Hydrothermal synthesis and growth mechanisms of different ZnO nanostructures and their gas-sensing properties

ZnO nanostructures with four different morphologies (nanoparticles, nanorods, mixtures of nanoparticles and nanorods as well as nanoflowers aggregated by nanoparticles and nanorods) were synthesized successfully via simple hydrothermal method. The crystalline structures of ZnO samples were characterized by the X-ray diffraction and the microscopic morphologies of ZnO samples were observed by the scanning electron microscopy. Besides, the probable growth mechanisms of ZnO nanostructures with four different morphologies were proposed. We found that Hexamethylenetetramine (HMT), the halogen ion F⁻ and the concentration of OH⁻ played a significant role in the morphology of ZnO nanocrystalline. In addition, further gas sensitivity measurements revealed that all the as-synthesized ZnO performed gas-sensing properties towards the ethanol gas with very low concentration. Furthermore, the gas-sensing properties of nanoflowers were much more excellent than the other three low-dimension nanostructures, which indicated that the splendid gas-sensing properties of ZnO nanoflowers were contributed to their large specific area.