INFIQC   05475
INSTITUTO DE INVESTIGACIONES EN FISICO- QUIMICA DE CORDOBA
Unidad Ejecutora - UE
congresos y reuniones científicas
Título:
Mechanism of Cu2O reduction by alcanethiols
Autor/es:
C. A. CALDERÓN; C. OJEDA; P. PAREDES OLIVERA; V. A. MACAGNO; E. M. PATRITO
Lugar:
La Plata
Reunión:
Simposio; 4to Encuentro de Física y química de Superficies (FyQS-IV).; 2009
Resumen:
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The interaction of 1-octanethiol,
1,8-octanedithiol, 1-hexadecanethiol and 16-mercaptohexadecanoic acid with
polycrystalline copper surfaces was investigated comparatively using forming
solutions with polar (0.05 M
NaOH solution) and apolar (n-hexane) solvents. The thiol layers were
formed on the freshly chemically polished copper surface as well as on the
anodically oxidized surface. The effects of the alkanethiol chain length and terminal group on the
blocking properties of the surface were investigated. We show for the first time that compact monolayers and multilayers can
be obtained from an alkaline forming solution. Copper oxides are completely
reduced in the alkaline forming solution for all the thiols investigated after
an immersion time of 45 minutes. On the contrary, the presence of a surface
oxide was always detected after the formation of the thiol layer in the
n-hexane solution. The mechanism of Cu2O reduction by thiols was
investigated by means of density functional theory calculations. The surface
reactions involve the protonation of the surface oxygen atoms of the oxide which
act as Lewis base sites. In the alkaline electrolyte, the proton transfer
involves the water molecules of the solvent whereas in the n-hexane solution
the proton transfer involves the SH group of the alkanethiol. The surface
reactions are not the rate limiting step because they have very low activation
energy barriers. The higher reduction rate observed in the alkaline thiol
solutions is due to the high concentration of the reacting water molecules,
whereas the lower reaction rate in the n-hexane solutions correlates with the
lower concentration of the reactant alkanethiol molecules.