Nanotech Cleans Up

The mesh of nanowires behind MIT's new material for absorbing oil and other organic pollutants, here shown at increasing magnifications (left to right).

Courtesy of Francesco Stellacci, MIT, and Nature Nanotechnology

Monday, June 16th, 2008--

How do you clean up an oil spill? In the future, maybe with a big towel made of tiny wires.

Since the start of this decade, about 200,000 metric tons of oil have spilled into the world’s waterways, according to the International Tanker Owners Pollution Federation. Finding a way to remove that oil quickly and effectively could minimize the damage to marine environments. Now, a team of researchers led by scientists at the Massachusetts Institute of Technology has created a membrane out of nanowires that can selectively sop up oil from water.

The nanowire membrane “looks like a piece of brown paper,” says Francesco Stellacci, an associate professor of materials science and engineering at MIT, “and the way we produce it is similar to making paper.” But instead of the wood fiber used to make paper, Stellacci and his colleagues use tiny wires made from manganese oxide to create their membrane. These nanowires, some 20 nanometers in diameter (one nanometer is 1 million times smaller than a human hair), are “interwoven like spaghetti” to create a sheet that looks and feels like paper, says the Italian scientist.

Now, how to get it to suck up oil? Any piece of paper is absorbent, says Stellacci--just think of Bounty, the paper towel dubbed “the quicker picker upper.” Stellacci’s nanopaper is like the famous paper towel, but it’s made to absorb only oil and not water. That’s a two-part process. The first step is to weave the nanowires together tightly. “Because it’s a very fine spaghetti mesh, it traps a lot of air on its surface and that keeps the water off,” he says.

The next step is to target the oil. To do that, the researchers coat the nanopaper with a polymer, siloxane vapor, that attracts oil. “It’s very selective,” says Stellacci. “It gets only the oil.” Back to the Bounty analogy, if you’ve got a spill of oil and water on the counter and you mop it up with the paper towel, it will pick up both. But if you use the nanopaper, it will soak up the oil, leaving the water on the counter.

Just how absorbent is it? According to Stellacci’s studies, the nanopaper can absorb up to twenty times its own weight. Make a big enough sheet of these nanowires, and you can soak up a lot of oil.

So far, the nanopaper has only been tested in the lab, but Stellacci is eager to try it out on a real spill. If it does work in a real-world setting, the nanopaper could be a blueprint for using nanomaterials to clean up the environment. Stellacci predicts that his nanopaper will work on more than oil. He thinks it will also remove other organic compounds from water, including solvents like benzene, used to make plastics, rubbers, and dyes, and toluene, used in paint thinner.

This research was published in the May 30th online edition of Nature Nanotechnology.

--Karin Vergoth