Avaliação dos efeitos da funcionalização por tratamento ácido no desempenho eletroanalítico de eletrodos modificados com nanotubos de carbono de paredes múltiplas

Abstract

The unique properties of carbon nanotubes make this material a target of great interest, with important applications in electroanalysis, highlighting its electrocatalytic properties as electrodic surface modifiers in the manufacture of electrochemical sensors. This work demonstrates that the electrochemical behavior of different molecules, such as drugs, including omeprazole and ciprofloxacin, phenolic compounds such as catechol, dopamine, hydroquinone and tert-butylhydroquinone, or even molecules with forensic interest such as 2,4,6- trinitrotoluene (TNT) on a glassy carbon electrode modified with multi-walled carbon nanotubes (MWCNTs) is affected by the acid functionalization of this material. Voltammetric and amperometric measurements showed that glassy carbon electrode modified with nonfunctionalized MWCNTs (NF-MWCNTs) presented better analytical performance in comparison with the electrode modified with the same material, but after the functionalization process using acid treatment (F-MWCNT). Changes in the surface area of the carbon nanomaterials and the removal of metallic impurities present in MWCNTs were effects observed after functionalization process with HNO3/H2SO4, and both processes contribute to the improved performance of NF-MWCNTs modified electrodes. Electrochemical impedance spectroscopy measurements revealed higher electron transfer rate when using NF-MWCNTs. Increase in voltammetric responses (up to 10-fold), higher slope values for the amperometric studies (up to 7-fold) and, for some cases, widening of the linear working range, were verified. Although acid functionalization introduced oxygenated groups and structural defects on the MWCNTs structure verified by surface characterization techniques which may contribute for electrocatalytic effect of MWCNTs, the presence of metallic impurities on non-treated MWCNTs, such as Fe, Mo and Co, play major role on the sensitivity of the electrochemical sensors. The functionalization removed almost completely the metallic residual impurities from MWCNTs and resulted in a decrease in the specific surface area of the material, which may have contributed to the loss in sensitivity of the sensors. This characteristic was exploited in both oxidation and reduction of electroactive species, providing the production of more sensitive amperometric and voltammetric sensors.