Abstract
Chemical sensors relying on graphene-based materials have been widely used for electrochemical determination of metal ions and have demonstrated excellent signal amplification. This study reports an electrochemically reduced graphene oxide (ERGO)/mercury film (HgF) nanocomposite-modified pencil graphite electrode (PGE) prepared through successive electrochemical reduction of graphene oxide (GO) sheets and an in situ plated HgF. The ERGO-PG-HgFE, in combination with dimethylglyoxime (DMG) and square-wave adsorptive cathodic stripping voltammetry (SW-AdCSV), was evaluated for the determination of Ni2+ in tap and natural river water samples. A single-step electrode pre-concentration approach was employed for the in situ Hg-film electroplating, metal-chelate complex formation, and non-electrolytic adsorption at –0.7 V. The current response due to nickel-dimethylglyoxime [Ni(II)-DMG2] complex reduction was studied as a function of experimental paratmeters including the accumulation potential, accumulation time, rotation speed, frequency and amplitude, and carefully optimized for the determination of Ni2+ at low concentration levels (μg L−1) in pH 9.4 of 0.1 M NH3–NH4Cl buffer. The reduction peak currents were linear with the Ni2+ concentration between 2 and 16 μg L−1. The limits of detection and quantitation were 0.120 ± 0.002 µg L−1 and 0.401 ± 0.007 µg L−1 respectively, for the determination of Ni2+ at an accumulation time of 120 s. The ERGO-PG-HgFE further demonstrated a highly selective stripping response toward Ni2+ determination compared to Co2+. The electrode was found to be sufficiently sensitive to determine metal ions in water samples at 0.1 µg L−1, well below the World Health Organization standards.
Acknowledgments
The following work was performed in collaboration with SensorLab, the University of the Western Cape and the National Research Foundation (NRF) of South Africa.