Chitosan-Network Hydrogels With Complementary Radiative Cooling Modes for Sustainable Thermal Management

Passive radiative cooling (PRC) provides a sustainable solution for building energy management. However, it still remains a huge challenge to fabricate cost-effective and scalable materials with complementary radiative cooling capabilities. Herein, chitosan (CS)-based hydrogels were fabricated by adding radiative cooling fillers—barium sulfate (BaSO 4 ), titanium dioxide (TiO 2 ), and silicon dioxide (SiO 2 ) to achieve selective enhancement of either solar reflectance or infrared emissivity. Through optimization of filler type and loading, CS/BaSO 4 and CS/TiO 2 hydrogels exhibit a peak solar reflectance of 87% (0.4–1.0 μm), enabling outdoor sub-ambient cooling of 7°C under peak solar radiation. The CS/SiO 2 hydrogel (S3-30) exhibits significantly improved atmospheric window emissivity of 88% (8–13 μm), facilitating efficient nighttime radiative heat dissipation. The imine-crosslinked CS networks provide excellent solid–liquid dual-phase stability, preventing water leakage while maintaining facile processability. More importantly, indoor simulations show that temperature is reduced by 2.2°C–4.2°C in model building, while 12-h outdoor field validation confirms stable sub-ambient performance. This work proposes a facile, versatile and biopolymer-based method to fabricate radiative cooling coatings with complementary functionalities, offering a new pathway toward sustainable thermal management in built environments.