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 fi lm, resulting in the removal of the p-toluene sulfonate. counter ions. On t he 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 treatmen t 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 relations hip between the amount of mercury electrolessly entrapped within the film a nd that being stripped off from the films was obtained (correlation coeffic ients range from 0.992 to 0.997, N = 4). Several characteristics of these m ercury-loaded polypyrrole films including the morphology, point of saturati on and the effect of interfering silver ions were then investigated. The ca pability of base-acid pretreated polypyrrole films to remove mercury by ele ctroless preconcentration in mercury-containing wastewater samples was then demonstrated. The mercury contents determined in these samples are compara ble to those obtained using inductively coupled plasma-atomic emission spec troscopy. 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 si mple, cheap and effective pollution control technology.