Piezoelectric photocatalytic self-cleaning hollow fiber ceramic membrane and preparation method and application thereof

Abstract

The present application relates to a kind of hollow fiber ceramic membrane materials with piezoelectric photocatalytic self-cleaning function and its preparation method.The preparation method of the membrane material includes two steps: first, prepare non-metal doped titanium dioxide nanotube photocatalyst, and it is immobilized on the surface of hollow fiber ceramic base membrane by vacuum assisted dip coating method and low temperature sintering method, form composite membrane with photocatalytic self-cleaning performance;Second, in-situ growth of calcium (Ca) doped BaTiO3 piezoelectric photocatalyst by hydrothermal method, further enhance its self-cleaning performance.The present application innovatively combines piezoelectric photocatalytic technology and membrane separation technology, significantly increases the specific surface area of catalyst, solves the problem of catalyst settlement and recovery in water treatment process.The composite membrane also improves the anti-fouling performance and separation flux of membrane, through the synergistic effect of piezoelectric effect and photocatalytic effect, organic pollutants on the surface of membrane are efficiently degraded, the service life of membrane is prolonged, and an effective solution for the self-cleaning of membrane is provided.The present application is suitable for industrial and environmental water treatment field.

Description

Technical Field

[0001] This invention relates to a self-cleaning hollow fiber ceramic membrane material, and more particularly to a piezoelectric photocatalytic self-cleaning hollow fiber ceramic membrane material and its preparation method. This membrane material is mainly used in industrial and environmental water treatment fields. Background Technology

[0002] Membrane separation technology is a technique that uses pressure to selectively allow certain components to permeate through a membrane to achieve the separation and purification of substances. This technology offers advantages such as no phase change, low energy consumption, high efficiency, and simple process. Ceramic membranes can be classified into flat sheet membranes, tubular membranes, and hollow fiber membranes based on their shape. Among them, hollow fiber membranes exhibit higher separation flux due to their larger membrane surface area. Compared with organic membranes, ceramic membranes show broader application prospects in industry due to their excellent resistance to acid and alkali corrosion, organic solvents, and high temperature and pressure. Despite the many advantages of membrane separation technology, membrane fouling is a problem in practical applications. Membrane fouling can severely shorten the service life of membranes, necessitating the search for clean and environmentally friendly methods to clean membrane materials. Currently, commonly used membrane cleaning methods include hydraulic cleaning, mechanical rinsing, and chemical cleaning. To reduce cleaning frequency, energy consumption, and secondary pollution, it is necessary to improve the structure and function of membrane materials to enhance their antifouling and self-cleaning capabilities.

[0003] Self-cleaning technology utilizes renewable energy to enable surfaces to automatically remove attached dirt, deposits, or contaminants without human intervention. This technology achieves its goals through functional materials, surface treatments, or physicochemical methods, aiming to maintain surface cleanliness and reduce maintenance frequency and costs. For example, by creating materials with specific wettability (superhydrophobic and superhydrophilic properties), the adsorption and accumulation of contaminants can be effectively prevented; or photocatalytic functional materials can generate free radicals under light irradiation, thereby degrading surface dirt; piezoelectric functional materials can be combined with external mechanical energy (such as wind, vibration, and water flow), causing piezoelectric polarization due to the relative displacement of positive and negative charges on their surface, altering the charge distribution on the membrane material surface and decomposing surface deposits; or self-cleaning microorganisms can be introduced onto the material surface to decompose or remove contaminants. Combining these self-cleaning technologies with membrane separation technology aims to promote the directional separation of charge carriers, thereby achieving redox reactions with contaminants and transforming environmental pollutants into harmless substances.

[0004] Piezoelectric catalysis typically involves crystals with non-centrosymmetric structures, such as barium titanate (BaTiO3), zinc oxide (ZnO), transition metal dichalcogenides (MoS2), and potassium niobate (KNbO3). BaTiO3, as a lead-free material, avoids the environmental and health hazards of lead, aligning with green chemistry principles. It possesses a high piezoelectric constant, enabling it to effectively generate charge under mechanical stress, thereby enhancing catalytic reaction efficiency. Furthermore, BaTiO3 exhibits excellent photocatalytic performance under visible light irradiation, contributing to the degradation and transformation of organic pollutants. Compared to other types of catalysts, barium titanate is not only readily available but also has mature preparation processes and good economic viability. Chinese invention patent (CN202011112614.0) discloses a BaTiO3 / KNbO3 composite piezoelectric photocatalyst in which BaTiO3 nanospheres with a particle size of 30-50 nm are uniformly distributed on prismatic KNbO3 using a hydrothermal method. The 0.3BaTiO3 / 0.7KNbO3 composite piezoelectric photocatalyst exhibits a significantly higher degradation effect within 180 min than the other two single piezoelectric materials, and the catalyst demonstrates excellent piezoelectric photocatalytic activity and stability. Furthermore, Chinese invention patent (CN202410186852.8) discloses a piezoelectric photocatalytic composite catalyst combining Na2Ti3O7 nanowires and Ba... 1-x Sr xTiO3 nanowires, Ag2O / Ag-BST materials, quartz fibers, and silica sol effectively improve the light conductivity and carrier migration efficiency of visible light, thereby enhancing wastewater treatment efficiency. However, most of these catalysts are difficult to recover and can easily cause secondary pollution. Therefore, piezoelectric photocatalytic materials can be combined with separation membrane materials, not only improving catalyst recovery efficiency but also fully utilizing renewable energy sources such as wind, hydro, and solar power. By optimizing the electronic structure design of the materials, energy and environmental benefits can be maximized. Chinese invention patent (CN202310727795.5) discloses a piezoelectric photocatalytic MoO3 / P(VDF-TrFE) nanocomposite membrane prepared by spin-coating. The nanocomposite membrane is prepared by spin-coating a casting solution of P(VDF-TrFE) and MoO3 onto a substrate. It exhibits high degradation efficiency for RhB dyes, and the preparation method is simple and low-cost. It displays both positive and inverse piezoelectric effects, but the generated electrical signal is relatively weak, and the long-term stability of the membrane has not yet been evaluated. Organic membranes exhibit poor resistance to degradation and aging by strong oxidizing free radicals, resulting in low throughput and treatment efficiency. Chinese invention patent (CN201611060410.0) discloses a piezoelectric ceramic filter membrane and its application device. This filter membrane is prepared by coating a mixture of piezoelectric materials and additives and then sintering. Its main purpose is to prevent clogging of the filter channels of the ceramic filter membrane through the piezoelectric effect, achieving a self-cleaning function while inhibiting contamination. Chinese invention patent (CN202011221203.5) discloses a porous SiO2 ceramic membrane prepared by gel casting. This method first obtains a ceramic green body, then polarizes the green body under high-temperature oil bath or air conditions, and finally calcines it at high temperature to obtain excellent piezoelectric properties. Unlike the traditional method of calcining before polarization, this invention allows the SiO2 grains in the green body to rotate and rearrange more effectively along the polarization electric field direction during polarization, thereby achieving higher piezoelectric performance at a lower polarization voltage. The prepared porous silica ceramic membrane exhibits a vibration signal value of 1–10 mV when a voltage is applied across its ends. Under an alternating electric field, the membrane generates in-situ vibrations and acoustic waves during separation, but the vibration signal value is low, limiting its effectiveness in reducing contaminants and membrane pore blockage, and improving separation efficiency. Chinese invention patent (CN202320563772.0) discloses a piezoelectric photocatalytic reaction device. By adjusting the reaction platform, stirring device, and illumination device, the photocatalytic reaction efficiency can be improved, allowing for the adjustment of light intensity, reaction liquid stirring rate, and ultrasonic frequency. This device is applicable to various photocatalysts. In photoelectric-piezoelectric synergistic catalysis, light and ultrasound serve as energy input sources. Light primarily excites charge carriers, while ultrasound excites alternating polarization fields. These periodically alternating polarization fields act as "charge pumps," "dragging" charges to the material surface to participate in the catalytic reaction, promoting charge carrier separation, thereby enhancing the degradation of contaminants on the membrane surface and the cross-current catalytic efficiency of the entire system.

[0005] This invention relates to a hollow fiber ceramic membrane material with piezoelectric photocatalytic self-cleaning function and its preparation method. The method mainly includes two steps: First, a non-metal-doped titanium dioxide nanotube photocatalyst is prepared and immobilized on the surface of a self-made or commercial hollow fiber ceramic substrate membrane using a vacuum-assisted dip-coating method and a low-temperature sintering method, thereby forming a hollow fiber ceramic composite membrane with photocatalytic self-cleaning properties. Subsequently, a calcium (Ca)-doped BaTiO3 piezoelectric photocatalyst is grown using a hydrothermal method and in situ grown on the surface of the composite membrane, finally obtaining a piezoelectric photocatalytic self-cleaning hollow fiber ceramic composite membrane. This invention innovatively combines piezoelectric photocatalysis technology with membrane separation technology, significantly increasing the specific surface area of ​​the catalyst and effectively solving the problems of catalyst sedimentation and recovery in water treatment processes. Furthermore, the composite membrane enhances the membrane's antifouling performance and separation flux. Through the synergistic effect of piezoelectric and photocatalytic effects, it can efficiently degrade organic pollutants on the membrane surface, thereby extending the membrane's service life and providing an effective solution for membrane self-cleaning, making it suitable for industrial and environmental water treatment. Summary of the Invention

[0006] This invention relates to a method for improving the self-cleaning performance of hollow fiber ceramic membranes by immobilizing piezoelectric photocatalysts on the membrane. Specifically, this invention uses commercially available or homemade hollow fiber ceramic membranes as the base membrane. Due to their large surface area, these membranes can bind more catalysts, thus providing more active sites for the catalytic reaction. This composite membrane significantly improves the membrane's hydrophilicity, antifouling properties, and piezoelectric photocatalytic self-cleaning performance, enabling rapid and effective separation of pollutants in water, thereby increasing the membrane's flux and antifouling performance. The preparation method of the hollow fiber ceramic membrane material with antifouling and piezoelectric photocatalytic self-cleaning properties mainly includes the following steps:

[0007] (1) Preparation of photocatalytic composite membrane:

[0008] ① Preparation of non-metallic element-doped titanium dioxide (TiO2) nanotube photocatalyst: Tubular sodium metatitanate (Na2Ti3O7) was prepared according to our previous Chinese invention patent (CN202310757330.4). Then, it was mixed with one of sulfur (S)-containing compounds, nitrogen (N)-containing compounds or carbon (C)-containing compounds in a certain mass ratio and ground. The mixture was then placed in a tube furnace and sintered for a period of time under an argon atmosphere and at a certain temperature to obtain a non-metallic element-doped TiO2 nanotube photocatalyst.

[0009] ② Vacuum filtration: The photocatalyst prepared in step ① above is uniformly dispersed in deionized water, and an appropriate volume of the dispersion is fixed on the outer surface of the hollow fiber ceramic substrate membrane by vacuum-assisted dip coating.

[0010] ③ Low-temperature sintering: Calcination at a certain temperature for a certain time yields a hollow fiber ceramic composite membrane with photocatalytic self-cleaning function;

[0011] (2) Formation of piezoelectric photocatalytic composite film:

[0012] ① Hydrothermal in-situ growth: The photocatalytic membrane is immersed in the above mixed solution by preparing a certain concentration of Na2Ti3O7, Ba(OH)2·8H2O and Ca(OH)2 solution, and hydrothermal growth is carried out at a certain temperature;

[0013] ② Vacuum sintering: Vacuum annealing is performed at a certain temperature and time to obtain a piezoelectric photocatalytic film (Mo / S-TiNTs@Ba). 1-x Ca x TiO3), x = 0 ~ 1.

[0014] In step (1)① above, the particle size range of TiO2 powder required for synthesizing Na2Ti3O7 is 3-5 μm; the concentration of NaOH solution is 8-12 mol / L; ultrasonic treatment at room temperature for 20-40 min is used to mix evenly; the reaction vessel is kept at 180-220℃ for 6-18 h; the sulfur-containing compound is selected from thiourea and carbon disulfide, the nitrogen-containing compound is selected from urea and melamine, and the carbon-containing compound is selected from polyvinyl alcohol and biomass carbon; the mass ratio of Na2Ti3O7 powder to one of the above compounds is 1:0.1-1:1; the argon atmosphere flow rate is 200 sccm, the tube furnace annealing temperature is 200℃-900℃, and the time is 1-2 h;

[0015] In step (1)② above, taking sulfur-doped TiO2 nanotubes (S-TiNTs) as an example, the ultrasonic dispersion concentration in deionized water is 0.05~0.5g / L; the pressure of the circulating water vacuum pump is -0.088MPa; and the base film is selected from Al2O3, mullite or commercial hollow fiber ceramic membrane.

[0016] In step (1)③ above, the calcination temperature of the high-temperature box furnace is 300~700℃, and the calcination time is 1~2h; the volume of the modified liquid is (V=50, 75, 100, 125, 150, 200mL);

[0017] In step (2)① above, the optimal ratio of the Mo / S-TiNTs membrane is 75-125 mL of filtration volume, which is used as the photocatalytic membrane. The concentrations of Na2Ti3O7, Ba(OH)2·8H2O and Ca(OH)2 are 15-35 mmol / L, 20-40 mmol / L and 25-35 mmol / L, respectively, wherein the molar ratio of Ba(OH)2·8H2O and Ca(OH)2 is 1:9-9:1, and the reaction vessel is kept at 180-220℃ for 0.125-6 h;

[0018] In step (2)② above, the vacuum annealing temperature of the tube furnace is 240~395℃ and the annealing time is 40~200min.

[0019] This invention offers the following beneficial technical effects: Based on existing TiO2 nanotube photocatalyst preparation technology, non-metallic doping enhances photocatalytic performance; further, in-situ growth of piezoelectric catalysts improves catalytic degradation performance during dynamic water treatment. The piezoelectric photocatalytic membrane separation device is easy to operate; the modified membrane exhibits excellent separation performance for wastewater containing organic matter, with a high flux recovery rate. It significantly reduces the impact of membrane surface fouling on the entire life cycle of the membrane material, reduces replacement costs, and provides a valuable reference for membrane self-cleaning. Attached Figure Description

[0020] Figure 1 (a) and (a1) are the hollow fiber ceramic substrate membranes (M0) prepared in the experimental comparative examples. Figure 1 (b) and (b1, the inset in b1 is magnified 10000 times) are piezoelectric photocatalytic hollow fiber ceramic films (M / S-TiNTs@Ba) prepared in Example 1. 0.7 Ca 0.3 Scanning electron microscope image of TiO3 surface.

[0021] Figure 2 The hollow fiber ceramic substrate membrane (M0) prepared in the experimental comparative example, the photocatalytic hollow fiber ceramic membrane (M / S-TiNTs) prepared in Example 1, and the piezoelectric photocatalytic hollow fiber ceramic membrane (M / S-TiNTs@Ba) are all examples of such membranes. 0.7 Ca 0.3 Comparison of water contact angles of TiO3.

[0022] Figure 3 The hollow fiber ceramic substrate membrane (M0) prepared in the experimental comparative example and the piezoelectric photocatalytic hollow fiber ceramic membrane (M / S-TiNTs@Ba) prepared in Example 1 are also mentioned. 0.7 Ca 0.3 The graph shows a comparison of the changes in permeation flux and TOC concentration of the membrane during the piezoelectric photocatalytic self-cleaning process (40 kHz, λ>320 nm, 0.1 MPa, flow rate: 1.7 L / min) of TiO3 in the separation of produced water from oil fields. The inset shows a comparison of the composite membrane after continuous filtration of produced water from oil fields for 1 hour (a), followed by cleaning with a xenon lamp and ultrasound for 30 minutes (b), and then cleaning with a xenon lamp and ultrasound for another 30 minutes (c).

[0023] Figure 4 It is the piezoelectric photocatalytic ceramic film (M / S-TiNTs@Ba) prepared in Implementation Case 1. 0.7 Ca0.3 Comparison of the effects of TiO3 on the separation of 500 mg / L tetracycline before and after. Detailed Implementation

[0024] Example 1:

[0025] (1) Preparation of photocatalytic composite membrane: First, Na2Ti3O7 and thiourea were mixed and ground at a mass ratio of 1:0.3. The mixture was placed in a tube furnace, evacuated, and then purged with 200 sccm of Ar atmosphere before sintering at 300℃ for 2 h to obtain S-doped TiO2 photocatalyst. Second, a 0.2 g / L deionized water solution of S-doped TiO2 photocatalyst was prepared, and 100 mL of the modified solution was uniformly immobilized on the outer surface of the mullite ceramic substrate membrane by vacuum-assisted dip coating. Then, the membrane was calcined at 300℃ for 2 h using a low-temperature sintering method to obtain a mullite / S-TiNTs ceramic membrane (M / S-TiNTs) with photocatalytic self-cleaning function.

[0026] (2) Preparation of piezoelectric photocatalytic composite film: First, a mixed solution of Ba(OH)₂·8H₂O and Ca(OH)₂ with a molar ratio of 7:3 was prepared, and the above M / S-TiNTs photocatalytic film was placed in it. Hydrothermal growth was performed at 200℃ for 30 min, followed by vacuum annealing at 260℃ for 60 min to obtain mullite / S-TiNTs@Ba 0.7 Ca 0.3 TiO3 piezoelectric photocatalytic film (M / S-TiNTs@Ba 0.7 Ca 0.3 TiO3).

[0027] Example 2:

[0028] (1) Same as step 1 in Example 1. The base film is selected as an alumina (Al2O3) hollow fiber ceramic membrane.

[0029] (2) Preparation of piezoelectric photocatalytic composite film: First, a mixed solution of Ba(OH)₂·8H₂O and Ca(OH)₂ with a molar ratio of 9:1 was prepared, and an M / S-TiNTs photocatalytic film was placed in it. Hydrothermal growth was performed at 200℃ for 30 min, followed by vacuum annealing at 395℃ for 180 min to obtain alumina / S-TiNTs@Ba 0.9 Ca 0.1 TiO3 piezoelectric photocatalytic film (M' / S-TiNTs@Ba 0.9 Ca 0.1 TiO3).

[0030] Experimental comparison example:

[0031] Selection and preparation of ceramic substrate membranes: Mullite and Al2O3 hollow fiber ceramic membranes were prepared by referring to our previously filed Chinese invention patents (CN202310757330.4) and (CN2024106420058).

[0032] Experimental results:

[0033] This invention provides a piezoelectric photocatalytic self-cleaning hollow fiber ceramic membrane material and its preparation method, mainly used for organic wastewater treatment. A composite membrane is obtained by immobilizing a novel piezoelectric photocatalyst on the surface of a hollow fiber ceramic membrane. This composite membrane exhibits excellent separation performance and good piezoelectric photocatalytic self-cleaning ability in tetracycline wastewater and oil-water separation performance tests.

[0034] Figure 1 (a,a1) and (b,b1) respectively show the hollow fiber mullite ceramic membrane (M0) prepared in the experimental comparative example and the piezoelectric photocatalytic hollow fiber ceramic membrane (M / S-TiNTs@Ba) in Example 1. 0.7 Ca 0.3 Scanning electron microscope (SEM) image of the TiO3 surface. The M0 substrate film exhibits a high aspect ratio and a distinctly cross-shaped mullite whisker structure; M / S-TiNTs@Ba 0.7 Ca 0.3 Scanning electron microscopy images of the TiO3 surface reveal S-TiNTs and Ba. 0.8 Ca 0.2 TiO3 has both nanotube and particulate structures and is tightly bonded to the base film.

[0035] Figure 2 The experimental comparative examples show the hollow fiber mullite ceramic membrane (M0) prepared in the experimental comparative examples, the M / S-TiNTs photocatalytic hollow fiber ceramic membrane in Example 1, and the M / S-TiNTs@Ba in Example 2. 0.7 Ca 0.3 A comparison of water contact angles of TiO3 piezoelectric photocatalytic hollow fiber ceramic membranes. The initial water contact angle (WCA) of the M / S-TiNTs membrane decreased from 40±5° for M0 to 10±5°, and the water droplet cooled to 0° on the M / S-TiNTs surface within 30 ms, significantly faster than the 90 ms for M0. Specifically, the M / S-TiNTs@Ba... 0.7 Ca 0.3 Water droplets on the TiO3 film surface cooled to 0°C within 10 ms, indicating a significant enhancement in the hydrophilicity of both the photocatalytic and piezoelectric photocatalytic films. This is mainly attributed to two factors: firstly, the increased content of hydrophilic substances, particularly S-TiNTs and Ba... 0.7 Ca 0.3The introduction of TiO3 increases the number of oxygen groups in the membrane; secondly, the smoother surface reduces the contact area between the membrane and oil droplets, further enhancing hydrophilicity. The enhanced surface hydrophilicity allows the membrane to bind more water molecules, forming a hydration layer that provides energy and a spatial barrier for oil droplet diffusion, thereby achieving underwater superoleophobicity.

[0036] Figure 3 The hollow fiber mullite ceramic membrane (M0) prepared in the experimental comparative example and the M / S-TiNTs@Ba in Example 1 are shown. 0.7 Ca 0.3 A comparison of the permeation flux changes of TiO3 piezoelectric photocatalytic hollow fiber ceramic membranes during piezoelectric photocatalytic self-cleaning (40 kHz, λ>320 nm, 0.1 MPa, flow rate: 1.7 L / min) after separating produced water from oilfields is presented. The results show that under pulsed pressure (0.1 MPa, flow rate: 1.7 L / min) for 1 hour per filtration cycle, the filtered composite membrane was simultaneously subjected to ultrasonic cleaning (40 kHz) and xenon lamp irradiation (λ>320 nm) for 30 minutes. Over time, the permeation flux of Mo decreased significantly, possibly due to its large pore size and rough surface. The concentration of produced water before separation was 1035 ppm, which decreased to 776 ppm after separation. In contrast, the permeation flux of M / S-TiNTs@Ba 0.7 Ca 0.3 The flux recovery rates of TiO3 were 94.5% and 93.6%, significantly higher than that of M0. After separation, the concentration in the produced water decreased to 13 ppm, demonstrating the stability of the piezoelectric photocatalytic active layer and showcasing the self-cleaning and regeneration capabilities of the composite membrane. The illustration shows the M / S-TiNTs@Ba prepared in Example 1. 0.7 Ca 0.3 Comparison of photos of a TiO3 piezoelectric photocatalytic hollow fiber ceramic membrane after (a) continuous filtration of oilfield produced water for 1 hour, (b) cleaning with xenon lamp and ultrasound for 30 minutes, and (c) cleaning with xenon lamp and ultrasound again for 30 minutes. After 1 hour of oil-water emulsion contamination, the membrane changed from white to brownish-yellow. After 30 minutes of ultrasonic and xenon lamp irradiation, the membrane color returned to light yellow, indicating that the piezoelectric photocatalyst effectively degraded the contaminants on the membrane surface. Under the same conditions, after another 1 hour of oil-water emulsion contamination, and then catalyzed by ultrasound and xenon lamp simultaneously for 30 minutes, the modified membrane surface returned to its original white color, proving that the reactive oxygen species (ROS) generated by the piezoelectric photocatalytic functional layer can effectively degrade contaminants on the membrane surface and have a certain degree of stability.

[0037] Figure 4 The M / S-TiNTs@Ba prepared in Example 1 are shown. 0.7 Ca 0.3Comparison of 500 mg / L tetracycline (TC) separation before and after using a TiO3 piezoelectric photocatalytic hollow fiber ceramic membrane. 500 mg / L TC was separated using an M / S-TiNTs@Ba 0.7 Ca 0.3 After six separations of 50 mL solution with TiO3, the concentration after separation decreased to 192.2 ± 10.0 mg / L, and the separation efficiency reached 61.6 ± 2.0%, indicating that the piezoelectric photocatalytic composite membrane has a good adsorption and separation effect on tetracycline.

[0038] This invention provides a method for preparing a self-cleaning hollow fiber ceramic membrane material, particularly a piezoelectric photocatalyst-modified hollow fiber ceramic membrane. This membrane offers the following advantages: the preparation method is simple; the membrane material exhibits excellent hydrophilicity and antifouling properties, as well as good piezoelectric photocatalytic self-cleaning ability; it maintains a high initial flux; and it significantly reduces the impact of membrane surface fouling on the entire life cycle of the membrane material, thereby reducing replacement costs. In summary, this invention provides a solid research foundation for industrial and environmental water treatment fields, and offers an effective solution for catalyst recovery and membrane self-cleaning.

Claims

1. A piezoelectric photocatalytic self-cleaning hollow fiber ceramic membrane, characterized in that: A hollow fiber ceramic composite membrane with photocatalytic self-cleaning properties was obtained by using self-made or commercially available hollow fiber ceramics as the base film and non-metallic element-doped titanium dioxide nanotubes as the photocatalyst, which were then immobilized on the surface of the ceramic base film using a vacuum-assisted dip-coating method and a low-temperature sintering method. Subsequently, a piezoelectric photocatalyst was grown in situ using a hydrothermal method to prepare a piezoelectric photocatalytic self-cleaning hollow fiber ceramic composite membrane. The specific preparation method of the above composite membrane is as follows: (1) Preparation of photocatalytic composite membrane: ① Preparation of non-metallic element-doped titanium dioxide (TiO2) nanotube photocatalyst: First, a magnetic oscillator and a certain amount of water were added to the lining of a polytetrafluoroethylene hydrothermal reactor. A certain concentration of NaOH was slowly added dropwise, and the mixture was stirred at room temperature for a certain time until the solution was uniformly mixed. A certain amount of TiO2 nanoparticles were added, and the mixture was stirred for a certain time to obtain a stable and uniform suspension. The magnetic oscillator was removed, and the inner liner of the reactor was embedded into the outer liner. After sealing, the reactor was placed in a high-temperature forced-air drying oven and heated for a period of time. After the reactor cooled, the product was removed from the lining of the hydrothermal reactor and treated by washing with water and acid until neutral to obtain tubular sodium tritiate (Na2Ti3O7). Then, it was mixed with one of the following: a sulfur-containing compound, a nitrogen-containing compound, or a carbon-containing compound, in a certain mass ratio and ground. The mixture was then placed in a tube furnace and sintered for a period of time under an argon atmosphere and at a certain temperature to obtain a non-metallic element-doped TiO2 nanotube photocatalyst. ② Vacuum filtration: The photocatalyst prepared in step ① above is uniformly dispersed in deionized water, and an appropriate volume of the dispersion is fixed on the outer surface of the hollow fiber ceramic substrate membrane by vacuum-assisted dip coating. ③ Low-temperature sintering: Calcination at a certain temperature for a certain time yields a hollow fiber ceramic composite membrane with photocatalytic self-cleaning function; (2) Formation of piezoelectric photocatalytic composite film: ① Hydrothermal in-situ growth: By preparing solutions of Na2Ti3O7, Ba(OH)2·8H2O and Ca(OH)2 of a certain concentration, the photocatalytic membrane is immersed in the above solutions and hydrothermal growth is carried out at a certain temperature; ② Vacuum sintering: Vacuum annealing is performed at a certain temperature and time to obtain the piezoelectric photocatalytic film Mo / S-TiNTs@Ba 1- x Ca x TiO3, x = 0.1~0.

9.

2. The piezoelectric photocatalytic self-cleaning hollow fiber ceramic membrane according to claim 1, characterized in that: In step (1), a 10 mol / L NaOH solution was slowly added dropwise to the lining of the reactor. The solution was mixed uniformly by magnetic stirring at room temperature for 5 min. 0.9785 g of TiO2 nanoparticles were added, and stirring was continued for 30 min to obtain a stable and uniform suspension. The magnetic stir bar was removed, and the inner liner of the reactor was embedded into the outer liner. After sealing, the reactor was placed in a high-temperature forced-air drying oven and heated to 150 °C for 12 h. After the reactor cooled, the product was removed from the oven and treated by water washing, acid washing, and magnetic stirring for 12 h until neutral, to obtain sodium tritiate nanotubes. The sulfur-containing compound was selected from thiourea and carbon disulfide, the nitrogen-containing compound was selected from urea and melamine, and the carbon-containing compound was selected from polyvinyl alcohol and biomass carbon. The mass ratio of Na2Ti3O7 powder to one of the above compounds was 1:0.1 to 1:

1. The argon atmosphere flow rate was 200 sccm, and the tube furnace sintering temperature was 200 °C to 900 °C. °C, for 1–2 hours.

3. The piezoelectric photocatalytic self-cleaning hollow fiber ceramic membrane according to claim 1, characterized in that: The base membrane is selected from either Al2O3 or mullite hollow fiber ceramic membrane; in the vacuum filtration step of the photocatalytic composite membrane preparation, the concentration of non-metallic element-doped TiO2 nanotubes in deionized water is 0.05-0.5 g / L; the pressure of the circulating water vacuum pump is -0.088 MPa.

4. The piezoelectric photocatalytic self-cleaning hollow fiber ceramic membrane according to claim 1, characterized in that: The volume of the non-metallic element-doped TiO2 nanotube aqueous solution is any one of 50, 75, 100, 125, 150, or 200 mL. After filtration, the solution is sintered in a high-temperature box furnace at a low temperature of 300 °C to 700 °C for 1 to 2 h to obtain a photocatalytic composite membrane.

5. The piezoelectric photocatalytic self-cleaning hollow fiber ceramic membrane according to claim 1, characterized in that: In the hydrothermal in-situ growth, the concentration of Na₂Ti₃O₇ was 15–35 mmol / L, and the concentrations of Ba(OH)₂·8H₂O and Ca(OH)₂ were 20–40 mmol / L and 25–35 mmol / L, respectively, with a molar ratio of Ba(OH)₂·8H₂O to Ca(OH)₂ of 1:9–9:

1. The reactor was kept at 180 °C–220 °C for 0.125–6 h, and the tube furnace was vacuum annealed at 240 °C–395 °C for 40–200 min to obtain the piezoelectric photocatalytic film Mo / S-TiNTs@Ba 1-x Ca x TiO3, x=0.1~0.9.

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