Superselective Removal of Lead from Water by Two-Dimensional MoS₂ Nanosheets and Layer-Stacked Membranes

Abstract

Point-of-use (POU) devices with satisfactory lead (Pb²⁺) removal performance are urgently needed in response to recent outbreaks of lead contamination in drinking water. This study experimentally demonstrated the excellent lead removal capability of two-dimensional (2D) MoS₂ nanosheets in aqueous form and as part of a layer-stacked membrane. Among all materials ever reported in the literature, MoS₂ nanosheets exhibit the highest adsorption capacity (740 mg/g), and the strongest selectivity/affinity toward Pb²⁺ with a distribution coefficient <i>K</i>_d that is orders of magnitude higher than that of other lead adsorption materials (5.2 × 10⁷ mL/g). Density functional theory (DFT) simulation was performed to complement experimental measurements and to help understand the adsorption mechanisms. The results confirmed that the cation selectivity of MoS₂ follows the order Pb²⁺ > Cu²⁺ ≫ Cd²⁺ > Zn²⁺, Ni²⁺ > Mg²⁺, K⁺, Ca²⁺. The membrane formed with layer-stacked MoS₂ nanosheets exhibited a high water flux (145 L/m²/h/bar), while effectively decreasing Pb²⁺ concentration in drinking water from a few mg/L to less than 10 μg/L. The removal capacity of the MoS₂ membrane is a few orders of magnitude higher than that of other literature-reported membrane filters. Therefore, the layer-stacked MoS₂ membrane has great potential for POU removal of lead from drinking water.