JP4426244B2 - Carbon nanotube production method and purification method - Google Patents
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本発明は炭素化合物を多孔性担体に金属触媒を担持させた基体上に接触させ熱分解し粗カーボンナノチューブを得て、ついで前記基体を除去することを特徴とするカーボンナノチューブの製造方法に関する。 The present invention relates to a method for producing carbon nanotubes, characterized in that a carbon compound is brought into contact with a substrate on which a metal catalyst is supported on a porous carrier, pyrolyzed to obtain crude carbon nanotubes, and then the substrate is removed.
また本発明はカーボンナノチューブに含有される不純物を取り除くためのカーボンナノチューブの精製方法に関する。特に本発明は、金属触媒を担持させた多孔性担体を含むカーボンナノチューブの精製方法に関する。 The present invention also relates to a carbon nanotube purification method for removing impurities contained in the carbon nanotube. In particular, the present invention relates to a method for purifying a carbon nanotube including a porous support on which a metal catalyst is supported.
カーボンナノチューブは炭素６員環からなるグラファイトシートが円筒状を形成した物質であり、優れた機械特性を利用した複合材料、半導体素子、導電材料、水素吸蔵材料などとしての実用化に向けた研究が進められている。カーボンナノチューブの製造方法として、初期には黒鉛電極のアーク放電を用いるアーク放電法や黒鉛にレーザーパルス光を照射するレーザー蒸発法が適用されたが、収量が少ないことやアモルファスカーボン等の不純物が多いなど、ナノチューブの工業的製造技術としては課題を有している。また、近年注目される手法として、炭素化合物を高温下で触媒金属微粒子に接触させて熱分解する化学気相成長法（以下、ＣＶＤ法とする）がある。ＣＶＤ法には、触媒金属を気相中に浮遊させる方法（特許文献１参照）や、シリカ粉末やアルミナ粉末などの多孔性担体に触媒金属を担持する方法（特許文献２参照）が知られている。特に多孔性担体を用いたＣＶＤ法は、担体の種類や温度条件を変えて単層や多層のカーボンナノチューブを作り分けることが可能であり、原料を気体として供給するため大量合成に適した方法として期待されている。 Carbon nanotubes are substances in which graphite sheets consisting of carbon 6-membered rings form a cylindrical shape, and research aimed at practical application as composite materials, semiconductor elements, conductive materials, hydrogen storage materials, etc. using excellent mechanical properties. It is being advanced. As the carbon nanotube production method, the arc discharge method using the arc discharge of the graphite electrode and the laser evaporation method of irradiating the graphite with laser pulse light were initially applied, but the yield was low and there were many impurities such as amorphous carbon. Thus, there are problems as an industrial manufacturing technique of nanotubes. Further, as a technique attracting attention in recent years, there is a chemical vapor deposition method (hereinafter referred to as a CVD method) in which a carbon compound is thermally decomposed by contacting with catalytic metal fine particles at a high temperature. Known CVD methods include a method in which a catalytic metal is suspended in a gas phase (see Patent Document 1) and a method in which a catalytic metal is supported on a porous carrier such as silica powder or alumina powder (see Patent Document 2). Yes. In particular, the CVD method using a porous carrier can change the type and temperature conditions of the carrier to produce single-walled or multi-walled carbon nanotubes, and is a suitable method for mass synthesis because the raw material is supplied as a gas. Expected.
篠原らは、多孔性珪酸塩の一種であるゼオライトに触媒金属としてＦｅ／Ｖを担持した粉末に、７００℃で窒素／アセチレン混合気体を接触させることによって多層のカーボンナノチューブを得たことを報告している（非特許文献１参照）。さらに、触媒金属にＦｅ／Ｃｏを用い、原料にアルゴン／アセチレン混合気体を用いて、６００−９００℃の温度条件下で単層のカーボンナノチューブが得られている（特許文献２参照）。 Shinohara et al. Reported that multi-walled carbon nanotubes were obtained by contacting a nitrogen / acetylene mixed gas at 700 ° C. with a powder in which Fe / V was supported as a catalyst metal on zeolite, a kind of porous silicate. (See Non-Patent Document 1). Furthermore, single-walled carbon nanotubes are obtained under a temperature condition of 600 to 900 ° C. using Fe / Co as the catalyst metal and an argon / acetylene mixed gas as the raw material (see Patent Document 2).
丸山らは、ゼオライトに触媒金属としてＦｅ／Ｃｏを担持した粉末に、７００−８００℃でアルゴン／エタノール混合気体を接触させることによって単層のカーボンナノチューブを得られることを報告している（非特許文献２参照）。 Maruyama et al. Reported that single-walled carbon nanotubes can be obtained by contacting an argon / ethanol mixed gas at 700-800 ° C. with a powder in which Fe / Co is supported on zeolite as a catalyst metal (non-patent document). Reference 2).
しかしながら、ゼオライトなどの無機多孔性担体を用いてＣＶＤ法で製造したカーボンナノチューブには、製造プロセスから必然的に触媒金属とともに多量の無機担体が不純物として混入している。 However, carbon nanotubes produced by the CVD method using an inorganic porous carrier such as zeolite are inevitably mixed with a large amount of inorganic carrier as an impurity together with the catalyst metal from the production process.
そのため、ＣＶＤ法で得られたカーボンナノチューブを工業的に利用するためには、これらの触媒金属および多孔性担体を除去して純度を上げることが必要である。 Therefore, in order to industrially use the carbon nanotubes obtained by the CVD method, it is necessary to remove these catalytic metals and the porous carrier to increase the purity.
ここで、触媒金属については、カーボンナノチューブを塩酸、硫酸、硝酸などの酸性溶液に浸漬する方法や、これらの酸性溶液で還流する方法によって除去可能であることが知られている。 Here, it is known that the catalyst metal can be removed by a method in which carbon nanotubes are immersed in an acidic solution such as hydrochloric acid, sulfuric acid, or nitric acid, or a method in which the carbon nanotube is refluxed with these acidic solutions.
また、ゼオライトなどの多孔性担体を除去する方法としては、フッ酸浸漬処理や２０００℃程度の熱処理によって除去できることが知られている（非特許文献３、特許文献２参照）。しかしながら、フッ酸のような反応性の高い酸で処理することや高温熱処理することによりカーボンナノチューブの分解や劣化がおこることが懸念される。 As a method for removing a porous carrier such as zeolite, it is known that it can be removed by hydrofluoric acid immersion treatment or heat treatment at about 2000 ° C. (see Non-Patent Document 3 and Patent Document 2). However, there is a concern that the carbon nanotubes may be decomposed or deteriorated by treatment with a highly reactive acid such as hydrofluoric acid or high temperature heat treatment.
本発明の課題はゼオライトなどの多孔性担体を効率良く除去し、高純度かつ高品質のカーボンナノチューブを得るためのカーボンナノチューブの製造方法を提供することを目的とする。 An object of the present invention is to provide a carbon nanotube production method for efficiently removing a porous carrier such as zeolite and obtaining high-purity and high-quality carbon nanotubes.
本発明者らは、上記目的を達成するため、多孔性担体に金属触媒を担持した基体に炭素化合物気体を接触させて熱分解するＣＶＤ法で製造したカーボンナノチューブを、特定の酸性溶液に浸漬処理して前記基体を除去することを特徴とするカーボンナノチューブの製造方法および精製方法を提供しうることを見出した。 In order to achieve the above object, the present inventors have immersed carbon nanotubes produced by a CVD method in which a carbon compound gas is brought into contact with a substrate carrying a metal catalyst on a porous carrier and thermally decomposed into a specific acidic solution. The present inventors have found that a method for producing and purifying carbon nanotubes characterized by removing the substrate can be provided.
本発明は、
１．炭素化合物を多孔性担体に金属触媒を担持させた基体上に接触させ熱分解し粗カーボンナノチューブを得て、ついでテトラフルオロホウ酸を含む酸性溶液に該粗カーボンナノチューブを浸漬処理することにより前記基体を除去することを特徴とするカーボンナノチューブの製造方法である。
The present invention
1. A carbon compound is brought into contact with a substrate on which a metal catalyst is supported on a porous carrier and thermally decomposed to obtain crude carbon nanotubes, and then the crude carbon nanotubes are immersed in an acidic solution containing tetrafluoroboric acid to thereby treat the substrate. This is a method for producing a carbon nanotube, characterized by removing water.
２．前記テトラフルオロホウ酸を含む酸性溶液がさらに塩酸を含み、テトラフルオロホウ酸と塩酸の混合比がテトラフルオロホウ酸１重量部に対して塩酸が０．1〜５０重量部であることを特徴とする上記に記載のカーボンナノチューブの製造方法である。 2. The acidic solution containing tetrafluoroboric acid further contains hydrochloric acid, and the mixing ratio of tetrafluoroboric acid and hydrochloric acid is 0.1 to 50 parts by weight with respect to 1 part by weight of tetrafluoroboric acid. This is a method for producing a carbon nanotube as described above.
３．テトラフルオロホウ酸を含む酸性溶液に浸漬する処理に加えて、塩酸を含む酸性溶液への浸漬処理を逐次併用して前記基体を除去することを特徴とする上記に記載のカーボンナノチューブの製造方法である。 3. In addition to the treatment of immersing in an acidic solution containing tetrafluoroboric acid, the substrate is removed by sequentially using an immersing treatment in an acidic solution containing hydrochloric acid. is there.
４．カーボンナノチューブを酸性溶液に浸漬処理する際に、マイクロウェーブを照射しながら加熱および加圧処理をおこなうことを特徴とする上記に記載のカーボンナノチューブの製造方法である。 4). The carbon nanotube production method according to the above, wherein when the carbon nanotube is immersed in an acidic solution, heating and pressure treatment are performed while irradiating microwaves.
５．金属触媒を担持させた多孔性担体を含む粗カーボンナノチューブを、テトラフルオロホウ酸を含む酸性溶液に浸漬処理して前記基体を除去することを特徴とするカーボンナノチューブの精製方法である。 5. A method for purifying carbon nanotubes, comprising immersing a crude carbon nanotube containing a porous carrier carrying a metal catalyst in an acidic solution containing tetrafluoroboric acid to remove the substrate.
６．浸漬処理後のカーボンナノチューブの純度が５０重量％以上１００重量％以下である上記に記載の製造方法により得られるカーボンナノチューブである。 6). It is a carbon nanotube obtained by the manufacturing method as described above, wherein the purity of the carbon nanotube after the immersion treatment is 50 wt% or more and 100 wt% or less.
７．浸漬処理後の多孔性担体の濃度が１．０重量％〜０重量％である上記に記載の製造方法により得られるカーボンナノチューブである。 7). It is a carbon nanotube obtained by the manufacturing method as described above, wherein the concentration of the porous carrier after the immersion treatment is 1.0% by weight to 0% by weight.
本発明のカーボンナノチューブの製造方法および精製方法により、高純度で欠陥の少ないカーボンナノチューブを得ることができる。 By the carbon nanotube production method and purification method of the present invention, carbon nanotubes with high purity and few defects can be obtained.
本発明のカーボンナノチューブの製造方法および精製方法について以下に説明する。
本発明においてカーボンナノチューブは、多孔性担体に金属触媒を担持した基体に原料炭素源となる炭素化合物気体を接触させて熱分解させるＣＶＤ法によって粗カーボンナノチューブを製造する。図１はＣＶＤ法によってカーボンナノチューブを製造するためのＣＶＤ装置の模式図である。ＣＶＤ装置は、電気炉、石英管、気体導入系、真空排気系、および石英管内で多孔性担体に金属触媒を担持した基体を保持するための石英ボートからなる。さらに図示されていないが、温度制御系、真空制御系、気体流量計などが設置されている。
The carbon nanotube production method and purification method of the present invention will be described below.
In the present invention, carbon nanotubes are produced by a CVD method in which a carbon compound gas serving as a raw material carbon source is brought into contact with a substrate having a metal catalyst supported on a porous carrier and thermally decomposed. FIG. 1 is a schematic view of a CVD apparatus for producing carbon nanotubes by a CVD method. The CVD apparatus includes an electric furnace, a quartz tube, a gas introduction system, a vacuum exhaust system, and a quartz boat for holding a substrate carrying a metal catalyst on a porous carrier in the quartz tube. Although not shown, a temperature control system, a vacuum control system, a gas flow meter, and the like are installed.
この装置を用い、粗カーボンナノチューブは以下の手順で好ましく製造される。予め調製した多孔性担体に金属触媒を担持した基体を石英ボートに載せ、石英管内に設置する。石英管を真空排気した後、気体導入系より不活性気体（アルゴン、窒素など）を導入しながら排気速度を調整して石英管内を一定圧力に保持する。さらに、電気炉をカーボンナノチューブの生成温度まで昇温した後、キャリア気体（例えば、アルゴン、窒素、水素またはそれらの混合気体等）と炭素化合物気体を適当な流量比で流して数分から数時間保持することで粗カーボンナノチューブを製造することができる。 Using this apparatus, the crude carbon nanotube is preferably produced by the following procedure. A substrate in which a metal catalyst is supported on a porous carrier prepared in advance is placed on a quartz boat and placed in a quartz tube. After evacuating the quartz tube, the inside of the quartz tube is maintained at a constant pressure by adjusting the exhaust speed while introducing an inert gas (argon, nitrogen, etc.) from the gas introduction system. Furthermore, after raising the temperature of the electric furnace to the carbon nanotube production temperature, a carrier gas (for example, argon, nitrogen, hydrogen, or a mixed gas thereof) and a carbon compound gas are allowed to flow at an appropriate flow ratio and held for several minutes to several hours. By doing so, crude carbon nanotubes can be produced.
なお、上記の製造方法で多孔性担体、金属触媒および生成温度条件を選ぶことにより、単層または多層のカーボンナノチューブを選択的に製造できる。 In addition, single-walled or multi-walled carbon nanotubes can be selectively produced by selecting a porous carrier, a metal catalyst, and a production temperature condition in the above production method.
上記の多孔性担体としては、無機酸化物構造体が用いられる。多孔性担体の公知の具体例はゼオライト、シリカ、アルミナ、マグネシア、ジルコニア、チタニア、およびそれらの組み合わせなどである。 An inorganic oxide structure is used as the porous carrier. Known specific examples of the porous carrier include zeolite, silica, alumina, magnesia, zirconia, titania, and combinations thereof.
また、触媒としては、例えば公知のＦｅ、Ｃｏなどの酢酸塩等の金属化合物が用いられるが、これに限定されるものではない。触媒の例としては、Ｆｅ、Ｃｏの他にＮｉ、Ｍｏ、Ｃｒ、Ｍｏ、Ｙ、Ｒｕ、Ｒｈ、Ｐｄ、Ｉｒ、Ｐｔなどの金属および化合物からなる群から選ばれる少なくとも一種が挙げられる。 Moreover, as a catalyst, although metal compounds, such as well-known acetates, such as Fe and Co, are used, for example, it is not limited to this. Examples of the catalyst include at least one selected from the group consisting of metals and compounds such as Ni, Mo, Cr, Mo, Y, Ru, Rh, Pd, Ir, and Pt in addition to Fe and Co.
触媒は、例えばエタノールなどの有機溶媒に多孔性担体と一緒に投入攪拌した後に乾燥させ、触媒微粒子の形で多孔性担体の表面／内部に担持したものを用いる。 As the catalyst, for example, a catalyst that is charged and stirred together with a porous carrier in an organic solvent such as ethanol and dried and supported on the surface / inside of the porous carrier in the form of catalyst fine particles is used.
カーボンナノチューブの原料炭素源となる炭素化合物は、公知のエタノール、メタノール、イソプロパノール、ブタノールなどのアルコール類やフェノール、アセトン、ベンゼンなどが挙げられ、これらを気化して用いる。また、メタン、エチレン、アセチレン、一酸化炭素などの気体を使用することができる。 Examples of the carbon compound serving as a carbon source material for carbon nanotubes include known alcohols such as ethanol, methanol, isopropanol, and butanol, phenol, acetone, benzene, and the like, which are used after being vaporized. Moreover, gases, such as methane, ethylene, acetylene, carbon monoxide, can be used.
以上説明した、多孔性担体に金属触媒を担持した基体に原料炭素源となる炭素化合物気体を接触させて熱分解するＣＶＤ法を用いて得られた粗カーボンナノチューブは、ゼオライトなどの多孔性担体と金属触媒が不純物として含まれているため、これらの不純物を除去して精製する必要がある。 As described above, the crude carbon nanotubes obtained by the CVD method in which the carbon compound gas serving as the raw material carbon source is brought into contact with the substrate on which the metal catalyst is supported on the porous carrier are thermally decomposed. Since the metal catalyst is contained as impurities, it is necessary to remove these impurities for purification.
次に、本発明における多孔性担体に金属触媒を担持した基体に炭素化合物気体を接触させて熱分解するＣＶＤ法で得られた粗カーボンナノチューブを精製する方法について説明する。 Next, a method for purifying crude carbon nanotubes obtained by a CVD method in which a carbon compound gas is brought into contact with a substrate carrying a metal catalyst on a porous carrier in the present invention and thermally decomposed will be described.
上記の方法で得られた粗カーボンナノチューブを、少なくともテトラフルオロホウ酸を含む酸性溶液に例えば数時間ないし数十時間浸漬処理してゼオライトなどの多孔性担体およびＦｅ、Ｃｏなどの金属触媒からなる基体を除去する。このとき使用する酸性溶液のテトラフルオロホウ酸の濃度は１％以上とすることが好ましく、さらに好ましい濃度は、５％以上、５０％以下である。テトラフルオロホウ酸の濃度が５％未満であると、カーボンナノチューブ中に含まれるゼオライトなどの多孔性担体およびＦｅ、Ｃｏなどの金属触媒を十分に溶解することができず、純度の高いカーボンナノチューブが得られない。また、テトラフルオロホウ酸の濃度が５０％を超えると、精製されたカーボンナノチューブの劣化や分解が生じてしまうことがある。 A substrate comprising a porous support such as zeolite and a metal catalyst such as Fe and Co by immersing the crude carbon nanotube obtained by the above method in an acidic solution containing at least tetrafluoroboric acid for several hours to several tens of hours, for example. Remove. The concentration of tetrafluoroboric acid in the acidic solution used at this time is preferably 1% or more, and more preferably 5% or more and 50% or less. When the concentration of tetrafluoroboric acid is less than 5%, a porous carrier such as zeolite and a metal catalyst such as Fe and Co contained in the carbon nanotube cannot be sufficiently dissolved, and a high purity carbon nanotube is obtained. I can't get it. Further, when the concentration of tetrafluoroboric acid exceeds 50%, the purified carbon nanotubes may be deteriorated or decomposed.
粗カーボンナノチューブの精製に用いる酸性溶液は、テトラフルオロホウ酸と塩酸の混合物を用いることも有効である。塩酸を加えることにより、Ｆｅ、Ｃｏなどの金属触媒をより確実にカーボンナノチューブから除去することができる。このときテトラフルオロホウ酸と塩酸の混合比はテトラフルオロホウ酸と塩酸の混合比がテトラフルオロホウ酸１重量部に対して塩酸が０．１〜５０重量部の範囲が好適である。テトラフルオロホウ酸に対すると塩酸の重量部が０．１未満では塩酸添加の効果が十分得られず、塩酸の重量部が５０より大きいとテトラフルオロホウ酸が希釈されるためゼオライトなど多孔性担体の除去が不十分となる。 It is also effective to use a mixture of tetrafluoroboric acid and hydrochloric acid as the acidic solution used for the purification of the crude carbon nanotubes. By adding hydrochloric acid, metal catalysts such as Fe and Co can be more reliably removed from the carbon nanotubes. At this time, the mixing ratio of tetrafluoroboric acid and hydrochloric acid is preferably such that the mixing ratio of tetrafluoroboric acid and hydrochloric acid is 0.1 to 50 parts by weight of hydrochloric acid with respect to 1 part by weight of tetrafluoroboric acid. When the weight part of hydrochloric acid is less than 0.1 with respect to tetrafluoroboric acid, the effect of adding hydrochloric acid is not sufficiently obtained, and when the weight part of hydrochloric acid is more than 50, tetrafluoroboric acid is diluted. Removal is insufficient.
少なくともテトラフルオロホウ酸を含む酸性溶液としては、上記の塩酸のほかに、硫酸、硝酸、酢酸などの酸性溶液を混合して用いることができる。 As an acidic solution containing at least tetrafluoroboric acid, an acidic solution such as sulfuric acid, nitric acid, and acetic acid can be mixed and used in addition to the above hydrochloric acid.
酸性溶液による粗カーボンナノチューブの精製方法として、少なくともテトラフルオロホウ酸を含む酸性溶液に浸漬する処理と、少なくとも塩酸を含む酸性溶液との浸漬処理とを逐次併用して前記基体を除去することも有効である。少なくともテトラフルオロホウ酸を含む酸性溶液で粗カーボンナノチューブを浸漬処理することにより、主としてゼオライトなどの多孔性担体を除去することができる。また、少なくとも塩酸を含む酸性溶液で粗カーボンナノチューブを浸漬処理することにより、主としてＦｅ、Ｃｏなどの金属触媒を除去することができる。 As a method of purifying crude carbon nanotubes with an acidic solution, it is also effective to remove the substrate by sequentially using a treatment of immersing in an acidic solution containing at least tetrafluoroboric acid and an immersing treatment with an acidic solution containing at least hydrochloric acid. It is. By immersing the crude carbon nanotube with an acidic solution containing at least tetrafluoroboric acid, a porous carrier such as zeolite can be mainly removed. Further, by immersing the crude carbon nanotubes with an acidic solution containing at least hydrochloric acid, it is possible to mainly remove metal catalysts such as Fe and Co.
粗カーボンナノチューブを上記の酸性溶液に浸漬処理する場合に、室温下で処理をおこなっても多孔性担体および金属触媒の除去効果が得られるが、反応を促進するために溶液の沸騰がおきない温度範囲で加温してもよい。好ましい温度範囲としては４０〜９５℃である。 When the crude carbon nanotubes are immersed in the above acidic solution, the effect of removing the porous support and the metal catalyst can be obtained even if the treatment is performed at room temperature, but the solution does not boil to accelerate the reaction. You may heat in the range. A preferred temperature range is 40 to 95 ° C.
あるいは、粗カーボンナノチューブを上記の酸性溶液に浸漬処理する場合に、密閉容器中でマイクロ波を照射しながら加熱および加圧処理を加えることも有効である。これにより、ゼオライトなどの多孔性担体および金属触媒の分解を促進して短時間で処理を完了することができる。好ましい加圧条件の範囲としては１〜１０ＭＰａである。 Alternatively, when the crude carbon nanotube is immersed in the above acidic solution, it is also effective to add heat and pressure treatment while irradiating microwaves in a sealed container. Thereby, decomposition | disassembly of porous supports, such as a zeolite, and a metal catalyst can be accelerated | stimulated, and a process can be completed in a short time. A preferable pressure condition range is 1 to 10 MPa.
以上説明した精製方法で得られたカーボンナノチューブの純度は、５０重量％以上、より好ましくは９５重量％以上１００重量％以下であり、実質的に多孔質担体を含まない高純度のカーボンナノチューブが得られる。 The purity of the carbon nanotube obtained by the purification method described above is 50% by weight or more, more preferably 95% by weight or more and 100% by weight or less, and a high-purity carbon nanotube substantially free of a porous carrier is obtained. It is done.
得られたカーボンナノチューブに含まれるゼオライトなどの多孔性担体の濃度は、１．０〜０重量％であり、極めて純度の高いカーボンナノチューブが得られる。
以上説明したカーボンナノチューブの精製方法は、高純度で欠陥の少ないカーボンナノチューブを得るための極めて有用な製造方法である。
The concentration of the porous carrier such as zeolite contained in the obtained carbon nanotubes is 1.0 to 0% by weight, and carbon nanotubes with extremely high purity can be obtained.
The carbon nanotube purification method described above is an extremely useful production method for obtaining carbon nanotubes with high purity and few defects.
以下、実施例により本発明方法をさらに詳しく具体的に説明する。ただしこれらの実施例は本発明の範囲を何ら限定するものではない。 Hereinafter, the method of the present invention will be described in more detail with reference to examples. However, these examples do not limit the scope of the present invention.
［実施例１］
多孔性担体にＹ型ゼオライト粉末（東ソー製；ＨＳＺ−３９０ＨＵＡ）を用い、触媒金属化合物に酢酸第二鉄と酢酸コバルトを用いて、Ｆｅ／Ｃｏ触媒をゼオライトに担持した。触媒の担持量はそれぞれ２．５重量％に調製した。その後、石英ボートに多孔性担体／触媒粉末を乗せてＣＶＤ装置の石英管内に設置して真空排気をおこない、Ａｒ流量１０ｍｌ／分で導入しながら室温から８００℃まで昇温した。所定の８００℃に達した後、エタノール蒸気を流量３０００ｍｌ／分で導入し、Ａｒ／エタノール雰囲気下で３０分間保持した。得られた粗カーボンナノチューブをレーザーラマン分光法（レーザー波長：５１４ｎｍ）で測定した結果を図２に示す。ラマンスペクトルから、波数１５９０ｃｍ−１付近のＧバンドと波数１５０〜３００ｃｍ−１のラジアルブリージングモードが検出され、単層のカーボンナノチューブが生成していることが確認された。ついで、得られた粗カーボンナノチューブ（カーボンナノチューブ／ゼオライト／金属触媒）を、濃度１７％のテトラフルオロホウ酸の酸性水溶液に、室温下で２４時間浸漬してゼオライトおよび金属触媒を除去した。精製前後のカーボンナノチューブについて、熱重量分析法（空気雰囲気、室温〜８００℃、１０度／分昇温）による減量率測定と、電子線マイクロアナライザーによる元素分析を実施しカーボンナノチューブの純度を比較した結果を表１に示す。なお、熱重量分析法での減量率は、試料の炭素重量率に相当することからカーボンナノチューブの純度と等価である。
[Example 1]
An Fe / Co catalyst was supported on zeolite using Y-type zeolite powder (manufactured by Tosoh; HSZ-390HUA) as the porous carrier, ferric acetate and cobalt acetate as the catalytic metal compound. The catalyst loading was adjusted to 2.5% by weight, respectively. Thereafter, the porous carrier / catalyst powder was placed on a quartz boat, placed in a quartz tube of a CVD apparatus, evacuated, and heated from room temperature to 800 ° C. while being introduced at an Ar flow rate of 10 ml / min. After reaching a predetermined 800 ° C., ethanol vapor was introduced at a flow rate of 3000 ml / min, and maintained for 30 minutes in an Ar / ethanol atmosphere. FIG. 2 shows the result of measuring the obtained crude carbon nanotube by laser Raman spectroscopy (laser wavelength: 514 nm). Raman spectra are detected radial breathing mode of wave number 1590 cm -1 vicinity of the G band and the wave number 150～300Cm -1, it was confirmed that single-walled carbon nanotubes are produced. Subsequently, the obtained crude carbon nanotube (carbon nanotube / zeolite / metal catalyst) was immersed in an acidic aqueous solution of tetrafluoroboric acid having a concentration of 17% at room temperature for 24 hours to remove the zeolite and the metal catalyst. The carbon nanotubes before and after purification were subjected to thermogravimetric analysis (air atmosphere, room temperature to 800 ° C., 10 ° C./minute temperature increase), weight loss measurement, and elemental analysis using an electron microanalyzer to compare the purity of carbon nanotube The results are shown in Table 1. Note that the weight loss rate in the thermogravimetric analysis method is equivalent to the carbon weight rate of the sample and is therefore equivalent to the purity of the carbon nanotube.
表１の結果から、精製前のカーボンナノチューブの熱重量分析法における減量率は４重量％、元素分析では大量のゼオライト（Ｓｉ）および金属触媒（Ｆｅ、Ｃｏ）が検出されカーボンナノチューブの純度は低いものであった。精製後のカーボンナノチューブの減量率は７７重量％で、ゼオライト構成元素のＳｉは検出されず少量の金属触媒（Ｆｅ、Ｃｏ）が残留していた。これより、酸性溶液の浸漬処理により純度７７重量％のカーボンナノチューブが得られることが確認された。 From the results in Table 1, the weight loss rate in the thermogravimetric analysis method of carbon nanotubes before purification is 4% by weight. In elemental analysis, a large amount of zeolite (Si) and metal catalysts (Fe, Co) are detected, and the purity of carbon nanotubes is low. It was a thing. The weight loss rate of the carbon nanotubes after purification was 77% by weight, and the zeolite constituent element Si was not detected, and a small amount of metal catalyst (Fe, Co) remained. From this, it was confirmed that carbon nanotubes having a purity of 77% by weight were obtained by the immersion treatment of the acidic solution.
さらに、精製後のカーボンナノチューブを誘導結合プラズマ発光分光法による定量分析を行なった結果、Ｓｉ含有量は０．０５重量％でＳｉＯ２換算したゼオライトの濃度は０．１１重量％であった。 Further, as a result of quantitative analysis of the purified carbon nanotubes by inductively coupled plasma emission spectroscopy, the Si content was 0.05% by weight and the zeolite concentration in terms of SiO 2 was 0.11% by weight.
［実施例２］
実施例１と同様条件のＣＶＤ法で得られた粗カーボンナノチューブを、テトラフルオロホウ酸１重量部に対して塩酸が３．０重量部からなる酸性水溶液に、室温下で２４時間浸漬してゼオライトおよび金属触媒を除去した。精製後のカーボンナノチューブの熱重量分析法の減量率から求めた純度は７５重量％で、元素分析ではゼオライト（Ｓｉ）は検出されずに金属触媒（Ｆｅ、Ｃｏ）のみが検出された。
[Example 2]
A crude carbon nanotube obtained by a CVD method under the same conditions as in Example 1 was immersed in an acidic aqueous solution consisting of 3.0 parts by weight of hydrochloric acid with respect to 1 part by weight of tetrafluoroboric acid at room temperature for 24 hours. And the metal catalyst was removed. The purity obtained from the weight loss rate of the purified carbon nanotubes by thermogravimetric analysis was 75% by weight. In elemental analysis, zeolite (Si) was not detected, but only metal catalysts (Fe, Co) were detected.
［実施例３］
実施例１と同様条件のＣＶＤ法で得られた粗カーボンナノチューブを、実施例１と同組成のテトラフルオロホウ酸からなる酸性水溶液に浸漬し、さらに密閉容器中でマイクロ波（出力：４００Ｗ）を照射し、温度８０℃，圧力１０ＭＰａで２０分間処理してゼオライトおよび金属触媒を除去してカーボンナノチューブを精製した。
得られたカーボンナノチューブの減量率から求めた純度は５９重量％で、元素分析ではゼオライト（Ｓｉ）は検出されずに金属触媒（Ｆｅ、Ｃｏ）のみが検出された。
[Example 3]
The crude carbon nanotubes obtained by the CVD method under the same conditions as in Example 1 were immersed in an acidic aqueous solution made of tetrafluoroboric acid having the same composition as in Example 1, and microwaves (output: 400 W) were applied in a sealed container. Irradiation was performed at a temperature of 80 ° C. and a pressure of 10 MPa for 20 minutes to remove the zeolite and the metal catalyst, thereby purifying the carbon nanotube.
The purity obtained from the weight loss rate of the obtained carbon nanotubes was 59% by weight, and zeolite (Si) was not detected by elemental analysis, but only metal catalysts (Fe, Co) were detected.
［実施例４］
多孔性担体にＹ型ゼオライト粉末（東ソー製；ＨＳＺ−３２０ＮＡＡ）を用い、触媒金属化合物に酢酸第二鉄と酢酸コバルトを用いて、Ｆｅ／Ｃｏ触媒をゼオライトに担持した。触媒の担持量はそれぞれ２．５重量％に調製した。その後、石英ボートに触媒粉末を乗せてＣＶＤ装置の石英管内に設置して真空排気をおこない、Ａｒ流量１０ｍｌ／分で導入しながら室温から６００℃まで昇温した。所定の６００℃に達した後、エタノール蒸気を流量３０００ｍｌ／分で導入し、Ａｒ／エタノール雰囲気下で３０分間保持した。得られた黒色の生成物をレーザーラマン分光法および透過型電子顕微鏡で分析した結果、多層カーボンナノチューブが生成していることが確認された。ついで、得られた粗カーボンナノチューブ（多層カーボンナノチューブ／ゼオライト／金属触媒）を、実施例３と同様条件で処理し、ゼオライトおよび金属触媒を除去してカーボンナノチューブを精製した。精製前後の純度分析結果を表２に示す。
[Example 4]
An Fe / Co catalyst was supported on zeolite using Y-type zeolite powder (manufactured by Tosoh; HSZ-320NAA) as a porous carrier, ferric acetate and cobalt acetate as catalyst metal compounds. The catalyst loading was adjusted to 2.5% by weight, respectively. Thereafter, the catalyst powder was placed on a quartz boat, placed in a quartz tube of a CVD apparatus, evacuated, and heated from room temperature to 600 ° C. while being introduced at an Ar flow rate of 10 ml / min. After reaching the predetermined 600 ° C., ethanol vapor was introduced at a flow rate of 3000 ml / min, and maintained for 30 minutes in an Ar / ethanol atmosphere. As a result of analyzing the obtained black product by laser Raman spectroscopy and a transmission electron microscope, it was confirmed that multi-walled carbon nanotubes were produced. Next, the obtained crude carbon nanotube (multi-walled carbon nanotube / zeolite / metal catalyst) was treated under the same conditions as in Example 3 to remove the zeolite and the metal catalyst, thereby purifying the carbon nanotube. Table 2 shows the results of purity analysis before and after purification.
精製後のカーボンナノチューブは純度９５重量％で、少量の金属触媒（Ｆｅ、Ｃｏ）が残留していた。 The purified carbon nanotubes had a purity of 95% by weight and a small amount of metal catalyst (Fe, Co) remained.
１．原料気体
２．金属触媒／多孔性担体
３．石英管
４．電気炉
1. Raw material gas2. 2. Metal catalyst / porous support Quartz tube 4. Electric furnace
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