Morphological Control of Zinc Oxide Nanoparticles Imaged with Scanning Electron Microscopy

An undergraduate laboratory experiment utilizing inorganic chemistry synthetic methods and characterization techniques for nanoscale materials is described. Zinc oxide nanocrystals in the wurtzite crystal structure of varying morphology were rapidly synthesized with aqueous hydrothermal conditions at 90 °C from aqueous solutions of zinc nitrate, hexamethylenetetramine, and a growth modifier additive. Single crystal hexagonal prisms were prepared as rods (typical aspect ratio = 5.5) with sodium glycolate as a growth modifier additive while trisodium citrate yielded hexagonal plates (typical aspect ratio = 0.7). Ethylenediamine and ammonia yielded columnar hexagonal pyramids (florets) and hexagonal dipyramids (daggers), respectively. All nanocrystals were isolated with vacuum filtration, and crystal morphology was observed with scanning electron microscopy. This interdisciplinary laboratory module prepares students for future work in the field and has been used in an upper division inorganic chemistry course and would be suitable for use in a physics curriculum as well.