Electrocatalytic nitrite oxidation at a Pt(II)-based Metallo-supramolecular polymer interface: Kinetic and mechanistic insights

Abstract

This study reports the synthesis of a novel Pt(II)-based metallo-supramolecular polymer (polyPt) employing 4 '-(4-pyridyl)-2,2 ':6 ',2 ''-terpyridine (4-py-tpy) as the coordinating ligand, which was subsequently utilized as an electrocatalytic modifier for the electrochemical detection of nitrite (NO2-). The synthesized polyPt was deposited onto a glassy carbon electrode (GCE) via drop-casting to construct the polyPt_GCE sensing platform. The morphology and structural characteristics of the polymer were examined by field-emission scanning electron microscopy (FESEM), while energy-dispersive X-ray spectroscopy (EDS) and Fourier-transform infrared spectroscopy (FTIR) were used to verify functional moieties and elemental composition. The coordination and stoichiometric interaction between Pt(II) and the 4-py-tpy ligand were confirmed by UV-visible spectrophotometric titration. X-ray photoelectron spectroscopy (XPS) further confirmed the presence of coordinated Pt(II) centers and the preservation of the metal-ligand composition in the polymer framework. Electrochemical characterization was carried out using electrochemical impedance spectroscopy (EIS) and cyclic voltammetry (CV). The interfacial kinetics of nitrite oxidation at the polyPt_GCE were investigated through scan-rate analysis based on the Laviron model together with pH-dependent studies over the range of 3.0 to 9.0. The obtained heterogeneous electron-transfer rate constant and charge-transfer coefficient indicate that nitrite oxidation proceeds via a diffusion-controlled and electrochemically irreversible process, in which mass transport governs the current response while interfacial electron transfer is highly favorable and not rate-limiting. Under optimized experimental conditions, the polyPt_GCE exhibited a linear response toward nitrite concentrations from 5 to 1000 mu M, with a limit of detection (LOD) of 0.76 mu M. The modified electrode showed satisfactory stability, reproducibility, and selectivity toward nitrite oxidation. Furthermore, recovery studies in tap, rain, and lake water matrices demonstrated the practical applicability of the proposed sensing platform. These results highlight the potential of coordination-driven Pt(II) supramolecular polymer frameworks as tunable electrocatalytic interfaces for nitrite detection and provide insight into the structure-activity relationship governing electrochemical nitrite oxidation.