JP5339099B2 - Method for synthesizing thin-film particles having a carbon skeleton - Google Patents

Description

  The present invention relates to a very thin film-like particle having a skeleton made of carbon.

  In recent years, the search and application of substances having a high shape anisotropy are rapidly progressing. In the case where a large number of such substances are combined with other substances, it is expected that various properties such as high strength will be exhibited by addition of a low fraction. In addition, if the shape is very thin (one-dimensional) or extremely thin planar (two-dimensional), and it is an electrically semiconductor or good conductor, quantum properties such as single or a small number of aggregates can be applied to electronic properties. It is expected to produce a positive effect.

As anisotropically-shaped substances having a carbon atom skeleton, graphite fibers and carbon nanotubes that are particularly thin are known in one dimension, and graphite, fluorinated graphite, graphite oxide, etc. are known in two dimensions. ing. Among these, graphite, fluorinated graphite, and graphite oxide are all multilayer structures in which two-dimensional basic layers are stacked, and the number of layers is generally very large. The basic layer of graphite is made of sp ² -bonded carbon and has a thickness of one carbon atom. The base layer of fluorinated graphite consists of a sp ³ bond carbon skeleton with a thickness of one or two carbon atoms counted in a zigzag carbon array similar to diamond, and fluorine bonded to both sides of the skeleton. With the structure. The basic layer of graphite oxide is composed of a carbon skeleton mainly composed of sp ³ bonds having a tendency of slightly sp ² bonds, and having a thickness equivalent to one or two carbon atoms counted in a zigzag carbon array, It is considered to have a structure in which acidic hydroxyl groups or the like are bonded to both sides (for example, “Graphite Intercalation Compound”, Chapter 5, Carbon Society of Japan, Realize Inc. (1990); T. Nakajima et al., Carbon, 26, 357 (1988); M. Mermoux et al., Carbon, 29, 469 (1991)).

  Examples of such a multilayer structure having a carbon skeleton separated into a large number of basic layers are those in which isoprene is polymerized between graphite layers (H. Shioyama, Carbon, 35, 1664 (1997)), graphite oxide There are those in which polyethylene oxide penetrates between layers (Y. Matsuo et al., Carbon, 34, 672 (1996)) and those in which aniline is polymerized between layers (Japanese Patent Laid-Open No. 11-263613).

JP-A-11-263613

“Graphite Intercalation Compound”, Chapter 5, Carbon Society of Japan, Realize (1990) T.A. Nakajima et al. Carbon, 26, 357 (1988). M.M. Mermoux et al. Carbon, 29, 469 (1991). H. Shioyama, Carbon, 35, 1664 (1997) Y. Matsuo et al. Carbon, 34, 672 (1996).

  However, in the separation example of these multilayer structures, the basic layer or an extremely thin layer close thereto is only present as a constituent component in the composite, and has not been stably taken out alone. That is, an extremely thin film-like particle that has a highly crystalline carbon skeleton and can exist as an independent particle has not been found.

  An object of the present invention is to provide such a thin film-like particle.

  In order to achieve the above object, the inventors selected graphite oxide, which is considered to be relatively easily separated, among the three types of multilayer structures described above, and further promotes the separation of the layers. Synthesis (oxidation and purification) was performed to obtain the desired thin film particles. The structure of this thin film-like particle is almost the same as the structure of graphite oxide known so far, but it has an extremely thin shape that has not been known so far, i.e., the thickness of the thin film-like particle is less than the spread in the plane direction. It has a very small shape. In terms of the number of layers inside the particle, it is less than 20 layers of the basic layer. As a result, the thin film-like particles could be deformed flexibly despite having a dense carbon skeleton.

  In addition, it is desirable to handle the thin-film particles dispersed in a liquid. However, not only water, which is a dispersion medium immediately after synthesis, but also exchange with other dispersion media is studied, Application deployment to other materials has been made easier. Further, as is known in ordinary graphite oxide, it was possible to reduce the thin film-like particles into thin film-like graphite particles having an almost graphite structure or an aggregate thereof.

  The thin film-like particles of the present invention are extremely thinner than the conventionally known graphite oxide and have a highly anisotropic shape. Therefore, it can be deformed flexibly despite having a dense carbon skeleton inside the particle, and various properties such as high strength can be achieved by adding a low fraction when compounding with other substances. Is expected to be expressed. Furthermore, when this thin film-like particle is reduced to an electronic state similar to graphite, it exhibits electrical conductivity and is expected to exhibit a two-dimensional quantum effect due to its extremely thin shape.

Optical micrograph of thin film particles (on glass plate) Transmission electron micrograph of thin film-like particles (a flat surface including many wrinkles, flat surfaces other than wrinkles cannot be recognized, black and thick portions are carbon microgrids) Transmission electron micrograph of thin film particles (enlargement of one cocoon) Transmission electron micrograph of aggregates of thin film particles reduced with aluminum and hydrochloric acid

  The raw material for the thin film-like particles of the present invention is preferably highly crystalline graphite with a developed layer structure. Such graphite is easy to be separated into thin film particles after the oxidation reaction because each basic layer is large and the existence frequency of sigma bonds connecting two adjacent basic layers is extremely low. On the other hand, in the case of graphite with an undeveloped layer structure and low crystallinity, oxidation occurs, but the layers are very poorly separated. More specifically, graphite having the diameter of the widest basic layer inside the particle approximately equal to the diameter of the particle and having a single multilayer structure throughout the particle is desirable. As such graphite, natural graphite (especially good quality), quiche graphite (especially made at high temperature), and highly oriented pyrolytic graphite are known. Each base layer of natural graphite and quiche graphite is a single crystal having a substantially single orientation, and each base layer of highly oriented pyrolytic graphite is an aggregate of many small crystals having different orientations. In the present invention, these graphites and expanded graphite in which the layers of these graphites are expanded in advance are used as raw materials.

The size of the graphite basic layer and the minute portion inside the basic layer can be estimated by the peak shape in X-ray diffraction, observation of an electron channeling contrast image by a scanning electron microscope, observation by a polarizing microscope, and the like. As another index, for example, it is also a standard that the electrical resistance is about 10 ⁻⁶ Ωm or less. However, since these indicators only indicate the possibility of separation of the layers, it is actually desirable to confirm the separation of the multilayer structure by performing oxidation and purification using the target graphite raw material.

It is desirable that impurities such as metal elements in the graphite are previously removed to about 0.5% or less. When there are many impurities, separation of a multilayer structure may be inhibited.
Since the particle size of graphite is reflected in the size of the thin film-like particles to be generated in the plane direction, it can be selected according to the size of the thin film-like particles to be synthesized. It can be synthesized essentially. However, as the particle diameter increases, the time required for oxidation increases. In addition, when it is desired to define the shape of the thin film-like particles to be generated in the planar direction, for example, as a square, it may be cut into a square in advance at the stage of the graphite raw material. However, when cutting, it is necessary to recognize the crystal orientation.

  For the oxidation of graphite in the present invention, the known Brodie method (using nitric acid and potassium chlorate), the Staudenmeier method (using nitric acid, sulfuric acid and potassium chlorate), the Hummers-Offeman method (sulfuric acid, sodium nitrate, permanganic acid) Can be used). Of these, oxidation proceeds particularly in the Hummers-Offeman method (WS Hummers et al., J. Am. Chem. Soc., 80, 1339 (1958); US Pat. No. 2,798,878 (1957)). This oxidation method is particularly recommended in the present invention.

  In these graphite oxidation methods, first, ions of the oxidant intrude into the graphite layer to form an intercalation compound. Thereafter, by adding water, the intercalation compound is hydrolyzed to become graphite oxide. Of these reactions, the formation of intercalation compounds takes time and depends on the particle size of the graphite. Therefore, it is desirable to change the time of coexistence with the oxidant depending on the particle size of the graphite so that the oxidant ions penetrate into the graphite particles as much as possible. As a result of investigation by the present inventors, in the case of the Hummers-Offeman method, intrusion of ions of about 10 μm or more per hour was observed at around 20 ° C., and therefore, at least 30 minutes per 10 μm of graphite particle diameter. As described above, it is desirable to oxidize graphite with an oxidation time of 3 hours or longer if possible.

  In the above-described graphite oxidation method, it is necessary to purify by removing the oxidant remaining in the reaction solution or ions generated by decomposition of the oxidant and components derived from the ions. In a known oxidation method, this purification is performed by washing with water or alcohol. In the present invention, in this purification step, components that remain in the reaction solution or between the layers and possibly interfere with the separation of the layers are more positively removed, thereby promoting the separation into thin film particles. That is, by removing as much as possible low molecules and small ions other than the dispersion medium coexisting in the liquid, the degree of ionic dissociation of acidic hydroxyl groups present in each layer of graphite oxide is increased, and each layer that can be regarded as ionic large particles Strengthen the electrostatic repulsion between them to promote separation of the multilayer structure.

As a result of investigations by the present inventors, for example, when the concentration of graphite oxide is about 1 wt% or less and the concentration of sulfuric acid is about 0.05 wt% or less, the separation of the multilayer structure proceeds rapidly. When the ion dissociation of sulfuric acid is calculated up to one stage, the concentration of small ions other than those derived from graphite oxide (including hydrogen ions generated by ion dissociation of graphite oxide) in the reaction solution is about 10 mol / m ³ or less. Therefore, it is desirable to purify the product so as to be less than this concentration. In general, the separation of the layers proceeds as the purification proceeds. Specifically, after adding water, the water is removed along with small ions. The water used is preferably of high purity.

  On the other hand, in order to advance separation of each layer, which is an ionic large particle, it is also important to increase the degree of ion dissociation of each layer by lowering the concentration of graphite oxide particles in the liquid during purification. Therefore, the concentration of the graphite oxide at the stage where the particles are uniformly dispersed by adding water is set to about 5 wt% or less, more desirably 1 wt% or less.

  In the Hummers-Offeman method, hydrogen peroxide is usually added after hydrolysis to decompose permanganate ions into manganese (IV) ions, then washed with water and removed together with other sulfate ions and potassium ions ( W. S. Hummers et al., J. Am. Chem. Soc., 80, 1339 (1958)). However, when it becomes neutral, the solubility of manganese ions decreases, and it may remain as a hydroxide of manganese or the like between layers. Therefore, it is desirable to thoroughly wash with a sulfuric acid aqueous solution or a mixed aqueous solution of sulfuric acid and hydrogen peroxide before washing with water.

  For the purification operation by specific washing, known means such as decantation, filtration, centrifugation, dialysis, ion exchange and the like may be used. Here, the smaller the particle diameter of the raw graphite, the more the thin film particles are increased due to the progress of layer separation, and the more the small ions are removed, the more the charge per unit volume of the thin film particles increases. . As a result, the repulsion between the particles becomes strong, and the degree of holding the dispersion medium (hydrating if it is water) becomes high, so that any purification operation becomes difficult. In this case, operations with relatively high purification efficiency are centrifugation, dialysis, and ion exchange, and operations that can be purified in a relatively short time are centrifugation. On the other hand, decantation and filtration become more difficult as the diameter of the thin film-like particles becomes smaller due to slow settling and blockage by the thin film-like particles. In order to temporarily reduce the repulsion between particles, the use of another solvent having a low dielectric constant or salting out may be appropriately combined.

  During purification, separation of the multilayer structure occurs spontaneously. In addition to this, when water is removed together with small ions and then water is added again to obtain a uniform dispersion, a stirring operation such as shaking is added, so that the separation is further promoted. Ultrasonic irradiation can also be used. However, since the basic structure of each layer tends to be destroyed and become smaller as the layers are separated, it is desirable to use it particularly when thin-film particles having a small diameter are to be generated.

  By refining as described above, the separation of the layers proceeds inside many particles, but a few particles that are not in a thin film form, in which the separation of the multilayer structure is insufficient, remain. This is an impurity in the raw material (graphite and other inorganic substances that are difficult to separate) or foreign matter mixed during oxidation and purification. Since these generally precipitate easily, they can be removed by decantation or very gentle centrifugation during purification.

  By the above operation, the separation of the layers proceeds inside many particles. On the other hand, the possibility of separation increases even in the part of the layers that are not separated, but because it is a large particle, there are many hydrogen bonds etc. between the layers inside the particle, making it substantially difficult to separate in a short time It may have become. Therefore, as a method for further promoting the separation of the layers, it is conceivable to dilute the purified dispersion and further strengthen the molecular movement of the dispersion medium and the movement of the thin film particles. Specifically, there are ultrasonic irradiation and heating to the dispersion. However, in the ultrasonic irradiation, the basic structure of each layer tends to be destroyed and become smaller as the layers are separated as described above. In addition, heating can be expected to increase the degree of ionic dissociation, but it is desirable that the temperature be not so high because particles may be partially reduced particularly at high temperatures. Specifically, the temperature is 50 to 150 ° C.

  Further, in order to selectively obtain particles having further separated layers, the particles may be separated by the difference in dispersibility. For example, decantation or relatively gentle centrifugation may be performed and the non-sedimented portion may be used.

By each of the above operations, a dispersion liquid in which extremely thin thin-film particles, which can be called nanofilms, are dispersed in water is completed.
If the dispersion of the thin film particles is dried at a high concentration as in general graphite oxide, a large number of particles aggregate and it becomes difficult to disperse again (conversely, Many studies on the structure are for this agglomerated solid and thin film particles like the present invention were not known). Therefore, when using these thin film-like particles for specific purposes, they should be treated as a dispersion as much as possible, including its storage, and agglomeration may occur by drying from a very low concentration dispersion, spray drying, freeze drying, etc. It is desirable to obtain a small number of thin film-like particles, to use as a dispersion, and to mix with other substances.

  When used as a dispersion, a dispersion medium other than water may be desirable depending on the application. In that case, use another dispersion medium in the middle of the above purification, or concentrate the dispersion liquid by centrifugation after purification to reduce water, add another solvent, and then concentrate by centrifugation after mixing. The dispersion medium may be exchanged by repeating this process. Here, since the thin film-like particles have a high polarity, the affinity with the polar dispersion medium having a high dielectric constant is high. If such a dispersion medium is used, the aggregation of the thin-film particles is small. Specifically, a dispersion medium having a relative dielectric constant of about 15 or more is desirable. In addition, when the two dispersion media are not compatible with each other when the dispersion medium is exchanged, the two dispersion media are exchanged via a third dispersion medium that is compatible with both of the two dispersion media. May be.

  Since the thin film-like particles obtained by the present invention have a functional group such as a hydroxyl group, it can be expected to react with, for example, formaldehyde, carboxylic acids, isocyanate esters, epoxy compounds and the like. In this case, if another molecule that reacts with the thin film-like particle has a plurality of functional groups or a functional group that generates a plurality of bonds, the thin film-like particles are cross-linked.

  When the thin film-like particles obtained in the present invention are mixed with another organic or inorganic polymerizable substance and the polymerizable substance is polymerized, a composite containing the thin film-like particles can be obtained. In this case, when the dispersion of the thin film particles is mixed with another polymerizable substance and polymerized after removing the dispersion medium, aggregation of the thin film particles in the composite can be minimized.

In the case where the thin film-like particles obtained in the present invention are expected to have electronic properties, it is desirable to reduce the thin-film particles to an electronic state mainly composed of sp ² bonds similar to graphite to enhance electrical conductivity. Various known reduction reactions and electrode reactions (electrolytic reduction) using a reducing agent can be used for the reduction. Especially when a reducing agent is used, if the basic layer cannot be decomposed, it can reach the inside of the multilayer particle. It is thought that complete reduction of is difficult. On the other hand, as a general behavior of graphite oxide, it is possible to make a graphite-like structure to the inside of the multilayer by heating, and if heating is performed in a state where a plurality of particles are aggregated, the interlayer inside the multilayer particle or between the plurality of particles It is known that a pi bond occurs and a macroscopic shape such as an ordinary graphite film can be imparted (J. Maire et al., Carbon, 6, 555 (1968)). Since the thin film-like particle of the present invention has a particularly thin shape, it becomes a single thin film-like graphite particle that can be called a carbon nanofilm or a graphite nanofilm by making a structure similar to graphite by similar heating. Such a single thin film-like graphite particle or a larger film-like structure in which a plurality of such thin-film graphite particles are aggregated in a planar shape is expected to exhibit a two-dimensional quantum effect on electronic properties. In specific use, for example, the thin film-like particles may be placed on a suitable substrate having high heat resistance, reduced by heating, and the obtained thin film-like graphite particles may be processed into a predetermined shape by various etching methods. .

  It is also possible to mix the thin film-like graphite particles with another polymerizable substance and polymerize the polymerizable substance to form a composite containing the thin-film-like graphite particles. For example, the composite is given electrical conductivity. It becomes possible.

Further, the thin film-like graphite particles may be a precursor of a new carbon structure such as a thin film-like diamond or a thin-film-like large hydrocarbon.
Since the thin film-like particles obtained by the present invention are thin structures having a dense carbon skeleton, including the reduced form thereof, the particles alone or a plurality of particles agglomerate in a planar shape to form a larger film. When it becomes a structure, it may become a selectively permeable or shielding film material such as elementary particles such as muons and protons, small ions, and small molecules.

EXAMPLES Hereinafter, although this invention is demonstrated in more detail using an Example, this invention is not limited by this.
Example 1
Natural graphite (manufactured by SCC Co., Ltd., SNO-25, purity 99.97 wt% or more, purified product excluding impurities by heating at 2900 ° C., average particle size 24 μm, particle size 4.6 μm or less and 61 μm or more are 5 wt each. %) 10 g and sodium nitrate (purity 99%) 7.5 g were put into an Erlenmeyer flask, sulfuric acid (purity 96%) 345 cm ³ was added, a stir bar was added, and this was stirred while cooling in a water bath containing ice water. 45 g of potassium permanganate (purity 99%) was gradually added in about 1 hour. Cooling was completed in 2 hours, and the mixture was allowed to stand at about 20 ° C. for 5 days while further gently stirring. The obtained high-viscosity liquid was added to 1000 cm ³ with stirring for about 1 hour with a 5 wt% sulfuric acid aqueous solution (the water used for dilution was one having a conductivity of less than 0.1 μS / cm (hereinafter the same)). The mixture was further stirred for 2 hours. Hydrogen peroxide (30 wt% aqueous solution) 30g was added to the obtained liquid, and it stirred for 2 hours.

Transfer this solution to ^three centrifuge bottles (with a capacity of about 400 cm ³ ), centrifuge (maximum rotation radius 17 cm (hereinafter the same), 1000 rpm, 10 minutes), and discard the supernatant (slightly mixed with sediment, the same applies hereinafter) And only precipitation. Furthermore, with the precipitate in a centrifuge bottle, add a mixed aqueous solution of 3 wt% sulfuric acid / 0.5 wt% hydrogen peroxide (about 6 to 4 times the precipitate, the magnification decreases as the operation proceeds). The operation was repeated 15 times by capping, shaking the bottle to redisperse the precipitate, centrifuging (3000 rpm, 20 minutes), and discarding the supernatant. A total of about 13 kg was used as the mixed aqueous solution.

The liquid to be added was changed to water, and redispersion, centrifugation (7000 rpm, 30 minutes) and discarding of the supernatant were repeated twice. Further, water was added for redispersion, and the mixture was allowed to stand for 1 day to precipitate only a small amount of particles (such as thick particles) that were likely to precipitate. The precipitate was removed, and the liquid that did not precipitate was centrifuged (7000 rpm, 30 minutes), and the supernatant was discarded. Except supernatant is high liquid fluidity hard little viscosity of precipitation and the top of the lower, totaled about 650 cm ^3.

After stirring this difficult-to-flow precipitate and a slightly high-viscosity liquid to make a homogeneous liquid, about 1/2 (the rest is used in Example 2) is divided into six centrifuge bottles, and water ( Re-dispersion, centrifugation (7000 rpm, 60 minutes), and discarding of the supernatant were repeated 20 times in total. Thereafter, a small amount of water was added and stirred to obtain a highly purified aqueous dispersion of thin film particles, 1350 cm ³ . A part of the liquid was dried, and the change in weight before and after drying resulted in a concentration of thin film particles in the liquid of 0.45 wt%.

  The obtained aqueous dispersion was placed on a glass plate and dried for about 10 days at a temperature of about 20 ° C. and a relative humidity of about 40%, and X-ray diffraction measurement was performed. A peak corresponding to 0.83 nm was obtained. This corresponds to the interlayer distance of generally known graphite oxide (when water is held between the layers).

  When a small amount of the obtained aqueous dispersion was placed on a glass plate and observed with an optical microscope (OM) after drying, large thin-film particles with a clear outline and a maximum spread in the plane direction of several tens of μm, and the entire surface of the glass plate There was a film-like material covering the film (particularly, it is highly likely that the particles are aggregates of thin particles as compared with the electron microscope observation described later). In addition, the particles transmitted light well, and observation with reflected light was suitable.

The same aqueous dispersion was diluted 100 times with water, then placed on a glass plate and dried to try to obtain an average value of the thickness of the thin film-like particles. When the average thickness of the particle aggregate dried and adhered from the liquid is calculated to be about 12 nm (the particle density is 2.1 g / cm ³ ), approximately 3 particles are spread on the entire surface where the liquid has spread. It was confirmed by OM observation that more than a certain degree was overlapped (particles were extremely thin but could be identified because of their higher reflectivity than glass). Accordingly, the average thickness of each thin film-like particle is less than 4 nm.

  Dilute the same aqueous dispersion approximately 200 times with methanol (purity 99.8%), add a small amount of finely pulverized natural graphite as a reference substance, and place it on a copper mesh with a carbon microgrid for electron microscope observation. Dried. This is observed in advance by OM, and after confirming a region where the thin film-like particles on the microgrid have a large overlap (a region with a lot of reflected light) and a region with a small overlap (a region with a small amount of reflected light), transmission electrons Image observation and electron diffraction (ED) measurement were performed with a microscope (TEM).

  In the low-magnification TEM image, almost no special pattern was observed in a wide range in any region, but a large number of linear patterns were observed in part. Further, in the ED, a region having a lot of overlap gave a complex ED image in which a plurality of sets of 6-fold symmetric ED images (similar to graphite) overlapped with each other. This confirms that a plurality of thin film-like particles (the inside of each particle has high crystallinity) overlap each other. On the other hand, the region with little overlap gave only one set of the same 6-fold symmetric ED images. From this, it was found that the particles were single thin-film particles (the inside of the particles had high crystallinity). The lattice spacing obtained from these ED images (the lattice spacing created by carbon inside each layer, not the spacing between layers) is calculated to be about 0.215 nm with reference to the ED image of natural graphite. It was. This value indicates that the thin film-like particles have a dense crystalline carbon skeleton. Further, from the disappearance angle of the ED image when the mesh is inclined together with the thin film-like particles, the thickness of the basic layer giving the ED image is about 0.4 nm.

  Furthermore, when a linear pattern contained in the single thin film-like particle was enlarged and observed in the TEM image, a stripe pattern corresponding to the crystal lattice was seen inside the linear pattern. This indicates that there is a portion perpendicular to the plane of the mesh (parallel to the traveling direction of the electron beam). That is, this part is a structure in which a part of the particles that are flat in the dispersion liquid is, for example, in a stage where the particles are trapped on the microgrid while being dried, and rises and returns perpendicular to the plane direction. ). The interval between the lattice fringes was about 0.3 to 0.6 nm. The upper limit of this value is 0.61 nm (M between the basic layers of graphite oxide (when the thickness of the carbon skeleton is one carbon atom, there are hydroxyl groups on both sides of the carbon skeleton, and there is very little water between layers). Mermoux et al., Carbon, 29, 469 (1991)), the lower limit is close to the graphite base layer spacing of 0.34 nm. Therefore, for example, it is highly possible that the basic layer of graphite oxide or the basic layer of graphite oxide is heated with an electron beam and reduced to become graphite, and further corresponds to an intermediate structure thereof. Also, assuming that half the width of the wrinkles corresponds to the thickness of the thin film particles, a number of wrinkles are observed for the plurality of thin film particles, and the thin film particles are thin and about 2 nm thick. The actual measurement was about 7 nm.

As described above, it has been found that the obtained thin film-like particles are extremely thin and that they can be deformed while being a dense carbon skeleton because they are thin.
Example 2
About half of the remaining liquid homogenized in Example 1 is a regenerated cellulose tube (cross-sectional area 5 cm ² , thickness 30 μm, molecular weight cut off 12000 to 14000, assuming a globular protein with a density of 1 g / cm ^3. Calculated to pass through particles having a diameter of about 3.5 nm or less) and sealed, and dialyzed with about 20 times as water as an external solution. The outer liquid was changed about 10 times every about 2 days, and then the inner liquid was taken out to obtain a highly purified aqueous dispersion of thin film particles, 450 cm ³ . The concentration was 1.5 wt%.

By OM observation and TEM observation, extremely thin particles similar to those in Example 1 were confirmed.
Example 3
A part of the aqueous dispersion of the thin film particles obtained in Example 1 is centrifuged (7000 rpm, 30 minutes), the supernatant is discarded, and a small portion of the remaining highly viscous liquid is taken out and placed in a glass bottle. Diluted about 100 times with water. The glass bottle containing the liquid was placed on a hot plate at 150 ° C., and the liquid was heated (boiled) for about 20 minutes.

  The liquid obtained was diluted about 10 times with methanol and placed on a copper mesh with carbon microgrid and dried. This was observed in advance by OM, and after confirming a region with a large overlap and a region with a small overlap of thin film particles on the microgrid, the region was observed with a TEM.

  In any region, wrinkles similar to those of Example 1 were observed, but the wrinkles were not as sharp as in Example 1. An attempt was made to observe wrinkles present in a region with little overlap at a high magnification. However, the observation was not possible because the wrinkles disappeared due to the thermal influence of a strong electron beam. On the other hand, the wrinkles in the overlapping region can be observed even though they are blurred because the wrinkled particles are reinforced by other particles without wrinkles. The thickness was less than about 1 nm. This is smaller than in the first embodiment. Considering the size of the functional group such as a hydroxyl group present on the surface of the base layer, the thickness of the base layer is about 0.61 nm (M. Mermoux et al., Carbon, 29, 469 (1991)). The thickness obtained was close to that of the base layer, and the original multilayer structure was considered to be almost completely separated.

Example 4
Natural graphite with a large particle size (manufactured by ESC Co., Ltd., purity 99.76 wt% or more, purified product excluding metal elements by heating at 2900 ° C, diameter of about 1.4 to 2.0 mm, thickness of 0.1 mm or less An aqueous dispersion of thin film-like particles was obtained in the same manner as in Example 1 except that 1 g was used and oxidized in a standing time of 10 days with extremely gentle stirring.

As a result of OM observation, the obtained particles had an average size of about 0.1 mm in the plane direction, but contained particles of about 0.3 mm or more.
Example 5
The aqueous dispersion of thin film particles obtained in Example 1 was put in a centrifuge bottle, and acetone (relative dielectric constant 20.7 at 25 ° C., purity 99.5%, about 2 to 4 times that of the aqueous dispersion, operation was The magnification was increased as it proceeded), and redispersion, centrifugation (7000 rpm, 30 minutes), and discarding the supernatant were repeated a total of 3 times. The obtained precipitate had a concentration of about 1.7 wt% and was a non-fluid mass.

  Furthermore, 2-butanone (relative dielectric constant 18.5 at 20 ° C., purity 99%, about 4 times that of acetone dispersion) was added to this lump in a centrifuge bottle, followed by redispersion and centrifugation (7000 rpm, 30 minutes) ) And discarding the supernatant were repeated 3 times. The obtained precipitate had a concentration of about 2.0 wt% and was a non-fluid mass.

  As described above, the thin film-like particles can form a dispersion system even with a liquid other than water. However, as the dielectric constant decreased, the repulsion between the particles became smaller, and it became easier to generate a precipitate with a higher concentration. Further, since the anisotropy of the shape was high, the surrounding dispersion medium was retained even at a low concentration of several percent, and the fluidity of the dispersion was significantly lowered.

  Furthermore, 2-butanone was added to the precipitate of the thin film-like particles containing 2-butanone, and the mixture was stirred and redispersed to obtain a 2-butanone dispersion containing about 0.5% of the thin film-like particles. This liquid was mixed with an epoxy resin (cresol novolak epoxy type, imidazoles in a curing agent, 60 wt% 2-butanone solution), and heated to 60 ° C. under reduced pressure to remove 2-butanone. By curing for 2 hours, a composite in which about 1.5 wt% of thin film-like particles were uniformly dispersed was obtained.

Example 6
The aqueous dispersion of thin film particles obtained in Example 1 was placed on a glass plate, and the same aqueous dispersion was diluted 200-fold with methanol onto a copper mesh with a carbon microgrid, In any case, the thin film-like particles were reduced by drying at about 20 ° C. and then heating at 200 ° C.

  When the electrical resistance of the reduced product on the glass plate (thickness: about 30 μm, spread: about 2 cm × 2 cm) was measured with an electrode interval of 1 mm using a normal electrical tester, it was about 800Ω (with the same measurement method) The low-oriented graphite sheet having a thickness of 0.5 mm was 1.5Ω). Further, when this reduced product was peeled off from the glass plate and heated at 1000 ° C., it was about 5Ω.

  When the shape of the particles placed on the copper mesh was observed with OM, the shape was hardly changed before and after heating at 200 ° C. In addition, the particles were slightly colored by heating, and the reflectance was increased, but it was translucent because of the small thickness on the mesh.

Example 7
The aqueous dispersion containing the thin film-like particles obtained in Example 4 was diluted with water and placed on a glass plate, dried at about 20 ° C. and heated at 200 ° C. to reduce the thin film-like particles. As a result of OM observation, the particles before reduction on the glass plate could only be distinguished by the difference in light and dark, whereas the particles that had already been identified after reduction became extremely easy to identify. In addition, particles that could be identified by a weak contrast between light and dark were visible on the entire surface of the glass. It is considered that the particles are slightly colored by the reduction and the reflectance is increased, so that even thinner particles can be identified. These particles were also translucent after the reduction.

Example 8
The aqueous dispersion containing the thin film-like particles obtained in Example 1 was diluted about 50 times with water, aluminum powder (purity 99.9%, average particle size 3 μm) and hydrochloric acid (35 wt% aqueous solution) were added, and ultrasonic waves were added. And tried to hydrogenate the thin film particles. At least the surface of the thin film-like particles was reduced to become hydrophobic and macroscopically black particles, and most of them floated on the liquid surface. The resulting particles were washed with water, collected with a small amount of water without drying, and placed in a container.

  The particles were dried and various measurements were performed. As a result of OM observation, the obtained particles were translucent. As a result of TEM observation, agglomerates of single or plural thin film-like particles that were randomly bent and deformed like crushed paper were confirmed. Further, when X-ray diffraction measurement was performed, it was found that the peak corresponding to 0.83 nm observed in the original thin film-like particles disappeared completely, and the orientation became extremely low due to deformation and aggregation.

  The thin film-like particles according to the present invention are extremely thin and can be deformed inside the particles while having a dense carbon skeleton. When the affinity with the dispersion medium decreases, self-aggregation like a linear flexible polymer occurs. It has been found that this may occur.

Example 9
Two platinum electrodes (the area in contact with the liquid is about 6 cm ² and the interval is 1 cm each) are placed in the aqueous dispersion containing the thin film particles obtained in Example 1, and direct current (about 0.02 A at 19 V) is applied. Applied. A high-viscosity deposit having the same color as that of the thin film-like particles was generated at the positive electrode (power supply standard), and a black deposit was generated at the negative electrode as hydrogen was generated.

  Each electrode was placed in water in a separate container and each deposit was separated from the electrode. The deposit on the positive electrode was dispersed again in water, and particles similar to the original thin film particles were observed by OM. This was thought to be a thin film-like particle in which the hydroxyl groups were slightly reduced and temporarily aggregated. Moreover, the product of the negative electrode was precipitated without being dispersed in water, and the same aggregate as in Example 8 was observed by OM. This was considered to be an aggregate formed by reducing the thin film-like particles before a part of the generated hydrogen became hydrogen molecules.

Comparative Example 1
Oxidation and purification were carried out in the same manner as in Example 1 using synthetic graphite (manufactured by TIMCAL AMERICA INC., TIMREX KS75, purity 99.9% or more, average particle diameter of about 15 μm) instead of natural graphite. Although it became a dispersion of particles having a high affinity with water, which was clearly different from the synthetic graphite as a raw material, the viscosity was lower than that of the dispersion in Example 1, and a higher concentration of precipitate was produced even by centrifugation.

  When observed by OM, the majority of the non-planar particles were present and the number of the planar particles was small. These were all transparent, but most of them were thick enough to be easily identified by transmitted light.

Comparative Example 2
Oxidation and purification of graphite were carried out in the same manner as in Example 1 except that the oxidation time was set to 2 hours and particles that were likely to precipitate were not removed.

  When observed by OM, most of the particles having a diameter of about 40 μm or less were transparent and had a thin planar shape. Larger particles, on the other hand, consist of non-planar and planar particles, both thick enough to be easily discerned by transmitted light, with the periphery of the particles being transparent but the central portion being black and opaque. It was. The central part was considered not oxidized.

Comparative Example 3
In the same manner as in Example 1, graphite was oxidized and the dispersion at the stage after washing with a mixed aqueous solution of 3 wt% sulfuric acid / 0.5 wt% hydrogen peroxide was observed with OM. Most of the particles were planar particles, but most of them were thick enough to be easily identified by transmitted light. From comparison with Example 1, it was found that the separation of the layers progressed at the stage of removing small ions.

Comparative Example 4
The aqueous dispersion of thin film particles obtained in Example 1 was heated to about 50 ° C. on a glass plate placed on a hot plate to remove water, and a solid dried product having a thickness of about 0.1 mm was obtained.

The obtained dried product was put into water and stirred for 6 hours. There were aggregates that could be discerned with the naked eye, and complete redispersion was difficult.
The present invention includes the following aspects.

  1. A skeleton made of carbon obtained by oxidizing graphite and having a thickness of 0.4 to 10 nm, a planar size of 20 nm or more, and being dispersible in a liquid having a relative dielectric constant of 15 or more Thin film-like particles.

2. A dispersion of thin film particles, wherein the thin film particles according to claim 1 are dispersed in a liquid having a relative dielectric constant of 15 or more.
3. A thin-film graphite particle or an aggregate of thin-film graphite particles obtained by reducing the thin-film particles according to claim 1.

  4). 2. The method for synthesizing thin film particles according to claim 1, wherein the raw material is graphite having a diameter of the widest basic layer substantially equal to the diameter of the particles and having a single multilayer structure as a whole. .

5. 2. The method for synthesizing thin film particles according to claim 1, wherein graphite from which impurities are removed to 0.5% or less is used as a raw material.
6). The method for synthesizing thin film particles according to claim 1, wherein the graphite is oxidized with an oxidation time of 30 minutes or more per 10 µm of particle diameter of graphite.

7). 2. The method for synthesizing thin film particles according to claim 1, wherein after oxidation of graphite, the oxidation product is purified by setting the concentration of small ions other than those derived from the oxidation product in the reaction solution to 10 mol / m ³ or less. .

8). The method for synthesizing thin film particles according to claim 1, wherein after oxidation of graphite, the oxidized product is purified by setting the concentration at the time of dispersion of the oxidized product in the reaction solution to 5 wt% or less.
9. The method for synthesizing thin film particles according to claim 1, wherein particles having insufficient separation of the multilayer structure are settled and removed during purification.

  10. 2. The method for synthesizing thin film particles according to claim 1, wherein the dispersion of the thin film particles is heated in a temperature range of 50 to 150 [deg.] C. to further separate the multilayer structure inside the thin film particles.

11. 3. The method for producing a dispersion of thin film particles according to claim 2, wherein the liquid serving as the dispersion medium is exchanged from water to another liquid having a different relative dielectric constant.
12 The method for synthesizing thin-film graphite particles or aggregates of thin-film graphite particles according to claim 3, wherein the thin-film particles according to claim 1 are reduced by heating, a reducing agent or an electrode reaction.

Claims (8)

A skeleton made of carbon obtained by oxidizing graphite and having a thickness of 0.4 to 10 nm, a planar size of 20 nm or more, and being dispersible in a liquid having a relative dielectric constant of 15 or more A method for synthesizing thin film particles having
An oxidation step for oxidizing graphite to produce graphite oxide, and a purification step for removing small ions other than those derived from graphite oxide in the reaction solution after the oxidation step,
The method for synthesizing thin film particles, wherein the purification step repeats a centrifugation step and a redispersion step.   The method for synthesizing thin film particles according to claim 1, wherein the redispersion step includes a stirring operation.   3. The method for synthesizing thin film particles according to claim 1, wherein natural graphite is used as a raw material graphite.   3. The method for synthesizing thin film particles according to claim 1, wherein graphite from which impurities are removed to 0.5% or less is used as raw material graphite.   5. The method for synthesizing thin film particles according to claim 1, wherein in the oxidation step, graphite is oxidized for an oxidation time of 30 minutes or more per 10 μm of graphite particle diameter.   The method for synthesizing thin film particles according to any one of claims 1 to 5, wherein, in the purification step, small ions other than those derived from graphite oxide in the reaction solution are removed by setting the concentration of graphite oxide to 5 wt% or less. .   A method for synthesizing thin film-like graphite particles, characterized in that the thin film-like particles obtained by the synthesis method according to any one of claims 1 to 6 are reduced by heating, a reducing agent or an electrode reaction. A method for synthesizing an aggregate of thin film-like graphite particles, wherein the thin-film particles obtained by the synthesis method according to claim 1 are reduced by heating, a reducing agent or an electrode reaction.