Reversible Tuning the Aspect Ratio and Plasmonic Shift of Gold Nanorods in Alkaline Environment: Growth, Etching and Rebuilding

The well-developed seed-mediated growth of gold nanorods (GNRs) is under the weakly acidic condition, and the aggregation of the GNRs usually takes place when the pH value is increased to alkalinity. In this study, GNRs have been successfully prepared in the alkaline environment using the reducibility of H₂O₂ under the alkaline condition (pH = 10), and the longitudinal localized surface plasmon resonance (LSPR) could be fine tuned within a wider wavelength range of 600 ~ 1050 nm by changing the concentration of silver ion. On the other hand, by using the strong oxidizability of the H₂O₂ under the acidic condition (pH = 3), the prepared GNRs could be etched completely, and the chloroauric acid, as the important raw material of preparing GNRs, could be retrieved. The recovered materials could be reused as the growth solution of GNRs, and the re-prepared GNRs have longer aspect ratio and stronger LSPR. This research reflects the cyclic utilization of noble metal along with preparation of GNRs in the weak alkaline environment.