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 ele ctrochromic activity, in dichloromethane containing 0.1 M tetrabutyl ammoni um perchlorate (TBAP) is reported at 1.4 V versus Ag/AgCl. The electrochemi stry based on cyclic voltammetric measurements in dichloromethane containin g TBAP show redox behavior of the polymer associated to doping and de-dopin g of ClO4-, ion within the polymer interstices. The polycarbazole matrix ob tained by the potentiostatic and potentiodynamic modes of electropolymeriza tion is characterized based on scanning electron microscopy, differential c alorimetry, and infrared spectroscopy. De-doping of the polymer is studied by electrochemical reduction in TBAP-free dichloromethane followed by incub ation of the polymer film in 1 M aqueous KCl-solution for 24 h. The open ci rcuit potential (OCP) of doped and de-doped polycarbazole modified electrod e under the present experimental conditions is found to 462 and 19 mV, resp ectively 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 polym er electrode to Cu(II) ion is reported. On the other hand, ClO4- doped poly mer 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 c hloride matrix membrane assembled over a polymer-modified electrode. The do ped polymer under this condition helps in maintaining charge stabilization across Pt/polymer and polymer/PVC interfaces. The lowest detection limit fo r the potassium ion sensor is 5 x 10(-5) M with a slope of 58 mV/decade for valinomycin-based sensor and 6.8 x 10(-5) M with a slope of 54 mV for dibe nzo-18-crown-6 carriers with a wide linearity. The typical potentiometric r esults on the sensitivity, detection limits, and OCP to K+ ion recorded usi ng present polymer are compared with the data recorded earlier using polyin dole and a similar neutral carrier-based PVC membrane. A comparison on elec trode 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. (C) 2000 John Wiley & Sons, Inc.