Carbon nanotube and preparation method thereof

Abstract

A method for preparing carbon nanotubes according to an embodiment of the present invention comprises the steps of: injecting a carbon source, a metal catalyst, a co-catalyst, and a carrier gas into a reactor; and heating the reactor to prepare the carbon nanotubes. The ratio of the molar flow rate of the carbon source to the molar flow rate of the metal catalyst is 350 to 1300.

Description

Technical Field

[0001] The present invention provides a carbon nanotube and a method for preparing the same. Background Art

[0002] Carbon nanotubes (CNTs) have excellent chemical stability, mechanical and physical properties, and high thermal conductivity, and thus are materials used in many fields.

[0003] Carbon nanotubes are classified into single-walled carbon nanotubes having a structure formed by curling and connecting the ends of a single layer of graphite structure, double-walled carbon nanotubes having a form in which two layers of single-walled carbon nanotubes form a coaxial structure, multi-walled carbon nanotubes composed of multiple single walls, and the like according to synthesis conditions.

[0004] Synthesis methods of carbon nanotubes include chemical vapor deposition, arc discharge method, laser ablation method, high-pressure chemical vapor deposition method, etc. In order to efficiently prepare carbon nanotubes, a method that can convert a carbon source with a high conversion rate and synthesize carbon nanotubes with high crystallinity is required. Summary of the Invention

[0005] (I) Technical Problems to be Solved

[0006] One technical problem of the present invention is to provide a method for preparing a carbon nanotube that can provide high-quality carbon nanotubes.

[0007] One technical problem of the present invention is to provide a carbon nanotube prepared by the above method.

[0008] (II) Technical Solutions

[0009] The method for preparing a carbon nanotube according to the present invention includes the following steps: injecting a carbon source, a metal catalyst, a cocatalyst, and a carrier gas into a reactor; and heating the reactor to prepare a carbon nanotube. The ratio of the molar flow rate of the carbon source to the molar flow rate of the metal catalyst is 350 to 1300.

[0010] In an exemplary embodiment, the ratio of the molar flow rate of the carbon source to the molar flow rate of the metal catalyst may be 400 to 700.

[0011] In an exemplary embodiment, the ratio of the molar flow rate of the carbon source to the molar flow rate of the cocatalyst may be 700 to 2600.

[0012] In an exemplary embodiment, the ratio of the molar flow rate of the metal catalyst to the molar flow rate of the cocatalyst may be 1 to 3.

[0013] In an exemplary embodiment, the molar flow rate ratio of the carbon source to the carrier gas may be from 0.002 to 0.01.

[0014] In an exemplary embodiment, the molar flow rate ratio of the metal catalyst to the carrier gas may be 0.7×10 -5 to 2.7×10 -5 .

[0015] In an exemplary embodiment, the carbon source may include at least one selected from alcohols having 1 to 10 carbon atoms, carboxylic acids having 1 to 10 carbon atoms, saturated aliphatic hydrocarbons having 1 to 10 carbon atoms, and unsaturated aliphatic hydrocarbons having 1 to 10 carbon atoms.

[0016] In an exemplary embodiment, the metal catalyst may include an organometallic compound containing at least one selected from iron, nickel, and cobalt.

[0017] In an exemplary embodiment, the cocatalyst may include at least one selected from thiophene, dimethyldisulfide, carbon disulfide, diphenyl sulfide, and benzothiophene.

[0018] In an exemplary embodiment, the carrier gas may include an inert gas and hydrogen.

[0019] In an exemplary embodiment, in the total volume flow rate of the carrier gas, the volume flow rate of hydrogen may be 10 vol% to 30 vol%.

[0020] In an exemplary embodiment, the conversion rate of the carbon source may be 2.1 - 10%. The conversion rate may be a percentage value of the number of carbon atoms contained in the carbon nanotubes relative to the total number of carbon atoms of the carbon source.

[0021] According to the present invention, there is provided a carbon nanotube having a Raman R value defined by Formula 1 of 40 to 50.

[0022] [Formula 1]

[0023] Raman R = I G / I D

[0024] In Formula 1, I G is the peak intensity of the absorption region of 1580 cm -1 to 1600 cm -1 in the Raman spectrum obtained by Raman analysis of the carbon nanotubes, and I D is the peak intensity of the absorption region of 1330 cm -1 to 1380 cm -1 in the Raman spectrum.

[0025] In an exemplary embodiment, the carbon nanotubes may include at least one selected from single-walled carbon nanotubes (SWCNT), thin-walled carbon nanotubes (TWCNT), and multi-walled carbon nanotubes (MWCNT).

[0026] In an exemplary embodiment, the average aspect ratio of the carbon nanotubes may be from 10,000 to 20,000. The average aspect ratio may be defined as the average of the ratio of the length to the diameter of the carbon nanotubes.

[0027] (III) Advantageous Effects

[0028] By the method for preparing carbon nanotubes according to an exemplary embodiment of the present invention, the proportion (conversion rate) of the carbon source converted into carbon nanotubes can be increased. Therefore, the production efficiency of carbon nanotubes can be improved.

[0029] The carbon nanotubes prepared by the method for preparing carbon nanotubes according to an exemplary embodiment of the present invention may have improved graphite crystallinity and may contain a low content of amorphous phase.

[0030] The carbon nanotubes prepared by the method for preparing carbon nanotubes according to an exemplary embodiment of the present invention may have a high aspect ratio, and thus may have a long-chain shape. Moreover, the surface area of the carbon nanotubes is large and they can be easily cut along the length direction. Therefore, the carbon nanotubes can be applied to various fields through simple processing techniques. Description of the Drawings

[0031] Figure 1 is a schematic cross-sectional view of an exemplary apparatus for preparing carbon nanotubes.

[0032] Figure 2 is a graph of the carbon source conversion rate and the I G / I D ratio according to the molar flow rate of the carbon source and the molar flow rate of the metal catalyst for the examples and comparative examples. Detailed Description

[0033] The method for preparing carbon nanotubes according to the present invention includes the step of adjusting the ratio of the molar flow rate of the metal catalyst to the molar flow rate of the carbon source to prepare carbon nanotubes. In addition, the carbon nanotubes prepared by the method according to the present invention may have improved graphite crystallinity.

[0034] Hereinafter, the present invention will be described in detail with reference to the drawings. However, this is merely an exemplary description, and the present invention is not limited to the specific embodiments described exemplarily.

[0035] According to an exemplary embodiment, carbon nanotubes can be prepared by floating catalyst chemical vapor deposition (FC-CVD). The floating catalyst chemical vapor deposition method is a method for synthesizing carbon nanotubes by continuously supplying a catalyst and a carbon source as a raw material while spraying. Therefore, different from batch synthesis, carbon nanotubes can be continuously produced.

[0036] Figure 1 is a schematic cross-sectional view of an exemplary carbon nanotube preparation apparatus. Referring to Figure 1 , a carbon source, a metal catalyst, a promoter, and a carrier gas are injected into the reactor 200, and then the reactor is heated to prepare carbon nanotubes.

[0037] The carbon source is a raw material for carbon nanotubes. The carbon source can be an organic compound that supplies carbon through decomposition or catalytic reaction at high temperature. The phase of the carbon source can be a liquid phase or a gas phase. Carbon atoms from the carbon source can diffuse into the catalyst particles, and carbon nanotubes can grow from the surface of the catalyst particles.

[0038] For example, the carbon source can include alcohols having 1 to 10 carbon atoms, carboxylic acids having 1 to 10 carbon atoms, saturated aliphatic hydrocarbons having 1 to 10 carbon atoms, and unsaturated aliphatic hydrocarbons having 1 to 10 carbon atoms, etc. These can be used alone or in combination of two or more.

[0039] For example, the alcohols having 1 to 10 carbon atoms can include methanol, ethanol, propanol, butanol, ethylene glycol, polyethylene glycol, etc.

[0040] For example, the carboxylic acids having 1 to 10 carbon atoms can include acetic acid, formic acid, etc.

[0041] For example, the saturated aliphatic hydrocarbons having 1 to 10 carbon atoms can include methane, ethane, propane, butane, pentane, hexane, etc.

[0042] For example, the unsaturated aliphatic hydrocarbons having 1 to 10 carbon atoms can include ethylene, acetylene, propyne, vinylacetylene, mesitylene, etc.

[0043] The metal catalyst itself can act as a catalyst, or the metal catalyst can be decomposed or reacted at high temperature to transform into an active catalyst or form active catalyst particles. Therefore, the active catalyst can promote the reaction of the carbon source, and thus carbon nanotubes can be generated.

[0044] The metal catalyst can include metal elements such as iron, nickel, cobalt, platinum, ruthenium, molybdenum, vanadium, etc., and can include oxides of the metal elements, for example. These can be used alone or in combination of two or more.

[0045] In an exemplary embodiment, the metal catalyst may comprise an organometallic compound comprising at least one selected from iron, nickel, and cobalt.

[0046] For example, the metal catalyst may comprise ferrocene acetyl, ferrocene methanol, diacetyl ferrocene, iron(II) acetylacetonate, ferrocene and other organometallic compounds containing iron, cobaltocene and other organometallic compounds containing cobalt, nickelocene and other organometallic compounds containing nickel, etc. These may be used alone or in combination of two or more.

[0047] The cocatalyst can inhibit the overgrowth of catalyst particles formed by the metal catalyst, thereby increasing the total surface area of the catalyst particles. Therefore, the preparation efficiency of carbon nanotubes can be improved. In addition, the cocatalyst can increase the rate of carbon atom diffusion to the surface of the catalyst particles, so the production rate of carbon nanotubes can be increased.

[0048] For example, the cocatalyst may comprise thiophene, dimethyl disulfide, carbon disulfide, diphenyl sulfide, benzothiophene, etc. These may be used alone or in combination of two or more.

[0049] The carrier gas can be injected as a medium that allows the carbon source, catalyst, and cocatalyst to flow (float) inside the reactor. The carrier gas may comprise an inert gas and hydrogen. The inert gas has chemical stability and less property of donating, accepting, or sharing electrons, so it can allow the reactants or products to flow and move without reacting with the carbon source or the prepared carbon nanotubes.

[0050] The inert gas may include, for example, helium, nitrogen, neon, argon, krypton, xenon, etc. These may be used alone or in combination of two or more.

[0051] Referring again to Figure 1 , the carbon source, the metal catalyst, and the cocatalyst may be added to the reactor 200 in the form of a mixture through the inlet 110. In addition, the carrier gas may be injected into the reactor 200 through the gas inlet 120.

[0052] Different from that shown in Figure 1 , the carbon source, the metal catalyst, and the cocatalyst may be added through each separate inlet, and a mixture of the carbon source, the metal catalyst, the cocatalyst, and the carrier gas may also be introduced through the inlet 110 without introducing a separate carrier gas through the gas inlet 120.

[0053] The flow rates of the carbon source, the metal catalyst, the cocatalyst, and the carrier gas may vary according to the scale of the reactor and their respective types.

[0054] For example, the carbon source can be added at a flow rate of 1 - 40 ml / hour. Alternatively, the carbon source can be added at a flow rate of 0.0169 - 0.675 mol / hour.

[0055] For example, the metal catalyst can be added at a flow rate of 9.44 - 378 mg / hour. Alternatively, the metal catalyst can be added at a flow rate of 5.07×10 -5 mol / hour to 2.03×10 -3 mol / hour.

[0056] For example, the cocatalyst can be added at a flow rate of 2.13 - 85.4 mg / hour. Alternatively, the cocatalyst can be added at a flow rate of 2.54×10 -5 mol / hour to 1.01×10 -4 mol / hour.

[0057] For example, the carrier gas can be injected at a flow rate of 2 - 20 L / minute. Alternatively, the carrier gas can be injected at a flow rate of 4.99 - 49.9 mol / hour.

[0058] According to an exemplary embodiment, the molar flow rate ratio of the carbon source to the metal catalyst is 350 to 1300. According to some embodiments, the molar flow rate ratio of the carbon source to the metal catalyst can be 400 to 700 or 440 to 680.

[0059] When the metal catalyst and the carbon source are added to the reactor at a molar flow rate ratio within the above range, the amount of the metal catalyst is appropriate, so that the reaction of the carbon source can be promoted without becoming an impurity.

[0060] When the molar flow rate ratio of the carbon source to the metal catalyst exceeds 1300, the amount of the carbon source is excessive compared to the metal catalyst, so that the production rate of carbon nanotubes may decrease.

[0061] When the molar flow rate ratio of the carbon source to the metal catalyst is less than 350, the metal catalyst instead becomes an impurity, which may inhibit the formation of carbon nanotubes and reduce the conversion rate of the carbon source to carbon nanotubes.

[0062] In an exemplary embodiment, the molar flow rate ratio of the carbon source to the cocatalyst can be 700 to 2600. According to some embodiments, the molar flow rate ratio of the carbon source to the cocatalyst can be 800 to 1400. Within the above range, the amount of the cocatalyst is appropriate, so that the activity of the catalyst can be increased without becoming an impurity.

[0063] In an exemplary embodiment, the ratio of the molar flow rate of the metal catalyst to the molar flow rate of the cocatalyst can be from 1 to 3. In some embodiments, the ratio of the molar flow rate of the metal catalyst to the molar flow rate of the cocatalyst can be from 1.5 to 2.5.

[0064] Within the above range, the effect of the cocatalyst promoting the metal catalyst can be enhanced, and at the same time, the cocatalyst will not become an impurity or cause side reactions in the reaction of the carbon source.

[0065] In an exemplary embodiment, the ratio of the molar flow rate of the carbon source to the molar flow rate of the carrier gas can be from 0.002 to 0.01. In some embodiments, the ratio of the molar flow rate of the carbon source to the molar flow rate of the carrier gas can be from 0.009 to 0.01.

[0066] In an exemplary embodiment, the ratio of the molar flow rate of the metal catalyst to the molar flow rate of the carrier gas can be 0.7×10 -5 to 2.7×10 -5 . In some embodiments, the ratio of the molar flow rate of the metal catalyst to the molar flow rate of the carrier gas can be 1.3×10 -5 to 2.1×10 -5 . Within the above range, the carbon source and the metal catalyst can flow inside the reactor in a more uniformly dispersed and mixed state, and the efficiency of the carbon nanotube formation reaction can be improved. Therefore, the productivity of carbon nanotubes can be improved.

[0067] In an exemplary embodiment, in the total volume flow rate of the carrier gas, the volume flow rate of hydrogen can be from 10 vol% to 30 vol%. Within the above range, hydrogen, which can act as a reducing gas, can promote the carbon nanotube formation reaction.

[0068] The reactor can be heated in a state where a carbon source, a metal catalyst, a cocatalyst, and a carrier gas are injected inside the reactor. Therefore, the carbon source and the metal catalyst can be decomposed to form carbon atoms and catalyst particles, and carbon nanotubes can grow on the surface of the catalyst particles, thereby carbon nanotubes can be prepared.

[0069] In an exemplary embodiment, the reactor can be heated to a temperature of 1000°C to 2000°C. In some embodiments, the reactor can be heated to a temperature of 1000°C to 1700°C, 1000°C to 1500°C, or 1000°C to 1300°C.

[0070] The formed carbon nanotubes can be discharged through the discharge port 300 to obtain. For example, they can be wound around the lower end of the discharge port 300 to obtain in the form of carbon nanotube fibers.

[0071] Therefore, the decomposition of the carbon source and the catalyst and the growth of carbon nanotubes can proceed smoothly.

[0072] In an exemplary embodiment, the conversion rate of the carbon source can be 2.1% to 10%. In some embodiments, the conversion rate of the carbon source can be 2.8% to 5% or 2.8% to 4.8%. Within the above range, the proportion of the carbon source converted into carbon nanotubes is high, thereby improving the production efficiency of carbon nanotubes.

[0073] The conversion rate can be defined as the percentage value of the number of carbon atoms contained in the carbon nanotubes relative to the total number of carbon atoms in the carbon source.

[0074] According to the present invention, a carbon nanotube is provided, and the Raman R value defined by Formula 1 of the carbon nanotube is 40 to 50.

[0075] [Formula 1]

[0076] Raman R = I G / I D

[0077] In Formula 1, I G is the peak intensity of the absorption region at 1580 cm -1 to 1600 cm -1 in the Raman spectrum obtained by Raman analysis of the carbon nanotubes, and I D is the peak intensity of the absorption region at 1330 cm -1 to 1380 cm -1 in the Raman spectrum.

[0078] In some embodiments, the Raman R value of the carbon nanotubes can be 43 to 47.

[0079] When the I G / I D value within the above range is satisfied, the carbon nanotubes have high graphite crystallinity and the content of the amorphous phase as defects can be less. Therefore, high-quality carbon nanotubes can be achieved.

[0080] In an exemplary embodiment, the carbon nanotubes can include at least one selected from single-walled carbon nanotubes (SWCNT), thin-walled carbon nanotubes (TWCNT), and multi-walled carbon nanotubes (MWCNT).

[0081] In an exemplary embodiment, the average aspect ratio of the carbon nanotubes can be 10,000 to 20,000. The average aspect ratio can be defined as the average value of the ratio of the length to the diameter of the carbon nanotubes.

[0082] Within the above range, a single carbon nanotube can be suitably used as a carbon nanofiber, and due to its large surface area, it can be suitably used as a conductive material for electrodes and the like.

[0083] Hereinafter, with reference to specific experimental examples, the embodiments of the present invention will be further described. The examples and comparative examples included in the experimental examples are only used to illustrate the present invention and are not used to limit the claims. Various modifications and changes can be made to the embodiments within the scope and technical concept of the present invention, which will be obvious to those skilled in the art, and such modifications and changes are naturally within the scope of the claims.

[0084] Examples 1 to 2 and Comparative Examples 1 to 3

[0085] Use Figure 1 The carbon nanotubes of the examples and comparative examples were prepared using the carbon nanotube preparation apparatus schematically shown in. Specifically, the metal catalyst, cocatalyst, carbon source, and carrier gas were set to the molar flow ratio or volume flow ratio shown in Table 1 below, and a mixture (feed) of the metal catalyst, cocatalyst, carbon source, and carrier gas was injected into the interior of the reactor 200 through the inlet 110. The temperature at the position of the raw material inlet 110 of the reactor 200 was set to 100 - 400 °C, and the temperature inside the reactor 200 was increased to 1000 - 1500 °C using the heating furnace 400. The carbon nanotubes prepared inside the reactor 200 were obtained from the discharge port 300. Ferrocene was used as the metal catalyst, thiophene was used as the cocatalyst, ethanol was used as the carbon source, and a mixed gas of argon and hydrogen was used as the carrier gas. Table 2 shows the contents of the carbon source, cocatalyst, and metal catalyst based on the weight flow rate of the mixture (feed).

[0086] [Table 1]

[0087]

[0088] [Table 2]

[0089]

[0090] Experimental Example 1: Calculation of the conversion rate of the carbon source

[0091] The carbon source conversion rates of each example and comparative example were calculated by calculating the percentage of the number of carbon atoms contained in the obtained carbon nanotubes relative to the total number of carbon atoms of the injected carbon source. The carbon source conversion rates of each example and comparative example are shown in Table 3.

[0092] Experimental Example 2: Raman analysis of carbon nanotubes

[0093] Raman analysis was performed on the carbon nanotubes of the examples and comparative examples under the following conditions to obtain Raman spectra. The peak intensity ratio (I -1 to 1600 cm -1 in the absorption region corresponding to the G band was calculated from the Raman spectrum and the peak intensity in the absorption region of about 1330 cm -1 to 1380 cm -1 corresponding to the D band (I G / I D ).

[0094] i) Raman spectrometer: inVia Raman Microscope, Renishaw (UK)

[0095] ii) Argon ion laser wavelength: 532 nm

[0096] iii) Exposure time: 10 seconds, number of mappings: 10 times

[0097] iv) Detector: 1024 StreamLine CCD, Renishaw (UK)

[0098] v) Laser power: 1%

[0099] vi) Magnification: 20 times

[0100] Figure 2 The graph of the carbon source conversion rate and the I G / I D ratio according to the ratio of the molar flow rate of the carbon source to the molar flow rate of the metal catalyst for the examples and comparative examples calculated according to Experimental Example 1 and Experimental Example 2 is shown. In addition, the specific values are also shown in Table 3 below.

[0101] [Table 3]

[0102]

[0103] See Figure 2 and Table 3. By the method of the examples, the carbon source is converted into carbon nanotubes with a high conversion rate, and the prepared carbon nanotubes have a high I G / I D ratio, so the carbon nanotubes have high graphite crystallinity.

[0104] However, the I G / I D ratio of the carbon nanotubes prepared in the comparative examples where the ratio of the molar flow rate of the carbon source to the molar flow rate of the metal catalyst is less than 350 or more than 1300 is lower than that of the carbon nanotubes of the examplesG / I D Ratio. Therefore, compared with the examples, the carbon nanotubes of the comparative examples contain more defects such as amorphous carbon and the like.

[0105] The content described above is merely an example of applying the principles of the present invention, and other components may be further included without departing from the scope of the present invention.

Claims

1. A method for preparing carbon nanotubes, comprising the following steps: Injecting a carbon source, a metal catalyst, a promoter, and a carrier gas into a reactor; And Heating the reactor to prepare carbon nanotubes, Wherein, the molar flow rate ratio of the carbon source to the metal catalyst is 350 to 1300.

2. The method for preparing carbon nanotubes according to claim 1, wherein, The molar flow rate ratio of the carbon source to the metal catalyst is 400 to 700.

3. The method for preparing carbon nanotubes according to claim 1, wherein, The molar flow rate ratio of the carbon source to the promoter is 700 to 2600.

4. The method for preparing carbon nanotubes according to claim 1, wherein, The molar flow rate ratio of the metal catalyst to the promoter is 1 to 3.

5. The method for preparing carbon nanotubes according to claim 1, wherein, The molar flow rate ratio of the carbon source to the carrier gas is 0.002 to 0.

01.

6. The method for preparing carbon nanotubes according to claim 1, wherein, The ratio of the molar flow rate of the metal catalyst to the molar flow rate of the carrier gas is 0.7×10 -5 to 2.7×10 -5 .

7. The method for preparing carbon nanotubes according to claim 1, wherein, The carbon source includes at least one selected from alcohols having 1 to 10 carbon atoms, carboxylic acids having 1 to 10 carbon atoms, saturated aliphatic hydrocarbons having 1 to 10 carbon atoms, and unsaturated aliphatic hydrocarbons having 1 to 10 carbon atoms.

8. The method for preparing carbon nanotubes according to claim 1, wherein, The metal catalyst includes an organometallic compound, and the organometallic compound includes at least one selected from iron, nickel, and cobalt.

9. The method for preparing carbon nanotubes according to claim 1, wherein, The promoter includes at least one selected from thiophene, dimethyl disulfide, carbon disulfide, diphenyl sulfide, and benzothiophene.

10. The method for preparing carbon nanotubes according to claim 1, wherein, The carrier gas includes an inert gas and hydrogen.

11. The method for preparing carbon nanotubes according to claim 10, wherein, In the total volume flow rate of the carrier gas, the volume flow rate of hydrogen is 10 vol% to 30 vol%.

12. The method for preparing carbon nanotubes according to claim 1, wherein, The conversion rate of the carbon source is 2.1 - 10%, and the conversion rate is the percentage value of the number of carbon atoms contained in the carbon nanotubes relative to the total number of carbon atoms of the carbon source.

13. A carbon nanotube, wherein the Raman R value of the carbon nanotube defined by Formula 1 is 40 to 50, [Formula 1] Raman R = I G / I D In Formula 1, I G is the peak intensity of the absorption region at 1580 cm -1 to 1600 cm -1 in the Raman spectrum obtained by Raman analysis of the carbon nanotubes, and I D is the peak intensity of the absorption region at 1330 cm -1 to 1380 cm -1 in the Raman spectrum.

14. The carbon nanotube according to claim 13, wherein, The carbon nanotube includes at least one selected from single-walled carbon nanotubes (SWCNT), thin-walled carbon nanotubes (TWCNT), and multi-walled carbon nanotubes (MWCNT).

15. The carbon nanotube according to claim 13, wherein, The average aspect ratio of the carbon nanotube is 10000 to 20000, and the average aspect ratio is defined as the average value of the ratio of the length to the diameter of the carbon nanotube.

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