Precipitation, stabilization and molecular modeling of ZnS nanoparticles in the presence of cetyltrimethylammonium bromide

Department of Analytical Chemistry and Material Testing, VŠB-Technical University of Ostrava, 17. listopadu 15, 708 33 Ostrava-Poruba, Czech Republic.
Journal of Colloid and Interface Science (Impact Factor: 3.37). 04/2012; 377(1):58-63. DOI: 10.1016/j.jcis.2012.03.073
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ZnS nanoparticles were precipitated in aqueous dispersions of cationic surfactant cetyltrimethylammonium bromide (CTAB). The sphere radii of ZnS nanoparticles calculated by using band-gap energies steeply decreased from 4.5 nm to 2.2 nm within CTAB concentrations of 0.4-1.5 mmol L(-1). Above the concentration of 1.5 mmol L(-1), the radii were stabilized at R=2.0 nm and increased up to R=2.5 nm after 24 h. The hydrodynamic diameters of CTAB-ZnS structures observed by the dynamic light scattering (DLS) method ranged from 130 nm to 23 nm depending on CTAB concentrations of 0.5-1.5 mmol L(-1). The complex structures were observed by transmission electron microscopy (TEM). At the higher CTAB concentrations, ZnS nanoparticles were surrounded by CTA(+) bilayers forming positively charged micelles with the diameter of 10nm. The positive zeta-potentials of the micelles and their agglomerates were from 16 mV to 33 mV. Wurtzite and sphalerite nanoparticles with R=2.0 nm and 2.5 nm covered by CTA(+) were modeled with and without water. Calculated sublimation energies confirmed that a bilayer arrangement of CTA(+) on the ZnS nanoparticles was preferred to a monolayer.

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    • "These nanomaterials are often prepared by chemical precipitation reactions known as ,,bottom-up " methods. (Sheikh, Barakat, , Kanjwal, Aryal, Khil, Kim 2009, Praus, Dvorsky, Horníková, Pospíšil, Kovář 2012, Praus, Dvorsky, Kovář, Trojková 2012) and at sizes of the order of 100 nm and below their volume fraction in the aqueous dispersion is usually completely minor. The significant issue during formation of a dry nanopowder from such dispersion is the drying process and an extremely small amount of solids. "
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