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/cm3 with mesopore ratios of 96 and 98% for 7 and 12 nm silica colloidal nanoparticles respectively.