Desenvolvimento e caracterização de eletrodos modificados com materiais nano-estruturados de carbono

Abstract

In this thesis the development of efficient electrochemical sensors based on carbon nanostructured materials (graphene and nanotubes) was demonstrated. For this, three synthesis methods were used (electrochemical, drop casting and interfacial). The performance of these sensors was investigated using, as model analytes, hydroquinone (HQ), catechol (CT) and dopamine (DP). In the first section, a glassy carbon electrode (GCE) was used as substrate for the manufacture of chemically (CRGO) and electrochemically reduced (ERGO) graphene oxide amperometric sensors. The CRGO-based sensor was produced using the drop casting method, while in the synthesis of the ERGO-based sensor the electrochemical method was employed. The cyclic voltammetry measurements showed a higher current signal to the CRGO compared to the ERGO, due to the higher number of graphene sheets found in the CRGO, as well as a greater roughness and consequently a higher electroactive area of this electrode (evidenced by microscopic surface techniques). In addition, electrochemical impedance spectroscopy (EIS) measurements revealed that both modified surfaces showed lower resistance to electron transfer than unmodified GCE. Through amperometric measurements using the BIA technique, lower detection limits (DL) were obtained (between 12 and 55 nmol L-1). In the second section, carbon nanotube (CNT) and CRGO films were prepared by the interfacial method. The electrochemical performance of the composite electrode was compared with those obtained for the electrode without modification and individually modified with CNT or CRGO films. EIS measurements showed that electronic transfer was facilitated on the surface of the composite electrode, however, there was no significant increase in the electroactive area of the CNT/CRGO electrode. Amperometric detection of the DP and CT by BIA technique showed the presence of synergistic properties between CNTs and CRGO in composite performance, which resulted in highly sensitive sensors with better performance than CNT- or CRGO-based electrochemical sensors. Finally, a forensic application using ERGO for the detection of cocaine and some adulterants found in seized samples by the Federal Police is presented.