JP4849437B2 - Method for producing three-walled carbon nanotube and composition containing three-walled carbon nanotube - Google Patents

Description

  The present invention relates to a method for producing three-walled carbon nanotubes and a composition containing three-walled carbon nanotubes, and more particularly to a method for producing three-walled carbon nanotubes having excellent characteristics and durability and a composition containing three-walled carbon nanotubes. is there.

  The carbon nanotube has a shape in which one surface of graphite is wound into a cylindrical shape. A single-walled carbon nanotube is formed by winding one layer, a double-walled carbon nanotube is formed by winding two layers, and a three-layer is formed. The rolled carbon nanotubes are called three-walled carbon nanotubes, and the carbon nanotubes of two or more layers are collectively called multi-walled carbon nanotubes.

  Since carbon nanotubes have excellent characteristics such as high mechanical strength and high conductivity, they are used as negative electrodes for fuel cells and lithium secondary batteries, and are made of composite materials of resins, metals, ceramics and organic semiconductors. It is expected as a material for high-strength resins, conductive resins, transparent conductive films, metal electrolyte powders, thermally conductive ceramics, and electromagnetic shielding materials. Furthermore, since the ratio L / D between the length L and the diameter D is large and the diameter is several nanometers, it is expected as a material for probes for scanning tunneling microscopes, field electron emission sources, solar cell elements, and nanotweezers. In addition, since it has a nano-sized space, it is expected as a material for adsorption materials such as hydrogen, medical nanocapsules, and MRI contrast agents.

  Carbon nanotubes with high expectations are required for high-purity carbon nanotubes in any application, and carbon nanotubes having a single diameter to about 5 layers with a small diameter are useful. From the viewpoint of durability, a double-walled or triple-walled carbon nanotube is particularly advantageous. In addition, a graphite layer having few defects is considered to be excellent in characteristics. In particular, the carbon nanotubes having 2 to 5 layers are expected to be used as a negative electrode material for a fuel cell or a lithium secondary battery, a heat dissipation material, and an electron emission material as a composite with metal or ceramics.

  Conventionally, as a carbon nanotube production method, an arc discharge method, a laser evaporation method, a chemical vapor deposition method, or the like is known (see Non-Patent Document 1). Among them, a catalytic chemical vapor deposition method is applied to a graphite layer. It is known as a method for producing high-quality carbon nanotubes with few defects at low cost (see Non-Patent Document 2). Furthermore, it is known that single-walled carbon nanotubes with high linearity can be synthesized with high purity by using alcohol as a raw material in catalytic chemical vapor deposition (see Non-Patent Document 3).

However, highly linear three-walled carbon nanotubes having both high characteristics and higher durability than double-walled carbon nanotubes could not be synthesized.
Yahachi Saito, Shunji Bando, Fundamentals of Carbon Nanotubes, Corona Inc., p17, 23, 47 Chemical Physics Letters 303 (1999), 117-124 Chemical Physics Letters 360 (2002), 229-234

  An object of the present invention is to provide a method for producing a three-walled carbon nanotube having excellent characteristics and durability and high linearity in a catalytic chemical vapor deposition method, and a composition containing the three-walled carbon nanotube.

The method for producing a three-walled carbon nanotube of the present invention that achieves the above object comprises bringing a carbon-containing compound into contact with a metal catalyst comprising metal particles having an average diameter of 10 nm or less at a temperature of 600 to 1000 ° C. A method for producing a carbon nanotube mainly composed of a nanotube , wherein the total pressure in the step of bringing the carbon-containing compound into contact with the metal catalyst is 5000 Pa or less, and the partial pressure of the carbon-containing compound is 150 Pa or more and 3000 Pa or less. Among 100 carbon nanotubes arbitrarily selected with a scanning electron microscope, the number of three-walled carbon nanotubes is 50 or more .

The three-walled carbon nanotube-containing composition of the present invention comprises (1) 50 or more of 100 carbon nanotubes arbitrarily selected by a transmission electron microscope, and (2) transmission-type electrons. The average of the distance between the bent portions in the three-walled carbon nanotube arbitrarily selected with a microscope is 100 nm or more, and (3) the maximum peak intensity in the range of 1560 to 1600 cm ⁻¹ is G, by resonance Raman scattering measurement. When the maximum peak intensity within the range of 1310 to 1350 cm ⁻¹ is D, the G / D ratio is 10 or more, and (4) the metal content by elemental analysis is 1% by weight or less. A composition containing three-walled carbon nanotubes that satisfies the requirements.

  According to the production method of the present invention, it is possible to efficiently synthesize three-walled carbon nanotubes having a high purity and a small diameter and being uniform. In addition, the three-walled carbon nanotube-containing composition according to the present invention can be a three-walled carbon nanotube excellent in linearity because it does not easily include a bent structure in each of the three-walled carbon nanotubes.

  The method for producing a three-walled carbon nanotube of the present invention is characterized in that a carbon-containing compound is brought into contact with a metal catalyst having an average diameter of metal particles of 10 nm or less at a temperature of 600 to 1000 ° C. Here, the type of the metal is not particularly limited, but preferably a Group 3-12 metal, more preferably a Group 5-11 metal. Among these, V, Mo, Mn, Fe, Co, Ni, Pd, Pt, Rh, W, Cu, and the like are particularly preferable, and Fe, Co, Ni, Mo, and Mn are more preferable. Here, the metal is not necessarily a zero-valent state. Although it can be presumed that the metal is in a zero-valent state during the reaction, it may be interpreted in the meaning of a compound containing a metal or a metal species. The metal is preferably fine particles. The fine particles have a particle size of 10 nm or less, preferably 0.5 to 10 nm. If the metal is a fine particle, a carbon nanotube with a small diameter is likely to be generated.

  The measurement method of the average diameter of a metal catalyst is a method of observing a product with an electron microscope after carbon nanotube synthesis. By using a transmission electron microscope, it is possible to measure the particle diameter of metal particles of the order of nm. In the present invention, the average diameter of the metal catalyst is obtained by measuring the particle diameters of 100 or more metal particles arbitrarily selected with a transmission electron microscope (magnification of 2 million times) and averaging the results. .

  In the production method of the present invention, the particle diameter of 100 or more arbitrarily selected metal particles is measured with a transmission electron microscope (magnification 2 million times), and the particle diameter of the metal catalyst is 2.3 to 4.5 nm. The number of certain metal catalysts is preferably 80% or more. By using metal particles having such a particle diameter as a catalyst, the diameter of the three-walled carbon nanotube can be adjusted.

  Although only one type of metal may be used or two or more types may be used, it is preferable to use two or more types. When two kinds of metals are used, it is particularly preferable to contain Fe, Co, Ni, Mo, and Mn. The type of metal and its role are not particularly limited, but for example, a group consisting of one or more metal elements makes it easier to synthesize carbon nanotubes by modifying hydrocarbons and consisting of one or more metal elements Other groups may be used for the synthesis of carbon nanotubes.

  The metal catalyst may be supported on a carrier or may not be supported. That is, it may exist independently as a metal particle having a particle diameter of 10 nm or less in the reaction tube. When not supported on a carrier, a method using a metal complex that is easily gasified as a raw material is preferably used.

  On the other hand, when the metal catalyst is supported on the carrier, the method for supporting the metal catalyst is not particularly limited. For example, a carrier is impregnated in a non-aqueous solution (for example, ethanol solution) or an aqueous solution in which a metal salt to be supported is dissolved, thoroughly dispersed and mixed, and then dried, and then nitrogen, hydrogen, an inert gas, or a mixed gas thereof Alternatively, the metal can be supported on the carrier by heating at a high temperature (300 to 600 ° C.) in a vacuum (impregnation method).

  The larger the amount of the metal catalyst supported, the higher the yield of carbon nanotubes. However, when the amount is too large, the particle diameter of the metal particles increases and the carbon nanotubes to be produced become thicker. When the amount of supported metal is small, the particle diameter of the supported metal becomes small and thin carbon nanotubes can be obtained, but the yield tends to be low. The optimum metal loading varies depending on the pore volume, outer surface area, and loading method of the carrier, but it is preferable to carry 0.1 to 20% by weight of metal with respect to the carrier. When two or more kinds of metals are used, the ratio is not limited.

  A carbon-containing compound is brought into contact with the carrier carrying the metal catalyst thus obtained at a temperature of 600 to 1000 ° C. to produce a three-walled carbon nanotube. The temperature which makes a catalyst and a carbon containing compound contact is 600-1000 degreeC, Preferably the range of 700-950 degreeC is good. When the temperature is lower than 600 ° C., the yield of carbon nanotubes is deteriorated. When the temperature is higher than 1000 ° C., there are restrictions on the material of the reactor to be used, and bonding between the carbon nanotubes starts. It becomes difficult to control the shape.

  In the production method of the present invention, the metal catalyst is preferably supported on a carrier. Although the kind of support | carrier is not specifically limited here, It is preferable that it is at least one chosen from a metal, an oxide, and carbon. In particular, the support is preferably an oxide such as zeolite, alumina, silica, titania, and magnesia, and each oxide may form a mesoporous material having mesopores.

  Here, the mesoporous material is a material having pores with a diameter of about 2 to 50 nm, and is synthesized by concerted self-assembly of a surfactant and an inorganic substance. Mesoporous materials have excellent basic physical properties as catalysts and adsorbents, such as a large specific surface area and high stability. The mesoporous pores of such a material are useful as pores for supporting a metal when carbon nanotubes are synthesized on a support. A typical material is mesoporous silica. The crystal structure of mesoporous silica is not particularly limited. For example, there are MCM-41 having a hexagonal structure developed by Mobil, MCM-48 having a cubic structure, and MCM-50 having a layered or lamellar structure. The MCM-41 structure in which hexagonal pores are arranged in parallel is preferably used.

  Zeolite is composed of a crystalline inorganic oxide having a pore size of molecular size. Here, the molecular size is a size range of molecules existing in the world, and generally means a range of about 0.2 nm to 2 nm. More specifically, a crystalline microporous material composed of crystalline silicate, crystalline aluminosilicate, crystalline metallosilicate, crystalline metalloaluminosilicate, crystalline aluminophosphate, crystalline metalloaluminophosphate, or the like. That is.

  Crystalline silicate, crystalline aluminosilicate, crystalline metallosilicate, crystalline metalloaluminosilicate, crystalline aluminophosphate, crystalline metalloaluminophosphate are not particularly limited, but for example, Atlas of Zeolite Structure Types ( Meyer, Olson, Baerocha, Zeolites, 17 (1/2), 1996) (Atlas of Zeolite Structure types (WM Meier, DH Olson, Ch. Baerlocher, Zeolites, 17 (1/2), 1996)) A crystalline inorganic porous material having a structure of Moreover, the zeolite in this invention is not limited to what is published in the said literature, The zeolite which has the novel structure synthesized one after another is included. Preferred zeolite structures are FAU type, MFI type, MOR type, BEA type, LTL type, and LTA type, which are easily available, but are not limited thereto.

  Zeolite has a silicate structure in which the skeleton has a heteroatom (atom other than Si) such as Si or Al or titanium at the center of the tetrahedron and oxygen at the apex of the tetrahedron. Therefore, it is most stable that a tetravalent metal enters the center of the tetrahedral structure, and heat resistance can be expected. Therefore, theoretically, a zeolite that does not substantially contain or contains a trivalent component such as Al has high heat resistance. As these production methods, a method of directly synthesizing by a conventionally known hydrothermal synthesis method or a method of removing a trivalent metal from the skeleton by post-treatment is preferably used.

  In the carrier used in the present invention, mesoporous pores may be formed by subjecting zeolite to an acid or alkali treatment. The acid treatment is treatment for bringing an oxide into contact with an acid, and the acid to be used is not particularly limited, but hydrofluoric acid, sulfuric acid, hydrochloric acid, nitric acid or a mixture thereof is preferable.

  The method for forming mesoporous pores of oxide by acid treatment is not particularly limited. For example, 1 to 100 g of the above oxide is impregnated in an aqueous solution of 0.01 to 1.00 M acid, and thoroughly stirred and dispersed and mixed at 0 to 100 ° C., then washed with water and dried at 50 to 200 ° C. By doing so, mesoporous pores can be formed.

  Alkali treatment is a method of forming mesoporous pores by bringing an oxide into contact with an alkali, and several treatments with alkali can be mentioned. The alkali to be used is not particularly limited, but sodium hydroxide, potassium hydroxide, cesium hydroxide, barium hydroxide, sodium carbonate, sodium bicarbonate or a mixture thereof is preferable. In particular, sodium hydroxide and potassium hydroxide are preferable.

  The method for forming mesoporous pores of oxide by alkali treatment is not particularly limited. For example, 1 to 100 g of the oxide is impregnated in an aqueous solution of 0.01 to 1.00 M alkali, dispersed and mixed with sufficient stirring at 0 to 100 ° C., washed with water, and dried at 50 to 200 ° C. By doing so, mesoporous pores can be formed.

  The carrier material preferably contains at least one selected from titanium, boron, and zirconium in an atomic ratio with silicon of 0.01 or more. By including at least one selected from titanium, boron and zirconium in the support, the catalytic activity can be controlled by the interaction between the metal catalyst supported on the support and the support, and the physical properties of the generated three-walled carbon nanotubes Easy to control. The atomic ratio of at least one selected from boron and zirconium to silicon is preferably 0.01 or more. If this ratio is less than 0.01, the influence on the catalyst activity of the carrier is small. On the other hand, when the ratio exceeds 0.1, the effect of suppressing the catalytic activity is exerted, and the synthesis amount of the three-walled carbon nanotube is reduced. For this reason, the atomic ratio of at least one selected from boron and zirconium to silicon is preferably 0.01 or more and 0.1 or less.

  In the production method of the present invention, it is preferable that the carrier has at least one peak in a region of 2 to 10 nm by pore distribution measurement by a nitrogen adsorption method. The specific surface area and pore distribution of the carrier used in the present invention can be determined from the physical adsorption of nitrogen at a liquid nitrogen temperature by a nitrogen adsorption method. That is, using a technique known as the BET method, gradually put nitrogen into a carrier placed under reduced pressure, take an adsorption isotherm of nitrogen from high vacuum to atmospheric pressure, and gradually reduce nitrogen when it reaches atmospheric pressure. The nitrogen desorption isotherm should be taken.

  In order to obtain the pore size distribution of a carrier having a pore size in the region of 2 to 10 nm, calculation is usually performed using a desorption isotherm. As a theoretical formula for obtaining the pore size distribution, the Dollimore-Heal method (hereinafter abbreviated as DH method) is known. The pore size distribution defined in the present invention is obtained from the desorption isotherm of nitrogen by the DH method, and has one or more peaks in this 2 to 10 nm region. When the carrier has at least one peak in the region of 2 to 10 nm in the pore distribution measurement, it means that the carrier has mesopores, which means that it is easy to carry metal particles having a size close to the mesopore diameter. To do.

  In general, the pore size distribution is obtained by taking the value (ΔVp / ΔDp) obtained by differentiating the pore volume (Vp) by the pore diameter (Dp) on the vertical axis and the pore diameter (Dp) on the horizontal axis. The pore volume can be determined from the area of this graph. Further, ΔVp / ΔDp, which is an index of the depth of the pore, is not particularly limited, but is preferably 1000 or more.

  In the production method of the present invention, the carrier preferably has a peak intensity change rate of 5% or less in X-ray diffraction before and after baking at 800 ° C. in air. The carrier used in the present invention has a rate of change of peak intensity of 5% or less in X-ray diffraction before and after firing at 800 ° C. in air. The carrier is fired at a temperature of 800 ° C. for 30 minutes in an atmosphere of dry air. The powder X-ray diffraction (XRD) is measured at room temperature before and after the firing, and two arbitrary peaks in those carriers are taken out, and the rate of change in the peak intensity ratio is 5% or less. Say. Since the peak intensity ratio varies depending on the preparation of the measurement sample, care must be taken so that the amount used for measurement is constant.

  The rate of change of the peak intensity in the X-ray diffraction before and after firing at 800 ° C. in air is 5% or less, indicating that there is substantially no structural change due to firing. Since it does not change, it is preferable.

  Whether or not there is a substantial structural change due to the firing of the carrier, is an exothermic peak appearing between 600 and 800 ° C. when differential thermal analysis (DTA) is performed up to 800 ° C. by raising the temperature at 5 ° C./min in a nitrogen atmosphere? I can judge it. In other words, it can be determined that those having no exothermic peak in the range of 600 to 800 ° C. have substantially no structural change up to 800 ° C.

  In the measurement after a temperature of 600 ° C., when the DTA curve goes up once and then goes down and the peak is before 800 ° C., an exothermic peak appears. If it is not possible to determine whether it is a peak or not, the base line is formed by linking the beginning and end of the curve, and the longest point at the intersection of the perpendicular line from the base line and the DTA curve is selected. However, the case where there is a length of 5 times or more the noise height is called a peak. Also, the temperature at the intersection is read and used as the peak of the exothermic curve.

  In the production method of the present invention, the carbon-containing compound preferably contains at least one selected from aliphatic hydrocarbons having 1 to 5 carbon atoms and alcohols having 1 to 5 carbon atoms.

  Examples of the aliphatic hydrocarbon having 1 to 5 carbon atoms include methane or ethane, ethylene, acetylene, propane, propylene, propyne, normal butane, isobutane, 1-butene, 2-butene, 1-butyne and 2-butyne. , Butadiene, normal pentane, isopentane, neopentane, cyclopentane, 1-pentene, 2-pentene, 2-methyl-1-butene, 3-methyl-1-butene, 3-methyl-2-butene and cyclopentene are preferred. It is done. As the alcohol having 1 to 5 carbon atoms, for example, methanol or ethanol, 1-propanol, 2-propanol, 1-butanol, 2-butanol, 1-pentanol, 2-pentanol, 3-pentanol and the like are preferably used. .

  Among these, methane, ethanol, and propanol are particularly preferable carbon-containing compounds for the synthesis of three-walled carbon nanotubes.

The manufacturing method of the present invention, the total pressure of the step of contacting a carbon-containing compound to the metal catalyst Ri der less 5000 Pa, and the partial pressure of the carbon-containing compound is Ru der than 3000Pa less 150 Pa.

When the total pressure of the step of contacting a carbon-containing compound to a metal catalyst is more than 5000 Pa, Ru tend to yield a 3-layer carbon nanotube decreases. Further, there is a tendency to decrease the partial pressure of 3-layer carbon nanotube is less than 150Pa yield of the carbon-containing compounds, Ru tend to four or more layers generating the multi-walled carbon nanotubes is facilitated exceeds 3000 Pa. By changing the partial pressure of the carbon-containing compound, the ease of adsorption of the carbon-containing compound to the catalyst, and the number of carbon atoms of the carbon-containing compound, the number of carbon nanotube layers to be generated can be controlled. In particular, it is more preferable to use propanol at a partial pressure of 150 Pa or more and 3000 Pa or less as the carbon-containing compound serving as the carbon source because three-walled carbon nanotubes are easily generated.

  The method for contacting the metal catalyst with the carbon-containing compound is not particularly limited. For example, the above-described metal catalyst can be placed in a heat-resistant reaction tube made of quartz, alumina, or the like installed in a tubular furnace, and contacted by flowing a carbon-containing compound gas under reduced pressure and heating. The contact method of the metal catalyst and the carbon-containing compound may be a method of spraying the catalyst or a method of bringing the catalyst into contact with stirring, in addition to the above method.

  The three-walled carbon nanotube obtained by the production method of the present invention preferably satisfies the following requirements.

That is, in the present invention, three layers of carbon nanotubes, in 100 carbon nanotubes arbitrarily selected with a transmission electron microscope, Ru Oh 50 or more is a three-layer carbon nanotube. The measurement method was observed with a transmission electron microscope at a magnification of 1,000,000 times, 10% or more of the visual field area was a carbon nanotube in a 150 nm square field of view, and 100 pieces arbitrarily extracted from a plurality of fields of view. The number of layers in the carbon nanotube is observed and measured, and the above measurement is evaluated with an average value obtained for 10 locations. The proportion of 3-layer carbon nanotube is less than 100 in 50 present, the mechanical strength and durability sufficiently exhibited and Lena are.

  In the present invention, it is preferable that 80 or more of 100 three-walled carbon nanotubes arbitrarily selected by a transmission electron microscope have an outer diameter in the range of 1.8 to 5.0 nm. The measurement method was observed with a transmission electron microscope at a magnification of 1,000,000, and the outer diameter of 100 three-walled carbon nanotubes arbitrarily extracted from a plurality of fields of view was measured. The number of the three-walled carbon nanotubes in the range of 5.0 nm is counted, and the above measurement is evaluated with an average value obtained for 10 places.

  Furthermore, in the present invention, the hydrogen concentration in the gas supplied to the reaction field for synthesizing the three-walled carbon nanotube is preferably 100 ppm or less. Although hydrogen acts to clean the catalyst surface, it simultaneously promotes sintering of the catalyst at high temperatures. When alcohol is used as the carbon raw material as in the present invention, since the alcohol itself has an action of cleaning the catalyst, the effect of adding hydrogen is not preferable because only the sintering effect takes precedence.

In the production method of the present invention, it is also preferable that the carrier is formed on a substrate. Here, the type of the substrate is not particularly limited, but the surface on which the carrier material is applied is preferably 1 mm ² or more, and more preferably 1 cm ² or more. Examples of the material of the substrate include glass, quartz glass, silicon, metal, and oxide. The method for forming the mesoporous material on the substrate is not particularly limited. For example, a mesoporous material synthesized in a powder form may be coated later, or may be formed on the substrate in that case. A three-layer carbon nanotube substrate can be obtained by supporting a metal catalyst on the film-formed mesoporous material and synthesizing the three-layer carbon nanotube.

  In the production method of the present invention, it is preferable that the three-walled carbon nanotubes are oriented and grown substantially vertically from the substrate. The three-walled carbon nanotubes are substantially aligned and grown in the vertical direction from the substrate. From the electron micrograph of the cross section of the substrate, the straight line connecting the upper and lower ends of the arbitrarily selected three-walled carbon nanotube and the substrate surface The angle formed by is averaged over 10 or more, and the result is 90 ° ± 10 °. Alignment growth in the vertical direction from the substrate shows good electron emission characteristics for field emission displays and solar cells.

  Further, the production method of the present invention is a method in which, in a reaction tube in which a carbon-containing compound and a metal catalyst are in contact with each other, a carbon-containing compound is reformed with a metal catalyst installed on the upstream side of the reaction tube, It is preferable to synthesize three-walled carbon nanotubes with a catalyst. Although the kind of metal of the metal catalyst installed in an upstream is not specifically limited, Preferably a 3-12 group metal, More preferably, a 5-11 group metal is used. Among these, V, Mo, Mn, Fe, Co, Ni, Pd, Pt, Rh, W, Cu, and the like are preferable, and Fe, Co, Ni, Mo, and Mn are more preferable.

The three-walled carbon nanotube-containing composition of the present invention satisfies the following requirements (1) to (4).
(1) Of 100 carbon nanotubes arbitrarily selected with a transmission electron microscope, 50 or more are three-layer carbon nanotubes.
(2) The average distance between the bent portions in the three-walled carbon nanotube arbitrarily selected by the transmission electron microscope is 100 nm or more.
(3) By resonance Raman scattering measurement, the maximum peak intensity in the range of 1560~1600cm ^-1 G, when the maximum peak intensity is D within the 1310～1350Cm ^-1, the ratio of G / D 10 or more.
(4) The metal content by elemental analysis is 1% by weight or less.

  Such a three-walled carbon nanotube-containing composition can be obtained by the method for producing a three-walled carbon nanotube of the present invention.

  Here, the bent portion in the three-walled carbon nanotube refers to a bent due to the presence of a 5-membered ring and a 7-membered carbon in the graphite structure of the carbon nanotube, and is a high-resolution transmission electron micrograph as shown in FIG. This refers to the portion where carbon nanotubes are bent and observed.

  In the three-walled carbon nanotube-containing composition of the present invention, the average distance from the bent portion to the bent portion is determined for any three-walled carbon nanotube selected with a high-resolution transmission electron microscope, and this is calculated as 10 or more three-layer carbon nanotubes. The averaged result for the nanotubes is preferably 100 nm or more. As the distance from the bent portion to the bent portion is longer, the linearity of the three-walled carbon nanotube is improved, and a three-walled carbon nanotube having higher conductivity and thermal conductivity is obtained. Since the distance between the bent portions is preferably as long as possible, it is preferably 300 nm or more, more preferably 500 nm or more, and most preferably 1 μm or more.

In addition, the quality of the three-walled carbon nanotube-containing composition of the present invention can be evaluated by Raman spectroscopy. In the Raman spectrum, the Raman shift found in the range of 1560 to 1600 cm ⁻¹ is called the G band derived from graphite, and the Raman shift found in the range of 1310 to 1350 cm ⁻¹ is the D band derived from defects in amorphous carbon or graphite. be called. The higher the G / D ratio, the higher the degree of graphitization, which means a higher quality carbon nanotube. The G / D ratio of the three-walled carbon nanotube in the present invention is preferably 10 or more. More preferably, it is 15 or more, and most preferably 20 or more.

  In addition, the three-walled carbon nanotube-containing composition of the present invention preferably has a metal content by elemental analysis of 1% by weight or less. When the metal content is high, there is a concern that it may become a foreign substance in a use added to a polymer and a medical and pharmaceutical use, and adversely affect the human body. In the method for producing a three-walled carbon nanotube of the present invention, since the catalytic metal is present at the interface between the support and the three-walled carbon nanotube, the three-walled carbon nanotube can be easily cut by cutting the three-walled carbon nanotube at the interface as described later. Nanotubes and metal catalysts can be separated. The metal content is preferably as low as possible, more preferably 0.5% by weight or less, and most preferably 0.1% by weight or less.

  In addition, the carbon nanotube-containing composition of the present invention may be used as it is synthesized, and is preferably used without the support material and the catalyst metal. The support material and the catalyst metal can be removed with an acid or the like. For example, when zeolite is used as the carrier and cobalt is used as the catalyst metal, zeolite can be removed with hydrofluoric acid and cobalt can be removed with hydrochloric acid, as described in Japanese Patent Application No. 2003-126211. Further, as described in Japanese Patent Application No. 2004-047182, zeolite can be removed even with an aqueous sodium hydroxide solution. Further, as described in Japanese Patent Application No. 2003-331240, zeolite, cobalt and carbon nanotubes can be separated and recovered individually by a separation method using two liquids of an organic solvent and water. In addition, as described in Japanese Patent Application No. 2003-126211, when it is desired to remove the amount of the catalytic metal to a high degree, it is preferable to perform a calcination treatment and then treat with an acid. This is because the metal is covered with a carbon compound such as graphite, and therefore, once the carbon around the catalyst is burned out, the metal can be efficiently removed by acid treatment.

  The three-walled carbon nanotube-containing composition of the present invention is useful as an electron emission material. For example, when the carbon nanotube-containing composition of the present invention is used as a field emission electron source, the applied voltage can be kept low because the diameter is small and charge concentration tends to occur. In addition, even when a voltage is applied for a long time, the lifetime is significantly longer than single-walled carbon nanotubes and double-walled carbon nanotubes.

  In addition, the present invention is useful as a transparent conductive film containing a three-walled carbon nanotube-containing composition, having a light transmittance of 85% or more and a surface resistance of 1000Ω / □ or less. Three-walled carbon nanotubes contain carbon nanotubes that exhibit metallic electrical conductivity because they are moderately thin and have little light transmission hindrance and are thicker than single-walled or double-walled carbon nanotubes. The rate is high, which is advantageous for applications that require electrical conductivity.

  EXAMPLES Hereinafter, the present invention will be specifically described by way of examples. However, the following examples are given for illustrative purposes and should not be used in any way as a limited interpretation of the present invention. .

<Example 1>
After evacuating the inside of a quartz tube with an inner diameter of 32 mm and confirming that the temperature became 10 Pa or less at a temperature of 850 ° C., ferrocene was 50 Pa, methane was 300 Pa, and the total pressure with high-purity argon gas (manufactured by High Pressure Gas Industry) was 1000 Pa. The gas was prepared and introduced for 20 minutes. After stopping the introduction of methane, only argon gas was supplied at 5 cc / min for 30 minutes, the temperature was cooled to room temperature, and a composition containing three-walled carbon nanotubes was taken out.

  When the composition containing the obtained three-walled carbon nanotube was observed with a high-resolution transmission electron microscope, the number of the three-layered carbon nanotubes was 60%. Carbon impurities other than carbon nanotubes (fullerene, nanoparticles, amorphous carbon, etc.) were hardly observed. The average outer diameter of the three-walled carbon nanotube was 2.5 nm. The average distance between the bends was about 600 nm. As for the structure of the terminal portion, 90% or more of the observed three-walled carbon nanotubes were open ends. Further, 80% or more of the particle diameter of the metal catalyst was 2.3 to 4.5 nm. The Raman G / D ratio was about 17. As a result of EDX elemental analysis after purification, the metal catalyst content was 0.07%.

<Example 2>
(Synthesis of MCM-41)
After adding 3.64 g of cetyltrimethylammonium bromide (CTAB: manufactured by Aldrich) and 1.45 g of tetramethylammonium hydroxide (TMAOH: manufactured by Aldrich) to 28.8 ml of ion-exchanged water at 35 ° C., fumed silica (manufactured by Aldrich) ) 2.4g was added and stirred for 1 hour. After aging for 20 hours, it was transferred to an autoclave and hydrothermally synthesized at 150 ° C. for 96 hours. After hydrothermal synthesis, the product was collected by filtration, washed, calcined at 550 ° C. for 8 hours, and then calcined at 800 ° C. for 1 hour.

(Support of metal salt on MCM-41)
0.03 g of iron nitrate nonahydrate (manufactured by Kanto Chemical Co., Ltd.) and 0.17 g of cobalt nitrate hexahydrate (manufactured by Kanto Chemical Co., Ltd.) were dissolved in 15 ml of ethanol (manufactured by Kanto Chemical Co., Ltd.). To this solution, 1.4 g of MCM-41 was added, treated with an ultrasonic cleaner for 30 minutes, ethanol was removed at a constant temperature of 60 ° C. and 120 ° C. and dried. Then, it heated at 400 degreeC in the air for 1 hour, and obtained the solid catalyst with which the metal salt was carry | supported by MCM-41 powder.

(Synthesis of a composition containing three-walled carbon nanotubes)
On the quartz wool at the center of a quartz tube having an inner diameter of 32 mm, 1.0 g of the solid catalyst prepared above was taken, and argon gas was supplied at 600 cc / min. The quartz tube was installed in an electric furnace, and the center temperature was heated to 930 ° C. (temperature raising time 60 minutes). After reaching 930 ° C., the inside of the reaction tube is evacuated, and after confirming that the pressure is 10 Pa or less, the gas is adjusted so that the total pressure of ethanol vapor is 1500 Pa and high-purity argon gas (manufactured by High Pressure Gas Industry) is 4000 Pa. Was prepared and introduced for 20 minutes. After the introduction of ethanol vapor was stopped, only argon gas was supplied at 5 cc / min for 30 minutes, the temperature was cooled to room temperature, and a composition containing three-walled carbon nanotubes was taken out.

(High-resolution transmission electron microscope analysis of a composition containing three-walled carbon nanotubes)
When the composition containing the carbon nanotubes obtained as described above was observed with a high-resolution transmission electron microscope, the carbon nanotubes were composed of a clean graphite layer as shown in FIG. Nanotubes were 70%. Carbon impurities other than carbon nanotubes (fullerene, nanoparticles, amorphous carbon, etc.) were hardly observed. The average outer diameter of the three-walled carbon nanotube was 2.6 nm. The average distance between the bends was about 800 nm. As for the structure of the terminal portion, 90% or more of the observed three-walled carbon nanotubes were open ends. Further, 80% or more of the particle diameter of the metal catalyst was 2.3 to 4.5 nm.

(Resonance Raman spectroscopic analysis of a composition containing three-walled carbon nanotubes)
The composition containing the carbon nanotubes obtained as described above was measured with a resonance Raman spectrometer (INF-300 manufactured by Horiba Joban Yvon) at a laser wave number of 630 to 650 cm ⁻¹ , and the G / D ratio was determined. 18 and the G band was split and observed.

(Purification / elemental analysis)
The composition containing carbon nanotubes obtained as described above was baked at 400 ° C. for 30 minutes in air, and then added to 50 cc of toluene (manufactured by Wako Pure Chemical Industries), and subjected to ultrasonic vibration for 40 minutes. Next, 50 cc of ion-exchanged water was added and vigorously stirred for 10 minutes. The black toluene phase and the gray aqueous phase were separated with a separatory funnel, and the toluene phase was filtered. It was confirmed by SEM and EDX (ISIS manufactured by Oxford) that the toluene phase was mainly composed of carbon nanotubes and the aqueous phase was mainly composed of MCM-41 and catalytic metal. As a result of EDX elemental analysis of the carbon nanotube composition recovered from the toluene phase, the iron content was 0.03% and the cobalt content was 0.2%.

<Example 3>
Cobalt nitrate hexahydrate (manufactured by Kanto Chemical Co.) 0.17 g was dissolved in ethanol (manufactured by Kanto Chemical Co., Ltd.) 15 ml. To this solution, 1.4 g of zeolite (manufactured by Toray Industries, Inc., borosilicate) was added, treated with an ultrasonic cleaner for 30 minutes, ethanol was removed at a constant temperature of 60 ° C. and 120 ° C. and dried. Thereafter, it was heated in air at 400 ° C. for 1 hour to obtain a solid catalyst in which a metal salt was supported on zeolite powder.

  On the quartz wool at the center of a quartz tube having an inner diameter of 32 mm, 1.0 g of the solid catalyst prepared above was taken, and argon gas was supplied at 600 cc / min. The quartz tube was installed in an electric furnace, and the center temperature was heated to 900 ° C. (temperature rising time 60 minutes). After reaching 900 ° C., the inside of the reaction tube was evacuated, and after confirming that the pressure became 10 Pa or less, propanol vapor was introduced at 2000 Pa for 20 minutes. After the introduction of propanol vapor was stopped, only argon gas was supplied at 5 cc / min for 30 minutes, the temperature was cooled to room temperature, and a composition containing three-walled carbon nanotubes was taken out.

  When the composition containing the obtained three-walled carbon nanotube was observed with a high-resolution transmission electron microscope, the number of the three-layered carbon nanotubes was 75%. Carbon impurities other than carbon nanotubes (fullerene, nanoparticles, amorphous carbon, etc.) were hardly observed. The average outer diameter of the three-walled carbon nanotube was 2.6 nm. The average distance between the bends was about 650 nm. As for the structure of the terminal portion, 90% or more of the observed three-walled carbon nanotubes were open ends. Further, 80% or more of the particle diameter of the metal catalyst was 2.3 to 4.5 nm. The Raman G / D ratio was about 18. As a result of EDX elemental analysis after purification, the metal catalyst content was 0.04%.

<Example 4>
0.17 g of nickel nitrate hexahydrate (manufactured by Wako Pure Chemical Industries, Ltd.) was dissolved in 15 ml of ethanol (manufactured by Kanto Chemical Co., Inc.). To this solution, 1.4 g of α-alumina (manufactured by Wako Pure Chemical Industries, Ltd.) was added, treated with an ultrasonic cleaner for 30 minutes, and ethanol was removed at a constant temperature of 60 ° C. and 120 ° C. and dried. Then, it heated in air at 400 degreeC for 1 hour, and obtained the solid catalyst by which the metal salt was carry | supported by the alpha alumina powder.

  On the quartz wool at the center of a quartz tube having an inner diameter of 32 mm, 1.0 g of the solid catalyst prepared above was taken, and argon gas was supplied at 600 cc / min. The quartz tube was installed in an electric furnace, and the center temperature was heated to 750 ° C. (temperature raising time 60 minutes). After reaching 750 ° C., the inside of the reaction tube is evacuated, and after confirming that the pressure is 10 Pa or less, the gas is adjusted so that the total pressure of ethane is 1500 Pa and the total pressure with high purity argon gas (manufactured by High Pressure Gas Industry) is 2000 Pa. Prepared and introduced for 20 minutes. After stopping the introduction of ethane, only argon gas was supplied at 5 cc / min for 30 minutes, the temperature was cooled to room temperature, and a composition containing three-walled carbon nanotubes was taken out.

  When the composition containing the obtained three-walled carbon nanotube was observed with a high-resolution transmission electron microscope, the number of the three-walled carbon nanotube was 55%. Carbon impurities other than carbon nanotubes (fullerene, nanoparticles, amorphous carbon, etc.) were hardly observed. The average outer diameter of the three-walled carbon nanotube was 2.4 nm. The average distance between the bends was about 550 nm. As for the structure of the terminal portion, 90% or more of the observed three-walled carbon nanotubes were open ends. Further, 80% or more of the particle diameter of the metal catalyst was 2.3 to 4.5 nm. The Raman G / D ratio was about 12. As a result of EDX elemental analysis after purification, the metal catalyst content was 0.02%.

<Example 5>
0.3 g of iron nitrate nonahydrate (manufactured by Kanto Chemical Co.) was dissolved in 15 ml of ethanol (manufactured by Kanto Chemical Co., Ltd.). To this solution, 1.4 g of magnesia (manufactured by Wako Pure Chemical Industries, Ltd.) was added, treated with an ultrasonic cleaner for 30 minutes, ethanol was removed at a constant temperature of 60 ° C. and 120 ° C. and dried. Then, it heated at 400 degreeC in the air for 1 hour, and obtained the solid catalyst by which the metal salt was carry | supported by the magnesia powder.

  On the quartz wool at the center of a quartz tube having an inner diameter of 32 mm, 1.0 g of the solid catalyst prepared above was taken, and argon gas was supplied at 600 cc / min. The quartz tube was installed in an electric furnace, and the center temperature was heated to 950 ° C. (temperature raising time 60 minutes). After reaching 950 ° C., the inside of the reaction tube is evacuated, and after confirming that the pressure is 10 Pa or less, the gas is adjusted so that the total pressure with 900 Pa of methane and high-purity argon gas (manufactured by High Pressure Gas Industry) is 3000 Pa. Prepared and introduced for 20 minutes. After stopping the introduction of methane, only argon gas was supplied at 5 cc / min for 30 minutes, the temperature was cooled to room temperature, and a composition containing three-walled carbon nanotubes was taken out.

  When the composition containing the obtained three-layer carbon nanotube was observed with a high-resolution transmission electron microscope, the number of the three-layer carbon nanotube was 65%. Carbon impurities other than carbon nanotubes (fullerene, nanoparticles, amorphous carbon, etc.) were hardly observed. The average outer diameter of the three-walled carbon nanotube was 2.7 nm. The average distance between the bends was about 750 nm. As for the structure of the terminal portion, 90% or more of the observed three-walled carbon nanotubes were open ends. Further, 80% or more of the particle diameter of the metal catalyst was 2.3 to 4.5 nm. The Raman G / D ratio was about 18. As a result of EDX elemental analysis after purification, the metal catalyst content was 0.09%.

<Example 6>
0.3 g of iron nitrate nonahydrate (manufactured by Kanto Chemical Co., Ltd.) and 0.16 g of molybdenum chloride (manufactured by Wako Pure Chemical Industries, Ltd.) were dissolved in 15 ml of ethanol (manufactured by Kanto Chemical Co., Ltd.). To this solution, 1.4 g of titania (manufactured by Wako Pure Chemical Industries, Ltd.) was added, treated with an ultrasonic cleaner for 30 minutes, ethanol was removed at a constant temperature of 60 ° C. and 120 ° C. and dried. Thereafter, the mixture was heated in air at 400 ° C. for 1 hour to obtain a solid catalyst in which a metal salt was supported on titania powder.

  On the quartz wool at the center of a quartz tube having an inner diameter of 32 mm, 1.0 g of the solid catalyst prepared above was taken, and argon gas was supplied at 600 cc / min. The quartz tube was placed in an electric furnace, and the center temperature was heated to 800 ° C. (temperature rising time 60 minutes). After reaching 800 ° C., the inside of the reaction tube is evacuated, and after confirming that the pressure is 10 Pa or less, the gas is adjusted so that the total pressure with propane is 1500 Pa and high-purity argon gas (manufactured by High Pressure Gas Industry) is 4000 Pa. Prepared and introduced for 20 minutes. After the introduction of propane was stopped, only argon gas was supplied at 5 cc / min for 30 minutes, the temperature was cooled to room temperature, and a composition containing three-walled carbon nanotubes was taken out.

  When the composition containing the obtained three-walled carbon nanotube was observed with a high-resolution transmission electron microscope, the number of the three-walled carbon nanotube was 55%. Carbon impurities other than carbon nanotubes (fullerene, nanoparticles, amorphous carbon, etc.) were hardly observed. The average outer diameter of the three-walled carbon nanotube was 2.5 nm. The average distance between the bends was about 700 nm. As for the structure of the terminal portion, 90% or more of the observed three-walled carbon nanotubes were open ends. Further, 80% or more of the particle diameter of the metal catalyst was 2.3 to 4.5 nm. The Raman G / D ratio was about 14. As a result of EDX elemental analysis after purification, the metal catalyst content was 0.08%.

<Example 7>
Manganese nitrate hexahydrate (manufactured by Wako Pure Chemical Industries, Ltd.) 0.17 g was dissolved in ethanol (manufactured by Kanto Chemical Co.) 15 ml. To this solution, 1.4 g of activated carbon (manufactured by Wako Pure Chemical Industries, Ltd.) was added, treated with an ultrasonic cleaner for 30 minutes, ethanol was removed at a constant temperature of 60 ° C. and 120 ° C. and dried. Then, it heated at 400 degreeC in the air for 1 hour, and obtained the solid catalyst with which the activated carbon powder carry | supported the metal salt.

  On the quartz wool at the center of a quartz tube having an inner diameter of 32 mm, 1.0 g of the solid catalyst prepared above was taken, and argon gas was supplied at 600 cc / min. The quartz tube was placed in an electric furnace, and the center temperature was heated to 650 ° C. (temperature rising time 60 minutes). After reaching 650 ° C., the inside of the reaction tube is evacuated, and after confirming that the pressure is 10 Pa or less, the gas is adjusted so that the total pressure with acetylene is 1500 Pa and high-purity argon gas (manufactured by High Pressure Gas Industry) is 5000 Pa. Prepared and introduced for 20 minutes. After stopping the introduction of acetylene, only argon gas was supplied at 5 cc / min for 30 minutes, the temperature was cooled to room temperature, and a composition containing three-walled carbon nanotubes was taken out.

  When the composition containing the obtained three-walled carbon nanotube was observed with a high-resolution transmission electron microscope, the number of the three-walled carbon nanotube was 55%. Carbon impurities other than carbon nanotubes (fullerene, nanoparticles, amorphous carbon, etc.) were hardly observed. The average outer diameter of the three-walled carbon nanotube was 2.3 nm. The average distance between the bends was about 550 nm. As for the structure of the terminal portion, 90% or more of the observed three-walled carbon nanotubes were open ends. Further, 80% or more of the particle diameter of the metal catalyst was 2.3 to 4.5 nm. The Raman G / D ratio was about 12. As a result of EDX elemental analysis after purification, the metal catalyst content was 0.03%.

<Example 8>
Nickel nitrate hexahydrate (manufactured by Wako Pure Chemical Industries, Ltd.) 0.17 g and cobalt nitrate hexahydrate (manufactured by Wako Pure Chemical Industries, Ltd.) 0.17 g were dissolved in 15 ml of ethanol (manufactured by Kanto Chemical Co., Inc.). To this solution, 3.0 g of porous stainless steel was added, treated with an ultrasonic cleaner for 30 minutes, ethanol was removed at a constant temperature of 60 ° C. and 120 ° C. and dried. Then, it heated at 400 degreeC in the air for 1 hour, and obtained the solid catalyst by which the metal salt was carry | supported by the stainless steel powder.

  On the quartz wool at the center of a quartz tube having an inner diameter of 32 mm, 1.0 g of the solid catalyst prepared above was taken, and argon gas was supplied at 600 cc / min. The quartz tube was installed in an electric furnace, and the center temperature was heated to 700 ° C. (temperature rising time 60 minutes). After reaching 700 ° C., the inside of the reaction tube was evacuated, and after confirming that the pressure was 10 Pa or less, 1-butanol was introduced at 1500 Pa for 20 minutes. After stopping the introduction of 1-butanol, only argon gas was supplied at 5 cc / min for 30 minutes, the temperature was cooled to room temperature, and a composition containing three-walled carbon nanotubes was taken out.

  When the composition containing the obtained three-walled carbon nanotube was observed with a high-resolution transmission electron microscope, the number of the three-walled carbon nanotube was 55%. Carbon impurities other than carbon nanotubes (fullerene, nanoparticles, amorphous carbon, etc.) were hardly observed. The average outer diameter of the three-walled carbon nanotube was 2.4 nm. The average distance between the bends was about 600 nm. As for the structure of the terminal portion, 90% or more of the observed three-walled carbon nanotubes were open ends. Further, 80% or more of the particle diameter of the metal catalyst was 2.3 to 4.5 nm. The Raman G / D ratio was about 14. As a result of EDX elemental analysis after purification, the metal catalyst content was 0.09%.

<Example 9>
0.3 g of iron nitrate nonahydrate (manufactured by Kanto Chemical Co.) was dissolved in 15 ml of ethanol (manufactured by Kanto Chemical Co., Ltd.). To this solution, 1.4 g of magnesia (manufactured by Wako Pure Chemical Industries, Ltd.) was added, treated with an ultrasonic cleaner for 30 minutes, ethanol was removed at a constant temperature of 60 ° C. and 120 ° C. and dried. Then, it heated at 400 degreeC in the air for 1 hour, and obtained the solid catalyst by which the metal salt was carry | supported by the magnesia powder.

  Separately, 0.16 g of molybdenum chloride (manufactured by Wako Pure Chemical Industries, Ltd.) was dissolved in 15 ml of ethanol (manufactured by Kanto Chemical Co., Ltd.), and 1.4 g of α-alumina (manufactured by Wako Pure Chemical Industries, Ltd.) was added to the solution. It processed for 30 minutes with the ultrasonic cleaner, ethanol was removed and dried under the constant temperature of 60 degreeC and 120 degreeC. Then, it heated in air at 400 degreeC for 1 hour, and obtained the solid catalyst by which the metal salt was carry | supported by the alpha alumina powder.

  Take 1.0 g of the molybdenum / α-alumina catalyst on the quartz wool on the upstream side of the reaction gas of the quartz tube with an inner diameter of 32 mm, and take 1.0 g of the solid catalyst prepared above on the quartz wool in the center, and add argon gas. It was supplied at 600 cc / min. The quartz tube was installed in an electric furnace, and the center temperature was heated to 900 ° C. (temperature rising time 60 minutes). After reaching 900 ° C., the inside of the reaction tube is evacuated, and after confirming that the pressure is 10 Pa or less, the gas is adjusted so that the total pressure with methane is 300 Pa and high-purity argon gas (manufactured by High Pressure Gas Industry) is 3000 Pa. Prepared and introduced for 20 minutes. After stopping the introduction of methane, only argon gas was supplied at 5 cc / min for 30 minutes, the temperature was cooled to room temperature, and a composition containing three-walled carbon nanotubes was taken out.

  When the composition containing the obtained three-walled carbon nanotube was observed with a high-resolution transmission electron microscope, the number of the three-layered carbon nanotubes was 70%. Carbon impurities other than carbon nanotubes (fullerene, nanoparticles, amorphous carbon, etc.) were hardly observed. The average outer diameter of the three-walled carbon nanotube was 2.6 nm. The average distance between the bends was about 750 nm. As for the structure of the terminal portion, 90% or more of the observed three-walled carbon nanotubes were open ends. Further, 80% or more of the particle diameter of the metal catalyst was 2.3 to 4.5 nm. The Raman G / D ratio was about 16. As a result of EDX elemental analysis after purification, the metal catalyst content was 0.09%.

<Comparative Example 1>
0.03 g of iron nitrate nonahydrate (manufactured by Kanto Chemical Co., Ltd.) and 0.17 g of cobalt nitrate hexahydrate (manufactured by Kanto Chemical Co., Ltd.) were dissolved in 15 ml of ethanol (manufactured by Kanto Chemical Co., Ltd.). To this solution, 1.4 g of zeolite (Titanosilicate manufactured by Toray Industries, Inc.) was added, treated with an ultrasonic cleaner for 30 minutes, and ethanol was removed at a constant temperature of 60 ° C. and 120 ° C. and dried. Thereafter, it was heated in air at 400 ° C. for 1 hour to obtain a solid catalyst in which a metal salt was supported on zeolite powder.

  On the quartz wool at the center of a quartz tube having an inner diameter of 32 mm, 1.0 g of the solid catalyst prepared above was taken, and argon gas was supplied at 600 cc / min. The quartz tube was placed in an electric furnace, and the center temperature was heated to 800 ° C. (temperature rising time 60 minutes). After reaching 800 ° C., the inside of the reaction tube is evacuated, and after confirming that the pressure is 10 Pa or less, the gas is adjusted so that the total pressure of acetylene is 6000 Pa and high-purity argon gas (manufactured by High Pressure Gas Industry) is 30000 Pa. Prepared and introduced for 20 minutes. After the introduction of acetylene was stopped, only argon gas was supplied at 5 cc / min for 30 minutes, the temperature was cooled to room temperature, and a composition containing carbon nanotubes was taken out.

  When the composition containing the obtained carbon nanotube was observed with a high-resolution transmission electron microscope, the number of carbon nanotubes with two layers was 60%, and no three-walled carbon nanotubes were observed. Carbon impurities other than carbon nanotubes (fullerene, nanoparticles, amorphous carbon, etc.) were hardly observed. The average outer diameter of the double-walled carbon nanotubes was 1.5 nm. The average distance between the bends was about 100 nm. As for the structure of the terminal portion, 90% or more of the observed double-walled carbon nanotubes were open ends. The Raman G / D ratio was about 6. As a result of EDX elemental analysis after purification, the metal catalyst content was 0.06%.

  Table 1 shows the production conditions and evaluation results of Examples 1 to 9 and Comparative Example 1.

<Example 10>
(Electron emission characteristics of a composition containing three-walled carbon nanotubes)
The three-walled carbon nanotube composition obtained in Example 2 was dispersed in 1-propanol and spray-coated on a stainless steel substrate having a diameter of 10 mmφ. The substrate was placed in a chamber of an emission profiler (manufactured by Tokyo Cathode), and the inside of the chamber was evacuated to 10 ⁻⁷ Pa. The substrate coated with carbon nanotubes was used as the cathode, the anode was placed facing the substrate, and the cathode / anode distance was set to 100 μm. As a result of applying a voltage between both electrodes, a current value due to emission was observed when 135 V was applied, and the current value reached 1000 μA / cm ² when 280 V was applied.

<Example 11>
(Transparent conductive film containing three-walled carbon nanotubes)
When 10 mg of the three-walled carbon nanotube composition obtained in Example 2 was added to ion-exchanged water, then 30 mg of sodium dodecylbenzenesulfonate was added, and ultrasonic vibration was added for 30 minutes to obtain a black suspension. It was. A few drops of this were dropped onto a PET film (10 cm ² ) and applied with a bar coater (No. 8). After drying the water, the light transmittance and the surface resistance were measured. The above coating operation was repeated several times, and as a result of measuring the surface resistance when the light transmittance was maintained at 85% or more, it was 550Ω / □.

  According to the present invention, a highly linear three-walled carbon nanotube can be synthesized with a high yield.

It is a high-resolution transmission electron microscope photograph figure of the bending part of a carbon nanotube. 3 is a high-resolution transmission electron microscope photograph of the three-walled carbon nanotube-containing composition obtained in Example 2. FIG.

Claims (18)

A method for producing a carbon nanotube mainly composed of a three-layer carbon nanotube by contacting a carbon-containing compound with a metal catalyst composed of metal particles having an average diameter of 10 nm or less at a temperature of 600 to 1000 ° C. The total pressure in the step of bringing the carbon-containing compound into contact with the metal catalyst is 5000 Pa or less, the partial pressure of the carbon-containing compound is 150 Pa or more and 3000 Pa or less, and three layers among 100 carbon nanotubes arbitrarily selected by a transmission electron microscope A method for producing a three- walled carbon nanotube, comprising 50 or more carbon nanotubes.   The method for producing a three-walled carbon nanotube according to claim 1, wherein the metal catalyst is supported on a carrier.   The method for producing a three-walled carbon nanotube according to claim 2, wherein the carrier is at least one selected from a metal, an oxide, and carbon.   The method for producing a three-walled carbon nanotube according to claim 3, wherein the oxide is at least one selected from zeolite, alumina, silica, titania, and magnesia.   The method for producing a three-walled carbon nanotube according to any one of claims 2 to 4, wherein the carrier has at least one peak in a region of 2 to 10 nm by pore distribution measurement by a nitrogen adsorption method.   The method for producing a three-walled carbon nanotube according to any one of claims 2 to 5, wherein the carrier has a peak intensity change rate of 5% or less in X-ray diffraction before and after baking at 800 ° C in air.   The method for producing a three-walled carbon nanotube according to any one of claims 1 to 6, wherein the metal catalyst contains at least one selected from iron, cobalt, nickel, molybdenum, and manganese.   8. The 3 according to claim 1, wherein the carbon-containing compound includes at least one selected from the group consisting of an aliphatic hydrocarbon having 1 to 5 carbon atoms and an alcohol having 1 to 5 carbon atoms. For producing single-walled carbon nanotubes. The method for producing a three-walled carbon nanotube according to any one of claims 1 to 8, wherein the carbon-containing compound is propanol. The 3-layer carbon nanotubes in 100 pieces of three-layer carbon nanotubes arbitrarily selected with a transmission electron microscope, or 80 present from claim 1 an outer diameter in the range of 5.0nm 1.8 9 The method for producing a three-walled carbon nanotube according to any one of the above. The method for producing a three-walled carbon nanotube according to any one of claims 1 to 10 , wherein a hydrogen concentration in a gas supplied to a reaction field for synthesizing the three-walled carbon nanotube is 100 ppm or less. The method for producing a three-walled carbon nanotube according to any one of claims 2 to 11 , wherein the carrier is formed on a substrate. The method for producing a three-walled carbon nanotube according to claim 12 , wherein the three-walled carbon nanotube is oriented and grown substantially vertically from the substrate. In the reaction tube in which the carbon-containing compound and the metal catalyst are in contact, the carbon-containing compound is modified with a metal catalyst installed on the upstream side of the reaction tube, and the three-walled carbon nanotube is formed with the metal catalyst installed on the downstream side of the reaction tube The method for producing a three-walled carbon nanotube according to any one of claims 1 to 13 , wherein The method for producing a three-walled carbon nanotube according to any one of claims 1 to 14 , wherein the number of metal catalysts having a particle diameter of the metal catalyst of 2.3 to 4.5 nm is 80% or more. A three-walled carbon nanotube-containing composition that satisfies the following requirements (1) to (4).
(1) Of 100 carbon nanotubes arbitrarily selected with a transmission electron microscope, 50 or more are three-layer carbon nanotubes.
(2) The average distance between the bent portions in the three-walled carbon nanotube arbitrarily selected by the transmission electron microscope is 100 nm or more.
(3) By resonance Raman scattering measurement, the maximum peak intensity in the range of 1560~1600cm ^-1 G, when the maximum peak intensity is D within the 1310～1350Cm ^-1, the ratio of G / D 10 or more.
(4) The metal content by elemental analysis is 1% by weight or less. An electron emission material comprising the three-walled carbon nanotube-containing composition according to claim 16 . A transparent conductive film comprising the three-walled carbon nanotube-containing composition according to claim 16 , having a light transmittance of 85% or more and a surface resistance of 1000Ω / □ or less.

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