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, MIT
researchers and colleagues report in the May 30 online issue of Nature
Nanotechnology.
 | | Oil Spill |
The scientists 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.
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.”
In addition to Stellacci and Kong (who is also affiliated
with MIT's Research Laboratory of Electronics, or RLE), other authors
are Jikang Yuan, a postdoctoral associate in MIT's Department of
Electrical Engineering and Computer Science (EECS) and RLE; Xiaogang
Liu, now at the National University of Singapore; Ozge Akbulut of the
Department of Materials Science and Engineering; Junqing Hu of the
National Institute for Materials Science in Japan; and Steven L. Suib
of the University of Connecticut, Storrs.
This work was primarily funded by the Deshpande Center for
Technological Innovation at MIT.
Posted 2nd June 2008
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