WO2017141689A1

WO2017141689A1 - Nanodiamond dispersion liquid, and production method therefor

Info

Publication number: WO2017141689A1
Application number: PCT/JP2017/003320
Authority: WO
Inventors: 木本訓弘; 山本由紀
Original assignee: 株式会社ダイセル
Priority date: 2016-02-17
Filing date: 2017-01-31
Publication date: 2017-08-24
Also published as: JPWO2017141689A1; TW201800337A; JP6902015B2

Abstract

Provided is a method for producing a high-purity single-digit nanodiamond dispersion liquid having only a very small amount of contaminant metal components, through a step for simply and efficiently removing fine metal powder mixed with the nanodiamond. The nanodiamond dispersion liquid production method according to the present invention is for obtaining a nanodiamond dispersion liquid which has a particle size D50 (median size) of 10 nm or less, and in which the total content of a Zr compound, an Al compound, an Y compound, an Fe compound, and a Hf compound (in terms of elemental Zr, Al, Y, Fe, and Hf; weight) is 50 ppm or less of nanodiamond contained in the dispersion liquid (weight), through step 1 for subjecting nanodiamond to a pulverization treatment using a pulverizer, step 2 for subjecting a mixture of the nanodiamond after the pulverization treatment and sulfuric acid to a heat treatment, and step 3 for removing sulfate radicals from the mixture after the heat treatment.

Description

Nanodiamond dispersion and method for producing the same

The present invention relates to a method for producing a nanodiamond dispersion including a step of eluting and removing a metal component mixed in by pulverization using a pulverizer such as a bead mill. This application claims the priority of Japanese Patent Application No. 2016-028004 for which it applied to Japan on February 17, 2016, and uses the content here.

In recent years, development of fine-grained diamond materials called nanodiamonds has been underway. For nanodiamonds, so-called single-digit nanodiamonds having a particle diameter of 10 nm or less may be required depending on applications. Techniques relating to such nanodiamond dispersions are described, for example, in Patent Document 1 and Patent Document 2 below.

Japanese Patent Laid-Open No. 2005-001983 JP 2010-126669 A

The nanodiamond having a primary particle size of 10 nm or less exhibits high mechanical strength, high thermal conductivity, high refractive index, and the like. However, since fine particles such as nanodiamonds have a large proportion of surface atoms (particularly surface atoms that are coordinately unsaturated), the sum of van der Waals forces that can act between surface atoms of adjacent particles is large. And is prone to aggregation. In addition to this, in the case of nanodiamonds, a phenomenon called agglutination can occur, in which coulomb interaction between crystal planes of adjacent crystallites contributes and is very tightly assembled. Since nanodiamond has such a unique property that crystallites or primary particles can interact in a superimposed manner as described above, the primary particles are highly dispersed in, for example, a solvent by dissociating the primary particles of nanodiamond. Creating a state is very difficult.

Nanodiamonds take the form of aggregates (secondary particles) in which primary particles are assembled by very strong interaction at the stage of being generated by detonation, for example. For the crushing from the secondary particles to the primary particles, a crushing process using a pulverizer such as a bead mill is often employed.

The bead mill is a machine for crushing and / or crushing using metal beads, and zirconia beads are mainly used as the metal beads. In some cases, a mill container having an inner wall coated with zirconia is used. When nanodiamonds are crushed using such a bead mill, it is a metal that is very difficult to separate and remove because it has a particle size of several tens of nm or less, which is derived from metal beads or a mill container. It was inevitable that the fine powder was mixed in the nanodiamond, and the problem was that the purity of the nanodiamond decreased due to the mixing of the metal fine powder.

Accordingly, an object of the present invention is to achieve a single-digit nanometer with a high purity, in which the amount of metal components mixed is extremely low, through a process of easily and efficiently removing metal fine powder of several tens of nm or less mixed in nanodiamonds by crushing treatment. The object is to provide a method for producing a diamond dispersion.

As a result of intensive studies to solve the above-mentioned problems, the present inventors have found that the metal component mixed by subjecting the nanodiamond to the crushing process using a pulverizer is subjected to heat treatment of the nanodiamond mixed with the metal component together with sulfuric acid. The metal component can be eluted in sulfuric acid, and the metal component can be efficiently removed from the nanodiamond by separating and removing the sulfuric acid eluted from the metal component. Since the nano-diamond from which the slag has been removed has already been crushed, it can be easily re-dispersed by mixing with a dispersion medium, even if it is agglomerated by the sulfuric acid treatment. It was found that a dispersion was obtained. The present invention has been completed based on these findings.

That is, the present invention is a nanodiamond dispersion having a particle diameter D50 (median diameter) of 10 nm or less through the following steps, and the total content of Zr compound, Al compound, Y compound, Fe compound, and Hf compound ( Provided is a method for producing a nanodiamond dispersion, in which a nanodiamond dispersion having a Zr, Al, Y, Fe, and Hf element conversion (weight) of 50 ppm or less of nanodiamond (weight) contained in the dispersion is obtained.
Step 1: Nano diamond is subjected to crushing treatment using a pulverizer Step 2: A mixture of nano diamond and sulfuric acid after crushing treatment is subjected to heat treatment Step 3: Sulfate radicals are removed from the mixture after the heat treatment

The present invention also provides the method for producing the nanodiamond dispersion liquid, wherein the nanodiamond subjected to step 1 is a detonation nanodiamond.

The present invention is also a dispersion of nanodiamond, wherein the nanodiamond in the dispersion has a particle diameter D50 (median diameter) of 10 nm or less, a Zr compound, an Al compound, a Y compound, an Fe compound, and an Hf compound. A nanodiamond dispersion liquid in which the total content (converted to Zr, Al, Y, Fe, Hf elements; weight) is 50 ppm or less of the nanodiamond (weight) in the dispersion liquid is provided.

That is, the present invention relates to the following.
[1] A nanodiamond dispersion having a particle diameter D50 (median diameter) of 10 nm or less through the following steps, and the total content of Zr compound, Al compound, Y compound, Fe compound, and Hf compound (Zr, Al , Y, Fe, Hf element conversion; weight) The manufacturing method of the nano diamond dispersion liquid which obtains the nano diamond dispersion liquid which is 50 ppm or less of the nano diamond (weight) contained in a dispersion liquid.
Step 1: Nano diamond is subjected to pulverization using a pulverizer Step 2: A mixture of nano diamond and sulfuric acid after pulverization is subjected to heat treatment Step 3: Sulfate radicals are removed from the mixture after the heat treatment [ 2] The method for producing a nanodiamond dispersion liquid according to [1], wherein the nanodiamond to be subjected to step 1 is a detonation nanodiamond.
[3] The nanodiamond subjected to the crushing treatment is a nanodiamond dispersion having a pH of 8 or more (preferably 8 to 12, particularly preferably 9 to 11, more preferably 9.5 to 11.5). [1] Or the manufacturing method of the nano diamond dispersion liquid as described in [2].
[4] The method for producing a nanodiamond dispersion liquid according to any one of [1] to [3], wherein a bead mill is used as a pulverizer.
[5] The method for producing a nanodiamond dispersion liquid according to any one of [1] to [3], wherein a bead mill using metal beads is used as a pulverizer.
[6] As a pulverizer, a bead mill formed of a material containing at least one selected from Zr compounds, Al compounds, Y compounds, Fe compounds, and Hf compounds is used. Any of [1] to [3] The manufacturing method of the nano diamond dispersion liquid as described in any one.
[7] Production of nanodiamond dispersion liquid according to any one of [1] to [3], wherein a bead mill using zirconia beads or a bead mill coated with zirconia on the inner wall of the mill container is used as a pulverizer. Method.
[8] In any one of [1] to [7], sulfuric acid having a concentration of 50% by weight or more (preferably 55% by weight or more, particularly preferably 60% by weight or more) is used as sulfuric acid in Step 2. The manufacturing method of nano diamond dispersion liquid of description.
[9] Any one of [1] to [8], wherein the amount of sulfuric acid used is 2 times or more (preferably 10 times or more, particularly preferably 20 times or more) of nanodiamond (solid content conversion). The manufacturing method of the nano diamond dispersion liquid as described in one.
[10] The nano according to any one of [1] to [9], wherein the mixture of nanodiamond and sulfuric acid is heat-treated at a temperature of 200 ° C. or higher (preferably 220 ° C. or higher, particularly preferably 240 ° C. or higher). A method for producing a diamond dispersion.
[11] The method for producing a nanodiamond dispersion liquid according to any one of [1] to [10], wherein the sulfate radical is at least one selected from sulfuric acid, sulfate ion, and metal sulfate.
[12] For removal of sulfate radicals, sulfuric acid eluted with at least one selected from Zr compounds, Al compounds, Y compounds, Fe compounds, and Hf compounds is separated and removed by water washing treatment and / or neutralization treatment. The method for producing a nanodiamond dispersion liquid according to any one of [1] to [11].
[13] The method for producing a nanodiamond dispersion according to [12], wherein the water-washing treatment is a treatment of repeatedly washing with water until the pH of the nanodiamond dispersion becomes 6 or more.
[14] The neutralization treatment is a treatment in which a basic substance or an aqueous solution thereof is added until the pH of the nanodiamond dispersion becomes 12 or more to precipitate a sulfate radical as a salt, according to [12] or [13]. A method for producing a nanodiamond dispersion liquid.
[15] A dispersion of nanodiamond, the particle diameter D50 (median diameter) of nanodiamond in the dispersion being 10 nm or less, and the total content of Zr compound, Al compound, Y compound, Fe compound, and Hf compound A nanodiamond dispersion in which the amount (Zr, Al, Y, Fe, Hf element conversion; weight) is 50 ppm or less of the nanodiamond (weight) in the dispersion.
[16] The nanodiamond dispersion according to [15], wherein the nanodiamond in the nanodiamond dispersion has a zeta potential at pH 8 to 12 of −60 to −20 mV.
[17] The nanodiamond dispersion liquid according to [15] or [16], wherein the dispersion medium for dispersing nanodiamond is water or an aqueous dispersion medium containing 50% by weight or more of water.

In this specification, the Zr compound, the Al compound, the Y compound, the Fe compound, and the Hf compound each include a single metal.

Since the manufacturing method of the nanodiamond dispersion liquid of the present invention has the above-described configuration, the metal component is efficiently removed by a simple method, the amount of the metal component mixed is extremely low, and the nanodiamond dispersion liquid having excellent dispersibility, That is, a single-digit nanodiamond dispersion can be produced.

Nanodiamond has high mechanical strength, electrical insulation, excellent thermal conductivity, deodorizing effect, and antibacterial effect, and the nanodiamond dispersion obtained by the production method of the present invention has the above characteristics. Since the nanodiamond is contained in a highly dispersed state, the above characteristics can be highly expressed. Therefore, it is suitably used as an abrasive, a conductivity imparting material, an insulating material, a deodorant, an antibacterial agent and the like.

[Production method of nanodiamond dispersion]
The method for producing a nanodiamond dispersion of the present invention is a nanodiamond dispersion having a particle diameter D50 (median diameter) of 10 nm or less through the following steps: a Zr compound, an Al compound, a Y compound, an Fe compound, and Hf A nanodiamond dispersion liquid in which the total content of compounds (in terms of Zr, Al, Y, Fe, Hf elements; weight) is 50 ppm or less of the nanodiamond (weight) contained in the dispersion liquid is obtained.
Step 1: Nano diamond is subjected to a crushing process using a pulverizer (hereinafter referred to as “crushing process step”).
Step 2: The mixture of nano diamond and sulfuric acid after the crushing treatment is subjected to a heat treatment (hereinafter, sometimes referred to as “sulfuric acid treatment step”).
Step 3: Remove sulfate radicals from the mixture after the heat treatment (hereinafter referred to as “sulfate radical removal step”).

The nanodiamond to be subjected to step 1 (cracking treatment step) is produced, for example, through the following production step and purification step (including an acid treatment step, an oxidation treatment step, a pre-cracking treatment step, etc.).

(Generation process)
Nanodiamonds can be produced, for example, by detonation. The detonation method includes an air-cooled detonation method and a water-cooled detonation method. In the present invention, the air-cooled detonation method is particularly preferable in that nanodiamonds having smaller primary particles can be obtained than the water-cooled detonation method. The detonation may be performed in an air atmosphere, or may be performed in an inert gas atmosphere such as a nitrogen atmosphere or an argon atmosphere. Therefore, the nanodiamond to be subjected to the crushing treatment in the above step 1 is preferably detonation nanodiamond, that is, nanodiamond produced by detonation, and more preferably air-cooled detonation nanodiamond, that is, air-cooled detonation. Is a nanodiamond produced by

In the detonation method, first, a molded explosive with an electric detonator is installed inside a pressure-resistant container for detonation. As the container, for example, a metal container such as iron is used. The volume of the container is, for example, 0.5 to 40 m ³ , preferably 2 to 30 m ³ . As the explosive, a mixture of trinitrotoluene (TNT) and cyclotrimethylenetrinitroamine, ie hexogen (RDX), can be used. The weight ratio of TNT to RDX (TNT / RDX) is, for example, in the range of 40/60 to 60/40.

In the generation process, the electric detonator is then detonated and the explosive is detonated in the container. Detonation refers to an explosion associated with a chemical reaction in which the reaction flame surface moves at a speed exceeding the speed of sound. At the time of detonation, crude nanodiamonds are generated by the action of the pressure and energy of the shock wave generated by the explosion, using carbon that is liberated due to partial incomplete combustion of the explosive used.

(Purification process)
The crude nanodiamond obtained through the production process contains metal oxides such as Al, Fe, Co, Cr and Ni contained in the vessel used for the production reaction (for example, Fe ₂ O ₃ , Fe ₃ O _4). , Co ₂ O ₃ , Co ₃ O ₄ , NiO, Ni ₂ O _3, etc.) are included as metallic impurities, and the metallic impurities cause nano diamond adhesion. In addition, by-products such as graphite may be included, and this graphite is derived from carbon that did not form nanodiamond crystals among the carbon released by partial incomplete combustion of the explosive used. This also causes nano diamond adhesion. The purification process is a process for removing these impurities.

(Purification step; acid treatment step)
The acid treatment step is a step of removing the metallic impurities mixed in the crude nanodiamond obtained through the generation step, and an acid is added to the crude nanodiamond dispersion obtained by dispersing the crude nanodiamond in water. The metal impurities are eluted by addition to the acid, and then the acid from which the metal impurities are eluted is separated and removed to remove the metal impurities. As the acid (particularly strong acid) used in the acid treatment, a mineral acid is preferable, and examples thereof include hydrochloric acid, hydrofluoric acid, sulfuric acid, nitric acid, aqua regia and the like. These can be used individually by 1 type or in combination of 2 or more types. The concentration of the acid used for the acid treatment is, for example, 1 to 50% by weight. The acid treatment temperature is, for example, 70 to 150 ° C. The acid treatment time is, for example, 0.1 to 24 hours. The acid treatment can be performed under reduced pressure, normal pressure, or increased pressure. As a method for separating and removing the acid from which the metallic impurities are eluted, it is preferable to carry out, for example, decantation. In decantation, it is preferable to wash the solids (including nanodiamonds) with water, and it is particularly preferable to repeat the water washing until the pH of the precipitation solution reaches 2 to 3, for example.

(Purification process; oxidation process)
The oxidation treatment step is a step of removing graphite (graphite) mixed in the crude nanodiamond obtained through the generation step, and a crude nanodiamond dispersion liquid obtained by dispersing the crude nanodiamond in water (preferably, The graphite is removed by causing an oxidizing agent to act on the nanodiamond dispersion obtained through the acid treatment step. Examples of the oxidizing agent include chromic acid, chromic anhydride, dichromic acid, permanganic acid, perchloric acid, and salts thereof. These can be used individually by 1 type or in combination of 2 or more types. The concentration of the oxidizing agent used in the oxidation treatment is, for example, 3 to 50% by weight. The amount of the oxidizing agent used in the oxidation treatment is, for example, 300 to 500 parts by weight with respect to 100 parts by weight of the rough nanodiamond subjected to the oxidation treatment. The oxidation treatment temperature is, for example, 100 to 200 ° C. The oxidation treatment time is, for example, 1 to 24 hours. The oxidation treatment can be performed under reduced pressure, normal pressure, or increased pressure. The oxidation treatment is preferably performed in the presence of an acid (particularly a mineral acid. Examples similar to the mineral acid used in the acid treatment step) can be performed from the viewpoint of improving the graphite removal efficiency. When an acid is used for the oxidation treatment, the acid concentration is, for example, 5 to 80% by weight. After such oxidation treatment, it is preferable to remove the supernatant, for example, by decantation. In decantation, it is preferable to wash the solid content (including the nanodiamond adherend) with water. Although the supernatant liquid at the beginning of water washing is colored, it is preferable to repeat the water washing of the solid content until the supernatant liquid becomes transparent visually.

(Purification step; pre-cracking treatment step)
In this step, an alkali and hydrogen peroxide are reacted with the solution containing the nanodiamond adherend obtained through the oxidation treatment step. Examples of the alkali include sodium hydroxide, ammonia, potassium hydroxide and the like. The alkali concentration is preferably 0.1 to 10% by weight, more preferably 0.2 to 8% by weight, and still more preferably 0.5 to 5% by weight. The concentration of hydrogen peroxide is preferably 1 to 15% by weight, more preferably 2 to 10% by weight, and still more preferably 4 to 8% by weight. The temperature for carrying out the reaction is, for example, 40 to 95 ° C., and the reaction time is, for example, 0.5 to 5 hours. The reaction can be performed under reduced pressure, normal pressure, or increased pressure. After the reaction, it is preferable to remove the supernatant by decantation.

In the pre-cracking treatment step, it is preferable to adjust the pH of the precipitate obtained by the above decantation. For example, an acid (for example, hydrochloric acid) is added to adjust the pH to, for example, 2 to 3. Is preferred.

In the pre-cracking treatment step, next, it is preferable to perform water washing by a centrifugal sedimentation method on the solid content (including the nanodiamond adherend) in the precipitation liquid. More specifically, an operation for performing solid-liquid separation on the precipitate or suspension using a centrifuge, an operation for separating the precipitate from the supernatant, and then ultrapure water for the precipitate. It is preferable to carry out a series of processes including the operation of adding and suspending, for example, repeatedly. This washing with water is preferably carried out until the electrical conductivity per 1% by weight of the solid content of the dispersion becomes, for example, 20 μS / cm or less (preferably 15 μS / cm or less). The dispersion after washing with water is preferably acidic, and its pH is, for example, in the range of 3.5 to 6.5, and preferably in the range of 4 to 6. Washing with water until the electrical conductivity value and pH value of the dispersion are within the above ranges is preferable in that it facilitates crushing of nanodiamonds (separation of primary particles from secondary particles) in the next step 1. .

In the pre-crushing treatment step, it is then preferable to adjust the pH of the nanodiamond aggregate-containing dispersion. From the viewpoint of dispersion stability, the pH of the nanodiamond aggregate-containing dispersion is, for example, 8 or more (for example, 8 to 12), preferably 9 or more (for example, 9 to 11), more preferably 9.5 to 10.5. The solid concentration (nanodiamond concentration) is preferably 2% by weight or more (for example, 2 to 15% by weight), more preferably 4% by weight from the viewpoint of obtaining a single-digit nanodiamond dispersion having a high concentration. % Or more (for example, 4 to 10% by weight).

[Step 1: Crushing treatment step]
Step 1 is, for example, a step of subjecting nanodiamond obtained by the above method (for example, nanodiamond in a nanodiamond aggregate-containing dispersion) to a pulverization process using a pulverizer. Even after being purified through the above-described purification process, for example, detonation nanodiamonds take the form of aggregates (secondary particles) in which the primary particles are assembled with very strong interactions. However, the primary particles of nanodiamond can be separated from the nanodiamond adherend (secondary particles) by subjecting to a crushing treatment.

Examples of the pulverizer include a bead mill, a ball mill, a jet mill, and an ultrasonic homogenizer. In the present invention, it is preferable to use a bead mill because nanodiamonds can be finely pulverized until, for example, the particle diameter D50 (median diameter) is 10 nm or less.

The bead mill is an apparatus having a configuration in which beads are filled in a mill container (or a crushing chamber) having a rotation shaft in the center. By rotating the rotation shaft, motion is given to the beads. The object is crushed by the strong shearing force generated by the movement. As the beads, those of various materials (for example, zirconia, zirconia-silica ceramics, glass, alumina, steel, etc.) are known. Beads (zirconia beads) are preferably used. Further, as the bead mill, a mill vessel whose inner wall is coated with zirconia can be used. The zirconia beads and zirconia coating are at least one selected from Zr compounds, Al compounds, Y compounds, Fe compounds, and Hf compounds (mainly ZrO ₂ , Y ₂ O ₃ , Al ₂ O ₃ , HfO). ₂ etc.) is included. The zirconia-silica ceramic beads mainly contain ZrO ₂ , Y ₂ O ₃ , SiO ₂ , and Al ₂ O ₃ .

After the completion of step 1, classification may be performed before applying to step 2 to remove coarse nanodiamond particles and the like. The classification process can be performed using, for example, a centrifuge. By performing the classification treatment, a nanodiamond dispersion having a more uniform particle size distribution can be obtained.

The so-called zeta potential of the nanodiamond in the nanodiamond dispersion obtained through the above steps is preferably −60 to −20 mV, more preferably −50 to −30 mV. The particle diameter D50 (median diameter) is, for example, 10 nm or less (preferably 8 nm or less, particularly preferably 6 nm or less).

[Step 2: Sulfuric acid treatment step]
Step 2 is a step of subjecting the mixture of nano-diamond and sulfuric acid after the crushing treatment obtained through Step 1 to a heat treatment. In Step 1, it is inevitable that a component derived from a pulverizer (a fine powder having a particle diameter D50 (median diameter) of, for example, 50 nm or less) is mixed into the nanodiamond by being subjected to a pulverization treatment using a pulverizer. . Total content of Zr compound, Al compound, Y compound, Fe compound, and Hf compound contained in nano diamond after pulverization treatment obtained through step 1 (in terms of Zr, Al, Y, Fe, Hf elements; weight) ) Is, for example, 3,000 ppm or more (for example, 3,000 to 15,000 ppm) of nanodiamond (weight). Therefore, in Steps 2 and 3, the components derived from the grinder mixed in Step 1 are removed.

The nanodiamond subjected to the sulfuric acid treatment step may be a nanodiamond dispersion or a nanodiamond dry powder. When the nanodiamond dispersion is subjected to this step, the nanodiamond dispersion obtained through step 1 can be used as it is, and when the nanodiamond dry powder is subjected to this step, the nanodiamond dispersion is obtained through step 1. The dried nanodiamond dispersion is subjected to a drying process (for example, spray drying using a spray dryer or evaporation to dryness using an evaporator) to prepare a dry powder and using it. Can do.

As the sulfuric acid, it is preferable to use one having a concentration of, for example, 50% by weight or more (preferably 55% by weight or more, particularly preferably 60% by weight or more).

The amount of sulfuric acid used is, for example, 2 volume times or more, preferably 10 volume times or more, particularly preferably 20 volume times or more of nanodiamond (solid content conversion). Use of sulfuric acid in the above range is preferable in that the components derived from the pulverizer can be efficiently removed.

The heat treatment temperature of the mixture of nanodiamond and sulfuric acid is, for example, 200 ° C. or higher (preferably 220 ° C. or higher, particularly preferably 240 ° C. or higher). The heat treatment time is, for example, 5 minutes or longer (preferably 15 minutes or longer, particularly preferably 30 minutes or longer). In the present invention, it is particularly preferable to perform the heat treatment by the reflux method in that the sulfuric acid concentration can be kept constant and the components derived from the pulverizer can be more efficiently removed.

The heat treatment can be performed using, for example, a sand bath, a hot air dryer, a microwave reaction device, or the like. The heat treatment can be performed under normal pressure or under pressure. By subjecting the mixture of nanodiamond and sulfuric acid to a heat treatment, components derived from the pulverizer mixed in nanodiamond can be eluted in sulfuric acid. For example, when using a bead mill using zirconia beads as a pulverizer, or a bead mill in which the inner wall of the mill container is coated with zirconia, the components derived from the pulverizer are, for example, Zr compound, Al compound, Y compound, Fe compound, And at least one selected from Hf compounds (mainly ZrO ₂ , Y ₂ O ₃ , Al ₂ O ₃ , HfO ₂ ). In addition, when a bead mill using zirconia-silica ceramic beads is used as a pulverizer, components derived from the pulverizer are mainly ZrO ₂ , Y ₂ O ₃ , SiO ₂ , and Al ₂ O ₃ .

[Step 3: Sulfate radical removal step]
Step 3 is a step of removing sulfate radicals from the mixture after the sulfuric acid treatment. More specifically, in the sulfuric acid treatment in step 2, it is a step of separating and removing sulfate radicals produced by the dissolution of components derived from the pulverizer into sulfuric acid. The sulfate radical includes unreacted sulfuric acid used in the sulfuric acid treatment step, sulfate ions, metal sulfate, and the like.

The method for separating and removing the sulfate radical is not particularly limited, and examples thereof include washing with water and neutralization. These can be performed singly or in combination of two or more. A preferred example of the present invention is a method in which treatment is performed in the order of water washing, neutralization and water washing.

In the water washing treatment, the solid content (including nanodiamonds) in the mixture after the sulfuric acid treatment is washed with water. The water washing treatment is preferably performed while removing the supernatant by decantation or centrifugation, and the pH of the supernatant of the mixture after the sulfuric acid treatment is, for example, 6 or more (eg, 6 to 7), It is preferable to repeat the water washing process until it becomes 6.5 or more.

The neutralization treatment is performed by adding a basic substance or an aqueous solution thereof. The sulfate radical can be precipitated as a salt by adding a basic substance or an aqueous solution thereof. Examples of the basic substance include alkali metal compounds (for example, alkali metal hydroxides such as sodium hydroxide and potassium hydroxide; alkali metal carbonates such as sodium carbonate and potassium carbonate; alkali metal carbonates such as sodium bicarbonate). Hydrogen salt; alkali metal carboxylate such as sodium acetate and potassium acetate; sodium alkoxide such as sodium methoxide and sodium ethoxide), alkaline earth metal compound (for example, alkaline earth such as magnesium hydroxide and calcium hydroxide) Metal hydroxides; alkaline earth metal carbonates such as magnesium carbonate and calcium carbonate; alkaline earth metal carboxylates such as magnesium acetate and calcium acetate; alkaline earth metal alkoxides such as magnesium ethoxide, etc.) .

In the present invention, it is preferable to add the basic substance or an aqueous solution thereof to a dispersion obtained by dispersing the precipitate obtained through the water washing treatment in water until the pH of the dispersion becomes 12 or more. .

After the neutralization treatment, the water washing treatment is preferably performed again, and the water washing treatment is preferably performed while removing the supernatant by decantation or centrifugation. In the present invention, it is preferable to repeatedly carry out the water washing treatment of the dispersion liquid obtained through the neutralization treatment until the pH of the supernatant becomes, for example, 11 to 12 (preferably 10 to 11). .

The precipitate (nanodiamond slurry) obtained through the water washing-neutralization-water washing treatment is excellent in redispersibility, and is mixed with a dispersion medium to disperse to primary particles as if dissolved. The nanodiamond dispersion liquid (preferably the primary particles of nanodiamond are dispersed as colloidal particles) whose nanodiamond particle diameter D50 (median diameter) is 10 nm or less (preferably 8 nm or less, particularly preferably 6 nm or less) A dispersion) is obtained. In this specification, “particle diameter D50” is a value that can be measured by a so-called dynamic light scattering method.

For example, the nano-diamond obtained by crushing using a bead mill using zirconia beads as a pulverizer or a bead mill equipped with a mill container with an inner wall coated with zirconia is mixed with components derived from the pulverizer. However, the components derived from the pulverizer can be removed by performing the above steps 1 to 3. Therefore, the total content of Zr compound, Al compound, Y compound, Fe compound, and Hf compound in the nanodiamond dispersion obtained by mixing the precipitate obtained through the above steps 1 to 3 with a dispersion medium ( Zr, Al, Y, Fe, Hf element conversion; weight) is 50 ppm or less of nanodiamond (weight) contained in the dispersion, that is, according to the production method of the present invention, inclusion of components derived from a pulverizer A nanodiamond dispersion whose amount is below the detection limit is obtained.

[Nanodiamond dispersion]
The nanodiamond dispersion liquid of the present invention is a nanodiamond dispersion liquid, in which the nanodiamond particle diameter D50 (median diameter) in the dispersion liquid is 10 nm or less, and a Zr compound, Al compound, Y compound, Fe compound, And the total content of Hf compounds (in terms of Zr, Al, Y, Fe, Hf elements; weight) is, for example, 200 ppm or less (preferably 100 ppm or less, particularly preferably 50 ppm or less) of nanodiamond (weight) in the dispersion. . The nanodiamond dispersion liquid of the present invention can be produced, for example, by the method for producing the nanodiamond dispersion liquid.

The nanodiamond contained in the nanodiamond dispersion is, for example, detonation nanodiamond (nanodiamond produced by detonation), preferably air-cooled detonation nanodiamond (nanodiamond produced by air-cooled detonation) ). Air-cooled detonation nanodiamonds are preferred in that a nanodiamond dispersion having a smaller particle diameter D50 (median diameter) is obtained because primary particles tend to be smaller than water-cooled detonation nanodiamonds.

The dispersion medium contained in the nanodiamond dispersion liquid is a medium for appropriately dispersing nanodiamonds. As the dispersion medium, it is preferable to use a solvent in which nanodiamonds can easily disperse, and examples thereof include water, methanol, ethanol, ethylene glycol, dimethyl sulfoxide, and N-methylpyrrolidone. These can be used alone or in combination of two or more. In the present invention, it is particularly preferable to use water or an aqueous dispersion medium containing 50% by weight or more of water because it is particularly excellent in dispersibility of nanodiamonds.

The zeta potential of nanodiamond affects the dispersion stability of nanodiamond in the dispersion medium. The zeta potential of the nanodiamond contained in the nanodiamond dispersion of the present invention at pH 8-12 is preferably −60 to −20 mV, more preferably −50 to −30 mV. Therefore, it is excellent in dispersibility and temporal dispersion stability. In the present specification, the zeta potential of the nanodiamond contained in the nanodiamond dispersion is a value measured for nanodiamond in the nanodiamond dispersion having a nanodiamond concentration of 0.2% by weight at 25 ° C. When it is necessary to dilute the stock solution of the nanodiamond dispersion for the preparation of the nanodiamond dispersion having a nanodiamond concentration of 0.2% by weight, ultrapure water is used as the diluent.

As described above, the nanodiamond dispersion liquid of the present invention is a single-digit nanodiamond dispersion liquid with extremely low content of components derived from a pulverizer and excellent dispersion stability. Therefore, the characteristics of nanodiamond (high mechanical strength) , Electrical insulation, excellent thermal conductivity, deodorant effect, antibacterial effect), and can be suitably used as an abrasive, conductivity imparting material, insulating material, deodorant, antibacterial agent, etc. be able to. For example, when the nanodiamond dispersion liquid of the present invention is added to a resin and used, the above-described excellent characteristics can be imparted to the resin by adding a small amount.

Hereinafter, the present invention will be described more specifically with reference to examples, but the present invention is not limited to these examples. The pH was measured using a pH meter (trade name “Lacom Tester PH110” manufactured by Nikko Hansen Co., Ltd.).

Example 1
<Purification process>
(Acid treatment process)
200 g of air-cooled detonation nano diamond cocoon (manufactured by Daicel Corporation) with a primary particle size of nano diamond of 4 to 6 nm was weighed, 2 L of 10 wt% hydrochloric acid aqueous solution was added, and heat-treated under reflux for 1 hour. Went. After cooling, it was washed with water until the pH of the precipitate became 2 by decantation, and the supernatant was removed as much as possible.

(Oxidation process)
After adding 2 L of 60 wt% sulfuric acid aqueous solution and 2 L of 50 wt% chromic acid aqueous solution to the precipitate obtained by decantation, heat treatment was performed under reflux for 5 hours. After cooling, washing was carried out by decantation until the coloring of the supernatant disappeared, and the supernatant was removed as much as possible. The particle diameter D50 (median diameter) of the nanodiamond aggregate in the obtained precipitation liquid was 2 μm.

(Processing before crushing)
Next, pre-crushing treatment was performed. Specifically, first, 1 L of a 10 wt% aqueous sodium hydroxide solution and 1 L of a 30 wt% aqueous hydrogen peroxide solution are added to the precipitate obtained by decantation in the above-described oxidation treatment step to form a slurry. The slurry was heat-treated for 1 hour under reflux under normal pressure conditions. The heat treatment temperature was 50 to 105 ° C. After cooling, the supernatant was removed by decantation. Next, hydrochloric acid is added to the precipitate obtained by this decantation to adjust the pH of the precipitate to 2.5, and then the solid content (including the nanodiamond adherent) in this precipitate is centrifuged. Washed with water. Specifically, an operation for performing solid-liquid separation on the precipitate or suspension using a centrifuge, an operation for separating the precipitate from the supernatant, and then ultrapure water for the precipitate. A series of processes including the operation of adding and suspending was repeated until the electrical conductivity of the suspension reached 56 μS / cm when the solid content concentration (nanodiamond concentration) was adjusted to 6% by weight. It was. The pH of the solution after such washing with water was 4.3.

<Crushing process>
Next, the crushing process was performed. Specifically, after adding a sodium hydroxide aqueous solution to 300 mL of the slurry (nanodiamond adherence-containing dispersion) obtained through the pre-crushing treatment step and adjusting the pH to 10, the beads mill dispersion was performed on the slurry. went. The apparatus used was a bead mill RMB manufactured by Imex Corporation. After filling 300 mL of zirconia beads having a diameter of 0.03 mm as a crushing medium, 300 mL of slurry adjusted to pH 10 was added, and the peripheral speed was set to 8 m / s, and crushing was performed for 120 minutes.

<Classification process>
The crushed liquid was collected, coarse particles were removed by classification operation by centrifugation, and a nanodiamond dispersion liquid was obtained. The resulting nanodiamond dispersion has a solid content concentration of 5.8%, a particle diameter D50 (median diameter) of 4.3 nm, an electric conductivity of 680 μS / cm, a pH of 9.34, and the zeta potential of the nanodiamond is − It was 48 mV.

Next, this nanodiamond dispersion was pulverized. Specifically, 100 mL of nanodiamond dispersion liquid was spray-dried. The apparatus used was a spray dryer type B-290 manufactured by Nippon Büch Corporation. This obtained nanodiamond powder (1). The metal component contained in the obtained nanodiamond powder (1) was subjected to ICP emission spectroscopic analysis. The results are shown in Table 1.

<Sulfuric acid treatment process>
300 mg of nanodiamond powder (1) was weighed, and 10 mL of 64 wt% sulfuric acid was added thereto to obtain a mixture (1). The resulting mixture (1) was refluxed on a sand bath set at 250 ° C. 40 minutes.

<Sulfate radical removal process>
The mixture (1) after the reflux treatment is centrifuged using a centrifugal separator (centrifugal force: 4,000 × g, centrifugation time: 10 minutes), and the precipitate (1) and the supernatant (1) ICP emission spectroscopic analysis was performed on the metal components contained in the supernatant (1). The results are shown in Table 1. In addition, the analysis result of supernatant liquid (1) described the value converted into metal component content in nano diamond powder.

Next, 30 mL of ultrapure water was added to the resulting precipitate (1) to suspend it, and a second centrifugation process was performed using a centrifuge to achieve solid-liquid separation. Centrifugal separation of the precipitate and supernatant after solid-liquid separation, suspension by adding ultrapure water to the precipitate, and further centrifugation The process was repeated until the pH of the solution became 7 to obtain a gray precipitate on which nanodiamonds had adhered.

To the obtained gray precipitate, 30 mL of 3N sodium hydroxide was added and left at room temperature for 1 hour, followed by centrifugation using a centrifuge (centrifugal force; 4,000 × g, centrifugation time; 10 After separating the precipitate from the supernatant, 30 mL of ultrapure water is added to the resulting precipitate to suspend it, and a second centrifugation process is performed using a centrifuge. Liquid separation was attempted. Centrifugal separation of the precipitate and supernatant after solid-liquid separation, suspension by adding ultrapure water to the precipitate, and further centrifugation This was repeated until the pH of the solution became 10. The supernatant liquid was removed to obtain a black precipitate on which nanodiamonds had adhered. When 30 mL of ultrapure water was added to the black precipitate, the nanodiamond was dispersed so as to dissolve, and a nanodiamond dispersion (nanodiamond concentration: 1% by weight) was obtained. The particle diameter D50 (median diameter) of the nanodiamond in the nanodiamond dispersion was 5.3 nm. Further, ICP emission spectroscopic analysis was performed on the metal component contained in the nanodiamond powder (2) obtained by evaporating and drying the water of the nanodiamond dispersion. The results are shown in Table 1.

From Table 1, the Zr element, Al element, Y element, Hf element, and Fe element content in the supernatant liquid (1) are all Zr element, Al element, Y element in the nanodiamond powder (1). Since the Zr element, Al element, Y element, Hf element, and Fe element were not detected from the nanodiamond powder (2), the above sulfuric acid The metal components (particularly, Zr compound, Al compound, Y compound, Hf compound, and Fe compound) derived from the bead mill using the zirconia beads contained in the nanodiamond powder (1) were removed by the treatment. I understood it.

<Nanodiamond concentration>
The nanodiamond content in the nanodiamond dispersion is determined by the precision balance of the weighed value of 3 to 5 g of the weighed dispersion and the dried product (powder) remaining after evaporation of water from the weighed dispersion by heating. Based on the weighed value, calculation was performed.

<Median diameter>
The particle diameter D50 (median diameter) of the nanodiamond contained in the nanodiamond dispersion is determined using a dynamic light scattering method (non-contact backscattering method) using an apparatus manufactured by Spectris (trade name “Zetasizer Nano ZS”). ). For the measurement sample, use a nanodiamond dispersion obtained by diluting with ultrapure water so that the nanodiamond concentration is 0.5 to 2.0% by weight and then irradiating with an ultrasonic cleaner. did.

<Zeta potential>
The zeta potential of the nanodiamond contained in the nanodiamond dispersion was measured by laser Doppler electrophoresis using an apparatus (trade name “Zetasizer Nano ZS”) manufactured by Spectris. As a measurement sample, a nanodiamond dispersion obtained by diluting with ultrapure water so that the nanodiamond concentration was 0.2% by weight and then irradiating with an ultrasonic cleaner was used. In addition, the pH of the nanodiamond dispersion subjected to the measurement was confirmed using a pH test paper (trade name “Three Band pH Test Paper”, manufactured by ASONE CORPORATION).

<ICP emission spectroscopy>
In the case of nanodiamond powder (1) and (2), 100 mg of powder was used as a measurement sample, and in the case of supernatant liquid (1), 1 mL of supernatant liquid diluted to 10 mL with ultrapure water was measured. Used as a sample.
The measurement sample was put in a magnetic crucible and subjected to dry decomposition in an electric furnace. This dry decomposition was carried out in three stages: 450 ° C. for 1 hour, followed by 550 ° C. for 1 hour, followed by 650 ° C. for 1 hour. After such dry decomposition, the residue in the magnetic crucible was evaporated to dryness by adding 0.5 mL of concentrated sulfuric acid to the magnetic crucible. Then, the obtained dried product was finally dissolved in 20 mL of ultrapure water. In this way, an analytical sample was prepared.
This analysis sample was subjected to ICP emission spectroscopic analysis using an ICP emission spectroscopic analyzer (trade name “CIROS120”, manufactured by Rigaku Corporation). The analysis sample was prepared so that the lower limit of detection of this analysis was 50 ppm by weight. In this analysis, SPEX standard solution (XSTC-22; mixed standard solution) and Kanto Chemical Co., Ltd. atomic absorption standard solution (Hf1000, Y1000, Zr1000) were used as the standard solution for the calibration curve. The sample was appropriately diluted and used in a sulfuric acid aqueous solution having the same concentration as the sulfuric acid concentration of the analysis sample. In this analysis, the measurement value obtained by operating and analyzing in the same manner with an empty crucible was subtracted from the measurement value for the measurement sample to obtain the metal component concentration in the measurement sample.

According to the method for producing a nanodiamond dispersion liquid of the present invention, it is possible to easily and efficiently remove a metal component and produce a nanodiamond dispersion liquid having an extremely low mixing amount of the metal component and excellent dispersibility. it can. And, the nanodiamond dispersion obtained by the production method of the present invention can highly express properties having high mechanical strength, electrical insulation, excellent thermal conductivity, deodorizing effect, antibacterial effect, It is suitably used as an abrasive, conductivity imparting material, insulating material, deodorant, antibacterial agent and the like.

Claims

Through the following steps, a nanodiamond dispersion liquid having a particle diameter D50 (median diameter) of 10 nm or less, the total content of Zr compound, Al compound, Y compound, Fe compound, and Hf compound (Zr, Al, Y, A method for producing a nanodiamond dispersion, wherein a nanodiamond dispersion having an Fe, Hf element conversion (weight) of 50 ppm or less of nanodiamond (weight) contained in the dispersion is obtained.
Step 1: Nano diamond is subjected to crushing treatment using a pulverizer Step 2: A mixture of nano diamond and sulfuric acid after crushing treatment is subjected to heat treatment Step 3: Sulfate radicals are removed from the mixture after the heat treatment
The method for producing a nanodiamond dispersion liquid according to claim 1, wherein the nanodiamond to be subjected to step 1 is detonation nanodiamond.
A nanodiamond dispersion, the nanodiamond particle diameter D50 (median diameter) in the dispersion is 10 nm or less, and the total content of Zr compound, Al compound, Y compound, Fe compound, and Hf compound (Zr , Al, Y, Fe, Hf element conversion; weight) is a nanodiamond dispersion liquid having 50 ppm or less of nanodiamond (weight) in the dispersion liquid.