KR20070098433A - Selection method of semiconducting singlewalled carbon nanotubes - Google Patents

Abstract

A method for selecting semiconductive single-walled carbon nanotubes is provided to select semiconductive carbon nanotubes having a certain diameter range on a large scale and with high purity through a simple process. A method for selecting semiconductive single-walled carbon nanotubes includes the steps of: adding carbon nanotubes to a poly(3-alkylthiophene) solution represented by a formula 1; dispersing the carbon nanotubes in the poly(3-alkylthiophene) solution; centrifuging the dispersion; and removing the poly(3-alkylthiophene) from the supernatant after centrifugation. In the formula 1, n is an integer of 450-500 and R is a straight and branched alkyl group having 6-12 carbon atoms.

Description

Selection method of semiconducting singlewalled carbon nanotubes

1 is a schematic process flow diagram of a screening method according to the present invention.

2 is a SEM photograph of carbon nanotubes before and after treatment according to an embodiment of the present invention.

3 is a Raman scattering test result of the carbon nanotubes treated by the embodiment of the present invention.

4 is a graph showing the 4-point probe measurement results of the carbon nanotubes treated by the embodiment of the present invention.

The present invention relates to a method for selecting single-walled carbon nanotubes having a specific chirality, and more particularly, to a method for selecting only semiconducting carbon nanotubes.

Carbon nanotubes are several nanometers to several tens of nanometers in diameter and tens of micrometers to hundreds of micrometers in length, having large anisotropy and having various shapes in the form of single walls, multi walls, or bundles. Have These carbon nanotubes have the properties of conductors or semiconductors depending on the shape of the coil (chirality), and the carbon nanotube powder is a mixture of semiconducting carbon nanotubes and metallic carbon nanotubes. Metallic, zig-zag structures are semiconducting. In the case of semiconducting carbon nanotubes, energy gaps vary depending on diameter and have a one-dimensional structure that gives a unique quantum effect. Indicates.

In addition, carbon nanotubes are highly dynamic (about 100 times as much as steel), have excellent chemical stability, have high thermal conductivity, and have hollow properties. . For example, memory devices, electronic amplifiers or gas sensors, electromagnetic shielding, electrode plates of electrochemical storage devices (secondary cells, fuel cells or super capacitors), field emission displays, Attempts or studies to apply to polymer composites have been actively made.

However, in order for the application technology of carbon nanotubes to be commercialized, it is necessary to obtain only carbon nanotubes having special chirality. For example, semiconductor carbon nanotubes are required for application to memory devices and sensors. Metallic carbon nanotubes are required for application to shielding agents. Therefore, it is necessary to develop a method of selectively preparing carbon nanotubes having a specific chirality or a method of selecting carbon nanotubes having a specific chirality.

Currently, the most common method for producing carbon nanotubes is to use chemical vapor deposition (CVD), which is difficult to selectively produce carbon nanotubes having a desired chirality. Therefore, attempts have been made to produce carbon nanotubes having specific chirality by using an electric discharge method or a laser deposition method. However, when the yield is low and the laser is used, the manufacturing cost is high and the complete property having only desired characteristics (conductor or semiconductor characteristics) is achieved. There was a difficulty in selection growth.

Therefore, first, studies have been made on methods for removing carbon nanotubes of unwanted characteristics after growing carbon nanotubes in the form of a mixture of semiconducting carbon nanotubes and metallic carbon nanotubes.

For example, a method using a surfactant called ODA (octadecylamine) has been proposed, but since the surfactant has to be removed after separating the chiral carbon nanotubes, there is a problem that the process is complicated and the yield is low.

In addition, a method of dispersing carbon nanotubes in a solution and then applying only metallic carbon nanotubes to an electrode by electrophoresis was proposed, but it was difficult to obtain a large amount of carbon nanotubes having low yield and selective chirality. (Krupke et al. Science 301, 344-347 (2003)).

On the other hand, the Republic of Korea Patent No. 0 377630, by connecting both ends of the carbon nanotubes in parallel to the electrode and applying a voltage in the form of pulse in a certain temperature range to remove the carbon nanotubes having a specific chirality to obtain only the desired chiral carbon nanotubes Although the method is disclosed, the process of connecting the carbon nanotubes in parallel is not easy, and there are disadvantages in that they are not suitable for obtaining a large amount of carbon nanotubes having specific chirality.

 Ming Zheng et al. Disclose a method for separating metallic single-walled carbon nanotubes and semiconducting single-walled carbon nanotubes wrapped by ssDNA of a specific sequence by anion exchange chromatography (Science 302, 1545-1548). (2003)). This method is expensive and has a problem in that the DNA is removed.

In addition, a method of separating metallic carbon nanotubes from semiconducting carbon nanotubes through amine functionalization has been proposed, but the method is required for the entire process, such as two hours for ultrasonic treatment for dispersion and 12 hours for centrifugation for separation. There is a problem that it takes too long (Yutaka Maeda et al., J. Am. Chem. Soc. 2005, 127, 10287-10290).

Therefore, the technical problem to be achieved by the present invention is to overcome the problems of the prior art, to provide a method for mass screening semiconducting carbon nanotubes having a specific range of diameter in a simple process.

The present invention to achieve the above technical problem,

Adding carbon nanotubes to a poly (3-alkylthiophene) solution of Formula 1;

Dispersing the carbon nanotubes in the poly (3-alkylthiophene) solution;

Centrifuging the dispersion; And

It provides a method for screening semiconducting carbon nanotubes comprising the step of removing the poly (3-alkylthiophene) from the supernatant after the centrifugation:

[Formula 1]

N is an integer of 450 to 500, and R is a straight or branched chain alkyl group having 6 to 12 carbon atoms.

According to one embodiment of the present invention, the carbon nanotubes and the poly (3-alkylthiophene) may be mixed in a ratio of 1: 1.5 to 1: 3 by weight.

In addition, the dispersion treatment method may be an ultrasonic treatment method.

According to another embodiment of the present invention, the centrifugation step may be performed at 15000 to 20000 rmp.

According to another embodiment of the present invention, the poly (3-alkylthiophene) can be removed by a gas phase heat treatment method.

According to another embodiment of the present invention, the method may further include purifying the carbon nanotubes before adding the carbon nanotubes to the poly (3-alkylthiophene).

In addition, the purification step of the carbon nanotubes may be by gas phase heat treatment purification method, acid treatment purification method or surfactant treatment purification method. Hereinafter, the present invention will be described in more detail.

The method for screening semiconducting carbon nanotubes according to the present invention comprises the steps of adding carbon nanotubes to a poly (3-alkylthiophene) solution of formula (1); Dispersing the carbon nanotubes in the poly (3-alkylthiophene) solution; Centrifuging the dispersion; And removing the poly (3-alkylthiophene) from the supernatant after the centrifugation, characterized in that the separation efficiency is high while treating a large amount of powder samples at once, unlike the conventional method:

[Formula 1]

N is an integer of 450 to 500, and R is a straight or branched chain alkyl group having 6 to 12 carbon atoms.

1 is a schematic process flowchart for explaining a method for screening semiconducting carbon nanotubes according to the present invention.

The carbon nanotubes used in the present invention may be a crude product before purification as well as purified carbon nanotubes. The method for preparing the carbon nanotubes is not particularly limited as long as it is a known method, and arc discharge, laser deposition, and high pressure carbon monoxide. Any crude product of carbon nanotubes prepared by the conversion method (HiPCo; High-Pressure Co Conversion), plasma chemical vapor deposition, or thermal chemical vapor deposition can be used.

Subsequently, a solution is prepared by dissolving poly (3-alkylthiophene) of Chemical Formula 1 in a solvent.

Poly (3-alkylthiophene) of the general formula (1) is n is 450 to 550 degree of polymerization. R is a straight or branched chain alkyl group having 6 to 12 carbon atoms, most preferably hexyl.

The solvent for preparing the poly (3-alkyl thiophene) solution is not particularly limited, and examples thereof include chloroform, THF, DMF, Toluene, and the like.

The poly (3-alkylthiophene) solution is added to the carbon nanotubes to obtain a mixture. In this case, the mixing ratio of carbon nanotubes to poly (3-alkylthiophene) is preferably 1: 1.5 to 1: 3 by weight. (The preferred weight ratio is not known until now.) Too low yields lower yields, too much yields higher yields, but degrades separation quality.

The carbon nanotubes are then dispersed in the poly (3-alkylthiophene) solution. In this case, the dispersion may be performed by ultrasonication and may be processed for 10 seconds to 5 minutes.

Through the dispersion, semiconducting carbon nanotubes having a specific diameter are selectively non-covalently bound to the poly (3-alkylthiophene). The reason why the specific diameter of the semiconducting carbon nanotubes can be selectively bonded is because of the distribution of abundant electrons around sulfur of the poly (3-alkylthiophene) and the selective bonding between the semiconducting carbon nanotubes and the poly Difference in reactivity between the alkyl group of (3-alkylthiophene) and semiconducting carbon nanotube or metallic carbon nanotube, or pi-conjugation and semiconducting carbon nanotube of poly (3-alkylthiophene) It is assumed that this is due to pi-pi stacking with .

The semiconducting carbon nanotubes bonded to the poly (3-alkylthiophene) have a diameter ranging from 0.95 nm to 1.12 nm.

The dispersion is then centrifuged to separate the precipitate from the supernatant consisting of the combination of semiconducting carbon nanotubes and poly (3-alkylthiophene). The precipitate contains a small amount of semiconducting carbon nanotubes excluding metallic carbon nanotubes and semiconducting carbon nanotubes in the specific diameter range.

Finally, the supernatant is decanted, and then poly (3-alkylthiophene) is removed from the semiconducting carbon nanotubes in the same manner as gas phase heat treatment.

When the carbon nanotubes used in the present invention are carbon nanotube crude products, the method may further include purifying the carbon nanotube crude products before mixing the carbon nanotubes with the poly (3-alkylthiophene) solution. In this way, it is preferable to remove the carbon mass or catalyst metal mass other than the carbon nanotubes through the purification step in order to finally obtain high purity semiconducting carbon nanotubes.

The purification step of the crude carbon nanotube product is not particularly limited as long as it is a conventional method, and may be by vapor phase heat treatment purification method, acid treatment purification method or surfactant treatment purification method. In the case of the acid treatment purification method, an aqueous solution of nitric acid or an aqueous solution of hydrochloric acid is used as an aqueous acid solution, and the crude product of carbon nanotubes is immersed in a purification bath containing such an aqueous solution of nitric acid or hydrochloric acid for 1 to 4 hours. He proceeds in a way. At this time, H ⁺ in the acid aqueous solution removes carbon lumps or carbon particles and Cl ⁻ or NO ₃ ⁻ serves to remove the catalyst metal lumps. Next, ultrapure water is supplied to a purification tank containing the mixed solution in which the carbon nanotubes are dispersed, and the acid aqueous solution is overflowed from the purification tank. Then, the washed result is a metal mesh having a size of 300 μm or less. Purified carbon nanotubes can be obtained by filtering carbon agglomerates, carbon particles, and catalyst metal agglomerates using a filter.

On the other hand, in the case of refining by the vapor phase heat treatment step, the carbon nanotube crude product is placed in a boat in the center of the reactor and heated, and when acidic purifying gas such as hydrochloric acid gas or nitric acid gas flows, hydrogen formed by pyrolysis of the refinery gas. ions of impurities such as carbon clusters, and other thermal decomposition products Cl ^- or NO ₃ ^- is to remove the catalyst metal mass.

Alternatively, the carbon nanotubes may be mixed with a surfactant such as SDS, and then centrifuged to obtain a supernatant, which may be added to acetone to form a precipitate, followed by filtration and purification.

Hereinafter, the present invention will be described in more detail with reference to preferred embodiments of the present invention, but the present invention is not limited thereto.

Example 1

Preparation of Purified Single Layer Carbon Nanotubes (SWNT)

1) Solubilization of SWNT by Surfactant (SDS)

80 mg SWNT (HiPCo), 2 g SDS (Sodium Dodecyl Sulfate, manufactured by J.T. Baker), and 200 ml ultrapure water (0.1 microfiltration. Invitrogen) were mixed in a 400 ml beaker. The beaker was sonicated for 30 minutes while cooling in an ice bath (Cole-Parmer Ultrasonic Processor 750 W). Centrifugation (Sorvall PR5C Plus, 12,500 rpm) at 4 ° C. for 4 hours. The supernatant was then carefully followed to yield a dark black homogeneous solution (SWNT + SDS).

1) Removal of SDS and Recovery of SWNT

15 ml of acetone was added to 5 ml of the above solution (SWNT + SDS) and stirred vigorously for several seconds to obtain a large amount of black precipitate.

The supernatant was removed by centrifugation (Sorvall RC5C Plus, 12,500 RPM) for 20 minutes.

The precipitate was washed three times by centrifugation (10 minutes each) with acetone to remove the supernatant to give pure SWNT without surfactant in acetone.

The nanotubes were collected by filtration with a PTFE membrane (Millipore, 0.45㎛). Bucky paper was obtained on the film. The bucky paper was carefully peeled off the membrane. The bucky paper was placed in a vacuum oven and dried overnight at 50 ° C. Obtained dried and purified SWNTs.

2 shows SEM images of SWNT before and after the purification step. Figure 2a is before purification and Figure 2b is after purification. From the figure, it can be seen that carbon nanotubes from which impurities such as amorphous carbon and metal catalysts are removed are obtained.

Separation of Semiconductor SWNTs from Metallic SWNTs

 20 mg of poly (3-hexylthiophene) (manufactured by Aldrich) was dissolved in 10 ml of chloroform to give a dark red solution. The solution was added to 10 mg SWNTs and another 10 ml chloroform. Sonication was performed for the time shown in Table 1 below. Then 1 ml ali ?? was taken to obtain samples 1-6. The samples were centrifuged at 14,000 rpm for 10 minutes. Precipitates of the top samples were analyzed by Raman spectroscopy and 4-point probes.

Sample 1 Sample 2 Sample 3 Sample 4 Sample 5 Sample 6 Ultrasonic Treatment Time 10 sec 30 seconds 1 minute 2 minutes 5 minutes 10 minutes

Test Example

For the precipitate obtained in Example 1, the diameter distribution and chiral distribution of carbon nanotubes were measured through Raman spectrum analysis, and the results are shown in FIG. 3. According to Figure 3 it can be seen that the peak of the semiconducting carbon nanotubes of a specific diameter range found in the untreated group is sharply lowered after the poly (3-hexylthiophene) treatment. In addition, it can be seen that the peaks of the semiconducting carbon nanotubes relatively out of the specific diameter range are increased. This indicates that semiconducting carbon nanotubes in the specific diameter range are mostly present in the supernatant rather than the precipitate after centrifugation.

The characteristics of the SWNT bucky paper on the membrane filter were also recorded in a 4-probe batch using an Agilent 4156 device parameter analyzer. Sheet resistance (R _s ) was evaluated using a low current-low bias linear regime and resistivity (ρ) was calculated using = tx R _s . The thickness (t) of the SWNT bucky paper was evaluated by Toncor Apha-Step Surface Profiler.

In the resistance value measured by the 4-point probe in FIG. 4, the resistance value before the poly (3-hexylthiophene) treatment decreased from 8.71 × 10 ⁻³ Ω · cm to 5.75 × 10 ⁻³ Ω · cm after the treatment. The results show that instead of reducing the semiconducting carbon nanotubes in the precipitate as in the previous Raman analysis, the resistance value is reduced due to the presence of the metallic carbon nanotubes.

According to the present invention described above, it is possible to maximize the applicability to other devices, such as memory devices or sensors because it can sort out the semiconducting carbon nanotubes in a specific diameter range in a short time in a short time through a simple process.

Claims (9)

Adding carbon nanotubes to a poly (3-alkylthiophene) solution of Formula 1; Dispersing the carbon nanotubes in the poly (3-alkylthiophene) solution; Centrifuging the dispersion; And A method for screening semiconducting carbon nanotubes comprising removing the poly (3-alkylthiophene) from the supernatant after centrifugation. [Formula 1]

N is an integer of 450 to 500, and R is a straight or branched chain alkyl group having 6 to 12 carbon atoms. The method of claim 1, wherein the carbon nanotubes to poly (3-alkylthiophene) are added in a ratio of 1: 1.5 to 1: 3 by weight. The method for sorting semiconducting carbon nanotubes according to claim 1, wherein the dispersion is performed by ultrasonic treatment. The method of claim 1, wherein the poly (3-alkylthiophene) is poly (3-hexylthiophene). The method of claim 1, wherein the poly (3-alkylthiophene) is removed by a vapor phase heat treatment method. The method according to claim 1, wherein the centrifugation is performed at 15000 to 20000 rpm. The method of claim 1, wherein the semiconducting carbon nanotubes have a diameter of 0.95 to 1.12 nm. 10. The method of claim 1, further comprising purifying the carbon nanotube crude product prior to mixing the carbon nanotubes with a poly (3-alkylthiophene) solution. Way. The method of claim 8, wherein the purification of the carbon nanotubes is carried out by a vapor phase heat treatment purification method, an acid treatment purification method or a surface active agent treatment purification method.

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