Combustion synthesis of nanocrystalline ZnO powders using zinc nitrate and glycine as reactants—influence of reactant composition

Zinc oxide (ZnO) has a wurtzite structure, a characteristic of semi-conductors, and is used in electronic ceramic devices [1, 2] and photo catalysts [3, 4]. Nanoscale particles possess different physical and chemical properties compared to bulk materials. Better sinterability, higher catalytic activity, and other unique properties may be expected because of their nano-sized crystallite, large surface area and different surface properties (such as surface defect), etc. At present, two methods are generally being used to obtain nanosized ZnO powder: vapor method and sol-gel method, which require high processing and chemicals costs, respectively [5], Therefore, the synthesis method of nano-sized ZnO powders can still be improved. Recently, several researchers proposed the solution combustion method to synthesize simple and mixed metal oxides [6–11]. Using this method, the heating and evaporation of metal nitrate solution with an organic compound (such as glycine, urea, or citric acid etc.) results in self-firing and generates intense heat by exothermic reaction. This intense heat is used to synthesize the ceramic powders. This novel approach has the advantages of inexpensive raw materials, a relatively simple preparation process, and a fine resulting powder with high homogeneity. Although there is little literature reporting that nanosized ZnO have been synthesized by this method [4, 5, 12, 13], there is also hardly any information available on the effects of reactant composition in the nature of combustion reaction phenomena on the properties of as-synthesized ZnO powders. In this work, the study of correlation among reactant composition, reaction phenomena, and product characteristics are undertaken. Glycine (NH2CH2COOH) was selected as the fuel since it is inexpensive and its combustion heat (−3.24 Kcal/g) is more negative when compared with urea (−2.98 Kcal/g) or citric acid (−2.76 Kcal/g). On the other hand, zinc nitrate [Zn(NO3)2·6H2O] is utilized in the present work because of its dual role of being the zinc source and the oxidant. The combustion reaction can be expressed (but over-simplified) as follows: