Interaction of Pb²⁺ ions in water with two-dimensional molybdenum disulfide

Abstract

The removal of heavy metal contaminants from water is important for public health, and recently many two-dimensional (2D) materials with high specific surface areas are being studied as promising new active components in water purification. In particular, 2D MoS 2 nanosheets have been used for the removal of various heavy metals, but usually in either in complex geometries and composites, or in the chemically exfoliated metallic 1T-MoS 2 phase. However, the interaction of heavy metals dissolved in water with unmodified semiconducting 2H-MoS 2 is not well studied. In this paper, we report a detailed fundamental investigation of how Pb 2+ ions interact with 2H-MoS 2 . We observe small solid clusters that form on the MoS 2 surfaces after exposing them to Pb(NO 3 ) 2 aqueous solutions as shown by atomic force microscopy and transmission electron microscopy, and for liquid phase exfoliated MoS 2 we observe the nanosheets precipitating out of dispersion along with insoluble solid granules. We use a combination of x-ray photoelectron spectroscopy and x-ray diffraction to identify these solid clusters and granules as primarily PbSO 4 with some PbMoO 4 . We put forth an interaction mechanism that involves MoS 2 defects acting as initiation sites for the partial dissolution in aqueous oxygenated conditions which produces MoO 4 2− and SO 4 2− ions to form the solids with Pb 2+ . These results are an important contribution to our fundamental understanding of how MoS 2 interacts with metal ions and will influence further efforts to exploit MoS 2 for water remediation applications.

Transition Metal Dichalcogenide–Silk Nanofibril Membrane for One-Step Water Purification and Precious Metal Recovery

“…Therefore, some particles appear on the membrane surface after Pb 2+ and Hg 2+ filtration. The adsorption process of Pb­(NO 3 ) 2 by MoS 2 occurs along with the oxidation and dissolution of MoS 2 at defect sites, further producing small clusters or particles of PbMoO 4 and PbSO 4 . As for the adsorption of Hg 2+ on the MoS 2 surface in the aqueous environment, some protrusions (i.e., MoO 3 ·H 2 O crystals) would be generated due to the surface oxidation during the Hg 2+ adsorption process. , …”

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

“…16,17 Although MoS 2 is a naturally occurring mineral, the direct use of bulk MoS in heavy metal remediation is impossible because the interlayer spacing (0.63 nm) is so small that targeted heavy metal ions are unable to access the interior sulfur atoms. Synthetic 2D MoS 2 nanomaterials (e.g., flower-like aggregates) have been explored as adsorbents for toxic transition metal (Hg 2+ , Pb 2+ , Ag + , Zn 2+ , Cd 2+ ) remediation, showing moderate-to-high adsorption capacities [18][19][20][21][22][23][24][25] . However, little investigation has been done to quantify the affinity and selectivity of MoS 2 -based adsorbents.…”

“…Two-dimensional (2D) molybdenum disulfide (MoS 2 ), one of the most widely researched transition metal dichalcogenides (TMDs), is an ideal adsorbent material for heavy metal remediation because of its large surface area, and is abundant active sulfur sites that have a high affinity to heavy metals. , Although MoS 2 is a naturally occurring mineral, the direct use of bulk MoS 2 in heavy metal remediation is impossible because the interlayer spacing (0.63 nm) is so small that targeted heavy metal ions are unable to access the interior sulfur atoms. Synthetic 2D MoS 2 nanomaterials (e.g., flower-like aggregates) have been explored as adsorbents for toxic transition metal (Hg 2+ , Pb 2+ , Ag + , Zn 2+ , Cd 2+ ) remediation, showing moderate-to-high adsorption capacities. − However, little investigation has been done to quantify the affinity and selectivity of MoS 2 -based adsorbents . The surface area of MoS 2 available for adsorption is also compromised due to the aggregation of MoS 2 nanosheets during hydrothermal synthesis.…”

Ultra‐Rapid Removal of Pb(II) Ions by a Nano‐MoS2 Decorated Graphene Aided by the Unique Combination of Affinity and Electrochemistry

“…Further, the deconvoluted Pb 4f spectrum (Figure 4E) appeared at 138.6 and 143.2 eV (≈4.6 eV difference in the value), corresponding to Pb 4f 7/2 and Pb 4f 5/2 , respectively, suggesting the presence of both Pb (II) and Pb (0). [ 85,86 ] The presence of Pb (0) is assigned to the reduction of Pb (II) by the O 2– /O – /S 2– groups. Thus, the results suggest the mechanism of affinity of S 2– and oxygen moieties with Pb (II) and the role of electrochemistry in the adsorption of Pb (II).…”