Synthesis and characterization of nano-sized ZnO powders by direct precipitation method

In this study, the precursor precipitates of Zinc oxide (ZnO) were obtained by a direct precipitation method via the reaction between Zinc nitrate (Zn(NO₃)₂) and Ammonium carbonate ((NH₄)₂CO₃) in aqueous solutions with proper concentration. X-ray diffraction (XRD) analysis demonstrated that the precursor precipitates of ZnO were Zn₄(CO₃)(OH)₆·H₂O. Both the Differential thermal analysis (DTA) and the thermal gravimetric analysis (TGA) curves of the precursor precipitates show that no further weight loss and thermal effect were observed at a temperature of above 550 °C. The precursor precipitates of ZnO were subjected to thermal calcinations and finally yielded the nano-sized ZnO powders. The calcined ZnO powders were characterized by XRD, Brunauer-Emmet-Teller analysis (BET), and scanning electron microscope (SEM), respectively. The XRD results indicated that the synthesized ZnO powders had a pure wurtzite structure and the average nano-particle sizes were about 35.2 nm. However, the inconsistency of ZnO particle sizes derived from the BET methods and the XRD analysis indicated that a fraction of nano-sized ZnO powders were in the form of aggregates, which was also verified by SEM and TEM image. In addition, both the SEM image and the TEM photograph demonstrated that the nano-sized ZnO particles were of a pseudo-spherical shape.