High-efficiency polylactic acid fluffy nanofiber membrane for filtering gases and particulate matter and its preparation method

Abstract

This invention provides a highly efficient polylactic acid (PLA) fluffy nanofiber membrane for filtering gases and particulate matter, and its preparation method. The method includes: step S1, preparing a stereocomposite crystalline (SC) membrane; step S2, preparing an SC-electret PLA fluffy nanofiber membrane; step S3, preparing a MOF-type nanocrystal growth precursor solution; and step S4, preparing a MOF-modified SC-electret PLA fluffy nanofiber membrane. The highly efficient PLA fluffy nanofiber membrane for filtering gases and particulate matter provided by this invention can be used in air purification, industrial waste gas treatment, and indoor environmental remediation. The MOF-modified SC-electret PLA fluffy nanofiber membrane prepared by this invention has advantages such as high fluffiness, high-efficiency low-resistance filtration performance, strong carbon fixation performance, and high formaldehyde and CO adsorption efficiency, effectively extending the application of PLA biomaterials in air purification and toxic gas capture.

Description

Technical Field

[0001] This invention relates to the field of fully degradable fiber membrane materials for air purification and adsorption of toxic gases, specifically to a polylactic acid fluffy nanofiber membrane for efficiently filtering gases and particulate matter and its preparation method. Background Technology

[0002] Air particulate pollution and the hazards of toxic gases are major environmental and public health problems facing the world. Air particulate matter, especially PM2.5... 0.3 and PM 2.5 Particulate matter can penetrate deep into the lungs and affect the heart and brain through blood circulation, leading to respiratory and cardiovascular diseases and even increasing the risk of premature death. Meanwhile, toxic gases such as CO2, CO, and volatile organic compounds pose a direct threat to human health and the ecological environment. CO2 contributes to climate change, while CO can cause poisoning. Therefore, developing multifunctional materials that can effectively address the problems of particulate matter pollution and the hazards of toxic gases is of great significance.

[0003] Metal-organic frameworks (MOFs) are porous materials formed by the coordination bonds between metal ions or metal clusters and organic ligands. Due to their unique structure and excellent properties, they show great potential for applications in gas adsorption, storage, catalysis, and sensing. These materials possess high porosity and tunability, allowing for specific surface areas up to 1000 m². 2 MOF materials, with a density of / g or higher, can be flexibly designed to meet specific application requirements. Most MOF materials possess good crystallinity and an ordered three-dimensional network structure, while different metal ions endow them with unique catalytic activity and selectivity. MOFs exhibit excellent performance in the adsorption and separation of gases such as CO2, CH4, and H2, demonstrating good catalytic properties suitable for organic synthesis and environmental catalysis. Therefore, MOF materials are becoming an important research subject in materials science, environmental science, and biomedicine, and it is hoped that more high-performance MOF materials will be developed in the future to meet the needs of different applications.

[0004] On the other hand, polylactic acid (PLA), an ideal green material derived from plant-extracted starch, is widely used in air filtration due to its excellent mechanical properties, biocompatibility, and non-toxicity. PLA not only possesses excellent degradation properties but also exhibits good biocompatibility. Furthermore, the presence of chiral centers in its molecular chain gives it shear piezoelectricity, enabling it to generate voltage autonomously under mechanical action without the need for external electric field polarization. This technique is simple, efficient, and easily scalable for industrial production. By combining MOF materials with PLA, the performance of the filter material can be significantly improved, and the advantages of MOF can be effectively utilized to achieve efficient capture of particulate matter and effective adsorption of harmful gases. Summary of the Invention

[0005] Objective: To meet the demand for high-efficiency air purification, this invention proposes an innovative method. First, SC crystals are prepared and added as electrets to polylactic acid (PLA) fibers to enhance interfacial polarization of the fiber membrane and promote the generation of deep charge traps. Simultaneously, a bulking agent is added to induce fiber bulking. Next, MOF-type nanocrystals are synthesized in situ on the surface of the bulky fibers using UV-assisted and microwave catalysis, ultimately obtaining a MOF-modified SC crystal electret PLA bulky nanofiber membrane with high bulkiness, high-efficiency low-resistance filtration performance, excellent carbon fixation performance, and efficient adsorption of formaldehyde and CO. This innovative material has significant practical implications for air purification and harmful gas capture, expanding the application scope of PLA biomaterials.

[0006] This invention provides a polylactic acid fluffy nanofiber membrane for efficiently filtering gases and particulate matter, and a method for preparing the same. The method includes the following steps:

[0007] Step S1: Preparation of stereocomposite crystal SC: Stereocomposite crystal SC is obtained by crystallizing polylactic acid (PLLA) and polylactic acid (PDLA).

[0008] Step S2: Preparation of SC crystal electret polylactic acid fluffy nanofiber membrane: First, polylactic acid is dissolved in a solvent to prepare a polylactic acid solution. Then, the stereocomposite crystal SC prepared in S1 is used as the electret material. The stereocomposite crystal SC is added to the polylactic acid solution. By adding a fluffing agent to the polylactic acid solution, an SC crystal electret polylactic acid fluffy nanofiber membrane with uniformly sized fibers is prepared by electrospinning process.

[0009] Step S3: Preparation of MOF-type nanocrystal growth precursor solution: Dissolve the metal salt, terephthalate reagent and imidazole reagent in a solvent respectively, and then slowly add the metal salt solution to the mixed solution of terephthalate reagent and imidazole reagent. After stirring and mixing evenly, the MOF-type nanocrystal growth precursor solution is obtained.

[0010] Step S4: Preparation of MOF-modified SC-electret polylactic acid fluffy nanofiber membrane: The SC-electret polylactic acid fluffy nanofiber membrane obtained in step S2 is immersed in the MOF-type nanocrystal growth precursor solution prepared in step S3. Under ultraviolet (UV) irradiation, the MOF-type nanocrystals are grown at a constant temperature using microwave-assisted catalysis. Stirring is used to ensure the uniformity of the size of the MOF-type nanocrystals grown on the fiber surface. After growth, the membrane is rinsed with the solution and allowed to stand and dry to obtain the MOF-modified SC-electret polylactic acid fluffy nanofiber membrane.

[0011] In step S1, the mass ratio of L-polylactic acid (PLLA) to D-polylactic acid (PDLA) ranges from 1:9 to 9:1.

[0012] In step S1, the crystallization treatment method includes at least one of solution method, melt blending method, freeze drying method, and phase transformation method;

[0013] The solution method includes: dissolving L-polylactic acid (PLLA) and D-polylactic acid (PDLA) in at least one of dimethylformamide, dichloromethane, chloroform, acetone, hexafluoroisopropanol, and ethyl acetate as solvents, with a stirring speed of 100–500 rpm, to obtain L-PLLA solution and D-PDLA solution respectively, wherein the mass ratio of L-PLLA to solvent is 5%–30%, and the mass ratio of D-PDLA to solvent is 5%–30%; then, stirring and mixing the L-PLLA solution and D-PDLA solution at a stirring speed of 100–500 rpm to obtain a mixed solution, and solidifying and crystallizing the mixed solution by solvent evaporation or gelation to obtain stereocomposite crystals SC; wherein the solvent evaporation temperature is 20℃–250℃, and the gelation temperature is 20℃–60℃;

[0014] The melt blending method includes: melting L-polylactic acid (PLLA) and D-polylactic acid (PDLA) at a high temperature of 170°C to 300°C, stirring at a speed of 100 to 500 rpm during melting, and cooling at a temperature of -10°C to 30°C to obtain stereocomposite crystals (SC).

[0015] The freeze-drying method includes: using at least one of dimethylformamide, dichloromethane, chloroform, acetone, hexafluoroisopropanol, and ethyl acetate as a solvent; adding L-polylactic acid (PLLA) and D-polylactic acid (PDLA) to the solvent respectively; setting the stirring speed to 100-500 rpm to obtain L-polylactic acid (PLLA) solution and D-polylactic acid (PDLA) solution respectively; wherein the mass ratio of L-polylactic acid (PLLA) to solvent is 5%-30% and the mass ratio of D-polylactic acid (PDLA) to solvent is 5%-30%; mixing the L-polylactic acid (PLLA) solution and the D-polylactic acid (PDLA) solution; stirring speed during mixing is 100-500 rpm; then freezing and molding at ultra-low temperature of -150℃ to -50℃; and drying at -20℃ to -49℃ to remove the solvent to form stereocomposite crystals SC.

[0016] The phase transformation method includes: using at least one of dimethylformamide, dichloromethane, chloroform, acetone, hexafluoroisopropanol, and ethyl acetate as a solvent, adding L-polylactic acid (PLLA) and D-polylactic acid (PDLA) to the solvent respectively, setting the stirring speed to 100-500 rpm to obtain L-polylactic acid (PLLA) solution and D-polylactic acid (PDLA) solution respectively, wherein the mass ratio of L-polylactic acid (PLLA) to solvent is 5%-30%, and the mass ratio of D-polylactic acid (PDLA) to solvent is 5%-30%, mixing the L-polylactic acid (PLLA) solution and the D-polylactic acid (PDLA) solution, stirring the solution at 100-500 rpm, and then setting the cooling temperature to -20℃ to -100℃, with a temperature change rate of 1℃ / min to 5℃ / min to form stereocomposite crystals SC.

[0017] In step S2, the polylactic acid solution contains 5% to 25% polylactic acid, the mass ratio of the stereocomposite crystal SC to polylactic acid is 1:20 to 1:2, the solvent used is at least one of dimethylformamide, dichloromethane, chloroform, acetone, hexafluoroisopropanol, and ethyl acetate, the leavening agent is at least one of cellulose acetate, polyvinyl alcohol, polyurethane, polycaprolactone, chitosan, and polylactic acid copolymer, and the mass ratio of the leavening agent to polylactic acid is 1:10 to 2:1.

[0018] In step S2, when using electrospinning, the output voltage of electrospinning is 5-35kV, the solution consumption rate is 0.5-4mL / h, the spinning winding speed is 100-1500rpm, the receiving distance is 8-30cm, the spinning temperature is 20-50℃, the humidity is 50%-90%, the average diameter of polylactic acid fluffy nanofibers is 200-990nm, and the thickness of the polylactic acid fluffy nanofiber membrane is 300-1000μm.

[0019] In step S3, the metal salt is at least one of zinc nitrate (magnesium nitrate, ferric nitrate, copper nitrate), zinc acetate (magnesium acetate, ferric acetate, copper acetate), zinc sulfate (magnesium sulfate, ferric sulfate, copper sulfate), zinc chloride (magnesium chloride, ferric chloride, copper chloride), and zinc oxide (magnesium oxide, ferric oxide, copper oxide).

[0020] In step S3, the terephthalate reagent is at least one of terephthalic acid, sodium terephthalate, ammonium terephthalate, dimethyl terephthalate, and ammonium hydrogen terephthalate.

[0021] The imidazole reagent is at least one of methylimidazolium, dimethylimidazolium, 2-aminobenzimidazole, 2-aminoimidazolium, 1-3-aminopropylimidazolium, 4-aminoimidazolium, and imidazolylbenzylbenzyl.

[0022] The solvent is at least one of dimethyl thionamide, dimethylformamide, deionized water, ethanol, methanol, n-butanol, isopropanol, ethylene glycol, and chloroform.

[0023] The mass ratio of the metal salt to the terephthalate reagent is 1:8-1:1;

[0024] The mass ratio of the metal salt to the imidazole reagent is 1:10 to 1:1;

[0025] The mass ratio of the metal salt to the solvent is 1:1000 to 1:50;

[0026] When stirring, the stirring speed is 100-600 rpm and the stirring time is 20-40 min.

[0027] In step S4, the microwave output power used is 300–1200 W, the growth temperature is 150–250 °C, the synthesis time is 20–100 min, the stirring speed is 10–300 rpm, and the ultraviolet (UV) light wavelength range is 100–400 nm with an irradiation intensity of 100–500 mW / cm². 2 The irradiation time is the same as the synthesis time. The ultraviolet (UV) light source is selected from at least one of mercury lamp, xenon lamp, LED UV light source, black light lamp, ultraviolet lamp tube, and nitrogen laser. The average particle size of the MOF nanocrystals is 100-990 nm.

[0028] In step S4, the drying method used is at least one of natural drying, hot air drying, freeze drying, vacuum drying, microwave drying, spray drying, flash drying, and radiation drying.

[0029] The present invention also provides a polylactic acid fluffy nanofiber membrane for efficiently filtering gases and particulate matter, which is prepared using the method described above.

[0030] The polylactic acid fluffy nanofiber membrane provided by this invention, which efficiently filters gases and particulate matter, can be used in scenarios such as air purification, industrial waste gas treatment, and indoor environmental remediation. In air purification equipment, this membrane can be integrated into the filter to efficiently remove fine particles and common harmful gases such as PM2.5 from the air. 2.5 This material effectively removes CO2, formaldehyde, and CO, improving air quality. In personal protective equipment, it can be used to manufacture masks, providing high breathability and low resistance while effectively filtering viruses, bacteria, and other air pollutants to meet high-efficiency protection needs. For industrial waste gas treatment, this material exhibits excellent performance in capturing dust and adsorbing toxic gases, achieving pollutant removal with low energy consumption and providing a new option for environmental protection equipment. Furthermore, this material is also suitable for indoor air purification products, such as air purifiers and ventilation filtration systems, helping to improve indoor environmental quality and protect people's respiratory health.

[0031] Beneficial Effects: This invention provides a highly efficient polylactic acid (PLA) fluffy nanofiber membrane for filtering gases and particulate matter, and its preparation method. By preparing an SC-electret PLA fluffy nanofiber membrane and using a microwave-catalyzed + UV-assisted in-situ growth method, MOF-type nanocrystals are synthesized on the surface of each fiber in the membrane, relying on the fluffy nature of the fibers, resulting in an SC-electret PLA fluffy nanofiber membrane fully loaded with MOF-type nanocrystals. The nanofiber membrane has a fiber diameter of 200–990 nm and a membrane thickness of 300–1000 μm. At a flow rate of 85 L / min, it effectively filters PM2.5. 0.3 Its filtration efficiency is 96.5%–97.8%, effective against PM2.5. 2.5 The filtration efficiency is 99.2%–99.7%, the air resistance is 100–140 Pa, the adsorption efficiency for CO2 is 80%–85%, the adsorption efficiency for formaldehyde is 82%–88%, and the adsorption efficiency for CO can reach over 80%. The preparation method is simple and the conditions are controllable. The prepared MOF-modified SC crystalline electret polylactic acid fluffy nanofiber membrane has advantages such as high fluffiness, high-efficiency and low-resistance filtration performance, strong carbon fixation performance, and high-efficiency formaldehyde and CO adsorption performance, effectively extending the application of polylactic acid biomaterials in air purification and toxic gas capture. Attached Figure Description

[0032] The present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments, and the advantages of the present invention in the above and / or other aspects will become clearer.

[0033] Figure 1 This is a flowchart of the method of the present invention.

[0034] Figure 2 This is a schematic diagram of the morphology of the SC crystals prepared in Example 1 observed by SEM.

[0035] Figure 3 This is a schematic diagram of the morphology of the SC crystalline electret polylactic acid fluffy fiber membrane prepared in Example 2, observed by SEM.

[0036] Figure 4 This is a schematic diagram of the morphology of the MOF-type nanocrystals prepared in Example 3, observed by SEM.

[0037] Figure 5 This is a schematic diagram of the morphology of the MOF-modified SC-crystal electret polylactic acid fluffy nanofiber membrane prepared in Example 4, observed by SEM. Detailed Implementation

[0038] Example 1

[0039] This embodiment provides a method for preparing a polylactic acid fluffy nanofiber membrane for efficiently filtering gases and particulate matter, including the following steps:

[0040] S11, Preparation of stereocomposite crystals (SC): PLLA and PDLA are crystallized by solution method. Specifically, 1g of PLLA and 1g of PDLA are dissolved in 10g of dichloromethane. After complete dissolution, the two solutions are mixed evenly at 300rpm and then solidified and crystallized at 180℃ to obtain SC crystals.

[0041] Preparation of S12 and SC crystal electret polylactic acid fluffy nanofiber membranes: Using the SC crystals prepared in S11 as electret materials, 0.1g of SC crystals were first dispersed in 3g of dichloromethane. Then, 0.5g of polylactic acid and 0.5g of cellulose acetate were dissolved in 7g of dichloromethane and mixed uniformly to prepare a spinning solution. Subsequently, 2mL of the spinning solution was used for electrospinning. The output voltage was set to 24kV, the solution feed rate was 1.5mL / h, the fiber winding speed was 500rpm, the spinning temperature was 40℃, and the humidity was 70%. SC crystal electret polylactic acid fluffy nanofiber membranes were spun, with an average fiber diameter of 800nm ​​and a membrane thickness of 900μm.

[0042] S13. Preparation of MOF-type nanocrystal growth precursor solution: First, dissolve 0.5g of zinc nitrate in 100mL of water, then dissolve 1.5g of terephthalic acid and 2.5g of methylimidazole in 100mL of water. Mix the solutions under magnetic stirring at 300rpm until completely dissolved, and stir for 30min to ensure complete mixing, thus obtaining the MOF-type nanocrystal growth precursor solution.

[0043] S14. Preparation of MOF-type SC electret polylactic acid fluffy nanofiber membrane: The SC electret polylactic acid fluffy nanofiber membrane obtained in S12 was immersed in the MOF-type nanocrystal growth precursor solution prepared in S13. Light with a wavelength of 300 nm was provided by a mercury lamp, and the irradiation intensity was set to 250 mW / cm². 2 Then, microwave-assisted catalytic growth was performed, with a microwave output power of 800W, a growth temperature of 200℃, a synthesis time of 50min, and a stirring speed of 100rpm. After the reaction was completed, the mixture was rinsed with deionized water and allowed to stand and dry to obtain a MOF-type SC-crystallized electret polylactic acid fluffy nanofiber membrane. The average size of the MOF-type nanocrystals synthesized on the nanofiber surface was 300nm.

[0044] Example 2

[0045] This embodiment provides a method for preparing a polylactic acid fluffy nanofiber membrane for efficiently filtering gases and particulate matter, including the following steps:

[0046] S21, Preparation of stereocomposite crystals (SC): PLLA and PDLA were crystallized by melt blending. Specifically, 1.2g of PLLA and 0.8g of PDLA were melted at a high temperature of 250℃ and mixed uniformly at a speed of 400rpm. Then, they were transferred to a 0℃ environment for rapid cooling and crystallization to obtain SC crystals.

[0047] Preparation of S22 and SC crystal electret polylactic acid fluffy nanofiber membrane: Using the SC crystal prepared in S21 as the electret material, firstly, 0.12g of SC crystal was dispersed in 3g of acetone, then 1.2g of polylactic acid and 0.8g of polyvinyl alcohol were dissolved in 7g of acetone, and then they were uniformly mixed to prepare a spinning solution. Subsequently, 1mL of the spinning solution was electrospun under the following conditions: output voltage of 35kV, solution feed speed of 0.5mL / h, fiber winding speed of 1000rpm, spinning temperature of 20℃, and humidity of 50%. SC crystal electret polylactic acid fluffy nanofiber membrane was spun into the membrane, wherein the average fiber diameter of the membrane was 700nm and the membrane thickness was 800μm.

[0048] S23. Preparation of MOF-type nanocrystal growth precursor solution: First, dissolve 0.8g of magnesium acetate in 100mL of ethanol. Then, dissolve 1.6g of sodium terephthalate and 8g of methylimidazole in 100mL of ethanol. Mix the solutions under magnetic stirring at 600rpm for 20min to obtain the MOF-type nanocrystal growth precursor solution.

[0049] S24. Preparation of MOF-type SC electret polylactic acid fluffy nanofiber membrane: The SC electret polylactic acid fluffy nanofiber membrane obtained in S22 was immersed in the MOF-type nanocrystal growth precursor solution prepared in S23. Light with a wavelength of 400 nm was provided by a xenon lamp, and the irradiation intensity was set to 100 mW / cm². 2 Then, microwave-assisted catalytic growth was performed, with a microwave output power of 400W, a growth temperature of 150℃, a synthesis time of 100min, and a stirring speed of 10rpm. After the reaction was completed, the mixture was rinsed with deionized water and allowed to stand and dry to obtain a MOF-type SC-crystallized electret polylactic acid fluffy nanofiber membrane. The average size of the MOF-type nanocrystals synthesized on the nanofiber surface was 400nm.

[0050] Example 3

[0051] This embodiment provides a method for preparing a polylactic acid fluffy nanofiber membrane for efficiently filtering gases and particulate matter, including the following steps:

[0052] S31. Preparation of stereocomposite crystals (SC): PLLA and PDLA were crystallized by freeze-drying. Specifically, 0.8g of PLLA and 1.2g of PDLA were dissolved in 10g of chloroform. After complete dissolution, the two solutions were mixed evenly at 300rpm. The mixture was then solidified at -100℃ and dried at -40℃ to remove the solvent, thus obtaining SC crystals.

[0053] Preparation of S32 and SC crystal electret polylactic acid fluffy nanofiber membrane: Using the SC crystal prepared in S31 as the electret material, firstly, 0.08g of SC crystal was dispersed in 2g of chloroform, then 1.6g of polylactic acid and 0.4g of polyurethane were dissolved in 8g of chloroform, and then they were uniformly mixed to prepare a spinning solution. Subsequently, 1mL of the spinning solution was electrospun under the following conditions: output voltage of 30kV, solution feed speed of 0.8mL / h, fiber winding speed of 1500rpm, spinning temperature of 30℃, and humidity of 60%. SC crystal electret polylactic acid fluffy nanofiber membrane was spun into the membrane, wherein the average fiber diameter of the fiber membrane was 750nm and the membrane thickness was 850μm.

[0054] S33. Preparation of MOF-type nanocrystal growth precursor solution: First, dissolve 0.5g of ferric sulfate in 100mL of methanol. Then, dissolve 4g of ammonium terephthalate and 0.7g of 2-aminobenzimidazole in 200mL of methanol. After complete dissolution, mix the above solutions under magnetic stirring at 500rpm and stir for 40min to ensure complete mixing, thus obtaining the MOF-type nanocrystal growth precursor solution.

[0055] S34. Preparation of MOF-type SC electret polylactic acid fluffy nanofiber membrane: The SC electret polylactic acid fluffy nanofiber membrane obtained in S32 was immersed in the MOF-type nanocrystal growth precursor solution prepared in S33. Light with a wavelength of 100 nm was provided by an LED UV light source, and the irradiation intensity was set to 500 mW / cm². 2 Then, microwave-assisted catalytic growth was performed, with a microwave output power of 700W, a growth temperature of 250℃, a synthesis time of 20min, and a stirring speed of 100rpm. After the reaction was completed, the mixture was rinsed with deionized water and allowed to stand and dry to obtain a MOF-type SC-crystallized electret polylactic acid fluffy nanofiber membrane. The average size of the MOF-type nanocrystals synthesized on the nanofiber surface was 200nm.

[0056] Example 4

[0057] This embodiment provides a method for preparing a polylactic acid fluffy nanofiber membrane for efficiently filtering gases and particulate matter, including the following steps:

[0058] S41. Preparation of stereocomposite crystals (SC): PLLA and PDLA were crystallized by phase transformation. Specifically, 1g of PLLA and 1g of PDLA were dissolved in 10g of dimethylformamide and 10g of chloroform, respectively. After complete dissolution, the two solutions were mixed evenly at 500rpm. Then, the cooling temperature was set to -80℃, the temperature change rate was set to 4℃ / min, and the solution stirring speed was set to 400rpm. After the solution was completely solidified and crystallized, SC crystals were obtained.

[0059] Preparation of S42 and SC crystal electret polylactic acid fluffy nanofiber membranes: Using the SC crystals prepared in S41 as electret materials, 0.3g of SC crystals were first dispersed in 4g of chloroform, and then 0.3g of polylactic acid and 0.4g of polyurethane were dissolved in 6g of dimethylformamide. The mixtures were then uniformly mixed to prepare a spinning solution. Subsequently, 1.4mL of the spinning solution was used for electrospinning. The output voltage was set to 20kV, the solution feed rate was 3mL / h, the fiber winding rate was 300rpm, the spinning temperature was 50℃, and the humidity was 50%. SC crystal electret polylactic acid fluffy nanofiber membranes were spun, with an average fiber diameter of 1000nm and a membrane thickness of 600μm.

[0060] S43. Preparation of MOF-type nanocrystal growth precursor solution: First, dissolve 1g of copper oxide in 100mL of methanol, then dissolve 2g of dimethyl terephthalate and 1g of 4-aminoimidazole in 100mL of water. Mix the solutions under magnetic stirring at 500rpm until completely dissolved, and stir for 30min to ensure complete mixing, thus obtaining the MOF-type nanocrystal growth precursor solution.

[0061] S44. Preparation of MOF-type SC electret polylactic acid fluffy nanofiber membrane: The SC electret polylactic acid fluffy nanofiber membrane obtained in S42 was immersed in the MOF-type nanocrystal growth precursor solution prepared in S43. A 200nm wavelength ultraviolet lamp was used to provide the irradiation intensity, which was set to 450mW / cm². 2 Then, microwave-assisted catalytic growth was performed, with a microwave output power of 900W, a growth temperature of 180℃, a synthesis time of 40min, and a stirring speed of 300rpm. After the reaction was completed, the mixture was rinsed with deionized water and allowed to stand and dry to obtain a MOF-type SC-crystallized electret polylactic acid fluffy nanofiber membrane. The average size of the MOF-type nanocrystals synthesized on the nanofiber surface was 250nm.

[0062] Comparative Example 1 (no fluffy fiber prepared)

[0063] MOF-modified SC-crystal electret polylactic acid fluffy nanofiber membranes were prepared using the method described in Example 1. The difference is that no fluffing agent was added during electrospinning in this example. Specifically, S11, preparation of stereocomposite crystals (SC): PLLA and PDLA were crystallized using a solution method. Specifically, 1g of PLLA and 1g of PDLA were dissolved in 10g of dichloromethane. After complete dissolution, the two solutions were mixed evenly at 300rpm, and then solidified and crystallized at 180℃ to obtain SC crystals. S12, preparation of SC crystal electret polylactic acid nanofiber membrane: The SC crystals prepared in S11 were used as electret materials. First, 0.1g of SC crystals were dispersed in 3g of dichloromethane. Then, 1g of polylactic acid was dissolved in 7g of dichloromethane. These were then mixed evenly to prepare a spinning solution. Subsequently, 2mL of the spinning solution was used for electrospinning, with the output voltage set at 24kV, the solution feed rate at 1.5mL / h, and the fiber winding speed at 50 ... Under conditions of 0 rpm, spinning temperature of 40℃, and humidity of 70%, SC crystalline electret polylactic acid nanofiber membranes were spun. S13, Preparation of MOF-type nanocrystal growth precursor solution: First, 0.5 g of zinc nitrate was dissolved in 100 mL of water. Then, 1.5 g of terephthalic acid and 2.5 g of methylimidazole were dissolved in 100 mL of water respectively. The solutions were mixed under magnetic stirring at 300 rpm for 30 min to obtain a complete MOF-type nanocrystal growth precursor solution. S14, Preparation of MOF-type SC crystalline electret polylactic acid fluffy nanofiber membrane: The SC crystalline electret polylactic acid nanofiber membrane obtained in S12 was immersed in the MOF-type nanocrystal growth precursor solution prepared in S13. Light with a wavelength of 300 nm was provided by a mercury lamp, and the irradiation intensity was set to 250 mW / cm². 2 Then, the growth was carried out by microwave-assisted catalysis, with the microwave output power of 800W, the growth temperature of 200℃, the synthesis time of 50min, and the stirring speed of 100rpm. After the reaction was completed, the mixture was rinsed with deionized water and dried to obtain MOF-modified SC crystalline electret polylactic acid fluffy nanofiber membrane.

[0064] Comparative Example 2 (In the preparation of MOF-modified SC electret polylactic acid fluffy nanofiber membrane, UV-assisted + microwave catalysis was not used to promote in-situ synthesis)

[0065] The MOF-modified SC-crystal electret polylactic acid (PLLA) fluffy nanofiber membrane was prepared using the method described in Example 2. The difference is that UV-assisted + microwave catalysis was not used to promote in-situ synthesis in this example. Specifically, S21, preparation of stereocomposite crystals (SC): PLLA and PDLA were crystallized by melt blending. Specifically, 1.2 g of PLLA and 0.8 g of PDLA were melted at 250°C and uniformly mixed at 400 rpm, then transferred to a 0°C environment for rapid cooling and crystallization to obtain SC crystals; S22, preparation of SC-crystal electret polylactic acid fluffy nanofiber membrane: The SC crystals prepared in S21 were used as the electret material. First, [the text abruptly ends here]. 0.12g of SC crystals were dispersed in 3g of acetone. Then, 1.2g of polylactic acid and 0.8g of polyvinyl alcohol were dissolved in 7g of acetone and mixed uniformly to prepare a spinning solution. 1mL of the spinning solution was then subjected to electrospinning under the following conditions: output voltage of 35kV, solution feed rate of 0.5mL / h, fiber winding speed of 1000rpm, spinning temperature of 20℃, and humidity of 50%. This spun SC crystal electret polylactic acid fluffy nanofiber membranes were formed. The average diameter is 700 nm and the film thickness is 800 μm; S23, Preparation of MOF-type nanocrystal growth precursor solution: First, dissolve 0.8 g of magnesium acetate in 100 mL of ethanol, then dissolve 1.6 g of sodium terephthalate and 8 g of methylimidazole in 100 mL of ethanol respectively. Mix the solutions under magnetic stirring at 600 rpm for 20 min until completely dissolved to obtain the MOF-type nanocrystal growth precursor solution; S24, MOF Preparation of SC-electret polylactic acid fluffy nanofiber membrane: The SC-electret polylactic acid fluffy nanofiber membrane obtained in S22 was immersed in the MOF-type nanocrystal growth precursor solution prepared in S23. The growth temperature was set to 150℃, the synthesis time was set to 100min, and the stirring speed was set to 10rpm. After the reaction was completed, it was rinsed with deionized water and dried to obtain MOF-electret polylactic acid fluffy nanofiber membrane. The average size of the MOF nanocrystals synthesized on the nanofiber surface was 400nm.

[0066] Comparative Example 3 (No MOF-type nanocrystals grown)

[0067] The method of Example 3 was basically adopted to prepare polylactic acid fluffy nanofiber membranes. The difference is that MOF-type nanocrystals were not grown on the surface of the polylactic acid fluffy nanofiber membrane in this example. Specifically, S31, preparation of stereocomposite crystals (SC): PLLA and PDLA were crystallized by freeze-drying. Specifically, 0.8g of PLLA and 1.2g of PDLA were dissolved in 10g of chloroform. After complete dissolution, the two solutions were mixed evenly at 300rpm, then solidified at -100℃, and then dried at -40℃ to remove the solvent, obtaining SC crystals; S32, preparation of SC crystal electret polylactic acid fluffy nanofiber membrane: The SC crystals prepared in S31 were used as electret materials. First, 0.08g of SC crystals were dispersed in 2g of chloroform, then... 1.6g of polylactic acid and 0.4g of polyurethane were dissolved in 8g of chloroform and then uniformly mixed to prepare a spinning solution. 1mL of this spinning solution was then electrospun under the following conditions: output voltage of 30kV, solution feed rate of 0.8mL / h, fiber winding speed of 1500rpm, spinning temperature of 30℃, and humidity of 60%. This spun SC electret polylactic acid fluffy nanofiber membranes were formed, with an average fiber diameter of 750nm and a membrane thickness of 850μm. To ensure consistency in the remaining steps, the prepared SC electret polylactic acid fluffy nanofiber membranes were placed in a methanol solution, and then illuminated with 100nm wavelength light from an LED UV light source at an intensity of 500mW / cm². 2 Then, the nanofiber membrane was grown by microwave-assisted catalysis with a microwave output power of 700W, a growth temperature of 250℃, a synthesis time of 20min, and a stirring speed of 100rpm. After the reaction was completed, the membrane was rinsed with deionized water and allowed to stand and dry to obtain the nanofiber membrane.

[0068] Structural characterization and performance testing:

[0069] Scanning electron microscopy (SEM) observation: The microstructure of SC crystals, SC crystal electret polylactic acid fluffy nanofiber films, MOF-type nanocrystals, and MOF-modified SC crystal electret polylactic acid fluffy nanofiber films were observed using a field emission scanning electron microscope (model JSM-7900F, NEC). Figure 2 , Figure 3 , Figure 4 and Figure 5 (As shown).

[0070] Nanofiber membrane thickness and fiber diameter testing: The thickness of the nanofiber membrane was tested using a micrometer; the fiber diameter was calculated using ImageJ software, and the average fiber diameter was obtained.

[0071] Filtration performance testing: The filtration performance of a 10cm diameter circular nanofiber membrane was tested using a self-built filtration performance testing system. The air flow rate was set to 85L / min, and the particle size range of the NaCl atomized particles generated by the aerosol generator was 0.3–2.5μm. The particle concentration upstream and downstream of the nanofiber membrane was measured using a P-Trak particle counter (model 3910, TSI, USA; model 3330, TSI, USA), and the air resistance was measured using a micromanometer (AP800, TSI, USA). Finally, the filtration efficiency and pressure drop were calculated.

[0072] CO2 adsorption performance test: Based on the self-built gas adsorption performance test platform, medical-grade CO2 with a concentration of 99.5% was used, and an appropriate amount of CO2 was introduced into the test bench using a standard commercial regulator. The concentration of CO2 was monitored in real time using a portable CO2 sensor, and the initial concentration and the concentration after 1 hour of adsorption were recorded. The adsorption efficiency of the nanofiber membrane for CO2 was calculated.

[0073] CO adsorption performance test: Based on other adsorption performance test platforms built independently, an appropriate amount of CO was introduced into the test bench through a standard commercial regulator. The CO concentration was monitored in real time using a portable CO sensor, and the initial concentration and the concentration after 1 hour of adsorption were recorded. The adsorption efficiency of the nanofiber membrane for CO was calculated.

[0074] Formaldehyde adsorption performance test: Based on the self-built gas adsorption performance test platform, a suitable amount of formaldehyde was introduced into the test bench using a standard commercial regulator. The formaldehyde concentration was monitored in real time using a formaldehyde sensor, and the initial concentration and the concentration after 1 hour of adsorption were recorded. The adsorption efficiency of the nanofiber membrane for formaldehyde was calculated.

[0075] Experimental results: The technical solution described in this embodiment is as follows Figure 1 As shown, the main experimental materials and preparation and modification methods in this embodiment are described in detail, which is helpful for the preparation of MOF-modified SC crystalline electret polylactic acid fluffy nanofiber membranes. Figure 2 The surface morphology of the SC crystals prepared in Example 1 is shown. It can be clearly observed that the SC crystals prepared by the solution method have a uniform morphology and size, which is beneficial for their addition as an electret material to polylactic acid (PLA) to improve its polarization properties. Figure 3As shown, the surface morphology of the SC crystal electret polylactic acid fluffy fiber membrane prepared in Example 2 is displayed. It can be seen that the fiber exhibits a random structure, and grooves appear in the fiber coding. This is beneficial to increasing the specific surface area of ​​the fiber membrane and can increase the contact sites for MOF-type nanocrystals to grow on the fiber surface. It can also be seen that there are protrusions in the fiber, which is mainly due to the addition of SC crystals. The addition of SC crystals can significantly improve the interfacial polarization performance of the fiber. At the same time, deep charge traps are generated at its interface, which is of great significance for better charge storage and improving the electrostatic adsorption capacity of the fiber membrane for particulate matter.

[0076] Figure 4 The surface morphology of the MOF-type nanocrystals prepared in Example 3 is shown. It can be observed that the MOF-type nanocrystals prepared by UV-assisted and microwave catalysis have a relatively uniform size, with an average size of approximately 200 nm. Furthermore, the combined effect of UV and microwave not only significantly shortens the synthesis time and improves the preparation efficiency of MOFs, but also helps to adjust the porosity and pore size distribution of MOFs, optimize their gas adsorption performance, and promote the self-assembly process of organic ligands and metal ions, increasing the stability and structural integrity of MOFs. In addition, Figure 5 The morphology of the MOF-type SC-type electret polylactic acid fluffy nanofiber membrane prepared in Example 4 is shown. It can be seen that MOF-type nanocrystals are uniformly grown on the surface of the fibers, which is of great significance for improving the filtration performance of the fiber membrane for particulate matter and the adsorption performance for gas.

[0077] Table 1 shows the performance test results of Examples 1-4 and Comparative Examples 1-3. As can be seen from the table, the nanofiber membranes of Examples 1-4 can reach a maximum thickness of 900 μm. The nanofiber membranes exhibit excellent bulkiness, which is beneficial for the growth of MOF-type nanocrystals on the fibers. Furthermore, by controlling the electrospinning process, the fiber diameter of the fiber membrane is controlled at the nanometer level, which is more conducive to the effective interception of ultrafine particles. Simultaneously, the performance of filtering PM at a high airflow rate of 85 L / min was also demonstrated. 2.5 and PM 0.3 The performance of PM was measured, as shown in Table 1. Examples 1-4 tested PM... 0.3 Its filtration efficiency can reach 96.5% to 97.8%, effective against PM2.5. 2.5The filtration efficiency can reach 99.2% to 99.7%. Compared with Comparative Examples 1 to 3, the examples show superior filtration performance. At the same time, the fluffy fiber structure is more conducive to air circulation, thereby significantly reducing the air resistance of the nanofiber membrane (below 140 Pa). Compared to Comparative Example 1, the superior filtration performance is due to the dense fiber structure, which contributes to high filtration efficiency but also results in high air resistance. Compared to Comparative Example 2, because UV-assisted + microwave catalysis was not used to promote the in-situ synthesis of MOF-type nanocrystals, it was difficult to achieve complete synthesis of nanocrystals in a short time. Therefore, a nanofiber membrane with a larger specific surface area could not be formed to improve filtration efficiency, leading to a decrease in particulate matter filtration performance. Compared to Comparative Example 3, the obtained SC crystalline electret polylactic acid fluffy nanofiber membrane, after being soaked in methanol and treated with UV and microwave, exhibited in-situ synthesis of MOF-type nanocrystals on the fiber surface. The presence of methanol eliminated the initial charge on the fiber membrane surface. Although the deep charge traps generated by interfacial polarization could retain some charge, the loss of a large amount of surface charge and the large fiber gaps inside the fiber membrane easily allowed fine particles to pass through, thus reducing PM2.5 filtration efficiency. 0.3 and PM 2.5 The filtration performance decreases, but due to the lack of MOF-type nanocrystals, the large pores actually ensure low air resistance.

[0078] Table 1

[0079]

[0080] Table 2 compares the adsorption performance of MOF-type SC-type electret polylactic acid fluffy nanofiber membranes for CO2, formaldehyde, and CO. It can be seen that the adsorption efficiencies for CO2 in Examples 1–4 are 83.6%–85.1%, for formaldehyde 82.1%–97.2%, and for CO 80.3%–96.2%. This is mainly due to the uniform growth of MOF-type nanocrystals on the fiber surface, which provides a higher specific surface area for the fiber membrane. The fluffy fibers provide more contact sites with the gas, thus enabling higher adsorption capacity. Furthermore, UV irradiation can optimize the pore structure of the MOF-type nanocrystals, thereby increasing their specific surface area and pore volume, and improving their adsorption capacity for gas, thus giving them greater potential in applications such as gas separation, storage, and capture.

[0081] Table 2

[0082]

[0083]

[0084] This demonstrates that the method described in this invention, by preparing SC crystals and adding them as electrets to polylactic acid fibers, enhances the interfacial polarization of the fiber membrane, promotes the generation of deep charge traps, and simultaneously adds a fluffing agent to induce fiber fluffing. Then, MOF-type nanocrystals are synthesized in situ on the surface of the fluffy fibers through UV-assisted and microwave catalysis, thereby obtaining a MOF-modified SC crystal electret polylactic acid fluffy nanofiber membrane with high fluffiness, high efficiency and low resistance filtration performance, strong carbon fixation performance, and high efficiency formaldehyde and CO adsorption performance. This is of great significance for extending the application of polylactic acid biomaterials in the fields of air purification and toxic gas capture.

[0085] This invention provides a highly efficient polylactic acid fluffy nanofiber membrane for filtering gases and particulate matter, and a method for preparing the same. Many methods and approaches exist for implementing this technical solution; the above description is merely a preferred embodiment of the invention. It should be noted that those skilled in the art can make various improvements and modifications without departing from the principles of this invention, and these improvements and modifications should also be considered within the scope of protection of this invention. All components not explicitly stated in this embodiment can be implemented using existing technologies.

Claims

1. A method for preparing a polylactic acid fluffy nanofiber membrane for filtering gases and particulate matter, characterized in that, Includes the following steps: Step S1: Preparation of stereocomposite crystal SC: Stereocomposite crystal SC is obtained by crystallizing polylactic acid (PLLA) and polylactic acid (PDLA). Step S2: Preparation of SC crystal electret polylactic acid fluffy nanofiber membrane: First, polylactic acid is dissolved in a solvent to prepare a polylactic acid solution. Then, the stereocomposite crystal SC prepared in S1 is used as the electret material. The stereocomposite crystal SC is added to the polylactic acid solution. By adding a fluffing agent to the polylactic acid solution, an SC crystal electret polylactic acid fluffy nanofiber membrane with uniformly sized fibers is prepared by electrospinning process. Step S3: Preparation of MOF-type nanocrystal growth precursor solution: Dissolve the metal salt, terephthalate reagent and imidazole reagent in a solvent respectively, and then slowly add the metal salt solution to the mixed solution of terephthalate reagent and imidazole reagent. After stirring and mixing evenly, the MOF-type nanocrystal growth precursor solution is obtained. Step S4: Preparation of MOF-modified SC-electret polylactic acid fluffy nanofiber membrane: The SC-electret polylactic acid fluffy nanofiber membrane obtained in step S2 is immersed in the MOF-type nanocrystal growth precursor solution prepared in step S3. Under ultraviolet (UV) irradiation, the MOF-type nanocrystals are grown at a constant temperature using microwave-assisted catalysis. Stirring is used to ensure the uniformity of the size of the MOF-type nanocrystals grown on the fiber surface. After growth, the membrane is rinsed with the solution and allowed to stand and dry to obtain the MOF-modified SC-electret polylactic acid fluffy nanofiber membrane.

2. The method according to claim 1, characterized in that, In step S1, the mass ratio of L-polylactic acid (PLLA) to D-polylactic acid (PDLA) ranges from 1:9 to 9:

1.

3. The method according to claim 2, characterized in that, In step S1, the crystallization treatment method includes at least one of solution method, melt blending method, freeze drying method, and phase transformation method; The solution method includes: dissolving L-polylactic acid (PLLA) and D-polylactic acid (PDLA) in at least one of dimethylformamide, dichloromethane, chloroform, acetone, hexafluoroisopropanol, and ethyl acetate as solvents, with a stirring speed of 100–500 rpm, to obtain L-PLLA solution and D-PDLA solution respectively, wherein the mass ratio of L-PLLA to solvent is 5%–30%, and the mass ratio of D-PDLA to solvent is 5%–30%; then, stirring and mixing the L-PLLA solution and D-PDLA solution at a stirring speed of 100–500 rpm to obtain a mixed solution, and solidifying and crystallizing the mixed solution by solvent evaporation or gelation to obtain stereocomposite crystals SC; wherein the solvent evaporation temperature is 20℃–250℃, and the gelation temperature is 20℃–60℃; The melt blending method includes: melting L-polylactic acid (PLLA) and D-polylactic acid (PDLA) at a high temperature of 170°C to 300°C, stirring at a speed of 100 to 500 rpm during melting, and cooling at a temperature of -10°C to 30°C to obtain stereocomposite crystals (SC). The freeze-drying method includes: using at least one of dimethylformamide, dichloromethane, chloroform, acetone, hexafluoroisopropanol, and ethyl acetate as a solvent; adding L-polylactic acid (PLLA) and D-polylactic acid (PDLA) to the solvent respectively; setting the stirring speed to 100-500 rpm to obtain L-polylactic acid (PLLA) solution and D-polylactic acid (PDLA) solution respectively; wherein the mass ratio of L-polylactic acid (PLLA) to solvent is 5%-30% and the mass ratio of D-polylactic acid (PDLA) to solvent is 5%-30%; mixing the L-polylactic acid (PLLA) solution and the D-polylactic acid (PDLA) solution; stirring speed during mixing is 100-500 rpm; then freezing and molding at ultra-low temperature of -150℃ to -50℃; and drying at -20℃ to -49℃ to remove the solvent to form stereocomposite crystals SC. The phase transformation method includes: using at least one of dimethylformamide, dichloromethane, chloroform, acetone, hexafluoroisopropanol, and ethyl acetate as a solvent, adding L-polylactic acid (PLLA) and D-polylactic acid (PDLA) to the solvent respectively, setting the stirring speed to 100-500 rpm to obtain L-polylactic acid (PLLA) solution and D-polylactic acid (PDLA) solution respectively, wherein the mass ratio of L-polylactic acid (PLLA) to solvent is 5%-30%, and the mass ratio of D-polylactic acid (PDLA) to solvent is 5%-30%, mixing the L-polylactic acid (PLLA) solution and the D-polylactic acid (PDLA) solution, stirring the solution at 100-500 rpm, and then setting the cooling temperature to -20℃ to -100℃, with a temperature change rate of 1℃ / min to 5℃ / min to form stereocomposite crystals SC.

4. The method according to claim 3, characterized in that, In step S2, the polylactic acid solution contains 5% to 25% polylactic acid, the mass ratio of the stereocomposite crystal SC to polylactic acid is 1:20 to 1:2, the solvent used is at least one of dimethylformamide, dichloromethane, chloroform, acetone, hexafluoroisopropanol, and ethyl acetate, the leavening agent is at least one of cellulose acetate, polyvinyl alcohol, polyurethane, polycaprolactone, chitosan, and polylactic acid copolymer, and the mass ratio of the leavening agent to polylactic acid is 1:10 to 2:

1.

5. The method according to claim 4, characterized in that, In step S2, when using electrospinning, the output voltage of electrospinning is 5–35 kV, the solution consumption rate is 0.5–4 mL / h, the spinning winding speed is 100–1500 rpm, the receiving distance is 8–30 cm, the spinning temperature is 20–50 °C, the humidity is 50%–90%, the average diameter of polylactic acid fluffy nanofibers is 200–990 nm, and the thickness of the polylactic acid fluffy nanofiber membrane is 300–1000 μm.

6. The method according to claim 5, characterized in that, In step S3, the metal salt is at least one of zinc nitrate, zinc acetate, zinc sulfate, zinc chloride, and zinc oxide.

7. The method according to claim 6, characterized in that, In step S3, the terephthalate reagent is at least one of terephthalic acid, sodium terephthalate, ammonium terephthalate, dimethyl terephthalate, and ammonium hydrogen terephthalate. The imidazole reagent is at least one of methylimidazolium, dimethylimidazolium, 2-aminobenzimidazole, 2-aminoimidazolium, 1-3-aminopropylimidazolium, 4-aminoimidazolium, and imidazolylbenzylbenzyl. The solvent is at least one of dimethyl thionamide, dimethylformamide, deionized water, ethanol, methanol, n-butanol, isopropanol, ethylene glycol, and chloroform. The mass ratio of the metal salt to the terephthalate reagent is 1:8-1:1; The mass ratio of the metal salt to the imidazole reagent is 1:10 to 1:1; The mass ratio of the metal salt to the solvent is 1:1000 to 1:50; When stirring, the stirring speed is 100-600 rpm and the stirring time is 20-40 min.

8. The method according to claim 7, characterized in that, In step S4, the microwave output power used is 300–1200 W, the growth temperature is 150–250 °C, the synthesis time is 20–100 min, the stirring speed is 10–300 rpm, and the ultraviolet (UV) light wavelength range is 100–400 nm with an irradiation intensity of 100–500 mW / cm². 2 The irradiation time is the same as the synthesis time. The ultraviolet light source is selected from at least one of mercury lamp, xenon lamp, LED UV light source, and black light lamp. The average particle size of MOF nanocrystals is 100-990 nm.

9. The method according to claim 8, characterized in that, In step S4, the drying method used is at least one of natural drying, hot air drying, freeze drying, vacuum drying, microwave drying, spray drying, flash drying, and radiation drying.

10. A polylactic acid fluffy nanofiber membrane for high-efficiency filtration of gases and particulate matter, characterized in that, Prepared using the method described in any one of claims 1 to 9.

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