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

Carbon paste electrodes (CPE) were modified with nitrogen-doped carbon nanotubes (N-CNTs) synthesized at 750 °C (N-CNT 750) and 850 °C (N-CNT 850), carboxyl functionalized carbon nanotubes (MWCNT COOH), and pristine carbon nanotubes (MWCNT). Their electrochemical properties were investigated and compared towards a common redox probe, potassium ferricyanide (K 3 [Fe(CN) 6 ]). The electrochemical responses were probed using cyclic voltammetry, and the results unveiled that modification with carbon nanotubes enhanced anodic peak currents (I pa) for the electrodes CPE/MWCNT COOH , CPE/N-CNT 750 and CPE/N-CNT 850 (I pa , p < 0.05 in relation to pure CPE). In particular, CPE modified with N-CNTs synthesized at 850 °C (CPE/N-CNT 850) exhibited better electrochemical response, with lower peak-to-peak potential separation (ΔE p , p < 0.05 in relation to pure CPE). Complementary studies were conducted to investigate the electroactive area (A) and heterogeneous electron-transfer kinetics (k 0). CPE/N-CNT 850 (0.034 ± 0.005 cm2) and CPE/MWCNT COOH (0.057 ± 0.002 cm2) presented more satisfactory results for the anodic and cathodic electroactive area (A), respectively. Kinetic studies revealed a higher k 0 (1.03 × 10−3 cm.s−1) for the CPE/N-CNT 850 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-CNT 850 and CPE/MWCNT COOH. The CPE/N-CNT 850 and CPE/MWCNT COOH electrodes show the best correlation of results, the presence of polar groups on the surface of MWCNT COOH and a higher amount of graphitic nitrogen bond of N-CNT 850 suggest that these CNTs are particularly promising for applications in electrochemical fields. [Display omitted] • CNTs synthesized in different conditions were employed as modifiers in carbon paste electrode. • CPE/N-CNT 850 and CPE/MWCNT COOH displayed more satisfactory results regarding the electroactive area using [Fe(CN) 6 ]3−/4−. • CPE/N-CNT 850 exposed a higher k 0 for the redox probe. • Electrodes modified with N-CNT 850 and MWCNT COOH exhibited improved sensing capabilities for acetaminophen determination. • MWCNT COOH with polar groups and N-CNT 850 with a higher amount of graphitic nitrogen bond could improve their electrochemical properties. [ABSTRACT FROM AUTHOR]