Synthesis of Zinc Oxide from Layered Zinc Hydroxide Prepared from Zinc Nitrate Aqueous Solution

Abstract

ZnO is widely used as a raw material of various electronic parts and cosmetics. The properties of ZnO particles depend on the morphologies of the crystals. So, it is important to control the morphology of ZnO particles to obtain desired properties. Layered zinc hydroxides are known as the precursor of ZnO because it can be easily synthesized and transformed to ZnO by aging in aqueous solution at relatively low temperature. Moreover, ZnO particles derived from the layered zinc hydroxides by aging in aqueous solutions show various forms which in difficult to obtain by the direct thermal decomposition of zinc hydroxides at a high temperature. In this report, ZnO was synthesized from a layered zinc hydroxide containing nitrate ions between layers, Zn5(OH)8(NO3)2 •2H2O (ZHN), as a precursor by aging under various conditions. Effects of the amount of deionized water, the concentrations of NaNO3 aqueous solutions and the temperature were investigated on the transition of ZHN to ZnO during aging. The formation ratio of ZnO increased with increasing the amount of deionized water and aging temperature. When the ZHN was aged in 200 mL deionized water, the formation ratio of ZnO was 70% even at 60℃ and increased to 95% at 90℃ and 120℃. The aging in NaNO3 aqueous solutions enhanced the formation of ZnO but the formation ratio largely decreased by aging in a 0.1 mol/L NaNO3 aqueous solution. When aging was carried out in NaNO3 aqueous solutions of 1×10-2 to 1×10-6 mol/L at 90℃ and 120℃, the ZnO formation ratio was almost above 95%. In the case of high formation ratio of ZnO, well crystalized rod-shaped particles, which is characteristic shape of ZnO, was obtained and the aspect ratios of ZnO particles decreased with increasing NaNO3 concentrations.

Effects of aging conditions on the morphologies of ZnO particles synthesized under hydrothermal conditions from layered zinc hydroxide as a precursor derivered from zinc acetate

“…The ZHA, on the other hand, including a large quantity of ZnO such as powders obtained by aging at 120°C in Zn(OCOCH 3 ) 2 and CH 3 COONa solutions in concentrations below 0.1 molL −1 , showed no or only very small endothermic peaks and much lower weight loss than the theoretical weight loss of ZHA (about 38%) [19,20]. This is probably because ZHA tends to agglomerate in high concentration electrolyte solutions, and it is difficult to dissolve ZHA to form ZnO [22]. Also, the weight loss of ZHA aged in CH 3 COONa solution was much lower than in the case of aging in Zn(OCOCH 3 ) 2 .…”