Adsorption of 2-methyl-2-butanol on bismuth single crystal planes

Abstract

Cyclic voltammetry, impedance and chronocoulometry have been employed for a quantitative study of 2-methyl-2-butanol ( tert-PenOH) adsorption at the bismuth single crystal plane ∣ aqueous Na 2SO 4 solution interface. The adsorption characteristics of tert-PenOH, obtained from the impedance and chronocoulometry measurements, are in reasonable agreement within the limits of surface charge densities −16< σ<2 μC cm −2. The adsorption characteristics (Gibbs energy of adsorption −Δ G° A; limiting Gibbs adsorption Γ max; limiting potential shift of zero charge E N; molecular interaction parameter a, etc.) of tert-PenOH depend on the crystallographic structure of the electrode surface. Comparison of the adsorption parameters for n-propanol ( n-PrOH), n-butanol ( n-BuOH), tert-butanol ( tert-BuOH), tert-PenOH and n-hexanol ( n-HexOH) shows that the adsorption activity and other parameters depend on the length and structure of the hydrocarbon radical of the organic compound studied. The adsorption activity of tert-PenOH increases in the order of Bi planes (001)<(111)<(01 1 ̄ ) as the interfacial density of the planes increases. The limiting Gibbs adsorption Γ max and the molecular interaction parameter a decrease in the order of planes (001)≥(111)>(01 1 ̄ ) . Very low Γ max and E N values for the Bi(01 1 ̄ ) plane indicate that tert-PenOH molecules probably have a flat orientation on the chemically most active Bi(01 1 ̄ ) single crystal plane. Comparison of the adsorption characteristics for the Bi ∣ tert-PenOH interface with the data for Au single crystal planes [8,9,12] and Hg [14,25] is given.