Hydrophilic ionic liquid-assisted control of the size and morphology of ZnO nanoparticles prepared by a chemical precipitation method

Abstract

ZnO nanoparticles (NPs) were prepared by a chemical precipitation method from zinc acetate dihydrate and NaOH using isopropanol as the reaction medium. The influence of an imidazolium-based hydrophilic ionic liquid (IL), 1-ethyl-3-methylimidazolium methylsulfate, [EMIM][MeSO₄] at different concentrations on the size and morpholgy of ZnO NPs was investigated. The NPs were characterized by Fourier transform-infrared, energy dispersive X-ray and UV-visible spectroscopy, along with X-ray diffraction, particle size analysis, field emission scanning electron microscopy and high resolution transmission electron microscopy. Pure nanocrystalline ZnO with a hexagonal wurtzite phase was formed in the system. The particle size of the NPs varied in the range of 2–55 nm depending on the concentration of the IL used during preparation. With increasing concentration of [EMIM][MeSO₄] the shape of the NPs also changed interestingly from spheres to flakes through nanorods. The use of the IL has been proved effective as a self directing agent and templating material for the successful preparation of ZnO nanostructures. Finally, the mechanism for preparation of ZnO NPs with controllable sizes and morphlogy has been established and the variation of size, shape and morphology has been explained in terms of hydrogen bonding –co–π–π* stacking interaction between the IL and NPs.