Cellulose based hierarchical structural colored wood composite material for daytime radiative cooling

Daytime radiative cooling (DRC) provides a sustainable strategy to reduce the reliance on traditional energy-consuming cooling methods, which would facilitate the realization of “carbon neutrality.” However, the existed daytime radiative cooling materials have mostly white or mirror appearances, limiting their applications. Herein, we report a hierarchical structured photonic radiative cooling material, the delignified wood is used as the cellulosic basement of the photonic radiative cooling material, and the structural colored photonic layer is prepared by a bottom-up self-assembly of cellulose nanocrystal (CNC) and xylan which has tunable structural colored appearance cross over the visible spectrum. It is noteworthy that the high reflection efficiency (95.0 %) in the solar band and high emission efficiency (93.0 %) in the atmospheric window of structural colored wood endows them with high radiative cooling efficiency. In addition, the incorporation of PDMS improves the hydrophobicity of these materials without affecting their radiative cooling properties. The outdoor cooling effect of structural colored CNC film and wood material reach to about 2.1 °C and 4.3 °C, respectively. Interestingly, patterned “CNC” coated on wood can be used as an outdoor decorative and radiative cooling functional material, which provides a viable option for the colorful energy-saving building materials.