Characterization of the surface redox process of caffeic acid adsorbed at glassy carbon electrodes modified with partially reduced graphene oxide

Abstract

This paper describes for the first time the caffeic acid (CA) electrochemical oxidation in 1.0M HClO4 and phosphate buffer solutions (PBS) of different pH at glassy carbon electrodes (GCE) modified with electrochemically partially reduced graphene oxide (GCE/ePRGO) using cyclic and square wave voltammetries. A quasi-reversible surface redox couple was found in all reaction media at this modified electrode. The Box-Behnken design (BBD) statistical experiments and the surface methodology (RSM) were used to optimize experimental variables to generate the GCE/ePRGO. Atomic force microscopy (AFM) and electrochemical impedance spectroscopy (EIS) were used as the techniques to characterize the surface of modified electrodes. EIS was also used to determine a tentative electrochemical area for the GCE/ePRGO.The Frumkin adsorption isotherm was the best which describes the specific interaction of CA with CGE/ePRGO. The thermodynamic and kinetics of the surface redox couple were studied in 1.0M HClO4. Therefore, we used the methods of the “quasi-reversible maximum” and the “splitting of the net SW voltammetric peak” to obtain information about the thermodynamic and kinetics of this surface redox couple. Averages values obtained for the formal potential and the anodic transfer coefficient were (0.638±0.005) V and (0.58±0.06), respectively. A value of 40s−1 was obtained for the overall formal rate constant. For comparison, CA electrochemical responses were also studied at bare GCE, and GCE modified with a dispersion of graphene oxide (GCE/GO).