Hierarchically structured composite with superhydrophobicity and radiative cooling for energy-saving buildings

Passive daytime radiative cooling (PDRC) with zero energy consumption and green is regarded as one of the most feasible solutions to replace conventional electrical cooling by reflecting sunlight spontaneously and radiating excess heat through atmospheric transparency windows to universe natural heat sink. However, traditional cool building materials are still very limited in practical applications due to contamination by dust, rain, etc., which reduces the cooling capacity in outdoor environments. Herein, we fabricate a hierarchically designed superhydrophobic daytime radiative composite (Al2O3-PDMS/Al2O3-PDMS@Ag/Al2O3-PDMS/SiO2) via facile bladeing film and electroless Ag plating methods, which have strong visible light reflectivity ∼91 % and high mid-infrared emissivity ∼97 %, effectively producing an ambient temperature drop of 13.8 °C on sunny days in direct outdoor sunlight. What's more, the composite has satisfactory superhydrophobicity with a water contact angle of 154°, making the composite self-cleaning so that the composite is not contaminated and effectively maintains splendid radiative cooling properties. Meanwhile, after prolonged immersion in hydrochloric acid and water shock, the composite retains superhydrophobicity and significant radiative cooling properties, which are of great significance for the sustainable development of energy-saving buildings.