Controlled precipitation methods: formation mechanism of ZnO nanoparticles

Zinc oxide nano-particles with different morphologies have been obtained by controlling different parameters of the precipitation process: solution concentration, pH and washing medium. The reactions leading to the formation of zinc metastable complexes were followed by potentiometric and conductimetric titrations. During the ethanol washing step the intermediate zinc complexes have been modified by weathering and solution processes which drived both the phase transformation reactions and the particles recrystallization. The nucleation of zinc alkoxides during this process is an “organic matrix-mediated” process, where the matrix is formed on the intermediate zinc complexes surface during the NH4OH addition to the solution of the zinc precursor. The existence of this matrix has been supported by FTIR. The transformation of the zinc metastable complexes during the washing with ethanol was followed with XRD. Through this process it is possible to obtain agglomerates of zinc oxide nanoparticles from a random network, as was revealed by SEM and TEM.