Materials scientists and engineers at Northwestern University in Evanston, Illinois and University of Surrey in the U.K. created two new synthetic materials with the largest reported amounts of internal surface area. The researchers published their findings online in the Journal of the American Chemical Society (paid subscription required).
The two new materials, known as NU-109 and NU-110, belong to a class of crystalline nanoscale structures known as metal-organic frameworks. These kinds of materials are extremely porous with structures made of metal oxide joints and organic struts. Metal-organic frameworks, like the two new Northwestern materials, are considered promising candidates for a range of applications, including storing natural gas in vehicles, chemical catalysts, and capturing carbon dioxide emissions.
The source of the materials’ value are their vast internal surface areas. If unfolded, one NU-110 crystal the size of a grain of salt would have a surface equal to a desk top. Extrapolated further, one gram of NU-110 would have an internal surface area that could cover 1.5 football fields.
The research team led by Northwestern chemistry professor Omar Farha (pictured at top) synthesized and simulated the two materials that claim the largest surface areas of any porous materials on record, where one kilogram of the material contains an internal surface area that could cover seven square kilometers. The researchers used a standard analytical technique for computing surface areas.
Farha and colleagues were able to access the high surface area of the materials through a technique using carbon dioxide to remove the solvents that get trapped in the pores of the material, thus reducing the amount of available space. Heat could remove the solvents, but also damage the material in the process. The carbon dioxide technique, say the researchers, removes the solvent gently and leaves the pores intact.
The technology developed at Northwestern to design and synthesize metal-organic frameworks is being commercialized by a start-up company, NuMat Technologies in Evanston. Farha, who led the research team, is also the company’s chief scientist. In July, NuMat received funding from the Department of Energy through the Gas Technology Institute to identify new porous materials, such as metal-organic frameworks, to speed the development of low-pressure natural gas tanks for vehicles.
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