Controlling simonkolleite crystallisation via metallic Zn oxidation in a betaine hydrochloride solution

Zinc oxide nanoparticles, with a hexagonal flake structure, are of significant interest across a range of applications including photocatalysis and biomedicine. Simonkolleite (Zn-5(OH)(8)Cl-2 center dot H2O), a layered double hydroxide, is a precursor for ZnO. Most simonkolleite synthesis routes require precise pH adjustment of Zn-containing salts in alkaline solution, and still produce some undesired morphologies along with the hexagonal one. Additionally, liquid-phase synthesis routes, based on conventional solvents, are environmentally burdensome. Herein aqueous ionic liquid, betaine hydrochloride (betaine center dot HCl), solutions are used to directly oxidise metallic Zn, producing pure simonkolleite nano/microcrystals (X-ray diffraction analysis, thermogravimetric analysis). Imaging (scanning electron microscopy) showed regular and uniform hexagonal simonkolleite flakes. Morphological control, as a function of reaction conditions (betaine center dot HCl concentration, reaction time, and reaction temperature), was achieved. Different growth mechanisms were observed as a function of the concentration of betaine center dot HCl solution, both traditional classical growth of individual crystals and non-traditional growth patterns; the latter included examples of Ostwald ripening and oriented attachment. After calcination, simonkolleite's transformation into ZnO retains its hexagonal skeleton; this produces a nano/micro-ZnO with a relatively uniform shape and size through a convenient reaction route.

Automated summary

Pure simonkolleite nano/microcrystals were synthesized by directly oxidizing metallic Zn using aqueous ionic liquid solutions. The morphology of the simonkolleite flakes was controlled by adjusting the concentration of the ionic liquid solution, reaction time, and temperature. After calcination, the simonkolleite transformed into hexagonal ZnO nanoparticles/microparticles, resulting in a convenient reaction route for obtaining ZnO with a relatively uniform shape and size.