Preparation of low density and high mesoporosity carbon aerogels by an organic/inorganic hybrid method

Carbon aerogels were synthesized by the solution-sol-gel polymerization of resorcinol (R) and formaldehyde (F) with silica colloidal nanoparticles as additives in a basic aqueous solution followed by supercritical drying, pyrolysis and HF etching. The R/F molar ratio was maintained at 0.5 and the concentration of R+F in solution was varied. The evolution of porosity from hydrogels to carbon aerogels was investigated by nitrogen adsorption. The effect of R+F concentration and size of the silica colloidal nanoparticles on porosity and mesopore ratios were investigated under the same concentration of silica colloidal nanoparticles at 15 g/100 mL. Results indicated that the volume shrinkage of carbon precursors during supercritical drying and pyrolysis can be reduced by the presence of silica colloidal nanoparticles. The mesopore ratio increased with increasing R+F concentration and porosity decreased with increasing size of the silica colloidal nanoparticles. When the R+F concentration was 20 g/100 mL, the densities of the carbon aerogels were 0.22 and 0.26 g/cm(3) with mesopore ratios of 96 and 98% for 7 and 12 nm silica colloidal nanoparticles respectively.