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

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 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 CTA+ on the ZnS nanoparticles was preferred to a monolayer.

Graphical abstractFigure optionsDownload full-size imageDownload high-quality image (166 K)Download as PowerPoint slideHighlights► Precipitation of ZnS nanoparticles in aqueous dispersion of cetyltrimethylammonium (CTA) surfactants. ► UV spectra of the nanoparticles measured and band-gap energies and radii calculated. ► Determination of zeta-potentials and diameters of the nanoparticles by DLS. ► Molecular simulations of the arrangements of CTA ions on the nanoparticle surface.