Synthesis and characterization of silica aerogels dried under ambient pressure bed on water glass

• Min. amount of TMCS was obtained through experiments for complete surface modification.
• Optimum volume ratio of H2O to water glass was gotten.
• Proper amount of DMF can uniform the PSD of as-prepared silica aerogels.
• More than 0.9 ml organics (some) can be absorbed by 1 cm3 of the silica aerogels.

In this paper, we report the experimental results on the synthesis of water glass based silica aerogels, which were dried under ambient pressure. Water glass was hydrolyzed and condensed in water using HCl as the catalyst. To minimize shrinkage during drying process, N,N-dimethylformamide (DMF), acting as drying control chemical additive (DCCA), was introduced. Before the ambient pressure drying, solvent exchange and surface modification were completed. In order to get hydrophobic aerogel, trimethylchlorosilane (TMCS) was used to modify the hydrophilic hydrogel surface. Here a large amount of TMCS can be saved compared with that in single step solvent exchange/surface modification method. The effects of DMF on the physical and textural properties of the resulting aerogels were investigated. When the molar ratio of Si in water glass to DMF is 2.23, the synthesized silica aerogels have better properties. Characterized by FT-IR, SEM, BET, etc., the resulting aerogels have well-developed mesoporous structure (mean pore size of ~ 15 nm) with super hydrophobicity (contact angle of 161°) and excellent absorption capacity of organic liquids.