AgAu Hollow Hexagonal Nanoplates for Ultrasensitive Tracking of Pesticides and Plasmonic Photocatalysis by Surface-Enhanced Raman Spectroscopy

Plasmonic metal nanostructures have been attracting great interest due to their unique optical and catalytic properties. Here, we report a simple and mild synthetic approach for the colloidal synthesis of AgAu hollow hexagonal nanoplates (AgAu HHNPs) with multitips through the careful choice of suitable reducing agents. In particular, when a relatively stronger reducing agent (e.g., ascorbic acid, AA) is employed, the deposition rate of Ag and Au adatoms on the walls is faster than the rate of outward diffusion rate of Ag atoms inside Ag nanoplates. This causes more Ag and Au adatoms to be diffused toward the tips of AgAu HHNPs. Interestingly, well-defined AgAu HHNP nanostructures with controlled multitips possess an enhanced localized electromagnetic field due to the tip effect. The produced nanomaterial exhibits sensitive trace detection of the pesticide residue by means of the surface-enhanced Raman spectroscopy (SERS) technique, in which the limit of detection (LOD) of rhodamine 6G is 10–13 M and the LOD of tetramethylthiuram disulfide (TMTD) is 10–9 M. Furthermore, it also shows a particularly high reaction rate for the six-electron reduction of p-nitrothiophenol to p-aminothiophenol on AgAu HHNPs. The entire reaction processes have been in situ monitored by SERS, revealing that molecular hydrogen in situ generated on the semiconductor AgCl dominates the plasmonic photocatalysis. The detailed understanding gained herein will help to disentangle the rational design mechanism of complex hollow nanostructures, as well as the relationship between structural configuration and resulting performance in SERS detection and plasmonic photocatalysis.