Competitive Chemisorption from Binary Surfactant Mixtures at Solid-Liquid Interfaces: Hydroquinone and Naphthodydroquinone at Smooth Polycrystalline Platinum in Aqueous Solutions

摘要

Competitive chemisorption of hydroquinone (HQ) and 1,4-naphthohydroquinone (NHQ) from aqueous solutions onto smooth polycrystalline plantinum has been studied at room temperature. Adsorption measurements were based on thin-layer electrochemical methods. When HQ and NHQ were both present at low concentrations (C superscript O < 0.1 mM), a mixed adsorbed layer was formed in which the two species were oriented flat. At higher total concentrations an orientational transition occurred, and for C superscript O > 1 mM the mixed adlayer consisted of both species oriented vertically. Preferential adsorption of NHQ over HQ was exhibited at all bulk compositions studied. A plot of surface mole fraction ratio (X sub NHQ surf/X sub HQ surf) against solution mole fraction ratio (X sub NHQ sol/X sub HQ sol) was linear in the concentration regime where both compounds were adsorbed edgewise and the molecular area requirements were identical. This linearity suggested that the mixed interactions between HQ and NHQ are very similar to the self-interactions for the pure compounds. The slope of this plot indicated that the initial adsorption rate constant of NHQ is at least twice as large as that of HQ.