Researchers at Waseda University in Japan have grown “forests” of carbon nanotubes (CNTs) longer than ever before. Using a new method, the team grew bunches of nanotubes up to 14 cm (5.5 in) long, which should help make it easier to scale up production of this versatile material.
The name is pretty descriptive – carbon nanotubes are tubes of carbon atoms with diameters just nanometers wide. Forests of these tubes have shown promise in making materials that are lightweight and strong, have useful optical properties, as well as better water filters, batteries and transistors.
The problem is and always has been around growing them in bulk. In past studies scientists have managed to grow individual nanotubes as long as 50 cm (19.7 in), but single tubes aren’t particularly useful. Forests of them, meanwhile, have struggled to stretch longer than about 2 cm (0.8 in).
Now, the researchers on the new study have managed to extend CNT forests to a much more practical 14 cm. To do so, they tackled several problems that usually stunt the growth of CNT forests – the first of which is to reduce the deterioration of the catalyst that feeds the tubes.
“In the conventional technique, the CNTs stop growing due to a gradual structural change in the catalyst, so we focused on developing a new technique that suppresses this structural change and allows the CNTs to grow for a longer period,” says Hisashi Sugime, lead author of the study.
Normally, the catalyst is an iron-aluminum oxide coated onto a silicon substrate, but for this study the team added a new layer of gadolinium. This reduced the rate that the catalyst deteriorated, but alone it only boosted the CNT forests to about 5 cm (2 in).
The extra length came by placing the catalyst into a cold-gas chemical vapor deposition chamber. The catalyst was heated to 750 °C (1,382 °F), and the team then added small concentrations of iron and aluminum vapors at room temperature. That fed the catalyst for 26 hours, giving it the time to grow the CNT forests to the record-breaking length.
Importantly, the team says that analysis of the resulting carbon nanotube forests showed that they were as pure and strong as those grown through other methods. That means the new technique should be able to make viable carbon nanotubes at production scale.
“This simple but novel method that drastically prolongs catalyst lifetime by supplying parts-per-million-level vapor sources is insightful for catalyst engineering in other fields such as petrochemistry and nanomaterial crystal growth,” says Sugime. “The knowledge herein could be pivotal to making nanomaterials a ubiquitous reality.”
The research was published in the journal Carbon. The carbon nanotubes growing can be seen in the time lapse video below.
Source: Waseda University