Anisotropic high-surface-area carbon aerogels

The subject of this paper is the investigation of the multiscale structure of a new series of carbon aerogels. These carbon aerogels are obtained by resorcinol resorcinol-formaldehyde sol-gel reactions in acetone in a single-step base catalysis (AB) or a double-step base-acid catalysis (ABA) followed by supercritical drying and pyrolysis at 1050 degreesC under nitrogen flow. Two complementary techniques were used: small-angle and wide-angle X-ray scattering (SAXS and WARS) and nitrogen adsorption. Carbon aerogels AB and ABA are distinguished by a high surface area (>600 m(2)g(-1)) and by multiscale structural features that are very different from those of carbon aerogels resulting from gels prepared under the same conditions but in an aqueous solution (WB). The anisotropy observed at the mesoscale for aerogels obtained in acetone is attributed to strain occurring in the extreme operating conditions near the critical gelation concentration limit. The SAXS measurements on AB carbon aerogel reveal the presence of a high surface area with the main pore size contribution being at the nanoscale, resulting from micropores not accessible to nitrogen at -196 degreesC. By combining SAXS and WAXS measurements, it is suggested that all carbon aerogels display structural narrow micropores. (C) 2004 Elsevier B.V. All rights reserved.