KR20170140907A - Method for fabricating reduced graphene oxide and its suspension - Google Patents

Abstract

Disclosed are methods of preparing reduced graphene oxide and a suspension of the same. According to one example, an aqueous graphite oxide (GO) solution containing glucose is prepared, and is subjected to a hydrothermal process to produce a reduced graphene oxide (RGO) gel. The RGO gel is then dispersed in an aqueous acetic acid solution, and water is removed therefrom to produce an RGO powder. Further, the RGO powder is added to a solvent containing dimethylformamide (DMF) and deionized (DI) water, and is subjected to ultrasonication for dispersing the RGO powder to produce an RGO suspension.

Description

TECHNICAL FIELD The present invention relates to a reducing graphene oxide and a suspension of the same,

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a technology for producing Reduced Graphene Oxide (RGO), and more particularly to a technique for producing RGO and its suspension.

The graphene has a two-dimensional monolayer structure in which carbon atoms are sp ² bonded to form a hexagonal honeycomb lattice. Graphene has not only a very large surface area per unit volume, but also excellent electrical conductivity and chemical stability, and thus attracts much attention in the field of electronic materials. Graphene, for example, has a very high intrinsic electron mobility, allowing electrons to move more than 100 times faster than silicon. In addition, graphene exhibits high visible light transmittance and does not lose its electrical properties even if it is physically deformed (e.g., bending or stretching). Due to these properties, graphene has received great attention as a material that can be applied to transparent conductive coatings, electronic devices, sensors, supercapacitors, batteries, solar cells, heat dissipation materials, smart window materials and transistors.

As a method of producing graphene, a mechanical peeling method, a chemical vapor deposition (CVD) method, an epitaxial growth method, a chemical reduction method, and the like are known. The mechanical peeling method is a method of obtaining graphene from a graphite sample using the adhesive force of the tape. The chemical vapor deposition method is a method of synthesizing graphene by using a transition metal which forms carbon or carbide alloy well at high temperature or adsorbs carbon well as a catalyst layer. The epitaxial growth method is a method of forming graphene on a silicon carbide substrate through pyrolysis of single crystal silicon carbide under high vacuum. In the chemical reduction method, graphite oxide (GO), which is oxidized graphite, is dispersed in a solvent and then reduced to obtain graphene, that is, reduced graphene oxide (RGO).

Among the above methods, the chemical reduction method is known as a typical graphene synthesis method capable of obtaining a large amount of high quality graphene. Among the chemical reduction methods, hydrothermal synthesis is the most common synthesis method. For example, Korean Patent Publication No. 10-2011-0121584, "Transition metal oxide / graphene complex using microwave-hydrothermal synthesis method and its production method ", discloses a transition metal oxide / Is disclosed.

However, when reducing graphene oxide (RGO) is produced using a chemical reduction method, it is not easy to remove the oxide group therein. As a way to overcome such disadvantages, a method of using a reducing agent as a predetermined reagent capable of efficiently reducing graphite oxide (GO) has been proposed. Hydrazine (N2H4), hydrazine hydrate (N2H4.H2O), and sodium borohydrate (NaBH4) are used as typical reducing agents. However, since these reducing agents are highly toxic, the produced RGO is not suitable for use in the biotechnology field, and has a problem of deteriorating the characteristics of graphene even by a small amount of residual impurities.

RGO produced by the hydrothermal method is usually in the form of a solid phase, that is, an RGO gel, by aggregation. Such RGO gels are difficult to utilize for the production of fine patterns or thin films of MEMS devices by utilizing graphene. Therefore, the RGO gel is usually dispersed in a predetermined solvent to be formed into a suspension to be used for producing a fine pattern constituting the device. However, in order to prepare a graphene thin film or transition metal oxide / graphene composite having excellent electrical properties, the dispersity of the RGO suspension must be high.

Korean Patent Publication No. 10-2011-0121584 Korean Patent No. 10-1485857

One of the problems to be solved by the present invention is to provide a reducing graphene oxide and a reducing graphene oxide which can efficiently remove remaining oxide groups without using a toxic substance as a reducing agent in the production of reduced graphene oxide (RGO) And to provide a method for producing a suspension thereof.

Another object to be solved by the present invention is to provide reduced graphene oxide having a very high dispersity and being applicable to the production of a device having a fine pattern and a method for producing a suspension thereof.

According to an aspect of the present invention, there is provided a method for preparing reduced graphene oxide comprising preparing an aqueous solution of graphite oxide (GO) to which glucose is added, adding a hydrothermal process ) To obtain a reduced graphene oxide (RGO) gel, and dispersing the RGO gel in an aqueous acetic acid solution to remove moisture to obtain an RGO powder.

According to an embodiment of the present invention, the weight ratio of the GO to the glucose may be 1: 0.001 to 1:36.

According to another aspect of the embodiment, the hydrothermal process may be performed at a temperature of 160 to 185 ° C. for 2 to 4 hours.

According to another aspect of the embodiment, the concentration of the aqueous acetic acid solution may be 0.05 to 2 M (mol).

According to an aspect of the present invention, there is provided a method for preparing a reduced graphene oxide suspension, comprising preparing an aqueous solution of graphite oxide (GO) to which glucose is added, adding hydrothermal (RGO) gel is obtained by applying an RGO gel to an aqueous solution of acetic acid, followed by dispersing the RGO gel in an aqueous solution of acetic acid and then removing moisture to obtain an RGO powder, and then adding dimethylformamide (DMF) And deionized water (DI water), and performing ultrasonication so that the RGO powder is dispersed in the solvent.

According to an embodiment of the present invention, the dimethylformamide and the deionized water may be mixed at a volume ratio of 1: 1.

According to the embodiment of the present invention described above, glucose and acetic acid are used as reducing agents to produce RGO from GO. As a result, since toxic substances are not used for the reduction of GO, it can be more usefully used for a biosensor such as a biosensor. And RGO have a very small particle size and are evenly dispersed with a very high dispersion so that they can be usefully used for producing devices having a fine pattern such as a micron scale or less.

BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 is a flow chart illustrating a method of making reduced graphene oxide and a suspension thereof, according to one embodiment of the present invention.
Figures 2a and 2b are diagrams schematically illustrating a process for preparing RGO and RGO suspensions, respectively.
3A and 3B are FESEM images of a graphene thin film using an RGO suspension prepared according to a conventional method and a graphene thin film using an RGO suspension prepared according to an embodiment of the present invention, respectively.

BRIEF DESCRIPTION OF THE DRAWINGS Fig. However, these drawings are only an example for easily describing the content and scope of technical ideas, and thus the technical scope thereof is not limited or changed. It will be apparent to those skilled in the art that various changes and modifications can be made within the scope of the technical idea based on these examples. Also, terms and words used in the present specification are terms selected in consideration of the functions in the embodiments, and the meaning of the terms may vary depending on the user, the intention or custom of the operator, and the like. Therefore, the terms used in the following embodiments are defined according to their definitions when they are specifically defined in this specification, and in the absence of a specific definition, they should be construed in a sense generally recognized by ordinary artisans. And if it is assumed herein that the first layer of material is formed on the second layer of material, it is understood that not only is the layer of first material formed directly on the second layer of material, Unless otherwise stated, it should be understood that all other third material layers are interposed between the first material layer and the second material layer (upper).

BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 is a flow chart illustrating a method of making Reduced Graphene Oxide (RGO) and its suspension according to one embodiment of the present invention. And Figures 2a and 2b are diagrams schematically illustrating a process for preparing RGO and RGO suspensions, respectively.

Referring first to FIG. 1, an aqueous solution of graphite oxide (GO) to which glucose is added is first prepared (S11). More specifically, the GO aqueous solution is first prepared in a predetermined vessel (for example, a beaker). At this time, ultrasonic treatment can be performed so that GO is dispersed evenly in water as a solvent. Then, a predetermined amount of glucose is added to the GO aqueous solution, and stirring can be performed so that the added glucose is mixed well with the aqueous GO solution.

According to one aspect of this embodiment, the glucose may be added in a relatively small amount or in an amount in excess. For example, the glucose may be mixed into the GO aqueous solution at a ratio of 1: 0.001 to 1: 36, based on the weight of the GO. Preferably, the glucose may be mixed at a ratio of 1:10 to 1:20, more preferably 1:18, based on the weight of the GO. If the glucose is mixed at a ratio of 1:20, preferably 1:18, the final product, an impurity of reduction agent that is not reactive with RGO, may remain. On the other hand, when the glucose is mixed at a ratio of less than 1:10, preferably 1:18, the time required to reduce GO, ultimately the time required to produce RGO, may be prolonged.

Then, a hydrothermal process in which the prepared GO aqueous solution prepared in step S11 is heated at a predetermined temperature for a predetermined time is applied to obtain Reduced Graphene Oxide (RGO) gel S12). Through the hydrothermal process, the carbohydrate (glucose) molecules are converted into homogeneous carbon nanospheres and nanotubes, and the substitution of RGO at the defect site occurs. The resultant RGO gel (see FIG. 2a) is not in a dry state but in a wet state, indicating that RGO is in a solid state. As an example, in the case of using about 52 mg of GO in step S11, the RGO gel obtained in step S12 can be about 28 mg.

According to this embodiment, the hydrothermal processing can be performed by any kind of apparatus commonly used in the art. For example, an apparatus such as an autoclave as shown in FIG. 2A may be used for the sequence, but there is no particular limitation on the type of manufacturer. According to one aspect of the present invention, a hydrothermal process or a synthesis process using an autoclave (see FIG. 2A) can be performed at a temperature of 160 to 185 ° C for 2 to 4 hours. Preferably, the hydrothermal process can be carried out at a temperature of about 180 DEG C for 2 hours. Typically, carbohydrates are known to transfer carbon at temperatures of 180 ° C or higher. However, when the temperature is too high in the hydrothermal process, the process is unsafe. On the other hand, if the temperature is too low, the reduction reaction of GO may not occur smoothly.

Then, the RGO gel obtained in step S12 is dispersed in a predetermined acidic aqueous solution such as an aqueous acetic acid solution (RGO disperse in acid solution, see FIG. 2A), and water is removed to obtain RGO powder (S13). At this time, ultrasonic treatment may be further performed so that the RGO gel can be uniformly dispersed evenly in the aqueous acetic acid solution. RGO powder can be obtained by removing water by a method known in the art. Here, the RGO powder may be referred to as RGO platelets or RGO particles with RGO in the form of small pieces (denoted acRGO Platelets in Figures 2a and 2b) .

According to one aspect of this embodiment, the aqueous acetic acid solution may have a concentration of about 0.05 to 2M, preferably about 1M. The preferred concentration of such an aqueous acetic acid solution is a relatively mild condition so that the finally obtained RGO is suitable for use in the biotechnology field. This is because, when the concentration of the acetic acid aqueous solution is relatively large, acetic acid may remain as an impurity in the RGO powder as the final product. On the other hand, when the concentration of acetic acid is relatively small, impurities such as glucose remaining can not be effectively removed.

As described above, according to the embodiment of the present invention, an RGO gel is synthesized using a hydrothermal method, and the GO aqueous solution to which glucose is added is hydrothermally treated. Finally, the RGO gel obtained through the hydrothermal treatment may be finally added to a weakly acidic aqueous solution such as an aqueous acetic acid solution, and then dispersed using ultrasound treatment or the like to finally obtain powdery RGO. And, RGO produced through the treatment with glucomac and acetic acid can be more usefully used in biotechnology such as biosensor because it does not use toxic substances for reduction of GO.

1, the RGO powder prepared in step S13 is placed in a solvent mixed with dimethylformamide (DMF) and deionized water (DI water), and then subjected to ultrasonic treatment to disperse the RGO ultrasonication is performed (S14). As a result, an RGO suspension in which RGO is evenly dispersed in a mixed solution of DMF and deionized water is produced.

2B, the RGO gel obtained as a result of step S12, that is, the RGO gel before being treated in an acidic solution, is subjected to an acidic treatment with an acidic solution to obtain an RGO powder (acRGO Platelets ). Then, the RGO powder is put into a predetermined container (for example, a beaker), and DMF and deionized water are then charged into the container at a ratio of 1: 1 and further subjected to ultrasonic treatment to form an RGO suspension.

Substantially RGO can be said to be a kind of surfactant. Because RGO has a hydrophilic part and a hydrophobic part. Therefore, a mixture of DMF and deionized water is suitable for making an RGO solution, that is, an RGO suspension. According to one aspect of the present invention, the mixing ratio of DMF and deionized water does not necessarily have to be 1: 1. However, in order to mix the RGO suspension more well and to better deposit the RGO in the manufacturing process of the fine device, It is preferable that the volume mixing ratio of the ionized water is 1: 1.

The RGO suspension prepared by the above method has a very small particle size of RGO and is evenly dispersed with a very high dispersion degree. Thus, the RGO suspension can be usefully used to produce fine patterns utilizing graphene, such as devices with micron-scale or smaller scales (e.g., small devices such as MEMS devices).

3A and 3B are FESEM images of a graphene thin film using an RGO suspension prepared according to a conventional method and a graphene thin film using an RGO suspension prepared according to an embodiment of the present invention, respectively. 3A, a graphene thin film formed from an RGO suspension formed according to the conventional method, as indicated by a circle on the image, is not properly dispersed in the RGO suspension to clog the surface of the graphene thin film, As shown in FIG. On the other hand, referring to FIG. 3B, it can be seen that the graphene thin film formed from the RGO suspension formed according to the method of the present invention has uniform characteristics over the entire surface.

The above description is only an example and should not be construed as being limited thereto. It is to be understood that the technical spirit of the present invention should be defined only by the invention disclosed in the claims, and all technical ideas within the scope of equivalents thereof should be construed as being included in the scope of the present invention. Therefore, it is apparent to those skilled in the art that the above-described embodiments can be modified and implemented in various forms.

Claims (7)

Preparing an aqueous solution of graphite oxide (GO) to which glucose is added;
Applying a hydrothermal process to the GO aqueous solution to obtain a reduced graphene oxide (RGO) gel; And
Dispersing the RGO gel in an aqueous acetic acid solution and then removing water to obtain an RGO powder. The method according to claim 1,
Wherein the weight ratio of the GO to the glucose is 1: 0.001 to 1:36. The method according to claim 1,
Wherein the hydrothermal treatment is carried out at a temperature of 160 to 185 DEG C for 2 to 4 hours. The method according to claim 1,
Wherein the concentration of the acetic acid aqueous solution is 0.05 to 2 M (mol). 4. Reduced graphene oxide produced by any one of claims 1 to 4. Preparing an aqueous solution of graphite oxide (GO) to which glucose is added;
Applying a hydrothermal process to the GO aqueous solution to obtain a reduced graphene oxide (RGO) gel;
Dispersing the RGO gel in an aqueous acetic acid solution and removing water to obtain RGO powder; And
(RGO) powder is introduced into a solvent mixed with dimethylformamide (DMF) and deionized water (DI), and ultrasonication is performed so that the RGO powder is dispersed. A process for preparing a pin oxide suspension. The method according to claim 6,
Wherein the dimethylformamide and the deionized water are mixed at a volume ratio of 1: 1.

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