Synthesis and Characterization of S@AgBr Core-Shell Nanoparticles

Abstract

Core–shell nanoparticles are gaining lots of importance recently due to their exciting applications in different fields like biomedical, pharmaceutical, electronics, catalysis etc. They also show new properties than the single materials when coated one material with other. In this report we studied the preparation and growth kinetics of sulfur nanoparticles as a core in aqueous surfactant medium and then the particle was coated with AgBr. The main objective of this project is to study the effects of different parameters like types of acids, surfactants, reactant concentration, temperature, and sonication on core particle size and growth rate. Finally to coat the core with AgBr in surfactant assisted medium.
The sulfur nanoparticles were preparation by well known acid catalyzed precipitation reaction from sodium thiosulphate in presence of surfactants. We used both inorganic and organic acids, the results show organic acid gives smaller size of sulfur particles. The size of the particles is also depends on the reactant concentration and acid to reactant ratio. The effect of different surfactants (TX-100, CTAB, SDBS, and SDS) on particle size was also studied and found the surfactant can significantly reduce the particle size with out changing the shape. The size reducing ability is not same for all the surfactants, depends on the types of surfactant. Anionic surfactant SDBS is more efficient for controlling the uniform size in both the acids medium. However, in CTAB solution, we got lower size particles in a certain reactant concentration range, and we got lowest 30 nm particles in this medium. Sulfur obtained by this method was orthorhombic or -sulfur with S8 structure
As the sulfur nanoparticles are formed by a precipitation reaction, therefore, the overall process can be subdivided in to three steps: nucleation, growth, and particle agglomeration. For this reaction nucleation is very fast so particle size is mainly controlled by particle growth and agglomeration. Actually, as reaction rate is very fast the growth rate is mainly depends on the diffusion of newborn particle from the bulk phase to surface of the nuclei. The growth and agglomeration rate are depend on some reaction parameters, like temperature, reactant concentration, presence of different surfactants, and also on surfactant concentration. Those parameters increase the diffusion rate show higher growth rate. The increase in temperature and reactant concentration increases the size of the particle. The presence of surfactants creates a charged surface layer on the hydrophobic sulfur particle after adsorption and ultimately reduces the growth rate and agglomeration. The particle growth rate also depends on the surfactant concentration, with increase surfactant concentration growth rate decreases, and become constant near to its CMC value.
The core sulfur particles were coated with AgBr to from S@AgBr core-shell particles in aqueous medium. The core shell particles were confirmed by DLS measurement and UV spectroscopy. The core surface was modified with CTAB miceller solution to make the coating favorable. The overall size and shell thickness can be controlled by varying the reactant concentration both the core and shell material. The core-shell particle also was characterized by TGA, DLS, SEM and BET.