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

A sensor based on graphite decoratedwith 2-hydroxy-1,4-naphthoquinonewas developed to monitor the Cd(II) and Zn(II) concentration in riverwaters. The concentration of heavy metals (HMs) in rivers continuestoincrease beyond regional background values, thereby impacting humanhealth and disrupting ecological balance. In this context, an electrochemicalsensing device to detect HM ions Zn(II) and Cd(II) in river watersis 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 surfacemodification 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 developedsensor exhibits excellent stability, reproducibility, repeatability,and selectivity in the presence of interferents. The optimal G/HNFQ-CPEsensitivity is reflected by the limits of detection (LOD, 0.28 & PLUSMN;0.02 & mu;mol L-1 for Zn and 0.21 & PLUSMN; 0.03 & mu;mol L-1 for Cd), limits of quantification(LOQ, 0.95 & PLUSMN; 0.09 & mu;mol L-1 for Zn and0.70 & PLUSMN; 0.11 & mu;mol L-1 for Cd), and linearworking range (0.47-93.8 & mu;mol L-1).DFT calculations were performed to obtain molecular insights intothe electrode/electrolyte solution interface. Finally, the sensorwas validated using the atomic absorption technique, which placesG/HNFQ-CPE as a promising electrode for Zn(II) and Cd(II) SWV detection.