Synthesis and characterization of ferrocenecarboxaldehyde immobilized on modified SiO₂–Al₂O₃ in nanoscale, application for determination of penicillamine

In this study, we prepared a stable covalently bonded ferrocene derivative (ferrocenecarboxaldehyde) over SiO₂–Al₂O₃ mixed-oxide in nanoscale size (Fe ions did not accumulate and were dispersed as Fe metal ion–nanoparticles). SiO₂–Al₂O₃ mixed-oxide was functionalized with 3-aminopropyl-triethoxysilane group and ferrocenecarboxaldehyde was covalently linked to the organo-functionalized SiO₂–Al₂O₃ mixed-oxide. Fourier transform infrared spectroscopy, UV–Vis, CHN elemental analysis, inductively coupled plasma optical emission spectroscopy (ICP–OES), scanning electron microscope (SEM), energy-dispersive X-ray spectroscopy, transmission electron microscopy (TEM), and cyclic voltammetry were used to characterize the synthesized materials. Nitrogen sorption measurements of the modified Si/Al mixed-oxide confirm the presence of the ferrocene molecules attached to the modified Si/Al mixed-oxide. The considerable decrease in the specific surface area clearly indicates functionalization of the surface of the mixed-oxide with ferrocene. The nitrogen and Fe contents of the organometallic-modified Si/Al mixed-oxide (SAPFE) were determined by elemental analysis and ICP–OES, respectively, which were then used to compute the immobilized SAPFE content. SEM and TEM images confirm that the metal particle (Fe ions) size distribution forms a continuum between the minimal (2–5 nm) and the maximal (about 50 nm) diameters. The organo-functionalized SiO₂–Al₂O₃ mixed-oxide was used as a mediator for the determination of penicillamine at pH 6.0. Under the optimum conditions at pH 6.0, the oxidation peak potential of penicillamine at the modified electrode shifts about 400 mV to less positive value than for the unmodified carbon paste electrode. Differential pulse voltammetry exhibited two wide linear dynamic ranges of 0.06–7.5 and 7.5–140 μmol L⁻¹ penicillamine. The detection limit was found to be 0.01 μmol L⁻¹ penicillamine. Kinetic parameters such as electron transfer coefficient and catalytic reaction rate constant were also determined using the electrochemical approaches. Finally, the modified electrode was used as a novel nanosensor for the determination of penicillamine in real samples such as drug, serum, and urine.