Method for preparing single-walled carbon nanotube by taking papermaking black liquor crude extract as raw material

Abstract

The invention discloses a method for preparing a single-walled carbon nanotube by using a papermaking black liquor crude extract as a raw material. The single-walled carbon nanotube can be obtained through the steps of dilute phosphoric acid solution-ultrasonic combined leaching, microwave pyrolysis, water vapor circulation gas bath, aerobic calcination and the like. The obtained single-walled carbon nanotube is good in quality, uniform in size, uniform in tube diameter distribution, high in purity, high in preparation efficiency, wide in raw material source, green and environment-friendly in preparation process, low in production cost, simple in preparation method and easy for industrial production. According to the method, resource utilization of the papermaking black liquor is effectively improved, high additional value is achieved, recycling and utilization of lignin, metal and other useful components in the black liquor can be achieved, environmental pollution and resource waste are avoided, the technological approach of turning waste into wealth is achieved, and the win-win purpose of economic benefits and environmental protection is achieved. The method for preparing the single-walled carbon nanotube based on the papermaking black liquor is provided for the first time, and a new idea and a new choice are provided for preparation of the carbon nanotube.

Description

Technical Field

[0001] The invention relates to the technical field of carbon material preparation, and in particular to a method for preparing single-walled carbon nanotubes by taking a crude extract of papermaking black liquor as a raw material. Background Art

[0002] Carbon nanotubes are an excellent one-dimensional nanomaterial, which can be divided into single-walled carbon nanotubes (SWNT), double-walled carbon nanotubes (DWNT) and multi-walled carbon nanotubes (MWNT) according to the number of layers forming the tube wall. Among them, single-walled carbon nanotubes can be regarded as seamless hollow tubes formed by curling a single layer of graphite around the central axis at a certain spiral angle. They have a very high aspect ratio and exhibit excellent mechanical, electrical, thermal, optical and other properties. Therefore, single-walled carbon nanotubes have potential and extensive application value in different fields such as composite materials, new energy battery electrode materials, optoelectronic devices, biomedicine, heat transfer elements, and biological and chemical sensors.

[0003] Papermaking black liquor is wastewater produced in the alkaline pulping process (caustic soda process and sulfate process), containing a large amount of suspended solids, organic pollutants and toxic substances. At present, papermaking industrial wastewater in my country accounts for about 10% of the total industrial wastewater in the country, and most of it is directly discharged into water bodies, which has caused increasingly obvious pollution to water resources and environment. Lignin is the main component of papermaking black liquor, and it is also the second largest natural polymer material in nature after cellulose. However, lignin has a complex structure and is difficult to decompose. Most of it is discharged into the sea with papermaking black liquor or burned after simple concentration. Not only does it fail to achieve comprehensive resource utilization, but it also places a great burden on the environment. Therefore, it has become an urgent problem to realize efficient resource utilization of lignin and turn it from waste to treasure.

[0004] Improving the resource utilization of lignin in papermaking black liquor has been a research hotspot in recent years. For example, invention patent CN105198262B discloses a method for preparing a high-efficiency concrete water reducer using papermaking black liquor, which uses a filter to remove insoluble matter, adds acetic acid and sulfuric acid to pre-treat the papermaking black liquor, and then concentrates the pre-treated papermaking black liquor to increase its lignin content, and then adds diethanolamine, acrylic acid, sodium persulfate and sodium methyl methacrylate sulfonate to prepare a high-efficiency concrete water reducer. Invention patent CN106179496B discloses a method for preparing a lignin-based hydrothermal carbon sulfonic acid catalyst, which uses alkaline lignin in industrial papermaking waste liquid as raw material, and prepares a hydrothermal carbon sulfonic acid catalyst through refining, purification, hydrothermal carbonization and sulfonation. Although the main component of papermaking black liquor is lignin, it is affected by various other complex substances, and the obtained product often still has the disadvantages of high impurity content and many by-products, thereby affecting the purity and application effect of the product. Therefore, it is of great significance to develop a new process for preparing high-purity products from papermaking black liquor, which can not only achieve high added value of papermaking black liquor, but also open up a new way for the resource utilization of papermaking black liquor biomass and expand its application scope. Summary of the invention

[0005] In view of the above problems existing in the prior art, the present invention provides a method for preparing single-walled carbon nanotubes using a crude extract of papermaking black liquor as a raw material, thereby solving the problems of widespread environmental pollution and waste of resources caused by papermaking black liquor, as well as high impurity content and a large number of by-products due to its complex composition.

[0006] To achieve the above object, the present invention adopts the following scheme: a method for preparing single-walled carbon nanotubes using crude extract of papermaking black liquor as raw material, comprising the following steps:

[0007] 1) Adding a dilute phosphoric acid solution to the crude extract of papermaking black liquor, and then placing it in an ultrasonic treatment for dilute phosphoric acid solution-ultrasonic combined leaching to obtain an acid leached product; in this way, the ultrasonic wave is used to assist the leaching with its strong penetrating power, concentrated energy and direct action, and cooperates with the dilute phosphoric acid to shorten the dissolution time of impurities, and preliminarily eliminate the impurities in the crude extract of papermaking black liquor.

[0008] 2) Using a water vapor circulation system, the acid-leached product obtained in step 1) is subjected to air bath washing pretreatment, and then centrifuged and vacuum dried to obtain a precursor; in this way, the circulating airflow takes away most of the retained ash impurities, avoiding the subsequent strong acid cleaning process that may be required.

[0009] 3) Passing protective gas into the microwave tube furnace 1 and the microwave tube furnace 2 of the two-cavity microwave heating furnace to exclude air, the microwave tube furnace 1 and the microwave tube furnace 2 are connected by a gas valve, placing the precursor obtained in step 2) in the microwave tube furnace 1, placing the precursor obtained in step 2) in the microwave tube furnace 1, and placing a shallow crucible containing nano-scale tungsten powder particles in the microwave tube furnace 2, then raising the temperatures of the microwave tube furnace 1 and the microwave tube furnace 2 to 1125-1325° C. at the same time, and then controlling the gas flow rate of the precursor vapor in the microwave tube furnace 1 to evenly enter the microwave tube furnace 2 through the gas valve, so that it fully reacts with the tungsten powder, and then cooling to room temperature, and collecting black powder; in this way, the protective atmosphere is passed before and after heating to prevent possible experimental risks, and the gas rate is based on maintaining a non-oxidizing atmosphere and preventing the generated carbon nanotubes from being taken away, which relatively saves the amount of protective gas and fully practices the concept of sustainable development. Microwaves can heat rapidly and intensively, and can quickly crack the carbon source in the crude extract of papermaking black liquor and form carbon vapor; at the same time, the same high temperature is maintained in another furnace chamber, allowing the carbon vapor to land on the nanoscale tungsten powder particles (as the heteronuclear growth substrate of single-walled carbon nanotubes) and grow to obtain single-walled carbon nanotubes. Among them, if the microwave heating temperature is too low, it is difficult to meet the thermodynamic growth conditions of carbon nanotubes, thereby forming impurities such as carbon microspheres; if the carbon vapor introduction rate is too fast, it will cause unstable airflow in the cranial cavity, and at the same time produce a variety of allotropes such as carbon fibers, spiral carbon, and carbon microspheres, reducing the purity of the carbon nanotubes. The preparation principle of the single-walled nanotubes of the present invention is as follows: Figure 1 As shown, at high temperature, carbon vapor uses tungsten atoms as a substrate to perform non-uniform nucleation growth. At this time, the critical nucleation work required is much lower than that of uniform nucleation growth. The precise control of the microwave heating temperature and the gas flow rate of the precursor by the present invention provides a stable thermodynamic growth environment for it.

[0010] 4) The black powder obtained in step 3) is heated to 180-200°C for aerobic calcination, and then placed in a water vapor circulation system for air bath washing, and then the washed product is vacuum dried to obtain the single-walled carbon nanotubes. In this way, by effectively controlling the temperature during aerobic calcination, a small amount of low-melting-point allotropes in the carbon nanotubes are effectively removed without affecting the precursor of the carbon nanotubes themselves; further, by using a circulating water vapor washing method, the large contact surface of the circulating washing is fully utilized to remove impurities and ash from the carbon nanotubes, and high-purity single-walled carbon nanotubes are obtained.

[0011] Preferably, the crude extract of papermaking black liquor refers to papermaking black liquor obtained by sequentially concentrating, sulfonating, and powder spraying and drying.

[0012] Preferably, the concentration of the dilute phosphoric acid solution in step 1) is 9% to 11%, and the power of the ultrasonic wave is 900 to 1100W.

[0013] Preferably, the vacuum degree of the vacuum drying is 0.005-0.01 MPa.

[0014] Preferably, the protective gas is argon gas, the purity of the protective gas is 99.99%, and the gas flow rate of the protective gas is 0.05-0.1 m 3 / h.

[0015] Preferably, the microwave heating rate in step 3) is 180-200°C / min.

[0016] Preferably, the air flow rate in step 3) is 0.05-0.1 m 3 / h, the reaction time is 20 to 30 minutes.

[0017] Another object of the present invention is to provide single-walled carbon nanotubes prepared by the above method.

[0018] Another object of the present invention is to provide the use of the above-mentioned single-walled carbon nanotubes in electrode materials, composite materials, flexible electronic devices or drug carriers. Specifically, they can be used as electrode material additives for secondary batteries and supercapacitors, catalyst carriers for fuel cells, composite materials for the aerospace field, flexible electronic devices in the semiconductor field, and drug carriers in the biomedical field.

[0019] Compared with the prior art, the present invention has the following beneficial effects:

[0020] 1. The present invention uses the crude extract of papermaking black liquor as raw material, and single-walled carbon nanotubes can be obtained through the steps of dilute phosphoric acid solution-ultrasonic combined leaching, microwave high-temperature cracking, water vapor circulation air bath and aerobic calcination. Through the precise control of the heating temperature of the microwave and the air flow rate of the precursor vapor, the obtained single-walled carbon nanotubes are of good quality, uniform size, uniform tube diameter distribution, and few by-products. Furthermore, the impurities in the product are greatly reduced through the steps of ultrasonic combination, water vapor circulation air bath and aerobic calcination, thereby improving the purity of the single-walled nanotubes. The present invention has high preparation efficiency, few by-products, a wide range of raw material sources, a green and environmentally friendly preparation process, low production cost, and a simple preparation method, which is easy to industrialize and produce, achieving the win-win goal of economic benefits and environmental protection, and has very important practical significance for the sustainable development of mankind and has good application prospects.

[0021] 2. The present invention effectively improves the resource utilization of papermaking black liquor, achieves high added value, can better solve the management problems faced by wood pulp papermaking black liquor, can realize the recovery and utilization of lignin in black liquor, and also avoids environmental pollution and resource waste, realizes the process of turning waste into treasure, and promotes the sustainable development of the economy. And for the first time, it is proposed to prepare single-walled carbon nanotubes based on papermaking black liquor, which provides a new idea and new choice for the preparation of carbon nanotubes. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 Schematic diagram of the preparation principle of single-walled nanotubes of the present invention.

[0023] Figure 2 This is a scanning electron microscope image of the single-walled nanotubes prepared in Example 1.

[0024] Figure 3 This is a scanning electron microscope image of the single-walled nanotubes prepared in Example 2.

[0025] Figure 4 This is a scanning electron microscope image of the single-walled nanotubes prepared in Example 3.

[0026] Figure 5 This is the XRD pattern of the single-walled nanotubes prepared in the present invention.

[0027] Figure 6 Scanning electron microscope image of single-walled nanotubes prepared in Comparative Example 1

[0028] Figure 7 This is a scanning electron microscope image of the single-walled nanotubes prepared in Comparative Example 2.

[0029] Figure 8 This is a scanning electron microscope image of the single-walled nanotubes prepared in Comparative Example 3. DETAILED DESCRIPTION

[0030] The present invention is further described in detail below in conjunction with specific examples. In the following examples, if no special description is given to the experimental methods, all are conventional operations, and the reagents used are commercially available.

[0031] The scanning electron microscope used in the following embodiments is Sigma300 (made in: Carl Zeiss Microscopy Limited), the X-ray diffractometer is D2PHASER (made in: Bruker AXS, Germany), the integrated constant temperature battery test box is MIHW-200-160CH (made in: Shenzhen Xinwell Electronics Co., Ltd.), the ultrasonic crusher is ZOLLO-650Y (Shanghai Zuole Instrument Co., Ltd.), and the experimental water is distilled water.

[0032] 1. A method for preparing single-walled carbon nanotubes using crude extract of papermaking black liquor as raw material.

[0033] Embodiment 1: The steps of this embodiment are as follows:

[0034] 1) The papermaking black liquor is sequentially concentrated, sulfonated, and powder-dried to obtain a crude papermaking black liquor extract, and then a 10% (v / v) dilute phosphoric acid solution is added to the crude papermaking black liquor extract, and then the extract is placed in an ultrasonic wave set at 1000W for 12 hours for dilute phosphoric acid solution-ultrasonic wave combined leaching to obtain an acid leached product.

[0035] 2) The acid-leached product obtained in step 1) is subjected to air bath washing pretreatment using a water vapor circulation system, and then centrifuged and vacuum dried for 12 hours while maintaining a vacuum degree of 0.01 MPa to obtain a precursor.

[0036] 3) Add 99.99% pure argon gas at a flow rate of 0.1m 3 / h is passed into the microwave tube furnace 1 and the microwave tube furnace 2 of the two-cavity microwave heating furnace to exclude air, the microwave tube furnace 1 and the microwave tube furnace 2 are connected by an air valve, 10g of the precursor obtained in step 2) is weighed and loaded into a shallow dry corundum crucible and placed in the microwave tube furnace 1, and a shallow crucible filled with nano-scale tungsten powder particles is placed in the microwave tube furnace 2, and then the microwave tube furnace 1 and the microwave tube furnace 2 are simultaneously raised to 1225°C, the heating rate is 180°C / min, and the gas flow rate of the precursor vapor in the microwave tube furnace 1 entering the microwave tube furnace 2 is controlled by the air valve to be 0.075m 3 / h, the reaction continued for 25 min, then cooled to room temperature and black powder was collected.

[0037] 4) The black powder obtained in step 3) is heated to 180-200° C. for aerobic calcination, and then placed in a water vapor circulation system for air bath washing. The washed product is then vacuum dried for 12 hours to obtain the single-walled carbon nanotubes. At the same time, the washing residue is concentrated by utilizing the density difference to recover the valuable metals therein.

[0038] The carbon nanotubes prepared in this example were observed under a scanning electron microscope. Figure 2 The results show that the prepared carbon nanotubes have a fairly regular fiber aspect ratio and uniform size. They are basically single-walled carbon nanotubes with a yield of 41%. There are no obvious carbon allotropes such as carbon fibers, helical carbon, and carbon microspheres.

[0039] Embodiment 2: The steps of this embodiment are as follows:

[0040] 1) The papermaking black liquor is sequentially concentrated, sulfonated, and powder-dried to obtain a crude papermaking black liquor extract, and then a 10% (v / v) dilute phosphoric acid solution is added to the crude papermaking black liquor extract, and then the extract is placed in an ultrasonic wave set at 1000W for 12 hours for dilute phosphoric acid solution-ultrasonic wave combined leaching to obtain an acid leached product.

[0041] 2) The acid-leached product obtained in step 1) is subjected to air bath washing pretreatment using a water vapor circulation system, and then centrifuged and vacuum dried for 12 hours while maintaining a vacuum degree of 0.01 MPa to obtain a precursor.

[0042] 3) Add 99.99% pure argon gas at a flow rate of 0.1m 3 / h is passed into the microwave tube furnace 1 and the microwave tube furnace 2 of the two-cavity microwave heating furnace to exclude air, the microwave tube furnace 1 and the microwave tube furnace 2 are connected by an air valve, 10g of the precursor obtained in step 2) is weighed and loaded into a shallow dry corundum crucible and placed in the microwave tube furnace 1, and a shallow crucible containing nano-scale tungsten powder particles is placed in the microwave tube furnace 2, and then the microwave tube furnace 1 and the microwave tube furnace 2 are simultaneously raised to 1125°C, the heating rate is 180°C / min, and the gas flow rate of the precursor vapor in the microwave tube furnace 1 entering the microwave tube furnace 2 is controlled by the air valve to be 0.075m 3 / h, the reaction continued for 25 min, then cooled to room temperature and black powder was collected.

[0043] 4) The black powder obtained in step 3) is heated to 180-200° C. for aerobic calcination, and then placed in a water vapor circulation system for air bath washing. The washed product is then vacuum dried for 12 hours to obtain the single-walled carbon nanotubes. At the same time, the washing residue is concentrated by utilizing the density difference to recover the valuable metals therein.

[0044] The carbon nanotubes prepared in this example were observed under a scanning electron microscope. Figure 3 The results show that the prepared carbon nanotubes have a fairly regular fiber aspect ratio and uniform size. They are basically single-walled carbon nanotubes with a yield of 33%. There are no obvious carbon allotropes such as carbon fibers, helical carbon, and carbon microspheres.

[0045] Embodiment 3: The steps of this embodiment are as follows:

[0046] 1) The papermaking black liquor is sequentially concentrated, sulfonated, and powder-dried to obtain a crude papermaking black liquor extract, and then a 10% (v / v) dilute phosphoric acid solution is added to the crude papermaking black liquor extract, and then the extract is placed in an ultrasonic wave set at 1000W for 12 hours for dilute phosphoric acid solution-ultrasonic wave combined leaching to obtain an acid leached product.

[0047] 2) The acid-leached product obtained in step 1) is subjected to air bath washing pretreatment using a water vapor circulation system, and then centrifuged and vacuum dried for 12 hours while maintaining a vacuum degree of 0.01 MPa to obtain a precursor.

[0048] 3) Add 99.99% pure argon gas at a flow rate of 0.1m 3 / h is passed into the microwave tube furnace 1 and the microwave tube furnace 2 of the two-cavity microwave heating furnace to exclude air, the microwave tube furnace 1 and the microwave tube furnace 2 are connected by an air valve, 10g of the precursor obtained in step 2) is weighed and loaded into a shallow dry corundum crucible and placed in the microwave tube furnace 1, and a shallow crucible filled with nano-scale tungsten powder particles is placed in the microwave tube furnace 2, and then the microwave tube furnace 1 and the microwave tube furnace 2 are simultaneously raised to 1325°C, the heating rate is 180°C / min, and the gas flow rate of the precursor vapor in the microwave tube furnace 1 entering the microwave tube furnace 2 is controlled by the air valve to be 0.075m 3 / h, the reaction continued for 25 min, then cooled to room temperature and black powder was collected.

[0049] 4) The black powder obtained in step 3) is heated to 180-200° C. for aerobic calcination, and then placed in a water vapor circulation system for air bath washing. The washed product is then vacuum dried for 12 hours to obtain the single-walled carbon nanotubes. At the same time, the washing residue is concentrated by utilizing the density difference to recover the valuable metals therein.

[0050] The carbon nanotubes prepared in this example were observed under a scanning electron microscope. Figure 4 The results show that the prepared carbon nanotubes have a fairly regular fiber aspect ratio and uniform size. They are basically single-walled carbon nanotubes with a yield of 39%. There are no obvious carbon allotropes such as carbon fibers, helical carbon, and carbon microspheres.

[0051] Furthermore, the single-walled carbon nanotubes prepared in Examples 1 to 3 were subjected to XRD testing, and the results were as follows: Figure 5 As shown. The results show that the XRD diffraction peaks of the carbon nanotubes of the present invention are displayed at 2θ=25° and 45°, corresponding to the (002) and (100) diffraction crystal planes, respectively, indicating that the main component is the carbon nanotubes with graphitized structure, wherein the position of the (002) crystal plane diffraction peak is used to determine the number of layers and diameter of the carbon nanotubes, and the position of the (100) crystal plane diffraction peak is used to characterize the structure and arrangement of the carbon nanotubes. The single-walled carbon nanotubes prepared by this method are of high purity and free of impurities.

[0052] Comparative Example 1: In this comparative example, the temperature of microwave tube furnace 1 and microwave tube furnace 2 is raised to 1025°C at the same time, and the gas flow rate of the precursor vapor entering the microwave tube furnace 2 is 0.15m 3 / h, and other steps are the same as in Example 1.

[0053] Comparative Example 2: In this comparative example, the temperature of microwave tube furnace 1 and microwave tube furnace 2 is raised to 925°C at the same time, and the gas flow rate of the precursor vapor entering the microwave tube furnace 2 is 0.175m 3 / h, and other steps are the same as in Example 1.

[0054] Comparative Example 3: In this comparative example, the temperature of microwave tube furnace 1 and microwave tube furnace 2 is raised to 725°C at the same time, and the gas flow rate of the precursor vapor entering the microwave tube furnace 2 is 0.175m 3 / h, and other steps are the same as in Example 1.

[0055] The products prepared in Comparative Examples 1 to 3 were observed under a scanning electron microscope. Figures 6 to 8 The results show that: the product of comparative example 1 has obvious carbon microsphere allotropes ( Figure 6 ), the product of comparative example 2 obviously contains various allotropes such as carbon fiber and carbon microspheres ( Figure 7 ), and the product of comparative example 3 even showed various allotropes such as carbon fiber, helical carbon, and carbon microspheres ( Figure 8 ). It can be seen that the carbon nanotubes obtained in the comparative example are of low purity and are prone to produce various allotropic byproducts such as carbon fibers, helical carbons, and carbon microspheres. This may be due to the low reaction temperature or unstable carbon source gas flow rate, which will greatly affect the application effect of single-walled carbon nanotubes in practice.

[0056] Finally, it should be noted that the above embodiments are only used to illustrate the technical solution of the present invention rather than to limit it. Although the applicant has described the present invention in detail with reference to the preferred embodiments, ordinary technicians in the field should understand that modifications or equivalent substitutions of the technical solution of the present invention without departing from the purpose and scope of the technical solution of the present invention should be included in the scope of the claims of the present invention.

Claims

1. A method for preparing single-walled carbon nanotubes using a crude extract of papermaking black liquor as a raw material, characterized in that: The following steps are involved: 1) adding a dilute phosphoric acid solution to the crude extract of papermaking black liquor, and then placing it in an ultrasonic treatment for dilute phosphoric acid solution-ultrasonic combined leaching to obtain an acid leached product; 2) using a water vapor circulation system to pre-treat the acid-leached product obtained in step 1) by gas bath washing, and then centrifuging and vacuum drying to obtain a precursor; 3) Passing protective gas into the microwave tube furnace 1 and the microwave tube furnace 2 of the two-cavity microwave heating furnace to exclude air, the microwave tube furnace 1 and the microwave tube furnace 2 are connected by a gas valve, placing the precursor obtained in step 2) in the microwave tube furnace 1, and placing a shallow crucible filled with nano-scale tungsten powder particles in the microwave tube furnace 2, then raising the temperature of the microwave tube furnace 1 and the microwave tube furnace 2 to 1125-1325° C. at the same time, and then controlling the gas flow rate of the precursor vapor in the microwave tube furnace 1 to evenly enter the microwave tube furnace 2 through the gas valve, so that it fully reacts with the tungsten powder, and then cooling to room temperature, and collecting black powder; 4) The black powder obtained in step 3) is heated to 180-200° C. for aerobic calcination, and then placed in a water vapor circulation system for air bath washing, and then the washed product is vacuum dried to obtain the single-walled carbon nanotubes.

2. The method for preparing single-walled carbon nanotubes using crude extract of papermaking black liquor as raw material according to claim 1, characterized in that: The crude extract of papermaking black liquor refers to the papermaking black liquor obtained by sequentially concentrating, sulfonating, and powder spraying and drying.

3. The method for preparing single-walled carbon nanotubes using crude extract of papermaking black liquor as raw material according to claim 1, characterized in that: The concentration of the dilute phosphoric acid solution in step 1) is 9% to 11%, and the power of the ultrasonic wave is 900 to 1100W.

4. The method for preparing single-walled carbon nanotubes using crude extract of papermaking black liquor as raw material according to claim 1, characterized in that: The vacuum degree of the vacuum drying is 0.005-0.01 MPa.

5. The method for preparing single-walled carbon nanotubes using crude extract of papermaking black liquor as raw material according to claim 1, characterized in that: The protective gas is argon gas, the purity of the protective gas is 99.99%, and the gas flow rate of the protective gas is 0.05-0.1m 3 / h.

6. The method for preparing single-walled carbon nanotubes based on crude extract of papermaking black liquor according to claim 1, characterized in that: The rate of microwave heating in step 3) is 180-200°C / min.

7. The method for preparing single-walled carbon nanotubes based on crude extract of papermaking black liquor according to claim 1, characterized in that: The airflow rate in step 3) is 0.05-0.1 m 3 / h.

8. The method for preparing single-walled carbon nanotubes based on crude extract of papermaking black liquor according to claim 1, characterized in that: The reaction time in step 3) is 20 to 30 minutes.

9. The single-walled carbon nanotube prepared by the method according to any one of claims 1 to 8.

10. Use of the single-walled carbon nanotube according to claim 9 in electrode materials, composite materials, flexible electronic devices or drug carriers.

Images