Chelating ligand-mediated synthesis of hollow ZnS microspheres and its optical properties

Monodispersed hollow ZnS microspheres have been successfully synthesized by a facile ethylenediamine tetraacetic acid (EDTA) mediated hydrothermal route. The sizes of the hollow spheres vary from 1.5 to 3.5 μm when the reaction temperature varied from 130 to 230 °C. The formation of these hollow spheres is attributed to the oriented aggregation of ZnS nanocrystals around the gas–liquid interface between H 2S and water. EDTA plays important role as chelating ligand and capping reagent, which regulates the release of Zn 2+ ions for the formation of ZnS hollow spheres. The products were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), UV–vis spectroscopy, photoluminescence, and Raman spectroscopy. The obtained ZnS hollow spheres show a sharp and photostable UV emission ∼370 nm, which is attributed to the recombination process associated with interstitial sulfur vacancy. Well crystalline ZnS hollow spheres with diameters ranging from 1.5 to 3.5 μm and shell thickness from 230 to 700 nm showing ultraviolet emission have been successfully synthesized through a novel one-step hydrothermal process using EDTA as the complexing agent. A suitable mechanism for the formation of ZnS hollow spheres is discussed.