Analysis of growth parameters for hydrothermal synthesis of ZnO nanoparticles through a statistical experimental design method

Nanocrystalline ZnO particles were synthesized from an aqueous solution composed of zinc acetate dihydrate (Zn(CH₃COO)₂• 2H₂O) and urea (H₂NCONH₂). A precipitating precursor, basic zinc carbonate (Zn₅(CO₃) ₂(OH)₆), was first formed by hydrothermally treating the solution at 120 °C for 2-4 h. Nanocrystalline ZnO particles were then obtained by calcining the precursors at 350-650 °C for 0.5-2 h. The synthesis products were characterized using thermogravimetry-differential scanning calorimetry-mass spectrometry, X-ray diffraction, scanning electron microscopy, transmission electron microscopy and photoluminescence techniques. Based on the experimental results, a possible reaction mechanism for the ZnO formation was proposed. The effects of experimental parameters (namely, the hydrothermal treatment time, the calcination time, and the calcination temperature) on the characteristics of the resulting ZnO products (i.e., the crystalline size and the photoluminescence properties) were analyzed by the Taguchi method to attain the optimum synthesis conditions. By using the appropriate parameters derived from this method, we verified that the optimized synthesis provided a yield of ∼70% and that the resulting ZnO particles possessed the characteristics of a ∼25 nm crystalline size and a satisfactory photoluminescence property.