Ionic Liquids Assisted Synthesis of ZnO Nanostructures： Controlled Size, Morphology and Antibacterial Properties

Systematic analysis about the exploitation of imidazolium based ionic liquids （ILs）, [BMIM] BF4 [ILl], [EMIM] BF4 ILL2] and [BMIM] PF6 [IL3] as the morphological template on the basic sol-gel method adopted synthesis of nanostructured zinc oxide （ZnO） is presented. X-ray diffraction （XRD）, particle size analysis （PSA） and scanning electron microscopy （SEM） have been employed for the characterization of structure and morphology of the synthesized ZnO particles. Well-defined capsule like shaped morphology with lower nanosize is observed for the ZnO nanoparticles with ILl than those with IL2 and IL3. This confirms that ILl served as an effective templating material due to their unique properties. Especially the effective aggregation of ZnO particles with a self-organized frame of ILl was the essential factor to produce the lower nanosized ZnO with capsule shaped structure. The synthesized ZnO samples with IL2 and IL3 fabricated the flake like shaped and rod like shaped morphologies in the range of nanoscale. The formed ZnO nanoparticles with IL2 exhibit higher nanosize than the ZnO nanoparticles produced by ILl, owing to shorter length of alkyl group in its cation which restricts steric effect and permits the nanoparticles to grow longer. Even though IL3 produced the discrete ZnO nanorods, the hydrophobic nature of IL3 created the higher nanosize than the ZnO nanoparticles formed by other two ionic liquids. Antibacterial properties of the synthesized ZnO nanostructures were investigated against Staphylococcus aureus （gram positive） and Escherichia coil （gram negative） bacteria by Agar diffusion test method. Microbial experiments indicate that the synthesized ZnO samples show a wide spectrum of antimicrobial activities and performed better against S. aureus than E. coil with the same concentration of ZnO.