Growth process, crystal size and alignment of ZnO nanorods synthesized under neutral and acid conditions

ZnO nanorods were synthesized by hydrothermal methods. The pH value is an important factors which affects the growth behavior and morphology of ZnO one dimensional (1D) nanostructures. ZnO nanorods immobilized on glass substrates were formed in aqueous solutions under neutral (pH = 7) and acid (pH = 5) conditions. In the neutral solution, well aligned ZnO nanorods with very small size, vertical orientation, high density and uniform distribution were produced, whereas ZnO nanorods with large dimensions were sparsely and obliquely arranged in the acid solution. Their growth process, chemical composition, crystal structure, and optical property were characterized by scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), X-ray diffraction (XRD) and photoluminescence (PL). It is revealed that the pH can change the chemical reactions and influence the extent of nucleation and crystal growth, thereby having a great effect on the crystal size and the alignment of ZnO nanorods. The crystal quality, structural defects, microstructural development and potential applications were also discussed.