A simple preparation technique for shape-controlled zinc oxide nanoparticles: Formation of narrow size-distributed nanorods using seeds in aqueous solutions

Various shapes of wurtzite-type ZnO nanoparticles were selectively produced in a simple aqueous system prepared by mixing ZnSO4 and NaOH solutions. Ellipsoidal nanoparticles were obtained by the addition of an alkaline agent into an acidic zinc solution (acidic route), while nanorods were grown by mixing a zinc precursor into an alkaline solution (basic route). The aspect ratio and size distribution of the nanorods grown through the basic routes were controlled by the addition of nanoparticles prepared by the acidic route as seeds. On the other hand, micrometric branching rods were obtained by dilution of the reaction solution in the basic routes. The morphological variation of ZnO particles is ascribed to the balance of the nucleation and crystal growth depending on the degree of the supersaturation. We successfully prepared narrow size-distributed rods with a nanometric width and a submicrometric length using the seed particles, because the presence of the seeds suppressed additional nucleation and then controlled the degree of the supersaturation for steady growth of the crystalline particles.