Electrospun nanofiber air filtration membrane with three-layer gradient structure polylactic acid, and preparation method and application thereof

Abstract

The application relates to a polylactic acid electrostatic spinning nanofiber air filtration membrane with a three-layer gradient structure, a preparation method and application thereof, polylactic acid / silicon dioxide nanofibers are prepared by using a blending method, the surfaces of the polylactic acid / silicon dioxide nanofibers are modified by fluorination through FOTS, the polylactic acid / silicon dioxide nanofibers are used as an outer super-hydrophobic layer, polylactic acid nanofibers and polylactic acid / MOF nanofibers are sequentially deposited, a kind of air filtration membrane with gradually decreasing fiber diameter and pore size is obtained by adjusting the content of polylactic acid, the content of polylactic acid relative to MOF and electrospinning parameters and the like, the air filtration membrane has high filtration efficiency, small resistance pressure drop, high ammonia gas adsorption performance, high dust holding capacity, self-cleaning performance, long service life and the like, and is suitable for the field of air purification.

Description

Technical Field

[0001] This invention relates to a composite filter material for particulate matter filtration and ammonia purification, specifically a polylactic acid electrospun nanofiber air filter membrane with a three-layer gradient structure, its preparation method and application, belonging to the field of nanofiber membrane preparation technology. Background Technology

[0002] With the development of industrialization and animal husbandry, air pollution has become a substantial threat to human health and the ecological environment. In particular, harmful gases such as particulate matter (PM) and ammonia (NH3) produced by livestock farms pose a significant threat to the environment and human health. Especially harmful gases with an aerodynamic diameter of less than 2.5 micrometers (PM2.5)... 2.5 Particulate matter (PM) easily penetrates the lungs and bronchi, while ammonia can cause acute health problems such as eye and nasal irritation and respiratory symptoms. Therefore, polluted air has a direct impact on human health. Air filtration is considered one of the most promising and effective technologies for mitigating this problem.

[0003] Currently, traditional air filter membranes are mainly made of materials such as polyethylene, glass fiber, and polypropylene. However, these membranes are relatively inefficient at capturing gaseous pollutants, primarily due to their inert surfaces and limited specific surface area. To effectively filter particulate matter and gaseous pollutants, air filter membranes need to incorporate multi-layered structures with specific functions. For example, combining activated carbon filter membranes with traditional air filter membranes can significantly improve filtration efficiency, but it also significantly increases pressure drop and energy consumption. Therefore, there is an urgent need to develop air filter membranes with high efficiency, multiple functions, and low pressure drop.

[0004] In recent years, with the development of nanotechnology, air filtration technology has been significantly improved. Electrospinning technology has become an ideal method for producing fiber filter membranes with defined dimensions, morphology, and functional components. By constructing multilayer gradient pore structures, highly efficient filter membranes with high filtration efficiency, low pressure drop, and long service life can be developed. However, most chemically synthesized polymers face a common problem: non-renewability, non-reusability, and non-biodegradability, which leads to secondary environmental problems. Therefore, developing natural or biodegradable polymer filter membranes is of significant scientific and technological importance for reducing environmental pollution and building a sustainable society. Polylactic acid (PLA) not only possesses excellent mechanical properties, good biocompatibility, and is non-toxic and mild, but also exhibits good biodegradability, making it an environmentally friendly polymer material. Furthermore, PLA exhibits shear piezoelectricity due to the chiral centers in its molecular chain, generating polarization and charge during breathing vibrations and friction without the need for external electric field polarization treatment, thereby promoting the electrostatic capture of PMs. These characteristics make PLA a promising candidate for application in the field of air filtration materials. Summary of the Invention

[0005] The main objective of this invention is to provide an air filter membrane with a three-layer gradient structure of polylactic acid electrospun nanofibers, its preparation method, and its application, so as to solve the problems of low filtration efficiency, high pressure drop, low dust holding capacity, and poor gas adsorption performance of current air filter membranes.

[0006] To achieve the above objectives, in a first aspect, the present invention provides a method for preparing a polylactic acid electrospun nanofiber air filter membrane with a three-layer gradient structure, comprising: electrospinning a polylactic acid / silica solution as an outer layer spinning solution to form an outer layer fiber; fluorinating the outer layer fiber with a mixed solution composed of n-hexane and 1H,1H,2H,2H-perfluorooctyltrichlorosilane (FOTS); electrospinning a polylactic acid solution as a middle layer spinning solution on one side of the outer layer fiber to form a middle layer fiber; and electrospinning a polylactic acid / UiO-66-NH2 solution as an inner layer spinning solution on one side of the middle layer fiber to form an inner layer fiber, thereby obtaining a composite membrane with a three-layer gradient structure.

[0007] Furthermore, the outer spinning solution is obtained by uniformly dispersing silica powder in a mixed solution of dichloromethane (DCM) and N,N-dimethylformamide (DMF), ultrasonically treating it for 1 hour, and then adding polylactic acid (PLA) particles to the mixed solution.

[0008] Furthermore, the volume ratio of DCM to DMF is 3:2.

[0009] Furthermore, the outer spinning solution contains 10 wt% PLA and 0.5-5 wt% silica.

[0010] Furthermore, the intermediate spinning solution is obtained by adding PLA particles to a mixed solution of DMF and DCM.

[0011] Furthermore, the volume ratio of DCM to DMF is 3:2.

[0012] Furthermore, the PLA mass fraction in the intermediate spinning solution is 10 wt%.

[0013] Furthermore, the inner spinning solution is prepared by uniformly dispersing UiO-66-NH2 particles in a mixed solution of DCM and DMF, ultrasonically treating for 1 hour, and then adding PLA particles and stirring at room temperature for 6 hours. The PLA mass fraction is 9-5 wt%, and the UiO-66-NH2 mass fraction is 1-7 wt%.

[0014] Furthermore, the volume ratio of DCM to DMF is 3:2.

[0015] Furthermore, the outer fiber layer is immersed in a mixed solution of hexane and FOTS, and then heat-treated at 45°C for 2 hours.

[0016] Furthermore, the volume ratio of hexane to FOTS is 2000:1.

[0017] Furthermore, the electrospinning parameters for the outer fiber are as follows: room temperature, average humidity of 35%, solution feed rate of 1.5 mL / h, current collector speed of 80 r / min, positive voltage of 16 kV, negative voltage of 5 kV, and collection distance of 20 cm.

[0018] Furthermore, the spinning parameters for the middle layer fiber are as follows: room temperature, average humidity of 35%, solution feed rate of 1.5 mL / h, current collector speed of 80 r / min, positive high voltage of 19 kV, negative high voltage of 5 kV, and collection distance of 20 cm.

[0019] Furthermore, the spinning parameters for the fourth step of the inner layer fiber are as follows: room temperature, average humidity of 35%, solution feed rate of 1.5 mL / h, current collector speed of 80 r / min, positive high voltage of 20 kV, negative high voltage of 5 kV, and collection distance of 20 cm.

[0020] Secondly, the present invention provides an air filter membrane with a three-layer gradient structure of polylactic acid electrospun nanofibers, comprising, from the inside out, an inner layer of polylactic acid / UiO-66-NH2 fibers, a middle layer of polylactic acid solution fibers, and an outer layer of fluorinated polylactic acid / silica solution fibers, wherein the diameter and pore size of the air filter membrane decrease sequentially from the outer layer of fibers to the inner layer of fibers.

[0021] Polylactic acid electrospun nanofiber air filter membrane for PM 0.5 It has a high filtration efficiency of 99.15% and a pressure drop of 89.65 Pa; the water contact angle of the outer fiber is 161°; and the dust holding capacity at 1000 Pa is 55.74 g / m³. 2 The dust residue remaining on the filter membrane surface after simple mechanical vibration and water rinsing is only 6g / m³. 2 The adsorption capacity for NH3 was 103.4 cm⁻¹. 3 / g.

[0022] Thirdly, the present invention provides the application of the above-mentioned polylactic acid electrospun nanofiber air filter membrane with a three-layer gradient structure in air filter materials.

[0023] Fourthly, the present invention provides an air filtration product comprising the above-mentioned polylactic acid electrospun nanofiber air filter membrane having a three-layer gradient structure.

[0024] The air filter membrane provided by this invention comprises an outer fluorinated polylactic acid / silica layer, a middle polylactic acid nanofiber layer, and an inner polylactic acid / UiO-66-NH2 nanofiber layer. First, polylactic acid / silica nanofibers are prepared using a blending method, and their surface is modified with FOTS to serve as a superhydrophobic outer layer. Then, polylactic acid nanofibers and polylactic acid / MOF nanofibers are deposited sequentially. By adjusting the polylactic acid content, the polylactic acid content relative to MOF, and electrospinning parameters, an air filter membrane with gradually decreasing fiber diameter and pore size is obtained. The preparation method is simple and practical, requiring less sophisticated equipment. It offers high filtration efficiency, low pressure drop, high ammonia adsorption capacity, high dust holding capacity, self-cleaning properties, and a long service life. Compared to traditional polylactic acid filter membranes and commercial glass fiber filter membranes, it exhibits superior filtration performance and is suitable for air purification applications. Attached Figure Description

[0025] The accompanying drawings, which form part of this application, are used to provide a further understanding of the invention. The illustrative embodiments of the invention and their descriptions are used to explain the invention and do not constitute an improper limitation of the invention.

[0026] In the attached diagram:

[0027] Figure 1 The morphology and structure of the three-layer composite filter membrane in the embodiments of the invention are characterized. Scanning electron microscope (SEM) images of the outer layer (a, d), the middle layer (b, e), and the inner layer (c, f), the average fiber diameter (g), pore size distribution (h), and average pore size (i) of the outer, middle, and inner layers.

[0028] Figure 2 The water contact angle of the outer fiber prepared in Example 1 of the invention.

[0029] Figure 3 Scanning electron microscope (SEM) image of UiO-66-NH2 (a). SEM image of the inner fiber (b). SEM and elemental distribution map of a single P5U7 fiber (c).

[0030] Figure 4 The graph shows the filtration performance results of the filter membranes, including the filtration efficiency and pressure drop of the outer (a), double (b), and triple (c) nanofiber layers. The quality factor (QF) of the outer (d), double (e), and triple (f) nanofiber layers with different particle sizes is also shown. The filtration efficiency (g) and PM2.5 levels of the PLA filter membrane, commercial glass fiber filter membrane, and FPLAS-1 / P19 / P5U7 filter membrane are also presented. 0.5 QF(h). PLA filter membranes, commercial glass fiber filter membranes, and FPLAS-1 / P19 / P5U7 filter membranes, as well as some reported air filter membranes, for PM2.5. 0.5Comparison of filtration efficiency and pressure drop (i).

[0031] Figure 5 For (a) the self-cleaning performance test of the FPLAS-1 / P19 / P5U7 filter membrane. (b)

[0032] (c) Slip angle (SA) of FPLAS-1 / P19 / P5U7 filter membrane. (d) Contact angle (CA) and slip angle (SA) of clean and dirty FPLAS-1 / P19 / P5U7 filter membrane after cleaning. (e) Contact angle (CAs) and slip angle (SAs) of FPLAS-1 / P19 / P5U7 filter membrane after 100 finger touch tests. (f) Pressure drop and (g) dust holding capacity (airflow velocity of 10.6 cm / s) of FPLAS-1 / P19 / P5U7 filter membrane, PLA filter membrane and commercial glass fiber filter membrane during one service cycle. (h) Optical images of the surface of FPLAS-1 / P19 / P5U7 filter membrane in initial, end-of-life, mechanical vibration and water washing conditions.

[0033] Figure 6 This is a schematic diagram showing the filtration efficiency and pressure drop of three different filter membranes for particles of different sizes (airflow velocity of 5.3 cm / s).

[0034] Figure 7 Adsorption capacity and mechanism of ammonia (NH3). (a) Ammonia adsorption isotherms of FPLAS-1 / P19 / P5U7, PLA, and commercial glass fiber filters at 25 °C. (b) Comparison of ammonia adsorption capacity of FPLAS-1 / P19 / P5U7, commercial glass fiber, PLA filters with other reported fiber filters. (c) Nitrogen adsorption-desorption curves of FPLAS-1 / P19 / P5U7, PLA, and commercial glass fiber filters. (d) Schematic diagram of ammonia adsorption via hydrogen bonding of NH2 groups in UiO-66-NH2.

[0035] Figure 8 (a) Schematic diagram of the preparation of the three-layer gradient composite filter membrane; (b) Schematic diagram of the fiber structure, PM gradient filtration and harmful gas adsorption process of the three-layer gradient composite filter membrane. Detailed Implementation

[0036] The embodiments of the present invention are described in detail below. The embodiments described below are exemplary and are only used to explain the present invention, and should not be construed as limiting the present invention. Where specific techniques or conditions are not specified in the embodiments, they are performed according to the techniques or conditions described in the literature in the art or according to the product instructions. In this invention, polylactic acid (PLA, molecular weight = 110,000), N,N-dimethylformamide (DMF, analytical grade, ≥99.5%), 2-amino-1,4-dicarboxylic acid (BDC-NH2, 98%), zirconium chloride (ZrCl4, 98%), and 1H,1H,2H,2H-perfluorooctyltrichlorosilane (FOTS, 97%) were purchased from Shanghai Maclean Biochemical Co., Ltd. Dichloromethane (DCM, analytical grade, ≥99.5%) was purchased from Tianjin Fuyu Fine Chemicals Co., Ltd. Silica (SiO2, 500 nm) and n-hexane (analytical grade, ≥99%) were purchased from Aladdin Industries, Inc. Unless otherwise specified, all reagents and instruments used are commercially available products. The room temperature in these embodiments was 22-28°C. The method for synthesizing UiO-66-NH2 nanoparticles in this invention follows the method described by Garibay et al. Typically: 1.43 g ZrCl4, 1.12 g BDC-NH2, and 70 mL DMF were mixed and sonicated for 5 minutes. The mixture was then transferred to a 100 mL stainless steel autoclave lined with polytetrafluoroethylene and reacted at 120°C for 24 hours. After cooling to room temperature, the mixture was centrifuged to separate the solids, and then washed three times with DMF. Finally, the precipitate was dried at 120°C for 6 hours.

[0037] In this invention, filtration performance is tested by dispersing simulated PM particles into a mixing chamber (length × height × width: 50 × 50 × 40 cm) via an aerosol diffuser and injection system. PM concentration (i.e., the amount of PM in 0.1 liters of air) is monitored by a dual PM laser sensor (A4-CG, Beijing Yishan Technology Co., Ltd., China). Filtration efficiency is determined by calculating the percentage decrease in PM concentration before and after filtration. Furthermore, the pressure drop across the filter membrane is recorded by a differential pressure gauge (DT-8890A, Shenzhen Huashengchang Machinery Industry Co., Ltd., China). PM 0.5 PM is defined as having an aerodynamic diameter of less than 0.5 micrometers. 0.5-1 PM represents aerodynamic diameters ranging from 0.5 to 1 micrometer. 1-2.5 PM represents aerodynamic diameters ranging from 1 to 2.5 micrometers. 2.5-5 PM represents aerodynamic diameters ranging from 2.5 to 5 micrometers. 5-10 PM represents aerodynamic diameters ranging from 5 to 10 micrometers.

[0038] This invention provides an air filter membrane with a reduced pore size gradient arranged from the outer layer to the inner layer, wherein the outer layer consists of fluorinated polylactic acid / silica nanofibers, polylactic acid nanofibers, and polylactic acid nanofibers arranged sequentially from the outer layer to the inner layer.

[0039] PLA / SiO2 nanofibers were first prepared using electrospinning technology and then fluorinated by immersion in a silane solution. Subsequently, PLA nanofibers and PLA / UiO-66-NH2 nanofibers were continuously spun using electrospinning technology to form an intermediate and inner layer, respectively. This process effectively captures particles of different sizes and adsorbs harmful gases.

[0040] To more clearly illustrate the structural features and effects of the present invention, the present invention will be described in detail below with reference to the accompanying drawings and specific embodiments.

[0041] Example 1

[0042] A method for preparing a polylactic acid-based three-layer gradient electrospun nanofiber air filter membrane includes the following steps:

[0043] The first step is to prepare the three spinning solutions:

[0044] Silica powder was uniformly dispersed in a mixed solution of DCM and DMF (volume ratio 3:2), and ultrasonically treated for 1 hour. PLA particles were then added to the SiO2 / DMF / DCM dispersion to obtain a PLA mass fraction of 10 wt% and a silica mass fraction of 1 wt%, which was used as the outer spinning solution. The FPLAS nanofiber layer was labeled as FPLAS-1.

[0045] PLA particles were added to a mixed solution of DMF and DCM (volume ratio 3:2) to obtain a solution with a PLA mass fraction of 10 wt%. This solution was applied at a positive voltage of 19 kV and used as the intermediate spinning solution; it was labeled as P19.

[0046] UiO-66-NH2 particles were uniformly dispersed in a mixed solution of DCM and DMF (volume ratio 3:2) and ultrasonically treated for 1 hour. PLA particles were then added to the UiO-66-NH2 / DMF / DCM dispersion and stirred at room temperature for 8 hours to form the inner layer spinning solution. The PLA mass fraction was 5 wt% and the UiO-66-NH2 mass fraction was 7 wt%. The PLA / UiO-66-NH2 layer was labeled as P5U7.

[0047] Step 2, Fluorinated polylactic acid / silica nanofiber outer layer:

[0048] The outer spinning solution was loaded into a 5 mL syringe, and an outer fiber membrane was obtained by electrospinning. The membrane (25 mm × 70 mm) was then immersed in a mixed solution of 50 mL n-hexane and 25 μL FOTS for 30 minutes, and then heat-treated at 45 °C for 2 hours to obtain a fluorinated nanofiber outer layer. The spinning parameters were: room temperature, average humidity of 35%, solution feed rate of 1.5 mL / h, current collector speed of 80 r / min, positive voltage of 16 kV, negative voltage of 5 kV, and collection distance of 20 cm.

[0049] The third step is the lamination of the outer and middle layers:

[0050] The fluorinated nanofiber outer layer was attached to an aluminum foil substrate on a roller. Then, the middle layer spinning solution was loaded into a 5 mL syringe, and the middle layer fiber membrane was spun by electrospinning to obtain a fluorinated polylactic acid / silica nanofiber outer layer and a polylactic acid middle layer composite membrane. The spinning parameters were: room temperature, average humidity of 35%, solution feed rate of 1.5 mL / h, current collector speed of 80 r / min, positive voltage of 19 kV, negative voltage of 5 kV, and collection distance of 20 cm.

[0051] The fourth step is the lamination of the outer, middle, and inner layers:

[0052] A composite film consisting of a fluorinated polylactic acid / silica nanofiber outer layer and a polylactic acid middle layer was attached to an aluminum foil substrate on a roller. Then, the inner layer spinning solution was loaded into a 5mL syringe, and the middle layer fiber membrane was spun out by electrospinning, yielding a fluorinated polylactic acid / silica nanofiber outer layer, a polylactic acid middle layer, and a polylactic acid...

[0053] / UiO-66-NH2 three-layer composite membrane; spinning parameters are: room temperature, average humidity of 35%, solution feed rate of 1.5mL / h, current collector speed of 80r / min, positive voltage of 20kV, negative voltage of 5kV, and collection distance of 20cm.

[0054] The prepared fiber membrane had a water contact angle of 161°, and the filtration membrane was effective against PM2.5. 0.5 It has a high filtration efficiency of 99.15%, a pressure drop of 89.65 Pa, and a dust holding capacity of 55.74 g / m³ at 1000 Pa. 2 ,like Figure 6 and 7 As shown, the amount of dust remaining on the filter membrane surface after simple mechanical vibration and water rinsing is only 5.9 g / m². 2 It exhibits excellent self-cleaning properties and reusability, with an adsorption capacity of 103.4 cm⁻¹ for NH₃. 3 / g.

[0055] Example 2

[0056] The difference between this embodiment and Embodiment 1 is that the silica mass fraction in the outer spinning solution is 0.5 wt%, and the FPLAS nanofiber layer is labeled as FPLAS-0.5.

[0057] Example 3

[0058] The difference between this embodiment and Embodiment 1 is that the silica mass fraction in the outer spinning solution is 3 wt%, and the FPLAS nanofiber layer is labeled as FPLAS-3.

[0059] Example 4

[0060] The difference between this embodiment and Embodiment 1 is that the silica mass fraction in the outer spinning solution is 5 wt%, and the FPLAS nanofiber layer is labeled as FPLAS-5.

[0061] Example 5

[0062] The difference between this embodiment and Embodiment 1 is that the positive high voltage in the middle spinning solution during the spinning process is 19KV, which is marked as P19.

[0063] Example 6

[0064] The difference between this embodiment and Embodiment 1 is that the inner spinning solution has a PLA mass fraction of 9 wt% and a UiO-66-NH2 mass fraction of 1 wt%, and is labeled as P9U1.

[0065] Example 7

[0066] The difference between this embodiment and Embodiment 1 is that the inner spinning solution has a PLA mass fraction of 7 wt% and a UiO-66-NH2 mass fraction of 3 wt%, and is labeled as P7U3.

[0067] Example 8

[0068] The difference between this embodiment and Embodiment 1 is that the inner spinning solution has a PLA mass fraction of 5 wt% and a UiO-66-NH2 mass fraction of 5 wt%, and is labeled as P5U5.

[0069] Example 9

[0070] The difference between this embodiment and Embodiment 1 is that the inner spinning solution has a PLA mass fraction of 5 wt% and a UiO-66-NH2 mass fraction of 7 wt%, and is labeled as P5U7.

[0071] The fiber morphology and pore structure of the optimal three-layer composite filter membrane are as follows: Figure 1As shown in (a) to (i), the outer layer is FPLAS-1, the middle layer is P19, and the inner layer is P5U7. The outer layer is prepared by electrospinning SiO2-containing fibers, followed by fluorination. The addition of SiO2 significantly alters the fiber surface, making its surface morphology rougher. Figure 1 (a) and (d) show that subsequent fluorination of the fibers resulted in the formation of numerous nanospheres (FPLAS-1) on the surface. The fiber surface morphology of the intermediate layer (PLA-19) is smooth, as... Figure 1 As shown in (b) and (e), the inner layer (P5U7) exhibits numerous nanoprotrusions, primarily due to doping with UiO-66-NH2. The average fiber diameters of FPLAS-1, PLA-19, and P5U7 are 947.21 nm, 609.60 nm, and 378.24 nm, respectively. Figure 1 As shown in (g). The pore size distribution of each layer is as follows. Figure 1 As shown in (h), the gradual decrease in interlayer pore size (FPLAS-1, PLA-19, and P5U7) is illustrated. The average pore sizes are 4.98 μm, 3.70 μm, and 1.91 μm, respectively. This pore size reduction is crucial for multi-stage filtration, effectively mitigating the risk of particle clogging within the filter membrane. For a given filter membrane thickness, the gradual decrease in pore size leads to a gradual increase in pressure drop, rather than a sudden increase; this structure allows the filter membrane to maintain low pressure drop and high dust holding capacity. Each layer was adjusted during electrospinning by modifying process parameters and the mass fraction of the polymer solution. Outer layers with different SiO2 concentrations exhibited a fiber morphology similar to FPLAS-1. The addition of appropriate SiO2 and subsequent fluorination increased the fiber roughness. Fluorination simultaneously reduced the fiber surface energy, thereby enhancing its hydrophobic characteristics. FPLAS-1 was chosen as the final outer layer of the composite filter membrane due to its superior contact angle of 161.4 degrees, as shown in Table 1 and... Figure 2 As shown. The fibers in the intermediate layer all exhibit a smooth surface morphology, and the average fiber diameter shows a decreasing trend with increasing voltage. P19 as the intermediate layer is beneficial for the formation of gradients in the fiber structure. UiO-66-NH2 was added to the inner layer to improve the adsorption performance of the filtration membrane. To enhance the loading capacity of UiO-66-NH2 in the inner layer, the electrospinning solution was adjusted by reducing the PLA content and increasing the UiO-66-NH2 nanoparticle content. SEM images of nanofibers with different UiO-66-NH2 contents are shown. Figure 3As shown in (b), in P9U1 and P7U3, the UiO-66-NH2 nanoparticles are completely encapsulated by fibers. When the mass fraction of UiO-66-NH2 relative to PLA is further increased, the fiber diameter of P5U5 is smaller than the particle size of the UiO-66-NH2 nanoparticles, exposing UiO-66-NH2 to the fiber exterior. The fibers of P5U7 are slightly larger than those of P5U5. Because many UiO-66-NH2 particles aggregate at the same cross-section of the fiber, not only is the fiber diameter increased, but more nanoparticles are also exposed. Figure 3 (c) shows that elements C, O, and Zr are uniformly distributed within a single fiber, indicating uniform loading of UiO-66-NH2 on the fiber. The water contact angles of the PLA / SiO2 and FPLAS layers are shown in Table 1.

[0072] Table 1

[0073] Before fluorination 136.1±1.5 137.7±3.5 141.8±3.9 134.4±2.6 129.9±0.3 After fluorination 142.1±2.5 157.8±0.9 161.4±1.8 157.3±2.3 145.1±2.7

[0074] Table 2

[0075] FPLAS-1 / P19 / P5U7 filter membrane 0.114 181 PLA filter membrane 0.072 81.31 Commercial glass fiber filter membrane 0.024 28.41

[0076] The thickness of the filter membrane was determined by comparing the QF values ​​of the filter membranes at different electrospinning times. The filtration performance of the outer, double-layer, and triple-layer filter membranes at different wind velocities is shown below. Figure 4 As shown. Figure 4 (a) The filtration efficiency of the middle and outer layers ranges from 33.01% to 86.94% (PM). 0.5 ), 35.05% to 87.58% (PM 0.5-1 ), 82.08% to 95.28% (PM 1-2.5 ), 87.36% to 99.45% (PM 2.5-5 ), 92.91% to 99.99% (PM 5-10 The pressure drop increased from 17.36 Pa to 31.68 Pa. The filtration efficiency of all outer layers increased with increasing particle size. This improvement is attributed to the screening filtration method playing a dominant role in intercepting particles in the outer layers. Figure 4 (d) shows that FPLAS-1 (30 minutes) reached PM 5-10 It boasts the highest QF, primarily due to its near-perfect filtration efficiency (99.99%). Meanwhile, FPLAS-1 (20 minutes) demonstrates superior performance against PM2.5. 2.5-5 The highest QF indicates its superior filtration performance for PM2.5-5. Considering that one function of the outer layer is to trap coarse particles (especially those with a diameter greater than 2.5 micrometers), FPLAS-1 (20 min) is the best choice as the outer layer for constructing the gradient structure of the composite filter membrane.

[0077] Figure 4(b) Demonstrates the filtration efficiency and pressure drop of various membrane combinations when adding intermediate layers of different thicknesses in FPLAS-1 (20 minutes). The above combinations are for PM... 1-2.5 Achieving a filtration efficiency of over 97.80%, the FPLAS-1 (20 minutes) / P19 (30 minutes) combination effectively filters PM2.5. 1-2.5 With the highest QF, such as Figure 4 As shown in (e). Simultaneously, the FPLAS-1 (20 minutes) / P19 (30 minutes) combination also achieved a PM reduction of over 90.02%. 0.5-1 The filtration efficiency is significantly high. Therefore, FPLAS-1 (20 minutes) and P19 (30 minutes) were selected as the outer and middle layer materials.

[0078] The filtration performance after further introducing an inner layer onto FPLAS-1 (20 min) / P19 (30 min) nanofibers is as follows: Figure 4 As shown in (c). All combined filter membranes can capture 100% of PM. 5-10 and PM 2.5-5 And its effect on PM 1-2.5 PM 0.5-1 and PM 0.5 The filtration efficiency still shows an increasing trend with the increase of inner layer electrospinning time. It is worth noting that the FPLAS-1 (20 minutes) / P19 (30 minutes) / P5U7 (40 minutes) (abbreviated as FPLAS-1 / P19 / P5U7) filter membrane achieved PM... 0.5 The optimal QF.

[0079] The filtration efficiencies of FPLAS-1 / P19 / P5U7 are respectively PM 0.5 99.15% of PM 0.5-1 99.25%, PM 1-2.5 PM 2.5-5 and PM 5-10 All are 100%, while their pressure drop is only 89.65 Pa. The filtration performance of PLA filter membranes, commercial glass fiber filter membranes, and FPLAS-1 / P19 / P5U7 is as follows: Figure 4 As shown in (g). All three types of filter membranes have high coarse particle filtration capabilities, but FPLAS-1 / P19 / P5U7 shows better performance for PM2.5. 0.5 The highest filtration efficiency and highest QF, such as Figure 4 As shown in (h). Furthermore, compared to other reported air filter membranes (such as CMM-70, PP / PVA, CMPM-1, and PPS / PPTA), FPLAS-1 / P19 / P5U7 exhibits significant advantages in filtration performance, such as... Figure 4As shown in (i), this illustrates the high efficiency and potential of multilayer gradient structure filtration membranes in the simultaneous capture of particulate and gaseous pollutants.

[0080] like Figure 5 As shown in (a), the prepared pigsty dust covering the surface of the FPLAS-1 / P19 / P5U7 filter membrane became clean after rinsing with water droplets. PLA nanofiber filter membranes and commercial glass fiber filter membranes still had many contaminant residues after rinsing. Furthermore, water droplets could slide off the surface of the FPLAS-1 / P19 / P5U7 filter membrane with a waterslip angle (SA) of 3°, as... Figure 5 As shown in (b), the excellent self-cleaning ability is attributed to the superior superhydrophobicity of the outer layer of FPLAS-1. The contact angle (CA) and sliding angle (SA) of the dirty FPLAS-1 / P19 / P5U7 filter membrane after cleaning were 159.2° and 4°, respectively. Figure 5 As shown in (c), WA and SA decreased by only 2.2° and 1° respectively compared to the clean filter membrane, demonstrating the recovery potential of the FPLAS-1 / P19 / P5U7 filter membrane. Figure 5 (d) demonstrates the mechanical stability of the self-cleaning properties of the FPLAS-1 / P19 / P5U7 filter membrane. After 100 touches, the sample remained hydrophobic, with a contact angle of 145° and a sliding angle of 6°, indicating that the FPLAS-1 / P19 / P5U7 filter membrane has good hydrophobic stability.

[0081] The lifespan and recyclability of the filter membrane were assessed by evaluating pressure drop and dust retention capacity (DHC) under different conditions and five different states. Figure 5 As shown in (f), during one test cycle, the initial pressure drop of the three filter membranes was higher than that of the other four states, due to the reduced pore size caused by residual particles within the filter membrane. Notably, the FPLAS-1 / P19 / P5U7 filter membrane exhibited the lowest pressure drop loss (pressure drop after water washing - initial pressure drop) of only 4.81 Pa, while the air permeability losses of the PLA filter membrane and the commercial glass fiber filter membrane were 13.18 Pa and 15.02 Pa, respectively. These differences indicate that the FPLAS-1 / P19 / P5U7 filter membrane maintained the highest filtration performance after one cycle. Figure 5 (g) shows that the DHC of the FPLAS-1 / P19 / P5U7 filter membrane, PLA filter membrane, and commercial glass fiber filter membrane at the end of their service life was 55.74 g / m³. 2 51.03g / m 2 and 47.36g / m 2The gradient structure of the FPLAS-1 / P19 / P5U7 filter membrane slows down the rapid increase in pressure drop and allows it to hold more particles, thus extending its service life. After rapid dust removal and regeneration via mechanical vibration and water washing, the DHC of the composite filter membrane, PLA filter membrane, and commercial glass fiber filter membrane were 1 g / m³. 2 3g / m 2 and 6g / m 2 . Figure 5 The optical image in (h) shows that the filter membrane is closest to its initial state after washing. In summary, the FPLAS-1 / P19 / P5U7 filter membrane not only has the highest DHC, but also exhibits excellent recyclability (at least within one cycle).

[0082] To evaluate the saturated adsorption capacity of the filter membranes, adsorption and desorption isotherm tests of NH3 were performed on three different filter membranes at 25℃ and 1.0 bar. Figure 8 As shown in (a), the FPLAS-1 / P19 / P5U7 filter membrane exhibits the highest volumetric adsorption capacity, approximately 103.4 cm³. 3 / g, followed by the PLA filter membrane at 39.7cm. 3 / g and 10.5cm of commercial glass fiber filter membrane 3 / g. Furthermore, the NH3 adsorption capacity of the three filter membranes in this work was compared with that of some fiber filter membranes in other studies, such as... Figure 8 As shown in (b), the FPLAS-1 / P19 / P5U7 filter membrane still shows considerable advantages in the competition compared to polyvinyl alcohol (PVA) fiber, activated carbon fiber cloth (ACFC), HKUST-1 deposited on polypropylene (PP) fiber (HKUST-1-PP), and atomic layer deposition (ALD) coated HKUST-1-PP pad (HKUST-1-PPALD).

[0083] The high NH3 adsorption capacity of FPLAS-1 / P19 / P5U7 is mainly attributed to the UiO-66-NH2 doping in the inner P5U7 layer. On one hand, the addition of UiO-66-NH2 enhances the physical adsorption capacity of the filter membrane. For example... Figure 7 As shown in (c) and Table 2, the FPLAS-1 / P19 / P5U7 filter membrane exhibits a higher total pore volume and a higher specific surface area. These properties enhance the interaction between UiO-66-NH2 and NH3, promoting pore filling at relatively low pressures. Furthermore, the organic linker groups (-NH2 functional groups) in UiO-66-NH2 can interact with NH3 through strong hydrogen bonding, such as... Figure 7 As shown in (d), these results highlight the high efficiency and practical potential of this composite filter membrane in filtering particulate and gaseous contaminants.

[0084] In this invention, a multifunctional air filter membrane with a three-layer gradient structure, consisting of an FPLAS layer, a PLA layer, and a PLA / UiO-66-NH2 layer, was successfully prepared. The three-layer nanofiber filter membrane exhibits a gradient decrease in pore size along its thickness, enabling continuous sieving of airborne particles of different sizes. Compared to PLA filter membranes and commercial glass fiber filter membranes, the FPLAS-1 / P19 / P5U7 filter membrane not only effectively filters PM2.5 particles... 0.5 It has a high filtration efficiency (99.15%) and a low pressure drop (89.65 Pa), and also exhibits good dust holding capacity (55.74 g / m³). 2 Meanwhile, the outer layer of the FPLAS-1 / P19 / P5U7 filter membrane has a high water contact angle (161.4°), a low sliding angle (3°), and high mechanical stability, exhibiting good self-cleaning performance and recyclability. Furthermore, compared to PLA filter membranes and commercial glass fiber filter membranes, the FPLAS-1 / P19 / P5U7 filter membrane has the highest adsorption capacity for NH3, such as... Figure 6 As shown, through simple mechanical vibration and water rinsing, the dust residue on the filter membrane surface is only 6g / m². 2 The three-layer gradient filtration membrane exhibits excellent self-cleaning properties and reusability. Compared to PLA and commercial glass fiber filtration membranes, it demonstrates the highest NH3 adsorption capacity of 103.4 cm³. 3 / g. Therefore, the prepared FPLAS-1 / P19 / P5U7 filter membrane has high filtration performance, high dust holding capacity, excellent self-cleaning performance and high NH3 adsorption capacity.

[0085] Although embodiments of the present invention have been shown and described above, it is understood that the above embodiments are exemplary and should not be construed as limiting the present invention. Those skilled in the art can make changes, modifications, substitutions and variations to the above embodiments within the scope of the present invention.

Claims

1. A method for preparing a polylactic acid electrospun nanofiber air filter membrane with a three-layer gradient structure, characterized in that: The process includes electrospinning an outer layer fiber using a polylactic acid / silica solution as the outer layer spinning solution, then fluorinating the outer layer fiber using a mixed solution of n-hexane and FOTS; and finally electrospinning an inner layer fiber on one side of the outer layer fiber using a polylactic acid solution as the middle layer spinning solution. The polylactic acid / UiO-66-NH2 solution is then used as the inner layer spinning solution to form inner layer fibers on one side of the middle layer fibers, resulting in a composite membrane with a three-layer gradient structure. The outer layer spinning solution is obtained by uniformly dispersing silica powder in a mixed solution of DCM and DMF, ultrasonically treating it, and then adding PLA particles. The outer layer spinning solution has a PLA mass fraction of 10wt% and a silica mass fraction of 0.5-5wt%. The middle layer spinning solution is obtained by adding PLA particles to a mixed solution of DMF and DCM. The middle layer spinning solution has a PLA mass fraction of 10wt%. The inner layer spinning solution is obtained by uniformly dispersing UiO-66-NH2 particles in a mixed solution of DCM and DMF, ultrasonically treating it for 1 hour, and then adding polylactic acid PLA particles and stirring at room temperature for 6 hours. The PLA mass fraction is 9-5wt%, and the UiO-66-NH2 mass fraction is 9-5wt%. The mass fraction is 1-7 wt%, and the mass fraction of PLA in the inner spinning solution relative to the total solute is 9 wt%-41.7 wt%.

2. The method for preparing a polylactic acid electrospun nanofiber air filter membrane with a three-layer gradient structure according to claim 1, characterized in that: The volume ratio of DCM to DMF in the outer spinning solution, middle spinning solution, and inner spinning solution is 3:

2.

3. The method for preparing the polylactic acid electrospun nanofiber air filter membrane with a three-layer gradient structure according to claim 1, characterized in that: The outer fiber layer is immersed in a mixed solution of hexane and FOTS, and then heat-treated at 45°C for 2 hours; the volume ratio of hexane to FOTS is 2000:

1.

4. The method for preparing a polylactic acid electrospun nanofiber air filter membrane with a three-layer gradient structure according to claim 1, characterized in that, The electrospinning parameters for the outer layer fiber are: room temperature, average humidity of 35%, solution feed rate of 1.5 mL / h, current collector speed of 80 r / min, positive voltage of 16 kV, negative voltage of 5 kV, and collection distance of 20 cm. The electrospinning parameters for the middle layer fiber are: room temperature, average humidity of 35%, solution feed rate of 1.5 mL / h, current collector speed of 80 r / min, positive voltage of 19 kV, negative voltage of 5 kV, and collection distance of 20 cm. The electrospinning parameters for the inner layer fiber are: room temperature, average humidity of 35%, solution feed rate of 1.5 mL / h, current collector speed of 80 r / min, positive voltage of 20 kV, negative voltage of 5 kV, and collection distance of 20 cm.

5. A polylactic acid electrospun nanofiber air filter membrane with a three-layer gradient structure prepared by the preparation method according to any one of claims 1 to 4, characterized in that: The air filter membrane comprises, from the inside out, an inner layer of polylactic acid / UiO-66-NH2 fiber, a middle layer of polylactic acid fiber, and an outer layer of fluorinated polylactic acid / silica fiber. The diameter and pore size of the air filter membrane decrease sequentially from the outer layer fiber to the inner layer fiber.

6. The application of the polylactic acid electrospun nanofiber air filter membrane with a three-layer gradient structure according to claim 5 in air filtration materials.

7. An air filtration product comprising a polylactic acid electrospun nanofiber air filter membrane having a three-layer gradient structure as described in claim 5.

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