Oil and Water

blue gloved hand holding chunk of black material, with dropper placing oil on it
Jeff Fitlow, Rice University

Mauricio Terrones and his colleagues have created spongy blocks of carbon nanotubes that have an astounding ability to absorb oil, separating it from seawater. The new material, which could be used to clean up oil spills in oceans, also has other novel applications related to electronics, materials science, and medicine.

Solid, spongy blocks of carbon nanotubes may be a big help in future oil-spill cleanups, according to researchers at Penn State and Rice University who created the new material. Formed using carbon and a dash of boron, these nanotube sponges have a remarkable ability to separate oil from seawater.

Mauricio Terrones, a professor of physics at Penn State and part of an international team including scientists from the United States, Spain, Belgium and Japan, explains that carbon nanotubes are tiny tubes with diameters ranging from one to 50 nanometers—much narrower than the width of a human hair. They are also 100 times stronger than steel and about one-sixth the weight.

“Our goal was to find a way to make three-dimensional networks of these carbon nanotubes that would form a macroscale fabric—a spongy block of nanotubes that would be big and thick enough to be used to clean up oil spills and to perform other tasks," Terrones says.

“We realized that the trick was adding boron—which is next to carbon on the periodic table—because boron helps to trigger the interconnections of the material. To add the boron, we used very high temperatures and ‘knitted’ the substance into the nanotube fabric.”

Terrones’ collaborator, Pulickel Ajayan, a professor of engineering at Rice, explains that the boron puts kinks and elbows into the nanotubes and promotes the formation of covalent bonds, which give the sponges their robust qualities. “The boron helps to tangle the sponges into a complex network,” Ajayan says.

Daniel Hashim, a Rice graduate student and member of the team, notes that the spongy carbon-nanotube blocks are special for two reasons. “First, they are superhydrophobic, which means that they hate water, so they float really well. Second, they are oleophilic, which means that they love—and thus absorb—oil. In fact, they can absorb 123 times their weight in oil,” Hashim says.

To demonstrate, he drops a nanotube sponge into a dish of water with used motor oil floating on top. The sponge soaks it up. He then removes the sponge and puts a match to it, burning off the oil, before returning the undamaged material to the water to absorb more.

“This material can be used repeatedly and stands up to abuse," Hashim says, adding that one sponge remained elastic even after 11,000 uses in the lab. “Another interesting feature of these nanotube sponges, which are 99 percent air, is that they conduct electricity and can easily be manipulated with magnets," Hashim says.

Members of the research team are now working on how to make larger sheets of the stuff. “For oil spills, you would have to make large-enough sheets or find a way to weld smaller sheets together," Ajayan notes. Terrones adds that the team is also looking to exploit the three-dimensional structure of the sponges for other applications.

“Oil-spill remediation and environmental clean-up are just the beginning of how useful these materials could be,” Terrones says. “We could use these materials to make more efficient and lighter batteries. We could use them as scaffolds for bone-tissue regeneration. We could even impregnate the sponge with polymers to fabricate robust and light composites for the automobile and plane industries.”

Mauricio Terrones, Ph.D., is professor of physics and of materials science and engineering at Penn State, terrones@phys.psu.edu.

Support for this research comes from the National Science Foundation, the Air Force Office of Scientific Research, and the Center for Nanophase Materials Science of Oak Ridge National Laboratory.

Last Updated May 30, 2012