Interaction Of Pb2+ Ions In Water With Two-Dimensional Molybdenum Disulfide

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 MoS2 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-MoS2 phase. However, the interaction of heavy metals dissolved in water with unmodified semiconducting 2H-MoS2 is not well studied. In this paper, we report a detailed fundamental investigation of how Pb2+ ions interact with 2H-MoS2. We observe small solid clusters that form on the MoS2 surfaces after exposing them to Pb(NO3)(2) aqueous solutions as shown by atomic force microscopy and transmission electron microscopy, and for liquid phase exfoliated MoS2 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 PbSO4 with some PbMoO4. We put forth an interaction mechanism that involves MoS2 defects acting as initiation sites for the partial dissolution in aqueous oxygenated conditions which produces MoO42- and SO42- ions to form the solids with Pb2+. These results are an important contribution to our fundamental understanding of how MoS2 interacts with metal ions and will influence further efforts to exploit MoS2 for water remediation applications.