Carbon nanotube metal organic framework composite fiber membrane, preparation method and application thereof

Abstract

The application relates to the technical field of composite fiber membrane materials, in particular to a carbon nanotube metal organic framework composite fiber membrane and a preparation method and application thereof. Zn(NO3)2.6H2O and Blm are dissolved in dimethylformamide, acidized carbon nanotubes are added, stirring is carried out for 30-60 min, then heating is carried out at 95-120 DEG C for 72-100 h, after being cooled to room temperature, centrifugal separation is carried out and washing is carried out with DMF, then drying is carried out at 75-85 DEG C for 15-30 h, and a ZIF-7 / CNTs composite is obtained; polyimide is dissolved in N, N dimethylacetamide, the ZIF-7 / CNTs composite is added, stirring is carried out for 5-8 h, a casting solution is obtained, the casting solution is extruded to form a hollow fiber through a spinneret, the hollow fiber is soaked in deionized water for 36-48 h, then the hollow fiber is continuously soaked in ethanol and n-hexane, the soaking solvent is replaced every 30 min, finally, the hollow fiber is dried in a vacuum oven at 60-80 DEG C for 24-48 h, and a composite fiber membrane material is obtained. The metal organic framework material and the carbon nanotubes are combined, and a composite membrane material with excellent gas permeability and selectivity is prepared.

Description

Technical Field

[0001] This invention relates to the field of composite fiber membrane materials technology, and in particular to carbon nanotube metal-organic framework composite fiber membranes, their preparation methods and applications. Background Technology

[0002] Membrane gas separation is a novel, efficient, and energy-saving separation technology that has been widely applied in industries such as petrochemicals and synthetic ammonia. Membrane helium extraction was first studied by Stern et al. in 1965, but its industrialization has progressed relatively slowly to date. Polyimide, as one of the best-performing special engineering plastics, possesses advantages such as good thermal stability, acid and alkali resistance, solvent resistance, stable molecular size, and good mechanical properties. Simultaneously, polyimide exhibits excellent gas selectivity, thus attracting significant attention in the field of gas separation. To overcome the limitations of gas permeability and selectivity, researchers have modified polymer molecules through various physical and chemical methods, such as adding inorganic particles to polymer systems, attempting to create polymer materials that combine excellent gas permeability and selectivity.

[0003] Metal-organic frameworks (MOFs) are a novel class of porous materials formed by the self-assembly of one or more metal centers and organic ligands. Their unique 3D structure endows them with ultra-high specific surface area, high porosity, controllable morphology and pore size, highly ordered distribution of metal active centers, and modifiability. After high-temperature carbonization, they can form various nanoporous carbon metal particles / metal oxides / single-atom structures of carbon-based materials. However, the degree of graphitization, pore retention, and structural integrity of different types of MOF materials during carbonization are quite limited, restricting the further development of MOF-derived materials in membrane gas separation. Carbon nanotubes are characterized by small size, large aspect ratio, and large specific surface area; however, the strong van der Waals forces and electrostatic interactions between the atoms of carbon nanotubes often lead to aggregation, resulting in a decline in material performance.

[0004] Therefore, it is of great significance to study how to combine metal-organic framework materials and carbon nanotubes to prepare composite membrane materials with both excellent gas permeability and selectivity. Summary of the Invention

[0005] In view of this, the purpose of this invention is to provide carbon nanotube-metal-organic framework composite fiber membranes, their preparation methods and applications, combining metal-organic framework materials and carbon nanotubes to prepare composite membrane materials with both excellent gas permeability and selectivity.

[0006] The present invention solves the above-mentioned technical problems through the following technical means:

[0007] The first aspect of the present invention is to provide a carbon nanotube metal-organic framework composite fiber membrane, wherein the composite fiber membrane is formed by spinning and extruding a mixture of polyimide and carbon nanotube metal-organic framework composite, wherein the polyimide comprises 2.1 to 4.5 parts by weight and the carbon nanotube metal-organic framework composite comprises 0.2 to 0.8 parts by weight.

[0008] In conjunction with the first aspect, in some embodiments, the carbon nanotube metal-organic framework composite comprises the following raw materials in parts by weight: 2.21 to 4.91 parts of Zn(NO3)2·6H2O, 1.32 to 4.17 parts of Blm, and 1.3 to 2.5 parts of acidified carbon nanotubes.

[0009] A second aspect of the present invention provides a method for preparing a carbon nanotube-metal-organic framework composite fiber membrane, comprising the following steps:

[0010] Zn(NO3)2·6H2O and Blm were dissolved in dimethylformamide, and acidified carbon nanotubes were added and stirred for 30-60 min. Then, the mixture was transferred to a Teflon stainless steel autoclave and heated at 95-120℃ for 72-100 h. After cooling to room temperature, the mixture was centrifuged and washed with DMF. Then, it was dried in a vacuum drying oven at 75-85℃ for 15-30 h to obtain the ZIF-7 / CNTs composite.

[0011] Polyimide was dissolved in N,N-dimethylacetamide, and ZIF-7 / CNTs composite was added. The mixture was stirred for 5–8 hours to obtain a casting solution. The solution was then extruded through a spinneret to form hollow fibers. The hollow fibers were soaked in deionized water for 36–48 hours, and then continuously soaked in ethanol and n-hexane for 2–10 hours, with the soaking solvent being changed every 30 minutes. Finally, the hollow fibers were dried in a vacuum oven at 60–80°C for 24–48 hours to obtain the composite fiber membrane material.

[0012] In conjunction with the second aspect, in some embodiments, the acidified carbon nanotubes are prepared as follows:

[0013] Concentrated sulfuric acid and concentrated nitric acid were added sequentially to the high-temperature treated multi-walled carbon nanotubes. The mixture was stirred ultrasonically at room temperature for 4–8 hours. The mixture was then diluted and allowed to stand until the carbon nanotubes precipitated. The supernatant was discarded, and the lower suspension was filtered through a polytetrafluoroethylene membrane with a pore size of 0.22 μm. The filtrate was repeatedly washed with distilled water until the pH of the filtrate was approximately 6. The filtered solid was then vacuum dried at 55–65 °C for 24–48 hours to obtain acidified carbon nanotubes.

[0014] In conjunction with the second aspect, in some embodiments, the high-temperature treatment is as follows: multi-walled carbon nanotubes are placed in a closed reactor filled with argon gas, and the reactor is heated to 1450-1600°C at a heating rate of 10°C / min, and then held at that temperature for 0.8-1.5 hours.

[0015] In conjunction with the second aspect, in some embodiments, the concentrated sulfuric acid is 120-150 parts by volume, and the concentrated nitric acid is 40-60 parts by volume.

[0016] In conjunction with the second aspect, in some embodiments, the mass fraction of Zn(NO3)2·6H2O is 2.21 to 4.91 parts, the mass fraction of Blm is 1.32 to 4.17 parts, and the mass fraction of acidified carbon nanotubes is 1.3 to 2.5 parts.

[0017] A third aspect of the present invention is to provide the application of the above-mentioned carbon nanotube metal-organic framework composite fiber membrane in helium separation and purification.

[0018] The carbon nanotube / metal-organic framework (MOF) composite fiber membrane of this invention utilizes the growth characteristics of MOFs on the surface of carbon nanotubes to synthesize a carbon nanotube / metal-organic framework (MOF) composite material, which is then combined with polyimide to prepare a hollow fiber membrane, thus obtaining the carbon nanotube / metal-organic framework composite fiber membrane. The combination of MOFs and CNTs can achieve multi-faceted complementarity and improvement in structure and performance. In the preparation method of the nanotube / metal-organic framework composite fiber membrane of this invention, the carbon nanotubes are acidified to introduce carboxyl groups onto the surface of multi-walled carbon nanotubes. This achieves both functional modification—providing homogeneous nucleation sites for MOF growth—and removal of small amounts of impurities and unreacted carbon particles introduced due to limitations in production conditions.

[0019] The carbon nanotube metal-organic framework composite fiber membrane of the present invention exhibits a high selectivity coefficient for helium. Gas detection experimental data show that, compared with pure polypropylene, the helium permeability coefficient is increased by 44.16%, the selectivity coefficient for He / CH4 is increased by 39.29%, and the selectivity coefficient for He / N2 is increased by 54.1%. Attached Figure Description

[0020] Figure 1 The PXRD spectra of CNTs, ZIF-7 / CNTs, and ZIF-7 simulated in Example 4 are shown. Detailed Implementation

[0021] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0022] Unless otherwise specified in the following examples, the conditions are as per standard conditions or the manufacturer's recommendations. Raw materials, equipment, or instruments whose manufacturers are not specified are all commercially available products.

[0023] This application utilizes the growth characteristics of MOFs on the surface of carbon nanotubes to synthesize a carbon nanotube / metal-organic framework (MOF) composite material, which is then used to prepare a hollow fiber membrane with polyimide, thus obtaining a carbon nanotube-metal-organic framework composite fiber membrane. The combination of MOFs and CNTs can achieve multi-faceted complementarity and improvement in both structure and performance. Carbon nanotube materials are characterized by their small size, large aspect ratio, and large specific surface area; however, strong van der Waals forces and electrostatic interactions exist between the atoms of carbon nanotubes, often leading to aggregation and a decrease in material performance. Therefore, to obtain a high-performance hybrid matrix membrane, this application functionalizes the carbon nanotubes to enable interaction between them and the polymer matrix. By acidifying the carbon nanotubes, carboxyl groups are introduced onto the surface of the multi-walled carbon nanotubes, achieving both functionalization—providing homogeneous nucleation sites for MOF growth—and removing small amounts of impurities and unreacted carbon particles introduced due to limitations in the production process.

[0024] The carbon nanotube-metal-organic framework composite fiber membrane of this application is prepared by spinning and extruding a mixture of polyimide and a carbon nanotube-metal-organic framework composite. The weight percentage of polyimide is 2.1–4.5 parts, and the weight percentage of the carbon nanotube-metal-organic framework composite is 0.2–0.8 parts. The preparation method is as follows:

[0025] 2.21–4.91 parts by weight of Zn(NO3)2·6H2O and 1.32–4.17 parts by weight of Blm were dissolved in dimethylformamide, and acidified carbon nanotubes were added and stirred for 30–60 min. Then the mixture was transferred to a Teflon stainless steel autoclave and heated at 95–120 °C for 72–100 h. After cooling to room temperature, the mixture was centrifuged and washed with DMF. Finally, it was dried in a vacuum drying oven at 75–85 °C for 15–30 h to obtain the ZIF-7 / CNTs composite.

[0026] Polyimide was dissolved in N,N-dimethylacetamide, and ZIF-7 / CNTs composite was added. The mixture was stirred for 5–8 hours to obtain a casting solution. The solution was then extruded through a spinneret to form hollow fibers. The hollow fibers were soaked in deionized water for 36–48 hours, and then continuously soaked in ethanol and n-hexane for 2–10 hours, with the soaking solvent being changed every 30 minutes. Finally, the hollow fibers were dried in a vacuum oven at 60–80°C for 24–48 hours to obtain the composite fiber membrane material.

[0027] Example 1

[0028] The preparation method of the carbon nanotube metal-organic framework composite fiber membrane in this embodiment is as follows:

[0029] (1) Modification of carbon nanotubes

[0030] Argon was used as a protective gas at a flow rate of 150 sights, and the heating rate was 10℃ / min. After reaching 1500℃, the mixture was treated for 1 hour. 2.0 g of high-temperature annealed multi-walled carbon nanotubes (p-MWCNTs) were weighed into a 250 mL three-necked flask, and 120 mL of concentrated sulfuric acid and 40 mL of concentrated nitric acid were added sequentially. The mixture was ultrasonically stirred at room temperature for 5 hours. The mixture was then diluted and slowly poured into a 5000 mL beaker. The mixture was allowed to stand until the carbon nanotubes precipitated. The supernatant was discarded, and the lower suspension was filtered through a 0.22 μm PTFE membrane. The filtrate was repeatedly washed with distilled water until the pH of the filtrate was approximately 6. After filtration, the filtrate was vacuum dried at 60℃ for 24 hours to obtain acidified carbon nanotubes (c-MWCNTs).

[0031] (2) Synthesis of ZIF-7 / CNTs composite material

[0032] 2.43 g Zn(NO3)2·6H2O and 1.49 g Blm were dissolved in 300 ml DMF and stirred for 30 min. Then, 1.5 g of the modified c-MWCNT was added and stirred for another 30 min. The solution was then transferred to a Teflon stainless steel autoclave and heated at 100 °C for 72 h. After cooling to room temperature, ZIF-7 was obtained by centrifugation and washed three times with DMF. The ZIF-7 / CNT composite material was then dried in a vacuum drying oven at 80 °C for 15 h.

[0033] (3) Preparation of hollow fiber membranes from ZIF-7 / CNTs and PI

[0034] 2.8g of PI was dissolved in 50ml of DMAc and stirred for several hours. Then, 0.2g of ZIF-7 / CNTs was added and stirred for another 5 hours to obtain a casting solution. This solution was then extruded through a spinneret to form hollow fibers. The volatile solvent evaporated on the outermost layer of the fiber, forming a primary ultrathin selective layer. The original fiber was stretched in the air gap and then placed in a tap water bath to form a porous network under the skin layer. The hollow fibers were collected and soaked in deionized water for 36 hours to remove residual solvents and non-solvents. Then, they were continuously soaked in ethanol and n-hexane for 2 hours, with the solvent being changed every 30 minutes. Finally, the hollow fibers were dried in a vacuum oven at 60℃ for 24 hours to obtain the final hollow fiber membrane material.

[0035] Example 2

[0036] The preparation method of the carbon nanotube metal-organic framework composite fiber membrane in this embodiment is as follows:

[0037] (1) Modification of carbon nanotubes

[0038] Argon was used as a protective gas at a flow rate of 150 sights, and the heating rate was 10℃ / min. After reaching 1500℃, the temperature was treated for 1 hour. 3.0 g of high-temperature annealed multi-walled carbon nanotubes (p-MWCNTs) were weighed into a 250 mL three-necked flask, and 135 mL of concentrated sulfuric acid and 45 mL of concentrated nitric acid were added sequentially. The mixture was ultrasonically stirred at room temperature for 6 hours. The mixture was then diluted and slowly poured into a 5000 mL beaker. The mixture was allowed to stand until the carbon nanotubes precipitated. The supernatant was discarded, and the lower suspension was filtered through a 0.22 μm PTFE membrane. The filtrate was repeatedly washed with distilled water until the pH of the filtrate was approximately 6. After filtration, the filtrate was vacuum dried at 60℃ for 36 hours to obtain acidified carbon nanotubes (c-MWCNTs).

[0039] (2) Synthesis of ZIF-7 / CNTs composite material

[0040] 3.54 g Zn(NO3)2·6H2O and 2.96 g Blm were dissolved in 400 ml DMF and stirred for 45 min. Then, 2.5 g of the modified c-MWCNT was added and stirred for another 60 min. The solution was then transferred to a Teflon stainless steel autoclave and heated at 100 °C for 96 h. After cooling to room temperature, ZIF-7 was obtained by centrifugation. The ZIF-7 was washed several times with DMF and then dried in a vacuum drying oven at 80 °C for 30 h to obtain the ZIF-7 / CNTs composite material.

[0041] (3) Preparation of ZIF-7 / CNTs and PI composite membrane:

[0042] 2.5g of PI was dissolved in 100ml of DMAc and stirred for several hours. Then, 0.5g of ZIF-7 / CNTs was added and stirred for another 8 hours to obtain a casting solution. This solution was then extruded through a spinneret to form hollow fibers. The volatile solvent evaporated on the outermost layer of the fiber, forming a primary ultrathin selective layer. The original fiber was stretched in the air gap and then placed in a tap water bath to form a porous network under the skin layer. The hollow fibers were collected and soaked in deionized water for 48 hours to remove residual solvents and non-solvents. Then, they were continuously soaked in ethanol and n-hexane for 10 hours, with the solvent being changed every 30 minutes. Finally, the hollow fibers were dried in a vacuum oven at 80℃ for 48 hours to obtain the final hollow fiber membrane material.

[0043] Example 3

[0044] The preparation method of the carbon nanotube metal-organic framework composite fiber membrane in this embodiment is as follows:

[0045] (1) Modification of carbon nanotubes

[0046] Argon was used as a protective gas at a flow rate of 150 sights, and the heating rate was 10℃ / min. After reaching 1500℃, the temperature was treated for 1 hour. 3.5 g of high-temperature annealed multi-walled carbon nanotubes (p-MWCNTs) were weighed into a 250 mL three-necked flask, and 150 mL of concentrated sulfuric acid and 50 mL of concentrated nitric acid were added sequentially. The mixture was ultrasonically stirred at room temperature for 4 hours. The mixture was then diluted and slowly poured into a 5000 mL beaker. The mixture was allowed to stand until the carbon nanotubes precipitated. The supernatant was discarded, and the lower suspension was filtered through a polytetrafluoroethylene membrane with a pore size of 0.22 μm. The filtrate was repeatedly washed with distilled water until the pH of the filtrate was approximately 6. After filtration, the filtrate was vacuum dried at 60℃ for 48 hours to obtain acidified carbon nanotubes (c-MWCNTs).

[0047] (2) Synthesis of ZIF-7 / CNTs composite material

[0048] 2.21 g Zn(NO3)2·6H2O and 1.32 g Blm were dissolved in 350 ml DMF and stirred for 40 min. Then, 1.3 g of the modified c-MWCNT was added and stirred for another 40 min. The solution was then transferred to a Teflon stainless steel autoclave and heated at 100 °C for 100 h. After cooling to room temperature, ZIF-7 was obtained by centrifugation. The ZIF-7 was washed three times with DMF and then dried in a vacuum drying oven at 80 °C for 20 h to obtain the ZIF-7 / CNTs composite material.

[0049] (3) Preparation of hollow fiber membranes from ZIF-7 / CNTs and PI

[0050] 2.1g of PI was dissolved in 50ml of DMAc and stirred for several hours. Then, 0.4g of ZIF-7 / CNTs was added and stirred for another 6 hours to obtain a casting solution. This solution was then extruded through a spinneret to form hollow fibers. The volatile solvent evaporated on the outermost layer of the fiber, forming a primary ultrathin selective layer. The original fiber was stretched in the air gap and then placed in a tap water bath to form a porous network under the skin layer. The hollow fibers were collected and soaked in deionized water for 40 hours to remove residual solvents and non-solvents. Then, they were continuously soaked in ethanol and n-hexane for 5 hours, with the solvent being changed every 30 minutes. Finally, the hollow fibers were dried in a vacuum oven at 70℃ for 24 hours to obtain the final hollow fiber membrane material.

[0051] Example 4

[0052] The preparation method of the carbon nanotube metal-organic framework composite fiber membrane in this embodiment is as follows:

[0053] (1) Modification of carbon nanotubes

[0054] Argon was used as a protective gas at a flow rate of 150 sights, and the heating rate was 10℃ / min. After reaching 1500℃, the mixture was treated for 1 hour. 3.0 g of high-temperature annealed multi-walled carbon nanotubes (p-MWCNTs) were weighed into a 250 mL three-necked flask, and 125 mL of concentrated sulfuric acid and 60 mL of concentrated nitric acid were added sequentially. The mixture was ultrasonically stirred at room temperature for 8 hours. The mixture was then diluted and slowly poured into a 5000 mL beaker. The mixture was allowed to stand until the carbon nanotubes precipitated. The supernatant was discarded, and the lower suspension was filtered through a 0.22 μm PTFE membrane. The filtrate was repeatedly washed with distilled water until the pH of the filtrate was approximately 6. After filtration, the filtrate was vacuum dried at 60℃ for 40 hours to obtain acidified carbon nanotubes (c-MWCNTs).

[0055] (2) Synthesis of ZIF-7 / CNTs composite material

[0056] 4.91 g Zn(NO3)2·6H2O and 4.17 g Blm were dissolved in 400 ml DMF and stirred for 60 min. Then, 2.0 g of the modified c-MWCNT was added and stirred for another 50 min. The solution was then transferred to a Teflon stainless steel autoclave and heated at 100 °C for 80 h. After cooling to room temperature, ZIF-7 was obtained by centrifugation. The ZIF-7 was washed several times with DMF and then dried in a vacuum drying oven at 80 °C for 25 h to obtain the ZIF-7 / CNTs composite material.

[0057] (3) Preparation of ZIF-7 / CNTs and PI composite membrane:

[0058] 4.5 g of PI was dissolved in 100 ml of DMAc. After stirring for several hours, 0.8 g of ZIF-7 / CNTs was added, and stirring was continued for 8 hours to obtain a casting solution. This solution was then extruded through a spinneret to form hollow fibers. The volatile solvent evaporated on the outermost layer of the fiber, forming a primary ultrathin selective layer. The original fibers were stretched in the air gap and then placed in a tap water bath to form a porous network under the skin layer. The hollow fibers were collected and soaked in deionized water for 48 hours to remove residual solvents and non-solvents. Then, they were continuously soaked in ethanol and n-hexane for 10 hours, with the solvent being changed every 30 minutes. Finally, the hollow fibers were dried in a vacuum oven at 80°C for 48 hours to obtain the final hollow fiber membrane material. Its PXRD spectrum is shown below. Figure 1 As shown.

[0059] Figure 1 The PXRD spectra of CNTs, ZIF-7 / CNTs, and ZIF-7 simulated in Example 4 are shown.

[0060] Gas permeability tests were conducted on the carbon nanotube-metal-organic framework composite fiber membranes prepared in Examples 1-4, using pure polypropylene hollow fiber membranes as a control group. The gas permeability and separation performance of the carbon nanotube-metal-organic framework composite fiber membranes prepared in Examples 1-4 were evaluated using the constant volumetric pressure method at room temperature. The test gases were He, CH4, and N2. The test results are shown in Table 1.

[0061] Table 1

[0062] Example Helium permeability (bar) <![CDATA[Selectivity coefficient for He / CH4]]> <![CDATA[Selectivity coefficient for He / N2]]> Example 1 161 99 167 Example 2 170 117 184 Example 3 167 113 181 Example 4 173 112 188 Pure polypropylene 120 84 122

[0063] The data in Table 1 show that the carbon nanotube metal-organic framework composite fiber membrane of the present invention exhibits a high selectivity coefficient for helium. Compared with pure polypropylene, the helium permeability coefficient is increased by 44.16%, the selectivity coefficient for He / CH4 is increased by 39.29%, and the selectivity coefficient for He / N2 is increased by 54.1%. Therefore, the carbon nanotube metal-organic framework composite fiber membrane of the present invention can be used for the separation and purification of helium.

[0064] The above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit it. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the spirit and scope of the present invention, and all such modifications and substitutions should be covered within the scope of the claims of the present invention. Technical aspects, shapes, and structures not described in detail in this invention are all well-known technologies.

Claims

1. A carbon nanotube metal-organic framework composite fiber membrane, characterized by, The composite fiber membrane is made by mixing and spinning extruding polyimide and carbon nanotube metal organic framework composite, the weight fraction of the polyimide is 2.1-4.5 parts, and the weight fraction of the carbon nanotube metal organic framework composite is 0.2-0.8 parts; The carbon nanotube metal organic framework composite comprises the following raw materials in weight fractions: Zn(NO3)2·6H2O 2.21-4.91 parts, Blm 1.32-4.17 parts, and acidified carbon nanotubes 1.3-2.5 parts; The preparation method of the carbon nanotube metal organic framework composite fiber membrane comprises the following steps: Zn(NO3)2·6H2O and Blm are dissolved in dimethylformamide, acidified carbon nanotubes are added and stirred for 30-60 min, then the mixture is moved into an autoclave and heated at 95-120℃ for 72-100 h, after cooling to room temperature, centrifugal separation and washing with DMF, and drying in a vacuum drying oven at 75-85℃ for 15-30 h, a ZIF-7 / CNTs composite is obtained; Polyimide is dissolved in N,N-dimethylacetamide, the ZIF-7 / CNTs composite is added, and stirring is performed for 5-8 h to obtain a casting solution, the casting solution is extruded through a spinneret to form a hollow fiber, the hollow fiber is immersed in deionized water for 36-48 h, then continuously immersed in ethanol and n-hexane for 2-10 h, the immersion solvent is replaced every 30 min, and finally the hollow fiber is dried in a vacuum oven at 60-80℃ for 24-48 h to obtain a composite fiber membrane material.

2. The carbon nanotube metal-organic framework composite fiber membrane according to claim 1, wherein, The acidified carbon nanotubes are prepared as follows: After high-temperature treatment, concentrated sulfuric acid and concentrated nitric acid are sequentially added to the multi-walled carbon nanotubes, ultrasonic stirring is performed at room temperature for 4-8 h, then the mixture is diluted, left to stand until the carbon nanotubes precipitate, the supernatant is poured off, the lower suspension is filtered through a polytetrafluoroethylene membrane with a pore size of 0.22 μm, repeatedly washed with distilled water until the filtrate pH≈6, and the filtered solid is vacuum dried at 55-65℃ for 24-48 h to obtain acidified carbon nanotubes.

3. The carbon nanotube metal-organic framework composite fiber membrane according to claim 2, wherein, The high-temperature treatment is as follows: the multi-walled carbon nanotubes are placed in a sealed reaction furnace with argon gas, the reaction furnace is heated at a rate of 10℃ / min to 1450-1600℃, and then held for 0.8-1.5 h.

4. The carbon nanotube metal-organic framework composite fiber membrane according to claim 3, wherein, The volume fraction of the concentrated sulfuric acid is 120-150 parts, and the volume fraction of the concentrated nitric acid is 40-60 parts.

5. The carbon nanotube metal-organic framework composite fiber membrane of claim 4, wherein, The mass fraction of Zn(NO3)2·6H2O is 2.21-4.91 parts, the mass fraction of Blm is 1.32-4.17 parts, and the mass fraction of acidified carbon nanotubes is 1.3-2.5 parts.

6. The carbon nanotube metal organic framework composite fiber membrane according to any one of claims 1-5, for use in helium gas separation and purification.

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