CN113860289B - Method for purifying carbon nano tube - Google Patents
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Abstract
The invention relates to the technical field of carbon nanotube purification, in particular to a method for purifying carbon nanotubes, which comprises the steps of mixing carbon nanotubes, an oxidant and dilute acid for reaction, and adding (6 multiplied by 10) into each 5g carbon nanotubes ‑3 ~32×10 ‑3 ) mol of oxidant and 150-600g H + And (3) carrying out post-treatment on dilute acid with the concentration of 1.8-20 mol/L after the reaction is finished to obtain the purified carbon nano tube. The method for purifying the carbon nano tube not only can effectively improve the purity of the carbon nano tube, but also has small influence on the surface structure of the carbon nano tube, has simple integral purification process and is beneficial to improving the dispersibility of the carbon nano tube.
Description
Technical Field
The invention relates to the technical field of carbon nanotube purification, in particular to a method for purifying carbon nanotubes.
Background
In industrial production, a transition metal (Fe, co, ni, etc.) or a compound thereof is generally required as a catalyst to produce carbon nanotubes, and a large amount of transition metal impurities remain in the carbon nanotubes produced by the catalyst. In order to remove these transition metal impurities, there are generally two purification methods. One is to use high-temperature heat treatment, the heat treatment temperature is about 2500 ℃, the other is to firstly carry out oxidation treatment at 300-900 ℃ on the carbon nano tube, and then use dilute hydrochloric acid solution for purification treatment.
In recent years, a few literature materials select concentrated nitric acid or concentrated sulfuric acid to process carbon nanotubes, for example, CN113003565a shows that the concentrated nitric acid or concentrated sulfuric acid is used as a treatment solution for purifying the carbon nanotubes, and the method has simple process and improves the purity of the carbon nanotubes to a certain extent, but the strong oxidation treatment seriously damages the surface structure of the carbon nanotubes, so that the conductivity of the carbon nanotubes is reduced. CN109650379B uses gradient oxidation and acid washing to purify single-wall carbon nanotubes, while improving the purity of carbon nanotubes and avoiding damage to the surface structure of carbon nanotubes, the overall process conditions are complex, and the purification cost is high, so there is room for improvement.
In view of the foregoing, the inventors have found that it is necessary to provide a method for purifying carbon nanotubes which can effectively improve the purity of carbon nanotubes, has little influence on the surface structure of carbon nanotubes, and is simple in overall process.
Disclosure of Invention
In order to solve the problem of complicated purification process of carbon nanotubes, the inventors consider that it is necessary to provide a method for purifying carbon nanotubes, which can not only effectively improve the purity of carbon nanotubes, have less influence on the surface structure of carbon nanotubes, have a simple overall process, but also facilitate improving the dispersibility of carbon nanotubes.
In a first aspect, the present application provides a method for purifying carbon nanotubes, which adopts the following technical scheme:
a method for purifying carbon nanotubes comprises the following steps: mixing carbon nanotubes, oxidant and dilute acid for reaction, adding (6×10) per 5g carbon nanotubes -3 ~32×10 -3 ) mol of oxidant and 150-600g H + And (3) carrying out post-treatment on dilute acid with the concentration of 1.8-20 mol/L after the reaction is finished to obtain the purified carbon nano tube.
In the purification reaction process of the carbon nano tube, the oxidation degree of the carbon nano tube is controlled by controlling the reaction of the dilute acid and the oxidant with the carbon nano tube in a specific mass ratio, and the structure of the carbon nano tube can be slightly destroyed under the oxidation degree, so that the transition metal impurities coated in the carbon nano tube are in contact reaction with the dilute acid solution, and the purification effect of the carbon nano tube is better; in addition, as dilute acid and oxidant are compounded in a specific mass ratio in the purification process, the oxidation degree of the carbon nano tube is low, so that the damage degree of the carbon nano tube structure is low, and the conductivity of the carbon nano tube is not obviously changed, so that the defect that the conductivity of the carbon nano tube is easy to be reduced after purification in the prior art is overcome; the method for purifying the carbon nano tube is simple and has small operation difficulty, and is favorable for reducing the treatment cost of the carbon nano tube, so that the purification treatment effect of the carbon nano tube is better.
In addition, in the pulping process, the carbon nanotubes are easy to break along the structural defect generated by the purification, and the tube length of the carbon nanotubes is shortened to improve the dispersibility of the carbon nanotubes, so that the problem that the carbon nanotubes are difficult to disperse at present is solved.
Preferably, the temperature of the reaction is 10-70 ℃, and the time of the reaction is 30-200min.
Under the reaction conditions, the carbon nano tube can be effectively purified, the structural damage degree of the carbon nano tube is small, the carbon nano tube can be better in purification effect and simultaneously maintain better conductivity, the purification reaction temperature of the carbon nano tube is low, the reaction time is short, the energy consumption for purifying the carbon nano tube can be effectively reduced, and therefore, the energy is effectively saved, and the method has higher economic value.
Preferably, the H + The concentration is 3.5-13.5 mol/L.
By oxidizing agent with a specific concentration of H + Under the cooperation, the oxidation degree of the carbon nano tube is better, so that transition metal impurities are not easy to remain after the carbon nano tube is purified, the purification degree of the carbon nano tube is higher, meanwhile, the structural damage degree of the carbon nano tube is lower, the conductivity of the carbon nano tube is not easy to drop, and the carbon nano tube can obtain better dispersibility in the pulping process.
Preferably, the dilute acid is a non-oxidizing acid.
Non-oxidative acids such as hydrochloric acid, carbonic acid, dilute sulfuric acid, silicic acid, metaaluminate and the like have weak oxidizing property, achieve the effect of purifying the carbon nanotubes after being cooperated with an oxidant, and simultaneously lead the carbon nanotubes to be difficult to excessively oxidize so as to reduce the conductivity.
Further, the non-oxidizing acid is dilute sulfuric acid. Compared with other non-oxidizing acids, the dilute sulfuric acid is not easy to generate toxic and harmful substances in the purification reaction process, has small overall pollution and is safe in reaction environment.
Preferably, the oxidant is one or more of potassium permanganate, potassium perchlorate, potassium dichromate and hydrogen peroxide solution, and the mass fraction of the hydrogen peroxide is not less than 20%.
The potassium permanganate, the hydrogen peroxide, the potassium perchlorate and the potassium dichromate have better oxidability, and the components can be matched with dilute sulfuric acid to better control the oxidation degree of the carbon nano tube, so that the surface damage degree of the carbon nano tube is reduced, the carbon nano tube obtains better purification effect and keeps better conductivity. The potassium perchlorate and the potassium dichromate are easy to produce polluted chlorine or heavy metal chromium after the carbon nano tube purification reaction, and the potassium permanganate and the hydrogen peroxide are safe and are not easy to produce toxic and harmful substances, so the application further selects the potassium permanganate and the hydrogen peroxide as oxidizing agents.
Preferably, the carbon nanotubes are one or a combination of two of original multi-wall carbon nanotubes, double-wall carbon nanotubes and single-wall carbon nanotubes.
The original multi-wall carbon nanotubes, single-wall carbon nanotubes and double-wall carbon nanotubes and their mixtures can obtain better purification effect under the above method, and simultaneously maintain better conductivity.
Preferably, the post-treatment is solid-liquid separation after the reaction is finished, and then the carbon nanotubes are washed to be neutral, so as to obtain the purified carbon nanotubes.
The post-treatment is simple, the operation is convenient, the purity of the obtained purified carbon nanotube is high, the conductivity change rate is small, and the dispersibility is good. Further, water is used as a liquid for washing the carbon nanotubes.
In a second aspect, the present application provides a carbon nanotube conductive paste, which adopts the following technical scheme:
the carbon nano tube slurry is prepared by purifying the carbon nano tube obtained by the method, a dispersing agent and a solvent according to the mass ratio of 1: (0.2-1): (5-125) and is formed by combining.
The preparation method of the carbon nano tube slurry comprises the steps of mixing and uniformly dispersing the carbon nano tube purified by the method, the dispersing agent and the solvent according to the mass ratio to obtain the carbon nano tube slurry.
The carbon nano tube purified by the method is uniformly dispersed in a solvent to obtain carbon nano tube slurry with high dispersibility and stability, and the slurry can be further applied to battery products as conductive slurry. The slurry is used as a raw material of the silicon anode material slurry, and the dispersibility of the carbon nano tube purified by the method is improved, so that the viscosity of the silicon anode material slurry and the resistivity of the silicon anode pole piece are reduced, and the electrochemical performance of the battery is improved.
In summary, the present application has the following advantages:
1. according to the method, the dilute acid, the oxidant and the carbon nano tube are controlled to be matched in a specific proportion, so that the effect of keeping better conductivity of the carbon nano tube while purifying the carbon nano tube is achieved, and the process for purifying the carbon nano tube is simple, convenient to implement and high in economic value.
2. The non-oxidative acid and the oxidant are matched in a specific proportion to control the oxidation degree of the carbon nano tube, so that the purification effect of the carbon nano tube is good, the surface structure damage is small, and the conductivity change of the carbon nano tube is small.
3. The carbon nanotube slurry prepared by the purified carbon nanotube has the advantages of high purity, good conductivity and good dispersibility, and has higher economic value.
Drawings
FIG. 1 is a process flow diagram of a method for purifying carbon nanotubes.
Fig. 2 is an SEM image of carbon nanotubes in the slurry prepared in application example 3.
Fig. 3 is an SEM image of carbon nanotubes in the slurry prepared in comparative example 1.
Fig. 4 is an SEM image of the purified carbon nanotube slurry prepared in application example 3 in a silicon negative electrode slurry.
Fig. 5 is an SEM image of the purified carbon nanotube slurry prepared in comparative example 1 in a silicon negative electrode slurry.
FIG. 6 is a Raman spectrum of the purified carbon nanotubes prepared in example 3 and comparative example 4.
Detailed Description
In the following examples, a process flow diagram of a method of purifying carbon nanotubes is shown in FIG. 1.
Example 1
A method for purifying carbon nanotubes comprises the following steps:
step (1), 5g of single-walled carbon nanotubes and 1g of potassium permanganate (6.3X10 -3 mol) was added to 150g of 9.38mol/L dilute sulfuric acid and reacted at 10℃for 30min.
And (2) carrying out suction filtration after the reaction is finished to separate solid from liquid, and washing the reacted single-walled carbon nanotubes with deionized water to be neutral to obtain the purified carbon nanotubes.
Experiment 2
A method for purifying carbon nanotubes comprises the following steps:
step (1), 5g of single-walled carbon nanotubes and 5g of potassium permanganate (31.6X10 -3 mol) was added to 600g of 0.94mol/L dilute sulfuric acid and reacted at 50℃for 200min.
And (2) carrying out suction filtration after the reaction is finished to separate solid from liquid, and washing the reacted single-walled carbon nanotubes with deionized water to be neutral to obtain the purified carbon nanotubes.
Example 3
A method for purifying carbon nanotubes comprises the following steps:
step (1), 5g of single-walled carbon nanotubes and 1.5 g of potassium permanganate (9.4X10 -3 mol) was added to 500g of 6.57mol/L dilute sulfuric acid and reacted at 30℃for 1 hour.
And (2) carrying out suction filtration after the reaction is finished to separate solid from liquid, and washing the reacted single-walled carbon nanotubes with deionized water to be neutral to obtain the purified carbon nanotubes.
Example 4
A method for purifying carbon nanotubes comprises the following steps:
step (1), 5g of single-walled carbon nanotubes and 5g of potassium permanganate (31.6X10 -3 mol) was added to 500g of 1.87mol/L dilute sulfuric acid and reacted at 30℃for 2 hours.
And (2) carrying out suction filtration after the reaction is finished to separate solid from liquid, and washing the reacted single-walled carbon nanotubes with deionized water to be neutral to obtain the purified carbon nanotubes.
Example 5
A method for purifying carbon nanotubes comprises the following steps:
step (1), 5g of single-walled carbon nanotubes and 2.5g of 30% by mass hydrogen peroxide (22.1X10 g) -3 mol) was added to 200g of 4.69mol/L dilute sulfuric acid and reacted at 30℃for 2 hours.
And (2) carrying out suction filtration after the reaction is finished to separate solid from liquid, and washing the reacted single-walled carbon nanotubes with deionized water to be neutral to obtain the purified carbon nanotubes.
Example 6
A method for purifying carbon nanotubes comprises the following steps:
step (1), 5g of multi-walled carbon nanotubes and 3.5g of potassium permanganate (22.1X10 -3 mol) was added to 200g of 4.69mol/L dilute sulfuric acid and reacted at 30℃for 1.5 hours.
And (2) carrying out suction filtration after the reaction is finished to separate solid from liquid, and washing the reacted multiwall carbon nanotubes with deionized water to be neutral to obtain the purified carbon nanotubes.
Example 7
A method for purifying carbon nanotubes comprises the following steps:
step (1), taking 5g of multi-walled carbon nanotubes and 5g of hydrogen peroxide (29.4X10) -3 mol) was added to 200g of 1.87mol/L dilute sulfuric acid and reacted at 30℃for 1.5 hours.
And (2) carrying out suction filtration after the reaction is finished to separate solid from liquid, and washing the reacted multiwall carbon nanotubes with deionized water to be neutral to obtain the purified carbon nanotubes.
Comparative example 1
5g of single-wall carbon nano tube is put into a tube furnace for pre-oxidation treatment at 500 ℃ for 2 hours, then 1.63mol/L of dilute hydrochloric acid is used for pickling, finally, after solid-liquid separation is carried out by a suction filtration method, the reacted single-wall carbon nano tube is washed to be neutral by deionized water, and the purified carbon nano tube is obtained.
Comparative example 2
5g of multi-wall carbon nano tube is put into a tube furnace to be pre-oxidized for 2 hours at 400 ℃, then 1.63mol/L of dilute hydrochloric acid is used for pickling, finally, after solid-liquid separation is carried out by a suction filtration method, the multi-wall carbon nano tube after reaction is washed to be neutral by deionized water, and the purified carbon nano tube is obtained.
Comparative example 3
The difference from example 3 is that: in the step (1), under the condition of not adding potassium permanganate, 5g of single-wall carbon nanotubes are added into 500g of 6.57mol/L dilute sulfuric acid, and the reaction is carried out for 30min at 10 ℃.
Comparative example 4
The difference from example 3 is that: in the step (1), the dilute sulfuric acid of 6.57mol/L is replaced by 13.14mol/L of concentrated sulfuric acid in an equivalent manner.
Application example 1
The carbon nanotube slurry is prepared by the following steps:
step a, dissolving 3.2g of sodium methylcellulose in 393.6g of water, and sanding for 10 minutes at a rotating speed of 4500r/min to obtain sodium methylcellulose dispersion.
Step b, adding 3.2g of the single-walled carbon nanotube purified in the embodiment 1 into the sodium methylcellulose dispersion liquid, and sanding for 60 minutes at the rotating speed of 4500r/min to obtain carbon nanotube slurry.
Application examples 2 to 5
The difference from application example 1 is that: in step b, the single-walled carbon nanotubes purified in example 1 were replaced with the single-walled carbon nanotubes purified in examples 2 to 5, respectively, in an equivalent manner in application examples 2 to 5.
Application example 6
The carbon nanotube slurry is prepared by the following steps:
step a, dissolving 15g of polyvinylpyrrolidone in 410g of water, and sanding for 10 minutes at a rotating speed of 4500r/min to obtain polyvinylpyrrolidone dispersion.
And b, adding 75g of the multi-wall carbon nano tube purified in the example 6 into the polyvinylpyrrolidone dispersion liquid, and sanding for 50 minutes at the rotating speed of 4500r/min for dispersion to obtain carbon nano tube slurry.
Application example 7
The difference from application example 6 is that: in step b, application example 7 replaced the multi-walled carbon nanotubes purified in example 6 with the same amount of multi-walled carbon nanotubes purified in example 7.
Blank sample 1
The difference from application example 3 is that: in step b, the single-walled carbon nanotubes purified in example 1 were replaced with the single-walled carbon nanotubes which were not purified in equal amounts.
Blank sample 2
The difference from application example 6 is that: in step b, the multi-walled carbon nanotubes purified in example 6 were replaced with the multi-walled carbon nanotubes which were not purified in equal amounts.
Comparative example 1 was used
The difference from application example 3 is that: in step b, the single-walled carbon nanotubes obtained in comparative example 1 were used in the same amount as those obtained in example 1.
Comparative example 2 was used
The difference from application example 6 is that: in step b, the multi-walled carbon nanotubes obtained in comparative example 2 were used in place of the multi-walled carbon nanotubes purified in example 6 in equal amounts.
Comparative example 3 was used
The difference from application example 3 is that: in step b, the single-walled carbon nanotubes obtained in comparative example 3 were used in place of the single-walled carbon nanotubes purified in example 1 in equal amounts.
Comparative example 4 was used
The difference from application example 3 is that: in step b, the single-walled carbon nanotubes obtained in comparative example 4 were used in place of the single-walled carbon nanotubes purified in example 1 in equal amounts.
Performance test
Experiment 1
The purity of the carbon nanotubes in each example was tested using a synchronous thermogravimetric analysis instrument model us TA Discovery SDT 650.
Experiment 2
The viscosity of the carbon nanotube slurry of each application example and the application comparative example was tested using a rheometer model An Dongpa RheolabQC.
Experiment 3
Viscosity and conductivity testing of carbon nanotube slurries
The negative electrode composite slurry is prepared by adopting the carbon nanotube slurry, the viscosity of the negative electrode composite slurry is tested, the prepared negative electrode composite slurry is coated on a copper foil for drying, and the resistivity of the film is tested by adopting a pole piece resistivity tester.
Wherein, the negative electrode composite slurry prepared by the carbon nano tube slurries of application examples 1-5 and comparative examples 1, 3 and 4 consists of the following components in percentage by mass: 96.4% by mass of silicon-graphite composite (capacity 500 mAh/g), 3.5% by mass of sodium carboxymethylcellulose and 0.1% by mass of carbon nanotube slurry prepared by using single-walled carbon nanotubes of comparative examples 1 to 5 and comparative examples 1, 3 and 4.
The negative electrode slurry prepared by the carbon nano tube slurry of the application examples 6-7 and the application comparative example 2 comprises the following components in percentage by mass: 95.5% of silicon-graphite composite material (capacity 500 mAh/g), 3.5% of sodium carboxymethylcellulose and 1% of carbon nanotube slurry prepared by using the multiwall carbon nanotubes of comparative example 2.
The test data for experiments 1-3 are detailed in Table 1.
TABLE 1
| Purity of carbon nanotubes | Viscosity of carbon nanotube paste (mPa. S) | Silicon cathode paste viscosity (mPa. S) | Resistivity of silicon negative electrode sheet (Ω cm) | |
| Application example 1 | 99.3% | 1256 | 3382 | 0.329 |
| Application example 2 | 99.2% | 1320 | 3408 | 0.337 |
| Application example 3 | 99.3% | 1300 | 3436 | 0.335 |
| Application example 4 | 99.4% | 1288 | 3375 | 0.324 |
| Application example 5 | 99.4% | 1290 | 3396 | 0.330 |
| Application example 6 | 99.5% | 1890 | 4639 | 2.418 |
| Application example 7 | 99.6% | 1800 | 4520 | 2.504 |
| Blank sample 1 | 85.0% | 4030 | 4210 | 0.658 |
| Blank sample 2 | 93.5% | 2400 | 5380 | 4.450 |
| Comparative example 1 was used | 96.4% | 3050 | 3954 | 0.345 |
| Comparative example 2 was used | 98.1% | 4500 | 5062 | 2.861 |
| Comparative example 3 was used | 88.3% | 3870 | 4048 | 0.583 |
| Comparative example 4 was used | 99.6% | 1240 | 3084 | 0.648 |
The data of application examples 1-7 and blank samples 1-2 in Table 1 show that, relative to the carbon nanotubes which are not subjected to purification treatment, the purity of the single-walled carbon nanotubes in examples 1-7 is greater than 99%, and the resistivity change rate of the single-walled carbon nanotubes in examples 1-7 applied to the silicon negative electrode sheet is smaller, which proves that the conductivity change of the single-walled carbon nanotubes after purification is not great, the structural damage degree of the single-walled carbon nanotubes after purification treatment is smaller, and the viscosity test of the carbon nanotube slurry and the viscosity test of the silicon negative electrode slurry show that the purification process of the single-walled carbon nanotubes is simple, and the operation is convenient. In addition, the viscosity of the carbon nanotube slurry in application examples 1 to 7 was reduced, and the carbon nanotubes were more easily dispersed in the solvent, thus proving that the dispersibility and stability of the carbon nanotubes were improved.
The data comparison of application example 3 and application comparative example 1, application example 6 and application comparative example 2 in table 1 shows that compared with the traditional pre-oxidation treatment purification method, the effect of purifying the carbon nanotubes and the conductivity of the purified carbon nanotubes are similar to those of the traditional pre-oxidation treatment purification method, but the method for purifying the carbon nanotubes is quite simple, convenient to operate, beneficial to reducing the operation difficulty and energy consumption of purifying the carbon nanotubes, and has higher economic value. In addition, as can be seen from fig. 2-5, the carbon nanotubes purified in embodiment 3 of the present application can be better dispersed in the solution system both in the slurry and in the silicon negative electrode slurry, while the carbon nanotubes in comparative example 1 are easy to be present in a agglomerated manner both in the slurry and in the silicon negative electrode slurry, and therefore, the carbon nanotubes purified in embodiment have the advantage of better dispersibility compared with the carbon nanotubes purified in comparative example 1.
As can be seen from comparison of the data of application example 3 and application comparative examples 3 to 4 in table 1, the results of application comparative example 3 show that the purification of carbon nanotubes using dilute sulfuric acid alone is poor without adding an oxidizing agent, and thus it is difficult to obtain carbon nanotubes with high purity, and in order to obtain carbon nanotubes with better purity, it is more preferable to use an oxidizing acid or an oxidizing agent or a combination of both having a high concentration as a reagent for purifying carbon nanotubes, as in application comparative example 4 while using a concentrated acid having a strong oxidizing property and an oxidizing agent as a reagent for purifying reaction, the purifying effect of carbon nanotubes is indeed expected. Referring to fig. 6, the ratio of IG/ID in the raman spectrum of the carbon nanotube in example 3 is 10.53, and the ratio of IG/ID in example 3 is larger, which indicates that the structure of the carbon nanotube after purification in example 3 is more complete and the conductivity is good, while the IG/ID of the carbon nanotube after purification in comparative example 4 is 4.21, which is significantly smaller than that in example 3, which indicates that the surface of the carbon nanotube in comparative example 4 has more functional groups introduced than that of the carbon nanotube in example 3, resulting in serious surface damage of the carbon nanotube after purification in comparative example 4, because the surface structure of the carbon nanotube is severely damaged after the concentrated sulfuric acid and the oxidizing agent are matched in comparative example 4, the conductivity of the carbon nanotube is reduced, which seriously affects the application of the carbon nanotube as a conductive agent in the battery field, and the prepared silicon negative electrode sheet has a relatively good purity after purification, and the resistivity change of the prepared silicon negative electrode sheet is not large, which proves that the surface of the carbon nanotube has relatively low conductivity after the dilute sulfuric acid is matched with potassium permanganate.
The present embodiment is merely illustrative of the present application and is not intended to be limiting, and those skilled in the art, after having read the present specification, may make modifications to the present embodiment without creative contribution as required, but is protected by patent laws within the scope of the claims of the present application.
Claims (8)
1. A method for purifying carbon nanotubes is characterized in thatIn the following steps: mixing carbon nanotubes, oxidant and dilute acid for reaction, adding (6×10) per 5g carbon nanotubes -3 ~32×10 -3 ) mol of oxidant and 150-600g H + The concentration of the dilute acid is 1.8-20 mol/L, the dilute acid is non-oxidizing acid, and the oxidant is one or a combination of more of potassium permanganate, potassium perchlorate, potassium dichromate and hydrogen peroxide solution; post-treatment is carried out after the reaction is finished, so as to obtain the purified carbon nano tube; the temperature of the reaction is 10-50 ℃, and the time of the reaction is 30-200min.
2. The method for purifying carbon nanotubes of claim 1, wherein: the H is + The concentration is 3.5-13.5 mol/L.
3. The method for purifying carbon nanotubes of claim 1, wherein: the non-oxidizing acid is dilute sulfuric acid.
4. The method for purifying carbon nanotubes of claim 1, wherein: the mass fraction of the hydrogen peroxide is not less than 20%.
5. The method for purifying carbon nanotubes of claim 1, wherein: the carbon nano tube is one or the combination of two of original multi-wall carbon nano tube, double-wall carbon nano tube and single-wall carbon nano tube.
6. The method for purifying carbon nanotubes of claim 1, wherein: and the post-treatment is to carry out solid-liquid separation after the reaction is finished, and wash the carbon nano tube to be neutral, so as to obtain the purified carbon nano tube.
7. The method of purifying carbon nanotubes of claim 6, wherein: water was used as a liquid for washing the carbon nanotubes.
8. A carbon nanotube paste characterized by: the carbon nanotubes purified by the method of any one of claims 1 to 7, a dispersant and a solvent in a mass ratio of 1: (0.2-1): (5-125) and is formed by combining.
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