Frozen Carbon Dioxide Templates Porous Materials

A new technique for creating porous materials has been developed by Andrew I. Cooper, James Long, and Haifei Zhang at the University of Liverpool, in England (J. Am. Chem. Soc. 2005, 127, 13482). The researchers dissolved the sugar acetate 1,2,3,4,6-pentaacetyl ß-D-galactose (BGAL) in liquid CO₂ within a stainless steel tube. They gradually lowered the tube into liquid nitrogen to freeze the CO₂. Then they slowly warmed the tube in dry ice, releasing gaseous CO₂ through a venting valve as it sublimed from the sample. The process converted the original BGAL powder into a solvent-free network of aligned tubular pores (shown). The researchers, who chose BGAL because it is highly soluble in CO₂ and is solid at room temperature, report that the technique works with other sugar acetates. Cooper notes that it could, in principle, be extended to CO₂-soluble polymers. The authors believe their aligned porous structures could find application in tissue engineering, for example, as scaffolds for aligned nerve cell growth.