Porosity and surface area of monolithic carbon aerogels prepared using alkaline carbonates and organic acids as polymerization catalysts

D. Fairén-Jiménez, F. Carrasco-Marín and C. Moreno-Castilla

Carbon aerogels were prepared by polymerization of a resorcinol–formaldehyde mixture using different polymerization catalysts such as: sodium or potassium carbonates, oxalic acid or para-toluenesulfonic acid. The carbon aerogel obtained with this last acid was further CO2-activated to 8.5% and 22% burn-off. All samples were characterized by N2 and CO2 adsorption at −196 and 0 °C, respectively, and by mercury porosimetry, scanning electron microscopy, and thermogravimetric analysis. Samples prepared using Na2CO3 were denser than those prepared using K2CO3. In addition, the density of samples prepared under acidic conditions was greater than that of samples prepared using alkaline carbonates as catalysts. Most of the carbon aerogels prepared were mesoporous with narrow pore size distributions. Results obtained showed that the nature of the acid used in the preparation of these aerogels only affected the gelation process. Finally, it is noteworthy that CO2 activation of the carbon aerogel prepared with para-toluenesulfonic acid as catalyst only increased and widened the microporosity and had virtually no effect on the mesoporosity.

June, 2006

Granular and monolithic activated carbons from KOH-activation of olive stones

Ruth Ubago-Pérez, Francisco Carrasco-Marín, David Fairén-Jiménez and Carlos Moreno-Castilla

Different activated carbons were prepared by KOH-activation of carbonized olive stones by varying the KOH/carbon weight ratio and the particle size of the precursor. The activated carbon with the best surface characteristics was furthermore steam-activated. Other activated carbon was obtained by using directly olive stones as raw material. In this case the precursor particles were broken by the KOH solution, obtaining an activated carbon with an extremely fine particle size. Different monoliths were prepared from this powder activated carbon by using a binder and pressure. All samples were characterized by N2 and CO2 adsorption at −196 and 0 °C, respectively, and scanning electron microscopy. Some samples were also characterized by benzene adsorption at 30 °C. Carbon monoliths were used to remove toluene from a toluene/air flow under dynamic conditions. Column bed characteristics were obtained from breakthrough curves. Amounts adsorbed at saturation were much higher than others reported in the literature and that were obtained by using different activated carbons.

June, 2006

Surface Area and Microporosity of Carbon Aerogels from Gas Adsorption and Small- and Wide-Angle X-ray Scattering Measurements

David Fairén-Jiménez, Francisco Carrasco-Marín, David Djurado, Françoise Bley, FranÇoise Ehrburger-Dolle, and Carlos Moreno-Castilla

A carbon aerogel was obtained by carbonization of an organic aerogel prepared by sol-gel polymerization of resorcinol and formaldehyde in water. The carbon aerogel was then CO2 activated at 800 °C to increase its surface area and widen its microporosity. Evolution of these parameters was followed by gas adsorption and small- and wide-angle X-ray scattering (SAXS and WAXS, respectively) with contrast variation by using dry and wet (immersion in benzene and m-xylene) samples. For the original carbon aerogel, the surface area, SSAXS, obtained by SAXS, is larger than that obtained by gas adsorption (Sads). The values become nearly the same as the degree of activation of the carbon aerogel increases. This feature is due to the widening of the narrow microporosity in the carbon aerogel as the degree of activation is increased. In addition, WAXS results show that the short-range spatial correlations into the assemblies of hydrocarbon molecules confined inside the micropores are different from those existing in the liquid phase.

November, 2005

Nanoporous carbon materials: Comparison between information obtained by SAXS and WAXS and by gas adsorption

FranÇoise Ehrburger-Dolle, David Fairén-Jiménez, Sandrine Berthon-Fabry, Patrick Achard, Françoise Bley, Francisco Carrasco-Marín, David Djurado, Carlos Moreno-Castilla and Isabelle Morfin