Fabrication of coenocytic Pd@CdS nanocomposite as a visible light photocatalyst for selective transformation under mild conditions

Coenocytic Pd@CdS nanocomposite has been successfully prepared via a facile wet chemistry approach. Its structure and properties have been characterized by a series of techniques, including field-emission scanning electron microscopy (FE-SEM), transmission electron microscopy (TEM), energy-dispersive X-ray spectroscopy (EDX), X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), ultra-violet/visible diffuse reflectance spectroscopy (DRS), nitrogen adsorption-desorption and electron spin resonance spectroscopy (ESR). The results demonstrate that the Pd nanoparticles as multiple cores are evenly distributed inside the photoactive CdS shell, forming a coenocytic nanostructure. It is found that the concentration of precursors and the intrinsic nature of noble metal colloids play essential roles in the growth process for such noble metal@semiconductor nanocomposite. Accordingly, a possible formation mechanism for the coenocytic Pd@CdS nanocomposite is proposed. The visible light photocatalytic activity of Pd@CdS has been evaluated by selective oxidation of a range of alcohols using molecular oxygen as oxidant under mild conditions. The results show that the coenocytic Pd@CdS exhibits enhanced photocatalytic activity as compared to blank-CdS obtained by the same procedure in the absence of Pd colloid nanoparticles as seeds. The enhanced photocatalytic performance of the coenocytic Pd@CdS can be ascribed to the coupling interaction of enhanced light absorption intensity, the longer lifetime of photogenerated charge carriers and its favorable adsorptivity. It is expected that our work could provide useful information for fabricating other core-shell nanocomposites and open an avenue to utilizing them in the field of photocatalytic selective organic transformations.