Synthesis and characterization of the first transparent silicon oxycarbide aerogel obtained through H2 decarbonization

Ambient dried aerogels (ambigels) have been synthesized from bis(triethoxysilyl)methane, BTEM and bis(triethoxysilyl)ethane, BTEE. The ambigels have been pyrolyzed at 800 and 1100 C in flowing H2 to obtain the corresponding SiOC aerogels. H2 gas reacts with organic moieties of the gel forming methane, which is eliminated in the gas phase and reduces the formation of a “free carbon” phase. The microstructural features of SiOC aerogels have been characterized by N2 sorption analysis while the molecular structure of SiOC has been studied by multinuclear solid state NMR (29Si, 1H, 13C) and FT-IR spectroscopy. When the BTEM ambigel is pyrolyzed in H2 flow at 800 C the decarbonization process is highly efficient and a bulk, transparent and colourless SiOC aerogel is obtained for the first time. The formation of a silicon oxycarbide network was verified by NMR and FT-IR studies.