Morphology-controlled growth of ZnO nanostructures using microwave irradiation: from basic to complex structures

Morphology-controlled growth of ZnO nano- and microstructures was achieved by microwave irradiation. Various basic ZnO structures, including nanorods, nanocandles, nanoneedles, nanodisks, nanonuts, microstars, microUFOs, and microballs were simply synthesized at a low temperature (90 degrees C) with low power microwave-assisted heating (about 50 W) and a subsequent aging process. These results could be obtained by changing the precursor chemicals, the capping agents, and the aging times. Even more complex ZnO structures, including ZnO bulky stars, cakes, and jellyfishes, were constructed by microwave irradiation to a mixture of the as-prepared basic ZnO structures and the solution I, IV, or V. This is a fast, simple, and reproducible method which does not require any template, catalyst, or surfactant but can control the morphology of ZnO crystals from simple to complex. Scanning electron microscopy (SEM), transmission electron microscopy (TEM), energy dispersive X-ray spectroscopy (EDX), and X-ray diffraction (XRD) were used to observe the morphology, crystallinity, and chemical composition of the ZnO structures. Growth mechanisms for shape-selective ZnO synthesis were proposed based on these results.