Electrochemical analysis of a PPV derivative thin film doped with ß-ketoimine calix[4]arene in the dark and under illumination for the detection of Hg2+ ions

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Conducting polymer can be used as the polymer matrix of the ion sensitive membrane (containing electroactive sites), which would exhibit intrinsic mixed ionic and electronic conductivity. In this work, a soluble poly(p-phenylene vinylene) derivative (MEH-PPV) has been used as the electroconducting polymer to immobilize the ß-ketoimine calix[4]arene derivative. Indium-thin oxide (ITO) electrode coated with the thin films of MEH-PPV and composite MEH-PPV/ß-ketoimine Cal[4] are designed for the determination of trace amounts of Hg2+ ions. Surface morphology properties were examined by atomic force microscopy (AFM) and scanning electron microscopy (SEM). The presented results show that the incorporation of calixarene derivative into MEH-PPV polymer improved the surface smoothness. Contact angle measurements were used to study hydrophobicity and surface energy properties of thin films. We observed that the best adhesion on the ITO surface is for the MEH-PPV/ß-ketoimine Cal[4] surface due to the presence of (OH) groups coming from the molecules of derivative calix[4]arene. Thin films were characterized by electrochemical impedance spectroscopy (EIS) in the dark and under illumination. The impedance behavior of the modified electrodes is modeled by an equivalent electrical circuit using the Z-View software. From the impedance plots, the bulk resistance and ionic conductivity of the membranes is an important factor determining the ability of ions to pass across the membrane. Marked differences in the ionic conductivity are observed as a function of the light excitation. The charge transfer processes at the electrode/electrolyte interface was carefully examined in the dark and under illumination. Optical excitation of both membranes revealed that the sensing activity of the MEH-PPV/ß-ketoimine Cal[4] modified electrode can improve the measuring sensitivity of Hg2+ ions compared to the MEH-PPV modified electrode.