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

Publication at Faculty of Mathematics and Physics |
2012

Abstract

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 ZnS-CTAB 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 scanning electron microscopy (SEM). At the higher CTAB concentrations, ZnS nanoparticles were surrounded by CTA(+) bilayers forming positively charged micelles with the diameter of 10 nm.

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 CFA(+) on the ZnS nanoparticles was preferred to a monolayer.