  The management of the abundant eggshell biowaste produced worldwide has
become a problematic issue due to the generated odor and microorganisms after
directly disposing eggshell biowaste in landfills. Herein, we propose a novel
method to convert the hazardous eggshell biowaste to valuable resources for
energy management applications. Eggshell-based films are fabricated by
embedding eggshell powders into polymer matrix to achieve highly efficient
sub-ambient daytime radiative cooling. Benefiting from the Mie scattering of
eggshell particles/air pores in the solar spectrum and strong emission of
eggshell in the mid-infrared (mid-IR) range, the eggshell-based films present
high reflection of 0.96 in the solar spectrum and high emission of 0.95 in the
mid-IR range, resulting in significant average temperature drop of 5{\deg}C and
12{\deg}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 novel means for an
environmentally friendly and sustainable management of the eggshell biowaste.
