Molecular Dynamics Studies
on the Adaptability of
an Ionic Liquid in the Extraction of Solid Nanoparticles
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Abstract
Recently, a number of publications have suggested that
ionic liquids
(ILs) can absorb solid particles. This development may have implications
in fields like
oil sand processing, oil spill beach cleanup, and water treatment.
In this Article, we provide a computational investigation of this
phenomenon via molecular dynamics simulations. Two particle surface
chemistries were investigated: (1) hydrocarbon-saturated and (2) silanol-saturated,
representing hydrophobic and hydrophilic particles, respectively.
Employing 1-butyl-3-methylimidazolium hexafluorophosphate ([BMIM][PF<sub>6</sub>]) as a model IL, these nanoparticles were allowed to equilibrate
at the IL/water and IL/hexane interfaces to observe the interfacial
self-assembled structures. At the IL/water interface, the hydrocarbon-based
nanoparticles were nearly completely absorbed by the IL, while the
silica nanoparticles maintained equal volume in both phases. At the
IL/hexane interface, the hydrocarbon nanoparticles maintained minimal
interactions with the IL, whereas the silica nanoparticles were nearly
completely absorbed by it. Studies of these two types of nanoparticles
immersed in the bulk IL indicate that the surface chemistry has a
great effect on the corresponding IL liquid structure. These effects
include layering of the ions, hydrogen bonding, and irreversible absorption
of some ions to the silica nanoparticle surface. We quantify these
effects with respect to each nanoparticle. The results suggest that
ILs likely exhibit this absorption capability because they can form
solvation layers with reduced dynamics around the nanoparticles