Rahmiana Zein

Electrochemical Determination of Chromium(VI) in River Water with Gold Nanoparticles–Graphene Nanocomposites Modified Electrodes

In this study, nanocomposites of ligand-free gold nanoparticles that are anchored onto the graphene surface (Graphene/AuNPs) were synthesized by a sonochemical method in a single reaction step. A highly sensitive amperometric sensor using Graphene/AuNPs is proposed for the determination of trace hexavalent chromium Cr(VI) in environmental water samples. Compared with a gold electrode, a glassy carbon electrode and a AuNPs modified glassy carbon electrode, the Graphene/AuNPs modified glassy carbon electrode exhibits the highest electrocatalytic activity and stability towards the reduction of Cr(VI), based on the results by cyclic voltammetry and electrochemical AC impedance studies. This study shows that the Graphene/AuNPs-based sensor can detect Cr(VI) with a low detection limit of 10 nM (∼0.5 μg/L), a wide dynamic range of 0 to 20 μM (R = 0.999) and very good selectivity and reproducibility. The electrode is applied to the determination of Cr(VI) in river samples with satisfactory recovery values.

Anodic Stripping Voltammetry for the Determination of Trace Cr(VI) with Graphite/Styrene-Acrylonitrile Copolymer Composite Electrodes

A square-wave anodic stripping voltammetry (SWASV) for the determination of trace amounts of hexavalent chromium Cr(VI) at a graphite/styrene-acrylonitrile (Graphite-SAN) copolymer composite electrode is described. This method involves a preconcentration step whereby the trace Cr(VI) was cathodically reduced to Cr(III) on an electrode surface in an acetate buffer (pH 5), followed by an anodic stripping technique with a square-wave voltammetric mode. It has been shown that the analytical sensitivity is significantly improved at the Graphite-SAN copolymer composite electrode in comparison with the conventional glassy carbon electrode, due to the strong interaction between Cr(III) and the nitrile end group of the SAN copolymer. The SWASV response was characterized with respect to the pH, deposition potential, possible interferences, etc. Under the optimal conditions, the stripping peak height linearly increased with the concentration of Cr(VI) in a range from 0 to 150 ng mL-1 with a correlation coefficient of 0.997, and a detection limit of 4.2 ng mL-1 was achieved based on signal-to-noise ratio of about 3. The Graphite-SAN composite electrode exhibited some interesting advantages, such as high mechanical rigid, easy surface renewable, higher sensitivity and better peak resolution in comparison with the results at conventional glassy carbon electrodes. They have been applied to the determination of Cr(VI) in real water samples with satisfactory recoveries.