Self-Cleaning and Self-Cooling Cellulose-Fiber-Based Hierarchical Composites

Passive daytime radiative cooling (PDRC) cools an object down by simultaneously reflecting sunlight and thermally radiating heat to the cold outer space through the Earth's atmospheric window. However, for practical applications, current PDRC materials are facing unprecedented challenges such as complicated and expensive fabrication approaches and performance degradation arising from surface contamination. Here, we develop scalable cellulose-fiber-based hierarchical composites with excellent self-cleaning and self-cooling capabilities, through air-spraying ethanolic polytetrafluoroethylene (PTFE) microparticles suspensions embedded within the micropores of the cellulose fiber. The formed superhydrophobic PTFE coating not only protects the cellulose-fiber-based paper from water wetting and dust contamination for real-life applications but also reinforces its solar reflectance by sunlight backscattering. It results in a sub-ambient cooling performance of 5°C and radiative cooling power of 104 W/m2 under direct solar irradiance of 834 W/m2 and 671 W/m2, respectively. The self-cleaning surface of the hierarchical composites extends its lifespan and keep its good cooling performance for outdoor applications. Additionally, dyed cellulose-fiber-based paper can absorb appropriate visible wavelengths to display specific colors and effectively reflect near-infrared lights to reduce solar heating, which synchronously achieves effective radiative cooling and aesthetic varieties.