Fabrication of a novel nano-composite carbon paste sensor based on silica-nanospheres functionalized with isatin thiosemicarbazone for potentiometric monitoring of Cu2+ ions in real samples

Abstract

The present paper describes the fabrication of a novel nano-structured organic–inorganic hybrid potentiometric sensor based on silica nanospheres functionalized with isatin thiosemicarbazone (ITC@APTES@SiO₂) as a neutral carrier for the rapid and sensitive determination of Cu(II) ions in real samples. Furthermore, multi-walled carbon nanotubes (MWCNTs) and room temperature ionic liquid (RTIL) (1-n-butyl-3-methylimidazolium tetrafluoroborate) have been used in the composition of carbon paste to improve its conductivity and transduction of the chemical signal to the electrical signal. The sensing material (ITC@APTES@SiO₂) was synthesized by immobilizing isatin thiosemicarbazone (ITC) onto aminopropyl functionalized silica nanospheres (APTES@SiO₂), and characterized by Fourier transform infrared (FT-IR) spectroscopy, solid-state ¹³C CPMAS and ²⁹Si CPMAS NMR spectroscopy, Brunauer–Emmett–Teller (BET) surface area analysis, X-ray diffraction (XRD), transmission electron microscopy (TEM) and elemental analysis. The nano-composite sensor exhibits a stable potential response to Cu(II) ions with a Nernstian slope of 29.3 ± 0.28 mV decade⁻¹ over a wide linear dynamic concentration range of 1.0 × 10⁻⁷ to 1.0 × 10⁻¹ M with a detection limit of 5.01 × 10⁻⁸ M. Furthermore, it demonstrates a fast response time of about 5 s, and can be used for at least 3 months without any significant variance in the potential. The potential response of the proposed sensor was found to be independent of pH in the range of 2.5–7. In addition, the electrode was found to be highly selective for Cu(II) ions with respect to alkali, alkaline earth, transition and heavy metal ions. The response mechanism of the nano-composite sensor was also investigated using UV-vis spectrophotometric analysis and the AC impedance technique. The practical utility of the developed sensor has also been reported for diverse real samples.