KR20110101668A - Manufacturing method of graphene compound with excellent dispersability in organic solvents - Google Patents

Abstract

The present invention relates to a method for producing a graphene compound, more specifically preparing a graphene oxide; And it relates to a method for producing a graphene compound excellent in dispersibility in an organic solvent comprising the step of reducing by adding phenylhydrazine to the graphene oxide. According to the preparation method of the present invention, by reducing the graphene oxide in one step using phenylhydrazine to prepare a graphene compound, graphene can be easily and stably dispersed in various organic solvents, using water or a surfactant. It is possible to realize a large dispersion concentration without reducing the manufacturing cost.

Description

Manufacturing method of graphene compound with excellent dispersability in organic solvents}

The present invention relates to a method for preparing a graphene compound having excellent dispersibility which can be directly dispersed in various organic solvents by reducing graphene oxide through a chemical reaction.

Graphene is a honeycomb two-dimensional thin film made of a layer of carbon atoms. When carbon atoms are chemically bonded by SP ² hybrid orbits, carbon atoms form two-dimensionally spread carbon hexagonal planes. The aggregate of carbon atoms having such a planar structure is graphene, and the thickness of 0.3 nm is only one carbon atom. . Graphene has become one of the hottest topics in physics since 2005, when the AKGeim research group at the University of Manchester, UK, introduced how to make thin, one-atom carbon films from graphite.

The most notable feature of graphene is that there is no effective mass of electrons in graphene, so the electrons behave as relativity particles moving at the speed of light. In addition, graphene has an abnormal half-integer quantum hall effect on electrons and holes. Because of this feature, it is possible to implement particle physics experiments indirectly through graphene, which could not be performed in the field of particle physics.

On the other hand, the conventional silicon-based semiconductor process technology can not manufacture a semiconductor device having a high density of less than 30nm class. This is because the thickness of the metal atom layer such as gold or aluminum deposited on the substrate is thermodynamically unstable and the metal atoms are entangled with each other to obtain a uniform thin film. This is because they become nonuniform at nanoscale.

However, graphene has the potential to overcome the integration limits of silicon-based semiconductor device technology. Graphene has a characteristic of changing its electrical resistance due to the change of charge density according to gate voltage because its characteristic is metallic and its thickness is very thin, which is several nm or less, which corresponds to the screening length. Since the electrical characteristics change according to the crystal orientation of the graphene, the user can express the electrical characteristics in the selection direction.

Metal transistors can be used to implement high-speed electronic devices because the mobility of charge carriers is large, and the charges of charge carriers can be changed from electrons to holes depending on the polarity of the gate voltage. It is expected to be. The characteristics of the graphene sheet can be used very effectively in the future carbon-based electrical devices or carbon-based electromagnetic devices.

However, although such graphene sheets have very useful properties, no method for economically, large-scale, and reproducible production has been developed until now. Known graphene can be classified into the following three ways.

The first method is to separate the ultrafine graphite layer using the cellophane tape. When the cellophane tape is attached to the graphite and then peeled off, a graphene thin film separated from the graphite may be obtained on the surface of the cellophane tape. However, in this method, depending on the quality of the adhesive tape, the number of layers of the graphene thin film separated from the graphite is not constant, the shape and the paper are not constant in the shape of torn paper, and electron beam lithography due to the large amount of useless thick graphite particles. There is a problem in that it is difficult to pattern the electrode, and it is impossible to obtain a graphene thin film in a large area.

The second method is an epitaxial growth method through pyrolysis of SiC under high vacuum. In this method, when SiC single crystal is heated at high vacuum and high temperature, SiC on the surface is decomposed and Si is sublimed and removed, and the remaining carbon atoms form graphene. However, this method uses SiC as a starting material.

The single crystal is very expensive, there is a problem that it is very difficult to obtain a large area of the graphene sheet, SiC itself should be used as a substrate, the SiC substrate had a problem that the performance is not good enough to use as an electronic material as SiO ₂ .

The third method is to use the chemical peeling action of the graphite compound. Based on the results of the study on the graphite compound, which is typically mixed with impurities, many researchers have proposed a method of chemical exfoliation. However, this method has not only succeeded in obtaining graphene, but only several hundred nanometers thick graphite fragments to date, and it may cause many defects because the chemicals inserted between the graphite layers are not completely removed. There was a problem.

In order to solve the above problems, the present inventors have confirmed that the present invention can be stably dispersed in an organic solvent by reducing graphene oxide using phenylhydrazine instead of hydrazine, which has been conventionally used, and completed the present invention.

Accordingly, an object of the present invention is to provide a method for producing a graphene compound which can be easily and stably dispersed in various organic solvents in one reaction while reducing the production cost.

In order to achieve the above object, the present invention comprises the steps of preparing graphene oxide; And it provides a method for producing a graphene compound excellent in dispersibility in an organic solvent comprising the step of reducing by adding phenylhydrazine to the graphene oxide.

In one embodiment of the present invention, the phenylhydrazine may be added in an amount of 10 to 10,000 parts by weight based on 100 parts by weight of graphite oxide.

In one embodiment of the present invention, the step of reducing by adding phenylhydrazine to the graphite oxide may be performed for 1 to 240 hours at a temperature of 0 ~ 100 ℃.

In one embodiment of the present invention, the graphene oxide may be formed by oxidizing graphite or expanded graphite (expanded graphite).

In one embodiment of the present invention, the concentration of the graphene oxide is 0.01 ~ 100 Mg / ml.

In one embodiment of the present invention, the graphene compound may have a dispersion concentration of 0.1 mg / ㎖ or more in an organic solvent.

The method for preparing a graphene compound having excellent dispersibility in an organic solvent according to the present invention is to stably reduce graphene to various organic solvents by preparing graphene compounds by reducing graphene oxide in one step using phenylhydrazine. It is possible to disperse, to realize a large dispersion concentration without using water or a surfactant, it is possible to reduce the manufacturing cost.

In addition, the graphene compound thus prepared has an advantage that it can be variously applied and applied to a conductive thin film, a polymer composition, a metal oxide, a semiconductor compound, a conductive ink, a photocatalyst, a battery, a super capacitor electrode, a fuel cell bipolar electrode, and the like.

Figure 1 shows the chemical change of the graphene surface when reducing the graphene oxide to phenylhydrazine according to an embodiment of the present invention.
Figure 2 shows the ultraviolet absorption spectrum of the graphene compound formed according to an embodiment of the present invention.
Figure 3 (a) is a XPS spectrum of graphene oxide, Figure 3 (b) is a deconvolution of the C1s spectrum of graphene oxide, Figure 3 (c) is a graphene compound formed according to an embodiment of the present invention 3 (d) shows the deconvolution of the C1s spectrum of the graphene compound, and FIG. 3 (e) shows the deconvolution of the N1s spectrum of the graphene compound.
Figure 4 shows the Raman spectrum of the graphene oxide and the graphene compound formed according to an embodiment of the present invention.
Figure 5 shows the XRD results of the graphene oxide and the graphene compound formed according to an embodiment of the present invention.
Figure 6 shows a cross-sectional SEM picture of the graphene paper formed in accordance with an embodiment of the present invention.

The present invention is characterized by providing a method for producing a graphene compound that can be stably dispersed in various organic solvents by reducing graphene oxide using phenylhydrazine in order to effectively disperse the graphene in an organic solvent.

Graphene has attracted attention as a promising nanomaterial, but has not been widely applied due to the problem that it is hardly dispersed in an organic solvent. According to the research results published so far, graphene may be formed by dispersing the solution phase using a small amount of water or a surfactant, modifying the surface through complex chemical methods, and making a dispersed phase using a surfactant or the like. It could be dispersed in solution, but has the disadvantage that there are many restrictions on solvent dispersion.

In addition, a method of using hydrazine when preparing a graphene compound by reducing graphene oxide has been studied. In this case, it is possible to disperse in an organic solvent in the presence of water. In order to disperse in a pure organic solvent, a surfactant was required, and the concentration which can stably disperse was also very low.

Accordingly, the inventors of the present invention, while studying a method for effectively dispersing the graphene, when phenyl hydrazine is reduced by dispersing the graphene can be dispersed easily and stably with a larger dispersion concentration than when using hydrazine. It was confirmed that there is.

Therefore, the present invention comprises the steps of preparing graphene oxide; And it provides a method for producing a graphene compound dispersible in an organic solvent comprising the step of reducing by adding phenylhydrazine to the graphene oxide.

In the present invention, "graphene" refers to a structure of graphite consisting of a plate of graphite hexagonal honeycomb pattern of 1 to 5 layers, and has very excellent electrical properties. In addition, the "graphene compound" is formed by reducing the graphene oxide suspension (suspension), means chemically converted graphene (chemically converted graphene, CCG).

In the present invention, 'phenylhydrazine' has a structure of Chemical Formula C ₆ H ₈ N ₂ and is also referred to as hydrazinobenzene. Pure is a colorless liquid, oxidized in the air, brownish, and when cooled, forms a plate or rod. It does not dissolve well in water but mixes well with ethanol, diethyl ether, chloroform and benzene. In the present invention, graphene was easily dispersed in various organic solvents using such phenylhydrazine.

According to the present invention, a stable graphene compound that can be dispersed in an organic solvent is prepared by reducing graphene oxide with a sufficient amount of phenylhydrazine at room temperature.

According to studies reported up to now, surfactants are used to stably disperse the graphene in an organic solvent (① J. AM. CHEM. SOC., Vol. 130, pp. 16201-16206 (2008), ② ADV MATER., Vol. 21, pp. 1679-1683 (2009)), Method of introducing functional groups on the surface of graphene using compounds of complex structure (CHEM. MATER., Vol. 21, pp3045-3047 (2009) Has been known.

However, the present invention suggests a method of stably maintaining a dispersed phase in the organic solvent by aggregating phenyl functional groups on the graphene surface and increasing the distance between the graphene layers and layers at the same time as reduction. There is a big feature. When the graphene oxide is reduced to phenylhydrazine, as shown in FIG. 1, the graphene shows chemical changes. Referring to FIG. 1, when phenylhydrazine is added to graphene oxide and reacted for 24 hours at room temperature to reduce the residue, phenyl functional groups remain on the graphene surface to change chemically on the graphene surface. You can see that happens. Through the chemical change of the graphene surface it can be easily dispersed in a large dispersion concentration in various organic solvents.

Hereinafter, each step of the method for preparing a graphene compound having excellent dispersibility in the organic solvent of the present invention will be described in more detail.

First, graphene oxide for preparing a graphene compound is prepared.

In the present invention, the graphene oxide is formed by oxidizing graphite or expanded graphite (expanded graphite), for example, may be formed by oxidizing with sulfuric acid (H ₂ SO ₄ ) and potassium permanganate (KMnO ₄ ). The expanded graphite may be formed by thermally expanding the expandable graphite using electromagnetic waves. For example, expandable graphite can expand up to about 150 times the original graphite volume.

In addition, the concentration of graphene oxide may be 0.01 to 100 mg / ml, preferably 0.1 to 10 mg / ml, but is not limited thereto. For example, the concentration of the synthesized graphite oxide suspension may be dried in a vacuum atmosphere at 80 ° C. for 24 hours to about 4 mg / ml, and may be diluted to a concentration of 0.01 to 4 mg / ml by deionized water. have.

Next, the prepared graphene oxide and phenylhydrazine are mixed at a predetermined ratio, and a process of reducing the graphene oxide at room temperature is performed. Here, phenylhydrazine may be added in an amount of 10 to 10,000 parts by weight, and preferably 50 to 1,000 parts by weight, based on 100 parts by weight of graphene oxide.

The reduction time of graphene oxide depends on the concentration of graphene oxide and on the weight ratio of graphene oxide / phenylhydrazine, and the reduction time may be 1 to 240 hours, preferably 24 to 120 hours. The graphene oxide dispersion is brown or yellow depending on the concentration of graphene oxide, and gradually changes from brown or yellow to black as graphene oxide is reduced. In addition, the reduction temperature of the graphene oxide may be 0 ~ 100 ℃, preferably 20 ~ 30 ℃.

The graphene compound prepared as described above may exhibit a dispersion concentration of 0.1 mg / ml or more in an organic solvent, and preferably, a dispersion concentration of 0.5 to 10 mg / ml. When the dispersion concentration in the organic solvent is less than the above value, a large amount of organic solvent must be used, and there is a problem that the reactor volume, solvent recovery, and treatment process are inefficient. At this time, the graphene compound according to the present invention can be dispersed in all conventionally used organic solvents, for example, as an organic solvent, methanol, N, N'-dimethylformamide (N, N'-dimethylformamide; DMF ), 1-methyl-2-pyrrolidinone (NMP), propylene carbonate (PC), dimethylacetamide (DMAc), ethylene glycol, dimethylsulphoxide; DMSO) and the like, but is not limited thereto.

Meanwhile, the graphene compound prepared according to the method of the present invention may form a transparent and conductive graphene thin film by spray deposition, spin coating, or the like. The graphene thin film thus formed has excellent electrical conductivity and may be applied to various fields.

According to the present invention, by reducing the graphene oxide in one step using phenylhydrazine to prepare a graphene compound, graphene can be easily and stably dispersed in various organic solvents, without using water or a surfactant. Dispersion concentration can be realized and manufacturing cost can be reduced.

In addition, the graphene compound dispersible in the organic solvent of the present invention can be used to give a particularly high conductivity to the polymer, conductive polymer (conducting polymer), conductive thin film, polymer composition, metal oxide, semiconductor compound, conductive ink, Photocatalyst, battery, supercapacitor electrode, electromagnetic interference shielding (EMI), electrostatic charge dissipation (ESD), fuel cell bipolar electrode, thermal conductive nanocomposite, etc. .

Hereinafter, the present invention will be described in detail with reference to embodiments and drawings. However, these examples are intended to illustrate the present invention in more detail, and the scope of the present invention is not limited to these examples.

< Example  1>

Graphene  Synthesis of Compound

In order to prepare a graphene compound that can be directly dispersed in an organic solvent, the present inventors mixed 100 ml of a 4 mg / ml graphite oxide suspension and 3 ml of phenylhydrazine at room temperature for 24 hours to reduce graphite oxide. Pin dispersions were prepared. Next, the graphene dispersion was filtered and then washed several times with water, methanol and DMF to remove phenylhydrazine that remained without reaction. The filter cake of the graphene compound thus obtained can be easily redispersed in various organic solvents.

On the other hand, in order to compare the reducing effect of phenyl hydrazine, a graphene compound was prepared by reducing graphene oxide using hydrazine as a comparative example. Table 1 below compares the characteristics of using hydrazine and phenylhydrazine for the reduction of graphene oxide.

Comparison of Reduction Characteristics of Graphene Using Hydrazine and Phenylhydrazine Hydrazine Phenylhydrazine Reducing medium Water, water and DMF mixture Water, organic solvent Reduction temperature 80 to 100 ℃ Room temperature Reduction time 1 to 24 hours 24 hours Electrical Conductivity of Graphene Paper * Reduction in water
Air drying: 7,200 S / m
Dry at 220 ℃: 11,800S / m
* Reduction in water + DMF
Drying in the air: 1700 S / m
Dry at 150 ℃: 16,000 S / m Dry at 50 ℃: 4700 S / m
Dry at 150 ℃: about 21,000S / m Dispersion degree in water-soluble condition 0.5 mg / ml or less 0.25mg / ml Dispersion in organic solvent 0.3 mg / ml or less [water + DMF (1: 9 v / v)]
0.03mg / ml or less (other organic solvents) 0.6mg / ml or more (DMAc, DMF, PC)
1.0 mg / ml or more (NMP) Dispersion in methanol impossible possible

As shown in Table 1, in the case of using hydrazine, it can be dispersed in the organic solvent in the presence of water, it was found that the concentration of the stable dispersion is very low, less than 0.03 mg / ㎖. Therefore, a surfactant is required to stably disperse in a pure organic solvent.

However, in the case of using phenylhydrazine as in the present invention, it was found to be stably dispersed in a large concentration in an organic solvent without water or a surfactant, and in organic solvents such as DMAc, DMF, and PC, more than 0.6 mg / ml, in particular NMP has a large dispersion concentration of 1.0 mg / ml or more. In addition, in methanol, it was not possible to disperse by conventional hydrazine reduction, but it was possible to disperse by phenylhydrazine reduction.

< Example  2>

Graphene  Elemental Analysis of Compounds

We analyzed the element of the graphene compound. As a result, as shown in Table 2 below, the C / O atomic ratio was 1.68 in graphene oxide (GO), and the graphene compound (CCG) reduced in phenylhydrazine was 9.51, which was reduced in phenylhydrazine. It was confirmed that the C / O atomic ratio was increased.

In addition, the content of nitrogen (N) did not contain nitrogen in the case of graphene oxide, graphene compound (CCG) was found to contain about 3% by weight. Through this, it was confirmed that the N bond appears in the graphene compound (CCG) by the reduction of phenylhydrazine.

Elemental Analysis Result (Unit: Weight%) sample Carbon (C) Oxygen (O) Hydrogen (H) Nitrogen (N) C / O C / N Graphene oxide 54.53 43.29 2.18 0 1.68 n / a Graphene compounds 83.75 11.72 1.54 2.99 9.51 32.67

< Example  3>

Graphene  UV absorption peak of the compound

The present inventors measured the ultraviolet absorption peak (UV absorbance peak) using a UV-vis spectrometer to examine the structural change characteristics of the graphene compound prepared in Example 1, the results are shown in FIG.

As a result, referring to Figure 2, the ultraviolet absorption spectrum of graphene oxide (GO) showed a strong absorption peak (strong absorbance peak) at 234nm, it showed a medium absorbance peak (shoulder absorbance peak) at 300nm. When phenylhydrazine was added to graphene oxide, the ultraviolet absorption peak of graphene oxide gradually redshifted over time, and the ultraviolet absorption amount increased during the reaction in the entire spectral region. This result indicates that the conjugated C═C bond is recovered by reduction of phenylhydrazine. After 15 hours of the addition of phenylhydrazine, the ultraviolet absorption peak shifted to 270 nm, and after 15 hours the absorption was saturated indicating that the reduction was complete.

< Example  4>

Graphene  Compound XPS  spectrum

The present inventors measured the X-ray Photoelectron Spectroscopy (XPS) spectrum to analyze the structural change characteristics of the graphene compound prepared in Example 1, the results are shown in Figure 3 (a) to Figure 3 (e) It was.

As a result, referring to FIGS. 3 (a) and 3 (b), the C1s XPS spectrum of graphene oxide (GO) shows three kinds of peaks assigned to oxygen-generating functional groups such as hydroxy, epoxide and carbonyl groups. Shows.

3 (c) and 3 (d), after the reduction to phenylhydrazine, these peaks are also present in the C1s XPS spectrum of the graphene compound (CCG), but the intensity of the peak appears much weaker than that of graphene oxide. These results indicate that most of the oxygen-generating functional groups have been removed. In addition, deconvolution of the C1s spectrum of the graphene compound (CCG) shows a new peak at 285.8 eV corresponding to CN binding.

< Example  5>

Graphene  Raman spectrum of the compound

The present inventors measured the Raman spectrum in order to analyze the structural change characteristics of the graphene compound prepared in Example 1, the results are shown in FIG.

As a result, referring to Figure 4, the Raman spectra of graphene oxide (GO) appeared two peaks at 1328cm ^{- 1} and 1595cm ^-1 , which corresponds to the D and G bands, respectively. G peak of the CCG is 1583㎝ ^- was red shifted to ^1, which is consistent with the reduced GO previously reported. The I (D) / I (G) ratio of CCG increased to 1.50 compared to 1.27 of GO, indicating that many small SP ² regions were formed during the reduction.

< Example  6>

Graphene  X-ray of the compound diffraction ( XRD ) analysis

The present inventors performed X-ray diffraction (XRD) analysis to characterize the graphene compound prepared in Example 1, and the results are shown in FIG.

As a result, referring to FIG. 5, when reducing graphene oxide to hydrazine (N ₂ H ₂ ), there is a wide peak of about 23 °, which generally corresponds to d interval of 3.8 kPa. However, in the case of reducing graphene oxide to phenylhydrazine as in the present invention, a d interval peak corresponding to d interval 6.1 mm appears at 14.50 °. As such, an increase in the d interval of the graphene compound (CCG) reduced with phenylhydrazine is due to the phenyl group being grafted on the surface of the graphene compound as reduction occurs as compared with when reduced with hydrazine. Can be explained. Through such a change, the graphene compound reduced with phenylhydrazine can be stably dispersed in an organic solvent.

< Example  7>

In organic solvent Graphene  Determination of Solubility of Compounds

The present inventors measured the solubility of the graphene compound prepared in Example 1, the results are shown in Table 3 below.

In order to measure the solubility, the filter cake of the graphene compound (CCG) prepared in Example 1 was prepared using N, N'-dimethylformamide (DMF), 1-methyl-2-pyrrolidinone. It was redispersed by sonication for 90 minutes in various solvents such as (1-methyl-2-pyrrolidinone (NMP) and propylene carbonate (PC). The solubility of the graphene compound in various solvents was determined by the following two methods.

First, the graphene compound suspension was centrifuged at 3000 rpm for 15 minutes. Next, 10 ml of the supernatant was taken, dried at 120 ° C. for 5 hours, and weighed to determine solubility for 12 hours under vacuum at 70 ° C.

Second, the graphene compound suspension was stored for 24 hours instead of centrifugation.

As a result, the graphene compound (CCG) was highly dispersed in the polar solvent, the concentration of the graphene compound was 1 mg / ㎖ or more in the NMP solvent.

Solubility measurement result menstruum Solubility (mg / ml) Centrifugation (15 minutes, 3000 rpm) 24 hours storage N, N'-dimethylformamide (DMF) 0.675 0.752 1-methyl-2-pyrrolidinone (NMP) 1.015 1.046 Propylene Carbonate (PC) 0.748 0.798

Therefore, through the above results, it was confirmed that when the graphene oxide is reduced using phenylhydrazine, it is stably dispersed in various organic solvents without water or surfactant.

< Example  8>

Graphene  Conductivity Measurement of Compound

The present inventors measured the electrical conductivity of the graphene compound prepared in Example 1, wherein the electrical resistance of the graphene paper prepared by filtration of the graphene compound (CCG) in the DMF suspension was determined by the 4-probe station method. Was measured.

As a result, the electrical conductivity of the graphene paper dried at 50 ℃ was 4770S / m, while the electrical conductivity of the graphene paper dried at 150 ℃ was measured to 20950S / m.

Meanwhile, the thickness of the graphene paper was measured by SEM image of the cross section. Referring to FIG. 6, the thickness of the graphene paper was about 2.8 μm.

So far I looked at the center of the preferred embodiment for the present invention. Those skilled in the art will appreciate that the present invention can be implemented in a modified form without departing from the essential features of the present invention. Therefore, the disclosed embodiments should be considered in an illustrative rather than a restrictive sense. The scope of the present invention is shown in the claims rather than the foregoing description, and all differences within the scope will be construed as being included in the present invention.

Claims (6)

Preparing graphene oxide; And
Reduction by adding phenylhydrazine to the graphene oxide
Method for producing a graphene compound excellent in dispersibility in an organic solvent comprising a. The method of claim 1,
The phenylhydrazine is a method for producing a graphene compound having excellent dispersibility in an organic solvent, characterized in that added to 10 to 10,000 parts by weight based on 100 parts by weight of graphite oxide. The method of claim 1,
Reducing the addition of phenylhydrazine to the graphite oxide is a method for producing a graphene compound having excellent dispersibility in an organic solvent, characterized in that performed for 1 to 240 hours at a temperature of 0 ~ 100 ℃. The method of claim 1,
The graphene oxide is a method for producing a graphene compound having excellent dispersibility in an organic solvent, characterized in that formed by oxidizing graphite or expanded graphite (expanded graphite). The method of claim 1,
The concentration of graphene oxide is 0.01 ~ 100 A method for producing a graphene compound having excellent dispersibility in an organic solvent, characterized in that it is mg / ml. The method of claim 1,
The graphene compound is a method for producing a graphene compound excellent in dispersibility in an organic solvent, characterized in that having a dispersion concentration of 0.1 mg / ㎖ or more in an organic solvent.

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