Fate and Transport of Molybdenum Disulfide Nanomaterials in Sand Columns

Research and development of two-dimensional transition metal dichalcogenides (TMDC) (e.g., molybdenum disulfide [MoS₂]) in electronic, optical, and catalytic applications has been growing rapidly. However, there is little known regarding the behavior of these particles once released into aquatic environments. Therefore, an in-depth study regarding the fate and transport of two popular types of MoS₂ nanomaterials, lithiated (MoS₂-Li) and Pluronic PF-87 dispersed (MoS₂-PL), was conducted in saturated porous media (quartz sand) to identify which form would be least mobile in aquatic environments. The electrokinetic properties and hydrodynamic diameters of MoS₂ as a function of ionic strength and pH were determined using a zeta potential analyzer and dynamic light scattering techniques. Results suggest that the stability is significantly decreased beginning at 10 and 31.6 mM KCl, for MoS₂-PL and MoS₂-Li, respectively. Transport study results from breakthrough curves, column dissections, and release experiments suggest that MoS₂-PL exhibits a greater affinity to be irreversibly bound to quartz surfaces as compared with the MoS₂-Li at a similar ionic strength. Derjaguin-Landau-Verwey-Overbeek theory was used to help explain the unique interactions between the MoS₂-PL and MoS₂-Li surfaces between particles and with the quartz collectors. Overall, the results suggest that the fate and transport of MoS₂ is dependent on the type of MoS₂ that enters the environment, where MoS₂-PL will be least mobile and more likely be deposited in porous media from pluronic-quartz interactions, whereas MoS₂-Li will travel greater distances and have a greater tendency to be remobilized in sand columns.