17O Solid-State NMR Study on Exposed Facets of ZnO Nanorods with Different Aspect Ratios.

The physical and chemical properties of metal oxide nanocrystals are closely related to their exposed facets, so the study on facet structures is helpful to develop facet/morphology-property relationships and rationally design nanostructures with desired properties. In this study, wurtzite ZnO nanorods with different aspect ratios were prepared by controlling the Zn2+/OH- ratio, temperature and time in hydrothermal processes. An O-17 solid-state NMR study was performed on these nanorods, after surface O-17 labeling, to explore the relationship of the O-17 NMR signals with the local surface structure of different exposed facets, i.e., nonpolar (10 (1) over bar0) and polar (0002) facets. It is observed that, one of the signals, the sharp component of a peak at -18.8 ppm, comprises the contribution from the oxygen ions on the polar (0002) facets, in addition to that from nonpolar (10 (1) over bar0) facets, which is confirmed by O-17 NMR spectra of ZnO nanorods with controlled aspect ratios and different thermal treatment conditions. This is important for accurately interpreting the O-17 NMR signal of ZnO-containing materials, especially when studying the facet-related mechanisms. The method applied here can also be extended to study the facet-dependent properties of other faceted oxide nanocrystals.