A comparative investigation of photocatalyst ZnO nanorods grown on different seed layers: influence of annealing temperature and atmosphere

Abstract

The seed layers were deposited on the activated glass lamellas by dip-coating using zinc solutions with and without diethanolamine (DEA). ZnO nanorods were grown on these two types of seed layers by chemical bath deposition (CBD) method at 95 degrees C. The nanorods were then annealed in air at 300, 400 and 500 degrees C and in an oxygen atmosphere at 400 and 500 degrees C. The influences of seed solution chemistry, annealing temperature and atmosphere on the structural properties of the ZnO nanorods were investigated via X-ray diffraction (XRD) and scanning electron microscopy (SEM). An improved vertical alignment of the nanorods along the c-axis was observed on the DEA-containing seed layer. Their diameters decreased with the increasing annealing temperature, whereas their crystallinities increased. Optical properties of the samples were also studied by ultraviolet-visible (UV-vis) and photoluminescence (PL) spectroscopies. Their optical band edges shifted to lower energies as the annealing temperature increased up to 400 degrees C. The PL intensities decreased with annealing at 500 degrees C in an oxygen atmosphere, which was attributed to the decrease in defect concentration. Their photocatalytic tests using AR88 azo dye and UVA irradiation revealed that the annealing process is beneficial in achieving improved color removals from the aqueous dye solutions. The well-aligned nanorods were successfully grown on the DEA-supported seed layer. However, their photocatalytic efficiencies remained relatively low, which was attributed to poor light interactions with their lateral surfaces.