Remarkable Acid Stability of Polypyrrole-MoS₄: A Highly Selective and Efficient Scavenger of Heavy Metals Over a Wide pH Range

The new material polypyrrole/MoS₄ ²⁻(MoS₄-Ppy), prepared by ion-exchange of NO₃- of NO₃-Ppy with MoS₄ ²⁻, displays high acid stability and excellent uptake for heavy metal ions such as Hg²⁺, Ag⁺, Cu²⁺, and Pb²⁺. The different maximum adsorption capacities (q_m) for Cu²⁺, Pb²⁺, Hg²⁺, and Ag⁺ depend on the various binding modes arising from the different thiophilicity of these metal ions. The removals of Ag⁺ and Pb²⁺ reach >99.6% within 5 min, and for highly toxic Hg²⁺, >98% removal achieves at 1 min. At strong acid limit, the exceptional q_m(Ag⁺) of 725 mg g⁻¹ places the MoS₄-Ppy at the top of materials for such removal. Uptake kinetics of Ag⁺, Hg²⁺, and Pb²⁺ is extremely fast: >99.9% removal rates at wide pH range (0.5–6) within 1–5 min. Also, at strongly acidic conditions (pH ≈ 1), for highly toxic Hg²⁺, <2 ppb concentration can be achieved, accepted as safe limit. The MoS₄-Ppy demonstrates an outstanding ability to separate low-concentrated Ag⁺ from high concentrated Cu²⁺ especially under strong acidic conditions (pH ≈ 1), showing a large separation factor SF_Ag/Cu (K_d ^Ag/K_d ^Cu) of 10⁵ (>100). MoS₄-Ppy is a superior and novel sorbent material for water remediation applications as well as precious metals recovery.