Waste Glass-Derived Hierarchically Porous All-Inorganic Coatings for Sustainable Daytime Radiative Cooling

Passive daytime radiative cooling (PDRC) is a promising thermal management technology, yet its widespread application is hindered by the high production costs and poor durability of traditional organic-based materials. Here, we presented a hierarchically porous, all-inorganic PDRC coating synthesized from industrial waste glass and alumina microparticles via low-temperature (600 °C) processing. Rather than serving merely as a cheap substitute, the alkali oxides inherent in waste glass act as natural fluxes, enabling partial melting. Concurrently, the steric hindrance of alumina restricts full densification, spontaneously constructing a highly scattering random photonic network. The optimized composite (50 wt.% waste glass/50 wt.% alumina) achieves 96% solar reflectance and 95% atmospheric window emittance. Field tests confirmed sub-ambient cooling of ~4.0 °C (day) and ~4.5 °C (night), yielding a peak net cooling power of 108.1 W/m2. Accelerated weathering and thermal shock (1000 °C) tests demonstrated sustained optical stability under extreme environmental stress.