Dispersion frequency technique to explain the charge transfer process involved in cadmium detection using aniline, N-phenylglycine and graphene oxide based electrochemical sensor

Abstract

A new technique, termed as dispersion frequency (DF) technique, based on Maxwell Wagner dispersion frequency, was proposed for the first time in an electrochemical sensor to explain the charge transfer mechanism involved, behind the sensing process. Dispersion frequency can be characterized by the maximum dispersion in capacitance, which is an interfacial relaxation effect, and occurs in systems where electric current passes through the electrode electrolyte interface across the double layer. In this work, this technique was used to explain the reason behind the improvement in the selectivity by varying the film thickness and amount of graphene oxide (GO), in composite (from aniline, N-phenylglycine and GO) films. For that purpose, electrochemical impedance spectroscopy (EIS) experiments were conducted, and the DF values were evaluated. It was found that the DF values decrease with film thickness and increase with the GO content when detecting Cd2+ in buffer. Also, the DF value changed (decreased) in presence of interfering species. Thus, it was demonstrated that the DF values could be used to predict and explain the interference effect. The behavior of the DF values was opposite to that of the barrier width (BW) values as studied in a previous work which too were a function of the film thickness and the GO content. Both explain independent physical phenomena which are related to the same charge transfer process. In this work, a correlation coefficient relating the barrier width and dispersion frequency values with respect to film thicknesses at any specific amount of GO content was evaluated. This correlation coefficient can be used to evaluate one parameter if the other is known for a series of film thicknesses by doing lesser number of EIS experiments.