Nanostructured ZnO with Tunable Morphology from Double-Salt Ionic Liquids as Soft Template.

Abstract

ZnO nanostructures with tunable morphology were synthesized by the hydrothermal method from two ionic liquids (ILs), 1-ethyl-3-methylimidazolium acetate [C2mim]CH3CO2 and 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide [C2mim](CF3SO2)2N and their corresponding double-salt ILs (DSILs). ILs served as soft templates. DSILs were noted for the production of smaller particle size along with uniformity compared to their pure IL counterparts. A changeover of the shape of ZnO from nano-prism to a hexagonal disk-like structure was observed with the addition of [C2mim]CH3CO2 in the medium during synthesis while nano-dice- and rod-shaped particles were obtained from [C2mim](CF3SO2)2N. The effect of concentration of both ILs was explored for the variations of size and shape, and at high concentrations, the morphology was distinct and sharp with uniform size in each case. The synthesized products exhibited excellent phase (wurtzite) purity and polycrystalline nature. The smallest crystallite size was acquired from DSILs, indicating the advantageous effect of the dual anions. The selective adsorption effect of [C2mim]CH3CO2 on certain facets promoted the growth of ZnO clusters along the [1010] direction, while [C2mim](CF3SO2)2N favored the growth along the [0001] direction. Consequently, DSILs rendered interpenetrating hexagonal disks due to the combined action of the anions for controlling the shape. The band gap energies of the nanoparticles (NPs) were consistent with the distribution of size. Extremely strong red emission and negligible UV emission for the synthesized ZnO NPs demonstrate their potential in the advancement of optoelectronic devices.