Electrochemical Determination of Cd, Cu, Pb, and Hg in Water and Food Using a Glassy Carbon Electrode Modified with Metal-Organic Framework, Polydiallyldimethylammonium, and Polydopamine

A functionalized Zr-based metal–organic framework (MOF) was synthesized using UiO-66 as the framework, polydiallyldimethylammonium (PDDA) as the interfacial modifier, and polydopamine (PDA) as the functionalizing agent through a straightforward one-pot hydrothermal reaction. The material underwent characterization through X-ray diffraction to determine its crystal structure, scanning electron microscopy and transmission electron microscopy to analyze its surface morphology and microstructure, and X-ray photoelectron spectroscopy to evaluate its elemental oxidation states. These analyses revealed that UiO-66-PDDA-PDA displayed well-dispersed PDA and an abundance of functionalized hydroxyl and amino groups. Utilizing this innovative functionalized MOF material, an electrochemical sensor was developed based on a UiO-66-PDDA-PDA-modified glassy carbon electrode for the simultaneous determination of Cd2+, Cu2+, Pb2+, and Hg2+. The fabricated electrochemical sensor exhibited excellent selectivity and rapid response to microgram levels of the mentioned heavy metal ions in tea, water, and dairy products using cyclic voltammetry. The sensor demonstrated remarkably low detection limits and stable relative standard deviations (RSDs) for the four heavy-metal ions. Furthermore, the electrochemical properties and applications of the modified electrode were investigated by optimizing operational parameters such as pH, deposition potential, and deposition time to improve the detection of trace ions. This approach offers a rapid screening method for inspectors to verify sample compliance.