The production of high surface area porous carbonaceous materials from polysiloxane

Nanoporous carbonaceous materials with high surface area were prepared by the pyrolysis of polymethyl(phenyl)siloxane resin (SR249) under vacuum at a controlled temperature (1250-1350℃) followed by leaching in hydrofluoric acid (HF). Their compositions and structures at different pyrolysis temperatures were investigated by X-ray diffraction, Raman spectroscopy, elemental analysis, transmission electron microscopy and N₂ adsorption. The SiO₂ phase in the pyrolysis products was regarded as a natural template and could be leached away by HF. The pyrolysis temperature and leaching had important effects on the compositions and structures of the carbonaceous materials. Their specific surface areas were very low (<55m²/g) before leaching, but the specific surface area and total pore volume increased significantly after leaching, and could be as high as 1148m²/g and 0.608cm³/g, respectively when pyrolysis was carried out at 1300℃. The pore size of all the samples after leaching was in the narrow range of 1-4nm. TEM showed that the free carbon phase, SiC nanocrystallines and silicon oxycarbide ceramics wrapped each other.