A three-dimensional nanofiber tubular filter membrane for water filtration and its preparation method

Abstract

To ensure a high dirt-holding capacity of the water filtration membrane and enhance the mechanical strength of the nanofibers, the present invention provides a three-dimensional nanofiber tubular filtration membrane for water filtration and a method for preparing the same. The method first prepares a quaternary ammonium salt chitosan / polyvinyl alcohol solution and electrospins it to produce a two-dimensional nanofiber membrane. The two-dimensional nanofiber membrane is then homogenized in anhydrous tert-butyl alcohol to produce a nanofiber dispersion. The nanofiber dispersion is freeze-dried in a mold to form a nanofiber aerogel. The transition from a two-dimensional to a three-dimensional structure significantly increases the dirt-holding capacity of the filtration membrane. Finally, the aerogel is heat-treated to further enhance its stability and improve its mechanical strength. The present invention is simple, practical, easily scalable, and has excellent filtration efficiency and water flux. Furthermore, the selected quaternary ammonium salt chitosan has an antibacterial effect, which enhances the antibacterial properties of the filtration membrane.

Description

Technical Field

[0001] The invention belongs to the technical field of water treatment equipment and relates to a three-dimensional nanofiber tubular filter membrane for water filtration and a preparation method thereof. Background Art

[0002] Membrane filters are water treatment devices that deeply filter and purify water according to specific usage requirements. The core technology of membrane filters lies in the filtration membrane within the filtration device. However, current membrane filtration systems face numerous drawbacks and challenges, including: 1) poor filtration selectivity and permeability, resulting in insufficient filtration performance when separating impurities from water; 2) membrane degradation under certain environmental conditions or after prolonged use, impacting long-term reliability; 3) high-performance membrane materials are expensive to produce, making them uneconomical; 4) membrane production and disposal processes can impact the environment, leading to pollution; and 5) membrane filtration systems lack antibacterial properties, lacking the ability to kill bacteria and other harmful microorganisms in water.

[0003] Nanofibers have attracted attention due to their highly porous structure, narrow pore size, and high specific surface area. One of the most effective technologies for producing nanofibers is electrospinning, and the resulting nanofibers can be used in a variety of fields, including water filtration. On the one hand, the pore size of nanofiber membranes is typically at the nanometer level, which can effectively intercept suspended particles and microorganisms in the water. The high specific surface area of ​​nanofiber membranes allows more pollutants to adhere to the membrane, which gives the fiber membrane a certain dirt holding capacity. However, as particles accumulate during the filtration process, the dirt holding capacity may decrease. On the other hand, the small diameter of nanofibers and the porous structure of the fibers result in low overall mechanical properties of the membrane. To address this problem, current research focuses on first ensuring the high dirt holding capacity of water filtration membranes and secondly on enhancing the mechanical strength of nanofibers. Summary of the Invention

[0004] To address the above problems, the present invention provides a three-dimensional nanofiber tubular filter membrane for water filtration and a method for preparing the same. The present invention first prepares a quaternary ammonium salt chitosan / polyvinyl alcohol (QCS / PVA) solution and obtains a two-dimensional nanofiber membrane by electrospinning; the two-dimensional nanofiber membrane is then immersed in anhydrous tert-butyl alcohol and homogenized to produce a nanofiber dispersion; the nanofiber dispersion is freeze-dried in a mold to form a nanofiber aerogel. The transition from a two-dimensional structure to a three-dimensional structure significantly increases the filter membrane's ability to hold pollutants; and finally, the aerogel is heat-treated to further enhance stability and improve the mechanical strength of the filter membrane. The present invention has the advantages of being simple, practical, easy to promote, and having excellent filtration efficiency and water flux. Furthermore, the selected quaternary ammonium salt chitosan has an antibacterial effect, which improves the antibacterial properties of the filter membrane.

[0005] In order to achieve the above object, the technical solution adopted by the present invention is: a method for preparing a three-dimensional nanofiber tubular filter membrane for water filtration, characterized by comprising the following steps:

[0006] S1: Preparation of quaternary ammonium chitosan / polyvinyl alcohol (QCS / PVA) solution and electrospinning to obtain a two-dimensional nanofiber membrane;

[0007] S2: 2D nanofiber membrane immersed in anhydrous tert-butyl alcohol and homogenized to produce nanofiber dispersion;

[0008] S3: The nanofiber dispersion is freeze-dried in a mold to form a three-dimensional nanofiber aerogel;

[0009] S4: The three-dimensional nanofiber aerogel was heat-treated at 150-200 °C to further enhance the stability and improve the mechanical strength of the filtration membrane.

[0010] In step S1, the preparation method of the quaternary ammonium salt chitosan (QCS) is as follows: dispersing chitosan in a NaBH4 / NaOH solution and stirring at 100-120°C, filtering, washing, and vacuum drying to obtain deacetylated chitosan, reacting the deacetylated chitosan with 2,3-epoxypropyltrimethylammonium chloride, filtering, purifying, and drying to obtain QCS; the mass ratio of the chitosan to NaBH4 is 10:0.9-1.1, preferably 10:1; the mass ratio of the deacetylated chitosan to 2,3-epoxypropyltrimethylammonium chloride is 1:2.5-3.2, preferably 1:2.8, and the purity of the prepared QCS is ≥98%.

[0011] Preferably, in step S1, the mass ratio of QCS to PVA in the quaternary ammonium chitosan / polyvinyl alcohol (QCS / PVA) solution is 1:3-7, preferably 1:5-6. More preferably, the final concentration of QCS in the QCS / PVA solution is 1-2%, and the final concentration of PVA is 6-8%.

[0012] Preferably, in step S1, the electrospinning conditions are: a steel needle nozzle with an inner diameter of 0.4-0.7 mm is used for spinning, the distance between the needle and the collecting plate is 15-18 cm, the spinning temperature is 25-30 ° C, the humidity is 50%-65% RH, the voltage at the spinneret is 25-30 kV, and the solution propulsion speed is 0.3-0.5 mL / h.

[0013] In step S2 of the present invention, the electrospun nanofiber membrane is immersed in anhydrous tert-butanol. Anhydrous tert-butanol is an organic solvent and is easily volatilized during the subsequent freeze-drying, which can ensure the stability and uniformity of the fiber. The nanofiber dispersion with a density of 50-100 g / L is obtained by homogenization in anhydrous tert-butanol.

[0014] In step S3, the nanofiber dispersion is placed in a polyurethane plastic sleeve mold for freeze drying. The mold consists of two parts, an inner part and an outer part. The inner part is a solid cylinder with a smaller radius, and the outer part is a hollow cylinder with a larger radius. The bottom end of the mold is blocked, and there is a hollow interlayer between the inner and outer layers. The inner diameter of the mold is 1~5 cm and the outer diameter is 1.5~8 cm. Two layers of cylindrical copper mesh with diameters of 1~5 cm and 1.5~8 cm can be placed inside the mold to support the three-dimensional nanofiber aerogel. The copper mesh has a pore size of 0.07~0.09 mm, a wire diameter of 0.04~0.06 mm, a thickness of 0.1~0.15 mm, and a density of 8.96~9.65 g / cm 3 .

[0015] The freeze drying in step S3 is preferably performed at -35 to -55°C for 45 to 50 hours.

[0016] The three-dimensional nanofiber tubular filter membrane prepared by the above method has a cylindrical copper mesh placed inside the membrane to support the three-dimensional nanofiber aerogel and enhance its overall mechanical properties. The three-dimensional nanofiber tubular filter membrane has high porosity and high specific surface area.

[0017] The present invention also discloses the application of three-dimensional nanofiber tubular filter membrane in water filtration. The nanofiber aerogel has a filtration efficiency of up to 97.34%, not less than 2500 L / m 2 h of water flux and an antibacterial rate higher than 98%.

[0018] The principle of the reaction between QCS and PVA in the present invention generally involves physical and chemical interactions between the two substances: the positively charged quaternary ammonium salt groups on QCS can electrostatically interact with hydroxyl groups, anionic substances, and other groups on PVA; the numerous hydroxyl groups on PVA molecules form hydrogen bonds with the amino groups of QCS; and during blending and spinning, the molecular chains of the two also penetrate each other to form a uniform mixture.

[0019] The ammonium group (-NH3 +) makes it carry a positive charge, and chitosan quaternary ammonium salt can be adsorbed to the negatively charged surface of bacteria through electrostatic interaction, destroying the integrity of the cells, increasing the permeability of the cell membrane, and leaking the cell contents, thereby inhibiting the growth and reproduction of bacteria. Therefore, the two-dimensional nanofibers containing quaternary ammonium salt chitosan have antibacterial properties. When the two-dimensional nanofiber membrane is innovatively prepared into a three-dimensional form, its overall specific surface area is significantly improved, the adsorption efficiency and the dirt holding capacity are significantly enhanced, and the material is given higher durability, so that it can also ensure a stable pollutant filtration effect during long-term use. Secondly, previous studies have shown that heat treatment can promote fiber bonding and thus improve mechanical strength. Therefore, the application of heat-treated three-dimensional structured nanofiber aerogel in the field of water filtration can successfully achieve the purpose of removing solid particles, suspended matter and other impurities in water, thereby achieving a water purification effect.

[0020] Compared with the prior art, the present invention has the following beneficial effects:

[0021] First, the three-dimensional nanofiber aerogel prepared by the present invention has a unique microscopic cell structure with small pores and large specific surface area, which gives it excellent physical properties: compared with a single nanofiber membrane, the three-dimensional structure of the nanofiber aerogel not only greatly improves the porosity of the material, but also forms abundant micropores on its surface. These microporous channels provide more passage paths for water molecules. Therefore, nanofiber aerogels show significant advantages in the water treatment process. They have both efficient filtering capabilities, which can effectively remove impurities and pollutants in water, and can ensure a high water flux, allowing water to pass quickly. The excellent filtration efficiency and water flux of aerogels make them ideal filter materials for a variety of high-performance water treatment applications.

[0022] Secondly, using QCS and PVA as matrices, the matrix solution can form continuous and stable nanofibers during the electrospinning process. The combination of PVA and QCS produces a synergistic effect. On the one hand, PVA improves the fiber-forming properties and mechanical strength of QCS, resulting in nanofiber membranes with better physical properties and stability. On the other hand, the antibacterial properties of QCS complement the deficiencies of PVA, resulting in the composite nanofiber membrane exhibiting superior antibacterial performance.

[0023] Finally, aerogel has a unique three-dimensional network structure, which gives it extremely rich pores and a high specific surface area, allowing it to effectively adsorb and accommodate more dirt. And because of the increase in surface area, the aerogel's dirt-holding capacity is significantly improved, and it can absorb more pollutants, enhancing its application effect under different environmental conditions. The high adsorption capacity of aerogel not only improves its water treatment efficiency, but also slows the material's dirt saturation rate, thereby significantly extending its service life, reducing the need for frequent material replacement, and further improving its cost-effectiveness and sustainability. By heat-treating the aerogel and combining the three-dimensional nanofiber aerogel with a copper mesh, the overall mechanical properties of the prepared filter are enhanced, making it suitable for application in real-world scenarios. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 Schematic diagram of the structure of the three-dimensional nanofiber tubular filter membrane of the present invention; in the figure, 1, copper mesh, 2, three-dimensional nanofiber aerogel filling matrix;

[0025] Figure 2 The three-dimensional nanofiber tubular filtration membrane of the present invention ( Figure 1 ) structural cross-section at AA; in the figure, 1, copper mesh, 2, three-dimensional nanofiber aerogel filling matrix;

[0026] Figure 3 is the SEM image of the unheated QCS / PVA nanofiber aerogel;

[0027] Figure 4 Fiber diameter of unheated QCS / PVA nanofiber aerogel (a) and fiber diameter of heated QCS / PVA nanofiber aerogel (b);

[0028] Figure 5 is the filtration efficiency of the QCS / PVA nanofiber aerogel produced by the reaction under different conditions in Examples 1-3;

[0029] Figure 6 is the pure water flux of the QCS / PVA nanofiber aerogel produced by the reaction under different conditions in Examples 1-3;

[0030] Figure 7 The antibacterial effect (a) and inhibition rate (b) of QCS / PVA nanofiber aerogel (NF-A2) and the control group without aerogel addition. DETAILED DESCRIPTION

[0031] The technical solution of the present invention is described in further detail below in conjunction with the accompanying drawings and specific embodiments. The following examples and drawings are used to illustrate the present invention, but are not intended to limit the scope of the present invention.

[0032] The mold used in this embodiment consists of two parts: an inner part and an outer part. The inner part is a solid cylinder with a smaller radius, and the outer part is a hollow cylinder with a larger radius. The bottom of the mold is blocked, and there is a hollow interlayer between the inner and outer layers. The inner diameter of the mold is 3 cm and the outer diameter is 4.5 cm. Two layers of cylindrical copper mesh with diameters of 3 cm and 4.5 cm respectively can be placed inside the mold to support the three-dimensional nanofiber aerogel. The copper mesh has a pore size of about 0.08 mm, a wire diameter of about 0.05 mm, a thickness of 0.125 mm, and a density of about 9.30 g / cm 3 .

[0033] The polyvinyl alcohol (PVA) 1799 used in this example has an alcoholysis degree of 98-99% mol / mol; manufacturer: Aladdin (China).

[0034] The chitosan used in this example has a deacetylation degree of ≥95% and a viscosity of 100-200 mPa.s. It was manufactured by Shanghai Macklin.

[0035] The preparation method of QCS in this embodiment is as follows:

[0036] (1) Preparation of deacetylated chitosan

[0037] Chitosan was dispersed in a 10% (w / w) NaOH solution containing 1% NaBH₄ (an antioxidant) to prepare 200 mL of a 10% (w / w) chitosan / NaOH solution. After stirring at 110°C for 5 hours, the solution was filtered through filter paper and washed with distilled water until neutral. The resulting material was filtered, rinsed first with methanol and then with acetone, and then vacuum-dried at 70°C overnight to obtain 17.8 g of deacetylated chitosan.

[0038] (2) QCS preparation

[0039] Deacetylated chitosan was dispersed in 85° C. distilled water to prepare 60 mL of a 10% (w / w) deacetylated chitosan solution.

[0040] 2,3-Epoxypropyltrimethylammonium chloride (21.3 mL, 111 mmol) was added to the deacetylated chitosan solution in 7.1 mL portions every 2 hours. After 10 hours of reaction, the clear, pale yellow reaction solution was poured into 4°C pure acetone (200 mL) while stirring and refrigerated overnight. The next day, the acetone was decanted, and the remaining gelatinous product was dissolved in pure methanol (100 mL). The solution was precipitated with 4:1 acetone-ethanol (250 mL), and the white product was collected by filtration. It was then further purified by washing with hot ethanol in a Soxhlet extractor for 24 hours. The final product was dried at 70°C overnight to obtain 10.2 g of quaternary ammonium chitosan with a purity of 98% and a degree of quaternization of 1.0.

[0041] Example 1: Preparation of three-dimensional nanofiber tubular filtration membrane

[0042] (1) Preparation of QCS / PVA nanofiber membrane by electrospinning: QCS / PVA solution was prepared by volume ratio of 30% QCS solution (QCS dissolved in deionized water, concentration 6.5wt%) and 70% PVA solution (PVA dissolved in deionized water at 80℃, concentration 9wt%), and electrospun on aluminum-coated paper. The electrospinning conditions were as follows: a steel needle nozzle with an inner diameter of 0.4-0.7 mm was used for spinning, the distance between the needle and the collecting plate was 15-18 cm, the spinning temperature was 25-30℃, the humidity was 50%-65% RH, the voltage at the spinneret was 30 kV, and the solution propulsion speed was 0.5 mL / h.

[0043] (2) The electrospun nanofibers were immersed in anhydrous tert-butyl alcohol and homogenized (using an IKA T25 homogenizer) to obtain a nanofiber dispersion with a density of 100 g / L;

[0044] (3) freeze-drying the nanofiber dispersion at -40 °C for 48 h to form a nanofiber aerogel in a mold;

[0045] (4) The stability of the freeze-dried aerogel was improved by heat treatment at 160 °C for 10 min, and the obtained aerogel was named NF-A1.

[0046] The structural diagram of the three-dimensional nanofiber tubular filter membrane of the present invention is as follows Figure 1 、 2 It includes a copper mesh 1 and a three-dimensional nanofiber aerogel filling matrix 2. A cylindrical copper mesh is placed inside the three-dimensional nanofiber tubular filter membrane to support the three-dimensional nanofiber aerogel.

[0047] Among them, the SEM image of the unheated QCS / PVA nanofiber aerogel is shown in Figure 2. Figure 3 As shown; the fiber diameter of the unheated QCS / PVA nanofiber aerogel (a) and the fiber diameter of the heated QCS / PVA nanofiber aerogel (b) are as shown Figure 4 As shown. Figure 4 It can be seen that after the nanofibers undergo heat treatment, their fiber diameter increases to a certain extent. Before heating, the fiber diameter is generally distributed around 0.55 μm, and after heating, the fiber diameter is generally distributed around 0.7 μm.

[0048] Example 2: Preparation of three-dimensional nanofiber tubular filtration membrane

[0049] (1) Preparation of QCS / PVA nanofiber membrane by electrospinning: QCS / PVA solution was prepared by volume ratio of 30% QCS solution (QCS was dissolved in deionized water, concentration of 5 wt%) and 70% PVA solution (PVA was dissolved in deionized water at 80 ℃, concentration of 11 wt%), and electrospun on aluminum-coated paper. The electrospinning conditions were as follows: a steel needle nozzle with an inner diameter of 0.4-0.7 mm was used for spinning, the distance between the needle and the collecting plate was 15-18 cm, the spinning temperature was 25-30 ℃, the humidity was 50%-65% RH, the voltage at the spinneret was 30 kV, and the solution propulsion speed was 0.5 mL / h.

[0050] (2) The electrospun nanofibers were immersed in anhydrous tert-butyl alcohol and homogenized (using an IKA T25 homogenizer) to obtain a nanofiber dispersion with a density of 100 g / L;

[0051] (3) freeze-drying the nanofiber dispersion at -40 °C for 48 h to form a nanofiber aerogel in a mold;

[0052] (4) The stability of the freeze-dried aerogel was improved by heat treatment at 160 °C for 10 min, and the obtained aerogel was named NF-A2.

[0053] Example 3: Preparation of three-dimensional nanofiber tubular filtration membrane

[0054] (1) Preparation of QCS / PVA nanofiber membrane by electrospinning: QCS / PVA solution was prepared by volume ratio of 30% QCS solution (QCS was dissolved in deionized water, concentration of 5 wt%) and 70% PVA solution (PVA was dissolved in deionized water at 80 ℃, concentration of 11 wt%), and electrospun on aluminum-coated paper. The electrospinning conditions were as follows: a steel needle nozzle with an inner diameter of 0.4-0.7 mm was used for spinning, the distance between the needle and the collecting plate was 15-18 cm, the spinning temperature was 25-30 ℃, the humidity was 50%-65% RH, the voltage at the spinneret was 30 kV, and the solution propulsion speed was 0.5 mL / h.

[0055] (2) The electrospun nanofibers were immersed in anhydrous tert-butyl alcohol and homogenized (using an IKA T25 homogenizer) to obtain a nanofiber dispersion with a density of 50 g / L;

[0056] (3) freeze-drying the nanofiber dispersion at -40 °C for 48 h to form a nanofiber aerogel in a mold;

[0057] (4) The stability of the freeze-dried aerogel was improved by heat treatment at 200 °C for 10 min, and the obtained aerogel was named NF-A3.

[0058] Red pigment nanoparticles (PNPs) were dispersed in pure water at a concentration of 66.7 μL / L. The particle size distribution of the PNPs was analyzed using a Malvern laser particle size analyzer (Mastersizer 2000). The separation performance of the nanofiber membrane for PNPs was studied at a preset pressure of 0.1 MPa. The filtration efficiency was calculated using the following equation:

[0059]

[0060] in, C f is the concentration of the feed solution (μL / L), C P is the concentration of the permeate solution (μL / L) calculated from the spectra measured by a UV-visible spectrophotometer (UV-2550, Shimadzu, China).

[0061] The filtration efficiency of QCS / PVA nanofiber aerogels generated under different reaction conditions in Examples 1-3 is as follows: Figure 5 As shown in the figure, the NF-A2 nanofiber aerogel has a maximum filtration efficiency of 97.34%, while the NF-A1 and NF-A3 aerogels have filtration efficiencies of 78.65% and 76.82%, respectively. This confirms that when the concentrations of PVA and QCS and the heat treatment temperature are varied within the selectable range, the three-dimensional nanostructures can maintain high filtration efficiency.

[0062] The pure water flux of the aerogel was tested by cross-flow filtration (SF-SA Membrane Separation Technology Co., Ltd.) after pre-pressing the aerogel at a preset pressure of 0.1 MPa for 10 minutes. The pure water flux of the nanofiber membrane was calculated using the flow equation:

[0063]

[0064] Where J is the pure water flux (L·m -2 ·h -1 ), Q is the volume of the solution being tested passing through the material (L), A is the effective area of ​​the material being tested (m 2 ), T is the sampling time (h).

[0065] The water flux test results of the filter membrane are as follows Figure 6 As shown in the figure, the water flux of the aerogel filtration membrane began to decline after the first 0.75 days. All the aerogel nanofiber membranes still maintained a water flux of not less than 2500 L / m after 3 days of filtration. 2 ·h -1 The water flux of NF-A2 can maintain a stable and high value for a long time.

[0066] NF-A2 aerogel was selected for antibacterial experiments. First, a single colony of Staphylococcus aureus and Escherichia coli was picked and cultured in 20 mL LB liquid medium for 12 h, and then the bacterial suspension was diluted to 10 6 CFU / mL for subsequent use. 5 mg of NF-A2 aerogel was crushed and dispersed in 1 mL of diluted bacterial suspension and incubated in a shaker at 37°C for 24 h. The bacterial solution without aerogel was used as the control group. Subsequently, 0.1 mL of bacterial culture was placed on an agar plate and incubated at 37°C overnight. Finally, an automatic colony counter (Shinesosupre G9) was used to measure the number of colonies and calculate the bacterial survival rate. The results of the antibacterial experiment are shown in Figure 2. Figure 7 As shown in (a) and (b), compared with the control group, the aerogel in the experimental group has obvious antibacterial properties, with an inhibition rate of 99% against Staphylococcus aureus and 100% against Escherichia coli.

[0067] In general, the three-dimensional nanofiber structure has higher water flux and filtration efficiency, and maintains good durability. This shows that the three-dimensional aerogel structure enables the filter membrane to maintain water flow while also ensuring a high dirt holding capacity of the filter membrane. The material also has obvious antibacterial properties, proving that the material has good application prospects.

[0068] The foregoing description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Those skilled in the art will readily appreciate that the present invention is susceptible to modification and variation. Any modifications, equivalent substitutions, or improvements made within the spirit and principles of the present invention shall be included within the scope of protection of the present invention.

Claims

1. A method for preparing a three-dimensional nanofiber tubular filter membrane for water filtration, characterized in that: The following steps are involved: S1: Prepare quaternary ammonium salt chitosan / polyvinyl alcohol solution and obtain two-dimensional nanofiber membrane by electrospinning; S2: 2D nanofiber membrane immersed in anhydrous tert-butyl alcohol and homogenized to produce nanofiber dispersion; S3: The nanofiber dispersion is freeze-dried in a mold to form a three-dimensional nanofiber aerogel; a cylindrical copper mesh is placed inside the mold to support the three-dimensional nanofiber aerogel; S4: The three-dimensional nanofiber aerogel is heat-treated at 150-200°C to obtain a three-dimensional nanofiber tubular filtration membrane.

2. The preparation method according to claim 1, wherein In step S1, the preparation method of quaternary ammonium salt chitosan is as follows: chitosan is dispersed in a NaBH4 / NaOH solution and stirred at 100-120°C, filtered, washed, and vacuum dried to obtain deacetylated chitosan, deacetylated chitosan is reacted with 2,3-epoxypropyltrimethylammonium chloride, filtered, purified, and dried to obtain quaternary ammonium salt chitosan.

3. The preparation method according to claim 1, wherein In the step S1, the mass ratio of quaternary ammonium chitosan to polyvinyl alcohol in the quaternary ammonium chitosan / polyvinyl alcohol solution is 1:3-7.

4. The preparation method according to claim 1, wherein In step S1, the electrospinning conditions are as follows: a steel needle nozzle with an inner diameter of 0.4-0.7 mm is used for spinning, the distance between the needle tip and the collecting plate is 15-18 cm, the spinning temperature is 25-30°C, the humidity is 50%-65% RH, the voltage at the spinneret tip is 25-30 kV, and the solution propulsion speed is 0.3-0.5 mL / h.

5. The preparation method according to claim 1, wherein In step S2, the nanofiber dispersion with a density of 50-100 g / L is obtained by homogenization in anhydrous tert-butanol.

6. The preparation method according to claim 1, wherein In step S3, the nanofiber dispersion is placed in a polyurethane plastic sleeve mold for freeze drying. The mold includes an inner and an outer part, the inner part is a solid cylinder, the outer part is a hollow cylinder, the bottom of the mold is blocked, and there is a hollow interlayer between the inner and outer layers. The inner diameter of the mold is 1-5 cm and the outer diameter is 1.5-8 cm. Two layers of cylindrical copper mesh with diameters of 1-5 cm and 1.5-8 cm, respectively, can be placed inside the mold to support the three-dimensional nanofiber aerogel. The copper mesh has an aperture of 0.07~0.09mm, a wire diameter of 0.04~0.06mm, a thickness of 0.1~0.15mm, and a density of 8.96~9.65 g / cm 3 .

7. The preparation method according to claim 1, wherein The freeze drying in step S3 is: freeze drying at -35 to -55°C for 45 to 50 hours.

8. The three-dimensional nanofiber tubular filtration membrane prepared by the method according to any one of claims 1 to 7, characterized in that: The invention comprises a copper mesh and a three-dimensional nanofiber aerogel filling matrix. A cylindrical copper mesh is placed inside the three-dimensional nanofiber tubular filter membrane to support the three-dimensional nanofiber aerogel.

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