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

Abstract

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 particles 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.