Led by Richard Li, a graduate student in MIT’s Department of Aeronautics and Astronautics, the team created carbon nanotubes using household ingredients rich in sodium, such baking soda, table salt and detergent pellets. Additionally, the team did it without the use of high heat that is usually required for the process. In doing so, the team demonstrated a brand new way to create carbon nanotubes.
Carbon nanotubes from salt
Prior to this study, scientists would use iron as the catalyst for creating carbon nanotubes. Here, a material such a carbon fiber would be coated in an iron-based catalyst, and then heated to over 1,400 F in a chamber filled with carbon dioxide and other carbon-rich gasses. At this temperature, the iron atoms draw the carbon out of the gasses. These eventually form individual tubes of carbon. Scientists dissolve the remaining catalyst, leaving behind pure carbon nanotubes.
Li's team came about the new method of creating carbon nanotubes by accident. They were researching ways of growing carbon nanotubes on different surfaces with different compounds using iron when they found that the resulting nanotubes looked a bit different. Upon further inspection, they discovered that a small quantity of sodium was causing the growth. This represented the first time that carbon nanotubes had been observed to grow from a sodium-based catalyst.
“Sodium and other alkali metals have not been explored for CNT catalysis,” said Brian Wardle, a team member who's a professor of aeronautics at MIT. “This work has led us to a different part of the periodic table.”
The team started testing the process using commercial grade sources of sodium such as baking soda, table salt and detergent, dissolving them in water and coating carbon fiber with the resulting solution. Eventually, the team moved on to tests using purified sodium. The team found that the carbon nanotubes grew out at about 896 F, a much lower temperature than with iron-based catalysts.
Sodium catalyst-grown carbon nanotubes have another advantage. With the traditional iron-based catalyst method, the carbon nanotubes must be isolated from the iron using a number of chemicals. With the sodium-based method however, the nanotubes come out without any contamination from the sodium – the creation process simply burns the sodium off.
Refining the process
At the moment, the carbon nanotubes created in this process do not posses the strength that carbon nanotubes are usually known for. This is because the walls of sodium-based carbon nanotubes don't align themselves in the crystal-like hexagonal configuration like the iron-based carbon nanotubes. With this in mind, Li hopes to further refine the process for creating carbon nanotubes from sodium.
Regardless of the quality of the carbon nanotubes created using sodium, the fact that the team discovered a new method of making the material represents a big step in carbon nanotube research.
Carbon nanotubes are seen to have a number of beneficial applications. Already, scientists are looking at how filters made from carbon nanotubes can remove heavy metals from water. More importantly, scientists are looking to carbon nanotubes as a way develop batteries that last longer and provide more power than current batteries.
That said, as with any new technology, carbon nanotubes also come with some risks. Research has warned that carbon nanotubes can lead to cancer if their particles end up being inhaled by people. This poses a great risk to those involved in their manufacture. With this in mind, scientists should take great care when conducting further research into carbon nanotubes so that their pros don't outweigh their cons.
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