SURFACE SPECIFIC ADSORPTION OF SACCHARIN ON IODINE-MODIFIED PT(111) ELECTRODES

Saccharin (o-benzoic sulfimide) preferentially adsorbs onto platinum(1 11)electrodes modified with the (3x3) iodine adlayers (theta(1) = 0.44 ). This is in contrast to platinum (111) electrodes modified with the (root 7x root 7)R19.1 degrees iodine adlayer (theta(1) = 0.43) where n o adsorption is detected. Saccharin adsorption was monitored through c hanges in the voltammograms associated with the oxidative desorption o f the strongly bound iodine adlayer and Ag underpotential deposition o n the iodine-modified electrode surfaces in acidic solutions. Simple m odeling calculations support the experimental observation and suggest that the preferential adsorptive behavior of saccharin is due to the e nhanced van der Waals interactions associated with the symmetric Pt(11 1)(3x3)-I adlayer structure. The Pt(111)(3x3)-I adlayer structure is o ne of two (3x3) iodine adlayer structures found to a comparable extent of coverage on name-annealed Pt(111) electrodes exposed to iodine for a longer duration than that leading to the formation of the Pt(111)(r oot 7x root 7)R19.1 degrees-I adlattice.