CdS nanoparticles were easily combined with TiO2 through a reaction in micro-emulsion by means of ultrasonic irradiation. The formation of a uniform layer of TiO2 on the CdS led to an increase of the size of nanoparticles. This is due to the appearance of a core–shell structure between the two combined semiconductors with a strong interface between them. TiO2 shell depths were in the range of 1.4–2.3 nm. Nano-scale depths of TiO2 layers on the CdS can be easily controlled by adjusting the concentration of TTIP (titanium tetra-isopropoxide). Important variables such as the preparation method, molar ratio of the reactants, and time of sonication were investigated. Ultrasonic irradiation can control the hydrolysis and condensation of TTIP and the formation of a gradient TiO2 shell around the CdS core. The nanoparticles were characterized by X-ray diffraction (XRD), UV–visible spectroscopy, energy dispersed analysis of X-ray (EDAX), HRTEM, SEM, and surface area measurements (BET).

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