Single nanomaterial level investigation of ZnO nanorod sulfidation reactions via position resolved confocal Raman spectroscopy

Abstract

Zinc oxide (ZnO) nanomaterials have been used as desulfurizing sorbents for gaseous streams, zinc sulfide (ZnS)-forming template lattices in nanomaterial synthesis, and agriculturally produced sulfur (S)-removing reagents from the environment. Although various nanoscale forms of ZnO have already been utilized widely for such purposes, there is currently a lack of fundamental insight into the sulfidation of ZnO nanomaterials at the single nanocrystal level. We demonstrate that position-resolved confocal Raman spectroscopy can be successfully used to reveal the sulfidation process of ZnO NRs occurring at the single nanomaterial level. We attained a single crystal level understanding of the facet-dependent sulfidation reactivity of ZnO NRs by tracking the same NRs with Raman spectroscopy before and after the sulfidation reaction and quantitatively analyzing various ZnS-induced phonon scattering intensities from different positions on the NRs. The trend in NR facet-dependent sulfidation reactivity is further substantiated by correlating it with the electron microscopy and fluorescence data measured from the same NRs. The insight obtained from this study may provide the much-needed fundamental knowledge base for designing optimal ZnO nanostructures beneficial to many technological and industrial applications exploiting the ZnO-to-ZnS conversion. Taken together with the well-established methods to synthesize ZnO nanomaterials of specific crystal shapes and structures, our findings from this study may be broadly applicable in formulating and optimizing more advanced, low-dimensional ZnO sorbents and scrubbers for highly effective S removal.