Stability of Substituted 4-Bromophenyl and 4-Nitrophenyl Groups Electrochemically Grafted at Carbon Electrode Surface

Abstract

The electrochemical reduction of an aryl diazonium tetrafluoroborate salt, dissolved in acetonitrile, at a carbon electrode surface allowed the grafting of aryl groups with the formation of a carbon-carbon bond. Groups such as 4-nitrophenyl and 4-bromophenyl were grafted at a glassy carbon electrode surface. The stability of these grafted groups, present at the glassy carbon electrode surface, was studied at various electrode potentials in aqueous media. In appropriate experimental conditions, the as-grafted groups severely inhibit the cyclic voltammetry response of selected redox probes. Thus, the reappearance and/or increase of an electrochemical response, after polarization, were taken as an indication that a modification of the grafted layer occurred. The results of this work demonstrated that polarization at very positive (ca. 1.8 V) and negative (ca. -2 V) potential is needed to observe and electrochemical response. Electrochemical impedance spectroscopy was also used to investigate the stability of the grafted layers. The impedance data usually tracks fairly well the cyclic voltammetry results, although the former appears to be more sensitive to changes that are occurring upon polarization of the modified electrode.