The effect of different alkaline catalysts on the formation of silica aerogels prepared by the sol–gel approach

Abstract

Due to the unique three-dimensional spatial network structure formed by SiO₂ nanoparticles and high surface aera, silica aerogel is a high-profile material in many fields. In the present study, by adopting the industrial water glass as the silicon source, silica aerogels had been prepared via the sol–gel approach followed by the ambient pressure drying process. The effects of different alkaline catalysts in terms of LiOH, NaOH, KOH, and NH₃·H₂O on the formation of silica aerogels were investigated. It was found that with the introduction of alkaline catalysts, the gel aging time dramatically decreased from 5840 to 31 min during the sol–gel process. Compared with the silica aerogels prepared without any catalyst, accordingly, the thermal stability was significantly improved, and the decomposition temperature increased from 375 to above 410 °C. Furthermore, the silica aerogels prepared with alkaline catalysts were featured in a distinctive double-pore structure. It was shown that the alkali metal ions might have an alkaline dissolution effect in the weakly acidic environment during the sol–gel process. Moreover, this effect might increase the contact area between different SiO₂ nanoparticles, which was benefit to maintain the three-dimensional spatial network structure and resulted in the silica aerogels with higher thermal stability. The alkaline dissolution effect had an influence on the pore size distribution of silica aerogels with a double pore structure at 1.7 and 32 nm as well as retained large pore volume at about 2.60–3.35 cm³/g.