An ultrasonic method for the synthesis, control and optimization of CdS/TiO2 core–shell nanocomposites
In this study, an ultrasonic method was utilized in combination with microemulsion to synthesize CdS/TiO2 core–shell nanoparticles and control their particle size and ultimately optimize the influential parameters. Moreover, response surface methodology (RSM) was used to optimize the thickness of the shell. Herein, four parameters, i.e. temperature (67–79 °C), synthesis retention time (45–105 min), TiO2 : CdS ratio (1.5–7.5) and the power of ultrasound waves (37–53 watt), were optimized to synthesize nanoparticles with an average size of up to 10 nm. A correlation equation was introduced for the size range of 10–90 nm, which was then proven to have excellent predictions. To verify the proposed model, two different sets of combinations were selected to synthesize 10 nm composites, and consequently, nanocomposites with the sizes of 10.4 and 10.9 nm were successfully synthesized. The power of ultrasound waves and retention time had the most influence on the size of the particles. Further experiments proved that the optical absorption spectrum of the composite particles was extended to the visible region. Furthermore, the formation of CdS/TiO2 core–shell nanocomposites was confirmed by different characterization techniques including XRD, TEM, EDAX, UV-vis, FTIR and DLS.