Ramírez EA, Cortés E, Rubert AA, Carro P, Benítez G, Vela ME, Salvarezza RC. Complex surface chemistry of 4-mercaptopyridine self-assembled monolayers on Au(111).
LANGMUIR : THE ACS JOURNAL OF SURFACES AND COLLOIDS 2012;
28:6839-6847. [PMID:
22497438 DOI:
10.1021/la204951u]
[Citation(s) in RCA: 15] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/31/2023]
Abstract
The adsorption of 4-mercaptopyridine on Au(111) from aqueous or ethanolic solutions is studied by different surface characterization techniques and density functional theory calculations (DFT) including van der Waals interactions. X-ray photoelectron spectroscopy and electrochemical data indicate that self-assembly from 4-mercaptopyridine-containing aqueous 0.1 M NaOH solutions for short immersion times (few minutes) results in a 4-mercaptopyridine (PyS) self-assembled monolayer (SAM) with surface coverage 0.2. Scanning tunneling microscopy images show an island-covered Au surface. The increase in the immersion time from minutes to hours results in a complete SAM degradation yielding adsorbed sulfur and a heavily pitted Au surface. Adsorbed sulfur is also the main product when the self-assembly process is made in ethanolic solutions irrespective of the immersion time. We demonstrate for the first time that a surface reaction is involved in PyS SAM decomposition in ethanol, a surface process not favored in water. DFT calculations suggest that the surface reaction takes place via disulfide formation driven by the higher stability of the S-Au(111) system. Other reactions that contribute to sulfidization are also detected and discussed.
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