Preparation of ambient pressure dried MTMS/TEOS co-precursor silica aerogel by adjusting NH4OH concentration

• MTMS/TEOS co-precursor aerogels via APD without surface modification were prepared.
• The effect of NH4OH on co-precursor aerogels was discussed in detail.
• The concentration of NH4OH was much lower than those in other co-precursor sol systems.
• The concentration of NH4OH deeply affected the sizes of primary particles and clusters.
• The molar ratio of NH4OH:(MTMS+TEOS) being 8.67 and the NH4OH concentration being 0.25 M were optimum.

Using tetraethoxysilane (TEOS) and methyltrimethoxysilane (MTMS) as co-precursors, hybrid silica aerogels were prepared via ambient pressure drying (APD) without further surface modification. Due to various precursors presenting different condensation rates, the effect of NH4OH used as catalyst was explored in detail to balance the condensation rates of the precursors. Several aspects including volume shrinkage, density, specific surface area, microstructure and thermal stability were characterized to confirm the optimal condensation condition. It was found that the sizes of primary particles and clusters of SiO2 increased at first and then decreased with the NH4OH concentration, which impacts the other characteristics of the samples seriously. At optimum, the samples achieved low density 0.107 g/cm3, high porosity 95.1%, specific surface area 705.6 m2/g and thermostability up to approximately 435 °C.