Feb 14, 2008 2:03 PM

UCLA chemists design new material to capture carbon dioxide emissions, culprit behind global warming

UCLA chemists report a major advance in reducing heat-trapping carbon dioxide emissions in the Feb. 15 issue of the journal Science. They have demonstrated that they can capture carbon dioxide – which contributes to global warming, rising sea levels and increased acidity of oceans.

Their research can lead to power plants efficiently capturing carbon dioxide before it’s released into the atmosphere without using toxic materials.

“The technical challenge of selectively removing carbon dioxide has been overcome,” said Omar M. Yaghi, UCLA’s Christopher S. Foote Chair Professor of Chemistry, and co-author of the Science paper. “Now we have structures that can be tailored precisely to capture carbon dioxide and store it like a reservoir, as we have demonstrated. No carbon dioxide escapes. Nothing escapes – unless you want it to do so. We believe this to be a turning point in capturing carbon dioxide before it reaches the atmosphere.”

Carbon dioxide is captured in a new class of materials that Yaghi and his group have designed, which they call ZIFs (zeolitic imidazolate frameworks). They are porous and chemically robust with large surface areas, can be heated to high temperatures without decomposition, and can be boiled in water or organic solvents for a week and still remain stable.

Rahul Banerjee, a postdoctoral research scholar in chemistry and Anh Phan, a graduate student in chemistry, who both work in Yaghi’s laboratory, synthesized 25 ZIF crystal structures, and demonstrated that three of them have high selectivity for capturing carbon dioxide.

“The selectivity of ZIFs to carbon dioxide is unparalleled by any other material,” said Yaghi, director of UCLA’s Center for Reticular Chemistry and a member of the California NanoSystems Institute. “Rahul and Anh were so successful at making new ZIFs that, for the purposes of reporting the results, I had to ask them to stop,” he added.

The inside of a ZIF can store gas molecules, while flaps that act like the chemical equivalent of a revolving door allow certain molecules to pass through and go inside the reservoir, while larger molecules or molecules of different shapes are blocked; carbon dioxide can be propelled inside.

“We can screen and select the one type of molecule we want to capture,” Phan said. “The beauty of the chemistry is that we have the freedom to choose what kind of door we want, and control what goes through the door.”

“The capture of carbon dioxide creates cleaner energy,” Yaghi said. “ZIFs in a smokestack would trap carbon dioxide in the pores prior to its delivery to its geologic storage space.”

Currently, the process for capturing carbon dioxide emission from a power plant requires toxic materials and takes 20 to 30% of the power plant’s energy output, Yaghi said. In contrast, ZIFs can pluck out carbon dioxide from other gases that are emitted and hold it.

“For each liter of ZIF, you can hold 83 liters of carbon dioxide,” Banerjee said. This amount is five times that stored by porous state-of-the-art carbon materials.

The word ZIF, Yaghi noted, is a Biblical word that describes a region of splendor. It is also a word that means comeliness and brightness. This name is quite fitting to this new class of materials, he said.

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