One step synthesis of ZnO nanoparticles in free organic medium: Structural and optical characterizations

Nano-sized ZnO particles are synthesized by the sol–gel method in aqueous medium without any annealing, ripening treatment or organic additive addition. The structure, morphology, and optical properties of these ZnO nanoparticles are characterized by X-ray Diffraction (XRD), Transmission Electron Microscopy (TEM) and Ultraviolet–visible spectroscopy (UV–vis) respectively. The effect of the synthesis temperature on the morphological (shape and size) and optical properties of these nanoparticles have been examined for temperatures varying from 0 to 80 °C. XRD analysis shows that the as-prepared particles crystallize in the Würtzite hexagonal phase even at very low synthesis temperatures. Meanwhile, Transmission Electron Microscopy observations reveal that the particles present a significant change in shape and size as the temperature increases. They take a flower shape, at very low temperatures, a conical or ellipsoidal shape when the temperature is ranging from 20 °C to 50 °C and a rodlike shape with a hexagonal section at elevated temperatures (>50 °C). Moreover, it has been observed that the increasing of the synthesis temperature leads to a net increase in the average particle size. It affects especially the length in the minor axis direction while the length in the major direction (c-axis) remains nearly constant. Optical properties, carried out by spectrophotometric measurements, indicate that increasing the temperature results in lower band gap energy values.