ROLE OF HYDROXYL IONS IN THE GROWTH OF 1-D ZINC OXIDE ON WIRE USING DIRECT HEATING METHOD

Abstract

One dimensional zinc oxide (1-D ZnO) array has been utilized for various application such as photocatalytic, solar cells, and light emitting diode. Low-temperature solution-based methods including hydrothermal, chemical bath deposition, and precipitation methods have been frequently employed for the growth of 1-D ZnO nanostructures. These methods are easy to handle, less expensive, and environmental friendly. However, the main drawback of solution-based methods is long growth duration of ZnO nanostructures varying from 2 to 12 hours. Direct heating method enables ZnO nanostructures to grow rapidly (less than 1 hour) on a metal substrate by employing the Joule heating effect. Under direct heating condition, the effect of hydroxyl ion (OH^?) on the formation of 1-D ZnO is crucial to investigate. In this work, ZnO submicron-rods were grown on kanthal wire with different OH^? concentrations. The formation of ZnO submicron-rods was verified by FESEM, TEM and XRD analyses. At low OH^- ion concentration, Zn(OH)₂ precipitates were formed in the bulk solution. With the increase of OH^- ion concentration, [Zn(OH)₄]^2- complexes were formed, which initiated the nucleation of ZnO on the kanthal wire surface. After direct heating for 10 minutes using 1.2M of OH^- ion, ZnO submicron-rods were fully grown on the wire with average diameter of 304 ± 78.6 nm. In conclusion, tailoring the OH^- ion concentration eliminated the formation of Zn(OH)₂ precipitates and increased the [Zn(OH)₄]^2- complexes which was favorable for the growth of 1-D ZnO in a controlled manner using direct heating method.