Eco-friendly Multiscale Nanostructure Aerogels for Energy Conservation via Radiative Cooling

Polymer-based radiative cooling materials are widely utilized in green building and carbon neutrality initiatives owing to their inherent optical properties, flexibility, and scalability. However, the optical performance of eco-friendly polymer-based materials requires further improvement to achieve high-efficiency radiative cooling. Herein, a multiscale nanostructure calcium carbonate (CaCO3)/polyvinyl alcohol aerogel (MNCPA) was designed and fabricated through an optical simulation-guided approach. The MNCPA exhibits a multiscale nanostructure comprising nanostrips (∼50 nm), CaCO3 nanoparticles (NPs, ∼400 nm), and nano-protrusions (∼900 nm). This multiscale configuration enables distributed reflection across the ultraviolet-visible (0.3-0.8 μm), short-wave near-infrared (0.8-1.1 μm), and long-wave near-infrared (1.1-2.5 μm) spectral bands, thereby significantly enhancing full-spectrum solar reflectivity. Furthermore, the infrared vibration characteristics of CaCO3 NPs, combined with the enlarged thermal radiation area provided by this multiscale architecture, enhance emissivity within the atmospheric transparency window (8-13 μm). Under outdoor solar exposure, a temperature reduction of ∼15.8 °C was achieved by the MNCPA, surpassing that of a commercial film by ∼5.1 °C. Additionally, building energy simulations using an MNCPA-integrated model demonstrated an average annual cooling energy conservation of ∼32.66 MJ m-2 relative to baseline consumption, corresponding to an energy saving ratio of ∼16.85%. This strategy provides a viable approach for advancing eco-friendly materials toward building energy conservation.