KR101618975B1 - Preparation method of graphene nanosheets - Google Patents

Abstract

The present invention relates to a method for producing a graphene nanosheet, and more particularly, to a method for manufacturing a graphene nanosheet using a poly ( p - phenylene vinylene) precursor, which is a kind of polyelectrolyte, as a stabilizer in peeling a graphite A graphene nanosheet can be obtained by forming a complex with graphene to obtain a non-defective graphene nanosheet stably dispersed at a high concentration on an aqueous medium without impairing function of the graphene, Nano-sheet.
The present invention can prevent structural degradation of bar-graphene and deterioration of intrinsic electrical properties of graphene, which are produced by separating graphene from graphite without oxidation process, and it is possible to prevent degradation of graphene due to residual impurities Lt; / RTI > In particular, the poly ( p - phenylenevinylene) precursor, which is a polyelectrolyte, is converted into a conjugated poly ( p - phenylene vinylene) through optical, thermal or chemical treatment, and does not act as an impurity. In addition, when a thin film of an electric or electronic device is formed using the aqueous medium graphene dispersion obtained according to the present invention, there is an advantage that a very simple coating method such as spray-casting can be used.

Description

TECHNICAL FIELD [0001] The present invention relates to a method of manufacturing graphene nanosheets,

The present invention relates to a method for producing a graphene nanosheet, and more particularly, to a method for manufacturing a graphene nanosheet using a poly ( p - phenylene vinylene) precursor, which is a kind of polyelectrolyte, as a stabilizer in peeling a graphite A graphene nanosheet can be obtained by forming a complex with graphene to obtain a non-defective graphene nanosheet stably dispersed at a high concentration on an aqueous medium without impairing the function of graphene, and a method for producing graphene nanosheets, Nano-sheet.

The present invention can prevent structural degradation of bar-graphene and deterioration of intrinsic electrical properties of graphene, which are produced by separating graphene from graphite without oxidation process, and it is possible to prevent degradation of graphene due to residual impurities Lt; / RTI > In particular, the poly ( p - phenylenevinylene) precursor, which is a polyelectrolyte, is converted into a conjugated poly ( p - phenylene vinylene) through optical, thermal or chemical treatment, and does not act as an impurity. In addition, when a thin film of an electric or electronic device is formed using the aqueous medium graphene dispersion obtained according to the present invention, there is an advantage that a very simple coating method such as spray-casting can be used.

Graphene, a carbon isotope, is a 2D-structured sheet-like material with an atomic level (~ 3 Å) in thickness. It has excellent mechanical and electrical properties and is suitable for chemical sensors, field-effect transistors and organic opto- (Organic optoelectronic device), which is a high-tech carbon material that can be applied to a wide range of fields. In recent years, composite materials such as graphene, graphene / conductive polymer, graphene / metal oxide, graphene / carbon nanotube, and graphene / metal nanoparticle have been widely used as a variety of electrode materials including touch screens, batteries, super capacitors, And so on.

For these diverse and potential applications, graphene is often required to be provided in a dispersed form in a liquid medium. Once a stable and environmentally stable dispersion is provided, a homogeneous thin film of nanometers to tens of micrometers in thickness can be readily formed by layered self-assembly techniques. That is, exfoliating layered materials such as graphite in an aqueous environment can be considered as a gateway technology because a wide range of solution-based process technologies can be applied in this case.

The Hummers method, which is most commonly known as a liquid phase stripping technique, is a technique for producing a single layer of graphene oxide (GO) by oxidizing graphite and stripping it in water. In the process of contacting graphite with an aqueous solution containing a strong oxidizing agent It is the mechanism by which graphene is formed as the graphene layers are oxidized and the layers are separated due to the repulsive forces present between the oxide layers. At this time, the graphene oxide is functionalized by an epoxide group, a hydroxyl group and a carboxyl group. On the other hand, graphene oxide is electrically insulated, and a process of reducing graphene oxide by various treatments such as chemical and thermal treatment is required.

However, this technique has a drawback that the risk of decomposing or destroying the material is very large, and the structure and electrical characteristics of the reduced graphene oxide (RGO) can not be completely restored by the structural and electrical properties of natural graphene have. Specifically, the conjugated structure of graphene is damaged in the oxidation / reduction process as described above, and the inherent electrical characteristics of graphene are deteriorated to a considerable extent.

In this respect, it is desirable to separate and disperse the graphene in the liquid phase in its original form without containing functional groups and intact, for example, by grafting the graphene from the graphite through sonication.

However, in this case, there still exists a problem that graphene is re-agglomerated by a strong van der Waals force acting between the sheets in order to minimize the surface free energy by using pure graphene. Further, ultrasonic treatment of graphite in an organic solvent can provide a better quality single layer to a few layer graphene, but in this case, the size of the flake produced is relatively small to be used for electrical and electronic applications and mechanical reinforcement applications Its practicality is low.

Alternatively, the surface free energy can be minimized by allowing the stabilizer to adsorb to the graphene surface using a stabilizer. At this time, effective stabilizers include surfactants, aromatic molecules capable of "pi-pi stacking ", aromatic polymers, and aromatic polyelectrolytes. The stabilizers act non-covalently with graphene by surface adsorption, micelle formation, and / or pi-pi interactions, thereby separating the graphene sheet and also allowing the separated sheets to be restacked To prevent it steric or electrostatic.

However, in this case, in order to obtain a graphene dispersion having a high concentration, a polymer and a surfactant having a higher concentration are required. As a result, an excess amount of a stabilizer remains in the dispersion. Such a dispersion containing an excessive amount of the stabilizer can not completely remove the excess stabilizer, and the concentration ratio of graphene to the stabilizer is lowered, which is a big obstacle to the use of the dispersion in a composite, a film, and an electric / electronic device. This surplus stabilizer also adversely affects the mechanical and electrical properties of the graphene loaded final product.

On the other hand, U.S. Published Patent Application No. 2013-0136684 discloses a method of forming a graphene-containing complex to produce a high-purity graphene nanosheet that is peeled and dispersed in a semiconductor polymer matrix. Specifically, the document discloses conjugates selected from thiophene-based oligomers and polymers, pyrene, phthalocyanine, polyphenylvinylidene, polyfluorene, polycarbazole, polyindolocarbazole, polytriarylamine, Gt; modified < / RTI > graphene.

However, this document relates to a technique for peeling expanded graphite in an organic solvent, 1,2-dichlorobenzene. 1,2-Dichlorobenzene has a high boiling point (180.5 DEG C) and is difficult to completely remove, There still exists a problem that it acts as an impurity in the thin film.

Thus, in the production of graphene nanosheets through peeling of graphite, graphene can be stably peeled and dispersed at a high concentration on an aqueous medium without causing impurities and using an organic solvent without impairing the inherent structure and properties of graphene, It is in urgent need of developing a new method that can make it possible.

U.S. Published Patent Application No. 2013-0136684

SUMMARY OF THE INVENTION The present invention has been made in order to solve the problems of the prior art as described above, and it is an object of the present invention to improve the method of chemical separation of existing graphene and to stably peel off graphene on an aqueous medium at a high concentration without using an oxidizing agent, The present invention also provides a method for producing a graphene nanosheet which can be dispersed.

According to an aspect of the present invention, there is provided a method of manufacturing a graphite intercalation compound comprising: (a) providing a graphite intercalation compound (GIC); (b) heating the graphite intercalation compound (GIC) in an argon (Ar) atmosphere to obtain expanded graphite; (c) dispersing the expanded graphite in a poly ( p -phenylene vinylene) precursor or a conductive conjugated polymer precursor using an ultrasonic treatment to form a complex of a graphene / conjugated polymer precursor; (d) maintaining the state of the dispersion so as to precipitate unstable aggregates in the resulting dispersion, followed by centrifugation; (e) taking a supernatant of the centrifuged dispersion and diluting with distilled water; And (f) collecting the sediment by centrifuging the diluted dispersion, and then redissolving the sediment in distilled water using ultrasonic treatment to obtain a water-based dispersion stabilized with a poly ( p -phenylene vinylene) precursor or a conductive conjugated polymer precursor And obtaining a medium graphene dispersion form. The present invention also provides a method for producing a graphene nanosheet.

In addition, the poly ( p -phenylene vinylene) precursor is transferred to a poly ( p -phenylenevinylene) conjugated polymer through thermal treatment or chemical treatment using an acid to become conductive. Of the present invention.

For example, the poly ( p -phenylene vinylene) precursor is represented by the following formula (A).

(A)

Wherein X is C ₄ H ₄ S (thiophene) or S (CH ₃ ) ₂ (sulfonium), R ₁ And R ₂ are each independently H, C ₄ H ₉ , CH ₃ O, C ₆ H ₁₃ O, C ₈ H ₁₇ O, C ₉ H ₁₉ O, C ₁₀ H ₂₁ O or 2-ethylhexyl)

Also, the conductive conjugated polymer precursor is a nonconductive conjugated polymer that can be converted to a conductive state by doping.

For example, the nonconductive conjugated polymer may be at least one selected from the group consisting of polyaniline, polypyrrole, polythiophene, polyacetylene, and derivatives thereof.

The method of manufacturing a graphene nanosheet according to the present invention is characterized in that heating in step (b) is performed at 1000 캜 for 30 seconds.

In addition, the present invention provides a method of manufacturing a graphene nanosheet, wherein the ultrasonic treatment in the step (c) is a probe ultrasonic treatment.

In addition, the collection and redispersion of the sediment in the step (f) is repeated 5 to 7 times.

Also, the ultrasonic treatment in the step (f) is performed in a low power sonic bath.

In the step (f), an aqueous medium graphene dispersion stabilized with a poly ( p -phenylene vinylene) precursor or a conductive conjugated polymer precursor having a concentration of 0.004 to 0.7 mg / mL is obtained. A method for producing a nanosheet is provided.

The present invention also provides a method of manufacturing a graphene nanosheet, wherein the graphene nanosheet is peeled to a level of less than five graphene layers.

Also, the present invention provides a method for producing a graphene nanosheet, which comprises obtaining a graphene nanosheet having a thickness of 2 to 10 nm.

In another aspect of the present invention, there is provided a graphene nanosheet in the form of an aqueous medium graphene dispersion stabilized with a poly ( p -phenylene vinylene) precursor or a conductive conjugated polymer precursor prepared according to the above method do.

Also, the graphene nanosheet is used as a thin film coating material of a thin film electronic device.

According to the method of manufacturing a graphene nanosheet according to the present invention, graphene is separated and formed from graphite without oxidizing / reducing process, thereby preventing structural damage to graphene and deterioration of electrical properties inherent to graphene.

In addition, a poly ( p - phenylene vinylene) precursor or a conductive conjugated polymer precursor, which is a polyelectrolyte, is used as a stabilizer to form a complex with graphene. By minimizing re - aggregation of the graphene sheet, Can be stably dispersed on the surface.

In addition, the use of an excess amount of a stabilizer, a surfactant, and an organic solvent is not used, and disadvantages due to the property of a product due to the residual impurities can be prevented. Specifically, the poly ( p -phenylene vinylene) precursor used in the present invention is converted into a conjugated poly ( p -phenylene vinylene) through thermal or chemical treatment in the future, and does not act as an impurity.

In addition, when the aqueous medium graphene dispersion obtained according to the present invention is used, a thin film can be formed by a very simple coating method such as spray-casting, and layer self-assembly of individual multi-layer graphene flakes It becomes very easy.

Furthermore, the graphene / PPV-pre composite obtained according to the present invention has the distinct advantage that it can be directly used as a photosensitive material due to the presence of poly ( p -phenylene vinylene).

BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 is a process flow diagram for the preparation of a graphene dispersion stabilized with a poly ( p -phenylene vinylene) precursor.
2 (a) is poly (p-phenylene vinylene), and the graphene UV-Vis spectrum of the dispersion stabilized with precursor 2 (b) is a poly-stabilized with (p-phenylene vinylene) precursor graphene (&Amp;_thetas; _ex = 532 nm, 6 mW).
Figure 3 (a) is an AFM image of graphene stabilized with a poly ( p -phenylene vinylene) precursor, Figure 3 (b) is the thickness profile of the selected graphene flakes, It is a histogram showing the thickness of graphene flakes ( N = 300).

Hereinafter, the present invention will be described in detail.

A method of manufacturing a graphene nanosheet according to the present invention comprises:

(a) providing a graphite intercalation compound (GIC);

(b) heating the graphite intercalation compound (GIC) in an argon (Ar) atmosphere to obtain expanded graphite;

(; hereinafter abbreviated to as "pre-PPV" herein Poly (p -phenylene vinylene) precursor) or conductive (p-phenylene vinylene) precursor (c) of poly using sonication ball-component polymer to the expanded graphite, Dispersing the dispersion in a conjugated polymer precursor to form a composite of a graphene / conjugated polymer precursor;

(d) maintaining the state of the dispersion so as to precipitate unstable aggregates in the resulting dispersion, followed by centrifugation;

(e) taking a supernatant of the centrifuged dispersion and diluting with distilled water; And

(f) The diluted dispersion is centrifuged to collect the precipitate, and the precipitate is redispersed in distilled water by ultrasonic treatment to obtain an aqueous medium stabilized with a poly ( p -phenylenevinylene) precursor or a conductive conjugated polymer precursor To obtain a graphene dispersion form (see Fig. 1).

That is, according to the present invention, a non-defective graphene nanosheet is formed on an aqueous medium by applying a polyelectrolyte, PPV-pre, as a stabilizer for graphene separation and dispersion. According to the present invention, -π interaction preserves the electronic conjugation of the graphene intact and preserves the intact cohesive graphene dispersion stabilized on the medium with a very high graphene / stabilizer yield. In particular, PPV-pre forms Lamellar sheets as well as the graphene layer, which allows smooth interaction with the graphene layer while retaining the graphene in its intact form without incorporating functional groups on the graphene surface can do.

In the present invention, the poly ( p -phenylene vinylene) precursor used for separating graphene from graphite is a non-conjugated polyelectrolyte, which is a thermally or chemically treated poly ( p -phenylene vinylene) It is a substance that becomes conductive through the transition. That is, the poly ( p -phenylene vinylene) precursor used as the stabilizer used in the present invention is converted into the conjugated poly ( p -phenylene vinylene) through optical, thermal or chemical treatment, There are advantages.

Available poly (p-phenylene vinylene), which is not particular limitation on the type of precursor, to, for example, a material represented by formula (A) Poly - can be used as (p-phenylene vinylene) precursor.

(A)

Wherein X is C ₄ H ₄ S (thiophene) or S (CH ₃ ) ₂ (sulfonium), R ₁ And R ₂ are each independently selected from the group consisting of H, C ₄ H ₉ , CH ₃ O, C ₆ H ₁₃ O, C ₈ H ₁₇ O, C ₉ H ₁₉ O, C ₁₀ H ₂₁ O or 2-ethylhexyl )to be)

Polyester represented by the formula A (p-phenylene vinylene) precursor is a poly by the application of heat or acid-an exemplary process by which transitions to the (p-phenylenevinylene) polymer conjugate are shown in Fig.

[Figure 1]

Also, in the present invention, the conductive conjugated polymer precursor used for separating graphene from graphite is a nonconductive (conjugated) polymer capable of being converted into a conductive conjugated polymer by doping, and the kind thereof is not particularly limited.

In one preferred embodiment, the conductive conjugated polymer precursor may be a nonconductive conjugated polymer such as polyaniline, polypyrrole, polythiophene, polyacetylene, and derivatives thereof.

The exemplary types of polyaniline, polypyrrole, polythiophene, and derivatives thereof usable as the nonconductive conjugated polymer and the transition process to the conductive conjugated polymer by doping are shown in FIGS. 2 to 4 below.

[Figure 2]

[Figure 3]

[Figure 4]

The step (a) is a step of preparing a graphite intercalation compound (GIC) as a graphite material for preparing the graphene nanosheet of the present invention by a solution peeling method.

In this step, the graphite intercalation compound (GIC) comprises i) mixing and stirring natural graphite flakes, concentrated sulfuric acid and fuming nitric acid; ii) slowly dropping and stirring the mixture in distilled water; iii) removing the clean supernatant liquid through decantation after maintaining the graphite particles in the resulting mixture to settle; And iv) repeatedly washing the graphite particles with distilled water, followed by centrifugation, followed by drying.

In the step (b), the prepared graphite intercalation compound (GIC) is heated to a predetermined temperature in an argon (Ar) atmosphere to thermally expand the graphite crystal.

Specifically, when the graphite intercalation compound (GIC) is heated (for example, at 1000 DEG C for 30 seconds), an intercalation agent bonded between graphene flat sheets undergoes a physical phase change from a liquid phase to a vapor phase The volume thereof increases, so that adjacent graphene layers in the expandable graphite become separated from each other.

) 또는 전도성 공액 고분자 전구체를 준비하고 이를 상기 팽창된 그래파이트와 함께 초음파 처리하여 그래핀/공액 고분자 전구체의 복합체(Graphene/Conjugated polymer precursor composite)를 형성함으로써, 그래파이트로부터 그래핀으로의 용액박리 및 분산을 수행하는 단계이다.In step (c), a poly ( p -phenylenevinylene) precursor (for example, a polyphenylene vinylene) precursor which is a polyelectrolyte as a material to be interposed between the separated graphene layers,

) Or a conductive conjugated polymer precursor is prepared and subjected to ultrasonic treatment together with the expanded graphite to form a graphene / conjugated polymer precursor composite, whereby the solution separation and dispersion from the graphite to the graphene can be carried out .

In this step, the ultrasonic processing can be performed through probe ultrasonic processing (probe ultrasonic processing), but is not limited thereto.

In addition, the present inventors have confirmed through experiments that graphene is not damaged or functionalized by a functional group by PPV-pre and high-power ultrasonic waves even when the above process is performed. That is, according to the present invention, it becomes possible to separate and disperse graphene in its original form without containing any functional groups in the liquid phase.

The steps (d) and (e) may be performed by precipitating unstable aggregates (e.g., some graphene agglomerates that are not bound to PPV-pre and re-aggregated) in a dispersion containing a complex of graphene / conjugated polymer precursor After filtration, only the supernatant of the dispersion is taken and diluted with distilled water.

In this step, the centrifugation and dilution method is not particularly limited, and can be carried out according to a conventional apparatus and method in the art.

In addition, the amount of the supernatant may be appropriately adjusted in accordance with the conditions, such that unstable aggregates are not included. For example, about 75% of the supernatant may be used after centrifugation.

In the step (f), the diluted dispersion is centrifuged again to collect sediments containing the complex of the graphene / conjugated polymer precursor, and then redispersed in an aqueous medium (for example, distilled water) using ultrasonic treatment, The step of preparing the graphene nanosheet according to the present invention in the form of a graphene dispersion stabilized on an aqueous medium with PPV-pre or a conductive conjugated polymer precursor.

In this step, the collection and redispersion of the sediment can be repeatedly carried out about 5 to 7 times (for example, 6 times), thereby obtaining a cleaner graphene nanosheet product (sediment).

In addition, the ultrasonic treatment may be performed in a low power sonic bath, but is not limited thereto.

According to the present invention, it is possible to obtain a graphene dispersion having a high concentration ranging from 0.004 to 0.7 mg / mL (for example, 0.4 mg / mL, 0.668 mg / mL and the like) without adding an excessive amount of stabilizer as in the prior art, The concentration is about 2 to 20 times higher than when using a solvent or a surfactant (0.002 to 0.3 mg / mL).

In addition, according to the present invention, graphite can be peeled off with a thin graphene sheet which is a minority layer of less than five layers (for example, two to four layers), and the graphene nanosheet (graphene flake) Or more.

According to another aspect of the present invention there is provided a graphene nanosheet in the form of an aqueous medium graphene dispersion stabilized with a poly ( p -phenylene vinylene) precursor or a conductive conjugated polymer precursor prepared according to the above process .

The graphene nanosheet according to the present invention can be suitably used as a thin film coating material of a thin film electronic device such as a field-effect transistor.

In addition, the graphene nanosheet (e.g., graphene / PPV-pre composite) according to the present invention can be used in a wide variety of applications including graphene / conductive polymers, graphene / metal oxides, graphene / carbon nanotubes, It can be utilized as a material of composite material, and it is expected that the characteristics of such composite material can be greatly improved.

Hereinafter, the present invention will be described in more detail with reference to Examples and Experimental Examples. It should be understood, however, that these examples are for illustrative purposes only and are not intended to limit the scope of the invention in any way.

Example : PPV - pre Stabilized Grapina  Preparation of dispersion

(1) Production of Expanded Graphite

1 g of natural graphite flakes (particle size = -10 mesh, Alfa Aesar, Korea), 30 mL of concentrated sulfuric acid (95%, Samchun Pure Chemical Co., Ltd., Korea), and fuming nitric acid (93%, Matsunoen Chemicals Ltd, Japan ) Were mixed and stirred well at room temperature for 24 hours.

40 mL of distilled water (Milli-Q Plus purification system) was slowly added dropwise, followed by stirring for 20 minutes.

The resulting mixture was allowed to settle for several hours to precipitate the graphite particles, and then the clean supernatant liquid was removed through decantation.

The obtained graphite particles were washed three times with distilled water, centrifuged at 4000 rpm for 15 minutes and then dried at 60 DEG C for 24 hours to obtain a graphite intercalation compound (GIC).

Then, the dried compound was placed in a long quartz tube filled with argon (Ar) and sealed with a rubber pad.

The quartz tube was placed in a tube furnace at 1000 ° C for 30 seconds to obtain an expanded graphite (EG) compound.

(2) Preparation of aqueous medium graphene dispersion stabilized with PPV-pre

)(0.6 mg/mL) 35 mL에 분산시킨 후, 프로브 초음파 처리(Cole-Parmer Vibracell CV33 Sonicator Probe Head, 21% of 750 W)를 120분 동안 수행하여 샘플을 제조하였다.0.21 g of the expanded graphite compound (GIC) was added to PPV-pre (

(0.6 mg / mL) and then subjected to probe ultrasonication (Cole-Parmer Vibracell CV33 Sonicator Probe Head, 21% of 750 W) for 120 minutes to prepare a sample.

The resulting dispersion was left overnight to allow unstable aggregates to settle and then centrifuged (Hettich Rotofix 32) at 500 rpm for 90 minutes.

After centrifugation, the upper 75% of the dispersion was transferred and diluted with distilled water.

Subsequently, the diluted dispersion was centrifuged (Supra 22K) at 8000 rpm for 1 hour, and the sediment was collected, and then the sediment was redispersed in distilled water.

After the washing procedure was repeated 6 times, the sediment dispersion was ultrasonicated (Wiseclean WUC-D10H) in a low power sonic bath for 10 minutes and redispersed in 10 mL of distilled water, A graphene dispersion stabilized with PPV-pre was finally obtained.

Experimental conditions

(1) The concentration of the graphene dispersion obtained according to the above examples was measured using a UV / Visible absorption spectroscopy (Perkin Elmer, Lambda 40) (using a 1 cm quartz cuvette).

(2) Physical properties of graphene flakes were investigated using Raman spectrometry (Raman-LTPL) (λ _ex = 532 nm).

(3) The AFM image of the graphene flake is used with a Nanoscope IV multimode atomic force microscope (AFM) (Veeco) (operating in tapping mode, using a Si cantilever with a scan speed of 0.5 Hz, 125 mm length) Respectively.

Experimental Example  One: Grapina  Spectroscopic Characterization of Dispersions Spectroscopic characterization ) And concentration measurement

The UV-Vis spectrum of the graphene dispersion (30-fold dilution) stabilized with PPV-pre after centrifugation (8000 rpm) is shown in Fig. 2 (a). The left and right cuvettes in Figure 2 (a) below represent the graphene and PPV-pre solution stabilized with diluted PPV-pre, respectively.

The dispersion was characterized by ultraviolet / visible light absorption spectroscopy. As shown in FIG. 2 (a), the spectrum showed a characteristic spectrum in the Visible-IR region (400 to 1100 nm). On the other hand, an absorption peak appeared at 268 nm, which is believed to be due to graphene's delocalized electron system.

According to the Lambert-Beer law (A = αCℓ, where C = concentration, ℓ = path length), the absorption coefficient α is related to Absorbance A and is an important parameter for characterizing any dispersion . The concentration of the graphene dispersion stabilized with PPV-pre was calculated up to 0.7 mg / mL (e.g., 0.668 mg / mL) when? At 660 nm was 1390 mL mg ^-1 m ^-1 , And about 2 to 20 times higher than when using a surfactant (0.002 to 0.3 mg / mL).

A graphene dispersion stabilized with such a high concentration of PPV-pre may be very useful for many practical applications, particularly thin-film electronics.

Experimental Example  2: PPV - pre Stabilized Grapina  Physical property evaluation

The physical properties of graphene stabilized with PPV-pre using Raman spectrum ([lambda] _ex = 532 nm, 6 mW) were investigated and are shown in Fig. 2 (b).

The Raman spectra of Figure 2 (b) below show a clear G band (~ 1580 cm ^-1 ) and a broad 2D band (~ 2700 cm ^-1 ), which is less than five layers per sp ² carbon and flake, respectively It corresponds to the characteristic of the pin. PPV-pre is a remarkable result in that Raman is inert. Especially, D band (~ 1350 cm ^-1 ) corresponding to the characteristic of sp ³ carbon content is kept low, which is caused by damage or functionalization of graphene by PPV-pre and high power sonication It means that you did not.

Experimental Example  3: PPV - pre Stabilized Grapina  Structural characterization

AFM measurements were performed to gain insight into the structural features of graphene stabilized with PPV-pre. As a sample for AFM measurement, a mica (freshly cleaved mica) substrate was dipped in a graphene dispersion (0.4 mg / mL) stabilized with PPV-pre.

The thickness of the exfoliated graphene flakes was determined and determined by tapping mode AFM of the dispersion dip coated on the mica substrate.

The AFM image of the graphene stabilized with PPV-pre, the thickness profile of the selected graphene flake and the histogram ( N = 300) of the observed graphene flake thickness are shown in Figs. 3 (a), 3 3 (c).

AFM height profiles of 300 graphene flakes show that 76% of graphene flakes have a thickness in the range of 2 to 10 nm, which corresponds to multilayer graphene. That is, it is understood that uniform graphite crystals of an alternating-layer (e.g., AB) structure are decomposed into bi- to few- graphene flakes and they are folded and entangled on the substrate. In general, most of these multilayer flakes were found to have lateral dimensions of ~ 1 um.

Claims (14)

(a) providing a graphite intercalation compound (GIC);
(b) heating the graphite intercalation compound (GIC) in an argon (Ar) atmosphere to obtain expanded graphite;
(c) dispersing the expanded graphite in a poly ( p -phenylene vinylene) precursor without using an organic solvent and a surfactant by ultrasonic treatment to form a complex of a graphene / poly ( p -phenylene vinylene) ;
(d) maintaining the state of the dispersion so as to precipitate unstable aggregates in the resulting dispersion, followed by centrifugation;
(e) taking a supernatant of the centrifuged dispersion and diluting with distilled water; And
(f) The diluted dispersion is centrifuged to collect the precipitate, and the precipitate is re-dispersed in distilled water using ultrasonic treatment to form an aqueous medium graphene dispersion stabilized with a poly ( p -phenylene vinylene) precursor ; ≪ / RTI >
The poly ( p -phenylenevinylene) precursor in the step (c) is a non-lyophilic polymer, which is converted into a poly ( p -phenylenevinylene) conjugated polymer through chemical treatment using a thermal treatment or an acid, ≪ / RTI >
A method for producing a graphene nanosheet.
The method according to claim 1,
Wherein the poly ( p -phenylene vinylene) precursor is represented by the following formula (A): < EMI ID =
(A)

In Formula A above, X is C ₄ H ₄ S (thiophene) or S (CH ₃ ) ₂ (sulfonium); R ₁ and R ₂ are each independently H, C ₄ H ₉ , CH ₃ O, C ₆ H ₁₃ O, C ₈ H ₁₇ O, C ₉ H ₁₉ O, C ₁₀ H ₂₁ O or 2-ethylhexyl.
The method according to claim 1,
Wherein the heating in step (b) is performed at 1000 占 폚 for 30 seconds.
The method according to claim 1,
Wherein the ultrasonic treatment in the step (c) is a probe ultrasonic treatment.
The method according to claim 1,
Wherein the collection and redispersion of the sediment in the step (f) is repeated 5 to 7 times.
The method according to claim 1,
Wherein the ultrasonic treatment in the step (f) is performed in a low power sonic bath.
The method according to claim 1,
Wherein the step (f) is to obtain an aqueous medium graphene dispersion stabilized with a poly ( p -phenylene vinylene) precursor having a concentration of 0.004 to 0.7 mg / mL.
The method according to claim 1,
Wherein the graphene nanosheet is produced by separating graphite to a level of less than five graphene layers.
The method according to claim 1,
Wherein the graphene nanosheet is obtained by graphen nanosheet having a thickness of 2 to 10 nm.
A graphene nanosheet in the form of an aqueous medium graphene dispersion stabilized with a poly ( p -phenylene vinylene) precursor, prepared according to the method of any one of claims 1 to 9.
11. The method of claim 10,
Wherein the graphene nanosheet is used as a thin film coating material of a thin film electronic device.
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