Effect of synthesis pH on the structure of carbon xerogels

Abstract

Mesoporous carbon xerogels were prepared from the sol-gel polymerization of resorcinol with formaldehyde (RF) followed by carbonization. The effect of the initial pH of the RF solution on the surface area, pore volume, pore size distribution and nanostructure was studied. A brief mechanism of polymerization is discussed. Typically, a lower initial pH yielded carbon xerogels with a higher surface area and pore volume, and a broader pore size distribution. The highest surface area and pore volume were around 620 m 2 g −1 and 0.8 cm 3 g −1, with a mean pore radius ranging from 4 to 6 nm and with 80% of the pore volume as mesopores. Transmission electron microscopy and X-ray diffraction revealed a surface morphology consisting of 10 nm diameter particles randomly oriented to produce a partially nanocrystalline structure in between graphite and activated carbon. Thermogravimetric and differential scanning calorimetric analyses disclosed a significant weight loss (50%) during a strongly exothermic carbonization process.