A purification method for single-walled carbon nanotubes

Abstract

This application discloses a method for purifying single-walled carbon nanotubes, belonging to the field of single-walled carbon nanotubes. The method includes the following steps: S1, mixing materials containing potassium permanganate, concentrated sulfuric acid, and raw single-walled carbon nanotube ash, and reacting them to obtain a reaction solution; S2, mixing materials containing the reaction solution and hydrogen peroxide, and filtering through a microporous membrane to obtain a solid; S3, washing the solid with water to obtain ultra-high purity single-walled carbon nanotubes; in step S3, the water washing is performed until the pH of the aqueous solution is 4-5. This method can remove metal nanoparticles coated with crystalline carbon particles, graphene sheets deeply wrapped with single-walled carbon nanotubes, and multi-walled carbon nanotubes, achieving a single-walled carbon nanotube purity higher than 99%.

Description

Technical Field

[0001] This application relates to a purification method for single-walled carbon nanotubes, belonging to the field of single-walled carbon nanotubes. Background Technology

[0002] Single-walled carbon nanotubes (SWCNTs) are one-dimensional tubular carbon nanomaterials with a single-layered wall. SWCNTs possess excellent physical and chemical properties and have broad application prospects in mechanics, electrical engineering, optics, and electronics. Currently, there are three most widely used methods for synthesizing SWCNTs: arc-discharge, laser-ablation, and chemical vapor deposition. However, the raw ash from these methods currently contains a considerable amount of carbon impurities and metal catalyst nanoparticle impurities. These carbon impurities typically include amorphous carbon, crystalline carbon spheres, multi-walled carbon nanotubes, graphite sheets, graphene sheets, and fullerene spheres, etc., while the metal catalyst particles are usually transition metal particles, commonly ferromagnetic metals (such as Fe and Ni). Moreover, these metal catalysts are nanoparticles, a significant portion of which are individually coated with crystalline carbon layers, forming a core-shell structure unit with a metal nanoparticle core and a crystalline carbon sphere outer shell, referred to in this invention as "crystalline carbon sphere particles coated with metal nanoparticles." These impurities have complex compositions, and most carbon impurities (graphite sheets, graphene sheets, crystalline carbon spheres, and multi-walled carbon nanotubes) often have higher thermal stability than single-walled carbon nanotubes, making them very difficult to remove. Metal particles coated within crystalline carbon spheres are particularly difficult to remove due to the crystalline carbon layer. Currently, most purification methods only remove metal particles exposed on the carbon impurities, failing to address metal nanoparticles coated with crystalline carbon particles. Furthermore, they are particularly ineffective at removing graphene sheets and multi-walled carbon nanotubes deeply encased in single-walled carbon nanotubes. Therefore, it is necessary to develop a purification method that can simultaneously remove all of these impurities, achieving a purification level of over 99% for single-walled carbon nanotubes.

[0003] This application draws upon the processing method of the prior art CN 106744817 A, but compared with the prior art, the scenario it addresses is different; the initial raw materials are more complex, and the corresponding purification difficulty is greatly increased. In the prior art CN106744817 A, the focus is on raw single-walled carbon nanotube solids, i.e., single-walled carbon nanotube solids with a purity of over 99%. (See the appendix to the specification of that prior art.) Figure 1 and attached Figure 2In the sample, we can clearly observe that no impurities other than single-walled carbon nanotubes were observed, which clearly verifies its purity of over 99%. However, the original single-walled carbon nanotube ash targeted in this application has a purity as low as 60%, and its components and structural relationships are very complex. In addition to single-walled carbon nanotubes, it contains amorphous carbon, crystalline carbon spheres, multi-walled carbon nanotubes, graphite sheets, graphene sheets, and fullerene spheres, among other impurities, and their interrelationships are extremely complex. Therefore, removing so many impurities is understandably difficult. In the prior art CN 106744817 A, the centrifugation washing process is performed until neutral (pH = 6-7) to remove residual reaction byproducts such as manganese ions, chloride ions, and hydrogen ions, ensuring that the final highly dispersed single-walled carbon nanotube solution is free of these impurity ions. The purpose of centrifuging and washing with water and controlling the pH at 4-5 in this application is to ensure that the non-single-walled carbon nanotube components such as carbon fragments and graphene sheets in the solution can be completely separated and removed in the next centrifugation process. Summary of the Invention

[0004] The existing technology CN 106744817 A can only peel off single (non-tube bundle) single-walled carbon nanotubes, and cannot purify the raw single-walled carbon nanotube ash containing a large number of impurities. Generally, the higher the purity of the raw material and the simpler the composition, the easier the purification is, and vice versa. In the field of single-walled carbon nanotubes, 1% purity means the presence of impurities in a complex system, and it also means that a 1% increase in purity will bring great difficulties to the purification work. This application, through the action of potassium permanganate and concentrated sulfuric acid, combined with specific washing and purification parameters, controls the pH at 4-5, enabling the purification of raw single-walled carbon nanotube ash containing a large number of complex system impurities. While achieving purification, controlling the order of raw material addition can preserve the original length of the single-walled carbon nanotubes as much as possible, effectively reducing the excessive shortening of single-walled carbon nanotubes caused by premature oxidation of the raw material by concentrated sulfuric acid, thus obtaining longer single-walled carbon nanotubes than in the prior art, and is expected to achieve better mechanical properties.

[0005] According to the first aspect of this application, a method for purifying single-walled carbon nanotubes is provided. This method can remove metal nanoparticles coated with crystalline carbon particles, graphene sheets deeply wrapped with single-walled carbon nanotubes, and multi-walled carbon nanotubes, and achieve a purity of single-walled carbon nanotubes higher than 99%.

[0006] A method for purifying single-walled carbon nanotubes includes the following steps:

[0007] S1. Mix materials containing potassium permanganate, concentrated sulfuric acid, and raw ash of single-walled carbon nanotubes, and react them to obtain a reaction solution.

[0008] S2. After mixing the materials containing the reaction solution and hydrogen peroxide, filter the mixture through a microporous membrane to obtain a solid.

[0009] S3. After washing the solid with water until the pH of the aqueous solution is 4-5, centrifuge to obtain ultra-high purity single-walled carbon nanotubes.

[0010] Optionally, in step S1, the purity of the single-walled carbon nanotubes in the original single-walled carbon nanotube ash is 60wt% to 95wt%.

[0011] Optionally, the content of amorphous carbon in the original single-walled carbon nanotube ash is 0wt% to 5wt%.

[0012] Optionally, the content of amorphous carbon in the original single-walled carbon nanotube ash is independently selected from any value of 0, 1 wt%, 2 wt%, 3 wt%, 4 wt%, 5 wt%, or any range between two.

[0013] Optionally, the content of metal nanoparticles in the original single-walled carbon nanotube ash is 0wt% to 15wt%.

[0014] Optionally, the content of metal nanoparticles in the original single-walled carbon nanotube ash is independently selected from any value or a range between 0, 1 wt%, 2 wt%, 3 wt%, 4 wt%, 5 wt%, 6 wt%, 7 wt%, 8 wt%, 9 wt%, 10 wt%, 11 wt%, 12 wt%, 13 wt%, 14 wt%, and 15 wt%.

[0015] Optionally, the purity of the ultra-high purity single-walled carbon nanotubes reaches 99wt% to 100wt%.

[0016] Optionally, in step S1, the impurities in the original single-walled carbon nanotube ash include at least one of crystalline carbon spheres, multi-walled carbon nanotubes, graphite sheets, graphene sheets, fullerene spheres, metal nanoparticles, and metal crystalline carbon particles.

[0017] Optionally, the metallic crystalline carbon particles are crystalline carbon spheres coated with metallic nanoparticles.

[0018] Optionally, the metallic carbon particles are embedded in the interlaced grid of single-walled carbon nanotubes and / or adhered to and / or bonded to the surface of the single-walled carbon nanotubes.

[0019] The crystalline carbon spheres include solid crystalline carbon spheres and closed hollow crystalline carbon spheres.

[0020] The particle size of the metal particles in the metal crystalline carbon particles is 1 nm to 100 nm; the particle size of the metal particles in the metal crystalline carbon particles is 3 nm to 50 nm; the particle size of the metal particles in the metal crystalline carbon particles is 5 nm to 30 nm.

[0021] The metallic crystalline carbon particles are 2nm to 100nm in size, and their size is larger than that of the metallic particles that coat their core.

[0022] The thickness of the crystalline carbon layer in the metallic crystalline carbon is at least one graphene sheet.

[0023] The shape of the crystalline carbon particles in the metal crystalline carbon particles can be a regular geometric solid shape or an irregular geometric solid shape.

[0024] The metal particles in the metal crystalline carbon particles may fill the entire hollow cavity of the crystalline carbon sphere, or they may not fill the hollow cavity of the crystalline carbon sphere.

[0025] Optionally, in step S1, the mass ratio of the original single-walled carbon nanotube ash to the potassium permanganate is 1:1 to 2.

[0026] Optionally, in step S1, the mass ratio of the original single-walled carbon nanotube ash to the potassium permanganate is independently selected from any value or a range between 1:1, 1:1.1, 1:1.2, 1:1.3, 1:1.4, 1:1.5, 1:1.6, 1:1.7, 1:1.8, 1:1.9, and 1:2.

[0027] Optionally, in step S1, the concentration of the concentrated sulfuric acid is 98 wt% to 100 wt%.

[0028] The amount of concentrated sulfuric acid used should be excessive compared to the amount of potassium permanganate used.

[0029] Optionally, the volume ratio of the sulfuric acid to the mass ratio of the potassium permanganate is 75 ml / g or higher.

[0030] Optionally, the mass ratio of potassium permanganate to the original single-walled carbon nanotube ash is 1:1 to 1:2.

[0031] Optionally, in step S1, the reaction conditions are as follows:

[0032] The temperature is 50℃~60℃;

[0033] The time is 2 to 3 hours.

[0034] Optionally, the reaction can be carried out in an oil bath.

[0035] Optionally, in step S2, the molar ratio of hydrogen peroxide to the reaction solution is greater than 1;

[0036] The reaction solution is measured by the manganese dioxide it contains, and the hydrogen peroxide is measured by the hydrogen peroxide it contains.

[0037] Optionally, in step S2, the microporous membrane filtration is further washed with hydrochloric acid.

[0038] Optionally, in step S3, after washing with water, centrifugation is performed to obtain the supernatant solution, which is then filtered and washed with water to obtain the ultra-high purity single-walled carbon nanotubes.

[0039] Optionally, the washing process includes high-speed centrifugal washing, filtration washing, and semi-permeable membrane washing.

[0040] The high-speed centrifugal washing refers to pouring the single-walled carbon nanotube solid obtained in the above steps into deionized water and stirring it thoroughly. Then, centrifuging it at high speed in a centrifuge allows the single-walled carbon nanotube solid to completely settle and separate into layers. After that, the supernatant is discarded, and deionized water is added to the centrifuge tube for thorough stirring and washing. Then, the tube is centrifuged again, and the layers are separated. The supernatant is then discarded. This centrifugal washing process is repeated 2-3 times.

[0041] Alternatively, the centrifugation conditions are as follows:

[0042] The rotational speed is 5000 rpm to 14000 rpm;

[0043] The time is 20 to 40 minutes.

[0044] Optionally, the following steps are included:

[0045] S1. Add the original ash of single-walled carbon nanotubes to a mixture containing potassium permanganate and concentrated sulfuric acid, and react to obtain a reaction solution.

[0046] S2. Add hydrogen peroxide to a mixture containing the reaction solution and water, and filter through a microporous membrane to obtain a solid.

[0047] S3. The solid is washed with water until the pH of the aqueous solution is 4-5, and then centrifuged to obtain ultra-high purity single-walled carbon nanotubes.

[0048] According to one embodiment of this application, the method of the present invention includes the following steps:

[0049] First, potassium permanganate solid was added to an excess of concentrated sulfuric acid solution and reacted completely. Then, the original single-walled carbon nanotube ash was added to the above solution and stirred evenly. The resulting reaction mixture was placed in an oil bath at 50℃~60℃ and stirred continuously for 2h~3h. The reaction mixture was diluted with deionized water, and then an excess of hydrogen peroxide solution was added to reduce and remove the generated manganese dioxide solid. After filtration through a microporous membrane and washing with hydrochloric acid solution, the obtained solid was washed with deionized water to remove some impurity ions from the solution. When the pH of the single-walled carbon nanotube mixed aqueous solution was 4~5, it was centrifuged at 5000~14000 rpm for 30 minutes. The upper homogeneous solution was taken out, and the solution was filtered and washed with deionized water. The collected black solid was ultra-high purity single-walled carbon nanotubes.

[0050] The beneficial effects that this application can produce include:

[0051] This application provides a method for purifying single-walled carbon nanotubes, which can remove metal nanoparticles coated with crystalline carbon particles, graphene sheets deeply wrapped with single-walled carbon nanotubes, and multi-walled carbon nanotubes, and achieve a purity of single-walled carbon nanotubes higher than 99%. Attached Figure Description

[0052] Figure 1 This is a schematic diagram of the cross-section of the microstructure of metallic carbon particles.

[0053] Figure 2 The image shown is a transmission electron microscope (TEM) image of the original single-walled carbon nanotubes from Example 1, with a scale bar of 100 nm.

[0054] Figure 3 The image shown is a transmission electron microscope (TEM) image of ultra-high purity single-walled carbon nanotubes from Example 1. The scale bar is 100 nm.

[0055] Figure 4 The image shown is a transmission electron microscope (TEM) image of the original single-walled carbon nanotubes from Example 2, with a scale bar of 200 nm.

[0056] Figure 5 This is a scanning electron microscope image of ultra-high purity single-walled carbon nanotubes from Example 2.

[0057] Figure 6 This is a transmission electron microscope image of Example 4. Detailed Implementation

[0058] The present application is described in detail below with reference to the embodiments, but the present application is not limited to these embodiments.

[0059] Unless otherwise specified, all raw materials used in the embodiments of this application were purchased through commercial channels.

[0060] The analysis method in the embodiments of this application is as follows:

[0061] Transmission electron microscopy (TEM, Tecnai F20, FEI Corporation, USA) was used for analysis.

[0062] X-ray photoelectron spectroscopy analysis was performed using an X-ray photoelectron spectrometer (XPS, Thermo Fisher, ESCALAB 250Xi).

[0063] Scanning electron microscopy analysis was performed using a field emission scanning electron microscope (FESEM, SU-8010, Hitachi, Japan).

[0064] Thermogravimetric analysis was performed using a simultaneous thermal analyzer (TG / DTA, STA449F3, Netzsch).

[0065] Component analysis was performed using scanning probe microscopy (AFM, Nanoscope Multimode IIIa, Veeco Instruments).

[0066] The single-walled carbon nanotube raw material disclosed in this application refers to impure single-walled carbon nanotubes, that is, single-walled carbon nanotubes containing some non-single-walled carbon nanotube impurities, including metal particle impurities and carbon impurities.

[0067] Example 1

[0068] 0.4 g of potassium permanganate solid was added to a beaker containing 15 ml of concentrated sulfuric acid (98 wt%). After the reaction was complete, 0.2 g of single-walled carbon nanotube ash was added. Figure 2 Pour the solution into the above solution, stir thoroughly, and then place it in a constant temperature oil bath at 50°C and stir for 2 hours. During this time, cover with a glass lid to prevent concentrated sulfuric acid from absorbing water. After cooling to room temperature, dilute with about 100 ml of deionized water while stirring continuously. Then add about 10 ml of 30% hydrogen peroxide solution, stir and react for 15 minutes, and then filter with a microporous membrane. The obtained black solid was directly poured into 100ml of 4% dilute hydrochloric acid and stirred and washed. Then it was filtered through a microporous membrane and washed with deionized water. The obtained black solid was then poured into 200ml of deionized water and stirred thoroughly. It was then centrifuged at 14000 rpm for 30 minutes. After separation, the supernatant was discarded. 200ml of deionized water was added to the centrifuge tube and stirred and washed thoroughly. The mixture was then centrifuged again, separated, and the supernatant was discarded. This centrifugation and washing process was repeated 2-3 times until the pH of the mixture was 5 when deionized water was added to the centrifuge tube. The mixture was then centrifuged again at 5000 rpm for 30 minutes, the supernatant was extracted, and the dispersion was collected. The mixture was then filtered through a microporous membrane to remove residual impurity ions. The collected black solid was the ultra-high purity single-walled carbon nanotube.

[0069] The centrifugation speed of 5000 revolutions refers to 5000 revolutions per minute.

[0070] The purity of the ultra-high purity single-walled carbon nanotubes is over 99 wt%. Figure 3 Elemental analysis using X-ray energy dispersive spectroscopy (EDS) showed no residual metallic impurities. Ten random transmission electron microscopy (TEM) images taken at different locations revealed two graphene flakes, with no multi-walled carbon nanotubes, carbon particles, metal particles, or other impurities detected. Similarly, ten random scanning electron microscopy (SEM) images taken at different locations also showed no graphene, multi-walled carbon nanotubes, carbon particles, metal particles, or other impurities.

[0071] The diameter of the ultra-high purity single-walled carbon nanotubes is significantly smaller than that of the original single-walled carbon nanotubes, and most of them are non-tube-bundle type single-walled carbon nanotubes.

[0072] The ultra-high purity single-walled carbon nanotubes have oxygen-containing groups attached to their surface, including hydroxyl groups, epoxy groups, carboxyl groups, and carbonyl groups. The oxygen content of the ultra-high purity single-walled carbon nanotubes is 29 at.%.

[0073] The raw ash of the single-walled carbon nanotubes is prepared by direct current arc method (see Journal of Physical Chemistry C, 113 (2009), 3612-16.); the purity of the raw ash of the single-walled carbon nanotubes is 60 wt%; the impurities in the raw ash of the single-walled carbon nanotubes include crystalline carbon spheres, graphite flakes, fullerene spheres, metallic crystalline carbon particles and amorphous carbon, wherein the content of metallic impurities is 15 wt% and the content of amorphous carbon is less than 5 wt%.

[0074] The metal particles in the metal crystalline carbon particles have a particle size of 1-100 nm; the metal particles in the metal crystalline carbon particles have a particle size of 3-50 nm; the metal particles in the metal crystalline carbon particles have a particle size of 5-30 nm; the metal crystalline carbon particles have a particle size of 2-100 nm.

[0075] In the original ash of single-walled carbon nanotubes, the single-walled carbon nanotubes exist in bundles, which are interwoven and randomly entangled with each other. Metallic crystalline carbon particles are embedded in the interwoven grid of single-walled carbon nanotubes, some of which are adhered to the surface of single-walled carbon nanotubes, and some are bonded to the surface of single-walled carbon nanotubes.

[0076] After centrifugation at 5000 rpm for 30 minutes, the sediment was analyzed and found to consist mostly of graphene sheets, with a small amount of large-tube single-walled carbon nanotubes. Additionally, partially exfoliated crystalline carbon spheres with a particle size of 150 nm were also found. The outer graphene carbon layer of these spheres had been partially exfoliated into graphene sheets. Due to the relatively large size of these crystalline carbon particles, they had not yet been completely oxidized and exfoliated. This indicates that the crystalline carbon spheres were oxidized and exfoliated into graphene oxide sheets throughout the process. The size of the graphene oxide sheets is positively correlated with the size of the crystalline carbon particles, while the degree of oxidation of the graphene sheets is negatively correlated with the size of the crystalline carbon particles.

[0077] Example 2

[0078] 0.4 g of potassium permanganate solid was added to a beaker containing 15 ml of concentrated sulfuric acid (98 wt%). After the reaction was complete, 0.2 g of single-walled carbon nanotube ash was added. Figure 4 Pour the solution into the above solution, stir thoroughly, and then place it in a constant temperature oil bath at 50°C and stir for 2 hours. During this time, cover with a glass lid to prevent concentrated sulfuric acid from absorbing water. After cooling to room temperature, dilute with about 100 ml of deionized water while stirring continuously. Then add about 10 ml of 30% hydrogen peroxide solution, stir and react for 15 minutes, and then filter with a microporous membrane. The obtained black solid was directly poured into 100ml of 4% dilute hydrochloric acid and stirred and washed. Then it was filtered through a microporous membrane and washed with deionized water. The obtained black solid was then poured into 200ml of deionized water and stirred thoroughly. It was then centrifuged at 14000 rpm for 30 minutes. After separation, the supernatant was discarded. 200ml of deionized water was added to the centrifuge tube and stirred and washed thoroughly. The mixture was then centrifuged again, separated, and the supernatant was discarded. This centrifugation and washing process was repeated 2-3 times until the pH of the mixture was 4 when deionized water was added to the centrifuge tube. The mixture was then centrifuged again at 10000 rpm for 30 minutes, the supernatant was extracted, and the dispersion was collected. The mixture was then filtered through a microporous membrane to remove residual impurity ions. The collected black solid was the ultra-high purity single-walled carbon nanotube.

[0079] The purity of the ultra-high purity single-walled carbon nanotubes is over 99 wt%. Elemental analysis by X-ray energy dispersive spectroscopy showed no residual metal impurities. No other impurities such as graphene, multi-walled carbon nanotubes, carbon particles, or metal particles were detected by transmission electron microscopy or scanning electron microscopy.

[0080] The diameter of the ultra-high purity single-walled carbon nanotubes is significantly smaller than that of the original single-walled carbon nanotubes, and most of them are non-tube-bundle type single-walled carbon nanotubes.

[0081] The surface of the ultra-high purity single-walled carbon nanotubes is coated with oxygen-containing groups, including hydroxyl groups, epoxy groups, carboxyl groups, and carbonyl groups.

[0082] The single-walled carbon nanotube raw ash is prepared by vapor deposition; the purity of the single-walled carbon nanotube raw ash is 75 wt%; the impurities in the single-walled carbon nanotube raw ash include crystalline carbon spheres, graphene sheets, fullerene spheres, metallic crystalline carbon particles and multi-walled carbon nanotubes, wherein the content of metallic impurities is 8 wt%.

[0083] The particle size of the metal particles in the metal crystalline carbon particles is 1-50 nm; the particle size of the metal particles in the metal crystalline carbon particles is 2-10 nm.

[0084] In the original ash of single-walled carbon nanotubes, the single-walled carbon nanotubes exist in bundles, which are interwoven and randomly entangled with each other. Metallic crystalline carbon particles are embedded in the interwoven grid of single-walled carbon nanotubes, some of which are adhered to the surface of single-walled carbon nanotubes, and some are bonded to the surface of single-walled carbon nanotubes.

[0085] Multi-walled carbon nanotubes were detected to be oxidized and peeled off into long graphene sheets in the centrifuged sediment, indicating that multi-walled carbon nanotubes can also be removed by this method.

[0086] Example 3

[0087] The difference between this embodiment and Embodiment 2 is that raw ash containing single-walled carbon nanotubes with purities of 90 wt% and 95 wt%, respectively, was used as the purification raw material. The raw ash was prepared by chemical vapor deposition. Impurities in the raw ash included crystalline carbon spheres, metallic carbon particles, and multi-walled carbon nanotubes. The ultra-high purity single-walled carbon nanotubes had a purity exceeding 99.9 wt%. Elemental analysis by X-ray energy dispersive spectroscopy showed no residual metal impurities. Transmission electron microscopy and scanning electron microscopy did not detect any other impurities such as graphene, multi-walled carbon nanotubes, carbon particles, or metal particles. However, large bundles of single-walled carbon nanotubes and a significant amount of graphene sheets were detected in the centrifuged sedimentation products.

[0088] Example 4

[0089] The difference between this embodiment and Example 1 is that a single-walled carbon nanotube sample with a purity of 99 wt% was used as the purification raw material. The single-walled carbon nanotubes were prepared by a direct current arc method (see Journal of Physical Chemistry C, 113 (2009), 3612-16). The impurities in the single-walled carbon nanotubes included crystalline carbon spheres, metallic crystalline carbon particles, and their coated metal particles, with the content of metal impurities being 1.0 wt%. The purity of the ultra-high purity single-walled carbon nanotubes reached over 99.9 wt%. Elemental analysis by X-ray energy dispersive spectroscopy showed no residual metal impurities detected, and no other impurities such as graphene, carbon particles, or metal particles were observed by transmission electron microscopy or scanning electron microscopy.

[0090] Example 5

[0091] The difference between this embodiment and Embodiment 2 is that the mass ratio of raw ash of single-walled carbon nanotubes to potassium permanganate solid is 1:1, and the mixture is stirred in a constant-temperature oil bath at 60°C for 3 hours. When the amount of potassium permanganate added is reduced, the recovery yield is lower than that of Embodiment 2, but ultra-high purity single-walled carbon nanotubes can still be obtained after separation.

[0092] Comparative Example 1

[0093] 0.4 g of potassium permanganate solid was added to a beaker containing 15 ml of concentrated sulfuric acid (98%). After the reaction was complete, 0.2 g of single-walled carbon nanotube ash was added. Figure 2Pour the solution into the above solution, stir thoroughly, and then place it in a constant temperature oil bath at 50°C and stir for 2 hours. During this time, cover with a glass lid to prevent concentrated sulfuric acid from absorbing water. After cooling to room temperature, dilute with about 100 ml of deionized water while stirring continuously. Then add about 10 ml of 30% hydrogen peroxide solution, stir and react for 15 minutes, and then filter with a microporous membrane. The obtained black solid was directly poured into 100ml of 4% dilute hydrochloric acid and stirred and washed. Then it was filtered through a microporous membrane and washed with deionized water. The obtained black solid was then poured into 200ml of deionized water and stirred thoroughly. It was then centrifuged at 14000 rpm for 30 minutes. After separation, the supernatant was discarded. An appropriate amount of deionized water was added to the centrifuge tube and stirred and washed thoroughly. The mixture was then centrifuged again, separated, and the supernatant was discarded. This centrifugation and washing process was repeated 4-6 times until the supernatant was neutral (pH=6-7). Finally, the centrifuged sediment was collected and about 200ml of deionized water was added. After stirring for 30 minutes, the resulting dispersion was divided into two parts. The dispersions were centrifuged at 5000 rpm and 14000 rpm for 30 minutes, respectively. The supernatant dispersion was carefully extracted and collected. The components in the two solutions were monitored by transmission electron microscopy. It was found that in addition to single carbon nanotubes, both solutions contained a considerable amount of graphene oxide sheets, with a volume content of about 5-15%. The explanation is that when the ions in the solution are completely washed away until the pH of the dispersion is 6-7, neither graphene oxide sheets nor single-walled carbon nanotubes are prone to aggregate, and the dispersion environment does not meet the conditions for separating and purifying them. We found that the oxidized and exfoliated single-walled carbon nanotubes have better solubility stability in weakly acidic solutions than graphene oxide sheets, which are more prone to aggregate in weakly acidic solutions. Similarly, in the initial centrifugation washing step, because the pH is below 4, both carbon nanotubes and graphene oxide are prone to aggregate and will settle together during centrifugation, failing to achieve the desired separation and purification.

[0094] The original ash of the single-walled carbon nanotubes described in this comparative example is the same as that in Example 1.

[0095] Comparative Example 2

[0096] The comparative example differs from Example 1 in the purity and composition of the original single-walled carbon nanotube ash. Specifically, the purity of the single-walled carbon nanotubes is 30 wt%, the content of amorphous carbon is higher at 24 wt%, and the content of metal nanoparticles is also 24 wt%. The final product after separation contains a large number of nano-carbon fragments, and the yield is very low, making it impossible to achieve ultra-high purity purification of single-walled carbon nanotubes. Amorphous carbon has many structural defects and poor chemical stability, and is preferentially oxidized into fine amorphous carbon fragments, while the single-walled carbon nanotubes and other carbon impurities do not react completely. Furthermore, these fine nano-carbon fragments are very difficult to separate and remove in solution.

[0097] Comparative Example 3

[0098] The difference between this comparative example and Example 2 is that the mass ratio of single-walled carbon nanotube ash to potassium permanganate solid was 1:4. The final product after separation contained a large amount of nano-carbon fragments and graphene oxide sheets, severely damaging the tubular structure of the single-walled carbon nanotubes and making purification impossible. When the amount of potassium permanganate added was too large, the single-walled carbon nanotubes were severely damaged and oxidized into graphene oxide sheets and fine amorphous carbon fragments, making ultra-high purity purification of single-walled carbon nanotubes impossible.

[0099] Comparative Example 5

[0100] The difference between this comparative example and Example 1 is that the centrifugation speed for the last separation was 4000 rpm. It was found that the centrifugation speed was too low to completely separate and remove impurities such as graphene oxide.

[0101] Comparative Example 6

[0102] The difference between this embodiment and Comparative Example 1 is that the raw material for single-walled carbon nanotubes used is a solid single-walled carbon nanotube with a purity of over 99% (see Journal of Physical Chemistry C, 113 (2009), 3612-16, prepared by purification method), and the feeding sequence is as follows: single-walled carbon nanotubes and potassium permanganate are added to concentrated sulfuric acid sequentially. In the resulting highly dispersed single-walled carbon nanotubes, over 95% of the single-walled carbon nanotubes have a length of less than 1 micrometer. However, when the feeding sequence is followed according to this application, 90% of the single-walled carbon nanotubes obtained in the final product have a length of more than 1 micrometer.

[0103] The above description is merely a few embodiments of this application and is not intended to limit this application in any way. Although this application discloses preferred embodiments as described above, it is not intended to limit this application. Any changes or modifications made by those skilled in the art without departing from the scope of the technical solution of this application using the disclosed technical content are equivalent to equivalent implementation cases and fall within the scope of the technical solution.

Claims

1. A method for purifying single-walled carbon nanotubes, characterized in that, Includes the following steps: S1. Mix materials containing potassium permanganate, concentrated sulfuric acid, and raw ash of single-walled carbon nanotubes, and react them to obtain a reaction solution. S2. After mixing the materials containing the reaction solution and hydrogen peroxide, filter the mixture through a microporous membrane to obtain a solid. S3. Wash the solid with water until the pH of the aqueous solution is 4-5, and then centrifuge to obtain ultra-high purity single-walled carbon nanotubes. In step S1, the purity of the single-walled carbon nanotubes in the original ash is 60wt%~95wt%.

2. The purification method according to claim 1, characterized in that, In step S1, the content of amorphous carbon in the original single-walled carbon nanotube ash is 0wt%~5wt%.

3. The purification method according to claim 1, characterized in that, In step S1, the content of metal nanoparticles in the original single-walled carbon nanotube ash is 0wt%~15wt%.

4. The purification method according to claim 1, characterized in that, In step S1, the mass ratio of the original single-walled carbon nanotube ash to the potassium permanganate is 1:1~2.

5. The purification method according to claim 1, characterized in that, In step S1, the impurities in the original single-walled carbon nanotube ash include at least one of crystalline carbon spheres, multi-walled carbon nanotubes, graphite sheets, graphene sheets, fullerene spheres, metal nanoparticles, and metal crystalline carbon particles.

6. The purification method according to claim 5, characterized in that, The metallic crystalline carbon particles are crystalline carbon spheres coated with metallic nanoparticles.

7. The purification method according to claim 5, characterized in that, The metallic crystalline carbon particles are embedded between the interlaced grids of single-walled carbon nanotubes and / or adhered to and / or bonded to the surface of single-walled carbon nanotubes.

8. The purification method according to claim 1, characterized in that, The purity of ultra-high purity single-walled carbon nanotubes reaches 99wt%~100wt%.

9. The purification method according to claim 1, characterized in that, In step S1, the concentration of the concentrated sulfuric acid is 98wt%~100wt%.

10. The purification method according to claim 1, characterized in that, In step S1, the volume ratio of the concentrated sulfuric acid to the mass ratio of the potassium permanganate is above 75 ml / g.

11. The purification method according to claim 1, characterized in that, In step S1, the reaction conditions are as follows: The temperature is 50℃~60℃; The time is 2 to 3 hours.

12. The purification method according to claim 1, characterized in that, In step S1, the reaction is carried out in an oil bath.

13. The purification method according to claim 1, characterized in that, In step S2, the molar ratio of hydrogen peroxide to the reaction solution is greater than 1; The reaction solution is measured by the manganese dioxide it contains, and the hydrogen peroxide is measured by the hydrogen peroxide it contains.

14. The purification method according to claim 1, characterized in that, In step S2, the microporous membrane filtration is also washed with hydrochloric acid.

15. The purification method according to claim 1, characterized in that, In step S3, after washing with water, centrifugation is performed to obtain the supernatant solution, which is then filtered and washed with water to obtain the ultra-high purity single-walled carbon nanotubes.

16. The purification method according to claim 1, characterized in that, In step S3, the water washing process includes high-speed centrifugal water washing, filtration water washing, and semi-permeable membrane water washing.

17. The purification method according to claim 15, characterized in that, The centrifugation conditions are as follows: The rotational speed is 5000 rpm to 14000 rpm; The time is 20 min to 40 min.

18. The purification method according to claim 1, characterized in that, Includes the following steps: S1. Add the original ash of single-walled carbon nanotubes to a mixture containing potassium permanganate and concentrated sulfuric acid, and react to obtain a reaction solution. S2. Add hydrogen peroxide to a mixture containing the reaction solution and water, and filter through a microporous membrane to obtain a solid. S3. The solid is washed with water until the pH of the aqueous solution is 4-5, and then centrifuged to obtain ultra-high purity single-walled carbon nanotubes.

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