In this work, some structural and optical properties of the zinc oxide (ZnO) nanoparticles were studied. The highly crystalline
ZnO nanoparticles were produced by the hydrothermal and sol–gel methods. The analyses of the XRD patterns, STEM images and
UV spectroscopy showed that the size of the nanoparticles prepared by oxalic acid was smaller than the ones by urea. The properties
of oxalic acid and urea were also investigated to determine the most effective crystallization process of ZnO nanoparticles.
It has been shown that pH, decomposition temperature and activity coefficient of the complexing agent have certain effects
on crystallization process.