WO2014080974A1 - Carbon nanotube and method for producing same - Google Patents

Carbon nanotube and method for producing same Download PDF

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WO2014080974A1
WO2014080974A1 PCT/JP2013/081375 JP2013081375W WO2014080974A1 WO 2014080974 A1 WO2014080974 A1 WO 2014080974A1 JP 2013081375 W JP2013081375 W JP 2013081375W WO 2014080974 A1 WO2014080974 A1 WO 2014080974A1
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sulfur
carbon nanotubes
carbon nanotube
chain
encapsulated
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PCT/JP2013/081375
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French (fr)
Japanese (ja)
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利彦 藤森
金子　克美
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国立大学法人信州大学
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    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01B—NON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
    • C01B32/00—Carbon; Compounds thereof
    • C01B32/15—Nano-sized carbon materials
    • C01B32/158—Carbon nanotubes
    • C01B32/168—After-treatment
    • C01B32/178—Opening; Filling
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01B—NON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
    • C01B32/00—Carbon; Compounds thereof
    • C01B32/15—Nano-sized carbon materials
    • C01B32/158—Carbon nanotubes
    • C01B32/168—After-treatment
    • C01B32/174—Derivatisation; Solubilisation; Dispersion in solvents

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  • the present invention relates to a carbon nanotube that can be used as a conductive material or the like by being combined with sulfur and a method for producing the same.
  • Non-patent Document 1 an encapsulated carbon nanotube in which fullerene, metal, or various compounds are encapsulated in the hollow of the carbon nanotube is known (Non-patent Document 1, Patent Documents 1 and 2).
  • Examples of composites of carbon nanotubes and sulfur include an example in which a sulfur compound is included in a carbon nanotube for the purpose of being used as a positive electrode material for a secondary battery (Patent Document 3), and an example in which sulfur is included in a carbon nanotube (non-patent document).
  • Patent Document 3 an example in which sulfur is included in a carbon nanotube for the purpose of being used as a positive electrode material for a secondary battery
  • Patent Document 3 an example in which sulfur is included in a carbon nanotube
  • the inventors have encapsulated sulfur in carbon nanotubes, so that one-dimensional nanospaces of carbon nanotubes are used as templates, and sulfur is arranged and accommodated in a chain, and sulfur is chained in the hollow space of carbon nanotubes.
  • the present inventors have found a phenomenon in which sulfur as an insulator is metallized at room temperature and normal pressure. That is, an object of the present invention is to provide a carbon nanotube having a novel configuration and action in which sulfur is included, and a method for producing the carbon nanotube.
  • the carbon nanotube according to the present invention is characterized in that a sulfur chain in which sulfur atoms are linked in a chain shape is included.
  • sulfur is included in the carbon nanotubes, the sulfur is chained in accordance with the one-dimensional nanospace of the carbon nanotubes, and is included as sulfur chains covalently bonded to each other.
  • sulfur is converted into a one-dimensional crystal by the nanospace of carbon nanotubes acting like a template, thereby sulfur is metallized.
  • the sulfur atoms included in the carbon nanotubes may be included as a linear structure or may be included as a zigzag structure. Even when encapsulated in a zigzag structure, the sulfur chain is a one-dimensional structure, and since sulfur atoms are encapsulated in a one-dimensional regular arrangement, it is referred to as a one-dimensional crystal in this specification.
  • the sulfur chain is encapsulated in the carbon nanotube as a linear structure, there may be a structure in which two sulfur chains are encapsulated in parallel.
  • the carbon nanotube encapsulating sulfur may be a single-walled carbon nanotube, a double-walled carbon nanotube, or a multi-walled carbon nanotube having two or more layers.
  • a sulfur-encapsulated carbon nanotube having conductivity it is necessary that a one-dimensional chain of sulfur is formed in a state where sulfur is encapsulated in the carbon nanotube, and a one-dimensional crystal of sulfur is formed.
  • Carbon nanotubes containing sulfur are particularly advantageous in that they have excellent conductivity.
  • the carbon nanotubes that form a one-dimensional sulfur-containing chain containing sulfur those having a hollow portion diameter (inner diameter) of about 0.4 to 2.0 nm can be used, and preferably the hollow portion diameter is 0.8. Those up to 1.5 nm can be used. Since the size of the sulfur atom is about 0.4 nm, the diameter of the hollow portion of the carbon nanotube needs to be 0.4 nm or more. When the diameter of the carbon nanotube is 2.0 nm or more, sulfur formed at normal temperature and normal pressure the diameter of the hollow portion of the carbon nanotube from the structure (S 8) is formed of or less is required 2.0 nm. In the experiment, sulfur was encapsulated in single-walled carbon nanotubes and double-walled carbon nanotubes, and it was confirmed that sulfur was encapsulated as a one-dimensional crystal in the hollow part of carbon nanotubes.
  • Carbon nanotubes in which sulfur chains are encapsulated are excellent in conductivity. Therefore, the sheet body containing carbon nanotubes containing sulfur can be suitably used as a conductive material.
  • the sulfur-encapsulated carbon nanotubes constituting this sheet include carbon nanotubes encapsulating a linear sulfur chain, carbon nanotubes encapsulating two linear sulfur chains in parallel, and a zigzag sulfur chain. Encapsulated carbon nanotubes can be used. Single-walled, double-walled, and multi-walled carbon nanotubes can be used as the carbon nanotubes. However, when single-walled carbon nanotubes are used, the carbon nanotubes have excellent conductivity.
  • a carbon nanotube and sulfur are accommodated in a sealed container, the container is vacuum-sealed, and the vacuum-sealed container is heated to a temperature of 718 K or higher to form sulfur in the carbon nanotube.
  • a manufacturing method comprising a step of encapsulating and a purification step of removing sulfur adhering to the outer surface of the carbon nanotube after encapsulating sulfur in the carbon nanotube can be suitably used.
  • the purification step includes a step of adding carbon nanotubes obtained in the step of encapsulating sulfur to carbon disulfide, preparing a dispersion of carbon nanotubes by ultrasonic irradiation, and filtering the dispersion of carbon nanotubes. It is characterized by that.
  • the carbon nanotube according to the present invention can be utilized as a conductive material in which sulfur chains are metallized by inclusion of sulfur in the carbon nanotubes in a chain shape, and the carbon nanotubes and sulfur are combined. And the use of sulfur can be expanded.
  • a carbon nanotube in which sulfur was accommodated in a chain shape in the hollow space of the carbon nanotube was produced by the following method.
  • Single-walled carbon nanotubes (SWCNT) and double-walled carbon nanotubes (DWCNT) were used as the carbon nanotubes.
  • a carbon nanotube open end treatment is performed.
  • Single-walled carbon nanotubes and double-walled carbon nanotubes are sealed in a glass tube through which gas flows, and an end-opening treatment is performed at 723 K for 1 hour while flowing oxygen gas at a rate of 100 ml / min.
  • Examples of the carbon nanotube open end treatment include acid treatment using hydrochloric acid and nitric acid, and ultrasonic treatment.
  • the open-end process using oxygen gas has the advantage that the open-end process can be efficiently performed and that the open-end process can be performed accurately by using a method that is easy to control such as temperature and gas flow rate.
  • Some commercially available carbon nanotubes are open-ended, but the open-end treatment improves the open-end rate and makes it easier to enclose sulfur.
  • the treatment for encapsulating sulfur in the carbon nanotubes subjected to the open end treatment was performed as follows. 10 mg of the single-walled carbon nanotube subjected to the open end treatment and 30 mg of sulfur (99.9999%) are put into a glass tube and vacuum sealed (step of vacuum sealing). Subsequently, the carbon nanotube which included sulfur was prepared by hold
  • the sample prepared by the above method was added to carbon disulfide and subjected to ultrasonic irradiation to obtain a carbon nanotube dispersion.
  • the dispersion contains sulfur separated from carbon nanotubes and carbon nanotubes containing sulfur. By filtering this dispersion, a carbon nanotube containing sheet-like sulfur is obtained. After repeating this process three times, unnecessary carbon disulfide was removed by maintaining at room temperature and under vacuum for 1 hour or longer (purification process), and carbon nanotubes containing sulfur after purification were obtained.
  • the obtained sample is a sheet.
  • the purpose of washing the carbon nanotubes with carbon disulfide is to remove sulfur adhering to the outer surface of the carbon nanotubes (sulfur S 8 found at room temperature and normal pressure). By ultrasonic treatment, sulfur that has entered the gaps between the carbon nanotube bundles can be removed. Sulfur present between the bundles of carbon nanotubes acts to increase the electrical resistivity.
  • FIG. 1 (a) shows that sulfur is arranged in two chains along the longitudinal direction of the carbon nanotubes in the hollow space of the single-walled carbon nanotubes. Each of the two sulfur chains is linearly arranged in a one-dimensional crystal form. The distance between the sulfur atoms of the two sulfur chains is 0.32 nm.
  • the carbon nanotube encapsulating sulfur is a one-dimensional crystal of sulfur formed by a one-dimensional nanospace, which is a hollow space of the carbon nanotube, acting like a template.
  • the inner diameter of the carbon nanotube in FIG. 1 (a) is 1.1 nm.
  • FIGS. 1B and 1C are TEM images of double-walled carbon nanotubes containing sulfur.
  • FIG. 1B shows that sulfur chains are encapsulated in a zigzag chain in the hollow space of the carbon nanotube.
  • FIG.1 (c) shows that the sulfur chain is included as a linear structure.
  • the inner diameter of the carbon nanotube shown in FIG. 1 (b) is 0.68 nm
  • the inner diameter of the carbon nanotube shown in FIG. 1 (c) is 0.60 nm.
  • the sulfur becomes a zigzag chain or a linear chain.
  • FIGS. 1 (b) and 1 (c) show the results of analyzing the intensity of the TEM image for the sample shown in FIGS. 1 (b) and 1 (c) in the longitudinal direction of the carbon nanotube and the direction perpendicular to the longitudinal direction. Show.
  • the interval between the sulfur atoms on one side of the sulfur chain in zigzag configuration shown in FIG. 2 (a) is 0.33 ⁇ 0.03 nm.
  • the interval between the sulfur atoms of the sulfur chain having a linear structure is 0.18 ⁇ 0.02 nm.
  • FIG. 3 shows X-ray diffraction patterns for single-walled carbon nanotubes containing sulfur and double-walled carbon nanotubes containing sulfur. For comparison, FIG. 3 also shows the measurement results for single-walled carbon nanotubes that do not contain sulfur (empty) and double-walled carbon nanotubes. The peaks appearing in the profiles of single-walled carbon nanotubes and double-walled carbon nanotubes indicate that sulfur is contained in a regularly arranged state in the hollow space of the carbon nanotubes.
  • FIG. 3 exemplifies the arrangement form of the contained sulfur and the peak corresponding to the sulfur interval in the arrangement. Multiple peaks appear in the graph because the sample used to measure the X-ray diffraction pattern contains carbon nanotubes with different inner diameters, and the spacing between the sulfur atoms contained in the carbon nanotubes. This is due to the existence of different (crystal spacing). As shown in the profile of the single-walled carbon nanotube in FIG. 3, sulfur may be included in a zigzag type in the case of sulfur-encapsulated single-walled carbon nanotubes.
  • the XRD profile shown in FIG. 3 shows an asymmetric profile unique to a one-dimensional crystal.
  • sulfur holds a chain structure by a covalent bond. From the above domain size, it is considered that sulfur encapsulated in carbon nanotubes constitutes a very long linear structure or one-dimensional crystal structure of zigzag structure in which sulfur atoms are arranged in units of several tens to several hundreds.
  • FIG. 6 shows a distance d between sulfur atoms of a linear sulfur chain obtained from the peak position of the XRD profile when the sample temperature is changed.
  • the sulfur chains encapsulated in the single-walled carbon nanotubes stably maintain a regular arrangement in the temperature range of 300 to 800K.
  • the sulfur chains encapsulated in the double-walled carbon nanotubes stably maintain a linear structure from room temperature to 500K, but a large peak shift appears above 500K. This indicates that when heated to about 500K or higher, the interval between sulfur atoms derived from the linear structure is extended.
  • FIGS. 7 (a) and 7 (b) show X-ray diffraction similarly measured for single-walled carbon nanotubes and double-walled carbon nanotubes containing sulfur chains in a zigzag structure at sample temperatures ranging from 300 to 800K. The behavior of specific peaks of the pattern (corresponding to the zigzag structure) is shown.
  • FIG. 8 shows the arrangement interval d of sulfur obtained from the peak position of the XRD profile.
  • the measurement results shown in FIGS. 5 to 8 show that the sulfur chains included in the carbon nanotubes stably maintain a linear structure or a zigzag structure in a temperature range of room temperature to about 500 K in vacuum, that is, this temperature. In the range, it means that the one-dimensional crystal structure is surely maintained. Even when the temperature exceeds 500 K, the linear structure or zigzag concept is maintained in the experimental temperature range, although the interval between sulfur atoms is extended.
  • FIG. 9 shows the result of measuring the distribution of sulfur in the single-walled carbon nanotube.
  • FIG. 9 shows a TEM image of a sulfur-encapsulated single-walled carbon nanotube, a carbon element mapping image at a portion corresponding to the TEM image (near the center of the image), and a sulfur element mapping image.
  • the carbon element mapping image and the sulfur element mapping image are compared, the position where the carbon is present and the position where the sulfur is present completely coincide with each other. This measurement result shows that sulfur is included in the carbon nanotubes at a high filling rate.
  • FIG. 10 shows a double-walled carbon nanotube TEM image containing sulfur, a carbon element mapping image at a portion corresponding to the TEM image, and a sulfur element mapping image. Also in the case of this sample, the carbon position and the sulfur position completely coincide, and it can be seen that sulfur is included in the carbon nanotubes at a high filling rate.
  • FIG. 11 shows an example of an XPS spectrum of sulfur in carbon nanotubes (2s sulfur).
  • the XPS spectrum of carbon (1s carbon) of the carbon nanotube is measured, the ratio of carbon to sulfur is obtained from the area ratio of the peak portion of the spectrum, and the sulfur filling rate is obtained, the sulfur inclusion is obtained.
  • the sulfur filling rate for the single-walled carbon nanotubes was 16 wt%, and the sulfur filling rate for the sulfur-encapsulated double-walled carbon nanotubes was 8.8 wt%.
  • FIGS. 12A and 12B show the results of measuring the sulfur filling rate in the carbon nanotubes by thermogravimetric analysis for sulfur-encapsulated single-walled carbon nanotubes and sulfur-encapsulated double-walled carbon nanotubes.
  • the curve in the graph is the differential spectrum.
  • Sulfur-encapsulated single-walled carbon nanotubes are stable up to 600K in the presence of oxygen, and as shown in FIG. 12 (a), the filling rate of sulfur is 12 wt%, as compared with single-walled carbon nanotubes not containing sulfur.
  • Sulfur-encapsulated double-walled carbon nanotubes are stable up to 900K in the presence of oxygen. From the thermogravimetric analysis of the double-walled carbon nanotubes not containing sulfur, the filling rate of sulfur could not be estimated clearly (FIG. 12 (b)).
  • FIG. 13 (a) is a Raman spectroscopic spectrum for sulfur-encapsulated single-walled carbon nanotubes and single-walled carbon nanotubes not containing sulfur.
  • FIG. 13B is a Raman spectroscopic spectrum for sulfur-encapsulated double-walled carbon nanotubes and double-walled carbon nanotubes not containing sulfur.
  • BWF (Breit-Wigner-Fano) corresponding to a metallic Raman band is increased for carbon nanotubes containing sulfur compared to carbon nanotubes not containing sulfur. is doing. BWF increases when metal contacts carbon nanotubes. That is, since BWF is increasing, it can be seen that the sulfur chain in contact with the carbon nanotube is metalized. Also in the Raman spectroscopic spectrum shown in FIG. 13 (b), the BWF of the double-walled carbon nanotube containing the sulfur chain is increased. That is, it shows that the sulfur chain encapsulated in the double-walled carbon nanotube is metallized. In the double-walled carbon nanotube, the metallized sulfur chain contacts only the inner-layer carbon nanotube. Therefore, the increase rate of BWF as a whole sample is inferior to single-walled carbon nanotubes.
  • FIG. 14 shows the measurement results for single-walled carbon nanotubes.
  • sulfur-encapsulated single-walled carbon nanotubes had a 55% decrease in resistivity compared to single-walled carbon nanotubes that did not contain sulfur.
  • Samples composed of single-walled carbon nanotubes that do not contain sulfur show semiconducting temperature dependence, and the electrical resistivity increases with decreasing temperature, whereas samples made of sulfur-encapsulated single-walled carbon nanotubes are mostly at temperature. There is no dependency.
  • the resistivity decreased by 87%.
  • the reason why the temperature dependence of the sample composed of sulfur-encapsulated single-walled carbon nanotubes is not observed can be explained by considering that the sulfur chains encapsulated in the carbon nanotubes are metallized.
  • the electron conduction path of the sulfur-encapsulated carbon nanotube includes a conduction path in the longitudinal direction of the carbon nanotube, a conduction path in the width direction of the carbon nanotube, and a conduction path in the longitudinal direction of sulfur contained in the carbon nanotube.
  • the above measurement result means that the conduction path by the conductive sulfur encapsulated in the carbon nanotube exhibits the same action as the metallic conduction path.
  • FIG. 15 shows the electrical resistivity of a sheet-like sample made from double-walled carbon nanotubes not containing sulfur and a sheet-like sample made from sulfur-containing double-walled carbon nanotubes over a temperature range of 2 to 300K. The measurement results are shown. Over a temperature range of 2 to 300 K, the resistivity of the sample made of sulfur-encapsulated double-walled carbon nanotubes is lower than that of the sample made of double-walled carbon nanotubes not containing sulfur. At 300K, the resistivity of the sample made of sulfur-encapsulated double-walled carbon nanotubes was reduced by 20% compared to the sample made of double-walled carbon nanotubes not containing sulfur.
  • Sulfur metallization is a phenomenon that occurs under extreme conditions above 90 GPa.
  • the above experimental results suggest that sulfur is metallized by inclusion in carbon nanotubes. If this sulfur is metallized, a novel consisting of sulfur and carbon nanotubes will be suggested.
  • Application development as a conductive material is possible. Sulfur exists in large quantities as a natural resource, but conventionally, it is rarely used as a functional material.
  • the sulfur-encapsulated carbon nanotube according to the present invention greatly opens up its use as a novel conductive material by a combination of sulfur and carbon nanotube.

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Abstract

[Problem] To provide carbon nanotubes provided with a novel structure encapsulating sulfur. [Solution] These carbon nanotubes are obtained by encapsulating a sulfur chain made up of sulfur atoms linked linearly, this sulfur chain takes on a one-dimensional crystal structure of a linear structure or zigzag structure, and excellent conductivity is actualized by metallization. Monolayer carbon nanotubes encapsulating sulfur have excellent conductivity, and sheets having excellent conductivity can be constructed using carbon nanotubes encapsulating sulfur.

Description

カーボンナノチューブ及びその製造方法Carbon nanotube and method for producing the same
　本発明は、硫黄と複合化することにより導電性材料等として利用することができるカーボンナノチューブ及びその製造方法に関する。 The present invention relates to a carbon nanotube that can be used as a conductive material or the like by being combined with sulfur and a method for producing the same.
　単体硫黄は無尽蔵に存在する天然資源であるにもかかわらず、その用途は安価な工業薬品が多く、機能性材料として積極的に有効活用されていない。カーボンナノチューブでは、カーボンナノチューブの中空内に、フラーレンあるいは金属、各種化合物を内包した内包型のカーボンナノチューブが知られている（非特許文献１、特許文献１、２）。カーボンナノチューブと硫黄とを複合化した例としては、二次電池の正極材料に利用する目的でカーボンナノチューブに硫黄化合物を内包した例（特許文献３）、カーボンナノチューブに硫黄を内包した例（非特許文献２）がある。 Despite being an inexhaustible natural resource, elemental sulfur is used for many industrial chemicals and is not actively used as a functional material. As the carbon nanotube, an encapsulated carbon nanotube in which fullerene, metal, or various compounds are encapsulated in the hollow of the carbon nanotube is known (Non-patent Document 1, Patent Documents 1 and 2). Examples of composites of carbon nanotubes and sulfur include an example in which a sulfur compound is included in a carbon nanotube for the purpose of being used as a positive electrode material for a secondary battery (Patent Document 3), and an example in which sulfur is included in a carbon nanotube (non-patent document). There is literature 2).
特開２０１２－４６３９３号公報JP 2012-46393 A 特開２０１１－２４６３３２号公報JP 2011-246332 A 特開２００７－２３４３３８号公報JP 2007-234338 A
　本件発明者は、カーボンナノチューブに硫黄を内包させることにより、カーボンナノチューブの一次元ナノ空間が鋳型として利用し、硫黄が鎖状に配列して収容されること、カーボンナノチューブの中空空間に硫黄が鎖状に収容されることにより、常温、常圧では絶縁体である硫黄が金属化する現象を見出し、本発明に想到した。
　すなわち、本発明は、硫黄を内包させてなる新規な構成及び作用を有するカーボンナノチューブ及びその製造方法を提供することを目的とする。 The inventors have encapsulated sulfur in carbon nanotubes, so that one-dimensional nanospaces of carbon nanotubes are used as templates, and sulfur is arranged and accommodated in a chain, and sulfur is chained in the hollow space of carbon nanotubes. As a result, the present inventors have found a phenomenon in which sulfur as an insulator is metallized at room temperature and normal pressure.
That is, an object of the present invention is to provide a carbon nanotube having a novel configuration and action in which sulfur is included, and a method for producing the carbon nanotube.
　本発明に係るカーボンナノチューブは、硫黄原子が鎖状に連なる硫黄鎖が内包されていることを特徴とする。
　カーボンナノチューブに硫黄を内包させると、硫黄はカーボンナノチューブの１次元ナノ空間にならって鎖状となり、互いに共有結合した硫黄鎖となって内包される。いいかえれば、硫黄は、カーボンナノチューブのナノ空間が鋳型のように作用して一次元結晶となり、これによって硫黄が金属化する。 The carbon nanotube according to the present invention is characterized in that a sulfur chain in which sulfur atoms are linked in a chain shape is included.
When sulfur is included in the carbon nanotubes, the sulfur is chained in accordance with the one-dimensional nanospace of the carbon nanotubes, and is included as sulfur chains covalently bonded to each other. In other words, sulfur is converted into a one-dimensional crystal by the nanospace of carbon nanotubes acting like a template, thereby sulfur is metallized.
　カーボンナノチューブに内包される硫黄原子は、直線構造として内包される場合と、ジグザグ構造となって内包される場合がある。ジグザグ構造で内包される場合も、硫黄鎖は一次元的な構造であり、硫黄原子が一次元的に規則的に配列して内包されることから、本明細書では一次元結晶と称する。
　硫黄鎖が直線構造としてカーボンナノチューブに内包される場合、並列に２つの硫黄鎖が内包される構造となることもある。 The sulfur atoms included in the carbon nanotubes may be included as a linear structure or may be included as a zigzag structure. Even when encapsulated in a zigzag structure, the sulfur chain is a one-dimensional structure, and since sulfur atoms are encapsulated in a one-dimensional regular arrangement, it is referred to as a one-dimensional crystal in this specification.
When the sulfur chain is encapsulated in the carbon nanotube as a linear structure, there may be a structure in which two sulfur chains are encapsulated in parallel.
　硫黄を内包させるカーボンナノチューブは、単層カーボンナノチューブであっても、二層カーボンナノチューブ、または二層以上の多層カーボンナノチューブであってもよい。ただし、導電性を備える硫黄内包カーボンナノチューブとするには、カーボンナノチューブに硫黄を内包させた状態で、硫黄の一次元鎖が形成され、硫黄の一次元結晶が形成される必要がある。硫黄を内包したカーボンナノチューブはとくに導電性に優れるという利点がある。 The carbon nanotube encapsulating sulfur may be a single-walled carbon nanotube, a double-walled carbon nanotube, or a multi-walled carbon nanotube having two or more layers. However, in order to obtain a sulfur-encapsulated carbon nanotube having conductivity, it is necessary that a one-dimensional chain of sulfur is formed in a state where sulfur is encapsulated in the carbon nanotube, and a one-dimensional crystal of sulfur is formed. Carbon nanotubes containing sulfur are particularly advantageous in that they have excellent conductivity.
　硫黄を内包して導電性を備える硫黄の一次元鎖を形成するカーボンナノチューブとしては、中空部分の径（内径）が0.4～2.0ｎｍ程度のものが使用でき、好適には中空部分の径が0.8～1.5ｎｍのものが使用できる。硫黄原子のサイズは0.4nm程度であるから、カーボンナノチューブの中空部分の径は0.4nm以上である必要があり、カーボンナノチューブの径が2.0nm以上の場合は、常温・常圧下で形成される硫黄の構造（S8）が形成されるからカーボンナノチューブの中空部分の径は2.0nm以下である必要がある。
　実験では、単層カーボンナノチューブと二層カーボンナノチューブに硫黄を内包させ、カーボンナノチューブの中空部分に硫黄が一次元結晶として内包されることを確かめた。 As the carbon nanotubes that form a one-dimensional sulfur-containing chain containing sulfur, those having a hollow portion diameter (inner diameter) of about 0.4 to 2.0 nm can be used, and preferably the hollow portion diameter is 0.8. Those up to 1.5 nm can be used. Since the size of the sulfur atom is about 0.4 nm, the diameter of the hollow portion of the carbon nanotube needs to be 0.4 nm or more. When the diameter of the carbon nanotube is 2.0 nm or more, sulfur formed at normal temperature and normal pressure the diameter of the hollow portion of the carbon nanotube from the structure (S 8) is formed of or less is required 2.0 nm.
In the experiment, sulfur was encapsulated in single-walled carbon nanotubes and double-walled carbon nanotubes, and it was confirmed that sulfur was encapsulated as a one-dimensional crystal in the hollow part of carbon nanotubes.
　硫黄鎖が内包されたカーボンナノチューブは導電性に優れている。したがって、硫黄を内包したカーボンナノチューブを含むシート体は、導電性材料として好適に利用することができる。
　このシート体を構成する硫黄内包カーボンナノチューブとしては、直線構造となる硫黄鎖が内包されたカーボンナノチューブ、並列に２つの直線構造となる硫黄鎖が内包されたカーボンナノチューブ、ジグザグ構造となる硫黄鎖が内包されたカーボンナノチューブが使用できる。カーボンナノチューブには単層、二層、多層カーボンナノチューブが使用できるが、単層カーボンナノチューブを使用した場合にとくに導電性に優れたものとなる。 Carbon nanotubes in which sulfur chains are encapsulated are excellent in conductivity. Therefore, the sheet body containing carbon nanotubes containing sulfur can be suitably used as a conductive material.
The sulfur-encapsulated carbon nanotubes constituting this sheet include carbon nanotubes encapsulating a linear sulfur chain, carbon nanotubes encapsulating two linear sulfur chains in parallel, and a zigzag sulfur chain. Encapsulated carbon nanotubes can be used. Single-walled, double-walled, and multi-walled carbon nanotubes can be used as the carbon nanotubes. However, when single-walled carbon nanotubes are used, the carbon nanotubes have excellent conductivity.
　硫黄を内包したカーボンナノチューブの製造方法としては、カーボンナノチューブと硫黄とを密封容器に収容し、容器を真空密封する工程と、前記真空密封した容器を718K以上の温度に加熱してカーボンナノチューブに硫黄を内包させる工程と、カーボンナノチューブに硫黄を内包させた後、カーボンナノチューブの外面に付着した硫黄を除去する精製工程と、を備える製造方法が好適に利用できる。
　前記精製工程においては、硫黄を内包させる工程により得られたカーボンナノチューブを二硫化炭素に加え、超音波照射してカーボンナノチューブの分散液を調製し、このカーボンナノチューブの分散液を濾過する工程を備えることを特徴とする。 As a method for producing carbon nanotubes containing sulfur, a carbon nanotube and sulfur are accommodated in a sealed container, the container is vacuum-sealed, and the vacuum-sealed container is heated to a temperature of 718 K or higher to form sulfur in the carbon nanotube. A manufacturing method comprising a step of encapsulating and a purification step of removing sulfur adhering to the outer surface of the carbon nanotube after encapsulating sulfur in the carbon nanotube can be suitably used.
The purification step includes a step of adding carbon nanotubes obtained in the step of encapsulating sulfur to carbon disulfide, preparing a dispersion of carbon nanotubes by ultrasonic irradiation, and filtering the dispersion of carbon nanotubes. It is characterized by that.
　本発明に係るカーボンナノチューブは、カーボンナノチューブに硫黄が鎖状に内包されることにより硫黄鎖が金属化され、カーボンナノチューブと硫黄とが複合化された導電性材料として利用することができ、カーボンナノチューブと硫黄の用途を拡大することができる。 The carbon nanotube according to the present invention can be utilized as a conductive material in which sulfur chains are metallized by inclusion of sulfur in the carbon nanotubes in a chain shape, and the carbon nanotubes and sulfur are combined. And the use of sulfur can be expanded.
硫黄を内包した単層カーボンナノチューブと二層カーボンナノチューブのTEM像である。It is a TEM image of the single-walled carbon nanotube and the double-walled carbon nanotube which included sulfur. 硫黄を内包した単層カーボンナノチューブと二層カーボンナノチューブについて、その長手方向と長手方向に直交する方向についてのTEM画像の強度を示すグラフである。It is a graph which shows the intensity | strength of the TEM image about the direction orthogonal to the longitudinal direction and the longitudinal direction about the single-walled carbon nanotube and the double-walled carbon nanotube which included sulfur. 硫黄を内包した単層カーボンナノチューブと二層カーボンナノチューブについてのX線回折パターンを示すグラフである。It is a graph which shows the X-ray-diffraction pattern about the single-walled carbon nanotube and the double-walled carbon nanotube which included sulfur. XRDプロファイルの一つのピークを示すグラフである。It is a graph which shows one peak of an XRD profile. 直線構造に硫黄が内包された単層カーボンナノチューブと二層カーボンナノチューブについて、サンプル温度を変えたときのX線回折パターンの挙動を示すグラフである。It is a graph which shows the behavior of the X-ray diffraction pattern when the sample temperature is changed about the single-walled carbon nanotube and the double-walled carbon nanotube in which sulfur is included in the linear structure. サンプル温度を変えたときの硫黄の間隔の変化を示すグラフである。It is a graph which shows the change of the space | interval of sulfur when changing sample temperature. ジグザグ構造に硫黄が内包された単層カーボンナノチューブと二層カーボンナノチューブについて、サンプル温度を変えたときのX線改選パターンの挙動を示すグラフである。It is a graph which shows the behavior of the X-ray refining pattern when the sample temperature is changed about the single-walled carbon nanotube and the double-walled carbon nanotube in which sulfur is included in the zigzag structure. サンプル温度を変えたときの硫黄の間隔の変化を示すグラフである。It is a graph which shows the change of the space | interval of sulfur when changing sample temperature. 硫黄内包単層カーボンナノチューブの炭素元素マッピング像と、硫黄元素マッピング像である。It is a carbon element mapping image of a sulfur inclusion single-walled carbon nanotube, and a sulfur element mapping image. 硫黄内包二層カーボンナノチューブの炭素元素マッピング像と、硫黄元素マッピング像である。It is a carbon element mapping image of a sulfur inclusion double-walled carbon nanotube, and a sulfur element mapping image. カーボンナノチューブ中における硫黄のXPSスペクトルである。2 is an XPS spectrum of sulfur in a carbon nanotube. 硫黄内包単層カーボンナノチューブと硫黄内包二層カーボンナノチューブについて、熱重量分析法による分析結果を示すグラフである。It is a graph which shows the analysis result by a thermogravimetric analysis about a sulfur inclusion single-walled carbon nanotube and a sulfur inclusion double-walled carbon nanotube. 硫黄内包カーボンナノチューブと硫黄を内包していないカーボンナノチューブについてのラマン分光スペクトルである。It is a Raman spectroscopic spectrum about a sulfur inclusion carbon nanotube and a carbon nanotube which does not contain sulfur. 硫黄を内包していない単層カーボンナノチューブと硫黄を内包した単層カーボンナノチューブから作製したシート体について電気抵抗率の温度変化を測定した結果を示すグラフである。It is a graph which shows the result of having measured the temperature change of the electrical resistivity about the sheet | seat body produced from the single wall carbon nanotube which does not include sulfur, and the single wall carbon nanotube which included sulfur. 硫黄を内包していない二層カーボンナノチューブと硫黄を内包した二層カーボンナノチューブから作製したシート体について電気抵抗率の温度変化を測定した結果を示すグラフである。It is a graph which shows the result of having measured the temperature change of the electrical resistivity about the sheet | seat body produced from the double-walled carbon nanotube which included sulfur and the double-walled carbon nanotube which included sulfur.
（硫黄内包カーボンナノチューブの製法）
　カーボンナノチューブの中空空間内に硫黄が鎖状に収容されたカーボンナノチューブは下記の方法により作製した。
　カーボンナノチューブには、単層カーボンナノチューブ（SWCNT)と、二層カーボンナノチューブ（DWCNT)を使用した。 (Production of sulfur-encapsulated carbon nanotubes)
A carbon nanotube in which sulfur was accommodated in a chain shape in the hollow space of the carbon nanotube was produced by the following method.
Single-walled carbon nanotubes (SWCNT) and double-walled carbon nanotubes (DWCNT) were used as the carbon nanotubes.
　まず、カーボンナノチューブの開端処理を行う。
　単層カーボンナノチューブと二層カーボンナノチューブを、ガスが流通するガラス管に封入し、100ml/minの速度で酸素ガス流通させながら、723Kで1時間の開端処理を行う。なお、カーボンナノチューブの開端処理としては、塩酸や硝酸などを用いる酸処理や、超音波処理がある。酸素ガスを用いる開端処理は、開端処理が効率的に行えることと、温度、ガス流速といった制御が容易な方法を利用することで、的確に開端処理が行えるという利点がある。市販品のカーボンナノチューブには開端されているものもあるが、開端処理を行うことで開端率が向上し、硫黄を内包させやすくすることができる。 First, a carbon nanotube open end treatment is performed.
Single-walled carbon nanotubes and double-walled carbon nanotubes are sealed in a glass tube through which gas flows, and an end-opening treatment is performed at 723 K for 1 hour while flowing oxygen gas at a rate of 100 ml / min. Examples of the carbon nanotube open end treatment include acid treatment using hydrochloric acid and nitric acid, and ultrasonic treatment. The open-end process using oxygen gas has the advantage that the open-end process can be efficiently performed and that the open-end process can be performed accurately by using a method that is easy to control such as temperature and gas flow rate. Some commercially available carbon nanotubes are open-ended, but the open-end treatment improves the open-end rate and makes it easier to enclose sulfur.
　開端処理をしたカーボンナノチューブに硫黄を内包させる処理は、次のようにして行った。
　開端処理した単層カーボンナノチューブ10mgと、硫黄（99.9999％）30mgとをガラス管に入れ、真空封止（真空密封する工程）する。次いで、電気炉中で873Ｋ、48時間保持することにより、硫黄を内包したカーボンナノチューブを調製（カーボンナノチューブに硫黄を内包させる工程）した。
　同様に、開端処理した二層カーボンナノチューブ10mgと、硫黄（99.9999％）30mgとをガラス管に入れ、真空封止した後、電気炉中で873Ｋ、48時間保持することにより、硫黄を内包したカーボンナノチューブを調製した。 The treatment for encapsulating sulfur in the carbon nanotubes subjected to the open end treatment was performed as follows.
10 mg of the single-walled carbon nanotube subjected to the open end treatment and 30 mg of sulfur (99.9999%) are put into a glass tube and vacuum sealed (step of vacuum sealing). Subsequently, the carbon nanotube which included sulfur was prepared by hold | maintaining for 48 hours at 873 K in an electric furnace (the process of including sulfur in a carbon nanotube).
Similarly, 10 mg of open-walled double-walled carbon nanotubes and 30 mg of sulfur (99.9999%) are placed in a glass tube, vacuum-sealed, and kept in an electric furnace at 873 K for 48 hours, thereby carbon containing sulfur. Nanotubes were prepared.
　上記方法により調製したサンプルを二硫化炭素に加え、超音波照射してカーボンナノチューブの分散液を得た。分散液はカーボンナノチューブから分離された硫黄と硫黄を内包したカーボンナノチューブを含む。この分散液を濾過することで、シート状の硫黄を内包したカーボンナノチューブを得る。この工程を３回、繰り返し行った後、室温・真空下で1時間以上保持することで不要な二硫化炭素を除去し（精製工程）、精製後の硫黄を内包したカーボンナノチューブを得た。得られた試料は、シート状のものである。
　カーボンナノチューブを二硫化炭素で洗浄する目的は、カーボンナノチューブの外面に付着した硫黄（常温・常圧でみられる硫黄S8）を除去するためである。超音波処理することにより、カーボンナノチューブバンドルの隙間に入り込んだ硫黄を除去することができる。カーボンナノチューブのバンドル間に存在する硫黄は電気抵抗率を上昇させるように作用する。 The sample prepared by the above method was added to carbon disulfide and subjected to ultrasonic irradiation to obtain a carbon nanotube dispersion. The dispersion contains sulfur separated from carbon nanotubes and carbon nanotubes containing sulfur. By filtering this dispersion, a carbon nanotube containing sheet-like sulfur is obtained. After repeating this process three times, unnecessary carbon disulfide was removed by maintaining at room temperature and under vacuum for 1 hour or longer (purification process), and carbon nanotubes containing sulfur after purification were obtained. The obtained sample is a sheet.
The purpose of washing the carbon nanotubes with carbon disulfide is to remove sulfur adhering to the outer surface of the carbon nanotubes (sulfur S 8 found at room temperature and normal pressure). By ultrasonic treatment, sulfur that has entered the gaps between the carbon nanotube bundles can be removed. Sulfur present between the bundles of carbon nanotubes acts to increase the electrical resistivity.
（TEM像観察）
　図１（a）、（b）、（c）は、硫黄を内包した単層カーボンナノチューブのTEM像である。図１（a）から、単層カーボンナノチューブの中空空間内に、カーボンナノチューブの長手方向に沿って硫黄が２本の鎖状に並んでいることがわかる。２本の硫黄鎖はそれぞれ一次元結晶状に直線的に配列している。２本の硫黄鎖の硫黄原子間の間隔は0.32nmである。この硫黄を内包したカーボンナノチューブは、カーボンナノチューブの中空空間である一次元ナノ空間が鋳型のように作用することにより、硫黄の一次元結晶が構成されたものである。図１（a）のカーボンナノチューブの内径は1.1nmである。 (TEM image observation)
1A, 1B, and 1C are TEM images of single-walled carbon nanotubes containing sulfur. FIG. 1 (a) shows that sulfur is arranged in two chains along the longitudinal direction of the carbon nanotubes in the hollow space of the single-walled carbon nanotubes. Each of the two sulfur chains is linearly arranged in a one-dimensional crystal form. The distance between the sulfur atoms of the two sulfur chains is 0.32 nm. The carbon nanotube encapsulating sulfur is a one-dimensional crystal of sulfur formed by a one-dimensional nanospace, which is a hollow space of the carbon nanotube, acting like a template. The inner diameter of the carbon nanotube in FIG. 1 (a) is 1.1 nm.
　図１（b）、（c）は、硫黄を内包した二層カーボンナノチューブのTEM像である。図１（b）は、カーボンナノチューブの中空空間内にジグザグの鎖状に硫黄鎖が内包されていることを示す。図１（c）は、硫黄鎖が直線構造として内包されていることを示す。
　図１（b）に示すカーボンナノチューブの内径は0.68nm、図１（c）に示すカーボンナノチューブの内径は0.60nmである。
　このように、カーボンナノチューブに硫黄を内包させると、硫黄はジグザグ型の鎖状となったり、直線型の鎖状となったりする。二層カーボンナノチューブに硫黄を内包させたものは、TEM観察時に内包物質がダメージを受けにくく、内包された硫黄の構造が見やすくなる。 FIGS. 1B and 1C are TEM images of double-walled carbon nanotubes containing sulfur. FIG. 1B shows that sulfur chains are encapsulated in a zigzag chain in the hollow space of the carbon nanotube. FIG.1 (c) shows that the sulfur chain is included as a linear structure.
The inner diameter of the carbon nanotube shown in FIG. 1 (b) is 0.68 nm, and the inner diameter of the carbon nanotube shown in FIG. 1 (c) is 0.60 nm.
In this way, when sulfur is included in the carbon nanotube, the sulfur becomes a zigzag chain or a linear chain. When a double-walled carbon nanotube is encapsulated with sulfur, the encapsulated material is less likely to be damaged during TEM observation, and the structure of the encapsulated sulfur is easy to see.
　図２（a）、（b）は、図１（b）、（c）に示したサンプルについて、カーボンナノチューブの長手方向と、長手方向に直交する方向について、TEM画像の強度を分析した結果を示す。図２（a）に示す、ジグザグ配置となっている硫黄鎖の一方側の硫黄原子の間隔は0.33±0.03nmである。図２（b）に示す、直線構造となる硫黄鎖の硫黄原子の間隔は0.18±0.02nmである。 2 (a) and 2 (b) show the results of analyzing the intensity of the TEM image for the sample shown in FIGS. 1 (b) and 1 (c) in the longitudinal direction of the carbon nanotube and the direction perpendicular to the longitudinal direction. Show. The interval between the sulfur atoms on one side of the sulfur chain in zigzag configuration shown in FIG. 2 (a) is 0.33 ± 0.03 nm. As shown in FIG. 2B, the interval between the sulfur atoms of the sulfur chain having a linear structure is 0.18 ± 0.02 nm.
（XRD解析）
　図３に、硫黄を内包した単層カーボンナノチューブと、硫黄を内包した二層カーボンナノチューブについてのX線回折パターンを示す。図３には、比較のため、硫黄を内包していない（empty)単層カーボンナノチューブと二層カーボンナノチューブについての測定結果をあわせて示した。
　単層カーボンナノチューブと二層カーボンナノチューブのプロファイルに表れているピークは、カーボンナノチューブの中空空間内において硫黄が規則的に配列した状態で内包されていることを示す。 (XRD analysis)
FIG. 3 shows X-ray diffraction patterns for single-walled carbon nanotubes containing sulfur and double-walled carbon nanotubes containing sulfur. For comparison, FIG. 3 also shows the measurement results for single-walled carbon nanotubes that do not contain sulfur (empty) and double-walled carbon nanotubes.
The peaks appearing in the profiles of single-walled carbon nanotubes and double-walled carbon nanotubes indicate that sulfur is contained in a regularly arranged state in the hollow space of the carbon nanotubes.
　図３に、内包された硫黄の配列形態と、その配列における硫黄の間隔に対応するピークを例示する。グラフ中に複数のピークが表れているのは、X線回折パターンの測定に使用したサンプル中に、内径が異なるカーボンナノチューブが混在しているためで、カーボンナノチューブに内包されている硫黄原子の間隔（結晶間隔）が異なるものが存在することによる。図３の単層カーボンナノチューブのプロファイルに示すように、硫黄内包単層カーボンナノチューブの場合もジグザグ型に硫黄が内包される場合もある。 FIG. 3 exemplifies the arrangement form of the contained sulfur and the peak corresponding to the sulfur interval in the arrangement. Multiple peaks appear in the graph because the sample used to measure the X-ray diffraction pattern contains carbon nanotubes with different inner diameters, and the spacing between the sulfur atoms contained in the carbon nanotubes. This is due to the existence of different (crystal spacing). As shown in the profile of the single-walled carbon nanotube in FIG. 3, sulfur may be included in a zigzag type in the case of sulfur-encapsulated single-walled carbon nanotubes.
　図３に示すXRDプロファイルは、一次元結晶に特有の非対称なプロファイルを示す。図４は、XRDプロファイルの一つのピークを拡大して示した例で、ピーク形状が非対称、すなわちカーボンナノチューブに内包された硫黄が一次元構造を備えることを示す。
　回折ピークの半値幅（ΔQ)から、カーボンナノチューブに内包された硫黄鎖のドメインサイズ（ξ＝2π/ΔQ)を見積もることができる。XRDプロファイルから、硫黄内包単層カーボンナノチューブにおける硫黄鎖のドメインサイズは35～45nm、硫黄内包二層カーボンナノチューブにおける硫黄鎖のドメインサイズは90～160nmであった。
　硫黄を内包したカーボンナノチューブの中空空間内では、硫黄は共有結合により鎖状構造を保持していると考えられる。上記ドメインサイズから、カーボンナノチューブに内包された硫黄は、硫黄原子が少なくとも数十個から数百個単位で並んだ、非常に長い、直線構造あるいはジグザグ構造の一次元結晶構造を構成すると考えられる。 The XRD profile shown in FIG. 3 shows an asymmetric profile unique to a one-dimensional crystal. FIG. 4 is an example of an enlarged view of one peak of the XRD profile, and shows that the peak shape is asymmetric, that is, sulfur encapsulated in the carbon nanotube has a one-dimensional structure.
From the half width (ΔQ) of the diffraction peak, the domain size (ξ = 2π / ΔQ) of the sulfur chain encapsulated in the carbon nanotube can be estimated. From the XRD profile, the sulfur chain domain size in the sulfur-encapsulated single-walled carbon nanotubes was 35 to 45 nm, and the sulfur chain domain size in the sulfur-encapsulated double-walled carbon nanotubes was 90 to 160 nm.
In the hollow space of the carbon nanotube encapsulating sulfur, it is considered that sulfur holds a chain structure by a covalent bond. From the above domain size, it is considered that sulfur encapsulated in carbon nanotubes constitutes a very long linear structure or one-dimensional crystal structure of zigzag structure in which sulfur atoms are arranged in units of several tens to several hundreds.
（熱的安定性）
　サンプルの温度を変えたときのXRDプロファイルから、カーボンナノチューブに内包された硫黄の規則的配列（結晶性構造）の熱的安定性を調べた。
　図５（a）、（b）は、硫黄鎖が直線状に内包された単層カーボンナノチューブと二層カーボンナノチューブについて、サンプル温度を300～800Kの範囲で変えて測定したX線回折パターンの特定のピーク（直線構造に対応する）についての挙動を示している。 (Thermal stability)
From the XRD profile when the temperature of the sample was changed, the thermal stability of the regular arrangement (crystalline structure) of sulfur contained in the carbon nanotube was investigated.
Figures 5 (a) and 5 (b) show the X-ray diffraction patterns measured for single-walled carbon nanotubes and double-walled carbon nanotubes in which sulfur chains are encapsulated in a straight line, with the sample temperature varied in the range of 300 to 800K. The behavior of the peak (corresponding to the linear structure) is shown.
　図６は、サンプル温度を変えたときのXRDプロファイルのピーク位置から求めた、直線構造の硫黄鎖の硫黄原子間距離ｄを示す。単層カーボンナノチューブに内包された硫黄鎖については、300～800Kの温度範囲において、安定的に規則的配列を保持している。また、二層カーボンナノチューブに内包された硫黄鎖については、室温から500Kまでは安定的に直線構造を保持しているが、500Kを超えると大きなピークシフトが表れる。これは、500K程度温度以上に加熱すると、直線構造に由来する硫黄原子の間隔が伸びることを示す。 FIG. 6 shows a distance d between sulfur atoms of a linear sulfur chain obtained from the peak position of the XRD profile when the sample temperature is changed. The sulfur chains encapsulated in the single-walled carbon nanotubes stably maintain a regular arrangement in the temperature range of 300 to 800K. In addition, the sulfur chains encapsulated in the double-walled carbon nanotubes stably maintain a linear structure from room temperature to 500K, but a large peak shift appears above 500K. This indicates that when heated to about 500K or higher, the interval between sulfur atoms derived from the linear structure is extended.
　図７（a）、（b）は、同様に、硫黄鎖がジグザグ構造に内容された単層カーボンナノチューブと二層カーボンナノチューブについて、サンプル温度を300～800Kの範囲で変えて測定したX線回折パターンの特定のピーク（ジグザグ構造に対応する）の挙動を示す。
　図８は、XRDプロファイルのピーク位置から求めた、硫黄の配列間隔ｄを示す。硫黄鎖がジグザグ構造に内包された場合も、直線構造に内包された場合と同様に、単層カーボンナノチューブに内包された硫黄鎖については、300～800Kの温度範囲において安定的にジグザグ構造を保持し、二層カーボンナノチューブに内包された硫黄鎖については、室温から500Kまでは安定的にジグザグ構造を保持する一方、500Kを超えると硫黄原子の間隔が伸びることを示している。 FIGS. 7 (a) and 7 (b) show X-ray diffraction similarly measured for single-walled carbon nanotubes and double-walled carbon nanotubes containing sulfur chains in a zigzag structure at sample temperatures ranging from 300 to 800K. The behavior of specific peaks of the pattern (corresponding to the zigzag structure) is shown.
FIG. 8 shows the arrangement interval d of sulfur obtained from the peak position of the XRD profile. When the sulfur chain is encapsulated in the zigzag structure, the sulfur chain encapsulated in the single-walled carbon nanotubes stably maintains the zigzag structure in the temperature range of 300 to 800K, as in the case of the encapsulated structure. In addition, the sulfur chains encapsulated in the double-walled carbon nanotubes stably maintain a zigzag structure from room temperature to 500K, while the interval between sulfur atoms increases when the temperature exceeds 500K.
　図５～８に示した測定結果は、カーボンナノチューブに内包された硫黄鎖は、真空中において、室温～500K程度の温度範囲において、安定的に直線構造あるいはジグザグ構造を保持すること、すなわちこの温度範囲においては、確実に一次元結晶構造を保持することを意味する。なお、500Kを超えた場合であっても、実験温度範囲においては、硫黄原子の間隔は伸びるものの、直線構造あるいはジグザグ構想は保持している。 The measurement results shown in FIGS. 5 to 8 show that the sulfur chains included in the carbon nanotubes stably maintain a linear structure or a zigzag structure in a temperature range of room temperature to about 500 K in vacuum, that is, this temperature. In the range, it means that the one-dimensional crystal structure is surely maintained. Even when the temperature exceeds 500 K, the linear structure or zigzag concept is maintained in the experimental temperature range, although the interval between sulfur atoms is extended.
（カーボンナノチューブ内の硫黄分布）
　図９は、単層カーボンナノチューブ内の硫黄の分布を測定した結果を示す。図９では、硫黄内包単層カーボンナノチューブのTEM像と、TEM像に該当する部位（像の中心付近）における炭素元素マッピング像と、硫黄元素マッピング像を示す。
　炭素元素マッピング像と硫黄元素マッピング像とを対比してみると、炭素が存在する位置と硫黄が存在する位置とが完全に一致している。この測定結果は、カーボンナノチューブ内に硫黄が高い充填率で内包されていることを示す。 (Sulfur distribution in carbon nanotubes)
FIG. 9 shows the result of measuring the distribution of sulfur in the single-walled carbon nanotube. FIG. 9 shows a TEM image of a sulfur-encapsulated single-walled carbon nanotube, a carbon element mapping image at a portion corresponding to the TEM image (near the center of the image), and a sulfur element mapping image.
When the carbon element mapping image and the sulfur element mapping image are compared, the position where the carbon is present and the position where the sulfur is present completely coincide with each other. This measurement result shows that sulfur is included in the carbon nanotubes at a high filling rate.
　図１０は、硫黄を内包した二層カーボンナノチューブTEM像と、TEM像に該当する部位における炭素元素マッピング像と、硫黄元素マッピング像を示す。このサンプルの場合も、炭素位置と硫黄位置とが完全に一致し、カーボンナノチューブ内に硫黄が高い充填率で内包されていることがわかる。 FIG. 10 shows a double-walled carbon nanotube TEM image containing sulfur, a carbon element mapping image at a portion corresponding to the TEM image, and a sulfur element mapping image. Also in the case of this sample, the carbon position and the sulfur position completely coincide, and it can be seen that sulfur is included in the carbon nanotubes at a high filling rate.
　図１１は、カーボンナノチューブ中における硫黄のXPSスペクトル（2ｓの硫黄）の例を示す。同様に、カーボンナノチューブの炭素（1ｓの炭素）のXPSスペクトルを計測し、スペクトルのピーク部分の面積比から、炭素と硫黄の比率を求め、カーボンナノチューブ中の硫黄の充填率を求めると、硫黄内包単層カーボンナノチューブについての硫黄充填率は16wt%、硫黄内包二層カーボンナノチューブについての硫黄充填率は8.8wt%であった。 FIG. 11 shows an example of an XPS spectrum of sulfur in carbon nanotubes (2s sulfur). Similarly, when the XPS spectrum of carbon (1s carbon) of the carbon nanotube is measured, the ratio of carbon to sulfur is obtained from the area ratio of the peak portion of the spectrum, and the sulfur filling rate is obtained, the sulfur inclusion is obtained. The sulfur filling rate for the single-walled carbon nanotubes was 16 wt%, and the sulfur filling rate for the sulfur-encapsulated double-walled carbon nanotubes was 8.8 wt%.
　図１２（a）、（b）は、硫黄内包単層カーボンナノチューブと、硫黄内包二層カーボンナノチューブについて、熱重量分析法により、カーボンナノチューブ中における硫黄の充填率を測定した結果を示す。燃焼条件はHe:O２＝8：2である。
　グラフ内のカーブは微分スペクトルである。硫黄内包単層カーボンナノチューブは酸素存在下において600Kまで安定であり、図１２（a）に示すように、硫黄を内包しない単層カーボンナノチューブとの比較から、硫黄の充填率は12wt%となる。
　硫黄内包二層カーボンナノチューブは酸素存在下においては、900Kまで安定である。硫黄を内包しない二層カーボンナノチューブについての熱重量分析からは硫黄の充填率は明確に見積もることができなかった（図１２（b））。 FIGS. 12A and 12B show the results of measuring the sulfur filling rate in the carbon nanotubes by thermogravimetric analysis for sulfur-encapsulated single-walled carbon nanotubes and sulfur-encapsulated double-walled carbon nanotubes. The combustion condition is He: O 2 = 8: 2.
The curve in the graph is the differential spectrum. Sulfur-encapsulated single-walled carbon nanotubes are stable up to 600K in the presence of oxygen, and as shown in FIG. 12 (a), the filling rate of sulfur is 12 wt%, as compared with single-walled carbon nanotubes not containing sulfur.
Sulfur-encapsulated double-walled carbon nanotubes are stable up to 900K in the presence of oxygen. From the thermogravimetric analysis of the double-walled carbon nanotubes not containing sulfur, the filling rate of sulfur could not be estimated clearly (FIG. 12 (b)).
（硫黄鎖の金属化）
　硫黄内包カーボンナノチューブの硫黄鎖の金属性を確かめるため、ラマン分光測定を行った。図１３（a）は、硫黄内包単層カーボンナノチューブと硫黄を内包していない単層カーボンナノチューブについてのラマン分光スペクトルである。図１３（b）は、硫黄内包二層カーボンナノチューブと硫黄を内包していない二層カーボンナノチューブについてのラマン分光スペクトルである。 (Sulfur chain metallization)
In order to confirm the metallic nature of the sulfur chain of the sulfur-encapsulated carbon nanotube, Raman spectroscopic measurement was performed. FIG. 13 (a) is a Raman spectroscopic spectrum for sulfur-encapsulated single-walled carbon nanotubes and single-walled carbon nanotubes not containing sulfur. FIG. 13B is a Raman spectroscopic spectrum for sulfur-encapsulated double-walled carbon nanotubes and double-walled carbon nanotubes not containing sulfur.
　図１３（a）に示すラマン分光スペクトルでは、硫黄を内包していないカーボンナノチューブに比べて、硫黄を内包したカーボンナノチューブについては金属的なラマンバンドに相当するBWF(Breit-Wigner-Fano)が増大している。カーボンナノチューブに金属が接触するとBWFが増大する。すなわち、BWFが増大していることから、カーボンナノチューブに接触している硫黄鎖が金属化されていることがわかる。
　図１３（b）に示すラマン分光スペクトルにおいても、硫黄鎖を内包した二層カーボンナノチューブのBWFが増大している。すなわち、二層カーボンナノチューブに内包された硫黄鎖が金属化されたことを示す。なお、二層カーボンナノチューブでは、金属化した硫黄鎖は内層のカーボンナノチューブのみに接触する。したがって、サンプル全体としてのBWFの増加率は、単層のカーボンナノチューブよりも劣っている。 In the Raman spectroscopic spectrum shown in FIG. 13 (a), BWF (Breit-Wigner-Fano) corresponding to a metallic Raman band is increased for carbon nanotubes containing sulfur compared to carbon nanotubes not containing sulfur. is doing. BWF increases when metal contacts carbon nanotubes. That is, since BWF is increasing, it can be seen that the sulfur chain in contact with the carbon nanotube is metalized.
Also in the Raman spectroscopic spectrum shown in FIG. 13 (b), the BWF of the double-walled carbon nanotube containing the sulfur chain is increased. That is, it shows that the sulfur chain encapsulated in the double-walled carbon nanotube is metallized. In the double-walled carbon nanotube, the metallized sulfur chain contacts only the inner-layer carbon nanotube. Therefore, the increase rate of BWF as a whole sample is inferior to single-walled carbon nanotubes.
（電気抵抗率の測定）
　硫黄を内包していない単層カーボンナノチューブから作製したシート状のサンプルと、硫黄を内包した単層カーボンナノチューブから作製したシート状のサンプルについて、2～300Kの温度範囲にわたり、４端子法により電気抵抗率を測定した。
　図１４は、単層カーボンナノチューブについての測定結果を示す。300Kにおいては、硫黄内包単層カーボンナノチューブは、硫黄を内包していない単層カーボンナノチューブと比較して抵抗率が55％減少した。
　硫黄を内包していない単層カーボンナノチューブからなるサンプルは、半導体的温度依存性を示し、低温になるとともに電気抵抗率が増大するのに対して、硫黄内包単層カーボンナノチューブからなるサンプルはほとんど温度依存性がみられない。2Kにおいては抵抗率が87％減少した。 (Measurement of electrical resistivity)
Electric resistance of sheet-like samples made from single-walled carbon nanotubes not containing sulfur and sheet-like samples made from single-walled carbon nanotubes containing sulfur over a temperature range of 2 to 300K by the 4-terminal method The rate was measured.
FIG. 14 shows the measurement results for single-walled carbon nanotubes. At 300K, sulfur-encapsulated single-walled carbon nanotubes had a 55% decrease in resistivity compared to single-walled carbon nanotubes that did not contain sulfur.
Samples composed of single-walled carbon nanotubes that do not contain sulfur show semiconducting temperature dependence, and the electrical resistivity increases with decreasing temperature, whereas samples made of sulfur-encapsulated single-walled carbon nanotubes are mostly at temperature. There is no dependency. At 2K, the resistivity decreased by 87%.
　硫黄内包単層カーボンナノチューブからなるサンプルについて温度依存性がみられない理由は、カーボンナノチューブに内包された硫黄鎖が金属化したと考えることによって説明できる。
　硫黄内包カーボンナノチューブの電子伝導パスとしては、カーボンナノチューブの長手方向への伝導パス、カーボンナノチューブの幅方向への伝導パス、カーボンナノチューブに内包された硫黄の長手方向への伝導パスがある。上記測定結果は、カーボンナノチューブに内包された導電性硫黄による伝導パスが金属的な伝導パスと同様の作用を示すことを意味する。 The reason why the temperature dependence of the sample composed of sulfur-encapsulated single-walled carbon nanotubes is not observed can be explained by considering that the sulfur chains encapsulated in the carbon nanotubes are metallized.
The electron conduction path of the sulfur-encapsulated carbon nanotube includes a conduction path in the longitudinal direction of the carbon nanotube, a conduction path in the width direction of the carbon nanotube, and a conduction path in the longitudinal direction of sulfur contained in the carbon nanotube. The above measurement result means that the conduction path by the conductive sulfur encapsulated in the carbon nanotube exhibits the same action as the metallic conduction path.
　図１５は、硫黄を内包していない二層カーボンナノチューブから作製したシート状のサンプルと、硫黄内包二層カーボンナノチューブから作製したシート状のサンプルについて、2～300Kの温度範囲にわたり、電気抵抗率を測定した結果を示す。
　2～300Kの温度範囲にわたり、硫黄内包二層カーボンナノチューブからなるサンプルの抵抗率は、硫黄を内包していない二層カーボンナノチューブからなるサンプルと比較して抵抗率が減少している。300Kにおいては、硫黄内包二層カーボンナノチューブからなるサンプルの抵抗率は、硫黄を内包していない二層カーボンナノチューブからなるサンプルに比較して20％減少した。 FIG. 15 shows the electrical resistivity of a sheet-like sample made from double-walled carbon nanotubes not containing sulfur and a sheet-like sample made from sulfur-containing double-walled carbon nanotubes over a temperature range of 2 to 300K. The measurement results are shown.
Over a temperature range of 2 to 300 K, the resistivity of the sample made of sulfur-encapsulated double-walled carbon nanotubes is lower than that of the sample made of double-walled carbon nanotubes not containing sulfur. At 300K, the resistivity of the sample made of sulfur-encapsulated double-walled carbon nanotubes was reduced by 20% compared to the sample made of double-walled carbon nanotubes not containing sulfur.
　硫黄内包二層カーボンナノチューブの場合も、測定温度2～300Kにおいて電気抵抗率が低下している理由は、カーボンナノチューブに内包された硫黄鎖が金属化していることによると考えられる。ただし、二層カーボンナノチューブの場合は、金属化した硫黄鎖と物理的に相互作用するのは、内層のカーボンナノチューブであるため、硫黄内包による電気抵抗率の温度依存性の変化量は単層カーボンナノチューブの場合にみられたほどには顕著にあらわれない。これは、二層カーボンナノチューブの外層のカーボンナノチューブと、金属化した硫黄鎖とが物理的に隔離されているため、サンプル全体としての電気伝導に大きく寄与しないためであると考えられる。 In the case of sulfur-encapsulated double-walled carbon nanotubes, the reason why the electrical resistivity decreases at a measurement temperature of 2 to 300 K is considered to be due to the metallization of the sulfur chains encapsulated in the carbon nanotubes. However, in the case of double-walled carbon nanotubes, it is the carbon nanotubes in the inner layer that physically interact with the metallized sulfur chains, so the amount of change in the temperature dependence of the electrical resistivity due to the inclusion of sulfur is Not as pronounced as in the case of nanotubes. This is considered to be because the carbon nanotubes in the outer layer of the double-walled carbon nanotubes and the metallized sulfur chains are physically separated, and thus do not greatly contribute to the electrical conduction of the entire sample.
　硫黄の金属化は、90GPa以上の極限条件下で発現する現象である。上記実験結果は、硫黄がカーボンナノチューブに内包されることにより、金属化されることを示唆するものであり、この硫黄が金属化される作用を利用すれば、硫黄とカーボンナノチューブとからなる新規な導電材料としての応用展開が可能である。
　硫黄は天然資源として大量に存在するが、従来は、機能性材料としてはほとんど利用されていない。本発明に係る硫黄を内包したカーボンナノチューブは、硫黄とカーボンナノチューブとの組み合わせにより、新規な導電材料としての用途を大きく開くものである。 Sulfur metallization is a phenomenon that occurs under extreme conditions above 90 GPa. The above experimental results suggest that sulfur is metallized by inclusion in carbon nanotubes. If this sulfur is metallized, a novel consisting of sulfur and carbon nanotubes will be suggested. Application development as a conductive material is possible.
Sulfur exists in large quantities as a natural resource, but conventionally, it is rarely used as a functional material. The sulfur-encapsulated carbon nanotube according to the present invention greatly opens up its use as a novel conductive material by a combination of sulfur and carbon nanotube.

Claims (10)

  1. 　硫黄原子が鎖状に連なる硫黄鎖が内包されていることを特徴とするカーボンナノチューブ。 A carbon nanotube characterized by containing sulfur chains in which sulfur atoms are linked in a chain.
  2. 　直線構造となる硫黄鎖が内包されていることを特徴とする請求項１記載のカーボンナノチューブ。 The carbon nanotube according to claim 1, wherein a sulfur chain having a linear structure is included.
  3. 　並列に２つの硫黄鎖が内包されていることを特徴とする請求項２記載のカーボンナノチューブ。 The carbon nanotube according to claim 2, wherein two sulfur chains are included in parallel.
  4. 　ジグザグ構造となる硫黄鎖が内包されていることを特徴とする請求項１記載のカーボンナノチューブ。 The carbon nanotube according to claim 1, wherein a sulfur chain having a zigzag structure is included.
  5. 　前記硫黄鎖が、単層カーボンナノチューブに内包されていることを特徴とする請求項１～４のいずれか一項記載のカーボンナノチューブ。 The carbon nanotube according to any one of claims 1 to 4, wherein the sulfur chain is encapsulated in a single-walled carbon nanotube.
  6. 　硫黄原子が鎖状に連なる硫黄鎖が内包されているカーボンナノチューブを含むことを特徴とするシート体。 A sheet body comprising carbon nanotubes containing sulfur chains in which sulfur atoms are linked in a chain.
  7. 　直線構造となる硫黄鎖が内包されているーボンナノチューブを含むことを特徴とする請求項６記載のシート体。 The sheet body according to claim 6, wherein the sheet body includes a bon nanotube in which a sulfur chain having a linear structure is included.
  8. 　ジグザグ構造となる硫黄鎖が内包されているカーボンナノチューブを含むことを特徴とする請求項６記載のシート体。 The sheet body according to claim 6, comprising a carbon nanotube in which a sulfur chain having a zigzag structure is included.
  9. 　カーボンナノチューブと硫黄とを密封容器に収容し、容器を真空密封する工程と、
    　前記真空密封した容器を718K以上の温度に加熱してカーボンナノチューブに硫黄を内包させる工程と、
    　カーボンナノチューブに硫黄を内包させた後、カーボンナノチューブの外面に付着した硫黄を除去する精製工程と、
    を備えることを特徴とする硫黄鎖を内包するカーボンナノチューブの製造方法     Storing the carbon nanotubes and sulfur in a sealed container, and vacuum-sealing the container;
    Heating the vacuum-sealed container to a temperature of 718K or higher to enclose sulfur in carbon nanotubes;
    A purification step of removing sulfur adhering to the outer surface of the carbon nanotube after encapsulating sulfur in the carbon nanotube;
    A method for producing a carbon nanotube containing a sulfur chain, comprising:
  10. 　前記精製工程においては、硫黄を内包させる工程により得られたカーボンナノチューブを二硫化炭素に加え、超音波照射してカーボンナノチューブの分散液を調製し、このカーボンナノチューブの分散液を濾過する工程を備えることを特徴とする請求項９記載のカーボンナノチューブの製造方法。
     
     
          The purification step includes a step of adding carbon nanotubes obtained in the step of encapsulating sulfur to carbon disulfide, preparing a dispersion of carbon nanotubes by ultrasonic irradiation, and filtering the dispersion of carbon nanotubes. The method for producing a carbon nanotube according to claim 9.


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