Decoupling Cellulose‐Photonic Material Interaction in Solar Scattering for Realizing Daytime Radiative Cooling

ABSTRACT Understanding the interaction between micro and nano assembly in optical composite scatters is important for developing high‐performance radiative cooling materials. In this work, taking cellulose as a proof of concept, a series of photonic materials (MgO, BaSO 4 , ZnO) are used to regulate the interaction between light and cellulose, aiming to modulate the sunlight scattering efficiency of cellulose‐based composite cooling materials (CCAs). By rearranging the structure of cellulose composite assembly at micro/nano scale in wet ball milling process, the cellulose‐photonic materials with the unique micro/nano structure are achieved. The nanoparticles can be anchored and dispersed onto the skeleton of cellulose, which can induce multiple sunlight reflection at the interface, thereby resulting in improved overall solar reflectance. The FDTD simulation demonstrated the backwards scattering is dominant in this complex system, different from pure cellulose scatters with a low refractive index. As a result, CCAs exhibited a high solar reflectance of 0.95 and high infrared emissivity of 0.94, and achieve subambient cooling of 6.6 °C during daytime under direct sunlight in summer in Nanjing. Energy simulation shows CCAs can save 57% cooling energy if it used in buildings in China. This work paves the way for developing high and stable biomass‐based daytime radiative cooling materials for thermal regulation.