Carbonation of BaSO₄ NPs Modified Alkali-Activated GGBS for Passive Daytime Radiative Cooling

In this study, alkali-activated granulated blast furnace slag (AAS) was selected as a low-carbon precursor for fabricating an inorganic radiative cooler via accelerated carbonation and BaSO4 nanoparticles (NPs) modification. The influence of the accelerated carbonation and BaSO4 dosages on the solar reflectance and thermal emittance were experimentally investigated, along with multiple analytical characterizations that provide insights into the correlation between phase/microstructure transformation and optical properties. Additionally, small-scale field tests were conducted to validate the cooling performance of the as-fabricated sample in outdoor environments. An energy balance analysis was subsequently performed to calculate the corresponding net cooling power. The results revealed that the synergy of carbonation and BaSO4 NPs significantly improved the solar reflectance from 10.3 to 83.9% while having negligible impact on the thermal emittance. Mechanism analysis indicated that the whitening effect of BaSO4 NPs and its capability to promote the formation of calcite and capillary pore were responsible for the improved solar reflectance. Outdoor measurements demonstrated an excellent passive cooling performance compared to the plain sample, with an average temperature drop of ∼10 °C in the midday, corresponding to a net cooling power of 59 W/m2. This work paves the way for upcycling waste slag into a high-performance passive cooling material while also capturing CO2 for energy-efficient buildings.