JP2020172406A - Method for producing surface-modified nanodiamond - Google Patents

Abstract

To provide a method for producing a surface-modified nanodiamond excellent in production efficiency and capable of obtaining the surface-modified nanodiamond having an amine-derived surface-modifying group by using various amines.SOLUTION: A method for producing a surface-modified nanodiamond comprises a liquid plasma treatment step of subjecting a mixed liquid containing nanodiamond and an amine to a liquid plasma treatment for obtaining a nanodiamond having a nitrogen atom-containing group derived from the amine on the surface. The amine is an amine represented by formula (1), and the total number of carbon atoms in the amine represented by formula (1) is preferably 26 to 60: RnNH3-n (1).SELECTED DRAWING: Figure 1

Description

The present invention relates to a method for producing surface-modified nanodiamonds. More specifically, the present invention relates to a method for producing surface-modified nanodiamond having an amine-derived nitrogen atom-containing group on the surface.

Nanodiamond is an ultrafine diamond having a very large specific surface area, and has high mechanical strength, electrical insulation, and excellent thermal conductivity. It also has deodorant effect, antibacterial effect, and chemical resistance. Therefore, it is used as an abrasive, a conductivity-imparting material, an insulating material, a deodorant, an antibacterial agent, and the like.

Nanodiamonds are generally synthesized by the detonation method. Nanodiamonds obtained by the detonation method often form adherents, and the adherents are crushed using a crusher such as a bead mill to increase the median diameter (D50) of the particles. So-called single digit nanodiamonds with a diameter of less than 10 nm can be obtained (see Patent Documents 1 and 2).

Nanodiamond is a heat-dissipating material, an optical material (for example, a high-performance film material), a material reinforcing material, a heat exchange flow medium, and a coating material (for example, an antibacterial coating material and a deodorant coating material) while taking advantage of the above-mentioned characteristics of nanodiamond. In order to develop into various applications such as abrasives, lubricants, and medical materials, the target surface modifying group is introduced into nanodiamond.

For example, for nanodiamonds whose surface has been modified with amines or ammonium, methods for obtaining the nanodiamonds include a method of acid chlorideizing a carboxy group existing on the surface of nanodiamonds and reacting with amines, a method of using an ammonium salt, and the like. Is known (see Patent Document 3 and Non-Patent Document 1).

Japanese Unexamined Patent Publication No. 2005-001983 JP-A-2010-126669 JP-A-2017-128482

Journal of American Chemical Society 131 (2009) 4594-4595

However, the method of acid chloride formation has a problem of inferior production efficiency because there is a problem in safety and a long reaction time. Further, in the method using an ammonium salt, the types of the ammonium salt itself are small, and the solvent that can be used is limited from the viewpoint of the dispersibility of the obtained modified nanodiamond.

Therefore, an object of the present invention is to provide a method for producing surface-modified nanodiamonds, which has excellent production efficiency and can obtain surface-modified nanodiamonds having surface-modifying groups derived from amines by using various amines. is there.

As a result of diligent studies to achieve the above object, the present inventor has made a method for producing surface-modified nanodiamonds, which comprises a step of subjecting a mixed solution containing nanodiamonds and amines to plasma treatment in the liquid to modify the surface of nanodiamonds. For example, it has been found that the production efficiency is excellent and it is possible to obtain surface-modified nanodiamonds having surface-modifying groups derived from amines by using various amines. The present invention has been completed based on these findings.

That is, the present invention comprises a surface-modified nanodiamond step of subjecting a mixed solution containing nanodiamond and amine to plasma treatment in liquid to obtain nanodiamond having a nitrogen atom-containing group derived from the amine on the surface. Providing a manufacturing method for.

The amine is an amine represented by the following formula (1), and the total number of carbon atoms in the amine represented by the formula (1) is preferably 26 to 60.
R _n NH _3-n (1)
(In formula (1), R represents a monovalent organic group, and n represents an integer of 1 to 3).

The R is preferably a linear or branched alkyl group having 1 to 22 carbon atoms.

The amine is preferably a secondary amine or a tertiary amine.

According to the method for producing surface-modified nanodiamonds of the present invention, it is possible to obtain surface-modified nanodiamonds having a surface-modifying group derived from the amines, which are excellent in production efficiency and using various amines.

It is a process drawing which shows one Embodiment of the manufacturing method of the surface-modified nanodiamond of this invention. It is a figure which shows the FT-IR spectrum of the nanodiamond obtained in Preparation Example 1. It is a figure which shows the FT-IR spectrum of the surface-modified nanodiamond obtained in Example 1. It is a figure which shows the FT-IR spectrum of the surface-modified nanodiamond obtained in Example 2. It is a figure which shows the FT-IR spectrum of the surface-modified nanodiamond obtained in Example 3.

[Manufacturing method of surface-modified nanodiamond]
The method for producing surface-modified nanodiamonds of the present invention is a step of subjecting a mixed solution containing nanodiamonds and amines to plasma treatment in liquid to obtain nanodiamonds having a nitrogen atom-containing group derived from the amine on the surface (plasma treatment in liquid). Step) is included. In addition, in this specification, the manufacturing method of the surface-modified nanodiamond of this invention may be simply referred to as "the manufacturing method of this invention".

Examples of nanodiamonds used in the submerged plasma treatment step include detonation nanodiamonds (that is, nanodiamonds produced by the detonation method) and high-temperature and high-pressure nanodiamonds (that is, nanodiamonds produced by the high-temperature and high-pressure method). ) Etc. can be mentioned. Above all, it is preferable to use detonation nanodiamonds because the particle size of the primary particles is a single digit nanometer and the dispersibility is excellent.

The detonation method includes an air-cooled detonation method and a water-cooled detonation method. Above all, the air-cooled detonation method is preferable from the viewpoint that nanodiamonds having smaller primary particles than the water-cooled detonation method can be obtained. Further, the detonation may be carried out in an atmospheric atmosphere, or may be carried out in an inert gas atmosphere such as a nitrogen atmosphere or an argon atmosphere. Therefore, the nanodiamonds used in the submerged plasma treatment step are preferably detonation nanodiamonds, that is, nanodiamonds produced by the detonation method, and more preferably air-cooled detonation nanodiamonds.

The production method of the present invention may include other steps such as a production step, a purification step, an oxygen oxidation step, a hydrogenation step, and a crushing step in addition to the submerged plasma treatment step. Examples of the purification step include an acid treatment step, an oxidation treatment step, an alkaline superwater treatment step, and a drying step.

FIG. 1 is a process diagram showing an embodiment of the manufacturing method of the present invention. One embodiment of the production method of the present invention shown in FIG. 1 includes a production step S1, an acid treatment step and S2, an oxidation treatment step S3, an oxygen oxidation step S4, a crushing step S4, and a submerged plasma treatment step S5. And at least include.

(Generation process)
In the production step (nanodiamond production step), for example, a crude nanodiamond product is produced by a detonation method. Specifically, first, a molded explosive equipped with an electric detonator is installed inside a pressure-resistant container for detonation, and a gas having a specific composition and the explosive used coexist in the container. , Seal the container. The container is made of iron, for example. The volume of the container is, for example, 0.5 to 40 m ³ . As the explosive, a mixture of trinitrotoluene (TNT) and cyclotrimethylene trinitroamine or hexogen (RDX) can be used. The mass ratio of TNT to RDX (TNT / RDX) is, for example, in the range of 40/60 to 60/40. The amount of explosive used is, for example, 0.05 to 2.0 kg.

In the production process, the electric detonator is then detonated to detonate the explosive in the container. Detonation is an explosion that accompanies a chemical reaction in which the flame surface on which the reaction occurs moves at a high speed that exceeds the speed of sound. At the time of detonation, nanodiamonds are produced by the action of the pressure and energy of the shock wave generated by the explosion, using the carbon released by the explosive used as a partial incomplete combustion as a raw material. Nanodiamond is a product obtained by the detonation method. First of all, between adjacent primary particles or crystallites, in addition to the action of van der Waals force, the Coulomb interaction between crystal planes contributes to make nanodiamond very strong. It assembles and becomes an adherent body.

In the production step, the container and its inside are then cooled by allowing it to cool at room temperature for about 24 hours. After this cooling, the nanodiamond crude products (including the nanodiamond adherents and soot produced as described above) adhering to the inner wall of the container are scraped off with a spatula. Collect the product. By the detonation method as described above, a crude product of nanodiamond particles can be obtained. In addition, a desired amount of crude nanodiamond product can be obtained by performing the above-mentioned production steps a required number of times.

(Acid treatment process)
In the acid treatment step, a strong acid is allowed to act on the raw material nanodiamond crude product, for example, in an aqueous solvent to remove the metal oxide. The nanodiamond crude product obtained by the detonation method tends to contain metal oxides, and these metal oxides are oxides of Fe, Co, Ni, etc. derived from containers and the like used in the detonation method. .. For example, by allowing a strong acid to act in an aqueous solvent, metal oxides can be dissolved and removed from the crude nanodiamond product (acid treatment). The strong acid used for this acid treatment is preferably a mineral acid, and examples thereof include hydrochloric acid, hydrofluoric acid, sulfuric acid, nitric acid, and aqua regia. As the strong acid, one kind may be used, or two or more kinds may be used.

The concentration of the strong acid used in the acid treatment is, for example, 1 to 50% by mass. The acid treatment temperature is, for example, 70 to 150 ° C. The acid treatment time is, for example, 0.1 to 24 hours. Further, the acid treatment can be performed under reduced pressure, normal pressure, or pressure. After such acid treatment, the solid content (including the nanodiamond adherent) is washed with water, for example, by decantation. It is preferable to repeatedly wash the solid content with water by decantation until the pH of the precipitate reaches, for example, 2-3. When the content of the metal oxide in the crude nanodiamond product obtained by the detonation method is small, the above acid treatment may be omitted.

(Oxidation process)
The oxidation treatment step is a step of removing graphite from the crude nanodiamond product using an oxidizing agent. The crude nanodiamond product obtained by the detonation method contains graphite (graphite), which does not form nanodiamond crystals out of the carbon released by the explosive used due to partial incomplete combustion. Derived from graphite. For example, graphite can be removed from the crude nanodiamond product by allowing an oxidizing agent to act in an aqueous solvent after undergoing the above acid treatment. Further, by allowing an oxidizing agent to act, an oxygen-containing group such as a carboxy group or a hydroxyl group can be introduced into the surface of nanodiamond.

Examples of the oxidizing agent used in this oxidation treatment include chromic acid, chromic anhydride, dichromic acid, permanganic acid, perchloric acid, nitric acid, mixtures thereof, and at least one acid selected from these and others. Examples of mixed acids with acids (such as sulfuric acid) and salts thereof. Above all, it is preferable to use a mixed acid (particularly, a mixed acid of sulfuric acid and nitric acid) because it is environmentally friendly and has an excellent action of oxidizing and removing graphite.

The mixing ratio of sulfuric acid and nitric acid (former / latter; mass ratio) in the mixed acid is, for example, 60/40 to 95/5, even under pressure near normal pressure (for example, 0.5 to 2 atm). For example, it is preferable in that graphite can be efficiently oxidized and removed at a temperature of 130 ° C. or higher (particularly preferably 150 ° C. or higher; the upper limit is, for example, 200 ° C.). The lower limit is preferably 65/35, more preferably 70/30. The upper limit is preferably 90/10, more preferably 85/15, and even more preferably 80/20. When the mixing ratio is 60/40 or more, the content of sulfuric acid having a high boiling point is high, so that the reaction temperature becomes, for example, 120 ° C. or more under pressure near normal pressure, and the graphite removal efficiency tends to improve. is there. When the mixing ratio is 95/5 or less, the content of nitric acid that greatly contributes to the oxidation of graphite increases, so that the efficiency of removing graphite tends to improve.

The amount of the oxidizing agent (particularly the mixed acid) used is, for example, 10 to 50 parts by mass, preferably 15 to 40 parts by mass, and more preferably 20 to 40 parts by mass with respect to 1 part by mass of the crude nanodiamond product. The amount of sulfuric acid used in the mixed acid is, for example, 5 to 48 parts by mass, preferably 10 to 35 parts by mass, and more preferably 15 to 30 parts by mass with respect to 1 part by mass of the crude nanodiamond product. The amount of nitric acid used in the mixed acid is, for example, 2 to 20 parts by mass, preferably 4 to 10 parts by mass, and more preferably 5 to 8 parts by mass with respect to 1 part by mass of the crude nanodiamond product.

When the above mixed acid is used as the oxidizing agent, a catalyst may be used together with the mixed acid. By using a catalyst, the efficiency of removing graphite can be further improved. Examples of the catalyst include copper (II) carbonate and the like. The amount of the catalyst used is, for example, about 0.01 to 10 parts by mass with respect to 100 parts by mass of the crude nanodiamond product.

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 pressure.

If the metal oxide that could not be completely removed remains on the nanodiamond even after the above acid treatment step, the primary particles interact very strongly with each other to form an aggregate (secondary). It takes the form of particles). In such a case, alkali and hydrogen peroxide may be allowed to act on the nanodiamond in an aqueous solvent. As a result, the metal oxide remaining on the nanodiamond can be removed, and the separation of the primary particles from the adherent can be promoted.

After the oxidation treatment step, it is preferable to remove the supernatant by, for example, decantation. Further, at the time of decantation, it is preferable to wash the solid content with water. Although the supernatant liquid at the beginning of washing with water is colored, it is preferable to repeatedly wash the solid content with water until the supernatant liquid becomes visually transparent.

(Drying process)
The production method of the present invention may include a drying step. For example, after evaporating the liquid content from the nanodiamond-containing solution obtained through the above oxidation treatment step using a spray drying device, an evaporator, or the like, the residual solid content generated thereby is heated and dried in a drying oven. dry. The heating and drying temperature is, for example, 40 to 150 ° C. By undergoing such a drying step, a nanodiamond adhering body (an adhering body of nanodiamond particles) can be obtained as a powder.

Further, the nanodiamond may be subjected to an oxidation treatment (for example, oxygen oxidation) or a reduction treatment (for example, hydrogenation treatment) in the gas phase, if necessary. By performing the oxidation treatment in the gas phase, nanodiamonds having many carboxy groups on the surface can be obtained. When a large number of carboxy groups are present on the surface, the reaction between amines and nanodiamonds is more likely to proceed in the subsequent submerged plasma treatment step, and the formation of nitrogen atom-containing groups such as amide groups and ammonium salts is promoted. Further, by performing the reduction treatment in the gas phase, nanodiamonds having many CH groups on the surface can be obtained. In particular, it is preferable to include an oxygen oxidation step from the viewpoint that the surface-modified nanodiamond can be easily obtained through the submerged plasma treatment step.

(Oxygen oxidation process)
The nanodiamond powder that has undergone the above purification step may be subjected to an oxygen oxidation step of heating in a gas atmosphere containing oxygen using a gas atmosphere furnace. In the oxygen oxidation step, specifically, nanodiamond powder is arranged in a gas atmosphere furnace, oxygen-containing gas is supplied or passed through the furnace, and the inside of the furnace reaches a temperature condition set as a heating temperature. Is heated and oxygen oxidation treatment is carried out. The temperature condition of this oxygen oxidation treatment is, for example, 250 to 500 ° C. In order to realize a negative zeta potential for the nanodiamond particles contained in the produced nanodiamond dispersion, the temperature condition of this oxygen oxidation treatment is preferably relatively high, for example, at 400 to 450 ° C. is there. Further, the oxygen-containing gas used in the oxygen oxidation step may be a mixed gas containing an inert gas in addition to oxygen. Examples of the inert gas include nitrogen, argon, carbon dioxide and helium. The oxygen concentration of the mixed gas is, for example, 1 to 35% by volume.

(Hydrogenation process)
In order to realize a positive zeta potential for the nanodiamond particles contained in the produced nanodiamond dispersion, a hydrogenation step may be performed after the oxygen oxidation step. In the hydrogenation step, the nanodiamond powder that has undergone the oxygen oxidation step is heated in a gas atmosphere containing hydrogen using a gas atmosphere furnace. Specifically, hydrogen-containing gas is supplied or passed through a gas atmosphere furnace in which nanodiamond powder is arranged, and the temperature inside the furnace is raised to the temperature condition set as the heating temperature to generate hydrogen. Chemical processing is carried out. The temperature condition of this hydrogenation treatment is, for example, 400 to 800 ° C. Further, the hydrogen-containing gas used in the hydrogenation step may be a mixed gas containing an inert gas in addition to hydrogen. Examples of the inert gas include nitrogen, argon, carbon dioxide and helium. The hydrogen concentration of the mixed gas is, for example, 1 to 50% by volume. In order to realize a negative zeta potential for the nanodiamond particles contained in the produced nanodiamond dispersion, the crushing step described later may be carried out without performing such a hydrogenation step.

(Crushing process)
Even after being purified through the above purification step, oxygen oxidation step, hydrogenation step, etc., the detonation method nanodiamond is an adherent (aggregated by very strong interaction between primary particles). There is a strong tendency to take the form of secondary particles). In order to separate many primary particles from the adherent, a crushing step may be performed after the purification step, the oxygen oxidation step, or the hydrogenation step. Specifically, first, nanodiamonds that have undergone an oxygen oxidation step or a subsequent hydrogenation step are suspended in pure water to prepare a slurry containing the nanodiamonds. In the preparation of the slurry, a centrifugation treatment may be performed to remove a relatively large aggregate from the nanodiamond suspension, or the nanodiamond suspension may be subjected to sonication treatment. Then, the slurry is subjected to a wet crushing process. The crushing treatment can be performed using, for example, a high shear mixer, a high shear mixer, a homomixer, a ball mill, a bead mill, a high-pressure homogenizer, an ultrasonic homogenizer, a colloid mill, or the like. A crushing treatment may be carried out by combining these. From the viewpoint of efficiency, it is preferable to use a bead mill.

A bead mill, which is a crusher or a disperser, includes, for example, a cylindrical mill container, a rotor pin, a centrifugation mechanism, a raw material tank, and a pump. The rotor pin has a common axis with the mill container and is configured to be rotatable at high speed inside the mill container. The centrifuge mechanism is located at the top of the mill vessel. In the bead milling by the bead mill in the crushing step, the above slurry as a raw material is transferred from the raw material tank to the lower part of the mill container by the action of a pump while the bead is filled in the mill container and the rotor pin is stirring the bead. (Including nanodiamond adhering material) is introduced. The slurry reaches the top of the mill vessel through the beads being stirred at high speed in the mill vessel. In this process, the nanodiamond adherents contained in the slurry are crushed or dispersed by contact with the violently moving beads. As a result, the crushing of nanodiamond adhering bodies (secondary particles) into primary particles proceeds. The slurry and beads that have reached the upper centrifuge mechanism in the mill container are centrifuged by the operating centrifugation mechanism using the difference in specific gravity, the beads stay in the mill container, and the slurry is sent to the centrifugation mechanism. It is discharged to the outside of the mill container via a hollow line slidably connected. The discharged slurry is returned to the raw material tank, and then put into the mill container again by the action of the pump (circulation operation). In such bead milling, the crushing medium used is, for example, zirconia beads, the diameter of which is, for example, 15-500 μm. The amount of beads (apparent volume) filled in the mill container is, for example, 50 to 80% of the volume of the mill container. The peripheral speed of the rotor pin is, for example, 8 to 12 m / min. The amount of slurry to be circulated is, for example, 200 to 600 mL, and the flow rate of the slurry is, for example, 5 to 15 L / hour. The processing time (circulation operation time) is, for example, 30 to 300 minutes. In the crushing step, a batch type bead mill may be used instead of the continuous type bead mill as described above.

By going through such a crushing step, a nanodiamond dispersion liquid containing the primary particles of nanodiamond dispersed as colloidal particles can be obtained.

For the slurry that has undergone the crushing step, a classification operation for removing coarse particles may be performed. For example, a classification device can be used to remove coarse particles from the slurry by a classification operation utilizing centrifugation. As a result, a black transparent nanodiamond dispersion liquid in which the primary particles of nanodiamond are dispersed as colloidal particles can be obtained.

A drying step may be performed on the nanodiamonds that have undergone the crushing step or the nanodiamonds that have undergone the crushing step and the classification operation. In the drying step, specifically, the dispersion liquid containing nanodiamond is subjected to a drying treatment to obtain a dry powder of nanodiamond. Examples of the drying treatment method include spray drying performed using a spray drying device and evaporative drying performed using an evaporator.

(Submerged plasma treatment process)
In the submerged plasma treatment step, a mixed solution containing nanodiamond and amine is treated with submerged plasma.

The amine used in the liquid plasma treatment step is not particularly limited, but an amine having one or more organic groups on the nitrogen atom constituting the amine is preferable. Examples of such amines include amines represented by the following formula (1).
R _n NH _3-n (1)

In the above formula (1), R represents a monovalent organic group. Examples of the monovalent organic group include a hydrocarbon group, a heterocyclic group, and a group in which two or more of these are bonded via a single bond or a linking group (a divalent group having one or more atoms). Be done. Examples of the linking group include a carbonyl group (-CO-), an ether bond (-O-), a thioether bond (-S-), an ester bond (-COO-), an amide bond (-CONH-), and a carbonate bond. (-OCOO-), and groups in which a plurality of these are linked are mentioned.

Examples of the above-mentioned hydrocarbon group include an aliphatic hydrocarbon group, an alicyclic hydrocarbon group, an aromatic hydrocarbon group, and a group in which these are bonded.

As the aliphatic hydrocarbon group, an aliphatic hydrocarbon group having 1 to 22 carbon atoms is preferable, and for example, a methyl group, an ethyl group, a propyl group, an isopropyl group, a butyl group, an isobutyl group, an s-butyl group and a t-butyl group are preferable. A linear or branched alkyl group having 1 to 22 carbon atoms such as a group, a pentyl group, a hexyl group, a decyl group, a dodecyl group and an octadecyl group; and a vinyl group, an allyl group, a 1-butenyl group and the like having 2 to 22 carbon atoms. Alkenyl group; Examples thereof include an alkynyl group having 2 to 22 carbon atoms such as an ethynyl group and a propynyl group.

As the alicyclic hydrocarbon group, a 3- to 22-membered alicyclic hydrocarbon group is preferable, and for example, a cyclopropyl group, a cyclobutyl group, a cyclopentyl group, a cyclohexyl group, a cyclooctyl group and the like having about 3 to 22 members. Alkyl group; cycloalkenyl group having about 3 to 22 members such as cyclopentenyl group and cyclohexenyl group; perhydronaphthalene-1-yl group, norbornyl group, adamantyl group, tricyclo [5.2.1.0 ^2,6 ] Decane-8-yl group, tetracyclo [4.4.0.1 ^2,5 . 1 ^7,10 ] Examples thereof include a bridging cyclic hydrocarbon group such as a dodecane-3-yl group.

As the aromatic hydrocarbon group, an aromatic hydrocarbon group having 6 to 14 carbon atoms is preferable, and examples thereof include a phenyl group and a naphthyl group.

The hydrocarbon group may have a substituent. Examples of the substituent include a halogen atom, an oxo group, a hydroxy group, a substituted oxy group (for example, an alkoxy group, an aryloxy group, an aralkyloxy group, an acyloxy group, etc.), a carboxy group, and a substituted oxycarbonyl group (for example, alkoxycarbonyl). Groups, aryloxycarbonyl groups, aralkyloxycarbonyl groups, etc.), substituted or unsubstituted carbamoyl groups, cyano groups, nitro groups, sulfo groups, heterocyclic groups and the like. Further, the hydroxy group and the carboxy group may be protected by a protecting group known in the field of organic synthesis. Further, a heterocyclic ring having an aromatic or non-aromatic attribute may be condensed on the ring of the alicyclic hydrocarbon group or the aromatic hydrocarbon group.

The above heterocyclic group is a group obtained by removing one hydrogen atom from the structural formula of the heterocycle. Examples of the heterocycle include aromatic heterocycles and non-aromatic heterocycles. Such a heterocycle is a 3 to 10-membered ring (preferably a 4- to 6-membered ring) having a carbon atom and at least one heteroatom (for example, an oxygen atom, a sulfur atom, a nitrogen atom, etc.) in the atoms constituting the ring. ), These fused rings can be mentioned. Specifically, a heterocycle containing an oxygen atom as a heteroatom (for example, a 3-membered ring such as an oxyran ring; a 4-membered ring such as an oxetane ring; a furan ring, a tetrahydrofuran ring, an oxazole ring, an isooxazole ring, a γ-butyrolactone ring). 5-membered rings such as 4-oxo-4H-pyran ring, tetrahydropyran ring, morpholin ring and the like; benzofuran ring, isobenzofuran ring, 4-oxo-4H-chromen ring, chroman ring, isochroman ring and the like. Fused rings; 3-oxatricyclo [4.3.1.1 ^4,8 ] undecane-2-one ring, 3-oxatricyclo [4.2.1.0 ^4,8 ] nonane-2-one ring , Etc.), heterocycles containing sulfur atoms as heteroatoms (eg, 5-membered rings such as thiophene ring, thiazole ring, isothiazole ring, thiazizole ring; 6-membered ring such as 4-oxo-4H-thiopyran ring) A 5-membered ring such as a fused ring such as a benzothiophene ring) or a heterocycle containing a nitrogen atom as a heteroatom (for example, a pyrrol ring, a pyrrolidine ring, a pyrazole ring, an imidazole ring, a triazole ring, etc.; 6-membered rings such as a ring, a pyrimidine ring, a pyrazine ring, a piperidine ring, a piperazine ring; an indole ring, an indolin ring, a quinoline ring, an acridin ring, a naphthylidine ring, a quinazoline ring, a fused ring such as a purine ring, etc.) and the like. In addition to the substituents that the hydrocarbon group may have, the heterocyclic group includes a C _1-4 alkyl group (for example, a methyl group, an ethyl group, etc.), a C _3-20 cycloalkyl group, and a C. _It may have a _6-14 aryl group (for example, a phenyl group, a naphthyl group, etc.) and the like.

As the R, an aliphatic hydrocarbon group is preferable from the viewpoint of excellent solubility in a solvent in liquid plasma treatment, reactivity with nanodiamonds, and dispersibility of the obtained surface-modified nanodiamonds in a solvent. A linear or branched alkyl group is preferable, and a linear or branched alkyl group having 1 to 22 carbon atoms is more preferable. Further, from the viewpoint of superior solubility in a solvent in liquid plasma treatment, reactivity with nanodiamond, and dispersibility of the obtained surface-modified nanodiamond in a solvent, an R of 1 or more (particularly 2 or more) is C _10-. It is preferably a ₂₂ alkyl group (particularly a C _14-22 alkyl group). In particular, when a bulky amine having R having a large number of carbon atoms is used, the effect of the plasma treatment in the liquid can be further obtained.

In the above equation (1), n is an integer of 1 to 3. Of these, 2 or 3 is preferable from the viewpoint of excellent solubility in a solvent in liquid plasma treatment, reactivity with nanodiamonds, and dispersibility of the obtained surface-modified nanodiamonds in a solvent. That is, the amine represented by the above formula (1) is preferably a secondary amine or a tertiary amine. When n is 2 or 3, the plurality of Rs may be the same or different.

The total number of carbon atoms in the amine represented by the above formula (1) is preferably 26 to 60, more preferably 30 to 40. When the total number of the carbon atoms is within the above range, the solubility in the solvent in the submerged plasma treatment, the reactivity with the nanodiamond, and the dispersibility of the obtained surface-modified nanodiamond in the solvent are further excellent.

The nanodiamond used in the submerged plasma treatment step may be nanodiamond powder or an aqueous dispersion of nanodiamond, but the aqueous dispersion of nanodiamond is easier in procedure. It is preferable because it has excellent reactivity with amines and can efficiently produce surface-modified nanodiamonds. Further, the nanodiamond used in the submerged plasma treatment step preferably has a carboxy group.

The particle size D50 (median diameter) of nanodiamond used in the submerged plasma treatment step is, for example, 5000 nm or less, preferably 100 nm or less, and more preferably 10 nm or less. The lower limit of the particle size D50 of nanodiamond is, for example, 1 nm.

As the submerged plasma treatment performed in the presence of nanodiamond and amine, a treatment based on a known or conventional submerged plasma method can be adopted. In the submerged plasma treatment, a high voltage pulse output is applied to the electrode from the submerged pulse plasma power supply device, plasma below the boiling point of the liquid is generated in the boiled bubbles near the electrode, and radical species are generated from the liquid. it can. Above all, a method capable of generating plasma in bubbles in a liquid by glow discharge is preferable.

A commercially available submerged plasma apparatus can be used for the submerged plasma treatment. The submerged plasma treatment conditions such as the distance between terminals, the voltage applied between terminals, the frequency, and the pulse width can be appropriately adjusted according to the type and ratio of amines to be modified into nanodiamonds. The distance between the terminals is, for example, 0.1 to 20 mm, preferably 0.3 to 10 mm, and more preferably about 0.5 to 5 mm. The voltage applied between the terminals is a voltage before the plasma applied between the terminals is generated, and is, for example, 1000 to 10000 V, preferably 2000 to 6000 V, and more preferably about 2500 to 5000 V. The frequency is, for example, 1 to 400 kHz, preferably 10 to 100 kHz, and more preferably about 20 to 50 kHz. The pulse width is, for example, 0.1 to 4 μs, preferably 0.5 to 4 μs, and more preferably about 1 to 4 μs. The treatment time is, for example, 1 minute or more (for example, 5 to 500 minutes), preferably 10 minutes or more (for example, 10 to 300 minutes), more preferably 20 minutes or more (for example, 20 to 250 minutes), and further preferably 30 minutes or more (for example, 30 minutes or more). For example, about 30 to 200 minutes). Further, the submerged plasma treatment is a treatment accompanied by heat generation, and the temperature is, for example, 20 to 100 ° C., preferably 30 to 80 ° C.

The solvent used for the in-liquid plasma treatment is not particularly limited, and may be a polar solvent or a low-polarity solvent (non-polar solvent). Water is preferable from the viewpoint of excellent dispersibility of the raw material nanodiamond, the viewpoint of the solubility of amine, and the viewpoint that it is preferable to use the nanodiamond aqueous dispersion as described above. Further, from the viewpoint of further improving the solubility of the amine used for surface modification and forming a uniform layer with water to maintain high reaction efficiency, it is preferable to use a polar solvent as a solvent other than water, and more preferably a protic. It is a polar solvent. Examples of the protonic polar solvent include alcohols such as methanol, ethanol, isopropyl alcohol and butanol (particularly alcohols having 1 to 4 carbon atoms); carboxylic acids such as formic acid and acetic acid. Of these, methanol and isopropyl alcohol are preferable. Further, from the viewpoint of improving the dispersibility of the obtained surface-modified nanodiamond, an organic solvent may be further added. Examples of the organic solvent include organic solvents used in the organic solvent dispersion of nanodiamond described later. As the organic solvent, a low-polarity solvent is still preferable, and benzene, toluene, and methyl isobutyl ketone are preferable. Since the submerged plasma treatment gives a strong energy to the reaction system, the reaction system may be a two-layer system consisting of an aqueous layer and an organic layer.

The amount of amine used for the plasma treatment in the liquid is, for example, about 200 to 10000 parts by mass, preferably 300 to 5000 parts by mass, and more preferably 500 to 2000 parts by mass with respect to 100 parts by mass of nanodiamond. When the amount of amine used is 200 parts by mass or more, the surface-modified nanodiamond produced is excellent in dispersibility in an organic solvent. When the amount of amine used is 10,000 parts by mass or less, the formation of by-products can be suppressed.

After completion of the reaction, the obtained reaction product is preferably subjected to a purification treatment (for example, washing, centrifugation, etc.).

Further, by subjecting the reaction product after the purification treatment to a drying treatment, a surface-modified nanodiamond powder can be obtained. Examples of the drying treatment method include vacuum heating drying (including spray drying performed using a spray drying device under reduced pressure and evaporative drying performed using an evaporator under reduced pressure).

As described above, nanodiamonds (surface-modified nanodiamonds) having a nitrogen atom-containing group derived from the amine as a surface-modifying group can be obtained depending on the amine used. Examples of the nitrogen atom-containing group include the amine-derived amide group and the amine-derived ammonium salt (amine salt). The surface-modified nanodiamond may have only one type of nitrogen atom-containing group, or may have two or more types. For example, it is presumed that when a secondary amine is used as the amine, an amide group is mainly formed, and when a tertiary amine is used as the amine, an ammonium salt is mainly formed.

Examples of the amine-derived amide group include an amide group formed by dehydration condensation of a hydrogen atom on a nitrogen atom in a primary amine or a secondary amine and OH in a carboxy group on the surface of nanodiamond. The amide group formed when the amine represented by the above formula (1) is used as the amine includes a group represented by the following formula (2a), a group represented by the following formula (2b), and the following formula. Examples thereof include the group represented by (2c). The carbon atoms in the formulas (2a) to (2c) are each bonded to the surface of the nanodiamond particles, and R is the same as that described above. However, n in the formula (2a) is 1 or 2, and the two Rs when n = 2 may be the same or different. The amide group may have only one kind, or may have two or more kinds.
-C (= O) NR _n (2a)
-C (= O) N (-R) -C (= O)-(2b)
{-C (= O)} ₃ N (2c)

Examples of the ammonium salt formed when the amine represented by the above formula (1) is used as the amine include an ammonium salt represented by the following formula (3). It should be noted that R and n in the formula (3) are the same as those described above, and when n is 2 or more, 2 or more Rs may be the same or different.
N ⁺ R _n H _4-n (3)

[Organic solvent dispersion of nanodiamond]
By dispersing the surface-modified nanodiamonds obtained by the production method of the present invention in an organic solvent, an organic solvent dispersion of surface-modified nanodiamonds can be obtained. The organic solvent dispersion is, for example, a mixture of the surface-modified nanodiamond and an organic solvent, subjected to dispersion treatment such as sonication and bead milling, and if necessary, purification treatment such as filtration treatment and centrifugation treatment. It can be manufactured by applying.

Examples of the organic solvent include protic organic solvents and aprotic organic solvents, and polar organic solvents and non-polar organic solvents. These may be used alone or in combination of two or more.

The SP value [(cal / cm ³ ) ^0.5 : Fedors calculated value] of the organic solvent at 25 ° C. is, for example, 7 to 23 (preferably 7 to 17, more preferably 7 to 15, still more preferably 7 to 13, and further. It is preferably 7 to 12, particularly preferably 7 to 10).

The relative permittivity of the organic solvent at 25 ° C. is, for example, 1 to 40 (preferably 2 to 35). The relative permittivity in this specification is a value described in the 5th edition of the Chemical Handbook, Basic Edition, Maruzen Co., Ltd., and the Chemical Society of Japan. For the relative permittivity, an organic solvent was injected into a glass cell with an ITO transparent electrode having a cell gap of 10 μm, and the electric capacity of the obtained cell was measured using a model 2353LCR meter (measurement frequency: 1 kHz) manufactured by NF Co., Ltd. It can also be obtained by measuring at 25 ° C. and 40% RH.

The SP value of the polar organic solvent at 25 ° C. is, for example, 10.0 or more (preferably 10.0 to 23.0, particularly preferably 10.0 to 15.0), and the non-polar organic solvent at 25 ° C. The SP value in the above is, for example, less than 10.0 (preferably 7.5 to 9.5, particularly preferably 8.0 to 9.3). The relative permittivity of the polar organic solvent at 25 ° C. is, for example, 15 to 40 (preferably 15 to 35, particularly preferably 18 to 35), and the relative permittivity of the non-polar organic solvent at 25 ° C. is For example, it is 1 or more and less than 15 (preferably 1 to 10, more preferably 1 to 5).

Examples of the protic organic solvent include methanol (SP value: 13.8, relative permittivity: 32.6), ethanol (SP value: 12.6, relative permittivity: 24.30), and 1-propanol (SP). Value: 11.8, relative permittivity: 20.1), monovalent alcohol having 1 to 5 carbon atoms such as isopropyl alcohol (SP value: 11.6, relative permittivity: 19.92); carbon such as ethylene glycol Examples thereof include polyhydric alcohols of several 2 to 5.

Examples of the aproton organic solvent include toluene (SP value: 9.14, specific dielectric constant: 2.379), o-xylene (SP value: 9.10), aromatic hydrocarbons such as benzene; cyclohexane and the like. Alicyclic hydrocarbons; aliphatic hydrocarbons such as n-hexane (SP value: 7.29); halogenated hydrocarbons such as carbon tetrachloride, methylene chloride, ethylene dichloride, chloroform; isopropyl ether, tetrahydrofuran (SP). Values such as ethers such as diethyl ether (SP value: 7.25); ethyl acetate (SP value: 8.75), esters such as butyl acetate (SP value: 8.70); acetone (SP value) : 9.07, specific dielectric constant: 20.7), methyl ethyl ketone (SP value: 8.99), methyl isobutyl ketone (MIBK, SP value: 8.4), cyclohexanone (SP value: 9.80) and other ketones. And so on.

Since the organic solvent dispersion contains the surface-modified nanodiamond that exhibits easy dispersibility in the organic solvent, the dispersibility of the nanodiamond can be maintained even if the nanodiamond concentration is adjusted to be high. The nanodiamond concentration in the organic solvent dispersion (total nanodiamond concentration including the surface-modified nanodiamond) is, for example, 0.0001% by mass or more, preferably 0.001% by mass or more, and more preferably 0.005% by mass. That is all. The upper limit of the nanodiamond concentration is, for example, 5% by mass.

The organic solvent dispersion may contain nanodiamonds other than the surface-modified nanodiamonds, but the ratio of the surface-modified nanodiamonds to all the nanodiamonds contained in the organic solvent dispersion of nanodiamonds is, for example, It is 50% by mass or more, preferably 75% by mass or more, and more preferably 95% by mass or more. The upper limit is 100% by mass. Therefore, the content of nanodiamonds other than the surface-modified nanodiamonds is, for example, 50% by mass or less, preferably 25% by mass or less, and more preferably 5% by mass, based on the total amount of nanodiamonds contained in the organic solvent dispersion of nanodiamonds. It is as follows. When the content of the surface-modified nanodiamond is 50% by mass or more, an organic solvent dispersion of nanodiamond containing nanodiamond in a highly dispersed state can be easily obtained.

The content of the organic solvent (the total amount when two or more kinds are contained) in the total amount of the organic solvent dispersion is, for example, 85.0 to 99.5% by mass, preferably 95.0 to 99.5% by mass.

The total content of the surface-modified nanodiamond and the organic solvent in the total amount of the organic solvent dispersion is, for example, 60% by mass or more, preferably 90% by mass or more. The upper limit is 100% by mass.

Since the organic solvent dispersion uses the surface-modified nanodiamond, the nanodiamond has excellent dispersibility in the organic solvent.

When a polar organic solvent is used as the organic solvent, the particle size D50 (median diameter) of nanodiamond in the organic solvent dispersion is, for example, 1000 nm or less, preferably 800 nm or less, and more preferably 700 nm or less. The lower limit of the particle size D50 of nanodiamond is, for example, 100 nm.

When a non-polar organic solvent is used as the organic solvent, the particle size D50 (median diameter) of nanodiamond in the organic solvent dispersion is, for example, 1000 nm or less, preferably 100 nm or less, and particularly preferably 50 nm or less. The lower limit of the particle size D50 of nanodiamond is, for example, 4 nm.

Further, since the organic solvent dispersion contains the surface-modified nanodiamonds, the nanodiamonds are high even when a protic polar organic solvent or a non-polar organic solvent, which has been difficult to disperse in the past, is used as the organic solvent. It can be contained in a dispersed state.

The organic solvent dispersion has excellent compatibility with the oil agent and the resin composition, and by adding the organic solvent dispersion of the surface-modified nanodiamond to the oil agent and the resin composition, nanodiamonds can be added to the oil agent and the resin composition. It can be evenly dispersed and can impart properties derived from nanodiamonds (for example, high mechanical strength, electrical insulation, excellent thermal conductivity, deodorant effect, antibacterial effect, chemical resistance, etc.). The oil or resin composition to which the organic solvent dispersion of nanodiamond is added is a heat radiation material, an optical material (for example, a high-performance film material), a material reinforcing material, a heat exchange flow medium, and a coating material (for example, an antibacterial coating). It can be preferably used as a material, a deodorant coating material), an abrasive, a lubricant, a medical material, and the like.

Hereinafter, the present invention will be described in more detail based on Examples, but the present invention is not limited to these Examples.

Preparation Example 1 (Preparation of nanodiamond aqueous dispersion)
A nanodiamond aqueous dispersion was produced through the following steps.

(Generation process)
First, the process of producing nanodiamonds by the detonation method was performed. In this step, first, a molded explosive equipped with an electric detonator was installed inside a pressure-resistant container for detonation, and the container was sealed. The container is made of iron and the volume of the container is 15 m ³ . As the explosive, 0.50 kg of a mixture of TNT and RDX was used. The mass ratio of TNT to RDX (TNT / RDX) in this explosive is 50/50. Next, the electric detonator was detonated and the explosive was detonated in the container (generation of nanodiamonds by the detonation method). Next, the temperature of the container and its inside was lowered by leaving it at room temperature for 24 hours. After this cooling, the crude nanodiamond products adhering to the inner wall of the container (including the adherents of nanodiamond particles and soot produced by the above-mentioned detonation method) are scraped off with a spatula, and the nanodiamonds are removed. The crude product was recovered.

(Acid treatment process)
Next, an acid treatment step was performed on the nanodiamond crude product obtained by performing the above-mentioned production step a plurality of times. Specifically, the slurry obtained by adding 6 L of 10% by mass hydrochloric acid to 200 g of the crude nanodiamond product was heat-treated for 1 hour under reflux under normal pressure conditions. The heating temperature in this acid treatment is 85 to 100 ° C. Next, after cooling, the solid content (including nanodiamond adherents and soot) was washed with water by decantation. The solid content was repeatedly washed with water by decantation until the pH of the precipitate was from the low pH side to 2.

(Oxidation process)
Next, an oxidation treatment step was performed. Specifically, 6 L of 98% by mass sulfuric acid and 1 L of 69% by mass nitric acid were added to a precipitate (including nanodiamond adherents) obtained through decantation after acid treatment to form a slurry, which was then added to form a slurry. This slurry was heat-treated for 48 hours under reflux under normal pressure conditions. The heating temperature in this oxidation treatment is 140 to 160 ° C. Next, after cooling, the solid content (including the nanodiamond adherent) was washed with water by decantation. The supernatant liquid at the beginning of washing with water was colored, and the solid content was repeatedly washed with water by decantation until the supernatant liquid became visually transparent.

(Drying process)
Next, 1000 mL of the nanodiamond-containing liquid obtained through the above-mentioned washing treatment was spray-dried (drying) using a spray-drying device (trade name "Spray Dryer B-290", manufactured by Nippon Buch Co., Ltd.). Process). As a result, 50 g of nanodiamond powder was obtained.

(Oxygen oxidation process)
Next, 4.5 g of the nanodiamond powder obtained as described above was allowed to stand in the core tube of a gas atmosphere furnace (trade name "gas atmosphere tube furnace KTF045N1", manufactured by Koyo Thermo System Co., Ltd.), and the core tube was placed. After continuing to pass nitrogen gas at a flow rate of 1 L / min for 30 minutes, the flowing gas is switched from nitrogen to a mixed gas of oxygen and nitrogen, and the mixed gas is passed through the core tube at a flow rate of 1 L / min. Continued. The oxygen concentration in the mixed gas is 4% by volume. After switching to the mixed gas, the temperature inside the furnace was raised to 400 ° C., which is the set heating temperature. The heating rate was 10 ° C./min up to 380 ° C., which is 20 ° C. lower than the set heating temperature, and 1 ° C./min from 380 ° C. to 400 ° C. thereafter. Then, while maintaining the temperature condition in the furnace at 400 ° C., the nanodiamond powder in the furnace was subjected to oxygen oxidation treatment (oxygen oxidation step). The processing time was 3 hours.

The zeta potential of the nanodiamond powder obtained as described above was measured by a laser Doppler electrophoresis method using an apparatus manufactured by Malvern (trade name “Zetasizer Nano ZS”). The nanodiamond dispersion liquid subjected to the measurement was diluted with ultrapure water so that the nanodiamond concentration was 0.2% by mass, and then subjected to ultrasonic irradiation with an ultrasonic cleaner. The zeta potential measurement temperature is 25 ° C. As a result of this measurement, the zeta potential of the nanodiamond dispersion was -38 mV.

(Crushing process)
Next, a crushing step was performed. Specifically, first, 0.9 g of nanodiamond powder and 29.1 mL of pure water that had undergone the above-mentioned oxygen oxidation step were added to a 50 mL sample bottle and mixed to obtain about 30 mL of slurry. Next, the slurry was subjected to a centrifugation treatment (centrifugal force of 20000 × g for 10 minutes) and a subsequent ultrasonic treatment. In the ultrasonic treatment, an ultrasonic irradiator (trade name "ultrasonic cleaner AS-3", manufactured by AS ONE Corporation) was used to irradiate the slurry with ultrasonic waves for 2 hours. .. After that, bead milling was performed using a bead milling device (trade name "parallel four-cylinder sand grinder LSG-4U-2L type", manufactured by IMEX Co., Ltd.). Specifically, 30 mL of slurry after ultrasonic irradiation and zirconia beads having a diameter of 30 μm are put into a 100 mL mill container, Vessel (manufactured by Imex Co., Ltd.) and sealed, and the device is driven to perform bead milling. Executed. In this bead milling, the input amount of zirconia beads is, for example, 33% with respect to the volume of the mill container, the rotation speed of the mill container is 2570 rpm, and the milling time is 2 hours.

Next, the slurry (suspension) that had undergone the crushing step as described above was subjected to a centrifugation treatment using a centrifugation device (classification operation). The centrifugal force in this centrifugation treatment was 20000 × g, and the centrifugation time was 10 minutes. Next, 10 mL of the supernatant of the nanodiamond-containing solution that had undergone the centrifugation treatment was collected. In this way, a nanodiamond aqueous dispersion in which nanodiamonds are dispersed in pure water was obtained.

Example 1
(Manufacturing of surface-modified nanodiamonds)
Next, a submerged plasma treatment step was performed. Specifically, 10 mL of the nanodiamond aqueous dispersion (nanodiamond concentration: 1% by mass) obtained in Preparation Example 1, 15 mL of water, 20 mg of dioctadecylamine, 25 mL of methanol, and 50 mL of isopropyl alcohol were mixed. , The mixture was sonicated. Next, this mixture was subjected to a submerged plasma device (trade name "MPP04-A4-200", manufactured by Kurita Seisakusho Co., Ltd.), a distance between terminals of 3 mm, an applied voltage between terminals of 3500 V, a frequency of 20 kHz, and a pulse width of 3.6 μs. Under the above conditions, plasma treatment in liquid was performed at 55 ° C. for 1 hour. Next, the solvent of the mixed solution subjected to the plasma treatment in the solution was distilled off under reduced pressure to recover the solid. Next, 20 mL of toluene was added to this solid, and after ultrasonic treatment, centrifugation (20,000 × g, 10 minutes) was performed to remove the supernatant, and the solid was recovered. Next, 40 mL of hexane was added to this solid, and after ultrasonic treatment, centrifugation (20,000 × g, 10 minutes) was performed to remove the supernatant, and the solid was recovered. Next, 60 mL of acetone was added to this solid, and after ultrasonic treatment, centrifugation (20,000 × g, 10 minutes) was performed to remove the supernatant, and the solid was washed with hexane to recover the solid, and surface-modified nanodiamonds were obtained. Obtained.

(Preparation of organic solvent dispersion)
The obtained surface-modified nanodiamonds are mixed with toluene (SP value obtained by the Fedors method at 25 ° C.: 9.14, 25 mL, relative permittivity at 25 ° C.: 2.379) and centrifuged (20000 × g, 10). Toluene dispersion of nanodiamond was obtained by removing the precipitate (nanodiamond concentration: 0.3% by weight). When the particle size of nanodiamonds in the toluene dispersion of nanodiamonds was measured by a dynamic light scattering method, the median size (particle size D50) was 42 nm.

Example 2
(Manufacturing of surface-modified nanodiamonds)
Mix 10 mL of the nanodiamond aqueous dispersion (nanodiamond concentration: 1% by mass) obtained in Preparation Example 1, 15 mL of water, 20 mg of dioctadecylmethylamine, 25 mL of methanol, and 50 mL of isopropyl alcohol to superimpose the mixture. Sonicated. Next, this mixture was subjected to a submerged plasma device (trade name "MPP04-A4-200", manufactured by Kurita Seisakusho Co., Ltd.), a distance between terminals of 1 mm, an applied voltage between terminals of 3500 V, a frequency of 20 kHz, and a pulse width of 3.6 μs. Under the above conditions, plasma treatment in liquid was performed at 65 ° C. for 1 hour. Next, the solvent of the mixed solution subjected to the plasma treatment in the solution was distilled off under reduced pressure to recover the solid. Next, 20 mL of toluene was added to this solid, and after ultrasonic treatment, centrifugation (20,000 × g, 10 minutes) was performed to remove the supernatant, and the solid was recovered. Next, 40 mL of hexane was added to this solid, and after ultrasonic treatment, centrifugation (20,000 × g, 10 minutes) was performed to remove the supernatant, and the solid was recovered. Next, 60 mL of acetone was added to this solid, and after ultrasonic treatment, centrifugation (20,000 × g, 10 minutes) was performed to remove the supernatant, and the solid was washed with hexane to recover the solid, and surface-modified nanodiamonds were obtained. Obtained.

(Preparation of organic solvent dispersion)
The obtained surface-modified nanodiamonds are mixed with toluene (SP value obtained by the Fedors method at 25 ° C.: 9.14, 25 mL, relative permittivity at 25 ° C.: 2.379) and centrifuged (20000 × g, 10). Toluene dispersion of nanodiamond was obtained by removing the precipitate (nanodiamond concentration: 0.3% by weight). When the particle size of nanodiamonds in the toluene dispersion of nanodiamonds was measured by a dynamic light scattering method, the median size (particle size D50) was 382 nm.

Further, the obtained surface-modified nanodiamonds were mixed with acetone (SP value obtained by the Fedors method at 25 ° C.: 9.07, 25 mL, relative permittivity at 25 ° C.: 20.7) and centrifuged (20000 × g). (10 minutes) to remove the precipitate to obtain an acetone dispersion of nanodiamonds (nanodiamond concentration: 0.3% by weight). When the particle size of nanodiamonds in the acetone dispersion of nanodiamonds was measured by a dynamic light scattering method, the median size (particle size D50) was 228 nm.

Example 3
(Manufacturing of surface-modified nanodiamonds)
10 mL of the nanodiamond aqueous dispersion (nanodiamond concentration: 1% by mass) obtained in Preparation Example 1, 15 mL of water, 20 mg of tridodecylamine, 25 mL of methanol, and 50 mL of isopropyl alcohol are mixed, and the mixture is sonicated. Processed. Next, this mixture was subjected to a submerged plasma device (trade name "MPP04-A4-200", manufactured by Kurita Seisakusho Co., Ltd.), a distance between terminals of 1 mm, an applied voltage between terminals of 3500 V, a frequency of 20 kHz, and a pulse width of 3.6 μs. Under the above conditions, plasma treatment in liquid was performed at 65 ° C. for 1 hour. Next, the solvent of the mixed solution subjected to the plasma treatment in the solution was distilled off under reduced pressure to recover the solid. Next, 20 mL of toluene was added to this solid, and after ultrasonic treatment, centrifugation (20,000 × g, 10 minutes) was performed to remove the supernatant, and the solid was recovered. Next, 40 mL of hexane was added to this solid, and after ultrasonic treatment, centrifugation (20,000 × g, 10 minutes) was performed to remove the supernatant, and the solid was recovered. Next, 60 mL of acetone was added to this solid, and after ultrasonic treatment, centrifugation (20,000 × g, 10 minutes) was performed to remove the supernatant, and the solid was washed with hexane to recover the solid, and surface-modified nanodiamonds were obtained. Obtained.

(Preparation of organic solvent dispersion)
The obtained surface-modified nanodiamonds are mixed with toluene (SP value obtained by the Fedors method at 25 ° C.: 9.14, 25 mL, relative permittivity at 25 ° C.: 2.379) and centrifuged (20000 × g, 10). Toluene dispersion of nanodiamond was obtained by removing the precipitate (nanodiamond concentration: 0.3% by weight). When the particle size of nanodiamonds in the toluene dispersion of nanodiamonds was measured by a dynamic light scattering method, the median size (particle size D50) was 139 nm.

Further, the obtained surface-modified nanodiamonds were mixed with acetone (SP value obtained by the Fedors method at 25 ° C.: 9.07, 25 mL, relative permittivity at 25 ° C.: 20.7) and centrifuged (20000 × g). (10 minutes) to remove the precipitate to obtain an acetone dispersion of nanodiamonds (nanodiamond concentration: 0.3% by weight). When the particle size of nanodiamonds in the acetone dispersion of nanodiamonds was measured by a dynamic light scattering method, the median size (particle size D50) was 210 nm.

Comparative Example 1
10 mL of the nanodiamond aqueous dispersion (nanodiamond concentration: 1% by mass) obtained in Preparation Example 1, 15 mL of water, 20 mg of dioctadecylamine, 25 mL of methanol, and 50 mL of isopropyl alcohol are mixed to obtain a mixed solution. It was. Then, 35 g of zirconia beads (manufactured by Tosoh Corporation, registered trademark "YTZ", diameter 30 μm) was added to the obtained mixed solution. After the addition, a homogenizer (trade name "UH-600S", manufactured by SMT Co., Ltd.) was used, and the treatment was carried out at 55 ° C. for 1 hour. Next, the solvent of the treated mixed solution was distilled off under reduced pressure to recover the solid. Next, 20 mL of toluene was added to this solid, and after ultrasonic treatment, centrifugation (20,000 × g, 10 minutes) was performed to remove the supernatant, and the solid was recovered. Next, 40 mL of hexane was added to this solid, and after ultrasonic treatment, centrifugation (20,000 × g, 10 minutes) was performed to remove the supernatant, and the solid was recovered. Next, 60 mL of acetone was added to this solid, and after ultrasonic treatment, centrifugation (20,000 × g, 10 minutes) was performed to remove the supernatant, and the solid was washed with hexane to recover the solid.

The obtained nanodiamonds are mixed with toluene (SP value obtained by the Fedors method at 25 ° C.: 9.14, 25 mL, relative permittivity at 25 ° C.: 2.379) and centrifuged (20000 × g, 10 minutes). However, nanodiamonds settled and a toluene dispersion of nanodiamonds could not be obtained. Therefore, in Comparative Example 1, it was determined that the surface-modified nanodiamond could not be obtained.

Comparative Example 2
10 mL of the nanodiamond aqueous dispersion (nanodiamond concentration: 1% by mass) obtained in Preparation Example 1, 15 mL of water, 20 mg of dioctadecylmethylamine, 25 mL of methanol, and 50 mL of isopropyl alcohol are mixed to prepare a mixed solution. Obtained. Then, 35 g of zirconia beads (manufactured by Tosoh Corporation, registered trademark "YTZ", diameter 30 μm) was added to the obtained mixed solution. After the addition, a homogenizer (trade name "UH-600S", manufactured by SMT Co., Ltd.) was used, and the treatment was carried out at 65 ° C. for 1 hour. Next, the solvent of the treated mixed solution was distilled off under reduced pressure to recover the solid. Next, 20 mL of toluene was added to this solid, and after ultrasonic treatment, centrifugation (20,000 × g, 10 minutes) was performed to remove the supernatant, and the solid was recovered. Next, 40 mL of hexane was added to this solid, and after ultrasonic treatment, centrifugation (20,000 × g, 10 minutes) was performed to remove the supernatant, and the solid was recovered. Next, 60 mL of acetone was added to this solid, and after ultrasonic treatment, centrifugation (20,000 × g, 10 minutes) was performed to remove the supernatant, and the solid was washed with hexane to recover the solid.

The obtained nanodiamonds are mixed with toluene (SP value obtained by the Fedors method at 25 ° C.: 9.14, 25 mL, relative permittivity at 25 ° C.: 2.379) and centrifuged (20000 × g, 10 minutes). However, nanodiamonds settled and a toluene dispersion of nanodiamonds could not be obtained. Therefore, in Comparative Example 2, it was determined that the surface-modified nanodiamond could not be obtained.

Comparative Example 3
10 mL of the nanodiamond aqueous dispersion (nanodiamond concentration: 1% by mass) obtained in Preparation Example 1, 15 mL of water, 20 mg of tridodecylamine, 25 mL of methanol, and 50 mL of isopropyl alcohol are mixed to obtain a mixed solution. It was. Then, 35 g of zirconia beads (manufactured by Tosoh Corporation, registered trademark "YTZ", diameter 30 μm) was added to the obtained mixed solution. After the addition, a homogenizer (trade name "UH-600S", manufactured by SMT Co., Ltd.) was used, and the treatment was carried out at 65 ° C. for 1 hour. Next, the solvent of the treated mixed solution was distilled off under reduced pressure to recover the solid. Next, 20 mL of toluene was added to this solid, and after ultrasonic treatment, centrifugation (20,000 × g, 10 minutes) was performed to remove the supernatant, and the solid was recovered. Next, 40 mL of hexane was added to this solid, and after ultrasonic treatment, centrifugation (20,000 × g, 10 minutes) was performed to remove the supernatant, and the solid was recovered. Next, 60 mL of acetone was added to this solid, and after ultrasonic treatment, centrifugation (20,000 × g, 10 minutes) was performed to remove the supernatant, and the solid was washed with hexane to recover the solid.

The obtained nanodiamonds are mixed with toluene (SP value obtained by the Fedors method at 25 ° C.: 9.14, 25 mL, relative permittivity at 25 ° C.: 2.379) and centrifuged (20000 × g, 10 minutes). However, nanodiamonds settled and a toluene dispersion of nanodiamonds could not be obtained. Therefore, in Comparative Example 3, it was determined that the surface-modified nanodiamond could not be obtained.

<Measurement method of median diameter by dynamic light scattering method>
It is a 50% volume cumulative diameter measured using a device manufactured by Spectris (trade name "Zeta Sizar Nano ZS"). The measured nanodiamond concentration of the organic solvent dispersion of nanodiamond is 0.3% by mass.

<FT-IR analysis>
The nanodiamonds in the nanodiamond aqueous dispersion obtained in Preparation Example 1 and the surface-modified nanodiamonds obtained in Examples 1 to 3 were subjected to FT-IR analysis by the following analyzer and analysis method.
Analytical device: Part number "FT / IR-6100", manufactured by JASCO Corporation Analytical method: Using 1 mg of sample, 100 mg of potassium bromide (for IR absorption measurement, manufactured by Wako Pure Chemical Industries, Ltd.) and a dairy bowl After pulverizing and mixing, 26.5 mg of this sample was pressure-molded at a pressure of 40 MPa for 3 to 5 minutes to prepare KBr pellets for analysis (KBr method).

The FT-IR spectrum of the nanodiamond obtained in Preparation Example 1 is shown in FIG. 2, the FT-IR spectrum of the surface-modified nanodiamond obtained in Example 1 is shown in FIG. 3, and the surface-modified nano obtained in Example 2 is shown in FIG. The FT-IR spectrum of the diamond is shown in FIG. 4, and the FT-IR spectrum of the surface-modified nanodiamond obtained in Example 3 is shown in FIG. 5, respectively. In Example 1, peaks derived from amide groups were observed near 1653 cm ^{-1 and} around 1420 cm ^-1 . From this, it is presumed that in Example 1, nanodiamonds having an amide group mainly derived from dioctadecylamine were obtained. Moreover, in Example 2, a peak derived from an ammonium salt was observed near 1600 cm ^-1 . From this, it is presumed that in Example 2, nanodiamonds having an ammonium salt mainly derived from dioctadecylmethylamine were obtained. Moreover, in Example 3, a peak derived from an ammonium salt was observed near 1602 cm ^-1 . From this, it is presumed that in Example 3, nanodiamonds having an ammonium salt mainly derived from tridodecylamine were obtained. The characteristic peaks observed in the surface-modified nanodiamonds obtained in Examples 1 to 3 are the peaks not observed in the nanodiamonds obtained in Preparation Example 1.

S1 production step S2 acid treatment step S3 oxidation treatment step S4 oxygen oxidation step S5 liquid plasma treatment step

Claims (4)

A method for producing surface-modified nanodiamonds, which comprises an in-liquid plasma treatment step of subjecting a mixed solution containing nanodiamonds and amines to plasma treatment in liquid to obtain nanodiamonds having a nitrogen atom-containing group derived from the amine on the surface. The production of the surface-modified nanodiamond according to claim 1, wherein the amine is an amine represented by the following formula (1), and the total number of carbon atoms in the amine represented by the formula (1) is 26 to 60. Method.
R _n NH _3-n (1)
(In formula (1), R represents a monovalent organic group, and n represents an integer of 1 to 3). The method for producing surface-modified nanodiamond according to claim 2, wherein R is a linear or branched-chain alkyl group having 1 to 22 carbon atoms. The method for producing surface-modified nanodiamond according to any one of claims 1 to 3, wherein the amine is a secondary amine or a tertiary amine.

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