Wrapping AgCl Nanostructures with Trimetallic Nanomeshes for Plasmon-Enhanced Catalysis and in Situ SERS Monitoring of Chemical Reactions.

Selective chemical control of multiple reactions is incredibly important for the fabrication of sophisticated nanostructures for functional applications. A representative example is the synthesis of plasmonic nanomaterial-silver chloride (AgCl) conjugates, where metal ions should be selectively reduced into metallic nanostructures for plasmon-enhanced catalytic activity, while the reducible AgCl nanomaterials remain intact despite the presence of a chemical reductant. In addition to the selectively controlled reduction, the plasmonic nanostructures should be appropriately designed for the high stability and photoefficiency of catalysts. In this study, we demonstrate how AgCl nanocubes and nanospheres could be comprehensively wrapped by plasmonic three-dimensional nanomesh structures consisting of gold, silver, and palladium by the selective reduction of their ionic precursors while the AgCl nanostructures remain intact. Complete trimetallic wrapping provided the absorption of visible light, while the porosity of the nanomesh structures exposed the photocatalytic AgCl surface to catalyze desired reactions. Platinum in place of palladium was examined to demonstrate the versatility of the wrapping scheme, resulting in an extraordinary catalytic activity. Importantly, the detailed chemical mechanism behind the trimetallic wrapping of the AgCl nanostructures was systematically investigated to understand the roles of each reaction component in controlling the chemical selectivity. The synthesized AgCl-trimetal nanoconjugates excellently exhibit both metal-based and plasmon-enhanced catalytic properties for the removal of environmentally harmful Cr6+. Moreover, their applications as surface-enhanced Raman-scattering (SERS) probes for the in situ monitoring of catalytic reduction in real-time and as single-nanoparticle SERS probes for molecular detection are thoroughly demonstrated.