New Material Sponges Up Pollutants, Leaving Water Clean
ARGONNE, Illinois, July 30, 2007 (ENS) - A unique type of porous material that can cleanse contaminated water and potentially purify hydrogen for use in fuel cells has been developed by scientists at the U.S. Department of Energy's Argonne National Laboratory.
Porous semiconducting aerogels were discovered by Argonne materials scientists Peter Chupas and Mercouri Kanatzidis, along with colleagues at Northwestern and Michigan State universities.
When the researchers submerged a speck of the aerogel in a solution of mercury-contaminated water they found that the gel removed more than 99.99 percent of the heavy metal.
The researchers believe that these gels can be used not only for environmental cleanup but also to remove impurities from hydrogen gas that could damage the catalysts in hydrogen fuel cells.
'When people talk about the hydrogen economy, one of the big questions they're asking is ‘Can you make hydrogen pure enough that it doesn't poison the catalyst?' Chupas said. 'While there's been a big push for hydrogen storage and a big push to make fuel cells, there has not been nearly as big a push to find out where the clean hydrogen to feed all that will come from.'
The aerogels act as a kind of sieve or selectively permeable membrane. Their unique chemical and physical structure will allow researchers to 'tune' their pore sizes or composition in order to separate particular poisons from the hydrogen stream.
'You can put in elements that bind the poisons that are in the stream or ones that bind the hydrogen so you let everything else fall through,' Chupas said. 'For example, gels made with open platinum sites would extract carbon monoxide, a common catalyst poison.'
The research team had not intended to create the aerogels, but their discovery proved fortunate, said Kanatzidis. Originally, the researchers had used surfactants to produce porous semiconducting powders instead of gels.
When one of the researchers ran the synthesis reaction without the surfactant, he noticed that gels would form time after time.
Kanatzidis says that because the material maintains its cohesion, it possesses an enormous surface area - one cubic centimeter of the aerogel could have a surface area as large as a football field.
The bigger the surface area of the material, the more efficiently it can bind other molecules, he said.
The paper, entitled 'Porous semiconducting gels and aerogels from chalcogenide clusters,' appears in the July 27 issue of the journal 'Science.'
The initial research into porous semiconducting surfactants was supported by a grant from the National Science Foundation.
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