Preparation and infrared emissivities of self-assembled ZnO spherical aggregates

The self-assembled zinc oxide (ZnO) spherical aggregates were prepared via the hydrothermal process in the presence of multi-functional additives. Multi-functional additives including oxalic acid, citric acid and sodium polyacrylate were demonstrated to be vital to the self-assembly of ZnO nanosheets, which constructs the spherical aggregates ultimately. The anions can conglutinate the surface of ZnO nuclei via ionic bonding, and the electrostatic attraction between Zn2+ and anions will promote polyacid counter anions to bridge ZnO nuclei. The infrared emissivity in 8–14 μm of ZnO nanosheets is 0.90, while the emissivity of spherical aggregate slightly decreases to 0.88. It is anticipated that the method can offer a potential solution to fabricate spherical aggregates of metal oxides nanoparticles.