A Comparative Analysis of the Properties of Zinc Oxide (ZnO) Nanoparticles Synthesized by Hydrothermal and Sol-Gel Methods

Objective: To study the structural, optical and conductivity properties of ZnO nanoparticles synthesized by two different methods such as hydrothermal and sol-gel methods. Methods/Analysis: ZnO is synthesized at various temperatures 100oC, 150oC and 200oC using hydrothermal method with oxalic acid and zinc acetate and using sol-gel method with sodium hydroxide, zinc chloride and zinc nitrate. Findings: For both methods, the average crystal size determined by X-ray Diffraction (XRD) is noted to be in the range 20–30 nm. The pattern confirmed the composition, crystallinity and the synthesized products are ZnO with high purity and the hexagonal phase. The absorption peak of ZnO nanoparticles has a blue-shift compared with that of the bulk. In hydrothermal method, the band gap is large (i.e) from 4.4–4.9 eV and in the sol-gel method 3.5–3.9 eV. ZnO nanoparticles synthesized by both methods exhibit similar luminescence. Scanning Electron Microscopy (SEM) pictures reveal the morphology as near-spherical prismatic nano particles for hydrothermal method and as nanoflakes for sol-gel method. The Energy Dispersive X-ray Spectroscopy (EDAX) analysis confirms the presence of ZnO only and no other element. The conductivity decreases with the growth temperature as well as the concentration of the ZnO samples by sol-gel method. In contrast, the conductivity of the sample prepared by hydrothermal method, increases with the growth temperature but decreases with the concentration. Novelty: In addition, conductivity of the synthesized ZnO nanoparticles is measured for various concentrations of ZnO. The results of both the methods are compared with each other and with those reported in the literature.