Abstract
Changes in the adsorption profiles of 1,4-naphthohydroquinone (NHQ) on smooth polycrystalline platinum electrodes in aqueous 1 M HClO 4 brought about by varying levels of surface-active organic impurities [typified by hydroquinone (HQ) and benzene] have been studied by thin-layer electrochemical techniques, 10 −5 M HQ is sufficient to alter the adsorption profile of NHQ; above 10 −4 M HQ, the packing density transitions prominent from pure NHQ solutions were completely suppressed. Similar results were obtained when benzene was used as the contaminant. Packing density measurements indicated that the subject surface-active impurities inhibited formation of flat-, but not edge-, adsorbed NHQ; this is in agreement with data from a previous study [M.P. Soriaga, J.H. White, D. Song and A.T. Hubbard, J. Electroanal. Chem., 171 (1984) 359] which showed that low-levels of iodide, a surface-active anion, enforced formation of edge-adsorbed NHQ even at (low) concentrations where flat-adsrobed species would have formed from pure NHQ solutions. The presence of surface-active impurities may help account for the profound differences in adsorption measurements reported in the literature for various aromatic compounds.
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