JP2014136653A - Method of manufacturing reduction type graphene oxide - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method of manufacturing metal non-dope or metal dope reduction type graphene oxide useful as a material for a capacitor and the like.SOLUTION: The graphene oxide is heated at 100 to 400°C. The graphene oxide is obtained by (1) a process of preparing suspension containing sulfonated graphite by conducting a laser ablation on a reaction medium containing 90 to 98 mass% of sulfuric acid with a metal or a metal compound, if the case may be, in a presence of solid acid catalyst for sulfonation, then adding 60 to 98 mass% of nitric acid and a strong oxidation agent, and (2) adding water and 25 to 40 mass% of hydrochloric acid to the obtained suspension to hydrolyze the sulfonated graphite.

Description

  The present invention relates to a manufacturing method for manufacturing reduced graphene (RGO) capable of providing excellent conductivity such as a capacitor.

  Graphene is called as a two-dimensional sheet (FIG. 1) in which carbon atoms are arranged in a network like a honeycomb at the atomic level, or a state in which the sheet is laminated in one to several layers. Since graphene behaves as particles without weight in graphene sheets, it exhibits an electron transport property that is an order of magnitude higher than Si crystals, the mainstream of semiconductor device materials that make up transistors and ultra-large scale integrated circuits. It is attracting attention as a high-performance electronic component material that changes to Furthermore, due to the structural characteristics of graphene composed of a stable hexagonal structure, graphene is very strong even in the form of a sheet, and has the possibility of being used in various applications as a stable material with little deterioration. Highly useful material.

On the other hand, while its usefulness has been recognized, it has been difficult to form graphene on a silicon substrate or a glass substrate in a film form. Initially, it was very laborious to transfer the graphite by peeling the graphite one by one with an adhesive theme. Therefore, the performance of the obtained graphene varies, and it cannot be said that it is sufficient in various performances. Recently, as described in Patent Document 1, for example, a chemical vapor deposition method under reduced pressure and high temperature has been developed in a vapor deposition chamber by converting a raw material constituting carbon into plasma.
However, the chemical vapor deposition method requires high vacuum conditions and high temperature conditions (for example, 300 ° C. or higher), has a large energy load, and has low production efficiency. It is very difficult to provide in the form.

In recent years, low-emission vehicles such as electric vehicles and hybrid vehicles have been developed from the perspectives of mitigating air pollution in large cities by automobile exhaust gas, promoting the use of alternative energy for petroleum, and reducing carbon dioxide emissions that contribute to the prevention of global warming. Popularization is required. In addition, with the introduction of distributed power sources based on natural energy such as solar power, wind power, and hydropower to power systems, various power storage devices are being developed. Development to increase the withstand voltage is underway. And as an electrochemical element used for a power storage device, for example, an electric double layer capacitor capable of high density and large capacity has attracted attention.
Since the capacity of the electric double layer capacitor is proportional to the surface area of the polarizable electrode, activated carbon having a large surface area is generally used as the material of the polarizable electrode. Activated carbon is produced by carbonizing a raw material having a high carbon content such as coconut shell, petroleum pitch, petroleum coke, etc. at a low temperature of 300 to 700 ° C. and then activating the raw material. For the activation, for example, an inorganic acid such as water vapor, hydrochloric acid, nitric acid, sulfuric acid, or a potassium salt such as potassium hydroxide is used, which contributes to an increase in production cost.

  Furthermore, in the conventional electric double layer capacitor, in order to increase the surface area of the polarizable electrode, the granulated activated carbon is uniformly dispersed in an electrolyte such as propylene carbonate. In practice, it is difficult to uniformly disperse the activated carbon in the electrolytic solution, and there is a problem that it is difficult to effectively utilize the surface area inherent to the activated carbon.

  The present inventor has found that a large-capacity capacitor can be produced when reduced graphene oxide is used instead of activated carbon as a material constituting the polarizable electrode, and the present invention has been achieved.

Republished Patent (A1) WO2005-021430

Therefore, the present invention, unlike graphene, can be used for applications such as capacitors, can be easily manufactured, and by combining various metals, a new reduced graphene oxide that exhibits extremely excellent conductivity and its It is contemplated to provide a manufacturing intermediate.
The present inventor has already filed an application regarding a method for producing graphene oxide useful as an intermediate for producing graphene.
The present inventor reduced graphene oxide by a simple reduction means to produce a reduced graphene oxide and an intermediate compound of graphene oxide and graphene. This compound is easier to handle (lower risk of dust explosion) than graphene oxide and can be easily doped or intercalated with metal, and as a result, compared to graphene, It has been found that a material exhibiting excellent conductivity and charge storage property can be produced. This compound can also be called metal-doped or intercalated reduced graphene oxide, and was found to be very excellent for use as a material such as a capacitor.

Accordingly, the inventors have provided useful materials such as capacitors that are superior to graphene, and further, metal doped or undoped via graphene oxide, which can be manufactured much more easily than graphene. The present invention has been achieved by providing a production method capable of producing reduced graphene oxide.
That is, the present invention relates to graphene oxide powder at a relatively low temperature (for example, 100 to 400 ° C., preferably 150 to 300 ° C.) and, if necessary, in the presence of an inert gas such as nitrogen. In addition, it is possible to produce metal-undoped reduced graphene oxide from graphene oxide by heating, and further, in the process of producing graphene oxide, a metal or a metal compound is blended, and graphene oxide of the previous applicant By applying this production method, metal-doped graphene oxide was produced and reduced in the same manner as described above to find that metal-doped reduced graphene oxide was obtained, and the present invention has been achieved.

In addition, graphene oxide can be manufactured using the following processes, for example.
That is, the following steps:
(1) In a reaction medium containing 90 to 98% by mass of sulfuric acid, laser ablation is performed in the presence of a solid acid catalyst for sulfonation, and then 60 to 98% by mass of nitric acid and a strong oxidizing agent are added with stirring. A step of preparing a suspension containing sulfonated graphite, and (2) a step of hydrolyzing the sulfonated graphite by adding water and 25 to 40% by mass of hydrochloric acid to the obtained suspension. ,
Can be prepared.
Here, the solid acid catalyst is suitably carbonized D glucose, and the strong oxidant is suitably potassium permanganate. Laser ablation is preferably performed by introducing a YAG laser into the reaction medium.
In this case, when graphene oxide is produced, the metal-doped or intercalated graphene oxide can be produced by adding a metal or a metal compound in the step (1).

It is a schematic diagram which shows the 1 layer structure of graphene. It is a schematic diagram of graphene oxide. 1 shows a diagram of an apparatus for producing reduced graphene oxide. FIG. The Raman spectrum figure of the graphene oxide obtained in the example is shown. The Raman spectrum figure of general graphene is shown. 4 is a Raman spectrum diagram of metal-non-doped reduced graphene oxide obtained in Example 2. FIG. 4 is a Raman spectrum diagram of silver-doped reduced graphene oxide obtained in Example 3. FIG. An electron micrograph of graphene oxide taken at 1000 times is shown. An electron micrograph of graphene oxide taken at a magnification of 5000 is shown. An electron micrograph of graphene oxide taken at 10000 times is shown. The electron micrograph of the graphene oxide image | photographed by 30000 times is shown. An electron micrograph of reduced graphene oxide taken at 1000 times is shown. An electron micrograph of reduced graphene oxide taken at a magnification of 5000 is shown. An electron micrograph of reduced graphene oxide taken at 10000 times is shown. An electron micrograph of reduced graphene oxide taken at 30000 times is shown.

Embodiments of the present invention will be described below.
1. Production of Graphene Oxide Graphene oxide as a raw material of the present invention is produced as follows.
First, graphite is sulfonated. In the sulfonation reaction, laser ablation is performed in the reaction medium in the presence of a solid acid catalyst and a strong oxidizing agent for sulfation in a concentrated sulfuric acid medium to sulphate the graphite particles while passing between the graphite particles. Nanosuspensions of sulfonated graphite particles can be prepared by expanding and refining the particles, and then adding concentrated nitric acid and strong oxidizer, preferably slowly, to further advance the sulfonated reaction. .
Here, the graphite or graphite particles used in the reaction may be natural or synthetic and preferably have a purity of 99% or more. When natural graphite is used as the graphite source, since impurities such as silica are present, it is preferable to use a product having a purity of 99% or more.
The amount of graphite used is, for example, 1 to 50 g, preferably 10 to 30 g, based on 100 ml of concentrated sulfuric acid.

The density | concentration of the concentrated sulfuric acid to be used is 90-98 mass%, for example, Preferably, it is 96-98 mass%.
In order to accelerate the sulfonation reaction of graphite, a solid acid catalyst for sulfonation is added to the sulfonation reaction together with concentrated sulfuric acid. Any solid acid catalyst can be used without particular limitation as long as it promotes sulfonation. The production method of the solid acid catalyst has already been described in, for example, Japanese Patent No. 4041409, Japanese Patent Publication No. 2012-149014, and re-published WO2007 / 029496, and products (for example, stocks of distributors) It can be obtained as carbonized D glucose 569 manufactured by company Human Systems).

The solid acid catalyst uses, for example, dehydration action and oxidation action of concentrated sulfuric acid (for example, 98%) and fuming sulfuric acid against carbon sources such as D-glucose, cellulose, naphthalene, and anthracene. It is carbonized and sulfonated at a high temperature of about 200 to 300 ° C. By sulfonated, the sulfonated graphite particles have an affinity for sulfuric acid, so that the dispersibility and interlayer expansion of the graphite particles by ablation in liquid described below can be further enhanced.
The amount of the solid acid catalyst is, for example, 0.1 to 10 g, preferably 0.5 to 5 g, for example, for carbonized D glucose as the solid acid catalyst with respect to 20 g of graphite. is there.

  Laser ablation is known per se and is used in water. In general, laser ablation is used to modify the surface of a material such as a metal to uniformly disperse it in water in the form of nanocolloid particles, and as a technique for producing a metal dispersion that does not settle. It has come to be used. For example, see “Laser ablation and its application” (Corona, 1999), Laser Society Laser Expo 2000 Special Seminar (April 2004), etc. When a pulse laser in the visible region is used, ablation occurs in water, and a large pressure plume is formed on the surface of the material for a short time, and this pressure is used to locally deform the metal surface. It is understood. In water, since the expansion of the plume is suppressed due to the inertia of the water, the plume pressure is 10 to 100 times that in the air and reaches several gigapascals (GPa). It is understood that this pressure generates shock waves and propagates through the material.

As a laser used for laser ablation, a YAG laser (wavelength, for example, 1.06 μm) that can be sent into a liquid by a glass fiber can be suitably used.
By performing laser ablation in the liquid under stirring in the liquid medium, the multilayer graphite interlayer distance is expanded by about three times, for example, in the presence of a solid acid catalyst suitable for sulfonation under strong sulfonation conditions. It becomes possible to introduce a sulfone group into the benzene ring of graphite, and a nano-dispersion of sulfonated graphite particles can be obtained.
The sulfonation reaction can be performed by performing laser ablation in a liquid while stirring graphite or graphite particles with a magnetic stirrer. By the laser ablation in the liquid, the graphite particles in the reaction vessel can be refined into a nanocolloid state and suspended. Laser ablation in the liquid generates strong pulses in the liquid for the graphite particles, thereby expanding the interlayer spacing of the graphite, and delamination and oxidation by the action of concentrated sulfuric acid and solid acid catalyst present. And sulphonation reaction can be carried out. Laser ablation is effective, for example, for a short time, for example, about 30 minutes.

In the sulphonation step, when a sulphonation reaction is performed in the presence of a metal or a metal compound, a metal-doped sulphone capable of preparing a metal-doped graphene oxide as an intermediate for producing a metal-doped reduced graphene oxide A suspension of graphite oxide is obtained.
As the metal used in this case, for example, various metals such as silver, palladium, copper, and zinc can be used. Moreover, as a metal, it can mix | blend with various forms, such as a metal oxide (zinc oxide etc.), a hydroxide, and a salt.
The amount of the metal to be blended or the compound thereof is preferably 0.01 to 5% by mass, preferably 0.1 to 3% by mass with respect to graphite as the metal.

  In the obtained sulfonated graphite particles, it is considered that sulfonic acid groups are present in a state where the sulfonic acid group enters the graphite layer or is bonded to the surface of the layer and bonded or added to the benzene ring.

Since the sulfonation reaction is an exothermic reaction, it is preferable to adjust the cooling temperature of the reaction vessel so that it does not boil and emit smoke in a water bath whose temperature is controlled outside.
In order to further proceed the sulphonation reaction on the graphite particles, concentrated nitric acid and a strong oxidizing agent are then added to the reaction medium with stirring.
The concentration of concentrated nitric acid used is, for example, 50 to 85% by mass, preferably 50 to 80% by mass, and more preferably 55 to 70% by mass. The amount of concentrated nitric acid is, for example, 5 to 50 g, preferably 10 to 30 g per 100 ml of concentrated sulfuric acid.
The amount of potassium permanganate as a strong oxidizing agent is, for example, 3 to 100 g, more preferably about 10 to 30 g, with respect to 100 ml of concentrated sulfuric acid. This provides a suspension of fully sulfonated graphite particles.
The doping metal may be blended at this point.

The sulfonated graphite particles thus obtained can then be hydrolyzed or desulfonated by adding water and concentrated hydrochloric acid to the reaction medium in which it is dispersed.
As water, generally purified water is used. For example, as water, distilled water, ion exchange water, or the like can be suitably used.
The amount of water used will be, for example, about 500 to 1200 ml, preferably about 700 to 900 ml, with respect to 100 ml of concentrated sulfuric acid. Water is preferably added slowly and with stirring, while suppressing the generation of heat of reaction with concentrated sulfuric acid present therein.
The concentration of concentrated hydrochloric acid used is, for example, 25 to 40% by mass, preferably 34 to 37% by mass. The amount of hydrochloric acid used is, for example, 5 to 20 g, preferably 8 to 12 g, with respect to 20 g of the strong oxidizer.

As a container used for the reaction, a container that is resistant to a highly reactive compound such as concentrated sulfuric acid, concentrated nitric acid, concentrated hydrochloric acid, or the like, such as a container made of borosilicate heat-resistant glass, is used.
After the hydrolysis reaction, impurities or unwanted substances float on the surface of the reaction medium by naturally cooling for about 5 to 60 minutes, preferably about 10 to 30 minutes.
The suspended impurities or unnecessary substances are removed, and the reaction product dispersed in the medium is separated into a solid phase and a liquid phase using a centrifugal separator. Next, the supernatant is discarded, and the paste-like solid phase can be dried by heating or 400 ml of water, the viscosity is lowered, and water is blown away by a spray drier or the like to obtain solid graphene oxide powder.

Formation of graphene oxide can be confirmed by a Raman spectrum. Similarly, the generation of metal-undoped reduced graphene oxide and metal-doped reduced graphene oxide can also be confirmed by a Raman spectrum.
When graphene oxide powder is measured with a high-resolution transmission electron microscope, the average thickness is 1 to 40 nm, and the diameter is about 2 to 90 μm.
Graphene oxide is assumed to have a functional group such as a hydroxyl group, an ether group, or a carboxyl group added to a benzene ring between layers or on the surface of the layer as in the conceptual diagram shown in FIG. .
The average particle diameter of the graphene oxide particles when measured by the electron microscope STM method is 2 to 40 nm in thickness and 4 to 80 μm in diameter.
The degree of oxidation can be easily confirmed by measurement such as X-ray photoelectron spectroscopy (XPS).

2. Manufacture of reduced graphene oxide Graphene oxide or metal-doped graphene oxide obtained as described above is different from graphene by performing gentle reduction, and compared with graphene oxide, hydroxyl group, carboxyl group, etc. Thus, a metal-undoped or metal-doped reduced graphene oxide having a structure in which the functional group is left is obtained.
Here, with reference to FIG. 3, a manufacturing process of the metal-undoped or metal-doped reduced graphene oxide will be described.
As a preferred embodiment, the metal undoped graphene oxide or the metal doped graphene oxide powder introduced into the reactor 2 heated by the heating device 2a such as a mantle heater is reduced while flowing a nitrogen stream from the nitrogen cylinder 1. In this case, since the obtained metal undoped or metal doped reduced graphene oxide is very fine and bulky, in this case, in order to efficiently collect the obtained metal undoped or metal doped reduced graphene oxide, Two collection devices 3 and 4 are employed. As such a collecting device, a commercially available product can be used, and for example, a silent cleaner manufactured by Osawa & Company can be used as appropriate.
In the case of using an inert gas, the flow rate of the inert gas can be employed without any particular limitation as long as it is a flow rate that allows reduction. The flow rate is, for example, generally 0.5 to 40 liters / minute (L / minute), and preferably about 5 to 30 liters / minute. During the reaction, the metal-undoped graphene oxide or the metal-doped graphene oxide is transferred to the inert gas while being reduced, and moves to the collection devices 3 and 4.
The reduction temperature is generally 100 to 400 ° C, preferably 150 to 300 ° C. When this temperature reaches 1100 ° C., complete reduction occurs and graphene is formed.

The metal-undoped or metal-doped reduced graphene oxide obtained in this way is very dispersible in water and has completely different properties from graphene due to the hydrophilic action of the functional groups present inside. . For this reason, the difference in structure with graphene is clear.
Unlike graphene, reduced graphene oxide is easily dispersed in water due to hydrophilic functional groups such as hydroxyl groups and carboxyl groups present in reduced graphene oxide. On the other hand, since graphene has no functional group, it can be dispersed only in a special and expensive lipophilic solvent. Further, the reduced graphene oxide can be confirmed to be different from the graphene oxide by the shift of the peak position from the Raman spectrum diagram.

  The obtained reduced graphene oxide, particularly the metal-doped reduced graphene oxide, is intercalated between layers as a metal ion when the doped metal ion is a multilayered reduced graphene oxide. When used as a capacitor, it has an excellent function. In addition, even if it is a single layer, it is bonded to another layer by an ionic bond or the like through a functional group of the single layer. Can fulfill.

  Hereinafter, the present invention will be described in more detail with reference to examples.

Production of graphene oxide Example 1: Production of metal-undoped graphene oxide A magnetic stirrer, a 1200 mL double-walled borosilicate heat-resistant glass reaction vessel, and a temperature-controlled hot water circulation apparatus were prepared.
First, put a magnet protected with acid-resistant ceramic in a borosilicate heat-resistant glass reaction vessel, and then put 20 g of graphite (Nippon Graphite Co., Ltd .: ACP1000) so as not to splash, so that it does not fly while stirring with a magnetic stirrer Into this, 100 ml of 98% concentrated sulfuric acid and 1 g of carbonized D-glucose (made in-house) as a solid acid catalyst were added little by little. Under stirring with a magnetic stirrer, a commercially available Yag laser transmitter was used, the tip of the glass fiber was set near the center of the liquid, and laser pulses were sent at 10 second intervals. Due to the action of laser ablation and concentrated sulfuric acid, the interlayer distance (height) of the graphite composed of multi-layer graphene is expanded three times, and the penetration of concentrated sulfuric acid is facilitated. The sulfonated action of sulphonated graphene was promoted to produce sulfonated graphene. Laser ablation was completed in about 30 minutes.
Next, 10 ml of concentrated nitric acid (60%) was injected little by little while paying attention to heat generation. Subsequently, potassium permanganate powder (manufactured by Wako Pure Chemical Industries, Ltd.) was gradually added to 100 ml of sulfuric acid while paying attention to heat generation of 20 g.
After stirring for 30 minutes with a magnetic stirrer, the oxidation reaction (sulphonation) was completed.
Next, 800 ml of pure water and 20 ml of 35 mass% concentrated hydrochloric acid were injected while paying attention to heat generation. After 30 minutes, the sulfonated graphene changed to graphene oxide and was uniformly dispersed in the aqueous medium.
When water and concentrated hydrochloric acid were added and stirred for 10 minutes, impurities or unnecessary substances floated and were removed by filtration. The generated graphene oxide was uniformly dispersed in the solution.
Next, the dispersion was placed in a centrifuge Himac CR-GIII (300000) manufactured by Hitachi Koki Co., Ltd. and operated at 7000 rpm for 10 minutes to obtain a solid layer.
After stopping, the supernatant is removed, 400 ml of water is added to the graphene oxide remaining at the bottom, and the water is uniformly dispersed in the water. Spray dryer: spray-dried using a spray dryer, and solid graphene oxide is removed. Obtained.
FIG. 4 is a Raman spectrum of the obtained graphene oxide. Raman spectrum is measured using AC-1 manufactured by iTRIX Corporation, exposure time 5.00 seconds, exposure count 10, background exposure count 32, laser 532 nm, grating 900 lines / mm, spectrometer The test was performed under the conditions of an aperture 50 μm pinhole and a laser output level 10.0 mW. Measurement points were measured at 3 to 5 points of the thinned sample, and the variation of the measurement results was evaluated. FIG. 4 shows that the measurement results at the three points are uniform. For comparison, a Raman spectrum of common graphene under the same conditions is shown in FIG.
When FIG. 4 is compared with FIG. 5, it is understood that the peak shape and position are clearly different between graphene oxide of the present invention and graphene, and graphene oxide is manufactured by the above manufacturing method. . Graphene oxide has a different structure from graphite. Graphite and graphene are not dispersible in water and are dispersed or dissolved only in a special solution, whereas the graphene oxide of the present invention is dispersible in water due to the influence of the hydrophilic functional group contained therein. Since the graphene oxide obtained in this manner is dispersed in water, the dispersion is cast on a flat surface such as a substrate, dried, and then reduced by a normal reduction method. Can be prepared.
8 to 11 show electron micrographs of graphene oxide obtained by photographing at magnifications of 1000 times, 5000 times, 10000 times, and 30000 times, respectively. It was found that a relatively large amount of granular graphene oxide exists.
The shooting conditions were obtained as a secondary electron image at an acceleration voltage of 5 kV using JSM-6010 InTouchScope manufactured by JEOL Ltd.

Example 2: Production of metal-undoped reduced graphene oxide A glass reactor heated by a mantle heater 2a while flowing a nitrogen stream from a nitrogen cylinder 1 at a flow rate of about 10 to 20 L / min using the apparatus of FIG. 20 g of metal-undoped graphene oxide was introduced into 2 and heated to about 170 ° C. to perform a reduction reaction. During the heating by the heater 2a, the graphene oxide powder is reduced while being floated in the container by the flow of the nitrogen stream, and then gradually, by the two collection devices 3 and 4 while being guided by the nitrogen stream. Collected as metal-undoped reduced graphene oxide.
FIG. 6 is a Raman spectrum diagram of the obtained metal undoped reduced graphene oxide.
When the Raman spectrum of reduced graphene oxide (Fig. 6) is compared with the Raman spectrum of graphene oxide (Fig. 4), the peak of the two peaks is higher in the graph of reduced graphene oxide. I understand. This shows that reduced graphene oxide is clearly different from graphene oxide. Further, as is clear from comparison with the graph of Raman spectrum of graphene, it can be clearly distinguished by different peaks as in the case of graphene oxide.
12 to 15 show electron micrographs of reduced graphene oxide obtained by photographing at magnifications of 1000 times, 5000 times, 10000 times, and 30000 times, respectively.

Example 3 Production of Silver Metal Doped Graphene Oxide and Silver Metal Doped Reduced Graphene Oxide In Example 1, in the sulfonation reaction step, silver was used as a metal in a concentrated sulfuric acid reaction medium. Compounding in an amount of 0.5% by mass, Example 1 was repeated to produce silver metal-doped graphene oxide.
Next, in the same manner as in Example 2, the silver metal-doped graphene oxide was reduced to obtain silver metal-doped reduced graphene oxide.
7 is a Raman spectrum diagram of the silver-doped reduced graphene oxide obtained in Example 3. FIG.
The Raman spectrum of the metal-doped reduced graphene oxide FIG. 7 shows that the peak height is lower and the peaks are gentler than the Raman spectrum of the metal-undoped reduced graphene oxide FIG.

Examples 4 and 5: Production of copper or zinc metal doped graphene oxide and copper or zinc metal doped reduced graphene oxide In Example 1, using copper or zinc oxide instead of silver as the metal or metal compound, Copper and zinc metal doped graphene oxide were prepared, respectively, and then copper and zinc metal doped reduced graphene oxide were prepared in the same manner as in Example 3.
The Raman spectrum of the obtained copper or zinc metal doped reduced graphene oxide was the same as that described in FIG.

Industrial Applicability The metal-undoped or metal-doped reduced graphene oxide obtained in the present invention is very useful as a capacitor material. In addition, metal-doped graphene oxide is useful as an intermediate in the production of these capacitor materials.

Claims (11)

A method for producing metal-doped graphene oxide, comprising the following steps:
(1) In a reaction medium containing 90 to 98% by mass of sulfuric acid, laser ablation is carried out in the presence of a sulfonated solid acid catalyst together with a metal or metal oxide, and then 60 to 98% by mass of nitric acid and strong Adding an oxidizing agent with stirring to prepare a suspension containing sulfonated graphite;
(2) adding water and 25-40 mass% hydrochloric acid to the resulting suspension to hydrolyze the sulfonated graphite;
A method for producing metal-doped graphene oxide, comprising:   The method according to claim 1, wherein the solid acid catalyst is carbonized D glucose.   The method of claim 1, wherein the strong oxidant is potassium permanganate.   The method of claim 1, wherein the laser ablation is performed with a YAG laser.   A method for producing metal-undoped reduced graphene oxide, the graphene oxide being heated at 100 to 400 ° C. The graphene oxide has the following steps:
(1) In a reaction medium containing 90 to 98% by mass of sulfuric acid, laser ablation is performed in the presence of a solid acid catalyst for sulfonation, and then 60 to 98% by mass of nitric acid and a strong oxidizing agent are added with stirring. Preparing a suspension containing sulfonated graphite,
And (2) adding water and 25-40% by mass hydrochloric acid to the resulting suspension to hydrolyze the sulfonated graphite,
The method according to claim 5, which is obtained by:   The process according to claim 5, wherein the heating is carried out in the presence of an inert gas.   The method according to claim 7, wherein the inert gas is nitrogen.   A method for producing metal-doped reduced graphene oxide, comprising heating the metal-doped graphene oxide obtained by the method according to claim 1 at 100 to 400 ° C.   The method according to claim 9, wherein heating is performed in the presence of an inert gas.   The method according to claim 10, wherein the inert gas is nitrogen.