Spectroelectrochemical and DFT Study of Thiourea Adsorption on Gold Electrodes in Acid Media

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Title: Spectroelectrochemical and DFT Study of Thiourea Adsorption on Gold Electrodes in Acid Media
Authors: Cheuquepán, William | Pérez Martínez, Juan Manuel | Orts Mateo, José M. | Rodes, Antonio
Research Group/s: Grupo de Espectroelectroquímica y Modelización (GEM)
Center, Department or Service: Universidad de Alicante. Departamento de Química Física | Universidad de Alicante. Instituto Universitario de Electroquímica
Keywords: Spectroelectrochemical | DFT study | Thiourea adsorption | Gold electrodes | Acid media
Knowledge Area: Química Física
Issue Date: 3-Jul-2014
Publisher: American Chemical Society
Citation: The Journal of Physical Chemistry C. 2014, 118(33): 19070-19084. doi:10.1021/jp503694m
Abstract: The adsorption of thiourea (TU) at Au(111) and Au(100) single crystal and evaporated gold thin-film electrodes with preferential (111) orientation was studied in perchloric acid solutions with TU concentrations below 0.1 mM. For this purpose, cyclic voltammetry with gold single crystals was combined with external reflection infrared spectroscopy and surface-enhanced infrared reflection–absorption spectroscopy under attenuated total reflection conditions (ATR-SEIRAS) with gold thin film electrodes. In situ surface enhanced Raman spectroscopy (SERS) experiments were also carried out with these latter samples. In addition, optimized geometries and theoretical harmonic vibrational frequencies, obtained from B3LYP/LANL2DZ, 6-31+G(d) calculations for TU and thioureate species adsorbed on Au clusters with (111) orientation, were used for the interpretation of the experimental spectra. ATR-SEIRAS experiments show irreversible adsorption of TU at 0.10 V, whereas the SERS experiments have confirmed the bonding of the TU molecule to the metal surface through the S atom. The optimized geometry obtained from density functional theory (DFT) calculations for adsorbed TU corresponds to unidentate bonding through the sulfur atom, with the Au–S bond slightly tilted (13°) from the surface normal, whereas the C–S bond appears to be tilted by 45°. In the case of adsorbed thioureate, under the application of an external electric field of 0.01 a.u., a bidentate asymmetrical bridge adsorption configuration is obtained with one N(H) and the S atoms bonded to Au in positions close to “top” adsorption sites and with the molecular plane perpendicular to the metal surface. The observation of an adsorbate band for the asymmetric NCN stretching in the experimental infrared spectra confirms the tilting of the S–C bond of the adsorbed TU at low potentials. Changes of the adsorbate bands in the ATR-SEIRA spectra at potentials around 0.60 vs reversible hydrogen electrode (RHE) can be interpreted on the basis of DFT results as due to the deprotonation of adsorbed TU to form adsorbed thioureate.
Sponsor: We thank the financial support from Ministerio de Economía y Competitividad (project CTQ2009-13142, Fondos FEDER), Generalitat Valenciana (ACOMP/2011/200 and ACOMP/2012/137, Fondos FEDER), and Universidad de Alicante.
URI: http://hdl.handle.net/10045/45578
ISSN: 1932-7447 (Print) | 1932-7455 (Online)
DOI: 10.1021/jp503694m
Language: eng
Type: info:eu-repo/semantics/article
Rights: © 2014 American Chemical Society
Peer Review: si
Publisher version: http://dx.doi.org/10.1021/jp503694m
Appears in Collections:INV - GEM - Artículos de Revistas

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