ZnO nanostructures decorated hollow glass microspheres as near infrared reflective pigment

Hollow glass microsphere/ZnO composite pigments were successfully prepared by a facile sol-gel method. ZnO coating layers composed of nanosheets, nanoplates, or nanoparticles were anchored at the surface of hollow glass microspheres by formation of Zn-O-Si bond. A reasonable growth mechanism for elucidating the formation of ZnO nanocoating was proposed. The results indicated that the near-infrared reflectance property of the composite pigments was strongly affected by the morphology of ZnO nanostructures. The nanoparticles structures exhibited higher near-infrared reflectance than that of nanosheets and nanoplates structures. The near-infrared solar reflectance of hollow glass microsphere/ZnO composite pigments was 95.7%, while the total solar reflectance of the composite pigment was as high as 97.2%. An approximately 11.1 °C decrease in outer surface temperature was obtained for the heat box coated with composite pigments. Therefore, hollow glass microsphere/ZnO composites are excellent near infrared reflective pigments for efficient solar reflective coatings designed for building facades and roofs.