Method for producing a cellulose composite separation membrane having piezoelectric effect

Abstract

The application discloses a preparation method of a cellulose composite separation membrane with a piezoelectric effect, and comprises the following steps: step 1, hydroxylation modification of inorganic piezoelectric fillers; step 2, preparation of a casting solution; step 3, blade casting; step 4, coupling treatment of phase separation-saponification regeneration-electric field polarization; and step 5, post-treatment after film formation. In the application, cellulose acetate is used as a film forming matrix, the inorganic piezoelectric fillers are subjected to hydroxylation modification, and a crystallization regulation component is introduced as a crystallization enhancement and interface regulation component; a non-solvent induced phase separation-in-situ saponification regeneration-synchronous electric field polarization coupling process is adopted, so that pore forming, crystal type reconstruction and dipole polarization are completed in one step, and a biomass-based piezoelectric composite separation membrane is constructed.

Description

Technical Field

[0001] This invention relates to the field of piezoelectric functional composite membrane materials, specifically a method for preparing a cellulose composite separation membrane with piezoelectric effect. Background Technology

[0002] Membrane separation technology, with its advantages of high efficiency and energy saving, no phase change required, and simple operation, has been widely used in seawater desalination, wastewater treatment, and wastewater reuse. However, membrane fouling remains a bottleneck restricting the long-term operation of membrane technology. Organic pollutants, microorganisms, colloids, etc., adsorb and clog the membrane surface or pores, leading to decreased flux, increased energy consumption, and shortened lifespan. Traditional physical and chemical cleaning are "post-treatment" strategies, which have limited effectiveness, are prone to membrane damage, and can cause secondary pollution. Therefore, developing green separation membrane materials with intrinsic antifouling properties has become a research hotspot.

[0003] The piezoelectric effect enables bidirectional conversion between mechanical and electrical energy. In the membrane separation process, the mechanical vibrations generated by fluid pressure during water treatment can induce in-situ micro-electric fields, dielectric forces, and reactive oxygen species on the membrane surface. This can inhibit pollutant adsorption and adhesion at the source, making it an effective way to construct intrinsically antifouling membranes and a cutting-edge antifouling strategy. Existing piezoelectric technologies or piezoelectric separation membranes mostly use petroleum-based fluoropolymers such as PVDF as the substrate, doping them with graphene oxide or inorganic salts, or combining them with electric field polarization (for example, application number 202411592692.3 discloses a piezoelectric nanofiltration membrane with electrodynamic anti-fouling function, its preparation method, and its application), to improve the piezoelectric phase content and antifouling performance of PVDF membranes. However, these fluorinated materials have drawbacks such as non-biodegradability, high environmental accumulation risk, and non-renewable raw materials, which contradict increasingly stringent global environmental regulations (such as fluorine bans) and "dual carbon" goals.

[0004] Cellulose, as the most abundant natural polymer in nature, has advantages such as being renewable, biodegradable, hydrophilic, and having excellent film-forming properties, making it an ideal green material to replace fluoropolymers. Studies have shown that cellulose possesses piezoelectric properties due to its non-centrosymmetric crystal structure (such as the triclinic crystal system of cellulose type I and the monoclinic crystal system of cellulose type II). However, the crystal structure limits its piezoelectric performance to be extremely weak; the piezoelectric output voltage of pure regenerated cellulose membranes is typically below 0.3V, or even only tens of millivolts, far from meeting the needs of practical applications.

[0005] To improve the piezoelectric properties of cellulose, theoretically, three strategies can be adopted: first, adding high-piezoelectric inorganic fillers (such as barium titanate, zinc oxide, etc.); second, directly using highly crystalline nanocellulose (such as CNC, CNF, MCC, etc.), but this is costly and difficult to form into separation membranes; third, constructing non-centrosymmetric crystalline structures by inducing crystallization through process control. However, conventional composite methods suffer from technical bottlenecks such as easy aggregation of inorganic fillers, weak interfacial bonding with the cellulose matrix, low cellulose crystallinity, weak piezoelectric response, and difficulty in synergizing membrane pore structure and flux-retention performance. Existing PVDF-based piezoelectric membrane preparation processes are also unsuitable for biomass cellulose systems and lack an integrated molding process for controlling the saponification crystal structure of the cellulose matrix, modifying the filler interface, and synergizing electric field polarization. Therefore, how to significantly improve the piezoelectric activity of cellulose-based membranes while maintaining their green properties and excellent separation performance is a technical challenge that urgently needs to be solved in this field. Summary of the Invention

[0006] To address the shortcomings of existing technologies, this invention provides a method for preparing a cellulose composite separation membrane with piezoelectric effect.

[0007] The technical solution of this invention to solve the aforementioned technical problem is to provide a method for preparing a cellulose composite separation membrane with piezoelectric effect, the method comprising the following steps: Step 1: The inorganic piezoelectric filler is surface-hydroxylated using a hydroxylation modification method to obtain hydroxylated inorganic piezoelectric filler; Step 2: Dissolve the film-forming polymer, the hydroxylated inorganic piezoelectric filler prepared in Step 1, the crystallization regulating component and the pore-forming agent completely in an organic solvent, and after standing to remove bubbles, obtain a homogeneous casting solution. Step 3: Uniformly coat the casting solution prepared in Step 2 onto the substrate surface to form a nascent liquid film; Step 4: Immerse the substrate with the nascent liquid film in an alkaline coagulation bath, and simultaneously apply a DC electric field to perform non-solvent-induced phase separation, in-situ saponification regeneration and electric field polarization synergistic treatment to solidify and form a cellulose solid-phase composite membrane. Step 5, Post-film treatment: Take out the cellulose solid-phase composite membrane obtained in step 4, soak it to remove residual organic solvents and pore-forming agents, and freeze-dry it to obtain a cellulose composite separation membrane with piezoelectric effect.

[0008] Compared with the prior art, the beneficial effects of the present invention are as follows: (1) In this invention, cellulose acetate is used as the film-forming matrix, inorganic piezoelectric filler is modified by hydroxylation, and crystallization regulation components are introduced as crystallization enhancement and interface regulation components. The non-solvent-induced phase separation-in-situ saponification regeneration-synchronous electric field polarization coupling process is adopted to complete pore formation, crystal reconstruction and dipole polarization in one step to construct a biomass-based piezoelectric composite separation membrane.

[0009] (2) Based on the inherent but weak piezoelectric properties of regenerated cellulose, this invention utilizes inorganic piezoelectric fillers to enhance the piezoelectric performance of the separation membrane, and simultaneously uses the heterogeneous nucleation effect of crystallization-regulated components to inhibit the aggregation of inorganic piezoelectric fillers, thereby improving the crystallization order of cellulose and improving the dispersibility of fillers; through saponification and regeneration, a type II monoclinic non-centrosymmetric crystal structure of regenerated cellulose is constructed, and the electric field polarization induces dipole orientation.

[0010] (3) The crystallization regulating component of the present invention acts as a crystallization nucleating agent, interface bridging agent and pore structure regulating agent. It induces the formation of a highly crystalline monoclinic cellulose type II crystal structure in the cellulose base film through hydrogen bonding and promotes the uniform dispersion of hydroxylated inorganic piezoelectric filler in the base film.

[0011] (4) The in-situ saponification hydrolysis of the present invention deacetylates cellulose acetate to generate regenerated cellulose, enriches the polymer hydroxyl groups and enhances the hydrophilicity of the separation membrane, and simultaneously constructs a type II monoclinic non-centrosymmetric crystal structure of regenerated cellulose, giving the matrix an intrinsic piezoelectric basis.

[0012] (5) The composite membrane obtained by this invention possesses the characteristics of being green and biodegradable, having excellent hydrophilicity, high porosity, high flux, and high retention and separation capabilities for dye / protein pollutants. It also exhibits intrinsic antifouling properties driven by piezoelectricity. During water treatment, it spontaneously generates a piezoelectric effect through pressure, forming charge repulsion and dielectric force to repel pollutants, and generates active oxygen in situ to inhibit microbial adhesion, thereby suppressing the adsorption and deposition of pollutants on the membrane surface. Its piezoelectric response voltage is 0.8~1.8V, and its pure water flux is ≥200L•m. -2 •h -1 With an organic dye rejection rate of ≥80% and a total pollution ratio of ≤40% for protein pollutants, it meets the long-term operation requirements of water treatment and can be widely used in the separation, purification, and resource reuse of organic dye wastewater, protein-based wastewater, and industrial organic wastewater. Attached Figure Description

[0013] Figure 1 The infrared spectrum of barium titanate in Example 1 of this invention; Figure 2 The infrared spectrum of barium titanate hydroxylated according to Example 1 of the present invention; Figure 3 This is a scanning electron microscope image of the surface morphology of the cellulose separation membrane in Comparative Example 1 of the present invention. Figure 4 This is a scanning electron microscope image of the surface morphology of the cellulose composite separation membrane in Example 6 of the present invention; Figure 5 The X-ray diffraction pattern of the cellulose separation membrane crystal structure of Comparative Example 1 of this invention is shown below. Figure 6The X-ray diffraction pattern of the cellulose composite separation membrane crystal structure in Example 6 of this invention is shown. Figure 7 This is a piezoelectric output voltage diagram of the cellulose separation membrane in Comparative Example 1 of the present invention; Figure 8 This is a piezoelectric output voltage diagram of the cellulose composite separation membrane in Example 6 of the present invention; Figure 9 The graph shows the filtration efficiency and antifouling ratio of the cellulose separation membrane in Comparative Example 1 of this invention. Figure 10 This is a graph showing the filtration efficiency and antifouling ratio of the cellulose composite separation membrane in Example 6 of the present invention. Detailed Implementation

[0014] Specific embodiments of the present invention are given below. These specific embodiments are only used to further illustrate the present invention in detail and do not limit the scope of protection of the present invention.

[0015] This invention provides a method for preparing a cellulose composite separation membrane with piezoelectric effect (hereinafter referred to as the method), which includes the following steps: Step 1, Hydroxylation modification of inorganic piezoelectric fillers: The inorganic piezoelectric fillers are surface-hydroxylated using a hydroxylation modification method to obtain hydroxylated inorganic piezoelectric fillers; Preferably, in step 1, the inorganic piezoelectric filler is barium titanate (BTO), zinc oxide, or molybdenum disulfide (preferably barium titanate).

[0016] Preferably, in step 1, the hydroxylation modification method is hydrogen peroxide oxidation, plasma treatment, or ultrasound-assisted chemical reaction.

[0017] Preferably, in step 1, the hydrogen peroxide oxidation method specifically involves: mixing the inorganic piezoelectric filler with hydrogen peroxide solution until homogeneous, and then refluxing the reaction; after the reaction is completed, centrifuging and retaining the precipitate, then washing until neutral, and drying to obtain the hydroxylated inorganic piezoelectric filler.

[0018] Preferably, in step 1, the concentration of the hydrogen peroxide solution is 30 wt%; the mass of the inorganic piezoelectric filler accounts for 4-6 wt% of the sum of the masses of the inorganic piezoelectric filler and the hydrogen peroxide solution. The process for achieving uniform mixing is as follows: using a water bath ultrasonic method, with a temperature of 20~65℃, a frequency of 20~45kHz, a power of 300~600W, and a time of 25~35min; The reflux reaction process is as follows: temperature 110~130℃, time 7~9h; The drying process is as follows: temperature 55~65℃, time 10~30h. Vacuum drying is preferred.

[0019] The hydroxyl content on the surface of inorganic piezoelectric fillers modified by hydrogen peroxide oxidation is increased by 75%~85%, while maintaining the integrity of their characteristic crystal structure with inherent piezoelectric properties; among them, barium titanate maintains the integrity of perovskite crystal structure, zinc oxide maintains the integrity of hexagonal wurtzite crystal structure, and molybdenum disulfide maintains the integrity of tetragonal crystal phase structure.

[0020] Preferably, in step 1, the plasma treatment method specifically involves: placing the inorganic piezoelectric filler in a plasma chamber, evacuating it, and then introducing water vapor and oxygen to maintain the working pressure at 20~100Pa; then turning on the radio frequency power supply, setting the discharge power to 100~250W, and the treatment time to 10~60min; then centrifuging and retaining the precipitate, washing to remove ungrafted material from the surface, and drying to obtain the hydroxylated inorganic piezoelectric filler.

[0021] Preferably, in step 1, the vacuum degree of the plasma chamber is 5~10 Pa; the volume ratio of water vapor to oxygen is 15~5:1. The drying process involves a temperature of 55-65℃ and a time of 12-24 hours. Vacuum drying is preferred.

[0022] The surface hydroxyl content of the inorganic piezoelectric filler modified by plasma treatment is increased by 50%~65%, while maintaining the integrity of its characteristic crystal structure with inherent piezoelectric properties; among them, barium titanate maintains the integrity of perovskite crystal structure, zinc oxide maintains the integrity of hexagonal wurtzite crystal structure, and molybdenum disulfide maintains the integrity of tetragonal crystal phase structure.

[0023] High-energy particles in the plasma act on the surface of the inorganic piezoelectric filler. Hydroxyl radicals (·OH) generated by the dissociation of water vapor can introduce hydroxyl groups, while oxygen helps to replenish reactive oxygen species and remove surface contaminants.

[0024] Step 2, Preparation of casting solution: The film-forming polymer, the hydroxylated inorganic piezoelectric filler prepared in step 1, the crystallization regulating component and the pore-forming agent are completely dissolved in an organic solvent. After standing and degassing, a homogeneous casting solution is obtained. Preferably, in step 2, the film-forming polymer is cellulose acetate (CA), specifically at least one of cellulose monoacetate, cellulose diacetate, and cellulose triacetate (CTA) with different degrees of substitution (preferably cellulose diacetate and / or cellulose triacetate). Preferably, in step 2, the crystallization regulating component is highly crystalline cellulose nanopowder, specifically at least one of microcrystalline cellulose (MCC), cellulose nanocrystals, and cellulose nanofibers.

[0025] Preferably, in step 2, the pore-forming agent is polyvinylpyrrolidone (PVP).

[0026] Preferably, in step 2, the organic solvent is at least one selected from 1,4-dioxane, N,N-dimethylformamide, N,N-dimethylacetamide, and N-methylpyrrolidone.

[0027] Preferably, in step 2, the mass percentages of each component in the casting solution are as follows: film-forming polymer 4~10wt% (preferably 7wt%), hydroxylated inorganic piezoelectric filler 0.25~1.0wt% (preferably 0.75wt%), crystallization regulating component 0.25~1.75wt% (preferably 1.50wt%), pore-forming agent 0.2~1.0wt% (preferably 0.7wt%), and the remainder being organic solvent.

[0028] Preferably, in step 2, the dissolution process is as follows: stirring is used at a speed of 600~1200 rpm, a temperature of 25~75℃, and a time of 6~10 hours. Preferably, in step 2, the standing degassing time is 20~28h, and the temperature is 20~45℃; Step 3, Film Forming: The casting liquid prepared in Step 2 is uniformly coated onto the substrate surface using a doctor blade to form a primary liquid film; Preferably, in step 3, the thickness of the doctor blade coating is 100~500μm.

[0029] Preferably, in step 3, the substrate is a clean, flat glass plate.

[0030] Step 4, Phase separation-saponification regeneration-electric field polarization coupling treatment: The substrate with the nascent liquid film is immersed in an alkaline coagulation bath, and a DC electric field is applied simultaneously to perform non-solvent-induced phase separation, in-situ saponification regeneration and electric field polarization synergistic treatment to solidify and form a cellulose solid phase composite membrane. Preferably, in step 4, the alkaline coagulation bath is a 0.1~1.0 mol / L aqueous solution of sodium hydroxide or potassium hydroxide; Preferably, in step 4, the immersion process is: the temperature is 20~40℃ and the time is 10~40min.

[0031] Preferably, in step 4, the intensity of the DC electric field is 100~1000V / mm (preferably 600V / mm), and its direction is perpendicular to the surface of the nascent liquid film.

[0032] Step 5, Post-film treatment: Take out the cellulose solid-phase composite membrane obtained in step 4, soak it to remove residual organic solvents and pore-forming agents, and freeze-dry it to obtain a cellulose composite separation membrane with piezoelectric effect.

[0033] Preferably, in step 5, the soaking process is as follows: soaking in deionized water for 20-48 hours at a temperature of 20-40°C.

[0034] Preferably, in step 5, the freeze-drying process is as follows: temperature -60~-20℃, time 12~48h.

[0035] The test method in this embodiment is as follows: The chemical structures of the inorganic piezoelectric filler before and after hydroxylation modification were characterized using a Fourier transform infrared spectroscopy (FTIR, Nicolet NEXUS-670, USA) via potassium bromide (KBr) pellet method. Specific test conditions were as follows: 4 cm⁻¹ -1 The resolution is between 4000 and 600 cm. -1 Scan the area 32 times; The microstructure of the separation membranes in the examples and comparative examples was observed using a field emission scanning electron microscope (FE-SEM, SU8010, Hitachi, Japan). All membrane samples were first freeze-dried, then vacuum sputtered with gold, and observed at 5kV. The crystallization properties of the separation membranes of the examples and comparative examples were characterized at room temperature in the range of 2θ = 5 to 60° using an X-ray diffractometer (Miniflex 600, Rigaku Corporation, Japan) equipped with a Cu Kα source (λ = 1.5406 Å). The scanning speed was 5° / min, the voltage was 40 kV, and the current was 150 mA. The piezoelectric properties of the separation membranes in the examples and comparative examples were tested using a piezoelectric performance testing device. The membrane samples were fixed and connected to an electrometer. The membrane samples were cyclically struck under a pressure of 0.1 MPa to form mechanical stimulation. The striking frequency of the linear motor system was adjusted to once per second. The open-circuit voltage signal output by the electrometer was measured and recorded. Cross-flow filtration antifouling test was conducted: the membranes under test were placed in the filtration device and pre-filtered with deionized water until the flux stabilized, and the initial water flux was recorded; then, the solution was switched to a prepared BSA simulated contaminant solution for dynamic cross-flow filtration, and the filtration flux was recorded periodically until the flux tended to stabilize, completing the contamination stage test; after that, the membranes were rinsed with deionized water, and the water flux after rinsing was recorded after the flux returned to stability; at the same time, the BSA contaminant solution and permeate were collected before and after filtration, and their absorbance was measured by ultraviolet spectrophotometer. The contaminant concentration was calculated by combining the BSA standard curve, and then the filtration efficiency (retention rate) of each membrane and the change in filtration efficiency before and after rinsing were calculated.

[0036] Example 1: Step 1, Barium titanate hydroxylation modification: BTO powder was dispersed in a 30wt% hydrogen peroxide solution, with the mass of BTO accounting for 5wt% of the sum of the masses of BTO and hydrogen peroxide solution; then it was placed in an ultrasonic device and ultrasonically treated at 25℃, 40kHz frequency, and 400W power for 30 min; then refluxed at 120℃ for 8 h; after the reaction was completed, the precipitate was centrifuged and retained, then washed with deionized water until neutral, and then vacuum dried at 60℃ for 12 h to constant weight to obtain hydroxylated barium titanate (BTO-OH), with a yield of approximately 76%; Step 2, Preparation of casting solution: 7 wt% CTA, 0.75 wt% BTO-OH, 0.25 wt% MCC, 0.7 wt% PVP and 91.3 wt% 1,4-dioxane were placed in a magnetic stirrer at 1000 rpm and stirred at 70°C for 8 h until completely dissolved into a homogeneous solution; then allowed to stand at 40°C for 24 h to remove bubbles, resulting in a homogeneous casting solution. Step 3, Film Forming: The casting solution is scraped and evenly coated onto the surface of a clean and flat glass plate using a doctor blade to form a 400μm thick nascent liquid film. Step 4, Phase separation-saponification regeneration-electric field polarization coupling treatment: The glass plate with the nascent liquid film obtained in Step 3 is immersed in a 25℃, 0.5mol / L NaOH aqueous solution coagulation bath, and a high voltage electric field of 600V / mm with the direction perpendicular to the surface of the nascent liquid film is applied simultaneously to perform non-solvent-induced phase separation, in-situ saponification regeneration and electric field polarization synergistic treatment and solidification for 30min to obtain a cellulose solid phase composite membrane; Step 5, Post-film treatment: Take out the cellulose solid-phase composite membrane obtained in step 4, soak it in deionized water at 25℃ for 24h to remove residual organic solvents and additives, and then freeze-dry it at -50℃ for 24h to obtain a cellulose composite separation membrane with piezoelectric effect (hereinafter referred to as cellulose composite separation membrane).

[0037] Depend on Figure 1 It can be seen that the unhydroxylated BTO nanoparticles only exhibit two characteristic absorption peaks, one of which is located at 1400 cm⁻¹. -1 The spectral band at that location corresponds to the -CO3 produced by barium carbonate (BaCO3) in BaTiO3. 2- The stretching vibration is located at 543cm. -1 The band at that location represents the Ti-O vibration of BaTiO3.

[0038] Depend on Figure 2 It can be seen that, in addition to exhibiting the two characteristic peaks of BTO, the BTO-OH nanoparticles also show a peak at 3427 cm⁻¹. -1 A relatively broad characteristic peak appeared at the point, which is attributed to the stretching vibration of surface -OH, indicating the introduction of hydroxyl groups into BTO.

[0039] The piezoelectric performance test results show that the output voltage of the cellulose composite separation membrane obtained in this embodiment is 0.50V.

[0040] The antifouling performance test results show that the separation efficiency of the cellulose composite separation membrane obtained in this embodiment is 69.4%, the cleaning efficiency is 59.51%, and the corresponding total contamination ratio is 40.95%, demonstrating high efficiency and low contamination characteristics.

[0041] Example 2: This embodiment is the same as Embodiment 1, except that in step 2, the mass percentage of MCC is 0.50 wt%. The piezoelectric performance test results show that the output voltage of the cellulose composite separation membrane obtained in this embodiment is 0.74V.

[0042] The antifouling performance test results show that the separation efficiency of the cellulose composite separation membrane obtained in this embodiment is 71.5%, the cleaning efficiency is 60.03%, and the corresponding total contamination ratio is 40.40%, demonstrating high efficiency and low contamination characteristics.

[0043] Example 3: This embodiment is the same as Embodiment 1, except that in step 2, the mass percentage of MCC is 0.75 wt%. The piezoelectric performance test results show that the output voltage of the cellulose composite separation membrane obtained in this embodiment is 1.05V.

[0044] The antifouling performance test results show that the separation efficiency of the cellulose composite separation membrane obtained in this embodiment is 72.8%, the cleaning efficiency is 60.44%, and the corresponding total contamination ratio is 40.13%, demonstrating high efficiency and low contamination characteristics.

[0045] Example 4: This embodiment is the same as Embodiment 1, except that in step 2, the mass percentage of MCC is 1.00 wt%. The piezoelectric performance test results show that the output voltage of the cellulose composite separation membrane obtained in this embodiment is 1.30V.

[0046] The antifouling performance test results show that the separation efficiency of the cellulose composite separation membrane obtained in this embodiment is 74.3%, the cleaning efficiency is 61.76%, and the corresponding total contamination ratio is 40.02%, demonstrating high efficiency and low contamination characteristics.

[0047] Example 5: This embodiment is the same as Embodiment 1, except that in step 2, the mass percentage of MCC is 1.25 wt%. The piezoelectric performance test results show that the output voltage of the cellulose composite separation membrane obtained in this embodiment is 1.65V.

[0048] The antifouling performance test results show that the separation efficiency of the cellulose composite membrane obtained in this embodiment is 75.4%, the cleaning efficiency is 61.97%, and the corresponding total contamination ratio is 39.57%, demonstrating high efficiency and low contamination characteristics.

[0049] Example 6: This embodiment is the same as Embodiment 1, except that in step 2, the mass percentage of MCC is 1.50 wt%. Depend on Figure 4 As can be seen, with the introduction of BTO-OH particles and the increase of MCC content, the surface roughness of the cellulose composite separation membrane obtained in this embodiment increases significantly and a porous structure appears. This is because instantaneous phase separation occurs during the phase transformation process. However, MCC and BTO-OH do not exhibit self-particle aggregation, indicating that they can form a uniform dispersion and stable anchoring with the cellulose matrix through hydrogen bonding.

[0050] Depend on Figure 6 It can be seen that the diffraction peak intensity of the cellulose composite separation membrane obtained in this embodiment is significantly enhanced. This is due to the high crystallinity of MCC itself, which can act as a heterogeneous crystal nucleating agent to induce the orderly arrangement of cellulose matrix molecular chains through intermolecular hydrogen bonding, reduce the proportion of amorphous regions, and thus effectively improve the overall crystallinity of the composite membrane, providing a key structural basis for enhancing dipole moment orientation and reducing charge relaxation loss.

[0051] The piezoelectric performance test results show (see) Figure 8 The output voltage of the cellulose composite separation membrane obtained in this embodiment is 1.80V.

[0052] The results of the anti-pollution performance test show (see) Figure 10 The cellulose composite separation membrane obtained in this embodiment has a separation efficiency of 75.9%, a cleaning efficiency of 62.24%, and a corresponding total contamination ratio as high as 38.95%, demonstrating high efficiency and low contamination characteristics.

[0053] Comparative Example 1: Step 1, Preparation of casting solution: Place 7wt% CTA, 0.7wt% PVP and 92.3wt% 1,4-dioxane in a magnetic stirrer at 1000 rpm and stir at 70℃ for 8 hours until completely dissolved into a homogeneous solution; then let stand at 40℃ for 24 hours to remove bubbles, and obtain a homogeneous casting solution. Step 2 of this comparative example is the same as step 3 of Example 1, step 3 of this comparative example is the same as step 4 of Example 1, and step 4 of this comparative example is the same as step 5 of Example 1, thus obtaining a cellulose separation membrane.

[0054] Depend on Figure 3 It can be seen that the surface of the cellulose separation membrane obtained in the comparative example exhibits a relatively dense and smooth porous separation membrane texture structure, indicating that neither phase separation nor saponification reaction has a significant impact on or damage to the membrane structure.

[0055] Depend on Figure 5 It can be seen that the cellulose separation membrane obtained in the comparative example has three diffraction peaks at 2θ=12.1°, 2θ=20.2° and 2θ=21.7°, which belong to the (110), (110) and (200) crystal planes of the cellulose polymer, respectively, showing typical regenerated cellulose type II crystallization characteristics. However, the crystallization peaks are relatively wide, and the surface pure cellulose separation membrane has poor crystallization performance.

[0056] The piezoelectric performance test results show (see) Figure 7 The output voltage of the cellulose separation membrane obtained in this comparative example is 0.25V.

[0057] The results of the anti-pollution performance test show (see) Figure 9 The cellulose separation membrane obtained in this comparative example had a separation efficiency of only 9.7% and a cleaning efficiency of only 26.7%, with a corresponding total contamination ratio as high as 72.88%, showing characteristics of low efficiency and high contamination.

[0058] Any aspects not covered in this invention are applicable to existing technologies.

Claims

1. A method for preparing a cellulose composite separation membrane with piezoelectric effect, characterized in that, The method includes the following steps: Step 1: The inorganic piezoelectric filler is surface-hydroxylated using a hydroxylation modification method to obtain hydroxylated inorganic piezoelectric filler; Step 2: Dissolve the film-forming polymer, the hydroxylated inorganic piezoelectric filler prepared in Step 1, the crystallization regulating component and the pore-forming agent completely in an organic solvent, and after standing to remove bubbles, obtain a homogeneous casting solution. The film-forming polymer is cellulose acetate; the crystallization regulating component is highly crystalline cellulose nanopowder. Step 3: Uniformly coat the casting solution prepared in Step 2 onto the substrate surface to form a nascent liquid film; Step 4: Immerse the substrate with the nascent liquid film in an alkaline coagulation bath, and simultaneously apply a DC electric field to perform non-solvent-induced phase separation, in-situ saponification regeneration and electric field polarization synergistic treatment to solidify and form a cellulose solid-phase composite membrane. Step 5, Post-film treatment: Take out the cellulose solid-phase composite membrane obtained in step 4, soak it to remove residual organic solvents and pore-forming agents, and freeze-dry it to obtain a cellulose composite separation membrane with piezoelectric effect.

2. The method for preparing the cellulose composite separation membrane with piezoelectric effect according to claim 1, characterized in that, In step 1, the inorganic piezoelectric filler is barium titanate, zinc oxide, or molybdenum disulfide; In step 1, the hydroxylation modification method is hydrogen peroxide oxidation, plasma treatment, or ultrasound-assisted chemical reaction.

3. The method for preparing the cellulose composite separation membrane with piezoelectric effect according to claim 2, characterized in that, In step 1, the hydrogen peroxide oxidation method specifically involves: mixing the inorganic piezoelectric filler with hydrogen peroxide solution until homogeneous, then refluxing the reaction; after the reaction is complete, centrifuging and retaining the precipitate, then washing until neutral, and drying to obtain the hydroxylated inorganic piezoelectric filler; The concentration of the hydrogen peroxide solution is 30 wt%; the mass of the inorganic piezoelectric filler accounts for 4-6 wt% of the sum of the masses of the inorganic piezoelectric filler and the hydrogen peroxide solution. The process for achieving uniform mixing is as follows: using a water bath ultrasonic method, with a temperature of 20~65℃, a frequency of 20~45kHz, a power of 300~600W, and a time of 25~35min; The reflux reaction process is as follows: temperature 110~130℃, time 7~9h; The drying process is as follows: temperature is 55~65℃, time is 10~30h.

4. The method for preparing the cellulose composite separation membrane with piezoelectric effect according to claim 2, characterized in that, In step 1, the plasma treatment method specifically involves: placing the inorganic piezoelectric filler in a plasma chamber, evacuating the chamber, and then introducing water vapor and oxygen to maintain the working pressure at 20~100Pa; then turning on the radio frequency power supply, setting the discharge power to 100~250W, and the treatment time to 10~60min; then centrifuging and retaining the precipitate, washing to remove ungrafted material from the surface, and drying to obtain the hydroxylated inorganic piezoelectric filler; The vacuum level of the plasma chamber is 5~10 Pa; the volume ratio of water vapor to oxygen is 15~5:1; The drying process is as follows: temperature is 55~65℃, time is 12~24h.

5. The method for preparing the cellulose composite separation membrane with piezoelectric effect according to claim 1, characterized in that, In step 2, the pore-forming agent is polyvinylpyrrolidone; In step 2, the organic solvent is at least one of 1,4-dioxane, N,N-dimethylformamide, N,N-dimethylacetamide, and N-methylpyrrolidone.

6. The method for preparing a cellulose composite separation membrane with piezoelectric effect according to claim 1 or 5, characterized in that, In step 2, the film-forming polymer is at least one of cellulose monoacetate, cellulose diacetate, and cellulose triacetate; In step 2, the crystallization control component is at least one of microcrystalline cellulose, cellulose nanocrystals, and cellulose nanofibers.

7. The method for preparing the cellulose composite separation membrane with piezoelectric effect according to claim 1, characterized in that, In step 2, the mass percentages of each component in the casting solution are as follows: film-forming polymer 4~10wt%, hydroxylated inorganic piezoelectric filler 0.25~1.0wt%, crystallization regulating component 0.25~1.75wt%, pore-forming agent 0.2~1.0wt%, and the remainder is organic solvent; In step 2, the dissolution process is as follows: stirring is used at a speed of 600~1200 rpm, a temperature of 25~75℃, and a time of 6~10 hours. In step 2, the standing time for degassing is 20~28 hours, and the temperature is 20~45℃.

8. The method for preparing the cellulose composite separation membrane with piezoelectric effect according to claim 1, characterized in that, In step 3, the coating thickness is 100~500μm; In step 3, the substrate is a clean, flat glass plate.

9. The method for preparing the cellulose composite separation membrane with piezoelectric effect according to claim 1, characterized in that, In step 4, the alkaline coagulation bath is a 0.1~1.0 mol / L aqueous solution of sodium hydroxide or potassium hydroxide; In step 4, the immersion process is as follows: temperature is 20~40℃, time is 10~40min; In step 4, the intensity of the DC electric field is 100~1000V / mm, and its direction is perpendicular to the surface of the nascent liquid film.

10. The method for preparing the cellulose composite separation membrane with piezoelectric effect according to claim 1, characterized in that, In step 5, the soaking process is as follows: soaking in deionized water for 20-48 hours at a temperature of 20-40°C; In step 5, the freeze-drying process is as follows: temperature -60~-20℃, time 12~48h.

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