Nanoporous Silica–Chitosan Aerogels for Thermal Insulation and Flame Retardancy

The significant accumulation of fly ash has resulted in serious environmental issues. It is imperative to find a safe and high-value method for reusing fly ash to effectively address this problem. Additionally, silica aerogels have gained attention as a promising material for energy conservation and thermal management. However, producing a silica aerogel with low production costs and superior overall properties is still a major challenge. In this study, silica–chitosan composite aerogels (SCA) were prepared from fly ash and chitosan. Amorphous silica is polymerized in situ on chitosan by hydrogen bonding and silyl-oxygen condensation. The resulting aerogels exhibited a fully formed block structure, extremely low density, exceptional flame retardancy, and notable mechanical properties (able to withstand 24,000 times the stress of its own mass). It is noteworthy that the nanopores and three-dimensional network structure endow SCA with excellent thermal insulation performance (with a thermal conductivity of 0.0474–0.0521 W m–1 K–1). The strategy presented here provides a cost-effective and straightforward approach to prepare SCA. The results demonstrate its considerable potential for practical use in energy-efficient and thermally insulated structures. Moreover, this approach offers a direct and high value-added solution to the problem of fly ash.