Solution-processable, robust and sustainable cooler via nano-structured engineering

Passive daytime radiative cooling (PDRC) materials simultaneously featuring aesthetic and safety distinctions demonstrate versatile applications beyond cooling buildings, while the integrated advantages of high strength, morphological reconfigurability, and sustainability remain challenging for the conventional PDRC materials. Herein, we designed a robust, custom-shaped and eco-friendly cooler via a scalable solution-processable strategy, involving the nano-scale assembly of nano cellulose (NC) and inorganic nanoparticle (e.g., ZrO2, SiO2, BaSO4, and hydroxyapatite). The robust cooler shows an interesting "brick-and-mortar" structure, where the NC constructs interwoven framework (as brick structure) and the inorganic nanoparticle uniformly locates in the skeleton (as mortar structure), collectively contributing to high mechanical strength (>80 MPa) and flexibility. In addition, the structural and chemical distinctions enable our cooler to show a high solar reflectance (>96 %) and mid-infrared emissivity (>0.9), demonstrating a sub-ambient average temperature drop of 8.8 °C in long-term outdoor environments. The high-performance cooler with robustness, scalability and environmental friendliness, serves as a competitive participant toward the advanced PDRC materials in our low-carbon society.