JP2014156370A - Manufacturing method of metallic oxide nanoparticle supporting carbon nanotube - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an efficient manufacturing method of a metallic oxide nanoparticle supporting carbon nanotube which is useful as a catalyst.SOLUTION: This invention provides a manufacturing method of a metallic oxide nanoparticle supporting carbon nanotube including a step of making a carbon nanotube (A) support metallic oxide nanoparticles by applying an electromagnetic wave to a mixture containing the specific carbon nanotube (A), a metallic oxide precursor (B), an alcohol compound (C) and water (D).

Description

  The present invention relates to a method for efficiently producing metal oxide nanoparticle-supported carbon nanotubes useful as a catalyst.

In recent years, in order to solve energy problems and environmental problems, various catalysts, for example, catalysts in which metal nanoparticles or metal oxide nanoparticles are supported on the surface of a carbon-based catalyst carrier have attracted attention.
As such a catalyst, for example, Patent Document 1 describes a catalyst including a carbon-based catalyst carrier and a metal particle layer adsorbed on the surface of the carbon-based catalyst carrier.

In addition, a method for producing metal oxide nanoparticles using a microwave or the like is known.
For example, Patent Document 2 describes a method for producing metal oxide fine particles, wherein a metal solution is hydrolyzed in a polyol solution containing a hydrolyzable metal compound and then irradiated with microwaves. Has been.

JP 2007-75811 A JP 2003-342007 A

  As described above, in recent years, various catalysts have attracted attention in order to solve energy problems and environmental problems, and development of higher performance catalysts has been demanded.

  This invention is made | formed in view of this situation, and it aims at providing the method of manufacturing efficiently the metal oxide nanoparticle carrying | support carbon nanotube useful as a catalyst.

  The present inventors have intensively studied to solve the above problems. As a result, when a mixture containing a carbon nanotube, a metal oxide precursor, an alcohol compound, and water having a specific relationship between the average diameter (Av) and the standard deviation (σ) of the diameter is irradiated with electromagnetic waves, the metal oxide Metal oxide particles are generated by hydrolysis and polycondensation reaction of the precursor, and as a result, it is possible to efficiently produce metal oxide nanoparticle-supported carbon nanotubes in which metal oxide nanoparticles are supported on carbon nanotubes. The headline and the present invention have been completed.

Thus, according to the present invention, the following methods (1) to (5) for producing the metal oxide nanoparticle-supported carbon nanotubes are provided.
(1) Carbon nanotube (A), metal oxide precursor (B), alcohol in which the average diameter (Av) and the standard deviation (σ) of the diameter satisfy the relational expression: 0.60> 3σ / Av> 0.20 A metal oxide nanoparticle-supporting carbon nanotube having a step of supporting a metal oxide nanoparticle on a carbon nanotube (A) by irradiating a mixture containing the compound (C) and water (D) with electromagnetic waves. Production method.
(2) The manufacturing method of the metal oxide nanoparticle carrying | support carbon nanotube as described in (1) whose content of water (D) is 0.01-5 mass% in the whole mixture.
(3) The manufacturing method of the metal oxide nanoparticle carrying | support carbon nanotube as described in (1) or (2) whose frequency of the electromagnetic waves to irradiate is 0.003-3000 GHz.
(4) Metal oxide nanoparticle carrying | supporting in any one of (1)-(3) whose average particle diameter is 1-20 nm and whose standard deviation of a particle size is 3 nm or less A method for producing carbon nanotubes.
(5) Metal oxide nanoparticle carrying | support carbon in any one of (1)-(4) whose loadings of a metal oxide nanoparticle are 1-30000 mass parts per 100 mass parts of carbon nanotubes (A). Nanotube manufacturing method.

  ADVANTAGE OF THE INVENTION According to this invention, the method of manufacturing efficiently the metal oxide nanoparticle carrying | support carbon nanotube useful as a catalyst is provided.

4 is a drawing-substituting photograph showing a field emission transmission electron microscope (FE-TEM) image of the carbon nanotubes carrying titanium oxide nanoparticles obtained in Example 1. FIG.

  In the method for producing a metal nanotube-supported carbon nanotube of the present invention, the average diameter (Av) and the standard deviation (σ) of the diameter satisfy a relational expression: 0.60> 3σ / Av> 0.20 ( A) A metal oxide nanoparticle is supported on a carbon nanotube (A) by irradiating a mixture containing a metal oxide precursor (B), an alcohol compound (C), and water (D) with electromagnetic waves. A step of causing

[Carbon nanotube (A)]
The carbon nanotube (A) used in the present invention has an average diameter (Av) and a standard deviation (σ) of the diameter satisfying a relational expression: 0.60> 3σ / Av> 0.20.
In the present invention, “carbon nanotube (A)” is a general term for a set of predetermined carbon nanotubes constituting the carbon nanotube, and “diameter” means an outer diameter of the predetermined carbon nanotube.

In the present invention, the average diameter (Av) and the standard deviation (σ) of the diameter of the carbon nanotube (A) are a sample average value and a sample standard deviation, respectively. They are obtained as an average value and a standard deviation when measuring the diameter of 100 randomly selected carbon nanotubes under observation with a transmission electron microscope. In the above relational expression, 3σ is obtained by multiplying the obtained standard deviation (σ) by 3.
By using carbon nanotubes (A) in which the average diameter (Av) and standard deviation (σ) satisfy the relational expression: 0.60> 3σ / Av> 0.20, metal oxide nanoparticles useful as a catalyst are supported. Carbon nanotubes can be obtained.

  Here, 3σ / Av represents the diameter distribution of the carbon nanotube (A), and the larger the value, the wider the diameter distribution. In the present invention, the diameter distribution is preferably a normal distribution.

  The diameter distribution of the carbon nanotube (A) can be calculated by observing with a transmission electron microscope. That is, under observation with a transmission electron microscope, the diameter of 100 randomly selected carbon nanotubes was measured, and the results were used to obtain the diameter on the horizontal axis and the frequency on the vertical axis. It is obtained by plotting the data and approximating with Gaussian. The value of 3σ / Av can also be increased by combining a plurality of types of carbon nanotubes obtained by different production methods, but in this case, it is difficult to obtain a normal distribution of diameters. In the present invention, the carbon nanotube (A) is composed of carbon nanotubes obtained by a single production method, or carbon nanotubes obtained by another production method in an amount that does not affect the diameter distribution of the carbon nanotubes. May be blended.

  The average diameter (Av) of the carbon nanotube (A) is preferably 0.5 nm or more and 15 nm or less from the viewpoint of obtaining metal oxide nanoparticle-supported carbon nanotubes useful as a catalyst.

The average length of the carbon nanotube (A) is preferably 0.1 μm to 1 cm. When the average length of the carbon nanotube (A) is within the above range, it becomes easy to form a metal oxide nanoparticle-supported carbon nanotube more useful as a catalyst.
The average length of the carbon nanotube (A) can be calculated, for example, by measuring 100 randomly selected carbon nanotubes using a transmission electron microscope.

The specific surface area of the carbon nanotube (A) is preferably 100 to 2500 m ² / g. When the specific surface area of the carbon nanotube (A) is within the above range, it becomes easy to form a metal oxide nanoparticle-supported carbon nanotube more useful as a catalyst.
The specific surface area of the carbon nanotube (A) can be determined by a nitrogen gas adsorption method.

  The carbon nanotubes constituting the carbon nanotube (A) may be single-walled or multi-layered.

  Moreover, the carbon nanotube which comprises a carbon nanotube (A) may have a functional group such as a carboxyl group introduced on its surface. The functional group can be introduced by a known oxidation treatment method using hydrogen peroxide, nitric acid or the like.

  The carbon nanotube (A) is a known method, for example, a substrate having a catalyst layer for producing carbon nanotubes (hereinafter sometimes referred to as a “CNT producing catalyst layer”) on the surface (hereinafter, referred to as “CNT producing substrate”). In addition, when a raw material compound and a carrier gas are supplied and carbon nanotubes are synthesized by chemical vapor deposition (CVD), a small amount of oxidant is present in the system. Thus, it can be obtained by a method (super growth method) of dramatically improving the catalytic activity of the catalyst layer for CNT production (WO 2006/011655 pamphlet).

The support for supporting the CNT production catalyst layer in the CNT production substrate is not particularly limited as long as it can carry the CNT production catalyst layer on the surface thereof.
Examples of the material of the support include metals such as iron, nickel, chromium, molybdenum, tungsten, titanium, aluminum, manganese, cobalt, copper, silver, gold, and platinum; alloys containing these metals; oxides containing the metals A semiconductor such as silicon; a non-metal such as quartz, glass, mica, graphite, diamond; and the like.
Examples of the shape of the support include a flat plate shape, a thin film shape, and a block shape.

  A conventionally known carbon nanotube production catalyst can be used as the catalyst constituting the CNT production catalyst layer. Specific examples include metal catalysts such as iron chloride, iron, iron-molybdenum, alumina-iron, alumina-cobalt, and alumina-iron-molybdenum.

  Examples of the raw material compound include hydrocarbon compounds such as methane, ethane, propane, ethylene, propylene, and acetylene; alcohol compounds such as methanol and ethanol; ketone compounds such as acetone; carbon monoxide;

Examples of the carrier gas include helium, argon, hydrogen, nitrogen, neon, krypton, carbon dioxide, and chlorine.
Examples of the oxidizing agent include water vapor, oxygen, ozone, hydrogen sulfide and the like. The content of the oxidizing agent in the gas phase is usually 10 ppm or more and 10,000 ppm or less.

The pressure in the reaction system is preferably 10 ² Pa to 10 ⁷ Pa (100 atmospheric pressure).
The temperature in the reaction system during the production of the carbon nanotube (A) can be appropriately determined according to the catalyst, the raw material compound, and the oxidizing agent. Usually, it is 400-1200 degreeC.

[Metal oxide precursor (B)]
The metal oxide precursor (B) is a compound that generates metal oxide nanoparticles by hydrolysis and polycondensation reaction. A metal oxide precursor (B) will not be specifically limited if it melt | dissolves in the solvent to be used, and produces | generates the target metal oxide nanoparticle.
As a metal oxide precursor (B), the complex and salt which consist of a cation (metal ion) and an anion are mentioned.
Examples of the cation constituting the metal oxide precursor (B) include titanium (IV) ion, zirconium (IV) ion, hafnium (IV) ion, silicon (IV) ion, zinc (II) ion, and tin (IV). Ions, indium (III) ions, and the like.
Examples of anions constituting the metal oxide precursor (B) include alkoxide ions such as methoxide ions, ethoxide ions, propoxide ions, isopropoxide ions, n-butoxide ions, t-butoxide ions; fluoride ions Halide ions such as chloride ion, bromide ion and iodide ion; acetate ion; sulfate ion; nitrate ion; oxalate ion;

Specific examples of the metal oxide precursor (B) include Ti (OCH ₃ ) ₄ , Ti (OC ₂ H ₅ ) ₄ , Ti (OnC ₃ H ₇ ) ₄ , Ti (OiC ₃ H ₇ ) ₄ , Ti ( OC ₄ H ₉ ) ₄ , TiCl ₄ , Zr (OCH ₃ ) ₄ , Zr (OC ₂ H ₅ ) ₄ , Zr (OnC ₃ H ₇ ) ₄ , ZrOiC ₃ H ₇ ) ₄ , Zr (OC ₄ H ₉ ) ₄ , ZrCl ₄ , Hf (OCH ₃ ) ₄ , Hf (OC ₂ H ₅ ) ₄ , Hf (OnC ₃ H ₇ ) ₄ , Hf (OiC ₃ H ₇ ) ₄ , Hf (OC ₄ H ₉ ) ₄ , HfCl _4, etc. However, it is not limited to these.
A metal oxide precursor (B) can be used individually by 1 type or in combination of 2 or more types.

  The metal oxide obtained from the metal oxide precursor (B) is a metal oxide contained in the metal oxide precursor (B). For example, titanium oxide, zirconium oxide, hafnium oxide, aluminum oxide And silicon oxide.

[Alcohol compound (C)]
The alcohol compound (C) is a compound having one or more hydroxyl groups in the molecule.
In the present invention, the alcohol compound (C) plays a role of promoting the hydrolysis / polycondensation reaction of the metal oxide precursor (B), stabilizing the generated metal oxide nanoparticles, and preventing aggregation. .
The alcohol compound (C) is not particularly limited as long as it can play these roles.

Examples of the alcohol compound (C) include monoalcohols such as methanol, ethanol, propanol, and butanol; ethylene glycol, propylene glycol, 1,3-butanediol, 1,4-butanediol, 2,3-butanediol, Examples include diols such as 1,5-pentanediol, 1,6-hexanediol, diethylene glycol, triethylene glycol, and tetraethylene glycol; cellosolves such as 2-methoxyethanol and ethylene glycol monoethyl ether; and the like. Especially, as alcohol compound (C), diols and cellosolves are preferable.
These alcohol compounds (C) can be used singly or in combination of two or more.

[Water (D)]
In the present invention, water (D) is used to advance the hydrolysis reaction of the metal oxide precursor (B). Examples of the water (D) used include distilled water and deionized water.

[Other ingredients]
The mixture used for this invention may contain another component in the range which does not prevent the effect of this invention. Examples of other components include a solvent (excluding the alcohol compound (C)), a dispersant, a surfactant, a pH adjuster, and the like. These may be appropriately known ones.

〔blend〕
The mixture used in the present invention is obtained, for example, by mixing carbon nanotubes (A), metal oxide precursor (B), alcohol compound (C), water (D) and other components, and dispersing the carbon nanotubes. be able to.

  A known method can be used for the mixing process and the dispersion process. Examples thereof include a method using a nanomizer, an optimizer, an ultrasonic disperser, a ball mill, a sand grinder, a dyno mill, a spike mill, a DCP mill, a basket mill, a paint conditioner, a high-speed stirring device, and the like.

Although content of a carbon nanotube (A) is not specifically limited, Preferably it is 0.001-10 mass% in the whole mixture.
Although content of a metal oxide precursor (B) is not specifically limited, Preferably it is 1.0 * 10 < ^-10 > -1.0 * 10 < ^-8 > mass% in the whole mixture.
The content of the alcohol compound (C) is not particularly limited. The alcohol compound (C) can also be used as a solvent.
The content of water (D) is not particularly limited as long as it is an amount capable of hydrolyzing the metal oxide precursor (B). The content of water (D) is preferably 0.01 to 5% by mass in the entire mixture.

[Electromagnetic wave irradiation]
In the present invention, the mixture is irradiated with electromagnetic waves. By irradiating the mixture with electromagnetic waves, the carbon nanotubes (A) absorb the electromagnetic waves to generate heat, and the mixture is efficiently heated. Thereby, the metal oxide precursor (B) is efficiently hydrolyzed by water (D), and the metal oxide nanoparticles are not in a free form in the mixture by the subsequent polycondensation reaction. It selectively deposits on the surface of (A) and is supported on the surface uniformly and with good adhesion.

  A publicly known method can be adopted as a method of irradiating electromagnetic waves. For example, according to a method as described in JP-T-2006-517260, metal oxide nanoparticle-supporting carbon nanotubes can be efficiently produced. The production of the metal oxide nanoparticle-supporting carbon nanotubes may be performed batchwise or continuously.

Specifically, by injecting the mixture into a tubular reactor as shown in the figure of the above publication or by installing the mixture and irradiating electromagnetic waves from the outside, the mixture is heated and the metal oxide precursor is heated. The hydrolysis / polycondensation reaction of the body proceeds, and as a result, carbon nanotubes carrying metal oxide nanoparticles are obtained.
The electromagnetic wave can be generated using a magnetron or a gyrotron.
The frequency of the electromagnetic wave to be irradiated is not particularly limited as long as the mixture is heated to promote the hydrolysis / polycondensation reaction of the metal oxide precursor and, as a result, the metal oxide nanoparticle-supported carbon nanotube can be obtained. However, 0.003-3000 GHz is preferable. By irradiating an electromagnetic wave having a frequency in such a range, the target metal oxide nanoparticle-supported carbon nanotube can be obtained more efficiently.
Although the temperature which heats a mixture by irradiating electromagnetic waves is based also on the solvent to be used, it is 85-350 degreeC normally.
The irradiation time is usually 10 seconds to 60 minutes, although it depends on the solvent used.

After the metal oxide nanoparticles are supported on the carbon nanotubes (A) by the above method, the reaction liquid containing the metal oxide nanoparticle-supported carbon nanotubes is separated from the supernatant and precipitate (metal oxide) by a centrifugal separation method or the like. The target metal oxide nanoparticle-supporting carbon nanotubes can be isolated by dividing the product into the product nanoparticle-supporting carbon nanotubes and removing the supernatant.
Moreover, you may further wash | clean the isolated metal oxide nanoparticle carrying | support carbon nanotube as needed. For example, after washing the metal oxide nanoparticle-supported carbon nanotubes in a cleaning solvent, the dispersion is separated into a supernatant liquid and metal oxide nanoparticle-supported carbon nanotubes by a centrifugal separation process. It can be performed by a method of removing.

  The metal oxide nanoparticles supported on the carbon nanotube (A) by the method of the present invention have a small average particle diameter and excellent uniformity. The average particle diameter of the metal oxide nanoparticles is preferably 1 to 20 nm, and the standard deviation of the particle diameter is preferably 3 nm or less.

  The metal oxide nanoparticle-supported carbon nanotube obtained by the method of the present invention preferably has a metal oxide nanoparticle support amount of 1 to 30000 parts by mass per 100 parts by mass of the carbon nanotube (A). If the loading amount of the metal oxide nanoparticles is within such a range, the catalytic performance of the carbon nanotubes carrying the metal oxide nanoparticles is improved, which is preferable.

According to the present invention, metal oxide nanoparticles are supported on carbon nanotubes (A) uniformly and with good adhesion, and the metal oxide nanoparticles-supported carbon nanotubes useful as a catalyst are efficiently produced. Can do.
The metal oxide nanoparticle carrying | support carbon nanotube obtained by this invention functions as a redox catalyst, and is useful for various uses. For example, when the metal oxide nanoparticles are titanium oxide nanoparticles, a catalyst constituting the cathode catalyst layer or anode catalyst layer of the fuel cell, a catalyst constituting the catalyst layer of the counter electrode of the dye-sensitized solar cell, nitrogen It is useful as an oxide removal catalyst.

[Example 1]
To a three-necked flask, 50 mL of 1,5-pentanediol, 0.03 g of carbon nanotubes, and 2 mL of water were added.
The carbon nanotubes had the following characteristic values:
Average diameter (Av): 3.3 nm, diameter standard deviation (σ): 0.64 nm, 3σ / Av: 0.58, average length: 100 μm, specific surface area: 800 m ² / g, mainly monolayer.
The contents of the three-necked flask were irradiated with ultrasonic waves at room temperature for 10 minutes using a bath-type ultrasonic cleaner [manufactured by BRANSON, 5510J-MT (42 kHz, 180 W)]. The contents were stirred in a three-necked flask and then irradiated again with ultrasonic waves for 10 minutes. Next, Ti (OC ₂ H ₅ ) ₄ was added to obtain a reaction dispersion.
The obtained dispersion for reaction was subjected to a supporting treatment by irradiating microwaves in accordance with the method of the example of JP-T-2006-517260 (frequency of irradiated electromagnetic wave: 2.45 GHz).
After the above supporting treatment, the dispersion after the reaction is separated into a colorless and transparent supernatant and a precipitate (carbon nanotubes supporting titanium oxide nanoparticles) by centrifugal separation (13,000 rpm for 5 minutes), and the supernatant is removed. As a result, the carbon nanotubes carrying titanium oxide nanoparticles were isolated. When the supported titanium oxide was analyzed by X-ray diffraction (XRD), it was confirmed that the anatase type useful in the application field was selectively produced.
Next, the isolated titanium oxide nanoparticle-supported carbon nanotubes were mixed with ethanol, and the titanium oxide nanoparticle-supported carbon nanotubes were dispersed by ultrasonic treatment (42 kHz, 180 W, 10 minutes) at room temperature. The dispersion was separated into a supernatant and titanium oxide nanoparticle-supported carbon nanotubes by centrifugation (13,000 rpm for 5 minutes), and the supernatant was removed to wash the titanium oxide nanoparticle-supported carbon nanotubes.

[Microscopic observation]
The cleaned titanium oxide nanoparticle-supported carbon nanotubes were mixed with ethanol and dispersed by ultrasonic treatment (42 kHz, 180 W, 10 minutes) at room temperature to obtain a sample for microscope observation. The carbon nanotubes carrying titanium oxide nanoparticles were observed using a field emission transmission electron microscope (FE-TEM) (FIG. 1), and from the images of 100 randomly selected titanium oxide nanoparticles, the average particle size of the titanium oxide nanoparticles The standard deviation of diameter and particle size was determined. The average particle diameter of the titanium oxide nanoparticles was 5 nm, and the standard deviation of the particle diameter was 1 nm. Moreover, the coverage of the carbon nanotube surface by the titanium oxide nanoparticle in the titanium oxide nanoparticle carrying | support carbon nanotube was 90%.

[Adhesion]
The titanium oxide nanoparticle-supporting carbon nanotubes dispersed in ethanol by the above method were again subjected to ultrasonic treatment (42 kHz, 180 W, 10 minutes) at room temperature. Using this dispersion as a sample, the carbon nanotubes carrying titanium oxide nanoparticles were observed by FE-TEM, and the change in the coating state of the carbon nanotube surface with the titanium oxide nanoparticles before and after the ultrasonic treatment was examined.
As a result of observation, the coating state of the titanium oxide nanoparticles was not substantially changed, and it was thus confirmed that the titanium oxide nanoparticle-supporting carbon nanotubes are those in which the titanium oxide nanoparticles are firmly supported.

Claims (5)

  The carbon nanotube (A), the metal oxide precursor (B), the alcohol compound (C) in which the average diameter (Av) and the standard deviation (σ) of the diameter satisfy the relational expression: 0.60> 3σ / Av> 0.20 ), And a mixture containing water (D), by irradiating the carbon nanotubes (A) with metal oxide nanoparticles by irradiating the mixture with electromagnetic waves, a method for producing metal oxide nanoparticle-supported carbon nanotubes.   The manufacturing method of the metal oxide nanoparticle carrying | support carbon nanotube of Claim 1 whose content of water (D) is 0.01-5 mass% in the whole mixture.   The manufacturing method of the metal oxide nanoparticle carrying | support carbon nanotube of Claim 1 or 2 whose frequency of the electromagnetic waves to irradiate is 0.003-3000 GHz.   The method for producing metal nanotube-supported carbon nanotubes according to any one of claims 1 to 3, wherein the metal oxide nanoparticles have an average particle diameter of 1 to 20 nm and a standard deviation of the particle diameter of 3 nm or less. .   The manufacturing method of the metal oxide nanoparticle carrying | support carbon nanotube in any one of Claims 1-4 whose loadings of a metal oxide nanoparticle are 1-30000 mass parts per 100 mass parts of carbon nanotubes (A).

Images