Effects of nanolayer versus nanosphere morphologies on radiative cooling

Passive radiative cooling has emerged as a promising solution to address the challenges of energy consumption and climate crisis. Calcium carbonate (CaCO₃) is a material seen in both cooling paints and snail shells for cooling purposes but with nanoparticle and multilayer morphologies, respectively, raising the question of how the morphology affects the radiative cooling performance. In this work, we calculate the optical performance of the calcite-air nanolayer and nanosphere composites using the Transfer Matrix Method and Mie theory combined with Monte Carlo simulation, respectively. Notably, the nanolayer composite, with a 60% volume fraction, has the maximum reflectance and optimizes at a nanolayer thickness of 300 nm. In comparison, spherical nanoparticles reach their optimum reflectance at around 500–600 nm diameter. Furthermore, nanolayers exhibit higher sky window emissivity of up to 6%, resulting in the highest figure of merit. These results highlight the unique behaviors of each morphology and underscore the need for distinct optimized parameters to achieve high solar reflection.