Nanowire 'Paper Towel' Designed to Clean Up Oil Spills

LiveScience.com Yahoo News 30 May 08;

A mat of nanowires with the touch and feel of paper could be an important new tool in the cleanup of oil and other organic pollutants, scientists announced today.

MIT researchers and colleagues say they have created a membrane that can absorb up to 20 times its weight in oil, and can be recycled many times for future use. The oil itself can also be recovered.

Some 200,000 tons of oil have already been spilled at sea since the start of the decade.

"What we found is that we can make 'paper' from an interwoven mesh of nanowires that is able to selectively absorb hydrophobic liquids - oil-like liquids - from water," said Francesco Stellacci, an associate professor in the Department of Materials Science and Engineering and leader of the work.

The results are detailed in the May 30 online issue of Nature Nanotechnology.

In addition to its environmental applications, the nanowire paper could also impact filtering and the purification of water, said Jing Kong, an assistant professor of electrical engineering in the Department of Electrical Engineering and Computer Science and one of Stellacci's colleagues on the work. She noted that it could also be inexpensive to produce because the nanowires of which it is composed can be fabricated in larger quantities than other nanomaterials.

Stellacci explained that there are other materials that can absorb oils from water, "but their selectivity is not as high as ours." In other words, conventional materials still absorb some water, making them less efficient at capturing the contaminant.

The new material appears to be completely impervious to water. "Our material can be left in water a month or two, and when you take it out it's still dry," Stellacci said. "But at the same time, if that water contains some hydrophobic contaminants, they will get absorbed."

Made of potassium manganese oxide, the nanowires are stable at high temperatures. As a result, oil within a loaded membrane can be removed by heating above the boiling point of oil. The oil evaporates and can be condensed back into a liquid. The membrane - and oil - can be used again.

Two key properties make the system work. First, the nanowires form a spaghetti-like mat with many tiny pores that make for good capillarity, or the ability to absorb liquids. Second, a water-repelling coating keeps water from penetrating into the membrane. Oil, however, isn't affected, and seeps into the membrane.

The membrane is created by the same general technique as its low-tech cousin, paper. "We make a suspension of nanowires, like a suspension of cellulose [the key component of paper], dry it on a non-sticking plate, and we get pretty much the same results," Stellacci said.

In a commentary accompanying the Nature Nanotechnology paper, Joerg Lahann of the University of Michigan concluded: "Stellacci and co-workers have provided an example of a nanomaterial that has been rationally designed to address a major environmental challenge."

Cleaning up: Nano 'towel' soaks up oil spills
Yahoo News 30 May 08;

Researchers in the United States announced Friday they had created a paper-like membrane made of nano-scale materials that could clean up oil pollution and other chemical spills.

The substance can absorb up to 20 times its own weight in oil and be recycled again and again for future use, while the oil itself can also be recovered and used, they reported in the specialist journal Nature Nanotechnology.

The novel material comprises wires made of potassium manganese oxide at the scale of 20 nanometres, or 20 billionths of a metre, in diameter.

Together, the wires form a "spaghetti-like mat" whose strands have tiny pores that are good at absorbing liquids.

The membrane is covered with a hydrophobic, or water-repelling, coating. As a result, water cannot penetrate the membrane -- but oil can.

"What we have found is that we can make 'paper' from an interwoven mesh of nanowires that is able to selectively absorb hydrophobic liquids from water," said lead researcher Francesco Stellacci, an associate professor of materials science at the Massachusetts Institute of Technology (MIT).

The membrane appears to be completely impervious to water, he said.

"Our material can be left in water a month or two, and when you take it out, it's still dry. But at the same time, if that water contains some hydrophobic contaminants, they will get absorbed."

This also opens the way for using the membrane as a water filter, the team said.

Oil that is snared by the membrane can be removed by heating above the boiling point of oil. The oil evaporates and can be condensed back into a liquid.

In a press release, MIT said the membrane can be fabricated more cheaply than other nano materials. In the same way that cellulose is used for making conventional paper, a suspension is dried on a non-sticking plate.

In a commentary, published in the same journal, University of Michigan chemical engineer Joerg Lahann questioned whether the membrane would be used commercially, given the cost -- and possible toxicity -- of manganese oxide.

"Even so, it clearly provides a blueprint that can guide the design of future nanomaterials for environmental applications," Lahann said. "Many other examples are expected to follow and will confirm the potential of nanomaterials for protecting the environment."

On May 5, French-led technologists said they had beefed up the performance of a nano-powder that stores carbon dioxide (CO2), in a step towards creating a a filter to catch greenhouse gases from vehicle exhausts.

A cubic metre (35 cubic feet) of the new substance, called MIL-101, is able to capture 400 cu. metres (14,125 cu. feet) of CO2, thanks to pores 3.5 nanometres (billionths of a metre) across, according to the National Centre for Scientific Research (CNRS).