Method for purifying single-walled carbon nanotubes based on supercritical fluid co-extraction

Abstract

The application discloses a single-walled carbon nanotube purification method based on supercritical fluid synergistic extraction, which comprises the following steps: mixing hydrogen peroxide aqueous solution with single-walled carbon nanotubes, heating under a certain pressure after CO2 is introduced, opening a UV lamp and stirring, and cooling and pressure releasing; mixing weak acid with a metal chelating agent uniformly and then adding the mixture into the above reaction kettle, heating under a certain pressure after CO2 is introduced, cooling and pressure releasing after the stirring reaction is completed. When the single-walled carbon nanotubes are purified, the single-walled carbon nanotubes are first treated by using H2O2 under the high-pressure environment of CO2 supercritical fluid, -OH free radicals are generated by decomposing H2O2 through UV light excitation, and amorphous carbon, graphite shell and metal impurities in the single-walled carbon nanotubes are oxidized; then, the remaining metal elements are first converted into metal salt solution by using supercritical CO2 fluid, acid and metal chelating agent, and then neutral organic molecular type metal chelates are generated, so that the purpose of high-efficiency impurity removal is achieved.

Description

Technical Field

[0001] This invention relates to the field of nanomaterial purification technology, and in particular to a purification method for single-walled carbon nanotubes based on supercritical fluid synergistic extraction. Background Technology

[0002] Single-walled carbon nanotubes (SWNTs) exhibit broad application prospects in electronic devices, composite materials, and energy storage due to their unique electrical, thermal, and mechanical properties. Currently, arc discharge is one of the most practical methods for preparing SWNTs; however, the resulting SWNTs typically contain a large number of metal catalyst particles (such as iron, cobalt, and nickel) and amorphous carbon impurities. These impurities severely affect the intrinsic properties and practical applications of SWNTs. Common purification methods include high-temperature heat treatment and wet chemical methods. High-temperature heat treatment typically uses different oxidizing gases at 300-700℃. While this method can remove impurities such as amorphous carbon and graphite flakes, the removal effect is limited, energy consumption is high, and it can damage the structure of SWNTs. Traditional wet chemical methods often use strong oxidizing acids such as concentrated sulfuric acid or concentrated nitric acid combined with hydrogen peroxide or potassium permanganate. Although this can effectively remove some metal impurities, the strong oxidation process can damage the structure of SWNTs, leading to decreased conductivity, and the waste liquid is difficult to treat, causing environmental pollution. For example, while the concentrated nitric acid or concentrated sulfuric acid method used in CN113003565A is simple, it severely damages the carbon nanotube structure. CN109650379B, although reducing damage through gradient oxidation and acid washing, is complex and costly. Supercritical fluid technology, using fluids above their critical temperature and pressure, has shown unique advantages in recent years as an emerging purification method. Supercritical carbon dioxide (sc-CO2) possesses gas-like high diffusivity and liquid-like good solubility, effectively penetrating carbon nanotube bundles. Under suitable conditions, it can remove metallic impurities encapsulated in carbon nanotubes without damaging their structure. Studies have shown that within a temperature range of 35-75℃ and a pressure range of 250-400 atm, sc-CO2 can achieve a metal impurity removal efficiency of up to 80% for the purification of Hipco and Swan single-walled carbon nanotubes. However, there is still room for improvement in the extraction efficiency relying solely on supercritical CO2, especially for metal catalyst particles tightly bound within the carbon nanotube structure.

[0003] Therefore, it is crucial to develop a method that can efficiently remove impurities from single-walled carbon nanotubes while preserving the original structural integrity of the single-walled carbon nanotubes to the greatest extent possible. Summary of the Invention

[0004] To address the aforementioned problems, the purpose of this invention is to provide a method for purifying single-walled carbon nanotubes based on supercritical fluid synergistic extraction, thereby solving the problems of existing carbon nanotube purification methods, such as damage to the single-walled carbon nanotube structure and limited impurity removal efficiency.

[0005] To achieve the above objectives, this invention first provides a method for purifying single-walled carbon nanotubes based on supercritical fluid synergistic extraction, comprising the following steps: (1) Mix hydrogen peroxide aqueous solution with single-walled carbon nanotubes and put them into a high-pressure heated and stirred reactor equipped with UV lamp. After CO2 is introduced, pressurize to 15-30 MPa and heat to 40-70℃. Turn on the UV lamp and start stirring. After stirring, reduce the pressure to 7 MPa, cool down and release the pressure. (2) After the weak acid and the metal chelating agent are mixed evenly, they are added to the reaction vessel of step (1). After CO2 is introduced, the pressure is increased to 15-30 MPa and heated to 40-80℃. At the same time, the CO2 fluid in the reaction vessel is kept in an outward flow state. After the reaction is completed by stirring, the temperature is reduced and the pressure is released. The material is taken out, washed and dried to obtain the purified single-walled carbon nanotubes.

[0006] In one embodiment of the present invention, the mass fraction of the hydrogen peroxide aqueous solution in step (1) is 30%, and the mass ratio of the hydrogen peroxide aqueous solution to the single-walled carbon nanotube is 3:1 to 7:1.

[0007] In one embodiment of the present invention, in step (1), the reactor contains a dual-channel gas inlet and outlet. Preferably, the pressure in the reactor is 20 MPa and the temperature is 55°C. The CO2 is high-purity CO2 with a purity of 99.9% or higher.

[0008] In one embodiment of the present invention, in step (1), the stirring time is 30~120min, preferably 100min.

[0009] In one embodiment of the present invention, in step (1), after stirring, the pressure is repeatedly reduced from 15-30 MPa to 7 MPa 2-5 times. That is, after reducing the pressure from 15-30 MPa to 7 MPa, the pressure is then increased back to 15-30 MPa and reduced to 7 MPa, and this process is repeated. The reason for repeatedly increasing and decreasing the pressure is that when the supercritical CO2 fluid flows through the interior of the single-walled carbon nanotubes, the repeated increase and decrease in pressure causes the CO2 gas to change between the supercritical fluid and gas states. The CO2 gas expands, thereby opening the aggregated single-walled carbon nanotubes, exposing the metal impurities, and facilitating subsequent impurity removal.

[0010] In one embodiment of the present invention, in step (2), the weak acid is formic acid or acetic acid, and the metal chelating agent is selected from at least one of acetylacetone, hexafluoroacetylacetone, sodium diethyldithiocarbamate, and 8-hydroxyquinoline.

[0011] In one embodiment of the present invention, in step (2), the mass ratio of the weak acid to the metal chelating agent is 2:1 to 6:1, preferably 4:1.

[0012] In one embodiment of the present invention, in step (2), the mass ratio of the mixed solution of weak acid and metal chelating agent to the single-walled carbon nanotubes in the reaction vessel is 40~80:1, preferably 70:1.

[0013] In one embodiment of the present invention, in step (2), the stirring reaction time is 60~180min, preferably 150min.

[0014] In one embodiment of the present invention, in step (2), the single-walled carbon nanotubes after stirring reaction are cleaned with anhydrous ethanol 2 to 5 times until the solution is colorless and transparent, and then vacuum dried at a temperature of 60-80°C for 3-6 hours.

[0015] The purification mechanism of this invention is as follows: First, H2O2 is introduced into the interior of single-walled carbon nanotubes under high pressure in a supercritical CO2 fluid environment. Then, UV light excitation causes H2O2 to decompose, generating a large number of -OH free radicals. These free radicals have extremely strong oxidizing power and can oxidize the amorphous carbon and graphite shells in the single-walled carbon nanotubes into CO and CO2. This removes impurities from the amorphous carbon and graphite shells while exposing metallic impurities. Simultaneously, some metallic impurities are oxidized into metal ions, such as Fe(OH)2. 3+ And it enters the H2O solution after the H2O2 reaction decomposes from the solid particles.

[0016] Then, under supercritical CO2 fluid conditions, acid and metal chelating agents are added to convert the remaining elemental metal into a metal salt solution, which then reacts with the metal chelating agent to generate neutral, organic molecular metal chelates. Metal chelates are solids at room temperature and pressure, but under supercritical CO2 fluid conditions, they are "super solvents" with extraordinary solubility for nonpolar / weakly polar organic molecules. The newly generated solid chelates immediately dissolve into the surrounding supercritical CO2 fluid, and the impurities are carried away by the continuously flowing supercritical CO2 fluid. Finally, the residual metal chelates in the single-walled carbon nanotubes are washed away with an organic solution.

[0017] The present invention also discloses a single-walled carbon nanotube prepared using the above purification method.

[0018] The present invention also discloses an application of the above-mentioned single-walled carbon nanotubes in the fields of electronic devices, composite materials and energy storage.

[0019] Beneficial effects: (1) In the purification of single-walled carbon nanotubes, the present invention first uses H2O2 to treat the single-walled carbon nanotubes under high pressure in a supercritical CO2 fluid environment. By exciting H2O2 with UV light, a large number of -OH free radicals are generated, which oxidize the amorphous carbon and graphite shells in the single-walled carbon nanotubes into CO and CO2, and at the same time oxidize the metal impurities. Then, on this basis, supercritical CO2 fluid, acid and metal chelating agent are used to convert the remaining metal elements into metal salt solutions, and then react with metal chelating agents to generate neutral, organic molecular metal chelates, so as to achieve the purpose of efficient impurity removal.

[0020] (2) In this invention, when using hydrogen peroxide to remove impurities, supercritical CO2 fluid is used. On the one hand, supercritical CO2 fluid assists in the decomposition of H2O2 to generate -OH free radicals. On the other hand, supercritical CO2 fluid can carry H2O2 into the interior of single-walled carbon nanotubes so that the generated free radicals can contact the single-walled carbon nanotubes more efficiently, thereby achieving the purpose of more efficient impurity removal.

[0021] (3) In the present invention, when using hydrogen peroxide to remove impurities, after removing impurities, the pressure of the reaction system is repeatedly adjusted. When the supercritical CO2 fluid flows through the interior of the single-walled carbon nanotube, the pressure is repeatedly increased and decreased, so that the CO2 gas changes between the two states of supercritical fluid and gas. The CO2 gas expands, thereby opening the aggregated single-walled carbon nanotube, exposing the metal impurities, which facilitates subsequent impurity removal.

[0022] (4) Compared with traditional methods that use high temperature and large amounts of strong acid for impurity removal, this method minimizes the damage to the single-walled carbon nanotube structure caused by high temperature and strong acid, thus maintaining the integrity of the single-walled carbon nanotube structure. This invention does not require the use of high temperature, and the supercritical CO2 fluid can be reused, making it more energy-efficient than traditional methods.

[0023] (5) The purification method of this invention can achieve a metal removal efficiency of over 97% in single-walled carbon nanotubes. Furthermore, it uses supercritical CO2 as the main solvent and a small amount of weak acid, replacing the large amount of strong acid reagents used in traditional methods, thus reducing the environmental harm caused by the incomplete treatment of large amounts of strong acid waste liquid. This method is applicable to the purification of single-walled carbon nanotubes obtained by various synthesis methods such as arc discharge and flotation, and has broad applicability. Attached Figure Description

[0024] Figure 1 The image shows the Raman spectrum of the original single-walled carbon nanotube sample. Figure 2The Raman spectrum of the purified single-walled carbon nanotube sample in Example 1; Figure 3 The Raman spectrum of the purified single-walled carbon nanotube sample in Comparative Example 1 is shown. Figure 4 This is a SEM image of the purified single-walled carbon nanotubes from Example 1; Figure 5 The image shows a SEM image of the purified single-walled carbon nanotubes from Comparative Example 1. Detailed Implementation

[0025] The technical solution of the invention will be described in detail below with reference to the accompanying drawings: The single-walled carbon nanotubes involved in this invention were prepared according to the preparation method of Example 1 in patent CN113860287A.

[0026] Example 1 A method for purifying single-walled carbon nanotubes includes the following steps: (1) Mix 50g of 30% H2O2 reagent with 10g of single-walled carbon nanotubes evenly, and put it into a high-pressure heating and stirring reactor equipped with a UV lamp. Seal the reactor, introduce high-purity CO2 and pressurize it to 20 MPa. Heat it to 55°C, turn on the UV lamp, and start stirring for 100 minutes. Then reduce the pressure from 20 MPa to 7 MPa. Repeat the pressure increase and decrease three times. Finally, cool it down to room temperature and then depressurize it to atmospheric pressure. (2) Mix 560g of formic acid and 140g of acetylacetone evenly and add them to the reactor. Seal the reactor, turn on the stirrer, and introduce high-purity CO2. First pressurize to 25 MPa, then heat and control the temperature to 70°C. At the same time, keep the supercritical CO2 fluid in the reactor in an outward flow state. After 150 minutes, first reduce to room temperature, then depressurize to atmospheric pressure, open the reactor, and take out the material.

[0027] (3) Wash the sample after step (2) with anhydrous ethanol until the solution is colorless and transparent, and then put it into a vacuum dryer and dry it at 70°C for 5 hours.

[0028] Example 2 is basically the same as Example 1, except that: in step one, the reaction pressure is 25 MPa and the temperature is 65 °C, and in step two, the formic acid is 400 g and the acetylacetone is 100 g.

[0029] Comparative Example 1 (Conventional Acid Treatment Method): 10g of the same original single-walled carbon nanotubes as in Example 1 was added to 1000mL of 5M nitric acid solution and refluxed at 80°C for 4 hours. After the reaction was completed, the nanotubes were centrifuged, washed with deionized water until neutral, and finally vacuum dried in a vacuum dryer for 3 hours.

[0030] Comparative Example 2 The difference between Comparative Example 2 and Example 1 is that step (1) is omitted, and acetylacetone is omitted in step (2). The specific steps are as follows: (1) Take 10g of single-walled carbon nanotubes and 560g of formic acid, mix them evenly, add them to the reactor, seal the reactor, turn on the stirrer, introduce high-purity CO2, first pressurize to 25Mpa, then heat, control the temperature to 70℃, and at the same time keep the supercritical CO2 fluid in the reactor in an outward flow state. After 150 minutes, first reduce to room temperature, then depressurize to atmospheric pressure, open the reactor, and take out the material.

[0031] (2) Wash the sample after step (1) with anhydrous ethanol until the solution is colorless and transparent, and then put it into a vacuum dryer and dry it at 70°C for 5 hours.

[0032] Comparative Example 3 The difference between Comparative Example 3 and Example 1 is that step (1) is omitted. The specific steps are as follows: (1) Take 10g of single-walled carbon nanotubes, mix them evenly with 560g of formic acid and 140g of acetylacetone, add them to the reactor, seal the reactor, start stirring, introduce high-purity CO2, first pressurize to 25Mpa, then heat, control the temperature to 70℃, and at the same time keep the supercritical CO2 fluid in the reactor in an outward flow state. After 150 minutes, first lower to room temperature, then depressurize to atmospheric pressure, open the reactor, and take out the material.

[0033] (2) Wash the sample after step (1) with anhydrous ethanol until the solution is colorless and transparent, and then put it into a vacuum dryer and dry it at 70°C for 5 hours.

[0034] Comparative Example 4 The difference between Comparative Example 4 and Comparative Example 3 is that supercritical CO2 fluid treatment is performed without introducing CO2. The specific steps are as follows: (1) Take 10g of single-walled carbon nanotubes, mix them with 560g of formic acid and 140g of acetylacetone, add them to the reactor, seal the reactor, start stirring, pressurize to 25Mpa, then heat, control the temperature at 70℃, continue for 150 minutes, first reduce to room temperature, then depressurize to normal pressure, open the reactor, and take out the material.

[0035] (2) Wash the sample after step (1) with anhydrous ethanol until the solution is colorless and transparent, and then put it into a vacuum dryer and dry it at 70°C for 5 hours.

[0036] Comparative Example 5 The difference between Comparative Example 5 and Example 1 is that CO2 is not introduced in step (1), and the pressure is not repeatedly increased or decreased after the reaction is completed.

[0037] (1) Mix 50g of 30% H2O2 reagent with 10g of single-walled carbon nanotubes evenly, and put it into a high-pressure heating and stirring reactor equipped with a UV lamp. Seal the reactor, first pressurize to 20Mpa, heat to 55℃, turn on the UV lamp, start stirring for 100 minutes, and finally cool down to room temperature and then depressurize to atmospheric pressure. (2) Mix 560g of formic acid and 140g of acetylacetone evenly and add them to the reactor. Seal the reactor, turn on the stirrer, and introduce high-purity CO2. First pressurize to 25 MPa, then heat and control the temperature to 70°C. At the same time, keep the supercritical CO2 fluid in the reactor in an outward flow state. After 150 minutes, first reduce to room temperature, then depressurize to atmospheric pressure, open the reactor, and take out the material.

[0038] (3) Wash the sample after step (2) with anhydrous ethanol until the solution is colorless and transparent, and then put it into a vacuum dryer and dry it at 70°C for 5 hours.

[0039] Comparative Example 6 The difference between Comparative Example 6 and Example 1 is that CO2 is not introduced in step (1).

[0040] (1) Mix 50g of 30% H2O2 reagent with 10g of single-walled carbon nanotubes evenly, and put it into a high-pressure heating and stirring reactor equipped with a UV lamp. Seal the reactor, first pressurize to 20 MPa, heat to 55°C, turn on the UV lamp, start stirring for 100 minutes, then reduce the pressure from 20 MPa to 7 MPa, and repeat the pressure increase and decrease 3 times. Finally, first cool down to room temperature, and then depressurize to atmospheric pressure. (2) Mix 560g of formic acid and 140g of acetylacetone evenly and add them to the reactor. Seal the reactor, turn on the stirrer, and introduce high-purity CO2. First pressurize to 25 MPa, then heat and control the temperature to 70°C. At the same time, keep the supercritical CO2 fluid in the reactor in an outward flow state. After 150 minutes, first reduce to room temperature, then depressurize to atmospheric pressure, open the reactor, and take out the material.

[0041] (3) Wash the sample after step (2) with anhydrous ethanol until the solution is colorless and transparent, and then put it into a vacuum dryer and dry it at 70°C for 5 hours.

[0042] Comparative Example 7 The difference between Comparative Example 7 and Example 1 is that the amount of H2O2 reagent added in step (1) is different.

[0043] (1) Mix 90g of 30% H2O2 reagent with 10g of single-walled carbon nanotubes evenly, and put it into a high-pressure heating and stirring reactor equipped with a UV lamp. Seal the reactor, introduce high-purity CO2 and pressurize it to 20 MPa. Heat it to 55°C, turn on the UV lamp, and start stirring for 100 minutes. Then reduce the pressure from 20 MPa to 7 MPa. Repeat the pressure increase and decrease 3 times. Finally, cool it down to room temperature and then depressurize it to atmospheric pressure. (2) Mix 560g of formic acid and 140g of acetylacetone evenly and add them to the reactor. Seal the reactor, turn on the stirrer, and introduce high-purity CO2. First pressurize to 25 MPa, then heat and control the temperature to 70°C. At the same time, keep the supercritical CO2 fluid in the reactor in an outward flow state. After 150 minutes, first reduce to room temperature, then depressurize to atmospheric pressure, open the reactor, and take out the material.

[0044] (3) Wash the sample after step (2) with anhydrous ethanol until the solution is colorless and transparent, and then put it into a vacuum dryer and dry it at 70°C for 5 hours.

[0045] Metal impurity content analysis: The iron and cobalt contents in the samples before and after purification were analyzed by inductively coupled plasma atomic emission spectrometry (ICP-AES). The results are shown in Table 1 below. Table 1. Content and removal rate of impurity metals in the original single-walled carbon nanotubes, Examples 1-2, and Comparative Examples 1-7.

[0046] Comparative Example 1 is a traditional acid treatment method. This method not only has a low total metal removal rate, but also damages the structure of single-walled carbon nanotubes. The structure of the purified single-walled carbon nanotubes was characterized by Raman spectroscopy. Figures 1-3 In Comparative Example 1, the D peak of the traditional acid treatment method showed a significant increase, indicating an increase in defects in the single-walled carbon nanotubes (such as...). Figure 3 As shown), the D peak (Raman shift around 1350, an indicator of graphitization and defect degree) in the G / D ratio of the sample of Example 1 did not change much compared with the original sample (e.g. Figure 2 As shown), and then combined with scanning electron microscopy (SEM) to characterize the image ( Figures 4-5 In contrast, the surface of the single-walled carbon nanotubes treated with conventional acid in Example 1 showed obvious etching and fracture marks, while the carbon nanotubes in Example 1 maintained a complete and smooth surface morphology and a high aspect ratio, indicating that the method of the present invention can better maintain the complete crystal structure of single-walled carbon nanotubes.

[0047] Compared to Example 1, Comparative Examples 2-4 did not utilize the process of using H2O2 under high pressure in a supercritical CO2 fluid environment to excite H2O2 decomposition via UV light to generate a large number of -OH free radicals for oxidation and removal of amorphous carbon and graphite sheets. This resulted in the metal impurities remaining encapsulated and not exposed, thus affecting the subsequent removal of metal impurities. Comparative Example 2 further omitted acetylacetone, failing to utilize the combination of acetylacetone and formic acid. This prevented the conversion of elemental metals into metal ions before reacting with acetylacetone to form neutral, organic metal chelates for removal. Instead, only some metal oxides were removed by reacting with formic acid under heating conditions; the elemental metals in the impurities remained, making the removal effect inferior to Comparative Example 3. Comparative Example 4, again based on Comparative Example 3, did not introduce CO2. Only pressure heating failed to generate a supercritical fluid, and formic acid and acetylacetone only reacted with metal impurities exposed on the outside of the single-walled carbon nanotubes for removal.

[0048] Compared to Example 1, Comparative Example 5 did not add CO2 and did not adjust the temperature and pressure parameters. Therefore, it could not produce a supercritical fluid, preventing H2O2 from first penetrating the interior of the single-walled carbon nanotubes and then using UV lamp irradiation to generate -OH radicals to oxidize the metal impurities inside the single-walled carbon nanotubes into metal ions, thus affecting the subsequent impurity removal effect. Comparative Example 6, based on Comparative Example 5, adjusted the temperature and pressure parameters. This process achieved a slightly better impurity removal effect than Comparative Example 5, possibly because the air expanded, partially exposing the metal impurities during pretreatment.

[0049] Compared with Example 1, Comparative Example 7 changed the ratio of H2O2 to single-walled carbon nanotubes, which exceeded the optimal ratio range, and the effect was slightly worse.

[0050] Total metal removal rate: Judging from the Fe and Mo metal content after purification in the table above, the total metal removal rate after purification in Examples 1 and 2 is significantly better than that of traditional acid washing and other comparative methods.

[0051] In summary, the single-walled carbon nanotube purification method based on supercritical fluid synergistic extraction provided by this invention can significantly better maintain the structural integrity of single-walled carbon nanotubes while efficiently removing metal impurities, and the process is environmentally friendly, thus having significant industrial application value.

[0052] The embodiments provided above are not intended to limit the scope of the invention, nor are the described steps intended to limit the order of execution. Any obvious modifications made to the invention by those skilled in the art based on existing common knowledge also fall within the scope of protection defined by the claims.

Claims

1. A method for purifying single-walled carbon nanotubes based on supercritical fluid synergistic extraction, characterized in that, Includes the following steps: (1) Mix hydrogen peroxide aqueous solution with single-walled carbon nanotubes and put them into a high-pressure heated and stirred reactor equipped with UV lamp. After CO2 is introduced, pressurize to 15-30 MPa and heat to 40-70℃. Turn on the UV lamp and start stirring. After stirring, reduce the pressure from 15-30 MPa to 7 MPa, then increase the pressure to 15-30 MPa and reduce it to 7 MPa. Repeat this process 2-5 times. Cool down and depressurize. The mass ratio of hydrogen peroxide aqueous solution to single-walled carbon nanotubes is 3:1 to 7:

1. (2) After the weak acid and the metal chelating agent are mixed evenly, they are added to the reaction vessel of step (1). After CO2 is introduced, the pressure is increased to 15-30 MPa and the temperature is increased to 40-80℃. At the same time, the CO2 fluid in the reaction vessel is kept in an outward flow state. After the reaction is completed by stirring, the temperature is reduced and the pressure is released. The material is taken out, washed and dried to obtain purified single-walled carbon nanotubes. The weak acid is formic acid or acetic acid, and the metal chelating agent is selected from at least one of acetylacetone, hexafluoroacetylacetone, sodium diethyldithiocarbamate, and 8-hydroxyquinoline.

2. The purification method according to claim 1, characterized in that, In step (1), the mass fraction of the hydrogen peroxide aqueous solution is 30%, the reaction vessel has dual channels for gas inlet and outlet, the CO2 is high-purity CO2 with a purity of 99.9% or higher, and the stirring time is 30~120min.

3. The purification method according to claim 1, characterized in that, In step (2), the mass ratio of the weak acid to the metal chelating agent is 2:1 to 6:

1.

4. The purification method according to claim 1, characterized in that, In step (2), the mass ratio of the mixed solution of weak acid and metal chelating agent to the single-walled carbon nanotubes in the reactor is 40~80:

1.

5. The purification method according to claim 1, characterized in that, In step (2), the stirring reaction time is 60~180 min.

6. The purification method according to claim 1, characterized in that, In step (2), the single-walled carbon nanotubes after stirring reaction are cleaned with anhydrous ethanol 2 to 5 times until the solution is colorless and transparent, and then vacuum dried at a temperature of 60-80℃ for 3-6 hours.

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