KR100996883B1 - Method of green synthesis of graphene nano-sheets and graphene nano-sheets - Google Patents

Abstract

PURPOSE: A manufacturing method of a graphene sheet processing the ultrasonic wave after irradiating microwave is provided to obtain the grapheme sheet at low cost and in a short manufacturing time without overusing the organic solvent for the use of the strong oxidized and the additional desquamation. CONSTITUTION: A manufacturing method of a graphene sheet comprises next steps. The graphitic structure having the arrangement in which the graphene layer oxidizes the AB laminating structure. The microwave in the graphitic structure is examined. The graphene layer combination is split by the ultrasonic wave. The graphitic structure is dipped in the hydrogen peroxide and processed with ultrasonic wave. The ammonium sulfate is added more in the hydrogen peroxide.

Description

Graphene sheet manufacturing method and the graphene sheet prepared by the method {Method of Green Synthesis of Graphene Nano-sheets and Graphene Nano-sheets}

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

Graphene is a monolayer of carbon atoms densely compacted in the benzene ring structure and forms blocks of various structures such as carbon black, carbon fiber, nanotubes and fullerene.

As such, graphene is an interesting 2D flat material composed of single-walled carbon atoms, with individual graphene sheets freed and immobilized with unique properties and promising for the production of nanoscale engineering and nanoscale equipment.

This is because graphene's unique properties make it very promising in field-effect transistors, lithium-ion batteries, hydrogen storage, molecular sensors and actuators by enhancing fillers 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 barb-up techniques such as thermal chemical vapor deposition (CVD), graphene allows the precursor particles to grow gradually in size from atomic or molecular species, i.e., the epigrowth of graphene on a substrate. It is synthesized by growth of graphene plateslets by epitaxial growth or CVD. In theory, the barb-up method has the ability to control size, shape, size distribution, agglomeration, etc., but in practice this is very difficult to realize. There are also environmental concerns about the release of PAH (polyaromatic hydrocarbon) (see California's 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 with Scotch tape, electrochemical methods using ionic liquids as solvents, and thermal and chemical exfoliation of expanded graphite oxide, have been achieved to obtain graphene monolayers. Has been developed for this purpose.

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

In particular, peeling individual graphene sheets from graphene oxide is the most common method and many techniques have been reported for obtaining monolayer graphene successfully, but this method for producing graphene platelets from graphite is known as sulfuric acid / permanganic acid. It is carried out using an oxidizing agent such as potassium (KMnO 4) followed by reduction or solvent etching with either hydrazine or alkali.

As a result, most of the chemical methods known to date rely heavily on the use of sulfuric acid / potassium permanganate (KMnO 4) or strong oxidizers such as carboxylic acid, formic acid, and overuse of organic solvents that are harmful to the environment for further exfoliation.

In addition, despite several environmentally-researched studies of the reduction of graphene oxide by either chemical or electrochemical methods, an integrated environmentally friendly approach has not yet been established for all processes of graphene synthesis. It is not developed.

The present inventors have completed the present invention by developing a graphene sheet manufacturing method suitable for large-scale synthesis and eco-friendly as a result of research efforts to solve the above problems.

Therefore, it is an object of the present invention to provide a process for the preparation of a process for the preparation of an integrated < RTI ID = 0.0 > acidic < / RTI > To provide an environment-friendly graphene sheet manufacturing method and the graphene sheet prepared by the method.

It is another object of the present invention 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 production time.

Still another object of the present invention is to provide a graphene sheet manufacturing method and a graphene sheet prepared by the method that can minimize the problems associated with excessive oxidation to obtain a high quality graphene sheet as well as a higher yield will be.

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

Oxidation step of the invention the oxidation of graphitizing the structure Gras pinned layer having an array of a complete laminate structure AB (AB stacking) in order to attain the object; A microwave irradiation step of performing microwave irradiation on the oxidized graphite structure; It provides a graphene sheet manufacturing method comprising; and an ultrasonic treatment step of sonicating the graphene layer binder consisting of several layers obtained after the irradiation step.

In a preferred embodiment, the oxidation step is sonicated by immersing the graphite 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 graphite structure.

In a preferred embodiment, the ammonium peroxy disulfate is added in a weight ratio of 0.05 to 2 relative 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 graphite 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 removal step of removing residual oxide groups from the graphene sheet obtained after the sonication step.

In a preferred embodiment, the removing step is performed by dispersing the graphene sheet in a hydrazine solution.

In a preferred embodiment, the graphite structure is graphite or carbon nanotubes.

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 another aspect, 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.

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, organic acids harmful to the environment for the use of sulfuric acid / potassium permanganate (KMnO 4) or strong oxidizing agents such as carboxylic acid and formic acid and further peeling action No excessive use of solvents 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.

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,
3 and 4 are graphs of the respective spectra results analyzed by XPS spectrometer and Raman spectrometer of graphene worms obtained by microwave irradiation in one embodiment of the present invention,
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 is a nanopropyllomitry image obtained by observing a graphene sheet obtained in one embodiment of the present invention with an atomic force microscope (AFM),
FIG. 8 is a graph showing the spectra of the graphene sheets obtained in one embodiment of the present invention through a Raman spectrometer and the analyzed spectra results. FIG.

The terms used in the present invention were selected as general terms as widely used as possible, but in some cases, the terms arbitrarily selected by the applicant are included. In this case, the meanings described or used in the detailed description of the present invention are considered, rather than simply the names of the terms. The meaning should be grasped.

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

However, the present invention is not limited to the embodiments described herein but may be embodied in other forms. Like reference numerals designate like elements throughout the specification.

First, the present invention is an oxidation step of oxidizing graphitizing structure having an array of pinned Gras a complete laminate structure AB (AB stacking); A microwave irradiation step of obtaining microwave graphene bonded to several layers by performing microwave irradiation on the oxidized graphite structure; And a sonication step of sonicating the graphene layer binder; and a technical feature of the graphene sheet including a graphene layer binder of several layers is easily obtained through microwave irradiation. The microwave irradiation step is performed at 150 to 550 W for 50 to 100 seconds using a microwave oven, preferably at 450 to 550 W for 85 to 95 seconds.

By introducing such a simple and simple microwave irradiation step, it is not necessary to use a strong oxidizing agent such as sulfuric acid / potassium permanganate (KMnO 4) or carboxylic acid or formic acid in the oxidation step, and an excessive amount of an organic solvent harmful to the environment Use may 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 graphite structure means all materials whose members are composed only of carbon, and include graphite (graphite), carbon black, carbon fiber, carbon nanotube, and the like. the stacked structure of a pinned layer can be provided at the best conditions for producing from the non-graphitizing structure having an array of a complete laminate structure AB (AB stacking) the preparation of a graphene sheet.

Example

Graphene Sheet Preparation from Graphite (Graphite)

Graphite from the graphene layers are arranged to complete a laminated structure AB (AB stacking) was obtained in the same way as to the graphene sheet.

1. Oxidation stage

Natural graphite, hydrogen peroxide (concentration 35%) and ammonium peroxydisulfate prepared in a glass tube were prepared at a ratio of 2: 1: 0.1 (concentration: 35%) and natural peroxide prepared with natural graphite (purity: 99%, average particle size: 200um), ammonium peroxydisulfate and hydrogen peroxide The graphite was immersed in the solvent in a weight ratio of.

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

2. Microwave irradiation stage

The glass tube was then placed in a microwave oven and irradiated at 500 W for 90 seconds. At this time, under the microwave irradiation, a rapid peeling phenomenon was observed, accompanied by lightening (lightening).

3. Ultrasonic Treatment Step

Graphene worms were subjected to dry sonication for 30, 60, and 60 minutes to obtain a graphene layer binder composed of several layers from graphene worms formed by the microwave irradiation. The best results were obtained when dry sonication for 90 minutes. 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 located in the range of 15 to 25 minutes.

The overall process is as shown in FIG.

Meanwhile, a step of removing residual 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.

Experimental Example 1

The graphene worms obtained by the microwave irradiation in the embodiment was observed by SEM and the shape photographs thereof are shown in FIG.

The principle of formation of graphene worms as a preliminary step for obtaining a graphene layer-bonded body is as follows. The microwave irradiation decomposes ammonium peroxydisulfate into releasing oxidation radicals which generate radicals that cause cutting of graphite sheets. Attack the defects on the graphite surface and then as reaction procedures the oxidized radicals are generated from the decomposition of hydrogen peroxide and inserted between the interlayer graphite layers to cause rapid expansion to form the graphene worms.

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

It can be seen from FIG. 3 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%.

In FIG. 4 Raman spectra show nearly equal full width half maximum (FWHM) of protruding D and G bands and intensity indicating the well-laminated characteristics of graphene nanosheets in the graphene worms.

Experimental Example 2

In Example, the graphene layered binder composed of few layers of fluffy graphene nanosheets obtained by dry sonication of the graphene worms was observed by SEM and TEM (FIG. In particular, 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, ultrasonication of graphene worms and / or graphene layer composites may cause acoustic cavitation near the surface, thereby causing ripping and shearing of small platelets This creates an erosion. 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 adjacent to the surface of the bubbles that withstand stable cavitation and cause nearby plaques to be shaved or torn away. 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, which are small enough and from sub-particles. This is because the separation of the graphite plates constituting the component is dominant, and the increase in irradiation time will result in the breaking of the graphite nanosheets on the leaf.

However, the present invention does not allow any of the above-mentioned processes to occur simultaneously 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. It is based on the prediction of the possibility, and it is possible to realize mass production of graphene sheet quickly and eco-friendly.

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 this scrolling phenomenon is not observed in the TEM photograph (b). The substrate in which the graphene sheets are gathered appears to affect the shape.

Experimental Example 4

The graphene sheet obtained in the example was observed with an atomic force microscope (AFM), and the nanopropylomimitri image is shown in FIG. 7.

AFM images such as those shown in FIG. 7 have traditionally been used to measure dimensions of discrete graphite sheets. 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 graphene surface dried on the substrate increases its visible thickness as measured by AFM. Also, although the perforated substrate (AAO) was used in the present invention, it was found that the bending needles were not minimized.

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 is an essential tool for characterizing carbon-containing materials, 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 band 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). Lt; RTI ID = 0.0 > G) < / RTI >

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

In addition, in the above experimental example, Raman spectra were obtained using an Invia reflex micro Raman spectrometer (Leniso), which was operated at 0.1 mW and had crystal laser excitation of 514.5 nm. SEM results photographs were recorded using a cold field emission scanning electron microscope (S-4700, Hitachi, Japan). TEM was performed on a JEOL JEM 2010 microscope operated at 200 kV using a perforated carbon coated copper grid. Both TEM and SEM experiments placed a very thinly dispersed drop on the relative substrates after precipitation and dried under atmospheric conditions. Nanoprofilometry was performed using a nanoview NV 200 with three interfero metric objective lenses and a vertical resolution of 0.5 nm manufactured by NanoSister Meze (Korea). .

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 is provided to those skilled in the art without departing from the spirit of the present invention. Various changes and modifications will be possible.

Claims (14)

Induced oxidation step of oxidizing the pinned graphitizing structure having an array of a complete laminate structure AB (AB stacking);
A microwave irradiation step of performing microwave irradiation on the oxidized graphite structure; And
And a sonication step of sonicating the graphene layer binder composed of several layers obtained after the irradiation step.
The oxidation step is a graphene sheet manufacturing method characterized in that the ultrasonic treatment by immersing the graphite structure in hydrogen peroxide.
delete The method of claim 1,
Wherein the oxidizing step further comprises adding ammonium peroxydisulfate to the hydrogen peroxide and immersing the graphitic structure in an ultrasonic treatment for 2 to 6 minutes.
The method of claim 3,
The ammonium peroxy disulfate is graphene sheet production method characterized in that the addition of 0.05 to 2 by weight relative to the hydrogen peroxide.
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 graphite structure in the microwave oven.
Induced oxidation step of oxidizing the pinned graphitizing structure having an array of a complete laminate structure AB (AB stacking);
A microwave irradiation step of performing microwave irradiation on the oxidized graphite structure; And
And a sonication step of sonicating the graphene layer binder composed of several layers obtained after the irradiation step.
The sonication step is a graphene sheet manufacturing method characterized in that the graphene layer binder is dispersed in an alcohol solvent and sonicated for 15 to 25 minutes.
7. The method according to any one of claims 1 to 6,
And a removing step of removing residual oxide groups from the graphene sheet obtained after the sonication step.
The method of claim 7, wherein
The removing step is a graphene sheet manufacturing method, characterized in that performed by dispersing the graphene sheet in a hydrazine solution.
7. The method according to any one of claims 1 to 6,
The graphitic structure is a graphene sheet manufacturing method, characterized in that the graphite or carbon nanotubes.
Induced oxidation step of oxidizing the pinned graphitizing structure having an array of a complete laminate structure AB (AB stacking);
A microwave irradiation step of performing microwave irradiation on the oxidized graphite structure; And
And a sonication step of sonicating the graphene layer binder composed of several layers obtained after the irradiation step.
The graphene layer binder is a graphene sheet manufacturing method, characterized in that obtained by the dry ultrasonic treatment after the irradiation step.
Induced oxidation step of oxidizing the pinned graphitizing structure having an array of a complete laminate structure AB (AB stacking);
A microwave irradiation step of performing microwave irradiation on the oxidized graphite structure; And
And a sonication step of sonicating the graphene layer binder composed of several layers obtained after the irradiation step.
The graphene layer binder is a graphene sheet manufacturing method characterized in that it has a curved or curled structure.
Induced oxidation step of oxidizing the pinned graphitizing structure having an array of a complete laminate structure AB (AB stacking);
A microwave irradiation step of performing microwave irradiation on the oxidized graphite structure; And
And a sonication step of sonicating the graphene layer binder composed of several layers obtained after the irradiation step.
The graphene layer binder is a graphene sheet manufacturing method, characterized in that the oxygen content is 1.41%.

delete delete

Images