ABSTRACT
The influence of cationic, anionic, and nonionic surfactants (S) on the characteristics of carbon xerogels was analyzed. The polymerization of resorcinol (R) and formaldehyde (F) was developed in an aqueous solution of S without any additional catalyst. The gels obtained were dried in air to obtain organic xerogels and then carbonized to carbon xerogels. The prepared samples were characterized by FTIR, TG, SEM, and N(2) and CO(2) adsorption. The formation of RF-S copolymers was observed for cationic and nonionic surfactants, but this was not observed for anionic S, probably because of repulsive electrostatic interactions between the two organic phases. Nevertheless, anionic S leads to a greater morphological transformation with the formation of nonporous needle particles associated with the higher pH induced by this S. Carbon xerogels are microporous materials with interesting molecular sieve behavior. The RF-S composites undergo greater shrinkage than do the pure RF xerogel; consequently, a narrower microporosity is obtained.
ABSTRACT
Carbon aerogels and xerogels were successfully prepared from phloroglucinol-phenol mixtures and characterized by different techniques to determine their potential. We examined the influence of the phloroglucinol/phenol ratio, reactant concentration, cure conditions, and drying method on the morphology and porosity of the samples. The gelation time was found to be independent of the phloroglucinol/phenol ratio in spite of the different reactivities of both monomers. In general, carbon aerogels have a high volume of mesopores and of micropores without diffusion restrictions. Carbon xerogels are denser materials without mesopores but with a well-developed microporosity that shows a strong molecular sieve effect. Therefore, while micro-/mesoporous carbon aerogels can be used as catalyst supports or VOC adsorbents, the microporous carbon xerogel could offer high selectivity in the separation of small molecules from gaseous mixtures.