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The reduction of 4-nitrobenzene diazonium electrografted layer: An electrochemical study coupled to in situ sum-frequency generation spectroscopy

Richard, William and Evrard, David and Busson, Bertrand and Humbert, Christophe and Dalstein, Laetitia and Tadjeddine, Abderrahmane and Gros, Pierre The reduction of 4-nitrobenzene diazonium electrografted layer: An electrochemical study coupled to in situ sum-frequency generation spectroscopy. (2018) Electrochimica Acta, 283. 1640-1648. ISSN 0013-4686

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Official URL: https://doi.org/10.1016/j.electacta.2018.07.073

Abstract

This work describes an electrochemical study of 4-nitrobenzene diazonium (4-NBD) reduction onto glassy carbon (GC) electrode coupled to in situ sum-frequency generation (SFG) spectroscopy. After 4-NBD grafting at 0.3 V vs. saturated calomel electrode (SCE) onto GC, SFG allowed a clear signal assigned to the symmetrical vibration mode of the nitro (NO2) groups to be observed at 1349 cm-1 or 1353 cm-1 depending on whether the spectrum was recorded in air or inside the solution. This result proved that 4-NBD grafting actually occurs at a potential as high as 0.3 V vs. SCE. The combination of SFG data and cyclic voltammetry (CV) also indicated that at such a potential, NO2 groups did not experience reduction process into hydroxylamine (NHOH) or amine (NH2) groups. The electrolysis of grafted NO2 moieties at -0.1 V was followed by CV and in situ by SFG. The exponential decay of the NO2 signal located at 1353 cm-1 vs. electrolysis time was in accordance with a charge transfer-limited reaction rate for a species immobilized at the electrode surface, and allowed a first order kinetic rate constant for NO2 reduction to be estimated k = 0.006 s-1. The integration of the peaks observed on the corresponding cyclic voltammograms (CVs) which were attributed to the NO/NHOH reversible system showed that the NO2 reduction produced both hydroxylamine and amine groups and was not quantitative. The fact that SFG spectroscopy was silent for long electrolysis time values suggested the remaining nitro groups to be located far from the electrode surface, as a consequence of an electron tunneling efficiency which decreased throughout the film thickness. Further electrolysis at -0.8 V allowed the remaining nitro groups to be reduced into NH2 with almost quantitative yields. All these results suggest the existence of a stratified layer during the electrolysis process, in which there is no limitation due to H+ diffusion in the organic film.

Item Type:Article
HAL Id:hal-01865382
Audience (journal):International peer-reviewed journal
Uncontrolled Keywords:
Institution:French research institutions > Centre National de la Recherche Scientifique - CNRS (FRANCE)
Université de Toulouse > Institut National Polytechnique de Toulouse - INPT (FRANCE)
Université de Toulouse > Université Toulouse III - Paul Sabatier - UPS (FRANCE)
Other partners > Université Paris-Sud 11 (FRANCE)
Laboratory name:
Funders:
Région Ile-de-France - European Union's Seventh Framework Programme (FP7/ 2012-2015) - Université Paris-Sud
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Deposited By: David Evrard
Deposited On:31 Aug 2018 12:05

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