Extraction of mercury and silver into base-acid treated polypyrrole films: a possible pollution control technology

Polypyrrole-para-toluene sulfonate films were treated sequentially in 0.5 M NaOH and 0.5 M HNO₃. The base treatment was reported to deprotonate the film, resulting in the removal of the p-toluene sulfonate counter ions. On the other hand, the acid treatment was found to result in reprotonation of the film and its return to an oxidised state. In this work, such a treatment of polypyrrole films was initially exploited in an electroless entrapment of mercury from standard solutions. An electrochemical stripping technique was used to remove the entrapped mercury from the film. A linear relationship between the amount of mercury electrolessly entrapped within the film and that being stripped off from the films was obtained (correlation coefficients range from 0.992 to 0.997, N = 4). Several characteristics of these mercury-loaded polypyrrole films including the morphology, point of saturation and the effect of interfering silver ions were then investigated. The capability of base-acid pretreated polypyrrole films to remove mercury by electroless preconcentration in mercury-containing wastewater samples was then demonstrated. The mercury contents determined in these samples are comparable to those obtained using inductively coupled plasma-atomic emission spectroscopy. Furthermore, using silver as an example, we were able to achieve electroless preconcentration of the metal into pretreated polypyrrole films following a time as short as 7 min. All these results tend to suggest that the base-acid pretreated polypyrrole films may find an application as a simple, cheap and effective pollution control technology.