Studies on polycarbazole‐modified electrode and its applications in the development of solid‐state potassium and copper(II) ion sensors

Electrochemical synthesis of polycarbazole, having better stability and electrochromic activity, in dichloromethane containing 0.1 M tetrabutyl ammonium perchlorate (TBAP) is reported at 1.4 V versus Ag/AgCl. The electrochemistry based on cyclic voltammetric measurements in dichloromethane containing TBAP show redox behavior of the polymer associated to doping and de‐doping of ClO ion within the polymer interstices. The polycarbazole matrix obtained by the potentiostatic and potentiodynamic modes of electropolymerization is characterized based on scanning electron microscopy, differential calorimetry, and infrared spectroscopy. De‐doping of the polymer is studied by electrochemical reduction in TBAP‐free dichloromethane followed by incubation of the polymer film in 1 M aqueous KCl solution for 24 h. The open circuit potential (OCP) of doped and de‐doped polycarbazole modified electrode under the present experimental conditions is found to 462 and 19 mV, respectively, versus SCE in 0.1 M NH₄NO₃. The de‐doped polymer shows remarkable sensitivity and selective to Cu(II) ion compared to its sensitivity for Fe³⁺, Ni²⁺, Co²⁺, Pb²⁺, and Cu⁺ ions. A typical response of the de‐doped polymer electrode to Cu(II) ion is reported. On the other hand, ClO doped polymer is used in the development of solid‐state K⁺ ion sensors using dibenzo‐18‐crown‐6/valinomycin as a neutral carrier–based, plasticized poly vinyl chloride matrix membrane assembled over a polymer‐modified electrode. The doped polymer under this condition helps in maintaining charge stabilization across Pt/polymer and polymer/PVC interfaces. The lowest detection limit for the potassium ion sensor is 5 × 10⁻⁵ M with a slope of 58 mV/decade for valinomycin‐based sensor and 6.8 × 10⁻⁵ M with a slope of 54 mV for dibenzo‐18‐crown‐6 carriers with a wide linearity. The typical potentiometric results on the sensitivity, detection limits, and OCP to K⁺ ion recorded using present polymer are compared with the data recorded earlier using polyindole and a similar neutral carrier–based PVC membrane. A comparison on electrode kinetics of these two polymer‐modified electrodes also has been made using the data on Tafel plots to study the relative kinetic polarizability based on ion‐exchange currents. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 75: 1749–1759, 2000