Ultrahigh-Strength, Fire-Safe, and Passive-Thermal-Regulating Alginate Aerogels Enabled by Dual-Cross-Linked Networks for Energy-Saving Applications

Building materials that integrate thermal insulation, fire safety, structural durability, and passive cooling are highly desirable for reducing building energy consumption. Achieving this combination in sustainable biomass-derived materials remains challenging. Here, a multifunctional sodium alginate-based aerogel (SPCA) was fabricated via directional freezing and reinforced by a dual-cross-linked framework formed through PA-mediated hydrogen bonding and Ca2+ coordination. The resulting network produced a denser, more uniform honeycomb-like porous structure, thereby strengthening the aerogel skeleton. SPCA achieved a compressive strength of 4.57 MPa and a compressive modulus of 37.97 MPa, along with improved water stability. Despite moderate structural densification, SPCA retained a low thermal conductivity of 0.044 W m–1 K–1 and outperformed several commercial insulation materials under both hot and cold conditions. The aerogel also exhibited rapid self-extinguishing behavior and enhanced char formation. Furthermore, the combined effects of thermal insulation and radiative cooling enabled effective daytime cooling, resulting in a temperature reduction of 4.2 °C under simulated solar irradiation and a maximum temperature drop of 7.2 °C under outdoor conditions. Model-house experiments demonstrated reductions in roof and indoor temperatures, while EnergyPlus simulations predicted annual cooling-energy savings across different climate regions. The work provides a promising strategy for developing structurally durable, fire-safe, and thermally functional biomass aerogels for energy-efficient buildings, with great potential for practical applications in thermal management.