Controlling the Morphology of Zinc Oxide Nanorods Crystallized from Aqueous Solutions: The Effect of Crystal Growth Modifiers on Aspect Ratio

The effect of growth modifiers on the morphology of zinc oxide (ZnO) nanorods crystallized from solution is characterized. During hydrolysis of zinc nitrate at pH = 7.6 and 75 °C, hexagonally prismatic ZnO crystals were grown in the presence of three growth modifiers: poly(diallyldimethylammonium chloride) (PDADMAC), sodium poly(styrene sulfonate) (PSS), and trisodium citrate. Using statistical analyses of scanning electron microscopy (SEM) images, crystal dimensions were quantified, and the median aspect ratio (ratio of prism length to width) was determined as a function of modifier concentration. In the absence of growth modifiers, the median crystal aspect ratio was 5.2. The aspect ratio was reduced to 4.7, 2.5, and 0.25 in the presence of, respectively, 67 nmol/L (nM) PDADMAC, 130 nM PSS, and 40 μmol/L (μM) citrate. These effects are explained in terms of both electrostatic and coordinative binding between growth modifier and crystal surface.