KR20100033263A - Method for controlling diameter of carbon nitride nanotubes using template - Google Patents

Abstract

PURPOSE: A diameter control method of a carbon nanotube using a template is provided to insure convenience of a process by selectively removing a metal on the outer surface of the template before growing the carbon nanotube. CONSTITUTION: A diameter control method of a carbon nanotube comprises the following steps: doping a metal precursor on a template; reducing the precursor by heat-treating under the hydrogen atmosphere; removing a metal on the outer surface of the template by processing with nitrogen plasma; and growing the carbon nanotube by providing methane gas. The template is an organic silica mesoporous template. The metal precursor is transition metal salt.

Description

Method for Controlling Diameter Of Carbon Nitride Nanotubes Using Template}

The present invention relates to a method for controlling the diameter of carbon nanotubes according to the pore size of the template by growing carbon nanotubes only from metals present in the pores of the template by removing metal particles present on the outer wall of the template. .

There are three major carbon structures in nature. In other words, C60 is a pencil-like graphite, diamond, and 60 carbon atoms called bucky balls. Ten carbon atoms are present on the large circle of the buckyball. The addition of 10 carbon atoms results in a C70 molecule with a slightly stretched center of the soccer ball. If 10 carbons are added again, the middle part becomes longer (C80). The continuous inflow of carbon atoms forms a tube shape. Carbon-nanotubes are very small tubes having diameters of several nm to several tens of nm.

In 1991, Dr. Ijima, Japan, observed the synthesis of fullerenes by the electric discharge method with an electron microscope, and revealed the existence of a soccer ball-like pleene and acicular structure (multi-layered carbon nanotube structure). History began (see Nature 1991 VOL. 354. 56). The carbon nanotubes refer to a new material in which hexagons made of six carbons are connected to each other to form a tubular shape. That is, a planar carbon structure in which honeycomb is formed by combining three carbon atoms is rolled up to form a tube tube. The thermal conductivity is about 1,000 times that of copper and the strength is about 100 times that of steel, so it is hardly broken. In addition, the carbon fiber can be broken even when only 1% is deformed, but the carbon nanotube can be tolerated without breaking even when 15% is deformed. In addition, the carbon nanotubes are attracting attention as new functional materials that are expected to have various applications in the microscopic or macroscopic aspects because they have a mechanically very strong, excellent chemical stability, high thermal conductivity, and a hollow structure. For example, attempts or studies to apply to memory devices, electronic amplifiers or gas sensors, electromagnetic shielding, secondary batteries, fuel cells or electrode capacitors of hydrogen capacitors, field emission displays, polymer composites, and the like have been made very actively.

In particular, many studies have been conducted due to the excellent electrical properties, and many studies have been recognized the possibility of carbon nanotubes as a nanodevice material. In particular, since the carbon nanotubes added with nitrogen show an effect of improving the electrical properties, the carbon nanotubes added with nitrogen as a hetero element show various application possibilities in the technical field to which the invention belongs. In order for carbon nanotubes to be used as nanodevice materials, they must be oriented carbon nanotubes having a small and uniform diameter distribution at specific locations on the substrate. To this end, it is necessary to use a template to produce a carbon nanotube having a diameter similar to the pore size of the template and a uniform diameter distribution.

As a method of manufacturing carbon nanotubes using a conventional template, a metal precursor is doped into a template using a hydrothermal method, and carbon nanotubes using a chemical vapor deposition (CVD) method. (An-hui Lu et al., Carbon, 43, 8, 1811, 2005). However, in the above method, the metal particles used as the catalyst are dispersed not only in the pores of the template, but also in the outer wall, so that the size of the carbon nanotubes is larger than the pore size of the template, and the diameters are nonuniform.

In order to solve the above problem, another conventional technique (D. Barreca et al., Microporous and Mesoporous Materials, 103, 142, 2007) used nitric acid to selectively remove metal particles present in the outer wall of the template. According to the above method, the carbon nanotubes grown in the template treated with nitric acid were able to improve the uniformity of the diameter of the carbon nanotubes compared with those not treated with nitric acid. However, even in this case, the carbon nanotubes grown on the outer wall of the template could not be controlled. In addition, when the treatment is performed by increasing the concentration of nitric acid, there is a possibility that even metal particles existing inside the pores of the template may be removed, and thus, there is a problem that it is difficult to selectively remove metal particles existing on the outer wall of the template.

In order to solve the above problems, the present invention is to provide a method for controlling the diameter of the carbon nanotubes by selectively removing the metal particles present on the outer wall of the template.

In order to achieve the above object, the present invention comprises the step of growing a carbon nanotube by doping a metal precursor (template) to the template, heat treatment in a hydrogen atmosphere, and then treatment with nitrogen plasma and methane gas, The present invention provides a method of controlling the diameter of carbon nanotubes.

In the present invention, just before growing the carbon nanotubes, only the metal present on the outer wall of the template can be selectively removed, thereby facilitating process convenience. In addition, since the carbon nanotubes are grown from the metal present only in the pores of the template, carbon nanotubes having a uniform diameter can be grown.

In addition, the diameter of the carbon nanotubes grown in accordance with the present invention is very similar to the pore size of the template, it is possible to precisely control the diameter of the carbon nanotubes by adjusting the pore size of the template. Accordingly, the industrial utilization is very large in various applications such as electron emission source, structural composite materials, nano devices.

The present invention provides a method for controlling the diameter of carbon nanotubes using a template.

Specifically, the diameter control method of carbon nanotubes comprises the steps of doping a metal precursor (metal precursor) to the template; Reducing by heat treatment in a hydrogen atmosphere; Treating the nitrogen plasma to remove metal present in the template outer wall; Supplying methane gas to grow carbon nanotubes.

The metal precursor is a precursor of a metal catalyst, and refers to a material that is reduced by heat treatment in a hydrogen atmosphere, and mainly uses a metal salt.

Preferably, the template may use an organosilica mesoporous template. Silica templates such as MCM-41 and SBA-15 may also be used, but the organosilica template is used in the present invention because the reactivity with the metal catalyst is inferior as compared with organosilica. In addition, since the metal catalyst must be doped in the pores of the template, a porous template is used.

Preferably, the metal precursor may use a transition metal salt. In this case, the metal precursor may be used without particular limitation, so long as it is a salt containing a transition metal, and generally, an acetate series and a chloride series are used. In addition, when using a metal precursor of 5wt% to the weight of the template, doping may be optimized in the template.

Preferably, the transition metal may use iron (Fe), nickel (Ni) or cobalt (Co).

Preferably, the heat treatment in the hydrogen atmosphere is carried out while flowing the hydrogen gas at a flow rate of 100 ~ 500sccm at the temperature of 200 ~ 400 ℃ and pressure of 200 ~ 400torr. At this time, a microwave oven may be used to provide a temperature of about 300 ° C., in which a metal precursor is adsorbed onto the template.

Preferably, the nitrogen plasma is carried out while flowing the nitrogen gas at a flow rate of 10 ~ 100sccm under the conditions of 10 ~ 20torr pressure and 500 ~ 1000W microwave power. In this case, the microwave was used as a plasma generating source, and in addition to the microwave, RF or a DC power source may be used.

Preferably, the methane gas is carried out while supplying at a temperature of 600 ~ 800 ℃ and a microwave power of 500 ~ 1000W at a pressure of 20 ~ 30 torr.

In the above, nitrogen gas and methane gas are reacted by plasma chemical vapor deposition (plasma CVD) to grow carbon nanotubes.

The present invention also provides a carbon nanotube of controlled diameter prepared by the above method.

Hereinafter, the contents of the present invention will be described in detail through Examples and Test Examples. However, these are intended to explain the present invention in more detail, and the scope of the present invention is not limited thereto.

<Examples>

(1) doping the template with metal salt

5 wt% Iron (II) acetate (molecular weight: 173.94, Aldrich), a metal catalyst, was dispersed well by sonication in 50 ml of DMF (N, N-Dimethylformamide) solution. Thereafter, the solution was spun at 2.45 Ghz, 700 W microwave for 90 seconds in 100 mg of an organic silica mesoporous template. As a result, the template was doped with a metal catalyst in the form of a metal salt.

(2) reduction of metal salts doped in the template

After the template was placed in a chamber, the internal pressure of the chamber was maintained at about 400 torr, and 200 sccm of hydrogen gas was flowed at a temperature of 300 ° C. for 2 hours. As a result, the metal catalyst particles doped in the template were reduced.

(3) Treatment of nitrogen plasma

Subsequently, 15 mg of the template doped with reduced metal catalyst particles (Fe) was dispersed in 3 ml of acetone, and then dip-coated on a SiO ₂ / Si wafer (4 cm × 4 cm). The dip-coated wafer was dried overnight in an oven and treated with nitrogen plasma to remove doped metal catalyst particles (Fe) on the template outer wall. The nitrogen plasma treatment was carried out by treating 85 sccm of nitrogen with a microwave power of 850 W for 1 minute under 20 torr pressure.

(4) treatment of methane gas

In addition, while nitrogen plasma was treated to the template, 15 sccm of methane gas (CH ₄ ) was supplied, and plasma reaction was performed. At this time, the temperature in the chamber was maintained at 750 ℃, pressure 23torr, the microwave power during the plasma reaction was performed for 10 minutes at 850W. As a result, carbon nanotubes were selectively grown only in the pores of the template, and nitrogen was added to the grown carbon nanotubes. The nitrogen is added during the nitrogen plasma treatment process.

Hereinafter, according to the above production example, it was confirmed through the test example that the carbon nanotubes with a controlled diameter were grown.

<Test Example 1>-Doping the template with a metal salt

HRTEM photographs, EDS analysis results and XPS analysis results were checked to see if the metal catalyst (Fe) was doped into the template.

In the HRTEM of FIG. 1A, the presence of the metal catalyst (Fe) in the template could not be confirmed, but the presence of the metal catalyst (Fe) was confirmed by the EDS analysis result. In addition, through the XPS analysis result of FIG. 1B, it is possible to confirm the coupling property of the template and the doped metal catalyst (Fe). The metal catalyst (Fe) is derived from a metal salt (Fe (II) acetate).

Test Example 2 Reduction of Metal Salt Doped to Template

In order to reduce the metal salt (Fe (II) acetate) present in the template of Test Example 1 to metal (Fe), hydrogen gas was treated at a temperature of 300 ° C. The reduced metal catalyst particles (Fe) can be confirmed by the HRTEM of FIG. 2, and it can be seen that Fe is uniformly doped in the pores and the outer wall of the template.

<Test Example 3>-Treatment of nitrogen plasma

Nitrogen plasma was treated to remove Fe present in the template outer wall of Test Example 2.

 In the HRTEM of FIG. 3A, it can be seen that most of the Fe particles are present in the pores of the template, through which the metal catalyst particles (Fe) doped on the outer wall of the template are removed. In addition, looking at the analysis results using XPS of Figure 3b, it can be seen that the intensity of Fe after the nitrogen plasma treatment is reduced, which indicates that the Fe catalyst particles are etched by nitrogen plasma. In addition, looking at the analysis results using SAXS of Figure 3c, it can be seen that the crystallinity change of the template doped with Fe in the pores. In other words, from the results of experiments in which the Full Width at Half Maximum (FWHM) before the nitrogen plasma treatment was 0.209 and the FWHM after the nitrogen plasma treatment was 0.215, the porosity of the template was changed in comparison with before and after the nitrogen plasma treatment. It can be seen that there is almost no.

In conclusion, the analysis of Figures 3a to 3c, it can be seen that when the nitrogen plasma treatment, Fe doped in the pores of the template is not removed, only Fe attached to the outer wall of the template is selectively removed.

Test Example 4-Treatment of Methane Gas

In order to remove Fe present on the outer wall of the template and grow carbon nanotubes containing nitrogen from the pores of the template, methane gas was treated together with the nitrogen plasma treatment of Test Example 3.

In the HRTEM of Figure 4, it can be seen that the carbon nanotubes to which nitrogen is selectively grown only in the pores of the template. From the Fe catalyst particles present in the 3.8 nm pores of the template, carbon nanotubes with a diameter of 3.4 nm having a size similar to the pore size were grown, indicating that the carbon nanotubes selectively grew only in the pores of the template. In addition, the node shown on the carbon nanotubes of the TEM picture shows the nitrogen added to the carbon nanotubes.

As described above, although described with reference to preferred embodiments and test examples of the present invention, those skilled in the art to which the present invention pertains without departing from the spirit and scope of the invention as set forth in the claims below. It will be understood that various modifications and changes can be made.

1A is an HRTEM photograph and an EDS analysis graph. The HRTEM image shows the doping of 5 wt% iron (II) acetate in the template (Template-Fe5 (MW)) using the microwave-assisted method, and the EDS analysis graph shows the Show that the ingredients are included.

Figure 1b is an XPS analysis graph, showing the coupling characteristics of the template and Fe of Figure 1a.

FIG. 2 is an HRTEM photograph, in which the template doped with iron acetate of FIG. 1A is reduced, thereby forming iron in pores.

Figure 3a is a HRTEM picture and TEM picture, showing that Fe was present on the outer wall of the template selectively removed by treatment with nitrogen plasma.

FIG. 3B is an XPS analysis graph in which a template before treatment of nitrogen plasma and a template after treatment of nitrogen plasma are compared. Template-Fe5 (MW) (r) shown in the drawing indicates that 5wt of iron acetate was reduced after doping the template, and Template-Fe5 (MW) (P) -Plasma Treatment was Template-Fe5 (MW) (r). It shows that nitrogen plasma treatment was carried out.

FIG. 3C is a SAXS analysis graph in which the template before the nitrogen plasma treatment is compared with the template after the nitrogen plasma treatment similarly to FIG. 3B.

4 is an HRTEM photograph and a TEM photograph, showing that the diameter of the carbon nanotubes selectively grown in the pores of the template is similar to the pore size of the template.

Claims (8)

In the carbon nanotube diameter control method, Doping a metal precursor to the template; Reducing by heat treatment in a hydrogen atmosphere; Treating the nitrogen plasma to remove metal present in the template outer wall; A method of controlling the diameter of carbon nanotubes comprising supplying methane gas to grow carbon nanotubes. The method of claim 1, wherein the template is an organosilica mesoporous template. The method of claim 1, wherein the metal precursor is a transition metal salt. The method of claim 3, wherein the transition metal is selected from the group consisting of iron (Fe), nickel (Ni), and cobalt (Co). The carbon nanotube diameter control method of claim 1, wherein the heat treatment in the hydrogen atmosphere flows hydrogen gas at a flow rate of 100-500 sccm at a temperature of 200-400 ° C. and a pressure of 200-400 torr. The method of claim 1, wherein the nitrogen plasma flows nitrogen gas at a flow rate of 10-100 sccm under a pressure of 10-20torr and a microwave power of 500-1000W. The carbon nanotube diameter control method of claim 1, wherein the methane gas is supplied under a microwave power of 500-1000 W at a temperature of 600-800 ° C. and a pressure of 20-30 torr. A carbon nanotube having a diameter controlled by the method of any one of claims 1 to 7.

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