Improving Electrochemical Pb²⁺ Detection Using a Vertically Aligned 2D MoS₂ Nanofilm

Abstract

Recent advancements in MoS₂ nanofilms have aided in the development for important water-related environmental applications. However, a MoS₂ nanofilm-coated sensor has yet to have been applied for heavy metal detection in water-related environmental samples. In this study, a novel vertically aligned two-dimensional (2D) MoS₂ (edge exposed) nanofilm was applied for <i>in situ</i> lead ion (Pb²⁺) detection. The developed sensor showed an excellent linear relationship toward Pb²⁺ between 0 and 20 ppb at -0.45 V vs Ag/AgCl using square wave anodic stripping voltammetry (SWASV) with the improved limit of detection (LOD) of 0.3 ppb in a tap water environment. The vertically aligned 2D MoS₂ sensor exhibited improved detection sensitivity (2.8 folds greater than a previous metallic [Bi] composite electrode) with lower relative standard deviation for repetitive measurements (<i>n</i> = 11), indicating enhanced reproducibility for Pb²⁺ detection. The vertically aligned 2D MoS₂ layers exhibited 2.6 times higher sensitivity than horizontally aligned 2D MoS₂ (basal plane exposed). Density functional theory calculations demonstrated that adsorption energy of Pb on the MoS₂ side edge was much higher (4.11 eV) than those on the basal plane (0.36 and 0.07 eV). In addition, the band gap center of vertical MoS₂ was found to be higher than the Pb²⁺ → Pb reduction potential level and capable of reducing Pb²⁺. Overall, the newly developed vertically aligned 2D MoS₂ sensor showed excellent performance for detecting Pb²⁺ in a real drinking water environment with good reliability.