Posted: May 10th, 2012 Nanotube 'sponge' has potential in oil spill cleanup ( Nanowerk News ) A carbon nanotube sponge that can soak up oil in water withunparalleled efficiency has been developed with help fromcomputational simulations performed at the Department of Energy's(DOE's) Oak Ridge National Laboratory. Carbon nanotubes, which consist of atom-thick sheets of carbonrolled into cylinders, have captured scientific attention in recentdecades because of their high strength, potential high conductivityand light weight. But producing nanotubes in bulk for specializedapplications was often limited by difficulties in controlling thegrowth process as well as dispersing and sorting the producednanotubes. ORNL's Bobby Sumpter was part of a multi-institutional researchteam that set out to grow large clumps of nanotubes by selectivelysubstituting boron atoms into the otherwise pure carbon lattice.Sumpter and Vincent Meunier, now of Rensselaer PolytechnicInstitute, conducted simulations on supercomputers, includingJaguar at ORNL's Leadership Computing Facility, to understand howthe addition of boron would affect the carbon nanotube structure. A carbon nanotube sponge developed with help from ORNL researchersholds potential as an aid for oil spill cleanup. |
"Any time you put a different atom inside the hexagonal carbonlattice, which is a chicken wire-like network, you disrupt thatnetwork because those atoms don't necessarily want to be part ofthe chicken wire structure," Sumpter said. "Boron has a differentnumber of valence electrons, which results in curvature changesthat trigger a different type of growth." Simulations and lab experiments showed that the addition of boronatoms encouraged the formation of so-called "elbow" junctions thathelp the nanotubes grow into a 3-D network. The team's results arepublished in Nature Scientific Reports ( "Covalently bonded three-dimensional carbon nanotube solidsvia boron induced nanojunctions" ). "Instead of a forest of straight tubes, you create aninterconnected, woven sponge-like material," Sumpter said.
"Becauseit 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 tothe human eye, is extremely efficient at absorbing oil incontaminated 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 densityof the sponge network, it will absorb up to 100 times its weight inoil." The material's mechanical flexibility, magnetic properties, andstrength lend it additional appeal as a potential technology to aidin oil spill cleanup, Sumpter says. "You can reuse the material over and over again because it's sorobust," he said. "Burning it does not substantially decrease itsability to absorb oil, and squeezing it like a sponge doesn'tdamage it either." The material's magnetic properties, caused by the team's use of aniron catalyst during the nanotube growth process, means it can beeasily controlled or removed with a magnet in an oil cleanupscenario.
This ability is an improvement over existing substancesused in oil removal, which are often left behind after cleanup andcan degrade the environment.
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