Schiff Base Ligands for Electrochemical Detection of Cd2+ in Water Samples: Performance and Theoretical Investigations.

Two ethylenediamine-based Schiff base ligands (L3 and L4) were designed and synthesized as electroactive materials for the selective electrochemical detection of Cd2+. The structural modification of the molecular scaffold was investigated to establish a relationship between molecular structure, electronic properties, and sensing performance. The ligands were characterized by 1H NMR, Fourier transform infrared, UV-Vis spectroscopy, and density functional theory (DFT) calculations, which confirmed their successful synthesis and favorable electronic properties. Electrochemical characterization by cyclic voltammetry and electrochemical impedance spectroscopy revealed enhanced charge-transfer efficiency at L3 and L4 modified glassy carbon electrodes. Differential pulse voltammetry demonstrated excellent Cd2+ sensing performance, with detection limits of 21 nmol.L-1 for L3/GCE and 17 nmol.L-1 for L4/GCE over a wide linear range of 1-240 nmol.L-1. L4/GCE exhibited superior performance, attributed to its favorable electronic properties and enhanced charge transfer, consistent with DFT results. Moreover, L4/GCE achieved recovery rates close to 100% in real water samples. These findings demonstrate the novelty of the proposed Schiff base functionalization strategy and highlight L4/GCE as a promising sensitive and selective platform for Cd2+ monitoring.