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A carbon
nanotube sponge that can soak up oil in water with unparalleled efficiency has
been developed with help from computational simulations performed at the U.S. Department
of Energy’s (DOE’s) Oak Ridge National Laboratory (ORNL).
Carbon
nanotubes, which consist of atom-thick sheets of carbon rolled into cylinders,
have captured scientific attention in recent decades because of their high
strength, potential high conductivity, and light weight. But producing
nanotubes in bulk for specialized applications was often limited by
difficulties in controlling the growth process as well as dispersing and sorting
the produced nanotubes.
ORNL’s Bobby
Sumpter was part of a multi-institutional research team that set out to grow
large clumps of nanotubes by selectively substituting boron atoms into the
otherwise pure carbon lattice. Sumpter and Vincent Meunier, now of Rensselaer
Polytechnic Institute, conducted simulations on supercomputers, including
Jaguar at ORNL’s Leadership Computing Facility, to understand how the addition
of boron would affect the carbon nanotube structure.
“Any time
you put a different atom inside the hexagonal carbon lattice, which is a
chicken wire-like network, you disrupt that network because those atoms don’t
necessarily want to be part of the chicken wire structure,” Sumpter said.
“Boron has a different number of valence electrons, which results in
curvature changes that trigger a different type of growth.”
Simulations and
laboratory experiments showed that the addition of boron atoms encouraged the
formation of so-called “elbow” junctions that help the nanotubes grow
into a 3D network. The team’s results are published in Nature Scientific Reports.
“Instead of
a forest of straight tubes, you create an interconnected, woven sponge-like
material,” Sumpter said. “Because it is interconnected, it becomes
three-dimensionally strong, instead of only one-dimensionally strong along the
tube axis.”
Further
experiments showed the team’s material, which is visible to the human eye, is
extremely efficient at absorbing oil in contaminated seawater because it
attracts oil and repels water.
“It loves
carbon because it is primarily carbon,” Sumpter said. “Depending on
the density of oil to water content and the density of the sponge network, it
will absorb up to 100 times its weight in oil.”
The material’s
mechanical flexibility, magnetic properties, and strength lend it additional
appeal as a potential technology to aid in oil spill cleanup, Sumpter says.
“You can
reuse the material over and over again because it’s so robust,” he said.
“Burning it does not substantially decrease its ability to absorb oil, and
squeezing it like a sponge doesn’t damage it either.”
The material’s
magnetic properties, caused by the team’s use of an iron catalyst during the
nanotube growth process, means it can be easily controlled or removed with a
magnet in an oil cleanup scenario. This ability is an improvement over existing
substances used in oil removal, which are often left behind after cleanup and
can degrade the environment.
The experimental
team has submitted a patent application on the technology through Rice University.
