Ferrocenium tetrachloromagnesate modified MWCNTs electrode for detection of bismuth(III) at the trace level in polluted aqueous solutions

This study presents the fabrication of a ferrocenium tetrachloromagnesate (FTM) modified multi-walled carbon nanotubes (MWCNTs) electrode for the voltammetric determination of bismuth ions (Bi3+) in aquatic environments. The FTM was synthesized from the reaction of mag­nesium chloride with ferrocene. The incorporation of FTM, a redox-active species, was shown to markedly improve electron transfer kinetics and overall electrochemical conductivity. Structural and morphological characterizations via Fourier transform infrared spectroscopy, transmission electron microscopy, energy dispersive x-ray, field emission scanning electron microscopy and X-ray diffraction confirmed the successful embedding of FTM within the electrode matrix. Electrochemical assessments using cyclic voltammetry, electrochemical impe­dance spectro­scopy, and chronocoulometry revealed that a 10 wt.% FTM loading provided the most optimal charge transfer and interfacial behaviour. Differential pulse stripping voltammetry further demonstrated the high sensitivity of the developed electrode, achieving an ultralow detection limit of 0.543 nM with two broad linear ranges of 1.0 nM to 0.1 and 1.0 µM to 0.1 mM for Bi3+. The sensor also exhibited remarkable reproducibility (RSD 8.67 %) and stability (RSD 7.77 %). Furthermore, excellent selectivity toward Bi3+ was maintained in the presence of potentially interfering ions such as Mn2+, La3+, Ni2+, Li+, Zn2+, Fe2+, Cd2+, Cu2+, Er2+ and Pb2+. Real water-sample analyses yielded recoveries of 89 to 104 %, confirming the practical feasibility of the electrode for environmental monitoring.