Substituted Nitroquinolines Immobilized in Multiwalled Carbon Nanotubes: An Unconventional Voltammetric Experiment.

Multiwalled carbon nanotube-glassy carbon electrodes (MWCNT-GCEs) were prepared and used to immobilize 5-nitroquinoline (5-NQ), 6-nitroquinoline (6-NQ) and 8-nitroquinoline (8-NQ). Cyclic voltammetry was used to study the conventional voltammetric behavior of these NQs dissolved in an aqueous alcoholic solution and compare them with the unconventional voltammetric behavior observed when the NQs were immobilized in a porous layer of MWCNTs. Increased currents and shift to lower overpotential can be explained by the change of the mass transport regime from semi-infinite diffusion to thin layer diffusion. Reduction peak potentials depended on the position of the nitro group (-NO₂ ) in the quinoline structure and the test cell pH. Reduction peak potential of -NO₂ was dependent on the mesomeric effect of the resonant structures and the inductive effect of the N heteroatom. ArNO/ArNHOH redox couple was electrogenerated in situ and immobilized on a nanostructured electrode network for all the studied NQs. The redox couple generated from 5-NQ was the most stable with 50% remaining at the 15th cycle. Even though the current intensity observed for 6-NQ was the largest, the stability of 6-NQ was 35% at the same voltammetric cycle. The lowest stability was observed for 8-NQ with only 25% remaining at the 15th cycle. [ABSTRACT FROM AUTHOR]