JP2003238131A - Random aggregate of thin particle with carbon skeletal structure - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a reduced form a random aggregate of thin particles with carbon skeletal structures. <P>SOLUTION: The random aggregate in which one or more thin particles are densely aggregated, is produced by partially or totally reducing the thin particles with the carbon skeletal structures in fluid. Having a large specific surface area, the aggregate is useful as an absorbent material for a low molecular weight compound or an ion, a catalyst and the negative electrode material of a battery. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a random agglomerate of thin film particles having a carbon skeleton.

[0002]

2. Description of the Related Art In recent years, the search for substances having high shape anisotropy and their applications have been rapidly progressing. As an anisotropic material having a carbon atom as a skeleton, one-dimensionally known graphite fibers and particularly thinned carbon nanotubes, and two-dimensionally known graphite, fluorinated graphite, graphite oxide, etc. ing. Of these, graphite, fluorinated graphite, and graphite oxide are all multilayer structures in which two-dimensional basic layers are stacked, and it is generally known that the number of layers is very large.
Furthermore, for graphite oxide, very thin ones with a small number of layers have been made (eg, NAKotov et al., Adv.M.
Ater., 8, 637 (1996)), the inventors of the present invention previously mentioned that it is desirable to call such graphite oxide (when the number of layers is one, for example, graphene oxide (graphene is the name of one layer of graphite)). ) And a graphite having a very small number of layers by reducing it (preferably called graphene when the number of layers is one). (Japanese Patent Application No. 2000-277307). Furthermore, the present inventors have obtained a particularly widespread thin film particle and a laminated aggregate in which thin film particles are laminated and expanded, and a reduced product thereof (Japanese Patent Application Nos. 2001-374537 and 20).
01-374538).

Here, the basic layer of graphite oxide is 1 carbon atom.
Carbon skeletons of one or two thicknesses (sp ³ carbon and sp ²
Consisting of carbon, sp ³ carbons and often), on both sides of the plane of the skeleton, such as acidic hydroxyl group is believed to have a structure bonded (e.g., T.Nakajima et al., Carbon, 26,357
(1988); M. Mermoux et al., Carbon, 29, 469 (1991)). When the thickness of the carbon skeleton is one carbon atom, hydroxyl groups are present on both sides of the carbon skeleton, and the amount of water between the layers is extremely small, the thickness of the basic layer is 0.61 nm. In addition, when the degree of oxidation is high and it is dried well, the oxygen contained in the oxidized graphite is 4
It is about 0 wt%.

The graphite oxide thin-film particles (hereinafter referred to as “oxidation-type thin-film particles”) are partially or completely reduced to be in an electronic state with many sp ² bonds similar to graphite, resulting in an electrical state. Higher conductivity. In particular, as a general behavior of graphite oxide, it is possible to form a graphite-like structure up to the inside of the multilayer by reduction by heating. It is known that an intermolecular force is generated between the particles to give a macroscopic shape such as an ordinary graphite film (J.Maire et al., Carbon, 6,555 (1968)). Oxidized thin film particles are reduced to thin film particles by the same heating (Japanese Patent Application No. 2000-277307).

Here, when the thin film particles are completely reduced, each basic layer of the thin film particles becomes a basic layer (graphene) of graphite. In the case of multi-layer particles, the interlayer distance substantially matches the interlayer distance of graphite, but the mutual positional relationship of the layers has a disordered structure that is more disturbed than that of graphite. Further, in the case of partial reduction, oxygen or the like remains in each basic layer, and the interlayer distance becomes larger than the interlayer distance of graphite.

The above-mentioned oxidized and reduced thin-film particles have a graphite oxide nanofilm (graphene oxide nanofilm if there is one layer) when the oxygen fraction is high, and a low oxygen fraction. When there is no oxygen, it can be called a graphite nanofilm (graphene nanofilm if there is one layer). Furthermore, as a unified approach, the oxidation type single-layer carbon nanofilm and multilayer carbon nanofilm, respectively,
It can be referred to as a reduced single-layer carbon nanofilm and a multi-layer carbon nanofilm. With the name of this carbon nanofilm, although it is a disordered layer as described above, there is no confusion caused by calling it graphite.

In such a thin film particle, each layer has a dense periodic carbon skeleton (a reduced type thin film particle has a particularly dense carbon skeleton with many pi electrons).
However, since the particles have a large spread as compared with the thickness, the particles can be deformed inside. Specifically, in the case of oxidized thin-film particles, when the affinity with the surrounding dispersion medium is relatively decreased, a shape that is bent and deformed like wrinkled thin paper is known. (For example, T.
Hwa et al., Phys. Rev. A44, R2235 (1991), X. Wen et al.,
Nature, 355, 426 (1992)). The deformed particles correspond to random agglomerates of thin film particles.

[0008]

However, in contrast to such a random agglomerate of oxidation type thin film particles, a random agglomerate of reduction type thin film particles has not been specifically known.

An object of the present invention is to provide a random agglomerate of the reduced thin film particles and a method for synthesizing the same.

[0010]

[Means for Solving the Problems] In order to achieve the above-mentioned object, the inventors of the present invention reduced an oxidative thin film particle in a dispersion liquid, or a random aggregate of an oxidizable thin film particle. The present invention relating to a random agglomerate of reduced-type thin film particles and a method for synthesizing the same was completed by studying reduction of a.

[0011]

BEST MODE FOR CARRYING OUT THE INVENTION For the oxidation type thin film particles (oxidation type carbon nanofilm) used in the present invention, Japanese Patent Application No.
000-277307 and Japanese Patent Application No. 2001-37453
As disclosed in 7 above, using graphite with few impurities and high crystallinity with a developed layer structure as a raw material, chemical or electrochemical oxidation is performed, and purification is performed to remove even smaller ions as much as possible, Use the one that has promoted spontaneous layer separation. Furthermore, as a method of particularly promoting the separation of layers, there is a method of heating a dispersion liquid of thin film particles at around 100 ° C.

As described above, a dispersion liquid, in which extremely thin thin film particles are dispersed in water, which can be called an oxidized carbon nanofilm, is synthesized.

The size of the thin film particles is such that the thickness (the direction of the c-axis in the raw material graphite) is 0.4 nm as a relatively small particle.
10 nm, preferably 0.4 nm to 5 nm, and the size in the plane direction (direction of a-axis and b-axis in raw graphite) is 2
It is 0 nm or more, preferably 200 nm or more, and more preferably 1 μm or more.

When the synthesis of the thin film particles is completed, the thin film particles are in the form of a dispersion liquid containing water as a dispersion medium. It is possible to replace the dispersion medium of this dispersion liquid with water, instead of water, with a highly polar liquid having a relative dielectric constant of about 15 or more, such as methanol, ethanol, acetone, or 2-butanone. As a means for using such a high-polarity liquid other than water as the main dispersion medium, a method of diluting by adding a sufficiently high-polarity dispersion medium other than water contained in the original dispersion liquid, There is a method in which a high-polarity dispersion medium other than water is added and then the supernatant is repeatedly removed by centrifugation and decantation to gradually exchange the high-polarity dispersion medium other than water.

The lower the permittivity of the dispersion medium, the lower the dielectric constant of the oxidation type thin film particles in the dispersion, the lower the affinity with the dispersion medium, and the more the aggregation progresses.

Various known reduction reactions using a reducing agent and electrode reactions (electrolytic reduction) can be used for the reduction of the oxidized thin film particles. However, especially when a reducing agent is used, complete reduction to the inside of the multilayer particles is considered difficult unless the basic layer is decomposed. On the other hand, the reduction by heating (J. Maire et al., Carbon, 6,555 (1968)), which is known as a general behavior of graphite oxide, can almost completely reduce the inside of the multilayer. As disclosed in Japanese Patent Application No. 2000-277307, the oxidized thin film-like particles are reduced into thin film-like particles by the same heating.

When the thin film particles are completely reduced, each basic layer of the thin film particles becomes a basic graphite layer (graphene). Interlayer distance (undefined for single layer)
Is almost the same as the interlayer distance of graphite, but the mutual positional relationship of the layers is a disordered structure that is a little more disturbed than that of graphite. In addition, the mutual positional relationship in the plane direction of the plurality of thin film particles has a very disordered (almost random) disordered layer structure, and further, there is a gap between the plurality of particles.

On the other hand, the degree of reduction of the thin film particles does not necessarily have to be perfect, and partial reduction may be used depending on the purpose. In this case, each basic layer contains oxygen and the like, and its interlayer distance is larger than that of graphite.

The reduction by heating is particularly carried out at 150 ° C to 200 ° C.
It rapidly occurs at around ℃, and further slowly progresses to 1000 ℃ or more in a non-oxidizing atmosphere or in vacuum. Further, it is expected that a larger crystal will be formed by pressing at a higher temperature. On the other hand, since it burns down in air at 600 ° C. or lower, only partial reduction in which oxygen or the like remains is possible. During the reduction by heating, desorption of water, oxygen, carbon compounds, etc. occurs. As a result, the oxygen fraction changes from about 40 wt% before reduction to about 0 to 35 wt%.

As described above, by heating at a relatively low temperature,
Oxidized thin film particles (oxidized carbon nanofilm)
From this, reduced thin film particles (reduced carbon nanofilm) are synthesized.

In the present invention, using the properties of the thin film particles as described above, a random agglomerate of reduced thin film particles is synthesized by the following two methods. The first method is to partially or completely reduce the oxidized thin film particles in the dispersion liquid (particularly, the aqueous dispersion liquid), reduce the affinity of the thin film particles for the dispersion medium, and carry out random coagulation. This is a method of producing aggregates. Each of the above methods can be used for the reduction in this case, but it is particularly preferable to use a reducing agent or to use a reducing agent and heating in combination. The second method is to use a dispersion medium having a relatively low dielectric constant and a little low affinity for the thin film particles to first generate random agglomerates of the oxidized thin film particles, and then use the dispersion medium. Take out the random agglomerates by removing by drying,
After that, it is a method of partial or complete reduction. It is particularly desirable to use heating for the reduction in this case.

In either method, when the concentration of the thin film particles in the dispersion is low, the number of aggregates of the single thin film particles is relatively large, and when the concentration is high, a plurality of thin film particles are formed. There are many agglomerates composed of particles. In addition, the lower the affinity between the thin film particles and the dispersion liquid, the more sharply and sharply each part of the particle is deformed, and each thin film particle (single thin film particle or multiple thin film particles Each thin film particle that constitutes an aggregate of particles shrinks smaller,
It becomes possible to aggregate at high density.

The random agglomerates of the reduced thin film particles obtained in the present invention have a structure in which each part of the thin film particles is bent and agglomerates randomly to form a gap between the respective parts, so It has a large specific surface area as compared with the case of stacking without bending and aggregating. Accordingly, it can be used as a low molecular weight or ion absorbing material, a catalyst, a negative electrode material of a battery, and the like.

[0024]

The present invention will be described in more detail with reference to the following examples, but the present invention is not limited thereto.

Example 1 Natural graphite (SNOC, SNO-25, purity 9)
9.97 wt% or more, purified product obtained by removing impurities and the like by heating at 2900 ° C., 10 g of average particle size of 24 μm, particle size of 4.6 μm or less and 61 μm or more of 5 wt% each, sodium nitrate (purity 99%) 7. 5 g, sulfuric acid (purity 96%) 621
g, and 45 g of potassium permanganate (purity 99%) were placed in a mixed solution, and the mixture was allowed to stand at about 20 ° C. for 5 days with gentle stirring. The obtained highly viscous liquid was added to 1000 cm ³ of 5 wt% sulfuric acid aqueous solution (water having a conductivity of less than 0.1 μS / cm was used for dilution (hereinafter the same)) with stirring for about 1 hour. , And stirred for another 2 hours. 30 g of hydrogen peroxide (30 wt% aqueous solution) was added to the obtained liquid,
Stir for 2 hours.

This solution was purified by centrifugation using a mixed aqueous solution of 3 wt% sulfuric acid / 0.5 wt% hydrogen peroxide and centrifugation using water to obtain an aqueous dispersion of thin film particles. From the weight change of a part of the liquid before and after drying, the concentration of thin film particles in the liquid was 0.45 wt%. In addition, in the elemental analysis of the thin film particles dried in vacuum at 40 ° C., oxygen is about 42 wt%,
Hydrogen was about 2 wt%.

The resulting aqueous dispersion was placed on a glass plate and dried, 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).

Dilute the same aqueous dispersion 100 times with water
And place it on a glass plate to dry, and then flatten the thickness of the thin-film particles.
I tried to get the average value. Dry from the liquid and put on a glass plate
Calculated the average thickness of a large number of attached particles is about 12 nm
(The particle density is 2.1 g / cm ³And if)
In addition, about 3 particles or more are overlaid on the entire surface where the liquid spreads
Was confirmed by optical microscope (OM) observation (grain
Although the child is extremely thin, it has a higher reflectance than glass,
I was able to separate). From this, the thickness of each thin film particle is an average
It was less than 4 nm. Also, in this observation, thin film particles
It is confirmed that the average size in the plane direction is about 20 μm.
It has been certified.

This aqueous dispersion of thin film particles of the oxidative type was diluted about 50 times with water to prepare an aluminum powder (purity 99.9).
%, Average particle size 3 μm) and hydrochloric acid (35 wt% aqueous solution) are added, ultrasonic irradiation is performed, and hydrogen treatment (reduction) of thin film particles is performed.
I went. At least the surface of the thin film particles was reduced to become hydrophobic and macroscopically black particles, and most of them floated on the liquid surface. The generated particles were washed with water by filtration, collected together with a small amount of water without being dried, and put in a container.

The particles were dried and various measurements were performed. OM
Upon observation, the particles obtained were translucent. Combined with the hydrophobic and macroscopically black color described above, the reduction of the thin film particles was considered to be incomplete. In addition, when observed by a scanning electron microscope (SEM), the paper was bent and deformed as if it had been wrinkled, and aggregated at high density.
Aggregates of single or multiple thin film particles were confirmed.
Further, when observed by a transmission electron microscope (TEM), a structure similar to SEM was confirmed at low magnification, and a sharp bending portion of the carbon skeleton was also confirmed at high magnification. Further, when X-ray diffraction measurement was performed, the peak corresponding to 0.83 nm completely disappeared, which confirmed that the random aggregate had extremely low orientation.

Example 2 As in Example 1, an aqueous dispersion of oxidized thin film particles having an average spread of about 20 μm and an average thickness of less than 4 nm was placed in a centrifuge bottle, and acetone (specific dielectric at 25 ° C.) was added. Rate 20.
7, purity 99.5%, about 2 to 4 times that of the aqueous dispersion, the magnification increases as the operation proceeds), redispersion and centrifugation (7000 rpm, 30 minutes), and discarding of the supernatant are repeated 3 times in total. It was The obtained precipitate has a concentration of about 1.7 wt%,
It was a lump without fluidity.

This precipitate was left under a reduced pressure to remove acetone, and a lump-like solid having a volume of several tens of minutes as compared with the original precipitate was obtained. As a result of SEM observation, a denser aggregate (which is considered to include a layered overlapping portion in addition to a random aggregation portion) was confirmed as compared with Example 1.

This agglomerate was removed from room temperature to 500 in about 10 hours.
The temperature was raised to 0 ° C., followed by heating and reduction to obtain a reduced random aggregate.

This reduced random agglomerate was placed in a closed container, hydrogen was introduced, and the hydrogen storage amount was measured from the pressure decrease. The storage amount was about 0.02 wt%.

[0035]

INDUSTRIAL APPLICABILITY The random agglomerates of thin film particles (reducing carbon nanofilms) having a skeleton made of reduced carbon according to the present invention are sharply and sharply bent at each part of the thin film particles to have a high density. Has an aggregated structure. Since this aggregate has a large specific surface area, it can be expected to be used as a low molecular weight or ion absorbing material, a catalyst, a negative electrode material of a battery, and the like.

[Brief description of drawings]

FIG. 1 is a scanning electron microscope image of a random aggregate of reduced thin film particles (synthesized by hydrogen treatment) (an example of the whole aggregate).

FIG. 2 is a scanning electron microscope image of a random aggregate of reduced thin film particles (synthesized by hydrogen treatment) (enlarged part of FIG. 1).

FIG. 3 is a transmission electron microscope image of a random aggregate of reduced thin film particles (synthesized by hydrogen treatment) (there is a sharp bend in the thin film particles in the center).

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Takuya Goto             22 Wadai, Tsukuba City, Ibaraki Mitsubishi Gas Chemical             Research Institute, Inc. (72) Inventor Mitsugu Taniguchi             22 Wadai, Tsukuba City, Ibaraki Mitsubishi Gas Chemical             Research Institute, Inc. F-term (reference) 4G046 CA01 CB09 CC10                 4G066 AA04B AA06D BA20 BA36                       BA50 CA38 FA03 FA11 FA17                       FA37

Claims (7)

[Claims] 1. The thickness obtained by oxidizing graphite is 0.4.
nm to 10 nm, the size in the plane direction is 20 nm or more,
Liquid having relative permittivity of 15 or more is lyophilic, and thin film particles having a skeleton made of carbon have an oxygen content of 0 to 35 wt.
A random agglomerate obtained by partially or completely reducing the amount to 1% and aggregating one or more. 2. The thin film particles are sharply and abruptly bent, and aggregated at a high density.
The random aggregate according to 1. 3. The method for synthesizing random aggregates according to claim 1 or 2, wherein the thin film particles are partially or completely reduced in a liquid. 4. The thin film particles are dispersed in a dispersion medium having a relatively low affinity for the thin film particles, the dispersion medium is removed, and then the particles are partially or completely reduced. The method for synthesizing a random aggregate according to claim 1 or claim 2. 5. A low molecular weight or ionic absorption material using the random aggregate according to claim 1. 6. A catalyst using the random aggregate according to claim 1. 7. A negative electrode material for a battery using the random aggregate according to claim 1.