Facile preparation of nanostructured ZnO via low-temperature hydrothermal method upon changing the precursor anion: The study of structural, morphological, and optical properties

The synthesis of ZnO nanostructures was carried out via a low-temperature hydrothermal route; using three different zinc precursors: ZnSO4, ZnCl2, and Zn(ac)2. X-ray diffraction analysis confirmed that all synthesized samples have high purity wurtzite hexagonal structure. The calculation of lattice parameters indicated that the precursor's anion and the hydrothermal time strongly affected the lattice parameters. The SO42- anion capped the polar surface growth, which leads to 2D nanostructures. However, the Cl- anion boosted growth along the c axis and inhibited the lateral axes, which lead to 1D nanostructures. The microstrain and crystallite size of the samples were determined using the Williamson-Hall (W-H), Size-Strain Plot, and Halder-Wagner (H-W) methods. The SEM images indicated morphological differences in the formation of the synthesized samples, confirming that the anion of the precursor and the hydrothermal time play a determining role in the shape of the ZnO nanostructures. All the ZnO samples show strong absorption in the ultraviolet region with an onset of absorbance in the range 250-335 nm; blue shifting was observed for all samples indicating a large bandgap, such as Eg(Cl-) > Eg(SO42-) > Eg(C2H3O2- ) and the Urbach energy that reflects the disorder was calculated, such that Eu(ZA6) > Eu(ZS6) > Eu(ZC6). There was a correlation between optical and structural proprieties: the bandgap decreased with increasing microstrain, however, Urbach energy increased.

Automated summary

In this study, ZnO nanostructures were synthesized using different zinc precursors, and characterized by X-ray diffraction analysis. It was found that the precursor's anion and hydrothermal time had a significant influence on the lattice parameters and morphology. The correlation between the morphology and optical properties of ZnO nanostructures was determined through SEM image observation and spectral analysis.