Scalable, Recyclable, and Sustainable Daytime Radiative Cooling Materials Engineered by Cellulose-Based Binary-Particle Scattering Architectures

Passive daytime radiative cooling has emerged as a promising zero-energy technology for reducing surface temperatures under direct sunlight. Recent advances in single-component cooling materials have improved solar reflectance and infrared emission. However, the fixed band gaps, refractive indices, and phonon modes of single fillers still impose intrinsic limitations, leading to unavoidable absorption dips and a restricted emissive bandwidth, thereby preventing these single-component cooling materials from maintaining strong cooling performance under intense solar irradiance. Here, we develop a composite material that incorporates binary BaSO4 and Al2O3 particles within a hierarchically porous cellulose acetate matrix. This hybrid binary-particles cellulose acetate material (BCA) enables a broadband solar reflectance of 96.0% and a mid-infrared emissivity of 95.2%. The BCA delivers daytime subambient cooling of up to 5.5 °C under solar irradiance of 1000 W·m-2 and reduces surface temperatures by more than 13 °C when applied to car exteriors, demonstrating its effectiveness for practical application under outdoor conditions. Energy modeling shows that the BCA delivers energy savings greater than 138 kWh·m-2 for building cooling in representative climates. The BCA also exhibits favorable cost performance, scalability, and recyclability, supporting its potential for large-scale implementation.