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Scientists at the U.S. Department of Energy's Argonne National Laboratory have identified a new technique for cleansing contaminated water and potentially purifying hydrogen for use in fuel cells, thanks to the discovery of an innovative type of porous material.
Argonne materials scientists Peter Chupas and Mercouri Kanatzidis, along with colleagues at Northwestern and Michigan State universities, created and characterized porous semiconducting aerogels at Argonne's Advanced Photon Source (APS). The researchers then submerged a fraction of a gram of the aerogel in a solution of mercury-contaminated water and 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 this kind of environmental cleanup, but also to remove impurities from hydrogen gas that could damage the catalysts in potential 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, which are fashioned from chalcogenides — molecules centered on the elements found directly under oxygen in the periodic table — are expected to be able to separate out the impurities from hydrogen gas much as they did the mercury from the water by acting as a sieve or selectively permeable membrane. The unique chemical and physical structure of the gels will allow researchers to "tune" their pore sizes or composition in order to separate particular poisons from the hydrogen stream.
Kanatzidis and his co-workers recognized that aerogels offered one remarkable advantage over powders, in that the material maintained its cohesion and therefore possessed an enormous surface area. One cubic centimeter of the aerogel could have a surface area as large as a football field, according to Kanatzidis. 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 Science.
The initial research into porous semiconducting surfactants was supported by a grant from the National Science Foundation. Use of the APS was supported by DOE, Office of Science, Office of Basic Energy Sciences.