How graphene is produced

Abstract

To provide a new method for producing graphene.SOLUTION: A method for producing graphene includes: preparing a non-aqueous liquid containing at least one first ion selected from the group consisting of alkali metal and ammonium, a first fluoride complex containing at least one first tetravalent atom selected from the group consisting of group IV to group XIV, at least one second ion selected from the group consisting of alkali metal and ammonium, a second fluoride complex containing at least one second trivalent or tetravalent atom selected from the group consisting of group VII, group X and group XI, and a non-aqueous hydrogen fluoride-containing liquid having a content of hydrogen fluoride of 20 mass% or more and 100 mass% or less; and bringing the non-aqueous liquid into contact with graphite, and obtaining graphene.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a method for producing graphene. [Background technology]

[0002] Graphene is a sheet-like material in which carbon atoms are covalently bonded in a hexagonal honeycomb pattern. Graphene is known as a single-layer or multi-layer material, and has high electron and hole mobility and high thermal conductivity. Single-layer graphene is also known as a zero-gap semiconductor, with no band gap. Furthermore, graphene has various optical properties, such as high absorption of white light. These properties of graphene have made it a promising material for use in a variety of fields.

[0003] Graphene can be obtained by exfoliating sheet-like graphene, in which hexagonal carbon atoms constituting graphite are two-dimensionally covalently bonded. Methods for exfoliating sheet-like graphene from graphite include physical, electrical, and chemical methods. Physical methods include a method in which graphite is exfoliated by applying shear force to the powder or graphite in an organic solvent using a mixer or the like. Electrical methods include a method in which graphite is used as an anode in an aqueous solution containing an electrolyte, a voltage is applied between the anode and cathode, and the graphite is oxidized and anionic electrolytes are inserted between the graphite layers, thereby exfoliating the graphite. Chemical methods include a method in which graphite is exfoliated by reacting it with an oxidizing agent such as potassium permanganate in an aqueous sulfuric acid solution (Patent Document 1). [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Special Publication No. 2013-544223 Summary of the Invention [Problem to be solved by the invention]

[0005] Graphene is expected to be a material that can be used in a variety of fields, and new methods for producing graphene are therefore required. [Means for solving the problem]

[0006] One aspect of the present invention is a method for producing graphene, comprising: preparing a non-aqueous liquid containing: a first fluoride complex including at least one first ion selected from the group consisting of alkali metals and ammonium and at least one tetravalent first atom selected from the group consisting of Groups 4 and 14; a second fluoride complex including at least one second ion selected from the group consisting of alkali metals and ammonium and at least one trivalent or tetravalent second atom selected from the group consisting of Groups 7, 10, and 11; and a non-aqueous hydrogen fluoride-containing liquid having a hydrogen fluoride content in the range of 20% by mass or more and 100% by mass or less; and contacting the non-aqueous liquid with graphite to obtain graphene.

[0007] According to one embodiment of the present invention, a novel method for producing graphene can be provided. [Brief explanation of the drawings]

[0008] [Figure 1] 1 is a flowchart illustrating a method for producing graphene. DETAILED DESCRIPTION OF THE INVENTION

[0009] Hereinafter, a method for producing graphene according to the present invention will be described based on one embodiment. However, the embodiment described below is an example for realizing the technical idea of ​​the present invention, and the present invention is not limited to the following graphene production method.

[0010] A method for producing graphene includes preparing a non-aqueous liquid containing: a first fluoride complex containing at least one first ion selected from the group consisting of alkali metals and ammonium and at least one tetravalent first atom selected from the group consisting of Groups 4 and 14; a second fluoride complex containing at least one second ion selected from the group consisting of alkali metals and ammonium and at least one trivalent or tetravalent second atom selected from the group consisting of Groups 7, 10, and 11; and a non-aqueous hydrogen fluoride-containing liquid having a hydrogen fluoride content in the range of 20% by mass or more and 100% by mass or less; and contacting the non-aqueous liquid with graphite to obtain graphene.

[0011] When the second fluoride complex in the non-aqueous liquid acts as an oxidizing agent and comes into contact with graphite, which is a stack of three-dimensionally bonded graphene sheets, each composed of hexagonal carbon atoms covalently bonded two-dimensionally. This extracts electrons from the surface of each graphene sheet, causing charges to accumulate on the surface of each graphene sheet. When charges of the same polarity accumulate on the surface of each stacked graphene sheet, electrostatic repulsion occurs between the graphene sheets, causing the gap between the graphene sheets to widen. The graphene is then exfoliated into sheets composed of two-dimensionally bonded hexagonal carbon atoms, yielding graphene. The first fluoride complex in the non-aqueous liquid is presumed to promote the extraction of electrons from the surface of graphene by the second fluoride complex, which acts as an oxidizing agent. This facilitates electrostatic repulsion between the graphene sheets, making it easier to exfoliate the graphene into sheets. This provides a novel method for producing graphene. Furthermore, the exfoliated graphene is fluorinated simultaneously with the exfoliation from the graphite. This method eliminates the need to produce graphene fluoride using graphene oxide, as disclosed in Patent Document 1, and allows graphene fluoride to be produced directly from graphite. Since the step of preparing graphene oxide is no longer necessary, graphene fluoride can be produced easily.

[0012] 1 is a flowchart showing an example of a method for producing graphene, which includes steps S101 of preparing a non-aqueous liquid containing a first fluoride complex, a second fluoride complex, and a non-aqueous hydrogen fluoride-containing liquid, and S102 of contacting the non-aqueous liquid with graphite to obtain graphene.

[0013] Preparing non-aqueous liquids First Fluoride Complex The first fluoride complex contains at least one first ion selected from the group consisting of alkali metals and ammonium, and at least one tetravalent first atom selected from the group consisting of Group 4 and Group 14. The first ion is Li + , Na + , K. + , Rb + , Cs + and NH4 + Preferably, it is at least one selected from the group consisting of Li + , Na + , K. + and NH4 + More preferably, it is at least one selected from the group consisting of Na + , K. + and NH4 + It is more preferable that the first atom is at least one selected from the group consisting of: (I) (II) (III) (IV ...) (IV)) (IV)) (IV)) (IV)) (IV)) (IV)) (IV)) (IV)) (IV)) (IV)) (IV)) (IV)) (IV)) (IV)) (IV)) (IV)) (IV)) (IV))))))))))))))))))))))))))))))))))))))))))))))))))

[0014] The first fluoride complex preferably has a composition included in the composition formula represented by the following formula (I). A12[M14+ F6] (I) (In formula (I), A1 represents an alkali metal and NH4 + and M1 is at least one first ion selected from the group consisting of Group 4 and Group 14.

[0015] In formula (I), A1 is K + , Na + and NH4 + It is preferable that M1 is at least one selected from the group consisting of Si, Ge, Ti, Zr and Sn.

[0016] The first fluoride complex is specifically K2[Si 4+ F6], Na2[Si 4+ F6], (NH4)2[Si 4+ F6], K2[Ge 4+ F6], Na2[Ge 4+ F6], (NH4)2[Ge 4+ F6], K2[Ti 4+ F6], Na2[Ti 4+ F6], (NH4)2[Ti 4+ F6], K2[Zr 4+ F6], Na2[Zr 4+ F6], (NH4)2[Zr 4+ F6], K2[Sn 4+ F6], Na2[Sn 4+ F6], and (NH4)2[Sn 4+ F6]. The first fluoride complex may be used singly or in combination of two or more kinds.

[0017] Secondary Fluoride Complexes The second fluoride complex contains at least one second ion selected from the group consisting of alkali metals and ammonium, and at least one trivalent or tetravalent second atom selected from the group consisting of Groups 7, 10, and 11. The second ion is Li + , Na + , K. + , Rb+ , Cs + and NH4 + Preferably, it is at least one selected from the group consisting of Li + , Na + , K. + and NH4 + More preferably, it is at least one selected from the group consisting of Na + , K. + and NH4 + It is more preferable that the second atom is at least one selected from the group consisting of: (I) Preferably, the second atom is at least one selected from the group consisting of Mn, Ni, Pd, Pt, Cu, Ag, and Au, and more preferably at least one atom selected from the group consisting of Mn, Ni, Pd, Pt, Cu, and Ag. It is preferable that the second ion contained in the second fluoride complex is at least one selected from the group consisting of K, Na, and ammonium, and the second atom contained in the second fluoride complex is at least one selected from the group consisting of Mn, Ni, Pd, Pt, Cu, Ag, and Au.

[0018] The second fluoride complex preferably has a composition included in the composition formula represented by the following formula (II-1) or a composition included in the composition formula represented by the following formula (II-2). A22[M2 4+ F6] (II-1) (In formula (II-1), A2 is an alkali metal and NH4 + and M2 is at least one tetravalent second atom selected from the group consisting of Groups 7 and 10. A2[M2 3+ F4] (II-2) (In formula (II-2), A2 is an alkali metal and NH4 + and M2 is at least one trivalent second atom selected from the group consisting of Group 11.

[0019] In the formula (II-1) or (II-2), A2 is K+ , Na + and NH4 + and M2 is preferably at least one selected from the group consisting of Mn, Ni, Pd, Pt, Cu, Ag, and Au.

[0020] The second fluoride complex is specifically K2[Mn 4+ F6], Na2[Mn 4+ F6], (NH4)2[Mn 4+ F6], K2[Ni 4+ F6], Na2[Ni 4+ F6], (NH4)2[Ni 4+ F6], K2[Pd 4+ F6], Na2[Pd 4+ F6], (NH4)2[Pd 4+ F6], K2[Pt 4+ F6], Na2[Pt 4+ F6], (NH4)2[Pt 4+ F6], K[Ag 3+ F4], Na[Ag 3+ F4], (NH4)[Ag 3+ F4], K[Au 3+ F4], Na[Au 3+ F4] and (NH4)[Au 3+ F4]. The second fluoride complex may be used singly or in combination of two or more.

[0021] The content of the second fluoride complex is preferably 5% by mass or more and 50% by mass or less, or may be 10% by mass or more and 40% by mass or less, or may be 15% by mass or more and 35% by mass or less, relative to 100% by mass of the total of the first fluoride complex and the second fluoride complex contained in the non-aqueous liquid. When the content of the second fluoride complex is 5% by mass or more and 50% by mass or less, relative to 100% by mass of the total of the first fluoride complex and the second fluoride complex contained in the non-aqueous liquid, the oxidizing power of the second fluoride complex causes it to extract electrons from the surface of sheet-like graphene in which hexagonal carbon atoms are two-dimensionally covalently bonded when it comes into contact with graphite, and the first fluoride complex promotes the electron extraction, collecting charge on the surface of the graphene sheet, facilitating electrostatic repulsion between each layer of the graphene sheet, thereby increasing the spacing between the layers of the graphene sheet and facilitating the production of graphene.

[0022] Non-aqueous hydrogen fluoride-containing liquid The non-aqueous hydrogen fluoride-containing liquid has a hydrogen fluoride content in the range of 20% by mass to 100% by mass. The non-aqueous hydrogen fluoride-containing liquid may be 100% by mass of liquid hydrogen fluoride under standard conditions (25°C, 1 atmospheric pressure). The hydrogen fluoride content in the non-aqueous hydrogen fluoride-containing liquid may be in the range of 20% by mass to 80% by mass, 30% by mass to 60% by mass, 20% by mass to 30% by mass, or 60% by mass to 80% by mass. The non-aqueous hydrogen fluoride-containing liquid may contain, in addition to hydrogen fluoride, a compound that is liquid under standard conditions (25°C, 1 atmospheric pressure) and has a boiling point of 120°C or higher. The non-aqueous hydrogen fluoride-containing liquid may contain at least one compound selected from the group consisting of heterocyclic compounds, amines, ureas, amides, carbamates, trialkylphosphines, ethers, esters, alcohols, and quaternary ammonium salts. Commercially available non-aqueous hydrogen fluoride-containing liquids include Olah's reagent, a pyridine-HF complex containing 70% by mass of hydrogen fluoride and pyridine. Other examples of non-aqueous hydrogen fluoride-containing liquids include triethylamine-HF complexes containing 28% by mass of hydrogen fluoride and triethylamine. Other examples of non-aqueous hydrogen fluoride-containing liquids include urea-HF complexes containing 65-75% by mass of hydrogen fluoride and urea, and DMPU-HF complexes containing 65% by mass of hydrogen fluoride and N,N'-dimethylpropylene urea.

[0023] Examples of heterocyclic compounds include alicyclic compounds having a ring selected from 1,3-propylene oxide, trimethylene sulfide, pyrrolidine, tetrahydrofuran, tetrahydrothiophene, piperidine, tetrahydropyran, and tetrahydrothiopyran, and heterocyclic aromatic compounds having a ring selected from furan, thiophene, pyrrole, pyrazole, imidazole, isoxazole, thiazole, thiadiazole, pyridine, pyridazine, pyrimidine, pyrazine, triazine, benzofuran, indole, thianaphthene, benzimidazole, benzoxazole, benzothiazole, benzotriazole, purine, quinoline, isoquinoline, quinoxaline, quinazoline, dibenzothiophene, acridine, and phenanthroline. The nitrogen-containing heterocyclic compound may contain fluorine, chlorine, or bromine.

[0024] The compound containing imidazole and fluorine includes an imidazolium salt represented by the following formula (1).

[0025] [ka]

[0026] In formula (1), R1 and R3 each independently represent an alkyl group having 1 to 4 carbon atoms; 2、 R 4、 and R5 each independently represent a hydrogen atom or an alkyl group having 1 to 4 carbon atoms. Some or all of R1 to R5 may be bonded to each other to form a ring. n represents a number from 1 to 4. Examples of alkyl groups having 1 to 4 carbon atoms include a methyl group, an ethyl group, an n-propyl group, an i-propyl group, and an n-butyl group. R 2、 R 4、 and R5 may be a hydrogen atom, a methyl group, or an ethyl group, or may be a hydrogen atom. In formula (1), n ​​is a number from 1 to 4 and does not necessarily have to be an integer. The number of n can be calculated from the elemental analysis value of the compound.

[0027] Specific examples of the compound represented by formula (1) include 1,3-dimethylimidazolium salt, 1,3,4-trimethylimidazolium salt, and 1-ethyl-3-methylimidazolium salt. 1-Ethyl-3-methylimidazolium salt is a salt that melts at room temperature. In addition, in formula (1), some or all of R1 to R5 may be bonded to each other to form a ring. Specific examples include 1,3-dimethylbenzimidazolium salt and 1-ethyl-3-methylbenzimidazolium salt.

[0028] Examples of oxygen-containing heterocyclic compounds containing fluorine, chlorine or bromine include 3-trichloromethylfuran, 3-tribromomethylfuran, 2,3-bis[trichloromethyl]benzofuran, and 2,3-bis[tribromomethyl]benzofuran.

[0029] Examples of sulfur-containing heterocyclic compounds containing fluorine, chlorine, or bromine in the compound include 2-trichloromethylthiophene, 3-trichloromethylthiophene, 2,3-bis[trichloromethyl]thiophene, 2,5-bis[trichloromethyl]thiophene, 3,4-bis[trichloromethyl]thiophene, 2-tribromomethylthiophene, 3-tribromomethylthiophene, 2,3-bis[tribromomethyl]thiophene, 2,5-bis[tribromomethyl]thiophene, 3,4-bis[tribromomethyl]thiophene, 2-trichloromethylthianaphthene, 2-tribromomethylthianaphthene, 4,6-bis[trichloromethyl]dibenzothiophene, and 4,6-bis[tribromomethyl]dibenzothiophene.

[0030] Examples of nitrogen-containing heterocyclic compounds containing fluorine, chlorine, or bromine in the compound include 2-trichloromethylpyrrole, 2-tribromomethylpyrrole, 4-chloro-3-trichloromethylpyrazole, 4-chloro-3,5-bis[trichloromethyl]pyrazole, 4-chloro-3-tribromomethylpyrazole, 4-chloro-3,5-bis[tribromomethyl]pyrazole, 1-methyl-3-trichloromethylpyrazole-4-carboxylate, 1,2-bis[trichloromethyl]imidazole, 1,3-bis[trichloromethyl]imidazole, 1,5-bis[trichloromethyl]imidazole, 1,5-bis[tribromomethyl]pyrazole, 1,2-bis[trichloromethyl]imidazole, 1,3-bis[trichloromethyl]imidazole, 1,5-bis[tribromomethyl]pyr ... Bis[trichloromethyl]imidazole, 2,5-bis[trichloromethyl]imidazole, 4,5-bis[trichloromethyl]imidazole, 1,2,5-tris[trichloromethyl]imidazole, 2,3,4-tris[trichloromethyl]imidazole, 1,2-bis[tribromomethyl]imidazole, 1,3-bis[tribromomethyl]imidazole, 1,5-bis[tribromomethyl]imidazole, 2,5-bis[tribromomethyl]imidazole, 4,5-bis[tribromomethyl]imidazole, 1,2,5-tris[tribromomethyl]imidazole [tribromomethyl]imidazole, 2,3,4-tris[tribromomethyl]imidazole, 2-trichloromethylpyridine, 3-trichloromethylpyridine, 4-trichloromethylpyridine, 2,3-2,5-bis[trichloromethyl]pyridine, 2,6-bis[trichloromethyl]pyridine, 3,5-bis[trichloromethyl]pyridine, 2-tribromomethylpyridine, 3-tribromomethylpyridine, 4-tribromomethylpyridine, 2,3-2,5-bis[tribromomethyl]pyridine, 2,6-bis[tribromomethyl]pyridine, 3,5-bis[tribromomethyl]pyridine bromomethyl]pyridine, 3-trichloromethylpyridazine, 3-tribromomethylpyridazine, 4-trichloromethylpyridazine, 4-tribromomethylpyridazine, 2,4-bis[trichloromethyl]pyrimidine, 2,6-bis[trichloromethyl]pyrimidine, 2,4-bis[tribromomethyl]pyrimidine, 2,6-bis[tribromomethyl]pyrimidine, 2,4-dichloro-5-trichloromethylpyrimidine, 2-trichloromethylpyrazine, 2-tribromomethylpyrazine, 1,3,5-trisbis[trichloromethyl]triazine, 1,3,5-Trisbis[tribromomethyl]triazine, 4-trichloromethylindole, 5-trichloromethylindole, 4-tribromomethylindole, 5-tribromomethylindole, 2-trichloromethylbenzimidazole, 2-tribromomethylbenzimidazole, 5-trichloromethyl-1H-benzotriazole, 5-tribromomethyl-1H-benzotriazole, 6-trichloromethylpurine, 6-tribromomethylpurine, 3-trichloromethylquinoline, 4-trichloromethylquinoline, 3-tribromomethylquinoline, 4-tribromomethylquinoline, 3-tri Examples of the chloromethylisoquinoline include chloromethylisoquinoline, 3-tribromomethylisoquinoline, 4-trichloromethylchinoline, 4-tribromomethylchinoline, 2-trichloromethylquinoxaline, 2-tribromomethylquinoxaline, 5-trichloromethylquinoxaline, 5-tribromomethylquinoxaline, 9-trichloromethylacridine, 9-tribromomethylacridine, 4-trichloromethyl-1,10-phenanthroline, 4-tribromomethyl-1,10-phenanthroline, 5-trichloromethyl-1,10-phenanthroline, and 5-tribromomethyl-1,10-phenanthroline.

[0031] Examples of oxygen- and nitrogen-containing heterocyclic compounds containing fluorine, chlorine, or bromine include 3,5-bis[trichloromethyl]isoxazole, 3,5-bis[tribromomethyl]isoxazole, 2-trichloromethylbenzoxazole, and 2-tribromomethylbenzoxazole.

[0032] Examples of sulfur- and nitrogen-containing heterocyclic compounds containing fluorine, chlorine, or bromine include 4,5-bis[trichloromethyl]thiazole, 4,5-bis[tribromomethyl]thiazole, 5-trichloromethyl-thiadiazole, 5-tribromomethyl-thiadiazole, 2-trichloromethylbenzothiazole, and 2-tribromomethylbenzothiazole.

[0033] Examples of amines include methylamine, ethylamine, dimethylamine, diethylamine, trimethylamine, triethylamine, n-propylamine, isopropylamine, n-butylamine, dibutylamine, tributylamine, diethylenetriamine, monoethanolamine, triethanolamine, 1,2-propylenediamine, monoisopropanolamine, diisopropanolamine, triisopropanolamine, o-toluidine, p-nitrotoluene, N-(2-aminoethyl)ethanolamine, aniline, piperazine, and triethylenetetramine.

[0034] Examples of ureas include urea, 1,1,3,3-tetramethylurea, 1,3-dimethyl-2-imidazolidinone, 1,3-diethyl-2-imidazolidinone, 1,3-di(n-propyl)-2-imidazolidinone, 1,3-di(n-butyl)-2-imidazolidinone, 1,3-dimethyl-3,4,5,6-tetrahydro-2(1H)-pyrimidinone, N,N'-dimethylpropylurea, N,N'-diethylpropylurea, N,N'-di(n-propyl)propylurea, and N,N'-di(n-butyl)propylurea.

[0035] Examples of amides include N,N'-dimethylformamide, N,N'-diethylformamide, N,N'-dimethylacetamide, and 1-methyl-2-pyrrolidone.

[0036] Examples of carbamic acids include carbamic acid and ethyl carbamate.

[0037] Examples of trialkylphosphines include hexamethylphosphoramide.

[0038] Examples of ethers include n-butyl ether, n-hexyl ether, anisole, phenetole, butylphenyl ether, amylphenyl ether, methoxytoluene, benzyl methyl ether, diphenyl ether, dibenzyl ether, 1,2-diethoxyethane, 1,2-dibutoxyethane, diethylene glycol dimethyl ether, diethylene glycol diethyl ether, and diethylene glycol dibutyl ether.

[0039] Examples of esters include n-butyl acetate, n-pentyl acetate, isopentyl acetate, cyclohexyl acetate, benzyl acetate, butyl propionate, isopentyl propionate, methyl benzoate, dimethyl phthalate, and γ-butyrolactone.

[0040] The alcohols are alcohols having a hydrocarbon group with 4 or more carbon atoms, such as 1-butanol, 2-methyl-1-propanol, 2-butanol, 2-methyl-2-propanol, butanol, 1-pentanol, 2-pentanol, 1-hexanol, 2-hexanol, 2-methyl-2-pentanol, 1-heptanol, 2-heptanol, 1-octanol, 1-nonanol, 1-decanol, 1-undecanol, and 1-dodecanol.

[0041] The quaternary ammonium salt includes a quaternary ammonium salt represented by the following formula (2).

[0042] [ka]

[0043] In formula (2), R6 represents an alkyl group having 1 to 4 carbon atoms, R7 represents a methoxymethyl group, a methoxyethyl group, or an ethoxymethyl group, and n represents a number from 1 to 4.

[0044] The quaternary ammonium salt represented by formula (2) is composed of a quaternary ammonium cation and a fluorohydrogenate anion. Examples of R6 in the quaternary ammonium cation include linear or branched alkyl groups having 1 to 4 carbon atoms. Specific examples include methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, and tert-butyl groups. Examples of R7 in the quaternary ammonium cation include methoxymethyl, methoxyethyl, and ethoxymethyl groups. Examples of the fluorohydrogenate anion include F(HF)n, where n is a number from 1 to 4. - Examples of the fluorohydrogenate anion include the fluorohydrogenate anion represented by the following formula: n does not necessarily have to be an integer, and is preferably a number of 1.5 or more and 3 or less, and more preferably a number of 2 or more and 2.5 or less.

[0045] Specific examples include N-methoxymethyl-N-methylpyrrolidinium fluorohydrogenate, N-methoxymethyl-N-ethylpyrrolidinium fluorohydrogenate, N-methoxymethyl-Nn-propylpyrrolidinium fluorohydrogenate, N-methoxymethyl-N-iso-propylpyrrolidinium fluorohydrogenate, N-methoxymethyl-Nn-butylpyrrolidinium fluorohydrogenate, N-methoxymethyl-N-iso-butylpyrrolidinium fluorohydrogenate, N-methoxymethyl-N-tert-butylpyrrolidinium fluorohydrogenate, N-methoxyethyl-N-methylpyrrolidinium fluorohydrogenate, N-methoxyethyl-N-ethylpyrrolidinium fluorohydrogenate, N-methoxyethyl-Nn-propylpyrrolidinium fluorohydrogenate, and N-methoxyethyl-N-iso-propylpyrrolidinium. Examples of the fluorohydrogenate include N-methoxyethyl-Nn-butylpyrrolidinium fluorohydrogenate, N-methoxyethyl-N-iso-butylpyrrolidinium fluorohydrogenate, N-methoxyethyl-N-tert-butylpyrrolidinium fluorohydrogenate, N-ethoxymethyl-N-methylpyrrolidinium fluorohydrogenate, N-ethoxymethyl-N-ethylpyrrolidinium fluorohydrogenate, N-ethoxymethyl-Nn-propylpyrrolidinium fluorohydrogenate, N-ethoxymethyl-N-iso-propylpyrrolidinium fluorohydrogenate, N-ethoxymethyl-Nn-butylpyrrolidinium fluorohydrogenate, N-ethoxymethyl-N-iso-butylpyrrolidinium fluorohydrogenate, and N-ethoxymethyl-N-tert-butylpyrrolidinium fluorohydrogenate.

[0046] The non-aqueous liquid is preferably prepared by adding a first fluoride complex and a second fluoride complex to a non-aqueous hydrogen fluoride-containing liquid. Alternatively, the first fluoride complex and the second fluoride complex may be added to the non-aqueous hydrogen fluoride-containing liquid while stirring the non-aqueous hydrogen fluoride-containing liquid to prepare the non-aqueous liquid. The order in which the first fluoride complex and the second fluoride complex are added to the non-aqueous hydrogen fluoride-containing liquid may be such that the first fluoride complex is added first and then the second fluoride complex is added, or the second fluoride complex is added first and then the first fluoride complex is added, or the first fluoride complex and the second fluoride complex may be added simultaneously to the non-aqueous hydrogen fluoride-containing liquid. Alternatively, the non-aqueous liquid may be prepared by mixing the first fluoride complex and the second fluoride complex and adding the resulting mixture to the non-aqueous hydrogen fluoride-containing liquid.

[0047] The total amount of the first fluoride complex and the second fluoride complex in the non-aqueous liquid is preferably 12 g / L to 120 g / L, and may be 15 g / L to 100 g / L, 18 g / L to 80 g / L, or 20 g / L to 70 g / L per 1 L of the non-aqueous hydrogen fluoride-containing liquid. When the total amount of the first fluoride complex and the second fluoride complex in the non-aqueous liquid is 12 g / L to 120 g / L, when the non-aqueous liquid comes into contact with graphite, the oxidizing power of the second fluoride complex extracts electrons from the surface of the graphene sheet, and the first fluoride complex promotes the electron extraction, collecting charge on the surface of each graphene sheet and facilitating electrostatic repulsion between the layers of each graphene sheet, thereby increasing the spacing between the layers of each graphene sheet and facilitating the production of graphene sheet.

[0048] contacting the graphite with a non-aqueous liquid Graphene is obtained by contacting graphite with a non-aqueous liquid. Examples of graphite include artificial graphite such as coke-based artificial graphite and pitch-based artificial graphite, and natural graphite such as spheroidized natural graphite, flake natural graphite and lump natural graphite.

[0049] The amount of graphite relative to 1 L of nonaqueous liquid is preferably in the range of 1 g / L to 5 g / L, and may be in the range of 1.5 g / L to 4 g / L, or may be in the range of 2 g / L to 3.5 g / L, per L of nonaqueous liquid. When the amount of graphite relative to 1 L of nonaqueous liquid is in the range of 1 g / L to 5 g / L, sheet-like graphene can be easily obtained when the nonaqueous liquid and the graphite come into contact with each other.

[0050] In the step of contacting the non-aqueous liquid with the graphite, the temperature of the non-aqueous liquid is preferably in the range of 10° C. or more and 40° C. or less, and may be in the range of 15° C. or more and 35° C. or less. The temperature of the non-aqueous liquid may be room temperature, and as long as the temperature is in the range of 10° C. or more and 40° C. or less, evaporation of the non-aqueous hydrogen fluoride-containing liquid contained in the non-aqueous liquid can be suppressed, and the non-aqueous liquid can be brought into contact with the graphite relatively safely.

[0051] The non-aqueous liquid is preferably brought into contact with the graphite while stirring. By bringing the non-aqueous liquid into contact with the graphite while stirring, the oxidizing power of the second fluoride complex contained in the non-aqueous liquid facilitates electron extraction from the surface of the sheet-like graphene in which hexagonal carbon atoms are two-dimensionally covalently bonded, and can further promote electron extraction by the first fluoride complex. This can collect charge on the surface of each sheet-like graphene, facilitate electrostatic repulsion between the layers of each sheet-like graphene, and increase the spacing between the layers of each sheet-like graphene, making it easier to obtain graphene. The non-aqueous liquid may be stirred at a speed ranging from 60 rpm to 1350 rpm, from 70 rpm to 1200 rpm, from 80 rpm to 1000 rpm, or from 90 rpm to 900 rpm.

[0052] After contacting graphite with a non-aqueous liquid to exfoliate the graphene, the supernatant non-aqueous liquid is removed and the graphene is dried as needed to obtain sheet-like graphene in which hexagonal carbon atoms are covalently bonded two-dimensionally.

[0053] The presence or absence of graphene can be confirmed by visually checking the state of dispersion in the non-aqueous liquid. The non-aqueous liquid after contact with graphite is subjected to ultrasonic treatment or the like, and visually inspected after a certain period of time. If the color of the non-aqueous liquid after contact with graphite is darker than that of the non-aqueous liquid before contact with graphite, it can be confirmed that sheet-like graphene has been exfoliated from the graphite that has come into contact with the non-aqueous liquid. Furthermore, the non-aqueous liquid that has come into contact with graphite can be uniformly dispersed by ultrasonic treatment or the like, centrifuged at 5000 rpm for 10 minutes, and the absorbance of the supernatant at 700 nm can be measured to confirm that sheet-like graphene has been exfoliated from the graphite that has come into contact with the non-aqueous liquid. Untreated graphite aggregates due to strong van der Waals forces and tends to precipitate in non-aqueous liquids, resulting in a supernatant liquid with an absorbance of approximately 0. However, when graphene is brought into contact with a non-aqueous liquid containing fluoride and bonded to fluorine, it is thought to remain dispersed in the non-aqueous liquid without agglomerating due to the electrostatic repulsion between the fluorine atoms, resulting in a darker color in the non-aqueous liquid and a higher absorbance in the supernatant.

[0054] The surface morphology of the resulting graphene can also be confirmed by measuring it using an atomic force microscope (AFM). An AFM is a type of microscope that detects the atomic force acting between a probe and a sample. The AFM probe is attached to the tip of a cantilever. The probe is brought into contact with the sample surface with a small force, and the surface morphology can be imaged by scanning the probe horizontally (X and Y directions) while feedback-controlling the probe-sample distance (Z direction) to maintain a constant cantilever deflection. Numerical processing of this image data allows for the quantification of nanoscale morphology. While various indices exist for quantifying nanoscale morphology, the Z-axis value can be used to confirm the successful production of graphene. It is known that the thickness of single-layer graphene measured by AFM is 1 nm, and the Z-axis value can be used to determine the number of graphene layers produced.

[0055] The nonaqueous solution contains a hydrogen fluoride-containing liquid, which allows fluorine ions to bond with the resulting exfoliated graphene, resulting in fluorine-containing fluorinated graphene. The fluorine in the resulting graphene acts as a charged impurity, creating an energy gap. This allows for a wider range of applications as a material for semiconductor devices, where the band gap is easier to control than in a state without a band gap (zero gap, 0 gap). Fluorinated graphene also easily adsorbs fluorine gas, making it suitable for use as a fluorine gas adsorbent. Furthermore, fluorinated graphene can be used as a water repellent material, taking advantage of the water-repellent properties of fluorine. Additionally, it can be used as an auxiliary agent for the formation of solid electrolyte interfacial membranes (SEI membranes) in the anode materials of lithium-ion batteries.

[0056] The resulting graphene contains fluorine, and the fluorine content is preferably in the range of 1 atomic % to 20 atomic % relative to the total amount of carbon, fluorine, and oxygen (100 atomic %), and may be in the range of 3 atomic % to 19 atomic % or 5 atomic % to 18 atomic %. When the fluorine content of the resulting graphene is in the range of 1 atomic % to 20 atomic % relative to the total amount of carbon, fluorine, and oxygen (100 atomic %), the fluorine behaves as a charged impurity, providing a sufficient energy gap and broadening the range of applications for the resulting graphene. The contents of each element, such as carbon, fluorine, and oxygen, contained in the graphene can be measured by measuring the surface of the resulting graphene using a commercially available X-ray photoelectron spectroscopy (XPS) or Electron Spectroscopy for Chemical Analysis (ESCA) device.

[0057] The resulting graphene contains fluorine, and the atomic ratio F / C of fluorine to carbon is preferably within a range of 0.01 to 0.3, or may be within a range of 0.02 to 0.25, or may be within a range of 0.03 to 0.20. When the atomic ratio F / C of fluorine to carbon contained in the graphene is within a range of 0.01 to 0.3, the fluorine behaves as a charged impurity, and a sufficient energy gap can be imparted, thereby broadening the applications of the resulting graphene.

[0058] The resulting graphene does not necessarily contain oxygen, and the oxygen content in the graphene is preferably in the range of 0 atomic % to 5 atomic % relative to the total of carbon and fluorine (100 atomic %), and may be in the range of 0.001 atomic % to 4 atomic %, 0.002 atomic % to 3 atomic %, or 0.003 atomic % to 2 atomic %. If oxygen is contained in the graphene, it is presumed that oxygen-containing groups are attached to the surface of the graphene, and since the oxygen-containing groups are hydrophilic, they may interfere with the properties of the fluorine contained in the graphene, such as water repellency. Therefore, the resulting graphene does not necessarily contain oxygen. [Example]

[0059] The present invention will be described in more detail below with reference to examples, but the present invention is not limited to these examples.

[0060] Example 1 Non-aqueous liquid preparation process 0.8 g of potassium hexafluorosilicate (K2SiF6) as the first fluoride complex and 0.2 g of potassium hexafluoromanganate (K2MnF6) as the second fluoride complex were weighed out, and these were added to 45 mL of a non-aqueous hydrogen fluoride-containing liquid, which was a pyridine-HF complex containing 70 mass % hydrogen fluoride and 30 mass % pyridine. The non-aqueous hydrogen fluoride-containing liquid was stirred to dissolve the potassium hexafluorosilicate and potassium hexafluoromanganate, thereby preparing a non-aqueous liquid.

[0061] Contact process between non-aqueous liquid and graphite A polytetrafluoroethylene (PTFE) stir bar was placed in a non-aqueous liquid adjusted to 25°C. While continuously stirring at 300 rpm using a magnetic stirrer, 0.1 g of graphite (flake graphite, product name: Graphite, manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) was added to the non-aqueous liquid and stirred for 72 hours. The liquid containing the non-aqueous liquid and graphene was collected and centrifuged at 25°C and 5,000 rpm for 5 minutes to precipitate graphene. A non-aqueous hydrogen fluoride-containing liquid was added, and the mixture was centrifuged under the same conditions to remove the supernatant. This operation of removing the supernatant was repeated three times to remove the second fluoride complex and the first fluoride complex remaining as impurities in the graphene. N-methyl-2-pyrrolidone (NMP) was then added to the precipitate, and the mixture was centrifuged at 5,000 rpm at 5°C for 5 minutes to collect the supernatant. The supernatant was collected three times to prevent any non-aqueous hydrogen fluoride-containing liquid from remaining in the NMP solvent after redispersion. NMP was then added to give a graphene dispersion with a graphene concentration of 3 mg / mL.

[0062] Comparative Example 1 The graphite before contact with the non-aqueous liquid was used as Comparative Example 1.

[0063] Evaluation and Results 1 Measurement of shape by AFM The graphene obtained by the manufacturing method according to Example 1 was fixed on a silicon substrate, and the height difference between the surface Z1 of the silicon substrate and the surface Z2 of the graphene was measured using an AFM. The results are shown in Table 1, and the AFM measurement conditions are shown below. The measurement was performed on two graphene samples obtained by the manufacturing method according to Example 1 (Example 1: Sample 1 and Sample 2). AFM measurement conditions Measurement equipment: AFM5400L (Hitachi High-Tech Science Corporation) Scanner diameter: 20 μm Scanning frequency: 1.0Hz Measurement area: 5 μm x 5 μm square Number of XY data: 256 x 256 Probe: SI-DF20 (material silicon, tip radius R10nm, probe depth 12.5μm)

[0064] [Table 1]

[0065] From the results shown in Table 1, it was confirmed that graphene with about five layers could be obtained because the height difference was about 5 nm.

[0066] Evaluation and Results 2 Surface measurement by XPS The atomic weights of the surfaces of the graphene obtained by the production method according to Example 1 and the graphite according to Comparative Example 1 were measured using XPS. The results are shown in Table 2, and the XPS measurement conditions are shown below. In Table 2, "ND" indicates that the value is below the detection limit. The detection limit is less than 0.1 atomic %. In Table 2, "-" indicates that the atomic weight of F was below the detection limit, and therefore the atomic ratio F / C could not be calculated. XPS measurement conditions Equipment: Quantera SXM (ULVAC-PHI, Inc.) X-ray source: Monochromatic Al Kα ray (hν 1486.6eV) Analysis area: 200 μmφ Pass energy: 224 eV

[0067] [Table 2]

[0068] From the results shown in Table 2, it was confirmed that the graphene obtained by the production method according to Example 1 contains fluorine, and the fluorine content is in the range of 1 atomic % to 20 atomic % relative to the total amount of carbon, fluorine, and oxygen (100 atomic %). It was presumed that the fluorine in the graphene obtained by the production method according to Example 1 behaves as a charged impurity, and can provide a sufficient energy gap. [Industrial Applicability]

[0069] Graphene obtained by the manufacturing method of the present disclosure can be used in semiconductor elements such as field-effect transistors, transparent conductive films, etc., and can be utilized in fields such as electronic sensors, transistors, batteries, fuel cells, solar cells, touch screens, display technology, lighting, etc. Graphene obtained by the manufacturing method of the present disclosure can also be utilized as a material for semiconductor elements that is easy to control, a material for fluorine gas adsorbents, and a material for water repellents.

Claims

1. preparing a non-aqueous liquid including: a first fluoride complex containing at least one first ion selected from the group consisting of alkali metals and ammonium, and at least one tetravalent first atom selected from the group consisting of Groups 4 and 14; a second fluoride complex containing at least one second ion selected from the group consisting of alkali metals and ammonium, and at least one trivalent or tetravalent second atom selected from the group consisting of Groups 7, 10, and 11; and a non-aqueous hydrogen fluoride-containing liquid having a hydrogen fluoride content in the range of 20% by mass to 100% by mass; bringing the non-aqueous liquid into contact with graphite to obtain graphene.

2. 2. The graphene production method according to claim 1, wherein, in preparing the non-aqueous liquid, a content of the second fluoride complex is in a range of 5 mass % or more and 50 mass % or less, relative to 100 mass % in total of the first fluoride complex and the second fluoride complex contained in the non-aqueous liquid.

3. 3. The graphene production method according to claim 1, wherein in preparing the nonaqueous liquid, a total amount of the first fluoride complex and the second fluoride complex is in a range of 12 g / L or more and 120 g / L or less per 1 L of the nonaqueous hydrogen fluoride-containing liquid.

4. 4. The graphene production method according to claim 1, wherein in preparing the non-aqueous liquid, the first fluoride complex and the second fluoride complex are added to the non-aqueous hydrogen fluoride-containing liquid to prepare the non-aqueous liquid.

5. 5. The method for producing graphene according to claim 1, wherein, in bringing the non-aqueous liquid into contact with the graphite, an amount of graphite relative to the non-aqueous liquid is in a range of 1 g / L or more and 5 g / L or less per 1 L of the non-aqueous liquid.

6. 6. The method for producing graphene according to claim 1, wherein, in bringing the non-aqueous liquid into contact with graphite, the temperature of the non-aqueous liquid is in the range of 10°C or higher and 40°C or lower.

7. The method for producing graphene according to claim 1 , wherein the non-aqueous liquid is brought into contact with the graphite while being stirred.

8. 8. The graphene production method according to claim 1, wherein, in preparing the non-aqueous liquid, the second ions contained in the second fluoride complex are at least one type selected from the group consisting of K, Na, and ammonium, and the second atoms are at least one type selected from the group consisting of Mn, Ni, Pd, Pt, Cu, Ag, and Au.

9. 8. The graphene production method according to claim 1, wherein, in preparing the non-aqueous liquid, the first fluoride complex has a composition included in a composition formula represented by the following formula (I): A1 ２ [M1 ４＋ F ６ ] (I) (In formula (I), A1 is an alkali metal and NH ４ ＋ and M1 is at least one first ion selected from the group consisting of Group 4 and Group 14.

10. 10. The graphene production method according to claim 1, wherein, in preparing the non-aqueous liquid, a first ion contained in the first fluoride complex is at least one type selected from the group consisting of K, Na, and ammonium, and the first atom is at least one type selected from the group consisting of Si, Ge, Ti, Zr, and Sn.

11. 10. The graphene production method according to claim 1, wherein, in preparing the non-aqueous liquid, the second fluoride complex has a composition included in a composition formula represented by the following formula (II-1) or a composition included in a composition formula represented by the following formula (II-2): A2 ２ [M2] ４＋ F ６ ] (I-1) (In formula (II-1), A2 is an alkali metal and NH ４ ＋ and M2 is at least one tetravalent second atom selected from the group consisting of Groups 7 and 10. A2M2 ３＋ F ４ ] (II-2) (In formula (II-2), A2 is an alkali metal and NH ４ ＋ and M2 is at least one trivalent second atom selected from the group consisting of Group 11.

12. 12. The graphene production method according to claim 1, wherein in preparing the nonaqueous liquid, the nonaqueous hydrogen fluoride-containing liquid contains at least one selected from the group consisting of heterocyclic compounds, amines, ureas, amides, carbamic acid esters, trialkylphosphines, ethers, esters, and alcohols.

13. 13. The method for producing graphene according to claim 1, wherein the obtained graphene contains fluorine, and the fluorine content is in the range of 1 atomic % or more and 20 atomic % or less, relative to a total of 100 atomic % of carbon, fluorine, and oxygen.

14. 13. The method for producing graphene according to claim 1, wherein the oxygen content of the obtained graphene is in the range of 0 atomic % or more and 5 atomic % or less, relative to a total of 100 atomic % of carbon, fluorine, and oxygen.

15. 15. The method for producing graphene according to claim 1, wherein the obtained graphene contains fluorine and has an atomic ratio F / C of fluorine to carbon in the range of 0.01 or more and 0.3 or less.

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