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 15g/100mL. 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 20g/100mL, the densities of the carbon aerogels were 0.22 and 0.26g/cm³ with mesopore ratios of 96 and 98% for 7 and 12nm silica colloidal nanoparticles respectively.