Organic and carbon xerogels derived from sodium carbonate controlled polymerisation of aqueous phenol-formaldehyde solutions

Abstract

Porous carbons were synthesized from aqueous sodium carbonate catalysed solutions of the low cost precursors phenol and formaldehyde, applying ambient pressure drying without prior solvent exchange. Many of the samples are found to crack during drying, however, the resulting porous carbons show porosities up to 80%, specific surface areas up to 746 m²/g, and micropore volumes up to 0.29 cm³/g; the mesopore volume and external surface area of the derived carbons, however, is small indicating the dominance of macropores. An unusual gelation kinetic, i.e., the formation of precipitating flakes instead of the classical sol–gel-transition is observed; this is likely due to nuclei growth from a metastable state in the phase diagram and makes it challenging to reproduce samples with well defined properties. Nevertheless mechanically stable macroporous monoliths, that survive the ambient pressure drying without prior solvent exchange can be synthesized; the system presented, however, seems not to be suitable as base system for highly mesoporous carbon samples (aerogels, cryogels, xerogels) or large scale production of porous carbon materials.