Bioinspired superhydrophobic cellulose-based thermal emitters with multiphase scattering structure for durable daytime radiative cooling

Abstract

Biomass-derived radiative cooling systems have garnered significant attention owing to their sustainable advantages. Cellulose demonstrates radiative cooling potential through C−C/C−O−C vibrational modes that enable thermal exchange with outer space. However, conventional cellulose materials face critical challenges including water sensitivity, UV degradation, and subpar radiative performance for outdoor applications. Inspired by the hierarchical structure of taro leaves, we developed a cellulose nanofibers (CNFs)-based multifunctional aerogel through pickering emulsion templating and freeze-drying strategies. The composite aerogel features a precisely engineered multiphase scattering architecture comprising polydimethylsiloxane (PDMS), CNFs, and nano-silica (nano-SiO₂). This unique design leverages refractive index mismatches to establish heterogeneous scattering interfaces, significantly enhancing broadband light management. The synergistic combination of PDMS’s low surface energy and nano-SiO₂-induced nanoscale roughness achieved exceptional super-hydrophobicity (water contact angle: 153.8°). The optimized aerogel emitter demonstrated outstanding photonic performance with 93.5 % solar reflectance and 98.5 % infrared emissivity, enabling a sub-ambient temperature drop of 7.51 °C under peak solar irradiance. Remarkably, the material maintained 95 % of initial cooling efficiency after 30 hours UV exposure (60 mW·cm^-²), attributable to the UV-blocking nano-SiO₂/PDMS matrix and stable scattering networks. This biomimetic design establishes a new paradigm for durable, high-performance radiative cooling materials through intelligent multiphase structural engineering.