EFFECT OF MOLECULAR-OXYGEN ON THE SURFACE-ENHANCED RAMAN INTENSITY OF ADSORBED MOLECULES ON SILVER, COPPER AND GOLD ELECTRODES

The effect of molecular oxygen (O2) on the surface-enhanced Raman intensities of pyridine (py) adsorbed on silver, copper and gold electrodes has been investigated. A fast decrease in the SERS intensity with the time of electrode exposure to an electrolyte solution saturated with O2 has been observed for py adsorbed on silver and copper electrodes. In the case of copper in solutions containing benzotriazole, the decrease in the SERS intensities was not so fast as for py. A less pronounced decrease in the SERS intensity with time of 02 exposure was observed for py adsorbed on gold electrodes. Part of the SERS intensity of py adsorbed on silver and copper is irreversibly lost after oxygen exposure at open circuit, while the SERS intensity of py adsorbed on gold is totally recovered. The results suggest that O2 reacts with the SERS-active sites, oxidizing them and precluding the short-range (charge-transfer) mechanism of enhancement from being effective. This oxidation of the SERS-active sites is irreversible for silver and copper, but reversible for gold electrodes.