JP7074907B2 - Nanodiamond organic solvent dispersion - Google Patents

Description

The present invention relates to a nanodiamond organic solvent dispersion liquid in which nanodiamond particles are dispersed in an organic solvent.

In recent years, the development of fine-grained diamond materials called nanodiamonds has been promoted. As for nanodiamonds, so-called single-digit nanodiamonds having a particle size of 10 nm or less may be required depending on the application. Nanodiamond particles, such as single-digit nanodiamonds, can exhibit high mechanical strength, high thermal conductivity, high refractive index, low coefficient of thermal expansion, etc., as do bulk diamonds.

However, since nanodiamond particles such as single-digit nanodiamonds generally have a large proportion of surface atoms (coordinating unsaturated), the total van der Waals force that can act between the surface atoms of adjacent particles is It is large and easy to aggregate. In addition to this, a phenomenon called agglutination can occur in which the Coulomb interaction between the crystal planes of adjacent crystal planes contributes and aggregates very strongly. Since the nanodiamond particles have such a unique property that the crystallites or the primary particles can interact with each other in a superimposed manner, the primary particles are dissociated and the nanodiamond particles are dispersed in a solvent or a resin material. Creating a state of affairs entails technical difficulties. In particular, in the process of dispersing nanodiamond particles in an organic solvent in order to prepare a nanodiamond organic solvent dispersion liquid, the nanodiamond particles often aggregate.

As a method for preventing agglomeration of nanodiamond particles and obtaining a nanodiamond dispersion liquid, the methods described in Patent Document 1 and Non-Patent Document 1 are known. In Patent Document 1, a nanodiamond aqueous dispersion is used as a starting material, a polar solvent having a boiling point higher than that of water is mixed with the nanodiamond aqueous dispersion, water is removed by an evaporator, and the polar solvent remains in the nano by a solvent substitution method. A diamond organic solvent dispersion is being prepared. Further, in Non-Patent Document 1, a nanodiamond dispersion liquid is produced by crushing a suspension containing nanodiamond with a bead mill or the like.

International Publication No. 2014/174150

Meijo University Faculty of Science and Engineering Research Report No. 50 2010 pp. 28-35 "Crushing and Dispersing Aggregated Nanodiamonds and Surface Chemistry of Primary Particles"

However, in the method described in Patent Document 1, since water is removed by an evaporator and the solvent is replaced, for example, only a solvent having a boiling point higher than that of water having a boiling point of 140 ° C. or higher can be applied, and an organic having a boiling point lower than that of water can be applied. It is not possible to obtain a nanodiamond organic solvent dispersion as a solvent. Further, in the method described in Non-Patent Document 1, only the nanodiamond dispersion liquid of nanodiamond having a positive zeta potential is obtained, and the dispersion liquid of nanodiamond having a negative zeta potential has not been reported.

Therefore, an object of the present invention is that nanodiamond particles having a negative zeta potential and an organic solvent which is a polar solvent having a low boiling point are dispersed and stabilized by dispersing the nanodiamond particles in the organic solvent while suppressing aggregation. It is to provide a solvent dispersion.

As a result of diligent studies to solve the above problems, the present inventors have dispersed the nanodiamond particles in an organic solvent which is a polar solvent having a low boiling point by substituting the solvent from the aqueous dispersion of nanodiamond using a permeable membrane. It has been found that a dispersion-stabilized nanodiamond organic solvent dispersion can be obtained. The present invention has been completed based on these findings.

That is, the present invention provides a nanodiamond organic solvent dispersion liquid containing nanodiamond particles having a negative zeta potential and an organic solvent having a boiling point of 120 ° C. or lower and a relative permittivity of 30 or more at 25 ° C.

Further, in the nanodiamond organic solvent dispersion liquid of the present invention, it is preferable that the organic solvent is methanol or acetonitrile.

Further, in the nanodiamond organic solvent dispersion liquid of the present invention, it is preferable that the nanodiamond particles are explosive nanodiamond particles.

Further, the nanodiamond organic solvent dispersion liquid of the present invention is preferably a dispersion liquid substituted with a permeable membrane solvent.

Further, the present invention uses a dialysate from a nanodiamond dispersion containing nanodiamond particles having a negative zeta potential in an organic solvent having a boiling point of 120 ° C. or lower and a relative permittivity of 30 or more at 25 ° C. Provided is a method for producing a nanodiamond organic solvent dispersion liquid for obtaining a nanodiamond organic solvent dispersion liquid of the organic solvent by membrane separation.

The nanodiamond organic solvent dispersion liquid of the present invention can be dispersed in an organic solvent which is a polar solvent having a low boiling point while suppressing aggregation of nanodiamond particles, and the nanodiamond particles can be dispersed and stabilized.

It is a figure which shows an example of the process of the manufacturing method of the nanodiamond organic solvent dispersion liquid of this invention.

[Nanodiamond organic solvent dispersion]
The nanodiamond organic solvent dispersion of the present invention contains nanodiamond particles having a negative zeta potential and an organic solvent having a boiling point of 120 ° C. or lower and a relative permittivity of 30 or more at 25 ° C. The nanodiamond organic solvent dispersion liquid of the present invention is preferably a dispersion liquid substituted with a permeable membrane solvent. The nanodiamond organic solvent dispersion liquid of the present invention can disperse nanodiamond particles in an organic solvent which is a polar solvent having a low boiling point and stabilize the dispersion while suppressing aggregation by substituting a permeable membrane solvent. can. Details of the permeable membrane solvent substitution will be described later in the method for producing a nanodiamond organic solvent dispersion.

The nanodiamond particles may be primary particles of nanodiamond or secondary particles of nanodiamond in which primary particles are aggregated. In the present invention, the nanodiamond primary particles refer to nanodiamonds having a particle size of 10 nm or less. The particle size D50 (median diameter) of the nanodiamond particles in the nanodiamond organic solvent dispersion of the present invention is, for example, 10 μm or less, preferably 500 nm or less, and more preferably 200 nm or less. The particle size D50 is the particle size of the primary particles of nanodiamond or the secondary particles obtained by assembling the primary particles. When the particle size D50 of the nanodiamond particles is 10 μm or less, a sufficient surface area per unit mass can be sufficiently secured, and for example, the functions as nanodiamonds (for example, mechanical strength, thermal conductivity, etc.) are efficiently exhibited. be able to.

The negative (negative) zeta potential in the nanodiamond particles means that the value of the zeta potential at pH 7 at 25 ° C. as measured by, for example, laser Doppler electrophoresis is negative. The zeta potential is, for example, −60 to −20 mV, preferably −50 to −25 mV, and more preferably −45 to −30 mV.

The proportion of the solid content in the nanodiamond organic solvent dispersion is, for example, 0.1 to 10% by mass, preferably 0.3 to 8% by mass, more preferably 0.5 to 6% by mass, and further preferably 1.0. ~ 4% by mass. Most of the solid content in the nanodiamond organic solvent dispersion is preferably nanodiamond particles, and the proportion of the nanodiamond particles in the solid content is, for example, 95% by mass or more, preferably 98% by mass or more, more preferably. Is 99% by mass or more, more preferably 100% by mass.

The proportion of nanodiamond particles in the nanodiamond organic solvent dispersion is, for example, 0.1 to 10% by mass, preferably 0.3 to 8% by mass, more preferably 0.5 to 6% by mass, and even more preferably 1. It is 0 to 4% by mass. The proportion of the organic solvent in the nanodiamond organic solvent dispersion of the present invention is, for example, 90 to 99.9% by mass, preferably 92 to 99.7% by mass, more preferably 94 to 99.5% by mass, still more preferably. Is 96-99% by mass.

(Nanodiamond particles)
Similar to bulk diamond, nanodiamond has a basic skeleton of sp ³ structure of carbon atom. The nanodiamond particles preferably have, for example, a hydroxyl group, a carboxyl group, a carbonyl group, an alkenyl group or the like as a group (surface functional group) bonded to a terminal carbon atom of the basic skeleton of nanodiamond.

The ratio of hydroxyl group-bonded carbon (C—OH) to the carbon contained in the nanodiamond particles is, for example, 7.0% or more, preferably 8.0% or more, more preferably 9.0% or more, still more preferably 10.0%. % Or more, particularly preferably 12.0% or more. The upper limit of the ratio of the hydroxyl group-bonded carbon is, for example, 40.0%. The hydroxyl group-bonded carbon means carbon in the basic skeleton of nanodiamond to which a hydroxyl group (−OH), which is a surface functional group, is bonded in the basic skeleton of nanodiamond. The proportion of the hydroxyl-bonded carbon can be measured, for example, by solid ¹³ C-NMR analysis.

The ratio of carboxyl carbon (C (= O) O) in the carbon contained in the nanodiamond particles is, for example, 0.1% or more, preferably 0.2% or more, more preferably 0.3% or more, still more preferable. Is 0.4% or more. The upper limit of the proportion of carboxyl carbon is, for example, 5.0%. The carboxyl carbon means carbon contained in a carboxyl group (-C (= O) O containing -COOH) which is a surface functional group. The proportion of carboxyl carbon can be measured, for example, by solid ¹³ C-NMR analysis.

The ratio of carbonyl carbon (C = O) in the carbon contained in the nanodiamond particles is, for example, 0.05% or more, preferably 0.1% or more, more preferably 0.2% or more, still more preferably 0. It is 3% or more. The upper limit of the proportion of carbonyl carbon is, for example, 5.0%. The carbonyl carbon means carbon contained in a carbonyl group (−C = O) which is a surface functional group. It is assumed that the carbon contained in -C (= O) O is not contained in the carbonyl carbon. The proportion of carbonyl carbon can be measured, for example, by solid ¹³ C-NMR analysis.

The ratio of hydrogen-bonded carbon to the carbon contained in the nanodiamond particles is, for example, 8.0% or more, preferably 9.0% or more, more preferably 10.0% or more, still more preferably 12.0% or more. The hydrogen-bonded carbon is carbon that is bonded to a hydrogen atom existing in a surface functional group. When the ratio of hydrogen-bonded carbon is 8.0% or more, it contributes to the stabilization of the surface carbon of nanodiamond. The proportion of hydrogen-bonded carbon can be measured, for example, by solid ¹³ C-NMR analysis.

The ratio of sp ³ carbon (carbon atom having a sp ³ structure) in the carbon contained in the nanodiamond particles is, for example, 45.0% or more, preferably 50.0% or more, more preferably 55.0% or more, still more preferable. Is 60.0% or more, particularly preferably 65.0% or more. The upper limit of the proportion of sp ³ carbon is 90.0%. The proportion of sp ³ carbon can be measured, for example, by solid ¹³ C-NMR analysis.

Examples of the nanodiamond particles include nanodiamond particles produced by the detonation method (nanodiamond particles produced by the detonation method), nanodiamond particles produced by the high temperature and high pressure method, and the like. Among them, the nanodiamond particles are preferably explosive nanodiamond particles because they are more excellent in dispersibility and nanodiamonds having a primary particle diameter of one digit nanometer can be easily obtained.

(Organic solvent)
The organic solvent in the nanodiamond organic solvent dispersion of the present invention has a boiling point of 120 ° C. or lower and a relative permittivity of 30 or more at 25 ° C. The boiling point is preferably 110 ° C. or lower, more preferably 105 ° C. or lower, still more preferably 100 ° C. or lower, particularly preferably 95 ° C. or lower, and most preferably 90 ° C. or lower. The lower limit of the boiling point is, for example, 50 ° C. The relative permittivity is preferably 31 or more, more preferably 32 or more. The upper limit of the relative permittivity is, for example, 80. The viscosity of the organic solvent is, for example, 0.1 to 3.0 cP, preferably 0.2 to 2.5 cP, and more preferably 0.3 to 2.0 cP. The boiling point, relative permittivity, and viscosity are described in, for example, the book "Solvent Handbook" (Kodansha, Teruzo Asahara / Niichiro Tokura / Shin Okawara / Manabu Senoo / Satoshi Kumano, ed.) And "Chemical Handbook 5th Edition". The values described in "Basics" (Maruzen Co., Ltd., Japan Chemistry Society) can be adopted.

The larger the relative permittivity, the greater the ability to dissolve the electrolyte. Generally, a solvent having a large relative permittivity (for example, a solvent having a relative permittivity of 30 or more) is called a polar solvent. When the relative dielectric constant of the organic solvent is 30 or more (polar solvent), the nanodiamond particles can be dispersed in the organic solvent by the electric charge on the surface of the nanodiamond particles, and the dispersed state can be maintained. can.

Examples of the organic solvent include methanol (boiling point 64.5 ° C., relative permittivity 33.1), acetonitrile (boiling point 81.6 ° C., relative permittivity 37.5), and formic acid (boiling point 100.8 ° C., relative permittivity). 58.5) can be mentioned. Of these, methanol and acetonitrile are preferable as the organic solvent. The boiling point in parentheses is 1 atm (760 mmHg), and the relative permittivity is a value at 25 ° C. (however, the relative permittivity of formic acid is a value at 16 ° C.).

(Manufacturing method of nanodiamond organic solvent dispersion)
The method for producing the nanodiamond organic solvent dispersion is, for example, a relative dielectric at a boiling point of 120 ° C. or lower and 25 ° C. using a dialysate from a nanodiamond dispersion containing nanodiamond particles having a negative zeta potential. This is a method for obtaining a nanodiamond organic solvent dispersion of the organic solvent by performing membrane separation in an organic solvent having a ratio of 30 or more. As the nanodiamond dispersion, a nanodiamond aqueous dispersion is preferable. When the nanodiamond dispersion liquid is a nanodiamond water dispersion liquid, it is a method of substituting the solvent from water with the organic solvent by using a dialysis membrane.

Hereinafter, as an example of the method for producing nanodiamond particles in the nanodiamond organic solvent dispersion liquid of the present invention, a method for obtaining the organic solvent dispersion liquid after obtaining the explosive method nanodiamond particles will be described. FIG. 1 is a process diagram showing an example of this method. This method includes a production step S1, a purification step S2, a crushing step S3, a classification step S4, and a solvent replacement step S5.

In the production step S1, the detonation method is performed under the condition that the gas (including a significant amount of oxygen) coexists with the air-cooled type, and nanodiamonds are produced. First, a molded explosive equipped with an electric detonator is installed inside a pressure-resistant container for detonation, and the container is placed in a state where the atmospheric composition normal pressure gas and the explosive used coexist in the container. Seal. The container is made of iron, for example, and 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 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, preferably 0.3 to 1.0 kg.

In the generation step S1, 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. The produced nanodiamond becomes a cohesive body in which adjacent primary particles or crystallites are very strongly aggregated by the action of van der Waals force and the interaction of Coulomb between crystal planes.

In the production step S1, the temperature of the container and its inside is then lowered by leaving it at room temperature for, for example, 24 hours. After this cooling, a spatula is used to scrape off the nanodiamond crude products (including the nanodiamond adherents and soot produced as described above) adhering to the inner wall of the container. Collect the product. By the air-cooled atmospheric coexistence detonation method as described above, a crude product of nanodiamond particles can be obtained. The detonation method, which is air-cooled and carried out under the condition that a gas having an atmospheric composition (containing a significant amount of oxygen) coexists, is suitable for producing nanodiamond particles having a large amount of functional groups on the surface of the primary particles. be. According to the air-cooled atmospheric coexistence detonation method, the growth of diamond nuclei from the raw material carbon is suppressed in the process of forming diamond crystallites, and part of the raw material carbon (some of which contains oxygen, etc.) is suppressed. It is believed that this is due to the formation of surface functional groups. Further, by performing the production step S1 as described above a required number of times, it is possible to obtain a desired amount of crude nanodiamond product. As the crude product of nanodiamond, a commercially available product may be used.

The purification step S2 includes an acid treatment in which a strong acid is allowed to act on the nanodiamond crude product obtained in the production step S1, for example, in an aqueous solvent. The nanodiamond crude product obtained by the detonation method tends to contain metal oxides, but this metal oxide is an oxide of Fe, Co, Ni, etc. derived from the container used in the detonation method. be. For example, the metal oxide can be dissolved and removed from the crude nanodiamond product by allowing a predetermined strong acid to act in an aqueous solvent (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. In the acid treatment, one kind of strong acid may be used, or two or more kinds of strong acids may be used. The concentration of the strong acid used in the acid treatment is, for example, 1-50% 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 to 3.

In the present embodiment, the purification step S2 includes an oxidation treatment for removing graphite from the crude nanodiamond product (nanodiamond adherent before completion of purification) using an oxidizing agent. The crude nanodiamond product obtained by the detonation method contains graphite (graphite), which forms nanodiamond crystals out of the carbon released by the explosive used due to partial incomplete combustion. Derived from carbon that did not. For example, after undergoing the above-mentioned oxidation treatment, graphite can be removed from the crude nanodiamond product by, for example, allowing a predetermined oxidizing agent to act in an aqueous solvent (oxidation treatment). Examples of the oxidizing agent used in this oxidation treatment include chromium acid, chromium anhydride, dichromic acid, permanganic acid, perchloric acid, and salts thereof. In the oxidation treatment, one kind of oxidizing agent may be used, or two or more kinds of oxidizing agents may be used. The concentration of the oxidizing agent used in the oxidation treatment is, for example, 3 to 50% by mass. 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 crude nanodiamond product 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 pressure. Further, the oxidation treatment is preferably performed in the coexistence of mineral acid from the viewpoint of improving the removal efficiency of graphite. Examples of the mineral acid include hydrochloric acid, hydrofluoric acid, sulfuric acid, nitric acid, and aqua regia. When mineral acid is used for the oxidation treatment, the concentration of the mineral acid is, for example, 5 to 80% by mass. After such an oxidation treatment, the solid content (including the nanodiamond adherent) is washed with water, for example, by decantation. Since the supernatant liquid at the beginning of washing with water is colored, it is preferable to repeatedly wash the solid content with water by decantation until the supernatant liquid becomes visually transparent.

Even after undergoing the above acid treatment and oxidation treatment, the detonation nanodiamond particles are in the form of cohesive particles (secondary particles) in which the primary particles interact very strongly with each other. Easy to take. In order to promote the separation of the primary particles from the adhered body, predetermined alkali and hydrogen peroxide may be allowed to act on the nanodiamond particles in an aqueous solvent. Thereby, for example, when the metal oxide that could not be completely removed by the above-mentioned acid treatment remains in the nano diamond, the metal oxide can be removed, and the nano diamond primary particles from the nano diamond adhering body can be removed. Separation is promoted (alkaline overwater treatment). Examples of the alkali used in this treatment include sodium hydroxide, ammonia, potassium hydroxide and the like. In this treatment, the concentration of alkali is, for example, 0.1 to 10% by mass, the concentration of hydrogen peroxide is, for example, 1 to 15% by mass, the treatment temperature is, for example, 40 to 100 ° C., and the treatment time is For example, 0.5 to 5 hours. Further, this treatment can be performed under reduced pressure, normal pressure, or pressure. After the supernatant is removed from the nanodiamond-containing solution that has undergone this treatment by, for example, decantation, the residue may be subjected to a drying treatment to obtain a dry powder. Examples of the drying treatment method include spray drying performed using a spray drying device and evaporative drying performed using an evaporator.

In this method, the crushing step S3 is then performed. Even after being purified through the above series of processes, detonation nanodiamonds are coagulants (secondary particles) in which the primary particles interact very strongly with each other. Easy to take form. The crushing step S3 is performed in order to separate many primary particles from the adhered body. Specifically, for a solution containing nanodiamonds that have undergone the above-mentioned purification process or the like in an aqueous solvent, the pH is adjusted to, for example, 8 to 12 using an alkaline solution to prepare a slurry, and then the slurry is solved. Perform the crushing process. The aqueous solvent means a solvent containing more than 50% by mass of water. As the alkaline solution for pH adjustment, for example, an aqueous sodium hydroxide solution or an aqueous ammonia solution can be used. By adjusting the pH to the alkaline side before the crushing treatment, the zeta potential of the nanodiamond particles after the crushing treatment can be set to a negative value, that is, the zeta potential can be set to a negative value. The solid content concentration or nanodiamond concentration of the slurry to be subjected to the crushing treatment is, for example, 1 to 6% by mass. 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, or a colloidal mill. A crushing treatment may be carried out by combining these. From the viewpoint of efficiency, it is preferable to use a bead mill. By going through the crushing step S3 as described above, it is possible to obtain a nanodiamond aqueous dispersion in which nanodiamond primary particles having a negative zeta potential are dispersed as colloidal particles.

In this method, the classification step S4 is then performed. Specifically, a classification operation for removing coarse particles is performed on the slurry that has undergone the crushing step S3. For example, a classification device can be used to remove coarse particles from the slurry by a classification operation utilizing centrifugation. A commercially available nanodiamond aqueous dispersion having a negative zeta potential may be used to obtain a nanodiamond organic solvent dispersion by performing the next solvent replacement step S5.

In this method, the solvent replacement step S5 is then performed. In the solvent replacement step S5, the nanodiamond organic solvent dispersion of the organic solvent is separated from the nanodiamond aqueous dispersion containing nanodiamond particles having a negative zeta potential in the organic solvent using a dialysis membrane. It is a step (transmission membrane solvent replacement step) for obtaining. In the nanodiamond organic solvent dispersion liquid of the present invention, the nanodiamond particles can be dispersed in the organic solvent which is a polar solvent having a low boiling point while suppressing aggregation by this step, and the nanodiamond particles can be dispersed and stabilized.

In the solvent replacement step S5, the nanodiamond aqueous dispersion is wrapped in a dialysis membrane, immersed in an organic solvent and stirred to prevent the nanodiamond particles from permeating the outside of the dialysis membrane, and the water inside the dialysis membrane is dialed. A nanodiamond organic solvent dispersion can be obtained inside the dialysis membrane by allowing it to permeate the outside of the membrane and allowing the organic solvent outside the dialysis membrane to permeate the inside of the dialysis membrane. Further, by exchanging the organic solvent (buffer) and repeating the above dipping and stirring 2 to 3 times as necessary, a nanodiamond organic solvent dispersion liquid having a lower water content can be obtained. The time for each immersion and stirring is, for example, about 1 to 5 hours.

The material of the dialysis membrane is not particularly limited as long as it is strong against organic solvents and has an appropriate molecular weight cut-off (MWCO), but examples thereof include cellulosic materials, and examples of cellulosic materials include regenerated cellulose (RC). Examples thereof include cellulose ester (CE), cupraammonium rayon (CR), cellulose acetate (CA), and saponified cellulose (SCA). In addition, as materials other than cellulose-based materials, polysulfone (PS), polyethersulfone (PES), polyester-based polymer alloy (PEPA), ethylene vinyl alcohol copolymer (EVAL), and polymethyl, which are synthetic polymer-based materials. Examples thereof include methacrylate (PMMA) and polyacrylonitrile copolymer (PAN). The molecular weight cut-off (MWCO) of the dialysis membrane is, for example, 500 to 50,000, preferably 1,000 to 30,000, more preferably 2,000 to 20,000, still more preferably 3,000 to 10, It is 000. If the molecular weight of the fraction is too small, solvent replacement cannot be performed efficiently, and if the molecular weight of the fraction is too large, the nanodiamond particles may permeate the dialysis membrane. As the dialysis membrane, a commercially available dialysis membrane can be used, and for example, a trade name "RC dialysis tube" (manufactured by Spectrum Co., Ltd.) can be used.

The amount of the organic solvent used in the solvent replacement step S5 is, for example, 3000 to 10000 parts by mass, preferably 4000 to 8000 parts by mass with respect to 100 parts by mass of the nanodiamond aqueous dispersion. The water content (based on mass) in the nanodiamond organic solvent dispersion is, for example, 2000 ppm or less, preferably 1500 ppm or less, more preferably 1000 ppm or less, still more preferably 900 ppm or less, and particularly preferably 800 ppm or less. The lower limit of the water content is, for example, 10 ppm.

As described above, a dispersion in which nanodiamond particles having a negative zeta potential are dispersed in an organic solvent solution, that is, a nanodiamond organic solvent dispersion can be produced.

Hereinafter, the present invention will be described in more detail based on examples, but the present invention is not limited to these examples. In addition, Example 2 is described as a reference example.

[Production Example 1: Production of Nanodiamond Aqueous Dispersion]
As the crude product of nanodiamond, air-cooled detonation nanodiamond soot (manufactured by Czech ALIT) having a primary particle size of nanodiamond of 4-6 nm was used. 220 g of air-cooled detonation nanodiamond soot was weighed, 10.7 L of a 10% hydrochloric acid aqueous solution was added, and then the mixture was heated under reflux for 1 hour (acid treatment). After cooling, the mixture was washed with water by decantation until the pH of the precipitate reached 2.5, and the supernatant was removed. Next, 4725 g of 98% sulfuric acid and 50 g of ultrapure water were added to 1625 g of the precipitate (solid content 125 g) (40 ° C. or lower). To this, 3050 g of an aqueous solution of chromic acid (1500 g of chromic acid) was added, and the mixture was heated under reflux (internal temperature: 141 ° C.) for 5 hours and then cooled to obtain 9450 g of a slurry solution (oxidation treatment). Then, it was washed with water by decantation until the coloration of the supernatant disappeared, and the supernatant was removed as much as possible to obtain a precipitate.

After adding 1 L of a 10% aqueous sodium hydroxide solution to the precipitate obtained above, heat treatment was carried out under reflux for 1 hour. After cooling, the supernatant was removed by decantation, 20% hydrochloric acid was added to adjust the pH to 2.5, and then water washing was performed by a centrifugal sedimentation method. Ultrapure water was added to the final centrifugal precipitate to adjust the solid content concentration to 8%, and the pH was adjusted to 10 with sodium hydroxide to obtain a pre-dispersion slurry. Bead mill dispersion was performed on the above pre-dispersion slurry. A wet disperser (trade name "Ultra Apex Mill UAM-015", manufactured by Kotobuki Kogyo Co., Ltd.) was used for the dispersion. After filling the wet disperser with zirconia beads having a diameter of 0.03 mm, which is a crushing medium, up to 60% of the volume of the crushing container, 300 mL of the pre-dispersion slurry is circulated at a flow rate of 10 L / h, and the peripheral speed of the wet disperser is 10 m. It was set to / s and crushed for 90 minutes. Then, the crushed liquid was recovered, and coarse particles were removed by a classification operation by centrifugation to obtain a nanodiamond aqueous dispersion (particle size distribution D50 = 5.4 nm).

The obtained nanodiamond aqueous dispersion was dried to remove water, and then solid ¹³ C-NMR analysis was performed by the following measurement method. In the solid ¹³ C-NMR analysis, the ratio of each carbon atom was 16.6% of hydroxyl-bonded carbon (C—OH) and carboxyl carbon (C (= O) O) with respect to the total carbon atoms contained in the nanodiamond. ) Was 0.5%, carbonyl carbon (C = O) was 0.4%, hydrogen-bonded carbon was 14.7%, and sp ³ carbon was 67.8%.

<Solid ¹³ C-NMR analysis>
Solid-state ¹³ C-NMR analysis was performed by a solid-state NMR method using a solid-state NMR apparatus (trade name "CMX-300 Infinity", manufactured by Chemagnetics). The measurement method and other conditions related to measurement are as follows.
Measurement method: DD / MAS method Measurement nuclear frequency: 75.188829 MHz ( ¹³ C nucleus)
Spectral width: 30.003 kHz
Pulse width: 4.2 μsec (90 ° pulse)
Pulse repetition time: ACQTM 68.26msec, PD 15sec
Observation point: 2048 (data point: 8192)
Reference substance: Polydimethylsiloxane (external standard: 1.56 ppm)
Temperature: Room temperature (about 22 ° C)
Sample rotation speed: 8.0 kHz

[Example 1: Production of nanodiamond organic solvent dispersion (methanol dispersion)]
7.0 g of the nanodiamond aqueous dispersion obtained in Production Example 1 above is placed in a dialysis membrane, trade name "spectrum dialysis tube": model number "RC dialysis tube pore 3" (molecular weight cut-off 3500, manufactured by Spectrum Co., Ltd.). rice field. The dialysis membrane containing the nanodiamond aqueous dispersion was immersed in 1 L of methanol (buffer) and stirred with a stirrer for 3 hours. Then, after exchanging 1 L of methanol (buffer), the operation of stirring with a stirrer for 3 hours was performed twice. As a result, by exchanging the solvent from the nanodiamond aqueous dispersion, 3.67 g of the dispersion (nanodiamond organic solvent dispersion) in which the nanodiamond particles were dispersed in methanol was obtained. This nanodiamond organic solvent dispersion was a black solution, and no separation or aggregation of nanodiamond particles was observed even after being left for a while. Therefore, the nanodiamond particles could be dispersed in methanol and stabilized.

[Example 2: Production of nanodiamond organic solvent dispersion (acetonitrile dispersion)]
In the same manner as in Example 1 except that the buffer was replaced with acetonitrile, 3.43 g of a dispersion liquid (nanodiamond organic solvent dispersion liquid) in which nanodiamond particles were dispersed in acetonitrile was obtained. This nanodiamond organic solvent dispersion was a black solution, and no separation or aggregation of nanodiamond particles was observed even after being left for a while. Therefore, the nanodiamond particles could be dispersed in acetonitrile to stabilize the dispersion.

The following measurements were performed on the nanodiamond organic solvent dispersions obtained in Examples 1 and 2 above. The measurement results are shown in Table 1.

<Solid content>
The solid content is calculated based on the weighed value of 3 to 5 g of the weighed solution and the weighed value of the dry matter (powder) remaining after evaporating the liquid content from the weighed solution by heating with a precision balance. did.

<amount of water>
The water content was measured using a Karl Fischer Moisture Meter, product name "CA-200" (manufactured by Mitsubishi Chemical Corporation). The average value measured 5 times was taken as the water content.

<Diameter D50>
The particle size D50 (median diameter) of the nanodiamond particles is a value measured by a dynamic light scattering method (non-contact backscattering method) using a device manufactured by Spectris (trade name "Zetasizer Nano ZS"). be. The nanodiamond dispersion subjected to the measurement has undergone ultrasonic cleaning for 10 minutes with an ultrasonic cleaner.

<Haze value>
The haze value is a value measured using a haze measuring device (trade name "Haze Meter 300A", manufactured by Nippon Denshoku Industries Co., Ltd.). Each sample liquid used for the measurement has undergone ultrasonic cleaning for 10 minutes with an ultrasonic cleaner. The thickness (inner dimension) of the measuring glass cell filled with the sample liquid and used for the measurement is 1 mm, and the optical path length in the sample according to the measurement is 1 mm.

S1 Generation step S2 Purification step S3 Crushing step S4 Classification step S5 Solvent replacement step

Claims (3)

The zeta potential is negative, the ratio of hydroxyl-bonded carbon to the total carbon atoms contained in nanodiamond is 7.0 to 40.0%, the ratio of carboxyl carbon is 0.1 to 5.0%, and carbonyl carbon. Nanodiamond particles having a ratio of 0.05 to 5.0%, a ratio of hydrogen-bonded carbon of 8.0% or more, and a ratio of sp ³ carbon of 45.0 to 90.0%, and a boiling point of 120 ° C. Hereinafter, a nanodiamond organic solvent dispersion liquid containing an organic solvent having a specific dielectric constant of 30 or more at 25 ° C. (excluding acetonitrile) and having a proportion of the nanodiamond particles of 1.0 to 10% by mass . The nanodiamond organic solvent dispersion liquid according to claim 1, wherein the organic solvent is methanol. The nanodiamond organic solvent dispersion according to claim 1 or 2, wherein the water content is 1500 mass ppm or less.

Images