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The development of highly sensitive and selective methods for the simultaneous determination of toxic heavy metal ions (HMIs), including Hg(II), Pb(II), and Cu(II), in environmental samples is one of the key challenges in modern electroanalysis, requiring novel electrode materials with enhanced adsorption and detection capabilities to address the issues of mutual interference and low sensitivity at trace concentration levels [1]. In this work, we propose the use of zinc ferrite nanoparticles (ZnFe2O4, ZFO), synthesized by the sol-gel method with subsequent calcination, as an effective electrode modifier to address this challenge.
The obtained ZFO nanoparticles possess a spinel structure, a small average size of approximately 11.2 nm, and a high specific surface area of 54.1 m2/g, as confirmed by X-ray diffraction (XRD) and transmission electron microscopy (TEM). The high specific surface area and well-developed mesoporous structure provide a large number of active sites for the adsorption of metal ions, which is a critical factor for the preconcentration step in stripping voltammetry. Electrochemical studies using cyclic voltammetry (CV) and differential pulse anodic stripping voltammetry (DPASV) demonstrated that ZFO-modified electrodes exhibit significantly higher analytical signals compared to bare glassy carbon electrodes (GCE) or precursor-based electrodes.
Under optimized conditions (0.1 M HAc-NaAc buffer, pH=5.0, deposition potential -1.2 V, deposition time 120 s), the ZFO/GCE electrode showed excellent analytical performance for both individual and simultaneous determination of HMIs. The limits of detection (LOD, S/N=3) for simultaneous analysis reached 0.92 nM for Hg(II), 5.11 nM for Pb(II), and 7.84 nM for Cu(II). The electrode also demonstrated high reproducibility (relative standard deviation (RSD) < 1%), repeatability (RSD = 0.785% for 15 measurements of Hg(II)), stability over 7 days (RSD = 3.24%), and good selectivity in the presence of common interfering ions such as Al(III), Na(I), Ni(II), Co(II), and others. Successful testing on real water samples from a reservoir spiked with Hg(II) showed high recovery rates (97.7–102.4%), confirming the material's suitability for environmental monitoring applications.
Thus, ZnFe2O4 nanoparticles synthesized by the sol-gel method represent a promising material for the fabrication of electrochemical sensors intended for the sensitive and selective simultaneous determination of toxic heavy metal ions in natural and wastewater.