KR102151983B1 - Manufacturing method of graphene oxides - Google Patents

Abstract

The present invention relates to a method for producing graphene oxide comprising the step of heat-treating by mixing graphite and metal carbonate, and the method for producing graphene oxide according to the present invention can produce graphene oxide in a short time without using a strong acid. There is an advantage.

Description

Graphene oxide manufacturing method {Manufacturing method of graphene oxides}

The present invention relates to a method for producing graphene oxide for producing graphene oxide using a metal carbonate.

Graphene refers to a new material that has a honeycomb-shaped structure through sp ² bonds of carbon atoms. Such graphene has advantages in transparency, electrical conductivity, thermal conductivity, and mechanical strength compared to thickness, and has a wide surface area. According to these advantages, graphene is being used in various advanced fields such as advanced electronic devices, sensors, super capacitors, and solar cells, and related research is being actively conducted.

Methods of producing such graphene are largely classified into a mechanical exfoliation method, a chemical vapor deposition method, an epitaxial growth method, and a chemical reduction method. Among these, the method that can be produced in a relatively large quantity at low cost is the chemical reduction method. Specifically, the chemical reduction method oxidizes graphite to produce graphene oxide, and then reduces it again to produce reduced graphene oxide (RGO). Due to the nature of the process, it is easy to mass-produce graphene. have.

Conventional methods for producing graphene oxide include the Hummer's method or the Brodie's method, and recently, it has been common to use the Modified Hummer's method, which is an improved Hummer method.

However, in the case of using the existing method, the oxidation reaction is carried out over concentrated sulfuric acid or nitric acid, which may cause a problem of high concentration sulfuric acid treatment, and there is a risk of explosion due to an exothermic reaction between concentrated sulfuric acid and water, For this reason, there is a problem that the purification process becomes very complicated.

Accordingly, the prior art (CARBON 2013, 64, pp. 225-229) aims to provide an improved improved Hummer method, but there is still a problem of causing environmental problems by using concentrated sulfuric acid.

CARBON 2013, 64, pp. 225~229

An object of the present invention is to provide a graphene oxide production method capable of producing graphene oxide without using a high concentration acidic solution.

Another object of the present invention is to provide a method for producing graphene oxide which can economically produce graphene oxide within a short time.

Another object of the present invention is to provide a method for producing graphene oxide, which simplifies the cleaning process because impurities are easily cleaned, and hardly contains impurities.

Another object of the present invention is to provide a method for producing graphene oxide that minimizes the discharge of liquid waste through a dry process.

Another object of the present invention is to provide a method for producing graphene oxide capable of producing a single layer of graphene oxide.

Another object of the present invention is to provide high-quality graphene oxide and reduced graphene oxide with minimal defects.

The method for producing graphene oxide according to the present invention includes a step of heat treatment by mixing graphite and metal carbonate.

In the method for manufacturing graphene oxide according to an embodiment of the present invention, the heat treatment may be performed by a dry process.

In the method for producing graphene oxide according to an embodiment of the present invention, the heat treatment in the heat treatment step may be performed at 500 to 1200°C.

In the method for producing graphene oxide according to an embodiment of the present invention, the weight ratio of graphite: metal carbonate mixed in the heat treatment step may be 1:1 to 10.

In the method for producing graphene oxide according to an embodiment of the present invention, the metal included in the metal carbonate may be a Group 1 metal.

In the method for producing graphene oxide according to an embodiment of the present invention, the heat treatment step may be performed for 10 minutes or more.

In the method for producing graphene oxide according to an embodiment of the present invention, a washing step of washing the primary oxide generated after the heat treatment step with 0.5 to 5% by weight aqueous inorganic acid solution may be further included.

The present invention also provides graphene oxide, and the graphene oxide according to the present invention may be prepared by a method for producing graphene oxide according to an embodiment of the present invention.

Graphene oxide according to an embodiment of the present invention may have a carbon/oxygen atom ratio of 1.75 or more contained in graphene oxide.

In the method for producing graphene oxide according to an embodiment of the present invention, the graphene oxide may have a zeta potential of -20 to -50 mV based on 1 mg of graphene oxide dispersed in 1 ml of water.

The present invention also provides a method for producing reduced graphene oxide, and the method for producing reduced graphene oxide according to the present invention includes the step of reducing graphene oxide prepared by the method for producing graphene oxide according to an embodiment of the present invention. It may be manufactured by.

The present invention has the advantage that graphene oxide can be prepared within a short time without using a high concentration acidic solution by heat-treating graphite and metal carbonate under a dry process. In addition, there is an advantage of being able to manufacture single-layer graphene oxide, which was difficult to find in the production of graphene oxide except for the conventional Hummer's method. Furthermore, since the product contained in the primarily generated oxide includes metal ions, it is easy to clean impurities.

1 is a diagram illustrating the surface of graphene oxide prepared according to an embodiment of the present invention.
FIG. 2 shows an X-ray Photoelectron Spectroscopy (XPS) analysis of graphene oxide according to Examples and Comparative Examples of the present invention.
3 shows Raman spectra of graphene oxide according to Examples and Comparative Examples of the present invention.
4 shows an X-ray diffraction spectrum (XRD) of graphene oxide according to Examples and Comparative Examples of the present invention.
5 shows the thermal stability of graphene oxide according to Examples and Comparative Examples of the present invention.
6 is a graph showing and measuring FT-IR of graphene oxide according to Examples and Comparative Examples of the present invention.
FIG. 7 is a diagram illustrating an embodiment of the present invention, a comparative example, and measuring contact angles, reflectances, and absorbances made of reduced graphene prepared by reducing them through heat treatment, respectively.

Hereinafter, a method for producing graphene oxide according to the present invention will be described in detail. At this time, unless there are other definitions in the technical and scientific terms used, they have the meanings commonly understood by those of ordinary skill in the technical field to which this invention belongs, and unnecessarily obscure the subject matter of the present invention in the following description. Description of possible known functions and configurations will be omitted.

In addition, the singular form used in the specification and the appended claims may be intended to include the plural form unless otherwise indicated in the context.

The units of% and ratio used without particular mention in the present invention mean weight% and weight ratio, and unless otherwise defined, it means the weight% that any one component of the total composition occupies in the composition.

The method for producing graphene oxide according to the present invention includes a step of heat treatment by mixing graphite and metal carbonate.

The present invention provides a method for producing graphene oxide, and the method for producing graphene oxide according to the present invention includes a step of heat treatment by mixing graphite and a metal carbonate.

The method for producing graphene oxide according to the present invention has advantages in that it is possible to produce graphene oxide within a short time without using a strong acid such as sulfuric acid, nitric acid or phosphoric acid, and that impurities can be easily removed.

Specifically, conventionally known Hummer's method, etc., by performing an oxidation reaction in a solvent such as concentrated sulfuric acid, it is difficult to treat concentrated sulfuric acid discharged as a waste liquid, and causes environmental problems in the process of dilution. Furthermore, the commonly used Hummer's method requires a long reaction time of at least 2 hours, typically 8 hours or more, and has a problem that it takes a long time to synthesize graphene oxide, and is produced when concentrated sulfuric acid is used as a solvent. There is a problem in that the graphene oxide may contain about 0.05 to 0.5% of sulfur as an impurity.

However, the method for producing graphene oxide according to the present invention does not require a strong acid, so that a waste liquid treatment problem does not occur, and a waste liquid treatment cost additionally generated during the production of graphene oxide can be reduced. In addition, since it is possible to manufacture graphene oxide even by heat treatment for a short time, there is an advantage that a large amount of graphene oxide can be produced within a short period of time. Further, the method for producing graphene oxide according to the present invention has the advantage of being able to produce graphene oxide with high purity even if the impurities contained after the heat treatment of graphite are metal oxides, so that cleaning is relatively easy, and a part of the cleaning process is omitted.

In the method for manufacturing graphene oxide according to an embodiment of the present invention, the heat treatment may be performed by a dry process. The graphene oxide production method according to an embodiment of the present invention has an advantage of preventing environmental pollution problems caused by strong acids and minimizing waste liquid by performing an oxidation reaction in a dry process without the above-described strong acid solvent.

In addition, a number of Hummer's methods have been used for the production of conventional graphene oxide because it has the advantage of being able to manufacture a single layer of graphene oxide despite environmental problems using strong acids. However, the method for producing graphene oxide according to the present invention has the advantage of being able to produce a single layer of graphene oxide without discharge of strong acid wastewater by a dry process, and the ratio of reduced graphene oxide to be produced later with such a single layer of graphene oxide. There is an advantage of being able to remarkably improve properties such as surface area and electrical conductivity.

Specifically, in the method for producing graphene oxide according to an embodiment of the present invention, the heat treatment in the heat treatment step may be 500 to 1200°C, specifically 600 to 1000°C, and more specifically 700 to 900°C. While improving the synthesis efficiency of graphene oxide in the above-described temperature range, there is an advantage of preventing a decrease in production efficiency of graphene oxide due to excessively high temperature.

In the heat treatment step, the atmosphere may be used without limitation as long as it is an atmosphere containing oxygen, and may be air as a non-limiting example.

In the graphene oxide production method according to an embodiment of the present invention, the weight ratio of the graphite: metal carbonate mixed in the heat treatment step is 1:1 to 10, specifically 1:1 to 6, more specifically 1:1 It may be to 4. While increasing the production yield of graphene oxide within the above-described range, it is possible to prevent a problem in which impurities are contained in graphene oxide to be produced later due to an excessive metal carbonate content. Furthermore, the metal included in the metal carbonate may be a Group 1 metal, specifically one or two or more selected from lithium, sodium and potassium, and more specifically, the metal carbonate is Li ₂ CO ₃ , Na ₂ CO ₃ and K It may be one or two or more selected from ₂ CO ₃ , but this is only an example of a Group 1 metal carbonate, and the present invention is not limited thereto.

In the method for producing graphene oxide according to an embodiment of the present invention, the heat treatment step may be performed without limitation for a period of time during which graphene oxide can be generated by the oxidation reaction of graphite, and for example, may be performed for 10 minutes or more. Preferably, it may be performed for 10 minutes to 120 minutes, more preferably 20 to 80 minutes, but this is only a preferred example and is not limited thereto. The graphene oxide manufacturing method according to an embodiment of the present invention, unlike the conventionally known graphene oxide manufacturing method, can produce graphene oxide that does not deteriorate physical properties compared to the case of using a conventional strong acid even in a short time reaction of 80 minutes or less. There is an advantage to be able to.

In other words, the method for producing graphene oxide according to an embodiment of the present invention includes the step of heat-treating graphite and metal carbonate in a short time, so that it is possible to produce graphene oxide by a simple method without using a strong acid. There is this.

In the graphene oxide production method according to an embodiment of the present invention, the graphite input in the heat treatment step may perform a graphene oxide production reaction in various particle size ranges, and the present invention is not limited to the particle size range of graphite. . Specifically, the particle size of the graphite may be 10 to 40000 µm, more specifically 30 to 2000 µm, but the present invention is not limited thereto. In addition, since the metal carbonate introduced in the heat treatment step is melted at the reaction temperature due to the process characteristics of the present invention, it is possible to manufacture graphene oxide without limiting the particle size.

The method of manufacturing graphene oxide according to an embodiment of the present invention may further include a cleaning step of cleaning the primary oxide generated through the heat treatment after the heat treatment step. At this time, one or two or more selected from water, C1 to C4 alcohol and acid aqueous solution may be used, and in the case of a solution commonly used for washing, it can be used without limitation. More preferably, the method for producing graphene oxide according to an embodiment of the present invention may perform a cleaning step through a weakly acidic cleaning solution from the viewpoint of dissolving and removing metal oxide, which is an impurity that may be included in the primary oxide. . Specifically, the metal oxide, which is an impurity that may be included in the primary oxide, may be one or two or more selected from Li ₂ O, Na ₂ O and K ₂ O, and a weakly acidic cleaning solution to remove the above-described basic metal oxide You can use In this case, the acid compound included in the weakly acidic cleaning solution may specifically use inorganic acids such as hydrochloric acid, nitric acid, sulfuric acid, or phosphoric acid to prevent the problem of impurities remaining in graphene oxide, but the present invention is not limited thereto. More preferably, in the method for producing graphene oxide according to an embodiment of the present invention, the washing step may be performed through an aqueous inorganic acid solution of 0.5 to 5% by weight, preferably 0.5 to 3% by weight, and furthermore, water and The inorganic acid aqueous solution may be alternately used for washing, but the present invention is not limited thereto.

The present invention also provides graphene oxide, and the graphene oxide according to the present invention may be prepared by the method for producing graphene oxide according to an embodiment of the present invention.

Graphene oxide according to an embodiment of the present invention may have a carbon/oxygen atom ratio of 0.1 to 3.0, more specifically 0.15 to 2. In addition, the zeta potential of the aqueous solution of graphene oxide may be -20 to -50 mV under the condition of pH 5 to 6. Preferably, it may be -30 to -50, more preferably -40 to -50, but is not limited thereto. This means that the oxygen-containing functional groups are introduced into graphene through an oxidation reaction, as compared to graphene oxide prepared using the Hummer's method or the Modified Hummer's method, which has been widely used in the past. That is, even if graphene oxide is produced without using a strong acid within a short period of time, graphene oxide having an equivalent level of zeta potential compared to the conventional method can be produced, and through this, it can be easily applied to various products such as electronic devices, coating materials, and fibers. It suggests that it can be used as an applicable material.

The present invention also provides a method for producing reduced graphene oxide, and the method for producing reduced graphene oxide according to the present invention includes the step of reducing graphene oxide prepared by the method for producing graphene oxide according to an embodiment of the present invention. do. In this case, the reduction can be used without limitation in the case of a method of reducing graphene oxide that is commonly used, and the present invention is not limited thereto.

Hereinafter, the present invention will be described in detail by examples. The embodiments described below are only to aid understanding of the invention, and the present invention is not limited to the embodiments.

[Example 1]

0.5 g of graphite with an average particle size of 2000 µm and 2.0 g of Li ₂ CO ₃ were put in an alumina crucible and mixed well. The mixed graphite and metal carbonate mixture was heat-treated at 850° C. for 30 minutes. The reactant after heat treatment is dissolved in water, washed once by centrifugation with water, and washed once with 1% by weight hydrochloric acid. Wash again by centrifugation three times with water, and the washed graphene oxide is dried at room temperature or stored in a dispersed state in water.

[Example 2]

It was prepared in the same manner as in Example 1, but graphene oxide was prepared by mixing the same amount of Na ₂ CO ₃ instead of Li ₂ CO ₃ .

[Example 3]

It was prepared in the same manner as in Example 1, but graphene oxide was prepared by mixing the same amount of K ₂ CO ₃ instead of Li ₂ CO ₃ .

[Comparative Example 1]

Graphene oxide was prepared using Brodie's method, and detailed conditions are summarized in Table 1.

[Comparative Example 2]

Graphene oxide was prepared using the Hummer's method, and detailed conditions are summarized in Table 1.

[Comparative Example 3]

Graphene oxide was prepared using a Modified Hummer's method using concentrated sulfuric acid as a solvent and potassium permanganate as an oxidizing agent, and detailed conditions are summarized in Table 1.

[Comparative Example 4]

Graphene oxide was prepared using a Modified Hummer's method using concentrated sulfuric acid as a solvent and potassium permanganate and sodium nitrate as oxidizing agents, and detailed conditions are summarized in Table 1.

Measurement of carbon/oxygen atomic ratio (C/O ratio)

Graphene oxide prepared according to Example 1 and Comparative Examples 1 to 4 was analyzed through elemental analysis, and the results are shown in Table 1.

At this time, the elemental analyzer was measured using Flash 1112, Thermo Fisher Scientific, Germany, and each element was oxidized by the dynamic flash combustion method and quantified with a TCD detector, and each element was separated through a column and graphene oxide. The ratio of elements was calculated by determining the amount (%) of C, O, H, and N contained in.

Referring to Table 1, it can be seen that the carbon/oxygen atomic ratio of graphene oxide prepared according to Example 1 of the present invention is not significantly different from the case of using an acid solvent such as concentrated sulfuric acid.

menstruum Oxidant Reaction time impurities Waste liquid discharge Carbon/oxygen atomic ratio Example 1 -
(Dry process) Li ₂ CO ₃ 30 minutes Li ₂ O About 3L 1.82 Example 2 -
(Dry process) Na ₂ CO ₃ 30 minutes Na ₂ O About 3L 0.67 Example 3 -
(Dry process) K ₂ CO ₃ 30 minutes K ₂ O About 3L 0.18 Comparative Example 1 H ₂ SO _4,
HNO ₃ KClO ₃ 10 hours ClO ₂ About 10L 2.16 Comparative Example 2 H ₂ SO ₄ NaNO ₃ ,
KMnO ₄ 2-8 hours NO _x ,
Mn ₂ O ₇ About 10L 2.25 Comparative Example 3 H ₂ SO ₄ KMnO ₄ 8 hours Mn ₂ O ₇ About 10L 1.68 Comparative Example 4 H ₂ SO ₄ NaNO ₃ ,
KMnO ₄ 120 hours NO _x ,
Mn ₂ O ₇ About 10L 2.23

Zeta potential Measure

The zeta potential of the graphene oxide prepared according to Example 1 and Comparative Example 3 was measured using a surface potential meter (Zetasizer 3000HS, Malvern; 10mW) using a 633 nm He-Ne laser. Specifically, the zeta potential was measured under conditions in which graphene oxide of Example 1 and Comparative Example 3 was dispersed at a concentration of 1 mg/mL in water (pH=5.5), and the results are shown in Table 2.

Zeta potential (mV) Example 1 -43.5 Comparative Example 3 -44.2

Referring to Table 2, it can be seen that there is no significant difference in the zeta potential compared to the case of using the commonly used Modified Hummer's method, and based on this, graphene oxide with similar physical properties can be produced without using a strong acid. can confirm. Furthermore, it can be seen that graphene oxide having high purity can be prepared only by simple washing with a weak acid as in the example.

Graphene oxide Surface analysis

The surface of graphene oxide prepared by the method according to Example 1 was analyzed by AFM (atomic force microscope), TEM (transmission electron microscope), and SEM (scanning electron microscope), and is shown in FIG. 1.

Referring to Figure 1, it can be seen that the graphene oxide prepared by the method according to Example 1 of the present invention is formed as a single layer, which is an effect that is difficult to deduce in other methods except for the conventional Hummers method, and is a single layer of graphene oxide. It can be predicted that graphene having more excellent physical properties can be prepared after reduction by manufacturing.

Graphene oxide Characterization

Graphene oxide prepared by the method according to Example 1, Example 2, Example 3, and Comparative Example 3 was C1s XPS (Thermo scientific, ESCA Probe), Raman analysis (Renishaw, 514 nm, Ar ⁺ ionlaser), X-ray Analysis through diffraction analysis (Rigaku Ultima IV X-ray diffractometer with Cu Kα radiation at a scanning rate of 5°C min ^-1 ), thermal stability analysis, and FT-IR (FT-IR-2501PC, SHIMADZU), respectively, Fig. 2 To Figure 6.

In Figures 2 to 6, 1M ₂ X refers to Example 1, 2M ₂ X refers to Example 2, 3M ₂ X refers to Example 3, 2-1M ₂ X, 2-2M ₂ X, 2-3M ₂ X Is a graphite: Na ₂ CO ₃ experiment with different weight ratios, 2-1M ₂ X is 1:1, 2-2M ₂ X is 1:2, 2-3M ₂ X is mixed at a mixing ratio of 1:3. Means that.

Contact angle , Reflectance and absorbance measurement

MSGO and H-GO obtained in Example 1 and Comparative Example 3 were reduced by heat treatment at 400° C. to obtain reduced graphene (MSrGO H-rGO), respectively, and formed in a sheet shape to determine their contact angle, reflectance and absorbance. Measured and shown in Figure 7.

Referring to the results of Figure 2, the graphene oxide prepared by Example 1 compared to the graphene oxide prepared by Comparative Example 3, the carbon-carbon double bond peak of the carbon-oxygen bond formed by the oxidation reaction. It shows a clearly distinct shape from the peak. In terms of this distinct form, Comparative Example 3 shows that various types of oxygen-containing functional groups are widely included on the graphene molecule, and in Example 1, the oxygen-containing functional groups are limited to specific functional groups, and thus there are fewer types. Suggests that. In addition, when it is seen that the peak value of the portion corresponding to the oxide of Example 1 is low, compared to Comparative Example 3, the number of oxidized carbons is relatively small, but the ratio of carbon-carbon double bonds corresponding to the surface area of graphene Can be confirmed that is high. On the other hand, it can be seen that the graphene oxide prepared in Example 1 in which a high concentration acidic solution is not used is similar in physical properties compared to the graphene oxide prepared using the conventional Hummer's method.

Referring to the results of FIG. 3, the graphene oxide prepared according to Example 1 shows a Raman absorption peak most similar to the graphene oxide prepared using the Hummer’s method.

Referring to the XRD results of FIG. 4, as oxygen functional groups are introduced between layers, delamination occurs, and a diffraction peak characteristic of graphene oxide at about 10° can be confirmed. Accordingly, when the results of FIGS. 2 to 4 are summarized, it can be seen that the present invention can produce graphene oxide at the level of a single layer at the same level as the conventional Hummer's method.

Referring to the results of the thermal stability experiment of FIG. 5, it can be seen that the graphene oxide produced by Example 1 exhibits the most similar behavior to the graphene oxide prepared using the conventional Hummer's method of Comparative Example 3.

Referring to the FT-IR experiment results of FIG. 6, Example 1 and Comparative Example 3 commonly show various absorption peaks due to oxygen-containing functional groups, and these results are consistent with the results of FIGS. 2 to 4. will be. However, the graphene oxide prepared by Example 1 has a more distinct form from the peak of the carbon-oxygen bond formed by the oxidation reaction in the carbon-carbon double bond peak compared to the graphene oxide prepared by Comparative Example 3. Showing. In view of this distinct form, Comparative Example 3 contains various types of oxygen-containing functional groups, whereas Example 1 suggests that the oxygen-containing functional groups are limited to specific functional groups, and thus there are fewer types. This is consistent with the results of FIG. 2.

From the results of FIG. 7, it can be seen that the contact angle of the graphene oxide prepared in Example 1 is higher than that of Comparative Example 3, and these results show a similar tendency even when each of them is reduced to form reduced graphene oxide. can confirm.

In terms of reflectance and absorbance, it can be seen that the reduced graphene prepared by reducing the graphene oxide prepared according to the embodiment of the present invention has a low reflectance and a high absorbance. It is believed that a black pigment with high absorbance and low reflectivity can be applied as a black matrix to a display panel.

Claims (12)

Mixing graphite and metal carbonate and performing heat treatment in an atmosphere containing oxygen by a dry process without a strong acid solvent; And washing the primary oxide generated after the heat treatment step with an aqueous 0.5 to 5% by weight inorganic acid aqueous solution. delete The method of claim 1,
The heat treatment in the heat treatment step is performed at 500 to 1200 ℃ graphene oxide manufacturing method. The method of claim 1,
Graphene mixed in the heat treatment step: the weight ratio of the metal carbonate is 1:1 to 10 graphene oxide production method. The method of claim 1,
The metal contained in the metal carbonate is a group 1 metal, graphene oxide production method. The method of claim 1,
The heat treatment step is a method for producing graphene oxide performed for 10 minutes or more. delete delete delete delete A method for producing reduced graphene oxide comprising the step of reducing the graphene oxide prepared by the method of any one of claims 1 and 3 to 6. delete

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