SERS investigation on 4-nitro-3-pyrazolecarboxylic acid adsorbed on palladium-doped silver nanoparticles

Surface-enhanced Raman scattering (SERS) spectroscopy, due to the giant enhancement factors of the Raman signal, is a powerful tool for the investigation of “in situ” catalytic reactions. Many efforts have been carried out to extend this technique from SERS-active metals (Ag, Au, and Cu) to more catalytically efficient metals like Pd, Ni, and Pt. We have prepared bimetallic colloids, composed of silver nanoparticles partially coated with Pd clusters, immobilized on quartz, in order to combine the SERS response of the noble metal with the catalytic efficiency of Pd. The interest in doping Ag nanoparticles with Pd is due to its potential ability in the catalysis of hydrogenation reactions. The catalytic activity of these bimetallic substrates was tested here for 4-nitro-3-pyrazolecarboxylic acid (NPC) by means of SERS spectroscopy. Environmental scanning electron microscopy (ESEM) and surface plasmon resonance (SPR) measurements were employed for the morphological characterization of the metal colloidal particles immobilized on quartz. The SERS spectra showed that the nitro group of NPC was reduced to amino group.