Synthesis, characterisation and ion transport studies on polypyrrole/deoxyribonucleic acid conducting polymer membranes
Thin films composed of polypyrrole/deoxyribonucleic acid (PPy/DNA) were prepared by potentiodynamic potentiostatic and galvanostatic methods from aqueous solutions containing pyrrole and salmon sperm DNA. This material was also grown as large free-standing membranes, and onto platinum sputter-coated polyvinylidene fluoride (PVDF) filters to form composite membranes. Electrochemical studies of this material indicated that it could be oxidised and reduced, inducing ion movement in and out of the surrounding solution. The results of elemental phosphorus analysis confirmed that DNA had been incorporated into the conducting polymer as a dopant, while four-point probe measurements on free-standing PPy/DNA membranes gave a conductivity of 0.11 S cm-1. UV-VIS spectroscopic studies of films grown onto indium/tin oxide coated glass were also consistent with the polymer being conducting in its oxidised form. Scanning electron microscopy and atomic force microscopy showed that the surface of free-standing membranes was relatively smooth. Transport of potassium and copper across composite PPy/DNA/Pt/PVDF membranes was achieved using an applied pulsed potential and source solutions containing these ions. However, under the same conditions no transport of calcium, magnesium or iron was observed. A Cu2+/Fe3 selectivity factor of 33 was calculated using metal ion fluxes obtained from a transport experiment performed using a source solution containing both of the above metal ions. This value is six times larger than Cu2 /Fe3 selectivity factors previously reported for conducting polymer membranes.
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