Nickel tungstate–graphene nanocomposite for simultaneous electrochemical detection of heavy metal ions with application to complex aqueous media

Abstract

We show for the first time that a composite of carbon and binary transition metal oxide, in the form of a reduced graphene oxide and nickel tungstate (RGO/NiWO₄) nanocomposite, is an effective material for electrochemical heavy metal ions detection. The multivalent electronic states of this composite show well-defined peaks of Cd(II), Pb(II), Cu(II) and Hg(II) during simultaneous detection, which is otherwise not observed for NiWO₄ NPs and RGO sheets. Simultaneous and selective detection of heavy metal ions in drinking water as well as in complex aqueous media such as carbonated drinks, milk and fruit juices has been successfully demonstrated. Differential pulse anodic stripping voltammetric (DPASV) method was adopted for detection because it partially suppresses the background current and improves signal which leads to a low limit of detection (LOD) when compared to linear sweep voltammetry (LSV). LOD for Cd(II), Pb(II), Cu(II) and Hg(II) ions were found to be 4.7 × 10⁻¹⁰ M, 3.8 × 10⁻¹⁰ M, 4.4 × 10⁻¹⁰ M and 2.8 × 10⁻¹⁰ M for individual detection and 1.0 × 10⁻¹⁰, 1.8 × 10⁻¹⁰, 2.3 × 10⁻¹⁰ and 2.8 × 10⁻¹⁰ M, for simultaneous detection, respectively. The effect of deposition time and deposition potential on the sensing parameter was studied in acetate buffer (pH = 5.0). The better sensitivity with the high capacitive current along with individual and simultaneous electrochemical detection of RGO/NiWO₄ nanocomposite is mainly attributed to its large surface area, good electronic conductivity, and better electron transport properties which lead to better catalytic response towards the heavy metal ions detection.