2 research outputs found

    Structural Evolutions of ZnS Nanoparticles in Hydrated and Bare States

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    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

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    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 Å (no water) to 28.5 Å). 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
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