KR20050110912A - Process for non-oxidative purification of carbon nanotube - Google Patents

Abstract

The present invention relates to a method for non-oxidative purification of carbon nanotubes (carbon nanotubes, CNTs), which is melted in an organic solvent and sonicated in accordance with the present invention, followed by centrifugation to remove residues. The method for purifying carbon nanotubes, which includes a process for producing carbon nanotubes, has a high yield, can obtain a debundlized state CNT having excellent purity and solubility, is easy to process, and the purification process is simple and economical. This can be useful.

Description

PROCESS FOR NON-OXIDATIVE PURIFICATION OF CARBON NANOTUBE}

The present invention relates to a method for non-oxidative purification of carbon nanotubes (carbon nanotubes, CNTs).

Carbon nanotubes are hexagonal honeycomb graphite surfaces in which one carbon atom is bonded to three other carbon atoms, which are rounded to a nano-sized diameter, and are large molecules having unique physical properties according to their size and shape. It is hollow, lightweight and has good electrical conductivity as copper, thermal conductivity as good as diamond and tensile strength as steel. According to the cylindrical coupling structure, the tube and the tube interact with each other and change from conductor to semiconductor without intentionally adding impurities. Depending on the shape of the roll, it may be divided into single walled nanotubes (SWNTs), multi-walled nanotubes (MWNTs), and rope nanotubes.

Due to the inherent physicochemical properties of CNTs, the demand for them is increasing in various industries. Therefore, various manufacturing methods of CNTs have been radically developed. However, impurities such as metal catalysts, graphite, or amorphous carbon particles, which are generated during the production of CNTs, are more thermally stable than CNTs, and thus, a purification process for obtaining high purity CNTs is very complicated. As a result, industrially available high-purity CNTs are expensive and are limited in their use. In particular, SWNTs are very useful as one-dimentional quantum wires due to their excellent metallic properties. Therefore, studies on CNT refining for industrial application are being actively conducted.

Conventional methods for refining CNTs are based on thermal and / or chemical oxidation, where the etching rate of amorphous carbon, which is an impurity, is faster than CNTs. (Chiang, I. et al. , J. Phys. Chem. B , 105, 8297-8301, 2001; Hu, H. et al. , J. Phys. Chem. B , 107, 13838-13840, 2003; US Pat. No. 5,698,175 And U. S. Patent No. 5,695, 734, etc.) However, this method of oxidative purification destroys CNT's inherent electrical properties and alters its chemical structure, resulting in a completely different material, which results in most CNTs as well as impurities in the purification process. There is also a problem that the yield is low along with the destruction. Recently, in order to solve CNT destruction of oxidative purification, filtration, Bandow, S., J. Appl. Phys. , 80, 1020, 1996; Bandow, S. et al., J. Phys. Chem. B , 101, 8839, 1997; Shelimov, KB et al. , Chem. Phys. Lett. , 282, 429, 1988), chromatograph, Duesberg, g.S. et al. , Chem. Commun. , 3 , 435, 1998; Zhao B. et al. , J. Am. Chem. Soc. , 123, 11673, 2001) and polymer-assisted purification process, Murphy, R. et al . , 6, J. Phys. Chem. B , 106, 3087-3091, 2002), but the problems of high cost and low yield are still limited in the wide range of industrial applications requiring mass production.

It is therefore an object of the present invention to provide a non-oxidative purification process of carbon nanotubes (CNTs) with excellent yields and economics.

In accordance with the above object, in the present invention, carbon nanotubes (CNT) are dissolved in an organic solvent, sonication and sonication, followed by centrifugation to remove residues. ) Provides a purification method.

Hereinafter, the present invention will be described in detail.

The present inventors intensively studied a high yield CNT deoxidation purification method, which consists of a simple process. The present invention includes a process of dissolving CNTs in an organic solvent, sonication, and centrifugation to remove residues. It has been found that the sonochemistry purification method not only yields CNTs in a debundlized state with high yield, good purity and solubility, but also is easy to process and the purification process is simple and economical.

The method of the present invention does not use any solubilizing agent or functional agent, but only melts CNTs in an organic solvent and ultrasonically grinds them, followed by centrifugation to take a supernatant to obtain high purity. Characterized by obtaining CNTs.

At this time, the organic solvent serves as a dispersion medium of the carbon nanotubes, and available organic solvents include aromatic solvents xylene, 1,2-dichlorobenzene, and the like. It may be used in an amount sufficient to melt. For example, it may be used in an amount of 1 to 50 ml, preferably 2 to 10 ml, per mg of carbon nanotubes.

Ultrasonic pulverization is a process of separating and melting an entangled bundle of CNT powders containing impurities into small bundles (or individual) CNTs and impurities to dissolve the CNTs homogeneously in an organic solvent. Preferably it can be carried out for 1 to 60 minutes, preferably 5 to 10 minutes at a frequency of 15 to 30 kHz.

Centrifugation may be carried out two or more times at 10 to 120 minutes at 1000 to 500000 g, preferably at 10 to 15 minutes at 1500 to 1800 g, for 30 to 60 minutes at 15000 to 18000 g, at 320000 to 360000 g The residue may be gradually removed by performing once each for 60 to 120 minutes.

According to the purification method of the present invention, impurities such as amorphous carbon, carbon nanoparticles, graphite, and the like contained in the carbon nanotube (CNT) powder can be effectively removed, and a CNT having a purity of 75% or more can be obtained.

Hereinafter, the present invention will be described in detail by way of examples.

However, the following examples are merely to illustrate the invention, but the content of the present invention is not limited to the following examples.

<Example 1>

Using the - (SWNT s (starting)) of the tip-type grinder to powder 5 ㎎ with 1,2-dichlorobenzene was melted in 10 ㎖ 50% amplified in the frequency ㎑ 20 for 5 minutes, conventional low-purity single-wall nanotubes Ultrasonic grinding. This was centrifuged at 1600 g for 10 minutes to separate the residue <B> and the supernatant. The separated supernatant was further centrifuged at 16000 g for 60 minutes to separate the supernatant <C> and the residue <D>, and the separated <C> was finally centrifuged at 350000 g for 30 minutes to almost 100%. close to the purity of the% p (purificated) - got the SWNT.

Scanning electron microscopy (SEM) analysis

The SEM (scanning electron microscopy, SEM S-4700) analyzer to Example 1 s- SWNT powder as a starting material in, during the first centrifugation during the remaining is water <B>, 2 car centrifugation supernatant using a <C> The detailed morphological characteristics of <D>, the residue from the second centrifugation, and the supernatant from the final centrifugation, p- SWNT, were analyzed.

As a result, as shown in a to d of FIG. 1 and a to d of FIG. 2, it can be seen that s- SWNT is mixed with SWNT and bulky impurities (a and b of FIG. 1). In the first centrifugation, it can be seen that graphite having a diameter of 10 μm or more is filtered out as a residue <B> (FIG. 1C). In addition, it can be seen that <D>, the residue during the second centrifugation, particles of particles having a diameter of 500 nm or more are filtered (FIG. 1 d), and the SWNTs in the supernatant <C> thus purified in the second centrifugation. It was confirmed that only and small particles and mixed (Fig. 2a). Finally, it can be seen that almost 100% of SWNTs were purified in a debundlized state in p- SWNTs (b to d of FIG. 2).

Thermogravimetric Analysis (TGA), Inductive Thermogravimetric Analysis (DTG), and Lorenzian Curve Fit

S- SWNT powder used as starting material in Example 1, residue <B> at the first centrifugation, <C> at the second centrifugation, and <D> at the second centrifugation, TGA, DTG And Lorenchean curves, and the results are shown in FIGS. 3A to 3D and Table 1 below.

Here, Figure 3a is the starting material of Example 1 s- SWNT powder, Figure 3b is the residue during the first centrifugal <B>, Figure 3c is the residual door during the second centrifugation <D>, Figure 3d is the secondary The supernatant at centrifugation is shown as <C>.

Sample Name Peak temperature (℃) Component Composition ratio Residual Ratio (%) s- SWNT diagram 3a 725.126 black smoke 42.294 4.53 680.992 SWNT 50.277 550.342 Carbon nano particles (CNPs) 6.4284 <B> Figure 3b 741.652 black smoke 6.87 0 692.189 black smoke 87.67 635.57 Amorphous carbon 5.45 <D> Fig. 3c 667.084 A-graphite 36.13 5.76 567.421 Amorphous carbon / B-graphite 50.64 341.79 Carbon nanoparticles 13.23 <C> degrees 3d 567.525 Amorphous carbon / B-graphite 20.11 0 613.617 SWNT 79.89

As a result, the residue <B> in the first centrifugation contained 95% graphite and 5% amorphous carbon, and no metal residue was observed. In addition, the residual <D> in the second centrifugation is 667 ℃ and 567 ℃ two graphite particles of 36% large graphite particles (A-graphite particles) and 50% small graphite particles (B-graphite particles) Peaks were observed, respectively, and it was found that CNT particles of 349.7 ° C. peak and 5.76% metal residue were also contained. On the other hand, it can be seen that <C>, the supernatant during the second centrifugation, contains about 80% SWNT and 20% amorphous carbon and graphite particles having a 613 ° C peak.

These results are consistent with the SEM analysis, indicating that the non-oxidation purification method of the present invention can effectively obtain high purity SWNTs.

Raman spectra

In Example 1, Raman scattering spectroscopic analysis of supernatant p- SWNT (a) and s- SWNT powder (b) used as starting material was carried out in the final centrifugation.

As a result, as shown in Figure 4, the radial breathing mode (RBM) showed two strong peaks at 172 and 182 cm ^-1 of p- SWNT, and 162 and 178 cm ^-1 of s- SWNT powder. These mean diameters of 1.39-1.53 nm ( p- SWNT) and 1.36-1.44 nm ( s- SWNT powder), respectively. The larger diameter of p - SWNTs compared to s- SWNT powders is due to better separation due to the purification process. In addition, the FWHM (full width at half maximum) and the tangential G-band of RBM are similar to each other, indicating that the purification process of the present invention does not damage carbon nanotubes. .

In addition, unlike the G-band, in the D-band, p- SWNT (1280 cm ^-1 ) shows a slightly increased peak compared to s- SWNT powder (1274 cm ^-1 ), which shows good symmetry and mean p of p- SWNT. This means an increase in the number of sp3 hybridized carbon in the condensed aromatic structures of the nanotubes as the length of the SWNTs decreases.

As discussed above, the non-destructive, non-destructive, non-destructive CNTs comprising melting the carbon nanotubes (CNTs) of the present invention in an organic solvent by ultrasonication. The oxidative sonochemistry purification method provides a high yield, mild, debundlized CNT with excellent purity and solubility, which is easy to process and simple to purify. Economical, they can be useful in a wide range of industries such as biomedical, materials engineering and semiconductors.

1 is a scanning electron microscope (SEM) analysis of single-walled nanotube powders (a and b) used as starting materials in Example 1, and residues (c and d) removed according to the present invention,

2 shows the results of SEM analysis of the supernatant (a) and the final purified single-wall nanotubes (b, c and d) after the second centrifugation in Example 1,

3A to 3D are thermogravimetric analysis (TGA), inductive thermogravimetric analysis (DTG) and Lorenzian curve fit of single-walled nanotube powders used as starting materials in Example 1 and residues removed in accordance with the present invention. ) Result,

FIG. 4 shows Raman spectra of the final purified single wall nanotube (a) and single wall nanotube powder (b) used as starting material in Example 1. FIG.

Claims (5)

A method of purifying carbon nanotubes comprising melting carbon nanotubes in an organic solvent and pulverizing them ultrasonically and then centrifuging to remove residues. The method of claim 1, Purification method characterized in that the organic solvent is an aromatic solvent. The method of claim 1, Ultrasonic grinding is a purification method, characterized in that performed for 1 to 60 minutes at a frequency of 10 to 100 Hz. The method of claim 1, Centrifugation is carried out at 1000 to 500000 g for 10 to 120 minutes. The method of claim 1, Purification method characterized in that the centrifugation process is carried out two or more times.