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 mu m 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. (c) 2014 Elsevier Ltd. All rights reserved.