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

Abstract

Point-of-use (POU) devices with satisfactory lead (Pb 2+ ) 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) MoS 2 nanosheets in aqueous form and as part of a layer-stacked membrane. Among all materials ever reported in the literature, MoS 2 nanosheets exhibit the highest adsorption capacity (740 mg/g), and the strongest selectivity/affinity towards Pb 2+ with a distribution coefficient K d that is orders of magnitude higher than that of other lead adsorption materials (5.2×10 7 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 MoS 2 follows the order Pb 2+ > Cu 2+ >> Cd 2+ > Zn 2+ , Ni 2+ > Mg 2+ , K + , Ca 2+ . The membrane formed with layer-stacked MoS 2 nanosheets exhibited a high water flux (145 L/ m 2 /h/bar), while effectively decreasing Pb 2+ concentration in drinking water from a few mg/L to less than 10 μg/L. The removal capacity of the MoS 2 membrane is a few orders of magnitude higher than that of other literature-reported membrane filters. Therefore, the layer-stacked MoS 2 membrane has great potential for POU removal of lead from drinking water.

Matrix effects on the performance and mechanism of Hg removal from groundwater by MoS2 nanosheets

“…Actually, a downward shift of binding energy has been observed in the case of Pb( ii ) removal by MoS 2 , in which Pb( ii ) binds to two neighboring S atoms with an equal bond length. 40 Hg( ii ) as a larger and softer Lewis acid is more likely to form a multi-bonding structure with S, in a similar manner to S–Hg–S arranged in a square planar configuration on the galena surface. 60 The TEM elemental mapping (Fig.…”

“…MoS 2 nanosheets were prepared by an established chemical exfoliation method following the approach reported previously, and the schematic illustration of the exfoliation process is shown in Fig. S1 † 40 . Briefly, 5 mL of 1.6 M n -butyllithium in hexane solution was added to ∼300 mg of bulk MoS 2 powder (∼2 µm, Sigma-Aldrich) and the suspension was stirred gently in a nitrogen-filled glovebox for 2 d. Then 40 mL hexane was added to the resulting solution mixture, and the excess organic reactants and byproducts were removed by centrifugation at 4000 rpm for 15 min to obtain the Li-intercalated MoS 2 sample.…”

“…Actually, the downward shift of binding energy has been observed in the case of Pb(II) removal by MoS2, in which Pb(II) binds to two neighboring S atoms with an equal bond length. 40 Hg(II) as a larger and softer Lewis acid is more likely to form multi-bonding structure with S, in a similar manner with S-Hg-S arranged in a square planar configuration on the galena surface. 60 The TEM elemental mapping (Figure S9 (i.e., the presence of Cl) could promote the redox reactions between Hg and MoS2, induce the vast generation of reduced Hg species (i.e., Hg 0 and monovalent Hg), and thus enhance the overall removal capacity of Hg by MoS2 nanosheets as compared to the removal in DI water.…”

“…[26][27][28] Generally, the highly efficient and selective Hg removal by MoS 2 nanosheets stems from their large surface area and abundant active sulfur sites that have strong Lewis acid/base so-so interactions with Hg. [29][30][31] Liu et al 32 used hydrothermally-synthesized MoS 2 to simultaneously remove Hg(II), Pb(II) and Cd(II) from the aqueous phase, and MoS 2 exhibited the highest removal efficiency for Hg(II) among the tested ions with a maximum adsorption capacity of 2409 mg g À1 . Jia et al 33 reported multi-layer adsorption of Hg(II) onto MoS 2 nanosheets via Hg-S complexation and electrostatic interactions.…”

The Modified Liquid‐Liquid Interface: The Effect of an Interfacial Layer of MoS2 on Ion Transfer

“…The existence of such a negative charge was established as a result of several examples of cationic species being encapsulated in MoS 2 structure [58,62–64] . Studies related to the surface charge of MoS 2 nanosheets have also shown that their dispersion maintains a negative zeta potential [65–68] . In addition, exfoliation of MoS 2 results in numerous defects such as sulphur vacancies in its surface [69,70] .…”