In-situ trapping and confining of highly redox active quinoline quinones on MWCNT modified glassy carbon electrode and its selective electrocatalytic oxidation and sensing of hydrazine

•A controlled electrochemical oxidation of 8-hydroxyquinoline (QL) on MWCNT surface•In-situ trapping and surface confinement of quinoline quinone (QLO) intermediate species•Precise identification of the molecular structure of the intermediate•Highly efficient electrocatalytic oxidation of hydrazine on MWCNT@QLO•Sensitive flow injection analysis of hydrazine using MWCNT@QLO as a detector

Organic redox mediator functionalized carbon nanomaterials has been considered the future of advanced nanomaterials owing to their exemplary behaviors. It is highly challenging to prepare stable functional carbon nanomaterials. Herein, we report a simple preparation of highly redox active and stable quinoline quinone (QLO) functionalized multiwalled carbon nanotube (MWCNT) modified glassy carbon electrode (GCE/MWCNT@QLO) by in-situ electrochemical oxidation of 8-hydroxyquinoline (QL) on a GCE/MWCNT in pH 7 phosphate buffer solution. Unlike the formation of electro-inactive and tarry polymeric products with electrochemical oxidation of QL at glassy carbon electrode, a multi-redox active QLO derivative intermediate was electro-generated as intermediate species and was trapped on a MWCNT modified electrode in this work. Specific pi-pi interaction between QL and MWCNT and its diffusion restrictive electrochemical oxidation process are keys for the selective entrapment of QLO on the underlying electrode. The QLO trapped MWCNT modified electrode (GCE/MWCNT@QLO) was characterized by Transmission electron microscope, X-ray photoelectron spectroscopy, Raman spectroscopy, Infrared spectroscopy, gas liquid chromatography coupled mass spectrometry and in-situ cyclic voltammetry (CV) electrochemical quartz crystal microbalance. CV of the GCE/MWCNT@QLO has displayed three well-defined redox peaks at E1/2 = -0.45 V (A1/C1), -0.1 V (A2/C2) and 0 V vs Ag/AgCl (A3/C3) corresponding to the electron-transfer behaviors of pyridinium ion, 2,3 and 5,8 diquinone functional groups of the MWCNT@QLO. The intermediate trapped modified electrode showed excellent electrocatalytic behavior and amperometric current-time sensing response to an environmental pollutant, hydrazine at 0 V vs Ag/AgCl in pH 7 phosphate buffer solution with a calibration plot linearity and detection limit values of 25-450 μM and 12 μM respectively without any interference from ascorbic acid, uric acid, cysteine and nitrate. In further, flow injection analysis coupled electrochemical of hydrazine at 0 V vs Ag/AgCl with a detection limit value 0.7 μM was also demonstrated.

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