Bio-skin inspired 3D porous cellulose/AlPO4 nano-laminated film with structure-enhanced selective emission for all-day non-power cooling

Abstract

Porous cellulose films have been reported as sustainable and highly-efficient non-power radiative cooling (PRC) materials but are still challenged by their insufficient atmospheric window (AM) emissivity and complex preparation technology. Herein, bio-mimetic skin structure inspired 3D porous cellulose acetate hybrid hollow AlPO₄ (3D PCA/h-AlPO₄) nano-laminated PRC film is creatively fabricated by a proposed solvent polarity matching strategy. Owing to the ultra-rapid extraction of high-quality solvent NMP by water relying on their stronger matching polarity, the PRC film self-forms ultra-rapidly within 5 min and is composed of skin-like wrinkle surface, porous matrix, and dense nanolayer. The wrinkle surface and dense h-AlPO₄ nanolayer has been demonstrated to have higher atmospheric window emissivity (∼94.7% and 96.6%) than the smooth surface (88.7%). The self-formed uniform cavities of about 2 μm can contribute to a high solar reflectivity (∼97%). As proof of concept, the bio-structural film is used for all-day cooling under different atmospheric radiations, and about 13.5 °C/5 °C (daytime high solar irradiance of 988 W m⁻²) and ∼1.5 °C/0.5 °C (nighttime) temperature reduction is realized at low/high (12 °C/35 °C) environment temperatures, respectively. We believe the bio-structure design and ultra-rapid film-formation strategy would inspire the development of polymer-based PRC materials for the highly-efficient energy saving applications.