Polymorphous ZnO Nanostructures: Zn Polar Surface-Guided Size and Shape Evolution Mechanism and Enhanced Photocatalytic Activity

This study proposes a simple, low-temperature chemical etching method for selective preparation of monodispersed, hexagonal, single-crystal ZnO nanostructures. The morphological evolution from nanoplates (NPs) to nanoseals (NSs), nanobowls (NBs), and nanorings (NRs) is initiated by positively charged (0001) Zn polar surface and driven by the principle of minimum energy. The relationship among the morphology, dimensions, and function of ZnO was determined by investigating polar planes, surface areas, energy bands, defects, optical properties, and catalytic activity for rhodamine B degradation. The ZnO NBs and ZnO NRs exhibit improved photocatalytic performance because of enhanced light harvesting and plasmonic resonance enhanced absorption. Surface recombination plays a key role in the apparent rate constant k for ZnO NBs with small size and those formed at low reaction temperatures. The photocatalytic activity of ZnO NBs formed at high reaction temperatures decreases with increasing size because of the decreased surface area.