Control of ZnO Morphology via a Simple Solution Route

Abstract

By decomposing Zn(OH)4 2- or Zn(NH3)4 2+ precursor in various solvents at suitable reaction conditions, zinc oxide with a diversity of well-defined morphologies was synthesized. Flowerlike ZnO built up by nanorods was obtained by treating Zn(OH)4 2- precursor in water at 180 °C for 13 h. Whereas a replacement of the solvent by n-heptane yields snow flakelike ZnO. The prismlike and the prickly spherelike ZnO were also prepared, respectively, by decomposing Zn(NH3)4 2+ or Zn(OH)4 2- in ethanol at 100 °C for 13 h. The rodlike ZnO was produced at 180 °C under the same condition for preparing prickly spherelike product. Besides these typical samples, ZnO in other morphologies was studied manipulatively by changing the reaction conditions of our solution route. Systematical condition-dependent experiments were compared comprehensively to reveal the formation and detailed growth process of ZnO nanosized crystallites and aggregates. The experimental results studied by X-ray diffraction, transmission electron microscopy, and scanning electron microscopy indicated that the solvent, precursor, solution basicity, and reaction temperature as well as time are responsible for the variations of ZnO morphologies.

Effect of Precursor Type on Zinc Oxide Formation and Morphology Development during Hydrothermal Synthesis

“…To examine the phase formation of ZnO depending on the precursor type, ZnO powders were synthesised under hydrothermal synthesis conditions at 100 °C for 0-3 hours using different precursors (ZnCl 2 was observed as a major phase with a small amount of zincite (zinc oxide) at t=0 min (Fig. 1).…”

“…In solution, the growth unit of a crystal is the complex that is formed by the connection of cation with OH -ions. In the supersaturation solution, zinc hydroxide gel dissolved in the solution complex with OH -ions forms growth units (Zn(OH) [2][3][4] ) by the attraction of ions as follows: Since the growth unit (Zn(OH) [2][3][4] ) incorporating into the crystal lattice take place by the dehydration reaction between OH -ligands, the growth habit of the ZnO crystal is related to OH -ligands at the interface or the reaction medium [8,9].…”

“…In this case, kinetically favored tiny crystallites nucleate first in supersaturated medium and are followed by the growth of larger particles (thermodynamically favored) due to the energy difference between large and smaller particles of higher solubility based on the GibbsThomson law [10]. The aqueous solution of zinc nitrate can produce Zn(OH) 2 aches the supersaturation degree of ZnO, ZnO nuclei will form spontaneously in the aqueous complex solution [7].…”

“…Because of these unique characteristic, zinc oxide (ZnO) is a very attractive materials for various applications such as conductive oxide, antistatic coating, sensors, band gap optoelectronic devices, pigments and an UV filters in sunscreens. Depending upon the different synthesis methods, it can be synthesised with various type of morphology such as rod like, sphere like, flower like or urchinlike morphologies [1][2][3]. The crystal structure, particle size and morphology of ZnO particles are important parameters which affect the properties of the powder and hence determine application areas.…”

“…Zang et al reported the controlling of ZnO morphology by using different precursor (Zn(OH) 4 2-and Zn(NH 3 ) 4 2-) and simple solution route. They founded that ZnO particles had a prismlike morphology after reaction process where NH 3 was formed as a by-product from Zn(NH 3 ) 4 2-whereas ZnO particles had a rod like or the flower like morphology depending on the concentration of OH -in the Zn(OH) 4 2-solution [2].…”