EXTRACTION OF SILVER BY POLYPYRROLE FILMS UPON A BASE-ACID TREATMENT

Polypyrrole films, synthesized in the presence of para-sulphonate, wer e treated sequentially in 0.5 M NaOH and 0.5 M HNO3. The base treatmen t resulted in deprotonation and removal of the pnra-toluene sulphonate ions, while the acid treatment resulted in reprotonation of the films and its return to an oxidized st;lte. Hence, in the presence of silve r (0.5-25 ppm) in 0.5 M HNO3, electroless reduction took place and sil ver metal was entrapped in the polypyrrole structure. Following the el ectroless preconcentration of silver at polypyrrole films, the metal c ontent of the remaining acidic solutions was analyzed by atomic absorp tion spectroscopy. The results showed a linear relationship (0.993 cor relation coefficient, N=7) between the concentration of silver removed (ppm g(-1)) and the original silver concentration (ppm), i.e. [Ag+](r emoved)=57.6[Ag+](original)-32.9, with the 95% confidence intervals of the slope and intercept of 6.5g(-1) and 72.6 ppm g(-1), respectively. Reproducible voltammetric stripping response of silver entrapped in p olypyrrole films was obtained for concentrations down to 1 ppm. By in situ preconcentration of silver with mercury, stripping responses fur films exposed to as low as 5 ppb silver were recorded. In this work, t he capability of pretreated polypyrrole films in removing silver by el ectroless preconcentration in several environmental samples was furthe r explored. (C) 1998 Elsevier Science B.V.