Eggshell Biowaste-Derived Flexible and Self-Cleaning Films for Efficient Subambient Daytime Radiative Cooling

The management of the abundant eggshell biowaste produced worldwide has become a problematic issue due to the generated odor and microorganisms after direct disposal of the eggshell biowaste in landfills. Herein, we propose a new method to convert the hazardous eggshell biowaste to valuable resources for energy management applications. Eggshell-based films are fabricated by embedding eggshell powders into a polymer matrix to achieve highly efficient subambient daytime radiative cooling. Benefiting from the Mie scattering of the eggshell particles/air pores in the solar spectrum and the strong emission of the eggshell in the mid-infrared (mid-IR) range, the eggshell-based films present a high reflection of 0.96 in the solar spectrum and a high emission of 0.95 in the mid-IR range, with notable average temperature reductions of 4.1 and 11 °C below the ambient temperature during daytime and nighttime, respectively. Moreover, the eggshell-based films exhibit excellent flexibility and self-cleaning properties, which are beneficial for practical long-term outdoor applications. Our proposed design provides a new means for environmentally friendly and sustainable management of eggshell biowaste.