In-Suspension Growth of ZnO Nanorods with Tunable Length and Diameter Using Polymorphic Seeds

Nanostructured zinc oxide (ZnO) is an important material that finds application in numerous fields spanning from catalysis to optoelectronics. Rodlike ZnO nanostructures are of particular interest, given their well-defined crystalline orientation and high surface area to volume ratio. In this work we show how the choice of precursor seeds determines the final morphology of in-suspension-grown ZnO nanostructures and can be used to tune their length and diameter. Free-standing ZnO nanorods were grown by controlled hydrolysis of zinc nitrate at 90 °C using hexamethylenetetramine as a source of ammonia which, in turn, provided OH anions. The ZnO growth was directed toward the formation of pencil-shaped nanorods (diameter ∼124 nm) using aqueous suspensions of ZnO nanopyramids (prepared by a nonhydrolytic sol–gel method), whereas their length depended on the concentration of the initial precursor. To prove the importance of the size of seeds and their morphology, ZnO nanotiles, nanoparticles, and nanocrystals were also used to seed the growth of ZnO nanostructures, giving nanorods of different lengths and diameters. The morphology of the nanostructures was investigated by SEM, TEM, and powder X-ray diffraction.