Solar-driven adaptive radiative cooling coating with polymer carbon dots-enhanced photoluminescence for urban skin

Abstract

Adaptive passive daytime radiative cooling coating adjusts cooling capacity on an as-needed basis, making it an advanced zero-energy building cooling technology for urban skin. Currently, research mostly focuses on temperature-driven mechanisms, constrained by the limited availability of phase change materials. To address this challenge, this study pioneers the fabrication of a Solar-driven Adaptive Radiative Cooling (SARC) coating, which can adjust cooling capacity based on solar irradiance. To achieve this objective, the polymer Carbon Dots (CDs), PEI/Poly(St-co-BA)@CDs, are innovatively incorporated in SARC coating as the photoluminescent materials to convert the absorbed solar energy into light energy. Notably, the polymer-based CDs enable the design of Smart Cooling Beads (SCBs) whose surfaces are hydrophilic, making it easier to get dissolved in aqueous solutions. Moreover, the CDs were evenly distributed on the surfaces of SCBs, allowing it to achieve a higher quantum yield, recorded as 33.6 %. Illustrated with an aqueous coating example for demonstration, the effective solar reflectance of developed SARC coating increases from 92.5 % to 95 % under solar radiation. Furthermore, the adaptive cooling performance (1.5 °C to 3.2 °C lower than static coatings) varies with solar radiation (from 220 W. m−2to 880 W. m−2), demonstrating an energy efficiency improvement. These findings validate the SARC coating as a simple, feasible, environmentally friendly, and scalable solution for the advancement of next-generation smart urban skin.