view:32743 Last Update: 2022-5-4
Electrochemical study of adsorption and electrooxidation of 4,4′‑biphenol on the glassy carbon electrode: determination of the orientation of adsorbed molecules
Electrochemical oxidation of 4,4′-biphenol has been studied in aqueous solution and acetone/water mixtures using cyclic voltammetry and chronocoulometry. Obtained results show that difusion and adsorption currents are mixed (weak adsorption). Weak adsorption was studied and proven by various methods. Semi-integral analysis and chronocoulometry were used as efective methods for determining surface coverage (i.e., initial surface excess) from voltammogram and chronocoulogram in the presence of weak adsorption. An initial surface excess (Γ*) was determined to be 0.43±0.02 nmol/cm2 for 4,4′-biphenol and 0.67 ± 0.03 nmol/cm2 for 4,4′-diphenoquinone by semi-integration and confrmed using chronocoulometry. A good agreement was observed between the results suggested by the applied methods. Eventually, the orientation of 4,4′-biphenol and 4,4′-diphenoquinone molecules adsorbed from solution onto the glassy carbon electrode was determined. Comparison of initial surface excess measurements with values calculated for various possible molecular orientations indicates that the dominant orientations of the adsorbed molecules (4,4′-biphenol and 4,4′-diphenoquinone) are edgewise. Calculations were based on covalent and Van der Waals radii as tabulated by Pauling.