Synthesis and characterization of 3D ZnO superstructures via a template-free hydrothermal method

The ZnO microrods and flower-like 3D superstructures have been synthesized via a template-free hydrothermal method. The prepared ZnO samples are characterized by powder X-ray diffraction (XRD) and scanning electron microscopy (SEM). It is found that the flower-like 3D ZnO superstructures can be obtained simply by tuning the volume ratio of Zn(OH)₂⁴⁻ precursor solution to water, or the volume ratio of ethylene glycol to water. When the volume ratio of Zn(OH)₄²⁻ precursor solution to water is 1:7, the flower-like 3D ZnO superstructures are obtained, in which the diameter of an individual pencil-like rod is about 1.0 μm, and the tip size is several nanometers. While when the volume ratio of Zn(OH)₄²⁻ precursor solution to ethylene glycol (EG) is 1:1, the flower-like 3D ZnO superstructure consists of hexagonal rods with about 500 nm in diameter. A plausible formation mechanism of flower-like 3D ZnO superstructures is discussed in detail.