Mechanism of Redox Reaction on Polypyrrole

Abstract

A concentration of bipolarons in doped polypyrrole (PPy) decreases on electrochemical reduction at an early stage while that of polarons increases. Further reduction increases the absorption intensity at 800 nm on expense of the peak intensity at 550 nm. Prolonged reduction produces a strong absorption at 400 nm and diminishes the intensities both at 550 nm and 800 nm. The trend of changes in absorption intensity at 800 nm repeats when the reduction system is fixed to pH = 3 by adding acetic acid. However, adding 0.01 mol of hydroquinone in the system lowers monotonically the absorption intensity at 800 nm on reduction. Cyclic voltammograms of the PPy change little after 7,000 cycles if hydroquinone is added to the system. Polarons are so reactive that PPy transforms into irreversible changes in the structure on the reduction process and the reactivity is retarded by adding hydroquinone in the system.

Characterization of Overoxidized Polypyrrole Colloids Imprinted with l-Lactate and Their Application to Enantioseparation of Amino Acids

“…The inset in Figure shows UV−vis absorption spectra of PPyPVP/ l -lactate colloids dispersed in water. Two bands at 450 and >850 nm diminished with increased polymerization pH, the latter having been assigned to electronic transition for bipolarons. , Disappearance of the bipolaron band at the high pH region, which is caused by destruction of the conjugated structure of polypyrrole as a result of the carbonyl group introduction (see Scheme ), indicates that peroxodisulfate leads to overoxidation after polymerization (path 1 in Scheme ).

3 Effect of pH on absorbance of 0.14 g L -1 colloids (A) untreated and (B) treated electrochemically.

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