A method for preparing a piezoelectric response type hybrid ceramic film

Abstract

The application discloses a preparation method of a piezoelectric response type hybrid ceramic membrane, and the piezoelectric response type hybrid ceramic membrane is prepared by using polyvinylidene fluoride powder as a membrane base material, using propylene carbonate or ethylene carbonate as a diluent, doping negative voltage ceramic modified nanoparticles, and doping appropriate inorganic piezoelectric nanoparticles, so that the piezoelectric performance of the membrane is obviously improved, and the relative content of the beta crystal form of the polyvinylidene fluoride membrane is improved by introducing a negative group on the membrane surface through surface grafting, so that the high efficient interception of humic acid and excellent anti-pollution effect are finally realized.

Description

Technical Field

[0001] This invention relates to the field of membrane separation technology, and in particular to a method for preparing a piezoelectric-responsive hybrid ceramic membrane. Background Technology

[0002] Natural water bodies are an important resource for obtaining freshwater, and the efficient removal of humic acid from them is a prerequisite for obtaining compliant freshwater. Among various water treatment technologies, membrane separation technology is one that can achieve deep separation. Fluoropolymers, represented by polyvinylidene fluoride (PVDF), are currently widely used materials for preparing porous membranes and for removing humic acid from natural water bodies. Because natural humic acid has a wide molecular weight distribution (10⁻¹⁰...),... 3 ~10 6 Conventional ultrafiltration membranes, relying solely on pore size sieving, are ineffective at removing humic acids (kDa). In particular, the functional groups in humic acids, such as C=O, C=C, and COOH, form numerous hydrogen bonds with H, O, and F groups on the ultrafiltration membrane surface, easily adhering to it and clogging the pores to form a dense filter cake layer. This causes irreversible fouling that is difficult to clean completely, severely impacting membrane lifespan and increasing operating costs. Besides having a suitable pore size, the membrane surface also needs strong hydrophilicity and a strong negative charge to enhance the repulsion of negatively charged humic acids, thereby reducing their fouling. Grafting hydrophilic, negatively charged groups (such as sulfonate, phosphonate, and carboxyl groups) onto the surface to improve its hydrophilicity and charge can reduce the adsorption of pollutants on the membrane surface.

[0003] Thermally induced phase separation is a commonly used technique for preparing polymer porous membranes, offering advantages such as easily controllable pore structure, high membrane mechanical properties, and convenient preparation processes. It is particularly suitable for preparing solvent-free polymer porous membranes at room temperature, and polyvinylidene fluoride (PVDF) porous membranes have already been prepared using this method. However, the steric hindrance effect of the grafted groups limits the density of grafted groups on the membrane surface. In other words, relying solely on grafting to increase the surface charge density and hydrophilicity has limited effect on improving antifouling performance and cannot significantly reduce humic acid adsorption. Therefore, compared to improving the surface charge density and hydrophilicity through surface grafting, developing hydrophilic membrane surfaces with higher charge density is particularly necessary for the deep treatment of surface water.

[0004] Piezoelectric materials are materials that exhibit a voltage between their two surfaces when subjected to pressure. Piezoelectric materials possess the piezoelectric effect, which is the phenomenon where certain dielectric materials, when subjected to external force in a specific direction, become polarized internally, thus generating a potential difference (electric field) between the two opposing surfaces of the material. Polyvinylidene fluoride (PVDF) is one of the few known organic polymers exhibiting a piezoelectric effect, primarily derived from its internal β-crystal structure. Compared to inorganic piezoelectric materials, the relatively low piezoelectric properties of organic materials mean that relying solely on the piezoelectric output of PVDF to increase the charge density on the film surface is insufficient.

[0005] Therefore, to address the above problems, this invention significantly improves the piezoelectric properties of the membrane by increasing the relative content of β-crystals in the polyvinylidene fluoride membrane and simultaneously doping it with an appropriate amount of inorganic piezoelectric modified ceramic nanoparticles during the membrane fabrication process. Furthermore, by introducing negatively charged groups onto the membrane surface through surface grafting, the surface charge density of the membrane can be significantly increased. Since the ultrafiltration membrane for water treatment is a pressure-driven membrane, it can generate more charges on the membrane surface under pulsed operating pressure, thereby further increasing the surface charge density. Ultimately, the enhanced electrostatic repulsion force achieves efficient retention of humic acid and excellent antifouling effect. Summary of the Invention

[0006] The purpose of this invention is to provide a method for preparing a piezoelectric responsive hybrid ceramic membrane. By doping an appropriate amount of inorganic piezoelectric nanoparticles, the electrical properties of the membrane are significantly improved. Furthermore, by introducing negatively charged groups on the membrane surface through surface grafting, the relative content of the β-crystal form of the polyvinylidene fluoride membrane is increased, ultimately achieving efficient retention of humic acid and excellent anti-fouling effect.

[0007] The technical solution of this invention is as follows: A method for preparing a piezoelectric responsive hybrid ceramic film, comprising the following steps: S1. Preparation of negatively charged piezoelectric ceramic modified nanoparticles: 90g of solvent, 10g of deionized water, and 1g of piezoelectric ceramic nanoparticles with hydroxyl groups on the surface were mixed and ultrasonically dispersed for 30min. Then, 1g of negatively charged silane coupling agent was added, and the mixture was mixed. The pH was adjusted to 6 with hydrochloric acid, and the reaction was carried out at room temperature for 4-6h. After the reaction, the nanoparticles were washed three times with anhydrous ethanol, each time using 600-900mL of anhydrous ethanol. Then, they were washed once with 600-900mL of deionized water. After centrifugation at 9000r / min for min, the supernatant was discarded, and the precipitate was dried in an oven at 80℃ for 12h to obtain negatively charged piezoelectric ceramic modified nanoparticles for later use. S2. Preparation of film-forming system: Take the dried polyvinylidene fluoride powder, diluent and negatively charged voltage-modified ceramic nanoparticles prepared in step S1 and add them to a stirrer. Mix at 50-70℃ for 2 hours to obtain a uniformly mixed slurry. Then degas under vacuum for 1 hour to obtain the film-forming system for later use. S3. Preparation of flat hybrid ceramic membrane: The film-forming system prepared in step S2 is fed through a feed tank with a doctor blade at the same temperature at 50-100℃, so that the film-forming system is coated on a stainless steel plate at the same temperature to form a flat membrane. After initial cooling in air for 10-20 seconds, it is further cured in deionized water at 25℃. Then, the membrane is taken out and soaked and washed with 25℃ deionized water extractant for 30-60 minutes to remove the diluent. It is then taken out and air-dried for later use. S4. Surface grafting: The membrane after being air-dried in step S3 is soaked in 5% hydrogen peroxide-dilute sulfuric acid pretreatment solution for 30 minutes, washed with deionized water and air-dried, then transferred to a UV reactor. Isopropanol solution is injected at a flow rate of 50 mL / min under a nitrogen atmosphere, with an irradiation distance of 10 cm. The treatment is continued for 1.5 h with irradiation intervals of 10 s after each irradiation of 20 s. After that, the membrane is rinsed with deionized water for 12 h to remove free monomers. After vacuum drying at room temperature, a piezoelectric hybrid ultrafiltration membrane with polyvinylidene fluoride surface grafted with polyacrylic acid is obtained, which is the piezoelectric responsive hybrid ceramic membrane.

[0008] In step 1 above, the solvent is anhydrous ethanol or methanol, the piezoelectric ceramic nanoparticles with hydroxyl groups on the surface are lead-free barium titanate or niobate-based piezoelectric ceramics, and the negatively charged silane coupling agent contains sulfonate, phosphonate or carboxyl functional groups.

[0009] Specifically, in step S1, the piezoelectric ceramic nanoparticles with hydroxyl-containing surfaces are barium titanate nanoparticles with hydroxyl-containing surfaces, potassium sodium metaniobate nanoparticles with hydroxyl-containing surfaces, barium strontium metaniobate nanoparticles with hydroxyl-containing surfaces, potassium sodium niobate nanoparticles with hydroxyl-containing surfaces, sodium bismuth titanate nanoparticles with hydroxyl-containing surfaces, or barium strontium niobate nanoparticles with hydroxyl-containing surfaces; the negatively charged silane coupling agent is triethoxysiloxane sulfonate, monosiloxane pyrophosphate, or triethoxysilane.

[0010] More specifically, in step S1 above, the piezoelectric ceramic nanoparticles with hydroxyl content on the surface have a particle size ≤100nm.

[0011] In step S2 above, the mass ratio of the polyvinylidene fluoride powder, diluent, and negatively charged voltage-modified ceramic nanoparticles is 25-30:66-73:2-4.

[0012] In step S2 above, the diluent is a water-soluble propylene carbonate or ethylene carbonate.

[0013] In step S3 above, the thickness of the scraper is 0.2 mm and the thickness of the stainless steel plate is 3 mm.

[0014] In step S4 above, the 5% hydrogen peroxide-dilute sulfuric acid pretreatment solution is made by mixing 5% hydrogen peroxide and 0.1M dilute sulfuric acid in a volume ratio of 3:1. The high-pressure mercury arc lamp of the ultraviolet reactor has an emission wavelength of 365nm and a power of 300W.

[0015] In step S4 above, the isopropanol solution contains 5% small molecule organic matter with negatively charged unsaturated bonds and 0.5% benzophenone photoinitiator; the small molecule organic matter with negatively charged unsaturated bonds is acrylic acid or vinyl phosphate.

[0016] In step S4 above, the β-crystal content of polyvinylidene fluoride in the piezoelectric responsive hybrid ceramic membrane is not less than 80%, and the pulse operating pressure is 0.1~0.4MPa.

[0017] Compared with the prior art, the present invention has the following beneficial effects: 1. The preparation method is simple. A piezoelectrically responsive charged-and-negative hybrid ultrafiltration membrane can be prepared simply by surface modification of inorganic ceramic nanoparticles, membrane preparation by thermally induced phase separation at a low temperature, and graft modification of the membrane surface. 2. The membrane has good retention and anti-fouling effects on humic acid; 3. This method is also applicable to various membrane types such as spiral wound membranes, multichannel membranes, and hollow fiber membranes. Attached Figure Description

[0018] Figure 1 Images of the sheet membranes (A is a polyvinylidene fluoride sheet membrane without doped negatively charged voltammetric ceramic modified nanoparticles (Comparative Example 1); B is a hybrid ceramic sheet membrane doped with negatively charged voltammetric ceramic modified nanoparticles (Example 1)). Figure 2 Infrared spectra (1730 cm⁻¹) of undoped polyvinylidene fluoride sheet film modified with negatively charged voltammetric ceramic nanoparticles (Comparative Example 1) and hybrid ceramic sheet film modified with negatively charged voltammetric ceramic nanoparticles (Example 1). -1 The peak near the grafted acrylic acid is the carboxyl group peak; 3000-3500 is the cm⁻¹ peak. -1 (Unreacted hydroxyl peaks on barium titanate surface); Figure 3 Surface zeta potential of polyvinylidene fluoride flat sheet film without doped negatively charged voltammetric ceramic modified nanoparticles (Comparative Example 1) and hybrid ceramic flat sheet film doped with negatively charged voltammetric ceramic modified nanoparticles (Example 1). Detailed Implementation

[0019] The technical approach of this invention in its specific implementation will be described in detail and completely. It should be noted that the implementation process and technical approach mentioned above represent only a small part of the key achievements involved in this invention, and do not list all the technical requirements in detail. Based on specific implementation schemes, all other specific embodiments obtained by those skilled in the art under the technical approach of this invention without creative effort are within the protection scope of this invention.

[0020] Example 1: S1. Preparation of negatively charged voltage-modified ceramic nanoparticles: 90g of anhydrous ethanol, 10g of deionized water, and 1g of barium titanate nanoparticles with hydroxyl groups on the surface were mixed and ultrasonically dispersed for 30min. Then, 1g of sulfonic acid triethoxysiloxane was added, and the pH was adjusted to 6 with hydrochloric acid. The reaction was carried out at room temperature for 4h. After the reaction, the nanoparticles were washed three times with 200mL of anhydrous ethanol each time, and then washed once with 200mL of deionized water. After centrifugation at 9000r / min for 8min, the supernatant was discarded, and the precipitate was dried in an oven at 80℃ for 12h to obtain negatively charged voltage-modified barium titanate ceramic nanoparticles.

[0021] S2. Preparation of film-forming system: 25 parts of dried polyvinylidene fluoride powder, 73 parts of propylene carbonate, and 2 parts of negatively charged barium titanate ceramic modified nanoparticles were mixed evenly in a batch stirrer at 70°C for 2 hours to form a slurry system. The mixture was then degassed under vacuum for 1 hour to obtain the film-forming system for preparing the hybrid membrane.

[0022] S3. Preparation of flat-plate hybrid ceramic membrane: The prepared film-forming system is simultaneously discharged from a feed tank with a thickness of 0.2 mm and a doctor blade at the same temperature at 50°C, so that the film-forming system is coated onto a stainless steel plate with a thickness of 3 mm at the same temperature to form a flat-plate membrane. After initial cooling in air for 10 seconds, it is further cured in deionized water at 25°C. Subsequently, the membrane is removed and immersed in 25°C deionized water extractant for 30 minutes to remove the diluent. After being air-dried, it is then used for subsequent grafting operations. S4. Surface grafting: The membrane obtained in S3 was immersed in a pretreatment solution (composed of 5% hydrogen peroxide and 0.1M dilute sulfuric acid, with a volume ratio of 3:1) for 30 minutes. After rinsing with deionized water and air-drying, it was transferred to an ultraviolet reactor (high-pressure mercury arc lamp with an emission wavelength of 365nm and a power of 300W). Under a nitrogen atmosphere, a 5% acrylic acid isopropanol solution (containing 0.5% benzophenone photoinitiator) was injected into the system at a flow rate of 50mL / min. The irradiation distance was 10cm, and the irradiation was stopped for 10s every 20s. The treatment was continued for 1.5h. The membrane was rinsed with deionized water for 12h to remove free monomers. After vacuum drying at room temperature, a piezoelectric responsive hybrid ceramic membrane with polyacrylic acid grafted onto the surface of polyvinylidene fluoride was obtained.

[0023] The membrane was found to contain 91.2% polyvinylidene fluoride (PVDF) β-crystals. Under a constant operating pressure of 0.1 MPa, the rejection rate for humic acid with a molecular weight of 10 kDa (tested according to the "Test Methods for Ultrafiltration Membranes" (GB / T 32360-2015)) was 43.7%, the membrane surface zeta potential was -39 mV (pH=7), and the flux recovery rate was 46.2%. Under a pulsed operating pressure of 0.1 MPa, the rejection rate for humic acid with a molecular weight of 10 kDa was 87.4%, the membrane surface zeta potential was -72 mV (pH=7), and the flux recovery rate was 84.8%.

[0024] Example 2: S1. Preparation of negatively charged voltage-modified ceramic nanoparticles: 90g of anhydrous methanol, 10g of deionized water, and 1g of barium titanate nanoparticles with hydroxyl groups on the surface were mixed and ultrasonically dispersed for 30min. Then, 1g of triethoxysiloxane sulfonate was added, and the pH was adjusted to 6 with hydrochloric acid. The reaction was carried out at room temperature for 4h. After the reaction, the nanoparticles were washed three times with 300mL of anhydrous ethanol each time, and then washed once with 300mL of deionized water. After centrifugation at 6000r / min for 10min, the supernatant was discarded, and the precipitate was dried in an oven at 80℃ for 12h to obtain negatively charged voltage-modified barium titanate ceramic nanoparticles.

[0025] S2. Preparation of film-forming system: 30 parts of dried polyvinylidene fluoride powder, 66 parts of propylene carbonate, and 4 parts of negatively charged barium titanate ceramic modified nanoparticles were mixed evenly in a stirrer at 50°C for 2 hours to form a slurry system. The mixture was then degassed under vacuum for 1 hour to obtain the film-forming system for preparing the hybrid membrane.

[0026] S3. Preparation of flat-plate hybrid ceramic membrane: The prepared film-forming system is simultaneously discharged from a feed tank with a thickness of 0.2 mm and a doctor blade at the same temperature at 100°C, so that the film-forming system is coated onto a stainless steel plate with a thickness of 3 mm at the same temperature to form a flat-plate membrane. After initial cooling in air for 20 seconds, it is further cured in deionized water at 25°C. Subsequently, the membrane is removed and immersed in 25°C deionized water extractant for 60 minutes to remove the diluent. After being air-dried, it is then used for subsequent grafting operations. S4. Surface grafting: The membrane obtained in S3 was immersed in a pretreatment solution (composed of 5% hydrogen peroxide and 0.1M dilute sulfuric acid, with a volume ratio of 3:1) for 30 minutes. After being washed with deionized water and air-dried, it was transferred to an ultraviolet reactor (high-pressure mercury emission wavelength 365nm, power 300W). Under a nitrogen atmosphere, a 5% acrylic acid isopropanol solution (containing 0.5% benzophenone photoinitiator) was injected into the system at a flow rate of 50mL / min. The irradiation distance was 10cm, and the irradiation was stopped for 10s every 20s. The treatment was continued for 1.5h. The membrane was rinsed with deionized water for 12h to remove free monomers. After vacuum drying at room temperature, a piezoelectric responsive hybrid ceramic membrane with polyacrylic acid grafted onto the surface of polyvinylidene fluoride was obtained.

[0027] The membrane was found to contain 91.5% polyvinylidene fluoride (PVDF) β-crystal form. Under a constant operating pressure of 0.4 MPa, it exhibited a 51.2% rejection rate for humic acid with a molecular weight of 10 kDa (tested according to the "Test Methods for Ultrafiltration Membranes" (GB / T 32360-2015)), a membrane surface zeta potential of -40 mV (pH=7), and a flux recovery rate of 52.8%. Under a pulsed operating pressure of 0.4 MPa, the rejection rate for humic acid with a molecular weight of 10 kDa was 98.9%, the membrane surface zeta potential was -94 mV (pH=7), and the flux recovery rate was 97.3%.

[0028] Example 3: S1. Preparation of negatively charged voltage-modified ceramic nanoparticles. 90g of anhydrous ethanol, 10g of deionized water, and 1g of barium strontium niobate nanoparticles with hydroxyl groups on their surface were mixed and ultrasonically dispersed for 30min. Then, 1g of monosiloxane pyrophosphate was added, and the pH was adjusted to 6 with hydrochloric acid. The reaction was carried out at room temperature for 6h. After the reaction, the nanoparticles were washed three times with 250mL of anhydrous ethanol each time, followed by one wash with 250mL of deionized water. After centrifugation at 7000r / min for 5min, the supernatant was discarded, and the precipitate was dried in an oven at 80℃ for 12h to obtain negatively charged voltage-modified barium strontium niobate ceramic nanoparticles.

[0029] S2. Preparation of the film-forming system. 30 parts of dried polyvinylidene fluoride powder, 66 parts of ethylene carbonate, and 4 parts of negatively charged barium strontium niobate ceramic modified nanoparticles were mixed uniformly in a batch stirrer at 50°C for 2 hours to form a slurry system. The mixture was then degassed under vacuum for 1 hour to obtain the film-forming system for preparing the hybrid membrane.

[0030] S3. Preparation of a flat-plate hybrid ceramic membrane. The prepared film-forming system is simultaneously fed into a feed bath with a thickness of 0.2 mm and a doctor blade at the same temperature at 100°C, allowing the film-forming system to be coated onto a 3 mm thick stainless steel plate at the same temperature to form a flat-plate membrane. After initial cooling in air for 10 seconds, it is further cured in deionized water at 25°C. Subsequently, the membrane is removed and immersed in 25°C deionized water extractant for 60 minutes to remove the diluent. After air drying, it is ready for subsequent grafting operations. S4. Surface Grafting. The membrane obtained in S3 was immersed in a pretreatment solution (composed of 5% hydrogen peroxide and 0.1M dilute sulfuric acid, with a volume ratio of 3:1) for 30 minutes. After rinsing with deionized water and air-drying, it was transferred to an ultraviolet reactor (high-pressure mercury emission wavelength 365nm, power 300W). Under a nitrogen atmosphere, a 5% acrylic acid isopropanol solution (containing 0.5% benzophenone photoinitiator) was injected into the system at a flow rate of 50mL / min. The irradiation distance was 10cm, and the irradiation was stopped for 10s every 20s. The treatment was continued for 1.5h. The membrane was rinsed with deionized water for 12h to remove free monomers. After vacuum drying at room temperature, a piezoelectrically responsive hybrid ceramic membrane with polyacrylic acid grafted onto the surface of polyvinylidene fluoride was obtained.

[0031] The membrane was found to contain 92.1% polyvinylidene fluoride (PVDF) β-crystal form. Under a constant operating pressure of 0.4 MPa, it exhibited a 51.7% rejection rate for humic acid with a molecular weight of 10 kDa (tested according to the "Test Methods for Ultrafiltration Membranes" (GB / T 32360-2015)), a membrane surface zeta potential of -40 mV (pH=7), and a flux recovery rate of 53.1%. Under a pulsed operating pressure of 0.4 MPa, the rejection rate for humic acid with a molecular weight of 10 kDa was 99.2%, the membrane surface zeta potential was -96 mV (pH=7), and the flux recovery rate was 97.6%.

[0032] Example 4: S1. Preparation of negatively charged voltage-modified ceramic nanoparticles. 90g of anhydrous ethanol, 10g of deionized water, and 1g of sodium bismuth titanate nanoparticles with hydroxyl groups on their surface were mixed and ultrasonically dispersed for 30min. Then, 1g of monosiloxane pyrophosphate was added, and the pH was adjusted to 6 with hydrochloric acid. The reaction was carried out at room temperature for 6h. After the reaction, the nanoparticles were washed three times with 300mL of anhydrous ethanol each time, followed by one wash with 300mL of deionized water. After centrifugation at 8000r / min for 8min, the supernatant was discarded, and the precipitate was dried in an oven at 80℃ for 12h to obtain negatively charged voltage-modified sodium bismuth titanate ceramic nanoparticles.

[0033] S2. Preparation of the film-forming system. 28 parts of dried polyvinylidene fluoride powder, 69 parts of ethylene carbonate, and 3 parts of sodium bismuth titanate ceramic modified nanoparticles with negative voltage charge were mixed uniformly in a batch stirrer at 50°C for 2 hours to form a slurry system. The mixture was then degassed under vacuum for 1 hour to obtain the film-forming system for preparing the hybrid film.

[0034] S3. Preparation of flat-sheet hybrid ultrafiltration membrane. The prepared membrane-forming system was simultaneously discharged from a feed tank with a thickness of 0.2 mm and a doctor blade at the same temperature at 90°C, so that the membrane-forming system was coated onto a stainless steel plate with a thickness of 3 mm at the same temperature to form a flat-sheet membrane. After initial cooling in air for 20 seconds, it was further cured in deionized water at 25°C. Subsequently, the membrane was removed and immersed in 25°C deionized water extractant for 60 minutes to remove the diluent. After being air-dried, it was then subjected to subsequent grafting operations. S4. Surface Grafting. The membrane obtained in S3 was immersed in a pretreatment solution (composed of 5% hydrogen peroxide and 0.1M dilute sulfuric acid, with a volume ratio of 3:1) for 30 minutes. After rinsing with deionized water and air-drying, it was transferred to an ultraviolet reactor (high-pressure mercury emission wavelength 365nm, power 300W). Under a nitrogen atmosphere, a 5% vinyl phosphoric acid isopropanol solution (containing 0.5% benzophenone photoinitiator) was injected into the system at a flow rate of 50mL / min. The irradiation distance was 10cm, and the irradiation was stopped for 10s every 20s, and the treatment was continued for 1.5h. After rinsing with deionized water for 12h to remove free monomers, the membrane was dried under vacuum at room temperature to obtain a piezoelectrically responsive hybrid ceramic membrane with polyvinylidene fluoride surface grafted with polyvinyl phosphoric acid.

[0035] The membrane was found to contain 90.7% polyvinylidene fluoride (PVDF) β-crystals. Under a constant operating pressure of 0.3 MPa, it exhibited a 49.2% rejection rate for humic acid with a molecular weight of 10 kDa (tested according to the "Test Methods for Ultrafiltration Membranes" (GB / T 32360-2015)), a membrane surface zeta potential of -40 mV (pH=7), and a flux recovery rate of 51.6%. Under a pulsed operating pressure of 0.3 MPa, the rejection rate for humic acid with a molecular weight of 10 kDa was 92.5%, the membrane surface zeta potential was -89 mV (pH=7), and the flux recovery rate was 91.5%.

[0036] Comparative Example 1: Preparation method of polyvinylidene fluoride sheet film without doped negatively charged voltage-modified ceramic nanoparticles S1. Preparation of negatively charged barium titanate ceramic modified nanoparticles: 90g of anhydrous ethanol and 10g of deionized water were mixed and ultrasonically dispersed for 30min. Then, 1g of triethoxysilane sulfonate was added, and the pH was adjusted to 6 with hydrochloric acid. The reaction was carried out at room temperature for 4h. After the reaction, the nanoparticles were washed three times with 200mL of anhydrous ethanol each time, and then washed once with 200mL of deionized water. After centrifugation at 9000r / min for 8min, the supernatant was discarded, and the precipitate was dried in an oven at 80℃ for 12h to obtain negatively charged barium titanate ceramic modified nanoparticles.

[0037] S2. Preparation of film-forming system: 25 parts of dried polyvinylidene fluoride powder, 73 parts of propylene carbonate, and 2 parts of negatively charged barium titanate ceramic modified nanoparticles were mixed evenly in a batch stirrer at 70°C for 2 hours to form a slurry system. The mixture was then degassed under vacuum for 1 hour to obtain the film-forming system for preparing the hybrid membrane.

[0038] S3. Preparation of flat-plate hybrid ceramic membrane: The prepared film-forming system is simultaneously discharged from a feed tank with a thickness of 0.2 mm and a doctor blade at the same temperature at 50°C, so that the film-forming system is coated onto a stainless steel plate with a thickness of 3 mm at the same temperature to form a flat-plate membrane. After initial cooling in air for 10 seconds, it is further cured in deionized water at 25°C. Subsequently, the membrane is removed and immersed in 25°C deionized water extractant for 30 minutes to remove the diluent. After being air-dried, it is then used for subsequent grafting operations. S4. Surface grafting: The membrane obtained in S3 was immersed in a pretreatment solution (composed of 5% hydrogen peroxide and 0.1M dilute sulfuric acid, with a volume ratio of 3:1) for 30 minutes. After being washed with deionized water and air-dried, it was transferred to an ultraviolet reactor (high-pressure mercury arc lamp with an emission wavelength of 365nm and a power of 300W). Under a nitrogen atmosphere, a 5% acrylic acid isopropanol solution (containing 0.5% benzophenone photoinitiator) was injected into the system at a flow rate of 50mL / min. The irradiation distance was 10cm, and the irradiation was stopped for 10s every 20s. The treatment was continued for 1.5h. The membrane was rinsed with deionized water for 12h to remove free monomers. After vacuum drying at room temperature, a piezoelectric hybrid ultrafiltration membrane with polyvinylidene fluoride surface grafted with polyacrylic acid was obtained.

[0039] The relative content of polyvinylidene fluoride β-crystal in the membrane was determined to be %, and the rejection rate of humic acid with a molecular weight of kDa (tested according to "Test Methods for Ultrafiltration Membranes" (GB / T 32360-2015)) was % under a constant operating pressure of 0.1 MPa, the membrane surface zeta potential was -39 mV (pH=7), and the flux recovery rate was %. Under a pulsed operating pressure of 0.1 MPa, the rejection rate of humic acid with a molecular weight of 10 kDa was %, the membrane surface zeta potential was -72 mV (pH=7), and the flux recovery rate was %.

[0040] It should be particularly noted that all similar substitutions and modifications are obvious to those skilled in the art. The above description is only an embodiment of the present invention and does not limit the patent scope of the present invention. Any equivalent structural or procedural transformations made using the content of the present invention specification, or any direct or indirect application of other related technical fields, are similarly included within the patent protection scope of the present invention.

Claims

1. A method for preparing a piezoelectrically responsive hybrid ceramic film, characterized in that: Follow these steps: S1. Preparation of negatively charged piezoelectric ceramic modified nanoparticles: 90g of solvent, 10g of deionized water and 1g of piezoelectric ceramic nanoparticles with hydroxyl groups on the surface are mixed and ultrasonically dispersed for 30min. Then, 1g of negatively charged silane coupling agent is added and mixed. The pH value is adjusted to 6 with hydrochloric acid and reacted at room temperature for 4-6h. After the reaction, the nanoparticles are washed 3 times with anhydrous ethanol, each time using 200-300mL of anhydrous ethanol. Then, they are washed once with 200-300mL of deionized water. After centrifugation at 6000-9000r / min for 5-10min, the supernatant is discarded and the precipitate is dried in an oven at 80℃ for 12h to obtain negatively charged piezoelectric ceramic modified nanoparticles for later use. S2. Preparation of film-forming system: Take the dried polyvinylidene fluoride powder, diluent and negatively charged voltage-modified ceramic nanoparticles prepared in step S1 and add them to a stirrer. Mix at 50-70℃ for 2 hours to obtain a uniformly mixed slurry. Then degas under vacuum for 1 hour to obtain the film-forming system for later use. The mass ratio of the polyvinylidene fluoride powder, diluent, and negatively charged voltage-modified ceramic nanoparticles is 25-30:66-73:2-4. S3. Preparation of flat hybrid ceramic membrane: The film-forming system prepared in step S2 is fed through a feed tank with a doctor blade at the same temperature at 50-100℃, so that the film-forming system is coated on a stainless steel plate at the same temperature to form a flat membrane. After initial cooling in air for 10-20 seconds, it is further cured in deionized water at 25℃. Then, the membrane is taken out and soaked and washed with 25℃ deionized water extractant for 30-60 minutes to remove the diluent. It is then taken out and air-dried for later use. S4. Surface Grafting: The membrane after being air-dried in step S3 is immersed in a 5% hydrogen peroxide-dilute sulfuric acid pretreatment solution for 30 minutes. The 5% hydrogen peroxide-dilute sulfuric acid pretreatment solution is a mixture of 5% hydrogen peroxide and 0.1M dilute sulfuric acid in a volume ratio of 3:

1. After being washed with deionized water and air-dried, it is transferred to a UV reactor. An isopropanol solution containing 5% negatively charged acrylic acid and 0.5% benzophenone photoinitiator is injected at a flow rate of 50 mL / min under a nitrogen atmosphere. The irradiation distance is 10 cm. The treatment is continued for 1.5 h with a 20 s irradiation interval followed by a 10 s irradiation stop. Then, the membrane is rinsed with deionized water for 12 h to remove free monomers. After vacuum drying at room temperature, a piezoelectric hybrid ultrafiltration membrane with polyacrylic acid grafted onto the surface of polyvinylidene fluoride is obtained, which is a piezoelectric responsive hybrid ceramic membrane.

2. The method for preparing a piezoelectrically responsive hybrid ceramic film according to claim 1, characterized in that: In step S1, the solvent is anhydrous ethanol or methanol, the piezoelectric ceramic nanoparticles with hydroxyl groups on the surface are lead-free barium titanate or niobate-based piezoelectric ceramics, and the negatively charged silane coupling agent contains sulfonate, phosphonate or carboxyl functional groups.

3. The method for preparing a piezoelectrically responsive hybrid ceramic film according to claim 1 or 2, characterized in that: In step S1, the piezoelectric ceramic nanoparticles with hydroxyl-containing surfaces are barium titanate nanoparticles with hydroxyl-containing surfaces, potassium sodium metaniobate nanoparticles with hydroxyl-containing surfaces, barium strontium metaniobate nanoparticles with hydroxyl-containing surfaces, potassium sodium niobate nanoparticles with hydroxyl-containing surfaces, sodium bismuth titanate nanoparticles with hydroxyl-containing surfaces, or barium strontium niobate nanoparticles with hydroxyl-containing surfaces; the negatively charged silane coupling agent is triethoxysiloxane sulfonate, monosiloxane pyrophosphate, or triethoxysilane.

4. The method for preparing a piezoelectrically responsive hybrid ceramic film according to claim 3, characterized in that: In step S1, the piezoelectric ceramic nanoparticles with hydroxyl content on the surface have a particle size ≤100nm.

5. The method for preparing a piezoelectric-responsive hybrid ceramic film according to claim 1, characterized in that: In step S2, the diluent is a water-soluble propylene carbonate or ethylene carbonate.

6. The method for preparing a piezoelectrically responsive hybrid ceramic film according to claim 1, characterized in that: In step S3, the thickness of the scraper is 0.2 mm, and the thickness of the stainless steel plate is 3 mm.

7. The method for preparing a piezoelectrically responsive hybrid ceramic film according to claim 1, characterized in that: In step S4, the high-pressure mercury arc lamp of the ultraviolet reactor has an emission wavelength of 365nm and a power of 300W.

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