Effects of octadecylammine molar concentration on the structure, morphology and optical properties of ZnO nanostructure prepared by homogeneous precipitation method

Pristine and octadecylammine (ODA)-capped ZnO nanostructures were synthesized via the homogeneous precipitation method at a bath temperature of 80 °C and annealed in air at 700 °C for 2 h. Various molar concentrations of ODA ranging from 0.3 to 15 mol% ODA were used to study the effect of ODA capping into ZnO nanostructures. The x-ray diffraction (XRD) analyses revealed the hexagonal wurtzite structure for all prepared samples. The estimated average crystallite sizes were found to be in the range of 46-72 nm. It was found that the crystallite sizes increased with an increase in the amount of ODA molar concentration. The surface morphology studied using scanning electron microscopy (SEM) showed flower-like shapes for pristine ZnO and cylindrical nanorods features for ODA-capped ZnO nanostructures. Elemental energy dispersive (EDS) and mapping analysis conducted on the samples shows homogeneous distribution of Zn, O, and C ions. The Ultraviolet-visible diffusion reflectance spectroscopy showed a decrease in the band gap with an increasing of ODA molar concentration. The photoluminescence (PL) results demonstrated that the luminescence intensity increased up to 10 mol% ODA. However, further increase in ODA molar concentration revealed the decrease on the luminescence intensity. The approach in the present study opened a new way to tune band gap and luminescence intensity using ODA.