A facile shape-selective growth of ZnO nanotips and graded nanowires from its oriented nanorods in a saturated ZnS solution

A facile solution-based route is developed for the preparation of distinctive ZnO nanostructures via a dissolution-growth of ZnO nanorods in a saturated ZnS solution at a water-bath temperature of 95 °C. In the dissolution-growth process, a series of novel morphologies including nanotips, tapered and graded nanowires can be conveniently achieved by simply changing the heating time. The pointed ends of the nanotips have a diameter of several nanometers, and the graded nanowires have a gradient change in diameter from a few to tens of nanometers along the longitudinal direction with the size of the thin end matching the Bohr exciton radius of ZnO. Furthermore, the formation mechanism from the ZnO nanorods to the nanotips, to the tapered and graded nanowires is discussed based on shape-evolution observations.