WO2020105646A1

WO2020105646A1 - Method for producing graphene, and graphene production equipment

Info

Publication number: WO2020105646A1
Application number: PCT/JP2019/045320
Authority: WO
Inventors: 橋本　英樹; 英孝阿相; 勇太仁科
Original assignee: 学校法人工学院大学; 国立大学法人岡山大学
Priority date: 2018-11-21
Filing date: 2019-11-19
Publication date: 2020-05-28
Also published as: JP7357936B2; JPWO2020105646A1

Abstract

Provided are: a method for producing graphene, the method including a stripping step for applying a voltage between a pair of electrodes 30, 32 in a state in which the pair of electrodes are disposed in an electrolyte solution 20 that includes water and at least one electrolyte selected from the group consisting of inorganic acids, inorganic salts, organic acids, and bases, and in which graphite 10 is disposed between the pair of electrodes without being in contact with the electrodes, whereby graphene is stripped from the graphite, and a recovery step for recovering the graphene generated by stripping from the graphite; and graphene production equipment for implementing the method.

Description

Graphene manufacturing method and graphene manufacturing apparatus

The present disclosure relates to a graphene manufacturing method and a graphene manufacturing apparatus.

Graphene, which is a sheet-like crystalline carbon composed of carbon atoms, has excellent properties such as conductivity, thermal stability, toughness, and flexibility, and is used in various devices such as semiconductor devices, solar cells, and transparent conductive films. Is expected to be used in the field of.

As a practical production method of graphene, a top-down method in which graphene is obtained by delamination using graphite as a starting material is drawing attention.
Generally, graphite is chemically exfoliated using strong oxidizer such as potassium permanganate and concentrated sulfuric acid (strong acid), which is an intercalant, to prepare graphene. Since a required reagent and a large amount of pure water are consumed, development of a new stripping method is required.

In recent years, attention has been paid to an electrochemical stripping method in which graphite is used as an electrode in an electrolytic solution to cause delamination of graphite to obtain graphene (see, for example, Patent Documents 1 to 7). For example, when graphite is used as an anode and low-concentration sulfuric acid is used to perform electrolysis at a relatively low voltage (for example, 10 V), the graphite can be exfoliated in a short time of less than 1 hour to obtain graphene.

On the other hand, a high voltage of 1100V was applied by immersing an anode, a cathode, and a graphite powder in an organic electrolytic solution containing tetrabutylammonium tetrafluoroborate (Bu ₄ NBF ₄ ) and N-methyl-2-pyrrolidone (NMP). After that, a method of obtaining graphene by performing high shearing treatment at 330000 / s for 1 hour is known (see Non-Patent Document 1).

Patent Document 1: Japanese Patent Application Laid-Open No. 2012-131691 Patent Document 2: Japanese Patent Publication No. 2016-534010 Patent Document 3: Japanese Patent Publication No. 2017-502168 Japanese Patent Document 4: Japanese Patent Publication No. 2017-538041 Japanese Patent Publication 5: International Publication No. 2012/073861 Patent Document 6: Japanese Unexamined Patent Publication No. 2018-35056 Patent Document 7: International Publication No. 2017/100968

It is predicted that the market for end products using graphene will reach several trillion yen in 2030, but the high-quality graphene currently on the market is extremely low because a cheap manufacturing method for graphene has not been established. It is expensive.
For example, when applying a method of producing graphene by energizing a graphite electrode as disclosed in Patent Documents 1 to 5, in order to obtain graphene to be used as an electrode, for example, polyimide is heated at about 3000 ° C. It is necessary to use the produced expensive graphite single foil or a molded body of graphite. Further, as the graphene is peeled off from the graphite electrode, the graphite electrode gradually becomes smaller, so it is necessary to replace the graphite electrode when it becomes small to some extent.

On the other hand, natural graphite powder can be obtained at low cost (about 1/100 of that of graphite single foil), but electrodes cannot be attached to graphite powder. Therefore, it is not possible to perform electrolytic treatment using natural graphite powder by the method of obtaining electric power by using graphite as an electrode to obtain graphene.
In this respect, according to the method disclosed in Non-Patent Document 1, it is possible to produce graphene from graphite powder, but an expensive organic electrolytic solution and a remarkably high voltage of 1100 V are required, and further, after the electrolysis, a machine is used. Shear treatment is required, and industrial applicability is extremely low.

The present disclosure has been made in view of the above circumstances, and provides a graphene manufacturing method and a graphene manufacturing apparatus that can use graphite particles or powder as a raw material and can relatively easily manufacture graphene. The purpose is to do.

Means for solving the above problems include the following aspects.
<1> A pair of electrodes is arranged in an electrolytic solution containing at least one electrolyte selected from the group consisting of an inorganic acid, an inorganic salt, an organic acid, and a base, and water, and between the pair of electrodes. A peeling step of peeling graphene from the graphite by applying a voltage between the pair of electrodes in a state where the graphite is arranged without contact with the pair of electrodes,
A recovery step of recovering graphene generated by peeling from the graphite,
Of producing graphene including.
<2> The method for producing graphene according to <1>, wherein the electrolytic solution contains sulfuric acid as the electrolyte.
<3> The method for producing graphene according to <2>, wherein the concentration of the sulfuric acid in the electrolytic solution is 1 mM or more and 0.5 M or less.
<4> The method for producing graphene according to any one of <1> to <3>, wherein the graphite is in the form of particles or powder.
<5> The method for producing graphene according to any one of <1> to <4>, in which a voltage is applied between the pair of electrodes in a state where the graphite is housed in a filter through which the electrolytic solution can pass. ..
<6> The method for producing graphene according to any one of <1> to <5>, in which the voltage applied between the pair of electrodes is in the range of 5 V to 80 V.
<7> A container containing an electrolytic solution containing at least one electrolyte selected from the group consisting of an inorganic acid, an inorganic salt, an organic acid, and a base, and water,
A pair of electrodes arranged in the container,
A power supply for applying a voltage between the pair of electrodes,
Between the pair of electrodes arranged in the container, graphite arrangement means for arranging graphite without contacting the pair of electrodes,
And a graphene manufacturing apparatus having the same.
<8> The graphene production apparatus according to <7>, wherein the graphite placement means includes a holding member that holds the graphite.
<9> The graphene production apparatus according to <8>, wherein the holding member contains the graphite and includes an insulating filter that is permeable to the electrolytic solution.
<10> The graphene production apparatus according to <7>, including a stirring device that disperses the graphite in the electrolytic solution by stirring the electrolytic solution.
<11> The graphene production apparatus according to any one of <7> to <10>, including a moving device that moves the graphite between the pair of electrodes.
<12> The graphene production apparatus according to any one of <7> to <11>, including a circulation device that circulates the electrolytic solution in the container.

According to the present disclosure, there are provided a graphene production method and a graphene production apparatus, which can use graphite particles or powder as a raw material and can relatively easily produce graphene.

It is a schematic diagram showing an example (first embodiment) of a graphene manufacturing device which performs a peeling process using a graphite board in a manufacturing method of graphene of the present disclosure. It is a schematic diagram showing other examples (2nd embodiment) of a graphene manufacturing device which performs a peeling process in a manufacturing method of graphene of this indication. It is a schematic diagram showing other examples (third embodiment) of a graphene manufacturing device which performs a peeling process in a manufacturing method of graphene of this indication. It is a figure which shows the relationship of the electrolytic solution (sulfuric acid) density | concentration when electrolysis processing is performed using a graphite plate as a bipolar electrode, electrolysis time, and the applied voltage between drive electrodes. It is a figure which shows the relationship of electrolyte solution (sulfuric acid) density | concentration, electrolysis time, and electrolyte solution temperature at the time of performing an electrolysis process using a graphite plate as a bipolar electrode. It is a figure which shows the sulfuric acid density | concentration of an electrolyte solution, the external appearance of the graphite plate after electrolysis, the peeling rate, and the average voltage value. It is a figure which shows the (A) optical microscope image and the (B) scanning electron microscope image of the graphene obtained by the electrolytic treatment of the graphite plate. It is a figure which shows the electrolysis time in the electrolysis process of a graphite plate, the applied voltage between drive electrodes, and the relationship of the change of a graphite plate. It is a figure which shows the electrolysis time at the time of electrolyzing a graphite plate, the electrolytic solution (sulfuric acid) density | concentration, and the relationship of temperature. It is a figure which shows the electrolysis time at the time of electrolytically processing a graphite plate, and the relationship of the mass change of the peeled material. It is a figure which shows the relationship of the ratio of the electrolysis time and the amount of exfoliation at the time of electrolytically treating a graphite plate. It is a figure which shows the (A) optical microscope image and (B) scanning electron microscope image of the graphene obtained at each time at the time of electrolytically treating a graphite plate. It is a figure which shows the electrolysis time at the time of electrolytically treating a graphite particle, the sample external appearance, and the relationship of voltage. It is a figure which shows the time-dependent change of the electrolytic solution temperature at the time of electrolyzing graphite particles. It is a figure which shows the (A) optical microscope image and the (B) scanning electron microscope image of the graphene obtained by carrying out the electrolytic treatment of the graphite particle. It is a figure which shows the electrolysis time, the external appearance of a sample, and the relationship of a voltage at the time of electrolyzing a graphite particle or powder. It is a figure which shows the time-dependent change of the electrolytic solution temperature at the time of electrolyzing graphite powder. It is a figure which shows the (A) optical microscope image and (B) scanning electron microscope image of the graphite powder (before electrolysis) and the graphene (after electrolysis) obtained by electrolytic treatment. It is a figure which shows the XRD pattern by the X-ray diffraction of the graphene produced by electrolyzing graphite before electrolysis, a graphite plate, particles, or powder, respectively. It is a schematic diagram showing other methods (an example of a graphene manufacturing device) which performs a peeling process in a manufacturing method of graphene of this indication. It is a schematic diagram showing other methods (an example of a graphene manufacturing device) which performs a peeling process in a manufacturing method of graphene of this indication. It is a schematic diagram showing other methods (an example of a graphene manufacturing device) which performs a peeling process in a manufacturing method of graphene of this indication. It is a schematic diagram showing other methods (an example of a graphene manufacturing device) which performs a peeling process in a manufacturing method of graphene of this indication.

Hereinafter, embodiments of the present disclosure will be described with reference to the drawings.
In the present specification, the numerical range represented by “to” means the range including the numerical values before and after “to” as the lower limit value and the upper limit value.
In addition, the term “process” in the present specification is not limited to an independent process, and even when it cannot be clearly distinguished from other processes, the term is used as long as the intended purpose of the process is achieved. included.

The inventors of the present invention have been earnestly studying to develop a new method for producing graphene by electrolytic stripping even for fine graphite samples such as particles and powders without directly applying electric current. Attempts were made to apply bipolar electrochemistry to graphite samples. In bipolar electrochemistry, a sample to be treated (bipolar electrode) is placed between insoluble drive electrodes, and a voltage is applied to the drive electrodes, and the potential gradient formed between the drive electrodes is used to create a bipolar electrode. On the other hand, it is a method of performing asymmetric electrolytic treatment.
Then, the present inventors used an electrolytic solution containing at least one electrolyte selected from the group consisting of an inorganic acid, an inorganic salt, an organic acid, and a base, and arranged graphite as a bipolar electrode between a pair of electrodes. It has been found that the graphene can be easily manufactured by applying a voltage to peel the graphite surface regardless of the shape of the graphite.

That is, in the method for producing graphene of the present disclosure, at least one electrolyte (hereinafter sometimes simply referred to as “electrolyte”) selected from the group consisting of an inorganic acid, an inorganic salt, an organic acid, and a base, and water. A pair of electrodes (may be referred to as “driving electrodes”) are arranged in an electrolyte solution containing (hereinafter, may be simply referred to as “electrolyte solution”), and between the pair of electrodes, In a state where graphite is arranged without contact with the pair of electrodes, a step of peeling graphene from the graphite by applying a voltage between the pair of electrodes, and a graphene produced by peeling from the graphite The method includes a collecting step of collecting.

(Electrolyte)
As the at least one electrolyte selected from the group consisting of an inorganic acid, an inorganic salt, an organic acid, and a base contained in the electrolytic solution, graphite is placed between a pair of electrodes to apply a voltage to the graphite. There is no particular limitation as long as the graphene can be peeled off. Examples of the electrolytic solution that can be used in the method for producing graphene of the present disclosure include an electrolytic solution containing sulfuric acid, phosphoric acid, oxalic acid, sodium sulfate, ammonium sulfate, potassium sulfate, potassium hydroxide, sodium hydroxide, or hydrogen peroxide. Or a mixed electrolytic solution containing two or more kinds of these electrolytes. From the viewpoint of easy exfoliation of graphene from graphite and availability, sulfuric acid is preferred as the electrolyte.
As the solvent, water can be used because it can be used as an electrolytic solution by dissolving the electrolyte to be used, and water is preferable from the viewpoint of handleability and cost. In addition to water, another solvent or additive may be added as long as it does not prevent the exfoliation of graphene from graphite by the method of the present disclosure.

-Electrolyte concentration-
When a sulfuric acid solution is used as the electrolytic solution, a low-concentration sulfuric acid solution that is easy to handle can be preferably used in the method for producing graphene of the present disclosure. If the concentration of sulfuric acid in the electrolytic solution is too low, it is difficult to conduct electricity between the drive electrodes, and it is difficult for graphite to peel off. If the concentration of sulfuric acid is too high, graphite is difficult to peel off. From the viewpoint of easily exfoliating graphene from graphite, the sulfuric acid concentration is preferably 1 mM to 0.5 M, more preferably 10 mM to 0.2 M, and particularly preferably 10 mM to 0.1 M.

-Electrolyte temperature-
The temperature of the electrolytic solution is not particularly limited, but if the temperature of the electrolytic solution is too low, the voltage applied between the driving electrodes may increase, while if it is too high, the driving electrodes (anode, cathode) may be energized during electrolysis. ), The temperature of the electrolytic solution rises, and the concentration of the electrolytic solution may change due to evaporation of the solvent. Therefore, the temperature of the electrolytic solution during electrolysis is, for example, preferably 5 to 70 ° C., more preferably 10 to 60 ° C., and particularly preferably 20 to 50 ° C.

(A pair of electrodes)
The drive electrode is not particularly limited as long as it is made of a material that is not corroded by the electrolytic solution and does not easily chemically change even when a voltage is applied. From the viewpoint of chemical stability, a platinum (Pt) electrode, a gold electrode, and a carbon electrode are preferable, and an electrode obtained by coating a highly corrosion-resistant metal (for example, titanium, tantalum, niobium, etc.) with platinum, gold or the like may be used, but particularly a Pt electrode. Is preferred.

-Applied voltage-
If the voltage applied between the pair of electrodes is too low, the exfoliation of graphite will not occur easily, and if it is too high, the power consumption will increase. From this viewpoint, the voltage applied between the pair of electrodes is preferably 5 to 80 V, more preferably 15 to 75 V, and particularly preferably 20 to 75 V.

-Electrode position-
The position of the pair of electrodes is not particularly limited as long as graphite is arranged between the electrodes and graphene can be separated from the graphite when a voltage is applied between the electrodes, but a higher voltage is required as the distance between the electrodes increases. Become. Therefore, the distance between the electrodes is preferably 5 to 100 mm, for example.

(Graphite)
The shape and size of graphite, which is a raw material for graphene, is not particularly limited, and may be any shape such as plate-like, rod-like, particle-like, and powder-like.
The graphite may be arranged between the pair of drive electrodes (anode and cathode), may be located between the anode and the cathode, or may be arranged on the cathode side or a position close to the anode side.

For example, when a graphite plate is used, it will gradually separate from the graphite plate as graphene with the passage of electrolysis time, and the graphite plate will gradually become smaller (thinner). Since the graphite plate functions not as a driving electrode but as a bipolar electrode that does not receive direct current, use it as a raw material for graphene until the part located between the driving electrodes in the electrolyte solution eventually disappears. You can

On the other hand, graphite obtained from nature (natural graphite) is usually in the form of particles or powder, and can be obtained at a lower cost than a graphite plate molded from natural graphite. In the method for producing graphene according to the present disclosure, it is not necessary to directly energize graphite itself, and therefore particulate or powdery graphite (natural graphite) can be preferably used.

An apparatus for carrying out the method for producing graphene of the present disclosure is not particularly limited, but for example, the peeling step can be suitably performed using a graphene production apparatus having the following configuration. That is, the graphene production apparatus of the present disclosure includes a container containing an electrolytic solution containing at least one electrolyte selected from the group consisting of an inorganic acid, an inorganic salt, an organic acid, and a base, and the container, Graphite for arranging graphite between the pair of electrodes arranged, a power supply for applying a voltage between the pair of electrodes, and the pair of electrodes arranged in the container without contacting the pair of electrodes Arranging means, and.

<First embodiment>
FIG. 1 schematically illustrates an example (first embodiment) of a graphene manufacturing apparatus that performs a peeling step in the graphene manufacturing method of the present disclosure. In the present embodiment, the pair of

electrodes

30, 32 are arranged in the container 40 in which the electrolytic solution 20 is stored, and the graphite plate 10 held by the holding member 12 such as a clip as the graphite arranging means is the pair of

electrodes

30, 32. The

electrodes

30 and 32 are arranged in a suspended state without coming into contact with the

electrodes

30 and 32.
Then, a voltage is applied between the

electrodes

30 and 32 to energize them. At this time, the graphite plate 10 functions as a bipolar electrode, and the graphene can be separated from the surface of the graphite plate 10 with the energization between the pair of

electrodes

30 and 32.

The graphene generated by peeling from the graphite plate 10 may be recovered from the electrolytic solution using a filter or the like, and then washed with water, alcohol or the like, if necessary, and dispersed in a solvent or dried. ..

<Second embodiment>
FIG. 2 schematically illustrates another example (second embodiment) of the graphene production apparatus that performs the peeling step in the graphene production method of the present disclosure. In the present embodiment, an insulating filter 14 that accommodates graphite between the pair of

electrodes

30 and 32 and that is permeable to the electrolytic solution 20 is arranged.
As described above, even when a voltage or a voltage is applied by arranging the particulate or powdery graphite in the electrolyte solution 20 between the

electrodes

30 and 32 in the electrolytic solution 20, the graphite in the filter 14 serves as a bipolar electrode. It can function and exfoliate graphene from graphite. In addition, in the present embodiment, the graphene generated by peeling from the graphite can be retained in the filter 14, so that it can be efficiently collected.

Even in the case where the graphite plate 10 shown in FIG. 1 is used for electrolytic treatment, if the graphite plate 10 is housed in the filter 14 shown in FIG. Therefore, it can be efficiently collected.

<Third embodiment>
FIG. 3 schematically illustrates another example (third embodiment) of the graphene manufacturing apparatus that performs the peeling step in the graphene manufacturing method of the present disclosure. In the present embodiment, a pair of

electrodes

30 and 32 are arranged facing each other along the side wall surface of the container 40, and graphite 50 in the form of particles or powder is dispersed in the electrolytic solution 20 between the pair of

electrodes

30 and 32. Has been done. With such a configuration, even if the graphite 50 is not housed in the filter 14, the graphite 50 is placed between the pair of

electrodes

30, 32 without contacting the

electrodes

30, 32 and functions as a bipolar electrode. Then, by applying a voltage between the

electrodes

30 and 32, the graphene can be separated from the graphite 50. When the particulate or powdery graphite 50 is dispersed in the electrolyte solution 20, some graphite may come into contact with one of the

electrodes

30, 32, but most of the graphite 50 has

electrodes

30, 32. The graphene can be separated from the graphite 50 by being disposed between the

electrodes

30 and 32 without making contact with the.
Alternatively, the electrolytic solution 20 may be stirred by a stirrer so that the particulate or powdery graphite 50 in the electrolytic solution 20 is placed between the

electrodes

30 and 32 as much as possible. For example, the stirrer 16 may be placed in the container 40 and stirred to suppress the precipitation of the graphite 50, and the graphene may be separated from the entire graphite 50 dispersed in the electrolytic solution, or air may be sent from a blower pump. You may stir by bubbling.

As described above, the specific mode of mainly performing the peeling step in the graphene manufacturing method of the present disclosure has been described, but the graphene manufacturing method and the manufacturing apparatus of the present disclosure are not limited to the above-described embodiments, and other embodiments may be used. It may be performed, and may include other steps other than the peeling step and the collecting step. As another step, for example, a step of sonicating an electrolytic solution containing graphene to miniaturize the graphene after the peeling step can be mentioned.

Also, in the peeling process, the electrolytic solution in the container may be circulated by using a circulation device. FIG. 15 shows an example of a method (graphene production apparatus) for exfoliating graphene from graphite while circulating an electrolytic solution. Note that FIG. 15 is a schematic view seen from above the container 40, and illustration of the power source connected to the

drive electrodes

30 and 32 is omitted. As shown in FIG. 15, a pipe 62 for circulating the electrolytic solution 20 is connected to both sides of the container 40, and the electrolytic solution 40 in the container 40 is circulated through the pipe 62 by a circulation pump 60. A rise in bath temperature can be suppressed. Further, by providing a trap (not shown) such as a filter for collecting the graphene separated from the graphite 10 in the middle of the tube 62, the graphene can be efficiently collected.

Alternatively, graphene may be peeled off while moving the graphite between the pair of electrodes by using a moving device that moves the graphite in the peeling step. 16 to 18 show an example of a method of exfoliating graphene while moving graphite (an example of a graphene manufacturing apparatus). 16 to 18, the electrolytic solution and the container are not shown. For example, as shown in FIG. 16 or FIG. 17, the graphite 10 is held in the in-plane direction of the electrodes 30 and 32 (direction perpendicular and horizontal to the direction in which the

electrodes

30 and 32 face each other) (see FIG. (Not shown) together with the

drive electrodes

30 and 32, or as shown in FIG. 18 (electrolyte solution and container are not shown), the filter 14 accommodating graphite in the form of particles or powder is driven electrode 30. , 32 may be used. Thus, if the graphene is peeled off while moving the graphite between the electrodes, it is possible to continuously process and mass production becomes possible.

The method and apparatus for manufacturing graphene of the present disclosure are not limited to the above-described embodiments, and a plurality of embodiments may be combined.

Hereinafter, the method for producing graphene of the present disclosure will be described more specifically with reference to Examples. However, each of these examples does not limit the present invention.
Experiments were conducted using a platinum plate as a driving electrode and various types of graphite samples as a bipolar electrode. The equipment used in the examples is as follows.
・ Structure observation: Optical microscope (OLYMPUS, BX51M)
Scanning electron microscope (JEOL, JSM-6701F)
・ Crystal structure analysis: X-ray diffraction method (Rigaku, MiniFlex600)

[Experimental example using graphite plate]
In order to investigate the optimum electrolytic solution concentration and the like when performing electrolytic treatment on graphite powder, the effect of electrolytic solution concentration on the exfoliation of graphite was investigated using a graphite plate.
As the electrolysis condition, a high current condition (constant current electrolysis of 5 A) was used, which was capable of peeling the graphite plate in a short time in direct DC electrolysis. With a distance between the driving electrodes of 20 mm, a sulfuric acid concentration of 1 mmol / dm ³ to 0.5 mol / dm ³ (1 mM to 0.1 mm) was applied to a graphite plate (sample immersion area: 6.7 cm ² ) having a width of 10 mm and a thickness of 1 mm. 5 M) and constant current electrolysis was performed for 60 minutes.

<Relationship between electrolyte concentration and voltage and liquid temperature>
The voltage during electrolysis was monitored under the above electrolysis conditions, and the voltage applied between the drive electrodes and the electrolyte temperature were plotted against electrolysis time (FIGS. 4A and 4B). Because of the high current electrolysis, the electrolyte temperature increased during the electrolysis, especially at the initial stage, at any concentration. The steady-state voltage value decreased with the increase of the electrolyte concentration, and the temperature increase was suppressed as the voltage decreased except for 1 mmol / dm ³ .

<Relationship between electrolytic solution concentration and peeling ratio>
The mass of the graphite plate before and after electrolysis was measured, and the peeling ratio was calculated. The appearance of the sample after electrolysis, the peeling ratio, and the average voltage value are shown together in FIG. 5 with respect to the sulfuric acid concentration of the electrolytic solution. As can be seen from the appearance photograph, it was found that the graphite plate was peeled off from the side of the drive electrode facing the cathode, and the degree of progress thereof depended on the electrolyte concentration. It was found that the peeling ratio increased as the sulfuric acid concentration increased, showed the maximum value at 20 mmol / dm ³ , and then decreased at 50 mmol / dm ³ or more.

FIG. 6 shows an optical microscope image and a scanning electron microscope (SEM) image of a peeled product obtained by performing electrolytic treatment at 20 mmol / dm ³ . Since a large number of flaky substances have been confirmed, even if the electricity is not directly applied, a graphite plate is placed between a pair of driving electrodes and subjected to electrolytic treatment, so that minute graphite is exfoliated and graphene is generated. It became clear. From the viewpoint of the peeling ratio, the optimum concentration of sulfuric acid was determined to be 20 mmol / dm ³ , and the voltage at this time was about 50 V, which is a voltage that can be sufficiently realized even in consideration of industrial use. I can say.

<Relationship between electrolysis time and peeling rate>
At the electrolysis time of 60 minutes, the graphite plate could not be completely peeled off, so the electrolysis time was examined. The results obtained by treating the electrolysis for 10 to 120 minutes are shown in FIGS. 7A to 9. After the treatment for 120 minutes, all the exposed parts of the graphite plate in the electrolytic solution were peeled off and disappeared (FIG. 7A). Although the voltage value fluctuated due to the change in the electrolytic solution temperature (Fig. 7B), reproducibility was confirmed in the basic electrolytic behavior. When the mass of the exfoliated product was measured, the exfoliated amount (ratio) increased as the electrolysis time increased (FIGS. 8A and 8B).
Further, when the structure of the exfoliated material obtained at each time was observed with an optical microscope image and a scanning electron microscope, it was confirmed that flaky substances were observed and that graphene was generated (FIG. 9). ..

[Experimental Example Using Graphite Particles or Graphite Powder]
Next, the same treatment was performed on the graphite particles (1 mm square) and the graphite powder (particle size 20 to 500 μm) at a sulfuric acid concentration of 20 mmol / dm ³ . At this time, in order to hold particles or powder in the electrolytic solution between the driving electrodes, a graphite sample was placed in an insulating filter bag and subjected to electrolytic treatment. The details of the experimental method are as follows.
(experimental method)
・ Sample (hold the sample in a bipolar electrode and an insulating filter bag)
Graphite particles (surface area: 6 mm ² )
Graphite powder (particle size: 20-500 μm)
-Electrolysis conditions Drive electrode: Pt plate (30 mm x 30 mm x 2 mm)
Distance between driving electrodes: 20 mm
Electrolyte: 20 mM sulfuric acid (10 ° C)
Current: 5A
Electrolysis time: 30 min
-Post-treatment (1) Filtration, washing (pure water, ethanol), ultrasonic treatment in N, N-dimethylformamide (DMF) (1 min)
(2) Dry after filtration and washing

<Electrolytic treatment using graphite particles>
First, an insulative filter bag containing one graphite particle was placed between the drive electrodes for electrolytic treatment. The sample appearance and voltage-time curve are shown in FIG. 10A, and the change in bath temperature with time is shown in FIG. 10B. The upper limit voltage of 75 V was reached at the initial stage of electrolysis, and the voltage dropped as the bath temperature increased, and finally reached about 55 V. During the electrolysis, the inside of the filter bag gradually turned black, and when the sample was checked after electrolysis for 30 minutes, it was found that the peeling was sufficiently completed by electrolysis for 30 minutes because no particles remained. When the structure of the peeled sample was confirmed by an optical microscope and SEM, graphene was generated (FIG. 11).

<Electrolytic treatment using graphite powder>
Further, graphite powder was housed in an insulating filter bag and subjected to electrolytic treatment in the same manner as graphite particles. The changes in electrolysis behavior and bath temperature were similar to those of particles (FIGS. 12A and 12B). Observation of the treated sample with an optical microscope and SEM confirmed that graphene was generated (FIG. 13).

-X-ray diffraction-
The sample before electrolysis and the sample (exfoliated product) produced by electrolytically treating the plate, particles and powder were analyzed by X-ray diffraction. The XRD pattern is shown in FIG. Since the sharp peak corresponding to the graphite (002) plane was sharply lowered by the electrolytic treatment, it was confirmed that delamination proceeded.
From the above results, it is understood that in the bipolar electrolysis of graphite using low-concentration sulfuric acid, not only the graphite plate but also fine graphite particles or graphite powder can be exfoliated to produce graphene.

In the graphene production method of the present disclosure, an electrolytic solution containing an inexpensive inorganic acid such as sulfuric acid can be used, and since the shape and size of graphite used as a raw material for graphene are not limited, inexpensive natural graphite powder is applied. By doing so, it is possible that graphene can be mass-produced at low cost.

10 graphite plate 12 holding member (an example of graphite arranging means)
14 Filter (an example of graphite placement means)
16 Stirrer 20

Electrolyte

30, 32 Electrode 40 Container 50 Graphite (particle or powder)
60 circulation pumps 62 tubes

The disclosure of Japanese Patent Application 2018-218478 filed on Nov. 21, 2018 is incorporated herein by reference in its entirety.
All publications, patent applications, and technical standards mentioned herein are to the same extent as if each individual publication, patent application, and technical standard were specifically and individually noted to be incorporated by reference, Incorporated herein by reference.

Claims

An inorganic acid, an inorganic salt, an organic acid, and an electrolytic solution containing at least one electrolyte selected from the group consisting of a base and water, a pair of electrodes is arranged, and between the pair of electrodes, the pair of electrodes. In a state in which graphite is arranged without contacting the electrodes of, a peeling step of peeling graphene from the graphite by applying a voltage between the pair of electrodes,
A recovery step of recovering graphene generated by peeling from the graphite,
Of producing graphene including.
The method for producing graphene according to claim 1, wherein the electrolytic solution contains sulfuric acid as the electrolyte.
The method for producing graphene according to claim 2, wherein the concentration of the sulfuric acid in the electrolytic solution is 1 mM or more and 0.5 M or less.
The method for producing graphene according to any one of claims 1 to 3, wherein the graphite is in the form of particles or powder.
The method for producing graphene according to any one of claims 1 to 4, wherein a voltage is applied between the pair of electrodes in a state where the graphite is housed in a filter through which the electrolytic solution can pass.
The method for producing graphene according to any one of claims 1 to 5, wherein the voltage applied between the pair of electrodes is in the range of 5V to 80V.
A container containing an electrolytic solution containing at least one electrolyte selected from the group consisting of inorganic acids, inorganic salts, organic acids, and bases; and water,
A pair of electrodes arranged in the container,
A power supply for applying a voltage between the pair of electrodes,
Between the pair of electrodes arranged in the container, graphite arrangement means for arranging graphite without contacting the pair of electrodes,
An apparatus for producing graphene including.
The graphene production apparatus according to claim 7, wherein the graphite placement means includes a holding member that holds the graphite.
The graphene production apparatus according to claim 8, wherein the holding member contains an insulating filter that contains the graphite and allows the electrolytic solution to pass therethrough.
The graphene production apparatus according to claim 7, further comprising a stirring device that disperses the graphite in the electrolytic solution by stirring the electrolytic solution.
The graphene production apparatus according to any one of claims 7 to 10, including a moving device that moves the graphite between the pair of electrodes.
The graphene production apparatus according to any one of claims 7 to 11, including a circulation device that circulates the electrolytic solution in the container.