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 potenti als explored, adsorption maximum coverage of the surface and the desor ption of PY at E= -1.8V (SCE) have been observed. At the negative pote ntials and polarization close to the potential of zero charge, PY mole cules at bismuth single crystal planes assume a tilted orientation, wi th the hydrocarbon ring facing the metal. The saturation coverage Gamm a(max) and the limiting capacity C-1 decrease, and the shift of zero c harge potential E-N, due to the displacement of surface water by a mon olayer 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 c onstant a and standard Gibbs energy of adsorption Delta G(ads)(0), hav e 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 t o Bi electrodes increases in the same direction of planes. The attract ive interaction between the adsorbed molecules rises in the sequence o f planes Bi(01 (1) over bar) < Bi(111) < Bi(111) as the superficial de nsity of atoms decreases. The absolute value of the Gibbs energy of ad sorption 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 t he adsorption activity of aliphatic compounds on Au is lower than on B i or on Hg we can conclude that there is a weak chemical interaction o f PY molecules with Au surface atoms. The Gibbs energy of adsorption o f PY on Ag is somewhat lower (3 to 5 kJmol(-1)) than for Bi and Hg ele ctrodes; this is caused mainly by the higher hydrophilicity of Ag elec trodes. The values of Gibbs energy of PY adsorption on Bi and Hg are c omparable and, accordingly, the differences between the metal-adsorbat e interaction are not large and the adsorption activity of PY increase s, when the hydrophilicity of electrodes decreases in the sequence Bi( 111) > Hg > Bi(001) > Bi(01 (1) over bar).