Sustainable Cellulose/Silica Composite Aerogels with Enhanced Mechanical Properties and Daytime Radiative Cooling Capability

Cellulose aerogels (CAs) typically suffer from poor mechanical resilience under compression due to adhesion effects between adjacent cellulose nano-building blocks. Here, we report the fabrication of cellulose/silica composite aerogels constructed of three-dimensional connected nanosheets by freezing and freeze-drying of mixed cellulose nanofiber (CNF) and silica nanobelt (SN) aqueous dispersions. The CNFs form the nanosheet skeletons, and the SNs are homogeneously distributed around the nanosheets. The integration of SNs into cellulose nanosheets effectively alleviates the adhesion effects between nanosheets and endows the sheet skeletons with elasticity and mechanical strength, leading to significantly enhanced flexibility and compressibility of the aerogel monoliths. The composite aerogels can fully recover under a compressive strain of up to 80%. Benefiting from the unique porous structure and abundant chemical bonds vibrating in mid-infrared region that is transparent in the atmosphere, the composite aerogel exhibits maximum solar reflectance of 98.3% in 0.3–2.5 μm and infrared emissions of 92.6% in the 8–13 μm range, enabling superior passive radiative cooling performance of the aerogels. Importantly, the composite aerogels after practical application are recoverable and biodegradable, indicating their sustainable nature. Our study addresses the challenge of poor mechanical properties of CAs and promotes their sustainable application for daytime radiative cooling.