2 research outputs found
Structural Evolutions of ZnS Nanoparticles in Hydrated and Bare States
Suitable optoelectronic properties
and the nontoxic nature of ZnS
quantum dots capacitate exciting applications for these nanomaterials
especially in the field of biomedical imaging. However, the structural
stability of ZnS nanoparticles has been shown to be challenging since
they potentially are prone to autonomous structural evolutions in
ambient conditions. Thus, it is essential to build an understanding
about the structural evolution of ZnS nanoparticles, especially in
aqueous environment, before implementing them for in vivo applications.
In this study we compared the structure of ZnS nanoparticles relaxed
in a vacuum and in water using a classical molecular dynamics method.
Structural analyses showed that the previously observed three-phase
structure of bare nanoparticles is not formed in the hydrated state.
The bulk of hydrated nanoparticles has more crystalline structure;
however, the dynamic heterogeneity in their surface relaxation makes
them more polar compared to bare nanoparticles. This heterogeneity
is more severe in hydrated wurtzite nanoparticles, causing them to
show larger dipole moments. Analyzing the structure of water in the
first hydration shell of the surface atoms shows that water is mainly
adsorbed to the nanoparticles’ surface through Zn–O
interaction, which causes the structure of water in the first hydration
shell to be discontinuous
Molecular Dynamics Study of the Role of Water in the Carbon Dioxide Intercalation in Chloride Ions Bearing Hydrotalcite
Molecular dynamics
simulation was used to study the role of water
in the intercalation of CO<sub>2</sub> with a model Mg–Al–Cl-hydrotalcite
mineral at ambient pressure and temperature. The ClayFF force field
was used along with a model Mg–Al–Cl-hydrotalcite containing
different amounts of water (H<sub>2</sub>O) and carbon dioxide (CO<sub>2</sub>) molecules in its interlayer spacing. It was observed that
high CO<sub>2</sub> content, say 3.85 mmol g<sup>–1</sup>,
could be achieved at low water concentrations or even without the
presence of water. However, high water concentrations (e.g., 2 H<sub>2</sub>O molecules/hydrotalcite unit cell, the maximum allowed water
concentration observed experimentally) could also yield similar CO<sub>2</sub> content, but in this case, the presence of water led to a
significant interlayer spacing expansion (from 23.0 Ã… (no water)
to 28.5 Ã…). The expansion was likely due to the change in the
orientation distribution of the CO<sub>2</sub> molecules. Analyzing
the orientation of CO<sub>2</sub> molecules revealed that they preferred
to orientate parallel to the mineral surface at low water concentrations.
However, as water concentration increased, CO<sub>2</sub> molecules
exhibited a wider range of orientations with a significant fraction
of them orienting more or less perpendicular to the mineral surface,
especially at high CO<sub>2</sub> contents. The observed change in
the orientation of CO<sub>2</sub> was attributed to the dipole interaction
between H<sub>2</sub>O and CO<sub>2</sub> molecules and the reduced
interaction between CO<sub>2</sub> and the hydroxyl groups on hydrotalcite.
Also, it was observed that water molecules formed extensive hydrogen
bond networks. All of the above findings seem to explain the contradicting
results reported in the literature that water is needed under certain
conditions to increase the amount of CO<sub>2</sub> captured by hydrotalcites.
Here, we showed that high amounts of CO<sub>2</sub> can be intercalated
with the presence of water