Solvent effects in adsorption of alkyl thiols on gold structures: A molecular simulation study

We carried out Monte Carlo simulations of gold nanocrystals (NCs) and (111) slabs covered with alkyl thiols, with and without explicit solvent (n-hexane), at T ) 300 K. Adsorption isotherms for propane- and octanethiol showed a phase behavior measured previously in experiments. Comparison of the adsorption isotherm of octanethiol in hexane on a (111) slab with experimental data suggests that, in this system, no thiolate bond was formed. The geometry of a gold surface strongly influences the formation and structure of the capping monolayer. On a (111) surface, attractive interactions between carbon chains are more pronounced than on a NC. This leads to a stronger penetration of the capping layer by the solvent. Adsorption selectivity for binary alkyl thiol mixtures is stronger in vacuum than in solution. The convex shape of the NCs also reduces the adsorption selectivity of binary thiol mixtures. This result shows that the solvent cannot be ignored in simulations.