WO2007058488A1

WO2007058488A1 - Method for manufacturing the high purity carbon nanotube film using dispersed solution of carbon nanotube

Info

Publication number: WO2007058488A1
Application number: PCT/KR2006/004834
Authority: WO
Inventors: Hee-Tae Jung; Dae-Hwan Jung; Sang Cheon Youn
Original assignee: Korea Advanced Institute Of Science And Technology
Priority date: 2005-11-16
Filing date: 2006-11-16
Publication date: 2007-05-24
Also published as: KR100754984B1; KR20070051979A

Abstract

The present invention relates to a method for preparing a high purity carbon nanotube film using a dispersed solution of carbon nanotube(CNT), and more particularly, to a method for preparing a high purity carbon nanotube film, the method comprising the steps of: (a) preparing highly purified dispersed solution of carbon nanotube having carboxyl group formed to add a coupling agent and base; (b) forming a CNT single layer by reacting the resulting dispersed solution with a substrate having exposed amine group on the surface thereof; (c) forming an organic amine layer on the CNT single layer by reacting the CNT single layer with an organic amine compound; (d) repeatedly laminating the CNTs by reacting CNT having exposed carboxyl group with the organic amine. According to the present invention, a high density CNT film having high purity can be prepared by repetitive amaide bond formation between the amine group on the surface of the substrate and the carboxyl group of CNT and thus it can be applied to bio-chips, bio-sensors, gas-sensors, a basic material of flat panel displays, bandable panel displays, transistors, transparent electrodes and a basic material of semiconductors.

Description

METHOD FOR MANUFACTURING THE HIGH PURITY CARBON NANOTUBE FILM USING DISPERSED SOLUTION

OF CARBON NANOTUBE

TECHNICAL FIELD

The present invention relates to a method for preparing a high purity carbon nanotube film using a dispersed solution of carbon nanotube(CNT), and more particularly, to a method for preparing a high purity carbon nanotube film with high density, the method comprising the steps of: (a) preparing a highly purified dispersed solution of carbon nanotube having carboxyl group formed to add a coupling agent and base; (b) forming a CNT single layer by reacting the resulting dispersed solution with a substrate having exposed amine group on the surface thereof; (c) forming an organic amine layer on the CNT single layer by reacting the CNT single layer with an organic amine compound; (d) repeatedly laminating the CNT by reacting CNT having exposed carboxyl group with the organic amine.

BACKGROUND ART

Carbon nanotube is an allotrope of carbon, which consists of carbons existing abundantly on the earth. They are tubular materials where a carbon atom is bound to other carbons in the form of a hexagonal honeycomb structure. Their diameter is about the size of a nanometer (i/io9 meter). Carbon nanotubes are known to have excellent mechanical properties, electrical selectivity, field emission properties and highly efficient hydrogen storage properties and be new and almost defect-free of all the existing materials. Because of their properties of excellent structural rigidity, chemical stability, ability to act as ideal one-dimensional (iD) "quantum wires" with either semiconducting or metallic behaviors and a large aspect ratio, carbon nanotubes exhibit a broad range of potential applications as a basic material of flat panel displays, transistors, energy reservoirs, etc., and as various sensors due to electrical properties of CNT (Dai, H., Ace. Chem. Res., 35:1035-1044, 2002).

In order to apply such properties more diversely, a purified single-walled carbon nanotube has been cut into short nanotube pieces using an acid. The cut carbon nanotube pieces have mainly -COOH chemical functional group at a part of ends and sidewall of the cut tube. The properties of the carbon nanotubes have been modified by chemical binding of various materials using these chemical functional groups. Further, there have been reported that -SH group was substituted for the functional group of carbon nanotube by chemical manipulation to fix on a gold surface (Nan, X. et al, J. Colloid Interface Sd., 245:311-8, 2002) and that carbon nanotube was immobilized in a multilayer structure using the electrostatic method (Rouse, J. H. et ah, Nano Lett., 3:59-62, 2003). However, the former has disadvantages in that it shows low carbon nanotube surface density and weak bonding because it can immobilize carbon nanotube only in a single layer, and the latter also has a fatal disadvantage in that there is a possibility of change innate properties of carbon nanotube and polymer molecules can be easily dissolved in solvent because of using mixed polymer.

To solve the above-mentioned problems, a patent relating to a method for laminating and patterning carbon nanotubes using chemical self assembly process

(KR 2004-0036526 Ai) was disclosed. The prior patent has an advantage in that it can provide a patterned film of CNT having an excellent conductivity in the processes of energy reservoirs, biosensors, semiconductors since it can easily form CNT patterns by forming a pattern on a surface-treated substrate using photolithography method to deposite CNTs in a single layer and multilayer using chemical self assembly process. However, it has disadvantages in that purified CNT film cannot be prepared since nitric acid was used in the purification and cutting processes of CNTs to result in large amount of impurities in the cut CNTs and the dispersed solution of CNTs coagulate due to the use of 0(7- azabenzotriazole-i-yl)-N,N,N',N'-tetramethyluronium hexafluorophosphate

(HATU) and N,N- diisopropylethylamine (DIEA) as a coupling agent and base during preparing CNT dispersed solution.

Meanwhile, the present inventors have developed a method for preparing a high density CNT film having exposed chemical functional group by laminating CNT on a substrate having exposed amine group using chemical linkage, but have not solved the above-mentioned problem due to using nitric acid in the purification and cutting processes of CNT.

In the case where CNT film is prepared using CNT containing large amount of impurities, there is a problem in that it is difficult to apply it to various sensors for measuring tiny changes and various materials, and in the case where a dispersed solution of CNT to be immobilized on a substrate coagulates, there is a problem in that a ununiform film is formed.

Therefore, there is an urgent demand for developing a method for preparing a high density CNT film having high purity which is uniformly fixed upon immobilizing a dispersed solution of CNTs on a substrate by maintaining high dispersion without containing impurities and coagulating the dispersed solution of CNTs.

Accordingly, the present inventors have made an extensive efforts to prepare a high density CNT film having high purity, and consequently found that a highly purified dispersed solution of CNT having formed carboxyl group was added with a coupling agent and base for maintaining dispersion to form a CNT single layer by allowing the resulting mixture solution to react with a substrate having amine group exposed on the surface thereof, and an organic amine layer was formed on the CNT single layer by allowing an organic amine compound to react with the CNT layer, and then the CNT is repeatedly depositted by allowing the organic amine to react with CNT having carboxyl group exposed, and thus, a high purity CNT film having high density was prepared, thereby completing the present invention.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide a method for a high density CNT film having high purity, the method comprising the steps of; (a) preparing a highly purified dispersed solution of carbon nanotube having formed carboxyl group to add a coupling agent and base so as to maintain high dispersion; (b) forming a CNT single layer by reacting the resulting mixture solution with a substrate having exposed amine group on the surface thereof; (c) forming an organic amine layer on the CNT single layer by reacting the CNT single layer with an organic amine compound; (d) repeatedly laminating the CNT by reacting the CNT layer having exposed carboxyl group with the organic amine, and a high density CNT film having high purity prepared using said method.

It is another object of the present invention to provide a method for modifying a CNT film so as to have both a functional group binding to the carboxyl group of CNT film having exposed carboxyl group and a chemical functional group selected from the group consisting of amine group, aldehyde group, hydroxy! group, thiol group and halogen and a high density CNT film having high purity prepared using the same.

To achieve the above object, in one aspect, the present invention provides a method for preparing a high purity CNT film, the method comprising the steps of: (a) (i) purifying a CNT using HCl; (ii) preparing a CNT having exposed carboxyl group by cutting the purified CNT with a mixture solution of H₂SO₄ and H₂O₂; and (iii) preparing a dispersed solution of the CNT having exposed carboxyl group by dispersing the CNT having exposed carboxyl group in a solvent to add with a coupling agent selected from the group consisting of 1,3-dicyclohexyl carbodiimide(DCC) and JV,i\T-carbonyliimidazole(CDI) and at least one base selected from the group consisting of ι-hydroxybenzotriazole(HOBt), 2- hydroxypyridine(HOPy), endo-JV-hydroxy-5-norbornene-2,3- dicarboximide(HONB), diisopropylethylamine(DIEA) and N- methylimidazole(NMI); (b) forming a CNT single layer on the surface of a substrate by amide bond formation between the amine group and the carboxyl group by reacting a substrate having an amine group exposed on the surface thereof with the dispersed solution of CNT having exposed carboxyl group prepared in step (a); (c) laminating CNT layers by reacting the dispersed solution of CNT having exposed carboxyl group, prepared in step (a) with the organic amine layer formed on the CNT layer after reacting the CNT single layer with an organic amine compound having at least two amine groups; and (d) forming a high density CNT film having exposed carboxyl group by repeating the step (c) n times to alternately laminate CNT layers and organic amine layers n times.

In the present invention, the CNT of (i) in the step (a) is preferably prepared by Hipco (high pressure CO disproportionation) process, and the solvent of the step (a) is preferably any one or more selected from the group consisting of N-methyl- 2-pyrrolidone(NMP), dimethyl acetamide(DMAc), dimethylformamide(DMF), cyclohexanone, ethylalcohol and chlorobenzene, more preferably, dimethylformamide(DMF) .

In the present invention, the coupling agent is preferably 1,3- dicyclohexylcarbodiimide(DCC) and the base is preferably 1- hydroxybenzotriazole(HOBt). In the present invention, the substrate of the step (b) is preferably any one or more material selected from the group consisting of glass, quartz, glass wafer, silicon wafer, melted silica, plastics and transparent polymer, and the substrate having exposed amine group on the surface thereof of the step (b) is preferably obtained by treating the substrate with any one or more selected from the group consisting of aminealkyloxysilane and aminealkylchlorosilane.

In the present invention, the organic amine compound having two or more amine groups is preferably a substance having a chemical formula of H₂N-Ri-NH₂, R₂- (NH₂)₃ θr R₃-(NH₂)₄; wherein Ri, R₂ and R₃ are independently a Ci_-20 saturated hydrocarbon, unsaturated hydrocarbon, aromatic organic group or Su_-20 silanes.

In another aspect, the present invention provides a high density CNT film having exposed carboxyl group, prepared by the above-described method.

In still another aspect, the present invention provides a method for preparing a high density CNT film, the method comprising modifying the CNT film having exposed carboxyl group so that chemical compound has both a functional group capable of binding to the carboxyl group and a chemical functional group selected from the group consisting of amine group, aldehyde group, hydroxyl group, thiol group and halogen.

In the present invention, the chemical compound is preferably any one or more selected from the group consisting of H₂N-Ri-NH₂, H₂N-R₂-SH, H₂N-R₃-OH, H₂N- R₄-CHO, or H₂N-R₅-COON, H₂N-R₆-X; wherein R₁, R₂, R₃, R₄, R₅ and R₆ are independently a C2-20 saturated hydrocarbon, unsaturated hydrocarbon or aromatic organic group, respectively and X is halogen elements or succinimdyl ester.

In yet another aspect, the present invention provides a high density CNT film having exposed chemical functional group selected from the group consisting of amine group, aldehyde group, hydroxyl group, thiol group and halogen, which is prepared by the above-described method.

The above and other objects, features and embodiments of the present invention will be more clearly understood from the following detailed description and accompanying claims.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. l is schematic view of the process for preparing a CNT by laminating CNT having exposed carboxyl group on a substrate having exposed amine group by amide bond formation.

FIG. 2 shows photographs by transmission electron microscope, comparing the inventive CNT cut using a mixture solution of sulfuric acid and H₂O₂ as described in Example i with CNT cut using a mixture solution of sulfuric acid and nitric acid according to the conventional method.

FIG. 3 shows an image comparing dispersion rate after a chemical compound inducing amide bond formation was dissolved in CNT which is highly dispersed in a solvent.

FIG. 4 is UV-vis-NIR (near infered ray) spectrophotometer graph showing a decrease in the penetration as the number of the inventive CNT layers increased.

FIG. 5 are photographs by scanning electron microscopy showing a comparison between a surface (a) of a substrate having CNT film formed by laminating CNT prepared by the conventional method 5 times and a surface (b) of a substrate having a high purity CNT film having high density formed by laminating the inventive CNT 5 times (left: magnification 5O,oooX, right: magnification ioo,oooX).

DETAILED DESCRIPTION OF THE INVENTION, AND PREFERRED EMBODIMENTS

The present invention relates to a method for preparing a high purity carbon nanotube film using a dispersed solution of carbon nanotube, and more particularly, to a method for preparing a high density CNT film having high purity, the method comprising the steps of; (a) preparing a dispersed solution of a highly purified carbon nanotube having formed carboxyl group to add with a coupling agent and base to the dispersed solution; (b) forming a CNT single layer by reacting the resulting mixture solution with a substrate having exposed amine group on the surface thereof; (c) forming an organic amine layer on the CNT single layer by reacting the CNT single layer with an organic amine compound; (d) repeatedly laminating CNTs by reacting the CNT layer having exposed carboxyl group with the organic amine.

A prefered embodiment for the preparation of CNT film according to the present invention is as follows.

The first step: Preparation of cut CNT having exposed carboxyl group

CNT, used in the present invention, is not particularly limited and may be a commercially available product or prepared by a conventional method to use. To apply amide bonds to the present invention, carboxyl groups should be exposed on the surface and/or both ends of CNT and pure CNT without having impurities is needed to obtain a high purity CNT film. The second step: Preparation of a dispersed solution of CNT remaining in a highly dispersed state

The prepared cut CNT having exposed carboxyl group was put into any one or more solvent selected from the group consisting of N-methyl-2-pyrrolidone(NMP), dimethyl acetamide(DMAc), dimethylformamide(DMF), cyclohexanone, ethylalcohol and chlorobenzene to disperse in a sonicator. The obtained dispersed solution of CNT should remain in a highly dispersed state during chemical reaction. According to the preparation method of the present invention, it is possible to remain in a highly dispersed state when a coupling agent, DCC (1,3- dicyclohexyl carbodiimide) or CDI (iV^JV'-carbonyldiimidazole) and any one or more base selected from the group consisting of HOBt (l-hydroxybenzotriazole), HOPy (2-hydroxypyridine), HONB (endo-iV-hydroxy-5-norbornene-2,3- dicarboximide), DIEA (diisopropylethylamine) and NMI (N-methylimiddazole) were used.

The third step: Preparation of a substrate having exposed amine group

As a substrate of the present invention, all kinds of substrates can be used as long as it is surface-treated with amine. Also, it can be prepared by immobilizing amine alkyloxysilane on the surface of a substrate to have an amine group exposed on the surface of the substrate, in which the substrate is a material selected from the group consisting of glass, quartz, glass wafer, silicon wafer, melted silica, plastics and transparent polymer and it is also possible to use commercially available substrate which had been surface-treated with amine.

The fourth step: Preparation of a CNT film

The dispersed solution of CNT having exposed carboxyl group, which remained in a highly dispersed state, prepared in the step 2, was reacted with the substrate having exposed amine group, prepared in the step 3 to form a CNT single layer on the substrate by amide bond formation between the carboxyl group and the amine group (FIG. ι(a)).

Then, the CNT single layer is reacted with an organic amine compound having two or more amine groups so as to reexpose amine group on the surface of CNT, and another CNT is laminated on the CNT single layer by reacting the dispersed solution of the CNT which remained in a highly dispersed state, prepared in the step 2, with CNT having exposed carboxyl group (FIG. l(b)).

Next, the CNT layers and the organic amine layers are alternately laminated n times by repetitively performing a chemical reaction between the CNT having exposed carboxyl group and the organic amine compound, i.e., amide bond formation to prepare a uniform CNT film having high density on the surface of the substrate (FIG. ι(c)).

The fifth step: Modifying the surface of CNT film

The CNT film having exposed carboxyl group, prepared in the step 4, can be modified using a chemical compound having both a functional group capable of binding to the carboxyl group and a chemical functional group (amine group, aldehyde group, hydroxyl group, thiol group and halogen). As a chemical compound that can be used for modification of CNT film, any one or more selected from the group consisting of H₂N-Ri-NH₂, H₂N-R₂-SH, H₂N-R₃-OH, H₂N-R₄- CHO, or H₂N-R₅-COON, H₂N-R₆-X can be used; wherein R₁, R₂, R₃, R₄, R₅ and R₆ are independently a C2-20 saturated hydrocarbon, unsaturated hydrocarbon or aromatic organic group, respectively, and X is halogen elements or succinimdyl ester.

Example The present invention will hereinafter be described in further detail by examples. However, it is to be understood that these examples can be modified into other various forms, and the scope of the present invention is not intended to be limited to such examples. Such examples are given to more fully describe the present invention for a person skilled in the art.

Example l: Preparation of cut CNT having exposed carboxyl group

5θθmg of CNT was heat-treateded in a furnace with a temperature of 365⁰C for 1 hour while air is injected at a flow of 0.1 SLM. The heat-trateded CNT was put into lL HCl to purify in a sonicator for 3 hours and filtered through a lμm filter to dry, then the above-discribed process was repeated 5 times. In order to cut the purified

CNT into CNT having exposed carboxyl group, the purified CNT was stirred in a mixture solution of H₂SO₄ and H₂O₂ (a volume ratio of 4:1) for 24 hours, then cut and diluted in a distilled water. The obtained suspension of CNT was filtered through a o.2μm filter and dried.

Comparative example 1: Comparision of CNT purity

CNT cut using a mixture solution of nitric acid and sulfuric acid was compared with the inventive CNT cut with respect to purity using HCl by TEM photograph (FIG. 2). As a result, the CNT cut using nitric acid and a mixture solution of nitric acid and H₂SO₄ contained a large amount of impurities (FIG. 2(a)), the inventive CNT cut using a mixture solution of H₂SO₄ and H₂O₂ and using HCl seldom contained impurities (FIG. 2(b)).

Example 2: Preparation of a dispersed solution of CNT remaining in a highly dispersed state

0.1 wt% of cut CNT having exposed carboxyl group, prepared in Example 1, was put into dimethylformamide (DMF solvent) to disperse in a sonicator for 10 hours, DCC (l^-dicyclohexylcarbodiimide) as an amide coupling agent and HOBt (l- hydroxybenzotriazole) as base were dissolved in a CNT-dispersed solvent at a concentration of 12 mM.

Comparative example 2: Comparision of dispersion rate of dispersed solution of CNT

Dispersion rate of the case where cut CNT was dissolved in a solvent to disperse and added with a conventional amide coupling agent and base was compared with that of the case where the dispersed solution of CNT was added with the inventive coupling agent and base, during the chemical reaction (FIG. 3).

As a result, in the case where o-(7-azabenzotriazole-i-yl)-N, N, N', N'- tetramethyluronium hexafluorophosphate (HATU)/N,N-diisopropylethylamine

(DIEA) used in prior art were dissolved in a highly dispersed solution of CNT, coagulation of CNT occurred right after the coupling agent and base were added to the dispersed solution (FIG. 3(a)), in the case where i-ethyl-3-(3- dimethylaminopropyl)-carbodiimide (EDC)/(NHS) were dissolved in a highly dispersed solution of CNT, coagulation of CNT occurred right after the coupling agent and base were added to the dispersed solution (FIG. 3(b)).

However, it was suggested that the highly dispersed solution of CNT remained in a highly dispersed state when DCC (i,3-dicyclorohexylcarboidiimide)/HOBt used in Example 2, were dissolved in a highly dispersed solution of CNT (FIG. 3(c)).

Example 3: Preparation of substrate having exposed amine group

A glass substrate was put into a toluene solution of o.2%(v/v) aminealkyloxysilane and allowed it to react for 1 hour at room temperature, then washed by soaking in a toluene solution 3 times, followed by drying in a vacuum oven for 20 minute at 120⁰C to prepare.

Example 4: Preparation of CNT film

The substrate having exposed amine group, prepared in Example 3, was allowed to react with the dispersed solution of CNT remaining in a highly dispersed state, prepared in Example 2 to form a CNT single layer on a substrate by amide bond formation between the amine group and the carboxyl group. Then, 0.1 M of oxydianyline as an organic amine compound was dissolved in dimethylformamaid(DMF) solvent, and the CNT fixed on the substrate was put into the resulting solution, and then allowed to react for 10 hours at room temperature to reexpose an amine group on the surface of CNT through a washing process using dimethylformamaid(DMF) and dichloromethane. The substrate having another side of amine group provided by the organic amine compound was put into the dispersed solution of CNT, prepared in Example 2 and allowed to react for 10 hours at room temperature, and then washed using dimethylformamaid(DMF) and dichloromethane to laminate another CNT on primarily formed CNT single layer.

Next, chemical reaction between CNT having exposed carboxyl group and an organic amine compound, i. e., amide bond formation was repetitively performed, and then the CNT layers and the organic amide layers are alternately laminated to prepare a high density CNT film with uniform surface. FIG. 4 shows the results of the penetration measured according to the number of CNT layers from the first lamination to the fifth lamination, and FIG. 5(b) shows a SEM photograph of CNT film fixed on a substrate after repeating the laminations 5 times.

Comparative example 3: Comparision of purity of CNT film CNT cut with a mixture solution of nitric acid and H₂SO₄ after purifying using a nitric acid and the inventive CNT cut with a mixture solution of H₂SO₄ and H₂O₂ after purifying using HCl were laminated 5 times by the same method as Example 4 and the obtained CNT film was observed using SEM photograph to compare 5 purity. As a result, CNT film obtained by using CNT cut with a mixture solution of nitric acid and H₂SO₄ after purifying using a nitric acid contained a large mount of impurities (FIG. 5(a)), and the inventive CNT film obtained by using CNT cut with a mixture solution of H₂SO₄ and H₂O₂ after purifying using HCl seldom contained impurities (FIG. 5(b)). As shown in FIG. 5(b), it was confirmed that the CNT film 0 according to the present invention has higher purity than that of CNT film of prior art and is formed uniformly with high density.

INDUSTRIAL APPLICABILITY 5

As described above, according to the present invention, a high purity CNT film can be prepared by fixing highly purified CNTs on the surface of the substrate, and a high density CNT film having high purity can be prepared uniformly by repetitive amaide bond formation between the amine group on the surface of the substrate O and the carboxyl group of CNT and thus it can be applied to bio-chips, bio-sensors, gas-sensors, a basic material of flat panel displays, bandable panel displays, transistors, transparent electrodes and a basic material of semiconductors.

While the present invention has been described with reference to the particular 5 illustrative embodiment, it is not to be restricted by the embodiment but only by the appended claims. It is to be appreciated that those skilled in the art can change or modify the embodiment without departing from the scope and spirit of the present invention.

Claims

THE CLAIMS What is claimed is:

1. A method for preparing a high density CNT film having high purity, the method comprising the steps of:

(a) (i) purifying a CNT using HCl; (ii) preparing a CNT having exposed carboxyl group by cutting the purified CNT with a mixture solution of H₂SO₄ and H₂O₂; and (iii) preparing a dispersed solution of the CNT having exposed carboxyl group by dispersing the CNT having exposed carboxyl group in a solvent to add with a coupling agent selected from the group consisting of 1,3-dicyclohexyl carbodiimide(DCC) and iV,JV-carbonyliimidazole(CDI) and at least one base selected from the group consisting of ι-hydroxybenzotriazole(HOBt), 2- hydroxypyridine(HOPy), endo-iV-hydroxy-5-norbornene-2,3- dicarboximide(HONB), diisopropylethylamine(DIEA) and N- methylimidazole(NMI);

(b) forming a CNT single layer on the surface of a substrate by amide bond formation between the amine group and the carboxyl group by reacting a substrate having an amine group exposed on the surface thereof with the dispersed solution of CNT having exposed carboxyl group, prepared in step (a); (c) laminating a CNT layer by reacting the dispersed solution of CNT having exposed carboxyl group, prepared in step (a) with the organic amine layer formed on the CNT layer after reacting the CNT single layer with an organic amine compound having at least two amine groups; and

(d) forming a high density CNT film having exposed carboxyl group by repeating the step (c) n times to alternately laminate CNT layers and organic amine layers n times.

2. The method according to claim 1, wherein the CNT of (i) in the step (a) is preferably prepared by Hipco (high pressure CO disproportionation) process.

3- The method according to claim l, wherein the solvent of the step (a) is preferably any one or more selected from the group consisting of N-methyl-2- pyrrolidone(NMP), dimethyl acetamide(DMAc), dimethylformamide(DMF), cyclohexanone, ethylalcohol and chlorobenzene.

4. The method according to claim 3, wherein the solvent is preferably dimethylformamide(DMF) .

5. The method according to claim 1, wherein the coupling agent is preferably 1,3- dicyclohexylcarbodiimide(DCC).

6. The method according to claim 1, wherein the base is preferably 1- hydroxybenzotriazole(HOBt) .

7. The method according to claim 1, wherein the substrate of the step (b) is preferably any one or more selected from the group consisting of glass, quartz, glass wafer, silicon wafer, melted silica, plastics and transparent polymer.

8. The method according to claim 1, wherein the substrate having exposed amine functional group on the surface thereof in the step (b) is preferably obtained by treating the substrate with any one or more selected from the group consisting of aminealkyloxysilane and aminealkylchlorosilane.

9. The method according to claim 1, wherein the organic amine compound having two or more amine groups is preferably a substance having a chemical formula of

H₂N-Ri-NH₂, R₂-(NH₂)₃ θr R₃-(NH₂)₄; wherein Ri, R₂ and R₃ are independently a Ci-20 saturated hydrocarbon, unsaturated hydrocarbon, aromatic organic group or Sii-20 silane.

10. A high density CNT film having exposed carboxyl group, prepared by the method of any one claim among claims i to 9.

11. A method for preparing a high density CNT film, the method comprising modifying the high density CNT film having exposed carboxyl groups of claim 10 so that a chemical compound have both a functional group capable of binding to the carboxyl group and a chemical functional group selected from the group consisting of amine group, aldehyde group, hydroxyl group, thiol group and halogen.

12. The method according to claim 11, wherein the chemical compound is any one or more selected from the group consisting of H₂N-Ri-NH₂, H₂N-R₂-SH, H₂N-R₃- OH, H₂N-R₄-CHO, or H₂N-R₅-COON, H₂N-R₆-X; wherein R₁, R₂, R₃, R₄, R₅ and R₆ are independently a C_2-20 saturated hydrocarbon, unsaturated hydrocarbon or aromatic organic group, respectively, and X is halogen elements or succinimdyl ester.

13. A high density CNT film having an exposed chemical functional group selected from the group consisting of amine group, aldehyde group, hydroxyl group, thiol group and halogen, prepared by the method of claims 11 or 12.