Synthesis of morphology-tunable ZnO nanostructures via the composite hydroxide mediated approach for photocatalytic applications

Morphology-tunable ZnO nanostructures were prepared via the composite hydroxide mediated approach by simply tuning the temperature of the molten composite hydroxides. The synthesized ZnO nanostructures were characterized by means of scanning electron microscopy, transmission electron microscopy, x-ray diffraction, photoluminescence spectrophotometry, x-ray photoelectron spectroscopy and UV–vis spectroscopy. As the temperature of molten composite hydroxides increased from 170 °C to 240 °C, the morphology of ZnO nanostructures evolved from nanoparticles and nanorods, to nanoflowers and nanoplates, and finally to hierarchical nanospheres and nanosheets. Photocatalytic analysis revealed that the photocatalytic activity of the synthesized ZnO nanostructures was heavily dependent on their morphology. It was found that the ZnO nanostructures synthesized at 220 °C exhibited the highest photocatalytic activity with its first-order rate constant of 0.1334 min−1. As a contrast, the ZnO nanostructures synthesized at 170 °C exhibited the lowest photocatalytic activity with its first-order rate constant of 0.0511 min−1. We have demonstrated the composite hydroxide mediated approach as a technically sound, environmentally friendly methodology for creating a wide range of ZnO nanostructures.