Fabrication of Ni–Co-Based Heterometallo-Supramolecular Polymer Films and the Study of Electron Transfer Kinetics for the Nonenzymatic Electrochemical Detection of Nitrite

Abstract

Here, we report the synthesis of a bimetallic supramolecular polymer (SMP) for fabricating an electrochemical nitrite sensor and study the reaction mechanism of the selective oxidation of nitrite by cyclic voltammetry (CV) simulation through the kinetic parameters evaluation. Symmetrical ligand-bearing terpyridine moieties [4′,4′′′′-(1,4-Phenylene)bis(2,2′:6′,2″-terpyridine)] were complexed with Ni(II) and Co(II) salts (Co:Ni:Ligand-0.5:0.5:1) (polyNiCo) to synthesize a heterometallo-SMP. The polyNiCo was characterized by using UV/vis spectrophotometric titration, SEM, EDS, FT-IR, EIS, and CV techniques. The molecular weight of the polymer was determined from the intrinsic viscosity measurement using the Mark–Houwink–Sakurada equation. While the spectroscopic data revealed the structural morphologies and properties of the polyNiCo, electroanalytical characterization studies confirmed the high electrochemical activity and suitability of the polyNiCo heterometallo-SMP as an electrochemical sensor. A glassy carbon electrode (GCE) was used as the base for fabricating ployNiCo_GCE and also for detecting the nitrite analyte through the oxidation process. The kinetics for the irreversible oxidation mechanism were studied using scan-rate and pH-variation methods. The electroactive surface area, electron transfer coefficient, heterogeneous electron transfer rate constant, etc. parameters were studied using the Butler–Volmer equations. We simulated the CV for the nitrite oxidation process at the polyNiCo_GCE based on the analysis of the kinetic parameters obtained from the electroanalytical experiments. An exceptional agreement between the experimental and the simulated CV was found, which confirmed the validity of the calculated kinetic parameters. Using CV and amperometry techniques, we studied the effectiveness of the polyNiCo_GCE for detecting the nitrite analyte at different concentrations. The amperometry technique showed a wide linear range of 2.5 μM–1.73 mM and a limit of detection (LOD) of 0.45 μM. The sensor was also tested for interference, stability, and reproducibility. Real sample analysis was performed using both CV and amperometry techniques, and the obtained results were compared with the results obtained by using standard solutions.