Sorption of U(VI) on the 4-mercaptopyridine self-assembled monolayer

The sorption of U(VI) on the 4-mercaptopyridine self-assembled monolayer (4-PyS-SAM) on Au(111) was studied by cyclic voltammetry. Cyclic voltammograms (CVs) of the 4-PyS-SAM working electrode were obtained by contact with 1 mM UO₂(NO₃)₂ solution, 1 mM UO₂(NO₃)₂ and 50 mM acetic acid solution, or 1 mM UO₂(NO₃)₂ and 50 mM oxalic acid solution for 6h at pH 4. The reduction current of U(VI) to U(V) was detected in the CV. The CV of the U(VI) associated 4-PyS-SAM after transport to U(VI)-free 0.1 M NaClO₄ solution showed that the reduction current was detected in the cases of UO₂(NO₃)₂ and U(VI)-acetate, but not in the case of U(VI)-oxalate solution, indicating that U(VI) was adsorbed on the 4-PyS-SAM from the UO₂(NO₃)₂ and U(VI)-acetate solutions, but not from U(VI)-oxalate solution. These results suggest that stability of U(VI)-4-PyS-SAM is not so high that U(VI)-4-PyS-SAM cannot be formed in the presence of 50 mM oxalate. (author)