New aerogels could purify hydrogen for fuel cells
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 a innovative type of porous material. Given that one of the most feasible ways to produce renewable and climate-neutral hydrogen is via biomass (overview), the research into purification techniques is of obvious interest to the biohydrogen community.
Argonne materials scientists Peter Chupas and Mercouri Kanatzidis, along with colleagues at Northwestern and Michigan State universities, created and characterized porous semiconducting aerogels (image, click to enlarge) 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. They publish their findings in an open-access article in the July 27 issue of Science. 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.
energy :: sustainability :: biomass :: bioenergy :: biofuels :: biohydrogen :: aerogel :: purification :: materials sciences ::
"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, he explained.
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. "When we saw that these chalcogenides would make a gel, we were amazed," said Kanatzidis. "We turned the flask upside down and nothing flowed."
Generally, such reactions produce only uninteresting precipitates at the bottom of the flask, he said, so that in this case, "we knew we had something special."
Kanatzidis and his co-workers recognized that aerogels offered one remarkable advantage over powders: because the material maintained its cohesion, it 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.
Previous experiments into molecular filtration had used oxides rather than chalcogenides as their chemical constituents. While oxides tend to be insulators, most chalcogenides are semiconductors, enabling the study of their electrical and optical characteristics. Kanatzidis hopes to examine the photocatalytic properties of these new gels in an effort to determine whether they can assist in the production, and not merely the filtration, of hydrogen.
Unlike periodic materials, which possess a consistent long-range structure, the gels formed by the Northwestern and Argonne researchers are highly disordered. As a result, conventional crystallographic techniques would not have effectively revealed the structure and behavior of the gels. The high-energy X-rays produced by the APS, however, allowed the scientists to take accurate readings of the atomic distances within these disorganized materials. "This is where the APS really excels. It's the only place that has a dedicated facility for doing these kinds of measurements, and it allows you to wash away a lot of old assumptions about what kinds of materials you can and cannot look at," Chupas said.
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.
Image: (A) Different building blocks used in chalcogel formation (blue spheres, metal centers; red spheres, chalcogenide atoms). (B and C) Monolithic hydrogel before (B) and after (C) supercritical drying, showing very little volume loss.
References:
Santanu Bag, Pantelis N. Trikalitis, Peter J. Chupas, Gerasimos S. Armatas, and Mercouri G. Kanatzidis, "Porous semiconducting gels and aerogels from chalcogenide clusters", Science 27 July 2007: Vol. 317. no. 5837, pp. 490 - 493, DOI: 10.1126/science.1142535
Argonne National Laboratory: New aerogels could clean contaminated water, purify hydrogen for fuel cells - July 27, 2007.
Article continues
Argonne materials scientists Peter Chupas and Mercouri Kanatzidis, along with colleagues at Northwestern and Michigan State universities, created and characterized porous semiconducting aerogels (image, click to enlarge) 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. They publish their findings in an open-access article in the July 27 issue of Science. 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?' 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. - Peter Chupas, Argonne National LaboratoryThe 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 kind of 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:
energy :: sustainability :: biomass :: bioenergy :: biofuels :: biohydrogen :: aerogel :: purification :: materials sciences ::
"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, he explained.
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. "When we saw that these chalcogenides would make a gel, we were amazed," said Kanatzidis. "We turned the flask upside down and nothing flowed."
Generally, such reactions produce only uninteresting precipitates at the bottom of the flask, he said, so that in this case, "we knew we had something special."
Kanatzidis and his co-workers recognized that aerogels offered one remarkable advantage over powders: because the material maintained its cohesion, it 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.
Previous experiments into molecular filtration had used oxides rather than chalcogenides as their chemical constituents. While oxides tend to be insulators, most chalcogenides are semiconductors, enabling the study of their electrical and optical characteristics. Kanatzidis hopes to examine the photocatalytic properties of these new gels in an effort to determine whether they can assist in the production, and not merely the filtration, of hydrogen.
Unlike periodic materials, which possess a consistent long-range structure, the gels formed by the Northwestern and Argonne researchers are highly disordered. As a result, conventional crystallographic techniques would not have effectively revealed the structure and behavior of the gels. The high-energy X-rays produced by the APS, however, allowed the scientists to take accurate readings of the atomic distances within these disorganized materials. "This is where the APS really excels. It's the only place that has a dedicated facility for doing these kinds of measurements, and it allows you to wash away a lot of old assumptions about what kinds of materials you can and cannot look at," Chupas said.
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.
Image: (A) Different building blocks used in chalcogel formation (blue spheres, metal centers; red spheres, chalcogenide atoms). (B and C) Monolithic hydrogel before (B) and after (C) supercritical drying, showing very little volume loss.
References:
Santanu Bag, Pantelis N. Trikalitis, Peter J. Chupas, Gerasimos S. Armatas, and Mercouri G. Kanatzidis, "Porous semiconducting gels and aerogels from chalcogenide clusters", Science 27 July 2007: Vol. 317. no. 5837, pp. 490 - 493, DOI: 10.1126/science.1142535
Argonne National Laboratory: New aerogels could clean contaminated water, purify hydrogen for fuel cells - July 27, 2007.
Article continues
Monday, July 30, 2007
Oil spill clean-up agents threaten coral reefs
Called the 'rainforests of the sea', coral reefs are an endangered ecosystem and are disappearing at an alarming rate due to numerous threats, including over-fishing, global warming and pollution, particularly oil spills. Besides hosting a rich diversity of marine organisms, these habitats are also potential sources of life-saving medicines and food for humans. Scientists looking for better ways to protect this important habitat have recently focused on the environmental impact of oil dispersants, detergents used break down oil spills into smaller, less harmful droplets.
In the new report, Shai Shafir and colleagues evaluated the effects of both crude oil and six commercial oil dispersants under laboratory conditions on the growth and survival of two important species of reef corals. The dispersants and dispersed oil droplets were significantly more toxic to the coral than the crude oil itself, the scientists report. The dispersants caused significant harm, including rapid, widespread death and delay in growth rates, to the coral colonies tested even at doses recommended by the manufacturers, they add.
It is estimated that 40% of global crude oil transport is conducted offshore with much of the traffic, taking place in tropical, coral reef-rich areas. This heavy maritime traffic of crude oils and their products is prone to accidents, resulting in major or minor spillages. Although the number of major oil spills has decreased in the past decade it is still, by far, the most serious threat to the marine environment:
energy :: sustainability :: crude oil :: petroleum :: oil spills :: biodiesel :: biodegradable :: biofuels :: coral reefs ::
Of the three major ways for treating marine oil spills (chemicals, mechanical containment booms, skimmers and sorbents, biological-biodegrading microorganisms), chemicals, mainly oil dispersants, are probably the most commonly used, the scientists say.
Dispersants are chemicals that contain surfactants and/or solvent compounds that break down floating oil into small droplets within the water-column, which makes the spill less likely to reach shore. Dispersed oil is subjected to natural forces such as waves and currents that promote dissolution of oil droplets.
Use of dispersants for treating oil spills is governed by local and national regulations determining, for instance, distance from shore and depth at which treatment is allowed. However, since most oil-tanker accidents occur near the shore, it is essential to evaluate the impacts of oil dispersants on organisms that live on the seabed, including sea grass populations and coral reefs.
Given that manufacturer-recommended dispersant concentrations proved to be highly toxic and resulted in mortality for all nubbins and that they were significantly more toxic than crude oil, the scientists rule out the use of any oil dispersant in coral reefs and in their vicinity.
The authors therefor urge decision-making authorities to carefully consider these results when evaluating possible use of oil dispersants as a mitigation tool against oil pollution near coral reef areas.
Image: Oil-spill clean-up agents are a threat to coral reefs, researchers say. Courtesy: Shai Shafir, The Hebrew University of Jerusalem.
References:
Shai Shafir, Jaap Van Rijn, and Baruch Rinkevich, "Short and Long Term Toxicity of Crude Oil and Oil Dispersants to Two Representative Coral Species", Environ. Sci. Technol., 41 (15), 5571 -5574, 2007. 10.1021/es0704582 S0013-936X(07)00458-0, Web Release Date: June 26, 2007, scheduled print edition August 1, 2007.
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