KR100611643B1 - method of processing carbon nanotubes - Google Patents

Abstract

The present invention relates to a surface treatment method of a powdery carbon structure such as carbon nanotubes, and performs surface treatment by irradiating a high energy cation beam to the powdery carbon structure to be treated in an atmosphere containing oxygen. According to the surface treatment method of the powdery carbon structure, carbon nanotubes having high dispersibility and solubility in organic solvents can be produced without using a chemical solvent such as a strong oxidizing agent, and contaminant by-products generated by acidic chemicals are generated. Instead, it can be processed in large quantities and provides an advantage of increasing yield.

Description

Method of Purifying Powdered Carbon Structures {method of processing carbon nanotubes}

1 is a process chart showing a purification process of a powdery carbon structure according to a preferred embodiment of the present invention,

2 is a view showing an example of an apparatus for performing a purification treatment of a powdery carbon structure according to the present invention,

Figure 3 is a graph showing the results measured by XPS for carbon nanotubes not irradiated with a proton beam,

4 is a graph showing the results of measuring carbon nanotubes irradiated with a proton beam by XPS.

<Description of Symbols for Main Parts of Drawings>

200: proton accelerator 220: chamber

The present invention relates to a method for purifying a powdery carbon structure, and more particularly, to a method for purifying a powdery carbon structure that can increase the dispersibility of the powdery carbon structure in an organic solvent.

Carbon nanotubes are usually carbon materials having a high aspect ratio ranging from 1 to 100 nanometers (nm) in diameter and from several nanometers (nm) to several tens of micrometers (μm) in length. .

Carbon nanotubes exhibit conductive or semiconducting properties depending on their structure, and are used as materials for forming display devices, secondary batteries, and electron emitting devices.

In addition, carbon nanotubes are being used as additives in various composite materials due to their high electrical conductivity, thermal stability, tensile strength and resilience.

Recently, as methods for producing high quality carbon nanotubes at low cost have been developed, various methods for applying carbon nanotubes as additives of composite materials have been attempted. For example, the use of carbon nanotubes as additives to enhance the functions of ultra-high strength structural composites formed by combining polymers and organic materials, functional composite materials using electronic shielding films, and high thermal conductivity is being investigated. .

It is important to effectively disperse the bundles of carbon nanotubes in a solvent in order to make functional composites containing carbon nanotubes. As an example, in order to make an ultrahigh-strength polymer composite material in which carbon nanotubes are dispersed, it is necessary to uniformly disperse carbon nanotubes in a polymer matrix.

However, carbon nanotubes have a problem of having very low dispersion in solvents due to long lengths and strong attraction between carbon nanotubes.

 In order to improve such a problem, a lot of researches have been conducted on a method for mixing carbon nanotubes with polymer materials after dispersing through chemical and physical pre-treatment processes.

Known methods up to now include a method of oxidizing the surface of the carbon nanotubes with a strong acid solution such as sulfuric acid, hydrochloric acid, nitric acid and the like to increase the dispersibility of the carbon nanotube material itself.

McCarthy has reported a method of treating carbon fiber surfaces with sulfuric acid in Polymer Chem. 30 (1): 420 (1990). This method is a method for forming a carboxyl group (COOH) on the surface of the carbon fiber, it is also disclosed in U.S. Patent No. 5,698,175 proposed by Hiura, which has the effect of removing impurities, and is useful for adding functional groups to the surface. It is known that it can be utilized. In addition, the treatment of the surface of the carbon nanotubes with a solution of sulfonic acid, alkali metal chloride and hydrogen peroxide may cause effective oxidation. 6,099,960 and 6,099,965.

In addition, as reported by Esumi in the process of dispersing carbon nanotubes containing nitric acid or nitric acid mixed with sulfuric acid (Carbon 34: 279-281 (1996)). have.

In addition, Korean Patent Application No. 2000-0030351 and Korean Patent Application No. 2001-0047617 disclose a method of treating carbon nanotubes based on an acid or an acid.

However, the method of chemically treating carbon nanotubes using an acid solution as listed above has the following problems.

First, the yield is low because the separation extraction must be repeated through centrifugation and filter for each treatment step using a large amount of acid solvent.

Second, the process is complicated, the process takes a lot of time, the process is expensive.

Third, it is difficult to treat by-products of chemicals generated in the treatment process, and these by-products may pollute the environment.

Because of these problems, wet chemical treatment is difficult to apply industrially to the processing of large amounts of carbon nanotubes.

On the other hand, as another method of increasing the dispersibility of carbon nanotubes, Korean Patent Application No. 2003-0029184 discloses a method of chemically and physically bonding organic molecules to carbon nanotubes so that organic molecules are wrapped around the surface of carbon nanotubes and treated. It is. However, this method has a significant increase in the solubility of the carbon nanotubes in the solvent, but the organic functional group is included on the surface of the carbon nanotubes, so that the reaction process is complicated and expensive.

In addition, when the carbon nanotubes are mixed with other plastics or polymers, the outer surface of the carbon nanotubes is hidden in the functional group, and thus the properties of the desired carbon nanotubes are not sufficiently expressed.

On the other hand, the wet and dry method for treating the surface is a method using oxidizing gas and ultraviolet rays, there is a Japanese Patent Publication No. 2000-095965 for carbon black and the method by the same ultraviolet irradiation in the case of carbon fiber ball is Japanese Patent Laid-Open No. 3-185176 It was reported in the issue. However, these methods also have a high surface absorption by the target carbon due to the characteristics of the irradiated ultraviolet rays, so that a small amount of treatment can be performed at the laboratory level, but there are limitations in commercialization for treating carbon nanostructures for mass industrial use.

The present invention has been made to improve the above problems, and an object of the present invention is to provide a method for purifying a powdery carbon structure which can increase the dispersibility of the powdery carbon structure in a solvent and has a high treatment speed.

In order to achieve the above object, the method for purifying a powdery carbon structure according to the present invention includes a cation beam irradiation treatment step of irradiating a cation beam to a powdery carbon structure to be treated in an atmosphere containing oxygen.

Preferably the cation beam is a proton beam is applied.

In addition, the proton energy of the proton beam is 20 keV to 50 MeV, more preferably 10 MeV is applied.

The powdery carbon structure includes at least one of carbon nanotubes, carbon fibers, and carbon black.

In addition, a wet treatment step of treating the treated carbon powder structure in an acidic aqueous solution before or after the cation beam irradiation treatment step; may be further included.

Hereinafter, a method of purifying a powdery carbon structure according to a preferred embodiment of the present invention will be described in detail with reference to the accompanying drawings.

1 is a process chart showing a method for purifying a powdery carbon structure according to the present invention.

Referring to the drawing, in the purification method of the carbon structure, the carbon structure to be treated is treated by irradiating a cation beam in an oxygen atmosphere (step 100).

Here, the oxygen atmosphere refers to an atmosphere in which oxygen alone or a gas mixed with oxygen, for example, air or a liquid, for example, water (H ₂ O) is applied. When water is applied, carbon nanotubes may be placed in a container containing water and irradiated with a cation beam.

In addition, the cation beam may be applied to a positively charged proton or heavy ions, preferably a proton.

In addition, powder type carbon structures that can be applied to proton beam irradiation include carbon nanotubes, carbon fibers, carbon black, and the like, which will be described below with reference to carbon nanotubes.

The proton beam irradiation time may be appropriately applied in consideration of the amount of carbon nanotubes to be treated, and as an example, 20 to 6000 seconds may be applied.

In addition, the amount of carbon nanotubes to be used for one irradiation may be appropriately applied to the extent that the proton beam is evenly irradiated.

In order to purify the carbon nanotubes used, a wet treatment process for treating carbon nanotubes in an acidic aqueous solution before or after proton beam irradiation may be further added.

The carbon nanotube purification method may be performed using various known particle accelerators capable of generating protons or heavy ions and irradiating the carbon nanotubes with appropriate energy.

Particle accelerator that can be applied to the present invention should be able to generate protons or heavy ions and emit them with appropriate energy, and the results of the present invention are not affected by such protons or heavy ion accelerators or methods. Is omitted. However, an example of an apparatus capable of generating and accelerating a proton beam to irradiate carbon nanotubes to improve understanding of the present invention will be described with reference to FIG. 2.

Referring to FIG. 2, a proton accelerator 200 and a chamber 220 are provided as a device for carrying out purification of carbon nanotubes.

The proton accelerator 200 is configured to accelerate and output the protons generated by the proton generator 210 that generates the protons.

In addition, the proton accelerator 200 may further include a device for dispersing or focusing the proton beam in an appropriate angular range so as to adjust the irradiation area of the proton beam.

In addition, in order to control the proton beam generated in the proton accelerator 200 to an appropriate energy range, a metal plate 221 such as a gold thin film or Havar may be disposed on the proton beam traveling path.

Preferably, the energy of the protons emitted from the proton accelerator 200 is applied within a range of 20 keV to 40 MeV, and more preferably, protons having an energy of 10 MeV in order to process tens to hundreds of grams of carbon nanotubes in a few minutes. The beam is applied.

On the other hand, the chamber 220 is formed to have an internal space and is provided to face the irradiation direction of the proton beam emitted from the proton accelerator 200.

In addition, the chamber 220 includes a stage 230 for mounting a container 240 containing carbon nanotubes to be treated, a gas inlet 221 for injecting oxygen or air therein, and oxygen or air injected therein. It has a structure having a gas outlet 222 to be.

Unlike this, the chamber 220 may be omitted, and the proton beam emitted from the proton accelerator may be installed and treated to irradiate the carbon nanotubes to be treated in the air.

On the other hand, if necessary, a heater (not shown) capable of raising the temperature inside the chamber 220 or a temperature controller for controlling the increase in temperature due to irradiation within a predetermined range may be further installed. However, the temperature inside the chamber 220 should be less than 550 degrees Celsius, the melting temperature of the carbon nanotubes.

Unlike this, of course, it can be reacted by proton beam irradiation at room temperature.

The stage 230 may be provided with an apparatus, for example, a vibration applying apparatus, an ultrasonic applying apparatus, etc., into which the carbon nanotube powder to be treated contained in the container 240 may be agitated.

Unlike the illustrated example, an automatic transfer device (not shown) capable of transferring the carbon nanotubes to be treated in the direction of proton beam irradiation may be installed instead of the stage 230 to process a large amount of carbon nanotubes. to be.

The process of purifying carbon nanotubes using such a device in the air atmosphere will be described in more detail.

First, the carbon nanotubes in powder form to be purified are placed in the container 240 and placed on the stage 230.

Then start the proton accelerator 200. Then, a reaction is performed in which the surface of the carbon nanotubes is treated by oxygen in the air introduced through the gas inlet 221 and the proton beam uniformly irradiated into the chamber 220.

In describing the reaction process, protons of energy of dozens of mega electron volts (MeV) irradiated from the proton accelerator 200 undergo energy transfer due to energy absorption on the surface of the carbon nanotubes. The carbon-carbon bonds are absorbed by the amorphous carbon atoms present in the carbon nanotubes by the irradiated proton beams to separate the carbon-carbon bonds. The generated carbon molecules are activated carbons containing radicals, and various carbon-oxygen complexes are formed on the surface of the carbon nanotubes by reaction of oxygen molecules with carbon. Representative complexes are C-O and C = O, and a carboxyl group (COO-) containing the same produces a chemical reaction that produces a final oxide on the surface.

In order to confirm the reaction results, the results of comparative measurements using X-ray photoelectron spectroscopy (XPS) for each of the irradiation with the proton beam and after the proton beam are shown in FIGS. 4 and 5.

4 is a distribution chart of carbon binding energy of carbon nanotubes before irradiation with a proton beam. Referring to FIG. 4, the binding energy of the 1s orbital of carbon is about 285 eV. In addition, the binding energy distribution is divided into four small peaks of a, b, c, and d, where the difference in energy is the weak amorphous carbon (a), sp2 carbon (b), and oxidized carbon elements of carbon. CO (c) and C = O (d) are shown, indicating that sp2 carbon (b), which forms the crystal of carbon nanotubes, has the highest distribution.

  5 is a surface analysis result of carbon nanotubes obtained after irradiating a proton beam having an energy of 10MeV for 1314 seconds. Again, it is divided into four small peaks of a, b, c, and d, and the difference in energy is before the irradiation the weak amorphous carbon (a), sp2 carbon (b), and the oxidized carbon elements CO (c) and C = O (d) can be seen, and many amorphous carbons (a) of carbon nanotubes are formed, and more oxidized CO (c) and C = O (d) are formed than sp2 carbon (b). Shows that The formed amorphous carbon (a) is formed by breaking the carbon-carbon bond of the carbon nanotube, so that it can easily react with external oxygen.

Carbon nanotubes oxidized to the surface through this reaction process has a high dispersibility to the solvent. The results will be described later through Examples 1 to 4 below.

Carbon nanotubes that can be applied to the purification process of the carbon nanotubes can be applied regardless of the previous manufacturing process and structure. That is, as the production method of carbon nanotubes known to date, electric discharge, laser deposition, vapor phase synthesis, plasma chemical vapor deposition, thermal chemical vapor deposition, etc. are known. It can be applied to all of these purification processes.

In addition, the above-described purification process may be applied to single-walled carbon nanotubes consisting of a single layer, multi-walled carbon nanotubes consisting of multiple layers, or carbon nanotubes having a different structure. .

In addition, as described above, the powdery carbon structure that can be applied to the proton beam irradiation includes carbon fibers, carbon black, and the like in addition to carbon nanotubes.

On the other hand, the purification method by proton beam irradiation can be combined with the conventional wet treatment method.

That is, after the carbon nanotubes are wet treated with an acid solution to remove impurities, a proton beam irradiation process is performed to irradiate the proton beam, or the proton beam is irradiated to the carbon nanotubes to be treated, and then an acidic solution is prepared. As a matter of course, the wet treatment may be performed to enhance oxidation of the surface of the carbon nanotubes.

Here, the wet treatment step using an acidic solution refers to a process of adding carbon nanotubes to an acidic solution generated by diluting nitric acid, hydrochloric acid, or sulfuric acid with water.

Hereinafter, exemplary embodiments of the present invention will be described with reference to Table 1 below to determine whether the carbon nanotubes purified by proton beam irradiation have high dispersibility in various solvents.

division menstruum Sample 1 (proton beam not irradiated) Sample 2 (proton beam irradiation) Example 1 DMF 30.6 mg / L 65.1 mg / L Example 2 1,2-Dichlorobenzene 42.1 mg / L 76.1 mg / L Example 3 THF 3.0 mg / L 15.3 mg / L Example 4 Pyridine 4.3 mg / L 12.6 mg / L

The solvents applied in the examples described in Table 1 are generally selected from several solvents used for dissolving polymers or organic matters, and single-walled carbon nanotubes without proton beam irradiation for each selected solvent (sample 1 And a single-walled carbon nanotube (denoted as sample 2) subjected to proton beam irradiation were visually observed for dispersibility, ie, solubility, and analyzed using UV-visible spectroscopy.

Sample 2 was applied to the carbon nanotubes irradiated with a proton beam having an energy of 10 MeV for 1324 seconds at room temperature under an air atmosphere.

As can be seen from Table 1, in Example 1 to which a DMF (N, N-dimethyl formamide) solvent is applied, the solubility of Sample 2 subjected to proton beam irradiation is about 213% higher than that of Sample 1. In Example 2, in which a dichlorobenzene (1, 2-dichlorobenzene) solvent was applied, the solubility of Sample 2 was 180% higher than that of Sample 1. In Example 3, in which THF (tetrahydrofuran) solution was applied, the solubility of Sample 2 was higher than that of Sample 1. 510% higher. Finally, in Example 4 to which a pyridine solvent was applied, the solubility of Sample 2 was about 293% higher than that of Sample 1.

On the other hand, the conditions different from the proton beam irradiation conditions of the embodiments described above through Table 1, that is, oxygen is forcibly supplied into the chamber 220, the separation distance and processing between the proton accelerator 200 and the carbon nanotubes After varying the amount of carbon nanotubes, the solubility in the organic solvent after irradiation of the proton beam for 486 seconds was confirmed to be increased by more than several hundred%.

Carbon nanotubes subjected to proton beam irradiation as can be seen through the above examples have a higher dispersibility before proton beam irradiation, regardless of the type of solvent.

As described above, according to the method for purifying the powdered carbon structure according to the present invention, it is possible to prepare carbon nanotubes having high dispersibility and solubility in an organic solvent without using a chemical solvent such as a strong oxidizing agent. It does not generate contaminant by-products from chemicals, enables mass processing in a short time, and provides an advantage of increasing yield.

Claims (5)

In the method of purifying the powdery carbon structure, And a cation beam irradiation treatment step of irradiating a powdered carbon structure to be treated with a cation beam in an atmosphere containing oxygen. The method of claim 1, wherein the cation beam is a proton beam. The method of claim 2, wherein the proton energy of the proton beam is 20 keV to 50 MeV. The method according to claim 1 or 2, The powdery carbon structure is a purification method of a powdery carbon structure, characterized in that it comprises at least one of carbon nanotubes, carbon fibers, carbon black. The method according to claim 1 or 2, And a wet treatment step of treating the treated carbon powder structure in an acidic aqueous solution before or after the cation beam irradiation treatment step.

Images