Sono-synthesis of core–shell nanocrystal (CdS/TiO2) without surfactant

A core–shell nanocomposite (CdS/TiO2) was synthesized at relatively low temperature (70 °C) with small particle sizes (∼11 nm). First, CdS nanoparticles were prepared by a combination of ultrasound and new micro-emulsion (O/W) without surfactant. Then the synthesized CdS was easily combined with TiO2 under sonication. The formation of uniform surface layer of TiO2 with depths of 0.75–1.1 nm on the CdS led to an increase of particle size. Ultrasonic irradiation can control the hydrolysis and condensation of titanium tetra-isopropoxide (TTIP) and the formation of TiO2 shell around the CdS core. This technique avoids some of the problems that exist in conventional microemulsion synthesis such as the presence of different additives and calcinations. It was found that nanocomposite particles extend the optical absorption spectrum into the visible region in comparison with pure TiO2 and pure CdS. In addition, a larger depth of TiO2 led to a red-shift of the absorption band in nanocomposite. The characterization of nanocomposites has been studied by HRTEM, TEM, XRD, EDAX, BET and, UV–vis.

► A novel method introduces for the synthesis of core–shell structure.
► Ultrasonic irradiation can control the formation of TiO2 shell around the CdS core.
► The nanocomposite extends the spectral response to the visible region.
► This technique avoids addition of different additives and calcinations.
► A larger depth of TiO2 led to a red-shift of the absorption band in nanocomposite.