Self-Assembled ZnS Nanostructured Spheres:  Controllable Crystal Phase and Morphology

We report a simple biomolecule-assisted synthesis of ZnS nanostructured spheres assembled from ZnS nanocrystals with the controllable crystal phase and morphology. l-Cysteine, a biomolecule, was used as the sulfur source and played a key role in the formation of ZnS nanostructured spheres. ZnS nanostructured spheres assembled from various ZnS nanocrystal building blocks, such as nanosheets, quantum dots, nanorods, and multimorphology nanocrystals, were successfully prepared by this simple method. The crystal phase of ZnS nanostructured spheres could be controlled by introducing ethanolamine or ethanediamine as a surface-modifying reagent in this synthetic system. The hexagonal ZnS nanocrystals were obtained in mixed solvents of water and ethanolamine at temperature as low as 95 °C. The growth mechanism of the nanostructured spheres assembled from nanorods was proposed. The optical properties of ZnS nanostructured spheres were investigated by ultraviolet−visible (UV−vis) absorption and photoluminescence (PL) spectra.