Adsorption of adenosine on (111) and (001) bismuth single crystal planes

Abstract

Abstract Cyclic voltammetry, impedance and chronocoulometry have been employed for quantitative study of adenosine (Ado) adsorption at the bismuth single crystal plane|0.05 M Na2SO4 aqueous solution interface. The adsorption of Ado on Bi planes reveals the existence of two capacity pits resulting in reversible, mainly physical adsorption at zero charge potential Eσ=0, and more stronger interaction at moderate positive charge densities. The adsorption isotherms, Gibbs adsorption energy ΔGads0, the limiting Gibbs adsorption Γmax, and other adsorption parameters have been determined. At potentials close to Eσ=0, the value of Γmax and the absolute value of ΔGads0 of Ado increase from Bi(111) to Bi(001). The very low values of Γmax and the limiting potential shift of zero charge EN≈0, caused by the replacement of the water monolayer by the monolayer of Ado, have beeen explained by the flat orientation of Ado molecules at Bi(111). The adsorbed Ado molecules at the Bi(001) plane have probably a tilted orientation, but with the value of EN≈0, i.e. the total dipole moment μ ≈0 . The molecular interaction parameter a in the Frumkin isotherm has a negative value and its negative decreases from Bi(001) to Bi(111) as the reticular density of planes increases.