Extraction of silver by polypyrrole films upon a base–acid treatment

Polypyrrole films, synthesized in the presence of para-sulphonate, were treated sequentially in 0.5 M NaOH and 0.5 M HNO3. The base treatment resulted in deprotonation and removal of the para-toluene sulphonate ions, while the acid treatment resulted in reprotonation of the films and its return to an oxidized state. Hence, in the presence of silver (0.5–25 ppm) in 0.5 M HNO3, electroless reduction took place and silver metal was entrapped in the polypyrrole structure. Following the electroless preconcentration of silver at polypyrrole films, the metal content of the remaining acidic solutions was analyzed by atomic absorption spectroscopy. The results showed a linear relationship (0.993 correlation coefficient, N=7) between the concentration of silver removed (ppm g−1) and the original silver concentration (ppm), i.e. [Ag+]removed=57.6[Ag+]original−32.9, with the 95% confidence intervals of the slope and intercept of 6.5 g−1 and 72.6 ppm g−1, respectively. Reproducible voltammetric stripping response of silver entrapped in polypyrrole films was obtained for concentrations down to 1 ppm. By in situ preconcentration of silver with mercury, stripping responses for films exposed to as low as 5 ppb silver were recorded. In this work, the capability of pretreated polypyrrole films in removing silver by electroless preconcentration in several environmental samples was further explored.