Adsorption of pyridine on the (111), (001) and (01(1)over-bar) faces of bismuth

The adsorption of pyridine (PY) on Bi(111), Bi(00 (1) over bar) single crystal electrodes has been studied in 0.1M aqueous NaF solution for concentrations of PY ranging from 1 to 200 mM. In the range of potentials explored, adsorption maximum coverage of the surface and the desorption of PY at E= -1.8V (SCE) have been observed. At the negative potentials and polarization close to the potential of zero charge, PY molecules at bismuth single crystal planes assume a tilted orientation, with the hydrocarbon ring facing the metal. The saturation coverage Gamma(max) and the limiting capacity C-1 decrease, and the shift of zero charge potential E-N, due to the displacement of surface water by a monolayer of PY, rises in the sequence of planes Bi(01 (1) over bar) < Bi(001) < Bi(111) as the vertical component of the orientation of the PY molecules increases. Adsorption isotherms, values of the attraction constant a and standard Gibbs energy of adsorption Delta G(ads)(0), have been determined. As in the case of other organic compounds studied, the activity of Bi planes increases in the sequence of planes Bi(111) < Bi(001) < Bi(01 (1) over bar). The partial change transfer from PY to Bi electrodes increases in the same direction of planes. The attractive interaction between the adsorbed molecules rises in the sequence of planes Bi(01 (1) over bar) < Bi(111) < Bi(111) as the superficial density of atoms decreases. The absolute value of the Gibbs energy of adsorption of PY increases in the sequence of electrodes Ag < Bi(111) < Hg < Bi(001) < Bi(01 (1) over bar) < Au(111) < Au(100) < Au(311), As the adsorption activity of aliphatic compounds on Au is lower than on Bi or on Hg we can conclude that there is a weak chemical interaction of PY molecules with Au surface atoms. The Gibbs energy of adsorption of PY on Ag is somewhat lower (3 to 5 kJmol(-1)) than for Bi and Hg electrodes; this is caused mainly by the higher hydrophilicity of Ag electrodes. The values of Gibbs energy of PY adsorption on Bi and Hg are comparable and, accordingly, the differences between the metal-adsorbate interaction are not large and the adsorption activity of PY increases, when the hydrophilicity of electrodes decreases in the sequence Bi(111) > Hg > Bi(001) > Bi(01 (1) over bar).