Studies on the formation and properties of polypyrrole doped with ionised β-cyclodextrins: influence of the anionic pendants

Abstract

Polypyrrole films doped with sulfonated β-cyclodextrin (PPy/sβ-CD) and carboxymethyl β-cyclodextrin (PPy/CMβ-CD) were formed on electropolymerisation of pyrrole in a solution of the cyclodextrin sodium salts. Lower rates of electropolymerisation were evident with the carboxymethyl β-CD and this was attributed to protonation of the carboxylate groups due to an increase in the interfacial pH at the electrode-solution interface. The PPy/sβ-CD and PPy/CMβ-CD films showed cation exchange behaviour with the ingress of Na + and its associated water molecules on reduction. The PPy/CMβ-CD film showed less electroactive behaviour which may be related to the lower number of anionic pendants on the CMβ-CD or to the possible precipitation of the less soluble neutral CD which arises due to the protonation of the carboxylate groups. The PPy/sβ-CD showed a high capacitance of 6.0 mF cm −2 corresponding to a specific capacitance of 71 F g −1 over a wide potential range extending from − 0.60 to 0.60 V vs SCE. Over-oxidation was observed at relatively low potentials, at about 0.60 V vs SCE. A diffusion coefficient of 6.47 × 10 −6 cm 2 s −1 and a rate constant of 3.73 × 10 −2 cm s −1 were obtained for the ferricyanide redox couple at the PPy/sβ-CD, indicating little or no inhibition of the ferricyanide redox reaction.

The selective electrochemical sensing of dopamine at a polypyrrole film doped with an anionic β−cyclodextrin

“…It is clear that the optimum current for the oxidation of DA is seen for formation potentials between 0.60 V and 0.83 V vs SCE. The lower peak currents observed when the polymer is formed at higher potentials are associated with the overÀoxidation of the polymer and the formation of a more insulating polymer film [34]. At the lower applied potentials, between 0.40 V and 0.50 V vs SCE, the doping levels are lower and as the oxidation of DA is connected to the presence of the SβCD, the lower doping levels result in poor detection.…”

“…It is clear that a prior reduction period gives rise to lower peak currents. This behaviour can be explained in terms of the cationÀexchange properties of the PPyÀSβCD films [26,34], where the ingress of Na þ ions occurs at lower applied potentials. This is illustrated in Fig.…”