Effect of Bonding Interactions between Arsenate and Silver Nanofilm on Surface-Enhanced Raman Scattering Sensitivity

The effect of Ca2+ on surface-enhanced Raman scattering (SERS) analysis of arsenate (As(V)) using Ag nanofilm was studied. Extended X-ray absorption fine structure (EXAFS) was used for the first time to investigate the bonding structures of adsorbed As(V) on the SERS substrate, as well as the mechanism of the Ca2+ effect on the SERS analysis of As (V). As(V) was found to be adsorbed on Ag nanofilm through formation of bidentate binuclear surface complexes (AgO)(2)AsO2- with an average As-Ag interatomic distance of 2.56 angstrom in the As(V) single adsorbate system, and through formation of a ternary surface complex (AgO)(CaO)(2)AsO+ with an average As-Ag distance of 3.03 angstrom in the presence of Ca2+. The formation of the ternary surface complex dramatically decreased the SEAS sensitivity and resulted in a shift of the SERS As(V) band from 780 cm(-1) for the As(V) system to 790 cm(-1) in the As(V)-Ca2+ binary adsorbate system. It was discovered that the negative effect of Ca2+ and Mg2+ was reduced dramatically by addition of F- into As (V) solution and groundwater samples. The fundamental information on the Ca2+ perturbance of surface interactions between As(V) and Ag will help in the development of SERS techniques for analysis of As(V) in contaminated groundwater.