Carbon material particle and method for producing the same

Abstract

To provide spherical carbon material particles and a method for producing the same.SOLUTION: The carbon material particles have a G-band in a Raman spectrum obtained by Raman spectroscopic analysis. The volume average particle diameter of the carbon material particles is 10 to 200 nm, and the carbon material particles are soluble in N, N-dimethylformamide. The carbon material particles can be obtained by dissolving a soluble carbon material in an organic solvent and mixing it with a poor solvent to precipitate the carbon material particles.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to spherical nano-carbon material particles and a method for producing the same.

Background Art

[0002] Carbon materials and carbon material particles (such as graphite, activated carbon, carbon black, graphene, carbon nanotubes, etc.) are used in a wide range of fields. Further, carbon material particles are used in energy fields such as batteries, automotive fields such as tires, and lubrication fields such as solid lubricants.

[0003] As carbon material particles, they are synthesized by various production methods such as chemical vapor deposition method and thermal decomposition method of organic substances (Patent Document 1, Non-Patent Documents 1-5).

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Non-Patent Documents

[0005]

Non-Patent Document 1

Non-Patent Document 2

Non-Patent Document 3

Non-Patent Document 4

Non-Patent Document 5

Summary of the Invention

Problems to be Solved by the Invention

[0006] As described above, carbon material particles are manufactured by various manufacturing methods, but energy and costs are required in the manufacturing methods, such as high temperature and the need for an inert atmosphere. Also, although the synthesis of particles with a particle size of several nm or several microns has been widely carried out, the synthesis of carbon material particles with a particle size of about several tens to 100 nm in between has been difficult. Further, in existing synthesis methods, aggregation of particles is also strong, and it has been difficult to use them as single particles (primary particles).

[0007] As a method for manufacturing by adjusting the particle size of carbon material particles, a spray firing method has been disclosed (Non-Patent Documents 1-2). By reducing the concentration during spraying, it is possible to synthesize nano-sized carbon material particles, but there is a problem that the concentration is very low and it is not suitable for mass production. Therefore, there has been a demand for a method for manufacturing carbon material particles with a desired particle size by a manufacturing method that is energy- and cost-saving, simple, and capable of mass production.

[0008] In view of the above situation, an object of the present invention is to provide spherical nano carbon material particles and a manufacturing method by reprecipitation of a soluble carbon material.

Means for Solving the Problems

[0009] The present inventor conducted various studies to achieve the above object and arrived at the present invention. That is, carbon material particles having a G band in a Raman spectrum obtained by Raman spectroscopic analysis, wherein the volume average particle size of the carbon material particles is 10 to 200 nm, and the carbon material particles are soluble in N,N-dimethylformamide. Further, a method for manufacturing carbon material particles, which includes a step of dissolving a soluble carbon material having a G band in a Raman spectrum obtained by Raman spectroscopic analysis in an organic solvent, and a step of mixing the carbon material solution obtained in the above step with a poor solvent to precipitate carbon material particles.

Effects of the Invention

[0010] By using the carbon material particles and the method for producing the same of the present invention, it is possible to simply produce carbon material particles having a desired particle size, and provide carbon material particles that can be used for lubrication applications and the like. [Brief description of the drawings]

[0011]

Figure 1

Figure 2

Figure 3

[0012] The present invention will be described in detail below. Note that a combination of two or more of the individual preferred embodiments of the present invention described below is also a preferred embodiment of the present invention.

[0013] [Carbon material particles] The carbon material particles of the present invention have a G band (1580 cm due to a benzene hexagonal mesh structure) in a Raman spectrum obtained by Raman spectroscopy. -1 In addition, the D band (at around 1350 cm due to defects and functional groups) -1 It is also preferable that the graphene has a peak in the G′ band (at about 2700 cm -1 It is also preferable that the particle has a peak in the vicinity of 100 nm. It is possible to select an appropriate wavelength for the excitation wavelength in the Raman spectrum. By having these peaks, the particle can be said to be made of a carbon material, and can exhibit the effects of a carbon material (lubricity, etc.).

[0014] The carbon material particles of the present invention have a volume average particle diameter of 10 to 200 nm as measured by particle size distribution measurement. Even for particle diameters that were conventionally difficult to manufacture, by using the carbon material particles of the present invention and the method for producing the same, it is possible to adjust the particle diameter to a desired value. The lower limit of the volume average particle diameter of the carbon material particles of the present invention is more preferably 12 nm or more, and even more preferably 15 nm or more. The upper limit of the volume average particle diameter is more preferably 150 nm or less, and even more preferably 120 nm or less. Further, the number average particle diameter of the carbon material particles of the present invention is preferably 10 to 200 nm, more preferably the lower limit is 12 nm or more, and even more preferably 14 nm or more. The upper limit of the number average particle diameter is more preferably 150 nm or less, and even more preferably 120 nm or less. The above volume average particle diameter and number average particle diameter are the average particle diameters measured by observation using the dynamic light scattering method (DLS) or SEM.

[0015] The carbon material particles of the present invention are soluble in a solvent, particularly N,N-dimethylformamide (DMF). General carbon materials (such as graphite, activated carbon, carbon black, graphene, carbon nanotubes, etc.) are insoluble in solvents. Some of them can be dispersed, but essentially, being soluble in a solvent means dissolving in the solvent, for example, passing through a membrane filter (such as 0.1 μm) when the liquid is passed through. On the other hand, general carbon materials cannot pass through. That is, the determination of solubility or not is as follows: after mixing the carbon material with the solvent to a concentration of 0.001% by mass, ultrasonic treatment is carried out for 1 hour, and when the obtained liquid is passed through a GL chromatographic disk (pore size 0.1 μm) manufactured by GL Sciences Inc., if the carbon material passes through the filter paper, it is considered soluble in that solvent. The fact that the carbon material to be coated is soluble in the solvent enables the application of the reprecipitation method, which is a feature of the manufacturing method of the present invention. However, in the case of general nanoparticles, although they are in a dispersed state, their size is small, so they can pass through the pores of the filter. Since the carbon material particles of the present invention can apply the reprecipitation method, when dissolved in a good solvent such as DMF, they are dissolved at the molecular level rather than in the form of particle shape. That is, "the carbon material particles are soluble in the solvent" means that after mixing with the solvent to a concentration of 0.001% by mass, ultrasonic treatment is carried out for 1 hour, and when the obtained liquid is passed through a GL chromatographic disk (pore size 0.1 μm) manufactured by GL Sciences Inc., the carbon material passes through the filter paper, and when the solution is cast on a silicon wafer, dried, and observed by SEM or transmission electron microscope (TEM), the original particle shape cannot be maintained (observed as a film or a lump).

[0016] In order to maintain good solubility and dispersibility, the carbon material particles of the present invention preferably have an oxygen-to-carbon ratio (O / C) of 0.1 or more by X-ray photoelectron spectroscopy (XPS). To maintain better solubility and dispersibility, 0.15 or more is preferable, 0.2 or more is more preferable, 0.25 or more is even more preferable, and 0.3 or more is most preferable.

[0017] The carbon material particles of the present invention preferably emit fluorescence. This enables their use as a fluorescence detector. Specifically, it is preferable that visible light fluorescence is emitted when excited with light of 350 nm. The wavelength of the fluorescence preferably has a peak in the range of 400 to 600 nm.

[0018] [Dispersion of carbon material particles] The dispersion of carbon material particles of the present invention is a dispersion in which the carbon materials of the present invention are dispersed without dissolution. That is, the main component (50% or more) of the dispersion medium is a poor solvent in which the carbon materials of the present invention do not dissolve. The dispersion medium may be one kind or a mixture of two or more kinds of solvents. Examples of the dispersion medium (poor solvent) include water, higher alcohols, hydrocarbons, aromatic hydrocarbons, ethers, esters, and the like. Any solvent that does not satisfy the above "the carbon material particles are soluble in the solvent" may be used as the poor solvent. Among them, water is preferable. Although the main component (50% or more) of the dispersion medium needs to be a poor solvent, other components such as other solvents (which may be good solvents) and additives (dispersants, antioxidants, preservatives, etc.) may be blended. The concentration of the poor solvent is preferably 50% or more, more preferably 60%, further preferably 70% or more, even more preferably 80% or more, and most preferably 90% or more. This results in a stably dispersed dispersion.

[0019] The concentration of the carbon material particles in the dispersion of carbon material particles of the present invention is preferably 0.01 to 50% by mass, more preferably 0.05 to 20% by mass, and most preferably 0.1 to 10% by mass. Being within this range enables application to various uses. The concentration can be adjusted by distilling off the solvent by heating or reduced pressure, or by concentrating using a membrane filter or ultrafiltration.

[0020] [Soluble carbon material] The soluble carbon material used in the present invention is soluble in a solvent. General carbon materials (such as graphite, activated carbon, carbon black, graphene, carbon nanotubes, etc.) are insoluble in a solvent. Although some can be dispersed, essentially, being soluble in a solvent means being able to dissolve in the solvent, for example, it can pass through a membrane filter (such as 0.1 μm) when the liquid is passed through. On the other hand, general carbon materials cannot pass through. That is, the determination of solubility is as follows: after mixing the carbon material with the solvent to a concentration of 0.001% by mass, ultrasonic treatment is performed for 1 hour, and when the resulting liquid is passed through a GL chromatodisk (pore size 0.1 μm) manufactured by GL Sciences Inc., if the carbon material passes through the filter paper, it is considered soluble in that solvent. The solubility of the carbon material in the solvent enables the precipitation (reprecipitation) of homogeneous particles.

[0021] The solvent in which the soluble carbon material used in the present invention is soluble is not particularly limited, and it may be a single solvent or a mixed solvent of two or more solvents. Examples of soluble solvents (good solvents) include nitrogen-containing solvents such as N,N-dimethylformamide and N-methylpyrrolidone, ketone solvents such as acetone and methyl ethyl ketone, ester solvents such as ethyl acetate, alcohol solvents such as methanol, ethanol, and 2-propanol, and halogen solvents such as chloroform. Among these, it is particularly preferable that it is soluble in N,N-dimethylformamide, acetone, and methanol.

[0022] The soluble carbon material used in the present invention has a peak in the Raman spectrum obtained by Raman spectroscopic analysis at the G band (around 1580 cm -1 derived from the benzene hexagonal network structure). Furthermore, it is also preferable that it has a peak at the D band (around 1350 cm -1 derived from defects and functional groups). Furthermore, it is also preferable that it has a peak at the G' band (around 2700 cm -1 derived from the graphene skeleton). By having these peaks, it can be characterized as having a skeleton as a carbon material.

[0023] The soluble carbon material used in the present invention preferably contains a component having a polystyrene-equivalent molecular weight of 1000 or more (that is, the maximum value of the molecular weight distribution is 1000 or more) as measured by GPC molecular weight measurement. This results in good reprecipitability. More preferably, it is 3000 or more, and even more preferably, it is 5000 or more.

[0024] The soluble carbon material used in the present invention can be obtained by firing a polyphenol such as phloroglucinol (a compound having two or more phenolic hydroxyl groups in its structure) at a low temperature of 300 °C or lower.

[0025] [Method for Producing Carbon Material Particles] The method for producing carbon material particles of the present invention includes a step of dissolving a soluble carbon material having a G band in a Raman spectrum obtained by Raman spectroscopic analysis in an organic solvent, and a step of mixing the carbon material solution obtained in the above step with a poor solvent to precipitate carbon material particles. When mixing, the poor solvent may be added to the carbon material solution, the carbon material solution may be added to the poor solvent, or the carbon material solution and the poor solvent may be simultaneously added to a container or the like and mixed.

[0026] In the method for producing carbon material particles of the present invention, as the good solvent and poor solvent to be used, those similar to those described above can be used.

[0027] In the method for producing carbon material particles of the present invention, the concentration of the soluble carbon material in the carbon material solution is preferably 0.1 to 30% by mass. This enables mass production of carbon material particles having a desired particle size. More preferably, it is 0.3 to 25% by mass, and even more preferably, it is 0.5 to 20% by mass.

[0028] In the method for producing carbon material particles of the present invention, the mixing ratio of the carbon material solution to the poor solvent is preferably in the range of 1:1 to 1:1000. This enables mass production of carbon material particles having a desired particle size. More preferably, it is 1:2 to 1:500, and even more preferably, it is 1:5 to 1:100.

[0029] In the method for producing carbon material particles of the present invention, the stirring conditions during the mixing of the carbon material solution and the poor solvent are not particularly limited, but from the viewpoint of achieving good mixing, it is preferable to perform a stirring treatment. This includes stirring by a stirrer and stirring such as introducing a liquid from a thin nozzle to form a vortex, and operations for well mixing the two liquids. Further, flow synthesis in which the solution and the poor solvent are respectively introduced from two pipes and mixed and prepared in one pipe or a microreactor is also preferable.

[0030] In the method for producing carbon material particles of the present invention, the temperature during production is not particularly limited, but it is preferably 0 to 100°C. From the viewpoint of cost, it is preferably around room temperature (10 to 40°C). The atmosphere during production is not particularly limited either, but an atmosphere under air, an inert atmosphere, etc. are preferable, and from the viewpoint of cost, an atmosphere under air is preferable.

Examples

[0031] The present invention will be described in more detail with reference to the following examples, but the present invention is not limited to only these examples. Unless otherwise specified, "parts" means "parts by mass" and "%" means "% by mass".

[0032] [Raman spectrum measurement] Microscopic laser Raman spectroscopic analysis was performed under the following apparatus and conditions. Apparatus: NRS-3100 manufactured by JASCO Corporation Measurement conditions: Excitation wavelength 532 nm, number of integrations 32 times

[0033] [X-ray photoelectron spectroscopy (XPS) measurement] XPS analysis was performed under the following apparatus and conditions to calculate O / C. Apparatus: AXIS-NOVAX manufactured by Shimadzu Kratos Co., Ltd. X-ray source · Output: AlKα - 100 W, pass energy 40 eV, neutralizing gun ON

[0034] [Particle size distribution] Particle size distribution analysis was performed under the following apparatus and conditions. Apparatus: ZETASIZER Nano-ZS manufactured by Malvern Panalytical Measurement conditions: Aqueous dispersion, particle refractive index 1.33

[0035] [Molecular weight measurement] The GPC measurement was carried out using the following apparatus and conditions, and the maximum molecular weight was estimated from the rising edge of the peak. Apparatus: HLC-8220GPC manufactured by Tosoh Corporation Column: TSKgel superH-RC Developing solvent: N,N-dimethylformamide (added with 0.1 mass% lithium bromide)

[0036] [Fluorescence analysis] The measurement of the emission and excitation spectra was carried out using the following apparatus and conditions. Apparatus: F-7000 manufactured by Hitachi High-Technologies Corporation Measurement conditions: Excitation wavelength 350 nm, sample concentration 0.01 mass%

[0037] [Lubrication property evaluation] The lubrication property evaluation was carried out using the following apparatus and conditions, and the average of the coefficient of kinetic friction at each sliding cycle was measured. Apparatus: Static and kinetic friction tester (manufactured by Trinity Lab Co., Ltd.) Contact: Surface contact made of 10 mm × 10 mm SUS, Substrate: SUS304 Load: 100 g, Sliding speed: 10 mm / sec, Sliding distance: 10 mm Number of sliding cycles: 100 times

[0038] [Preparation examples 1 and 2 of soluble carbon materials] Using a glass tube oven, phloroglucinol was heated at 250 °C (preparation example 1) or 300 °C (preparation example 2) for 1 hour under the atmosphere to obtain soluble carbon materials (1) and (2). The maximum molecular weight of soluble carbon material (1) was 7000 and the O / C was 0.31, while the maximum molecular weight of soluble carbon material (2) was 320000 and the O / C was 0.30. The G band and D band were observed by Raman spectroscopy respectively.

[0039] [Examples 1 - 5] The soluble oxygen material (1) was dissolved in N,N - dimethylformamide (DMF). The concentrations at that time were 0.5, 1.0, 2.5, 5.0, and 10 mass% (in the order of Examples 1 to 5). 0.1 g of each solution was taken and added to 10 g of ion - exchanged water being stirred with a magnetic stirrer, and reprecipitation was carried out to obtain a carbon material particle dispersion. The dispersion was filtered through a 0.025 μm membrane filter to collect the particles. From fluorescence analysis, fluorescence having a peak around 480 nm was observed. For reference, the Raman spectroscopy analysis and SEM observation results of the carbon material particles obtained in Example 5 are shown in FIGS. 1 and 2. Note that all of the obtained carbon material particles were soluble in DMF and were observed in a film - like form (i.e., once dissolved and solidified) by SEM observation on a silicon wafer.

[0040] [Example 6] The soluble carbon material (1) was dissolved in acetone at a concentration of 10 mass%. 0.1 g of the solution was taken and added to 10 g of ion - exchanged water being stirred with a magnetic stirrer, and reprecipitation was carried out to obtain a carbon material particle dispersion. From fluorescence analysis, fluorescence having a peak around 480 nm was observed.

[0041] [Example 7] The soluble carbon material (2) was dissolved in DMF at a concentration of 10 mass%. 0.1 g of the solution was taken and added to 10 g of ion - exchanged water being stirred with a magnetic stirrer, and reprecipitation was carried out to obtain a carbon material particle dispersion.

[0042] [Example 7] The soluble carbon material (1) was dissolved in acetone at a concentration of 10 mass%. 0.1 g of the solution was taken and added to 10 g of hexane being stirred with a magnetic stirrer, and reprecipitation was carried out to obtain a carbon material particle dispersion.

[0043] The particle size, maximum molecular weight, and O / C of the obtained carbon material particles were as shown in Table 1. From Raman spectroscopy analysis, the G - band and D - band were confirmed in all samples.

[0044]

Table 1

[0045] The carbon material particles obtained in Example 5 were made into a 0.1% aqueous dispersion, and their lubricating properties were compared with those of Comparative Example 1 (water only). The results are shown in Fig. 3. In the case of water only, the coefficient of friction (COF) was small initially, but increased as the number of sliding cycles increased. The carbon material particles obtained in Example 5 showed a constant COF value of 0.3 from the initial stage to the later stage, indicating good rolling lubrication properties. As can also be confirmed from the SEM observation results, since the carbon material particles of the present invention are spherical in shape, they exhibit rolling lubrication properties.

[0046] By using the carbon material particles of the present invention and the method for producing the same, carbon material particles having a desired particle diameter can be utilized and can be used in lubrication applications and the like.

Claims

1. Carbon material particles having a G band in a Raman spectrum obtained by Raman spectroscopic analysis, wherein the volume average particle diameter of the carbon material particles is 10 to 200 nm, and the carbon material particles are soluble in N,N-dimethylformamide. Carbon material particles characterized by this.

2. A dispersion liquid containing the carbon material particles according to Claim 1 and a poor solvent.

3. A step of dissolving a soluble carbon material having a G band in a Raman spectrum obtained by Raman spectroscopic analysis in an organic solvent, A method for producing carbon material particles, comprising a step of mixing the carbon material solution obtained in the above step with a poor solvent to precipitate carbon material particles.

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