Showing papers by "Juan A. Squella published in 2016"

Electrochemistry and XPS of 2,7-dinitro-9-fluorenone immobilized on multi-walled carbon nanotubes

Abstract: We report that glassy carbon electrodes (GCE) modified with multi-walled carbon nanotubes (MWCNTs) can be derivatized with 2,7-dinitro-9-fluorenone (2,7-NFN). The derivatization procedure involves simple immersion of the MWCNT-modified electrode in a solution containing 2,7-NFN. SEM images indicate that the MWCNTs form a twisted, three-dimensional array that remains attached to the GCE surface. Both electrochemical and spectroscopic measurements (XPS) indicate that 2,7-NFN is immobilized on the electrode, most probably by being trapped within the pockets of the mentioned three-dimensional array. The electrode with the immobilized 2,7-NFN is sufficiently stable to resist washing but allows both its manipulation and reduction to form the hydroxylamine derivative. This derivative can be oxidized to form a nitroso compound. Both the nitroso and hydroxylamine derivatives are also trapped within the MWCNT surface pockets. Furthermore, depending on the selected working potential, the nature of the encapsulated compound, i.e., nitro, nitroso, or hydroxylamine derivative and mixtures thereof, can be selected. All these redox pathways were verified by cyclic voltammetry and XPS.

Electrocatalysis of NADH on 3,5-Dinitrobenzoic Acid Encapsulated on Multiwalled Carbon Nanotube-Modified Electrode

Abstract: We report that glassy carbon electrode (GCE) modified with multiwalled carbon nanotubes (MWCNTs) can encapsulate or entrap 3,5-dinitrobenzoic acid (35DNB) generating a 35DNB-MWCNTGC electrode. After electrochemical reduction in situ of only one nitro group of 35DNB, it turns into the hydroxylamine derivative (R-NHOH), which can be further oxidized to the nitroso derivative (R-NO). Then, R-NO/R-NHOH redox couple was electrogenerated in situ by cycling the potential between 0.20 and −0.20 V vs Ag/AgCl. The very well-defined and persistent redox couple was characterized with a formal potential, E o ’ = −28 mV vs Ag/AgCl at a scan rate of 20 mV s−1. Using the Laviron’s plot, a transfer coefficient, α = 0.45, and an electron transfer rate constant, k s = 10.5 s−1, for the electron transfer of the couple R-NO/R-NHOH, were calculated. This redox reaction results to be a very efficient mediator for electrocatalytic NADH oxidation. The 35DNB-MWCNTGC electrode efficiently catalyzes the oxidation of NADH with a decrease of more than 0.60 V vs Ag/AgCl in the overpotential compared to the bare GCE and a difference of 0.25 V vs Ag/AgCl with respect to the situation without mediator. The preparation of the electrode is very easy and not time-consuming.