Abstract
Ordered mesoporous silicon nitrides with a high nitrogen content (32 wt %) were synthesized by using polycarbosilane (PCS) as a ceramic precursor and mesoporous carbon CMK-8 as a hard template via nanocasting synthesis. Small-angle X-ray scattering, TEM, and nitrogen sorption analyses showed that the mesoporous silicon nitride products have a 3-D bicontinuous cubic mesostructure (Ia (3) over bard) similar to KIT-6, a specific BET surface area of 384 m(2) g(-1), a large pore volume of 0.71 cm(3) g(-1), and a narrow pore size distribution at the mean value of 5.7 nm. The PCS precursor can be transformed into silicon nitride by reactive pyrolysis under ammonia atmosphere. The nitrogen protected 1400 degrees C crystallization process is a key step for the synthesis of ordered mesoporous silicon nitrides. The secondary impregnation-pyrolysis cycle can reduce the structural shrinkage and improve the mesostructural regularity.