“The tubes looked a little funny, and Rich and the team carefully peeled the onion back, as it were, and it turns out a small quantity of sodium, which we suspected was inactive, was actually causing all the growth,” Wardle says.įor the most part, iron has been the traditional catalyst for growing CNTs. Li and his colleagues were experimenting with ways to grow CNTs on various surfaces by coating them with different solutions of iron-containing compounds, when the team noticed the resulting carbon nanotubes looked different from what they expected. Researchers then use various techniques to dissolve the catalyst, leaving behind pure carbon nanotubes. At temperatures of up to 800 degrees Celsius, the iron starts to draw carbon atoms out of the gas, which glom onto the iron atoms and to each other, eventually forming vertical tubes of carbon atoms around individual carbon fibers. A material of interest, such as carbon fibers, is coated in a catalyst - usually an iron-based compound - and placed in a furnace, through which carbon dioxide and other carbon-containing gases flow. Researchers typically grow CNTs on various materials through a process called chemical vapor deposition.

As such, researchers have explored coating various surfaces with CNTs to produce stronger, stiffer, tougher materials.

The bond between carbon atoms is extraordinarily strong, and when patterned into a lattice, such as graphene, or as a tube, such as a CNT, such structures can have exceptional stiffness and strength, as well as unique electrical and chemical properties. Each tube is made from a rolled up lattice of hexagonally arranged carbon atoms. Under a microscope, carbon nanotubes resemble hollow cylinders of chicken wire. Li’s MIT co-authors are postdocs Erica Antunes, Estelle Kalfon-Cohen, Luiz Acauan, and Kehang Cui alumni Akira Kudo PhD ’16, Andrew Liotta ’16, and Ananth Govind Rajan SM ’16, PhD ’19 professor of chemical engineering Michael Strano, and professor of aeronautics and astronautics Brian Wardle, along with collaborators at the National Institute of Standards and Technology and Harvard University. “Using sodium as a catalyst really unlocks the kinds of surfaces you can grow nanotubes on.” “In aerospace composites, there are a lot of polymers that hold carbon fibers together, and now we may be able to directly grow CNTs on polymer materials, to make stronger, tougher, stiffer composites,” says Richard Li, the study’s lead author and a graduate student in MIT’s Department of Aeronautics and Astronautics. The researchers say that sodium may make it possible for carbon nanotubes to be grown on a host of lower-temperature materials, such as polymers, which normally melt under the high temperatures needed for traditional CNT growth.

In a study published this week in the journal Angewandte Chemie, the team reports that sodium-containing compounds found in common household ingredients are able to catalyze the growth of carbon nanotubes, or CNTs, at much lower temperatures than traditional catalysts require. Baking soda, table salt, and detergent are surprisingly effective ingredients for cooking up carbon nanotubes, researchers at MIT have found.

Carbon nanotubes