Voltammetric response of a copper(II) complex incorporated in silica-modified carbon-paste electrode

This work describes the preparation, characterization and use of the comple x formed by Cu(II) with 3-aminopropyltriethoxysilane immobilized on silica gel, incorporated into a carbon-paste electrode. The electrochemical studie s were carried out in deaerated, 0.1 mol l(-1) KCl solution through cyclic voltammetry by scanning the potential from +1.0 to -1.0 V. Two redox proces ses were observed that could be assigned to Cu(II)/Cu(I). The formal standa rd potentials, E-0' (where E-0'=(E-pa+E-pc)/2; E-pa the anodic and E-pc the cathodic peak potentials), of the first and second redox couples were calc ulated, giving 94 and -274 mV vs. Ag/AgCl, respectively. The dependence of peak potential on the sweeping rate, indicated a quasi-reversible behavior. From the plot of I-p vs. nu(1/2) (I-p is the peak current and nu the scan rate), a straight Line was obtained at low scan rates (<20 mV s(-1)), which means that the current-potential curves are controlled by diffusive transp ort. This behavior is similar to that usually observed for solution species , although the complex in this case is adsorbed on the matrix. Our results show that the modified electrode presents catalytic activity for oxygen red uction because the saturation of the solution in the cell with pure oxygen causes a considerable enhancement of the cathodic peak current, The analysi s of the current-potential curves recorded at the rotating disk electrode i ndicates that the copper-complex catalyzes the four-electron reduction of O -2 to H2O. Chronoamperometric measurements show the potentiality of the use of this working electrode as an amperometric sensor for dissolved dioxygen in aqueous media. (C) 1999 Elsevier Science B.V. All rights reserved.