Synthesis of Polypyrrole Induced by [Fe(CN)6]3− and Redox Cycling of [Fe(CN)6]4−/[Fe(CN)6]3−

Abstract

Chemical synthesis of the conducting polymer polypyrrole induced by [Fe(CN)₆]^3- is reported. Reaction kinetics were characterized spectrophotometrically. Reaction rate was evaluated at several different pH levels in the presence of [Fe(CN)₆]^3- and [Fe(CN)₆]^4- ions. The formation of polypyrrole at aerobic and anaerobic conditions was evaluated. We report that at anaerobic conditions [Fe(CN)₆]^4- cannot initiate oxidative polymerization, while its oxidized form [Fe(CN)₆]^3- successfully initiates and maintains the pyrrole polymerization reaction. The formation of polypyrrole was also observed in the solution containing a pyrrole monomer, [Fe(CN)₆]^4- and dissolved oxygen due to re-oxidation (redox cycling) of [Fe(CN)₆]^4- into [Fe(CN)₆]^3- by dissolved oxygen. Experiments to determine the polymerization reaction rate were performed and showed the highest rate in the presence of 0.5 mM of [Fe(CN)₆]^3- at pH 9.0, while the polymerization reaction performed at pH 7.0 was determined as the slowest. This investigation opens new horizons for the application of [Fe(CN)₆]^4-/[Fe(CN)₆]^3--based redox cycling reactions in the synthesis of the conducting polymer polypyrrole and potentially in the formation of other conducting polymers which can be formed by oxidative polymerization.