Synthesis of solar heat-reflective ZnTiO3 pigments with novel roof cooling effect

Abstract TiO2 and ZnO based white paints are used worldwide to keep the buildings cool by reflecting solar heat flux. However, the cooling effect and lifetime of such coatings are limited by their band gap and fair reflectivity. Herein, scale-up synthesis of pure hexagonal ZnTiO3 pigment with an optical band gap of 3.75 eV is developed. It is found that the solar absorptance of the as-grown ZnTiO3 pigment is only 0.115, which is 0.038 and 0.044 lower in relation to the conventional ZnO and TiO2 pigments, respectively. Furthermore, the actual outdoor roof cooling test was performed at noon on a sunny day in summer. Interestingly, results found that while the ZnO white paint can decrease the roof temperature from 70.1 °C to 59.8 °C, the ZnTiO3 paint cools the roof from 70.1 °C to 55.2 °C. Compared to the 10.3 °C roof cooling effect of ZnO paint, the as-fabricated ZnTiO3 paint has a roof cooling effect as high as 14.9 °C, which is much more attractive for energy saving applications.