Electrochemical response of carbon paste electrodes modified with carbon nanotubes: Effects of temperature of nitrogen doping and oxygen functionalization

Abstract

Carbon paste electrodes (CPE) were modified with nitrogen-doped carbon nanotubes (N-CNTs) synthesized at 750 °C (N-CNT750) and 850 °C (N-CNT850), carboxyl functionalized carbon nanotubes (MWCNTCOOH), and pristine carbon nanotubes (MWCNT). Their electrochemical properties were investigated and compared towards a common redox probe, potassium ferricyanide (K3[Fe(CN)6]). The electrochemical responses were probed using cyclic voltammetry, and the results unveiled that modification with carbon nanotubes enhanced anodic peak currents (Ipa) for the electrodes CPE/MWCNTCOOH, CPE/N-CNT750 and CPE/N-CNT850 (Ipa, p < 0.05 in relation to pure CPE). In particular, CPE modified with N-CNTs synthesized at 850 °C (CPE/N-CNT850) exhibited better electrochemical response, with lower peak-to-peak potential separation (ΔEp, p < 0.05 in relation to pure CPE). Complementary studies were conducted to investigate the electroactive area (A) and heterogeneous electron-transfer kinetics (k0). CPE/N-CNT850 (0.034 ± 0.005 cm2) and CPE/MWCNTCOOH (0.057 ± 0.002 cm2) presented more satisfactory results for the anodic and cathodic electroactive area (A), respectively. Kinetic studies revealed a higher k0 (1.03 × 10−3 cm.s−1) for the CPE/N-CNT850 electrode. Differential pulse voltammetry was employed for the electrochemical detection of Acetaminophen (AC). The response was linear for an AC concentration range from 66.2 to 259.7 μmol L−1, with the lowest detection limit (LOD) of 0.37 μmol L−1 and the highest sensitivity of 0.244 ± 0.002 μA L μmol−1 for the respective electrodes CPE/N-CNT850 and CPE/MWCNTCOOH. The CPE/N-CNT850 and CPE/MWCNTCOOH electrodes show the best correlation of results, the presence of polar groups on the surface of MWCNTCOOH and a higher amount of graphitic nitrogen bond of N-CNT850 suggest that these CNTs are particularly promising for applications in electrochemical fields.