Interaction of halide and halate ions with colloidal silver and their influence on surface-enhanced Raman scattering of pyridine with near-infrared excitation

Abstract

The interactions between halide and halate ions and colloidal silver surfaces are studied by surface-enhanced Raman spectroscopy (SERS) with excitation in the near-infrared (NIR) wavelength region. The interaction strength of halide ions with silver surface decreases in the order I − > Br > Cl − while the enhancements of the Raman modes of pyridine caused by addition of these ions range in the order of Cl − ≈ Br − > I −. ClO 3 − and BrO 3 − ions in silver colloids give rise to SERS bands at about 226 and 158 cm −1, respectively, while IO 3 − ions on colloidal silver surface result in two Raman bands at about 750 and 334 cm −1. These results indicate that the interactions of ClO 3 − and BrO 3 − ions with silver surface are through their lone pair electrons of Cl and Br. Nevertheless, IO 3 − ions bond to silver surface through their negatively charged O −. The interaction strength of halate ions with silver are measured to be BrO 3 − > ClO 3 ≈ IO 3 −. The enhancements of the Raman modes of pyridine caused by addition of halate ions increase in the order ClO 3 − < IO 3 − < BrO 3. These ions contribute not only to the electromagnetic enhancement but also to the chemical enhancement in the NIR-SERS. BrO 3 − ions are able to create about 2.2 and 3.7 times more surface active sites on colloidal silver surface than ClO 3 − and IO 3 − ions do.