Carbon Nanotube-Loaded Nafion Film Electrochemical Sensor for Metal Ions: Europium

Abstract

A Nafion film loaded with novel catalyst-free multiwalled carbon nanotubes (MWCNTs) was used to modify a glassy carbon (GC) electrode to detect trace concentrations of metal ions, with europium ion (Eu³⁺) as a model. The interaction between the sidewalls of MWCNTs and the hydrophobic backbone of Nafion allows the MWCNTs to be dispersed in Nafion, which was then coated as a thin film on the GC electrode surface. The electrochemical response to Eu³⁺ was found to be ∼10 times improved by MWCNT concentrations between 0.5 and 2 mg/mL, which effectively expanded the electrode surface into the Nafion film and thereby reduced the diffusion distance of Eu³⁺ to the electrode surface. At low MWCNT concentrations of 0.25 and 0.5 mg/mL, no significant improvement in signal was obtained compared with Nafion alone. Scanning electron microscopy and electrochemical impedance spectroscopy were used to characterize the structure of the MWCNT–Nafion film, followed by electrochemical characterization with Eu³⁺ via cyclic voltammetry and preconcentration voltammetry. Under the optimized conditions, a linear range of 1–100 nM with a calculated detection limit of 0.37 nM (signal/noise = 3) was obtained for determination of Eu³⁺ by Osteryoung square-wave voltammetry after a preconcentration time of 480 s