Control growth of single crystalline ZnO nanorod arrays and nanoflowers with enhanced photocatalytic activity

Single crystalline vertical nanorod arrays and nanoflowers of ZnO have been grown in situ on cheap zinc foils under hydrothermal conditions, by means of hexamethylenetetramine and ethanolamine, respectively. Their morphologies and crystal structures are characterized by X-ray diffraction, scanning electron microscopy, and high-resolution transmission electron microscopy. The nanorods and flowers of ZnO grew along the $$ \{ 10\bar{1}1\} $$ and $$ \{ 0001\} $$ planes, respectively. Both types of ZnO display high photocatalytic ability toward the degradation of methylene orange under UV irradiation. The ZnO nanorods show better performance than that of the ZnO nanoflowers, and the $$ \{ 10\bar{1}1\} $$ facets of the ZnO nanorods have higher photoactivity than that of the $$ \{ 000\bar{1}\} $$ or $$ \{ 10\bar{1}0\} $$ crystal planes. This is because the weaker coordinated O atoms on the surface are more likely to be saturated by H atoms in aqueous solution, thereby releasing more free OH radicals. A facile method was developed for selective control synthesis of ZnO nanoflowers and nanorod arrays on Zinc foil, with the assistance of ethanolamine and the hexamethylenetetramine, respectively. The illustration shows the time evolution of the two ZnO structures.