JP2006111458A - Method for producing double wall carbon nanotube and composition containing double wall carbon nanotube - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for producing a double wall carbon nanotube which enables to efficiently synthesize the double wall carbon nanotube with small and uniform diameter, and a composition containing the double wall carbon nanotube obtainable by this method. <P>SOLUTION: The carbon nanotube mainly comprising double wall carbon nanotubes is produced by preparing a material satisfying all of the following three conditions: (1) exhibiting ≥300 m<SP>2</SP>/g specific surface area measured by the nitrogen adsorption method, (2) having at least one peak in a region of 1-10 nm pore diameters, (3) showing a change rate of peak intensity of ≤5 % in X-ray diffraction between before and after firing at 800°C in air, making the material carry a metal catalyst, and bringing the carried catalyst into contact with an alcohol at 600-950°C. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a method for producing a double-walled carbon nanotube and a composition containing a double-walled carbon nanotube. More specifically, the present invention relates to a double-walled carbon nanotube capable of efficiently synthesizing a thin-walled and uniform double-walled carbon nanotube. The present invention relates to a production method and a double-walled carbon nanotube-containing composition obtained from the production method.

  The carbon nanotube has a shape in which one surface of graphite is wound into a cylindrical shape. A single-walled carbon nanotube is wound in one layer, a double-walled carbon nanotube is wound in two layers, and is wound in multiple layers. This was called multi-walled carbon nanotube. Since carbon nanotubes have high mechanical strength and high conductivity, they are used as negative electrodes for fuel cells and lithium secondary batteries, and as high strength resins and conductive resins made of composite materials of resins, metals and organic semiconductors. It is expected as a material for transparent conductive films, metal electrolyte powders, electromagnetic shielding materials and the like.

  Furthermore, since L / D (ratio of length / diameter) is large and the diameter is several nm, 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. In any application, high-purity carbon nanotubes are required, and as carbon nanotubes, single-walled or double-walled carbon nanotubes with a small diameter are advantageous. Are better.

  Conventionally, arc discharge methods, laser evaporation methods, chemical vapor deposition methods, and the like are known as methods for producing carbon nanotubes (see Non-Patent Document 1). Among these, catalytic chemical vapor deposition is known as a method for inexpensively producing high-quality carbon nanotubes with few defects in the graphite layer (see Non-Patent Document 2). Furthermore, according to the catalytic chemical vapor deposition method, it is known that the number of carbon nanotubes can be controlled to a single layer or 2 to 5 layers (see Non-Patent Document 3).

As a preferable method of the catalytic chemical vapor deposition method, a method in which a catalyst is supported alone is known (see Non-Patent Document 4), and an oxide is often used as the carrier. However, it is difficult to control the physical properties of the carbon nanotubes to be uniform, and it has been extremely difficult to efficiently synthesize a double-walled carbon tube having a small diameter and a uniform diameter.
Yahachi Saito, Shunji Bando [Author] “Basics of Carbon Nanotubes”, Corona Inc., p17, 23, 47 Chemical Physics Letters 303 (1999), 117-124 Chemical Physics Letters 360 (2002), 229-234 Tanaka Kazuyoshi [ed.] “Carbon Nanotubes – Challenge to Nanodevices”, Kagaku Dojin, p74-76

An object of the present invention is to provide a method for producing a double-walled carbon nanotube capable of efficiently synthesizing a double-walled carbon nanotube having a small diameter and a uniform diameter, and a resulting composition containing the double-walled carbon nanotube. .

  Another object of the present invention is to provide a method for producing a double-walled carbon nanotube that makes it possible to efficiently synthesize double-walled carbon nanotubes that are less likely to contain a bent structure in individual double-walled carbon nanotubes and that have excellent linearity, and the same It is in providing the composition containing a double-walled carbon nanotube obtained.

  Still another object of the present invention is to provide a method for producing a double-walled carbon nanotube that makes it possible to efficiently synthesize a high-purity double-walled carbon nanotube-containing composition containing carbon nanotubes, and the resulting double-walled carbon nanotube-containing composition. It is to provide a composition.

The method for producing a double-walled carbon nanotube according to the present invention that solves the above-described object comprises supporting a metal catalyst on a carrier using a material that satisfies all the following requirements (1) to (3) as a carrier, The carbon nanotube which has a double-walled carbon nanotube as a main component by making it contact with is manufactured.
(1) Show 300 m < ² > / g or more by the specific surface area measurement by a nitrogen adsorption method.
(2) It has at least one or more peaks in a region having a pore diameter of 1 to 10 nm in pore distribution measurement by a nitrogen adsorption method.
(3) The rate of change of peak intensity in X-ray diffraction before and after baking at 800 ° C. in air is 5% or less.

Moreover, the double-walled carbon nanotube-containing composition of the present invention is characterized by satisfying all the following requirements (1) to (4).
(1) Of 100 carbon nanotubes arbitrarily selected with a transmission electron microscope, 80 or more are double-walled carbon nanotubes.
(2) The average distance between the bent portions in the double-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.

According to the present invention, the carrier carrying the metal catalyst as described above has at least one peak in the region of 2 to 10 nm with a specific surface area of 300 m ² / g or more, and X-rays before and after baking at 800 ° C. in air. A material having a rate of change in peak intensity of 5% or less in diffraction and contacting with alcohol at 600 to 950 ° C. to efficiently synthesize uniform double-walled carbon nanotubes with high carbon purity and small diameter. Can do. In addition, according to the present invention, it is possible to obtain a double-walled carbon nanotube that is unlikely to include a bent structure in each double-walled carbon nanotube and has excellent linearity.

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 the liquid nitrogen temperature. Using a technique known as the BET method, nitrogen is gradually introduced into a carrier placed under reduced pressure, an adsorption isotherm of nitrogen at 0 to atmospheric pressure is taken, and when the atmospheric pressure is reached, nitrogen is gradually reduced. The desorption isotherm may be taken. If the specific surface area determined by this method is 300 m ² / g or more, it means that the carrier is porous, which means that the catalyst particles are easily supported on the outer surface.

  In order to obtain the pore size distribution of a mesoporous portion including a region having a pore size of 1 to 10 nm, it is usually calculated using a desorption isotherm. As a theoretical formula for obtaining the pore size distribution, a Dollimore-Heal method (hereinafter abbreviated as DH method) is known. The pore size distribution defined in the present invention is determined by the DH method from the nitrogen desorption isotherm.

  Generally, the pore size distribution is obtained by taking the pore diameter on the horizontal axis and ΔVp / ΔRp on the vertical axis, and the pore volume in the present invention can be obtained from the area of this graph. Here, Rp represents the radius of the pore, and Vp represents the volume when the adsorbed nitrogen is liquefied. ΔVp / ΔRp is preferably 1000 or more. By having at least one peak in the region of 1 to 10 nm in pore distribution measurement, it means that the carrier has mesopores, and it means that it is easy to carry metal particles having a size close to the mesopore diameter. .

  The carrier used in the present invention has a peak intensity change rate of 5% or less in X-ray diffraction before and after baking at 800 ° C. in air. When powder X-ray diffraction (XRD) is performed at room temperature before and after, any two peaks of the carrier are taken out, and the rate of change in the peak intensity ratio is 5% or less. Note that the peak intensity ratio may vary depending on the preparation of the measurement sample.

  The presence or absence of substantial structural change is also judged by whether or not an exothermic peak appears 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. be able to. That is, it can be judged that the structure having no exothermic peak in the range of 600 to 800 ° C. has substantially no structural change up to 800 ° C.

  When the DTA curve once rises up and down after 600 ° C. and the peak is before 800 ° C., an exothermic peak appears. If it is not possible to judge whether it is a peak or not, connect the point where the curve starts to climb and the point where it falls completely to the base line, select the longest point where the vertical line from the baseline intersects the curve, and the length is A case where the length is five times or more the height of noise is called a peak. Also, the temperature at the intersection is read and used as the peak of the exothermic curve.

  In the present invention, the carrier is not particularly limited, but silica, alumina, magnesia, titania, and zeolite are preferably used, and each oxide may form a mesoporous material having mesopores.

  Here, the mesoporous material is a material having pores having a diameter of about 2 to 50 nm. Synthesized by concerted self-organization of surfactant and inorganic material. 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, Bauercher, Zeolites, 17 (1/2), 1996) (Atlas of Zeolite Structure types (WM Meier, DH Olson, Ch.
Baerlocher, Zeolites, 17 (1/2), 1996)), which is a crystalline inorganic porous material. Moreover, the zeolite in this invention is not limited to what is published in this literature, The zeolite which has the novel structure synthesized one after another is included. Preferred 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.

The zeolite may be subjected to acid or alkali treatment to form mesoporous pores.
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 an oxide is impregnated in an aqueous solution of 0.01 to 1.00 M acid, thoroughly stirred and dispersed at 0 to 100 ° C., washed with water, and dried at 50 to 200 ° C. As a result, mesoporous pores can be formed.

  Alkali treatment is a method of forming mesoporous pores by bringing alkali into contact with an oxide, and examples thereof include some treatment with alkali. 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 an 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. As a result, mesoporous pores can be formed.

In the present invention, the support material preferably contains at least one selected from titanium, boron and zirconium in an atomic ratio of 0.01 or more with silicon. 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 resulting double-walled carbon nanotube Easy to control. The atomic ratio of at least one selected from boron and zirconium to silicon is preferably 0.01 or more. When this ratio is 0.01 or less, the influence on the catalyst activity of the carrier is small. On the other hand, when the ratio is 0.1 or more, the effect of suppressing the catalytic activity is exerted, and the synthesis amount of the double-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.

  Next, a method for supporting a metal on the carrier will be described.

  Although the kind of metal is not specifically limited, A group 3-12 metal, Most preferably, a group 5-11 metal is used. 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 preferably have a particle size of 0.5 to 10 nm. If the metal is fine particles, thin carbon nanotubes are likely to be generated.

  Although only one type of metal may be supported or two or more types of metal may be supported, it is preferable to support two or more types of metal. When two kinds of metals are supported, it is particularly preferable to contain Fe, Co, Ni, Mo, and Mn.

  The method for supporting the metal on the carrier is not particularly limited. For example, an oxide 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 mixture thereof The metal can be supported on the oxide by heating at a high temperature (300 to 600 ° C.) in gas or vacuum (impregnation method).

  The larger the amount of metal supported, the higher the yield of carbon nanotubes. However, if the amount is too large, the particle diameter of the metal becomes large and the carbon nanotubes produced become thick. If 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.

  Alcohol is brought into contact with the metal-supported oxide thus obtained at 600 to 950 ° C. to produce a double-walled carbon nanotube. The temperature which makes a catalyst and alcohol contact is 600-950 degreeC, Preferably the range of 700 to 900 degreeC is good. When the temperature is lower than 600 ° C., the yield of carbon nanotubes is deteriorated, and when the temperature is higher than 950 ° C., there are restrictions on the material of the reactor to be used, and the bonding between the carbon nanotubes starts. It becomes difficult to control the shape.

  For example, methanol or ethanol, propanol, or butanol is preferably used as the alcohol. Of these, ethanol is the most preferred alcohol.

  The pressure in the step of bringing the alcohol into contact with the catalyst is preferably 1000 Pa or less, and the partial pressure of the alcohol is preferably 1 Pa or more and 100 Pa or less. If the pressure in the step of bringing the catalyst into contact with alcohol is higher than 1000 Pa, the yield of the double-walled carbon nanotubes is remarkably lowered, which is not preferable. Moreover, when the partial pressure of alcohol is lower than 1 Pa, the yield of double-walled carbon nanotubes is remarkably reduced, and when the partial pressure is higher than 100 Pa, the production of multi-walled carbon nanotubes is promoted, which is not preferable.

There is no particular limitation on the method of contacting the catalyst and the carbon-containing compound. For example, this can be achieved by placing the above-described catalyst in a heat-resistant reaction tube made of quartz, alumina, or the like installed in a tubular furnace and flowing alcohol gas under reduced pressure and heating. In addition to the above method, the catalyst and alcohol may be contacted by a method of spraying the catalyst or a method of bringing the catalyst into contact with stirring.

  The carbon nanotube-containing composition obtained by the production method of the present invention is characterized by satisfying the following requirements.

  That is, 80 or more of 100 carbon nanotubes arbitrarily selected by a transmission electron microscope are double-walled carbon nanotubes. The measurement method is, for example, observation with a transmission electron microscope at a magnification of 1 million, carbon nanotubes of 10% or more of the visual field area in a 150 nm square visual field, and 100 arbitrarily extracted from a plurality of visual fields. Eighty or more of the carbon nanotubes are double-walled carbon nanotubes, and the above measurement is evaluated with an average value obtained at 10 locations.

  Further, in the present invention, out of 100 double-walled carbon nanotubes arbitrarily selected by a transmission electron microscope, 80 or more have an outer diameter in the range of 1.5 to 4.0 nm. The measurement method is, for example, observing with a transmission electron microscope at a million magnification, measuring the outer diameter of 100 double-walled carbon nanotubes arbitrarily extracted from a plurality of fields of view, and 80 or more having the outer diameter. It is in the range of 1.5 to 4.0 nm, and the above-mentioned measurement is evaluated with an average value obtained at 10 locations.

  In the present invention, the hydrogen concentration in the gas supplied to the reaction field for synthesizing the double-walled carbon nanotube is 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 hydrogenation effect is not preferred because only the sintering effect takes precedence.

Further, the present invention is characterized in that a mesoporous material carrying a catalyst is formed on a substrate. Here, the type of the substrate is not particularly limited, but the surface on which the mesoporous material is applied is preferably 1 mm ² or more, and more preferably 1 cm ² or more. Examples of the material 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 double-walled carbon nanotube substrate can be obtained by synthesizing double-walled carbon nanotubes on the film-formed mesoporous material.

  In the present invention, the double-walled carbon nanotubes are substantially oriented and grown in the vertical direction from the substrate. The fact that the substrate is substantially aligned and grown in the vertical direction means that, for example, the angle formed by the straight line connecting the upper and lower ends of the double-walled carbon nanotubes arbitrarily selected from the electron micrograph of the substrate cross section and the substrate surface Is averaged over 10 or more and the result is 90 ° ± 10 °. By orientation growth, it exhibits good electron emission characteristics for field emission displays and solar cells.

The carbon nanotube composition obtained by the present invention is a double-walled carbon nanotube-containing composition that satisfies all the following requirements (1) to (4).
(1) Of 100 carbon nanotubes arbitrarily selected with a transmission electron microscope, 80 or more are double-walled carbon nanotubes.
(2) The average distance between the bent portions in the double-walled carbon nanotube arbitrarily selected by the transmission electron microscope is 100 nm or more.
(3) According to resonance Raman scattering measurement, when the maximum peak intensity in the range of 1560 to 1600 cm −1 is G and the maximum peak intensity in the range of 1310 to 1350 cm −1 is D, the ratio of G / D is 10 or more.
(4) The metal content by elemental analysis is 1% by weight or less.

  Here, the bent portion in the double-walled carbon nanotube refers to a bent due to the presence of a carbon 5-membered ring and a 7-membered ring in the graphite structure of the carbon nanotube, and is shown in the high-resolution transmission electron micrograph of FIG. As mentioned above, the carbon nanotube is a portion observed in a bent state in the length direction.

  In the double-walled carbon nanotube-containing composition of the present invention, the average of the distance from the bent portion to the bent portion is determined for any two-walled carbon nanotube selected by a high-resolution transmission electron microscope, and this is calculated as 10 or more double-walled carbon nanotubes. The average result for the nanotubes is 100 nm or more. As the distance from the bent portion to the bent portion is longer, the linearity of the double-walled carbon nanotube is improved, and a double-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.

Moreover, the double-walled carbon nanotube-containing composition according to the present invention can be evaluated by Raman spectroscopy. In the Raman spectrum, the Raman shift seen in the vicinity of 1590 cm ⁻¹ is called a G band derived from graphite, and the Raman shift seen in the vicinity of 1350 cm ⁻¹ is called a D band derived from defects in amorphous carbon or graphite. The higher the G / D ratio, the higher the degree of graphitization, which means a higher quality carbon nanotube. The double-walled carbon nanotube in the present invention has a G / D ratio of 10 or more. More preferably, it is 15 or more, and most preferably 20 or more.

  Moreover, the double-walled carbon nanotube-containing composition according to the present invention refers to a composition whose metal content by elemental analysis is 1% by weight or less. When the metal content is high, there is a concern that it may become a foreign substance or adversely affect the human body in the use added to the polymer and the medical and pharmaceutical use. In the method for synthesizing the double-walled carbon nanotubes according to the present invention, since the catalytic metal exists at the interface between the support and the double-walled carbon nanotube, as described later, the double-walled carbon nanotube is easily cut by cutting the double-walled carbon nanotube at the interface. Carbon 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, but it is preferable to use it 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. Also, zeolite can be removed with an aqueous sodium hydroxide solution. Furthermore, zeolite, cobalt and carbon nanotubes can be separated and recovered individually by a separation method using two liquids of an organic solvent and water. Moreover, when it is desired to remove the amount of the catalyst metal to a high degree, it is preferable to perform the treatment with an acid after performing the firing treatment. 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 double-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.

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
(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, the mixture was transferred to an autoclave and hydrothermally synthesized at 150 ° C. for 48 hours or 96 hours. After hydrothermal synthesis, the product was collected by filtration, washed, calcined at 550 ° C. for 8 hours, and calcined at 800 ° C. for 1 hour. Hereinafter, the 48-hour synthesized product is abbreviated as MCM-41 (48), and the 96-hour synthesized product is abbreviated as MCM-41 (96).

  Next, 3.64 g of cetyltrimethylammonium bromide (CTAB: manufactured by Aldrich) and 1.45 g of tetramethylammonium hydroxide (TMAOH: manufactured by Aldrich) were added to 28.8 ml of ion-exchanged water at 35 ° C., and then MCM-41. (48) 2.4 g 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 140 hours. After hydrothermal synthesis, the product was collected by filtration, washed, calcined at 550 ° C. for 8 hours, and calcined at 800 ° C. for 1 hour. Hereinafter, this sample is abbreviated as 2MCM-41 (140), and the three samples combined with the MCM-41 (48) and MCM-41 (96) are collectively referred to as MCM-41.

(Measurement of pore size distribution of MCM-41)
Using the synthesized MCM-41, the nitrogen adsorption amount is measured at a liquid nitrogen temperature (77K) with a nitrogen adsorption amount measuring apparatus (BELSOAP36 manufactured by Nippon Bell), and the pore size distribution is obtained by the DH method from the data of the desorption curve. It was. The result is shown in FIG.

In FIG. 2, Rp represents the radius of the pore, and Vp represents the volume when adsorbed nitrogen is liquefied. The peak position of the pore distribution was 3.48 nm for MCM-41 (48), 3.48 nm for MCM-41 (96), and 4.19 nm for 2MCM-41 (140). The specific surface area was MCM-41 (48) in ^{829m 2 / g, MCM-41} (96) in ^{833m 2 / g, 2MCM-41} (140) in 903m ² / g.

(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 a double-walled carbon nanotube)
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 was evacuated, and after confirming that the pressure became 10 Pa or less, ethanol vapor was introduced for 20 minutes so that the pressure became 100 Pa. After the introduction of ethanol vapor was stopped, high-purity acetylene gas (manufactured by High Pressure Gas Industry) was supplied at 5 cc / min for 30 minutes, the temperature was cooled to room temperature, and a composition containing double-walled carbon nanotubes was taken out. As a result of X-ray diffraction of the carrier, the rate of change in peak intensity was less than 5%.

(High-resolution transmission electron microscope analysis of a composition containing double-walled carbon nanotubes)
When the composition containing carbon nanotubes obtained as described above was observed with a high-resolution transmission electron microscope, as shown in FIGS. 3, 4, and 5, the carbon nanotubes were composed of a clean graphite layer. The number of carbon nanotubes with two layers was 80% or more. Carbon impurities other than carbon nanotubes (fullerene, nanoparticles, amorphous carbon, etc.) were hardly observed.

(Resonance Raman spectroscopic analysis of a composition containing double-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 Gioban Yvon), and the G / D ratio was determined. As a result, the MCM-41 (48) was 15, MCM-41 (96) was 12, and 2 MCM-41 (140) was 13, indicating high-quality double-walled carbon nanotubes.

Example 2
(Synthesis of mesoporous materials by Sol-Gel method)
Tetraethyl orthosilicate (TEOS: manufactured by Aldrich), special grade ethanol (manufactured by Wako Pure Chemical Industries, Ltd.), hydrochloric acid (manufactured by Wako Pure Chemical Industries, Ltd.), and ion-exchanged water in a molar ratio of 1: 3: 5 × 10 ⁻⁵ : 1. In addition, after refluxing for 1 hour, a hydrochloric acid solution of CTAB was added to obtain a composition having the following molar ratio.
TEOS: EtOH: HCl: H ₂ O: CTAB = 1: 20: 4 × 10 ⁻³ : 5: 0.1
The composition was stirred for 48 hours and then allowed to dry at room temperature for 3 days. After pulverization, calcination was performed at 550 ° C. for 8 hours, and then calcination was performed at 800 ° C. for 1 hour to obtain a mesoporous material (hereinafter abbreviated as SG).

(Measurement of pore size distribution of SG)
Using the synthesized SG, the nitrogen adsorption amount was measured at a liquid nitrogen temperature (77K) with a nitrogen adsorption amount measuring apparatus (BELSOAP36 manufactured by Nippon Bell Co., Ltd.), and the pore size distribution was determined by the DH method from the data of the desorption curve. The result is shown in FIG.

In FIG. 2, Rp represents the radius of the pore, and Vp represents the volume when adsorbed nitrogen is liquefied. The peak position of the pore distribution was 2.52 nm. The specific surface area was 899 m ² / g.

(Support of metal salt on SG)
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 SG 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 SG powder.

(Synthesis of a composition containing a double-walled carbon nanotube)
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 was evacuated, and after confirming that the pressure became 10 Pa or less, ethanol vapor was introduced for 20 minutes so that the pressure became 100 Pa. After stopping the introduction of ethanol vapor, high-purity acetylene gas (manufactured by High Pressure Gas Industry) was supplied at 5 cc / min for 30 minutes, the temperature was cooled to room temperature, and a composition containing double-walled carbon nanotubes was taken out. As a result of X-ray diffraction of the carrier, the rate of change in peak intensity was less than 5%.

(High-resolution transmission electron microscope analysis of a composition containing double-walled carbon nanotubes)
When the composition containing carbon nanotubes obtained as described above was observed with a high-resolution transmission electron microscope, as shown in FIG. 6, the carbon nanotubes were composed of clean graphite layers, and the number of layers was two. Of the carbon nanotubes were 80% or more. Carbon impurities other than carbon nanotubes (fullerene, nanoparticles, amorphous carbon, etc.) were hardly observed.

(Resonance Raman spectroscopic analysis of a composition containing double-walled carbon nanotubes)
The composition containing carbon nanotubes obtained as described above was measured with a resonance Raman spectrometer (INF-300 manufactured by Horiba Joban Yvon), and the G / D ratio was determined. As a result, 11 and high-quality double-walled carbon nanotubes I found out.

Example 3
(Measurement of pore size distribution of borosilicate)
The nitrogen adsorption amount is measured at a liquid nitrogen temperature (77K) with a nitrogen adsorption amount measuring apparatus (BELSOAP36 manufactured by Nippon Bell Co., Ltd.) using a borosilicate manufactured by NM Chemcat, and the pore size distribution is obtained by the DH method from the data of the desorption curve. It was. As a result, the peak position of the pore distribution was 2.50 nm. The specific surface area was 328m ² / g.

(Support of metal salt on borosilicate)
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 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. Then, it heated at 400 degreeC in the air for 1 hour, and obtained the solid catalyst by which metal salt was carry | supported by SG powder.

(Synthesis of a composition containing a double-walled carbon nanotube)
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 was evacuated, and after confirming that the pressure became 10 Pa or less, ethanol vapor was introduced for 20 minutes so that the pressure became 100 Pa. After the introduction of ethanol vapor was stopped, high-purity acetylene gas (manufactured by High Pressure Gas Industry) was supplied at 5 cc / min for 30 minutes, the temperature was cooled to room temperature, and a composition containing double-walled carbon nanotubes was taken out. As a result of X-ray diffraction of the carrier, the rate of change in peak intensity was less than 5%.

(High-resolution transmission electron microscope analysis of a composition containing double-walled carbon nanotubes)
When the composition containing the carbon nanotubes obtained as described above was observed with a high-resolution transmission electron microscope, as shown in FIG. 7, the carbon nanotubes were composed of clean graphite layers, and the number of layers was two. Of the carbon nanotubes were 80% or more. Carbon impurities other than carbon nanotubes (fullerene, nanoparticles, amorphous carbon, etc.) were hardly observed.

(Resonance Raman spectroscopic analysis of a composition containing double-walled carbon nanotubes)
The composition containing carbon nanotubes obtained as described above was measured with a resonance Raman spectrometer (INF-300 manufactured by Horiba Joban Yvon), and the G / D ratio was determined. As a result, 14 and high-quality double-walled carbon nanotubes were obtained. I found out.

Example 4
(Creation of field electron emission source)
50 mg of the carbon nanotube obtained in Example 1 and 100 ml of acetone were placed in a 100 ml beaker, and ultrasonic waves were irradiated for 30 minutes. Separately, this dispersion was placed in a beaker containing a copper plate, and allowed to stand to spontaneously evaporate acetone to obtain a copper plate having carbon nanotubes deposited on the surface.
(Evaluation of field electron emission ability)
The obtained copper plate was used as a cathode so as to face the anode electrode, and this bipolar structure was introduced into an evaluation chamber to evaluate the field electron emission ability. As a result, the carbon nanotubes obtained in this example showed good field electron emission ability.

Comparative Example 1
The same operation as that after the loading of the metal salt in Example 1 was carried out using silicalite having no pores in the mesopore region by BET measurement (untreated silicalite, manufactured by NV Chemcat), but carbon nanotubes were obtained. There wasn't.

It is a high resolution transmission electron microscope photograph illustrating a bent portion in a carbon nanotube. FIG. 3 is a pore diameter distribution curve diagram of mesoporous pores obtained by analyzing the mesoporous material and borosilicate used for the carrier material in the present invention by the DH method. It is a high-resolution transmission electron microscope photograph figure of the carbon nanotube containing composition synthesize | combined using MCM-41 (48) in this invention. It is a high-resolution transmission electron microscope photograph figure of the carbon nanotube containing composition synthesize | combined using MCM-41 (96) in this invention. It is a high-resolution transmission electron microscope photograph figure of the carbon nanotube containing composition synthesize | combined using 2MCM-41 (140) in this invention. 1 is a high-resolution transmission electron micrograph of a carbon nanotube-containing composition synthesized using a sol-gel method mesoporous material in the present invention. 1 is a high-resolution transmission electron micrograph of a carbon nanotube-containing composition synthesized using borosilicate in the present invention.

Explanation of symbols

Rp Pore radius Vp Volume when adsorbed nitrogen is liquefied

Claims (15)

A carbon nanotube mainly composed of a double-walled carbon nanotube is obtained by supporting a metal catalyst on the support using a material satisfying all of the following requirements (1) to (3) and contacting the support with alcohol at 600 to 950 ° C. A method for producing a double-walled carbon nanotube, which is characterized in that it is produced.
(1) Show 300 m < ² > / g or more by the specific surface area measurement by a nitrogen adsorption method.
(2) It has at least one or more peaks in a region having a pore diameter of 1 to 10 nm in pore distribution measurement by a nitrogen adsorption method.
(3) The rate of change of peak intensity in X-ray diffraction before and after baking at 800 ° C. in air is 5% or less.   In the measurement of pore distribution by the nitrogen adsorption method of the carrier, when the radius of the pore is represented by Rp and the volume when the adsorbed nitrogen is liquefied is represented by Vp, the peak height in the region where the pore diameter is 1 to 10 nm is high. The method for producing a double-walled carbon nanotube according to claim 1, wherein the thickness (ΔVp / ΔRp) is 1000 or more.   The method for producing a double-walled carbon nanotube according to claim 1 or 2, wherein the carrier material is a mesoporous material mainly composed of silicon.   The method for producing a double-walled carbon nanotube according to claim 3, wherein the carrier material is a mesoporous material having an MCM-41 structure.   The method for producing a double-walled carbon nanotube according to claim 1 or 2, wherein the carrier material is zeolite.   The method for producing a double-walled carbon nanotube according to any one of claims 1 to 5, wherein the carrier material contains at least one selected from titanium, boron, and zirconium in an atomic ratio of 0.01 or more with respect to silicon.   The method for producing a double-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.   The method for producing a double-walled carbon nanotube according to any one of claims 1 to 7, wherein the pressure in the step of bringing the metal catalyst into contact with the alcohol is 1000 Pa or less, and the partial pressure of the alcohol is 1 Pa or more and 100 Pa or less.   The method for producing a double-walled carbon nanotube according to any one of claims 1 to 8, wherein 80 or more of the 100 carbon nanotubes arbitrarily selected from the produced carbon nanotubes with a transmission electron microscope are double-walled carbon nanotubes.   Any one of 100 double-walled carbon nanotubes arbitrarily selected from the produced carbon nanotubes with a transmission electron microscope has 80 or more in the range of 1.5 to 4.0 nm in outer diameter. A method for producing a double-walled carbon nanotube as described in 1.   The method for producing a double-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 double-walled carbon nanotube is 100 ppm or less.   The method for producing a double-walled carbon nanotube according to any one of claims 1 to 11, wherein a mesoporous material having an MCM-41 structure is formed on a substrate.   The method for producing a double-walled carbon nanotube according to claim 12, wherein the double-walled carbon nanotube is substantially oriented and grown vertically from the substrate. A double-walled carbon nanotube-containing composition that satisfies all the following requirements (1) to (4).
(1) Of 100 carbon nanotubes arbitrarily selected with a transmission electron microscope, 80 or more are double-walled carbon nanotubes.
(2) The average distance between the bent portions in the double-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 double-walled carbon nanotube-containing composition according to claim 14.

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