Highly micro- and mesoporous oxycarbide derived materials from HF etching of silicon oxycarbide materials

Abstract

[EN] Highly micro-mesoporous silicon oxycarbide-derived carbon materials (SiOC-DC) with elevated specific surface area up to 895 mg and high pore volumes of mesopores (0.3 cmg) and micropores (0.2 cmg) have been obtained by direct etching of SiOC with HF. Initial organic-inorganic hybrids were synthesized by the sol-gel method employing triethoxysilane and polydimethylsiloxane (PDMS) of different molecular weights (550, 1750 and 4200 gmol). These hybrids were pyrolyzed from 1100 to 1400 °C. Short PDMS chains (550 gmol) within the hybrid structure rendered dense SiOC materials after pyrolysis, however long PDMS chains (1750 and 4200 gmol) produced highly micro-mesoporous SiOC materials up to 1300 °C. The etching of SiOC employing HF produced the selective removing of silica nano-domains and as a result highly micro-mesoporous SiOC-DC materials were created. In dense SiOC the HF attack is favoured at the highest temperatures (1400 °C) when the SiOC is more phase separated. On the other hand, in porous SiOC there is an agreement between the pyrolysis temperature and the porosity and, therefore the SiOC materials are etched easier at 1200 °C. SiOC-DC materials are composed by a porous glassy network enriched with carbon (graphene-like carbon and turbostratic carbon) and SiC which present an incipient crystallization.