Low-density, thermally stable silica aerogels enabled by a novel physical sedimentation template method by ambient pressure drying

This study presents a novel strategy for fabricating silica aerogels using a physical blending-sedimentation template method combined with an ambient pressure drying process. By employing inert graphite as a template and adjusting the template-to-sol mass ratio and gelation temperature, the sedimentation process is guided to regulate the dynamic “destruction-reconstruction” of the sol-gel system, thereby optimizing its three-dimensional network structure. The resulted aerogel exhibits excellent properties, including low density (0.134 g cm −3 ) and thermal conductivity (0.018 W m −1 K −1 ) as well as high specific surface area (602.68 m 2 g −1 volume (1.24 mL g −1 ). However, its thermal stability is still very low. In contrast, active templates, such as Al 2 O 3 , Kaolin and TiO 2 , are utilized to promote the formation of Al–O–Si and Ti–O–Si bridging bonds, which not only effectively tune the pore structure, but also significantly enhance thermal stability. Specifically, the aerogel prepared with the Al 2 O 3 template demonstrates the lowest density of 0.129 g cm −3 and thermal conductivity of 0.015 W m −1 K −1 , coupled with the largest pore diameter (13.41 nm) and volume (1.79 mL g −1 ). More importantly, it can retain 70% of the original mass at the temperature approaching 800 °C. This simple and cost-effective method allows for easy template recovery and reuse, offering a feasible pathway for the large-scale production of silica aerogels with potential applications in thermal insulation, high-temperature catalysis, and adsorption.