Natural silk nanofiber aerogel/SiO2 microsphere composite film with unique hierarchical structure for thermal insulation and high-performance radiative cooling

Passive radiative cooling improves the cooling performance of materials by reflecting radiant heat from sunlight and mid-infrared wavelengths. However, radiative cooling power will be significantly reduced due to the absorption of sunlight and poor thermal insulation performance of the emitter. To improve the emissivity and radiation intensity of the emitter, aerogel films with excellent layered structure and high mechanical toughness were constructed by silk nanofibers and PVA. Meanwhile, SiO2 nano-microspheres are added to improve the radiative thermal conductivity of the film in all incident directions. The prepared SNF/SiO2 aerogels have low thermal conductivity (0.037 W m−1 K−1) and high mid-infrared emissivity (94.3 % for a thickness of 0.5 cm), which can cope with the reduction of radiative cooling performance due to solar energy absorption. The SNF-10 % SiO2 aerogel film exhibited a daytime cooling power of 112.3 W m−2 and was below the ambient temperature of 14.6 °C under direct sunlight. Furthermore, the SNF/SiO2 aerogel has good mechanical elasticity, thermal insulation, and air filtration properties, demonstrating the high stability of its hierarchical structure. This study provides more options for the application of natural silk aerogels in the field of thermal performance.