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: 3.55). 04/2012; 377(1):58-63. DOI: 10.1016/j.jcis.2012.03.073
Source: PubMed

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 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.

1 Bookmark
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: Physics and chemistry of very small particles emanate from a long-term tradition of colloidal chemistry. An important area of contemporary nanotechnologies is preparation of nanoparticles with size lower than 100 nm by top-down and bottom-up methods. Bottom-up methods turned out to be more suitable for preparation of nanoparticles than methods based of various chemical reactions. In our previous works we referred about preparation of ZnS nanoparticles with size about 3-5 nm stabilized by cationic surfactants like cetyltrimethylammonium bromide (CTAB) in aqueous dispersions by chemical precipitation of zinc acetate and sodium sulphide. CTAB was found to significantly influence size of ZnS nanoparticles. A basic requirement for their photocatalytic properties is maximal reactive surface area. For practical manipulation these nanoparticles were deposited on caring larger particles which formed dray powders. In this work, a new method for preparation of composite of ZnS nanoparticles and montmorillonite ZnS-MMT in aqueous environment is presented. The ZnS-MMT nanocomposite was formed by cavitation implosion of ZnS nanoparticles into MMT pores. As a result of very high impact velocities at collisions of ZnS nanoparticles and MMT particles increase of a number of ZnS nanoparticles in ZnS-MMT can be expected. The method of cavitation deposition utilizes implosion of cavitation bubbles, which were formed by nucleation on external surface of dispersed particles. Extreme dynamics of implosion collapse of cavitation bubbles leads to formation of high impact pressures up to tents GPa in final implosion phase. Density of nanoparticles in the aqueous dispersion is very high and cavitation bubbles nucleated on walls of the caring MMT particles catch photoactive ZnS nanoparticles on expanding surface with high probability. At the end of tensile stress in liquid a bubble implosion collapse as well as a collision between both particles happen. The deposition happens with high frequency and energy. Performed analyses showed that the method of cavitation deposition lead to increase of specific surface area at cca 214 % of that originated by standard mechanical shaking. The total content of ZnS in the ZnS-MMT composite increased from 7 wt. % (shaking) to 10.5 wt. %. If ZnS nanoparticles are bound to surface of a caring material in a monolayer arrangement then nanocomposite photocatalytic efficiency should be proportional to product of specific surface area and a total content of deposited ZnS. Hence, the photocatalytic efficiency of ZnS-MMT nanocomposite prepared by the cavitation method was about 300 % in comparison with the composite prepared by shaking.
    NSTI-NANOTECH 2014, Washington; 06/2014
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: Zinc sulfide, both as a bulk material and in nanocrystalline form, is a valuable luminescent material with important applications. Doped ZnS nanoparticles of around 5 nm are the material of choice for optoelectronic applications running in the UV region owing to their significant quantum size effect. This paper concerns detailed structural, spectroscopic and crystal field studies of ZnS nanoparticles, both pure and doped with Mn2+ ions, successfully synthesized at room temperature using a simple reverse micelle technique in the Triton X-100/cyclohexane medium. The resulting ZnS sphalerite phase small-size nanoparticles (3–5 nm) have a much larger energy band gap (~ 4.7 eV) than that reported for the bulk ZnS (3.6 eV), thus confirming a pronounced quantum confinement effect. The electron paramagnetic resonance data provided evidence for the existence of two distinct environments for Mn2+ ions: the interior (core) and near the surface of the nanoparticles. The presence of an Mn2+-characteristic orange emission centered at 600 nm confirmed that our samples were properly doped with Mn2+ ions, as the 4T1→6A1 radiation transition could arise only on the basis of Mn2+ ions incorporated into the ZnS nanoparticles. To the best of our knowledge, our finding include the longest decay time component for the orange emission ever observed, timed at about 3.3 ms. The experimental excitation spectra were analyzed and the transitions assigned using the exchange charge model of theory of crystal field, which allowed to calculate the energy level scheme of the Mn2+ ions. The results presented in this paper provide us with detailed information about the ZnS sphalerite nanocrystals studied and can be readily applied to other similar systems.
    Journal of Luminescence 02/2014; 146:133-140. · 2.14 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: Core/shell CdS/ZnS nanoparticles were modelled in the Material Studio environment and synthesizedby one-pot procedure. The core CdS radius size and thickness of the ZnS shell composed of 1–3 ZnS monolayers were predicted from the molecular models. From UV–vis absorption spectra of the CdS/ZnScolloid dispersions transition energies of CdS and ZnS nanostructures were calculated. They indicatedpenetration of electrons and holes from the CdS core into the ZnS shell and relaxation strain in the ZnSshell structure. The transitions energies were used for calculation of the CdS core radius by the Schrödingerequation. Both the relaxation strain in ZnS shells and the size of the CdS core radius were predicted bythe molecular modelling.The ZnS shell thickness and a degree of the CdS core coverage were characterized by the photocatalyticdecomposition of Methylene Blue (MB) using CdS/ZnS nanoparticles as photocatalysts. The observedkinetic constants of the MB photodecomposition (kobs) were evaluated and a relationship between kobsand the ZnS shell thickness was derived. Regression results revealed that 86% of the CdS core surface wascovered with ZnS and the average thickness of ZnS shell was about 12% higher than that predicted bymolecular modelling.
    Applied Surface Science 01/2014; 292:813-822. · 2.54 Impact Factor


Available from
May 19, 2014