| Description |
Surface-enhanced Raman scattering (SERS) spectroscopy is a sensitive tool that can be used to probe chemistry at metal-solution interfaces. To control the interfacial activity of ionic species at the metal surface, the metal-surface potential is controlled with a potentiostat, while SERS provides an in situ method to observe the interfacial chemistry. In this work, SERS studies are carried out with potential control to investigate monolayer self-assembly, acid-base chemistry, ion-pair interactions, and reduction of electroactive anions at chemically-modified silver surfaces. Adsorption and self-assembly of 11-mercaptoundecanoic acid on silver was monitored by SERS. The time-dependent profiles of Raman spectra indicate a multistep self-assembly process, which involves participation of both thiol and carboxylate groups in the adsorption process and depends on the solvent, solution pH, and surface potential. The acid-base chemistry of 2-mercaptobenzoic acid (2-MBA) immobilized on a silver surface was also investigated. The benzoate form and benzoic acid form of 2-MBA could be identified spectroscopically to determine the relative populations of the bound ligand. In addition, shifts in the carboxylate stretching mode of 2-MBA revealed interactions between the benzoate group and the silver surface, which could be displaced by other anions in solution. It was found that applied potential has significant effects on the proton dissociation equilibrium of immobilized 2-MBA, an effect arising from the changes in the interfacial pH relative to bulk solution. Adsorption of cetylpyridinium (CP+) and its interaction with nitrobenzenesulfonate (NB-) on a 1-dodecanthiol (C12) modified silver surface was also studied. The binding of NB- to the C12 surface relies on its ion-pairing with CP+. Adsorption of CP+ and ion-pair stability on the C12 surface can be modulated by electrolyte concentration. The results provide understanding of surfactant adsorption and ion interactions involved in ion-interaction chromatography. SERS and cyclic voltammetry were used to investigate reduction of NB- on bare and C12-modified silver surfaces in the presence of CP+. The reduction was identified by the disappearance of the NO2 symmetric stretching mode and frequency shifts in the ring breathing mode. Ion-pair accumulation of NB- can be observed on C12 surface, and its repeatable reduction was studied by cyclic voltammetry and SERS. |
