JP2003054922A - Structure including carbon-coated catalyst nanoparticle, method of making such structure, and method of producing carbon nanostructure therefrom - Google Patents

Abstract

PROBLEM TO BE SOLVED: To increase the productivity of carbon nanotubes of high quality. SOLUTION: The composite carbon structures that contain carbon-coated catalyst nanoparticles, and that are used in subsequent arc-discharge or laser ablation methods to produce carbon nanostructures, particularly single walled nanotubes in an increased amount and of a well-defined quality. Also, a method of making the composite carbon structures, and a method of using the composite carbon structures to produce carbon nanostructures, such as SWNTs. Further, a catalyst support for CVD growth of carbon nanostructures, wherein the catalyst support includes carbon-coated catalyst nanoparticles. Also, a method of making the catalyst support, and a method of using the catalyst support to grow carbon nanostructures by CVD.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to carbon-coated nanometer-sized particles (nanoparticles), and more particularly to carbon-coated catalyst nanoparticles. Furthermore, the present invention relates to a method for producing carbon nanostructures from carbon-coated catalyst nanoparticles.

[0002]

BACKGROUND OF THE INVENTION Most of the previous work on one-dimensional carbon nanostructures such as single-walled nanotubes (SWNTs), multi-walled nanotubes (MWNTs) and carbon nanofibers has been
It has been synthesized using powder catalysts starting from at least the micrometer scale. For example, "Helica
l Microtubuls of Graphiti
c Carbon ", by S.C. Iijima, Nat
ure, vol. 354, Nov. 7,1991, pp
56-58, "Single-Shell Carbo
n Nanotubes of 1-nm diameter
ter ”, byS. Iijima, Nature, vo
l. 363, June. 17, 1993, pp603-
605, "Production of Carbon
Nanotubes ", by C. Journet
et al. Appl. Phys. Aug. 1998,
vol. 67, pp. 1-9, "Nanotubes
from Carbon ", by P. W. Ajaya
n, Chem. Rev. , 1999, vol. 99,
p. 1787, and "Gas-phase Puri.
fiction of Single-wall C
arbon Nanotubes], by J. L. Z
immanman et al, Chem. Mate
r. , 2000, vol. 12, p. See 1361.

A schematic diagram of a typical reaction using a micrometer size catalyst is shown in FIG. As shown in FIG. 5, graphite powder 1 of micrometer size
0 and micrometer sized oxide coated catalyst particles 12 are reactants in carbon rods used as anodes in typical arc discharges or as source materials in typical laser ablation. The reactants are exposed to heating by arc discharge or laser ablation to produce the desired SWNT structure. 1 ms, as represented by arrow X
During the first part of the shorter reaction, the reactants are exposed to heat above 4000 K in the reaction zone. As a result of this part of the reaction, the micrometer-sized particles are first produced as intermediate products, micrometer-sized carbon particles 14, oxygen substances 16, metal-carbon clusters 18, oxides 20 and nanometer-sized carbon particles. Crushed to 30. Then, in the second part of the reaction, which occurs after 1 ms, the temperature decreases as the product is removed from the heat source (either the arc of the arc discharge or the laser of the laser ablation), as represented by the arrow Y, Certain carbon-coated catalyst particles 1, metal chips 24
The SWNTs 22, the amorphous carbon 28, the oxide 20, and the nanometer-sized carbon particles 30 are formed from the intermediate product.

However, the use of micrometer sized catalysts can lead to low catalyst productivity, and thus involves some drawbacks which result in low content and purity of the final product produced in the reaction zone.

First, these micrometer-sized catalysts do not exhibit catalytic activity until they are broken into nanoscale (ie, nanometer-sized) clusters, even clusters on the sub-nanoscale. However, the reaction time is generally very short. For example, SWNT
In the case of laser ablation synthesis of, the time available for SWNT growth is less than 1 second. Therefore, there is not enough time to break all the catalyst into usable particles that are small enough. For this reason, the use of catalyst particles is inefficient when they are used in micrometer size.

Secondly, end products, such as soot from laser ablation or arc discharges containing the desired carbon nanostructures, are not preferred because the metal catalyst particles are not fully utilized during very short reaction times. Contains high metal particle content. That is, since the catalyst is not completely depleted during the reaction, there is a large amount of unused catalyst in the final product and thus the final product is not pure.

Thirdly, these micrometer-sized metal powders, when used as catalysts, are usually unfavorably coated with a thin layer of metal oxide, which thin layer therefore contains oxygen in the reaction zone. Gives off a substance. And oxygen substances (O ₂ , O ⁻ , O ^{2 −} , etc.) are carbon substances (C ⁺ ,
C2 ⁺ , C3 ^+, etc.), whereby oxygenates interfere with the formation of well-defined carbon structures. Therefore, due to oxygen interference, the desired carbon nanostructure product contains defects and produces a significant amount of amorphous carbon.

Fourth, these micrometer sized catalysts are not mixed with carbon in advantageous proportions. That is, there is too much catalyst for carbon in a given cubic micrometer sized volume, which results in lower catalyst productivity and lower end product purity.

In the prior art, carbon coated metal nanoparticles have also been produced. See, eg, US Pat. No. 5,965,267 by Nolan et al.
However, Nolan does not recognize these carbon-coated metal nanoparticles as catalysts for producing carbon nanostructures. That is, Nolan carbon-coated metal nanoparticles are the final products and are used as thermal composites (such as adhesives in heat sinks), reinforced composites and magnetic particle recording media.

[0010]

The object of the present invention is to overcome the drawbacks of the prior art. More specifically, the object of the present invention is to use the catalyst particles more efficiently in the production of carbon nanostructures, and in particular SWNTs.
Furthermore, it is an object of the present invention to increase the production purity of carbon nanostructures, by reducing the amount of metal catalyst particles present after the nanostructure production process, eg laser ablation or arc discharge. Furthermore, it is an object of the present invention to reduce the amount of manufacturing defects in the carbon nanostructures and the amount of amorphous carbon by reducing the oxygen material in the reaction zone that forms the desired carbon nanostructures. Is. Further, the object of the present invention is to
Increasing the catalyst productivity by obtaining an advantageous catalyst-to-carbon ratio in a given cubic micrometer-sized volume, and producing a higher purity of carbon nanostructures.

[0011]

SUMMARY OF THE INVENTION To overcome the above-referenced problems, other problems and deficiencies in the prior art, the present invention provides a nanometer sized catalyst that is smaller than the conventionally used micrometer sized catalyst particles. Provide particles (catalyst nanoparticles). Since catalyst nanoparticles smaller than a few hundred nanometers are already on a small scale, they are easily used during the short reaction times associated with the production of carbon nanostructures. That is, the catalyst nanoparticles do not have to be crushed from the micrometer size to be used, they are easier to use as such, leading to higher efficiency in using the catalyst particles. These catalytic nanoparticles are used to form carbon-catalyst rods, which can be used, for example, for the production of carbon nanostructures by laser ablation or arc discharge.

Since it is not necessary to crush catalyst nanoparticles to crush micrometer-sized catalyst particles,
The catalyst nanoparticles are more completely depleted during the short reaction times associated with the production of carbon nanostructures. Thus, as-produced carbon nanostructures are purer because the catalyst nanoparticles are more completely depleted during carbon nanostructure synthesis. That is, since the catalyst nanoparticles are exhausted more efficiently and completely, the amount of catalyst particles remaining in the as-produced carbon nanostructure is small.

Furthermore, the catalytic nanoparticles according to the invention are coated with carbon. The morphology of the carbon coating can vary from the amorphous graphite layer to the aligned graphite layer. Since the carbon coated catalyst nanoparticles are coated with carbon, they are not oxidized and therefore do not carry oxygen substances into the reaction zone. And since the catalyst particles of the present invention do not carry oxygen substances into the reaction zone, the desired carbon nanostructures have fewer defects and produce less amorphous carbon.

Moreover, because the catalyst nanoparticles are coated with carbon, the carbon to catalyst ratio is more advantageous on a cubic micrometer size scale, whereby the use of catalyst particles is more efficient. That is, the catalyst nanoparticles are uniformly distributed in the carbon on a scale that is the same dimension as the size of the desired carbon nanostructure final product. Thus, the catalyst particles and carbon readily interact to enhance catalyst productivity and, in turn, enhance the purity of the desired carbon nanostructures.

The carbon-coated catalyst nanoparticles can be used in various methods for producing carbon nanostructures, such as laser ablation, arc discharge and CVD. When used in laser ablation or arc discharge, carbon coated catalytic nanoparticles are formed into rods or other structures by mixing those particles with carbon particles and a binder. When used in CVD, carbon coated catalyst nanoparticles are deposited on the catalyst support material. The present invention includes rods or other structures, methods of making such rods and methods of using such rods to make SWNTs. Further, the invention includes catalyst support materials having carbon coated catalyst nanoparticles thereon, methods of making such catalyst supports, and methods of using such catalyst supports.

More particularly, the present invention relates to carbon coated catalyst nanoparticles, each of which comprises nanometer sized catalyst particles surrounded by a carbon coating, carbon nanoparticles, and said carbon coated catalyst nanoparticles. The above and other objects and advantages are achieved by providing a composite carbon structure for producing a carbon nanostructure, which comprises a binding agent that binds to

Further, the present invention includes a step of using the above-mentioned composite carbon structure as a first electrode, and a step of performing an arc discharge using the first electrode and a second electrode containing carbon. The above and other objects and advantages are achieved by providing a method of manufacturing SWNTs.
Alternatively, the above-mentioned composite carbon structure can be used as a source material in laser ablation for manufacturing SWNTs.

Still further, the present invention provides soot by, for example, performing a first arc discharge between a first electrode containing a carbon rod filled with a catalyst and a second electrode containing pure carbon. And collecting the soot, grinding the soot and mixing the soot with a binder material to form a first intermediate product, pressing the first intermediate product, and thereafter Heating the first intermediate product and subsequently cooling the first intermediate product, thus forming the composite carbon structure, to produce a composite carbon structure for the production of carbon nanostructures. The above and other objects and advantages are achieved by providing a method of doing so.

Alternatively, instead of generating soot by arcing, the soot can be generated by any other suitable method, such as laser ablation using a carbon rod filled with catalyst.

Still further, the present invention is directed to carbon-coated catalyst nanoparticles, each containing nanometer-sized catalyst particles surrounded by a carbon coating, and an inorganic catalyst support material uniformly mixed with said carbon-coated catalyst nanoparticles. The above and other objects and advantages are achieved by providing a catalyst support for CVD, including and.

Further, the present invention includes the steps of forming the above-mentioned catalyst carrier, heating the catalyst carrier, and supplying a carbon source to the catalyst carrier in order to grow carbon nanostructures. The above and other objects and advantages are achieved by providing a method of forming carbon nanostructures by CVD.

Finally, the invention provides a carbon coating, for example by performing a first arc discharge between a first electrode comprising a carbon rod filled with a catalyst and a second electrode comprising carbon. Generating soot containing catalyst nanoparticles, collecting the soot, and purifying the soot by removing particles other than the carbon-coated catalyst nanoparticles in the soot, thus producing purified soot. A method for producing a catalyst for CVD of carbon nanostructures, which comprises the steps of: suspending the purified soot in a solvent and dispersing the purified soot on a catalyst support material. By accomplishing the above and other objects and advantages.

Again, instead of generating soot by arc discharge, any other suitable method can be used, for example laser ablation of carbon rods filled with catalyst.

[0024]

The above and other objects and advantages of the present invention will become more apparent by describing in detail the preferred representative embodiments of the present invention with reference to the accompanying drawings. . In the drawings, similar numbers refer to
Throughout the several figures, similar or corresponding parts are represented.

Carbon-coated nanoparticles, eg catalyst nanoparticles, are mainly abundant in soot produced by laser ablation or arc discharge of carbon-metal composites. These carbon coated catalyst nanoparticles are generally very stable at ambient conditions due to the carbon coating. However, it is possible to release the catalytic nanoparticles from the carbon coating rapidly at sufficiently high temperatures. Once the particles are released from the carbon coating in an inert atmosphere, the catalytic nanoparticles become very active, and the particles are made by suitable techniques (laser ablation, electric arc discharge or simple arc discharge, chemical vapor deposition (CVD)). Etc.) and controlling the growth conditions (temperature, pressure, etc.), and can be used as a catalyst for the synthesis of one-dimensional carbon nanostructures such as SWNTs and carbon nanofibers of various shapes.

According to the present invention, these carbon coated catalyst nanoparticles are formed into carbon rods or other structures. The shape of the rod or other structure is not critical and can be any shape suitable for arc discharge or laser ablation. The carbon coated catalyst nanoparticles can be used as-produced in the initial laser ablation method or the arc discharge method. Alternatively, the carbon coated catalyst nanoparticles can be treated or purified prior to using the particles to form carbon rods or other structures. This rod or other structure can then be used in a second laser ablation or arc discharge or CVD to produce high purity defined carbon nanostructures.

The composition of the catalyst nanostructure is, for example, Ni,
It can be a pure metal such as Co or a metal carbide such as YC ₂ and CeC ₂ . Although these metals and metal carbides are preferred, the catalyst nanoparticles of the present invention can be used as catalysts in the production of carbon nanostructures such as Mo, LaC ₂ , Gd, three-dimensional (3D) transition metals, lanthanide series metals, and the like. It can be any composition of particles suitable for use. The latter group is not as effective as the former group and is more expensive. Therefore, the former group is preferred.

The shape of the catalytic nanoparticles is not as important as their size. Thus, the catalytic nanoparticles can have any shape, such as spheres, cubes, cones, or any irregular shape. On the other hand, the size of the catalytic nanoparticles is more important, which is between 0.1 nm and 100 nm.
It is in the range of nm. This range is, for example, SWNT, M
It is advantageous for manufacturing one-dimensional carbon nanostructures such as WNT and bamboo-like carbon nanofibers. Here, smaller size particles are beneficial for the production of SWNTs and MWNTs, whereas larger size particles are beneficial for the production of carbon nanofibers. Preferably, the size of the catalytic nanoparticles is in the range 1 nm to 50 nm.
The preferred range is easy to produce and is most abundant in soot produced from laser ablation or arc discharge performed on carbon-metal composite rods. The size of the catalytic nanoparticles can be controlled by controlling the carbon to metal ratio in the carbon rod used for initial laser ablation or arc discharge. The higher the carbon to metal ratio, the smaller the average size of the catalytic nanoparticles. If the size of the catalyst nanoparticles is too small,
Catalytic nanoparticles are difficult to manufacture and are therefore expensive. On the other hand, if the size of the catalyst nanoparticles is too large, the catalyst nanoparticles must first be crushed before use, as discussed above for micrometer sized catalyst particles, so that the catalyst nanoparticles are of high purity alignment. It is neither effective nor efficient in producing carbon nanostructures.

As mentioned above, the carbon coating on the catalytic nanoparticles can vary from amorphous carbon to ordered graphite layers. If amorphous carbon is used, it should be sufficient to completely surround the catalytic nanoparticles. When using a graphite layer, it is generally formed concentrically around the catalytic nanoparticles. The number of graphite layers can range from 1-100 most commonly found in soot produced by laser ablation or arc discharge,
The number of graphite layers is preferably in the range 1-10. The number of graphite layers does not depend on the size of the underlying catalyst nanoparticles, but rather can be determined as follows. If less than one graphite layer is present, the catalytic nanoparticles are not well protected from oxidation. The same applies if there is not enough amorphous carbon to completely surround the catalyst nanoparticles. On the other hand,
If there are too many graphite layers, the catalytic nanoparticles will
It is not effectively used to form the desired carbon nanostructures. That is, if there are too many graphite layers, there is not enough time during the reaction to fracture the carbon coating to the point where the catalyst nanoparticles are exposed for use as a catalyst. Similarly, there is too much amorphous carbon, ie, for example, the MWN surrounding the catalyst nanoparticles.
If there are too many T walls, the catalytic nanoparticles will not be effectively used as catalysts in forming carbon nanostructures.

The concentration of carbon coated catalyst nanoparticles used in the rod or other structure may be varied by laser ablation, arc discharge, CVD, etc. to produce the desired carbon nanostructure from the rod or other structure. Varies based on method of manufacture.

When using the laser ablation method or the arc discharge method, carbon rods are used as both a catalyst and a carbon source for the growth of the desired carbon nanostructures. If there is too much metal catalyst (ie too much carbon coated catalyst nanoparticles), there will be metal left in the final product and, worse, impurities will increase. On the other hand, if there is not enough metal catalyst (ie, too few carbon-coated catalyst nanoparticles), there is not enough catalytic activity to conveniently produce carbon nanostructures. Ideally, the goal is to use just enough metal catalyst to produce the desired carbon nanostructures. Therefore, according to the present invention, the weight percentage of carbon coated catalyst nanoparticles is in the range of 1-80. Here, less carbon coated catalyst nanoparticles are required for laser ablation than required for arc discharge. The balance of the rod or other structure is carbon, preferably pure carbon. Further, in these methods, the weight percent of carbon coated catalyst nanoparticles is preferably in the range of 2-30.

A schematic diagram of a typical reaction using nanometer-sized catalyst particles according to the present invention is shown in FIG.
As shown in FIG. 1, nanometer-sized carbon particles 3
0 and carbon-coated catalyst nanoparticles 1 are reactants in a carbon rod used, for example, as a first electrode in a typical arc discharge or as a source material in a typical laser ablation. To produce the desired SWNT nanostructures 22, the reactants are exposed to heat, for example by laser ablation or arc discharge. As represented by arrow X, during the first part of the reaction shorter than 1 ms, the reactants are exposed to heat above 400 K in the reaction zone. As a result of this part of the reaction, the nanometer-sized particles are easily broken into intermediate products, smaller nanometer-sized carbon particles 30 and metal-carbon clusters 18. Then, in the second part of the reaction, which occurs after 1 ms, the temperature decreases as the product is removed from the heat source (either the arc of the arc discharge or the laser of the laser ablation), as represented by the arrow Y, the product. Carbon coated catalyst particles 1
And the SWNT 22 with the metal tip 24 is easily formed from an intermediate product.

Compared to the representative prior art reaction shown in FIG. 5, the present invention achieves a lower impurity product while at the same time achieving a higher percentage of the desired SWNTs.

On the other hand, when using the CVD method, rods (or other articles containing carbon-coated catalytic nanoparticles, usually carriers)
Is mainly used as a catalyst. Another carbon source is introduced into the reaction zone in such a CVD process. Also, C
The temperature in the VD method (400 to 1200 ° C., preferably 800 to 1200 ° C.) is the temperature in laser ablation or arc discharge (typically to require more catalyst for the CVD reaction to produce the desired carbon nanostructure). In general, it is lower than about 4000 ° K). Therefore, the concentration of carbon-coated catalyst nanoparticles for the CVD method is 5
˜95% by weight (wt%). Preferably, the concentration of carbon coated catalyst nanoparticles is 20-95% by weight.
Is. In this case, the remainder is a carrier material that acts as a separator to prevent the metal from aggregating as it melts during the CVD reaction. The carrier material is, for example, an inert inorganic material such as Al ₂ O ₃ , SiO ₂ , silica wafer, porous aluminum film, silica zeolite.

[0035]

Example 1 In this example, SWNTs are prepared by arc discharge of a carbon rod containing carbon coated Ni and CeC ₂ nanoparticles. First, a carbon rod containing carbon coated catalyst nanoparticles is formed. Secondly, arc discharge is performed using the carbon rod manufactured in the first step.

Preparation of Carbon Rods Containing Carbon Coated Catalyst Nanoparticles A pure carbon rod measuring 1.5 × 1.5 × 10 cm was used as the cathode and metal (15 wt% Ni, 6
By wt% CEC ₂₎ arc discharge using carbon rods which are uniformly filled, soot and cathode deposition discharge (cat
hode deposit discharge) was generated. Soot and deposits were generated under the following conditions. 7
A pure helium atmosphere of 00 torr was used as a buffer gas.
The current density was set to 180 A / cm ² . Voltage 30 ~
It was automatically controlled to be between 40V. The soot and deposits formed contained 5-20 wt% SWNTs.
A representative TEM image of this soot is shown in Figure 2A.

The soot and deposits are collected, ground well and then a binder material 1-5, such as pitch or carbon paste.
Mixed with wt%. Although carbon-containing binders are preferred, they are not required. Any suitable binder can be used. Further, the amount of binder should be sufficient so that the rod is strong and easy to handle. The mixture was then filled into stainless steel molds measuring 1 × 10 × 10 cm and pressed under high pressure, ie 1-10 ton / cm ² . The size and shape of the mold is not critical as long as sufficient pressure can be applied to mold the soot, cathode deposits and binder into a fixed shape that is easy to handle. After pressing, the pressed soot containing carbon coated catalyst nanoparticles was placed in a furnace with a mold and heat treated at 400-800 ° C. for 10 hours in a vacuum, Ar atmosphere or other inert gas atmosphere. . The furnace temperature and heating time can be different. For example, shorter times can be used in conjunction with higher temperatures and longer times can be used in conjunction with lower temperatures. The key elements are to completely dry and / or solidify the binder and to prevent the carbon coated catalyst nanoparticles from being incinerated. After complete cooling, ie cooling to room temperature, the pressed soot was released from the mold and then cut into 1 × 1 × 20 cm smaller bars. Although the mold and pressed soot were allowed to cool completely in this example, this is not essential.

Soot pressed (and thus smaller bars cut from it) as it was released from the mold
Contains a high percentage of nanometer sized metal catalyst particles coated with carbon, ie carbon coated catalyst nanoparticles. These carbon coated catalyst nanoparticles are highly oxygen and chemical attack resistant. Furthermore, the carbon coated catalyst nanoparticles in these smaller carbon rods are almost in the range of 1-20 nm. The metal percentage is 20% by weight, where Ni is in the form of a pure metal whereas Ce is in the form of a carbide. To prevent the adsorption of oxygen and moisture on the carbon rods, the carbon rods are stored in an inert atmosphere until normally used.

These smaller rods were then used in a second arc discharge as described below.

Arc Discharge of the Smaller Carbon Rod Prepared Above The pure carbon rod (1.5 × 1.5 × 10 cm) was then used as the cathode in the second arc discharge and the smaller carbon rod prepared above was used as the anode. . The conditions for this second arc discharge were the same as the conditions described above for the first arc discharge. That is, a 700 torr pure helium atmosphere was used as the buffer gas. Current density is 1
It was set to 80 A / cm ² . The voltage was automatically controlled to be between 30 and 40V. The soot and deposits produced in this second arc discharge consisted of 40-60 wt% SWN.
It contained T. A typical TEM image of this soot is shown in FIG.
It is shown in B.

Therefore, the SWN in the second arc discharge
The T content was significantly higher than in the first arc discharge. This can be seen from the comparison between FIGS. 2A and 2B. However, the arc conditions for each arc discharge were exactly the same except for the composition of the anode. Therefore, the higher SWNT content in the second arc discharge is due to the use of carbon-coated catalyst nanoparticles with high catalyst productivity and low oxygen content as metal catalysts. More specifically, a high SWNT content (a) directly exhibits catalytic activity when released from the carbon coating, (b) prevents the catalytic nanoparticles from being oxidized, which in turn contains oxygen in the arc plasma region. Carbon-coated catalyst nano-particles, which provide a good mixture of carbon and metal catalysts, which dramatically reduces the rates (if the catalyst particles were to be oxidized, they would burn out immediately in air). It depends on the nature of the particles.

Note that in this example the carbon soot and deposits were used as collected from the first arc discharge and they were not first purified before forming the anode for the second arc discharge. It is important to do. Therefore, expensive and time consuming purification processes are not needed to achieve this high yield of SWNTs. Alternatively, the second
If the soot and deposits from the first arc discharge are purified before forming the arc discharge anode of
To remove particles other than carbon coated catalyst nanoparticles),
It is possible to obtain even higher percentages of SWNTs.

Example 2 Carbon coating C used as a catalyst in this example
o Bamboo-like carbon nanofibers are manufactured from nanoparticles by CVD.

Catalyst Preparation Carbon coated catalyst nanoparticles were prepared by arc discharge operation. Specifically, a pure carbon rod was used as a cathode, and a carbon rod uniformly filled with 20 wt% Co was used as an anode. The conditions of arc discharge were the same as in Example 1. Collects soot and deposits produced by the arc discharge, which
It was found to contain amorphous carbon, carbon nanotubes, fullness, small amounts of metal not coated with carbon at all, and carbon-coated catalyst nanoparticles. Therefore,
To further improve the quality of the carbon coated catalyst nanoparticles, i.e. to remove particles other than carbon coated catalyst nanoparticles, the soot and deposits are exposed to concentrated nitric acid, filtered and washed with pure water for purification. Produced carbon coated catalyst nanoparticles.
A TEM image of the purified carbon coated catalyst nanoparticles is shown in FIG. The purified carbon coated catalyst nanoparticles were then suspended in acetone for dispersion on the silica wafer catalyst support.

Instead of using concentrated nitric acid to purify the carbon coated catalyst nanoparticles, any other suitable method can be used. Also, instead of the silica wafer catalyst support, any other suitable support such as, for example, AlO ₂ , SiO ₂ , porous aluminum film or silica zeolite can be used.

Chemical Vapor Deposition Carbon monoxide (CO) was selected as the carbon source. Before the CO reaches the carbon-coated catalyst nanoparticles on the support, 400
Preheated to ~ 1000 ° C. At this temperature, the majority of CO tends to decompose, so that C _n ⁺ is available for reaction with the catalyst, where n is a natural number. C
At the same time as O was preheated, the catalyst support was heated in a furnace having a temperature between 800 and 1200 ° C. At this temperature, the catalytic metal in the carbon coating begins to melt and begin to emerge. Then, the preheated gas phase was introduced into the furnace containing the catalyst support. Upon introduction of the gas phase into the furnace, the carbon coating is partially etched by the small amount of undecomposed CO, thus leaving the catalyst nanoparticles out of the carbon coating. As the catalyst exits the carbon coating and contacts the gas phase (including C _n ⁺ from cracked CO gas), the catalyst exhibits strong catalytic activity for the growth of carbon nanofibers.

In this example, as shown in FIGS. 4A-E, bamboo-shaped nanofibers were manufactured by the following mechanism. The carbon coated catalyst nanoparticles 1 are shown in FIG. 4A,
It comprises catalytic nanoparticles 2 surrounded by a carbon coating 4. The carbon coated catalyst nanoparticles 1 are 800 to 1
Being heated in a furnace at a temperature of 200 ° C., the catalytic nanoparticles 2 begin to melt into the metal catalyst 2 ′ and to emerge from the carbon coating 4 as shown in FIG. Furthermore, _{C n} which is preheated to a temperature in the range of vapor (400 to 1000 ° C.
⁽ Including ⁺ and CO) is introduced into the furnace and the carbon coating 4
Are either etched by CO in the gas phase or opened due to the higher temperature of the coating, thus becoming the carbon shell 4 '. In any case, the metal catalyst 2 '
Begins to exit the carbon shell 4 ', as shown in Figure 4C. At this point, carbon from the gas phase dissolves in the metal catalyst 2'and migrates through the catalyst 2'towards the carbon shell 4 ', while the catalyst exits the carbon shell 4'further, as shown in FIG. The second carbon shell 4 ″ is left behind as shown in FIG. As the catalyst repeats the process of dissolving carbon (the carbon then migrates through the catalyst towards the previously formed carbon shell), then as it exits the carbon shell, the catalyst becomes bamboo-like as shown in Figure 4E. To form carbon nanofibers.

Although carbon monoxide was used as the carbon source in this example, any other suitable carbon source such as organic compounds, CH ₄ and benzene can be used. Furthermore, although bamboo-like nanofibers were produced in this example, various other shapes of carbon nanofibers could be obtained by controlling the growth temperature, vapor phase composition and catalyst particle size, as is known in the art. It is possible to grow.

Advantages of the Invention The present invention provides nanometer sized catalyst particles (catalyst nanoparticles) that are much smaller than the conventionally used micrometer sized catalyst particles. Since the catalyst nanoparticles are already such small scale particles, they are readily used during the short reaction times associated with the production of carbon nanostructures. That is, the catalytic nanoparticles need not be crushed from the micrometer size to be used,
They are easier to use as they are, thus leading to higher efficiency in the use of catalyst particles. These catalytic nanoparticles are used to form carbon-catalyst rods, which can be used, for example, for the production of carbon nanostructures by laser ablation or arc discharge.

Since it is not necessary to crush the catalyst nanoparticles to crush micrometer-sized catalyst particles,
The catalyst nanoparticles are more completely depleted during the short reaction times associated with the production of carbon nanostructures. Thus, as-produced carbon nanostructures are purer because the catalyst nanoparticles are more completely depleted during carbon nanostructure synthesis. That is, since the catalyst nanoparticles are exhausted more efficiently and completely, the amount of catalyst particles remaining in the as-produced carbon nanostructure is small.

Furthermore, the catalytic nanoparticles according to the invention are coated with carbon. The morphology of the carbon coating can vary from the amorphous graphite layer to the aligned graphite layer. Since the carbon coated catalyst nanoparticles are coated with carbon, they are not oxidized and therefore do not carry oxygen substances into the reaction zone. And since the catalyst particles of the present invention do not carry oxygen substances into the reaction zone, the desired carbon nanostructures have fewer defects and produce less amorphous carbon.

Finally, because the catalyst nanoparticles are coated with carbon, the carbon to catalyst ratio is more advantageous on a cubic micrometer size scale, whereby the use of catalyst particles is more efficient. That is, the catalyst nanoparticles are evenly distributed in the carbon on a scale that is the same dimension as the size of the desired carbon nanostructures. Thus, the catalyst particles and carbon readily interact to enhance catalyst productivity and, in turn, enhance the purity of the desired carbon nanostructures.

Without departing from the spirit and scope of the present invention as defined in the claims, structures coated with carbon coated catalyst nanoparticles according to the present invention, methods of making said structures and said structures are used. It is considered that many modifications to the method are possible.

[Brief description of drawings]

FIG. 1 is a schematic view of the formation mechanism of SWNTs when carbon-coated catalyst nanoparticles are used as a starting material.

FIG. 2A is an image of soot produced in a first arc discharge of the present invention made with a conventional catalyst in a representative TEM image of soot produced in an arc discharge.

FIG. 2B is a representative TEM image of soot produced in an arc discharge, an image of soot produced by using carbon-coated catalyst nanoparticles, ie according to the second arc discharge according to the invention.

FIG. 3 is a TEM image of purified carbon-coated catalyst nanoparticles for CVD growth of carbon nanostructures.

4A-E are schematic diagrams of the growth mechanism for bamboo-like carbon nanofibers.

FIG. 5 is a schematic diagram of the formation mechanism of SWNTs manufactured from conventional micrometer-sized starting materials.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 Carbon-coated catalyst nanoparticles 2 Nanometer-sized catalyst particles 2'Metal catalyst 4 Carbon coating 4'Carbon shell 4 '' Second carbon shell 10 Graphite powder 12 Oxide-coated metal particles 14 Micrometer-sized carbon particles 16 Oxygen Material 18 Metal-carbon cluster 20 Oxide 22 Single-walled carbon nanotube (SWNT) 24 Metal tip 28 Amorphous carbon 30 Nanometer-sized carbon particles X First reaction arrow Y representing a temperature higher than 4000 K and a time shorter than 1 ms. Second reaction arrow representing a temperature below 4000 K and a time longer than 1 ms

Claims (49)

[Claims] 1. Carbon-coated catalyst nanoparticles, each of which comprises nanometer-sized catalyst particles surrounded by a carbon coating, carbon nanoparticles, and a binder for binding the carbon-coated catalyst nanoparticles to the carbon nanoparticles. A composite carbon structure for producing a carbon nanostructure, comprising: 2. The carbon structure according to claim 1, wherein each of the nanometer-sized catalyst particles has a size in the range of 0.1 to 100 nm. 3. The carbon structure according to claim 1, wherein each of the nanometer-sized catalyst particles has a size in the range of 1 to 50 nm. 4. The carbon structure of claim 1, wherein each of the nanometer-sized catalyst particles is selected from the group consisting of Ni, Co, YC ₂ and CeC ₂ . 5. The carbon coatings each being at least one graphite layer completely surrounding each one of the nanometer sized catalyst particles.
The carbon structure according to. 6. The carbon structure of claim 5, wherein each of the carbon coatings comprises substantially concentric 1-100 graphite layers surrounding each one of the nanometer sized catalyst particles. 7. The carbon structure of claim 5, wherein each of the carbon coatings comprises 1 to 10 substantially concentric graphite layers completely surrounding each one of the nanometer sized catalyst particles. 8. The carbon structure according to claim 1, wherein the carbon catalyst nanoparticles constitute 1 to 80% by weight of the carbon structure. 9. The carbon structure according to claim 1, wherein the carbon-coated catalyst nanoparticles constitute 2 to 30% by weight of the carbon structure. 10. The carbon structure according to claim 1, wherein the binder comprises carbon. 11. The carbon structure of claim 1, wherein the binder is present in an amount sufficient to be strong enough to handle the carbon structure. 12. The binder is 1 to 1 of the carbon structure.
The carbon structure according to claim 1, which constitutes 5% by weight. 13. The carbon structure according to claim 1, wherein the carbon structure has a rod shape. 14. A step of using the composite carbon structure according to claim 1 as a first electrode, and an arc discharge using the first electrode and a second electrode containing carbon. A method of manufacturing SWNTs, the method including: 15. The SW according to claim 14, wherein the first electrode is an anode and the second electrode is a cathode.
Method for manufacturing NT. 16. The step of carrying out the arc discharge comprises the step of placing the anode and the cathode in a buffer atmosphere of helium, and the step of carrying out the anode and the cathode at 30-40.
Subjecting the voltage to a voltage between V and the method of manufacturing a SWNT according to claim 15. 17. The step of carrying out the arc discharge comprises:
The method of manufacturing SWNTs according to claim 15, comprising consuming the anode in time. 18. A SW including a step of forming the composite carbon structure according to claim 1, and a step of performing laser ablation on the composite carbon structure.
Method for manufacturing NT. 19. A step of generating soot using a carbon rod filled with a catalyst, collecting the soot, grinding the soot, and mixing the soot with a binder material to produce a first intermediate product. And pressing the first intermediate product, then heating the first intermediate product and subsequently cooling the first intermediate product, thus forming the composite carbon structure. A method for producing a composite carbon structure for producing a carbon nanostructure, comprising: 20. In the step of generating soot, a first arc discharge is performed between an anode containing a carbon rod filled with the catalyst and a cathode containing pure carbon in order to generate soot. The method for producing the composite carbon structure according to claim 19, which comprises: 21. The step of performing the first arc discharge comprises Ni and CeO 2 as the catalyst in the anode.
21. The composite carbon structure according to claim 20, comprising the steps of using ₂ ; placing the anode and the cathode in a buffered atmosphere of helium; and subjecting the anode and the cathode to a voltage between 30-40V. A method of manufacturing. 22. The step of mixing the soot with a binder material comprises mixing the soot with 1 to 5 wt% carbon-based binder to form the first intermediate product. A method for producing the described composite carbon structure. 23. The method of manufacturing a composite carbon structure according to claim 19, wherein the pressing step includes pressing the first intermediate product at a pressure of 1 to 10 ton / cm ² . 24. The step of heating the first intermediate product includes heating the pressed first intermediate product from 400 to 800.
24. A method of making a composite carbon structure according to claim 23, comprising placing in a furnace having an inert atmosphere at a temperature of 0 C for 10 hours. 25. The method of manufacturing a composite carbon structure according to claim 24, wherein the cooling step includes cooling to room temperature. 26. A CVD method comprising carbon-coated catalyst nanoparticles, each of which comprises nanometer-sized catalyst particles surrounded by a carbon coating, and an inorganic catalyst support material homogeneously mixed with said carbon-coated catalyst nanoparticles. Catalyst carrier. 27. The catalyst carrier according to claim 26, wherein each of the nanometer-sized catalyst particles has a size in the range of 0.1 to 100 nm. 28. The nanometer-sized catalyst particles each having a size in the range of 1 to 50 nm.
The catalyst carrier according to item 1. 29. The catalyst carrier according to claim 26, wherein each of the nanometer-sized catalyst particles is selected from the group consisting of Ni, Co, YC ₂ and CeC ₂ . 30. The catalyst carrier according to claim 26, wherein each of the carbon coatings is at least one graphite layer that completely surrounds each of the nanometer-sized catalyst particles. 31. The catalyst support of claim 30, wherein each of the carbon coatings comprises substantially concentric 1-100 graphite layers surrounding each one of the nanometer sized catalyst particles. 32. The catalyst carrier of claim 30, wherein each of the carbon coatings comprises 1 to 10 substantially concentric graphite layers surrounding each one of the nanometer sized catalyst particles. 33. The catalyst carrier of claim 26, wherein the carbon-coated catalyst nanoparticles make up 5 to 95% by weight of the carbon carrier. 34. The catalyst support of claim 26, wherein the carbon-coated catalyst nanoparticles make up 20-95% by weight of the carbon support. 35. The inorganic catalyst carrier is Al ₂ O ₃ or S.
iO _2, silica wafer, a catalyst carrier according to claim 26 which is selected from the group consisting of porous aluminum film and silica zeolites. 36. A step of forming the catalyst support according to any one of claims 26 to 35, a step of heating the catalyst support, and a carbon source for the catalyst support for growing a carbon nanostructure. And a step of forming a carbon nanostructure by CVD. 37. The step of heating the catalyst carrier comprises 40
37. A method of forming a carbon nanostructure according to claim 36, comprising placing the catalyst support in a furnace at a temperature of 0 to 1200 <0> C. 38. The method of forming a carbon nanostructure according to claim 37, wherein the furnace temperature, the carbon source and the catalyst particle size are selected to form a bamboo-like carbon fiber. 39. The step of heating the catalyst carrier comprises 80
37. A method of forming a carbon nanostructure according to claim 36, comprising placing the catalyst support in a furnace at a temperature of 0 to 1200 <0> C. 40. The method of forming a carbon nanostructure according to claim 36, further comprising the step of preheating the carbon source, which is performed before the step of supplying the carbon source to the catalyst support. 41. The step of preheating the carbon source comprises 400
41. The method of forming a carbon nanostructure of claim 40, comprising heating the carbon source to a temperature of ~ 1000 <0> C. 42. The method of forming a carbon nanostructure according to claim 36, wherein the step of supplying the carbon source includes supplying the carbon source in a gas phase. 43. The step of supplying the carbon source comprises CO,
Method of forming a carbon nanostructure according to claim 42 including providing the CH ₄ and carbon source selected from the group consisting of benzene. 44. A step of generating the soot from a carbon rod filled with a catalyst so that the soot contains the carbon-coated catalyst nanoparticles, and collecting the soot, and at the same time, the carbon-coated catalyst nanoparticles in the soot. Purifying the soot by removing particles other than, thus producing purified soot,
Suspending the purified soot in a solvent and dispersing the purified soot on a catalyst support material, a method for producing a catalyst for CVD of carbon nanostructures. 45. In the step of generating soot, a first arc discharge is performed between an anode including a carbon rod filled with the catalyst and a cathode including pure carbon in order to generate soot. 45. A method of making a catalyst according to claim 44 comprising: 46. The step of performing the first arc discharge comprises Ni and CeO 2 as the catalyst in the anode.
46. A catalyst according to claim 45 comprising the steps of using ₂ ; placing the anode and cathode in a buffered atmosphere of helium; and subjecting the anode and cathode to a voltage between 30-40V. Method. 47. The catalyst of claim 44, wherein the step of purifying the soot comprises forming a solution containing the soot and nitric acid, filtering the soot, and washing the soot with water. Method. 48. The step of suspending the purified soot in the solution includes: acetone, water, benzene, alcohol,
45. A method of making a catalyst according to claim 44 comprising suspending the purified soot in a solvent selected from the group consisting of toluene and chloroform. 49. The step of dispersing the soot on the catalyst support material comprises the step of sooting on a catalyst support material selected from the group consisting of Al ₂ O ₃ , SiO ₂ , silica wafers, porous aluminum films and silica zeolites. 45. A method of making a catalyst according to claim 44, comprising dispersing.