JP2001335310A - Method of refining carbon substance with nano-structure - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a refining method capable of removing metal particles of a catalyst without damaging a carbon with a nano-structure. SOLUTION: This method comprises a first process wherein the metal particles in the carbon substance are removed by refluxing in solvent the carbon substance with the nano-structure, which is produced using the metallic catalyst, and a second process wherein an amorphous carbon is vaporized and removed by heat-treating the refluxed carbon substance. Process 1, 2 are alternately repeated several times. The carbon substance is preferably refluxed in an acid or an alkaline solvent in the first process and the refluxed carbon substance is preferably heat-treated in the range of 200 to 700 deg.C in the second process. The above heat-treatment of the second time is conducted at a temperature higher than that selected from the above range of temperature the first time treatment and is also still within the above range of temperature. The carbon substance having the nano-structure is a carbon nano-tube.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method for purifying a carbon material having a nanostructure such as C60 fullerene, carbon nanotube, and graphite nanofiber.

[0002]

2. Description of the Related Art Carbon materials having a structure on the order of nanometers, such as C60 fullerenes, carbon nanotubes, and graphite nanofibers (hereinafter referred to as carbon materials having a nanostructure) are known. The carbon material having the nanostructure is expected to be applied to various uses such as a one-dimensional thin wire, a catalyst, a cold cathode device, and a hydrogen storage material due to the mechanical properties and structural properties derived from the special structure. .

[0003] The carbon material having the nanostructure is, for example, Fe, C in an inert gas such as argon or helium.
o, an iron group element such as Ni, a rare earth element such as Gd, Y, La, Ce, and Nd; a platinum group element such as Pd, Rh, and Pt, or a mixture thereof; Can be produced by arc discharge between the carbon electrodes using the carbon electrodes prepared as described above (Z. Phys. D, 40, 4).
21-424 (1997), Nature, vol.
388, 756-758, 21, Aug. (199
7)).

However, since the carbon material having a nanostructure manufactured as described above contains metal particles used as a catalyst, when the carbon material is used for a cold cathode device, a hydrogen storage material, or the like, And does not work well. Therefore, conventionally, various purification methods for removing the metal particles from the carbon material having the nanostructure have been proposed. For example, a carbon material having the nanostructure manufactured as described above is prepared by using a 2.6M nitric acid solution. And remove the metal particles by dissolving the same in nitric acid.
A method of suspending in water of H10 and filtering is known (Science, vol. 280, 1253-125).
6, May, (1998)).

[0005] However, since the metal particles of the catalyst are included in amorphous carbon which is inevitably produced as a by-product during the production of the carbon material having the nanostructure, it is attempted to remove the metal particles by the above method. Then, the conditions must be strict and there is a disadvantage that the carbon material having the nanostructure itself may be damaged.

[0006]

SUMMARY OF THE INVENTION An object of the present invention is to provide a purification method which can eliminate such inconveniences and remove metal particles of a catalyst without damaging carbon having a nanostructure. I do.

[0007]

In order to achieve the above object, the present invention provides a method for purifying a carbon material having a nanostructure produced using a metal catalyst, wherein the carbon material is refluxed in a solvent. A first step of dissolving and removing metal particles of a catalyst contained in the carbon material in the solvent and subdividing amorphous carbon inevitably produced as a by-product during the production of the carbon material; The method is characterized in that a carbon material is heat-treated to vaporize and remove the finely divided amorphous carbon and a second step of stabilizing the structure of the carbon material is alternately performed a plurality of times.

[0008] According to the purification method of the present invention, first, at the reflux of the first step of the first step, free metal particles are dissolved and removed in the solvent, and the metal particles are inevitable in the production of the carbon material. Amorphous carbon by-produced is subdivided. However, at this time, the amorphous carbon is merely subdivided, and the metal particles contained in the amorphous carbon cannot be removed.

Then, in the first heat treatment in the second step, the amorphous carbon is vaporized and removed, thereby exposing the metal particles contained in the amorphous carbon. The heat treatment has the effect of stabilizing the structure of the carbon material having the nanostructure, but the effect of vaporizing the amorphous carbon is greater in the first time. The heat treatment may be performed after filtering the carbon substance from the solvent, or may be performed in the solvent.

Then, by the second reflux in the first step, the metal particles exposed as described above are removed, and the amorphous carbon is further subdivided. In the second and subsequent heat treatment steps, the amorphous carbon is vaporized and removed, and the metal particles included in the amorphous carbon are exposed. The effect of stabilizing is greater.

Therefore, the purification method of the present invention removes the metal particles at a high rate without damaging carbon having the nanostructure by performing the first step and the second step a plurality of times. be able to.

Further, in the purification method of the present invention, a first step of refluxing the carbon substance in an acid or an alkali, and a second step of heating the refluxed carbon substance at a temperature in the range of 200 to 700 ° C. After performing the above steps, the first step and the second step are repeated again.

Preferably, the reflux in the first step is performed in an acid or an alkali in order to chemically dissolve the metal particles of the catalyst and subdivide the amorphous carbon. As the acid, nitric acid, sulfuric acid, hydrochloric acid, hydrogen peroxide and the like can be used, and as the alkali, sodium hydroxide and the like can be used.

[0014] The heat treatment in the second step may include:
A temperature in the range of 200 to 700 ° C. in order to vaporize and remove the amorphous carbon enclosing the metal particles of the catalyst, to expose the metal particles, or to stabilize the structure of the carbon material having the nanostructure. It is preferable to carry out in. If the temperature is less than 200 ° C., it is difficult to vaporize the amorphous carbon, and if it is more than 700 ° C., the carbon material having the nanostructure may be damaged.

In the refining method of the present invention, the first step and the second step can be repeated a plurality of times to improve the removal rate of the metal particles. Tend to increase the damage of the carbon material provided with. Therefore, in the purification method of the present invention, it is preferable that the first step and the second step are alternately repeated twice.

At this time, in the second step of the second step, in order to stabilize the structure of the carbon material having the nanostructure, the temperature is higher than the temperature of the first heat treatment selected from the above range, and The heat treatment is preferably performed at a temperature within the range.

Examples of the carbon material having the nanostructure used in the present invention include a carbon nanotube.

[0018]

Next, embodiments of the present invention will be described in more detail with reference to the accompanying drawings. FIG. 1 is a diagram showing a change in weight of metal particles of a catalyst contained in a carbon material having a nanostructure at each stage of the purification method of the present embodiment, and FIG. It is a diagram which shows the result of the Raman spectrometry of the carbon material which has a structure, and FIG. 3 thru | or FIG.

In this embodiment, first, Ni: Y: C =
Using a 1: 1: 98 carbon electrode, arc discharge was performed at a current of 100 A and a voltage of 30 V under a helium atmosphere of 0.055 MPa, and a carbon nanotube was synthesized as a carbon material having a nanostructure to obtain Sample 1. Sample 1
Means N2 used as a catalyst in addition to carbon nanotubes
It contains i and Y metal particles, amorphous carbon inevitably produced as by-products, and inevitable impurities.

Next, 800 mg of the sample 1 was put into 600 ml of 1M nitric acid, and sufficiently stirred so as to be uniformly dispersed. Then, as the first step of the present invention, 120 ° C.
And refluxed for 48 hours. With this process,
Of the metal particles used as the catalyst, coarse particles in the free state and inevitable impurities are mainly removed, and amorphous carbon is subdivided.

After the reflux, the sample solution is ultrafiltered with a nitric acid-resistant filter (pore size: 0.2 μm), and the pH is adjusted to about pH with deionized water.
The carbon nanotubes were neutralized and washed until the carbon nanotubes reached 5. The carbon nanotubes were collected. The collected carbon nanotubes are collected in air at 90
Sample 2 was obtained by sufficiently drying at ° C.

Next, as a second step in the first step of the present invention, the sample 2 was placed in a heating furnace maintained at 400 ° C. in an air atmosphere, and subjected to a heat treatment for 2 hours. With this process,
The finely divided amorphous carbon is vaporized and removed to expose the metal particles of the catalyst contained in the amorphous carbon. At this time, since the amorphous carbon has been subdivided in advance as described above,
It is possible to prevent the carbon nanotubes from being locally heated and burned out. The obtained carbon nanotube was used as Sample 3.

Next, the sample 3 was put into deionized water, and was sufficiently dispersed by radiating ultrasonic waves for 15 minutes. 60 m of the sample 3 thus dispersed.
g was added to 60 ml of 1M nitric acid, and sufficiently stirred so as to be uniformly dispersed. Then, as a second step of the present invention, reflux was performed at 120 ° C. for 24 hours. By this treatment, the metal particles of the catalyst exposed in the previous step are removed, and the remaining amorphous carbon not removed in the first second step is further subdivided. However, since the amorphous carbon is mostly removed in the first second step, the reflux treatment mainly removes the metal particles of the catalyst.

The sample solution after the reflux was subjected to the same treatment as in the first step of the first time to collect carbon nanotubes. The collected carbon nanotubes were used as Sample 4.

Next, as a second step of the second step of the present invention, the sample 4 was placed in a heating furnace maintained at 450 ° C. in an air atmosphere and subjected to a heat treatment for 20 minutes. By this processing, of the remaining amorphous carbon that was not removed in the first step of the second step, the one that was subdivided in the second step of the first step was removed, and the structure was stabilized. A carbon nanotube is obtained. However, since the amorphous carbon is mostly removed in the first second step as described above, the heat treatment mainly stabilizes the structure of the carbon nanotube. The obtained carbon nanotube was used as Sample 5.

Next, the contents (mg) of the metal particles were measured by subjecting the samples 1 to 5 to thermal analysis. FIG.
The change in the content of the metal particles when 100 mg of sample 1 was prepared and the treatment of each step was sequentially performed is shown. From FIG. 1, 17 mg per 100 mg for sample 1 immediately after production.
It is clear that the content of the metal particles was finally reduced to 0.7 mg per 100 mg in Sample 5, and the content was removed at a high rate.

Next, the results of Raman spectroscopic analysis of Samples 2 to 5
The results are shown in FIG. From FIG. 2, the sample number increases.
About 160, indicating the presence of carbon nanotubes.
cm ^-1The peak at the position of
The amount of carbon nanotubes decreases,
It is clear that the amount is increasing.

Next, FIGS. 3 to 7 show simulated electron micrographs of Samples 1 to 5. FIG.

FIG. 3A is a simulated view of an electron microscope photograph of Sample 1 at a magnification of 92,500, and FIG.
It is an enlarged view of (a) and is a mimetic view of a 920,000-fold electron microscope photograph of sample 1. 3 (a) and 3
According to (b), the metal particles 2 are scattered between the fibrous carbon nanotubes 1.

FIG. 4 is a copy of an electron micrograph of Sample 2 at a magnification of 92,500, and it is clear that the number of metal particles 2 is reduced as compared with FIG. 3A.

FIG. 5 is a mimetic diagram of an electron micrograph of the sample 3 at a magnification of 92,500. Compared with FIG. 4, the metal particles 2 are increased, but this is due to the first heat treatment in the second step. As a result, the amorphous carbon was removed, and the total volume of the sample was reduced. As a result, the metal particles 2 relatively increased. In FIG. 5, the structure of the carbon nanotube 1 is stabilized by the heat treatment, and the outline of the carbon nanotube 1 is clearer than in FIG.

FIG. 6A is a simulated view of an electron micrograph of the sample 4 at a magnification of 92,500, and FIG.
It is an enlarged view of (a) and is a mimetic view of a 920,000 times electron microscope photograph of sample 4. 6 (a) and 6
According to (b), it is clear that the metal particles 2 hardly exist between the fibrous carbon nanotubes 1.

FIG. 7 is an electron micrograph of Sample 5 at the same magnification as in FIG. 6B. According to FIG.
Compared to (b), the outline of the carbon nanotube 1 is clear, and it is clear that the crystal plane is clear.

From the above results, according to the purification method of this embodiment, the carbon nanotubes 1 can be
It is clear that the metal particles 2 of the catalyst can be removed at a high rate.

In the present embodiment, the reflux in the first step is performed in nitric acid. However, the solvent used for the reflux may be any solvent that can dissolve and remove the metal particles of the catalyst. Alternatively, other acids such as sulfuric acid, hydrochloric acid, and hydrogen peroxide, alkalis such as sodium hydroxide, or hot water may be used.

In this embodiment, the first step and the second step
Step 2 is alternately repeated twice.
The step and the second step may be repeated one or more times as long as the carbon nanotube 1 is not excessively damaged.

[Brief description of the drawings]

FIG. 1 is a diagram showing a change in weight of a metal particle of a catalyst contained in a carbon material having a nanostructure in each stage of a purification method of the present invention.

FIG. 2 is a diagram showing the results of Raman spectroscopic measurement of a carbon material having a nanostructure at each stage of the purification method of the present invention.

FIG. 3 is a schematic view of an electron micrograph of a carbon material having a nanostructure in one stage of the purification method of the present invention.

FIG. 4 is a schematic view of an electron micrograph of a carbon material having a nanostructure in one stage of the purification method of the present invention.

FIG. 5 is a schematic view of an electron micrograph of a carbon material having a nanostructure in one stage of the purification method of the present invention.

FIG. 6 is a schematic view of an electron micrograph of a carbon material having a nanostructure in one stage of the purification method of the present invention.

FIG. 7 is a schematic view of an electron micrograph of a carbon material having a nanostructure in one stage of the purification method of the present invention.

[Explanation of symbols]

 1. Carbon material having a nanostructure 2. Metal particles

Claims (4)

[Claims] In a method for purifying a carbon material having a nanostructure manufactured using a metal catalyst, the carbon material is refluxed in a solvent to dissolve metal particles of a catalyst contained in the carbon material in the solvent. A first step of removing amorphous carbon inevitably produced as a by-product during the production of the carbon material, and a heat treatment of the refluxed carbon material to vaporize the finely divided amorphous carbon. And a second step of stabilizing the structure of the carbon material alternately a plurality of times. 2. A first step of refluxing the carbon material in an acid or alkali, and a step of removing the refluxed carbon material from 200 to 7
The purification method according to claim 1, wherein after performing the second step of performing heat treatment at a temperature in the range of 00C, the first step and the second step are repeated again. 3. The method according to claim 2, wherein in the second step of the second step, the heat treatment is performed at a temperature higher than the temperature of the first heat treatment selected from the range and within the range. Item 4. The purification method according to Item 2. 4. The method according to claim 1, wherein the carbon material having the nanostructure is a carbon nanotube.