Recyclable cellulose nanocrystals xerogel with thermally insulating and radiative cooling

Passive radiative cooling technology provides a sustainable method to minimize building's energy consumption and maintain indoor cooling by reflecting solar light and emitting heat to outer space. However, designing a radiative cooler that achieves high solar reflectance and mid-infrared emissivity while meeting the outdoor practical applications is still a challenge. Herein, we proposed a kind of cellulose nanocrystals (CNCs)-based thermal insulating xerogel through cross-linking with poly (ethylene glycol) diacrylate (PEGDA), and followed by fluorinated treatment. The as-prepared xerogel exhibits a low thermal conductivity of 0.0671 W/mK, high solar reflectivity of ∼92.52 %, high mid-infrared emissivity of ∼94.45 %, as well as excellent self-cleaning properties. The coupling of excellent thermal insulation and radiative cooling endows the xerogel with superior thermal management properties, achieving a temperature drop of ∼13 °C at daytime, and meanwhile, its cooling performance can be maintained across various weather conditions. In addition, the applications of xerogel were extended to food and ice preservation. More importantly, the CNCs-based xerogel can be recycled in a straightforward manner or naturally degraded in outdoor environment, which ensured its sustainability. This study can help to a comprehensive understanding of the radiative cooling behavior of xerogels and guide to an approach to develop the high-performance green and sustainable radiative cooling porous material.