On Porosity of Carbon Aerogels from Sol-Gel Polymerization of Phenolic Novolak and Furfural

Carbon aerogels were prepared by sol-gel polymerization of phenolic novolak and furfural followed by supercritical drying and pyrolysis. The porosity and morphologies of carbon aerogels were characterized by nitrogen adsorption, apparent density, He- pycnometer method, and transmission electronic microscopy (TEM). Effect of ratios of phenolic novolak to furfural (Ra) and total concentration of reactants (C) in sol-gel step on porosity and morphologies of carbon aerogels was investigated. The carbon aerogels synthesized are rich in meso- and macropores. The Ra determines the cross-linking density of polymers, thereby the compatibility of the polymers, and ultimately the shrinkage of gels in the drying and pyrolysis. The network sizes and the porosity of organic and carbon aerogels are mainly determined by Ra. The C has no effect on volume shrinkage of gels in drying and pyrolysis and has only dilute effect in determining bulk density of organic and carbon aerogels, and ultimately the porosity of carbon aerogels. Conversion of mesopores to micro- and macropores is observed, which is related to combination of C and Ra, and determines the partition of micro-, meso- and macropores.