Keep Cool: Polyhedral ZnO@ZIF-8 Polymer Coatings for Daytime Radiative Cooling

Abstract

Effective daytime radiative cooling materials with high solar reflectance and strong infrared emittance can greatly reduce the cooling demand of buildings without any energy consumption, which is a great application potential in the field of energy. Nanoparticle-based radiator is a simple and inexpensive solution for daytime radiative cooling. However, it is difficult for traditional oxide pigment nanoparticles to realize daytime radiative cooling under strong sunlight because of their low reflectance. Here, we report an inexpensive ZnO@ZIF-8 nanoparticle-based radiative cooling coating, which simultaneously achieves sunlight reflection and thermal radiation. ZnO@ZIF-8 polymer coatings can exhibit both high solar reflectance (0.90 ± 0.01) and infrared emittance (0.95 ± 0.01, 8–13 μm). The polyhedral morphology and the unoriented pores of the ZnO@ZIF-8 polymer coating significantly enhance the scattering of sunlight. Even under a nonradiative heat exchange condition, the temperature on the coating surface could be decreased by 7.6 °C when compared with that of the substrate under a solar intensity of 1000 W m–2. Owing to their superior optical capability and simple methods, ZnO@ZIF-8 polymer coatings are promising to be widely utilized and produced. This work is of great significance for designing advanced novel ZnO nanoparticle-based radiators, which provide daytime radiative cooling.