Abstract
Rationally controlled multistage hydrothermal methods have been developed to prepare different types of hierarchical zinc oxide (ZnO) nanostructures with high surface-to-volume ratios and more exposed polar facets. Four types of hierarchical ZnO nanostructures, i.e. nanobrushes (ZNBs), nanoleaves (ZNLs), hierarchical nanodisks (HNDs) and nanoflakes (ZNFs), assembled from initial mono-morphological nanostructures, i.e. nanowires (ZNWs) and nanodisks (ZNDs), were produced from sequential nucleation and growth after a hydrothermal process. Hierarchical nanostructures with 1D nanowire and 2D nanodisk building blocks were realized using zinc nitrate and zinc sulphate as the source of zinc ions, respectively. Compared to their initial mono-morphological counterparts, the grown hierarchical nanostructures demonstrated superior gas sensing properties. ZNLs and ZNFs showed a significant improvement in the sensitivity and fast response to acetone. In addition to the high surface-to-volume ratio, due to the ultrathin sheet building blocks, the enhanced gas sensing properties of the ZNLs and ZNFs are chiefly ascribed to the increased proportion of exposed (0001) polar facets. The current study offers a path for the structure induced development of gas sensing properties by designing a necessary nanostructure, which could be used to fabricate high performance nanostructured gas sensors based on other metal oxides.