Effect of zinc-hydroxo species on the growth of one-dimensional ZnO nanostructures

Abstract

One-dimensional ZnO nanostructures were grown on ZnO seed layer by hydrothermal method using zinc nitrate (Zn(NO3)2) and sodium hydroxide (NaOH) as precursors. The concentrations of NaOH and Zn(NO3)2 were varied from 40 mM to 680 mM and kept constant, respectively. Effects of increasing the hydroxide ions on the concentration of zinc-hydroxo species in the solution were studied using thermodynamic simulation software. The simulated results showed that Zn(OH)2 and Zn(OH)3- concentrations tended to decrease but Zn(OH)42- was non-linearly increased when the concentration of NaOH at room temperature was increased. After the growth of ZnO, the samples were characterized by FESEM and UV-vis to investigate the morphology and transmittance spectra, respectively. The results showed that the rod density of ZnO nanostructures was decreased due to lower concentrations of Zn(OH)2 and Zn(OH)3- species affecting ZnO nucleation mode. On the other hand, Zn(OH)42- was competitively higher and involved in growing 1-D ZnO nanostructures on the nucleation layer resulting in larger diameter and longer length of nanostructures. For the UV-vis results, the % transmittance spectra in visible region of grown ZnO nanostructures with NaOH concentrations from 40 to 360 mM were more than 70% but too low transmittance for 520 mM.