SURFACE-ENHANCED RAMAN-SCATTERING OF CO2 DISSOLVED IN AQUEOUS COLLOIDAL SOLUTIONS OF SILVER AND GOLD

The observation of surface-enhanced Raman scatterings (SERS) from CO2 molecules dissolved in aqueous solutions of silver and gold colloids measured with 850 nm near-IR excitation is reported. Different types of surface enhancement and surface-enhanced Raman spectra were observed. The SERS spectrum of CO2 on colloidal gold is in good agreement with the spectrum of CO2 dissolved in water. Two different types of SERS spectra were found for CO2 on colloidal silver. They can be assigned to physisorbed and/or weakly chemisorbed CO2 molecules and to strongly bonded CO2- negatively charged surface radicals, respectively. The enhancement factor for the stretching mode of carbon dioxide is estimated to be of the order of 10(2)-10(4), depending on the kinds of metal and types of adsorption, which demonstrates that SERS on colloidal silver or gold particles in solution offers possibilities for detecting CO2 dissolved in liquids at low concentrations.