Desenvolvimento e aplicação do eletrodo de folhas de grafite obtido por deposição química de vapor a pressão atmosférica para determinação eletroquímica de cafeína

Abstract

Graphite-based electrochemical sensors are constantly innovated, with this in mind, in order to obtain a versatile, environmentally friendly and easy to manufacture sensor, this research involved the synthesis of micrometric graphite sheets (GS) was proposed, through the pyrolysis of toluene. The synthesis process via Atmospheric Pressure Chemical Vapor Deposition (APCVD) applied in this work is advantageous as it does not require the use of metallic catalysts, substrates, vacuum, plasma or hydrogen flow, these being necessary when deals with traditional CVD synthesis. To characterize the GS as a working electrode, morphological and physical-chemical characterizations of the material were carried out using techniques such as: SEM, TEM, FTIR, EDS, XRD, Raman and Contact Angle. The electrochemical behavior was evaluated in the presence of different redox media, these being potassium hexacyanoferrate (III) (K4Fe(CN)6) and hexaminruthenium chloride (III), thus obtaining ∆Epic equivalent to 0.38 V and 0.16 V , respectively, when in neutral medium (KCl 0.1 M), the behavior in acidic (pH=2.0) and alkaline (pH=12.0) medium was also evaluated. The electroactive area of the GS electrode was evaluated, estimated at 0.177 cm2, with a geometric area of 0.1 cm2 . With the aim of evaluating the resistance to charge transfer, electrochemical impedance spectroscopy was performed, obtaining the Rct equivalent to 12271 Ω for the GS, and in order to compare resistance data, the Rct of 3692 Ω was obtained with the electrode conventional glassy carbon under the same conditions. Aiming to apply the GS electrode in electroanalysis, the detection and quantification of caffeine in different types of commercial drinks was carried out. The results obtained show that the GS electrode presents a linear response in a caffeine concentration range (0.68-1477.26 µM), with R2 of 0.99. The limit of detection (LOD) estimated at 0.68 µM suggests greater sensitivity than other conventional sensors, such as glassy carbon and BDD, for example. When comparing electrochemical determinations and highperformance liquid chromatography measurements, an average percentage variation of 1.2% was observed. With these results, it is possible to highlight the potential use of this sensor as an analytical, portable, reliable, low-cost and high-efficiency tool. to determine caffeine in different types of samples