Nanotubos de carbono no desenvolvimento de sensores eletroquímicos

Abstract

Carbon nanotubes (CNTs) have attracted great interest in electroanalysis. This material shows important properties as high charge transfer rate, high surface area and the presence of functional groups that make the sensors based on CNTs are attractive to be modified with several species. Metallic phthalocyanines (MPc) are well recognized for their excellent electrocatalytic properties and can be electrostatically adsorbed onto CNTs, where the CNT-MPc system shows a synergic and electrocatalytic effect. Thus, this work aims to characterize the electrocatalytic properties of CNTs, after a functionalization step of CNTs in an oxidizing media. Another objective is the development of electrochemical sensors based in functionalized CNTs modified with metallic phthalocyanines for the determination of environmental and medicinal substances. The CNTs were functionalized in oxidizing media (mixture 1:3 HNO3/H2SO4). The micro-structural analysis was characterized by FTIR and the FEGSEM and TEM microscopy, in which was observed that the functionalization step decreases the diameter of the tubes, unlocks the edge plans and increases the density of functional groups. The electrochemical characteristics of CNTs were examined by cyclic voltammetry and electrochemical impedance spectroscopy, in which these tests showed that the functionalized CNTs shift for more negative values the oxidation potential of redox couple [Fe(CN)6]4-/3-, as the electron transfer resistance, increase in oxidation and reduction current besides the improvement in the reversibility of the system. An electrochemical methodology were developed for the detection of pesticides 4-nitrophenol (4-NP), carbaryl, and glyphosate (Gly) in natural waters. For each pesticide used a specific sensor was constructed based on CNTs and metallic phthalocyanines. Medicinal substances (catecholamines) were also evaluated and developed sensors based on CNTs modified with cobalt phthalocyanine were developed. The proposed electrochemical sensors presented highly electrocatalytic and sensitive in the determination of pesticides and catecholamines. The proposed methodology were compared with the official methods of analysis and noted that the sensors yielded the detection limits required, demonstrating that electrochemical sensors based on CNTs become an alternative for the development of highly sensitive, rapid and low cost methodologies.