Composite nanofiltration membrane, preparation method and application thereof in filtering emerging pollutants

Abstract

The application provides a composite nanofiltration membrane, a preparation method and application thereof in filtering emerging pollutants. The composite nanofiltration membrane comprises a macroporous base membrane support layer, an oriented hollow nanofiber intermediate layer and a filtration skin layer, wherein the oriented hollow nanofiber intermediate layer is loaded on the macroporous base membrane support layer, the oriented hollow nanofiber intermediate layer comprises oriented and hollow polymer nanofibers with internal hollow cavities, and the surface of the filtration skin layer has a wrinkle structure along the arrangement direction of the hollow polymer nanofibers. The structure of the hollow polymer nanofibers of the composite nanofiltration membrane provided by the application provides sufficient water phase monomer storage space, forms an ultrathin, high-crosslinking-degree polyamide layer with regular wrinkle structures on both sides of the hollow polymer nanofibers, effectively shortens the transmission path of water molecules, reduces the permeation resistance, and realizes the synchronous improvement of the membrane permeability and selectivity.

Description

Technical Field

[0001] This application relates to the field of water treatment, and in particular to a composite nanofiltration membrane, its preparation method, and its application in filtering emerging pollutants. Background Technology

[0002] With the rapid growth of the global population and the acceleration of industrialization, the demand for freshwater is constantly increasing. Among the many desalination technologies, nanofiltration technology has attracted much attention due to its excellent permeability, low energy consumption, and effective removal of contaminants such as personal care products, endocrine disruptors, and pharmaceuticals. However, the unavoidable balance between permeability and selectivity remains a key obstacle for the industrial application and technological advancement of nanofiltration membranes. Therefore, an increasing number of researchers are focusing on the strategy of introducing an intermediate layer.

[0003] Previous studies have shown that using nanomaterials such as MOFs, COFs, nanowires, nanotubes, nanocrystals, or nanosheets as the interlayer in composite nanofiltration membranes has significantly improved membrane performance. However, these nanomaterials often present problems such as uneven nanomaterial distribution, high material costs, leaching, leakage, and even secondary water pollution when used as interlayers. Electrospun nanofibers, with their high specific surface area, three-dimensional interconnected porous structure, and flexible surface chemical tunability, have become an ideal platform for constructing interlayers. Nanofiber interlayers can not only effectively smooth the substrate surface, but their rich pore structure also holds promise for providing low-resistance channels for water transport. However, in studies using electrospun nanofibers as interlayers, there are still many problems in effectively utilizing their structure. Furthermore, secondary modification of nanofiber interlayers still presents issues of nanomaterial leaching and leakage. Existing methods for preparing electrospun hollow nanofibers for constructing support layers suffer from the adverse effect of nanofiber support layer swelling. Therefore, effectively utilizing the structural role of nanomaterials to optimize nanofiber interlayers is an effective strategy for improving nanofiltration membrane performance and a problem that urgently needs to be solved. Summary of the Invention

[0004] To address the aforementioned technical problems, this application provides a composite nanofiltration membrane, its preparation method, and its application in filtering emerging pollutants. The composite nanofiltration membrane provided by this application, due to the inclusion of an oriented hollow nanofiber interlayer, provides ample storage space for aqueous monomers within the hollow polymer nanofiber structure. This effectively increases the total amount of piperazine (PIP) aqueous monomers participating in the interfacial polymerization reaction. Simultaneously, the hollow polymer nanofiber structure moderately inhibits the diffusion behavior of piperazine (PIP) aqueous monomers. This slow-release effect allows the interfacial polymerization reaction to proceed under more controllable kinetic conditions, promoting the formation of a wrinkled filter layer structure, effectively improving separation performance, and achieving a simultaneous improvement in membrane permeability and selectivity. Furthermore, the preparation method of this application has the advantages of simple operation and low manufacturing cost. The composite nanofiltration membrane provided by this application for filtering or retaining emerging pollutants exhibits significant stability and anti-fouling performance in retaining emerging pollutants.

[0005] This application provides a composite nanofiltration membrane, comprising a macroporous base membrane support layer, an oriented hollow nanofiber intermediate layer, and a filter skin layer. The macroporous base membrane support layer is composed of a hydrophilic organic material. The oriented hollow nanofiber intermediate layer is loaded on the macroporous base membrane support layer and comprises oriented hollow polymer nanofibers, each having an internal hollow cavity. The filter skin layer is formed on the surface of the oriented hollow nanofiber intermediate layer and / or the surface of the macroporous base membrane support layer. The surface of the filter skin layer has a wrinkled structure along the orientation of the hollow polymer nanofibers in the oriented hollow nanofiber intermediate layer.

[0006] Preferably, the oriented hollow nanofiber interlayer is an oriented hollow polyvinylidene fluoride (PVDF) nanofiber interlayer.

[0007] Preferably, the macroporous membrane support layer is a polyethersulfone (PES) membrane, and the filter layer is a polyamide (PA) layer.

[0008] Preferably, the thickness of the polyamide layer is 50 nm to 82 nm.

[0009] On the other hand, this application, such as Figure 1 As shown, a method for preparing a composite nanofiltration membrane is provided, comprising the following steps:

[0010] S1. Obtain a hydrophilic macroporous base membrane support layer;

[0011] S2. An oriented hollow nanofiber intermediate layer is prepared by coaxial electrospinning and loaded onto the macroporous base film support layer to form a composite substrate;

[0012] S3. Perform an interfacial polymerization reaction on the composite substrate to prepare a filter layer.

[0013] Preferably, the macroporous base membrane support layer obtained in step S1 is a polyethersulfone (PES) base membrane layer, the oriented hollow nanofiber intermediate layer prepared by coaxial electrospinning in step S2 is an oriented hollow polyvinylidene fluoride (PVDF) nanofiber intermediate layer, the composite substrate is formed by loading the oriented hollow polyvinylidene fluoride (PVDF) nanofiber intermediate layer on the polyethersulfone (PES) base membrane layer, and the filter skin layer prepared in step S3 is a polyamide (PA) layer.

[0014] Preferably, step S2 includes:

[0015] S21. Prepare electrospinning solutions, including preparing a polyvinylidene fluoride (PVDF) electrospinning shell solution and a polyvinylpyrrolidone (PVP) electrospinning core solution.

[0016] S22. Electrospinning the electrospinning shell solution and the electrospinning core solution simultaneously using coaxial electrospinning to obtain the oriented hollow polyvinylidene fluoride (PVDF) nanofiber intermediate layer.

[0017] Preferably, in step S21, the electrospinning solution is prepared by the following steps: dissolving a certain mass-volume percentage of polyvinylidene fluoride (PVDF) in a mixed solvent of N,N-dimethylformamide (DMF) and acetone in a certain volume ratio to prepare an electrospinning shell solution; and completely dissolving a certain mass percentage of polyvinylpyrrolidone (PVP) powder in a mixed solvent of N,N-dimethylformamide (DMF) and N,N-dimethylacetamide (DMAc) in a certain volume ratio to prepare an electrospinning core solution.

[0018] Preferably, the method for preparing the electrospinning shell solution in step S21 includes: dissolving polyvinylidene fluoride (PVDF) in a mixed solvent of N,N-dimethylformamide (DMF) and acetone at a volume ratio of 3:1, completely dissolving it under constant temperature conditions to prepare an electrospinning shell solution with a polyvinylidene fluoride (PVDF) concentration of 15% (w / v), and allowing it to stand at 15°C to 25°C for more than 24 hours.

[0019] Preferably, the method for preparing the electrospinning core layer solution in step S21 includes: dissolving polyvinylpyrrolidone (PVP) in a mixed solvent of N,N-dimethylformamide (DMF) and N,N-dimethylacetamide (DMAc) in a volume ratio of 1:1, completely dissolving it under constant temperature conditions to prepare an electrospinning core layer solution with a polyvinylpyrrolidone (PVP) mass percentage of 30%, and letting it stand for more than 24 hours.

[0020] Preferably, the coaxial electrospinning method is completed by a coaxial electrospinning device. Under the condition of collector rotation, the electrospinning time is set to 5 to 20 minutes, and the electrospinning shell solution and the electrospinning core solution are electrospinned simultaneously.

[0021] Preferably, the conditions for electrospinning are as follows: applying a voltage of 18 kV, maintaining the relative humidity of the environment at 40%RH to 50%RH, setting the collector rotation speed to 700 rpm, the propulsion speed of the electrospinning shell solution to 2.0 mL / h, the propulsion speed of the electrospinning core solution to 1.5 mL / h, and setting the electrospinning duration to 10 minutes.

[0022] Preferably, step S3 includes:

[0023] S31. The composite substrate is immersed in an aqueous solution containing a polyamine compound, and after a first specified time, excess aqueous solution is removed from the side of the composite substrate to which the filter layer is to be formed, to obtain a pretreated membrane.

[0024] S32. To uniformly disperse the aqueous solution on the surface of the pretreated membrane;

[0025] S33. Pour an organic phase solution containing polyacrylamide compounds onto the pretreated membrane and carry out an interfacial polymerization reaction. After a second specified time, remove the excess organic phase solution to obtain a composite nanofiltration membrane with a polyamide (PA) layer.

[0026] Preferably, step S3 further includes the steps of preparing an aqueous solution and an organic solution, wherein the aqueous solution containing the polyamine compound is a piperazine (PIP) aqueous solution, and the organic solution containing the polyacrylamide compound is a 1,3,5-benzenetricarboxyl chloride (TMC) organic solution.

[0027] Preferably, the first specified time is 3 to 7 minutes, and the second specified time is 1 to 6 minutes.

[0028] Specifically, in a further detailed implementation, such as Figure 2 As shown, the specific preparation method of the composite nanofiltration membrane of this application by coaxial electrospinning includes the following steps:

[0029] S1-1: Pretreatment of polyethersulfone (PES) based film;

[0030] S2-1: Prepare the electrospinning shell layer solution and electrospinning core layer solution required for the intermediate layer of oriented hollow polyvinylidene fluoride (PVDF) nanofibers;

[0031] S3-1: Electrospinning the electrospinning shell layer solution and the electrospinning core layer solution simultaneously for a certain period of time to prepare the oriented hollow polyvinylidene fluoride (PVDF) nanofiber intermediate layer, and loading it onto the polyethersulfone (PES) base film to form a composite substrate.

[0032] S4-1: Place the composite substrate with the side of the oriented hollow polyvinylidene fluoride (PVDF) nanofiber intermediate layer facing upward on a flat plate, and carry out an interfacial polymerization reaction on this side to obtain a polyamide (PA) layer with selective permeability.

[0033] Preferably, step S2-1 includes:

[0034] S2-11. The steps for preparing the electrospinning shell solution are as follows: Polyvinylidene fluoride (PVDF) is dissolved in a mixed solvent of N,N-dimethylformamide (DMF) and acetone at a volume ratio of 3:1. The solution is then heated to 60°C in a water bath and stirred for 10 hours until completely dissolved. After stirring, the solution is allowed to stand at 15°C to 25°C for 24 hours to degas, thus preparing an electrospinning shell solution with a PVDF concentration of 15% (w / v).

[0035] S2-12. The steps for preparing the electrospinning core layer solution are as follows: Dissolve polyvinylpyrrolidone (PVP) in a mixed solvent of N,N-dimethylformamide (DMF) and N,N-dimethylacetamide (DMAc) at a volume ratio of 1:1. Then, heat the solution to 60°C using a water bath and stir for 10 hours until completely dissolved. After stirring, allow it to stand for 24 hours to prepare an electrospinning core layer solution with a polyvinylpyrrolidone (PVP) content of 30% by mass.

[0036] Preferably, in step S3-1, the electrospinning shell solution and the electrospinning core solution are poured into two 10 mL syringes, each containing 5 mL. The electrospinning shell solution and the electrospinning core solution are simultaneously electrospinned for 10 minutes and loaded onto a polyethersulfone (PES) base film to obtain a composite substrate. After electrospinning, the composite substrate is immersed in anhydrous ethanol solution for 1 minute, followed by a water bath for 1 hour, then removed and dried to obtain a polyethersulfone (PES) base film loaded with an oriented hollow polyvinylidene fluoride (PVDF) nanofiber interlayer.

[0037] Preferably, in step S3-1, the electrospinning conditions are as follows: spinning voltage 18 kV, ambient relative humidity maintained at 40% RH to 50% RH, collector rotation speed 700 rpm, electrospinning shell layer solution propulsion speed 2.0 mL / h, electrospinning core layer solution propulsion speed 1.5 mL / h, round trip distance fixed at 150 mm, and moving speed 32 mm / s.

[0038] Preferably, the preparation of the polyamide (PA) layer in step S4-1 includes:

[0039] S4-11. Immerse the composite substrate in an aqueous solution, and after complete immersion for a first specified time, pour off the excess aqueous solution and make the aqueous solution on the surface evenly dispersed.

[0040] S4-12. Slowly pour the organic phase solution onto the composite substrate treated in S4-11 to carry out the interfacial polymerization reaction, and remove the excess organic phase solution after the second specified time.

[0041] S4-13. After the membrane treated in S4-12 is dried in the air, it is cured to obtain a composite nanofiltration membrane with a polyamide (PA) layer.

[0042] Preferably, the first specified time is 3 to 7 minutes, more preferably 4 minutes and 30 seconds; the second specified time is 1 to 6 minutes, more preferably 2 minutes; after the interface polymerization, it is air-dried for 30 to 90 seconds, more preferably 60 seconds, and then cured in an oven for 5 minutes.

[0043] Preferably, the aqueous phase solution is a piperazine (PIP) aqueous phase solution, and the organic phase solution is a 1,3,5-benzenetricarboxylic acid chloride (TMC) organic phase solution.

[0044] Preferably, before step S4-11, the polyethersulfone (PES) base film with the loaded oriented hollow polyvinylidene fluoride (PVDF) nanofiber interlayer is placed flat on a clean glass plate and fixed around the edges using a frame and rubber rings.

[0045] In another aspect, this application provides a composite nanofiltration membrane prepared by any of the preparation methods described in another aspect of this application.

[0046] In another aspect, this application provides the use of the aforementioned composite nanofiltration membrane in filtering emerging pollutants, wherein the emerging pollutants include at least one pollutant selected from methylparaben (MP), propylparaben (PP), benzylparaben (BP), sulfamethoxazole (SMX), and trimethoprim (TMP).

[0047] The beneficial effects of this application lie in the construction of an oriented hollow nanofiber interlayer on a hydrophilic macroporous membrane support layer. The macroporous membrane surface is gradually covered by nanofibers, while the pore size remains essentially unchanged, and the surface hydrophilicity is altered. The hollow fiber structure of the oriented hollow nanofiber interlayer stores a large number of amine monomers, reducing the diffusion of aqueous monomers and optimizing the permeation conditions for water molecules. Furthermore, the filter skin surface has a wrinkled structure along both sides of the fiber structure of the oriented hollow nanofiber interlayer, effectively improving separation performance. While maintaining the retention effect, it achieves a simultaneous improvement in membrane permeability and selectivity, exhibiting significant stability and antifouling performance in the retention of emerging pollutants. The composite nanofiltration membrane and its preparation method of this application have the advantages of simple operation and low material cost, providing a superior option for composite nanofiltration membranes and their preparation in the field of water treatment. Attached Figure Description

[0048] To more clearly illustrate the technical solutions in the embodiments of this application or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0049] Figure 1 This is a schematic diagram of the preparation process of the composite nanofiltration membrane of this application;

[0050] Figure 2 This is a schematic diagram of the preparation process of the composite nanofiltration membrane according to a specific embodiment of this application;

[0051] Figure 3 Schematic diagrams of the oriented hollow nanofiber morphology of composite nanofiltration membranes in different comparative examples and embodiments of this application;

[0052] Figure 4a , 4b This is a schematic diagram showing the porosity and average pore size of the composite nanofiltration membranes in different comparative examples and embodiments of this application;

[0053] Figure 5a , 5b This is a schematic diagram showing the dynamic contact angle of the composite nanofiltration membranes in different comparative examples and embodiments of this application;

[0054] Figure 6 The above are schematic diagrams of surface scanning electron microscopy (SEM) of composite nanofiltration membranes in different comparative examples and embodiments of this application.

[0055] Figure 7 Figures showing the characterization results of the polyamide layer thickness of the composite nanofiltration membrane in different comparative examples and embodiments of this application;

[0056] Figure 8 This is a schematic diagram of the roughness atomic force microscopy (AFM) of the composite nanofiltration membranes in different comparative examples and embodiments of this application;

[0057] Figure 9a , 9b This is a schematic diagram of the ultraviolet-visible spectrum of piperazine (PIP) aqueous monomer diffusion during the interfacial polymerization reaction of composite nanofiltration membranes in different comparative examples and embodiments of this application.

[0058] Figure 10a This is a schematic diagram showing the water contact angle (WCA) of the composite nanofiltration membranes in different comparative examples and embodiments of this application;

[0059] Figure 10b This is a schematic diagram of the Zeta potential of the composite nanofiltration membranes in different comparative examples and embodiments of this application;

[0060] Figure 11a This is a schematic diagram of the Fourier transform infrared (FTIR) spectra of the chemical properties of the composite nanofiltration membranes in different comparative examples and embodiments of this application;

[0061] Figure 11b This is a schematic diagram of X-ray photoelectron spectroscopy (XPS) of the chemical properties of the composite nanofiltration membranes in different comparative examples and embodiments of this application;

[0062] Figure 12a , 12b These are schematic diagrams of polyethylene glycol (PEG) retention and pore size distribution curves of composite nanofiltration membranes in different comparative examples and embodiments of this application.

[0063] Figure 13 Schematic diagrams showing the pure water permeation flux and Na2SO4 salt rejection effect of composite nanofiltration membranes in different comparative examples and embodiments of this application;

[0064] Figure 14a , 14b Schematic diagrams showing the permeation flux and retention performance of composite nanofiltration membranes for different salts in different comparative examples and embodiments of this application;

[0065] Figure 15 This is a schematic diagram illustrating the removal effect of composite nanofiltration membranes on emerging pollutants in different comparative examples and embodiments of this application;

[0066] Figures 16a-16c This is a schematic diagram illustrating the operational stability of the composite nanofiltration membrane according to a preferred embodiment of this application.

[0067] Figures 17a-17c This is a schematic diagram illustrating the antifouling performance of the composite nanofiltration membrane according to a preferred embodiment of this application. Detailed Implementation

[0068] To make the technical means, creative features, objectives and effects of this application easier to understand, the following description, in conjunction with specific illustrations, further elaborates on this application.

[0069] One aspect of this application provides a composite nanofiltration membrane, comprising a macroporous base membrane support layer, an oriented hollow nanofiber intermediate layer, and a filter skin layer. The macroporous base membrane support layer is composed of a hydrophilic organic material. The oriented hollow nanofiber intermediate layer is loaded on the macroporous base membrane support layer and comprises oriented hollow polymer nanofibers. The filter skin layer is formed on the surface of the oriented hollow nanofiber intermediate layer and / or the surface of the macroporous base membrane support layer. The surface of the filter skin layer has a wrinkled structure along the orientation of the hollow polymer nanofibers in the oriented hollow nanofiber intermediate layer.

[0070] In one specific embodiment, the oriented hollow nanofiber interlayer is an oriented hollow polyvinylidene fluoride (PVDF) nanofiber interlayer, the macroporous base membrane support layer is a polyethersulfone (PES) base membrane, and the filter skin layer is a polyamide (PA) layer. Further, the polyamide (PA) layer is an ultrathin layer with a thickness of 50 nm to 82 nm, a crosslinking degree of 55.32% to 73.97%, and a water contact angle of 35.7° to 54°. The preferred composite nanofiltration membrane exhibits a water permeation flux of up to 24.91 L·m⁻²·h⁻¹·bar⁻¹ and a salt rejection rate of 96.45% to 97.62%.

[0071] The composite nanofiltration membrane provided in this application has the following main properties and structure: a skin layer thickness of 50 nm to 82 nm; a crosslinking degree of 55.32% to 73.97%; a water contact angle of 35.7° to 54°; a Zeta potential of -45.2 mV to 1.15 mV; and in the preferred embodiment, the polyamide (PA) layer of the composite nanofiltration membrane has a thickness of 54.2 ± 0.5 nm, a water flux of up to 24.91 L·m⁻²·h⁻¹·bar⁻¹, a salt rejection rate of 96.45% to 97.62%, and a Cl⁻ / SO₄²⁻ selectivity of 17.3 to 101.4.

[0072] In this embodiment, the polyethersulfone (PES) base membrane serves as a macroporous substrate. After depositing an oriented hollow polyvinylidene fluoride (PVDF) nanofiber interlayer, the macroporous structure on the PES base membrane surface is gradually covered by the oriented hollow PVDF nanofibers, altering the hydrophilicity while maintaining the pore size essentially unchanged, forming a novel substrate morphology that influences the morphology and performance of the polyamide (PA) layer. The polyamide (PA) layer surface exhibits a wrinkled structure along the alignment direction of the hollow polymer nanofibers in the oriented hollow nanofiber interlayer. Simultaneously, the hollow fiber structure guides the transport of more water molecules, effectively improving the membrane's separation performance. The composite nanofiltration membrane in this embodiment has an ultrathin polyamide (PA) layer. The polyamide (PA) layer surface exhibits a wrinkled structure along both sides of the fiber structure of the oriented hollow nanofiber interlayer. The hydrophilicity, high crosslinking degree, and excellent electronegativity of the PES base membrane play a positive role in improving its separation performance, achieving high water permeation flux while maintaining good retention.

[0073] Another aspect of this application provides the use of the aforementioned composite nanofiltration membrane in filtering emerging pollutants, said emerging pollutants including at least one pollutant selected from methylparaben (MP), propylparaben (PP), benzylparaben (BP), sulfamethoxazole (SMX) and trimethoprim (TMP).

[0074] This application also provides a method for preparing a composite nanofiltration membrane, such as... Figure 1 As shown, it includes the following steps:

[0075] S1. Obtain a hydrophilic macroporous base membrane support layer;

[0076] S2. An oriented hollow nanofiber intermediate layer is prepared by coaxial electrospinning and loaded onto a macroporous base membrane support layer to form a composite substrate;

[0077] S3. Perform interfacial polymerization on the composite substrate to prepare the filter skin.

[0078] In a specific embodiment, the macroporous base membrane support layer is a polyethersulfone (PES) base membrane layer, the oriented hollow nanofiber interlayer prepared by coaxial electrospinning in step S2 is an oriented hollow polyvinylidene fluoride (PVDF) nanofiber interlayer, the composite substrate is composed of an oriented hollow polyvinylidene fluoride (PVDF) nanofiber interlayer loaded on the polyethersulfone (PES) base membrane layer, and the filter skin layer prepared in step S3 is a polyamide (PA) layer with a thickness of 50 nm to 82 nm.

[0079] Further, step S2 includes: S21, preparing an electrospinning solution, including preparing a polyvinylidene fluoride (PVDF) electrospinning shell solution and a polyvinylpyrrolidone (PVP) electrospinning core solution; S22, simultaneously electrospinning the electrospinning shell solution and the electrospinning core solution by coaxial electrospinning to obtain an oriented hollow polyvinylidene fluoride (PVDF) nanofiber intermediate layer.

[0080] In step S21, the electrospinning solution is prepared by the following steps: a certain mass-volume percentage of polyvinylidene fluoride (PVDF) is dissolved in a mixed solvent of N,N-dimethylformamide (DMF) and acetone in a certain volume ratio to prepare an electrospinning shell solution; a certain mass-volume percentage of polyvinylpyrrolidone (PVP) powder is completely dissolved in a mixed solvent of N,N-dimethylformamide (DMF) and N,N-dimethylacetamide (DMAc) in a certain volume ratio to prepare an electrospinning core solution. In this application, the electrospinning shell solution is preferably prepared by dissolving polyvinylidene fluoride (PVDF) in a mixed solvent of N,N-dimethylformamide (DMF) and acetone in a volume ratio of 3:1, completely dissolving it under constant temperature conditions to prepare an electrospinning shell solution with a PVDF concentration of 15% (w / v), and allowing it to stand at 15°C to 25°C for at least 24 hours. The electrospinning core solution is preferably prepared by dissolving polyvinylpyrrolidone (PVP) in a mixed solvent of N,N-dimethylformamide (DMF) and N,N-dimethylacetamide (DMAc) in a volume ratio of 1:1, completely dissolving it under constant temperature conditions to prepare an electrospinning core solution with a polyvinylpyrrolidone (PVP) mass percentage of 30%, and allowing it to stand for at least 24 hours.

[0081] Coaxial electrospinning is performed using an electrospinning apparatus. At a certain rotation speed, the electrospinning time is set to 5 to 20 minutes, simultaneously performing coaxial electrospinning on both the shell solution and the core solution. Preferred electrospinning conditions in this application are: an applied voltage of 18 kV, an ambient relative humidity maintained at 40% RH to 50% RH, a collector rotation speed of 700 rpm, a shell solution feed rate of 2.0 mL / h, a core solution feed rate of 1.5 mL / h, and a electrospinning duration of 10 minutes.

[0082] Step S3 includes: S31, immersing the composite substrate in an aqueous solution containing a polyamine compound, and removing excess aqueous solution after a first specified time, such as 3 to 7 minutes, to obtain a pretreated membrane; S32, uniformly dispersing the aqueous solution on the surface of the pretreated membrane; S33, pouring an organic solution containing a polyacrylamide compound onto the pretreated membrane to carry out an interfacial polymerization reaction, and removing excess organic solution after a second specified time, such as 1 to 6 minutes, to obtain a composite nanofiltration membrane with a polyamide (PA) layer. In this application, the aqueous solution is a piperazine (PIP) aqueous solution, and the organic solution is a 1,3,5-benzenetricarboxylic acid chloride (TMC) organic solution.

[0083] In a further embodiment, a composite nanofiltration membrane is prepared by coaxial electrospinning, wherein the macroporous base membrane support layer is a polyethersulfone (PES) base membrane layer, the oriented hollow nanofiber intermediate layer is an oriented hollow polyvinylidene fluoride (PVDF) nanofiber intermediate layer, and the filter skin layer is a polyamide (PA) layer. Figure 2 As shown, the specific preparation method includes the following steps:

[0084] S1-1: Pretreatment of polyethersulfone (PES) based film;

[0085] S2-1: Prepare the electrospinning shell layer solution and electrospinning core layer solution required for the intermediate layer of oriented hollow polyvinylidene fluoride (PVDF) nanofibers;

[0086] S3-1: Electrospinning the shell layer solution and the core layer solution simultaneously for a certain period of time to prepare an oriented hollow polyvinylidene fluoride (PVDF) nanofiber intermediate layer, which is then loaded onto a polyethersulfone (PES) base film to form a composite substrate.

[0087] S4-1: Place the composite substrate with the side of the oriented hollow polyvinylidene fluoride (PVDF) nanofiber intermediate layer facing upward on a flat plate, and carry out an interfacial polymerization reaction on this side to obtain a polyamide (PA) layer with selective permeability.

[0088] Specifically, in step S1-1, the polyethersulfone (PES) base film is pretreated, including: cutting it to a suitable size, which is 15 cm × 15 cm in this embodiment, fixing it on yellow release paper, soaking it, and performing a neutral treatment.

[0089] Step S2-1 includes: S2-11, the steps for preparing the electrospinning shell solution are as follows: dissolve polyvinylidene fluoride (PVDF) in a mixed solvent of N,N-dimethylformamide (DMF) and acetone in a volume ratio of 3:1, then heat it to 60°C in a water bath and stir for 10 hours until completely dissolved. After stirring, let it stand at 15°C to 25°C for 24 hours to degas, thus preparing an electrospinning shell solution with a polyvinylidene fluoride (PVDF) concentration of 15% (w / v). S2-12. The steps for preparing the electrospinning core layer solution are as follows: dissolve polyvinylpyrrolidone (PVP) in a mixed solvent of N,N-dimethylformamide (DMF) and N,N-dimethylacetamide (DMAc) in a volume ratio of 1:1, then heat it to 60°C in a water bath and stir for 10 hours until completely dissolved. After stirring, let it stand for 24 hours to prepare an electrospinning core layer solution with a polyvinylpyrrolidone (PVP) mass percentage of 30%.

[0090] In step S3-1, 5 mL of the electrospinning shell solution and 5 mL of the electrospinning core solution are poured into two 10 mL syringes respectively. The electrospinning shell solution and the electrospinning core solution are simultaneously electrospinned using a screw-type coaxial needle and loaded onto a polyethersulfone (PES) substrate. After electrospinning, the PES substrate with the oriented hollow polyvinylidene fluoride (PVDF) nanofiber intermediate layer is immersed in anhydrous ethanol solution for 1 minute, followed by a water bath for 1 hour. It is then removed and dried to obtain the composite substrate. The preferred coaxial electrospinning conditions are: spinning voltage 18 kV, ambient relative humidity maintained at 40% RH to 50% RH, collector rotation speed 700 rpm, propulsion speed of the electrospinning shell solution 2.0 mL / h, propulsion speed of the electrospinning core solution 1.5 mL / h, round-trip distance fixed at 150 mm, and moving speed 32 mm / s.

[0091] Before step S4-11, place the composite substrate flat on a clean glass plate and fix it around the edges using a frame and rubber rings.

[0092] Aqueous and organic phase solutions were prepared. In this embodiment, a 0.5 wt% aqueous solution of piperazine (PIP) was prepared using water as a solvent and placed in a brown bottle; a 0.1% (w / v) organic phase solution of 1,3,5-benzenetricarboxylic acid chloride (TMC) was prepared using n-hexane as a solvent and placed in a brown bottle.

[0093] The preparation of the polyamide (PA) layer in step S4-1 includes: S4-11, pouring piperazine (PIP) aqueous solution into the frame to ensure that the polyethersulfone (PES) base film supporting the oriented hollow polyvinylidene fluoride (PVDF) nanofiber interlayer is immersed in the piperazine (PIP) aqueous solution for 3 to 7 minutes, preferably 4 minutes and 30 seconds, and then pouring off the excess aqueous solution. The piperazine (PIP) aqueous solution on the surface can be uniformly dispersed by a rubber collection roller; S4-12, 1, A 3,5-benzenetricarboxylic acid chloride (TMC) organic phase solution is slowly poured onto the composite substrate treated in S4-11 to carry out an interfacial polymerization reaction for 1 to 6 minutes, preferably 2 minutes. Afterward, excess 1,3,5-benzenetricarboxylic acid chloride (TMC) organic phase solution is removed. In S4-13, the membrane treated in S4-12 is air-dried for 30 to 90 seconds, preferably 60 seconds, and then cured in an oven for 5 minutes to obtain a composite nanofiltration membrane with a polyamide (PA) layer. After preparation, the composite nanofiltration membrane can be stored in deionized water at 4°C.

[0094] To further illustrate the impact of the preparation method of this application on the composite nanofiltration membrane, this application uses the above-mentioned preparation method to conduct different comparative examples and embodiments. In the comparative examples and embodiments, the polyethersulfone (PES) base membrane obtained without electrospinning treatment is labeled as PES, the composite substrate obtained when the electrospinning time is 10 min and the electrospinning core layer solution advance speed is 0 mL / h is labeled as PES-OS, and the composite nanofiltration membranes prepared by the interfacial polymerization process are labeled as TFC and TFC-OS, respectively; the composite substrates obtained when the electrospinning core layer solution is prepared using 20%, 30%, and 40% by mass percentage of polyvinylpyrrolidone (PVP) and the electrospinning time is 10 min are labeled as PES-O-H1, PES-O-H2, and PES-O-H3, respectively, and the composite nanofiltration membranes prepared by the interfacial polymerization process are labeled as TFC-O-H1, TFC-O-H2, and TFC-O-H3, respectively.

[0095] Comparative Example 1 of this application is a blank composite nanofiltration membrane without a nanofiber interlayer. The resulting membrane is labeled TFC, and the preparation steps include:

[0096] 1. Cut the polyethersulfone (PES) base film to a size of 15 cm × 15 cm and fix it on yellow release paper for later use.

[0097] 2. Preparation of electrospinning shell solution: Dissolve polyvinylidene fluoride (PVDF) in a mixed solvent of N,N-dimethylformamide (DMF) and acetone in a volume ratio of 3:1. Then heat the solution to 60°C in a water bath and stir for 10 hours until completely dissolved. After stirring, allow the solution to stand at 15°C to 25°C for 24 hours to degas, thus preparing an electrospinning shell solution with a polyvinylidene fluoride (PVDF) concentration of 15% (w / v).

[0098] The steps for preparing the electrospinning core layer solution are as follows: dissolve polyvinylpyrrolidone (PVP) in a mixed solvent of N,N-dimethylformamide (DMF) and N,N-dimethylacetamide (DMAc) in a volume ratio of 1:1, then heat the solution to 60°C in a water bath and stir for 10 hours until completely dissolved. After stirring, let the solution stand for 24 hours to prepare an electrospinning core layer solution with a polyvinylpyrrolidone (PVP) content of 30% by mass.

[0099] 3. Pour 5 mL of the electrospinning shell solution and 5 mL of the electrospinning core solution into two 10 mL syringes respectively. Apply a spinning voltage of 18 kV, maintain the relative humidity of the environment at 40% RH to 50% RH, set the collector rotation speed to 700 rpm, the propulsion speed of the electrospinning shell solution to 2.0 mL / h, the propulsion speed of the electrospinning core solution to 1.5 mL / h, the round-trip distance to be fixed at 150 mm, and the moving speed to 32 mm / s. Set the electrospinning time for the inner and outer spinning solutions to 0 min using a screw-type coaxial needle. No nanofiber intermediate layer is formed on the collector surface wrapped with polyethersulfone (PES) base film. Subsequently, immerse the polyethersulfone (PES) base film in anhydrous ethanol solution for 1 min, bathe in water for 1 hour, remove it, and dry it in a 50°C oven for 4 hours to obtain a substrate without a nanofiber intermediate layer.

[0100] 4. Prepare a 0.5 wt% piperazine (PIP) aqueous solution in a 50 mL brown bottle using deionized water as the solvent, and sonicate for 30 min. Prepare a 0.1% (w / v) 1,3,5-benzenetricarboxylic acid (TMC) organic solution in a 50 mL brown bottle using n-hexane as the solvent, and sonicate for 30 min to completely dissolve it, thus obtaining a 1,3,5-benzenetricarboxylic acid (TMC) organic solution.

[0101] The prepared composite substrate was placed flat on a clean glass plate and fixed and leak-proofed using a stainless steel frame and rubber ring, with the side of the substrate without the nanofiber interlayer to be subjected to interfacial polymerization facing upwards.

[0102] Pour 50 mL of the prepared piperazine (PIP) aqueous solution into the frame, soak the PES base membrane for 4 minutes and 30 seconds, then pour off the excess aqueous solution, remove the stainless steel frame and rubber ring to obtain the pretreated membrane.

[0103] Roll a rubber roller over the surface of the pretreated membrane to uniformly disperse the aqueous phase solution. Pour 50 mL of the prepared 1,3,5-benzenetricarboxylic acid chloride (TMC) organic phase solution into the frame, react for 2 minutes, and then pour off the excess organic phase solution. After air drying for 60 seconds, place it in an oven to cure for 5 minutes to obtain a composite nanofiltration membrane with a selectively permeable polyamide (PA) layer.

[0104] The composite nanofiltration membrane prepared above was stored in deionized water at 4°C.

[0105] The composite nanofiltration membrane prepared in Comparative Example 1 is labeled TFC, with an average pore diameter mostly distributed around 140 nm. Tests showed a crosslinking degree of 55.32%, a water contact angle of approximately 54°, a water permeation flux of 10.3 L·m⁻²·h⁻¹·bar⁻¹, a salt rejection rate of 97.62%, and a Cl⁻ / SO₄²⁻ selectivity of 17.3.

[0106] Comparative Example 2: The difference between Comparative Example 2 and Comparative Example 1 is that the electrospinning time is 10 min, the propulsion speed of the electrospinning core layer solution is 0 mL / h, and other process conditions are the same as those in Comparative Example 1.

[0107] The oriented solid polyvinylidene fluoride (PVDF) nanofiber interlayer prepared in Comparative Example 2 was labeled PVDF-OS, and the prepared composite nanofiltration membrane was labeled TFC-OS. The average pore diameter was mostly distributed at around 140 nm. Testing showed that the nanofiltration membrane prepared in Comparative Example 2 had a crosslinking degree of 69.06%, a water contact angle of approximately 46.9°, a water permeation flux of 22.87 L·m⁻²·h⁻¹·bar⁻¹, a salt rejection rate of 97.39%, and a Cl⁻ / SO₄²⁻ selectivity of 92.6.

[0108] Example 1: The difference between Example 1 and Comparative Example 1 is that when preparing the electrospinning core layer solution, 20% polyvinylpyrrolidone (PVP) by mass was used, the electrospinning time was 10 min, and other process conditions were the same as those in Comparative Example 1.

[0109] The oriented hollow polyvinylidene fluoride (PVDF) nanofiber interlayer prepared in Example 1 is labeled PVDF-O-H1, and the prepared composite nanofiltration membrane is labeled TFC-O-H1. The average pore diameter is mostly distributed at around 140 nm. Testing showed that the composite nanofiltration membrane prepared in Example 1 had a crosslinking degree of 72.73%, a water contact angle of approximately 38.6°, a water permeation flux of 23.74 L·m⁻²·h⁻¹·bar⁻¹, a salt rejection rate of 96.45%, and a Cl⁻ / SO₄²⁻ selectivity of 95.7.

[0110] Example 2: The difference between Example 2 and Comparative Example 1 is that when preparing the electrospinning core layer solution, 30% polyvinylpyrrolidone (PVP) by mass was used, the electrospinning time was 10 min, and other process conditions were the same as those in Comparative Example 1.

[0111] In Example 2, the oriented hollow polyvinylidene fluoride (PVDF) nanofiber interlayer was labeled PVDF-O-H2, and the prepared composite nanofiltration membrane was labeled TFC-O-H2. The average pore diameter was mostly distributed around 140 nm. Testing showed a crosslinking degree of 73.97%, a water contact angle of approximately 35.7°, a water permeation flux of 24.91 L·m⁻²·h⁻¹·bar⁻¹, a salt rejection rate of 96.81%, and a Cl⁻ / SO₄²⁻ selectivity of 101.4.

[0112] Example 3: The difference between Example 3 and Comparative Example 1 is that when preparing the electrospinning core layer solution, 40% polyvinylpyrrolidone (PVP) by mass was used, the electrospinning time was 10 min, and other process conditions were the same as those in Comparative Example 1.

[0113] In Example 3, the oriented hollow polyvinylidene fluoride (PVDF) nanofiber interlayer was labeled PVDF-O-H3, and the prepared composite nanofiltration membrane was labeled TFC-O-H3. The average pore diameter was mostly distributed around 140 nm. Testing showed that the nanofiltration membrane prepared in the above examples had a crosslinking degree of 70.27%, a water contact angle of approximately 36.3°, a water permeation flux of 24.67 L·m⁻²·h⁻¹·bar⁻¹, a salt rejection rate of 97.33%, and a Cl⁻ / SO₄²⁻ selectivity of 96.1.

[0114] As can be seen from the comparative examples and embodiments above, this application uses coaxial electrospinning technology to prepare a composite nanofiltration membrane. An oriented hollow nanofiber interlayer is successfully constructed on a polyethersulfone (PES) base membrane layer, and a composite nanofiltration membrane with excellent selective permeability is prepared based on interfacial polymerization. Furthermore, the oriented hollow nanofiber interlayer loading in the composite nanofiltration membrane provided by this application alters a series of physicochemical properties of the PES base membrane surface, such as hydrophilicity and roughness. The new morphology of the oriented hollow nanofiber interlayer also affects the morphology and performance of the polyamide (PA) layer. Simultaneously, the PES base membrane forms a novel substrate morphology, with moderate hydrophilicity, a mild reaction interface, and controllable monomer diffusion, providing a stable interfacial reaction for the reaction between the piperazine (PIP) aqueous solution and the 1,3,5-benzenetricarboxylic acid (TMC) organic solution, thereby resulting in higher crosslinking degree and excellent separation performance.

[0115] To better illustrate this, this application used a series of analytical instruments, including scanning electron microscopy (SEM), atomic force microscopy (AFM), and Fourier transform infrared spectroscopy (FTIR), to analyze the morphology, physicochemical properties, and separation performance of different composite nanofiltration membranes. The separation performance and removal efficiency of emerging pollutants were also evaluated. Compared with TFC and TFC-OS, TFC-O-H1, TFC-O-H2, and TFC-O-H3 exhibited increased crosslinking degree, decreased water contact angle, and a maximum water permeation flux of 24.91 L·m⁻²·h⁻¹·bar⁻¹. The results showed that, under the condition of using a polyvinylpyrrolidone (PVP) electrospinning core layer solution with a mass percentage of 30%, the composite substrate could regulate the diffusion of piperazine (PIP) aqueous monomers and optimize the water molecule transport path during the interfacial polymerization reaction. The prepared TFC-O-H2 membrane had the best separation performance, with a water permeation flux of 24.91 L·m⁻²·h⁻¹·bar⁻¹ and a salt rejection rate of 96.81%, indicating that the rejection effect on emerging pollutants was also well maintained.

[0116] In the electrospinning process, electrospinning core layer solutions are prepared using polyvinylpyrrolidone (PVP) powder with different mass percentages, such as... Figure 3 As shown, Figure 3 a, b, and c in the figures represent the cross-sectional morphologies of the intermediate layers of oriented hollow polyvinylidene fluoride (PVDF) nanofibers obtained under conditions where polyvinylpyrrolidone (PVP) powder was 20 wt%, 30 wt%, and 40 wt%, respectively. Figure 3 As can be seen, the outer diameters of the three groups of oriented hollow polyvinylidene fluoride (PVDF) nanofibers are not significantly different, all falling within the range of 1.30 μm to 1.40 μm. However, the inner diameters show a considerable variation, from... Figure 3As shown in a, the PVDF-O-H1 increased from approximately 0.29 μm to... Figure 3 The c in the figure shows that the PVDF-O-H3 is approximately 0.97 μm. This trend indicates that, during coaxial electrospinning, appropriately increasing the concentration of the electrospinning core solution can effectively expand the internal cavities of the fiber. From Figure 3 From above, these oriented hollow polyvinylidene fluoride (PVDF) nanofibers all maintain a continuous, interconnected tubular structure, with no obvious collapse or perforation observed. Notably, the significant increase in the volume of the hollow cavities within the fibers facilitates the storage of more aqueous amine monomers before interfacial polymerization, laying the structural foundation for the subsequent formation of high-performance composite nanofiltration membranes with wrinkled structures.

[0117] The porosity and average pore size of nanofiber interlayer composite substrates prepared by different modification processes of polyethersulfone (PES) based films were characterized, and the results are shown in Figure 4. Figure 4a In the study, the porosity of the polyethersulfone (PES)-based film was 58.65%. However, after introducing an oriented hollow polyvinylidene fluoride (PVDF) nanofiber interlayer, the porosity of the composite substrate showed a significant increasing trend. Specifically, the porosity of the PES-OS composite substrate increased to 60.84%, while the porosities of the PES-O-H1, PES-O-H2, and PES-O-H3 composite substrates further increased to 62.21%, 63.55%, and 63.71%, respectively. This result indicates that the introduction of hollow nanofibers can effectively improve the porosity of the composite substrate. This is because the hollow structure of the oriented hollow PVDF nanofibers can form a large number of interconnected interstitial channels, increasing the pore volume ratio within the substrate. The average pore size test results of the composite substrate are shown below. Figure 4b As shown, the average pore size of each composite substrate film is within a small range of 138.7 nm to 141.1 nm, with no significant difference, indicating that the introduction of oriented hollow nanofibers did not affect the overall pore size of the composite substrate.

[0118] Figure 5a , 5b This is a schematic diagram showing the dynamic contact angle of the composite nanofiltration membranes in different comparative examples and embodiments of this application. From... Figure 5aIt can be observed that the dynamic contact angle changes of PES-O-H1, PES-O-H2, and PES-O-H3 membranes all fall between those of PES and PES-OS membranes. This indicates that the hydrophilicity / hydrophobicity of the substrate surface was successfully altered after hollow modification of the nanofiber structure, exhibiting a controllable gradient and moderate hydrophilicity / hydrophobicity. Compared to the solid nanofiber-modified PES-OS membrane, the increased hydrophilicity of PES-O-H1, PES-O-H2, and PES-O-H3 membranes is attributed to the integrity of the internal channel structure. The moderately hydrophilic / hydrophobic interface constructed by the method in this application ensures the uniform spreading of the aqueous monomer on the substrate surface, providing a stable and controllable reaction interface for the homogeneous reaction of the interfacial polymerization reaction. It also reduces structural defects in the polyamide layer caused by excessive monomer permeation or insufficient monomer reserves, laying a crucial interfacial foundation for the subsequent preparation of high-performance composite nanofiltration membranes.

[0119] To further illustrate that the change in dynamic contact angle is due to the structural advantages of hollow nanofibers and to exclude the influence of the hydrophilic PES substrate, this application tested the water contact angle of the composite substrate and the nanofiber interlayer of the corresponding composite nanofiltration membrane. Figure 5b As shown, the PVDF-OS intermediate layer of oriented solid polyvinylidene fluoride (PVDF) nanofibers remained stable after a certain degree of reduction, while the dynamic water contact angle of the oriented hollow polyvinylidene fluoride (PVDF) nanofiber intermediate layers PVDF-O-H1, PVDF-O-H2, and PVDF-O-H3 all decreased to 0° within 15 s. This is because, on the one hand, the slit-shaped pores formed between the parallel-arranged oriented nanofibers facilitate permeation and transport during filtration, thereby enhancing hydrophilicity; on the other hand, the hollow structure inside the hollow nanofibers can provide excellent through-water channels during water permeation, which is conducive to the permeation and storage of water molecules, which is equivalent to changing the hydrophilicity at the physical level.

[0120] Surface morphology typically affects the separation performance of nanofiltration membranes. To further illustrate the influence of hollow nanofiber interlayers with different orientations on the morphology of polyamide (PA) layers, the surfaces of different composite nanofiltration membranes were characterized using scanning electron microscopy (SEM). The results are as follows: Figure 6 As shown, Figure 6 As shown in Figure a, on the surface of the TFC membrane, due to unconstrained polymerization, the polyamide (PA) layer molecular chains randomly nucleate, grow, and aggregate, ultimately forming a polyamide (PA) layer with poor uniformity and low effective specific surface area. Introducing a solid nanofiber interlayer, as... Figure 6As shown in b, in the TFC-OS membrane, the inhibition of the diffusion rate of the aqueous piperazine (PIP) monomer causes the polyamide (PA) layer to form biomimetic structural folds resembling centipedes along both sides of the fiber. After controlling the cavity structure of the intermediate layer of the oriented hollow nanofibers, as shown in Figure b, Figure 6 As shown in Figures c, d, and e, the prepared TFC-O-H1, TFC-O-H2, and TFC-O-H3 membranes exhibit a further increase in surface wrinkles. This may be attributed to the fact that, compared to solid nanofiber interlayers, oriented hollow nanofiber interlayers have a storage and slow-release effect on aqueous monomers, which enhances interfacial instability during the interfacial polymerization reaction, thereby generating more wrinkled structures. However, in the TFC-O-H3 membrane, the unstable deformation of the interlayer fiber structure disrupts the orderly diffusion of monomers, leading to excessive aggregation of polyamide (PA) layer molecular chains, thus reducing the surface wrinkle degree.

[0121] like Figure 6 As shown, the surface morphology of the TFC membrane and different composite nanofiltration membranes was characterized using scanning electron microscopy (SEM). Figure 6 As shown in Figure a, the polyamide (PA) layer of the TFC membrane exhibits a disordered nodular structure formed by traditional interfacial polymerization, accompanied by macroporous defects. The TFC-OS membrane with a solid nanofiber interlayer, as shown in Figure a... Figure 6 As shown in b, its surface polyamide layer exhibits a bamboo-like pleated structure distributed along the oriented fibers, based on the template effect of nanofibers. TFC-O-H1, TFC-O-H2, and TFC-O-H3, which introduce oriented hollow nanofiber intermediate layers, are shown in... Figure 6As shown in Figures c, d, and e, the wrinkled structure of the polyamide layer on its surface undergoes a highly significant change. The wrinkles are tightly distributed along the alignment direction of the hollow polymer nanofibers, exhibiting a zipper-like distribution. Furthermore, the number, distribution, and structural continuity of the wrinkles are far superior to those of the TFC and TFC-OS films, indicating that the introduction of the oriented hollow nanofiber interlayer significantly promotes the formation of wrinkles on the polyamide layer surface and enhances the wrinkling degree of the membrane surface. This phenomenon can be attributed to the fact that the oriented hollow nanofibers have interconnected internal cavities and a higher specific surface area, enabling controllable adsorption, storage, and slow release of aqueous piperazine monomers. This allows for precise regulation of the interfacial polymerization kinetics, resulting in a more uniform and complete interfacial polymerization process for the formation of the polyamide (PA) layer. In addition, the oriented hollow nanofibers form an ordered fiber support framework on the substrate surface, providing directional active sites for the nucleation and growth of the polyamide (PA) layer. This guides the polyamide molecular chains to grow oriented and stack orderly along the fiber axis, ultimately forming a continuous wrinkled structure distributed along the alignment direction of the hollow polymer nanofibers. This highly wrinkled structure, induced by the oriented hollow nanofiber interlayer, can significantly increase the effective permeation area of ​​the polyamide (PA) layer. Without sacrificing the membrane retention performance, it provides more low-resistance transport channels for water molecules and lays a key structural foundation for the significant improvement of the permeation performance of composite nanofiltration membranes.

[0122] Combining SEM and AFM, Figure 7 The polyamide (PA) layer thickness of different composite nanofiltration membranes was systematically characterized. Cross-sectional SEM results show that the TFC membrane without a nanofiber interlayer, such as... Figure 7 As shown in Figure a, a significant collapse structure appears at the interface between the polyamide (PA) layer and the composite substrate. The cross-section of the polyamide (PA) layer lacks a clear and continuous phase interface, thus making precise quantitative determination of uniform thickness impossible. Further analysis using AFM... Figure 7 After quantitative analysis of the membrane cross-section shown in a1, the thickness of the TFC membrane polyamide (PA) layer was approximately 152.37 nm. Figure 7 As shown in a2, the cross-sectional structure of the polyamide (PA) layer was significantly improved after the introduction of the nanofiber interlayer, forming a continuous, complete polyamide (PA) layer with a clear interface. Figure 7 As shown in b and b2, the average thickness of the polyamide (PA) layer in the TFC-OS film is 81.4 ± 0.6 nm. Figure 7As can be seen from c and c2, d and d2, and e and e2, TFC-O-H1, TFC-O-H2, and TFC-O-H3 achieved further reductions in the polyamide (PA) layer thickness. Among them, the polyamide (PA) layer thickness of the TFC-O-H2 film is lower than that of all other composite films, at only 54.2 ± 0.5 nm. This can be attributed to the precise control of the interfacial polymerization process by the hollow nanofiber interlayer, which is also confirmed by Figure 9. Although the solid nanofiber interlayer improved the wettability of the substrate and achieved preliminary optimization of the polyamide (PA) layer thickness, the solid structure has poor controllability of monomer adsorption and release behavior. In this embodiment, the oriented hollow nanofiber interlayer, with its interconnected internal hollow cavity structure and controllable hydrophilic-hydrophobic balance, forms a precise control system of "monomer adsorption-storage-slow release": On the one hand, by adsorbing and storing sufficient piperazine monomers through the internal hollow cavity structure, monomers are continuously and smoothly supplied to the two-phase reaction interface on demand during the interfacial polymerization process, relying on the confinement effect of the structure. This avoids the violent cross-linking and overgrowth caused by local excess of monomers, thereby promoting the rapid formation of an ultrathin polyamide (PA) layer. On the other hand, the hydrophilic-hydrophobic balance interface constructed by the hollow nanofiber interlayer allows the aqueous monomers to be spread into a uniform and thin layer on the substrate surface, strictly confining the interfacial polymerization reaction to the two-phase interface region, thus spatially reducing the thickness of the polyamide (PA) layer. At the molecular scale, the oriented hollow nanofiber interlayer achieves multi-level precise control of the interfacial polymerization process by reconstructing the monomer concentration and promoting the full cross-linking of the polyamide network, ultimately synergistically obtaining a high-performance composite nanofiltration membrane with a wrinkled structure.

[0123] To further investigate the influence of the nanofiber interlayer on the morphology of the composite nanofiltration membrane, Figure 8 The surface roughness of different composite nanofiltration membranes was analyzed. For example... Figure 8 The roughness statistics from a to e show that the TFC membrane has a low roughness, indicating a relatively smooth surface. The roughness of the TFC-OS membrane increases significantly to 76.1 nm, which can be explained by the template effect of solid nanofibers on the membrane surface, resulting in a denser protrusion structure. The increased wrinkles further enhance the surface roughness. The TFC-O-H2 membrane, prepared using oriented hollow nanofibers, shows a decrease in roughness to 64.5 nm. This indicates that the ordered diffusion of the piperazine (PIP) aqueous monomer weakens the intensity of the reaction interface and confines the interfacial polymerization reaction to a localized interface, thereby reducing the membrane surface roughness.

[0124] During interfacial polymerization, the diffusion behavior of piperazine (PIP) aqueous monomers into the organic phase directly affects the polyamide (PA) layer. Therefore, UV-Vis spectrophotometry was used to systematically characterize the regulatory effect of composite substrates with different nanofiber interlayers on the diffusion of piperazine (PIP) aqueous monomers. Figure 9a The full-wavelength scanning spectrum shown indicates that all composite nanofiltration membranes with different nanofiber interlayers exhibit a characteristic absorption peak of piperazine (PIP) at 294 nm. Among them, the TFC-O-H2 membrane has the lowest absorption peak intensity, indicating that the diffusion of piperazine (PIP) aqueous monomers is restricted during the interfacial polymerization reaction, which is consistent with the trend of polyamide (PA) layer thickness variation. Figure 9b The diffusion kinetics curves further demonstrate that the TFC-O-H2 membrane reaction interface has the lowest amount of piperazine (PIP) aqueous monomer and the slowest diffusion rate. The unique through-hole structure of the hollow fiber achieves precise control of "adsorption-storage-slow release" through capillary action and structural resistance.

[0125] The wettability and charge properties of composite nanofiltration membrane surfaces are key factors affecting their permeation selectivity and antifouling ability. Figure 10 shows the hydrophilicity and hydrophobicity properties of different composite nanofiltration membranes evaluated by static water contact angle testing, and the Zeta potential values ​​of the membrane surface under different pH conditions were measured using a Zeta potentiometer. Figure 10a In the static water contact angle (WCA) test, the TFC-O-H2 membrane surface contact angle was 35.7°, the lowest among the different composite nanofiltration membranes in this application embodiment, demonstrating its superior surface hydrophilicity. This improvement is due to the hollow nanofiber cavity structure storing a large amount of piperazine (PIP) aqueous monomers. During the interfacial reaction, the diffusion inhibition of piperazine (PIP) aqueous monomers results in a relatively large amount of aqueous solution remaining after the interfacial polymerization reaction, forming more polar groups such as carboxyl and amino groups on the membrane surface, thereby improving hydrophilicity. Subsequently, the Zeta potential of different composite nanofiltration membranes was tested, such as... Figure 10b The results showed that the surfaces of different composite nanofiltration membranes exhibited negative electronegativity within a pH range of 3 to 11. Among them, the TFC-O-H2 membrane exhibited the strongest electronegativity, reaching a Zeta potential of -45.2 mV under strongly alkaline conditions at pH 11. This can be explained by the fact that after the hollow nanofiber interlayer induced the formation of a wrinkled structure in the polyamide (PA) layer, the remaining aqueous monomers enriched the surface of the polyamide (PA) layer with carboxyl groups and fully exposed them, significantly increasing the negative charge sites on the surface of the composite nanofiltration membrane, thus exhibiting extremely strong electronegativity.

[0126] As shown in Figure 11, the chemical properties of different composite nanofiltration membranes were evaluated using methods such as ATR-FTIR and XPS. Figure 11aThe ATR-FTIR spectra of the samples show that the chemical composition of the polyamide (PA) layer remains unchanged despite the introduction of an oriented hollow nanofiber interlayer. Specifically, the FTIR spectra of the different composite nanofiltration membranes show distinct absorption bands at 1624 cm⁻¹ (amide I: C=O stretching vibration), 1575 cm⁻¹ (amide II: CN vibration / N–H stretching), 1485 cm⁻¹ (aromatic C–H planar bending), 1410 cm⁻¹ (aromatic C=C vibration), and 1245 cm⁻¹ (COC vibration), confirming the successful synthesis of the aromatic polyamide (PA) layer. Figure 11b XPS results for different composite nanofiltration membranes showed three characteristic peaks with binding energies of approximately 284.8 eV (C1s), 399.5 eV (N1s), and 532.0 eV (O1s). In Table 1, the TFC-O-H2 membrane achieved a higher degree of crosslinking. This enhancement is attributed to the cavity structure of the oriented hollow nanofiber interlayer restricting the diffusion of the stored piperazine (PIP) aqueous monomers, enabling the reaction with TMC to form a composite nanofiltration membrane with a highly crosslinked polyamide (PA) layer. This is highly advantageous for the smaller average pore size and narrow pore size distribution, facilitating precise ion separation.

[0127] Table 1. XPS elemental analysis and crosslinking degree of various composite nanofiltration membranes

[0128]

[0129] Figure 12 shows the retention rates of neutral organic solute PEG (Mw = 200, 400, 600, 800, 1000 Da) for different composite nanofiltration membranes, and the results were plotted using a nonlinear fitting model based on the log-normal distribution between the retention rate and the solute Stokes radius. As shown in Figure 12a, with increasing PEG molecular weight, the retention rates of PEG for different composite nanofiltration membranes gradually increase, consistent with the retention pattern of traditional nanofiltration membranes. The TFC membrane has a MWCO of 695 Da, while the TFC-OS, TFC-O-H1, TFC-O-H2, and TFC-O-H3 membranes, after introducing a nanofiber interlayer, show significantly reduced MWCOs to 600 Da, 547 Da, 483 Da, and 547 Da, respectively. This indicates that the introduction of the nanofiber interlayer significantly improves the retention capacity of neutral small molecule solutes. Furthermore, the membrane pore size probability density distribution curves were obtained using the retention rates. Figure 12bThe results showed that after modification with hollow nanofibers, the pore size of the membrane surface decreased and the distribution became more concentrated, indicating that the polyamide (PA) layer became denser after being regulated by the hollow nanofiber interlayer. This change is consistent with the trend of crosslinking degree in Table 1. This structural improvement is attributed to the continuous and slow release of piperazine (PIP) aqueous monomers during interfacial polymerization, which prolongs the controllable interfacial polymerization process, inhibits the disordered and non-uniform growth of the polyamide (PA) layer, and ultimately forms a polyamide layer with smaller pore size and more uniform distribution.

[0130] Figure 13 The separation performance of various composite nanofiltration membranes was tested and evaluated using permeability and rejection rate, respectively. Figure 13 As can be seen, the pure water permeation flux of the TFC membrane is approximately 10.3 L·m⁻²·h⁻¹·bar⁻¹. After introducing the nanofiber interlayer, the permeability of the TFC-OS, TFC-O-H1, TFC-O-H2, and TFC-O-H3 membranes all showed significant improvement. Among them, the flux of the TFC-OS membrane with the solid nanofiber interlayer increased to about 22.9 L·m⁻²·h⁻¹·bar⁻¹. The TFC-O-H1, TFC-O-H2, and TFC-O-H3 membranes with the oriented hollow nanofiber interlayer achieved further flux improvements. The TFC-O-H2 membrane achieved the highest permeation flux of approximately 24.9 L·m⁻²·h⁻¹·bar⁻¹, which is about 2.4 times the flux of the original TFC membrane, while maintaining a Na₂SO₄ rejection rate comparable to that of the TFC membrane. This demonstrates that by introducing an oriented hollow nanofiber interlayer, the "trade-off" effect of traditional nanofiltration membranes is effectively overcome, achieving a significant increase in water permeation flux while maintaining high retention performance. This substantial increase in water permeation flux stems from the dual structural optimization of the base membrane and the polyamide layer: First, the nanofiber interlayer, through its high porosity and interconnected fiber network structure, forms a "groove effect," providing water molecules with more and less-resistance transport channels, thus providing the structural basis for the increased water permeation flux. The TFC-O-H2 membrane further optimizes the permeation process due to its excellent hollow cavity structure. Furthermore, the oriented hollow nanofiber interlayer regulates the formation of a highly wrinkled and ultra-thin polyamide (PA) layer, significantly reducing the mass transfer resistance of the polyamide layer during permeation. Simultaneously, the continuous and defect-free polyamide (PA) layer ensures that the membrane's retention effect is not affected. It is noteworthy that the permeation flux of the TFC-O-H3 membrane shows a slight decrease, which may be due to the slightly thicker polyamide (PA) layer hindering water molecule transport to some extent. In summary, in the embodiments of this application, the hollow nanofiber intermediate layer structure of the TFC-O-H2 membrane achieves an optimal balance between the mass transfer resistance of the base membrane and the permeation resistance of the polyamide (PA) layer, laying a solid foundation for subsequent high-performance separation.

[0131] To systematically evaluate the separation performance and practical application performance of composite nanofiltration membranes, this application selected four typical inorganic salts in the water treatment field—Na₂SO₄, MgSO₄, MgCl₂, and NaCl—as separation targets. Under operating pressure of 5 bar and feed concentration of 1000 ppm, the water permeation flux and salt rejection performance of different composite nanofiltration membranes were tested, and the results are shown in Figure 14. Figure 14a In the water permeation flux test, the flux of different composite nanofiltration membranes with nanofiber intermediate layers was significantly increased in all salt solutions. The flux for different salts showed the following trend: NaCl > MgCl2 > MgSO4 > Na2SO4. This is because high-retention salts generate stronger concentration polarization and osmotic backpressure effects. That is, the higher the salt rejection rate, the greater the concentration difference between the membrane surface and the feed solution, the more severe the concentration polarization, and the higher the local osmotic pressure on the membrane surface. This offsets some of the effective operating driving force, ultimately leading to a decrease in water permeation flux. As shown in Figure 14b, the salt rejection test results show that all nanofiltration membranes exhibited a consistent rejection rate for the four inorganic salts in the order Na2SO4 > MgSO4 > MgCl2 > NaCl, which is opposite to the permeability trend. The rejection rates of Na2SO4 and MgSO4 remained stable above 95%, while the rejection rate of NaCl was below 30%, achieving efficient separation of monovalent and divalent salts.

[0132] To comprehensively evaluate the application value of modified nanofiltration membranes, Figure 15Typical organic pollutants widely detected in water bodies were selected as targets for removal: paraben preservatives, including methylparaben (MP), propylparaben (PP), and benzylparaben (BP), as well as antibiotic pollutants sulfamethoxazole (SMX) and trimethoprim (TMP). The removal capabilities of different composite nanofiltration membranes for small molecule organic pollutants were tested. Overall, the TFC-OS, TFC-O-H1, TFC-O-H2, and TFC-O-H3 membranes showed significantly higher retention rates than the TFC membrane. Among them, the TFC-O-H2 membrane exhibited the best removal effect, achieving a retention rate of over 85% for benzylparaben (BP), sulfamethoxazole (SMX), and trimethoprim (TMP) with molecular weights greater than 200 Da, demonstrating excellent removal capabilities for small molecule organic pollutants. From the perspective of pollutant rejection patterns, the rejection rate of paraben homologues generally increases with increasing molecular weight, specifically methylparaben (MP) at 152 Da, propylparaben (PP) at 180 Da, and benzylparaben (BP) at 228 Da. The TFC membrane exhibits extremely limited removal capacity for low molecular weight parabens (MP and PP), with rejection rates of only 19.88% and 24.39%, respectively. In contrast, the TFC-O-H2 membrane significantly improves the rejection rates of MP and PP to 35.36% and 37.76%, respectively, and the rejection rate of BP further increases from 85.31% to 94.32%, fully demonstrating the significant enhancement of the sieving capacity of composite nanofiltration membranes with oriented hollow nanofiber interlayers for small molecule organic matter. For antibiotic pollutants, TFC-OS, TFC-O-H1, TFC-O-H2, and TFC-O-H3 membranes also exhibited excellent removal effects. Sulfamethoxazole (SMX) and trimethoprim (TMP) have molecular weights of 253 Da and 290 Da, respectively. The TFC membranes showed retention rates of only 61.35% and 63.39% for these two compounds, while the TFC-O-H2 membrane increased the retention rates to 89.35% and 89.32%, respectively, achieving highly efficient removal of antibiotic-related micropollutants from water. These results demonstrate that composite nanofiltration membranes can significantly enhance the removal capacity of trace organic pollutants in water, showing good application potential in advanced drinking water treatment and wastewater treatment.

[0133] As shown in Figure 16a, within the pressure range of 1 bar to 6 bar, the water permeation flux of the TFC-O-H2 membrane exhibits a linear relationship with the operating pressure, indicating its strong resistance to compaction. Figure 16b shows the synchronous variation trend of water permeability and Na2SO4 rejection rate of the TFC-O-H2 membrane under different Na2SO4 concentration gradients. As shown, with the increase of feed concentration, the Na2SO4 rejection rate also increases. This is because the increase in ion concentration enhances the concentration polarization on the surface of the TFC-O-H2 membrane, thereby increasing the Na2SO4 rejection rate. However, due to the increase in osmotic pressure caused by the increase in feed concentration, the related water permeability decreases significantly. Figure 16c The long-term operational stability of the TFC-O-H2 membrane at 5 bar pressure was demonstrated. During the entire 50-hour operation, the Na2SO4 rejection rate and water permeability remained stable. These results indicate that the incorporation of a hollow nanofiber interlayer can meet the pressure resistance and long-term stability requirements of the TFC-O-H2 membrane.

[0134] Figure 17 shows a comparison of the antifouling performance of TFC membrane and TFC-O-H2 membrane in the organic pollution cycle. Figures 17a-17cUsing bovine serum albumin (BSA), salicylic acid (SA), and hyaluronic acid (HA) solutions as model contaminants, the normalized flux decay curves of two membranes during a 3-hour continuous filtration process were recorded. The results showed that the flux of both membranes exhibited a pattern of "rapid initial decrease followed by a gradual slowdown." This is because in the initial stage of fouling, contaminants are rapidly adsorbed or deposited on the membrane surface, clogging some membrane pores and forming an initial fouling layer, leading to a sharp decrease in flux. As filtration continues, a stable and compressible filter cake layer gradually forms on the membrane surface, slowing the flux decay rate and tending towards equilibrium. Notably, throughout the entire fouling stage and after subsequent physical cleaning, the normalized flux of the TFC-O-H2 membrane was consistently significantly higher than that of the TFC membrane, indicating its superior anti-fouling and fouling recovery capabilities. The superior antifouling performance of TFC-O-H2 membranes is due to two main factors. First, the water contact angle on the membrane surface is as low as 35.7°, significantly better than that of TFC membranes. This highly hydrophilic surface facilitates the formation of a dense hydration layer at the membrane-water interface. This hydration layer effectively prevents the adsorption of hydrophobic or amphiphilic organic pollutants such as bovine serum albumin (BSA), hyaluronic acid (HA), and salicylic acid (SA) onto the membrane surface. Second, TFC-O-H2 membranes have a stronger negative surface charge, with a Zeta potential of −45.2±0.3mV. During filtration, they exhibit a stronger electrostatic repulsion effect on similarly negatively charged organic pollutants, especially under neutral or alkaline conditions, thus delaying the accumulation of pollutants on the membrane surface. These synergistic effects are further confirmed by the fouling index: the total fouling rate (Rt) and irreversible fouling rate (Rir) of TFC-O-H2 membranes are reduced, while the flux recovery rate (FRR) is increased. In summary, the introduction of the hollow nanofiber interlayer not only improves the separation performance of the membrane, but also endows the TFC-O-H2 membrane with excellent resistance to organic fouling by enhancing hydrophilicity, negative charge and optimizing surface morphology, laying the foundation for its long-term stable operation in the treatment of actual complex water bodies.

[0135] The composite nanofiltration membrane of this application is prepared by coaxial electrospinning a hollow nanofiber interlayer membrane on a macroporous base membrane. The loading of the hollow nanofiber interlayer alters a series of physicochemical properties of the macroporous base membrane surface, such as hydrophilicity and roughness, and the new morphology of the hollow nanofiber interlayer affects the morphology and performance of the polyamide (PA) layer. Simultaneously, the hydrophilic macroporous base membrane forms a novel substrate morphology. The moderate hydrophilicity, mild reaction interface, and controllable monomer diffusion provide a stable interfacial reaction for the interfacial polymerization reaction, resulting in higher crosslinking degree and excellent separation performance. The composite nanofiltration membrane provided in this application, at a preferred concentration, produces a TFC-O-H2 membrane with optimal separation performance: a water flux of 24.91 L·m⁻²·h⁻¹·bar⁻¹, a salt rejection rate of 96.81%, and a Cl⁻ / SO₄²⁻ selectivity of 101.4.

[0136] Furthermore, the composite nanofiltration membrane provided in this application exhibits high removal rates for emerging pollutants. It achieves a 94.32% rejection rate for neutral pollutant BP and an 89.35% removal rate for negatively charged antibiotic pollutant SMX. It demonstrates excellent stability in anti-fouling experiments, with flux recovery rates (FRR) for BSA, SA, and HA increased to 84.6% for BSA, 81.7% for SA, and 93.3% for HA.

[0137] In summary, the composite nanofiltration membrane provided in this application improves the removal rates of emerging pollutants in water treatment, such as small-molecule neutral hydrophobic pollutants methylparaben (MP), propylparaben (PP), and benzylparaben (BP), and exhibits high removal rates for charged pollutants sulfamethoxazole (SMX) and trimethoprim (TMP). The nanofiltration membrane provided in this application demonstrates excellent stability in antifouling experiments, showing improved flux recovery rates for bovine serum albumin (BSA) solution, hyaluronic acid (HA), and salicylic acid (SA), and exhibits strong chemical stability and durability. Therefore, the composite nanofiltration membrane provided in this application not only has high permeability but also demonstrates excellent removal efficiency of emerging pollutants, antifouling performance, stability, and durability.

[0138] In fact, the embodiments of this application only preferred the materials and preparation methods for the composite nanofiltration membrane. In actual use, a hydrophilic macroporous base membrane support layer is used, on which an oriented hollow nanofiber intermediate layer is formed. After interfacial polymerization reaction, an ultrathin, highly cross-linked filter skin with a regular pleated structure is formed, which effectively shortens the transport path of water molecules, reduces the permeation resistance, and thus significantly improves the water permeation flux.

[0139] The above provides a detailed description of a composite nanofiltration membrane, its preparation method, and its application. For those skilled in the art, appropriate adjustments can be made to the specific implementation methods and application scope without departing from the technical concept of this application; therefore, the content of this specification should not be construed as a limitation on the scope of protection of this application.

Claims

1. A composite nanofiltration membrane, characterized in that, The membrane comprises a macroporous base membrane support layer, an oriented hollow nanofiber intermediate layer, and a filter skin layer. The macroporous base membrane support layer is composed of a hydrophilic organic material. The oriented hollow nanofiber intermediate layer is loaded on the macroporous base membrane support layer and includes oriented hollow polymer nanofibers with internal hollow cavities. The filter skin layer is formed on the surface of the oriented hollow nanofiber intermediate layer and / or the surface of the macroporous base membrane support layer. The surface of the filter skin layer has a wrinkled structure along the orientation of the hollow polymer nanofibers in the oriented hollow nanofiber intermediate layer.

2. The composite nanofiltration membrane as described in claim 1, characterized in that, The intermediate layer of the oriented hollow nanofiber is an oriented hollow polyvinylidene fluoride (PVDF) nanofiber intermediate layer.

3. The composite nanofiltration membrane as described in claim 2, characterized in that, The macroporous base membrane support layer is a polyethersulfone (PES) base membrane, and the filter layer is a polyamide (PA) layer.

4. The composite nanofiltration membrane as described in claim 3, characterized in that, The thickness of the polyamide layer is 50 nm to 82 nm.

5. A method for preparing a composite nanofiltration membrane, characterized in that, Includes the following steps: S1. Obtain a hydrophilic macroporous base membrane support layer; S2. An oriented hollow nanofiber intermediate layer is prepared by coaxial electrospinning and loaded onto the macroporous base film support layer to form a composite substrate; S3. Perform an interfacial polymerization reaction on the composite substrate to prepare a filter layer.

6. The method for preparing the composite nanofiltration membrane as described in claim 5, characterized in that, The macroporous base membrane support layer obtained in step S1 is a polyethersulfone (PES) base membrane layer. The oriented hollow nanofiber intermediate layer prepared by coaxial electrospinning in step S2 is an oriented hollow polyvinylidene fluoride (PVDF) nanofiber intermediate layer. The composite substrate is formed by loading the oriented hollow polyvinylidene fluoride (PVDF) nanofiber intermediate layer onto the polyethersulfone (PES) base membrane layer. The filter skin layer prepared in step S3 is a polyamide (PA) layer.

7. The method for preparing the composite nanofiltration membrane as described in claim 6, characterized in that, Step S2 includes: S21. Prepare electrospinning solutions, including preparing polyvinylidene fluoride (PVDF) electrospinning shell solution and polyvinylpyrrolidone (PVP) electrospinning core solution. S22. Electrospinning the electrospinning shell solution and the electrospinning core solution simultaneously using coaxial electrospinning to obtain the oriented hollow polyvinylidene fluoride (PVDF) nanofiber intermediate layer.

8. The method for preparing the composite nanofiltration membrane as described in claim 7, characterized in that, In step S21, the electrospinning solution is prepared by the following steps: polyvinylidene fluoride (PVDF) is dissolved in a mixed solvent of N,N-dimethylformamide (DMF) and acetone to prepare an electrospinning shell solution; polyvinylpyrrolidone (PVP) powder is completely dissolved in a mixed solvent of N,N-dimethylformamide (DMF) and N,N-dimethylacetamide (DMAc) to prepare an electrospinning core solution.

9. The method for preparing the composite nanofiltration membrane as described in claim 8, characterized in that, The preparation method of the electrospinning shell solution in step S21 includes: dissolving polyvinylidene fluoride (PVDF) in a mixed solvent of N,N-dimethylformamide (DMF) and acetone in a volume ratio of 3:1, completely dissolving it under constant temperature conditions to prepare an electrospinning shell solution with a polyvinylidene fluoride (PVDF) concentration of 15% (w / v), and letting it stand at 15°C to 25°C for more than 24 hours.

10. The method for preparing the composite nanofiltration membrane as described in claim 8, characterized in that, The preparation method of the electrospinning core layer solution in step S21 includes: dissolving polyvinylpyrrolidone (PVP) in a mixed solvent of N,N-dimethylformamide (DMF) and N,N-dimethylacetamide (DMAc) in a volume ratio of 1:1, completely dissolving it under constant temperature conditions to prepare an electrospinning core layer solution with a polyvinylpyrrolidone (PVP) mass percentage of 30%, and letting it stand for more than 24 hours.

11. The method for preparing the composite nanofiltration membrane according to any one of claims 8 to 10, characterized in that, The coaxial electrospinning method is completed by a coaxial electrospinning device. Under the condition of collector rotation, the electrospinning time is set to 5 minutes to 20 minutes, and the electrospinning shell solution and the electrospinning core solution are electrospinned simultaneously.

12. The method for preparing the composite nanofiltration membrane as described in claim 11, characterized in that, The conditions for electrospinning are as follows: an 18 kV voltage is applied, the relative humidity of the environment is maintained at 40% RH to 50% RH, the collector rotation speed is set to 700 rpm, the propulsion speed of the electrospinning shell solution is 2.0 mL / h, the propulsion speed of the electrospinning core solution is 1.5 mL / h, and the electrospinning time is set to 10 minutes.

13. The method for preparing the composite nanofiltration membrane as described in claim 6, characterized in that, Step S3 includes: S31. The composite substrate is immersed in an aqueous solution containing a polyamine compound, and after a first specified time, excess aqueous solution is removed from the side of the composite substrate to which the filter layer is to be formed, to obtain a pretreated membrane. S32. To uniformly disperse the aqueous solution on the surface of the pretreated membrane; S33. Pour an organic phase solution containing polyacrylamide compounds onto the pretreated membrane and carry out an interfacial polymerization reaction. After a second specified time, remove the excess organic phase solution to obtain a composite nanofiltration membrane with a polyamide (PA) layer.

14. The method for preparing the composite nanofiltration membrane as described in claim 13, characterized in that, Step S3 further includes the steps of preparing an aqueous phase solution and an organic phase solution, wherein the aqueous phase solution containing the polyamine compound is a piperazine (PIP) aqueous phase solution, and the organic phase solution containing the polyacrylamide compound is a 1,3,5-benzenetricarboxyl chloride (TMC) organic phase solution.

15. The method for preparing the composite nanofiltration membrane as described in claim 14, characterized in that, The first specified time is 3 to 7 minutes, and the second specified time is 1 to 6 minutes.

16. The use of the composite nanofiltration membrane according to any one of claims 1 to 4 in filtering emerging pollutants, characterized in that, The emerging contaminants include at least one contaminant selected from methylparaben (MP), propylparaben (PP), benzylparaben (BP), sulfamethoxazole (SMX), and trimethoprim (TMP).

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