KR20170032566A

KR20170032566A - Carbon nanotubes having improved crystallinity

Info

Publication number: KR20170032566A
Application number: KR1020150130049A
Authority: KR
Inventors: 강경연; 우지희; 조동현; 이승용; 장형식
Original assignee: 주식회사 엘지화학
Priority date: 2015-09-15
Filing date: 2015-09-15
Publication date: 2017-03-23
Also published as: CN107074548A; WO2017048053A1

Abstract

The present invention relates to a method for chlorinating a residual metal in a carbon nanotube by reacting the metal remaining in the carbon nanotube with a chlorine containing compound at a first temperature in a vacuum or an inert atmosphere to chlorinate the residual metal, &Lt; / RTI > , The average value of the intensity ratios (I _G / I _D ) of the G band and the D band measured by Raman spectroscopy in comparison with the pre-purification carbon nanotubes was compared with the pre-purification carbon nanotubes Thereby providing carbon nanotubes having an increase of 20% or more.

Description

CARBON NANOTUBES HAVING IMPROVED CRYSTALLINITY < RTI ID = 0.0 >

The present invention provides a carbon nanotube having improved crystallinity by removing impurities contained in carbon nanotubes produced by reacting with a chlorine-containing compound.

Generally, carbon nanotubes (hereinafter referred to as "CNTs") have a diameter of about 3 to 150 nm, specifically about 3 to 100 nm, and a cylindrical carbon tube whose length is several times the diameter, for example, 100 times or more Quot; These CNTs are composed of layers of ordered carbon atoms and have different types of cores. Such CNTs are also referred to as carbon fibrils or hollow carbon fibers, for example.

The CNT can be generally manufactured by an arc discharge method, a laser evaporation method, a chemical vapor deposition method, or the like. Among them, the arc discharge method and the laser evaporation method are difficult to mass-produce, and there is a problem that economical efficiency is lowered due to an excessive cost of producing an arc or a cost of purchasing a laser apparatus.

In chemical vapor deposition, carbon nanostructures are produced by dispersing and reacting metal catalyst particles and a hydrocarbon-based raw material gas in a fluidized bed reactor at a high temperature. That is, the metal catalyst reacts with the raw material gas while floating in the fluidized bed reactor by the raw material gas to grow the carbon nanostructure.

Carbon nanotubes exhibit nonconductive, conductive or semiconducting properties due to their inherent chirality. The carbon atoms are connected by a strong covalent bond. The tensile strength of the carbon nanotubes is about 100 times greater than that of steel. The carbon nanotubes are excellent in flexibility and elasticity, And is chemically stable. Due to its size and specific properties, it is industrially important in the production of composites, and has high utility in the fields of electronic materials, energy materials and various other fields. For example, the carbon nanotube may be applied to an electrode of an electrochemical storage device such as a secondary cell, a fuel cell, or a super capacitor, an electromagnetic wave shield, a field emission display, or a gas sensor.

However, the catalyst metal used in the production of carbon nanotubes is treated as an impurity when the carbon nanotubes are to be used, and the basic physical properties such as thermal stability and chemical stability are reduced by the metal impurities. Therefore, at this time, there is a need for a method of improving basic physical properties of the carbon nanotubes by purifying only the carbon nanotubes.

The present invention provides a carbon nanotube in which the residual metal contained in the produced carbon nanotube is removed to thereby significantly improve thermal stability.

According to an aspect of the present invention, there is provided a method for producing a carbon nanotube, comprising: reacting a metal remaining in a carbon nanotube with a chlorine-containing compound at a first temperature in a vacuum or an inert atmosphere to chlorinate the residual metal; And

Evaporating and removing the chlorinated residual metal in an inert gas or vacuum atmosphere at a second temperature higher than the first temperature;

&Lt; / RTI >

(I _G / I _D ) of the G band and the D band measured by Raman spectroscopy is increased by 20% or more as compared to the pre-purification carbon nanotube.

The second temperature T ₂ may be at a temperature of T ₁ + 300 ° C or higher.

The first temperature is selected at 500 ° C to 1000 ° C, and the second temperature is selected at 800 ° C to 1500 ° C.

Further, the temperature at which the purified carbon nanotubes start to be oxidized may be 550 ° C or higher.

In addition, the metal impurity content remaining in the purified carbon nanotube may be 50 ppm or less.

Further, the purification process of reacting with the above-mentioned chlorine-containing compound to evaporate the residual metal requires N ₂ Gas or a vacuum atmosphere.

The carbon nanotubes may be prepared by using a metal catalyst containing cobalt (Co), and may contain at least one metal component selected from among iron (Fe), molybdenum (Mo), vanadium (V) It can be more inclusive.

The carbon nanotubes may have a Co content of 40 ppm or less after the purification process.

In addition, the carbon nanotubes may be one produced by chemical vapor deposition (CVD) on a fluidized bed reactor.

In addition, the carbon nanotube may be in the form of an Entangle or a Bundle.

In addition, the chlorine-containing compound may be chlorine (Cl ₂ ) gas or trichloromethane (CHCl ₃ ) gas.

Further, the first temperature may be 700 ° C to 900 ° C, and the second temperature may be 900 ° C to 1500 ° C.

The carbon nanotube according to the present invention reacts with a chlorine compound at a high temperature to remove the residual metal generated in the production process of the carbon nanotube using the metal catalyst, thereby effectively removing impurities such as residual metal Can be removed. Particularly, the chlorine gas treatment process proceeding at the first temperature, which is relatively low temperature, and the chlorine metal removal process proceeding to the second temperature in the nitrogen (N ₂ ) or vacuum atmosphere, can increase the metal removal efficiency remaining in the carbon nanotube , And the second step proceeds in a nitrogen or vacuum atmosphere, so that chlorine remaining in the carbon nanotubes can be removed together. The physical properties of the carbon nanotubes can be further improved. In particular, oxidation stability and conductivity due to the improvement of the crystallinity can be improved, and this can be useful as a composite material of a metal composite and a conductive polymer.

Fig. 1 shows SEM images of the carbon nanotubes of Example 1 and Comparative Example 1 before and after purification.
2 is a graph showing TEM_EDX results of carbon nanotubes before and after purification.
3 is a graph comparing G band and D band measured by Raman spectroscopy for the carbon nanotubes of Example 1 and Comparative Example 1. FIG.

The terms and words used in the present specification and claims should not be construed as limited to ordinary or dictionary meanings and the inventor can properly define the concept of the term to describe its invention in the best possible way And should be construed in accordance with the principles and meanings and concepts consistent with the technical idea of the present invention.

Hereinafter, the present invention will be described in detail.

According to a preferred embodiment of the present invention,

Reacting a metal remaining in the carbon nanotube with a chlorine-containing compound at a first temperature in a vacuum or an inert atmosphere to chlorinate the residual metal; And

Evaporating and removing the chlorinated residual metal at a second temperature higher than the first temperature;

, The average value of the intensity ratio (I _G / I _D ) of the G band and the D band measured by Raman spectroscopy is increased by 20% or more as compared with the pre-purification carbon nanotubes.

The present invention uses a method of removing residual metal generated from a metal catalyst used in a manufacturing process of carbon nanotubes by chlorinating the residual metal by reacting with a chlorine containing compound at a high temperature, Method can be used to purify the carbon nanotubes, whereby deterioration of physical properties due to metal impurities such as residual metals can be improved. Particularly, in the thermal stability, before the oxidation start temperature of the purified carbon nanotubes is refined, The carbon nanotubes can exhibit an increase rate of 100 DEG C or higher, and can be more efficiently used for a flame retardant or a metal composite which can be used in a high temperature environment.

According to one embodiment, the first temperature is selected from 500 ° C to 1000 ° C, and the second temperature is selected from 800 ° C to 1500 ° C.

Further, the content of the metal impurities remaining in the carbon nanotubes after the purification process may be reduced by 10 to 100 times that before the purification, that is, almost all the remaining metal is removed. This is because the chlorinated metal has a boiling point It is possible to utilize the principle of evaporating the liquefied or gaseous metal to a higher temperature through the chlorination process by utilizing the low characteristic compared with the metal. Since this utilizes the high-temperature reaction of the gas phase, There is an advantage that it does not cause physical damage.

Hereinafter, the purification process of the carbon nanotubes will be described in more detail.

Reacting the metal remaining in the produced carbon nanotube with a chlorine-containing compound at a first temperature in a vacuum or inert gas atmosphere to chlorinate the residual metal; And And evaporating and removing the chlorinated residual metal at a second temperature higher than the first temperature.

According to one embodiment, the chlorine-containing compound may be chlorine (Cl ₂ ) or trichloromethane (CHCl ₃ ) gas. Since the chlorine-containing compound is low in reactivity with the carbon nanotubes, the damage to the produced carbon nanotubes can be further reduced.

The first temperature (T ₁ ) at which chlorination of the metal takes place may be 500 ° C to 1000 ° C, and more preferably 700 ° C to 900 ° C. The chlorination reaction of metal impurities such as catalytic metal in the carbon material may not be smooth at a temperature lower than 500 ° C.

The heating process after the chlorination of the metal is performed at a second temperature (T ₂ ) which is higher than the first temperature (T ₁ ). Specifically, T ₂ may be a temperature of T ₁ + 300 ° C or higher, The second temperature may be in the range of 800 ° C to 1500 ° C, preferably 900 ° C to 1400 ° C. If the temperature is lower than 900 ° C or lower than the first temperature, the removal reaction of the chlorinated metal is not smooth Residual metals and chlorinated metals may remain in the carbon nanotubes and act as impurities, which may deteriorate the physical properties of the carbon nanotubes. In addition, at a temperature of 1500 占 폚 or higher, catalytic graphitization may occur due to the residual metal, and metal removal may not be easy.

Also, the chlorination reaction performed at the first temperature may be maintained for about 10 minutes to 1 hour so that the chlorination process of the residual metal is completed more completely. The total flow rate depends on the size of the charged carbon nanotube and the reactor Can be adjusted.

After the chlorination step, the evaporation and removal of the chlorinated metal at the second temperature may be performed in an inert gas or a vacuum atmosphere for 30 minutes to 300 minutes, which removes only the chlorinated residual metal without affecting the carbon nanotube It should be within range. In addition, the evaporation and removal of the chlorinated metal can be carried out while alternately forming a vacuum atmosphere and an inert gas atmosphere, which can further enhance the removal efficiency.

Further, the chlorination reaction of the residual metal may occur in a vacuum or nitrogen gas atmosphere. More specifically, a reaction in which the residual metal is chlorinated by introducing a chlorine-containing compound gas after raising the temperature of the reactor or the reactor filled with the carbon nanotube to a vacuum or nitrogen atmosphere to a first temperature can be performed. In this case, in the chlorination step performed at the first temperature, only the chlorination reaction of the metal may mainly occur, and the removal reaction by evaporation of the chlorinated residual metal may occur mainly at the second temperature. At this time, in the evaporation and removal process of the residual metal, the introduction of the chlorine-containing compound is stopped and the inside of the reactor or the inside of the reactor is converted into the vacuum atmosphere, so that evaporation of the chlorinated metal can occur more smoothly.

In this case, the vacuum atmosphere means a pressure of 1 torr or less, and the inert gas means an inert gas such as nitrogen (N ₂ ) or argon (Ar). In addition, the second step in which the evaporation and the chlorination metal removal reaction take place may be carried out at a pressure of 500 torr to 800 torr, preferably 600 to 700 torr. In addition, the chlorine metal and chlorine compound removal and evaporation processes proceeding to the second temperature can be alternately applied in a vacuum and inert gas atmosphere, and can be applied in a pulse form. Specifically, a vacuum may be formed up to 1 torr, and then an inert gas may be injected again after a certain period of time to apply a pressure of up to 500 torr. After that, vacuum may be repeatedly formed. The remaining residual metal can be removed and the purification efficiency can be further increased.

The metal impurity content of the carbon nanotubes from which the residual metal is removed by the above method may be 50 ppm or less, and the metal impurities of the carbon nanotubes can be measured by ICP analysis. According to one embodiment, the carbon nanotube may be a metal catalyst containing a metal such as cobalt (Co) or iron (Fe) as a main component. In this case, the content of the main metal may be 40 ppm or less And the total content may be 50 ppm or less.

The above-described method for purifying carbon nanotubes can effectively remove residual metals such as catalyst metals while suppressing damage or cutting of carbon nanotubes or solidifying carbon nanotubes with amorphous carbon material, It is possible to provide a carbon nanotube having improved mechanical properties and physical properties by suppressing physical damage or cutting of the carbon nanotube. In particular, it is possible to provide a carbon nanotube that is remarkably improved in thermal stability Can be provided.

The carbon nanotube according to the present invention may be one produced by growing a carbon nanotube by a chemical vapor synthesis method (CVD) through decomposition of a carbon source using a supported catalyst, and the catalytic metal carried on the supported catalyst may be a carbon nanotube Is not particularly limited.

Examples of the catalytic metal include at least one kind of metal selected from the group consisting of Groups 3 to 12 of the 18-element type periodic table recommended by IUPAC in 1990. Among them, at least one kind of metal selected from the group consisting of 3, 5, 6, 8, 9 and 10 is preferable, and iron (Fe), nickel (Ni), cobalt (Co), chromium (Cr) At least one metal selected from the group consisting of Mo, W, V, Ti, Ru, Rh, Pd, Pt and rare- Particularly preferred. Examples of the catalyst metal precursor include inorganic salts such as nitrates, sulfates and carbonates of catalyst metals, organic salts such as nitrates and acylates, organic complexes such as acetylacetone complexes, organic metal compounds and the like And is not particularly limited as long as it is a compound containing a catalytic metal.

It is widely known to control the reaction activity by using two or more of these catalytic metals and catalytic metal precursor compounds. For example, at least one element selected from iron (Fe), cobalt (Co), and nickel (Ni) and at least one element selected from titanium (Ti), vanadium (V), and chromium (Cr), molybdenum (Mo), and tungsten (W) can be exemplified. The metal catalyst may preferably be cobalt (Co) as a main component and further include at least one metal selected from iron (Fe), molybdenum (Mo), chromium (Cr), and vanadium (V).

The catalyst used in the carbon nanotube generation step is specifically a catalytically active metal precursor, _{Co (NO 3) 2 -6H 2O} , (NH 4) 6 Mo 7 O 24 -4H 2 O, Fe (NO 3) 2 -6H ₂ O or Ni (NO ₃ ) ₂ -6H ₂ O) dissolved in distilled water and then wet-impregnating the solution with a carrier such as Al ₂ O ₃ , SiO ₂ or MgO.

The catalyst may be a catalyst prepared by treating a catalytically active metal precursor with a support such as Al (OH) ₃ , Mg (NO ₃ ) ₂ or colloidal silica together with ultrasonic waves.

The catalyst may be prepared by a sol-gel method using a chelating agent such as citric acid or tartaric acid so that the catalytically active metal precursor can be dissolved in water, Or by co-precipitation of the active metal precursor.

In the method of the present invention, by bringing the supported catalyst and the carbon-containing compound into contact with each other under a heating region.

In the catalyst preparation process, it is preferable to use a supported catalyst using an impregnation method, which is higher than the bulk density processing catalyst when the supported catalyst is used, The possibility of occurrence of fine particles due to attrition which may occur during the fluidization process can be reduced and the mechanical strength of the catalyst itself is also excellent and the reactor operation can be stabilized.

The aluminum-based support which can be used in the present invention may be at least one member selected from the group consisting of Al ₂ O ₃ , AlO (OH) ₃ and Al (OH) ₃ , preferably alumina (Al ₂ O ₃ ). The aluminum (Al) -based support may further include at least one selected from the group consisting of ZrO ₂ , MgO, and SiO ₂ . The aluminum (Al) -based support may have a spherical or potato-like shape and may be composed of a material having a porous structure, a molecular sieve structure, a honeycomb structure, or another suitable structure so as to have a relatively high surface area per unit mass or volume.

According to one embodiment, a method for producing a supported catalyst for CNT synthesis according to the present invention comprises:

(1) mixing a support in a metal aqueous solution containing a catalyst component precursor and an active component precursor to form an aqueous solution containing the supported catalyst precursor;

(2) aging the impregnated aqueous solution containing the supported catalyst precursor to obtain a mixture;

(3) vacuum drying the mixture to coat the catalyst component and the active component on the surface of the support; And

(4) firing the resultant obtained by the vacuum drying to form a supported catalyst.

The carbon nanotubes can be prepared by a chemical vapor phase synthesis method in which carbon nanotubes are grown by a chemical vapor phase synthesis method by decomposing a carbon source using the catalyst.

Specifically, in the chemical vapor phase synthesis method, the carbon nanotube catalyst is introduced into a fluidized bed reactor, and at 500 to 900 ° C., at least one carbon source selected from saturated or unsaturated hydrocarbons having 1 to 4 carbon atoms, or a mixture of hydrogen and nitrogen Or by injecting gas. The step of growing a carbon nanotube by injecting a carbon source into the catalyst for preparing a carbon nanotube may be performed for 30 minutes to 8 hours.

The carbon source is a saturated or unsaturated hydrocarbon group having 1 to 4 carbon atoms, such as ethylene (C ₂ H _4), acetylene (C ₂ H _2), methane (C ₂ H _4), propane (C ₃ H _8), such as one But is not limited thereto. Also, the mixed gas of hydrogen and nitrogen transports the carbon source, prevents the carbon nanotube from burning at high temperature, and helps decompose the carbon source.

The carbon nanotubes produced using the supported catalyst according to the present invention can be obtained in the form of a potato or spherical aggregate having a particle size distribution value (D _cnt ) of 0.5 to 1.0. For example, a catalyst obtained by impregnating and calcining a catalyst component and an active component into a spherical or potato-shaped granular support has a spherical or potato-like shape without a large change in shape, and the aggregated carbon nanotube aggregate grown on such a catalyst also has a shape The shape of the spherical or potato-like shape is enlarged only by a large diameter without a large change of the shape. Here, the spherical shape or the potato shape refers to a three-dimensional shape such as a spherical shape or an elliptical shape having an aspect ratio of 1.2 or less.

The particle size distribution value (D _cnt ) of the carbon nanotubes is defined by the following formula (1).

[Formula 1]

Dcnt = [Dn ₉₀ -Dn ₁₀ ] / Dn ₅₀

Dn ₉₀ is the number average particle size measured under the 90% standard in the absorbing mode using a Microtrac particle size analyzer after 3 hours of placing the CNT in the distilled water, Dn ₁₀ is the number average particle size measured under the 10% standard, And Dn ₅₀ is the number average particle size measured under the standard of 50%.

The particle size distribution value may preferably be 0.55 to 0.95, more preferably 0.55 to 0.9.

In the present invention, the carbon nanotubes may be of a bundle type or a non-bundled type having a flatness ratio of 0.9 to 1. The term " bundle " used in the present invention means a plurality of carbon nanotubes Refers to a bundle or rope configuration in which the tubes are arranged side by side or tangled. The 'non-bundle or entangled type' is a shape without a uniform shape such as a bundle or a rope shape. In case of the bundle type, the CNT bundle may have a diameter of 1 to 50 μm.

The flatness is defined by the following formula (2).

[Formula 2]

Flatness = the shortest diameter passing through the center of the CNT / the maximum diameter passing through the center of the CNT.

In the present invention, the carbon nanotube has a bulk density of 80 to 250 kg / m ³ . Specifically, the bulk density is defined by the following formula 3, and the density distribution of the carbon nanotubes can provide a specific range of the present invention.

[Formula 3]

Bulk density = CNT weight (kg) / CNT volume (m ³ )

In the present invention, the carbon nanotube may have an average particle diameter of 100 to 800 μm and a strand diameter of the carbon nanotube may be 10 to 50 nm.

The metal component remaining in the form of fine powder or impurity in the carbon nanotube having the above properties is reacted with a chlorine compound in a high temperature atmosphere to form a metal chlorides, thereby lowering the boiling point thereof. The temperature of the metal chlorides above the boiling point The carbon nanotubes can be purified using a process of evaporating and removing the carbon nanotubes under the condition that the carbon nanotubes can be purified. The carbon nanotubes produced by this method can have improved physical properties, and in particular, improved thermal stability, The present invention can be advantageously used for a carbon composite material used in an environment of < RTI ID = 0.0 >

EXAMPLES Hereinafter, the present invention will be described in detail with reference to Examples and Comparative Examples. However, the present invention is not limited to these Examples, but is merely an example for further illustrating the present invention.

Comparative Example One

Carbon nanotubes were synthesized on a lab scale fixed bed reactor using a Co / Fe containing metal catalyst for CNT synthesis. Specifically, the CNT synthesis catalyst prepared in the above process was attached to the middle portion of a quartz tube having an inner diameter of 55 mm, and then heated to a temperature of 650 ° C in a nitrogen atmosphere and maintained. While flowing hydrogen gas at a flow rate of 60 sccm And then synthesized for 2 hours to synthesize a main nanotube agglomerate of an entangled (non-bundle) type. The shape of the carbon nanotubes is shown in Fig.

Example One

20 g of the carbon nanotubes prepared in Comparative Example 1 were placed in a firing furnace. The furnace was evacuated to 1 torr and the temperature was raised to 900 캜. Next, chlorine (Cl ₂ ) gas was supplied to 680 torr. Thereafter, the temperature was raised to 1400 占 폚, held in a vacuum atmosphere for 2 hours, and then vacuum-cooled. The shape of the purified carbon nanotubes is shown in Fig.

TEM_EDX was measured to observe the change in the constitutional elements of the surface of the carbon nanotubes of Example 1 and Comparative Example 1 and is shown in Fig. The surface elements of the carbon nanotubes before and after the purification (Comparative Example 1) and after the purification (Example 1) were analyzed through a TEM-EDX analyzer. As a result, no specific elements other than carbon were detected on the surface of the purified carbon nanotubes . That is, the peaks detected before and after purification were the same, and there was no generation of additional peaks after purification. Therefore, it was found that there was no change in the carbon nanotubes due to Cl used in purification.

I _G / I _D by Raman spectroscopy of the carbon nanotubes of Example 1 and Comparative Example 1 was measured at a laser wavelength of 532 nm using a DXR Raman Microscope (Thermo Electron Scientific Instruments LLC). The results of Raman analysis are shown in FIG. 3, and I _G / I _D values were obtained and shown in Table 1.

division Cl ₂ treatment I _G / I _D ratio Average Standard Deviation Relative standard deviation (%) Example 1 O 0.99 0.01 1.38 Comparative Example 1 X 0.77 0.02 2.35

From the results of Table 1, it was found that the I _G / I _D value of the carbon nanotubes of Example 1 purified by the purification method according to the present invention was increased by 20% or more, indicating that the carbon nanotubes purified by the method of the present invention Indicating that the crystallinity of the tube is significantly improved. In addition, the results show that the standard deviation and the relative standard deviation% are decreased, which indicates that the purification process is performed uniformly on the whole sample, and secondly, the effect of improving the crystallinity from the purification process is also improved. It is possible to produce carbon nanotubes having even homogeneity of crystallinity by exerting an even effect.

Therefore, the method for purifying carbon nanotubes according to the present invention can provide carbon nanotubes excellent in crystallinity without changing the shape and elements of the carbon nanotubes.

While the present invention has been particularly shown and described with reference to specific embodiments thereof, those skilled in the art will appreciate that such specific embodiments are merely preferred embodiments and that the scope of the present invention is not limited thereby. something to do. It is therefore intended that the scope of the invention be defined by the claims appended hereto and their equivalents.

Claims

Reacting a metal remaining in the carbon nanotube with a chlorine-containing compound at a first temperature in a vacuum or an inert gas atmosphere to chlorinate the residual metal; And
Evaporating and removing the chlorinated residual metal to a second temperature (T ₂ ) of a temperature higher than the first temperature (T ₁ );
, The average value of the intensity ratio (I _G / I _D ) of the G band and the D band measured by Raman spectroscopy is increased by 20% or more as compared with the pre-purification carbon nanotube, .

The method according to claim 1,
Wherein an average value of an intensity ratio (I _G / I _D ) of the G band to the D band measured by Raman spectroscopy is 0.9 to 1.5.

The method according to claim 1,
Wherein the standard deviation of the average value of IG / ID measured by Raman spectroscopy is reduced by 40% or more as compared with the pre-purification carbon nanotube.

The method according to claim 1,
And the second temperature (T ₂ ) proceeds at a temperature of T ₁ + 300 ° C or higher.

The method according to claim 1,
Wherein the first temperature is selected from 500 ° C to 1000 ° C, and the second temperature is selected from 800 ° C to 1500 ° C.

The method according to claim 1,
Wherein the step of evaporating by the second temperature and the step of removing the chlorinated metal proceed in a vacuum or an inert gas atmosphere.

The method according to claim 1,
Wherein the refined carbon nanotubes have an oxidation initiation temperature of 550 DEG C or more.

The method according to claim 1,
And the content of metal impurities remaining in the purified carbon nanotubes is 50 ppm or less.

The method according to claim 1,
Wherein the carbon nanotubes are produced using a metal catalyst containing cobalt (Co).

10. The method of claim 9,
Wherein the carbon nanotube is produced using a metal catalyst further comprising at least one metal component selected from the group consisting of Fe, Mo, V, and Cr.

10. The method of claim 9,
The carbon nanotube having a Co content of 40 ppm or less after the step of purifying the carbon nanotubes.

The method according to claim 1,
Wherein the carbon nanotubes are prepared by chemical vapor deposition (CVD) on a fluidized bed reactor.

The method according to claim 1,
Wherein the carbon nanotube is in the form of an Entangle or a Bundle.

The method according to claim 1,
Wherein the chlorine-containing compound is chlorine (Cl ₂ ) gas or trichloromethane (CHCl ₃ ) gas.

The method according to claim 1,
Wherein the first temperature is 700 ° C to 900 ° C, and the second temperature is 900 ° C to 1500 ° C.