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Staff Accomplishments

Teaching an Old Material New Tricks

January 2007
Researchers discover material has a talent for absorbing gases Frustrated carbon-based crystals may help solve a frustrating carbon-based problem, reducing carbon dioxide emissions from the world's power plants. Recently, researchers at Pacific Northwest National Laboratory and University of Missouri-Columbia developed a new class of materials by frustrating the crystal structure with small amounts of toluene, a clear liquid used in manufacturing paints and fingernail polish. The crystals are composed of bowl-shaped calixarene molecules. When the researchers added large quantities of toluene, the bowls filled with toluene and could not accept gas molecules. When they removed all of the toluene, the bowls collapsed. A small amount of toluene, though, prevented or frustrated the collapse of the bowls, allowing them to accept gas molecules. "This material appears to be very promising for separating carbon dioxide from gas mixtures," said PNNL's Praveen Thallapally, the principal investigator. "It absorbs more carbon dioxide under standard temperature and pressure conditions than many materials in use today." In addition, this material could be used to purify hydrogen, an important step in using hydrogen as an alternative fuel. Previous studies by these researchers show that the frustrated calixarenes can remove nitrogen, carbon dioxide and other impurities from a hydrogen stream. While calixarenes were discovered in the late 1800s, the crystalline form was considered impervious to gases. Scientists believed gases simply flowed around the crystals, not interacting with them. The researchers explored frustrated calixarenes using single crystal x-ray and powder diffraction system equipped with a beryllium cell. "This is a one-of-a-kind piece of equipment," said PNNL's Wayne Martin, Applied Geology and Geochemistry Group Manager. The instrument is able to detect the phase transformation as it happens at variable temperatures and pressures, letting the researchers observe materials phenomena that were impossible to study before. This research is just the tip of the iceberg. The team is developing more frustrated crystals to absorb gases and has just published an article in New Journal of Chemistry on one calixarene that absorbs methane, the major component in natural gas. Researchers are now focusing on other calixarene derivatives and metal-organic frameworks. "These materials could aid in pollution prevention, gas storage, separations, sensor applications and other purposes, yet undiscovered," noted PNNL Fellow and co-investigator Pete McGrail. The funding for the project stems from Laboratory Directed Research & Development (LDRD) and the Office of Fossil Energy.

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