title: Formation of amorphous zinc citrate spheres and their conversion to crystalline ZnO nanostructures.
abstract: We report a method for synthesizing zinc citrate spheres at a low temperature (90 °C) under normal atmospheric pressure. The spherical structures were amorphous and had an average diameter of ∼1.7 μm. The amorphous zinc citrate spheres could be converted into crystalline ZnO nanostructures in aqueous solutions by heating at 90 °C for 1 h. By local dissolution of the zinc citrate spheres, nucleation and growth of ZnO occurred on the surfaces of the amorphous zinc citrate spheres. The morphologies and exposed crystal faces of the crystalline ZnO nanostructures (structure I: oblate spheroid; structure II: prolate spheroid; structure III: hexagonal disk; structure IV: sphere) could be controlled simply by varying the solution composition (solutions I, II, III, or IV) in which the as-prepared amorphous zinc citrate spheres were converted. The concentration of citrate anions and solution pH played a decisive role in determining the morphologies and exposed crystal faces of the crystalline ZnO nanostructures. On the basis of experimental results, we propose a plausible mechanism for the conversion of amorphous zinc citrate spheres into the variety of observed ZnO structures.
authors.affiliation: Department of Chemical Engineering, Pohang University of Science and Technology (POSTECH), San 31, Hyoja-Dong, Nam-Gu, Pohang, Gyungbuk, Korea 790-784.
authors.forename: Seungho
authors.initials: S
authors.lastname: Cho
authors.forename: Ji-Wook
authors.initials: JW
authors.lastname: Jang
authors.forename: Alum
authors.initials: A
authors.lastname: Jung
authors.forename: Sung-Hyun
authors.initials: SH
authors.lastname: Lee
authors.forename: Jaeguen
authors.initials: J
authors.lastname: Lee
authors.forename: Jae Sung
authors.initials: JS
authors.lastname: Lee
authors.forename: Kun-Hong
authors.initials: KH
authors.lastname: Lee