A piezoelectric nanofiltration membrane with electric anti-scaling function and its preparation method and application

Abstract

The present invention discloses a piezoelectric nanofiltration membrane with electric anti-scaling function and its preparation method and application, which belongs to the field of membrane water treatment technology. The present invention dopes two-dimensional conductive nanosheets into the traditional PVDF piezoelectric membrane and performs phase separation in an alternating electric field, thereby preparing a piezoelectric base membrane with a high β-PVDF content and a crystal orientation structure, and then performs interfacial polymerization to form a nanofiltration membrane with piezoelectric activity. The present invention increases the β-phase PVDF content in the base membrane by adding two-dimensional conductive nanosheets to the base membrane, thereby enhancing the piezoelectric properties of the base membrane itself. On the other hand, by synchronously applying an alternating electric field during the film making process, the two-dimensional conductive nanosheets are induced to be oriented and form conductive synapses on the surface of the base membrane, and then after interfacial polymerization, the conductive synapses can penetrate into the polyamide layer and form a conductive network, and finally the base membrane piezoelectric signal is transmitted to the surface of the nanofiltration membrane, thereby giving the nanofiltration membrane piezoelectric properties and electric anti-scaling function.

Description

Technical Field

[0001] The invention belongs to the technical field of membrane water treatment, and in particular relates to a piezoelectric nanofiltration membrane with electric anti-scaling function, and a preparation method and application thereof. Background Art

[0002] In recent years, the global demand for water has increased significantly. Nanofiltration technology has been widely used in deep treatment of drinking water, purification of brackish water, reuse of industrial wastewater and desalination of seawater due to its excellent removal performance of inorganic ions. However, the inorganic scaling problem faced by nanofiltration membranes in actual applications has restricted the development of nanofiltration membranes. How to effectively alleviate inorganic scaling in the nanofiltration process has become a key issue in the development of nanofiltration membranes. Among them, inorganic scaling in nanofiltration membranes mainly includes inorganic salts such as calcium carbonate (CaCO3), calcium sulfate (CaSO4), and barium sulfate (BaSO4). These scaling deposits on the membrane surface or in the membrane pores will form a dense pollution layer, reduce the mass transfer efficiency, and cause the water flux to continue to decrease with the increase of operating time. The traditional methods for removing inorganic scaling from nanofiltration membranes mainly include physical cleaning (such as backwashing and ultrasonic cleaning) and chemical cleaning (cleaning with acid, alkali or chelating agent solution). However, these methods have obvious disadvantages. Physical cleaning can easily damage the membrane structure and reduce the service life of the membrane, while chemical cleaning can easily lead to chemical agent residues, which is not friendly to the environment. In addition, frequent cleaning operations increase operating costs and system complexity, making it difficult to completely solve the scaling problem, leading to long-term performance degradation of the membrane.

[0003] In response to the scaling problem of nanofiltration membranes, electric field-assisted membrane fouling control technology has shown unique advantages. However, traditional electric-assisted membrane fouling technology usually relies on external power supply, which increases energy consumption and makes it difficult to meet the development requirements of green and low-carbon membrane separation technology. In response to this problem, new membrane fouling control technologies based on the intrinsic piezoelectric properties of membrane materials have gradually become viable alternatives. Polyvinylidene fluoride is not only one of the most widely used membrane-making polymers, but also a typical organic piezoelectric material (β-phase PVDF). Unlike traditional conductive membranes or electric field-assisted membrane fouling control technologies, PVDF piezoelectric membranes can directly convert redundant mechanical energy in the pressure-driven membrane separation process into membrane surface potential energy through their inherent electromechanical coupling characteristics (i.e., piezoelectric characteristics), thereby slowing down the development of membrane fouling through a series of electrochemical actions. Therefore, new piezoelectric nanofiltration membranes based on the piezoelectric properties of PVDF-based membranes show great potential in anti-scaling.

[0004] However, using the piezoelectric properties of PVDF for anti-fouling of nanofiltration membranes still faces certain challenges. Since the preparation of nanofiltration membranes requires interfacial polymerization on the surface of the PVDF base membrane, and the polyamide functional layer formed by interfacial polymerization is not conductive, this limits the transmission of the base membrane piezoelectric signal to the surface of the nanofiltration membrane, ultimately making it difficult for the nanofiltration membrane to effectively express the piezoelectric properties and unable to give the nanofiltration membrane the ideal electric anti-fouling function. Summary of the invention

[0005] In order to solve the above technical problems, the present invention proposes a piezoelectric nanofiltration membrane with electric anti-scaling function and a preparation method and application thereof.

[0006] To achieve the above object, the present invention provides the following technical solutions:

[0007] The present invention provides a method for preparing a piezoelectric nanofiltration membrane with an electric anti-scaling function, comprising the following steps: subjecting a polymer casting liquid doped with two-dimensional conductive nanosheets to phase separation under an alternating electric field to prepare a piezoelectric base membrane with conductive synapses on the surface; then subjecting the piezoelectric base membrane to interfacial polymerization to prepare a polyamide layer, and allowing the conductive synapses to penetrate deeply into the polyamide layer and form a conductive network, thereby obtaining the piezoelectric nanofiltration membrane with an electric anti-scaling function.

[0008] Preferably, the diameter of the two-dimensional conductive nanosheet is 50-250 nm, and the aspect ratio is (500-2000):1; the two-dimensional conductive nanosheet includes nanosilver and / or nanozinc.

[0009] Preferably, the method for preparing the piezoelectric base film having conductive synapses on the surface comprises the following steps:

[0010] (1) dispersing a two-dimensional conductive nanosheet, a porogen and a polymer in an organic solvent, heating, stirring and standing to degas, to obtain a casting solution doped with the two-dimensional conductive nanosheet;

[0011] (2) coating the casting liquid doped with two-dimensional conductive nanosheets obtained in step (1) on a substrate, and then immersing the substrate in a coagulation bath set in an alternating electric field for phase separation until the casting liquid is completely gelled, thereby obtaining a piezoelectric base film with conductive synapses on the surface.

[0012] Preferably, in step (1), the amounts of the porogen, polymer and organic solvent are 4wt%, 18wt% and 78wt% respectively; the amount of the two-dimensional conductive nanosheets is 0.3-2wt% of the total mass of the porogen, polymer and organic solvent.

[0013] Preferably, in step (1), the porogen includes polyvinyl pyrrolidone and / or polyethylene glycol; the polymer includes polyvinylidene fluoride; and the organic solvent includes one of N-methylpyrrolidone, N,N-dimethylformamide, dimethyl sulfoxide, and dimethylacetamide.

[0014] Preferably, in step (1), the temperature of the heating and stirring is 40 to 70° C., and the speed of the heating and stirring is 200 to 400 rpm.

[0015] Preferably, in step (2), the intensity of the alternating electric field is 200-800 V / mm, and the frequency of the alternating electric field is 10-100 Hz; and the coagulation bath is pure water.

[0016] Preferably, the aqueous phase of the interfacial polymerization is a piperazine aqueous solution with a concentration of 1.5 wt%, and the organic phase is a trimesoyl chloride solution with a concentration of 1 wt%; the trimesoyl chloride solution is prepared by dissolving trimesoyl chloride in an organic solvent.

[0017] The present invention provides a piezoelectric nanofiltration membrane with electric anti-scaling function prepared by the preparation method described in the above technical scheme.

[0018] The present invention also provides the application of the piezoelectric nanofiltration membrane with electric anti-scaling function described in the above technical solution in membrane water treatment.

[0019] Compared with the prior art, the present invention has the following advantages and technical effects:

[0020] The present invention dopes two-dimensional conductive nanosheets in a conventional PVDF piezoelectric film and separates the two-dimensional conductive nanosheets in an alternating electric field, thereby preparing a piezoelectric base film with a high β-PVDF content and a crystal orientation structure, and then subjecting the base film to interfacial polymerization to form a nanofiltration membrane with piezoelectric activity. The present invention adds two-dimensional conductive nanosheets to the base film, thereby increasing the β-phase PVDF content in the base film, thereby enhancing the piezoelectric properties of the base film itself. On the other hand, by synchronously applying an alternating electric field during the film-making process, the two-dimensional conductive nanosheets are induced to be oriented and form conductive synapses on the surface of the base film, and then after interfacial polymerization, the conductive synapses can penetrate into the polyamide layer and form a conductive network, and finally conduct the base film piezoelectric signal to the surface of the nanofiltration membrane, thereby giving the nanofiltration membrane piezoelectric properties and electric anti-scaling function. In the process of pressure-driven membrane separation, the piezoelectric base film can respond to the mechanical energy of the system to generate a piezoelectric potential, and then conduct the piezoelectric signal to the surface of the polyamide layer through its conductive synapses, thereby enhancing the anti-scaling ability of the piezoelectric nanofiltration membrane.

[0021] The piezoelectric nanofiltration membrane with electric anti-scaling function provided by the present invention has significantly improved ability to inhibit calcium sulfate (CaSO4) scaling compared to traditional nanofiltration membranes. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] The drawings constituting a part of the present application are used to provide a further understanding of the present application. The illustrative embodiments and descriptions of the present application are used to explain the present application and do not constitute an improper limitation on the present application. In the drawings:

[0023] Figure 1 A schematic flow chart of a method for preparing a piezoelectric nanofiltration membrane with electric anti-scaling function provided by the present invention;

[0024] Figure 2 It is a schematic diagram of the in-situ piezoelectric signal testing device of the present invention;

[0025] Figure 3 XRD patterns of the piezoelectric nanofiltration membranes prepared in Examples 1-5 and Comparative Example 1;

[0026] Figure 4 It is a piezoelectric signal output diagram of the piezoelectric nanofiltration membrane prepared in Examples 1-5 and Comparative Example 1;

[0027] Figure 5 It is a piezoelectric signal output diagram of the piezoelectric nanofiltration membrane prepared in Examples 3, 6-7 and Comparative Example 2;

[0028] Figure 6 It is a piezoelectric signal output diagram of the piezoelectric nanofiltration membrane prepared in Example 3 and Comparative Examples 3-4;

[0029] Figure 7 It is a piezoelectric signal output diagram of the piezoelectric nanofiltration membrane prepared in Example 3 and Comparative Examples 5-6;

[0030] Figure 8 It is a piezoelectric signal output diagram of the piezoelectric nanofiltration membrane prepared in Examples 3, 9-11 and Comparative Examples 7-8;

[0031] Fig. 9 The membrane flux recovery rate diagram of the piezoelectric nanofiltration membranes prepared in Examples 1-11 and Comparative Examples 1-8. DETAILED DESCRIPTION

[0032] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0033] In order to make the above-mentioned objects, features and advantages of the present invention more obvious and easy to understand, the present invention is further described in detail below with reference to the accompanying drawings and specific embodiments.

[0034] An embodiment of the present invention provides a method for preparing a piezoelectric nanofiltration membrane with an electric anti-scaling function, comprising the following steps: subjecting a polymer casting liquid doped with two-dimensional conductive nanosheets to phase separation under an alternating electric field to prepare a piezoelectric base membrane with conductive synapses on the surface; then subjecting the piezoelectric base membrane to interfacial polymerization to prepare a polyamide layer, and allowing the conductive synapses to penetrate into the interior of the polyamide layer and form a conductive network, thereby obtaining the piezoelectric nanofiltration membrane with an electric anti-scaling function.

[0035] The present invention dopes two-dimensional conductive nanosheets in a conventional PVDF piezoelectric film and separates the two-dimensional conductive nanosheets in an alternating electric field, thereby preparing a piezoelectric base film with a high β-PVDF content and a crystal orientation structure, and then subjecting the base film to interfacial polymerization to form a nanofiltration membrane with piezoelectric activity. The present invention adds two-dimensional conductive nanosheets to the base film, thereby increasing the β-phase PVDF content in the base film, thereby enhancing the piezoelectric properties of the base film itself. On the other hand, by synchronously applying an alternating electric field during the film-making process, the two-dimensional conductive nanosheets are induced to be oriented and form conductive synapses on the surface of the base film, and then after interfacial polymerization, the conductive synapses can penetrate into the polyamide layer and form a conductive network, and finally conduct the base film piezoelectric signal to the surface of the nanofiltration membrane, thereby giving the nanofiltration membrane piezoelectric properties and electric anti-scaling function. In the process of pressure-driven membrane separation, the piezoelectric base film can respond to the mechanical energy of the system to generate a piezoelectric potential, and then conduct the piezoelectric signal to the surface of the polyamide layer through its conductive synapses, thereby enhancing the anti-scaling ability of the piezoelectric nanofiltration membrane.

[0036] In a preferred embodiment, the diameter of the two-dimensional conductive nanosheet is 50-250nm, more preferably 50-100nm; the aspect ratio of the two-dimensional conductive nanosheet is (500-2000):1, more preferably (600-1000):1; the two-dimensional conductive nanosheet includes nanosilver and / or nanozinc. The present invention applies an alternating electric field during the film formation process and controls the diameter and aspect ratio of the two-dimensional conductive nanosheet so that the two-dimensional conductive nanosheet can form conductive synapses on the surface of the base film. The present invention controls the diameter of the two-dimensional conductive nanosheet within the above range to provide more conductive paths. Under the action of the electric field, the migration ability of the carriers is enhanced, thereby improving the overall conductivity; for nanosheets with smaller diameters, at the microscopic scale, the limited volume may limit the movement of the carriers, resulting in a decrease in conductivity. The present invention controls the aspect ratio (i.e., the long and thin shape) of the two-dimensional conductive nanosheets within the above range, so that the nanosheets can form a more regular network structure when arranged. The regular network structure can not only provide a more continuous current conduction path, but also reduce the obstacles in charge transmission, thereby improving conductivity. In addition, the increase in the diameter of the two-dimensional conductive nanosheets can generally improve the conductivity, but too large an aspect ratio may lead to increased brittleness; while nanosheets with high aspect ratios help to form a more regular network structure and promote effective current transmission, but too high an aspect ratio may affect the stability of the structure. Therefore, the use of two-dimensional conductive nanosheets with diameters and aspect ratios within the above ranges can form the most stable conductive channel.

[0037] In a preferred embodiment, the method for preparing the piezoelectric base film having conductive synapses on the surface comprises the following steps:

[0038] (1) dispersing a two-dimensional conductive nanosheet, a porogen and a polymer in an organic solvent, heating, stirring and standing to degas, to obtain a casting solution doped with the two-dimensional conductive nanosheet;

[0039] (2) coating the casting liquid doped with two-dimensional conductive nanosheets obtained in step (1) on a substrate, and then immersing the substrate in a coagulation bath set in an alternating electric field for phase separation until the casting liquid is completely gelled, thereby obtaining a piezoelectric base film with conductive synapses on the surface.

[0040] In a preferred embodiment, in step (1), the amounts of the porogen, polymer and organic solvent are 4wt%, 18wt% and 78wt% respectively; the amount of the two-dimensional conductive nanosheet is 0.3-2wt% of the total mass of the porogen, polymer and organic solvent, and more preferably 0.3-1wt%. The amount of the two-dimensional conductive nanosheet in the present invention will affect the piezoelectric properties of the piezoelectric nanofiltration membrane. As the amount of the two-dimensional conductive nanosheet increases, the electrical signal will first increase and then decrease. When the amount of the two-dimensional conductive nanosheet is too much, the piezoelectric properties of the piezoelectric nanofiltration membrane will be adversely affected.

[0041] In a preferred embodiment, in step (1), the porogen includes polyvinyl pyrrolidone (PVP) and / or polyethylene glycol (PEG); the polymer includes polyvinylidene fluoride (PVDF); and the organic solvent includes one of N-methylpyrrolidone (NMP), N,N-dimethylformamide (DMF), dimethyl sulfoxide (DMSO), and dimethylacetamide (DMAC).

[0042] In a preferred embodiment, in step (1), the temperature of the heating and stirring is 40-70° C., and the speed of the heating and stirring is 200-400 rpm. The present invention forms a homogeneous casting solution by heating and stirring.

[0043] In a preferred embodiment, in step (1), the standing degassing time is 24 hours.

[0044] In a preferred embodiment, in step (2), the strength of the alternating electric field is 200 to 800 V / mm, more preferably 400 to 600 V / mm. The present invention uses a strong alternating electric field for phase separation, which can promote the effective arrangement of electric dipoles inside the material, make the arrangement more orderly, enhance the polarization effect of the membrane material, and improve its piezoelectric effect.

[0045] In a preferred embodiment, in step (2), the frequency of the alternating electric field is 10 to 100 Hz, more preferably 50 to 100 Hz. The frequency of the alternating electric field in the present invention affects the piezoelectric properties of the piezoelectric nanofiltration membrane. As the frequency of the alternating electric field increases, the electrical signal tends to increase. However, when the frequency of the alternating electric field is too high, the membrane material may not be able to respond in time and follow the change of the electric field, resulting in a lag in the rearrangement of the dipoles, thereby disrupting the directional arrangement of the dipoles and reducing the piezoelectric performance. When the frequency is close to infinity, it is approximately considered a direct current electric field, and no conductive synapses will be formed.

[0046] In a preferred embodiment, in step (2), the coagulation bath is pure water.

[0047] In a preferred embodiment, in step (2), the phase separation time is 20 minutes. In the present invention, too short a phase separation time will reduce the piezoelectric performance of the piezoelectric nanofiltration membrane.

[0048] In a preferred embodiment, in step (2), the substrate is a glass plate; after coating the casting liquid doped with two-dimensional conductive nanosheets on the substrate, the method further includes using a wet film preparation device to form the casting liquid into a flat plate with a thickness of 250 μm.

[0049] In a preferred embodiment, the aqueous phase of the interfacial polymerization is a piperazine (PIP) aqueous solution with a concentration of 1.5wt%, and the organic phase is a trimesoyl chloride solution with a concentration of 1wt%; the trimesoyl chloride solution is prepared by dissolving trimesoyl chloride (TMC) in an organic solvent, and the organic solvent is n-hexane. The present invention uses the piperazine aqueous solution as the aqueous phase and the trimesoyl chloride solution as the organic phase to form a polyamide layer on the surface of the piezoelectric base film through interfacial polymerization.

[0050] The present invention provides a piezoelectric nanofiltration membrane with electric anti-scaling function prepared by the preparation method described in the above technical scheme.

[0051] The present invention also provides the application of the piezoelectric nanofiltration membrane with electric anti-scaling function described in the above technical solution in membrane water treatment.

[0052] Unless otherwise specified, the raw materials in the examples of the present invention were purchased from commercial sources.

[0053] Example 1

[0054] A method for preparing a piezoelectric nanofiltration membrane with electric anti-scaling function, the specific steps are as follows, and the process flow is shown in Figure 1 :

[0055] (1) An organic solvent NMP, a polymer PVDF and a porogen PVP are mixed in a ratio of 78 wt%:18 wt%:4 wt%, and then 0.3 wt% of the total weight of NMP, PVDF and PVP is added into the mixture, and then the mixture is heated in a water bath at 50°C and mechanically stirred at 300 rpm for 10 h, and then allowed to stand for degassing for 24 h to obtain a casting solution doped with nanosilver flakes; wherein the diameter of the nanosilver flakes is 100 nm and the aspect ratio is 600:1.

[0056] (2) coating the casting liquid doped with nanosilver flakes obtained in step (1) on a glass plate, and then forming it into a flat plate with a thickness of 250 μm using a wet film preparation device, and then immersing the glass plate with the casting liquid in a coagulation bath set in an alternating electric field for phase separation, wherein the intensity of the alternating electric field is 400 V / mm, the frequency is 50 Hz, and the phase separation time is 20 min, until the casting liquid is completely gelled, thereby obtaining a piezoelectric base film with conductive synapses on the surface.

[0057] (3) Using a clamp, the conductive synaptic surface of the piezoelectric base film obtained in step (2) is flattened and fixed upward, and a 1.5 wt % piperazine aqueous solution is evenly coated on the surface of the piezoelectric base film, fully contacted for 20 minutes, and then the excess piperazine aqueous solution is removed with a roller, and then a 1 wt % benzyl chloride n-hexane solution is evenly poured on the membrane surface, fully contacted for 1 minute, and then the excess solution on the membrane surface is washed off with n-hexane, and the membrane is placed in an oven for drying to obtain a piezoelectric nanofiltration membrane with electric anti-scaling function, which is recorded as PI-PVDF@Ag 0.3 -NFM.

[0058] Example 2

[0059] A method for preparing a piezoelectric nanofiltration membrane with electric anti-scaling function, the specific steps are as follows, and the process flow is shown in Figure 1 :

[0060] (1) An organic solvent NMP, a polymer PVDF and a porogen PVP are mixed in a ratio of 78 wt%:18 wt%:4 wt%, and then 0.5 wt% of the total weight of NMP, PVDF and PVP is added into the mixture, and then the mixture is heated in a water bath at 50°C and mechanically stirred at 300 rpm for 10 h, and then allowed to stand for degassing for 24 h to obtain a casting solution doped with nanosilver flakes; wherein the diameter of the nanosilver flakes is 100 nm and the aspect ratio is 600:1.

[0061] (2) coating the casting liquid doped with nanosilver flakes obtained in step (1) on a glass plate, and then forming it into a flat plate with a thickness of 250 μm using a wet film preparation device, and then immersing the glass plate with the casting liquid in a coagulation bath set in an alternating electric field for phase separation, wherein the intensity of the alternating electric field is 400 V / mm, the frequency is 50 Hz, and the phase separation time is 20 min, until the casting liquid is completely gelled, thereby obtaining a piezoelectric base film with conductive synapses on the surface.

[0062] (3) Using a clamp, the conductive synaptic surface of the piezoelectric base film obtained in step (2) is flattened and fixed upward, and a 1.5 wt % piperazine aqueous solution is evenly coated on the surface of the piezoelectric base film, fully contacted for 20 minutes, and then the excess piperazine aqueous solution is removed with a roller, and then a 1 wt % benzyl chloride n-hexane solution is evenly poured on the membrane surface, fully contacted for 1 minute, and then the excess solution on the membrane surface is washed off with n-hexane, and the membrane is placed in an oven for drying to obtain a piezoelectric nanofiltration membrane with electric anti-scaling function, which is recorded as PI-PVDF@Ag 0.5 -NFM.

[0063] Example 3

[0064] A method for preparing a piezoelectric nanofiltration membrane with electric anti-scaling function, the specific steps are as follows, and the process flow is shown in Figure 1 :

[0065] (1) An organic solvent NMP, a polymer PVDF and a porogen PVP are mixed in a ratio of 78 wt%:18 wt%:4 wt%, and then 1 wt% of the total weight of NMP, PVDF and PVP is added into the mixture, and then the mixture is heated in a water bath at 50°C and mechanically stirred at 300 rpm for 10 h, and then allowed to stand for degassing for 24 h to obtain a casting solution doped with nanosilver flakes; wherein the diameter of the nanosilver flakes is 100 nm and the aspect ratio is 600:1.

[0066] (2) coating the casting liquid doped with nanosilver flakes obtained in step (1) on a glass plate, and then forming it into a flat plate with a thickness of 250 μm using a wet film preparation device, and then immersing the glass plate with the casting liquid in a coagulation bath set in an alternating electric field for phase separation, wherein the intensity of the alternating electric field is 400 V / mm, the frequency is 50 Hz, and the phase separation time is 20 min, until the casting liquid is completely gelled, thereby obtaining a piezoelectric base film with conductive synapses on the surface.

[0067] (3) Using a clamp, the conductive synaptic surface of the piezoelectric base film obtained in step (2) is flattened and fixed upward, and a 1.5 wt % piperazine aqueous solution is evenly coated on the surface of the piezoelectric base film, fully contacted for 20 minutes, and then the excess piperazine aqueous solution is removed with a roller, and then a 1 wt % benzyl chloride n-hexane solution is evenly poured on the membrane surface, fully contacted for 1 minute, and then the excess solution on the membrane surface is washed off with n-hexane, and the membrane is placed in an oven for drying to obtain a piezoelectric nanofiltration membrane with electric anti-scaling function, which is recorded as PI-PVDF@Ag 1.0 -NFM.

[0068] Example 4

[0069] A method for preparing a piezoelectric nanofiltration membrane with electric anti-scaling function, the specific steps are as follows, and the process flow is shown in Figure 1 :

[0070] (1) An organic solvent NMP, a polymer PVDF and a porogen PVP are mixed in a ratio of 78 wt%:18 wt%:4 wt%, and then 1.5 wt% of the total weight of NMP, PVDF and PVP is added, and then heated in a water bath at 50° C. and mechanically stirred at 300 rpm for 10 h, and then allowed to stand for degassing for 24 h to obtain a casting solution doped with nanosilver flakes; wherein the diameter of the nanosilver flakes is 100 nm and the aspect ratio is 600:1.

[0071] (2) coating the casting liquid doped with nanosilver flakes obtained in step (1) on a glass plate, and then forming it into a flat plate with a thickness of 250 μm using a wet film preparation device, and then immersing the glass plate with the casting liquid in a coagulation bath set in an alternating electric field for phase separation, wherein the intensity of the alternating electric field is 400 V / mm, the frequency is 50 Hz, and the phase separation time is 20 min, until the casting liquid is completely gelled, thereby obtaining a piezoelectric base film with conductive synapses on the surface.

[0072] (3) Using a clamp, the conductive synaptic surface of the piezoelectric base film obtained in step (2) is flattened and fixed upward, and a 1.5 wt % piperazine aqueous solution is evenly coated on the surface of the piezoelectric base film, fully contacted for 20 minutes, and then the excess piperazine aqueous solution is removed with a roller, and then a 1 wt % benzyl chloride n-hexane solution is evenly poured on the membrane surface, fully contacted for 1 minute, and then the excess solution on the membrane surface is washed off with n-hexane, and the membrane is placed in an oven for drying to obtain a piezoelectric nanofiltration membrane with electric anti-scaling function, which is recorded as PI-PVDF@Ag 1.5 -NFM.

[0073] Example 5

[0074] A method for preparing a piezoelectric nanofiltration membrane with electric anti-scaling function, the specific steps are as follows, and the process flow is shown in Figure 1 :

[0075] (1) An organic solvent NMP, a polymer PVDF and a porogen PVP are mixed in a ratio of 78 wt%:18 wt%:4 wt%, and then 2 wt% of the total weight of NMP, PVDF and PVP is added, and then heated in a water bath at 50° C. and mechanically stirred at 300 rpm for 10 h, and then allowed to stand for degassing for 24 h to obtain a casting solution doped with nanosilver flakes; wherein the diameter of the nanosilver flakes is 100 nm and the aspect ratio is 600:1.

[0076] (2) coating the casting liquid doped with nanosilver flakes obtained in step (1) on a glass plate, and then forming it into a flat plate with a thickness of 250 μm using a wet film preparation device, and then immersing the glass plate with the casting liquid in a coagulation bath set in an alternating electric field for phase separation, wherein the intensity of the alternating electric field is 400 V / mm, the frequency is 50 Hz, and the phase separation time is 20 min, until the casting liquid is completely gelled, thereby obtaining a piezoelectric base film with conductive synapses on the surface.

[0077] (3) Using a clamp, the conductive synaptic surface of the piezoelectric base film obtained in step (2) is flattened and fixed upward, and a 1.5 wt % piperazine aqueous solution is evenly coated on the surface of the piezoelectric base film, fully contacted for 20 minutes, and then the excess piperazine aqueous solution is removed with a roller, and then a 1 wt % benzyl chloride n-hexane solution is evenly poured on the membrane surface, fully contacted for 1 minute, and then the excess solution on the membrane surface is washed off with n-hexane, and the membrane is placed in an oven for drying to obtain a piezoelectric nanofiltration membrane with electric anti-scaling function, which is recorded as PI-PVDF@Ag 2.0 -NFM.

[0078] Example 6

[0079] A method for preparing a piezoelectric nanofiltration membrane with electric anti-scaling function, the specific steps are as follows, and the process flow is shown in Figure 1 :

[0080] (1) An organic solvent NMP, a polymer PVDF and a porogen PVP are mixed in a ratio of 78 wt%:18 wt%:4 wt%, and then 1 wt% of the total weight of NMP, PVDF and PVP is added into the mixture, and then the mixture is heated in a water bath at 50°C and mechanically stirred at 300 rpm for 10 h, and then allowed to stand for degassing for 24 h to obtain a casting solution doped with nanosilver flakes; wherein the diameter of the nanosilver flakes is 100 nm and the aspect ratio is 600:1.

[0081] (2) coating the casting liquid doped with nanosilver flakes obtained in step (1) on a glass plate, and then forming it into a flat plate with a thickness of 250 μm using a wet film preparation device, and then immersing the glass plate with the casting liquid in a coagulation bath set in an alternating electric field for phase separation, wherein the intensity of the alternating electric field is 400 V / mm, the frequency is 10 Hz, and the phase separation time is 20 min, until the casting liquid is completely gelled, thereby obtaining a piezoelectric base film with conductive synapses on the surface.

[0082] (3) Using a splint, the conductive synaptic surface of the piezoelectric base membrane obtained in step (2) is flattened and fixed upward, and a 1.5 wt % piperazine aqueous solution is evenly coated on the surface of the piezoelectric base membrane, and fully contacted for 20 minutes. Then, the excess piperazine aqueous solution is removed with a roller, and then a 1 wt % benzyl chloride n-hexane solution is evenly poured on the membrane surface, and fully contacted for 1 minute. Then, the excess solution on the membrane surface is washed off with n-hexane, and the membrane is placed in an oven for drying to obtain a piezoelectric nanofiltration membrane with electric anti-scaling function.

[0083] Example 7

[0084] A method for preparing a piezoelectric nanofiltration membrane with electric anti-scaling function, the specific steps are as follows, and the process flow is shown in Figure 1 :

[0085] (1) An organic solvent NMP, a polymer PVDF and a porogen PVP are mixed in a ratio of 78 wt%:18 wt%:4 wt%, and then 1 wt% of the total weight of NMP, PVDF and PVP is added into the mixture, and then the mixture is heated in a water bath at 50°C and mechanically stirred at 300 rpm for 10 h, and then allowed to stand for degassing for 24 h to obtain a casting solution doped with nanosilver flakes; wherein the diameter of the nanosilver flakes is 100 nm and the aspect ratio is 600:1.

[0086] (2) coating the casting liquid doped with nanosilver flakes obtained in step (1) on a glass plate, and then forming it into a flat plate with a thickness of 250 μm using a wet film preparation device, and then immersing the glass plate with the casting liquid in a coagulation bath set in an alternating electric field for phase separation, wherein the intensity of the alternating electric field is 400 V / mm, the frequency is 100 Hz, and the phase separation time is 20 min, until the casting liquid is completely gelled, thereby obtaining a piezoelectric base film with conductive synapses on the surface.

[0087] (3) Using a splint, the conductive synaptic surface of the piezoelectric base membrane obtained in step (2) is flattened and fixed upward, and a 1.5 wt % piperazine aqueous solution is evenly coated on the surface of the piezoelectric base membrane, and fully contacted for 20 minutes. Then, the excess piperazine aqueous solution is removed with a roller, and then a 1 wt % benzyl chloride n-hexane solution is evenly poured on the membrane surface, and fully contacted for 1 minute. Then, the excess solution on the membrane surface is washed off with n-hexane, and the membrane is placed in an oven for drying to obtain a piezoelectric nanofiltration membrane with electric anti-scaling function.

[0088] Comparative Example 1

[0089] A method for preparing a piezoelectric nanofiltration membrane, the specific steps are as follows:

[0090] (1) The organic solvent NMP, the polymer PVDF and the porogen PVP were mixed in a ratio of 78 wt %: 18 wt %: 4 wt %, heated in a water bath at 50° C. and mechanically stirred at 300 rpm for 10 h, and then allowed to stand for degassing for 24 h to obtain a casting solution.

[0091] (2) The casting liquid obtained in step (1) is coated on a glass plate, and then made into a flat plate with a thickness of 250 μm using a wet film preparation device. The glass plate with the casting liquid is then immersed in a coagulation bath set in an alternating electric field for phase separation. The intensity of the alternating electric field is 400 V / mm, the frequency is 50 Hz, and the phase separation time is 20 min, until the casting liquid is completely gelled to obtain a piezoelectric base film.

[0092] (3) Using a splint, the piezoelectric base film obtained in step (2) is laid flat and fixed with the convex surface facing upward, and a 1.5 wt % piperazine aqueous solution is evenly coated on the surface of the piezoelectric base film, and fully contacted for 20 minutes. Then, the excess piperazine aqueous solution is removed with a roller, and then a 1 wt % benzyl chloride n-hexane solution is evenly poured on the surface of the film, and fully contacted for 1 minute. Then, the excess solution on the surface of the film is washed off with n-hexane, and the film is placed in an oven for drying to obtain a piezoelectric nanofiltration membrane, which is recorded as PI-PVDF@Ag0-NFM.

[0093] Comparative Example 2

[0094] A method for preparing a piezoelectric nanofiltration membrane, the specific steps are as follows:

[0095] (1) An organic solvent NMP, a polymer PVDF and a porogen PVP are mixed in a ratio of 78 wt%:18 wt%:4 wt%, and then 1 wt% of the total weight of NMP, PVDF and PVP is added into the mixture, and then the mixture is heated in a water bath at 50°C and mechanically stirred at 300 rpm for 10 h, and then allowed to stand for degassing for 24 h to obtain a casting solution doped with nanosilver flakes; wherein the diameter of the nanosilver flakes is 100 nm and the aspect ratio is 600:1.

[0096] (2) The casting liquid doped with nanosilver flakes obtained in step (1) is coated on a glass plate, and then formed into a flat plate with a thickness of 250 μm using a wet film preparation device. The glass plate with the casting liquid is then immersed in a pure water coagulation bath until the casting liquid is completely gelled to obtain a piezoelectric base film.

[0097] (3) Using a clamp, the convex surface of the piezoelectric base film obtained in step (2) is laid flat and fixed upward, and a 1.5 wt % piperazine aqueous solution is evenly coated on the surface of the piezoelectric base film, and fully contacted for 20 minutes. Then, the excess piperazine aqueous solution is removed with a roller, and then a 1 wt % benzyl chloride n-hexane solution is evenly poured on the surface of the film, and fully contacted for 1 minute. Then, the excess solution on the surface of the film is washed off with n-hexane, and the film is placed in an oven for drying to obtain a piezoelectric nanofiltration membrane.

[0098] The piezoelectric nanofiltration membranes prepared in Examples 1-5 and Comparative Example 1 were subjected to XRD tests. The test results are shown in Figure 3 .Depend on Figure 3 It can be seen that with the increase of the content of nanosilver flakes in the casting solution, the content of β-PVDF in the piezoelectric nanofiltration membrane increases accordingly. When the content of nanosilver flakes exceeds a certain value, the content of β-PVDF decreases accordingly.

[0099] Under room temperature, the piezoelectric nanofiltration membranes prepared in Examples 1-5 and Comparative Example 1 were subjected to water electrical signal testing using a platinum-titanium dual-electrode system under the action of a diaphragm pump, and the test was performed after the signal was stable. The schematic diagram of the device used in the test process is shown in Figure 2, test results see Figure 4 .Depend on Figure 4 It can be seen that the content of nanosilver flakes in the casting solution will affect the piezoelectric properties of the piezoelectric nanofiltration membrane. Comparing Examples 1-5 and Comparative Example 1, in the presence of alternating electric field polarization, as the content of nanosilver flakes increases, the measured electrical signal tends to first increase and then decrease. When the content of nanosilver flakes exceeds a certain value, it will have an adverse effect on the piezoelectric signal.

[0100] Under room temperature, the piezoelectric nanofiltration membranes prepared in Examples 3, 6-7 and Comparative Example 2 were subjected to water electrical signal testing using a platinum-titanium dual-electrode system under the action of a diaphragm pump, and the test was performed after the signal was stable. The schematic diagram of the device used in the test process is shown in Figure 2 , test results see Figure 5 .Depend on Figure 5 It can be seen that when 1wt% of nanosilver flakes are doped, whether electric field polarization is performed and the frequency of the alternating electric field will also affect the piezoelectric properties of the piezoelectric nanofiltration membrane. Comparison of Examples 3, 6-7 and Comparative Example 2 shows that the presence or absence of electric field polarization and the frequency of the alternating electric field further affect the piezoelectric signal output of the piezoelectric nanofiltration membrane by affecting the formation of membrane conductive synapses.

[0101] Example 8

[0102] The difference from Example 3 is that the nano silver sheet in step (1) is replaced by a nano zinc sheet, and the remaining steps are the same as Example 3.

[0103] Comparative Example 3

[0104] The difference from Example 3 is that in step (1), the diameter of the nanosilver flakes is 300 nm, and the remaining steps are the same as Example 3.

[0105] Comparative Example 4

[0106] The difference from Example 3 is that in step (1), the diameter of the nanosilver flakes is 20 nm, and the remaining steps are the same as Example 3.

[0107] Under room temperature, the piezoelectric nanofiltration membrane prepared in Example 3 and Comparative Examples 3-4 was used to test the electrical signal in water using a platinum-titanium dual-electrode system under the action of a diaphragm pump. The test was performed after the signal was stable. The schematic diagram of the device used in the test process is shown in Figure 2 , test results see Figure 6 .Depend on Figure 6 It can be seen that the diameter of the nanosilver flakes will also affect the piezoelectric signal output of the piezoelectric nanofiltration membrane.

[0108] Comparative Example 5

[0109] The difference from Example 3 is that in step (1), the aspect ratio of the nanosilver flakes is 300:1, and the remaining steps are the same as Example 3.

[0110] Comparative Example 6

[0111] The difference from Example 3 is that in step (1), the aspect ratio of the nanosilver flakes is 3000:1, and the remaining steps are the same as Example 3.

[0112] Under room temperature, the piezoelectric nanofiltration membrane prepared in Example 3 and Comparative Examples 5-6 was used to test the electrical signal in water using a platinum-titanium dual-electrode system under the action of a diaphragm pump. The test was performed after the signal was stable. The schematic diagram of the device used in the test process is shown in Figure 2 , test results see Figure 7 .Depend on Figure 7 It can be seen that the aspect ratio of the nanosilver flakes will also affect the piezoelectric signal output of the piezoelectric nanofiltration membrane.

[0113] The piezoelectric signal results of the piezoelectric nanofiltration membranes prepared in Example 8 and Comparative Examples 3-6 are shown in Table 1.

[0114] Table 1 Piezoelectric signals of piezoelectric nanofiltration membranes prepared in Example 8 and Comparative Examples 3-6

[0115] Example 8 Comparative Example 3 Comparative Example 4 Comparative Example 5 Comparative Example 6 Piezoelectric signal / mV 900 500 300 400 350

[0116] It can be seen from Table 1 that the piezoelectric signal of the piezoelectric nanofiltration membrane prepared in Example 8 of the present invention is 900 mV, while the piezoelectric signals of Comparative Examples 3-6 are significantly reduced after changing the diameter or aspect ratio of the nanosilver flakes.

[0117] Example 9

[0118] The difference from Example 3 is that in step (2), the intensity of the alternating electric field is 200 V / mm, and the remaining steps are the same as Example 3.

[0119] Example 10

[0120] The difference from Example 3 is that in step (2), the intensity of the alternating electric field is 600 V / mm, and the remaining steps are the same as Example 3.

[0121] Embodiment 11

[0122] The difference from Example 3 is that in step (2), the intensity of the alternating electric field is 800 V / mm, and the remaining steps are the same as Example 3.

[0123] Comparative Example 7

[0124] The difference from Example 3 is that in step (2), the intensity of the alternating electric field is 100 V / mm, and the remaining steps are the same as Example 3.

[0125] Comparative Example 8

[0126] The difference from Example 3 is that in step (2), the intensity of the alternating electric field is 900 V / mm, and the remaining steps are the same as Example 3.

[0127] Under room temperature, the piezoelectric nanofiltration membranes prepared in Examples 3, 9-11 and Comparative Examples 7-8 were tested for electrical signals in water using a platinum-titanium dual-electrode system under the action of a diaphragm pump. The test was performed after the signal was stable. The schematic diagram of the device used in the test process is shown in Figure 2 , test results see Figure 8 .Depend on Figure 8 It can be seen that the intensity of the applied alternating electric field will affect the piezoelectric signal output of the piezoelectric nanofiltration membrane.

[0128] The piezoelectric signal results of the piezoelectric nanofiltration membranes prepared in Example 3 and Comparative Examples 7-8 are shown in Table 2.

[0129] Table 2 Piezoelectric signals of piezoelectric nanofiltration membranes prepared in Example 3 and Comparative Examples 7-8

[0130] Example 3 Comparative Example 7 Comparative Example 8 Piezoelectric signal / mV 1000 150 400

[0131] It can be seen from Table 2 that the piezoelectric signal of the piezoelectric nanofiltration membrane prepared in Example 3 of the present invention is 1000 mV, while the piezoelectric signal of Comparative Examples 7-8 is significantly reduced after changing the intensity of the applied alternating electric field.

[0132] Performance Test:

[0133] (1) Membrane flux

[0134] The flux experiment was carried out using a cross-flow filtration device. The effective filtration area of ​​the nanofiltration membrane module was 7 cm 2 , and connected to a 5.0L water storage tank, cross-flow filtration was performed at a pressure of 0.48MPa, and the permeate was collected and weighed using Ohaus Adventurer ProBalanceAV8101, and the relevant data were recorded using Collect6.1 software. In the piezoelectric nanofiltration membrane flux evaluation experiment, the piezoelectric nanofiltration membrane pure water flux (J0(L / m 2 h)) The calculation method is shown in formula (1), where V is the permeate volume (L), A is the effective filtration area (m 2 ), Δt is the filtration time (h). The pure water flux of the piezoelectric nanofiltration membrane of Examples 1-11 and Comparative Examples 1-8 is shown in Table 3-4.

[0135]

[0136] Table 3 Pure water flux of piezoelectric nanofiltration membrane prepared in Examples 1-11

[0137]

[0138] Table 4 Pure water flux of piezoelectric nanofiltration membrane prepared in Comparative Examples 1-8

[0139]

[0140] It can be seen from Table 3-4 that the pure water flux of the piezoelectric nanofiltration membrane prepared in Examples 1-11 of the present invention can reach 50-60 L / m 2 Compared with Example 3, the pure water flux of the piezoelectric nanofiltration membrane prepared in Comparative Example 1 was reduced by 2 L / m 2 h, the pure water flux of the piezoelectric nanofiltration membrane prepared in Comparative Example 2 decreased by 10L / m 2 h, the pure water flux of the piezoelectric nanofiltration membrane prepared in Comparative Example 3 decreased by 15L / m 2 h, the pure water flux of the piezoelectric nanofiltration membrane prepared in Comparative Example 4 decreased by 5L / m 2 h, the pure water flux of the piezoelectric nanofiltration membrane prepared in Comparative Example 5 decreased by 6L / m 2 h, the pure water flux of the piezoelectric nanofiltration membrane prepared in Comparative Example 6 decreased by 10 L / m 2 h, the pure water flux of the piezoelectric nanofiltration membrane prepared in Comparative Example 7 decreased by 5L / m 2 h, the pure water flux of the piezoelectric nanofiltration membrane prepared in Comparative Example 8 decreased by 3L / m 2 h. This shows that changing the diameter and aspect ratio of the nanosheets also has a certain effect on the flux of the piezoelectric nanofiltration membrane.

[0141] (2) Anti-scaling performance

[0142] The anti-pollution performance of the piezoelectric nanofiltration membrane was evaluated by cross-flow filtration experiment. The pollutant used was 20 mM / L calcium sulfate solution, the filtration pressure was 0.48 MPa, the continuous filtration time was 8 h, and the flux (J) was measured after the filtration was completed. F ), then use deionized water to physically flush the contaminated membrane surface for 5 minutes, and then use deionized water to measure the nanofiltration membrane flux (Jc) at this time, and calculate the final membrane flux recovery rate (η), that is, the membrane anti-pollution performance. The calculation method of the membrane flux recovery rate is shown in formula (2), where J0 is the pure water flux. The anti-pollution performance of the piezoelectric nanofiltration membrane of Examples 1-11 and Comparative Examples 1-8, that is, the flux recovery rate, is shown in Fig. 9 .

[0143]

[0144] Fig. 9 The anti-pollution performance of the piezoelectric nanofiltration membranes of Examples 1-11 and Comparative Examples 1-8. Fig. 9It can be seen that compared with Example 3, Comparative Example 1 did not add nanosilver flakes, and the flux recovery rate of the membrane decreased by nearly 45%; Comparative Example 2 did not apply an alternating electric field, and the flux recovery rate of the membrane decreased by nearly 52%; Comparative Examples 3-4 changed the diameter of the nanosilver flakes, and the flux recovery rates of the membranes decreased by nearly 27% and 40%, respectively; Comparative Examples 5-6 changed the aspect ratio of the nanosilver flakes, and the flux recovery rates of the membranes decreased by nearly 35% and 32%, respectively; Comparative Examples 7-8 changed the intensity of the alternating electric field, and the flux recovery rates of the membranes decreased by nearly 52% and 38%, respectively.

[0145] The above are only preferred specific implementations of the present application, but the protection scope of the present application is not limited thereto. Any changes or substitutions that can be easily thought of by a person skilled in the art within the technical scope disclosed in the present application should be included in the protection scope of the present application. Therefore, the protection scope of the present application should be based on the protection scope of the claims.

Claims

1. A method for preparing a piezoelectric nanofiltration membrane with electric anti-scaling function, characterized in that: The following steps are involved: The polymer casting liquid doped with two-dimensional conductive nanosheets is phase separated under an alternating electric field to prepare a piezoelectric base film with conductive synapses on the surface; the piezoelectric base film is then subjected to interfacial polymerization to prepare a polyamide layer, and the conductive synapses are allowed to penetrate into the polyamide layer and form a conductive network, thereby obtaining the piezoelectric nanofiltration membrane with electric anti-scaling function; the polymer includes polyvinylidene fluoride.

2. The preparation method according to claim 1, characterized in that: The diameter of the two-dimensional conductive nanosheet is 50-250 nm, and the aspect ratio is (500-2000):1; the two-dimensional conductive nanosheet comprises nano-silver and / or nano-zinc.

3. The preparation method according to claim 1, characterized in that: The method for preparing the piezoelectric base film having conductive synapses on the surface comprises the following steps: (1) dispersing a two-dimensional conductive nanosheet, a porogen and a polymer in an organic solvent, heating, stirring and standing to degas, to obtain a casting solution doped with the two-dimensional conductive nanosheet; (2) coating the casting liquid doped with two-dimensional conductive nanosheets obtained in step (1) on a substrate, and then immersing the substrate in a coagulation bath set in an alternating electric field for phase separation until the casting liquid is completely gelled, thereby obtaining a piezoelectric base film with conductive synapses on the surface.

4. The preparation method according to claim 3, characterized in that: In step (1), the amounts of the porogen, polymer and organic solvent are 4wt%, 18wt% and 78wt% respectively; the amount of the two-dimensional conductive nanosheet is 0.3-2wt% of the total mass of the porogen, polymer and organic solvent.

5. The preparation method according to claim 3 or 4, characterized in that: In step (1), the porogen includes polyvinyl pyrrolidone and / or polyethylene glycol; the polymer includes polyvinylidene fluoride; and the organic solvent includes one of N-methylpyrrolidone, N,N-dimethylformamide, dimethyl sulfoxide, and dimethylacetamide.

6. The preparation method according to claim 3, characterized in that: In step (1), the temperature of the heating and stirring is 40 to 70° C., and the speed of the heating and stirring is 200 to 400 rpm.

7. The preparation method according to claim 3, characterized in that: In step (2), the intensity of the alternating electric field is 200-800 V / mm, and the frequency of the alternating electric field is 10-100 Hz; and the coagulation bath is pure water.

8. The preparation method according to claim 1, characterized in that: The aqueous phase of the interfacial polymerization is a piperazine aqueous solution with a concentration of 1.5 wt %, and the organic phase is a trimesoyl chloride solution with a concentration of 1 wt %; the trimesoyl chloride solution is prepared by dissolving trimesoyl chloride in an organic solvent.

9. A piezoelectric nanofiltration membrane with electrokinetic anti-scaling function prepared by the preparation method according to any one of claims 1 to 8.

10. Use of the piezoelectric nanofiltration membrane with electric anti-scaling function as claimed in claim 9 in membrane water treatment.

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