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Trapping light in a "cage." (light energy storage)

Using a "molecular cage" to trap light energy and then store it chemically, scientists have been able to mimic photosynthesis. This marks an important step in the field of solar energy research, according to Prabir Dutta, professor of chemistry, Ohio State University. "Our hope is that, down the road, we can use this trapped light energy to make hydrogen fuels or methane. We're doing in a sense what plants do during photosynthesis--turning light energy into chemical energy."

For years, scientists have been able to store light energy chemically using systems that utilize the ability of a donor molecule--one that becomes charged when exposed to light--to transfer its electric charge to an acceptor molecule. However, these systems have a hard time preventing the wasteful "back electron transfer" reaction, whereby the acceptor molecule simply passes its charge back to its donor and the stored energy is lost.

Current systems only can slow down that wasteful process, but, by adding a third molecule--an "ultimate acceptor"--to his system, Dutta has accomplished a long-term charge separation. "The first acceptor passes its charge to the ultimate acceptor instead of back to the donor."

Then, to make sure the charge doesn't find its way back to the donor, Dutta's system physically isolates the donor by trapping it within a zeolite "cage." Zeolites are crystals with channels and cavities that are just big enough to fit small molecules. The donor molecule, trisbipyridine ruthenium, is trapped within the zeolite, thus isolating it.

He tested his theory by suspending a powdered form of the zeolite complex in solution, then shining light on it to stimulate irradiation from the sun. "As the solution absorbed electrons, it darkened. In a sense, the zeolite complex plays the same role as chlorophyll in plants: It helps to convert light energy to chemical energy." In plants, the chemical energy may be released as an animal digests the vegetation, in the form of heat as wood is burned, or as fossil fuel is burned.

Dutta can access the energy stored in the ultimate acceptor, using it to perform such work as creating hydrogen or methane fuels. Compared to other solar systems, in which energy is trapped, but not accessible, the energy stored has a much greater potential for accessibility. "We still have a lot of work to do to increase the efficiency of our system, but this is the first time anyone has been able to accomplish any long-term storage. It's the first step in the long road to practical, viable solar energy technology."
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Publication:USA Today (Magazine)
Date:Jun 1, 1994
Previous Article:Using light to "spy" on materials.
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