Method for synthesizing single walled carbon nanotubes using ultrasonic spraying

Abstract

The present invention relates to a method for synthesizing single walled carbon nanotubes and single walled carbon nanotubes synthesized by the synthesis method. The synthesis method comprises the steps of: preparing a catalyst solution containing a catalyst precursor and an organic solvent; ultrasonically spraying the catalyst solution at an oscillator intensity of 50 kHz or more to form catalyst droplets; injecting the catalyst droplets into a reactor through a carrier gas; and injecting a carbon source into the reactor to react the catalyst droplets with the carbon source.

Description

Synthesis method of single-walled carbon nanotubes using ultrasonic spraying

[0001] The present invention relates to a synthesis method capable of economically synthesizing single-walled carbon nanotubes having high purity by controlling the size of catalyst droplets through ultrasonic spraying.

[0002] Carbon nanotubes (CNTs) are polymeric carbon isotopes in which carbon atoms are interconnected in a hexagonal honeycomb pattern. Depending on the number of carbon walls, they can be classified into single-walled carbon nanotubes (SWCNTs) and multi-walled carbon nanotubes (MWCNTs).

[0003] To synthesize the above single-walled carbon nanotubes (SWCNTs), it is necessary to control the catalyst particle size to 3 nm or less. To achieve this, devices such as plasma and lasers, or carriers, have been used to form catalysts with fine particle sizes. However, these devices, such as plasma and lasers, are expensive, increasing the unit price of single-walled carbon nanotubes and reducing economic feasibility.

[0004] Meanwhile, attempts have been made to secure the economic feasibility of single-walled carbon nanotubes by synthesizing them using nozzles or bubblers capable of micro-injection. However, when the nozzle is applied, the pressure drop and temperature drop at the nozzle tip cause the liquid catalyst solution to condense, forming large catalyst droplets. This leads to the enlargement of the catalyst particles, resulting in the production of multi-walled carbon nanotubes, carbon shells, or carbon nanofibers instead of single-walled carbon nanotubes. In addition, when the bubbler is applied, there is a limitation in that the mass production of single-walled carbon nanotubes is low because the amount of catalyst injected is small.

[0005] Therefore, there is a need for a technology that can economically manufacture single-walled carbon nanotubes with high purity.

[0006] The inventors of the present invention have conducted various studies to solve the above-mentioned conventional problems, and as a result, they have confirmed that single-walled carbon nanotubes with excellent physical properties can be synthesized in high yield by reacting catalyst droplets formed through ultrasonic spraying performed under specific conditions with a carbon source.

[0007] Accordingly, the object of the present invention is to provide a method for synthesizing single-walled carbon nanotubes capable of economically synthesizing single-walled carbon nanotubes having high purity and high crystallinity.

[0008] In order to solve the above problem, the present invention provides a method for synthesizing single-walled carbon nanotubes, comprising the steps of: preparing a catalyst solution containing a catalyst precursor and an organic solvent; forming catalyst droplets by ultrasonic spraying the catalyst solution with a vibrator intensity of 50 KHz or higher; injecting the catalyst droplets into a reactor via a transport gas; and injecting a carbon source into the reactor to react the catalyst droplets with the carbon source.

[0009] In addition, the present invention provides a single-walled carbon nanotube synthesized by the method for synthesizing the single-walled carbon nanotube.

[0010] The present invention synthesizes single-walled carbon nanotubes through a process of forming uniform, fine-sized catalyst droplets through ultrasonic atomization performed under specific conditions. Therefore, compared to conventional techniques that suffer from the problem of forming large catalyst droplets, the present invention can synthesize the desired single-walled carbon nanotubes with high yield. Accordingly, the present invention can realize high-purity and high-crystallization of single-walled carbon nanotubes, and through this, purification efficiency can be maximized with minimal resources in the subsequent purification process.

[0011] In addition, since the present invention can synthesize single-walled carbon nanotubes by applying a CVD synthesis device, it is advantageous for mass production, thereby securing economic feasibility (price competitiveness), which is an important aspect in the synthesis of single-walled carbon nanotubes.

[0012] Figures 1 and 2 are images of carbon nanotubes confirmed using a transmission electron microscope (TEM) in Test Example 1.

[0013] Figure 3 is an image of a carbon nanotube confirmed using a scanning electron microscope (SEM) in Test Example 2.

[0014] Figure 4 is a graph showing the results of analyzing carbon nanotubes using Raman spectroscopy in Test Example 2.

[0015] Hereinafter, the present invention will be described in detail. Herein, the present invention is not limited to the contents disclosed below, and may be modified in various forms as long as the gist of the invention is not changed.

[0016] The word "comprising" or "including" in this specification is intended to specify particular features, regions, steps, processes, elements and / or components, and does not exclude the presence or addition of other features, regions, steps, processes, elements and / or components, unless specifically stated to the contrary.

[0017] In this specification, the description that one component is connected or coupled with another component includes both direct connection or coupling between these components or indirect connection or coupling through another component.

[0018] In this specification, singular expressions are interpreted to include the singular or plural as interpreted in the context, unless otherwise specified.

[0019] All numbers and expressions indicating the amounts of components, reaction conditions, etc. described in this specification can be modified by the term “about” in all cases unless otherwise specified.

[0020] The terms first, second, etc. described in this specification are used to describe various components, and the components should not be limited by the terms, and the terms are used only for the purpose of distinguishing one component from another.

[0021]

[0022] Synthesis method of single-walled carbon nanotubes

[0023] The present invention can efficiently inject and disperse a catalyst having a particle size required for the synthesis of single-walled carbon nanotubes (e.g., a catalyst having a particle size of 3 nm or less) into a reactor by forming catalyst droplets having a uniform and fine size through ultrasonic spraying, thereby economically synthesizing single-walled carbon nanotubes having high purity and high crystallinity.

[0024] Specifically, the method for synthesizing a single-walled carbon nanotube according to the present invention comprises the steps of (S-1) preparing a catalyst solution containing a catalyst precursor and an organic solvent; (S-2) forming catalyst droplets by ultrasonically spraying the catalyst solution with a vibrator intensity of 50 KHz or higher; (S-3) injecting the catalyst droplets into a reactor via a transport gas; and (S-4) injecting a carbon source into the reactor to react the catalyst droplets with the carbon source, which will be described in detail as follows.

[0025]

[0026] S-1: Preparation of catalyst solution

[0027] The above step S-1 is a step for preparing a catalyst solution containing a catalyst precursor and an organic solvent. Specifically, the catalyst solution can be prepared (manufactured) by adding and dissolving the catalyst precursor in the organic solvent.

[0028] The above organic solvent is not particularly limited as long as it is a commonly known organic solvent capable of dissolving the catalyst precursor.

[0029] According to the present invention, the organic solvent may have a surface tension of 30 mN / m or less. Specifically, the surface tension of the organic solvent may be 28 mN / m or less, 26 mN / m or less, 24 mN / m or less, or 23 mN / m or less, but is not limited thereto. For example, the surface tension of the organic solvent may be 17 to 30 mN / m, 19 to 27 mN / m, 21 to 25 mN / m, or 22 to 23 mN / m. The surface tension of the organic solvent can be measured by the commonly known Ring Method or Wilhelmy Plate Method.

[0030] Additionally, the organic solvent may have a density of, but is not limited to, 0.90 g / cc or less, 0.88 g / cc or less, 0.85 g / cc or less, 0.83 g / cc or less, or 0.80 g / cc or less.

[0031] According to the present invention, the organic solvent may have a ratio (s / d) of surface tension (s) and density (d) of 33 or less. Specifically, the ratio (s / d) of the organic solvent may be 32.5 or less, 31 or less, 30 or less, 29 or less, or 28.5 or less, but is not limited thereto. For example, the ratio (s / d) of the organic solvent may be 26 to 33, 27 to 31.5, 27.5 to 30.5, 27.5 to 29.5, or 27.5 to 28.5.

[0032] Since the surface tension and the ratio (s / d) of the organic solvent are each within the above range, the size of the catalyst droplets can be finely controlled, and thus, a catalyst having a particle size of 3 nm or less required for the synthesis of single-walled carbon nanotubes can be evenly dispersed (scattered) within the reactor, so that single-walled carbon nanotubes having high purity and high crystallinity can be synthesized at a high yield.

[0033] Specifically, the organic solvent may be at least one selected from the group consisting of an alcohol solvent, an aromatic solvent, a ketone solvent, and an ether solvent. The alcohol solvent is not particularly limited, but may specifically include methanol, ethanol, or a combination thereof. The aromatic solvent is not particularly limited, but may specifically include benzene, toluene, or a combination thereof. The ketone solvent is not particularly limited, but may specifically include acetone. The ether solvent is not particularly limited, but may specifically include tetrahydrofuran (THF).

[0034] The above catalyst precursor is not particularly limited as long as it is a commonly known catalyst precursor used in the synthesis of single-walled carbon nanotubes.

[0035] Specifically, according to the present invention, the catalyst precursor may include at least one selected from the group consisting of ferrocene, ferrocenecarboxylic acid, ferrocenecarboxaldehyde, ferrocenemethanol, iron(II) fumarate, iron(II) oxalate, iron(III) acetylacetonate, iron(II) chloride solution, iron(III) citrate, and iron(II) gluconate hydrate.

[0036] According to the present invention, the content of the catalyst precursor included in the catalyst solution may be 0.05 to 10 wt% based on the total weight of the catalyst solution. Specifically, the content of the catalyst precursor may be 0.05 to 8 wt%, 0.05 to 6 wt%, 0.05 to 4 wt%, 0.08 to 2 wt%, or 0.1 to 1 wt% based on the total weight of the catalyst solution, but is not limited thereto. When the content of the catalyst precursor is within the above range, the size of the catalyst droplets and the catalyst can be controlled to a required level, thereby synthesizing single-walled carbon nanotubes in a high yield.

[0037] Meanwhile, the catalyst solution may be comprised of the organic solvent and the catalyst precursor. Specifically, the catalyst solution may be comprised of only the organic solvent and the catalyst precursor, without including any carrier, additive, etc., thereby enabling the synthesis of single-walled carbon nanotubes with high purity and high crystallinity.

[0038]

[0039] S-2: Formation of catalyst droplets

[0040] The above S-2 step is a step of forming catalyst droplets by ultrasonic spraying the prepared catalyst solution with a vibrator intensity of 50 KHz or higher. Specifically, the catalyst solution is introduced into an ultrasonic spraying device equipped with an ultrasonic vibrator, and through a process of ultrasonic spraying with a vibrator intensity of 50 KHz or higher, catalyst droplets having a fine size can be formed. Here, the catalyst droplets may refer to liquid droplets having catalyst seeds dispersed in an organic solvent.

[0041] According to the present invention, the vibrator intensity may be 50 KHz or more, 100 KHz or more, 500 KHz or more, 800 KHz or more, 1,000 KHz or more, 1,500 KHz or more, 2,000 KHz or more, 3,000 KHz or more, or 3,500 KHz or more, and may be 5,000 KHz or less, 4,500 KHz or less, or 4,000 KHz or less, but is not limited thereto. Specifically, the vibrator intensity may be 50 to 4,500 KHz, 200 to 4,300 KHz, 800 to 4,200 KHz, 800 to 4,000 KHz, 1,300 to 4,000 KHz, or 1,600 to 4,000 KHz. When the vibrator intensity applied during the ultrasonic spraying is within the above range, catalyst droplets having a size controlled to a required level can be formed.

[0042] Specifically, according to the present invention, the size of the catalyst droplets formed through the ultrasonic spraying may be 3 to 10 μm. For example, the size of the catalyst droplets may be, but is not limited to, 3.5 to 10 μm, 4 to 8 μm, 4.5 to 6 μm, or 4.5 to 5 μm. Since the size of the catalyst droplets is within the above range, a catalyst having a particle size of 3 nm or less can be injected and dispersed into a reactor, thereby enabling the synthesis of single-walled carbon nanotubes having high purity at a high yield. The size of the catalyst droplets is a value measured by calculating the particle structure with a scattered light pulse by irradiating a laser beam and multiplying the scan speed by the duration of the pulse, and may mean, for example, the average particle diameter of the catalyst droplets.

[0043]

[0044] S-3: Injection of catalyst droplets

[0045] The above S-3 step is a step of injecting the formed catalyst droplets into the reactor via a transport gas. Specifically, the catalyst droplets can be injected into the reactor through a process of supplying the catalyst droplets to the flow of transport gas that is injected into the transport gas injection line and moves into the reactor.

[0046] According to the present invention, the transport gas may have an injection flow rate of 0.1 to 1,000 slm. Specifically, the injection flow rate of the transport gas may be, but is not limited to, 0.1 to 500 slm, 0.5 to 300 slm, 0.5 to 100 slm, 1 to 50 slm, 1 to 10 slm, or 1.5 to 5 slm. When the injection flow rate of the transport gas is within the above range, a uniform and fine-sized catalyst droplet is injected in a constant amount, thereby enabling the synthesis of single-walled carbon nanotubes with a high yield. The unit of the injection flow rate, slm, means standard liter per minute.

[0047] The above-mentioned transport gas is not particularly limited as long as it is a gas that can smoothly transport the catalyst droplets without affecting the size and activity of the catalyst droplets. Specifically, the transport gas may include, but is not limited to, one or more selected from the group consisting of argon (Ar), nitrogen (N2), hydrogen (H2), and helium (He).

[0048] These transport gases may be injected into the reactor simultaneously with the carbon source described later through a single line, or may be injected into the reactor separately from the carbon source described later through a separate line.

[0049]

[0050] S-4: Reaction of catalyst droplets and carbon source

[0051] The above S-4 step is a step of injecting a carbon source into a reactor into which catalyst droplets have been injected via the transport gas, thereby reacting the catalyst droplets with the carbon source. Specifically, single-walled carbon nanotubes can be synthesized through a process of reacting catalyst droplets having a uniform and fine size with a carbon source. For example, by injecting catalyst droplets controlled to have a size of 3 to 10 μm into the reactor, a catalyst (catalyst seed) having a particle size of 3 nm or less (specifically, 1.8 to 2.3 nm) is dispersed (dispersed) in the reactor. By injecting the carbon source into the reactor in which the catalyst (catalyst seed) exists, the catalyst and the carbon source react, thereby synthesizing the single-walled carbon nanotubes desired in the present invention in a high yield.

[0052] The above carbon source is not particularly limited as long as it is a commonly known carbon source used in the synthesis of single-walled carbon nanotubes. Specifically, the carbon source is methane (CH4), ethane (C2H6), propane (C3H8), butane (C4H 10), acetylene (C2H2), ethylene (C2H4), carbon black, artificial graphite, and natural graphite, but is not limited thereto.

[0053] The carbon source may have an injection flow rate of 0.1 to 100 slm. Specifically, the injection flow rate of the carbon source may be, but is not limited to, 0.1 to 50 slm, 0.1 to 30 slm, 0.1 to 10 slm, 0.1 to 5 slm, or 0.1 to 1 slm. When the injection flow rate of the carbon source is within the above range, the reaction efficiency of the catalyst droplets and the carbon source is optimized, so that single-walled carbon nanotubes can be synthesized in a high yield.

[0054] According to the present invention, the carbon source may be injected into the reactor together with an activating gas. The activating gas reduces an oxide film or the like present on the surface of the catalyst (catalyst seed) derived from the catalyst droplets, thereby activating the surface of the catalyst and improving the reaction efficiency with the carbon precursor. The activating gas is not particularly limited, but may specifically include at least one selected from the group consisting of hydrogen (H2), oxygen (O2), air, and vaporized water.

[0055] The injection flow rate of the above-mentioned activating gas may be 0.1 to 100 slm. Specifically, the injection flow rate of the above-mentioned activating gas may be 0.1 to 50 slm, 0.1 to 30 slm, 0.15 to 10 slm, 0.15 to 5 slm, or 0.2 to 1 slm, but is not limited thereto. When the injection flow rate of the above-mentioned activating gas is within the above range, the reaction efficiency of the above-mentioned catalytic droplets and the above-mentioned carbon source is optimized, so that single-walled carbon nanotubes can be synthesized in a high yield.

[0056] According to the present invention, the reaction temperature of the catalyst droplets and the carbon source may be 650 to 1,100°C when considering the reaction efficiency. Specifically, the reaction temperature may be 700 to 1,050°C, 750 to 1,000°C, or 800 to 950°C, but is not limited thereto.

[0057] Additionally, the reaction between the catalyst droplets and the carbon source may be a chemical vapor deposition (CVD) reaction. The possibility of the chemical vapor deposition reaction facilitates the mass production of single-walled carbon nanotubes, thereby ensuring the economic feasibility (price competitiveness) of single-walled carbon nanotubes.

[0058] Meanwhile, according to the present invention, the particle size of the unreacted catalyst remaining in the reactor after the reaction between the catalyst droplets and the carbon source is completed may be 3 to 50 nm. Specifically, the particle size of the unreacted catalyst may be 3 to 30 nm, 3 to 10 nm, 4 to 10 nm, or 5 to 10 nm, but is not limited thereto. As the particle size of the unreacted catalyst is within the above range, single-walled carbon nanotubes having high purity can be synthesized in high yield.

[0059]

[0060] single-walled carbon nanotubes

[0061] The single-walled carbon nanotube according to the present invention is synthesized using the above-described synthesis method. Such single-walled carbon nanotubes can exhibit excellent electrical properties and high purity.

[0062] The single-walled carbon nanotube may have an electrical conductivity of 500 S / cm or more, 700 S / cm or more, or 900 S / cm or more (e.g., 600 to 1,500 S / cm, 750 to 1,300 S / cm, or 900 to 1,250 S / cm), but is not limited thereto.

[0063] In addition, the single-walled carbon nanotube may have a carbon purity of 70% or more and a synthesis yield of 500% or more. Specifically, the single-walled carbon nanotube may have a carbon purity of 70 to 99.9%, 80 to 99%, or 90 to 98%, and a synthesis yield of 700 to 2,500%, 900 to 2,300%, or 1,000 to 2,000%, but is not limited thereto.

[0064] The present invention is described in more detail through the following examples. However, the scope of the present invention is not limited to these examples.

[0065]

[0066] [Example 1]

[0067] Ferrocene (C), a catalyst precursor 10 H 10 Fe) 0.4 g was dissolved in 399.6 g of ethanol to prepare a catalyst solution with a concentration of 0.1 wt%.

[0068] Next, the catalyst solution was injected into an ultrasonic spraying device equipped with an ultrasonic vibrator, and ultrasonic spraying was performed at a vibrator strength of 1,600 KHz to form catalyst droplets having a uniform shape and being evenly distributed. Here, the size of the formed catalyst droplets was measured using an FBRM (Focused Beam Reflectance Measurement) system, and the size was confirmed to be 5 ㎛ or less. Next, in order to inject the catalyst droplets into the reactor, argon (Ar) gas, which is a transport gas, was injected at 1.5 slm through a transport gas injection line, so that the catalyst droplets were injected into the reactor having an internal temperature of 900°C. Meanwhile, separately from the argon (Ar) gas, 0.15 slm of methane (CH4) gas, which is a carbon source (carbon precursor), and 0.2 slm of hydrogen (H2) gas, which is an activating gas, were injected through a carbon source injection line to cause a high-temperature catalytic reaction between the catalyst droplets and the methane (CH4) gas within the reactor, and carbon nanotubes were synthesized through the reaction. After completion of the reaction, the particle size of the unreacted catalyst remaining within the reactor was analyzed using a transmission electron microscope (TEM), and the particle size was confirmed to be 10 nm or less. In addition, it was also confirmed that catalyst aggregates larger than 20 nm were not formed.

[0069]

[0070] [Example 2]

[0071] Carbon nanotubes were synthesized by performing the same process as in Example 1, except that a catalyst solution with a concentration of 2.5 wt% was used. At this time, the catalyst solution was ferrocene (C), which is a catalyst precursor. 10 H 10Fe) was dissolved in 390 g of ethanol to prepare the catalyst. Meanwhile, the size of the catalyst droplets formed through the FBRM system was confirmed to be 5 μm or less. In addition, the particle size of the unreacted catalyst was confirmed to be 10 nm or less through a transmission electron microscope, and it was also confirmed that catalyst aggregates larger than 20 nm were not formed.

[0072]

[0073] [Example 3]

[0074] Carbon nanotubes were synthesized using the same process as in Example 1, except that the vibrator intensity of the ultrasonic atomizer was adjusted to 100 KHz. The size of the catalyst droplets formed through the FBRM system was confirmed to be 5 to 10 μm. In addition, the particle size of the unreacted catalyst was confirmed to be greater than 10 nm through a transmission electron microscope, and the formation of catalyst aggregates of 50 nm or less was also confirmed.

[0075]

[0076] [Example 4]

[0077] Carbon nanotubes were synthesized by performing the same process as in Example 1, except that a catalyst solution with a concentration of 2.5 wt% was used. At this time, the catalyst solution was ferrocene (C), which is a catalyst precursor. 10 H 10 Fe) was dissolved in 390 g of methanol to produce a catalyst droplet. Meanwhile, the size of the catalyst droplets formed through the FBRM system was confirmed to be less than 5 μm. In addition, since the vapor pressure increased by more than 200% compared to the case where ethanol was used due to the use of methanol, it was confirmed that the catalyst droplets were vaporized during the process of being transferred into the reactor, and most of the catalyst droplets did not reach the reactor, but rather condensed catalyst was attached to the inner wall of the transfer pipe.

[0078]

[0079] [Example 5]

[0080] Carbon nanotubes were synthesized by performing the same process as in Example 1, except that a catalyst solution with a concentration of 2.5 wt% was used. At this time, the catalyst solution was ferrocene (C), which is a catalyst precursor. 10 H 10 Fe) was dissolved in 390 g of toluene to prepare a catalyst solution. Meanwhile, the size of the catalyst droplets formed through the FBRM system was confirmed to be less than 10 μm. In addition, the particle size of the unreacted catalyst was confirmed to be 10 to 50 nm through a transmission electron microscope.

[0081]

[0082] [Example 6]

[0083] Carbon nanotubes were synthesized by performing the same process as in Example 1, except that a catalyst solution with a concentration of 2.5 wt% was used. At this time, the catalyst solution was ferrocene (C), which is a catalyst precursor. 10 H 10 Fe) was dissolved in 390 g of benzene to prepare a catalyst. Meanwhile, the size of the catalyst droplets formed through the FBRM system was confirmed to be less than 10 μm. In addition, the particle size of the unreacted catalyst was confirmed to be 10 to 50 nm through a transmission electron microscope.

[0084]

[0085] [Example 7]

[0086] Carbon nanotubes were synthesized by performing the same process as in Example 1, except that a catalyst solution with a concentration of 2.5 wt% was used. At this time, the catalyst solution was ferrocene (C), which is a catalyst precursor. 10 H 10 Fe) was dissolved in 390 g of acetone to prepare the catalyst. Meanwhile, the size of the catalyst droplets formed through the FBRM system was confirmed to be less than 10 μm. In addition, the particle size of the unreacted catalyst was confirmed to be 10 to 50 nm through a transmission electron microscope.

[0087]

[0088] [Example 8]

[0089] Carbon nanotubes were synthesized by performing the same process as in Example 1, except that a catalyst solution with a concentration of 2.5 wt% was used. At this time, the catalyst solution was ferrocene (C), which is a catalyst precursor. 10 H 10 Fe) was dissolved in 390 g of tetrahydrofuran (THF) to prepare a catalyst solution. Meanwhile, the size of the catalyst droplets formed through the FBRM system was confirmed to be less than 10 μm. In addition, the particle size of the unreacted catalyst was confirmed to be 10 to 50 nm through a transmission electron microscope.

[0090]

[0091] [Comparative Example 1]

[0092] Carbon nanotubes were synthesized using the same process as in Example 1, except that the vibrator intensity of the ultrasonic atomizer was adjusted to 40 KHz. The size of the catalyst droplets formed through the FBRM system was confirmed to be 15 to 40 μm. In addition, the particle size of the unreacted catalyst was confirmed to be greater than 20 nm through a transmission electron microscope, and the formation of catalyst aggregates greater than 100 nm was also confirmed.

[0093]

[0094] [Comparative Example 2]

[0095] Ferrocene (C), a catalyst precursor 10 H 10 Fe) 0.4 g was dissolved in 399.6 g of ethanol to prepare a catalyst solution with a concentration of 0.1 wt%.

[0096] Next, the catalyst solution was injected into a device equipped with a spray nozzle to form and spray catalyst droplets, and then the catalyst droplets were transferred into a reactor having an internal temperature of 900°C. At this time, a mixed gas of argon (Ar) gas, methane gas, and hydrogen gas was used for spraying and transporting the catalyst droplets, and the operating pressure was 5 kg / cm 2Carbon nanotubes were synthesized through the reaction of the above catalyst droplets and the above methane gas. Afterwards, the particle size of the unreacted catalyst was confirmed to be greater than 200 nm through a transmission electron microscope.

[0097]

[0098] The properties of the organic solvents used in the preparation of the catalyst solution in each of the above examples and comparative examples are summarized and shown in Table 1 below.

[0099]

[0100] Organic solvent Ethanol Methanol Toluene Benzene Acetone THF Classification Alcohol Alcohol Aromatic Aromatic Ketone Ether Surface tension (mN / m) 22.1 2 2.7 28.4 28.9 25.2 26.4 Density (g / cc) 0.79 0.79 0.87 0.88 0.78 0.89 Surface tension / density ratio 28.0 2 8.7 3 2.6 3 2.8 3 2.3 2 9.7 Use of ethanol: Examples 1, 2, 3 / Comparative examples 1, 2 Use of methanol: Example 4 Use of toluene: Example 5 Use of benzene: Example 6 Use of acetone: Example 7 Use of tetrahydrofuran: Example 8

[0101]

[0102] [Experimental Example 1] Confirming Synthesis Results

[0103] The carbon nanotubes synthesized in each of the examples and comparative examples were confirmed using a transmission electron microscope, and the results are shown in FIGS. 1 and 2.

[0104] Referring to FIGS. 1 and 2, it can be seen that in the examples, the synthesis of single-walled carbon nanotubes (SWCNTs) targeted by the present invention was successfully achieved, whereas in the comparative examples, mainly multi-walled carbon nanotubes (MWCNTs) were synthesized.

[0105]

[0106] [Experimental Example 2] Synthesis Results and Crystallinity Verification

[0107] The carbon nanotubes synthesized in Example 2 were confirmed using a scanning electron microscope, and the crystallinity was analyzed using radial breathing mode (RBM) of Raman spectroscopy, and the results are shown in FIGS. 3 and 4.

[0108] Referring to FIGS. 3 and 4, it can be confirmed that in Example 2, the synthesis of uniform and highly crystalline single-walled carbon nanotubes (SWCNTs) was successfully achieved.

[0109]

[0110] [Experimental Example 3] Synthesis Results and Crystallinity Confirmation

[0111] The shape of the carbon nanotubes (SWCNT or MWCNT) synthesized in each of the examples and comparative examples was confirmed through the presence or absence of the RBM (Radial Breathing Mode) of Raman spectroscopy, and the results are shown in Table 2 below.

[0112]

[0113] Example 1 Example 2 Example 3 Example 4 Example 5 Example 6 Example 7 Example 8 Comparative Example 1 Comparative Example 2 Catalyst type Ferrocene Ferrocene Ferrocene Ferrocene Ferrocene Ferrocene Ferrocene Ferrocene Catalyst amount (g) 0.4 10 0.4 10 10 10 10 10 10 0.4 0.4 Organic solvent type Ethanol Ethanol Ethanol Methanol Toluene Benzene Acetone THF Ethanol Ethanol Solvent amount (g) 399.6 390 399.6 390 390 390 390 390 399.6 399.6 Oscillator intensity (KHz) 1,600 1,600 1001,600 1,600 1,600 1,600 1,600 40- Catalyst droplet size (㎛) ≤5≤55~10≤5≤10≤10≤1015~40-Ar gas (slm) 1.51.51.51.51.51.51.51.51.51.51.51.5Hydrogen gas (slm) 0.20.20.20.20.20.20.20.20.20.20.20.2Reaction temperature (℃) 900900900900900900900900900900900Unreacted catalyst particle size (nm) ≤10≤10>10≤1010~5010~5010~5010~50>20>200CNT TypeSWCNTSWCNTSWCNT+MWCNTSWCNTSWCNT+MWCNTSWCNT+MWCNTSWCNT+MWCNTSWCNT+MWCNTMWCNTMWCNTSWCNTDiameter (nm) 1.4~1.81.4~1.81.4~1.81.4~1.81.4~1.81.4~1.81.4~1.81.4~1.8--

[0114] Referring to Table 2 above, it was confirmed that the examples according to the present invention, which synthesize carbon nanotubes by forming catalyst droplets through ultrasonic spraying, controlled the size of the catalyst droplets to 10 ㎛ or less, so that single-walled carbon nanotubes (SWCNTs) were well synthesized. In addition, it was confirmed that the particle size of the unreacted catalyst was 50 nm or less, and catalyst aggregates exceeding 50 nm were not formed.

[0115] Furthermore, in the case of Example 2, it was confirmed that the production amount of single-walled carbon nanotubes (SWCNTs) increased by more than 1000% compared to Example 1. In addition, in the case of Examples 5 to 8, since an aromatic organic solvent was used in the preparation of the catalyst solution, tar was generated during the synthesis of carbon nanotubes, which lowered the purity of the carbon nanotubes. However, it was also confirmed that the solubility of ferrocene, which is a catalyst precursor, was excellent at more than 1000%.

[0116] On the other hand, in the case of Comparative Example 1 where the vibrator intensity is less than 50 KHz during ultrasonic spraying, it was confirmed that multi-walled carbon nanotubes and / or carbon nanofibers, not single-walled carbon nanotubes, were synthesized due to insufficient control of the size of the catalyst droplets. In addition, in the case of Comparative Example 2 where the catalyst droplets are formed through a spray nozzle, a pressure drop occurs at the tip of the nozzle, and due to a temperature drop caused by the pressure drop, huge catalyst droplets are formed, resulting in the generation of huge catalysts with particle sizes of 20 to 25 nm. Therefore, it was confirmed that in Comparative Example 2 as well, multi-walled carbon nanotubes (diameter: 15 to 18 nm) and / or carbon nanofibers, not single-walled carbon nanotubes, were synthesized.

Claims

A step of preparing a catalyst solution containing a catalyst precursor and an organic solvent; A step of forming catalyst droplets by ultrasonically spraying the catalyst solution with a vibrator intensity of 50 KHz or higher; A step of injecting the above catalyst droplets into a reactor via a transport gas; and A method for synthesizing a single-walled carbon nanotube, comprising the step of injecting a carbon source into the reactor and reacting the catalyst droplets with the carbon source. In the first paragraph, A method for synthesizing single-walled carbon nanotubes, wherein the organic solvent has a surface tension of 30 mN / m or less. In the first paragraph, A method for synthesizing a single-walled carbon nanotube, wherein the organic solvent has a ratio (s / d) of surface tension (s) and density (d) of 33 or less. In the first paragraph, A method for synthesizing a single-walled carbon nanotube, wherein the catalyst precursor comprises at least one selected from the group consisting of ferrocene, ferrocenecarboxylic acid, ferrocenecarboxaldehyde, ferrocenemethanol, iron(II) fumarate, iron(II) oxalate, iron(III) acetylacetonate, iron(II) chloride solution, iron(III) citrate, and iron(II) gluconate hydrate. In the first paragraph, A method for synthesizing a single-walled carbon nanotube, wherein the content of the catalyst precursor included in the catalyst solution is 0.05 to 10 wt% based on the total weight of the catalyst solution. In the first paragraph, A method for synthesizing a single-walled carbon nanotube, wherein the above-mentioned vibrator strength is 800 to 4,000 KHz. In the first paragraph, A method for synthesizing single-walled carbon nanotubes, wherein the formed catalyst droplets have a size of 3 to 10 μm. In the first paragraph, A method for synthesizing a single-walled carbon nanotube, wherein the particle size of the unreacted catalyst remaining after the reaction between the above catalyst droplets and the above carbon source is completed is 3 to 50 nm. In the first paragraph, A method for synthesizing single-walled carbon nanotubes, wherein the above carbon source has an injection flow rate of 0.1 to 100 slm. In the first paragraph, The above carbon source is injected into the reactor together with an activation gas, A method for synthesizing single-walled carbon nanotubes, wherein the above-mentioned activating gas has an injection flow rate of 0.1 to 100 slm. In the first paragraph, A method for synthesizing single-walled carbon nanotubes, wherein the above transport gas has an injection flow rate of 0.1 to 1,000 slm. In the first paragraph, A method for synthesizing a single-walled carbon nanotube, wherein the reaction temperature of the catalyst droplet and the carbon source is 650 to 1,100°C. In the first paragraph, A method for synthesizing single-walled carbon nanotubes, wherein the reaction between the above catalyst droplets and the above carbon source is a chemical vapor deposition (CVD) reaction. A single-walled carbon nanotube synthesized by the method for synthesizing a single-walled carbon nanotube of claim 1.

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