Single-crystal spherical carbon nanoparticles

Abstract

The present invention relates to single-crystal spherical carbon nanoparticles, each characterized by being a single crystal, being spherical, and having an average particle diameter of 1 nm to 30 nm. Single-crystal spherical carbon nanoparticles according to the present invention can generate fluorescence at a high fluorescence quantum efficiency by means of excitation via light of a wide wavelength range stretching from ultraviolet light to visible light, and can increase the fluorescence quantum efficiency of conventionally known carbon nanoparticles to 10% or higher. Single-crystal spherical carbon nanoparticles according to the present invention are non-toxic to living organisms held by compound semiconductors formed from cadmium, selenium, tellurium, or the like, and can therefore be used in drug delivery. Furthermore, single-crystal spherical carbon nanoparticles according to the present invention are spherical, and therefore can be packed with an electrode material, etc. for solar cells or secondary ion batteries at a high density and can be used as an electrode material for solar cells as well as negative electrodes of lithium-ion batteries.

Description

Single-crystal spherical carbon nanoparticles

[0001] The present invention relates to single-crystal spherical carbon nanoparticles.

[0002] Carbon nanoparticles are nanoparticles made of carbon atoms, and those with a particle diameter of less than 10 nm are also called carbon quantum dots. Quantum dots formed from metal elements such as CdSe and CdTe and exhibiting fluorescence are known. However, these quantum dots are not suitable for use inside the human body, and therefore, alternative materials have been sought.

[0003] It is known that carbon nanoparticles can be produced by a top-down or bottom-up method. Known top-down methods for producing carbon nanoparticles include, for example, laser ablation, arc discharge, and electrochemical techniques to produce carbon nanoparticles from carbon materials of at least micron size, such as graphite, carbon nanotubes, and diamond. In contrast, known bottom-up methods for producing carbon nanoparticles include, for example, a method known as the hydrothermal method, in which pure water or an organic solvent is heat-treated under high-temperature and high-pressure conditions, and a method using chemical vapor deposition (CVD).

[0004] When using carbon nanoparticles for drug delivery in the human body, they must be hydrophilized. This can be achieved by oxidation in the atmosphere, or by dispersing the nanoparticles in an aqueous solution with a surfactant and then hydrophilizing the nanoparticle surface with an oxidizing agent. Hydrophilization of carbon nanoparticles in an aqueous solution using surfactants requires a post-treatment washing process to remove the surfactant, making this a complex process.

[0005] Claim 1 of Patent Document 1 describes a carbon nanoparticle phosphor containing carbon atoms, oxygen atoms, nitrogen atoms, and optionally hydrogen atoms. Due to the presence of C-N bonds and C-O bonds, the carbon nanoparticle phosphor can be dispersed in an aqueous solution. Claim 9 of Patent Document 1 discloses that the carbon nanoparticle phosphor is produced by a method including a step of hydrothermal synthesis of a solution in which an organic substance selected from the group consisting of citric acid, benzoic acid, glucose, fructose, and sucrose, amines, and one or more selected from inorganic acids and acetic acid are dissolved in an aqueous solvent. The spatial lattice, which is structural information about the carbon nanoparticle phosphor, is not disclosed.

[0006] Patent Document 2 describes a carbon composite for oxygen reduction catalysts (claim 1) that includes nanosheet-shaped graphene oxide or a reduced product thereof and carbon quantum dots. It also describes that the carbon quantum dots may be carbon obtained by a conventional hydrothermal reaction, for example, by heating an aqueous solution containing a carbon source compound such as citric acid and a nitrogen source compound such as ethylenediamine at a temperature above the boiling point of water (claim 6,

[0031] , etc.). These carbon quantum dots differ from the single-crystal spherical carbon nanoparticles of the present invention, and it is not disclosed that the carbon nanoparticle phosphors are single-crystal and spherical.

[0007] Patent Document 3 describes a method for producing luminescent nanocarbon (claim 1,

[0013] ) that includes a reaction step of reacting a raw material solution containing a carbon source compound and a nitrogen source compound by a solvothermal synthesis method or the like. This luminescent nanocarbon is produced by hydrothermal synthesis similar to the production method in Patent Document 1, but does not disclose that the carbon nanoparticle fluorescent material is a single crystal and spherical.

[0008] Patent Document 4 describes a method for forming carbon dots, which includes (a) mixing carbon powder with sulfuric acid and nitric acid to form a carbon powder mixture; (b) heating the carbon powder mixture under reflux to form a refluxed carbon powder mixture; and (c) cooling the refluxed carbon powder mixture. (d) neutralizing the refluxed carbon powder mixture to form a neutralized carbon powder mixture containing solubilized carbon dots (claim 1,

[0036] ). By using an acid in step (a), the carbon powder is oxidized to a quantum size of 1.5 to 6 nm (

[0037] ,

[0038] ). The carbon dots prepared by the above method have abundant carboxyl groups on their surfaces and may have negative charges on the carboxyl groups (

[0048] ). Because carbon dots have abundant carboxyl groups on their surfaces, they differ from the single-crystalline spherical carbon nanoparticles of the present invention. Patent Document 4 also does not disclose that carbon nanoparticle phosphors are single-crystalline and spherical.

[0009] Patent Document 5, owned by the applicant of the present application, describes a method for producing semiconductor microparticles (claim 1) using a fluid processing device equipped with relatively rotating processing surfaces that can approach and separate. Specific examples of the semiconductor element are described as elements selected from the group consisting of silicon, germanium, carbon, and tin (

[0037] ). However, no specific examples are described in which the semiconductor element is carbon. Even based on Patent Document 5, single-crystalline spherical carbon nanoparticles cannot be obtained.

[0010] Patent Document 6, owned by the applicant of the present application, describes a method for producing crystals made of fullerenes (claim 1) by using a fluid treatment device equipped with relatively rotating treatment surfaces that can approach and separate. This production method is a method for recrystallizing fullerenes using fullerenes as raw materials in advance, but is not a method for producing fullerenes themselves. As described above, Patent Document 6 does not disclose that the carbon nanoparticle phosphors are single crystals and spherical.

[0011] Non-Patent Document 1 describes that carbon tetrachloride is reduced with a hydride reducing agent such as lithium aluminum hydride to form carbon quantum dots, which are then reacted with arylamine in the presence of a platinum catalyst to synthesize amine-terminated carbon quantum dots. ２ The carbon quantum dots are different from the single-crystal spherical carbon nanoparticles of the present invention because they have a group. Furthermore, it is not disclosed that carbon quantum dots are single-crystal spherical.

[0012] WO2018 / 163955 JP 2019-155349 JP 2021-183548 JP 2019-511442 Patent 4458202 Patent 4363495

[0013] Journal of Materials Chemistry, Volume 2, pp. 6025-6031 (2014)

[0014] The object of the present invention is to provide carbon nanoparticles that can emit blue to red fluorescence when excited by ultraviolet to visible light at wavelengths, can be used as fluorescent markers that can be injected into the body as almost non-toxic drug delivery agents, and can be used to densely pack electrode materials for secondary batteries.

[0015] As a result of intensive research to solve the above-mentioned problems, the present inventors have found that single-crystal spherical carbon nanoparticles, which are single crystals, spherical, and have an average particle size of 1 nm to 30 nm, are single crystals without grain boundaries that reduce luminous efficiency, and therefore can produce high fluorescence quantum efficiency when excited by light of a wide wavelength range from ultraviolet to visible light, and can be used as a fluorescent marker for drug delivery and can be packed densely into electrode materials for secondary batteries, thereby completing the present invention.

[0016] [1] Single-crystal spherical carbon nanoparticles characterized by being single-crystal, spherical, and having an average particle size of 1 nm to 30 nm. [2] The single-crystal spherical carbon nanoparticles according to [1], which are hexagonal. [3] The single-crystal spherical carbon nanoparticles according to [2], which are formed from a simple lattice, a rhombohedral lattice, or a space lattice consisting of a simple lattice and a rhombohedral lattice. [4] Using the perimeter (Z) and area (S) of a projected image of the single-crystal spherical carbon nanoparticles observed with a transmission electron microscope, the perimeter (Z) and area (S) of the projected image of the single-crystal spherical carbon nanoparticles are calculated by the mathematical formula: 4πS / Z ２ The single-crystal spherical carbon nanoparticles according to any one of [1] to [3], wherein the average circularity calculated by the above formula is 0.9 or more.

[0017] [5] In the IR absorption spectrum, 2800 cm －１ ~2950cm －１ It shows an absorption peak in the wave number range of 900 cm －１ ~1900cm －１ 1000 cm obtained by waveform separation of the wave number range －１ ~1100cm －１ The area of ​​the absorption peak is 900 cm －１ ~1900cm －１ [6] The single-crystal spherical carbon particles according to any one of [1] to [4], wherein the area of ​​the wavenumber range of 1650 cm is 15% or less of the total area of ​​the single-crystal spherical carbon particles according to any one of [1] to [4]. －１ ~1550cm －１ The intensity of the peak of I Ｇ and 1250 cm －１ ~1350cm －１ The intensity of the peak of I Ｄ When I Ｄ / I Ｇ The single-crystal spherical carbon nanoparticles according to any one of [1] to [5], wherein the ratio of

[0018] [7] The single-crystalline spherical carbon nanoparticles according to any one of [1] to [6], which exhibit a fluorescence maximum in the wavelength range of 400 nm to 600 nm in the fluorescence spectrum. [8] The single-crystalline spherical carbon nanoparticles according to any one of [1] to [6], which exhibit a fluorescence maximum in the wavelength range of 900 cm in the IR absorption spectrum. －１ ~1900cm －１ The wave number range is separated into 1300 cm －１~1400cm －１ The area of ​​the absorption peak is 900 cm －１ ~1900cm －１ The single-crystal spherical carbon nanoparticles according to any one of [1] to [7], wherein the area of ​​the single-crystal spherical carbon nanoparticles is 10% or less of the total area in the wavenumber range of [1] to [7].

[0019] The single-crystalline spherical carbon nanoparticles of the present invention are single crystals without grain boundaries that reduce fluorescence efficiency, and therefore can emit fluorescence with high fluorescence quantum efficiency when excited by light of a wide wavelength range from ultraviolet light to visible light, making it possible to increase the fluorescence quantum efficiency of conventionally known carbon nanoparticles to 10% or more. Furthermore, the single-crystalline spherical carbon nanoparticles of the present invention are not toxic to living organisms, as are compound semiconductors formed from cadmium, selenium, tellurium, etc., and can therefore be used for drug delivery. Furthermore, because the single-crystalline spherical carbon nanoparticles of the present invention are spherical, they can be densely packed with electrode materials for solar cells and secondary ion batteries, and can be used as anodes for lithium ion batteries and electrode materials for solar cells.

[0020] 1 shows a TEM image of the single-crystal spherical carbon nanoparticles prepared in Example 1-1. The single-crystal spherical carbon nanoparticles prepared in Example 1-2 have a wave number of 2700 cm. －１ ~3050cm －１ The IR spectrum of the single-crystal spherical carbon nanoparticles prepared in Example 1-2 at a wave number of 900 cm －１ ~1900cm －１ 1 shows the waveform separation of the IR spectrum at a wavenumber of 1250 cm for the single-crystal spherical carbon nanoparticles prepared in Example 1-3. This shows the normalized fluorescence spectrum of the single-crystal spherical carbon nanoparticles prepared in Example 1-3, i.e., the normalized fluorescence spectrum obtained by changing the excitation wavelength from 300 nm to 750 nm in 40 nm increments, with the maximum intensity set to 1.0. This shows the relationship between excitation wavelength and fluorescence peak wavelength, prepared based on the results of FIG. 4. This shows the excitation wavelength dependence of the fluorescence peak wavelength for the single-crystal spherical carbon nanoparticles prepared in Example 1-3. This shows the normalized fluorescence spectrum of the single-crystal spherical carbon nanoparticles prepared in Example 1-3 at a wavenumber of 1250 cm for the single-crystal spherical carbon nanoparticles prepared in Example 1-3. －１ From 1700 cm －１1 shows the Raman scattering spectrum at 2θ of 42° to 46° for the single-crystal spherical carbon nanoparticles produced in Examples 1-1 to 1-3. 1 shows the X-ray diffraction patterns at diffraction angles (2θ) of 42° to 46° for the single-crystal spherical carbon nanoparticles produced in Examples 3-1 to 3-3. 1 shows the normalized fluorescence spectrum of the single-crystal spherical carbon nanoparticles produced in Example 3-3, i.e., the normalized fluorescence spectrum obtained by varying the excitation wavelength from 240 nm to 360 nm with the maximum intensity set to 1.0.

[0021] Hereinafter, embodiments of the present invention will be described. However, the present invention is not limited to only the embodiments described below. Furthermore, examples of application to luminescent materials that generate fluorescence will be described as examples, but the uses of the single-crystalline spherical carbon nanoparticles of the present invention are not limited to these.

[0022] 1. Single-crystal spherical carbon nanoparticles The single-crystal spherical carbon nanoparticles of the present invention are single-crystal, spherical, and have an average particle diameter of 1 nm to 30 nm. If the average particle diameter is 30 nm or more, high-density packing becomes difficult when the single-crystal spherical carbon nanoparticles are used as a secondary battery negative electrode material. The single-crystal spherical carbon nanoparticles are hexagonal. The hexagonal space lattice can have a simple lattice structure or a rhombohedral lattice structure. The single-crystal spherical carbon nanoparticles are preferably calculated using the perimeter (Z) and area (S) of a projected image of the single-crystal spherical carbon nanoparticles observed with a transmission electron microscope, using the formula: 4πS / Z ２ The average circularity calculated by the formula (1) is 0.9 or more, more preferably 0.92 or more, and even more preferably 0.95 or more. When utilizing the fluorescence from single-crystal spherical carbon nanoparticles, the average particle size of the single-crystal spherical carbon nanoparticles is preferably 1.2 nm to 10 nm, more preferably 1.5 nm to 7 nm, and even more preferably 2 nm to 5 nm.

[0023] Carbon has a variety of structures, including sp ２Graphene layers based on C=C bonds made of carbon atoms with hybrid orbitals, graphite in which these graphene layers are stacked in the c-axis direction, and carbon nanotubes are also known. However, because these do not have a band gap, excited electrons generated by excitation light and electron vacancies (positive holes) left by the excited electrons immediately recombine, and do not produce fluorescence. ２ Carbon, which consists of carbon atoms with hybrid orbitals, needs some way to create a band gap. One way to do this is to use sp ２ sp produced by breaking the bond region of a carbon atom with a hybrid orbital and bonding with a carbon atom or an element other than a carbon atom ３ The purpose is to introduce a bond between carbon atoms with hybrid orbitals. ３ The bond of carbon atoms having hybrid orbitals can generate C—H bonds or C—O bonds by bonding hydrogen or oxygen to the edge of the graphene layer. Therefore, it is preferable to use carbon particles having a structure in which graphene layers constituting the single-crystal spherical carbon nanoparticles are stacked, with C—H bonds existing within the graphene layers and C—O bonds existing at the edge of the graphene layers. The presence of C—O bonds in the single-crystal spherical carbon nanoparticles can be confirmed by, for example, a peak at 2800 cm, which is attributed to the stretching vibration of the C—H bond, in the IR absorption spectrum. －１ ~2950cm －１ and the 1000 cm wavenumber region attributed to the stretching vibration of the C-O bond. －１ ~1100cm －１ The single-crystal spherical carbon nanoparticles of Example 1-2 can be confirmed by the presence of absorption in the wave number region of 2925 cm as shown in FIGS. －１ and 2852 cm －１ There is an absorption peak due to a C-H bond at 1097 cm －１ The presence of an absorption peak due to the C-O bond in sp ３ It is possible to confirm the structural changes that contribute to the creation of the band gap due to the presence of carbon atoms with hybrid orbitals.

[0024] The single crystal spherical carbon particles preferably have an IR absorption spectrum of 2800 cm －１~2950cm －１ It shows an absorption peak in the wave number range of 900 cm －１ ~1900cm －１ 1000 cm obtained by waveform separation of the wave number range －１ ~1100cm －１ The area of ​​the absorption peak (stretching vibration of the C-O bond) is 900 cm －１ ~1900cm －１ The monocrystalline spherical carbon particles preferably have a C—O bond ratio of 15% or less, more preferably 2% or more and 15% or less, even more preferably 2% or more and 10% or less, and even more preferably 2% or more and 8.5% or less of the total area in the wave number range.

[0025] The single crystal spherical carbon particles preferably have a Raman scattering spectrum of 1650 cm －１ ~1550cm －１ The intensity of the peak of I Ｇ and 1250 cm －１ ~1350cm －１ The intensity of the peak of I Ｄ When I Ｄ / I Ｇ The ratio of the carbon nanoparticles to the surface area of ​​the carbon nanoparticles is 1.0 or less, preferably 0.95 or less, more preferably 0.85 or less, even more preferably 0.65 or less, and even more preferably 0.55 or less.

[0026] The single-crystal spherical carbon particles are preferably single-crystal spherical carbon nanoparticles that exhibit a fluorescence maximum in the wavelength range of 400 nm to 600 nm in the fluorescence spectrum. The single-crystal spherical carbon particles are preferably single-crystal spherical carbon nanoparticles that exhibit a fluorescence maximum in the wavelength range of 900 cm in the IR absorption spectrum. －１ ~1900cm －１ The wave number range is separated into 1300 cm －１ ~1400cm －１ The area of ​​the absorption peak is 900 cm －１ ~1900cm －１ The area of ​​the C—N bond in the wave number range is preferably 10% or less, more preferably 8% or less, and even more preferably 6.5% or less.

[0027] Fluorescence from carbon nanoparticles is known to occur through three different mechanisms: (A) sp ３ (B) Control of fluorescent color by controlling physical factors, such as changing the band gap of electronic energy depending on the particle size of carbon nanoparticles into which carbon atoms with hybrid orbitals have been introduced (known as the quantum effect). (B) Control of fluorescent color mediated by surface substituents, by treating the carbon nanoparticle surface with various chemical substances to chemically bond various substituents, such as alkyl groups and amino groups with different molecular chain lengths, to the silicon nanoparticle surface. (C) Control of fluorescent color by chemical factors, utilizing compositional changes mediated by oxygen and nitrogen contained in carbon nanoparticles.

[0028] The single-crystalline spherical carbon nanoparticles of the present invention generate fluorescence through the synergistic action of (A) the quantum effect mechanism and (C) the oxygen-mediated mechanism, among the three mechanisms (A) to (C) described above. This mechanism differs from the amino-terminated carbon nanoparticles of Non-Patent Document 1, which use the quantum effect mechanism (A) and the surface modification mechanism (B). The single-crystalline spherical carbon nanoparticles of the present invention preferably generate a fluorescence maximum in the wavelength range of 400 nm to 600 nm.

[0029] 2. Method for Producing Single-Crystalline Spherical Carbon Nanoparticles The single-crystalline spherical carbon nanoparticles of the present invention can be produced, for example, by mixing a liquid containing raw materials for single-crystal spherical carbon nanoparticles (Liquid B) with a reducing liquid (Liquid A) containing metallic lithium and a condensed aromatic compound in a thin film fluid formed between two processing surfaces that are arranged opposite to each other and are capable of approaching and separating from each other, with at least one of the processing surfaces rotating relative to the other.

[0030] (Single-crystalline spherical carbon nanoparticle raw material solution (solution B)) The raw material for single-crystalline spherical carbon nanoparticles is not particularly limited as long as it is a substance that can precipitate single-crystalline spherical carbon nanoparticles by reduction. Preferred raw materials include carbon tetrahalides, more preferably carbon tetrachloride, carbon tetrabromide, carbon tetraiodide, etc., and even more preferably carbon tetrachloride, carbon tetrabromide, etc.

[0031] The solvent for the single-crystalline spherical carbon nanoparticle raw material solution is not particularly limited, as long as it can reduce the raw material for single-crystalline spherical carbon nanoparticles to precipitate single-crystalline spherical carbon nanoparticles, and is an inert substance that does not affect the reduction reaction. Preferred examples of the solvent include ethers, more preferably tetrahydrofuran (THF), dioxane, 1,2-dimethoxyethane (DME), diethylene glycol dimethyl ether, diethylene glycol diethyl ether, diethyl ether, polyethylene glycol dimethyl ether, or mixtures thereof, and even more preferably THF or DME.

[0032] (Residual Water Content of Solvent) It is necessary to use a solvent having a residual water content of 10 ppm or less for use in the present invention. The reason for this is that when single-crystal spherical carbon nanoparticles are produced in a solvent by a reduction reaction, if the residual water content exceeds 10 ppm, the oxidation reaction of the graphene layers becomes significant, causing distortion in the graphite structure produced by stacking the graphene layers in the c-axis direction, and if the graphene layers cannot be stacked on each other, single-crystal spherical carbon nanoparticles will not be obtained.

[0033] (Single-crystalline spherical carbon nanoparticle reduced solution (solution A)) The reducing agent contained in the single-crystalline spherical carbon nanoparticle reduced solution is not particularly limited as long as it can reduce the raw material for single-crystalline spherical carbon nanoparticles contained in the single-crystalline spherical carbon nanoparticle raw material solution and precipitate single-crystalline spherical carbon nanoparticles. Examples of the reducing agent include a combination of metallic lithium and a condensed aromatic compound.

[0034] Examples of condensed aromatic compounds include those that can transfer one electron from metallic lithium to the condensed aromatic compound to generate lithium ions and condensed aromatic compound anions (radical anions). The condensed aromatic compound anions that have undergone one electron transfer have one electron in the lowest unoccupied molecular orbital (LUMO) of the condensed aromatic compound. For example, when carbon tetrachloride is used as the raw material for single-crystalline spherical carbon nanoparticles, the reduction potential of carbon tetrachloride is -1.9 V. Therefore, in order to reduce carbon tetrachloride to carbon nanoparticles, the potential of the condensed aromatic compound anions must be more noble than -1.9 V. Here, the potential is a value relative to a silver (Ag) / silver chloride (AgCl) reference electrode (reference electrode). Examples of condensed aromatic compounds with a potential lower than −1.9 V include naphthalene (−2.53 V), DBB (−2.87 V), biphenyl (−2.68 V), 1,2-dihydronaphthalene (−2.57 V), phenanthrene (−2.49 V), anthracene (−2.04 V), pyrene (−2.13 V), and mixtures thereof, with naphthalene, DBB, and biphenyl being preferred. On the other hand, tetracene (−1.55 V) and azulene (−1.62 V) are not suitable for the reduction of carbon tetrachloride.

[0035] The molar ratio of metallic lithium to condensed aromatic compound is, for example, 1:1 to 1:5, preferably 1:1 to 1:1.2, and more preferably 1:1 to 1:15. The molar ratio of metallic lithium to the raw material for single-crystalline spherical carbon nanoparticles is, for example, 10:1 to 1.2:1, preferably 7:1 to 1.5:1, and more preferably 5:1 to 3:1. It is preferable to use metallic lithium in excess of the raw material for single-crystalline spherical carbon nanoparticles. Using an excess amount makes it possible to prepare single-crystalline spherical carbon nanoparticles. If metallic lithium is used in an amount three-quarters of the raw material for single-crystalline spherical carbon nanoparticles, the nanoparticles will not be completely reduced, and chlorine atoms derived from the raw material will remain in the single-crystalline spherical carbon nanoparticles, resulting in polycrystalline and non-spherical nanoparticles. Examples of solvents for the reduced solution of single-crystalline spherical carbon nanoparticles include the solvents described above used in the raw material for single-crystalline spherical carbon nanoparticles. The concentration of metallic lithium in the reduced solution of single-crystal spherical carbon nanoparticles is not particularly limited, but is determined according to the molar ratio of metallic lithium to the raw materials of the single-crystal spherical carbon nanoparticles.

[0036] (Preparation of reducing solution at low temperature) An alkali metal can be dissolved in an ether-based organic solvent in the coexistence of a condensed aromatic compound. However, at a dissolution temperature of 0°C or higher, the anion of the condensed aromatic compound becomes unstable, and a chemical reaction between the condensed aromatic compound and the alkali metal atom occurs, resulting in a problem of impairing the effectiveness of the reducing solution. For example, when naphthalene (molecular formula: C) is added to a condensed aromatic compound, １０ H ８ ), when lithium (Li) is used as the alkali metal, C １０ H ７ The problem is that the generation of compounds such as Li tends to cause changes in the concentration of naphthalene anions, which act as reducing agents. For this reason, in the production method of the present invention, the temperature of the solution prepared in the step of preparing the reduced solution of single-crystalline spherical carbon nanoparticles is maintained below 0°C, allowing the condensed aromatic compound anions to exist stably and suppressing decomposition of the condensed aromatic compound anions.

[0037] The condensed aromatic compound anion, generated by electron transfer from metallic lithium to a condensed aromatic compound, can bond via Coulomb force with the metallic lithium cation generated by the electron transfer. However, this raises concerns about changes in reducing power due to back electron transfer from the condensed aromatic compound anion to the lithium cation. Fluctuations in reducing power affect the particle size distribution of the resulting single-crystalline spherical carbon nanoparticles. Therefore, to suppress fluctuations in reducing power due to back electron transfer, the lithium cation and the condensed aromatic compound anion must be bound by Coulomb force via the solvent molecules. It is known that the state of anions and cations in such solutions can be confirmed by measuring ultraviolet-visible absorption spectroscopy. According to this, even in the case of metallic lithium, when metallic lithium and naphthalene are dissolved in tetrahydrofuran, an ether-based organic solvent, the state in which THF is present is 60% to 80% at 25°C, but when metallic sodium and naphthalene are dissolved in THF, it is known that the sodium cation and naphthalene anion are directly bonded by Coulomb force, with almost no THF present.

[0038] The solvent can be introduced by lowering the temperature of the solvent. In other words, "using a solvent" means that the lithium cation and the condensed aromatic compound anion are respectively surrounded by solvent molecules, resulting in a solvated cation and a solvated anion, and the solvents are in contact with each other. This type of solvent-mediated contact state between the cation and the anion can be generated within the solution, allowing the condensed aromatic compound anion to exist stably and suppressing back electron transfer from the condensed aromatic compound anion to the lithium cation. In a solution state where such a solution structure is prepared in advance, even if a reducing solution prepared at a temperature above 0°C in a state where solvation is not fully achieved or where a distribution in the solvated state occurs is lowered during the preparation of carbon nanoparticles, solvation is not necessarily complete, resulting in variations in reducing power and causing a distribution in particle size of the carbon nanoparticles within the solution. At low temperatures, ions are directly bonded to each other by Coulomb forces and are in equilibrium. Even if the solution is cooled to a low temperature during the preparation of carbon nanoparticles, it is difficult for solvent molecules to overcome the Coulomb forces and penetrate between the cations and anions. Therefore, the temperature during the preparation of the solution is important.

[0039] (Method for Producing Single-Crystalline Spherical Carbon Nanoparticles) The single-crystal spherical carbon nanoparticles of the present invention can be produced, for example, by mixing a liquid (liquid B) containing raw materials for single-crystal spherical carbon nanoparticles with a reducing liquid (liquid A) containing metallic lithium and a condensed aromatic compound in a thin film fluid formed between two processing surfaces arranged opposite each other, which are capable of approaching and separating each other and at least one of which rotates relative to the other. Examples of the apparatus used in the production method of the present invention include the fluid processing apparatus proposed by the applicant of the present application and described in JP 2009-112892 A. The device includes a stirring vessel having a circular inner circumferential surface and a stirring tool attached to the stirring vessel with a small gap between it and the inner circumferential surface. The stirring vessel has at least two fluid inlets and at least one fluid outlet. A first fluid to be treated containing one of the reactants is introduced into the stirring vessel through one of the fluid inlets, and a second fluid to be treated containing a different reactant is introduced into the stirring vessel through the other fluid inlet via a different flow path from the first fluid to be treated. At least one of the stirring vessel and the stirring tool rotates at a high speed relative to the other, turning the fluid to be treated into a thin film, and reacting reactants contained in at least the first and second fluids to be treated within this thin film. Other examples of fluid treatment devices based on the same principle are described in Patent Documents 6 and 7.

[0040] Preferably, single-crystalline spherical carbon nanoparticles are produced by mixing a liquid (liquid B) containing raw materials for the single-crystalline spherical carbon nanoparticles with the reduced liquid (liquid A) in the thin film fluid. The single-crystalline spherical carbon nanoparticles are produced in two steps: first, graphene layers are formed as nuclei for the single-crystalline spherical carbon nanoparticles, and then these layers are stacked on top of each other to form single-crystalline spherical carbon nanoparticles. Even when the reaction is initiated by bringing liquid B into contact with liquid A at a temperature below 5°C, the frequency of nuclei for single-crystalline spherical carbon nanoparticle growth is low, and therefore the frequency of contact between graphene layers, which are the nuclei for single-crystalline spherical carbon nanoparticles, is also low. Therefore, the growth of the single-crystalline spherical carbon nanoparticles is less susceptible to changes in the concentration of the raw material liquid due to the growth of surrounding single-crystalline spherical carbon nanoparticles, and the supply of raw materials necessary for the growth of the single-crystalline spherical carbon nanoparticles is uniform.

[0041] The temperature of the single-crystal spherical carbon nanoparticle reduced solution (Solution A) introduced into the thin film fluid formed between two processing surfaces arranged opposite to each other, capable of approaching and separating, at least one of which rotates relative to the other, can be, for example, −30° C. to 25° C., preferably −10° C. to 25° C., and more preferably 0° C. to 25° C. In Examples 1 and 3, production was carried out with the temperature of Solution A at 17° C., and as a result, single-crystal spherical carbon nanoparticles that were single-crystal, spherical, and emitted fluorescence with a high fluorescence quantum efficiency could be produced.

[0042] The temperature of the single-crystal spherical carbon nanoparticle raw material liquid (liquid B) introduced into the thin film fluid formed between two processing surfaces arranged opposite to each other, capable of approaching and separating, at least one of which rotates relative to the other, can be, for example, −10° C. to 25° C., preferably 0° C. to 25° C., and more preferably 10° C. to 25° C. In Examples 1 to 3, production was carried out with the temperature of liquid B set to 23° C., and as a result, single-crystal spherical carbon nanoparticles that were single-crystal, spherical, and emitted fluorescence with a high fluorescence quantum efficiency could be produced.

[0043] In the production of single-crystal spherical carbon nanoparticles, for example, lithium chloride is produced as a by-product. Because lithium chloride has high solubility in the reaction solvent, it can be easily separated from the single-crystal spherical carbon nanoparticles by centrifugation.

[0044] 3. Uses of Single-Crystalline Spherical Carbon Nanoparticles The single-crystalline spherical carbon nanoparticles of the present invention can be used, for example, as a light-emitting element, a light-emitting material that emits fluorescence, a negative electrode of a lithium ion battery, an electrode material for a solar cell, and a bonding material for a substrate of a semiconductor device.

[0045] The present invention will be further described below with reference to examples, but the present invention is not limited to these examples.

[0046] (Transmission Electron Microscope (TEM): Preparation of Sample for TEM Observation) The single-crystal spherical carbon nanoparticles obtained in the Examples and Comparative Examples were dispersed in THF in a container at a concentration of approximately 0.001%. The container containing the resulting dispersion was introduced into a glove box under an argon atmosphere, and the dispersion was dropped onto a carbon support film and dried to prepare a sample for TEM observation.

[0047] (TEM Observation) A transmission electron microscope JEM-2100 (manufactured by JEOL Ltd.) was used for TEM observation of the single-crystal spherical carbon nanoparticles. The above-mentioned TEM observation sample was used as the specimen. The observation conditions were an acceleration voltage of 200 kV and an observation magnification of 10,000 times or more. The particle diameter was calculated from the distance between the maximum outer circumferences of the single-crystal spherical carbon nanoparticles observed by TEM, and the average value (average particle diameter) of the results of measuring the single-crystal spherical carbon nanoparticle diameter for 50 particles was calculated.

[0048] (Infrared (IR) Absorption Spectrum) The IR absorption spectrum of the single-crystal spherical carbon nanoparticles was measured by the attenuated total reflection (ATR) method using a Fourier transform infrared spectrophotometer FT / IR-6600 (manufactured by JASCO Corporation). The measurement conditions were a resolution of 4.0 cm －１The number of accumulations was 128, a diamond prism (ATR PRO470-H, an accessory for the FT / IR-6600) was used, and the angle of incidence was 45°. The number of accumulations was 128, and a diamond prism (PKS-D1F) (wide area: refractive index 2.4) was incorporated into the ATRPRO ONE, an accessory for the FT / IR-6600, and the angle of incidence was 45°. The infrared (IR) absorption spectra measured for the single-crystalline spherical carbon nanoparticles produced in the examples and the polycrystalline carbon nanoparticles produced in the comparative examples are referred to as IR spectra.

[0049] (Fluorescence Spectrum) The fluorescence spectrum of the single-crystal spherical carbon nanoparticles was measured using a spectrofluorometer FT-6500 (manufactured by JASCO Corporation). The sample used was the above-mentioned sample for TEM observation. The sample solution dispersed in THF was placed in a quartz cell (optical path length: 1 cm) in an argon atmosphere glove box, the top was sealed, and the cell was then removed from the glove box for measurement. The measurement conditions were an excitation bandwidth of 3 nm, a fluorescence bandwidth of 3 nm, a response of 0.1 seconds, a scanning speed of 100 nm / min, and a data acquisition interval of 0.5 nm. Similarly, the fluorescence spectrum of 9,10-diphenylanthracene, used as a reference substance for relative fluorescence quantum efficiency, was measured under the same conditions.

[0050] (Pattern separation of fluorescence spectrum) The measured fluorescence spectrum of the single-crystalline spherical carbon nanoparticles was subjected to waveform separation to calculate the relative fluorescence quantum efficiency to that of 9,10-diphenylanthracene, and the area % of the fluorescence spectrum showing a peak at 430 nm was calculated. The waveform separation was performed using the waveform separation software built into the FT / IR-6600 used in the IR absorption spectrum measurement.

[0051] (Relative Fluorescence Quantum Efficiency) The fluorescence quantum efficiency of a fluorescent substance can be evaluated by the efficiency of fluorescence generated in response to excitation light. In the present invention, the fluorescence quantum efficiency of the single-crystal spherical carbon nanoparticles was calculated as a relative value to the fluorescence quantum efficiency of 9,10-diphenylanthracene, which is a reference substance, set at 1.0. 9,10-diphenylanthracene has a fluorescence quantum efficiency of 1.0 at a fluorescence peak wavelength of 430 nm. The relative fluorescence quantum efficiency was calculated by the following formula (1): Φ ｘ =Φ ｓ (F ｘ / F ｓ ) (A ｓ / A ｘ ) (I ｓ / I ｘ ) (n ｘ ２ / n ｓ ２ ) (1) (wherein x represents single-crystal spherical carbon nanoparticles, s represents 9,10-diphenylanthracene, Φ ｘ is the relative fluorescence quantum efficiency of single-crystal spherical carbon nanoparticles. ｓ is the quantum efficiency of 9,10-diphenylanthracene. F is the area of ​​the fluorescence spectrum. A is the absorbance at the excitation wavelength. I is the intensity of the excitation light. n is the refractive index of the solvent used.] In the present invention, for 9,10-diphenylanthracene as the reference substance and the single-crystal spherical carbon nanoparticles, the measurement conditions of the spectrofluorometer that measures fluorescence, such as the excitation light bandpass width, fluorescence bandpass width, scanning speed, data acquisition interval, and measurement sensitivity, are all constant, and the same solvent, THF, is used. Therefore, (I ｓ / I ｘ ) (n ｘ ２ / n ｓ ２ ) is 1.0. Therefore, it was calculated from the areas of the fluorescence spectra of the THF dispersion of single-crystal spherical carbon nanoparticles and the THF solution of 9,10-diphenylanthracene, and the absorbance values ​​at the time of measurement.

[0052] (Ultraviolet-Visible: UV-Vis Absorption Spectrum Measurement) The UV-Vis (ultraviolet-visible) absorption spectrum of the single-crystal spherical carbon nanoparticles was measured using an ultraviolet-visible-near-infrared spectrophotometer (product name: V-770, manufactured by JASCO Corporation). The measurement range was 200 nm to 900 nm, with a sampling rate of 0.2 nm and a slow measurement speed. A 10 mm thick quartz cell for liquids was used for the measurement. To calculate the relative fluorescence quantum efficiency of the single-crystal spherical carbon nanoparticles, the nanoparticles were diluted with THF so that the absorbance over a wavelength range of 300 nm to 400 nm was 0.05 or less, and then measured. The absorbance of a THF solution of 9,10-diphenylanthracene was measured under similar measurement conditions.

[0053] (Circularity) The circularity was calculated as an index for evaluating the sphericity of single-crystal spherical carbon nanoparticles as follows. The circularity of the single-crystal spherical carbon nanoparticles was determined by approximating the image obtained by TEM observation as an ellipse using TEM image software iTEM (manufactured by Olympus Soft Imaging Solutions GmbH). Next, from the analysis results of the TEM image analysis software, the major axis (D), perimeter (Z), and area (S) of the ellipse, which is the projected image of the single-crystal spherical carbon nanoparticles, were determined. The values ​​of perimeter (Z) and area (S) were used to calculate 4πS / Z. ２ was calculated and used as the circularity. The closer the circularity value is to 1, the closer the particle is to a sphere, and when the particle shape is a perfect sphere, the circularity is a maximum of 1. In addition, the average value of the major axis (D) of the ellipses was calculated and used as the average particle size. Measurements were performed on 50 independent single-crystal spherical silicon nanoparticles.

[0054] (X-ray Diffraction: XRD) For X-ray diffraction (XRD) measurement, an EMPYREAN powder X-ray diffractometer (manufactured by Malvern Panalytical Division of Spectris Inc.) was used. The measurement conditions were: measurement range: 10 to 100 [°2θ], Cu anticathode, tube voltage: 45 kV, tube current: 40 mA, and scan rate: 0.013° / min.

[0055] (Raman Scattering Spectrum Measurement) The Raman scattering spectrum of the single-crystal spherical carbon nanoparticles was measured using a PR-1w palmtop Raman spectrophotometer manufactured by JASCO Corporation. The wavelength of the excitation laser light was 785 nm, the output of the laser light was 5 mW, and the wavelength was 3 cm.－１ / pixel, measurement wave number is 200 cm －１ ~3000cm －１ It was decided.

[0056] Example 1 In Example 1, the raw material carbon tetrachloride (CCl ４ A THF solution of the above (single-crystalline spherical carbon nanoparticle raw material solution) was reduced using a THF solution of metallic lithium dissolved in naphthalene (single-crystalline spherical carbon nanoparticle reduced solution) to produce single-crystalline spherical carbon nanoparticles. Table 1 shows the formulations of Examples 1-1 to 1-4.

[0057]

[0058] The solvent used in Example 1 was ultra-dehydrated tetrahydrofuran (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) with a residual moisture content of 10 ppm or less. A single-crystalline spherical carbon nanoparticle reduced solution (Liquid A) and a single-crystalline spherical carbon nanoparticle raw material solution (Liquid B) were prepared in a glove box under an argon atmosphere. Specifically, the single-crystalline spherical carbon nanoparticle reduced solution (Liquid A) was prepared by dissolving metallic lithium to a concentration of 0.4 mol / L in a THF solution containing naphthalene dissolved at a preparation temperature of -5°C using a glass-coated magnetic stirrer. Similarly, carbon tetrachloride, the single-crystalline spherical carbon nanoparticle raw material for Liquid B, was dissolved in THF and stirred for at least 60 minutes using a glass-coated magnetic stirrer. Substances indicated by chemical formulas or abbreviations in Table 1 are represented by CCl. ４ represents carbon tetrachloride (manufactured by Kanto Chemical Co., Ltd.), Li represents metallic lithium (manufactured by Kishida Chemical Co., Ltd.), C １０ H ８ is naphthalene (manufactured by Kanto Chemical Co., Ltd.).

[0059] Next, the prepared single-crystalline spherical carbon nanoparticle reduced solution (solution A) and single-crystalline spherical carbon nanoparticle raw material solution (solution B) were mixed using a fluid treatment device described in Patent Document 6 by the applicant of the present application. Here, the fluid treatment device described in Patent Document 6 is the device described in Figure 1 (A) of the same publication, in which the opening d2 of the second introduction part has a concentric ring shape surrounding the central opening of the processing surface 2, which is a ring-shaped disk. Specifically, a single-crystalline spherical carbon nanoparticle reduced solution or a single-crystalline spherical carbon nanoparticle raw material solution, which is liquid A, was introduced from the first introduction part d1 between the processing surfaces 1 and 2. While the processing unit 10 was operating at a rotation speed of 500 rpm to 5,000 rpm, a single-crystalline spherical carbon nanoparticle raw material solution or a single-crystalline spherical carbon nanoparticle reduced solution, which is liquid B, different from the liquid introduced as liquid A, was introduced from the second introduction part d2 between the processing surfaces 1 and 2. The single-crystalline spherical carbon nanoparticle raw material solution and the single-crystalline spherical carbon nanoparticle reduced solution were mixed in the thin film fluid, and single-crystalline spherical carbon nanoparticles were precipitated between the processing surfaces 1 and 2. A discharge liquid containing single-crystalline spherical carbon nanoparticles was discharged from between the processing surfaces 1 and 2 of the fluid processing device. The discharged single-crystalline spherical carbon nanoparticle dispersion was recovered in a beaker via a vessel.

[0060] Table 2 shows the operating conditions of the fluid treatment apparatus of Example 1. The introduction temperatures (liquid delivery temperatures) and introduction pressures (liquid delivery pressures) of liquid A and liquid B shown in Table 2 were measured using a thermometer and a pressure gauge installed in the sealed introduction paths (first introduction part d1 and second introduction part d2) communicating between the processing surfaces 1 and 2. The introduction temperature of liquid A shown in Table 2 is the actual temperature of liquid A under the introduction pressure in the first introduction part d1, and the introduction temperature of liquid B is the actual temperature of liquid B under the introduction pressure in the second introduction part d2.

[0061]

[0062] A wet cake sample was prepared from the single-crystal spherical carbon nanoparticle dispersion discharged from the fluid processing device and collected in a beaker. The preparation method was performed according to a conventional method. The discharged single-crystal spherical carbon nanoparticle dispersion was collected, and the single-crystal spherical carbon nanoparticles were precipitated from the collected solution by centrifugation (at 30,190 G for 2 hours), and the supernatant was separated. Subsequently, ultrasonic cleaning with THF and precipitation were repeated, and the finally obtained single-crystal spherical carbon nanoparticles were dried at -0.10 MPaG at 25°C for 20 hours to obtain a dry powder.

[0063] 1 shows a TEM image of the single-crystal spherical carbon nanoparticles of Example 1-1. Similar results were confirmed for the single-crystal spherical carbon nanoparticles of Examples 1-2 to 1-4. The lattice fringes were observed in one direction, confirming that the nanoparticles were single crystals.

[0064] (C—H bond) FIG. 2 shows the IR spectrum of the single-crystal spherical carbon nanoparticles of Example 1-2 at a wave number of 2700 cm －１ ~3050cm －１ The results of measurements in the region of 2855 cm are shown. －１ absorption and 2920 cm －１ The absorption peak of is attributed to the stretching vibration of the C—H bond, and it was confirmed that the single-crystalline spherical carbon nanoparticles were hydrogenated. The same was confirmed for Examples 1-1, 1-3, and 1-4.

[0065] FIG. 3 shows the IR spectrum of the single-crystal spherical carbon nanoparticles of Example 1-2 at a wave number of 900 cm －１ ~1900cm －１ The results of waveform separation after measurement in the region are shown below. The peak wavenumber of each band after waveform separation and the relative area ratio are shown in parentheses. Waveform separation was performed using the waveform separation software built into the FT / IR-6600.

[0066] (C—O bond) The IR spectrum in FIG. 3 is divided into 10 parts by waveform separation, and the IR spectrum is －１ ~1100cm －１The absorption in this wavenumber region is attributed to C—O bonds. The ratio of the total area of ​​band 9 and band 10, which were separated into this wavenumber region, to the total area (C—O bond ratio) was 10.7%. The C—O bond ratio is preferably 2% or more and 15% or less. If it is less than 2%, it becomes difficult to disperse the single-crystal spherical carbon nanoparticles in an aqueous solution, and if it exceeds 15%, the circularity of the single-crystal spherical carbon nanoparticles will be 0.9 or less, and they will be farther from a spherical shape, which will disadvantageously lead to a decrease in the relative fluorescence quantum efficiency.

[0067] The C—O bonds of single-crystalline spherical carbon nanoparticles can be generated by reducing single-crystalline spherical carbon nanoparticles in ultra-dehydrated tetrahydrofuran (THF), a grade of THF specified to have a residual moisture content of 10 ppm or less, using moisture controlled to a constant level of 10 ppm or less. Because the graphene layer is highly reactive immediately after the reduction reaction, the single-crystalline spherical carbon nanoparticles can be protected by a gentle oxidation reaction caused by a certain amount of moisture. Protecting the surface of the single-crystalline spherical carbon nanoparticles in this way reduces variations due to oxidation during the cleaning and recovery process. This cleaning and recovery process basically requires first dissolving residual organic matter in a THF solvent and then rinsing with pure water, but some oxidation reaction occurs during this cleaning and recovery process.

[0068] (C—N bond) C—N bond is generated by reaction with the outermost surface of the graphene layer that was not protected by oxygen due to exposure to the air atmosphere during the cleaning and recovery process of single-crystal spherical carbon nanoparticles. Since no nitrogen-containing raw materials or solvents are used in the reduction reaction of single-crystal spherical carbon nanoparticles, C—N bond is generated after the reaction of single-crystal spherical carbon nanoparticles. Therefore, nitrogen does not have a significant effect on the fluorescent properties of the single-crystal spherical carbon nanoparticles, but it also makes it possible to terminate defects with nitrogen. In the IR spectrum of FIG. 3, C—N bond is generated at 1300 cm －１ ~1400cm －１ Since it has absorption in the wavenumber region, the peak wavenumber is 1357 cm －１The band 7 corresponds to this band, and the relative area ratio (ratio of C—N bonds) is 6.2%. Since C—N bonds, together with C—O bonds, have the effect of terminating defects in which bonds between carbon atoms in the graphene layer are broken, the ratio of C—N bonds is preferably 10% or less. This C—N bond may not be detected in cases where C—O bonds terminate carbon atom bond defects.

[0069] The C-H bonds of the single-crystal spherical carbon nanoparticles confirmed in Figure 2 can hydrophobize the surface of the single-crystal spherical carbon nanoparticles, allowing the single-crystal spherical carbon nanoparticles to be well dispersed in organic solvents. However, the results in Figure 2 also confirm that the coexistence of C-O bonds enables the nanoparticles to be dispersed in aqueous solvents.

[0070] Figure 4 shows the fluorescence spectrum of the single-crystalline spherical carbon nanoparticles of Examples 1-3. The fluorescence spectra are normalized with the maximum intensity of the fluorescence spectrum obtained for each excitation wavelength set to 1.0, and are the results of varying the excitation wavelength from 320 nm to 580 nm in 20 nm increments. The results in Figure 4 confirm that the fluorescence of the single-crystalline spherical carbon nanoparticles of Examples 1-3 exhibits a maximum peak between 400 nm and 600 nm, depending on the excitation wavelength.

[0071] Figure 5 is a graph showing the relationship between excitation wavelength and fluorescence peak wavelength, created based on the results of Figure 4. It shows the excitation wavelength dependence of the fluorescence peak wavelength of the single-crystalline spherical carbon nanoparticles of Examples 1-3. It is known that as the particle size of single-crystalline spherical carbon nanoparticles increases, the fluorescence peak wavelength shifts to the longer wavelength side, and therefore it is believed that fluorescence is obtained from nanoparticles whose particle size has gradually increased.

[0072] This change in the fluorescence peak wavelength of the single-crystal spherical carbon particles can be explained by the quantum effect (A) of the three mechanisms (A) to (C). That is, the fluorescence peak wavelength of the single-crystal spherical carbon nanoparticles is thought to shift to shorter wavelengths because the band gap increases as the particle size of the single-crystal spherical carbon nanoparticles decreases, resulting in a shift to shorter wavelengths, a result of the quantum effect mechanism (A). Furthermore, the single-crystal spherical carbon nanoparticles of the present invention are not surface-modified with alkyl groups, amino groups, or the like, and therefore do not employ the surface modification mechanism (B) of the three mechanisms. Therefore, the fluorescence is thought to be generated by a synergistic effect of the oxygen-mediated mechanism (C) due to oxygen being bonded to the single-crystal spherical carbon particles, and the quantum effect mechanism (A).

[0073] 6 shows the Raman scattering spectrum of the single-crystal spherical carbon nanoparticles of Examples 1-3. For comparison, the Raman scattering spectrum of particles obtained by crushing the graphite crucible in a mortar is shown. The Raman scattering spectrum of graphite has a peak at 1650 cm －１ From 1550cm －１ Only in the wavenumber region of Ｇ When the bonds of the graphene layers are disrupted and defects occur in the graphite, a peak called a band appears at 1300 cm －１ From 1450 cm －１ To I Ｄ Since a peak called a band appears, the spectral intensity ratio between the two, I Ｄ / I Ｇ The defect of the carbon material can be estimated by the value of I. Ｇ The band intensity is set to 100, and I Ｄ The results are a relative comparison of the band intensities, and the I of the single crystal spherical carbon particles produced in Examples 1-3 Ｄ / I Ｇ The ratio was 0.23, confirming that there were few bond defects.

[0074] 7 shows the XRD patterns of the single-crystal spherical carbon particles of Examples 1-1, 1-2, and 1-4. The graphite crystals are sp ２Graphene layers, each consisting of planar layers of C=C bonds formed by carbon atoms with hybrid orbitals, are stacked in the c-axis direction. In hexagonal graphite, the spatial lattice can be a simple lattice or a rhombohedral lattice. The peaks at diffraction angles 2θ of 42.2° and 44.6° are observed in a simple lattice with a hexagonal structure, whereas the peak at 2θ of 43.3° is observed in a rhombohedral lattice. This result indicates that in single-crystalline spherical carbon nanoparticles with a hexagonal structure, when the spatial lattice is a simple lattice, two graphene layers, designated as layers A and B, form a layered structure such as ABABAB... In the case of a rhombohedral lattice, three graphene layers, designated as layers A, B, and C, form a layered structure such as ABCABCABC... . The average lattice spacing was calculated by dividing the sum of two values ​​of lattice spacing calculated by the Bragg's equation from the diffraction peak angles observed at diffraction angles 2θ = 44.6° and 2θ = 43.3° by 2, to obtain an arithmetic mean value. This was measured for 10 samples, and then the sum of these values ​​was divided by 10 to obtain the average lattice spacing.

[0075] Table 3 shows the average particle size, average circularity, crystal structure, average lattice spacing of graphene layers, C—O bond ratio obtained by IR spectrum, and I obtained by Raman scattering spectrum of the single-crystal spherical carbon nanoparticles of Examples 1-1 to 1-4. Ｄ / I Ｇ The ratio and relative fluorescence quantum efficiency are shown.

[0076]

[0077] Comparative Example 1 The formulation of Comparative Example 1 was the same as that of Example 1 shown in Table 1, but the disk rotation speed was reduced to 600 rpm and 500 rpm as shown in Table 4 to produce single-crystal spherical carbon nanoparticles. Table 5 shows the results for the obtained single-crystal spherical carbon particles. By reducing the disk rotation speed to less than 700 rpm, no change was observed in the crystal structure, but the average circularity was less than 0.9, and I Ｄ / I Ｇ As the ratio increased from 1.0 and the number of defects increased compared to Example 1, the relative fluorescence quantum efficiency became a low value of 5% or less.

[0078]

[0079]

[0080] Example 2 Example 2 shows the results of single-crystalline spherical carbon nanoparticles produced when the single-crystalline spherical carbon particle reduced solution was set at temperatures below 0°C, i.e., -10°C and 10°C, and the disk rotation speeds were 5,000 rpm and 3,500 rpm. The compositions of the single-crystalline spherical carbon nanoparticle reduced solution and the single-crystalline spherical carbon nanoparticle raw material solution were the same as in Example 1, and the production was carried out under the conditions shown in Table 1. Table 6 shows the production conditions for Example 2, and the results of the obtained single-crystalline spherical carbon nanoparticles are shown in Table 7. For the single-crystalline spherical carbon nanoparticles produced in Example 2, the lower the temperature of the single-crystalline spherical carbon nanoparticle reduced solution (solution A), the smaller the average particle size, but the relative fluorescence quantum efficiency was 10% or more.

[0081]

[0082]

[0083] Comparative Example 2 The formulation of Comparative Example 2 was the same as that of Example 1 shown in Table 1, but as shown in Table 8, the disk rotation speed was reduced to 700 rpm, and single-crystal spherical carbon particles were produced at temperatures of the single-crystal spherical carbon nanoparticle reduction solution (solution A) of -10°C and 10°C. Table 9 shows the results of the produced single-crystal spherical carbon nanoparticles. The single-crystal spherical carbon nanoparticles produced at a disk rotation speed of 700 rpm and a solution A temperature of 10°C or less had an average circularity of less than 0.9, and the defect abundance ratio calculated from Raman scattering spectrum was I. Ｄ / I Ｇ The ratio was increased to 1.0 or more, and the relative fluorescence quantum efficiency was reduced to a low value of 5% or less.

[0084]

[0085]

[0086] In Example 3, the formulations of solutions A and B were the same as those in Table 1, and single-crystalline spherical carbon nanoparticles were produced by varying the flow rate ratio of solution B (single-crystalline spherical carbon nanoparticle raw material solution) to solution A (single-crystalline spherical carbon nanoparticle reduced solution). Table 10 shows the production conditions for single-crystalline spherical carbon nanoparticles. Table 11 shows the results for the obtained single-crystalline spherical carbon nanoparticles.

[0087]

[0088]

[0089] 8 shows the XRD pattern of the single-crystal spherical carbon nanoparticles obtained in Example 3. In Example 3-1, a diffraction peak at a diffraction angle 2θ of 43.25° due to a hexagonal rhombohedral space lattice and a diffraction peak at 44.6° due to a hexagonal simple lattice are observed. In Examples 3-2 and 3-3, a diffraction peak at a diffraction angle 2θ of 43.25° due to a rhombohedral space lattice is observed, and results were obtained that indicated that most of the lattice was a rhombohedral lattice. In Example 3-3, a peak was also observed at 43.5°, which was determined to be due to a rhombohedral lattice.

[0090] Figure 9 shows the fluorescence spectrum of the single-crystal spherical carbon nanoparticles produced in Example 3-3. The fluorescence peak wavelength measured at excitation wavelengths of 240 nm to 360 nm was 420 nm, indicating no excitation wavelength dependency. The fluorescence peak wavelength of Example 1-3 shown in Figure 4 exhibits excitation light dependency, with the fluorescence peak wavelength shifting toward longer wavelengths as the excitation wavelength becomes longer. However, the structure of the single-crystal spherical carbon nanoparticles in this case corresponds to a hexagonal crystal structure in which a simple lattice and a rhombohedral lattice are mixed, as shown in Figure 7. Since Example 3-3 only shows results for the rhombohedral lattice, the difference in the excitation light dependency of the fluorescence peak wavelength is thought to be due to differences in the spatial lattice of the single-crystal spherical carbon particles.

[0091] In the production of single-crystalline spherical carbon nanoparticles, the effect of increasing the flow rate of the single-crystalline spherical carbon nanoparticle reduced solution (Liquid A) compared to the flow rate of the single-crystalline spherical carbon nanoparticle raw material solution (Liquid B) is manifested in the fact that the reduction reaction rate is increased, producing a large number of minute graphene layers, and these minute graphene layers are stacked together in the c-axis direction, thereby producing smaller single-crystalline spherical carbon nanoparticles. In this way, by increasing the flow rate of the single-crystalline spherical carbon nanoparticle reduced solution (Liquid A) compared to the flow rate of the single-crystalline spherical carbon nanoparticle raw material solution (Liquid B), the symmetry of the fluorescence spectrum was improved, and fluorescence with a narrow fluorescence spectrum half-width of 70 nm and high color purity was obtained.

[0092] The single-crystalline spherical carbon nanoparticles of the present invention are single crystals without grain boundaries that reduce fluorescence efficiency, and therefore can emit fluorescence with high fluorescence quantum efficiency when excited by light of a wide wavelength range from ultraviolet light to visible light, making it possible to increase the fluorescence quantum efficiency of conventionally known carbon nanoparticles to 10% or more. Furthermore, the single-crystalline spherical carbon nanoparticles of the present invention are not toxic to living organisms, as are compound semiconductors formed from cadmium, selenium, tellurium, etc., and can therefore be used for drug delivery. Furthermore, because the single-crystalline spherical carbon nanoparticles of the present invention are spherical, they can be densely packed with electrode materials for solar cells and secondary ion batteries, and can be used as anodes for lithium ion batteries and electrode materials for solar cells.

Claims

1. A single-crystalline spherical carbon nanoparticle, which is single-crystalline, spherical, and has an average particle diameter of 1 nm to 30 nm.

2. The single-crystalline spherical carbon nanoparticle according to Claim 1, which is hexagonal.

3. The single-crystalline spherical carbon nanoparticle according to Claim 2, which is formed from a simple lattice, a rhombohedral lattice, or a space lattice composed of a simple lattice and a rhombohedral lattice.

4. Using the perimeter (Z) and area (S) of the projected image of the single-crystalline spherical carbon nanoparticles observed by an electron microscope, the mathematical formula: 4πS / Z 2 The single-crystalline spherical carbon nanoparticles according to claim 1, wherein the average value of the circularity calculated by the formula is 0.9 or more.

5. In the IR absorption spectrum, an absorption peak is shown in the wavenumber range of 2800 cm -1 to 2950 cm -1 and 900 cm -1 to 1900 cm -1 The area of the absorption peak in the wavenumber range of 1000 cm -1 to 1100 cm -1 obtained by waveform separation is 15% or less with respect to the total area of the wavenumber range of 900 cm -1 to 1900 cm -1 The single-crystalline spherical carbon particles according to any one of claims 1 to 4.

6. In the Raman scattering spectrum, the intensity of the peak at 1650 cm -1 to 1550 cm -1 is defined as I G , and when the intensity of the peak at 1250 cm -1 to 1350 cm -1 is defined as I D , the single-crystalline spherical carbon nano-particles according to any one of claims 1 to 4, wherein the ratio of I D / I G is 1.0 or less.

7. The single-crystalline spherical carbon nanoparticle according to any one of Claims 1 to 4, which produces a fluorescence maximum in a wavelength range of 400 nm to 600 nm in a fluorescence spectrum.

8. In the IR absorption spectrum, the wavenumber range of 900 cm -1 to 1900 cm -1 is waveform-separated, and the area of the absorption peak in the range of 1300 cm -1 to 1400 cm -1 is 10% or less of the total area of the wavenumber range of 900 cm -1 to 1900 cm -1 The single-crystalline spherical carbon nanoparticles according to any one of claims 1 to 4.