Photocatalytic cement-based passive cooling composites: The synergy between radiative cooling and self-cleaning mechanisms
Daoru Liu, J.C.O. Zepper, Daiwei Fan, Qingliang Yu
Abstract
Radiative cooling holds promise in combating climate change by reducing energy consumption. However, organic radiative coolers face fabrication complexities, weak environmental reliability, and limited self-cleaning capabilities. To overcome these challenges, we present autoclaved cement pastes, inorganic passive coolers with exceptional energy-free cooling and self-cleaning properties, achieved through a straightforward hydrothermal process. The inorganic cooler incorporating 28 wt.% alumina exhibits impressive solar reflectivity (0.91), atmospheric window emissivity (0.91), radiative cooling power (−11.0 W/m2), and effective evaporative cooling (>8 h, 25 W/m2). The high solar reflectivity is attributed to tailored nano/micro particles and pores inducing strong Mie scattering within the solar spectral range (λ = 280–2500 nm). The theoretical cooling properties are validated by the outdoor on-site measurements, and the roles of moisture inside the cooler matrix are verified. Additionally, the cooler formulation featuring 14 wt.% nanosilica and 14 wt.% alumina demonstrates remarkable self-cleaning capabilities, eliminating approximately 68% of surface contaminants within 30 min. This self-cleaning performance stems from the evolution of C–S–H phases, leading to the formation of massive nano C-(A)-S-H "honeycombs" with "nanowires", enhancing mass adsorption and photocatalytic quantum effects at abundant active sites. This study would open new avenues for scalable, energy-free cement-bound cooling materials for building engineering and align with the UN's sustainable development goals.