Polypyrrole-Mo_3S_(13): An Efficient Sorbent for the Capture of Hg~(2+) and Highly Selective Extraction of Ag~+ over Cu~(2+)

摘要

The new material Polypyrrole—Mo_3S_(13) (abbr. Mo_3S_(13)—Ppy) is a new material prepared by ion-exchange between Ppy-NO_3 and (NH_4)_2Mo_3S_(13). The Mo_3S_(13)— Ppy was designed to exhibit strong selectivity for Ag~+ and highly toxic Hg~(2+) in mixtures with other ions. It displays an apparent selectivity ranking of Hg~(2+) > Ag~+ > Co~(2+), Ni~(2+), Cu~(2+), Zn~(2+), Cd~(2+), and Pb~(2+). The strong affinity of Mo_3S_(13)-Ppy for Ag~+ and Hg~(2+) was confirmed with extremely high distribution coefficients (K_d) (~10~7 mL/g) and remarkable removal efficiencies (>99.99%), resulting in <1 ppb concentrations of these ions. Furthermore, Mo_3S_(13)—Ppy achieved excellent separation selectivity for Ag~+ from Cu~(2+) (even at a high Cu~(2+)/Ag~+ ratio, the molar ratio of 867 and mass ratio of 500) because of the special structure of Mo_3S_(13)~(2-) and its component Mo~(4+) and (S_2)~(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 (Ag~0) crystals on the surface of Mo_3S_(13)—Ppy.