WO2004035883A2 - Nano-carbone fibreux et procede d'elaboration - Google Patents

Nano-carbone fibreux et procede d'elaboration Download PDF

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WO2004035883A2
WO2004035883A2 PCT/KR2003/002182 KR0302182W WO2004035883A2 WO 2004035883 A2 WO2004035883 A2 WO 2004035883A2 KR 0302182 W KR0302182 W KR 0302182W WO 2004035883 A2 WO2004035883 A2 WO 2004035883A2
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catalyst
carbon
hydrogen
preparation
fibrous
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PCT/KR2003/002182
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English (en)
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WO2004035883A3 (fr
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Seong Ho Yoon
Mochida Isao
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Nexen Nano Tech Co., Ltd
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Priority claimed from KR10-2002-0063641A external-priority patent/KR100483802B1/ko
Priority claimed from KR1020030049473A external-priority patent/KR100713609B1/ko
Priority claimed from KR1020030049472A external-priority patent/KR100726368B1/ko
Application filed by Nexen Nano Tech Co., Ltd filed Critical Nexen Nano Tech Co., Ltd
Priority to AU2003271224A priority Critical patent/AU2003271224A1/en
Priority to US10/531,831 priority patent/US20060008408A1/en
Publication of WO2004035883A2 publication Critical patent/WO2004035883A2/fr
Publication of WO2004035883A3 publication Critical patent/WO2004035883A3/fr

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    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B82—NANOTECHNOLOGY
    • B82Y—SPECIFIC USES OR APPLICATIONS OF NANOSTRUCTURES; MEASUREMENT OR ANALYSIS OF NANOSTRUCTURES; MANUFACTURE OR TREATMENT OF NANOSTRUCTURES
    • B82Y30/00—Nanotechnology for materials or surface science, e.g. nanocomposites
    • 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
    • C01B32/16—Preparation
    • C01B32/162—Preparation characterised by catalysts
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B82—NANOTECHNOLOGY
    • B82Y—SPECIFIC USES OR APPLICATIONS OF NANOSTRUCTURES; MEASUREMENT OR ANALYSIS OF NANOSTRUCTURES; MANUFACTURE OR TREATMENT OF NANOSTRUCTURES
    • B82Y40/00—Manufacture or treatment of nanostructures
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01B—NON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
    • C01B2202/00—Structure or properties of carbon nanotubes
    • C01B2202/20—Nanotubes characterized by their properties
    • C01B2202/34—Length
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01B—NON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
    • C01B2202/00—Structure or properties of carbon nanotubes
    • C01B2202/20—Nanotubes characterized by their properties
    • C01B2202/36—Diameter

Definitions

  • This invention relates to fibrous nanocarbons, especially to ladder-structured and pair-structured fibrous nanocarbons and the preparations of the same.
  • the fibrous nanocarbons of this invention can be used as the fillers of polymer and ceramic composites, catalyst support for fuel cell, catalyst supports for organic unit reaction, gas storing materials for methane and hydrogen, anodic and conductive materials for lithium secondary battery, and electrode materials for high performance electric double layered capacitor.
  • This invention relates to the ladder structured fibrous nanocarbons and the pair structured fibrous nanocarbons and its preparation method.
  • Carbon nanotube usually has a hollow fibrous nano-structure with the diameter of larger than 0.4nm. Carbon nanotube has a structure of concentrically-stacked hexagonal planes which are almost aligned along to the fiber axis.
  • Single Wall Carbon Nanotube (SWNT) has most fundamental structure because it is composed of only one concentric hexagonal plane, where Multi Wall Carbon Nanotube (MWNT) are usually composed of more than two concentrical hexagonal planes. SWNT has the range of diameter from 0.4 ⁇ 2.0 nm and MWNT has the range of diameter from 3.5-50 nm.
  • Carbon nanofibers have been classified their structures into three typical alignments of graphitic hexagonal planes such as platelet, herringbone and tubular ones (ref: N.M. Rodriguez, A. Chambers, R.T.K. Baker, Catalytic Engineering of Carbon nanostructures. Langmuir 1995; 11(10): 3862-3866).
  • Platelet carbon nanofibers showed the perpendicular alignment of graphitic hexagonal planes to the fiber axis and herringbone or .feather ones did the inclined alignment with 20 - 80 degrees to the fiber axis, which can not maintain the continued tubular structures in the fibrous forms like carbon nanotubes.
  • Tubular carbon nanofiber which has the parallel alignment of graphitic hexagonal planes to the fiber axis resembles or is the same with carbon nanotube according to its definition. There may be much more varieties of fibrous structures in term of transient alignments and surface roughness.
  • Such carbon nanofibers can usually prepared by catalytic synthesis of gases or hydrocarbons over the metals that are mainly composed of metals of VI B such as Fe, Ni, Co.
  • Fibrous nanocarbon can be defined as a fibrous nanocarbon which has a diameter or width of 0.46 - several hundreds nano meters and aspect ratios (ratio of length over diameter) of over 4. Fibrous nanocarbons can be classified into carbon nanotubes and carbon nanofibers according to the diameters or widths and structure of their fibrous forms.
  • Hyperion Catalytic International Inc. claimed MWNT or tubular carbon nanofibers of fibrous structured carbons which had a hollow fibril with 8-15 concentrically-stacked carbon hexagonal planes, having inner diameter of around 5 nm and outer diameters of 3.5 - 70 nm. [JP 62-50000943]
  • Boehm, Murayama, and Rodriguez also reported the preparations of carbon nanofibers or filamentous carbons individually by the catalytic pyrolysis of carbon monoxide and hydrocarbons over the transition metals of Fe, Ni, and Co. (ref: Boehm, Carbon, 11, 583 (1973); H. Murayama, T. Maeda, Nature, 245,791; N.M. Rodriguez, 1993. J. Mater. Res. 8: 3233)).
  • bamboo-like carbon nanofibers have been known to have the hollow nano-fibrous structure with periodically connected inner wall surface by the graphene knobs, remaining closed inner space.
  • Chen et al prepared bamboo-like carbon nanofibers by the catalytic pyrolysis of ethylene over the Cu-Ni alloy over the reaction temperature of 720°C. (ref: Carbon 39 (2001) 1467-1475, Formation of bamboo-shaped carbon filaments and dependence of their morphology on catalyst composition and reaction conditions, Jiuling Chen, Yongdan Li , Yanmei Ma , Yongning Qin, Liu Chang).
  • Kajiura et al. also reported bamboo-like carbon nanofibers obtained by the arc-discharge method, (ref: Carbon 40 (2002) 2423-2428, High-purity fibrous nanocarbon deposit on the anode surface in hydrogen DC arc-discharge, Hisashi Kajiura, Houjin Huang, Shigemitsu Tsutsui , Yousuke Murakami, a Mitsuaki Miyakoshi). Their reports were limited to deal with the bamboo-like carbon nano-structure in which the closed inner space by the periodical knob of joint was blockaded by the wall of graphene sheets.
  • the present invention was designed to solve the problems of conventional carbon nanofibers as described above, and specifically the purpose of this invention is to provide fibrous nanocarbons with ladder or pair structures to be used for various fields such as pigments, inks, films, coating materials, and composites, especially with transparency.
  • the present invention purposed to provide a high yield preparation of the fibrous nanocarbons with ladder or pair structures to be used as a high-efficient material for overall industry, for examples, a catalyst support of fuel cells; a gas storage medium for hydrogen or methane; and an electrode or conductor in lithium secondary battery and super EDLC (Electric Double Layered Capacitor).
  • a catalyst support of fuel cells for examples, a catalyst support of fuel cells; a gas storage medium for hydrogen or methane; and an electrode or conductor in lithium secondary battery and super EDLC (Electric Double Layered Capacitor).
  • this invention discloses a ladder-structured fibrous nanocarbons, concerning a uni-modally- or bi-modally-formed fibrous nanocarbons, which is characterized by (1) the sp 2 hybrid carbon content of more than 95% per total content; (2) the interlayer spacing (doo 2> d-spacing of C(002) profiles determined by X-ray diffraction method) of 0.3360nm ⁇ 0.3800nm; (3) the (002) plane stacking of more than 4 layers and the aspect ratio of more than 20; (4) the fiber cross-section's width/thickness of 2.0nm ⁇ 800nm; (5) the inclination angle of hexagonal plane alignment to the fiber axis of 0 ⁇ 85 degrees; and (6) carbon hexagonal planes stacking along the fiber axis, forming knots (nodes) at intervals of 5 nm ⁇ 100 nm, sharing partly the structure or stacking layers with the opposite side hexagonal planes and connecting periodically to each other, consequently forming ladder
  • a pair-structured fibrous nanocarbon of this invention concerns the uni-modally or bi-modally grown fibrous nanocarbons, which is characterized by (1) the sp 2 hybrid carbon content of more than 95% per total content; (2) d 002 of 0.3360nm ⁇ 0.3800nm; (3) the (002) plane stacking of more than 8 layers; (4) the width/thickness of fiber cross-section of 2.0 nm ⁇ 800 nm; (5) the aspect ratio is more than 20; and (6) bonding of two unit fibers formed by said (1) ⁇ (5) features, being induced by the interaction between the two unit fibers in the beginning of formation, also leaving a uniform interval of O. ⁇ nm ⁇ 30nm.
  • this invention discloses preparation method of said ladder- or pair-structured fibrous nanocarbons, characterized by catalytic pyrolysis of carbon source gas or liquid, wherein said catalysts are prepared in the form of unsupported bulk or powder metals, wherein the reduction of said metals by hydrogen provides reduced forms, and simultaneously very fine metal particles are obtained by roles of hydrogen or hydrogen radical during said reduction process.
  • transition metals active to aforementioned carbon sources such as Fe, Ni or Co are used as primary metals, and, in order to assist fine-particle formation of said primary metals, secondary metals inactive to said carbon sources are added in 5 ⁇ 95wt%, providing uniformly finer metal particles, which are used as unsupported metal catalysts in this invention.
  • Metal catalysts as prepared above are used as fibrous nanocarbon preparation catalysts, wherein the preparation of fibrous nanocarbons in this invention is attained through introduction of 3-phase gas mixtures of hydrocarbons, hydrogen, and helium at 0.5 ⁇ 30 seem per 1 mg catalysts, wherein said hydrogen partial pressure is selected in 2 - 95 v/v%, the heat treatment is performed at temperatures of 380 - 750°C for 2 min ⁇ 48 h.
  • Ladder- and pair-structured fibrous nanocarbons as described above and proved by Examples in this invention have advantages of using both inner and outer surfaces for adsorption in any time, differing from bamboo-like carbon nanotubes of closed inner space or conventional carbon nanotubes which are connected to outer space just in the parts of defects, partial surfaces, or tube tips formed by removal of catalysts. Therefore, ladder- and pair-structured fibrous nanocarbons in this invention enable uniform interval doping of metals or inorganic materials to said fibrous nanocarbons, developing novel applications such as gas storage of methane and so on; conventional catalyst supports; and electrical energy storage.
  • Figure 1 illustrates HR-SEM photograph of the present ladder-structured fibrous nanocarbons produced in Example 1.
  • Figure 2A and Figure 2B illustrate TEM photographs of ladder-structured fibrous nanocarbon and enlarged image of the same.
  • Figure 3A and Figure 3B illustrate 30 degree tilted TEM photograph of ladder-structured fibrous nanocarbon and enlarged image of the same.
  • Figure 4 illustrates the structural model of fibrous nanocarbon shown in Figure 1.
  • Figure 5 illustrates HR-SEM photograph of carbon nanotube produced in Comparative Example 1
  • Figure 6 illustrates TEM photograph of carbon nanotube produced in Comparative Example 1
  • Figure 7 illustrates low magnified HR-SEM photograph of the present pair-structured fibrous nanocarbons produced in Example 3.
  • Figure 8 illustrates high magnified HR-SEM photograph of the present pair-structured fibrous nanocarbons produced in Example 3.
  • Figure 9A, Figure 9B and Figure 9C illustrate STM photograph, real probe scanning profile the cross-section, and conjectured profile of the cross-section of the present pair-structured fibrous nanocarbons produced in Example 3, respectively.
  • Figure 10A and Figure 10B illustrate TEM photographs of the side and plane views of the present pair-structured fibrous nanocarbons produced in Example 3.
  • Figure 11 illustrates HR-SEM photograph of the present pair-structured fibrous nanocarbons produced in Example 4.
  • Figure 12 illustrates TEM photograph of the present pair-structured fibrous nanocarbons produced in Example 4.
  • Figure 13 illustrates the structural models of pair-structured fibrous nanocarbons in Example 3 and Example 5. Best mode for carrying out the Invention
  • fibrous nanocarbons in the present invention and preparation methods thereof. First, the overall description is given, and the details of this invention are provided by Examples, compared to Comparative Examples. In following Examples and Comparative Examples, the fibrous nanocarbons are referred as 'ladder-structured fibrous nanocarbon' when the structure resembles a ladder, and 'pair-structured fibrous nanocarbon' when the structure are formed by bonding of two unit fibers.
  • Ladder-structured fibrous nanocarbon in this invention is not yet reported on the properties and application of the same, hence a novel materiaUt ⁇ hich is formed by bonding at uniform intervals, simultaneously with formation and growth of two unit carbon nanofibers, wherein the inner side of the fibrous nanocarbon is open and connected to the outer space.
  • Ladder-structured fibrous nanocarbons in this invention concerns a uni-modally- or bi-modally-formed fibrous nanocarbon, which is characterized by (1) the sp 2 hybrid carbon content of more than 95% per total content; (2) the interlayer spacing (doo2, d-spacing of C(002) profiles determined by X-ray diffraction method) of 0.3360nm ⁇ 0.3800nm; (3) the (002) plane stacking of more than 4 layers and the aspect ratio of more than 20; (4) the fiber cross-section width/thickness of 2.0nm ⁇ 800nm; (5) the 0 ⁇ 85 degree inclination angle of hexagonal plane alignment for each unit carbon nanofibers to the fiber axis; and (6) carbon hexagonal planes stacking along the fiber axis, forming knots (nodes) at intervals of 5 nm - 100 nm, sharing partly the structure or stacking layers with the opposite side hexagonal planes and connecting periodically to each other, consequently forming ladder-like structure, wherein the
  • Carbon hexagonal planes of said ladder-structured fibrous nanocarbon align as shown in Figures 1-3, for example, ladder-structured fibrous nanocarbons produced at 500°C in Example 1 have a tubular structure, wherein the carbon hexagonal planes align at 0.1 ⁇ 5 degree to the fiber axis, but the hexagonal plane stacking connected to each other at 15 nm intervals aligns perpendicular to the fiber axis.
  • the inner space formed by connective units is open to outer space
  • the alignment of carbon hexagonal planes is characterized by (1) angled alignment at 0.1 ⁇ 20 degree to the fiber axis in the range of 2 ⁇ 80 nm the fiber cross-section width/thickness, and angled alignment at 20 - 85 degree to the fiber axis in the range of 80 ⁇ 800 nm the fiber cross-section width/thickness, and (2) the tendency that the each fibril cross-section width/thickness increases according to increase of primary metal (active to carbon sources) content in the catalyst composition or increase of synthesis temperature.
  • supported catalysts which are prepared by finely dispersing active metals on supports, are used for fibrous nanocarbon production wherein carbon source gases are pyrolyzed at prescribed temperatures by using said supported catalysts.
  • catalysts such as transition metals is attained by strong interaction of oxygen atom or heteroatom negative charge, or ion exchange principle.
  • oxygen atom or heteroatom negative charge or ion exchange principle.
  • iron nitrate or acetate containing oxygen of strong negative charge is dispersed on alumina, and reduced in hydrogen gas mixtures, resulting in active supported-metal catalyst.
  • Preparation method of ladder-structured fibrous nanocarbon in this invention is similar with conventional methods in terms of using catalytic pyrolysis of gaseous or liquid carbon sources such as CO or hydrocarbons of 1 ⁇ 4 carbon atoms, but the catalyst is not a supported one but bulk metal or particulate metal catalyst.
  • said bulk metal or particulate metal catalyst is necessary to experience segregation process by roles of hydrogen or hydrogen radical during the catalyst reduction process, to be formed as very fine metal particles.
  • transition metals such as Fe, Ni or Co active to said carbon sources are used as primary metals, with 5 - 95wt% addition of secondary metals inactive to said carbon sources in order to assist fine-particle formation, providing uniformly finer metal particles, which are used as unsupported metal catalysts in this invention.
  • metals such as Mn, Mo, Cr, W, and Ni which show no carbon yield from carbon monoxide are added 5 ⁇ 95wt% as secondary metals for fine dispersion of iron particles, providing alloy catalysts which are used as fibrous nanocarbon preparation catalysts.
  • metals such as Co and Ni which show high carbon yield from ethylene in prescribed gas mixture composition at prescribed temperatures are used as primary metals, and metals such as Fe, Mn, Mo, Cr, and W at addition of 5 ⁇ 95wt% which show no carbon yield from ethylene are effective as secondary metals for dispersion of primary metals.
  • cobalt-molybdenum (Co-Mo) catalyst certain amounts of cobalt nitrate and ammonium molybdate aqueous solutions are first prepared.
  • excess amounts of ammonium bicarbonate or oxalic acid must be added into the mixed solutions for obtaining the precipitate of mixed metal carbonates.
  • the obtained mixed metal carbonates must be fully dried in vacuum at 80°C for over 8 h after filtering and rinsing.
  • the obtained mixed metal carbonates are calcined for 2D10 h at 400°C under the air atmosphere for obtaining mixed metal oxides.
  • the obtained Co-Mo oxides are first reduced for 0.5 ⁇ 40 h at the temperature ranges of 450 - 550°C under the hydrogen-helium mixed gases of certain ratios. Specifically, the volume percentage of hydrogen should be 1 ⁇ 40 to the volumes of helium. After the first reduction, obtained Co-Mo alloy should be cooled to room temperature for the passivation of the surface with the appropriate oxidation conditions. For the passivation, the desirable amounts oxygen to nitrogen and period are 0.5 ⁇ 10 volume percent and 10 ⁇ 120 min, respectively.
  • the obtained Co-Mo alloy metal contains the compositions of cobalt 80 ⁇ 99 weight percents, more desirably 85 ⁇ 95 weight percents. Mo compositions are not completely reduced, containing oxygen less than 0.01 ⁇ 90 percents over the 1 weight percent of Mo.
  • compositions of cobalt in Co-Mo catalyst is more than 99 %, the prepared fibrous nanocarbons contains some of different structured carbons or showed the values of aspect ratio (length of fibrous nanocarbon/width of fibrous nanocarbon) less than 20.
  • Co-Mo catalyst For the preparation of fibrous nanocarbons using aforementioned Co-Mo catalyst, Co-Mo catalyst must be second reduced for 0.5 - 12 h at the temperature ranges of 450 ⁇ 550°C under the hydrogen-helium mixed gases of certain ratios. Specifically, the volume percentage of hydrogen should be 5 ⁇ 40 to the volumes of helium. If the temperature and period for the second reduction are shorter or lower than 0.5 h or 450°C, Co metal shows none or very low activity to the carbon source for the fiber growth. If the temperature and period for the second reduction are longer or higher than 12 h or 550°C, a severe sintering of separated Co metal occurs, resulting in very heterogeneous structures and dimensions of fibrous nanocarbons.
  • this invention also concerns a method for producing a substantially uniform plurality of essentially ladder-structured or paired, discrete fibrous nanocarbons which comprises contacting for an appropriate period of time and at a suitable pressure, suitable metal-containing particles with a suitable gaseous, carbon-containing gas, at a temperature between about 380°C and 750°C.
  • the mixture of ethylene, carbon monoxide and hydrogen are introduced by the exact control of flow rate with mass flow controller.
  • the desirable flow rate and partial pressure of carbon containing gas are 0.5 ⁇ 30 seem per 1 mg of catalyst and 10 ⁇ 95% of carbon containing gas, respectively.
  • the addition of 1 ⁇ 50 volume% of carbon monoxide per ethylene to carbon containing gas are desirable.
  • the period for the reaction is 2 min ⁇ 48 h.
  • the ladder-structured fibrous nanocarbon and the pair-structured fibrous nanocarbon prepared in this invention have clearly different structures with bamboo-like structure, showing the width of 2.0 - 800 nm and open knobs in every 5 - 100 nm in inner side of fibrous nanocarbons, and relatively developed graphitic structure which are very suitable as fillers for the applications of transparent conductive materials, transparent or non-transparent electromagnetic shielding materials, high thermal or electric conductive materials, anodic or conductive materials of lithium or air secondary batteries, electrodic materials for EDLC, and catalyst supports for the fuel cells and organic unit reactions.
  • the obtained Co-Mo oxides are first reduced for 0.5 h at the temperature ranges of 500°C under the hydrogen-helium mixed gases of certain ratios. Specifically, the volume percents of hydrogen were 10 to the total volume. After the first reduction, obtained Co-Mo alloy was cooled to room temperature for the passivation of the surface with the appropriate oxidation conditions. For the passivation, the desirable amounts oxygen to nitrogen and period are 5 volume percent and 30 min, respectively.
  • the obtained Co-Mo alloy metal contains the compositions of cobalt 89.4 weight percents.
  • Co-Mo catalyst For the preparation of fibrous nanocarbons using aforementioned Co-Mo catalyst, 30 mg of Co-Mo catalyst was second reduced for 2 h at 480°C under the hydrogen-helium mixed gases (The partial pressure of hydrogen is 20 volume % to the total volume).
  • Graphitization properties of the fibrous nanocarbons were analyzed in X-ray diffraction (Rigaku Geigerflex II; CuK ⁇ , 40KV, 30mA, Stepwise Method) at 2 ⁇ 5 ⁇ 90°. From the diffraction, the average (002) plane interlayer spacing (d002, hereinafter) and the average stacking height of (002) planes (Lc (002), hereinafter) were obtained according to the JSPS procedure (The 117 th committee in Japan society for the promotion of science. Tanso, 36, 25-34 (1963)).
  • the surface areas of the fibrous nanocarbons were calculated by using the Dubinin equation from the nitrogen isotherm at -190°C.
  • Table 1 shows d002, Lc (002), and the surface areas of the fibrous nanocarbons produced in corresponding examples.
  • the fibrous nanocarbons as prepared above shows a composed structure of two unit tubular carbon nanofibers wherein the hexagonal planes align angled to the fibrous nanocarbon axis (the angle 0.1 ⁇ 5°), distinct from carbon nanotube as described above.
  • Two unit carbon nanofibers are bridged periodically with carbon plane knobs by around 15 nm distant, forming ladder structure.
  • the average diameters or widths of the fibrous nanocarbons were measured by observation of 300 thousand magnified images through SEM monitor in random selection of 500 fibrous nanocarbons.
  • the average diameter of the fibrous nanocarbon produced above was 23nm and 75% of fibrous nanocarbons ranged 12 ⁇ 32 nm diameters.
  • the aspect ratio of the fibrous nanocarbon produced above was more than 200.
  • Examples 2 below illustrate production of fibrous nanocarbons under the same or different conditions over the same or different catalysts, and average diameters, d002, Lc(002), and surface areas of fibrous nanocarbons produced in corresponding Examples or Comparative examples are summarized in Tables 1 and 2, comparing with the comparative examples.
  • Co-Mo catalyst For the preparation of fibrous nanocarbons using aforementioned Co-Mo catalyst, 30 mg of Co-Mo catalyst was second reduced for 2h at 550°C under the hydrogen-helium mixed gases (The partial pressure of hydrogen is 20 volume % to the total volume).
  • Table 1 shows d002, Lc (002), the surface areas and average width or breadth of the fibrous nanocarbons produced in corresponding example.
  • the fibrous nanocarbons as prepared above shows a composed structure of two unit tubular carbon nanofibers wherein the hexagonal planes align angled to the fibrous nanocarbon axis (the angle 0.1 - 5°), distinct from carbon nanotube as described above.
  • Two unit carbon nanofibers are bridged periodically with carbon plane knobs by around 15 nm distant, forming ladder structure.
  • the average diameters or widths of the fibrous nanocarbons were measured by observation of 300 thousand magnified images through SEM monitor in random selection of 500 fibrous nanocarbons.
  • Carbon Black(CB)-supported Fe/Ni mixture or alloy (6/4 w/w) catalyst was prepared as follows. The mixture of the adequate amounts of iron nitrate and nickel nitrate was dissolved in 200 ml distilled water, and then
  • the slurry was dried in a rotary evaporator at 80°C under 40 Torr, providing a CB-supported Fe/Ni (6/4) catalyst (5% metal content per CB).
  • Table 1 shows d002, Lc(002), the surface areas and the average diameter of the carbon nanotube produced in corresponding examples.
  • the morphology and structure of carbon nanotube produced above were examined under a high resolution scanning electron microscope (HR-SEM, Jeol, JSM 6403F) and a transmission electron microscope (TEM, Jeol, JEM 201 OF) as shown in Figures 5 and 6.
  • the carbon nanotubes as prepared above shows a tubular structure wherein the hexagonal planes align angled to the fibrous nanocarbon axis (the angle below 5°), which is almost align along to the fiber axis.
  • the carbon nanotubes have flat planes and continuous hollow cores therein as examined under high resolution scanning electron microscope. As observed by transmission electron microscope shown in Figure 6, the carbon nanotubes have circular cross sections, and the widths of the carbon nanotubes are smaller than those of the hollow cores.
  • the aspect ratio which shows the fiber dimension is more than 100.
  • the average diameters or widths of the fibrous nanocarbons were measured by observation of 300 thousand magnified images through TEM monitor in random selection of 500 fibrous nanocarbons.
  • Catalyst of 30 mg prepared as in Example 1 was set in the furnace as described in Example 1. The reduction was performed in the gas mixture of 200 seem hydrogen/helium (20v/v% hydrogen partial pressure) at 600°C for 2 h, and then the reaction was performed in the gas mixture of 200 seem ethylene/hydrogen (80v/v% hydrogen partial pressure) at 600°C for 2 h, providing 1333 mg fibrous nanocarbons, which have no connection unit between fibrils.
  • Figures 7 show the SEM photographs of the pair-structured fibrous nanocarbon of this invention.
  • Low magnification can not discrete the combined structure of two unit carbon nanofibers because of low resolution, where the higher magnification can discrete the pair structure which is composed of two independently grown unit carbon nanofibers.
  • Pair-structured fibrous nanocarbon illustrates the ribbon-like or hexagonal column as shown in Figures of 9 - 11.
  • the width of cross-section decreases with increasing the preparation temperature.
  • the hexagonal cross-section may be induced from the shape of active catalyst (ref: S. H. Yoon, A. Tanaka, S. Y. Lim, Y. Korai, I. Mochida, B. Ahn, K. Yokogawa, C. W. Park, 3-dimensional structure of carbon nanofiber: carbon nano rod, Proceedings of international symposium on carbon, 2003, Oviedo, Spain, 8-1, 76).
  • This invention discloses that such separated hexagonal shaped very fine metal catalyst is further divided into two particles with plane symmetry and independent two same carbon nanofibers are grown over the divided catalyst particles.
  • Two independently grown unit carbon nanofibers compose the pair-structured fibrous nanocarbon with the combination of two fiber units by the Van der Waals force.
  • Pair-structured fibrous nanocarbons in the present invention have feather (herringbone), tubular, and columnar (platelet) structure whose carbon hexagonal planes are laminated at certain angles to the fiber axis, being formed by bonding of two ribbon- or plate-shape unit carbon nanofibers of trapezoidal cross section at regular distance by means of interaction between said two unit fibers, distinctly differing from conventional carbon nanotubes which have general circular cross section which involves hollow core of a regular size with the concentric carbon hexagonal stacking.
  • Pair-structured fibrous nanocarbon of this invention concerns the uni-modally or bi-modally grown fibrous nanocarbons, which is characterized by (1) the sp 2 hybrid carbon content of more than 95% per total content; (2) d 0 0 2 of 0.3360nm ⁇ 0.3800nm, the (002) plane stacking of more than 8 layers; (3) the width/thickness of fiber cross-section of 2.0 nm ⁇ 800 nm, and the fiber thickness ranges 1.0 ⁇ 400 nm; (4) the aspect ratio is more than 20, (5) bonding of two unit carbon nanofibers with said (1) - (4) features at 0.4nm ⁇ 30nm distance by the interaction between the two unit fibers (Van der Waals Force) in the beginning of fiber formation, (6)the hexagon-shaped cross section formed by two trapezoids as shown in Figures 7 - 11 , (7) the width of 2.0 ⁇ 800 nm and the thickness of 2.0 ⁇ 800 nm in said cross section, (8) in pair-structured fibrous nanocarbon with said (1)
  • Carbon hexagonal plane alignment or texture in the pair-structured fibrous nanocarbon tends to depend on the texture of the unit fibers.
  • the unit fiber at 600°C as prepared in Example 3 shows a platelet (columnar) texture where the carbon hexagonal planes align at angles of 75 ⁇ 90 degree to the fiber axis.
  • Pair-structured fibrous nanocarbon which is formed by bonding of two said unit fibers also shows platelet (columnar) texture.
  • pair-structured fibrous nanocarbon in the case of preparation of pair-structured fibrous nanocarbon at relatively low temperature such as 520oC as in Example 4, unit fibers which have the hexagonal alignment at 0.1 ⁇ 75 degree to the fiber axis bond by two units by inter-particle force or Van der Waals force, resulting in pair-structured fibrous nanocarbons which appear to have herringbone (feather) structure.
  • said pair-structured fibrous nanocarbon shows hexagon cross section originating from trapezoid-shaped cross section of said unit fibers, distinctly differing from conventional herringbone carbon nanofibers with circular cross section.
  • pair-structured fibrous nanocarbon The distance between two unit fibers which constitute the pair-structured fibrous nanocarbon is so small as 1 ⁇ 5 nm in preparation at high temperatures such as 600°C as in Example 3 as shown in Figure 10, but shows relatively large values of 5 ⁇ 20 nm in preparation at low temperatures such as 520°C as in Example 4 as shown in Figure 12.
  • Figure 13 illustrates a schematic model of pair-structured fibrous nanocarbon.
  • pair-structured fibrous nanocarbon in this invention is formed as a single body through bonding of two unit fibers by inter-fiber force or Van der Waals force, showing the inner side open to the outer space, distinctly differing from conventional carbon nanotubes.
  • pair-structured fibrous nanocarbon in this invention shows a hexagon shape of the cross section, where the unit fibers with trapezoid-shaped cross section are very close in the inter-fiber distance. Differing from pair-structured fibrous nanocarbons prepared at high temperatures, pair-structured fibrous nanocarbons prepared at relatively low temperatures are found to show the cross section close to a regular hexagon and relatively large inter-fiber distance between two unit fibers.
  • multi-walled carbon nanotubes as prepared in Example 6 are shown in SEM and TEM of Figures 5 and 6.
  • SEM image of Figure 5 carbon nanofibers have cleaner surface than pair-structured fibrous nanocarbon in this invention, and at a high magnification, a separation part as in this pair-structured fibrous nanocarbon is never found, which reflects that said multi-walled carbon nanotubes are formed totally as a single unit body having a continuous hollow core.
  • carbon nanotubes have the feature that the size of wall comprising the stacking of carbon hexagonal planes is generally smaller than the size of inner hollow.
  • Preparation method of pair-structured fibrous nanocarbon in this invention is similar with conventional methods in terms of using catalytic pyrolysis of gaseous or liquid carbon sources, but the catalyst is not a supported one but bulk metal or particulate metal catalyst. Also, said bulk metal or particulate metal catalyst is necessary to experience segregation process by roles of hydrogen or hydrogen radical during the catalyst reduction process, to be formed as very fine metal particles. To obtain more uniform fine particles of said catalysts through said segregation process, transition metals active to carbon sources, such as Fe, Ni or Co are used as primary metals, with 5 ⁇ 95wt% addition of secondary metals inactive to said carbon sources in order to assist fine-particle formation, providing unsupported metal catalysts for producing pair-structured fibrous nanocarbon in this invention.
  • transition metals active to carbon sources such as Fe, Ni or Co are used as primary metals, with 5 ⁇ 95wt% addition of secondary metals inactive to said carbon sources in order to assist fine-particle formation, providing unsupported metal catalysts for producing pair-structured fibr
  • metals such as Mn, Mo, Cr, W, and Ni which show no carbon yield from carbon monoxide are added 5 ⁇ 95wt% as secondary metals for fine dispersion of iron particles, providing alloy catalysts which are used as fibrous nanocarbon preparation catalysts.
  • metals such as Co and Ni which show high carbon yield from ethylene in prescribed gas mixture composition at prescribed temperatures are used as primary metals, and metals such as Fe, Mn, Mo, Cr, and W at addition of 5 ⁇ 95wt% which show W
  • Fe-Mn iron-manganese
  • the passivation is performed under gas mixture containing
  • Fe-Mn catalysts 20 0.5-10v/v% oxygen in nitrogen, argon or helium for 10-120 min.
  • the Fe content is 5 - 95wt%, preferably 20 - 85wt%.
  • the passivation is performed under gas mixture containing 1 ⁇ 5v/v% oxygen in nitrogen, argon or helium for 30 min.
  • the Fe content is 5 - 95wt%, preferably 20 -
  • the reduction condition is the same with said catalyst reduction condition, and the temperature and time are recommended as 450-550°C and 0.5 - 12 h, respectively.
  • the reduction temperature of lower than 450°C or the reduction time of less than 30 min provide no fully-reduced catalyst to show no or little activity
  • the reduction temperature of higher than 550°C or the reduction time of more than 12 h lead to sintering of fine particles which have been formed by said segregation process during hydrogen reduction, consequently resulting in inactive catalyst for production of fibrous nanocarbons due to loss of independency.
  • Fe-Mn alloy catalysts as prepared above are dispersed on boat or plate of alumina or silica, or are set in a floating or flow furnace, and the CO/hydrogen mixture of 0.5 - 30 seem per 1 mg catalyst (preferably, 1 - 10 seem) is introduced to said furnace for prescribed time, providing pair-structured fibrous nanocarbon, wherein said gas mixture contains 10 - 95v/v% hydrogen partial pressure, the temperature is proper at 380 - 750°C (preferably, 520 - 700°C), and the time is proper for 2 min - 48 h (preferably, 20 min - 24 h).
  • the pair-structured fibrous nanocarbon can be produced at high yields of 1.5 - 60 times per catalyst weight depending on production conditions, the reaction for 8 h providing the carbon yield of 30 times per catalyst weight.
  • the pair-structured fibrous nanocarbon comprising two unit fibers with very clean surface can be attained.
  • reaction temperatures of higher than 750°C lead however to the deactivation of catalyst, producing almost no fibrous nanocarbon.
  • the reaction time of less than 30 min provides very small yield which is not economical, and the reaction time of more than 48 h shows no further yield increase, rather undesirably inducing aggregation of fibers produced and decreasing independency of individual fibers.
  • Pair-structured fibrous nanocarbon in this invention shows 2.0 ⁇ 800 nm fiber diameters and 0.5 - 30 nm inter-unit fiber distances, and also has the relatively developed graphitic structure depending on the reaction temperature, being expected for various applications as aforementioned in
  • the obtained mixed metal carbonates are calcined for 5 h at 400°C under the air flow of 200sccm for obtaining mixed metal oxides.
  • the obtained Fe-Mn oxides are first reduced for 0.5 h at the temperature ranges of 500 degree C under the hydrogen-helium mixed gases of certain ratios. Specifically, the lo volume percents of hydrogen were 10 to the total volume. After the first reduction, obtained Fe-Mn alloy was cooled to room temperature for the passivation of the surface with the appropriate oxidation conditions. For the passivation, the desirable amounts oxygen to nitrogen and period are 5 volume percent and 30 min, respectively.
  • Fe-Mn catalyst For the preparation of fibrous nanocarbons using aforementioned Fe-Mn catalyst, 30 mg of Fe-Mn catalyst was second reduced for 2 h at 480 degree C under the hydrogen-helium mixed gases (The partial pressure of hydrogen is 20 volume % to the total volume(IOOsccm)).
  • Graphitization properties of pair-structured fibrous nanocarbons were analyzed in X-ray diffraction (Rigaku Geigerflex II; CuK ⁇ , 40KV, 30mA, Stepwise Method) at 2 ⁇ 5 - 90°. From the diffraction, the average (002) plane interlayer spacing (d002, hereinafter) and the average stacking height of (002) planes (Lc(002), hereinafter) were obtained according to the JSPS procedure (Otani Sugio, et al. Carbon Fibers. Nihon Kindaihensyusya; Tokyo, 1983). The surface areas of the fibrous nanocarbons were calculated by using the Dubinin equation from N2 BET isotherms. Table 2 shows d002, Lc (002), the surface areas and the width/thickness of the fibrous nanocarbons produced in corresponding examples.
  • the pair-structured fibrous nanocarbons as prepared above shows a composed structure of two unit platelet carbon nanofibers wherein the hexagonal planes align angled to the fibrous nanocarbon axis (the angle 85
  • Carbon hexagonal planes were found to align almost perpendicular to the fiber axis, and the cross section of the fibers was found to shape a hexagon as shown in the scanned profile of scanning tunneling microscope of Figure 9.
  • the width of the fibers shapes oblong trapezoid where the side and front shape of the fibers are different.
  • the front observation does not show bonding of two unit fibers, but the side observation shows the single fiber formation from two plate-shaped unit fibers of trapezoidal cross section.
  • the aspect ratio which shows the fiber dimension is more than 80.
  • the average diameters or widths of the fibrous nanocarbons were measured by observation of 300 thousand magnified images through SEM monitor in random selection of 500 fibrous nanocarbons.
  • the pair-structured fibrous nanocarbons as prepared above shows a composed structure of two unit platelet carbon nanofibers wherein the hexagonal planes align angled to the fibrous nanocarbon axis (the angle 85
  • the average diameters or widths of the fibrous nanocarbons were measured by observation of 300 thousand magnified images through SEM monitor in random selection of 500 fibrous nanocarbons.
  • the inter-spacing between the two unit carbon nanofibers shows 4.2 nm as shown in Figure 10.
  • Table 2 shows d002, Lc (002), the surface areas and the width/thickness of the fibrous nanocarbons produced in corresponding examples.
  • the pair-structured fibrous nanocarbons as prepared above shows a composed structure of two unit platelet carbon nanofibers wherein the hexagonal planes align angled to the fibrous nanocarbon axis (the angle 85
  • the average diameters or widths of the fibrous nanocarbons were measured by observation of 300 thousand magnified images through SEM monitor in random selection of 500 fibrous nanocarbons.
  • Table 2 shows d002, Lc (002), the surface areas and the width/thickness of the fibrous nanocarbons produced in corresponding examples.
  • the pair-structured fibrous nanocarbons as prepared above shows a composed structure of two unit platelet carbon nanofibers wherein the hexagonal planes align angled to the fibrous nanocarbon axis (the angle 85
  • the average diameters or widths of the fibrous nanocarbons were measured by observation of 300 thousand magnified images through SEM monitor in random selection of 500 fibrous nanocarbons.
  • the inter-spacing between the two unit carbon nanofibers shows 5.8 nm.
  • Catalyst as in Example 3 (Fe/Mn 3/7) was set in the middle of a quartz tube (45 mm inner diameter) in the horizontal furnace as used in catalyst preparation, and the mixture of 200sccm hydrogen/helium (20v/v% hydrogen partial pressure) was flowed at 500°C for 2 h on purpose of catalyst reduction, and then the reaction was performed at 480°C for 12 h, providing almost no pair-structured fibrous nanocarbon.
  • the ladder and pair-structured fibrous nanocarbons in this invention which is different from conventional filamentous carbons, carbon nanofibers and carbon nanotubes, have open structure. Therefore, the fibrous nanocarbon of this invention is expected as a superior material for practical applications such as transparent conductive composites; transparent electromagnetic shields; lithium secondary battery, EDLC(Electric Double Layered Capacitor), and air cells; catalyst supports for fuel cells or organic reactions; electrification blocks for solar cells; electric desalination electrodes; gas storage; isotope separator; and removal of SO x or NO x .

Abstract

L'invention concerne différents types de nanocarbone fibreux, en particulier du type à structure en échelle et en paire, ainsi que leur élaboration. Précisément, les produits décrits peuvent être utilisés pour les applications suivantes: matériaux moléculaires composites, supports de catalyseur pour pile à combustible, supports de catalyseur pour réaction organique, moyen de stockage de gaz pour méthane et hydrogène, électrodes ou conducteurs pour batterie secondaire au lithium, et électrodes pour condensateurs électriques à double couche. Ces produits sont caractérisés par: une structure de type graphite, avec une teneur en carbone hybride sp2 supérieure à 95 % par rapport à la teneur totale; un intervalle intercouche (d002, intervalle d des profils C(002) déterminé par la technique de diffraction des rayons X) de 0,3360 nm ~ 0,3700 nm; un empilement en plan (002) de plus de quatre couches (ou équivalant à 1,5 nm); un rapport d'aspect supérieur à 10; une section transversale/épaisseur de fibre de 5 nm ~ 500 nm; et une structure en échelle et en paire sans âme creuse continue.
PCT/KR2003/002182 2002-10-17 2003-10-17 Nano-carbone fibreux et procede d'elaboration WO2004035883A2 (fr)

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