Metal transport studies on inherently conducting polymer membranes containing cyclodextrin dopants

Conducting polymer membranes consisting of polypyrrole (PPy) doped with sulfated α-cyclodextrin (α-CDS) or sulfated β-cyclodextrin (β-CDS) were prepared electrochemically using aqueous solutions, containing pyrrole and the respective cyclodextrins. The N:S ratio for both polymers were very similar and indicated that there was approximately 4.5 pyrrole for every deprotonated sulfate group. The electrical conductivities of PPy·α-CDS and PPy·β-CDS were found to be 0.7 S cm−1 and 0.4 S cm−1, respectively. Cyclic voltammetry studies showed that the two polymers were electroactive and generally gave similar electrochemical responses when immersed in the same elecrolyte solution. Electrochemically controlled transport of alkali metal ions, alkaline earth metal ions and transition metal ions was demonstrated across composite membranes prepared by depositing PPy·α-CDS or PPy·β-CDS onto platinum sputter-coated polyvinylidene filters. PPy·β-CDS coated membranes proved to be significantly more permeable towards most metal ions examined than either PPy·α-CDS coated membranes or any other membranes previously examined. The one exception to this was copper ions, which were transported to a much greater extent across composite PPy·α-CDS membranes. Significant increases in the permeability of both membranes towards copper and in the case of composite PPy·β-CDS membranes iron, were obtained by altering the pulsed potential used to initiate metal ion transport.