Honda Motor Co., Ltd. (JP) received U.S. Patent 7,767,186 for microwave treatment of carbon nanotubes to separate metallic-type carbon nanotubes from semiconductor carbon nanotubes.
Honda inventors Avetik Harutyunyan and Toshio Tokune developed a method for treating carbon nanotubes with microwave energy to selective remove metallic-type carbon nanotubes is provided. A sample containing carbon nanotubes is positioned in a microwave cavity at a location corresponding to a maximum in the electric field component of a stationary wave having a microwave frequency. The sample is exposed to the microwave energy for a sufficient period of time to increase the proportion of semiconducting-type carbon nanotubes within the sample.
Alternatively, a sample consisting essentially of metallic-type and semiconducting-type carbon nanotubes is exposed to microwave energy for a sufficient period of time to increase the proportion of semiconducting-type carbon nanotubes within the sample.
Single-walled carbon nanotubes are a material with many potential industrial and research uses. Potential applications for carbon single-walled nanotubes (SWNTs) composed of carbon include such diverse areas as nanodevices, field emitters, improved capacitors, high strength composite materials, and hydrogen storage. Realizing the full potential of carbon nanotubes within these technologies, however, will require further study into the properties of carbon nanotubes. Some of the barriers to achieving this potential are due to limitations in current carbon nanotube synthesis methods.
The end product for many carbon nanotube synthesis techniques is a mixture of carbon nanotubes, amorphous carbon, and some type of metal particles used as a growth catalyst. The metal particles used for the growth catalyst are often metal nanoparticles composed of a ferromagnetic material such as iron, cobalt, or nickel. Additionally, the carbon nanotubes themselves are formed in a mixture of sizes and shapes. In particular, the desired carbon SWNTs are usually a mixture of carbon SWNTs with semiconducting-type properties and carbon SWNTs with metallic-type properties. The ratio of metallic type-nanotubes versus semiconducting-type nanotubes is controlled in part by the process used to synthesize the nanotubes.
The Honda invention provides a method for increasing the proportion of semiconducting-type nanotubes in a carbon nanotube sample. In an embodiment, a microwave cavity is configured to produce a stationary wave at a desired microwave frequency. A carbon nanotube sample containing both semiconducting-type and metallic-type carbon nanotubes is placed in the cavity at a location corresponding to a maximum in the electric field component of a stationary wave of a microwave frequency. The carbon nanotube sample is then exposed to the stationary wave at the desired microwave frequency. The carbon nanotube sample is exposed for a sufficient period of time to destroy or damage carbon nanotubes with metallic-type properties while causing minimal or no damage to carbon nanotubes with semiconducting-type properties.
The method provides for increasing the proportion of semiconducting-type nanotubes in a carbon nanotube sample that does not contain additional ferromagnetic or conductive materials. In an embodiment, a carbon nanotube sample consisting essentially of semiconducting-type and metallic-type carbon nanotubes is placed in a microwave cavity. The carbon nanotube sample is then exposed to microwave energy for a sufficient period of time to destroy carbon nanotubes with metallic properties while causing minimal or no damage to carbon nanotubes with semiconducting properties.
The method provides for increasing the proportion of semiconducting-type nanotubes in a carbon nanotube sample that does not contain additional ferromagnetic or conductive materials. In an embodiment, a carbon nanotube sample consisting essentially of semiconducting-type and metallic-type carbon nanotubes is placed in a microwave cavity. The carbon nanotube sample is then exposed to microwave energy for a sufficient period of time to destroy carbon nanotubes with metallic properties while causing minimal or no damage to carbon nanotubes with semiconducting properties.
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