Nanofiber membranes for removing short-chain pfas in water, and methods of use and regeneration thereof

Abstract

The application discloses a nanofiber membrane for removing short-chain PFASs in water, characterized in that the nanofiber membrane is a flexible membrane-shaped material formed by cross-linking and reinforcing of specially-made nanoscale flexible fibers arranged in a disorderly interlaced manner by glutaraldehyde, the specially-made nanoscale flexible fibers are flexible fibers of a multi-component system formed by mixed combination of a main component of flexible thermoplastic polyurethane (TPU) and polyethylene imine (PEI), and the flexible fibers have a microstructure of a nanophase separation surface of the two main components on the surface of the flexible fibers. The application further discloses an application method and a regeneration method of the nanofiber membrane. The application can more efficiently adsorb and remove short-chain PFASs in water, and has the advantages of simple preparation, low development cost and being conducive to regeneration and utilization.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of water treatment, and particularly relates to a nanofiber membrane for removing short-chain PFASs in water and an application and regeneration method thereof. BACKGROUND

[0002] Per- and polyfluoroalkyl substances (PFASs) are a class of organic compounds artificially synthesized containing highly fluorinated hydrophobic carbon chains (C n F 2n+1- ) and are almost ubiquitous in the environment due to their unique physicochemical properties. However, studies have found that PFASs have environmental persistence and potential toxicity, and in recent years, PFASs have been regarded as a new class of emerging pollutants and have attracted public attention. At present, the research on PFASs mainly focuses on long-chain PFASs, among which perfluorooctanoic acid (PFOA) and perfluorooctanesulfonic acid (PFOS) are the most studied compounds among emerging persistent organic pollutants. PFOS and PFOA have been strictly limited or banned in many countries. In order to reduce the environmental hazards related to long-chain PFASs or evade regulation, manufacturers have begun to mass-produce and use short-chain PFASs as substitutes, which has led to a sharp increase in the number of short-chain PFASs in the environment. Compared with traditional long-chain PFASs, these short-chain PFASs as substitutes may have relatively low bioaccumulation and toxicity, but they still exhibit strong environmental persistence and have stronger long-distance transport capacity, and have gradually become the main component of PFASs in the water environment.

[0003] Traditional biochemical treatment methods face great challenges in removing PFASs from water. Compared with processes such as photolysis, ozone decomposition, and electrochemical oxidation, which have harsh reaction conditions and high energy consumption, adsorption has the advantages of simple operation, high cost-effectiveness, and high treatment effect. Therefore, adsorption has broad application prospects in the field of PFASs water pollution remediation. Traditional adsorbent materials, such as activated carbon materials, have poor removal efficiency for perfluorooctanoic acid in water and cannot be regenerated. Currently, the methods for removing perfluorinated compounds from water are mainly divided into two categories: patents CN102489260B, CN102500338B, CN105776404A, and CN103408103A involve traditional adsorbent materials, which use cotton, cellulose, nylon, and reverse osmosis membrane materials to remove perfluorinated compounds from water, respectively, and have certain popularization potential. However, due to low removal efficiency or high cost, industrial application is limited. Patents CN104193056B, CN108264127A, and CN105001371B use methods such as light radiation, photocatalysis, molecular imprinting, and induced electrochemistry to degrade trace amounts of perfluorinated compounds in water, but due to harsh conditions, difficult operation, high energy consumption, and other reasons, actual application cannot be widely promoted. The recent patent CN114920907B covalent organic framework material amino-functionalized porous aromatic framework compound has high efficiency and selectivity in adsorbing PFASs, but the material preparation process is relatively complicated, and the cost of raw materials is high. In addition, most of the current patents have limited attention to short-chain perfluorinated and polyfluorinated compounds.

[0004] Therefore, there is a need to develop a material that can efficiently adsorb and remove short-chain PFASs from water, and reduce the difficulty of the preparation process and the production cost. SUMMARY

[0005] To overcome the shortcomings of the prior art, the technical problem to be solved by the present application is how to provide a nanofiber membrane that can more efficiently adsorb and remove short-chain PFASs from water, and reduce the difficulty of the preparation process, so that it has the characteristics of simple preparation, low development cost, and is conducive to recycling.

[0006] To solve the above technical problems, the technical scheme adopted by the present application is as follows:

[0007] A nanofiber membrane for removing short-chain PFASs from water, characterized in that the nanofiber membrane is a flexible membrane-shaped material formed by cross-linking and reinforcing special nanoscale flexible fibers arranged in a disorderly and interlaced manner with glutaraldehyde, the special nanoscale flexible fibers are flexible fibers formed by mixing and combining flexible thermoplastic polyurethane (TPU) and polyethyleneimine (PEI) into a multi-component system, and the flexible fibers have a microstructure of a nanophase separation surface of the two main components on the surface of the flexible fibers.

[0008] Wherein, the nano-phase separation refers to the nano-level phase separation structure, and the phase separation refers to the rearrangement of binary or multi-component mixture, and each component forms a phase (crystal phase) in a certain spatial area (under microscopic vision). In this way, in the fiber membrane product, due to the microcrystalline groups of flexible thermoplastic polyurethane (TPU) and polyethylene imine (PEI) on the fiber surface, the hydrophobic effect of polyurethane (TPU) and the electrostatic effect of a large number of protonated amino groups on polyethylene imine are integrated, and the two synergistically adsorb perfluoro and polyfluorinated compounds (PFASs), which can achieve the effect of efficiently removing perfluoroalkyl compounds in water.

[0009] Further, the content ratio of the flexible thermoplastic polyurethane (TPU) and the polyethylene imine (PEI) is in the range of (1-4):1.

[0010] This is because when TPU:PEI is greater than 4:1, i.e. the proportion of PEI is less than 25%, the nano-phase separation on the surface of the flexible fiber is not obvious, which seriously affects the adsorption of PFASs on the material. When TPU:PEI is less than 1:1, i.e. the proportion of PEI is greater than 50%, the nanofiber formed by electrospinning is not uniform and is easy to stick together, and the adsorption of PFASs does not increase with the increase of the content of PEI. Therefore, considering the adsorption efficiency and cost, the optimal ratio of TPU and PEI is (1-4):1.

[0011] Further, the nanofiber membrane is prepared by the following steps:

[0012] S1 thermoplastic polyurethane (TPU) and polyethylene imine (PEI) are added to a mixed solvent of acetone and N,N-dimethylformamide (DMF) in a certain proportion, the obtained solution is stirred uniformly, and after being fully dissolved, a spinning solution containing thermoplastic polyurethane / polyethylene imine is prepared;

[0013] S2 the prepared spinning solution is loaded into a syringe, and electrospinning technology is used for spinning to obtain flexible nanofiber;

[0014] S3 the obtained flexible fiber is collected and immersed in a glutaraldehyde solution for crosslinking to obtain a preliminary product membrane;

[0015] S4 the preliminary product membrane is repeatedly washed with deionized water and soaked overnight to remove unreacted substances on the surface; after drying, a finished product membrane is obtained.

[0016] The nanofiber material prepared in the scheme has the characteristics of high specific surface area, strong renewability, easy functional modification, etc., and shows great potential in the field of water pollutant adsorption. Among them, the electrospinning technology for preparing nanofiber material has the advantages of simple operation, easy control of pore size, good stability, etc., and is a prior art, and the process will not be described here. However, the electrospun nanofiber prepared from a single polymer usually has limited pollutant removal capacity. Thermoplastic polyurethane (TPU) is composed of hard segments and soft segments, in which the hard segment is a group such as urethane with strong polarity and rigidity, there is a strong hydrogen bond between molecules, and it can produce intermolecular hydrogen bond with other polar groups such as amino, carboxyl, etc. Polyethyleneimine (PEI) is a water-soluble polymer, which contains a large number of primary and secondary amine sites on the molecular chain. These amine sites are easily protonated to obtain positive charges in a wide pH range, which is beneficial to the electrostatic adsorption of anionic PFASs in water. Therefore, the characteristics of the present scheme are to mix the above two polymers in a certain proportion, dissolve them in a suitable solvent, and prepare a nanophase separation high specific surface area nanofiber material by controlling the environmental conditions. In this way, a high specific surface area material with both hydrophobic effect and electrostatic effect with polar groups is obtained, and through the synergistic effect of hydrophobicity and electrostaticity, the purpose of removing short-chain anionic PFASs is achieved. At the same time, the above preparation process itself has the advantages of simple operation, convenient preparation, stable and reliable effect, etc.

[0017] Further, in step S1, the mixed solution is subjected to magnetic stirring at room temperature, and after being fully dissolved, ultrasonic treatment is used to remove bubbles.

[0018] In this way, the stirring efficiency can be better improved, and the elimination of bubbles can better ensure the quality and effect of subsequent spinning.

[0019] Further, in step S1, the thermoplastic polyurethane has a molecular weight of 120-150 thousand, and the polyethyleneimine has a molecular weight of 50% aqueous solution of 5.0-7.5 thousand.

[0020] In this way, the two kinds of molecules can be uniformly mixed to form a high molecular solution of interpenetrating network, achieving a better nanospinning effect.

[0021] Further, in step S1, the mass ratio of thermoplastic polyurethane to polyethyleneimine is 1:1-4:1, and the mass ratio of acetone to N,N-dimethylformamide is 1:1-4:1.

[0022] In this way, the thermoplastic polyurethane and the polyethyleneimine are fully dissolved, and the high molecules are interlaced with each other. Due to the different evaporation speeds of the two solvents in the electrospinning process, the thermoplastic polyurethane and the polyethyleneimine produce nanoscale phase separation, and the formed nanofiber membrane has a unique nanophase separation structure, which has good adsorption effect on PFASs.

[0023] Further, in step S2, the mass percentage of the spinning solution of the thermoplastic polyurethane and the polyethylene imine is 15%-25%, the spinning voltage is 15-20 kV, and the flow rate is 0.5-1.0 mL / h.

[0024] In this way, uniform nanofibers can be spun, and the average diameter of the nanofibers is about 200 nm.

[0025] Further, in step S3, the obtained flexible fiber is added to a 1%-5% glutaraldehyde solution for cross-linking and fixing, and the cross-linking time is 1-2 hours.

[0026] In this way, the polyethylene imine is further cross-linked to form a stable flexible fiber membrane material, avoiding the loss of polyethylene imine during the adsorption process.

[0027] Further, in step S4, the membrane is placed in a vacuum drying oven and dried at 25°C for 24 h to obtain a finished membrane.

[0028] In this way, the membrane surface is better protected from damage during drying.

[0029] The application also discloses a method for using the nanofiber membrane as an adsorption material to remove PFASs pollutants in water, characterized in that the nanofiber membrane is fixed on a stirring rod, the stirring rod is placed in a solution to be adsorbed, and stirring is performed to adsorb, and the stirring rod is removed after adsorption is completed.

[0030] In this way, the method is convenient to operate and has excellent adsorption effect. In the application process, the four common PFASs are perfluorooctanoic acid (PFOA), perfluoropropionic acid (PFHxA), perfluoro-2-methyl-3-oxa hexanoic acid (GenX), and perfluorobutyric acid (PFBA), among which PFHxA, GenX, and PFBA are considered short-chain perfluorinated compounds.

[0031] Further, the pH value of the solution to be adsorbed is adjusted to be between 4 and 7. The optimal pH value for PFOA, PFHxA, and GenX is 4, and the optimal pH value for PFBA is 6. After the adjustment, the adsorption effect can be better improved. Due to hydrophobic and electrostatic interactions, the adsorption capacity of PFOA, PFHxA, and GenX is 0.75, 0.68, and 0.65 mmol / g, respectively, at a pH of 4, and the adsorption capacity of PFBA is 0.38 mmol / g at a pH of 6.

[0032] The present invention also discloses a method for regenerating the nanofiber membrane, characterized in that the nanofiber membrane after adsorption is used is added to a mixed regeneration solution of sodium chloride and methanol, stirred for 5-15 minutes (preferably 10 minutes), taken out, immersed again in pure water, stirred for 5-15 minutes (preferably 10 minutes), taken out and air-dried naturally.

[0033] In this way, based on the ion exchange effect of sodium chloride and the dissolution and partitioning effect of methanol, the PFAS adsorbed on the surface of the nanofiber membrane can be rapidly desorbed.

[0034] Furthermore, 1% sodium chloride by mass is added to a 70% methanol solution to form a mixed regeneration solution of sodium chloride and methanol.

[0035] In the mixed regeneration solution with the above-mentioned proportions, adsorption and desorption cycles were performed. After five cycles, the adsorption capacity of the TPU / PEI nanofiber membrane for the four PFAS compounds remained almost identical to that of the initial membrane. TPU / PEI nanofibers exhibit good renewability and a simple separation process, demonstrating potential for green and efficient application in the remediation of PFAS pollution in water bodies.

[0036] Therefore, compared with existing inventions, the beneficial technical effects of the present invention are as follows:

[0037] 1. The raw materials selected for the synthesis of the TPU / PEI nanofiber membrane prepared by this invention are common polymers and organic reagents, which are low in cost and environmentally friendly. 2. The preparation process of the TPU / PEI nanofiber membrane prepared by this invention is controllable and simple to operate. 3. The TPU / PEI nanofiber membrane prepared by this invention has good adsorption performance for both long-chain and short-chain perfluorinated and polyfluorinated compounds. 4. The nanofiber membrane prepared by this invention has strong anti-interference ability; even under the influence of high concentrations of humic acid (up to 10 mg / L) and sodium chloride (up to 5 mg / L), the adsorption rate can still reach 65-85% of the initial value. 5. The regeneration process of the TPU / PEI nanofiber membrane prepared by this invention is simple, with good regeneration performance and fast regeneration speed; the adsorption capacity remains basically unchanged after five cycles of adsorption and desorption treatment.

[0038] In summary, this invention can efficiently adsorb and remove short-chain PFASs from water, and has the advantages of simple preparation, low development cost, and easy regeneration. Attached Figure Description

[0039] Figure 1 This is a schematic diagram of the preparation process of the nanofiber membrane (i.e., TPU / PEI nanofiber membrane) of the present invention.

[0040] Figure 2 for Figure 1 A schematic diagram of the molecular structure of the functional components on the surface of the nanofiber membrane prepared in this process.

[0041] Figure 3 Figure 1 is a scanning electron microscope image of the nanofiber membrane prepared in Example 1. Figure 1 Figure 2 is a scanning electron microscope image of the nanofiber membrane prepared in Example 2.

[0042] Figure 4 Figure 3 is an infrared spectrum of the thermoplastic TPU and TPU / PEI nanofiber membrane. Figure 4 is a high-resolution C 1s spectrum of the TPU / PEI nanofiber membrane.

[0043] Figure 5 is a high-resolution N 1s spectrum of the TPU / PEI nanofiber membrane. Figure 5 Figure 6 is an XPS spectrum of the TPU / PEI nanofiber membrane before and after adsorbing PFOA. Figure 5 Figure 7 is a high-resolution C 1s spectrum of the TPU / PEI nanofiber membrane before and after adsorbing PFOA. Figure 5 Figure 8 is a high-resolution N 1s spectrum of the TPU / PEI nanofiber membrane before and after adsorbing PFOA. Figure 9 is an adsorption kinetics plot of the TPU / PEI nanofiber membrane adsorbing four PFASs.

[0044] Figure 10 is an adsorption isotherm plot of the TPU / PEI nanofiber membrane adsorbing four PFASs. Figure 6 Figure 11 is a plot of the effect of humic acid (HA) on the adsorption of four PFASs by the TPU / PEI nanofiber membrane. Figure 6 Figure 12 is a plot of the regeneration and reusability of the TPU / PEI nanofiber membrane. Figure 13 is a plot of the regeneration and reusability of the TPU / PEI nanofiber membrane.

[0045] Figure 14 is a plot of the regeneration and reusability of the TPU / PEI nanofiber membrane. Figure 7 Figure 15 is a plot of the regeneration and reusability of the TPU / PEI nanofiber membrane. Figure 16 is a plot of the regeneration and reusability of the TPU / PEI nanofiber membrane.

[0046] Figure 17 is a plot of the regeneration and reusability of the TPU / PEI nanofiber membrane. Figure 8 Figure 18 is a plot of the regeneration and reusability of the TPU / PEI nanofiber membrane. DETAILED DESCRIPTION DETAILED DESCRIPTION

[0047] The application will be further described in detail below with reference to specific examples. DETAILED DESCRIPTION DETAILED DESCRIPTION A nanofiber membrane for removing short-chain PFASs from water, characterized in that the nanofiber membrane is a flexible membrane-shaped material formed by cross-linking and reinforcing special nanoscale flexible fibers arranged in a disorderly and interlaced manner with glutaraldehyde, and the special nanoscale flexible fibers are flexible fibers formed by a multi-component system in which the main components are a mixture of flexible thermoplastic polyurethane (TPU) and polyethyleneimine (PEI), and the flexible fibers have a microstructure of a nanophase separation surface of the two main components on the surface of the flexible fibers.

[0049] DETAILED DESCRIPTION DETAILED DESCRIPTION

[0050] The nano-phase separation refers to a nano-level phase separation structure, and the phase separation refers to a structure in which a binary or multi-component mixture is rearranged to form a phase (crystal phase) in a certain spatial region (under microscopic vision). In this way, in the fiber membrane product, due to the microcrystalline groups of the flexible thermoplastic polyurethane (TPU) and the polyethylene imine (PEI) on the fiber surface, the hydrophobic effect of the thermoplastic polyurethane (TPU) and the electrostatic effect of a large number of protonated amino groups on the polyethylene imine are integrated, and the two synergistically adsorb perfluoro and polyfluorinated compounds (PFASs), so that the effect of efficiently removing perfluoroalkyl compounds in water can be achieved.

[0051] The content ratio of the flexible thermoplastic polyurethane (TPU) and the polyethylene imine (PEI) is in the range of (1-4):1.

[0052] This is because when TPU:PEI is greater than 4:1, i.e., the PEI proportion is less than 25%, the nano-phase separation on the surface of the flexible fiber is not obvious, which seriously affects the adsorption of PFASs on the material. When TPU:PEI is less than 1:1, i.e., the PEI proportion is greater than 50%, the nanofiber formed by electrospinning is not uniform and is prone to adhesion, and the adsorption of PFASs does not increase with the increase of the PEI content. Therefore, considering the adsorption efficiency and cost, the optimal ratio of TPU and PEI is (1-4):1.

[0053] In this embodiment, the nanofiber membrane is prepared by the following steps:

[0054] S1 thermoplastic polyurethane (TPU) and polyethylene imine (PEI) are added to a mixed solvent of acetone and N,N-dimethylformamide (DMF) in a certain proportion, and the obtained solution is stirred uniformly and dissolved sufficiently to prepare a spinning solution containing thermoplastic polyurethane / polyethylene imine;

[0055] S2 the prepared spinning solution is loaded into a syringe, and electrospinning technology is used for spinning to obtain flexible nanofibers;

[0056] S3 the obtained flexible nanofibers are collected and immersed in a glutaraldehyde solution for crosslinking to obtain a preliminary product membrane;

[0057] S4 the preliminary product membrane is repeatedly washed with deionized water and soaked overnight to remove unreacted substances on the surface; after drying, a finished product membrane is obtained.

[0058] Nanofiber materials have high specific surface area, strong renewability, and easy functional modification, and show great potential in the field of water pollutant adsorption. Among them, electrospinning technology for preparing nanofiber materials has the advantages of simple operation, easy control of pore size, and good stability, and is a prior art, and the process will not be described here. However, the electrospun nanofiber prepared from a single polymer usually has limited pollutant removal capacity. Thermoplastic polyurethane is composed of hard segments and soft segments, wherein the hard segment is a urethane group with strong polarity and rigidity, and there is a strong hydrogen bond between molecules, and it can also produce intermolecular hydrogen bond with other polar groups such as amino and carboxyl groups. Polyethyleneimine (PEI) is a water-soluble polymer, and its molecular chain contains a large number of primary and secondary amine sites. These amine sites can be easily protonated to obtain positive charges in a wide pH range, which is beneficial to the electrostatic adsorption of anionic PFASs in water. Therefore, the feature of the present scheme is to mix the above two polymers in a certain proportion, dissolve them in a suitable solvent, and prepare a nanophase separation high specific surface area nanofiber material by controlling the environmental conditions. In this way, a high specific surface area material with both hydrophobic effect and electrostatic effect with polar groups is obtained, and through the synergistic effect of hydrophobicity and electrostaticity, the purpose of removing short-chain anionic PFASs is achieved. At the same time, the above preparation process itself has the advantages of simple operation, convenient preparation, stable and reliable effect, etc.

[0059] In step S1, the mixed solution is stirred by magnetic force at room temperature, and after being fully dissolved, ultrasonic treatment is used to remove bubbles.

[0060] In this way, the stirring efficiency can be better improved, and the elimination of bubbles can better ensure the quality and effect of subsequent spinning.

[0061] In step S1, the thermoplastic polyurethane has a molecular weight of 120-150 thousand, and the polyethyleneimine has a molecular weight of 50% aqueous solution of 5.0-7.5 thousand.

[0062] In this way, the two kinds of molecules can be uniformly mixed to form a high molecular solution of interpenetrating network, and a better nanospinning effect can be achieved.

[0063] In step S1, the mass ratio of thermoplastic polyurethane to polyethyleneimine is 1:1-4:1, and the mass ratio of acetone to N,N-dimethylformamide is 1:1-4:1.

[0064] In this way, the thermoplastic polyurethane and the polyethyleneimine are fully dissolved, and the high molecular weight is interlaced, and the nanofiber membrane formed has a unique nanophase separation structure, and has good adsorption effect on PFASs.

[0065] In step S2, the mass percentage of the thermoplastic polyurethane and the polyethylene imine spinning solution is 15%-25%, the spinning voltage is 15-20kV, and the flow rate is 0.5-1.0 mL / h.

[0066] In this way, uniform nanofibers can be spun, and the average diameter of the nanofibers is about 200 nm.

[0067] In step S3, the obtained flexible fiber is added to a 1%-5% glutaraldehyde solution for cross-linking and fixing, and the cross-linking time is 1-2 hours.

[0068] In this way, the polyethylene imine is further cross-linked to form a stable nanofiber membrane material, and the loss of the polyethylene imine during the adsorption process is avoided.

[0069] In step S4, the membrane is placed in a vacuum drying box and dried at 25℃ for 24 h to obtain a finished product.

[0070] In this way, the membrane surface is better protected from damage during drying.

[0071] The application further discloses an application method of the nanofiber membrane as an adsorption material for removing PFAS pollutants in water, and the method is characterized in that the nanofiber membrane is fixed on a stirring rod, the stirring rod is placed in a solution to be adsorbed, and stirring is performed to adsorb, and the stirring rod is removed after the adsorption is completed.

[0072] In this way, the application method has the characteristics of convenient operation and excellent adsorption effect. In the application process, the four common PFASs are perfluorooctanoic acid (PFOA), perfluoropropionic acid (PFHxA), perfluoro-2-methyl-3-oxa hexanoic acid (GenX), and perfluorobutyric acid (PFBA), wherein PFHxA, GenX, and PFBA can be regarded as short-chain perfluorinated compounds.

[0073] In the application method, the pH value of the solution to be adsorbed is adjusted to be between 4 and 7. The optimal pH value is 4 for PFOA, PFHxA, and GenX, and the optimal pH value is 6 for PFBA. In this way, the adsorption effect can be better improved. Due to hydrophobic and electrostatic interactions, the adsorption capacity of PFOA, PFHxA, and GenX is 0.75, 0.68, and 0.65 mmol / g respectively when the pH value is 4, and the adsorption capacity of PFBA is 0.38 mmol / g when the pH value is 6.

[0074] The application further discloses a regeneration method of the nanofiber membrane, and the method is characterized in that the nanofiber membrane after being used for adsorption is added to a mixed regeneration liquid of sodium chloride and methanol, stirred for 5-15 minutes (preferably 10 minutes), taken out, immersed in pure water again, stirred for 5-15 minutes (preferably 10 minutes), taken out, and naturally dried.

[0075] Thus, based on the ion exchange of sodium chloride and the solubility distribution of methanol, PFASs adsorbed on the surface of the nanofiber membrane can be quickly desorbed.

[0076] In the method, 1% sodium chloride by mass is added to a 70% methanol solution to form a mixed regeneration liquid of sodium chloride and methanol.

[0077] Figure 1 A schematic diagram of the preparation process of the nanofiber membrane of the present application. Figure 1 The left part of the middle picture shows a step of mixing and stirring a thermoplastic polyurethane (TPU) and a polyethylene imine (PEI) to prepare a spinning solution, the upper part of the middle picture shows a step of spinning by using a syringe and cross-linking, and the right part of the middle picture shows a microstructure of the prepared membrane product and a molecular structure formula of a surface functional component substance.

[0078] Figure 2 A schematic diagram of the preparation process of the nanofiber membrane of the present application. Figure 1 The right part of the middle picture shows a schematic diagram of the molecular structure formula in an enlarged view. As can be seen from the right part of the middle picture, Figure 2 It can be seen that the surface functional component substance of the membrane product of the present embodiment is a thermoplastic polyurethane and a polyethylene imine. The two high molecular chains of the thermoplastic polyurethane and the polyethylene imine are interlaced with each other, and the urethane bond on the thermoplastic polyurethane and the amino group on the polyethylene imine can form intermolecular hydrogen bonds. In addition, the amine group on the polyethylene imine and glutaraldehyde undergo a cross-linking reaction, which plays a role of cross-linking fixation.

[0079] Figure 3 A schematic diagram of the preparation process of the nanofiber membrane of the present application. Figure 1 A scanning electron microscope image of the nanofiber membrane prepared in the present embodiment. Figure 3 The upper right corner of the middle picture is a schematic diagram in an enlarged view. As can be seen from the upper right corner of the middle picture, Figure 3 It can be seen from the middle picture that the nanofiber membrane prepared in the present embodiment is microscopically formed by a number of layers of fibers in the same horizontal direction arranged in a disorderly interlaced manner, and the fibers and the fibers have interlaced and interconnected pore spaces, which can accommodate a large amount of adsorbate into the pores, and at the same time Figure 3 The upper right corner of the middle picture is a schematic diagram in an enlarged view. As can be seen from the upper right corner of the middle picture, Figure 2 It can be seen from the middle picture that the nanofiber membrane prepared in the present embodiment is microscopically formed by a number of layers of fibers in the same horizontal direction arranged in a disorderly interlaced manner, and the fibers and the fibers have interlaced and interconnected pore spaces, which can accommodate a large amount of adsorbate into the pores, and at the same time

[0080] Figure 4 The infrared spectra of the TPU raw material and the TPU / PEI nanofiber membrane. As can be seen from the figure, compared with the infrared spectrum of the TPU raw material, the TPU / PEI nanofiber membrane has a new absorption peak at 1648 cm -1 A new absorption peak is generated, which is a new group C=N generated by the cross-linking reaction of PEI and glutaraldehyde.

[0081] Figure 5 (a) XPS spectra of TPU / PEI nanofiber membrane before and after adsorbing PFOA. Figure 5 (b-c) High-resolution C1s spectra of TPU / PEI nanofiber membrane before and after adsorbing PFOA. Figure 5 (d-e) High-resolution N 1s spectra of TPU / PEI nanofiber membrane before and after adsorbing PFOA. Figure 5 As can be seen from (a), compared with the TPU / PEI nanofiber membrane before adsorption, a new binding band (F 1s) was generated after the TPU / PEI nanofiber membrane adsorbed PFOA. Figure 5 As can be seen from (b-c), compared with the TPU / PEI nanofiber membrane before adsorption, two new characteristic peaks appeared in the C1s spectrum after the TPU / PEI nanofiber adsorbed PFOA, which were located at 291.64 eV and 293.97 eV, corresponding to CF2 and CF3 functional groups. Figure 5 As can be seen from (d-e), compared with the TPU / PEI nanofiber membrane before adsorption, the proportion of amine / imine and protonated amino peaks changed significantly after the TPU / PEI nanofiber adsorbed PFOA, indicating that the amino group played an important role in the PFOA adsorption process.

[0082] Figure 6 (a) Adsorption kinetics of TPU / PEI nanofiber membrane for four PFASs (PFOA, PFHxA, GenX and PFBA); Figure 6 (b) Adsorption isotherm of TPU / PEI nanofiber for four PFASs (PFOA, PFHxA, GenX and PFBA). From Figure 6 As can be seen from (a), the adsorption rates of the four PFASs were close, with PFBA being the fastest; the adsorption kinetics of the four PFASs on the TPU / PEI nanofiber membrane was fitted with pseudo-first-order kinetics and pseudo-second-order kinetics, and the pseudo-second-order kinetics fitting was better, indicating that hydrophobic interaction and chemical adsorption played an important role. Figure 6 As can be seen from (b), the adsorption isotherm of the four PFASs on the TPU / PEI nanofiber membrane was fitted with Langmuir and Frendlich models, and PFOA, PFHxA and GenX were better fitted with Frendlich model, indicating that the adsorption type was multilayer adsorption. The maximum saturated adsorption capacity of PFOA, PFHxA, GenX and PFBA obtained by Langmuir model fitting was: 1.41, 1.10, 1.01, 0.96 mmol / g, indicating that TPU / PEI had high adsorption for both long-chain and short-chain PFASs.

[0083] Figure 7 Figure for the effect of humic acid (HA) on the adsorption of four PFASs by TPU / PEI nanofiber membranes. From the figure, it can be seen that the adsorption capacity of PFOA, PFHxA, GenX and PFBA all decreased with the addition of HA, but even when the concentration of humic acid was as high as 10 mg / L, their adsorption capacity could still reach 65%-85% of that without the addition of humic acid.

[0084] Figure 8 Figure for the regeneration and reusability of TPU / PEI nanofiber membranes. From the figure, it can be seen that after 5 cycles, the adsorption capacity of TPU / PEI nanofiber membranes for PFOA, PFHxA, GenX and PFBA is still close to that of the initial membrane, indicating that TPU / PEI nanofiber membranes have good regenerability and reusability.

Claims

1. A nanofiber membrane for removing short chain PFASs in water, characterized by, The nanofiber membrane is a flexible membrane material formed by cross-linking and reinforcing specially made nano-scale flexible fibers arranged in a random and interwoven manner with glutaraldehyde. The specially made nano-scale flexible fibers are flexible fibers with a multi-component system formed by a mixture of flexible thermoplastic polyurethane and polyethyleneimine as the main components. The surface of the flexible fibers has a microstructure with the two main components separated in a nano-phase state. The ratio of the flexible thermoplastic polyurethane to polyethyleneimine is in the range of (1-4):

1.

2. The nanofiber membrane for removing short-chain PFASs in water according to claim 1, wherein, Nanofiber membranes are prepared using the following steps: S1. Thermoplastic polyurethane and polyethyleneimine are added to a mixed solvent of acetone and N,N-dimethylformamide in a certain proportion. The resulting solution is stirred evenly and fully dissolved to obtain a spinning solution containing flexible thermoplastic polyurethane / polyethyleneimine. S2 The prepared spinning solution is loaded into a syringe and electrospinning is performed to produce nanoscale flexible fibers. The flexible fibers collected in S3 were immersed in a glutaraldehyde solution for cross-linking to obtain a preliminary membrane. S4 repeatedly rinses the initial membrane with deionized water and soaks it overnight to remove unreacted substances on the surface; after drying, the finished membrane is obtained.

3. The nanofiber membrane for removing short-chain PFASs in water according to claim 2, characterized by, In step S1, the mixed solution is magnetically stirred at room temperature to fully dissolve it, and then ultrasonic treatment is used to remove air bubbles.

4. The nanofiber membrane for removing short-chain PFASs in water according to claim 2, characterized by, The thermoplastic polyurethane used in step S1 has a molecular weight of 120,000-150,000 and a polyethyleneimine molecular weight of 50,000-75,000 in a 50% aqueous solution.

5. The nanofiber membrane for removing short-chain PFASs in water according to claim 2, wherein In step S1, the mass ratio of thermoplastic polyurethane to polyethyleneimine is 1:1-4:1, and the mass ratio of acetone to N,N-dimethylformamide is 1:1-4:

1.

6. The nanofiber membrane for removing short-chain PFASs in water according to claim 2, characterized by, In step S2, the mass percentage of the spinning solution of thermoplastic polyurethane and polyethyleneimine is 15%-25%, the spinning voltage is 15-20kV, and the flow rate is 0.5-1.0 mL / h.

7. The nanofiber membrane for removing short-chain PFASs in water according to claim 2, wherein In step S3, the obtained flexible fibers are added to a 1%-5% glutaraldehyde solution for cross-linking fixation, and the cross-linking time is 1-2 hours; In step S4, the membrane is placed in a vacuum drying oven and dried at 25°C for 24 hours to obtain the finished membrane.

8. The method of using the nanofiber membrane for removing short-chain PFASs from water as described in any one of claims 1-7, characterized in that, The nanofiber membrane was fixed on a stirring rod, the stirring rod was placed in the solution to be adsorbed, and the mixture was stirred thoroughly to carry out adsorption. After the adsorption was completed, the stirring rod was removed. Adjust the pH of the solution to be adsorbed to between 4 and 7.

9. The method for regenerating the nanofiber membrane for removing short-chain PFASs from water as described in any one of claims 1-7, characterized in that, After the nanofiber membrane has been used up, add it to a mixed regeneration solution of sodium chloride and methanol, stir for 5-15 minutes, remove it, immerse it again in pure water, stir for 5-15 minutes, remove it and let it air dry naturally.

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