Research Achievements

October 29, 2019 

Dietary fiber effectively purifies carbon nanotubes

A dietary fiber can help separate out semiconducting carbon nanotubes used for making transistors for flexible electronics.

 

A new, cheaper method easily and effectively separates two types of carbon nanotubes. The process, developed by Nagoya University researchers in Japan, could be up-scaled for manufacturing purified batches of single-wall carbon nanotubes that can be used in high-performance electronic devices. The findings were published in the journal Applied Physics Express.

 

Single-wall carbon nanotubes (SWCNTs) have excellent electronic and mechanical properties, making them ideal candidates for use in a wide range of electronic devices, including the thin-film transistors found in LCD displays. A problem is that only two-thirds of manufactured SWCNTs are suitable for use in electronic devices. The useful semiconducting SWCNTs must be separated from the unwanted metallic ones. But the most powerful purification process, known as aqueous two-phase extraction, currently involves the use of a costly polysaccharide, called dextran.

 

Organic chemist Haruka Omachi and colleagues at Nagoya University hypothesized that dextran's effectiveness in separating semiconducting from metallic SWCNTs lies in the linkages connecting its glucose units. Instead of using dextran to separate the two types of SWCNTs, the team tried the significantly cheaper isomaltodextran, which has many more of these linkages.

 

A batch of SWCNTs was left for 15 minutes in a solution containing polyethylene glycol and isomaltodextrin and then centrifuged for five minutes. Three different types of isomaltodextrin were tried, each with a different number of linkages and a different molecular weight. The team found that metallic SWCNTs separated to the bottom isomaltodextrin part of the solution, while the semiconducting SWCNTs floated to the top polyethylene glycol part.

 

The type of isomaltodextrin with high molecular weight and the most linkages was the most (99%) effective in separating the two types of SWCNTs. The team also found that another polysaccharide, called pullulan, whose glucose units are connected with different kinds of linkages, was ineffective in separating the two types of SWCNTs. The researchers suggest that the number and type of linkages present in isomaltodextrin play an important role in their ability to effectively separate the carbon nanotubes.

 

The team also found that a thin-film transistor made with their purified semiconducting SWCNTs performed very well.

 

Isomaltodextrin is a cheap and widely available polysaccharide produced from starch that is used as a dietary fiber. This makes it a cost-effective alternative for the SWCNT extraction process. Omachi and his colleagues are currently in discussions with companies to commercialize their approach. They are also working on improving the performance of thin-film transistors using semiconducting SWCNTs in flexible displays and sensor devices.

 

 

Figure: The unwanted metallic SWCNTs deposited at the bottom of the solution,

while the wanted semiconducting ones floated to the top.

 

 

The article, "Aqueous two-phase extraction of semiconducting single-wall carbon nanotubes with isomaltodextrin and thin-film transistor applications," was published in Applied Physics Express at DOI: 10.7567/1882-0786/ab369e

 

Authors: Haruka Omachi, Tomohiko Komuro, Kaisei Matsumoto, Minako Nakajima, Hikaru Watanabe, Jun Hirotani, Yutaka Ohno, and Hisanori Shinohara

 

For more information, contact:

Associate Professor Haruka Omachi

Research Center for Materials Science, Nagoya University

Email: omachi@chem.nagoya-u.ac.jp

 

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About Nagoya University

Nagoya University has a history of about 150 years, with its roots in a temporary medical school and hospital established in 1871, and was formally instituted as the last Imperial University of Japan in 1939. Although modest in size compared to the largest universities in Japan, Nagoya University has been pursuing excellence since its founding. Six of the 18 Japanese Nobel Prize-winners since 2000 did all or part of their Nobel Prize-winning work at Nagoya University:  four in physics - Maskawa and Kobayashi in 2008, and Akasaki and Amano in 2014  - and two in Chemistry - Noyori in 2001 and Shimomura in 2008. In mathematics, Mori did his Fields Medal-winning work at Nagoya University. A number of other important discoveries have been made at Nagoya University, including the Okazaki DNA Fragments by Reiji and Tsuneko Okazaki in the 1960s; and depletion forces by Asakura and Oosawa in 1954.

 

 

 

 

 

 

 

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