Electrochemical impedance detection of Hg2+, Ni2+ and Eu3+ ions by a new azo-calix[4]arene membrane

Due to their recognition properties and efficiency for the detection of toxic metals, calixarenes have already found applications in the design of chemical sensors based on using an electrochemical transduction. In this study, a new chromogenic azo-calix[4]arene derivative was deposited on gold electrode by spin coating to develop a new electrochemical sensor. Adhesion and morphological properties of the membrane have been firstly developed using contact angle measurements and scanning electronic microscopy (SEM) respectively. Electrochemical impedance spectroscopy (EIS) is used to study the response of the calixarenes membrane in contact with aqueous solutions of various metallic cations. The impedance behavior of the structures has been modeled by an equivalent circuit using the Z-View software. This technique has shown a selective response of this membrane towards Hg2+, Ni2+ and Eu3+. The differences in selectivity are found to be represented by variations in the resistance of the membrane (Rm) and in the charge transfer resistance (Rct) of the interface. Variation of CPE1 and CPE2 have been also investigated which were correlated to the porosity of the film and the exchange of the charge between the substrate and the electrolyte respectively.