obtained: when 1.5 wt% graphene oxide was added, it was found from FTIR and XRD that the piezoelectric performance of PVDF itself was improved, indicating that blending graphene oxide could improve the piezoelectric performance of the PVDF composite ultrafiltration membrane itself.

[0103] Example 7

[0104] A preparation method of a PVDF composite ultrafiltration membrane with underwater piezoelectric activity (without polarization):

[0105] (1) First, 0.1 wt% graphene oxide (GO) (with a diameter of 50 nm) was dispersed in 75.9 wt% organic solvent NMP under ultrasonic action, and then polymer PVDF and pore-forming agent PVP were added to this solution in a ratio of 20 wt%:4 wt% (the total mass percentage of GO, NMP, PVDF, and PVP was 100%). Subsequently, it was heated in a water bath at 60 °C and dissolved with mechanical stirring at 400 rpm for 8 h, and then left to stand for defoaming for 24 h to obtain a casting solution.

[0106] (2) The casting solution was coated on a glass plate and made into a flat shape with a wet film maker, with a thickness of 250 μm. The glass plate with the casting solution was directly immersed in a pure water coagulation bath, and the temperature of the coagulation bath was maintained at room temperature (25 °C). The membrane was taken out until the casting solution was completely gelled to obtain a PVDF porous membrane.

[0107] (3) The hydrophobic modification solution was uniformly coated on the surface of the PVDF porous membrane (the dosage ratio of the hydrophobic modification solution to the area of the PVDF porous membrane was 5 mL:1 cm 2 ), and a pressure of 10 kPa was maintained during the coating process. The coating time was 30 min. Subsequently, the coated membrane was left to stand at room temperature for 24 h to ensure that n-hexane completely volatilized to obtain a PVDF composite ultrafiltration membrane.

[0108] The hydrophobic modified solution consists of 2 wt% triethoxy(1H,1H,2H,2H-nonafluorohexyl)silane and 98 wt% n-hexane.

[0109] The PVDF composite ultrafiltration membrane prepared in this example was tested for underwater electrical signals using a platinum-titanium double electrode system under the action of a peristaltic pump, and the peristaltic pump provided a pulsed pressure of 90 kPa.

[0110] It was determined that the average piezoelectric output signal of the PVDF composite ultrafiltration membrane prepared in this example was 100 mV.

[0111] Example 8

[0112] A preparation method of a PVDF composite ultrafiltration membrane with underwater piezoelectric activity (without polarization):

[0113] (1) First, 0.3 wt% graphene oxide (GO) (with a diameter of 50 nm) was dispersed in 75.7 wt% organic solvent NMP under ultrasonic action, and then polymer PVDF and pore-forming agent PVP were added to this solution in a ratio of 20 wt%:4 wt% (the total mass percentage of GO, NMP, PVDF, and PVP was 100%). Subsequently, it was heated in a water bath at 60 °C and dissolved with mechanical stirring at 400 rpm for 8 h, and then left to stand for defoaming for 24 h to obtain a casting solution.

[0114] (2) The casting solution was coated on a glass plate and made into a flat shape with a wet film former, with a thickness of 250 μm. The glass plate with the casting solution was directly immersed in a pure water coagulation bath, and the temperature of the coagulation bath was maintained at room temperature (25 °C). After the casting solution was completely gelled, the membrane was taken out to obtain a PVDF porous membrane.

[0115] (3) The hydrophobic modified solution was uniformly coated on the surface of the PVDF porous membrane (the dosage ratio of the hydrophobic modified solution to the area of the PVDF porous membrane was 5 mL:1 cm 2 ), and a pressure of 10 kPa was maintained during the coating process. The coating time was 30 min. Subsequently, the coated membrane was left to stand at room temperature for 24 h to ensure that the n-hexane completely volatilized, obtaining a PVDF composite ultrafiltration membrane.

[0116] The hydrophobic modified solution consists of 2 wt% triethoxy(1H,1H,2H,2H-nonafluorohexyl)silane and 98 wt% n-hexane.

[0117] The PVDF composite ultrafiltration membrane prepared in this example was tested for underwater electrical signals using a platinum-titanium double electrode system under the action of a peristaltic pump, and the peristaltic pump provided a pulsed pressure of 90 kPa.

[0118] It was determined that the average piezoelectric output signal of the PVDF composite ultrafiltration membrane prepared in this example was 130 mV.

[0119] Example 9

[0120] Preparation method of a PVDF composite ultrafiltration membrane with underwater piezoelectric activity (without polarization):

[0121] (1) First, under ultrasonic action, 0.5 wt% graphene oxide (GO) (with a diameter of 50 nm) is dispersed in 75.5 wt% organic solvent NMP. Then, according to the ratio of 20 wt%:4 wt%, polymer PVDF and pore-forming agent PVP are added to this solution (the total mass percentage of GO, NMP, PVDF, and PVP is 100%). Subsequently, it is heated in a water bath at 60 °C and dissolved with mechanical stirring at 400 rpm for 8 h, and left to stand for degassing for 24 h to obtain a casting solution.

[0122] (2) The casting solution is coated on a glass plate and made into a flat shape with a wet film former, with a thickness of 250 μm. The glass plate with the casting solution is directly immersed in a pure water coagulation bath, and the temperature of the coagulation bath is maintained at room temperature (25 °C). After the casting solution is completely gelled, the membrane is taken out to obtain a PVDF porous membrane.

[0123] (3) The hydrophobic modification solution is evenly coated on the surface of the PVDF porous membrane (the dosage ratio of the hydrophobic modification solution to the area of the PVDF porous membrane is 5 mL:1 cm 2 ), and a pressure of 10 kPa is maintained during the coating process. The coating time is 30 min. Subsequently, the coated membrane is left to stand at room temperature for 24 h to ensure that n-hexane completely volatilizes, obtaining a PVDF composite ultrafiltration membrane.

[0124] The hydrophobic modification solution consists of 2 wt% triethoxy(1H,1H,2H,2H-nonafluorohexyl)silane and 98 wt% n-hexane.

[0125] The PVDF composite ultrafiltration membrane prepared in this example is used to test the underwater electrical signal under the action of a peristaltic pump using a platinum-titanium double electrode system. The peristaltic pump provides a pulsed pressure of 90 kPa.

[0126] It is measured that the average piezoelectric output signal of the PVDF composite ultrafiltration membrane prepared in this example is 150 mV.

[0127] Example 10

[0128] Preparation method of a PVDF composite ultrafiltration membrane with underwater piezoelectric activity (without hydrophobic modification):

[0129] (1) First, 0.1 wt% graphene oxide (GO) (with a diameter of 50 nm) was dispersed in 75.9 wt% organic solvent NMP under ultrasonic action. Then, polymer PVDF and pore-forming agent PVP were added to this solution in a ratio of 20 wt%:4 wt% (the total mass percentage of GO, NMP, PVDF, and PVP is 100%). Subsequently, it was heated in a water bath at 60 °C and dissolved with mechanical stirring at 400 rpm for 8 h, and then left standing for defoaming for 24 h to obtain a casting solution.

[0130] (2) The casting solution was coated on a glass plate and made into a flat shape with a wet film preparation device, with a thickness of 250 μm. The glass plate with the casting solution was immersed in a pure water coagulation bath set in a negative direct current electric field for phase separation and synchronous polarization. The electric field strength was 600 V / mm and the time was 15 min. The temperature of the coagulation bath was maintained at room temperature (25 °C). After the casting solution was completely gelled, the membrane was taken out to obtain a PVDF composite ultrafiltration membrane.

[0131] The PVDF composite ultrafiltration membrane prepared in this example was used to test the underwater electrical signal under the action of a peristaltic pump using a platinum-titanium double electrode system. The peristaltic pump provided a pulsed pressure of 90 kPa.

[0132] After testing, when 0.1 wt% graphene oxide was added and coupled with the in-situ polarization of the electric field without hydrophobic modification, it was found that under the platinum-titanium double electrode system, the average piezoelectric output signal of this PVDF composite ultrafiltration membrane was 100 mV. This shows that the electrical signal generated by the electromechanical coupling effect is affected by the double electric layer, resulting in the weakening of its transmission in water.

[0133] Example 11

[0134] A preparation method of a PVDF composite ultrafiltration membrane with underwater piezoelectric activity (without hydrophobic modification):

[0135] (1) First, 0.3 wt% graphene oxide (GO) (with a diameter of 50 nm) was dispersed in 75.7 wt% organic solvent NMP under ultrasonic action. Then, polymer PVDF and pore-forming agent PVP were added to this solution in a ratio of 20 wt%:4 wt% (the total mass percentage of GO, NMP, PVDF, and PVP is 100%). Subsequently, it was heated in a water bath at 60 °C and dissolved with mechanical stirring at 400 rpm for 8 h, and then left standing for defoaming for 24 h to obtain a casting solution.

[0136] (2) Coating the casting solution on a glass plate, making it into a flat shape with a wet film former, with a thickness of 250 μm. Immerse the glass plate with the casting solution in a pure water coagulation bath set in a negative DC electric field for phase separation and synchronous polarization. The electric field strength is 600 V / mm, and the time is 15 min. Keep the temperature of the coagulation bath at room temperature (25 °C). After the casting solution is completely gelled, take out the membrane to obtain the PVDF composite ultrafiltration membrane.

[0137] Testing the underwater electrical signals of the PVDF composite ultrafiltration membrane prepared in this example using a platinum-titanium double electrode system under the action of a peristaltic pump. The peristaltic pump provides a pulsed pressure of 90 kPa.

[0138] After testing, when adding 0.3 wt% graphene oxide and coupling the in-situ polarization effect of the electric field without hydrophobic modification, it is found that under the platinum-titanium double electrode system, the average piezoelectric output signal of this PVDF composite ultrafiltration membrane is 150 mV. This shows that the electrical signals generated by the electromechanical coupling effect are affected by the electric double layer, resulting in the weakening of their transmission in water.

[0139] Example 12

[0140] A preparation method of a PVDF composite ultrafiltration membrane with underwater piezoelectric activity (without hydrophobic modification):

[0141] (1) First, disperse 0.5 wt% graphene oxide (GO) (with a diameter of 50 nm) in 75.5 wt% organic solvent NMP under ultrasonic action. Then, add polymer PVDF and pore-forming agent PVP to this solution according to a ratio of 20 wt%:4 wt% (the total mass percentage of GO, NMP, PVDF, and PVP is 100%). Subsequently, heat it in a water bath at 60 °C and dissolve it with mechanical stirring at 400 rpm for 8 h, and let it stand for defoaming for 24 h to obtain the casting solution.

[0142] (2) Coating the casting solution on a glass plate, making it into a flat shape with a wet film former, with a thickness of 250 μm. Immerse the glass plate with the casting solution in a pure water coagulation bath set in a negative DC electric field for phase separation and synchronous polarization. The electric field strength is 600 V / mm, and the time is 15 min. Keep the temperature of the coagulation bath at room temperature (25 °C). After the casting solution is completely gelled, take out the membrane to obtain the PVDF composite ultrafiltration membrane.

[0143] Testing the underwater electrical signals of the PVDF composite ultrafiltration membrane prepared in this example using a platinum-titanium double electrode system under the action of a peristaltic pump. The peristaltic pump provides a pulsed pressure of 90 kPa.

[0144] After testing, when 0.5 wt% graphene oxide was added, under the in-situ polarization effect of the coupled electric field and without hydrophobic modification, it was found that in the platinum-titanium double-electrode system, the average piezoelectric output signal of this PVDF composite ultrafiltration membrane was 200 mV. This indicates that the electrical signal generated by the electromechanical coupling effect is affected by the double electric layer, resulting in the weakening of its transmission in water.

[0145] Example 13

[0146] A preparation method of a PVDF composite ultrafiltration membrane with underwater piezoelectric activity (electric field polarization intensity 100 V / mm):

[0147] (1) First, under ultrasonic action, 0.5 wt% graphene oxide (GO) (with a diameter of 50 nm) was dispersed in 75.5 wt% organic solvent NMP. Then, according to the ratio of 20 wt%:4 wt%, the polymer PVDF and the pore-forming agent PVP were added to this solution (the total mass percentage of GO, NMP, PVDF, and PVP is 100%). Subsequently, it was heated in a water bath at 60 °C and dissolved with mechanical stirring at 400 rpm for 8 h, and then left to stand for defoaming for 24 h to obtain a casting solution.

[0148] (2) The casting solution was coated on a glass plate and made into a flat shape with a wet film preparation device, with a thickness of 250 μm. The glass plate with the casting solution was immersed in a pure water coagulation bath set in a negative DC electric field for phase separation and synchronous polarization. The electric field intensity was 100 V / mm and the time was 15 min. The temperature of the coagulation bath was maintained at room temperature (25 °C). After the casting solution was completely gelled, the membrane was taken out to obtain a PVDF porous membrane.

[0149] (3) The hydrophobic modification solution was uniformly coated on the surface of the PVDF porous membrane (the dosage ratio of the hydrophobic modification solution to the area of the PVDF porous membrane is 5 mL:1 cm 2 ), and a pressure of 10 kPa was maintained during the coating process. The coating time was 30 min. Subsequently, the coated membrane was left to stand at room temperature for 24 h to ensure that n-hexane completely volatilized, obtaining a PVDF composite ultrafiltration membrane.

[0150] The hydrophobic modification solution consists of 2 wt% triethoxy(1H,1H,2H,2H-nonafluorohexyl)silane and 98 wt% n-hexane.

[0151] The PVDF composite ultrafiltration membrane prepared in this example was tested for underwater electrical signals using a platinum-titanium double-electrode system under the action of a peristaltic pump, and the peristaltic pump provided a pulsed pressure of 90 kPa.

[0152] It was determined that the average piezoelectric output signal of the PVDF composite ultrafiltration membrane prepared in this example was 200 mV.

[0153] Example 14

[0154] Preparation method of a PVDF composite ultrafiltration membrane with underwater piezoelectric activity (changing the long-chain silane used in the hydrophobic modification solution to short-chain silane):

[0155] (1) First, disperse 0.5 wt% graphene oxide (GO) (with a diameter of 50 nm) in 75.5 wt% organic solvent NMP under ultrasonic action. Then, add polymer PVDF and pore-forming agent PVP to this solution in a ratio of 20 wt%:4 wt% (the total mass percentage of GO, NMP, PVDF, and PVP is 100%). Subsequently, heat in a water bath at 60 °C and dissolve with mechanical stirring at 400 rpm for 8 h, and let it stand for defoaming for 24 h to obtain a casting solution.

[0156] (2) Coat the casting solution on a glass plate, and use a wet film former to make it into a flat shape with a thickness of 250 μm. Immerse the glass plate with the casting solution in a pure water coagulation bath set in a negative DC electric field for phase separation and synchronous polarization. The electric field strength is 600 V / mm, and the time is 15 min. Keep the temperature of the coagulation bath at room temperature (25 °C). After the casting solution is completely gelled, take out the membrane to obtain a PVDF porous membrane.

[0157] (3) Uniformly coat the hydrophobic modification solution on the surface of the PVDF porous membrane (the area ratio of the amount of the hydrophobic modification solution to the PVDF porous membrane is 5 mL:1 cm 2 ), and maintain a pressure of 10 kPa during the coating process. The coating time is 30 min. Subsequently, let the coated membrane stand at room temperature for 24 h to ensure that n-hexane completely volatilizes, and obtain a PVDF composite ultrafiltration membrane.

[0158] The hydrophobic modification solution is composed of 2 wt% triethoxymethylsilane and 98 wt% n-hexane.

[0159] Test the underwater electrical signal of the PVDF composite ultrafiltration membrane prepared in this example using a platinum-titanium double electrode system under the action of a peristaltic pump. The peristaltic pump provides a pulsed pressure of 90 kPa.

[0160] It is measured that the average piezoelectric output signal of the PVDF composite ultrafiltration membrane prepared in this example is 250 mV.

[0161] Example 15

[0162] Preparation method of a PVDF composite ultrafiltration membrane with underwater piezoelectric activity (the size of graphene oxide is 0.2 nm):

[0163] (1) First, 0.1 wt% graphene oxide (GO) (with a diameter of 0.2 nm) was dispersed in 75.9 wt% organic solvent NMP under ultrasonic action. Then, polymer PVDF and pore-forming agent PVP were added to this solution in a ratio of 20 wt%:4 wt% (the total mass percentage of GO, NMP, PVDF, and PVP is 100%). Subsequently, it was heated in a water bath at 60 °C and dissolved with mechanical stirring at 400 rpm for 8 h, and then left to stand and defoam for 24 h to obtain a casting solution.

[0164] (2) The casting solution was coated on a glass plate and made into a flat shape with a wet film former, with a thickness of 250 μm. The glass plate with the casting solution was immersed in a pure water coagulation bath set in a negative direct current electric field for phase separation and synchronous polarization. The electric field strength was 600 V / mm and the time was 15 min. The temperature of the coagulation bath was maintained at room temperature (25 °C). After the casting solution was completely gelled, the membrane was taken out to obtain a PVDF porous membrane.

[0165] (3) The hydrophobic modification solution was uniformly coated on the surface of the PVDF porous membrane (the dosage ratio of the hydrophobic modification solution to the area of the PVDF porous membrane was 5 mL:1 cm 2 ), and a pressure of 10 kPa was maintained during the coating process. The coating time was 30 min. Subsequently, the coated membrane was left to stand at room temperature for 24 h to ensure that n-hexane completely volatilized, obtaining a PVDF composite ultrafiltration membrane.

[0166] The hydrophobic modification solution was composed of 2 wt% triethoxy(1H,1H,2H,2H-nonafluorohexyl)silane and 98 wt% n-hexane.

[0167] The PVDF composite ultrafiltration membrane prepared in this example was used to test the underwater electrical signal under the action of a peristaltic pump using a platinum-titanium double electrode system. The peristaltic pump provided a pulsed pressure of 90 kPa.

[0168] It was measured that the average piezoelectric output signal of the PVDF composite ultrafiltration membrane prepared in this example was 200 mV.

[0169] Example 16

[0170] A preparation method of a PVDF composite ultrafiltration membrane with underwater piezoelectric activity (the size of graphene oxide is 500 nm):

[0171] (1) First, 0.1 wt% graphene oxide (GO) (with a diameter of 500 nm) was dispersed in 75.9 wt% organic solvent NMP under ultrasonic action. Then, the polymer PVDF and the pore-forming agent PVP were added to this solution in a ratio of 20 wt%:4 wt% (the total mass percentage of GO, NMP, PVDF, and PVP is 100%). Subsequently, it was heated in a water bath at 60 °C and dissolved with mechanical stirring at 400 rpm for 8 h, and then left to stand for degassing for 24 h to obtain a casting solution.

[0172] (2) The casting solution was coated on a glass plate and made into a flat shape with a wet film applicator, with a thickness of 250 μm. The glass plate with the casting solution was immersed in a pure water coagulation bath set in a negative direct current electric field for phase separation and synchronous polarization. The electric field strength was 600 V / mm and the time was 15 min. The temperature of the coagulation bath was maintained at room temperature (25 °C). After the casting solution was completely gelated, the membrane was taken out to obtain a PVDF porous membrane.

[0173] (3) The hydrophobic modification solution was uniformly coated on the surface of the PVDF porous membrane (the ratio of the dosage of the hydrophobic modification solution to the area of the PVDF porous membrane was 5 mL:1 cm 2 ), and a pressure of 10 kPa was maintained during the coating process. The coating time was 30 min. Subsequently, the coated membrane was left to stand at room temperature for 24 h to ensure that n-hexane completely volatilized, obtaining a PVDF composite ultrafiltration membrane.

[0174] The hydrophobic modification solution was composed of 2 wt% triethoxy(1H,1H,2H,2H-nonafluorohexyl)silane and 98 wt% n-hexane.

[0175] The PVDF composite ultrafiltration membrane prepared in this example was used to test the underwater electrical signal under the action of a peristaltic pump using a platinum-titanium double electrode system. The peristaltic pump provided a pulsed pressure of 90 kPa.

[0176] It was measured that the average piezoelectric output signal of the PVDF composite ultrafiltration membrane prepared in this example was 150 mV.

[0177] Example 17

[0178] A preparation method of a PVDF composite ultrafiltration membrane with underwater piezoelectric activity (the polarization electric field is a positive direct current electric field):

[0179] (1) First, 0.1 wt% graphene oxide (GO) (with a diameter of 50 nm) was dispersed in 75.9 wt% organic solvent NMP under the action of ultrasound. Then, polymer PVDF and pore-forming agent PVP were added to this solution in a ratio of 20 wt%:4 wt% (the total mass percentage of GO, NMP, PVDF, and PVP is 100%). Subsequently, it was heated in a water bath at 60 °C and dissolved with mechanical stirring at 400 rpm for 8 h, and then left to stand and defoam for 24 h to obtain a casting solution.

[0180] (2) The casting solution was coated on a glass plate and made into a flat shape with a wet film preparation device, with a thickness of 250 μm. The glass plate with the casting solution was immersed in a pure water coagulation bath set in a positive direct current electric field for phase separation and synchronous polarization. The electric field strength was 600 V / mm and the time was 15 min. The temperature of the coagulation bath was maintained at room temperature (25 °C). After the casting solution was completely gelated, the membrane was taken out to obtain a PVDF porous membrane.

[0181] (3) The hydrophobic modification solution was evenly coated on the surface of the PVDF porous membrane (the area ratio of the amount of the hydrophobic modification solution to the PVDF porous membrane is 5 mL:1 cm 2 ), and a pressure of 10 kPa was maintained during the coating process. The coating time was 30 min. Subsequently, the coated membrane was left to stand at room temperature for 24 h to ensure that n-hexane completely volatilized, obtaining a PVDF composite ultrafiltration membrane.

[0182] The hydrophobic modification solution consists of 2 wt% triethoxy(1H,1H,2H,2H-nonafluorohexyl)silane and 98 wt% n-hexane.

[0183] The PVDF composite ultrafiltration membrane prepared in this example was used to test the underwater electrical signal under the action of a peristaltic pump using a platinum-titanium double electrode system. The peristaltic pump provided a pulsed pressure of 90 kPa.

[0184] It was measured that the average piezoelectric output signal of the PVDF composite ultrafiltration membrane prepared in this example was 250 mV.

[0185] Effect Example 1

[0186] The piezoelectric properties (electrical signals) of PVDF composite ultrafiltration membranes (Examples 1 - 6) prepared by blending different contents of graphene oxide (GO) were measured. The results are shown in Figure 5 .

[0187] It can be seen from Figure 5 that as the content of GO increases, the piezoelectric signal of the PVDF composite ultrafiltration membrane first increases and then decreases, reaching a maximum of 1200 mV. Compared with the PVDF composite ultrafiltration membrane without blending graphene oxide, the piezoelectric output signal is increased by 5 times. This shows that the content of blended graphene oxide has a significant effect on the piezoelectric properties of the PVDF piezoelectric separation membrane.

[0188] Effect Example 2

[0189] Piezoelectric properties (electrical signals) of PVDF composite ultrafiltration membranes prepared in Measurement Example 2 (Poling - 0.1 wt%), Example 3 (Poling - 0.3 wt%), Example 4 (Poling - 0.5 wt%), Example 7 (nPoling - 0.1 wt%), Example 8 (nPoling - 0.3 wt%), and Example 9 (nPoling - 0.5 wt%) are shown in Figure 6 。

[0190] From Figure 6 it can be seen that on the basis of the same content of blended graphene oxide, after in-situ polarization under an electric field, the piezoelectric signal of the membrane in water is 5 times higher than that of the membrane without in-situ polarization under an electric field, which demonstrates the important role of in-situ polarization under an electric field by comparison.

[0191] Effect Example 3

[0192] Piezoelectric properties (electrical signals) of PVDF composite ultrafiltration membranes prepared in Measurement Example 2 (Hob - 0.1 wt%), Example 3 (Hob - 0.3 wt%), Example 4 (Hob - 0.5 wt%), Example 10 (0.1 wt%), Example 11 (0.3 wt%), and Example 12 (0.5 wt%) are shown in Figure 7 。

[0193] From Figure 7 it can be seen that on the basis of the same content of blended graphene oxide, after hydrophobic modification, the piezoelectric signal of the membrane in water is 5 times higher than that of the unmodified PVDF composite ultrafiltration membrane, which demonstrates the key role of hydrophobic modification by comparison.

[0194] Effect Example 4

[0195] Piezoelectric properties (electrical signals) of PVDF composite ultrafiltration membranes prepared in Example 4 (Hob - PM0.5 - Poling 600) and Example 13 (Hob - PM0.5 - Poling 100) under different electric field strengths are shown in Figure 8 。

[0196] From Figure 8 it can be seen that on the basis of completely the same other conditions, the PVDF composite ultrafiltration membrane prepared by applying an electric field strength of 600 V / mm during the phase inversion process has a piezoelectric signal in water 5 times higher than that of the PVDF composite ultrafiltration membrane prepared by applying an electric field strength of 100 V / mm.

[0197] Effect Example 5

[0198] Measurement Example 4 (Hob-C 12 H 19 F9O3Si-PM0.5-Poling) and Example 14 (Hob-C7H 18 O3Si-PM0.5-Poling) The piezoelectric properties (electrical signals) of PVDF composite ultrafiltration membranes prepared with silanes of different chain lengths are shown in Figure 9 .

[0199] From Figure 9 it can be seen that on the basis of exactly the same other conditions, the PVDF composite ultrafiltration membrane prepared with long-chain silane (triethoxy(1H,1H,2H,2H-nonafluorohexyl)silane) (C 12 H 19 F9O3Si) during the hydrophobic modification process has a piezoelectric signal in water that is 5 times higher than that of the composite PVDF ultrafiltration membrane prepared with short-chain silane (triethoxymethylsilane) (C7H 18 O3Si).

[0200] Effect Example 6

[0201] Measure the fouling resistance of the PVDF composite ultrafiltration membranes prepared in Example 1 (Hob-PM0-Poling), Example 9 (Hob-PM 0.5 -nPoling), Example 12 (PM 0.5 -Poling), and Example 4 (Hob-PM 0.5 -Poling) against bovine serum albumin (BSA). The results are shown in Figure 10 .

[0202] Measurement of the anti-fouling performance of ultrafiltration membranes (i.e., the fouling resistance to bovine serum albumin (BSA)):

[0203] At the beginning of the filtration experiment, place the PVDF ultrafiltration membrane sample in the ultrafiltration cup and pre-press the PVDF ultrafiltration membrane with deionized water at 0.1 MPa for 60 min to obtain a stable initial flux denoted as J0. Subsequently, change the filtration water body to a 20 mg / L bovine serum albumin solution, adjust the pressure to 0.09 MPa. Considering that the initial fluxes of different PVDF ultrafiltration membrane samples are different, measure the steady-state flux of the PVDF ultrafiltration membrane sample when the permeate volume reaches 500 mL and denote it as J p . After that, perform a simple physical cleaning with deionized water, and then measure the pure water flux of the PVDF ultrafiltration membrane sample again and denote it as J c . The anti-fouling performance of the PVDF ultrafiltration membrane can be evaluated by the total fouling resistance (R t ), the irreversible fouling resistance (R i ), and the reversible fouling resistance (R r) It is evaluated that the total fouling resistance refers to the proportion of the water flux loss after fouling to the pure water flux, which is calculated according to formula (1); the reversible fouling resistance refers to the proportion of the flux recovered by simple physical cleaning to the pure water flux before fouling, which is calculated according to formula (2); the irreversible fouling resistance refers to the proportion of the flux that is still difficult to recover after physical cleaning to the pure water flux before fouling, which is calculated according to formula (3).

[0204]

[0205]

[0206]

[0207] From Figure 10 it can be seen that on the basis of the same other conditions, the total fouling resistance of the PVDF composite ultrafiltration membrane added with GO to BSA is reduced by more than 3 times compared with the PVDF composite ultrafiltration membrane without GO added; the total fouling resistance of the PVDF composite ultrafiltration membrane with electric field polarization to BSA is reduced by more than 3 times compared with the PVDF composite ultrafiltration membrane without electric field polarization; the total fouling resistance of the PVDF composite ultrafiltration membrane with hydrophobic modification to BSA is reduced by 4 times compared with the PVDF composite ultrafiltration membrane without hydrophobic modification. Among them, the irreversible resistance of the PVDF composite ultrafiltration membrane prepared by blending graphene oxide, in-situ electric field polarization and hydrophobic modification to BSA drops to 0.05, and its anti-fouling performance is significantly improved.

[0208] Effect Example 7

[0209] Measure the piezoelectric properties (electrical signals) of the PVDF composite ultrafiltration membranes prepared in Example 2 (GO-50nm) and Example 15 (GO-0.2nm) with different diameters of graphene oxide. The results are shown in Figure 11 .

[0210] From Figure 11 it can be seen that on the basis of the same other conditions, the piezoelectric signal of the PVDF composite ultrafiltration membrane prepared with graphene oxide with a diameter of 50nm in water is 1 time higher than that of the composite PVDF ultrafiltration membrane prepared with graphene oxide with a diameter of 0.2nm.

[0211] Effect Example 8

[0212] Measure the piezoelectric properties (electrical signals) of the PVDF composite ultrafiltration membranes prepared in Example 2 (GO-50nm) and Example 16 (GO-500nm) with different diameters of graphene oxide. The results are shown in Figure 11 .

[0213] From Figure 11It can be seen that, on the basis that other conditions are exactly the same, the piezoelectric signal of the PVDF composite ultrafiltration membrane prepared using graphene oxide with a diameter of 50 nm in water is 1 time higher than that of the composite PVDF ultrafiltration membrane prepared using graphene oxide with a diameter of 500 nm.

[0214] Effect Example 9

[0215] The piezoelectric properties (electric signals) of the PVDF composite ultrafiltration membranes prepared by using polarization electric fields with different electricities in Determination Example 2 (negative DC electric field polarization) and Example 17 (positive DC electric field polarization) were measured. The results are shown in Figure 12 .

[0216] From Figure 12 it can be seen that, on the basis that other conditions are exactly the same, the piezoelectric signal of the PVDF composite ultrafiltration membrane prepared by using negative DC electric field polarization in water is 1 time higher than that of the composite PVDF ultrafiltration membrane prepared by using positive DC electric field polarization.

[0217] Through comparison, it is illustrated that the blending of graphene oxide, in-situ electric field polarization, and hydrophobic modification play a synergistic role in enhancing the piezoelectric properties of the membrane to achieve the anti-pollution effect.

[0218] The above-described embodiments are only descriptions of the preferred modes of the present invention, and do not limit the scope of the present invention. Without departing from the design spirit of the present invention, various deformations and improvements made by those of ordinary skill in the art to the technical solutions of the present invention shall fall within the protection scope determined by the claims of the present invention.

Claims

1. A method for preparing a PVDF composite ultrafiltration membrane having underwater piezoelectric activity, characterized in that: The following steps are involved: The casting solution is prepared by using graphene oxide, organic solvent, porogen and PVDF as raw materials; The casting solution is coated on a flat plate, and then immersed in a pure water coagulation bath set in a negative electrode DC electric field for phase separation and synchronous polarization to obtain a PVDF porous membrane; Performing hydrophobic modification on the PVDF porous membrane to obtain the PVDF composite ultrafiltration membrane; The casting solution comprises the following raw materials in percentage by weight: 0.1-1.5% graphene oxide, 17-24% PVDF, 0.5-4% porogen, and the remainder organic solvent; The intensity of the electric field is 200 to 800 V / mm, and the time of phase separation and synchronous polarization is 5 to 30 minutes; The hydrophobic modification method comprises the following steps: uniformly coating the hydrophobic modification solution on the surface of the PVDF porous membrane and maintaining a pressure of 5 to 80 kPa during the coating process; the ratio of the amount of the hydrophobic modification solution to the area of ​​the PVDF porous membrane is 1 to 7 mL: 1 cm 2 ; The hydrophobic modification solution is composed of the following raw materials in percentage by mass: 0.5-5% long-chain silane and 95-99.5% n-hexane; the long-chain silane includes triethoxy (1H, 1H, 2H, 2H-nonafluorohexyl) silane, trichloro (1H, 1H, 2H, 2H-tridecafluorooctyl) silane or 1H, 1H, 2H, 2H-perfluorodecyltriethoxysilane.

2. The preparation method according to claim 1, characterized in that: The diameter of the graphene oxide is 0.5-100 nm.

3. The preparation method according to claim 1, characterized in that: The organic solvent includes N-methylpyrrolidone, N,N-dimethylformamide, dimethyl sulfoxide or dimethylacetamide; and / or the porogen includes polyvinylpyrrolidone, polyethylene glycol or lithium chloride.

4. The preparation method according to claim 1, characterized in that: The graphene oxide, organic solvent, porogen and PVDF are heated and stirred to prepare the casting solution; the heating and stirring temperature is 45 to 75° C.; The thickness of the casting solution on the flat plate is 150-350 μm.

5. A PVDF composite ultrafiltration membrane prepared by the preparation method according to any one of claims 1 to 4.

6. Use of the PVDF composite ultrafiltration membrane according to claim 5 in water purification.

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