Investigating Cd²⁺ ion sensing with palygorskite-carbon paste electrodes: optimizing performance through Doehlert design

In this study, the potential use of a novel electrode composed of palygorskite, a natural nanomaterial with a hollow structure, for the detection of Cd²⁺was investigated. Moreover, the electrode’s efficiency under various operating conditions was assessed through response surface methodology. For this purpose, cyclic voltammetry, electrochemical impedance spectroscopy, and scanning electron microscopy were utilized along with Doehlert experimental design methodology. The findings demonstrated that the electrode’s sensitivity was enhanced by using HCl solution (10⁻² M) as a supporting electrolyte or by increasing Cd²⁺ ion concentration. Additionally, the weights of the effects of the factors on electrode sensitivity followed the order Cd²⁺ concentration > pH > scan rate. The estimated limit of detection was approximately 2.03 × 10⁻⁴ mol/L; however, experimentally, Cd²⁺ concentrations as low as 5 × 10⁻⁵ M could be detected. The electrode exhibited selectivity in detecting Cd²⁺ and Pb²⁺ ions in arable land. Furthermore, it could be regenerated through a mild chemical treatment involving cation exchange. On the other hand, the electrode/solution interface could be likened to an electric circuit comprising solution resistance (162 Ω.cm²), charge transfer resistance (19.850 Ω.cm²), double-layer capacitor (11.3 × 10⁻⁶ Fs^(α-1)), and Warburg diffusion element (150 s⁻¹). These data as well as the electrode’s performance were mainly discussed in the sight of the physical and structural characteristics of palygorskite.