JP2000290008A - Method for purifying carbon tube - Google Patents

Abstract

PROBLEM TO BE SOLVED: To purify carbon tubes, in particular single-wall carbon nanotubes by dispersing a crude product containing carbon tubes in a colloidal gold solution, removing the solvent and heating the crude product in an atmosphere of oxygen to selectively adsorb fine gold particles on a carbon impurity. SOLUTION: A crude product containing carbon tubes is dispersed in a colloidal gold solution, the solvent is removed from the colloidal gold solution containing the crude product and the crude product is heated in an atmosphere of oxygen to purify the carbon tubes. The diameter of fine gold particles contained in the colloidal gold solution is preferably 1-100 nm and water or an organic solvent such as an alcohol is used as the solvent of the solution. The solvent is removed by air drying. The heating temperature after the removal of the solvent is about 300-500 deg.C. The purity of carbon tubes is controlled by adjusting the heating temperature and heating time.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for purifying carbon tubes from crude carbon tube products containing carbon impurities, and more particularly to a method for purifying carbon tubes suitable for single-wall carbon nanotubes.

[0002]

2. Description of the Related Art Carbon tubes are cylindrical carbon molecules. Among them, carbon tubes called carbon nanotubes are needle-like carbon molecules whose diameter is on the order of nanometers, and graphene (single-layer graphite sheet)
Has a cylindrical shape. A graphene cylinder having a concentric multilayer structure is called a multi-wall carbon nanotube, and a graphene cylinder consisting of a single-layer graphene cylinder is called a single-wall carbon nanotube.

As a method for synthesizing single-wall carbon nanotubes, a laser ablation method is well known. This is a method in which a carbon target mixed with a metal such as cobalt or nickel as a catalyst is heated to a high temperature and irradiated with a powerful laser. By this method, a large amount of single-walled carbon nanotubes can be obtained. However, this method has a problem that unnecessary carbon impurities such as fullerene and amorphous carbon particles are mixed into the crude product.

With respect to multi-walled carbon nanotubes, a heating oxidation method has been effective as a purification method. For example, Nature, No. 367
Volume, p. 519, as reported in 1994,
When the multiwall carbon nanotube crude product is heated in an oxygen atmosphere, carbon impurities can be oxidized and removed. However, this purification method cannot be directly applied to single-walled carbon nanotubes. This is because the carbon impurities generated in the laser ablation method are generally larger than the impurities generated in synthesizing the multi-wall carbon nanotube, and require long-time oxidation. Therefore, under the oxidation conditions for removing impurities, most of the single-wall carbon nanotubes are also oxidized.

[0005] To avoid this problem, various purification methods have been proposed. One of the methods is an ultrafiltration method. This is the Journal of Physical Chemistry (Journal of Physical Chemistry).
misry), vol. 101, p. 8839, 1997.
This is a method of filtering single-walled carbon nanotubes using a filter that transmits submicron substances, as reported in 1998. However, this method
The crude product must have a high purity in advance, and there are limitations on the applicable crude product.

As another method for purifying single-walled carbon nanotubes, a nitric acid boiling method is known. This method is based on Advanced Materials (Adv)
advanced Materials), Vol. 10, No. 61
As reported in page 1, 1998, a single-walled carbon nanotube crude product is dispersed in concentrated nitric acid and refluxed at a high temperature to oxidize carbon impurities. However, this purification method damages the surface of the single-walled carbon nanotube, so that a high-quality single-walled carbon nanotube cannot be obtained.

As a method superior to these purification methods, a purification method using fine gold particles is disclosed in JP-A-8-91816.
No. in the official gazette. This purification method is
Journal of Applied Physics (Japan)
nice Journal of Applied P
Physics, Vol. 32, p. 2809, 1993, which utilizes the fact that when gold becomes fine particles it acts as a catalyst and has the property of oxidizing carbon at low temperatures. In this method, gold is vapor-deposited simultaneously with the synthesis of single-walled carbon nanotubes, and as a result, impurities are removed by performing a heat treatment in a oxygen atmosphere on a crude product to which gold has adhered. This method has an advantage that it is possible to selectively oxidize only the region to which the fine gold particles are attached, and that unnecessary damage is not given to the single-walled carbon nanotube.

[0008] The purification method using fine gold particles has advantages over other purification methods. However, when the fine gold particles adhere to single-walled carbon nanotubes, the carbon nanotubes are oxidized and cut therefrom. there were. Since oxidation of the carbon nanotube proceeds from the tip, when cutting occurs, oxidation proceeds from there. Therefore, the yield of carbon nanotubes is reduced.

Usually, the adsorption of the fine gold particles is performed during the synthesis of the single-walled carbon nanotube. That is, a gold vapor deposition machine is provided in the nanotube synthesizer, and gold vapor deposition is performed simultaneously during synthesis. The gold molecules flying to the carbon surface aggregate with each other to form fine gold particles. This phenomenon occurs not only on carbon impurities but also on carbon nanotubes.

When this crude product is heated in an oxygen atmosphere, the fine gold particles adhering to the carbon impurities efficiently oxidize the impurities, but the fine gold particles adhering to the carbon nanotubes cut the carbon nanotubes.

[0011]

SUMMARY OF THE INVENTION An object of the present invention is to improve the above-mentioned disadvantages of the prior art, and in particular, to make it possible to selectively adsorb fine gold particles to carbon impurities, thereby providing a high quality carbon tube. It is intended to provide a novel method for purifying a carbon tube, which enables purification of a carbon tube.

[0012]

SUMMARY OF THE INVENTION The present invention basically employs the following technical configuration to achieve the above object. That is, a first aspect of the method of purifying a carbon tube according to the present invention is a method of purifying a carbon tube, wherein a first step of dispersing a crude product containing the carbon tube in a colloidal gold solution; A second step of removing the solvent from the colloidal gold solution containing: and a third step of heating the crude product in an oxygen atmosphere.
According to an aspect, the diameter of the gold fine particles contained in the colloidal gold solution is 1 nm to 100 nm, and in a third aspect, the solvent of the gold colloid solution is water. According to a fourth aspect, the solvent for the gold colloid solution is an organic solvent such as alcohol, and a fifth aspect is the second step. The removal of the solvent in the step is characterized in that the solvent is removed by natural drying. In a sixth embodiment, the heating temperature in the third step is 300 ° C. to 500 ° C. Characterized in that
The seventh aspect is characterized in that the purity of the carbon tube is controlled by adjusting the heating temperature or the heating time in the third step.

[0013]

BEST MODE FOR CARRYING OUT THE INVENTION A method for purifying a carbon tube according to the present invention comprises a first step of dispersing a crude product containing a carbon tube in a colloidal gold solution, and removing a solvent from the colloidal gold solution containing the crude product. A second step of removing;
A third step of heating the crude product in an oxygen atmosphere;
It is characterized by including.

The above-mentioned colloidal gold solution is obtained by dispersing fine gold particles in a solvent. The diameter of gold particles is 1n
m to 100 nm. Water is generally used as a solvent. When the crude carbon tube product is dispersed in the gold colloid solution, the fine gold particles are selectively adsorbed to carbon impurities. At this time, a surfactant such as benzalkonium chloride may be added to promote the adsorption.

Next, the solvent is removed from the crude product to which the fine gold particles are adsorbed by natural drying. Even after this step, the fine gold particles remain in a state of being adsorbed by the carbon impurities. After separating the solvent, the crude product is heated in an oxygen atmosphere,
The carbon impurities are oxidized from the region where the fine gold particles are adsorbed. The catalytic effect of the fine gold particles is effective at 300 ° C. or higher.
However, if the temperature exceeds 500 ° C., the carbon tube is oxidized. Therefore, the optimum temperature range is from 300 ° C. to 500 ° C.

[0016]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A method for purifying a carbon tube according to the present invention includes a first step of dispersing a crude product containing a carbon tube in a colloidal gold solution, and a step of removing a solvent from the colloidal gold solution containing the crude product. And a third step of heating the crude product in an oxygen atmosphere.

Hereinafter, a specific example of the method for purifying a carbon tube according to the present invention will be described in more detail. Single-wall carbon nanotubes are synthesized, for example, by the following method. As a target, a carbon rod containing 0.3 atomic percent of nickel and cobalt is prepared.
The target is heated at a high temperature in an electric furnace (for example, 1200
° C), and irradiating the target with a pulse laser while flowing an inert gas such as argon. As a result, a crude product containing single-walled carbon nanotubes is obtained.

In this method, about 50% of carbon impurities are mixed. Carbon tubes and single-walled carbon nanotubes may be synthesized by other synthesis methods such as an arc discharge method or a chemical vapor deposition method. As a result, the purification method of the present invention is also effective for the obtained crude product. It is. As the gold colloid solution, a solution containing 1011 gold fine particles having a diameter of 10 nm per 1 cm ³ is used. The diameter of the gold particles is 1n
The range from m to 100 nm is effective for the purification method of the present invention. Although water was used as the solvent, an organic solvent such as alcohol is also effective for the purification method of the present invention. The number of gold particles per unit volume can be changed according to the degree of adsorption.

The above-mentioned crude product of carbon nanotubes is added to a colloidal gold solution and dispersed by ultrasonic treatment. When the ultrasonic treatment is performed for about 1 hour, the crude carbon nanotube product is uniformly dispersed in the gold colloid solution.
After dispersing the carbon nanotubes in the colloidal gold solution, the solvent is removed by natural drying. For separation of the solvent, a rotary evaporator or the like may be used. When the crude product after the solvent separation is observed with a scanning electron microscope, as shown in FIG. 1, it is observed that the fine gold particles are adsorbed on carbon impurities other than carbon nanotubes.

Thereafter, the crude product on which the fine gold particles are adsorbed is
Heat treatment is performed in the air using an electric furnace. In this example, the heat treatment was performed at a temperature of 300 ° C. for 10 minutes. In addition, by adjusting the heating time and heating temperature,
The purity of the carbon nanotube can be controlled.
By performing the oxidation treatment for a sufficiently long time, it is possible to cut the carbon nanotubes.

When the electron microscope observation after the heat treatment is performed,
As shown in FIG. 2, a single-walled carbon nanotube from which carbon impurities have been removed is confirmed. Also when applied to a carbon tube such as a multi-wall carbon nanotube, the effect of quickly removing impurities is confirmed.

[0022]

The method for purifying a carbon tube according to the present invention is constituted as described above, so that it is possible to selectively adsorb fine gold particles to carbon impurities and to purify a high quality carbon tube. Becomes Above all,
Effective purification of single-walled carbon nanotubes becomes possible.

[Brief description of the drawings]

FIG. 1 is a schematic view of a crudely purified single-walled carbon nanotube attached to fine gold particles obtained in one example of the present invention.

FIG. 2 is a schematic view of a purified single-walled carbon nanotube obtained in one example of the present invention.

[Explanation of symbols]

 1 Single-wall carbon nanotube 2 Carbon impurity 3 Fine gold particles

Claims (7)

[Claims] 1. A method for purifying a carbon tube, comprising: a first step of dispersing a crude product containing a carbon tube in a colloidal gold solution; and a second step of removing a solvent from the colloidal gold solution containing the crude product. And a third step of heating the crude product in an oxygen atmosphere. 2. The method according to claim 1, wherein the gold fine particles contained in the gold colloid solution have a diameter of 1 nm to 100 nm. 3. The method for purifying a carbon tube according to claim 2, wherein the solvent of the gold colloid solution is water. 4. The method according to claim 2, wherein the solvent of the colloidal gold solution is an organic solvent such as alcohol. 5. The method for purifying a carbon tube according to claim 1, wherein the removal of the solvent in the second step comprises removing the solvent by natural drying. 6. The heating temperature in the third step is 300
The method for purifying a carbon tube according to claim 1, wherein the temperature is in a range of from ° C to 500 ° C. 7. The purification of a carbon tube according to claim 1, wherein the purity of the carbon tube is controlled by adjusting a heating temperature or a heating time in the third step. Law.