KR20090006912A - Method and apparatus for modifying carbon nanotube using plasma - Google Patents

Abstract

A reforming method of a carbon nanotube is provided to improve solubility and dispersibility of the carbon nanotube by binding various plasma species on a surface of the carbon nanotube and to separating or refining SWCNT of metallic and semiconductive properties. A reforming method of a carbon nanotube comprises steps of: synthesizing the carbon nanotube; refining the synthesized carbon nanotube; irritating the plasma in the refined-processed carbon nanotube; and processing the refined-processed carbon nanotube in an acidic aqueous solution before or after a plasma processing step.

Description

Method and apparatus for reforming carbon nanotube using plasma {METHOD AND APPARATUS FOR MODIFYING CARBON NANOTUBE USING PLASMA}

The present invention relates to a method and apparatus for reforming carbon nanotubes, and more particularly, to a method and apparatus for reforming carbon nanotubes using plasma so that the carbon nanotubes have high dispersibility and solubility in a liquid solvent and optionally have high chemical reactivity. It is about.

Recently, interest in nanotechnology has been increasing, and research and technology development on carbon nanotubes consisting of only carbon atoms have been actively conducted. Carbon nanotubes are a structure in which a single graphite surface made of sp ² bonds is rolled round. Generally, the characteristics of carbon nanotubes are determined by the angle at which the graphite surface is dried or the diameter of the tube.

Carbon nanotubes are conductive or semiconducting depending on their structure and are used for display devices, secondary battery electrodes, electron-emitting devices, fuel storage transport media, and AFM / STM probes. Carbon nanotubes are also used as additives in various composite materials due to their high electrical conductivity, thermal stability, tensile strength and resilience.

It is important to effectively disperse the bundles of carbon nanotubes in a solvent in order to make functional composites containing carbon nanotubes. For example, in order to make ultra-high strength polymer composites in which carbon nanotubes are dispersed, carbon nanotubes must be uniformly dispersed in a polymer matrix. However, carbon nanotubes have a problem of having a very low dispersion in a solvent due to long length and strong attraction between carbon nanotubes.

In order to improve this problem, a lot of researches have been conducted on techniques for mixing carbon nanotubes with polymer materials by having a dispersing force through chemical and physical pretreatment. Known methods to oxidize the surface of carbon nanotubes with a solution of sulfuric acid, nitric acid, hydrochloric acid, hydrogen peroxide, etc. in order to improve the dispersibility of the carbon nanotube itself, and the Korean Patent Registration No. 10-0579319 A method for surface modification of carbon nanotubes by irradiating ultraviolet rays in an atmosphere is disclosed.

However, the method of chemically treating carbon nanotubes using the solutions listed in the conventional method has a low yield since the separation extraction through centrifugation and filter is repeated for each processing step using a large amount of acid solvent. The process is complicated, time consuming and expensive. In addition, the chemicals and by-products generated during the treatment must be treated and there is a problem of causing environmental pollution.

Single-Wall Carbon Nanotubes (hereinafter referred to as "SWCNTs") show metal or semiconductor properties depending on the asymmetry of the molecules, and SWCNTs generally have both properties. Metal SWCNTs are highly desirable as conductive thin films and transparent electrodes, and semiconductor SWCNTs are showing great industrial demand for field effect transistors.

However, there is no method of synthesizing the SWCNT of the metallic properties and the semiconductor SWCNT selectively of the SWCNT synthesis method yet, but it is possible to synthesize twice as many semiconductor SWCNTs than the metallic SWCNT. This is an important drawback for applications where pure SWCNT is essential. For example, metallic SWCNTs reduce the on / off current ratio of field emission transistors, while semiconductor SWCNTs reduce the conductivity of thin films. Therefore, in order to realize the potential of SWCNTs, there is an urgent need for a method of efficiently separating SWCNTs having two characteristics or selective purification of two SWCNTs.

 Semiconductive SWCNTs are separated from metallic SWCNTs from SWCNTs with carboxyl functional groups with the help of Octadeclyamine or Porphyrins. On the other hand, the metallic SWCNTs are separated from the semiconducting SWCNTs using bromine complex or Dielectrophoresis. However, the amount of separated metallic SWCNTs is very small. Metallic and semiconducting SWCNTs surrounded by DNA are separated by anion exchange chromatography, but this method is expensive and has a problem of DNA removal from SWCNTs.

In order to solve the above problems, by covalently bonding various plasma species to the surface of carbon nanotubes, carbon nanotube reforming method and apparatus for improving the solubility and dispersibility of carbon nanotubes and separating or purifying metallic and semiconducting SWCNTs are provided. There is an object of the present invention.

Carbon nanotube reforming method for achieving the above object comprises the steps of synthesizing the carbon nanotubes; Purifying the synthesized carbon nanotubes; And a plasma treatment step of irradiating plasma to the purified carbon nanotubes to be treated.

And a wet treatment step of treating the carbon nanotubes to be treated with an acidic aqueous solution before or after the plasma treatment step.

The plasma processing step may include loading carbon nanotubes in a container to expose the carbon nanotubes to plasma; A plasma gas injection step of selecting and injecting the plasma gas; A plasma ON step of generating the plasma; A processing time control step of controlling the plasma exposure time; A plasma off step of blocking the plasma generation; And collecting the plasma treated carbon nanotubes. Modification method of carbon nanotubes.

After the plasma treatment step, the treated carbon nanotubes are dispersed in a solvent, and then the pH of the dispersion is adjusted to a range of 7 to 14.

The solvent is characterized by consisting of distilled water, chloroform, isopropanol, dimethylformamide, methylpyrrolidinone, decane, tetrahydrofuran, dichloroethane or mixtures thereof.

The solvent is characterized in that it comprises a selected dispersant consisting of a surfactant, a water soluble polymer or a mixture thereof.

The plasma treatment step is characterized in that it is carried out at a temperature of -10 ℃ to 800 ℃.

In the plasma treatment step, the plasma is characterized in that generated at a pressure of 10 ^-6 Torr to 5 atm.

In the plasma treatment step, the plasma is a fluorine containing an inert gas such as argon and helium, fluorine such as hydrogen (H ₂ ), nitrogen (N ₂ ), oxygen (O ₂ ), CF ₄ , NF ₃ , SF ₆ Gas, hydrocarbon gas such as methane (CH ₄ ), ethylene (C ₂ H ₄ ), acetylene (C ₂ H ₂ ), nitrogen dioxide (NO ₂ ), nitrogen monoxide (NO), carbon dioxide (CO ₂ ), carbon monoxide (CO) , Ammonia (NH ₃ ) gas or a mixed gas of the above-mentioned gases, hydrogen peroxide (H ₂ O ₂ ), methanol (CH ₃ OH), ethanol (C ₂ H ₅ OH), acetone ( CH ₃ COCH ₃ ) and a hydrocarbon liquid having 6 to 20 carbon atoms.

The carbon nanotubes to be treated are carbon black, carbon fiber or fullerene.

In the plasma processing step, the plasma is a radio frequency plasma, a high frequency plasma, a dielectric barrier discharge plasma, an AC or DC glow discharge plasma, a middle frequency plasma, an arc plasma, a corona discharge. It is characterized by consisting of a plasma or a mixture thereof.

In addition, the object is a plasma chamber in which the gas inlet and the gas outlet is formed; A carbon nanotube container installed inside the chamber and containing carbon nanotubes to be modified; And a plasma generating device installed inside the chamber and irradiating plasma to the container.

One side of the plasma chamber is characterized in that the vacuum device including a vacuum pump is provided.

The carbon nanotube container is characterized in that the carbon nanotube is provided with a vibration applying device or an ultrasonic application device that can be stirred so as to be uniformly modified by the plasma.

The carbon nanotube container is characterized in that the stage is provided with a stage for adjusting the separation distance between the plasma and the carbon nanotubes.

According to the present invention, carbon nanotubes can be modified to have high dispersibility and solubility in a solvent on the surface of carbon nanotubes by using various plasmas without using chemicals such as strong oxidizing agents.

In addition, according to the present invention it is possible to separate the high yield of m-SWCNT and s-SWCNT by selectively providing a difference in chemical reactivity to the SWCNT by using a plasma chemical reaction.

Therefore, the carbon nanotube application field can be further expanded by the present invention.

Hereinafter, a method of modifying carbon nanotubes using plasma according to an embodiment of the present invention will be described in detail with reference to the accompanying drawings.

1 is a process flow diagram illustrating a carbon nanotube reforming process using plasma according to an embodiment of the present invention.

Referring to Figure 1, it shows a process flow from the synthesis (S20) step of the typical carbon nanotubes (S70) step.

First, carbon nanotubes are synthesized (S20). Carbon nanotube synthesis methods that are well known to date include electric discharge, laser deposition, vapor phase synthesis, thermal chemical vapor deposition, and plasma chemical vapor deposition. The carbon nanotubes include multi-walled carbon nanotubes (MWCNT) and single-walled carbon nanotubes (SWCNT). Carbon nanotubes synthesized by various physicochemical methods as described above may or may not include transition metals depending on the synthesis method.

Next, the synthesized carbon nanotubes are purified (S30). That is, in the synthesis process, the carbon nanotubes containing the transition metal are removed by the physicochemical treatment method, and amorphous carbon is also removed in this process. The physicochemical treatment means heat treatment in an oxidizing atmosphere such as 400 ^° C. to 800 ^° C. air or an inorganic strong acid such as hydrochloric acid or sulfuric acid.

Next, the purified carbon nanotubes are modified (S100). That is, in the present invention, a reforming method using plasma is applied to achieve the reforming effect (dispersibility and solubility improvement, metallic carbon nanotube purification, semiconductor carbon nanotube purification).

If the plasma is classified according to the generated pressure, it may be classified into a low pressure plasma and a high pressure plasma. In general, the low pressure plasma may vary in pressure depending on the application, but in the carbon nanotube reforming according to the embodiment of the present invention, a plasma generated at a pressure of 10 ⁻⁶ Torr to several hundred Torr is generally preferred, and a high pressure plasma is referred to as hundreds of Torr to 5 Refers to plasma generated at a pressure of atm. The low pressure and high pressure plasma may include radio frequency plasma, high frequency (0.3 GHz to 20 GHz) plasma, dielectric barrier discharge plasma, AC or DC glow discharge, middle frequency plasma, arc plasma. , Corona discharge plasma. In general, in the case of a low pressure discharge plasma, its characteristics are in the form of a glow discharge such as a fluorescent lamp and the temperature of the plasma gas is room temperature.

Depending on the method used in the carbon nanotube reforming step (S100), it is possible to exhibit modification effects such as dispersibility and solubility improvement, metallic carbon nanotube purification, and semiconducting carbon nanotube purification. This will be described later.

Through the carbon nanotube reforming (S100) step, the carbon nanotube filtering step (S50) and the carbon nanotube dispersion manufacturing step (S60) step lead to carbon nanotube application (S70).

The carbon nanotube reforming step (S100) will be described in detail. The carbon nanotube reforming step (S100) step includes a CNT Loading (S101) step of placing the carbon nanotubes in a container to expose the plasma, and the plasma reforming effect described above. Plasma gas injection (S102) to select and inject suitable plasma gas, plasma on (S103) generating plasma, processing time control (S104) controlling plasma exposure time, plasma off (S105), CNT collection (S106) step.

In the CNT Loading (S101) step, the temperature of the container on which the carbon nanotubes are loaded may be delayed or accelerated by cooling or heating the chemical reaction with the plasma, and the temperature of the container may be controlled at -10 ° C to 800 ° C. have.

When the low pressure plasma is applied in the plasma gas injection step S102, the pressure is controlled at 10 ⁻⁶ Torr to several hundred Torr while maintaining the selected plasma gas atmosphere. In addition, when the carbon nanotubes in powder form are applied in the plasma reforming step S100, the carbon nanotube powder may be mixed or flipped again for uniform modification of the carbon nanotubes. Of course, by controlling the time in the processing time control step (S104) to achieve a uniform modification, of course.

The carbon nanotubes obtained in the plasma reforming step S100 may be subjected to the carbon nanotube filtering step S50 filtered by wet treatment with the inorganic strong acid solution described above. In addition, the plasma-modified carbon nanotubes may undergo a carbon nanotube dispersion preparation (S60) step of dispersing in a solvent to prepare a dispersion, and may adjust the pH of the prepared carbon nanotube dispersion to a range of 7 to 14 and dispersibility. It can be sonicated for further enhancement.

The solvent of the resulting dispersion after plasma reforming is preferably composed of distilled water, chloroform, isopropanol, dimethylformamide, methylpyrrolidinone, decane, tetrahydrofuran, dichloroethane and mixtures thereof. In addition, the solvent may include a dispersant consisting of a surfactant, a water-soluble polymer and a mixture thereof. The plasma-modified carbon nanotubes and carbon nanotube dispersions are applied to various fields as the powder itself or as the dispersion itself (S70). On the other hand, the carbon nanotube reforming method by the plasma treatment can of course be combined with the conventional wet treatment method.

Plasma modification effects of the above-described dispersibility and solubility of carbon nanotubes, metallic carbon nanotube refining, and semiconducting carbon nanotube refining are determined according to the selected plasma gas.

, O ₂ ^{- -} for example, oxygen as the plasma gas (O ₂₎ is O, including the electrons in the plasma will be described a reaction process when the inlet, O ^+, O ₂ ^+, molecular oxygen radicals, oxygen radicals, O _There are various types of plasma species such as ₃ , which separate the carbon-carbon (CC) bonds to the amorphous carbon atoms present in the carbon nanotubes. In addition, a plasma chemical reaction occurs to generate a carboxyl group (COO-) on the surface of carbon nanotubes by reaction with carbon. This reaction takes several seconds to several minutes, and the modified carbon nanotubes have high dispersibility and solubility in a solvent.

Carbon structures, such as carbon nanotubes, begin to oxidize in an oxidative atmosphere around 500 degrees Celsius, and in the case of SWCNT, partial oxidation may occur even at 800 degrees Celsius. In addition, considering the temperature of the container of the carbon nanotubes controlled at -10 ℃ to 800 ℃ described above, the plasma treatment is preferably carried out at a temperature of -10 ℃ to 800 ℃. In addition, impurities remaining in the carbon nanotube purification (S30) step described in FIG. 1 may also be removed. The modified carbon nanotubes may be dispersed in a solvent, and then the pH of the resulting carbon nanotube dispersion may be adjusted to a range of 7 to 14 and sonicated to further improve dispersibility.

In addition, in order to increase dispersibility and solubility in a solvent, plasma treatment of carbon nanotubes using not only oxygen but also hydrogen, fluoride gas, and hydrocarbon gas shows hydrophobic to superhydrophobic, hydrophilic to superhydrophilic properties depending on the gas used. The same properties make it possible to have high dispersibility in the solvent. In addition, it can be plasma-treated using the gases listed above to make the functional group required on the surface of the carbon nanotubes.

As described above, metallic SWCNTs (m-SWCNTs) and semiconductor SWCNTs (s-SWCNTs) coexist in single-walled carbon nanotubes. According to a journal published in Synthetic Metals (Vol. 2, Issues 3-4, pp. 171-176, year 1980), the graphite surface is formed by nitronium ions (NO ₂ ⁺ ). It was introduced that it can be easily attacked.

That is, nitronium ions capture pi ( π ) electrons in graphite while increasing the binding energy with the graphite surface. Compared to single-walled carbon nanotubes and graphite, except for the strain effect, SWCNT has graphite-like pie electrons on its surface. Since m-SWCNTs have a much higher electron charge density than s-SWCNTs, nitronium ions can attack the m-SWCNT's walls and further decompose the walls to selectively separate s-SWCNTs from m-SWCNTs. From this principle, s-SWCNT can be easily separated using plasma reforming method.

Nitrogen dioxide plasma, for example, produces abundant nitrinium ions that effectively attack and decompose m-SWCNTs to yield high yields of s-SWCNTs. It is also possible to use nitrogen monoxide or a mixed gas of oxygen and nitrogen instead of nitrogen dioxide. The modified carbon nanotubes may be dispersed in a solvent to make an s-SWCNT dispersion, and the pH of the dispersion may be adjusted to 7 to 14, and the dispersion may be sonicated for better dispersibility.

In addition, a high yield of m-SWCNT can be obtained through selective oxidation of s-SWCNTs. In general, m-SWCNTs have a higher chemical reactivity than s-SWCNTs. However, in the case of hydrogen peroxide, weak hole dopant, and plasma treatment, s-SWCNT can be made to have higher chemical reactivity, so it is selective by various oxygen radicals such as oxygen atom, ozone, etc. generated in hydrogen peroxide plasma. By s-SWCNT can be oxidized to obtain a high yield of m-SWCNT. The modified carbon nanotubes can be dispersed in a solvent to form an m-SWCNT dispersion, the pH of the dispersion is adjusted to 7 to 14, and the dispersion can be sonicated for better dispersibility.

The solvent of the dispersion produced after the plasma reforming may be composed of distilled water, chloroform, isopropanol, dimethylformamide, methylpyrrolidinone, decane, tetrahydrofuran, dichloroethane and mixtures thereof. In addition, the solvent may include a dispersant consisting of a surfactant, a water-soluble polymer and a mixture thereof.

2 is an example of a reforming apparatus capable of performing a method for reforming carbon nanotubes using plasma according to an embodiment of the present invention.

Referring to FIG. 2, the reforming apparatus 500 of the present invention includes a plasma chamber 90, a plasma generating apparatus 50, and a carbon nanotube container 72.

The plasma chamber 90 is provided with a plasma gas inlet 80 and an outlet 82. When the low pressure plasma is applied, a vacuum component including a vacuum pump (not shown) may be provided at one side of the chamber 90.

The carbon nanotube 70 contained in the carbon nanotube container 72 may be installed to be stirred such that the carbon nanotube 70 is uniformly modified by the plasma 60, for example, a vibration applying device or an ultrasonic application device. The carbon nanotube container 72 may have a batch form or an in-line form.

In addition, a stage (not shown) may be installed in the carbon nanotube container 72 to adjust the separation distance between the plasma 60 and the carbon nanotubes 70.

In order to change the physical and chemical properties of the carbon nanotubes 70, the plasma gas is an inert gas such as argon and helium, hydrogen (H ₂ ), nitrogen (N ₂ ), oxygen (O ₂ ), CF ₄ , NF ₃ , Fluoride gas containing fluorine such as SF ₆ , hydrocarbon gas such as methane (CH ₄ ), ethylene (C ₂ H ₄ ), acetylene (C ₂ H ₂ ), nitrogen dioxide (NO ₂ ), nitrogen monoxide (NO), carbon dioxide Hydrogen peroxide (H ₂ O ₂ ), methanol (CH ₃ OH) which can be (CO ₂ ), carbon monoxide (CO), ammonia (NH ₃ ) gas or a mixture of the above-listed gases , Ethanol (C ₂ H ₅ OH), acetone (CH ₃ COCH ₃ ) and may include a hydrocarbon liquid having 6 to 20 carbon atoms, in this case, the gas inlet may be further provided with a device for liquid evaporation.

The process of reforming the carbon nanotubes using the plasma generator 50 in a plasma atmosphere will be described in more detail.

First, the carbon nanotubes to be modified are placed on the carbon nanotube container 72, and then the plasma generator 50 is operated. In the case of low pressure plasma, a vacuum pump is operated to vacuum the inside of the plasma chamber 90. The gas introduced through the inlet 80 is generated by the plasma apparatus 50, and the plasma is applied to the used gas. Accordingly, the surface of the carbon nanotubes is modified by chemically active species (ions, electrons, radicals) and ultraviolet rays generated during plasma generation.

1 is a process flow diagram illustrating a carbon nanotube reforming process using plasma according to an embodiment of the present invention.

2 is a cross-sectional view of a carbon nanotube reformer showing a preferred embodiment of the carbon nanotube reforming method using a plasma according to an embodiment of the present invention.

<Description of Signs of Major Parts of Drawings>

50: plasma generating device 60: plasma

70: carbon nanotube 72: carbon nanotube container

90: plasma chamber

Claims (15)

In the modification method of carbon nanotubes, Synthesizing the carbon nanotubes; Purifying the synthesized carbon nanotubes; And And a plasma treatment step of irradiating plasma to the purified carbon nanotubes to be treated. The method of claim 1, And a wet treatment step of treating the treated carbon nanotubes in an acidic aqueous solution before or after the plasma treatment step. The method of claim 1, The plasma treatment step, Loading the carbon nanotubes in a container to expose the carbon nanotubes to the plasma; A plasma gas injection step of selecting and injecting the plasma gas; A plasma ON step of generating the plasma; A processing time control step of controlling the plasma exposure time; A plasma off step of blocking the plasma generation; And Collecting the plasma treated carbon nanotubes; and modifying the carbon nanotubes. The method of claim 1, After the plasma treatment step, After dispersing the treated carbon nanotubes in a solvent, the carbon nanotube reforming method characterized in that to adjust the pH of the dispersion in the range of 7 to 14. The method of claim 4, wherein The carbon nanotube reforming method, characterized in that the solvent consists of distilled water, chloroform, isopropanol, dimethylformamide, methylpyrrolidinone, decane, tetrahydrofuran, dichloroethane or a mixture thereof. The method of claim 5, wherein Wherein said solvent comprises a selected dispersant comprising a surfactant, a water-soluble polymer, or a mixture thereof. The method of claim 1, The plasma treatment step, Carbon nanotube reforming method characterized in that carried out at a temperature of -10 ^o C to 800 ^o C. The method of claim 1, In the plasma processing step, The plasma is carbon nanotube reforming method, characterized in that generated at a pressure of 10 ^-6 Torr to 5 atm. The method of claim 1, In the plasma processing step, The plasma is an inert gas such as argon and helium, hydrogen (H ₂ ), nitrogen (N ₂ ), oxygen (O ₂ ), fluorinated gas containing fluorine such as CF ₄ , NF ₃ , SF _6, and methane (CH ₄ ), Hydrocarbon gases such as ethylene (C ₂ H ₄ ), acetylene (C ₂ H ₂ ), nitrogen dioxide (NO ₂ ), nitrogen monoxide (NO), carbon dioxide (CO ₂ ), carbon monoxide (CO), ammonia (NH ₃ ) Gas or a mixture of the gases listed above, hydrogen peroxide (H ₂ O ₂ ), methanol (CH ₃ OH), ethanol (C ₂ H ₅ OH), acetone (CH ₃ COCH ₃ ) Carbon nanotube reforming method characterized in that any one selected from a hydrocarbon liquid having 6 to 20 carbon atoms. The method of claim 1, The carbon nanotubes to be treated are carbon black, carbon fibers or fullerenes. The method of claim 1, In the plasma processing step, The plasma may be a radio frequency plasma, a high frequency plasma, a dielectric barrier discharge plasma, an AC or DC glow discharge plasma, a middle frequency plasma, an arc plasma, a corona discharge plasma, or a mixture thereof. Carbon nanotube reforming method, characterized in that made. In the apparatus for modifying carbon nanotubes, A plasma chamber in which a gas inlet and a gas outlet are formed; A carbon nanotube container installed inside the chamber and containing carbon nanotubes to be modified; And And a plasma generator installed inside the chamber and irradiating plasma to the vessel. The method of claim 12, One side of the plasma chamber is a carbon nanotube reformer, characterized in that a vacuum device including a vacuum pump is provided. The method of claim 12, The carbon nanotube reformer is characterized in that the carbon nanotube reformer is provided with a vibration applying device or an ultrasonic application device that can be stirred so that the carbon nanotube is uniformly modified by the plasma. The method of claim 12, The carbon nanotube container is a carbon nanotube reformer, characterized in that the stage is provided with a stage for adjusting the separation distance between the plasma and the carbon nanotube.

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