Detection and sorption study of dioxouranium(VI) ions onN-(2-mercaptopropionyl)glycine-modified silver colloid by surface-enhanced Raman scattering

Abstract

An aqueous silver colloid activated at 514 nm with 10-3 M N-(2-mercaptopropionyl)glycine (MPG) involves surface-active sites for the complexation of uranyl ions and displays the νs UO22+ SER spectrum at 840 cm-1, allowing uranyl detection at concentrations as low as 5×10-9 M. This level of detection competes successfully with spectrophotometric and fluorimetric determination. A quantitative study of the SER spectra as a function of total uranyl concentrations in the colloid, ranging between 5×10-9 and 1×10-5 M, shows that half of the sorption sites are occupied by uranyl for a total uranyl concentration of about 10-7 M; from this value, a 100-fold concentration increase induces only a twofold enhancement of the uranyl band at 840 cm-1, although no appreciable change of the colloid appears. As a result of an analysis of the uranyl complexation either in solution or simultaneously with several sorbed MPG molecules, the surface site concentration for uranyl sorption in the colloid used is estimated to be close to 10-8 M. This value corresponds to about one complexation site per primary particle of silver, perhaps at contacts between aggregated particles. At such sites, MPG molecules bonded to the metal surfaces through S—Ag bonds still involve amide and carboxylate groups free to coordinate an uranyl ion. The mean enhancement of the Raman cross-section of uranyl at the surface complexation sites reaches 3×105 with respect to uranyl nitrate aqueous solution. © John Wiley & Sons, Ltd.