Phosphorylated cellulose-based hybrid aerogels with flame retardancy and hydrophobicity for passive radiative cooling

scattering centers and a high mid-infrared emittance of 95.0% associated with multiple infrared-active vibrational modes within the atmospheric window. Consequently, the M-PCB-1 aerogel delivers outstanding daytime cooling performance, achieving a temperature difference of up to 19.2 °C relative to the chamber ambient temperature under controlled xenon-lamp irradiation. Furthermore, the aerogel exhibits excellent thermal insulation (0.054 W/m·K) and robust chemically integrated fire safety. Phosphorylation endows the PCNF framework with phosphate-promoted char-forming flame retardancy, while the thermally stable BaSO₄ particles provide an additional physical barrier effect, resulting in a residual mass of 65.4% at 800 °C and an 88.6% reduction in total heat release. Additionally, the Cassie-Baxter wetting state endows the surface with high hydrophobicity, a water contact angle of approximately 145°, low water adhesion, and self-cleaning properties. Global building energy simulations suggest that integrating this aerogel into the modeled building envelope could reduce annual cooling-energy consumption by up to 13% under the specified assumptions. This work presents a sustainable, high-performance material paradigm for next-generation energy-efficient building thermal management.