Synthesis of core-shell structured CdS@CeO2 and CdS@TiO2 composites and comparison of their photocatalytic activities for the selective oxidation of benzyl alcohol to benzaldehyde

Core-shell structured CdS@CeO2 and CdS@TiO2 composites were fabricated, with the aim of systematically comparing the influence of shell layer composition on the photocatalytic activity of CdS. The obtained samples were characterized by the means of transmission electron microscopy (TEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), nitrogen adsorption-desorption, and UV-vis diffuse reflectance spectroscopy (DRS). It was found that the core-shell structured CdS@CeO2 and CdS@TiO2 have been successfully constructed and the absorption edge exhibits a slight blue-shift after coating CeO2 or TiO2 shell layer. The selective oxidation of benzyl alcohol indicates that the photocatalytic activities of the synthesized samples show an increasing tendency in the order of CeO2 < CdS < CdS@TiO2 < CdS@CeO2-90 < CdS@CeO2-180 (CdS@CeO2 samples treated at 90 degrees C and 180 degrees C were denoted as CdS@CeO2-90 and CdS@CeO2-180, respectively). It was revealed that the redox couple Ce4+/Ce3+ in CeO2 shell not only promotes the separation of electron-hole pairs but also favors the transfer of electrons from the inner layer of CeO2 shell to its outer layer. Hydrothermal treatment can increase the contents of Ce3+ and chemisorbed oxygen, by which the photocatalytic activity can be enhanced. The radical scavenging experiments proved that in acetonitrile solution O-center dot(2)- and hble are the main reactive species responsible for the transformation from benzyl alcohol to benzaldehyde. (C) 2016 Elsevier B.V. All rights reserved.