Porous structure of organic and carbon aerogels synthesized by sol-gel polycondensation of resorcinol with formaldehyde

Organic aerogels were synthesized via the sol-gel polycondensation of resorcinol with formaldehyde in a slightly basic aqueous solution and followed by supercritical drying with carbon dioxide. As a result of characterization by nitrogen adsorption, the resorcinol-formaldehyde (RF) aerogels were mesoporous materials with high surface areas and had few micropores. The surface area of the RF aerogel was controlled by the mole ratio of resorcinol to basic catalyst (R/C). On the other hand, the mesopore volume of RF aerogel changed greatly with R/C or the ratio of resorcinol to water (R/W). The RF aerogel having a monodisperse porous structure was prepared under the conditions of low R/C or high R/W. As R/C increased or R/W decreased. the porous structure of the aerogel became dispersed. Carbon aerogels were obtained by pyrolyzing the RF aerogels at 1223 K, and the aerogel had larger surface areas than the RF aerogels. It was found that micropores in the carbon aerogels were formed during pyrolysis of the RF aerogels. When the RF aerogel having a monodisperse porous structure was pyrolyzed, the mesopore volume of the carbon aerogel was smaller than that of the original RF aerogel. The mesopore volume increased by the pyrolysis of the RF aerogel having a dispersed porous structure. (C) 1997 Elsevier Science Ltd.