Synthesis of resorcinol–formaldehyde/silica composite aerogels and their low-temperature conversion to mesoporous silicon carbide

Resorcinol–formaldehyde/silica composite (RF/SiO2) gels were acid-catalyzed formed in one pot at 27 °C within 60 min, and then dried to aerogels with supercritical fluid CO2. After carbonization in nitrogen atmosphere and a magnesiothermic reaction at 700 °C, RF/SiO2 aerogels were successfully converted to monolithic mesoporous silicon carbide (SiC aerogels). The starting RF/SiO2 aerogels had an interpenetrating organic/inorganic network and the resulting SiC products preserved monolithic mesoporous morphology similar to the original templates. The as-synthesized SiC aerogels consisted of nanocrystalline β-SiC, possessed a BET surface area of 232 m2/g and showed sufficient mesoporosity. They had a direct band gap of about 3.2 eV (less than that of bulk β-SiC) and showed photoluminescence at room temperature. The mechanisms about the formation of RF/SiO2 gels and the conversion to SiC aerogels were discussed. Potentially, the reported method can be used to convert many metal or semimetal oxide/carbon composite aerogels to carbide aerogels at relatively low temperature for many catalytic, electronic, photonic and thermal applications.

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► One-pot synthesis of RF/SiO2 aerogels is time-efficient.
► Acids as catalysts and acetonitrile as co-solvent are used for the one-pot synthesis.
► RF/SiO2 aerogels are converted into mesoporous SiC at low temperature of 700 °C.
► Mesoporous SiC preserves delicate structure of aerogels.