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

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 C-13 CPMAS and Si-29 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 x 10(-7) to 1.0 x 10(-1) M with a detection limit of 5.01 x 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.