WO2011083896A1

WO2011083896A1 - Method for the fabricating graphene nanosheets, and graphene nanosheets fabricated using the method

Info

Publication number: WO2011083896A1
Application number: PCT/KR2010/002552
Authority: WO
Inventors: 오일권; 스리다바다하남비; 전진한
Original assignee: 전남대학교산학협력단
Priority date: 2010-01-08
Filing date: 2010-04-23
Publication date: 2011-07-14
Also published as: KR100996883B1

Abstract

The present invention relates to a method for the green synthesis of graphene from graphite or graphite oxide, and more particularly, to a method for the green synthesis of graphene nanoshheets, which is environmentally friendly and appropriate for large-scale synthesis, as well as to graphene nanosheets fabricated using the method.

Description

【Specification】

[Name of invention]

Graphene sheet manufacturing method and graphene sheet prepared by the above method

The present invention relates to a graphene manufacturing method, and more particularly, to a graphene sheet manufacturing method suitable for large-scale synthesis and environmentally friendly, and a graphene sheet prepared by the above method.

<2>

Background Art

Graphene is a monolayer in which carbon atoms are densely compacted in the benzene ring structure, making blocks of various structures such as carbon black, carbon fiber, nanoleuubles, and fullerenes.

Graphene is an interesting 2D flat material composed of single-layered carbon atoms. The freely fixed individual graphene sheets have unique properties and are promising for the production of nanoscale engineering and nanoscale equipment.

In other words, graphene's unique properties make it a very promising application in field-effect transistors, lithium-ion batteries, hydrogen storage, molecular sensors, and actuators by strengthening layering agents in high-performance polymer nanocomposites.

Since the first report of producing graphene by mechanical peeling (pilling method), many techniques have been classified and developed under the top down method and the bottom up method.

In bar-up techniques such as thermal chemical vapor deposition (CVD), graphene is characterized by progressive growth in size of precursor particles from atomic or molecular species, ie graphene on a substrate. It is synthesized by growing epitaxial growth of or graphene platelets by CVD. In theory, the barb-up technique has the ability to control size, shape, size distribution, and agglomeration, but in practice this is very difficult to realize. There is also an environmental concern for the release of PAH (polyaromatic hydrocarbon) (see California Environmental Protection Agency (EPA) Order), although CVD can produce high quality graphenes. More common top-down techniques include stripping of individual graphene sheets from graphite structures such as expanded graphite and carbon nanotubes. Many techniques, including physical methods by hand stripping of individual graphene layers using Scotch tape, electrochemical methods using dissociative liquids as solvents, and thermal and chemical exfoliation of expanded graphite oxide, have been employed. Has been developed to obtain.

In the top-down process, graphitic microstructures such as graphite, carbon fiber, and carbon nanotubes are the starting materials, and individual graphene layers are cut out by physical, electrochemical or chemical routes. Peeling off

<ιο> In particular, peeling individual graphene sheets from graphene oxide is the most common method, and many techniques have been reported to obtain successfully graphene graphene, but this method for producing graphene plates from graphite has been reported. Is carried out using an oxidizing agent such as sulfuric acid / potassium permanganate (KMn04) followed by reduction with either hydrazine or alkali: or solvent etching.

<ιι> As a result, most of the chemical methods known to date are sulfuric acid / potassium permanganate

(KMn04) or the use of strong oxidizing agents such as carboxylic acids, formic acid, and excessive use of organic solvents harmful to the environment for further exfoliation.

In addition, although there have been some environmentally friendly studies on the reduction of graphene oxide by either chemical or electrochemical methods, an integrated environmentally friendly approach for all processes of graphene synthesis to date. This is not yet developed.

<13>

[Detailed Description of the Invention]

[Technical problem]

As a result of research efforts to solve the above problems, the present inventors have developed an eco-friendly graphene sheet manufacturing method suitable for large-scale synthesis and completed the present invention. ᅳ

Therefore, it is an object of the present invention to provide all processes of graphene synthesis without the use of sulfuric acid / potassium permanganate (KMn04) or strong oxidizing agents such as carboxylic acid, formic acid and excessive use of environmentally harmful organic solvents for further exfoliation. It is to provide an integrated environmentally friendly graphene sheet manufacturing method and the graphene sheet made by the method. Another object of the present invention is to provide a graphene sheet manufacturing method suitable for large scale synthesis and a graphene sheet prepared by the method through low cost and short manufacturing time.

Another object of the present invention is to minimize the problems associated with excessive oxidation to obtain a high quality graphene sheet as well as a graphene sheet manufacturing method having a higher yield and the graphene sheet prepared by the method To provide.

The objects of the present invention are not limited to the above-mentioned objects, and other objects not mentioned will be clearly understood by those skilled in the art from the following description.

<19>

Technical Solution

In order to achieve the above object, the present invention provides a graphene layer having a perfect lamination structure (9

oxidizing the graphite structure having an array of stackings; A microwave irradiation step of performing microwave irradiation on the oxidized nibble structure; It provides a graphene sheet manufacturing method comprising a; and an ultrasonic treatment step of sonicating the graphene layer conjugate consisting of several layers obtained after the irradiation step. ᅳ

In a preferred embodiment, the oxidation step is sonicated by immersing the intumescent structure in hydrogen peroxide.

In a preferred embodiment, the oxidation step is sonicated for 2 to 6 minutes by further adding ammonium peroxy disulfate to the hydrogen peroxide and immersing the flammable structure.

In a preferred embodiment, the ammonium peroxy disulfate is added at 0.05 to 2 weight ¾ with respect to hydrogen peroxide.

In a preferred embodiment, the microwave irradiation step is performed at 150 to 550 W for 50 to 100 seconds after placing the oxidized structure in the microwave oven.

In a preferred embodiment, the sonication step is sonicated for 15 to 25 minutes by dispersing the graphene layer binder in an alcohol solvent.

In a preferred embodiment, the method further includes a removing step of removing residual oxide groups from the graphene sheet obtained after the sonication step.

In a preferred embodiment, the removing step is hydrazine of the graphene sheet It is carried out by dispersing in solution.

In a preferred embodiment, the flammable structure is a flaky or carbon nanotube.

In a preferred embodiment, the graphene layer binder is obtained by dry sonication after the irradiation step.

In a preferred embodiment, the graphene layer binder has a curved or curled structure.

In a preferred embodiment, the graphene layer binder has an oxygen content of 1.41%. In addition, the present invention provides a graphene sheet, characterized in that produced by the graphene manufacturing method of any one of claims 1 to 12.

In a preferred embodiment, the graphene sheet has an undulation that increases the visible thickness.

Advantageous Effects

The present invention has the following excellent effects.

First, according to the graphene sheet manufacturing method of the present invention and the graphene sheet prepared by the method, it is harmful to the environment for the use of sulfuric acid / potassium permanganate (KMn04) or strong oxidizing agents such as carboxylic acid and formic acid and for further exfoliation. There is no need for excessive use of organic solvents, which is integrated and environmentally friendly for all processes of graphene sheet synthesis.

According to the graphene sheet manufacturing method of the present invention and the graphene sheet produced by the method is suitable for the synthesis of large-scale graphene sheet through low cost and short manufacturing time. According to the graphene sheet manufacturing method of the present invention and the graphene sheet produced by the method can minimize the problems associated with excessive oxidation to obtain a high quality graphene sheet as well as have a higher yield.

[Brief Description of Drawings]

1 is a representative view showing a pure graphene manufacturing process proposed in an embodiment of the present invention,

Figure 2 is a SEM observation of the graphene worms obtained by microwave irradiation in one embodiment of the present invention,

Figures 3 and 4 are obtained by microwave irradiation in one embodiment of the present invention Each spectra results graph analyzed by XPS spectrometer and Raman spectrometer of laffin worms,

5 is a photograph of the results obtained by observing the graphene layer binder obtained in an embodiment of the present invention by SEM and TEM,

6 is a photograph of the results obtained by observing the graphene sheet obtained in an embodiment of the present invention by SEM and TEM,

FIG. 7 illustrates a nanopropyllomitry image obtained by observing a graphene sheet obtained in one embodiment of the present invention with an atomic force microscope (AFM).

8 is a graphene sheet obtained in an embodiment of the present invention by analyzing the Raman spectrometer and the analyzed spectra graph.

[Best Mode for Implementation of the Invention]

The terminology used in the present invention is a general term that has been widely used as far as possible, but in some cases, the term is arbitrarily selected by the applicant. In this case, the terminology used herein is not simply a name of the term. The meaning should be grasped in consideration of the meaning used or used.

Hereinafter, with reference to the accompanying drawings and preferred embodiments will be described in detail the technical configuration of the present invention.

However, the present invention is not limited to the embodiments described herein and may be embodied in other forms. Like numbers refer to like elements throughout the specification.

First, the present invention provides an oxidation step of oxidizing a flaw structure having a graphene layer having a perfect stack structure stacking); A microwave irradiation step of obtaining a graphene layer binder composed of several layers by performing microwave irradiation on the oxidized graphite structure; And an ultrasonic wave treatment step of ultrasonically treating the graphene layer binder. The graphene sheet manufacturing method includes a graphene layer binder having several layers, particularly through microwave irradiation. . The microwave irradiation step is performed using 150 to 550W for 50 to 100 seconds using microwave oven, preferably 450 to 550W for 85 to 95 seconds.

This very simple and convenient microwave irradiation step eliminates the need for the use of strong oxidants such as sulfuric acid / potassium permanganate (KMn04) or carboxylic acids or formic acid in the oxidation step, and the environment for further exfoliation. Of harmful organic solvents Excessive use can be excluded.

In addition, low cost and short manufacturing time make it possible to synthesize high quality graphene sheets on a large scale.

In the present invention, the inductible structure refers to all materials whose members are composed only of carbon, and include graphite (array), carbon black, carbon fiber, carbon nanotube, and the like. The lamination structure of the graphene layer constituting the lamination structure can provide the optimum manufacturing conditions for producing the graphene sheet from an abrupt structure having a perfect array of stacking Aβ stack structure.

<54>

<55> Example

<56> Graphene Sheet Preparation from Graphite

Graphene sheets were obtained from graphite in which graphene layers were arranged in perfect ^ laminate stacking).

<58>

1. Oxidation stage

Natural graphite (purity 99¾, average particle size 200ura), ammonium peroxy disulfate and hydrogen peroxide were prepared to prepare natural graphite, hydrogen peroxide (concentration 35%) and ammonium peroxy disulfate prepared in a glass tube. The graphite was immersed in the solvent in a weight ratio of 1: 0.1.

The glass tube was sonicated for 3 minutes in an ultrasonic apparatus of known configuration.

<62>

2. Microwave irradiation step

And then 90 seconds after placing the glass tube in a microwave oven.

Irradiated at 500W. At this time, rapid peeling was observed under microwave irradiation, accompanied by lightening.

<65>, <66> 3. Ultrasonic Treatment Step

Graphene worms were dry sonicated for 30, 60, and 60 minutes to obtain several layers of graphene layer binders from graphene worms formed by microwave irradiation. Best results obtained after 90 minutes of dry sonication All. In some cases, the graphene layer binder may be obtained only by microwave irradiation. Thereafter, the obtained graphene layer binder was dispersed in ethyl alcohol and sonicated for 20 minutes to obtain individually separated graphene sheets.

Here, another alcohol solvent may be used instead of ethyl alcohol, and the sonication time is preferably in the range of 15 to 25 minutes.

The overall process is as shown in FIG.

Meanwhile, a step of removing the remaining oxide groups from the graphene sheet obtained after the sonication step may be further performed, for example, dispersing the obtained graphene sheet in a hydrazine solution.

<71>

<72> Experimental Example 1

The graphene worms obtained by the microwave irradiation in the embodiment was observed by SEM and the shape photographs are shown in FIG. 2, and the spectra result graphs analyzed through the XPS spectrometer and the Raman spectrometer were shown in FIGS. 3 and 4, respectively. Shown in

Herein, the principle of forming graphene worms, which is a preliminary step for obtaining the graphene layer binder, shows that ammonium peroxydisulfate is decomposed into radical releasing radical radicals that cause the cutting of graphite sheets due to microwave irradiation. The radicals attack the defects on the graphite surface, and then as reaction reactions, the radicals of the oxide are generated from the decomposition of hydrogen peroxide and are inserted between the interlayer graphite layers to cause rapid expansion, leading to graphene walls. It is formed.

FIG. 2, which shows SEM photographs of the graphene worms, shows a uniform distance between balloons of the graphene worms, suggesting that there was a uniform expansion along the c-axis of graphite. At this time, the peeling rate (exfoliation coefficient: ratio of the volume V _GIC of the graphite-inserted compound to the volume V _EG of graphite) was found to be 150. Characteristics of graphene worms such as pore structure, porosity, sphericity of pores, and fractal dimensions were analyzed by Image J, image analysis software.

3 shows that most of the oxygen moieties of the XPS spectra are lost during microwave treatment, indicating that the oxygen content in the worms is as low as 1.41%. Can be.

Raman spectra in FIG. 4 is an intensity that indicates the well stacked characteristics of graphene nanosheets in the graphene worms and the protruding D and G bands of nearly equal full width half maximum (FWHM). Shows.

<78>

<79> Experimental Example 2

The graphene layered binder composed of few layers of fluffy graphene nanosheets obtained by dry sonication of the graphene worms in the Example was observed by SEM and TEM (FIG. 5 d). 5 is shown, in particular the SEM micrographs (a, b, c in FIG. 5) show the presence of curled up or onion-like structures. It is well known that sharp edges and facets are less stable than structures with smooth bends and curls or that the formation of a sphere is caused by the need to minimize surface area. Therefore, it can be seen that the bending of the graphene sheet under microwave irradiation is a surface stress-induced pressure phenomenon that leads to the formation of an ellipsoidal structure composed of weakly attached graphene sheets.

On the other hand, sonicating graphene worms and / or graphene layer composites causes acoustic cavitation near the surface, thereby tearing and shearing platelets. This creates a partial erosion that leads to. Inertial cavitation, also caused by the violent collapse of the bubble, causes the plates to tear away, and the released graphene nanosheets can further activate adjacent plates. Micro streaming can also occur close to the surface of the bubbles that withstand stable cavitation and cause the adjacent plates to be shaved or torn apart. Another explanation by Chen et al., Who proposed ultrasonic irradiation due to the fragile nature of exfoliated graphite particles, suggests that most of the particles cause shortened accordion-like particles, the shorter particles being much smaller and sub-particles. This is because the separation of the graphite plates constituting the above components is dominant and also the increase in irradiation time will result in the breaking of the graphite nanosheets on the leaf.

However, the present invention is directed to all of the processes described above due to various parameters such as balloon size of the graphene worms, viscosity of the medium, particle size distribution, etc., which affect the degree of dissipation and formation of these acoustic cavities. Can happen simultaneously It is derived from the prediction of the possibility, and by realizing such a possibility, the mass production of graphene sheets is possible quickly and eco-friendly.

<83>

<84> Experimental Example 3

The graphene sheets obtained in the examples were observed by SEM and TEM, and the photographs are shown in FIG. 6.

The SEM photograph (a) of FIG. 6 shows the scrolling of the sheets while the scrolling phenomenon is not observed in the TEM photograph (b). The substrate in which the graphene sheets are gathered seems to affect the morphology.

<87>

<88> Experimental Example 4

The graphene sheet obtained in Example was subjected to an atomic force microscope:

Aminopropyl) was shown in Figure 7 by observation with AFM).

AFM images such as those shown in FIG. 7 have traditionally been used to measure the dimensions of isolated sheets of flanks. However, image distortion in atomic force microscopy (AFM) of thin films may be due to the limited size of the AFM tip. The degree of distortion in the image depends on the relative sharpness of the tip and the surface properties. Although graphene is flat, it is very wavy due to its thin size and is bistable by bringing distortion to the measured thickness. So a non-invasive technique using monochromatic optical light used to test the thickness of the graphene layers was used here.

The graphene sheet also has a lateral dimension of several micrometers and a thickness of 2 nm comparable to the thickness measured by AFM, and has the properties of a fully peeled graphene oxide sheet. The undulation of the dried graphene surface on the substrate increases its visible thickness as measured by AFM. It was also found that the bends were not minimized, although perforated substrate M0 was used in the present invention.

<92>

<93> Experimental Example 5

The graphene sheet obtained in the Example was analyzed by Raman spectrometer and the analyzed spectra result graph is shown in FIG. 8.

Raman spectra are essential for characterizing carbon-containing materials. This is because its shape makes it possible to distinguish between monolayer and multilayer samples. In addition to the almost total absence of the D band (although nodules were observed in the D bend region) as shown in Fig. 8, the G bands appeared sharp, suggesting that four peaks suggesting that high purity graphene can be obtained (Fig. 8). A single G-peak was shown that could not be entangled.

<96>

The experimental examples show that a high-quality graphene (nano) sheet can be obtained through a manufacturing method such as the embodiment of the present invention, which can be quickly and environmentally friendly, simple, and mass production from graphite.

<98>

In addition, in the above experimental example, Raman spectra was obtained using an Invia reflex micro Raman spectrometer (Reniso), which was operated in O.lmW and had a crystal laser excitation of 514.5 nm. SEM results photographs were recorded using a Dune Field Emission Scanning Electron Microscope (S-4700, Hitachi, Japan). TEM was performed on a JEOL JEM 2010 microscope operated at 200 kV using a carbon coated copper grid with holes. TEM and SEM experiments were both placed on a drop of very diluted relative substrates after precipitation and dried at atmospheric conditions. Nanoprofilometry was performed using a nanoview NV 200 with three interfero metric objective lenses, manufactured by Nanosister Metz (Korea), and a vertical resolution of 0.5 nm. It became.

<100>

As described above, the present invention has been illustrated and described with reference to preferred embodiments, but is not limited to the above-described embodiments, and the general knowledge in the art to which the present invention pertains does not depart from the spirit of the present invention. Various changes and modifications will be possible by those who have the responsibility.

Claims

[Range of request]

[Claim 1]

An oxidation step in which the graphene layer oxidizes an abrupt structure having a perfect stacking arrangement;

A microwave irradiation step of performing microwave irradiation on the oxidized graphite structure; And

A method for producing a graphene sheet comprising a; ultrasonic treatment step of sonicating the graphene layer binder consisting of several layers obtained after the irradiation step.

[Claim 2]

The method according to claim 1,

The oxidation step is a graphene sheet manufacturing method characterized in that the ultrasonic treatment by immersing the graphite structure in hydrogen peroxide.

[Claim 3]

According to claim 12,

The oxidation step is a graphene sheet manufacturing method characterized in that the addition of ammonium peroxy disulfate to the hydrogen peroxide further and sonicated for 2 to 6 minutes by immersing the flammable structure.

[Claim 4]

The method of claim 3,

The ammonium peroxy disulfate is graphene sheet production method characterized in that the addition of 0.05 to 2 weight ¾ to hydrogen peroxide.

[Claim 5]

The method of claim 1,

The microwave irradiation step is a graphene sheet manufacturing method characterized in that carried out at 150 to 550W for 50 to 100 seconds after placing the oxidized structure in the microwave oven ᅳ

[Claim 6]

The method of claim 1,

The sonication step is a graphene sheet manufacturing method characterized in that the graphene layer binder is dispersed in an alcohol solvent sonicated for 15 to 25 minutes.

[Claim 7]

The method of claim 1,

And a removing step of removing the residual oxide group from the graphene sheet obtained after the sonication step.

[Claim 8]

The method of claim 7,

The removing step is a graphene sheet manufacturing method characterized in that is carried out by dispersing the graphene sheet in a hydrazine solution.

[Claim 9]

The method of claim 1,

The graphitic structure is a graphene sheet manufacturing method, characterized in that by abyss or carbon nanotubes.

[Claim 10]

The method of claim 1,

The graphene layer binder is a graphene sheet manufacturing method characterized in that it is obtained by dry ultrasonic charging after the irradiation step.

[Claim 11]

In U, at least

The graphene layer binder is a graphene sheet manufacturing method characterized in that it has a curved or curled structure. '

[Claim 12] The method of claim 1,

The graphene layer binder is a graphene sheet manufacturing method, characterized in that the oxygen content is 1.41%.

[Claim 13]

A graphene sheet characterized by being produced by the graphene manufacturing method of any one of claims 1 to 12.

[Claim 14]

The method of claim 13,

The graphene sheet is a graphene sheet characterized in that it has an undulation to increase the visible thickness (undulation).