Green synthesis of fluorine-containing polyimide aerogels toward passive daytime radiative cooling for energy saving

Traditional organic passive daytime radiative cooling (PDRC) materials have attracted extensive attention due to their abundant chemical structures and flexible mechanical properties. However, their flammability and ultraviolet radiation degradation seriously limited their sustainable application. Herein, a chemical-physical dual strategy is proposed by introducing fluorine and silica nanoparticles into a traditional polyimide aerogel to reshape both the chemical and microstructure and give birth to fluorine and silica functionalized polyimide composite aerogels (FSPI), showing PDRC with inherent flammability and ultraviolet radiation resistance. Owing to the presence of fluorine and silica, the FSPI aerogels show high solar reflectance (∼92.8 %) in the wavelength of 0.78–1.1 μm and high IR emissivity (∼93.0 %) among 8–13 μm, thus fulfilling a passive sub-ambient cooling of ∼9.4 °C at daytime. Meanwhile, the fluorine and silica also endow the FSPI with outstanding thermal stability (T_{-5 %}, ∼524 °C), hydrophobicity (water contact angle ∼120.4°), anti-aging, and flame-retardant (PHRR, 13.1 W g⁻¹) performances, making them ideal candidates for sustainable cooler in building energy saving. This study provides a general and powerful route toward organic PDRC materials for anti-aging, flame-retardant, and water-resistance applications.