Carbon xerogels synthesized via phenol–formaldehyde gels

Abstract

A new synthesis route for organic and carbon xerogels based on the low cost precursors phenol and formaldehyde was developed. The combination of n-propanol as solvent and acidic catalysis leads to homogeneous, highly porous monolithic samples. The conversion of the gel into an organic xerogel is performed via drying at ambient conditions. The organic samples as well as the carbon samples show densities between 0.29 and 1.17 g/cm 3 (porosities up to 88%). The impact of different synthesis parameters – such as the type and concentration of the catalyst, the mass content of phenol and formaldehyde in the initial solution, the molar ratio of phenol to catalyst or the molar ratio of formaldehyde to phenol – on the microstructure and morphology were evaluated and key synthesis parameters identified. Furthermore a monofunctional phenol was applied as an additional parameter to control the sol–gel process. Small-angle X-ray scattering (SAXS) measurements performed during the sol–gel transition provide information on the evolution of the gel structure. The carbons derived via pyrolysis of the organic xerogels were characterized with SAXS, nitrogen sorption and electron microscopy. Electron microscopy images show the typical network of cross linked primary particles that is also characteristic for resorcinol-based aerogels and xerogels. The as received carbon samples show specific surface areas up to 572 m 2/g, micropore volumes up to 0.24 cm 3/g, external surface areas up to 150 m 2/g and mesopore volumes up to 0.69 cm 3/g. Energy dispersive X-ray (EDX) reveals an almost pure carbon phase with only oxygen impurities.