Manufacturing method and manufacturing apparatus for nanodiamond

Abstract

To appropriately classify nanodiamonds.SOLUTION: The method includes a step (S3) of adding acid to a dispersion liquid in which nanodiamonds are dispersed in water, and a centrifugal separation step (S4) of centrifuging the dispersion liquid to which acid has been added, wherein the nanodiamonds are classified by centrifugal separation into nanodiamonds that are a precipitate and nanodiamonds dispersed in a supernatant liquid.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a method and an apparatus for manufacturing nanodiamond.

Background Art

[0002] Nanoparticles refer to particles having a particle size on the order of nanometers (1 to 100 nm). Nanodiamond is an example of hydrophobic nanoparticles. Methods for producing nanodiamond include the High Pressure and High Temperature (HPHT) method, the Chemical Vapor Deposition (CVD) method, the detonation method, and the like.

[0003] In the method for producing a nanodiamond dispersion described in Patent Document 1, a nanodiamond crude product produced by the detonation method is purified, a chemical disintegration treatment is performed on the purified nanodiamond, and a solution containing the nanodiamond subjected to the chemical disintegration treatment is centrifuged. Then, the above chemical disintegration treatment and the above centrifugation are repeated for the precipitate after centrifugation until the supernatant after centrifugation becomes black and transparent. As a result, a nanodiamond dispersion, which is a black and transparent supernatant, is collected.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] Nanodiamonds produced using various methods have various particle sizes. Therefore, it is required to classify the above nanodiamonds according to particle size. Usually, a centrifuge is used for the above classification.

[0006] However, with a general centrifuge where the centrifugal force is less than 100,000 g, it is difficult to classify nanodiamonds with a particle size of 50 nm or less. To classify such nanodiamonds, an ultracentrifuge with a centrifugal force of 100,000 g or more is required. However, the above ultracentrifuge is significantly more expensive than the above centrifuge, and it is difficult to appropriately classify according to the size of the nanodiamonds.

[0007] One aspect of the present invention aims to appropriately classify nanodiamonds or obtain nanodiamonds with uniform sizes.

Means for Solving the Problems

[0008] To solve the above problems, a method for manufacturing nanodiamonds according to one aspect of the present invention includes an additional step of adding an acid to a dispersion in which nanodiamonds are dispersed in water, and a centrifugation step of centrifuging the dispersion to which the acid has been added. By the centrifugation, the nanodiamonds are classified into nanodiamonds as a precipitate and nanodiamonds dispersed in the supernatant.

[0009] A method for manufacturing nanodiamonds according to another aspect of the present invention includes an additional step of adding an acid to a dispersion in which nanodiamonds are dispersed in water, and a centrifugation step of centrifuging the dispersion to which the acid has been added. Among the precipitate and the supernatant generated by the centrifugation, the centrifugation step of obtaining the precipitate as nanodiamonds is included.

[0010] A nanodiamond manufacturing apparatus according to still another aspect of the present invention includes an additional device for adding an acid to a dispersion in which nanodiamonds are dispersed in water, and a centrifugation device for centrifuging the dispersion to which the acid has been added. By the centrifugation, the nanodiamonds are classified into nanodiamonds as a precipitate and nanodiamonds dispersed in the supernatant.

Advantages of the Invention

[0011] According to one aspect of the present invention, it is possible to appropriately classify nanodiamonds or obtain nanodiamonds with uniform sizes.

Brief Description of the Drawings

[0012]

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Best Mode for Carrying Out the Invention

[0013] 〔Embodiment 1〕 Hereinafter, an embodiment of the present invention will be described with reference to FIGS. 1 and 2.

[0014] FIG. 1 is a flowchart showing the flow of a method for manufacturing nanodiamond in the present embodiment. As shown in FIG. 1, first, a dispersion in which nanodiamond is sufficiently dispersed in water is prepared (S1). As the above-mentioned nanodiamond, those prepared and purified by any method such as the high-temperature high-pressure method or the detonation method can be used. A commercially available product may be used as the above-mentioned nanodiamond.

[0015] Next, centrifugation is repeated on the above dispersion using a centrifuge (S2). Then, by taking out the supernatant, a dispersion of nanodiamond having an average particle size of 50 nm or less can be prepared. When using a commercially available product of nanodiamond having an average particle size of 50 nm or less, step S2 can be omitted. The above particle size is the diameter when the nanodiamond is assumed to be a spherical particle, and is an index of the size of the nanodiamond.

[0016] Next, an acid is added to the above dispersion and stirred sufficiently (S3, additional step). At this time, although the reason will be described later, it is considered that a plurality of nanodiamonds are clustered. When relatively large nanodiamonds among nanodiamonds having a particle size of 50 nm or less are clustered, the particle size of the cluster becomes larger than 50 nm. The reason for this will be described later. Also, as the above acid, any acid or a combination thereof can be used. It is desirable that the above acid is at least one of hydrochloric acid and a weak acid.

[0017] Examples of inorganic acids contained in the above weak acids include acetic acid, hydrogen sulfide, carbonic acid, phosphoric acid, and the like. Examples of organic acids contained in the above weak acids include oxalic acid, citric acid, formic acid, lactic acid, tartaric acid, succinic acid, malic acid, and the like. Further, a weakly acidic salt such as calcium carbonate may be used as the above weak acid.

[0018] Next, centrifugation is performed using a centrifuge, and among the precipitate and supernatant liquid thus generated, the precipitate is recovered (S4, centrifugation step). As the above centrifuge, a general centrifuge with a centrifugal force of less than 100,000 g may be used.

[0019] At this time, clusters with a particle size larger than 50 nm precipitate by the above centrifugation. Therefore, among the nanodiamonds with a particle size of 50 nm or less, the nanodiamonds with a relatively large particle size are included in the above precipitate, while the nanodiamonds with a relatively small particle size are included in the above supernatant liquid. Thereby, the nanodiamonds with a relatively large particle size and the nanodiamonds with a relatively small particle size can be appropriately classified using a centrifuge. Further, by recovering the above precipitate, among the nanodiamonds with a particle size of 50 nm or less, the nanodiamonds with a relatively large particle size can be appropriately obtained using a centrifuge. From the above, the method for producing nanodiamonds according to the present embodiment is industrially advantageous compared to the case of using an ultracentrifuge, high-performance liquid chromatography, or the like.

[0020] Next, using the supernatant as a dispersion, an acid is added and thoroughly stirred (S5). At this time, the concentration of the acid in the dispersion to which the acid is added is increased compared to the previous time (S5). Then, the process returns to step S4 and the above process is repeated (repetition step). Due to the increase in the acid concentration, among the nanodiamonds contained in the supernatant, the nanodiamonds with relatively large particle sizes further cluster, and the particle size of the clusters becomes larger than 50 nm. Then, by centrifugation in step S4, the nanodiamonds contained in the supernatant can be classified into the nanodiamonds with relatively large particle sizes and the nanodiamonds with relatively small particle sizes using a centrifuge. Therefore, by repeating steps S4 and S5, the acid concentration can be increased step by step and centrifuged, and as a result, the nanodiamonds with a particle size of 50 nm or less can be classified by particle size.

[0021] Figure 2 is a block diagram showing a schematic configuration of a nanodiamond manufacturing apparatus that executes the above-described method for manufacturing nanodiamonds. As shown in Figure 2, the nanodiamond manufacturing apparatus 1 includes an acid addition device 2 (addition device), a centrifugation device 3, and a control device 4.

[0022] The acid addition device 2 adds an acid to a dispersion in which nanodiamonds are sufficiently dispersed in water based on a set concentration. Further, the acid addition device 2 adds an acid to the supernatant created by the centrifugation device 3 as a dispersion based on a set concentration. The dispersion to which the acid is added is sent to the centrifugation device 3. Since a known injection device that injects water containing an acid into a solution can be used as the acid addition device 2, its details are omitted.

[0023] The centrifugation device 3 performs centrifugation on the dispersion from the acid addition device 2 to separate it into a precipitate and a supernatant. While the precipitate is recovered, the supernatant is sent to the acid addition device 2 as a dispersion. Since a known centrifuge that centrifuges a solution can be used as the centrifugation device 3, its details are omitted.

[0024] The control device 4 comprehensively controls the acid addition device 2 and the centrifugal separation device 3, and is constituted by a computer including, for example, a CPU (Central Processing Unit) and a memory. Then, the operation control of various configurations is performed by causing the computer to execute a control program. The control device 4 instructs the acid addition device 2 and the centrifugal separation device 3 to execute the method of nanodiamond shown in FIG. 1.

[0025] The present invention is not limited to the above-described embodiments, and various modifications are possible within the scope shown in the claims. Embodiments obtained by appropriately combining the technical means disclosed in different embodiments are also included in the technical scope of the present invention.

Example

[0026] An example of the present invention will be described below.

[0027] In this example, commercially available nanodiamond (manufactured by Element Six, trade name Micron+MDA M0.10) having an average particle size of about 100 nm was used. 1000 mg of the above nanodiamond was dispersed in 100 cm of ultrapure water produced by an ultrapure water production device (manufactured by Merch, model number Milli-Q IQ7005) using an ultrasonic cleaner (manufactured by AS ONE, model number VS-100III) to prepare a nanodiamond dispersion. 3 Thereafter, the above nanodiamond dispersion was centrifuged at 13000 rpm for 15 minutes using a centrifuge (manufactured by the former Hitachi Koki Co., Ltd. (now Eppendorf Highmark Technologies), main body model number CF15R, angle rotor model number T15A41), and a precipitate PR1 and a supernatant SP1 were obtained.

[0028]

[0029] ​When the average particle size of the nanodiamond was measured by the dynamic light scattering (DLS) method using a particle size measuring device (Zetasizer Nano ZSP, manufactured by Malvern) for the dispersion liquid PR1a in which the precipitate PR1 was dispersed in the ultrapure water by the ultrasonic cleaner, it was larger than about 50 nm. The same was true when the average particle size of the nanodiamond was measured for the dispersion liquid PR1a using a transmission electron microscope (TEM) (model number H-7650, manufactured by Hitachi High-Technologies Corporation).

[0030] On the other hand, the measured value of the average particle size of the nanodiamond in the supernatant SP1 was 50 nm or less in both DLS and TEM. Also, it was confirmed in both DLS and TEM that the nanodiamond in the supernatant SP1 had a large variation in particle size.

[0031] Next, hydrochloric acid (HCl) with a molar concentration of 1 M (manufactured by Fujifilm Wako Pure Chemical Corporation, reagent grade (Guaranteed Reagent)) was added to the supernatant SP1 and stirred for 1 hour to make the final concentration of hydrochloric acid 0.5 mM. Next, when centrifugation was performed at 13,000 rpm for 15 minutes using the centrifuge, a precipitate PR2 and a supernatant SP2 were obtained. Next, the hydrochloric acid with a molar concentration of 1 M was added to the supernatant SP2 and stirred for 1 hour to make the final concentration of hydrochloric acid 2.5 mM. Next, when centrifugation was performed at 13,000 rpm for 15 minutes using the centrifuge, a precipitate PR3 and a supernatant SP3 were obtained.

[0032] Next, hydrochloric acid with a molar concentration of 1 M was added to the supernatant SP3 and stirred for 1 hour to adjust the final concentration of hydrochloric acid to 5.0 mM. Next, using the centrifuge, centrifugation was performed at 13,000 rpm for 15 minutes, obtaining a precipitate PR4 and a supernatant SP4. Next, hydrochloric acid with a molar concentration of 1 M was added to the supernatant SP4 and stirred for 1 hour to adjust the final concentration of hydrochloric acid to 10.0 mM. Then, using the centrifuge, centrifugation was performed at 13,000 rpm for 15 minutes, obtaining a precipitate PR5 and a supernatant SP5.

[0033] Figure 3 is a diagram showing an example of an image of the supernatant SP1 after centrifugation without adding hydrochloric acid, taken by TEM. Referring to Figure 3, it can be understood that nanodiamonds ND with various particle sizes are present in the supernatant SP1.

[0034] Figure 4 is a diagram showing an example of an image of dispersions PR2a - PR5a obtained by dispersing precipitates PR2 - P5, which were centrifuged after gradually increasing the concentration of hydrochloric acid, in ultrapure water, taken by TEM. In the example of Figure 4, the hydrochloric acid contained in precipitates PR2 - PR5 was purified and removed by ultracentrifugation. Referring to Figure 4, it can be understood that as the concentration of hydrochloric acid increases, the particle size of nanodiamonds ND tends to become uniform.

[0035] Figure 5 is a graph showing the particle size distribution calculated from the analysis of the TEM images of each of the dispersions PR2a - PR5a, presented as a box - whisker plot and a frequency distribution. In the box - whisker plot, the points indicated by the rectangles are the average values. The average particle sizes of the dispersions PR2a - PR5a were 26.33 nm, 20.52 nm, 19.22 nm, and 16.35 nm, respectively. Referring to Figure 5, it can be understood that as the concentration of hydrochloric acid increases, the particle size of nanodiamonds ND becomes smaller. Incidentally, for the dispersions PR2a - PR5a, the average particle sizes calculated from the number distribution of particle sizes obtained by measurement using DLS were 47.39 nm, 34.12 nm, 40.97 nm, and 33.89 nm, respectively.

[0036] (Discussion) The above particle size measuring device has a function of measuring the particle size of nanodiamond by DLS, and also has a function of measuring the zeta potential of nanodiamond by the electrophoretic light scattering method. Therefore, as a result of measuring the particle size and zeta potential of nanodiamond using the above particle size measuring device, it was found that the nanodiamond with a lower zeta potential and a larger particle size was more likely to precipitate with the addition of hydrochloric acid.

[0037] From this, the following phenomenon can be considered. That is, in a dispersion in which nanodiamond is sufficiently dispersed in water, water molecules participate with nanodiamond around the nanodiamond, so that the nanodiamond is stably dispersed in water. By adding hydrochloric acid to the above dispersion, the water molecules that participated with the nanodiamond are removed, and the nanodiamond becomes unstable, and a plurality of nanodiamonds cluster for stabilization.

[0038] Nanodiamonds with a large particle size cluster several of them, so that the particle size of the cluster becomes about 50 nm and precipitates by centrifugation of the above centrifuge. On the other hand, for nanodiamonds with a small particle size, as the acid concentration increases, the number of particles in the cluster increases, and the particle size of the cluster becomes about 50 nm, and it precipitates by centrifugation of the above centrifuge. Therefore, by increasing the acid concentration stepwise and performing centrifugation, nanodiamonds can be classified according to particle size.

Example

[0039] Another embodiment of the present invention will be described below. In this example, 500 mg of commercially available nanodiamond similar to that in Example 1 was dispersed in 50 cm of ultrapure water produced by the same ultrapure water production device as in Example 1 using the same ultrasonic cleaner as in Example 1 to prepare a nanodiamond dispersion. 3 Thereby, a nanodiamond dispersion was prepared.

[0040] Next, centrifugation was performed on the above-mentioned nano-diamond dispersion using the same centrifuge as in Example 1 at 8000 rpm for 5 minutes, 10000 rpm for 5 minutes, 12000 rpm for 5 minutes, and 13000 rpm for 15 minutes. Furthermore, when centrifugation was performed at 25000 rpm for 15 minutes using an ultracentrifuge (manufactured by Beckman Coulter, trade name Optima Max), a precipitate PR11 and a supernatant SP11 were obtained. Regarding the above-mentioned supernatant SP11, the average particle size by DLS was 25 nm.

[0041] Next, the same hydrochloric acid as in Example 1 was added to the above-mentioned supernatant SP11 and stirred for 1 hour to adjust the final concentration of hydrochloric acid to 0.1 mM. Next, when centrifugation was performed at 10000 rpm for 5 minutes using the above centrifuge, a precipitate PR12 and a supernatant SP12 were obtained. Next, the above hydrochloric acid was added to the above supernatant SP12 and stirred for 1 hour to adjust the final concentration of hydrochloric acid to 0.25 mM. Next, when centrifugation was performed at 10000 rpm for 5 minutes using the above centrifuge, a precipitate PR13 and a supernatant SP13 were obtained.

[0042] Next, the above hydrochloric acid was added to the above supernatant SP13 and stirred for 1 hour to adjust the final concentration of hydrochloric acid to 0.5 mM. Next, when centrifugation was performed at 10000 rpm for 5 minutes using the above centrifuge, a precipitate PR14 and a supernatant SP14 were obtained. Next, the above hydrochloric acid was added to the above supernatant SP14 and stirred for 1 hour to adjust the final concentration of hydrochloric acid to 1.0 mM. Next, when centrifugation was performed at 10000 rpm for 5 minutes using the above centrifuge, a precipitate PR15 and a supernatant SP15 were obtained. Next, the above hydrochloric acid was added to the above supernatant SP15 and stirred for 1 hour to adjust the final concentration of hydrochloric acid to 2.0 mM. Next, when centrifugation was performed at 10000 rpm for 5 minutes using the above centrifuge, a precipitate PR16 and a supernatant SP16 were obtained.

[0043] Next, the precipitates PR12 to P16 after centrifugation with the concentration of hydrochloric acid increased stepwise were dispersed in ultrapure water to prepare dispersions PR12a to PR16a. Then, for each of the above dispersions PR12a to PR16a, the average value of the particle size was calculated from the number distribution of the particle sizes obtained from the measurement by the above DLS.

[0044] Figure 6 is a graph showing the relationship between the concentration of hydrochloric acid and the average value of the above particle size for each of the above dispersions PR12a to PR16a. Referring to Figure 6, it can be understood that even when the concentration of hydrochloric acid is lower than that in Example 1, the average value of the particle size of the nanodiamond ND tends to decrease as the concentration of hydrochloric acid increases, similar to Example 1.

Example

[0045] Another example of the present invention will be described below.

[0046] To the supernatant SP11 prepared in Example 2, acetic acid (manufactured by Nacalai Tesque, reagent grade) with a molar concentration of 1 M was added and stirred for 1 hour to make the final concentration of acetic acid 1.0 mM. Next, using the same centrifuge as in Example 1, centrifugation was performed at 10,000 rpm for 5 minutes, and a precipitate PR22 and a supernatant SP22 were obtained. Next, to the above supernatant SP22, the above acetic acid was added and stirred for 1 hour to make the final concentration of acetic acid 2.5 mM. Next, using the above centrifuge, centrifugation was performed at 10,000 rpm for 5 minutes, and a precipitate PR23 and a supernatant SP23 were obtained.

[0047] Next, acetic acid was added to the supernatant SP23 and stirred for 1 hour to adjust the final concentration of acetic acid to 5.0 mM. Next, centrifugation was performed at 10,000 rpm for 5 minutes using the centrifuge, resulting in a precipitate PR24 and a supernatant SP24. Next, acetic acid was added to the supernatant SP24 and stirred for 1 hour to adjust the final concentration of acetic acid to 10.0 mM. Next, centrifugation was performed at 10,000 rpm for 5 minutes using the centrifuge, resulting in a precipitate PR25 and a supernatant SP25. Next, acetic acid was added to the supernatant SP25 and stirred for 1 hour to adjust the final concentration of acetic acid to 20.0 mM. Next, centrifugation was performed at 10,000 rpm for 5 minutes using the centrifuge, resulting in a precipitate PR26 and a supernatant SP26.

[0048] Next, dispersions PR22a to PR26a were prepared by dispersing the precipitates PR22 to P26 after centrifugation with the acetic acid concentration increased stepwise in ultrapure water. Then, for each of the dispersions PR22a to PR26a, the average value of the particle size was calculated from the number distribution of the particle sizes obtained from the measurement by the DLS.

[0049] FIG. 7 is a graph showing the relationship between the acetic acid concentration and the average value of the particle size for each of the dispersions PR22a to PR26a. Referring to FIG. 7, it can be understood that as the acetic acid concentration increases, the average value of the particle size of the nanodiamond ND tends to decrease.

Example

[0050] Another embodiment of the present invention will be described below.

[0051] To the supernatant SP11 prepared in Example 2, citric acid monohydrate (manufactured by Nacalai Tesque, reagent grade) with a molar concentration of 100 mM was added and stirred for 1 hour to make the final concentration of citric acid 0.1 mM. Next, using the same centrifuge as in Example 1, centrifugation was performed at 10,000 rpm for 5 minutes, and a precipitate PR32 and a supernatant SP32 were obtained. Next, to the above supernatant SP32, the above citric acid was added and stirred for 1 hour to make the final concentration of citric acid 0.25 mM. Next, using the above centrifuge, centrifugation was performed at 10,000 rpm for 5 minutes, and a precipitate PR33 and a supernatant SP33 were obtained.

[0052] Next, to the above supernatant SP33, the above citric acid was added and stirred for 1 hour to make the final concentration of citric acid 0.5 mM. Next, using the above centrifuge, centrifugation was performed at 10,000 rpm for 5 minutes, and a precipitate PR34 and a supernatant SP34 were obtained. Next, to the above supernatant SP34, the above citric acid was added and stirred for 1 hour to make the final concentration of citric acid 1.0 mM. Next, using the above centrifuge, centrifugation was performed at 10,000 rpm for 5 minutes, and a precipitate PR35 and a supernatant SP35 were obtained. Next, to the above supernatant SP35, the above citric acid was added and stirred for 1 hour to make the final concentration of citric acid 2.0 mM. Next, using the above centrifuge, centrifugation was performed at 10,000 rpm for 5 minutes, and a precipitate PR36 and a supernatant SP36 were obtained.

[0053] Next, dispersions PR32a to PR36a were prepared by dispersing the precipitates PR32 to P36 after centrifugation with the concentration of citric acid increased stepwise in ultrapure water. Then, for each of the above dispersions PR32a to PR36a, the average value of the particle size was calculated from the number distribution of the particle sizes obtained from the measurement by the above DLS.

[0054] Figure 8 is a graph showing the relationship between the concentration of citric acid and the average value of the above particle size for each of the above dispersions PR32a to PR36a. Referring to Figure 8, it can be understood that as the concentration of citric acid increases, the average value of the particle size of the nanodiamond ND tends to decrease.

[0055] From the above Examples 1 to 4, it is considered that the acid added to the nanodiamond dispersion may be any acid such as hydrochloric acid, acetic acid, citric acid, sulfuric acid, nitric acid, etc.

Explanation of symbols

[0056] 1 Manufacturing apparatus for nanodiamond 2 Acid addition device (addition device) 3 Centrifugal separation device 4 Control device

Claims

1. An additional step of adding an acid to a dispersion in which nanodiamonds are dispersed in water, A centrifugation step of centrifuging the dispersion to which the acid has been added, wherein the centrifugation classifies the nanodiamonds into nanodiamonds as a precipitate and nanodiamonds dispersed in the supernatant liquid. A method for producing nanodiamonds, comprising:

2. An additional step of adding an acid to a dispersion in which nanodiamonds are dispersed in water, A centrifugation step of centrifuging the dispersion to which the acid has been added, wherein the precipitate is obtained as nanodiamonds among the precipitate and the supernatant liquid generated by the centrifugation. A method for producing nanodiamonds, comprising:

3. Further comprising a repetition step of repeating the additional step and the centrifugation step using the supernatant liquid as the dispersion, The repetition step increases the concentration of the acid in the dispersion to which the acid has been added with each repetition. The method for producing nanodiamonds according to claim 1 or 2.

4. The acid is at least one of hydrochloric acid and a weak acid. The method for producing nanodiamonds according to claim 1 or 2.

5. An additional device for adding an acid to a dispersion in which nanodiamonds are dispersed in water, A centrifugation device for centrifuging the dispersion to which the acid has been added, wherein the centrifugation classifies the nanodiamonds into nanodiamonds as a precipitate and nanodiamonds dispersed in the supernatant liquid. A manufacturing apparatus for nanodiamonds, comprising:

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