Zinc oxide flower-like synthesized under hydrothermal conditions

One-dimensional zinc oxide with flower like configuration was synthesized onto a conductor glass substrate (fluorine-doped tin oxide - FTO) at 90 °C during 4 and 16 h. The zinc oxide formation occurs without any use of pre-seed layer or reactants to increase ionic strength of medium, neither addition of surfactant to act as capping agents for controlling morphology or special treatment on the commercial FTO substrate, making this an efficient and inexpensive procedure. X-ray diffraction analysis evidences a structure composed by single crystal in the wurtzite phase. The flower-like configuration observed by field emission scanning electronic microscopy images was promoted by the interaction between the reactant used to prepare the initial solution with pH adjusted at 10.5. This pH value is found, by titration study (triplicate) and in agreement with many reports in the literature, to promote the powder formation of zinc oxide with flower-like configuration. Tubular ZnO flower-like formation on the FTO was attributed to etching caused by ammonia in high concentration during the hydrothermal synthesis. In addition, our experimental results combined with theoretical ab initio calculation lead us to propose that the formation of tubular flower-like zinc oxide films proceeds in three steps, when prepared by hydrothermal process at different times (at T = 90 °C).