Researchers Design World's Lowest-Density Crystals for Use in Clean Energy

Chemists at the University of California - Los Angeles (UCLA) said they have designed new organic structures for the storage of voluminous amounts of gases for use in alternative energy technologies.

The research, published on April 13 in the journal Science, demonstrates how the design principles of reticular chemistry have been used to create three-dimensional covalent organic frameworks, which are entirely constructed from strong covalent bonds and have high thermal stability, high surface areas and extremely low densities.

The team of researchers comprises chemists from the Center for Reticular Chemistry at UCLA's California NanoSystems Institute and the departments of chemistry and biochemistry at UCLA.

Led by Omar Yaghi, UCLA professor of chemistry and biochemistry, the team has developed a class of materials in which components can be changed nearly at will. Reticular chemistry, the brainchild of Yaghi, is the chemistry of linking molecular building blocks by strong bonds into predetermined structures. The principles of reticular chemistry and the ability to construct chemical structures from these molecular building blocks have led to the creation of new classes of materials of exceptional variety.

The covalent organic frameworks, or COFs (pronounced "coffs"), one of these new classes of materials, are the first crystalline porous organic networks. A member of this series, COF-108, has the lowest density reported of any crystalline material.

"These are the first materials ever made in which the organic building blocks are linked by strong bonds to make covalent organic frameworks," Yaghi said. "The key is that COFs are composed of light elements, such as boron, carbon and oxygen, which provide thermal stability and great functionality."

COF-108, the latest advance in reticular chemistry development, has a high surface area, with more than 4,500 meters per gram. "One gram, unraveled, could cover the surface area of approximately 30 tennis courts," Yaghi said.

In the push to develop methods to control greenhouse gas emissions, some of the biggest challenges have been finding ways to store hydrogen for use as a fuel, to use methane as an alternative fuel and to capture and store carbon dioxide from power plant smokestacks before it reaches the atmosphere. Yaghi and his colleagues believe COFs are uniquely suited for all these applications because of their functional flexibility and their extremely light weight and high porosity.

Through reticular chemistry, Yaghi has developed a process whereby it is possible to utilize the arsenal of organic building blocks to construct a large number of new COF structures with components that can be easily designed to suit a particular application. The pore size and pore functionality of these materials can be varied at will.

For more on Yaghi's research, visit http://www.chem.ucla.edu/dept/Faculty/yaghi.html.

This article originally appeared in the 04/01/2007 issue of Environmental Protection.

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