Carbon Nanotube-Loaded Nafion Film Electrochemical
Sensor for Metal Ions: Europium
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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 (Eu<sup>3+</sup>) 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 Eu<sup>3+</sup> 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 Eu<sup>3+</sup> 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 Eu<sup>3+</sup> 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 Eu<sup>3+</sup> by Osteryoung square-wave
voltammetry after a preconcentration time of 480 s