Table salt, detergent, and baking soda are effective ingredients for creating carbon nanotubes, researchers at MIT have found out.
This surprising study was published this week in the journal Angewandte Chemie, the team reports that compounds that contain sodium are found in common household ingredients are able to catalyze the growth of carbon nanotubes, or CNTs, at much lower temperatures than the traditional catalysts require.
The researchers say that the sodium makes it possible for carbon nanotubes to be grown on host materials that have lower-temperature, such as polymers, which melt under the high temperatures needed for traditional CNT growth.
"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. "Using sodium as a catalyst really unlocks the kinds of surfaces you can grow nanotubes on."
Under a microscope, carbon nanotubes are the same as hollow cylinders of chicken wire. Each tube is made from a lattice of hexagonally arranged carbon atoms that are rolled-up. The bond between carbon atoms is strong and when patterned into a lattice, such as a graphene, or as a tube, such structures can have stiffness and strength as well as unique electrical and chemical properties. Researchers have explored coating various surfaces with CNTs to make stiffer, tougher and stronger materials.
Researchers typically grow CNTs through a process called chemical vapor deposition, and they do it through various materials. The material of interest, such as carbon fibers, is coated in a catalyst and placed in a furnace, in which carbon dioxide and other carbon-containing gases flow.
When the temperature hits 800 degrees Celsius, the iron starts to draw carbon atoms out of the gas, which then gloms onto the iron atoms and to each other, forming vertical tubes of carbon atoms around the individual carbon fibers.
Li and his team of researchers were experimenting with ways to grow CNTs on different surfaces by coating them with different solutions of iron-containing compounds when they noticed the resulting carbon nanotubes looked different from what they expected.
"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.
Iron has been the traditional catalyst for growing CNTs. Wardle says that this is the first time that they have seen sodium getting a similar effect.
"Sodium and other alkali metals have not been explored for CNT catalysis," Wardle says. "This work has led us to a different part of the periodic table."
"A large part of CNT research is not on growing them, but on cleaning them -getting the different metals used to grow them out of the product," Wardle says. "The neat thing with sodium is, we can just heat it and get rid of it, and get pure CNT as a product, which you can't do with traditional catalysts."