Synthesis and Characterization of Silica/Carbon Composite Aerogels

摘要

A series of monolithic silica/resorcinol-formaldehyde (silica/RF) aerogels have been prepared by a simple one-step sol-gel process of 3-aminopropyltriethoxysilane (APTES), resorcinol ?, and formaldehyde (F) in ethanol, followed by drying with supercritical CO_2. The silica/carbon composite aerogels were obtained by pyrolysis of the silica/RF aerogels under N_2 atmosphere. The silica/carbon composite aerogels exhibit low densities (0.1241-0.2751 g/cm~3) and high porosities (>84%). The pore morphologies of the composite aerogels have been investigated in detail by nitrogen sorption measurements, scanning electron microscopy, and transmission electron microscopy. The surface areas of these composite aerogels result from the contribution of macropores, mesopores, and micropores. Combustion in air or etching in HF solution can remove carbon or silica from the silica/carbon composite aerogels and yields monolithic or cracked unitary silica or carbon aerogels. The study indicates that when the starting APTES/R molar ratio is high (sample 3SiOC-C and 2SiOC-C), the silica framework is the supporting framework; and for low starting APTES/R ratio samples (sample SiOC-3C, SiOC-2C, and SiOC-C), the carbon framework is the supporting framework. Remarkably, carbon aerogels with high surface areas of 2000 m~2/g can be obtained after removing silica frameworks of composite aerogels of 3SiOC-C and 2SiOC-C.