Electrochemical Investigations of 4‑Methoxypyridine
Adsorption on Au(111) Predict Its Suitability for Stabilizing Au Nanoparticles
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Abstract
A thermodynamic
analysis of the adsorption of 4-methoxypyridine
(MOP) on Au(111) surfaces is presented in an effort to determine its
propensity to stabilize metal nanoparticles. The adsorption of MOP
is compared and contrasted to the adsorption of 4-dimethylaminopyridine
(DMAP), the latter of which is well-known to form stable Au nanoparticles.
Electrochemical studies show that MOP, like most pyridine derivatives,
can exhibit two different adsorption states. The electrical state
of the metal, the pH of the solution, and the surface crystallography
determine whether MOP adopts a low-coverage, π-bonded orientation
or a high-coverage, σ-type orientation. A modified Langmuir
adsorption isotherm is used to extract free energies of adsorption
which are roughly 10% stronger for DMAP compared to MOP at equivalent
conditions when expressed on a rational basis. The higher adsorption
strength is attributed to DMAP’s greater Lewis basicity. Qualitatively,
MOP and DMAP adsorption are found to be completely analogous, implying
that MOP-protected gold particles should be stable under conditions
that favor the high-coverage adsorption state. Using a previously
reported, single-phase synthesis, this is shown to be the case