Estudo do efeito do pré-tratamento ácido em eletrodos de folha de grafite pirolisadas na detecção de catecol e resorcinol

Abstract

Phenolic compounds, such as catechol and resorcinol, are used in various industrial fields. Often, inappropriate disposal of these isomers causes contamination and can reach rivers. Therefore, when these products be in contact with humans, they cause harm to health and therefore it is necessary to monitor them. Thus, as one of the forms of control, electrochemical sensors are excellent choices as they have high efficiency, ease of measurement and decentralization, in addition to low production costs. In this study, pyrolytic graphite sheet (PGS) electrodes were used as a working electrode in the production of an electrochemical sensor to determine the presence of these pollutants in water. To the limits of determination and quantification to be optimized, a surface treatment was carried out using acidic solutions to modify the surface of the electrode and thus improve the interaction at the interface between the surface of the working electrode and the solution. Therefore, the electrodes were activated with nitric acid solutions (PGSNA) using cyclic voltammetry and amperometry. After this treatment surface exfoliation of the electrode was promoted and subsequently improved the electroactive area and interaction with the pollutant solution. After acid treatment, PGS demonstrated an increase in the electroactive area from 2,06x10-7 to 2,32x10-7 cm² and improved sensitivity observed in electrochemical characterization studies. Other studies, such as SEM and RAMAN, also emphasized the differences that occurred. In the analytical curves, PGS-NA demonstrated a better profile and sensitivity when compared to PGS without any treatment. The values obtained for the detection limit of catechol were 0,58 and 1,17 μmol. L-1 for PGS-NA and PGS, respectively. Resorcinol’s detection limit was 11,21 to 0,16 μmol. L-1 also for PGS-NA and PGS, respectively. The electrodes also performed stability studies, standard addition, and interference testing, where again the treated electrodes obtained better results. Finally, from studies of the calibration curves, different behavior was observed for PGS-NA in the presence of resorcinol. In the resorcinol oxidation mechanism, a polymeric film is formed and deposited on the surface of the electrode, which can reduce its contact with the solution, causing a reduction in current in subsequent measurements. This point was confirmed by electrochemical impedance spectroscopy tests carried out with the redox probe and by decreasing currents in the calibration curves. However, for the analyzes of catechol calibration curves, different behavior was observed, that is, after resorcinol measurements on the same electrode, the next measurements using only catechol showed an increase in current. As these compounds are isomers, it is possible that there is a better interaction between them made possible by the electrolytic medium, which results in better sensitivity to the catechol solution after the influence of resorcinol. Finally, the treated electrodes demonstrated better performance in determining the presence of resorcinol and catechol isomers, demonstrating that monitoring in effluents is possible.