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

Abstract

In recent years, core/shell nanocomposite materials have shown an increasing interest due to their unique optical and electronic properties [1]. The uniform deposition of inorganic material on the small core particles is often problematic [2]. Ultrasound is an easy and effective method under the mild conditions for preparing these kinds of nonmaterials [3, 4]. It can improve the contact of the two components, crystallinity, and formation of uniform coating [4-5]. In this study, the core-shell nanocomposites with small particle size (~11 nm) were synthesized at a relatively low temperature (70oC). The CdS nanoparticles have prepared with a new induced micro-emulsion (O/W) by ultrasound without surfactant and it was easily combined with TiO2 under sonication. The formation of uniform layer of TiO2 with the depths of 0.75 – 1.1 nm on the CdS led to an increase of the size of nanoparticles. Ultrasonic irradiation can control the hydrolysis and condensation of TTIP (titanium tetra-isopropoxide) and the formation of a gradient TiO2 shell around the CdS core. This technique avoids some problems that normally exist in conventional microemulsion synthesis such as the presence of different additives and calcinations. It is found that modification of TiO2 with CdS particles extends the optical absorption spectrum into the visible region in comparison with pure TiO2 and pure CdS. Increasing the TiO2 led to a red-shift of the absorption band in nanocomposite. The characterization of nanocomposites has been studied by HRTEM, TEM, XRD, BET and UV-vis spectroscopy.