WO2007139244A1

WO2007139244A1 - A carbon nanotube of which surface is modified by transition metal coordination, and a method for modifying the same

Info

Publication number: WO2007139244A1
Application number: PCT/KR2006/002087
Authority: WO
Inventors: Ha Jin Lee; Haeseong Lee; Tinh Nguyen
Original assignee: Korea Basic Science Institute
Priority date: 2006-05-30
Filing date: 2006-05-30
Publication date: 2007-12-06

Abstract

Disclosed is a carbon nanotube having a modified surface through transition metal coordination. The carbon nanotube includes a carbon nanotube having a surface where a π-electron exists, and a transition metal ion being coordinate-bonded by electron -sharing of the π-electron existing in the surface of the carbon nanotube. A carbon nanotube further includes an organic material coordinate-bonded to the transition metal ion. A method of manufacturing the carbon nanotube is also disclosed.

Description

[DESCRIPTION]

[Invention Title]

A carbon nanotube of which surface is modified by transition metal

coordination, and A method for modifying the same

[Technical Field]

The present invention relates to carbon nanotubes having surfaces

modified by transition metal coordination and methods of modifying the same.

More specifically, this invention relates to carbon nanotubes to the surfaces of

which a transition metal is coordinate-bonded and an organic material is

coordinate-bonded to the transition metal, and methods of manufacturing the

same.

[Background Art]

In recent years, nano technology has become highly of interest. In

particular, research and development on nano technology have been focused on

carbon nanotubes in terms of quantity and quality.

A carbon nanotube has a peculiar appearance due to much higher aspect

ratio than any other material made so far. The tube diameter is on the order of

nanometers while its length is more than the order of micrometers.

The carbon nanotube is a carbon allotrope formed of carbon elements

enriched in the earth. A carbon nanotube is structured in a way that one carbon is combined with three other carbons to form a planar structure of

hexagonal honeycomb pattern, which is then rolled up to form a tube. It can be

categorized into several types by the shapes and methods of rolled-up tube and

the number of walls constituting a tube.

That is, the carbon nanotube may be categorized into a multi-walled

nanotube (MWNT) and a single-walled nanotube (SWNT). The multi-walled

nanotube includes two or more walls and the single-walled nanotube includes

only single wall. Owing to their structural difference, their properties become

different from each other. For example, SWNTs tend to be entangled to form a

nanorope since larger surface area of SWNTs induces stronger interaction than

that of MWNTs.

A carbon nanotube has many attractions in its properties such as good

electrical conductivity, high mechanical strength and Young's modulus, etc.

These advantages allow us to seek various applications such as electron emitters

for FED (field emission display) and white light source, electrodes of secondary

Lithium ion battery, transportation and storage medium for fuel battery,

nano-wires, probes of AFM/STM, field effect transistors (FET),

high-performance composites and so on.

In spite of their versatility, there is a critical disadvantage in practical

applications. Due to the strong van der Waals interaction with other carbon nanotubes, it is very difficult for the nanotubes to be dissolved or dispersed. In

order to overcome this limitation in its applications, many approaches have been

attempted. For example, a chemical functional group is introduced into the

carbon nanotube to modify the physical and chemical properties thereof to

thereby improve its dispersibility within solvents and consequently provide

applicability for electronic nano elements.

In a typical method for chemically modifying a carbon nanotube, the

carbon nanotube is treated in a strong acid for a long period of time such that a

carboxylic group is introduced at the ends of or in the wall of carbon nanotube

to modify the nanotube through coordinate-bonding. However, this method

requires a long process time and has a low yield rate for the carbon nanotube

recovered after the process. In addition, the recovered nanotube itself has a

significant damage to adversely affect its electrical conductivity.

[Disclosure]

[Technical Problem]

Accordingly, the present invention has been made in an effort to solve

the problems occurring in the prior art. It is an object of the invention to

provide a carbon nanotube of which surface is modified through transition metal

coordination to thereby have an improved dispersibility, and a method of

modifying the carbon nanotube. In addition, another object of the invention is to provide a carbon

nanotube having hydrophobic or hydrophilic property through coordinate-bonding

of an organic material to the transition material, and a modification method

thereof.

[Technical Solution]

To achieve the above objects, according to an aspect of the invention, there

is provided a carbon nanotube having a chemically modified surface through

transition metal coordination. The carbon nanotube comprises a carbon nanotube

having a surface where a π-electron exists, and a transition metal ion being

coordinate-bonded by electron- sharing of the π-electron existing in the surface

of the carbon nanotube.

Preferably, the carbon nanotube may further comprise an organic material

being coordinate-bonded to the transition metal ion.

Preferably, the organic material includes a compound containing a carboxylic

group.

Preferably, the carboxylic compound includes EDTA or stearic acid.

Preferably, the transition metal ion includes any one selected from the group

consisting of Cu¹⁺, Cu²⁺, Fe²⁺, Fe³⁺, Ru²⁺, Ru³⁺, Cr²⁺, Cr³⁺, Mo⁰, Mo⁺, Mo²⁺, Mo³⁺,

W²⁺, W³⁺, Rh³⁺, Rh⁴⁺, Co⁺, Co²⁺, Re²⁺, Re³⁺, Ni⁰, Ni⁺, Ni²⁺, Mn³⁺, Mn⁴⁺, V²⁺, V³⁺,

Pd²⁺, Pt²⁺, Zn⁺, Zn²⁺, Au⁺, Au²⁺, Ag⁺ and Ag²⁺. Preferably, the carbon nanotube includes a single-walled carbon nanotube

(SWNT) or a multi-walled carbon nanotube (MWNT).

According to another aspect of the invention, there is provided a method of

chemically modifying a carbon nanotube through transition metal coordination.

The method comprises the steps of a) introducing a transition metal ion into a

solvent, and b) immersing a carbon nanotube into the solvent containing the

transition metal ion to form a carbon nanotube -transition metal composite

through coordinate-bonding between the carbon nanotube and the transition metal

ion.

Preferably, the method may further comprise the steps of c) introducing an

organic material into a solvent, and d) immersing the carbon nanotube-transition

metal composite formed in the step b) into the solvent containing the organic

material to form a carbon nanotube-transition metal-organic material composite

through coordinate -bonding between the carbon nanotube-transition metal

composite and the organic material.

Preferably, the organic material in the steps c) and d) includes a compound

containing a carboxylic group.

Preferably, the carboxylic compound includes EDTA or stearic acid.

Preferably, the transition metal ion includes any one selected from the group

consisting of Cu¹⁺, Cu²⁺, Fe²⁺, Fe³⁺, Ru²⁺, Ru³⁺, Cr²⁺, Cr³⁺, Mo⁰, Mo⁺, Mo²⁺, Mo³⁺, W²⁺, W³⁺, Rh³⁺, Rh⁴⁺, Co⁺, Co²⁺, Re²⁺, Re³⁺, Ni⁰, Ni⁺, Ni²⁺, Mn³⁺, Mn⁴⁺, V²⁺, V³⁺,

Pd²⁺, Pt²⁺, Zn⁺, Zn²⁺, Au⁺, Au²⁺, Ag⁺ and Ag²⁺.

Preferably, the carbon nanotube includes a single-walled carbon nanotube or

a multi-walled carbon nanotube.

Preferably, the solvent includes an organic solvent or an aqueous solvent.

Preferably, the steps b) and d) includes the step of immersing the carbon

nanotube and the carbon nanotube-transition metal composite respectively into

the solvent and uniformly dispersing the mixture using a dispersing means.

Preferably, the dispersion using the dispersing means is carried out

through an ultrasonic treatment, through a refluxing treatment by stirring and

heating inside of a container, or using a homogenizer.

[Advantageous Effects]

The present invention can provide a hydrophilic or hydrophobic carbon nanotube

having an improved dispersibility and a modification method thereof. In addition,

a desired functional group can be introduced onto the surface of a carbon

nanotube, under alleviated reaction conditions, in organic or aqueous solvent,

within 2 hours at room temperature, without minimizing damage on the surface

of carbon nanotube.

That is, according to the invention, the process time can be dramatically

reduced, and the yield of carbon nanotube recovered after the process is very high. In the recovered carbon nanotube, its own damage is very small and thus

its electrical conductivity is not affected, dissimilar to the conventional carbon

nanotube.

As described above, the surface of carbon nanotube can be

characteristically controlled through its chemical functional radicals. Thus, this

characteristic control plays an important role in modeling the dispersion of

carbon nanotube within various solvents and polymer matrixes. It will further

advance carbon nanotube-based nano-composites and nano-devices.

[Description of Drawings]

Fig. 1 is a schematic view showing a process for modifying a carbon

nanotube according to the present invention!

Figs. 2a and 2b are TEM photographs showing a single-walled carbon

nanotube and a multi-walled carbon nanotube respectively;

Figs. 3a and 3b are TEM images showing CuCl₂-SWNT and

CuCb-MWNT according to the invention;

Figs. 4a and 4b are TEM images showing CuCl₂-SWNT-EDTA and

CuCl₂-MWNT-EDTA according to the invention;

Figs. 5a and 5b are TEM images showing CUCI₂-SWNT-SA and

CUCI₂-MWNT-SA according to the invention;

Fig. 6 is an AFM image showing CuCl₂-SWNT and CuCl₂-MWNT according to the invention;

Fig. 7 shows the result of Raman spectrometric analysis for SWNT

modified according to the invention!

Fig. 8 shows the result of FT-IR analysis for SWNT obtained according

to the invention;

Fig. 9 shows the TGA result for CuCl₂-SWNT-EDTA obtained according

to the invention;

Fig. 10 shows the TGA result for CUCI₂-SWNT-SA obtained according to

the invention;

Fig. 11 shows a water absorption curve with relative humidity for SWNT

modified according to the invention!

Fig. 12 shows the results of UV-VIS spectrometric analysis for

CuCl2-SWNT-EDTA/SA obtained according to the invention, where the analysis

has been carried out immediately and one hour after an ultrasonic treatment; and

Fig. 13 shows the area difference in light absorbance for

CuCb-SWNT-EDTA/SA of the invention, depending upon the solvent polarities

and duration time.

[Mode for Invention]

Hereinafter, exemplary embodiments of the invention will be explained in

details with reference to the accompanying drawings. As shown in Fig. 1, the present invention relates to a carbon nanotube on

the surface of which π-electrons are rich. The carbon nanotube is modified by

coordinate bond with a transition metal, which has an empty d-orbital to thereby

be easily bonded with the π-electron. Therefore, agglomeration and the like,

which is caused by Van Der Waal's force between nanotubes, can be prevented

to thereby enable to dramatically improve dispersibility.

The transition metal may be any one selected from the group consisting of

Cu¹⁺, Cu²⁺, Fe²⁺, Fe³⁺, Ru²⁺, Ru³⁺, Cr²⁺, Cr³⁺, Mo⁰, Mo⁺, Mo²⁺, Mo³⁺, W²⁺, W³⁺, Rh³⁺,

Rh⁴⁺, Co⁺, Co²⁺, Re²⁺, Re³⁺, Ni⁰, Ni⁺, Ni²⁺, Mn³⁺, Mn⁴⁺, V²⁺, V³⁺, Pd²⁺, Pt²⁺, Zn⁺,

Zn²⁺, Au⁺, Au²⁺, Ag⁺ and Ag²⁺.

In addition, secondarily an organic material is coordinate-bonded to the

transition metal ion that is primarily coordinate-bonded to the carbon nanotube.

In this way, hydrophobic or hydrophilic property is provided to the carbon

nanotube formed by coordinate bond with a transition metal. Preferably, the

organic material may include EDTA and stearic acid containing a carboxylic

group, which is capable of secondary coordinate-bond with transition metals. In

case of EDTA, hydrophilic (COOH) property is provided to the carbon nanotube.

In case of the stearic acid, hydrophobic (CH3) is provided to the carbon

nanotube. In this way, hydrophilic or hydrophobic can be selectively provided,

depending upon the environment where the carbon nanotube is applied, thereby further improving the dispersibility of carbon nanotube. For example, the

hydrophilic carbon nanotube comes to have a higher dispersibility in a polar

solvent.

This transition metallization/coordination technique can be used to

functionalize both a singe wall carbon nanotube and a multi-walled carbon

nanotube.

On the other hand, the carbon nanotube is chemically modified through

transition metal coordination as follows: a) a transition metal ion is introduced

into a solvent, b) a carbon nanotube is immersed into the solvent mixed with the

transition metal ion, thereby forming a carbon nanotube-transition metal

composite through coordinate -bond between the carbon nanotube and the

transition metal ion.

Thereafter, preferably, c) an organic material is introduced into the solvent,

and d) the carbon nanotube-transition metal composite is immersed into the

solvent mixed with the organic material to thereby form a carbon

nanotube-transition metal-organic material composite through coordination

between the carbon nanotube-transition metal composite and the organic material.

Preferably, in the b) and d) steps, the carbon nanotube and the carbon

nanotube-transition metal composite are immersed into the solvent and dispersed

uniformly using a dispersing means. As an alternative for ultrasonic treatment, in the step of forming the carbon

nanotube-transition metal composite and the carbon nanotube-transition

metal-organic material composite, stirring and heating can be carried out inside

of a container to reflux, or a homogenizer can be employed. This dispersing

treatment disperses the carbon nanotube and the carbon nanotube-transition

metal composite uniformly in the solvent to avoid agglomeration thereof, thereby

resulting in spontaneous coordinate bonding between the carbon

nanotube-transition metal composite and the organic material.

In the following examples, a single-walled carbon nanotube or a

multi-walled carbon nanotube, as shown in Fig. 2, is used.

(Example 1)

CuCl₂-SWNT

10 mg of SWNT is mixed with 20 mL of CuCk 2H2θ-methanol solution and

an ultrasonic treatment (20 KHz) is performed at room temperature for 2 hours.

The ultrasonic treated SWNT solution is centrifugally separated to recover

precipitates, which are rinsed twice with 20 mL of methanol to obtain a black

precipitate through a vacuum drying. Fig. 3a is a TEM photography showing

CuCk-SWNT obtained in this example. In this image, black spots are CuCb

particles coordinate -bonded to the SWNT. It can be seen that a plurality of

CuCb particles are bonded to the single-walled carbon nanotube. In addition, Table 1 summaries the results of electron probe micro-analysis for CuCb-SWNT

obtained according to the invention and an SWNT before modification. As can

be seen from Table 1, Cu and Cl has been found only in the CuCb-SWNT

according to the invention.

[Table 1]

(Example 2)

CuCb-MWNT

This example is the same as the example 1, except that MWNT, instead of

SWNT, is used in the synthesis of CuCl₂-MWNT. Fig. 3b shows a TEM image

showing CuCl₂-MWNT obtained according to the invention. In Fig. 3b, black

spots are CuCl₂ particles coordinate-bonded to MWNT. Thus, it can be seen

that a plurality of CuCl₂ particles are bonded to the multi-walled carbon

nanotube.

(Example 3)

CuCb-SWNT-EDTA 20 mg of CuCl₂-SWNT is mixed with 20 mL of 0.25 M EDTA

(ethylenediaminetetraacetic acid) solution and an ultrasonic treatment (20 KHz) is

performed at room temperature for 1 hour. The ultrasonic treated solution is

centrifugally separated at 14,000 rpm for 20 minutes to recover precipitates,

which are rinsed twice with 10 mL of H₂O and 10 mL of ethanol to obtain a

black precipitate through a vacuum drying. Fig. 4a is a TEM photography

showing CuCb-SWNT-EDTA obtained in this example, which looks different

from the image of Fig. 3a where only transition metal is coordinated. The

surface of the single-walled carbon nanotube^~CuCl₂ composite has been modified

with COOH to become hydrophilic.

(Example 4)

CuCb-MWNT-EDTA

This example is the same as the example 3, except that CuCk-MWNT,

instead of CuCl₂-SWNT, is used in the synthesis of CuCl₂-SWNT-EDTA. Fig.

4b shows a TEM image showing CuCl₂- SWNT-EDTA obtained in this example,

which looks different from the image of Fig. 3b where only transition metal is

coordinated. The surface of the multi-walled carbon nanotube-CuCl₂ composite

has been modified with -COOH to become hydrophilic.

(Example 5)

This example is the same as the example 3, except that 20 mL of 50 mM

stearic acid-ethanol solution, instead of 20 mL of 0.25 M EDTA solution, is used

in the synthesis of CuCl₂-SWNT-EDTA. Fig. 5b shows a TEM image showing

CuCh-SWNT-SA obtained in this example, which looks different from the image

of Fig. 3b where only transition metal is coordinated. The surface of the

single-wall carbon nanotube-CuCb composite has been modified with -CH3 to

become hydrophobic.

(Example 6)

CUCI₂-MWNT-SA

This example is the same as in the example 5, except that CuCb-MWNT,

instead of CuCl₂-SWNT, is used in the synthesis of CUCI₂-SWNT-SA. Fig. 5b

shows a TEM image showing CUCI₂-MWNT-SA obtained in this example,

which looks different from the image of Fig. 3b where only transition metal is

coordinated. The surface of the multi-walled carbon nanotube^~CuCl₂ composite

has been modified with -CH3 to become hydrophobic.

Fig. 6 is an AFM (atomic force microscope) image for SWNT and MWNT

reacted with CuCl₂ according to the invention. The AFM measurement of the

carbon nanotube reacted with CuCl₂ has found that transition metal particles

having a size of 3 nm are combined to the carbon nanotube wall. The particle

size matches those of metal particles shown in the TEM images of Figs. 3 to 5. Fig. 7 shows the result of Raman Spectrometric analysis for SWNT

modified according to the invention. The positions of RBM, D and G-band for

four specimens have not been changed. When the surface of single-wall carbon

nanotube is modified with transition metals, D/G ratio (WΪG) has been increased

to 0.13 (0.07 before being modified). This means that the surface of a

single-walled carbon nanotube has been modified with transition metals. In

addition, where the single-walled carbon nanotube, which has been modified with

a transition metal, is modified again with an organic material, i.e., EDTA or SA,

it has been increased to above 0.2. It means that the single-walled carbon

nanotube modified with a transition metal has been modified again with other

materials.

Fig. 8 shows the FT-IR result for a single-walled carbon nanotube modified

according to the invention. When only EDTA exists, the C=O stretching mode

has been viewed at 1689 cm^"1. When CuCk is combined with EDTA, the

stretching mode is separated into 1726 cm^"1 (C=O asymmetrical stretching mode)

and 1590 cm^"1 (C=O symmetrical stretching mode). When a carbon nanotube

modified with CuCk according to the invention is reacted with EDTA, the

stretching mode appears at 1722, 1573 cm \ which means that the carbon

nanotube modified with CuCb has been combined with EDTA.

Figs. 9a and 9b are the results of TGA (thermal gravimetric analysis) under nitrogen atmosphere and with a temperature increment of 10°C/min with four

materials, which are SWNT, CuCb-SWNT according to the invention,

SWNT-CuCk-EDTA according to the invention, and physically mixed

SWNT-CuCl₂ and EDTA. In Fig. 9a, first, in case of SWNT and CuCl₂-SWNT

according to the invention, as the temperature increases, its weight decreases

slowly. In case of CuCl₂-SWNT-EDTA according to the invention, however, a

sudden decrease in its weight has been viewed at around 300 °C, which

corresponds to decomposition of the organic material EDTA. This sudden

change of weight is similar to a sudden decrease of weight in Fig. 9b, which is

caused by decomposition of EDTA at 261.6 ^°C when CuCl₂-SWNT and EDTA are

physically mixed (not chemically reacted). That is, it can be seen from Figs. 9a

and 9b that, in case of SWNT-CUCI₂-EDTA according to the invention,

SWNT-CuCl₂ has been chemically combined with EDTA.

Figs. 10a and 10b are the results of TGA (thermal gravimetric analysis)

under nitrogen atmosphere and with a temperature increment of 10^°C/min with

four materials, which are SWNT, CuCl₂-SWNT according to the invention,

SWNT-CUCI₂-SA according to the invention, and physically mixed SWNT-CuCl₂

and SA. In Fig. 10a, first, in case of SWNT and CuCl₂-SWNT according to the

invention, as the temperature increases, its weight decreases slowly. In case of

CUCI₂-SWNT-SA according to the invention, however, a sudden decrease in its weight has been viewed at around 270 "C, which corresponds to decomposition of

the organic material SA. This sudden change of weight is similar to a sudden

decrease of weight in Fig. 10b, which is caused by decomposition of SA at 18

0^°C when CuCb-SWNT and SA are physically mixed (not chemically reacted).

That is, it can be seen from Figs. 10a and 10b that, in case of

SWNT-CuCk-SA according to the invention, SWNT-CuCb has been chemically

combined with SA.

Fig. 11 shows a water absorption curve with relative humidity. At a higher

relative humidity (80%), the hydrophilic CuCl₂-SWNT-EDTA according to the

invention has a higher rate of water uptake, rather than the hydrophobic

CuCb-SWNT-SA according to the invention. It can be seen from the above

results that the surface of a carbon nanotube modified according to the invention,

i.e., the surface of CuCl₂-SWNT-EDTA and CUCI₂-SWNT-SA has been modified

to have hydrophilic and hydrophobic properties respectively.

Fig. 12 is a graph showing the absorbance measured using a UV

spectrophotometer in order to observe dispersibility of the carbon nanotube

modified in two solvents (DMF: polar, THF: non-polar) having polarities different

from each other. In case of both nanotubes, the absorbance has been decreased

when measured one hour after dispersion, rather than when measured

immediately after dispersion. This means that the concentration has been decreased over time due to re-aggregation of carbon nanotube. Fig. 13 shows

the area difference of light absorbance over time with respect to the absorbance

area of 700 nm to 1000 nm in Fig. 12, in order to experiment a relative stability

of hydrophilic/hydrophobic carbon in hydrophilic/hydrophobic solvents. It can be

seen that the smaller area difference means the more stable dispersion in the

solvent. It has been found out that the hydrophilic carbon nanotube modified

with EDTA is more stably dispersed in the DMF and the hydrophobic carbon

nanotube modified with SA is more stably dispersed in the THF.

[Industrial Applicability]

As described above, the surface of carbon nanotube can be characteristically

controlled through its chemical functional radicals. Thus, this characteristic

control plays an important role in modeling the dispersion of carbon nanotube

within various solvents and polymer matrixes. It will further advance carbon

nanotube-based nano-composites and nano-devices.

Although the present invention has been described with reference to

several preferred embodiment, the description is illustrative of the invention and

is not to be construed as limiting the invention. Various modifications and

variation may occur to those skilled in the art, without departing from the spirit

and scope of the invention, as defined by the appended claims.

Claims

[CLAIMS]

[Claim 1]

A carbon nanotube having a modified surface through transition metal

coordination, the carbon nanotube comprising:

a carbon nanotube having a surface where a π-electron exists; and

a transition metal ion being coordinate-bonded by electron -sharing of the π

-electron existing in the surface of the carbon nanotube.

[Claim 2]

The carbon nanotube as claimed in claim 1, further comprising an organic

material being coordinate-bonded to the transition metal ion.

[Claim 3]

The carbon nanotube as claimed in claim 2, wherein the organic material

includes a compound containing a carboxylic group.

[Claim 4]

The carbon nanotube as claimed in claim 3, wherein the carboxylic

compound includes EDTA or stearic acid.

[Claim 5]

The carbon nanotube as claimed in claim 1 or 2, wherein the transition

metal ion includes any one selected from the group consisting of Cu¹⁺, Cu ⁺, Fe ⁺,

Fe³⁺, Ru²⁺, Ru³⁺, Cr²⁺, Cr³⁺, Mo⁰, Mo⁺, Mo²⁺, Mo³⁺, W²⁺, W³⁺, Rh³⁺, Rh⁴⁺, Co⁺, Co²⁺, Re²⁺, Re³⁺, Ni⁰, Ni⁺, Ni²⁺, Mn³⁺, Mn⁴⁺, V²⁺, V³⁺, Pd²⁺, Pt²⁺, Zn⁺, Zn²⁺, Au⁺, Au²⁺,

Ag⁺ and Ag²⁺.

[Claim 6]

The carbon nanotube as clamed in claim 1 or 2, wherein the carbon

nanotube includes a single-walled carbon nanotube or a multi-walled carbon

nanotube.

[Claim 7]

A method of chemically modifying a carbon nanotube through transition

metal coordination, the method comprising the steps of:

a) introducing a transition metal ion into a solvent; and

b) immersing a carbon nanotube into the solvent containing the transition

metal ion to form a carbon nanotube-transition metal composite through

coordinate-bonding between the carbon nanotube and the transition metal ion.

[Claim 8]

The method as claimed in claim 7, further comprising the steps of:

c) introducing an organic material into a solvent; and

d) immersing the carbon nanotube-transition metal composite formed in the

step b) into the solvent containing the organic material to form a carbon

nanotube-transition metal-organic material composite through coordinate-bonding

[Claim 9]

The method as claimed in claim 8, wherein the organic material in the

steps c) and d) includes a compound containing a carboxylic group.

[Claim 10]

The method as claimed in claim 9, wherein the carboxylic compound

includes EDTA or stearic acid.

[Claim 11]

The method as claimed in claim 7 or 8, wherein the transition metal ion

includes any one selected from the group consisting of Cu¹⁺, Cu²⁺, Fe²⁺, Fe³⁺,

Ru²⁺, Ru³⁺, Cr²⁺, Cr³⁺, Mo⁰, Mo⁺, Mo²⁺, Mo³⁺, W²⁺, W³⁺, Rh³⁺, Rh⁴⁺, Co⁺, Co²⁺, Re²⁺,

Re³⁺, Ni⁰, Ni⁺, Ni²⁺, Mn³⁺, Mn⁴⁺, V²⁺, V³⁺, Pd²⁺, Pt²⁺, Zn⁺, Zn²⁺, Au⁺, Au²⁺, Ag⁺ and

Ag²⁺.

[Claim 12]

The method as claimed in claim 7 or 8, wherein the carbon nanotube

includes a single-walled carbon nanotube or a multi-walled carbon nanotube.

[Claim 13]

The method as claimed in claim 7 or 8, wherein the solvent includes an

organic solvent or an aqueous solvent.

[Claim 14]

The method as claimed in claim 7 or 8, wherein the steps b) and d) includes the step of immersing the carbon nanotube and the carbon

nanotube-transition metal composite respectively into the solvent and uniformly

dispersing the mixture using a dispersing means.

[Claim 15]

The method as claimed in claim 14, wherein the dispersion using the

dispersing means is carried out through an ultrasonic treatment, through a

refluxing treatment by stirring and heating inside of a container, or using a

homogenizer.