Carbon aerogels prepared by autocondensation of flavonoid tannin

Abstract

The first carbon aerogels prepared by autocondensation of condensed (flavonoid) tannin, a cheap renewable resource extracted from Mimosa barks, are presented. Mixing aqueous solutions of tannin and sodium silicate indeed produced the very fast gelation of tannins, thus leading to organic hydrogels which were first converted into organic aerogels by supercritical drying, and then into carbon aerogels after pyrolysis at 900 °C. Subsequent dissolution of the silica nanoparticles thus formed within the carbon structure further increased significantly the porosity of the materials. Silica thus appeared to be both the gelation catalyst and a pore-directing agent. In this work, the influence on the porosity of the silica/tannin ratio and of the nature of the etching agent used for removing the silica was thoroughly investigated by combining several techniques. The conditions for producing either the most porous materials or those with the highest surface areas were identified and discussed.