Lead ion (Pb2+) electrochemical sensors based on novel Schiff base ligands

In this study, a novel bidentate Schiff base ligand, namely (1E,1′E,2E,2′E)-N,N′-(butane-1,4-diyl)bis(3-(2-methoxyphenyl)prop-2-en-1-imine) (L¹), and a tetradentate Schiff base ligand, namely N1,N2-bis(2-(((1E,2E)-3-(4-(dimethylamino)phenyl)allylidene)amino)ethyl)ethane-1,2-diamine (L²), were successfully synthesized through a simple procedure. The synthesized Schiff base ligands were characterized by scanning electron microscopy (SEM) analysis, attenuated total reflectance-Fourier transform infrared spectroscopy (ATR-FTIR), nuclear magnetic resonance (NMR) and ultraviolet-visible (UV-vis) spectroscopy. Moreover, the thermal behavior was studied through thermogravimetric (TG)/differential thermogravimetric (DTG)/differential thermal (DT) analyses under a nitrogen atmosphere. Subsequently, the features and performances of the synthesized ligands (L¹ and L²) as electrochemical sensors for the detection of heavy metal ions (HMIs) have been investigated. A different behavior was noticed using these two ligands, with L¹ being the best candidate for developing a modified screen-printed carbon electrode (L¹/SPCE) electrochemical Pb²⁺ sensor. To improve further the performances, gold nanoparticles (AuNPs) were deposited by an electrochemical process on the L¹/SPCE platform. The developed AuNPs-L¹/SPCE sensor displayed enhanced lead ion sensing with a high sensitivity of 56.78 μA μM⁻¹ cm⁻² and a detection limit of 0.298 μM. This novel sensor demonstrated promising performances for the detection of Pb²⁺ ions in real seawater with no sample treatment.