Square-Wave Voltammetric Detection of Zn(II) and Cd(II) with a Graphite/Carbon Paste Electrode Decorated with 2-Hydroxy-1,4-naphthoquinone

The concentration of heavy metals (HMs) in rivers continues to increase beyond regional background values, thereby impacting human health and disrupting ecological balance. In this context, an electrochemical sensing device to detect HM ions Zn(II) and Cd(II) in river waters is herein reported. It consists of graphite (G) decorated with 2-hydroxy-1,4-naphthoquinone (HNFQ) incorporated in a carbon paste electrode (CPE), and the G surface modification with HNFQ was characterized by cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS), and chronocoulometry (CC). The electroanalytical behavior and detection of Zn(II) and Cd(II) were evaluated by square-wave voltammetry (SWV) and CV. The developed sensor exhibits excellent stability, reproducibility, repeatability, and selectivity in the presence of interferents. The optimal G/HNFQ-CPE sensitivity is reflected by the limits of detection (LOD, 0.28 ± 0.02 μmol L–1 for Zn and 0.21 ± 0.03 μmol L–1 for Cd), limits of quantification (LOQ, 0.95 ± 0.09 μmol L–1 for Zn and 0.70 ± 0.11 μmol L–1 for Cd), and linear working range (0.47–93.8 μmol L–1). DFT calculations were performed to obtain molecular insights into the electrode/electrolyte solution interface. Finally, the sensor was validated using the atomic absorption technique, which places G/HNFQ-CPE as a promising electrode for Zn(II) and Cd(II) SWV detection.