Study on adsorption states by Surface-enhanced Raman Spectroscopy

SERS has been used as a state-resolving probe to study the adsorption state s. In the case of pyridine (Py) adsorbed on the Ag electrode surface, the e quilibrium and transition between two adsorbed states, i.e., the perpendicu lar mode adsorbed through the nitrogen lone-pair electrons and the flat mod e through the Ic electrons of the aromatic ring, were studied. It was found that in the low pyridine concentration or the initial stage of adsorption, the flat mode was favored.: While the concentration became higher and the adsorption tended to equilibrium, the adsorbed molecules would transit to t he perpendicular mode. The similar phenomenon was also observed when changi ng the applied electric potential and the pH value of the solution. In the case of the adsorption of Methylene Blue (MB) on the HNO3-etched silver sur face, the influence of Cl- ions on the adsorption states of MB was investig ated. It showed that MB molecules adsorbed on the silver surface tended to transform from the "lying-down" state to the "end-on" state while adding Cl - ions.