Use of carbon paste electrodes as a novel strategy to study adsorption mechanism of silver ions onto functionalized grapefruit peel

Abstract In order to study the adsorption mechanism of silver ions onto adsorbents prepared from grapefruit peels functionalized with urea and melamine, carbon paste electrodes (CPE) were prepared and cyclic voltammetry studies were carried out. The electrochemical results showed that for the case of CPE containing the adsorbent functionalized with urea, there is one oxidation signal at 0.0 V vs. MSE attributable to the oxidation of silver that was adsorbed onto the amino groups present on its surface. On the other hand, in the CPE that contained the adsorbent functionalized with melamine, two oxidation signals were observed at 0.0 V and −0.1 V vs. MSE attributable to silver adsorbed to the surface, but indicating the presence of two different energy adsorption sites: The first of them associated with amino groups and the second with carboxyl groups. The results were complemented with infrared spectroscopy techniques, X-ray photoemission spectroscopy, and dispersive energy spectroscopy and immersion microcalorimetry. From the results obtained it was possible to define the mechanism of adsorption of the metal on each of the adsorbents studied. The electrochemical study has provided valuable information to elucidate the mechanism of adsorption, adequately complemented with conventional spectroscopic techniques has achieved a broad characterization of the amino-functionalized organic matrix, so that this analytical technique is shown as a new alternative to study superficial chemical changes in functionalized materials.