JP6709913B2 - Method for producing catalyst carrier for producing carbon nanotube, and method for producing carbon nanotube - Google Patents
Method for producing catalyst carrier for producing carbon nanotube, and method for producing carbon nanotube Download PDFInfo
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- 239000003054 catalyst Substances 0.000 title claims description 170
- 239000002041 carbon nanotube Substances 0.000 title claims description 59
- 238000004519 manufacturing process Methods 0.000 title claims description 18
- OKTJSMMVPCPJKN-UHFFFAOYSA-N Carbon Chemical compound [C] OKTJSMMVPCPJKN-UHFFFAOYSA-N 0.000 title claims description 14
- 229910021393 carbon nanotube Inorganic materials 0.000 title claims description 9
- 239000000395 magnesium oxide Substances 0.000 claims description 53
- CPLXHLVBOLITMK-UHFFFAOYSA-N magnesium oxide Inorganic materials [Mg]=O CPLXHLVBOLITMK-UHFFFAOYSA-N 0.000 claims description 53
- AXZKOIWUVFPNLO-UHFFFAOYSA-N magnesium;oxygen(2-) Chemical compound [O-2].[Mg+2] AXZKOIWUVFPNLO-UHFFFAOYSA-N 0.000 claims description 53
- 239000000463 material Substances 0.000 claims description 47
- 229910052751 metal Inorganic materials 0.000 claims description 39
- 239000002184 metal Substances 0.000 claims description 39
- 238000000034 method Methods 0.000 claims description 32
- 238000000137 annealing Methods 0.000 claims description 29
- 239000013078 crystal Substances 0.000 claims description 14
- 239000010409 thin film Substances 0.000 claims description 14
- 238000002441 X-ray diffraction Methods 0.000 claims description 12
- 239000000843 powder Substances 0.000 claims description 12
- 230000015572 biosynthetic process Effects 0.000 claims description 11
- 230000003647 oxidation Effects 0.000 claims description 11
- 238000007254 oxidation reaction Methods 0.000 claims description 11
- 239000000758 substrate Substances 0.000 claims description 11
- 229910052742 iron Inorganic materials 0.000 claims description 9
- 229910052760 oxygen Inorganic materials 0.000 claims description 9
- QVGXLLKOCUKJST-UHFFFAOYSA-N atomic oxygen Chemical compound [O] QVGXLLKOCUKJST-UHFFFAOYSA-N 0.000 claims description 8
- 239000001301 oxygen Substances 0.000 claims description 8
- 229910052759 nickel Inorganic materials 0.000 claims description 6
- 238000001228 spectrum Methods 0.000 claims description 5
- 238000004544 sputter deposition Methods 0.000 claims description 4
- 238000000576 coating method Methods 0.000 claims description 2
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- 239000010410 layer Substances 0.000 description 23
- XEEYBQQBJWHFJM-UHFFFAOYSA-N iron Substances [Fe] XEEYBQQBJWHFJM-UHFFFAOYSA-N 0.000 description 22
- 239000007864 aqueous solution Substances 0.000 description 21
- 239000007789 gas Substances 0.000 description 15
- 239000002245 particle Substances 0.000 description 14
- 238000010438 heat treatment Methods 0.000 description 13
- XKRFYHLGVUSROY-UHFFFAOYSA-N Argon Chemical compound [Ar] XKRFYHLGVUSROY-UHFFFAOYSA-N 0.000 description 12
- NLXLAEXVIDQMFP-UHFFFAOYSA-N Ammonia chloride Chemical compound [NH4+].[Cl-] NLXLAEXVIDQMFP-UHFFFAOYSA-N 0.000 description 8
- XUIMIQQOPSSXEZ-UHFFFAOYSA-N Silicon Chemical compound [Si] XUIMIQQOPSSXEZ-UHFFFAOYSA-N 0.000 description 8
- 238000004833 X-ray photoelectron spectroscopy Methods 0.000 description 8
- 230000002378 acidificating effect Effects 0.000 description 8
- 239000010703 silicon Substances 0.000 description 8
- 239000000126 substance Substances 0.000 description 7
- 238000003786 synthesis reaction Methods 0.000 description 7
- UHOVQNZJYSORNB-UHFFFAOYSA-N Benzene Chemical compound C1=CC=CC=C1 UHOVQNZJYSORNB-UHFFFAOYSA-N 0.000 description 6
- 229910052786 argon Inorganic materials 0.000 description 6
- 239000002131 composite material Substances 0.000 description 6
- 238000009792 diffusion process Methods 0.000 description 6
- 239000011261 inert gas Substances 0.000 description 6
- 238000001755 magnetron sputter deposition Methods 0.000 description 6
- 229910052710 silicon Inorganic materials 0.000 description 6
- 238000006243 chemical reaction Methods 0.000 description 5
- 150000002739 metals Chemical class 0.000 description 5
- IJGRMHOSHXDMSA-UHFFFAOYSA-N Atomic nitrogen Chemical compound N#N IJGRMHOSHXDMSA-UHFFFAOYSA-N 0.000 description 4
- LFQSCWFLJHTTHZ-UHFFFAOYSA-N Ethanol Chemical compound CCO LFQSCWFLJHTTHZ-UHFFFAOYSA-N 0.000 description 4
- VEXZGXHMUGYJMC-UHFFFAOYSA-N Hydrochloric acid Chemical compound Cl VEXZGXHMUGYJMC-UHFFFAOYSA-N 0.000 description 4
- HSFWRNGVRCDJHI-UHFFFAOYSA-N alpha-acetylene Natural products C#C HSFWRNGVRCDJHI-UHFFFAOYSA-N 0.000 description 4
- 235000019270 ammonium chloride Nutrition 0.000 description 4
- 238000005229 chemical vapour deposition Methods 0.000 description 4
- 238000009826 distribution Methods 0.000 description 4
- 125000002534 ethynyl group Chemical group [H]C#C* 0.000 description 4
- 229910052732 germanium Inorganic materials 0.000 description 4
- GNPVGFCGXDBREM-UHFFFAOYSA-N germanium atom Chemical compound [Ge] GNPVGFCGXDBREM-UHFFFAOYSA-N 0.000 description 4
- VNWKTOKETHGBQD-UHFFFAOYSA-N methane Chemical compound C VNWKTOKETHGBQD-UHFFFAOYSA-N 0.000 description 4
- 239000000203 mixture Substances 0.000 description 4
- TWNQGVIAIRXVLR-UHFFFAOYSA-N oxo(oxoalumanyloxy)alumane Chemical compound O=[Al]O[Al]=O TWNQGVIAIRXVLR-UHFFFAOYSA-N 0.000 description 4
- 239000002356 single layer Substances 0.000 description 4
- 238000012360 testing method Methods 0.000 description 4
- 238000001016 Ostwald ripening Methods 0.000 description 3
- 230000003213 activating effect Effects 0.000 description 3
- 238000004458 analytical method Methods 0.000 description 3
- 229910052799 carbon Inorganic materials 0.000 description 3
- 230000000052 comparative effect Effects 0.000 description 3
- 239000010408 film Substances 0.000 description 3
- 239000010419 fine particle Substances 0.000 description 3
- 239000001307 helium Substances 0.000 description 3
- 229910052734 helium Inorganic materials 0.000 description 3
- SWQJXJOGLNCZEY-UHFFFAOYSA-N helium atom Chemical compound [He] SWQJXJOGLNCZEY-UHFFFAOYSA-N 0.000 description 3
- 239000011777 magnesium Substances 0.000 description 3
- UGFAIRIUMAVXCW-UHFFFAOYSA-N Carbon monoxide Chemical compound [O+]#[C-] UGFAIRIUMAVXCW-UHFFFAOYSA-N 0.000 description 2
- FYYHWMGAXLPEAU-UHFFFAOYSA-N Magnesium Chemical compound [Mg] FYYHWMGAXLPEAU-UHFFFAOYSA-N 0.000 description 2
- 238000000026 X-ray photoelectron spectrum Methods 0.000 description 2
- 239000003570 air Substances 0.000 description 2
- 150000003863 ammonium salts Chemical class 0.000 description 2
- 230000005540 biological transmission Effects 0.000 description 2
- 229910002091 carbon monoxide Inorganic materials 0.000 description 2
- 230000007547 defect Effects 0.000 description 2
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- 238000007865 diluting Methods 0.000 description 2
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- YBMRDBCBODYGJE-UHFFFAOYSA-N germanium oxide Inorganic materials O=[Ge]=O YBMRDBCBODYGJE-UHFFFAOYSA-N 0.000 description 2
- 229910002804 graphite Inorganic materials 0.000 description 2
- 239000010439 graphite Substances 0.000 description 2
- 239000001257 hydrogen Substances 0.000 description 2
- 229910052739 hydrogen Inorganic materials 0.000 description 2
- 125000004435 hydrogen atom Chemical class [H]* 0.000 description 2
- 229910052749 magnesium Inorganic materials 0.000 description 2
- 230000008018 melting Effects 0.000 description 2
- 238000002844 melting Methods 0.000 description 2
- 238000001000 micrograph Methods 0.000 description 2
- 229910052757 nitrogen Inorganic materials 0.000 description 2
- PVADDRMAFCOOPC-UHFFFAOYSA-N oxogermanium Chemical compound [Ge]=O PVADDRMAFCOOPC-UHFFFAOYSA-N 0.000 description 2
- 239000010453 quartz Substances 0.000 description 2
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- 229910052594 sapphire Inorganic materials 0.000 description 2
- 239000010980 sapphire Substances 0.000 description 2
- 238000000926 separation method Methods 0.000 description 2
- VYPSYNLAJGMNEJ-UHFFFAOYSA-N silicon dioxide Inorganic materials O=[Si]=O VYPSYNLAJGMNEJ-UHFFFAOYSA-N 0.000 description 2
- 229910052814 silicon oxide Inorganic materials 0.000 description 2
- 230000002194 synthesizing effect Effects 0.000 description 2
- 238000002230 thermal chemical vapour deposition Methods 0.000 description 2
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- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 description 2
- 125000004432 carbon atom Chemical group C* 0.000 description 1
- 239000000969 carrier Substances 0.000 description 1
- 230000003197 catalytic effect Effects 0.000 description 1
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- 230000003287 optical effect Effects 0.000 description 1
- 238000012764 semi-quantitative analysis Methods 0.000 description 1
- 239000002109 single walled nanotube Substances 0.000 description 1
- 239000002904 solvent Substances 0.000 description 1
- 238000005477 sputtering target Methods 0.000 description 1
- 238000003860 storage Methods 0.000 description 1
Description
本発明は、極めて大きな長さを有する単層カーボンナノチューブ（以下、ＣＮＴと記す）を高効率かつ高純度で製造するための触媒担持体、成長基材、およびこの基材を用いてＣＮＴを成長させる方法に関する。 INDUSTRIAL APPLICABILITY The present invention grows CNTs using a catalyst carrier, a growth base material, and a growth base material for producing single-walled carbon nanotubes (hereinafter referred to as CNTs) having an extremely large length with high efficiency and high purity. Regarding how to make.
ＣＮＴは、ｓｐ2炭素原子だけで構成される円筒状の主骨格を有する物質であり、優れた機械特性、熱・電気伝導性、分子貯蔵能、金属触媒担持能等を有することから、樹脂やセラミックス、金属との複合材料、電池電極材料等への展開が期待されている。特に長さが１００μｍ、好ましくは１ｍｍを超える長尺なＣＮＴは、会合しやすいために複合材料中で互いにコンタクトを取りやすい。このような特性に起因し、長尺なＣＮＴは混合される材料に対して高い熱・電気伝導性の付与が可能であり、また高い機械強度を有する複合材料を提供することができる。 CNT is a substance having a cylindrical main skeleton composed only of sp 2 carbon atoms, and has excellent mechanical properties, thermal/electrical conductivity, molecular storage ability, metal catalyst supporting ability, etc. It is expected to be applied to ceramics, composite materials with metals, and battery electrode materials. In particular, long CNTs having a length of 100 μm, preferably more than 1 mm, are likely to come into contact with each other in the composite material because they easily associate with each other. Due to such characteristics, the long CNTs can impart high heat/electrical conductivity to the materials to be mixed, and can provide a composite material having high mechanical strength.
高純度のＣＮＴを製造する方法として、化学気相成長（ＣＶＤ）法において、炭素原料ガスとともに触媒賦活物質をＣＮＴ成長基材に担持された触媒に接触させる技術が知られている（非特許文献１から６）。ここで触媒は、ＦｅやＣｏ、Ｎｉ等のＣＮＴの成長に活性を示す金属（以下活性金属と記す）を含む微粒子であり、ＣＮＴ成長基材は触媒が互いに近接して触媒担持体に担持された構造をとる。この製造方法では、触媒担持体に酸化アルミニウムを用いることによって、ＣＮＴが基材の表面に対して垂直方向に成長し、ＣＮＴの垂直配向体を形成することができる。 As a method for producing high-purity CNT, there is known a technique in a chemical vapor deposition (CVD) method in which a catalyst activating substance is brought into contact with a catalyst supported on a CNT growth base material together with a carbon source gas (Non-Patent Document 1). 1 to 6). Here, the catalyst is fine particles containing a metal (hereinafter referred to as an active metal) which is active in the growth of CNTs such as Fe, Co, and Ni, and the CNT growth base material is such that the catalysts are supported on the catalyst carrier in close proximity to each other. Have a different structure. In this manufacturing method, by using aluminum oxide for the catalyst carrier, CNTs grow in the direction perpendicular to the surface of the base material, and a vertically aligned CNT body can be formed.
基材上に成長したＣＮＴを複合材料等へ利用するためには、基材から剥離する必要がある。通常、基材上に成長したＣＮＴの垂直配向体を基材から分離する際には、根元から物理的にはがし取るという方法が採用される。この方法では、基材からＣＮＴをはがし取るための機械が必要になるだけでなく、合成条件によってはＣＮＴと基材とが強く固着されるために、全てのＣＮＴを回収することができないことがある。一方、ＣＮＴの基材からの剥離方法としては他に、ＣＮＴが接する触媒担持体を溶解することによって、ＣＮＴを基材から分離する方法が知られている。（例えば、非特許文献２）。 In order to use the CNT grown on the base material in a composite material or the like, it is necessary to peel it from the base material. Usually, when separating the vertically aligned CNTs grown on the substrate from the substrate, a method of physically peeling from the root is adopted. This method requires not only a machine for peeling off the CNTs from the base material, but also the CNTs and the base material are strongly fixed to each other depending on the synthesis conditions, so that all the CNTs cannot be recovered. is there. On the other hand, as another method of separating the CNT from the base material, a method is known in which the CNT is separated from the base material by dissolving the catalyst carrier in contact with the CNT. (For example, nonpatent literature 2).
本発明の目的は、垂直に配向した長さ１ｍｍ以上の単層ＣＮＴを成長させるための触媒担持体を提供し、さらに垂直方向に１ｍｍ以上成長させたＣＮＴを酸性あるいは塩基性水溶液に浸してＣＮＴを触媒担持体から剥離することができる触媒担持体を提供することである。さらに触媒担持体を備えるＣＮＴ成長基材、さらに触媒担持体を備えるＣＮＴ成長基材を用いて１ｍｍを超える極めて長い垂直方向に配向した単層ＣＮＴを短時間で合成することが可能となるＣＮＴ成長方法を提供することである。 An object of the present invention is to provide a catalyst carrier for growing vertically aligned single-walled CNTs having a length of 1 mm or more, and further immersing the CNTs grown in a vertical direction of 1 mm or more in an acidic or basic aqueous solution. It is to provide a catalyst carrier which can be peeled from the catalyst carrier. Furthermore, using a CNT growth base material provided with a catalyst support, and a CNT growth base material provided with a catalyst support, it is possible to synthesize a single-walled CNT oriented in an extremely long vertical direction exceeding 1 mm in a short time. It is to provide a method.
このような課題を解決するために本発明では、以下の手段を提供することとした。 In order to solve such a problem, the present invention provides the following means.
[１] 酸化マグネシウムを含む触媒担持体であり、前記酸化マグネシウムの平均結晶子径Ｄは１３ｎｍよりも大きく１００ｎｍよりも小さく、ここで前記平均結晶子径Ｄは、前記触媒担持体のＸ線回折パターンに以下の数１を適用することによって算出され、
[２] 前記触媒担持体が基材上に設けられていることを特徴とする[１]に記載の触媒担持体
[３] 前記触媒担持体上に、活性金属を含む触媒を有することを特徴とする、[１]に記載の触媒担持体。
[４] 前記触媒は前記触媒担持体の表面から深さ７ｎｍよりも浅い領域を備え、かつ前記領域は酸化数が０の前記活性金属を含み、前記深さおよび前記活性金属の酸化数は、前記カーボンナノチューブ成長基材を不活性ガスで満たされた７５０℃の加熱炉に導入して５分間保持した後、加熱炉から取り出し室温に冷却し、Ｘ線光電子分光法を用いて前記活性金属の深さ方向の分布と酸化状態を評価することで見積もられる、[３]に記載の触媒担持体。
[５] [１]に記載の触媒担持体上に触媒を備えるＣＮＴ成長基材。
[６] 酸化マグネシウムを備える触媒担持体を形成する工程と、前記触媒担持体を７５０℃以上１６５０℃以下の温度範囲でアニーリングを行う工程と、前記触媒担持体上に触媒を設ける工程と、前記触媒上にカーボンナノチューブを成長させる工程とを備えるカーボンナノチューブの製造方法。
[1] A catalyst carrier containing magnesium oxide, wherein the average crystallite diameter D of the magnesium oxide is larger than 13 nm and smaller than 100 nm, wherein the average crystallite diameter D is the X-ray diffraction of the catalyst carrier. Calculated by applying the following equation 1 to the pattern,
[2] The catalyst carrier according to [1], wherein the catalyst carrier is provided on a base material.
[3] The catalyst carrier according to [1], which has a catalyst containing an active metal on the catalyst carrier.
[4] The catalyst has a region shallower than a depth of 7 nm from the surface of the catalyst carrier, and the region contains the active metal having an oxidation number of 0, and the depth and the oxidation number of the active metal are The carbon nanotube growth base material was introduced into a heating furnace at 750° C. filled with an inert gas, held for 5 minutes, taken out of the heating furnace, cooled to room temperature, and subjected to X-ray photoelectron spectroscopy to measure the active metal content. The catalyst carrier according to [3], which is estimated by evaluating the distribution in the depth direction and the oxidation state.
[5] A CNT growth substrate provided with a catalyst on the catalyst carrier according to [1].
[6] a step of forming a catalyst carrier provided with magnesium oxide, a step of annealing the catalyst carrier in a temperature range of 750° C. to 1650° C., a step of providing a catalyst on the catalyst carrier, And a step of growing carbon nanotubes on a catalyst.
垂直に配向した長さ１ｍｍ以上の単層ＣＮＴを成長させることができ、さらに垂直方向に１ｍｍ以上成長させたＣＮＴを酸性あるいは塩基性水溶液に浸すことにより触媒担持体から剥離することができる。 Vertically oriented single-walled CNTs having a length of 1 mm or more can be grown, and the CNTs grown vertically of 1 mm or more can be peeled from the catalyst carrier by immersing them in an acidic or basic aqueous solution.
以下、本出願で開示される発明の各実施形態について、図面を参照しつつ説明する。但し、本発明は、その要旨を逸脱しない範囲において様々な形態で実施することができ、以下に例示する実施形態の記載内容に限定して解釈されるものではない。 Hereinafter, embodiments of the invention disclosed in the present application will be described with reference to the drawings. However, the present invention can be implemented in various forms without departing from the scope of the invention, and is not construed as being limited to the description of the embodiments illustrated below.
図面は、説明をより明確にするため、実際の態様に比べ、各部の幅、厚さ、形状等について模式的に表される場合があるが、あくまで一例であって、本発明の解釈を限定するものではない。本明細書と各図において、既出の図に関して説明したものと同様の機能を備えた要素には、同一の符号を付して、重複する説明を省略することがある。 In order to make the description clearer, the drawings may schematically show the width, thickness, shape, etc. of each part as compared with the actual mode, but this is merely an example and limits the interpretation of the present invention. Not something to do. In the present specification and the drawings, elements having the same functions as those described in regard to the drawings already shown are designated by the same reference numerals, and duplicate description may be omitted.
以下の実施形態によりもたらされる作用効果とは異なる他の作用効果であっても、本明細書の記載から明らかなもの、または、当業者において容易に予測し得るものについては、当然に本発明によりもたらされるものと理解される。 Even if other operational effects different from the operational effects brought about by the embodiments below are obvious from the description of the present specification or can be easily predicted by those skilled in the art, naturally, according to the present invention. Understood to be brought.
（第１実施形態）
図１（Ａ）は触媒担持体の概略図、さらに、触媒担持体の上に触媒が担持された概略図を示す。図１（Ａ）に示すように触媒担持体１０４の表面には、ＣＮＴを成長させるための触媒１０６が設けられる。触媒１０６はＦｅ、Ｃｏ、Ｎｉなどの金属を一種、あるいは複数種含むことができる。触媒担持体１０４の上に触媒１０６が担持された基材をＣＮＴ成長基材１００とする。触媒担持体１０４には、酸化マグネシウム以外の酸化物が含まれていてもよいが、水溶液に浸漬させたときに成長したＣＮＴを触媒担持体から剥離しやすくする観点から、触媒担持体における酸化マグネシウムの含有率は好ましくは５０ｗｔ％以上、より好ましくは７５ｗｔ％、より好ましくは８５ｗｔ％以上、より好ましくは９０ｗｔ％、より好ましくは９５ｗｔ％以上であることが好ましい。触媒担持体１０４は特定な形状に限定されず、板状や球状であっても良い。
(First embodiment)
FIG. 1A shows a schematic view of a catalyst carrier, and further shows a schematic view of the catalyst carried on the catalyst carrier. As shown in FIG. 1A, a catalyst 106 for growing CNTs is provided on the surface of the catalyst carrier 104. The catalyst 106 can contain one or more metals such as Fe, Co, and Ni. A base material in which the catalyst 106 is supported on the catalyst support 104 is referred to as a CNT growth base material 100. The catalyst carrier 104 may contain an oxide other than magnesium oxide, but from the viewpoint of facilitating separation of CNTs grown when immersed in an aqueous solution from the catalyst carrier, magnesium oxide in the catalyst carrier is used. The content of is preferably 50 wt% or more, more preferably 75 wt%, more preferably 85 wt% or more, more preferably 90 wt%, more preferably 95 wt% or more. The catalyst carrier 104 is not limited to a particular shape and may be plate-like or spherical.
ここで触媒担持体１０４は酸化マネシウムの多結晶体を備える。この多結晶体は、Ｘ線回折パターンに対して以下に示すシェラー式（式１）を適用して算出した平均結晶子径Ｄが１３ｎｍよりも大きく１００ｎｍより小さい、１３ｎｍよりも大きく５０ｎｍより小さい、あるいは２０ｎｍよりも大きく５０ｎｍより小さい結晶子を備える。 Here, the catalyst carrier 104 comprises a polycrystal of manesium oxide. This polycrystalline body has an average crystallite diameter D calculated by applying the following Scherrer formula (Formula 1) to the X-ray diffraction pattern, which is larger than 13 nm and smaller than 100 nm, larger than 13 nm and smaller than 50 nm, Alternatively, it has a crystallite larger than 20 nm and smaller than 50 nm.
ここで、Ｋ、λ、Ｂ、θはそれぞれ、Ｘ線回折スペクトルにおけるシェラー定数、入射光の波長、回折線幅、ブラック角であり、シェラー定数にはＫ＝０．９４が適用される。また、平均結晶子径Ｄとは、Ｘ線回折パターンに現れる酸化マグネシウムの（１１１）面、（２００）面、（２２０）面、（３１１）面、（２２２）面由来の各回折ピークにシェラー式を適用して算出した結晶子径の平均である。 Here, K, λ, B, and θ are the Scherrer constant in the X-ray diffraction spectrum, the wavelength of incident light, the diffraction line width, and the black angle, respectively, and K=0.94 is applied to the Scherrer constant. In addition, the average crystallite diameter D is Scherrer at each diffraction peak derived from the (111) plane, (200) plane, (220) plane, (311) plane, and (222) plane of magnesium oxide that appears in the X-ray diffraction pattern. It is the average of the crystallite diameters calculated by applying the formula.
本実施形態では、酸化マグネシウムを含む触媒担持体１０４の平均結晶子径Ｄは１３ｎｍよりも大きく１００ｎｍより小さい範囲を備える。これにより、下記に述べる複合酸化物を含む層１１４の形成の抑制が可能となり、かつ、下記に述べるオストワルド熟成の抑制が可能となる。 In this embodiment, the average crystallite diameter D of the catalyst carrier 104 containing magnesium oxide is in the range of more than 13 nm and less than 100 nm. This makes it possible to suppress the formation of the layer 114 containing a complex oxide described below and also suppress the Ostwald ripening described below.
平均結晶子径Ｄが１３ｎｍより小さい場合、触媒担持体１０４における結晶粒界が多いために、結晶粒界を経由した活性金属の触媒担持体１０４内部への拡散が起こりやすい。その結果、図２（Ａ）に示すように、触媒１０６の粒子を構成する活性金属が触媒担持体１０４を構成する酸化マグネシウムと反応し、マグネシウムとの複合酸化物を含む層１１４が形成される。例えば触媒１０６中の活性金属がＦｅの場合には、以下の式（２）、（３）で示す反応が生じ、Ｆｅが＋２価で存在するＦｅxＭｇ1-xＯやＦｅが＋３価で存在するＭｇＦｅ2Ｏ4といった複合酸化物を含む層１１４を形成するため、短時間で触媒活性が失われる。その結果、ＣＮＴが成長しにくい。 When the average crystallite diameter D is smaller than 13 nm, there are many crystal grain boundaries in the catalyst carrier 104, so that the active metal easily diffuses into the catalyst carrier 104 via the crystal grain boundaries. As a result, as shown in FIG. 2A, the active metal forming the particles of the catalyst 106 reacts with the magnesium oxide forming the catalyst carrier 104 to form a layer 114 containing a complex oxide with magnesium. .. For example, when the active metal in the catalyst 106 is Fe, the reactions shown by the following formulas (2) and (3) occur, and Fe x Mg 1-x O and Fe in which the divalent Fe exists are +3 valent. Since the layer 114 containing the existing complex oxide such as MgFe 2 O 4 is formed, the catalytic activity is lost in a short time. As a result, it is difficult for CNTs to grow.
層１１４ができていることを確かめるためには、“活性金属の拡散試験”と名付ける以下に定義した試験が有効である。 To confirm that layer 114 is formed, the test defined below, entitled "Active Metal Diffusion Test", is useful.
“活性金属の拡散試験”は以下の方法で行われる。触媒１０６が担持された触媒担持体１０４（すなわちＣＮＴ成長基材１００）をヘリウム、アルゴン等の不活性ガスで満たされた７５０℃の加熱炉に導入して５分間保持した後、加熱炉から取り出し室温に冷却する。この試料における活性金属の深さ方向の分布と酸化状態をＸ線光電子分光法（ＸＰＳ）による深さ方向分析で評価する。 The "active metal diffusion test" is performed by the following method. The catalyst carrier 104 carrying the catalyst 106 (that is, the CNT growth base material 100) was introduced into a heating furnace at 750° C. filled with an inert gas such as helium or argon, held for 5 minutes, and then taken out from the heating furnace. Cool to room temperature. The distribution of the active metal in the depth direction and the oxidation state in this sample are evaluated by the depth direction analysis by X-ray photoelectron spectroscopy (XPS).
平均結晶子径Ｄが１３ｎｍよりも大きく１００ｎｍよりも小さい場合、触媒担持体１０４における結晶粒界が少ないために、結晶粒界を経由した活性金属の触媒担持体１０４内部への拡散が起こりにくい。そのため、図３で示すように、活性金属が触媒担持体１０４内部へ拡散する領域１１６の最深部が触媒担持体１０４の表面（上面）から７ｎｍに存在し、７ｎｍより深い領域には存在しない、あるいはＸＰＳで活性金属由来のピークが検出されない。さらに、この領域１１６には０価の状態の活性金属が含まれる。すなわち、ＣＮＴ成長に活性な０価の活性金属が触媒担持体１０４表面近傍に存在するために、ＣＮＴが成長しやすい。 When the average crystallite diameter D is larger than 13 nm and smaller than 100 nm, the number of crystal grain boundaries in the catalyst carrier 104 is small, so that the active metal does not easily diffuse into the catalyst carrier 104 via the crystal grain boundaries. Therefore, as shown in FIG. 3, the deepest part of the region 116 in which the active metal diffuses into the catalyst carrier 104 exists 7 nm from the surface (upper surface) of the catalyst carrier 104, and does not exist in a region deeper than 7 nm. Alternatively, the peak derived from the active metal is not detected by XPS. Further, this region 116 contains active metal in a zero-valent state. That is, since a zero-valent active metal active for CNT growth exists near the surface of the catalyst carrier 104, CNTs are likely to grow.
平均結晶子径Ｄが１３ｎｍ以下の場合、触媒担持体１０４における結晶粒界が多いために、結晶粒界を経由した活性金属の触媒担持体１０４内部への拡散が起こりやすい。図３で示す活性金属が触媒担持体１０４内部へ拡散する領域１１６は触媒担持体１０４の表面（上面）から７ｎｍよりも深く存在し、かつ活性金属は＋２価あるいは＋３価の酸化数で存在し、０価の酸化数は存在しない。あるいはＸＰＳで０価の活性金属由来のピークが検出されない。 When the average crystallite diameter D is 13 nm or less, since there are many crystal grain boundaries in the catalyst carrier 104, the active metal easily diffuses into the catalyst carrier 104 via the crystal grain boundaries. The region 116 where the active metal shown in FIG. 3 diffuses into the catalyst carrier 104 exists deeper than 7 nm from the surface (upper surface) of the catalyst carrier 104, and the active metal exists with an oxidation number of +2 or +3. There is no zero-valent oxidation number. Alternatively, a peak derived from a 0-valent active metal is not detected by XPS.
平均結晶子径Ｄが１００ｎｍを超える場合、結晶子表面で活性金属の拡散が起こりやすく、その結果、図２（Ｂ）に示すように、小さい粒子がより小さく、大きい粒子がより大きくなるオストワルド熟成と呼ばれる微粒子サイズの変化が誘発されるために、単層ＣＮＴが成長しにくい。例えば、エーシーエスナノ、２０１０年、第４巻、ｐ．８９５−９０４には、平滑な酸化アルミニウムの単結晶を触媒担持体に用いた場合、蒸着膜を用いた場合と較べてオストワルド熟成が極めて容易に起こり、ＣＮＴの垂直配向体がほとんど成長しないことが報告されている。また、平均結晶子径Ｄが１００ｎｍを超える酸化マグネシウムの単結晶を触媒担持体に用いた場合、長さが２ｍｍを超える長尺ＣＮＴが合成されたと報告されているが、得られるＣＮＴは多層である（非特許文献３）。単層ＣＮＴも合成可能であるが、その長さは６０μｍにとどまっている（非特許文献４）。 When the average crystallite diameter D exceeds 100 nm, diffusion of the active metal is likely to occur on the crystallite surface, and as a result, as shown in FIG. 2B, small particles are smaller and large particles are larger. It is difficult for single-walled CNTs to grow due to the change in the size of fine particles called ". For example, AC S-Nano, 2010, Volume 4, p. In 895-904, when a smooth aluminum oxide single crystal is used as a catalyst carrier, Ostwald ripening occurs extremely easily as compared with the case where a vapor deposition film is used, and a vertical aligned body of CNT hardly grows. It has been reported. It is also reported that when a single crystal of magnesium oxide having an average crystallite diameter D of more than 100 nm is used as a catalyst carrier, a long CNT having a length of more than 2 mm is synthesized, but the obtained CNT is a multilayer. (Non-patent document 3). Single-walled CNTs can also be synthesized, but their length is limited to 60 μm (Non-Patent Document 4).
本実施形態では、酸化マグネシウムを含む触媒担持体１０４の平均結晶子径Ｄを１３ｎｍよりも大きく１００ｎｍより小さい範囲で制御する。これにより、複合酸化物を含む層１１４の形成の抑制が可能となり、かつ、オストワルド熟成の抑制が可能となる。このように触媒担持体１０４の構造を制御することにより、後述するＣＮＴの成長工程において、触媒１０６の数密度とサイズを長時間維持することができる。そのためＣＮＴの成長が長時間持続され、図１（Ｃ）に示すように、長さＬが１ｍｍを超える長尺な単層ＣＮＴ１１２を成長させることが可能である。 In the present embodiment, the average crystallite diameter D of the catalyst carrier 104 containing magnesium oxide is controlled within a range larger than 13 nm and smaller than 100 nm. This makes it possible to suppress the formation of the layer 114 containing the composite oxide and also suppress Ostwald ripening. By controlling the structure of the catalyst carrier 104 in this manner, the number density and size of the catalyst 106 can be maintained for a long time in the CNT growth step described later. Therefore, the growth of CNTs continues for a long time, and as shown in FIG. 1C, it is possible to grow a long single-walled CNT 112 having a length L exceeding 1 mm.
触媒担持体１０４の作製方法、およびこれを用いるＣＮＴの合成方法を図４（Ａ）乃至（Ｃ）および図１（Ｃ）を用いて説明する。 A method for manufacturing the catalyst carrier 104 and a method for synthesizing CNTs using the catalyst carrier 104 will be described with reference to FIGS. 4A to 4C and 1C.
触媒担持体１０４は酸化マグネシウム粉末１０４をアニールして作られる（図４（Ａ））。アニーリングは例えば電気炉などの炉内での熱処理によって行うことができる。この時のアニーリングの温度は、酸化マグネシウムの平均結晶子径を１３ｎｍ以上とし、かつ酸化マグネシウムの融解を抑えるために６００℃以上２８００℃以下、より好ましくは７００℃以上１６５０℃以下であることが好ましい。アニーリングは窒素やアルゴンなどの不活性ガス、あるいは空気や酸素の存在下で行ってもよいが、触媒担持体１０４中の酸素欠陥の発生を防止するため、酸素を含む雰囲気下でアニーリングを行うことが好ましい。アニーリング時間は適宜選択でき、例えば５分から１時間、１０分から３０分、あるいは１５分から２０分とすることができる。このアニーリングにより触媒担持体１０４の結晶が成長し、含有する酸化マグネシウムの平均結晶子径Ｄが１３ｎｍよりも大きく１００ｎｍより小さく、１３ｎｍよりも大きく５０ｎｍより小さく、あるいは２０ｎｍよりも大きく５０ｎｍより小さい触媒担持体１０４が得られる。 The catalyst carrier 104 is made by annealing the magnesium oxide powder 104 (FIG. 4(A)). Annealing can be performed by heat treatment in a furnace such as an electric furnace. At this time, the annealing temperature is preferably 600° C. or more and 2800° C. or less, more preferably 700° C. or more and 1650° C. or less, in order to set the average crystallite diameter of magnesium oxide to 13 nm or more and to suppress the melting of magnesium oxide. .. The annealing may be performed in the presence of an inert gas such as nitrogen or argon, or air or oxygen, but in order to prevent the generation of oxygen defects in the catalyst carrier 104, the annealing should be performed in an atmosphere containing oxygen. Is preferred. The annealing time can be appropriately selected and can be, for example, 5 minutes to 1 hour, 10 minutes to 30 minutes, or 15 minutes to 20 minutes. Crystals of the catalyst carrier 104 grow by this annealing, and the average crystallite diameter D of the magnesium oxide contained therein is larger than 13 nm and smaller than 100 nm, larger than 13 nm and smaller than 50 nm, or larger than 20 nm and smaller than 50 nm. The body 104 is obtained.
引き続き、触媒１０６を形成する。まず触媒１０６に含まれる金属を含有する触媒層１２０を形成する（図４（Ｂ））。触媒層１２０の形成には真空蒸着法や有機金属ＣＶＤ（ＭＯＣＶＤ）法、スパッタリング法を適用することができ、典型的には高周波マグネトロンスパッタリング法が用いられる。触媒層１２０の厚さは１ｎｍ以上１０ｎｍ以下、あるいは１ｎｍ以上３ｎｍ以下、典型的には１．８ｎｍとすることができる。触媒１０６に含まれる金属としてＦｅ、Ｃｏ、Ｎｉなどの金属が挙げられる。 Subsequently, the catalyst 106 is formed. First, the catalyst layer 120 containing the metal contained in the catalyst 106 is formed (FIG. 4B). A vacuum deposition method, a metal organic chemical vapor deposition (MOCVD) method, or a sputtering method can be applied to the formation of the catalyst layer 120, and a high frequency magnetron sputtering method is typically used. The thickness of the catalyst layer 120 can be 1 nm or more and 10 nm or less, or 1 nm or more and 3 nm or less, typically 1.8 nm. Examples of the metal contained in the catalyst 106 include metals such as Fe, Co and Ni.
引き続き触媒層１２０に対して加熱を行い、粒子状の触媒１０６を形成する（図４（Ｃ）。加熱は電気炉などの炉内において、例えば６００℃から７００℃で行うことができる。加熱は還元雰囲気で行うことができ、例えば水素を含むガス中で行うことができる。以上の工程により、触媒１０６が作製される。 Subsequently, the catalyst layer 120 is heated to form the particulate catalyst 106 (FIG. 4C). The heating can be performed in a furnace such as an electric furnace at 600° C. to 700° C., for example. It can be performed in a reducing atmosphere, for example, in a gas containing hydrogen, and the catalyst 106 is manufactured through the above steps.
なお、触媒層１２０の形成工程を省き、触媒１０６の粒子を直接触媒担持体１０４上に形成してもよい。 The step of forming the catalyst layer 120 may be omitted, and the particles of the catalyst 106 may be directly formed on the catalyst carrier 104.
ＣＮＴは熱ＣＶＤ法によって形成することができる。具体的には、上述した工程で作製された触媒１０６を電気炉などの加熱炉に設置する。その後、ベンゼンやアセチレン、一酸化炭素、メタン、エタノールなどのＣＮＴ成長用のガス、および水などの触媒賦活物質を加熱炉内に供給し、６００℃から１２００℃の温度範囲で加熱することで、触媒１０６表面からＣＮＴの化学的成長を開始することができる。炉内にはアセチレンを希薄するためのヘリウムやアルゴンなどの不活性ガスを供給してもよい。その結果、図１（Ｃ）に模式的に示すようにＣＮＴ成長基材１００の表面に対して垂直な方向に配向した単層ＣＮＴ１１２を得ることができる。 The CNT can be formed by the thermal CVD method. Specifically, the catalyst 106 manufactured in the above steps is placed in a heating furnace such as an electric furnace. Then, a gas for CNT growth such as benzene, acetylene, carbon monoxide, methane, and ethanol, and a catalyst activating substance such as water are supplied into the heating furnace and heated in a temperature range of 600°C to 1200°C. Chemical growth of CNTs can be initiated from the surface of the catalyst 106. An inert gas such as helium or argon for diluting acetylene may be supplied into the furnace. As a result, a single-layer CNT 112 oriented in a direction perpendicular to the surface of the CNT growth base material 100 can be obtained as schematically shown in FIG.
以上の工程により、単層構造を有し、かつ、長さが１ｍｍを超える長尺のＣＮＴを短時間で効率よく合成することができる。 Through the above steps, a long CNT having a single-layer structure and having a length of more than 1 mm can be efficiently synthesized in a short time.
酸化マグネシウムは、酸性あるいは塩基性水溶液に可溶性がある。したがって成長した１ｍｍを超える極めて長い単層ＣＮＴが担持された触媒担持体１０４を酸性水溶液あるいは塩基性水溶液に浸漬させる工程により、全ての、あるいは実質的に全ての単層ＣＮＴを触媒担持体１０４から剥離することが可能となる。具体的には、酸性水溶液としてアンモニウム塩水溶液や塩酸、典型的には塩化アンモニウム水溶液を使用することができる。 Magnesium oxide is soluble in acidic or basic aqueous solutions. Therefore, all or substantially all of the single-walled CNTs are removed from the catalyst-supported body 104 by the step of immersing the grown catalyst-supported body 104 supporting extremely long single-walled CNTs exceeding 1 mm in an acidic aqueous solution or a basic aqueous solution. It can be peeled off. Specifically, an ammonium salt aqueous solution or hydrochloric acid, typically an ammonium chloride aqueous solution, can be used as the acidic aqueous solution.
（第２実施形態）
図１（Ｂ）は触媒担持体が基材上に設けられた概略図、さらに、前記触媒担持体の上に触媒が担持された概略図を示す。図１（Ｂ）に示すように、媒担持体１０４の表面には、ＣＮＴを成長するための触媒１０６が設けられる。触媒１０６はＦｅ、Ｃｏ、Ｎｉなどの金属を一種、あるいは複数種含むことができる。触媒担持体１０４には、酸化マグネシウム以外の酸化物が含まれていてもよいが、水溶液に浸漬させたときに成長したＣＮＴを触媒担持体から剥離しやすくする観点から、触媒担持体における酸化マグネシウムの含有率は好ましくは５０ｗｔ％以上、より好ましくは７５ｗｔ％、より好ましくは８５ｗｔ％以上、より好ましくは９０ｗｔ％、より好ましくは９５ｗｔ％以上であることが好ましい。触媒担持体１０４は基材１０２の上に設けられる。基材１０２の材料には特に制限はなく、石英やシリコン、ゲルマニウム、グラファイト、サファイア（酸化アルミニウム）などであってもよい。シリコンやゲルマニウムを用いる場合、基材１０２の表面にシリコンやゲルマニウムの酸化物の薄膜が形成されていてもよい。基材１０２は特定な形状に限定されず、板状や球状であってもよい。
(Second embodiment)
FIG. 1B shows a schematic view in which a catalyst carrier is provided on a substrate, and further a schematic view in which a catalyst is carried on the catalyst carrier. As shown in FIG. 1B, a catalyst 106 for growing CNTs is provided on the surface of the medium carrier 104. The catalyst 106 can contain one or more metals such as Fe, Co, and Ni. The catalyst carrier 104 may contain an oxide other than magnesium oxide, but from the viewpoint of facilitating separation of CNTs grown when immersed in an aqueous solution from the catalyst carrier, magnesium oxide in the catalyst carrier is The content of is preferably 50 wt% or more, more preferably 75 wt%, more preferably 85 wt% or more, more preferably 90 wt%, more preferably 95 wt% or more. The catalyst carrier 104 is provided on the base material 102. The material of the base material 102 is not particularly limited, and may be quartz, silicon, germanium, graphite, sapphire (aluminum oxide), or the like. In the case of using silicon or germanium, a thin film of silicon or germanium oxide may be formed on the surface of the base material 102. The base material 102 is not limited to a particular shape, and may have a plate shape or a spherical shape.
基材１０２上に設けられた触媒担持体１０４の作製方法、およびこれを用いるＣＮＴの合成方法を図５（Ａ）乃至（Ｄ）を用いて説明する。 A method for manufacturing the catalyst carrier 104 provided on the base material 102 and a method for synthesizing CNT using the catalyst carrier 104 will be described with reference to FIGS.
まず、基材１０２上に酸化マグネシウムの薄膜を形成し、触媒担持体１０４を形成する（図５（Ａ））。基材１０２に特に制限はないが、後述する加熱やアニーリング工程において耐熱性を示す材料であることが好ましい。具体的には石英やシリコン、ゲルマニウム、グラファイト、サファイア（酸化アルミニウム）などであることができる。シリコンやゲルマニウムを用いる場合、基材１０２の表面にシリコンやゲルマニウムの酸化物の薄膜が形成されていてもよい。 First, a thin film of magnesium oxide is formed on the base material 102 to form the catalyst carrier 104 (FIG. 5A). The base material 102 is not particularly limited, but a material that exhibits heat resistance in the heating and annealing steps described below is preferable. Specifically, it may be quartz, silicon, germanium, graphite, sapphire (aluminum oxide), or the like. In the case of using silicon or germanium, a thin film of silicon or germanium oxide may be formed on the surface of the base material 102.
触媒担持体１０４は、例えばスパッタリング法、電子ビーム蒸着法、酸化マグネシウム微粒子の分散液を塗布し乾燥後焼成する方法（塗布法）、マグネシウム薄膜の酸化、典型的にはマグネトロンスパッタリング法などを用いて形成することができる。膜厚は１５ｎｍ以上１０００ｎｍ以下、あるいは５０ｎｍ以上２００ｎｍ以下とすることができる。 The catalyst carrier 104 is formed by, for example, a sputtering method, an electron beam evaporation method, a method of applying a dispersion liquid of magnesium oxide fine particles, followed by drying and baking (coating method), oxidation of a magnesium thin film, typically a magnetron sputtering method. Can be formed. The film thickness can be 15 nm or more and 1000 nm or less, or 50 nm or more and 200 nm or less.
その後、アニーリングを行う。アニーリングは例えば電気炉などの炉内での熱処理によって行うことができる。この時のアニーリングの温度は、酸化マグネシウムの平均結晶子径を１３ｎｍ以上とし、かつ酸化マグネシウムと基材１０２の融解を抑えるために６００℃以上２８００℃以下、より好ましくは７００℃以上１６５０℃以下であることが好ましい。アニーリングは窒素やアルゴンなどの不活性ガス、あるいは空気や酸素の存在下で行ってもよいが、触媒担持体１０４中の酸素欠陥の発生を防止するため、酸素を含む雰囲気下でアニーリングを行うことが好ましい。アニーリング時間は適宜選択でき、例えば５分から１時間、１０分から３０分、あるいは１５分から２０分とすることができる。このアニーリングにより触媒担持体１０４の結晶が成長し、平均結晶子径Ｄが１３ｎｍよりも大きく１００ｎｍより小さく、１３ｎｍよりも大きく５０ｎｍより小さく、あるいは２０ｎｍよりも大きく５０ｎｍより小さい触媒担持体１０４が得られる（図５（Ｂ））。 After that, annealing is performed. Annealing can be performed by heat treatment in a furnace such as an electric furnace. The annealing temperature at this time is such that the average crystallite diameter of magnesium oxide is 13 nm or more and 600° C. or more and 2800° C. or less, more preferably 700° C. or more and 1650° C. or less in order to suppress melting of the magnesium oxide and the base material 102. Preferably. The annealing may be performed in the presence of an inert gas such as nitrogen or argon, or air or oxygen, but in order to prevent the generation of oxygen defects in the catalyst carrier 104, the annealing should be performed in an atmosphere containing oxygen. Is preferred. The annealing time can be appropriately selected and can be, for example, 5 minutes to 1 hour, 10 minutes to 30 minutes, or 15 minutes to 20 minutes. Crystals of the catalyst carrier 104 grow by this annealing, and a catalyst carrier 104 having an average crystallite diameter D larger than 13 nm and smaller than 100 nm, larger than 13 nm and smaller than 50 nm, or larger than 20 nm and smaller than 50 nm is obtained. (FIG. 5(B)).
上述の工程で作製された触媒担持体１０４上に触媒１０６を形成する。触媒１０６は、まず触媒１０６に含まれる金属を含有する触媒層１２０を形成する（図５（Ｃ））。触媒層１２０には真空蒸着法や有機金属ＣＶＤ（ＭＯＣＶＤ）法、スパッタリング法を適用することができ、典型的には高周波マグネトロンスパッタリング法が用いられる。触媒層１２０の厚さは１ｎｍ以上１０ｎｍ以下、あるいは１ｎｍ以上３ｎｍ以下、典型的には１．８ｎｍとすることができる。触媒１０６に含まれる金属としてＦｅ、Ｃｏ、Ｎｉなどの金属が挙げられる。 The catalyst 106 is formed on the catalyst carrier 104 manufactured in the above process. The catalyst 106 first forms the catalyst layer 120 containing the metal contained in the catalyst 106 (FIG. 5C). A vacuum deposition method, a metal organic CVD (MOCVD) method, or a sputtering method can be applied to the catalyst layer 120, and a high frequency magnetron sputtering method is typically used. The thickness of the catalyst layer 120 can be 1 nm or more and 10 nm or less, or 1 nm or more and 3 nm or less, typically 1.8 nm. Examples of the metal contained in the catalyst 106 include metals such as Fe, Co and Ni.
引き続き触媒層１２０に対して加熱を行い、粒子状の触媒１０６を形成する（図５（Ｄ）。加熱は電気炉などの炉内において、例えば６００℃から７００℃で行うことができる。加熱は還元雰囲気で行うことができ、例えば水素を含むガス中で行うことができる。以上の工程により、触媒１０６が作製される。 Subsequently, the catalyst layer 120 is heated to form the particulate catalyst 106 (FIG. 5D). The heating can be performed, for example, at 600° C. to 700° C. in a furnace such as an electric furnace. It can be performed in a reducing atmosphere, for example, in a gas containing hydrogen, and the catalyst 106 is manufactured through the above steps.
なお、触媒層１２０の形成工程を省き、触媒１０６の粒子を直接触媒担持体１０４上に形成してもよい。 The step of forming the catalyst layer 120 may be omitted, and the particles of the catalyst 106 may be directly formed on the catalyst carrier 104.
ＣＮＴは熱ＣＶＤ法によって形成することができる。具体的には、上述した工程で作製されたＣＮＴ成長基材１００を電気炉などの加熱炉に設置する。その後、ベンゼンやアセチレン、一酸化炭素、メタン、エタノールなどのＣＮＴ成長用のガス、および水などの触媒賦活物質を加熱炉内に供給し、６００℃から１２００℃の温度範囲で加熱することで、触媒１０６表面からＣＮＴの化学的成長を開始することができる。炉内にはアセチレンを希薄するためのヘリウムやアルゴンなどの不活性ガスを供給してもよい。その結果、図１（Ｃ）に模式的に示すようにＣＮＴ成長基材１００の表面に対して垂直な方向に配向した単層ＣＮＴ１１２を得ることができる。 The CNT can be formed by the thermal CVD method. Specifically, the CNT growth base material 100 manufactured in the above process is installed in a heating furnace such as an electric furnace. Then, a gas for CNT growth such as benzene, acetylene, carbon monoxide, methane, and ethanol, and a catalyst activating substance such as water are supplied into the heating furnace and heated in a temperature range of 600°C to 1200°C. Chemical growth of CNTs can be initiated from the surface of the catalyst 106. An inert gas such as helium or argon for diluting acetylene may be supplied into the furnace. As a result, a single-layer CNT 112 oriented in a direction perpendicular to the surface of the CNT growth base material 100 can be obtained as schematically shown in FIG.
以上の工程により、単層構造を有し、かつ、長さが１ｍｍを超える長尺のＣＮＴを短時間で効率よく合成することができる。 Through the above steps, a long CNT having a single-layer structure and having a length of more than 1 mm can be efficiently synthesized in a short time.
酸化マグネシウムは、酸性あるいは塩基性水溶液に可溶性がある。したがって成長した１ｍｍを超える極めて長い単層ＣＮＴが担持された触媒担持体１０４を酸性水溶液あるいは塩基性水溶液に浸漬させる工程により、全ての、あるいは実質的に全ての単層ＣＮＴを触媒担持体１０４から剥離することが可能となる。具体的には、酸性水溶液としてアンモニウム塩水溶液や塩酸、典型的には塩化アンモニウム水溶液を使用することができる。 Magnesium oxide is soluble in acidic or basic aqueous solutions. Therefore, all or substantially all of the single-walled CNTs are removed from the catalyst-supported body 104 by the step of immersing the grown catalyst-supported body 104 supporting extremely long single-walled CNTs exceeding 1 mm in an acidic aqueous solution or a basic aqueous solution. It can be peeled off. Specifically, an ammonium salt aqueous solution or hydrochloric acid, typically an ammonium chloride aqueous solution, can be used as the acidic aqueous solution.
本実施例では、触媒担持体１０４の作製、およびそれを用いたＣＮＴの合成例に関して説明する。 In this example, the production of the catalyst carrier 104 and an example of CNT synthesis using the same will be described.
［１．触媒担持体］
酸化マグネシウム粉末を予め７５０℃に加熱した電気炉に挿入し、空気環境下で２０分間加熱した（アニーリング）後、室温まで冷却した。
[1. Catalyst carrier]
The magnesium oxide powder was inserted into an electric furnace preheated to 750° C., heated in an air environment for 20 minutes (annealing), and then cooled to room temperature.
［２．ＣＮＴ垂直配向体の合成］
ＣＮＴ垂直配向体の合成は、、図４（Ｂ）、（Ｃ）、および図１（Ｃ）に示すように、前記アニーリングの処理を行った酸化マグネシウム粉末に対して触媒層１２０の形成工程、触媒１０６の粒子の形成工程、およびＣＮＴ成長工程を順次行うことにより実施した。具体的には、前記酸化マグネシウム粉末に対して１００Ｗで２分間スパッタ処理した後、高周波マグネトロンスパッタリング（２０Ｗ、４６ｓｅｃ）により１．８ｎｍの鉄を蒸着し、触媒層１２０を形成した。
[2. Synthesis of vertically aligned CNTs]
As shown in FIGS. 4(B), 4(C), and 1(C), the synthesis of the CNT vertical alignment body is performed by forming the catalyst layer 120 on the magnesium oxide powder subjected to the annealing treatment. The step of forming particles of the catalyst 106 and the step of growing CNT were sequentially performed. Specifically, the magnesium oxide powder was sputtered at 100 W for 2 minutes, and 1.8 nm of iron was deposited by high frequency magnetron sputtering (20 W, 46 sec) to form the catalyst layer 120.
続いて触媒１０６の粒子の形成工程として、予め６５０℃に加熱した電気炉に触媒粒子形成工程用のガスを流し、担持体Ａまたは担持体Ｂを導入した。粒子形成工程用のガスの流量と組成は以下の通りである。
全流量：１０００ｓｃｃｍ
Ｈ2：９０％
Ｈｅ：１０％
Subsequently, in the step of forming the particles of the catalyst 106, the gas for the step of forming the catalyst particles was caused to flow in the electric furnace preheated to 650° C., and the carrier A or the carrier B was introduced. The flow rate and composition of the gas for the particle forming process are as follows.
Total flow rate: 1000 sccm
H 2 : 90%
He: 10%
引き続くＣＮＴ成長工程として、７５０℃に加熱した電気炉にＣＮＴ成長工程用のガスを流し、担持体Ａまたは担持体Ｂを導入した。ＣＮＴ成長工程用のガス流量と組成は以下の通りである。反応時間、すなわちガスと触媒１０６との接触時間は１０分であった。
全流量：１０００ｓｃｃｍ
Ｃ2Ｈ2：０．４％
Ｈ2Ｏ：２００ ｐｐｍ
Ｈｅ：残部
In the subsequent CNT growth step, the gas for the CNT growth step was passed through an electric furnace heated to 750° C., and the carrier A or the carrier B was introduced. The gas flow rate and composition for the CNT growth process are as follows. The reaction time, that is, the contact time between the gas and the catalyst 106 was 10 minutes.
Total flow rate: 1000 sccm
C 2 H 2 : 0.4%
H 2 O: 200 ppm
He: balance
以上により、１ｍｍを超える長さの垂直方向に配向した単層ＣＮＴが得られた。 From the above, a single-walled CNT having a length of more than 1 mm and oriented in the vertical direction was obtained.
［３．ＣＮＴの担持体からの剥離］
触媒担持体の上に形成されたＣＮＴの垂直配向体を基材から剥離するために、ＣＮＴの垂直配向体が成長した触媒担持体を、０．１Ｍの塩化アンモニウム水溶液１０ｍＬに２４時間浸漬させた。ＣＮＴの垂直配向体が担持体から剥離され、水溶液中を浮遊した。
[3. Peeling of CNT from carrier]
In order to separate the vertically aligned CNTs formed on the catalyst carrier from the substrate, the catalyst carrier on which the vertically aligned CNTs had grown was immersed in 10 mL of a 0.1 M ammonium chloride aqueous solution for 24 hours. .. The vertically aligned CNTs were separated from the carrier and floated in the aqueous solution.
本実施例では、シリコン基板を基材１０２として用いた触媒担持体１０４とＣＮＴ成長基材１００の作製、およびそれを用いたＣＮＴの合成例に関して説明する。 In this example, a catalyst carrier 104 using a silicon substrate as a base material 102 and a CNT growth base material 100, and an example of CNT synthesis using the same will be described.
［１．触媒担持体］
基材１０２として、表面に５００ｎｍの熱酸化膜を有する幅１０ｍｍ、長さ１０ｍｍ、厚さ０．６２５ｍｍのシリコン基板を用いた。基材１０２上に触媒担持体１０４を形成するため、１１０ｎｍの酸化マグネシウム薄膜を高周波マグネトロンスパッタリングにより蒸着した。スパッタリングターゲットには酸化マグネシウムを用い、アルゴン流量９．５ＳＣＣＭ、酸素流量０．５ＳＣＣＭの条件下、２００Ｗの電圧で１００分間の蒸着を行った。続いて予め７５０℃に加熱した電気炉に上記基材１０２を挿入し、空気環境下で２０分間加熱した（アニーリング）後、室温まで冷却した。以下この実施例で作製した触媒担持体を担持体Ａと記す。
[1. Catalyst carrier]
As the base material 102, a silicon substrate having a width of 10 mm, a length of 10 mm, and a thickness of 0.625 mm having a thermal oxide film of 500 nm on its surface was used. In order to form the catalyst carrier 104 on the base material 102, a 110 nm magnesium oxide thin film was deposited by high frequency magnetron sputtering. Magnesium oxide was used as a sputtering target, and vapor deposition was performed at a voltage of 200 W for 100 minutes under the conditions of an argon flow rate of 9.5 SCCM and an oxygen flow rate of 0.5 SCCM. Subsequently, the base material 102 was inserted into an electric furnace preheated to 750° C., heated in an air environment for 20 minutes (annealing), and then cooled to room temperature. Hereinafter, the catalyst carrier prepared in this example is referred to as a carrier A.
［２．比較担持体］
比較用の触媒担持体として、前記アニーリングを実施しないこと以外は担持体Ａと同様の手順で触媒担持体を作製した。この担持体を担持体Ｂと記す。
[2. Comparison carrier]
As a catalyst carrier for comparison, a catalyst carrier was prepared by the same procedure as that of the carrier A except that the annealing was not performed. This carrier is referred to as carrier B.
［３．ＣＮＴ垂直配向体の合成］
ＣＮＴ垂直配向体の合成は、図５（Ｃ）、（Ｄ）、および図１（Ｃ）に示すように、担持体Ａあるいは担持体Ｂに対して触媒層１２０の形成工程、触媒１０６の粒子の形成工程、およびＣＮＴ成長工程を順次行うことにより実施した。具体的には、担持体Ａまたは担持体Ｂの表面を１００Ｗで２分間スパッタ処理した後、高周波マグネトロンスパッタリング（２０Ｗ、４６ｓｅｃ）により１．８ｎｍの鉄を蒸着し、触媒層１２０を形成した。
[3. Synthesis of vertically aligned CNTs]
As shown in FIGS. 5(C), 5(D), and 1(C), the synthesis of the vertically aligned CNTs is performed by forming the catalyst layer 120 on the carrier A or the carrier B and the particles of the catalyst 106. It was carried out by sequentially performing the forming step and the CNT growing step. Specifically, the surface of the carrier A or the carrier B was sputtered at 100 W for 2 minutes, and then 1.8 nm of iron was deposited by high frequency magnetron sputtering (20 W, 46 sec) to form the catalyst layer 120.
続いて触媒１０６の粒子の形成工程として、予め６５０℃に加熱した電気炉に触媒粒子形成工程用のガスを流し、担持体Ａまたは担持体Ｂを導入した。粒子形成工程用のガスの流量と組成は以下の通りである。
全流量：１０００ｓｃｃｍ
Ｈ2：９０％
Ｈｅ：１０％
Subsequently, in the step of forming the particles of the catalyst 106, the gas for the step of forming the catalyst particles was caused to flow in the electric furnace preheated to 650° C., and the carrier A or the carrier B was introduced. The flow rate and composition of the gas for the particle forming process are as follows.
Total flow rate: 1000 sccm
H 2 : 90%
He: 10%
引き続くＣＮＴ成長工程として、７５０℃に加熱した電気炉にＣＮＴ成長工程用のガスを流し、担持体Ａまたは担持体Ｂを導入した。ＣＮＴ成長工程用のガス流量と組成は以下の通りである。反応時間、すなわちガスと触媒１０６との接触時間は１０分であった。
全流量：１０００ｓｃｃｍ
Ｃ2Ｈ2：０．４％
Ｈ2Ｏ：２００ ｐｐｍ
Ｈｅ：残部
In the subsequent CNT growth step, the gas for the CNT growth step was passed through an electric furnace heated to 750° C., and the carrier A or the carrier B was introduced. The gas flow rate and composition for the CNT growth process are as follows. The reaction time, that is, the contact time between the gas and the catalyst 106 was 10 minutes.
Total flow rate: 1000 sccm
C 2 H 2 : 0.4%
H 2 O: 200 ppm
He: balance
［４．ＣＮＴの評価］
図６（Ａ）、（Ｂ）はそれぞれ、担持体Ａと担持体Ｂを用いて作製した単層ＣＮＴの垂直配向体の電子顕微鏡（ＳＥＭ）像ある。アニーリング工程を含む担持体Ａからは１ｍｍを超える高さのＣＮＴ１１２が形成されていることがわかる（図６（Ａ））。一方、アニーリング工程を含まない担持体Ｂ上に形成されたカーボンナノチューブ１１２の高さは５０μｍ程度に留まったことがわかる（図６（Ｂ））。
[4. Evaluation of CNT]
6(A) and 6(B) are electron microscope (SEM) images of a vertically aligned body of single-walled CNTs produced using the carrier A and the carrier B, respectively. It can be seen that CNTs 112 having a height of more than 1 mm are formed from the carrier A including the annealing step (FIG. 6(A)). On the other hand, it can be seen that the height of the carbon nanotubes 112 formed on the carrier B, which does not include the annealing step, remained at about 50 μm (FIG. 6(B)).
図７（Ａ）、（Ｂ）はそれぞれ、担持体Ａと担持体Ｂを用いて作製した単層ＣＮＴの垂直配向体を担持体Ａ、あるいは担持体Ｂからピンセットを用いて剥離し、溶媒中に分散させた後、透過型電子顕微鏡用グリッドに塗布し乾燥させた試料の電子顕微鏡（ＴＥＭ）像である。担持体Ａを用いた場合は単層ＣＮＴが主生成物として生成したこと（図７（Ａ））、および担持体Ｂを用いた場合は２層ＣＮＴが主生成物として生成していることがわかる（図７（Ｂ））。生成したＣＮＴ垂直配向体（フォレスト）の高さと、ＴＥＭ観察から評価した単層ＣＮＴ、２層および３層以上の多層ＣＮＴの割合（％）を表１にまとめる。 FIGS. 7(A) and 7(B) respectively show a vertically aligned single-walled CNT prepared by using the carrier A and the carrier B, peeled from the carrier A or the carrier B using tweezers, and then in a solvent. FIG. 3 is an electron microscope (TEM) image of a sample that was dispersed in a sample, applied to a grid for a transmission electron microscope, and dried. When the carrier A was used, single-walled CNTs were produced as the main product (FIG. 7A), and when the carrier B was used, the two-layered CNTs were produced as the main product. It is understood (Fig. 7(B)). Table 1 shows the heights of the vertically aligned CNTs (forests) and the proportions (%) of the single-walled CNTs, the two-layered, and the multi-layered CNTs having three or more layers evaluated from the TEM observation.
［５．ＣＮＴの担持体からの剥離］
担持体Ａの上に形成されたＣＮＴの垂直配向体を基材から剥離するために、ＣＮＴの垂直配向体が成長した担持体Ａを、０．１Ｍの塩化アンモニウム水溶液１０ｍＬに２４時間浸漬させた。ＣＮＴの垂直配向体全体が担持体から剥離され、水溶液中を浮遊した。
[5. Peeling of CNT from carrier]
In order to separate the vertically aligned CNTs formed on the carrier A from the substrate, the carrier A on which the vertically aligned CNTs had grown was immersed in 10 mL of a 0.1 M ammonium chloride aqueous solution for 24 hours. .. The entire vertically aligned CNTs were peeled from the carrier and floated in the aqueous solution.
［６．触媒担持体の結晶径の評価］
担持体Ａと担持体Ｂにおける触媒担持体１０４である酸化マグネシウム薄膜の結晶子径を微小角入射Ｘ線回折によって評価した。図８（Ａ）は、担持体Ａと担持体Ｂの微小角入射Ｘ線回折の測定結果を示したものである。ここで、(ア)、(イ)、(ウ)、(エ)、（オ）はそれぞれ、酸化マグネシウム（ＭｇＯ）の（１１１）面、（２００）面、（２２０）面、（３１１）面、（２２２）面に由来する回折ピークである。図８（Ａ）から明らかなように、担持体Ａの方が担持体Ｂよりも尖鋭な回折ピークを与えており、アニーリングにより触媒担持体１０４を形成するＭｇＯを含む結晶子が粒成長したと推察される。各回折ピークにシェラーの式を適用して算出された結晶子径をそれぞれ表２、３に示す。ここでシェラーの式は、以下の式４で表現され、Ｄ、Ｋ、Ｂ，θはそれぞれ結晶子径、シェラー定数、ピークの回折線幅、ブラック角を示す。なお、光学系による回折線の広がりの影響による補正は、Ｓｉ単結晶（１１１）の測定を実施し、その回折線幅０．０４°を用いた。ここで、結晶子の外形が立方体で大きさの分布を持たないと仮定し、シェラー定数Ｋには０．９４を適用した。各ピークから求めた結晶子径の平均値、すなわち平均結晶子径Ｄは担持体Ａでは２０ｎｍ、担持体Ｂでは１３ｎｍであった。
[6. Evaluation of crystal size of catalyst carrier]
The crystallite diameter of the magnesium oxide thin film, which is the catalyst carrier 104 in the carriers A and B, was evaluated by minute angle incident X-ray diffraction. FIG. 8A shows the measurement results of the small-angle incidence X-ray diffraction of the carrier A and the carrier B. Here, (A), (B), (C), (D), and (O) are the (111) plane, (200) plane, (220) plane, and (311) plane of magnesium oxide (MgO), respectively. , (222) plane-derived diffraction peaks. As is clear from FIG. 8(A), the carrier A gives a sharper diffraction peak than the carrier B, and it is found that the crystallites containing MgO forming the catalyst carrier 104 have grown due to annealing. Inferred. The crystallite sizes calculated by applying the Scherrer's formula to each diffraction peak are shown in Tables 2 and 3, respectively. Here, the Scherrer's equation is expressed by the following Equation 4, and D, K, B, and θ indicate the crystallite diameter, the Scherrer constant, the peak diffraction line width, and the black angle, respectively. The correction due to the influence of the spread of the diffraction line by the optical system was carried out by measuring the Si single crystal (111) and using the diffraction line width of 0.04°. Here, assuming that the outer shape of the crystallite is cubic and has no size distribution, 0.94 is applied to the Scherrer constant K. The average value of the crystallite size obtained from each peak, that is, the average crystallite size D was 20 nm for the carrier A and 13 nm for the carrier B.
［７．活性金属の拡散試験］
ここでは、触媒１０６を構成するＦｅと触媒担持体１０４を構成するＭｇＯの反応がアニーリングによって抑制されるかどうかを明らかにすることを目的とし、Ｘ線光電子分光法（ＸＰＳ）を用いて分析を行った。
[7. Diffusion test of active metal]
Here, for the purpose of clarifying whether the reaction between Fe forming the catalyst 106 and MgO forming the catalyst support 104 is suppressed by annealing, an analysis is performed using X-ray photoelectron spectroscopy (XPS). went.
担持体Ａおよび担持体Ｂに対して、前述の触媒層１２０の形成工程と触媒１０６の粒子形成工程を施した後、７５０℃のＨｅ雰囲気下で５分間保持し、その後室温まで冷却した。これらの基材についてＸＰＳにて深さ方向分析を行い、各深度におけるＦｅの半定量分析と電荷状態の評価を行った。図８（Ｂ）は各深度におけるＦｅ２ｐ軌道のエネルギーに対応する領域のＸＰＳスペクトルを示す。担持体Ａ、担持体ＢともにＦｅ２ｐ３/２とＦｅ２ｐ１/２に由来する光電子ピークがそれぞれ７０５ｅＶから７１７ｅＶの領域と７２０ｅＶから７３０ｅＶの領域に観測されており、Ｆｅの存在が確認できる。さらにＦｅ２ｐ３/２に由来する光電子ピークの電子結合エネルギーに着目すると、担持体Ａではピークトップを７０７ｅＶ、７１１ｅＶに有するピークが確認されたのに対し、担持体Ｂでは主にピークトップを７１１ｅＶに有するピークのみが確認された。このことは、担持体ＢではほとんどのＦｅが＋２価の酸化状態あるいは＋３価の酸化状態で存在しているのに対し、担持体Ａでは酸化状態だけでなく金属状態（すなわち０価）で存在するＦｅも含まれていることがわかる。したがって下記反応式（５）、（６）に基づくＦｅとＭｇＯの反応がアニーリングを施した担持体Ａでは抑制されているといえる。 After carrying out the catalyst layer 120 forming step and the catalyst 106 particle forming step on the support A and the support B, the support A and the support B were held in a He atmosphere at 750° C. for 5 minutes, and then cooled to room temperature. The depth direction analysis was performed on these base materials by XPS, and the semi-quantitative analysis of Fe at each depth was performed and the charge state was evaluated. FIG. 8B shows an XPS spectrum of a region corresponding to the energy of the Fe2p orbit at each depth. Photoelectron peaks derived from Fe2p3/2 and Fe2p1/2 were observed in the regions of 705 eV to 717 eV and in the regions of 720 eV to 730 eV of both the carrier A and the carrier B, and the existence of Fe can be confirmed. Further, focusing on the electron binding energy of the photoelectron peak derived from Fe2p3/2, it was confirmed that the carrier A has peak tops at 707 eV and 711 eV, whereas the carrier B mainly has peak tops at 711 eV. Only the peak was confirmed. This means that most of Fe is present in the support B in the +2 valent oxidation state or the +3 valence oxidation state, whereas the support A is present in the metal state (that is, 0 valence) as well as the oxidation state. It can be seen that Fe is included. Therefore, it can be said that the reaction between Fe and MgO based on the following reaction formulas (5) and (6) is suppressed in the annealed carrier A.
また、Ｆｅの深さ分布に着目すると担持体Ａでは最表面からの深さが少なくとも６．１ｎｍでＦｅ２ｐ由来の光電子ピークが完全にノイズに埋もれて検出できないのに対し、担持体Ｂでは最表面からの深さが少なくとも１０．９ｎｍまで検出された。担持体Ａでは、ＦｅとＭｇＯの反応が抑制されたことでＦｅの触媒担持体１０４内部への拡散が抑制されていると考えられる。 Further, focusing on the depth distribution of Fe, the carrier A has a depth from the outermost surface of at least 6.1 nm and the photoelectron peak derived from Fe2p is completely buried in noise and cannot be detected, while the carrier B has the outermost surface. Was detected up to at least 10.9 nm. It is considered that in the carrier A, the reaction of Fe and MgO was suppressed, so that diffusion of Fe into the catalyst carrier 104 was suppressed.
以上述べたように、本発明に係る触媒担持体は、極めて長い単層ＣＮＴを与え、かつ水溶液に浸漬させることで成長したＣＮＴを基材から容易に剥離することが可能であることがわかった。 As described above, it was found that the catalyst carrier according to the present invention can easily separate the grown CNTs from the base material by giving extremely long single-walled CNTs and immersing them in an aqueous solution. ..
１００：触媒を担持した触媒担持体（ＣＮＴ成長基材）
１０２：基材
１０４：触媒担持体
１０６：触媒
１１２：カーボンナノチューブ
１１４：複合酸化物の含有層
１１６：領域
１２０：触媒層
100: Catalyst carrier carrying a catalyst (CNT growth base material)
102: base material 104: catalyst carrier 106: catalyst 112: carbon nanotube 114: composite oxide containing layer 116: region 120: catalyst layer
Claims (9)
アニーリング後の前記酸化マグネシウム粉末または前記酸化マグネシウム薄膜上に、前記酸化マグネシウム粉末または前記酸化マグネシウム薄膜に接する触媒を形成する工程と、
前記触媒上にカーボンナノチューブを成長させる工程とを備え、
前記平均結晶子径Ｄは、Ｘ線回折ピークに以下の式を適用することによって決定され、
A step of forming a catalyst in contact with the magnesium oxide powder or the magnesium oxide thin film on the magnesium oxide powder or the magnesium oxide thin film after annealing ,
A step of growing carbon nanotubes on the catalyst ,
The average crystallite size D is determined by applying the following formula to the X-ray diffraction peaks,
前記アニーリング後の前記酸化マグネシウム粉末または前記酸化マグネシウム薄膜上に、前記酸化マグネシウム粉末または前記酸化マグネシウム薄膜に接する触媒を形成する工程とを含み、 A step of forming a catalyst in contact with the magnesium oxide powder or the magnesium oxide thin film on the magnesium oxide powder or the magnesium oxide thin film after the annealing,
前記平均結晶子径Ｄは、Ｘ線回折ピークに以下の式を適用することによって決定され、 The average crystallite size D is determined by applying the following formula to the X-ray diffraction peaks,
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