A Simple Strategy for Fabrication of "Plum-Pudding" Type Pd@CeO2 Semiconductor Nanocomposite as a Visible-Light-Driven Photocatalyst for Selective Oxidation

The Pd@CeO2 semiconductor nanocomposite with "plum-pudding" structure has been fabricated successfully via a facile low-temperature hydrothermal reaction of polyvinylpyrrolidone (PVP)-capped Pd colloidal partiles and cerium chloride precursor followed by a calcination process in air. Different characterization techniques, including X-ray diffraction (XRD), field-emission scanning electron microscopy (FE-SEM), transmission scanning electron microscopy (TEM), energy-dispersive X-ray spectroscopy (EDX), UV-vis diffuse reflectance spectra (DRS), X-ray photoelectron spectra (XPS), photoluminescence spectra (PL), nitrogen adsorption-desorption, and electron spin resonance spectra (ESR), have been used to investigate the structure and properties of the Pd@CeO2 nanocomposite. It is found that the nanosized Pd particles are evenly dispersed into the matrix of CeO2, thus forming a plum-pudding structure, i.e., multi-Pd core@CeO2 shell configuration. This unique nanostructure endows the Pd@CeO2 nanocomposite with enhanced activity and selectivity toward the visible-light-driven oxidation of various benzylic alcohols to corresponding aldehydes using dioxygen as oxidant at room temperature and ambient pressure compared with a supported Pd/CeO2 nanocomposite and nanosized CeO2 powder. The formation of the multi-Pd core@CeO2 shell structure can be understood by a synergistic interaction of heterogeneous seeded growth process, monolayer-capped core coalescence, and shell re-encapsulation. Together with the previous report, it can be concluded that the intrinsic structure nature of noble metal colloids is able to play a key role in affecting the formation process of noble metal core@semiconductor shell nanocomposites, by which we can realize the design and preparation of different specific core-shell nanostructures with atomic scale accuracy. It is hoped that our current work could open promising prospects of the fabrication of multimetal core@semiconductor shell nanocomposites and their application to visible-light-driven selective organic transformations.