XIV
h
International Conference on Molecular Spectroscopy, Białka Tatrzańska 2017
84
T3: O–3
The effect of concentration on the surface-enhanced
Raman scattering of p-aminothiophenol
Maria Rosa Lopez-Ramirez
1
, Daniel Aranda Ruiz
1
, Francisco Jose Avila Ferrer
1
,
Juan F. Arenas
1
, Juan C. Otero
1
, and Juan Soto
1
1
Department of Physical Chemistry, Faculty of Science, University of Málaga, E-29071 Málaga,
Spain, e-mail: mrlopez@uma.es
The organic compound p-aminothiophenol (pATP, HS-Ph-NH
2
) has become very popular
because it is often used for checking the enhancement capability of each new SERS substrate
due to its very intense SERS spectra. SERS of pATP on silver electrode is significantly different
from its ordinary Raman spectra and it is very dependent on the particular conditions of the
SERS experiment. In this work the effect of adsorbate concentration on the potential dependent
SERS spectra of pATP recorded on a silver electrode has been studied using NaClO
4
as
electrolyte. On the other hand, MS-CASPT2 have been performed in order to help the analysis
of the experimental results by computing resonance Raman spectra of selected structural models
of the metal−adsorbate surface complex.
It was found that the spectra are dependent on adsorbate concentration and dominated by a
resonant charge transfer (CT) mechanism, where the charge is always transferred from the
adsorbate to the metal. The relative SERS enhancements are due to Franck−Condon factors
related to the CT process, and there are not intensified bands through Herzberg−Teller
contributions. Furthermore, the Raman signals of the SERS recorded at low concentration arise
from at least three different molecular species: (i) pATP bonded to silver electrode through
sulfur atom (Ag
n
-S
−
-Ph-NH
2
); (ii) pATP bonded to silver electrode through both sulfur and
nitrogen atoms (Ag
n
-S
−
-PhNH
2
-Ag
m
); (iii) The azo derivative p,p′-dimercaptoazobenzene (or its
nitrene precursor).
Fig. 1. Potential dependent SERS spectra of p-aminothiophenol: (a) 10
−3
M; (b) 10
−6
M, in NaClO
4
on silver electrode at excitation wavelength of 785 nm.
Keywords: p-aminothiophenol, SERS, silver electrode, ab initio calculations.
Acknowledgment
This research has been supported by the Spanish Ministerio de Economía y Competitividad (Projects:
CTQ2012-31846 and CTQ2015-65816-R). F.J.A. thanks MINECO for contract Juan de la Cierva IJCI-
2014-21333.
References
[1] M.R. Lopez-Ramirez, D. Aranda Ruiz, F.J. Avila Ferrer, J.F. Arenas, J.C. Otero, J. Soto, J. Phys.
Chem. C 120 (2016) 19322.
[2] F. Avila, D.J. Fernández, J.F. Arenas, J.C. Otero, J. Soto, Chem. Commun. 47 (2011) 4210.
XIV
h
International Conference on Molecular Spectroscopy, Białka Tatrzańska 2017
85
T3: O–4
Potential-dependent in situ spectroscopy during interfacial
electrochemical reactions of organic corrosion inhibitors
Ying-Hsuan Chen
1
, and Andreas Erbe
1,2
1
Department of Interface Chemistry and Surface Engineering, Max-Planck-Institut für
Eisenforschung GmbH, Max-Planck-Straße 1, 40237 Düsseldorf, Germany, e-mail:y.h.chen@mpie.de
2
Department of Materials Science and Engineering, NTNU, Norwegian University of Science and
Technology, 7491 Trondheim, Norway
2-Mercaptobenzothiazole (MBT) is known as one of the most effective corrosion inhibitors
of copper for 40 years. During the inhibition process, MBT is supposed to react with copper
forming a passivating layer (CuMBT complex) to prevent further corrosion [1]. The complex
electrochemical and chemical processes between copper, electrolyte, copper oxides, and the
inhibitor films are not fully understood, in particular, why the passivating layer is so stable and
so protective. In this work, this mechanism was investigated by in situ infrared (IR)
spectroscopy, in situ Raman spectroscopy and in situ UV/VIS spectroscopic ellipsometry,
coupled with electrochemical experiments. The attenuated total reflection (ATR) technique was
applied in IR spectroscopy to study MBT during electrochemical processes at the solid/liquid
interface [2].
The temporal evolution of IR spectra at open circuit potential showed a rearrangement of
MBT at the interface. Interfacial structure was also dependent on the electrode potential. In
Raman spectra, the red shift of band at 1400 cm
–1
at low electrode potential showed a difference
between surface species and bulk species of CuMBT. The potential-dependent increase of
thickness, which was obtained from ellipsometric spectra, indicated the formation of a CuMBT
complex layer. Besides, the inhibition of oxide formation was examined in this work as well. It
was shown that after the copper surface was treated with MBT solution, the formation of copper
oxide was inhibited because of the disappearance of oxide related peak in Raman spectra. Based
on these results, the final goal is to engineer molecular structures of corrosion inhibitors based
on their reactivity, their tendency to adsorb on the metal and their tendency to passivate a
surface.
Fig. 1. The time-dependent IR spectra.
Keywords: corrosion inhibitor; 2-mercaptobenzothiazole; in situ interface spectroscopy
Acknowledgment
Y.-H. C. acknowledges Deutscher Akademischer Austauschdienst (DAAD) for the financial support, the
International Max Planck Research School for Surface and Interface Engineering in Advanced Materials
and the members of Interface Spectroscopy group for lots of help.
References
[1] M. Finšgar, J. Jackson, Corrosion Science 86 (2014) 17.
[2] S. Nayak, P.U. Biedermann, M. Stratmann, A. Erbe, Phys. Chem. Chem. Phys. 15 (2013) 5771.
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