Layered Metal Chalcophosphate (K-MPS-1) for Efficient, Selective, and ppb Level Sequestration of Pb from Water

Abstract

Sequestration of heavy metal ions from water is an important issue in chemistry. Herein, we report the detailed Pb2+ adsorption and ion exchange kinetics of a potassium intercalated layered metal thiophosphate, K0.48Mn0.76PS3.H2O (K-MPS-1), which is capable of efficient removal of Pb2+ (>99%) from very dilute concentrations (1–100 ppb). K-MPS-1 can selectively capture Pb2+ even in the presence of other monovalent and divalent cations such as Na+, Ca2+, and Mg2+ with high separation factor. K-MPS-1 can operate within a broad pH range of 2–12 effectively with high distribution coefficient (KdPb) of 5.36 × 105 mL/g, following pseudo second order kinetics. Initially, K+ intercalation in MnPS3 (MPS-1) increases the interlayer spacing and subsequently creates Mn2+ vacancy to maintain charge neutrality and destroy the center of symmetry of the P2S6 unit. Finally, Pb2+ kicks out K+ ions from the interlayer and sits into Mn2+ vacant sites in MPS-1 which further helps to regain the center of symmetry of the structure. K-MPS-1 has achieved Pb2+ removal capacity of 393.5 ± 8 mg/g following Langmuir–Freundlich adsorption model. K-MPS-1 is effective to capture Pb2+ far below the mark of tolerance level (15 ppb, USA-EPA) of drinking water.