US20090191116A1

US20090191116A1 - Porous filamentous nanocarbon and method of forming the same

Info

Publication number: US20090191116A1
Application number: US12/335,664
Authority: US
Inventors: Seong Ho Yoon; Isao Mochida; Seong Yop Lim
Original assignee: Suntel Co Ltd
Current assignee: VINATECH CO Ltd
Priority date: 2004-12-30
Filing date: 2008-12-16
Publication date: 2009-07-30
Also published as: JP4819061B2; EP1833755A1; WO2006071066A1; CA2593117A1; EP1833755A4; JP2008526663A; US20100202958A1; KR20070087697A; US20090004095A1; CA2593117C; CN101124153A; CN101124153B

Abstract

A method for forming a porous filamentous nanocarbon involves radially forming a tunnel-like mesopore from an outer periphery toward the central axis of a filamentous nano carbon by attaching a material having a metal catalyst on an outer periphery of the filamentous nanocarbon and removing a carbon hexagonal plane through gasification in virtue of the metal catalyst.

Description

CROSS REFERENCE TO RELATED APPLICATION

This application is a divisional of prior application Ser. No. 11/813,079, filed Aug. 1, 2008 the entirety of which is incorporated herein by reference.

TECHNICAL FIELD

The present invention relates to a porous filamentous nanocarbon where mesopores are formed on an outer periphery thereof, and more particularly, to a porous filamentous nanocarbon in which the mesopores are radially formed from an outer periphery toward a fiber axis thereof along an arrangement direction of a carbon hexagonal plane.

BACKGROUND

As researches for porous materials with porosity are actively conducted recently, methods for manufacturing them are well known to the public. In particular, with regard to a method for manufacturing an activated charcoal and an activated carbon fiber and a method for manufacturing a fibrous nanocarbon and a carbon nanotube using a metal catalyst, a number of patents and theses are widely known. Herein, the carbon nanotube is a hollow carbon nanotube of which the diameter is 80 nm or less. According to such a general activation method, a porous carbon material, which is typically called an activated carbon, is formed by forming plenty of micropores on the surface of the carbon material.
Two methods for manufacturing the activated charcoal and the activated carbon fiber are well known to the public. One is a method in which a carbon-based material undergoes a heat treatment at a temperature in a range of 300° C. to 1,100° C. for a predetermined time in an ambient of water vapor, air, carbon dioxide, or the like, to thereby manufacture the activated charcoal and the activated carbon fiber. The other one is a method in which a heat treatment is performed over the carbon-based material at a temperature in a range of 300° C. to 1,100° C. for a predetermined time in a salt having an alkali metal such as potassium hydroxide, sodium hydroxide, or the like, and a separate rinsing and a drying process are sequentially performed so as to fabricate the activated charcoal and the activated carbon fiber.
In the International Patent Publication No. W08603455, filed on 1986 by Hyperion Catalytic International Inc. in U.S.A., there has been announced a technology for a carbon nanotube with a hollow tubular structure of which a fiber diameter is in a range of 3.5 nm to 70 nm, where a carbon hexagonal plane is concentrically arranged along a fiber axis. The carbon nanotube is mainly classified into a single wall carbon nanotube (SWNT) in which a carbon hexagonal plane is configured with one sheet of a single wall, and a multi wall carbon nanotube (MWNT) configured with multi-walls. It becomes generally known that the fiber diameter of the SWNT ranges from 0.4 nm to 3.5 nm, and the fiber diameter of the MWNT ranges from 2.5 nm to 50 nm.
It is widely known a method for manufacturing a filamentous nanocarbon by thermally decomposing carbon monoxide and hydrocarbon gas as a carbon source upon a metal catalyst. For example, U.S. Pat. No. 4,565,683 discloses a method for manufacturing a filamentous carbon, where a fiber is formed in 1 u long or greater by thermally decomposing carbon monoxide and hydrocarbon or the like at 540˜800° C. using a catalyst such as iron oxide, iron, nickel, etc. In addition, Baker and Rodriguez et al. have announced a method for manufacturing a carbon nanofiber of which surface area is in a range of 50 u/g to 800 u/g, by thermally decomposing hydrocarbon at 500˜700° C. using a catalyst such as iron, nickel, cobalt, etc. Furthermore, Boehm et al. and Murayama and Rodriguez et al. have announced a method for manufacturing a filamentous nanocarbon by thermally decomposing hydrocarbon using a transition metal such as iron, cobalt, nickel, or alloy catalyst thereof (Bohem, Carbon, 11, 583 (1973); H. Murayama, T. Maeda, Nature, 245, 791; Rodriguez, N. M., 1993, J. Master. Res. 8(3233)).
Among various carbon nanofibers, there are a carbon nanofiber with a platelet structure in which the carbon hexagonal plane is arranged perpendicular to the fiber axis, and a carbon nanofiber with a Herringbone structure in which the carbon hexagonal plane is inclined with respect to the fiber axis at 20˜80° (Rodriguez, N. M., 1993, J. Master. Res. 8 (3233)). They do not have hollows therein, which is a significant difference from the nanotube. FIGS. 1 a, 1 b and 1 c are transmission electron microscope (TEM) images illustrating a carbon nanotube, a platelet filamentous nanocarbon, and a herringbone filamentous nanocarbon, respectively. Since all the activated charcoal, the carbon nanotube, and the filamentous nanocarbon have large surface area, they may be applied to an adsorbent or a catalyst support. Because they have micropores of which sizes are 2 nm or smaller, they are effective for adsorbing small-size molecules such as a gas detrimental to an environment, a halogenated hydrocarbon contaminating water, or the like. Therefore, they may be applied to a removal of a contaminant caused by the exhaust gas of a factory, a purification of drinking water, and so forth. However, it is difficult to apply them to an adsorbent for a polymer, or a catalyst support for converting polymer material such as petroleum. In order that the activated charcoal, the filamentous nanocarbon, etc, may be applied to these cases, it is necessary to manufacture an absorbent having mesopores of which sizes are very uniform with low cost, wherein the size of the mesopore is in a range of 2 nm to 100 nm.
Several technologies for forming mesopores have been well known to the public.
According to one technology, a material that contains a removable moiety, of some sizes, is polymerized so as to incorporate the moiety into a solid product. The moiety is removed, leaving a porous solid having pores. For example, if firing a polymer mixed with an organic material and an inorganic material, the organic material is burnt out so that there occurs a fine pore in the inorganic material, of which size is correspondent to that of the organic material. The resultant porous solid can have a very narrow pore size distribution in the mesopore range, however, the preparation of such materials is very expensive and time consuming.
Recently, a research result for synthesizing a material having mesopores using silica and silica alumina has been published, which is referred to as MCM-41 and M41-S disclosed in U.S. Pat. No. 5,108,725 and U.S. Pat. No. 5,378,440. However, because this is electrically an insulator and is very unstable in alkali solution, it is not adaptive for applying it to a fuel cell, a battery, an electrolysis battery, capacitor, etc.
Another technology is related to a synthesis of a carbon material selectively having mesopores therein. In detail, a polymer as a carbon source is injected into a template such as zeolite, alumina, silica, and so forth, having mesopores therein. Alternatively, a pyrolytic carbon is chemically deposited on the template from hydrocarbon gas. Thereafter, the template is removed using fluoric acid or the like. However, this method has also disadvantages that its fabrication cost is too high, and productivity is too poor in consideration of fabrication period and production amount.
Meanwhile, since most of the solid with the mesopores fabricated by the above methods has a particulate shape, it has difficulties in filtering despite the advantage of having high specific surface area.

TECHNICAL PROBLEM

The present invention provides a porous filamentous nanocarbon including a filamentous nanocarbon having mesopores of which porosity is high and each pore size is uniform, in which the size of the mesopore is in a range of 20 nm to 30 nm, and a method for manufacturing the same.
The present invention also provides a porous filamentous nanocarbon for an absorbent for separating a polymer such as protein or the like, a chromatography material, an electrode material for a fuel cell, electrochemical reaction, and so forth, and a method for manufacturing the same.
The present invention further provides a porous filamentous nanocarbon for removing inconvenience for treatment thereof, by forming a solid with mesopores in a filamentous shape of which the diameter is several nanometers, not forming the solid with mesopores in a particulate shape, and a method for manufacturing the same.
Embodiments of the present invention provide porous filamentous nanocarbons having a mesopore, wherein the mesopore is a tunnel-like pore which is radially formed from an outer periphery of the filamentous nanocarbon toward the central axis of the filamentous nanocarbon.
In some embodiment, the filamentous nanocarbon is a nanocarbon with a platelet structure in which carbon hexagonal planes are vertically stacked with respect to the central axis. Alternatively, the filamentous hexagonal plane is a nanofiber with a Herringbone structure which is formed in the V-shape as being inclined at an angle in a range of 20 to 80° with respect to the central axis. Herein, the mesopore is formed along the arrangement direction of the carbon hexagonal planes.
In other embodiments, the filamentous nanocarbon has the diameter in a range of 2 to 100 nm, e.g., preferably in a range of 10 to 200 nm, and an aspect ratio of 4 or higher, e.g., preferably 10 or higher. The mesopore has the size in a range of 2 to 100 nm, e.g., preferably in a range of 2 to 30 nm, and the porosity of at least 20% or greater, e.g., preferably 50% or greater.
In further embodiments of the present invention, there are provided methods for forming a porous filamentous nanocarbon, the method including radially forming a tunnel-like mesopore from an outer periphery toward the central axis of a filamentous nano carbon by attaching a material having a metal catalyst on an outer periphery of the filamentous nanocarbon and removing a carbon hexagonal plane through gasification in virtue of the metal catalyst.
In further other embodiments, the mesopore is formed according as a predetermined portion of the filamentous nanocarbon on which the metal catalyst is attached selectively reacts with the metal catalyst. Accordingly, the predetermined portion of the carbon hexagonal plane is removed, and the mesopore is formed along the arrangement direction of the carbon hexagonal plane. Because of the selective reaction, it is possible to control the size of the tunnel-like mesopore and the porosity according to the size of the metal catalyst attached on the filamentous nanocarbon or nano-drilling conditions.
Thus, since the nano-sized mesopore of which the diameter is in a range of 2 nm to 30 nm is formed on the outer periphery of the filamentous nanocarbon, the porous filamentous nanocarbon may be applied to the separation/absorption of protein, petroleum, and so forth, and an electrode for a fuel cell.
According to the present invention, it is possible to obtain a porous filamentous nanocarbon having mesopores of which porosity is high and each pore size is uniform, in which the size of the mesopore is in a range of 20 nm to 30 nm. This porous filamentous nanocarbon may be variously applied to an adsorbent, a chromatography material, a catalyst support, etc. Meanwhile, it is possible to more enhance the conductivity between particles in virtue of a filamentous shape when applying the inventive nanocarbon to electrochemical applications requiring conductivity. In addition, the present invention provides an advantageous merit of removing inconvenience for treatment thereof, e.g., filtering, because a solid with mesopores has a filamentous shape of which the diameter is several nanometers instead of a particulate shape.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 a is a transmission electron microscope (TEM) images showing a filamentous nanocarbon having a tubular structure;

FIG. 1 b is a TEM showing photographs a filamentous nanocarbon having a platelet structure;

FIG. 1 c is a TEM images showing a filamentous nanocarbon having a Herringbone structure;

FIG. 2 is a schematic view and TEM images illustrating a filamentous nanocarbon with a tubular structure according to the present invention;

FIG. 3 is a schematic view and TEM images illustrating a filamentous nanocarbon with a platelet structure according to the present invention;

FIG. 4 is a schematic view and TEM images illustrating a filamentous nanocarbon with a Herringbone structure according to the present invention;

FIG. 5 is a schematic view and TEM images illustrating a filamentous nanocarbon in which mesopores are formed by nano-drilling according to the present invention;

FIGS. 6 to 9 are TEM images illustrating a filamentous nanocarbon in which mesopores are formed by nano-drilling process according to the present invention; and

FIG. 10 is a graph illustrating electrochemical activity in comparison of the filamentous nanocarbon according to the present invention with the prior art.

DETAILED DESCRIPTION

FIG. 1 are high resolution transmission electron microscope (TEM) images showing conventional filamentous nanocarbons having three representative structures such as a tubular structure, a platelet structure, and a Herringbone structure, respectively, and also illustrates typical 2-dimensional models corresponding to the respective structures.
FIGS. 2 to 4 illustrate that the filamentous nanocarbons with the three structures are formed by finely stacking nano-rods, which are structural units. That is, a tunnel-like mesopore according to the present invention is formed based on a new structure of a filamentous nanocarbon configured with the stacked carbon nano-rods.
The nano-rod, which is a basic unit constituting the filamentous nanocarbon, has a structure where fullerene tubes are overlapped along the same axis and one end thereof is closed, wherein the fullerene tube cluster is configured as a cylindrical shape such that carbon hexagonal planes are overlapped with each other (refer to FIG. 3 a). In general, the nano-rod is configured as a hexagonal prism having 4˜6 number of coaxes, of which each diameter is about 2.5 nm and each size is in a range of 20 nm to 80 nm. Detail descriptions for the nano-rod are disclosed more fully in the thesis of S.-H. Yoon et al. (S.-H. Yoon, S. Lim, S.-h. Hong, I. Mochida, B. An, K. Yokogawa. 2004, Carbon, 42(15), 3087-3095; B. An, K. Yokogawa, S. Lim, S.-H. Yoon, 1. Mochida. In: Carbon 2004 International Conference, Brown University: RI (USA), 2004).
In the present invention, nano-sized mesopores are formed on an outer periphery of the filamentous nanocarbon using a nano-drilling process. If a nano catalyst is attached on the outer periphery of the filamentous nanocarbon, and then a heat treatment is performed over the filamentous nanocarbon on which the nano catalyst is attached in hydrogen or oxygen ambient, there occurs a hydrogenation or an oxidation gasification reaction so that there is formed a tunnel penetrating from the outer surface into an interior, of which a size is corresponding to that of the nano catalyst. A drilling pattern formed by the inventive method is not random in comparison with the prior art, but is uniformly formed along the arrangement direction of the carbon hexagonal plane. Accordingly, the nano catalyst under hydrogenation or oxidation ambient removes the filamentous nanocarbon from a portion on which the nano catalyst is attached along the stacked structure of the nano-rods, to thereby form the nano tunnels by drilling the filamentous nanocarbon. Referring to FIG. 5, it is shown that the predetermined portion of the nano-rod is removed and thus the tunnel is formed.
This reaction is caused by gasification of the metal with respect to carbon due to hydrogen, oxygen, or the like. The reason the mesopore is formed in a shape of the tunnel is that the decomposition of the carbon plane due to the gasification occurs along the alignment direction of the nano-rod units, which are formed as a hexagonal prism of the carbon hexagonal plane, because the surface forming sidewalls of the carbon hexagonal plane is more reactive than the base surface. Accordingly, the nanodrilling reaction progresses along a major axis of the nano-rod from the outer periphery of the filamentous nanocarbon to the center of the fiber. This is possible by preferentially gasifying and removing the nano-rods where the catalyst is attached on an end thereof in hydrogen or oxygen ambient. At this time, since one or more nano-rods may react with reaction gas by means of the catalyst, there is formed the nano tunnel of which width is 2˜30 nm greater than the diameter of the nano-rod. Therefore, there are formed the tunnel shaped mesopores radially along the alignment axis of the nanorods from the outer periphery toward the center of the fiber.
The metal catalyst for nano-drilling, i.e., gasification, may employ an element in the groups V, VI, VII, and [ ] of the periodic table. Preferably, the catalyst is iron (Fe), cobalt (Co), nickel (Ni), molybdenum (Mo), vanadium (V), chromium (Cr), platinum (Pt), palladium (Pd), ruthenium (Ru), copper (Cu), silver (Ag), zinc (Zn), tin (Sn), and an alloy thereof. It is preferable that the alloy catalyst employ Ni—Cu, Fe—Ni, Fe—Pt, Fe—Mo, Ni—Mo, Co—Mo, Pt—Ru, etc. It is preferable that the size of the catalyst be in a range of 2 nm to 50 nm. In case of too small, there occurs micropores. On the contrary, in case of too large, a great amount of the filamentous nanocarbon may be removed.
It is preferable that the reaction gas for activation employs hydrogen gas or oxygen gas. Furthermore, carbon dioxide (CO2 gas, sulfur dioxide (SO2) gas, nitrogen monoxide (NO) gas, nitrogen dioxide (NO2) gas, and water may be used as the reaction gas. If the reaction conditions are not appropriately controlled in the activation process, the graphite layer of the nano-rod may be melt or be inserted into an intermediate so that it is very important to adjust the process temperature. For instance, it is preferable to perform the activation process at 400˜1,200° C., more preferably at 500˜900° C., in case of hydrogenation. In addition, it is preferable to perform the activation process at 100˜500° C., more preferably at 200˜400° C., in case of oxidation.
Reference will now be made in detail to the preferred embodiments of the present invention, examples of which are illustrated in the accompanying drawings. However, the present invention is not limited to the embodiments illustrated herein after, and the embodiments herein are rather introduced to provide easy and complete understanding of the scope and spirit of the present invention.
To begin with, a method for manufacturing a filamentous nanocarbon used in the present invention will be set forth in brief herebelow.
First, a method for manufacturing a filamentous nanocarbon with a tubular structure will be illustrated. First of all, Fe/Ni alloy used as a metal catalyst is fabricated as a following method. A nickel nitride and an iron nitride are dissolved in distilled water at room temperature. Next, ammonium bicarbonate is added and stirred. Precipitate produced from this solution is washed with distilled water and ethanol, and then is dried in vacuum state. The dried precipitate is fired at 400° C. in dry air ambient so as to fabricate Fe—Ni oxide. The Fe—Ni oxide is reduced at 400° C. in H₂/He ambient. Thereafter, an aftertreatment is processed again at room temperature in O₂/He ambient to thereby obtain Fe—Ni alloy catalyst. The catalyst fabricated by this method is put into a quartz tube in a reaction furnace. Afterwards, a heat treatment is performed at 625° C. for 2 hours in H₂/He ambient. Thereafter, a heat treatment is performed at 625° C. for 2 hours while inflowing mixture gas of CO/H₂, to thereby obtain a carbon fiber.
The fabricated carbon fiber has such a structure that a carbon hexagonal plane is parallel with a fiber axis and a hollow exists therein. (FIG. 2). The outer diameter of the fiber is in a range of 5 to 35 nm, and an aspect ratio is 30 or higher. FIG. 2 a is a TEM image, and FIG. 2 b is an illustrative view setting forth a stacked structure of nano-rods. FIGS. 2C and 2D are scanning tunneling microscope (STM) images of the surface of the fiber. It is possible to observe that the nano-rods are interconnected and stacked from the drawings.
Second, a method for manufacturing a filamentous nanocarbon with a platelet structure will be illustrated. After fabricating an Fe catalyst from iron nitride using the aforementioned method, the Fe catalyst is put into the quartz tube in the reaction furnace. Thereafter, a heat treatment is performed at 600° C. for 2 hours while inflowing mixture gas of CO/H2 The fabricated carbon fiber has the platelet structure where the carbon hexagonal plane is stacked perpendicular to the fiber axis (FIG. 3). The outer diameter of the fiber is in a range of 90 nm to 300 nm, and an aspect ratio is 30 or higher. FIGS. 3 a and 3 b are TEM images and FIG. 3 c is an STM image of the surface of the nanocarbon. FIG. 3 d is an illustrative view setting forth a stacked structure of nano-rods. It is possible to observe that the nano-rod is stacked perpendicular to the fiber axis from the drawings.
Third, a method for manufacturing a filamentous nanocarbon with a Herringbone structure will be illustrated. After fabricating a Ni—Cu alloy catalyst from nickel nitride and copper nitride using the aforementioned method, the Ni—Cu alloy catalyst is put into the quartz tube in the reaction furnace. Thereafter, a heat treatment is performed at 580° C. for 2 hours in H₂/He ambient while inflowing mixture gas of ethylene/hydrogen so as to obtain a carbon fiber. The fabricated carbon fiber has such a Herringbone structure that the carbon hexagonal plane is formed in the V-shape with respect to the fiber axis at an angle of 20˜80° (FIG. 4). The outer diameter of the fiber is in a range of 80 nm to 350 nm, and an aspect ratio is 30 or higher. FIGS. 4 a and 4 b are TEM images and FIG. 4 c is an STM image of the surface of the fiber. FIG. 4 d is an illustrative view setting forth a stacked structure of nano-rods. It is possible to observe that the nano-rod is stacked as being inclined with respect to the fiber axis at a predetermined angle from the drawings.
Next, there will be illustrated a method for manufacturing a porous filamentous nanocarbon using a nano-drilling process of the present invention herebelow.

EMBODIMENT I

The nickel particle used for a nano-drill catalyst is attached on the outer periphery of the Herringbone filamentous nanocarbon by dipping and dispersing the Herringbone filamentous nanocarbon in nickel nitride solution. The filamentous nanocarbon is vacuum dried at 150° C. to fabricate a nanofiber on which the nickel catalyst is attached. The filamentous nano-carbon is put into the quartz tube in the reaction furnace. Thereafter, a heat treatment is performed at 800° C. for 2 hours in mixture gas of H₂/He ambient.
The fabricated porous filamentous nanocarbon, as illustrated in a TEM image in FIG. 6, becomes a very porous nanofiber in which the nano tunnels are formed. The nano tunnel is formed along the arrangement direction of the carbon hexagonal plane without any change in the structure of the filamentous nanocarbon. The nano tunnel has a diameter in a range of 5 to 30 nm. The specific surface area and a volume of the mesopore are measured to be 352 u/g and 0.42 u/g, respectively, using ₂NBrunauer-Emitter-Teller (BET) method.

EMBODIMENT 2

The nickel particle used for a nano-drill catalyst is attached on the outer periphery of the Herringbone filamentous nanocarbon by dipping and dispersing the Herringbone filamentous nanocarbon in nickel nitride solution. The filamentous nanocarbon is vacuum dried at 150° C. to fabricate a nanofiber on which the nickel catalyst is attached. The filamentous nano-carbon on which the nickel catalyst is attached is put into the quartz tube in the reaction furnace. Thereafter, a heat treatment is performed at 350° C. for 3 hours in O₂ambient.
The fabricated porous filamentous nanocarbon, as illustrated in a TEM image in FIG. 7, becomes a very porous nanofiber in which the nano tunnels are formed. The nano tunnel is formed along the arrangement direction of the carbon hexagonal plane without any change in the structure of the filamentous nanocarbon. The nano tunnel has a diameter in a range of 2 to 10 nm. Herein, although the average size of the mesopore is smaller than that of the first embodiment, the mesopores are uniformly distributed in comparison with the first embodiment. The specific surface area and a volume of the mesopore are measured to be 298 u/g and 0.39 u/g, respectively, using ₂N BET method.

EMBODIMENT 3

Iron particles used for a nano-drill catalyst are attached on the outer periphery of the Herringbone filamentous nanocarbon by dipping and dispersing the Herringbone filamentous nanocarbon in iron nitride solution. The filamentous nanocarbon is vacuum dried at 150° C. to fabricate a nanofiber on which the iron catalyst is attached. The filamentous nano-carbon on which the iron catalyst is attached is put into the quartz tube in the reaction furnace. Thereafter, a heat treatment is performed at 850° C. for 3 hours in mixture gas of He/H2 ambient.
The fabricated porous filamentous nanocarbon, as illustrated in a TEM image in FIG. 8, becomes a very porous nanofiber in which the nano tunnels are formed. The nano tunnel is formed along the arrangement direction of the carbon hexagonal plane. However, since a graphitization partially occurs at the same time with the gasification due to the catalyst unlike the first and second embodiments, a carbon structure around the mesopore is slightly changed so as to fabricate a porous material having good graphitizability around the mesopore. The specific surface area and a volume of the mesopore are measured to be 254 u/g and 0.33 u/g, respectively, using 2N BET method.

EMBODIMENT 4

The nickel particle used for a nano-drill catalyst is attached on the outer periphery of the platelet filamentous nanocarbon by dipping and dispersing the platelet filamentous nanocarbon in nickel nitride solution. The filamentous nanocarbon is vacuum dried at 150° C. to fabricate a nanofiber on which the nickel catalyst is attached. The filamentous nano-carbon on which the nickel catalyst is attached, is put into the quartz tube in the reaction furnace. Thereafter, a heat treatment is performed at 800° C. for 3 hours in mixture gas of H₂/He ambient.
The fabricated porous filamentous nanocarbon, as illustrated in a TEM image in FIG. 9, becomes a very porous nanofiber in which the nano tunnels are formed. The nano tunnel is formed along the arrangement direction of the carbon hexagonal plane without any change in the structure of the filamentous nanocarbon. The nano tunnel has a diameter in a range of 6 to 32 mm. The specific surface area and a volume of the pore are measured to be 154 u/g and 0.24 u/g, respectively, using ₂NBET method.

COMPARATIVE EXAMPLE 1

In the first comparative example, a conventional alkali cactivation method is applied to the Herringbone filamentous nanocarbon. A mixture of the Herringbone filamentous nanocarbon and KOH (nanocarbon:KOH=1:4 w/w) is put on a pan. Thereafter, a heat treatment is performed at 850° C. for 2 hours in mixture gas of H₂/He ambient.
From a TEM image, it is observed that predetermined portions of the carbon hexagonal plane are removed at a regular space, forming a ladder shape. According to the BET result, it is understood that micropores of which specific surface area and size are 154 u/g and 1.0 nm, respectively, are formed. Therefore, it is known that the conventional alkali cactivation method is not adaptive for selectively forming mesopores of the inventive porous filamentous nanocarbon.

COMPARATIVE EXAMPLE 2

The nickel particle used for a nano-drill catalyst is attached on the outer periphery of the Herringbone filamentous nanocarbon by dipping and dispersing the filamentous nanocarbon with butte structure in nickel nitride solution. The filamentous nanocarbon is vacuum dried at 150° C. to fabricate a nanofiber on which the nickel catalyst is attached. The filamentous nano-carbon on which the nickel catalyst is attached is put into the quartz tube in the reaction furnace. Thereafter, a heat treatment is performed at 800° C. for 3 hours in mixture gas of H₂/He ambient.
Unlike the embodiments, it is known that the filamentous nanocarbon of the second comparative example shows a weight change before and after the reaction is less than 5%. This is well observed in the TEM image that the micropores are not formed uniformly. The specific surface area and a volume of the pore are measured to be 122 u/g and 0.21 u/g, respectively, using ₂NBET method. Thus, it is known that the inventive nano-drilling method is not effective for a tubular filamentous nanocarbon, i.e., the carbon nanotube. As the result of the second comparative example, considering that the nano-drilling method is not effective for the tubular structure in which the end portion of the nano-rod is not exposed, the fabrication of the tunnel-like mesopores according to the nano-drilling of the present invention is performed such that the catalyst attached on the exposed end portion of the nano-rod deems to selectively gasify the nano-rods therearound.

COMPARATIVE EXAMPLE 3

The nickel particle used for a nano-drill catalyst is attached on a carbon black by dipping and dispersing the carbon black in nickel nitride solution. The carbon black is vacuum dried at 150° C. to fabricate the carbon black on which the nickel catalyst is attached. The carbon black on which the nickel catalyst is attached on is put into the quartz tube in the reaction furnace. Thereafter, a heat treatment is performed at 800° C. for 3 hours in mixture gas of H₂/He ambient.
There is little weight change before and after the reaction, and thus it is known that the nano-drilling method according to the present invention is not effective for the carbon black.
Examples in which the porous filamentous nanocarbon fabricated by the nanodrilling method of the present invention is applied will be illustrated herebelow.
First, the porous filamentous nanocarbon can be applied to an adsorbent and a chromatography.
Since the mesopore of the porous filamentous nanocarbon according to the present invention has a maximum pathway of about 200 nm long, it takes about 2 seconds for molecules to diffuse from one end of the mesopore to the other end. In this manner, the diffusion time is very short so that it is very effective for the inventive nanocarbon to be applied to the adsorbent and the chromatography. In particular, in case of the chromatography, it is very adaptively used for separating biologically important molecules such as enzyme, steroid, alkaloid, hormone, protein, and so forth.
Second, the porous filamentous nanocarbon can be applied to a catalyst support. Due to the short diffusion pathway as described above, it may be importantly applied to the conversion of the polymer material, e.g., synthesis of steroid and enzyme, refinement of petroleum, or the like.
Third, the porous filamentous nanocarbon can be applied to an electrode for electrochemical reaction. The filamentous nanocarbon according to the present invention is dipped into the catalyst metal solution and is coated with the catalyst metal, to thereby form an electrode on the surface of the porous filamentous nanocarbon. Since the material so fabricated is resistant to alkali or acid, it is possible to apply the inventive nanocarbon to electrochemical reaction requiring severe environments. For instance, the coated Pt—Ru catalyst may be used as a catalyst for oxidizing methanol in methanol fuel cell. FIG. 10 is a cyclic voltammogram illustrating methanol oxidation using Pt—Ru catalyst electrode and Ag/AgCl electrode, which shows an activity measured in the preset invention about two times greater than the prior art.
The porous filamentous nanocarbon of the present invention may be variously applied to an adsorbent, a chromatography material, a catalyst support, etc. That is, it is possible to apply the porous filamentous nanocarbon to the separation/absorption of protein, petroleum, and so forth, and an electrode for a fuel cell.

Claims

1. A method for forming a porous filamentous nanocarbon, the method comprising:

radially forming a tunnel-like mesopore from an outer periphery toward the central axis of a filamentous nano carbon by attaching a material having a metal catalyst on an outer periphery of the filamentous nanocarbon and removing a carbon hexagonal plane through gasification in virtue of the metal catalyst.

2. The method of claim 1, wherein the metal catalyst includes at least one selected from the groups, V, VI, VII, and □ of the periodic table.

3. The method of claim 2, wherein the metal catalyst is at least one selected from the group consisting of iron (Fe), nickel (Ni), copper (Cu), platinum (Pt), manganese (Mn), vanadium (V), and an alloy thereof.

4. The method of claim 1, wherein the mesopore is formed according as a pre-determined portion of the filamentous nanocarbon on which the metal catalyst is attached is removed through a selective gasification reaction in virtue of the metal catalyst.

5. The method of claim 4, wherein the mesopore is formed along the arrangement direction of the carbon hexagonal plane as the predetermined portion of the carbon hexagonal plane on which the metal catalyst is attached is removed through the selective gasification reaction.

6. The method of claim 1, wherein a reactant for gasifying the carbon hexagonal plane in virtue of the metal catalyst includes hydrogen gas.

7. The method of claim 6, wherein the gasification temperature is in a range of 500° C. to 900° C.

8. The method of claim 1, wherein a reactant for gasifying the carbon hexagonal plane in virtue of the metal catalyst includes oxygen gas.

9. The method of claim 8, wherein an activation temperature is in a range of 200° C. to 400° C.