KR101415175B1 - Preparation method of graphene by thermal plasma - Google Patents

Abstract

The present invention relates to a graphene manufacturing method using thermal plasma. Specifically, the present invention provides a high quality graphene manufacturing method which does not use metal nanopowder used as a catalyst and a post process by providing a method of synthesizing high purity few layer graphene by increasing voltages applied to both ends of plasma by injecting hydrogen with argon as thermal plasma generating gas in a graphene manufacturing method, thereby being capable of being useful for application.

Description

Preparation method of graphene by thermal plasma using thermal plasma [0002]

The present invention relates to a method for producing graphene using thermal plasma.

Graphene is a conductive material with a thickness of one layer of atoms, with the carbon atoms forming a honeycomb arrangement in a two-dimensional fashion. It has become an important model for studying various low-dimensional nano phenomena as graphite when accumulated in three dimensions, carbon nanotubes when dried one-dimensionally, and fulleren which is a zero-dimensional structure as a ball. Graphene is not only very stable structurally and chemically, but it is also predicted that electrons can be used about 100 times faster than silicon and about 100 times more current than copper. The characteristics of graphene were experimentally confirmed in 2004, when the method of separating graphene from graphite was found.

Graphene has the advantage that it is very easy to fabricate 1D or 2D nanopatterns because it consists of carbon, which is a relatively light element, and it can control the semiconductor-conductor properties as well as the variety of chemical bonds It is possible to manufacture a wide range of devices such as sensors and memories. Graphene was selected as one of the world's 100 best future technologies by MIT in 2008. In recent years, the Korea Chemical Technology Institute and the Samsung Economic Research Institute have also selected graphene-related technologies as the top ten technologies to change our lives within 10 years. .

Domestic graphene research is still in its infancy so far that small-scale national projects have been launched last year, far behind the US, Japan and Europe.

In spite of the excellent electrical, mechanical and chemical properties of graphene mentioned above, since the high-purity synthesis method has not been developed in the past, studies on practical applicable techniques have been limited. In the conventional mass synthesis method, graphite was mechanically pulverized and dispersed in a solution, followed by self-assembly to form a thin film. The advantage of being able to synthesize at a relatively low cost is that the electrical and mechanical properties of a number of graphene pieces are not as expected due to their overlapping structures.

Due to the rapidly increasing demand for flat panel displays, the global transparent electrode market is expected to grow to 20 trillion won within the next 10 years. Due to the nature of the display industry in Korea, the domestic demand for transparent electrodes has reached several hundred billion won every year, but most of them are dependent on imports. Indium tin oxide (ITO), which is a typical transparent electrode, has been widely applied to displays, touch screens, and solar electric appliances. Recently, due to the depletion of indium, the price has risen and urgent development of alternative materials has been required. In addition, due to the property of ITO which is easy to break, the application has been greatly restricted as a next generation electronic product which can be folded, bent or stretched. Graphene, on the other hand, was expected to have the advantage of being capable of short circuiting and patterning in a relatively simple manner while having excellent stretchability, flexibility and transparency. These graphene electrodes are expected to have an innovative effect not only on import substitution effects but also on the entire electronic industry technology of the next generation flexible electronic industry if future technology can be established.

However, when such graphenes are generally made by chemical vapor deposition (CVD), impurities are contained in the layered structure of the graphene, and impurities are mixed in the layered structure. Thus, the inherent electrical conductivity and transparency There is a problem that it is difficult to secure

In addition, although a method of manufacturing high purity graphene is proposed in "Development and application of large area / high purity graphene manufacturing technology based on roll to roll using chemical vapor deposition method, Department of Mechanical Design, Sungkyunkwan University, 2012.10, Kim Hyung Keun" There is a problem in that it is difficult to produce graphene having excellent light transmittance because the control of the 2D peak which can be called a graphene specific peak is not properly performed.

Therefore, the inventors of the present invention confirmed that it can not be a useful means for fabricating graphene having high light transmittance although it may be useful for producing large-area graphene in the case of the conventional invention, The present inventors have completed the present invention by confirming that high purity graphene can be manufactured by injecting hydrogen together with argon as a gas to increase the voltage applied across both ends of the plasma.

It is an object of the present invention to provide a method of manufacturing graphene using thermal plasma.

The present invention

1) introducing a carbon-based reaction gas and a hydrogen gas into a reactor;

2) injecting hydrogen into the reactor together with argon as a generated gas to generate a thermal plasma, thereby providing a method of manufacturing graphene using thermal plasma.

The present invention can provide a high temperature environment required for graphene growth by using thermal plasma in the production of graphene and increase the reactivity and inject hydrogen together with argon as a thermal plasma generation gas to increase the voltage applied across the plasma By synthesizing high-purity fine grain graphene, high-quality graphene can be produced and used without using the metal nano powder used as a post-treatment process and catalyst in the conventional method.

BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 is a schematic diagram of an overall experimental setup of a non-transferred arc plasma system for the production of graphene using thermal plasma.
2 is a schematic diagram of a path of hydrogen gas injected into a plasma torch nozzle.
3 is a graph showing Raman spectroscopic results according to the distance between the plasma torch nozzle and the graphite substrate. (a) is 10 cm, and (b) is 14 cm.
4 is a graph showing Raman spectroscopic results according to the surface treatment of hydrogen gas (route A). (a) is 1.0 L / min, (b) is 2.0 L / min, and (c) is 3.0 L / min.
FIG. 5 is a graph showing Raman spectroscopic results (532 nm / 3 mW, NRS-3100, 532 nm wavelength, JASCO) according to surface treatment of hydrogen gas and increase in plasma voltage (path B). (a) is 1.0 L / min, (b) is 1.0 L / min, and (c) is 1.5 L / min.
6 is a graph showing the ratio of the D peak to the G peak according to the hydrogen gas flow rate injected into the path B. FIG.
FIG. 7 is a graph showing the FE-TEM analysis result of the synthesized graphene. The number of layers of graphene was confirmed in (a) and (b), and in (c) and (d)

Hereinafter, the present invention will be described in detail.

The present invention

1) introducing a carbon-based reaction gas and a hydrogen gas into a reactor;

2) injecting hydrogen into the reactor together with argon as a generated gas to generate a thermal plasma, thereby providing a method of manufacturing graphene using thermal plasma.

Step 1) is a step of injecting a carbon-based reaction gas and hydrogen gas into the reactor.

The carbon-based reaction gas is preferably at least one selected from the group consisting of methane (CH ₄ ), ethane (C ₂ H ₆ ), ethene (C ₂ H ₄ ) and ethene (C ₂ H ₂ ) Do not.

The carbon-based gas was used as a carbon source to generate graphene and hydrogen gas was introduced to improve the quality of graphene.

Step 2) is a step of generating thermal plasma by injecting hydrogen together with argon as a generation gas to the reactor.

The thermal plasma is an ionization gas composed of electrons, ions, atoms and molecules generated from a plasma torch using a DC arc or a high frequency induction coupled discharge, and is a high-speed jet having an extremely high temperature and high activity ranging from several thousands to several tens of thousands K .

In the present invention, the thermal plasma jet is generated by a direct current plasma apparatus. In the plasma apparatus, argon gas, air, hydrogen gas or a mixture thereof may be used as a thermal plasma generating gas. Preferably, a mixed gas of argon and hydrogen is used do.

In the thermal plasma generating gas described above, argon is an element of group 8, and thus electrons are easily released even by a relatively small amount of energy, and inert gases are generally used for generation of thermal plasma since they have little effect on chemical reactions. If hydrogen is mixed with the argon gas, the surface treatment of the graphene and the voltage of the plasma are increased, so that the quality of the graphene is improved.

In the present invention, the flow rate of the hydrogen gas is preferably 0.5 to 3.0 L / min, more preferably 0.5 to 1.5 L / min, but is not limited thereto.

When the flow rate of the hydrogen gas is less than 0.5 L / min, the effect of the hydrogen gas is insignificant in the step of injecting the carbon-based reaction gas and the hydrogen gas into the reactor. If the flow rate of the hydrogen gas is more than 3.0 L / min, The economical efficiency is reduced because hydrogen gas is excessively injected in comparison with the general carbon and hydrogen ratio for forming the fins. In addition, in the step of generating thermal plasma by injecting hydrogen together with argon as a generating gas into the reactor, when the flow rate of the hydrogen gas is 1.5 L / min or more, the plasma voltage greatly increases, .

The substrate is preferably one selected from the group consisting of a graphite substrate, a silicon substrate, a transition metal substrate, and a composite substrate, but is not limited thereto.

(See FIG. 1) of the experimental apparatus of the method of manufacturing graphene using the thermal plasma of the present invention and a schematic diagram of the hydrogen gas path injected into the plasma torch (see FIG. 2).

An argon gas (15 L / min) was flowed between the cathode of the plasma torch and the anode nozzle in a plasma generating gas and discharged. In order to control the growth temperature condition of graphene, the distance between the plasma torch nozzle and the graphite substrate was adjusted to 14 cm. Additional hydrogen gas was injected into the plasma torch in two ways (Path A and Path B). The effect of improving the quality of graphene by the surface treatment of hydrogen gas was confirmed by injecting 1.0 to 3.0 L / min of hydrogen gas together with 1.0 L / min of methane gas and 1.0 L / min of the path A. In the path B, argon gas And hydrogen gas 0.5 ~ 1.5 L / min were injected to increase the plasma voltage from 21.0 V to 34.8 V. The plasma current was 300 A and the atmospheric pressure was experimented. The flow rate of all gases was controlled by MFC (Mass Flow Controller, MKP, MPR-3000). The quality of the resulting graphene was measured using a Raman spectrometer (RFC-100 / S, 1064 nm wavelength, 100 mW laser power, Brukers), (NRS-3100, 532 nm wavelength, 3 mW laser power, JASCO) 2100F, JEOL).

(RFC-100 / S, Brukers) by controlling the distance between the graphite substrate and the plasma torch nozzle. As a result, the distance between the plasma torch nozzle and the graphite substrate was graphened at a distance of 14 cm (See Fig. 3).

The results of Raman spectroscopy (RFC-100 / S, Brukers) were confirmed by injecting hydrogen gas with methane gas into the reaction tube nozzle (path A) to analyze the graphene generated by injecting hydrogen gas together with methane gas. As the flow rate of the hydrogen gas increased, the 2D peak became larger and sharp, and the CH peak near 2850 / cm decreased as hydrogen was injected, and the D peak was also larger, so that the thickness of graphene It was confirmed that the graft was defective due to a low D peak and a low quality graphene was synthesized (see FIG. 4).

In order to analyze the graphene generated by injecting hydrogen gas together with argon gas, hydrogen gas was injected into the reaction tube nozzle (path B) together with argon gas to observe Raman spectroscopic results (RFC-100 / S, Brukers) , It was confirmed that as the flow rate of the hydrogen gas increases, the D peak sharply decreases and graphene of better quality is synthesized (see FIGS. 5 and 6).

Analysis of high-quality graphene using a transmission electron microscope (TEM) revealed that graphene's handkerchief pattern was confirmed and that the total number of graphene was less than 10, so that a Few Layer Graphene (See Fig. 7)

Hereinafter, the present invention will be described in detail with reference to Examples and Experimental Examples. However, the following Examples and Experimental Examples are merely illustrative of the present invention, and the present invention is not limited by the following Examples and Experimental Examples.

< Example > Thermal plasma  Used Grapina  Produce

High - quality graphene was synthesized by decomposing methane gas (CH ₄ ) carbon in gas phase using thermal plasma.

Specifically, the experimental apparatus comprises a plasma torch, a reactor, a power supply, and a scrubber. The plasma torch, the reactor, and the chamber were cooled by cooling water (Fig. 1). Argon gas of 15 L / min was used as the plasma discharge gas. Argon gas was flowed between the cathode of the plasma torch and the anode nozzle in a plasma generating gas and discharged. The distance between the plasma torch nozzle and the graphite substrate was adjusted to control the growth temperature condition of graphene. The distance was adjusted to 10 and 14 cm. The additional hydrogen gas was injected in two ways (route A and route B), and the effect of improving the quality of graphene by surface treatment of hydrogen gas was confirmed by injecting hydrogen gas together with methane gas into route A, And the argon gas, which is a plasma generating gas, was injected in the path B, thereby confirming the effect of improving the quality of graphene by increasing the plasma voltage.

Further, hydrogen gas was injected into the plasma torch (FIG. 2). The hydrogen gas injected into path A was controlled at 1 to 3 L / min, and the hydrogen gas injected into path B was controlled at 0.5 to 1.5 L / min. The voltage change varied from 21.0 V to 34.8 V. The flow rate of the methane gas injected into the plasma region was fixed at 1 L / min, and the plasma current was 300 A, atmospheric pressure. The flow rate of all gases was controlled by MFC (Mass Flow Controller, MKP, MPR-3000). The resulting graphene was analyzed using two types of Raman spectroscopy (RFC-100 / S, 1064 nm wavelength, 100 mW laser power, Brukers), (NRS-3100, 532 nm wavelength, 3 mW laser power, JASCO) , JEOL) were used to confirm their quality and characteristics.

< Experimental Example  1> plasma torch  Analysis of effect of distance between nozzle and graphite substrate

Raman spectroscopic results (RFC-100 / S, Brukers) were confirmed by controlling the temperature by adjusting the distance between the graphite substrate and the plasma torch nozzle.

In general, the growth temperature of graphene is known to be 850 ~ 1200 ℃. However, since the temperature of the plasma used in this experiment reaches from several thousands to several tens of thousands, it is impossible to measure the general thermal conductivity. Therefore, Raman spectroscopic results (RFC-100 / S, Brukers) were confirmed by adjusting the temperature by adjusting the distance between the graphite substrate and the plasma torch nozzle. There are generally three peaks in graphene. The D peak observed at 1340 / cm indicates the defect of graphene, the G peak observed at 1580 / cm is the peak observed in graphite material, and the 2D peak observed at 2700 / It is a peak that confirms the number of layers of the pin.

As a result, in case of (a) having a distance of 10 cm between the graphite substrate and the plasma torch nozzle, a large amount of a soot peak was observed at 2500 to 3200 / cm, and a distance between the graphite substrate and the plasma torch nozzle was 14 (b), charcoal peaks were observed much less than the preceding line (a), and three common peaks (G, D, 2D) were observed, so that when the distance between the plasma torch nozzle and the graphite substrate was 14 cm (Fig. 3).

< Experimental Example  &Lt; 2 &gt; &gt; Grapina  Analysis (path A)

In order to analyze the graphene generated by injecting hydrogen gas with methane gas, hydrogen gas was injected into the reaction tube nozzle (route A) together with methane gas to observe Raman spectroscopic results (RFC-100 / S, Brukers).

Specifically, the distance between the graphite substrate and the plasma torch nozzle, which is the production-compatible temperature, was fixed at 14 cm, and hydrogen gas was injected into the reaction tube nozzle (path A) together with methane gas Only the surface treatment effect was observed without affecting the plasma voltage.

As a result, the charcoal peak of graphene (RFC-100 / S, Brukers) disappearing due to the flow rate of hydrogen gas, and as the flow rate of hydrogen gas was increased, the 2D peak became larger and sharpened and the peak of 2850 / cm The CH peak also decreased with the injection of hydrogen, and the D peak was also found to be large (FIG. 4).

From the above results, it can be confirmed that the graphene layer has a lower number of layers with thin and sharp 2D peaks, and the defect of graphene is large with a large D-peak, so that low-quality graphene is synthesized.

< Experimental Example  &Lt; 3 &gt; &gt; generated by injecting hydrogen gas together with argon gas Grapina  Analysis (Path B)

Raman spectroscopic results (RFC-100 / S, Brukers) were observed by injecting hydrogen gas with argon gas through a reaction tube nozzle (path B) to analyze the graphene generated by injecting hydrogen gas together with argon gas.

Specifically, hydrogen gas was injected into the reaction tube nozzle (path B) with argon gas at a flow rate of 0.5 to 1.5 L / min in order to reduce the D peak, which was shown in Experimental Example 2. The plasma voltage was 21.0 V to 34.8 V Respectively.

As a result, it is a Raman spectroscopic result according to the surface treatment of the hydrogen gas and the increase of the plasma voltage. (532 nm / 3 mW, NRS-3100, JASCO) It was confirmed that the D peak sharply decreases as the flow rate of hydrogen gas increases (FIG. 5).

Also, it was confirmed that as the flow rate of the hydrogen gas increases, the D peak decreases greatly, and when the hydrogen gas is further injected, a better quality graphene is synthesized (FIG. 6).

< Experimental Example  4> High quality Grapina  analysis

High-quality graphene was analyzed using a transmission electron microscope (TEM) for analysis.

Specifically, in Experimental Example 3, hydrogen gas was injected at a flow rate of 1.5 L / min into a reaction tube nozzle (path B) together with argon gas, and the resulting graphene was analyzed by FE-TEM (JEM-2100F, JEOL) The synthesized graphene was analyzed.

As a result, (a) and (b) visually confirmed that the number of graphene layers was about 7 to 8 layers, and (c) and (d) confirmed graphene handkerchief patterns.

From the above results, it was confirmed that the total number of graphenes was less than 10, so that a fur layer graphene was formed (FIG. 7).

Claims (6)

i) injecting methane gas (CH4) and hydrogen gas into a reactor through a first path within a plasma torch nozzle, while applying heat to the plasma torch in a reactor equipped with a plasma torch and a substrate;
ii) injecting argon gas (Ar) and hydrogen gas into the reactor through a second path within the plasma torch nozzle in the reactor of step i) to produce a thermal plasma.
Method of manufacturing graphene using thermal plasma.
The method of claim 1, wherein the distance between the plasma torch and the substrate in the reactor of step i) is 14 cm.
The method of claim 1, wherein the flow rate of the hydrogen gas in step i) is 1.0 to 3.0 L / min.
The method according to claim 1, wherein the flow rate of hydrogen gas in step ii) is 1.5 L / min.
delete The method of claim 1, wherein the substrate of step 2) is one selected from the group consisting of a graphite substrate, a silicon substrate, a transition metal substrate, and a composite substrate.

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