Bio-based and fireproof radiative cooling aerogel film: Achieving higher sustainability and safety

Even though significant advantages in the energy-free regulation of temperature are presented, the practical applications of radiative cooling materials in buildings and human surfaces still involve many safety issues, especially for fire hazards of polymer-based materials. Meanwhile, renewable and environmentally friendly materials are urgently needed to develop suitable radiative cooling materials with no adverse environmental impact. Herein, a chitosan-derived composite aerogel film with high solar reflection provided by the addition of melamine-phytic acid (MA/PA) hybrids is designed and prepared, presenting radiative cooling and fireproof performances. The instinct deep-yellow color of chitosan (CS) is successfully shielded by high-reflective MA/PA hybrids, while IR emissivity of up to 90.4 % and solar reflectivity of ∼ 89.3 % are achieved. In outdoor environments, this composite aerogel shows sub-ambient temperature drops of ∼ 4.3 °C and ∼ 3.1 °C in cloudless and cloudy weather, presenting a robust cooling effect. In addition, CS-MA/PA composite aerogel film with 3 mm thickness can isolate the fire of ∼ 500 °C, showing superior fire safety attributed to the synergistic flame retardant effects among chitosan, phytic acid, and melamine, which suppress the initial growth of fire and promote the rapid formation of protective char layer. This work provides a bio-based, fire-safe, and radiative cooling material to decrease the energy consumption of temperature regulation with a more environmentally friendly and safer approach, further promoting the practical application of radiative cooling materials.