We report the use of 2,6-dimethylphenyl isocyanide (2,6-DMPI) as a molecular probe for characterizing the overgrowth of Pd on Ag nanocubes using surface-enhanced Raman scattering (SERS). When 2,6-DMPI binds to Ag via s donation from σ* orbitals of isocyanide to d-band of Ag, the stretching frequency for the NC bond, νNC, shows a blue shift. In comparison, when 2,6-DMPI binds to Pd via π-back donation from d-band of Pd to the π* antibonding orbital of isocyanide, the νNC band exhibits a red shift. More significantly, the isocyanide group could anchor to Pd atoms in an atop, bridge, or hollow configuration with a continuous red shift in νNC, making it possible to resolve the atomic structures of Pd on the surface of Ag nanocubes during the overgrowth. We also demonstrate the possibility of directly introducing 2,6-DMPI to the original growth solution for in situ monitoring the real-time atomic arrangements of Pd during the overgrowth in the liquid phase and under ambient condition. The change in νNC could provide detailed information for the reduction, deposition, and diffusion process as the overgrowth progresses. With atomic sensitivity, this in situ method could shed light on the mechanistic details in the seeded overgrowth. This work would support the rational design of bimetallic nanocrystals with other noble metals like Pt, Rh, Ir, and Ru.

Probing the atomic arrangement of palladium on silver nanocrystals with an isocyanide-based reporter by surface-enhanced Raman scattering

256th National Meeting (2018)

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