Controlled fabrication of nanostructured ZnO particles and porous thin films via a modified chemical bath deposition method

Abstract

ZnO precipitates and thin solid films were prepared, respectively, in the same solution via a modified chemical bath deposition method. In the solution with distilled water as solvent and zinc nitrate hydrate, hexamethylene tetramine as reactants, a novel microsphere with nanometer holes separated by thin flakes and ZnO hierarchical structure with rod like branches were formed after 24 h at 60 °C. Through controlling the deposition time and the concentration of solution, the pure porous thin solid films can be fabricated. When the citric acid as capping molecules was added into the solution, the precipitates were the pure microspheres and the ZnO hierarchical structure vanished completely. After annealing at 250 °C for 1 h, the thin flakes have been torn off and consisted of the small ZnO nanoparticles with the average size 10 nm. The porous surface of microspheres was maintained. However, after annealing at 400 °C for 1 h,the microspheres have been deformed and became compact. On the other hand, the thin solid films became more exiguous with the bigger surface areas in the solution with citric acid. In the solution with methanol as solvent, the precipitates were the pure ZnO hierarchical structure with rice like branches and the porous microspheres disappeared entirely. The experimental results were studied by X-ray diffraction (XRD), field-emission scanning electron microscopy (FESEM), TG-DSC and the possible mechanisms about the effects of citric acid and solvent on tailoring the size and morphology of ZnO were considered.