JP6833243B2 - Method for producing graphene and chemically modified graphene - Google Patents

Description

The present invention relates to graphene and a method for producing chemically modified graphene.

Graphene is a two-dimensional sheet composed of carbon and has excellent conduction properties, so it is a material that is attracting attention especially in the field of electronics. Graphene has been produced so far by a CVD method in which graphene is produced on a copper substrate by flowing methane gas or the like under high temperature and vacuum, and graphene is stripped from high-purity graphite using scotch tape. , Mechanical stripping method that transfers to the substrate, ^{chemical stripping method that intercalates graphene with Li +,} etc., and bottom-up organic synthesis method that synthesizes nanographene using benzene analog as a starting material. can give.

As a method for producing graphene using plasma generated in water, a pair of carbon electrodes are immersed in water or an aqueous solution to form a pulse under the conditions of a voltage of 1 kV to 2 kV, a pulse width of 0.5 μs to 4 μs, and a frequency of 5 kHz to 50 Hz. A method of forming graphene from a carbon electrode by applying a voltage to the carbon electrode to generate glow discharge plasma has been proposed (Patent Document 1). In this method, the energy acting between carbon electrodes is limited to a very small amount by generating glow discharge plasma, which is a low-temperature plasma in a non-equilibrium state in which the temperature of electrons and neutral particles is low, although the electron temperature is high. When a plasma active species collides with a carbon electrode, the carbon component is peeled off from the surface of the carbon electrode in the form of graphene.

In addition, a bandgap can be imparted by chemically modifying graphene in which the bandgap does not exist. By chemical modification such as hydrogenation, halogenation, nitrogenation, and introduction of defects, adsorption ability and luminescence can be exhibited, or it can be applied to hydrogen storage and the like. In order to chemically modify graphene, a method of introducing nitrogen into graphene by flowing nitrogen by a CVD method, a method of physically adsorbing a donor or acceptor compound to graphene, and in halogenation, Fluorine, chlorine plasma methods, photochemical reactions, and methods using microwaves have been reported.

However, these production methods are not suitable for mass synthesis, and in most cases, strict control of conditions such as temperature and atmosphere is required.

Japanese Unexamined Patent Publication No. 2014-152095

An object of the present invention is to provide a simple and large-scale method for synthesizing graphene, nanographene, and chemically modified graphene.

The present invention provides a simple and large amount of method for synthesizing graphene, nanographene, and chemically modified graphene. Further, the present invention is a method in which pulse plasma by spark discharge or pulse plasma by instantaneous arc discharge is repeatedly applied in a pulse shape between a pair of carbon electrodes immersed in a solvent, which is desired by selecting a solvent and an applied voltage. This is a method for synthesizing a large amount of chemically modified graphene in a simple manner. A pair of carbon electrodes are immersed in a solvent containing an element to be chemically modified, and a predetermined voltage is applied to generate pulse plasma between the carbon electrodes. Provided is a method of generating and synthesizing a graphene chemically modified with a desired element.

Specific embodiments of the present invention are as follows.
[1] A method for producing graphene.
A method characterized in that a pair of carbon electrodes are immersed in a solvent, spark discharges are repeatedly generated between the pair of carbon electrodes in a pulsed manner, and graphene is formed from the pair of carbon electrodes.
[2] A method for producing graphene.
Immerse a pair of carbon electrodes in a solvent
A pulsed plasma is repeatedly generated by periodically applying a voltage of 10 V or more and 500 V or less, a rising period of 1 μs or more and 50 μs or less, and a pulse width of 10 μs or more and 200 μs or less to the pair of carbon electrodes. ,
A method characterized by forming graphene from the pair of carbon electrodes.
[3] The method according to [1] or [2], wherein the solvent is water, an aqueous sodium hydroxide solution, tetrahydrofuran, methanol, ethanol, or toluene.
[4] The method according to any one of [1] to [3], wherein the graphene formed is nanoparticles of a solid solution.
[5] The method according to any one of [1] to [4], wherein the voltage applied to the pair of carbon electrodes is controlled to control the dimensions of graphene formed.
[6] A method for producing chemically modified graphene.
A pair of carbon electrodes are immersed in a solvent containing atoms constituting a chemically modified group, and spark discharges are repeatedly generated between the pair of carbon electrodes in a pulsed manner to form a chemically modified graphene from the pair of carbon electrodes. A method characterized by that.
[7] A method for producing chemically modified graphene.
A pair of carbon electrodes are immersed in a solvent containing atoms constituting a chemically modifying group.
Pulse plasma is repeatedly generated by periodically applying a pulsed voltage to the pair of carbon electrodes under the conditions of a voltage of 10 V or more and 500 V or less, a rise time of 1 μs or more and 50 μs or less, and a pulse width of 10 μs or more and 200 μs or less. ,
A method characterized by forming chemically modified graphene from the pair of carbon electrodes.
[8] The method according to [6] or [7] , wherein the atom constituting the chemically modifying group is N, F, Cl, Br, I, F, or S.
[9] Solvents containing atoms constituting the chemically modifying group are dichloromethane, chloroform, carbon tetrachloride, 1,1,2,2-tetrachloroethane, trifluoroacetic acid, and 1,3,5-trifluorobenzene methanol solution. , Liquid bromine, 1,1,2,3-tetrabromoethane, bromoform, carbon tetrabromide hexane solution, methyl iodide, iodine solution, diiodomethane, iodoform methanol solution, acetonitrile, ammonia, carbon disulfide or molten sulfur solution The method according to [6] or [7].
[10] The method according to any one of [6] to [9] , wherein the chemically modified graphene formed is nanoparticles of a solid solution.
[11] The method according to any one of [6] to [10], wherein the voltage applied to the pair of carbon electrodes is controlled to control the dimensions of the chemically modified graphene formed.

In the production method of the present invention, pulse plasma is generated between a pair of carbon electrodes by spark discharge or instantaneous arc discharge in a solvent. The arc discharge plasma is a thermal plasma having a high particle density and a local thermal equilibrium state in which the temperature of ions and neutral particles is substantially equal to the electron temperature. Spark discharge is superior in production volume.

By repeating spark discharge or momentary arc discharge in a liquid in a pulse shape, the carbon electrode material momentarily evaporates to an ionized (plasma) state, and carbon atoms agglomerate during cooling and remain at room temperature. Graphene is synthesized in. Since the nanoparticles are synthesized in the liquid and the synthesized nanoparticles are suspended in the liquid, the aggregation of the nanoparticles can be prevented. The synthesized nanoparticles may precipitate in the liquid, but at this time, the nanoparticles do not aggregate. Here, agglutination is a concept that indicates that nanoparticles are bonded to each other and are difficult to separate by stirring. As described above, in the present embodiment, the agglomeration of nanoparticles, which has been a problem in the conventional method, does not occur. Therefore, it can be obtained in a state where nanoparticles are dispersed.

Further, in the method of the present invention, unlike the method using a DC arc discharge in vacuum or air that has been studied conventionally, repeated spark discharge or instantaneous arc discharge in a liquid is repeatedly used in a pulsed manner. Due to the instantaneous plasma state and the quenching effect, it is possible to synthesize not only nanographene but also semi-stable phases such as modified graphene.

The voltage periodically applied between the pair of carbon electrodes is in the range of 10 V or more and 500 V or less, preferably 30 V or more and 400 V or less. At this time, the current peak value fluctuates from several A to several 100 A, for example, 1 A or more and 200 A or less, preferably 1 A or more and 50 A or less, and more preferably 1 A or more and 20 A or less. The current average value is several A or less, for example, 0.1 A or more and 10 A or less. The pulse width is in the range of 10 μs or more and 200 μs or less, preferably 10 μs or more and 100 μs or less, and more preferably 10 μs or more and 50 μs or less. When the pulse current is output, the rising period of the pulse current is, for example, 1 μs or more and 50 μs or less, preferably 1 μs or more and 20 μs or less. At this time, the pulse interval is not limited, but is preferably 5 ms or more and 20 ms or less.

By controlling the voltage applied between the pair of carbon electrodes, the dimensions of the obtained graphene can be controlled. For example, when water is used as a solvent, the larger the applied voltage, the smaller the size of graphene, and it is possible to produce graphene up to a size of several tens of nm. By appropriately controlling the applied voltage and pulse conditions, a fine and uniform single-layer graphene sheet can be synthesized.

In the method of the present invention, when a chemically modified graphene is produced, a pair of carbon electrodes are immersed in a solvent containing an element to be chemically modified, and spark discharge plasma or arc discharge plasma is repeated in a pulse shape under the above conditions. Apply. The solvent containing the element to be chemically modified is not particularly limited as long as it contains the desired element, volatile, flammable, it is preferably selected in consideration of toxicity. For example, when it is desired to chemically modify with a halogen element, a solvent containing a chlorine atom, a fluorine atom, a bromine atom and an iodine atom can be used. Examples of the solvent containing chlorine atoms include dichloromethane (CH ₂ Cl ₂ ), chloroform (CHCl ₃ ), carbon tetrachloride (CCl ₄ ), 1,1,2,2-tetrachloroethanene (CHCl ₂ CHCl ₂ ), and the like. It can be preferably mentioned. As the solvent containing a fluorine atom, trifluoroacetic acid (CF ₃ COOH), 1,3,5-trifluorobenzene methanol solution and the like can be preferably mentioned. Solvents containing bromine atoms include bromine (Br ₂ ), which is liquid at room temperature, 1,1,2,3-tetrabromoethane (CHBr ₂ CHBr ₂ ), bromoform (CHBr ₃ ), and carbon tetrabromide (CBr _4). ) A hexane solution or the like can be preferably mentioned. Preferred examples of the solvent containing an iodine atom include methyl iodide (CH ₃ I), iodine solution (I ₂ ), diiodomethane (CH ₂ I ₂ ), and iodoform methanol solution. Alternatively, when chemical modification with a nitrogen atom is desired, acetonitrile (C ₂ H ₃ N), ammonia (NH ₃ ) and the like can be preferably mentioned. When it is desired to chemically modify with a sulfur atom, carbon disulfide (CS ₂ ), a melted sulfur solution, or the like can be preferably mentioned.

When a solvent containing chlorine atom, fluorine atom, bromine atom, iodine atom, chlorine atom, sulfur atom, etc. is used, fluorine atom, bromine atom, iodine atom, chlorine atom, sulfur atom, etc. become carbon when plasma is generated. It binds to produce modified graphene.

The amount of elements that can be introduced into graphene by this method increases as the substance is unstable as a solvent. For example, between carbon tetrachloride and chloroform, carbon tetrachloride is a stable solvent with a larger number of chlorine atoms, so chloroform, which is a more unstable solvent, can introduce more chlorine atoms. it can.

Further, in this manufacturing method, the production amount can be increased only by increasing the discharge area, and there is no technical restriction on the increase in the discharge area. Therefore, this production method is suitable for mass production of nanoparticles in a solid solution.

According to the present invention, for example, the following effects can be obtained.
(1) Nanographene up to several tens of nm can be produced. The size of graphene can be controlled by changing the applied voltage, the amount of current, and the solvent.
(2) By changing the solvent, graphene chemically modified with graphene, nanographene, nitrogen, boron, phosphorus, halogen elements (fluorine, chlorine, bromine, iodine) and chalcogen (sulfur, selenium, tellurium) can be produced. It can also be controlled in terms of the amount and dimensions of its introduction. For example, N-doping can be performed for ammonia, acetonitrile, etc., and Cl-doping can be performed for chloromethane, chloroform, etc., and this amount can be adjusted by the type and concentration of the solvent.
(3) Regarding chloroformation, 27.4% of chloro can be introduced as an element ratio when chloroform is used.
(4) The production time can be significantly shortened, and depending on the solvent, production can be performed in a few minutes.
(5) Mass synthesis is possible, and depending on the solvent, gram scale synthesis is possible per hour. For example, a voltage of 1 kHz and 240 V is applied to a graphite electrode immersed in chloroform in a 200 mL beaker for 20 minutes to obtain 0.72 g (2.16 g / h) of Cl-doped graphene.
(6) It is an inexpensive manufacturing method because it has low electrical energy and does not require a high vacuum or a high voltage power supply.

It is explanatory drawing which shows the schematic structure of the manufacturing apparatus used in the manufacturing method of this invention. 5 is an XPS chart of each sample synthesized in Example 1. It is an XPS chart of the N-doped graphene synthesized in Example 2. It is an XPS chart of the N-doped graphene synthesized in Example 2. 3 is an XPS chart of Cl-doped graphene synthesized in Example 3. FIG. 5 is an XPS chart of F-doped graphene synthesized in Example 4. FIG. 5 is an XPS chart of Br-doped graphene synthesized in Example 5. It is an XPS chart of the I-doped graphene synthesized in Example 6. FIG. 5 is an XPS chart of S-doped graphene synthesized in Example 7. FIG. 5 is a photograph showing a situation after applying submerged pulse plasma (spark discharge) between graphite electrodes for 15 minutes in Example 8. 6 is an AFM observation image of the graphene sheet synthesized in Example 9. 6 is an AFM observation image of the Cl-doped graphene sheet synthesized in Example 10. It is a structural formula showing chemical modification to graphene / nanographene. It is a graph which shows the potential image photograph of the Cl-doped graphene sheet measured by the Kelvin probe force microscope and the potential difference between two points.

Embodiment

Hereinafter, the present invention will be specifically described with reference to the accompanying drawings, but the present invention is not limited thereto.

FIG. 1 is an explanatory diagram showing an example of a schematic configuration of a nanoparticle manufacturing apparatus 1 used for carrying out the method of the present invention. The nanoparticle production apparatus 1 includes, for example, a power supply apparatus 10, a pair of carbon electrodes 20, a reaction vessel 30, and a vibration apparatus 50. The reaction vessel 30 contains water, an aqueous solution, or a solvent 40 containing an element to be chemically modified (hereinafter, simply abbreviated as “solvent or the like 40”). The vibrating device 50 can be omitted.

The power supply device 10 may periodically output a voltage in the range of 10 V or more and 500 V or less in a pulsed manner in order to generate a pulsed spark discharge plasma or an arc discharge plasma between the pair of carbon electrodes 20. There are no particular restrictions. In consideration of safety and the need for a special device, the power supply device 10 is preferably used in the range of 30 V or more and 400 V or less. In consideration of energy efficiency, the power supply device 10 is used, for example, in the range of 0.1 A or more and 10 A or less on a time average. The current peak value at this time appears in the range of several A or more and several 100 A or less, for example, 1 A or more and 200 A or less, preferably 50 A or less, and more preferably 20 A or less. The rising period of the pulse current is, for example, 1 μs or more and 50 μs or less, preferably 1 μs or more and 20 μs or less.

The pair of carbon electrodes may be vibrated periodically or intermittently. When vibration is applied, graphene deposited between the electrodes is less likely to stay, and discharge is efficiently performed, which is preferable.

As the pair of carbon electrodes 20, carbon electrodes having a desired shape and size such as a rod shape, a wire shape, and a plate shape can be used. A high-purity graphite electrode (99.99% or more) is preferable for synthesizing graphene with controlled chemical modification, but the purity and raw material may be changed as needed.

The solvent or the like 40 not only performs a submerged pulse discharge between the pair of carbon electrodes 20, but also has an effect of temporarily storing a product due to the submerged pulse discharge. The amount of the solvent or the like 40 is not particularly limited, but at least in the reaction vessel 30, at least a part of the pair of carbon electrodes 20 can be present in the solvent or the like 40 and can be scattered and disappear by the pulse discharge in the liquid. However, it is desirable that the amount is such that the diffusibility of the product due to the pulse discharge in the liquid is not lost in the solvent. The temperature of the solvent or the like 40 at the time of discharge is not particularly limited and depends on the type, but usually, discharge is performed in the range of room temperature to 300 ° C. If the temperature of the solvent or the like 40 is too high, the vapor pressure of the solvent or the like 40 rises, and if the solvent or the like 40 is a flammable liquid, there is a possibility of ignition due to electric discharge. On the other hand, if the temperature of the solvent or the like 40 is too low, the viscosity of the solvent or the like 40 may increase and the diffusibility of the product due to the pulse discharge in the liquid may be impaired. The temperature of the solvent and the like 40 is preferably set in consideration of these. For example, when the solvent or the like 40 is water, the temperature range is preferably 20 ° C. to 80 ° C., and when the solvent or the like 40 is chloroform, the temperature range is preferably 20 ° C. to 50 ° C.

The vibrating device 50 gives vibration to the pair of carbon electrodes 20. By giving vibration to the carbon electrode 20, it is possible to prevent the precipitates formed on the surface of the carbon electrode 20 from staying on the surface of the electrode 20 and efficiently perform the discharge. The vibrating device 50 may periodically vibrate the carbon electrode 20, or may vibrate continuously or intermittently. Further, in order to prevent the concentration and temperature of the solvent and the like 40 near the pair of carbon electrodes 20 from changing due to the progress of the reaction and to efficiently cool the surfaces of the pair of carbon electrodes 20, the nanoparticle manufacturing apparatus 1 May include a mechanism for flowing the solvent or the like 40, such as a stirrer.

In the graphene or chemically modified graphene according to the present invention, an appropriate amount of a desired solvent or the like 40 is charged in the reaction vessel 30, a pair of carbon electrodes 20 are immersed in the solvent or the like 40, and a desired voltage is applied by the power supply device 10 to form a pair. It can be manufactured by repeatedly generating pulsed plasma of spark discharge or arc discharge between the carbon electrodes 20 of the above. By repeatedly acting the pulse plasma, graphene is formed on the surface of the carbon electrode 20 and cooled instantaneously, and preferably the graphene is separated from the surface of the carbon electrode 20 by the vibration applied to the surface of the carbon electrode 20 by the vibrating device 50. It can be diffused in 40 such as a solvent.

Hereinafter, the present invention will be described in detail with reference to Examples. In the following examples, unless otherwise specified, "current (A)" means an average value, not a current peak value.

[Example 1]
Two columnar graphite electrodes (purity 99.99995%, Φ = 6.15 mm) were immersed in a 200 ml beaker containing the solvent shown in Table 1, and the electrodes were vibrated under the conditions shown in Table 1. The voltage was periodically applied in a pulse shape (pulse interval: 8 to 17 ms), pulsed plasma of spark discharge was repeatedly generated between the graphite electrodes, graphene and chemically modified graphene were synthesized and analyzed by XPS. The XPS chart is shown in FIG. Sample No. Reference numeral 1 is a graphene electrode as a control. FIG. 2 is a C1s spectrum. In each spectrum, the solid line of the separated spectrum shows the C = C bond, and the broken line shows the CH bond. From FIG. 2, it can be seen that graphene having relatively few structural defects and oxygen functional groups can be synthesized by using a solvent containing water or an alcohol-based OH group. Further, in toluene, since C ₆₀ is produced, almost no oxygen functional group is observed.

Table 2 shows the abundance ratio of each group.

Table 3 shows the abundance ratio of each element.

Since this method uses spark discharge, the current is extremely large compared to glow discharge, and it is suitable for mass production. In addition, modified graphene can be easily synthesized by converting the liquid into a halogen solution or the like.

[Example 2]
Two graphite electrodes are immersed in a 200 ml beaker containing the solvent shown in Table 4, and while vibrating the electrodes, a pulsed spark discharge is generated under the conditions shown in Table 4 to synthesize N-doped graphene. Then, it was analyzed by XPS. The XPS charts are shown in FIGS. 3 and 4. The left side of FIG. 3 shows No. 3 using acetonitrile as a solvent. It is a C1s spectrum for 8 samples, and the right side of FIG. 3 shows the same No. It is an N1s spectrum of 8 samples. The left side of FIG. 4 shows No. 1 using ammonia as a solvent. It is a C1s spectrum for 9 samples, and the right side of FIG. 4 shows the same No. It is an N1s spectrum for 9 samples. In the spectra on the left side and the side of FIG. 3, the solid line of the separated spectrum shows the CN bond, and the broken line shows the C = C bond. In the spectra on the right side of FIG. 3 and the right side of FIG. 4, the solid lines of the separated spectra are CN bonds. The binding mode of N is as shown in Chemical formula 1.

Table 5 shows the abundance ratio of each group.

Table 6 shows the abundance ratio of each element.

From the N1s spectra of FIGS. 3 and 4, it can be seen that when acetonitrile and ammonia are used as the solvents, N is introduced mainly in the pyrolic type (see the structural formula Pyrroleic below).

Table 7 shows the abundance ratios of N-introduced pyrrolic, pyridine, graphite and oxide types.

[Example 3]
Two graphite electrodes are immersed in a 200 ml beaker containing the solvent shown in Table 8 to generate a pulsed spark discharge under the conditions shown in Table 8 while vibrating the electrodes to synthesize Cl-doped graphene. Then, it was analyzed by XPS. The XPS chart is shown in FIG. The upper part of FIG. 5 is the C1s spectrum, the solid line of the separated spectrum shows the C—Cl bond, and the broken line shows the C = C bond. The lower part of FIG. 5 is a Cl2p spectrum. As shown in the upper part of FIG. 5, in the C1s spectrum, the peak of C-Cl and the peak of C-OH overlap. Therefore, when the Cl-doping ratio (Cl / C + Cl) was calculated from the peak of the Cl2p spectrum, it was found. CH ₂ Cl ₂ , CHCl ₃ , and CCl ₄ were 9.75%, 29.67%, and 12.62%, respectively. The _{yield for CHCl 3} was 2.16 g per hour.

Table 9 shows the abundance ratio of each group.

Table 10 shows the abundance ratio of each element.

Introduction amount of Cl for graphene, the most stable as the solvent is the lowest CHCl _3, then it can be seen that the decrease in the order of _CCl 4, _{CH 2} Cl 2.

[Example 4]
Two graphite electrodes are immersed in a 200 ml beaker containing the solvent shown in Table 11, and while vibrating the electrodes, a pulsed spark discharge is generated under the conditions shown in Table 11 to synthesize F-doped graphene. Then, it was analyzed by XPS. The XPS chart is shown in FIG. The upper part of FIG. 6 shows _{the case where CF 3} COOH is used as the solvent, and the lower part of FIG. 6 shows the case where 1,3,5-trifluorobenzene is used as the solvent. The left side is the C1s spectrum and the right side is the F1s spectrum. .. In the C1s spectrum, the solid line of the separated spectrum shows the CF bond, and the broken line shows the C = C bond. The CF bond can also be confirmed in the F1s spectrum.

Table 12 shows the binding energy values of each functional group.

Table 13 shows the abundance ratio of each element.

[Example 5]
Br-doped graphene is synthesized by immersing two graphite electrodes in a 200 ml beaker containing the solvent shown in Table 14 and generating a pulsed spark discharge under the conditions shown in Table 14 while applying vibration to the electrodes. Then, it was analyzed by XPS. The XPS chart is shown in FIG. The left side of FIG. 7 shows _{the case where Br 2} is used as the solvent, the center of FIG. 7 shows the case where CHBr _{2 and} CHBr ₂ are used as the solvent, and the right side of FIG. 7 shows the case where CBr ₄ is used as the solvent. The upper part is the C1s spectrum and the right side is the Br3d spectrum. In the C1s spectrum, the solid line of the separated spectrum shows the bond between C and F, and the broken line shows the C = C bond. A peak of the C-Br group is observed near 286.2 eV, and C-Br binding can be confirmed in the Br3d spectrum.

Table 15 shows the abundance ratio of each element.

[Example 6]
Two graphite electrodes are immersed in a 200 ml beaker containing the solvent shown in Table 16 to generate a pulsed spark discharge under the conditions shown in Table 16 while vibrating the electrodes to synthesize I-doped graphene. Then, it was analyzed by XPS. The XPS chart is shown in FIG. The lower part of FIG. 8 shows _{the case where CH 3} I is used as the solvent, the upper part of FIG. 8 shows the case where I ₂ is used as the solvent, the left side is the C1s spectrum, the upper right side is the I3d spectrum, and the lower right side is the Br3d spectrum. Is. In the C1s spectrum, the solid line of the separated spectrum is the CI bond, and the broken line is the peak of the C = C bond. In the C1s spectrum, the peak of the CI group is observed near 285.8 eV, and in the I3d spectrum, the bond of CI can be confirmed in the vicinity of 621 eV.

Table 17 shows the abundance ratio of each element.

[Example 7]
Two graphite electrodes are immersed in a 200 ml beaker containing the solvent shown in Table 18, and while vibrating the electrodes, spark discharge is generated in a pulsed manner under the conditions shown in Table 18 to synthesize S-doped graphene. Then, it was analyzed by XPS. The XPS chart is shown in FIG. The solid line of the separated spectrum is the CS bond, the broken line is the peak of the C = C bond, and the peak of the CS group is observed near 285.6 eV.

[Example 8]
Two graphite electrodes are immersed in a beaker containing water as a solvent, and the voltage is changed to 60V, 100V, 200V and 240V while giving vibration to the electrodes, and submerged pulse plasma (spark discharge) between the graphite electrodes. ) Was applied for 15 minutes to synthesize a graphene sheet. The pulse interval was 8-17 ms. The graphene obtained after the reaction is shown in FIG. 10, and the yield of the graphene actually obtained is shown in Table 20. It can be seen that the amount of graphene obtained increases as the applied voltage increases.

[Example 9]
Using of _{H 2} O as a solvent, by changing the voltage 60V, 100 V, the 200V and 240V, by applying a liquid in pulsed plasma (spark discharge) while applying vibration to the electrode between the carbon electrodes were synthesized graphene sheet. The pulse interval was 8-17 ms. The obtained graphene solution was added dropwise to mica and dried, and AFM measurement was performed. The AFM image of the graphene sheet is shown in FIG. Table 21 shows the dimensions of the graphene nanosheets read from the AFM observation image. The higher the applied voltage, the smaller the dimensions of the graphene nanosheets.

[Example 10]
_{A graphene sheet was synthesized by using CHCl 3} as a solvent, changing the voltage to 60V, 100V, 200V and 240V, and applying submerged pulse plasma (spark discharge) while applying vibration to the electrodes between the carbon electrodes. The pulse interval was 8-17 ms. The graphene was subjected to ultrasonic treatment for 2 hours, the obtained graphene was centrifuged at 4800 rpm for 1 hour, the obtained solution was dropped and dried on a Si substrate, and AFM measurement was performed. The AFM image of the Cl-doped graphene sheet obtained at a voltage of 240 V is shown in FIG. From the AFM observation image, it can be seen that graphene nanosheets having a diameter of several tens of nm are obtained.

[Physical characteristics]
In the present invention, by changing the solvent, graphene chemically modified with nitrogen, boron, phosphorus, halogen elements (fluorine, chlorine, bromine, iodine) and chalcogen (sulfur, selenium, tellurium) can be produced, and its physical properties. Can also be controlled. For example, a sample obtained by immersing two graphite electrodes in a 200 ml beaker containing the solvent shown in Table 8 to synthesize Cl-doped graphene under the conditions shown in Table 8, dropping these onto a Si substrate, and drying the sample. It was measured with a Kelvin probe force microscope (KPFM). Taking the case of CH ₂ Cl ₂ as an example, two points are taken from the potential image shown in the left figure of FIG. 14 , and a graph showing the potential between these two points (indicated by the white line in the figure) and the thickness of the sheet. There is a 14 right. When the potential decreases, the potential image is displayed in black, and in the graph on the right, it can be seen that the voltage of the substrate decreases from 430 mV to 390 mV. Further comparing the potential image when using _{CH 2 Cl 2, CHCl 3,} CCl 4, I The amount of doping is to increase, it can be seen that the potential image KPFM is reduced. General halogen-doped graphene behaves as p-type, but as the amount of doping increases, the contact potential difference of chemically modified graphene, that is, the value of the work function decreases, approaching the behavior of N-type semiconductors. Understand.

The chemically modified graphene obtained by the synthetic method of the present invention has excellent conduction characteristics like graphene and can control the band gap, so that it can also be used as a semiconductor device. Therefore, it can be expected to be used in FETs, sensors, electrodes, etc. Moreover, since the catalytic activity is very excellent from a chemical point of view, it can be expected as a catalyst for electrodes. In addition, by using chemically modified graphene or an oxidation-treated graphene, excellent proton conductivity can be exhibited, and it is expected as a material for energy creation such as fuel cells, solar cells, and capacitors. In addition, it is possible to control the affinity between the layers of the laminated graphene and the solvent, and it can be expected as a separation film for gas and solution.

Claims (4)

It ’s a method of manufacturing graphene.
Immerse a pair of carbon electrodes in water and
A voltage of 10 V or more and 500 V or less, a rise time of 1 μs or more and 50 μs or less, and a pulse width of 10 μs or more and 200 μs or less are periodically applied to the pair of carbon electrodes to repeatedly generate spark discharge. ,
A method characterized by forming graphene from the pair of carbon electrodes. The method of claim 1, wherein the voltage applied to the pair of carbon electrodes is controlled to control the dimensions of the graphene formed. A method for producing chemically modified graphene.
Dichloromethane, chloroform, carbon tetrachloride, trifluoroacetic acid, 1,3,5-trifluorobenzene, liquid bromine, 1,1,2,3-tetrabromoethane, carbon tetrabromide, methyl iodide, iodine solution, or A pair of carbon electrodes are immersed in a solvent that is carbon disulfide.
A voltage of 10 V or more and 500 V or less, a rise time of 1 μs or more and 50 μs or less, and a pulse width of 10 μs or more and 200 μs or less are periodically applied to the pair of carbon electrodes to repeatedly generate spark discharge. ,
A method characterized by forming a chemically modified graphene selected from Cl-doped graphene, F-doped graphene, Br-doped graphene, I-doped graphene, and S-doped graphene from the pair of carbon electrodes. The method according to claim 3 , wherein the voltage applied to the pair of carbon electrodes is controlled to control the dimensions of the chemically modified graphene formed.