In Situ

ZnO is one of the most widely applied nanomaterials, and the vast majority of ZnO nanoparticles are synthesized from aqueous solutions of inexpensive salts. Here we present the first in situ powder X-ray diffraction (PXRD) study of the formation of ZnO nanoparticles under hydrothermal conditions. An aqueous Zn(NO3)(2) and NaOH precursor gel was studied at three different temperatures (150, 200, and 250 degrees C) by in situ PXRD, and Rietveld refinements of the data were used to extract crystal structure and nanostructural information. Interesting trends in the evolution of crystallite size and twin faulting with temperature were established. The morphology of the synthesized crystallites depends on temperature and reaction time; at high temperatures and long reaction times almost isotropic crystallites are formed, while the anisotropy increases with shorter synthesis times and lower temperatures. Furthermore, the twin fault probability decreases with reaction time and increasing reaction temperature. Under the present synthesis conditions, a minimum ZnO crystallite size of around 14 nm in the a-direction and 22 nm in the c-direction is observed