Fabrication of ZnO nanoparticles with various aspect ratios through acidic and basic routes

Nanoscale ZnO grains and rods having various aspect ratios were selectively synthesized through acidic and basic routes, respectively, in an aqueous system at 60 °C. Equiaxial nanograins were obtained by the addition of NaOH into an acidic solution of ZnSO₄ (acidic route). On the other hand, nanorods with an aspect ratio ∼12 were prepared by the introduction of ZnSO₄ into a basic solution of NaOH (basic route). The aspect ratio of ZnO nanoparticles was changed by the preparation routes, whereas the final pH of the solutions was the same. The variation of pH in the reaction system influenced the density of homogeneous nucleation and the crystal growth along the c axis. The morphological control of one-dimensional ZnO particulate materials with nanosized diameters and lengths was successfully achieved using the simple mixing techniques.