In-situ MOFized stereocomplex polylactic acid micro / nano fiber self-powered filter membrane and preparation method thereof

Abstract

This invention provides an in-situ MOF-modified stereocomposite polylactic acid (PLLA) micro / nanofiber self-powered filter membrane and its preparation method. The method comprises the following steps: ZIF-8 nanocrystals with uniform morphology and stable dimensions are prepared using a combination of microwave-assisted synthesis and template method. The ZIF-8 dispersion is then co-spun with a L-type polylactic acid (PLLA) / D-type polylactic acid (PDLA) blend solution using a combination of electrospraying and electrospinning to prepare the in-situ MOF-modified stereocomposite polylactic acid (PLLA) micro / nanofiber self-powered filter membrane. The prepared in-situ MOF-modified stereocomposite polylactic acid (PLLA) micro / nanofiber self-powered filter membrane exhibits controllable bead and mesoporous morphology, as well as the high specific surface area and surface activity imparted by ZIF-8, resulting in high filtration performance, excellent triboelectric output performance, and good self-cleaning ability. It has broad application prospects in the fields of personal protective equipment and intelligent monitoring.

Description

Technical Field

[0001] This invention belongs to the field of fiber filtration membrane technology, and particularly relates to an in-situ MOF-modified stereocomposite polylactic acid micro / nanofiber self-powered filter membrane and its preparation method. Background Technology

[0002] Particulate matter (PM) pollution has a significant impact on the economy and public health. Because fine PM (aerodynamic diameter ≤ 2.5 μm, i.e., PM2.5) can carry large numbers of bacteria and viruses into the human respiratory system and cause harm, efficient and low-energy strategies are needed to protect the public from severe PM pollution. Simultaneously, to mitigate plastic pollution and microplastic hazards associated with traditional filter materials, the demand for biodegradable air filter materials that effectively remove PM is increasing. Polylactic acid (PLA) is non-toxic, highly biocompatible, and completely biodegradable, making it a promising candidate for widespread application in the air filtration field.

[0003] However, traditional polylactic acid fiber membranes still have the following problems when used as air filtration membranes: (1) relatively low filtration efficiency; (2) poor self-cleaning ability; (3) weak triboelectric output performance.

[0004] Therefore, there is an urgent need to improve polylactic acid fiber filter membranes so that they can be better applied to air filtration. Summary of the Invention

[0005] The purpose of this invention is to overcome the shortcomings of the prior art and provide an in-situ MOF-modified stereocomposite polylactic acid micro / nanofiber self-powered filter membrane and its preparation method, so as to meet the demand for long-lasting air filter membranes.

[0006] The specific technical solution is as follows:

[0007] An in-situ MOF-modified stereocomposite polylactic acid micro / nanofiber self-powered filter membrane is prepared from spinning solution A, spinning solution B, and electro-sprayed ZIF-8 stock solution; the filter membrane has an average nanofiber diameter of 150-1000 nm, an average microfiber diameter of 1-10 μm, a bead size of 1-20 μm, a fiber surface mesopore size of 50-500 nm, and a fiber membrane thickness of 20-600 μm.

[0008] Furthermore, the spinning solution A includes a PLLA / PDLA blend, the mass fraction of which is 0.1–7 wt%; the spinning solution B includes a PLLA / PDLA blend, the mass fraction of which is 8–18 wt%.

[0009] A method for preparing the above-described in-situ MOF-modified stereocomposite polylactic acid micro / nanofiber self-powered filter membrane includes the following steps:

[0010] S1. Preparation of ZIF-8 crystals: ZIF-8 dispersion was prepared by microwave-assisted synthesis of 2-methylimidazole solution and zinc salt, and ZIF-8 crystals were obtained after extraction and drying.

[0011] S2. Preparation of ZIF-8 electro-injection stock solution: Disperse the ZIF-8 crystals obtained in S1 in a solvent and add a dispersant to obtain a stable and uniform electro-injection ZIF-8 stock solution.

[0012] S3. Preparation of electrospinning solution A: PDLA and PLLA are mixed at a certain molar ratio and then dissolved in a mixed solvent composed of a good solvent and a bad solvent to prepare spinning solution A (low concentration);

[0013] S4. Preparation of electrospinning solution B: PDLA and PLLA are mixed in a certain molar ratio and then dissolved in a mixed solvent composed of a good solvent and a bad solvent to prepare spinning solution B (high concentration);

[0014] S5. Preparation of in-situ MOF-based stereocomposite polylactic acid micro / nanofiber self-powered filter membrane: The ZIF-8 electrospraying solution obtained in S2, the spinning solution A obtained in S3, and the spinning solution B obtained in S4 were used to prepare fiber membranes by simultaneous electrospraying / electrospinning. After in-situ annealing, a self-powered MOF-based stereocomposite polylactic acid micro / nanofiber filter membrane was formed.

[0015] Furthermore, in step S1, at least one of the water-soluble zinc salts zinc nitrate, zinc chloride, zinc sulfate, and zinc acetate is used, wherein the concentration of the zinc salt is 0.01–5 mol / L, and the molar ratio of 2-methylimidazole to the zinc salt is 40:1 to 1:40.

[0016] Furthermore, in step S1, the microwave reactor output power is 100-1500W, the reaction temperature is 40-200℃, and the reaction time is 20-120min.

[0017] Furthermore, the dispersant used in step S2 is at least one of polyvinylpyrrolidone, dodecyltrimethylammonium bromide, sodium dodecyl sulfate, and sodium dodecylbenzene sulfonate, and the mass ratio of ZIF-8 to the dispersant is 1:10 to 1:1000.

[0018] Furthermore, the solvent used in step S2 is at least one of dimethylformamide, dichloromethane, chloroform, N-methylpyrrolidone, hexafluoroisopropanol, methanol, ethanol, isopropanol, and glycerol, and the mass fraction of ZIF-8 in the dispersion is 0.01 to 10 wt%.

[0019] Furthermore, the good solvent used in step S3 is at least one of dichloromethane, trichloromethane, N,N-dimethylformamide, N-methylpyrrolidone, hexafluoroisopropanol, tetrahydrofuran, and ethyl acetate, and the bad solvent is at least one of methanol, ethanol, isopropanol, glycerol, butanol, ethylene glycol, and propylene glycol; the molar ratio of PDLA to PLLA in spinning solution A is 1:0.1 to 1:20, the volume ratio of bad solvent to good solvent is 1:1 to 1:10, and the mass fraction of PLLA / PDLA blend in spinning solution A is 0.1 to 7 wt%.

[0020] Furthermore, the good solvent used in step S4 is at least one of dichloromethane, trichloromethane, N,N-dimethylformamide, N-methylpyrrolidone, hexafluoroisopropanol, tetrahydrofuran, and ethyl acetate, and the bad solvent is at least one of methanol, ethanol, isopropanol, glycerol, butanol, ethylene glycol, and propylene glycol; the molar ratio of PDLA to PLLA in spinning solution B is 1:0.1 to 1:20, the volume ratio of bad solvent to good solvent is 1:1 to 1:100, and the mass fraction of PLLA / PDLA blend in spinning solution B is 8 to 18 wt%.

[0021] Furthermore, in step S5, the diameter of the electrospinning needle is 0.06–1.54 mm, the applied electrostatic field voltage is 10–60 kV, the spinning temperature is 20–65 °C, and the relative humidity of the environment is 25%–85%.

[0022] Furthermore, in step S5, the consumption rate of ZIF-8 electrospray solution is 0.1–10 mL / h, the consumption rate of spinning solution A is 0.1–10 mL / h, the consumption rate of spinning solution B is 0.1–10 mL / h, and the receiving distance is 10–30 cm.

[0023] Furthermore, in step S5, the average diameter of the fibers obtained from spinning solution A is 150–1000 nm, and the average diameter of the fibers obtained from spinning solution B is 1–10 μm.

[0024] Compared with the prior art, the present invention has the following advantages and beneficial effects:

[0025] (1) In the preparation method of the in-situ MOF-based stereocomposite polylactic acid micro / nanofiber self-powered filter membrane of the present invention, stereocomposite polylactic acid is prepared by co-spinning of L-polylactic acid (PLLA) and D-polylactic acid (PDLA) to increase the β crystal content and improve the triboelectric output performance. By utilizing the concentration gradient difference of the PDLA / PLLA mixed solution, a micro / nano hierarchical structure is constructed to achieve controllable adjustment of the bead morphology and quantity. By constructing a "polymer-poor solvent-good solvent" ternary system, a controllable mesoporous structure is generated in situ under the phase separation induced by the poor solvent.

[0026] (2) The in-situ MOF-modified stereocomposite polylactic acid micro / nanofiber self-powered filter membrane of the present invention endows the fibers with high specific surface area and surface activity through the beaded / porous structure and the anchoring of ZIF-8 on the fiber surface, thereby improving filtration performance, reducing air resistance, increasing the fiber friction contact area and improving friction output performance. At the same time, the beaded structure and ZIF-8 help to build a superhydrophobic surface, giving the fiber membrane good self-cleaning ability.

[0027] (3) The specific surface area of ​​the in-situ MOF-modified stereocomposite polylactic acid micro / nanofiber self-powered filter membrane of the present invention reaches 330.5-850.5 m². 2 / g, PM0.3 filtration efficiency is 98.3~99.8%, PM2.5 filtration efficiency is 98.8~99.9%, air resistance is less than 100Pa at a flow rate of 85L / min, high dielectric constant (0.65-0.98F / m) and high output performance (output voltage up to 25.6V).

[0028] (4) The in-situ MOF-based stereocomposite polylactic acid micro / nanofiber self-powered filter membrane of the present invention has high filtration performance, excellent triboelectric output performance and good self-cleaning ability, and has broad application prospects in the fields of personal protection and intelligent monitoring. Attached Figure Description

[0029] Figure 1 This is a flowchart of the preparation method of the present invention;

[0030] Figure 2 The image shows a scanning electron microscope image of the in-situ MOF-modified stereocomposite polylactic acid micro / nanofiber self-powered filter membrane obtained in Example 2.

[0031] Figure 3 The water contact angle diagrams are shown for the polylactic acid fiber membranes obtained in Example 2(a) and Comparative Example 2(b);

[0032] Figure 4 Figures show the self-cleaning performance of the polylactic acid micro / nanofiber self-powered filter membrane obtained in Example 2 before (a) and after (b, c) testing. Detailed Implementation

[0033] The following combination Figure 1-4 The detailed description of specific embodiments of the present invention is only for the purpose of providing further explanation of the present invention, and does not constitute a limitation of the present invention.

[0034] Triboelectric nanogenerators (TENGs) are an emerging energy harvesting device capable of effectively collecting various forms of low-frequency mechanical energy. Studies have shown that TENGs can generate high open-circuit voltages of tens to hundreds of volts without ozone emissions, demonstrating significant potential for air pollution control. TENGs can filter PM through the generated triboelectric charge, a technique known as triboelectric air purification. Integrating TENGs into filters allows for the continuous supply of electrostatic charges to the filters, resulting in more efficient adsorption of small particles. Furthermore, TENG-based wearable electronics have been applied in medical monitoring systems to monitor the respiratory status of infected patients, obtaining a wealth of physiologically relevant information and potential disease clues.

[0035] Metal-organic frameworks (MOFs) are novel nanoporous materials composed of a central metal ion or metal cluster and organic ligands coordinated together. They possess repeating structures and ordered spatial arrangements. Compared to traditional porous materials, MOFs exhibit higher specific surface area and porosity, while also possessing characteristics such as uniform structure, numerous adsorption sites, controllable size, and tunable pore size. MOFs can be chemically modified without altering their topology, enabling their application in the fabrication of triboelectric nanogenerators and the expansion of triboelectric series.

[0036] This invention employs a combination of microwave-assisted synthesis and template methods to optimize the preparation conditions of ZIF-8 nanocrystals. Stereoscopic composite polylactic acid is prepared by co-spinning a mixture of L-polylactic acid (PLLA) and D-polylactic acid (PDLA), thereby increasing the content of electroactive β-crystals and improving triboelectric output performance. Utilizing the concentration gradient difference of the PDLA / PLLA mixed solution, micro / nano hierarchical structures are constructed, allowing for controllable adjustment of bead morphology and quantity. By constructing a ternary system of "polymer-poor solvent-good solvent," controllable mesoporous structures are generated in situ under poor solvent-induced phase separation. High-dielectric, high-specific-surface-area ZIF-8 is anchored on the fiber surface using an electrospray method, increasing the specific surface area and surface activity, resulting in fiber membranes with high filtration efficiency, excellent triboelectric output performance, and good self-cleaning function.

[0037] Example 1

[0038] A method for preparing an in-situ MOF-modified stereocomposite polylactic acid micro / nanofiber self-powered filter membrane includes the following steps:

[0039] S1. Preparation of ZIF-8 crystals: 2-methylimidazole solution and zinc acetate were mixed (mass ratio of 2-methylimidazole solution and zinc acetate was 40:1), and then ZIF-8 crystals were synthesized by microwave-assisted synthesis (microwave reactor output power was 1500W, reaction temperature was 200℃, and reaction time was 20min).

[0040] S2. Preparation of ZIF-8 electro-spray stock solution: ZIF-8 crystals were dispersed in dimethylformamide, and then polyvinylpyrrolidone dispersant was added to obtain ZIF-8 electro-spray stock solution (the mass ratio of ZIF-8 to dispersant was 1:10, and the mass fraction of ZIF-8 in the dispersion was 10wt%).

[0041] S3. Preparation of electrospinning solution A: PDLA and PLLA are mixed at a molar ratio of 1:10 as the matrix polymer, and dissolved in a mixed solvent composed of dichloromethane and ethanol (volume ratio of dichloromethane and ethanol is 1:10) to prepare a spinning solution A with a concentration of 7wt%.

[0042] S4. Preparation of electrospinning solution B: PDLA and PLLA are mixed at a molar ratio of 1:15 as the matrix polymer, and dissolved in a mixed solvent composed of dimethylformamide and ethanol (volume ratio of dimethylformamide and ethanol is 1:100) to prepare a spinning solution B with a concentration of 18wt%.

[0043] S5. Preparation of in-situ MOF-modified stereocomposite polylactic acid micro / nanofiber self-powered filter membrane: The ZIF-8 electrospray stock solution (4 mL, needle diameter 0.84 mm, consumption rate 0.8 mL / h) obtained in S12, the spinning solution A (4 mL, needle diameter 0.84 mm, consumption rate 0.8 mL / h) obtained in S13, and the spinning solution B (4 mL, needle diameter 0.84 mm, consumption rate of B 0.8 mL / h) obtained in S14 were subjected to electrospray / electrospinning (electrospinning voltage 20 kV, spinning voltage 60 kV, spinning temperature 40 ℃, relative humidity 85%, receiving distance 17 cm), and annealed at 40 ℃ for 8 h to prepare the in-situ MOF-modified stereocomposite polylactic acid micro / nanofiber self-powered filter membrane.

[0044] The obtained filter membrane has an average nanofiber diameter of 500 nm, an average microfiber diameter of 2 μm, an average pore size of 58 nm, an average bead size of 10 μm, and a fiber membrane thickness of 100 μm.

[0045] Example 2

[0046] A method for preparing an in-situ MOF-modified stereocomposite polylactic acid micro / nanofiber self-powered filter membrane includes the following steps:

[0047] S1. Preparation of ZIF-8 crystals: 2-methylimidazole solution and zinc sulfate phase were mixed (mass ratio of 2-methylimidazole solution to zinc nitrate was 1:1), and then ZIF-8 was synthesized by microwave-assisted synthesis (microwave reactor output power was 800W, reaction temperature was 160℃, and reaction time was 40min).

[0048] S2. Preparation of ZIF-8 electro-spray stock solution: ZIF-8 was dissolved in dichloromethane, and then dodecyltrimethylammonium bromide dispersant was added to obtain ZIF-8 electro-spray stock solution (the mass ratio of ZIF-8 to dispersant was 1:1000, and the mass fraction of ZIF-8 in the dispersion was 0.01wt%).

[0049] S3. Preparation of electrospinning solution A: PDLA and PLLA are mixed at a molar ratio of 1:7 as the matrix polymer, and dissolved in a mixed solvent composed of chloroform and methanol (the volume ratio of chloroform and methanol is 1:10) to prepare a spinning solution A with a concentration of 1wt%.

[0050] S4. Preparation of electrospinning solution B: PDLA and PLLA are mixed at a molar ratio of 1:14 as the matrix polymer, and dissolved in a mixed solvent composed of N-methylpyrrolidone and glycerol (the volume ratio of N-methylpyrrolidone and glycerol is 1:1) to prepare a spinning solution B with a concentration of 8wt%.

[0051] S5. Preparation of in-situ MOF-modified stereocomposite polylactic acid micro / nanofiber self-powered filter membrane: The ZIF-8 electrospray stock solution (8 mL, needle diameter 0.51 mm, consumption rate 0.8 mL / h) obtained in S22, the spinning solution A (10 mL, needle diameter 0.21 mm, consumption rate 1.0 mL / h) obtained in S23, and the spinning solution B (10 mL, needle diameter 0.34 mm, consumption rate 1.0 mL / h) obtained in S24 were subjected to electrospray / electrospinning (electrospinning voltage 10 kV, electrospinning voltage 30 kV, spinning temperature 40 ℃, relative humidity 85%, receiving distance 15 cm), and annealed at 40 ℃ for 12 h to prepare the in-situ MOF-modified stereocomposite polylactic acid micro / nanofiber self-powered filter membrane.

[0052] The obtained filter membrane has an average nanofiber diameter of 350 nm, an average microfiber diameter of 5.6 μm, an average pore size of 128 nm, an average bead size of 8.5 μm, and a fiber membrane thickness of 200 μm.

[0053] Example 3

[0054] A method for preparing an in-situ MOF-modified stereocomposite polylactic acid micro / nanofiber self-powered filter membrane includes the following steps:

[0055] S1. Preparation of ZIF-8 crystals: 2-methylimidazolium solution and zinc fluoride were mixed (mass ratio of 2-methylimidazolium solution to zinc fluoride was 8:1), and then ZIF-8 was synthesized by microwave-assisted synthesis (microwave reactor output power was 1000W, reaction temperature was 100℃, and reaction time was 30min).

[0056] S2. Preparation of ZIF-8 electro-spray stock solution: ZIF-8 was dissolved in chloroform, and then sodium dodecyl sulfate dispersant was added to obtain ZIF-8 electro-spray stock solution (the mass ratio of ZIF-8 to dispersant was 1:40, and the mass fraction of ZIF-8 in the solution was 0.75wt%).

[0057] S3. Preparation of electrospinning solution A: PDLA and PLLA are mixed at a molar ratio of 1:6 as the matrix polymer, and dissolved in a mixed solvent composed of dimethylformamide and isopropanol (the volume ratio of dimethylformamide and isopropanol is 1:4) to prepare a spinning solution A with a concentration of 5wt%.

[0058] S4. Preparation of electrospinning solution B: PDLA and PLLA are mixed at a molar ratio of 1:12 as the matrix polymer, and dissolved in a mixed solvent composed of ethyl acetate and propylene glycol (volume ratio of ethyl acetate and propylene glycol is 1:7) to prepare a spinning solution B with a concentration of 15wt%.

[0059] S35. Preparation of in-situ MOF-modified stereocomposite polylactic acid micro / nanofiber self-powered filter membrane: The ZIF-8 electrospray stock solution (18 mL, needle diameter 0.21 mm, consumption rate 1.2 mL / h) obtained in S32, the spinning solution A (12 mL, needle diameter 0.21 mm, consumption rate 1.0 mL / h) obtained in S33, and the spinning solution B (12 mL, needle diameter 0.84 mm, consumption rate 1.0 mL / h) obtained in S34 were subjected to electrospray / electrospinning (electrospinning / electrospinning voltage was 25 kV, spinning temperature was 40℃, relative humidity was 40%, and receiving distance was 15 cm), and annealed at 40℃ for 24 h to prepare the in-situ MOF-modified stereocomposite polylactic acid micro / nanofiber self-powered filter membrane.

[0060] The obtained filter membrane has an average nanofiber diameter of 800 nm, an average microfiber diameter of 5 μm, an average pore size of 35 nm, an average bead size of 11.5 μm, and a fiber membrane thickness of 420 μm.

[0061] Example 4

[0062] An in-situ MOF-modified stereocomposite polylactic acid micro / nanofiber self-powered filter membrane and its preparation method include the following steps:

[0063] S1. Preparation of ZIF-8 crystals: 2-methylimidazole solution and zinc iodide were mixed (mass ratio of 2-methylimidazole solution to zinc iodide was 20:1), and then ZIF-8 crystals were synthesized by microwave-assisted synthesis (microwave reactor output power 500W, reaction temperature 120℃, reaction time 120min).

[0064] S2. Preparation of ZIF-8 electro-spray stock solution: Dissolve ZIF-8 in N-methylpyrrolidone, and then add sodium dodecylbenzenesulfonate dispersant to obtain ZIF-8 electro-spray stock solution (the mass ratio of ZIF-8 to dispersant is 1:10, and the mass of ZIF-8 in the solution is 5wt%).

[0065] S3. Preparation of electrospinning solution A: PDLA and PLLA are mixed at a molar ratio of 1:5 as the matrix polymer, and dissolved in a mixed solvent composed of chloroform and n-butanol (the volume ratio of chloroform and n-butanol is 1:5) to prepare a spinning solution A with a concentration of 15wt%.

[0066] S4. Preparation of electrospinning solution B: PDLA and PLLA are mixed at a molar ratio of 1:10 as the matrix polymer, and dissolved in a mixed solvent composed of tetrahydrofuran and ethylene glycol (volume ratio of tetrahydrofuran and ethylene glycol is 0.1:5) to prepare a spinning solution B with a concentration of 25wt%.

[0067] S5. Preparation of in-situ MOF-modified stereocomposite polylactic acid micro / nanofiber self-powered filter membrane: The ZIF-8 electrospray stock solution (18 mL, needle diameter 0.34 mm, consumption rate 1.5 mL / h) obtained in S42, the spinning solution A (12 mL, needle diameter 0.34 mm, consumption rate 2 mL / h) obtained in S43, and the spinning solution B (12 mL, needle diameter 0.84 mm, consumption rate 2 mL / h) obtained in S44 were subjected to electrospray / electrospinning (electrospinning / electrospinning voltage was 45 kV, spinning temperature was 60 ℃, relative humidity was 45%, and receiving distance was 15 cm), and annealed at 60 ℃ for 12 h to prepare the in-situ MOF-modified stereocomposite polylactic acid micro / nanofiber self-powered filter membrane.

[0068] The obtained filter membrane has an average nanofiber diameter of 800 nm, an average microfiber diameter of 5 μm, an average pore size of 35 nm, an average bead size of 12.4 μm, and a fiber membrane thickness of 400 μm.

[0069] Comparative Example 1

[0070] The stereocomposite polylactic acid (PLLA) micro / nanofiber membrane was prepared using the method described in Example 1. The difference was that ZIF-8 was not added in this example. Specifically, PDLA and PLLA were mixed at a molar ratio of 1:10 as the matrix polymer, and dissolved in a mixed solvent of dichloromethane and ethanol (volume ratio of dichloromethane to ethanol: 1:0.1) to prepare a spinning solution A with a concentration of 7 wt%. PDLA and PLLA were mixed at a molar ratio of 1:15 as the matrix polymer, and dissolved in a mixed solvent of dimethylformamide and ethanol (volume ratio of dimethylformamide to ethanol: 1:0.1) to prepare a spinning solution B with a concentration of 18 wt%. Subsequently, the obtained spinning solution A (4 mL, needle diameter 0.84 mm, consumption rate 0.8 mL / h) and spinning solution B (4 mL, needle diameter 0.84 mm, consumption rate of B 0.8 mL / h) were subjected to multi-needle electrospinning (electrospray voltage 20 kV, spinning voltage 60 kV, spinning temperature 40 °C, relative humidity 85%, receiving distance 17 cm), and annealed at 40 °C for 8 h to prepare a stereocomposite polylactic acid micro / nanofiber filter membrane.

[0071] The obtained filter membrane has an average nanofiber diameter of 654 nm, an average microfiber diameter of 5.3 μm, an average pore size of 158 nm, an average bead size of 8.5 μm, and a fiber membrane thickness of 100 μm.

[0072] Comparative Example 2

[0073] The stereocomposite polylactic acid (PLA) micro / nanofiber membrane was prepared using the method described in Example 2. The difference was that the ZIF-8 crystals prepared in Example 2 were dried by high-speed centrifugation before use. Then, the ZIF-8 crystal powder was added to spinning solution A and spinning solution B for electrospinning. Specifically, PDLA and PLLA were mixed at a molar ratio of 1:7 as the matrix polymer and dissolved in a mixed solvent of chloroform and methanol (volume ratio of chloroform to methanol: 1:10) to prepare spinning solution A with a concentration of 1 wt%. PDLA and PLLA were mixed at a molar ratio of 1:14 as the matrix polymer and dissolved in a mixed solvent of N-methylpyrrolidone and glycerol (volume ratio of N-methylpyrrolidone to glycerol: 1:1) to prepare spinning solution B with a concentration of 8 wt%.

[0074] Subsequently, ZIF-8 crystal powder was added to spinning solution A and spinning solution B (mass fractions of 10% and 15%, respectively) for multi-needle electrospinning. The spinning parameters were set as follows: spinning solution A (10 mL, needle diameter of 0.21 mm, consumption rate of 1.0 mL / h) and spinning solution B (10 mL, needle diameter of 0.34 mm, consumption rate of B of 1.0 mL / h) for multi-needle electrospinning (electrospinning voltage of 30 kV, spinning temperature of 40 °C, relative humidity of 85%, receiving distance of 15 cm). The mixture was then annealed at 40 °C for 12 h to prepare a stereocomposite polylactic acid micro / nanofiber membrane.

[0075] The obtained filter membrane has an average nanofiber diameter of 350 nm, an average microfiber diameter of 5 μm, an average pore size of 156 nm, and a fiber membrane thickness of 380 μm.

[0076] Structural characterization and performance testing

[0077] Tensile property testing: The obtained nanofiber membrane was cut into tensile test strips. The tensile properties of the composite membrane were tested using a universal tensile testing machine (model 4403, sensor 100N) from Instron, USA, according to the ASTM D638-2003 standard for testing the tensile properties of plastics. At least three parallel test samples were required for each group, and the average value was taken as the result.

[0078] Surface potential test: The surface potential of the nanofiber membrane was tested using a non-contact electrostatic meter (VM54XQS, Quatek, USA). The test height was 2 cm, and the temperature and humidity were kept constant at 25℃ and 45%. Twenty data points were randomly collected for each sample and the average value was taken.

[0079] Filtration performance testing: The fiber membrane (area 113.04 cm²) was tested using an LZC-K type automatic filter media tester (Suzhou Huada Instrument Equipment Co., Ltd.). 2 The air filtration performance was tested with a gas flow rate of 85 L / min and the NaCl atomized crystals generated by the aerosol generator having a particle size range of 0.1–10 μm. At least three different locations were tested for each group of fiber membranes, and the average value was taken.

[0080] Water contact angle test: The contact angle (CA) was measured using a 2μL droplet with a JC2000D1 contact angle system (Shanghai Zhongchen). The average CA value was obtained from three different regions of the test sample.

[0081] Self-cleaning performance test: The fiber membrane is placed on a glass inclined plate, and pollutant particles (indoor dust) are scattered on the surface of the fiber membrane, causing the surface of the fiber membrane to be contaminated with dust. Then, the airflow of the air pump achieves high-speed shearing (water droplets are dropped onto the surface of the fiber membrane through a plastic dropper) to remove the particles from the fiber surface, thus achieving the membrane's re-cleaning and reusability.

[0082] The results are shown in Tables 1-3. Tables 1, 2, and 3 compare the test results of specific surface area, dielectric constant, surface potential, mechanical properties, filtration performance, output performance, and water contact angle of the in-situ MOF-modified stereocomposite polylactic acid micro / nanofiber self-powered filter membranes obtained in the examples and comparative examples, respectively.

[0083] Table 1. Test results of dielectric constant and surface potential of in-situ MOF-modified stereocomposite polylactic acid micro / nanofiber self-powered filter membrane

[0084]

[0085] In Table 1, Examples 1-4 exhibited high specific surface areas due to the anchoring of ZIF-8 on the fiber surface. Examples 1-4 and Comparative Example 2 also showed extremely high surface potentials (8.5-14.8 kV). Furthermore, the surface potential of the filter membranes in Examples 1-4 hardly decreased over time, confirming their extremely high long-term stability. In Table 1, the dielectric constants of Examples 1-4 were significantly improved compared to Comparative Example 1. The high specific surface area, high surface potential, high dielectric constant, and enhanced nanofiber confinement properties make microporous nanofibers an ideal platform for molecular sieving and adsorption separation, typically exhibiting stronger loading capacity and lower air resistance.

[0086] Table 2. Test results of specific surface area, mechanical properties, and filtration performance of in-situ MOF-modified stereocomposite polylactic acid micro / nanofiber self-powered filter membrane

[0087]

[0088] In Table 2, Examples 1-4 all showed filtration efficiencies of over 98% for both PM0.3 and PM2.5. Comparative Example 1 demonstrated that at lower surface potentials, the filtration efficiencies of the fiber membrane for PM0.3 and PM2.5 were lower than at higher potentials, with a filtration efficiency of 70.3% for PM0.3 and 72.4% for PM2.5.

[0089] In Table 2, the tensile strength of the fiber membranes in Examples 1-4 ranged from 19.6 to 33.5 MPa, significantly higher than that in Comparative Examples 1-2. This is because ZIF-8 fills the vacancies on the fiber surface, reducing surface defects and improving tensile strength. However, as the ZIF-8 content increases, the tensile strength of the fiber membrane first increases and then decreases. This is mainly because ZIF-8 can act as a nucleation point during stereocomposite processing, promoting crystal growth and improving the crystallinity of polylactic acid fibers. This increases the number of physical crosslinking points in the molecule, thus improving mechanical properties. However, excessive ZIF-8 content can also increase stress concentration points in the fibers and weaken heterogeneous nucleation, leading to a decrease in tensile strength. Therefore, adding an appropriate amount of ZIF-8 helps improve the strength of the nanofiber membrane. Table 3. Test results of output performance and water contact angle of in-situ MOF-modified stereocomposite polylactic acid micro / nanofiber self-powered filter membrane.

[0090]

[0091] In Table 3, the triboelectric output performance of Examples 1-4 ranges from 16.9 to 25.6 V, significantly higher than that of Comparative Examples 1-2. This is mainly because the introduction of ZIF-8 between the fibers increases the frictional area between them. Simultaneously, the high electron conversion capability of ZIF-8, combined with the improved fiber stacking pattern due to the beaded / porous structure, increases the fiber-to-fiber contact area (e.g., ...). Figure 2 As shown), this increases the output voltage of the fiber membrane. Simultaneously, the increased water contact angle is mainly due to the synergistic effect of the hydrophobic ZIF-8 and the beaded structure, giving the fiber membrane self-cleaning capabilities (e.g., ...). Figure 3 and Figure 4 (As shown).

[0092] This demonstrates that the technical solution proposed in this invention enables the in-situ MOF-modified stereocomposite polylactic acid micro / nanofiber self-powered filter membrane to possess excellent filtration performance, triboelectric output performance, and self-cleaning ability. These are likely due to: (1) utilizing the solubility gradient difference in the solution to form a beaded structure in the fibers, while simultaneously constructing a "non-good solvent-good solvent-polymer" ternary system, and using the principle of phase separation induced by the non-good solvent to generate a controllable mesoporous structure in situ on the surface of the stereocomposite polylactic acid fiber. The beaded / mesoporous structure improves the fiber stacking mode, reduces air resistance, and provides more binding sites for ZIF-8 on the fiber surface, increasing the specific surface area and surface activity of the fiber and enhancing the adsorption capacity for particulate matter; (2) The synergistic effect of the beaded structure and the uniformly attached ZIF-8 on the fiber surface enables the fiber to form a superhydrophobic surface, which greatly reduces the adhesion of dirt. When subjected to mechanical forces such as airflow and water, dirt can automatically detach from the ZIF-8 surface, thereby achieving self-cleaning; (3) Due to the large specific surface area and frictional contact area of ​​ZIF-8, as well as higher electron exchange capacity, the triboelectric output performance of the fiber membrane is significantly improved; (4) The stereocomposite polylactic acid obtains a high degree of crystallinity and a regular chain conformation through inter-chain hydrogen bond interaction, which enhances the mechanical properties and filtration performance of the fiber membrane.

[0093] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. An in-situ MOF-modified stereocomposite polylactic acid micro / nanofiber self-powered filter membrane, characterized in that, The filter membrane is prepared from spinning solution A, spinning solution B, and electro-sprayed ZIF-8 stock solution; the average diameter of the nanofibers is 150~1000 nm, the average diameter of the microfibers is 1~10 μm, the size of the beads is 1~20 μm, the size of the mesopores on the fiber surface is 50~500 nm, and the thickness of the fiber membrane is 20~600 μm. Spinning solution A includes a PLLA / PDLA blend, with a mass fraction of 0.1-7 wt% in spinning solution A; spinning solution B includes a PLLA / PDLA blend, with a mass fraction of 8-18 wt% in spinning solution B; the molar ratio of PDLA to PLLA in both spinning solution A and spinning solution B is 1:0.1-1:

20. Both spinning solution A and spinning solution B contain solvents including good solvents and bad solvents. The good solvent is at least one of dichloromethane, trichloromethane, N,N-dimethylformamide, N-methylpyrrolidone, hexafluoroisopropanol, tetrahydrofuran, and ethyl acetate. The bad solvent is at least one of methanol, ethanol, isopropanol, glycerol, butanol, ethylene glycol, and propylene glycol. The volume ratio of bad solvent to good solvent in spinning solution A is 1:1 to 1:

10. The volume ratio of bad solvent to good solvent in spinning solution B is 1:1 to 1:

100.

2. A method for preparing the in-situ MOF-modified stereocomposite polylactic acid micro / nanofiber self-powered filter membrane according to claim 1, characterized in that, Includes the following steps: S1. Preparation of ZIF-8 crystals: ZIF-8 dispersion was prepared by microwave-assisted synthesis of 2-methylimidazole solution and zinc salt, and ZIF-8 crystals were obtained after extraction and drying. S2. Preparation of ZIF-8 electro-injection stock solution: Disperse the ZIF-8 crystals obtained in S1 in a solvent and add a dispersant to obtain a stable and uniform electro-injection ZIF-8 stock solution. S3. Preparation of electrospinning solution A: PDLA and PLLA are mixed in a certain molar ratio and then dissolved in a mixed solvent composed of a good solvent and a bad solvent to prepare electrospinning solution A; S4. Preparation of electrospinning solution B: PDLA and PLLA are mixed in a certain molar ratio and then dissolved in a mixed solvent composed of a good solvent and a bad solvent to prepare electrospinning solution B; S5. Preparation of in-situ MOF-based stereocomposite polylactic acid micro / nanofiber self-powered filter membrane: The ZIF-8 electrospraying solution obtained in S2, the spinning solution A obtained in S3, and the spinning solution B obtained in S4 were used to prepare fiber membranes by simultaneous electrospraying / electrospinning. After in-situ annealing, a self-powered MOF-based stereocomposite polylactic acid micro / nanofiber filter membrane was formed.

3. The method for in-situ MOF-based stereochemical composite polylactic acid micro / nanofiber self-powered filter membrane according to claim 2, characterized in that, The water-soluble zinc salt used in step S1 is at least one of zinc nitrate, zinc chloride, zinc sulfate, and zinc acetate, with a concentration of 0.01~5 mol / L and a molar ratio of 2-methylimidazole to zinc salt of 40:1~1:

40.

4. The method for in-situ MOF-based stereochemical composite polylactic acid micro / nanofiber self-powered filter membrane according to claim 2, characterized in that, In step S1, the microwave reactor output power is 100~1500 W, the reaction temperature is 40~200 ℃, and the reaction time is 20~120 min.

5. The method for in-situ MOF-based stereochemical composite polylactic acid micro / nanofiber self-powered filter membrane according to claim 2, characterized in that, The dispersant used in step S2 is at least one of polyvinylpyrrolidone, dodecyltrimethylammonium bromide, sodium dodecyl sulfate, and sodium dodecylbenzene sulfonate, with a mass ratio of ZIF-8 to the dispersant of 1:10 to 1:1000.

6. The method for in-situ MOF-based stereochemical composite polylactic acid micro / nanofiber self-powered filter membrane according to claim 2, characterized in that, The solvent used in step S2 is at least one of dimethylformamide, dichloromethane, chloroform, N-methylpyrrolidone, hexafluoroisopropanol, methanol, ethanol, isopropanol, and glycerol, and the mass fraction of ZIF-8 in the dispersion is 0.01~10wt%.

7. The method for in-situ MOF-based stereochemical composite polylactic acid micro / nanofiber self-powered filter membrane according to claim 2, characterized in that, In step S5, the diameter of the electrospinning needle is 0.06~1.54 mm, the applied electrostatic field voltage is 10~60kV, the spinning temperature is 20~65 ℃, and the relative humidity is 25%~85%. In step S5, the consumption rate of ZIF-8 electrospray solution is 0.1~10 mL / h, the consumption rate of spinning solution A is 0.1~10 mL / h, the consumption rate of spinning solution B is 0.1~10 mL / h, and the receiving distance is 10~30 cm.

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