Colored Reflective Paints with Doped ZnO Fillers for High Cooling Capabilities

Colored reflective paints are attractive for building cooling and aesthetics. However, coloration of the paints could paradoxically increase the solar absorption, decreasing the cooling capabilities. In this work, we introduced a novel coloration strategy by using metal ion-doped ZnO nanoparticles as fillers to achieve chromatic paints with high cooling capabilities. With inorganic binder of aqueous K2SiO3 solution, it observed that the Mg-doping enabled the paint to deliver a high cooling power of 103.8 W/m2, while Fe-, Cu- and Co-doping strategies created pale buff (L* = 84.6, a* = 2.9, b* = 16.3), olive green (L* = 66.8, a* = −7.9, b* = 18.7), and pale gray (L* = 81.5, a* = −0.6, b* = 2.1) colors with highly remained cooling power of 83.9, 75.4 and 61.1 W/m2, respectively. Physical characterizations indicated that the maintained crystal structures and similar band gaps could be the main reasons for high cooling capabilities of the colored paints. In addition, the high temperature differences and strong adhesion capabilities of paints on concrete substrates enabled them to present promising cooling energy savings for buildings.