Low temperature structure tunability of zinc oxide nanostructures using milk protein casein

Spherical, flower and rod-like zinc oxide nanostructures have been successfully biosynthesized at 70 °C in the presence of milk protein casein through a simple precipitation method. The concentration of casein in an alkaline medium determines the structure of zinc oxide. The chemical synthesis of highly crystalline zinc oxide nanostructures is accomplished at relatively low processing temperature using casein. X-ray diffraction studies confirm the phase purity and crystalline nature of zinc oxide nanostructures. Morphological changes in the samples were identified through electron microscopic images. Casein linkage with the ZnO nanostructures was confirmed by Fourier Transform Infra-red spectroscopy. The role of casein on the morphological features has been explained on the basis of its self-assembling nature, copolymerization, and secondary structure formation. The effects of morphological change in the optical properties are studied using a UV-visible absorption and photoluminescence spectroscopy. The results indicate that casein is a good mediator for the morphology-controlled growth of nanostructures at moderately low temperatures.