Influence of alkaline compounds on the porosity of resorcinol-formaldehyde xerogels

Carbon xerogels (CX) were prepared by means of the sol-gel polymerization of resorcinol with formaldehyde using the following alkaline additives: NaOH, Ca(OH)2, Na2CO3, NaHCO3 and Li2CO3. Their porous and chemical structures were studied in depth using several characterization techniques. It was found that anion has a greater influence on the porous structure than cation since, in most of the cases studied, carbonate-based carbon xerogels have a larger pore size than their sodium and calcium hydroxide-based counterparts (i.e., a pore size of around 95 nm for carbon xerogels based on OH– vs. ca. 1000 nm in the case of carbonate-based xerogels, for a specific value of pH, dilution and resorcinol/formaldehyde molar ratio). In addition, it was possible to remove the source of the sodium of the synthesis process, a highly corrosive element that damages the devices and equipment used in post-treatments. Both types of hydroxide lead to carbon xerogels with identical porous and chemical properties, except in their impurity content, which is smaller in the case of the sample produced from Ca(OH)2.