Structural Evolutions of ZnS Nanoparticles in Hydrated and Bare States
M Khalkhali and HB Zeng and QX Liu and H Zhang, JOURNAL OF PHYSICAL CHEMISTRY C, 120, 7870-7884 (2016).
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.
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