METHOD FOR SEPARATING DETONATION NANODIAMONDS

Abstract

Disclosed is a method for separating nanodiamond clusters synthesized by a detonation method having a size of 100 nm˜1,000 nm into nanodiamonds of 100 nm or less—more specifically, into uniformly sized nanodiamonds in the range of 5 nm˜50 nm, free of metal and alkaline impurities and ready to quantitatively attach functional groups on the surface of the nanodiamonds for applications such as thin film precursor materials, drug delivery systems and cosmetics compositions.

Claims

1. A method for separating nanodiamond clusters comprising the steps of: adding nanodiamond clusters to deionized water; adding alcohol to the deionized water to form a mixed aqueous solution; applying ultrasound to the mixed aqueous solution to separate the nanodiamond cluster.

2. The method according to claim 1, wherein the mixed aqueous solution is maintained at a temperature of 25˜100° C.

3. The method according to claim 1, wherein nanodiamond clusters are added to the deionized water in the ratio of 0.1˜20 parts per weight of nanodiamond clusters to 100 parts per weight of deionized water.

4. The method according to claim 1, wherein the boiling point of the alcohol is lower than the boiling point of water.

5. The method according to claim 1, wherein the volume ratio of the deionized water to alcohol is 1:0.1˜10.

6. The method according to claim 1, further comprising a pH controlling step comprised of adding an alkaline agent or an acid to the mixed aqueous solution before, during or after the step of applying ultrasound to the mixed aqueous solution.

7. The method according to claim 6, wherein the acid is an inorganic acid or an organic acid free of metal or halogen elements.

8. The method according to claim 6, wherein the mixed aqueous solution has a pH value increased to within the range of 3˜12.

9. The method according to claim 6, wherein the alkaline agent is a non-metallic base.

10. The method according to claim 6, wherein the alkaline agent is a non-metallic amine base.

11. The method according to claim 6, wherein the mixed aqueous solution comprises a zeta potential value in the range of −100˜100 mV as a result of adding the alkaline agent.

12. The method according to claim 1, wherein the applied ultrasound has a frequency in the range of 2 kHz˜40 kHz.

13. The method according to claim 1, further comprising a step of recovering the nanodiamond particles by centrifugation after the step of applying ultrasound to the mixed aqueous solution.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0023] FIG. 1 shows a conventional method of separating nanodiamonds using milling;

[0024] FIGS. 2-13 show results of particle analysis of nanodiamonds in dispersion solutions according to Examples 1˜8 and Comparative Examples 1˜4.

DETAILED DESCRIPTION OF THE INVENTION

Best Mode

[0025] The present invention relates to a method for separating nanodiamond clusters produced by detonation synthesis from a cluster size of hundreds of nanometers to sizes in the range of several to several tens of nanometers. The present invention also relates to nanodiamonds and nanodiamond dispersion solutions produced by the same method.

[0026] FIG. 1 shows the method of separating nanodiamonds using the conventional technology of milling. Referring to FIG. 1, a single particle phase nanodiamond (10) as defined in the present invention refers to a single particle phase nanodiamond having a diamond crystal structure (SP3) at the core (1) and a graphite layer (2) surrounding it, where the size of the core (1) is approximately 4˜7 nm and the thickness of the graphite layer (2) is 1 nm.

[0027] The cluster of detonation nanodiamond (DND) (100) as defined in the present invention refers to an agglomeration of tens to hundreds of single particle phase (10) nanodiamonds.

[0028] Multiple particle phase nanodiamonds (30) as defined in the present invention refers to a size of nanodiamonds that is in between single particle phase (10) nanodiamonds and a DND cluster (100) as shown in FIG. 1. For example, several single particle phase nanodiamonds (10) and preferably up to ten single particle phase nanodiamonds are referred to as multiple particle phase nanodiamonds (30) for the purposes of the present invention.

[0029] Again referring to FIG. 1, the nanodiamond cluster (100) is an agglomeration of single particle phase nanodiamonds (10) which is enclosed in a skin (20) of graphite surrounding its surface.

[0030] The present invention provides a method for separating and removing the graphite layer (20) from the surface of the nanodiamond clusters (100) and a method for separating the agglomerated nanodiamonds into individual single particle phase nanodiamonds (10) and multiphase nanodiamonds (30).

[0031] The separation method of the present invention includes a hydration step, a solvent mixture step and a separation step. The method may also include a pH control step and a recovery step for the nanodiamond particles.

[0032] The hydration step involves adding the nanodiamond cluster (100) in to deionized water and hydrating it. Here, the nanodiamond cluster refers to the soot produced as a result of the detonation synthesis. The preferred diamond content of the soot is 10%˜90%. It is also possible to include a process for eliminating carbon and graphite formed on the surface of the nanodiamond cluster although it is not necessarily required.

[0033] The nanodiamonds being subject to the hydration process are DND cluster powders synthesized by detonation as previously described. There is no limit to the size of the powders and it may be in the range of 500 nm˜1000 nm.

[0034] The duration required for the hydration step may be 10˜100 minutes, and may preferably be 30˜60 minutes. The hydration may be performed at a temperature in the range of 30˜100° C. and preferably in the range of 60˜80° C.

[0035] The weight of the nanodiamond cluster being added to the solution may be 0.1˜20 parts by weight based on 100 parts of deionized water and may preferably be 1˜10 parts by weight based on 100 parts of deionized water.

[0036] As a result of the hydration process described above, water molecules permeate into the DND cluster (100) and in-between the single particle phase nanodiamonds (10), sufficiently wetting them.

[0037] The step of adding alcohol is performed by adding alcohol directly to the hydrated nanodiamond solution.

[0038] Commonly known alcohols, for example, alkyl alcohol, ethyl alcohol, propyl alcohol as well as dihydric and trihydric alcohols etc. may be used in the alcohol adding step described above.

[0039] It is preferable to use alcohols having a boiling point that is lower than water and more preferably at least one of methyl alcohol, ethyl alcohol and propyl alcohol or a combination thereof.

[0040] The proportion of alcohol added to the solution may be 1:0.1˜10 (deionized water:alcohol) and preferably 1:0.5˜10 (deionized water:alcohol).

[0041] The present invention may include the step of applying ultrasound to the solution after adding a solvent to the mixture.

[0042] The applied ultrasound may have a frequency of 2 kHz˜40 kHz.

[0043] The power of the applied ultrasound may be in the range of 100 W˜2000 W, and more specifically in the range of 500 W˜1500 W. The duration of ultrasound application may be in the range of 1 hr˜10 hrs and preferably in the range of 3 hrs˜6 hrs.

[0044] The temperature of the solution during ultrasound application may be in the range of 30˜100° C. and preferably in the range of 70˜90° C. and most preferably maintained at a temperature below the boiling point of the above mentioned alcohol. The pressure within the reaction chamber may be maintained in the range of 1˜100 atmospheres and more specifically in the range of 1˜10 atmospheres.

[0045] The solution may be stirred while applying the ultrasound.

[0046] Cavitation caused by the ultrasound increases the boiling effect of the mixed solution of water and alcohol thereby facilitating the break-up of the nanodiamond cluster (100).

[0047] Specifically, water and alcohol molecules that permeate into the crevices of the DND cluster start to form bubbles under the influence of ultrasound. In addition, alcohol rapidly evaporates at the boiling point of the mixed water-alcohol solution adding to the bubbling effect of the ultrasound. The combined effects of the boiling solvent and the ultrasound create high energy bubbles packed with powerful impact forces inside the DND clusters (100) that break them up and separate them from within.

[0048] There were many previous attempts to employ ultrasound to break up DND clusters (100). However, relying solely on ultrasound required more time and did not have a significant effect.

[0049] The pH of the mentioned solution may be raised to a value in the range of 3˜12 and preferably in the range of 5˜12. More specifically, alkaline agents may be added to the solution to control its pH before, during or after applying the ultrasound. Alternatively, acids may be added to the solution to control its pH. For such purposes, it is desirable to use inorganic or organic acids that are free of metal or halogen elements. For example, H.sub.2SO.sub.4 may be used.

[0050] As for alkaline agents, a non-metallic base, and preferably an amine base alkaline agent may be used. Among the amine based alkaline agents, NH.sub.4OH (NH.sub.3) is the most preferable. The reason for NH.sub.4OH being most preferable is because NH.sub.3 is highly soluble in water and it has the advantage of being easy to add to or remove from water. In addition, the following energy scheme is realized on the surface of the nanodiamond cluster: First, H is dissociated from COOH existing on the surface of the nanodiamond (ND) cluster to give ND-COO—+H+. As the pH of the solution is gradually increased from acidic to neutral and then to alkaline, the surface of the nanodiamond cluster maintains an absolute value of zeta potential that remains above a certain level due to the characteristics of ND-COO—, and therefore puts the nanodiamond cluster in a state that is easier to break up.

[0051] Eventually, by adding the alkaline agent, it is possible to significantly prevent the re-agglomeration of the single particle phase (10) nanodiamonds having COOH functional groups on its surface.

[0052] As a result of adding the alkaline agent to the solution, the zeta potential value of the solution may fall in the range of −100˜100 mV and preferably in the range of −50˜50 mV.

[0053] In the initial particle separation stage of the present invention, the inclusion of metal components as well as highly reactive halogen ion compounds has been prevented. Only those non-metallic compounds, such as H.sub.2O, EtOH, MeOH, NH.sub.4OH, CH.sub.3COOH etc., that are basically composed of the same elements (substances) that compose DND (C, H, O, N) have been used because they are compounds made up of substances that do not remain in the system before and after the reaction. In addition, ultrasound is applied as an auxiliary means to increase the efficiency of the overall separation while adding the alkaline agent contributes to maintaining the distance between the separated particles.

[0054] Repeating the series of steps of the present invention causes the separated particles to become continuously smaller and the color of the separated dispersions to turn from the initial gray (approximately 200 nm or more) to blue (200 nm˜100 nm) and further to black (100 nm or less) that is transparent and has no turbidity. Eventually, transparent nanodiamonds with particle sizes 100 nm and less are obtained. Further, the separated particle size may reduce to 50 nm or less and ultimately converge to the level of 5 nm.

[0055] The described method of the present invention may comprise additional steps after the step of applying ultrasound that include a step of separating the nanodiamonds from the solution and a step of drying.

[0056] After the ultrasonic step, a separation and drying step which may involve centrifugation or vacuum distillation and high temperature spray drying or oven drying may result in the recovery of separated nanodiamond particles in its solid phase.

[0057] The steps of the present invention may be repeated in series at least once. In addition, the recovered nanodiamond powders may be used industrially by mixing with other solids, liquids or gases.

[0058] Another aspect of the present invention relates to the nanodiamonds produced by the steps described herein. The average particle size of the nanodiamond powder may be 100 nm or less, and preferably in the range of 5˜50 nm.

[0059] The present invention also relates to the dispersion of the mentioned nanodiamond powders dispersed in water or other solvents. The dispersion has the features of changing color depending on the concentration of the solution. The results of UV/VIS spectroscopy on the nanodiamonds obtained may be as follows.

Mode of Invention

[0060] The description above may be explained by the following test procedures and results.

EXAMPLE 1

[0061] Approximately 200 g of nanodiamond clusters synthesized by the detonation reaction method was added to 4 L of deionized water and stirred for 60 minutes while heating the solution up to 80° C. 400 mL of ethanol was added to the solution and stirred for approximately 10 more minutes. NH.sub.4OH was then added to the solution increasing the pH of the solution to a value of 8 or above. Thereafter, ultrasonic treatment was performed for 120 minutes on the solution with a frequency of 2˜4 kHz. The recovered particle slurry was then subject to centrifugation for separation at 10,000 rpm for 30 minutes. The particle distribution of the separated diamond particles is listed in the following Table 1.

EXAMPLE 2

[0062] Approximately 200 g of nanodiamond clusters synthesized by the detonation reaction method was added to 3 L of deionized water and stirred for 60 minutes while heating the solution up to 80° C. 1 L of EtOH was added to the solution and then NH.sub.4OH was added to raise the pH value of the solution to 8 or more, after which ultrasonic treatment was performed for 120 minutes at a frequency of 2˜4 kHz. The resulting particle slurry was then subject to centrifugation for separation. The speed of the centrifuge was 10,000 rpm for 1 hr.

EXAMPLE 3

[0063] 200 g of nanodiamond clusters synthesized by the detonation reaction method was added to 2 L of deionized water and stirred for 60 minutes at room temperature. 2 L of EtOH was added to the solution and then NH.sub.4OH was added to raise the pH value of the solution to 8 or more, after which ultrasonic treatment was performed for 120 minutes at a frequency of 2˜4 kHz. The resulting particle slurry was then subject to centrifugation for separation. The speed of the centrifuge was 10,000 rpm for 60 minutes. The particle distribution of the separated diamond particles is listed in the following Table 1.

EXAMPLE 4

[0064] 200 g of nanodiamond clusters synthesized by the detonation reaction method was added to 1 L of deionized water and stirred for 60 minutes while heating the solution up to 80° C. 3 L of EtOH was added to the solution and then NH.sub.4OH was added to raise the pH value of the solution to 8 or more, after which ultrasonic treatment was performed for 240 minutes at a frequency of 2˜4 kHz. The resulting particle slurry was then subject to centrifugation for separation. The speed of the centrifuge was 10,000 rpm for 2 hours. The particle distribution of the separated diamond particles is listed in the following Table 1.

EXAMPLE 5

[0065] 200 g of nanodiamond clusters synthesized by the detonation reaction method was added to 1 L of deionized water and stirred for 60 minutes while heating the solution up to 80° C. 3 L of EtOH was added to the solution and then NH.sub.4OH was added to raise the pH value of the solution to 8 or more, after which ultrasonic treatment was performed for 240 minutes at a frequency of 2˜4 kHz. The resulting particle slurry was then subject to centrifugation for separation. The speed of the centrifuge was 10,000 rpm for 2 hours. The particle distribution of the separated diamond particles is listed in the following Table 1.

EXAMPLE 6

[0066] 200 g of nanodiamond clusters synthesized by the detonation reaction method was added to 2 L of deionized water and stirred for 60 minutes while heating the solution up to 80° C. 2 L of EtOH was added to the solution and then NH.sub.4OH was added to raise the pH value of the solution to 8 or more, after which ultrasonic treatment was performed for 240 minutes at a frequency of 2˜4 kHz. The resulting particle slurry was then subject to centrifugation for separation. The speed of the centrifuge was 10,000 rpm for 2 hours. The particle distribution of the separated diamond particles is listed in the following Table 1.

EXAMPLE 7

[0067] 200 g of nanodiamond clusters synthesized by the detonation reaction method was added to 2 L of deionized water and stirred for 60 minutes while heating the solution up to 80° C. 2 L of EtOH was added to the solution and then NH.sub.4OH was added to raise the pH value of the solution to 8 or more, after which ultrasonic treatment was performed for 240 minutes at a frequency of 2˜4 kHz. The resulting particle slurry was then subject to centrifugation for separation. The speed of the centrifuge was 10,000 rpm for 1 hour. The particle distribution of the separated diamond particles is listed in the following Table 1.

EXAMPLE 8

[0068] 200 g of nanodiamond clusters synthesized by the detonation reaction method was added to 3 L of deionized water and stirred for 60 minutes while heating the solution up to 80° C. 1 L of methanol was added to the solution and then NH.sub.4OH was added to raise the pH value of the solution to 8 or more, after which ultrasonic treatment was performed for 240 minutes at a frequency of 2˜4 kHz. The resulting particle slurry was then subject to centrifugation for separation. The speed of the centrifuge was 10,000 rpm for 1 hour. The particle distribution of the separated diamond particles is listed in the following Table 1.

COMPARATIVE EXAMPLE 1

[0069] 200 g of nanodiamond clusters synthesized by the detonation reaction method was added to 4 L of deionized water and stirred for 60 minutes while heating the solution up to 80° C. NaOH was then added to the solution increasing the pH of the solution to a value of 8 or above. Thereafter, ultrasonic treatment was performed for 240 minutes on the solution with a frequency of 2˜4 kHz. The recovered particle slurry was then subject to centrifugation for separation at 10,000 rpm for 1 hour. The particle distribution of the separated diamond particles is listed in the following Table 1.

COMPARATIVE EXAMPLE 2

[0070] 200 g of nanodiamond clusters synthesized by the detonation reaction method was added to 4 L of deionized water and stirred for 60 minutes while heating the solution up to 80° C. NaCl and NaOH were then added to raise the pH value of the solution to 8 or more, after which ultrasonic treatment was performed for 240 minutes at a frequency of 2˜4 kHz. The resulting particle slurry was then subject to centrifugation for separation. The speed of the centrifuge was 10,000 rpm for 1 hour. The particle distribution of the separated diamond particles is listed in the following Table 1.

COMPARATIVE EXAMPLE 3

[0071] 200 g of nanodiamond clusters synthesized by the detonation reaction method was added to 4 L of deionized water and stirred for 60 minutes while heating the solution up to 80° C. NaCl and NaOH were then added to raise the pH value of the solution to 8 or more, after which ultrasonic treatment was performed at a frequency of 2˜4 kHz. The resulting particle slurry was then subject to centrifugation for separation. The speed of the centrifuge was 10,000 rpm for 1 hour. The particle distribution of the separated diamond particles is listed in the following Table 1.

COMPARATIVE EXAMPLE 4

[0072] 200 g of nanodiamond clusters synthesized by the detonation reaction method was added to 4 L of deionized water and stirred for 60 minutes while heating the solution up to 80° C. The solution was then subject to ultrasonic treatment for 60 seconds. The particle distribution of the separated diamond particles is listed in the following Table 1.

Measurement of Particle Size Distribution

[0073] Measurement of particle size distribution of the nanodiamond particles separated from the nanodiamond clusters was performed using a Malvern Zetasizer® on the dispersion solutions of Examples 1˜8 (FIGS. 2-9) and Comparative Examples 1˜4 (FIGS. 10˜13) and are graphically shown in FIGS. 2-13 and listed in Table 1 below.

TABLE-US-00001 TABLE 1 Average Particle Size Median Size Particle Size Color of Example No. (nm) (nm) Distribution (nm) Particle Impurities Example 1 90 66.1 10~300 Gray Not applicable Example 2 65 46.6 18~180 Blackish gray Not applicable Example 3 61 47.2 18~160 Blackish gray Not applicable Example 4 23 18.0 7~60 Black Not applicable Example 5 21 16.8 5~50 Black Not applicable Example 6 28 22.3 13~70  Black Not applicable Example 7 43 29.1 10~120 Black Not applicable Example 8 43 32.1 15~130 Black Not applicable Comparative 85 68.7 30~230 Brownish Na Example 1 gray Comparative 75 52.1 20~220 Blackish gray Na Example 2 Comparative 174 76.6 30~700 Black-gray Cl Example 3 Comparative 488 419.7 170~850  Gray Not applicable Example 4

[0074] Referring to Table 1, Examples 1˜8 list an average particle size of 120 nm or less, and for Examples 2˜8 the average size is in general about 50 nm. Examples 4˜8 in particular, show a particle size distribution of 100 nm or less and a very small average particle size of 20˜50 nm, which are black in color. In general, the color of the dispersion solution of nanodiamonds is gray for particles of 200 nm or more, blue for particles of 100˜200 nm and clear black with no turbidity for particles of 100 nm or less. The majority of the examples given in the present invention display a color of black or blackish gray which confirms that the nanodiamond particles separated and dispersed are of 100 nm or less in size.

[0075] Due to the metal additives, it can be seen that impurities such as Na and Cl exist in Comparative Examples 1˜3. For Comparative Example 1, as much as 0.7 wt. % was detected. Through the given examples, it was confirmed that nanodiamonds could be separated without the use of zirconium or ceramic beads or the use of metal containing compounds (e.g. NaCl). In addition, as shown in Examples 1˜8 since there was no introduction of Na during the separation process of the nanodiamonds the impurity content was nil.

[0076] In Comparative Examples 1˜4, only water was used as the solvent and as a result, the particle size distribution was 30˜850 nm and the average particle size was 85˜488 nm, indicating that the nanodiamond particles did not separate completely from the nanodiamond clusters.

[0077] While the present invention has been particularly shown and described with reference to exemplary embodiments as given above, they are for purposes of illustration only and are not intended to limit the scope of protection of the present invention.

INDUSTRIAL APPLICATIONS

[0078] The method for separating nanodiamonds of the present invention provides nanodiamond particles of 5˜50 nm, which are uniform in size and absent of metal or alkaline impurities and therefore may be used as precursor materials for thin films, drug delivery systems or cosmetic compositions and the like.