METHOD FOR CONTINUOUSLY SYNTHESIZING CARBON NANOTUBES

Abstract

The present disclosure relates to a method for continuously synthesizing carbon nanotubes using a plasma treated catalyst. The method for continuously synthesizing carbon nanotubes comprises: a plasma treating step of preparing metal nanoparticles by plasma treating metal salts in an H.sub.2 or NH.sub.3 atmosphere; a first mixture preparing step of preparing an emulsion mixture by mixing a solvent and a surfactant; a second mixture preparing step of preparing a second mixture by mixing the emulsion mixture and a carrier gas; and a reacting step of forming carbon nanotubes by introducing the second mixture and metal nanoparticles into a heated reactor. Accordingly, the catalyst can be prepared by reducing metal salts at a relatively low temperature and in a shorter time, the yield of the carbon nanotubes can be increased, and the diameter of the carbon nanotubes can be uniformly controlled, thereby enabling an economical and mass production of carbon nanotubes.

Claims

1. A method of continuously synthesizing carbon nanotubes, the method comprising: a plasma treating step of producing metal nanoparticles by performing plasma treatment on a metal salt in an H.sub.2 or NH.sub.3 atmosphere; a first mixture preparing step of preparing an emulsion mixture by mixing a solvent with a surfactant; a second mixture preparing step of preparing a second mixture by mixing the emulsion mixture with a carrier gas; and a reacting step of introducing the second mixture and metal nanoparticles into a heated reactor to form carbon nanotubes.

2. The method of claim 1, wherein in the plasma treating step, the plasma treating is performed in a gaseous atmosphere basically comprising H.sub.2 or NH.sub.3 atmosphere and additionally comprising nitrogen gas and a Group 18 inert gas.

3. (canceled)

4. The method of claim 1, further comprising an oxygen plasma treating step in which plasma treating is performed in an oxygen atmosphere after the plasma treating step.

5. The method of claim 1, wherein the plasma treating step is performed at a pressure in a range of 0.2 to 2.5 Torr.

6. The method of claim 1, wherein the plasma treating step is performed in a temperature range of 50 C. to 300 C. in a frequency range of 15 to 30 kHz.

7. The method of claim 1, wherein in the first mixture preparing step, the solvent is a carbon-containing solvent or a carbon-free solvent, and wherein when the carbon-free solvent is used in the first mixture preparing step, a carbon source gas is added in the second mixture preparing step.

8. A method for manufacturing carbon nanotubes, the method comprising: a mixing step of preparing a mixed solution by mixing a solvent, a metal precursor, and a support; a first heating step of preparing a catalyst support by heating the mixed solution under vibration; a dispersing step of preparing a catalyst dispersion solution by dispersing the catalyst carrier in a reducing solution; an electron beam applying step of irradiating the catalyst dispersion solution with an electron beam; a second heating step of preparing a functional catalyst support by heating after filtering the catalyst dispersion mixture that has undergone the electron beam irradiation step; and a synthesizing step of preparing carbon nanotubes by reacting the functional catalyst support with a carbon source.

9. The method of claim 8, wherein the mixing step is performed by mixing 0.1 to 2.0 parts by weight of metal precursor in 100 parts by weight of solvent and then adding 0.5 to 5.0 parts by weight of support.

10. The method of claim 8, wherein the first heating step is performed in a multi-step heating method in which the mixture is subjected to vibration and heated to a temperature range of 60 C. to 120 C., then the vibration is stopped and the mixture is heated to 150 C. to 250 C.

11. The method of claim 8, wherein the reducing solution is an aqueous solution containing an alcohol having 1 to 3 carbon atoms and a reducing agent.

12. The method of claim 11, wherein the reducing agent includes at least one of hydrazine, LiBH.sub.4, NaBH.sub.4, ethylene oxide, formaldehyde, formic acid, and polyol.

13. The method of claim 8, wherein the electron beam is applied with a density current of 100 to 500 A/cm 2 and an acceleration voltage in a range of 300 to 600 keV.

14. The method of claim 13, wherein the electron beam is applied for a duration of 3 to 10 minutes.

15. The method of claim 8, wherein the heating temperature in the second heating step may be in a range of 500 C. to 1000 C.

16. The method of claim 8, wherein a plasma treating step is further performed between the second heating step and the synthesizing step in which the functional catalyst support is plasma treated.

17. A method of manufacturing a branched carbon nanotube having improved hydrophilicity, the method comprising: a pretreating step of discharging an acidic solution mixed with carbon nanotubes in water; a heat treating step of preparing a support by heat treating the carbon nanotubes obtained through the pretreating step; a catalyst structure body preparing step of preparing a catalyst structure body in which a catalyst is supported on a support by mixing the support, a solvent, and a catalyst precursor and then reducing the catalyst precursor; and a carbon nanotube synthesizing step of preparing a branched carbon nanotubes by reacting the catalyst structure body with a carbon source.

18. The method of claim 17, wherein the pretreating step comprises: a first pretreating step of mixing the carbon nanotubes in an acidic solution and then treating them with ultrasonic waves; and a second pretreating step of discharging the mixture that has undergone the first pretreating step by plasma underwater.

19. The method of claim 17, wherein the heat treating step is a step of heat treating the pretreated carbon nanotubes in an oxygen atmosphere at a temperature in a range of 280 C. to 550 C. for 20 to 80 minutes.

20. The method of claim 17, wherein the catalyst structure body preparing step comprises: a first step of preparing a precursor mixture by mixing the support, the solvent, and the catalyst precursor; a second step of preparing a supported catalyst by drying the precursor mixture at a temperature in a range of 90 C. to 120 C.; a third step of preparing a catalyst structure body by mixing the supported catalyst with a reducing solution and then stirring; and a fourth step of filtering and washing the catalyst structure body.

21. (canceled)

22. The method of claim 20, wherein the reducing solution comprising at least one selected from the group consisting of hydrazine, LiBH.sub.4, NaBH.sub.4, ethylene oxide, formaldehyde, formic acid, and polyol.

Description

EXPERIMENTAL EXAMPLE 1

[0084] Metal nanoparticles were prepared by reducing FeCl.sub.3 in a gaseous atmosphere containing hydrogen gas, nitrogen gas, or argon gas under conditions as shown in Table 1 below, with the pressure maintained at about 1.0 Torr, and by generating a plasma with a temperature of 100 C. using a high-frequency bipolar direct current pulse generator with a frequency of 22 kHz. The oxygen plasma treatment stage was performed in an oxygen atmosphere where 02 was supplied at a flow rate of 110 sccm for about 10 minutes while maintaining the frequency, temperature, pressure, etc. The water concentration (number/cm 3) of metal nanoparticles of about 15 to 100 nm size was measured for about 20 minutes using a portable connection particle counter (CPC, Kanomax Model 3800), and the metal nanoparticle generation rate (%) was calculated through Formula 1 below.

Metal nanoparticle production rate (%)={(R.sub.2R.sub.1)/R.sub.1}100 (Formula 1)

[0085] (Where R.sub.2 is the number concentration of metal nanoparticles after the reaction, and R.sub.1 is the number concentration of metal nanoparticles before the reaction.)

TABLE-US-00001 TABLE 1 Metal nanoparticles Hydrogen Nitrogen production (v/v) gas gas Argon gas rate (%) Comparative 2 72.3 Example 1 Comparative 2 5 78.6 Example 2 Comparative 2 5 0.005 81.9 Example 3 Example 1 2 5 0.01 90.4 Example 2 2 5 0.1 93.5 Example 3 2 5 0.3 95.0 Example 4 2 5 0.45 97.8 Example 5 2 5 0.5 98.1 Example 6 2 5 0.55 97.4 Example 7 2 5 0.07 94.2 Example 8 2 5 0.1 91.1 Example 9 2 5 1.0 90.5 Comparative 2 5 1.3 87.1 Example 4 Comparative 2 5 1.7 79.9 Example 5 Comparative 2 5 2 71.7 Example 6

[0086] As shown in Table 1, when the metal nanoparticle production rate was greater than 90%, it may be seen that hydrogen gas, nitrogen gas, and argon gas were mixed at a volume ratio (v/v) of about 2:5:0.01 to about 1.0.

[0087] On the other hand, in Comparative Example 1 and Comparative Example 2 including only hydrogen gas and nitrogen gas, the metal nanoparticle production rate was less than 80%, and in Comparative Examples 3 to 6 which the contents of hydrogen, nitrogen, and argon gases are outside the above range, the metal nanoparticle production rate was less than 90%.

[0088] Therefore, it was found that when hydrogen gas, nitrogen gas, and argon gas were mixed in a volume ratio (v/v) of about 2:5:0.011.0, the generation rate of metal nanoparticles was excellent, and the highest at a volume ratio (v/v) of about 2:5:0.5.

EXPERIMENTAL EXAMPLE 2

[0089] The results of manufacturing carbon nanotubes using metal nanoparticles prepared according to Examples 1 to 9 and Comparative Examples 1 to 6 of Example 1 as catalysts are shown in Table 2 below.

[0090] Metal nanoparticles were supplied by injecting argon, a carrier gas, into the reactor at a flow rate of 100 sccm. In addition, after mixing 6 parts by weight of alkyl glucoside with 100 parts by weight of benzene as a solvent, argon, a carrier gas, was sprayed at a flow rate of 100 sccm and supplied into the reactor, while the temperature of the reactor was maintained at 800 C.

[0091] The prepared carbon nanotubes were observed with a scanning electron microscope (SEM) to measure the diameter, and the carbon nanotube yield (%) was calculated through Formula 2 below.

Yield (%)={amount of produced carbon nanotubes (g)/amount of supplied metal salt (g)}100(Formula 2)

TABLE-US-00002 TABLE 2 Carbon nanotube Yield (%) Diameter Comparative Example 1 744 62.78 20.5 Comparative Example 2 1,699 62.27 21.9 Comparative Example 3 1,749 68.92 18.0 Example 1 1,905 70.98 8.7 Example 2 2,011 69.85 8.4 Example 3 2,075 70.23 7.9 Example 4 2,114 69.47 8.0 Example 5 2,122 69.98 7.4 Example 6 2,068 70.13 7.7 Example 7 2,081 70.29 8.2 Example 8 2,058 69.16 8.9 Example 9 2,003 68.92 9.0 Comparative Example 4 1,884 64.38 11.7 Comparative Example 5 1,694 66.64 16.9 Comparative Example 6 1,731 62.76 19.6

[0092] As shown in Table 2 above, in the case of Examples 1 to 9, the yield of carbon nanotubes exceeded 2,000%, the diameter of the manufactured carbon nanotubes was constant at about 70 nm, and the standard deviation was also maintained between about 74 and 90. On the other hand, in the case of Examples 1 to 6, the yield of carbon nanotubes was less than 2,000%, the diameter of the carbon nanotubes was manufactured in the range of about 62 to 69 nm, and the standard deviation was calculated to be about 11 to 22, which confirms the difficulty in controlling the uniformity of the carbon nanotubes manufactured.

[0093] Through Comparative Examples 1 and 2, it was found that when nitrogen gas was added, the yield of carbon nanotubes increased by about 2 times or more, and when argon gas was added through Comparative Examples 2 and 3, the yield of and the diameter of the carbon nanotubes increased simultaneously.

[0094] Furthermore, through Comparative Examples 3 to 6 and Examples 1 to 9, it was found that when the volume ratio of hydrogen gas and nitrogen gas is 2:5, the content of argon gas that can simultaneously control the yield and diameter of carbon nanotubes by increasing the content of argon gas is in the range of 0.01 to 1.0 v/v, and the most excellent content of argon gas is 05 v/v.

EXPERIMENTAL EXAMPLE 3

[0095] Metal nanoparticles and carbon nanotubes were manufactured in the same manner as in Experiment 1 and Experiment 2 under the conditions shown in Table 3 below, and the metal nanoparticle production rate and carbon nanotube yield were calculated using Formulae 1 and 2, and the manufactured carbon nanotubes were observed under a scanning electron microscope (SEM) to measure the diameters.

TABLE-US-00003 TABLE 3 Metal Carbon nanoparticle nanotube Hydrogen Nitrogen Argon production yield Diameter (v/v) gas gas gas rate (%) (%) (nm) Comparative 0.5 0.5 90.2 1,628 62.51 11.6 Example 7 Example 10 1 5 0.5 95.4 2,001 68.94 9.7 Example 5 2 5 0.5 98.1 2,122 69.98 7.4 Example 11 3 5 0.5 99.2 2,108 69.72 8.6 Example 12 5 5 0.5 99.2 2,074 68.86 9.3 Comparative 6 5 0.5 99.6 1,997 68.84 16.4 Example 8 Comparative 8 5 0.5 99.8 1,804 67.47 26.1 Example 9

[0096] As shown in Table 3 above, the yield of the carbon nanotubes manufactured according to Example 7 with a hydrogen gas content of less than 1 v/v was less than 2000%, and it can be seen that the diameter of the carbon nanotubes was not controlled.

[0097] On the other hand, in the case of Comparative Examples 8 and 9, where the hydrogen gas content exceeded 5 V/V, the metal nanoparticles production rate was quite high, about 995% or more, but the yield of carbon nanotubes was less than 2000%, and it was confirmed that the diameter of the prepared carbon nanotubes was not controlled smoothly.

[0098] Therefore, considering both the metal nanoparticle production rate, the carbon nanotube yield, and the carbon nanotube diameter control aspects, it was found that the results were excellent when the hydrogen gas content was about 1 to 5 V/V, as in the case of Example 5 and Examples 10 to 12, and that the measurement results were best when the volume ratio (v/v) of hydrogen gas, nitrogen gas, and argon gas was about 2:5:0.5, as in Example 5.

[0099] A method of manufacturing carbon nanotubes, according to another embodiment of the present disclosure, the method including: a mixing step of mixing a solvent, a metal precursor, and a support to prepare a mixture solution; a first heating step of heating the mixture solution under vibration to prepare a catalyst support; a dispersing step of dispersing the catalyst support in a reducing solution to prepare a catalyst dispersion solution; an electron beam irradiating step in which the catalyst dispersion solution is irradiated with an electron beam; a second heating step in which the mixture obtained through the electron beam irradiating step is filtered and then heated to produce a functional catalyst support; and a synthesizing step in which a carbon nanotube is manufactured by reacting the functional catalyst support with a carbon source.

[0100] First, the mixing step is a step of adsorbing the metal precursor to the support by mixing the solvent, the metal precursor, and the support. In this step, the mixture may be obtained by mixing 100 parts by weight of the solvent with 0.1 to 2.0 parts by weight of the metal precursor to uniformly disperse the metal precursor, followed by 0.5 to 5.0 parts by weight of the support, which, if performed in this order, may cause the metal precursor to being more uniformly dispersed and adsorbed on the support.

[0101] At this time, after mixing the support together, stirring may be performed for 30 minutes to 2 hours at a stirring speed of 300 to 600 rpm.

[0102] The solvent is used as a dispersion medium for adsorbing and supporting the metal precursor on the support by uniformly dispersing the support and the metal precursor and is at least one selected from the group consisting of aromatic hydrocarbons, aliphatic hydrocarbons, alcohol compounds, and water. For example, benzene, toluene, xylene, etc., may be used as aromatic hydrocarbons, hexane, heptane, octane, etc., may be used as aliphatic hydrocarbons, and ethanol, propyl alcohol, polyethylene glycol, etc., may be used as alcohol compounds.

[0103] In particular, it is preferable to use an alcohol compound as a solvent, and more preferably, polyethylene glycol may be used. In this case, the effect of uniformly dispersing the metal precursor in the solvent can be achieved without the use of a separate surfactant, thereby preventing the deterioration of the accessibility between the metal precursor and the support due to the surfactant, and no post-processing is required to remove the surfactant, which is more effective in terms of reaction efficiency and process efficiency.

[0104] The metal precursor is a metal salt that is a precursor of the catalyst for forming the carbon nanotubes, in which the metal salt may include at least one metal salt of oxides, nitrides, borides, fluorides, bromides, sulfides, chlorides, and carbonate salts of at least one metal selected from the group consisting of iron (Fe), cobalt (Co), nickel (Ni), platinum (Pt), palladium (Pd), molybdenum (Mo), and vanadium (V).

[0105] These metal precursors may be mixed in an amount of 0.1 to 2.0 parts per 100 parts of solvent, and it is preferred that the metal precursors are mixed in the above content in the mixing step since the amount of metal salt supported by the support is small when the content of the metal precursors is less than 0.1 part per 100 parts of solvent, and the support efficiency is low when the content of the metal precursors is more than 2.0 part per 100 parts of solvent since there is no additional increase in the amount of support.

[0106] The support is a support to which a metal precursor is adsorbed, and the type is not particularly limited but may be a carbon-based support, for example, being at least one or more selected from the group consisting of carbon black, activated carbon powder, carbon nanotube, carbon nanowire, and fullerene.

[0107] Such a support may be porous and preferably has a specific surface area in a range of 200 to 600 m 2/g in order to increase metal precursor supporting efficiency and carbon nanotube synthesizing efficiency.

[0108] The porous support may preferably be a carbon-based support whose specific surface area is increased by ozonation, and in this case, ozonation of the carbon-based support has the advantage that the specific surface area is not only increased by ozone but also has the advantage of further improving the adsorption efficiency when the metal catalyst is subsequently adsorbed due to the introduction of oxygen-based functional groups.

[0109] Specifically, it is preferable to supply ozone at a flow rate of 80 to 250 mg/min at a temperature of 250 C. to 380 C. to the carbon-based support as described above and ozonate the support for 1 to 4 hours. At this time, if the flow rate of ozone is less than 80 mg/min, the processing time increases excessively, and the workability decreases, and if the flow rate of ozone exceeds 250 mg/min, the pressure in the reactor increases rapidly, and it is difficult to preserve the porous support powder.

[0110] In addition, when the ozonation time is less than 1 hour, the effect of increasing the specific surface area and introducing functional groups by ozone is insignificant, and when the ozonation time exceeds 4 hours, the specific surface area may decrease due to the closure of micropores on the surface of the carbon-based support, so it is preferable to perform the ozonation treatment under the conditions described above.

[0111] Next, the first heating step is to prepare the catalyst support by heating the mixture obtained through the previous mixing step by applying vibration.

[0112] By heating under vibration in this step, agglomeration between the metal precursor and the support or agglomeration between the support and the support is prevented in the process of adsorption of the metal precursor to the support, so that the metal precursor is uniformly dispersed and adsorbed on the support, and a catalyst support of a more constant size can be formed, which has the advantage of improving the reliability of the carbon nanotubes since carbon nanotubes with a constant size and constant properties are synthesized in the subsequent synthesis of carbon nanotubes.

[0113] This step can be performed in a multi-step heating method, specifically, the mixture solution is vibrated and heated to a temperature range of 60 C. to 120 C. for 10 to 80 minutes, then the vibrations are stopped and the mixture solution is heated to 150 C. to 250 C. for 1 to 30 hours.

[0114] This primary vibration and heating at relatively low temperatures allow for uniform dispersion and adsorption of the metal precursor on the support. Furthermore, by heating to the temperature range as described above, solvent losses can be minimized while improving the adsorption efficiency of the metal precursor to the support by heat.

[0115] Then, by secondarily heating to a relatively high temperature while eliminating vibration, the solvent can be completely removed to form a particulate catalyst support, and the absence of vibration prevents damage to the support due to collision between the supports, dislodging of the metal precursor, etc.

[0116] At this time, the vibration may be applied by vibrating the reactor containing the mixture solution in a vertical or horizontal direction, preferably with an amplitude of 0.5 to 5 mm and a frequency of 0.5 to 5 kHz. When the intensity of the vibration is small, the dispersion effect obtained by applying the vibration is insignificant, and especially when the frequency exceeds 5 kHz, the damage to the support is caused by the collision energy generated by the collision of the support with each other in the mixture solution, and the size of the support is uneven, so it is desirable to apply the vibration under the above conditions.

[0117] Next, a dispersing step of preparing a catalyst dispersion solution by dispersing the catalyst support obtained through the first heating step in a reducing solution is performed. Through this step, the metal precursor may be reduced to the metal, and at the same time, the catalytic activity may be improved.

[0118] The reducing solution is an aqueous solution containing an alcohol having 1 to 3 carbon atoms and a reducing agent, and the alcohol having 1 to 3 carbon atoms may be at least one or more selected from the group consisting of methanol, ethanol, and propanol, and the reducing agent may be at least one or more of hydrazine, LiBH.sub.4, NaBH.sub.4, ethylene oxide, formaldehyde, formic acid, and polyol.

[0119] The reducing solution may include 1 to 30 parts by weight of alcohol and 0.01 to 1 part by weight of a reducing agent per 100 parts by weight of water. By using an aqueous alcohol solution instead of water as a solvent for the reducing solution, the catalyst support can be uniformly dispersed in the reducing solution without a separate surfactant. In addition, since active species generated in the subsequent electron beam irradiating step can be controlled by alcohol, damage to the catalyst support can be prevented, and since no impurities are generated, a catalyst support with higher purity can be produced.

[0120] Next, an electron beam irradiating step of irradiating the catalyst dispersion solution with an electron beam is performed. This step involves irradiating the catalyst dispersion with an electron beam to control the particle diameter of the reduced metal and the particle diameter of the support in order to form carbon nanotubes of consistent and uniform size and properties in the subsequent carbon nanotube synthesizing step. In addition, the strength of the support itself can be improved by strengthening the molecular bonds of the support that are connected by weak bonds by electron beam irradiation.

[0121] In this step, the electron beam applied to the catalyst dispersion may have a density current amount of 100 to 500 A/cm 2, an accelerating voltage of 300 to 600 keV, and an irradiation time of 3 to 10 minutes.

[0122] When the density current amount, acceleration voltage, and irradiation time of the electron beam are less than the above range, it is difficult to obtain the above effects by electron beam irradiation, and when the above range is exceeded, excessive electron beam irradiation may cause problems such as breaking the bond between the metal and the support or damaging the support, so it is preferable to apply the electron beam under conditions within the above range.

[0123] Next, a second heating step is performed in which the mixture obtained through the electron beam irradiating step is filtered and then heated to prepare a functional catalyst support.

[0124] The second heating step is a step of preparing a functional catalyst support in which metal particles, which are catalysts, are coated on the surface and pores of the support by heating catalyst support particles obtained by filtering the mixture obtained through the electron beam irradiating step.

[0125] In this step, the heating temperature may be 500 C. to 1000 C., preferably 800 C. to 1000 C., and it has the advantage that by heating in such a temperature range, the crystallinity of the support itself increases, thereby improving the strength of the support, while at the same time obtaining a functional catalyst support of the form described above. At this time, when the heating temperature exceeds 1000 C., pores may be rather closed due to excessive crystallization, and the specific surface area of the support may decrease. Therefore, heat treating is preferably performed in the above-described temperature range.

[0126] In the second heating step, heating may be performed for 1 to 18 hours, preferably 2 to 10 hours.

[0127] Then, a synthesizing step may be performed to synthesize the carbon nanotubes by reacting the functional catalyst support obtained by the second heating step with a carbon source. A plasma treating step may be further performed between the second heating step and the synthesizing step to plasma treat the functional catalyst support, and in such a plasma treating step, the strength of the support itself may be improved, and the bonding force between the metal and the support may be improved.

[0128] At this time, plasma treating is preferably performed under a vacuum of 1 to 100 Torr and a temperature of 200 C. to 500 C. in a nitrogen or inert gas atmosphere, and when performed under these conditions, performance enhancement effects can be obtained without damage to the support or metal.

[0129] Finally, the synthesizing step is a step of synthesizing carbon nanotubes by reacting the functional catalyst support obtained through the above process with a carbon source using the metal supported on the functional catalyst support as a catalyst. Through this, carbon nanotubes having a uniform particle size and physical properties can be synthesized.

[0130] The method of synthesizing the carbon nanotubes in this step is not particularly limited and may be applied to, for example, arc discharge method, laser vaporization method, CVD method, catalytic synthesis method, plasma synthesizing method, continuous vapor synthesizing method, etc., but is not limited thereto.

[0131] For example, carbon nanotubes may be manufactured by putting the functional catalyst support in a quartz boat and placing the quartz boat inside a reactor.

[0132] For example, continuous carbon nanotubes manufacturing may be performed by dispersing the functional catalyst support in a solvent and continuously supplying the functional catalyst support into a reactor while proceeding with a carbon nanotube synthesizing reaction.

[0133] In this case, the functional catalyst support is made in the form of a colloidal solution in a solvent such as water or an organic solvent, which is finely dispersed or sprayed into the reactor to make the particle droplets of the colloidal solution suspended in the gas, and they exist as gas-phase colloids for a period of time, thereby enabling the continuous synthesis of two-dimensional or three-dimensional carbon nanotubes in the gas phase.

[0134] A method of making the dispersion solution or colloidal solution obtained by dispersing the functional catalyst support in a solvent into a gas phase, or suspending the dispersion solution in a gas, is not particularly limited and can be performed by any method known in the art, such as direct spraying, siphon spraying, atomization, and the like.

[0135] On the other hand, when dispersing the functional catalyst support in a solvent such as water or an organic solvent, a surfactant may be added in an amount that does not adversely affect the carbon nanotube synthesizing reaction in order to prevent agglomeration and uniform dispersion of the functional catalyst support. The type of surfactant used at this time is not particularly limited.

[0136] In the carbon nanotube synthesizing step, the carbon source may be an organic compound selected from the group consisting of, for example, carbon monoxide, a saturated or unsaturated aliphatic hydrocarbon having 1 to 6 carbon atoms, or an aromatic hydrocarbon having 6 to 10 carbon atoms, and such carbon source may have 1 to 3 heteroatoms selected from the group consisting of oxygen, nitrogen, chlorine, fluorine, and sulfur. These carbon sources may partially or completely replace the solvent in the colloidal solution or may be further mixed, and in the case of further mixing, the carbon sources may be introduced together into the reactor when the colloidal solution is sprayed into the reactor, and the reaction occurs.

[0137] In particular, when water is used as a solvent for colloidal solutions, a separate carbon source must be supplied during the reaction.

PREPARATION EXAMPLE 1

[0138] Production of Functional Catalyst Support

[0139] A mixture of 100 parts by weight of polyethylene glycol and 0.5 parts by weight of FeCl.sub.3, a metal precursor, was mixed with 1.0 parts by weight of a support, and stirring was performed at a speed of 380 rpm for 90 minutes to adsorb the metal precursor onto the support. At this time, as the support, carbon nanotubes having a BET specific surface area of 370 m.sup.2/g ozonated for 200 minutes at a flow rate of 100 mg/min at 280 C. were used.

[0140] Next, the mixture solution of the above polyethylene glycol, metal precursor, and support was heated to 78 C., and a vibration with an amplitude of 2 mm and a frequency of 2.3 kHz was applied for 30 min to make the mixture solution uniformly dispersed, and then the vibration was stopped, and the mixture solution was raised to 180 C. and heated for 8 hours to obtain a catalyst support in which the metal precursor was uniformly adsorbed on the support.

[0141] Then, the catalyst support was mixed in a reducing solution in which 100 parts by weight of water, 5 parts by weight of methanol, and 0.05 parts by weight of LiBH.sub.4 as a reducing agent were mixed at a weight ratio of 100:5, and an electron beam of density current 230 A/cm 2 and an acceleration voltage of 400 keV was applied for 7 minutes.

[0142] Next, the mixture was filtered, and the powder component was heated at 850 C. for 4 hours to produce a functional catalyst support.

[0143] Carbon Nanotube Synthesis

[0144] 0.25 g of the previously produced catalyst structure body was placed in a quartz boat, placed in the center of a 27 mm diameter quartz tube located in the furnace, and the temperature of the furnace was increased to 800 C. by supplying argon (Ar) gas at a flow rate of 100 ml/min.

[0145] Then, while argon (Ar) gas containing 2 vol % of vaporized benzene was injected into the reactor, carbon nanotubes were synthesized for 30 minutes.

EXPERIMENTAL EXAMPLE 4

[0146] The carbon nanotubes were synthesized using the same method as in Example 1 above, but the electron beam irradiation conditions were varied as shown in Table 4, and the carbon nanotubes were synthesized using each functional catalyst support using the same method as in the previous Example, and the diameter distribution and BET specific surface area of each carbon nanotube were measured, and the synthesis yield was calculated, and the results are shown in Table 4. At this time, in Table 4, Comparative Example 11 is a case in which the functional catalyst support was used by omitting the electron beam irradiating step. Scanning electron microscopy (SEM) photographs of each synthesized carbon nanotube were taken, and the diameters of 10 random strands, including the thinnest and thickest, were measured, and the mean values and standard deviations were calculated and listed in Table 4.

Synthesis yield (%)=[amount of manufactured carbon nanotubes (g)/amount of supplied metal salt (g)]100(Formula 3)

TABLE-US-00004 TABLE 4 BET Diameter specific distribution Density Irradiation surface Average Synthesis current time area value Standard yield (A/cm.sup.2) (minutes) (m.sup.2/g) (nm) deviation (%) Example 11 230 7 450 62.8 9.6 1,526 Example 12 250 9 444 65.5 8.8 1,458 Example 13 280 4 459 65.1 9.7 1,424 Comparative 306 68.5 45.2 1,035 Example 11 Comparative 80 5 428 63.2 25.5 1,128 Example 12 Comparative 550 4 355 61.7 18.2 1,366 Example 13 Comparative 280 2 436 65.7 19.5 1,141 Example 14 Comparative 250 11 328 60.8 12.5 985 Example 15

[0147] Referring to the experimental results in Table 4, it was found that in Examples 11 to 13, carbon nanotubes having a high specific surface area and a uniform diameter distribution were obtained.

[0148] On the other hand, in the case of Comparative Examples 11 to 15, the diameter distribution was non-uniform, and the synthesis yield was low, and the specific surface area of Comparative Examples 11, 13, and 15 were significantly lower than that of other samples.

[0149] In particular, when Example 12 and Comparative Example 15 are compared together, it is found that when the density current amount is the same and the irradiation time exceeds 10 minutes, the specific surface area decreases rapidly, the uniformity of the diameter distribution decreases, and the synthesis yield decreases significantly, which is believed to be the result of problems such as damage to the support or changes in the bonding structure of the catalyst metal due to the excessively long electron beam irradiation time.

[0150] Furthermore, when Example 13 and Comparative Example 14 are examined together, it is found that the diameter distribution and synthesis yield are significantly reduced even when the irradiation time is less than 3 minutes, which is believed to be due to the fact that the particle size of the reduced metal is not controlled by the electron beam irradiation due to the excessively short irradiation time.

[0151] Therefore, from the present experimental results, it can be confirmed that in order to improve the specific surface area of the carbon nanotubes in the synthesis of carbon nanotubes, uniformize the diameter distribution, and improve the synthesis yield, in the electron beam irradiating step of the method for manufacturing carbon nanotubes according to one embodiment of the present disclosure, the electron beam is preferably applied for 3 to 10 minutes under the condition of a density current amount of 100 to 500 A/cm 2 and an acceleration voltage of 300 to 600 keV.

[0152] Another embodiment of the present disclosure is a method of manufacturing a branched carbon nanotube with improved hydrophilicity, in which a plurality of Y junctions is formed on a straight central carbon nanotube, and branch carbon nanotubes extending from the central carbon nanotube are formed at these Y junctions to form a branched carbon nanotube having an overall tree-like shape.

[0153] These branched carbon nanotubes have a plurality of Y junctions and have excellent stability and electrochemical efficiency when used as an electrochemical material.

[0154] A method of manufacturing branched carbon nanotubes according to one embodiment of the present disclosure, the method including: a pretreating step of immersing the carbon nanotubes in an acidic solution; a heat treating step of heat treating the carbon nanotubes obtained through the pretreating step to prepare a support; a catalyst structure body manufacturing step of preparing a catalyst structure body in which a catalyst is bound to a support by mixing the support with a solvent and a catalyst precursor and reducing the catalyst precursor; and a carbon nanotube synthesizing step of manufacturing a branched carbon nanotube by reacting the catalyst structure body with a carbon source.

[0155] First, the pretreating step is performed by immersing the carbon nanotubes in an acidic solution to create physical defects on the surface of the carbon nanotubes used as supports for the catalyst in order to adsorb the metal catalyst particles to the defect sites in a later step and to induce the growth of branching carbon nanotubes.

[0156] Specifically, this step includes: a first pretreating step in which the carbon nanotubes are immersed in an acidic solution and sonicated; and a second pretreating step of discharging the mixture subjected to the first pretreatment step into underwater plasma.

[0157] The first pretreating step is to immerse the carbon nanotubes in an acidic solution and sonicate them to uniformly disperse the carbon nanotubes in the acidic solution, in which the acidic solution may be an aqueous solution of a weak acid including at least one weak acid selected from the group consisting of acetic acid, formic acid, lactic acid, benzoic acid, propionic acid, citric acid, malonic acid, adipic acid, and tartaric acid.

[0158] When the acidic solution used in the first pretreating step is an aqueous solution of a strong acid including sulfuric acid, hydrochloric acid, nitric acid, or phosphoric acid, physical defects of the carbon nanotubes can be induced by the first pretreating step alone, but there is a problem that the amount of physical defects is excessively increased due to the strong acid and a brush or brush-like carbon nanotube with a central carbon nanotube as a center is formed instead of a branched carbon nanotube, so it is preferable to use the weak acidic aqueous solution described above as the acidic solution.

[0159] The first pretreating step can be performed at 80 C. to 130 C. for 1 to 5 hours, during which the carbon nanotubes are uniformly dispersed and hydrophilic functional groups are bonded to the carbon nanotubes by the simultaneous action of heat and a weak acid, giving the carbon nanotubes hydrophilic properties.

[0160] The second pretreating step is to generate radicals by generating a pulsed underwater plasma discharge in an aqueous solution of a weak acid in which the carbon nanotubes are immersed and to cause more physical defects in the carbon nanotubes by the radicals generated. At the same time, the radicals generated by the plasma discharge bind to the physical defects of the carbon nanotubes and hydrophilize the carbon nanotubes to be used as supports, thereby improving the hydrophilicity of the resulting branched carbon nanotubes and enhancing their dispersibility in various solvents.

[0161] In addition, since various contaminants included in the mixture used for the reaction are removed through the plasma discharge, there is an advantage in that more pure and stable support can be manufactured.

[0162] At this stage, the underwater plasma discharge can be applied with a frequency of 3 to 6 kHz, a pulse width of 3 to 5 seconds, and a power of 600 to 1200 W. These plasma discharge conditions induce the generation of plasma and the formation of physical defects in the carbon nanotubes by the plasma discharge. At the same time, it is desirable to maintain the above discharge conditions during the underwater plasma discharge, as it is a condition for shaping the final branched carbon nanotubes into a branched shape with a plurality of Y junctions rather than a brush or brush shape or a straight shape.

[0163] The second pretreating step may be performed at a temperature range of 10 C. to 60 C. for a period of 30 minutes to 2 hours. It is preferred that the plasma treating is performed during the above-described process time since the formation rate of physical defects is low when the process is performed at a temperature lower than the above-described temperature conditions or for a shorter period of time, and the formation of branched structures is prevented due to excessive defect formation when the process is performed at a temperature higher than the above-described temperature conditions or for a longer period of time, which results in a deterioration of the physical and electrical properties of the carbon nanotubes finally obtained.

[0164] Next, a heat treating step of preparing a support by heat treating the carbon nanotubes obtained through the pretreating step is performed. The carbon nanotubes obtained through the pretreating step can be filtered and washed before being used for the heat treating step, which removes contaminants and amorphous carbon on the surface of the carbon nanotubes to obtain more pure carbon nanotubes. The carbon nanotubes obtained here are used as supports for supporting catalysts in a later step.

[0165] In this step, the pretreated carbon nanotubes are heat treated under an oxygen atmosphere for 20 to 80 minutes at a temperature range of 280 C. to 550 C., where oxygen atmosphere means oxygen alone or a gas containing oxygen, such as air. Since the carbon nanotubes are heat treated under an oxygen atmosphere, the functional groups that confer hydrophilicity to the surface of the carbon nanotubes are retained so that the hydrophilicity of the carbon nanotubes used as support can be maintained in subsequent steps.

[0166] At this step, when the heat treating temperature or time is below the above range, the purification effect is minimal, and when the temperature or time exceeds the above range, there is a problem that the physical properties or hydrophilicity of the carbon nanotube to be used as a support may be deteriorated by excessive heat treating, so it is desirable to perform the heat treating within the process conditions described above.

[0167] The catalyst structure body preparing step is a step of forming a catalyst structure body in which the catalyst is bonded to the support by mixing the carbon nanotubes obtained through the heat treating step, that is, the support together with a solvent and a catalyst precursor. Through this step, the catalyst precursor is bound and reduced to the region where the physical defect of the carbon nanotube occurs so this region acts as a Y-junction formation region and enables the manufacturing of the branched carbon nanotubes.

[0168] This step is performed in a multi-step manner and specifically includes: a first step of mixing the support with a solvent and a catalyst precursor to prepare a precursor mixture; a second step of drying the precursor mixture at a temperature range of 90 C. to 120 C. to prepare a support catalyst; a third step of mixing the support catalyst with a reducing solution and stirring to prepare a catalyst structure body; and a fourth step of filtering and washing the catalyst structure body.

[0169] First, the first step is a step of preparing a precursor mixture by mixing the support, solvent, and catalyst precursor. The support is a carbon nanotube obtained through the previous heat treating step.

[0170] The solvent is used as a dispersion medium for adsorbing and supporting the metal precursor on the support by uniformly dispersing the support and the catalyst precursor and is at least one selected from the group consisting of aromatic hydrocarbons, aliphatic hydrocarbons, alcohol compounds, and water. For example, benzene, toluene, xylene, etc., may be used as aromatic hydrocarbons, hexane, heptane, octane, etc., may be used as aliphatic hydrocarbons, and ethanol, propyl alcohol, polyethylene glycol, etc., may be used as alcohol compounds.

[0171] In particular, it is preferable to use an alcohol compound, particularly polyethylene glycol, as a solvent. In this case, the catalyst precursor can be uniformly dispersed in the solvent without using a separate surfactant. Accordingly, it is possible to prevent deterioration of accessibility between the catalyst precursor and the support by the surfactant, and since a post-process for removing the surfactant is not required, it is more effective in terms of reaction efficiency and process efficiency.

[0172] The catalyst precursor is a metal salt that is a precursor of the catalyst for forming the carbon nanotubes, in which the metal salt may include at least one metal salt of oxides, nitrides, borides, fluorides, bromides, sulfides, chlorides, and carbonate salts of at least one metal selected from the group consisting of iron (Fe), cobalt (Co), nickel (Ni), platinum (Pt), palladium (Pd), molybdenum (Mo), and vanadium (V).

[0173] In this step, the precursor mixture may include 0.1 to 10 parts by weight of the support and 0.1 to 1.2 parts by weight of the catalyst precursor per 100 parts by weight of the solvent. When the content of the support in the precursor mixture is less than 0.1 part by weight, the productivity of the supported catalyst is lowered, and when the content of the support exceeds 10 parts by weight, the catalyst adsorption efficiency to the support is lowered even if the content of the catalyst precursor is increased, so it is preferable to include the content of the support within the above weight range. At this time, in order to maximize such an effect, more preferably, the support may be included in an amount of 0.5 to 3 parts by weight.

[0174] Since the amount of the catalyst precursor is also within a range to maximize the supporting efficiency of the support, the precursor mixture preferably includes components within the above-described content range.

[0175] This step can be performed by first mixing the solvent and the catalyst precursor, and then mixing the support into this mixture and stirring at a stirring speed of 300 to 600 rpm for 2 to 4 hours. Through this step, a physical defect is caused by the underwater plasma discharge, and the catalyst precursor, which is a metal salt, can be adsorbed by the radicals formed at the physical defect site, and the catalyst metal can be bound to the physical defect site in the subsequent reduction process.

[0176] At this step, the precursor mixture may further include a catalyst functional enhancer, which helps the metal precursor to adsorb onto the support in a uniform and constant size in a solvent environment without separate surfactants and prevents excessive agglomeration of metal particles during the reduction process. Therefore, when a catalyst functional enhancer is added, carbon nanotubes with uniform physical properties can be grown, and the yield of branched carbon nanotubes can be increased.

[0177] Such catalytic functional enhancers may include at least one of indole, imidazole, and hectorite compounds, in which case the hectorite compounds may include 2-hydrogenated tallowbenzylmonium hectorite, disteardimonium hectorite, quaternium-18 hectorite, or stearalkonium hectorite.

[0178] The catalyst functional enhancer may be mixed together in the mixing step of the solvent and the catalyst precursor and may be included in an amount of 17 to 58 parts by weight per 100 parts by weight of the catalyst precursor.

[0179] Preferably, at least one first compound selected from the group consisting of indole and imidazole and a second compound that is a hectorite compound may be used together since such a combination results in a better effect than when the first and second compounds were each used alone.

[0180] In this case, the first compound and the second compound can be mixed in a weight ratio of 1:03 to 07, and when used in a range outside this mixing ratio, the effect of improving the catalytic function is rather poor due to factors such as stability deterioration, and it is difficult to see the effect of improving the carbon nanotube yield, so it is preferable to use them together within the weight range described above.

[0181] Next, the second step is a step of obtaining a supported catalyst by filtering and drying the mixture obtained through the first step. In this step, drying can be performed at a temperature range of 90 C. to 120 C. for 2 to 10 hours, which minimizes the adsorption of the catalyst precursor to the sites where the support is not physically defective, allowing the subsequent growth of branched carbon nanotubes only in the sites where the support is physically defective, and after this step, the supported catalyst in the form of a dry powder can be obtained.

[0182] Next, the third step is a step of preparing a catalyst structure body by mixing the supported catalyst obtained through the second step with a reducing solution and stirring to reduce the catalyst precursor to a catalyst metal.

[0183] This step may be performed by mixing the supported catalyst with the reducing solution and heating and stirring for 1 to 4 hours at a stirring speed of 300 to 600 rpm in a temperature range of 20 C. to 200 C.

[0184] In this step, the reducing solution includes a solvent and a reducing agent and may include at least one of hydrazine, LiBH.sub.4, NaBH 4, ethylene oxide, formaldehyde, formic acid, and polyol.

[0185] The reducing solution may include 0.01 to 0.5 parts by weight of the reducing agent relative to 100 parts by weight of the solvent. When the content of the reducing agent is out of the above weight range, it is preferable that the reducing agent is included within the above weight range because a sufficient reduction of the metal salt does not occur or economic efficiency is reduced.

[0186] The fourth step is a step of removing an unreacted reducing agent by filtering the catalyst structure body from the mixture obtained through the third step and washing with a solvent. At this time, the solvent used for the reducing solution may be used as the solvent used for washing.

[0187] On the other hand, the above step of synthesizing carbon nanotubes is a step of synthesizing carbon nanotube branches from a physical defect region of the catalyst structure by reacting the previously obtained catalyst structure with a carbon source and a branched carbon nanotube having a plurality of Y junctions can be synthesized through this step.

[0188] The method of synthesizing the carbon nanotubes in this step is not particularly limited, and may be applied to, for example, arc discharge method, laser vaporization method, CVD method, catalytic synthesis method, plasma synthesis method, continuous vapor synthesis method, etc., but is not limited thereto.

[0189] For example, carbon nanotubes may be manufactured by placing the catalyst structure in a quartz boat and placing the quartz boat inside a reactor.

[0190] For example, continuous manufacturing two-dimensional or three-dimensional Y-branched carbon nanotubes can be performed by dispersing the catalyst structure body in a solvent and continuously supplying the dispersant into a reactor to proceed with a carbon nanotube synthesis reaction.

[0191] In this case, the catalyst structure body is made in the form of a colloidal solution in a solvent such as water or an organic solvent, which is finely dispersed or sprayed into the reactor to make the particle droplets of the colloidal solution suspended in the gas, and they exist as gas phase colloids for a period of time, thereby enabling the continuous synthesis of two-dimensional or three-dimensional carbon nanotubes in the gas phase.

[0192] A method of making the dispersion solution or colloidal solution obtained by dispersing the catalyst structure body in a solvent into a gas phase, or suspending the dispersion solution in a gas, is not particularly limited and can be performed by any method known in the art, such as direct spraying, siphon spraying, atomization, and the like.

[0193] On the other hand, when dispersing the catalyst structure body in a solvent such as water or an organic solvent, a surfactant may be added in an amount that does not adversely affect the carbon nanotube synthesizing reaction in order to prevent agglomeration and uniform dispersion of the catalyst structure body. The type of surfactant used at this time is not particularly limited.

[0194] In the carbon nanotube synthesizing step, the carbon source may be an organic compound selected from the group consisting of, for example, carbon monoxide, a saturated or unsaturated aliphatic hydrocarbon having 1 to 6 carbon atoms, or an aromatic hydrocarbon having 6 to 10 carbon atoms, and such carbon source may have 1 to 3 heteroatoms selected from the group consisting of oxygen, nitrogen, chlorine, fluorine, and sulfur. These carbon sources may partially or completely replace the solvent in the colloidal solution or may be further mixed, and in the case of further mixing, the carbon sources may be introduced together into the reactor when the colloidal solution is sprayed into the reactor, and the reaction occurs. In particular, when water is used as a solvent for colloidal solutions, a separate carbon source must be supplied during the reaction.

PREPARATION EXAMPLE 2

[0195] Production of Catalyst Structure Body

[0196] First, the carbon nanotubes were immersed in an aqueous propionic acid solution, heated to 90 C., and ultrasonicated for 2 hours. Thereafter, the temperature was then lowered to 35 C., and an underwater plasma was generated with a frequency of 5 kHz, a pulse width of 4 seconds, and a power of 800 W for a total of minutes to induce physical defects in the carbon nanotubes, which were then filtered and washed with water to prepare carbon nanotubes with physical defects, which were then heat treated in an oxygen atmosphere at 450 C. for 60 minutes to prepare the support.

[0197] Next, 0.5 parts by weight of catalyst precursor, FeCl.sub.3, was mixed with 100 parts by weight of polyethylene glycol as a solvent, 4.5 parts by weight of the support was mixed, and stirred for 3 hours at a stirring speed of 400 rpm to prepare a precursor mixture.

[0198] Next, the precursor mixture was filtered and dried at 105 C. for 4 hours to obtain a supported catalyst, which was mixed with a reducing solution and stirred at 120 C. for 2 hours at a stirring speed of 400 rpm to reduce the catalyst precursor to produce a catalyst structure body. At this time, as the reducing solution, a reducing solution containing 0.2 parts by weight of LiBH.sub.4 as a reducing agent based on 100 parts by weight of polyethylene glycol was used.

[0199] Next, a catalyst structure body was finally produced by filtering the catalyst structure body from the mixture and washing with polyethylene glycol.

[0200] Carbon Nanotube Synthesis

[0201] 0.25 g of the previously produced catalyst structure body was placed in a quartz boat and placed in the center of a 27 mm diameter quartz tube located in the furnace, and the temperature of the furnace was increased to 1000 C. by supplying helium gas at a flow rate of 100 ml/min.

[0202] Then, while injecting hydrogen gas containing 2 vol % of vaporized benzene into the reactor, carbon nanotubes were synthesized for 30 minutes.

EXPERIMENTAL EXAMPLE 5

[0203] A catalyst structure body was prepared using the same method as in Preparation Example 2, but the catalyst structure body was produced by changing the underwater plasma application conditions in the catalyst structure body preparing step as shown in Table below. Thereafter, carbon nanotubes were synthesized using the catalyst structure body of each Example and Comparative Example as a catalyst, using the same method as in Example 2, and the synthesis yield, surface resistance, BET specific surface area, and water dispersion of the carbon nanotubes were measured, and the results are shown in Table 5.

[0204] The synthesis yield was confirmed by calculating according to the following Formula (4).

Synthesis yield (%)=[amount of manufactured carbon nanotubes (g)/amount of supplied metal salt (g)]100(Formula 4)

[0205] The surface resistivity was measured by heating and molding a mixture of 27% by weight of carbon nanotubes, 96.5% by weight of polycarbonate polymer, and 0.8% by weight of additives including stabilizers, lubricants, and antioxidants to produce specimens with a thickness of 3.0 mm and a length of 11.4 mm, and then measuring the surface resistivity of each specimen using an SRM-110 (Pinion).

[0206] The water dispersibility was determined by mixing each carbon nanotube in water at a concentration of 0.1% by weight, dispersing for 1 minute with an ultrasonic wave having an output of 110 W at 20 KHz, and then determining whether precipitates were generated. It was evaluated as X when the precipitate occurred and as O when the precipitate did not occur.

TABLE-US-00005 TABLE 5 Plasma application conditions Measurement result Pulse Synthesis Surface Specific Frequency width yield resistance surface Water (kHz) (seconds) (%) (/sq.) area (m.sup.2/g) dispersibility Example 21 5 4 1,012 10.sup.4 or less 495 Example 22 4 4 958 10 or less 511 Comparative 2 4 941 2.7 10.sup.5 389 X Example 21 Comparative 7 4 786 5.8 10.sup.5 473 Example 22 Comparative 5 2 688 1.2 10.sup.5 406 Example 23 Comparative 5 6 624 9.2 10.sup.6 395 Example 24

[0207] When looking at the experimental results in Table 5, in the case of Examples 21 and 22, it was confirmed that the surface resistance was significantly lower than that of Comparative Examples, and the synthesis yield and specific surface area also had excellent values.

[0208] In particular, when comparing the experimental results of Example 21, Example 22, Comparative Example 21, and Comparative Example 22, respectively, the results of Comparative Example 21 and Comparative Example 22 are significantly lower than those of the Embodiments. This is believed to be due to the fact that when preparing the catalyst structure body for synthesizing the carbon nanotubes of the Comparative Examples, the frequency of the applied plasma is excessively low or high, resulting in the insufficient formation of physical defects in the catalyst structure body by the plasma, resulting in a decrease in the adsorption efficiency of the metal catalyst precursor, or excessive formation of physical defects, resulting in damage to the shape of the central column of the branched carbon nanotube.

[0209] In addition, in the case of Comparative Example 21, it was confirmed that the water dispersibility was lower than that of other carbon nanotubes because precipitation occurred during water dispersion.

[0210] On the other hand, when referring to the results of Example 21 together with the results of Comparative Examples 23 and 24, it can be seen that the results of Example 21 are significantly superior, which is judged to be due to the problem that the pulse width of the plasma is formed excessively short or long, similar to the reason above.

[0211] Therefore, it can be concluded from the present experimental results that the plasma is preferably applied at a frequency of 3 to 6 kHz and [0212] a pulse width of 3 to 5 seconds in the production of the catalyst structure body.

EXPERIMENTAL EXAMPLE 6

[0213] A catalyst structure body and carbon nanotubes were prepared using the same method as in Preparation Example 2, but a catalyst functional enhancer was further added when preparing the precursor mixture during the production of the catalyst structure body.

[0214] At this time, the catalyst functional enhancer was added in the weight shown in Table 2, and in this case, the weight shown in Table 6 is the weight with respect to 100 parts by weight of the catalyst precursor, and the synthesis yield of the carbon nanotubes manufactured according to each Example was calculated using the same method as in Example 5, and the results are shown in Table 6.

TABLE-US-00006 TABLE 6 Catalyst functional enhancer (parts by weight) Weight Disteardimonium ratio Synthesis Indole (A) hectorite (B) (B/A) yield (%) Example 21 0 1,012 Example 23 8.8 0 1,248 Example 24 9.2 1,017 Example 25 7.4 2.0 0.27 1,289 Example 26 6.8 2.3 0.34 1,564 Example 27 6.2 3.2 0.52 1,683 Example 28 5.6 3.7 0.66 1,660 Example 29 5.3 3.9 0.74 1,257

[0215] When looking at the experimental results of Table 6, it was found that the synthesis yields increased when a catalyst functional enhancer was added during the preparation of the precursor mixture.

[0216] When looking at the results of Examples 23 to 29 in Table 6, it was found that the synthesis yield increased more when the indole or hectorite compound was used as a catalyst functional enhancer than when used alone. In the case of Examples 26 to 28, it was confirmed that a particularly significant increase was exhibited.

[0217] From these results, it can be seen that the yield of carbon nanotube synthesis is increased when a catalyst functional enhancer is used in the preparation of the precursor mixture. In particular, when indole and hectorite compounds are used in a weight ratio of 1:03 to 07 as a catalyst functional enhancer, a more significant yield improvement effect can be obtained by increasing the stability of the precursor mixture and improving the function of the catalyst.

INDUSTRIAL APPLICABILITY

[0218] The present disclosure relates to a continuous carbon nanotubes synthesizing method using a plasma-treated catalyst, in which metal nanoparticles are prepared by plasma treating a metal salt, and continuous carbon nanotubes manufacturing is performed by reacting the metal salt with a carbon source in the gas phase, without adding a separate reducing agent, so that the carbon nanotubes of the present disclosure can be used industrially.