Improvement in the performance of a zinc ion-selective potentiometric sensor using modified core/shell Fe3O4@SiO2 nanoparticles

Abstract

A novel, simple, accurate and sensitive zinc ion-selective potentiometric sensor was fabricated by modifying the surface of Fe₃O₄@SiO₂ nanoparticles using a ligand (L) prepared by a coupled reaction between (3-aminopropyl)trimethoxysilan (APTMS) and 2-hydroxy-3-methoxybenzaldehyde (2-H-3-MBA). The prepared Fe₃O₄ nanoparticles were characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray powder diffraction (XRD) and Fourier transform infrared (FTIR). In addition, Fe₃O₄@SiO₂, Fe₃O₄@SiO₂–APTMS, and Fe₃O₄@SiO₂–L were characterized by FTIR. X-ray photoelectron spectroscopy was used to confirm the surface modification of the Fe₃O₄@SiO₂ nanoparticles. The effects of individual variables such as the amount of graphite powder, Fe₃O₄@SiO₂–L and sodium tetraphenylborate (NaTPB) used in the composition of the carbon paste electrode (CPE) in addition to their possible interactions were investigated and optimized using a central composite design (CCD) under response surface methodology (RSM). The optimal values of graphite powder, Fe₃O₄@SiO₂–L and NaTPB in a proper amount of paraffin oil obtained were 72, 15 and 6 mg, respectively. The prepared electrode applied for sensing Zn²⁺ ions demonstrated a linear range of 2.5 × 10⁻⁶ to 1.00 × 10⁻¹ mol L⁻¹. The detection limit, slope and response time of this sensor were found to be 10⁻⁶ mol L⁻¹, 29.451 and 14 s, respectively. The potentiometric response of the prepared electrode based on Fe₃O₄@SiO₂–L was independent of the pH of the test solution over the pH range of 4–6, which is an advantage of this electrode having a neutral working pH. This sensor was successfully used for the sensitive determination of trace amounts of Zn²⁺ in samples of water. The moderate selectivity coefficient evaluated by the fixed interference method (FIM) indicated an efficient discriminating ability of the proposed electrode for Zn²⁺ ion assessment. It was also found to be well repeatable and reproducible.