Preparation of zinc sulfide and cadmium zinc sulfide nanometer sized particles in aqueous micellar media

Abstract

In this study cadmium dodecylsulfate, Cd(DS)2 and zinc dodecylsulfate, Zn(DS)2 functionalized surfactants were prepared and characterized by determination of their cmc and aggregation number using conductivity and fluorescence quenching respectively. The cadmium surfactant was found to have a cmc of 1.1 x lQ-3 mol dm-3 and an aggregation number of 109. The zinc surfactant was found to have similar values 1.2 x lQ-3 mol dm-3 for the cmc and an aggregation number of 106. The functionalized surfactants were reacted with sulfide to prepare Zinc sulfide, cadmium sulfide and a variety of cadmium zinc sulfide nanoparticle dispersions. Stable zinc sulfide dispersions were prepared with particles prepared at concentrations below the cmc of Zn(DS)2 having radii of ea. 3nm and those prepared at concentrations above the cmc of the surfactant had radii of ea. 2 nm. The particle radii were calculated using NedeljkoviC's equation, which relates the wavelength of absorption onset to particle radius. Colloidally stable cadmium sulfide particles were prepared however, Nedeljkovic' s equation had no solutions for the wavelengths of absorption onset measured for CdS dispersions. Furthermore Cadmium sulfide, was not found to be stable with respect to photodegradation. Particles were produced using different admixtures of Zn(DS)2 and NaDS, and particle sizes similar to those obtained when Zn(DS)2 was the only surfactant were reported in each case. When the experiment was performed in the presence of rapid mixing, aggregation was observed at those compositions which lied below the cmc curve. Cadmium zinc sulfide dispersions were prepared using mixtures of Zn(DS)2 and Cd(DS)2 above the cmc of the surfactants. The CdS character was found to predominate in U1ese particles. Particles were also produced in the presence of cationic and nonionic surfactants. However, none of these were found to have any long term colloidal stability.