Anti-perfluorinated substance adsorbing nanofiber membrane and method for manufacturing the same

Abstract

The application provides an anti-perfluorinated substance adsorption nanofiber membrane and a preparation method thereof, and belongs to the technical field of environmental functional materials. The preparation method comprises the following steps: melt blending ethylene-vinyl alcohol copolymer and cellulose acetate, melt spinning treatment, extracting by acetone to obtain nanofibers; dispersing the nanofibers in a solvent for high-speed shearing, and crosslinking treatment to obtain a crosslinked nanofiber suspension; coating the crosslinked nanofiber suspension on a polypropylene fabric substrate, and drying treatment to obtain a nanofiber membrane; soaking the nanofiber membrane in an alkaline solution, and washing and drying with water to obtain an anti-perfluorinated substance adsorption nanofiber membrane. The application utilizes two-phase polymer blending and selective extraction technology to construct a high-porosity nanofiber network, and adjusts and controls the chemical properties of the fiber surface through crosslinking treatment and alkaline solution soaking, so as to realize the physical interception of particulate matter and the low adsorption characteristics of perfluorinated substances.

Description

Technical Field

[0001] This application relates to the field of environmental functional materials technology, specifically to a nanofiber membrane resistant to the adsorption of perfluorinated substances and its preparation method. Background Technology

[0002] Per- and polyfluoroalkyl (PFAS) compounds are widely used in industrial and consumer products due to their unique physicochemical properties. However, due to their persistent pollution and health risks, developing a highly sensitive and accurate detection method is crucial for environmental monitoring and risk assessment. Sample pretreatment significantly impacts the accuracy of the final results throughout the PFAS analysis process. While traditional solid-phase extraction (SPE) techniques are widely used, they are prone to clogging and exhibit severe non-specific adsorption when processing actual water samples containing suspended particulate matter, leading to unexpected adsorption losses of the target analytes and underestimation of trace PFAS detection results. To overcome the limitations of traditional materials, existing publicly available technologies have proposed using nanofiber membranes for PFAS detection. However, these technologies still suffer from issues such as mismatch between application methods and sampling scenarios, complex preparation processes, and limitations on large-scale application.

[0003] Therefore, there is an urgent need to develop a special filter membrane that can simultaneously achieve efficient retention of particulate matter and extremely low PFAS adsorption loss in the sampling and filtration process, so as to ensure the accuracy of trace PFAS detection from the sampling source to the analytical endpoint, and fill the technical gap in the pre-sampling treatment process of existing technologies. Summary of the Invention

[0004] In view of the technical problems existing in the background art, this application provides a nanofiber membrane for adsorption of perfluorinated substances and its preparation method. The nanofiber membrane prepared by this method, through innovative material composite and structural design, can not only efficiently intercept suspended particulate matter in water samples, but also significantly reduce the non-specific adsorption of perfluorinated substances, thereby ensuring the accuracy of trace perfluorinated substance detection from the sampling source to the analysis endpoint.

[0005] To achieve the above objectives, in a first aspect, this application proposes a method for preparing a nanofiber membrane resistant to the adsorption of perfluorinated substances, comprising: Ethylene-vinyl alcohol copolymer and cellulose acetate are melt-blended to obtain a melt blend; The melt blend was melt-spun and then extracted with acetone to obtain nanofibers. Nanofibers are dispersed in a solvent and subjected to high-speed shearing to obtain a nanofiber suspension; A cross-linking agent was added to the nanofiber suspension and stirred to obtain a cross-linked nanofiber suspension. A cross-linked nanofiber suspension was coated onto a polypropylene fabric substrate and dried to obtain a nanofiber membrane. The nanofiber membrane was immersed in an alkaline solution, washed with water and dried to obtain a nanofiber membrane resistant to the adsorption of perfluorinated substances.

[0006] Furthermore, the mass ratio of ethylene-vinyl alcohol copolymer to cellulose acetate is 2:(3-8).

[0007] Furthermore, the melt blending temperature is 210℃-225℃; and / or, The draw rate for melt spinning is 700 m / min to 900 m / min.

[0008] Furthermore, the solvent is a mixed solution of deionized water and isopropanol; the volume ratio of isopropanol to deionized water is 1:(1-3), and the mass ratio of nanofibers to the mixed solution of deionized water and isopropanol is (1-10):100.

[0009] Furthermore, the high-speed shearing speed is 10,000 rpm to 12,000 rpm, and the high-speed shearing time is 15 min to 20 min.

[0010] Furthermore, the crosslinking agent is a glutaraldehyde solution; the mass fraction of the glutaraldehyde solution is 10%-25%, and the volume ratio of the glutaraldehyde solution to the nanofiber suspension is (1-10):100; and / or, The cross-linking treatment time is 0.5h-3h.

[0011] Furthermore, the coating thickness is 10μm-25μm; and / or, The drying temperature is 20℃-70℃.

[0012] Furthermore, the alkaline solution includes at least one of sodium hydroxide solution and potassium hydroxide solution, and the concentration of the alkaline solution is 1.0 mol / L to 3.0 mol / L; and / or, Soaking time is 0.5h-5h.

[0013] Secondly, this application proposes a nanofiber membrane resistant to perfluorinated substances, which is prepared by the above-described method for preparing nanofiber membranes resistant to perfluorinated substances.

[0014] Furthermore, the pore size range of the nanofiber membrane resistant to perfluorinated substances is 100nm-800nm.

[0015] The beneficial technical effects of this application are as follows: In this application, a nanofiber membrane material with extremely low non-specific adsorption for perfluorinated substances is constructed through a synergistic strategy combining physical structure regulation and surface chemical modification. This method integrates topological design with surface inertization treatment, achieving the technical goal of adsorption rate below 5% during perfluorinated substance sampling, and solving the key problem of detection accuracy being affected by adsorption loss in traditional sampling materials. By addressing the aforementioned issues, this invention anticipates achieving the following technical effects: the prepared nanofiber membrane exhibits a significantly lower adsorption loss rate for typical PFAS (such as perfluorooctanoic acid PFOA, perfluorooctane sulfonic acid PFOS, etc.) compared to existing commercially available filter membranes (such as polytetrafluoroethylene PTFE, nylon membranes) and functionalized enrichment membranes in existing technologies, achieving a filtration recovery rate of over 90%; the membrane material possesses a uniform nanofiber network structure with controllable pore size, effectively retaining particles larger than 0.22 μm, meeting the general requirements for environmental water sample filtration; the preparation process is simple, efficient, and reproducible, suitable for large-scale production; this membrane can be used as a disposable filtration consumable, is compatible with conventional filtration devices, and is easily promoted and applied in environmental monitoring laboratories and field sampling sites.

[0016] The above description is merely an overview of the technical solution of this application. In order to better understand the technical means of this application and to implement it in accordance with the contents of the specification, and to make the above and other objects, features and advantages of this application more obvious and understandable, specific embodiments of this application are given below. Attached Figure Description

[0017] To more clearly illustrate the technical solution of this application, the accompanying drawings used in this application will be briefly described below. Obviously, the drawings described below are merely some embodiments of this application. For those skilled in the art, other drawings can be obtained from these drawings without any creative effort.

[0018] Figure 1 A comparison of the infrared spectra of the nanofiber membrane without alkali soaking provided in Comparative Example 1 of this application and the nanofiber membrane against perfluorinated substance adsorption provided in Example 1 of this application. Figure 2 A photograph of the water contact angle of the nanofiber membrane against perfluorinated substances provided in Example 1 of this application; Figure 3 A photograph of the water contact angle of a nanofiber membrane that has not been soaked in alkaline solution, provided in Comparative Example 1 of this application; Figure 4 This is a SEM image of the perfluorinated nanofiber membrane provided in Example 1 of this application; Figure 5 This is a SEM image of the nanofiber membrane provided in Comparative Example 1 of this application that has not been soaked in alkali solution. Detailed Implementation

[0019] The embodiments of the technical solution of this application will now be described in detail with reference to the accompanying drawings. These embodiments are only used to more clearly illustrate the technical solution of this application and are therefore merely examples, and should not be used to limit the scope of protection of this application.

[0020] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application pertains; the terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the application; the terms “comprising” and “having”, and any variations thereof, in the specification, claims, and foregoing description of the drawings are intended to cover non-exclusive inclusion.

[0021] In this document, the term "embodiment" means that a particular feature, structure, or characteristic described in connection with an embodiment may be included in at least one embodiment of this application. The appearance of this phrase in various places throughout the specification does not necessarily refer to the same embodiment, nor is it a separate or alternative embodiment mutually exclusive with other embodiments. It will be explicitly and implicitly understood by those skilled in the art that the embodiments described herein can be combined with other embodiments.

[0022] The "range" disclosed in this application is defined by a lower limit and an upper limit. A given range is defined by selecting a lower limit and an upper limit, which define the boundaries of a particular range. Ranges defined in this way can include or exclude endpoints and can be arbitrarily combined; that is, any lower limit can be combined with any upper limit to form a range. For example, if ranges of 60-120 and 80-110 are listed for a specific parameter, it is expected that ranges of 60-110 and 80-120 are also included. Furthermore, if minimum range values ​​of 1 and 2 are listed, and if maximum range values ​​of 3, 4, and 5 are listed, then the following ranges are all expected: 1-3, 1-4, 1-5, 2-3, 2-4, and 2-5. In this application, unless otherwise stated, the numerical range "ab" represents a shortened representation of any combination of real numbers between a and b, where a and b are real numbers. For example, the numerical range "0-5" indicates that all real numbers between "0-5" have been listed in this article; "0-5" is simply a shortened representation of these numerical combinations. Furthermore, when a parameter is stated as an integer ≥2, it is equivalent to disclosing that the parameter is, for example, an integer such as 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0023] Unless otherwise specified, all embodiments and optional embodiments of this application can be combined to form new technical solutions.

[0024] Unless otherwise specified, all technical features and optional technical features of this application may be combined to form new technical solutions.

[0025] Unless otherwise specified, all steps in this application may be performed sequentially or randomly, preferably sequentially. For example, the method includes steps (a) and (b), indicating that the method may include steps (a) and (b) performed sequentially, or it may include steps (b) and (a) performed sequentially. For example, the mention that the method may also include step (c) indicates that step (c) may be added to the method in any order. For example, the method may include steps (a), (b), and (c), or it may include steps (a), (c), and (b), or it may include steps (c), (a), and (b), etc.

[0026] Unless otherwise specified, the terms "comprising" and "including" as used in this application are open-ended. For example, "comprising" and "including" may mean that other components not listed may also be included or contained.

[0027] In the description of the embodiments in this application, the term "and / or" is merely a description of the relationship between related objects, indicating that three relationships can exist. For example, A and / or B can represent: A existing alone, A and B existing simultaneously, and B existing alone. Additionally, the character " / " in this document generally indicates that the preceding and following related objects have an "or" relationship.

[0028] The embodiments of this application will be described in further detail below with reference to the accompanying drawings and examples. The detailed description of the following embodiments and the accompanying drawings are used to illustrate the principles of this application by way of example, but should not be used to limit the scope of this application, that is, this application is not limited to the described embodiments.

[0029] Per- and polyfluoroalkyl substances (PFAS) are widely used in industrial and consumer products due to their unique physicochemical properties. However, because of their persistent pollution and health risks, developing a highly sensitive and accurate detection method is crucial for environmental monitoring and risk assessment. In the entire PFAS analysis process, sample pretreatment has a significant impact on the accuracy of the final results. While traditional solid-phase extraction (SPE) techniques are widely used, they are prone to clogging and exhibit severe non-specific adsorption when processing actual water samples containing suspended particulate matter. This leads to unexpected adsorption losses of the target analytes, resulting in underestimated trace PFAS detection results. Furthermore, SPE is cumbersome and inefficient. To overcome the limitations of traditional materials, existing publicly available technologies have proposed using nanofiber membranes for PFAS detection. However, these technologies still suffer from issues such as mismatch between application methods and sampling scenarios, complex preparation processes, and limitations on large-scale application.

[0030] Therefore, there is an urgent need to develop a special filter membrane that can simultaneously achieve efficient retention of particulate matter and extremely low PFAS adsorption loss in the sampling and filtration process, so as to ensure the accuracy of trace PFAS detection from the sampling source to the analytical endpoint, and fill the technical gap in the pre-sampling treatment process of existing technologies.

[0031] To address the aforementioned technical problems, in a first aspect, this application proposes a method for preparing a nanofiber membrane resistant to the adsorption of perfluorinated substances, comprising: Ethylene-vinyl alcohol copolymer and cellulose acetate are melt-blended to obtain a melt blend; The melt blend was melt-spun and then extracted with acetone to obtain nanofibers. Nanofibers are dispersed in a solvent and subjected to high-speed shearing to obtain a nanofiber suspension; A cross-linking agent was added to the nanofiber suspension and stirred to obtain a cross-linked nanofiber suspension. A cross-linked nanofiber suspension was coated onto a polypropylene fabric substrate and dried to obtain a nanofiber membrane. The nanofiber membrane was immersed in an alkaline solution, washed with water and dried to obtain a nanofiber membrane resistant to the adsorption of perfluorinated substances.

[0032] In this application, cellulose acetate and ethylene-vinyl alcohol copolymer are thermodynamically incompatible. Through melt blending, a sea-island structure can be formed, with cellulose acetate as the continuous phase (sea phase) and ethylene-vinyl alcohol copolymer as the dispersed phase (island phase). During melt spinning, the island phase ethylene-vinyl alcohol copolymer is refined and elongated along the fiber axis under shear and stretching, forming ultrafine fiber bundles embedded in the cellulose acetate sea phase. Subsequently, utilizing the difference in solubility between cellulose acetate and ethylene-vinyl alcohol copolymer, acetone is used for selective extraction. The cellulose acetate sea phase is dissolved and eluted, while the ethylene-vinyl alcohol copolymer island phase retains its original fiber morphology, resulting in ethylene-vinyl alcohol copolymer ultrafine fibers. This ultimately constructs an interpenetrating nanofiber network structure with high specific surface area and high porosity, providing a structural basis for subsequent physical interception. The obtained nanofibers are subjected to high-speed shearing to mechanically shorten them and eliminate fiber aggregation and entanglement, thereby obtaining a uniform and stable suspension. The fiber aspect ratio is then adjusted to precisely control the film-forming pore size. A crosslinking agent is added to the nanofiber suspension and stirred to introduce covalent bridging between the ethylene-vinyl alcohol copolymers, inhibiting swelling and enhancing the structural stability of the nanofibers. The crosslinked nanofibers are then uniformly loaded onto a polypropylene nonwoven fabric substrate. Utilizing the low affinity of polypropylene for perfluorinated substances, additional adsorption interference from the substrate is further avoided. Finally, alkaline immersion selectively converts residual acetyl groups on the nanofiber surface into hydroxyl groups, forming a high-density hydrogen bond network and improving hydrophilicity. After binding with water to form a dense and stable bound water layer, the hydrophobic properties of the perfluorinated substances repel them, thereby shielding the fiber body from potential hydrophobic attraction or electrostatic interactions between the fiber and the perfluorinated substances, reducing the accessibility of adsorption sites, and achieving an anti-perfluorinated substance adsorption effect.

[0033] In some embodiments, the mass ratio of ethylene-vinyl alcohol copolymer to cellulose acetate is 2:(3-8).

[0034] In this embodiment, controlling the mass ratio of ethylene-vinyl alcohol copolymer to cellulose acetate to be 2:(3-8) ensures a balance between fiber structure integrity and high porosity and high specific surface area. A higher proportion of ethylene-vinyl alcohol copolymer results in larger diameter fibers; a lower proportion results in smaller diameter fibers. The fiber diameter affects the pore size of the subsequently prepared nanofiber membrane. The nanofiber membrane prepared from finer fibers has a smaller pore size. While meeting basic pure water flux and interception efficiency requirements, the pore size can be flexibly adjusted according to actual application needs.

[0035] In some embodiments, the melt blending temperature is 210°C-225°C.

[0036] In this embodiment, the temperature of melt blending is controlled at 210℃-225℃. The ethylene-vinyl alcohol copolymer is completely melted, and cellulose acetate is in a flowable viscous state. The viscosities of the two melts are similar. After physical blending, the surface of the melt blend is smooth and can withstand a high stretching speed, giving the melt blend stability and spinnability.

[0037] In some embodiments, the draw rate of melt spinning is 700 m / min to 900 m / min.

[0038] In this embodiment, the stretching speed is controlled at 700m / min-900m / min. The melt stream extruded by melt spinning is subjected to moderate and continuous stretching force, which causes the continuous phase droplets of cellulose acetate and the dispersed phase of ethylene-vinyl alcohol copolymer to deform in synergy, be stretched and oriented into slender nanofibers, improve the strength and modulus of the finished fiber, and ensure the stability of continuous spinning and fiber quality.

[0039] In some embodiments, the solvent is a mixed solution of deionized water and isopropanol, the volume ratio of isopropanol to deionized water is 1:(1-3), and the mass ratio of nanofibers to the mixed solution of deionized water and isopropanol is (1-10):100.

[0040] In this embodiment, nanofibers are dispersed in a mixed solution of deionized water and isopropanol. By controlling the volume ratio of deionized water and isopropanol as well as the mass ratio of nanofibers to the mixed solution, the density and surface tension of the water and isopropanol mixture can be used to reduce the precipitation or agglomeration of nanofibers, forming a uniform suspension state and protecting the porous structure of nanofibers.

[0041] In some embodiments, the high-speed shearing speed is 10,000 rpm to 12,000 rpm, and the high-speed shearing time is 15 min to 20 min.

[0042] In this embodiment, the high-speed shearing speed is controlled at 10,000 rpm-12,000 rpm, and the high-speed shearing time is 15 min-20 min. The nanofibers are appropriately cut, and the fiber length distribution is narrowed to obtain a nanofiber suspension with relatively uniform length. This is beneficial to improve the uniformity of subsequent film formation and control the film pore size.

[0043] In some embodiments, the crosslinking agent is a glutaraldehyde solution with a mass fraction of 10%-25% and a volume ratio of glutaraldehyde solution to nanofiber suspension of (1-10):100.

[0044] In this embodiment, a glutaraldehyde solution with a mass fraction of 10%-25% was selected as the crosslinking agent. The ethylene-vinyl alcohol copolymer molecular chains of the nanofibers contain a large number of side hydroxyl groups (-OH), while the glutaraldehyde molecule has a highly reactive aldehyde group (-CHO) at each end. The two aldehyde groups of a glutaraldehyde molecule can undergo acetal reactions with the hydroxyl groups on different ethylene-vinyl alcohol copolymer chains, forming stable ether bonds (-O-CH2-O-) between the molecular chains. By controlling the volume ratio of glutaraldehyde solution to nanofiber suspension to (1-10):100, the reaction consumes the hydrophilic hydroxyl groups, reducing the overall hydrophilicity of the nanofibers and making it difficult for water molecules to penetrate. At the same time, the network structure formed by crosslinking restricts the mobility of the molecular chains, further inhibiting swelling and thus improving the stability of the nanofiber structure.

[0045] In some embodiments, the crosslinking treatment time is 0.5h-3h.

[0046] In this embodiment, by controlling the depth of the crosslinking reaction, covalent bridging is allowed to gradually penetrate from the fiber surface to the internal core, thereby achieving gradient regulation from surface shaping to bulk reinforcement. A crosslinking treatment of 0.5h-3h can uniformly penetrate the entire nanofiber skeleton through the crosslinked network, endowing it with resistance to hydrolysis and swelling, and improving the structural stability of the nanofibers.

[0047] In some embodiments, the coating thickness is 10 μm-25 μm.

[0048] In this embodiment, the coating thickness is controlled to be 10μm-25μm, which facilitates the formation of a continuous nanofiber functional layer. Within this thickness range, the nanofiber liquid film is uniformly spread, and after drying, a complete and interconnected nanofiber network can be obtained, ensuring its filtration and retention function for particulate matter. At the same time, it avoids delamination and peeling that may occur due to excessive coating thickness, thus improving the stability of the process.

[0049] In some embodiments, the drying temperature is 20°C-70°C.

[0050] In this embodiment, the drying temperature is controlled at 20℃-70℃. This mild drying temperature allows the solvent to evaporate smoothly, which is beneficial for the nanofibers to build an interpenetrating nanofiber network with high specific surface area and high porosity, maintaining the filtration retention performance. At the same time, it can reduce bubbling that may be caused by the wet film surface drying too quickly, reduce drying shrinkage stress, and reduce the risk of peeling of the nanofiber network from the substrate and thermal deformation.

[0051] In some embodiments, the alkaline solution includes at least one of sodium hydroxide solution and potassium hydroxide solution, and the concentration of the alkaline solution is 1.0 mol / L to 3.0 mol / L.

[0052] In this embodiment, the alkaline solution can be at least one of sodium hydroxide solution and potassium hydroxide solution. Sodium hydroxide hydrolysis, due to the smaller radius of sodium ions, allows for more uniform penetration within the nanofiber pores, resulting in a moderate hydrolysis rate. This effectively controls polar functional groups, reduces the membrane's adsorption performance for perfluorinated substances, and minimizes erosion of the nanofiber framework. Potassium ions, with their larger radius, exhibit stronger hydrolysis; their concentration can be appropriately adjusted to reduce perfluorinated substance adsorption while maintaining the integrity of the fiber membrane structure. Controlling the alkaline solution concentration to 1.0 mol / L–3.0 mol / L provides sufficient hydroxide ion concentration to drive the hydrolysis reaction, achieving a controllable balance between hydrolysis efficiency and nanofiber structure.

[0053] In some embodiments, the soaking time is 0.5h-5h.

[0054] In this embodiment, the soaking time is controlled to be 0.5h-5h, which ensures sufficient contact between the alkaline solution and the nanofiber surface and allows for controlled hydrolysis. While effectively reducing active sites that can participate in hydrogen bonding and electrostatic interactions, and weakening the hydrophobic association effect with perfluorocarbon chains, the complete porous network structure of the nanofibers is preserved. This reduces the non-specific adsorption tendency of the nanofiber membrane for perfluorinated substances and minimizes the retention and accumulation of perfluorinated substances on the membrane surface during filtration.

[0055] Secondly, this application proposes a nanofiber membrane resistant to perfluorinated substances, which is prepared by the above-described method for preparing nanofiber membranes resistant to perfluorinated substances.

[0056] It is understood that the bio-resistant perfluorinated substance adsorption nanofiber membrane has all the beneficial effects of the above-mentioned preparation methods of the perfluorinated substance adsorption nanofiber membrane, and will not be elaborated here.

[0057] In some embodiments, the pore size range of the nanofiber membrane resistant to perfluorinated substances is 100 nm to 800 nm.

[0058] In this embodiment, the pore size range of the anti-perfluorinated substance adsorption nanofiber membrane is 100nm-800nm, which can effectively intercept particulate matter in the sample and meet the general requirements for environmental water sample filtration.

[0059] It should be noted that this application is not limited to the above-described embodiments. The above embodiments are merely examples, and any embodiments with the same structure and effect as the technical concept within the scope of this application are included in the technical scope of this application. Various modifications that can be conceived by those skilled in the art to the embodiments, and other ways of constructing embodiments by combining some of the constituent elements, are also included in the scope of this application without departing from the spirit of this application.

[0060] The following are some specific embodiments. It should be noted that the embodiments described below are exemplary and are only used to explain this application, and should not be construed as limiting this application. Where specific techniques or conditions are not specified in the embodiments, they shall be performed in accordance with the techniques or conditions described in the literature in this field or according to the product instructions. Reagents or instruments whose manufacturers are not specified are all conventional products that can be obtained commercially.

[0061] I. Preparation Method Example 1 The ethylene-vinyl alcohol copolymer, after being thoroughly dried and dehydrated, was added to a twin-screw extruder at a mass ratio of 2:8 with cellulose acetate, and melt-blended at 210°C to obtain a melt blend. The obtained melt blend was melt-spun at a drawing speed of 800 m / min. After forming, the fibers were collected and extracted with acetone for 24 hours to obtain nanofibers. The obtained nanofibers were dispersed in a mixed solution of isopropanol and deionized water in a volume ratio of 1:1, and dispersed at 10,000 rpm for 15 min using an ultra-high-speed shear machine to obtain a nanofiber suspension with a mass fraction of 5%. With a volume ratio of glutaraldehyde solution to nanofiber suspension of 3:100, glutaraldehyde solution with a mass fraction of 20% was added to the obtained nanofiber suspension and magnetically stirred for 1 hour to obtain cross-linked nanofiber suspension. The obtained cross-linked nanofiber suspension was coated onto a polypropylene nonwoven fabric substrate with a coating thickness controlled at 25 μm, and then dried in an oven at 60 °C for 2 hours to obtain a nanofiber membrane. The obtained nanofiber membrane was placed in a 3 mol / L sodium hydroxide solution and soaked for 3 hours. After being removed, it was repeatedly washed with deionized water until neutral and then dried naturally at room temperature to obtain the nanofiber membrane for adsorbing perfluorinated substances as described in Example 1.

[0062] Example 2 The ethylene-vinyl alcohol copolymer, after being thoroughly dried and dehydrated, was added to a twin-screw extruder at a mass ratio of 2:8 with cellulose acetate, and melt-blended at 220°C to obtain a melt blend. The obtained melt blend was melt-spun at a drawing speed of 900 m / min. After forming, the fibers were collected and extracted with acetone for 36 hours to obtain nanofibers. The obtained nanofibers were dispersed in a mixed solution of isopropanol and deionized water in a volume ratio of 1:2, and dispersed at 12,000 rpm for 20 min using an ultra-high-speed shear machine to obtain a nanofiber suspension with a mass fraction of 7.5%. With a volume ratio of glutaraldehyde solution to nanofiber suspension of 5:100, 10% glutaraldehyde solution was added to the obtained nanofiber suspension and magnetically stirred for 2 hours to obtain a cross-linked nanofiber suspension. The obtained cross-linked nanofiber suspension was coated onto a polypropylene nonwoven fabric substrate with a coating thickness controlled at 15 μm, and then dried in an oven at 50 °C for 3 hours to obtain a nanofiber membrane. The obtained nanofiber membrane was placed in a 1.5 mol / L potassium hydroxide solution and soaked for 2 hours. After being removed, it was repeatedly washed with deionized water until neutral and then dried naturally at room temperature to obtain the nanofiber membrane for adsorbing perfluorinated substances as described in Example 2.

[0063] Example 3 The ethylene-vinyl alcohol copolymer, after being thoroughly dried and dehydrated, was added to a twin-screw extruder at a mass ratio of 3:7 with cellulose acetate and melt-blended at 215°C to obtain a melt blend. The obtained melt blend was melt-spun at a drawing speed of 900 m / min. After forming, the fibers were collected and extracted with acetone for 30 hours to obtain nanofibers. The obtained nanofibers were dispersed in a mixed solution of isopropanol and deionized water in a volume ratio of 1:3, and dispersed at 12,000 rpm for 15 min using an ultra-high-speed shear machine to obtain a nanofiber suspension with a mass fraction of 4%. With a volume ratio of glutaraldehyde solution to nanofiber suspension of 2:100, glutaraldehyde solution with a mass fraction of 25% was added to the obtained nanofiber suspension and magnetically stirred for 1.5 hours to obtain cross-linked nanofiber suspension. The obtained cross-linked nanofiber suspension was coated onto a polypropylene nonwoven fabric substrate with a coating thickness controlled at 18 μm and then naturally dried at 20°C to obtain a nanofiber membrane. The obtained nanofiber membrane was placed in a 3 mol / L sodium hydroxide solution and soaked for 0.5 h. After being removed, it was repeatedly washed with deionized water until neutral and then dried naturally at room temperature to obtain the nanofiber membrane for adsorbing perfluorinated substances as described in Example 3.

[0064] Example 4 The ethylene-vinyl alcohol copolymer, after being thoroughly dried and dehydrated, was added to a twin-screw extruder at a mass ratio of 2:3 with cellulose acetate, and melt-blended at 225°C to obtain a melt blend. The obtained melt blend was melt-spun at a drawing speed of 700 m / min. After forming, the fibers were collected and extracted with acetone for 24 hours to obtain nanofibers. The obtained nanofibers were dispersed in a mixed solution of isopropanol and deionized water in a volume ratio of 1:1, and dispersed at 12,000 rpm for 15 min using an ultra-high-speed shear machine to obtain a nanofiber suspension with a mass fraction of 10%. A glutaraldehyde solution with a mass fraction of 25% was added to the obtained nanofiber suspension at a volume ratio of 1:10 and the mixture was magnetically stirred for 3 hours to obtain a cross-linked nanofiber suspension. The obtained cross-linked nanofiber suspension was coated onto a polypropylene nonwoven fabric substrate with a coating thickness controlled at 10 μm, and then dried in an oven at 70 °C for 1 hour to obtain a nanofiber membrane. The obtained nanofiber membrane was placed in a 1 mol / L sodium hydroxide solution and soaked for 5 hours. After being removed, it was repeatedly washed with deionized water until neutral and then dried naturally at room temperature to obtain the nanofiber membrane for adsorbing perfluorinated substances as described in Example 4.

[0065] Comparative Example 1 Unlike Example 1, this method does not involve immersion in an alkaline solution. The remaining steps are largely the same and will not be repeated here. This yields the nanofiber membrane of Comparative Example 1.

[0066] Comparative Example 2 Unlike Example 1, no glutaraldehyde solution was added for crosslinking treatment. The remaining steps were roughly the same and will not be described in detail here, resulting in the nanofiber membrane of Comparative Example 2.

[0067] Comparative Example 3 Perfluorinated adsorption performance was tested using a commercially available PES (polyethersulfone) needle filter. The filter membrane is composed of hydrophobic polyethersulfone and contains sulfone groups and aromatic rings on its surface, which can simulate the PFAS analysis deviation caused by membrane-solute hydrophobic interaction and specific adsorption during the filtration process.

[0068] Comparative Example 4 Perfluorinated adsorption performance was tested using a commercially available PTFE (polytetrafluoroethylene) needle filter. The filter membrane is made of polytetrafluoroethylene, and its fluorinated carbon skeleton has potential fluorine affinity adsorption with PFAS.

[0069] Comparative Example 5 Perfluorinated adsorption performance was tested using a commercially available RC (regenerated cellulose) needle filter. This filter membrane is made of regenerated cellulose and contains hydrophilic hydroxyl functional groups, which can reduce the hydrophobic adsorption of PFAS.

[0070] Comparative Example 6 Perfluorinated adsorption performance was tested using a commercially available MCE (mixed cellulose ester) needle filter. This filter membrane is composed of mixed cellulose ester and contains multiple functional groups such as hydroxyl and ester groups. Its surface chemistry is complex, and its adsorption performance for PFAS needs to be comprehensively evaluated.

[0071] II. Testing Methods 1. Test procedure for the perfluorinated adsorption performance of the filter membrane: (1) First, cut the prepared filter membrane into a circle with a diameter of 13 mm, and then assemble it into a needle filter that matches the standard Luer connector for later use.

[0072] (2) Accurately transfer an appropriate amount of PFAS mixed standard stock solution, dilute it with methanol-water (volume ratio 1:9), and prepare a mixed standard working solution with a mass concentration of 1 μg / L for each target compound. Take 5 mL with a syringe and connect it to the standard Luer connector in step (1) for filtration. Discard the first 0.5 mL of filtrate, collect 1.0 mL of filtrate in a polypropylene injection bottle, add 0.05 ng of internal standard, mix well, and prepare for testing. At the same time, set up an unfiltered sample as a control sample.

[0073] 2. Formula for calculating the adsorption rate of PFAS by the filter membrane: Adsorption rate = (1 - C2 / C1) × 100% (I) In formula (I): C1 is the concentration of PFAS in the unfiltered control sample (ng / L); C2 is the concentration of PFAS in the filtered sample (ng / L).

[0074] 3. Testing instruments and testing procedures Testing equipment: Ultra-high performance liquid chromatography-tandem mass spectrometry (ACQUITY UPLC Xevo TQ-S): electrospray ionization source (ESI), 50 μL quantitative loop and perfluorinated trapping column (Isolator Column, 2.1 mm × 50 mm), chromatographic column was Acquity UPLC BEH C18 (2.1 mm × 100 mm, 1.7 μm). All were products of Waters Corporation, USA.

[0075] Chromatographic conditions: Mobile phase A was ammonium acetate aqueous solution (2 mmol / L, pH 8.0), mobile phase B was methanol; gradient elution conditions are shown in Table 1, flow rate 0.2 mL / min, column temperature 40℃, injection volume 50 μL.

[0076] Mass spectrometry conditions: Electrospray ionization (ESI) was used with multiple reaction monitoring (MRM) in negative ion mode. Ion source temperature was 450℃, spray voltage was -4500V, and mass spectrometry parameters are detailed in Tables 2 and 3.

[0077] The internal standard method is used for quantification, and the sample concentration is calculated according to the following formula (II): C i =(C x -C0)×1.1(II) In formula (II): C iC represents the concentration (ng / L) of component i in the sample. x C0 represents the concentration (ng / L) of component i in the sample calculated from the standard curve; C0 represents the concentration (ng / L) of component i in the blank sample; and 1.1 represents the dilution factor of the sample.

[0078] Table 1 lists the gradient elution condition parameters. Table 2 shows the mass spectrometry parameters of PFAS. Table 3 shows the mass spectrometry parameters of the internal standard. Note: "*" represents a quantitative ion pair.

[0079] III. Analysis of Test Results for Each Embodiment and Comparative Example Table 4 shows the adsorption rates of 22 perfluorinated substances for the nanofiber membranes provided in Examples 1-4 and the filter membranes provided in Comparative Examples 1-6. Table 5 shows the pure water flux and particulate matter interception rate of the nanofiber membranes provided in Examples 1-4 and Comparative Examples 1-6. Results analysis: The adsorption rates of the nanofiber membranes provided in Examples 1-4 and the filter membranes provided in Comparative Examples 1-6 for 22 perfluorinated substances are shown in Table 4. Among the 22 tested perfluorinated substances, except for perfluorohexanoic acid (PFHxA), the other 21 substances showed the lowest adsorption rates under the conditions of this example. By adjusting the process conditions of raw material ratio, melt blending temperature, alkali concentration and soaking time, crosslinking treatment time, coating thickness, melt spinning drawing speed, and high-speed shearing speed and time, low adsorption rates (≤9.8%) for various perfluorinated substances can be achieved in Examples 1-4, and even the adsorption rate of some perfluorinated substances is 0%. The overall adsorption rate of Examples 1-4 is lower than that of Comparative Examples 1-6.

[0080] Figure 1The infrared spectra of the nanofiber membrane without alkali soaking in Comparative Example 1 and the anti-perfluorinated substance adsorption nanofiber membrane provided in Example 1 of this application are compared. Under the same test conditions, the infrared light transmittance of the anti-perfluorinated substance adsorption nanofiber membrane prepared in Example 1 is increased, indicating that the nanofiber membrane of Example 1 successfully constructed a hydrophilic layer on the surface of the nanofiber after alkali soaking, which changed the chemical environment of the functional groups on the fiber surface. Comparative Example 1 lacks the step of alkali soaking treatment, and the acetyl groups remaining on its fiber surface cannot form a high-density hydrogen bond network. Therefore, the hydrophilicity of the fiber membrane is limited, but it still shows strong adsorption performance for perfluorinated substances. Figure 2 The image shows the water contact angle of the nanofiber membrane against perfluorinated substances provided in Example 1 of this application. The water contact angle is only 35°, indicating that the nanofiber membrane is hydrophilic and can effectively block hydrophobic perfluorinated substance molecules from contacting the fiber body. Figure 3 The image shows the water contact angle of the nanofiber membrane in Comparative Example 1, which was not soaked in alkaline solution. The water contact angle reaches 71°, indicating hydrophobicity and specific adsorption of perfluorinated substances. Comparative Example 2 lacks the cross-linking treatment step, and its fiber surface contains a large number of hydroxyl groups. When ionized groups are introduced through subsequent alkaline soaking, the uncross-linked molecular chains undergo severe swelling and even partial dissolution, leading to fiber surface remodeling. This re-exposes adsorption sites that were originally shielded by the hydration layer, resulting in strong adsorption performance for perfluorinated substances. Comparative Examples 3-6 use filters made from membranes of different materials. Except for the RC nanofiber membrane used in Comparative Example 5, which exhibits a certain level of low adsorption (0.2%-61.4%), the other membrane materials all showed varying degrees of specific adsorption for different perfluorinated substances, and the overall adsorption rates were higher than those in the embodiments of this application.

[0081] Figure 4 The image shows an SEM image of the nanofiber membrane for resisting perfluorinated substance adsorption provided in Example 1 of this application. The uniform porous fiber structure is visible, with the fibers clearly interwoven. Figure 5 The SEM image shows the nanofiber membrane in Comparative Example 1 that was not soaked in alkaline solution. It is evident that the fiber network is disordered and entangled, with low porosity, and its particulate matter interception rate remains at the same level as in Example 1. Comparative Example 2, lacking cross-linking, suffers from decreased mechanical strength of the fiber membrane, making it prone to detachment and resulting in a drop in interception efficiency to 95%. Table 5 shows that the average pure water flux of the nanofiber membranes prepared in Examples 1-4 at 0.05 MPa is 7500-25000 L / (m²). 2Compared to the commercially available filter membranes used in Comparative Examples 3-6, the nanofiber membranes prepared in this example exhibit superior permeability and high water production efficiency. As the proportion of ethylene-vinyl alcohol copolymer increases, the fiber diameter gradually increases, the porosity between fibers increases, and the pure water flux increases. The fiber solids content in the suspension and the thickness of the fiber layer also jointly affect the membrane pore size and porosity. For fibers of the same diameter, higher suspension solids content and greater thickness result in lower pure water flux and higher particulate matter interception efficiency. In summary, by changing the proportion of ethylene-vinyl alcohol copolymer, the stretching speed, and controlling the suspension solids content and coating thickness, the fiber diameter, membrane pore size, and porosity can be controlled, thereby achieving adjustment of water flux and meeting the requirements for intercepting particulate matter of different diameters.

[0082] In summary, this application constructs an ethylene-vinyl alcohol copolymer nanofiber network through a two-component blend of ethylene-vinyl alcohol copolymer and cellulose acetate, followed by selective extraction of cellulose acetate with acetone. Combined with glutaraldehyde crosslinking, alkaline surface polarity regulation, and the low surface energy of the polypropylene nonwoven fabric substrate, the synergistic effect ensures that the adsorption rate of various perfluorinated substances, such as perfluorooctanoic acid (PFOA) and perfluorooctane sulfonic acid (PFOS), is stably controlled below 10%, even as low as 5% in Example 1. Compared to the comparative filter membrane's adsorption loss of up to 100% for perfluorinated substances, this invention significantly reduces the non-specific adsorption loss of target analytes during sampling, significantly improving the accuracy and reliability of subsequent detection results. This ensures a pure water flux of 7500 L / (m³). 2 Under the premise of ·h), it can effectively intercept particles larger than 0.22μm, meeting the general requirements for environmental water sample filtration.

Claims

1. A method for preparing a nanofiber membrane resistant to the adsorption of perfluorinated substances, characterized in that, include: Ethylene-vinyl alcohol copolymer and cellulose acetate are melt-blended to obtain a melt blend; The melt blend was melt-spun and extracted with acetone to obtain nanofibers; The nanofibers were dispersed in a solvent and subjected to high-speed shearing to obtain a nanofiber suspension; A crosslinking agent is added to the nanofiber suspension and stirred to obtain a crosslinked nanofiber suspension through crosslinking treatment; The cross-linked nanofiber suspension was coated onto a polypropylene fabric substrate and dried to obtain a nanofiber membrane. The nanofiber membrane is immersed in an alkaline solution, washed with water and dried to obtain the nanofiber membrane that resists the adsorption of perfluorinated substances.

2. The method for preparing the nanofiber membrane resistant to perfluorinated substance adsorption according to claim 1, characterized in that, The mass ratio of the ethylene-vinyl alcohol copolymer to the cellulose acetate is 2:(3-8).

3. The method for preparing the nanofiber membrane resistant to perfluorinated substance adsorption according to claim 1, characterized in that, The melt blending temperature is 210℃-225℃; and / or, The draw rate of the melt spinning is 700 m / min to 900 m / min.

4. The method for preparing the nanofiber membrane resistant to perfluorinated substances according to claim 1, characterized in that, The solvent is a mixed solution of deionized water and isopropanol, the volume ratio of isopropanol to deionized water is 1:(1-3), and the mass ratio of nanofibers to the mixed solution of deionized water and isopropanol is (1-10):

100.

5. The method for preparing the nanofiber membrane resistant to perfluorinated substance adsorption according to claim 1, characterized in that, The high-speed shearing speed is 10,000 rpm to 12,000 rpm, and the high-speed shearing time is 15 min to 20 min.

6. The method for preparing the nanofiber membrane resistant to perfluorinated substances according to claim 1, characterized in that, The crosslinking agent is a glutaraldehyde solution with a mass fraction of 10%-25%, and the volume ratio of the glutaraldehyde solution to the nanofiber suspension is (1-10):100; and / or, The crosslinking treatment time is 0.5h-3h.

7. The method for preparing the nanofiber membrane resistant to perfluorinated substance adsorption according to claim 1, characterized in that, The coating thickness is 10μm-25μm; and / or, The drying process is carried out at a temperature of 20℃-70℃.

8. The method for preparing the nanofiber membrane resistant to perfluorinated substances according to claim 1, characterized in that, The alkaline solution includes at least one of sodium hydroxide solution and potassium hydroxide solution, wherein the concentration of the alkaline solution is 1.0 mol / L to 3.0 mol / L; and / or, The soaking time is 0.5h-5h.

9. A nanofiber membrane resistant to the adsorption of perfluorinated substances, characterized in that, It is prepared by the method for preparing nanofiber membranes resistant to perfluorinated substances as described in any one of claims 1-8.

10. The nanofiber membrane for resisting perfluorinated substance adsorption according to claim 9, characterized in that, The pore size range of the nanofiber membrane resistant to perfluorinated substances is 100nm-800nm.

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