Abstract
Colloidal nanodispersions of ZnS have been prepared using aqueous micellar solution of two cationic surfactants of trimethylammonium/pyridinium series with different head groups i.e., cetyltrimethylammonium chloride (CTAC) and cetyltrimethylpyridinium chloride (CPyC). The role of these surfactants in controlling size, agglomeration behavior and photophysical properties of ZnS nanoparticles has been discussed. UV–visible spectroscopy has been carried out for determination of optical band gap and size of ZnS nanoparticles. Transmission electron microscopy and dynamic light scattering were used to measure sizes and size distribution of ZnS nanoparticles. Powder X-ray analysis (Powder XRD) reveals the cubic structure of nanocrystallite in powdered sample. The photoluminescence emission band exhibits red shift for ZnS nanoparticles in CTAC compared to those in CPyC. The aggregation behavior in two surfactants has been compared using turbidity measurements after redispersing the nanoparticles in water. In situ evolution and growth of ZnS nanoparticles in two different surfactants have been compared through time-dependent absorption behavior and UV irradiation studies. Electrical conductivity measurements reveal that CPyC micelles better stabilize the nanoparticles than that of CTAC.
Highlights
The synthesis of ultrafine semiconducting particles is of great technological and scientific interest due to their superior physical and optical properties
For the synthesis of Zinc sulfide (ZnS) nanoparticles, Zn(OAc)2Á2H2O (99.5%), Na2SÁxH2O (55–58% assay), all were of analytical grade obtained from central drug house (CDH)
The cetyltrimethylpyridinium chloride (CPyC) is effective in quenching the luminescence [31] due to the ability of N-atom in pyridinium cation to seize the electrons from the surface states of nanoparticles making the electron transfer easy. These results indicate that the photophysical properties of ZnS nanoparticles depend up on the size and surface passivation, which might help to further understand the physical mechanism of ZnS nanoparticles that give rise to PL properties
Summary
The synthesis of ultrafine semiconducting particles is of great technological and scientific interest due to their superior physical and optical properties. Attempts have been made to prepare, stabilize and isolate homogeneously dispersed ZnS nanoparticles with and without capping agents [4–7]. When these clean nanoparticles aggregate, they lose their nanoscale sizes and corresponding properties. Extensive structural, kinetic and thermodynamic studies have been performed to explore the fundamental understanding of surfactant–water system including the effect of additives on micellization [8–10]. Still there are conflicting opinions on some aspects the studies regarding factors controlling the synthesis and stabilization of nanoparticles in aqueous surfactant solutions. It is quite difficult to scale up a general method for the nanoparticles synthesis using surfactants, because numerous parameters with different influences enter in to consideration, while studying a particular system
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