JP2007051058A - Method for manufacturing carbon nanotube - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for manufacturing carbon nanotubes, in which an aggregation phenomenon of catalyst nanoparticles can be prevented and the diameters of grown carbon nanotubes can be controlled to be uniform. <P>SOLUTION: In the method for manufacturing the carbon nanotubes, catalyst nanoparticles are subjected to a surface modifying treatment using a surface modifying agent of a molecular substance containing a silicon element, e.g., 3-aminopropyltriethoxysilane, and the carbon nanotubes are each grown on each catalyst nanoparticle subjected to the surface treatment so that the diameters of the carbon nanotubes are controlled by the surface treatment. Thereby, the carbon nanotubes can be each grown to have a diameter controlled by the surface three-dimensional stabilization due to silicon oxide-based deposit deposited on the surface of each catalyst nanoparticle by the decomposition of the surface modifying agent. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to carbon nanotubes, and more particularly, to a method for producing carbon nanotubes, which can improve the surface of catalyst nanoparticles and uniformly adjust the diameter of carbon nanotubes grown on the catalyst nanoparticles.

  The carbon nanotube has a diameter of 1 to 5 nm, and has anisotropy that is structurally large as the length increases from several μm to several hundred μm. It is known that such a carbon nanotube can have a conductive or semiconducting property depending on the diameter and the chirality. As a result, many studies are underway to use carbon nanotubes in various electronic devices.

  The carbon nanotubes are, for example, a method using arc discharge, a method using laser, a method using carbon monoxide (CO) under conditions of high temperature and high pressure, or a thermal chemical vapor deposition synthesis method. It can manufacture by the method like this.

  At this time, the diameter of the carbon nanotubes grown by the CVD method is very strongly dependent on the size of the catalyst nanoparticles. However, the catalyst nanoparticles exhibit a very strong surface free energy, which tends to aggregate easily at the process temperature utilized for CVD growth.

  Catalyst nanoparticles have a very high surface area to volume ratio and also have a low melting point compared to the bulk, which can be agglomerated at the temperatures used during the growth of carbon nanotubes. In addition, since the catalyst nanoparticles tend to be aggregated at such a high temperature, the aggregation phenomenon of the catalyst nanoparticles occurs very easily. Thereby, the diameter of the carbon nanotube can be grown to a diameter larger than the size of the used catalyst nanoparticles.

  In order to prevent such agglomeration of catalyst nanoparticles, a method using neutral nanoparticles that are physically separated between active catalyst nanoparticles can be considered. A method of preventing aggregation by embedding the catalyst nanoparticles in a porous supporter is also conceivable. However, there are many restrictions on the application of such a method to carbon nanotubes, and there are significant restrictions on their use.

  Since such a method introduces a second element substantially other than the catalyst nanoparticles, such as neutral nanoparticles or a porous supporter, such a second element was synthesized. A process of removing from carbon nanotubes is required. In addition, the density of the active catalyst nanoparticles per unit area is low, and the density of the carbon nanotubes synthesized is low.

  And although a porous supporter is mainly comprised with a metal oxide, a metal oxide is generally an insulator. Therefore, it does not meet the demand for growing carbon nanotubes on a conductive supporter in order to apply carbon nanotubes as an electrical connector. Therefore, development of a method capable of preventing the aggregation phenomenon of catalyst nanoparticles during the growth of carbon nanotubes and controlling the diameter of the synthesized carbon nanotubes is required.

  An object of the present invention is to provide a carbon nanotube production method that can prevent the aggregation phenomenon of catalyst nanoparticles and can uniformly control the diameter of the carbon nanotubes to be grown.

  According to one aspect of the present invention, a catalyst nanoparticle is subjected to a surface modification treatment with a surface modifier of a molecular substance containing silicon element, and the surface treatment is performed on the surface of the catalyst nanoparticle. And a step of growing the carbon nanotubes so as to be controlled.

  Another aspect of the present invention is a process of dispersing the catalyst nanoparticles in a solvent, and adding a surface modifier of a molecular substance containing silicon element to the dispersion, thereby dispersing the dispersed catalyst nanoparticles. The diameter is controlled by the surface treatment on the surface of the catalyst, the step of applying the dispersion on the substrate, and the catalyst nanoparticles deposited on the substrate by the application of the dispersion. A process for growing carbon nanotubes, and a method for producing carbon nanotubes.

  Further, another aspect of the present invention is the step of dispersing the catalyst nanoparticles in a solvent, and adding the surface modifier of a molecular substance containing silicon element and amine functional group to the dispersion. The diameter of the catalyst nanoparticles is controlled by the surface treatment on the surface of the catalyst nanoparticles, the step of applying the dispersion onto the substrate, and the catalyst nanoparticles deposited on the substrate by applying the dispersion. And a method of growing carbon nanotubes as described above.

  The catalyst nanoparticles may be formed of transition metal nanoparticles having a size distribution having a standard deviation of about 15% or less by a wet chemical synthesis method.

  The surface modifier is a molecular substance including at least one functional group selected from the group including a silane group, a siloxane group, and a silsesquioxane group.

The surface modifier is a molecular substance including at least one functional group selected from the group including —NH ₂ , —COOH, —CONH ₂ and —SH functional groups.

  The surface modifier includes 3-aminopropyltriethoxysilane (hereinafter referred to as APS).

  The surface modifier can be added directly or in solution to the dispersion.

  The step of growing the carbon nanotubes may be performed by CVD in which a carbon source gas is provided on the catalyst nanoparticles and decomposed to synthesize the carbon nanotubes.

  The CVD is thermal CVD for thermally decomposing the carbon source gas or plasma enhanced CVD for performing plasma.

  The carbon nanotubes may be grown with a controlled diameter by surface steric stabilization by a silicon oxide-based deposit deposited on the surface of the catalyst nanoparticles by decomposition of the surface modifier.

  The dispersion solvent includes any one selected from the group consisting of n-hexane, chloroform, toluene, water and ethanol.

  The step of applying the dispersion onto the substrate is performed by any one coating method selected from the group including spin coating, dip coating, spray coating, and paddle coating.

  The substrate is a glass or silicon substrate.

  The substrate is a substrate with a layer including any one conductive material selected from the group including Au, Ag, TiN, ITO, and TaN.

  According to the present invention, the surface of the catalyst nanoparticles can be improved by surface-treating the surface of the catalyst nanoparticles using a surface modifier containing silicon element, for example, APS. The surface of the catalyst nanoparticles whose surface has been improved by APS is sterically stabilized during the synthesis of the carbon nanotubes, whereby the diameter of the carbon nanotubes can be controlled. Accordingly, it is possible to substantially grow carbon nanotubes having a uniform diameter on the conductive film quality by eliminating the occurrence of the aggregation state of the catalyst nanoparticles.

  Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings. However, the embodiments of the present invention can be modified into various other forms, and the scope of the present invention should not be construed as being limited by the embodiments described below. The embodiments of the present invention should preferably be construed as provided to those skilled in the art to more fully describe the present invention.

  In an embodiment of the present invention, a wet chemical synthesis method is used to uniformly adjust the size when producing catalyst nanoparticles. The wet chemical synthesis method is known as a method capable of uniformly forming catalyst particles in a nano size. Accordingly, the catalyst nanoparticles used in the embodiment of the present invention may have a uniform size, for example, a uniform size of about 3 to 4.5 nm in diameter.

In an embodiment of the present invention, a technique for binding a surface modifier to the surface of such catalyst nanoparticles is presented in order to control the diameter of carbon nanotubes grown from the catalyst nanoparticles. The surface modifier presented in the embodiment of the present invention is understood to be bonded to the catalyst nanoparticles and decomposed to deposit a silicon oxide-based (SiO ₂ based) surface modification layer on the surface of the catalyst nanoparticles. sell.

  As the surface modifier, for example, a molecule containing a silicon (Si) element, such as APS, can be used. Such a surface modifier such as APS has an amine group as a terminal group, and the amine group is a catalyst nanoparticle while the adhesion of silicon oxide to the surface of the catalyst nanoparticle is controlled by the silane group. It plays the role of binding the APS molecule to the.

  Since the silicon oxide-based deposition layer with such a surface modifier is partially deposited on the surface of the catalyst nanoparticles, the surface area of the catalyst nanoparticles is eventually reduced to control the growth of carbon nanotubes. It can be understood that the effect of suppressing an increase in the diameter of the carbon nanotubes grown is realized. When carbon nanotubes are grown on the catalyst nanoparticles having a surface modifier bonded to the surface, the silicon-based deposition layer portion deposited on the surface of the catalyst nanoparticles by decomposition of the APS molecules is substantially the catalyst nanoparticles. It can be understood that the diameter of the carbon nanotubes to be grown is controlled by adjusting the surface area of the carbon nanotubes. Thereby, the diameter of the carbon nanotubes to be grown can be controlled substantially in accordance with the size of the catalyst nanoparticles.

  1 to 3 are drawings schematically illustrating a method of manufacturing a carbon nanotube according to an embodiment of the present invention.

  Referring to FIG. 1, a catalyst nanoparticle 100 having a uniform size, for example, a size of about 3 to 4.5 nm, is prepared by a wet chemical synthesis method. Wet chemical synthesis methods are known as methods that provide nanoparticles of very uniform set size, morphology and composition. Since the diameter of the carbon nanotube is largely determined by the size of the catalyst nanoparticle 100, it is very important to make the size of the catalyst nanoparticle 100 uniform. At this time, the particle size distribution of the catalyst nanoparticles 100 is desirably adjusted to have a standard deviation within 15%.

  Such catalyst nanoparticles 100 may be understood as transition metal nanoparticles. Transition metal nanoparticles are known to act as a catalyst in a reaction in which carbon elements are synthesized into carbon nanotubes. Examples of such transition metal nanoparticles include iron (Fe) nanoparticles.

  The surface of the catalyst nanoparticle 100 is treated with the surface modifier 200. At this time, the surface modifier 200 may be understood as a molecular substance containing silicon element (Si). For example, APS can be used as such a surface modifier 200.

Such molecular substances include functional groups or functional groups containing silicon element, for example, functional groups such as —NH ₂ , —COOH, —CONH ₂ , —SH in addition to silane groups, siloxane groups, or silsesquioxane groups. It can be understood as a molecule further having At this time, the number of functional groups containing silicon is not limited, and molecules containing at least one silicon-containing functional group can be used as such a surface modifier 200.

Such a functional group such as —NH ₂ , —COOH, —CONH ₂ , and —SH serves to allow the molecules of the surface modifier 200 to be bound to the catalyst nanoparticles 100. Can be understood. For example, in the case of APS, an amine group serves to bind APS 200 to the surface of the catalyst nanoparticle 100 while a silane group acts. Such a bond can be understood as a chemical bond, a covalent bond or a bond by weak interaction, for example, a bond by Van der Waals interaction.

  In the process of bonding the surface modifier 200 to the catalyst nanoparticles 100, first, the substantially pure surface modifier 200 is directly added to a dispersion in which the catalyst nanoparticles 100 are dispersed in a solvent (nano particle dispersion). Can be done. Alternatively, it may be performed by adding a solution formed by dissolving the surface modifier 200 in a suitable solvent to the nanoparticle dispersion. At this time, the surface modifier 200 may be added to the solution or directly to the nanoparticle dispersion and then stirred so that the surface modifier 200 is bonded to the catalyst nanoparticles 100.

  At this time, since the surface modifier 200 is substantially bonded to the surface of the catalyst nanoparticles 100, there is no substantial limitation on the degree to which the surface modifier 200 is added to the dispersion. Therefore, a sufficient amount of the surface modifier 200 may be introduced.

  Referring to FIG. 2, the catalyst nanoparticles 100 having an improved surface treated with the surface modifier 200 are deposited on the substrate 300. At this time, the catalyst nanoparticles 100 may be deposited on the conductive layer 400 on the substrate 300. This is because it is more suitable for applications using carbon nanotubes for electrical connection.

  The conductive layer 400 may be a conductive material layer such as gold (Au), silver (Ag), ITO, titanium nitride (TiN), or tantalum nitride (TaN). Such catalytic nanoparticles 100 may be deposited directly on a substrate 300, such as a silicon substrate or a glass substrate, without the introduction of such a conductive layer 400.

  At this time, a deposition liquid containing the catalyst nanoparticles 100 treated with the surface modifier 200 is prepared, and this deposition process can be performed using the deposition liquid. At this time, the dispersion liquid can be used as the deposition liquid. Accordingly, the deposition liquid may include a solvent that disperses the catalyst nanoparticles 200, and n-hexane, chloroform, toluene, water, ethanol, or the like may be used as the solvent.

  Such a deposition liquid (or dispersion) may be applied on the substrate 300 using a solution-based coating technique to deposit the catalyst nanoparticles 100 on the conductive layer 400 on the substrate 300. As such a coating technique, spin coating, dip coating, paddle coating, spray coating, or the like can be used.

  Meanwhile, since the surface modifier 200 is bonded to the surface of the catalyst nanoparticles 100, the surface modifier 200 is configured to help the catalyst nanoparticles 100 to be deposited on the conductive layer 400 or the substrate 300. The molecular material may further include a terminal functional group that can bind to the substrate 300 or the conductive layer 400. For example, it can further comprise a hydrophilic functional group. Since APS has a hydrophilic property, it can have a property capable of being bonded to the substrate 100 such as silicon.

  Referring to FIG. 3, catalyst nanoparticles 100 surface-treated or improved by the surface modifier 200 are deposited on the conductive layer 400, and carbon nanotubes 500 are grown on the deposited catalyst nanoparticles 100. At this time, the growth of the carbon nanotube 500 may be performed by a CVD-based synthesis method, for example, thermal CVD or plasma strengthening.

A carbon source gas, for example, acetylene gas (C ₂ H ₂ ) is provided on the catalyst nanoparticles 100 surface-treated with the surface modifier 200, and a temperature higher than a temperature at which such a carbon source gas is decomposed, The carbon nanotube 500 is grown by providing a temperature of about 650 ° C. When plasma is introduced, since the plasma accelerates such a decomposition process, the reaction temperature can be further lowered.

  At this time, the diameter of the carbon nanotubes 500 to be grown largely depends on the size of the catalyst nanoparticles 100, but the surface modifier 200 bonded to the catalyst nanoparticles 100 has a diameter of the carbon nanotubes 500 to be grown. Do the role to control. The surface modifier 200, for example, APS, is decomposed to form a silicon oxide-based deposit 201 on the surface of the catalyst nanoparticle 100.

  The amine group of APS serves to provide a bond that binds APS to the surface of the catalyst nanoparticle 100 while the silicon oxide-based deposit 201 is attached by the silane group. By decomposing APS, silane-based silicon is attached to the surface of the catalyst nanoparticle 100 as a silicon oxide-based deposit 201. In such a silicon oxide deposit 201 region, the carbon nanotube synthesis reaction is difficult to proceed. For example, on the surface of such a silicon oxide deposit 201, the movement of carbon radicals or carbon elements is suppressed, thereby suppressing the growth of the carbon nanotubes 500.

  Since the active surface of the catalyst nanoparticle 100 is adjusted so as to be substantially reduced by the adhesion of the deposit 201, it is possible to prevent the occurrence of a phenomenon in which the catalyst nanoparticle 100 is aggregated between each other due to excessive carbon reaction. . That is, the aggregation phenomenon of the catalyst nanoparticles 100 is suppressed by stabilization related to the spatial (or steric) arrangement of atoms or molecules on the surface of the catalyst nanoparticles 100, which is embodied by the bonded surface modifier 200, Thereby, the diameter of the carbon nanotube 500 is controlled.

  Since the aggregation phenomenon of the catalyst nanoparticles 100 is suppressed, the carbon nanotubes 500 can be grown to a diameter determined mainly depending on the size of the catalyst nanoparticles 100. Accordingly, the carbon nanotube 500 can be grown and synthesized so as to have a diameter substantially equivalent to the size of the catalyst nanoparticle 100. Since the catalyst nanoparticles 100 are formed to have a very uniform size by a wet chemical synthesis method, the carbon nanotubes 500 grown on the catalyst nanoparticles 100 having a uniform size are also synthesized to have a very uniform size. Is done.

4 and 5 are Scanning Electron Microscope (SEM) photographs of carbon nanotubes taken to explain the effects of the carbon nanotube manufacturing method according to the embodiment of the present invention. FIGS. 4 and 5 illustrate synthetic growth by thermal CVD providing C ₂ H ₂ gas at a temperature of about 650 ° C. using iron (Fe) catalyst nanoparticles surface-treated with APS according to an embodiment of the present invention. It is a SEM photograph of the carbon nanotube made. In comparison, FIG. 6 is an SEM photograph of carbon nanotubes and the like that are synthetically grown when APS is not used.

  Comparing the SEM photograph of FIGS. 4 and 5 with the SEM photograph of FIG. 6, when the catalyst nanoparticles surface-treated using APS are used, the diameter of the carbon nanotube is further increased than in the SEM photograph of FIG. It can be seen that the growth was fine, uniform and dense.

  As mentioned above, although this invention was demonstrated in detail through specific embodiment, this invention is not limited to this, The deformation | transformation and improvement are possible by those skilled in the art within the technical idea of this invention.

  The present invention is suitably used in the related technical field of carbon nanotubes.

1 is a schematic view illustrating a carbon nanotube manufacturing method according to an embodiment of the present invention. 1 is a schematic view illustrating a carbon nanotube manufacturing method according to an embodiment of the present invention. 1 is a schematic view illustrating a carbon nanotube manufacturing method according to an embodiment of the present invention. It is the SEM photograph of the carbon nanotube imaged in order to explain the effect of the manufacturing method of the carbon nanotube by the embodiment of the present invention. It is the SEM photograph of the carbon nanotube imaged in order to explain the effect of the manufacturing method of the carbon nanotube by the embodiment of the present invention. It is a SEM photograph of the carbon nanotube manufactured as a comparative example of the present invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 100 Catalyst nanoparticle 200 Surface modifier 201 Deposit 300 Substrate 400 Conductive layer 500 Carbon nanotube

Claims (23)

A step of surface-modifying the catalyst nanoparticles with a surface modifier of a molecular substance containing silicon element;
And a step of growing carbon nanotubes on the surface-treated catalyst nanoparticles so that a diameter is controlled by the surface treatment.   The method of claim 1, wherein the catalyst nanoparticles are formed of transition metal nanoparticles having a size distribution having a standard deviation of approximately 15% or less by a wet chemical synthesis method. .   2. The carbon according to claim 1, wherein the surface modifier is a molecular substance including at least one functional group selected from a group including a silane group, a siloxane group, and a silsesquioxane group. Nanotube manufacturing method. 2. The surface modifier is a molecular substance including at least one functional group selected from the group including —NH ₂ , —COOH, —CONH ₂ and —SH functional groups. The manufacturing method of the carbon nanotube as described in any one of.   The method for producing a carbon nanotube according to claim 1, wherein the surface modifier contains 3-aminopropyltriethoxysilane. The step of treating with the surface modifier comprises
Preparing a dispersion in which the catalyst nanoparticles are dispersed;
The method for producing carbon nanotubes according to claim 1, comprising a step of adding the surface modifier directly or in solution to the dispersion. The step of growing the carbon nanotubes comprises:
The method for producing carbon nanotubes according to claim 1, wherein the method is performed by chemical vapor deposition in which a carbon source gas is provided and decomposed on the catalyst nanoparticles to synthesize the carbon nanotubes.   8. The carbon nanotube according to claim 7, wherein the chemical vapor deposition is thermal chemical vapor deposition for thermally decomposing the carbon source gas or plasma enhanced chemical vapor deposition for performing plasma. Production method.   The carbon nanotube is grown with a controlled diameter by surface steric stabilization by a silicon oxide-based deposit deposited on the surface of the catalyst nanoparticles by decomposition of the surface modifier. Item 2. A method for producing a carbon nanotube according to Item 1. Dispersing catalyst nanoparticles in a solvent;
Adding a surface modifier of a molecular substance containing silicon element to the dispersion to improve the surface of the dispersed catalyst nanoparticles;
Applying the dispersion on a substrate;
A step of growing carbon nanotubes on the catalyst nanoparticles deposited on the substrate by application of the dispersion so that the diameter is controlled by the surface treatment. Method.   The method for producing carbon nanotubes according to claim 10, wherein the dispersion solvent contains any one selected from the group consisting of n-hexane, chloroform, toluene, water and ethanol.   11. The carbon according to claim 10, wherein the surface modifier is a molecular substance including at least one functional group selected from a group including a silane group, a siloxane group, and a silsesquioxane group. Nanotube manufacturing method. 11. The surface modifier is a molecular substance including at least one functional group selected from the group including —NH ₂ , —COOH, —CONH ₂ and —SH functional groups. The manufacturing method of the carbon nanotube as described in any one of. The step of applying the dispersion on the substrate includes:
The method for producing carbon nanotubes according to claim 10, wherein the method is performed by any one coating method selected from the group including spin coating, dip coating, spray coating, and paddle coating. The substrate is a glass or silicon substrate;
11. The method of claim 10, wherein the substrate is a substrate with a layer containing any one conductive material selected from the group consisting of Au, Ag, TiN, ITO, and TaN. .   The carbon nanotubes are grown with a controlled diameter by surface steric stabilization by a silicon oxide-based deposit deposited on the surface of the catalyst nanoparticles by decomposition of the surface modifier. The method for producing a carbon nanotube according to claim 10. Dispersing catalyst nanoparticles in a solvent;
Adding a surface modifier of a molecular substance containing silicon element and amine functional group to the dispersion to treat the surface of the dispersed catalyst nanoparticles;
Applying the dispersion on a substrate;
A step of growing carbon nanotubes on the catalyst nanoparticles deposited on the substrate by application of the dispersion so that the diameter is controlled by the surface treatment. Method.   The method for producing a carbon nanotube according to claim 17, wherein the surface modifier contains 3-aminopropyltriethoxysilane.   The carbon according to claim 17, wherein the surface modifier is a molecular substance including at least one functional group selected from the group including a silane group, a siloxane group, and a silsesquioxane group. Nanotube manufacturing method.   The carbon nanotube is grown with a controlled diameter by surface steric stabilization by a silicon oxide-based deposit deposited on the surface of the catalyst nanoparticles by decomposition of the surface modifier. Item 18. A method for producing a carbon nanotube according to Item 17. Providing catalyst nanoparticles; and
Treating the surface of the catalyst nanoparticles with a surface modifier containing silicon;
A method of growing carbon nanotubes on the catalyst nanoparticles treated with the surface modifier containing silicon.   The method of claim 21, wherein the diameter of the carbon nanotube is controlled by treating a surface of the catalyst nanoparticle. The method for producing carbon nanotubes according to claim 21, wherein the catalyst nanoparticles include iron nanoparticles.