Evolution of space-efficient and facet-specific ZnO 3-D nanostructures and their application in photocatalysis

We report new structural designs to dramatically increase the surface area of the ZnO nanostructure without compromising the small volume much. Space-efficient and facet-specific ZnO 3-D nanostructures, namely {101}-stacked nanocones and {100}-nanoforest, have been prepared by facet-selective etching and oriented nanocrystal growth, respectively. Grain boundary etching of multiwalled ZnO hexagonal nanocones leads to polar {101} facet-maximized ZnO stacked nanocones and oriented nanocolumn growth on ZnO hexagonal nanocones generates {100} facet maximized ZnO nanoforests. These facet-specific ZnO nanostructures offer opportunities for examination of their facet-dependent photocatalytic properties. Compared to the original ZnO hexagonal nanocone structures, these new ZnO 3-D structures exhibit a much higher photocatalytic property for photodegradation of organic dye, rhodamine B. Specifically, {101} stacked nanocones with a polar {101} plane maximized structure and high density of oxygen vacancies have shown the best performance among structures examined. We also demonstrate a great photocatalytic performance of the Au supported 3-D ZnO nanostructures with well-defined facets and high surface area.