CdS@TiO₂ and ZnS@TiO₂ core-shell nanocomposites: synthesis and optical properties

Abstract

Reverse micellar route was used to synthesize CdS@TiO₂ and ZnS@TiO₂ core-shell nanocomposites. Titanium hydroxyacylate has been used for the first time as the shell-forming agent for the formation of TiO₂ shell over CdS and ZnS which ensures the formation of shell over the core nanoparticle due to its slow rate of hydrolysis and thus forms core-shell nanocomposites. HRTEM studies show 3-5 nm sulphide nanoparticles forming the core. A strong quantum confinement for bare nanoparticles and core-shell nanocomposites was observed from the blue shift of the absorption band of these nanocomposites. The size of CdS and ZnS, calculated from spectroscopic studies, corroborated with that observed from HRTEM studies. 2-Mercaptoethanol (used as a capping agent) was found to restrict the size of the CdS core in these nanostructures which resulted in further shift of the absorption and emission bands towards lower wavelength. No quenching in the emission band of CdS was observed for the core-shell nanostructures. In contrast to CdS@TiO₂, the optical properties of ZnS@TiO₂ core-shell nanostructures do not show any shift in the absorption band when compared to bare ZnS nanoparticles.