KR20190117923A - Manufacturing method of graphene oxides - Google Patents

Abstract

The present invention relates to a method for manufacturing graphene oxides, comprising a step of heat treatment by mixing graphite and metal carbonate. The method for manufacturing graphene oxides according to the present invention can manufacture graphene oxides in a short time without using a strong acid. In addition, a product contained in oxide produced primarily contains metal ions, thereby allowing easy cleaning of impurities.

Description

Manufacturing method of graphene oxides

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

Graphene refers to a new material having a honeycomb structure in which carbon atoms are sp ² bonds. Such graphene has the advantages of transparency, electrical conductivity, thermal conductivity, and mechanical strength in comparison with thickness, and also has a wide surface area. According to these advantages, graphene is used in various advanced fields such as advanced electronic devices, sensors, supercapacitors, and solar cells, and related research is being actively conducted.

Such graphene production methods include mechanical peeling, chemical vapor deposition, epitaxial growth, and chemical reduction. Among these methods, a relatively low mass production method is possible by chemical reduction. Specifically, the chemical reduction method produces graphene oxide by oxidizing graphite, and then reduces the graphene oxide, thereby producing reduced graphene oxide (RGO). have.

Conventionally, the Hummer method (Hummer's method) or the Brodie method (Brodie's method) may be used to prepare graphene oxide. Recently, it has been common to use an improved Hummer method (Modified Hummer's method), which is an improvement of the Hummer method.

However, if the conventional method is used, high concentration sulfuric acid treatment may be problematic by performing oxidation reaction on concentrated sulfuric acid or nitric acid, and there is a risk of explosion due to exothermic reaction between concentrated sulfuric acid and water, and a large amount of wastewater is generated. For this reason, there is a problem that the purification process is very complicated.

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

CARBON 2013, 64, pp. 225-229

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

Another object of the present invention is to provide a graphene oxide production method that can economically produce graphene oxide in a short time.

Still another object of the present invention is to provide a method for producing graphene oxide, in which impurities are easily washed to simplify the cleaning process and hardly contain impurities.

Still another object of the present invention is to provide a method for producing graphene oxide, which minimizes the discharge of liquid waste in a dry process.

Still another object of the present invention is to provide a graphene oxide manufacturing method capable of producing a single layer of graphene oxide.

It is still another object of the present invention 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 graphene oxide manufacturing method according to an embodiment of the present invention, the heat treatment may be performed by a dry process.

In the graphene oxide manufacturing method according to an embodiment of the present invention, the heat treatment step of the heat treatment may be performed at 500 to 1200 ℃.

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

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

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

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

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

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

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

The present invention has the advantage that the graphene oxide can be produced in a short time without using a high concentration of acidic solution by heat-treating the graphite and metal carbonate in a dry process. In addition, there is an advantage in that it is possible to manufacture a single layer graphene oxide, which was difficult to find in the manufacture of graphene oxide except the Hummer's method. Furthermore, the product included in the oxide produced primarily includes metal ions, so that impurities can be easily cleaned.

Figure 1 shows the analysis of the surface of the graphene oxide prepared by the embodiment of the present invention.
FIG. 2 illustrates X-ray photoelectron spectroscopy (XPS) analysis of graphene oxide according to examples and comparative examples of the present invention.
Figure 3 shows the Raman spectrum of graphene oxide according to the Examples and Comparative Examples of the present invention.
Figure 4 shows the X-ray diffraction spectrum (XRD) of the graphene oxide according to the Examples and Comparative Examples of the present invention.
Figure 5 shows the thermal stability of the graphene oxide according to the Examples and Comparative Examples of the present invention.
6 is a graph illustrating the measurement and FT-IR of graphene oxide according to Examples and Comparative Examples of the present invention.
FIG. 7 shows examples of the present invention, a comparative example, and a measurement of contact angle, reflectance, and absorbance of reduced graphene, which are prepared by reducing them through heat treatment.

Hereinafter, a graphene oxide manufacturing method according to the present invention will be described in detail. In this case, unless there is another definition in the technical terms and scientific terms used, it has the meaning that is commonly understood by those of ordinary skill in the art, unnecessarily obscure the subject matter of the present invention in the following description Description of known functions and configurations that may be omitted.

Also, the singular forms used in the specification and the appended claims may be intended to include the plural forms as well, unless the context clearly indicates otherwise.

Units of% and ratio used without particular mention in the present invention mean weight% and weight ratio, and unless otherwise defined, means weight% of any one of the total compositions 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 mixing and heat treating graphite and metal carbonate.

The graphene oxide production method according to the present invention is capable of producing graphene oxide in a short time without using a strong acid such as sulfuric acid, nitric acid or phosphoric acid, and has the advantage of easy removal of impurities.

Specifically, Hummer's method, which is widely known in the art, is difficult to treat concentrated sulfuric acid discharged to waste liquid by performing an oxidation reaction on a solvent such as concentrated sulfuric acid, and there is a problem of causing environmental problems in the process of diluting it. Furthermore, Hummer's method, which is commonly used, requires a long reaction time of at least 2 hours, typically 8 hours or more, and thus requires a long time for synthesizing graphene oxide. There is a problem that sulfur may be included in the graphene oxide as impurities about 0.05 to 0.5%.

However, the graphene oxide manufacturing method according to the present invention does not require a strong acid does not cause the problem of the treatment of waste liquid, it is possible to reduce the waste liquid treatment costs additionally generated during the production of graphene oxide. In addition, it is possible to produce graphene oxide even by a heat treatment for a short time, there is an advantage that can produce a large amount of graphene oxide in a short time. Furthermore, the method for producing graphene oxide according to the present invention is an impurity included after the heat treatment of the graphite is a metal oxide, relatively easy to clean, there is an advantage that can produce a high purity graphene even by eliminating some of the cleaning process.

In the graphene oxide manufacturing method according to an embodiment of the present invention, the heat treatment may be performed by a dry process. Graphene oxide manufacturing method according to an embodiment of the present invention, by performing the oxidation reaction in a dry process without the above-mentioned strong acid solvent has the advantage of preventing the environmental pollution problem by strong acid, and minimize the waste fluid.

In addition, the Hummer's method has been used in the manufacture of graphene oxide in the prior art because it has the advantage of producing graphene oxide in a single layer despite environmental problems using a strong acid. However, the graphene oxide manufacturing method according to the present invention has a merit that a single layer of graphene oxide can be produced without the discharge of strong acid wastewater by a dry process, and the ratio of the reduced graphene oxide which is subsequently produced by such a single layer of graphene oxide There is an advantage that can significantly improve characteristics such as surface area and electrical conductivity.

Specifically, the heat treatment of the heat treatment step in the graphene oxide manufacturing method according to an embodiment of the present invention may be 500 to 1200 ℃, specifically 600 to 1000 ℃, more specifically 700 to 900 ℃. While improving the synthesis efficiency of graphene oxide in the above-described temperature range, there is an advantage that can be prevented from lowering the production efficiency of graphene oxide due to excessively high temperature.

Atmosphere in the heat treatment step may be used without limitation as long as the atmosphere containing oxygen, it may be air as one non-limiting example.

In the graphene oxide production method according to an embodiment of the present invention, the weight ratio of graphite to the metal carbonate mixed in the heat treatment step is 1: 1 to 10, specifically 1: 1 to 6, more specifically 1: 1 To 4 may be. While increasing the production yield of graphene oxide in the above-described range, it is possible to prevent the problem that impurities are contained in the graphene oxide to be produced later with excessive metal carbonate content. Further, 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 may be 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 one example of the Group 1 metal carbonate, the present invention is not limited thereto.

In the graphene oxide manufacturing method according to an embodiment of the present invention, the heat treatment step may be carried out without limitation during the time to produce the graphene oxide by the oxidation reaction of the graphite, for example may be performed for 10 minutes or more. Preferably 10 to 120 minutes, more preferably 20 to 80 minutes can be carried out but this is a preferred example and not limited thereto. Graphene oxide manufacturing method according to an embodiment of the present invention, unlike the conventionally known graphene oxide manufacturing method, it is possible to prepare a graphene oxide that does not cause a decrease in physical properties compared to the case of using a conventional strong acid even a short time of 80 minutes or less There are advantages to it.

In other words, the graphene oxide manufacturing method according to an embodiment of the present invention comprises the step of mixing the graphite and metal carbonate heat treatment in a short time, without the use of strong acid, it is possible to manufacture the graphene oxide in a simple method There is this.

In the graphene oxide manufacturing method according to an embodiment of the present invention, the graphite injected in the heat treatment step may perform the graphene oxide production reaction in various particle size range, the present invention is not limited to the particle size range of graphite. . Specifically, the graphite may have a particle size of 10 to 40000 μm, more specifically 30 to 2000 μm, but the present invention is not limited thereto. In addition, the metal carbonate added in the heat treatment step is melted at the reaction temperature in accordance with the process characteristics of the present invention, it is possible to produce graphene oxide without limiting the particle size.

The graphene oxide manufacturing method 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. In this case, the washing may use one or two or more selected from water, C1 to C4 alcohol and aqueous acid solution, and can be used without limitation in the case of a solution used for washing in general. More preferably, the graphene oxide manufacturing method according to an embodiment of the present invention may perform a cleaning step through a weakly acidic cleaning liquid in view of dissolving and removing metal oxides that are impurities included in the primary oxide. . Specifically, the metal oxide as 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 for removing the above-described metal oxide basic. Can be used. 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 in order to prevent a problem of impurities remaining in graphene oxide, but the present invention is not limited thereto. More preferably, in the graphene oxide production method according to an embodiment of the present invention, the washing step may be performed through an aqueous solution of inorganic acid of 0.5 to 5% by weight, preferably 0.5 to 3% by weight, and further, water and Alternately, the inorganic acid aqueous solution may be used for washing, but the present invention is not limited thereto.

The present invention also provides graphene oxide, the graphene oxide according to the present invention may be prepared by the graphene oxide production method 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 at a pH of 5 to 6 may be -20 to -50 mV. Preferably, it may be -30 to -50, more preferably -40 to -50, but is not limited thereto. This means that the surface potential is similar to graphene oxide prepared using Hummer's method or Modified Hummer's method, which is conventionally used, and that oxygen-containing functional groups are introduced into graphene through oxidation. That is, even if graphene oxide is produced without using a strong acid within a short time, graphene oxide having the same zeta potential can be prepared as compared to the conventional method, and thus, it is easily applied to various articles such as electronic devices, coating materials, and fibers. It can be used as applicable material.

The present invention also provides a method for producing reduced graphene oxide, the method for producing reduced graphene oxide according to the present invention includes reducing the 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 the reduction method of the commonly used graphene oxide, the present invention is not limited thereto.

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

Example 1

0.5 g of graphite having an average particle size of 2000 μm and 2.0 g of Li ₂ CO ₃ are added to an alumina crucible and mixed well. The mixed graphite and metal carbonate mixture is heat treated at 850 ° C. for 30 minutes. The heat treated reaction product is dissolved in water, washed once with centrifugation with water, and then washed once with 1 wt% hydrochloric acid. Again washed with centrifugation three times with water, and the washed graphene oxide is dried at room temperature or stored in a state dispersed in water.

Example 2

Prepared in the same manner as in Example 1, but instead of Li ₂ CO ₃ Na ₂ CO ₃ by mixing the same amount to prepare a graphene oxide.

Example 3

Prepared in the same manner as in Example 1, but instead of Li ₂ CO ₃ K ₂ CO ₃ by mixing the same amount to prepare a graphene oxide.

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 Modified Hummer's method using concentrated sulfuric acid as a solvent and potassium permanganate as an oxidant, and detailed conditions are summarized in Table 1.

[Comparative Example 4]

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

Determining the Carbon / Oxygen Ratio

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

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

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

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

Zeta potential  Measure

The zeta potential of graphene oxide prepared by Example 1 and Comparative Example 3 was measured by a surface potential meter (Zetasizer 3000HS, Malvern; 10mW) using a He-Ne laser of 633nm. Specifically, the zeta potential was measured under the conditions (pH = 5.5) in which the graphene oxides of Example 1 and Comparative Example 3 were dispersed in water at a concentration of 1 mg / mL, respectively, 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 zeta potential compared to the case of using the commonly used Modified Hummer's method. Based on this, it is possible to produce graphene oxide of similar properties without using a strong acid. can confirm. Furthermore, it can be seen that high purity graphene oxide can be produced by simple washing with a weak acid as in the example.

Graphene oxide  Surface analysis

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

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 in a single layer, which is difficult to derive from other methods except the conventional Hummers method, the graphene oxide of a single layer It can be expected that the graphene can be produced more excellent physical properties after reduction after the production.

Graphene oxide  Characterization

Graphene oxide prepared by the method according to Example 1, Example 2, Example 3 and Comparative Example 3 was subjected to C1s XPS (Thermo scientific, ESCA Probe), Raman analysis (Renishaw, 514 nm, Ar ⁺ ionlaser), X-ray Analyze by 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. To FIG. 6.

2 to 6, 1M ₂ X means Example 1, 2M ₂ X means Example 2, 3M ₂ X means Example 3, 2-1M ₂ X, 2-2M ₂ X, 2-3M ₂ X Was experimented by varying the weight ratio of graphite: Na ₂ CO ₃ , 2-1M ₂ X is 1: 1, 2-2M ₂ X is 1: 2, 2-3M ₂ X is 1: 3 mixed in a mixing ratio Means that.

Contact angle , Reflectance and absorbance measurements

MSGO and H-GO obtained in Example 1 and Comparative Example 3 were reduced by heat treatment at 400 ° C. to obtain reduced graphene oxide (MSrGO H-rGO), respectively, and they were formed into a sheet to form their contact angles, reflectances, and absorbances. Measured and shown in FIG.

Referring to the results of Figure 2, the graphene oxide prepared by Example 1 compared with the graphene oxide prepared by Comparative Example 3 carbon-carbon double bond peak of the carbon-oxygen bond formed by the oxidation reaction It is clearly distinguished from the peaks. In this distinctive form, Comparative Example 3 shows that various types of oxygen-containing functional groups are widely contained on the graphene molecules, and in Example 1, oxygen-containing functional groups are limited to specific functional groups, and thus are of fewer types. Suggesting that. In addition, when the peak value of the portion corresponding to the oxide of Example 1 is low, the ratio of carbon-carbon double bonds corresponding to the surface region in graphene, while the number of oxidized carbon relatively small compared to Comparative Example 3 Is high. On the other hand, it can be seen that the graphene oxide prepared through Example 1, which does not use a high concentration of acidic solution, is similar in terms of physical properties as compared with graphene oxide prepared using a conventional Hummer's method.

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

Referring to the XRD results of FIG. 4, it can be seen that diffraction peaks characteristic of graphene oxide at about 10 ° occur due to the intercalation as oxygen groups are introduced into the layers. Therefore, when combining the results of Figures 2 to 4 it can be seen that the present invention can produce a single layer graphene oxide at a level equivalent to the conventional Hummer's method.

Referring to the thermal stability test results of Figure 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 results of the FT-IR experiment of FIG. 6, Example 1 and Comparative Example 3 show various absorption peaks by oxygen-containing functional groups in common, and these results are consistent with those of FIGS. 2 to 4. will be. However, the graphene oxide prepared in Example 1 has a form in which the carbon-carbon double bond peak is more distinct from the peak of the carbon-oxygen bond formed by the oxidation reaction, compared to the graphene oxide prepared in Comparative Example 3. Is showing. In view of such a distinctive form, Comparative Example 3 suggests that the oxygen-containing functional group is limited to a specific functional group, and thus the type is smaller in comparison with the various types of oxygen-containing functional groups. It is consistent with the result of FIG.

As a result of Figure 7, it can be seen that the contact angle of the graphene oxide prepared in Example 1 compared to Comparative Example 3 is high, these results are shown to have a similar tendency even when the reduced graphene oxide is formed by reducing them, respectively. can confirm.

In terms of reflectance and absorbance, the reduced graphene oxide prepared by reducing the graphene oxide prepared according to the embodiment of the present invention may have a low reflectance and high absorbance. Black pigments with high absorbance and low reflectance can be applied to the display panel as a black matrix.

Claims (12)

Graphene oxide manufacturing method comprising the step of heat treatment by mixing the graphite and metal carbonate. The method of claim 1,
The heat treatment step is a graphene oxide manufacturing method performed by a dry process. The method of claim 1,
The heat treatment of the heat treatment step is a graphene oxide manufacturing method performed at 500 to 1200 ℃. The method of claim 1,
Graphite 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 included in the metal carbonate is a group 1 metal graphene oxide manufacturing method. The method of claim 1,
The heat treatment step is a graphene oxide manufacturing method that is performed for 10 minutes or more. The method of claim 1,
Graphene oxide manufacturing method further comprises a washing step of washing the primary oxide produced after the heat treatment step with 0.5 to 5% by weight aqueous solution of inorganic acid. Graphene oxide prepared by the method of any one of claims 1 to 7. The method of claim 8,
The graphene oxide is a graphene oxide graphene oxide is a carbon / oxygen atom ratio of 1.75 or more. The method of claim 8,
The graphene oxide has a zeta potential of -20 to -50 mV based on 1 mg of graphene oxide dispersed in 1 ml of water. A method for producing reduced graphene oxide having a high specific surface area comprising the step of reducing the graphene oxide prepared by the method of any one of claims 1 to 7. A conductive ink composition comprising the reduced graphene oxide of claim 11.

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