Improvement of mesoporosity of carbon cryogels by ultrasonic irradiation

Mesoporous carbon gels are usually obtained by pyrolyzing resorcinol-formaldehyde (RF) gels, which are synthesized via the sol-gel polycondensation of resorcinol with formaldehyde in a slightly basic aqueous solution followed by drying. However, meso-porous carbon gels cannot be prepared under the conditions of high catalyst concentration or high pH of RF solution even by using supercritical drying or freeze drying. In this work, mesoporosity of carbon cryogels is improved by ultrasonic irradiation to RF solution. It is found that the gelation time of RF solution becomes greatly short by ultrasonic irradiation and that ultrasonic can improve mesoporosity of carbon cryogels prepared at high catalyst concentration (C/W). Although the carbon cryogels prepared from C/W = 80mol/m(3) have no mesopores, the carbon sonogels prepared by ultrasonic irradiation under the same catalyst condition have sharp mesopore size distribution. The utilization of ultrasonic in the preparation of RF gel is an interesting way in improving mesoporosity of carbon gels prepared at high C/W or pH. (C) 2004 Elsevier Ltd. All rights reserved.