Rational design and synthesis of bifunctional metal nanocrystals for probing catalytic reactions by surface-enhanced Raman scattering

This report highlights recent progress in the rational design, synthesis, and applications of bimetallic nanocrystals with integrated SERS and catalytic activities. The ultimate goal is to develop bifunctional nanocrystals as a SERS probe for monitoring a catalytic reaction in situ. We first introduce seeded growth as a facile and powerful route to the syntheses of bifunctional nanocrystals with catalytic activities arising from Au or Pd, in addition to plasmonic properties originating from Ag or Au. Specifically, we discuss two distinctive pathways, namely conformal and site-selected deposition of a second metal on the surface of a noble-metal nanocrystal seed, for the fabrication of bifunctional nanocrystals with controlled composition and morphology. We then discuss the application of these bifunctional nanocrystals as unique probes for in situ SERS monitoring of the Au or Pd-catalyzed reduction of 4-nitrothiophenol to 4-aminothiophenol by NaBH4 and the Ag-catalyzed oxidation of 4-aminothiophenol to trans-4,4-dimercaptoazobenzene by the O-2 from air. We conclude this review with perspectives on the future development.