Highly stable and nonflammable hydrated salt nanocapsules with inorganic-organic composite shell for sustainable building technology

Inorganic hydrated salts show great potential for use in low-temperature energy storage. Nevertheless, drawbacks, such as phase separation, liquid leakage, and inherent supercooling, restrict their application in sustainable building technology. Here, nanoencapsulated phase change materials (NePCMs) was designed by combination of hydrated salt and inorganic-organic composite shell to enhance the thermal energy storage of buildings. Using a two-step method, PMMA and TiO2, considered excellent shell materials, were harmoniously combined on the surface of Na2HPO4·12H2O core. The latent heat of the nanocapsules was approximately 139.6 kJ/kg. After undergoing 500 heating and cooling cycles, the latent heat of nanocapsules only degraded by approximately 5 %. Leakage of water was not observed following heating of the NePCMs to 60 °C for 1 h. The supercooling degree of the nanocapsules decreased to around 0.7 °C. The hybrid PMMA-TiO2 shell was designed to improve shape stability, reduce water loss, and enhance mechanical properties. Through burning experiments, it was confirmed that NePCMs had good flame-retardant properties. Thus, hydrated salt nanocapsules with inorganic-organic composite shell are an ideal candidate for use as building materials for effective thermal management and fire protection.