Various white MOF-based cryogels for passive daytime radiative cooling

Abstract

Passive radiative cooling technology is a pressing need in contemporary society, yet it remains in its nascent stages, necessitating further research endeavors. In this study, a series of metal–organic framework (MOF)-based cryogels have been synthesized through the freeze-drying method. The presence of abundant pore structures and chemical bonds (such as C–O, C–H, C–N, PO, Ti–O, and C–OH) endows these MOF-based cryogels with high solar reflectance values exceeding 90% and high mid-infrared emissivity levels surpassing 95%. These MOF-based cryogels can reduce the temperature by at least 10 °C and up to 15.1 °C under direct sunlight. Notably, the structures and optical properties of these MOF-based cryogels remain unchanged after being exposed to sunlight for 7 days and immersed in water for 30 days, indicating their good performance durability. Following accelerated ultraviolet aging and multiple freeze–thaw cycles, the cryogels’ macroscopic appearances and microscopic morphologies remain intact, validating their exceptional weatherability. Furthermore, their recyclability and sustainable performance render them well-suited for applications as radiative cooling materials. The integration of MOFs and cryogels not only advances radiative cooling technology but also establishes a novel research platform for materials in this field.