KR20130079144A

KR20130079144A - Graphene carbon-nanotube composite and spray pyrolysis process for preparing same

Info

Publication number: KR20130079144A
Application number: KR1020120130391A
Authority: KR
Inventors: 송이화
Original assignee: 제일모직주식회사
Priority date: 2011-12-31
Filing date: 2012-11-16
Publication date: 2013-07-10

Abstract

In the graphene-carbon nanotube composite according to the present invention, graphene and a metal catalyst are added to a solvent to prepare a catalyst precursor solution, spray the catalyst precursor solution into a reactor using a droplet generator, and Sprayed droplets are prepared by the step of synthesizing the graphene-carbon nanotube composites through pyrolysis while passing through a reaction furnace. The graphene-carbon nanotube composite of the present invention has a weight ratio of graphene and carbon nanotubes in a range of 2: 1 to 1: 5. In the graphene-carbon nanotube composite according to the present invention, graphene and carbon nanotubes form a three-dimensional network, and the specific surface area is in the range of 300 to 2000 m 2 / g, and has excellent electrical conductivity.

Description

Graphene-carbon nanotube composite using spray pyrolysis process and graphene-carbon nanotube composite manufactured by the same method {Graphene Carbon-nanotube Composite and Spray Pyrolysis Process for Preparing Same}

The present invention relates to a graphene-carbon nanotube composite. More specifically, it relates to a new method for producing a graphene-carbon nanotube composite of the present invention and a graphene-carbon nanotube composite prepared by the method.

Recently, carbon nanotubes, fullerenes, and graphenes are being actively used as allotropees of carbon in new materials. A carbon allotrope refers to a substance composed of carbon but different in physical or chemical properties because of its different structure. Among the carbon allotrope, graphite is a carbon layer is bonded by van der Waals attractive force to form a three-dimensional structure by stacking layers, carbon nanotube (CNT) is a structure in which the carbon layer is dried one-dimensionally, fullerene (hole) Graphene is a two-dimensional honeycomb structure that has a thickness of one layer of atoms. Graphene is a conductor having a theoretical surface area of about 2000 m 2 / g or more, electron mobility of about 200,000 cm ² / Vs, and electron mobility of about 100 times that of silicon. In addition, the electrical resistance value of graphene is very small, about 2/3 of the electrical resistance value of copper, the breaking strength is 42 N / m, and the Young's modulus value is similar to diamond, and the mechanical strength is excellent. Due to such excellent characteristics of graphene, attempts to actively apply graphene to electrodes and composites have been actively made.

Graphene synthesis methods known to date include chemical vapor deposition (CVD) and chemical methods. When graphene is synthesized by chemical vapor deposition, high quality graphene may be synthesized, and the graphene may be used in a transparent electrode or a flexible display.

On the other hand, the graphene prepared by the chemical method is prepared from natural graphite, oxidize the natural graphite to graphene oxide (graphene oxide) using acid, and then ultrasonically dispersed in water, separated by one layer, and then reducing agent or Prepared by reducing with heat. However, graphene produced by this method essentially has many defects. In addition, the chemical method including the wet process has a relatively low specific surface area by the lamination of the graphene during the drying process, there is a problem that the graphene fragments are finely divided in the ultrasonic dispersion step.

In order to solve this problem of the chemical method, a research has been conducted to prepare a graphene-carbon nanotube composite by inserting metal particles between graphene or dispersing carbon nanotubes together. When synthesizing the graphene-carbon nanotube composite, when the expensive carbon nanotubes are dispersed together with the graphene to produce the graphene-carbon nanotube composite, the manufacturing cost is high and it is not economical. -There is a problem that can not synthesize the carbon nanotube composite material.

Therefore, the present inventors have developed a graphene-carbon nanotube composite having a high specific surface area and excellent electrical conductivity by forming a three-dimensional network of graphene and carbon nanotubes by using a spray pyrolysis process.

An object of the present invention is to provide a graphene-carbon nanotube composite having a wide specific surface area and excellent electrical conductivity by forming a three-dimensional network of graphene and carbon nanotubes.

Another object of the present invention is to provide a new method for producing a graphene-carbon nanotube composite having a wide specific surface area and excellent electrical conductivity by forming a three-dimensional network of graphene and carbon nanotubes.

Still another object of the present invention is to provide a method for preparing a new graphene-carbon nanotube composite having excellent process efficiency and economy.

Still another object of the present invention is to provide a new method of preparing a graphene-carbon nanotube composite.

The above and other objects of the present invention can be achieved by the present invention described below.

Graphene-carbon nanotube composite production method according to the present invention comprises the steps of preparing a catalyst precursor solution containing a graphene, a solvent, and a metal catalyst, spraying the catalyst precursor solution, and sprayed droplets in the reactor ( It is characterized by consisting of a step of synthesizing the graphene-carbon nanotube composite via a reaction furnace.

The solvent is an organic solvent having 5 or less carbon atoms in the main chain, preferably ethanol, methanol, or propanol. As the metal catalyst, peroxine, iron chloride, cobalt nitrite or a mixture thereof may be preferably used, and the amount of the metal catalyst is preferably used in the range of 0.01 to 0.5 mol / l relative to the solvent. In the step of preparing the catalyst precursor solution, graphene is preferably included in an amount of 0.5 to 2 mg / ml relative to the solvent.

Spraying the catalyst precursor solution sprays the catalyst precursor solution into the reactor using a droplet generator, and uses an ultrasonic nozzle for the droplet generator. It is preferable that the droplets of the catalyst precursor solution sprayed using the ultrasonic nozzle have a size of 5 to 50 µm.

The carrier gas is supplied to the reactor through which the graphene-carbon nanotube composite is synthesized via the liquid crystal generator. The carrier gas is preferably an inert gas such as argon or nitrogen, methane or propane. As for the temperature of a reactor, 600-1500 degreeC is preferable.

As described above, the graphene-carbon nanotube composite of the present invention sprays the catalyst precursor solution into the reactor using a droplet generator, and pyrolysis the sprayed droplets through the reactor. Since it is manufactured by the spray pyrolysis process (Spray Pyrolysis Process) can be said.

In the graphene-carbon nanotube composite according to the present invention, graphene and carbon nanotubes form a three-dimensional network. The graphene-carbon nanotube composite has a specific surface area in the range of 300 to 2000 m 2 / g, a weight ratio of graphene and carbon nanotubes in the range of 2: 1 to 1: 5, and excellent electrical conductivity. Such graphene-carbon nanotube composite can produce a supercapacitor.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Reference will now be made in detail to the preferred embodiments of the present invention, examples of which are illustrated in the accompanying drawings.

The present invention provides a graphene-carbon nanotube composite having a high specific surface area and excellent electrical conductivity by forming a three-dimensional network of graphene and carbon nanotubes, and provides a new process with excellent process efficiency and economical efficiency and an eco-friendly method. It has the effect of the invention.

Figure 1 is a schematic diagram showing a manufacturing process of the graphene-carbon nanotube composite by the spray pyrolysis process of the present invention.
Figure 2 (a) is a SEM picture of the graphene-carbon nanotube composite prepared in Example 1, Figure 2 (b) is a graph showing the results of EDS analysis.

The present invention relates to a graphene-carbon nanotube composite, a novel method for producing a graphene-carbon nanotube composite, and a graphene-carbon nanotube composite prepared by the method.

Hereinafter, the graphene-carbon nanotube composite of the present invention and the graphene-carbon nanotube composite of the present invention will be described in detail.

Grapina -Production method of carbon nanotube composite

Method for producing a graphene-carbon nanotube composite according to the present invention comprises the steps of preparing a catalyst precursor solution containing a graphene, a solvent, and a metal catalyst, spraying the catalyst precursor solution, sprayed droplets reaction (reaction through a furnace) and the graphene-carbon nanotube composite is synthesized.

In one embodiment of the present invention, the method for producing a graphene-carbon nanotube composite is prepared by adding a graphene and a metal catalyst to a solvent to prepare a catalyst precursor solution, using a droplet generator to convert the catalyst precursor solution into a reactor Spraying, and sprayed droplets are synthesized through pyrolysis via a reaction furnace to synthesize graphene-carbon nanotube composites.

The present invention may further comprise the step of synthesizing the graphene before preparing the catalyst precursor solution.

(1) Graphene Synthesis Step

Graphite used in the synthesis of graphene may be used as natural graphite without limitation, preferably expanded natural graphite (expanded graphite or exfoliated graphite) can be used.

As a method for synthesizing graphene with graphite, there is a chemical method represented by chemical vapor deposition (CVD) or Hummer's Method, an acid expansion method, or an ultrasonic separation method. When graphene is synthesized by a chemical method such as a hummer method, since graphene oxide is generated as an intermediate product and a defect occurs, it is preferable to synthesize the graphene by an acid expansion method or an ultrasonic separation method.

As the acid used in the acid expansion method, it is preferable to use an acid generally used, such as sulfuric acid or nitric acid, as a mixed solution. The temperature at the time of acid treatment is 50-200 degreeC, Preferably it is 50-100 degreeC, More preferably, it is good to process below the breaking point of the acidic solution to be used. The acid treatment time may vary from 1 to 24 hours depending on the acid treatment temperature, and preferably, treatment is performed within 1 to 5 hours. After the acid treatment, the acid-treated graphite solution is filtered to remove the solution, and further washed with water or diluted hydrochloric acid solution before filtration to increase the filtration efficiency. At this time, if the diluted hydrochloric acid solution is used instead of water, there is an advantage that the exothermic phenomenon occurs when using water.

By heat treatment of the acid-treated graphite without a separate drying process, graphene is synthesized as ions trapped in the graphite are released as a gas. The heat treatment temperature can be made at 200 to 2000 ℃, for effective gas release is preferably made at 500 to 1200 ℃, more preferably at 700 to 1200 ℃. Inert gas such as nitrogen, argon, helium may be used as the gas used for the heat treatment, and a mixture of hydrogen gas may be used to remove defects of graphene that may be generated due to high temperature acid treatment.

(2) Preparation step of catalyst precursor solution

The catalyst precursor solution for synthesizing the graphene-carbon nanotube composite of the present invention is prepared by dissolving a graphene and a metal catalyst in a solvent. After graphene is uniformly dispersed in a solvent, a metal catalyst is further dissolved to prepare a catalyst precursor solution.

The solvent can be used without limitation as long as it is a carbon-containing organic solvent that can be a carbon source. However, in the ultrasonic spraying method, it is preferable to use an organic solvent having 5 or less carbon atoms in the main chain, such as ethanol, methanol, propanol and the like.

Graphene is preferably mixed in a concentration that can be uniformly dispersed in a solvent, it may be included in 0.1 to 5 mg / ml, preferably 0.5 to 2 mg / ml compared to the solvent.

As the metal catalyst, metal ions such as iron (Fe), cobalt (Co), and nickel (Ni), which can grow and synthesize carbon nanotubes, can be used. Preferably, a metal catalyst which can be dissolved and ionized in an organic solvent such as ethanol may be used, and more preferably, Ferrocene, iron chloride, and cobalt nitrate may be used alone or in combination thereof. It can be used as a mixture of.

The metal catalyst is preferably included in an amount of 0.01 to 0.5 mol / l relative to the solvent. In the case of containing a metal catalyst of less than 0.01 mol / l, the amount of carbon nanotubes synthesized between the graphene is small, the aggregation between the graphene may occur, and if the metal catalyst containing more than 0.5 mol / l metal catalyst particles The reactivity of these compounds increases the synthesis yield of carbon nanotubes.

(3) spraying catalyst precursor solution

The prepared catalyst precursor solution is sprayed into the reactor 3 using the droplet generator 2. Figure 1 is a schematic diagram showing a manufacturing process of the graphene-carbon nanotube composite by the spray pyrolysis process of the present invention.

As shown in Figure 1, the graphene-carbon nanotube composite manufacturing apparatus of the present invention is a droplet generator (2) for spraying the catalyst precursor solution, the sprayed droplet is synthesized into the graphene-carbon nanotube composite It consists of a high temperature reactor 3 and a collector 4 for collecting the synthesized graphene-carbon nanotube composite.

An ultrasonic nozzle is used for the droplet generator 2. It is preferable that the droplets of the catalyst precursor solution sprayed using the ultrasonic nozzle have a size of 5 to 50 µm. The carrier gas is supplied to the reactor 3 through which the graphene-carbon nanotube composite is synthesized via the liquid crystal generator 2. In order to measure the amount of carrier gas supplied, a gas flow meter 1 is installed before the liquid crystal generator 2. The carrier gas is preferably an inert gas such as argon or nitrogen, methane, or propane. As for the temperature of a reactor, 600-1500 degreeC is preferable.

As a spraying method for introducing the catalyst precursor solution into a high temperature synthesis reactor, various spraying methods such as an ultrasonic nozzle method and a general nozzle method may be used. Among them, an ultrasonic nozzle method capable of giving sufficient residence time for synthesizing carbon nanotubes is preferable.

When using the normal nozzle method, the droplet size of the catalyst precursor produced is 100 μm or more. When the size of the droplet is 100 μm or more, it is difficult to synthesize graphene-carbon nanotubes because the drying step, the reaction / synthesis step, and the firing step in the reactor are difficult to occur in a single step.

However, when using the ultrasonic nozzle method, since the droplet size is sprayed into the reactor is 5 to 50 ㎛, it can be synthesized in a single process. However, the size of the sprayed droplets can be changed depending on the concentration of the precursor and the intensity of the ultrasonic wave.

The sprayed droplets can be moved into the high temperature reactor 3 by the carrier gas, and the velocity, the reactor temperature and the length of the carrier gas determine the time for which the droplets remain in the reactor. When the residence time is short, the catalyst ion becomes a catalyst particle, and it is difficult to complex the graphene with the growth of carbon nanotubes from the catalyst particle. If the residence time is long, the reaction yield is low. Therefore, the supply speed of the carrier gas may be determined in consideration of the residence time of the droplets. Preferably, the carrier gas may be supplied at a feed rate of 0.2 to 3 LPM (l / min).

(4) Synthesis step of graphene-carbon nanotube composite

The droplets of the sprayed catalyst precursor solution pass through the high temperature reactor 3 through the carrier gas supplied to the reactor, and thermally decompose and grow the carbon nanotubes on the metal catalyst, thereby gradually increasing the graphene-carbon nanotubes. Is synthesized.

As a carrier gas, argon, nitrogen, or the like, which is an inert gas, may be used, and at the same time, methane, propane, or the like may be mixed and used together with argon, nitrogen, hydrogen, and the like to auxiliaryly supply a carbon source.

In the present invention, since an organic solvent capable of forming carbon nanotubes is used in the droplets, graphene-carbon nanotube composites can be synthesized using argon and nitrogen gas, which are inert gases, without supplying a separate carbon source. Therefore, the post-treatment process of the expensive carbon source gas discharged unreacted is not necessary, and there is no fear that a problem such as an explosion may occur because the carbon source gas does not pass the high temperature gas furnace. Therefore, it is more preferable to use inert gases argon and nitrogen as carrier gases.

The reactor is a long, high-temperature device that can secure a sufficient residence time while giving a high temperature. The temperature of the reaction furnace is 600-1500 degreeC, Preferably it is 700-1100 degreeC. The reactor has a length of 1 to 3 m, it is preferably designed to ensure a minimum residence time of at least 5 seconds.

Under the conditions of the temperature and residence time of the reactor, the metal catalyst contained in the catalyst precursor solution supplied to the reactor is thermally decomposed together with the carbon source of the solution or gaseous carbon sources such as methane and propane, whereby Nanotubes are synthesized.

In the case of the synthesized carbon nanotubes, the diameter and the length of the carbon nanotubes may be changed according to the reaction conditions such as the type of metal ions dissolved in the precursor and the reaction temperature. In one example, the synthesized carbon nanotube length is proportional to the time that the droplets stay in the reactor.

The synthesized graphene-carbon nanotube composite is collected in the collector 4, the synthesis of the graphene-carbon nanotube composite is completed. The graphene-carbon nanotube composite synthesized by the spray pyrolysis process of the present invention has excellent electrical conductivity by efficiently forming a three-dimensional network of graphene and linear carbon nanotubes. Carbon nanotubes grown from metal catalysts serve to prevent graphene from being stacked again by forming a three-dimensional structure as well as an electrical bridge connecting graphene and graphene in terms of conductivity.

Figure 2 (a) is a SEM picture of the graphene-carbon nanotube composite prepared in Example 1, Figure 2 (b) is a graph showing the results of EDS analysis. As shown in Figure 2, the graphene-carbon nanotube composite of the present invention is the catalyst particles are placed between the graphene layer in the ion state in the synthesis step of graphene, carbon nanotubes while solving the lamination problem of graphene As it grows, graphene is dispersed. In addition, graphene and carbon nanotubes form a dense network, and the network improves electrical conductivity.

When synthesizing the graphene-carbon nanotube composite using the spray pyrolysis apparatus of the present invention, it is possible to continuously synthesize the graphene-carbon nanotube composite, shorten the synthesis time, and the post-synthesis cleaning process and Since a post-treatment process such as a heat treatment process is not required, the graphene-carbon nanotube composite may be synthesized by an environmentally friendly method.

Grapina Carbon Nanotube Composite

The present invention may be better understood by the following examples, which are for the purpose of illustrating the invention and are not intended to limit the scope of protection defined by the appended claims.

Example

Example One

Graphene prepared by ultrasonic separation method was dispersed in ethanol at a concentration of 1 mg / ml, and then ferrocene (ferrocene) was dissolved in a concentration of 0.1 M / L to prepare a precursor solution. The precursor solution was sprayed onto the spray pyrolysis apparatus in the form of droplets using argon gas as a carrier gas by ultrasonic spraying. Precursor droplets were synthesized into a graphene-carbon nanotube composite while passing through a high temperature reactor at 900 ° C. having a length of 1 m. After collecting the synthesized complex collected in a filter, the specific surface area was measured according to the following physical property measurement method is shown in Table 1 below.

Comparative Example One

The same procedure as in Example 1 was conducted except that a precursor solution containing no catalyst was prepared.

Specific surface area How to measure

The specific surface area was measured using the Brunauer-Emmett-Teller (BET) method. After determining the adsorption-desorption amount of nitrogen using a Model NOVA 4200 instrument, it was measured using the BET method. Degassing was performed at 200 ° C. for 2 hours prior to measurement to remove impurities physically adsorbed to the measurement sample.

Specific Surface Area (BET) Example 1 350 Comparative Example 1 30

As shown in Table 1, it can be seen that the graphene-carbon nanotube composite prepared in Example 1 has a significantly larger specific surface area (BET) than Comparative Example 1. Figure 2 (a) is a SEM picture of the graphene-carbon nanotube composite prepared in Example 1, Figure 2 (b) is a graph showing the results of EDS analysis. The SEM photograph shows that the plate-like material and the linear carbon nanotubes form a dense network, and the results of the EDS analysis show that the plate-like material is composed of carbon (C) rather than iron (Fe). It can be seen that.

As described above, the graphene-carbon nanotube composite of the present invention can be seen that graphene and carbon nanotubes form a three-dimensional network to prevent re-lamination of graphene and have an excellent specific surface area. For this reason, the graphene-carbon nanotube composite of the present invention can be suitably used as an electrode material of various batteries such as secondary batteries and supercapacitors having excellent electrical conductivity.

It will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the spirit and scope of the invention as defined by the appended claims.

Claims

Preparing a catalyst precursor solution comprising graphene, a solvent, and a metal catalyst; Spraying the catalyst precursor solution; The sprayed droplets are passed through a reaction furnace (reaction furnace) and the graphene-carbon nanotube composite is synthesized; Method of producing a graphene-carbon nanotube composite using a spray pyrolysis process (Spray Pyrolysis Process) comprising a.

The method of claim 1, further comprising preparing graphene before the preparation of the catalyst precursor solution.

The method of claim 1, wherein the spraying of the catalyst precursor solution is sprayed using an ultrasonic nozzle in a droplet generator.

The method of claim 1, wherein the graphene is included in the catalyst precursor solution at 0.5 to 2 mg / ml relative to the solvent.

The graphene of claim 1, wherein the metal catalyst is selected from the group consisting of peroxine, iron chloride, cobalt nitrite, and mixtures thereof, and is included in the catalyst precursor solution at 0.01 to 0.5 mol / l relative to the solvent. -Carbon nanotube composite production method.

The method of claim 4, wherein the solvent is an organic solvent having 5 or less carbon atoms in the main chain.

The method of claim 6, wherein the organic solvent is ethanol, methanol, or propanol.

The method of claim 3, wherein the droplet of the catalyst precursor solution sprayed using the ultrasonic nozzle is 5 to 50 ㎛.

The method of claim 1, wherein the carrier gas supplied to the reactor is an inert gas, methane, or propane.

10. The method of claim 9, wherein the inert gas is argon or nitrogen.

The method of claim 1, wherein the temperature of the reactor is 600 to 1500 ℃.

Graphene-carbon nanotube composite prepared by the method of any one of claims 1 to 11.

Graphene-carbon nanotube composite, characterized in that the graphene and carbon nanotubes form a three-dimensional network.

The graphene-carbon nanotube composite according to claim 13, wherein the graphene-carbon nanotube composite has a specific surface area (BET) of 300 to 2000 m 2 / g.

The graphene-carbon nanotube composite according to claim 13, wherein the graphene and carbon nanotubes are included in a weight ratio of 2: 1 to 1: 5.

A supercapacitor made of the graphene-carbon nanotube composite according to any one of claims 13 to 15.