JP2012184134A - Method for producing carbon material - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a carbon material having a high content rate of a thin-layer graphite which is, so to speak, an aggregate of graphene.SOLUTION: A carbonization step for carbonizing a woody raw material originated in a plant by a carbonization furnace under an inert gas atmosphere is performed, and a graphitization step for graphitizing a carbide obtained via the carbonization step at a temperature of ≥2,000°C under an inert gas atmosphere is performed, to thereby obtain a thin-layer graphite-enriched carbon material.

Description

  The present invention relates to a method for producing a carbon material. Specifically, the carbon material has a smooth surface having an average crystallite size of 5 nm or more, an interlayer distance of 0.340 nm to 0.347 nm, and a stacking number of 15 or less. The present invention relates to a method for producing a thin layer graphite (hereinafter simply referred to as a thin layer graphite) with high efficiency.

Since the discovery of fullerenes and carbon nanotubes, electronic nanocarbon materials have attracted a great deal of attention as basic materials for nanoscience and nanotechnology. These carbon materials are used in various composite materials because of their excellent properties such as high strength, high elastic modulus, and high conductivity. With the development of electronics technology in recent years, it is expected to be used as a conductive filler for electromagnetic shielding materials and antistatic materials, or as a filler for electrostatic coating on resins and fillers for transparent conductive resins. Has been. In addition, it is expected to be applied to electric brushes, variable resistors and the like as a material having high slidability and wear resistance. Furthermore, since it has high conductivity, heat resistance, and electromigration resistance, it has attracted attention as a wiring material for devices such as LSI.
In particular, in 2004, a single graphite sheet (graphene) was discovered and attracted great interest as a fundamental problem of solid state physics of Dirac-type fermions and from the aspect of applied technologies such as electronic devices / spin devices. I'm calling. Unlike fullerenes and nanotubes with closed ends, graphene forms an electronic state different from those because the sheet end face is an open end, and expresses unique electronic, magnetic, and chemical properties. It is being clarified from recent theories and experiments, and is expected to develop as a carbon-based molecular device. At the same time, the problem of graphene edge activity is closely related to the problem of electron transfer in secondary batteries and the like, and an important contribution to battery technology is expected.

  Currently, graphene is produced by a method of producing flakes by carefully peeling high crystalline graphite such as HOPG or scaly natural graphite with tape, or by producing ultrasonic flakes after being dispersed in tetrahydrofuran. The method is known. Also, Affune et al. Was attached to a highly oriented pyrolytic graphite (HOPG) substrate at an appropriate concentration by electrophoretic method and was heated at 1600 ° C. in an argon atmosphere, and one nanographene was obtained. (Non-patent Document 1).

A. M.M. Affoun, B.M. L. V. Prasad, H.M. Sato, T .; Enoki, Y. et al. Kaburagi and Y.K. Hisayama: Chem. Phys. Lett. 348, 17 (2001).

However, the graphene layer obtained in this way is about 100 nm ² at most, and the place where graphene is formed cannot be controlled. Industrially, in order to produce graphene, it is important to find a raw material having a precursor structure suitable for graphene production. Coal tar and asphalt, which are fossil fuels, have been used for a long time as raw materials for producing artificial graphite, but no method for producing graphene using these as raw materials has been reported. At the initial stage of carbonization, a laminated structure of an aromatic compound is formed, and a polymerization reaction is started. Therefore, it is considered difficult to produce graphene directly.

  In view of the above circumstances, an object of the present invention is to provide a technique for industrially producing graphene by a simple method. Specifically, a carbon material having a high content of thin-layer graphite that can be said to be an aggregate of graphene is provided. It is to provide.

  On the other hand, woody biomass materials are attracting attention as carbon materials that are less likely to cause environmental problems. Such raw materials are rich in cellulose and lignin. Although these compounds have low aromaticity, they contain a six-membered ring and also have sp3 bonds such as an oxygen bridge structure, so that lamination of aromatic compounds is inhibited during the carbonization reaction. It cannot become carbon. Therefore, it is interesting as a raw material that can produce graphene that is a single mesh surface.

〔Constitution〕
The characteristic configuration of the carbon material production method of the present invention for solving the above technical problem is:
A carbonization step of carbonizing a plant-derived wood-based material in an inert gas atmosphere in a carbonization furnace is performed, and the carbide obtained through the carbonization step is graphitized at a temperature of 2000 ° C. or higher in an inert gas atmosphere. Perform the graphitization process,
Thin layer graphite-enriched carbon material having a smooth surface with an average crystallite size of 5 nm or more, an interlayer distance of 0.340 nm to 0.347 nm, and a high content of thin layer graphite having 15 or less layers There is in point to get.
The thin-layer graphite referred to in the present invention is a compound having a structure similar to the partial structure of graphite as shown in FIG. 9, and each layer of graphite is laminated so as not to lose the physical properties as graphene. Thus, the crystallite size refers to the size of the range in which the laminated structure extends in a planar shape in the figure, and the interlayer distance refers to the distance between the surfaces when each layer is a plane. These can be easily determined by X-ray diffraction, and the number of stacked nuclear phases and planarity can be confirmed by an electron micrograph.

[Function and effect]
When a carbonization step of carbonizing a plant-derived wood-based material in a carbonization furnace in an inert gas atmosphere is performed, the organic matter contained in the wood-based material is carbonized and converted into a carbide having few heteroatoms. When performing a graphitization step of graphitizing this carbide at a temperature of 2000 ° C. or higher in an inert gas atmosphere, the carbide usually has a graphite structure in which a structure in which a number of smooth carbon layers are stacked gradually grows. In this case, first, sp2 bonds of the carbon layer grow to form a large number of carbon layers having a graphene structure, and the carbon layers are laminated to grow to form a graphite structure. This was confirmed experimentally by the present inventors.
That is, when the graphitization step is performed, a thin layer graphite (having a smooth surface having an average crystallite size of 50 nm or more and an interlayer distance of 0.340 nm to 0.347 nm during the graphitization step, It was confirmed that a carbon material having 15 layers or less is hereinafter simply referred to as such. Here, the interlayer distance of the thin graphite is sufficiently longer than the interlayer distance of the graphite, and the smooth surface is in a form that grows as a crystal having high smoothness and sufficiently large, and is clearly defined as carbide and graphite before graphitization. It has a structure that can be distinguished.
Further, it has been clarified by experiments described later that good thin-layer graphite does not grow when the graphitization step is performed at less than 2000 ° C.

  Such a thin layer graphite is expected to be structurally different from the carbides and graphites and can exhibit physical properties different from those of conventional carbon materials. For example, it is expected to be applied to semiconductor materials. Therefore, when performing the graphitization process, it is possible to obtain a thin-layer graphite-enriched carbon material by capturing the state of high content of the thin-layer graphite, and effectively utilizing the excellent physical properties of the thin-layer graphite. It is now possible to provide a carbon material that can be used.

〔Constitution〕
Moreover, it is preferable that the said woody raw material derived from a plant is sugarcane bagasse obtained by squeezing sugarcane.

[Function and effect]
Since the plant-derived woody material originally contains heteroatoms, carbon atoms are first carbonized to remove the heteroatoms while arranging the carbon skeleton into a six-membered ring, and then dehydrogenated from the six-membered carbon skeleton, Although it is considered necessary to grow sp2 bonds, the sugarcane bagasse contains a sufficient amount of cellulose and lignin, which are the basis of a six-membered ring structure, and also contains a lot of sp3 structures. This is considered to be the result of promoting the growth of the graphene structure of each layer rather than the growth of the laminated structure, and is considered to be a raw material suitable for obtaining a thin-layer graphite-enriched carbon material.

〔Constitution〕
Moreover, it is preferable that the content rate of the said thin layer graphite is 20% or more.

[Function and effect]
As described above, the physical properties of the thin-layer graphite-enriched carbon material are considered to be those that reflect the physical properties of the thin-layer graphite. However, if the content is too low, The physical properties of graphite that has been excessively graphitized appear strongly, and the physical properties of thin-layer graphite may not be sufficiently reflected. Therefore, it is preferable that the content rate of the said thin layer graphite is 20% or more. The content of the thin-layer graphite is obtained as a ratio of the peak at 2θ = 26 ° from the peak area ratio obtained by separating the 002 diffraction line by powder X-ray diffraction (XRD) using the pseudo-Voigt function. It is.

〔Constitution〕
Furthermore, while performing the carbonization process which carbonizes sugarcane bagasse obtained by squeezing sugarcane in an inert gas atmosphere in a carbonization furnace, the carbide | carbonized_material obtained through the said carbonization process is 2000 degreeC or more under inert gas atmosphere It is preferable to perform a graphitization step of graphitizing at a temperature of 2500 ° C. or lower.

[Function and effect]
That is, according to this thin layer graphite-enriched carbon material production method, it is known from the embodiments described later that a graphite layer content of about 30% can be obtained if the graphitization step is performed at 2000 ° C. or higher. If the temperature of the graphitization step is 2500 ° C. or less, it can be said that this is a production method that can be easily carried out industrially.

  Therefore, it is possible to provide a novel carbon material reflecting the physical properties of the thin-layer graphite, and utilization in various application fields can be expected.

Figure of carbon material graphitized bagasse at 1600 ° C Figure of carbon material graphitized bagasse at 1800 ° C Figure of carbon material graphitized bagasse at 2000 ° C Illustration of carbon material graphitized bagasse at 2200 ° C Illustration of carbon material graphitized bagasse at 2400 ° C Illustration of carbon material graphitized bagasse at 2600 ° C Illustration of carbon material graphitized bagasse at 2800 ° C Comparison of main X-ray diffraction peaks of carbon materials at different graphitization temperatures Conceptual diagram of thin graphite of the present invention

  Below, the manufacturing method of the carbon material of this invention is demonstrated. Preferred examples are described below, but these examples are described in order to more specifically illustrate the present invention, and various modifications can be made without departing from the spirit of the present invention. The present invention is not limited to the following description.

The carbon material production method of the present invention is, for example, a carbonization step of carbonizing a plant-derived woody raw material such as sugarcane bagasse obtained by pressing sugarcane in a carbonization furnace in an inert gas atmosphere to obtain a carbide. ,
A graphitization step is sequentially performed in which the carbide obtained through the carbonization step is graphitized in an inert gas atmosphere at a target temperature of 2000 ° C. or more for 0.5 to 3 hours. Here, a heating furnace is used in which the ambient temperature can be raised to 500 ° C./H up to 2000 ° C., 200 ° C./H from 2000 ° C. to 2500 ° C., and 50 ° C./H above 2500 ° C. In addition, the present inventors have experimentally known that the heating rate in the graphitization step and the holding time at the target temperature do not significantly affect the structure of the obtained carbon material.

  As a result, when analyzed by X-ray, a thin-layer graphite having a smooth surface with an average crystallite size of 5 nm or more, an interlayer distance of 0.340 nm to 0.347 nm, and a stacking number of 15 or less is 20 It has been found that a thin-layer graphite-enriched carbon material can be obtained that is contained at a high rate of ˜30%.

  Below, the more detailed embodiment of the manufacturing method of the carbon material of this invention is shown.

Embodiment
The bagasse previously dried at 100 ° C. was carbonized in a carbonization furnace at 1000 ° C. for 3 hours in a carbonization furnace, and then graphitized at various temperatures (1600-2800 ° C.) for 3 hours in an argon atmosphere. The obtained graphitized bagasse was subjected to structural analysis by X-ray diffraction measurement and TEM observation.
1 to 7 show the relationship between the firing temperature of the graphitized bagasse obtained and the structural analysis results, and Table 1 summarizes the structural characteristics of the thin-layer graphite contained in the obtained graphitized bagasse. .

  FIG. 5 shows a micrograph (TEM) (a) and X-ray diffraction (XRD) (b) of a carbon material graphitized with bagasse at 2400 ° C. A uniform graphite sheet from this micrograph is observed. When the edge part of a sheet is expanded, it turns out that it forms with the thin layer graphite laminated | stacked about 15 layers. Further, from this micrograph, it can be seen that about 30% of the carbon material has a thin graphite structure. Further, when observing the micrograph, from the X-ray diffraction result shown in FIG. 5B, when observing a peak with a diffraction angle of 2θ = 25 ° to 27 ° observed as one characteristic of the thin graphite, 2θ = 26. Crystallization (graphitization) has progressed from the observation of a peak at 0 ° C. From the peak position, the thin graphite produced here has a structure in which a graphene structure with an interlayer distance of 0.340 nm to 0.347 nm is laminated. I know that there is. Further, from the X-ray diffraction results, when a peak at a diffraction angle 2θ = 42 ° to 43 ° observed as another characteristic of the thin-layer graphite is observed, the crystallite size is about 5 nm and the thin-layer graphite content is 38.9%. You can see that (Note that the X-ray diffraction results and the analysis method are based on Hiroyuki Fujimoto et.al Carbon, 39, (2001) 1753-1761, which has obtained an approximate expression by extending Debye's scattering intensity equation. The content of the thin-layer graphite is a peak at a diffraction angle 2θ = 26 ° with respect to the total peak intensity at a diffraction angle 2θ = 25 ° to 27 ° when the 002 diffraction line is waveform-separated using the pseudo-Voigt function. (It is obtained as a percentage of strength.)

  FIG. 6 shows a micrograph (TEM) (a) and X-ray diffraction (XRD) (b) of a carbon material graphitized at 2600 ° C. bagasse. A uniform graphite sheet from this micrograph is observed. When the edge part of a sheet is expanded, it turns out that it forms with the thin layer graphite laminated | stacked about 15 layers. Further, from this micrograph, it can be seen that about 30% of the carbon material has a thin graphite structure. When observing the micrograph, from the X-ray diffraction result shown in FIG. 6B, when observing a peak at a diffraction angle 2θ = 25 ° to 27 ° observed as one characteristic of the thin-layer graphite, 26.5. Since the peak near 0 ° begins to grow, and the interlayer distance of the thin graphite corresponding to this peak is 0.3354 nm to 0.340 nm, although the thin graphite has been formed, each layer has a graphene-like property. It can be seen that it has begun to change to graphite properties. Further, from the X-ray diffraction results, it is found that the crystallite size is about 5 nm when the peak at the diffraction angle 2θ = 42 ° to 43 ° is observed.

  FIG. 7 shows a micrograph (TEM) (a) and X-ray diffraction (XRD) (b) of a carbon material obtained by graphitizing bagasse at 2800 ° C. A uniform graphite sheet from this micrograph is observed. When the edge part of a sheet is expanded, it turns out that it forms with the thin layer graphite laminated | stacked about 15 layers. Moreover, it can be seen from this micrograph that about 48% of the carbon material has a thin graphite structure. Moreover, when observing a micrograph, from the X-ray diffraction result shown in FIG. 7B, when a peak at a diffraction angle 2θ = 25 ° to 27 ° observed as one characteristic of thin-layer graphite is observed, 26.5. Since the peak near 0 ° begins to grow further and the interlayer distance of the thin graphite corresponding to this peak is 0.3354 nm to 0.340 nm, each layer is beginning to change to graphitic properties, but the thin graphite It can be seen that the production amount of is also increasing. Further, from the X-ray diffraction result, it is found that the crystallite size is about 15 nm when the peak at the diffraction angle 2θ = 42 ° to 43 ° is observed.

  FIGS. 3 and 4 show a micrograph (TEM) (a) and X-ray diffraction (XRD) (b) of a carbon material graphitized with bagasse at 2000 ° C. and 2200 ° C. (2200 ° C. is XRD only). A uniform graphite sheet from this micrograph is observed. When the edge part of a sheet is expanded, it turns out that it forms with the thin layer graphite laminated | stacked about 12 layers. Further, from this micrograph, it can be seen that about 30% of the carbon material has a thin graphite structure. When the micrograph is observed, from the X-ray diffraction result shown in FIG. 6 (b), when a peak at a diffraction angle 2θ = 25 ° to 27 ° observed as one characteristic of the thin-layer graphite is observed, it is around 26 °. And the interlayer distance of the thin graphite corresponding to this peak is 0.3354 nm to 0.340 nm, which indicates that each layer of the thin graphite begins to have graphene properties. Moreover, the thin-layer graphite contained in the obtained carbon material has a relatively high ratio of 29.4% and 27.2%.

  Moreover, when the example (refer FIG. 1, 2) which performed the graphitization process at 1600 degreeC and 1800 degreeC is seen, from the X-ray-diffraction result, the diffraction angle 2theta = 25 degrees observed as one characteristic of thin-layer graphite- The 27 ° peak is not observed, and it can be seen that the layer structure of the thin graphite is not formed or is very small even if it is generated.

  In the case where the graphitization process is performed at 1600 ° C. and 1800 ° C., as shown in FIGS. 3 to 7, in the example where the graphitization process is performed at 2000 ° C. to 2800 ° C., a peak near 26 ° appears. It can be seen that a layered structure of thin graphite is formed.

  Therefore, it can be seen that the carbon material containing the thin-layer graphite intended in the present application can be obtained at 2000 ° C. or higher, and that the graphitization step is preferably performed at 2000 ° C. to 2500 ° C.

  When the enlarged views near the diffraction angle 2θ = 26 ° of the thin X-ray diffraction peak are superimposed (see FIG. 8), the diffraction angle 2θ observed as one characteristic of the thin-layer graphite as the graphitization process temperature is increased. = 26 ° peak increased, and when the temperature was further increased, the peak near the diffraction angle 2θ = 26.5 ° began to increase, indicating that graphitization progressed.

Claims (5)

A carbonization step of carbonizing a plant-derived wood-based material in an inert gas atmosphere in a carbonization furnace is performed, and the carbide obtained through the carbonization step is graphitized at a temperature of 2000 ° C. or higher in an inert gas atmosphere. Perform the graphitization process,
Thin layer graphite-enriched carbon material having a smooth surface with an average crystallite size of 5 nm or more, an interlayer distance of 0.340 nm to 0.347 nm, and a high content of thin layer graphite having 15 or less layers A method for producing a carbon material.   The method for producing a carbon material according to claim 1, wherein the plant-derived woody material is sugarcane bagasse obtained by squeezing sugarcane.   The method for producing a carbon material according to claim 1 or 2, wherein the content of the thin-layer graphite is 20% or more.   While performing the carbonization process which carbonizes sugarcane bagasse obtained by squeezing sugarcane in an inert gas atmosphere in a carbonization furnace, the carbide obtained through the said carbonization process is 2000 ° C or more and 2500 ° C under an inert gas atmosphere. The manufacturing method of the carbon material which performs the graphitization process graphitized at the following temperatures.   An average crystallite size obtained by the method for producing a carbon material according to any one of claims 1 to 4 is 5 nm or more, a smooth surface having an interlayer distance of 0.340 nm to 0.347 nm is provided, and the number of stacked layers is 15 A thin-layer graphite-enriched carbon material having a high content of thin-layer graphite that is lower than the layer.