Bio-based phytic acid modified silica–alumina aerogels with lightweight, low-smoke, and fire-safe insulation performance

The demand for lightweight and fire-safe thermal insulation materials in civil and industrial applications has been continuously increasing. Silica aerogels are attractive candidates owing to their ultralow density and low thermal conductivity, but their high flammability and insufficient thermal stability limit broader engineering applications. Incorporating inorganic components such as alumina has been considered an effective strategy to enhance skeletal stability, giving rise to silica–alumina aerogels with improved high-temperature resistance. In this work, phytic acid (PA), a naturally occurring phosphorus-rich compound, was employed as both an acid catalyst and modifier to prepare phosphorus-containing silica–alumina aerogels (ASAs/PA) via supercritical drying. The optimized sample (ASAs/PA-2, TEOS/PA = 1:1.5 ×10⁻³) exhibited a low density of 0.0854 g/cm³ and a thermal conductivity of 24.9 mW/m/K. Compared with pure silica aerogels (SA), its peak heat release rate and total heat release were reduced by 82.0 % and 44.1 %, and by 44.4 % and 18.0 % compared with silica–alumina aerogels (ASAs), demonstrating enhanced flame retardancy arising from phosphorus–aluminum combined interactions. Additionally, the total smoke production (TSP) was significantly reduced, with a reduction of over 95 %, confirming the strong smoke-suppression effect of PA. ASAs/PA showed improved stability at 1000 °C, but reduced stability at 800 °C and 1200 °C compared with ASAs, indicating a trade-off between flame retardancy and high-temperature structural stability. These results highlight the potential of PA modified silica-alumina aerogels as lightweight, fire resistant, and sustainable thermal insulation composites for building and engineering applications, while also underscoring the importance of balancing flame retardancy with high temperature structural stability. • Phytic acid (PA) was introduced as both a catalyst and a modifier into silica–alumina aerogels to prepare ASAs/PA. • The ASAs/PA-2 (Si/Al molar ratio = 1:1, TEOS/PA molar ratio = 1:1.5 ×10⁻³) exhibited low density (0.0854 g/cm³) and low thermal conductivity (24.9 mW/m·K). • PA incorporation significantly reduced pHRR (44.4 %) and THR (18.0 %) of ASAs, and suppressed smoke release by over 95 % (TSP 0.01 m²), confirming its strong fire-safety effect. • In ASAs/PA, PA inhibits combustion through radical quenching of phosphorus-containing species in gas phase and strengthens the char structure in condensed phase via phosphorus–aluminum interactions, thereby enhancing flame retardancy. • ASAs/PA shows higher thermal stability than SA, and compared with ASAs, it showed slightly lower stability at 800 °C and 1200 °C but slightly higher stability at 1000 °C.