Preparation of multi-interfacial ZnO particles and their growth mechanism

ZnO particles with multi-interfacial morphologies such as flower-like shape, prickly sphere and flocculence structure, were synthesized by hydrothermal process under atmospheric pressure at about 373 K by adjusting zinc contained salts and the dosage of NaOH. Kinetic investigations on the growth of the related multi-interfacial ZnO revealed that the process consisted of two first-order reactions, and the reaction rate constants of the nucleation (k1) were less than those of the crystal growth (k2). For several kinds of zinc salts, say Zn(NO3)2·6H2O, Zn(CH3COO)2·2H2O, ZnSO4·7H2O or ZnCl2, the k1 are 0.057, 0.054, 0.054 and 0.094 min−1, respectively, and accordingly, the values of k2 are 0.413, 0.357, 0.116 and 0.025 min−1. The electronegativity of the anions and the basicity of the solutions are the key factors which govern the process of the crystallization and sequentially the morphology of the particles. The possible mechanism for the growth of the multi-interfacial morphologies is proposed that the positive surfaces ((0 0 0 1) and/or image planes) are inclined to enrich negative ions, leading to restraining the essentially dominant growth along c-axis and sequentially the morphology.