Sol-Gel Growth of Hexagonal Faceted ZnO Prism Quantum Dots with Polar Surfaces for Enhanced Photocatalytic Activity

The hexagonal faceted ZnO quantum dots (QDs) about 3-4 nm have been prepared via a sol-gel route by using oleic acid (OA) as the capping agent. It is revealed by electron diffraction patterns and high resolution transmission electron microscopy lattice images that the profile surfaces of the highly crystalline ZnO QDs are mainly composed of {100} planes, with the Zn-terminated (001) faces and the opposite (00 (1) over bar) faces presented as polar planes. Compared with spherical ZnO QDs, the hexagonal faceted ZnO QDs show enhanced photocatalytic activity for photocatalytic decomposition of methylene blue. A mechanism for the enhanced photocatalytic activity of the hexagonal faceted ZnO QDs for degradation of methylene blue is proposed. In addition to the large specific surface areas due to small size and high crystalline, the enhanced photocatalytic activity can mainly be ascribed to the special hexagonal morphology. The Zn-terminated (001) and O-terminated (00 (1) over bar) polar faces are facile to adsorb oxygen molecules and OH- ions, resulting in a greater production rate of H2O2 and OH center dot radicals, hence promoting the photocatalysis reaction. The synthesized hexagonal-shaped ZnO QDs with high photocatalytic efficiency will find widespread potential applications in environmental and biological fields.