Polypyrrole–Mo3S13: An Efficient Sorbent for the Capture of Hg2+and Highly Selective Extraction of Ag+over Cu2+

The new material Polypyrrole–Mo3S13(abbr.Mo3S13–Ppy) is a new material prepared by ion-exchange between Ppy-NO3and (NH4)2Mo3S13. The Mo3S13–Ppy was designed to exhibit strong selectivity for Ag+and highly toxic Hg2+in mixtures with other ions. It displays an apparent selectivity ranking of Hg2+> Ag+≥ Co2+, Ni2+, Cu2+, Zn2+, Cd2+, and Pb2+. The strong affinity of Mo3S13–Ppy for Ag+and Hg2+was confirmed with extremely high distribution coefficients (Kd) (∼107mL/g) and remarkable removal efficiencies (>99.99%), resulting in <1 ppb concentrations of these ions. Furthermore, Mo3S13–Ppy achieved excellent separation selectivity for Ag+from Cu2+(even at a high Cu2+/Ag+ratio, the molar ratio of 867 and mass ratio of 500) because of the special structure of Mo3S132–and its component Mo4+and (S2)2–. This is promising for the direct extraction of low-grade silver from copper-rich minerals. The maximum Ag uptake capacity of 408 mg/g is redox-based and surprisingly involves the deposition of large, millimeter sized, metallic silver (Ag0) crystals on the surface of Mo3S13–Ppy.