Synthesis and structural characterisation of CdS nanoparticles prepared in a four-components "water-in-oil" microemulsion

Nanostructured semiconductor particles are currently under intense investigation because of their enhanced photoreactivity and photocatalytic properties due to the quantum-size effect and the dependence of the photophysical and photochemical properties on their size as it approaches the exciton diameter. This increasing interest has led to the development of several synthetic procedures to prepare and stabilise uniform crystallites. In this paper, we report a novel synthetic pathway to obtain cadmium sulphide (CdS) nanoparticles in a quaternary "water-in-oil" microemulsion formed by a cationic surfactant cetyltrimethylammonium bromide (CTAB), pentanol, n-hexane and water. The synthesis of CdS in this system is achieved by mixing two microemulsions containing Cd(NO3)2 and Na2S, respectively. The nanocrystals have been characterised by using UV--visible spectroscopy and Transmission Electron Microscopy to investigate the influence of various parameters of the particles' formation and stability in solution. Capping of nanoparticles with suitable organic molecules has been performed in order to increase their stability and afford solubility in a wide range of solvents.