Atomistic mechanisms of ZnO aggregation from ethanolic solution: ion association, proton transfer, and self-organization.

We report on atomistic simulations related to the nucleation of zinc oxide nanocrystals from ethanolic solution. The underlying mechanisms are explored from the very initial stage of Zn2+ and OH(-) ion association to the formation of nanometer-sized aggregates counting up to 250 ions. The embryonic aggregates consist of zinc and hydroxide ions, only. At later stages of aggregate growth, proton transfer reactions at the aggregate-solvent interface account for the formation of O(2-) ions and induce the precipitation of zinc oxide. After the association of around 150 ions, ZnO domains were found to nucleate in the central region of the [Znx(OH)yOz]2x-y-2z) aggregates. In the course of further ion association and condensation reactions, progressive self-organization leads to an extended core in which the ions are arranged according to the wurtzite structure.