Structural Evolutions of ZnS Nanoparticles in Hydrated and Bare States

Abstract

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 threephase 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.

Size effect on atomic structure in low-dimensional Cu-Zr amorphous systems

“…The first peak distance becomes larger as particle size increases. A similar observation is also found in nanometer-sized crystalline ZnS particles 42 , 43 . To dig out details of local atomic structure in particles, the core-and-shell model in the inset of Fig.…”

RETRACTED ARTICLE: Atomic insight into hydration shells around facetted nanoparticles

“…Bulk magnetite preferentially grows in (111) orientation 25,28 , while (110) 27 and (001) planes are also energetically stable and occur 30 . Combined experimental and theoretical studies on water structures around magnetite or maghemite nanoparticles do not exist to our knowledge, and are sparse even for other industrially relevant material classes, such as hematite 23 , TiO 2 31 , or ZnS 32 . The majority of the studies to date concern the adsorption of individual water molecules, dimers or trimers from the gas phase 18,25–28,33 and only few address multiple layers in a condensation regime to mimic bulk water surroundings 23,31 .…”

In-Depth Study of ZnS Nanoparticle Surface Properties with a Combined Experimental and Theoretical Approach

“…This is shown by the sharpening of wide-angle X-ray scattering reflections and by the small-angle data which exclude the occurrence of particle growth. This behavior was later explained by Khalkhali et al by describing ZnS NPs as three-layer systems, constituted by (i) an internal crystalline core, (ii) an intermediate layer, and (iii) a topmost layer which, by interacting with the environment, modifies its structure driving the plastic deformations of the intermediate layer and the elastic deformation of the internal core …”