Carbon nanotube composition, catalyst for producing carbon nanotubes, method for producing carbon nanotubes, and carbon nanotubes

Abstract

The purpose of the present invention is to provide: a carbon nanotube composition containing carbon nanotubes that are semiconductive and have a high chirality uniformity; a catalyst for manufacturing carbon nanotubes with which it is possible to produce carbon nanotubes that are semiconductive and have a high chirality uniformity; a method for manufacturing carbon nanotubes in which the catalyst is used; and carbon nanotubes manufactured using the manufacturing method.　This carbon nanotube composition contains a metal and carbon nanotubes, the metal containing Ni as well as Sn and / or Sb, and the carbon nanotubes being single-walled and semiconductive.

Description

[Technical Field]

[0001] The present invention relates to a carbon nanotube composition, a catalyst for producing carbon nanotubes, a method for producing carbon nanotubes, and carbon nanotubes. This application claims priority based on international application PCT / JP2021 / 035526 filed on September 28, 2021, the contents of which are incorporated herein by reference. [Background technology]

[0002] A single-walled carbon nanotube is a material with a structure in which a single graphene sheet, composed of six-membered carbon rings, is rolled into a cylindrical shape. It is known that the electronic state of a single-walled carbon nanotube is determined by the axial winding of the graphene (chirality), and whether it is metallic or semiconducting. Semiconducting single-walled carbon nanotubes are attracting attention as materials for transistors and sensors, and as coated semiconductor materials for RFID (radio frequency identifier) ​​tags, for example.

[0003] Known methods for controlling the properties of single-walled carbon nanotubes include template growth, separation, and chemical vapor deposition (CVD). Template growth is a method for growing new nanotubes using the tip (cap) or a partially cut microstructure of a carbon nanotube as a template. Separation is a method for chemically separating carbon nanotubes into metallic carbon nanotubes and semiconducting carbon nanotubes using a separating agent (Patent Document 1). Chemical vapor deposition (CVD) is a method for depositing carbon nanotubes by supplying a raw material gas onto a catalyst (nucleus) (Patent Document 2). Patent Document 2 describes the use of metal fine particles as a catalyst, which are formed by placing a substrate on which metal ions and ruthenium ions are laid in a synthesis furnace and heating it under reducing conditions. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Patent Publication No. 2021-80121 [Patent Document 2] Japanese Patent Application Laid-Open No. 2015-93807 Summary of the Invention [Problem to be solved by the invention]

[0005] With the template growth method, it is difficult to achieve a high yield. With the separation method, the separating agent tends to remain on the single-walled nanotubes after separation, making it difficult to stabilize the quality. With the CVD method, it is difficult to uniform the chirality characteristics of the resulting carbon nanotubes.

[0006] The present invention has been made in consideration of the above problems, and aims to provide a carbon nanotube composition containing carbon nanotubes that have semiconducting properties and highly uniform chirality characteristics, a catalyst for producing carbon nanotubes that can produce carbon nanotubes that have semiconducting properties and highly uniform chirality characteristics, a method for producing carbon nanotubes using the catalyst, and carbon nanotubes produced using the production method. [Means for solving the problem]

[0007] The present inventors discovered that by using alloy particles containing Ni and at least one of Sn and Sb as a catalyst and heating a carbon source in the presence of the catalyst, it is possible to produce carbon nanotubes that have semiconducting properties and highly uniform chirality characteristics, and thus completed the present invention. Therefore, the present invention has the following aspects.

[0008] [1] A metal and a carbon nanotube, wherein the metal contains any one of Ni—Sn, Ni—Sn—Fe, Ni—Sb, and Ni—Sn—Fe containing Ni3Sn. Contains alloy particlesThe carbon nanotube composition comprises a single-walled carbon nanotube, a semiconducting carbon nanotube, and any one of a (6,5) chirality carbon nanotube, an (8,7) chirality carbon nanotube, and a (7,5) chirality carbon nanotube. [2] before The carbon nanotube composition according to [1] above, wherein at least one end of the carbon nanotubes is attached to the surface of the particle. [3] The carbon nanotube composition according to [1] or [2], which contains Ni at 1 ppm by mass or more and Sn and / or Sb at 1 ppm by mass or more.

[0009] [4] before The carbon nanotube composition according to [1] or [2], wherein the purity of the (6,5) chirality carbon nanotubes is 60% or more. [5] before The carbon nanotube composition according to [1] or [2], wherein the purity of the (8,7) chirality carbon nanotubes is 60% or more. [6] before The carbon nanotube composition according to [1] or [2], wherein the purity of the (7,5) chirality carbon nanotubes is 60% or more.

[0010] [7] Ni -Sn and, Ni- Sn -Fe, Ni- Sb , and Ni 3 Any of the Sn-containing Ni-Sn-Fe A catalyst for producing carbon nanotubes, comprising alloy particles containing the above-mentioned formula, wherein the carbon nanotubes include any one of (6,5) chirality carbon nanotubes, (8,7) chirality carbon nanotubes, and (7,5) chirality carbon nanotubes. [8] The catalyst for producing carbon nanotubes according to [7], wherein the Ni content per 1 part by mass of the total content of Sn and Sb in the alloy particles is in the range of 0.5 parts by mass or more and 10.0 parts by mass or less. [9] The catalyst for producing carbon nanotubes according to [7] or [8], wherein the alloy particles further contain Fe.

[10] The catalyst for producing carbon nanotubes according to [9], wherein the content of Fe per 1 part by mass of the total content of Sn and Sb in the alloy particles is in the range of 0.1 parts by mass or more and 5.0 parts by mass or less.

[11] The catalyst for producing carbon nanotubes according to [7] or [8] above, wherein the alloy particles are supported on porous particles.

[0011]

[12] Contains Ni-Sn and any of Ni-Sn-Fe, Ni-Sb, and Ni3Sn. Contains alloy particles A method for producing carbon nanotubes, comprising: a preparation step of preparing a catalyst; and a production step of heating a carbon source in the presence of the catalyst to produce carbon nanotubes including any one of (6,5) chirality carbon nanotubes, (8,7) chirality carbon nanotubes, and (7,5) chirality carbon nanotubes.

[0012]

[13] The method for producing carbon nanotubes according to

[12] , wherein in the producing step, the carbon source is heated in the presence of a catalyst at a heating temperature of 650° C. or less.

[14] The method for producing carbon nanotubes according to

[12] , wherein the heating temperature when the carbon source is heated in the presence of the catalyst in the producing step is 700° C. or more and 750° C. or less.

[15] The method for producing carbon nanotubes according to

[12] , further comprising an annealing step of annealing the carbon source in the presence of the catalyst after the preparing step and before the producing step.

[0013]

[16] The method for producing carbon nanotubes according to

[12] , wherein in the generating step, the carbon source is a carbon-containing gas, and the carbon-containing gas is converted into plasma and brought into contact with the catalyst.

[17] In the producing step, the carbon source is CarriedThe method for producing carbon nanotubes according to

[12] , wherein the carbon nanotubes are produced by heating in the presence of porous particles. [Effects of the Invention]

[0015] According to the present invention, it is possible to provide a carbon nanotube composition containing carbon nanotubes that have semiconducting properties and have highly uniform chirality characteristics. Also, according to the present invention, it is possible to provide a catalyst for producing carbon nanotubes that can produce carbon nanotubes that have semiconducting properties and have highly uniform chirality characteristics, a method for producing carbon nanotubes using the catalyst, and carbon nanotubes produced using the method. [Brief explanation of the drawings]

[0016] [Figure 1A] 1 is a fluorescence emission spectrum showing the relationship between the wavelength of excitation light irradiated onto the carbon nanotube composition obtained in Example 1 and the intensity of fluorescence having a wavelength of 970 nm generated by irradiation with the excitation light. [Figure 1B] 1 is a three-dimensional fluorescence spectrum showing the relationship between the wavelength of excitation light irradiated onto the carbon nanotube composition obtained in Example 1, and the wavelength and intensity of fluorescence generated by irradiation with the excitation light. [Figure 2] FIG. 1 is a diagram showing the configuration of an example of a plasma CVD apparatus that can be used in the carbon nanotube manufacturing method of the present embodiment. [Figure 3] 1 is a conceptual diagram showing the structure of metal particles contained in the carbon nanotube composition obtained in Example 2. FIG. [Figure 4] 1 is an X-ray photoelectron spectroscopy spectrum of the carbon nanotube composition obtained in Example 2. [Figure 5] 10 is a three-dimensional fluorescence spectrum showing the relationship between the wavelength of excitation light irradiated onto the carbon nanotube composition obtained in Example 10, and the wavelength and intensity of fluorescence generated by irradiation with the excitation light. [Figure 6]Figures 6(a) to 6(f) are three-dimensional fluorescence spectra showing the relationship between the wavelength of excitation light irradiated onto the carbon nanotube compositions obtained in Examples 11 to 16 and the wavelength and intensity of the fluorescence generated by irradiation with that excitation light. [Figure 7] FIG. 1 is a diagram showing the relationship between the heating temperature in the production process of Examples 11 to 16 and the purity of (6,5) and (8,7) chiral carbon nanotubes. [Figure 8] 10 is a three-dimensional fluorescence spectrum showing the relationship between the wavelength of excitation light irradiated onto the carbon nanotube composition obtained in Example 17, and the wavelength and intensity of fluorescence generated by irradiation with the excitation light. [Figure 9] 10 is a three-dimensional fluorescence spectrum showing the relationship between the wavelength of excitation light irradiated onto the carbon nanotube composition obtained in Example 18, and the wavelength and intensity of fluorescence generated by irradiation with the excitation light. [Figure 10] 10 is a three-dimensional fluorescence spectrum showing the relationship between the wavelength of excitation light irradiated onto the carbon nanotube composition obtained in Example 19, and the wavelength and intensity of fluorescence generated by irradiation with the excitation light. [Figure 11] 10 is a three-dimensional fluorescence spectrum showing the relationship between the wavelength of excitation light irradiated onto the carbon nanotube composition obtained in Example 20, and the wavelength and intensity of fluorescence generated by irradiation with the excitation light. DETAILED DESCRIPTION OF THE INVENTION

[0017] The present embodiment will be described in detail below with reference to the drawings as appropriate. The drawings used in the following description may show characteristic portions enlarged for the sake of clarity, and the dimensional ratios of each component may differ from the actual ones. The materials, dimensions, etc. exemplified in the following description are merely examples, and the present invention is not limited thereto. Appropriate modifications may be made within the scope of the present invention.

[0018] (Carbon nanotube composition) The carbon nanotube composition of the present embodiment contains a metal and carbon nanotubes. The metal in the carbon nanotube composition is an alloy containing Ni and either or both of Sn and Sb. That is, the metal may be any of a Ni-Sn alloy, a Ni-Sb alloy, and a Ni-Sn-Sb alloy. These alloys may further contain Fe. These alloys may be present in the carbon nanotube composition in the form of alloy particles. The alloy particles in the carbon nanotube composition may be a catalyst used in producing the carbon nanotubes. At least one end of the carbon nanotube may be attached to the surface of the alloy particle.

[0019] The content of alloy particles in the carbon nanotube composition may be, for example, 1 or more per 100 carbon nanotubes. The average particle size of the alloy particles may be in the range of 1 nm to 50 nm. The content and average particle size of the alloy particles can be measured, for example, using a scanning transmission electron microscope-energy dispersive X-ray analyzer (STEM-EDX). The content of alloy particles can be obtained by counting the number of alloy particles attached to 100 carbon nanotubes observed using STEM-EDX. The average particle size of the alloy particles can be obtained by calculating the average particle size of 100 alloy particles measured using STEM-EDX.

[0020] The Ni content of the carbon nanotube composition may be 1 ppm by mass or more. The Sn content may be 1 ppm by mass or more. The Sb content may be 1 ppm by mass or more. The Fe content may be 1 ppm by mass or more. There are no particular upper limits on the contents of Ni, Sb, Sn, and Fe. For example, the total content of Ni, Sb, and Sn (when Fe is included, the total content of Ni, Sb, Sn, and Fe) may be 30% by mass or less, 20% by mass or less, or 10% by mass or less. The contents of these metals can be obtained, for example, by filtering a mixture of the carbon nanotube composition and an acid and measuring the metal content in the obtained filtrate using an ICP atomic emission spectrometer.

[0021] The carbon nanotube composition may contain Ni, Sn, and Sb in an amount such that, when EDX elemental analysis is performed on a range containing 100 or more carbon nanotubes, a peak of at least one of Ni, Sn, and Sb is detected. The range containing 100 or more carbon nanotubes has an EDX spot diameter of, for example, 1 μm.

[0022] Carbon nanotubes are single-walled and semiconducting. Examples of semiconducting carbon nanotubes include carbon nanotubes with chirality properties of (6,5), (7,5), (6,4), (7,3), (8,3), and (8,7).

[0023] The carbon nanotube composition of this embodiment may selectively contain (6,5) chirality carbon nanotubes. The purity of the (6,5) chirality carbon nanotubes in the carbon nanotube composition may be 60% or more, or 80% or more.

[0024] The carbon nanotube composition of this embodiment may selectively contain (8,7) chirality carbon nanotubes, which have a chirality property of (8,7). The purity of the (8,7) chirality carbon nanotubes in the carbon nanotube composition may be 50% or more, 60% or more, or 80% or more.

[0025] The carbon nanotube composition of this embodiment may selectively contain (7,5) chirality carbon nanotubes. The purity of the (7,5) chirality carbon nanotubes in the carbon nanotube composition may be 60% or more, or 75% or more.

[0026] The content and purity of each chiral carbon nanotube are values ​​measured by fluorescence emission spectroscopy, which will be described below, or values ​​calculated by fitting a spectrum obtained by ultraviolet-visible-near-infrared absorption spectroscopy.

[0027] As an example, a method for measuring the content and purity of (6,5) chiral carbon nanotubes by fluorescence emission spectroscopy will be described. First, the carbon nanotube composition is irradiated with light (excitation light), and the wavelength and intensity of the light emission (fluorescence) generated when the electrons in the carbon nanotubes return from an excited state to a ground state are measured. Figure 1A shows a fluorescence emission spectrum showing the relationship between the wavelength of the excitation light irradiated on the carbon nanotube composition obtained in Example 1 (described below) and the intensity of the fluorescence emitted at a wavelength of 970 nm. In the fluorescence emission spectrum of Figure 1A, the peak in the excitation light wavelength range of 540 to 620 nm represents the fluorescence peak due to (6,5) chiral carbon nanotubes. This fluorescence emission spectrum is measured by changing the wavelength of the excitation light. For example, the excitation light is changed in 4 nm intervals within the range of 450 to 750 nm, and the fluorescence emission spectrum from 900 nm to 1450 nm at 20 nm intervals is repeatedly measured using an InGaAs detector.

[0028] Next, a three-dimensional fluorescence spectrum showing the relationship between the wavelength of excitation light, the wavelength of fluorescence, and its intensity is created from the obtained multiple fluorescence emission spectra. Figure 1B is a three-dimensional fluorescence spectrum showing the relationship between the wavelength of excitation light irradiated to the carbon nanotube composition obtained in Example 1 described below and the wavelength and intensity of fluorescence generated by irradiation with that excitation light. In Figure 1B, the horizontal axis represents the wavelength of fluorescence, and the vertical axis represents the wavelength of excitation light. The fluorescence intensity is indicated by the shade of color. That is, the darker the color, the higher the fluorescence intensity. In Figure 1B, the region where the excitation light wavelength is in the range of 540 to 620 nm and the fluorescence wavelength is in the range of 950 to 1000 nm represents the fluorescence intensity due to (6,5) chirality carbon nanotubes. Furthermore, the region where the excitation light wavelength is in the range of 625 to 675 nm and the fluorescence wavelength is in the range of 1000 to 1050 nm represents the fluorescence intensity due to (7,5) chirality carbon nanotubes.

[0029] The content of (6,5) chiral carbon nanotubes is the integral value (synthesis amount) I of the fluorescence intensity of (6,5) chiral carbon nanotubes. (6,5) The content of (7,5) chiral carbon nanotubes is correlated with the integral value I of the fluorescence intensity of (7,5) chiral carbon nanotubes. (7,5) Therefore, the purity (%) of the (6,5) chirality carbon nanotubes can be calculated using the following formula (1): Purity (%)=I (6,5) / (I (6,5) +I (7,5) )×100···(1)

[0030] The carbon nanotube composition of this embodiment may contain impurities. The impurities are, for example, substances that are inevitably mixed in from raw materials or the manufacturing process. The impurities are, for example, metals other than Ni, Sn, Sb, and Fe, and surfactants. The content of the impurities is, for example, 100 ppm by mass or less. The content of the impurities may be 50 ppm by mass or less, or 10 ppm by mass or less.

[0031] The carbon nanotube composition of this embodiment, configured as described above, can be produced by chemical vapor deposition (CVD) using alloy particles containing Ni and either or both of Sn and Sb as a catalyst, and the amount of impurities mixed in during the production process can be reduced compared to carbon nanotubes produced by conventional separation methods. Furthermore, since the carbon nanotubes are single-walled and have semiconducting properties, the carbon nanotube composition of this embodiment can be advantageously used, for example, as a material for transistors or sensors, or as a coated semiconductor.

[0032] In the carbon nanotube composition of this embodiment, if the metal is present in the form of particles, the metal particles can be removed by treating the carbon nanotube composition with acid, making it relatively easy to achieve high purity. Furthermore, if the purity of the (6,5) chirality carbon nanotubes is 60% or more, the chirality characteristics of the carbon nanotubes are uniform, so that transistors, sensors, and coated semiconductors manufactured using these tend to have stable characteristics.

[0033] (Catalyst for carbon nanotube production) The catalyst for producing carbon nanotubes of this embodiment is for producing carbon nanotubes having semiconducting properties. The catalyst of this embodiment includes alloy particles containing Ni and either or both of Sn and Sb. That is, the alloy particles may be Ni-Sn alloy particles, Ni-Sb alloy particles, or Ni-Sn-Sb alloy particles. The Ni content of the alloy particles may be in the range of 0.5 to 10.0 parts by mass per part by mass of the total content of Sn and Sb. The Ni content per part by mass of the total content of Sn and Sb may be in the range of 0.5 to 7.5 parts by mass, or in the range of 0.5 to 2.0 parts by mass.

[0034] The alloy particles may further contain Fe. The Fe content of the alloy particles may be in the range of 0.1 parts by mass to 5.0 parts by mass per part by mass of the total content of Sn and Sb. The Fe content per part by mass of the total content of Sn and Sb may be in the range of 0.5 parts by mass to 5.0 parts by mass, or in the range of 0.5 parts by mass to 2.0 parts by mass.

[0035] The alloy particles may be composite particles supported on porous particles, such as zeolite particles, magnesium oxide particles, silica particles, activated carbon, perlite, vermiculite, and diatomaceous earth.

[0036] When the porous particles are zeolite particles, the skeletal structure of the zeolite particles can be F-type, A-type, X-type, Y-type, etc., and from the viewpoint of improving chirality selectivity, F-type is preferred. When the skeletal structure of the zeolite particles supporting the alloy particles is F-type, (6,5) chirality carbon nanotubes can be selectively grown.

[0037] The content of alloy particles in the composite particles may be, for example, 0.5% by mass to 10.0% by mass in terms of the total content of Ni, Sn, Sb, and Fe. The content of alloy particles may be 0.5% by mass to 5.0% by mass, or 1.0% by mass to 5.0% by mass. The contents of Ni, Sn, Sb, and Fe in the porous particles are values ​​obtained by filtering a mixture of the composite particles and acid and measuring the metal contents in the obtained filtrate.

[0038] The average particle size of the composite particles may be in the range of 500 nm or more and 10 μm or less. The average particle size of the alloy particles in the composite porous particles may be in the range of 1 nm or more and 50 nm or less. The average particle size of the composite particles and alloy particles can be measured using STEM-EDX. The average particle size of the composite particles and alloy particles is a value obtained by calculating the average value of the particle sizes of 100 composite particles and alloy particles measured using STEM-EDX.

[0039] The method for producing the composite particles will be described by taking as an example a case where the alloy particles are Ni-Sn alloy particles. First, nickel salt, tin salt, and porous particles are added to a solvent to prepare a mixed dispersion in which the nickel salt and tin salt are dissolved and the porous particles are dispersed. As the nickel salt and tin salt, acetate salts can be used. The solvent is not particularly limited as long as it dissolves the nickel salt and tin salt, and for example, a monohydric alcohol can be used.

[0040] Next, the resulting mixed dispersion is heated and dried while being stirred. The heating temperature of the mixed dispersion is, for example, a temperature equal to or higher than the boiling point of the solvent. The heating temperature of the mixed dispersion may be equal to or lower than the boiling point of the solvent + 5°C. As a result, the nickel salt and tin salt dissolved in the mixed dispersion are precipitated on the surfaces of the porous particles, and composite particles in which alloy particles are supported on the surfaces of the porous particles are produced.

[0041] The catalyst of this embodiment configured as described above contains Ni, and therefore functions as a catalyst for producing carbon nanotubes. Furthermore, since it contains at least one of Sn and Sb, the uniformity of the chirality characteristics of the resulting carbon nanotubes is improved. When the Ni content per 1 part by mass of Sn or Sb content of the alloy particles is in the range of 0.5 parts by mass to 10.0 parts by mass, (6,5) chiral carbon nanotubes can be produced with higher priority.

[0042] When the alloy particles further contain Fe, the production efficiency of carbon nanotubes is improved. When the content of Fe in the alloy particles is in the range of 0.1 to 5.0 parts by mass per part by mass of the total content of Sn and Sb, the production efficiency of (6,5) chiral carbon nanotubes is further improved.

[0043] When alloy particles are supported on porous particles, the alloy particles are less likely to aggregate, and therefore, by using composite particles in which alloy particles are supported on porous particles, the production efficiency of carbon nanotubes is further improved.

[0044] (Method of manufacturing carbon nanotubes) The method for producing carbon nanotubes of this embodiment includes a step of preparing a catalyst containing Ni and Sn or Sb, and a step of producing carbon nanotubes by heating a carbon source in the presence of the catalyst. The catalyst can be any of the above-mentioned catalysts for producing carbon nanotubes.

[0045] The carbon source used in the production step is a substance that supplies carbon atoms that form carbon nanotubes. The carbon source may be solid, liquid, or gaseous. Examples of solid and liquid carbon sources that can be used include those that generate gaseous carbon sources by heating. Examples of gaseous carbon sources that can be used include organic carbon-containing compounds and carbon-containing gases such as carbon monoxide and carbon dioxide. The organic carbon-containing compound may have 1 to 6 carbon atoms. Examples of organic carbon-containing compounds that can be used include hydrocarbons, alcohols, and ketones. The hydrocarbons may be linear hydrocarbons or cyclic hydrocarbons. The hydrocarbons may be saturated hydrocarbons or unsaturated hydrocarbons. Furthermore, some or all of the hydrogen atoms in the hydrocarbons may be substituted with fluorine.

[0046] In the above-mentioned production step, the heating temperature when the carbon source is heated in the presence of a catalyst can be, for example, 650° C. or lower. When the heating temperature is within the above range, (6,5) chiral carbon nanotubes can be produced with higher priority. Furthermore, the heating temperature when the carbon source is heated in the presence of a catalyst can be, for example, 700° C. to 750° C. When the heating temperature is within the above range, the chirality selectivity changes from (6,5) to (8,7), and as a result, (8,7) chiral carbon nanotubes can be produced with higher priority.

[0047] The generating step may be performed using a plasma CVD method or a thermal CVD method. For example, from the viewpoint of increasing the purity of the resulting (6,5) chirality carbon nanotubes, it is preferable to carry out the production process using a plasma CVD method. In the case of the plasma CVD method, carbon nanotubes can be grown at a lower temperature than in the case of the thermal CVD method, and as a result, the purity of the (6,5) chirality carbon nanotubes can be increased compared to the case of the thermal CVD method. The heating temperature in the plasma CVD method can be 475°C or higher and 800°C or lower (e.g., 475°C).

[0048] From the viewpoint of increasing the purity of the resulting (8,7) chirality carbon nanotubes, either plasma CVD or thermal CVD can be used, provided that the temperature range is such that the chirality selectivity is (8,7).

[0049] The method for producing carbon nanotubes according to this embodiment may further include an annealing step of annealing the carbon source in the presence of a catalyst after the preparation step and before the production step. The heating temperature during the annealing step may be 20°C or higher and 300°C or lower (e.g., 200°C), and the heating time may be 0.1 hours or higher and 3 hours or lower (e.g., 2 hours). The annealing step is preferably performed under reduced pressure, for example, in a vacuum.

[0050] By annealing the carbon source in the presence of a catalyst in the annealing step, the chirality selectivity of the carbon nanotubes obtained after the production step changes from (6,5) to (7,5), resulting in the preferential production of (7,5) chiral carbon nanotubes.

[0051] When performing the annealing process, from the perspective of further increasing the purity of the obtained (7,5) chirality carbon nanotubes, the composition ratio of the catalyst can be adjusted in the preparation process. For example, when the catalyst is Ni-Sn-Fe alloy particles, when the mass ratio of Ni to the total mass of Ni-Sn-Fe alloy particles is a, the mass ratio of Sn is b, and the mass ratio of Fe is c, it can be adjusted so that the magnitude relationship of the mass ratios is a < b < c.

[0052] When performing the annealing process, from the perspective of further increasing the purity of the obtained (7,5) chirality carbon nanotubes, the heating temperature can also be adjusted in the above generation process. In this case, the heating temperature in the above generation process can be 475 °C or higher and 600 °C or lower (for example, 500 °C), and the heating time can be 0.5 minutes or longer and 10 minutes or shorter (for example, 2 minutes).

[0053] <{ In this way, by performing an annealing treatment (annealing process) before the (α) generation process, adjusting the composition ratio of the catalyst in the (β) annealing treatment and preparation process, or performing the (γ) annealing treatment, adjusting the composition ratio of the catalyst in the preparation process, and adjusting the heating temperature in the above generation process, (7,5) chirality carbon nanotubes can be generated more preferentially, and the purity can be further increased.

[0054] In addition, in the above generation process, the carbon source may be heated in the presence of a catalyst and porous particles to generate carbon nanotubes. When the porous particles are zeolite particles, examples of the framework structure of the zeolite particles include F-type, A-type, X-type, Y-type, etc. From the perspective of improving chirality selectivity, the F-type is preferred. When the framework structure of the zeolite particles supporting the alloy particles is F-type, Ni3Sn is generated more preferentially, and carbon nanotubes having a specific chirality, for example, (6,5) chirality carbon nanotubes, can be selectively grown.

[0055] FIG. 2 is a diagram showing the configuration of an example of a plasma CVD apparatus that can be used in the carbon nanotube manufacturing method of this embodiment. 2 includes a raw material gas supply unit 10, a reaction unit 20, and a pressure adjustment unit 30. The raw material gas supply unit 10 is connected to one end of the reaction unit 20 via a first connection unit 41. The pressure adjustment unit 30 is connected to the other end of the reaction unit 20 via a second connection unit 42.

[0056] The raw material gas supply unit 10 supplies a raw material gas to the reaction unit 20. The raw material gas supply unit 10 has a carbon-containing gas tank 11 that stores a carbon-containing gas that serves as the raw material gas. The carbon-containing gas tank 11 is connected to the first connection unit 41 via a gas flow regulator 12. However, the configuration of the raw material gas supply unit 10 is not limited thereto. For example, the raw material gas supply unit 10 may have a supply device for a dilution gas that dilutes the carbon-containing gas. For example, hydrogen gas or nitrogen gas can be used as the dilution gas.

[0057] The reaction unit 20 brings the raw material gas supplied from the reaction unit 20 into contact with the catalyst-holding substrate 1, and reacts the raw material gas to produce carbon nanotubes. The reaction unit 20 has a reaction tube 21, a substrate support 22 for supporting the catalyst-holding substrate 1 arranged inside the reaction tube 21, a plasma generator 23, and a heating furnace 24. The substrate support 22 is supported by a second connecting part 42. The catalyst-holding substrate 1 is a substrate having a catalyst layer containing the above-mentioned catalyst. The catalyst-holding substrate 1 is fixed to a tip part 22a of the substrate support 22. The plasma generator 23 is arranged on the outer periphery of the reaction tube 21, at a position between the position where the catalyst-holding substrate 1 is arranged and the first connecting part 41. The heating furnace 24 is arranged on the outer periphery of the reaction tube 21, at a position where the catalyst-holding substrate 1 is arranged.

[0058] The pressure adjusting unit 30 adjusts the pressure inside the reaction tube 21 of the reaction unit 20. The pressure adjusting unit 30 has a turbo pump 31 and a rotary pump 32. The turbo pump 31 is connected to the second connecting unit 42 via a valve. The rotary pump 32 is connected to the turbo pump 31.

[0059] Carbon nanotubes are produced using the plasma CVD apparatus 100 as follows. First, the turbo pump 31 and the rotary pump 32 of the pressure adjusting unit 30 are operated to adjust the pressure inside the reaction tube 21 of the reaction unit 20. The pressure inside the reaction tube 21 is not particularly limited, but may be, for example, in the range of 1 Pa to 100 Pa. Alternatively, the pressure inside the reaction tube 21 may be atmospheric pressure.

[0060] Next, in the raw material gas supply unit 10, a carbon-containing gas serving as a raw material gas is supplied to the reaction unit 20 using the gas flow regulator 12. The flow rate of the raw material gas supplied to the reaction unit 20 is, for example, in the range of 1 sccm to 100 sccm as the flow rate of the carbon-containing gas.

[0061] Next, in the reaction section 20, the plasma generator 23 is operated to convert the raw material gas into plasma. Furthermore, the heating furnace 24 is operated to heat the catalyst holding substrate 1. The temperature of the heating furnace 24 is, for example, in the range of 475°C or higher and 750°C or lower. Then, the plasmatized raw material gas is brought into contact with the catalyst layer of the heated catalyst holding substrate 1, and carbon nanotubes are produced on the surface of the catalyst.

[0062] The produced carbon nanotubes can be collected by peeling them off from the catalyst-holding substrate 1. The collected carbon nanotubes are usually a carbon nanotube composition to which alloy particles of the catalyst are attached.

[0063] According to the carbon nanotube manufacturing method of this embodiment configured as described above, carbon nanotubes are produced using the above-mentioned catalyst, so that (6,5) chirality carbon nanotubes, (8,7) chirality carbon nanotubes, or (7,5) chirality carbon nanotubes can be preferentially obtained. Furthermore, in the carbon nanotube manufacturing method of this embodiment, the raw material gas is converted into plasma, so the carbon nanotube production efficiency is improved. Note that the raw material gas may be brought into contact with the catalyst holding substrate 1 without converting the raw material gas into plasma.

[0064] The carbon nanotubes obtained by the carbon nanotube manufacturing method of this embodiment are (6,5) chirality carbon nanotubes, (8,7) chirality carbon nanotubes, or (7,5) chirality carbon nanotubes with high purity. Therefore, transistors, sensors, and coated semiconductors manufactured using the carbon nanotubes of this embodiment tend to have stable characteristics. [Example]

[0065] [Example 1] A mixed dispersion was obtained by adding 0.50 parts by mass of nickel acetate (Ni amount), 0.50 parts by mass of tin acetate (Sn amount), and 99.00 parts by mass of zeolite (F type, manufactured by Tosoh Corporation, product name "HSZ-720KOA") to ethanol. The mixed dispersion was heated to 85°C while stirring and dried. The structure of the dried product was analyzed using STEM-EDX. The metal content of the dried product was determined by filtering a mixture of the dried product and acid, and measuring the metal content in the filtrate using an ICP atomic emission spectrometer. The dried product was confirmed to be composite particles in which Ni-Sn alloy particles were supported on zeolite particles, with a Ni content of 0.50% by mass and a Sn content of 0.50% by mass.

[0066] Next, a carbon nanotube composition was produced using the composite particles obtained, using the plasma CVD apparatus shown in FIG. First, the composite particles were placed on a substrate to prepare a catalyst-supporting substrate. The obtained catalyst-supporting substrate was placed in the reaction section of a plasma CVD apparatus. Next, a carbon nanotube composition was produced under the following conditions using methane gas as the raw material gas.

[0067] Inner diameter of reaction tube: 5cm Plasma generator RF power: 28W Distance between plasma generator and catalyst support substrate: 40 cm Furnace temperature: 550℃ Pressure inside the reaction tube: 60 Pa Flow rate of raw gas: 20 sccm of methane gas Response time: 120 seconds

[0068] After the production was completed, the catalyst-supporting substrate was removed from the plasma CVD apparatus. The produced carbon nanotubes were peeled off from the catalyst-supporting substrate to recover the carbon nanotube composition. The recovered carbon nanotube composition was mixed with water, and the resulting carbon nanotube composition dispersion was processed using a centrifuge. The supernatant carbon nanotubes were recovered and dried to obtain the carbon nanotube composition.

[0069] [Example 2] Composite particles were produced in the same manner as in Example 1, except that 0.50 parts by mass of iron acetate (Fe amount) was further added to the mixed dispersion and the amount of zeolite was 98.50 parts by mass, and a carbon nanotube composition was produced using the resulting composite particles. The resulting composite particles had a structure in which Ni-Sn-Fe alloy particles were supported on zeolite particles, and had a Ni content of 0.50% by mass, a Sn content of 0.50% by mass, and a Fe content of 0.50% by mass.

[0070] [Example 3] Composite particles were produced in the same manner as in Example 2, except that the amounts of nickel acetate, tin acetate, and iron acetate were 0.75 parts by mass as Ni, 0.10 parts by mass as Sn, and 0.25 parts by mass as Fe, and the amount of zeolite was 98.90 parts by mass, and a carbon nanotube composition was produced using the resulting composite particles. The resulting composite particles had a structure in which Ni-Sn-Fe alloy particles were supported on zeolite particles, and had a Ni content of 0.75% by mass, a Sn content of 0.10% by mass, and a Fe content of 0.25% by mass.

[0071] [Example 4] Composite particles were produced in the same manner as in Example 3, except that the amount of tin acetate was 0.25 parts by mass in terms of Sn and the amount of zeolite was 98.75 parts by mass, and a carbon nanotube composition was produced using the resulting composite particles. The resulting composite particles had a structure in which Ni-Sn-Fe alloy particles were supported on zeolite particles, and had a Ni content of 0.75% by mass, a Sn content of 0.25% by mass, and a Fe content of 0.25% by mass.

[0072] [Example 5] Composite particles were produced in the same manner as in Example 3, except that the amount of tin acetate was 0.50 parts by mass in terms of Sn and the amount of zeolite was 98.50 parts by mass, and a carbon nanotube composition was produced using the resulting composite particles. The resulting composite particles had a structure in which Ni-Sn-Fe alloy particles were supported on zeolite particles, and had a Ni content of 0.75% by mass, a Sn content of 0.50% by mass, and a Fe content of 0.25% by mass.

[0073] [Example 6] Composite particles were produced in the same manner as in Example 2, except that the amounts of nickel acetate, tin acetate, and iron acetate were 1.50 parts by mass as Ni, 1.50 parts by mass as Sn, and 1.25 parts by mass as Fe, and the amount of zeolite was 95.75 parts by mass, and a carbon nanotube composition was produced using the resulting composite particles. The resulting composite particles had a structure in which Ni-Sn-Fe alloy particles were supported on zeolite particles, and had a Ni content of 1.50% by mass, a Sn content of 1.50% by mass, and a Fe content of 1.25% by mass.

[0074] [Comparative Example 1] Composite particles were produced in the same manner as in Example 1, except that tin acetate and iron acetate were not added, the amount of nickel acetate was 0.50 parts by mass in terms of Ni, and the amount of zeolite was 99.50 parts by mass, and a carbon nanotube composition was produced using the resulting composite particles. The resulting composite particles had a structure in which Ni particles were supported on zeolite particles, and the Ni content was 0.50% by mass.

[0075] Comparative Example 2 Composite particles were produced in the same manner as in Example 1, except that nickel acetate and iron acetate were not added, the amount of tin acetate was 0.50 parts by mass in terms of Sn, and the amount of zeolite was 99.50 parts by mass, and a carbon nanotube composition was produced using the resulting composite particles. The resulting composite particles had a structure in which Sn particles were supported on zeolite particles, and the Sn content was 0.50% by mass.

[0076] Comparative Example 3 Composite particles were produced in the same manner as in Example 1, except that nickel acetate and tin acetate were not added, the amount of iron acetate was 0.50 parts by mass in terms of Fe, and the amount of zeolite was 99.50 parts by mass, and a carbon nanotube composition was produced using the resulting composite particles. The resulting composite particles had a structure in which Fe particles were supported on zeolite particles, and the Fe content was 0.50% by mass.

[0077] The carbon nanotube compositions obtained in Examples 1 to 6 and Comparative Examples 1 to 3 were measured for the content and purity of (6,5) chiral carbon nanotubes, the presence or absence of metal particles, the metal content, and the layer structure by the following methods. The results are shown in Table 1.

[0078] (Content and purity of (6,5) chiral carbon nanotubes) Measurements were made using the above-mentioned fluorescence emission spectroscopy. In this example, the amount of powder measured, the amount of dispersion solution, and the fluorescence measurement conditions were all kept constant, so the approximation that fluorescence intensity ∝ content holds true. The content of (6,5) chirality carbon nanotubes is the integral value of the fluorescence intensity from (6,5) chirality carbon nanotubes.

[0079] (Presence or absence of metal particles, composition, layer structure) One hundred carbon nanotubes were observed using STEM-EDX to confirm the layer structure of the carbon nanotubes. Next, particles with a particle diameter of 1 nm or more attached to the surface of the carbon nanotubes were subjected to elemental analysis using EDX to determine whether they were metal particles. The composition of the metal particles was analyzed using EDX. Carbon nanotubes with a number of metal particles of 1 or more per 100 carbon nanotubes were considered to contain metal particles.

[0080] [Table 1]

[0081] The results in Table 1 confirm that the carbon nanotubes obtained in Examples 1 to 6 were carbon nanotube compositions containing alloy particles containing Ni and Sn or Ni, Sn, and Fe. Examples 1 to 6, which used Ni-Sn alloy particles or Ni-Sn-Fe alloy particles as the catalyst, showed improved purity of (6,5) chiral carbon nanotubes compared to Comparative Examples 1 to 3, which used Ni, Sn, and Fe particles alone. In particular, Examples 2 to 6, which used Ni-Sn-Fe alloy particles, showed an increased content of (6,5) chiral carbon nanotubes compared to Example 1, which used Ni-Sn alloy particles. These results confirm that Sn contained in the catalyst acts to preferentially produce (6,5) chiral carbon nanotubes, and Fe acts to increase the amount of (6,5) chiral carbon nanotubes produced.

[0082] The carbon nanotube composition obtained in Example 2 was analyzed using an XPS (X-ray photoelectron spectroscopy) instrument. The obtained X-ray photoelectron spectroscopy spectrum is shown in Figure 4. Quantitative analysis of the carbon, Fe, Ni, and Sn detected in the X-ray photoelectron spectroscopy spectrum using the XPS instrument revealed that the carbon content was 77.5 mass%, the F content was 4.6 mass%, the Ni content was 12.5 mass%, and the Sn content was 5.4 mass%.

[0083] The structure of the metal particles contained in the carbon nanotube composition obtained in Example 2 was analyzed by crystal structure analysis using XRD, elemental analysis using EDX, and electron diffraction pattern analysis using STEM. The resulting structure of the metal particles is shown conceptually in FIG. 3. As shown in FIG. 3, metal particle 50 had a core-shell structure having a core 51 and a shell 56 covering core 51. Core 51 was composed of a Ni phase 52 (Ni:fcc-Ni phase) with a face-centered cubic lattice structure, a phase 53 (Ni+Fe:fcc-Ni) in which part of the Ni phase with a face-centered cubic lattice structure was substituted with Fe, a phase 54 (Ni+Sn:hcp-Ni) in which part of the Ni phase with a hexagonal close-packed structure was substituted with Sn, and a Ni3Sn phase containing Ni3Sn, Ni3Sn2, Ni3Sn4, etc. x The shell portion 56 contained crystalline NiO and amorphous NiO. x The portion of the phase 55 has a shell portion 56 with a reduced thickness, or Ni3Sn x It was confirmed that a part of phase 55 was exposed. x It is believed that phase 55 has the effect of preferentially growing carbon nanotubes so that the chirality is (6,5).

[0084] [Example 7] A carbon nanotube composition was produced in the same manner as in Example 2, except that the temperature of the heating furnace was set to 500° C. The carbon nanotubes obtained had a (6,5) chirality carbon nanotube content of 1962 counts and a purity of 77.2%.

[0085] [Example 8] A carbon nanotube composition was produced in the same manner as in Example 2, except that before supplying the raw material gas to the reaction tube, the temperature of the heating furnace was set to 550°C and the catalyst holding substrate was heated for 2 minutes, and then the temperature of the heating furnace was set to 500°C, and the raw material gas was supplied to the reaction tube. The carbon nanotubes obtained had a production amount of (6,5) chirality carbon nanotubes of 95,484 counts and a purity of 96.1%. By performing pretreatment by heating the catalyst at 550°C, the purity was improved even when the heating temperature during carbon nanotube production was set to 475°C, which is lower than 500°C.

[0086] [Example 9] A mixed dispersion was obtained by adding 0.50 parts by mass of nickel acetate (Ni amount), 0.50 parts by mass of antimony acetate (Sb amount), and 99.00 parts by mass of zeolite to ethanol. The obtained mixed dispersion was heated to a temperature of 85°C while stirring and dried in the same manner as in Example 1 to obtain composite particles. The obtained composite particles had a structure in which Ni-Sb alloy particles were supported on zeolite particles, and had a Ni content of 0.50% by mass and an Sb content of 0.50% by mass.

[0087] Using the obtained composite particles, a carbon nanotube composition was produced in the same manner as in Example 1. The obtained carbon nanotubes were a carbon nanotube composition containing Ni—Sb alloy particles. The carbon nanotubes were single-walled, and the purity of (6,5) chirality carbon nanotubes was 87%, with a content of (6,5) chirality carbon nanotubes of 53,923 counts. It was confirmed that the Ni—Sb alloy particles, like the Ni—Sn alloy particles, are useful for producing semiconducting carbon nanotubes including (6,5) chirality carbon nanotubes.

[0088] [Example 10] Prior to the production step, an annealing treatment was carried out (annealing step) at a methane gas flow rate of 20 sccm, a pressure in the reaction tube of 60 Pa, a furnace temperature of 550°C, and a reaction time of 120 seconds, and the production step was carried out at an RF power of 50 W in the plasma generator and a furnace temperature of 475°C. Except for this, composite particles and a carbon nanotube composition were produced in the same manner as in Example 2. Figure 5 shows a three-dimensional fluorescence spectrum showing the relationship between the wavelength of the excitation light irradiated on the carbon nanotube composition obtained in Example 10 and the wavelength and intensity of the fluorescence generated by irradiation with that excitation light. The metal particles in the obtained composite particles were Ni-Sn-Fe alloy particles containing Ni3Sn, and the obtained carbon nanotubes had a (6,5) chirality carbon nanotube content of 16,800 counts and a purity of 96%.

[0089] [Examples 11 to 16] Composite particles and carbon nanotube compositions were produced in the same manner as in Example 2, except that the heating furnace temperature during the production process was 650°C, 675°C, 690°C, 700°C, 710°C, and 725°C. Figures 6(a) to 6(f) show three-dimensional fluorescence spectra indicating the relationship between the wavelength of the excitation light irradiated on the carbon nanotube compositions obtained in Examples 11 to 16 and the wavelength and intensity of the fluorescence generated by irradiation with that excitation light. Figure 7 also shows the relationship between the heating temperature during the production process and the purity of (6,5) and (8,7) chiral carbon nanotubes.

[0090] The metal particles in the composite particles obtained in Examples 11 to 16 were all Ni-Sn-Fe alloy particles containing Ni3Sn. Furthermore, it was confirmed that when the synthesis temperature was raised to 700°C or higher, the chirality selectivity changed from (6,5) to (8,7), and the purity of the (8,7) chirality carbon nanotubes increased. This is presumably because the (8,8) chirality carbon nanotubes grew from Ni3Sn(0001) and then changed to (8,7), which is (n,n-1), resulting in the preferential production of the (8,7) chirality carbon nanotubes.

[0091] [Example 17] Composite particles and a carbon nanotube composition were produced in the same manner as in Example 2, except that a thermal CVD apparatus was used under the following conditions: Figure 8 shows a three-dimensional fluorescence spectrum showing the relationship between the wavelength of the excitation light irradiated onto the carbon nanotube composition obtained in Example 17, and the wavelength and intensity of the fluorescence generated by irradiation with that excitation light.

[0092] Temperature inside the chamber: 700℃ Pressure inside the chamber: 60Pa Flow rate of raw gas: 20 sccm of methane gas Response time: 120 seconds

[0093] The metal particles in the composite particles obtained in Example 17 were Ni-Sn-Fe alloy particles containing Ni3Sn. The yield of the (8,7) chirality carbon nanotubes obtained was 9150 counts, with a purity of 68.7%. It was confirmed that the purity of the (8,7) chirality carbon nanotubes could be increased by synthesizing them using thermal CVD at a heating temperature of 700°C or higher instead of plasma CVD.

[0094] [Example 18] Composite particles and a carbon nanotube composition were produced in the same manner as in Example 2, except that an annealing treatment was performed in a vacuum at a heating temperature of 200°C for 3 hours before the production step. Figure 9 shows a three-dimensional fluorescence spectrum showing the relationship between the wavelength of the excitation light irradiated on the carbon nanotube composition obtained in Example 18 and the wavelength and intensity of the fluorescence generated by irradiation with that excitation light.

[0095] The metal particles in the composite particles obtained in Example 18 were Ni-Sn-Fe alloy particles containing Ni3Sn. The yield of the (7,5) chirality carbon nanotubes obtained was 34,000 counts, with a purity of 60.1%. It was confirmed that annealing before the production process changed the chirality selectivity from (6,5) to (8,7), and the purity of the (7,5) chirality carbon nanotubes increased.

[0096] [Example 19] Composite particles and a carbon nanotube composition were produced in the same manner as in Example 18, except that in the preparation step, the raw materials were adjusted so that the Ni content, Sn content, and Sn content in the composite particles were 0.3 mass%, 0.45 mass%, and 0.6 mass%, respectively. A three-dimensional fluorescence spectrum showing the relationship between the wavelength of the excitation light irradiated to the carbon nanotube composition obtained in Example 19 and the wavelength and intensity of the fluorescence generated by irradiation with that excitation light is shown in Figure 10.

[0097] The metal particles in the composite particles obtained in Example 19 were Ni-Sn-Fe alloy particles containing Ni3Sn. The yield of the (7,5) chirality carbon nanotubes obtained was 14,700 counts, with a purity of 72.5%. It was confirmed that the purity of the (7,5) chirality carbon nanotubes could be increased by adjusting the raw materials in the preparation process so that the mass ratio was (Ni content) < (Sn content) < (Fe content), and then annealing the raw materials.

[0098] [Example 20] Composite particles and a carbon nanotube composition were produced in the same manner as in Example 19, except that the heating furnace temperature during the production process was set to 500°C. Figure 11 shows a three-dimensional fluorescence spectrum showing the relationship between the wavelength of the excitation light irradiated onto the carbon nanotube composition obtained in Example 20 and the wavelength and intensity of the fluorescence generated by irradiation with that excitation light.

[0099] The metal particles in the composite particles obtained in Example 20 were Ni-Sn-Fe alloy particles containing Ni3Sn. The yield of the (7,5) chirality carbon nanotubes obtained was 7,880 counts, with a purity of 79.9%. It was confirmed that the purity of the (7,5) chirality carbon nanotubes could be further increased by adjusting the raw materials in the preparation process so that the mass ratio was (Ni content) < (Sn content) < (Fe content), followed by annealing, and further lowering the synthesis temperature. [Explanation of symbols]

[0100] 1. Catalyst support substrate 10. Raw material gas supply section 11 Carbon-containing gas tank 12 Gas flow regulator 20 Reaction section 21 Reaction tube 22 Substrate support material 22a Tip 23 Plasma Generator 24 Furnace 30 Pressure adjustment unit 31 Turbo pump 32 Rotary pump 41 1st connection part 42 2nd connection part 50 metal particles 51 Core 52 Ni phase with face-centered cubic lattice structure 53 A phase in which part of the Ni phase with a face-centered cubic lattice structure is replaced by Fe 54 A phase in which part of the Ni phase with a hexagonal close-packed structure is replaced by Sn 55 Ni3Sn x phase 56 Shell part 100 Plasma CVD equipment

Claims

1. a metal and a carbon nanotube, The metals include Ni—Sn, Ni—Sn—Fe, Ni—Sb, and Ni ３ The alloy particles contain any one of Ni—Sn—Fe containing Sn, The carbon nanotube composition, wherein the carbon nanotubes are single-walled and semiconducting, and include any one of (6,5) chiral carbon nanotubes, (8,7) chiral carbon nanotubes, and (7,5) chiral carbon nanotubes.

2. A carbon nanotube composition as described in claim 1, wherein at least one of the ends of the carbon nanotubes is attached to the surface of the particle.

3. 3. The carbon nanotube composition according to claim 1, comprising 1 mass ppm or more of Ni and 1 mass ppm or more of both Sn and Sb.

4. 3. The carbon nanotube composition according to claim 1, wherein the purity of the (6,5) chirality carbon nanotubes is 60% or more.

5. 3. The carbon nanotube composition according to claim 1, wherein the purity of the (8,7) chirality carbon nanotubes is 60% or more.

6. 3. The carbon nanotube composition according to claim 1, wherein the purity of the (7,5) chirality carbon nanotubes is 60% or more.

7. Ni-Sn, Ni-Sn-Fe, Ni-Sb, and Ni ３ A catalyst for producing carbon nanotubes, comprising alloy particles containing any of Ni—Sn—Fe containing Sn, The catalyst for producing carbon nanotubes, wherein the carbon nanotubes include any one of (6,5) chiral carbon nanotubes, (8,7) chiral carbon nanotubes, and (7,5) chiral carbon nanotubes.

8. 8. The catalyst for producing carbon nanotubes according to claim 7, wherein the content of Ni per part by mass of the total content of Sn and Sb in the alloy particles is in the range of 0.5 parts by mass to 10.0 parts by mass.

9. 9. The catalyst for producing carbon nanotubes according to claim 7, wherein the alloy particles further contain Fe.

10. 10. The catalyst for producing carbon nanotubes according to claim 9, wherein the content of Fe in the alloy particles is in the range of 0.1 parts by mass to 5.0 parts by mass per part by mass of the total content of Sn and Sb.

11. 9. The catalyst for producing carbon nanotubes according to claim 7, wherein the alloy particles are supported on porous particles.

12. Ni-Sn, Ni-Sn-Fe, Ni-Sb, and Ni ３ a preparation step of preparing a catalyst containing alloy particles containing any of Ni—Sn—Fe containing Sb; and a production step of heating a carbon source in the presence of the catalyst to produce carbon nanotubes including any one of (6,5) chiral carbon nanotubes, (8,7) chiral carbon nanotubes, and (7,5) chiral carbon nanotubes.

13. 13. The method for producing carbon nanotubes according to claim 12, wherein the carbon source is heated in the presence of the catalyst at a temperature of 650°C or less in the producing step.

14. 13. The method for producing carbon nanotubes according to claim 12, wherein the carbon source is heated in the presence of the catalyst at a temperature of 700°C or higher and 750°C or lower in the producing step.

15. The method for producing carbon nanotubes according to claim 12, further comprising an annealing step of annealing the carbon source in the presence of the catalyst after the preparing step and before the producing step.

16. The method for producing carbon nanotubes according to claim 12, wherein in the producing step, the carbon source is a carbon-containing gas, and the carbon-containing gas is converted into plasma and brought into contact with the catalyst.

17. The method for producing carbon nanotubes according to claim 12 , wherein in the producing step, the carbon source is heated in the presence of porous particles carrying the catalyst to produce carbon nanotubes.

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