Surface Chemistry of 4-Mercaptobenzoic Acid Self-Assembled on Ag(111) and Ag Nanoparticles.

Abstract

The adsorption of 4-mercaptobenzoic acid (MBA) on Ag(111) and Ag nanoparticles (AgNPs) has been studied by X-ray photoelectron spectroscopy (XPS), electrochemical techniques, high-resolution transmission electron microscopy (HRTEM), and density functional theory (DFT) calculations. Results show that MBA molecules adsorb intact on the Ag (111) surface via a thiolate bond, arranged in a (√3 × 4) lattice with coverage θ = 0.25. The phase diagram built using DFT data shows that this lattice is more stable than the dense (√7 × √7)R19.1 MBA lattices on reconstructed Ag(111) surfaces. No significant amounts of sulfide were found neither on the Ag(111) surfaces nor on MBA-protected AgNPs, suggesting that the Ag core@Ag-sulfide shell structure where thiolates could be grafted cannot be applied to the MBA-protected AgNPs. Slow degradation of the MBA protective layer in ambient conditions on the AgNPs results in disulfide formation and AgNP sintering.