Highly strength and flame-retardant aerogel cooler with reticular porous structures for building energy saving

Despite the significant advantages of radiative cooling polymer-based materials in terms of cost-effective temperature regulation, there are still some problems associated with their practical use in buildings, including the fire hazards and low compressive strength. Herein, this work reports a highly strength and flame-retardant chitosan-based aerogel cooler with reticular porous structures for building energy saving. The resultant hybrid aerogel cooler consisting of chitosan/AlCl3/polyvinyl alcohol (CAP) network and silica sols displayed various outstanding features, such as high solar reflectivity (97.4 %) and infrared emissivity (91.5 %), and hydrophobic performance. The excellent radiative cooling performance is further demonstrated by outdoor test where achieves more than 9 degrees C below the ambient temperature during direct sunlight. In addition, the hybrid aerogel cooler showed exceptional fire-retardant properties (self-extinguished in 1.1 s). Compared with the CAP aerogel, the CAP/silica hybrid aerogel has higher mechanical strength (1.57 MPa), indicating the cross-linking of silica sols with polymer framework improve the mechanical strength. Building simulations of potential cooling energy saving demonstrate that by using composite aerogel as the envelopes can save 33.9 % of energy consumption compared to the building baseline for Nanjing. This work not only highlights the potential of chitosan as widely available biocompatible polymer for thermal management in buildings, but also provides a novel route to combine radiative cooling and flame retardancy in chitosan-based composites, leading to expanded applications.