4.8 Article

Synergistic Effect of Metal Cations and Visible Light on 2D MoS2 Nanosheet Aggregation

Journal

ENVIRONMENTAL SCIENCE & TECHNOLOGY
Volume 55, Issue 24, Pages 16379-16389

Publisher

AMER CHEMICAL SOC
DOI: 10.1021/acs.est.1c03576

Keywords

2D nanomaterials; molybdenum disulfide; environmental behavior; aggregation and sedimentation; visible light

Funding

  1. National Nature Science Foundation of China [22076075, 41907296]
  2. China Postdoctoral Foundation [2020M682776]
  3. SUSTech-MIT Joint Center for Mechanical Engineering Education and Research and State Environmental Protection Key Laboratory of Integrated Surface Water-Groundwater Pollution Control
  4. National Science Foundation under the NSF Center for Sustainable Nanotechnology [CHE-2001611]

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The aggregation behavior of single-layer MoS2 nanosheets is influenced by cations in environmental conditions, with trivalent cations having a smaller impact compared to divalent and monovalent cations. Visible light irradiation also accelerates the aggregation process of nanosheets, even in the presence of natural organic matter.
Aggregation significantly influences the transport, transformation, and bioavailability of engineered nanomaterials. Two-dimensional MoS2 nanosheets are one of the most well-studied transition-metal dichalcogenide nanomaterials. Nonetheless, the aggregation behavior of this material under environmental conditions is not well understood. Here, we investigated the aggregation of single-layer MoS2 (SL-MoS2) nanosheets under a variety of conditions. Trends in the aggregation of SL-MoS2 are consistent with classical Derjaguin-Landau-Verwey-Overbeek (DLVO) colloidal theory, and the critical coagulation concentrations of cations follow the order of trivalent (Cr3+) < divalent (Ca2+, Mg2+, Cd2+) < monovalent cations (Na+, K+). Notably, Pb2+ and Ag+ destabilize MoS2 nanosheet suspensions much more strongly than do their divalent and monovalent counterparts. This effect is attributable to Lewis soft acid-base interactions of cations with MoS2. Visible light irradiation synergistically promotes the aggregation of SL-MoS2 nanosheets in the presence of cations, which was evident even in the presence of natural organic matter. The light-accelerated aggregation was ascribed to dipole-dipole interactions due to transient surface plasmon oscillation of electrons in the metallic 1T phase, which decrease the aggregation energy barrier. These results reveal the phase-dependent aggregation behaviors of engineered MoS2 nanosheets with important implications for environmental fate and risk.

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