Gels dried under supercritical and ambient conditions: a comparative study and their subsequent conversion to silica–carbon composite aerogels

Abstract

In present work, we have prepared gels with various compositions of methyltrimethoxysilane—3-(2,3- epoxypropoxy) propyltrimethoxysilane (MTMS-GPTMS) using a two-step acid base sol–gel process. To make a comparative study between the two common drying routes, we prepared gels under supercritical and also under ambient conditions. The density of the supercritically dried hybrid aerogels lies between 0.18 and 0.31 gcm-3, while the density of the ambient dried ones ranges between 0.35 and 0.42 gcm-3. The surface area of MTMS-0.25 GPTMS aerogel dried under supercritical conditions, has been found to be 464 m2 g-1 with a pore volume and average pore diameter of 1.24 cm3 g-1 and 11 nm respectively. The same composition dried under ambient conditions is found to have similar properties i.e. a BET surface area of 439 m2 g-1, pore volume of 1.22 cm3 g-1 and average pore diameter of 11 nm. The aerogels were later pyrolyzed yielding silica/carbon composite aerogels. The pyrolized aerogels possessed a surface area as high as 207 m2 g-1 with a total pore volume of 0.98 cm3 g-1. The pyrolysed aerogels were also calcined to yield carbon free materials.