(71g) Colloidal Low-Temperature Synthesis of Zinc Oxide Nanoparticles

Zinc oxide has (ZnO) found its important applications in optoelectronic devices, catalysts, sensors, and varistors. Because of its wide band gap of 3.37 eV, ZnO has gained attraction as a potential material for low-voltage luminescence and short wavelength applications. In addition, ZnO has efficient exciton emission at room temperature due to its high exciton binding energy of 60 meV. ZnO powders have been prepared by several methods including sol-gel, gas-phase condensation, and liquid-phase chemical condensation. There are only a few cases where pure hexagonal ZnO nanoparticles were obtained. In this work, ZnO nanoparticles were synthesized from anhydrous ZnCl2 and urea at low temperatures by a simple colloidal chemistry method. Ethylene glycol was used as the reaction medium. Tetramethylammonium hydroxide (TMAH) was used to adjust the pH of the reaction solution. No ZnO particles were formed without TMAH. The reaction solution was typically heated to 150 C. The ZnO nanoparticles were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), photoluminescence (PL) spectroscopy, transition electron microscopy (TEM), and thermogravimetric analysis (TGA)/differential scanning calorimetry (DSC). The ZnO nanoparticles synthesized had a hexagonal structure and were uniform in both shape and size.