CONTROL OF MESOPOROUS STRUCTURE OF ORGANIC AND CARBON AEROGELS

Resorcinol-formaldehyde (RF) 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 diox ide. Mesoporous carbon aerogels were then obtained by pyrolyzing the R F aerogels in an inert atmosphere. The control of mesoporous structure of the aerogels was studied by changing the amount of resorcinol (R), formaldehyde (F), distilled water (W) and sodium carbonate (basic cat alyst) (C) used in the polycondensation. As a result of characterizati on by nitrogen adsorption, the mesopore radius of the RF aerogel was c ontrolled in the range of 2.5-9.2 nm by changing the mole ratio of res orcinol to sodium carbonate (R/C) and the ratio of resorcinol to water used as diluent (R/W). Although the aerogels shrank by 1-4 nm during pyrolysis, the shape of pore size distribution of the RF aerogel was k ept. It was found that the mesopore radius of carbon aerogel ranged fr om 2.0 to 6.1 nm. As the pyrolysis temperature increased, the peak rad ius of pore size distribution was kept the same despite the fact that the pore volume decreased because of shrinkage. Adsorption isotherms o f ethane and ethylene were measured on the aerogels prepared. As the p yrolysis temperature increased, the amounts of ethane adsorbed became larger than those of ethylene adsorbed on the aerogels. The aerogels p yrolyzed at 1000 degrees C had the same adsorption characteristics of ethane and ethylene as the activated carbons did. (C) 1998 Elsevier Sc ience Ltd. All rights reserved.