Formation of CdS nanoparticles in mixed cationic-anionic surfactant vesicle system

CdS nanoparticles were prepared in a mixed vesicle dispersions of the simple cationic and anionic surfactants, i.e. decyltrimethylammonium bromide and sodium 10-undecenoate, from Cd²⁺ or CdEDTA^2- and H₂S. UV-visible spectra were used to characterize the CdS particles formed. The particle size (in diameter) varied from 2.7 to > 5.0 nm, depending on the preparation conditions. When the pH is between 9.4 and 10.0, at which the vesicles have the maximum entrapping efficiency, the smallest particles with good stability and relative narrow dispersion are obtained. The inner and outer surfaces are all available for the formation of ultrafine CdS particles. The CdS nanoparticles generated from Cd²⁺ are obviously smaller and much more stable than those generated from CdEDTA^2-.